Constructing Iron Vacancies in Thiospinel FeIn₂S₄ to Modulate Fe D‐Band Center and Accelerate Sodiation Kinetics Enabling High‐Rate and Durable Sodium Storage

Abstract The bimetallic synergies effect and combined conversion/alloying mechanism endow thiospinel FeIn₂S₄ with great potential as an anode material for sodium‐ion batteries (SIBs). However, their inconsistent synthesis, severe volumetric expansion, and sluggish reaction kinetics typically lead to unsatisfactory cyclic stability and rate capability. Herein, bimetallic organic framework derived FeIn₂S₄@N/S‐C microrods with Fe vacancies is presented for fast, durable, and reversible sodium storage. The presence of Fe vacancies significantly modulates the d‐band center of Fe and decreases the strength of the Fe─S bond for facilitating the sodiation reaction kinetics jointly. Moreover, a thin and stable solid electrolyte interface film with inorganic‐rich components is formed by Fe vacancies induction. Combined with the N, S co‐doped porous carbon matrix, the optimal sample delivers an excellent rate capability of 381 mAh g⁻¹ at 10 A g⁻¹ and a stable cyclic performance (448 mAh g⁻¹ after 500 cycles at 1 A g⁻¹). Furthermore, the assembled full‐cells also exhibit superior electrochemical performance with 87.5% capacity retention after rate and long‐term cyclic evaluations. This work presents a promising strategy for the structural regulation of bimetallic sulfides as advanced anodes for SIBs.