Sulfide-based Solid Electrolytes Research Articles

Self-Templated 3D Sulfide-Based Solid Composite Electrolyte for Solid-State Sodium Metal Batteries.

Rechargeable solid-state sodium metal batteries (SSMBs) experience growing attention owing to the increased energy density (vs Na-ion batteries) and cost-effective materials. Inorganic sulfide-based Na-ion conductors also possess significant potential as promising solid electrolytes (SEs) in SSMBs. Nevertheless, due to the highly reactive Na metal, poor interface compatibility is the biggest obstacle for inorganic sulfide solid electrolytes such as Na3SbS4 to achieve high performance in SSMBs. To address such electrochemical instability at the interface, new design of sulfide SE nanostructures and interface engineering are highly essential. In this work, a facile and straightforward approach is reported to prepare 3D sulfide-based solid composite electrolytes (SCEs), which utilize porous Na3SbS4 (NSS) as a self-templated framework and fill with a phase transition polymer. The 3D structured SCEs display obviously improved interface stability toward Na metal than pristine sulfide. The assembled SSMBs (with TiS2 or FeS2 as cathodes) deliver outstanding electrochemical cycling performance. Moreover, the cycling of high-voltage oxide cathode Na0.67Ni0.33Mn0.67O2 (NNMO) is also demonstrated in SSMBs using 3D sulfide-based SCEs. This study presents a novel design on the self-templated nanostructure of SCEs, paving the way for the advancement of high-energy sodium metal batteries.

Establishing laser cutting of components for sulfide-based solid-state batteries

The demand for safe, power- and energy-dense, low-cost batteries is constantly increasing due to the global shift toward renewable energy sources and the associated need for battery electric vehicles and grid-level energy storage. However, current-generation lithium-ion batteries are struggling to meet the requirements and are reaching their physicochemical limits regarding energy density. Solid-state battery technology promises to improve the current state of the art in electrochemical energy storage and has proven itself in research, although not yet in commercial applications. One of the main challenges in bringing the technology to the market is the limited knowledge and research on the production of solid-state batteries with commercially viable technologies. This study investigates the application of laser cutting technology to improve the cutting process in the production of sulfide-based solid-state batteries. Challenges such as the production atmosphere, handling of the components, and differences compared to conventional battery components are discussed. Using a picosecond laser source, the influence of the pulse frequency, peak fluence, scanning speed, and laser passes was investigated to identify appropriate parameters for cutting sulfide-based composite cathodes. The findings were then successfully applied to the cutting of sulfide-based solid electrolyte separators. An improvement in edge quality compared to mechanical punching is demonstrated, marking a crucial step toward the commercialization of solid-state batteries.

A Sulfide‐Based Solid Electrolyte With High Humid Air Tolerance for Long Lifespan All‐Solid‐State Sodium Batteries

AbstractSulfide‐based superionic conductors present great promise to achieve high energy density and safety for all‐solid‐state sodium batteries (ASSSBs). However, the poor electrolyte/electrode interface compatibility and humid air stability seriously hinder their deployment in ASSSBs. Herein, a series of high‐performance Na3‐□Sb1‐4x(SnWCaTi)xS4 sulfide‐based solid electrolytes (SSEs) are reported by coupling the vacancy effect with configurational entropy, which displays an excellent interface stability against sodium metal and an extraordinary tolerance toward the moist atmosphere, even for water. The optimized electrolyte effectively inhibits the detrimental mixed ion‐electron conducting interphase formation, achieving the ultra‐stable operation of Na–Na symmetric cell up to 1000 h. Furthermore, the Na+ diffusion kinetics is obviously enhanced by increasing the Na sites local anisotropy and Na vacancies. Eventually, the assembled TiS2//Na5Sn ASSSBs deliver a remarkable reversible capacity of 211.6 mAh g−1 at 0.5C with a long‐term cycling performance of 450 cycles at room temperature. More importantly, it achieves a steady running up to 100 cycles at 1C even if this electrolyte is placed in the air with a dew temperature of 13.8 °C for 30 min, the highest values in the state‐of‐the‐art sulfide‐based ASSSBs. The well‐designed SSEs open a new avenue for realizing the advanced and powerful ASSSBs.

PVDF Binder in All-Solid-State Lithium Batteries with NCM/Sulfide/PVDF Cathode, Oxide/PEO SE Layer, and Li-metal Anode

Sulfide-based solid electrolyte such as Li6PS5Cl (LPSCl) is unstable in contact with Li metal electrode due to decomposing to by-product resulting in poor performance. Therefore, the introduction of an interlayer to suppress reactivity is essential. In this study, instead of an interlayer, an oxide/polymer composite electrolyte was applied to suppress side reactions, while a sulfide-based electrolyte was used at the cathode to improve interfacial control between the cathode and the electrolyte. All-solid-state lithium batteries (ASLBs) were prepared by applying sulfide-based solid electrolyte (argyrodite, Li6PS5Cl) including NCM424, polyvinylidene fluoride (PVDF), and Super-P in a composite cathode layer, and a composite solid electrolyte (CSE) layer by mixing an oxide-based solid electrolyte (garnet, Al-doped Li7La3Zr2O12 (LLZO)), polymer (PEO, polyethylene oxide) and lithium metal as the anode. In this study, NCM424 powder was coated with LiNbO3 to prevent chemical reaction with the sulfide electrolyte. As the PVDF binder was applied to the cathode of the ASLB, the discharge capacity of the cell was approximately 163 mAh g−1 at 70 °C, 0.1 C, and 4.2 V cut-off and its capacity retention was 83% after 50 cycles. The effects of the PVDF were evaluated using both pouch-type cells. The capacity and cycle retention are greatly dependent on the PVDF content of the cathode materials and the drying temperature during the fabrication of the cathode. When the cathode with PVDF binder was dried at 130 °C, initial cycling was required for activation of the pouch cell, and it was possible to overcome this by adding a plasticizer.

Cradle-to-gate life cycle assessment of cylindrical sulfide-based solid-state batteries

PurposeSolid-state batteries (SSBs) are a current research hotspot, as they are safer and have a higher energy density than state-of-the-art lithium-ion batteries (LIBs). To date, their production only occurs on a laboratory scale, which provides a good opportunity to analyze the associated environmental impacts prior to industrialization. This paper investigates the environmental impacts of the production of cylindrical SSB, to identify environmental hotspots and optimization potentials.MethodsHere, an attributional cradle-to-gate life cycle assessment (LCA) is performed, focusing on SSBs that use a NMC811/lithium germanium phosphorous sulfide (LiGPS) composite cathode, a sulfide-based solid separator electrolyte, and a lithium metal anode. The life cycle impact assessment (LCIA) is performed in Umberto 11 using the Environmental Footprint 3.1 method with primary and literature data and the Evoinvent 3.9 database for background data.Results and discussionThe results show climate change impacts of 205.43 kg CO2 eq./kwh (for the base case), with hotspots primarily attributable to the electrolyte and cathode production, and more specifically to the LiPS and LiGPS synthesis as well as to the cathode active material. Additionally, the scenario analysis shows that an upscaling of the LiPS and LiGPS synthesis reduces environmental impacts across all assessed impact categories. In addition, it was shown that the use of an in situ anode further improves the overall environmental performance, while the use of alternative cathode active materials, such as NMC622 and LFP did not lead to any improvements, at least with reference to the storage capacity.ConclusionThe article highlights the environmental hotspots of sulfide-based SSB production, namely electrolyte and catholyte synthesis. The results show that upscaling the synthesis reduces the environmental impact and that cells with higher energy density show a favorable environmental performance. However, SSBs are still in the development stage and no final recommendation can be made at this time.

Are Sulfide‐Based Solid‐State Electrolytes the Best Pair for Si Anodes in Li‐Ion Batteries?

AbstractThe integration of Si‐based anodes within sulfide‐based solid electrolyte (SSE) Li‐ion batteries (LIB) has emerged as a promising avenue of research and development, attracting increasing interest in recent years. This work comprehensively examines the latest research directions and major strides in this field. It covers the key advances in the design and engineering of nano‐ and micro‐structured Si anode architectures, and strategies of surface modification. Additionally, it explores the impacts of external pressure, the role of binders and conductive additives, and the implications of varying Si particle size. Beyond providing a detailed account of the evolution of Si anodes within SSE LIBs, this work also identifies critical research challenges that urgently need addressing. These include the electrochemical‐mechanical evolution behavior and failure mechanism of Si anodes in SSE LIBs, strategies for structural and interface modifications, methods for preparing Si electrodes, advancements in high‐performance SSEs, and the development of scalable technologies for SSE thin films. Moreover, it discusses high‐energy cathodes tailored for Si‐based SSE LIBs. The identified research priorities are set to offer crucial guidance and insights, supporting the ongoing investigations and innovations in this dynamic area of research.

Stable Anode-Free All-Solid-State Lithium Battery through Tuned Metal Wetting on the Copper Current Collector

Stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li6PS5Cl, LPSCl) is achieved by tuning wetting of lithium metal on “empty” copper current-collector. Lithiophilic 1 μm Li2Te is synthesized by exposing the collector to tellurium vapor, followed by in-situ Li activation during the first charge. The Li2Te significantly reduces the electrodeposition/electrodissolution overpotentials and improves Coulombic efficiency (CE). During continuous plating experiments using half-cells (1 mA cm-2), the accumulated thickness of electrodeposited Li on Li2Te-Cu is more than 70 μm, which is the thickness of Li foil counter-electrode. Full AF-ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryo-FIB sectioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector-SE interface. Electrodissolution is uniform and complete, with Li2Te remaining structurally stable and adherent. By contrast, unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal”, dendrites that extend into SE, and thick non-uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory and mesoscale calculations provide complementary insight regarding nucleation-growth behavior. Unlike for conventional liquid-electrolyte metal batteries, the role of current collector/support lithiophilicy has not been explored for emerging AF-ASSBs.

Phase Field Damage Framework for Modeling Thin-Film Silicon Anodes in All-Solid-State Batteries

Recent advancements in solid electrolyte research have revived interest in the concept of silicon anodes for All-Solid-State Batteries (aSSBs). Tan et al. have recently proposed stable cyclic performance of micro-grain size pure silicon anodes paired with sulfide-based solid electrolytes [1]. This development has opened pathways toward potential aSSBs without encountering dendrite growth issues. This rediscovery of the thin-film a-silicon anodes concept has sparked computational interest in simulating the fracture-chemo-mechanical silicon lithiation mechanism. Understanding chemical reactions during lithiation and crack evolution during de-lithiation processes are intriguing topics. Especially, elastic-plastic deformation coupled with phase-field continuous fracture is crucial in comprehending the underlying physics and enhancing performance of battery cell through reverse engineering approaches.In this work, we develop a thermodynamically consistent deformation-diffusion-damage coupled framework to model the evolution of dense, thin-film-like a-silicon anodes during lithiation and delithiation. During delithiation, tensile stress develops inside the film as the lithiated film overcomes the initial stack pressure and compressive stress prevalent during lithiation. As tensile stress and strain evolve, randomly distributed weak spots lead to crack nucleation. This fracture occurs throughout the silicon film, forming sharp vertical cracks, and depending on surface conditions along the solid-state electrolyte, some interfacial cracks may emerge, leading to permanent contact loss and resulting in capacity reduction.From the model, we observed “mud crack” like phenomena, where crack distribution is not controlled by particle’s property, but entire cluster’s thickness matters. While flat model suggests that one that nucleate the crack was weak spots where they make stress concentration over entire body, whether they can evolve into big vertical crack mostly governed by connectivity of such weak spot maps. However, from our interface roughness model, what governs the crack evolution most was not the randomly distributed weak spot, but its geometric relative thickness difference between one another. Due to manufacturing process, perfect interface is hard to be achieved and such geometric irregularity always exist, thus, additive and binder studies along the silicon anode and its interface between sse would be key to achieve long and stable life span for a-silicon based aSSBs. Reference [1] Tan, Darren HS, et al. "Carbon-free high-loading silicon anodes enabled by sulfide solid electrolytes." Science 373.6562 (2021): 1494-1499.

Effect of Chemical Doping on Ion Transport in Sulfide Solid Electrolytes

Rechargeable solid-state batteries (SSBs) offer tremendous promise as a safe and energy-dense storage technology for use in electric transportation, robotics, and portable electronics. Lithium argyrodites (e.g., Li7PS6, and its halogen-doped derivatives) have emerged as a lucrative class of solid-state electrolytes (SSEs) for SSBs owing to their high Li-ion conductivity (~10-3 S/cm), good elastic stiffness (~30 GPa), and low flammability. Meanwhile, sulfide-based solid electrolytes such as Na3SbS4 (NSS) also showcase substantial potential for SSBs with their high theoretical specific capacity, enhanced safety, and abundance of resources. Despite their promise, both lithium and sodium-based SSBs remain far from commercialization due to lack of atomic-scale understanding of ion-conduction, charge transport, structural evolution, and interfacial reactions (e.g., dendrite growth, electrolyte decomposition etc.). Here we employ a combination of density functional theory calculations, ab initio molecular dynamics simulations, and nudged elastic band calculations to understand ion transport mechanism in chemically doped lithium argyrodites and NSS.In lithium-based systems, using accurate materials modeling, we design fluorine-containing argyrodite electrolytes that offers enhanced Li-ion conduction facilitated by unique Li-disorder induced by fluorine and other halogen co-dopants. Our results show the opening up of new pathways for Li inter-cage hops in these fluorine -containing argyrodite electrolytes which increases the Li-ion conductivity. In the case of sodium-based systems, we focus on atomic-scale mechanisms underlying Na-ion conduction in the presence of cation dopants. Ab initio molecular dynamics simulations reveal the significant impact of cation dopants on NSS, where the introduction of charge-compensating Na-vacancies enhances Na-ion conduction. The size of the cation dopant is found to be a critical factor, with examples such as Ca-doped NSS (rCa2+ / rNa+ = 0.98) showing a conductivity approximately 10 times that of pristine NSS, while larger Ba2+ as a dopant (rBa2+ / rNa+ = 1.35) hinders Na-ion hops due to local strain, resulting in a Na-ion conductivity ~5 times that of NSS. We will discuss these results in the context of accelerating design of novel solid-state electrolytes for long-lived, stable, and high-energy density SSBs.

Interfaces Comprehension at Electrodes on Sulfide-Based Solid State Batteries

The increasing demand for safe, highly efficient, and cost-effective energy storage systems has accelerated the development of solid-state batteries (SSBs) with lithium metal (LiM) anodes. This technology offers remarkable advantages over conventional lithium-ion batteries with liquid electrolytes; from improved safety with non-flammable electrolyte to higher gravimetric and volumetric energy density enabled using LiM anode along with the multilayered bipolar stacking cell fabrication. The combination of solid electrolyte (SE) mechanical strength, flexibility, and safety against self-ignition allows for optimized battery design to meet the specific requirements.1–4 In recent years, soft, flexible, and easily deformable sulfide-based solid electrolytes have received significant attention due to their attractive mechanical properties, high conductivity, and feasibility of processing at ambient temperature, which makes them appealing candidates for upscaling the technology to large format devices.2,4,5 Despite the high ionic conductivity and attractive mechanical properties of sulfide-based SSBs, this chemistry still faces key challenges to encompass fast rate and long cycling performance, mainly arising from the dynamic and complex solid-solid interfaces. Solid-state materials are characterized by a significant impact of interface-related phenomena on their functional characteristics, such as mechanical properties, conductivity mechanisms, or electrochemical performance. For SSBs with ceramic or glass-ceramic electrolytes, the stacking of the composite cathode, the SE and the LiM anode leads to multiple interfaces from voids, cracks, secondary phases from chemical and electrochemical reactions and grain boundaries.6,7 As electrochemical kinetics is governed by the contact area at the interface, ensuring the adhesion between the electrolyte and active electrode materials is the key to obtain high performance devices, especially at fast rates.The goal of the present work is to provide understanding on the complex solid-solid interfaces regulating sulfide-based battery performance. As shown in Figure 1, cells under different configurations with LPSCl, Li or In metal anodes, and LiNi0.6Mn0.2Co0.2O2 (NMC622)-based composite cathodes have been systematically studied aiming to bring insights on the dynamic interfaces at component level dominating processes during cell operation. From a multi-configurational approach and an advanced deconvolution of electrochemical impedance signals into distribution of relaxation times, we disentangle intricate underlying interfacial processes taking place at the battery components and that play major role on the overall performance. For the Li metal solid-state batteries, the cycling performance is highly sensitive to the chemomechanical properties of the cathode active material, the formation of the SEI, and processes ascribed to Li diffusion in the cathode composite and in the space-charge layer. The outcomes of this work aim to facilitate the design of sulfide solid-state batteries and provide methodological inputs for battery ageing assessment.(1) Zheng, F.; Kotobuki, M.; Song, S.; Lai, M. O.; Lu, L. Review on Solid Electrolytes for All-Solid-State Lithium-Ion Batteries. Journal of Power Sources 2018, 389, 198–213. https://doi.org/10.1016/j.jpowsour.2018.04.022.(2) Randau, S.; Weber, D. A.; Kötz, O.; Koerver, R.; Braun, P.; Weber, A.; Ivers-Tiffée, E.; Adermann, T.; Kulisch, J.; Zeier, W. G.; Richter, F. H.; Janek, J. Benchmarking the Performance of All-Solid-State Lithium Batteries. Nat Energy 2020, 5 (3), 259–270. https://doi.org/10.1038/s41560-020-0565-1.(3) Schnell, J.; Günther, T.; Knoche, T.; Vieider, C.; Köhler, L.; Just, A.; Keller, M.; Passerini, S.; Reinhart, G. All-Solid-State Lithium-Ion and Lithium Metal Batteries – Paving the Way to Large-Scale Production. Journal of Power Sources 2018, 382, 160–175. https://doi.org/10.1016/j.jpowsour.2018.02.062.(4) Kim, K. J.; Balaish, M.; Wadaguchi, M.; Kong, L.; Rupp, J. L. M. Solid‐State Li–Metal Batteries: Challenges and Horizons of Oxide and Sulfide Solid Electrolytes and Their Interfaces. Advanced Energy Materials 2021, 11 (1), 2002689. https://doi.org/10.1002/aenm.202002689.(5) Liu, S.; Zhou, L.; Han, J.; Wen, K.; Guan, S.; Xue, C.; Zhang, Z.; Xu, B.; Lin, Y.; Shen, Y.; Li, L.; Nan, C. Super Long‐Cycling All‐Solid‐State Battery with Thin Li 6 PS 5 Cl‐Based Electrolyte. Advanced Energy Materials 2022, 12 (25), 2200660. https://doi.org/10.1002/aenm.202200660.(6) Pesci, F. M.; Bertei, A.; Brugge, R. H.; Emge, S. P.; Hekselman, A. K. O.; Marbella, L. E.; Grey, C. P.; Aguadero, A. Establishing Ultralow Activation Energies for Lithium Transport in Garnet Electrolytes. ACS Appl. Mater. Interfaces 2020, 12 (29), 32806–32816. https://doi.org/10.1021/acsami.0c08605.(7) Chen, R.; Li, Q.; Yu, X.; Chen, L.; Li, H. Approaching Practically Accessible Solid-State Batteries: Stability Issues Related to Solid Electrolytes and Interfaces. Chem. Rev. 2020, 120 (14), 6820–6877. https://doi.org/10.1021/acs.chemrev.9b00268. Figure 1

Atmospheric Influences on Li6PS5Cl Separators and the Resulting Ionic Conductivity for All-Solid-State Batteries

All-solid-state batteries (ASSBs), defined through a solid electrolyte, are emerging as a promising solution to address current challenges in energy and power density demands for electromobility. Within the various possible types of solid electrolytes, sulfide-based materials exhibit advantageous high ionic conductivities. However, due to the strong reactivity of sulfides, atmospheric exposure can lead to the formation of toxic hydrogen sulfide and additionally negatively impact the resulting battery performance. Both factors present key challenges for ASSB production, as they necessitate the development of a material-adapted, economically viable and safe process atmosphere. In the present study, the influence of different production atmospheres on sulfide-based solid electrolytes is experimentally investigated. For this purpose, sulfide sheets are exposed to defined atmospheres with dynamic air fluctuations at dew points ranging from −60 °C to 0 °C. The resulting ionic conductivities indicate a dependency on the prevailing dew point and exposure time with a discernible impact on performance even at dew points of −60 °C within atmospheres with constant air circulation. With the acquired results, a detailed and knowledge-based selection and design of dry room production atmospheres for ASSB cell assembly is possible, which is a necessary step for further industrialization.

Triple-doped Argyrodite Sulfide Electrolyte with Improved Air Stability and Lithium Compatibility for All-Solid-State Li-Metal Batteries

The shift to electric vehicles has highlighted challenges associated with lithium-ion batteries, and the need for safer and higher-energy–density all-solid-state batteries. However, sulfide-based solid electrolytes face problems with moisture reactivity and poor Li metal compatibility. In this study, we synthesized a Li5.4Al0.1P1−xSbxS4.7−2.5xO2.5xCl1.3 electrolyte, employing a dual-doping strategy inspired by the “hard and soft acids and bases” theory to enhance ionic conductivity, air stability, and Li metal compatibility. Sb–O dopants were introduced into Cl–Al-doped argyrodite solid electrolytes, achieving an optimized electrolyte with controlled dopant concentration. The electrolyte exhibited high ionic conductivity, excellent air stability, and Li metal compatibility. The all-solid-state Li metal battery showed promising initial discharge capacity. The improved air stability of Sb–O-doped electrolytes is attributed to the formation of Sb–S and P–O bonds, which reduces H2S emission by 78 % upon moisture exposure, effectively suppressing reactions with moisture. Enhanced Li metal compatibility induces the formation of Li–Sb alloy at the anode interface, inhibiting the growth of Li-dendrites. The Li symmetric cell demonstrates high critical current density and outstanding cycling stability. This study offers a sulfide electrolyte design for all-solid-state Li metal batteries, showcasing its potential for practical application with high air stability and Li metal compatibility.

Rationally Designed Li-Ag Alloy with In-Situ-Formed Solid Electrolyte Interphase for All-Solid-State Lithium Batteries.

All-solid-state lithium batteries (ASSLBs) with sulfide-based solid electrolytes have attracted significant attention as promising energy storage devices, owing to their high energy density and enhanced safety. However, the combination of a lithium metal anode and a sulfide solid electrolyte results in performance degradation, owing to lithium dendrite growth and the side reactions of lithium metal with the solid electrolyte. To address these issues, a Ag-based Li alloy with a favorable solid electrolyte interphase (SEI) was prepared using electrodeposition and applied to the ASSLB as an anode. The electrochemically formed SEI layer on the Li-Ag alloy primarily comprised LiF and Li2O with high mechanical strength and Li3N with high ionic conductivity, which suppressed the formation of lithium dendrites and short-circuiting of the cell. The symmetric cell with the Li-Ag alloy achieved a critical current density of 1.6 mA cm-2 and maintained stable cycling for over 2000 h at a current density of 0.6 mA cm-2. Consequently, the all-solid-state lithium cell assembled with the Li-Ag alloy anode with SEI, Li6PS5Cl solid electrolyte, and LiNi0.78Co0.10Mn0.12O2 cathode delivered a high discharge capacity of 185 mAh g-1 and exhibited good cycling performance in terms of cycling stability and rate capability at 25 °C.

Isotropic cell design enables low-pressure lithium metal solid-state batteries

Solid-state batteries that utilize sulfide-based solid-electrolytes, such as the argyrodite Li6PS5Cl, have become one of the most promising directions for next-generation energy storage. However, one remaining technical challenge for such materials has been the requirement of large pressures during operation. This challenge grows as the size of the cells increase as the pressure must be uniformly distributed over a larger-and-larger area. In this work, we introduce an isotropic cell design to pressurize the cell with perfect homogeneity, which is ensured by using a fluid pressurization medium. By achieving perfect homogeneity, the magnitude of the pressure necessary to stabilize the material is greatly reduced. Using such an isotropic cell design, lithium-metal solid-state pouch cells achieve remarkable extreme-fast-charging performance even at a low-pressure of only 2 MPa.

Accelerated Li Penetration and Crack Propagation Due to Mechanical Degradation of Sulfide-Based Solid Electrolyte.

This work presents quantitative investigations into the relationships between lithium dendrite growth in the defects of Li6PS5Cl (LPSCl) solid electrolyte (SE), crack nucleation and propagation in the SE, and the associated mechanical forces driving these dendrites and cracks. Two different growth modes for lithium dendrites are identified by ex situ scanning electron microscopy (SEM) observation: longitudinal cracking inside pores in the SE and lateral penetration along boundaries of the SE particles. These in situ TEM tests reveal that concentrated Li plating in a nano-sized defect on the LPSCl surface will lead to the nucleation and propagation of cracks into the LPSCl under a stress much smaller than the expected mechanical strength of the LPSCl material. This unexpected mechanical degradation is caused by a reduction in the mechanical strength of LPSCl during electrochemical charge/discharge cycling, resulting from a disorder in the crystal structure of LPSCl as revealed by DFT simulations. Due to this mechanical degradation of LPSCl, the threshold force necessary to initiate crack growth is much lower than the previously expected force to drive dendrite growth.

Microstructure-chemomechanics relations of polycrystalline cathodes in solid-state batteries

Lithium-nickel-manganese-cobalt-oxides (NMC) embedded in solid-electrolytes are being extensively applied as composite cathodes to match the high energy density of metallic anodes. During charge/discharge, the cathode composite often degrades through the evolution of micro-cracks within the grains, along the grain boundaries, and delamination at the particle-electrolyte interface. Experimental evidence has shown that regulating the morphology of grains and their crystallographic orientations is an effective way to relieve the volume-expansion-induced stresses and cracks, consequently stabilizing the electrochemical performance of the electrode. However, the interplay among the crystal orientation, grain morphology, and chemo-mechanical behavior has not been holistically studied. In that context, a thermodynamically consistent computational framework is developed to understand the role of microstructural modulation on the chemo-mechanical interactions of a polycrystalline NMC secondary particle embedded in a sulfide-based solid electrolyte. A phase-field fracture variable is employed to consider the initiation and propagation of cracks. A set of diffused phase-field parameters is adopted to define the transition of chemo-mechanical properties between the grains, grain boundaries, electrolyte, and particle-electrolyte interfaces. This modeling framework is implemented in the open-source finite element package MOOSE to solve three state variables: concentration, displacement, and phase-field damage parameter. A systematic parametric study is performed to explore the effects of aspect ratio, the crystal orientation of grains, and the interfacial fracture energy through the chemo-mechanical analysis of the composite electrode. The findings of this study offer predictive insights for designing solid-state batteries that provide stable performance with reduced fracture evolution.

The improvement of electrochemical performance by mixing InF3 in Li5.3PS4.3Cl1.7 solid electrolyte

All-solid-state batteries (ASSBs) employing solid electrolytes (SE) are currently gaining attention as next-generation energy storage devices. Solid electrolytes exhibit higher energy densities and operation across a wide temperature range than liquid electrolytes. The solid electrolyte acts as a separator, providing higher mechanical strength than polymer separators. This helps prevent cell deterioration and short circuit issues caused by lithium dendrite growth during charge – discharge cycles. Consequently, lithium metal, previously challenging to apply in conventional lithium-ion batteries, can be utilized as an anode electrode material. Sulfide-based solid electrolytes offer advantageous mechanical properties and high ionic conductivity. However, their narrow chemical/electrochemical stability window poses challenges. During the charging-discharging process of a battery with a lithium metal anode, a reduction decomposition reaction of the solid electrolyte occurs. On the other hand, Lithium Fluoride (LiF) exhibits low electronic conductivity due to a wide band gap but has a broad electrochemical stability window. In this study, we prepared a mixture of Li5.3PS4.3Cl1.7 with InF3 to generate an artificial solid electrolyte interphase (SEI) containing LiF. We confirmed the structural properties using powder X-ray diffraction (XRD). The XRD pattern showed the maintenance of the argyrodite structure, with only an increase in the peak intensity corresponding to InF3. The optimized solid electrolyte-based ASSB demonstrated a higher initial discharge capacity of 172.8 mAh/g, a coulombic efficiency of 78.54 %, and a capacity retention rate of 93.6 %, outperforming ASSBs based on the bare solid electrolyte (Li5.3PS4.3Cl1.7).

Insights into Lithium Sulfide Glass Electrolyte Structures and Ionic Conductivity via Machine Learning Force Field Simulations.

Sulfide-based solid electrolytes (SEs) are important for advancing all-solid-state batteries (ASSBs), primarily due to their high ionic conductivities and robust mechanical stability. Glassy SEs (GSEs) comprising mixed Si and P glass formers are particularly promising for their synthesis process and their ability to prevent lithium dendrite growth. However, to date, the complexity of their glassy structures hinders a complete understanding of the relationships between their structures and properties. This study introduces a new machine learning force field (ML-FF) tailored for lithium sulfide-based GSEs, enabling the exploration of their structural characteristics, mechanical properties, and lithium ionic conductivities. Using molecular dynamic (MD) simulations with this ML-FF, we explore the glass structures in varying compositions, including binary Li2S-SiS2 and Li2S-P2S5 as well as ternary Li2S-SiS2-P2S5. Our simulations yielded consistent results in terms of density, elastic modulus, radial distribution functions, and neutron structure factors compared to DFT and experimental work. Our findings reveal distinct local environments for Si and P within these glasses, with most Si atoms in edge-sharing configurations in Li2S-SiS2 and a mix of corner- and edge-sharing tetrahedra in the ternary Li2S-SiS2-P2S5 composition. For lithium ionic conductivity at 300 K, the 50Li2S-50SiS2 glass displayed the lowest conductivity at 2.1 mS/cm, while the 75Li2S-25P2S5 composition exhibited the highest conductivity at 3.6 mS/cm. The ternary glass showed a conductivity of 2.6 mS/cm, sitting between the two. Moreover, an in-depth analysis of lithium ion diffusion over the MD trajectory in the ternary glass demonstrated a significant correlation between diffusion pathways and the rotational dynamics of nearby SiS4 or PS4 tetrahedra. The ML-FF developed in this study provides an important tool for exploring a broad spectrum of solid-state and mixed former sulfide-based electrolytes.

Cost-effective synthesis of sulfide-based solid electrolytes without using Li2S

Solid electrolytes possess highly attractive potential which can improve safety properties and achieve high energy density when they replace the conventional liquid electrolytes in Li-ion batteries. Sulfide-based solid electrolytes have received considerable attention owing to their high ionic conductivities and good wettability due to their soft nature. These materials are typically synthesized using Li2S as a precursor. However, Li2S is expensive and thus cannot be widely used to prepare sulfide-based solid electrolytes for all-solid-state batteries (ASSBs). Here, we propose a novel approach to synthesize a sulfide-based solid electrolyte without using Li2S as a precursor. In this method, the starting powders of Li2O, Mg, and S were converted into Li2S and MgO by ball milling. The Li2S-MgO composite was then sequentially milled with P2S5 and LiBH4, and a BH4-substituted thiophosphate solid electrolyte was synthesized. The resulting Li3PS4-LiBH4-MgO composite exhibited a high ionic conductivity of 7.2 mS cm–1 at 25 °C, and the ASSB prepared using the solid electrolyte functioned well. The thiophosphate local structure of the prepared samples was examined by Raman and 31P solid-state nuclear magnetic resonance spectroscopies. Although the ionic conductivity slightly decreased upon MgO addition, the thiophosphate local structure was maintained. Moreover, the presence of MgO improved the chemical stability of the electrolyte in air.

Synthesis and Comprehensive Analytical Study of β-Li3PS4 Stabilization by Ca- and Ba-Codoped Li3PS4.

Sulfide-based solid electrolytes with high Li+ conductivity, such as Li3PS4, are key materials for the realization of all-solid-state Li+ batteries. One approach to achieving high Li+ conductivity is to combine crystalline-phase stabilization at high temperatures with the introduction of defects at room temperature. In this work, this approach was verified by codoping Li3PS4 with two kinds of divalent cations. The resulting structural changes were comprehensively investigated both experimentally and computationally. The high-temperature β-Li3PS4 phase of Li3PS4 could be stabilized at room temperature by adjusting the amount of Ca or Ba doping. The synthesized samples doped with divalent cations were found to have conductivities about 2 orders of magnitude higher than that of the γ-Li3PS4 phase at room temperature. The resultant Li+ conductivity at room temperature was also higher than that expected from interpolation of results for nondoped β-Li3PS4. It is believed that the structural changes produced by the divalent cation doping contribute to this increase in conductivity. The stability of the β-Li3PS4 phase with divalent cation doping was also demonstrated using density-functional-theory calculations for models with equivalent compositions to the synthesized samples. The Li+ positions obtained by structural optimization calculations showed the presence of diverse and disordered Li sites in the Ca-doped lattice. Such structural changes can contribute to cascade processes involving Li+ collisions, referred to as the "billiard-ball" mechanism, which cannot occur in nondoped β-Li3PS4. This series of experiments involving the synthesis and analyses of β-Li3PS4 with divalent cation doping provides a way to enhance Li+ conductivity through structural modification and optimization.