Effect of rare earth ions doping on properties of LiFePO4/C cathode material

LiFe_0.99RE_0.01PO₄/C cathode material was synthesized by solid-state reaction method using FeC₂O₄·2H₂O, Li₂CO₃, NH₄H₂PO₄, RE(NO₃)₃·nH₂O as raw materials and glucose as a carbon source. The doping effects of rare earth ions, such as La³⁺, Ce³⁺, Nd³⁺, on the structure and electrochemical properties of LiFePO₄/C cathode material were systematically investigated. The as-prepared samples were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size analysis. The electrochemical properties were investigated in terms of constant-current charge/discharge cycling tests. The XRD results showed that the rare earth ions doping did not change the olivine structure of LiFePO₄, and all the doped samples were of single-phase with high crystallinity. SEM and particle size analysis results showed that the doping of La³⁺, Ce³⁺ and Nd³⁺ led to the decrease of particle size. The electrochemical results exhibited that the doping of La³⁺ and Ce³⁺ could improve the high-rate capability of LiFePO₄/C cathode material, among which, the material doped with 1% Ce³⁺ exhibited the optimal electrochemical properties, whose specific discharge capacities could reach 128.9, 119.5 and 104.4 mAh/g at 1C, 2C and 5C rates, respectively.