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

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.