From Mechanism to Metrics: Quantitative Insights into Moisture Stability of Solid-State Electrolytes

Sulfide and halide solid-state electrolytes (SSEs) are promising for next-generation battery systems, yet their poor moisture stability remains a critical challenge. Despite extensive research on materials design and protection strategies, the lack of standardized, quantitative methods for evaluating moisture stability is a fundamental barrier to translating SSEs into practical technologies. In this Perspective, we survey the literature on moisture stability of sulfide and halide SSEs and critically examine testing practices, including humidity levels, exposure duration, sample form, and postexposure heat treatment─which all vary widely and impede cross-study comparison. We highlight that postexposure heat treatment, often underreported, can strongly influence the apparent recovery of ionic conductivity and structure. We call for standardized protocols and reporting metrics to enable fair benchmarking, reproducibility, and clearer identification of truly effective stabilization strategies for reliable, manufacturable solid-state batteries.