Nanocrystalline transition metal ferrite thin films prepared by an electrochemical route for Li-ion batteries

Nanocrystalline ferrite MFe2O4 (M = Cu, Ni, Co) thin films have been prepared by an electrochemical route involving cathodic electrodeposition of MFe2 alloys and further anodization of the alloy films at room temperature. XRD measurements showed that those films are polycrystalline with spinel tetragonal structure for CuFe2O4, and cubic structure for NiFe2O4 and CoFe2O4, respectively. The uniform MFe2O4 films without cracks and pinholes were observed in SEM measurement, and the estimated grain average sizes of as-prepared ferrite films were about 50 nm. The electrochemical measurements showed that MFe2O4 thin film electrodes delivered a reversible capacity of 450–460 mAh g−1 at 10 μA cm−2 in the voltage range of 0.01–3.0 V and more than 75% reversible capacity still remained up to 100 cycles. Our results showed that MFe2O4 thin films could be used as promising anode materials for thin film lithium-ion batteries.