Dual‐Binder‐Enabled 18‐µm‐Thick High‐Conductivity Sulfide Electrolyte Film for High‐Energy‐Density All‐Solid‐State Batteries

The development of ultrathin, high ionic conductivity sulfide solid‐state electrolytes (SSEs) film is essential for achieving high‐energy‐density all‐solid‐state batteries (ASSBs). However, conventional chemically inert binders inevitably impede Li‐ion transport kinetics within SSE films, and the underlying Li‐ion transport mechanisms remain elusive. In this work, we report an Li‐ion‐conductive polymer binder (LiTFSI‐PMEMA) and integrate it with SSEs via dry processing to fabricate an ultrathin SSE film (USF). The resulting USF is only 18 µm thick and exhibits a high ionic conductivity of 1.56 mS cm ‒1 . By combining cryogenic transmission electron microscopy (cryo‐TEM), solid‐state nuclear magnetic resonance (ssNMR), and theoretical simulations, we propose an Li + transport model in which the SSE phase provides the dominant conduction pathway, while the polymer binder and SSEs/polymer contact regions can assist local Li + transport continuity between neighboring SSE particles. When implemented in ASSBs, the USF exhibits exceptional interfacial compatibility and kinetic stability, enabling a long‐term cycling life with 70.3% capacity retention over 1500 cycles. Furthermore, a LiNi 0.7 Co 0.2 Mn 0.1 O 2 ||USF||nSi pouch cell delivers a high stack‐level energy density of 322.7 Wh kg ‒1 . This work provides crucial insights into the multiphase Li‐ion transport kinetics and demonstrates a scalable manufacturing strategy for sulfide‐based ASSBs.