CoFe 2O 4 and NiFe 2O 4 synthesized by sol-gel procedures for their use as anode materials for Li ion batteries
Cobalt and nickel spinel ferrites with CoFe 2O 4 and NiFe 2O 4 stoichiometries have been prepared by a sol-gel process based on a vacuum sublimation of a citrate precursor. Several samples of CoFe 2O 4 were obtained by varying the conditions of citrate precursor formation and further annealing. SEM images demonstrated the strong influence of synthesis parameters on the morphologies of secondary and primary particles. The formation of layered flake-like aggregates defining a macroporous system is assumed to improve the electrolyte-electrode contact in iron-containing samples. An enhanced electrochemical performance was achieved for samples annealed at high temperatures, especially for CoFe 2O 4 heated at 1000 °C for 24 h. Capacity values higher than 700 mAh g -1 was recorded after 75 cycles. 57Fe Mössbauer spectroscopy was used to clarify aspects of the mechanism of the electrochemical reaction.