Insights on Na₃PS₄ Solid-State Electrolyte Dry Films: Interfacial Stability and Dry Room Compatibility

The state-of-the-art pellet type sodium solid-state batteries (NaSSBs) suffer from inadequate humidity stability and poor mechanical properties, resulting in non-negligible ohmic losses, limited crucial current density, and low energy density. To address these challenges, a dry process was proposed to fabricate Na₃PS₄ (NPS) film with only 0.2 wt % polytetrafluoroethylene (PTFE) binders. The density functional theory results revealed that PTFE with hydrophobic groups improves the moisture stability by reducing the available adsorption sites for H₂O on the surface. Furthermore, NaSSBs comprising an NPS film and NaCrO₂ (NCO) cathode exhibited a high specific discharge capacity of 119.6 mAh·g^–1 with an initial Coulombic efficiency (ICE) of 99.33%. After 24-h exposure of NPS film to a dry room (RH, 0.1%), a high conductivity retention of 90% and stable cycling can be achieved for 100 cycles with a capacity retention of 83.5%, representing a significant advancement toward scaling up and practical application of NaSSBs.