AC Impedance Analysis of the Degeneration and Recovery of Argyrodite Sulfide-Based Solid Electrolytes under Dry-Room-Simulated Condition

Toward the development of all-solid-state batteries with enhanced performance, this study describes the investigation of the degeneration mechanism under low-humid conditions of an argyrodite-type sulfide-based solid electrolyte. The degeneration of the electrolyte with moisture occurs even under the condition of super-low humidity in a dry room with a dew point (dp) as low as −50 °Cdp. Formation of hydrogen sulfide is detected when the electrolyte is exposed to dry air with −20 °Cdp. The results of impedance measurements suggest that the grain surface of the electrolyte is degenerated with moisture, resulting in a decrease in the lithium-ion conductivity at the grain boundary. The degenerated electrolyte surface can be partially recovered by heating at 170 °C in vacuo, although a small degeneration in bulk may occur in the heating process.