High Ionic Conductivity and Cost-Effective Halide Solid Electrolyte Enabled by Long-Range Cooperative Transport in Bi-Doped Li2ZrCl6

Li₂ZrCl₆ (LZC), a halide-based solid-state electrolyte, combines high ionic conductivity with cost-effectiveness, yet its atomic-scale ion transport mechanisms and doping strategies are insufficiently understood. Using first-principles calculations and ab initio molecular dynamics (AIMD) simulations, we first evaluated the intrinsic Li-ion migration behavior in bulk LZC. Potential energy surface analysis based on Li-ion site energies, combined with AIMD calculations, confirms the potential promotional effect of bismuth (Bi) cation doping on bulk ionic conductivity, increasing it to 10.93 mS cm^–1 and reducing the activation energy to 241.77 meV. Experimental results also demonstrate that Bi doping significantly enhances the electrical conductivity of LZC. This improvement is attributed to a transition from short- to long-range cooperative Li-ion migration. Additionally, 50% bromine (Br) substitution helped to reduce energy fluctuations caused by cation disorder, leading to a more uniform migration pathway. Statistical analysis across multiple solid-state electrolyte (SSE) systems further showed that shorter nearest-neighbor Li–Li distances are strongly correlated with higher conductivity and lower activation energies. This work highlights the importance of local structure and short-range interactions in halide SSEs and proposes a Bi-doped LZC as a cost-effective, high-performance candidate for next-generation solid-state batteries.