Properties Of Solid Electrolyte Interphase Research Articles

New Nitrate Additive Enabling Highly Stable and Conductive SEI for Fast‐Charging Lithium Metal Batteries

AbstractPolyester‐based electrolytes formed via in situ polymerization, have been regarded as one of the most promising solid electrolyte systems. Nevertheless, it is still a great challenge to address the issue of their high reactivity with metallic lithium anode by optimizing the components and properties of solid electrolyte interphase (SEI). Herein, a new class of N‐containing additive, isopropyl nitrate (ISPN) that can be miscible with ester solvents is demonstrated, and a chemically stable and ion‐conductive LiF‐Li3N composite SEI is constructed. In addition, ISPN can induce the formation of anion‐enriched solvation structures and reduces the desolvation barrier of Li+, resulting in fast transport of Li+. With the addition of ISPN, ionic conductivity of the electrolyte has nearly doubled, reaching as high as 5.3 × 10−4 S cm−1. What's more, the LiFePO4 (LFP)|ISPN‐PTA|Li cell exhibits exceptional cycle stability and fast charging capabilities, maintaining stable cycling for 850 cycles at 10 C rate. Even when paired with the high‐voltage cathode, the LiNi0.6Co0.2Mn0.2O2 (NCM622)|ISPN‐PTA|Li cell achieves an impressive capacity retention of 97.59% after 165 cycles at 5 C. This study offers a novel approach for ester‐based polymer electrolytes, paving the way toward the development of stable and high‐energy Li metal battery technologies.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically‐Stable Low‐Temperature Lithium‐Ion Batteries

AbstractGraphite (Gr)‐based lithium‐ion batteries with admirable electrochemical performance below −20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+‐solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically‐stable solid electrolyte interphase (SEI) without compromising strong Li+‐solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature‐dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low‐temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e−) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4‐based, inorganics‐enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e− blocking and rapid desolvation, and as a result, much suppressed Li‐metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low‐temperature battery performances. Overall, our work originally provides visualized guides to improve low‐temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

(Invited) Multiscale Modeling and Machine Learning Investigation of Battery Interphase Dynamics

In recent years, the solid electrolyte interphase (SEI) has emerged as a critical component in the development of efficient and durable electrochemical storage systems. Understanding the dynamics and properties of SEI is paramount for the enhancement of battery performance and longevity. This study presents a novel multi-scale simulation approach, incorporating Hybrid Ab Initio Reactive Molecular Dynamics (HAIR), to elucidate the intricate mechanisms governing SEI formation and evolution. Our methodology involves simulation under operando conditions, closely mimicking real-world scenarios, to provide insights into the molecular interactions and structural changes within the SEI layer. By leveraging HAIR, we bridge the gap between quantum mechanical precision and the expansive temporal-spatial scales of molecular dynamics, facilitating a more comprehensive understanding of SEI behavior [1,2]. Furthermore, we integrate machine learning (ML) techniques to refine our predictive models. These ML algorithms are trained on a rich dataset derived from HAIR simulations, enabling the prediction of key electrochemical properties, including chemical composition and electronic structure. The application of machine learning significantly enhances our ability to forecast SEI evolution under various operational conditions. A critical aspect of our research is the prediction of X-ray photoelectron spectroscopy (XPS) and Coulombic Efficiency (CE) outcomes [3]. By simulating these properties, we provide valuable predictions that align closely with experimental data, thereby validating our simulation framework. In summary, our study offers a groundbreaking perspective on SEI analysis, merging the fidelity of HAIR with the predictive power of machine learning. This approach not only deepens our fundamental understanding of SEI properties but also paves the way for the development of more efficient and durable electrochemical storage systems. Our findings hold significant implications for the future of battery technology and underscore the importance of advanced simulation techniques in electrochemical research. Reference 1. Liu Y; Yu PP; Sun QT; Wu Y; Xie M; Yang H; Cheng T*; Goddard WA; ACS Energy Lett. 2021, 6, 2320.2. Liu Y; Sun QT; Yue BT; Zhang YY; Cheng T*; J. Mater. Chem. A 2023, 11, 14640.3. Sun QT; Xiang Y; Liu Y; Xu L; Leng TL; Ye YF; Fortunelli A*; Goddard WA*; Cheng T*; J. Phys. Chem. Lett. 2022, 13, 8047. Figure 1

Investigating Temperature-Dependent Dynamics of SEI Growth and Battery Degradation

Several studies have contributed to the current understanding of the temperature-dependent behavior of solid-electrolyte interphase (SEI) formation in lithium-ion batteries and its impact on battery capacity and lifespan. Liu et al. developed a thermal-electrochemical model that revealed the complex interplay between diffusivity, reaction kinetics, and temperature on SEI growth1. Leng et al. presented an electrochemistry-based electrical model to examine the temperature's effect on battery aging2. Alipour et al. reviewed temperature-dependent electrochemical properties3, while Lubhani Mishra et al. provided a detailed physics-based analysis of battery degradation and temperature inhomogeneities4. These studies collectively indicate higher temperatures accelerating and promoting growth of compact and less permeable SEI structures leading to an increase in capacity loss and cell resistance, and lower temperatures resulting in slow ionic transport through the SEI also causing higher ohmic loss. In the present work, we study SEI growth and resulting effect on battery capacity fade using continuum scale modeling under the assumption of constant battery cell temperature as well as considering actual dynamically changing temperature data from experiments. SEI growth under these two considerations is compared and the comparison is used in determining scenarios where considering dynamically varying temperature is crucial for accuracy. The detailed analysis of the internal states from the simulation results contributes to the understanding of the effect of the thermal dynamics on battery cell degradation due to SEI growth. To achieve these objectives, a physics-based model, specifically the Single Particle Model (SPM), is utilized. The model uses temporal temperature data obtained from past experimental studies as well as temperature dependent properties of SEI provided in the literature as inputs for this investigation. The ultimate aim of this study is to better understand how temperature influences SEI characteristics, thereby contributing to improved battery performance and longevity across diverse thermal environments. References Liu, L., Park, J., Lin, X., Sastry, A. M., & Lu, W. (2014). A thermal-electrochemical model that gives spatial-dependent growth of solid electrolyte interphase in a Li-ion battery. Journal of power sources, 268, 482-490.Leng, F., Tan, C. M., & Pecht, M. (2015). Effect of temperature on the aging rate of Li-ion battery operating above room temperature. Scientific reports, 5(1), 12967.Alipour, M., Ziebert, C., Conte, F. V., & Kizilel, R. (2020). A review on temperature-dependent electrochemical properties, aging, and performance of lithium-ion cells. Batteries, 6(3), 35.Mishra, L., Subramaniam, A., Jang, T., Garrick, T. R., & Subramanian, V. R. (2022, October). Model Development for Temperature-Dependent Degradation in Large Format Lithium-Ion Batteries. In Electrochemical Society Meeting s 242 (No. 28, pp. 1075-1075). The Electrochemical Society, Inc.

Effect of Solid Electrolyte Interphase Heterogeneity on the Lithium Deposition Dynamic: A Phase-Field Approach

Lithium dendrites formation is an inherent drawback in the development of all solid-state lithium batteries technology. These issues remain unsolved due to the multiple and competing troubleshooting during lithium plating and stripping. The inhomogeneous mechanical and chemical properties of the Solid Electrolyte Interphase (SEI) [1] lead to uneven current distribution and unsmooth lithium plating and stripping [2,3,4]. A fine understanding of the relationship between the SEI composition and the dynamic of dendrite growth under polarization is not well established. All computational studies are based on homogeneous SEI on the top of the lithium electrode [5, 6]. The local deformation of the SEI under polarization may lead to several mechanical defect such as cracking and therefore a dendrite nucleation. To link the crack dynamic to the current density, we developed a novel multiphase-field approach in order to probe the first instants of the dendrite formation. Indicative variables are used in order to define dynamics phases of lithium electrode (in black on the figure), electrolyte (green) and two SEI domains (blue and red) and their interaction. This method allows to consider the SEI as a multi-domains object, where each region has its own (chemical, mechanical and ion transport) properties. Our results show that a smaller current density result in homogeneous deposition (top row on the figure), where a high current leads to a fracture of the SEI and a dendrite growth (bottom row). We highlighted the influence of SEI properties such as the thickness, the ratio between SEI domains or the surface tension on the deposition dynamic.On the left of the figure, the simulation box constituted of lithium (in black color) in contact with a solid electrolyte interphase constituted of a dense (blue) and porous (red) SEI, and electrolyte (green). The dynamic evolution of lithium and SEI, under low and high current density 0.12 and 12 mA/cm² are reported on top and bottom figures respectively.

Rational Design of Electrolyte Additives for Improved Solid Electrolyte Interphase Formation on Graphite Anodes: A Study of 1,3,6-Hexanetrinitrile

The construction of a thin, uniform, and robust solid electrolyte interphase (SEI) film on the surface of active materials is pivotal for enhancing the overall performance of lithium-ion batteries (LiBs). However, conventional electrolytes often fail to achieve the desired SEI characteristics. In this work, we introduced 1,3,6-hexanetrinitrile (HTCN) in the baseline electrolyte (BE) of 1.0 M LiPF6 in Ethylene Carbonate/Dimethyl Carbonate (EC/DMC) (3:7 by volume) with 5 wt.% fluoroethylene carbonate (FEC), denoted as BE-FH. By systematically investigating the influence of FEC: HTCN weight ratios on the electrochemical performance of graphite anodes, we identified an optimal composition (FEC:HTCN = 5:4 by weight, denoted as BE-FH54) that demonstrated greatly improved initial Coulombic efficiency, rate capability, and cycling stability compared with the baseline electrolyte. Deviations from the optimal FEC:HTCN ratio resulted in the formation of either small cracks or excessively thick SEI layers. The enhanced performance of BE-FH54-based LiB is mainly ascribed to the synergistic effect of FEC and HTCN in forming a robust, thin, homogeneous, and ion-conducting SEI. This research highlights the importance of rational electrolyte design in enhancing the electrochemical performance of graphite anodes in LiBs and provides insights into the role of nitrile-based additives in modulating the SEI properties.

Lamellar sulfonated acid polymer-initiated in situ construction of robust LiF-rich SEI enabling superior charge transport for ultrastable and fast charging silicon anodes

The extreme volume expansion of the silicon (Si) anodes during repeated cycles seriously induces undesirable interfacial side reactions, forming an unstable solid electrolyte interphase (SEI) that degrades the electrode integrity and cycle stability in lithium-ion batteries, limiting their practical applications. Despite considerable efforts to stabilize the SEI through surface modification, challenges persist in the development of high-performance Si anodes that effectively regulate intrinsic SEI properties and simultaneously facilitate electron/ion transport. Here, a highly conductive and organic electrolyte-compatible lamellar p-toluenesulfonic acid-doped polyaniline (pTAP) layer is proposed for constructing a robust artificial SEI on Si nanoparticles to achieve fast charging, long-term cycle lifespan and high areal capacity. The spatially uniform pTAP layer, formed through a facile direct-encapsulation approach assisted by enriched hydrogen bonding, contributes to the effective formation of in situ SEI with an even distribution of the LiF-rich phase in its interlamination spaces. Furthermore, the integrated artificial SEI facilitates isotropic ion/electron transport, increased robustness, and effectively dissipates stress from volume changes. Consequently, a notably high rate performance of 570 mA h g−1, even at a substantially high current density of 10 A g−1, is achieved with excellent cyclic stability by showing a superior capacity over 1430 mA h g−1 at 1 A g−1 after 250 cycles and a high areal capacity of ca. 2 mA h cm−2 at 0.5 C in a full cell system. This study demonstrates that the rational design of conductive polymers with SEI modulation for surface protection has great potential for use in high-energy-density Si anodes.

Effects of Electrolyte Solvent Composition on Solid Electrolyte Interphase Properties in Lithium Metal Batteries: Focusing on Ethylene Carbonate to Ethyl Methyl Carbonate Ratios

This study investigated the influence of variations in the mixing ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) on the composition and effectiveness of the solid electrolyte interphase (SEI) in lithium-metal batteries. The SEI is crucial for battery performance, as it prevents continuous electrolyte decomposition and inhibits the growth of lithium dendrites, which can cause internal short circuits leading to battery failure. Although the properties of the SEI largely depend on the electrolyte solvent, the influence of the EC:EMC ratio on SEI properties has not yet been elucidated. Through electrochemical testing, ionic conductivity measurements, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the formation of Li2CO3, LiF, and organolithium compounds on lithium surfaces was systematically analyzed. This study demonstrated that the EC:EMC ratio significantly affected the SEI structure, primarily owing to the promotion of the formation of a denser SEI layer. Specifically, the ratios of 1:1 and 1:3 facilitated a uniform distribution and prevalence of Li2CO3 and LiF throughout the SEI, thereby affecting cell performance. Thus, precise control of the EC:EMC ratio is essential for enhancing the mechanical robustness and electrochemical stability of the SEI, thereby providing valuable insights into the factors that either enhance or impede effective SEI formation.

Elucidating the role of polar functional groups in fluorinated polymer artificial interphase for stable lithium anodes

The properties of solid electrolyte interphase (SEI) are pivotal for stable lithium (Li) metal anodes. However, the process of formation and ion transport behavior of lithium fluoride (LiF) through the polar groups of organic fluorinated artificial SEI has not been clearly elucidated. Herein we demonstrate that the key role of polar functional groups in fluorinated polymer artificial SEI (FPASEI) is elucidated by using 2,2,2-trifluoroethylacrylate (TFEA) through radical polymerization. Density functional theory and ab initio molecular dynamics calculations demonstrate that the abundant CO polar groups in TFEA contribute a large number of electrons, thereby facilitating the degradation kinetics of CF bond cleavage in lithium bis(trifluoromethanesulfonyl)imide salt to yield LiF. Moreover, the presence of CF, COC, and CO groups in TFEA facilitate the migration of Li+ towards interchain regions through cation-dipole interaction, leading to dendrite-free Li deposition. The implementation of FPASEI in a Li||Li cell results in 500 h of Li plating/stripping cycling at 1 mA cm−2 and retains a capacity retention rate of 80 % after 265 cycles in Li||LiNi0.8Co0.1Mn0.1O2 cell. This study not only emphasizes the critical role of polar groups in artificial SEI but also presents a promising strategy for achieving stable Li metal batteries.

Revealing Lithium Nitrate-Mediated Solid-Electrolyte Interphase of Lithium Metal Anode via Cryogenic Transmission Electron Microscopy.

The cycle stability of lithium metal anode (LMA) largely depends on solid-electrolyte interphase (SEI). Electrolyte engineering is a common strategy to adjust SEI properties, yet understanding its impact is challenging due to limited knowledge on ultrafine SEI structures. Herein, using cryogenic transmission electron microscopy, we reveal the atomic-level SEI structure of LMA in ether-based electrolytes, focusing on the role of LiNO3 additives in SEI modulation at different temperature (25 and 50 °C). Poor cycle stability of LMA in the baseline electrolyte without LiNO3 additives stems from the Li2CO3-rich mosaic-type SEI. Increased LiNO3 content and elevated operating temperature enhance cyclic performance by forming bilayer or multilayer SEI structures via preferential LiNO3 decomposition, but may thicken the SEI, leading to reduced initial Coulombic efficiency and increased overpotential. The optimal SEI features a multilayer structure with Li2O-rich inner layer and closely packed grains in the outer layer, minimizing electrolyte decomposition or corrosion.

Additive-Driven Nanoscale Architecture of Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy.

In Li metal batteries (LMBs), which boast the highest theoretical capacity, the chemical structure of the solid electrolyte interphase (SEI) serves as the key component that governs the growth of reactive Li. Various types of additives have been developed for electrolyte optimization, representing one of the most effective strategies to enhance the SEI properties for stable Li plating. However, as advanced electrolyte systems become more chemically complicated, the use of additives is empirically optimized. Indeed, their role in SEI formation and the resulting cycle life of LMBs are not well-understood. In this study, we employed cryogenic transmission electron microscopy combined with Raman spectroscopy, theoretical studies including molecular dynamics (MD) simulations and density functional theory (DFT) calculations, and electrochemical measurements to explore the nanoscale architecture of SEI modified by the most representative additives, lithium nitrate (LiNO3) and vinylene carbonate (VC), applied in a localized high-concentration electrolyte. We found that LiNO3 and VC play distinct roles in forming the SEI, governing the solvation structure, and influencing the kinetics of electrochemical reduction. Their collaboration leads to the desired SEI, ensuring prolonged cycle performance for LMBs. Moreover, we propose mechanisms for different Li growth and cycling behaviors that are determined by the physicochemical properties of SEI, such as uniformity, elasticity, and ionic conductivity. Our findings provide critical insights into the appropriate use of additives, particularly regarding their chemical compatibility.

Li-Ion Battery Material Impedance Analysis II: Graphite and Solid Electrolyte Interphase Kinetics

Li-ion battery graphite electrodes form a solid-electrolyte-interphase (SEI) which is vital in protecting the stability and efficiency of the cell. The SEI properties have been studied extensively in the context of formation and additives, however studying its kinetic features after formation have been neglected. In this study we show the dynamic resistive behavior of the SEI after formation. Via electrochemical impedance spectroscopy measurements on Cu-foil after SEI formation we show how the SEI shows a potential-dependent resistance which can be explained by a change in charge carriers (Li+) in the SEI. Additional measurements on graphite exhibit a similar behavior and allow us to separate the charge transfer kinetics from the SEI resistance, showing that the SEI resistance is the dominating resistance in the graphite kinetics. Measurements on pre-formed electrodes also show how the SEI resistance changes when in contact with electrolyte of different LiPF6 salt concentrations, with the resistance decreasing for increasing salt concentrations. Ultimately, we show that the SEI resistance affects Li-plating by acting as an offset to the plating reaction but does not affect the nucleation overpotential itself.

Efficient Chemical Prelithiation with Modificatory Li+ Solvation Structure Enabling Spatially Homogeneous SEI toward High Performance SiOx Anode†

Comprehensive SummaryChemical prelithiation is widely proven to be an effective strategy to address the low initial coulombic efficiency (ICE) of promising SiOx anode. Though the reagent composition has been widely explored, the Li+ solvation structure, which practically plays the cornerstone role in the prelithiation ability, rate, uniformility, has rarely been explored. A novel environmentally‐friendly reagent with weak solvent cyclopentyl methyl ether (CPME) is proposed that enables both improved ICE and spatial homogeneous solid electrolyte interphase (SEI). And the prelithiation behavior and mechanism were explored focused on the Li+ solvation structure. Both theoretical investigation and spectroscopic results suggest that weak solvent feature of CPME reduces the solvent coordination number and decreases the Li+ desolvation energy. The optimized Li+ solvation structure enables high‐efficiency prelithiation that ensures the horizontal homogenization and mechanical properties of SEI. Moreover, the accompanied CPME molecules preferentially occupy positions in initial SEI, reducing the likelihood of LiPF6 decomposition and promoting longitudinal homogenization of SEI. Consequently, the efficient and homogenous prelithiation enables impressive ICE of 109.52% and improved cycling performance with 80.77% retained after 300 cycles via just 5 min soaking. Furthermore, the full cells with LiNi0.83Co0.12Mn0.05O2 (NCM831205) cathode display an enhancement in the energy density of 179.74% and up to 648.35 Wh·kg–1.

Surface Work Function Modifier to Modulate Electrolyte Decomposition on Negative Electrode in Lithium‐Ion Batteries

AbstractThe persistent decomposition of electrolytes on graphite and silicon electrodes in lithium‐ion batteries (LIBs) is typically mitigated by the formation of a solid electrolyte interphase (SEI). However, the inadequate formation and chemo‐mechanical degradation of SEI leads to re‐exposure of electrode to electrolyte, contributing to the deterioration of LIBs. To address this issue, tris(2,4‐pentanedionato)indium(III) (InAc) is incorporated into the work function tailoring additive. While conventional additives strengthen the chemo‐mechanical properties of SEI through compositional modifications derived from specific elements, InAc uniquely alters charge transfer across the electrode surface, facilitated by high or low work function layer. This additive establishes an interlayer between the SEI and graphite/SiO surfaces, attributed to its tailored lowest unoccupied molecular orbital energy level. Consequently, the exposure of graphite surface to the electrolyte is minimized by interlayer during cycling. The interlayer possesses a higher work function than lithiated graphite and suppresses further electrolyte decomposition on graphite. In contrast, the interlayer on SiO decreases work function of SiO surface, which promotes the formation of inorganic SEI on SiO. Hence the degradation of SEI is suppressed with LiIn layer at SiO electrode. This leads to a reduction in the ongoing accumulation of SEI, thereby enhancing durability of LIBs.

Nanoscale Visualization of Lithium Plating/Stripping Tuned by On‐site Formed Solid Electrolyte Interphase in All‐Solid‐State Lithium‐Metal Batteries

AbstractThe interfacial processes, mainly the lithium (Li) plating/stripping and the evolution of the solid electrolyte interphase (SEI), are directly related to the performance of all‐solid‐state Li‐metal batteries (ASSLBs). However, the complex processes at solid‐solid interfaces are embedded under the solid‐state electrolyte, making it challenging to analyze the dynamic processes in real time. Here, using in situ electrochemical atomic force microscopy and optical microscopy, we directly visualized the Li plating/stripping/replating behavior, and measured the morphological and mechanical properties of the on‐site formed SEI at nanoscale. Li spheres plating/stripping/replating at the argyrodite solid electrolyte (Li6PS5Cl)/Li electrode interface is coupled with the formation/wrinkling/inflating of the SEI on its surface. Combined with in situ X‐ray photoelectron spectroscopy, details of the stepwise formation and physicochemical properties of SEI on the Li spheres are obtained. It is shown that higher operation rates can decrease the uniformity of the Li+‐conducting networks in the SEI and worsen Li plating/stripping reversibility. By regulating the applied current rates, uniform nucleation and reversible plating/stripping processes can be achieved, leading to the extension of the cycling life. The in situ analysis of the on‐site formed SEI at solid‐solid interfaces provides the correlation between the interfacial evolution and the electrochemical performance in ASSLBs.

Nanoscale Visualization of Lithium Plating/Stripping Tuned by On-site Formed Solid Electrolyte Interphase in All-Solid-State Lithium-Metal Batteries.

The interfacial processes, mainly the lithium (Li) plating/stripping and the evolution of the solid electrolyte interphase (SEI), are directly related to the performance of all-solid-state Li-metal batteries (ASSLBs). However, the complex processes at solid-solid interfaces are embedded under the solid-state electrolyte, making it challenging to analyze the dynamic processes in real time. Here, using in situ electrochemical atomic force microscopy and optical microscopy, we directly visualized the Li plating/stripping/replating behavior, and measured the morphological and mechanical properties of the on-site formed SEI at nanoscale. Li spheres plating/stripping/replating at the argyrodite solid electrolyte (Li6 PS5 Cl)/Li electrode interface is coupled with the formation/wrinkling/inflating of the SEI on its surface. Combined with in situ X-ray photoelectron spectroscopy, details of the stepwise formation and physicochemical properties of SEI on the Li spheres are obtained. It is shown that higher operation rates can decrease the uniformity of the Li+ -conducting networks in the SEI and worsen Li plating/stripping reversibility. By regulating the applied current rates, uniform nucleation and reversible plating/stripping processes can be achieved, leading to the extension of the cycling life. The in situ analysis of the on-site formed SEI at solid-solid interfaces provides the correlation between the interfacial evolution and the electrochemical performance in ASSLBs.

Formation Processes of a Solid Electrolyte Interphase at a Silicon/Sulfide Electrolyte Interface in a Model All-Solid-State Li-Ion Battery.

Understanding the electrochemical reactions at the interface between a Si anode and a solid sulfide electrolyte is essential in improving the cycle stabilities of Si anodes in all-solid-state batteries (ASSBs). Highly dense Si films with very low roughnesses of <1 nm were fabricated at room temperature via cathodic arc plasma deposition, which led to the formation of a Si/sulfide electrolyte model interface. Li (de)alloying through the model interface hardly occurred during the first cycle, whereas it proceeded stably in subsequent cycles. Hard X-ray photoelectron spectroscopy and neutron reflectometry directly revealed that the reduction or oxidation of the interfacial component or Li3PS4 electrolyte occurred during the first cycle. Consequently, an interfacial layer with a thickness of 13 nm and primarily composed of Li2S, SiS2, and P2S5 glasses was formed during the first cycle. The interfacial layer acted as a Li-conductive, electron-insulating solid electrolyte interphase (SEI) that provided reversible (de)lithiation. Our model interface directly demonstrates the electrochemical reaction processes at the Si/Li3PS4 interface and provides insights into the structures and electrochemical properties of SEIs to activate the (de)lithiation of Si anodes using a sulfide electrolyte.

Decoupling Interfacial Kinetics Realizes 5C Fast Charging of Potassium‐Ion Batteries Using Graphite Anode

AbstractImproving interfacial kinetics is the key to realizing extreme fast charging (XFC) of graphite‐based potassium ion batteries (PIBs). The electrolyte engineering is commonly used for solid electrolyte interphase (SEI) design. However, this strategy adjusts both ion solvation structure and (de)solvation kinetics simultaneously, thus making it difficult to explicitly reveal the linkage between SEI properties and interfacial kinetics. Herein, the content of inorganic species in preformed SEI on graphite surface is precisely regulated and uncovered its critical role in improving the interfacial kinetics. The charge transfer kinetics on graphite/electrolyte interphase is found to be the rate limitation step upon XFC. Meanwhile, the increased inorganic species in SEI plays a decisive role in optimizing the charge transfer rather than the kinetics of naked K+ crossing SEI. Through unlocking the anodic charge transfer limitation with ultra‐inorganic rich SEI, the graphite//Prussian blue analogs full cells achieve a superior XFC ability (13 min charge to 80%) with a specific capacity of 103 mAh g−1 at 5 C. This work provides a fundamental understanding of the relationship between SEI properties and interfacial kinetics during XFC, which enables the rational design of SEI chemistry for fast‐charging PIBs.

Insights from Li and Zn systems for advancing Mg and Ca metal batteries.

The inherent limitations of lithium (Li)-ion batteries have sparked interest in exploring alternative technologies, especially those relying on metallic anodes: monovalent Li and divalent zinc (Zn), magnesium (Mg), and calcium (Ca) metals. In particular, Mg and Ca metal batteries offer significant advantages based on the natural abundance of their raw materials and high energy-storage capabilities resulting from the bivalency of the carrier ions. Yet, these battery systems are far from commercialization, and the lack of reliable electrolytes constitutes a primary concern. The formation of ion-insulating passivation layers on these metallic anodes and their inferior desolvation kinetics have long been recognized as formidable hurdles in the way of optimizing the electrolyte composition. These impediments call for innovative strategies in electrolyte engineering and an extensive analysis of the resulting solid-electrolyte-interphase (SEI) layer. In this review, we introduce recent pioneering studies of divalent Mg and Ca metal batteries that have been concerned with these issues. This review particularly focuses on drawing an analogy with Li and Zn metal batteries in terms of the relative advancement and by benchmarking against the strategies developed for these analogous systems. The areas of interest include a fundamental understanding of the thermodynamics and evolution of the morphology of metallic anodes, a correlation between the electrolyte and SEI compositions, state-of-the-art electrolyte strategies to realize reversible (de)plating of Mg and Ca, and new perspectives on the SEI properties and their relevance to corrosion and the calendar life. We finally encourage researchers in the community to delve into these emerging areas by linking with successful stories in the analogous systems, but identifying distinct aspects of Mg and Ca batteries that still require attention.