Fe1-xS/Fe g-C3N4 heterostructure encapsulated into S/N-doped carbon nanofibers as an efficient anode material for sodium ion batteries

Iron sulfides have shown great promise as anode materials for sodium-ion batteries (SIBs) due to their high storage capacity and low cost. However, their practical implementation is hindered by significant volume expansion and poor electronic conductivity. In this investigation, ultrafine Fe1-xS nanoparticles with dual protection from iron-modified graphitic carbon nitride (g-C3N4) and sulfur/nitrogen-doped one-dimensional carbon fiber were successfully fabricated through a designed strategy. The introduction of carbon fiber significantly accelerates the transport of electrons and ions as well as the reaction dynamics. Additionally, the in-situ hybridization of iron-modified g-C3N4 encapsulated in carbon fibers during pyrolysis leads to a heterogeneous structure between g-C3N4 and Fe1-xS species. This not only restricts the growth of Fe1-xS particles, but also greatly accelerate electron and ion transport as well as reaction kinetics. The resultant g-C3N4/Fe1-xS@NSCFs-0.15 composite demonstrated a stable discharge capacity of 577 mAh g(-1) after 100 cycles at 0.1 A g(-1), with a retained capacity of 451 mAh g(-1) after 100 cycles at 1 A g(-1). Our results indicate that the dual-protection structural characteristics of the iron-modified graphitic carbon nitride and S/N-doped one-dimensional carbon fiber can enhance the electrode performance of Fe1-xS, Meanwhile, the amount of urea added is crucial for regulating the fine structure.