Interfacial Instability and Induced Safety Failure Mechanisms in Sulfide Solid Electrolytes

Sulfide solid electrolytes (SSEs) are promising for all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity, mechanical deformability, and interfacial compatibility. However, SSE interfaces with anodes, cathodes, conductive additives, and current collectors are unstable, triggering safety failures like capacity degradation, internal resistance build-up, thermal runaway, and short circuits. This review summarizes recent progress on interface-induced safety failure mechanisms in sulfide-based ASSLBs, focusing on interface types, failure mechanisms, and thermal/mechanical degradation under multi-field coupling. We survey interface modification strategies and highlight advanced characterization techniques for probing interfacial phenomena. Key challenges and future research directions are discussed. Integrating recent findings, we identify interfacial instability as the primary bottleneck governing safety failures, providing a theoretical and technical framework for rational interface design, performance optimization, and safety enhancement. Throughout this review, we use SSE as the standard abbreviation for sulfide solid electrolytes.