High-Frequency Impedance Spectroscopic Analysis of Argyrodite-Type Sulfide-Based Solid Electrolyte upon Air Exposure

Sulfide-based solid electrolytes have attracted considerable attention for application in solid-state lithium batteries because of their high ionic conductivities, suitable mechanical properties, and successful operation with various active anode and cathode materials. However, sulfides react with traces of moisture to generate toxic H2S gas. This undesirable degradation reaction reduces lithium ionic conductivity, which is crucial to solid-state batteries. To understand the effect of moisture degradation on solid electrolyte particles, impedance spectroscopic measurements at high frequencies (up to 100 MHz) were performed at various temperatures. From the spectral analysis results, we separated the impedance components into grain boundaries and the internal bulk of the solid electrolyte particles before and after exposure to moist air. By calculating the activation energy of lithium ionic conduction from the temperature dependence of each impedance component (Arrhenius plot), we determined that the impedance and activation energy of the grain boundaries between the solid electrolyte particles increased. This indicates that lithium ionic conduction between the solid electrolyte particles was inhibited during the initial stage of exposure to moist air.