硅-石墨电极降解机理研究

Silicon/graphite material is one of the most promising anodes for high-performance lithium-ion batteries. However, the considerable deformation occurring during the charge/discharge process leading to its degradation hinders its application. Research on the electrochemical performance of silicon/graphite anode have mainly focused on its cyclic performance and microscopic mechanism, whilst the correlation between electrochemical performance and the mechanical deformation of batteries at the cell level is in few numbers. In this study, the electrochemical performance and cycling performance of the cells in Ah-level silicon/graphite anode pouch cells with different SiO weight ratios (5 wt.%, 10 wt.%, and 20 wt.%) in the anode, and LiNi0.8Co0.1Mn0.1 as the cathode are investigated by quantitative analysis. It is found that cells with different SiO weight ratios in anodes under a different state of charge (SOC) and state of health (SOH) demonstrate remarkable differences in electrochemical impedance characteristics. The results show that SOC, SOH and the weight ratios of SiO are the main factors affecting the impedance characteristics for batteries with silicon/graphite anode, which is deeply related to the change in the thickness of the electrode during lithiation/delithiation. This research facilitates the application of EIS in battery management and the design of silicon/graphite anode lithium-ion batteries.

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Batteries used in space applications can be exposed to large temperature-swings. During these large temperature-swings, the battery electrolyte can undergo a phase transformation from a liquid to a solid and back to a liquid. The nature of the solvent and the type of salt influence the crystallization processes. Herein, we aim to understand how pressure build-up in confined regions of an electrode (e.g., pores) influences degradation processes in silicon-oxide graphite anodes undergoing freeze-thaw dynamics. Our results show that high porosity electrodes lead to a greater density of nucleation sites for electrolyte crystallization. Local pressure build-up at pores results in active material loss and decreased cycle lifetime in batteries exposed to extreme temperature swings.

Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon–graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li+ crosstalk between silicon and graphite, consequent Li+ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li+ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li+ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm−2 has a cycle life of >750 cycles the volumetric energy density of 800 Wh L−1 in a commercial cell format. The degradation in silicon-graphite anodes is originated from Li ion crosstalk between silicon and graphite, and the pressure-induced staging transition of the graphite. Here, the authors demonstrate a prismatic cell with improved volumetric energy density and cycle stability by targeted solving above issues.

Graphite is the most used anode material for current-generation lithium-ion batteries due to its beneficial cycle life, availability and reasonable rate capability. Still, the modest capacity of 372 mAhg-1 represents a bottleneck in the pursuit of high-energy density anodes. Enabling much higher theoretical capacities of 3600 mAhg-1 [1], silicon represents a promising candidate as anode material for next generation batteries. However, the alloying-based lithiation mechanism of silicon is accompanied by a large volumetric change of up to 300% upon cycling, leading to fast degradation due to electrode pulverization, continuous SEI formation and extensive electrolyte consumption. Even though shallow cycling of silicon anodes has been demonstrated in laboratory scale cells [2], the mixing of silicon with graphite is considered the most viable approach to lift energy density while maintaining appropriate cycle life. Due to the fundamentally different kinetics and potentials of Li insertion and extraction of both materials, the development of silicon-graphite composite electrodes is not straightforward. One of the key questions for optimization is how the incorporation of silicon impacts the (de)lithiation behavior of graphite as a function of the silicon:graphite mass ratio, operating current and electrode potential. While lithiation of graphite in composite electrodes of 15 wt% silicon has been shown to occur in a similar manner as pure graphite, higher fractions of silicon are expected to exert more stress on the graphite and represent kinetic barriers for Li diffusion. This study presents results from in-situ X-ray diffraction experiments (XRD) of silicon-graphite/Li half cells conducted at the European Synchrotron Radiation Facility (ESRF). Serving as a reference, the current-dependent (de)lithiation behavior of a pure graphite/Li half cell has been thoroughly investigated and systematically compared to the (de)lithiation behavior of two selected silicon-graphite composite anodes (silicon:graphite ratio of 30:70 and 70:30, respectively) exposed to the same formation cycle and C-rate protocol. An optimized and novel measurement setup was used, based on a perforated current collector of the anode, providing a complete picture of the graphite in-plane and interplanar structural changes as well as the evolution of semicrystalline silicon peaks which would usually be obscured by the current collector signal. By correlating the electrochemical features (voltage curve and differential capacity plot) with the in-situ diffraction data, it was possible to identify and assign the occurrence and absence of dilute-stage and ordered graphite intercalation compounds (GICs) for the respective electrodes, yielding an in-depth insight into the graphite state of charge upon (de)lithiation and how it is influenced by the silicon content and applied C-rate. As expected, the silicon is (de)lithiated within the entire potential range, whereas graphite is most electrochemically active at potentials lower than 260 mV. In both composite electrodes, graphite attains a lower lithiation degree compared to pure graphite. This is because the high theoretical capacity of silicon results in high specific currents, ultimately challenging the rate capability of graphite. Moreover, the high delithiation overpotential encountered in the composite electrodes results in a highly asymmetrical lithiation/delithiation behavior of graphite. Also, graphite lithiation is less uniform in the composite anodes, indicated by the coexistence of dilute GICs upon (de)lithiation, compared to pure graphite where dilute phases are fully consumed (formed) as (de)lithiation progresses. Surprisingly, the in-situ XRD studies did not reveal signs of structural degradation and strain of graphite as a result of mechanical interaction with silicon. Instead, the volume change of graphite is well correlated with the amorphization of crystalline, unreacted silicon and the volume evolution of silicon crystallites upon charge-discharge. To mitigate the observed effects, the work suggests nanostructuring and advanced electrode architectures towards higher utilization and more homogeneous lithiation of graphite. Overall, the study provides a demonstration of a suitable operando cell for studies of anodes for Li-based systems, and aids the rational design of silicon-graphite composite anodes. References: [1] M.N. Obrovac and L. Christensen, Electrochem. Solid State Letters (2004) vol. 7, A93-A96 [2] T. Eguchi, K. Sawada, M. Tomioka and S. Kumagi, Electrochim. Acta (2021), 394, 139115. [3] K.P. C. Yao, J. S. Okasinski, K. Kalaga, J. D. Almer, and D. P. Abraham, Adv. Energy Mater. (2019), 9, 1803380 Figure caption: A: Structure of the in-situ coin cell. B: Image of the electrode backside, showing the perforated current collector, the electrode active material and the spots of acquired diffractograms. C: In-situ XRD plot, voltage curve and differential capacity plot of a 30:70 silicon:graphite electrode operated at C/5. Five different stages of the (de)lithiation process are denoted. Figure 1

The reaction processes in Li‐ion batteries can be highly heterogeneous at the electrode scale, leading to local deviations in the lithium content or local degradation phenomena. To access the distribution of lithiated phases throughout a high energy density silicon‐graphite composite anode, correlative operando SAXS and WAXS tomography are applied. In‐plane and out‐of‐plane inhomogeneities are resolved during cycling at moderate rates, as well as during relaxation steps performed at open circuit voltage at given states of charge. Lithium concentration gradients in the silicon phase are formed during cycling, with regions close to the current collector being less lithiated when charging. In relaxing conditions, the multi‐phase and multi‐scale heterogeneities vanish to equilibrate the chemical potential. In particular, Li‐poor silicon regions pump lithium ions from both lithiated graphite and Li‐rich silicon regions. This charge redistribution between active materials is governed by distinct potential homogenization throughout the electrode and hysteretic behaviors. Such intrinsic concentration gradients and out‐of‐equilibrium charge dynamics, which depend on electrode and cell state of charge, must be considered to model the durability of high capacity Li‐ion batteries.

This research paper investigates the influence of varying silicon oxide (SiOx) content on the performance and aging of lithium-ion cells. In-depth investigations encompass charge and discharge curves, thickness changes, electrolyte degradation, gas evolution, and chemical analysis of cells with different silicon oxide proportions in the anode and their associated cathodes. The results show that a higher silicon oxide content in the anode increases the voltage hysteresis between charge and discharge. Moreover, the first-cycle efficiencies decrease with a higher silicon oxide content, attributed to irreversible LixSiy formation and the subsequent loss of active lithium from the cathode during formation. The anodes experience higher thickness changes with increased silicon oxide content, and peaks in differential voltage curves can be correlated with specific anode active materials and their thickness change. A gas analysis reveals conductive salt and electrolyte intermediates as well as silicon-containing gaseous fragments, indicating continuous electrolyte decomposition and silicon oxide aging, respectively. Additionally, a chemical analysis confirms increased silicon-derived products and electrolyte degradation on electrode surfaces. These findings underscore the importance of a holistic aging investigation and help understand the complex chemical changes in electrode materials for designing efficient and durable lithium-ion cells.

An attractive approach to increase the Li+-storage capacity of anode materials in Lithium-ion batteries (LiBs), is to replace or combine the routinely-applied graphite (372 mAh g-1) with higher-capacity materials. Among others, silicon (Si) with a theoretical capacity of 3579 mAh g-1 is a promising candidate [1]. Silicon is not yet been used as an anode material in its pure form, due to its low conductivity and volume increase of up to 300 % during lithiation. This two-step expansion (1st: Si + 2 Li+ + 2 e- → SiLi2.0; 2nd: SiLi2.0 + 1.5 Li+ + 1.5 e- → SiLi3.5) is a source of mechanical stress that can ultimately lead to battery failure. Furthermore, the initial lithiation of crystalline silicon (c-Si + 3.5 Li+ + 3.5 e- → SiLi3.5) causes an amorphization of the pristine crystalline lattice. This structural change causes further degradation of the material, which can hardly be avoided [2]. The main degradation mechanisms resulting from expansion and amorphization are I) The uncontrolled formation of a passivation layer due to the cyclic volume change taking place during (de-)lithiation, which leads to a continuous break-up and reformation of the solid electrolyte interphase (SEI). II) The pulverization of particles resulting in mechanical stress and the electrical isolation of particles or particle fragments delaminating from the electrode [3]. The first mechanism discussed is more dominant for nanometer scaled particles (nm-Si), while the second mechanism occurs mostly for particles in the micrometer range (µm-Si). Our approach combines, nm- or µm-sized Si particles with different matrix materials. By incorporating the particles into an either graphitic or soft carbon-like support, we aim to increase the conductivity of the electrode material and gain additional buffer space thereby reducing interparticle mechanical stress [4]. On the one hand, the systems of carbon-based anode materials are already well understood in terms of electrode composition, processing parameters, electrolyte compatibility, formation of a stable SEI and the resulting high cycling stability. On the other hand, the observed degradation mechanisms will occur with different predominance in different Si/C composites depending on the Si particle size and the chosen carbon matrix. However, the latter is not completely understood. We will address these issues by comparing different Si/C-composites consisting of nm-Si-particles or µm-Si particles in a reduced graphite oxide (rGO) matrix and in a graphite-matrix. Electrochemical methods, such as galvanostatic cycling, impedance spectroscopy and dq/dU-analysis in 2- and 3-electrode setups, were coupled with optical and spectroscopical techniques (e.g. XRD, FTIR, SEM) to trace back the electrochemically measurable degradation of the electrode to structural changes during formation and cycling. Particular attention was paid to the localization and analysis of defect areas with increased degradation by correlating the optical and spectroscopical results data with the lithiation and delithiation processes. Considering the different SoC levels, we can identify the ongoing aging of the different electrode materials. Based on this, we propose the use of soft carbon-like structures such as rGO as a matrix material for Si/C composites due to its higher cycling stability under the investigated conditions. References [1] Jeschull, F., Surace, Y., Zürcher, S., Lari, G., Spahr, M. E., Novák, P. u. Trabesinger, S.: Graphite Particle-Size Induced Morphological and Performance Changes of Graphite–Silicon Electrodes. Journal of The Electrochemical Society 167 (2020) 10, S. 100535 [2] Graf, M., Berg, C., Bernhard, R., Haufe, S., Pfeiffer, J. u. Gasteiger, H. A.: Effect and Progress of the Amorphization Process for Microscale Silicon Particles under Partial Lithiation as Active Material in Lithium-Ion Batteries. Journal of The Electrochemical Society 169 (2022) 2, S. 20536 [3] Dienwiebel, I., Winter, M. u. Börner, M.: Visualization of Degradation Mechanisms of Negative Electrodes Based on Silicon Nanoparticles in Lithium-Ion Batteries via Quasi In Situ Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy. The Journal of Physical Chemistry C 126 (2022) 27, S. 11016–11025 [4] Müllner, S., Held, T., Schmidt-Rodenkirchen, A., Gerdes, T. u. Roth, C.: Reactive Spray Drying as a One-Step Synthesis Approach towards Si/rGO Anode Materials for Lithium-Ion Batteries. Journal of The Electrochemical Society 168 (2021) 12, S. 120545

Silicon (Si) anodes are considered promising candidates for next-generation lithium-ion batteries (LIBs) due to their high theoretical capacity (≈10 times that of graphite). However, the substantial volume expansion during cycling (>300%) results in the degradation of the solid electrolyte interphase (SEI) and pulverization of Si anodes. Herein, an AlF3 coating layer is introduced onto commercial Si-C composites (Si-C@AF-x) as an artificial SEI layer, which effectively modulates the interfacial environment with higher kinetics and stability. The Si-C@AF-1 anode achieves excellent cycling stability (capacity of 916.0 mA h g-1 after 100 cycles at 0.5 C and retention of 91.6%) and rate capability (549.7 mA h g-1 at 3.0 C). Even under extreme temperatures, the AlF3 coating layer can still support the fast and stable operation of the Si-C@AF-1 electrode, and the Si-C@AF-1||NCM811 full cell delivers 85.2% capacity retention after 100 cycles at 0.5 C. This work proves the effectiveness of designing a robust artificial SEI for enhancing the interfacial kinetics and stability, which also fits well with the commercial-scale production of electrode materials, thereby highlighting its strong commercialization potential for high-durability LIBs.

Silicon graphite anodes have emerged as promising candidates to replace conventional graphite anodes due to their higher theoretical capacity and ability to store more lithium ions. However, the significant volume expansion of silicon during lithiation and delithiation cycles results in severe mechanical degradation and rapid capacity fade, limiting their practical application. Additionally, the realisation of electrodes with high Si content are further limited by poor diffusion kinetics, resulting in an insufficient rate capability performance and lithium trapping. In this study carbon nanotubes (CNTs) are incorporated into the silicon graphite anode matrix as a strategy to mitigate these issues and enhance the cycling performance of LIBs. The CNTs, with their unique mechanical, electrical, and chemical properties, offer numerous benefits, including enhanced structural integrity, improved electrical conductivity, and increased lithium-ion diffusion kinetics. We investigated the effect of different ratios of CNTs on the cycling performance of silicon graphite anodes. The electrochemical performance of the composite electrodes were systematically evaluated using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Preliminary results show that the addition of CNTs to silicon graphite anodes significantly improves their cycling stability and rate capability. The composites exhibit reduced capacity fade, improved coulombic efficiency, and enhanced rate performance compared to silicon graphite anodes absent of the CNTs, facilitated by faster lithium-ion diffusion kinetics, leading to improved electrochemical performance.

The expansion of renewable causing a rising demand for affordable and improved energy storage systems. Lithium-ion batteries (LIB) are one of the most promising technologies for this achievement, with further improvements to be made in terms of new materials and an advanced electrode architecture. As a new generation electrode material to be included in LIB, silicon is in the focus of the today’s investigations. Silicon offers one order of magnitude higher theoretical specific capacity (3579 mAh/g) compared to the state-of-the-art material graphite (372 mAh/g). However, during lithiation of silicon a volume expansion of up to 300 % takes place. Due to the huge volume expansion tremendous mechanical degradation of the anode occurs, resulting in a drop in capacity and a shorten lifetime. Laser induced forward transfer (LIFT) is applied in this study as printing technology to develop enhanced silicon-graphite electrode compositions and electrode architectures. LIFT was performed using a pulsed nanosecond UV-laser with a maximum power of 10 W and repetitions rate of up to 30 kHz. For the LIFT process of anodes, polyacrylic acid (PAA) is used as binder, in contrast to the polyvinylidene fluoride (PVDF) binder commonly used for LIFT assisted printing of electrodes. PAA is a more appropriate binder for silicon-containing anodes than PVDF. In addition, also a customized architecture using subtractive and additive laser process techniques is introduced for an increase in lifetime of batteries containing silicon-based electrodes. For this purpose, graphite electrodes were structured with an ultrashort pulse laser with pattern widths of 100 µm. Subsequently, silicon rich slurry was printed into the patterns to increase the areal capacity. The as-prepared electrodes have spatially separated graphite and silicon regions. The respective electrodes were electrochemically cycled in half-cells and charged at different C-rates up to 5C to investigate their lithiation capability. After the rate capability analysis, the cells were cycled at C/2 to investigate the long-term degradation. The cells with the printed electrodes were cycled for more than 450 cycles with a capacity fade of 5 %. At their end-of-life, the cells were analyzed post-mortem. Finally, full-cells were assembled with cathodes containing NMC 622 as the active cathode material. Subsequently to the cell priming a lifetime analysis was performed at a C-rate of C/2 and cycle stability as well as lithium loss during cycling were evaluated.

Silicon (Si) is regarded as one of the most promising anode materials for high-energy-density lithium (Li)-ion batteries (LIBs). However, Li insertion/extraction induced large volume change, which can lead to the fracture of the Si material itself and the delamination/pulverization of electrodes, is the major challenge for the practical application of Si-based anodes. Herein, a facile and scalable multilayer coating approach was proposed for the large-scale fabrication of functionally gradient Si/graphite (Si/Gr) composite electrodes to simultaneously mitigate the volume change-caused structural degradation and realize high capacity by regulating the spatial distributions of Si and Gr particles in the electrodes. Both our experimental characterizations and chemomechanical simulations indicated that, with a parabolic gradient (PG) distribution of Si through the thickness direction that the two Si-poor surface layers guarantee the major mechanical support and the middle Si-rich layer ensures the high capacity, the as-prepared PG-Si/Gr electrode can not only effectively improve the stability of the electrode structure but also efficiently enable high capacity and stable electrochemical reactions. Consequently, the PG-Si/Gr electrode with a mass loading of 3.15 mg cm-2 exhibited a reversible capacity of 579.2 mAh g-1 (1.82 mAh cm-2) after 200 cycles at 0.2C. Even with a mass loading of 8.45 mg cm-2, the PG-Si/Gr anodes still delivered a high reversible capacity of 4.04 mAh cm-2 after 100 cycles and maintained excellent cycling stability. Moreover, when paired with a commercial LiNi0.5Mn0.3Co0.2O2 (NCM532) cathode (9.56 mg cm-2), the PG-Si/Gr||NCM532 full cell revealed an initial reversible areal capacity of 1.64 mAh cm-2 and sustained a stable areal capacity of 0.94 mAh cm-2 at 0.2C after 100 cycles.

This study focuses on optimizing composite anodes through varying Si@TiO2 core-shell nanoparticle percentages in graphite. Material characterization reveals the morphological transformation of graphite and silicon nanoparticles into composite anodes. Electrochemical tests, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS), provide essential insights into the electrochemical behavior of these composites. In the cycling tests, Graphite with 5% core-shell (GrCS5), Graphite with 10% core-shell (GrCS10), and Graphite with 15% core-shell (GrCS15) show initial discharge capacities of 568, 675, and 716 mAh/g, retaining 76%, 75%, and 72% after 100 cycles, respectively. Conversely, the Gr/Si composite, commencing with 728 mAh/g, exhibits rapid degradation, retaining 54% after 100 cycles. Moreover, the EIS analysis reveals higher values of ohmic, solid electrolyte interphase, and charge transfer resistances in Graphite with 10% silicon (GrSi10) compared to other composite anodes after 100 cycles. The examination of the lithium diffusion coefficient indicates that GrCS5 demonstrates superior lithium diffusion kinetics, displaying the highest coefficient among all composite anodes. The research objective is to identify the optimal composite anode composition through quadrant analysis, considering specific capacity and lithium diffusivity after 100 cycles. In conclusion, integrating Si@TiO2 core-shell nanoparticles in graphite anodes improves their performance, with GrCS10 demonstrating notable effectiveness

Li‐ion battery degradation processes are multi‐scale, heterogeneous, dynamic, and depend on the battery usage. Degradation mechanisms during overcharge of LiNiO2 are well known at the material level featuring O2 gas release and concomitant surface reconstruction of LiNiO2. However, there are still debates regarding the role of the high voltage phase formation, so called O1, on gas production. Moreover, little information is available on the effect of produced gases on the cell components (anode or sensors), or the effect of overcharge on electrode level behavior. In this work, we simultaneously measure the gas evolution using operando mass spectrometry while spatially resolving nanostructure and crystallographic lattice parameter changes using operando micro small/wide angle X‐ray scattering (SAXS/WAXS) mapping during the formation and overcharge of a LiNiO2/Graphite─Silicon pouch cell. This new correlated operando characterization experiment allowed to (1) confirm the absence of O1 phase even with substantial gas produced at end of charge, (2) unveil the effect of gases on reference electrode and (3) show that overcharge increases in‐plane reaction heterogeneities by creating local degraded regions lagging behind the ensemble electrochemistry. These findings will be important to optimize ageing of devices based on similar chemistries, in particular Ni‐rich cathodes, while showing the strength of correlated characterization leading to more efficient and robust information on complex mechanisms.

Reasons for abrupt capacity fading in commercial LiNi0.8Co0.1Mn0.1O2 (NCM811)/SiOx-graphite pouch batteries were evaluated using electrochemical methods. These approaches consist of charge and discharge curves, differential curves and electrochemical impedance spectroscopy (EIS), and some advanced verification techniques constituting scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The predominance testament concerning capacity attenuation through experimental verification after the battery is disassembled proves that the silicon-based anode material deteriorates further, bringing about a significant number of cracks with the progression of cycles. In addition, electrolyte enters into the cracks, generating the excessive growth of the solid electrolyte interface (SEI) and the expansion of impedance, which eventually causes the failure of conductive networks, dilemma of ion transmission and increment in polarization, ultimately contributing to lithium dendrites.

Silicon is a promising anode material due to its high theoretical capacity, but its extreme volume change (>300%) during cycling leads to contact loss, electrode delamination, and crack propagation, ultimately compromising mechanical integrity. While operando imaging captures morphological evolution, it remains insufficient to resolve the coupled electrochemical, mechanical, and microstructural dynamics that govern degradation. Here, a microstructure-resolved digital twin model of SiOx/graphite composite electrodes is presented to diagnose electrochemo-mechanical behavior. A 3D structure reconstructed from high-resolution FIB-SEM tomography is integrated into a coupled simulation framework that captures Li⁺ diffusion, interfacial electrochemical reactions, and concentration-dependent mechanical strain. Simulations reveal that volumetric expansion distorts internal conduction pathways-enhancing electronic conduction via broadened solid-solid interfaces while impeding ion transport through increased tortuosity. Moreover, charge-rate-dependent analysis shows that the charging rate governs the balance between the state of charge (SoC) and local stress. Increasing the rate from 0.5C to 4C reduces stress by limiting the SoC level, thereby mitigating mechanical degradation and enhancing cycling stability. This digital twin framework enables quantitative diagnostics of stress-driven failure and offers design guidelines for the development of mechanically robust, high-performance silicon-based anodes.

High-performance lithium-ion batteries (LIBs) are in increasing demand for a variety of applications in rapidly growing energy-related fields including electric vehicles. To develop high-performance LIBs, it is necessary to comprehensively understand the degradation mechanism of the LIB electrodes. From this viewpoint, it is crucial to investigate how the electrical properties of LIB electrodes change under charging and discharging. Here, we probe the local electrical properties of LIB electrodes with nanoscale resolution by scanning spreading resistance microscopy (SSRM). Via quantitative and comparative SSRM measurements on pristine and degraded LIB anodes of Si-C composites blended with graphite (Gr) particles, the electrical degradation of the LIB anodes is visualized. The electrical conductivity of the Si-C composite particles considerably degraded over 300 cycles of charging and discharging, whereas the Gr particles maintained their conductivity.

Silicon (Si), which delivers higher capacity than that of graphite, is an adequate material for enhancing the energy densities of lithium-ion batteries (LIBs). However, rapid capacity deterioration has made it difficult for practical use and commercialization. Furthermore, there is limited understanding regarding the degradation conditions and mechanisms of Si anode. Thus, our study aims to elucidate the degradation behavior and conditions of Si anodes while exploring the underlying degradation mechanisms. To investigate the degradation conditions of Si anodes, we conducted electrochemical experiments on NCM||Si full cells under various conditions. Cycling under sparse and ample electrolyte conditions was compared. It revealed stable cycling up to 400 cycles under sufficient conditions, while a rapid deterioration was observed after 200 cycles under sparse conditions. Additionally, we compared cycling performance under room temperature and elevated temperature conditions. Unlike conventional graphite-based LIBs, which typically exhibit more unstable cycling at high temperatures than room temperatures, NCM||Si full cells demonstrated more stable cycling behavior at elevated temperatures. While a sharp degradation occurred after approximately 200 cycles at room temperature, high temperatures yielded a remarkable 99.8% Coulombic efficiency and stable cycling beyond 300 cycles. Moreover, cycling performance was compared at low and high C-rates. At low C-rates, lifetimes exceeding 300 cycles were observed, whereas at high C-rates, rapid degradation commenced around 250 cycles. Through degradation condition experiments, we confirmed that Si anodes experience accelerated degradation with sparser electrolytes, lower temperatures, and higher C rates. Conditions of low temperature and high C-rate kinetically limit the movement of electrons and Li ions. Therefore, we hypothesized that the observed degradation behavior of Si may be attributed to restricted kinetics. To investigate this, we conducted Electrochemical impedance spectroscopy (EIS) measurements on Si, Si/Gr composite, and graphite (Gr) anodes across various states of charge (SOC). Our findings revealed pronounced differences in resistance behavior among these materials throughout the lithiation process. While graphite exhibited a linear resistance increase with lithiation, the Si/Gr composite maintained low resistance. However, pure Si anodes exhibited low resistance up to SOC60 but sharply increased resistance, quadrupling at SOC80. This observation suggests that Si encounters a significant kinetic barrier at high SOC ranges, which likely serves as a primary trigger for degradation. To enhance our comprehension of the degradation mechanism, we examined electrode surfaces post-cycling through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In the degraded Si electrode after 200 cycles, we observed pits scattered throughout the electrode surface which appeared to result from repeated expansion and contraction cycles. Furthermore, through EDS image analysis, we noted a significant increase in F peak content in areas where the Si peak had decreased. These observations suggest a correlation between the degradation of Si electrodes and an increase in side-reaction with electrolytes. It is known that Si undergoes a structural transformation from amorphous to crystalline, forming an over-lithiated structure, within a voltage range of less than 50 mV. Unlike graphite, which undergoes lithiation by intercalation, Si undergoes lithiation by chemical transformation, resulting in different products depending on the operating voltage. Therefore, understanding the actual driving voltage range of Si anodes is crucial for deducing the products of Si during charging and discharging. Thus, we conducted a three-electrode experiment in NCM||Si full cells. During the charging and discharging, the actual operating voltage of the Si electrode was observed to range from 0.031V to 2V. Similarly, in NCM||SiGr full cells, the actual operating voltage of the SiGr electrode ranged from 0.073V to 0.85V. Given that charging and discharging of the Si electrode occur even below 50mV, it suggests the presence of overcharged crystalline Si. To confirm the existence of this crystalline Si, we additionally conducted X-ray diffraction (XRD) and dQ/dV analysis. XRD analysis of degraded electrodes exhibited that as the cycle increased, indicating accelerated degradation, the peak of crystalline Si increased. The trend of increasing crystalline peak with progressing degradation was also confirmed through dQ/dV analysis. In conclusion, We observed the degradation behavior on Si electrodes and confirmed that the generation of over-lithiated crystalline Si is the main degradation cause. This discovery is expected to contribute to the future development of Si-based LIBs by providing valuable insights into achieving long cycles of Si anodes.

Silicon with a high gravimetric capacity of 3579 mAh g-1 of the pure material becomes increasingly common in the anode of lithium-ion batteries to increase energy density on the full cell level. However, silicon changes its volume excessively during (de-)lithiation making it prone to ageing. In commercial cells, it is typically applied as SiOx in small quantities in a composite anode together with graphite. Gas analytical studies of Gr/SiOx||NMC622 cells with varying silicon content and carbonate-based electrolyte are presented. The electrolyte consists of 1M LiPF6 in EC:DEC (1:1, v/v) + 5 wt-% FEC. The focus of this study is on investigations of ageing processes such as electrolyte decomposition during formation cycling. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. The different cell specifications were examined by operando mass spectrometry (MS) and post-mortem gas chromatography-mass spectrometry (GC-MS). Strong gas formation leads to a loss of electrolyte, which can cause the cell to dry out and consequently limit the cycle life. Gas analysis is a suitable method to identify decomposition products as well as to illustrate degradation reactions. Operando MS can be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge. Furthermore, a post-mortem GC-MS analysis was performed to identify the individual substances qualitatively. The cyclic formation of several degradation products can be determined. Among others, carbon dioxide, hydrogen as well as ethane are identified as characteristic decomposition products of the electrolyte. In addition, the decomposition path of the conducting salt can be detected. Another main result is the evidence of the presence of silicon-containing gaseous fragments as a function of the Si-content in the composite anode. These gas analytical studies of silicon graphite composite anodes provide an important contribution to the understanding of the degradation reactions taking place. The results shown help to illustrate them and give information about the influence of the silicon content on electrolyte degradation. Figure 1

Among anode materials for next-generation lithium-ion batteries, silicon derivatives play a key role, but their main degradation mechanisms were not yet observed in real-time. In this work, the microstructural evolution of a composite graphite - SiOx electrode was examined operando using an ionic liquid electrolyte and scanning electron microscopy during tenfold constant current application. On the electrode level, significant particle movement with large local strains that may result from binder damage or particle - binder interface cracking was observed. Novel continuous operando observation on particle level of the composite electrode in a liquid electrolyte was realized. On the particle level, irreversible deformation occurred but no indication for cracking was found. The focus of this article lies on the detailed presentation and discussion of the operando method and the used sample holder as well as the reliability and the interpretation of the combined microscopic and electrochemical data.

Promoting energy density while maintaining outstanding cycling stability and fast-charging ability is a key objective for the widespread utilization of lithium-ion batteries. Unfortunately, the most promising batteries with silicon/graphite (Si/Gr) composite anodes still face the issues of instability and high cost. The cognition of instinctive lithiation behavior between Si and Gr is incomplete. Here, the (de)intercalation and (de)alloying process is distinguished by increment capacity analysis, and the capacity degradation of each phase transform process is quantified with different current rates. The capacity contribution of graphite is easily inhibited by the alloying process of Si, which leads to an incomplete utilization of graphite. Besides, the Li+ accumulation in Si will deteriorate the cycling stability of the anode. The interplay between Si and graphite under different current rates is concluded, which will benefit the material engineering and help to improve the life span of Si-containing batteries.

High‐energy‐density lithium‐ion batteries are crucial for accelerating the widespread adoption of electric vehicles. Silicon monoxide/graphite (SiO/Gr) composite anodes have attracted considerable attention as promising candidates for increasing energy density. However, severe capacity degradation caused by the large volume changes of SiO during charge–discharge cycles remains a major obstacle to commercialization. One effective strategy to address this issue is to limit the charge/discharge operating voltage range (swing range) of the SiO anode. In this study, a cathode design composed of single‐crystalline and polycrystalline LiNi0.8Co0.1Mn0.1O2(NCM811) with a bimodal particle size distribution is proposed to effectively control the charge–discharge operating range of the SiO anode within a full‐cell. This design leverages the reaction heterogeneity of the cathode particles to induce an increase in overpotential at the end of discharge, effectively lowering the discharge endpoint potential of the anode. This design strategy enables stable cycling performance without compromising full‐cell energy density by selectively controlling the discharge depth of SiO in the SiO/Gr anode. The effectiveness of this design is validated through various electrochemical analyses and real‐time operando X‐ray Diffraction (XRD), demonstrating that it is an efficient strategy to enhance the long‐term cycle stability of SiO/Gr anodes without sacrificing energy density.

The rapid expansion of the electric vehicle market has accelerated the development of lithium-ion batteries with extended driving ranges, enhanced power output, and prolonged cycle life. In this context, SiOx has emerged as a promising next-generation anode material, offering a high theoretical capacity (700~1600 mAh g-1) and relatively moderate volumetric expansion (~150%) compared to pure silicon (~400%). This characteristic enables the use of thinner electrodes for equivalent capacities, potentially shortening lithium-ion transport distances and thereby allowing faster charging. Despite these advantages, the substantial volume changes of SiOx during cycling remain a significant challenge. In particular, excessive volume expansion can lead to structural degradation and mechanical stress within the electrode, ultimately resulting in the loss of electrical contact due to current collector delamination, active material debonding, and particle pulverization. Such degradation disrupts both electrical and binder connectivity, leading to poor electrical conductivity and diminished electrochemical performance. Therefore, it is crucial to achieve a comprehensive understanding and quantitative assessment of the mechanical stresses generated during charging. However, directly visualizing micro-scale structural changes and internal stresses is inherently difficult. To overcome these limitations, we employed digital-twin simulations to elucidate the coupled electrochemical and mechanical responses of SiOx/graphite composite electrodes under various charging rates. Using the finite volume method, we analyzed real-time structural changes and mechanical stresses during lithiation. Additionally, we used the high-resolution FIB-SEM imaging to provide an accurate 3D reconstruction of the SiOx/graphite composite electrode morphology. The simulated voltage profiles closely matched experimental measurements, confirming the accuracy of our simulation results. Our findings demonstrate that faster charging reduces the state of lithiation due to polarization effects, whereas slower charging leads to more significant volumetric changes and localized stress concentrations. These stresses were particularly pronounced around SiOx agglomerates and at SiOx/graphite interfaces, underscoring the importance of controlling SiOx distribution to mitigate localized stress. Moreover, the simulations reveal that severe volume expansion can induce pore blockage and increase ionic transport distances, ultimately affecting electrode porosity and tortuosity. By facilitating quantitative assessments of mechanical stress in realistic electrode structures, this digital-twin simulation provides invaluable insights for electrode design and enables early evaluation of mechanical stability. These insights will help pave the way for the development of more durable and reliable SiOx-based electrodes in lithium-ion batteries.

This study investigates the calendar ageing behaviour of NMC811//SiOx-graphite 21700 cylindrical cells (LGM50), which were held at varying states of charge (SoC), for up to 70 weeks at 4 different temperatures. Throughout the ageing study, capacity and internal resistance were monitored, and significant capacity loss over time, with greater loss at high SoC and temperature, were observed. A combination of electrochemical testing and post-mortem characterisation techniques point to the anode, more specifically, the silicon-oxide particles, as the driver of capacity fade through unstable solid-electrolyte interface dynamics, leading to the gradual loss of lithium inventory. Despite the greatest capacity loss being at ~80% SoC and the apparent improvement in capacity retention at higher SoCs, i.e. the “spoon-shape effect”, the degradation is most pronounced at 100% SoC, driven by the instability of the silicon-oxide SEI. This is demonstrated by post-calendar ageing cycling of the cells, where those aged at 100% SoC degraded at a faster rate than 80% SoC.

Utilizing multiple active materials is one method for increasing the gravimetric capacity of lithium-ion battery anodes while balancing material-based tradeoffs for high-performing battery technologies. Silicon is a popular anode material due to its high capacity. However, when paired with graphite, silicon often comprises only a small fraction (<15%) of the active anode material due to its high-volume expansion upon lithiation, which causes rapid degradation. Mixing active materials not only affects finite properties such as capacity and degradation rate but also changes lithiation dynamics due to differences in lithiation reaction kinetics and material heterogeneity. “Transfer-lithiation” is a phenomenon that has been recently observed in silicon-graphite anodes during a rest period after lithiation. 1 During transfer-lithiation, lithium typically crosses from graphite to silicon within the anode without an external exchange of current. Transfer lithiation can result in a change in the electrode’s state of health, volume expansion, and open-circuit voltage. The effects of transfer lithiation are rate-, material-, and composition-dependent and should be characterized and considered when designing mixed active material electrodes for advanced batteries. In this work, transfer-lithiation in anodes containing silicon nanoparticles and coal-derived soft carbon active materials are investigated and preliminary results are discussed. Samples of coal-derived soft carbon heat treated at different temperatures are tested to observe the effects of varying microstructures on transfer-lithiation. First, thermodynamic analysis using pseudo-OCV is coupled with modeling to establish the thermodynamic lithiation behavior of the materials. 2 Then, transfer-lithiation is investigated during rest periods following lithiation/delithiation pulses at varied applied currents. Overall, this work emphasizes material property performance relationships regarding lithiation dynamics and methods for observing transfer-lithiation phenomena. References: L. Frankenstein et al., ChemSusChem , e202401290 (2024). A. Paul et al., J. Electrochem. Soc. , 171 , 023501 (2024).

Silicon anode is an appealing alternative to enhance the energy density of lithium-ion batteries due to its high capacity, but it suffers from severe capacity fade caused by its fast degradation. The crossover of dissolved transition-metal (TM) ions from the cathode to the anode is known to catalyze the decomposition of electrolyte on the graphite anode surface, but the relative impact of dissolved Mn2+ versus Ni2+ versus Co2+ on silicon anode remains to be delineated. Since all three TM ions can dissolve from LiNi1-x-y Mnx Coy O2 (NMC) cathodes and migrate to the anode, here a LiFePO4 cathode is paired with SiOx anode and assess the impact by introducing a specific amount of Mn2+ or Ni2+ or Co2+ ions into the electrolyte. It is found that Mn2+ ions cause a much larger increase in SiOx electrode thickness during cycling due to increased electrolyte decomposition and solid-electrolyte interphase (SEI) formation compared to Ni2+ and Co2+ ions, similar to previous findings with graphite anode. However, with a lower impedance, the SEI formed with Mn2+ protects the Si anode from excessive degradation compared to that with Co2+ or Ni2+ ions. Thus, Mn2+ ions have a less detrimental effect on Si anodes than Co2+ or Ni2+ ions, which is the opposite of that seen with graphite anodes.

Silicon (Si) has been well recognized as a promising candidate to replace graphite because of its earth abundance and high‐capacity storage, but its large volume changes upon lithiation/delithiation and the consequential material fracturing, loss of electrical contact, and over‐consumption of the electrolyte prevent its full application. As a countermeasure for rapid capacity decay, a composite electrode of graphite and Si has been adopted by accommodating Si nanoparticles in a graphite matrix. Such an approach, which involves two materials that interact electrochemically with lithium in the electrode, necessitates an analytical methodology to determine the individual electrochemical behavior of each active material. In this work, a methodology comprising differential plots and integral calculus is established to analyze the complicated interplay among the two active batteries and investigate the failure mechanism underlying capacity fade in the blend electrode. To address performance deficiencies identified by this methodology, an aluminum alkoxide (alucone) surface‐modification strategy is demonstrated to stabilize the structure and electrochemical performance of the graphite‐Si composite electrode. The integrated approach established in this work is of great importance to the design and diagnostics of a multi‐component composite electrode, which is expected to be high interest to other next‐generation battery system.

Silicon–carbon (Si–C) composite anodes are a promising pathway to enhance the energy density of lithium-ion batteries (LIBs), yet the substantial volume changes of silicon during (de)lithiation cause mechanical degradation, capacity fading, and safety risks that hinder practical use. To address these challenges, we develop an electrochemical–thermal–mechanical coupled model tailored for LIBs with Si–C anodes. Built upon the Newman pseudo-two-dimensional framework, the multi-scale model integrates particle-, electrode-, and cell-level submodels. Electrochemical–mechanical coupling is captured through intercalation-induced particle expansion and cell-level thermal expansion, while bidirectional electrochemical–thermal coupling is introduced via a lumped thermal model with temperature-dependent electrochemical kinetics. The model is validated against experimental data, accurately reproducing current–voltage profiles, temperature rise, and displacement under various operating conditions. Simulations further reveal the distinct contributions of silicon and graphite: although silicon accounts for only a small fraction of anode mass, it can contribute 30% to the capacity of the cell owing to the high specific capacity of Si. At the same time, while silicon particles undergo volume changes exceeding 300%, the overall cell expansion remains below 7.5% due to structural dilution effects from other components. These findings establish a quantitative link between silicon content, electrochemical behavior, and cell expansion, providing theoretical guidance for the rational design of high-energy-density LIBs.

The rapidly growing demands on energy storage technologies over the last decade have imposed further requirements for the high energy/power density, safety, and durability of lithium-ion batteries (LIBs). Si/C composite materials have attracted enormous research interest as the most promising candidates for the anodes of next-generation lithium-ion batteries, owing to their high energy density and mechanical buffering property. However, the major disadvantage of materials with ultra-high capacities, such as Si-based materials, is the significant volume change during cycling, which further leads to mechanical and electrochemical degradation. However, a sophisticated and quantitative understanding of the highly electrochemical-mechanical coupling behaviors is still lacking. A comprehensive computational model is indispensable in the developing process of the excellent performance of anode material due to the low-realizability, inconvenience, and high-cost of experiments, which also provides powerful tools for fabrication guidance of novel Si/C composites designs. Hence, a multiphysics modeling framework is established with a detailed geometric description to quantitatively reveal the underlying governing mechanisms of Si/C composite anode behaviors. We studied the effects of the Si weight percentage, the Si-related particle distribution, the Si-related particle size, the mechanical constraint, and the binder domain gradient on the battery performance regarding the potential behavior, capacity delivery, mechanical stress/strain, Li plating, and polarization evolution. In our study, we used silicon monoxide (SiO) as the Si element source and graphite (Gr) as the C element source. Results discover that an 8-10 wt% of SiO would be an optimal choice regarding capacity delivery and minimizing Li plating under 1C constant current charging condition. Positioning SiO particles near the separator and reducing the sizes of SiO particles are also demonstrated to be beneficial for electrochemical performance with trivial influence on mechanical mismatch. In addition, the mechanical constraint demonstrates a balanced effect on the overall performance of cells and the local behaviors of particles. Our findings also indicate that reducing the proportion of carbon-binder domain (CBD) in the upper domain (near the anode surface) compared to the lower domain (near the current collector) positively influences electrochemical performance, particularly in terms of capacity and Li plating. However, such an arrangement introduces potential risks of mechanical failures and we recommend to incorporate a higher proportion of CBD alongside the SiO particles. Finally, an anode design with a lower CBD proportion in the upper domain exhibits superior rate performance. This study explores the multiphysics behavior of Si/C anodes material using a comprehensive methodology combining experimental and FEA techniques, systematically revealing the coupling mechanism among various physical fields, as well as providing efficient and powerful tools in the design, development, and evaluation of high energy density lithium-ion batteries.

The utilization of polymeric binders is indispensable in the implementation of silicon/carbon anode materials in high-energy-density lithium-ion batteries (LIBs). This necessity arises from their pivotal function in upholding structural integrity. However, current water-based binders solely focus on binder adhesion, neglecting the crucial interaction with the carbon material. In this work, a composite binder (CMC-CPAM-SBR) was constructed by combining Styrene Butadiene Rubber (SBR) with cationic polyacrylamide (CPAM) network binder with self-healing carboxymethyl cellulose (CMC). This innovative binder formulation was designed to enhance the performance of Si@C/graphite composite anodes. A capacity retention rate of 92.86% was achieved after 100 cycles, which represents the improvement over the performance of electrodes utilizing the CMC-CPAM binder, which only retained a capacity of 84.53% after the same number of cycles. A full battery with a capacity of 1992.8 mAh was designed, and the battery capacity remained at 80.6% of its capacity after completing 500 cycles. This research presents an effective technique for manufacturing high-performance anode materials.

Composite electrodes, especially silicon/carbon (Si/C) anodes, present significant opportunities for advancing the energy density of lithium-ion batteries (LIBs). However, challenges emerge, particularly in performance metrics when a high weight percentage of Si beyond 8-10 wt.% is employed 1. A nuanced understanding of the solid electrolyte interphase (SEI) in Si/C composites is imperative to overcome these limitations and enhance energy density. Conventional techniques such as ex-situ X-ray photoelectron spectroscopy and cryogenic electron microscopy face inherent drawbacks, including exposure to ultrahigh vacuum and the need for solvent washing, potentially altering the SEI layer 2. In contrast, nano-FTIR, utilizing Fourier transform infrared near-field spectroscopy, overcomes these challenges, enabling non-destructive probing of the SEI layer's chemistry and structure at room temperature within an inert atmosphere 3–5. In this study, we engineer custom-patterned electrodes featuring amorphous Si on atomically flat highly ordered pyrolytic graphite (HOPG) to emulate model composite electrodes. Leveraging nano-FTIR spectroscopy, near-field nanoscale white-light imaging, and atomic force microscopy measurements, our investigation reveals that the SEI on HOPG is enriched in organic lithium ethylene decarbonate (LiEDC), while the SEI on lithiated silicon unveils the presence of inorganic Li2CO3. Notably, we unveil a unique "mixed" SEI layer zone at the Si/HOPG interface, comprising a mixture of dominant SEI species from the surfaces of both the lithiated Si and the HOPG. The coexistence of these species suggests the formation of an SEI layer with presumably unique physicochemical properties, forming along Si-C interfaces in Si/C composite electrodes. These findings provide a comprehensive approach to studying model composite electrodes and offer valuable insights into optimizing the surface passivation of Si/C composite electrodes for high-performance LIBs. Acknowledgments This research was supported by the US Department of Energy (DOE)’s Vehicle Technologies Office under the Silicon Consortium Project directed by Brian Cunningham and managed by Anthony Burrell. References V. G. Khomenko and V. Z. Barsukov, Electrochim Acta, 52, 2829–2840 (2007). J. Wu, M. Ihsan-Ul-Haq, Y. Chen, and J. K. Kim, Nano Energy, 89, 106489 (2021). X. He, J. M. Larson, H. A. Bechtel, and R. Kostecki, Nat Commun, 13, 1398 (2022). I. Yoon, J. M. Larson, and R. Kostecki, ACS Nano, 17, 6943–6954 (2023). A. Dopilka, Y. Gu, J. M. Larson, V. Zorba, and R. Kostecki, ACS Appl Mater Interfaces, 15, 6755–6767 (2023).

The adoption of silicon-graphite composites as anode materials for the next generation of lithium-ion batteries with enhanced specific capacity requires complex technological efforts in order to mitigate the problem of the quick performance fading of electrodes due to the mechanical degradation of materials. The matter is currently being addressed in terms of electrolyte components, polymer binders, materials structure and morphology itself, as well as current collector design, which differ greatly in cost and scalability. The present work describes the efficacy of Cu foil perforation—a simple, low-cost, and easily scalable approach—as a means of Si/C composite anode performance stabilization during extensive charge-discharge cycling. The NMC||Si/C pouch-type full cells demonstrated over 90% of initial capacity retention after 100 charge-discharge cycles in the case of a 250 µm perforated Cu foil used as a current collector, compared to only 60% capacity left in the same conditions for plain Cu foil as an anode. The obtained result is related to the prevention of anode material delamination off the foil surface as a result of silicon expansion and contraction, which is achieved through the formation inter-penetrating metal-composite structure and the presence of “stitches”, connecting and holding both sides of the electrode tightly attached to the current collector.

Numerous volume changes and sluggish kinetics causing irreversible Li-trapping and, consequently, a dramatic capacity decline during cycling are the main challenges facing Si-based anodes in all-solid-state batteries (ASSBs). The incorporation of carbon and Si significantly combats volume change and enhances electronic transport but cannot eliminate Li-trapping. Herein, we partially solve this issue by adding Li3.75Si alloy into a Si/C composite as a Li reservoir by making either a bilayer electrode or a blended electrode. We demonstrate that the bilayer electrode has superior cycling performance but suffers from soft shorting problems at high current density. This contrasts with the blended electrode, which exhibits a three-fold higher electrode critical current density (CCD), as captured from a self-designed three-electrode cell, but with limited cycling performance. In addition, we present the positive effect of adding a solid electrolyte (SE) to the blended electrode and show that ASSBs having Ni-rich cathodes and SE-containing blended negative electrode can achieve 500 stable cycles at 0.8 mA/cm2 and 183 cycles at 3 mA/cm2 due to the enhanced ionic/electronic percolations. Altogether, these results provide further insights into achieving long-lifespan, high-rate, and dendrite-free Si-based ASSBs through regulation of the electrode structure and composition.

Silicon (Si) is regarded as one of the most promising anode materials for Li‐ion batteries (LIBs) owing to its high specific capacity of 3579 mAh g–1 and low redox potential. However, large volume changes in Si during lithiation/delithiation cycles lead to microcrack formation in the electrode and rupture of the solid electrolyte interphase (SEI) layer, resulting in poor cycling stability. In this regard, Si/carbon (Si/C) composites have been widely explored to mitigate the volume changes in Si and increase the Li‐ion kinetics. However, the mechanochemically unstable SEI layer is still challenging for the development of high‐energy‐density Si/C anodes. In this study, polyvinylpyrrolidone (PVP) is introduced as a mechanochemically boosting electrode additive (MBEA) to enhance the chemical and mechanical stability as well as the electrochemical performance of Si/C composite anodes in LIBs. PVP can stabilize the anode interface by forming a robust inorganic‐rich SEI layer, which improves the Li‐ion kinetics owing to its chemical stability and mechanical integrity. Furthermore, PVP on the surface of Si/C composite anodes enhances the binding affinity, including the adhesion and cohesion properties of the active materials. In these regards, the Si/C anodes with MBEA (Si/C‐MBEA) exhibit excellent electrochemical performance with alleviated volume changes compared with the pristine Si/C anode. This study presents a facile and practical approach for the development of high‐performance Si‐based anodes for next‐generation LIBs.

Silicon is a prime candidate for next-generation lithium-ion batteries (LIBs) due to its high theoretical gravimetric capacity (~3500 mAh g -1 ) and low reduction potential (< 0.4 V vs. Li). However, Si displays extreme expansion, on the order of 300 %, over the course of lithiation. Volume changes in Si during (de)lithiation not only impacts performance of the electrode through delamination and particle isolation but also poses a serious strain problem for battery systems engineering. Several strategies, including prelithiation and particle engineering, have been developed to ameliorate problems associated with volume changes of silicon anodes. In this work, we deposited nano-sized silicon onto various carbon scaffolds (porous and non-porous) via silane (SiH 4 ) chemical vapor deposition (CVD) at elevated temperature to form a silicon-carbon composite (Si/C). The carbon scaffold serves to anchor the nanoparticles to a larger conducting particle and provides void space for the silicon to expand into. We investigated the expansion/contraction characteristics of electrodes containing the Si/C composite and compared the data with those containing a sub-micron size silicon (without a carbon scaffold) using in-situ dilatometry ( Figure 1 ). The Si electrode exhibited an expansion of ~300 % at the end of lithiation; only a portion of this expansion was reversible upon delithiation. On the other hand, the Si/C electrode with a scaffold made of acetylene black showed a ~35% expansion and complete reversibility upon delithiation. In this presentation, the relative expansions of these electrodes and their reversibility will be correlated with other electrochemical properties such as capacity, impedance, and voltage profiles. Physicochemical properties, such as particle morphology, silicon content, and scaffold textural properties of the materials will also be discussed. Figure 1. Electrode expansion vs. capacity for Si (black) and Si/C composite (red) electrodes over the course of lithiation (solid line) and delithiation (dashed line). Figure 1

Silicon (Si) has been considered as the most promising anode material for next-generation high-capacity Li-ion batteries due to its very high theoretical specific capacity. However, the large deformation associated with (de)lithiation and its detrimental consequences like pulverization, loss of electrical contact, and subsequent capacity loss, have long been a roadblock in deploying high-capacity electrodes. Grafting small amounts of Si with graphite has been proven to utilize the higher capacity of silicon and the stability of graphite. The intricacies of interactions between the two active materials and their effect on the overall performance of the composite electrode are still not well known. Here, we present a novel fully coupled multiphysics electrochemical-mechanical model based on 3D microstructure extracted from X-ray tomography scans of Si-C composite electrode. The theoretical framework integrates the large deformation and viscoplastic response of Si, and the two-way coupling between diffusion and interfacial reactions with mechanical stress. The resolution of the pore phase from the silicon and graphite phases allows for the simulation of the Li+ ion kinetics in the composite electrode and influence of the microstructure. The model is employed to study the phenomena of preferential lithiation, crosstalk between active materials, partial utilization due to mechanical influences, and develop strategies to maximize the specific capacity. Lastly, we also explore the potential and avoidance of mechanical damage within active materials and interfacial delamination. The first-of-its-kind 3D microstructure resolved, multi-material model presents a novel tool to simulate the performance of Si-C composite electrode and decode the depth of interactions between the active materials.

Silicon (Si) anodes offer excellent lithium storage capacity for lithium‐ion batteries but face practical limitations due to significant volume expansion and low intrinsic electrical conductivity. These issues lead to side reactions that consume the electrolyte and impede ion‐electron transport, resulting in low areal loading (<2 mg cm⁻²) and restricted energy density. To address this, a scalable method is developed using spray drying of commercial graphite flakes (s‐Gr) and nanosilicon particles (n‐Si), followed by chemical vapor deposition to create microscale Si/C anodes (s‐Gr/n‐Si/VGs). Thin vertical graphene nanosheets (VGs) are grown on the surfaces and within the internal pores, forming a robust, micron‐sized Si/C spherical composite material. The VGs construct the conductive network, allowing the electrodes to operate at high areal loadings without pulverization and promoting LiF‐enriched solid electrolyte interphase for improved cycling stability. The s‐Gr/n‐Si/VGs maintain a capacity of 641.9 mAh g⁻¹ after 1000 cycles at 11.0 mg cm⁻², retaining 95.9% capacity. In pouch cells with NCM811 cathodes, the 5.0 Ah‐level cells achieved 80.0% capacity retention after 510 cycles at 1.0 C. This research provides a feasible pathway for manufacturing high‐performance, low‐cost, and scalable Si/C anodes suitable for high‐energy‐density lithium‐ion batteries.

Silicon (Si) anode is the most promising alternative for next generation lithium-ion batteries (LIBs) owing to large theoretical capacity, low working voltage and abundant natural resources. However, tremendous volume change of Si during the (de)lithiation processes causes repetitive formation of solid electrolyte interphase (SEI) layers, loss of electrical contact and electrodes pulverization, limiting its commercial application. Herein, we fabricate an interconnected hollow Si-C nanospheres/graphite composite via a facile and scalable approach. Notably, hollow Si-C nanospheres and graphite are homogeneously combined by using the surfactants as surface modifiers of graphite and introducing carbon dioxide (CO2) into magnesiothermic reduction reaction, resulting in the enhanced compatibility between hollow Si-C nanospheres and graphite, and the well-established electrical conductive network. The resultant Si-C nanospheres/graphite composite anode with carbon content of 59 wt% delivers a large reversible specific capacity of 662 mAh g-1 and a high capacity retention of 65.7% at 0.5 A g-1 after 200 cycles. Such excellent rate performance and superior cycling performance are attributed to high electrical conductivity and buffering effect of graphite, superior compatibility between hollow Si-C spheres and graphite, uniform distribution of both Si-C nanospheres with a unique hollow architecture and graphite flakes inside the composites and well-established interconnected electrical conductive carbon networks, which can effectively alleviate Si volume expansion and maintain good electrical contact during cycling. This strategy provides insights into designing Si-based anodes for practical LIBs.

The structural evolution of silicon oxide/graphite (SiOx/Gr) composite anodes under SiOx expansion is systematically investigated to address the lack of in‐depth studies on the mechanical disparities between Si‐based materials and graphite during operation. In this work, the electrode structure evolution is evaluated with a series of composite anodes with different SiOx/Gr ratios through electrochemical performance tests and structural characterization, focusing on pore growth and solid electrolyte interphase (SEI) renewal induced by active material volume changes. The results reveal that the continuous volume change of SiOx leads to uneven stress distribution within the electrode, which further causes mechanical fatigue and structural fractures of active materials. Notably, the replacement of modified SiOx material with artificial coating improves structural integrity and cycling performance, enabling the composite anode to maintain a capacity of 373 mAh·g‐1 even at 1 A·g‐1 after 1000 cycles. These findings demonstrate that optimizing stress distribution and structural evolution is critical for enhancing the mechanical stability and electrochemical performance of SiOx/Gr composite anodes. This study provides fundamental insights into the failure mechanisms of SiOx/Gr composite anodes and highlights the necessity of rational electrode design strategies to develop high‐capacity, long‐cycle‐life anode materials for next‐generation lithium‐ion batteries.

The primary failure behavior of Si‐based anodes is electrode fracture, which results from significant volume changes during electrochemical cycling. Binders play an essential role in maintaining electrode integrity. However, conventional binders often exhibit insufficient mechanical properties, leading to structural failure under stress. Inspired by the mussel byssus which contains metal coordination bonds to achieve toughness, this work proposes a dual‐dynamic network that integrates self‐healing ability and toughness through hydrogen bonds and metal coordination into a soft isoprene backbone. The extensibility of the crafted structure enables deformation exceeding 1300%, which is remarkably higher than most reported binders. Different from the self‐healing binders with single reversible bonds which have limited mechanical properties, the dual‐dynamic network combines rapid repair via hydrogen bonds with sufficient toughness from coordination bonds. In addition, the carboxyl groups retained during grafting provide interaction with the Si surface. Accordingly, the SiC and SiOx electrodes with as‐made binder achieve good cycling stability (retention of 83.3% and 86.8% after 300 cycles, respectively). The LiPF6//SiC full cell retains 96% after 150 cycles at 0.2C, and NCM811//SiC cell achieves retention of 84.2% after 200 cycles at 0.5 C. The implementation of this self‐healing binder provides a novel paradigm for rationally engineering the multi‐function binders.

Silicon-Graphite composite electrodes are a rapidly developing area of research and commercialization. Increasing the energy density of current Li-ion battery technology can be done by simply creating silicon/graphite composite electrodes. It is well known that the failure of these silicon/graphite composite electrodes stems from the expansion of the silicon during cycling that causes mechanical degradation, excessive SEI formation, and electrode shift loss. Development of a suitable binder will be crucial to the success of these composites. In this work we explore the benefits of CMC/SBR binder used in conjunction with single walled carbon nanotubes. These nanotubes are thought to be effective in increasing mechanical strength of the electrodes and increase the electrical connectivity between particles within the formed electrode. When the Si/graphite electrode cycles, it is believed that the SWCNTs help keep the active particles electrically connected and, hence, electrochemically active. The pouch cells studied here are shown to exhibit minimal loss of active mass in the negative electrode but experience capacity loss due to continued negative electrode SEI growth leading to lithium inventory or shift loss.

Silicon-graphite anodes offer a practical route to increase the energy density of lithium-ion batteries (LIBs), but their widespread adoption is hampered by cyclic instability due to huge volume changes of silicon during lithiation/delithiation process. Another fallout of LIBs capacity gain is growing safety concerns due to fire risks, associated with the uncontrolled release of chemical energy. Herein, we test a hexakis(fluoroethoxy)phosphazene (HFEPN) as a multifunctional electrolyte additive designed to mitigate both issues. The flammability of HFEPN-containing electrolytes was evaluated using a self-extinguishing time test, while the electrochemical performance was assessed in Si/C composite||NMC pouch cells under a progressively accelerated cycling protocol. It is shown that the additive fully imparts flame-retardant properties to the electrolyte at a 15 wt% loading. Despite forming a more stable solid–electrolyte interphase (SEI) with enhanced interfacial kinetics the additive did not improve the cycling stability of the Si/C-based cells. The cells with 15 wt% HFEPN retained 43% of capacity after 70 cycles, comparable to 46.5% for the reference electrolyte. The diffusion limitations imposed by the increased electrolyte viscosity are assumed to offset the interfacial benefits of the additive. Thus, alongside the improved synthetic route, this study demonstrates that while HFEPN functions as an effective flame retardant and SEI modifier, its practical benefits for silicon anodes are limited at high concentrations by detrimental effects on electrolyte transport properties and should be improved in future molecular design efforts.

This study presents a multiphysics simulation approach to optimize graphite-buffered bilayer anodes for enhanced energy density in lithium-ion batteries, assessing the electrochemical impact of diverse inner-layer materials, including silicon, hard carbon, lithium titanate (LTO), and metallic lithium, in pure and graphite-composite forms. A coupled finite-element model implemented in COMSOL Multiphysics 6.2 was used to integrate spherical lithium diffusion, charge conservation, and the solid electrolyte interphase (SEI) formation kinetics. The evaluated anode structure consisted of a 60 µm-thick bilayer: a 30 µm graphite surface layer coupled with a 30 µm inner layer of alternative active materials. Simulations were performed using an NMC622 cathode, LiPF6 in EC:EMC electrolyte, at room temperature, under a charge rate of 1 C, considering realistic particle sizes (graphite: 2.5 µm; Si: 0.1 µm; hard carbon: 2.5 µm; LTO: 0.2 µm; Li metal: 0.5 µm), and evaluated over 2000 cycles. The hard carbon/graphite configuration exhibited a capacity fade of 5.8% compared with 7.1% in pure graphite. Additionally, the SEI thickness decreased to 0.20 µm (from 0.25 µm), the overpotential dropped to −17 mV (from −59 mV), and the electrolyte consumption was reduced to 20.8% (from 42.9%). The analysis highlights hard carbon and LTO inner layers as optimal trade-offs between capacity and cycle stability, whereas silicon and lithium metal significantly increased the initial capacity but accelerated SEI formation and impedance growth. These findings demonstrate the graphite-buffered bilayer’s potential to decouple interfacial degradation from high-capacity materials, providing valuable guidelines for the design of advanced lithium-ion battery anodes.

No abstract available

The current energy density of Li‐ion capacitors (LICs) is unfavorable for industrial applications, due to the asymmetrical electrochemical kinetics between the anode and cathode. Herein, the energy density of composite anode materials is increased by optimizing the mass ratio between graphite (Gr) and nano‐Si to enable the solid electrolyte interface (SEI) to effectively buffer the large volume changes of Si during lithiation/delithiation. A twice‐repeated prelithiation method is used to stabilize the SEI and eliminate the irreversible capacity of the composite anodes. Variation of the Gr:nano‐Si mass ratio of the composite anode from 0 to 40 mass% shows that, although the LIC with a Gr:nano‐Si mass ratio of 80:20 (Gr80Si20) exhibits the highest energy density (91.9 Wh kg−1), its energy density deteriorates drastically after 10 000 cycles, retaining only 34.8% of its initial energy density. Conversely, the LIC with the composite anode with a Gr:nano‐Si mass ratio of 60:40 (Gr60Si40) has slightly lower energy density (87.3 Wh kg−1) but demonstrates outstanding cycling performance with energy density retention of 87.2% after 10 000 cycles. These findings highlight the potential of incorporating Gr/nano‐Si composite anodes into LICs for high‐energy‐density industrial applications.

The practical application of silicon (Si)-based anodes faces challenges due to severe structural and interphasial degradations. These challenges are exacerbated in lithium-ion batteries (LIBs) employing Si-based anodes with high-nickel layered oxide cathodes, as significant transition-metal crossover catalyzes serious parasitic side reactions, leading to faster cell failure. While enhancing the mechanical properties of polymer binders has been acknowledged as an effective means of improving solid-electrolyte interphase (SEI) stability on Si-based anodes, an in-depth understanding of how the binder chemistry influences the SEI is lacking. Herein, a zwitterionic binder with an ability to manipulate the chemical composition and spatial distribution of the SEI layer is designed for Si-based anodes. It is evidenced that the electrically charged microenvironment created by the zwitterionic species alters the solvation environment on the Si-based anode, featuring rich anions and weakened Li+-solvent interactions. Such a binder-regulated solvation environment induces a thin, uniform, robust SEI on Si-based anodes, which is found to be the key to withstanding transition-metal deposition and minimizing their detrimental impact on catalyzing electrolyte decomposition and devitalizing bulk Si. As a result, albeit possessing comparable mechanical properties to those of commercial binders, the zwitterionic binder enables superior cycling performances in high-energy-density LIBs under demanding operating conditions.

Lithium-ion batteries (LIBs) have been employed across a diverse range of applications, spanning from small portable devices to large electric vehicles and stationary energy storage systems. With the growing market for electric devices, the demand for rechargeable batteries with higher energy densities than conventional LIBs has increased. Graphite (Gr), of which theoretical capacity is 372 mAh g-1, is utilized as anode material in current LIBs because of its cycle stability, low price, and high conductivity. Despite these advantages, the graphite anode has used its maximum utilization, which has reached its theoretical capacity. Therefore, silicon (Si), of which theoretical capacity is 3579 mAh g-1, has emerged to achieve more higher energy density than that of Gr. Silicon anode, however, undergoes extremely large volume expansion during alloying/dealloying process, leading to pulverization, loss of electrical contact, and excessive solid electrolyte interface (SEI) layer formation. Eventually, this large volume expansion reduces cell life. Despite intensive effort for Si-dominant electrodes, a real application of this strategy to battery industry is unsure. In this regard, gradual replacement of Gr to Si is adaptable in practical perspective. For the practical use of graphite/Si electrodes, the research on the long-term cycling performance of wide temperature range is highly important. However, most research has mainly focused on charge/discharge mechanisms in short cycles or conducted experiments with half cells, which do not represent the actual commercial battery systems. Therefore, research on the aging mechanism of composite anode under conditions similar to real operating environments is needed. To reveal the aging mechanism of composite anode, full cell configuration with high mass loading electrodes was used for the electrochemical performance test. Under wide temperature range, different cycling performance were observed. The cell reassembly experiment is conducted to figure out which electrodes is mainly contributed to the capacity loss of full cell during cycling. From this experiment, the anode degraded more rapidly. Through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we observed changes in the morphology of the electrodes with varying cycle numbers and temperatures. The composite anode is degraded during cycling, and notably, a peculiar structure of SEI was observed. Additionally, secondary-ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS) is conducted to analyze the SEI structure, which determines the cycle life of batteries. The deeper understanding of the mechanism of long-term cycling performance will provide as primary key for the commercialization of composite anode design. Figure 1. a Scheme of the capacity loss of anode and cathode harvested from full coin cell after long-term cycling performance. b Voltage profiles of lithium half cell with aged anode and pristine electrode. c Voltage profiles of lithium half cell with aged cathode and pristine electrode. Figure 1

Calendar aging of Li-ion batteries with Si/graphite electrodes was investigated within this study. A total of 121 single-layer pouch full cells with either graphite or Si/graphite (3.0 wt−%, 5.8 wt−% and 20.8 wt−% Si) anodes and NMC622 cathodes with the same N/P ratio were built on pilot-scale. Calendar aging was studied at SoC 30%, 60%, and 100%, as well as temperature (25 °C, 45 °C, 60 °C) and time dependence. The aging data was analyzed in terms of capacity fade and a square-root behavior was observed. Differential voltage analysis (DVA) has been performed as a function of aging time. The observed temperature and time dependence is best described by time dependent, 3D Arrhenius plots. Post-Mortem analysis (SEM, EDX, GD-OES) is applied to investigate the changes on electrode and material level. Conclusions are drawn on the main aging mechanisms for calendar aging of Li-ion cells with Si/graphite anodes and differences between Si/graphite and pure graphite anodes are discussed. The Si-containing cells show a combination of lithium inventory loss and a loss of accessible Si active material, both caused by SEI growth.

Silicon-based anodes offer high specific capacities to enhance the energy density of lithium-ion batteries, but are severely hindered by the immense volume expansion and subsequent breakage of the solid-electrolyte-interphase (SEI) during cycling. Herein, we utilize an effective strategy, known as direct-contact prelithiation, to mitigate the challenges associated with expansion and surface instability in SiOx/graphite (SG) anodes. It involves introducing lithium into the anode via physical contact with lithium metal and electrolyte before cycling. Prelithiation of SG anodes with an advanced localized high-concentration electrolyte is shown to develop a mechanically robust artificial SEI that tolerates better the electrode volume expansion. The modified SG anode paired with the high-Ni cathode LiNi0.90Mn0.05Co0.05O2 delivers a high initial capacity of 191 mA h g-1 with 80% capacity retention over 150 cycles, compared to 46% retention with a conventional electrolyte. The bolstered SEI layer with reduced surface reactivity is due to the reduced electrolyte consumption and regulated SEI formation during cycling. Furthermore, the advanced electrolyte and fortified SG anode help reduce cathode degradation, transition-metal dissolution, and loss of active lithium. This study highlights viable prelithiation strategies to stabilize Si-based anodes for high-energy-density batteries through electrolyte design.

Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are considered the most effective electrolyte additives for improving the solid electrolyte interphase (SEI) of Si-containing anodes while lithium difluorophosphate (LiDFP) is known to improve the interphases of cathode materials and graphite. Here, we combine VC, FEC, and different amounts of LiDFP in a highly-concentrated electrolyte to investigate the effect on Si-dominant anodes in detail. Cycle life tests, electrochemical impedance spectroscopy and rate tests with anode potential monitoring were conducted in Si/NCM pouch cells. The results reveal that adding LiDFP to the electrolyte improves all performance criteria of the full cells, with a concentration of 1 wt.% being the optimal value for most cases. Post-mortem analyses using scanning electron microscopy and x-ray photoelectron spectroscopy showed that a more beneficial SEI film was formed for higher LiDFP concentrations, which led to less decomposition of electrolyte components and a better-maintained anode microstructure.

The electrolyte additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) improve the lifetime of lithium‐ion batteries with silicon‐containing anodes by their reduction yielding a more stable solid electrolyte interphase (SEI). However, the reductive decomposition mechanism of FEC and VC has not yet been fully clarified. For this purpose, we investigate the electrolyte decomposition in LiNi0.6Co0.2Mn0.2O2 (NCM622)/silicon‐graphite pouch cells containing either 1 M LiPF6 in FEC:dimethyl carbonate (DMC) or 1 M LiPF6 in VC:DMC using high‐performance liquid chromatography, gas chromatography, X‐ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry. Based on the molar consumptions of FEC and VC, and the cumulative irreversible capacities, we show that three electrons are consumed for every reduced FEC molecule, and that one electron is consumed for every reduced VC molecule. Based on the results, reactions of the FEC reduction are proposed yielding LiF, Li2CO3, Li2C2O4, HCO2Li, and a PEO‐type polymer. Furthermore, the reaction of the VC reduction is proposed yielding lithium‐containing, polymerized VC. During formation, the capacity loss of the cells is induced by lithium trapping in LixSiy/LixSiOy under the SEI and by lithium trapping in the SEI. During subsequent cycling, only lithium trapping in the SEI triggers the capacity loss.

Slurry solid fraction is often treated as an innocuous battery electrode processing parameter at the laboratory scale. In fact, articles that put a number to the water content of their slurries are few and far between. However, recent studies from our group have shown that the slurry solid fraction can have a significant impact on the electrochemical performances of the resulting electrodes. The present research aims to highlight the importance of optimising this parameter by demonstrating its impact throughout the electrode preparation and testing processes of Si-graphite electrodes for Li-ion batteries. Silicon, graphite, a conductive additive of graphene nanoplatelet (GnP) and a partially neutralized PAA-based binder (PAH0.8Na0.2, pH ≈ 4, Mw = 1084k, 393k or 7.6k g/mol) were dispersed in a variable amount of deionized water, yielding slurries of different solid fractions according to equation 1: Eq. 1 SF = (mSi + mGr + mGnP) / mSlurry An initial impact of the slurry solid fraction can be seen in the adsorption of the binder onto the active material and conductive additive in aqueous conditions. Gel permeation chromatography of the polymer remaining in the liquid phase after slurry dispersion reveals a strong preferential adsorption of high-molecular weight PAA, mainly on the silicon particles, that is even more pronounced at higher solid fraction. This localized polymer distribution affects its ability to fulfill its functions as a binder and an artificial solid-electrolyte interphase (SEI), which can later be seen in the irreversible capacity loss that arises from both electrical disconnections and SEI formation during cycling. The solid fraction is also a principal determinant of the rheological properties of the slurry, namely its viscosity under shearing and storage and loss moduli. Shear-thinning behavior is favourable to ensure homogeneous dispersion of matter in the electrode slurry and avoid creating surface defects during the coating process. Increasing the solid fraction leads to shear-thickening behavior in slurries with high-molecular weight binders. As such, large agglomerates of silicon and multiple surface defects are observed in these electrodes. On the other hand, the storage and loss moduli of the slurry will determine its stability during the drying process where there is a risk of sedimentation. The effects of the slurry solid fraction can also be seen in the dried electrodes. For example, the mechanical properties (hardness, elasticity) of the electrodes made with low-solid fraction slurries are comparatively poor, as measured by nanoindentation. Conversely, 4-point probe testing shows that electrodes made with high-solid fraction slurries are more resistive due to the presence of large silicon particles covered in a high concentration of polymer. The numerous impacts of the slurry solid fraction across the electrode preparation and testing processes culminate in a strong dependence of the resulting electrochemical performances on this often-neglected parameter. An optimal solid fraction is determined for the given materials. Formulations with different binder molecular weights are also compared at different solid fractions to illustrate the importance of this optimization step in drawing accurate and meaningful conclusions on the materials at study. References: Ligneel, E.; Lestriez, B.; Hudhomme, A.; Guyomard, D. Effects of the Solvent Concentration (Solid Loading) on the Processing and Properties of the Composite Electrode. J. Electrochem. Soc. 2007, 154 (3), A235. https://doi.org/10.1149/1.2431316. Porcher, W.; Lestriez, B.; Jouanneau, S.; Guyomard, D. Design of Aqueous Processed Thick LiFePO4 Composite Electrodes for High-Energy Lithium Battery. J. Electrochem. Soc. 2009, 156 (3), A133. https://doi.org/10.1149/1.3046129. Xiong, J.; Dupré, N.; Mazouzi, D.; Guyomard, D.; Roué, L.; Lestriez, B. Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode. ACS Appl. Mater. Interfaces 2021, 13 (24), 28304–28323. https://doi.org/10.1021/acsami.1c06683.

Silicon (Si) anodes have attracted considerable attention for high-energy-density lithium-ion batteries (LIBs), owing to their high theoretical capacity (>3500 mAh g−1 at room temperature), low reaction potential (<0.4 V vs. Li/Li+), and natural abundance. However, the repeated volume changes of Si during the lithiation/delithiation process induce critical complications, such as the pulverization of Si particles, formation of a thick solid-electrolyte-interphase (SEI) layer, and electrode delamination, resulting in poor cycle performance. To mitigate these complications, several strategies have been proposed, including the nano/microstructural design of Si, employing a Si/C composite, and using multifunctional binders. Regarding the choice of the binder, the conventional poly(vinylidene fluoride) (PVDF) is inadequate as it cannot accommodate a large hoop stress because of its weak van der Waals force. Compatible binders, such as carboxymethyl cellulose, poly(acrylic acid) (PAA), and poly(vinyl alcohol), have been generally employed to improve the electrochemical performance of Si anodes. Although binders with abundant functional groups (e.g., –OH, –COOH, –CN, and –NH2) prevent the delamination of Si anodes from the current collector, they suffer from brittleness due to their serious chain-entanglement network and strong interactions, leading to a high glass transition temperature (Tg ). Moreover, polymeric binders with poor stretchability and self-healing ability degrade the structural integrity of the Si anode during repeated volume changes. Further, low ionic conductivity deteriorates the transport of Li ions in the Si anode, thereby impeding the effectiveness of fast-charging systems. Therefore, various physicochemical properties of a polymeric binder are required to improve the electrochemical performance of Si anodes besides adhesion property. First, stretchability and a high elastic modulus are essential for a binder to endure the stress of large volume expansions and recover to the original state after the lithiation process. A Si anode incorporating a rigid and stiff polymeric binder could crack and become damaged, resulting in drastic capacity decay and safety issues. Second, the self-healing ability is required for a binder to spontaneously recover from the damage induced by the significant volume changes. The mechanical fracture of Si particles induces the loss of the active material and exposes a highly reactive surface to the electrolyte. Third, in the LIB system, the rate performance highly depends on the ionic conductivity as well as the electronic conductivity. Thus, a binder with high ionic conductivity is highly desired to enhance the Li-ion diffusion coefficients and achieve a high-rate-performance. A binder design that satisfies the three requirements above is desperately desired. a series of poly(Li[3-sulfopropylmethacrylate]-r-acrylic acid) (PLSA) polymers with different moiety ratios was synthesized from 3-sulfopropyl acrylate lithium salt (Li[SPMA]) and acrylic acid (AA) monomers. Subsequently, glycerol, as a thermally stable plasticizer (high boiling point: 290 °C), was added to the polymer matrix to lower the Tg and maintain the softness of the polymers after water evaporation. The hydroxyl groups in the glycerol interact with the oxygen in the polymers, enhancing ion solvation for rapid Li-ion conduction. The ionic side chain of the polymer, as a mechanical modulator, formed the crosslinking via the electrostatic interaction between the polymers, conferring the stretching and self-healing properties. Furthermore, the mobile Li ions in the side chain enhanced the ionic conductivity of the polymers. Meanwhile, the carboxylic acid group (–COOH) in AA interacted with the current collectors (i.e., copper (Cu) foil) and the silanol groups (–SiOH) from the Si particles via hydrogen bonding, enhancing the adhesion properties. The rationally designed polymers with excellent physicochemical properties (i.e., high stretchability, rapid self-healing ability, and high ionic conductivity) were introduced as polymeric binders in the Si anode in LIBs. The Si anode with the PLSA75 binder (Si–PLSA75) exhibited stable cycling performance, retaining 81.2% of its initial capacity after 300 cycles at 0.5 C (1.5 A g−1) and exhibiting outstanding rate performance (815 mAh g−1 at 5 C (15 A g−1)). Moreover, compared with the Si–PAA, the half-cell with Si–PLSA exhibited lower internal resistance and higher diffusion coefficients of the Li ion during the whole lithiation/delithiation process. Based on the outstanding electrochemical performance in Si anodes, Si/graphite (Si/Gr) blend anode was also tested with PLSA binder which could afford around 840 mAh g-1. The blended anode with PLSA75 also maintained 82.7% of its initial capacity after 200 cycles at 0.5 C. Furthermore, the blended anode was paired with a nickel (Ni)-rich cathode, LiNi0.8Co0.1Mn0.1O2, for the full-cell test, and the full cell still delivered a reversible capacity of 139.2 mAh g−1 after 200 cycles at 0.5 C. This work provides insights into the rational design of polymeric binders for achieving Si anodes with fast-charging and stable cycling performance.

Since the first commercialization of lithium-ion batteries (LIBs), LIBs have become an important power source for wireless electronics, electric vehicles (EVs), and other renewable energy storage systems due to their high energy density and operating voltage. The higher energy density of LIBs indicates that the electrode material can store more energy per unit mass or volume. Currently, with the high capacity demands of EV batteries and the use of high-capacity LIBs in a variety of devices, anode material capacity requirements are also rising rapidly. However, graphite, the most widely used anode material in commercial LIBs, has challenges in enhancing the energy and power density of LIBs due to its limited theoretical specific capacity (372 mAh g-1) and restricted rate capability. Hence, most battery industries have focused on forming graphite-silicon composites through the blending of silicon (Si) and graphite. Si has an ultrahigh theoretical specific capacity of 3579 mAh g-1 (Li15Si4), which is roughly 10 times higher than the specific capacity of graphite, and has a low redox potential (0.4 V vs Li/Li+). However its excellent properties, the Si-based anode undergoes a severe volume expansion (up to 300 %) during the repetitive lithiation/delithiation process. The resulting physical change causes the breakdown/restoration of the solid electrolyte interphase (SEI) layer over the surface of the Si. This phenomenon causes electrolyte decomposition, degradation of Coulombic efficiency, the loss of active lithium ions, and the formation of an unstable SEI layer. To address the inherent problems of Si, countless researches have been conducted to improve the electrochemical performance and long-term cycle stability of graphite-Si composite electrodes through nanostructure engineering, composite optimization, and surface modification. Nevertheless, graphite-Si composite electrodes continue to encounter challenges (e.g., electrode pulverization and delamination), constraining the incorporation of Si active materials into the composite. Therefore, it is imperative to devise a new graphite-Si composite for high-performance LIBs. In this work, we used polyvinylpyrrolidone (PVP) as an electrode additive and investigated how it affects SEI components and volume expansion issues. PVP, a component of LiF and Li3N, can produce high-quality SEI in the field. We verified this via X-ray photoelectron spectroscopy(XPS). In addition, when we evaluated Li metal cells, we discovered that the electrode with PVP had better capacity retention and battery performance than the electrode without PVP, and when we reviewed full cells, we discovered that the rate characteristics were improved and volume expansion was reduced. This work explores a simple strategy for employing electrode additives to improve long-term cycle stability and high-rate performance.

The energy density of lithium-ion batteries (LIBs) can be meaningfully increased by utilizing Si-on-graphite composites (Si@Gr) as anode materials, because of several advantages, including higher specific capacity and low cost. However, long cycling stability is a key challenge for commercializing these composites. In this study, to solve this issue, we have developed a multifunctional polymeric artificial solid-electrolyte interphase (A-SEI) protective layer on carbon-coated Si@Gr anode particles (making Si@Gr/C-SCS) to prolong the cycling stability in LIBs. The coating is made of sulfonated chitosan (SCS) that is crosslinked with glutaraldehyde promoting good ionic conduction together with sufficient mechanical strength of the A-SEI. The focused ion beam-scanning electron microscopy and high-resolution transmission electron microscopy images show that the SCS is uniformly coated on the composite particles with thickness in nanometer. The anodes are investigated in Li metal cells Si@Gr/C-SCS||Li metal) and lithium-ion full-cells (LiNi0.6Co0.2Mn0.2O2 (NCM-622)||Si@Gr/C-SCS) to understand the material/electrode intrinsic degradation as well as the impact of the polymer coating on active lithium losses because of the continuous SEI (re)formation. The anode composites exhibit a high capacity reaching over 600 mAh g-1, and even without electrolyte optimization, the Si@Gr/C-SCS illustrates a superior long cycle life performance of up to 1000 cycles (over 67% capacity retention). The excellent long-term cycling stability of the anodes was attributed to the SCS polymer coating acting as the A-SEI. The simple polymer coating process is highly interesting in guiding the preparation of long-cycle-life electrode materials of high-energy LIB cells.

This study presents the synthesis, characterization, and electrochemical performance evaluation of carbon@silicon (C@Si) and graphite@carbon@silicon (G@C@Si) nanocomposites as potential anode materials for lithium-ion batteries (LIBs). Employing a combination of mechanical milling and carbonization using citric acid, we developed nanocomposites exhibiting unique core-shell structures, as confirmed by detailed SEM and TEM analysis. The G@C@Si nanocomposite displayed superior electrochemical performance, delivering an initial discharge capacity of 1724 mAh g-1 and a high initial Coulombic efficiency of 87.37%. The nanocomposite demonstrated remarkable cycling durability with a discharge capacity of 1248 mAh g-1 over 200 cycles and an average Coulombic efficiency of 99.1% and high-capacity retention of about 83%. Notably, a high capacity of 1325 mAh g-1 was observed at a high 3C rate, and the electrode showed excellent resilience by rapidly recovering to a discharge capacity of 1637 mAh g-1 when the C rate was reduced back to 0.5C. Electrochemical impedance spectra revealed a reduced charge transfer resistance of approximately 43 Ω in the G@C@Si nanocomposite as compared to that of C@Si (∼56 Ω) and nano-Si (105 Ω), indicating enhanced lithium-ion diffusion due to the integration of graphite. Postcycle electrode analysis revealed excellent structural integrity, with minimized volume changes in both C@Si and G@C@Si. XPS studies revealed a thinner SEI layer formation in the G@C@Si electrode compared to C@Si. The C@Si core-shell formation through the citric acid treatment of nano-Si and integration of graphite by mechanical milling significantly boosts the electrochemical performance of the G@C@Si nanocomposite. These findings suggest that the G@C@Si nanocomposite offers immense potential for utilization in high-capacity and high-efficiency LIBs.

No abstract available

Constructing a stable solid electrolyte interphase (SEI) on high-specific-capacity silicon (Si) anode is one of the most effective methods to reduce the crack of SEI and improve the cycling performance of Si anode. Herein, the authors construct a reinforced and gradient SEI on Si nanoparticles by an in-situ thiol-ene click reaction. Mercaptopropyl trimethoxysilane (MPTMS) with thiol functional groups (SH) is first grafted on the Si nanoparticles through condensation reaction, which then in-situ covalently bonds with vinylene carbonate (VC) to form a reinforced and uniform SEI on Si nanoparticles. The modified SEI with sufficient elastic Lix SiOy can homogenize the stress and strain during the lithiation of Si nanoparticles to reduce their expansion and prevent the SEI from cracking. The Si nanoparticles-graphite blending anode with the reinforced SEI exhibits excellent performance with an initial coulombic efficiency of ≈90%, a capacity of 1053.3 mA h g-1 after 500 cycles and a high capacity of 852.8 mA h g-1 even at a high current density of 3 A g-1 . Moreover, the obtained anode shows superior cycling stability under both high loadings and lean electrolyte. The in-situ thiol-ene click reaction is a practical method to construct reinforced SEI on Si nanoparticles for next-generation high-energy-density lithium-ion batteries.

The incorporation of silicon monoxide (SiO) into graphite anodes improves the energy density of lithium‐ion batteries. However, it falls short of the long‐term durability of pure graphite, and research on their cycling performance remains limited. This study observes a sudden capacity decay in graphite/SiO anodes during long‐term cycling at room temperature (RT) and a moderate C‐rate. This decay arises from the mechanical degradation of SiO, leading to the formation of a “SiO‐SEI crust” that consumes lithium ions. This phenomenon does not occur at higher temperatures or lower C‐rates, implying that larger diffusion‐induced stress from lithium‐ion gradients at RT and 1 C accelerates SiO degradation. Furthermore, introducing a relaxation step to reduce the lithium‐ion gradient mitigates this sudden capacity decay, supporting diffusion‐induced stress as a critical factor in the degradation mechanism. These findings emphasize the role of diffusion‐induced stress in the performance degradation of Si‐based batteries and provide valuable insights for enhancing the lifespan of composite anodes.

This study explores the effects of transition metal (TM) ions—Ni, Co, Mn, and Fe—on the solid-electrolyte interphase (SEI) formation and electrochemical behavior of graphite and silicon (Si) anodes in lithium-ion...

The integration of micro-sized silicon (μm-Si) with high theoretical capacity and structurally stable graphite (Gr) has great potential in promoting the next generation of lithium-ion battery anodes. However, the application of Gr/μm-Si anodes is impeded by the excessive solid electrolyte interphase (SEI) accumulation and electrical disconnection caused by μm-Si swelling and fracturing. Herein, a multifunctional carbon layer (MCL) composed of in situ grown carbon nanotubes (CNTs) and pyrolytic carbon derived from polyacrylonitrile is prepared  to optimize Gr/μm-Si anode material. The pyrolytic carbon serves to anchor the CNTs and isolate the μm-Si surface from the electrolyte, mitigating side reactions and ensuring stable SEI formation. The CNTs create a robust three-dimensional conductive network, providing mechanical buffering for μm-Si volume expansion while enhancing electron and ion transport. Accordingly, the Gr/Si@MCL anode exhibits a discharge specific capacity of 503.6 mAh g-1, maintaining an exceptionally low capacity decay of just 0.031% per cycle after 500 cycles at a current density of 1 A g-1. Furthermore, the Gr/Si@MCL||LiFePO4 full-cell demonstrates excellent performance, particularly with a high energy density of 347 Wh kg-1. These results highlight the potential of the proposed structure design for advancing the practical deployment of Gr/μm-Si anodes in next-generation energy storage devices.

Silicon-carbon (Si/C) composites hold great promise as substitutes for conventional graphite anodes in high-specific-energy lithium-ion batteries (LIBs). However, their performance is hindered by silicon's substantial volume expansion during cycling, which can lead to electrode degradation. Traditional poly(acrylic acid) (PAA) binders often struggle to maintain electrode integrity under these conditions. To address this challenge, polyether modified polyurethane acrylic (PUMA) is used as physicochemical cocrosslinking polymer. PUMA offers superior mechanical properties, elasticity, and interfacial stability, enabling it to effectively accommodate silicon's volume changes and prevent electrode fracture. Through a simple preparation process, we used PUMA as a slurry additive in combination with PAA to form a functional composite binder, facilitating the construction of a stable and robust SEI film. This is conducive to alleviating the volume expansion of silicon and ensuring the cycling stability of the electrode. In Si/C450 half-cells, electrodes enhanced by our binder show a remarkable longevity, maintaining 97.26% of their capacity post 200 cycles at 0.5 C. The full cells Si/C450||NCM811 display a notable performance, achieving a capacity retention of 82.10% after 100 cycles at 0.2 C. These findings underscore the potential of our innovative binder design in enhancing the efficacy of silicon-based anodes in high-energy LIBs.

The commercialization of silicon‐based anodes is affected by their low initial Coulombic efficiency (ICE) and capacity decay, which are attributed to the formation of an unstable solid electrolyte interface (SEI) layer. Herein, a feasible and cost‐effective prelithiation method under a localized high‐concentration electrolyte system (LHCE) for the silicon–silica/graphite (Si–SiO2/C@G) anode is designed for stabilizing the SEI layer and enhancing the ICE. The thin SiO2/C layers with –NH2 groups covered on nano‐Si surfaces are demonstrated to be beneficial to the prelithiation process by density functional theory calculations and electrochemical performance. The SEI formed under LHCE is proven to be rich in ionic conductivity, inorganic substances, and flexible organic products. Thus, faster Li+ transportation across the SEI further enhances the prelithiation effect and the rate performance of Si–SiO2/C@G anodes. LHCE also leads to uniform decomposition and high stability of the SEI with abundant organic components. As a result, the prepared anode shows a high reversible specific capacity of 937.5 mAh g−1 after 400 cycles at a current density of 1 C. NCM 811‖Li‐SSG‐LHCE full cell achieves a high‐capacity retention of 126.15 mAh g−1 at 1 C over 750 cycles with 84.82% ICE, indicating the great value of this strategy for Si‐based anodes in large‐scale applications.

The anisotropic lithiation-induced expansion of crystalline silicon leads to uneven volume expansion and extreme stress concentration. This issue will be effectively mitigated by employing an isotropic amorphous structure. Here, an isotropic porous amorphous silicon (aSi) was prepared using a simple and safe method, followed by mechanical mixing with graphite to form an aSi/graphite composite (aSG60). Experimental results demonstrate that the isotropic nature and porous structure of aSi effectively suppress volume change during Li+ insertion and extraction. The aSG60 delivers a capacity of 1219.0 mAh g-1 at 1 A g-1, with a 70 % capacity retention after 200 cycles. Notably, the composite exhibits a volume expansion of only 38 % after 50 cycles, significantly lower than the 85 % observed in the micro‑silicon/graphite composite (uSG60) with a similar silicon content. These findings highlight the potential of aSi as a promising material for high-performance silicon-based anodes.

With the growing demand for high energy density and fast-charging/high-rate performance, understanding the thermodynamic and kinetic behavior of graphite/silicon composite anodes has become increasingly important. In this study, graphite/Si alloy composite electrodes containing 0–50 wt% silicon alloy were investigated using a three-electrode pouch cell combined with in situ dilation. Through this analysis, the changes in porosity after the formation cycles were determined, while the lithium-ion diffusion coefficient (DLi+) was calculated based on the Weppner–Huggins equation. In addition, the resistance components were quantitatively evaluated by pulse polarization and electrochemical impedance spectroscopy (EIS). This study elucidates the effect of porosity evolution, induced by irreversible expansion with varying silicon content, on the electrode's electrochemical behavior. For the YNG-30% electrode, irreversible expansion during the formation process increased the porosity from 32.3% to 55.0%. As a result, the transport pathways for solvated Li+ were expanded, and the charge-transfer resistance (Rct) decreased, leading to enhanced interfacial and interparticle diffusion in the graphite staging region. In contrast, in the silicon-dominant region, intrinsic thermodynamic and kinetic limitations resulted in higher overpotential at the beginning of charge and the end of discharge. Consequently, the role of silicon is not limited to increasing capacity but serves as a structural design element for achieving fast-charging and high-rate performance. These findings highlight that porosity optimization is a key factor for improving electrode performance.

Silicon-based materials, including pure Si, silicon oxide (SiO x ), and silicon nitride (SiN x ), have recently gained significant attention as promising anode materials for lithium-ion batteries due to the increasing interest in development of high energy density cells. Compared to graphite, the traditional candidate, elemental Si possesses a superior density (2.3 g ∙ cm -3 ) compared to graphite ( 2.2 g ∙ cm -3 ). Furthermore, Si exhibits significantly higher specific energy densities both volumetrically (9660 mAh∙cm⁻³) and gravimetrically (4200 mAh∙g⁻¹), greatly exceeding graphite, which has volumetric and gravimetric capacities of 840 mAh∙cm⁻³ and 372 mAh∙g⁻¹, respectively. However, despite of these promising potentials of the application of Si as anode materials, persistent challenges remain associated with the tremendous volume change upon cycling, graphite typically experiences maximum 10 % during lithiation, while Si expands more than three times of the original volume. Additionally, its limited electronic and ionic conductivity can lead to trapping effects, where lithium is irreversibly captured during the dealloying process, resulting in rapid capacity loss and poor cycling performance. Nevertheless, its volume expansion remains non-negligible and poses challenges for practical applications. To address these issues, current researches often combine SiO x with graphite, leveraging graphite's high conductivity and volume-buffering capability to improve the overall performance of the electrodes. Several methods exist to monitor the volume change of lithium batteries at different scales. At the microscopic crystallographic level, volume changes can be tracked using X-ray diffraction (XRD), in which variations in lattice parameters, such as the d-spacing, indicate changes in the spacing between crystalline planes. There are however also limitations on this methodology. Primarily, XRD peaks only represent crystalline structures, and silicon particles typically become amorphous after initial lithiation. Moreover, electrodes possess complex porous structures containing non-crystalline and inactive particles. Thus, macroscopic electrode expansion cannot be fully represented solely by changes in the spacing within crystalline active particles. To gain a more comprehensive monitoring of the volumetric behavior on the electrode level, in-situ electrochemical dilatometry is developed which enables the monitoring of a single electrode ‘s overall volume change during cycling. This work investigates the volumetric behavior of SiO x /Graphite composite electrodes and the mechanisms underlying the competitive lithiation behavior during the lithiation and delithiation processes. By adjusting the SiOₓ content, a series of electrodes with different theoretical capacities were fabricated in-house and prepared for lateral tests. Their thickness changes during charge and discharge were monitored in real-time using in-situ dilatometry. Prior to the investigation of the electrode, the SiO x was first characterized using XRD to determine the disproportioned Si and Si suboxides. Additionally, the topological structures of the electrode surfaces and cross-sections were examined via scanning electron microscopy (SEM) With increasing SiO x content the expansion rate of the electrodes became more pronounced, indicating the significant impact of SiO x on the mechanical properties of the electrodes during lithiation and delithiation. Furthermore, for the electrodes with 25 wt.% SiO x , ex-situ XRD analysis were performed at different charge/discharge cut-off voltages after two formation cycles at C/20 rate, revealing the alloying and the dealloying mechanism of SiO x at different lithiation states and its correlation with expansion behavior as well as the phase transition of the graphite particles. The morphological changes of the corresponding electrodes under different cut-off voltages were also examined under SEM as well. The experimental results demonstrate that the phase transformation process of SiO x is closely related to the expansion behavior of the electrode, and the observed hysteresis mainly arises from the incomplete reversibility of SiO x during delithiation. This work provides important experimental insights into the expansion mechanisms of silicon-based composite electrodes and their relationship with electrochemical behavior, offering theoretical support for optimizing the mechanical stability of silicon-based anode materials. Figure 1

The commercialization of silicon anodes requires polymer binders that are both mechanically robust and electrochemically stable in order to ensure that they can accommodate the volume expansion experienced during cycling. In this study, we examine the use of both low and high molecular weight (MW) polyacrylic acids (PAAs), and sodium polyacrylates (Na-PAAs), at different degrees of partial neutralization, as a possible binder candidate for use in silicon graphite anodes. High MW PAAs were found to have stable capacity retentions of 672 mAh g–1 for over 100 cycles, whereas with the low MW PAAs the capacity was found to already have declined to 373 mAh g–1 after the first 30 cycles. Furthermore, the partial neutralization of Na-PAA binder system was found to provide superior cycling performances, as compared to non-neutralized or fully neutralized PAA systems. The high MW and partially neutralized PAAs were also found to provide the electrode coatings with higher cohesion strengths, which allow for the electrodes’ microstructure to be more effectively maintained over several cycles. Overall, these findings suggest that partially neutralized and higher MW PAAs are the more suitable polymer binder candidates for use within silicon–graphite anodes.

Silicon-Graphite (Si-Gr) composite is widely studied as a viable alternative to harness Silicon’s high energy density while mitigating its volume expansion as a Lithium-ion cell anode. The present study adopts...

Silicon-graphite composite anodes (CAs) are promising for energy-dense lithium-ion batteries offering a significant increase in specific capacity through silicon, while leveraging graphite’s cycling stability. However, CAs endure substantial volume expansion potentially reaching up to 300% during lithiation thereby presenting varying modes of chemo-mechanical degradation over long-term cycling. In this study, we develop a microstructure-aware thermo-electrochemical model that incorporates the mechanistic interactions from both active materials thereby quantifying their coupled degradation response under fast charging. We focus on the interplay between three primary degradation modes: volume expansion, lithium plating and solid electrolyte interphase growth to assess the relative degradation signatures arising from both active materials. We reveal the existence of preferential lithiation dynamics in CAs that impact its in-operando volume expansion and lithium plating behavior. Furthermore, the implications of cycle-to-cycle variation in anode microstructure due to volume expansion and operating conditions will be explored. We also deduce the influence of silicon content in CAs that govern the trade-offs between energy density, electrochemical performance and long-term cycling stability. This work presents critical insights into the design of silicon-graphite CAs with superior cycling stability by understanding their intrinsic degradation mechanisms.

Automotive battery manufacturers are working to improve the individual cell and overall pack design1 by increasing durability, performance, and range, while reducing cost, and active material volume change2–8 is a key aspect that needs to be considered during this design process. Recently, silicon oxide-graphite composite anodes9,10 are being explored to increase total anode capacity while maintaining a tolerable amount of cell level reversible volume expansion due to the relatively lower reversible volume change of the silicon oxide compared to pure battery grade or metallurgical grade silicon. To predict the blended anode response and contribution to the overall cell volume change, we integrated the mechanical behavior of the individual active materials with the multi-species, multi-reaction model11–15 to predict the state-of-lithiation of the active materials in the cell at a given potential. The resulting simulations illustrate the tradeoff in volume change between the silicon oxide and the graphite during cell operation. This type of modeling approach will allow designers to virtually consider the impact of cell level and pack level design changes on overall system mechanical performance for automotive and grid storage applications, namely that relatively small addition of silicon containing materials can drive a significant increase in the volume change at the cell level, as demonstrated by the 5 wt% addition of silicon oxide accounting for half of the overall volume change in the cell16. In this work, we start with the model derivation from a single porous electrode volume change model at low rate2, consider dual electrode interaction3 and elevated rates4, add the competing equilibrium potential consideration5,7,17 to govern lithium split between active materials during charge or discharge with the MSMR model12, functional forms of the active material volume change6 based on experimental data, and extend the two particle model from previous rate dependent studies8 to a blended electrode in order to capture the state-of-charge dependency between the two active materials. References T. R. Garrick, Y. Zeng, J. B. Siegel, and V. R. Subramanian, J. Electrochem. Soc., 170, 113502 (2023). T. R. Garrick, K. Kanneganti, X. Huang, and J. W. Weidner, J. Electrochem. Soc., 161, E3297 (2014). T. R. Garrick, X. Huang, V. Srinivasan, and J. W. Weidner, J. Electrochem. Soc., 164, E3552 (2017). T. R. Garrick et al., J. Electrochem. Soc., 164, E3592 (2017). D. J. Pereira, J. W. Weidner, and T. R. Garrick, J. Electrochem. Soc., 166, A1251 (2019). D. J. Pereira et al., J. Electrochem. Soc., 167, 080515 (2020). D. J. Pereira, A. M. Aleman, J. W. Weidner, and T. R. Garrick, J. Electrochem. Soc., 169, 020577 (2022). T. R. Garrick et al., J. Electrochem. Soc., 171, 073507 (2024). C. Berg, R. Morasch, M. Graf, and H. A. Gasteiger, J. Electrochem. Soc., 170, 030534 (2023). A. Amin et al., J. Electrochem. Soc., 170, 020523 (2023). D. R. Baker and M. W. Verbrugge, Journal of The Electrochemical Society, 165, A3952 (2018). T. R. Garrick et al., J. Electrochem. Soc., 170, 060548 (2023). T. R. Garrick et al., J. Electrochem. Soc., 171, 023502 (2024). A. Paul et al., ECS Adv., 3, 042501 (2024). A. Paul et al., J. Electrochem. Soc., 171, 023501 (2024). T. R. Garrick et al., Journal of The Electrochemical Society, 171, 103509 (2024). Brian J. Koch et al 2024 J. Electrochem. Soc. 171 123505 Figure 1

Silicon-graphite (Si-Gr) composite electrodes, which are based on high-capacity silicon mixed with conductive graphite with low volume expansion, have garnered significant interest due to their excellent electrochemical performance and stability. However, increasing the silicon content in the composite electrodes accelerates degradation, leading to a limitation in achieving higher energy density. In addition, Si-Gr composite electrodes undergo multi-stage reactions of silicon and graphite, resulting in complex reaction kinetics and intricate volume change behaviors. Therefore, it is challenging to analyze the impact of each active material's reaction on the electrode degradation. Furthermore, as the degradation of composite electrodes has primarily been understood and studied in the context of silicon's significant volume expansion and degradation, there is a lack of research evaluating the influence of graphite reactions. Despite having a low volume expansion upon lithiation, graphite occupies a significant volume fraction in the composite electrode and exhibits a relatively consistent arrangement. Therefore, it is anticipated that graphite would also influence electrode structural changes and the consequent electrode defect formation. In this study, we observe the average stress corresponding to the electrochemical reactions of the charge/discharge processes of Si-Gr composite electrodes in situ. The average stress can be understood as the internal pressure build-up within the electrode due to the volume expansion of the reactions. The stress and the reaction capacity were differentiated with respect to potential to analyze the contributions of each reaction on the volume change and the internal force evolution. Interestingly, graphite reactions generally induced higher stress than those of silicon during the lithiation process, and their stress per capacity increased as the State of Charge (SoC) increased. These results indicate that graphite can significantly contribute to the stress inside the electrode even though it exhibits a much lower expansion rate than silicon. Moreover, stress behavior that contradicts the silicon volume contraction was also observed during silicon delithiation. This result can be attributed to the stress-relieving phenomenon of the binder, highlighting the importance of the interaction between the active materials and binders. To observe the initial degradation of the composite electrode, repeated charge-discharge cycles were conducted, revealing intervals of unstable stress variation. Subsequent examination using ex-situ SEM showed that debonding and fracture at the interface between graphite and silicon/binder were the primary causes. Furthermore, EDS, XPS, and indentation analysis showed that such structural defects were caused by changes in the silicon-binder structure due to SEI formation. As confirmed by the micro indentation test, the viscoelastic binder and silicon were transformed into a brittle silicon-binder structure. Consequently, it failed to sufficiently dampen the forces generated by the active materials’ volume change resulting in the defects. These research findings contribute to a fundamental understanding of the stability of Si-Gr composite electrodes and our method can be expanded to various energy electrodes of different materials and compositions to enhance understanding of their behavior and contribute to their stability improvement. Choi, J., G. Kim, and S.Y. Kim, Silicon Graphite Composite Anode Degradation: Effects of Silicon Ratio, Current Density, and Temperature. Energy Technology, 2023. Ghamlouche, A., M. Müller, F. Jeschull, and J. Maibach, Degradation Phenomena in Silicon/Graphite Electrodes with Varying Silicon Content. Journal of The Electrochemical Society, 2022. 169(2). Wetjen, M., et al., Differentiating the Degradation Phenomena in Silicon-Graphite Electrodes for Lithium-Ion Batteries. Journal of The Electrochemical Society, 2017. 164(12): p. A2840-A2852. Berhaut, C.L., et al., Multiscale Multiphase Lithiation and Delithiation Mechanisms in a Composite Electrode Unraveled by Simultaneous Operando Small-Angle and Wide-Angle X-Ray Scattering. ACS Nano, 2019. 13(10): p. 11538-11551. Yao, K.P.C., et al., Operando Quantification of (De)Lithiation Behavior of Silicon–Graphite Blended Electrodes for Lithium ‐Ion Batteries. Advanced Energy Materials, 2019. 9(8). Sethuraman, V.A., et al., Real-time stress measurements in lithium-ion battery negative-electrodes. Journal of Power Sources, 2012. 206: p. 334-342. Schweidler, S., et al., Volume Changes of Graphite Anodes Revisited: A Combined Operando X-ray Diffraction and In Situ Pressure Analysis Study. The Journal of Physical Chemistry C, 2018. 122(16): p. 8829-8835. Liu, X.H., et al., Size-dependent fracture of silicon nanoparticles during lithiation. ACS Nano, 2012. 6(2): p. 1522-31. Lee, H.-J., et al., Lithiation Pathway Mechanism of Si-C Composite Anode Revealed by the Role of Nanopore using In Situ Lithiation. ACS Energy Letters, 2022. 7(8): p. 2469-2476. Ogata, K., et al., Revealing lithium–silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy. Nature Communications, 2014. 5(1).

To increase the volumetric energy density modern high-energy Lithium-Ion cells consist of Graphite/Silicon ($\mathbf{G r} / \mathbf{S i}$) composite negative electrodes. Due to the high volume expansion of up to 300% caused by (de)lithiation of Si, challenges arise by the usage of $\mathbf{G r} / \mathrm{Si}$-electrodes to prevent accelerated degradation. Therefore, accurate models to predict the cell expansion and pressure are of increasing interest. To investigate the mechanical behavior, half-cell Equivalent Circuit Models (ECMs) are coupled with a solid and liquid diffusion model in this article. The current density distribution among $\mathbf{S i}$ - and Gr -particles is determined by the assumption of an ideal parallel-connected of the active materials. An electrochemical dilatometer is used to measure the electrode expansion. Based on these measurements and literature values of volume changes of the crystal structure, changes of the pore volume are estimated. For the cell expansion and force development a visco-elastic model is implemented by using a spring in serial to a Kelvin-Voigt-Model. Simulations show high agreement with experimental data and literature values regarding cell voltage and expansion.

With rapidly increasing demand for high energy density, silicon (Si) is greatly expected to play an important role as the anode material of lithium-ion batteries (LIBs) due to its high specific capacity. However, large volume expansion for silicon during the charging process is still a serious problem influencing its cycling stability. Here, a Si/C composite of vertical graphene sheets/silicon/carbon/graphite (VGSs@Si/C/G) is reported to address the electrochemical stability issues of Si/graphite anodes, which is prepared by adhering Si nanoparticles on graphite particles with chitosan and then in situ growing VGSs by thermal chemical vapor deposition. As a promising anode material, due to the buffering effect of VGSs and tight bonding between Si and graphite particles, the composite delivers a high reversible capacity of 782.2 mAh g-1 after 1000 cycles with an initial coulombic efficiency of 87.2%. Furthermore, the VGSs@Si/C/G shows a diffusion coefficient of two orders higher than that without growing the VGSs. The full battery using VGSs@Si/C/G anode and LiNi0.8 Co0.1 Mn0.1 O2 cathode achieves a high gravimetric energy density of 343.6 Wh kg-1 , a high capacity retention of 91.5% after 500 cycles and an excellent average CE of 99.9%.

The 3D battery concept applied on silicon–graphite electrodes (Si/C) has revealed a significant improvement of battery performances, including high-rate capability, cycle stability, and cell lifetime. 3D architectures provide free spaces for volume expansion as well as additional lithium diffusion pathways into the electrodes. Therefore, the cell degradation induced by the volume change of silicon as active material can be significantly reduced, and the high-rate capability can be achieved. In order to better understand the impact of 3D electrode architectures on rate capability and degradation process of the thick film silicon–graphite electrodes, we applied laser-induced breakdown spectroscopy (LIBS). A calibration curve was established that enables the quantitative determination of the elemental concentrations in the electrodes. The structured silicon–graphite electrode, which was lithiated by 1C, revealed a homogeneous lithium distribution within the entire electrode. In contrast, a lithium concentration gradient was observed on the unstructured electrode. The lithium concentration was reduced gradually from the top to the button of the electrode, which indicated an inhibited diffusion kinetic at high C-rates. In addition, the LIBS applied on a model electrode with micropillars revealed that the lithium-ions principally diffused along the contour of laser-generated structures into the electrodes at elevated C-rates. The rate capability and electrochemical degradation observed in lithium-ion cells can be correlated to lithium concentration profiles in the electrodes measured by LIBS.

No abstract available

Mechanical changes in active materials with large volume expansion such as silicon and nickel not only affect the electrochemical performance of modern batteries but also pose a great challenge to their mechanical design due to pressure increase during operation. We show that the large expansion and consequently changing mechanical properties of silicon and nickel strongly affect the electrochemical and mechanical performance. A multi-scale electrochemical model is developed, parameterized, and validated for a pouch cell with a SiOx-graphite anode (22 wt.-% SiOx) and an NMC|811 cathode. Mechanical parameters such as expansion and compressive properties are determined experimentally using an in-house-developed high-precision cell press and electrode dilatometer, thus parameterizing a semi-empirical mechanical model. We employ a new characterization technique to measure mechanical changes in the cell in-operando and propose a phenomenological parameterization where physical modeling is not yet sufficient. Through electrode porosity, we show that mechanical and electrochemical performance are interdependent, as the latter is reduced upon expansion and pressure development. On the one hand, the active material of the anode seems to expand into the pores at increased pressure, and on the other hand, the mechanical deformation of the cell components can no longer be neglected.

Microscale silicon particles have a higher specific capacity but larger volume expansion than graphite particles, leading to particle decoupling and lifetime limitations. This study investigates a wide range of external mechanical pressures from zero (ZP-0.00 MPa) to high (HP-0.50 MPa) pressure to determine the optimal pressure for high rate capability, cyclic lifetime, energy density, low temperature rise, and low cell thickness gain. The cells are characterized by rate tests and impedance spectroscopy, and are aged until 70% state-of-health (SoH). The post-mortem analysis after 70% SoH and thickness measurements over 360 cycles in a compression test bench offer insights into the thickness gain. Electrochemical results reveal an immediate reduction in discharge capacity upon transitioning from normal pressure (NP-0.20 MPa) to ZP, with NP and HP exhibiting superior performance over aging. The impedance was reduced initially and over aging for higher mechanical pressures, especially the cathode contact resistance, resulting in lower temperature rises during the rate tests. Overall, applying higher pressures reduced the anode and cell thickness gain. Moreover, the porosity decreased with increasing pressure, as determined by mercury intrusion porosimetry and pycnometer measurements. The anode mass increase correlates to the total charge throughput, which is pressure-dependent and the highest for NP.

Silicon-based anode in Li-ion batteries has received much attention due to its extremely high theoretical capacity which can support high-energy-density battery system. However it suffers seemingly insurmountable barriers including volume expansion and capacity fading during repetitive cycling. In this work, we demonstrated a new kind of silicon/carbon (Si/C) composite design to address the issues in the silicon-based anode application via building a three-dimensional structure of nano Si and carbide-derived-graphite (CDG). Unique cavity-structured CDG made from SiC powder via scalable high temperature treatment, could supply a conductive host for the well-dispersed nano Si particles. CDG/Si composite get improved cycle stability and maintained high capacity of 637 mAh g−1 after 500 cycles. Rate performance of CDG/Si was also enhanced, which should be attributed to good electrolyte accessibility and short ion diffusion distance of CDG to enhance electrode kinetics. In addition, CDG was verified to accommodate higher content of Si of 60%, to achieve higher capacity of 1800 mAh g−1. This work provided a good alternative of carbon matrix for Si/C anode, and it is anticipated that this kind of carbide derived graphite might be of great interest to the further development of high-capacity Si-based anode in Li-ion batteries.

While silicon can significantly enhance the energy density of lithium-ion battery (LiB) anodes, its volume expansion of +280% in the fully lithiated Li 15 Si 4 state and the resulting poor cycle life have limited its use in commercial applications. This study investigates a novel silicon-carbon (Si/C) composite anode material, composed of a carbon host structure infiltrated by silicon. The Si/C performance characteristics is compared with those of state-of-the-art graphite (Gra) and silicon-dominant (Si) anodes in full-cells with an NCA cathode. Full-cell charge and discharge rate tests show the same rate capability for the Si/C and Si anodes, which outperform the Gra anode. For a capacity retention of 80%, the cycle life of the full-cells with the Si/C anode of ∼650 cycles far exceeds the ∼200 cycles obtained with the Si anode but is still short of the ∼1000 cycles obtained with the graphite anode. The projected stack-level gravimetric/volumetric energy densities assuming commercial separator and current collector properties are ∼7%/∼16% higher for the Si/C compared to the graphite anode, approaching the ∼15%/∼20% energy density gains of the Si anodes. Consequently, this Si/C composite is a promising anode active material for LiBs, offering a combination of high energy density, rate capability, and lifetime.

This study presents a scalable and cost-effective spray-drying method for synthesizing graphite/silicon/carbon nanotube (G-Si-CNT) composites as high-performance anodes for lithium-ion batteries. By integrating graphite fines, nano-silicon (nSi), and a low loading (1 wt%) of single-walled CNTs, the resulting composites exhibit enhanced cycling stability and rate capability. The spray-drying process ensures uniform particle morphology and strong adhesion between components, effectively mitigating the mechanical degradation typically caused by silicon’s volume expansion during cycling. Electrochemical tests reveal that the G-15% nSi-1%CNT composite achieves a capacity retention of 95.3% after 100 cycles with a discharge capacity of 630 mAh·g-1 (3.15 mAh·cm-2), outperforming CNT-free counterparts. While CNTs increase solid electrolyte interphase-related losses due to higher surface area, their mechanical and conductive benefits outweigh this drawback. Impedance spectroscopy and post-mortem analyses confirm reduced charge-transfer resistance and improved structural integrity due to CNTs incorporation. The use of low-cost by-products from natural graphite spheroidization and low CNTs content offers significant economic advantages, positioning these composites as promising candidates for scalable, high-energy lithium-ion battery anodes.

No abstract available

In this paper, a Si@EG composite was prepared by liquid phase mixing and the elevated temperature solid phase method, while polyaniline was synthesized by the in situ chemical polymerization of aniline monomer to coat the surface of nano-silicon and exfoliated graphite composites (Si@EG). Pyrolytic polyaniline (p-PANI) coating prevents the agglomeration of silicon nanoparticles, forming a good conductive network that effectively alleviates the volume expansion effect of silicon electrodes. SEM, TEM, XRD, Raman, TGA and BET were used to observe the morphology and analyze the structure of the samples. The electrochemical properties of the materials were tested by the constant current charge discharge and cyclic voltammetry (CV) methods. The results show that Si@EG@p-PANI not only inhibits the agglomeration between silicon nanoparticles and forms a good conductive network but also uses the outermost layer of p-PANI carbon coating to effectively alleviate the volume expansion of silicon nanoparticles during cycling. Si@EG@p-PANI had a high initial specific capacity of 1491 mAh g−1 and still maintains 752 mAh g−1 after 100 cycles at 100 mA g−1, which shows that it possesses excellent electrochemical stability and reversibility.

An analytical model is proposed to investigate properties of composite electrodes that utilize more than one active material. We demonstrate how the equations can be applied to aid in the design of electrodes by comparing silicon-graphite and tin-graphite composite negative electrodes as examples with practical relevance. Based on simple assumptions, the results show how volume expansion tolerance and initial porosity are important factors for the achievable gravimetric and volumetric capacities as well as volumetric energy density. A Si-alloy/graphite composite electrode is used as an experimental system to corroborate the formulated analysis. Kinetic limitations are also addressed based on a novel heuristic approach.

Silicon-dominant (Si) anodes with microscale silicon particles meet the requirements of high energy density and low costs due to its ten times higher theoretical electrochemical capacity of 3579 mAh/gSi (Li15Si4) compared to graphite,1 lifetime extension due to partial lithiation,1-2 and high abundance and economic availability due to existing industrial infrastructure.1-2 The major drawback of silicon is the large volume expansion of nearly 300% upon full lithiation. This hinders the broad application of silicon as an active anode material due to continuous SEI (re-) formation and electrochemical milling of particles. Additionally, the volume expansion impacts the overall electrode stability, leading to thickness changes, the disruption of the electronic pathways, and the decoupling of particles. Although the approach of partial lithiation of microscale1 Si eases these effects by lowering the overall volume expansion, these problems still exist.2,3 In this work, the effect of different mechanical cell pressures on lithium-ion batteries with partially lithiated silicon-dominant anodes is investigated with 5.4 Ah multilayer pouch cells as a follow-up study of our previous work with laboratory T-Cells.3 Methodologically, a novel cell holder and pressure device were developed and validated to apply different mechanical cell pressures. Our investigation covers a pressure range from uncompressed as zero (ZP, 0.00 MPa) to high (HP, 0.50 MPa) external cell pressure to determine the optimal pressure for high rate capacity, cyclic lifetime, energy density, and low thickness gain. The cells were tested by checkup cycles at C/10, rate tests up to 3C, and cycled at C/2 until 70% state of health (SoH). Electrochemical impedance spectroscopy was conducted at different SoHs to quantify the effect of mechanical pressures on the impedance response.4 The post-mortem analysis after reaching 70% SoH and operando thickness measurements in a compression test5 bench give insights into the electrode and cell thickness gain. In the electrochemical results, the discharge capacity Q DCH was immediately reduced by decreasing the mechanical pressure from 0.20 MPa to 0.00 MPa or 0.05 MPa, both for the cells in the cell holder (see inset in Figure 1a) and the compression test bench (not shown). This pressure change was also quantified by an increased charge-averaged full cell potential during charging and a decreased charge-averaged full cell potential during discharging. The impedance was reduced for higher mechanical pressure, especially the cathode contact resistance initially and over aging, resulting in lower temperature increases during the rate tests. The capacity retention Q DCH and the total charge throughput were increased to 360 cycles until 70% SoH for higher mechanical pressures at NP (normal pressure, 0.20 MPa) and HP (see Figure 1) compared to 181 cycles for ZP. Overall, applying higher mechanical pressures reduced the thickness increase, as shown by operando thickness measurements and the post-mortem analysis. A dependency of the reversible thickness on the charged capacity was found. Moreover, the porosity decreased with increasing pressure, which was measured with mercury intrusion porosimetry (MIP) and pycnometry. The anode mass increase correlates to the total charge throughput, which is pressure-dependent and the highest for NP. Our findings demonstrate that applying the optimal mechanical cell pressure is significant when using microscale silicon-dominant anodes. We recommend a mechanical pressure of 0.50 MPa for increased rate capacity, minimizing impedance, heat evolution, and thickness gain, and 0.20 MPa for increased energy density. Acknowledgments: S.F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany) under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank the research battery production team of iwb at TUM for the multi-layer pouch cell production. We also thank Wacker Chemie for kindly providing the microscale silicon material. References: [1] Jantke et al. Silicon-Dominant Anodes Based on Microscale Silicon Particles under Partial Lithiation with High Capacity and Cycle Stability. Journal of The Electrochemical Society 2019, 166, A3881–A3885. [2] Haufe, S.; Bernhard, R.; Pfeiffer, J. Revealing the Failure Mechanism of Partially Lithiated Silicon-Dominant Anodes Based on Microscale Silicon Particles. Journal of The Electrochemical Society 2021, 168, 080531. [3] Friedrich et al. Effect of Mechanical Pressure on Lifetime, Expansion, and Porosity of Silicon Dominant Anodes in Laboratory Lithium-Ion Cells. ECS Meeting Abstract A04-0538. [4] Helmer et al. Deconvolution of an Soc-Dependent Contact Resistance in a Multilayer Pouch Cell Using Impedance Spectroscopy ECS Meeting Abstracts MA2023-01(2):618-618. [5] Aufschläger et al. High precision measurement of reversible swelling and electrochemical performance of flexibly compressed 5 Ah NMC622/graphite lithium-ion pouch cells. Journal of Energy Storage 2023, 59, 106483. Figure 1

Integrating silicon (Si) and graphitic carbon into micron-sized composites by spray-drying holds great potential in developing advanced anodes for high-energy-density lithium-ion batteries (LIBs). However, common graphite particles as graphitic carbon are always too large in three-dimensional size, resulting in inhomogeneous hybridization with nanosized Si (NSi); in addition, the rate capability of graphite is poor owing to sluggish intercalation kinetics. Herein, we integrated graphite nanosheets (GNs) with NSi to prepare porous NSi-GN-C microspheres by spray-drying and subsequent calcination with the assistance of glucose. Two-dimensional GNs with average thickness of ∼80 nm demonstrate superior lithium storage capacity, high conductivity, and flexibility, which could improve the electronic transfer kinetics and structural stability. Moreover, the porous structure buffers the volume expansion of Si during the lithiation process. The obtained NSi-GN-C microspheres manifest excellent electrochemical performance, including high initial coulombic efficiency of 85.9%, excellent rate capability of 94.4% capacity retention after 50 repeated high-rate tests, and good cyclic performance for 500 cycles at 1.0 A g−1. Kinetic analysis and in situ impedance spectra reveal dominant pseudocapacitive behavior with rapid and stable Li+ insertion/extraction processes. Ex situ morphology characterization demonstrates the ultra-stable integrated structure of the NSi-GN-C. The highly active GN demonstrates great potential to improve the lithium storage properties of Si, which provides new opportunity for constructing high-performance anodes for LIBs.

All-Solid-State Batteries (ASSBs) are increasingly perceived as a viable substitute to Li-ion batteries, primarily due to their enhanced safety and energy density. ASSBs utilize a non-flammable solid electrolyte, significantly reducing the risk of fire hazards. Furthermore, they can operate under a broader temperature and voltage spectrum. This research aims to optimize the composition of anode electrode materials, comprised of a particle mixture of Active Material (AM), Solid Electrolyte (SE), and conductive additive. Graphite, a frequently used AM, is favored for its low voltage characteristics and its low volume expansion during charge cycling. Additionally, graphite's low Young Modulus is beneficial in preventing the build-up of substantial stresses within the battery cell. Silicon (Si) is another appealing material due to its high gravimetric capacity, which is up to ten times greater than that of graphite. However, during Li insertion, the crystalline structure transitions to an amorphous state, resulting in a substantial expansion of up to 300%, which triggers a significant accumulation of stress. Numerous strategies have been explored to alleviate the stress build-up resulting from expansion by adding graphite or carbon nanotubes (CNTs). The latter provides void spaces which can accommodate the volumetric expansion. Furthermore, the CNTs possess the capacity to retain the electrode's structure during volume expansion, which is advantageous for maintaining structural integrity, preserving solid-solid contacts, and enhancing the electrical conduction network. Owing to these factors, ASSBs with the addition of CNTs have demonstrated improved cycling performance. 1 Simulating Si composite solid-state anodes presents a significant challenge due to the stress induced by localized Si particles. The substantial expansion of Si can lead to the formation of shell voids in minute localized regions surrounding the microscopic Si particles. This complexity makes it difficult to simulate the dynamics using traditional finite element (FE) based mechanical models. An alternative solution is to employ the Discrete Element Method (DEM) which is a type of particle-based models that solve for Newton's laws of motion for each particle. While continuum models are instrumental in deterministically calculating the properties of bulk materials, DEMs can be utilized to compute particle slippage and the evolution of void regions between individual particles, which influence the local contact area of solid-solid interactions. In our previous research,2 we developed a multiscale chemo-mechanical DEM model for Si anode solid-state batteries. This model encompasses two stages: fabrication and cell operation. During the fabrication stage, particles were simulated within a high-pressure mold, for which we devised an elasto-plastic contact model. Throughout the cell operation stage, we simulated Li insertion and AM volume expansion. However, in current study it was observed that during charge cycling in confined cell volume, the pressure exceeded levels that are acceptable for practical applications. Furthermore, during discharge, the contact areas between particles declined and AM progressively lost its ability to form an electronic percolative chain, reducing the discharge capacity. We successfully incorporated CNTs into the DEM model by linking particles into elongated fibers, each with robust adhesive fusion bonds. The electronic percolation network and interface contact areas saw significant improvement with the addition of CNTs. By further implementing this model, we can determine the optimal composition of Si, graphite and CNTs based on several performance indicators, including the electrode's power density and capacity fade. The study will be broadened to simulate various geometrical configurations, such as a particle mixture of Si and graphite, and coated Si and SE particles on CNT structures. Acknowledgements We gratefully acknowledge the support of the Japan Science and Technology Agency (JST) through the JST-Mirai Program, Grant number JPMJMI24G1. References L. Hu, X. Yan, Z. Fu, J. Zhang, Y. Xia, W. Zhang, Y. Gan, X. He, and H. Huang, ACS Appl. Energy Mater., 5, 14353–14360 (2022). M. So, S. Yano, A. Permatasari, T. D. Pham, K. Park,. and G. Inoue, Journal of Power Sources, 546, 231956 (2022).

Silicon (Si) is a promising active anode material for next-generation lithium-ion batteries due to its high theoretical electrochemical capacity of 3579 mAh/gSi (Li15Si4) and low costs using microscale Si particles.1,2 However, the wide usage of Si as an active anode material is hindered due to its lower lifetime compared to graphite anodes. The degradation in silicon-containing batteries can be suppressed by partial lithiation strategies,2,3,4 with applications for automotive cells leading to improved lifetime.5 However, the lifetime problem still exists in partially lithiated microscale Si particles with lower volume expansion2,3 with ≈200 cycles for one-third silicon utilization, i.e., 1200 mAh/gSi 2. Moreover, we confirmed in our previous study6 as reported by Wetjen et al.4 and Haufe et al.2 that lower cell discharge cut-off voltages and thus higher silicon delithiation potentials versus Li+/Li led to accerlated aging and should be avoided. Thus, the motivation for this study is to avoid these high anode delithiation potentials by operating the cells in a high full cell state of charge (SoC) and to investigate the influence of different SoC windows on lifetime with laboratory 182.1 ± 0.7 mAh/gNCA Swagelok T-cells comprising a microscale silicon-dominant anode and a NCA cathode. The electrode-specific aging is monitored with the lithium metal reference electrode based on the anode and cathode potentials and pulse tests. To investigate the aging in different SOC regimes, three cycling conditions were chosen in the low (LV), middle (MV) and high voltage (HV) window and compared to cells cycled between 2.8 and 4.2 V as full voltage6. The voltage window of LV, MV and HV were chosen to represent cycling between 0-50%, 25-75%, and 50-100% SOC, respectively. Formation and checkups were the same for all cells with 2.80 V to 4.20 V. After reaching the end-of-life criterion of 55% state of health (SoH), the cells were disassembled and anode and cathodes were re-assembled in half-cells for a post-mortem analysis to reveal loss of lithium inventory (LLI) and loss of active material of the anode LAMAn, and the cathode LAMCat of the respective full-cells. Complementary to the electrochemical aging, dilatometer measurements7 were conducted to quantify the electrode expansion for the different silicon anode SoC windows since particle decoupling is expected to be one of the major aging mechanisms for microscale silicon2, which is expected for high electrode expansions. For the electrochemical results, the lifetime can be drastically increased from ≈230 to ≈560 equivalent full cycles (EFCs) for operating the full cell in the HV compared to the FV window, as shown in Fig. 1a. One EFCs is defined as the total charge throughput for charging and discharging one cycle normalized to the capacity of the initial checkup cycle. Over aging, the full cell degradation correlates very well with the end of discharge potential of the silicon anodes. Moreover, the electrode-specific pulse results show strong anode degradation while the cathode remains intact. The post-mortem results reveal LLI as most dominenat aging mode, which was very similar for all voltage windows. The HV cells showed both the highest LAMNE and LAMPE, whereas LAMNE was more dominant compared to LAMPE. The silicon amorphization was the lowest for the LV anodes and the highest for the HV anodes at the same SoH. The dilatometer results show that the silicon electrode expansion is the lowest for the low lithiation, i.e., LV, and the highest for the highest lithiation, i.e., HV. From the dilatometry results, we conclude that the mechanical electrode stability does not limit lifetime. Our results demonstrate that lifetime can be significantly improved by a factor of ≈2.4 based on the EFCs if operating cells with silicon dominant anodes in high SoCs and that low SoCs should be avoided. Acknowledgments: S. F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany) under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank our student worker, Maximilian Reichl, for the fabrication of the NCA coatings. We also thank Wacker Chemie AG for kindly providing the microscale silicon material. References: [1] Jantke et al. Journal of The Electrochemical Society 2019, 166, A3881–A3885. [2] Haufe et al. Journal of The Electrochemical Society 2021, 168, 080531. [3] Li et al. Electrochiminca Acta 2019, 295, 778-786. [4] Wetjen et al. Journal of The Electrochemical Society 2018, 165, A1503-A1514 [5] Mikheenkova et al. Journal of The Electrochemical Society 2023, 170, 080503 [6] Friedrich et al. ECS Meeting Abstract 2023 A04-0538. [7] Spingler et al. Journal of The Electrochemical Society 2021, 168, 040515 Figure 1

The rapid development photovoltaic industry has generated a huge amount of waste ultra-fine silicon cutting powder. The management and value-added recovery of silicon cutting waste is highly important for both environmental remediation and economic efficiency. In this work, silicon waste was used as a cost-effective raw material for the preparation of silicon/graphite anode for lithium-ion batteries. First, porous Si embedded with Ag particles (pSi/Ag) was produced by silver-assisted chemical etching (Ag-ACE). Then, pSi/Ag was loaded on a micron-sized graphite matrix (pSi/Ag/G), and organic carbon (C) produced by the pyrolysis of polyvinylpyrrolidone (PVP) acted as a link to closely connect pSi/Ag and graphite to form the pSi/Ag/C/G composite. The incorporated Ag particles and the porous structure improve electron transfer and mitigate the volume expansion effect of silicon. The novel design and structure of the anode can maintain the integrity of the electrode during cycling, and thus strongly improve cycling stability. The prepared pSi/Ag/C/G composite exhibited a large initial discharge capacity of 2353 mAh/g at 0.5 A/g and good initial coulombic efficiency of 83%, delivering a high capacity of 972 mAh/g at 1 A/g after 200 cycles. This work confirmed the possibility of the preparation of lithium battery silicon-carbon anode from silicon waste and provides a promising new avenue for value-added utilization of silicon cutting waste materials.

A silicon nanoparticle–graphite nanosheet composite was prepared via a facile ball milling process for use as the anode for high-rate lithium-ion batteries. The size effect of Si nanoparticles on the structure and on the lithium-ion battery performance of the composite is evaluated. SEM and TEM analyses show a structural alteration of the composites from Si nanoparticle-surrounded graphite nanosheets to Si nanoparticle-embedded graphite nanosheets by decreasing the size of Si nanoparticles from 250 nm to 40 nm. The composites with finer Si nanoparticles provide an effective nanostructure containing encapsulated Si and free space. This structure facilitates the indirect exposure of Si to electrolyte and Si expansion during cycling, which leads to a stable solid–electrolyte interphase and elevated conductivity. An enhanced rate capability was obtained for the 40 nm Si nanoparticle–graphite nanosheet composite, delivering a specific capacity of 276 mAh g−1 at a current density of 1 C after 1000 cycles and a rate capacity of 205 mAh g−1 at 8 C.

Silicon/silicon oxides/graphite (Si/SiOx/G) composite with high capacity and excellent cycling performance has been synthesized via high temperature treatment, HF etching and high-energy ball milling for mixture of silicon oxide and graphite. The chemical composition and morphology of the sample was characterized by XRD, SEM and TEM. Large numbers of nanopores were formed in the as-prepared composite, providing three-dimensional transmission pathways for lithium ions and electrons. After 100 cycles, the electrode kept an excellent reversible capacity of 804.2mAh·g-1. The excellent electrochemical properties are mainly attributed to the uniform distribution of silicon particles in amorphous silicon oxide, the buffering effect of porous structure and the improvement of conductivity of the composite by graphite.

Lithium (Li) plating, triggered by fast charging and low temperature, will cause performance degradation and safety concerns for lithium-ion batteries (LIBs). However, strategically limited and controlled Li deposition might be advantageous for enhancing energy density. The detailed mechanism and regulation for performance improvement are yet to be fully explored. This study meticulously modulates the overlithiation capacity to regulate Li plating and probes its effects on the stability of high-capacity silicon/graphite (Si/Gr) electrodes through consecutive cycling and over the calendar aging period. The Si/Gr electrode (20 wt% Si) with a 20% overlithiation degree exhibits enhanced reversible capacity in comparison to the pristine Si/Gr electrode. This improvement is attributed to precision-controlled Li deposition, the increased electrochemical utilization of Si and Gr above 0 V, and the additional intercalation/alloying reactions below 0 V, which decelerate the progression of capacity degradation and significantly boost the electrochemical performance of Si/Gr electrodes. Moreover, this tailored Si/Gr electrode with a 20% overlithiation degree attenuates the deterioration associated with calendar aging. This research not only elucidates the intricate interplay and mechanisms of Li plating on Si/Gr electrodes during overlithiation but also presents a new understanding and approach to advance the performance of LIBs and extend their service lifespan.

No abstract available

Given the rising importance of energy storage for the technological future, the development of new storage technologies becomes critical. Lithium-ion batteries are a promising technology, in particular for electric mobility, because of their high energy density and specific energy. Among the different lithium technologies, the use of nickel-rich NMC positive electrodes and silicon-graphite negative electrodes (NMC/Si-Gr) allows for notably high specific energy values. However, this battery technology can have a short cycle life under certain conditions. As cycle life is a key issue for automotive applications, it is important to evaluate which factors can lead to an earlier degradation of NMC/Si-Gr batteries. This paper provides a long term cycling study of a commercial NMC/Si-Gr battery, including different types of cycling conditions, both static and dynamic, with the aim to identify which factors can shorten the cycle life of the technology. The state of health of the cells is measured and analyzed via capacity measurements and electrochemical impedance spectroscopy.

Amorphous Si thin films with different thicknesses were deposited on synthetic graphite electrodes by using a simple and scalable one-step physical vapor deposition (PVD) method. The specific capacities and rate capabilities of the produced electrodes were investigated. X-ray diffraction, scanning electron microscopy, Raman spectroscopy, profilometry, cyclic voltammetry, galvanostatic techniques, and in situ Raman spectroscopy were used to investigate their physicochemical and electrochemical properties. Our results demonstrated that the produced Si films covered the bare graphite electrodes completely and uniformly. Si-coated graphite, Si@G, with an optimal thickness of 1 μm exhibited good stability, with an initial discharge capacity of 628.7 mAhg-1, a capacity retention of 96.2%, and a columbic efficiency (CE) higher than 99% at C/3. A discharge capacity of 250 mAh g-1 was attained at a high current rate of 3C, which was over 2.5 times that of a bare graphite electrode, thanks to the high activated surface area (1.5 times that of pristine graphite) and reduced resistance during cycling.

The impact of the binding, solution structure, and solution dynamics of poly(vinylidene fluoride) (PVDF) with silicon on its performance as compared to traditional graphite and Li1.05Ni0.33Mn0.33Co0.33O2 (NMC) electrode materials was explored. Through refractive index (RI) measurements, the concentration of the binder adsorbed on the surface of electrode materials during electrode processing was determined to be less than half of the potentially available material resulting in excessive free binder in solution. Using ultrasmall-angle neutron scattering (USANS) and small-angle neutron scattering (SANS), it was found that PVDF forms a conformal coating over the entirety of the silicon particle. This is in direct contrast to graphite-PVDF and NMC-PVDF slurries, where PVDF only covers part of the graphite surface, and the PVDF chains make a network-like graphite-PVDF structure. Conversely, a thick layer of PVDF covers NMC particles, but the coating is porous, allowing for ion and electronic transport. The homogeneous coating of silicon breaks up percolation pathways, resulting in poor cycling performance of silicon materials as widely reported. These results indicate that the Si-PVDF interactions could be modified from a binder to a dispersant.

Challenges such as mechanical degradation and limited cycle life persist for high energy density lithium-ion batteries with silicon/graphite composite anodes. In this research work, the patterns of degradation of cells with silicon/graphite composite and NMC622 cathode are examined at varied cycling conditions and applied external pressure or pretension. The most notable outcome of this analysis is that cells cycled between 0 and 100 State-of-Charge (SoC) exhibit the most accelerated aging process. Increasing the pretension force effectively restrains the irreversible expansion of the cells, and has a positive effect on capacity retention. In this research, a comprehensive experiment was conducted involving 46 cells subjected to diverse cycling conditions, voltage windows, pretension forces, and temperatures. Reference performance tests (e.g. HPPC and 1/20 C-rate charge tests) are conducted regularly for analysis of degradation mechanisms. The capacity fade, resistance growth, and thickness increase are correspondingly shown in Figures 1, 2, and 3 with ampere hour throughput as the x-axis. The legend columns indicate test conditions, including C-rate, SoC window during cycling, temperature (in degrees Celsius), and pretension force (in psi). As is shown in all figures, there is a substantial dependence on the SoC window for cycling. To be specific, a rapid rate of capacity loss, resistance increase, and thickness increase occurs in the cell group cycled over the full SoC window (plotted in blue). Cells cycled under full SoC windows also exhibit an early accelerated fading (knee [1]) of capacity and accelerated increase (elbows [2]) of resistance and thickness. According to [3], this accelerated aging could be a consequence of side reactions and increased mechanical stress within the silicon particle when operating across a broad potential range. Meanwhile, for the cell group with restrained cycle windows (plotted in gray) the cells have not yet reached any knee, and have a relatively linear capacity loss. It should be noted that, within the range of partial cycling windows examined, cells subjected to a cycling range of 50-100 exhibit the most rapid degradation, which aligns with the conclusions presented in [4] due to the time at elevated potential. In Figure 2, the elevated temperature (depicted in red) exhibits a significant influence on the increase in resistance, potentially attributed to the growth of the solid electrolyte interface (SEI), but minimal impact on capacity loss. Maintaining other conditions constant and comparing cells under 25 psi and 15 psi (marked with hollow circles and filled circles, respectively), it is evident that a higher pretension force has a positive effect on cell capacity loss. Simultaneously, in Figure 3, the pretension force at 25 psi (marked with hollow circles) effectively restrains the irreversible expansion of the cells. The results are similar to the degradation pattern outlined in [5], it is observed that employing a high pretension force facilitates the mitigation of both degradation and expansion. As highlighted in [6], heightened temperatures lead to accelerated resistance growth. Nevertheless, the impact of various C-rates on degradation remains inconclusive [6]. This research systematically analyzed cell-level degradation through an extensive array of experiments, providing valuable insights into the intricate dynamics of capacity fade, resistance increase, and thickness growth. The study's revelation that the cycle window exerts a pronounced impact on battery health could offer crucial guidance for the design of Battery Management Systems (BMS). Moreover, the work establishes a foundational basis for future research, particularly in exploring electrode-level degradation patterns. These contributions collectively enhance the understanding of energy storage systems, offering practical implications for optimizing battery performance and longevity in various applications. [1]Attia, Peter M., et al. "“Knees” in lithium-ion battery aging trajectories." Journal of The Electrochemical Society 169.6 (2022): 060517. [2] Strange, Calum, et al. "Elbows of internal resistance rise curves in Li-ion cells." Energies 14.4 (2021): 1206. [3] Verbrugge, Mark, et al. "Fabrication and characterization of lithium-silicon thick-film electrodes for high-energy-density batteries." Journal of The Electrochemical Society 164.2 (2016): A156. [4] Xu, Bolun, et al. "Modeling of lithium-ion battery degradation for cell life assessment." IEEE Transactions on Smart Grid 9.2 (2016): 1131-1140. [5] Mohtat, Peyman, et al. "Reversible and irreversible expansion of lithium-ion batteries under a wide range of stress factors." Journal of The Electrochemical Society 168.10 (2021): 100520. [6] Pannala, Sravan, et al. "An Experimental Correlation of Degradation with Cell Reversible and Irreversible Expansion Measurement in Pouch Cells." Electrochemical Society Meeting Abstracts 243. No. 2. The Electrochemical Society, Inc., 2023. Figure 1

As the electric vehicle market keeps growing up, the importance of achieving good technical characteristics is increasingly important. The most common technology for EV energy storage is the use of battery packs, in particular, lithium-ion batteries (LIBs). One of the most promising solutions is based on nickel-rich positive electrodes and silicon-graphite negative electrodes. This paper shows an evaluation of nickel-rich/silicon-graphite LIBs, using several cycling tests under different regimes for evaluating the impact of the different aspects that are important in a EV, such as high current charging. The batteries state of health is evaluated via capacity measurement, efficiency calculation and impedance measurements.

No abstract available

Electric vehicles are consistently being adopted by the consumer market. The associated range anxiety of purchasing an electric vehicle can be partially put at ease by looking at real driving data that shows the average driving distance in a day is under 75 km. These limited driving days represent days with a partial battery cycle. Partial cycling ranges are an interesting area of research particularly for silicon-graphite composite electrodes, where different cycling ranges can have large impacts on the lifetime of the cell. In this study, we investigate the two active anode materials of metallurgical silicon and a silicon-carbon composite at five cycling ranges: 60-0%, 80-0%, 100-0%, 100-40%, and 100-60%. The cells used in this study contribute ~70% of their capacity from silicon or Si-C representing an interesting difference from silicon/graphite composite anodes featuring minimal silicon capacity. The cycling ranges that focus on cycling the graphite portions of the electrode and only occasionally use the silicon capacity show great capacity retention over their lifetime. Whereas the cells using predominantly using silicon capacity experience rapid capacity fading. This choice becomes an important distinction when trying to extend the lifetime of a vehicle’s battery pack.

The growing demand for high‐capacity, fast‐charging lithium‐ion batteries in electronic devices and electric vehicles has increased interest in silicon–graphite composite anodes. This study investigates the effect of binder composition on the electrochemical performance of composite electrodes containing 24 wt% silicon. Water‐soluble binders—polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and their crosslinked form (c‐PAA‐CMC)—are used to fabricate electrodes designated as PAA0 (CMC 100%), PAA50 (50% PAA–50% CMC), and PAA100 (PAA 100%). All electrodes are subjected to 1C galvanostatic cycling for 100 cycles. The PAA100 electrode exhibits the highest capacity retention (43.41%), compared to PAA50 (36.09%) and PAA0 (25.27%), highlighting the superior stability of the PAA binder. Scanning electron microscopy images reveal fewer surface cracks in PAA100 electrodes, indicating improved mechanical integrity. Electrochemical impedance spectroscopy (EIS) results show that the PAA100 electrode had up to 60% lower resistance, suggesting enhanced charge transport and interface stability. The findings suggest that PAA promotes early SEI formation and preserves electrode integrity during cycling. However, due to the high reactivity of silicon, continuous SEI growth contributes to irreversible capacity loss. Overall, the study underscores the importance of binder selection in improving the durability and fast‐charging performance of high‐silicon‐content lithium‐ion batteries.

In silicon/graphite (Si/Gr) composite electrodes for lithium‐ion batteries, which have recently garnered significant attention, the competitive (de)lithiation between Si and Gr is recognized as crucial for understanding the internal electrochemical processes. In this work, an in‐situ method to characterize this competitive behavior is proposed, utilizing a self‐developed electrode curvature measurement system. After validating the parallel electrode configuration and the model battery, curvature measurements are simultaneously conducted on the parallel Si and Gr cantilevered electrodes throughout electrochemical cycling. Subsequently, by calibrating the correlation between capacity and curvature of the Gr electrode, the capacity evolution of Si and Gr within the Si/Gr electrode is determined, shedding light on the underlying competitive (de)lithiation behavior. During lithiation, the process transitions from “Si‐dominant” to “Gr‐dominant” and eventually reaching a “synchronous” stage. For delithiation, it moves from “Gr‐dominant” to “Si‐dominant”. The method proposed in this work, based on the measurement of macroscopic electrode deformation, offers a novel perspective for characterizing competitive (de)lithiation in electrodes with multiphase active materials.

Silicon–graphite blend electrodes offer higher specific capacity than pure graphite and are increasingly used in high-energy lithium-ion batteries. This study proposes and validates a method to predict the heat generation in such blends under low-rate cycling conditions. The heat flow of individual silicon and graphite electrodes is measured using isothermal micro-calorimetry, while their pseudo-open-circuit potentials are recorded. The single-component data was combined to calculate blend potential, current distribution, and total heat generation across various silicon-to-graphite ratios. Three blend electrodes with different amounts of nanometer-sized silicon were fabricated for validation. In addition, a dual calorimetric setup was developed to simultaneously measure the current and the heat flow contributions from both active material components during cycling. The calculated electrochemical and thermal behavior were in good agreement with the experimental data, confirming that heat generation in silicon–graphite blends can be predicted using a linear combination of individual component contributions. This supports the applicability of the rule of mixtures under low-rate conditions. The proposed method enables accurate prediction of blend electrode thermal behavior based solely on single-component data, reducing the need to fabricate blend electrodes. In addition, the dual calorimeter setup provides a new tool for decoupling component-specific heat contributions in composite electrodes.

Application of silicon-based anode is significantly challenged by low initial Coulombic efficiency (ICE) and poor cyclability. Traditional pre-lithiation reagents often pose safety concerns due to their unstable chemical nature. Achieving a balance between water-stability and high ICE in prelithiated silicon is a critical issue. Here, we present a lithium-enriched silicon/graphite material with an ultra-high ICE of ≥110% through a high-stable lithium pre-storage methodology. Lithium pre-storage prepared a nano-drilled graphite material with surficial lithium functional groups, which can form chemical bonds with adjacent silicon during high-temperature sintering. This results in an unexpected O-Li-Si interaction, leading to in-situ pre-lithiation of silicon nanoparticles and providing high stability characteristics in air and water. Additionally, the lithium-enriched silicon/graphite materials impart a combination of high ICE, high specific capacity (620 mAh g-1), and long cycling stability (> 400 cycles). This study opens up a promising avenue for highly air and water-stable silicon anode prelithiation methods.

Silicon (Si), with high theoretical specific capacity, the most promising anode material to replace graphite in lithium‐ion battery (LIB) systems, is studied. The large volume changes during cycling cause cracking, fragmentation of Si, and electrical isolation of the Si active material from the current collector. The combined use of Si and graphite (Si‐Gr) provides the best option to achieve high energy densities in commercial LIB systems. The different physical and chemical surface properties of silicon and graphite necessitate designing a binder capable of restraining volume changes. The present study focuses on the effectiveness of crosslinking naturally abundant and water‐soluble tamarind gum (TG) with polyacrylic acid (PAA) as binder. Crosslinking of TG and PAA, confirmed by FTIR, has aided an optimum balance between the binding strength, swelling, and better electrode integrity during the cycling than PAA‐based anodes. It exhibits an initial specific capacity of 872 mAh/g and coulombic efficiency of 70%. The capacity retention is ≈60% at the end of 900 cycles. The crosslinked TG‐PAA binder facilitates Li+ transportation there by maintaining rate capability in the anode. The results provide a promising avenue for pursuing environment‐friendly processing of high‐capacity LIBs with an extended cycle life using crosslinked biopolymer as binder.

No abstract available

Silicon-Graphite (Si-Gr) composite electrodes, composed of heterogeneous active materials, combine the high capacity of silicon with the conductivity and stability of graphite. These anodes, known for their excellent electrochemical performance and cycle stability, are gaining attention as potential replacements for graphite electrodes [1]. However, their long-term cycle stability is not as good as graphite's, and the higher the silicon content, the quicker the degradation occurs. Thus, it is necessary to improve this aspect [2]. The primary reason for the degradation of cycle stability in Si-Gr composite electrodes is the repeated growth of the Solid Electrolyte Interphase (SEI) during the cycling process [3]. Initially, the SEI forms around the active material, and as the cycling progresses, it extends over the entire electrode [4, 5]. During this process, the electrochemical performance of the active materials within the electrode decreases, and occasionally recovers. This fluctuation is influenced by the repeated growth of the SEI. When the residual stress inside the electrode exceeds the yield point, electrode cracking occurs. Unintentionally, these cracks shorten the ion transport pathways, which in turn can restore the electrochemical performance [5]. However, this interpretation is based on the observed capacity reduction and changes in electrode structure ex-situ. Therefore, there are inherent limitations in clearly delineating the step-by-step processes that result in internal structural changes and crack formation within the electrode. Additional analysis is required to further investigate these phenomena. In this study, to understand the internal structural changes of the Si-Gr composite electrode during high-speed, long-term cycling, we monitored the changes in electrode stress states in-situ during 200 cycles at 1C [6]. Additionally, by varying the silicon ratio, we aimed to comprehend the role of each active material over the long term. In Figure 1a, the observed capacity and stress changes in the 6% Si electrode are overlaid values of the two active materials' reactions. To analyze the stress behavior characteristics due to the volumetric behavior of each active material, as shown in Figures 1b and 1c, the capacity and stress were differentiated to distinguish the contributions of each material (dQ/dV, dσ/dV). Additionally, by calculating the differential stress to differential capacity (dσ/dQ), as shown in Figure 1d, we understood the changes in the electrode structure at the reaction point of Silicon (Si1 for Li3.75Si → LixSi). By further analyzing these results and compiling data from different ratios of active materials, we aim to analyze the changes in internal electrode structure and the causes of crack formation in long-term, based on high-speed charging/discharging. Figure 1

In this study, we present a facile technique for producing the amorphous carbon-coated Silicon (Si) mixed with commercial graphite (Gt) as anode active material for lithium-ion batteries. The carbon is coated onto Si particles with a simple two-steps process from a low-cost alcohol-based source, namely furfuryl alcohol. The carbon-coated Si is then mixed with the Gt and the amount of Si is varied to obtain a stable cycling performance. The best cycling performance is obtained when the Si@C weight ratio with respect to Gt is adjusted to 10%. The cell containing the optimized Si@C anode able to deliver 408 mAh g−1 capacity after 100 cycles at 0.2C rate while the commercial state-of-the-art Gt anode only delivers a capacity of 303 mAh g−1 after 100 cycles. The materials are further characterized by Fourier-transform infrared (FTIR) spectroscopy, Scanning Electronic Microscopy coupled with Energy Dispersive Spectrometry (SEM/EDS), Particle Size Analyzer (PSA), Raman, X-ray Diffraction (XRD), and High-Resolution Transmission Electron Microscopy (HR-TEM) coupled with energy dispersive spectrometry and Selected Area Electron Diffraction (SAED). Electrochemical characterizations like Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) analysis of the half-cells are carried out. Finally, the post-mortem analysis of the cells is carried out using SEM/EDS, post-cycling CV, and EIS.

Silicon is a promising negative electrode material for high-energy batteries, but its volume changes during cell cycling cause rapid degradation, limiting its loading to about 10 wt.% in conventional graphite/Si composite electrodes. Overcoming this threshold requires evidence-based design for the formulation of advanced electrodes. Here we combine multimodal operando imaging techniques, assisted by structural and electrochemical characterizations, to elucidate the multiscale electro-chemo-mechanical processes in graphite/Si composite negative electrodes. We demonstrate that the electrochemical cycling stability of Si particles strongly depends on the design of intraparticle nanoscale porous structures, and the encapsulation and loss of active Si particles result in excessive charging current being directed to the graphite particles, increasing the risk of lithium plating. We also show that heterogeneous strains are present between graphite and Si particles, in the carbon-binder domain and the electrode’s porous structures. Focusing on the volume expansion of the electrode during electrochemical cycling, we prove that the rate performance and Si utilization are heavily influenced by the expansion of the carbon-binder domain and the decrease in porosity. Based on this acquired knowledge, we propose a tailored double-layer graphite/Si composite electrode design that exhibits lower polarization and capacity decay compared with conventional graphite/Si electrode formulations. Multimodal operando imaging reveals how multiscale structural design affects lithiation heterogeneity and electrochemical cycling stability in graphite/silicon composite battery electrodes.

Silicon‐graphite (Si/Gr) composite electrodes are widely used in commercial Li‐ion batteries to enhance capacity while balancing mechanical stability. This study investigates the electrochemical behavior of high‐silicon‐content (30 wt%) Si/Gr blends using a decoupled blend cell setup. By analyzing the contributions of individual components, we assess their effective C‐rates and charge distribution throughout the cycling process. The results confirm the non‐additive nature of Si/Gr electrochemistry, demonstrating significant variations in C‐rates between silicon and graphite, particularly during delithiation. The study also explores an alternative Si/Gr‐Gr decoupled blend setup to better represent lower silicon content electrodes. Our findings provide insight into lithium electrode dynamics and the complexities of designing blended electrodes with materials of significantly different capacities. This work contributes to the understanding of silicon’s role in composite anodes and offers valuable guidelines for designing high‐silicon‐content electrodes with improved electrochemical performance.

4.5 V‐class lithium‐ion batteries (LIBs) pairing LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes with silicon‐majority graphite (SmG, >1500 mAh g−1) anodes can surpass 400 Wh kg−1, but their cycling stability, safety, and low‐temperature operation are constrained by the difficulty in constructing stable interphase. This study reports a hybrid‐sulfonamide electrolyte (HSE) that can survive the aggressive chemistry of high‐voltage NMC811 and programs a self‐limiting inorganic interphase on Si by leveraging the electron‐limited onset at the Si||electrolyte junction. At first lithiation, the semiconductor characteristic and native SiOx create a space‐charge (depletion) region, so the anionic‐structure‐like sulfonamides bias first‐electron reduction, seeding lithium halide/chalcogenide inorganics that are electronically insulating yet Li+‐permeable. The resulting thin, dense layer suppresses electron tunneling, dissolution, and resists crack‐induced stress concentration during Si expansion—thereby self‐limiting further growth. Consequently, NMC811||SmG coin cells with the HSE retain 80% capacity after 500 cycles at 4.5 V and ≈5 mAh cm−2 and operate over a wide range of temperature from −40 to 60 °C, markedly outperforming the carbonate electrolyte. 1.4 Ah pouch cells maintain 80.0% of initial capacity after 1150 cycles and exhibit thermal stability up to 300 °C. This work establishes self‐limiting interphase formation on Si as a practical electrolyte design target for high‐energy LIBs.

Because of its high specific capacity, the silicon-graphite composite (SGC) is regarded as a promising anode for new-generation lithium-ion batteries. However, the frequently employed two-section preparation process, including the modification of silicon seed and followed mixture with graphite, cannot ensure the uniform dispersion of silicon in the graphite matrix, resulting in a stress concentration of aggregated silicon domains and cracks in composite electrodes during cycling. Herein, inspired by powder engineering, the two independent sections are integrated to construct multistage stable silicon-graphite hybrid granules (SGHGs) through wet granulation and carbonization. This method assembles silicon nanoparticles (Si NPs) and graphite and improves compatibility between them, addressing the issue of severe stress concentration caused by uncombined residue of Si NPs. The optimal SGHG prepared with 20% pitch content exhibits a highly reversible specific capacity of 560.0 mAh g-1 at a current density of 200 mA g-1 and a considerable stability retention of 86.1% after 1000 cycles at 1 A g-1 . Moreover, as a practical application, the full cell delivers an outstanding capacity retention of 85.7% after 400 cycles at 2 C. The multistage stable structure constructed by simple wet granulation and carbonization provides theoretical guidance for the preparation of commercial SGC anodes.

As a prominent next-generation anode material for high-capacity applications, silicon stands out due to its potential. Crystalline silicon, which offers a higher initial capacity compared to its amorphous counterpart, presents challenges in practical applications due to its poor cycling performance. In this study, we prepared composites of crystalline and amorphous silicon with graphite, assembled pouch-type full cells, and evaluated their suitability for practical use. The material incorporating amorphous silicon demonstrated superior performance at both high and low rates, as well as various temperatures. Additionally, the changes in cell thickness during charge and discharge, i.e., the volume changes in the anode material, are significantly related to cycling performance. We examined the microscopic interactions between silicon and lithium atoms using molecular dynamics simulations. Our observations indicate that lithium migration within amorphous silicon, which has lower activation energy, is much easier than in crystalline silicon. In crystalline silicon, lithium penetration is greatly influenced by the orientation of the crystal planes, resulting in anisotropic volume expansion during lithiation.

No abstract available

Despite its pronounced impact on charge transport and local stress‐field regulation, interfacial curvature remains an underexplored design parameter for silicon anodes. Here, we report a silicon anode encapsulated by a molecularly curved, sp 3 ‐rich graphite framework constructed via high‐energy ball milling. This curvature‐defect architecture transforms the typically inert graphite host into an active mediator for interfacial charge redistribution and stress relaxation. The curvature induces built‐in work‐function gradients and local electric fields that direct Li + /electron transport and suppress early stress hotspots; concurrently, curvature‐enhanced sp 3 ‐C sites catalyze in situ Si─C bond formation and drive interfacial charge redistribution, leading to partial Si de‐electronation and reversible core contraction. These coupled mechanisms homogenize 3D stress propagation, suppress crack initiation during lithiation. This curvature‐field‐stress coupling effectively overcomes the long‐standing challenge of multistage stress accumulation and unstable interfacial charge dynamics at the silicon‐graphite anode interface, thereby contributing to enhanced rate capability and long‐term cycling stability. Electrochemical characterizations reveal that the composite exhibits ultralow capacity decay (∼0.025% per cycle over 1200 cycles at 1 A g −1 ) and retains ∼492 mA h g −1 at 5 A g −1 . This curvature‐defect paradigm provides a scalable, mechanistically grounded pathway to activate inert graphite hosts and design stress‐tolerant, long‐lived silicon‐carbon anodes.

In order to increase the practical capacity of standard graphite anode and to overcome the drawbacks of pure silicon anode material due to its large volume change, graphite electrodes mixed with silicon nanoparticles are under development. In this work, various types of graphite anodes mixed with 10 wt% silicon nanoparticles were fabricated in view of film thickness and mixing ratio of binder materials. Additionally, free-standing structures were generated on silicon/graphite electrodes by applying ultrafast laser ablation. The mechanical stress within the electrodes can be significantly reduced by means of laser generated artificial porosity. Galvanostatic and cyclic voltammetry measurements reveal that the cells with structured electrodes exhibit excellent electrochemical properties and improved lithium-ion transport kinetic in comparison to cells with unstructured electrodes (reference). Furthermore, cell impedance was investigated by applying electrochemical impedance spectroscopy. Fresh cells with structured electrodes indicate a lower impedance only at full lithiated state. After cycling, these cells exhibit lower impedance at different depth of discharge probably due to a reduced mechanical and chemical degradation compared to reference cells.

High-weight-percentage silicon (Si) in graphite (Gr) anodes face commercialization hurdles due to fundamental and interrelated challenges. Nevertheless, using the existing manufacturing line, the optimized Si/Gr ratio is the most efficient and valuable way to fabricate high-energy-density lithium-ion batteries (LIBs). Still, literature has not thoroughly examined the Si/Gr ratio. This study addresses this critical gap by systematically evaluating Si content (5-20 wt %) in commercial graphite. The goal is to optimize the Si/Gr ratio for exceptional specific capacity while mitigating inherent Si limitations like cyclic stability and first-cycle irreversible capacity loss. This work employs a multidirectional approach, including in situ electrochemical impedance spectroscopy for interface analysis, rate capability assessment (up to 3 C-rate), Li diffusion coefficient measurement, and thorough cyclic stability evaluation. Increasing the silicon (Si) weight percent from 10% to 15% in the Si15Gr75 composite anode resulted in significant improvements in the first lithiation and delithiation capacities by approximately 16.8% and 16.0%, respectively. The Si15Gr75 cell delivered a high initial Coulombic efficiency of roughly 82.9%, nearly equivalent to a pure graphite anode. Furthermore, the Si15Gr75 Li cell exhibited excellent cyclic stability at a current rate of 0.5 C, retaining about 60% of its capacity after 215 cycles. Additionally, full-cell testing against a commercial NMC622 cathode showcases excellent performance across various current rates (0.1-0.5 C). This study paves the way for the development of high-energy-density LIBs by providing valuable insights into the optimization of Si/Gr composite anodes for commercial viability.

Novel alginate-based binders containing either catechol (d-Alg) or sulfonate (s-Alg) functional groups were developed and characterized to improve the capacity decay performance and better stability of Li-ion batteries. The electrochemical performance of silicon–graphite (Si/Gr) anode with alginate-based binders were compared to the commonly used CMC/SBR binder. The active material in the anodes was the ball-milled Si/Gr (20:80 wt%) powder mixture. A comprehensive electrochemical study was carried out through rate capability test, cycle test, differential capacity analysis (dQ/dV), and electrochemical impedance spectroscopy (EIS). The functionalized s-Alg binder showed the lowest electrolyte uptake (11.5%) and the highest tensile strength (97 MPa). Anodes with s-Alg exhibited high initial capacity (1250 mAh g−1) and improved decay performance (580 mAh g−1 at 0.2 C), by ~ 65% higher compared to CMC/SBR binder. The influence of pH value of s-Alg binder preparation showed that anodes prepared at pH 3 of s-Alg exhibit better performance, reaching 800 and 750 mAh g−1 at 0.1 and 0.2 C, respectively, due to the stronger bonding formation and compactness of anode layer which providing low charge transfer and solid electrolyte interface resistance.

The impact of mechanical pressure on electrode stability in full-cells comprising microscale silicon-dominant anodes and NCA cathodes was investigated. We applied different mechanical pressures using spring-compressed T-cells with metallic lithium reference electrodes enabling us to analyze the electrode-specific characteristics. Our investigation covers a wide pressure range from 0.02 MPa (low pressure - LP) to 2.00 MPa (ultra high pressure - UHP) to determine the optimal pressure for cyclic lifetime and energy density. We introduce an experimental methodology considering single-component compression to adjust the cell setup precisely. We characterize the cells using impedance spectroscopy and age them at C/2. In the post-mortem analysis, cross-sections of the aged anodes are measured with scanning electron microscopy. The images are analyzed with regard to electrochemical milling, thickness gain, and porosity decrease by comparing them to the pristine state. The results indicate that cycling at UHP has a detrimental effect on cycle life, being almost two-fold shorter when compared to cycling at normal pressure (NP, 0.20 MPa). Scanning electron microscopy showed a dependency of the thickness and the porosity of the aged silicon anodes on the applied pressure, with coating thickness increasing and porosity decreasing for all pressure settings, and a correlation between thickness and porosity.

Lithium-ion batteries (LIBs) are critical components in various electronic devices and electric vehicles, driving the need for enhanced performance and efficiency. Graphite has been a popular choice as an anode material due to its stability and conductivity. However, to meet the increasing demand for higher energy densities, silicon has emerged as a promising candidate owing to its high theoretical specific capacity [1]. In this study, we explore the behavior of graphite/silicon (Gr/Si) composite anodes for LIBs. Our investigation focuses on varying the silicon content within the composite anode (ranging from 0% to 20%) to understand its impact on the electrochemical performance. We employ micro-scale simulations by discrete element method (DEM) to provide insights into the evolution of the electrode morphology, including intercalation, particle size distribution, porosity, and tortuosity [1]. Moreover, to analyze the lithiation and delithiation processes, voltage, and energy density considering the morphological of anode, we utilize LIB simulation with Gr/Si, 1.0 M LiPF6 solution in EC-EMC solvent, and lithium metal were used for the anode, electrolyte, and cathode, respectively. The evaluation used three different constant charging rate (C-rate) conditions (0.5 C, 1 C and 2 C). This approach allows us to elucidate the structural evolution and mechanical stability of the composite anode during charge-discharge cycles. Additionally, Gr/Si electrodes display voltage hysteresis, attributed to the influence of the charge-discharge history on the equilibrium potential of the lithium-silicon intercalation reaction [2]. Through simulations, we can explore how the silicon content affects this voltage hysteresis. It becomes more pronounced with a higher content of silicon and at lower states of charge (SOCs). Furthermore, increasing the charging rate will amplify the hysteresis. Our comprehensive analysis aims to provide valuable insights into the intricate interplay between material composition, electrode morphology, and electrochemical performance, facilitating the development of high-performance LIBs with improved energy density and cycling stability. This detailed abstract highlights the computational framework, specific simulation methods, and key variables involved in the investigation of Gr/Si composite anodes, providing a more in-depth overview of the research approach and objectives. Acknowledgement: This research was carried out under the project (Grant Number JPMJMI24G1) supported by the JST-Mirai Program, Japan. References: M. So, S. Yano, A. Permatasari, T.D. Pham, K. Park, G. Inoue, Mechanism of silicon fragmentation in all-solid-state battery evaluated by discrete element method, J. Power Sources. 546 (2022) 231956. D.R. Baker, M.W. Verbrugge, X. Xiao, An approach to characterize and clarify hysteresis phenomena of lithium-silicon electrodes, J. Appl. Phys. 122 (2017) 165102.

To guarantee the minimum safety of Li-ion battery, quasi-solid electrolyte such as gel polymer is one of potential candidates by retarding the fire. With the safety issue, the requirement of higher energy density is still main issue for the next generation Li-ion battery. To enhance the energy density, Silicon (Si) is well known as potential anode due to its much higher theoretical specific capacity than that of graphite. Nevertheless, Si’s large volumetric changes during cycles hinder its application for the next generation Li-ion battery. Here, specially designed process to prelithiate Si nanostructures with size of several hundred nanometers were developed, and physical mixture of Si and graphite was applied to coin-type full cell with quasi-solid electrolyte. Specifically, Si nanostructures were obtained from recycled kerf-loss from Si wafering process for PV application. Those Si nanostructures were annealed with Li-sources such as Li 2 CO 3 in reduction atmosphere. Simultaneously, Carbon (C) sources (gasified Toluene) was injected to reactor to form C-layer to gain electrical conductivity of Si. Prelithiated Si and graphite were mixed with various Si’s weight ratios from 5 to 20%, and the mixture was applied as anode material with Ni-rich cathode and gel electrolyte for assembly of coin-type cell. Specific capacity of prelithiated Si exhibited around 2,000 mAh/g with high initial capacity of higher than 88%. Microstructure of the Si nanostructures were studied by using XRD, SEM and HR-TEM analysis. Gel electrolyte was applied not only for separator but also for inside of cathode and anode. Also, interface properties especially between anode materials and gel electrolyte were precisely investigated through the EIS (Electrochemical Impedance Spectroscopy) measurements to enhance the cycle performances. This quasi-solid-state Li-ion battery can solve the safety problem as well as low energy density at the same time.

Silicon (Si) is a promising next-generation anode for high-energy-density lithium-ion batteries. The application of silicon/carbon (Si/C) composites with high Si content is hindered by the huge volume change and insecure electrochemical interface of the Si anode. Herein, chemical-expanded graphite (CEG) is used as a carbon matrix to form Si@CEG/C composites with an embedded structure. CEG with an abundant pore structure and electropositivity can well disperse and accommodate a mass of Si nanoparticles (Si NPs). With the flexibility and porosity of CEG, the embedded structure of Si NPs fixed in an expanded graphite layer can adopt the volume change of Si NPs and offer the abundant path of diffusion of lithium-ion, which leads to a moderate cycle and rate performance. Si@CEG/C exhibits a high reversible capacity of 1232.4 mA h g-1 at a current density of 0.5 A g-1 and with a capacity retention rate of 87% after 200 cycles. This embedded structure of Si/C composites built by CEG is meaningful for the structure design of the Si-based anode with higher specific capacity, active material utilization, and satisfactory cycle stability.

To guarantee the minimum safety of Li-ion battery, quasi-solid electrolyte such as gel polymer is one of potential candidates by retarding the fire. With the safety issue, the requirement of higher energy density is still main issue for the next generation Li-ion battery. To enhance the energy density, Silicon (Si) is well known as potential anode due to its much higher theoretical specific capacity than that of graphite. Nevertheless, Si’s large volumetric changes during cycles hinder its application for the next generation Li-ion battery. Here, specially designed process to prelithiate Si nanoparticles with size of several hundred nanometers were developed, and physical mixture of Si and graphite was applied to coin-type full cell with quasi-solid electrolyte. Specifically, Si nanoparticles were annealed with Li-sources such as Li2CO3 or LiOH in reduction atmosphere. Simultaneously, Carbon (C) sources such as Toluene or ethylene was injected to Si nanoparticles to form C- layer to gain electrical conductivity of Si. Prelithiated Si and graphite were mixed with various composition from 0:100 to 50:50 (in wt.%), and the mixture was applied as anode material with Ni-rich cathode and gel electrolyte for assembly of coin-type cell. Specific capacity of prelithiated Si exhibited around 1,300 mAh/g with extremely high initial capacity of 88%. Microstructure of the Si nanoparticles were studied by using XRD, SEM and HR-TEM analysis. Various gel electrolyte was applied not only for separator but also for inside of cathode and anode. Effect of types and compositions of gel electrolytes on electrochemical properties such as cycle performance of quasi-solid-state Li-ion battery was investigated. Also, interface properties especially between anode materials and gel electrolyte were precisely investigated through the EIS (Electrochemical Impedance Spectroscopy) measurements to enhance the cycle performances. This quasi-solid-state Li-ion battery can solve the safety problem as well as low energy density at the same time.

Silicon–graphite (Si@G) anodes are receiving increasing attention because the incorporation of Si enables lithium-ion batteries to reach higher energy density. However, Si suffers from structure rupture due to huge volume changes (ca. 300%). The main challenge for silicon-based anodes is improving their long-term cyclabilities and enabling their charge at fast rates. In this work, we investigate the performance of Si@G composite anode, containing 30 wt.% Si, coupled with a LiNi0.8Co0.15Al0.05O2 (NCA) cathode in a pouch cell configuration. To the best of our knowledge, this is the first report on an NCA/Si@G pouch cell cycled at the 5C rate that delivers specific capacity values of 87 mAh g−1. Several techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and gas chromatography–mass spectrometry (GC–MS) are used to elucidate whether the electrodes and electrolyte suffer irreversible damage when a high C-rate cycling regime is applied, revealing that, in this case, electrode and electrolyte degradation is negligible.

This study investigates the calendar aging of lithium-ion batteries with graphite-silicon anodes using float current analysis. While float current analysis is already a proven method for assessing aging in cells with graphite-based anodes, the presence of silicon introduces additional complexities due to its voltage hysteresis. We address this by comparing the results for the scaling factor separately for charge and discharge. The scaling factor is initially derived from charge and discharge GITT measurements on fresh cells, including an aging-induced shift among both electrode curves. This approach enables quantification of SEI growth I_(SEI growth) , and cathode lithiation current I_CL bridging measured results for float currents with capacity loss rate. As a result, the scaling factor during charge delivered the most meaningful results regarding fitted aging currents. By extending the estimation method based on the Arrhenius equation across temperatures from 5°C to 50°C, our model is validated against measured float currents, improving the predictive accuracy of long-term aging trends in silicon-containing anodes. Electrochemical impedance spectroscopy provided further insights into degradation mechanisms, revealing a strong correlation between cathode lithiation by salt decomposition and resistance increase at high voltages (≥4.15 V), confirmed by pulse tests at 100% SOC showing a sharp resistance increase at elevated voltages

The ever-increasing share of electric vehicles in the mobility sector urgently calls for an increase in the production capacity of high-power and high-energy lithium-ion batteries with low production costs. A gravimetric energy density of about 350 Wh/kg flanked by a volumetric energy densities of at least 750 Wh/L were defined as ambitious goals from the European Union to be achieved by 2025. For this purpose, novel, high-capacity anode materials containing significant silicon content should be utilized in next generation batteries. At room temperature, silicon has a theoretical specific capacity of 3579 mAh/g which is one order of magnitude higher compared to the state-of-the-art graphite anode material (372 mAh/g). The volume change which silicon undergoes during lithiation and delithiation and the thereby caused mechanical stresses inside the composite electrode, which lead to loss of electrical contact and delamination, are an obstacle for its implementation in industrial battery production. While many researchers focus on other promising approaches to facilitate the usage of silicon in electrodes, for example pre-lithiation, the usage of graphite-silicon composites, or carbon coating on the silicon particles, here, the implementation of additional porosity via laser patterning is pursued. A water-based silicon/graphite slurry concept for the large-scale electrode production is used. There, the silicon nanoparticles’ agglomerates are destroyed and the silicon is finely dispersed using a ball mill, while the slurry homogenization is finalized using a disk stirrer. This facilitates the production of electrode sheets on a roll-to-roll coater, delivering enough material for the high power, high repetition rate roll-to-roll laser patterning process, both of which exhibit a technology readiness level of 5 to 6. The slurry and electrode characterizations are performed using laser induced breakdown spectroscopy (LIBS) for both the binder and lithium spatial distribution, the cyclability and lifetime of the electrodes is assessed in pouch cells with NMC 622 as counter electrode, and the lithiation of the composite material is determined with cyclic voltammetry. Scanning electron, digital and light microscopy are used for the characterization of the laser patterning, while chemical analysis is used to assess the composition of the electrode and the silicon oxidation during water-based manufacturing.

Silicon (Si)‐based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re‐formation of the solid electrolyte interphase and consumption of active lithium. The pre‐lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si‐based LIB full‐cells and enable their practical implementation. Here, the use of lithium squarate (Li2C4O4) as low‐cost and air‐stable pre‐lithiation additive for a LiNi0.6Mn0.2Co0.2O2 (NMC622)‐based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full‐cells is reported, which grows linearly with the initial amount of Li2C4O4, due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre‐lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre‐lithiation additive.

Rice husk is produced in a massive amount worldwide as a byproduct of rice cultivation. Rice husk contains approximately 20 wt% of mesoporous SiO2. We produce mesoporous silicon (Si) by reducing the rice husk-originating SiO2 using a magnesio-milling process. Taking advantage of meso-porosity and large available quantity, we apply rice husk-originating Si to lithium ion battery anodes in a composite form with commercial graphite. By varying the mass ratio between these two components, trade-off relation between specific capacity and cycle life was observed. A controllable pre-lithiation scheme was adopted to increase the initial Coulombic efficiency and energy density. The series of electrochemical results suggest that rice husk-originating Si–graphite composites are promising candidates for high capacity lithium ion battery anodes, with the prominent advantages in battery performance and scalability.

No abstract available

The SiOx/graphite composite is recognized as a promising anode material for lithium-ion batteries (LIBs), owing to the high theoretical capacity of SiOx combined with the excellent stability of graphite. However, the inherent disadvantage of volume expansion in silicon-based anodes places significant challenges on the solid electrolyte interphase (SEI) and severely degrades the electrochemical performance. Rational formulation of electrolyte, including its additives, is crucial in accommodating and optimizing the composition of the SEI and enhancing the cell performance. In this work, we present a comparative study of vinylene carbonate (VC) and lithium difluoro(oxalate)borate (LiDFOB) additives combined with fluoroethylene carbonate (FEC) in the electrolyte for SiOx/graphite∥LiNi1-x-y-zCoxMnyAlzO2 full cells. VC outperformed LiDFOB as an additive, delivering higher capacity cycling, higher Coulombic efficiency, and better cycle stability up to 400 cycles. XPS and impedance analyses reveal that LiDFOB contributed to SEI/CEI with both a lower proportion of LiF and a higher proportion of poly(VC), which tended to produce higher cell impedance. XRD and XANES further indicated that using the LiDFOB additive, the NCMA cycled to a shallower degree than that of the VC additive. Although the VC additive maintained a higher capacity up to 400 cycles, microstrain and SEM analyses show a higher strained NCMA along with clear evidence of cracking over the surface of the NCMA particle in VC-based electrolyte but not in LiDFOB. This suggests that the negative influence of LiDFOB at the anode (inferior SEI) supersedes the negative impact of both a cracked NCMA and a deeper cycled NCMA and SiOx-based anode.

Li-ion batteries (LiBs) are one of the best solutions for energy storage due to their high capacity, high power, and cyclability1,2. The increasing need for energy storage to supply electric vehicles demands continuous innovation to optimize the LiBs, specifically the manufacturing parameters to fabricate these devices. The battery production requests improved materials, cell designs, greener manufacturing processes, and recycling3,4. For instance, developing an improved anode material could be a good approach for optimizing the LiB energy density. A blend of graphite and silicon is a promising negative electrode due to the combined stability of graphite with the high theoretical capacity of silicon5,6. Since adding silicon changes the manufacturing parameters already established for commercial graphite electrode fabrication, our goal is to understand the impact of the manufacturing process, such as the calendaring effect on the properties of the silicon/graphite blend electrodes. These electrodes were prepared with two different silicon percentages, 8%, and 15%, compared to pure graphite. We investigate the morphological changes, electrochemical aging, and tortuosity when decreasing the porosity from 55% to 30% for both electrodes to evidence the porosity threshold for obtaining adequate electrode properties. Manufacturing optimization is time and cost-consuming. Modeling approaches are an excellent choice to decrease LiB fabrication scraps. We are developing machine learning and physical models of the 3D silicon-graphite electrode fabrication process within our ARTISTIC project7, and these optimization results will help to validate them. S. Chu and A. Majumdar, Nature, 488, 294–303 (2012). J. B. Goodenough and K.-S. Park, J. Am. Chem. Soc., 135, 1167–1176 (2013). J. Li, J. Fleetwood, W. B. Hawley, and W. Kays, Chem. Rev., 122, 903–956 (2022). F. M. Zanotto et al., Batter. Supercaps, 5 (2022). M. T. McDowell, S. W. Lee, W. D. Nix, and Y. Cui, Adv. Mater., 25, 4966–4985 (2013). F. Jeschull et al., J. Electrochem. Soc., 167, 100535 (2020). C. Liu, O. Arcelus, T. Lombardo, H. Oularbi, and A. A. Franco, J. Power Sources, 512, 230486 (2021).

The (de)lithiation process and resulting atomic and nano-scale morphological changes of a a-Si/c-FeSi2/graphite composite negative electrode are investigated within a Li-ion full-cell at several current-rates (C-rates) and after prolonged cycling by simultaneous operando synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS). WAXS allows the probing of the local crystalline structure. In particular, the observation of the graphite (de)lithiation process, revealed by the LixC6 Bragg reflections, enables access to the respective capacities of both graphite and active silicon. Simultaneously and independently, information on the silicon state of (de)lithiation and nano-scale morphology (1 nm to 60 nm) is obtained through SAXS. During lithiation, the SAXS intensity in the region corresponding to characteristic distances within the a-Si/c-FeSi2 domains increases. The combination of the SAXS/WAXS measurements over the course of several charge/discharge cycles, in pristine and aged electrodes, provides a complete picture of the current-rate (C-rate) dependent sequential (de)lithiation mechanism of the a-Si/c-FeSi2/graphite anode. Our results indicate that, within the composite electrode, the active silicon volume does not increase linearly with lithium insertion and point toward the important role of the electrode morphology to accommodate the nanoscale silicon expansion, an effect that remains beneficial after cell ageing and most probably explains the excellent performance of the composite material.

Failure mechanisms associated with silicon-based anodes are limiting the implementation of high-capacity lithium-ion batteries. Understanding the aging mechanism that deteriorates the anode performance and introducing novel-architectured composites offer new possibilities for improving the functionality of the electrodes. Here, the characterization of nano-architectured composite anode composed of active amorphous silicon domains (a-Si, 20 nm) and crystalline iron disilicide (c-FeSi2 , 5-15 nm) alloyed particles dispersed in a graphite matrix is reported. This unique hierarchical architecture yields long-term mechanical, structural, and cycling stability. Using advanced electron microscopy techniques, the nanoscale morphology and chemical evolution of the active particles upon lithiation/delithiation are investigated. Due to the volumetric variations of Si during lithiation/delithiation, the morphology of the a-Si/c-FeSi2 alloy evolves from a core-shell to a tree-branch type structure, wherein the continuous network of the active a-Si remains intact yielding capacity retention of 70% after 700 cycles. The root cause of electrode polarization, initial capacity fading, and electrode swelling is discussed and has profound implications for the development of stable lithium-ion batteries.

Silicon (Si) is a promising negative electrode material for high-energy automotive batteries, but its significant volume changes during cycling cause rapid degradation, limiting its loading to just 10 wt.% in commercial graphite/Si composite negative electrodes as a compromise between energy density and cycle life. Overcoming this threshold requires evidence-based design of advanced electrodes. Here we combine operando optical microscopy, synchrotron X-ray CT 4D imaging, digital image/volume correlation and machine learning-assisted image processing techniques, to elucidate the multiscale electro-chemo-mechanical processes in graphite/µ-Si composite negative electrode. Presented with multimodal high-resolution videos, here we show the expansion of porous µ-Si particles strongly depend on the morphology of the intra-particle porosity. One dimensional tubular porosity is conducive to suppressed volume expansion and cracking compared to planar porosity, which incurs highly anisotropic particle strain and crack. Moreover, the encapsulation and loss of active Si particles result in excessive charging current being directed to the graphite particles, thereby increasing the risk of premature lithium plating—an overlooked safety concern. Surprisingly, the electrode expansion is not necessarily governed by Si; rather, its influence only becomes pronounced at high SOCs during the first lithiation cycle but is dominated by graphite in the subsequent cycles. Severe thickness expansion (20%) and reduction in nano-pores (from 43% to 21%) are observed in the CBD, undermining accessible capacity and fast charging capability. Finally, in response to the five identified major challenges in graphite/µ-Si composite electrodes, we develop a double-layered graphite/µ-Si composite negative electrode, which demonstrates significantly lower polarization and mitigated capacity decay compared to its homogeneous counterparts. Overall, this study provides a comprehensive framework for advancing Si-based negative electrodes through hierarchical engineering, from particle level to the 3D architecture of the electrode. Figure 1

Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70 wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200 mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200 mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30% Si electrode, crystalline Si amorphization at potentials <110 mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70% Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

Silicon is a promising alternative to graphite anodes for achieving high-energy-density in lithium-ion batteries (LIBs) because of its high theoretical capacity (3579 mAh g-1). However, silicon anode must be developed to address its disadvantages, such as volume expansion and low electronic conductivity. Therefore, the use of silicon as composed with graphite and carbon anode materials is investigated, which requires properties such as a spherical morphology for high density and encapsulation of silicon particles in the composite. Herein, a graphite@silicon@carbon (Gr@Si@C) micro-sized spherical anode composite is synthesized by mechanofusion process. This composite comprises an outer surface, middle layer, and core pore, which are formed by the capillary force arising from 2D structured graphite and pitch properties. This structure effectively addresses the intrinsic issues associated with Si. Gr@Si@C exhibits a high capacity of 1622 mAh g-1 and capacity retention of 72.2% after 100 cycles, with a high areal capacity 4.2 mAh cm-2. When Gr@Si@C is blended with commercial graphite, the composite exhibits high capacity retention and average Coulombic efficiency after cycling. The Gr@Si@C blended electrode exhibits a high energy density of 820 Wh L-1 with ≈16% metallic Si in the electrode (40 wt.% composite), enabling the realization of practical commercial LIBs.

The present work deals with the postcycling analysis of the graphite‐based composite anodes, graphite reinforced with bare silicon nanoparticles (GrSi), and Si@TiO2 core–shell nanoparticles (GrCS), for lithium‐ion batteries. The electrochemical behavior is recorded through galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) tests. The postcyclic analysis is done using material and structural characterization. The GrSi anode demonstrates a higher initial specific capacity but lower cyclic stability relative to the GrCS anode. The capacity retention for the GrSi anode is ≈57%, while for the GrCS anode it is ≈75%. After cycling, the EIS analysis indicates that GrSi anode exhibits higher resistance than GrCS anodes. The cross‐sectional appearance of cycled anodes reveals minimal changes in the surface morphology of the GrCS anode, with a ≈75% thickness increase for the GrSi anode and ≈35% for the GrCS anode. The changed electrochemical behavior is attributed to the change in the composition of the solid–electrolyte interphase layer, as confirmed by X‐ray photo spectroscopy, and minor loss in crystallinity of GrCS anode material, as confirmed by X‐ray diffraction. The study provides insights into the mechanisms governing material degradation during the electrochemical processes in the composite anodes.

Silicon-based anodes are extensively studied as an alternative to graphite for lithium ion batteries. However, silicon particles suffer larges changes in their volume (about 280%) during cycling, which lead to particles cracking and breakage of the solid electrolyte interphase. This process induces continuous irreversible electrolyte decomposition that strongly reduces the battery life. In this research work, different silicon@graphite anodes have been prepared through a facile and scalable ball milling synthesis and have been tested in lithium batteries. The morphology and structure of the different samples have been studied using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning and transmission electron microscopy. We show how the incorporation of an organic solvent in the synthesis procedure prevents particles agglomeration and leads to a suitable distribution of particles and intimate contact between them. Moreover, the importance of the microstructure of the obtained silicon@graphite electrodes is pointed out. The silicon@graphite anode resulted from the wet ball milling route, which presents capacity values of 850 mA h/g and excellent capacity retention at high current density (≈800 mA h/g at 5 A/g).

This study reports a graphite-core, multiphase gradient C–Si–N composite architecture for Si-containing graphite-based negative electrodes in lithium-ion batteries. The increase in electrode thickness is used as a practical metric of expansion-driven degradation. The composite is prepared by the simultaneous nitridation and carbonization of a graphite core–Si precursor using polyvinylpyrrolidone (PVP) as the N source. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy indicates a quasi-continuous radial trend in the relative N signal toward the outer shell, consistent with preferential N enrichment near the particle exterior. This spatially distributed N arrangement may spatially separate the Si-rich expansion-prone region from the carbon-rich exterior containing nitrides and other N-bearing species, thereby enabling stress partitioning. The shell architecture is designed to disperse expansion-induced stress and stabilize the electrode–electrolyte interface. During electrochemical cycling, the C–Si–N electrode with 10% PVP preserves its core–shell morphology and exhibits the smallest average electrode thickness expansion (~58% after 40 cycles, based on four independent cells). The reduced thickness growth is discussed in relation to a mechanically robust Si–N matrix (Si3N4-like/SiNx-like), potential Li–N interphase species, and N-containing carbon, together with the post-mortem morphology and electrochemical impedance evolution. This study presents reduced swelling as an electrode-level trend versus nominal PVP addition, along with associated nitride-related signatures, thereby highlighting spatially graded stress buffering as an electrode-level design principle.

For the past decade, silicon (Si) as a material for negative electrodes of Li-ion batteries has been considered among the most promising candidates for replacing commonly used graphite. However, Si-based electrodes suffer from severe degradation, which depends on the type of Si materials used. Generally, the degradation of Si is mainly viewed in terms of particle fracturing during lithiation accompanied by constant growth of the solid electrolyte interphase (SEI). At the same time, the reversed process, delithiation, has received little attention. The present work demonstrates the morphological changes of the Si components of electrodes occurring during electrochemical cycling through electron microscopy analyses. These changes are rationalized through the migration of Si, resulting in the formation of Si dendrites embedded in SEI. With the assistance of ReaxFF modeling, we demonstrate that the delithiation predominantly drives this process. The present study reveals that fracturing of Si particles is not the only cause for degradation, as the Si surfaces dramatically change after prolonged cycling, resulting in the formation of Si dendrites.

Abstract Si‐based anodes can increase specific energy and energy density of Li ion batteries. However, the volume‐induced material stress and capacity loss necessitates only a partial Si utilization within composite anodes, typically with state‐of‐the‐art graphite, so called Si/Gr composites. In this work, various Si nanowires (SiNWs), a promising Si architecture for these composites, are investigated and modified via pre‐lithiation. Though, charged pre‐lithiated anodes show potentials below 0 V vs. Li|Li+ in the initial cycles, they do not show indications for metallic Li, which is likely a hint for a triggered surface Li depletion in course of a continuous “transfer‐lithiation” from lithiated Gr to Si, which is indicated by decreasing LiC6 and increasing Li x Si y signals via nuclear magnetic resonance (NMR), X‐ray diffraction (XRD) as well as shifts in capacities of respective voltage plateaus during discharge after storage. A relevant contribution of self‐discharge is unlikely as shown by a stable open‐circuit‐voltage during storage in charged state and similar subsequent discharge capacities, being consequently a hint for an intra‐electrode capacity shift. The process of transfer lithiation is finally validated via solid‐state 7Li NMR for varied Si morphology, i. e., amorphous and crystalline, as well as during pre‐lithiation with passivated lithium metal powder (PLMP).

In this study, Si@TiO2 core‐shell nanoparticles are synthesized using the peptization technique, resulting in a thin and uniform TiO2 coating layer over silicon nanoparticles. This coating layer serves the purpose of controlling the structural degradation of the silicon nanoparticles. These core‐shell nanoparticles are then reinforced into the natural graphite with the potential to be used as a composite anode material (Graphite/Si@TiO2) for Li‐ion batteries. The developed composite material exhibits an initial specific capacity of ≈675 mAh/g at 0.5 A/g, and after 100 cycles it retains the capacity of 75 %. Compared with Graphite/Si composite anode, the developed composite anode material shows improved cyclic stability. The pre‐and post‐cycling morphological analysis of Graphite/Si and Graphite/Si@TiO2 composite anode reveals the degradation behavior. It is assumed that the TiO2 coating provides a protective shield for the silicon particles, preventing their interaction with the electrolyte and causing less material to deposit over the anode surface. Electrochemical Impedance Spectroscopy (EIS) analysis supports these findings, with the Graphite/Si composite anode exhibiting higher resistance than the Graphite/Si@TiO2 anode. In conclusion, the study demonstrates the potential of using Si@TiO2 core‐shell nanoparticles as a reinforcing agent for natural graphite to develop high‐performance composite anode material for Li‐ion batteries. 

Silicon nanoparticles with median size of 51 nm are prepared by sand mill from waste silicon, and then carbon interweaved silicon nanoparticles/graphite anode materials are designed. Due to the size of silicon nanoparticles is restricted below critical fracture size of 150 nm as well as the rational decoration of carbon and graphite, fracture of silicon nanoparticles and volume deformation of active materials are highly alleviated, leading to low impedance, enhanced electrochemical reaction kinetics and good electronic connection between active materials and current collector. Furthermore, delithiation reversibility of the formed crystalline Li15Si4 alloy is enhanced. As a result, the anode with 10.5 wt.% content of Si (including SiOx) delivers a properly high initial reversible capacity of 505 mA h g-1, high cycling stability with capacity retentions of 86.3 % and 91.5 % at 0.1 and 1 A g-1 after 500 cycles, respectively. After cycling at a series of higher current densities, the reversible capacity recovers to original level completely (100 % recovery) when the current density is set back to original value, exhibiting outstanding rate performance. The results indicate that silicon-carbon anode can achieve high cycling performances with enhanced delithiation reversibility of the formed crystalline Li15Si4 alloy by restricting size of silicon nanoparticles and decoration of carbon materials, which are discussed systematically. The SiNPs are recycled from waste Si, and synthetic strategy of anode materials is very facile, cost-effective and nontoxic, which has potential for industrial production.

Si-based anode materials have attracted considerable attention for use in high-capacity lithium-ion batteries (LIBs), but their practical application is hindered by huge volume changes and structural instabilities that occur during lithiation/delithiation and low-conductivity. In this regard, we report a novel Si-nanocomposite by modulating the ultrathin surface oxide of nano-Si at a low temperature and highly conductive graphene-graphite matrix. The Si nanoparticles are synthesized by high-energy mechanical milling of micro-Si. The prepared Si/SiOx@C nanocomposite electrode delivers a high-discharge capacity of 1355 mAh g-1@300th cycle with an average Coulombic efficiency of 99.5% and a discharge capacity retention of ∼88% at 1C-rate (500 mA g-1). Remarkably, the nanocomposite exhibits a high initial Coulombic efficiency of ∼87% and excellent charge/discharge rate performance in the range of 0.5-5C. Moreover, a comparative investigation of the three different electrodes nano-Si, Si/SiOx, and Si/SiOx@C are presented. The exceptional electrochemical performance of Si/SiOx@C is owing to the nanosized silicon and ultrathin SiOx followed by a high-conductivity graphene-graphite matrix, since such a nanostructure is beneficial to suppress the volume changes of silicon, maintain the structural integrity, and enhance the charge transfer during cycling. The proposed nanocomposite and the synthesis method are novel, facile, and cost-effective. Consequently, the Si/SiOx@C nanocomposite can be a promising candidate for widespread application in next-generation LIB anodes.

Silicon, with its high specific capacity, is a highly promising material for lithium-ion battery anodes. To enhance durability, it is commonly combined with graphite in composite anodes. Despite this, the electrochemical dynamics between silicon and graphite are not yet fully understood. Modeling serves as an important tool for analyzing and improving batteries, but current models lack comprehensive representation of the coupled electrochemical and structural behavior of silicon-graphite blended electrodes. Herein, we present a comprehensive model for blended Si/Gr electrodes that incorporates the distinct properties and kinetics of each material. Our approach accounts for the dependence of electrode thickness and solid volume fraction on silicon content. Additionally, a memory-hysteresis variable is introduced to represent accurately silicon’s path-dependent voltage hysteresis. Our model reveals how silicon content influences the lithiation and delithiation dynamics, demonstrating that increased silicon enhances specific capacity. Our model predictions agree well with experimental data and provide insights into how silicon content affects electrolyte distribution and electrode thickness.

Herein, we improved the performance of Si/graphite (Si/C) composite anodes by introducing a highly adhesive co-polyimide (P84) binder and investigated the relationship between their electrochemical and adhesion properties using the 90° peel test and a surface and interfacial cutting analysis system. Compared to those of conventional poly(vinylidene fluoride) (PVdF)-based electrodes, the cycling performance and rate capability of P84-based Si/C anodes were improved by 47.0% (372 vs 547 mAh g–1 after 100 cycles at a 60 mA g–1 discharge condition) and 33.4% (359 vs 479 mAh g–1 after 70 cycles at a 3.0 A g–1 discharge condition), respectively. Importantly, the P84-based electrodes exhibited less pronounced morphological changes and a smaller total cell resistance after cycling than the PVdF-based ones, also showing better interlayer adhesion (Fmid) and interfacial adhesion to Cu current collectors (Finter).

The degradation mechanisms of commercial graphite–SiOx/NCA battery related to the aging process in full cell under cycling conditions at three different temperatures, namely, 10, 25, and 45°C, have been studied via post-mortem analysis, emphasizing the high-energy-density graphite–SiOx anode behaviour. The aging process of the full battery has been studied by non-destructive electrochemical methods. Then, to gain more understanding on the mechanisms that govern the graphite–SiOx degradation, full cells are disassembled, and the anodes are studied by physicochemical analysis techniques, electron microscopy techniques, and electrochemical characterizations. The battery cycled at 25°C, between 2.5 and 4.2 V, shows higher cyclability than those cycled at 45 and 10°C, at SoH 80 %. Under these conditions, the structural and morphological changes undergo by graphite–SiOx and SiOx particles, respectively, and the loss of active material, together with the solid electrolyte interphase growth explain the anode degradation.

Silicon is a promising active material for Li-ion battery negative electrodes because of its high theoretical specific capacity as compared to the standard graphite materials (3579 mAh/g vs 372 mAh/g). However, the capacity retention of Si-based anodes is negatively impacted by the Si expansion during lithiation (up to ~300% for Li15Si4 compared to ~10% for LiC6) and subsequent contraction during delithiation. The primary sources of this capacity fade are the delamination of the anode material from the current collector, the isolation of active material, and uncontrolled solid electrolyte interphase (SEI) formation. A resilient polymer binder network can help mitigate the effects of the expansion and contraction of silicon particles and prolong the cycle life of Si-based electrodes. Polyacrylic acid (PAA) is a prevalent binder material for Si-based and Si-Graphite composite electrodes that features carboxylic acid functional groups, which can bind to the native silanol layer on silicon particles. It is known to increase the adhesion of the electrode to the current collector and the cohesion strength of the bulk electrode, as well as act as an artificial SEI layer. The present study aims to optimize the PAA binder formulation in respect to several key parameters, namely its neutralisation degree, substituting cation, polymer molecular weight, and coverage ratio. Previous work from our group on silicon-graphite composite electrodes with a partially neutralized PAA binder yielded promising results. In fact, the simple addition of metal hydroxide has the double effect of increasing the slurry pH and forming carboxylate groups along the polymer chains. The former brings the active materials further away from their isoelectric points (pH ≈ 2.35 for silicon and pH ≈ 4 for graphite), preventing flocculation, while the latter increases interactions between the polymer chains through carboxylate-cation attractive interactions. The strength of these interactions depends on their nature. Monovalent metal cations (Na+, Li+) promote weaker dipole interactions while polyvalent cations (Mg2+, Zn2+, Ca2+) create stronger coordination bonds. These interactions have been shown to improve the mechanical properties of the dried electrodes, as well as their capacity retention over cycling in previous studies. Furthermore, the predominant trend in literature is to use a commercially available, high-molecular weight PAA for electrochemical studies. However, these long polymer chains require a more intensive synthesis process and run the risk of folding in on themselves due to intramolecular interactions, especially after the addition of polyvalent cations. Shorter chains are easier to synthesize but are typically thought to be less effective as binders due to their small size compared to the active material particles. High-, intermediate- and low-molecular weight PAA binders are compared in this study to verify these hypotheses. In a final step, an ideal polymer coverage ratio – a compromise between capacity retention and energy density – is determined for each binder formulations. The impact of each of these binder parameters is explored through a variety of characterisation techniques carried out at each electrode processing and testing step. The relative adsorption of each polymer formulation during the slurry dispersion step is studied by gel permeation chromatography. Next, the rheological properties of each slurry under shearing are compared, namely the viscosity, which relates to slurry milling and tape-casting conditions, and the storage and loss moduli, which affect the slurry stability and the electrode coating homogeneity. Next, the mechanical properties of the electrodes are determined by nanoindentation and the coating resistivities are measured with a 4-point probe. The electrochemical performances are ultimately compared to identify optimal binder characteristics for increased capacity retention. In sum, the impacts of the PAA chain length and partial neutralisation through the addition of various metal hydroxides are elucidated. Ideal coverage ratios are also determined for each formulation and an optimized, PAA-based binder for silicon-graphite composite electrodes is highlighted. References: Obrovac, M. N. Si-Alloy Negative Electrodes for Li-Ion Batteries. Curr. Opin. Electrochem. 2018, 9, 8–17. https://doi.org/10.1016/j.coelec.2018.02.002. Meyssonnier, C.; Merabet, A.; Dupré, N.; Paireau, C.; Lestriez, B. Critical Binder‐to‐Powders Coverage Ratio for Faster Graphite/SiOx Electrode Formulation Optimization. Small Methods 2024, 8 (8), 2301370. https://doi.org/10.1002/smtd.202301370. Vanpeene, V.; Huet, L.; Villanova, J.; Olbinado, M.; Marone, F.; Maire, E.; Roué, L.; Devic, T.; Lestriez, B. Deciphering the Benefits of Coordinated Binders in Si‐Based Anodes by Combined Operando/In Situ and Ex Situ X‐Ray Micro‐ and Nano‐Tomographies. Adv. Energy Mater. 2024, 2403741. https://doi.org/10.1002/aenm.202403741. Jiang, H.; Wei, C.; Yasmin, S.; Obrovac, M. N. Deconvoluting Slurry Rheology from Binder Performance in Si-Based Anodes. J. Electrochem. Soc. 2023, 170 (12), 120522. https://doi.org/10.1149/1945-7111/ad136f.

Silicon's high specific capacity makes it a highly promising anode material for lithium-ion batteries. To improve its durability, it is often combined with graphite in composite anodes. However, the electrochemical interactions between silicon and graphite remain not fully understood. While modeling is a valuable tool for battery analysis and optimization, existing models do not fully capture the coupled electrochemical and structural behaviors of silicon-graphite electrodes. In this work, we develop a comprehensive model for blended Si/Gr electrodes that accounts for the distinct properties and kinetics of each component. Our approach considers how silicon content influences electrode thickness and solid volume fraction. Furthermore, we introduce a memory-hysteresis variable to accurately describe silicon’s path-dependent voltage hysteresis. The model illustrates the impact of silicon content on lithiation and delithiation processes, showing that higher silicon fractions lead to increased specific capacity. Our predictions align well with experimental data and offer insights into how silicon content affects electrolyte distribution and electrode thickness.

Silicon is one of the most promising anode materials for next-generation high-energy-density lithium-ion batteries (LIBs), but it suffers from low conductivity and huge volume variation during lithiation/delithiation. In this work, graphite/silicon/graphite hybrid anodes with unique multilayered structures, called SG/Si/SG and SG/(Si/SG)5, are assembled on copper collectors using magnetron sputtering combined with a coating process. This strategy utilizes the graphite layer to alleviate the volume change of Si and prevent direct contacts of Si with both a current collector and an electrolyte to protect the falling off of the active material from the current collector and to inhibit side reactions. The as-fabricated SG/Si/SG anode has an initial lithiation capacity of 589.4 mAh g-1 with an initial Coulombic efficiency (ICE) of 86.5%. After 300 cycles at 1C, it maintains a specific capacity of 381.8 mAh g-1, with a remarkable capacity retention of 102.3%. Furthermore, under a high loading of ∼7.4 mg cm-2, the SG/(Si/SG)5 anode exhibits an initial areal capacity of 3.433 mAh cm-2 (specific capacity of 463.9 mAh g-1) and an ICE of 89.9%. After 100 cycles at 0.1C, it maintains an areal capacity of 2.024 mAh cm-2 (specific capacity of 290.2 mAh g-1), corresponding to a capacity retention of 67.8%. The multilayered carbon-silicon anode, with SG/(Si/SG)n configuration, should be practically useful for high-energy-density LIBs manufacture.

Artificial graphite (FSN) additive is employed as internal structural label for projecting cyclability of Si material native electrode in a mass ratio of Si/FSN = 1.0 in Li ion battery (LIB). Results of operando X-ray diffraction analysis on Si-FSN negative electrode in LIB demonstrate that one can evaluate the lithiation and delithiation affinity of active material by referring phase transition delay of graphite as affected by experimental splits in a formation process of LIB. We prove that a thin layer of surface amorphous structure and residual lattice strain are formed in Si by high energy ball-milling treatment. Those manipulations improve Li intercalation kinetics and thus enabling a capacity fading of less than 10% (from 1860 to 1650 mAhg−1) for Si negative electrode in 50 cycles. Of utmost importance, this study discloses a robust assessment for revealing mechanism on amorphous and strain related silicide formation and predicting cyclability of negative electrode by quantitative phase evolution rate of FSN additive in LIB.

Abstract Silicon–Graphite (SiGr) blended anodes represent a promising approach for enhancing the energy density of commercial Li‐ion batteries (LIBs). However, the ≈300% volume change of the silicon component during lithiation and delithiation induces significant mechanical stress, leading to particle cracking and pulverization that compromise electrode stability. This study presents the first evidence of controlled Si lithiation in Si‐rich blended anodes, where a crystalline silicon (c‐Si) core remains unreacted while the outer shell undergoes complete amorphization. Operando synchrotron X‐ray diffraction analysis of SiGr anodes over five consecutive cycles reveals a reversible lithiation of c‐Si, which was not previously reported. Complementary transmission electron microscopy (TEM) analysis of focused ion beam (FIB)‐prepared lamellae from cycled electrodes confirms the formation of an amorphous shell and preservation of the c‐Si core. These findings validate the feasibility of a partial lithiation strategy for SiGr anodes and provide unprecedented insights for the design of mechanically stable electrodes. Additionally, the interpretation of lithiation/delithiation differential capacity plots is discussed in light of the observed structural evolution, offering both fundamental and practical advancements for the development of robust SiGr anodes for high‐energy‐density LIBs.

Enhanced EV market penetration requires durability of the battery with high energy throughput. For long-term cycle stability of silicon-graphite anode capable of high energy density, the reversible redox reactions are crucial. Here, we unveil intriguing electrochemical phenomena such as crosstalk of lithium ion ($Li^{+}$) between silicon and graphite, $Li^{+}$ accumulation in silicon, and capacity depression of graphite under high pressure, which engender the irreversible redox reactions. Active material properties, i.e. the size of silicon and the hardness of graphite, silicon-graphite anode, are modified based on the unveiled results to enhance the reaction homogeneity and reduce subsequent degradation. Owing to the property change of the anode active materials, silicon-graphite anode paired with high nickel cathode allows the prismatic cell with 8.7 Ah to reach cycling performance over 750 cycles with volumetric energy density of 665 $Whl^{-1}$, which is corresponding to 800 $Whl^{-1}$ in the prismatic cell with 87 Ah. Finally, the cycling performance can be tailored by the design of electrode regulating $Li^{+}$ crosstalk. Our findings provide electrochemical insights into degradation mechanisms and a promising direction on the progressive improvement of materials and the design of electrodes in silicon-graphite anode.

Li-ion batteries contain excess anode area to improve manufacturability and prevent Li plating. These overhang areas in graphite electrodes are active but experience decreased Li+ flux during cycling. Over time, the overhang and the anode portions directly opposite to the cathode can exchange Li+, driven by differences in local electrical potential across the electrode, which artificially inflates or decreases the measured cell capacity. Here, we show that lithiation of the overhang is less likely to happen in silicon anodes paired with layered oxide cathodes. The large voltage hysteresis of silicon creates a lower driving force for Li+ exchange as lithium ions transit into the overhang, rendering this exchange highly inefficient. For crystalline Si particles, Li+ storage at the overhang is prohibitive, because the low potential required for the initial lithiation can act as thermodynamic barrier for this exchange. We use micro-Raman spectroscopy to demonstrate that crystalline Si particles at the overhang are never lithiated even after cell storage at 45 oC for four months. Since the anode overhang can affect the forecasting of cell life, cells using silicon anodes may require different methodologies for life estimation compared to those used for traditional graphite-based Li-ion batteries.

Linking electrode microstructure to electrochemical performance is essential for optimizing Li-ion batteries. However, this requires mechanistic 4D observations at ultimate spatio-temporal scales, which remains elusive. Here we demonstrate the use of operando synchrotron X-ray nano-holo-tomography combined with Digital Volume Correlation to track chemomechanical dynamics at both particle (local) and electrode (averaged) scales. Quantitative scale-bridging image analysis is applied to a high-capacity silicon-graphite anode during its formation cycle. Our findings reveal that local diffusion properties, graphite particle morphology and position in the electrode, distance to silicon clusters, surface contact with electrolyte and mechanical deformations, all have a direct impact on the local electrochemical activity and irreversibility - but these parameters are not equally important. Particularly, we identify fast diffusion channels that play a key role and counterbalance intrinsic depth-dependent reaction heterogeneities due to ionic/electronic diffusion limitations. The various structural factors that determine Gr-Si battery performance beyond ensemble properties are classified using a scale of influence, providing a practical framework for the optimization of materials and electrode manufacturing.

Silicon is a promising anode material for next-generation lithium-ion batteries due to its exceptionally high specific capacity (3600 mAh g$^{-1}$), significantly exceeding that of conventional graphite. However, its practical application is hindered by substantial volume expansion (300-400%) during lithiation, leading to mechanical degradation and capacity fade. A graphite-coated silicon core-shell structure has been proposed to mitigate these issues by combining silicon's capacity with graphite's structural stability. Despite this, experimental studies have shown that the usable capacity of such composite electrodes can remain low, often below 40% at 1C, especially under high-rate cycling. In this work, we develop a physics-based electrochemical model to investigate the charge-discharge behaviour, rate limitations, and degradation mechanisms of silicon-graphite core-shell anodes. The model incorporates lithium transport, interfacial kinetics, evolving contact area due to silicon expansion, and a simplified cracking framework to capture loss of active material. Results are validated against key experimental trends and used to explore the effects of particle size, shell thickness, and charge protocol, offering insights into the design of more durable and efficient Si-based composite anodes.

Si-anodes have long been candidates thanks to an expected ten-fold increase in capacity compared to graphite. However, details of the mechanisms governing their degradation remain elusive, hindering science-guided development of long-lived Si-based anodes. Here we demonstrate how the latest developments in cryo-atom probe tomography enable the in-depth analysis of the electrode and electrolyte, and their interface at atomic-level.

As silicon is approaching its theoretical limit for the anode materials in lithium battery, searching for a higher limit is indispensable. Herein, we demonstrate the possible of achieving ultrahigh capacity over 6500 mAh g-1 in silicon-carbon composites. Considering the numerous defects inside the silicon nanostructures, it is deduced the formation of quasi-Bose Einstein condensation should be possible, which can lead to the low viscosity flow of lithium-ions through the anode. At a charge-discharge rate of 0.1C (0.42 A g-1), the initial discharge specific capacity reaches 6694.21 mAh g-1, with a Coulomb efficiency (CE) of 74.71%, significantly exceeding the theoretical capacity limit of silicon. Further optimization of the anode material ratio results in improved cycling stability, with a discharge specific capacity of 5542.98 mAh g-1 and a CE of 85.25% at 0.1C. When the initial discharge capacity is 4043.01 mAh g-1, the CE rises to 86.13%. By training a multilayer perceptron with material parameters as inputs and subsequently optimizing it using a constrained genetic algorithm, an initial discharge specific capacity of up to 7789.55 mAh g-1 can be achieved theoretically. This study demonstrates that silicon-carbon composites have great potential to significantly enhance the energy density of lithium-ion batteries.

Silicon (Si) anodes attract a lot of research attention for their potential to enable high energy density lithium-ion batteries (LIBs). Many studies focus on nanostructured Si anodes to counteract deterioration. In this work, we model LIBs with Si nanowire (NW) anodes in combination with an ionic liquid (IL) electrolyte. On the anode side, we allow for elastic deformations to reflect the large volumetric changes of Si. With physics-based continuum modeling we can provide insight into usually hardly accessible quantities like the stress distribution in the active material. For the IL electrolyte, our thermodynamically consistent transport theory includes convection as relevant transport mechanism. We present our volume-averaged 1d+1d framework and perform parameter studies to investigate the influence of the Si anode morphology on the cell performance. Our findings highlight the importance of incorporating the volumetric expansion of Si in physics-based simulations. Even for nanostructured anodes - which are said to be beneficial concerning the stresses - the expansion influences the achievable capacity of the cell. Accounting for enough pore space is important for efficient active material usage.

Moving to larger cell formats in lithium-ion batteries increases overall useable energy but introduces inhomogeneities that influence aging. This study investigates degradation in 21700-type cells with NCM cathodes and graphite/SiOx anodes under cyclic aging, using in operando neutron diffraction, neutron depth profiling, and X-ray computed tomography. Prolonged cycling causes lithium loss, observed on the cathode side as reduced NCM unit cell change during cycling. On the anode side, this loss appears as diminished formation of the fully lithiated LiC6 phase. Differential voltage analysis during aging reveals not only lithium inventory loss but also active anode material loss. Diffraction data confirm this through shifts in the LiC12 transition and LiC6 onset to lower capacities, requiring less lithium to trigger the transitions. Lithium concentration profiles across electrode positions show depletion in the cathode, while elevated concentrations in the anode indicate increased solid-electrolyte interphase formation, suggesting lithium consumed from the cathode deposits on the anode side. CT measurements show that intrinsic inhomogeneities inside the cells have a stronger influence on the macroscopic structure than aging-induced changes, indicating that the observed capacity fade primarily originates from microscopic degradation processes within the electrodes. Overall, the combined techniques provide direct evidence of lithium loss, active material degradation, and spatially dependent aging mechanisms in large-format cylindrical cells.

Silicon is one of the most promising anode materials for Lithium-ion batteries. Silicon endures volume changes upon cycling, which leads to subsequent pulverization and capacity fading. These drawbacks lead to a poor lifespan and hamper the commercialization of silicon anodes. In this work, a hybrid nanostructured anode based on silicon nanoparticles (SiNPs) anchored on vertically aligned carbon nanotubes (VACNTs) with defined spacing to accommodate volumetric changes is synthesized on commercial macroscopic current collector. Achieving electrodes with good stability and excellent electrochemical properties remain a challenge. Therefore, we herein tune the active silicon areal loading either through the modulation of the SiNPs volume by changing the silicon deposition time at a fixed VACNTs carpet length or through the variation of the VACNT length at a fixed SiNPs volume. The low areal loading of SiNPs improves capacity stability during cycling but triggers large irreversible capacity losses due to the formation of the solid electrolyte interphase (SEI) layer. By contrast, higher areal loading electrode reduces the quantity of the SEI formed, but negatively impacts the capacity stability of the electrode during the subsequent cycles. A higher gravimetric capacity and higher areal loading mass of silicon is achieved via an increase of VACNTs carpet length without compromising cycling stability. This hybrid nanostructured electrode shows an excellent stability with reversible capacity of 1330 mAh g-1 after 2000 cycles.

Silicon suboxide is currently considered as a unique candidate for lithium ion batteries anode materials due to its considerable capacity. However, no adequate information exist about the role of oxygen content on its performance. To this aim, we used density functional theory to create silicon suboxide matrices of various Si:O ratios and investigated the role of oxygen content on the structural, dynamic, electronic properties and lithiation behavior of the matrices. Our study demonstrates that the O atoms interact strongly with the inserted Li atoms resulting in a disintegration of the host matrix. We found that higher concentration of oxygen atoms in the mixture reduces its relative expansion upon lithiation, which is a desirable quality for anode materials. It helps in preventing crack formation and pulverization due to large fluctuations in volume. Our study also demonstrate that a higher oxygen content increases the lithium storage capacity of the anode. However, it can also cause the formation of stable complexes like lithium silicates that might result into reversible capacity loss as indicated by the voltage-composition curves. The study provides valuable insights into the role of oxygen in moderating the interaction of lithium in silicon suboxide mixture in microscopic details.

A series of experiments were conducted using the STM instrument, which involves a conducting tip probe to analyse sample surfaces by measurements of a tunnelling current. In this experiment, STM was used to (1) determine the lattice constant of Highly Oriented Pyrolytic Graphite (HOPG) by acquiring atomic resolution images of its surface, (2) measure the work functions of gold (Au) and HOPG samples using the STS mode and, (3) compare the variation of the Local Density of States (LDOS) of gold, graphite and Silicon (Si) samples with respect to bias voltage V. Experimental values of the lattice constant of HOPG and work functions for gold and graphite were determined as 0.27 +/- 0.2 nm, 0.7 +/- 0.1 eV and 0.5 +/- 0.1 eV respectively. The lattice constant deviated slightly from the literature value of 0.246 nm, whereas the work functions deviated significantly from the literature values of 5.40 eV for gold and 4.62 eV for graphite. The LDOS for gold was found to be the highest, followed by graphite, then silicon. These findings will be discussed.

The role of additives such as FEC in extending the calendar life of silicon anodes beyond the cycling benefits is still not fully understood. Herein, the calendar life of high-loading Si (80 wt%) using baseline 1.2 M LiPF6 in EC-EMC electrolyte versus adding 10 wt% FEC is investigated over months. Over 8 days of aging, FEC leads to a 13-fold reduction in irreversible capacity loss in Si-LiFePO4 full cells. Cells without FEC are projected to fall below 80% of their initial capacity within approx. 22 days versus approx. 279 days with FEC. Symmetric Si-Si cells from harvested electrodes show greater increase in interphase resistance without FEC, whereby an increase of 10.81 Ohms is measured for 0 wt% FEC vs. only 3.37 Ohms for 10 wt% FEC over 2 months. Power law modeling of this long-term interphase resistance finds mixed transport-reaction growth behavior in FEC-free cells, suggesting significant dissolution, whereas cells with 10 wt% FEC added display a diffusion-controlled impedance growth behavior, suggesting a robust surface passivation film. Post-mortem FTIR and XPS confirm polycarbonate enrichment of the SEI, which was discovered to predominantly emerge from FEC self-polymerization during the idle aging. When the Si electrodes aged with and without FEC are harvested and reassembled into full cells with the same electrolytes used at aging, the first-cycle coulombic efficiency is 71% for 0 wt% FEC versus 97% for 10 wt% FEC. Subsequent cycling maintains over 99.7% CE with 10 wt% FEC, surpassing the pre-aging CE of 98.8%. This elevated CE indicates better passivation provided by the polymer fragments formed during aging compared to electrochemically formed SEI where no strong polymer FTIR signal is found. The self-polymerization during idle aging with additives such as FEC is therefore an opportune in situ mechanism to further engineer in extending the life of Si-based batteries.

The growth of the semiconductor and solar industry has been exponential in the last two decades due to the computing and energy demands of the world. Silicon (Si) is one of the main constituents for both sectors and, thus, is used in large quantities. As a result, a lot of Si waste is generated mainly by these two industries. For a sustainable world, the circular economy is the key; thus, the waste produced must be upcycled/recycled/reused to complete the circular chain. Herein, we show that an upcycled/recycled Si can be used with carbon as a composite anode material, with high Si content (~40 wt.%) and loading of 3-4 mAh/cm^2 for practical use in lithium-ion batteries. The unique spherical jackfruit-like structure of the Si-C composite can minimize the total lithium inventory loss compared to the conventional Si-C composite and pure Si, resulting in superior electrochemical performance. The superior electrochemical performance of Si-C composites enables the cell energy density of ~325 Wh/kg (with NMC cathode) and ~260 Wh/kg (with LFP cathode), respectively. The results demonstrate that Si-based industrial waste can be upcycled for high-performance Li-ion battery anodes through a controllable, scalable, and energy-efficient route.

Li-ion batteries are ineluctably subjected to external mechanical loading or stress gradient. Such stress can be induced in battery electrode during fabrication and under normal operation. In this paper, we develop a model for stresses generated during lithiation in the thin plate electrode considering the effects of external mechanical loading. It is found that diffusion-induced stresses are asymmetrically distributed through the thickness of plate due to the coupling effects of asymmetrically distributed external mechanical stress. At the very early stage during Li-ions insertion, the effects of the external mechanical loading is quite limited and unobvious. With the diffusion time increasing, the external mechanical loading exerts a significant influence on the evolution of stresses generated in the electrode. External compressed electrode is inclined to increase the value of stresses generated during lithiation, while external tensed electrode tends to decrease the value of stresses, and as the diffusion time increases, the effects of the external mechanical loading on the stresses generated during lithiation become more obvious.

We report real-time average stress measurements on composite silicon electrodes made with two different binders [Carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF)] during electrochemical lithiation and delithiation. During galvanostatic lithiation at very slow rates, the stress in a CMC-based electrode becomes compressive and increases to 70 MPa, where it reaches a plateau and increases slowly thereafter with capacity. The PVDF-based electrode exhibits similar behavior, although with lower peak compressive stress of about 12 MPa. These initial experiments indicate that the stress evolution in a Si composite electrode depends strongly on the mechanical properties of the binder. Stress data obtained from a series of lithiation/delithiation cycles suggests plasticity induced irreversible shape changes in contacting Si particles, and as a result, the stress response of the system during any given lithiation/delithiation cycle depends on the cycling history of the electrode. While these results constitute the first in-situ stress measurements on composite Si electrodes during electrochemical cycling, the diagnostic technique described herein can be used to assess the mechanical response of a composite electrode made with other active material/binder combinations.

The formation of passivating films is a common aging phenomenon, for example in weathering of rocks, silicon, and metals. In many cases, a dual-layer structure with a dense inner and a porous outer layer emerges. However, the origin of this dual-layer growth is so far not fully understood. In this work, a continuum model is developed, which describes the morphology evolution of the solid-electrolyte interphase (SEI) in lithium-ion batteries. Transport through the SEI and a growth reaction governed by the SEI surface energies are modelled. In agreement with experiments, this theory predicts that SEI grows initially as a dense film and subsequently as a porous layer. This dynamic phase transition is driven by the slowing down of electron transport as the film thickens. Thereby, the model offers a universal explanation for the emergence of dual-layer structures in passivating films.

High-energy-density lithium metal batteries require electrolytes that enable fast ion transport and form a stable solid-electrolyte interphase (SEI) to sustain high-rate cycling, a process that remains challenging to capture experimentally. Here, we develop a Deep Potential-based machine learning molecular dynamics (MLMD) framework, trained on extensive ab initio datasets and validated against experimental transport properties, to resolve early-stage SEI nucleation at lithium metal interfaces with quantum accuracy. We find that at the Li-metal interface, 3.5 M LiTFSI/DMC induces spontaneous, thermally activated reduction reactions, yielding rapidly growing thick anion-derived SEIs enriched in O/F-containing species. In contrast, 1.5-2.5 M LiTFSI/DMC and 1 M LiPF6/EMC/DMC/EC form thinner, LiF-dominated interphases with slower growth kinetics. Our modeling results are consistent with experimental observations, where 3.5 M LiTFSI enhances cycling stability and rate capability, while lower concentrations result in weaker passivation. Our MLMD framework efficiently captures the electrolyte transport and early-stage SEI formation mechanisms in LMBs.

Silicon anodes promise high energy densities of next-generation lithium-ion batteries, but suffer from shorter cycle life. The accelerated capacity fade stems from the repeated fracture and healing of the solid-electrolyte interphase (SEI) on the silicon surface. This interplay of chemical and mechanical effects in SEI on silicon electrodes causes a complex aging behavior. However, so far, no model mechanistically captures the interrelation between mechanical SEI deterioration and accelerated SEI growth. In this article, we present a thermodynamically consistent continuum model of an electrode particle surrounded by an SEI layer. The silicon particle model consistently couples chemical reactions, physical transport, and elastic deformation. The SEI model comprises elastic and plastic deformation, fracture, and growth. Capacity fade measurements on graphite anodesand in-situ mechanical SEI measurements on lithium thin films provide parametrization for our model. For the first time, we model the influence of cycling rate on the long-term mechanical SEI deterioration and regrowth. Our model predicts the experimentally observed transition in time dependence from square-root-of-time growth during battery storage to linear-in-time growth during continued cycling. Thereby our model unravels the mechanistic dependence of battery aging on operating conditions and supports the efforts to prolong the battery life of next-generation lithium-ion batteries.

Cycle life is critically important in applications of rechargeable batteries, but lifetime prediction is mostly based on empirical trends, rather than mathematical models. In practical lithium-ion batteries, capacity fade occurs over thousands of cycles, limited by slow electrochemical processes, such as the formation of a solid-electrolyte interphase (SEI) in the negative electrode, which compete with reversible lithium intercalation. Focusing on SEI growth as the canonical degradation mechanism, we show that a simple single-particle model can accurately explain experimentally observed capacity fade in commercial cells with graphite anodes, and predict future fade based on limited accelerated aging data for short times and elevated temperatures. The theory is extended to porous electrodes, predicting that SEI growth is essentially homogeneous throughout the electrode, even at high rates. The lifetime distribution for a sample of batteries is found to be consistent with Gaussian statistics, as predicted by the single-particle model. We also extend the theory to rapidly degrading anodes, such as nanostructured silicon, which exhibit large expansion on ion intercalation. In such cases, large area changes during cycling promote SEI loss and faster SEI growth. Our simple models are able to accurately fit a variety of published experimental data for graphite and silicon anodes.

This work proposes a semi-empirical model for the SEI growth process during the early stages of lithium-ion battery formation cycling and aging. By combining a full-cell model which tracks half-cell equilibrium potentials, a zero-dimensional model of SEI growth kinetics, and a semi-empirical description of cell thickness expansion, the resulting model replicated experimental trends measured on a 2.5 Ah pouch cell, including the calculated first-cycle efficiency, measured cell thickness changes, and electrolyte reduction peaks during the first charge dQ/dV signal. This work also introduces an SEI growth boosting formalism that enables a unified description of SEI growth during both cycling and aging. This feature can enable future applications for modeling path-dependent aging over a cell's life. The model further provides a homogenized representation of multiple SEI reactions enabling the study of both solvent and additive consumption during formation. This work bridges the gap between electrochemical descriptions of SEI growth and applications towards improving industrial battery manufacturing process control where battery formation is an essential but time-consuming final step. We envision that the formation model can be used to predict the impact of formation protocols and electrolyte systems on SEI passivation and resulting battery lifetime.

This research is a theoretical study that simulates the volume expansion of a prelithiated silicon nanowire during lithium ion insertion and the application of an electric current. Utilizing density functional theory (DFT) the ground state energy E_g (x) of prelithiated silicon (Li_xSi) is define as a function of the lithium ion (Li+) concentration (x). As the Li+ are increased, E_g (x) becomes increasingly stable from x=1.00 through x=2.415 and decreases in stability as the lithium ion concentration becomes x >2.415 until full lithiation of the silicon nanowire is reached at x=3.75. After the determination of the lithiated silicon ground state energies an electric current is applied to the lithiated silicon nanowire at varies Li+ concentrations x. It was discovered that the volume expansion began at approximately x=3.25 and increased to over 300% of the original volume of a pristine silicon nanowire at x=3.75 which at this point was full lithiation. This is in sharp contrast to prior research studies where the ground state energy was not considered. In previous studies the computation of the volume expansion starts approximately at x=0.75 and produces a continuous nonlinear volume expansion until the process was terminated at full lithiation.

This computational research study analyzes the increase of the specific charge capacity that comes with the reduction of the anisotropic volume expansion during lithium ion insertion within silicon nanowires. This research paper is a continuation from previous work that studied the expansion rate and volume increase. It has been determined that when the lithium ion concentration is decreased by regulating the amount of Li ion flux, the lithium ions to silicon atoms ratio, represented by x, decreases within the amorphous lithiated silicon (a-LixSi) material. This results in a decrease in the volumetric strain of the lithiated silicon nanowire as well as a reduction in Maxwell stress that was calculated and Youngs elastic module that was measured experimentally using nanoindentation. The conclusion as will be seen is that as there is a decrease in lithium ion concentration there is a corresponding decrease in anisotropic volume and a resulting increase in specific charge capacity. In fact the amplification of the electromagnetic field due to the electron flux that created detrimental effects for a fully lithiated silicon nanowire at x = 3.75 which resulted in over a 300 percent volume expansion becomes beneficial with the decrease in lithium ion flux as x approaches 0.75, which leads to a marginal volume increase of 25 percent. This could lead to the use of crystalline silicon, c-Si, as an anode material that has been demonstrated in many previous research works to be ten times greater charge capacity than carbon base anode material for lithium ion batteries.

This computational research study will analyze the multi-physics of lithium ion insertion into a silicon nanowire in an attempt to explain the electrochemical kinetics at the nanoscale and quantum level. The electron coherent states and a quantum field version of photon density waves will be the joining theories that will explain the electron-photon interaction within the lithium-silicon lattice structure. These two quantum particles will be responsible for the photon absorption rate of silicon atoms that are hypothesized to be the leading cause of breaking diatomic silicon covalent bonds that ultimately leads to volume expansion. It will be demonstrated through the combination of Maxwell stress tensor, optical amplification and path integrals that a stochastic analyze using a variety of Poisson distributions that the anisotropic expansion rates in the <110>, <111> and <112> orthogonal directions confirms the findings ascertained in previous works made by other research groups. The computational findings presented in this work are similar to those which were discovered experimentally using transmission electron microscopy (TEM) and simulation models that used density functional theory (DFT) and molecular dynamics (MD). The refractive index and electric susceptibility parameters of lithiated silicon are interwoven in the first principle theoretical equations and appears frequently throughout this research presentation, which should serve to demonstrate the importance of these parameters in the understanding of this component in lithium ion batteries.

Lithium-ion batteries (LIBs) are crucial for the green economy, powering portable electronics, electric vehicles, and renewable energy systems. The solid-electrolyte interphase (SEI) is vital for LIB operation, performance, and safety. SEI forms due to thermal instability at the anode-electrolyte interface, with electrolyte reduction products stabilizing it as an electrochemical buffer. This article aims to enhance the parametrization of the ReaxFF force field for accurate molecular dynamics (MD) simulations of SEI in LIBs. Focus is on Lithium Fluoride (LiF), an inorganic salt with favorable properties in the passivation layer. The protocol heavily relies on Python libraries for atomistic simulations, enabling robust automation of reparameterization steps. The proposed configurations and dataset enable the new ReaxFF to accurately represent the solid nature of LiF and improve mass transport property prediction in MD simulations. Optimized ReaxFF surpasses previous force fields by adjusting lithium diffusivity, resulting in a significant improvement in room temperature prediction by two orders of magnitude. However, our comprehensive investigation reveals ReaxFF's strong sensitivity to the training set, challenging its ability to interpolate the potential energy surface. Consequently, the current ReaxFF formulation is suitable for modeling specific phenomena by utilizing the proposed interactive reparameterization protocol and constructing a dataset. This work is an important step towards refining ReaxFF for precise reactive MD simulations, shedding light on challenges and limitations in force field parametrization. The demonstrated limitations underscore the potential for developing more advanced force fields through our interactive reparameterization protocol, enabling accurate and comprehensive MD simulations in the future.

The interface between liquid water and the Pt(111) metal surface is characterized structurally and thermodynamically via reactive molecular dynamics (MD) simulations within the ReaxFF framework. The formation of a distinct buckled adsorbate layer and subsequent wetting layers is tracked via the course of the waters density as well as the distribution of the H2O molecules with increasing distance to the metal surface. Hereby, also the Two Phase Thermodynamics method (2PT) has been utilized for studying the course of entropy as well as the translational, rotational and vibrational entropic contributions throughout the Pt(111)/H2O interface. A significant reduction of the entropy compared to the bulk value is observed in the adsorbate layer ($S$ = 31.05$\pm$2.48\,J/molK ) along with a density of 3.26$\pm$0.06g/cm$^{3}$. The O-O interlayer distribution allows direct tracing of the water ordering and a quantified comparison to the ideal hexagonal adlayer. While the adsorbate layer at the Pt surface shows the occurrence of hexagonal motifs, this near-order is already weakened in the wetting layers. Bulk behavior is reached at 15$\mathrm{\mathring{A}}$ distance from the Pt(111) metal. Introducing an electric field of 0.1 V/$\mathrm{\mathring{A}}$ prolongs the ordering effect of the metal surface into the liquid water.

We report in situ measurements of stress evolution in a silicon thin-film electrode during electrochemical lithiation and delithiation by using the Multi-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrate constraint, the silicon electrode initially undergoes elastic deformation, resulting in rapid rise of compressive stress. The electrode begins to deform plastically at a compressive stress of ca. -1.75 GPa; subsequent lithiation results in continued plastic strain, dissipating mechanical energy. Upon delithiation, the electrode first undergoes elastic straining in the opposite direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms plastically during the rest of delithiation. The plastic flow stress evolves continuously with lithium concentration. Thus, mechanical energy is dissipated in plastic deformation during both lithiation and delithiation, and it can be calculated from the stress measurements; we show that it is comparable to the polarization loss. Upon current interrupt, both the film stress and the electrode potential relax with similar time-constants, suggesting that stress contributes significantly to the chemical potential of lithiated-silicon.