Interface Stability and Kinetics of Sulfide Electrolytes in all‐Solid‐State Batteries

All-solid-state batteries (ASSBs) are considered promising candidates for next-generation energy storage systems, offering superior safety and energy density compared to conventional liquid-based batteries. However, achieving stable long-term cycling remains a significant challenge due to complex interfacial reactions, so interfacial stability has become a critical focus in the design and development of ASSBs. In this study, we present a comprehensive computational thermodynamic analysis of sulfide-based solid electrolytes (SEs) and their various interfaces in ASSBs, with particular emphasis on cathode/SE, SE/interlayer, SE/coating, cathode/interlayer, cathode/coating and lithium-silicon alloy/SE anode interfaces. The (electro)chemical stabilities of these interfaces are systematically evaluated. Our findings reveal that phosphate and sulfide-type cathodes exhibit high thermodynamic stability when paired with sulfide SEs owing to favorable chemical bonding and compatibility. Furthermore, interlayers and coatings of cathode materials, such as phosphates and binary halides, notably improve interface stability by mitigating detrimental side reactions, making them particularly advantageous for long-term cycling. For the lithium-alloy anode, incorporation of silicon markedly improves stability by lowering the reaction energy, with the stabilization effect intensifying as the Si content increases. Kinetic analyses reveal that the interphase at Li_xSi/Li₆PS₅Cl interface exhibits lower activation energy barriers for lithium-ion migration compared to the bulk phases, thereby enhancing ionic transport.