Ultrathin Sulfide/PVDF-HFP Composite Electrolyte for Solid-State Sodium Metal Batteries

Rechargeable solid-state sodium batteries that utilize solid electrolytes (SEs) have garnered considerable attention due to their enhanced safety and abundant sodium resources. Solid composite electrolytes (SCEs) that disperse the fine ceramic particles in a polymer matrix provide a viable approach to addressing these challenges. Nevertheless, intensive efforts have been devoted to inorganic oxide-based conductors, while the studies on SCEs with sulfide-based Na-ion conductors are rarely reported. In this work, we report the preparation of ultrathin, flexible, and stable SCE with adjustable thickness (20–65 μm) by embedding microsized Na3SbS3Se (NSSE) particles in a polymer (PVDF-HFP) matrix. NSSE-SCE exhibits the highest ionic conductivity of 1.31 × 10–4 S cm–1 at room temperature, one order higher than that of a polymer electrolyte. In addition, the critical current density (CCD) for a 20 μm NSSE-SCE membrane is estimated to be 1.1 mA cm–2. The assembled Na|SCE|TiS2 solid-state batteries with the smallest thickness demonstrate the best electrochemical performance, which delivers a discharge capacity of 182 mA h g–1 and shows stable cycling up to 300 cycles, as well as great rate performance. This work presents a solid composite electrolyte with sulfide-based Na-ion conductors and contributes to the development of solid-state Na metal batteries.