Interfacial engineering in sulfide-based all-solid-state batteries: from cathode/anode interfaces to electrolyte modification

Sulfide-based all-solid-state batteries (ASSBs) have attracted considerable attention because sulfide solid electrolytes combine high ionic conductivity with favorable mechanical properties. However, their practical application is still limited by interfacial instability, where electrochemical reactions, transport resistance, and mechanical contact loss are strongly coupled. This review summarizes recent progress in interfacial engineering of sulfide-based ASSBs, covering cathode and anode interfaces as well as modification of sulfide solid electrolytes. Representative strategies for high-voltage oxide cathodes, lithium metal, and silicon anodes are discussed with emphasis on interphase chemistry, Li⁺ transport, and contact stability. Bulk and surface regulation of sulfide electrolytes, together with thin-film processing, are also examined. These studies suggest that effective interface design should focus not simply on suppressing reactions, but on forming stable interphases that maintain ionic transport while limiting electronic leakage and mechanical degradation. Future development will require closer integration of interfacial chemistry, electrode architecture, and scalable processing under practical cell conditions.