Super‐High Sodium‐Ion Conductivity of Na$_{2.9}$Sb$_{0.9}$W$_{0.1}$S$_4$ at Low Pressures by Systematic Pressure and Temperature Treatments

Sodium-ion solid electrolytes with high ionic conductivity at low mechanical pressures are essential for the practical implementation of solid-state batteries. We investigated the combined influence of pressure and temperature on the conductivity of the sulfide-based sodium electrolyte Na$_{2.9}$Sb$_{0.9}$W$_{0.1}$S$_4$. A series of thermo-mechanical protocols were applied in which the pellets were first subject to high-pressure compaction (≤ 664 MPa) and subsequently annealed at 250°C for 1 h under a constant pressure (97 MPa). Electrochemical impedance spectroscopy (EIS) was performed to monitor the ionic conductivity. The most effective protocol (664 MPa → 250°C, 97 MPa) yielded a record superionic conductivity of 44.7 mS cm$^{−1}$ at pressures ≥ 18 MPa. After one week under constant pressure (97 MPa), and subsequent relaxation to 1.3 MPa, the conductivity remained at 13.1 mS cm$^{−1}$. Lower-pressure treatment also caused high conductivity (9.1 mS cm$^{−1}$ at 1.3 MPa), demonstrating the material's robustness. Powder X-ray diffraction confirmed a pressure-induced transition from tetragonal to cubic modifications of Na$_{2.9}$Sb$_{0.9}$W$_{0.1}$S$_4$, correlating with the conductivity enhancement. ... mehrThe results demonstrate that systematic pressure and temperature treatments afford super-high sodium-ion conductivity in Na$_{2.9}$Sb$_{0.9}$W$_{0.1}$S$_4$ at pressures compatible with industrial battery manufacturing, highlighting its promise as a solid electrolyte for next-generation sodium-ion batteries.