Impacts of site-selective oxygen introduction on structural stabilization, moisture stability, and battery performance in sulfide-based argyrodite

With sulfide-based solid electrolytes (SEs), all-solid-state batteries (ASSBs) have gained attention as next-generation secondary batteries. However, the issue of hydrogen sulfide gas generation, which is critical for ASSB commercialization, remains unresolved. While the introduction of oxygen improves moisture stability, it results in significant degradation in ionic conductivity and cell performance, and the mechanism behind moisture stabilization is unknown. Here, we investigate the effect of site-selective oxygen substitution at the Wyckoff 16e site of a PS₄ unit in a sulfide-based argyrodite, which induces structural stabilization, and its influence on moisture stability and cell performance. By synthesizing a novel halide-rich composition-based Li_5.33PS_4.27O_0.12Cl_1.55 (HR-LiPSOCl), substantial improvements in moisture stability, a high discharge capacity of 212 mAh g⁻¹, and 85 % capacity retention over 200 cycles are demonstrated. An ultra-high areal capacity cell of 28 mAh cm^-2 (215 mg cm^-2) and a pouch cell with an energy density of 870 Wh L^-1 are fabricated to evaluate the performance of HR-LiPSOCl. Additionally, the site-selective characteristic of oxygen in argyrodite and the mechanism behind the improved stability are clarified. This study aims to provide innovative insights into improving the performance of solid electrolytes in a simple and effective manner while using a composition that minimizes the amount of expensive Li₂S, ensuring cost-efficiency. Understanding the oxygen substitution mechanism and its contribution to moisture stabilization will further advance the commercialization of solid electrolytes.