High‐Conductivity Active Interface Layer for Active Lithium Reservoir in Micro‐Silicon‐Based All‐Solid‐State Batteries

Sulfide‐based all‐solid‐state lithium‐ion batteries (ASSLIBs) employing fully active, carbon‐free micro‐silicon (µSi) anodes present significant potential for high energy density, enhanced safety, and reduced cost. However, their practical application is challenged by inherent issues such as sluggish reaction kinetics, substantial volume expansion, and low Coulombic efficiency, which collectively degrade overall electrochemical performance. Herein, an interfacial engineering strategy is developed to construct an active interface layer on µSi particles via a mechanochemical cold‐pressing method. The resulting Li─Si alloy layer acts as an active lithium reservoir, which enables active lithium reservoir. Furthermore, this spontaneously formed active layer exhibits high ionic/electronic conductivities and accommodates volume changes due to its favorable mechanical properties, thereby improving electrode reaction kinetics and structural stability. ASSLIBs fabricated with LiNi 0.83 Co 0.12 Mn 0.05 O 2 cathode and modified µSi anode deliver a high initial specific capacity of 182.55 mAh g −1 and retain a capacity retention of 89.2% after 200 cycles at 0.1 C. This work offers a facile interfacial engineering technique for constructing self‐compensating lithium reservoirs and promotes the development of high‐energy‐density silicon‐based solid‐state batteries.