Bottom-up in situ formation of Fe₃O₄ nanocrystals in a porous carbon foam for lithium-ion battery anodes

A facile and scalable process for the in situ formation of Fe ₃O₄ nanocrystals in a pre-formed carbon foam (CF) (Fe ₃O₄/CF) was developed, which involved impregnation of an aqueous iron nitrate solution onto CF followed by controlled thermal treatment in an inert atmosphere. N₂ adsorption/desorption and BET measurements showed that the CF was a mesoporous carbon with a high pore volume and specific surface area. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction measurement, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) revealed that 5-50 nm Fe₃O ₄ nanocrystals at a high loading of 78.7 wt% were formed preferentially in the confined pores of CF. When tested for anode material in a Li ion half-cell, the Fe₃O₄/CF composite was far superior to unsupported Fe₃O₄ nanocrystals, exhibiting significantly improved Coulombic efficiencies and cycling stability and achieving >780 mA h g^-1 after 50 deep charge-discharge cycles with >95% cycling efficiency.