Engineering Interfacial Chemistry of Spinel Indium Sulfides via Iron‐Substitution‐Mediated Selective Catalysis for High‐Performance Sodium‐Ion Batteries

ABSTRACT Tailoring the decomposition dynamics of salts and solvents at the electrode–electrolyte interface is crucial for constructing a high‐quality solid electrolyte interphase (SEI) and achieving high‐performance sodium‐ion batteries (SIBs). Herein, we propose an iron‐substitution strategy to selectively catalyze salt–solvent decomposition and thereby realize a high‐quality SEI. Specifically, spinel indium sulfide with intrinsic indium vacancies (V In ‐In 3 S 4 ) predominantly adsorbs and promotes the reduction of ether molecules, forming a thick, nonuniform, and NaF‐deficient SEI layer. Conversely, Fe substitution eliminates the unfavorable indium vacancies and selectively catalyzes the preferential dissociation of P─F bond in PF 6 − anion while weakening C─O bond cleavage in ether molecules, thereby facilitating rapid NaF formation. Moreover, the Fe substitution greatly enhances the affinity of Fe‐In 3 S 4 toward NaF, facilitating rapid and uniform NaF deposition. As a result, a thin (∼8.0 nm), uniform, and ultra‐stable NaF‐rich SEI layer forms on Fe‐In 3 S 4 , enabling a high initial Coulombic efficiency (∼92.3%, 0.5 A g −1 ), remarkable rate capability (457.2 mAh g −1 at 10 A g −1 ), and long cycle life (0.011% capacity decay per cycle over 2000 cycles at 5 A g −1 ). The Fe‐substitution strategy also demonstrates universality across various electrolyte systems, offering a powerful approach to modulate interfacial chemistry and unlock the potential for high‐performance SIB anodes.