LiFe_1-x(Ni_0.98Co_0.01Mn_0.01)_xPO₄/C (x = 0.01, 0.03, 0.05, 0.07) as cathode materials for lithium-ion batteries

LiFe_1-x(Ni_0.98Co_0.01Mn_0.01)_xPO₄/C (x = 0.01, 0.03, 0.05, 0.07) is prepared by using spent electroless nickel plating solution as a raw material. The mechanism of the reaction is investigated by the analyses of thermogravimetric and differential scanning calorimeter (TG/DSC) and X-ray diffraction (XRD). It is found that the formation of LiFe_1-x(Ni_0.98Co_0.01Mn_0.01)_xPO₄/C starts at 300 °C, and above 500 °C, the product can be ascribed to LiFe_1-x(Ni_0.98Co_0.01Mn_0.01)_xPO₄/C. The structure, morphology and electrochemical properties of the samples are characterized by XRD, scanning electron microscope (SEM), electrochemical impedance spectroscopy(EIS) and charge/discharge tests. The results show that the Ni, Co and Mn multi-doping does not destroy the olivine structure of LiFePO₄ and is beneficial to the uniform distribution of particles, which improves the electrochemical properties of the samples. Especially, LiFe_0.97(Ni_0.98Co_0.01Mn_0.01)_0.03PO₄/C exhibits the best cycling stability and rate capability among all the samples. Its initial discharge capacity is 150.6 mAh g⁻¹ with the capacity retention of 98.8% after 100 cycles at 1 C. Even at 10 C, it still shows a high discharge capacity of 116.5 mAh g⁻¹.