Engineering Interfacial Chemistry of Spinel Indium Sulfides via Iron-Substitution-Mediated Selective Catalysis for...

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-In₃S₄) 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 PF₆ ^- 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-In₃S₄ 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-In₃S₄, 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.