Preparation and characterization of Na-doped LiFePO sub(4)/C composites as cathode materials for lithium-ion batteries

To improve the performance of LiFePO sub(4), single phase Li sub(1-)xa sub()xePO sub(4)/C (x = 0, 0.01, 0.03, 0.05) samples are synthesized by in situ polymerization restriction-carbonthermal reduction method. The effects of Na doping are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that doped Na ion does not destroy the lattice structure of LiFePO sub(4), while enlarges the lattice volume. Electrochemical test results show that the Li sub(0.97)Na sub(0.03)FePO sub(4)/C sample exhibits the best electrochemical performance with initial special discharge capacity of 158 mAh g super(-1) at 0.1 C. EIS results demonstrate that the charge transfer resistance of the sample decreases greatly by doping an appropriate amount of Na.