Mechanistic insights into high performance W6+-doped Li3YCl6 solid state electrolytes: synergy of vacancies and lattice softening

Abstract

Halide solid-state electrolytes (SSEs) are promising candidates for next-generation all-solid-state batteries due to their favorable combination of ionic conductivity and electrochemical stability. However, further boosting their ionic conductivity to exceed organic liquid electrolytes remains a critical challenge. Herein, we propose a high-valence cation substitution strategy using W⁶⁺ to enhance the performance of Li₃YCl₆. Notably, the utilization of low-cost tungsten precursors makes this strategy particularly effective in reducing the overall material cost of the electrolyte. Through first-principles calculations and molecular dynamics simulations, we reveal that W⁶⁺ doping triggers a synergistic enhancement mechanism: it not only introduces a high concentration of Li⁺ vacancies but also induces significant lattice softening. Specifically, the introduction of W⁶⁺ improves lattice flexibility of the anion framework, leading to a reduced bulk modulus of 15.66 GPa (vs. 21.20 GPa for pristine Li₃YCl₆) and broadened Li⁺ diffusion pathways. Consequently, the optimized composition, Li_2.52Y_0.84W_0.16Cl₆, exhibits a superior room-temperature ionic conductivity of 20.69 mS cm⁻¹ with a low activation energy of 0.22 eV. This study demonstrates that W⁶⁺ doping could simultaneously optimize Li⁺ vacancy concentration and structural flexibility, offering a promising electrolyte candidate that combines high ionic conductivity, cost-effectiveness, and structural stability for solid-state batteries.