High energy ball-milled iron sulfides with thin carbon layer coating (BM-FeS/C composites) were prepared by the simple and economical process. Ball-milled process, followed by carbon coating, reduced the particle size and increased the electrical conductivity. When employed as sodium-ion battery anodes, BM-FeS/C composites showed extremely high electrochemical performance with reversible specific capacity of 589.8 mAh·g^-1 after 100 cycles at a current density of 100 mA·g^-1. They also exhibited superior rate capabilities of 375.9 mAh·g^-1 even at 3.2 A·g^-1 and 423.6 mAh·g^-1 at 1.5 A·g^-1. X-ray absorption near edge structure analysis confirmed the electrochemical pathway for conversion reaction of BM-FeS/C composites.

Iron sulfides have been considered as one of the most promising candidates for sodium ion battery anode materials due to their high theoretical capacity and low cost. In this work, spindle-like Fe₇S₈ with nitrogen-doped carbon (Fe₇S₈/N-C) nanohybrids are successfully synthesized via a solvothermal method by sulfidation iron-based metal organic framework (FeMOF). As sodium ion battery anodes, Fe₇S₈/N-C nanohybrids exhibit high reversible capacity of 450.8 mAh·g^-1 at 200 mA·g^-1, and 406.7 mAh·g^-1 at 500 mA·g^-1 even after 500 cycles. They also show excellent rate properties and delivering the capacity of 327.8 mAh·g^-1 at a very high current density of 3.2 A·g^-1. These outstanding electrochemical performances can be attributed to the unique structure of Fe₇S₈/N-C nanohybrids. The nanoscale dimension in their size can be beneficial for facile ion and electron transports. Furthermore, the stable nitrogen doped carbon frameworks can also improve electrical conductivity and relieve the problems related to volume expansion. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy analyses have been performed to study reactions occurred in spindle-like Fe₇S₈/N-C nanohybrid electrode at both bulk and surface.