High‐Entropy Tailored UCl ₃ ‐Type Halides With Enhanced Ionic Conduction and Stability for All‐Solid‐State Sodium Batteries

Designing advanced halide-based solid electrolytes (SEs) combining high ionic conductivity and exceptional (electro)chemical stability is crucial for all-solid-state Na-ion batteries (ASSNIBs). However, most sodium-based halide systems remain restricted in high-voltage ASSNIB applications, due to their low conductivity from blocked ion-diffusion channels, and insufficient oxidation stability caused by anionic anti-oxidant bottlenecks. Here, we design a high‑entropy CeCl₃-based composition, NaLa0.472Ce0.472Ta0.155Nb0.155Zr0.155Cl₆ (HE-CeCl₃), which exhibits an optimal ionic conductivity over 10⁻³ S cm⁻¹ and enhanced stability. Local structural distortions incorporated into the HE-CeCl₃ structure give rise to promoted inter-site Na-ion exchanges so that they can percolate through contiguous one-dimensional migration pathways along the c-axis with flattened energy barriers. Moreover, the HE-CeCl₃ configuration enables suppressed Cl⁻ oxidation kinetics and enhanced thermodynamic stability, thereby delivering robust high-voltage stability (4.46 V vs. Na⁺/Na) and good solvent tolerance, showing great potential for wet-processed ultrathin electrolyte films. When coupled with a Na₃(VOPO₄)₂F cathode, ASSNIBs with HE-CeCl₃ catholyte present long-term stability (88.3% capacity retention at 0.3 C after 600 cycles in mold-type cells) and high areal capacity (1.7 mAh cm⁻² in pouch-type cells). This work provides a versatile high-entropy design strategy for simultaneously enhancing ion conduction and (electro)chemical stability in sodium-ion conductors, accelerating the development of practical ASSNIBs.