Influence of Anion Charge on Li Ion Diffusion in aNew Solid-State Electrolyte, Li 3 LaI 6

Based on density functional theory calculations of iodide-type compounds Li3MI6 (M = Sc, Y, and La), Li3LaI6 with stable octahedral Li occupation is theoretically found to meet the requirements of high lithium ionic conductivity, deformability, and chemical and electrochemical stability simultaneously, which sulfide-type solid-state electrolytes alone have not achieved so far. The underlying mechanism of superior lithium ion conduction in such a halide superionic conductor with stable octahedral Li occupations compared to the spinel ones with tetrahedral Li occupations has been uncovered. The Li migration enthalpies of those materials with face-centered-cubic anion frameworks are found to be not only strongly related to the ratio of anion charge over bond length (|qanion|/d) but also dependent on the lithium ion coordination number, which could be a universal design principle for searching new superionic conductors.