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

Abstract

ABSTRACT 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 CeCl 3 ‐based composition, NaLa 0.472 Ce 0.472 Ta 0.155 Nb 0.155 Zr 0.155 Cl 6 (HE‐CeCl 3 ), which exhibits an optimal ionic conductivity over 10 −3 S cm −1 and enhanced stability. Local structural distortions incorporated into the HE‐CeCl 3 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‐CeCl 3 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 Na 3 (VOPO 4 ) 2 F cathode, ASSNIBs with HE‐CeCl 3 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.