Preparation and characterization of Na<sub>2.88</sub>Sb<sub>0.88</sub>W<sub>0.12</sub>S<sub>4−</sub><i><sub>x</sub></i>O<i><sub>x</sub></i> solid electrolyte

For the practical application of all-solid-state batteries, it is necessary to improve the performance of the solid electrolytes. We previously reported the fabrication of Na2.88Sb0.88W0.12S4, which showed the highest ionic conductivity among Na+ conducting sulfide solid electrolytes. In this study, we focused on the anion substitution of Na2.88Sb0.88W0.12S4 and evaluated oxygen substitution. Samples of Na2.88Sb0.88W0.12S4−xOx (0 ≤ x ≤ 0.5) were fabricated by a mechanochemical process and subsequent heat treatment, and structural analysis and electrochemical evaluation were performed. The solid solution of oxygen was found to proceed in the range of x ≤ 0.3. The oxygen substitution decreased the ionic conductivity, but it maintained a high ionic conductivity of more than 10−3 S cm−1. The reduction tolerance was improved by the oxygen substitution based on cyclic voltammetry measurements. An all-solid-state Na–Sn/TiS2 cell using the Na2.88Sb0.88W0.12S3.7O0.3 electrolyte operated at room temperature.