Chemo-mechanical interfacial stabilization using elastic ion-conductive polymers in sulfide-based all-solid-state batteries

Solid-state sulfide electrolytes offer higher safety, eliminating leakage/explosion risks associated with liquid electrolytes while providing liquid-like ionic conductivity. However, they suffer from chemical instability and poor interparticle contact that degrade interfaces during cycling. This study attempts to address these limitations by introducing a composite electrolyte, in which a crosslinked ethylene oxide-based elastic ion-conductive polymer (E-ICP) forms an interpenetrating buffer within a porous Li₆PS₅Cl (LPSCl) scaffold. The E-ICP is produced via in situ copolymerization of ethylene glycol methyl ether acrylate monomer with a minor fraction of poly(ethylene glycol) dimethacrylate crosslinker. This ion-conductive network mitigates interfacial contact loss, provides additional Li⁺ transport pathways, and accommodates chemo-mechanical volume fluctuations owing to its elastic and adhesive characteristics. Spectroscopic analyses confirm suppressed interfacial side reactions with LPSCl. Li–In symmetric cells using the composite electrolyte exhibit stable cycling over 2500 h. Cross-sectional analyses reveal intact, crack-free cathode/electrolyte interfaces after cycling. In situ monitoring of internal cell pressure during cycling further validates the buffering capability of E-ICP. The combined chemical stability and mechanical elasticity of the E-ICP minimize delamination and interfacial degradation. The proposed approach provides a practical route for stabilizing sulfide-based solid electrolytes for next-generation batteries.