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_2.88Sb_0.88W_0.12S₄, with conductivity superior to that of the benchmark electrolyte, Li₁₀GeP₂S₁₂. Partial substitution of antimony in Na₃SbS₄ 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_2.88Sb_0.88W_0.12S₄. 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.