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.