High-performance flexible CoFe₂O₄/N-doped carbon nanofiber composite anode materials for sodium-ion batteries

Graphite is traditionally used as an anode material but is unsuitable for use in sodium-ion batteries because it has a low specific capacity and poor safety characteristics, it is therefore necessary to develop alternative anode materials. Flexible CoFe₂O₄ nanoparticle/N-doped carbon nanofiber films were prepared by electrospinning and calcination. The advantages of this process included inexpensive starting materials, easy preparation, and suitability for commercialization. The inherent shortcomings of CoFe₂O₄, such as poor electronic conductivity and large changes in volume, were mitigated via elemental doping and the formation of composites with high-quality carbon materials. Nitrogen-doped carbon nanofibers with large specific surface areas and superior mechanical properties were used as the supporting skeleton of the material. These nanofibers limited the volume expansion of CoFe₂O₄ throughout the cycling process and increased the ion diffusion velocity in the material. The optimal integration of nanoscale CoFe₂O₄ particles, which possess a higher theoretical specific capacity, with a nitrogen-doped carbon nanofiber conductive framework featuring a crosslinked three-dimensional structure facilitated the infiltration of the electrolyte into the electrode. This integration reduced the diffusion distance of sodium ions and effectively reduced the volume expansion of the material, as well as damage to the material during the electrochemical reaction. After 200 cycles at a current density of 0.1 A g⁻¹, it provided a high sodium storage capacity of 365.7 mA h g⁻¹. The capacity was maintained at 176.3 mA h g⁻¹ even at a high current density of 2 A g⁻¹. Exhibits good cycle stability.