A size-dependent interfacial passivation strategy for achieving long-cycle and high-rate performance of silicon anodes in sulfide solid-state batteries

Silicon (Si) is considered an important candidate anode material for sulfide-based all-solid-state batteries (ASSBs), yet its pronounced volume variation during cycling readily induces solid-solid interfacial instability, severely limiting its electrochemical performance. In this study, the interfacial evolutions and failure mechanisms of Si anodes with different particle sizes are systematically investigated. The results reveal that the size effects of Si govern the local electrochemical sintering capability and interfacial stability at the Si/SSE interface. Nanosized Si (nSi) exhibits faster kinetics; however, its dense surface oxide layer and point-contact interfacial configuration hinder the formation of a continuous passivation interphase, leading to interfacial separation and impedance growth during cycling. In contrast, microsized Si (mSi) can undergo localized plastic deformation and particle fusion under stack pressure, forming a stable two-dimensional passivation interphase and thereby enhancing cycling stability, although its rate capability remains limited. Based on the above analysis, a size-dependent interfacial passivation strategy is proposed, and a micro/nano size-integrated Si anode architecture is constructed to synergistically optimize interfacial stability and transport kinetics. This study elucidates the mechanism by which Si particle size regulates local electrochemical sintering and interfacial stability, providing new insights into the design of Si-based ASSBs anodes with high stability and fast kinetics.