Enhancement of capacity at high charge/discharge rate and cyclic stability of LiFePO4/C by nickel doping

By introducing nickel chemical into the precursor sol of LiFePO₄, a series of Ni-doped LiFePO₄ composite cathode materials, denoted as LiFe_1???x Ni _x PO₄/C (x?=?0, 0.01, 0.03, 0.05 and 0.10) were prepared by a spray drying–carbothermal approach. The materials were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical impedance spectrum etc. It is found that the doping of nickel with appropriate amount caused a slight shift of diffraction peaks towards higher angles and enhanced the dispersion of nanoprimary particles, which could be observed from their XRD patterns and SEM images. For the sample with 3 mol% Ni doing, the charge transfer resistance reduced from 52.4?Ω of LiFePO₄ to 18.7?Ω of LiFe_0.97Ni_0.3PO₄/C, and the potential interval of the redox peaks reduced from 0.51 to 0.40 V, indicating the better reversible of Ni-doped materials. For the sample LiFe_0.97Ni_0.03PO₄/C, its initial discharge capacities at various rates are 169.2 (0.2 C), 156.2 (1.0 C), 147.9 (2.0 C), 135.5 (5.0 C), and 94.0 (10.0 C)?mAh g^?1, respectively, enhanced by 55.2 % (at 5.0 C) and 82.1 % (at 10.0 C) compared with LiFePO₄. Furthermore, after 200 cycles of charge/discharge at 0.5 C, the capacity of LiFe_0.97Ni_0.03PO₄/C only decreased 8.8 %, but over 25 % decrease was observed for LiFePO₄/C.