Hopping Rate and Migration Entropy as the Origin of Superionic Conduction within Solid-State Electrolytes

Inorganicsolid-state electrolytes (SSEs) have gainedsignificantattention for their potential use in high-energy solid-state batteries.However, there is a lack of understanding of the underlying mechanismsof fast ion conduction in SSEs. Here, we clarify the critical parametersthat influence ion conductivity in SSEs through a combined analysisapproach that examines several representative SSEs (Li3YCl6, Li3HoCl6, and Li6PS5Cl), which are further verified in the xLiCl-InCl3 system. The scaling analysis on conductivityspectra allowed the decoupled influences of mobile carrier concentrationand hopping rate on ionic conductivity. Although the carrier concentrationvaried with temperature, the change alone cannot lead to the severalorders of magnitude difference in conductivity. Instead, the hoppingrate and the ionic conductivity present the same trend with the temperaturechange. Migration entropy, which arises from lattice vibrations ofthe jumping atoms from the initial sites to the saddle sites, is alsoproven to play a significant role in fast Li+ migration.The findings suggest that the multiple dependent variables such asthe Li+ hopping frequency and migration energy are alsoresponsible for the ionic conduction behavior within SSEs.