Enhanced sodium ion conductivity in Na₃VS₄ by P-doping

All-solid-state sodium-ion batteries are promising candidates for renewable energy storage applications, owing to their high safety, high energy density, and the abundant resources of sodium. The critical factor for an all-solid-state battery is having a sodium solid electrolyte that has high Na ion conductivity at room temperature and outstanding thermal stability, low flammability, and long battery lifespan. Herein, a new Na ion solid-state electrolyte, Na₃VS₄, is prepared by a solid state reaction. It shows conductivity of ∼1.16 × 10^-8 to 1.46 × 10^-6 S cm^-1 from 25 to 100 °C. The sodium ion conductivity was enhanced to ∼1.49 × 10^-7 to 1.20 × 10^-5 S cm^-1 through P substitution for V in the composition Na₃P_0.1V_0.9S₄. Such sodium ion conduction enhancement could be attributed to P substitution for V leading to a wider Na migration path and the generation of sodium vacancies.