First-principles study on selenium-doped Li10GeP2S12 solid electrolyte: Effects of doping on moisture stability and Li-ion transport properties

Improving moisture stability without degrading the ionic conductivity of Li10GeP2S12 (LGPS) based solid-state electrolytes (SSEs) is one of the key issues in developing all-solid-state lithium batteries. Herein, we report the reactivity of the LGPS surface towards H2O, subsequent hydrolysis reactions for the H2S formation, and effective methods to suppress the H2S evolution on the LGPS surface using density functional theory (DFT) calculations. The pristine LGPS surface is highly unstable towards H2O at room temperature, where H2O dissociation occurs spontaneously. However, the H2O adsorption and its activation are weakened upon the Se substitution on the LGPS surface. By doping the Se atom on LGPS, the H2S evolution can be suppressed and significantly improve the chemical stability of the LGPS surface. In addition, we predict the Li+ ion transport properties of both pristine and Se-doped LGPS compounds using ab initio molecular dynamics (AIMD) simulations. The Se-doped LGPS material has a similar bandgap to pristine LGPS; it can have similar decomposition products and low electronic conductivity. The predicted ionic conductivity of Se-doped LGPS is found to be slightly lower than the pristine. We propose replacing sulfur with Se atom as an effective strategy to improve the moisture stability of the LGPS compound.