Engineering CSFe Bond Confinement Effect to Stabilize Metallic‐Phase Sulfide for High Power Density Sodium‐Ion Batteries

Abstract

AbstractMetallic‐phase iron sulfide (e.g., Fe7S8) 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 Fe7S8‐based anode. Herein, Fe7S8 encapsulated in carbon‐sulfur bonds doped hollow carbon fibers (NHCFs‐S‐Fe7S8) is designed and synthesized for sodium‐ion storage. The NHCFs‐S‐Fe7S8 including metallic‐phase Fe7S8 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‐Fe7S8 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‐Fe7S8 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.