High-Entropy-Driven Moderate Lattice Distortion Improves Ionic Conductivity and High-Voltage Stability of Halide Solid-State Electrolytes

Developing advanced halide solid-state electrolytes (SSEs) with both high ionic conductivity and high-voltage stability is crucial for high-energy all-solid-state batteries (ASSBs). However, conventional strategies such as simple cation substitution or anion engineering for achieving these properties simultaneously often require compromising one for the other. Herein, a high-entropy strategy is employed to design and synthesize Li3-4xIn1-6xFexYxZr2xHf2xCl₆ (0 ≤ x ≤ 0.05) through multication substitution in Li₃InCl₆ (LIC). Li2.92In0.88Fe0.02Y0.02Zr0.04Hf0.04Cl₆ (HE-LIC) featuring moderate lattice distortion achieves the highest ionic conductivity of 1.136 mS cm⁻¹ at 25 °C and improved high-voltage stability. Based on theoretical calculations and experimental findings, the tailored distortion elongates Li1-Cl bonds (2.6616 vs 2.6531 Å in LIC) to facilitate Li⁺ conduction, while confining Cl⁻ distribution to inhibit oxidation. ASSBs with HE-LIC and LiCoO₂ cathode deliver a discharge capacity of 151.13 mAh g⁻¹ and 81.17% capacity retention after 100 cycles at 0.5 C under 4.5 V. Even at 4.6 V, a discharge capacity of 165.98 mAh g⁻¹ with 80.63% retention after 50 cycles at 0.5 C is achieved. These findings demonstrate the potential of high-entropy-driven moderate lattice distortion for advanced SSEs in high-voltage ASSBs.