Electrochemical Stability and Li Ion Diffusion Kinetics of Grain Boundaries in Li₁₀GeP₂S₁₂ Solid Electrolyte

Inorganic solid electrolytes (SEs) such as Li10GeP2S12 (LGPS) have received significant attention due to their fire safety, high ionic conductivity, and compatibility with lithium (Li) anodes which can enable high capacity all solid-state batteries. However, recent experimental studies have reported poor performance and unexpected behavior of SEs, apparently resulting from the interfaces and defects like grain boundaries (GBs). In this study, using first-principles calculations and kinetic Monte Carlo simulations, we investigate the stability, electronic character, and ion diffusion kinetics of LGPS GBs. The results show that Li-ion mobility significantly decreases at the GB interface. Furthermore, detailed defect state analysis indicates that it is not favorable for a neutral Li atom formation (by combining a Li ion and an electron trapped at the GB) leading to the nucleation of Li clusters and dendrite growth at the GB. From these results, it is confirmed that the GB of LGPS is an important factor to control the ion conducting characteristics of LGPS and that the electrochemical properties of sulfide SEs could be improved by constructing the engineered interfaces between its grains.