Formation Process of Na 3 SbS 4 Solid Electrolyte via a Liquid‐Phase Reaction Using Acetonitrile

Antimony-based sulfide solid electrolyte Na3SbS4 with good moisture stability is attractive for practical application in all-solid-state sodium batteries. Liquid-phase reaction is a facile and widely-used strategy, but the specific reactions in synthetic process and related mechanisms are still unclear. Herein, the reaction processes of synthesizing Na3SbS4 by liquid-phase reaction of Na2S, Sb2S3 and S in acetonitrile (ACN) are extensively investigated. A colorless supernatant and dark green precipitate are obtained after reacting for 24 h, the raw materials are negligible in supernatant. More importantly, the post-treatment temperature is investigated and the tetragonal Na3SbS4 (t-Na3SbS4) with high ionic conductivity (0.46 mS cm−1 at 25 °C) is obtained after heating at 450 °C for 3 h. Remarkably, the direct stacking of electrolyte is developed and t-Na3SbS4 is further prepared into a free-standing sheet-type solid electrolyte membrane using polytetrafluoroethylene (PTFE) fibrillation, then an ionic conductivity is achieved (0.17 mS cm−1 at 25 °C).