Selenium Doping Enhances the Conductivity of Liquid Phase Synthesized Na₃PS₄ as a Solid Electrolyte for All Solid State Sodium Batteries

A scalable, cost‐effective liquid‐phase synthesis method has shown promise for producing Na 3 PS 4 solid electrolytes. However, the ionic conductivity of the resulting solid electrolyte has been insufficient for applications in all‐solid state sodium batteries. In this work, solid electrolytes in which selenium (Se) partially substitutes phosphorus (P) in the series Na 3+x P 1‐x Se x S 4 (0.000 ≤ x ≤ 0.150) are successfully synthesized via the liquid‐phase method. The newly synthesized solid electrolytes retain the cubic structure of the glass‐ceramic and demonstrate ionic conductivity comparable to Na 3 PS 4 prepared by the ball‐milling method. The synthesized samples are effectively applied in all‐solid‐state sodium batteries containing a TiS 2 ‐solid electrolyte composite as the cathode and Na 15 Sn 4 as the anode, achieving an initial capacity of ≈125 mAh g − 1 based on the weight of the TiS 2 .