Engineering Li ₂ ZrCl ₆ with Ga ³⁺ /Ge ⁴⁺ Doping for High Ionic Conductivity and Stable Interfaces in Solid-State Batteries

The solid electrolyte Li₂ZrCl₆ has attracted significant attention due to its low cost and good compatibility with high-voltage cathode materials. Although it exhibits considerable ionic conductivity at room temperature, it still falls short of the requirements for widespread application. Doping has proven effective in enhancing the ionic conductivity of Li₂ZrCl₆. In this work, the potential of Li_2.5Zr_0.75Zn_0.25Cl₆, Li_2.25Zr_0.75Ga_0.25Cl₆, and Li₂Zr_0.75Ge_0.25Cl₆ as solid electrolytes is investigated using density functional theory and ab initio molecular dynamics simulations based on first principles, with the doping-induced enhancement mechanism analyzed at the atomic scale. Moreover, the electrochemical window and phase stability of these materials are examined by using the Pymatgen tool. Results indicate that the nature of the dopant and a lithium-rich strategy are key factors influencing the Li⁺ conductivity of Li_2.25Zr_0.75Ga_0.25Cl₆. Compared to pristine Li₂ZrCl₆, Li_2.25Zr_0.75Ga_0.25Cl₆ shows significantly improved ionic conductivity, attributed to a reduced migration energy barrier and additional migration pathways in the ab plane. Furthermore, more isosurfaces at the interface suggest that Ga³⁺ incorporation enhances Li⁺ conduction between Li₂ZrCl₆ and Li₂S. This study provides a microscopic understanding of how elemental doping improves ion transport, contributing to the development of advanced solid electrolytes and all-solid-state batteries.