High Ionic Conductivity and Cost-Effective Halide Solid Electrolyte Enabled by Long-Range Cooperative Transport in Bi-Doped Li ₂ ZrCl ₆

Li 2 ZrCl 6 (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.