Isovalent Multi-Component Material Design for Stabilizing Cubic-Li₇La₃Zr₂O₁₂ with Excellent Li Mobility

The cubic phase of Li₇La₃Zr₂O₁₂ (LLZO) is promising candidate for replacing traditional liquid-state electrolytes, due to their high ionic conductivity, high chemical stability to Li metal, and a wide electrochemical window. However, under ambient conditions, the tetragonal phase is the ground state, while the cubic phase can be stabilized above 650°C. To address this polymorphic issue, doping strategies have been widely attempted. However, conventional aliovalent dopants frequently results in a reduction in Li ion mobility and the induction of undesired phase transformations. In this study, we propose a novel multi-component doping strategy to stabilize the cubic phase of LLZO while maintaining high Li ion mobility. The practical isovalent ions and their combinations are screened using density-functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations, identifying the most stable multi-component alloy configuration that can stabilize the robust cubic phase of LLZO. Our results demonstrate that the Li₇La₃(Zr, Hf, Ce, Ru)₂O₁₂ composition achieves a stable cubic phase at low temperatures, which we was further validated through experimental synthesis. This proposed doping strategy has the potential to advance the development of high-performance all-solid-state batteries.