锂电池氟化SEI的形成机制

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.

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.

The strategic formulation of a compatible electrolyte plays a pivotal role in extending the longevity of lithium-metal batteries (LMBs). Here, we present findings on a partially fluorinated electrolyte distinguished by a subdued solvation affinity towards Li+ ions and a concentrated anion presence within the primary solvation layer. This distinctive solvation arrangement redirects the focal points of reactions from solvent molecules to anions, facilitating the predominant involvement of anions in the creation of a LiF-enriched solid-electrolyte interphase (SEI). Electrochemical assessments showcase effective Li+ transport kinetics, diminished overpotential polarization for Li nucleation, and prolonged cycling durability in Li||Li cells employing the partially fluorinated electrolyte. When tested in Li||NCM811 cells, the designed electrolyte delivers a capacity retention of 89.30% and exhibits a high average Coulombic efficiency of 99.80% over 100 cycles with a charge-potential cut-off of 4.6 V vs. Li/Li+ under the current density of 0.4 C. Furthermore, even at a current density of 1C, the cells maintain 81.90% capacity retention and a high average Coulombic efficiency of 99.40% after 180 cycles. This work underscores the significance of weak-solvation interaction in partially fluorinated electrolytes and highlights the crucial role of solvent structure in enabling the long-term stability and high-energy density of LMBs.

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.

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.

Silicon oxide–graphite is a promising high-capacity anode material for next-generation lithium-ion batteries (LIBs). However, despite using a small fraction (≤5%) of Si, it suffers from a short cycle life owing to intrinsic swelling and particle pulverization during cycling, making practical application challenging. High-nickel (Ni ≥ 80%) oxide cathodes for high-energy-density LIBs and their operation beyond 4.2 V have been pursued, which requires the anodic stability of the electrolyte. Herein, we report a nonflammable multi-functional fluorinated ester–based liquid electrolyte that stabilizes the interfaces and suppresses the swelling of highly loaded 5 wt% SiO–graphite anode and LiNi0.88Co0.08Mn0.04O2 cathode simultaneously in a 3.5 mAh cm−2 full cell, and improves cycle life and battery safety. Surface characterization results reveal that the interfacial stabilization of both the anode and cathode by a robust and uniform solid electrolyte interphase (SEI) layer, enriched with fluorinated ester-derived inorganics, enables 80% capacity retention of the full cell after 250 cycles, even under aggressive conditions of 4.35 V, 1 C and 45 °C. This new electrolyte formulation presents a new opportunity to advance SiO-based high-energy density LIBs for their long operation and safety.

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.

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 development of solid-state batteries is often hindered by interfacial instability, particularly between the electrolyte and the lithium metal anode. To address this challenge, we fabricate a bilayer solid-state electrolyte composed of Li3InCl6 and Li6PS5Cl, which demonstrates excellent mutual compatibility and high ionic conductivity. Furthermore, a robust, LiF-rich solid electrolyte interphase (SEI) was pre-formed on the lithium metal anode via a pre-treatment strategy in a fluoroethylene carbonate-containing electrolyte. This dual design not only ensures stable interfacial contact but also effectively suppresses interfacial side reactions. When integrated into an all-solid-state lithium metal battery with a LiCoO2 cathode, the assembled cell delivers exceptional cycling stability, retaining over 85% of its initial capacity after 100 cycles at a rate of 0.2C. This work highlights the synergistic role of a compatible bilayer electrolyte and an artificial LiF-rich SEI in enabling high-performance and long-lasting solid-state lithium metal batteries.

Aluminum (Al) foil is regarded as a promising anode for lithium‐ion batteries (LIBs) owing to its high theoretical capacity, low lithiation/delithiation potential, and natural abundance. However, Al‐foil‐based LIBs are currently confined to operate at room temperature, owing to the deterioration of solid electrolyte interphase (SEI) at high/low temperatures, which ultimately renders Al anode unable to endure significant volumetric changes during alloying/de‐alloying under extreme temperatures. Herein, wide temperature (WT) cyclability of Al‐based LIBs are realized for the first time by designing an Al‐phobic SEI. A thin, robust Al‐phobic LiF‐rich SEI layer with high mechanical strength (1.08 GPa) is in situ constructed in all‐fluorinated electrolyte featured with anion‐dominated solvation structure. This Al‐phobic interphase, which bonds weakly with the Al anode, is capable of accommodating volume expansion, mitigating the electrode pulverization, and reducing dead LixAl. Consequently, the Li||Al half‐cells exhibit a high Coulombic efficiency of 99.6% at 25 °C and maintain operational stability over the temperature range of −20–60 °C. The Al||LiNi0.8Mn0.1Co0.1O2 full cells deliver considerable capacities of 165.4 mAh g−1 at −20 °C and 223.2 mAh g−1 at 60 °C (based on cathode). This work represents a critical step of Al‐based LIBs for WT applications.

In recent work1 we introduced our first-principles based coarse-grained kinetic Monte Carlo (kMC) approach to investigate the behavior of the Li anode/electrolyte interface during cycling. Here we will report new insights obtained from numerous tests using the same kMC approach, where we examine the correlations between plating and SEI on the long-term battery performance. We analyze the effects of varying current rates on the rates of specific reactions and consequently on the changes induced in the SEI composition and Coulombic efficiencies during cycling. Our model system is a fluorinated electrolyte characterized in previous studies using theory and experiments. 2 In parallel, we discuss the results of classical molecular dynamics simulations to examine similar phenomena. References (1) Perez-Beltran, S.; Kuai, D.; Balbuena, P. B. SEI Formation and Lithium-Ion Electrodeposition Dynamics in Lithium Metal Batteries via First-Principles Kinetic Monte Carlo Modeling. ACS Energy Letters 2024, 9, 5268-5278. DOI: 10.1021/acsenergylett.4c02019. (2) Tan, S.; Kuai, D.; Yu, Z.; Perez-Beltran, S.; Rahman, M. M.; Xia, K.; Wang, N.; Chen, Y.; Yang, X.-Q.; Xiao, J.; et al. Evolution and Interplay of Lithium Metal Interphase Components Revealed by Experimental and Theoretical Studies. Journal of the American Chemical Society 2024, 146 (17), 11711-11718. DOI: 10.1021/jacs.3c14232.

Lithium metal battery (LMB) is a potential next-generation battery that can provide higher energy density than Li-ion batteries. However, during fast charging, lithium dendrites growth occur at the surface of Li metal anode, resulting in short circuiting, thermal runaway, and fire event. Under high-voltages beyond 4.2 V, lithium dendrites growth and structural degradation of cathode active material will be accelerated, leading to faster performance fade and higher risk of short circuiting. Herein, we demonstrate the significant impacts of fluorinated organic additive that enables ultrafast charging 400 cycles performance of Li//Mn-rich LMB under extreme conditions of 20 C (charged in 3 minutes) and charge cut-off voltage of 4.8 V, without lithium dendrites. Stable performance and high tolerance to extreme conditions are ascribed to the additive-derived formation of uniform and robust solid electrolyte interphase (SEI) layers at Li metal anode and Mn-rich cathode. Studies of the correlation between SEI stability, performance, and battery safety will be discussed in the meeting. Acknowledgements This research was supported by the Ministry of Trade, Industry & Energy (20007034) and National Research Foundation grant funded by the Ministry of Science and ICT (2019R1A2C1084024 & RS-2023- 00217581) of Korea.

Lithium iron phosphate (LFP) batteries are widely expanded in electrical vehicles and energy storage systems (ESS) due to their enhanced safety and low cost. However, their low temperatures performance is a major obstacle for their applications. The sluggish Li+ iondiffusion within electrode at low temperatures suppresses the lithiation or de-lithiation process and ion transport through solid electrolyte interphase (SEI), resulting in poor discharge capacity. To overcome these problems, the electrolytes with improved ionic conductivity and reduced de-solvation energy are being actively investigated. Among them, ester-based solvents have been preferred due to their low viscosity and freezing point. In this study, we applied dual co-solvent systems by combining ester and fluorinated ester that decrease de-solvation energy. Due to the reduction of viscosity, charge transfer and SEI resistance, the LFP cell with dual co-solvent electrolytes exhibited excellent discharge capacity and cycling performance at sub-ambient temperatures. Various analyses such as electrochemical impedance spectroscopy, FT-IR, Raman, NMR, and XPS were used to investigate the electrochemical behavior, solvation structure and chemical composition of the SEI layer. Our study provides new design principles for enhancing the low temperature performance of LFP batteries.

Lithium metal batteries (LMBs) require an electrolyte with high ionic conductivity as well as high thermal and electrochemical stability that can maintain a stable solid electrolyte interphase (SEI) layer on the lithium metal anode surface. The borate anions tetrakis(trifluoromethyl)borate ([B(CF3)4]−), pentafluoroethyltrifluoroborate ([(C2F5)BF3]−), and pentafluoroethyldifluorocyanoborate ([(C2F5)BF2(CN)]−) have shown excellent physicochemical properties and electrochemical stability windows; however, the suitability of these anions as high-voltage LMB electrolytes components that can stabilise the Li anode is yet to be determined. In this work, density functional theory calculations show high reductive stability limits and low anion–cation interaction strengths for Li[B(CF3)4], Li[(C2F5)BF3], and Li[(C2F5)BF2(CN)] that surpass popular sulfonamide salts. Specifically, Li[B(CF3)4] has a calculated oxidative stability limit of 7.12 V vs. Li+/Li0 which is significantly higher than the other borate and sulfonamide salts (≤6.41 V vs. Li+/Li0). Using ab initio molecular dynamics simulations, this study is the first to show that these borate anions can form an advantageous LiF-rich SEI layer on the Li anode at room (298 K) and elevated (358 K) temperatures. The interaction of the borate anions, particularly [B(CF3)4]−, with the Li+ and Li anode, suggests they are suitable inclusions in high-voltage LMB electrolytes that can stabilise the Li anode surface and provide enhanced ionic conductivity.

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.

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.

The lithium transport number determination of fluorinated ether (1,2-(1,1,2,2-tetrafluoroethoxy) ethane, TFEE)-based localized highly concentrated electrolytes (LHCEs) with 1,2-dioxolane (DOL) and dimethoxyethane (DME) as solvents has been explored using molecular dynamics simulations, nuclear magnetic resonance spectroscopy, Bruce-Vincent’s method, and low-frequency electrochemical impedance spectroscopy (EIS). We showcase that the TFEE-DOL LHCE has a as high as 0.65 but, on the other hand, exhibits low Coulombic efficiency (<90%) and poor stability vs Li metal anodes, i.e., in a lithium metal battery (LMB) setting. In contrast, the TFEE-DME LHCE shows high Coulombic efficiency (98.9%) and stability, despite a much lower (0.25). A significant migration resistance through the porous solid electrolyte interphase (SEI) for the former is the likely explanation, as revealed by EIS and assisted by scanning electron microscopy and X-ray photoelectron spectroscopy experiments. We thus find the interfacial properties at the Li metal anode to be more crucial than the ionic transport through the bulk of the electrolyte for LMB performance. We therefore propose that the focus should be put on the full (operando) impedance spectra of Li metal anodes in contact with electrolytes, since it enables the characterization of the interphase layer(s), rather than solely determining the (bulk) of the electrolytes.

Modification of lithium metal (LM) with a stable solid electrolyte interface leading to the possibilities of ambient assembly of a lithium metal battery (LMB) is of tremendous interest in the development of low-cost, safe batteries. Herein, LM surface modifications via direct as well as polymer electrolyte surface modification approaches consisting of hot pressing in air are demonstrated for the development of a stable solid electrolyte interface (SEI). The SEI at the polymer-lithium metal interface has in situ formed LiF and defective graphene, making the solid-state batteries cyclable even at high current densities (10 mA cm-2). This modification brings enhanced cyclability (>1000 cycles (1 h per cycle) for Li||Li cells at 6 mA cm-2; and >200 cycles for Li||NMC at 1 C) with a high Li+ transference number (0.62 ± 0.08) to the electrolyte operating at room temperature. Here, an optimized thin film of fluorinated graphite polymer was used for the modification, bringing air stability to the lithium anode along with fire resistance after the modification, addressing the key safety concerns with the direct use of metallic lithium. This method opens the possibilities of high performance LMBs with their assembly devoid of high inert conditions, thereby bringing down the cost of battery technology.

Lithium (Li) metal offers exceptional energy density as an anode material, but its uncontrolled electrodeposition and unstable interphase formation during cycling remain critical barriers to practical implementation. In addition, its extreme reactivity toward ambient moisture necessitates highly energy‐intensive dry room facilities, substantially increasing the cost and energy footprint of battery manufacturing. Here, we introduce a molecularly engineered artificial solid electrolyte interphase (SEI) that combines moisture tolerance and lithiophilicity to enable ambient‐processable Li metal anodes. A polyethyleneimine (PEI) partially substituted with fluoroalkyl moieties is designed as the protective layer, in which the nitrogen‐rich backbone guides uniform Li⁺ flux, while the fluorinated side chains impart hydrophobicity to block ambient moisture and simultaneously induce the in situ formation of LiF‐rich SEI species. A comprehensive set of analyses during humidity exposure qualitatively elucidates the protective function of the artificial SEI and quantitatively tracks corrosion products in ambient environments. Various electrochemical and depth‐resolved post‐mortem analyses demonstrate that the fluorinated PEI‐based artificial SEI effectively protects Li metal under ambient conditions while enabling fast interfacial kinetics and stable long‐term cycling. This work provides a viable pathway toward energy‐efficient Li metal battery manufacturing and offers new molecular‐level insights into the design of protective artificial interphases.

Polymer electrolytes‐based batteries are suffering great degradation due to the irreversible lithium deposition and increased impedance at sub‐zero temperature, which is related with Li+ conductivity of bulk electrolyte (σBulk) and ionic conductivity of solid electrolyte interface (σSEI). Thereby, an artificial SEI layer has coated on Li anode through in situ polymerizing polyester with fluorinated porphyrin, which could accelerate Li+ desolvation and conductivity of SEI. Then, the dual‐salt eutectic polymer electrolyte tolerate is employed to accelerate Li+ transfer through optimize their solvation structure. The matching factor is calculated to evaluate the synergistic effect of σBulk and σSEI on low‐temperature Li+ mobility. Thus, homogenize the Li+ flux during Li‐plating is achieved by marching the Li+ diffusion rate (δ = 1.92), which significantly mitigate overpotential aggravation and suppress dendrite nucleation. Overall, such marching factor could provide a theoretical parameter for evaluating the low‐temperature tolerability of solid‐state lithium batteries (SSBs), which would useful for improving batteries’ durability, safety and flexibility.

No abstract available

The introduction of 1,3,5-trifluorobenzene (F3B) as an additive for lithium-ion battery electrolytes can produce a LiF-rich solid electrolyte interface (SEI). Meanwhile, F3B has superior thermal stability compared with traditional fluorinated additives and is less likely to produce hydrogen fluoride to damage the cathode.

In this work, dimethoxyethane (DME) and 1,3-dioxolane (DOL) are studied as the co-solvent of an advanced electrolyte for fast charging of Li-ion batteries by using lithium bis(fluorosulfonyl)imide (LiFSI) as a salt and fluorinated ethylene carbonate (FEC) as an additive. It is shown that even when used with LiFSI and FEC, neither DME nor DOL constitute a suitable electrolyte for Li-ion batteries, either because of their inability to form a robust solid-electrolyte interphase (SEI) with graphite (Gr) anodes or because of their oxidative instability against oxygen released from the delithiated LiNi0.80Co0.10Mn0.10O2 (NCM811) and LiNi0.80Co0.15Al0.05O2 (NCA), respectively. However, using 30% FEC as the co-solvent can make 1:1 DME/DOL mixture compatible with high-voltage Li-ion batteries and combining it with conventional ethylene carbonate (EC) and ethyl methyl carbonate (EMC) significantly enhances the fast charging capability of Li-ion batteries. As a result, an advanced electrolyte composed of 1.2 m (molality) LiFSI 1:1:1:2 DME/DOL/EC/EMC + 10% FEC (all by wt.) offers much improved fast-charging performances in terms of capacity and capacity retention for a 200 mAh Gr/NCA pouch cell, compared with a 1.2 m LiFSI 3:7 EC/EMC baseline electrolyte. AC impedance analysis reveals that the significant improvement is attributed to a much reduced charge transfer resistance, while the advanced electrolyte has little effect on the bulk and SEI resistances.

The severe capacity fade of lithium-ion cells with silicon-dominant anodes has hindered their widescale commercialization. In this work, we link cell capacity fade to the heterogeneous physicochemical evolution of silicon anodes during battery cycling. Through a multilength scale characterization approach, we demonstrate that silicon particles near the anode surface react differently from those near the copper current collector. In particular, near the anode surface we find an amorphized wispy silicon encased in a highly fluorinated matrix of electrolyte-reduction products. In contrast, closer to the current collector, the silicon retains more of its initial morphology and structure, suggesting the presence of isolated particles. The results show that the accessibility of active silicon to lithium ions varies across the anode matrix. Material and cell designs, which minimize electrode expansion resulting from the in-filling of pores with the solid electrolyte interphase (SEI), are needed to enhance anode homogeneity during the electrochemical cycling.

In the quest for environmentally friendly and safe batteries, moving from fluorinated electrolytes that are toxic and release corrosive compounds, such as HF, is a necessary step. Here, the effects of electrolyte fluorination are investigated for full cells combining silicon–graphite composite electrodes with LiNi1/3Mn1/3Co1/3O2 (NMC111) cathodes, a viable cell chemistry for a range of potential battery applications, by means of electrochemical testing and postmortem surface analysis. A fluorine-free electrolyte based on lithium bis(oxalato)borate (LiBOB) and vinylene carbonate (VC) is able to provide higher discharge capacity (147 mAh gNMC–1) and longer cycle life at C/10 (84.4% capacity retention after 200 cycles) than a cell with a highly fluorinated electrolyte containing LiPF6, fluoroethylene carbonate (FEC) and VC. The cell with the fluorine-free electrolyte is able to form a stable solid electrolyte interphase (SEI) layer, has low overpotential, and shows a slow increase in cell resistance that leads to improved electrochemical performance. Although the power capability is limiting the performance of the fluorine-free electrolyte due to higher interfacial resistance, it is still able to provide long cycle life at C/2 and outperforms the highly fluorinated electrolyte at 40 °C. X-ray photoelectron spectroscopy (XPS) results showed a F-rich SEI with the highly fluorinated electrolyte, while the fluorine-free electrolyte formed an O-rich SEI. Although their composition is different, the electrochemical results show that both the highly fluorinated and fluorine-free electrolytes are able to stabilize the silicon-based anode and support stable cycling in full cells. While these results demonstrate the possibility to use a nonfluorinated electrolyte in high-energy-density full cells, they also address new challenges toward environmentally friendly and nontoxic electrolytes.

Developing a safe and long-lasting lithium (Li) metal battery is crucial for high-energy applications. However, its poor cycling stability due to Li dendrite formation and excessive Li pulverization is the major hurdle for its practical applications. Here, we present a silica (SiO2) nanoparticle-dispersed colloidal electrolyte (NDCE) and its design principle for suppressing Li dendrite formation. SiO2 nanoclusters in the NDCE play roles in enhancing the Li+ transference number and increasing the Li+ diffusivity in the vicinity of the Li-plating substrate. The NDCE enables less-dendritic Li plating by manipulating the nucleation-growth mode and extending Sand's time. Moreover, SiO2 can interplay with the electrolyte components at the Li-metal surface, enriching fluorinated compounds in the solid electrolyte interface layer. The initial control of the Li plating morphology and SEI structure by the NDCE leads to a more uniform and denser Li deposition upon subsequent cycling, resulting in threefold enhancement of the cycle life. The efficacy of the NDCEs has been further demonstrated by the practical battery design, featuring a commercial-level cathode and thin Li-metal (40 μm) anode.

Silicon is the preferred choice for lithium-ion battery anodes due to its high theoretical capacity and low lithiation potential. However, achieving high areal capacity with silicon anodes in solid-state batteries (SSBs) is challenging because of poor electronic and ionic conductivity, as well as chemo-mechanical instability at the silicon|solid electrolyte (Si|SE) interfaces. Here, we propose fabricating and testing composite anodes made of nanosized Si powder embedded in partially fluorinated graphene (Si-FG) and Li6PS5Cl (LPSCl) sulfide SE. X-ray photoelectron spectroscopy revealed that the in situ formation of LiF-rich SEI can protect against SE decomposition at the interface in the Si-FG-LPSCl composite anode. FIB-SEM and EIS analyses also indicate a stable structure and low interfacial resistance after one cycle for a composite anode containing FG. The incorporation of partially FG enhances both electronic (through heterojunction formation with Si) and ionic conductivities, buffers significant volume changes, and ensures chemo-mechanical stability in the composite anode. The Si-FG-LPSCl composite anode in SSBs delivered high discharge/charge capacities of 3499/2994 mAh g–1 at a C-rate of C/20 and an ICE of 85.6% in a half cell. This work provides valuable insights for advancing high-capacity Si composite anodes to meet future energy needs.

The application of lithium–sulfur (Li‐S) batteries is severely limited by the shuttle effect and sluggish sulfur conversion at the cathode, as well as the instability of the Li anode interface. Catalyst design and the construction of a stable solid electrolyte interphase (SEI) are key strategies to overcome these challenges. Herein, a bifunctional catalyst is reported prepared by incorporating atomically dispersed chromium (Cr) sites into lithiated zeolites. This approach not only accelerates the conversion of sulfur species and effectively suppresses the shuttle effect, but also leverages residual sodium (Na) ions from the Na‐exchanged zeolite to form a robust fluorinated Li/Na hybrid SEI on the Li anode, thereby enhancing specific capacity and cycling stability. As a result, the Li─S battery employing this catalyst delivers an initial capacity of 1130.3 mAh g −1 at 0.5C and maintains 957.4 mAh g −1 after 100 cycles, and demonstrates impressive rate performance with a capacity of 701.3 mAh g −1 at 5C. Moreover, the pouch cell achieves an energy density of 366 Wh kg −1 , underscoring its exceptional potential for practical applications.

Silicon (Si)-based materials have been considered as one of the most promising anodes for the development of high-energy-density lithium-ion batteries (LIBs). However, poor interfacial stability and structural degradation are critical challenges for the successful application of Si-based anodes in LIBs. Herein, the use of a novel fluorinated carbonate (trifluoropropylene carbonate, TFPC) with high reduction potential and rapid film-forming ability as an electrolyte cosolvent is reported, which overcomes the deterioration of the electrode structure that hinders the battery quality. X-ray photoelectron spectroscopy combined with Fourier transform infrared spectroscopy technology investigated the composition and distribution of the solid electrolyte interface (SEI) layer formed on the Si/C anode. Notably, a stable SEI with an organic and inorganic bilayer structure was formed in this electrolyte design, and excellent mechanical properties and ionic conductivity were achieved. Moreover, the Li intercalation mechanism is elucidated by in situ Raman characterization. Benefited from this unique SEI, the Si/C-based batteries exhibit compelling cycling and rate performance. This work provides an in-depth understanding of the Li intercalation mechanism of the Si/C electrode, as well as a novel electrolyte, for high-performance LIBs.

No abstract available

No abstract available

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.

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.

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.

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.

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.

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.

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.

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.

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.

Silicon-carbon (Si/C) anodes have emerged as promising alternatives to conventional graphite anodes for high-energy lithium-ion batteries (LIBs), owing to their higher specific capacity than graphite and enhanced cycling stability over pure silicon. However, the unstable solid electrolyte interphase (SEI) due to large volume changes during cycling is still a key bottleneck limiting their electrochemical performance. To address this critical limitation, the present study introduces wheat gluten (WG), a biomass-derived material from wheat, as a low-cost and sustainable binder for Si/C anodes. WG, rich in organic functional groups such as -COOH and -NH2, exhibits unique coordination capabilities with Li+. When employed as a binder, WG effectively induces the formation of Li+ solvated structures that weaken solvent coordination at the electrode surface/interface. This behavior facilitates the preferential growth of a LiF-rich SEI, thereby enhancing interfacial stability and mitigating capacity fade. Consequently, Si/C anodes employing WG binder (Si/C-WG) demonstrate remarkable cycling performance, delivering 95.9% capacity retention after 300 cycles at 0.5 A g-1, far surpassing that of conventional poly(vinylidene difluoride) (PVDF) binder, which retains only 59.5%. This study presents a novel strategy for designing functional binders optimized for Si/C anodes, offering critical insights to advance the development of high-performance anode materials in LIBs.

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.

The sulfide-type solid electrolyte (SE) is a promising candidate for realizing all-solid-state batteries (ASSBs) due to its good mechanical properties and high ionic conductivity. However, challenges such as limited electrochemical stability, inadequate solid-solid contact with the electrode, and reactivity with lithium often lead to dendrite growth and electrolyte reduction. A simple, solvent-free method was developed to form a robust artificial interphase between lithium metal and the solid electrolyte to address these issues. This was achieved by incorporating a composite electrolyte composed of Li6PS5Cl, polyethylene glycol (PEG), and lithium bis(fluorosulfonyl)imide (LiFSI), leading to the in-situ formation of a LiF-rich interfacial layer. This interphase effectively suppresses electrolyte reduction and enhances lithium-ion diffusion. Notably, the PEG additive improves the mechanical strength of the electrolyte by enhancing adhesion between sulfide particles. It also increases the flexibility of the Li6PS5Cl solid electrolyte, improving physical contact with the lithium anode and acting as a protective barrier to prevent direct SE-Li interaction, thus reducing electrolyte decomposition. As a result, Li/Li symmetric cells exhibited excellent cycling stability, maintaining performance for over 3000 hours at a current density of 0.1 mA cm-2, while the composite solid electrolyte achieved a critical current density of 4.75 mA cm-2. This study underscores the synergistic benefits of combining an artificial solid electrolyte interphase (SEI) with composite solid electrolytes, paving the way for high-performance all-solid-state lithium metal batteries (ASSLBs).

No abstract available

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Volume expansion of the Si-C anode during the charging/discharging process causes continuous fracture/formation of the solid electrolyte interface (SEI), which leads to rapid capacity fading. Here, we designed a MgF2-modified separator (MF-PP) to construct a fluorine-rich SEI layer by generating more LiF. The robust SEI layer formed can alleviate the volume stress and prevent crack growth in Si-C electrodes. After 450 cycles, the Si-C||MF-PP half cell retained a reversible capacity of 543.2 mAh g-1, while the LFP||MF-PP||Si-C full cell maintained a reversible capacity of 103.4 mAh g-1 with high Coulombic efficiency after 100 cycles. This facile and low-cost separator modification strategy provides an easily scalable approach to develop stable Si-based anodes for next-generation high-energy-density systems.

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.

Multi‐scale simulation is an important basis for constructing digital batteries to improve battery design and application. LiF‐rich solid electrolyte interphase (SEI) is experimentally proven to be crucial for the electrochemical performance of lithium metal batteries. However, the LiF‐rich SEI is sensitive to various electrolyte formulas and the fundamental mechanism is still unclear. Herein, the structure and formation mechanism of LiF‐rich SEI in different electrolyte formulas have been reviewed. On this basis, it further discussed the possible filming mechanism of LiF‐rich SEI determined by the initial adsorption of the electrolyte‐derived species on the lithium metal anode (LMA). It proposed that individual LiF species follow the Volmer–Weber mode of film growth due to its poor wettability on LMA. Whereas, the synergistic adsorption of additive‐derived species with LiF promotes the Frank‐Vander Merwe mode of film growth, resulting in uniform LiF deposition on the LMA surface. This perspective provides new insight into the correlation between high LiF content, wettability of LiF, and highperformance of uniform LiF‐rich SEI. It disclosed the importance of additive assistant synergistic adsorption on the uniform growth of LiF‐rich SEI, contributing to the reasonable design of electrolyte formulas and high‐performance LMA, and enlightening the way for multi‐scale simulation of SEI.

Poly(acrylic acid) copolymers containing nitrile and hydroxyl groups are synthesized through free radical polymerization and used as binders for silicon anodes. The characteristics of these poly(acrylic acid) copolymers are that they can be further in situ cross-linked through the Ritter reaction. The cross-linked binder (c-PACH-2) can simultaneously address the challenges of mechanical degradation, sluggish kinetics, and interfacial instability in the Si anode. The cross-linked architecture can mitigate volume expansion and prevent particle pulverization via elastic stress dissipation. Concurrently, ionic pathways and hopping sites accelerate Li+ diffusion, enabling superior rate capability. Density functional theory calculations and X-ray photoelectron spectroscopy analyses reveal c-PACH-2's preferential reduction to form a robust LiF-rich SEI film, reducing parasitic reactions. The c-PACH-2 binder delivers exceptional electrochemical performance, and the c-PACH-2@Si||Li cell has a capacity retention of 67.2% after 100 cycles at 0.2 C. This covalent network design integrates mechanical resilience and ion transport in the binders for the Si anode, offering an effective strategy for developing high-performance batteries.

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.

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH4 N2 S) is introduced as a new catalyzing agent for LiNO3 reduction to form robust inorganic-rich SEI layers containing abundant Li3 N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO3 - and TFSI- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li3 N, LiF, and Li2 S/Li2 S2 . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO4  full-cells.

Lithium (Li) metal anodes face critical challenges of dendritic growth and poor cycling stability, largely due to the inherent trade‐off within the solid electrolyte interphase (SEI) between high ionic conductivity and robust mechanical/electron‐insulating properties. To resolve this dilemma, an anode‐wide, hybrid SEI that synergistically combines a Li3N‐rich phase for rapid ion transport with a LiF‐rich phase for mechanical stability and electronic insulation is designed and constructed. This unique interface is achieved via a novel two‐step process: a metallurgical treatment to pre‐seed a 3D lithiophilic scaffold with a Li3N precursor, followed by the in situ electrochemical formation of LiF during cycling. This architecture, featuring well‐matched ion/electron transport properties, facilitates the uniform Li plating/stripping kinetics and effectively suppresses dendrite growth. Consequently, the engineered anode demonstrates unprecedented stability, cycling for over 8000 h in a symmetric cell. In a full‐cell configuration, it maintains ≈93.1% of its capacity after 1000 cycles at a high rate of 10 C. Furthermore, an assembled pouch cell delivers a specific discharge capacity of ≈100 mAh g−1 after 300 cycles. This work presents a powerful strategy of combining metallurgical pre‐seeding with electrochemical formation to engineer multi‐functional, bulk‐integrated interfaces, paving the way for high‐rate, long‐cycling lithium metal batteries.

No abstract available

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 silicon-based materials are the desirable anodes for next-generation lithium-ion batteries; however, the large volume change of Si during charging/discharging process causes electrode fracture and unstable solid-electrolyte interphase (SEI) layer, which severely impair its stability and Coulombic efficiency. Herein, the bundle of silicon nanoparticles are encapsulated in the robust micrometer-sized MXene frameworks, in which the MXene nanosheets are pre-crumpled by the capillary compression force to effectively buffer the stress induced by the volume change, and the abundant covalent bonds (Ti-O-Ti) between adjacent nanosheets formed through a facile thermal self-crosslinking reaction further guarantee the robustness of the MXene architecture. Both factors stabilize the electrode structure. Moreover, the abundant fluorine terminations on MXene nanosheets contribute to an in situ formation of a highly compact, durable and mechanically robust LiF-rich solid-electrolyte interphase layer outside the frameworks upon cycling, which not only shuts down the parasitic reaction between Si and organic electrolyte but also enhances the structural stability of MXene frameworks. Benefiting from these merits, the as-prepared anodes deliver a high specific capacity of 1797 mAh g-1 at 0.2 A g-1, and a high capacity retention of 86.7% after 500 cycles at 2 A g-1 with an average Coulombic efficiency of 99.6%. Significantly, this work paves the way for other high-capacity electrode materials with a strong volume effect.

Regulating the electrolyte decomposition to evolve a LiF-rich solid-electrolyte interphase (SEI) can reduce the energy barrier of the interfacial Li-ion transport toward fast-charging lithium-ion batteries. Due to the sluggish decomposition kinetics, LiPF6, as a widely used Li salt in commercial cells, is unable to build a LiF-rich SEI. Therefore, expensive fluorinated electrolyte additives are needed. Herein, to eliminate the use of extra fluorinated species, based on the subtle electrochemical decomposition of LiPF6 occurring ∼2.28 V vs. Li+/Li at 80°C, we developed a temperature-potential coupled formation (TPCF) protocol, which incorporates a constant-voltage step (2.28 V) at 80°C to stimulate LiPF6 decomposition deeply, thereby generating a high-quality SEI uniformly covering the graphite particle surfaces. This TPCF-derived SEI is thin and dense, full of LiF grain boundaries, which could reduce the energy barriers of Li+ desolvation and interfacial Li+ diffusion. Simultaneously, this SEI exhibits a higher work function, effectively suppressing electron leakage to reduce the degeneration of the electrolyte and interphase. Consequently, after a simple TPCF process, the assembled graphite||LiFePO4 full cell achieves stable cycling at a 6C rate, retaining 80% of its capacity after 3304 cycles and 70.5% after 8940 cycles, outperforming the counterparts.

No abstract available

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.

Sustained release refers to a formulation designed to gradually and consistently release active ingredients over an extended period. In liquid electrolytes, sudden release of active components leads to thick and porous solid‐electrolyte interphases (SEIs), which increase polarization voltage and degrade cycling stability. Herein, a sustained‐release polyvinylidene difluoride (SR‐PVDF) solid polymer electrolyte is presented, using dimethylformamide (DMF) and high‐boiling‐point fluoroethylene carbonate (FEC) as co‐solvents during the electrolyte preparation process. The slow evaporation of salt‐soluble FEC induces a dense bulk configuration with a β‐phase‐rich structure and promotes the formation of a sub‐micron, salt‐rich surface with sustained release characteristics. This salt‐rich surface, with a confined FEC solvate structure primarily consisting of contact ion pairs and aggregates, controls the release of TFSI− anions and FEC, producing a highly oriented LiF‐Li2O bi‐layer SEI during a prolonged cycling life. The SR‐PVDF shows a high ambient ionic conductivity of 0.59 mS cm−1 and a high critical current density of 10 mA cm−2 in Li||Li symmetric cells. Tested in Li||LiFePO4 full cells, it achieves a high‐rate capability of 97.9 mAh g−1 at 20C and long‐term cyclability with over 12000 cycles at 10C. The stable cycling of the LiNi0.8Mn0.1Co0.1O2 cathode further demonstrates its compatibility in high‐energy solid‐state batteries.

Lithium-sulfur (Li-S) batteries are considered to be one of the most promising energy storage batteries due to their high energy density. Sulfurized polyacrylonitrile (SPAN) receives increasing interest as a competitive cathode material for sulfur can be trapped in pyrolyzed polymer backbones via the formation of chemical bonds. However, Li-S batteries with SPAN suffer from dendrite growth and electrically isolated Li loss during cycling, which presents a significant safety hazard and short lifespan. The construction of a robust solid electrolyte interface (SEI) can effectively inhibit the formation of Li dendrites. In this study, we construct a Li3PO4/LiF-rich SEI by introducing lithium fluorophosphate (LiDFP) additive and in situ polymerization of electrolyte simultaneously. The gel polymer electrolyte is in situ generated with encapsulation of the organic liquid component in a poly(vinylidene carbonate) skeleton, resulting in an oxidative stability up to 4.8 V (vs Li/Li+). The in situ/ex situ microscopic observation reveals a dense Li deposition behavior. A steady cycling exceeding 1500 h with a low voltage hysteresis is achieved for symmetric Li||Li batteries at a current density of 0.1 mA cm-2. Furthermore, a decent capacity retention and approaching 100% Coulombic efficiency are present for the Li-S battery with a SPAN cathode over long-termcycling. This study offers a valuable reference for the construction of advanced solid-state Li-S batteries.

The practical application of lithium metal anodes is hindered by uncontrolled dendrite growth, which compromises battery safety and cyclability. Conventional strategies focus on modifying electrolyte compositions or interfacial coatings but fail to fundamentally regulate lithium deposition at the nanoscale. Here, Electrostatic catalysis‐driven asymmetric solid‐electrolyte interphase (SEI) formation, achieved via a pulsed positive voltage pretreatment, is introduced. This process induces site‐selective decomposition of electrolyte components, generating LiF‐rich SEI on flat surfaces and Li2O‐rich SEI in surface pits, thereby directing lithium plating into pits and suppressing dendrite formation. Experimental and computational studies reveal that electrostatic enrichment of PF6− anions at positively charged interfaces accelerates their decomposition, while pit regions, depleted of anions, promote solvent‐derived Li2O formation. Lithium metal anodes with this asymmetric SEI exhibit stable cycling for over 350 h at 1 mA cm−2, outperforming conventional SEI. Full cells paired with LiCoO2 (LCO) cathodes achieve 96.1% capacity retention after 400 cycles at 1 C, compared to 56.8% for conventional SEI. These findings introduce electrostatic catalysis as a powerful interfacial engineering strategy, enabling high‐performance lithium metal batteries through precise SEI control.

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.

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.

Lithium fluoride (LiF)-rich solid electrolyte interphases (SEIs) are promising for improving the safety and durability of lithium-based batteries due to their mechanical strength, thermal stability, and chemical inertness. However, a fundamental understanding of the behaviors of LiF under coupled thermal and mechanical stress conditions, commonly encountered during battery cycling and abuse, remains unclear. In this study, we investigate the thermal-mechanical responses of LiF at the nanoscale using molecular dynamics simulations and phonon analysis. LiF exhibits excellent mechanical stability under uniaxial and torsional loading with its fracture threshold surpassing the typical stress levels encountered in operating batteries. In contrast, the thermal conductivity (k) of LiF is highly sensitive to the strain and temperature: tensile strain leads to a ∼50% reduction in k at 300 K, which is primarily attributed to phonon softening, increased anharmonicity, and suppressed group velocities; compressive strain enhances k by up to ∼300%, due to phonon hardening and improved phonon velocities; elevated temperatures also degrade k by increasing phonon scattering. These results reveal the strain-temperature coupling effects on the behaviors of LiF, where its ability to dissipate heat can be severely compromised under inhomogeneous strains or elevated temperatures. Such thermomechanical coupling effects may cause localized heat accumulation in LiF-rich SEIs, accelerating degradation under harsh conditions. Our findings provide atomic-level insights into the coupled and coevolving effects of thermal and mechanical stresses in SEI performance and emphasize the importance of optimizing both mechanical and thermal properties for safer battery interfaces.

No abstract available

Lithium metal batteries have become potential high-energy storage devices because lithium metal has excellent theoretical capacity and low reduction potential. Unfortunately, the reckless growth of lithium dendrites leads to the decrease in Coulombic efficiency and the attenuation of cycle performance. Herein, we propose a collaborative assembly approach for a fluorine-enriched heterostructured solid electrolyte interphase (SEI) on lithium metal to enable stable and ultralong-life lithium metal batteries. The fluorine-enriched heterostructured SEI consists of an artificial precursor substrate K2ZrF6 and an epigenetically assembled LiF layer, and the composite structure cooperatively realizes the rapid conduction of Li+ ions and inhibits the formation of lithium dendrites. Benefiting from the heterostructured SEI, the symmetric cell exhibits an ultralong-time stable cycle of more than 7000 h at a high current and capacity density (4 mA cm-2 and 4 mA h cm-2, respectively), much longer than that of the lithium cell. Besides, the LiFePO4 full battery (LFP||Li-Zr) enables substantially enhanced cyclability over 800 cycles at 1 C. This work paves the way for dendrite-free and long-life lithium metal batteries with well-balanced heterostructured SEI engineering.

The electrocatalytic lithium-mediated nitrogen reduction reaction (Li-NRR) is considered as a promising alternative to the energy-intensive Haber-Bosch route. However, the solid electrolyte interphase that is derived from the electrolyte easily hinders the diffusion and nucleation of Li+, which ultimately suppresses N2 activation and the subsequent protonation process. Herein, we successfully construct surface oxygen vacancies (Ov) on commercial BaTiO3 (BTO) nanoparticles and further drive the phase transition from cubic/tetragonal to rhombohedral, which enhances the ferroelectricity of Ov-enriched BaTiO3 (BTOV) and produces orderly arranged dipoles. Systematic experimental and computational results validate that Ov-induced orderly arranged dipoles readily bind anions in the electrolyte and promote their reduction to form a LiF-rich SEI. The optimized anion-derived SEI enhances the Li+ transfer kinetics and effectively facilitates the uniform nucleation of Li+, which enables lower energy of Li+ desolvation and the reactant crossing the SEI. Thus, the as-prepared BTOV delivers a faradaic efficiency of 93.01% and an NH3 yield rate of 6.94 nmol s-1 cm-2 at -0.5 V which achieves more than a 45-fold performance improvement compared to the BTO counterpart. This work opens new horizons for the introduction of orderly arranged dipoles to modulate SEI chemistry and further enhance the intrinsic activity of the Li-NRR.

High‑nickel layered oxides, particularly LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811), are regarded as front-runners for next-generation lithium-ion battery cathodes due to their high energy density and reduced cobalt content. However, their practical implementation is hindered by rapid surface degradation, oxygen evolution, and severe lattice collapse under high-voltage operation. Here, we propose a dynamic cathode-electrolyte interphase (CEI) engineering strategy via a synergistic AlF dual surface modification, which concurrently stabilizes the bulk lattice and protects the interface. Fluorination with ammonium fluoride (NH₄F) promotes the formation of a dense, LiF-enriched CEI, while a conformal Al₂O₃ nanoshell provides adaptive protection against parasitic reactions and mechanical stress. The dual-modified NCM811 exhibits outstanding electrochemical performance, delivering a high initial discharge capacity of 227 mAh g-1 at 0.1C and maintaining 93.2 % capacity retention over 500 cycles at 0.2C. In-situ and ex-situ analyses, including X-ray diffraction and electrochemical impedance spectroscopy, reveal significant suppression of lattice distortion and interfacial resistance under high-voltage cycling. This scalable and cost-effective approach offers a universal platform for enabling high-voltage stability in Ni-rich cathodes, advancing their commercialization in high-energy lithium-ion batteries.

Lithium (Li) metal batteries are considered the most promising high‐energy‐density electrochemical energy storage devices of the next generation. However, the unstable solid–electrolyte interphase (SEI) derived from electrolytes usually leads to high impedance, Li dendrites growth, and poor cyclability. Herein, the ferroelectric BaTiO3 with orderly arranged dipoles (BTOV) is integrated into the polypropylene separator as a functional layer. Detailed characterizations and theoretical calculations indicate that surface oxygen vacancies drive the phase transition of BaTiO3 materials and promote the ordered arrangement of dipoles. The strong dipole moments in BTOV can adsorb TFSI− and NO3− anions selectively and promote their preferential reduction to form a SEI film enriched with inorganic LiF and LiNxOy species, thus facilitating the rapid transfer of Li+ and restraining the growth of Li dendrites. As a result, the Li–Li cell with the BTOV functional layer exhibits enhanced Li plating/stripping cycling with an ultra‐long life of over 7000 h at 0.5 mA cm−2/1.0 mAh cm−2. The LiFePO4 || Li (50 µm) full cells display excellent cycling performance exceeding 1760 cycles and superior rate performance. This work provides a new perspective for regulating SEI chemistry by introducing ordered dipoles to control the distribution and reaction of anions.

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 effectiveness of a solid electrolyte interphase (SEI) in lithium metal batteries (LMBs) is crucial for the reversible deposition and dissolution of lithium (Li). Herein, a multi‐valent cation (MVC) is proposed approach to enable superior LMB performance without increasing conducting salt concentration, thus reducing the cost and environmental footprint of LMBs. In this approach, a minimal amount of magnesium carbonate (MgCO3) of 0.05 m is added to a lithium hexafluorophosphate (LiPF6) based electrolyte, which effectively scavenges hydrogen fluoride (HF) generated from hydrolysis of LiPF6. Concurrently, the HF scavenging process dissolves MgCO3 microparticles and releases Mg2+ cations. It is noteworthy that multivalent Mg2+ cations, due to their high charge density, enrich the electric double layer with anions that preferentially decompose to form an anion‐derived SEI. Consequently, the MVC approach facilitates enhanced reversibility of Li metal deposition and dissolution, as well as stable galvanostatic cycling of LiNi0.8Mn0.1Co0.1O2 (NMC811)||Li cells. This approach provides a highly effective pathway for designing anion‐derived SEI, offering new insights into the control of Li metal interfaces.

Li metal is highly sought after as a negative electrode material due to its high specific capacity and low electrode potential. However, the brittle solid electrolyte interphase and undesirable coulombic efficiency have severely hindered its commercial application. Here we propose a formation mechanism of stable solid electrolyte interphase based on the de-solvation of heteroalkali cations rather than the simple electrostatic shielding effect. Cesium trifluoroacetate (CsTFA), characterized by high electron-donor anion and weak solvent-binding heteroalkali cation, was incorporated into commercial electrolytes to foster an inorganic-rich solid electrolyte interphase. The de-solvation of absorbed Cs+ dominates the initial solid electrolyte interphase formation on the Li surface. Simultaneously, the preferential reduction of TFA- promotes the enrichment of LiF within the solid electrolyte interphase. Owing to the synergistic effect of CsTFA, Li | |Cu half cells deliver a high CE of 99.77%, and Li | |LFP full cells exhibit satisfactory stability over 300 cycles with a 94.3% capacity retention at a negative/positive electrode capacity ratio of 1.36. Moreover, the added CsTFA in conventional ester electrolyte demonstrates improved stability of Li | |NCM811 full cells with an 80% capacity retention over 222 cycles at a negative/positive electrode capacity ratio of 1. The commercialization of lithium metal batteries has been hampered by intractable safety concerns due to their high reactivity. Here, authors use CsTFA as additive in commercial electrolytes to foster a stable solid electrolyte interphase and improve the electrochemical performance of the Li metal negative electrode.

Lithium (Li) metal anode (LMA) is highly considered as a desirable anode material for next-generation rechargeable batteries because of its high specific capacity and the lowest reduction potential. However, uncontrollable growth of Li dendrites, large volume change, and unstable interfaces between LMA and electrolyte hinder its practical application. Herein, a novel in situ formed artificial gradient composite solid electrolyte interphase (GCSEI) layer for highly stable LMAs is proposed. The inner rigid inorganics (Li2 S and LiF) with high Li+ ion affinity and high electron tunneling barrier are beneficial to achieve homogeneous Li plating, while the flexible polymers (poly(ethylene oxide) and poly(vinylidene fluoride)) on the surface of GCSEI layer can accommodate the volume change. Furthermore, the GCSEI layer demonstrates fast Li+ ion transport capability and increased Li+ ion diffusion kinetics. Accordingly, the modified LMA enables excellent cycling stability (over 1000 h at 3 mA cm-2 ) in the symmetric cell using carbonate electrolyte, and the corresponding Li-GCSEI||LiNi0.8 Co0.1 Mn0.1 O2 full cell demonstrates 83.4% capacity retention after 500 cycles. This work offers a new strategy for the design of dendrite-free LMAs for practical applications.

A novel electrolyte additive, 3, 3, 3‐trifluoropropylmethyldimethoxysilane (TFPMDS), is first proposed to modify both the cathode and the anode of lithium‐ion batteries at the same time. Charging/discharging tests demonstrate that the electrolyte with 1 wt% TFPMDS not only greatly improves the capacity retention of LiNi0.5Mn1.5O4 (LNMO)//Li cell (29.6%→90.8%) and graphite//Li cell (68.1%→98.3%), but also successfully ensures the long‐term cycle stability of LNMO//graphite pouch cell at 4.9 V. Further electrochemical measurements combining with spectroscopic characterization and theoretical calculations indicate that TFPMDS additive displays three principal functions: 1) Be preferentially oxidized to build a robust cathode electrolyte interphase (CEI) enriched in F/Si species with F‐rich nature of strong oxidation‐resistance. 2) Be able to scavenge the hazardous HF, F−, and H+ through its strong binding with these species and thus to protect LNMO at high‐voltage. 3) Be preferentially adsorbed on the graphite surface to form a “framework”, and to co‐construct an elastic solid electrolyte interphase (SEI) after the reduction of ethylene carbonate. Importantly, the Si─O group within TFPMDS is especially important for constructing a “molecular bridge” at the CEI/SEI interphase coupling the inorganic and organic species to improve its compatibility, stability, and elasticity.

The Li-mediated nitrogen reduction reaction (Li-NRR) has been proposed as one of the most promising ambient production routes for green ammonia. However, the effect of the applied potential (Ewe) on the reaction performance and the properties of the solid electrolyte interphase (SEI) remain poorly understood. Herein, we combine potential controlled experiments using a reliable LixFePO4 based reference electrode with post-mortem SEI characterization techniques, wherein we observe both an increase in the LiF concentration in the SEI, originating from LiTFSI decomposition, and the Faradaic efficiency (FENH3) with an increasing Ewe. The transition from a predominantly organic SEI at low Ewe (−3.2 VSHE) to a LiF-enriched layer at higher Ewe indicates the existence of kinetic barriers for the SEI formation reactions. Moreover, thicker and denser SEI structures observed at a higher Ewe enhance the Li-NRR by improving the mass transport regulation between reactant species. However, these thicker and denser SEI morphologies lead to current instabilities due to dynamic SEI thickening and breakdown. In Li-mediated electrochemical N₂ reduction to ammonia, selectivity and activity are governed by the solid electrolyte interphase (SEI). This study reveals how the applied potential shapes the SEI properties and composition, thereby influencing reaction performance.

No abstract available

Solid polymer electrolytes (SPEs) hold great promise for future applications of high‐energy lithium metal batteries (LMBs). Unfortunately, inadequate room‐temperature ionic conductivity, sluggish interfacial charge transport, and uncontrolled electrode/electrolyte interface reactions severely limit their widespread applications. Herein, poly(1,3‐dioxolane) electrolytes (PDEs) are prepared in situ by introducing lithium difluorophosphate (LiDFP, LiPO2F2) as a multifunctional additive, which not only achieves excellent ionic conductivity but facilitates interfacial charge transport. Meanwhile, a high‐mechanical‐stability organic–inorganic hybrid solid electrolyte interphase (SEI) is formed by the synergistic effect of PDEs and LiDFP. The enrichment of LiF and LixPOyFz species in SEI formed by the preferential reduction of LiDFP ensures outstanding mechanical stability, and the ring‐opening polymerization of 1,3‐dioxolane provides the SEI excellent adaptability to the repetitive volume changes of lithium metal anode, which mitigates crack and regeneration of SEI and reduces side reactions between active Li and electrolytes. Therefore, based on PDEs, the symmetric Li cell enables steady cycling for 2000 h. The Li‐LiFePO4 cell achieves superior long‐term cycling stability (over 1200 cycles) and wide operating temperature (−20 ∼ 60 °C). Also, the Li‐LiNi0.6Mn0.2Co0.2O2 exhibits favorable cycling stability. This study provides solutions to ongoing pain point issues of SPEs and facilitates practical applications of SPEs in high‐energy LMBs.

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.

No abstract available

To date, it is extensively believed that ether electrolytes are incompatible with graphite anode in Li-ion batteries due to detrimental solvent co-intercalation and exfoliation. Here, we provide design criteria of ether electrolytes for reversible graphite anode without the high salt concentration. In short, for ether electrolytes, the reductive stability of anions (or their solvated complex) and the solid-electrolyte interphase (SEI) govern the reversibility of graphite anode. Exfoliation and co-intercalation are not the root cause of as-documented cell failures using graphite anodes. While reductive-instable lithium bis(fluorosulfonyl)imide (LiFSI) is the optimal salt paired with DOL, reductive-stable LiBF4 finds applications with DME. Individual 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) based electrolytes can enable ~99.9% Coulombic efficiency with excellent capacity retention and fast-charge capability using natural graphite. In DOL electrolytes, weakened Li-solvent interaction and preferential reduction of FSI anion coordinated with Li-ion contribute to homogeneous SEI enriched with inorganic species, for example, LiF. Therefore, electrolyte reduction and Li-DOL co-intercalation are inhibited. In DME electrolytes, we show that LiBF4 has limited reduction, majorly on the edge site. We discover that a self-terminating, heterogeneous interphase based on grainy LiF proves to be desirable for operating Li-solvent co-intercalation. Taking advantage of the anisotropic characteristics of natural graphite, we conducted a holistic investigation into the nature, function, and formation of the heterogeneous SEI. In these studies, we clarify a long-lasting confusing issue in LIBs community-that is, the compatibility between ether electrolytes and graphite anode. Our findings not only shed light on the enigmatic interphase formed by ether electrolytes but also offer critical insights into future electrolyte design for graphite anodes operated under extreme conditions.

Significance Li metal is one of the most promising anodes for rechargeable batteries due to its large capacity, but its performance is plagued by high chemical reactivity, forming an unstable Li–electrolyte interface. Lithium fluoride has been recently touted as a promising material to improve this interface; however, its intrinsic protective role for Li remains uncertain, hindering design of improved Li interfaces. We demonstrate that the LiF-enriched interface undergoes significant modification as Li+ ions are cycled through it, and thus that the ensuing solid electrolyte interphase (SEI) repair process from the electrolyte is critical to achieve Li protection. Lithium is the most attractive anode material for high-energy density rechargeable batteries, but its cycling is plagued by morphological irreversibility and dendrite growth that arise in part from its heterogeneous “native” solid electrolyte interphase (SEI). Enriching the SEI with lithium fluoride (LiF) has recently gained popularity to improve Li cyclability. However, the intrinsic function of LiF—whether chemical, mechanical, or kinetic in nature—remains unknown. Herein, we investigated the stability of LiF in model LiF-enriched SEIs that are either artificially preformed or derived from fluorinated electrolytes, and thus, the effect of the LiF source on Li electrode behavior. We discovered that the mechanical integrity of LiF is easily compromised during plating, making it intrinsically unable to protect Li. The ensuing in situ repair of the interface by electrolyte, either regenerating LiF or forming an extra elastomeric “outer layer,” is identified as the more critical determinant of Li electrode performance. Our findings present an updated and dynamic picture of the LiF-enriched SEI and demonstrate the need to carefully consider the combined role of ionic and electrolyte-derived layers in future design strategies.

Unstable interface between highly reductive Li metal and a conventional liquid electrolyte leads to uncontrollable Li dendrites and Li pulverization, thus limiting the practical applications of Li metal batteries with high energy density. Herein, a fluorinated quasi-solid polymer electrolyte is synthesized to stabilize Li metal via the C-F/LiF enriched SEI derived from the fluorinated polymer skeleton. Benefiting from the homogenized ion plating/stripping process guided by lithiophilic C-F and rapid Li+ transportation assisted by LiF, Li dendrites and Li pulverization are suppressed. As a result, the Li||Li symmetrical cell with the fluorinated quasi-solid polymer electrolyte remains stable over 1400 h at a current density of 0.3 mA cm-2. LiNi0.8Co0.1Mn0.1O2||Li battery delivers a long-term cycling performance, where the capacity retains 87.77% of its initial state after 300 cycles at 0.5 C in the voltage range from 2.8 to 4.4 V.

Despite significant progress, lithium (Li) anodes still fall short of consistently achieving the >99.9% Coulombic efficiency (CE) required for >1,000 cycles. This limitation stems from uncontrolled reactions at the solid electrolyte interphase (SEI), which leads to uneven Li plating and stripping, ongoing electrolyte degradation, and depletion of active Li. While advancements in electrolyte formulations are ongoing, efforts to design more effective electrolytes remain hampered by an incomplete understanding of the specific mechanisms behind capacity loss during cycling. Recent progress in quantitative analysis of cycled lithium (Li) anodes has significantly deepened our understanding of root causes of capacity loss. Foundational research by Meng et al. introduced titration gas chromatography (TGC) as a technique to measure the amount of metallic lithium (Li⁰) that becomes trapped in electrode remnants during repeated cycling. Their findings showed that Li⁰ is the primary contributor to capacity loss at moderate Coulombic efficiencies (CE), and reducing Li⁰ can enhance battery performance. 1 However, at very high CE levels, the dominant cause of capacity loss shifts to solid electrolyte interphase (SEI) formation. 2 In this talk, we will present our efforts to expand on chemical titration methods by integrating them with gas chromatography (GC), inductively coupled plasma (ICP) spectroscopy, NMR, and other liquid-phase techniques, making them suited to provide chemical information on SEI composition and partitioning of capacity loss. In addition to Li⁰, these methods allow us to precisely identify how capacity loss relates to various trapped phases, including semicarbonates (ROCO₂Li), lithium carbide (Li₂C₂), olefins (RLi), lithium fluoride (LiF), lithium oxide (Li 2 O), and overall Li loss among others, enabling a clearer connection between these components and CE trends across diverse electrolytes and as a function of cycling. 3,4 Most recently, we conducted a statistical analysis on SEI titration data across a broad electrolyte set and identified a strong correlation between CE and SEI Li₂O content that exceeds that with LiF content, revealing Li 2 O to be the most universally beneficial SEI phase identified to date and challenging a longstanding belief in the field that LiF is the most important ionic SEI component. 4 Titration methods can also reveal how SEI phases couple to Li 0 formation: by enriching electrolytes with CO 2 gas additives, we found that SEI Li 2 CO 3 content, which supports high Li + SEI conductivity, is anticorrelated with Li 0 and positively correlated with CE, providing insight into the possible function of Li 2 CO 3 in the interphase. 5 Finally, we will discuss broader efforts to improve analytical methods to bring accounting of lost Li inventory ever-closer to 100% in cycled cells. Fang, J. Li, M. Zhang et al. , Nature 2019,572, 511–515. M. Hobold, J. Lopez, R. Guo, et al. , Nature Energy 2021, 6, 951-960. M. Hobold and B. M. Gallant, ACS Energy Letters 2022, 7, 3458-3466. M. Hobold, C. Wang, K. J. Steinberg, Y. Li, and B. M. Gallant, Nature Energy , 2024, 9, 580–591. K. Steinberg and B. M. Gallant, Journal of the Electrochemical Society , 2024, 171, 8, 080530.

A principle of suppressing Li dendrite in solid-state electrolytes is proposed and demonstrated using LiF-rich SEI experimentally. Solid-state electrolytes (SSEs) are receiving great interest because their high mechanical strength and transference number could potentially suppress Li dendrites and their high electrochemical stability allows the use of high-voltage cathodes, which enhances the energy density and safety of batteries. However, the much lower critical current density and easier Li dendrite propagation in SSEs than in nonaqueous liquid electrolytes hindered their possible applications. Herein, we successfully suppressed Li dendrite growth in SSEs by in situ forming an LiF-rich solid electrolyte interphase (SEI) between the SSEs and the Li metal. The LiF-rich SEI successfully suppresses the penetration of Li dendrites into SSEs, while the low electronic conductivity and the intrinsic electrochemical stability of LiF block side reactions between the SSEs and Li. The LiF-rich SEI enhances the room temperature critical current density of Li3PS4 to a record-high value of >2 mA cm−2. Moreover, the Li plating/stripping Coulombic efficiency was escalated from 88% of pristine Li3PS4 to more than 98% for LiF-coated Li3PS4. In situ formation of electronic insulating LiF-rich SEI provides an effective way to prevent Li dendrites in the SSEs, constituting a substantial leap toward the practical applications of next-generation high-energy solid-state Li metal batteries.

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The shuttle effect of lithium polysulfides (LiPSs) and the instability of the solid electrolyte interphase (SEI) lead to lithium dendrite growth and severe corrosion of lithium anodes (Li-anodes) for lithium-sulfur...

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As the holy-grail material, the Li-metal anode has been considered the potential anode of the next generation of Li-metal batteries (LMBs). However, issues of undesirable dendrite growth and unsatisfactory reversibility of the Li-plating/stripping process during the electrochemical cycling impede further application of LMBs. Herein, we innovatively introduce fluorinated graphene (F-Gr) species as a sacrificial effective electrolyte additive into EC/EMC-based electrolyte, which effectively triggers LiF-enriched (composition) and organic/inorganic species uniform-distributed (structure) SEI film architecture that features robustness and denseness, as well as good stability. With the F-Gr additive, efficient Li-metal anode protection (dendrite-free morphology on Li-metal surface and improved Li plating/stripping reversibility during electrochemical cycling) and significantly enhanced long-term lifespan of LMBs is achieved. Remarkably, classical electrochemical techniques, combined with the surface-sensitive characterizations (XPS and TOF-SIMS), comprehensively and systematically highlight critical structure-activity relationships between the SEI architecture (both composition and structure) and electrochemical performance. These techniques provide deep insights into the optimal electrolyte designation of Li-metal anode in LMBs.

Li metal is regarded as the most promising battery anode to boost energy density. However, being faced with the hostile compatibility between the Li anode and traditional carbonate electrolyte, its large-scale industrialization has been in a distressing circumstance due to severe dendrite growth caused by unsatisfying solid electrolyte interphase (SEI). With this regard, accurate control over the composition of the SEI is urgently desired to tackle the electrochemical and mechanical instability at the electrolyte/anode interface. Herein, we report a rationally designed fluorinated carbamate-based electrolyte employing LiNO3 as one of the main salts to induce the preferable anion decomposition to achieve a homogeneous and inorganic (LiF, Li3N, Li2O)-rich SEI. Thus, this electrolyte achieves a high Coulombic efficiency of 99% of the Li metal anode, a stable cycling over 1000 h for Li|Li symmetric cells, more than 100 cycles in 40-μm-thin Li|high-loading-NCM811 full batteries, and >50 cycles in Cu|LiFePO4 pouch cells, which is a promising electrolyte for highly reversible Li metal batteries.

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Lithium metal anodes have attracted extensive attention owing to their high theoretical specific capacity. However, the notorious reactivity of lithium prevents their practical applications, as evidenced by the undesired lithium dendrite growth and unstable solid electrolyte interphase formation. Here, we develop a facile, cost-effective and one-step approach to create an artificial lithium metal/electrolyte interphase by treating the lithium anode with a tin-containing electrolyte. As a result, an artificial solid electrolyte interphase composed of lithium fluoride, tin, and the tin-lithium alloy is formed, which not only ensures fast lithium-ion diffusion and suppresses lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible tin-lithium alloy formation and enabling lithium plating underneath it. With such an artificial solid electrolyte interphase, lithium symmetrical cells show outstanding plating/stripping cycles, and the full cell exhibits remarkably better cycling stability and capacity retention as well as capacity utilization at high rates compared to bare lithium. Here the authors report a simple method to create a solid electrolyte interphase that is tightly anchored onto the surface of lithium metal anode. This artificial structure suppresses dead and dendrite Li and stores Li via formation of alloys, enabling impressive battery performance.

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The artificial solid electrolyte interphase (SEI) layer is capable of protecting lithium anodes and preventing side reactions with electrolytes. The development of inorganic/organic composite hybrid SEI can be considered as an efficient strategy to combine the merits of high lithium ion conductivity, high mechanical modulus, and high flexibility. However, it still poses a great challenge to solve the agglomeration problem in these composite SEI to maintain the strong interaction between SEI and lithium metal. Herein, an inorganic/organic bilayer ultra‐thin SEI (P‐FEM@Li) derivative from reactive fluorinated copolymer (P‐FEM) is prepared and shows ultra‐large Young's modulus (> 75 GPa). The robust inorganic LiF‐rich layer provides superior ionic conductivity and large modulus, while the flexible organic polymer layer regulates lithium ions transport and interphase compatibility. The lithium anodes with P‐FEM induced bilayer SEI demonstrate stable cycles for more than 4400 h at 1 mA cm−2 and the average coulombic efficiency (CE) of Li||P‐FEM@Cu is 99.78% after 100 cycles. Moreover, the P‐FEM@Li||NCM811 punch cell with 428 Wh kg−1 exhibits a high‐capacity retention of 73% after 175 cycles. This work provides a new way to prepare practical SEI for lithium anodes.

Significance The “fluorinated interphase” is often seen as a catch-all solution for enhancing battery performance, despite LiF having a high Li-ion diffusion barrier. This study emphasizes evaluating its effects case-by-case. We developed weakly solvating electrolytes to tailor solid–electrolyte interphase (SEI) microstructures for fast-charging and low-temperature Li-ion batteries. Our work focuses on the role of LiF size and distribution in regulating Li-ion diffusion. Experimental results reveal that a fluorine-rich SEI with excessive, dense LiF impedes Li-ion transport, whereas a dispersed LiF-based SEI favors battery performance. Physics-based finite element simulations further elucidate how an optimized SEI microstructure facilitates charge transport across the electrode, offering a feasible approach to better batteries in extreme environments.

Fluorinated electrolytes based on fluoroethylene carbonate (FEC) have been considered as promising alternative electrolytes for high-voltage and high-energy capacity lithium-ion batteries (LIBs). However, the compatibility of the fluorinated electrolytes with graphite negative electrodes is unclear. In this paper, we have systematically investigated, for the first time, the stability of fluorinated electrolytes with graphite negative electrodes, and the result shows that unlike the ethylene carbonate (EC)-based electrolyte, the FEC-based electrolyte (EC was totally replaced by FEC) is incapable of forming a protective and effective solid electrolyte interphase (SEI) that protects the electrolyte from runaway reduction on the graphite surface. The reason is that the lowest unoccupied molecular orbital energy levels are also lowered by the introduction of fluorine into the solvent, and the FEC solvent has poorer resistance against reduction, leading to instability on the graphite negative electrode. To tackle this problem, two lithium salts of lithium bis(oxalato)borate and lithium difluoro(oxalato)borate (LiDFOB) have been investigated as negative-electrode film-forming additives. Incorporation of only 0.5 wt % LiDFOB to a FEC-based electrolyte [1.0 M LiPF6 in 3:7 (FEC–ethyl methyl carbonate)] results in excellent cycling performance of the graphite negative electrode. This improved property originates from the generation of a thinner and better quality SEI film with little LiF by the sacrificial reduction of the LiDFOB additive on the graphite negative electrode surface. On the other hand, this additive can stabilize the electrolyte by scavenging HF. Meanwhile, the incorporated LiDFOB additive has positive influence on the interphase layer on the positive electrode surface and significantly decreases the amount of HF formation, finally leading to improved cycling stability and rate capability of LiNi0.5Mn1.5O4 electrodes at a high cutoff voltage of 5 V. The data demonstrate that the LiDFOB additive not only exhibits a superior compatibility with graphite but also improves the electrochemical properties of high-voltage spinel LiNi0.5Mn1.5O4 positive electrodes considerably, confirming its potential as a prospective, multifunctional additive for 5 V fluorinated electrolytes in high-energy capacity lithium-ion batteries (LIBs).

Designing the solid-electrolyte interphase (SEI) is critical for stable, fast-charging, low-temperature Li-ion batteries. Fostering a “fluorinated interphase”, SEI enriched with LiF, has become a popular design strategy. Although LiF possesses low Li-ion conductivity, many studies have reported favorable battery performance with fluorinated SEIs. Such a contradiction suggests that optimizing SEI must extend beyond chemical composition design to consider spatial distributions of different chemical species. In this work, we demonstrate that the impact of a fluorinated SEI on battery performance should be evaluated on a case-by-case basis. Sufficiently passivating the anode surface without impeding Li-ion transport is key. We reveal that a fluorinated SEI containing excessive and dense LiF severely impedes Li-ion transport. In contrast, a fluorinated SEI with well dispersed LiF (i.e., small LiF aggregates well mixed with other SEI components) is advantageous, presumably due to the enhanced Li-ion transport across heterointerfaces between LiF and other SEI components. A new electrolyte, 1M LiPF 6 in 2-methyl tetrahydrofuran (2MeTHF), yields a fluorinated SEI with dispersed LiF. This electrolyte allows anodes of graphite, μSi/graphite composite, and pure Si to all deliver a stable Coulombic efficiency of 99.9% and excellent rate capability at low temperatures. Pouch cells containing layered cathodes also demonstrate impressive cycling stability over 1,000 cycles and exceptional rate capability down to -20°C. Through experiments and theoretical modeling, we have identified a balanced SEI-based approach that achieves stable, fast-charging, low-temperature Li-ion batteries.

Abstract A sturdy solid electrolyte interphase (SEI) is imperative for extending the calendar‐life of Si anodes in lithium‐ion batteries (LIBs). However, carbonate electrolytes form unstable interphases, hindering their practical implementation. Alternatively, fluorinated sulfonylimide (FSI−/TFSI−) based ionic liquid (IL) electrolytes, coupled with Li‐imide salts, enable anion‐derived SEI formation, thereby enhancing capacity retention. However, the functional role of these anions in directing SEI formation and evolution within IL‐based systems is poorly understood. Moreover, the mechanistic interplay between the decomposition pathways of symmetric and asymmetric anions in governing interfacial chemistry remains elusive. Herein, we investigate the chemistry and morphology of SEIs formed using various imidazolium‐based ILs containing both symmetric and asymmetric anions. We reveal that the synergistic interactions between symmetrical bis(fluorinated sulfonyl)imide anions and imidazolium cations facilitate an inorganic‐rich (LiF/LiOH) inner and a Li2SO4/polymeric outer layer SEI, conformally coating the 3D Si interface. The complementary effects of inorganic‐rich and polymer components, featuring key Li2SO4 species, reinforce mechanical integrity and flexibility, suppressing pulverization and enabling reversible capacity of 2489 mAh/g at 1C over 250 cycles. Correlating electrochemical performance with surface analysis provides critical insights into the impact of fluorinated sulfonylimide on passivation behavior and battery performance, guiding future design of ionic liquid electrolytes for LIBs.

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.

Rechargeable lithium (Li) metal batteries face persistent challenges in maintaining stable electrochemical performance, attributed to Li metal's high reactivity and the SEI's instability. Electrolyte composition plays a crucial role in reducing parasitic reactions at the Li metal anode and establishing a stable SEI. In this study, a novel fluorinated cyclic ether was synthesized, exhibiting enhanced electrochemical stability and minimizing Li-ion coordination capability. Its role in manipulating SEI formation was demonstrated, showcasing a bilayer SEI with a Li2O-rich inner layer and a LiF-rich outer layer, ensuring impressive stability and reversibility of Li metal anodes. The developed electrolyte showed significant enhancement in calendar life and cycling stability of Li (50 µm)||NMC811 (4 mAh/cm2) cells, leading to prototype pouch cells with a remarkable cycling stability of 80% capacity for up to 470 cycles, achieving 410 Wh/kg. This work highlights the potential of electrolyte engineering in advancing next-generation Li metal batteries towards high-energy-density applications.

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.

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

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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.

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

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.

No abstract available

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.

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.

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.

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 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 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 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 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.

SEM and EDS techniques are carried out to demonstrate the variation of morphology and chemical compound on the surface of graphite anode, which suggest a well‐accepted concept that the manganese ions have serious influence on the reversible capacity fade of graphite anode in lithium ion batteries. Based the main chemical compounds of the inorganic layer on the graphite surface, the evolution steps of graphite structure damaged by Mn ions are derived. Although the amount of deposited manganese ions is small, these play an important role in the catalytic decomposition of the electrolyte. Moreover, Raman analysis shows that the structure of the graphite anode becomes irregular at initial SEI formation cycles and tends to be stable at subsequent cycles. This structure variation is probably generated from the manganese ion deposition and the solid electrolyte interphase (SEI) film formation. According to the capacity tests, the cycling performance of NCM811/graphite lithium‐ion batteries could be improved 50% by FEC additive and B2O3 surface coating. FEC additive maybe benefit graphite forming a stable SEI film in the early stages of cycling to suppress the damage of Mn2+ ions, then improving the cycling performance.

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.

Incorporating functional fluorinated additives into the electrolyte has demonstrated a promising strategy for improving the electrochemical and interfacial stability of silicon‐based anode materials. In previous studies, these additives are claimed responsible for formation of a fluorinated solid electrolyte interphase (SEI) owing to matched orbital energy level with the other electrolyte components. The electric double layer (EDL) created via ionic‐electronic coupling at a (sub)nanoscale shows potential influence on the initial SEI formation at the anode, yet the underlying relationship among electrolyte additive, EDL and SEI remains obscure. Here, it is shown that, introduction of 0.5 wt.% trimethylsilyl trifluoromethanesulfonate (TMSOTF) additive into a conventional LiPF6‐based electrolyte helps to refine the EDL configuration, allowing stronger participation of additive molecules and counter anions for building a fluoride‐rich layers during initial SEI formation. This dynamic maintenance of an inorganic‐rich matrix (LiF, LixPOyFz, and LixSy) throughout the electrochemical process results in a SEI with optimized chemical composition, enhancing Li+ transport, mechanical strength, and structural integrity. Consequently, a SiOx (x≈1) anode exhibits improved cycling and rate performance, and electrode conformality. This work helps to clarify the EDL‐SEI interplay and provide guidelines for rational design of kinetically‐stable SEI on a high‐capacity anode with substantial volume variations.

In this work we explore how an electrolyte additive (fluorinated ethylene carbonate – FEC) mediates the thickness and composition of the solid electrolyte interphase formed over a silicon anode in situ as a function of state-of-charge and cycle. We show the FEC condenses on the surface at open circuit voltage then is reduced to C-O containing polymeric species around 0.9 V (vs. Li/Li+). The resulting film is about 50 Å thick. Upon lithiation the SEI thickens to 70 Å and becomes more organic-like. With delithiation the SEI thins by 13 Å and becomes more inorganic in nature, consistent with the formation of LiF. This thickening/thinning is reversible with cycling and shows the SEI is a dynamic structure. We compare the SEI chemistry and thickness to 280 Å thick SEI layers produced without FEC and provide a mechanism for SEI formation using FEC additives.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode/electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8Co0.1Mn0.1O2 /SiOx-graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt.% LiTFTCP into a LiPF6-carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

A fluorinated amide molecule with two functional segments, namely, an amide group with a high donor number to bind lithium ions and a fluorine chain to expel carbonate solvents and mediate the formation of LiF, was designed to regulate the interfacial chemistry. As expected, the additive preferably appears in the first solvation sheath of lithium ions and is electrochemically reduced on the anode, and thus an inorganic-rich solid electrolyte interphase is generated. The morphology of deposited lithium metal evolves from brittle dendrites into a granular shape. Consequently, the Li||LiFePO4 cell shows an excellent capacity retention of 92.7% at a high rate of 5 C after 800 cycles. Besides, the Li||LiNi0.8Co0.1Mn0.1O2 cell succeeds to maintain 98.1% of the initial capacity after 100 cycles at 1 C. Our designing of N,N-diethyl- 2,3,3,3-tetrafluoropropionamide (denoted as DETFP) highlights the importance of a "high donor number" and may shed light on the design principles of electrolytes for high performance batteries.

Constructing a LiF-rich solid electrolyte interphase (SEI) is a feasible strategy for inhibiting lithium (Li) dendrites of Li metal anodes (LMAs). However, selecting appropriate F-containing additives with efficient LiF contribution is still under active research. Herein, a series of fluorinated additives with diverse F/C molar ratios are investigated, and we demonstrate that the hexafluoroglutaric anhydride (F6−0) holds the best capability to derive the LiF-rich SEI in regular carbonate electrolytes (RCEs). To ameliorate the decomposition kinetics of the F6−0, LiNO3 (LNO) as an adjuvant is further introduced in the system. As a result, the reduction efficiency of F6−0 is increased to 91% under the F6−0/LNO synergistic effect, enabling the LMA with a uniform LiF-rich SEI in the RCE with merely 4 vol. % F6−0/LNO (F6L) addition. The LiNi0.8Co0.1Mn0.1O2||Li-20μm full-cell with the F6L also showcases better cycling and rate performances than the cases with other F-containing additives. A F-containing additive with efficient LiF contribution is urgent for Li metal batteries. The authors report a hexafluoroglutaric anhydride additive with a 91% conversion, enabling the Li metal anode with a LiF-rich interphase in regular electrolyte.

Gel polymer electrolytes (GPEs) based on deep eutectic electrolyte (DEE) show great promise for safe, high‐energy lithium metal batteries (LMBs). However, interfacial instability and limited fast‐charging capability remain challenges. Herein, an in situ polymerized fluorinated eutectic‐based electrolyte (named PDEE−UBP) is developed through molecular synergy engineering. The DEE consists of trifluoroacetamide (TFA) with a strongly electron‐withdrawing group ─CF3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). A stabilized interphase is constructed through a triangular additive synergy strategy, involving 2‐(3‐(6‐methyl‐4‐oxo‐1,4‐dihydropyrimidin‐2‐yl)ureido)ethyl methacrylate (UPyMA), lithium difluoro(oxalato)borate (LiDFOB) and tris(trimethylsilyl)phosphate (TMSP). The self‐healing function of UPyMA mitigates stress from lithium dendrite growth, improving lithium deposition uniformity. LiDFOB and TMSP promote the formation of a stable cathode electrolyte interphase. PDEE−UBP exhibits high ionic conductivity (2.83 mS cm−1 at 25 °C), wide electrochemical stability window (5.6 V vs Li/Li+), and a high Li⁺ transference number (0.68). Its moderately coordinated solvation structure weakens Li+−solvent interactions, lowers Li+ transport barriers, and enhances rate performance. Consequently, Li||LiFePO4 (LFP) cells deliver excellent 10 C performance with 84.7% capacity retention over 1000 cycles. Li||LiCoO2 (LCO) cells retain 92.7% after 1000 cycles at 3 C under 4.5 V. Additionally, PDEE−UBP demonstrates compatibility with 4.9 V LiNi0.5Mn1.5O4 cathodes. This work offers a promising approach for developing high‐voltage, fast‐charging GPEs for LMBs.

With their considerable capacity and structurally favorable characteristics, layered transition metal oxides have become strong contenders for cathode use in sodium-ion batteries (SIBs). Nevertheless, their practical deployment is challenged by pronounced capacity loss, predominantly induced by unstable cathode–electrolyte interphase (CEI) at elevated voltages. In this study, difluoroethylene carbonate (DFEC) is introduced as a functional electrolyte additive to engineer a robust and uniform CEI. The fluorine-enriched CEI effectively suppresses parasitic reactions, mitigates continuous electrolyte decomposition, and facilitates stable Na+ transport. Consequently, Na/NaNi1/3Fe1/3Mn1/3O2 (Na/NFM) cells with 2 wt.% DFEC retain 78.36% of their initial capacity after 200 cycles at 1 C and 4.2 V, demonstrating excellent long-term stability. Density functional theory (DFT) calculations confirm the higher oxidative stability of DFEC compared to conventional solvents, further supporting its interfacial protection role. This work offers valuable insights into electrolyte additive design for high-voltage SIBs and provides a practical route to significantly improve long-term electrochemical performance.

The development of high-energy-density lithium metal batteries (LMBs) using carbonate electrolytes is severely hindered by unstable interfacial chemistry, leading to uncontrolled lithium dendrite growth and rapid performance degradation. Given that the electrode/electrolyte interface property is highly dependent on the interface interactions, this work introduces 1,4-dithiane (1,4-DH), an environmentally benign cyclic thioether, as a multifunctional additive for stabilizing electrode-electrolyte interfaces in conventional carbonate electrolytes without fluorinated solvents. The 1,4-DH additive exhibits preferentially adsorption on both Li metal anodes and NCM811 (LiNi0.8Co0.1Mn0.1O2) cathodes, displacing solvent molecules from electrode surfaces to suppress solvent decomposition while driving localized PF6 - enrichment at the electrode interfaces via a robust binding interaction. The additive undergoes preferential self-decomposition during cycling to form sulfur-rich SEI (solid-electrolyte-interphase)/CEI (cathode electrolyte interphase), promoting synergistic decomposition of PF6 - simultaneously to form inorganic-dominated interphases (LiF, Li2S). As a result, the lithium iron phosphate full cell achieves 87.54% capacity retention and 99.99% average coulombic efficiency over 3000 cycles. Crucially, 1,4-DH stabilizes NCM811 cathodes against cracking, enabling prolonged cycle stability at 4.8 V. The additive further demonstrates exceptional adaptability under extreme conditions (-10 and 60 °C) and practical pouch cell configurations. This work provides a practical strategy for durable LMBs via non-fluorinated electrolyte engineering.

Silicon (Si) anode holds great potential to advance the energy-density of lithium-ion batteries (LIBs) owing to its high theoretical capacity (up to 3500 mAh g-1) and low operating potential (0.3 V vs. Li/Li+). However, the substantial volume changes (up to 300%) during the lithiation/delithiation process lead to the mechanical fracture of particles and the formation of unstable solid electrolyte interphase (SEI) layer, particularly under lean-additive electrolyte conditions. The unstable SEI layer triggers excessive electrolyte decomposition and loss of active materials, ending up with severe capacity decay and low Coulombic efficiency. Preventing those chronic issues, interface engineering through functional binders offers a practical approach to enhance the stability of SEI layer and maintain electrode integrity. Here, we report two different polymeric binders for Si-based anodes. Firstly, a rationally designed polymeric binder that constructs a stable SEI layer on Si-based anodes by preferentially reducing fluorinated functional groups to produce lithium fluoride (LiF). This uniform and thin SEI layer effectively preserves the structural morphology of Si particles during cycling, improving the structural stability of electrodes. Moreover, the LiF-enriched SEI layer substantially enhances electrolyte stability, preventing further decomposition, ensuring high electrolyte retention during cycling, and enabling high-energy-density lithium-ion batteries. Secondly, to utilize the micro-Si anodes in solid-state batteries, we have designed a covalently cross-linkable polymer binder with gel polymer electrolytes during the thermal curing. This secures an intimate contact of electrode-electrolyts and thus significantly extends the battery cycle life even with a record-breaking high-energy density (>1300 Wh/L). Our studies highlight the promising potential of this new binder for the formation of a sustainable electrode-electrolyte interface thereby promoting the commercialization of Si anodes in high-energy-density LIBs under practical electrolyte conditions.

Optimizing the electrode/electrolyte interface structure is the key to realizing high-voltage Li-metal batteries (LMBs). Herein, a functional electrolyte is introduced to synergetically regulate the interface layer structures on the high-voltage cathode and the Li-metal anode. Saccharin sodium (NaSH) as a multifunctional electrolyte additive is employed in fluorinated solvent-based electrolyte (FBE) for robust interphase layer construction. On the one hand, combining the results of ex-situ techniques and in-situ electrochemical dissipative quartz crystal microbalance (EQCM-D) technique, it can be seen that the solid electrolyte interface (SEI) layer constructed by NaSH-coupled fluoroethylene carbonate (FEC) on Li-metal anode significantly inhibits the growth of lithium dendrites and improves the cyclic stability of the anode. On the other hand, the experimental results also confirm that the cathode-electrolyte interface (CEI) layer induced by NaSH-coupled FEC effectively protects the active materials of LiCoO2 and improves their structural stability under high-voltage cycling, thus avoiding the material rupture. Moreover, theoretical calculation results show that the addition of NaSH alters the desolvation behavior of Li+ and enhances the transport kinetics of Li+ at the electrode/electrolyte interface. In this contribution, the LiCoO2 ǁLi full cell containing FBE+NaSH results in a high capacity retention of 80% after 530 cycles with a coulombic efficiency of 99.8%.

Controlling solid electrolyte interphase (SEI) in batteries is crucial for their efficient cycling. Herein, we demonstrate an approach to enable robust battery performance that does not rely on high fractions of fluorinated species in electrolytes, thus substantially decreasing the environmental footprint and cost of high-energy batteries. In this approach, we use very low fractions of readily reducible fluorinated cations in electrolyte (∼0.1 wt%) and employ electrostatic attraction to generate a substantial population of these cations at the anode surface. As a result, we can form a robust fluorine-rich SEI that allows for dendrite-free deposition of dense Li and stable cycling of Li-metal full cells with high-voltage cathodes. Our approach represents a general strategy for delivering desired chemical species to battery anodes through electrostatic attraction while using minute amounts of additive.

Silicon, as potential next‐generation anode material for high‐energy lithium‐ion batteries (LIBs), suffers from substantial volume changes during (dis)charging, resulting in continuous breakage and (re‐)formation of the solid electrolyte interphase (SEI), as well as from consumption of electrolyte and active lithium, which negatively impacts long‐term performance and prevents silicon‐rich anodes from practical application. In this work, fluorinated phosphazene compounds are investigated as electrolyte additives concerning their SEI‐forming ability for boosting the performance of silicon oxide (SiOx)‐based LIB cells. In detail, the electrochemical performance of NCM523 || SiOx/C pouch cells is studied, in combination with analyses regarding gas evolution properties, post‐mortem morphological changes of the anode electrode and the SEI, as well as possible electrolyte degradation. Introducing the dual‐additive approach in state‐of‐the‐art electrolytes leads to synergistic effects between fluoroethylene carbonate and hexafluorocyclotriphosphazene‐derivatives (HFPN), as well as enhanced electrochemical performance. The formation of a more effective SEI and increased electrolyte stabilization improves lifetime and results in an overall lower cell impedance. Furthermore, gas chromatography‐mass spectrometry measurements of the aged electrolyte with HFPN‐derivatives as an additive compound show suppressed ethylene carbonate and ethyl methyl carbonate decomposition, as well as reduced trans‐esterification and oligomerization products in the aged electrolyte.

Li metal batteries using Li metal as negative electrode and LiNi1-x-yMnxCoyO2 as positive electrode represent the next generation high-energy batteries. A major challenge facing these batteries is finding electrolytes capable of forming good interphases. Conventionally, electrolyte is fluorinated to generate anion-derived LiF-rich interphases. However, their low ionic conductivities forbid fast-charging. Here, we use CsNO3 as a dual-functional additive to form stable interphases on both electrodes. Such strategy allows the use of 1,2-dimethoxyethane as the single solvent, promising superior ion transport and fast charging. LiNi1-x-yMnxCoyO2 is protected by the nitrate-derived species. On the Li metal side, large Cs+ has weak interactions with the solvent, leading to presence of anions in the solvation sheath and an anion-derived interphase. The interphase is surprisingly dominated by cesium bis(fluorosulfonyl)imide, a component not reported before. Its presence suggests that Cs+ is doing more than just electrostatic shielding as commonly believed. The interphase is free of LiF but still promises high performance as cells with high LiNi0.8Mn0.1Co0.1O2 loading (21 mg/cm2) and low N/P ratio (~2) can be cycled at 2C (~8 mA/cm2) with above 80% capacity retention after 200 cycles. These results suggest the role of LiF and Cs-containing additives need to be revisited. Fluorinated interphases are often pursued as a design strategy for Li metal batteries. In contrast, here the authors show that an electrolyte with a non-fluorinated solvent and CsNO3 additive results in an LiF-free but inorganic-rich interphase that enables fast-charging of Li metal batteries.

Solid electrolyte interphases generated using electrolyte additives are key for anode-electrolyte interactions and for enhancing the lithium-ion battery lifespan. Classical solid electrolyte interphase additives, such as vinylene carbonate and fluoroethylene carbonate, have limited potential for simultaneously achieving a long lifespan and fast chargeability in high-energy-density lithium-ion batteries (LIBs). Here we report a next-generation synthetic additive approach that allows to form a highly stable electrode-electrolyte interface architecture from fluorinated and silylated electrolyte additives; it endures the lithiation-induced volume expansion of Si-embedded anodes and provides ion channels for facile Li-ion transport while protecting the Ni-rich LiNi0.8Co0.1Mn0.1O2 cathodes. The retrosynthetically designed solid electrolyte interphase-forming additives, 5-methyl-4-((trifluoromethoxy)methyl)-1,3-dioxol-2-one and 5-methyl-4-((trimethylsilyloxy)methyl)-1,3-dioxol-2-one, provide spatial flexibility to the vinylene carbonate-derived solid electrolyte interphase via polymeric propagation with the vinyl group of vinylene carbonate. The interface architecture from the synthesized vinylene carbonate-type additive enables high-energy-density LIBs with 81.5% capacity retention after 400 cycles at 1 C and fast charging capability (1.9% capacity fading after 100 cycles at 3 C). Interface architecture generated from electrolyte additives is a key element for high performance lithium-ion batteries. Here, the authors present that a stable and spatially deformable solid electrolyte interphase mitigates interfacial degradation of Si-embedded anodes and Ni-rich cathodes.

Rechargeable room-temperature sodium-sulfur (RT Na-S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate an all-fluorinated electrolyte, containing 2,2,2-trifluoro-N, N-dimethylacetamide (FDMA) solvent, 1,1,2,2-tetrafluoroethyl methyl ether (MTFE) anti-solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na-S batteries. A NaF- and Na3N-rich cathode electrolyte interphase derived from FDMA and FEC enables a "quasi-solid-phase" Na-S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes Na anode via a tailored solvation structure. The as-developed RT Na-S batteries deliver a high capacity, long lifespan, and enhanced safety.

Introducing a small dose of electrolyte additive in solid polymer electrolytes (SPEs) is an appealing strategy for improving the quality of solid-electrolyte-interphase (SEI) layer formed on lithium metal (Li°) anode, thereby extending the cycling life of solid-state lithium metal batteries (SSLMBs). In this work, we report a new type of SPEs comprising a low-cost, fluorine-free salt, lithium tricyanomethanide (LiTCM), as main conducting salt, and a fluorinated salt, lithium bis(fluorosulfonyl)imide (LiFSI), as electrolyte additive for enhancing the performance of SPE-based SSLMBs. Our results demonstrate that a homogeneous and stable SEI layer is readily formed on the surface of Li° electrode through the preferential reductive decomposition of LiFSI, and, consequently, the cycle stabilities of Li° || Li° and Li° || LiFePO4 cells are significantly improved after the incorporation of LiFSI as additive. The intriguing chemistry of salt anion revealed in this work may expedite the large-scale implementation of SSLMBs in the near future.

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.

Despite its ultrahigh theoretical capacity and ultralow redox electrochemical potential, the practical application of lithium metal anodes is still hampered by severe dendrite growth and unstable solid electrolyte interphase (SEI). Herein, a self‐assembled lithiophilic interface (SALI) for regulating Li electroplating behavior is constructed by introducing a meticulously synthesized Ni‐bis(dithiolene)‐based molecule (NiS4‐COOH) into a hybrid fluorinated ester‐ether electrolyte. The NiS4‐COOH molecules with carboxyl functional groups can spontaneously anchor on the Li metal surface to form a SALI, whose abundant Ni‐bis(dithiolene) sites can effectively reduce the initial Li deposition overpotential and guide the subsequent uniform Li electrodeposition. Moreover, due to the interaction between the coordination unsaturated Ni atom and the negatively charged PF6−, the NiS4‐COOH additive can significantly change the ionic coordination environment in the electrolyte, which is greatly conducive to suppressing PF6− decomposition, optimizing SEI composition and accelerating Li‐ion transfer. Consequently, the NiS4‐COOH‐modified electrolyte leads to impressive electrochemical performance of Li||LiFePO4 and Li||LiNi0.8Co0.1Mn0.1O2 batteries, delivering ultrahigh Coulombic efficiencies, considerable capacity retention, and good rate performance even at high areal active material loadings. This study presents the great potential of SALIs derived from multifunctional metal‐organic hybrid electrolyte additives toward high‐specific‐energy Li metal batteries.

Nickel-rich layered oxides are currently considered the most practical candidates for realizing high-energy-density lithium metal batteries (LMBs) due to their relatively high capacities. However, undesired nickel-rich cathode-electrolyte interactions hinder their applicability. Here, we report a satisfactory combination of an antioxidant fluorinated ether solvent and an ionic additive that can form a stable, robust interfacial structure on the nickel-rich cathode in ether-based electrolytes. The fluorinated ether 1,1,2,2-tetrafluoroethyl-1H,1H,5H-octafluoro-pentyl ether (TFOFE) introduced as a cosolvent into ether-based electrolytes stabilizes the electrolytes against oxidation at the LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode, while simultaneously preserving the electrochemical performance of the Li metal anode. Lithium difluoro(bisoxalato) phosphate (LiDFBP) forms a uniform cathode electrolyte interphase that limits the generation of microcracks inside secondary particles and undesired dissolution of transition metal ions such as nickel, cobalt, and manganese from the cathode into the electrolyte. Using TFOFE and LiDFBP in ether-based electrolytes provides an excellent capacity retention of 94.5% in a Li|NCM811 cell after 100 cycles and enables the delivery of significantly increased capacity at high charge and discharge rates by manipulating the interfaces of both electrodes. This research provides insights into advancing electrolyte technologies to resolve the interfacial instability of nickel-rich cathodes in LMBs.

Solid electrolyte interphase (SEI) formation in lithium ion cells prepared with advanced electrolytes is investigated by solid state multinuclear (7Li, 19F, 31P) magnetic resonance (NMR) measurements of electrode materials harvested from cycled cells subjected to an accelerated aging protocol. The electrolyte composition is varied to include the addition of fluorinated carbonates and triphenyl phosphate (TPP, a flame retardant). In addition to species associated with LiPF6 decomposition, cathode NMR spectra are characterized by the presence of compounds originating from the TPP additive. Substantial amounts of LiF are observed in the anodes as well as compounds originating from the fluorinated carbonates.

Lithium‐rich manganese‐based layered oxides (LRMOs) are promisingly used in high‐energy lithium metal pouch cells due to high specific capacity/working voltage. However, the interfacial stability of LRMOs remains challenging. To address this question, a novel armor‐like cathode electrolyte interphase (CEI) model is proposed for stabilizing LRMO cathode at 4.9 V by exploring partially fluorinated electrolyte formulation. The fluoroethylene carbonate (FEC) and tris (trimethylsilyl) borate (TMSB) in formulated electrolyte largely contribute to the formation of 4.9 V armor‐like CEI with LiBxOy and LixPOyFz outer layer and LiF‐ and Li3PO4‐rich inner part. Such CEI effectively inhibits lattice oxygen loss and facilitates the Li+ migration smoothly for guaranteeing LRMO cathode to deliver superior cycling and rate performance. As expected, Li||LRMO batteries with such electrolyte achieve capacity retention of 85.7% with high average Coulomb efficiency (CE) of 99.64% after 300 cycles at 4.8 V/0.5 C, and even obtain capacity retention of 87.4% after 100 cycles at higher cut‐off voltage of 4.9 V. Meanwhile, the 9 Ah‐class Li||LRMO pouch cells with formulated electrolyte show over thirty‐eight stable cycling life with high energy density of 576 Wh kg−1 at 4.8 V.

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.

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.

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.

To develop K-ion batteries, the potassium metal reactivity in a half-cells must be understood. Here, it is shown first that the K metal leads to the migration of the electrode degradation species to the working electrode surface so that half-cells' solid electrolyte interphase (SEI) studies cannot be trusted. Then, the K metal reactivity was studied by combining gas chromatography (GC)-mass spectrometry, GC/Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis after storage in ethylene carbonate/diethylene carbonate (EC/DEC) wo/w 0.8 M KPF6 or KFSI. A comparison with Li stored in EC/DEC wo/w 0.8 M LiPF6 was also performed. Overall, full electrolyte degradation pathways were obtained. The results showed a similar alkali reactivity when stored in EC/DEC with the formation of a CH3CH2OCO2M-rich SEI. For a MPF6-based electrolyte, the reactivity was driven by the PF6- anion (i) forming mostly LiF (Li metal) or (ii) catalyzing the solvent degradation into (CH2CH2OCOOK)2 and CH3CH2OCOOK as main SEI products with additional C2H6 release (K metal). This highlights the higher reactivity of the K system. With KFSI, the reactivity was driven by the FSI- anion degradation, leading to an inorganic-rich SEI. These results thus explain the better electrochemical performance often reported in half-cells with KFSI compared to that with KPF6. Finally, the understanding of these chemically driven electrolyte degradation mechanisms should help researchers to design robust carbonate-based electrolyte formulations for KIBs.

No abstract available

Spinel LiMn2O4 (LMO) is a well-known cathode material for lithium-ion batteries. In order to elucidate the molecular mechanism of the solid electrolyte interface (SEI) formation and the effect of an additive, vinylene carbonate (VC), we systematically studied the spontaneous and electrochemical reactions of solvents and a salt (LiPF6) in electrolytes with LMO in the absence and presence of VC. X-ray photoelectron spectroscopy (XPS) results of the LMO surfaces after soaking in the electrolyte solutions showed that the carbonate solvents as well as VC spontaneously decomposed on the LMO surfaces to form new compounds, such as alcohols, ethers, and carboxylates. The ratio of the produced LiF to MnF2 was similar for both with and without VC. Considering these spontaneously formed initial SEI components, we then investigated the variation of the SEI compositions during the initial electrochemical process until 3.8 V vs. Li+/Li. The role of the additive was studied and found that the electrochemical reaction of VC produced more organic compounds and led to an increase in the LiF/MnF2 ratio of the SEI layer. Based on the hard and soft acid and base theory, we proposed the mechanisms of the SEI formation via spontaneous and electrochemical reactions on the LMO thin film cathode with and without VC.

No abstract available

Solid electrolyte interphase (SEI) critically governs lithium (Li) battery performance. Yet, understanding the native SEI remains challenging due to the lack of techniques capable of depth profiling of the interphase layer under electrolyte conditions (wet-SEI). In this work, cryogenic X-ray photoelectron spectroscopy (cryo-XPS) coupled with argon gas cluster ion beam (GCIB) sputtering was developed to extensively investigate the vitrified wet-SEI of Li metal batteries without chemical damage. First, the combined cryo-XPS and GCIB platform captures the full composition of the native SEI in the presence of electrolyte, which comprises organic polymeric hydrocarbons and inorganic species like LiCx, LiF, LiOx, and Li2CO3. These results are significantly distinct from conventional XPS characterizations of dry-SEI (i.e., SEI without electrolyte) showing a depletion of inorganic species and thus highlight the strength of this hybrid approach in revealing the real motif of the native SEI. Second, a graded SEI architecture has been revealed with electrochemical decomposition products (LiF and Li2CO3) dominating the electrolyte-facing region, and chemically derived species (LiOx and LiCx) accumulating at the electrode-facing region. Lastly, this approach is capable of scrutinizing the dynamic evolution of SEI during Li deposition, unravelling a compositional shift from electrochemical SEI to a graded complex SEI architecture, with a thickness increase from the nanometer- to micrometer-scale. Therefore, depth-resolved cryo-XPS serves as a promising methodology for elucidating the dynamic heterogeneous chemical signatures across evolving solid-liquid interfaces in electrocatalysis and energy storage processes.

Tin (IV) sulfide (SnS2) is a promising anode material for Li‐ion batteries (LIBs) due to its high practical reversible capacity of 623 mAhg−1. However, its cycling stability is relatively poor and its long‐term degradation during cycling is not yet thoroughly investigated. In this work, a post‐mortem analysis of SnS2 electrodes was performed at pristine state, after the 1st cycle and at 80 % state‐of‐health. The analysis compared water‐based (Na‐CMC/SBR) and NMP‐based (PVDF) electrodes revealing insights into their degradation mechanisms and electrochemical performance. During the first cycle, SnS2 converts into Sn and Li2S identified by XRD, causing particle cracking and exfoliation. XPS and Raman spectroscopy identified Sn, SnFx, LiF, Li2S and carbonates species forming the solid electrolyte interphase (SEI), while in‐situ dilatometry revealed up to 60 % irreversible expansion after the first cycle. These species are also found after at 80 % SOH along with an increase in fluorine species, SEI thickness and interfacial resistance. Water‐based electrodes exhibited better cycling stability, with 80 wt.% SnS2 and 10 wt.% binder retaining 80 % capacity after 180+ cycles. These findings underscore the critical role of binder choice and processing in enhancing SnS2 anodes’ durability and capacity retention, paving the way for sustainable, high‐performance LIB anodes.

Quasi-solid polymer electrolyte (QPE) lithium (Li)-metal battery holds significant promise in the application of high-energy-density batteries, yet it suffers from low ionic conductivity and poor oxidation stability. Herein, a novel self-built electric field (SBEF) strategy is proposed to enhance Li+ transportation and accelerate the degradation dynamics of carbon-fluorine bond cleavage in LiTFSI by optimizing the termination of MXene. Among them, the SBEF induced by dielectric Nb4C3F2 MXene effectively constructs highly conductive LiF-enriched SEI and CEI stable interfaces, moreover, enhances the electrochemical performance of the QPE. The related Li-ion transfer mechanism and dual-reinforced stable interface are thoroughly investigated using ab initio molecular dynamics, COMSOL, XPS depth profiling, and ToF-SIMS. This comprehensive approach results in a high conductivity of 1.34 mS cm-1, leading to a small polarization of approximately 25 mV for Li//Li symmetric cell after 6000 h. Furthermore, it enables a prolonged cycle life at a high voltage of up to 4.6 V. Overall, this work not only broadens the application of MXene for QPE but also inspires the great potential of the self-built electric field in QPE-based high-voltage batteries.

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

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.

In this article BF3 etching is applied to fabricate basic SEI (B‐SEI) layers enriched with LiF and LixBFy. Artificial solid electrolyte interface (A‐SEI) with a “stromatolite” structure is formed on top of the B‐SEI growth during the charge‐discharge cycles. The structure of A‐SEI is characterized laterally and longitudinally by distribution of TEM elements and depth‐profile XPS, providing evidence for the elucidation of a new lattice‐tuning Li+ “layered” deposition‐type SEI structure. At the same time, the SEI is kept from electrolyte erosion fracturing during deposition, resulting in the growth of dendrites along the fracture and significantly enhanced cycling stability under high‐rate cycling conditions. In particular, A‐SEI endows significantly enhanced cycling capability to the full battery at high cycling rate and high current density. The full cell of A‐SEI@Li||LiPF6||LFP exhibits an extended lifetime after 2000 cycles at current densities up to 10 C, and still process a CE above 99.0%.

An operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) with simultaneous in situ electrochemical impedance spectroscopy (EIS) has been developed and applied to study the solid electrolyte interphase (SEI) formation on copper current collectors in Li ion batteries. The findings are backed by EIS simulations and complementary analytical techniques, such as online electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS). The evolution of mass and the mechanical properties of the SEI are directly correlated to the electrode impedance. Electrolyte reduction at the anode carbon active material initiates dissolution, diffusion, and deposition of reaction side products throughout the cell and increases electrolyte viscosity and the ohmic cell resistance as a result. On Cu the reduction of CuO x and HF occurs at >1.5 V and forms an initial LiF-rich interphase while electrolyte solvent reduction at <0.8 V vs Li+/Li adds a second, less rigid layer on top. Both the shear storage modulus and viscosity of the SEI generally increase upon cycling but-along with the SEI Li+ diffusion coefficient-also respond reversibly to electrode potential, likely as a result of Li+/EC interfacial concentration changes. Combined EIS-EQCM-D provides unique prospects for further studies of the highly dynamic structure-function relationships of electrode interphases in Li ion batteries.

No abstract available

The formation of a solid electrolyte interphase (SEI) on the surface of Li 4 Ti 5 O 12 (LTO) has become a highly controversial topic in literature with arguments for it and against it. However, the literature supporting the formation of an SEI layer typically suggests that a layer forms upon cycling of a cell, although the layer is probed after disassembling. Cubic mesostructured LTO with crystallite domain sizes between 3 and 4 nm and uniform pores with diameters ≤ 8nm was synthesized. The mean pore size was controlled between 4 to 8 nm through the use of a triblock amphipathic co-polymer having a tunable hydrophobic block as template, and by thermal treatment. The LTO morphology obtained was spherical and evolved upon heat treatment. These materials had excellent electrochemical performance, including high rate capability and capacity retention. The LTO material was subjected to operando SANS and XPS experiments that reveal that the highly debated SEI formed at potentials as high as 2.2 V, first as a LiF-rich layer that was followed by the growth of a carbonaceous layer. These SEI products formed on the smaller pores first before forming on the mesopores.

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.

No abstract available

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.

No abstract available

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 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.

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.

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.

A novel low-concentration electrolyte with lithium nitrate as the sole salt enables flame-retardant lithium metal batteries featuring a 4.4 V stability window, dendrite-free Li deposition, and stable cycling through a LiF/Li 3 N SEI.

Lithium bis(fluorosulfonyl)imide (LiFSI) is widely used in lithium-metal batteries to form a stable lithium fluoride (LiF)-based solid electrolyte interphase (SEI). However, the FSI⁻ itself fails to create a protective passivation layer on aluminum (Al) current collectors, leading to Al3⁺ dissolution and severe corrosion. While fluorinated ether solvents have shown promise in mitigating Al corrosion, the mechanisms remain unclear. Here, the role of cation solvations and ion pairing structures is shown in corrosion mitigation. 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB), a 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE)/1,2-dimethoxyethane (DME) mixture, and non-fluorinated ethers are evaluated in 1 m LiFSI. FDMB promoted the formation of AlF₃ while preventing corrosion under extreme conditions (e.g., 4.5 V vs Li/Li⁺, 60 °C). Electrochemical and DFT analyses showed that FDMB underwent favorable defluorination in coordination with both Li⁺ and Al3⁺ that arose from the oxidizing Al surface. Meanwhile, the formation of aggregated ion pairs between Li+ and FSI⁻ inhibited the generation of soluble Al3+ species coordinated with FSI-. Modifying FDMB with alkyl chains further enhanced the anti-corrosive effects by reducing the solubility of Al3+ species. In contrast, DME/TTE exhibited more Al corrosion, similar to tetraethylene glycol dimethyl ether (TEGDME), due to less favorable defluorination by the limited solvation of Li+ and Al3+ on TTE.

Engineering a stable solid electrolyte interphase (SEI) is critical for suppression of lithium dendrites. However, formation of desired SEI by formulating electrolyte composition is very difficult due to complex electrochemical reduction reactions. Here, instead of try-and-error of electrolyte composition, we design a Li-11 wt% Sr alloy anode to form SrF2-rich SEI in fluorinated electrolytes. Density functional theory (DFT) calculation and experimental characterization demonstrate that SrF2-rich SEI has a large interfacial energy with Li metal and a high mechanical strength, which can effectively suppress the Li dendrite growth by simultaneously promoting the lateral growth of deposited Li metal and the SEI stability. The Li-Sr/Cu cells in 2M LiFSI-DME shows an outstanding Li plating/stripping Coulombic efficiency of 99.42% at 1 mA cm-2 with a ca-pacity of 1 mAh cm-2 and 98.95% at 3 mA cm-2 with a capacity of 2 mAh cm-2, respectively. The symmetric Li-Sr/Li-Sr cells also achieve a stable electrochemical performance of 180 cycles at an extremely high current density of 30 mA cm-2 with a capacity of 1 mAh cm-2. When paired with LiFePO4 (LFP) and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes, Li-Sr/LFP cells in 2M LiFSI-DME electrolytes and Li-Sr/NMC811 cells in 1M LiPF6 in FEC:FEMC:HFE electrolytes also maintain excellent capacity retention. Designing SEI by regulating Li metal anode composition opens up a new and rational avenue to suppress Li dendrites.

No abstract available

No abstract available

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.