Surface Degeneration of Li3PS4-LiI Glass-Ceramic Electrolyte by Exposure to Humidity-Controlled Air and Its Recovery by Thermal Treatment

Sulfide-based solid electrolytes are desirable for use in all -solid-#1: Pristine 79% retention state batteries owing to their high ionic conductivity and plasticity. However, they generally degrade upon exposure to water and can generate toxic hydrogen sulfide even in dry-room atmospheres. To prevent their degradation, surface stabilization is required and further research into the degradation mechanism is necessary. In the present study, the stability of Li3PS4-LiI glass ceramic (LPSI) has been examined under low-humidity conditions. In contrast to an argyrodite-type solid electrolyte, exposure of LPSI to dry air with a dew point of -20 degrees C resulted in low H2S-gas generation and reduced ionic conductivity of LPSI. Since the conductivity mostly recovered after vacuum heating at 100 degrees C, the H2S generation is not considered to be the major reason for the reduction in conductivity. On the contrary, it is suggested that water molecules are present on the LPSI powder particles after dry-air exposure, resulting in the formation of a degraded LPSI layer and low ionic conductivity, and that most of the water molecules are removed during vacuum heating, resulting in the recovery of conductivity. Furthermore, optimal vacuum-heating conditions were obtained from X-ray diffraction and temperature -programmed desorption-mass spectrometry measurements, indicating an optimal temperature and heating time of 100 degrees C and 2 h, respectively. Impedance measurements were used to probe the degradation of the surface layer. The condition of the surface layer was affected by the pellet-forming pressure, and it was easier to detect the degradation of the surface layer when the pellets were formed at low pressures. This paper contributes to the formulation of guidelines for the development of water-resistant solid electrolytes. Znorm(Im) / omega cm 1500 1000 500 0 1000 2000 3000 Znorm(Re) / omega cm #3: Vacuum-heated (100 degrees C, 2 h) #2: After exposure for 1 h at -20 degrees C dp

Automated summary

This study examines the stability of Li3PS4-LiI glass ceramic (LPSI) under low-humidity conditions and found that exposure to dry air at -20 degrees C resulted in low H2S gas generation and reduced ionic conductivity. Vacuum heating can recover most of the conductivity, indicating that H2S generation is not the main reason for the conductivity reduction. It is suggested that water molecules on the LPSI powder particles after dry-air exposure lead to the formation of a degraded LPSI layer and low ionic conductivity.