Effective Solid Electrolyte Interphase Research Articles

Au-embedded mesoporous molecular sieve enables robust organic/inorganic hybrid solid electrolyte interphase for high-performance lithium metal batteries

The solid electrolyte interphase (SEI) determines the lithium (Li) deposition behavior for long-term lithium metal batteries. However, the naturally formed fragile SEI would cause the nonuniform lithium deposition and random dendrite growth due to weak interaction of the heterogeneous distributed inorganic and organic species. Herein, we designed Au-embedded mesoporous molecular sieve as an electrolyte modifier to feasibly form a robust organic/inorganic hybrid SEI. Such hybrid SEIs, composed of Si-O interlinked polycarbonates (poly(CO3)) which is derived from the Au-induced electrocatalytic polymerization of EC (ethylene carbonate), possess an ultrahigh Young’s modulus of 11.6 GPa, achieving uniform lithium deposition and suppression of lithium dendrites. Assembled by the Au@MCM-41-modified electrolyte, the Li||Li symmetrical cells exhibit a recyclable behavior of Li deposition/dissolution over 900 h at 0.5 mA cm−2, and the Li||LFP (LiFePO4) full cells maintain a high capacity of 123 mAh g−1 even after 300 cycles at 1.0 C. This work explores a new route to in situ develop a robust and effective SEI for prospective lithium metal batteries in practical application and social requirement.

Synergistic Effect of Lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)Imide (LiDFTFSI) and Vinylene Carbonate (VC) on High Performance of NMC811║Graphite Cells

Lithium-ion batteries (LIBs) have gained increasing importance in energy storage systems, driven by the growing demands of grid storage, automotive, and portable consumer applications. To meet the need for high energy density batteries, one promising approach involves the utilization of high capacity layered transition metal oxide cathodes, such as nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811), which can deliver a high reversible specific capacity of over 180 mAh·g-1 [1,2]. However, due to the structural and interfacial instability[3], nickel-rich NMC cathode still faces challenges in long-term galvanostatic cycling. For these reasons, design of novel electrolyte formulations, which enable formation of an effective cathode electrolyte interphase (CEI), is highly desirable. Recent studies have highlighted the cross-talk between the cathode and anode, indicating that the evolution of the solid electrolyte interphase (SEI) can impact the formation of the CEI[4]. Thus, establishing an effective SEI/CEI pair is essential for achieving long-term cycling of nickel-rich NMC cathode-based cells. Electrolyte optimization plays a crucial role in facilitating the formation of a desirable SEI/CEI pair, leading to an improved cell performance and longevity. Lithium (difluoromethanesulfonyl)(trifluoro-methanesulfonyl)imide (LiDFTFSI) has proven to be promising in solid-polymer-electrolyte batteries due to the good SEI/CEI formation ability and suppressed Al-dissolution[5]. Additionally, LiDFTFSI exhibits also good compatibility with Li-metal batteries[6], heralding promising applications in Li-ion batteries. However, there is lack of systematic research investigating the potential impact of LiDFTFSI on the cathode as well as on resulting CEI formation and dynamics.In this work, we demonstrated enhanced galvanostatic cycling performance of NMC811||graphite cells achieved by utilizing LiDFTFSI and lithium hexafluorophosphate (LiPF6) in a blended salt organic carbonate-based electrolyte formulation. Comprehensive electrochemical and post mortem analysis revealed that the LiDFTFSI alone can effectively mitigate the structural changes in the NMC811 electrode by facilitating the formation of modified CEI. However, the continued growth of an inhomogeneous CEI, caused by the cross-talk effect between electrodes, adversely affected long-term cycling stability. To address this, vinylene carbonate (VC) was introduced to the electrolyte. Synergistic effect with LiDFTFSI leads to the formation of effective and uniform SEI and CEI. As a result, 720 charge/discharge cycles were achieved in NMC811||graphite cells with LiDFTFSI and VC containing electrolytes at 1C while maintaining 80% state-of-health (SOH80%).

Building a Flexible and Highly Ionic Conductive Solid Electrolyte Interphase on the Surface of Si@C Anodes by Binary Electrolyte Additives.

Si@C as a high specific capacity anode material for lithium batteries (LIBs) has attracted a lot of attention. However, the severe volume change during lithium de-embedding causes repeated rupture/reconstruction of the solid electrolyte interphase (SEI), resulting in poor cycling stability of the Si-based battery system and thus hindering its application in commercial batteries. Using electrolyte additives to form an excellent SEI is considered to be a cost-effective method to meet this challenge. Here, the classical film-forming additive vinyl carbonate (VC), and the newly emerging lithium salt additive lithium difluorophosphate (LiDFP), are chosen as synergistic additives to improve the electrode-electrolyte interface properties. Final results show that the VC additive generates flexible polycarbonate components at the electrode/electrolyte interface, preventing the fragmentation of Si particles. However, the organic components show high impedance, inhibiting the fast transport of Li+. This defect can be supplemented from the decomposition substances of the LiDFP additive. The derived inorganic products, such as LiF and Li3PO4, can strengthen the reaction kinetics of the electrode, reduce the interfacial impedance, and promote the Li+ transport. Thus, the synergistic effect of VC and LiDFP additives builds an effective SEI with good flexibility and high ionic conductivity and then significantly improves the cycling and rate stability of Si@C anodes. The experimental results show that the utilization of LiDFP and VC additives to modify the Si@C anode interface enhances the capacity retention of the Si@C/Li half-cell after 100 cycles from 68.2% to 85.1%. Besides, the possible mechanism of action between VC and LiDFP is proposed by using the spectral characterization technique and density functional theory (DFT) calculations. This research opens up a new possibility for improvement of SEI, and provides a simple way to achieve high-performance Si-based LIBs.

Operando Investigation of Solid Electrolyte Interphase Formation, Dynamic Evolution, and Degradation During Lithium Plating/Stripping.

The solid electrolyte interphase (SEI) dictates the stability and cycling performance of highly reactive battery electrodes. Characterization of the thin, dynamic, and environmentally sensitive nature of the SEI presents a formidable challenge, which calls for the use of microscopic, time-resolved operando methods. Herein, we employ scanning electrochemical microscopy (SECM) to directly probe the heterogeneous surface electronic conductivity during SEI formation and degradation. Complementary operando electrochemical quartz crystal microbalance (EQCM) and ex situ X-ray photoelectron spectroscopy (XPS) provide comprehensive analysis of the dynamic size and compositional evolution of the complex interfacial microstructure. We have found that stable anode passivation occurs at potentials of 0.5 V vs Li/Li+, even in cases where anion decomposition and interphase formation occur above 1.0 V. We investigated the bidirectional relationship between the SEI and lithium plating-stripping, finding that plating-stripping ruptures the SEI. The current efficiency of this reaction is correlated to the anodic stability of the SEI, highlighting the interdependent relationship between the two. We anticipate this work will provide critical insights on the rational design of stable and effective SEI layers for safe, fast-charging, and long-lifetime lithium metal batteries.

Vanillin: An Effective Additive to Improve the Longevity of Zn Metal Anode in a 30 m ZnCl2 Electrolyte

AbstractIt remains a challenge to design aqueous electrolytes to secure the complete reversibility of zinc metal anodes. The concentrated water‐in‐salt electrolytes, e.g., 30 m ZnCl2, are promising candidates to address the challenges of the Zn metal anode. However, the pure 30 m ZnCl2 electrolyte fails to deliver a smooth surface morphology and a practically relevant Coulombic efficiency. Herein, it is reported that a small concentration of vanillin, 5 mg mLwater−1, added to 30 m ZnCl2 transforms the reversibility of Zn metal anode by eliminating dendrites, lowering the Hammett acidity, and forming an effective solid electrolyte interphase. The presence of vanillin in the electrolyte enables the Zn metal anode to exhibit a high Coulombic efficiency of 99.34% at a low current density of 0.2 mA cm−2, at which the impacts of the hydrogen evolution reaction are allowed to play out. Using this new electrolyte, a full cell Zn metal battery with an anode/cathode capacity (N/P) ratio of 2:1 demonstrates no capacity fading over 800 cycles.

Constructing Solid Electrolyte Interphase for Aqueous Zinc Batteries

AbstractProblems of zinc anode including dendrite and hydrogen evolution seriously degrade the performance of zinc batteries. Solid electrolyte interphase (SEI), which plays a key role in achieving high reversibility of lithium anode in aprotic organic solvent, is also beneficial to performance improvement of zinc anode in aqueous electrolyte. However, various studies about interphase for zinc electrode is quite fragmented, and lack of deep understanding on root causes or general design rules for SEI construction. And water molecules with high reactivity brings serious challenge to the effective SEI construction. Here, we reviewed the brief development history of zinc batteries firstly, then summarized the approaches to construct SEI in aqueous electrolyte. Furthermore, the formation mechanisms behind approaches are systematically analyzed, together with discussion on the SEI components and evaluation on electrochemical performance of zinc anode with various types of SEI. Meanwhile, the challenge between lab and industrialization are also discussed.

Constructing Solid Electrolyte Interphase for Aqueous Zinc Batteries.

Problems of zinc anode including dendrite and hydrogen evolution seriously degrade the performance of zinc batteries. Solid electrolyte interphase (SEI), which plays a key role in achieving high reversibility of lithium anode in aprotic organic solvent, is also beneficial to performance improvement of zinc anode in aqueous electrolyte. However, various studies about interphase for zinc electrode is quite fragmented, and lack of deep understanding on root causes or general design rules for SEI construction. And water molecules with high reactivity brings serious challenge to the effective SEI construction. Here, we reviewed the brief development history of zinc batteries firstly, then summarized the approaches to construct SEI in aqueous electrolyte. Furthermore, the formation mechanisms behind approaches are systematically analyzed, together with discussion on the SEI components and evaluation on electrochemical performance of zinc anode with various types of SEI. Meanwhile, the challenge between lab and industrialization are also discussed.

The Relationship between Ionic Conductivity and Solvation Structures of Localized High-Concentration Fluorinated Electrolytes for Lithium-Ion Batteries.

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

Effect of prelithiation with passivated lithium metal powder on passivation films on high-energy NMC-811 and SiCx electrodes

The effect of prelithiation using passivated lithium metal powder (PLMP) pressed onto SiCx anodes is reported for NMC-811‖ SiCx cells with high energy mass loadings. The effect of prelithiation degree and storage time after cell assembly on the formation and growth of the solid electrolyte interphase (SEI) was elucidated by impedance spectroscopy (EIS) and operando solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy, which allowed determining the optimal storage period for the prelithiated cells. The galvanostatic intermittent titration technique (GITT) was used to compare apparent Li+ diffusion coefficients in prelithiated and non-prelithiated SiCx electrodes. Furthermore, we show that the electrochemical performance of NMC-811‖ SiCx cells can be dramatically improved by prelithiation using PLMP. In particular, cycle life at 80% state of health (SoH) is almost tripled, increasing from 80 to 228 cycles. Moreover, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray (EDX) analysis show that the composition of the cathode electrolyte interphase (CEI) is also markedly modified compared with non-prelithiated reference cells. In particular, the amount of LixPFyOz species is reduced as prelithiation using PLMP promotes a more effective SEI layer on the SiCx electrode, richer in LiF and Li3PO4, and richer in organic components that probably also contribute to the enhanced cycling stability.

Critical roles of synthesis temperature and an effective solid electrolyte interphase in improving the electrochemical performance of carbon coated Fe3BO5 anode at high C-rates

Samples of core/yolk-shell structured, carbon-coated vonsenite (Fe3BO5) are synthesized by the solid-state method and utilized as conversion-type anode materials. The core consists of vonsenite nanoparticles, while the shell is composed of a defective (partially graphitized) carbon layer. A higher synthetic temperature leads to the formation of larger amounts of metallic impurities as a result of the carbothermal reduction. The electrochemical characteristics of the sample synthesized at a lower temperature (600 °C) are better than those of the samples synthesized at higher temperatures and without the carbon coating. This can be attributed to the smaller-sized crystallites having the least amount of metallic impurities and a better-formed solid electrolyte interphase (SEI). This optimized sample demonstrates an outstanding reversible specific discharge capacity of 976 mAh g-1 at a current density of 0.05 A g-1. Long cyclability test at an ultra-high C-rate of 5 A g-1 outlines the critical role of an effective SEI and carbon coating. Remarkably, this sample is able to sustain even further electrochemical abuse, and shows electrochemical activity up to a C-rate of 20 A g-1, thus validating the usefulness of this material as a safe and stable anode for fast charging-discharging Li-ion battery applications.

Regulating Inorganic and Organic Components to Build Amorphous-ZnFx Enriched Solid-Electrolyte Interphase for Highly Reversible Zn Metal Chemistry.

The introduction of inorganic crystallites into a solid-electrolyte interphase (SEI) is an effective strategy for improving the reversibility of the Zn metal anode (ZMA). However, the structure-performance relationship of the SEI is not fully understood because the existing forms of its inorganic and organic components in their pristine states are not resolved. Here, a highly effective SEI is constructed for ZMA using a bisolvent electrolyte and resolved its composition/structure by cryogenic transmission electron microscopy. This highly fluorinated SEI with amorphous inorganic ZnFx uniformly distributed in the organic matrix is largely different from the common mosaic and multilayer SEIs with crystalline inorganics. It features improved structural integrity, mechanical toughness, and Zn2+ ion conductivity. Consequently, the ZMA exhibits excellent reversibility with an enhanced plating/stripping Coulombic efficiency of 99.8%. The ZMA-based full cell achieves a high Zn utilization ratio of 54% at a practical areal capacity of 3.2mAhcm-2 and stable cycling over 1800h during which the accumulated capacity reached 5600mAhcm-2 . This research highlights the detailed structure and composition of amorphous SEIs for highly reversible metal anodes.

A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High‐Concentration Electrolytes over Electrochemical Performance of Lithium‐Ion Batteries

AbstractLocalized high‐concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)‐ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.

A Systematic Study on the Effects of Solvating Solvents and Additives in Localized High-Concentration Electrolytes over Electrochemical Performance of Lithium-Ion Batteries.

Localized high-concentration electrolytes (LHCEs) based on five different types of solvents were systematically studied and compared in lithium (Li)-ion batteries (LIBs). The unique solvation structure of LHCEs promotes the participation of Li salt in forming solid electrolyte interphase (SEI) on graphite (Gr) anode, which enables solvents previously considered incompatible with Gr to achieve reversible lithiation/delithiation. However, the long cyclability of LIBs is still subject to the intrinsic properties of the solvent species in LHCEs. Such issue can be readily resolved by introducing a small amount of additive into LHCEs. The synergetic decompositions of Li salt, solvating solvent and additive yield effective SEIs and cathode electrolyte interphases (CEIs) in most of the studied LHCEs. This study reveals that both the structure and the composition of solvation sheaths in LHCEs have significant effect on SEI and CEI, and consequently, the cycle life of energetically dense LIBs.

Solid electrolyte interphase-ization of Mg2+-blocking layers for lithium ions in anode-free rechargeable lithium metal batteries

A novel concept of solid electrolyte interphase (SEI)-ization of Mg2+-blocking layers for Li+ ions and its effect on their deposition in anode-free rechargeable Li-metal batteries (AFLMBs) has been introduced. The deposition quality of Li on Cu current collectors (CCs) has been improved by the addition of a moderate amount of Mg(N(CF3SO2)2)2 co-salt in Li+-containing carbonate-based electrolytes (Li–Mg electrolytes). Additional analyses revealed that thin, dense, and stable surface layers exhibiting permeability for Li+ and impermeability for Mg2+ ions were formed in Li–Mg electrolytes, significantly suppressing the Li dendrite growth and enhancing the deposited Li metal/Cu CC surface binding. As a result, the Mg2+-blocking layers acted as effective SEI layers from the perspective of Li+ ions, positively influencing the electrochemical performance of the AFLMB full cells.

Lithiated Copper Polyphthalocyanine with Extended π‐Conjugation Induces LiF‐Rich Solid Electrolyte Interphase toward Long‐Life Solid‐State Lithium‐Metal Batteries

AbstractThe composition of the solid electrolyte interphase (SEI) is crucial to stably operate solid‐state batteries based on lithium‐metal anodes. In this work, the redox state of the PVDF‐b‐PTFE (PVT) solid polymer electrolyte is regulated by introducing fully conjugated copper polyphthalocyanine metal (CuPcLi), improving the electron transfer kinetics to accelerate the decomposition of fluorinated ingredients. As a result, an effective SEI with enriched lithium fluoride forms in situ at the Li/electrolyte interface, which enhances the Li‐ion transport kinetics and regulates the lithium deposition behavior, delivering ultra‐stable lithium plating/stripping performance over 2000 h in the Li//Li half‐cell. In addition, the chemisorption between Cu2+and O atoms from TFSI−restrains the movement of anions in the electrolyte, and the CuPcLi improves the lithium ion release, exhibiting a high lithium‐ion conductivity of 0.8 mS cm−1and a high lithium‐ion transference number of 0.74. As a result, the solid polymer electrolyte of PVT‐10CuPcLi paired with LiFePO4delivers fantastic cyclic performance with a capacity retention of 92% even after 1000 cycles at 1 C at room temperature. When paired with high‐voltage LiNi0.6Co0.2Mn0.2O2(NCM622) cathode, the cells can be operated at 1 C with superior capacity retention over 88% after 300 cycles.

Effect of the Electric Double Layer (EDL) in Multicomponent Electrolyte Reduction and Solid Electrolyte Interphase (SEI) Formation in Lithium Batteries

Electrolytes, consisting of salts, solvents, and additives, must form a stable solid electrolyte interphase (SEI) to ensure the performance and durability of lithium(Li)-ion batteries. However, the electric double layer (EDL) structure near charged surfaces is still unsolved, despite its importance in dictating the species being reduced for SEI formation near a negative electrode. In this work, a newly developed model was used to illustrate the effect of EDL on SEI formation in two essential electrolytes, the carbonate-based electrolyte for Li-ion batteries and the ether-based electrolyte for batteries with Li-metal anodes. Both electrolytes have fluoroethylene carbonate (FEC) as a common additive to form the beneficial F-containing SEI component (e.g., LiF). However, the role of FEC drastically differs in these electrolytes. FEC is an effective SEI modifier for the carbonate-based electrolyte by being the only F-containing species entering the EDL and being reduced, as the anion (PF6-) will not enter the EDL. For the ether-based electrolyte, both the anion (TFSI-) and FEC can enter the EDL and be reduced. The competition of the two species within the EDL due to the surface charge and temperature leads to a unique temperature effect observed in prior experiments: the FEC additive is more effective in modulating SEI components at a low temperature (-40 °C) than at room temperature (20 °C) in the ether-based electrolyte. These collective quantitative agreements with experiments emphasize the importance of incorporating the effect of the EDL in multicomponent electrolyte reduction reactions in simulations/experiments to predict/control the formation of the SEI layer.

Effective SEI Formation via Phosphazene‐Based Electrolyte Additives for Stabilizing Silicon‐Based Lithium‐Ion Batteries

AbstractSilicon, 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.

Molecular dynamics simulations of fluoroethylene carbonate and vinylene carbonate as electrolyte additives for Li-ion batteries

ABSTRACT Contemporary electrolyte additives have captivated the attention of researchers since additives were reported to play a very crucial role in supporting the formation of an effective solid electrolyte interphase (SEI) in the case of silicon if used as an anode. The choice of a good solvent with additives demonstrates a significant impact on the solvation and diffusivity of lithium ions. Fluoroethylene carbonate (FEC) and Vinylene carbonate (VC) were extensively used additives for increasing the lifespan of Li-ion batteries (LIBs). In the current study, structural, dynamical, and transport properties of six different systems were investigated by applying classical molecular dynamics (MD) simulations. The properties obtained from the simulations suggested system E consisting of DMC, 1M LiPF, and 10% FEC, to be the best medium for the electrolytes for LIBs, since the diffusion coefficient of Li ions and ionic conductivity of LiPF were estimated to be of high values for the system E. However, before the evaluation of the transport properties, the structural properties in terms of radial distribution functions and spatial distribution functions were evaluated for DMC molecules with reference to DMC, Li, and PF ions. The structure data were also found to be in fair agreement with experimental and previous simulation results reported so far. Based on the finding of this study, it was suggested that DMC as a solvent with a 10% FEC additive could be considered a good medium for electrolytes for the improved performance of LIBs compared to VC as an additive to DMC.

Deciphering the effects of electrolyte concentration on the performance of lithium batteries by correlative surface characterization.

The formation of solid electrolyte interphase (SEI) and lithium ion intercalation are two crucial processes in lithium ion batteries. Given the complexity and challenges involved in investigating real batteries, a combination of model batteries comprising well-defined ultrathin graphite electrodes with surface-sensitive techniques can provide valuable information on these processes. Here, a comparative study of the performance of batteries using regular- and high-concentration electrolytes (RCE and HCE) is presented, aided by a myriad of correlative surface science techniques. It is found that the SEI formed in HCE possesses a thinner organic layer and more inorganic substances. Such an effective SEI protects the graphite electrode and facilitates the processes of Li+ intercalation/deintercalation, thereby improving the reversibility and cycling stability of the battery, superior to those with RCE. Moreover, the battery performance can be readily tuned by switching the electrolytes. The good cycling stability of the battery can still be maintained in RCE after the preformation of a robust SEI on the ultrathin graphite electrode in HCE. This work highlights the importance of electrolyte-modulated SEI formation to battery performance and provides powerful platforms to comprehensively study the SEI formation and ion intercalation processes.

Insights into Electrolytic Pre-Lithiation: A Thorough Analysis Using Silicon Thin Film Anodes.

Pre-lithiation via electrolysis, herein defined as electrolytic pre-lithiation, using cost-efficient electrolytes based on lithium chloride (LiCl), is successfully demonstrated as a proof-of-concept for enabling lithium-ion battery full-cells with high silicon content negative electrodes. An electrolyte for pre-lithiation based on γ-butyrolactone and LiCl is optimized using boron-containing additives (lithium bis(oxalato)borate, lithium difluoro(oxalate)borate) and CO2 with respect to the formation of a protective solid electrolyte interphase (SEI) on silicon thin films as model electrodes. Reversible lithiation in Si||Li metal cells is demonstrated with Coulombic efficiencies (CEff ) of 95-96% for optimized electrolytes comparable to 1 m LiPF6 /EC:EMC 3:7. Formation of an effective SEI is shown by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). electrolytic pre-lithiation experiments show that notable amounts of the gaseous product Cl2 dissolve in the electrolyte leading to a self-discharge Cl2 /Cl- shuttle mechanism between the electrodes lowering pre-lithiation efficiency and causing current collector corrosion. However, no significant degradation of the Si active material and the SEI due to contact with elemental chlorine is found by SEM, impedance, and XPS. In NCM111||Si full-cells, the capacity retention in the 100th cycle can be significantly increased from 54% to 78% by electrolytic pre-lithiation, compared to reference cells without pre-lithiation of Si.