Boosting Lithium-Ion Transport in Halide Solid-State Electrolytes by Aliovalent Substitution for All-Solid-State Lithium-Ion Batteries

Abstract

The development of high-performance solid-state electrolytes (SSEs) is critical for advancing all-solid-state lithium-ion batteries (ASSLIBs). Halide SSEs exhibit promising attributes, including high ionic conductivity and compatibility with high-voltage cathodes, yet challenges remain in optimizing their ion transport pathways. Here, we report a novel aliovalent substitution strategy by introducing Nb⁵⁺ into the Li₂ZrCl₆ lattice to synthesize Li₂₋ₓZr₁₋ₓNbₓCl₆ (0≤x<1) halide SSEs. Through mechanical ball milling and annealing, Nb⁵⁺ substitution induces lithium vacancy generation, expands 3D Li⁺ migration channels, and reduces activation energy. The optimized Li₁.₈Zr₀.₈Nb₀.₂Cl₆ achieves a room-temperature ionic conductivity of 1.03 × 10⁻³ S cm⁻¹, doubling that of pristine Li₂ZrCl₆, with an ultralow activation energy of 0.327 eV. Structural analyses and climbing-image nudged elastic band (CI-NEB) calculations reveal enhanced Li⁺ transport along both c-axis and a-b planes due to lattice contraction and vacancy redistribution. ASSBs assembled with LiCoO₂ cathodes and Li-In alloy anodes demonstrate superior rate capability (100 mAh g⁻¹ at 1 C) and cycling stability (91.4% capacity retention after 100 cycles). This work not only demonstrates a novel aliovalent doping strategy for halide SSEs but also provides critical insights into optimizing ion transport pathways, paving the way for next-generation energy storage systems.