A Synergistically Interlocked Ultrathin yet Robust Composite Electrolyte for Solid‐State Lithium Metal Batteries

ABSTRACT Solid‐state electrolytes (SSEs) offer a safer alternative to flammable liquids but face challenges like high interfacial resistance, low ionic conductivity, and inferior mechanical strength. Herein, a molecular bridging and interfacial stitching strategy is employed to construct a synergistically interlocked composite electrolyte, where a robust aramid nanofiber (ANF) network serves as a multifunctional molecular bridge that weaves a resilient network to securely anchor rigid Li 6 . 5 La 3 Zr 1 . 5 Ta 0 . 5 O 12 (LLZTO) particles in the soft poly(ethylene oxide) (PEO) matrix. This architecture provides robust mechanical integrity and dual‐channel Li‐ion conduction, overcoming the rigidity‐flexibility trade‐off in SSEs. The resulting ultrathin (∼3 µm) composite electrolyte (denoted as ANF@PLL) exhibits high ionic conductivity (0.68 mS cm −1 at 30°C), exceptional mechanical strength (∼20 MPa), and a wide electrochemical stability window (5.7 V). Li||ANF@PLL||Li symmetric cells achieve stable cycling over 2500 h, while the Li||ANF@PLL||LFP full cells deliver remarkable long‐term cycling stability (101.2 mAh g −1 after 1000 cycles at 0.5C) and rate performance (up to 10C). Furthermore, flexible pouch cells assembled with this electrolyte maintain stable electrochemical performance under high temperature (∼180°C) and harsh mechanical deformation, highlighting the significant potential of this molecular‐scale interface engineering strategy for practical high‐performance all solid‐state lithium metal batteries (ASSLMBs).