Superionic conductivity in halide solid electrolyte enabled by lattice extension

Halide solid electrolytes have recently attracted significant attention due to their promising combination of high ionic conductivity, excellent electrochemical stability, and favorable mechanical properties. In this study, a lattice extension strategy is employed to enable a series of Li₂ZrCl_6-xI_x (LZCI_x, 0 ≤ x ≤ 2) solid electrolytes. The incorporation of I⁻ ions into the Li₂ZrCl₆ lattice not only preserves the original crystal structure but also expands the lattice, enhances structural disorder, and significantly boosts ionic conductivity. Among the synthesized electrolytes, Li₂ZrCl₅I exhibited a room-temperature ionic conductivity of 1.06 mS cm⁻¹, four times that of pristine Li₂ZrCl₆, and a low activation energy of 0.32 eV. Ab initio molecular dynamics (AIMD) and bond valence site energy (BVSE) calculations reveal that I⁻ doping constructs a broader three-dimensional lithium-ion migration network, reducing the energy barrier and facilitating superior ion transport. When integrated into all-solid-state batteries (ASSBs) with TiS₂ cathodes, Li₂ZrCl₅I electrolytes demonstrated exceptional electrochemical performance, including high initial Coulombic efficiency (97.01 %), excellent capacity retention (88 % over 500 cycles at 1C), and robust rate capability. Notably, the Li₂ZrCl₅I −based ASSBs maintained stable operation under high active-material loading conditions (90 % TiS₂). These findings highlight the potential of iodide-substituted halides as advanced SSEs for next-generation energy storage systems, providing a novel approach to improving ionic transport and electrochemical performance in ASSBs.