Preparation and Electrochemical Performances of Vanadium or Nickel Doped Lithium Iron Phosphates

In this paper,the vanadium or nickel doped cathode material LiFePO₄ for lithium ion battery was synthesized by solvothermal method,using water/ethanol as the solvent.The crystal phases and microstructures of the samples were characterized by XRD and SEM,respectively.Furthermore,the electrochemical performances of LiFePO₄/carbon composites were studied by the methods of constant AC impedance and cyclic voltammetry.Through the constant current charge and discharge test,the results indicate that the difference between the charge and discharge voltage of the samples doped by vanadium and nickel ions is smaller than that of the undoped sample.The samples with 1% vanadium ion doping and 1% nickel ion doping respectively have an initial discharge specific capacity of 124.9 mAh/g and 113.5 mAh/g at 2.5～4.3 V,0.2 C and room temperature.And the sample with 1% vanadium ion doping has the best cycle performance with 114.4 mAh/g of specific discharge capacity and 91.59% of capacity retention rate after 50 cycles.The sample with 1% nickel ion doping has the highest initial discharge specific capacity of 103.1 mAh/g at 0 ℃.