An insight into intrinsic interfacial properties between Li metals and Li10GeP2S12 solid electrolytes

Abstract

Density functional theory simulations and experimental studies were performed to investigate the interfacial properties, including lithium ion migration kinetics, between lithium metal anode and solid electrolyte Li₁₀GeP₂S₁₂(LGPS). The LGPS[001] plane was chosen as the studied surface because the easiest Li⁺ migration pathway is along this direction. The electronic structure of the surface states indicated that the electrochemical stability was reduced at both the PS₄- and GeS₄-teminated surfaces. For the interface cases, the equilibrium interfacial structures of lithium metal against the PS₄-terminated LGPS[001] surface (Li/PS₄–LGPS) and the GeS₄-terminated LGPS[001] surface (Li/GeS₄–LGPS) were revealed based on the structural relaxation and adhesion energy analysis. Solid electrolyte interphases were expected to be formed at both Li/PS₄–LGPS and Li/GeS₄–LGPS interfaces, resulting in an unstable state of interface and large interfacial resistance, which was verified by the EIS results of the Li/LGPS/Li cell. In addition, the simulations of the migration kinetics show that the energy barriers for Li⁺ crossing the Li/GeS₄–LGPS interface were relatively low compared with the Li/PS₄–LGPS interface. This may contribute to the formation of Ge-rich phases at the Li/LGPS interface, which can tune the interfacial structures to improve the ionic conductivity for future all-solid-state batteries. This work will offer a thorough understanding of the Li/LGPS interface, including local structures, electronic states and Li⁺ diffusion behaviors in all-solid-state batteries.