Boosting reaction kinetics of polycrystalline phase Fe7S8/FeS2 heterostructures encapsulated in hollow carbon nanofibers for superior fast sodium storage

Abstract

Metal sulfides have been regarded as highly competitive anode materials for fast sodium storage due to their excellent redox reversibility and comparatively great electron properties. Nevertheless, metal sulfides suffer from serious structure collapse and capacity attenuation during fast cycling. Herein, the iron-based sulfide polycrystalline phase material grown in situ on hollow carbon nanofibers was synthesized (NHCFs-Fe₇S₈/FeS₂). The construction of the polycrystalline phase is an effective strategy to enhance electron and ion transport, and improve the reaction kinetics of sodium ions. Meanwhile, the construction of a carbon network can effectively alleviate the volume expansion in the process of fast charge/discharge and maintain the stability of the structure. Thanks to these unique characteristics, NHCFs-Fe₇S₈/FeS₂ exhibits a significantly enhanced electrochemical performance, which reveals outstanding long-term cycling stability (595.7 mA h g⁻¹ at 1.0 A g⁻¹ after 1000 cycles) and rate properties (154.7 mA h g⁻¹ at 50.0 A g⁻¹ and 107.0 mA h g⁻¹ at 100.0 A g⁻¹). The structure decoration method of metal sulfides can provide effective guidance for the design of other high-performance electrode materials for fast-charging sodium-ion batteries.