Sulfide-based Solid Electrolytes Research Articles

(Invited) Strategies for Enhancing the Stability of the Electrode-Electrolyte Interphase in Sulfide-Based Solid-State Batteries

In recent years, all solid-state batteries (SSBs) have gained significant attention as the next-generation energy storage device due to their high energy density, improved safety, and enhanced stability. Sulfide-based solid electrolytes (SEs) have garnered significant attention among various inorganic materials for their exceptional properties, including high ionic conductivity and robust mechanical properties. These features make them promising candidates for SSBs, ensuring both manufacturability and long-term cycle life. For example, Li-argyrodites (e.g., Li6PS5X, and X = Cl, Br, I) and Na-thioantimonate (e.g., Na2.88Sb0.88W0.12S4) offer high ionic conductivities (> 10-3 S/cm) that are comparable to those of liquid electrolytes. However, its practical application is still under-achieved due to a few technical challenges. Among the various issues, our focus is on the electrode-electrolyte interphase, which degrades the cycle life of the SSBs.At the cathode-electrolyte interphase, narrow electrochemical window (1.71 V – 2.01 V) of Li6PS5X unwantedly prompt the oxidative decomposition of solid-electrolyte. At the anode-electrolyte interphase, Li-argyrodite SEs can be easily reduced by Li metal or oxidized by cathode active materials because of its narrow electrochemical window (1.71 V – 2.01 V). The resulting byproducts at electrode-electrolyte interphases can unwantedly lead to capacity fading and an increase in cell resistance. Additionally, SSBs made with the Li-argyrodite SEs suffer from Li-dendrite penetration during repeated cycles and consequent internal short circuits.To address these challenges, we propose strategies for passivating the interphases between the cathode and the solid electrolyte, as well as between the metallic anode and the electrolyte in solid-state batteries (SSBs). Through a combinatorial study, we aim to elucidate the extent and severity of interfacial side reactions in solid-state batteries (SSBs). In addition, the optimal coating strategies of LiNbO3 for cathodes and Li3N coating on metallic Li anode will be discussed. The optimized Li3N as an artificial solid electrolyte interphase (SEI) layer on the metallic Li anode enables more than 5000 cycles without failure in symmetrical cells.Furthermore, we will also highlight a strategy for passivating the electrode-electrolyte interphases of Na-based solid-state batteries (SSBs) that employ thioantimoniate as the electrolyte material. The approaches to passivate the cathode and metallic Na anode will be presented. Comprehensive electrochemical and spectroscopic studies will be conducted to identify the source of degradation and elucidate the improvement mechanisms associated with each strategy.

Investigating the Mechanisms of Li Dendrite Formation in Sulfide Solid Electrolytes for All-Solid-State Batteries

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.

PVDF-HFP via Localized Iodization as Interface Layer for All-Solid-State Lithium Batteries with Li6PS5Cl Films.

All-solid lithium (Li) metal batteries (ASSLBs) with sulfide-based solid electrolyte (SEs) films exhibit excellent electrochemical performance, rendering them capable of satisfying the growing demand for energy storage systems. However, challenges persist in the application of SEs film owing to their reactivity with Li metal and uncontrolled formation of lithium dendrites. In this study, iodine-doped poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) as an interlayer (PHI) to establish a stable interphase between Li metal and Li6PS5Cl (LPSCl) films is investigated. The release of I ions and PVDF-HFP produces LiI and LiF, effectively suppressing lithium dendrite growth. Density functional theory calculations show that the synthesized interlayer layer exhibits high interfacial energy. Results show that the PHI@Li/LPSCl film/PHI@Li symmetrical cells can cycle for more than 650h at 0.1mA cm-2. The PHI@Li/LPSCl film/NCM622 cell exhibits a distinct enhancement in capacity retention of ≈26% when using LiNi0.6Mn0.2Co0.2O2 (NCM622) as the cathode, compared to pristine Li metal as the anode. This study presents a feasible method for producing next-generation dendrite-free SEs films, promoting their practical use in ASSLBs.

Enhanced Electrochemical Stability and Extended Cycle Life in Sulfide-Based All-Solid-State Batteries: The Role of Li10 SnP2 S12 Coating on Ni-Rich NCM Cathode.

Recently, sulfide-based all-solid-state batteries (ASSBs) have attracted great attention because of their excellent safety and high energy density. However, by-products formed from side-reactions between the oxide-based cathodes and sulfide-based solid electrolytes (SEs) increase the interfacial resistance and degrade the cell performance. Suppression of this interfacial resistance is thus critical. In this study, the extraordinarily high stability of the cathode/SE interface is discovered when a Li10 SnP2 S12 (LSnPS) is applied to a cathode buffer layer. The electrochemical properties of the cathode interface at high potential are improved by synthesizing a core-shell structure cathode using LSnPS. The synthesized LSnPS is uniformly coated on a Li2 ZrO3 -coated LiNi0.8 Co0.1 Mn0.1 O2 (LZO-NCM) surface using the cost-efficient mechano-fusion method. The ASSB with LSnPS-coated LZO-NCM as the cathode and Li6 PS5 Cl (argyrodite, LPSCl) as the SE exhibited a capacity of 192 mAh g-1 and excellent cycle retention of ≈75% after 500 charge/discharge cycles. In addition, the degradation mechanism at the cathode/SE interface is investigated. The results indicated that LSnPS stabilizes the interface between NCM and argyrodite, thereby inhibiting the decomposition of the SE. This technology is expected to contribute to the commercialization of cathode materials for sulfide-based ASSBs due to its enhanced cycle performance, low-cost material application, and eco-friendly process.

Synthesis and Characterization of Na3SbS4 Solid Electrolytes via Mechanochemical and Sintered Solid-State Reactions: A Comparative Study

A sulfide-based solid electrolyte is an enticing non-organic solid-state electrolyte developed under ambient conditions. Na3SbS4, a profoundly enduring substance capable of withstanding exceedingly elevated temperatures and pressures, emerges as a focal point. Within this investigation, we employ dual distinct techniques to fabricate Na3SbS4, encompassing ball milling and the combination of ball milling with sintering procedures. A remarkable ionic conductivity of 3.1 × 10−4 S/cm at room temperature (RT), coupled with a meager activation energy of 0.21 eV, is achieved through a bifurcated process, which is attributed to the presence of tetragonal Na3SbS4 (t-NSS). Furthermore, we delve into the electrochemical performance and cyclic longevity of the Na2/3Fe1/2Mn1/2O2|t-NSS|Na system within ambient environs. It reveals 160 mAh/g initial charge and 106 mAh/g discharge capacities at 0.01 A/g current density. Furthermore, a cycle life test conducted at 0.01 A/g over 30 cycles demonstrates stable and reliable performance. The capacity retention further highlights its enduring energy storage capabilities. This study underscores the sustainable potential of Na3SbS4 as a solid-state electrolyte for advanced energy storage systems.

Flexible and thin sulfide-based solid electrolyte sheet with Li+-ion conductive polymer network for all-solid-state lithium-ion batteries

All-solid-state lithium batteries (ASSLBs) with solid electrolytes are promising battery systems capable of improving the safety and energy density of current lithium-ion batteries. Reducing the thickness of the solid electrolyte while preventing the short circuit between the anode and cathode is imperative to increase the energy density of ASSLBs. Sulfide-based solid electrolytes have high ionic conductivities; however, they are brittle, difficult to be processed into a thin film, and challenging to form stable interfaces with electrodes of large volume change. In this study, flexible thin-solid electrolyte sheets with Li+-ion conductive polymer network were prepared and characterized for ASSLB applications. They exhibited higher ionic conductance and superior mechanical properties than those of pristine Li6PS5X (argyrodite) pellets. The all-solid-state lithium-ion cell (graphite/LiNi0.7Co0.15Mn0.15O2) with a solid electrolyte sheet delivered a high discharge capacity of 182.5 mAh g−1 and showed good cycling stability at 0.33 C and 25 ℃, demonstrating that flexible and thin sheets are promising solid electrolytes for ASSLBs operating at room temperature.

Trimethylsilyl Compounds for the Interfacial Stabilization of Thiophosphate-Based Solid Electrolytes in All-Solid-State Batteries.

Argyrodite-type Li6 PS5 Cl (LPSCl) has attracted much attention as a solid electrolyte for all-solid-state batteries (ASSBs) because of its high ionic conductivity and good mechanical flexibility. LPSCl, however, has challenges of translating research into practical applications, such as irreversible electrochemical degradation at the interface between LPSCl and cathode materials. Even for Li-ion batteries (LIBs), liquid electrolytes have the same issue as electrolyte decomposition due to interfacial instability. Nonetheless, current LIBs are successfully commercialized because functional electrolyte additives give rise to the formation of stable cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) layers, leading to supplementing the interfacial stability between electrolyte and electrode. Herein, inspired by the role of electrolyte additives for LIBs, trimethylsilyl compounds are introduced as solid electrolyte additives for improving the interfacial stability between sulfide-based solid electrolytes and cathode materials. 2-(Trimethylsilyl)ethanethiol (TMS-SH), a solid electrolyte additive, is oxidatively decomposed during charge, forming a stable CEI layer. As a result, the CEI layer derived from TMS-SH suppresses the interfacial degradation between LPSCl and LiCoO2 , thereby leading to the excellent electrochemical performance of Li | LPSCl | LiCoO2 , such as superior cycle life over 2000 cycles (85.0% of capacity retention after 2000 cycles).

Transforming Li3PS4 Via Halide Incorporation: a Path to Improved Ionic Conductivity and Stability in All‐Solid‐State Batteries

AbstractTo enhance Li+ transport in all‐solid‐state batteries (ASSBs), harnessing localized nanoscale disorder can be instrumental, especially in sulfide‐based solid electrolytes (SEs). In this investigation, the transformation of the model SE, Li3PS4, is delved into via the introduction of LiBr. 31P nuclear magnetic resonance (NMR)unveils the emergence of a glassy PS43− network interspersed with Br−. 6Li NMR corroborates swift Li+ migration between PS43− and Br−, with increased Li+ mobility indicated by NMR relaxation measurements. A more than fourfold enhancement in ionic conductivity is observed upon LiBr incorporation into Li3PS4. Moreover, a notable decrease in activation energy underscores the pivotal role of Br− incorporation within the anionic lattice, effectively reducing the energy barrier for ion conduction and transitioning Li+ transport dimensionality from 2D to 3D. The compatibility of Li3PS4 with Li metal is improved through LiBr incorporation, alongside an increase in critical current density from 0.34 to 0.50 mA cm−2, while preserving the electrochemical stability window. ASSBs with 3Li3PS4:LiBr as the SE showcase robust high‐rate and long‐term cycling performance. These findings collectively indicate the potential of lithium halide incorporation as a promising avenue to enhance the ionic conductivity and stability of SEs.

Protective NaSICON Interlayer between a Sodium-Tin Alloy Anode and Sulfide-Based Solid Electrolytes for All-Solid-State Sodium Batteries.

This paper presents a suitable combination of different sodium solid electrolytes to surpass the challenge of highly reactive cell components in sodium batteries. The focus is laid on the introduction of ceramic Na3.4Zr2Si2.4P0.6O12 serving as a protective layer for sulfide-based separator electrolytes to avoid the high reactivity with the sodium metal anode. The chemical instability of the anode|sulfide solid electrolyte interface is demonstrated by impedance spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The Na3.4Zr2Si2.4P0.6O12 disk shows chemical stability with the sodium metal anode as well as the sulfide solid electrolyte. Impedance analysis suggests an electrochemically stable interface. Electron microscopy points to a reaction at the Na3.4Zr2Si2.4P0.6O12 surface toward the sulfide solid electrolyte, which does not seem to affect the performance negatively. The results presented prove the chemical stabilization of the anode-separator interface using a Na3.4Zr2Si2.4P0.6O12 interlayer, which is an important step toward a sodium all-solid-state battery. Due to the applied pressure that is mandatory for battery cells with sulfide-based cathode composite, the use of a brittle ceramic in such cells remains challenging.

Nanoporous silicon fiber networks in a composite anode for all-solid-state batteries with superior cycling performance

All-solid-state batteries comprising Si anodes are promising materials for energy storage in electronic vehicles because their energy density is approximately 1.7 times higher than that of graphite anodes. However, Si undergoes severe volume changes during cycling, resulting in the loss of electronic and ionic conduction pathways and rapid capacity fading. To address this challenge, we developed composite anodes with a nanoporous Si fiber network structure in sulfide-based solid electrolytes (SEs) and conductive additives. Nanoporous Si fibers were fabricated by electrospinning, followed by magnesiothermic reduction. The total pore volume of the fibers allowed pore shrinkage to compensate for the volumetric expansion of Li12Si7, thereby suppressing outward expansion and preserving the Si-SE (or conductive additive) interface. The network structure of the lithiated Si fibers compensates for electronic and ionic conduction pathways even to the partially delaminated areas, leading to increased Si utilization. The anodes exhibited superior performance, achieving an initial Coulombic efficiency of 71%, a reversible capacity of 1474 mAh g−1, and capacity retention of 85% after 40 cycles with an industrially acceptable areal capacity of 1.3 mAh cm−2. The proposed approach can reduce the constraint pressure during charging/discharging and may have practical applications in large-area all-solid-state batteries.

New Insights of Infiltration Process of Argyrodite Li6PS5Cl Solid Electrolyte into Conventional Lithium-Ion Electrodes for Solid-State Batteries

All-solid-state lithium-ion batteries based on solid electrolytes are attractive for electric applications due to their potential high energy density and safety. The sulfide solid electrolyte (e.g., argyrodite) shows a high ionic conductivity (10−3 S cm−1). There is an open question related to the sulfide electrode’s fabrication by simply infiltrating methods applied for conventional lithium-ion battery electrodes via homogeneous solid electrolyte solutions, the structure of electrolytes after drying, chemical stability of binders and electrolyte, the surface morphology of electrolyte, and the deepening of the infiltrated electrolyte into the active materials to provide better contact between the active material and electrolyte and favorable lithium ionic conduction. However, due to the high reactivity of sulfide-based solid electrolytes, unwanted side reactions between sulfide electrolytes and polar solvents may occur. In this work, we explore the chemical and electrochemical properties of the argyrodite-based film produced by infiltration mode by combining electrochemical and structural characterizations.

Improved interfacial compatibility and ionic conductivity of SnI4 Co-doping Li-argyrodite sulfide electrolyte for all-solid-state lithium batteries

Despite lithium-argyrodite electrolytes have attracted great attention due to the high ionic conductivity and relatively lower cost, their applications are hindered by the inferior air stability and poor Li compatibility. Herein, we report a Sn/I co-doping the Li6PS5Cl strategy to overcome above obstacles. The optimized LPSC-0.05SnI4 exhibits high ionic conductivity of 3.9 × 10−3 S cm−1 at room temperature, and improved air stability. More importantly, an in situ formed LiI-rich interface on the lithium anode is introduced through the LPSC-0.05SnI4. As a result, the Li/LPSC-0.05SnI4/Li symmetric batteries deliver high critical current density of 1.45 mA cm−2 and a remarkable steady Li plating/stripping performance over 6000 h at 0.1 mA cm−2. The assembled LNO@NMC811/LPSC-0.05SnI4/Li all-solid-state batteries display prominent capacity and cycling stability. This work provides a practical and effective method for designing versatile and high-performance sulfide-based solid electrolytes.

Structural analysis and ionic conduction mechanism of sulfide-based solid electrolytes doped with Br

Sulfide glasses can exhibit notable ionic conductivity because of annealing-associated crystallization. One well-known example is Li7P3S11. Our research showed that adding bromine (Br) to Li3PS4 sulfide glass results in a similar crystal structure and high ionic conductivity comparable to that of another compound Li10GeP2S12. This structure differs from the PS4 anion framework of Li3PS4. In addition, the ionic conductivity decreases owing to a structural transition to the β-phase. Herein, we present our findings on the local structure of Li3PS4 sulfide glass and its crystallized glass ceramic with the addition of Br. This analysis relies on the pair distribution function analysis obtained from high-energy X-ray diffraction. Moreover, using the bond valence sum method, we verified that incorporating Br promotes the formation of Li ionic conduction pathways. Our results indicate that precise control over the anion molecular structure by introducing halogens holds promise for achieving high Li-ion conductivity.

Investigation of the Reaction Mechanism of All-Solid-State Lithium-Sulfur Batteries by Operando in Situ Raman Spectroscopy

In recent years, all-solid-state lithium-sulfur batteries (ASSLSBs) with sulfide-based solid electrolytes have become a leading energy storage system due to their high ionic conductivity, ultra-high energy density, high safety, and low cost. There have been many challenges with the practical applications of Li-S batteries, however, as a result of the sluggish redox kinetics of lithium polysulfide (LPS) and its shuttling effects. Single-atom catalysts (SACs) with atomically dispersed metal-based sites have proven to be promising electrocatalysts in Li-S batteries. To construct the ASSLSBs, we design and develop MoS2/SnS2 and Fe SACs with MoS2/SnS2 cathodes, Li5.4PS4.4Cl1.6 sulfide-based solid electrolytes, and Li-In anode. In the current study, in situ Raman spectroscopy is used to determine the LPS species in the sulfur cathode with SACs and without SACs during the ASSLSBs cycling. The aim is to understand the charge-discharge mechanism and the influence of SACs on the dissolution of sulfur and poly-sulfides. As compared to the MoS2/SnS2 cathode, the Fe@MoS2/SnS2 cathode exhibit the highest catalytic LPS conversion. In addition, the Fe@MoS2/SnS2 cathode delivers a high discharge capacity and long-cycling performance with high coulombic efficiency in ASSLSBs. In operando in situ Raman studies, SACs provide important new insights into the charge-discharge reaction mechanism for the next generation of ASSLSBs.

Novel Symmetric Cell Design for Analyzing All-Solid-State Battery Electrode

All-solid-state lithium batteries (ASSBs) with sulfide-based solid electrolytes (SSEs) have drawn much attention recently for the next-generation batteries. But there are some obstacles to overcome for their practical use. The SSE|cathode interface with poor contact and (electro)chemical instability is the subject of special interest, since it critically aggravates the core performance of battery, including cycling stability and rate capability. In addition to the interfacial property, it has been widely known that Li+ transport characteristics inside the cathode is another key factor in terms of fast and efficient operation of all the lithium battery systems, including the ASSBs. Thus, it goes without saying that the accurate characterization of the interfacial and bulk properties of the cathode is essential to develop the ASSBs.There are limited numbers of test cells to analyze the interface and bulk properties of the battery. First, a conventional half-cell includes Li metal as a counter electrode (CE), which is assumed to have a negligible resistance compared to that of the working electrode (i.e., cathode). It has been reported, however, that the effect of Li CE on total electrochemical signal cannot be disregarded. Moreover, the relative contribution of Li CE to total signal is increasing with the use of the state-of-the-art cathode, whose resistance is getting dramatically lower with technological progress. That is, it is getting difficult to obtain a reliable cathode response by using the two-electrode half-cell configuration. Second, a three-electrode test cell provides the signal of each electrode separately and has been extensively used for the electrochemical analysis. When one uses it for the ASSBs, however, the signals can be erroneous due to the structural distortion caused by the reference electrode (RE) insertion and its own chemical instability, which is especially severe in ASSBs with SSEs. Finally, an alternative cell design to avoid the above problems is a symmetric cell including two identical electrodes facing each other. A general symmetric cell is fabricated by charging/discharging two unit-cell, disassembling them, and re-assembling the identical electrodes to face each other. Unfortunately, a series of such procedure, esp. disassembling/re-assembling, is not applicable to the ASSB systems.In this study, a novel non-destructive potential-controllable symmetric cell (PCSC) is proposed for ASSBs. It features a porous temporary CE (TCE) in parallel between two symmetric electrodes. TCE works as an acceptor or provider of Li to charge or discharge, thereby controls the electrode potential. Symmetric electrodes are then evaluated electrochemically after disconnecting the TCE. As a case study, we investigated and comparatively analyze the electrochemical characteristics of an ASSB cathode, LiNbO3-coated LiNi0.8Co0.1Mn0.1O2, obtained from the conventional test cells and PCSC. Figure presents the impedance spectra of test cells. The two-electrode half-cell impedance is noticeably affected by Li CE over a wide frequency range and the three-electrode cell impedance suffers from severe noise probably caused by RE in the low frequency region. This indicates that both test cells are not suitable for interpreting reliably the interfacial and bulk properties of the cathode. In contrast, the impedance spectra from the PCSC have similar trend to that of three-electrode cell, but provides much more stable impedance spectra, allowing more accurate estimation of interface and bulk characters. In this presentation, the results obtained from DC techniques, such as galvanostatic method, are also comparatively analyzed with conventional test cells and our PCSC. Moreover, the reliability of the estimated values from the PCSC will be discussed by the comparison with those of the previous works. Figure 1

Investigation of Sulfide-Based Solid Electrolytes (SSE) Sensitivity Towards Humidity

All-solid-state lithium-ion batteries (ASSBs) represent a new generation of energy storage tools containing only solid components. They are of great interest to researchers and manufacturers thanks to their high energy density, which makes them promising candidates for electric transport applications. Among different types of solid-state electrolytes for lithium-ion batteries (LIBs), sulfide-based electrolytes (SSEs) have several advantages, such as high ionic conductivity and malleability [1, 2]. However, one of their main drawbacks is a high sensitivity towards air humidity [3]. Fast reaction of the SSEs with water results in the degradation of their structure and release of toxic gas (H2S) when exposed to even low concentrations of humidity. This factor leads to significant process cost and safety issues associated with mass production of ASSBs with sulfide-based SEs.The purpose of the present work is to study in details reactivity of SSEs towards humidity by following two main directions: The development of a flow-through setup that allows a better identification and highly precise quantification of gases (H2S or others) generated during reaction between water (humidity) and commercial SSEs: this flow-through setup intends to solve problems usually encountered when using closed-type setups, which are the most used setups in the literature[3, 4]. These problems include over-concentration of detected gases and low reproducibility of measurements;Physico-chemical and electrochemical characterizations of pristine and humidity exposed-SSEs in order to reveal the main factors affecting sensitivity towards humidity and to understand the degradation mechanisms. First, the efficiency of the flow-through gas analysis setup developed had been validated: H2S detection curves obtained for commercial SSE powders (Li6PS5Cl, Li6PS5Br, Li7P3S11, Li3PS4, Li10GeP2S12) in contact with humid Argon (30 to 200 ppm H2O in Ar) are highly reproducible (see example in Fig. 1 and Table 1). Measurements conducted at different humidity levels allowed accessing kinetics of water-induced degradation reactions involved. SSE powders characterizations using XRD, Raman, XPS, SEM, EIS, granulometry before and after exposure to humidity provided an insight into degradation-related phenomena taking place: morphology deterioration, loss of structure and conductive structural groups, drastic increase of ionic resistance. A relationship between the structure of SSE and its reactivity towards water was found and described.Refs[1] Energy Storage Mater. 2018, 14, 58–74 ; [2] Nano Energy 2021, 83, 105858 ; [3] Solid State Ion. 2011, 182 (1), 116–119 ; [4] Chem. Mater. 2020, 32 (6), 2664–2672. Figure 1

Optimizing Sulfur Utilization in High Loading Cathode for All-Solid-State Lithium-Sulfur Battery

All Solid-state Lithium-Sulfur battery (ASSLSB) possesses a great promise in providing a safe, high energy density, and low cost battery technology for vehicle electrification and grid energy storage. To achieve practically high specific energy in ASSLSB (e.g., >400 Wh/Kg), sulfur cathodes with high areal capacity (>6 mAh cm-2) are essentially needed to offset the relatively low working voltage of elemental sulfur cathode (1.9 V vs. Li). This requires high mass loading sulfur cathodes by maximizing both sulfur content in the whole electrode and sulfur utilization rate to reduce the parasitic weights. An optimal electrode architecture featuring sufficiently connected sulfur/solid electrolyte/carbon triple interfaces is desired to enable sulfur’s fast accessibility to electron and Li-ion simultaneously. Due to the non-flowability of those three solid components, however, it is very hard to maximize the contact of trip solid phases, which need new insights of the materials design and processing technology.This work looks at carbon microstructures and their impact on triple-point contact between electrochemically active sulfur, carbon, and the solid-state electrolyte (SSE) that comprises most composite cathodes in ASSLSB systems. While significant work has gone into understanding and developing novel carbon host structures for liquid Li-S cells for improving sulfur utilization, polysulfide trapping, better understanding is needed for ASSLSBs. Specifically, how sulfur infiltration, loading, and spatial distribution within the porous carbon host impacts sulfur utilization. Understanding how the infiltrated sulfur that resides in the porous carbon host connects with both carbon and solid electrolyte networks across the whole electrode structure and maintains its robustness during the repeated cell cycling is needed to achieve full utilization in high sulfur loading electrodes. The solid sulfur cathode system examined in the present study is a composite of porous carbon, sulfur, and a sulfide-based solid electrolyte. A combination of porous carbon hosts is investigated and correlated to the cell performance at practical conditions. Advanced characterization and computational tools are used to further elucidate the key parameters for high sulfur utilization in ASSLSBs with high sulfur loading cathodes. Details of the study will be presented and discussed at the meeting.Reference:(1) Nagata, H. and Y. Chikusa (2016). "All-Solid-State Lithium–Sulfur Battery with High Energy and Power Densities at the Cell Level." Energy Technology 4(4): 484-489(2) Banerjee, A., et al. (2020). "Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes." Chemical Reviews 120(14): 6878-6933.

Controls Stack Pressure Induced Fracture Using Microstructural Modulation in Solid-State Batteries

All-solid-state batteries (ASSBs) provide higher energy densities and safer alternatives to Li-ion batteries by incorporating Li-metal anode and inflammable solid electrolytes. To match the increased capacity of metallic anodes, ASSBs require high-energy-density cathode materials such as LiNixCoyMn1-x-yO2 (also known as NMC cathode) blended with a solid-state electrolyte (SSE). However, a key challenge is resolving the interfacial incompatibility between the active particulate material and the solid-state electrolyte within these composite cathodes. To obtain intimate contact between SSE and the active material, an external load (or stack pressure) needs to be applied during the processing and service life of cell. Nevertheless, such densification of cathode composites can lead to grain boundary fracture and/or complete particle disintegration. Therefore, the present work utilizes a microstructural modulation procedure to alleviate stack pressure-induced fracture in a polycrystalline cathode. Accordingly, a thermodynamically consistent computational framework is developed to understand the interplay between the stack pressure, microstructural modulation, and fracture behavior for polycrystalline NMC secondary particles embedded in a sulfide-based solid electrolyte. A phase-field fracture variable is employed to consider the initiation and propagation of cracks in the active material and SSE. This modeling framework is implemented in the open-source finite element package (MOOSE) to solve three state variables: concentration, displacement, and the phase-field damage parameter. A systematic parametric study is performed to explore the effects of stack pressure, aspect ratio, and the crystal orientation of grains on the chemo-mechanical performance of the composite electrode. We also quantitatively validate the numerical model with experimental investigation using state-of-the-art Nano-CT (Compact tomography) technique. The findings of this study offer predictive insights for designing solid-state batteries with reduced fracture evolution and stable performance. Figure 1

Usage of Co-Solvent for Fabricating the Composite Cathode for Sulfide-Based All-Solid-State Lithium Batteries

In recent decades, lithium-ion batteries (LIBs) have been widely used in electric vehicles and large-scale energy storage systems. However, current LIBs using the flammable organic electrolytes have a safety issue. Therefore, all-solid-state lithium batteries (ASSLBs) with enhanced safety and high energy density are in the spotlight. Among many solid electrolytes, sulfide-based solid electrolytes with high ion conductivity and ductile property are the most promising. In order to develop the ASSLBs, the composite cathode with high mass loading is imperative, which can be fabricated by the wet process suitable for mass production. Polar solvents can disperse a binder with polar groups well, but it may cause severe dissolution of sulfide solid electrolytes in the composite cathode. Therefore, we tried to use co-solvent that can disperse a polymer binder well and prevent the dissolution of sulfide solid electrolyte. Cycling performance of ASSLBs employing the wet-type composite cathode was evaluated and will be reported.

High-Voltage Degradation of Ni-Rich Cathode Materials in All-Solid-State Batteries

Lithium-ion battery (LIB) has been widely used as electrochemical energy storage devices in a variety of fields in our daily lives. In particular, recently there are strong market demands in the energy storage systems and electric vehicles, mainly due to its high energy and power densities. However, the customers’ strong needs for the safer and longer-lasting battery than commercial ones have sparked special interest in all-solid-state lithium battery (ASSB), which has a great possibility of replacing the conventional LIB that uses liquid electrolyte solution. Though much effort has been made for its practical applications, there are still a number of critical issues involved in the electrode/cell design, fabrication, scale-up, efficient operating conditions, etc. Upper cut-off voltage is one of the most important parameters, having a determinative effect on the energy density and cycling stability of the ASSB esp. when one uses Ni-rich layered oxide cathodes. Actually, the upper cut-off voltage is treated with high priority also in the LIB systems. In the case of the LIB, the secondary particle cracking is followed by gap-filling with electrolyte during the repetitive high voltage charging, giving additional electrochemical active area. Whereas, the particle cracking in the ASSB usually leads to the isolation of the primary particles. In addition, it is reported that the interface between active materials and solid electrolyte is degraded in a complex manner due to simultaneous chemical side reactions (e.g. cathode electrolyte interphase (CEI) formation) and mechanical breakdown (e.g. contact loss between electrolyte and particle), different from that of the LIB. Therefore, an analysis of cathode degradation in the ASSB needs to be dealt with in a different way from that in the LIB.In this work, the degradation of ASSB, consisting of sulfide-based solid electrolyte and Ni-rich cathode, undergoing the high voltage charge cycling is systematically studied using the electrochemical techniques. For this purpose, first, the deterioration tendency of reversible capacity and cell resistance was analyzed in constant current-constant voltage (CC-CV) charging mode at different upper cut-off voltages (CC charging) and the following charging times (CV charging). In addition, the effect of charging rate on the degradation trend was investigated in terms of the duration time that the cathode potential stays higher than a specific potential value in CC charging mode. It was confirmed that there are particular degradation tendencies of capacity and resistance for upper cut-off voltage and duration time, and the empirical relations were accordingly derived. Notably, the degradation trends between capacity and resistance were observed differently, strongly indicative of different governing factor for each degradation process. In the experiments at various charging rates, the lower charging rate led to larger degradation of the cathode. It is suggested that the application of a driving force for irreversible phase transition (i.e., from H2 to H3) for longer time at lower charging rate is the most probable reason.In order to more clearly understand the governing factors affecting high voltage cathode degradation, the degradation trends of capacity and resistance at the aforementioned operating conditions were thoroughly investigated using incremental capacity-differential voltage (IC-DV) analysis and electrochemical impedance spectroscopy (EIS), respectively. From the IC-DV analysis, it proved that the loss of active materials (LAM) is accelerated at higher cut-off voltage, longer duration time, and lower charging rate, indicating that the LAM might be one of the governing factors for capacity degradation. It is notable, by the way, that the interfacial resistance of the cathode was considerably increased at high voltage charging and implies the loss of lithium inventory (LLI) due to the CEI formation could be another major degradation mode. Accordingly, we tried to estimate the contribution of LLI to total degradation from the comparison of half-cell and full-cell analyses. On the other hand, from the EIS analysis, it was found that the increasing rate of the interfacial resistance was far higher than the decreasing rate of capacity. This tells us that the degradation of the cathode|electrolyte interface is mainly responsible for the resistance or power degradation at high voltage charging. In this presentation, the deterioration modes of ASSB at various high voltage charging conditions are explained in terms of the interface and bulk of the cathode. Moreover, the strategy to minimize the degradation at high voltage charging will be discussed.