Interfacial Degradation Electrochemistry of Micro‐Silicon Anodes in Solid‐State and Liquid Electrolytes

ABSTRACT Micro‐silicon (m‐Si) is a promising next‐generation anode material for lithium‐ion batteries (LIBs), but its practical use is limited by severe volume expansion, particle pulverization, and unstable solid electrolyte interphase (SEI) formation. Recently, solidelectrolyte (SE)‐free m‐Si electrodes in all‐solid‐state batteries (ASSBs) have attracted attention as a strategy to reduce direct contact between SEs and electrode components. This architecture can suppress parasitic interfacial reactions while maximizing the active Si content. However, whether SE‐free m‐Si electrodes can deliver sufficient electrochemical performance and interfacial stability to replace conventional LIB systems remains unclear. Here, we systematically compare the degradation behavior of m‐Si electrodes in liquid‐ and solid‐electrolyte systems by correlating electrochemical performance with interface‐level structural evolution. The results reveal distinct degradation pathways depending on the electrolyte environment. In LIBs, m‐Si undergoes continuous pulverization accompanied by repeated SEI rupture and unstable SEI growth at the particle–electrolyte interface. In contrast, ASSBs promote a film‐like transformation of m‐Si with limited interfacial reactivity, improved structural integrity, and enhanced electrochemical stability. These findings clarify the critical role of electrolyte type in governing Si anode degradation and provide design guidelines for high‐energy‐density Si‐based batteries.