锂电池氟化SEI的形成机制

Progress in commercializing solid polymer electrolytes (SPEs) for lithium metal batteries (LMBs) has been impeded by challenges, like concentration polarization, non‐uniform Li+ flux, and an unstable solid electrolyte interface (SEI), which contribute to dendrite formation. To address these issues, silica framework (SF)‐based single‐ion conductors are proposed, featuring a unique solvation channel composed of a fluorinated segment, a high‐dipole zwitterion, and a rotation‐motion‐driven ion‐hopping medium. This design promotes low resistance at the cathode/electrode interface, suppresses dendrite growth at the anode/electrolyte interface, and maintains a uniform Li+ flux. This results show that continuous ion channels within a robust framework enhance Li‐ion dissociation and transport, achieving high ionic conductivity (σDC =  8.8  × 10−4 S cm−1), a modulus of 0.9 GPa, a high lithium transference number (≈0.83), and an extended electrochemical stability window (up to 5.2 V) at 25 °C. This design fosters the formation of a hybrid organic/inorganic SEI layer composed of Li2CO3, LiF, and Li2O, enabling ultra‐stable Li plating/stripping for over 4000 h at 0.1 mA cm−2. Furthermore, the full cells demonstrate excellent rate performance and long‐term cycling stability and capacity retention (81% for Li||LFP and 86% for Li||NCM811 after 400 cycles at 1 C) and high coulombic efficiency, offering a promising strategy to stable LMBs.

As an emerging class of eutectic mixtures, deep eutectic gel electrolytes (DEGEs) exhibit unique advantages in lithium metal batteries (LMBs), particularly due to their high ionic conductivity and tunable molecular interactions. However, it is challenging to realize high interfacial stability between DEGEs and lithium metal. We developed a series of DEGEs utilizing fluorinated amides, which leverage the electron-withdrawing effects of fluorine to precisely modulate the lowest unoccupied molecular orbital (LUMO) energy levels of amides and their binding affinities for Li+. A bidirectional screening criterion is proposed, integrating the LUMO energy levels of amides and the desolvation barriers of solvated Li+ ions. Among the tested amides, 2,2,2-trifluoro-N-methylacetamide (C═Oα3F) demonstrates the lowest LUMO energy level and desolvation energy barrier. The declined LUMO energy level facilitates the formation of a uniform and robust SEI layer enriched with LiF and Li3N. Meanwhile, the reduced Li+ desolvation energy barrier renders more anions to participate in the solvation process, and this synergistic solvent-anion-derived SEI mechanism further reinforces SEI stability. Additionally, the C═Oα3F-DEGE exhibits superior nonflammability and a high ionic conductivity of 1.24 mS cm-1. The enhanced properties enable the corresponding Li||Li symmetric battery to achieve stable cycling for over 9000 h and the Li||LiFePO4 battery counterpart to deliver an impressive lifespan of 2500 cycles with 81.7% capacity retention. These results underscore the advantages of C═Oα3F-DEGE over other fluorinated amide-based systems, providing new insights into the development of high-performance deep eutectic gel electrolytes.

Introducing fluorinated electrolyte additives to construct LiF-rich solid-electrolyte interphase (SEI) on Si-based anodes is proven an effective strategy for coping with its massive volume changes during cycling. However, most current research on fluorine-containing additives focuses on their thermodynamics of decomposition, lacking studies on the correlation between the molecular structure of additives and their decomposition kinetics. Herein, two fluorinated ester additives, diethyl fluoromalonate (F1DEM) and diethyl 2,2-difluoromalonate (F2DEM) were designed and synthesized. Through combining a wealth of characterizations and simulations, it is revealed that despite the similar reduction thermodynamics, the favorable reduction kinetics of single-fluorinated F1DEM facilitate a LiF-rich layer during the early stage of SEI formation, contributing to the formation of a more robust SEI on SiOx anode compared to the difluorinated F2DEM. Consequently, the proposed additive achieves excellent cycling stability (84 % capacity retention after 1000 cycles) for 5 Ah 21700 cylindrical batteries under practical testing conditions. By unveiling the role of reaction kinetics, a long-overlooked aspect for the study of electrolyte additives, this work sheds light on how to construct a stable SEI on Si-based anodes.

Lithium metal batteries (LMBs) employing high-voltage cathode present a promising pathway toward high-energy-density energy storage systems. However, critical challenges have hindered their practical application, including lithium dendrite proliferation, unstable solid-electrolyte interphase (SEI), and limited oxidative stability of conventional 1,2-dimethoxyethane (DME)-based electrolytes. Herein, we rationally design a siloxane-based electrolyte system featuring enhanced oxidative stability through solvent molecular engineering. The Si-O bonding in siloxanes demonstrates superior bond energy compared to conventional C-O bonds in DME, which enables remarkable oxidative stability and the compatibility of high-voltage LMBs. Through in-operando Raman spectroscopy and molecular dynamics simulations, we reveal that more FSI- anion coordinates with Li+ to construct the solvation sheath in siloxane-based electrolyte. This unique coordination environment facilitates anion-derived SEI formation dominated by LiF/Li3N inorganic components, effectively suppressing dendrite growth and enhancing interfacial stability. The optimized electrolyte (DMS-3) enables exceptional electrochemical performance: Li||Cu cells achieve a high Coulombic efficiency of 99.4 % for 1000 cycles (0.5 mA cm-2) and 98.8 % for 800 cycles (1.0 mA cm-2). Li||LiNi0.8Co0.1Mn0.1O2 full cell with 89.82 % capacity retention after 500 cycles at 1.0 C. The practical validation using 1.2 Ah Li||LiNi0.8Co0.1Mn0.1O2 pouch cell demonstrated 92.26 % capacity retention after 110 cycles (0.3/0.5 C). This work establishes a molecular design paradigm for electrolyte engineering, providing critical insights for developing high-voltage LMBs.

Achieving high energy density has always been the goal of lithium-ion batteries (LIBs). SiOx has emerged as a compelling candidate for use as a negative electrode material due to its remarkable capacity. However, the huge volume expansion and the unstable electrode interface during (de)lithiation, hinder its further development. Herein, we report a facile strategy for the synthesis of surface fluorinated SiOx (SiOx@vG-F), and investigate their influences on battery performance. Systematic experiments investigations indicate that the reaction between Li+ and fluorine groups promotes the in-situ formation of stable LiF-rich solid electrolyte interface (SEI) on the surface of SiOx@vG-F anode, which effectively suppresses the pulverization of microsized SiOx particles during the charge and discharge cycle. As a result, the SiOx@vG-F enabled a higher capacity retention of 86.4% over 200 cycles at 1.0 C in the SiOx@vG-F||LiNi0.8Co0.1Mn0.1O2 full cell. This approach will provide insights for the advancement of alternative electrode materials in diverse energy conversion and storage systems.

The interfacial stability of localized high-concentration electrolytes (LHCEs) with fluorinated (F2DEE) or chlorinated (Cl2DEE) ether solvents critically controls lithium metal battery performance. However, atomistic mechanisms driving their solid electrolyte interphase (SEI) formation remain unclear. We systematically compare the decomposition pathways of 1LiFSI-1.6F2DEE-3TTE and 1LiFSI-1.6Cl2DEE-3TTE on Li metal using multiscale simulations: classical molecular dynamics (CMD), ab initio molecular dynamics (AIMD), and density functional theory (DFT). CMD simulations show unique electric double layer (EDL) reorganization under charging; both LHCEs retain FSI- anions within 6 Å of the Li anode, contrasting with conventional low-concentration electrolytes. This spatial selectivity enables AIMD simulations with two configurations (FSI--near and FSI--far interfaces). Results reveal that FSI- reduction (with solvent participation) dominates over TTE dissociation, with calculated SEI fragment ratios (F/Cl/S) matching the experimental XPS trend. Electronic structure analysis via projected density of states, bond evolution, and Bader charge transfer clarifies decomposition sequences. DFT identifies key dehalogenation differences: F2DEE requires 0.11 eV energy barrier for defluorination, while Cl2DEE undergoes spontaneous barrierless dechlorination. This explains higher organic carbon content in Cl2DEE-derived SEI observed experimentally. Our work establishes a multiscale framework correlating solvation evolution, EDL dynamics, and SEI mechanisms, providing atomistic design guidelines for stable high-voltage lithium battery electrolytes.

Uncontrolled ion transport, fragile solid electrolyte interphase (SEI), and unstable lithium-plated microstructures in the anode are key factors inducing the growth of lithium dendrites and hindering the development of lithium metal batteries (LMBs). In this paper, a fluorinated graphene/polyacrylonitrile composite flexible material is simultaneously designed as the separator and the anode host, forming a comprehensive improved structure (optimized separator-SEI-host system) to enhance the LMB performance. The host and separator are modified with F, O-co-doped graphene, inducing the formation of a stable artificial SEI. Meanwhile, the Li+ transport behavior was improved, and the Li deposition was well-guided. Thanks to this exquisite design, 7000 h of dendrite-free cycling and a low polarization of 10 mV are achieved by the symmetric cell at 1 mA cm-2 and 1 mAh cm-2. At the same time, the full battery assembled with lithium iron phosphate established a 72% capacity retention and a 99.7% Coulombic efficiency after 1400 cycles. Moreover, impressive performances were also achieved when pairing with an NCM cathode. Our study demonstrates a strategy for LMB performance optimization, facilitating the practical application of LMB.

Controlling the structure and chemistry of solid electrolyte interphase (SEI) underpins the stability of electrolyte-electrode interface, and is crucial for advancing rechargeable lithium metal batteries (LMBs). Here, we utilized photo-controlled copolymerization to achieve the on-demand synthesis of fluorosulfonyl fluoropolymers as unprecedented artificial SEI layers on Li metal anodes. This work not only enables instant formation of a hybrid polymer-inorganic interphase that consists of a polymer-enriched top layer and a LiF-fortified bottom layer, originating from a single polymeric component, but also imparts various desirable physical properties (e.g., good mechanical strength and flexibility, high ion conductivity, low overpotential) to SEI via a single-to-divergent strategy. Model reactions and structural characterizations supported the formation of a divergent fluorinated interphase, which furnished prolonged stabilization of Li deposition, high coulombic efficiency and improved cycling behavior in electrochemical experiments. This work highlights the great potential of exploring reactive polymers as versatile coatings to stabilize Li metal anodes, providing a promising avenue to solve electrode-electrolyte interfacial problems for LMBs.

Electrolytes play a crucial role in enhancing the cycling stability and overall lifespan of lithium metal batteries (LMBs). However, conventional electrolytes achieve ununiform and low ionic conductivity solid electrolyte interphase (SEI), leading to uncontrolled lithium dendrite growth and dead lithium formation, rendering them inadequate for meeting the performance of high energy density LMBs. Herein, a 1,2-difluorobenzene (1,2-dFBn) is introduced as antisolvent in fluorinated electrolyte which is composed of fluoroethylene carbonate (FEC) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The low energy level of the lowest unoccupied molecular orbital (LUMO) and the high fluorine-donating ability of 1,2-dFBn jointly modify the solvation structure and electrode/electrolyte interphase chemistry. As a result, this simple electrolyte formulation enables the Li||Li symmetric cells exhibit remarkable stability, enduring 700 h of continuous cycling under 2 mA cm-2 and Li||Cu cell achieve an impressive average Coulombic efficiency (CE) of 99.76%. Moreover, the full cell assembled with electrochemically deposited lithium capacity of 5 mAh cm-2 and LiFePO4 (LFP) as cathode achieves exceptional performance, maintaining a discharge specific capacity of 134.9 mAh g-1 while retaining 95.1% capacity at 2C after 1000 cycles. This study offers a plausible ratio design for fluorinated electrolyte, which achieving high CE and long-life LMBs.

This investigation employs first‐principles calculations to explore the interaction between imidazolium ionic liquids (ILs) and fluoride additives on lithium metal surface. Our focus lies in the comprehensive analysis of three distinct categories of fluorinated additives, each differing in their degree of fluorination. The computations reveal that fluorination plays a significant role in determining both the ionic conductivity and the formation of the solid–electrolyte interphase (SEI) film. Specifically, heightened fluorination enhances the oxidative stability of the system but diminishes the strength of solvent binding, resulting in the formation of larger salt/anion clusters and a decrease in ionic conductivity. Conversely, increased fluorination facilitates the interaction between fluorinated additives and the lithium metal surface, thereby aiding in the formation of a stable SEI film characterized by an abundance of inorganic LiF components. This is important as it serves to suppress dendrite growth and mitigate interface side reactions. Considering the combined influences of ionic conductivity and film formation, 1FP is suggested as the optimal candidate for pyridine‐based additive systems, with FEC preferred for cyclic ester‐based additive systems and BC for chain ester‐based additive systems. This study provides theoretical references for the design of ionic liquid‐fluorinated additive electrolyte systems that can protect the lithium metal anode.

Long cycle life was realized on a fluorinated, Au doped titanium silicalite modified Cu (ATSF-5/Cu) current collector by Li affinity of Au nanoparticles, microporous properties of titanium silicalite and the formation of the LiF-rich SEI layer.

Passivation of both anode and cathode surfaces by the inorganic-rich solid electrolyte interphases (SEI) is a very efficient approach to extent the cycle life of rechargeable high-voltage lithium (Li) metal batteries (LMBs). In this work, a fluorinated ether with weakly-solvating ability, termed DB, was used as a diluent as well as a co-solvent in the localized high-concentration electrolyte (LHCE) system, which contains LiFSI salt, 1,2-dimethoxyethane solvent, and DB. Dissimilar to most reported inert diluents, DB is demonstrated to form an anion-rich solvation sheath and partially participate in the solvation structure as well, resulting in the relatively weakened FSI--Li+ coordination, which significantly enhanced anion decomposition kinetics at the Li metal surface, promoting the formation of inorganic-rich SEI. With an optimized electrolyte, the SEIs of both the anode and cathode consist of inorganic-rich components with F, N, S, and O-containing species. Consequently, the full-cell with Li metal and NMC811 cathode at 4.4 V achieved long cycle life of 478 cycles at 80% capacity retention, which provides new perspective toward practical high-voltage battery systems.

Graphite-based Li-ion batteries require the formation of a solid electrolyte interphase (SEI) on the surface of the anode to prevent solvent co-intercalation and graphite exfoliation. Materials such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) that have been successfully deployed as SEI layer forming additives show limited utility under high voltage and high temperature conditions due to low electrochemical and/or thermal stability.1-3 Development of Li-ion batteries that meet the needs of automotive and other electrification applications require advanced electrolyte additives that can support operation under extreme conditions. Koura has developed fluorinated additives that demonstrate improved stability and performance over conventional SEI layer forming additives under the high temperature and high voltage conditions relevant to the automotive industry. In this study, the performance of Koura’s fluorinated additives was compared to common commercial additives in the multiple cell designs, including 4.3V Gr/NMC811, to identify candidates to replace VC and FEC. Testing included 45°C cycling and 60°C storage. It has been found that these materials reduce gassing and increase capacity retention during high-temperature battery operation. To gain a fundamental understanding of how these molecules function in the battery, including mechanisms of solvation, interfacial behavior, and bulk reactivity; and how the structure of the molecule contributes to its properties and behavior, comprehensive post-test analysis was conducted, including gas composition analysis and quantification via gas chromatography, bulk electrolyte composition analysis via NMR spectroscopy, and surface layer characterization via XPS and SEM. Also, performance of multiple structural variants was examined to develop a structure-property relationship to guide rational design of additives for advanced Li-ion batteries. This presentation will summarize Koura’s efforts to supply advanced fluorinated materials for Li-ion batteries that satisfy the arduous demands of current and future applications. Specifically, we will present data showing the capability of fluorinated Koura materials to replace and/or enable existing Li-ion additives under extreme operating conditions, specifically high temperature and/or voltage. Multiple structures will be compared, where appropriate, to highlight our fundamental understanding of the structure-property relationships critical to designing next generation materials. References: Tobias Teufl et al 2023 J. Electrochem. Soc. 170 020531 Daniel Pritzl et al 2017 J. Electrochem. Soc. 164 A2625 Hiroshi Haruna et al 2017 J. Electrochem. Soc. 164 A6278

Localized high-concentration electrolytes (LHCEs) combine a diluent with a high-concentration electrolyte, offering promising properties. The ions, solvent, and diluent interact to form complex heterogeneous liquid structures, where high salt concentration clusters are embedded in the diluent. Optimizing LHCEs for desired electrolyte properties like high ionic conductivity, low viscosity, and effective solid electrolyte interphase (SEI) formation ability within the vast chemical and compositional design space requires deeper understanding and theoretical guidance. We investigated the structures and conductivities of LHCEs based on a fluorinated solvent with two different diluents at varying concentrations. 2,2,3,3-Tetrafluoropropyl trifluoroacetate (TFPTFA) enters the solvation cluster due to its stronger Li-ion interactions, whereas 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE) enters only at extremely high diluent concentrations. The ionic conductivity increases with decreasing diluent concentrations, with a slope change during cluster percolation. Overall, TFETFE demonstrates higher effectiveness than TFPTFA, forming higher local salt concentration clusters and resulting in higher ionic conductivity.

Lithium (Li) metal has received significant attention as an anode material for next-generation batteries due to its high theoretical capacity and low redox potential. However, the high reactivity of Li metal leads to the formation of a native layer on its surface, inducing nonuniform Li+ flux at the electrolyte/Li metal interface, which promotes the growth of Li metal dendrites. In this study, perfluorooctyltriethoxysilane (PFOTES) was vaporized to chemically react with the native layer and modify the Li metal surface. This gas-solid reaction removes the native layer while simultaneously forming a homogeneous solid electrolyte interphase (SEI) layer. The Si-O-Si network formed through condensation reactions between PFOTES molecules, combined with the fluorinated carbon chain of PFOTES, facilitates rapid Li+ kinetics at the Li metal/electrolyte interface. Consequently, the exchange current density of PFOTES-modified Li (PFOTES-Li) increased to 0.2419 mA cm-2, which is 20 times higher than that of Bare-Li (0.0119 mA cm-2). The SEI layer derived from PFOTES effectively mitigates Li pulverization and the formation of dead Li during the long-term cycling. As a result, the PFOTES-Li||LiNi0.8Mn0.1Co0.1O2 full cell exhibits an excellent discharge capacity of 203.4 mAh g-1 under a high areal loading of 4.2 mAh cm-2. This study demonstrates a gas-solid reaction strategy for removing the native layer from the Li metal surface while forming a stable SEI layer, thereby ensuring high Li+ conductivity and mechanical stability, thus improving the cycling stability of Li metal batteries.

High-performance Li-ion/metal batteries working at a low temperature (i.e., <−20 °C) are desired but hindered by the sluggish kinetics associated with Li+ transport and charge transfer. Herein, the temperature-dependent Li+ behavior during Li plating is profiled by various characterization techniques, suggesting that Li+ diffusion through the solid electrolyte interface (SEI) layer is the key rate-determining step. Lowering the temperature not only slows down Li+ transport, but also alters the thermodynamic reaction of electrolyte decomposition, resulting in different reaction pathways and forming an SEI layer consisting of intermediate products rich in organic species. Such an SEI layer is metastable and unsuitable for efficient Li+ transport. By tuning the solvation structure of the electrolyte with a lower lowest unoccupied molecular orbital (LUMO) energy level and polar groups, such as fluorinated electrolytes like 1 mol L−1 lithium bis(fluorosulfonyl)imide (LiFSI) in methyl trifluoroacetate (MTFA): fluoroethylene carbonate (FEC) (8:2, weight ratio), an inorganic-rich SEI layer more readily forms, which exhibits enhanced tolerance to a change of working temperature (thermodynamics) and improved Li+ transport (kinetics). Our findings uncover the kinetic bottleneck for Li+ transport at low temperature and provide directions to enhance the reaction kinetics/thermodynamics and low-temperature performance by constructing inorganic-rich interphases.

The investigation of high-performance polymer-based electrolytes holds significant importance for advancing the development of next-generation lithium metal batteries (LMBs). In this work, a quasi-solid-state electrolyte (EFA-G) comprising pyrrolidinium type polymeric ionic liquids and fluoropolymers was synthesized through a photoinitiated free radical copolymerization process in the presence of solvate ionic liquids. EFA-G not only exhibited high ionic conductivity (9.87 × 10-4 S cm-1) but also had a wide electrochemical stability window (0-5.0 V vs Li+/Li). The improvement in Li+ transport number (tLi+ = 0.33) of EFA-G was attributed to the enhancement of the Li+ migration ability and the hindrance of anion mobility. Due to the shielding effect of the polymeric ionic liquid on the lithium electrode and the formation of a LiF-rich solid electrolyte interphase (SEI), EFA-G supported stable long-term plating/stripping cycling (>1000 h) of lithium symmetric cells. Li/LFP cells assembled with EFA-G at 30 °C exhibited excellent battery performance with a discharge specific capacity of 78.1 mA h g-1 at 8 C and long cycling life (>600 cycles) with high discharge specific capacity (127.8 mA h g-1 after 600 cycles). EFA-G also enabled decent performance for high-voltage cathode batteries. This work provides insights into the design of high-performance polymer-based electrolytes for LMBs.

Effective electrolyte compositions are of primary importance in raising the performance of lithium-ion batteries (LIBs). Recently, fluorinated cyclic phosphazenes in combination with fluoroethylene carbonate (FEC) have been introduced as promising electrolyte additives, which can decompose to form an effective dense, uniform, and thin protective layer on the surface of electrodes. Although the basic electrochemical aspects of cyclic fluorinated phosphazenes combined with FEC were introduced, it is still unclear how these two compounds interact constructively during operation. This study investigates the complementary effect of FEC and ethoxy(pentafluoro)cyclotriphosphazene (EtPFPN) in aprotic organic electrolyte in LiNi0.5 Co0.2 Mn0.3 O ∥ SiOx /C full cells. The formation mechanism of lithium ethyl methyl carbonate (LEMC)-EtPFPN interphasial intermediate products and the reaction mechanism of lithium alkoxide with EtPFPN are proposed and supported by Density Functional Theory calculations. A novel property of FEC is also discussed here, called molecular-cling-effect (MCE). To the best knowledge, the MCE has not been reported in the literature, although FEC belongs to one of the most investigated electrolyte additives. The beneficial MCE of FEC toward the sub-sufficient solid-electrolyte interphase forming additive compound EtPFPN is investigated via gas chromatography-mass spectrometry, gas chromatography high resolution-accurate mass spectrometry, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy, and scanning electron microscopy.

The formation of a stable solid electrolyte interphase (SEI) layer is crucial for enhancing the safety and lifespan of Li metal batteries. Fundamentally, a homogeneous Li+ behavior by controlling the chemical reaction at the anode/electrolyte interface is the key to establishing a stable SEI layer. However, due to the highly reactive nature of Li metal anodes (LMAs), controlling the movement of Li+ at the anode/electrolyte interface remains challenging. Here, an advanced approach is proposed for coating a sacrificial layer called fluorinated self-assembled monolayer (FSL) on a boehmite-coated polyethylene (BPE) separator to form a stable SEI layer. By leveraging the strong affinity between the fluorine functional group and Li+, the rapid formation of a LiF-rich SEI layer in the cell production and early cycling stage is facilitated. This initial stable SEI formation promotes the subsequent homogeneous Li+ flux, thereby improving the LMA stability and yielding an enhanced battery lifespan. Further, the mechanism behind the stable SEI layer generation by controlling the Li+ dynamics through the FSL-treated BPE separator is comprehensively verified. Overall, this research offers significant contributions to the energy storage field by addressing challenges associated with LMAs, thus highlighting the importance of interfacial control in achieving a stable SEI layer.

Reduction at the anode can affect electrolyte decomposition, solid electrolyte interphase (SEI) formation and growth, and thus the lithium solvation/de-solvation near the SEI, and ultimately lead to various perilous side reactions such as inactive lithium formation. Lithium ions solvated in the electrolyte solution along with salt anions diffuse towards the surface of the electrode. At the charged surface, these solvated ions can undertake different pathways leading to various reductive decomposition products to subsequently form the SEI. The transfer of electrons from the electrode to the salt anions form inorganic SEI products. The SEI layer gradually thickens during repeated charge/discharge cycles due to electron exposure to electrolyte or electrolyte diffusion to the anode surface. This gradual thickening of SEI layer decreases active lithium ions, solvents, and salts and increases cell resistance and lowers the cell capacity and Coulombic efficiency. Essentially, the choice of electrolytes has a significant influence on the formation of an SEI and its underlying chemical and mechanical properties. Optimizing the electrolytes is crucial for an SEI formation since the properties of the SEI significantly affect the lithium-ion batteries’ cyclability, life time, capacity retention, high power density, rate capability, and safety. One approach of stabilizing the SEI is to utilize an electrolyte with high concentration of salt, also known as High-Concentration Electrolytes (HCEs). This approach modifies the Li+ solvation structure to form contact ion pairs (CIP) and aggregates (AGG) while decreasing solvent-separated ion pairs (SSIPs) so that the salt anion, such as FSI-, is preferentially decomposed to form a robust LiF-rich SEI. LiF is considered a beneficial SEI component to block electron transport. By introducing a diluent (a non-solvating solvent) in the HCE to form Localized High Concentration Electrolyte (LHCE), the disadvantages of the HCE, such as low ionic conductivity, high viscosity and high cost, can be minimized while retaining the highly concentrated salt-solvent clusters as they are in the HCE. LHCEs based on fluorinated solvents and diluents can further stabilize the electrode-electrolyte interface. Recent studies showed that the presence of fluorine in the SEI, either in the form of simple inorganic fluorides (LiF) or organofluoro-moieties, brought positive impacts such as expanded electrochemical stability window and high ionic transport. Fluorinated solvents can shift the oxidation stability to a higher voltage compared to their nonfluorinated counterparts. Fluorinated electrolytes enable a high lithium plating Coulombic efficiency and suppresses lithium dendrite formation to a greater extent. In this work we focused on identifying the selection rules for the diluent for designing LHCEs to preserve or improve the local high salt concentration clusters to facilitate the formation of an inorganic rich anion derivative film on the anode as well as to enhance ionic conductivity to enable fast charging. Some of the important properties to consider while selecting a diluent are: - diluent molecules must offer little or no solubility to the salt so that they have minimal participation in the solvation clusters, they must be readily miscible with the solvating solvent so that they dissolve and remove some solvent molecules from the clusters; effectively increasing the salt concentration in the solvation clusters, diluents should be distributed on the periphery of salt-solvent clusters, diluents should have low viscosity, to reduce the overall viscosity of the formulated electrolyte, which in turn improves the ionic conductivity since the low viscosity of diluents allow for higher mobility of the ionic clusters. We analyzed LHCEs consisting of different diluents and diluent molar ratios in a comparative fashion to understand their properties in retaining or improving the structures of the high concentration salt-solvent clusters and improving ionic conductivity. We varied the diluent molar ratio to understand its relationship to increasing salt concentration gradients in the center of the solvent-salt clusters. We also analyzed the relationship between diluent molar ratio and ionic conductivity and found that an optimum diluent molar ratio exists for which the ionic conductivity can be maximized. Our findings serve as design guidelines for practical applications of LHCEs.

As a full cell system with attractive theoretical energy density, challenges faced by Li-O2 batteries (LOBs) are not only the deficient actual capacity and superoxide-derived parasitic reactions on the cathode side but also the stability of Li-metal anode. To solve simultaneously intrinsic issues, multifunctional fluorinated graphene (CFx, x = 1, F-Gr) was introduced into the ether-based electrolyte of LOBs. F-Gr can accelerate O2- transformation and O2--participated oxygen reduction reaction (ORR) process, resulting in enhanced discharge capacity and restrained O2--derived side reactions of LOBs, respectively. Moreover, F-Gr induced the F-rich and O-depleted solid electrolyte interphase (SEI) film formation, which have improved Li-metal stability. Therefore, energy storage capacity, efficiency, and cyclability of LOBs have been markedly enhanced. More importantly, the method developed in this work to disperse F-Gr into an ether-based electrolyte for improving LOBs' performances is convenient and significant from both scientific and engineering aspects.

Low cycling Coulombic efficiency (CE) and messy Li dendrite growth problems have greatly hindered the development of anode-free Li-metal batteries (AFLBs). Thus, functional electrolytes for uniform lithium deposition and lithium/electrolyte side reaction suppression are desired. Here, we report a locally fluorinated electrolyte (LFE) medium layer surrounding Cu foils to tailor the chemical compositions of the solid-electrolyte interphase (SEI) in AFLBs for inhibiting the immoderate Li dendrite growth and to suppress the interfacial reaction. This LFE consists of highly concentrated LiTFSI dissolved in a fluoroethylene carbonate and/or succinonitrile plastic mixture. The CE of Cu||LiNi0.8Co0.1Mn0.1O2 (NCM811) AFLB increased to a high level of 99% as envisaged, and the cycling ability was also highly improved. These improvements are facilitated by the formation of a uniform, dense, and LiF-rich SEI. LiF possesses high interfacial energy at the LiF/Li interface, resulting in a more uniform Li deposition process as proved by density functional theory (DFT) calculation results. This work provides a simple yet utility tech for the enhancement of future high-energy-density AFLBs.

Fluorinated linear organic solvents have great potential in improving the safety and lifetime of next-generation Li metal batteries. However, this group of solvents is underexplored. Here, we investigate the molecular and interfacial reactivity properties of seven partially and fully fluorinated linear carbonates designed based on conventional solvents. Using density functional theory, we find the highest occupied molecular orbital levels decrease with increasing substitution of the fluorinated functional groups, implying that fluorination, to a first approximation, improves the stability toward high voltage cathodes. On the basis of the simulated decomposition mechanisms and statistical analyses, we find that a fluorinated linear carbonate with partial fluorination at the methyl component is more accessible in terms of degradation and LiF nascence formation, leading to a potentially LiF-rich solid electrolyte interphase (SEI). The molecular design concepts and the computational techniques presented are transferable to ester and ether systems, facilitating the navigation in a large chemical design space.

Metallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries.

LiCoO2 batteries for 3C electronics demand high charging voltage and wide operating temperature range, which are virtually impossible for existing electrolytes due to aggravated interfacial parasitic reactions and sluggish kinetics. Herein, we report an electrolyte design strategy based on a partially fluorinated ester solvent (i.e., DFEA) that achieves a balance between weak Li+-solvent interactions, sufficient salt dissociation, high interfacial stability, and superior thermal stability to address the aforementioned challenges. The resulting high-voltage wide-temperature electrolyte (HWE) not only possesses low desolvation energy, fast Li+ transport, high oxidation stability, excellent thermal-abuse tolerance and non-flammability, but also enables the formation of both inorganic-rich cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI). Owing to the above merits, this HWE endows the highly stable operation of LiCoO2 cathodes under an ultra-high voltage of 4.7 V and Graphite||LiCoO2 batteries in an ultra-wide temperature range of -30 to 70 °C. Meanwhile, a 1.7 Ah-level 4.6 V Graphite||LiCoO2 pouch cell with a high energy density of 240 Wh kg-1 also delivers excellent cycling stability, representing a significant advancement in the design of electrolytes towards ultra-high voltage and ultra-wide temperature batteries.

Constructing a robust solid electrolyte interphase (SEI) is extremely critical to developing high-energy-density silicon (Si)-based lithium-ion batteries. However, it is still elusive how to accurately manipulate the chemical composition and structure of the SEI layer. Herein, a LiF-dominated SEI film intertwined by a highly elastic polymer is achieved by regulating the defluorination mechanism of the fluorinated carbonate additive on the Si electrode surface. The experimental and computational results confirm that the decomposition route of trans-difluoroethylene carbonate (DFEC) molecules can be significantly altered in the presence of lithium difluoro(oxalato)borate (LiDFOB) additive. The induction of direct defluorination of DFEC step by LiDFOB, as opposed to the breaking of C-O bonds without LiDFOB addition, is crucial in ensuring the exclusive formation of LiF-dominated SEI and maintaining the cyclic structure of DFEC. The defluorinated DFEC easily polymerizes to form poly(vinylene carbonate), enhancing the elasticity of the SEI. The resulting LiF-dominated SEI film with a polymer interwoven outer layer shows enhanced ionic conductivity and mechanical stability, which can effectively accelerate electrode reaction kinetics and maintain the structural stability of the Si electrode. As a result, the Si electrode with the electrolyte containing the designed dual-additive exhibits superior cycling stability and excellent rate performance, delivering a high reversible capacity of 1487.3 mAh g-1 after 1000 cycles at 2 A g-1.

Regulating interfacial chemistry at lithium (Li) anodes is vital for constructing robust solid‐electrolyte interphase (SEI) and achieving reliable Li metal batteries (LMBs). Herein, an electrode‐based strategy is proposed to regulate adsorption/defluorination kinetics of fluorinated electrolyte species by incorporating mechanochemically generated Li2O nanoparticles into the Li/Li22Sn5 composite electrode, thereby constructing a LiF‐rich SEI. This approach fundamentally differs from conventional methods that rely on concentrated salts or complex electrolyte formulations. Spectroscopic characterizations combined with density functional theory simulations confirm that the integrated‐Li2O nanoparticles strongly adsorb FEC and PF6– anions and promote their spontaneous defluorination, facilitating the preferential formation of LiF within the SEI. This inorganic‐rich interphase homogenizes Li deposition and mitigates electrolyte corrosion even at 60 °C. Consequently, the composite electrode delivers a high average Coulombic efficiency of 99.0% over 50 plating/stripping cycles in carbonate electrolyte at 1 mA cm−2 and 1 mAh cm−2. Paired with LiCoO2 cathodes, it achieves outstanding cyclability with 87.0% capacity‐retention at a low negative‐to‐positive ratio of 2:1 and 84.8% capacity‐retention under lean‐electrolyte conditions (20 µL) after 200 cycles over a wide voltage range of 2.8–4.5 V. This work highlights regulating adsorption/defluorination kinetics as an effective route to engineer LiF‐rich SEI and enable high‐performance LMBs.

Lithium (Li)-metal batteries are promising next-generation energy storage systems. One drawback of uncontrollable electrolyte degradation causes them to form a fragile and nonuniform solid electrolyte interface (SEI). In this study, we proposed a fluorinated carbon nanotube (CNT) macrofilm (CMF) on Li metal as a hybrid anode, which can regulate the redox state at anode/electrolyte interface. Due to the favorable reaction energy between plating Li and fluorinated CNTs, the metal can be fluorinated directly to a LiF-rich SEI during the charging process, leading to a high Young's modulus (~2.0 GPa) and fast ionic transfer (~2.59×10-7 S cm-1). The obtained SEI can guide the homogeneous plating/stripping of Li during electrochemical processes while suppressing dendrites growth. In particular, the hybrid endowed full cells with substantially enhanced cyclability allows for high-capacity retention (~99.3%) and remarkable rate capacity. This work can extend fluorination technology into a platform to control artificial SEI formation in Li-metal batteries giving it stability with long-life performance.

In this study, a porous organic polymer with "charge storage" properties was prepared and doped into a polymer composite solid electrolyte to study the effect of sufficient charge transfer on the decomposition of lithium salts. The results show in contrast to porphyrins, the unique structure of POF allows for charge transfer between each individual porphyrin. Therefore, during TFSI- decomposition to the formation of LiF, TFSI- can obtain sufficient charge, thereby promoting the break of C-F and forming the LiF-rich SEI. Compared with single porphyrin (0.423 e-), POF provides 2.7 times more charge transfer to LiTFSI (1.147 e-). The experimental results show that Li//Li symmetric batteries equipped with PEO-POF can be operated stably for more than 2700 h at 60 °C. Even the Li//Li (45 μm) symmetric cells are stable for more than 1100 h at 0.1 mA cm-1. In addition, LiFePO4//PEO-POF//Li batteries have excellent cycling performance at 2 C (80% capacity retention after 750 cycles). Even LiFePO4//PEO-POF//Li (45 μm) cells have excellent cycling performance at 1 C (96% capacity retention after 300 cycles). Even when the PEO-base is replaced with a PEG-base and a PVDF-base, the performance of the cell is still significantly improved.

Lithium fluoride (LiF)‐rich solid electrolyte interface (SEI) is critical for enabling the stable operation of polymer‐based all‐solid‐state lithium‐metal batteries (ASSLMBs). Precisely controlling the C─F dissociation chemistry in fluorine‐containing lithium salts to construct a LiF‐rich SEI is a logically viable but still challenging approach. Current strategies for constructing LiF‐rich SEI primarily focus on designing non‐metal polar groups and related structures. In contrast, approaches leveraging metal‐based electron donors to facilitate charge transfer for C─F bond cleavage and LiF formation remain largely unexplored. Herein, a dual‐enhanced charge transfer mechanism through prelithiation strategy is proposed in solid polymer electrolyte (SPE) for C─F bond cleavage. The charge transfer occurs between LiTFSI and the introduced metal sites and further enhanced by lithiation design, thereby achieving a robust LiF‐rich SEI. The achieving SPEs enable an excellent cyclability of Li|Li cell over 3800 h at 0.3 mA cm−2. Li||LiFePO4 ASSLMBs demonstrate a high Coulombic efficiency of ≈100% and a stability of 1200 cycles with capacity retention of 80% at 2C. The corresponding pouch cell delivers a high average areal capacity of 2.41 mAh cm−2 over 1600 h. This work offers a novel approach for constructing LiF‐rich SEI toward durable ASSLMBs.

No abstract available

Silicon (Si) anodes hold great promise for enhancing the energy density of lithium‐ion batteries (LIBs). However, issues such as slow intrinsic kinetics and unstable interfaces caused by significant volume changes hinder the practical deployment of Si anodes. Fast charging is desired by Si‐related issues that worsen Li plating and dead Li, making it essential to overcome these for safe, reversible charging. Herein, a novel approach is proposed by combining structural design and solid electrolyte interface (SEI) modulation to enable efficient and safe fast charging of LIBs. 3D porous micro‐particles consisting of Si nanosheets coated with a pitch‐based carbon layer are successfully prepared. This design provides enhanced ion transport pathways while maintaining the material's intrinsic rate performance and tap density. Furthermore, the designed localized high‐concentration electrolyte (LHCE) exhibits a lower Li+ desolvation energy barrier and leads to the formation of a LiF‐rich SEI, mitigating the Li plating “tip effect” during fast charging, maintaining interface stability, and demonstrating high Coulombic efficiency. Overall, this study highlights the synergistic importance of structure design and SEI regulation in enhancing LIB anodes for fast charging, aiding in developing superior, safe energy storage.

The practical application of lithium‐metal batteries (LMBs) remains impeded by uncontrollable Li dendrite growth and unstable solid‐state electrolyte interphase (SEI) on lithium‐metal anodes. Constructing the inorganic‐rich SEI is considered as an effective strategy to realize the dense Li deposition and inhibit interfacial side reactions, thereby improving the lifespans of LMBs. Herein, an anion‐reduction‐catalysis mechanism is proposed to design a LiF‐rich SEI utilizing 2D tellurium (Te) nanosheets as catalysts, which are homogenously implanted on the substrate. Lithiophilic Te nanosheets can induce uniform Li nucleation and deposition through in situ lithiation reactions, while the resulting product Li2Te can reduce the energy barrier for anion decomposition and promote the generation of LiF in the SEI. Consequently, Li dendrite growth and interfacial side reactions are effectively suppressed, enabling long‐cycle‐life LMBs. The Te‐modified electrode in half‐cells delivers superior cycle life exceeding 500 cycles and a high average Coulombic efficiency of 97.8% at 5 mAh cm−2. The high‐energy‐density (405 Wh kg−1) pouch cells pairing the Te‐modified Li anodes with high‐mass‐loading LiNi0.9Co0.05Mn0.05O2 (NCM90) cathodes exhibit stable cycling performance with a high average Coulombic efficiency of 99.3% in carbonate electrolytes. This work provides a promising anion catalyst design for LiF‐rich SEI and paves the way for developing high‐energy‐density LMBs.

Gel polymer electrolytes (GPEs) with high flame‐retardant concentration can remarkably reduce the thermal runaway risk of lithium metal batteries (LMBs). However, higher flame‐retardant content in GPEs always leads to increased leakage of active component and severe lithium corrosion, which greatly hinders the service life of LMBs. Herein, GPEs with high‐loading triphenyl phosphate (TPP) are originally fabricated by coaxial electrospinning and stabilized by dual confinement effects, including chemisorption of polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP), and physical encapsulation of polyacrylonitrile (PAN)/PVDF‐HFP. These effects arise from the strong polar interactions between the −CF3 group in PVDF‐HFP and P=O group in TPP, as well as the superior anti‐swelling property of PAN. To mitigate TPP‐induced corrosion during cycling, the optimized Li anode is armored with LiF‐rich solid electrolyte interphase (SEI) layer through immersing it in fluoroethylene carbonate‐containing electrolyte. As expected, the corresponding Li||Li symmetric cells deliver long‐term stable cycling behavior over 2400 h at 0.5 mA cm−2, and the LiFePO4||Li batteries hold a high‐capacity retention ratio of 81.7% after 6000 cycles at 10 C with excellent flame retardancy. These findings offer new insight into designing the SEI layer for lithium metal in flame‐retardant electrolytes, thus promoting the development and application of high‐security LMBs.

Lithium metal anodes are considered highly promising electrode materials due to their exceptional theoretical capacity and low reduction potential. However, their path to large-scale commercialization has been obstructed by significant challenges such as uncontrolled volume expansion, severe side reactions, and dendrite formation. To tackle these issues, our study introduces a covalent modification of separators using tannic acid (TA) and Co2+, coupled with the application of an external magnetic field. This innovative approach promotes the adsorption of CO32- ions while inhibiting the uptake of F- ions on the TA-Co/PP separators, leading to the formation of a LiF-rich solid electrolyte interface on the anode surface. Such modifications significantly enhance the electrochemical performance of lithium metal batteries. Remarkably, with the aid of the magnetic field, batteries featuring these modified separators maintained a Coulombic efficiency of 90% over 650 cycles at 1 mA cm-2. Additionally, under challenging conditions at 60 °C and 4 mA cm-2, the polarization voltage of Li symmetric cells utilizing TA-Co/PP separators is maintained at just 20 mV. This successful demonstration underlines the potential of our method to catalyze the broader adoption and commercialization of lithium metal batteries across varied temperature spectra.

Due to its good mechanical properties and high ionic conductivity, the sulfide-type solid electrolyte (SE) can potentially realize all-solid-state batteries (ASSBs). Nevertheless, challenges, including limited electrochemical stability, insufficient solid–solid contact with the electrode, and reactivity with lithium, must be addressed. These challenges contribute to dendrite growth and electrolyte reduction. Herein, a straightforward and solvent-free method was devised to generate a robust artificial interphase between lithium metal and a SE. It is achieved through the incorporation of a composite electrolyte composed of Li6PS5Cl (LPSC), polyethylene glycol (PEG), and lithium bis(fluorosulfonyl)imide (LiFSI), resulting in the in situ creation of a LiF-rich interfacial layer. This interphase effectively mitigates electrolyte reduction and promotes lithium-ion diffusion. Interestingly, including PEG as an additive increases mechanical strength by enhancing adhesion between sulfide particles and improves the physical contact between the LPSC SE and the lithium anode by enhancing the ductility of the LPSC SE. Moreover, it acts as a protective barrier, preventing direct contact between the SE and the Li anode, thereby inhibiting electrolyte decomposition and reducing the electronic conductivity of the composite SE, thus mitigating the dendrite growth. The Li|Li symmetric cells demonstrated remarkable cycling stability, maintaining consistent performance for over 3000 h at a current density of 0.1 mA cm–2, and the critical current density of the composite solid electrolyte (CSE) reaches 4.75 mA cm–2. Moreover, the all-solid-state lithium metal battery (ASSLMB) cell with the CSEs exhibits remarkable cycling stability and rate performance. This study highlights the synergistic combination of the in-situ-generated artificial SE interphase layer and CSEs, enabling high-performance ASSLMBs.

The interface structure of the electrode is closely related to the electrochemical performance of lithium‐metal batteries (LMBs). In particular, a high‐quality solid electrode interface (SEI) and uniform, dense lithium plating/stripping processes play a key role in achieving stable LMBs. Herein, a LiF‐rich SEI and a uniform and dense plating/stripping process of the electrolyte by reducing the electrolyte concentration without changing the solvation structure, thereby avoiding the high cost and poor wetting properties of high‐concentration electrolytes are achieved. The ultra‐low concentration electrolyte with an unchanged Li+ solvation structure can restrain the inhomogeneous diffusion flux of Li+, thereby achieving more uniform lithium deposition and stripping processes while maintaining a LiF‐rich SEI. The LiIICu battery with this electrolyte exhibits enhanced cycling stability for 1000 cycles with a coulombic efficiency of 99% at 1 mA cm–2 and 1 mAh cm–2. For the LiIILiFePO4 pouch cell, the capacity retention values at 0.5 and 1 C are 98.6% and 91.4%, respectively. This study offers a new perspective for the commercial application of low‐cost electrolytes with ultra‐low concentrations and high concentration effects.

Lithium fluoride (LiF) at the solid electrolyte interface (SEI) contributes to the stable operation of polymer-based solid-state lithium metal batteries. Currently, most of the methods for constructing lithium fluoride SEI are based on the design of polar groups of fillers. However, the mechanism behind how steric hindrance of fillers impacts LiF formation remains unclear. This study synthesizes three kinds of porous polyacetal amides (PAN-X, X=NH2, NH-CH3, N-(CH3)2) with varying steric hindrances by regulating the number of methyl substitutions of nitrogen atoms on the reaction monomer, which are incorporated into polymer composite solid electrolytes, to investigate the regulation mechanism of steric hindrance on the content of lithium fluoride in SEI. The results show that bis(trifluoromethanesulfonyl)imide (TFSI-) will compete for the charge without steric effect, while excessive steric hindrance hinders the interaction between TFSI- and polar groups, reducing charge acquisition. Only when one hydrogen atom on the amino group is replaced by a methyl group, steric hindrance from the methyl group prevents TFSI- from capturing charge in that direction, thereby facilitating the transfer of charge from the polar group to a separate TFSI- and promoting maximum LiF formation. This work provides a novel perspective on constructing LiF-rich SEI.

Electrochromic devices (ECDs) offer significant energy‐saving potential for applications such as smart windows and displays by modulating optical properties in response to electrical stimuli. However, their widespread adoption is limited by challenges associated with electrolyte stability and the formation of a robust solid‐electrolyte interphase (SEI). In this study, a novel quasi‐solid polymer electrolyte (QSPE) based on a UV‐curable matrix of poly(ethylene glycol) diacrylate (PEGDA) incorporated with poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) [P(VDF‐TrFE‐CFE), abbreviated as PVTC] is presented. The high dielectric constant of PVTC facilitates lithium‐ion transport, while electrochemical cycling triggers partial dehydrofluorination, thereby promoting in situ formation of a LiF‐rich SEI layer on WO3 surface. The optimized electrolyte exhibits excellent properties, including high optical transparency (88.7%), ionic conductivity (1.76 mS cm−1), and mechanical robustness. When applied in ECDs, PVTC enables outstanding performance, achieving 86.29% optical retention from the 5000th to the 40 000th cycle and 98.78% charge retention after 50 000 charge–discharge cycles. Furthermore, prototype demonstrations in smart windows and electrochromic sunglasses validate the scalability and flexibility of the proposed system, highlighting a promising strategy for advancing durable, high‐performance ECDs through innovative electrolyte design.

The solid electrolyte interphase (SEI) formed by the conventional constant-current process is often uneven and fragile, leading to low initial Coulombic efficiency, which induces rapid capacity degradation of silicon (Si) anodes. To obtain stable and uniform SEI, a pulse voltage method is proposed to construct a lithium fluoride(LiF) rich bilayer SEI on the Si anode surface, which selectively involves more anions in the SEI formation reaction by applying pulse voltage perturbations without altering the composition of the electrolyte. In-depth research has found that the pulse voltage protocol establishes an oscillation screening mechanism for anions, facilitating the arrival and decomposition of more anions on the surface of the Si anode to form a LiF-rich bilayer SEI. Such SEI exhibits high mechanical stability and rapid lithium-ion transport kinetics, achieving the initial Coulombic efficiency (ICE) of the Si anode improved to 90.8% and an enhanced capacity retention rate.

No abstract available

Lithium-oxygen batteries have a wide application due to their ultra-high theoretical energy density. However, uncontrollable lithium dendrites and highly reactive oxygen species greatly cause the corrosion of lithium anodes and the degradation of the electrolytes. In our work, we introduce 4-Methylbenzenesulfonyl Fluoride (4-MBSF) as a highly efficient film-forming additive. It can form a stable inorganic-organic composite solid electrolyte interfacial layer and inhibit the growth of lithium dendrites to stabilize the lithium anode, thus dramatically enhancing the lives of lithium-oxygen batteries. The sulfonyl fluoride group of 4-MBSF can react with LiOH to form a LiF-rich protective layer on the lithium metal surface, which can improve stripping/deposition stability and ionic conductivity. Besides, the π-conjugation of the benzene ring can improve the flexibility of the solid electrolyte interphase (SEI) layer to accommodate volume changes of the lithium anode during cycling and inhibit the attacks of the reactive oxygen species. The cycle life of lithium-oxygen batteries with 4-MBSF is prolonged to 400 cycles.

Silicon (Si) anodes hold exceptional promise for high-energy-density lithium-ion batteries (LIBs) due to their ultrahigh theoretical capacity (~4200 mAh g⁻¹). However, their commercialization is severely hindered by the significant volume expansion (~300%) and unstable solid electrolyte interphase (SEI). Conventional SEI, predominantly composed of organic species, suffers from low ionic conductivity, low electronic insulation and poor mechanical robustness, leading to rapid capacity decay. Herein, we propose an interface engineering strategy by decorating Si nanoparticles with an in-situ conversed MgF₂ layer (with coating integrity of 94.6%). During initial lithiation, the applied MgF₂ layer is in-situ conversed into SEI film with high ionic conductivity, electronic insulation and better mechanical adaptability. The prepared Si@MgF₂-1 anode achieves a high initial coulombic efficiency (91.7%), superior rate capability (2000 mAh g⁻¹ at 10 C), and remarkable cycling stability (1794.9 mAh g-1 after 500 cycles). Full-cell based on the Si@MgF₂-1 anode and NCM811 cathode further validate the practicality of this approach. The robust conversion strategy for the construction of a mechanically adaptive LiF-rich SEI layer holds significant promise for the advancement of durable silicon-based LIBs.

No abstract available

Amorphous silicon oxycarbide (SiOC) demonstrates high capacity for anode material of lithium‐ion batteries (LIBs). However, its low initial coulombic efficiency (ICE), poor electrical conductivity, and unstable solid electrolyte interphase (SEI) present significant challenges for practical application. Here, porous SiOC hierarchical spheres are elaborated by pyrolysis of cooperatively self‐assembled mesostructure, followed by an alkaline chemical etching process. Moreover, their electronic conductivity and mechanical strength are enhanced by decorating with well‐dispersed Fe/FeO nanoparticles (NPs). The cooperative interaction between the 3D nanoporous SiOC framework and its interconnected hierarchical structure provides rapid diffusion pathways and facilely accessible active sites for Li + ion insertion. The enhanced electronic and ionic conductivity of SiOC‐Fe anode facilitates the formation of a robust LiF‐rich SEI layer, which is found to be ionically more conductive and enables effective passivation of the anode/electrolyte interface, thereby ensuring long‐term cycling stability. Owing to the special nanostructure engineering and SEI, our prepared SiOC‐Fe anode exhibits an excellent cycling stability (635.3 mAh g −1 after 1200 cycles at 1.0 A g −1 ) as well as outstanding rate performance (277.3 mAh g −1 at 2.0 A g −1 ). Furthermore, the full cells assembled with an LiFePO 4 cathode demonstrate a high specific capacity of 140.0 mAh g −1 after 100 cycles. The work provides valuable insights into designing SiOC‐based anodes through metal NPs modification and nano‐morphologies construction for advanced LIBs.

Li metal is regarded as the "Holy Grail" in the next generation of anode materials due to its high theoretical capacity and low redox potential. However, sluggish Li ions interfacial transport kinetics and uncontrollable Li dendrites growth limit practical application of the energy storage system in high-power device. Herein, separators are modified by the addition of a coating, which spontaneously grafts onto the Li anode interface for in situ lithiation. The resultant alloy possessing of strong electron-donating property promotes the decomposition of lithium bistrifluoromethane sulfonimide in the electrolyte to form a LiF-rich alloy-doped solid electrolyte interface (SEI) layer. High ionic alloy solid solution diffusivity and electric field dispersion modulation accelerate Li ions transport and uniform stripping/plating, resulting in a high-power dendrite-free Li metal anode interface. Surprisingly, the formulated SEI layer achieves an ultra-long cycle life of over 8000 h (20,000 cycles) for symmetric cells at a current density of 10 mA cm-2. It also ensures that the NCM(811)//PP@Au//Li full cell at ultra-high currents (40 C) completes the charging/discharging process in only 68 s to provide high capacity of 151 mAh g-1. The results confirm that this scalable strategy has great development potential in realizing high power dendrite-free Li metal anode.

The generation of solid electrolyte interphase (SEI) largely determines the comprehensive performance of all-solid-state batteries. Herein, a novel "carrier-catalytic" integrated design is strategically exploited to in situ construct a stable LiF-LiBr rich SEI by improving the electron transfer kinetics to accelerate the bond-breaking dynamics. Specifically, the high electron transport capacity of Br-TPOM skeleton increases the polarity of C-Br, thus promoting the generation of LiBr. Then, the enhancement of electron transfer kinetics further promotes the fracture of C-F from TFSI- to form LiF. Finally, the stable and homogeneous artificial-SEI with enriched lithium dihalide is constructed through the in-situ co-growth mechanism of LiF and LiBr, which facilitatse the Li-ion transport kinetics and regulates the lithium deposition behavior. Impressively, the PEO-Br-TPOM paired with LiFePO4 delivers ultra-long cycling stability over 1000 cycles with 81% capacity retention at 1C while the pouch cells possess 88% superior capacity retention after 550 cycles with initial discharge capacity of 145 mAh g-1at 0.2C in the absence of external pressure. Even under stringent conditions, the practical pouch cells possess the practical capacity with stable electric quantities plateau in 30 cycles demonstrates its application potential in energy storage field.

The composition and physiochemical properties of the solid electrolyte interphase (SEI) significantly impact the electrochemical cyclability of the Li metal. Here, we introduce a trace dual-salt electrolyte additive (TDEA) that accelerates LiF production from FEC decomposition and improves the LiF distribution, resulting in earlier LiF precipitation and the formation of a LiF-rich SEI on the Li anode. TDEA at a millimolar-level concentration was found to alter the morphology of deposited Li, suppress Li dendrite formation, and increase the cycling time and operating current density for Li anodes. Li∥NCM811 full cells using TDEA-based electrolytes exhibited approximately two times longer lifespan than those without additives. Additionally, the TDEA-based electrolytes enabled a high energy density of 347 Wh kg-1 for 500-mAh pouch cells, maintaining stable cycling over 180 cycles under stringent conditions (N/P = 1.26 and E/C = 2.2 g A h-1). Our findings suggest that the proposed TDEA strategy offers a promising path to achieving high-performance Li metal batteries.

Lithium metal batteries (LMBs) are the best candidates for high‐energy density system. However, the unstable solid electrolyte interphase (SEI) caused by notorious lithium dendrite growth and huge volume fluctuation under practical conditions hinders its commercialization. Here, a functional copolymer composed of monomer is designed with ordered −CF2− groups grafted to viscoelastic backbone to provide homogeneous and self‐adapting in situ LiF‐rich interface. Hence, the robust interface facilitates rapid Li+ flux and suppresses dendritic Li growth. Furthermore, an elastic composite lithium metal anode (FELMA) based on the designed functional copolymer is fabricated through a cost‐effective approach. The FELMA shows excellent cycle stability with ultra‐low volume expansion rate of 0.16% per cycle after 200 cycles at the condition of 3 mA cm−2–3 mAh cm−2. The full batteries assembled with high‐loading LiNi0.8Co0.1Mn0.1O2 (NCM811, 4.1 mAh cm−2) cathode can maintain 80% capacity retention after 320 cycles under N/P = 2.17 and E/C = 2.68 g Ah−1, with the cycling life increased by 220% than Li||NCM811. A prototype 418 Wh kg−1 pouch cell (5.16 Ah) with N/P ratio of 0.88 and E/C ratio of 2.39 g Ah−1 shows stable cycling.

Metal‐organic framework materials (MOFs) with hierarchical porosity, structural tunability, and rich redox‐active centers have attracted intensive attention as potential substitutes for carbonaceous anode materials. However, the practical commercialization of MOFs still remains a challenge, due to uncontrollable performance degradation. Inspired by the prolonged lifespans of traditional anode materials with LiF‐rich solid electrolyte interface (SEI), the roles of LiF are examined in enhancing the cycle stability of MOFs, with copper benzenedicarboxylate (Cu‐BDC) as an example. By adjusting the electrolyte composition, the cycle performance of Cu‐BDC material is optimized, due to the generation of LiF‐rich SEI. In the optimal 3 M LiPF6 electrolyte, the formed SEI membrane is the thinnest, and the LiF content is the highest, so the Cu‐BDC shows a specific charge/discharge capacity of 378/387.2 mAh g−1 after 100 cycles at 100 mA g−1, comparing to less than 200 mAh g−1 in the electrolyte with 1% vinyl carbonate.

High–energy density lithium (Li) metal batteries (LMBs) are promising for energy storage applications but suffer from uncontrollable electrolyte degradation and the consequently formed unstable solid-electrolyte interphase (SEI). In this study, we designed self-assembled monolayers (SAMs) with high-density and long-range–ordered polar carboxyl groups linked to an aluminum oxide–coated separator to provide strong dipole moments, thus offering excess electrons to accelerate the degradation dynamics of carbon-fluorine bond cleavage in Li bis(trifluoromethanesulfonyl)imide. Hence, an SEI with enriched lithium fluoride (LiF) nanocrystals is generated, facilitating rapid Li+ transfer and suppressing dendritic Li growth. In particular, the SAMs endow the full cells with substantially enhanced cyclability under high cathode loading, limited Li excess, and lean electrolyte conditions. As such, our work extends the long-established SAMs technology into a platform to control electrolyte degradation and SEI formation toward LMBs with ultralong life spans. Description SAM to the rescue During cycling of lithium metal batteries, the formation of dendrites on the electrodes can cause failure of the battery over time. Liu et al. were able to enhance lithium stripping and plating using self-assembled monolayers (SAMs) containing carboxylic groups. The SAMs are deposited on the aluminum oxide–coated polypropylene separator and promote the formation of a lithium fluoride–rich solid electrolyte interphase that shows greater overall stability and enhanced lithium ion transport. —MSL Self-assembled monolayers help build a LiF-rich solid electrolyte interphase for a long-life-span Li metal anode.

The solid electrolyte interphase (SEI) of rich lithium halides can effectively regulate the uniform deposition of lithium, suppress the formation and growth of lithium dendrites, and consequently enhance the overall electrochemical performance of batteries. In current research, the construction of multi‐component lithium halide SEI primarily relies on chemical bond breaking, which involves longer formation pathways for lithium halides and presents inherent limitations. In this study, the ionic liquid is grafted onto the porous polymer, facilitating the in‐situ formation of LiBr through the direct ionic transformation of Br − , thereby streamlining the reaction pathway. Meanwhile, the pyridine unit in the porous polymer can promote the fracture of the C─F bond in LiTFSI, forming a LiF‐rich SEI. Ultimately, the LiF/LiBr co‐growing lithium double halide SEI is constructed on lithium anode, which effectively inhibited the lithium dendrites growth. The experimental results demonstrate that the Li//PEO‐PBrILs//Li battery stably cycled for 4000 h at the current density of 0.1 mA cm −1 . The LiFePO 4 //PEO‐PBrILs//Li battery maintains a capacity retention rate of 80.2% after 800 cycles at 1 C. Even at 30 °C, the LiFePO 4 //PEO‐PBrILs//Li battery maintains a capacity retention of 94% after 200 cycles. This study presents a novel approach for constructing various lithium halides SEI.

Solid-state electrolytes can guarantee the safe operation of high-energy density lithium metal batteries (LMBs). However, major challenges still persist with LMBs due to the use of solid electrolytes, that is, poor ionic conductivity and poor compatibility at the electrolyte/electrode interface, which reduces the operational stability of solid-state LMBs. Herein, a novel fiber-network-reinforced composite polymer electrolyte (CPE) was designed by combining an organic plastic salt (OPS) with a bicontinuous electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li7La3Zr2O12 (LLZO) membrane. The presence of LLZO in the composite helps to promote the dissociation of FSI- from OPSs. Subsequently, the dissociated FSI- is then involved in the formation of a LiF-rich solid electrolyte interphase (SEI) layer on the lithium anode via a reductive decomposition reaction, which was affirmed by theoretical calculations and experimental results. Due to the LiF-rich SEI layer, the Li/Li symmetric cell was able to demonstrate a long cyclic life of over 2600 h at a current density of 0.1 mA cm-2. More importantly, the as-prepared CPE achieved a high ionic conductivity of 2.8 × 10-4 S cm-1 at 25 °C, and the Li/LiFePO4 cell based on the CPE exhibited a high discharge capacity and 83.3% capacity retention after 500 cycles at 1.0 C. Thus, the strategy proposed in this work can inspire the future development of highly conductive solid electrolytes and compatible interface designs toward high-energy density solid-state LMBs.

Stabilizing a solid electrolyte interface (SEI) film on the Si surface is a prerequisite for realizing silicon (Si) anode applications. Interfacial engineering is one of the effective strategies to construct stable SEI films on Si surfaces and improve the electrochemical performance of the Si anodes. This work develops a silver (Ag)-decorated mucic acid (MA) buffer interface on the Si surface and the obtained Si@MA*Ag anode retains 1567 mAh g-1 after 500 cycles at 2.1 A g-1 and exhibits 1740 mAh g-1 at 126 A g-1, which are significantly higher than those of the bare Si anode of 247 and 145 mAh g-1 under the same conditions, respectively. Analysis indicates that the improved electrochemical performance is because of the depressed volume effect of the Si particles and the sustained integrity of the electrode laminate during cycling, the enhanced lithium diffusion on the Si surface, and the improved electronic conductivity of the Si anode, as well as the facilitated formation of inorganic components in the SEI film.

Fast-charging lithium-ion batteries (LIBs) have been severely hampered by the slow development of their electrolytes. Herein, we demonstrate that the size effect of solvent sheath would pose a great effect on the fast-charging performance of LIBs. Three similar ethers, including diethyl ether (DEE), dipropyl ether (DPE), and dibutyl ether (DBE), were mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and lithium bis(fluorosulfonyl)imide (1 M) to form an electrolyte for fast-charging LIBs, respectively. The results showed that it is more difficult to form ternary graphite intercalation compounds (GICs) in the electrolyte with a larger solvation sheath. The DEE electrolyte can form stable GICs and generate an inner LiF-rich solid electrolyte interphase (SEI), lowering the diffusion barrier of Li+. Therefore, the graphite anode powered by the DEE electrolyte can maintain a capacity of 190 mAh g-1 at 4 C after 500 cycles. This kind of size effect of solvation sheath is also applicable to lithium metal batteries.

Lithium (Li) is a promising anode material for all‐solid‐state Li metal batteries (ASSLMBs) due to its high energy density. However, the interface incompatibility of Li/solid electrolyte and uneven Li deposition induces the penetration of Li dendrites. Herein, a multifunctional rich‐LiF/Mg artificial solid electrolyte interphase (SEI) layer is constructed from a MgF2‐PVDF‐HFP film to passivate the Li anode and achieve effective inhibition of Li dendrites. Notably, the triggered LixMg alloys rivet the Li6PS5Cl (LPSCl) electrolyte and Li anode together well, producing satisfactory interface contact and reducing overpotential. The mechanism of LiF and LixMg alloys to enhance the stability of the Li/LPSCl interface is further elucidated by density functional theory (DFT). Moreover, the synergistic interaction of LiF with high interfacial energy and LixMg alloys with low diffusion barrier promotes uniform deposition of Li during plating/stripping and structural stability. Therefore, the modified Li‐symmetric cell exhibits ultra‐high critical current density (2.0 mA cm−2) and considerable cyclic stability (more than 1000 h at 0.5 mA cm−2). Remarkably, NCM//LPSCl//3% MgF2‐PVDF‐HFP@Li ASSLMBs exhibit considerable long‐term cycle stability (86.9% capacity retention after 100 cycles at 0.2 C). This work highlights the critical role of the intermediate passivating layer in mitigating side reactions and preventing Li penetration.

Recycling graphite anodes is critical due to the high economic and environmental costs of producing battery‐grade graphite. However, traditional recycling primarily regenerates graphite powder through complex steps like separation and purification. In spent graphite anode materials, the primary cause of electrochemical failure is the surface formation of a thick, poorly conductive solid electrolyte interphase (SEI) layer. Herein, a decarbonization‐fluorination strategy is developed to directly regenerate spent graphite electrodes. The process can convert the poorly conductive SEI layer into a highly conductive LiF‐rich layer by reacting Li2CO3 present in the SEI with an NH4F solution. This reconstructed interface boosts ionic conductivity, lowers interfacial resistance, and creates a fast pathway for lithium ions. The regeneration graphite electrode exhibits a high specific capacity of 303.9 mAh g−1 at 0.5 C and a capacity retention of 92.3% after 500 cycles. The LiNi0.8Co0.1Mn0.1O2 (NCM811)//regenerated graphite pouch cell (550 mAh) shows a 92% capacity retention after 200 cycles at 1 C. Furthermore, its areal capacity is 4.9 times higher than that of a spent graphite pouch cell. The techno‐economic analysis indicates cost reductions ≈78% compared to conventional approaches. This work lays the foundation for a more sustainable technology for the direct recovery of graphite electrodes.

No abstract available

The electrode/electrolyte interfaces play an important role in the electrochemical reaction kinetics to alleviate the severe polarization and voltage hysteresis in lithium primary batteries. Herein, C5 F5 N is proposed as an electrolyte additive to tune the characteristics of the electrode/electrolyte interfaces. The Li/CFx primary battery with C5 F5 N additive exhibits an excellent discharge-specific capacity of 981.4 mAh g-1 (0.1 C), a remarkable high-rate capability of 598 mAh g-1 (15 C), and an outstanding energy/power density of 1068.7 Wh kg-1 /24362.5 W kg-1 . It also shows remarkable storage performance with 717.2 mAh g-1 at 0.1 C after storage at 55 °C for 2 months. The excellent performance of the Li/CFx batteries is closely related to the improved and stable Li3 N/LiF-rich homogeneous interfaces induced by the C5 F5 N additive, which results in uniform distribution of Li+ flux, facilitated electrochemical kinetics, and increased rate capability of Li/CFx battery. Therefore, C5 F5 N is expected to be a promising electrolyte additive, and the related electrode/electrolyte interface engineering provides an effective and facile strategy to increase the performance of the lithium primary battery.

Inorganic LiF is generally a desirable component in solid electrolyte interface (SEI) for graphite anode due to its electronic insulation, low Li+ diffusion barrier, high modulus and good chemical stability. Herein, fluorinated carbon (CFx) was incorporated into graphite material, which exhibited a high discharge potential prior to electrolyte decomposition and in-situ formed a crystalline LiF-based SEI with improved Li+ diffusion rate. The optimized graphite anode therefore demonstrated a fast-charging capability with 124 mAh g-1 at high rate of 8 C and a remarkable capacity retention of 83.8% at the low temperature of -30 oC compared to that at 25 oC. Furthermore, the optimized graphite|LiFePO4 full cell exhibited a significantly high discharge capacity of 109 mAh g-1 at -30 oC, corresponding to a notable 77.3% room-temperature capacity retention. These findings highlight a facile strategy to attain a LiF-rich SEI for high-performance lithium-ion batteries.

Lithium (Li) dendrite growth in a routine carbonate electrolyte (RCE) is the main culprit hindering the practical application of Li metal anodes. Herein, we realize the regulation of the LiPF6 decomposition pathway in RCE containing 1.0 M LiPF6 by introducing a "self-polymerizing" additive, ethyl isothiocyanate (EITC), resulting in a robust LiF-rich solid electrolyte interphase (SEI). The effect of 1 vol % EITC on the electrode/electrolyte interfacial chemistry slows the formation of the byproduct LixPOFy. Such a LiF-rich SEI with EITC polymer winding exhibits a high Young's modulus and a uniform Li-ion flux, which suppresses dendrite growth and interface fluctuation. The EITC-based Li metal cell using a Li4Ti5O12 cathode delivers a capacity retention of 81.4% over 1000 cycles at 10 C, outperforming its counterpart. The cycling stability of 1 Ah pouch cells was further evaluated under EITC. We believe that this work provides a new method for tuning the interfacial chemistry of Li metal through electrolyte additives.

A solid electrolyte interphase (SEI) with robust mechanical property and high ionic conductivity is imperative for high-performance lithium metal batteries since it can efficiently impede the growth of notorious lithium dendrites. However, it is difficult to form such a SEI directly from an electrolyte. In this work, a crowding dilutant modified ionic liquid electrolyte (M-ILE) has been developed for this purpose. Simulations and experiments indicate that the 1,2-difluorobenzene (1,2-dfBen) dilutant not only creates a crowded electrolyte environment to promote the interaction of Li+-FSI-, leading to abundant aggregate ion pairs (AGGs), but also participates in the reduction to construct a robust and high ionic-conductive SEI. With this M-ILE, Li/LiFePO4 cells achieve a capacity retention of 96% over 250 cycles with 9.5 mg cm-2 mass loading, and Li/LiNi0.5Co0.2Mn0.3O2 cells also deliver a discharge capacity of 132 mAh g-1 with a high retention of 88% after 100 cycles. Therefore, the use of a crowding diluent is considered to be an efficient way to construct an advanced SEI for a Li anode.

Commercial Li-ion batteries use LiPF6-based carbonate electrolytes extensively, but there are many challenges associated with them, like dendritic Li growth and electrolyte decomposition, while supporting the aggressive chemical and electrochemical reactivity of lithium metal batteries (LMBs). This work proposes 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFM) as a multifunctional electrolyte additive, constructing protective solid-/cathode-electrolyte interphases (SEI/CEI) on the surfaces for both lithium metal anode (LMA) and Ni-rich cathode to solve these challenges simultaneously. The highly fluorinated group (-CF3) of the HFM molecule contributes to the construction of SEI/CEI films rich in LiF that offer excellent electronic insulation, high mechanical strength, and surface energy. Accordingly, the HFM-derived LiF-rich interphases can minimize the electrolyte-electrode parasitic reactions and promote uniform Li deposition. Also, the problems of LiNi0.8Co0.1Mn0.1O2 particles' inner microcrack evolution and the growth of dendritic Li are adequately addressed. Consequently, the HFM additive enables a Li/LiNi0.8Co0.1Mn0.1O2 cell with higher capacity retention after 200 cycles at 1 C than the cell with no additive (74.7 vs 52.8%), as well as a better rate performance, especially at 9 C. Furthermore, at 0.5/0.5 mAh cm-2, the Li/Li symmetrical battery displays supersteadfast cyclic performance beyond 500 h when HFM is present. For high-performance LMBs, the HFM additive offers a straightforward, cost-effective route.

Developing high-energy-density lithium metal batteries (LMBs) necessitates robust solid electrolyte interphases (SEIs) capable of enduring prolonged cycling. While lithium fluoride (LiF) is recognized as crucial for lithium metal anode (LMA) protection, the effects of different LiF sources in SEIs remain insufficiently understood. In this study, we systematically introduce single fluorine sources─anion LiF, solvent LiF, and native LiF─into a fluoride-free electrolyte system to elucidate the impact of LiF originating from different sources on the SEI composition and properties. Results reveal that SEI performance depends not only on LiF content but also on coexisting organic components. During deep cycling, solvent-derived LiF-rich SEIs, containing elevated LiF and organics, offer superior LMA protection ability. These SEIs maintain structural integrity during significant volume changes, effectively suppressing dead Li formation and achieving enhanced Coulombic efficiency. This work reexamines LiF's protective mechanisms while advancing SEI chemistry understanding, providing critical insights for developing high-performance LMBs.

The initial Coulombic efficiency (ICE) of lithium‐ion batteries, quantifying the irreversible Li+ loss during the first cycle, is critical for determining practical energy density. Many electrode materials exhibit substandard ICEs (<90%) due to excessive formation of solid electrolyte interphase (SEI). Traditional strategies modifying SEI formation mainly focus on the generating process but often consume extra Li+ and yield limited improvements. Here, a strategy is introduced that targets the terminating process of SEI formation, usually impeded by interfacial parasitic reactions, to achieve ICEs exceeding 90%. Using TiO2 as a model electrode, it is demonstrated that equivalent chemical fluorination suppresses the parasitic reaction between phosphorus pentafluoride (PF₅) and surface hydroxyl groups (─OH), early terminating SEI formation. Interfacial analysis and theoretical simulations reveal that this approach reduces organic SEI formation while preserving the beneficial LiF‐rich inner SEI layer. As a result, the fluorinated TiO2 anode exhibits an ICE of 92.1%, significantly higher than the 74.1% of pristine TiO2, without compromising other electrochemical performance metrics. Pouch cell tests confirm the practical applicability of the method. This work provides deep insights into mechanisms of terminating SEI formation and opens a new pathway for optimizing the battery performances through inherent SEI manipulation.

In situ polymerization strategies hold great promise for enhancing the physical interfacial stability in solid-state batteries, yet (electro)chemical degradation of polymerized interfaces, especially at high voltages, remains a critical challenge. Herein, we find interphase engineering is crucial for the polymerization process and polymer stability and pioneer an in situ polymerization-fluorination (Poly-FR) strategy to create durable interfaces with excellent physical and (electro)chemical stabilities, achieved by designing a bifunctional initiator for both polymerization and on-surface lithium donor reactions. The integrated in situ fluorination converts Li2CO3 impurities on LiNi0.8Co0.1Mn0.1O2 (NCM811) surfaces into LiF-rich interphases, effectively inhibiting the aggressive (de)lithiation intermediates and protecting the interface from underlying chemical degradation, thereby surpassing the stability limitations of polymerization alone. Furthermore, the Poly-FR mediated symmetric Li|Li cells achieve an impressive cycling stability of up to 12,000 h. Solid-state cells with NCM811 cathodes and Li metal anodes realize an ultrastable cycling performance of 400 cycles with 83.4% retention at a high voltage of 4.5 V. This work points toward advanced in situ polymerization and beyond.

Formation cycling is a critical process aimed at improving the performance of lithium ion (Li-ion) batteries during subsequent use. Achieving highly reversible Li-metal anodes, which would boost battery energy density, is a formidable challenge. Here, formation cycling and its impact on the subsequent cycling are largely unexplored. Through solid-state nuclear magnetic resonance (ssNMR) spectroscopy experiments, we reveal the critical role of the Li-ion diffusion dynamics between the electrodeposited Li-metal (ED-Li) and the as-formed solid electrolyte interphase (SEI). The most stable cycling performance is realized after formation cycling at a relatively high current density, causing an optimum in Li-ion diffusion over the Li-metal-SEI interface. We can relate this to a specific balance in the SEI chemistry, explaining the lasting impact of formation cycling. Thereby, this work highlights the importance and opportunities of regulating initial electrochemical conditions for improving the stability and life cycle of lithium metal batteries.

Prelithiation has been widely accepted as one of the most promising strategies to compensate for the loss of active substance and to improve the initial Coulombic efficiency in silicon-based anodes for advanced high-energy-density batteries. But because of their unstable solid electrolyte interface (SEI) layer and low initial Coulombic efficiency, they expand in volume during prelithiation and react with moisture, which makes commercialization a difficult process. Herein, we have developed a strategy using lithium bis(fluorosulfonyl)imide (LiFSI) treatment to eliminate redundant lithium and generate LiF-based inorganic compounds on the surface of the prelithiated electrode. Such method not only reduces the reactiveness of the prelithiated anode but also enhances the ionic conductivity of the SEI. The rich LiF surface works as an artificial SEI, and according to electrochemical evaluation, the initial Coulombic efficiency of the prelithiated silicon anode treated with LiFSI can reach 92.9%. This technique not only increases the battery’s energy density but also its cycle stability, resulting in superior capacity retention and a longer cycling life.

Employing functional additives can facilitate the formation of stable solid electrolyte interphase (SEI), which has emerged as a promising strategy to improve the electrochemical properties of lithium metal batteries (LMBs). Typical SEI containing inorganic components, such as lithium fluoride (LiF) and lithium nitride (LiNxOy and Li3N), have been confirmed to construct an ideal SEI for LMBs. Here, we designed and synthesized a novel molecule named BTFN to act as an SEI‐forming additive containing fluorine and nitro groups. The strong electron‐withdrawing effect greatly reduces the lowest unoccupied molecular orbital (LUMO) energy, facilitating its preferential decomposition during the SEI‐forming process. An SEI with rich LiF, LiNxOy, and Li3N forms after its preferential and complete decomposition, greatly enhancing stabilization and uniformity. The lifespan of symmetric LMBs with BTFN significantly increases more than 12 times under the same conditions; the Li/SPE/LFP full batteries cycle more than four times the contrast batteries with a capacity retention of 99.7%. This work provides some experiences and opinions for exploring complex SEI‐forming additives.

Silicon-based anodes have been attracting attention due to their high theoretical specific capacity, but their low initial Coulombic efficiency (ICE) seriously hinders their commercial application. Direct contact prelithiation is considered to be one of the effective means of solving this problem. By means of prelithiation, a specific solid electrolyte interphase (SEI) was constructed, which inhibited the volume expansion of the SiO/C composite anode during prelithiation and reduced the local current generated when the lithium source was in contact with the anode. On the one hand, it can reduce the side reactions derived from the decomposition of electrolytes in the prelithiation process, and on the other hand, it can slow down the prelithiation process and inhibit the volume expansion of the SiO/C composite anode in the prelithiation process. The results of XPS, TOF-SIMS, and other tests show that the use of an electrolyte whose main component is LiTFSI can construct SEI film whose main component is LiF, which to a certain extent can slow down the rate of prelithiation, reduce the local current generated when the lithium source is in contact with the negative electrode, minimize the occurrence of side reactions, and inhibit the volume expansion of the negative electrode material. The full battery assembled with NCM111 positive electrode still exhibits 83.5% capacity retention after 500 cycles at 1 C current density. These studies provide some ideas to enhance the performance of silicon-based materials.

It is critical to design the solvents or additives to provide high oxidation stability of electrolyte and good solid-electrolyte interphase (SEI) in lithium secondary batteries. In this work, we used quantum chemical calculations to evaluate carbonates with various fluorinated patterns to satisfy the requirements of antioxidation, stabilize SEI films, and modify solvation structures. The thermodynamic cycle method was used to calculate the oxidation and reduction potentials of a series of fluorinated linear (dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) and cyclic carbonates (ethylene carbonate, propylene carbonate, and 2,3-butanediol cyclic carbonate) vs Li+/Li. Both quantity and position of fluorine substitutions have a significant impact on the oxidation and reduction potentials according to correlation analyses. The instinctive causes for the potential change were the influence of the fluorinated position on the frontier orbital. We further studied lithium-ion coordinated fluorinated carbonates and found that the binding energy is mostly determined by electrostatic interaction according to the energy decomposition analysis. Fluorination will weaken the coordination ability of carbonates, which is demonstrated by their electrostatic potential distributions. Furthermore, it was found that the linear carbonate fluorinated at the α-position under reduction reaction easily produces LiF in situ, which was beneficial to the construction of good SEI. Finally, we provide some suggestions for the development of fluorinated carbonates based on the theoretical studies in this work.

Solid electrolyte interphase (SEI) plays an important role in regulating the interfacial ion transfer and safety of Lithium-ion batteries (LIBs). It is unstable and readily decomposed releasing much heat and gases and thus triggering thermal runaway. Herein, in situ heating X-ray photoelectron spectroscopy is applied to uncover the inherent thermal decomposition process of the SEI. The evolution of the composition, nanostructure, and the released gases are further probed by cryogenic transmission electron microscopy, and gas chromatography. The results show that the organic components of SEI are readily decomposed even at room temperature, releasing some flammable gases (e.g., H2 , CO, C2 H4 , etc.). The residual SEI after heat treatment is rich in inorganic components (e.g., Li2 O, LiF, and Li2 CO3 ), provides a nanostructure model for a beneficial SEI with enhanced stability. This work deepens the understanding of SEI intrinsic thermal stability, reveals its underlying relationship with the thermal runaway of LIBs, and enlightens to enhance the safety of LIBs by achieving inorganics-rich SEI.

Lithium metal batteries are considered highly promising candidates for the next-generation high-energy storage system. However, the growth of lithium dendrites significantly hinders their advance, particularly under high current densities, due to the formation of unstable solid electrolyte interphase (SEI) layers. In this study, we demonstrate that molybdenum-based MXenes, including Mo2CTx , Mo2TiC2Tx , and Mo2Ti2C3Tx , form more stable LiF/Li2CO3 SEI layers during lithium plating, compared to the conventional Cu electrode. Among these, the bimetallic Mo2Ti2C3Tx MXene, with its higher fluorine terminations, produces the most stable LiF-rich SEI layer. The formation of this stable inorganic SEI layer significantly reduces the nucleation overpotential for lithium deposition, promotes uniform Li deposition, and suppresses dendrite growth. Consequently, the Mo2Ti2C3Tx substrate achieved prolonged cycling stability of approximately 544 cycles with coulombic efficiency of ~99.79% at high current density of 3 mA cm-2 and capacity of 1 mAh cm-2. In full cells, the Mo2Ti2C3Tx anode, paired with an NCM622 cathode, maintained capacity retention of 70% over 100 cycles with high cathode loading of 10 mg cm-2. Our approach highlights the potential of Mo-based MXenes to improve the performance of lithium metal batteries, making them promising candidates for the next-generation energy storage system.

Lithiophilic substrates have been shown to improve the electrochemical performance of lithium metal anodes. The MXene-BN/Cu 3D current collector was prepared by a filtration method. The artificial solid electrolyte interface (SEI) layer composed of Li3N and LiF was formed on the surface of MXene-BN/Cu during the Li deposition process. Volume changes can be effectively relieved by this special 3D structure. The artificial SEI film reduced the critical dendrite growth length, inhibited Li dendrite growth, and stabilized the electrochemical cycle. MXene-BN/Cu exhibited highly reversible cycling properties during lithium metal deposition with a high Coulombic efficiency of ∼ 98.0% over 500 cycles. Furthermore, LiBH4 was produced during the Li deposition process. This study presents a promising strategy for developing dendrite-free Li anodes for use in lithium metal batteries.

Fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) are electrolyte additives that significantly influence the formation of the solid electrolyte interphase (SEI) during the initial cycling of lithium-ion batteries (LIBs). While FEC has been partially explored, the reductive decomposition mechanism of DFEC, particularly its kinetic and thermodynamic behaviour, remains poorly understood. In this work, we employ density functional theory (DFT) simulations to systematically investigate the thermodynamic (free energy, ΔG) and kinetic (free energy barrier, ΔG‡) parameters governing the reductive decomposition pathways of FEC and DFEC. The results indicate that both additives predominantly undergo direct two-electron reduction processes to form LiF and CO as the primary products. DFEC exhibits thermodynamic and kinetic behavior comparable to that of FEC. Notably, DFEC features a unique double-defluorination pathway that generates additional LiF, potentially enhancing SEI stability. Mayer bond order (MBO) and atomic dipole moment corrected Hirshfeld (ADCH) charge analyses further reveal that the Li+ coordination facilitates the defluorination process. These findings offer new insights into the decomposition of DFEC and confirm its ability to form LiF-rich SEI layers, highlighting DFEC as a promising electrolyte additive for stable and high-performance LIBs.

Lithium metal is the ideal candidate to replace conventional carbonaceous anodes due to its high theoretical specific capacity of 3860 mAh/g and low negative thermodynamic potential of -3.040 V vs. SHE [1]. Most organic electrolytes are unstable in the presence of Li metal and are reduced to form a solid-electrolyte interphase (SEI). One strategy to mitigate electrolyte decomposition is by upshifting the Li electrode redox potential. Ko et al. report positive shifts of up to 0.6 V in the Li electrode potential can influence coulombic efficiency [2]. In recent years, LiFSI-DME and LiFSI-FEC electrolytes with different concentrations have demonstrated highly reversible Li metal plating and stripping coulombic efficiencies of up to 99.1% [3] and 99.64% [4], respectively. While Qian et al. and Suo et al. briefly commented on the increased amount of inorganic content in the SEI, LiFSI concentration’s role on Li metal redox potential and SEI composition remains unclear. Organic species at the Li anode/electrolyte interphase are measured using a recently developed in-situ FTIR method. Cell level performance is evaluated by measuring coulombic efficiency. Complimentary techniques such as NMR and Raman are used to learn about the solvation structure as well as inorganic and soluble electrolyte decomposition products [5]. Novel insight into the relationship between SEI species, Li redox potential, and coulombic efficiency are presented. References Cheng, Xin-Bing, et al. "Toward safe lithium metal anode in rechargeable batteries: a review." Chemical reviews 117.15 (2017): 10403-10473. Ko, Seongjae, et al. "Electrode potential influences the reversibility of lithium-metal anodes." Nature Energy 7.12 (2022): 1217-1224. Qian, Jiangfeng, et al. "High rate and stable cycling of lithium metal anode." Nature communications 6.1 (2015): 6362. Suo, Liumin, et al. "Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries." Proceedings of the National Academy of Sciences 115.6 (2018): 1156-1161. Hestenes, Julia C., et al. "Transition metal dissolution mechanisms and impacts on electronic conductivity in composite LiNi0. 5Mn1. 5O4 cathode films." ACS Materials Au 3.2 (2022): 88-101.

The main challenges in rechargeable batteries, especially when aiming for high energy density, arise from the limited electrochemical stability window of current state-of-the-art electrolytes. Negative electrode active materials, such as silicon, tin oxide and others, whose capacity is many times higher than that of graphite, often exhibit large volume expansion upon lithiation and therefore the SEI formed on their surface is unstable. The most popular strategy for improving their cycling stability is the use of electrolyte additives that are reduced at potentials more positive than the electrolyte solvents. Their decomposition products are incorporated in the SEI, leading to a more stable electrode/electrolyte interface. One of the most-investigated electrolyte additives is fluoroethylene carbonate (FEC), because it has been shown to lead to a significant performance enhancement of Si- and Sn-based anodes. Many reaction pathways have been proposed, however there is currently no agreement on the exact type of chemical compounds constituting the decomposition products, nor on the exact mechanism for FEC decomposition. To address these questions, we conducted a systematic study that tracked the morphological and chemical changes during electrochemical decomposition of FEC. We have found that despite FEC often being referred as a “film-forming” additive, the first stage of its decomposition leads instead to the formation of spherical particles, consisting mainly of lithium fluoride (see figure below);1 only later a carbonate-rich film covers the entire electrode, covering as well the LiF-rich spheres. This phenomenon has been overlooked before likely due to very simple reason, disclosed in our contribution. A detailed investigation using XPEEM—a surface-sensitive analytical technique with high lateral resolution—as a function of electrolyte composition shows that fluorine in the later-formed carbonate film comes from the electrolyte salt, while all fluorine from FEC decomposition resides in the spherical particles, formed upon FEC reduction. In addition, we have found that the size and amount of particles strongly depend on the cell medium, where electrolytes with higher dielectric constant lead to larger particle size, as does the presence of the high-capacity electroactive materials in the electrode, both contributing to the final properties of FEC-derived SEI. The results of this study provide a deeper understanding of how fluorine-containing additives work and enables tuning of the SEI properties to the desired morphological and chemical outcome by using the laws of simple crystal-growth theory by adjusting the inter-cell environment. This work demonstrates that, with the right analytical tools, the true nature of the even seemingly very-well studied compounds can be revealed and a full understanding of their decomposition mechanisms can be clarified. Acknowledgement This research was supported by InnoSuisse (Project number 18254.2) References Y. Surace, D. Leanza, M. Mirolo, Ł. Kondracki, C.A.F. Vaz, M. El Kazzi, P. Novák, S. Trabesinger, Energy Storage Materials 2022, 44, 156-167. Figure 1

No abstract available

Micron-sized Si-based materials are promising anodes due to their high capacity, low cost, and ease of production, yet in application they suffer from severe volume expansion upon lithiation, which puts mechanical stress on the solid electrolyte interphase (SEI) that leads to premature capacity decay. Constructing a robust SEI with high Li+ conductivity is crucial in addressing this challenge, but most SEI regulation strategies for Si-based anodes come at the expense of manufacturability and cost. A novel and low-cost combination of additives comprised of 3 wt% trimethyl phosphate (TMP) and 5 wt% fluoroethylene carbonate (FEC) in carbonate electrolyte (BE-TF) was used to generate a bilayer SEI architecture specifically tailored for Si-based anodes by a sequential decomposition mechanism, where the lithium fluoride (LiF)-rich inner layer suppresses the volume expansion and the Li3PO4-rich outer layer forms a barrier that shields inner particles from detrimental side reactions. A high capacity retention of 88% after 200 cycles at 1 A g-1 can be achieved in a battery with a micron-sized SiOx (0 < x < 2) anode using BE-TF electrolyte. Additionally, an industrial-grade 3.5 Ah NCM||Gr-micron-sized SiOx pouch cell using BE-TF electrolyte could maintain long-term stability after 1000 cycles with high-capacity retention of >81% at a high charging rate of 3 C.

This study investigates the electrochemical performance, stability, and decomposition mechanisms of fluorine-based electrolytes in large-scale cylindrical Ni-rich lithium-ion batteries (LIBs) under high-voltage conditions (up to 4.8 V). We examine fluoroethylene carbonate (FEC) and di-fluoroethylene carbonate (DFEC) in electrolyte formulations and their effects on battery longevity, gas evolution, and solvation dynamics. While FEC is known for improving the solid electrolyte interphase (SEI), DFEC remains underexplored. Using molecular dynamics (MD) simulations, density functional theory (DFT) calculations, and electrochemical analysis, we identify key solvation properties, ion transport characteristics (tLi+, CIP%), and electronic structures influencing electrolyte stability. The 1.2 M LiPF6 in DMC/FEC/DFEC (4:0.5:0.5% v/v) electrolyte achieves the highest capacity retention (85.11% after 1,000 cycles), with DFEC reducing solvation shell binding energy and stabilizing electrolyte performance. Differential electrochemical mass spectrometry (DEMS) and nuclear magnetic resonance (NMR) spectroscopy reveal that FEC leads to higher CO2 production via ring-opening and de-fluorination to vinylene carbonate (VC), while DFEC reduces gas evolution. These insights provide a holistic framework for optimizing high-energy electrolyte formulations, supporting the development of safer, more efficient LIBs for electric vehicles and energy storage applications.

Introduction There is a growing need for high-capacity lithium-ion batteries as a power source for electric vehicles and a backup power source for renewable energy. Si negative electrodes, which have about ten times the capacity of conventional graphite electrodes, are expected to be used practically to increase the capacity of lithium-ion batteries. However, there are still issues that need to be addressed before Si electrodes can be used practically. One of them is the decomposition of electrolytes on the negative electrode surface. In conventional lithium-ion batteries, a small amount of additive such as FEC is added to the electrolyte to suppress electrolyte decomposition. However, suppression of the electrolyte decomposition is still difficult for Si electrodes. On the other hand, it has been found that lithium fluoride (LiF) in the SEI film formed from the decomposition products of the electrolyte improves charge and discharge properties of Si electrode.1-3 In this study, we aimed to suppress electrolyte decomposition and improve cycle life by forming a LiF layer as an artificial SEI on the Si electrode using a thin-film technique. Experimental Amorphous Si thin films, 100 nm in thickness, were prepared on copper foil by RF magnetron sputtering. Subsequently, LiF layers were deposited on the Si surfaces by sputtering with varying thicknesses. The thickness of the LiF layers was measured by a stylus surface profiler. The LiF-coated Si films were transferred to an Ar-filled glovebox without exposure to air and punched into disks 13 mm in diameter. A coin-type half-cell (CR2032) was assembled with the LiF-coated Si film as a working electrode and a Li disk of 14 mm in diameter as a counter electrode. A solution of 1 M LiPF6 dissolved in a mixture of ethylene carbonate and diethyl carbonate was used as an electrolyte. Charge and discharge characteristics were measured with a C/3 rate in a thermostatic chamber at 30°C. After cycling, the coin cells were disassembled in the glovebox, the Si electrodes were rinsed with dimethyl carbonate, and the Si electrode surfaces were observed with a scanning electron microscope (SEM). Result and Discussion Figure 1 shows variations in discharge capacity of the Si film electrodes with and without LiF coating. The discharge capacity of the Si electrode without LiF rapidly dropped after 10 cycles, but LiF coating significantly improved cyclability. Capacity retention at the 100th cycle, compared to that at the 5th cycle, increased from 4% without LiF to 52% with LiF coating. LiF coating also improved initial Coulombic efficiency from 89.9% to 92.5%, suggesting that LiF coating suppresses electrolyte decomposition. Si electrode surfaces after 30 cycles were observed by SEM as shown in Fig. 2. Exfoliation of the Si film without LiF was observed in many areas after 30 cycles, but it was suppressed by LiF coating. LiF coating is effective in improving the cycle performance of Si negative electrodes as an artificial SEI. Acknowledgments This work was supported by GteX Program Japan Grant Number JPMJGX23S3 and JSPS KAKENHI Grant Number 2201967. References [1] M. Haruta et al., Electrochimica Acta 267 (2018) 94. [2] M. Haruta et al., J. Electrochem. Soc. 165 (2018) A1874. [3] M. Haruta et al., Nanoscale 19 (2018) 17257. Figure 1

Lithium metal batteries (LMBs) have attracted tremendous attention due to their ultrahigh energy density. However, fluoroethylene carbonate (FEC), a commonly used additive in traditional ester-based electrolytes, is usually over-reduced during cycling, leading to form an extra-thick solid electrolyte interphase (SEI) which hinders the transport of Li+ and deteriorates fast charging performance. Herein, we propose a decomposition-competition-driven strategy to control the growth of SEI. Acetonitrile (AN) preferentially decompose to form a nitrogen-containing SEI due to low Lowest Unoccupied Molecular Orbital (LUMO) energy level (-2.96 eV), high polarity, and favorable wettability, which exhibits a capacity of inhibiting the decomposition of FEC. As a result, the polarization voltage of the cell is remarkably stable. Furthermore, AN reconstructs the solvation structure, accelerates Li+ desolvation and increases the Li+ transference number and diffusion coefficient. Benefiting from the optimized electrolyte system, Li||Li cells demonstrate stable cycling over 3300 h at 1 mA cm- 2, and Li||LFP cells retain 155 mAh g- 1 after 500 cycles at 1 C with 91.57% capacity retention. Additionally, excellent rate and long-cycle performance can also be achieved in high-voltage Li||NCM811 cells. This work provides new insights into enhancing interfacial and transport properties of electrolytes for practical LMBs.

Understanding and controlling solid-electrolyte interphase (SEI) formation to stabilize cell performance is a significant challenge for next-generation Li-ion battery technologies. In recent years, computational modeling has become an essential tool in providing fundamental insights into SEI properties and dynamics. However, neither atomistic nor continuum-level approaches alone can capture the complexities of SEI chemistry across all relevant length and time scales. In this work, a continuum-level model is developed that is informed by reaction mechanisms obtained from first-principle calculations. The atomistically informed continuum-level model is used to understand electrolyte degradation, including the decomposition of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC). The model presented here is the most chemically complex continuum-level SEI model in the literature to date. The SEI model is calibrated against experimental irreversible leakage currents and shows qualitative agreement with expected SEI growth trends. The model framework is expected to accelerate fundamental understanding of SEI formation, facilitate mechanism development feedback, and dynamically interact with experimental insights. Figure 1

Improving the quality of the solid-electrolyte interphase (SEI) layer is highly imperative to stabilize the Li-metal anodes for the practical application of high-energy-density batteries. However, controllably managing the formation of robust SEI layers on the anode is challenging in state-of-the-art electrolytes. Herein, we discuss the role of dual additives fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2, LiPF) within the commercial electrolyte mixture (LiPF6/EC/DEC) considering their reactivity with Li metal anodes using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Synergistic effects of dual additives on SEI formation mechanisms are explored systematically by invoking different electrolyte mixtures including pure electrolyte (LP47), mono-additive (LP47/FEC and LP47/LiPF), and dual additives (LP47/FEC/LiPF). The present work suggests that the addition of dual additives accelerates the reduction of salt and additives while increasing the formation of a LiF-rich SEI layer. In addition, calculated atomic charges are applied to predict the representative F1s X-ray photoelectron (XPS) signal, and our results agree well with the experimentally identified SEI components. The nature of carbon and oxygen-containing groups resulting from the electrolyte decompositions at the anode surface is also analyzed. We find that the presence of dual additives inhibits undesirable solvent degradation in the respective mixtures, which effectively restricts the hazardous side products at the electrolyte-anode interface and improves SEI layer quality.

In order to improve the performance of lithium-ion batteries (LIBs), novel electrolytes are of primary importance. Recently, fluorinated cyclic phosphazene derivatives in combination with fluoroethylene carbonate (FEC) are mentioned in the literature as a promising electrolyte additive combination, which can decompose to form a dense, uniform, and thin protective layer on the surface of the anode and cathode electrode.[1,2] Additionally, suppressing further electrolyte decomposition and electrode corrosion, thus protecting the structural destruction of the electrodes, are mentioned within this electrolyte composition.[1–3] Furthermore, galvanostatic charge and discharge experiments with different cell composition materials demonstrate that fluorinated cyclic phosphazene compounds as additional additive material tend to improve cycling stability.[1,3,4] Although the electrochemical aspects of cyclic fluorinated phosphazene compounds combined with FEC are briefly introduced, it is still not fully clear how these two compound classes interact constructively during operation mode. Thus, the positive synergistic effect of FEC/Hexafluorocyclotriphosphazene (HFPN)-derivatives on the electrochemical performance during cell operation is not enlightened. The focus of this study is to investigate the complementary effect of FEC and ethoxy(pentafluoro)cyclotriphosphazene (EtPFPN) as additive compounds in an aprotic organic electrolyte in LiNi0.5Co0.2Mn0.3O (NCM523) SiOx/C full cells. Furthermore, the formation mechanism of lithium ethyl methyl carbonate (LEMC)-EtPFPN interfacial products and the reaction mechanism of lithium alkoxide with EtPFPN are proposed and supported with DFT measurements. Additionally, a new effect of FEC regarding the SEI formation will be introduced. The EtPFPN decomposition compounds in the electrolyte after the SEI formation have been investigated via gas chromatography-mass spectrometry (GC-MS) and gas chromatography-high resolution mass spectrometry (GC-HRMS). The electrode electrolyte interface investigation of the SEI has been performed via in-situ shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) and scanning electron microscopy (SEM). Constant current cycling is conducted, and in-situ Raman measurements characterize the deposition of electrolyte components and LEMC-EtPFPN traces on the SiOx/C anode material during the SEI formation. Finally, the interplay between EC, EMC, Li-alkoxide, LEMC, FEC, and EtPFPN has been visualized schematically via a reaction mechanism postulated based on analytical data of the electrolyte. [1] A. Ghaur, C. Peschel, I. Dienwiebel, L. Haneke, L. Du, L. Profanter, A. Gomez‐Martin, M. Winter, S. Nowak, T. Placke, Adv Energy Mater 2023, 2203503. [2] J. Liu, X. Song, L. Zhou, S. Wang, W. Song, W. Liu, H. Long, L. Zhou, H. Wu, C. Feng, Z. Guo, Nano Energy 2018, 46, 404–414. [3] Q. Liu, Z. Chen, Y. Liu, Y. Hong, W. Wang, J. Wang, B. Zhao, Y. Xu, J. Wang, X. Fan, L. Li, H. bin Wu, Energy Storage Mater 2021, 37, 521–529. [4] Y.-H. Liu, M. Okano, T. Mukai, K. Inoue, M. Yanagida, T. Sakai, J Power Sources 2016, 304, 9–14.

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No abstract available

Silicon-based anodes offer high energy density but suffer from significant volume variations, leading to an unstable solid electrolyte interphase (SEI). To enhance SEI stability, numerous electrolyte additives have been designed to decompose on the anode and form desirable SEI components (e.g., LiF). However, their electrochemical reduction kinetics on the anode surface compete with other electrolyte components, leading to suboptimal interfacial decomposition efficiency and a less stable SEI structure. Here, inspired by bioremediation strategies in petroleum pollution treatment, we introduce a proton acceptor that reacts with fluoroethylene carbonate (FEC), a commercially established additive, to generate an intermediate. Such an intermediate lowers the reduction kinetic barrier, accelerating the formation of LiF and enriching it in the inner layer of the SEI. Compared to the randomly distributed LiF structure, the resulting SEI exhibits better mechanical stability and lithium-ion conduction, effectively accommodating volume changes and mitigating stress concentration caused by local overlithiation. As a result, the electrochemical performance surpasses that of previously reported works. This intermediate-based strategy significantly improves the utilization efficiency of commercial additives, offering a practical direction for future electrolyte design.

The solid electrolyte interphase (SEI) layer is essential for battery performance and safety due to its electron insulation and Li-ion conduction. However, issues such as ongoing electrolyte decomposition and Li dendrite growth often arise. The most common strategy for improving the SEI is using electrolyte additives. However, the growth mechanism of the SEI with additives remains unclear. In this study, we use operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) to monitor in real time the nanoscale processes at the electrode–electrolyte interface during battery operation. We investigate how the additive fluoroethylene carbonate (FEC) influences the formation and properties of the SEI, as well as the growth and dissolution of Li dendrites. Our study shows that FEC decomposes early, allowing the nucleation and growth of LiF nanoparticles (NPs) that create a dense, uniform, and thin SEI layer. Interestingly, our analysis reveals that these NPs have structural defects that could influence ionic and electronic conductivity. The real-time observations show that the FEC-based SEI facilitates the formation of dense and short Li metals, whereas the FEC-free SEI leads to the growth of long Li whiskers with thinner roots than tips. This structural difference influences their dissolution mechanism: in FEC-rich electrolytes, the strong contact between Li metal and the electrode ensures complete dissolution, while in FEC-free electrolytes, partial dissolution occurs, leaving behind inactive Li metal. These findings emphasize the crucial role of additives in shaping the growth mechanism and the local structure of the SEI, thereby regulating the growth and dissolution of Li metal.

The compatibility of lithium metal with organic solvents is the most crucial for lithium metal batteries (LMBs). Even though ether solvents show excellent compatibility toward lithium metal, the reactivity of the ether solvents at elevated temperatures and high voltages hinders their utilization in lithium metal battery systems. In this study, a high‐temperature ether electrolyte is designed comprising lithium oxalyldifluoroborate (LiODFB), diethylene glycol dibutyl ether (DGDE), 3‐methoxypropionitrile (MPN), and fluorinated ethylene carbonate (FEC), which is abbreviated as MDF electrolyte. The presence of MPN in the electrolyte changes the solvation structure, thereby facilitating increased redox reactions of ODFB− and synergizing with FEC to build a robust solid electrolyte interface (SEI), effectively inhibiting lithium dendrites growth and solvent decomposition. Consequently, the MDF electrolyte exhibits not only long cyclic stability and high coulombic efficiency in Li||Cu and Li||Li cells but also excellent cyclic characteristics in both Li||LiFePO4 (LFP) and Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cells. Remarkably, these cells demonstrate stable operation even when exposed to higher temperatures of up to 80 °C, while the Li||NCM811 cell maintains consistent cyclic stability at an elevated voltage level of 4.5 V.

Solid‐state polymerized electrolytes exhibit advantageous properties, making them optimal candidates for next‐gen commercial solid‐state batteries. However, these electrolytes present significant challenges in terms of long‐term cycling stability, energy density, and safety. In this study, a ternary eutectic solid electrolyte (TESE) is prepared by combining deep eutectic solvents (DESs), polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP), and fluorinated ethylene carbonate (FEC). TESE also facilitates uniform lithium deposition, interfacial stability, and long‐cycle stability. N‐Methylacetamide in DESs preferentially occupies the lithium dissolution sheath, which in turn initiates a concentration gradient‐driven decomposition of FEC and stimulates the generation of inorganic solid electrolyte interphase (SEI) layers. The lithium metal and graphite soft pack full batteries are successfully assembled, demonstrating that Li/P‐0.8‐FEC/LFP exhibits excellent long‐cycle performance, with a capacity of 139.9 mAh g−1 after 500 cycles at 1 C 25 °C, accompanied by 97.8 % capacity retention. Furthermore, the Gr/P‐0.8‐FEC/LFP commercial solid‐state flexible pack full cell exhibits stable cycling performance at a high rate of 1 C. Moreover, the device exhibits remarkable safety in a series of rigorous safety tests, including 100 repeated bendings, pinning, 7100 N force extrusion, and cutting. The study results demonstrate that the electrolyte exhibits excellent cycling performance and safety characteristics, indicating significant potential for commercialization.

The interfacial instability of graphite anodes at high temperatures critically undermines the safety and fast‐charging capability of lithium‐ion batteries. To overcome this challenge, trimethylsilyl‐2,2‐difluoro‐2‐fluorosulfonylacetate (TD) is proposed as a multifunctional electrolyte additive that significantly enhances anode performance through synergistic adjacent element induction and solvation‐weakening effects. The sulfur atom in TD's sulfonyl group induces an adjacent‐element effect, catalyzing the transformation of PF 6 − derivatives into stable LiF and Li 3 PO 4 species. Simultaneously, TD self‐decomposition forms a robust, multi‐layered solid electrolyte interphase (SEI), comprising both organic ((TMS) 2 O) and inorganic (Li 2 S, Li 2 SO 4 ) components, thereby substantially improving thermal stability. Furthermore, TD weakens Li⁺–solvent interactions, notably by decreasing the coordination number of fluoroethylene carbonate (FEC), which enhances interfacial kinetics and stability. Consequently, graphite anodes employing TD‐modified electrolytes exhibit remarkable fast‐charging performance, achieving 300 mAh·g −1 at 10C and 60 °C, along with superior cyclability. NCM811/graphite pouch cells retain 87.8% capacity after 200 cycles at 60 °C, while cylindrical cells at full state of charge display reduced self‐discharge across various temperatures. This work presents a novel electrolyte design strategy based on synergistic molecular effects, offering critical insights for developing advanced LIBs suited for extreme operating conditions.

Lithium‐ion batteries (LIBs), widely used in electric vehicles (EVs) and other applications, are increasingly expected to deliver higher energy densities and stable performance over a wide temperature range, posing stringent challenges for advanced electrolyte design. However, achieving these properties remains challenging with currently commercialized ethylene carbonate (EC)‐based electrolytes. Herein, a propylene carbonate (PC)‐based electrolyte system is reported, employing hexafluorobenzene (HFB) and fluoroethylene carbonate (FEC) as synergistic additives. Specifically, HFB facilitates compatibility with graphite anodes through selective interfacial adsorption, while the decomposition of FEC stabilizes the solid electrolyte interphase (SEI), mitigating the formation of high‐impedance interfaces. This tailored electrolyte exhibits superior ionic conductivity, excellent oxidative stability, and broad temperature tolerance. When validated at 4.5 V, high‐loading NCM811/graphite cells achieve nearly full capacity over 100 cycles at low temperatures (−20 °C), with pouch cells retaining 80% of their capacity after 470 cycles. These findings underscore the effectiveness of strategic additive engineering in advancing the development of PC‐based electrolytes for practical LIBs.

The transition to sustainable energy systems necessitates the widespread adoption of electrified transportation and grid-scale renewable energy storage. Lithium metal batteries (LMBs) have emerged as a promising candidate offering high specific capacity (3860 mAh g⁻¹) and low electrode potential (-3.04 V vs. SHE). However, their commercialization is severely hindered by the thermal instability of liquid electrolytes, which predisposes these systems to catastrophic thermal runaway (TR) under abusive conditions. This study investigates the thermo-electrochemical behavior of LMBs across three distinct electrolytes: (i) 1.0 M LiPF 6 in EC/EMC (3:7), (ii) the same with 2% FEC and 1% VC as additives, and (iii) 1.0 M LiTFSI in DOL/DME (1:1) representing carbonate-based, additive-enhanced, and ether-based electrolytes, respectively. Through calorimetric analysis, chemical characterization, and physics-based modeling, the effect of electrolyte composition on solid-electrolyte interphase (SEI) formation and decomposition pathways under thermal abuse are elucidated. A strong correlation between SEI chemistry and thermal runaway onset is identified, revealing critical stability differences dictated by electrolyte formulation. To facilitate systematic comparison across formulations, a new quantitative metric for thermal robustness is introduced. These findings provide mechanistic insights into electrolyte-induced instabilities and establish design principles for the development of safer, high-performance LMBs for next-generation energy storage systems.

Lithium metal batteries (LMBs) paired with high – voltage cathodes like Li and Mn-rich (LMR) offer high energy density exceeding 400 Wh/kg. However, their commercial adoption is hindered by electrolyte decomposition, cathode electrolyte interface (CEI) instability, dendrite formation, and capacity fade due to structural degradation at high voltages (> 4.6 V). In this study, we present a novel dual – salt localized high-concentration electrolyte (D-LHCE) formulation. This D-LHCE integrates LiPF 6 and LiTFSI in a fluoroethylene carbonate (FEC), Dimethyl carbonate (DMC), with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as a diluent. The dual-salt strategy aims to optimize solvation by enhancing the formation of contact ion pairs (CIP) and aggregates (AGG). This innovative electrolyte formulation is tailored to enhance the stability of both the cathode-electrolyte interphase (CEI) and the solid-electrolyte interphase (SEI) on the lithium metal anode, mitigating oxidative decomposition and parasitic reactions that degrade battery performance. The D-LHCE demonstrated a solvation structure with dual salts AGGs and CIPs, analyzed using Raman and 7 Li NMR. For example, Raman spectroscopy showed a shift in peaks at 745 cm -1 for coordinated PF₆ - and 741 cm -1 for TFSI - indicating a solvation structure dominated by CIP and AGG resulted from reduced free solvent molecules. 7 Li NMR exhibited upfield shifts such as -1.258 ppm and -1.322 ppm indicating enhanced Li-ion interaction with both PF 6 - and TFSI - anions, a synergic effect resulted in D-LHCE. Electrochemical property of D-LHCE was compared with a series of electrolytes including a baseline (1 M LiPF 6 in EC/EMC), FEC-baseline (1 M LiPF 6 in FEC/DMC), and single-salt LHCEs (3 M LiPF 6 or 3 M LiTFSI in FEC/DMC with TTE), and D-LHCE (2 M LiPF 6 + 1 M LiTFSI in FEC/DMC with TTE). Attributed to its increased interionic interaction and a reduction in the HOMO energy, the D-LHCE presented its superior anodic stability up to 4.75 V vs.Li , compared with the baseline (4.3 V vs.Li ) and the single-salt LHCE (4.6 V vs.Li ) electrolytes. As a result, D-LHCE electrolyte significantly extended the cycle life of LMR/Li cells, achieving 90.2% capacity retention after 100 cycles at 25 o C, compared to 21.9% with the baseline. The influence of D-LHCE on the properties of SEI and CEI layers in LMR/Li cells were investigated after 100 cycles at 25 o C. X-ray photoelectron spectroscopy (XPS) shows that Li SEI layer in D-LHCE has LiF rich composition (74.8%) compared with the baseline electrolyte (56.1% LiF), with no detectable Mn signals, indicating robust protection against transition metal dissolution. In addition, scanning electron microscopy (SEM) reveals that D-LHCE produces a compact and uniform SEI layer on Li, whereas the baseline electrolyte produces thicker and porous SEI with significant cracks. The CEI on aged LMR cathodes also benefits significantly from D-LHCE. XPS analysis revealed a thin, LiF-rich CEI layer (60.9%) on LMR compared to the baseline electrolyte (31.7% LiF). SEM images show minimal surface deposits on LMR after 100 cycles in D-LHCE, unlike the thick layers in baseline and FEC-baseline samples. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses indicate a low interfacial impedance (R int = 40.4 Ω in D-LHCE vs. 168.4 Ω in baseline), reflecting suppressed CEI growth. These results, demonstrating enhanced CEI stability, will be discussed in detail in the presentation.

The solid electrolyte interphase (SEI) governs key electrochemical properties in batteries. While additive-driven SEI engineering constitutes the most promising strategy for tailoring interfacial composition, the impact of specific additives on SEI's dynamic evolution remains unresolved. Herein, we performed operando neutron reflectometry (NR) to quantitatively resolve the SEI's structural dynamics under cycling conditions. Employing model additives with well-defined decomposition mechanisms, fluoroethylene carbonate (FEC) and vinylene carbonate (VC), we establish a robust operando NR framework that enables transferable mechanistic insights for emerging additive systems. Our data reveal contrasting SEI architectures: FEC produces a thin, inorganic-rich SEI (LiF-dominant) that enhances mechanical integrity and cycling stability, while VC yields a flexible organic-dominated SEI which mitigates stress-induced microcracking. These findings provide atomically resolved design principles for advanced electrolyte additives via operando interfacial analysis, advancing high-energy-density Li-ion batteries and beyond.

Fluoroethylene carbonate (FEC), as a key electrolyte component, has been extensively employed across diverse electrolyte systems owing to its excellent compatibility with different anode materials. However, its mechanistic role on the cathode side remains under debate due to the strong electron-withdrawing nature of the fluorine incorporation. Here, we demonstrate that lithium difluoro(oxalate)borate (LiDFOB) can effectively trigger the latent cathode-side functionality of FEC through a rationally designed dual-additive electrolyte. At the LiNi0.9Co0.05Mn0.05O2 cathode, oxidative cleavage of LiDFOB generates BOF2 intermediates that activate FEC and direct its decomposition toward LiF and B-O/B-F-rich inorganic species, constructing a compact and resilient cathode-electrolyte interphase (CEI). Simultaneously, the coupled reduction of FEC and DFOB- at the lithium metal anode yields a boron-rich, LiF-enriched solid electrolyte interphase (SEI) that enhances interfacial compatibility and suppresses dendrite growth. These LiDFOB-enabled, FEC-mediated interfacial pathways significantly improve ion transport and durability, delivering 73.4% capacity retention of Li||NCM9055 full cells after 1000 cycles at 4.7 V, versus 55.1% for the base electrolyte.

The interfacial reaction of a silicon anode is very complex, which is closely related with the electrolyte components and surface elements' chemical status of the Si anode. It is crucial to elucidate the formation mechanism of the solid electrolyte interphase (SEI) on the silicon anode, which promotes the development of a stable SEI. However, the interface reaction mechanism on the silicon surface is closely related to the surface components. This work systematically investigates the interfacial reaction mechanism on silicon materials with three representative coatings of graphene, TiO2, and SiO2 by ex situ X-ray photoelectron spectroscopy (XPS) and dynamic analysis in operando attenuated total reflection-Fourier transform infrared (ATR-FTIR), in situ revealing the different ring-opening mechanisms of fluoro-ethylene carbonate (FEC) and ethylene carbonate (EC) on different silicon surfaces with varying electrical conductivities. Due to the different ring-opening mechanisms, the final decomposition product of FEC on the graphene/electrolyte interface is stable LiF, while on the oxide (native SiO2 or emerging TiO2) interface, it forms an unstable solid lithium compound •CH2CHFOCO2Li. This study demonstrates that the formation mechanism of the SEI on silicon-based electrodes is related to the electron conductivity of surface elements, providing a theoretical basis for further optimization of silicon-based composite materials.

Most modification strategies of polyethylene oxide (PEO)‐based solid polymer electrolyte focus on improving the room temperature ionic conductivity, while disregarding its inherent flammability that poses substantial safety hazard. Herein, a self‐extinguishing quasi‐solid‐state polymer electrolyte (PTTF‐SPE), which combines excellent room temperature electrochemical properties and high safety, has been developed by introducing triethyl phosphate (TEP) as a low‐cost and highly effective flame retardant. The cross‐linking structure derived from ‐CH2‐CH2‐O‐ segments of tetramethylene glycol dimethyl ether (TEGDME) and PEO makes a contribution to a high amorphous state of polymer. A robust solid electrolyte interphase (SEI) formed by preferential decomposition of fluoroethylene carbonate (FEC) that acts as a film‐forming additive, which can prevent TEP from degradation at lithium metal anode. The optimized PTTF‐SPE exhibits high ionic conductivity (0.54×10‐3 S/cm) and lithium transference number (0.71) at room temperature. The LiFePO4||Li battery demonstrates excellent cycle life over 500 cycles at 0.5 C with a high average discharge capacity of 131 mAh/g. A symmetric Li||Li battery that operating for 850 hours indicates a good compatibility of PTTF‐SPE towards lithium metal. This work provides a new idea for developing high‐energy‐density and high‐safety lithium‐metal batteries (LMBs) for room temperature.

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.

The use of high-nickel NMC811 cathode and SiOx-Gr anode can greatly improve the overall energy densities of lithium-ion batteries. However, the unfavorable solid electrolyte interphase (SEI) layer generated from the decomposition of EC-based electrolytes lead to the poor cycling stability of NMC811||SiOx-Gr cells. Here we report an electrolyte design of 1.5 M LiPF6 dissolved in FEC/MA/BN 2:2:6 by volume, which can form thin, robust, and homogeneous SEI layer to greatly improve the charge transfer at the electrode-electrolyte interface. Importantly, the designed electrolyte shows an outstanding low temperature performance that it can deliver a capacity of 123.3 mAh g–1 after 50 cycles at -20℃ with a current density of 0.5 C, overwhelming the standard EC-based electrolyte (1.2 M LiPF6 EC/EMC 3:7 by volume) with a capacity of 35.7 mAh g–1. The electrolyte also has a superior rate performance that it achieves a capacity of 122.5 mAh g-1 at a high current density of 10 C. Moreover, the LTE electrolyte holds the great potential of extreme fast-charging ability because of the large part of CC contribution in the CCCV charging model at high charging current densities.

As the most promising high energy density technology, lithium metal batteries are associated with serious interfacial challenges because the electrolytes employed are unable to meet the requirements of both electrodes simultaneously, namely, the systems that work for Li metal are highly likely to be unsuitable for the cathode, and vice versa. In this study, we investigate the synergistic effects of lithium bis (oxalate) borate (LiBOB), fluoroethylene carbonate (FEC) and adiponitrile (ADN) to develop a formula that is compatible with both elements in the battery. The solid–electrolyte interphase (SEI) multi-layer generated from LiBOB and FEC successfully protects the electrolyte from the lithium and suppresses the decomposition of ADN on lithium, identified by the tiny amounts of isonitriles on the surface of the anode. Simultaneously, most of the ADN molecules remain and protect the cathode particles via the absorption layer of the nitrile groups, in the same way that this process works in commercial lithium-ion batteries. Benefiting from the stable interfacial films formed synchronously on the anode and cathode, the Li/LiNi0.8Co0.1Mn0.1O2 cells with an area capacity of ~3 mAh cm−2 operate stably beyond 250 cycles and target the accumulated capacity to levels as high as ~653.4 mAh cm−2. Our approach demonstrates that electrolyte engineering with known additives is a practical strategy for addressing the challenges of lithium batteries.

Solid electrolyte interphase (SEI), determined by the components of electrolytes, can endow batteries with the ability to repress the growth of Li dendrites. Nevertheless, the mechanism of commercial carbonates on in situ‐generated SEI and the consequential effect on cycling performance is not well understood yet, although some carbonates are well used in electrolytes. In this work, quantum chemical calculations and molecular dynamics are used to reveal the formation mechanisms of SEI with carbonate‐based electrolyte additives on the atomic level. It is confirmed that the Li‐coordinated carbonate species are the leading participant of SEI formation and their impact on battery performance is clarified. Fluoroethylene carbonate (FEC) exhibits a completely different behavior from vinyl ethylene carbonate (VEC), ethylene carbonate (EC), and vinylene carbonate (VC). High reduction potential Li+‐coordinated additives, e.g. FEC and VEC can dominate the formation of SEI by excluding propylene carbonate (PC) and LiPF6 from the decomposition, and the corresponding Li||Li symmetric cells show enhanced long‐term performance compared with those with pure PC electrolyte, while the low reduction priority additives (e.g., EC and VC) cannot form a uniform SEI by winning the competitive reaction.

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 advancement of Li-metal batteries is significantly impeded by the presence of unstable solid electrolyte interphase and Li dendrites upon cycling. Herein, we present an innovative approach to address these issues through the synergetic regulation of solid electrolyte interphase mechanics and Li crystallography using yttrium fluoride/polymethyl methacrylate composite layer. Specifically, we demonstrate the in-situ generation of Y-doped lithium metal through the reaction of composite layer with Li metal, which reduces the surface energy of the (200) plane, and tunes the preferential crystallographic orientation to (200) plane from conventional (110) plane during Li plating. These changes effectively passivate Li metal, thereby significantly reducing undesired side reactions between Li and electrolytes by 4 times. Meanwhile, the composite layer with suitable modulus (~1.02 GPa) can enhance mechanical stability and maintain structural stability of SEI. Consequently, a 4.2 Ah pouch cell with high energy density of 468 Wh kg−1 and remarkable capacity stability of 0.08% decay/cycle is demonstrated under harsh condition, such as high-areal-capacity cathode (6 mAh cm−2), lean electrolyte (1.98 g Ah−1), and high current density (3 mA cm−2). Our findings highlight the potential of reactive composite layer as a promising strategy for the development of stable Li-metal batteries. The application of Li-metal batteries (LMBs) is impeded by unstable solid electrolyte interphase (SEI) and uncontrollable Li dendrites growth. Here, the authors present an YF3/PMMA composite layer to achieve high-performance LMBs via the synergetic regulation of SEI mechanics and Li crystallography.

The limited salt dissociation efficiency and unstable (Li(DMF)x)+ solvation structures in poly(vinylidene fluoride) (PVDF)‐based solid‐state electrolytes (SSEs) significantly impede both high‐rate ion transport and electrode‐electrolyte interfacial stability. However, developing SSEs that combine high ionic conductivity (>1 mS cm−1) with stable electrode‐electrolyte interfaces remains a major scientific challenge. Here, a high‐voltage solid‐state lithium‐metal battery is presented employing a PVDF‐SCS (PVDF modified with benzenesulfonylated chitosan) electrolyte. The nitrogen‐based anionic receptors in sulfonamide chitosan (SCS) facilitated lithium salt dissociation through preferential anion‐cation pair disruption, thereby enhancing the free Li⁺ concentration. Crucially, the electron‐deficient nitrogen centers exhibit strong coordination with lithium salt anions, promoting their electrochemical reduction and forming a stable, anion‐derived solid electrolyte interphase (SEI). Consequently, the PVDF‐SCS electrolyte demonstrates an elevated Li⁺ conductivity of 1.35 mS cm−¹ and effectively mitigates dendritic growth, enabling a stable operation of Li|PVDF‐SCS|NCM523 full batteries for 400 cycles at a high voltage of 4.3 V. This work demonstrates the anion engineering can simultaneously enhance Li+ transport and interfacial stability, paving the way for high‐performance solid‐state batteries.

Residual solvents in vinylidene fluoride (VDF)‐based solid polymer electrolytes (SPEs) have been recognized as responsible for their high ionic conductivity. However, side reactions by the residual solvents with the lithium (Li) metal induce poor stability, which has been long neglected. This study proposes a strategy to achieve a delicate equilibrium between ion conduction and electrode stability for VDF‐based SPEs. Specifically, 2,2,2‐trifluoro‐N,N‐dimethylacetamide (FDMA) is developed as the nonside reaction solvent for poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVHF)‐based SPEs, achieving both high ionic conductivity and significantly improved electrochemical stability. The developed FDMA solvent fosters the formation of a stable solid electrolyte interphase (SEI) through interface reactions with Li metal, effectively mitigating side reactions and dendrite growth on the Li metal electrode. Consequently, the Li||Li symmetric cells and Li||LiFePO4 cells demonstrate excellent cycling performance, even under limited Li (20 µm thick) supply and high‐loading cathodes (>10 mg cm−2, capacity >1 mAh cm−2) conditions. The stable Li||LiCoO2 cells operation with a cutoff voltage of 4.48 V indicates the high‐voltage stability of the developed SPE. This study offers valuable insights into the development of advanced VDF‐based SPEs for enhanced lithium metal battery performance and longevity.

Lithium fluoride (LiF) facilitates robust and fast‐ion‐transport solid electrolyte interphase (SEI) in lithium metal batteries. Fluorinated solvents/salts are ubiquitously employed to introduce LiF into SEI through electrochemical decomposition, but this approach is usually at the expense of their continuous consumption. A direct approach to fluorinate SEI that employs crystal LiF is limited by its poor solubility in the current battery electrolyte formulation. Dissolving crystal LiF in high‐dielectric‐constant solvents, like ethylene carbonate (EC) is nearly neglected. Herein, the feasibility of directly fluorinating SEI by the addition of crystal LiF in aprotic electrolyte with the assistance of EC is verified, and its mechanisms in fluorination of SEI and anti‐acidification of electrolyte are explored. The dissolved LiF is encapsulated by solvent‐/salt‐derived organic skins to promote the fluorinated SEI. Meanwhile, the presence of LiF in electrolyte alters hazardous thermodynamic equilibrium, suppressing the production of acid species to mitigate electrolyte acidification and SEI degradation. Such collective benefits yield a capacity retention ratio of ≈88% after 150 cycles at a high areal capacity (4.5 mAh cm−2) in Li||NCM622 cells. This facile and effective fluorination of SEI contributes to an in‐depth understanding of SEI formation and rational design of well‐performing lithium metal batteries.

The interfacial instability of naturally fragile solid electrolyte interphase (SEI) on lithium leads to dendritic deposition, inferior cycling stability and substantially low coulombic efficiency of metal batteries. The performance of metal anodes can be improved by creating a robust passivation layer/artificial SEI. Along the same line, the modification of Li anode using sodium fluoride (NaF) is proposed to create a protective layer that mitigates dendrite growth and electrolyte decomposition. The proposed modification substantially improves the cycle life with >500 cycles in carbonate solvents at 1 mA cm-2 and areal capacity 0.5 mAh cm-2 in Li||Li symmetrical cells. The post-mortem analyses of cycled lithium reveal a smooth surface with no visible dendrites. In contrast, the unmodified lithium is covered with mossy metal deposits. The efficacy of NaF modification in improving the striping/plating behavior of lithium is also demonstrated using Aurbach's method. The improved performance is attributed to the formation of a stable SEI facilitated by the NaF layer, promoting preferred Li+ mass-transfer and mitigated electrolyte degradation as suggested by the post-mortem characterization and computational studies. The substantial improvement in the long-term performance of lithium cobalt oxide in the presence of NaF-modified lithium further underscores the practical utility of this relatively simple SEI modulation strategy.

The use of the “Holy Grail” lithium metal anode is pivotal to achieve superior energy density. However, the practice of a lithium metal anode faces practical challenges due to the thermodynamic instability of lithium metal and dendrite growth. Herein, an artificial stabilization of lithium metal was carried out via the thermal pyrolysis of the NH4F salt, which generates HF(g) and NH3(g). An exposure of lithium metal to the generated gas induces a spontaneous reaction that forms multiple solid electrolyte interface (SEI) components, such as LiF, Li3N, Li2NH, LiNH2, and LiH, from a single salt. The artificially multilayered protection on lithium metal (AF-Li) sustains stable lithium stripping/plating. It suppresses the Li dendrite under the Li||Li symmetric cell. The half-cell Li||Cu and Li||MCMB systems depicted the attributions of the protective layer. We demonstrate that the desirable protective layer in AF-Li exhibited remarkable capacity retention (CR) results. LiFePO4 (LFP) showed a CR of 90.6% at 0.5 mA cm–2 after 280 cycles, and LiNi0.5Mn0.3Co0.2O2 (NCM523) showed 58.7% at 3 mA cm–2 after 410 cycles. Formulating the multilayered protection, with the simultaneous formation of multiple SEI components in a facile and cost-effective approach from NH4F as a single salt, made the system competent.

Utilizing the "Holy Grail" lithium metal anode is crucial for attaining high energy density1. Nevertheless, employing a lithium metal as anode faces practical challenges due to thermodynamic instability and dendrite growth1-2. An artificial stabilization of lithium metal mainly employed to mitigate the electrolyte decomposition, dead lithium metal formation and dendrite growth3. A facile and cost effective gas treatment of lithium metal was carried out using thermal pyrolysis of NH4F salt to generate HF(g) and NH3(g). An exposure of lithium metal to the generated gas induces a spontaneous reaction that forms multilayer protection with multiple solid electrolyte interface (SEI) components, such as LiF, Li3N, Li2NH, LiNH2, and LiH from a single salt. The formation energy (ΔEf) using DFT-D3 calculations coupled with depth profile XPS and XRD measurements proven the formation of these reaction products. An operando optical microscope (Operando OM) observation on plating/stripping phenomena in symmetric cells under conventional carbonate electrolyte (1 M LiPF6 EC/DEC (1:1 v/v)) operated at 3 and 5 mA cm−2 current density demonstrate the advantage of protection layer on suppression of lithium dendrite. Furthermore, the artificial multilayer protection on lithium sustains stable lithium reversibility and overpotential under varied cell configuration both symmetric cell, Li||Li and half-cells, under Li||Cu and Li||MCMB systems. We demonstrate that the desirable protective layer with LiFePO4 (LFP) showed a capacity retention (CR) of 90.6% at 0.5 mA cm−2 after 280 cycles, and LiNi0.5Mn0.3Co0.2O2 (NCM523) showed 58.7% at 3 mAcm−2 after 410 cycles. Formulating the multi-layered protection, with the simultaneous formation of multiple SEI components in a facile and cost-effective approach from NH4F as a single salt, making the system competent. References Taklu, B. W.; Su, W.-N.; Chiou, J.-C.; Chang, C.-Y.; Nikodimos, Y.; Lakshmanan, K.; Hagos, T. M.; Serbessa, G. G.; Desta, G. B.; Tekaligne, T. M.; Ahmed, S. A.; Yang, S.-C.; Wu, S.-H.; Hwang, B. J., Mechanistic Study on Artificial Stabilization of Lithium Metal Anode via Thermal Pyrolysis of Ammonium Fluoride in Lithium Metal Batteries. ACS Applied Materials & Interfaces 2024, 16 (14), 17422-17431. Moon, S.; Park, H.; Yoon, G.; Lee, M. H.; Park, K.-Y.; Kang, K., Simple and effective gas-phase doping for lithium metal protection in lithium metal batteries. Chemistry of Materials 2017, 29 (21), 9182-9191. Taklu, B. W.; Nikodimos, Y.; Bezabh, H. K.; Lakshmanan, K.; Hagos, T. M.; Nigatu, T. A.; Merso, S. K.; Sung, H.-Y.; Yang, S.-C.; Wu, S.-H., Air-stable iodized-oxychloride argyrodite sulfide and anionic swap on the practical potential window for all-solid-state lithium-metal batteries. Nano Energy 2023, 112, 108471. Figure 1. Schematic illustration for the formation of an artificial multilayered protection via gas treatment and its effect on lithium plating. Figure 1

Abstract The uncontrollable formation of Li dendrites has become the biggest obstacle to the practical application of Li-metal anodes in high-energy rechargeable Li batteries. Herein, a unique LiF interlayer woven by millimeter-level, single-crystal and serrated LiF nanofibers (NFs) was designed to enable dendrite-free and highly efficient Li-metal deposition. This high-conductivity LiF interlayer can increase the Li+ transference number and induce the formation of ‘LiF–NFs-rich’ solid–electrolyte interface (SEI). In the ‘LiF–NFs-rich’ SEI, the ultra-long LiF nanofibers provide a continuously interfacial Li+ transport path. Moreover, the formed Li–LiF interface between Li-metal and SEI film renders low Li nucleation and high Li+ migration energy barriers, leading to uniform Li plating and stripping processes. As a result, steady charge–discharge in a Li//Li symmetrical cell for 1600 h under 4 mAh cm−2 and 400 stable cycles under a high area capacity of 5.65 mAh cm−2 in a high-loading Li//rGO–S cell at 17.9 mA cm−2 could be achieved. The free-standing LiF–NFs interlayer exhibits superior advantages for commercial Li batteries and displays significant potential for expanding the applications in solid Li batteries.

The solid electrolyte interphase (SEI) with lithium fluoride (LiF) is critical to the performance of lithium metal batteries (LMBs) due to its high stability and mechanical properties. However, the low Li ion conductivity of LiF impedes the rapid diffusion of Li ions in the SEI, which leads to localized Li ion oversaturation dendritic deposition and hinders the practical applications of LMBs at high‐current regions (>3 C). To address this issue, a fluorophosphated SEI rich with fast ion‐diffusing inorganic grain boundaries (LiF/Li3P) is introduced. By utilizing a sol electrolyte that contains highly dispersed porous LiF nanoparticles modified with phosphorus‐containing functional groups, a fluorophosphated SEI is constructed and the presence of electrochemically active Li within these fast ion‐diffusing grain boundaries (GBs‐Li) that are non‐nucleated is demonstrated, ensuring the stability of the Li || NCM811 cell for over 1000 cycles at fast‐charging rates of 5 C (11 mA cm−2). Additionally, a practical, long cycling, and intrinsically safe LMB pouch cell with high energy density (400 Wh kg−1) is fabricated. The work reveals how SEI components and structure design can enable fast‐charging LMBs.

Separator modification is a facile approach for ensuring stable cycling of lithium metal batteries. Here, a hybrid polymer coated separator with high Young's modulus and ion conductivity is designed by integrating proton‐doped polyaniline (PANi) nanosheets with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP). Density functional theory (DFT) calculation confirms that the proton‐doped PANi nanosheets interact with TFSI− anions and its 2D confinement effect induces conformational transition of PVDF to the polar β phase. These synergistic effects optimize Li+ transport. Besides, finite element simulations and in situ optical microscopy indicate that the conjugated structure of PANi promotes electron delocalization and homogenizes the potential across lithium anode surface, guiding a uniform Li+ flux and dense lithium deposition. Moreover, the hybrid polymer coating leads to the formation of LiF‐enriched SEI on lithium metal surfaces. As a result, Li||Li symmetric batteries with the hybrid polymer coated separator exhibit stable cycling for over 2000 h at a current density of 10 mA cm⁻2. In additoin, Li||LFP batteries using the modified separator has a stable cycling for over 200 cycles at 3 C, maintaining a capacity of 99.25 mAh g⁻¹ with a high areal loading of 13.5 mg cm⁻2.

Metallic lithium is the most competitive anode material for next‐generation lithium (Li)‐ion batteries. However, one of its major issues is Li dendrite growth and detachment, which not only causes safety issues, but also continuously consumes electrolyte and Li, leading to low coulombic efficiency (CE) and short cycle life for Li metal batteries. Herein, the Li dendrite growth of metallic lithium anode is suppressed by forming a lithium fluoride (LiF)‐enriched solid electrolyte interphase (SEI) through the lithiation of surface‐fluorinated mesocarbon microbeads (MCMB‐F) anodes. The robust LiF‐enriched SEI with high interfacial energy to Li metal effectively promotes planar growth of Li metal on the Li surface and meanwhile prevents its vertical penetration into the LiF‐enriched SEI from forming Li dendrites. At a discharge capacity of 1.2 mAh cm−2, a high CE of >99.2% for Li plating/stripping in FEC‐based electrolyte is achieved within 25 cycles. Coupling the pre‐lithiated MCMB‐F (Li@MCMB‐F) anode with a commercial LiFePO4 cathode at the positive/negative (P/N) capacity ratio of 1:1, the LiFePO4//Li@MCMB‐F cells can be charged/discharged at a high areal capacity of 2.4 mAh cm−2 for 110 times at a negligible capacity decay of 0.01% per cycle.

The practical application of lithium metal batteries (LMBs) is hindered by the issues of flammable electrolytes, lithium dendrites and the resulting thermal runaway. Designing flame‐retardant electrolytes with high performance is a valid strategy to break the current dilemma. In this work, the flame retardant of triphenyl phosphate (TPP) is elaborately encapsulated into the polymer shell of polyacrylonitrile (PAN) and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) to realize the controllable release of TPP during the soaking process. The resulting TPP@PAN/PVDF‐HFP fiber membrane holds high thermal stability, high mechanical strength, and low swelling rate, which is essential for the preparation of flame‐retardant gel polymer electrolyte (GPE). As demonstrated, the TPP@PAN/PVDF‐HFP GPE can deliver high Li+ transference number of 0.877, low interfacial activation energy barrier of 26.6 kJ mol−1 and heterogeneous SEI composition of Li3PO4/Li2CO3/LiF. The corresponding Li||Li cells achieve stable voltage polarization over 1000 h, and the Li||Cu cells display high plating/stripping CE of 99.1%. Meanwhile, the optimized Li||LiFePO4 batteries exhibit high reversible capacity of 158 mAh g−1 after 200 cycles at 0.5 C, and present outstanding fire resistance through the thermal runaway and puncture test. This study will open window for the design of high‐safety electrolytes to promote the practical application of LMBs.

Poly(vinylidene fluoride) (PVDF)‐based solid‐state electrolytes face critical challenges of sluggish ion transport and interfacial instability in lithium metal batteries, exacerbated by crystalline rigidity and residual organic solvents. Herein, a composite solid‐state electrolyte (M3‐xPVH) integrating oxygen‐vacancy‐rich nanowires into a PVDF‐HFP matrix, which establishes the abundant continuous ion transport pathways and the customized ionic microenvironments, is designed. MoO3‐x nanowires (SNWs) with abundant oxygen vacancies not only promote the flexibility of polymer chains and capture Li⁺ to form continuous ion transport pathways for obtaining high ion conductivity of 7.58×10−4 S cm−1, but also selectively bind dimethylformamide to customize the ionic microenvironment for accelerating Li⁺ desolvation and enhancing interfacial stability. Importantly, oxygen‐vacancy‐rich nanowires repel anions via charge repulsion and favor anion decomposition, thus forming an inorganic‐rich SEI. Remarkably, Li metal anode achieves ultra‐long cycling (>8000 h at 0.1 mA cm−2) and demonstrates excellent performance paired with the high‐voltage cathode NCM811. This work pioneers a novel strategy for designing high‐performance solid‐state electrolytes by synergistically engineering material dimensionality and defect chemistry, unlocking new possibilities for next‐generation lithium‐metal batteries.

Solid polymer electrolytes (SPEs) are regarded as promising candidates for developing high energy-density Li metal batteries because of their flexible processability and low cost. However, the application of SPEs is still inherently impeded by the mediocre ionic conductivity and unstable Li/electrolyte interface. In this work, the silver fluoride (AgF) additive is introduced to optimize the ionic conductivity of PEO and induce the formation of stable solid electrolyte interphase (SEI) layer between Li metal and SPEs interface, thereby inhibiting the growth of lithium dendrites. AgF can be complex with anions to promote the dissociation of Li+-TFSI- ion pairs, improving the mobility of Li+ ions, as confirmed by experimental and computational studies. Moreover, the AgF converses to LiF and Li-Ag alloys via in-situ electrochemical reaction with Li anode, which can not only prevent the Li metal from parasitic reactions, but also reduce the concentration gradient of Li+ ions. Hence, the Li|Li symmetric cell containing PEO-3 % AgF electrolyte demonstrates stable cyclability for 1800 h at 0.2 mA cm-2 (60 °C). When paired with a commercial LiFePO4 cathode, the resulting all-solid-state Li-metal battery delivers remarkable cyclic performance of 126.9 mAh g-1 after 400 cycles (0.5 C). This work provides a new approach for the development of composite solid-state electrolyte films and lithium metal anodes in all-solid-state batteries.

Regulating the composition of solid-electrolyte-interphase (SEI) is the key to construct high-energy density lithium metal batteries. Here we report a selective catalysis anionic decomposition strategy to achieve a lithium fluoride (LiF)-rich SEI for stable lithium metal batteries. To accomplish this, the tris(4-aminophenyl) amine-pyromeletic dianhydride covalent organic frameworks (TP-COF) was adopted as an interlayer on lithium metal anode. The strong donor-acceptor unit structure of TP-COF induces local charge separation, resulting in electron depletion and thus boosting its affinity to FSI-. The strong interaction between TP-COF and FSI- lowers the lowest unoccupied molecular orbital (LUMO) energy level of FSI-, accelerating the decomposition of FSI- and generating a stable LiF-rich SEI. This feature facilitates rapid Li+ transfer and suppresses dendritic Li growth. Notably, we demonstrate a 6.5 Ah LiNi0.8Co0.1Mn0.1O2|TP-COF@Li pouch cell with high energy density (473.4 Wh kg-1) and excellent cycling stability (97.4 %, 95 cycles) under lean electrolyte 1.39 g Ah-1, high areal capacity 5.7 mAh cm-2, and high current density 2.7 mA cm-2. Our selective catalysis strategy opens a promising avenue toward the practical applications of high energy-density rechargeable batteries.

Traditionally, dendrite growth is considered to be one of the reasons leading to poor performance of lithium metal. However, it is found that the growth of dendrites does not necessarily reduce the coulombic efficiency of lithium metals. Here, the relationships among morphologies, SEI composition and the coulombic efficiency of lithium metal have been systematically studied. By comparing different kinds of morphologies of lithium metal and the electrolytes, we discovered that SEI composition showed a great influence on the coulombic efficiency of lithium metal owing to the enhanced desolvation of SEI by ionic compounds such as lithium fluoride and lithium nitride. In addition, we further developed new method analyzing EIS of symmetric Li-Li cell to study the properties of SEI.

All-solid-state lithium metal batteries have emerged as a promising solution to overcoming the energy density and safety challenges associated with conventional lithium-ion batteries. Solid polymer electrolytes, particularly those based on poly(vinylidene fluoride) (PVDF) and dimethylformamide (DMF), demonstrate significant potential. However, interfacial side reactions between residual DMF solvents and lithium metal present substantial challenges. In this study, we investigate the in situ formation of solid electrolyte interphase protective layers to mitigate these side reactions. By incorporating F-rich additives, such as fluoroethylene carbonate and lithium difluorophosphate, we successfully establish a dual-layer inorganic SEI structure characterized by an outer LiF layer and an inner Li2O layer. Consequently, our approach extends the cycle life of lithium symmetric batteries to 3000 h. Additionally, the Li||LiFePO4 solid-state battery demonstrates exceptional stability, enduring 400 cycles at a 1C rate with an impressive capacity retention of 84%. This strategic methodology effectively leverages the benefits of residual solvents, ensuring both enhanced battery efficiency and long-term operational stability for PVDF-based all-solid-state lithium metal batteries.

Lithium-sulfur (Li-S) batteries offer high theoretical gravimetric capacities at low cost relative to commercial lithium-ion batteries. However, the solubility of intermediate polysulfides in conventional electrolytes leads to irreversible capacity fade via the polysulfide shuttle effect. Highly concentrated solvate electrolytes reduce polysulfide solubility and improve the reductive stability of the electrolyte against Li metal anodes, but reactivity at the Li/solvate electrolyte interface has not been studied in detail. Here, reactivity between the Li metal anode and a solvate electrolyte (4.2 M LiTFSI in acetonitrile) is investigated as a function of temperature. Though reactivity at the Li/electrolyte interface is minimal at room temperature, we show that reactions between Li and the solvate electrolyte significantly impact the solid electrolyte interphase (SEI) impedance, cyclability, and capacity retention in Li-S cells at elevated temperatures. Addition of a fluoroether cosolvent to the solvate electrolyte results in more fluoride in the SEI which minimizes electrolyte decomposition, reduces SEI impedance, and improves cyclability. A 6 nm AlF3 surface coating is employed at the Li anode to further improve interfacial stability at elevated temperatures. The coating enables moderate cyclability in Li-S cells at elevated temperatures but does not protect against capacity fade over time.

Lithium (Li) metal is considered as a highly promising anode material for next-generation rechargeable batteries due to its ultrahigh theoretical capacity (3860 mAh g-1) and the lowest redox potential (-3.04 V vs standard hydrogen electrode (SHE)). Nevertheless, its practical application is significantly impeded by uncontrolled dendrite formation, unstable solid electrolyte interphase (SEI), and low Coulombic efficiency, which collectively compromise cycling stability and safety. In this work, we present a fluorine and nitrogen codoped porous carbon (FNC) framework as an engineered host for regulating lithium nucleation and interfacial chemistry. Nitrogen doping enhances surface lithiophilicity and reduces nucleation overpotential, while fluorine incorporation facilitates the in situ formation of a LiF-rich SEI layer with superior mechanical robustness and chemical stability. The FNC host promotes planar lithium deposition and mitigates electrolyte decomposition and volume fluctuations. Compared with nitrogen-doped carbon (NC) and bare copper substrates, the FNC@Cu electrode exhibits markedly lower overpotential and dendrite-free horizontal lithium growth, leading to suppressed dead Li accumulation and enhanced reversibility. It achieves a Coulombic efficiency (CE) of 94% over 100 cycles at 2 mA cm-2 and retains 97% over 300 cycles under lean-lithium conditions. Full cell tests with LiFePO4 cathodes reveal a stable cycling performance with 95.1% capacity retention after 250 cycles (N/P ratio = 1.5), highlighting the practical viability of the FNC framework. These results underscore the efficacy of heteroatom codoping and interfacial design for realizing high-performance, lean-lithium metal batteries.

Construction of quasi-solid-state lithium metal batteries (LMBs) by in situ polymerization is considered a key strategy for the next generation of energy storage systems with high specific energy and safety. Poly(1,3-dioxolane) (PDOL)-based electrolytes have attracted wide attention among researchers, benefiting from the low cost and high ionic conductivity. However, interfacial deterioration and uncontrollable growth of lithium dendrites easily appeared in LMBs due to the high reactivity of lithium metal, resulting in the failure of LMBs. In this work, a strategy is developed of using Ga(OTF)3 as the initiator to obtain a PDOL-based gel electrolyte (GaPD). In addition, a hybrid stable solid electrolyte interphase (SEI) of lithium fluoride/Li2O/Li-Ga alloys is observed on the surface of lithium metal. Combined with density functional theory calculations, the hybrid SEI shows high affinity toward Li+, indicating that a uniform deposition of Li+ could be achieved. Therefore, the Li/GaPD/Li cell operates stably for 1600 h at room temperature. In addition, the LiFePO4/GaPD/Li cell retains a capacity retention rate of 90.2% over 200 cycles at 1 C. This work provides a reference for the practical application of in situ polymerization technology in high-performance and safe LMBs.

Lithium (Li) metal anodes are considered one of the most promising anodes for high-performance batteries with ultra-high specific energy density. However, uncontrolled dendrite growth and the unsuitability of common systems for high voltage hinder the development of Li metal batteries with long cycle life. Herein, we report a rationally designed artificial solid electrolyte interphase (SEI) for Li metal anodes, incorporating LiNO3 and lithium difluoro(oxalato)borate (LiDFOB) as additives within a porous poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer skeleton (referred to as PNF). LiNO3 and LiDFOB can release and synergistically react at the electrode surface, leading to the in situ generation of a homogeneously distributed inorganic/organic SEI during the electrochemical process. This SEI improves homogeneity, ionic conductivity and mechanical stability, contributing to the suppression of electrolyte side reactions and Li dendrite growth. Moreover, a uniform CEI with high Li+ conductivity can be constructed on the NCM811 particles, further enhancing the structural integrity of the NCM811 cathode. As a result, the artificial SEI layer on Li metal anodes enables stable cycling of Li-Cu half cells in an ester-based electrolyte and Li-LiNi0.8Mn0.1Co0.1O2 full cell even at a high voltage of 4.5 V. This work provides new insights into designing homogeneous SEIs for Li metal batteries.

Reactive negative electrodes like lithium (Li) suffer serious chemical and electrochemical corrosion by electrolytes during battery storage and operation, resulting in rapidly deteriorated cyclability and short lifespans of batteries. Li corrosion supposedly relates to the features of solid-electrolyte-interphase (SEI). Herein, we quantitatively monitor the Li corrosion and SEI progression (e.g., dissolution, reformation) in typical electrolytes through devised electrochemical tools and cryo-electron microscopy. The continuous Li corrosion is validated to be positively correlated with SEI dissolution. More importantly, an anti-corrosion and interface-stabilizing artificial passivation layer comprising low-solubility polymer and metal fluoride is designed. Prolonged operations of Li symmetric cells and Li | |LiFePO4 cells with reduced Li corrosion by ~74% are achieved (0.66 versus 2.5 μAh h−1). The success can further be extended to ampere-hour-scale pouch cells. This work uncovers the SEI dissolution and its correlation with Li corrosion, enabling the durable operation of Li metal batteries by reducing the Li loss.

The heterogeneity and continuous cracking of the static solid electrolyte interphase (SEI) are one of the most critical barriers that largely limit the cycle life of lithium (Li) metal batteries. Herein, we report a fatigue-free dynamic supramolecular ion-conductive elastomeric interphase (DSIEI) for a highly efficient and dendrite-free lithium metal anode. The soft phase poly(propylene glycol) backbone with loosely Li+-O coordinating interaction was responsible for fast ion transport. Simultaneously, the supramolecular quadruple hydrogen bonds (H-bonds) in the hard phases endow the elastomeric interphase with mechanical enhancement, while gradient H-bonds can dissipate strain energy via the sequential bonding cleavage. Such a design affords superior mechanical robustness, high ionic conductivity, gradient energy dissipation, and high Li+ transference number. Besides, anion enrichment in DSIEI assists in situ construction of a lithium fluoride-rich inner layer upon cycling. The resultant biomimetic bilayer structure enables the symmetric cells with superior cyclability of over 600 h at a high current density of 10 mA cm-2. Moreover, the DSIEI allows stable operation of the full cells under constrained conditions of limited lithium excess, a high-loading LiNi0.8Co0.1Mn0.1O2 cathode, and a low negative/positive capacity (N/P) ratio. This work presents a powerful strategy for deigning artificial SEI and achieving high-energy-density Li metal batteries.

One of the most challenging issues in the practical implementation of high‐energy‐density anode‐free lithium‐metal batteries (AFLMBs) is the sharp capacity attenuation caused by the mechanical degradation of the solid electrolyte interphase (SEI). However, developing an artificial SEI to address this issue remains a challenge due to the trade‐off between ionic conductivity and mechanical robustness for general ionic conducting films. In this study, a tenacious composite artificial SEI with integrated heterostructure of lithium fluoride (LiF) and lithium phosphorus oxynitride (LiPON) is prepared using a co‐sputtering approach to achieve both high ionic conductivity and fracture toughness. The embedded LiF domain has an extremely high Young's modulus and surface energy compared with those of bulk LiPON film, enabling a significant increase in fracture toughness by an order of magnitude. Most importantly, the interface between LiPON and LiF in the integrated structure generates additional fast Li+‐transport pathways, providing the artificial SEI with a conductivity higher than 10−6S cm−1. Consequently, the artificial SEI implementation significantly increases the cycling lifetime of the corresponding AFLMBs by >250%. This study highlights the importance of fracture toughness for the structural integrity of batteries and provides suggestions for designing viable SEI materials for high‐performance AFLMBs.

Lithium metal‐graphene host composite is a promising anode material for high‐energy‐density Li battery owing to its three‐dimensional structure, micro‐level controllable thickness and ultrahigh specific capacity. However, we discover that the hydroxyl/carboxyl functional groups in the reduced graphene oxide (rGO) host are likely to be reduced into lithium carbonate composition in the solid‐electrolyte interphase (SEI), which resulted in severe lithium dendrite growth that deteriorate its electrochemical performances. Here, we develop a magnesium anchoring strategy that selectively bond the Mg ion with the hydroxyl/carboxyl groups in rGO host, generating an electrolyte‐derived lithium fluoride‐dominant SEI instead of oxygen groups‐derived, lithium carbonate‐dominant SEI. By anchoring 0.60% of Mg in the rGO host using a facile compositing‐pyrolysis approach, Li dendrite growth in anode can be significantly suppressed, and the cycling stability of Li metal full cells can be prolonged by 200%. These findings give new insight into the mechanism of SEI formation in Li metal anode, and provide a new design strategy for restraining the reduced reaction of hydroxyl/carboxyl groups in graphene to stabilize the composite anode of lithium metal battery.

The argyrodite-type solid electrolyte (SE) Li6PS5Cl (LPSCl), recognized for its high ionic conductivity and low-temperature processability, offers substantial potential for enabling lithium metal anodes in all-solid-state batteries (ASSBs), promising high energy densities with enhanced safety. However, lithium dendrite penetration and unstable solid electrolyte interphase (SEI) formation hinder stable cycling at high current densities. This work presents a synergistic strategy to address these challenges by combining mild sintering of LPSCl pellets with the deposition of a lithium fluoride (LiF) passivation layer on 50 µm thick lithium metal. Optimized sintering at 80°C improves surface uniformity and densifies the LPSCl pellets, reducing porosity and increasing ionic conductivity. Complementarily, the deposition of a uniform 65 nm LiF layer on lithium via electron beam evaporation, reduces interfacial resistance, and stabilizes SEI formation. This dual modification doubles the critical current density of lithium symmetric cells from 1.1 to 2.2 mA cm-2. In full cells configurations with LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes, remarkable cycling stability is achieved over 2700 cycles (at 1 mA cm-2, 1.5 mAh cm-2), with 75% capacity retained after 1500 cycles. This study provides a practical approach for improving both SE pellet quality and lithium-SE interfacial stability, paving the way for the reliable implementation of thin lithium metal in next-generation ASSBs.

Gel polymer electrolytes (GPEs) show great promise for lithium metal batteries (LMBs), yet achieving a durable Li anode remains challenging due to the instability of the solid electrolyte interphase (SEI) layer. Regulating the Li + solvation structure is a critical approach to construct an effective SEI layer on the Li anode. In this work, a nanofiber membrane with polyethylenimine‐iodine (PEI‐I)/PAN complex core and polyacrylonitrile/polyvinylidene fluoride‐co‐hexafluoropropylene (PAN/PVDF‐HFP) polymer sheath (P‐I/P@P/P) is elaborately designed and prepared via the electrospinning method. The synergistic effect between the three‐dimensional matrix and the slowly released PEI‐I additive not only suppresses the combustion property of traditional GPEs, but also promotes the lithium‐ion desolvation and the generation of inorganic SEI layer on Li anode. As demonstrated, the optimized P‐I/P@P/P GPE delivers a high Li + transference number of 0.88, high ionic conductivity of 2.34 mS cm −1 , and heterogeneous SEI composition of Li 3 N/Li 2 CO 3 /LiF. The corresponding Li||Li cell achieves stable voltage polarization for 1000 h at 5 mA cm −2 , and the Li||Cu cell displays a high Coulombic efficiency of 97.84%. Satisfyingly, the targeted Li||LiFePO 4 battery exhibits an impressive capacity retention ratio of 97% after 3000 cycles. These findings offer a design paradigm for functional GPEs to drive the implementation of high‐energy‐density LMBs in practical scenarios.

High-voltage lithium (Li) metal batteries are promising candidates for next-generation batteries. To enable high-voltage Li metal batteries, an electrolyte having high anodic stability and excellent compatibility with Li metal anodes is essential. Here, we report a gel electrolyte comprising poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and a highly concentrated electrolyte of lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL), which provides both high anodic stability and high Coulombic efficiency of Li metal anodes. This gel electrolyte achieves the deposition of dense Li metal with larger particles. We have found that the FSI−–Li+ association is intensified in the presence of PVDF–HFP, leading to the formation of a low-resistance solid electrolyte interphase (SEI) enriched with LiF and sulfurous compounds derived from FSI−. These results suggest that the SEI with a superior Li+ transport property as well as the liquid-retaining ability of the gel electrolyte facilitate the deposition of dense Li and thus effectively prevents Li loss owing to electrolyte decomposition and dead Li formation, resulting in high Coulombic efficiency of Li metal anodes. We have also demonstrated the stable charge/discharge cycling of a high-voltage Li metal battery with a 5 V-class LiNi0.5Mn1.5O4 cathode using the gel electrolyte.

The solid electrolyte interphase layer that forms on the surface of the negative electrode in Li-ion batteries is crucial for battery cycle/calendar life, rate performance and safety. This 10's of nanometers layer is formed from the decomposition of the liquid electrolyte and its passivation properties are very sensitive to its formation and aging conditions. Despite this critical role, there is still a lack of fundamental understanding of how its structure and composition relate to its stability and passivation performance. Amongst the SEI products that form during the decomposition of liquid electrolyte, lithium fluoride (LiF) is a ubiquitous component and many attribute its presence to be a determining factor of a well passivated interface. Despite the importance, LiF’s nanostructure and distribution within the SEI layer is rarely investigated due to the lack of suitable characterization techniques. X-ray photoelectron spectroscopy (XPS) is the main tool to identify LiF in the SEI layer, but its micron scale lateral resolution precludes any nanometer scale mapping of LiF’s distribution which limits its ability to identify the role LiF plays in the SEI layer. Recently our group has been characterizing the SEI layer of Li-ion negative electrodes with nano-Fourier transform infrared spectroscopy (nano-FTIR).1,2 Nano-FTIR is a scanning probe technique based in a typical atomic force microscope (AFM) in which a broadband laser illuminates a metallic tip/sample interface. The metallic tip acts as an antenna, focusing the infrared light adjacent to the interface and creating a near-field interaction. By operating in constant tapping mode and due to the nonlinearity of the near-field signal on the tip/sample distance, the corresponding backscattered light from the near-field interaction with the sample can be separated from the background with lock-in amplification. The result is IR reflection and absorption spectra with lateral resolution close to the tip radius (ca. 20 nm). This far exceeds the diffraction limited resolution of typical IR microscopy (~10’s µm) creating new opportunities for IR characterization on nanometer length scales. In this talk, we’ll discuss our recent work related to utilizing synchrotron-based nano-FTIR to characterize and image LiF in the SEI layer of Li-ion based negative electrodes. The synchrotron infrared light source allows the detection of photons out to the far-IR (322 cm-1 limit) which enables the detection of the vibrational modes of Li containing inorganic phases such as LiF, Li2O, and LiH. By comparing model thin film LiF nano-FTIR spectra with experimental spectra take from the surfaces of Cu, Si thin film, and a novel metallic glass anode, we can gauge the heterogeneity of the LiF in the SEI layer and then suggest different LiF formation mechanisms. Based on the results, we believe that nano-FTIR with a synchrotron based light source will be a key tool to unravelling the nanoscale structure of the SEI layer due to its nanoscale chemical sensitivity and nondestructive nature. 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. This research used resources of the Advanced Light Source from beamline 2.4, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. References (1) Dopilka, A.; Gu, Y.; Larson, J. M.; Zorba, V.; Kostecki, R. Nano-FTIR Spectroscopy of the Solid Electrolyte Interphase Layer on a Thin-Film Silicon Li-Ion Anode. ACS Appl. Mater. Interfaces 2023, 15 (5), 6755–6767. (2) He, X.; Larson, J. M.; Bechtel, H. A.; Kostecki, R. In Situ Infrared Nanospectroscopy of the Local Processes at the Li/Polymer Electrolyte Interface. Nature Communications 2022, 13 (1), 1398.

The solid electrolyte interphase (SEI) is considered to be the key to the performance of lithium metal batteries (LMBs). The analysis of the SEI and cathode electrolyte interphase (CEI) composition (especially F 1s spectra) by X-ray photoelectron spectroscopy (XPS) has become a consensus among researchers. However, the surface-sensitive XPS characterization is susceptible to LiF artifacts due to several factors, leading to the overexaggerated role of LiF in the analysis of the SEI and CEI. In this paper, we conduct a systematic study on the reasons for the LiF artifacts in the XPS characterization of LMBs. The decomposition of the SEI and CEI components under argon ion sputtering, the reaction between Li2CO3 and LiPF6 in the electrolyte, influence of different sample pretreatments, the selection of the XPS measurement region, and the measurement time on the resulting spectra are investigated. The results indicate that the high content of LiF in the SEI and CEI may be attributed to the LiF artifacts, and the role of LiF in the SEI may be overexaggerated as a consequence. This work sounds an alarm about the potential misuse of argon ion sputtering and the lack of rigorous XPS characterization in SEI studies. This work also helps to set up standardized XPS characterization to provide a more accurate understanding of the role of SEI components.

Electrolyte interfaces with freshly plated lithium metal are crucial for the development of reservoir‐free all‐solid‐state batteries (ASSBs). This study provides an in‐depth characterization of the polyethylene oxide (PEO) lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) interphase with lithium metal resembling reservoir‐free cell conditions. Using an in situ setup in both secondary ion mass spectrometry (SIMS) and X‐ray photoelectron spectroscopy (XPS), the dynamic evolution of the solid electrolyte interphase (SEI) layer is investigated at 60 °C. Lithium metal plating is conducted with an electron flood gun, ensuring controlled lithium deposition and enabling direct identification of intermediate reaction products. Time‐of‐flight‐ (ToF‐) and Orbitrap‐SIMS are employed to provide high‐resolution insights into the formation of inorganic and organic SEI components coming from PEO and LiTFSI degradation after plating. XPS further reveals chemical transformations occurring at the interface. Additionally, coulometric titration time analysis (CTTA) captures the kinetic aspect of PEO: LiTFSI reaction with lithium metal, highlighting the influence of molecular weight and salt concentration on initial reaction speed and long‐term stability. By integrating high‐resolution SIMS analysis with surface‐sensitive XPS and electrochemical methods, a comprehensive approach is offered to better understand the dynamic behavior of the polymer electrolyte | lithium metal interphase under conditions relevant to reservoir‐free battery concepts.

Lithium fluoride (LiF) is a ubiquitous component in the solid electrolyte interphase (SEI) layer in Li-ion batteries. However, its nanoscale structure, morphology, and topology, important factors for understanding LiF and SEI film functionality, including electrode passivity, are often unknown due to limitations in spatial resolution of common characterization techniques. Ultrabroadband near-field synchrotron infrared nanospectroscopy (SINS) enables such detection and mapping of LiF in SEI layers in the far-infrared region down to ca. 322 cm–1 with a nanoscale spatial resolution of ca. 20 nm. The surface sensitivity of SINS and the large infrared absorption cross section of LiF, which can support local surface phonons under certain circumstances, enabled characterization of model LiF samples of varying structure, thickness, surface roughness, and degree of crystallinity, as confirmed by atomic force microscopy, attenuated total reflectance FTIR, SINS, X-ray photoelectron spectroscopy, high-angle annular dark-field, and scanning transmission electron microscopy. Enabled by this approach, LiF within SEI films formed on Cu, Si, and metallic glass Si40Al50Fe10 electrodes was detected and characterized. The nanoscale morphologies and topologies of LiF in these SEI layers were evaluated to gain insights into LiF nucleation, growth, and the resulting nuances in the electrode surface passivity.

The use of poly(1,3-dioxolane) (PDOL) electrolyte for lithium batteries has gained attention due to its high ionic conductivity, low cost, and potential for large-scale applications. However, its compatibility with Li metal needs improvement to build a stable solid electrolyte interface (SEI) toward metallic Li anode for practical lithium batteries. To address this concern, this study utilized a simple InCl3 -driven strategy for polymerizing DOL and building a stable LiF/LiCl/LiIn hybrid SEI, confirmed through X-ray photoelectron spectroscopy (XPS) and cryogenic-transmission electron microscopy (Cryo-TEM). Furthermore, density functional theory (DFT) calculations and finite element simulation (FES) verify that the hybrid SEI exhibits not only excellent electron insulating properties but also fast transport properties of Li+ . Moreover, the interfacial electric field shows an even potential distribution and larger Li+ flux, resulting in uniform dendrite-free Li deposition. The use of the LiF/LiCl/LiIn hybrid SEI in Li/Li symmetric batteries shows steady cycling for 2000 h, without experiencing a short circuit. The hybrid SEI also provided excellent rate performance and outstanding cycling stability in LiFePO4 /Li batteries, with a high specific capacity of 123.5 mAh g-1 at 10 C rate. This study contributes to the design of high-performance solid lithium metal batteries utilizing PDOL electrolytes.

The chemical composition of the solid electrolyte interphase (SEI) at the Li anode/electrolyte interface is critical to the performance of lithium metal batteries. Herein, we designed a functional ionic salt (DG-Cl) with a π-conjugated structure, aiming to enhance the electronic delocalization of the filler to regulate the bond-breaking kinetics and promote the formation of the effective components of the SEI. Density functional theory (DFT) verifies that DG-Cl is capable of releasing Cl− directionally under an electric field and subsequently combining with Li+ to form LiCl. Simultaneously, DG-Cl can anchor TFSI−via cation vacancies. Besides, through its strong electron delocalization capability, DG-Cl could facilitate the cleavage of C–F bonds of TFSI− during the binding process (with charge transfer reaching up to 1.8453e−), thereby promoting the formation of more LiF. XPS and TOF-SIMS confirmed the in situ uniform co-growth of LiF–LiCl on the SEI, which facilitates the Li-ion transport kinetics and regulates the lithium deposition behavior. Impressively, the lithium symmetric batteries deliver ultralong cycling stability over 4000 hours at 0.1 mA cm−2 and over 2200 hours at 0.2 mA cm−2 while the Li/LiFePO4 full cells possess 82.04% capacity retention after 800 cycles at 2C. Besides, this approach to regulating electron transfer at the molecular level guarantees the outstanding cycling performance of pouch cells. After 150 cycles, the battery retention rate was 96.6%. This work proposes a new approach to achieving high-performance and stable lithium metal batteries (LMBs).

The performance of rechargeable batteries is strongly influenced by the solid-electrolyte interphase (SEI), and a comprehensive understanding of SEI formation from the atomic level is crucial for effective battery design. The dynamics of the electrode-electrolyte interface is important and needs to be considered when evaluating the mechanism of the SEI formation. Here, we employed ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculations to examine interfacial behaviors and LiF formation. Through molecular dynamics and structure sampling, we successfully constructed an electrochemical stability diagram correlating the thermodynamic free energy with the potential, which is determined by the work function of electrode surfaces. DFT calculations revealed that LiF formation at the graphite-electrolyte interfaces occurs easily via the intermediate LiHF complex. Interestingly, LiF tends to be solvated by solvents rather than directly deposited onto electrode surfaces (e.g., the Au electrode), a phenomenon we identify as a critical determinant of the porous and uneven nature of the LiF layer observed on graphite electrodes. Our finding offers new mechanistic insights into LiF formation at graphite-electrolyte interfaces.

Liquid electrolytes, consisting of salts, solvents, and additives, must form a stable solid electrolyte interphase (SEI) to ensure the performance and durability of lithium(Li)-ion batteries. However, the electric double layer (EDL) structure near charged surfaces is still unsolved, despite its importance in dictating the species being reduced for SEI formation near a negative electrode. Recently, we have developed an interactive Molecular Dynamics -Density Functional Theory -data statistics (MD-DFT-data) model to investigate the reduction reactions of multicomponent electrolytes within the EDL. We will illustrate the effect of EDL on SEI formation in two essential electrolytes, the carbonate-based electrolyte for Li-ion batteries and the ether-based electrolyte for batteries with Li-metal anodes. Our results reveal that the role of fluoroethylene carbonate (FEC) additive differs drastically in the two electrolytes as an SEI modifier to form the beneficial F-containing SEI component (e.g., LiF). The competition among the cations, anions, and various species in the solvents with a charged surface at different temperatures can all jointly determine the EDL structure and therefore the SEI compositions. [1] While the classical Poisson–Boltzmann EDL model developed for fully solvated ions face new challenges in high-concentration liquid electrolytes (HCE), localized high-concentration liquid electrolytes (LHCE) as well as solid electrolytes (SE), new theoretical developments are required. We will introduce a new DEL model in SE and SEI by solving the DFT-informed Poisson–Fermi–Dirac equation and demonstrate how it can be used for interlayer thickness design. [2] [1] Wu, Q.S, McDowell, M.T., & Qi, Y., Journal of the American Chemical Society 145 (4), 2473-2484 (2023) [2] Swift, M.W., Swift, J.W. & Qi, Y. Modeling the electrical double layer at solid-state electrochemical interfaces. Nat Comput Sci 1, 212–220 (2021)

Two kinds of charge transfer reactions are critical for the performance and life of lithium battery: the desired ion transfer reaction occurring during each charge/discharge cycle, , and the undesired electron transfer reactions leading to the parasitic chemical decomposition of the electrolyte and solid electrolyte interphase (SEI) formation/growth. The heterogeneous multi-component nature of SEI dominates its ionic and electronic transport properties and controls these two charge transfer reactions. Density Functional Theory (DFT)-informed multiscale modeling has been providing valuable insights under the scarcity of quantitative experiments. For example, the LiF/Li2CO3 interface was demonstrated to increase the ionic conductivity of mixed SEI nanocomposite by forming an ionic space charge region near the interface and promoting more Li-ion interstitials in Li2CO3, although LiF itself has low Li-ion conducting carriers and conductivity. To form a LiF-rich SEI layer, the electrolyte compositions need to be designed. Since the SEI formation occurs on the charged surface, the electric double layer (EDL) structure near the charged surfaces needs to be incorporated into the modeling. Here interactive classical molecular dynamics (MD), DFT, and data statistical analysis were combined to illustrate the effect of EDL on SEI formation in two essential electrolytes, the carbonate-based electrolyte for Li-ion batteries and the ether-based electrolyte for batteries with Li-metal anodes. It was found the effectiveness of adding fluoroethylene carbonate (FEC) to form the beneficial F-containing SEI component (e.g., LiF) varies with the electrolyte and temperature, because of the interplay of ion-solvent interactions with the surface charge. These integrated modeling provided quantitative guidance for electrolyte/SEI/Li-metal interface design.

The solid-electrolyte interphase (SEI) that forms on lithium ion battery (LIB) anodes prevents degradation-causing transfer of electrons to the electrolyte. Grain boundaries (GBs) between different SEI components, like LiF, have been suggested to accelerate Li+ transport. However, using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that GBs enhance electron tunneling in thin LiF films by 1-2 orders of magnitude, depending on the bias. Extrapolating to thicker films using the Wentzel-Kramers-Brillouin (WKB) method emphasizes that safer batteries require passivation of GBs in the SEI.

Abstract Modifying the current collector is a promising strategy to enable Li metal anodes with minimal Li consumption. Herein, a scalable electrodeposition method is introduced to construct 3D ZnO/Zn(OH)2 nanosheets on Cu foil (ZOH NSs–Cu foil). Cu(OH)2 nanowires are first formed via anodization, followed by electroconversion of Cu2+ and Zn2+ ions. DFT calculations reveal that the ZOH NSs–Cu foil exhibits high Li adsorption energy, imparting strong lithiophilicity and lowering the Li nucleation overpotential. The 3D nanosheet structure provides a large electrochemically active surface, reducing the effective current density. Furthermore, ZOH NSs–Cu foil exhibits low charge transfer resistance and promotes a Li2O/LiF‐rich solid electrolyte interphase (SEI) layer, further reducing interfacial resistance. SEM analysis and simulations confirm uniform Li deposition on ZOH NSs–Cu foil. In asymmetric cells (1 mAh cm−2 at 1 mA cm−2), ZOH NSs–Cu foil supports stable cycling for over 400 cycles. Furthermore, a full cell coupling a LiFePO4 (LFP) cathode with a Li@ZOH NSs–Cu foil anode retains high capacity with ≈100% Coulombic efficiency over 350 cycles at 1 C, even at an N/P ratio of ≈1.9. This binder‐free, scalable approach offers precise Li deposition control and excellent electrochemical performance, advancing the practical application of Li metal anodes.

A comprehensive understanding of the solid‐electrolyte interphase (SEI) in lithium‐ion batteries is crucial for improving energy efficiency, battery performance, and safety. In this study, a transformer‐based instance segmentation framework, integrating deep convolutional neural networks is introduced with a feature pyramid network (FPN), to quantitatively analyze High‐Resolution Transmission Electron Microscopy (HRTEM) images and explain the complex microstructural features of the SEI. The model is trained on a dataset of simulated HRTEM images generated using Density Functional Theory (DFT)‐optimized grain boundary (GB) structures and calibrated with experimental microscope parameters. The model achieves robust segmentation performance, with training and validation mean intersection over union (mIOU) values of 0.98 and 0.96, respectively. On unseen test data, the model attains mean area match (AM) scores of 91.4% for GBs, 92.3% for Li2CO3, 91.7% for LiF, 88.7% for LiOH, and 88.6% for Li2O. These quantitative results highlight the model's high fidelity and its ability to capture subtle variations in crystallographic orientations and material contrasts. By enabling detailed, statistically grounded segmentation of SEI components, the approach offers valuable insights into ion transport and degradation mechanisms, paving the way for more resilient and efficient energy storage solutions.

Polyethylene oxide (PEO)-based electrolytes face critical challenges of interfacial instability and lithium dendrites in ASSLMBs. Herein, porous BiF3 nanoparticles with channel structures and reactivity were synthesized via a one-step precipitation method and introduced into PEO to construct a novel composite solid-state electrolyte (CPE) with enhanced interfacial stability and high ionic conductivity. Density functional theory (DFT) calculations verify that BiF3 nanoparticle promotes lithium salt dissociation, thereby increasing the mobility of free Li+, while its channel architecture establishes more paths for Li+ transport. Furthermore, BiF3 undergoes an in situ alloying reaction with the lithium anode to form LixBi and LiF, so as to build a gradient composite solid electrolyte interphase (SEI), which demonstrates exceptional interfacial stability and rapid Li+ transport kinetics, effectively inhibiting lithium dendrite propagation. As a result, Li|Li symmetrical cell with PEO-5%BiF3 CPE achieves stable cycling over 6000 h at 0.1 mA cm-2 without short-circuiting, and its Li|LFP full cell exhibits exceptional electrochemical performance across a wide temperature range (45-90°C). Moreover, it also demonstrates excellent cycling stability and capacity retention in Li|NCM811 system. Notably, the excellent electrochemical performance and safety of Li|PEO-5%BiF3 CPE|LFP pouch cell demonstrate good application potential.

No abstract available

The hard carbon (HC) anode materials demonstrate high capacity and excellent rate performance in lithium-ion batteries. However, HC anodes suffer from excessive loss of Li+ ions during the formation of the solid electrolyte interphase (SEI) film, leading to poor cycling stability, which hinders their large-scale applications. Herein, a facile pre-lithiation strategy is proposed to achieve multi-functional precompensation of carbon nanofibers (CNFs) anodes. Both experimental and density functional theory (DFT) calculation results revealed that the strategy compensated for the loss of Li+ ions and reacted with four structures of CNFs during pre-lithiation, including tiny graphite domains, CO-containing functional groups, defects, and micropores. Furthermore, the lithium in pre-lithiated carbon nanofibers (pCNFs) existed in various forms, consisting of LiC24 and LiC18, Li─O─C, quasi-metallic lithium, and Li+ ions. Moreover, the uniformly distributed lithium on the surface of pCNFs induced the formation of denser and more robust LiF/Li2CO3-rich SEI film, which promoted Li+ ions transport. As a result, pCNFs showed more stable cycling performance (369.8 mAh g-1, almost no decay for 1500 cycles). This work provides deeper insight into chemical pre-lithiation and offers a simple and mild strategy for highly stable batteries.

Lithium-ion (Li-ion) batteries are key to modern society, but they pose safety risks because of thermal runaway and ignition. In this study, we explored the use of hybrid aqueous electrolytes to enhance the safety and performance of Li-ion batteries, focusing on the solid-electrolyte interface (SEI) formed on lithium titanate (Li 4 Ti 5 O 12 ; LTO) electrodes. To achieve this, we employed high-resolution transmission electron microscopy (HRTEM) and density functional theory (DFT) calculations to analyze the microstructure and stability of the SEI layer. Further, we prepared LTO and LiMn 2 O 4 (LMO) electrodes, assembled full cells with hybrid aqueous electrolytes, and carried out electrochemical testing. The HRTEM analysis revealed the epitaxial growth of a LiF SEI layer on the LTO electrode, which has a coherent lattice structure that enhances electrochemical stability. The DFT calculations confirmed the energetic favorability of the LiF-LTO interface, indicating strong adhesion and potential for epitaxial growth. The full cell demonstrated excellent discharge performance, showing a notable improvement in coulombic efficiency after the initial cycle and sustained capacity over 100 cycles. Notably, the formation of a dense, crystalline LiF SEI layer on the LTO electrode is crucial for preventing continuous side reactions and maintaining mechanical stability during cycling. The experimental results, supported by the DFT results, highlight the importance of the orientational relationship between the SEI and the electrode in improving battery performance. The integration of experimental techniques and computational simulations has led to the development of an LTO/LMO full cell with enhanced discharge capabilities and stability. The study provides insights into the growth mechanisms of the SEI layer and its impact on battery performance, demonstrating the potential of hybrid aqueous electrolytes in advancing lithium-ion battery technology. The findings affirm the viability of this approach for optimizing next-generation Li-ion batteries, which can promote the development of safer and more reliable energy storage solutions.

In-situ polymerized gel electrolytes (GPE) are the promising next generation of electrolytes for high-energy batteries, integrating the multiple advantages of liquid and all solid state electrolytes. Herein, we synthesized GPE with Poly(ethylene glycol) acrylate (PEGDA) in order to understand how GPE efficiently inhibits lithium dendrite formation and growth. The effects of PEGDA on the lithium ion solvated structure are investigated using density functional theory (DFT) and ab-initio molecular dynamics (AIMD), which are also supported by the Raman result. The GPE electrolytes with the optimal PEGDA concentration exhibit the high transference numbers (tLi+ = 0.72) and ionic conductivity (σ = 3.24 mS cm -1). The lithium symmetric battery using GPE achieves a stable cycle with 1200h in comparison to 320h in liquid electrolytes (LE), possibly owing to the high content of LiF (17.9%) in the Solid Electrolyte Interphase (SEI) film of the GPE cell. The observed facile concentration/electric field gradient also accounts for high super cyclic performance through the finite element method (FEM). Besides, a LiCoO2|GPE|Li cell demonstrates superior capacity retention of 87.09% for 200 cycles, promising guidelines for the design of high specific energy lithium batteries.

No abstract available

Li metal batteries (LMB) are crucial for electrifying transportation and aviation. Engineering electrolytes to form desired solid-electrolyte interphase (SEI) is one of the most promising approaches to enable stable long-lasting LMBs. Among the liquid electrolytes explored, fluoroethylene carbonate (FEC) has seen great success in leading to desirable SEI properties for enabling stable cycling of LMBs. Given the many facets to desirable SEI properties, numerous descriptors and mechanisms have been proposed. In order to build a detailed mechanistic understanding, we analyze varying degrees of fluorination of the same prototype molecule, chosen to be ethylene carbonate (EC) to tease out the interfacial reactivity at the Li metal/electrolyte. Using density functional theory (DFT) calculations, we study the effect of mono-, di-, tri- and tetra- fluorine substitution of EC on its reactivity with Li surface facets in the presence and absence of Li salt. We find that the formation of LiF at early stage of SEI formation, posited as a desirable SEI component, depends on the F abstraction mechanism rather than the number of fluorine substitution. The best illustration of this is cis- and trans-difluoro EC, where F-abstraction is spontaneous with trans case while the cis case needs to overcome a non-zero energy barrier. Using a Pearson correlation map, we find that the extent of initial chemical decomposition quantified by the associated reaction free energy is linearly correlated with the charge transferred from the Li surface and the number of covalent-like bonds formed at the surface. The effect of salt and the surface facet have a much weaker role on determining the decompositions at the immediate electrolyte/electrode interfaces. Putting all of this together, we find that tetra-FEC could act as high-performing SEI modifier as it leads to a more homogeneous, denser LiF containing SEI. Using this methodology, future investigations will explore -CF3 functionalization and other backbone molecules (linear carbonates).

Abstract In this work we aim towards the molecular understanding of the solid electrolyte interphase (SEI) formation at the electrode electrolyte interface (EEI). Herein, we investigated the interaction between the battery‐relevant ionic liquid (IL) 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP‐TFSI), Li and a Co3O4(111) thin film model anode grown on Ir(100) as a model study of the SEI formation in Li‐ion batteries (LIBs). We employed mostly X‐ray photoelectron spectroscopy (XPS) in combination with dispersion‐corrected density functional theory calculations (DFT‐D3). If the surface is pre‐covered by BMP‐TFSI species (model electrolyte), post‐deposition of Li (Li+ ion shuttle) reveals thermodynamically favorable TFSI decomposition products such as LiCN, Li2NSO2CF3, LiF, Li2S, Li2O2, Li2O, but also kinetic products like Li2NCH3C4H9 or LiNCH3C4H9 of BMP. Simultaneously, Li adsorption and/or lithiation of Co3O4(111) to LinCo3O4 takes place due to insertion via step edges or defects; a partial transformation to CoO cannot be excluded. Formation of Co0 could not be observed in the experiment indicating that surface reaction products and inserted/adsorbed Li at the step edges may inhibit or slow down further Li diffusion into the bulk. This study provides detailed insights of the SEI formation at the EEI, which might be crucial for the improvement of future batteries.

Succinonitrile (SN)‐based in situ polymerized solid‐state electrolytes (SIPSSEs) for lithium batteries have attracted considerable attention due to their high ionic conductivity, wide electrochemical stability window (ESW), and potential for large‐scale applications. Despite these advantages, the polar cyano groups in SN molecules lead to significant interfacial problems upon direct contact with metallic lithium (Li), including unstable solid electrolyte interface (SEI) and the growth of Li dendrites, which impede the further application of SIPSSEs to solid‐state lithium metal batteries (SSLMBs). To address these challenges, here a GaF3‐modified SIPSSE (GSNE) is developed by incorporating GaF3 and fluoroethylene carbonate to passivate metallic Li and employing ethoxylated trimethylolpropane triacrylate to anchor SN molecules. As a result of this strategic electrolyte component design, GSNE achieves an ionic conductivity of 1.3 × 10−3 S cm−1 at 30 °C as well as wide ESW up to 4.6 V. Additionally, a LiF/Li3N/LixGa hybrid SEI is formed on the metallic Li surface through an in situ alloying reaction. This hybrid SEI demonstrates superior interfacial stability and fast Li⁺ transport kinetics, as confirmed by various advanced characterization techniques and theoretical calculations. Consequently, LiFePO4/GSNE/Li cells exhibit excellent rate performance and cycling stability. This work provides new insights into the designing of long‐lifespan SIPSSEs‐based SSLMBs.

Abstract Natural graphite, with its lower production cost, higher capacity, and superior electrical conductivity than artificial graphite, currently accounts for approximately 40% of the global lithium‐ion battery anode market. However, the inadequate compatibility of natural graphite with commercial carbonate ester electrolytes leads to irreversible capacity loss, reduce coulombic efficiency, and rapid capacity decline during cycling. Applying an oxygen‐deficient titanium dioxide (TiO2‐x) protective layer to natural graphite anodes has been noted as a successful method for improving their structural integrity and cycling stability; however, the fragile solid–electrolyte interphase (SEI) limits their fast‐charging capability. In this study, nitrogen atoms are strategically incorporated into the TiO2‐x surface structures, creating a lychee‐like primary interphase that regulated the interfacial electrochemistry and facilitated the development of a LiF‐dominated SEI. The robust LiF‐dominated SEI, as examined through ex situ X‐ray photoelectron spectroscopy analysis and kinetic evaluations, successfully mitigates interfacial side reactions and enhances bulk charge transfer. Consequently, the modified natural graphite anodes exhibit improved capacities at higher current densities, delivering a stable reversible capacity of 388.9 mAh g−1 after 200 cycles at a rate of 5 C.

Poly(ethylene oxide) (PEO)-based solid-state polymer electrolyte (SPE) is a promising candidate for the next generation of safer lithium-metal batteries. However, the serious side reaction between PEO and lithium metal and the uneven deposition of lithium ions lead to the growth of lithium dendrites and the rapid decline of battery cycle life. Building a LiF-rich solid electrolyte interface (SEI) layer is considered to be an effective means to solve the above problems. Here, porous organic polymers (POPs) with aromatic structures and non-aromatic structures were synthesized and introduced into the PEO-based SPE as fillers to explore the effect of aromatic structures on LiF-rich SEI formation. The results show that the POPs containing aromatic groups could catalyze the decomposition of LiTFSI to form a stable LiF-rich SEI layer and inhibit the growth of lithium dendrites. The discharge capacity of the LFP/Li battery is 103 mA h g−1 after 500 cycles at 1C (100 °C). It provides a promising way to improve the stability of the solid electrolyte matrix and SEI layer.

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Poly(ethylene oxide) (PEO)‐based solid composite electrolytes suffer from poor conductivity and lithium dendrite growth, especially toward the metallic lithium metal anode. In this study, succinonitrile (SN) is incorporated into a PEO composite electrolyte to fabricate an electrode‐compatible electrolyte with good electrochemical performance. The SN‐doped electrolyte successfully inhibits the lithium dendrite growth and facilitates the SEI layer formation, as determined by the operando nanofocus wide‐angle X‐ray scattering (nWAXS), meanwhile, stably cycled over 500 h in Li/SN‐PEO/Li cell. Apart from the observation of lithium dendrite, the robust SEI layer formation mechanism in the first cycle is investigated in the SN‐enhanced composite electrolyte by nWAXS. The inorganic electrochemical reaction products, LiF and Li3N, are found to initially deposit on the electrolyte side, progressively extending toward the lithium metal anode. This growth process effectively protected the metallic lithium, inhibited electron transfer, and facilitated Li⁺ transport. The study not only demonstrates a high‐performance interfacial‐stable lithium metal battery with composite electrolyte but also introduces a novel strategy for real‐time visualizing dendrite formation and SEI growth directing at the interface area of electrolyte and metallic lithium.

The notorious issues of lithium (Li) dendrite growth and volume change hinder the practical applications of Li metal anodes. LiF as a key component of the solid electrolyte interface (SEI) governs Li+ transport and deposition, yet the formation of LiF consumes the anions (PF6-/TFSI-) in the electrolyte, preventing the stable cycling of Li anodes. Herein, fluorine (F)-doped hollow carbon (FHC) was synthesized and used to construct a composite current collector with FHC as an F-rich buffer layer for modifying the Cu foil. The F content provided by FHC not only mitigates the anion (PF6-/TFSI-) consumption but also enhances the stability of SEI. The hollow structure of FHC with abundant internal space can accommodate deposited Li to relieve the volume change during cycling. Besides, the significantly improved specific surface area of the electrode effectively reduces the local current density to achieve a homogeneous Li deposition. Due to the above cooperation, the symmetrical cell of Cu@FHC-Li||Cu@FHC-Li maintains stable cycling for more than 1800 h with a hysteresis voltage of 19 mV. In addition, full cell coupling with LiFePO4 cathode delivers excellent long-term cycling and rate performance. This work provides an effective route for developing stable Li metal anodes.

Lithium metal batteries have been regarded as typical representative of high-energy storage systems. However, the lithium dendrite growth and fragile solid electrolyte interface (SEI) leads to safety issues and unsatisfactory...

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Silicon monoxide (SiO) anode offers high theoretical capacity but suffers from poor intrinsic conductivity, sluggish interfacial kinetics, and unstable electrode-electrolyte interphase. Heterogeneous coating can partially alleviate these issues, yet interfacial resistance between coating layers still limits fast-charging performance. Herein, we design a dual-coated SiO anode featuring a high-work-function N-doped carbon layer and a low-work-function TiN layer to create a built-in electric field (BEF) at the heterointerface. This BEF promotes directional Li+ transport, substantially lowering interfacial resistance and accelerating ion diffusion kinetics. Consequently, the developed TiN-SiO/C anode achieves exceptional rate performance (758 mA h g-1 at 5 A g-1) and long-term cycling stability (694.5 mA h g-1 after 800 cycles at 2 A g-1). Moreover, the BEF fosters an inorganic-rich SEI (LiF/LixTiN) with reduced Li+ migration energy (37.74 kJ mol-1), improving interfacial mechanical integrity and electrochemical stability. This work highlights work-function-engineered heterointerfaces as a powerful strategy toward high-performance battery materials.

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