High Ionic Conductivity Achieved in Li₃Y(Br₃Cl₃) Mixed Halide Solid Electrolyte via Promoted Diffusion Pathways and Enhanced Grain Boundary

The development of all-solid-state batteries is limited by the low ionic conductivity of solid electrolytes. Beyond sulfides and oxides, halides represent another family of solid electrolytes with high Li + conductivity and good stability. Here we report the design, synthesis, electrochemical testing, and crystal structure characterization of a halide compound, Li 3 Y(Br 3 Cl 3 ). A room-temperature conductivity of 7.2 mS/cm is achieved in Li 3 Y(Br 3 Cl 3 ) via hot-pressing at 170 °C. Crystal structure characterizations using synchrotron X-ray and neutron diffraction reveal the existence of Li at the tetrahedral sites and the 3D diffusion pathways. Electrochemical impedance spectroscopy results reveal the improved grain boundary contact and the lower grain boundary resistance after the hot-pressing process, which also boost the overall conductivity. All-solid-state batteries using Li 3 Y(Br 3 Cl 3 ) as the electrolyte demonstrate high capacity and good rate performance at room temperature. The new findings open up opportunities for the design of halide ionic conductors and the development of all-solid-state batteries.