Mg-substituted olivine LiFePO4 for secondary lithium ion batteries

Mg-substituted olivine LiFePO₄ samples with various substituted contents were prepared via a two-step method. The crystal structures of the as-prepared LiFe_1-xMg_xPO₄ (x=0, 0.02, 0.1, 0.2) were detected by X-ray diffraction, and no impurities found. The electrochemical performances of the LiFe_1-xMg_xPO₄ cathodes were evaluated by charge/discharge test, cyclic voltammetry, and electrochemical impedance spectroscopy. Compared with the blank sample LiFePO₄, the Mg-substituted LiFe_1-xMg_xPO₄ shows improved discharge capacities as well as better cycle life, among which LiFe_0.9Mg_0.1PO₄ has the lowest charge transfer resistance, which results in the best electrochemical performances, namely, an initial discharge capacity of 123mAh/g, and a capacity retention more than 92%.