Atomic insights into the oxidative degradation mechanisms of sulfide solid electrolytes

Abstract

Electrochemical degradation of solid electrolytes is a major roadblock in the development of solid-state batteries. Combining X-ray absorption spectroscopy characterization, first-principles simulations, and machine learning, here we report the atomic-scale oxidative degradation mechanisms of sulfide electrolytes using Li 3 PS 4 (LPS) as a model system. The degradation begins with a decrease of Li neighbor affinity to S atoms, followed by the formation of S-S bonds as the PS 4 tetrahedron deforms. After the first cycle, the PS 4 motifs become strongly distorted, and PS 3 motifs start to form. The distortion of PS 4 and the formation of S-S bonds are correlated with an increased interfacial impedance. We identify the spectral fingerprints of the local structural evolution and use them as a proxy for the electrochemical stability of phosphorus sulfide electrolytes, as demonstrated in argyrodite Li 6 PS 5 Cl. This study provides guidance for controlling macroscopic reactions through microstructural engineering and can advance the rational design of sulfide electrolytes.