A sodium-ion sulfide solid electrolyte with unprecedented conductivity at room temperature

Solid electrolytes are key materials to enable solid-state rechargeable batteries, a promising technology that could address the safety and energy density issues. Here, we report a sulfide sodium-ion conductor, Na 2.88 Sb 0.88 W 0.12 S 4 , with conductivity superior to that of the benchmark electrolyte, Li 10 GeP 2 S 12 . Partial substitution of antimony in Na 3 SbS 4 with tungsten introduces sodium vacancies and tetragonal to cubic phase transition, giving rise to the highest room-temperature conductivity of 32 mS cm −1 for a sintered body, Na 2.88 Sb 0.88 W 0.12 S 4 . Moreover, this sulfide possesses additional advantages including stability against humid atmosphere and densification at much lower sintering temperatures than those (>1000 °C) of typical oxide sodium-ion conductors. The discovery of the fast sodium-ion conductors boosts the ongoing research for solid-state rechargeable battery technology with high safety, cost-effectiveness, large energy and power densities. Solid-state rechargeable batteries using solid electrolytes instead of liquid ones could address the safety and energy density issues. Here the authors report a Na-ion solid electrolyte Na 2.88 Sb 0.88 W 0.12 S 4 which exhibits record high ionic conductivity of 32 mS/cm at room temperature.