Engineering CSFe Bond Confinement Effect to Stabilize Metallic‐Phase Sulfide for High Power Density Sodium‐Ion Batteries

Abstract

Metallic-phase iron sulfide (e.g., Fe₇ S₈ ) is a promising candidate for high power density sodium storage anode due to the inherent metal electronic conductivity and unhindered sodium-ion diffusion kinetics. Nevertheless, long-cycle stability can not be achieved simultaneously while designing a fast-charging Fe₇ S₈ -based anode. Herein, Fe₇ S₈ encapsulated in carbon-sulfur bonds doped hollow carbon fibers (NHCFs-S-Fe₇ S₈ ) is designed and synthesized for sodium-ion storage. The NHCFs-S-Fe₇ S₈ including metallic-phase Fe₇ S₈ embrace higher electron specific conductivity, electrochemical reversibility, and fast sodium-ion diffusion. Moreover, the carbonaceous fibers with polar CSFe bonds of NHCFs-S-Fe₇ S₈ exhibit a fixed confinement effect for electrochemical conversion intermediates contributing to long cycle life. In conclusion, combined with theoretical study and experimental analysis, the multinomial optimized NHCFs-S-Fe₇ S₈ is demonstrated to integrate a suitable structure for higher capacity, fast charging, and longer cycle life. The full cell shows a power density of 1639.6 W kg^-1 and an energy density of 204.5 Wh kg^-1 , respectively, over 120 long cycles of stability at 1.1 A g^-1 . The underlying mechanism of metal sulfide structure engineering is revealed by in-depth analysis, which provides constructive guidance for designing the next generation of durable high-power density sodium storage anodes.