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 Li_3-4<i>x</i>In_1-6<i>x</i>Fe_<i>x</i>Y_<i>x</i>Zr_2<i>x</i>Hf_2<i>x</i>Cl₆ (0 ≤ <i>x</i> ≤ 0.05) through multication substitution in Li₃InCl₆ (LIC). Li_2.92In_0.88Fe_0.02Y_0.02Zr_0.04Hf_0.04Cl₆ (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.