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

Alluaudite-type Na2+2xFe2-x(SO4)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 Na2.5Fe1.75(SO4)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 3d-O 2p 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.