Elastic Ion‐Conducting Layer Enables Stable Si‐Based All‐Solid‐State Batteries

Si‐based all‐solid‐state batteries with sulfide solid electrolytes are strong contenders for next‐generation high‐safety, high‐energy‐density batteries. However, Si‐based anodes inevitably suffer from irreversible delamination and side reactions at the rigid Si/solid electrolyte interface during cycling, making it challenging to achieve long cycle life. Here, we develop an elastic ion‐conducting layer on the Si surface that transforms the rigid interface into a conformal and recoverable elastic contact, achieving highly stable Si anode. The layer comprises a lithium bis(fluorosulfonyl)imide‐containing block copolymer, whose hydrogen‐bond‐rich hard domains provide mechanical robustness and elasticity. Ion‐conductive soft segments, together with an in situ‐formed inorganic‐rich solid electrolyte interphase on the Si surface, construct a three‐dimensional ion transport network. This interfacial architecture simultaneously mitigates interfacial stress and accelerates lithium‐ion transport within the Si anode. Consequently, the full‐cell exhibits stable cycling over 10,000 cycles at a high rate of 5C (8.7 mA cm −2 ), and the 0.6 Ah pouch cell retains 91% capacity after 650 cycles. Such interfacial layer holds great promise for accelerating the commercialization of Si‐based all‐solid‐state batteries.