Ionic conduction mechanism and design of amorphous Li₂O–TaCl₅ solid electrolytes

Amorphous oxyhalides have emerged as promising solid-state electrolytes (SSEs) owing to their structural flexibility and high ionic conductivity. However, the origins of fast Li⁺ transport in these disordered structures remain unclear. Here, atomistic simulations reveal the microscopic mechanisms governing Li⁺ diffusion in amorphous xLi₂O–TaCl₅ electrolytes. We identified two synergistic structural factors that control ion transport: (i) a stable, interconnected oxygen-bridged framework of Ta polyhedra, which forms continuous diffusion pathways; and (ii) reduced Li–Cl coordination, which alleviates local confinement. Together, these features enhance the connectivity of the Li⁺ diffusion pathways and promote correlated Li⁺ migration. To validate and further amplify these effects, F is substituted into the amorphous oxyhalide. The optimized composition (LTOC-8%F) exhibits enhanced structural characteristics consistent with this mechanism, and a corresponding elevated theoretical room-temperature ionic conductivity of 7.22 mS cm⁻¹. This study reveals the origins of fast ion transport in amorphous oxyhalide SSEs and establishes a mechanism-informed design strategy.