Environmental Stability of Li 6 PS 5 Cl 0.5 Br 0.5 Electrolyte During Lithium Battery Manufacturing and a Simplified Test Protocol

In this study, we investigate the environmental stability of the sulfide-based argyrodite solid electrolyte Li 6 PS 5 Cl 0 . 5 Br 0 . 5 , a promising candidate for all-solid-state lithium batteries due to its high ionic conductivity and favorable mechanical properties. Despite its potential, the material’s sensitivity to ambient air humidity presents challenges for large-scale battery manufacturing. Moisture exposure leads to performance degradation and the release of toxic hydrogen sulfide (H 2 S) gas, raising concerns for workplace safety. The objectives of this study are to validate the electrolyte synthesis process, evaluate the effects of air humidity exposure on its reactivity and ionic conductivity, and establish a standardized protocol for assessing environmental stability. We report a synthesis method based on ball milling and heat treatment that achieves an ionic conductivity of 2.11 mS/cm, along with a fundamental study incorporating modeling and formulation approaches to evaluate the electrolyte’s environmental stability. Furthermore, we introduce a simplified testing method for assessing environmental stability, which may serve as a benchmark protocol for the broader class of argyrodite solid electrolytes.