Two-Step Fluorination Route Enabling Li₂ZrCl₆ Solid Electrolytes Towards High-Voltage Li Batteries

Cost-effective Zr-based chloride electrolytes are attractive for practical all-solid-state lithium batteries, but their limited oxidative stability restricts their use with high-voltage cathodes. Fluorine incorporation can enhance the high-voltage stability of chloride electrolytes, yet the strong electrostatic interaction between F^- and Li⁺ and the kinetic limitations of conventional one-step synthesis often compromise Li⁺ transport and compositional homogeneity. Herein, we propose a two-step synthesis strategy coupled with Zn/F co-modification to regulate anion incorporation and local structural disorder in Li₂ZrCl₆-based electrolytes. This stepwise pathway promotes multicomponent solid-state reactions, facilitates Cl/F anion co-occupancy, and resolves the tradeoff between high-voltage stability and ionic transport. The optimized composition achieves an improved overall performance including oxidation stability, mechanical deformability, and ion transport. When paired with high-voltage LiCoO₂ cathodes, the optimized solid electrolyte enables a high discharge capacity, together with good rate capability and cycling performance. Interfacial analyses reveal that F-containing species redistribute toward the cathode surface during cycling, forming a LiF-rich cathode-electrolyte interphase that suppresses oxidative decomposition and maintains intimate solid-solid contact. This work provides an effective reaction pathway engineering strategy for developing high-voltage-compatible Zr-based halide electrolytes through dual-halogen chemistry and aliovalent cation modification.