Preparation and characterization of Na_2.88Sb_0.88W_0.12S_4−xO_x solid electrolyte

Abstract

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 Na_2.88Sb_0.88W_0.12S₄, which showed the highest ionic conductivity among Na⁺ conducting sulfide solid electrolytes. In this study, we focused on the anion substitution of Na_2.88Sb_0.88W_0.12S₄ and evaluated oxygen substitution. Samples of Na_2.88Sb_0.88W_0.12S_4−xO_x (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 Na_2.88Sb_0.88W_0.12S_3.7O_0.3 electrolyte operated at room temperature.