New Types of Binder for Ceramic Solid Electrolyte Films: Sulfide Electrolyte, Lithium Metal, Interfaces and Cyclability

Bulk-type all solid-state lithium-ion battery electrodes are manufactured by compressing composite powder of active material and solid electrolyte powder. This compression increases contact area between the powder particles and reduces ion transportation resistance in the electrode. In many cases, mechanical characteristics of the solid electrolyte and active material are different, and complex stress distribution is generated in the compressed composite powder. In authors previous studies, ion transportation characteristics of electrode with soft active material and hard active material are studied experimentally and numerically. The electrode with soft active material has high ionic conductivity due to high stress is applied to the solid electrolyte in the electrode and high contact area between solid electrolyte powder is achieved. As showed from this study, Young’s modulus of active material is an important factor of ionic transportation in electrode of all solid-state battery. Based on this result, solid electrolyte the Young's modulus of the solid electrolyte is also an important factor of ionic transportation in electrode. Therefore, in this study, we conducted experiments and numerical simulation of ionic conductivity of the electrode with changing the Young’s modulus of the solid electrolyte to elucidate the influence of Young’s modulus of the solid electrolyte on ionic transportation characteristics of the electrode.Two solid electrolytes are employed in this study. One is sulfide solid electrolyte of Li5.5PS4.5Br1.5. This solid electrolyte is made by mechanical milling with vibration mill and heat treatment. The other is halide solid electrolyte of Li3InCl6. This halide solid electrolyte is made with wet process from LiCl and InCl3. These solid electrolytes are mixed with dummy active material of ZrO2 and nylon. The dummy active materials used to simulate only ionic transportation by a solid electrolyte and mechanical conditions. Young’s modulus of ZrO2 is about 200 GPa and is almost same as Young’s modulus of hard active materials such as LCO and NCM. Young’s modulus of nylon is about 6 GPa and is almost same as Young’s modulus of soft active materials such as graphite. From these two solid electrolytes and two dummy active materials, four dummy electrodes.Fig.1 illustrates effective Young’s modulus of Li5.5PS4.5Br1.5 powder and Li3InCl6 powder measured with changing the applied pressure from 0MPa to 100MPa. From this figure, the Young’s modulus of Li5.5PS4.5Br1.5 is from 100MPa to 700MPa and that of Li3InCl6 is about half of Li5.5PS4.5Br1.5. Therefore, it can be said that, compared to sulfide solid electrolyte, halide solid electrolyte is relatively soft solid electrolyte.Fig.2 illustrates relative ionic conductivity as a function of the volumetric fraction of dummy active material. Here, the ionic conductivity is normalized by the ionic conductivity of pure solid electrolyte (= 0% volumetric fraction of dummy active material). As shown in fig.2 (a), the relative ionic conductivity of sulfide solid electrolyte and halide solid electrolyte are almost same when the dummy active material is soft (nylon). However, in the case with hard dummy active material (ZrO2), as shown in fig.2 (b), the relative ionic conductivity with halide solid electrolyte is lower than that with sulfide solid electrolyte at high dummy active material volumetric fraction. With hard active material, mechanical pillar is generated by active material in the electrode and strain of the solid electrolyte is low. In the case with sulfide solid electrolyte, relatively high stress can be generated with the low strain, but in the case with halide solid electrolyte, stress is relatively low with the low strain. This is because, as shown in fig.1, Young’s modulus of sulfide solid electrolyte is higher than that of the halide solid electrolyte, and high stress for high ionic conductivity can be generated even with low strain in the case with sulfide solid electrolyteThis Study is supported by JKA foundation (2021M-188) Figure 1

Introduction Conventional lithium-ion batteries (LIBs) have found widespread small and large applications. However, safety issues and capacity degradation of the cells, in general, can occur due to the use of toxic and flammable liquid electrolytes [1]. As one of the next-generation LIBs, solid-state lithium batteries (SSBs) have the potential to replace liquid electrolyte LIBs due to their safety and potentially high energy density [2]. The key component of SSBs is the solid-state electrolyte (SSE). Sulfide and halide-based solid electrolytes are among the hot topics in solid electrolyte research for SSBs. Despite the advantages of solid electrolytes, such as good compatibility with high-voltage cathode materials and soft fabrication. However, the poor chemical and electrochemical stability of sulfide and halide-based solid electrolytes towards Li metal has a critical problem that causes the degradation of the lithium/solid electrolyte interface due to the formation of side reaction components that leads to inhibiting lithium kinetics [3]. Results and Discussion Here, we have shown that a combination of halide and argyrodite (Li6PS5Cl) solid electrolytes can lead to the prevention of the formation of unfavorable interactions between solid electrolytes and lithium metal anode. The combination of halide and argyrodite (Li6PS5Cl) in the Li/Li symmetric cell can stabilize cycle life and increase the high critical current density (CCD) from C/20 to C/2 in comparison with the pure halide and argyrodite electrolytes. Furthermore, compared to the original halide and argyrodite electrolytes, a high initial coulombic efficiency and cycle life can be maintained when combined with a full Li/NCM cell. This approach to improving halide-based SSBs can provide a fairly simple and efficient strategy. Acknowledgements This project has received funding from the European Union's Horizon Europe programme for research and innovation under grant agreement No. 101069681 (HELENA project).

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Nanoscale Mapping of Extrinsic Interfaces in Hybrid Solid Electrolytes

The escalating demand for sustainable energy storage solutions, driven by the depletion of fossil fuels has stimulated extensive research in advanced battery technologies. Over the past two decades, global primary energy consumption, initially satisfied by non-renewables, has raised environmental concerns. Despite the availability of renewable sources like solar and wind, storage challenges propel innovation in batteries. Lithium-ion batteries (LIBs) have gained recognition for their high energy density and cost-effectiveness. However, issues such as safety concerns, dendrite formation, and limited operational temperatures necessitate alternative solutions. A promising approach involves replacing flammable liquid electrolytes with non-flammable solid electrolytes (SEs). SEs represent a transformative shift in battery technology, offering stability, safety, and expanded temperature ranges. They effectively mitigate dendrite growth, enhancing battery reliability and lifespan. SEs also improve energy density, making them crucial for applications like portable gadgets, electric vehicles, and renewable energy storage. However, challenges such as ionic conductivity, chemical and thermal stability, mechanical strength, and manufacturability must be addressed. This review paper briefly identifies SE types, discusses their advantages and disadvantages, and explores ion transport fundamentals and all-solid-state batteries (ASSBs) production challenges. It comprehensively analyzes sulfide SEs (SSEs), focusing on recent advancements, chemical and electrochemical challenges, and potential future improvements. Electrochemical reactions, electrolyte materials, compositions, and cell designs are critically assessed for their impact on battery performance. The review also addresses challenges in ASSB production. The objective is to provide a comprehensive understanding of SSEs, laying the groundwork for advancing sustainable and efficient energy storage systems.

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, high ionic conductivity allowing improved all-solid-state batteries performances at room temperature but suffer of moisture exposure that could induce H2S generation.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1) and the lowest electrochemical potential (-3.03V vs ENH). Ceramic solid electrolytes and especially sulfide composite solid electrolyte have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. At the same time, the chemical nature and composition of ceramic solid electrolyte can affect the dendrite growth by the interfacial chemical and electrochemical stability with lithium metal. In parallel, the sulfide solid electrolyte reacts with all components constituting the positive electrode as active material, electronic conductor, binder, current collector... Hence, all interfaces can generate side reaction, increase of polarisation, and so rapid battery fading. As demonstrated in literature, an important average pressure increase during cycling and aging can’t allow a future commercialisation of this technology. The safety is a crucial point and the generation of H2S in the case of all-solid-state battery based on sulfide electrolyte during scale-up phase and operation must be take into account and evaluated specifically.In this field and since a few years, Hydro-Quebec has decided to conduct specific research on all-solid ceramic batteries and especially in the field of sulfide-based ceramic electrolytes. Based on Hydro-Québec's knowledge with polymers, a solution of all-solid composite battery with ceramic tendency has been developed by generating several industrial properties at the different levels of the battery. The interaction previously observed in positive electrode mixture without binder have been resolved and integrated in slurry. In parallel, the impact between solid electrolyte ceramic film composition, density, reactivity with lithium metal and flexibility were studied to offer high conductivity and easily manipulation. Unlike the general perception that the sulfide electrolyte is not compatible with lithium metal, we successfully stabilized the lithium metal interface reaching the cycle life more than 700 cycles under industry-relevant pressure conditions at moderate temperature under pouch-cell configuration. The constraints of the use of li-ion equipment’s, cost reduction and safety have been considered at each level with quantitative measurements.Different parameters can influence the performances and aging of all solid state ceramic battery. To explore them, various electrochemical technics and associated specific treatments can be developed to extract and identify each phenomenon and ensure the better development of this technology. A specific sequential methodology will be presented with different examples from the materials, interfaces with lithium metal, pseudo-composites and temperature effects up to aging of total all-solid–state ceramic battery based on sulfide technology. The different improvements in positive composite electrode, in solid electrolyte ceramic film and in lithium metal interfaces will be explained. The presentation will show how technical and economical issues of sulfide electrolyte can be addressed to bring the technology closer to the market

As the primary use of Li-ion batteries shifts from small electronic devices to electric vehicles, there is a need to increase the stability and energy density of Li-ion batteries. In order to achieve high energy density, use of lithium metal as an anode has being considered due to its high theoretical capacity (3860 mAh g-1) and low reduction potential (-3.04 V vs. SHE). However, the liquid electrolyte used in Li-ion batteries is not only dangerous due to the risk of fire in case of leakage, but also has the disadvantage of shortening the lifetime of the battery due to the generation of lithium dendrites during cycling when lithium metal is used as anode. To overcome these disadvantages, all-solid-state batteries using solid electrolytes have emerged, which are expected to improve safety and cycling stability even when using lithium metal anodes. Among the various types of solid electrolytes, sulfide solid electrolytes are widely used due to their high ionic conductivity and ductility, which allows easy formation of good interfaces, resulting in high performance all-solid-state batteries.To date, many attempts have been made to use lithium metal anodes with solid electrolytes, but dendrite growth has not been completely suppressed.1 Dendrite growth is affected by many interface-related factors, such as void ratio, grain size, elastic modulus, reductive decomposition products, and electrical conductivity of the electrolyte, which must be clarified before the use of lithium metal anodes can be realized.2 It is essential to observe and analyse the changes during electrochemical tests in order to reveal the formation of Li dendrites under the conditions in which actual real cells operate. We have attempted to elucidate the dynamic structural changes at the interface using multimodal/multiscale operando X-ray CT under an applied pressure, as well as the reactions taking place at the interface by observing the interface products using X-ray absorption spectroscopy. In this study, X-ray diffraction, X-ray absorption spectroscopy, time-resolved impedance measurements and multi scale operando X-ray CT are used to determine the electrochemical and chemical mechanisms of Li dendrite formation in different sulfide solid electrolytes. By investigating and comparing the particle size, porosity, doping effect of halides and reduction resistance of solid electrolytes used in lithium metal solid-state batteries, the mechanism of Li dendrite growth and how each factor affects dendrite growth are investigated.Here, we discuss Li3PS4, halogen-doped Li3PS4, and argyrodite-based Li6PS5Cl as typical sulfide-based solid electrolytes; Li3PS4 is known to have a low elastic modulus, and a simple cold press could be used to reduce the inter-particle voids. However, Li3PS4 has a very narrow potential difference, which resulted in unwanted oxidation and reduction byproducts during battery cycling. The high electronic conductivity of the reduction products at the interface also led to the formation of electronic pathways, resulting in the concentration of current in several locations and ultimately triggering the formation of Li dendrites. On the other hand, in argyrodite Li6PS5Cl, the formation of an interfacial phase with low electronic conductivity, which is mainly composed of lithium chloride at the interface, suppresses the reduction reaction and thus the formation of Li dendrites. In the presentation, the relationship between the lithium dendrite formation and the operating conditions such as temperature and pressure will also be presented.

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect the dendrite growth by the interfacial chemical and electrochemical stability with lithium metal forming solid electrolyte interphase as a passivating layer. Since the lithium dendrites have to grow through this layer, its composition should play an important role in the dendrite formation. Moreover, it is known that the stack can be easily deformed because lithium dendrite growth with a high shear modulus, indicating that the solid electrolyte and its interface with lithium metal should be sufficiently strong to endure the pressure originating from lithium dendrite growth. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and grain-boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.Different parameters can influence the lithium dendrite growth and the critical current density in ceramic all-solid-state configuration, such as the solid electrolyte chemical composition, particle size, and the compactness of ceramic solid electrolyte. The pressure effect on the electrochemical performances of sulfide electrolytes was investigated. The pressure affects resistive grain boundaries, contact between lithium metal and solid electrolyte and lithium plating. As, the kinetics of reaction is derived from thermodynamic parameters, the temperature can affect the plating/stripping phenomena. These different parameters and the relationship between them will be presented and explained through complete studies based on sulfide solid electrolytes with the combination of various chemical and electrochemical techniques.

The low cost, safe and high energy storage technology is needed to ensure a continuous energy supply from renewal energy sources. However, current Li-ion batteries (LiBs) are facing challenges to fulfil the safety and high energy and power demands of fast-growing market of electric vehicles (EVs). In particular, liquid organic electrolytes used in conventional LIBs have raised the safety issues due to serious fire risk. Solid state batteries (SSBs) are considered to provide better safety as compared to LIBs because of solid electrolytes (SEs) are used in SSBs instead of flammable organic liquid based electrolytes [1-4].The various types of solid electrolytes have already been reported for SSBs which can be divided into oxides, sulfides, halides and polymers based on their properties, advantages and disadvantages [5]. Among these solid electrolytes, sulfide solid electrolytes have advantages over other due to high conductivity and ductile nature of sulfides [6]. The discovery of Li10GeP2S12 solid electrolyte called LGPS structured sulfide electrolyte have shown great potential to replace liquid electrolyte as ionic conductivity of LGPS was found 1.2×10-2 S cm-1 at room temperature comparable to the conductivity of organic liquid electrolyte [7]. However, Li10GeP2S12 electrolyte suffers with poor cyclability in solid state batteries due to reduction of Ge+4 ions to Ge0, and instable against lithium metal anode. Moreover, germanium (Ge) is a rare and expensive element, which limits the industrial application of Li10GeP2S12 [8, 9].Therefore, in the present work, we have developed LGPS structured based new Ge free solid electrolytes with high conductivity and better electrochemical stability. The phase identification of newly synthesized solid electrolytes is done by X-ray diffractometer technique along with Rietveld refinement analysis. The conductivity of prepared solid electrolytes is determined by electrochemical impedance spectroscopy. The ionic conductivity of newly synthesised electrolytes has reached upto 0.67 mS cm-1 at room temperature. The electrochemical analysis of prepared solid electrolytes is done using Li-metal in both side (in symmetric cell) as well as using standard cathode and anode materials (full cell).

Compared with oxide, halide, and polymer‐based solid electrolytes, Li‐ion conducting sulfide solid electrolytes exhibit remarkable ionic conductivity, electronic conductivity, and exceptional thermal and mechanical properties. Despite these advantages, the susceptibility of sulfide electrolytes to air and the formation of lithium dendrites on the anode hinder their large‐scale commercial application. In this study, we propose a doping strategy involving the nitrogen (N) element in sulfide electrolyte Li5.5PS4.5Cl1.5 (LPSCl) with inherently high ionic conductivity. We have successfully synthesized Li5.5+xPS4.5−xNxCl1.5(x = .025, .05, .07, .10) solid electrolytes by enhancing their air stability through doping. The modified electrolyte material demonstrates stable cycling performance exhibiting superior air stability compared to Li5.5PS4.5Cl1.5. The results indicate that the doped sulfide solid electrolyte effectively suppresses the growth of lithium dendrites, thereby enhancing the compatibility between the lithium metal anode and sulfide solid electrolyte.

1. Introduction Solid electrolyte is the key material for the all solid state lithium ion battery, which possesses higher safety than current lithium ion battery with organic electrolyte solvent. In addition to the safety advantage, solid electrolyte can operate under wider range of temperature, and has higher chemical stability against high voltage cathode material. So far, many researches on oxide and sulfide solid state electrolyte are reported, and particularly, sulfide electrolyte attracts many interests because of its higher lithium ion conductivity (1-3). Among various solid state electrolytes, Li2S-P2S5 based sulfide electrolyte is one of the most promising materials, and it is known that ion conductivity of sulfide electrolyte depends on its chemical component ratio and heat treatment temperature (4, 5). In order to optimize the component ratio and heat treatment condition, the detail analysis during the heat treatment is quite important. In this study, chemical changes and crystallization behaviors of Li2S / P2S5= 70 : 30 system are investigated. 2. Experimental The sulfide electrolytes were synthesized from Li2S and P2S5 by mechanical milling using a planetary ball mill apparatus. The mixture of reagent grade crystal of Li2S and P2S5 with the ratio 70 : 30 was put into the zirconia pot and mixed about 30 hours under N2 atmosphere. The obtained glass sample was heated under Ar atmosphere from room temperature to 270 °C for 1 hour to obtain glass ceramics sample. For the in situ measurement during heat treatment, the glass sample was put into glass capillary in the Ar atmosphere glove box and sealed under the same atmosphere. The structural changes of the glass sample during heat treatment were investigated by in situX-ray diffraction (crystallization behavior) and Raman spectroscopy (chemical structural changes). The generated gases during heat treatment can be detected by TPD-MS (temperature programmed desorption MS). 3. Results and discussions Figure 1 shows Raman spectra of glass and glass ceramics sample. The observed Raman bands are assigned to PS stretching of PS4 3- and P2S7 4- structure. From the comparison of Raman spectra, spectral sharpening of each Raman bands of glass ceramics sample is observed and the change is derived from the crystallization of the glass sample. To investigate what happened during the crystallization process, the gas generated during the heat treatment were analyzed (Figure 2). H2S is detected from around 100 °C to 250 °C and S compounds are also detected from 200 °C, and the generation maximum is around 350 to 400 °C. In the in situ Raman spectra (Figure 3), the Raman band of polysulfide can be detected around 500 cm-1 from 200 °C, and the temperature of polysulfide generation is coincide with the detection temperature of S compounds by TPD-MS. The origin of sulfur generation around 350 to 400 °C and the relationship with crystallization behavior will be discussed in the presentation considering the data of in situXRD diffraction patterns. References (1)F. Mizuno, A. Hayashi, K. Tadanaga, M. Tatsumisago, Adv. Mater. 17, 918 (2005) (2)F. Mizuno, A. Hayashi, K. Tadanaga, M. Tatsumisago, Electrochem. Solid-State Lett. 8, A603 (2005) (3) N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto, and A. Matsui, Nat. Mater. 10, 682 (2011) (4) A. Hayashi, K. Minami, M. Tatsumisago, J Solid State Electrochem. 4, 1761(2010) (5) M. Eom, J. Kim, S. Noh, D. Shin, J. Power Sources 284, 44 (2015) Figure 1

Sulfide-based all-solid-state batteries using a lithium metal anode are expected to be next-generation batteries due to their extremely high energy density. In order to use the lithium metal as the anode, suppressing dendrite of lithium metal during charge/discharge processes is essentially important. It has been reported that lithium dendrite formation occurs not from the lithium/sulfide solid electrolyte interface, but in the sulfide solid electrolyte, isolated from the interface1, 2. The formation of lithium dendrite within the sulfide solid electrolyte is caused by electron conduction in the sulfide solid electrolyte and at the sulfide solid electrolyte/void interface3. However, fundamental information on the mechanism of lithium dendrite formation in a sulfide solid electrolyte caused by its electron conduction is lacking. In this study, the three-dimensional morphological changes of the lithium dendrite in Li3PS4, which is a typical sulfide solid electrolyte, were observed directly using multimodal/multiscale operando computed tomography (CT) under an applied pressure.Li/Li3PS4/Li cells were constructed in a diameter of 10 mm and 1 mm for the critical current density measurements and X-ray CT measurements by using SPring-8 BL20XU respectively. X-ray CT images for behavior change with the electrochemical operation were collected in micro and nano scales at 25 °C every 30 mins. After a series of data processing steps, these images were converted to cross-sectional slices that were then stacked together to render a 3D reconstruction of the cell. The 3D imaging data coupled with precise species segmentation show that the lithium metal deposition start point is spatially separated from the lithium metal anode. The gradient in thickness of a lithium filament with repeated charging, widening the plating-susceptible region horizontally in the process and eventually led to cell failure. The lithium nucleation initiates along the pre-existing voids where local electronic conductivities are high during the plating. The deposition then widens from the nucleation across the electrolyte horizontally. Accompanied with streak fracture widening through the Li3PS4, does a Li/Li3PS4/Li cell finally short circuit. By combining the multimodal/multiscale operando X-ray computed tomography with X-ray absorption spectroscopy and electrochemical impedance spectroscopy measurements, we revealed that the electronic conduction of reductive decomposition products and the solid electrolyte/void interface cause the lithium deposition within the Li3PS4. These results suggests that the suppression of reductive decomposition and sulfide solid-state electrolytes with low electronic conductivity plays significant roles in suppressing the growth of lithium dendrites in the solid-state electrolyte layer.

A New General Paradigm for Understanding and Preventing Li Metal Penetration through Solid Electrolytes

In the last decade, lithium metal has burgeoned into a potential anode material from Li-ion battery to next generation battery systems because of the low redox potential (-3.040 V vs SHE.) and high gravimetric energy density [1-3]. Unlike conventional batteries, the major challenges to be addressed in lithium metal anodes are the dendritic growth, continuous lithium depletion, rapid capacity loss and low Columbic efficiency [4]. These challenges can be averted using electrolyte additives or creating artificial solid electrolyte (SEI) interphases [5]. In the present work, nanostructured transition metal sulfide (MS) and lithium transition metal sulfide (LMS) are used as artificial SEI on lithium metal anode by modifying the lithium metal/electrolyte interfaces and homogenous lithium deposition.The nanostructured transition metal sulfide and lithium transition metal sulfide were synthesized by a simple wet chemical route at relatively low temperatures (150-200 °C). The synthesized LMS were typically of high purity and were filtered, washed, ball-milled, and calcined prior to use in the battery. The microstructure, structure and chemical analysis of the synthesized metal sulfide was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Figure 1(a) shows the morphology of the ball-milled LMS as a layered structure with varying sizes of 10 µm to 100 nm. The EDS analysis of the ball-milled powder majorly showed an M/S ratio of 1:1 and 1:2.The LSM was deposited on Li metal substrate by sputtering technique from a LSM target in Ar atmosphere. This film deposition was carried out at different sputtering time (10 sec -100 sec) and processing pressures. Homogeneous deposition of this LSM of few tens of nanometers thickness was successfully achieved. The electrochemical performance of the LSM artificial SEI was investigated in symmetric cells of two coated Li electrodes and compared to bare Li (Figure 1(b)). At different current densities of 0.5 and 1 mA/cm2, repeated Li plating and stripping revealed an enhanced cycling performance of metal sulfide coated Li compared to bare Li electrode. To better understand the interfacial stability, electrochemical impedance spectroscopy (EIS) studies were performed at different stages of cycling. The cycling performance of coated and bare Li anode was performed in a full cell containing NMC811 as cathode. After cycling, the microstructural changes in lithium metal anode were explored using SEM. Figure 1: (a) SEM image of the ball-milled layered lithium metal sulfide and (b) Time-voltage profiles of the symmetric cells with Li anode and coated Li anode at the current density of 0.5 mA/cm2 References [1] D. Lin, Y. Liu, Y.Cui, “Reviving the Lithium Metal Anode for High-Energy Batteries”, Nature Nanotechnology, 12 (2017), 194-206.[2] D. Aurbach, B.D. McCloskey, L.F. Nazar, P.G. Bruce, “Advances in Understanding the Mechanisms Underpinning Lithium-air Batteries”, Nature Energy, 1 (2016) 16128.[3] W. Xu, J. Wang, F. Ding, X.Chen, E. Nasybulin, Y. Zhang, J.G. Zhang, “Lithium metal Anodes for Rechargeable Batteries”, Energy and Environmental Science, 7 (2014) 513-537.[4]J. Liu, Z. Bao, Y. Cui, E.J. Dufek, J.B. Goodenough, P. Khalifah, Q. Li, B.Y. Liaw, P. Liu, A. Manthiram, Y.S. Meng, V.R. Subramanian, M.F. Toney, V.V. Viswanathan, M.S. Whittingham, J. Xia, W. Xu, J. Yang, X.Q. Yang, J.G. Zhang, "Pathways for Practical High-Energy Long Cycling Lithium Metal Batteries", Nature Energy, 4 (2019) 180-186.[5] K Kim, M. Balaish, M. Wadaguchi, L. Kong, J. Rupp, “Solid State Batteries: Solid-State Li-metal Batteries: Challenges and Horizons of Oxide and Sulfide Solid Electrolytes and their Interfaces”, Advanced Energy Materials, 11 (2021) 2170002 Figure 1

Long cycle life all-solid-state batteries enabled by solvent-free approach for sulfide solid electrolyte and cathode films