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 LiNi0.7Co0.2Mn0.1O2||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.