Iron-based composite oxides as alternative negative electrodes for lithium-ion batteries

Nanosized lithiated iron oxides with 10 and 50 wt.% SiO₂ were prepared by a sol–gel method using 1 M Fe(NO₃)₃ · 9H₂O and 1 M LiNO₃ aqueous solutions in a stoichiometric ratio of 1:1 and colloidal silica. Dried xerogel was calcinated at 700 °C for 4 h in air. The X-ray data of samples synthesized using 10% and 50% SiO₂ showed the presence of a mixture of two phases: α-LiFeO₂ and Li_1−x Fe₅O₈ (0 < x ≤ 0.1) for a sample containing 10% SiO₂ and LiFe(SiO₃)₂ and Fe₂O₃ (h) for a sample with 50% SiO₂. The electrochemical behaviour of the compounds was investigated galvanostatically within the 0.01–3.0 V range at a current density of 0.80 mA cm⁻². The Li/Li _x Fe _y O _z (10%) · SiO₂ cell showed a high initial reversible capacity of 1,080 mA h g⁻¹ and a capacity of 600 mA h g⁻¹ at the 30th cycle. Accounting these results is the presence of a SiO₂ phase which stabilizes the structure of the active mass on cycling. The mean charge voltage (1.8 V) and the discharge voltage of 1.0 V versus Li⁺ reference electrode as well as the high reversible capacity indicate that this material is suitable for use as anode in lithium-ion batteries.