Enhanced High-Rate Capability and Long Cycle Stability of FeS@NCG Nanofibers for Sodium-Ion Battery Anodes

The development of advanced hierarchical anode materials has recently become essential to achieving high-performance sodium-ion batteries. Herein, we developed a facile and cost-effective scheme for synthesizing graphene-wrapped, nitrogen-rich carbon-coated iron sulfide nanofibers (FeS@NCG) as an anode for SIBs. The designed FeS@NCG can provide a significant reversible capacity of 748.5 mAh g^-1 at 0.3 A g^-1 for 50 cycles and approximately 3.9-fold higher electrochemical performance than its oxide analog (Fe₂O₃@NCG, 192.7 mAh g^-1 at 0.3 A g^-1 for 50 cycles). The sulfur- and nitrogen-rich multilayer package structure facilitates efficient suppression of the porous FeS volume expansion during the sodiation process, enabling a long cycle life. The intimate contact between graphene and porous carbon-coated FeS nanofibers offers strong structural barriers associated with charge-transfer pathways during sodium insertion/extraction. It also reduces the dissolution of polysulfides, enabling efficient sodium storage with superior stable kinetics. Furthermore, outstanding capacity retention of 535 mAh g^-1 at 5 A g^-1 is achieved over 1010 cycles. The FeS@NCG also exhibited a specific capacity of 640 mAh g^-1 with a Coulombic efficiency of above 99.8% at 5 A g^-1 at 80 °C, indicating its development prospects in high-performance SIB applications.