The Ab Initio Calculations on the Areal Specific Resistance of Li-Metal/Li₇La₃Zr₂O₁₂ Interphase

The solid–solid interfacial impedance between the garnet electrolyte and Li metal anode is one of the major challenges for garnet's application in all-solid-state batteries. The areal specific resistance (ASR) is investigated by ab initio calculations in this article, to predict the intrinsic ASR as lower limitation. The Li ion migration across the interphase is divided into two steps: 1) Li "intercalation" from Li-metal to the LLZO, forming a Li-rich interphase beneath the surface of LLZO, and 2) Li migration in the Li-rich interphase within LLZO. The first step is investigated by climbing image nudged elastic band (CI-NEB), resulting in barrier energy lower than 0.37 eV compared to experimental 0.34 eV of the garnet bulk phase. The second step is investigated by ab initio molecular dynamic simulations (AIMD), indicating that the Li-rich interphase's conductivity is lower by about 1–2 orders of magnitude compared to the bulk phase. As a result, the sum theoretical intrinsic ASR is as low as 0.01 Ω cm², suggesting high ASR in practicable battery arises from surficial impurity Li₂CO₃ rather than intrinsic ionic resistance. However, difficulties of removing Li₂CO₃ lie in that Li₇La₃Zr₂O₁₂ can thermodynamically decompose into reactive Li₂O to form high resistant Li₂CO₃.