Mitigating Lattice Distortion of Iron‐Sulfate Cathode via Quasi‐Perfect Ordered Motif for High‐Temperature Sodium‐Ion Batteries

Abstract

ABSTRACT Alluaudite‐type Na 2+2x Fe 2−x (SO 4 ) 3 demonstrates significant industrial promise as a cathode candidate in sodium‐ion batteries for mitigating the supply risks associated with scarce metals. However, a major challenge stems from intrinsic lattice distortion necessitated by its thermo‐deficient synthesis below 400 °C. This structural heterogeneity became uncontrollable during high‐temperature electrochemical cycling, resulting in severe polyhedral fracture and electrochemical decay. Herein, we achieve highly stable cycling of Na 2.5 Fe 1.75 (SO 4 ) 3 cathode through a quasi‐perfect ordered crystal design that exploits dipole interactions between polar bonds with specific low‐frequency microwave (50 Hz). This enhanced ordering strengthens covalent Fe 3 d –O 2 p hybridization, significantly mitigates crystalline defects and stress accumulation, thereby enabling redox reactions and polyhedral evolution to proceed reversibly during deep (de)sodiation. The quasi‐perfect ordering suppresses heterogeneous electrolyte reactions and preserves interfacial integrity throughout extended cycling. Consequently, the developed cathode exhibits remarkable cyclability at 4.5 V, exceeding 4000 cycles at 25 °C and nearly 400 cycles at 60 °C, further validated in pouch cells.