Manufacturing High-Energy-Density Sulfidic Solid-State Batteries

Sulfide-based all-solid-state batteries (ASSBs) have ushered in a new era of energy storage technology, offering the tantalizing prospect of unprecedented energy density and safety. However, the poor electrode-electrolyte interface between Li anodes and sulfide solid electrolytes has hindered its practical application. In this review, the primary focus lies in the current fundamental understanding, challenges, and optimization strategies regarding the interface chemistries between sulfide solid electrolytes and Li anode. First, an in-depth discussion is conducted and provides a detailed summary of the interfacial challenges that exist between the Li anode and sulfide solid electrolytes. Among these challenges, poor interfacial compatibility and stability stand out as the two crucial issues. Subsequently, effective approaches are systematically explored to surmount these issues. These encompass the component optimization and structural design of the bulk anode, doping and coating strategies of the sulfide solid electrolytes, and interface design between the Li anode and sulfide solid electrolytes. Finally, the insights are present into the limitations of current studies, perspectives, and recommendations for the further development of sulfide-based solid-state batteries, aiming to offer a comprehensive and enlightening overview for interface engineering, which is of great significance for the integration of applicable all-solid-state Li metal batteries (ASSLMBs).

Interface compatibility between sulfide solid electrolytes and Ni-rich oxide cathode materials: factors, modification, perspectives

All-solid-state batteries (ASSBs) working at room and mild temperature have demonstrated inspiring performances over recent years. However, the kinetic attributes of the interface applicable to the subzero temperatures are still unidentified, restricting the low-temperature interface design and operation. Herein, a host of cathode interfaces are constructed and investigated to unlock the critical interface features required for cryogenic temperatures. The unstable interface between LiNi0.90Co0.05Mn0.05O2 (Ni90) and Li6PS5Cl (LPSC) sulfide solid electrolyte (SE) results in unfavorable cathode-electrolyte interphase (CEI) and sluggish lithium-ion transport across the CEI. After inserting a Li2ZrO3 (LZO) coating layer, the activation energy of the Ni90@LZO/sulfide SE interface can be reduced from 60.19 kJ mol-1 to 41.39 kJ mol-1 owing to the suppressed interfacial reactions. Through replacing the LPSC SE and LZO coating layer by the Li3InCl6 (LIC) halide SE, both a highly stable interface and low activation energy (25.79 kJ mol-1) can be achieved, thus realizing an improved capacity retention (26.9%) at -30 °C for the Ni90/LIC/LPSC/Li-In ASSB. Moreover, theoretical evaluation clarifies that cathode/SE interfaces with high ionic conductivity and low energy barrier are favorable to the Li+ conduction through the interphase and the Li+ transfer across the cathode/interphase interface. These critical understandings may provide guidance for low-temperature interface design in ASSBs.

Surface to bulk design empowering Ni-rich layered oxide cathode in sulfide-based All-Solid-State batteries

Sulfide solid electrolytes are promising materials for next-generation all-solid-state lithium batteries due to their high ionic conductivity, mechanical properties, and compatibility with advanced electrodes like lithium metal. Recent advancements have focused on optimizing synthesis techniques, including both solid-phase and liquid-phase methods, alongside strategic doping modifications that enhance ionic conductivity and improve chemical stability. Despite these improvements, challenges remain, particularly in stabilizing interfaces between sulfide solid electrolytes and electrodes, as chemical reactivity leads to resistive layers and reduced battery performance. Efforts to address these challenges involve protective coatings, surface engineering, and advanced structural modifications. Additionally, sulfide solid electrolytes face environmental sensitivity, with exposure to air and moisture leading to degradation. To counter this, strategies such as hybrid electrolyte systems and surface treatments are being investigated to ensure long-term stability under various conditions. This review summarizes recent developments in sulfide solid electrolytes synthesis, doping modification, and interface engineering, while outlining future directions needed for the successful commercialization of all-solid-state lithium batteries, positioning sulfide-based electrolytes as key components for advancing battery safety, efficiency, and energy density.

All-solid-state batteries (ASSBs) using inorganic solid electrolytes are expected to achieve high safety and high energy density as alternatives to conventional lithium-ion batteries using liquid electrolytes. However, in many cases, rate capability of ASSBs is poor compared with that of the conventional liquid system. This is because the contact interface between solid active materials and solid electrolyte is insufficient, resulting in high resistance for electrochemical properties. The solid electrode-electrolyte interface in ASSBs is related to the morphological structure such as porosity and mixed state. It has been confirmed that pressurization reduces the grain boundaries of solid electrolytes and improves conductivity1). From this improvement, it is generally known that applying high pressure when assembling ASSBs improves the contact area of the solid-solid interface, including electrode and electrolyte interface. However, the effect of pressure on particle-particle contact and battery performance is not understood enough. In this study, we investigated the effect of pressure-induced three-dimensional structure on the electrochemical properties of ASSBs by using X-ray computed tomography (CT). ASSBs were prepared at various stack pressures using a composite cathode consisting of oxide active materials LiNi1/3Co1/3Mn1/3O2 (NCM), sulfide solid electrolyte Li10GeP2S12 (LGPS), and acetylene black. Electrochemical properties were investigated in ASSBs of NCM composite cathode|LGPS solid-electrolyte|In-Li anode. The charge–discharge measurements were performed using various stack pressure, which indicates that the capacity increases as the stack pressure increases. To analyze the factors behind this result in terms of the internal structure of the ASSBs, we performed X-ray CT with synchrotron radiation at 20 keV using a homemade operando measurement cell that electrode diameter is 1 mm. This measurement system allows us to analyze the three-dimensional structure of composite cathode during monitoring applied pressure, electrochemical measurements, and X-ray CT measurements. From the X-ray CT data, we succeeded in quantifying the changes in the porosity of the composite cathode and the contact state between the active material and electrolytes by changing the pressure. Quantitative analysis revealed that the porosity and contact state correlate with the charge–discharge properties. Additionally, CT analysis revealed that the voids are preferentially presented near active materials and these voids spread the horizontal direction (not pressurization direction), resulting in different porosities of composite cathode and solid electrolyte layer. Since it was confirmed that voids remained in the vicinity of the active material even when the pressurization was continued, controlling these voids decreases the voids of the entire cathode layer. Pressure dependencies on AC impedance during X-ray CT measurements showed that the apparent conductivity of ASSBs increases linearly as the confinement stack pressure increases. This result is caused by suggesting that the decrease in porosity and tortuosity in cathode layer, which is detected by CT analysis. Additionally, date of tortuosity shows over-pressurization may bypass Lithium conduction path. The improved internal structure such as contact state due to pressurization enhances the apparent conductivity and charged-discharge characteristics of ASSBs. With the latest synchrotron radiation measurement technology and image processing technology, high-precision analysis has become possible.1) Jean-Marie Doux, Yangyuchen Yang, Darren H. S. Tan, Han Nguyen, Erik A. Wu, a Xuefeng Wang, Abhik Banerjeea and Ying Shirley Meng, J. Mater. Chem. A, 8, 5049, (2020).

Stabilizing the interface between high-Ni oxide cathode and Li6PS5Cl for all-solid-state batteries via dual-compatible halides

Silicon is widely recognized as a promising anode material for all-solid-state batteries (ASSBs) due to exceptional specific capacity, abundant availability, and environmental sustainability. However, the considerable volume expansion and particle fragmentation of Si during cycling lead to significant performance degradation, limiting its practical application. Herein, the development of a pre-lithiated Si-based composite anode (c-Li1Si) is presented, designed to address the key challenges faced by Si-based anodes, namely severe volume changes and low electrochemical stability. The c-Li1Si anodes are prepared by incorporating Li₁Si powders with Li6PS5Cl (LPSCl) sulfide solid electrolyte (SSE), forming a dense structure that enhances conductivity and mitigates structural degradation. The ASSBs with c-Li1Si-60 anode exhibit outstanding electrochemical performance, including excellent rate capability and capacity retention of 84.4% after 1000 cycles at 1C and exceptional performance even at low anode-to-cathode capacity ratios (N/P ratio) of 1.68. EIS and pressure measurements reveal improved reaction kinetics and reduced volume expansion. X-ray micro-CT and SEM further confirmed the introduction of LPSCl effectively alleviated volume changes and maintained electrode structural integrity, contributing to enhanced electrochemical performance. These results underscore the potential of the c-Li1Si anode to overcome the intrinsic limitations of Si-based anodes, offering a promising pathway toward high-energy-density ASSBs.

All-solid-state batteries (ASSBs) are expected to have less safety concern than Lithium-ion batteries with organic liquid electrolyte (LIBs) because flammable liquid electrolytes are not used in ASSBs. The thermal behaviors in LIBs have widely discussed in many literatures1. However, thermal behaviors of ASSBs have not investigated much.In this study, to clarify the self-heating phenomenon of our prototype ASSB with Argyrodite-type solid electrolyte we have performed calorimetric studies and gas analyses. In the calorimetric measurement, an accelerated rate calorimetry (ARC) was used to compare the starting temperature of self-heating in ASSB to that in LIB. It was found that the self-heating of ASSB takes place at 200-300ºC which was significantly higher than that in LIB.To identify the endothermic and exothermic peaks in the calorimetric profile and to estimate the amount of heat generation in ASSB, a Calvet-type calorimeter (C600) and a differential scanning calorimeter (DSC) were used with a heating rate of 1 ℃/min under Ar atmosphere for a full cell and electrode layers of the ASSB, respectively. The exothermic peaks at 200- 300℃ for charged ASSB (at ca. 4.1 V) mostly corresponded to those for the cathode layer which was extracted from the charged ASSB. The crystal structure change of the cathode layer charged at ca. 4.1 V associated with temperature change was analyzed by X-ray diffraction (XRD) to understand the reaction mechanism. The XRD peaks for the active material and the solid electrolyte in the cathode layer were disappeared at 200-300ºC. It was suggested that the heat generation at 200- 300ºC were mainly caused by the reaction between the cathode active material and the solid electrolyte.We also analyzed the evolved gas during the heating of ASSB using a temperature-programmed desorption-mass spectrometry (TPD-MS). The detailed mechanism will be discussed on-site.AcknowledgmentsThis study was carried out in SOLiD-EV project supported by NEDO (New Energy and Industrial Technology Development Organization).References Xuning Feng, Minggao Ouyang, Xiang Liu, Languang Lu, Yong Xi, Xiangming He, Energy Storage Materials 10 (2018) 246-267.

Objective: Despite recent global efforts to establish all-solid-state batteries (ASSB) as potentially safe and stable high-energy and high-speed storage technology, long-term performance, specific power, and economic viability remain challenging. However, efficient and short ionic and electronic transport pathways and optimized interfacial contacts between the cell materials and compounds are essential. This poses a significant challenge for the microstructure of cathodes and a careful design and tailoring of anodes and separators in ASSB, which rely solely on solid-state contacts. Here, we present our recent work on ASSB with thiophosphate electrolytes conducted within the German Competence Cluster for Solid-State Batteries (FestBatt). Our work aims to investigate relevant parameters in different cell components on material, electrode, and cell level, such as the importance of particle size distributions, microstructures, and kinetic factors to optimize ASSB cathodes, separators, and anodes. Methodology: The work will be presented in four sections, which showcase key challenges as well as optimization strategies mainly focusing on cathode composites, but also discussing selected examples for separators and anodes in ASSB with thiophosphate electrolytes. Further, an outlook for relevant production steps of ASSB electrodes and cells will be given. For these studies, we mainly conducted focused ion beam scanning electron microscopy tomography, electrochemical impedance spectroscopy, cycling experiments on ASSB cells with thiophosphate solid electrolytes. Results: Fast conducting solid electrolytes are necessary to ensure sufficient transport in composite cathodes but does not represent the only key factor for high-quality cathode composites in ASSB. In our studies, we aimed to optimize the microstructure of composite cathodes consisting of intercalation-type active material and a thiophosphate-based solid electrolyte. We varied the particle size distribution of the solid electrolyte to create various cathode microstructures and assessed the effectiveness of electronic and ionic conduction pathways using partial conductivities. We used both electronically and ionically blocking electrodes for electrochemical impedance spectroscopy measurements to quantify the respective partial conductivities. Our analysis revealed that the particle size of the solid electrolyte significantly influences the charge transport and electrochemical performance of the cathodes. Additionally, using FIB-SEM tomography, we created detailed 3D reconstructions of the cathode microstructure and correlated the obtained partial conductivities with microstructural descriptors such as tortuosity factors, identifying possible kinetic bottlenecks. We found that minimizing residual porosity, which blocks ion and electron transport, is necessary to optimize cathode microstructures and enhance ASSB performance. Moreover, high-performance anodes, along with protective concepts, are crucial for establishing dense, high-energy ASSB cells. Lithium metal anodes may not be the ultimate solution, and silicon anodes can pose advantages, e. g. in terms of electrochemical stability for thiophosphate separators. Discussion: Our studies demonstrate the importance of optimizing the microstructure of cathodes and carefully designing Si anodes for improved ASSB cells. By manipulating the particle size distribution of the solid electrolyte, we achieved more efficient electronic and ionic transport pathways, leading to improved battery performance. The presented work is primarily published in references 1-5, detailing key challenges and showcasing optimization strategies for these topics. Beyond that, diversity in materials, research teams, and approaches is crucial for long-term successful development of ASSB. Acknowledgement: Scientific and administrative coordination of the BMBF Competence Cluster for Solid-State Batteries (FestBatt), FB2-Koord (03XP0431), and cell platform Thiophosphates, FB2-Thio (03XP0430A).

Lithium-ion batteries (LIBs) have played a pivotal role in advancing energy storage technologies, enabling high-demand applications such as electric vehicles and renewable energy storage systems. Despite their widespread use, LIBs face significant challenges in terms of energy density and intrinsic safety issues. These challenges have spurred interest in all-solid-state batteries (ASSBs), which utilize solid electrolytes (SEs) to offer safe alternatives to conventional liquid electrolyte-based LIBs. Among the various types of SEs explored to date, halide SEs exhibit improved compatibility with high-voltage oxide cathodes, as compared with sulfide-based SEs. Thus, halide SEs may be utilized as cathode coating materials for ASSBs using sulfide SEs with high ionic conductivity. However, the specific material properties that determine the chemical/electrochemical characteristics of halide coatings have not been clearly studied yet.In this study, we synthesize lithium yttrium chloride (Li3YCl6, LYC) SEs using different methods (solid-state synthesis and ammonium-assisted liquid-phase synthesis) at various heat-treatment temperatures to control phase compositions and crystal structures. These allow us to systematically explore the phase-structure-property relationship of LYC SEs and their roles as coating materials for LiNi0.90Co0.05Mn0.05O2 (NCM). Our experimental findings reveal that the phase, crystal structure and crystallinity of LYC significantly influence the microstructure, ionic conductivity, interfacial compatibility, and thermal stability of LYC-coated NCM (NCM@LYC). The crystal structure and crystallinity of synthesized LYC SEs are explored by Rietveld refinement of X-ray diffraction patterns. Notably, LYC SEs prepared via wet synthesis under optimal heat-treatment conditions exhibit superior Li-ion transport kinetics due to the enhanced crystallinity of phase-pure LYC. This leads to the improved interfacial resistances of NCM@LYC, as evidenced by impedance analyses of NCM composite electrodes. Therefore, the NCM@LYC composite electrodes with the optimized LYC SE show significant improvement in rate capability and cycle lifetimes. This research elucidates the critical role of the synthesis conditions in controlling the properties of halide coating materials and thus in improving the interfacial kinetics and stability of composite cathodes of ASSBs. The insights gained from the phase-structure-property relationships provide valuable guidelines for the development of highly conductive and stable SEs for next-generation batteries.

Enabling stable and high areal capacity solid state battery with Ni-rich cathode via failure mechanism study

All-solid-state batteries (ASSBs) employing sulfide solid electrolytes (SEs) are widely recognized as promising candidates for future energy storage owing to their excellent ionic conductivity, facile processability, and compatibility with high-energy electrodes. When integrated with Ni-rich layered oxides and Li metal, sulfide SEs enable energy densities and safety margins beyond those of conventional lithium-ion batteries. Yet their practical application is hindered by complex electrochemo-mechanical degradation that originates from intertwined electrochemical reactions and mechanical instability. Electrochemical reactions such as SE oxidation and interfacial decomposition can both induce and be exacerbated by mechanical degradation, e.g., active material cracking and interfacial contact loss. These coupled processes highlight that sustainable interfacial stability is not simply a matter of chemical passivation or mechanical reinforcement, but requires strategies that address both issues simultaneously. In this Feature Article, we review the origins and evolution of electrochemo-mechanical degradation in sulfide-based ASSBs, elucidate its detrimental impact on cell performance, and propose potential strategies for its mitigation. By providing a unified view of electrochemo-mechanical challenges, this work outlines a roadmap toward practical and reliable sulfide-based ASSBs.

Surface coating is essential for the cathode materials applied in all-solid-state batteries (ASSBs) based on sulfide electrolytes because of the instability of the cathode/sulfide interface. In contrast with those for general lithium ion batteries (LIBs) using a liquid electrolyte, the coating materials for ASSBs require different functional properties such as high ionic conductivity, low reactivity with sulfide electrolytes, and low electronic conductivity. In addition to LiNbO3, which is the most popular coating material for ASSBs, LiTaO3 is another highly promising coating material, and both materials mostly satisfy these requirements. In this work, LiTaO3 and LiNbO3 were used to coat the surface of LiNi0.82Co0.12Mn0.06O2 cathodes for ASSBs. Further, the effects of two different coating methods, postcoating and precursor-based (PB) coating, were characterized and compared. The postcoating method simply forms a coating layer, whereas the PB coating method offers an additional doping effect owing to the diffusion of coating ions into the cathode structure. Surface coating considerably increased the capacity of the ASSB cathodes under all experimental conditions. With the same coating amount and method, the effect of the LiTaO3 coating was similar or superior to that of the LiNbO3 coating. Compared with the postcoating method, however, the PB coating method resulted in a superior rate capability and cyclic performance, which was mostly attributed to the doping effect of Ta or Nb. An X-ray photoelectron spectroscopy analysis confirmed that both the LiTaO3 and LiNbO3 coatings suppressed side reactions. Among the coatings we examined, the LiTaO3 coating prepared by the PB method most effectively enhanced the electrochemical performance of the cathodes for sulfide electrolyte-based ASSBs.

Sulfide glasses are expected as solid electrolytes for all-solid-state batteries because of high lithium ion conductivities. The sulfide electrolyte powders pressed at ambient temperature have much lower grain boundary resistance compared to oxide electrolytes. The all-solid-state batteries using Li2S-P2S5 solid electrolytes have thus good interfaces between solid electrodes and solid electrolytes because of a favorable formability of sulfide electrolytes [1]. On the other hand, a high capacity of the batteries was retained during charging and discharging for hundreds of cycles [2]. This would be due to the fact that sulfide solid electrolytes maintain electrode/electrolyte contacts against volume change of electrode materials during Li insertion/extraction. Consequently, these facts indicate the superiority of sulfide solid electrolytes in terms of mechanical properties. However, their mechanical properties have rarely been reported because such compounds are generally unstable in air. Recently, our group has succeeded in evaluating the elastic modulus of Li2S-P2S5 sulfide electrolytes [3]. The Young’s moduli of Li2S-P2S5 glasses are about 18-25 GPa and these moduli are lower than those of oxide solid electrolytes such as cubic Li7La3Zr2O12, which is reported as 149.8 ±0.4 GPa at a relative density of ~97% [4].Various properties such as stability or conductivity of Li2S-P2S5 glasses are changed by adding a third component to Li2S-P2S5 glasses. We reported that the addition of oxides as a third component to Li2S-P2S5 sulfide glasses improved the electrochemical stability and chemical stability in air [5,6]. On the other hand, lithium-ion conductivities of Li2S-P2S5 sulfide glasses are increased by adding LiI [7]. These sulfide glasses are thus attractive electrolytes to apply for all-solid-state batteries because of the superior stability or conductivity. However, their mechanical properties have not been investigated.In this study, (70-x)Li2S·xLi2O·30P2S5 (x=0, 10, 20 mol%), 70Li2S·(30-y)P2S5·yP2O5 (y=0, 3, 10 mol%) and (100-z)(0.75Li2S·0.25P2S5)·zLiI (z=0, 5, 10, 20, 30 mol%) sulfide glass electrolytes were prepared by mechanical milling. The formability of the glass powders was investigated by powder compression tests. A partial substitution of oxides for sulfides lowered the formability of glasses, while the addition of LiI to sulfides improved the formability. Furthermore, Young’s moduli of these glasses were evaluated by ultrasonic wave velocity measurements. The Young’s moduli increased with an increase in the P2O5 content, while those decreased with an increase in the LiI content.