Cooperatively assembled, nitrogen-doped, ordered mesoporous carbon/iron oxide nanocomposites for low-cost, long cycle life sodium-ion batteries

Single pot, multi-component assembly of resol (carbon source), Pluronic F127, tetraethylorthosilicate (TEOS), dicyandiamide (nitrogen source) and iron nitrate (iron oxide source) yields nitrogen-doped ordered mesoporous carbon/iron oxide nanocomposites on carbonization. Etching the silica derived from the TEOS generates micropores in the carbon framework. The incorporation of iron oxide and nitrogen doping of the carbon tends to decrease the surface area; at approximately 3.7 wt% nitrogen and 21 wt% iron oxide (OMC-3.7-21), the surface area decreases from 2162 m²/g for the undoped ordered mesoporous carbon (OMC) to 974 m²/g and the pore volume decreases from 1.62 cm³/g to 0.6 cm³/g due to deformation of the nanostructure by crystallization of γ-Fe₂O₃ nanoparticles and N-doping of the carbon. Despite the decreased surface area, the reversible capacity when used as anodes in a sodium ion battery is increased from 110 mAh/g (undoped OMC) to 275 mAh/g (OMC-3.7-21) due to high capacity from the γ-Fe₂O₃ nanoparticles and the improved capacity associated with nitrogen doping of carbon. These nitrogen-doped ordered mesoporous carbon/iron oxide nanocomposites exhibit good cycle stability with almost 99% capacity retention after 350 charge/discharge cycles. The combination of low-cost and excellent electrochemical performance makes these mesoporous nanocomposites promising anode materials for sodium-ion batteries.