Spindle-like Fe₇S₈/N-doped carbon nanohybrids for high-performance sodium ion battery anodes

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.