Doping supervalent rare earth ion in LiFePO4/C through hydrothermal method

• LiFe0.95M0.05PO4/C (M = Sm, Eu, Yb) composite has been synthesized via hydrothermal method first time.
• Novel dopants Sm, Eu, Yb ion are beneficial to improving electrochemical performances of LiFePO4/C.
• Doping rare earth ion can accelerate preferable orientation of cathode material in Lithium ion battery.

Hydrothermal synthesized LiFePO4/C and LiFe0.95M0.05PO4/C (M = Sm, Eu, Yb) are studied in this paper. The samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis and Brunauer–Emmett–Teller (BET). The electrochemical performance is evaluated via galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The hydrothermal synthesized particles are nano scale level. The results show that the first discharge capacity of the as-prepared LiFePO4/C and LiFe0.95M0.05PO4/C (M = Sm, Eu, Yb) is 109.4 mAh/g, 153.6 mAh/g, 144.0 mAh/g and 160.7 mAh/g at 0.2 C, respectively, and reduces to 65.1 mAh/g, 147.7 mAh/g, 141.3 mAh/g and 152.6 mAh/g after 20 cycles, respectively. The specific surface area of LiFePO4/C and LiFe0.95M0.05PO4/C (M = Sm, Eu, Yb) is 18.3 m2/g, 25.2 m2/g, 21.5 m2/g and 25.4 m2/g, respectively. The exchange current density for LiFe0.95M0.05PO4/C (M = Sm, Eu, Yb) composite is 121 mA·g− 1, 89.8 mA·g− 1, 138.8 mA·g− 1, respectively, which is much larger than that for LiFePO4/C, 12.5 mA·g− 1. The result of cyclic voltammetry indicates that the difference between anode peak potential and cathode peak potential reduces and the reversibility of electrochemical reaction is enhanced at doped electrode materials. The electrochemical performances are apparently improved due to doping supervalent rare earth ion in LiFePO4/C.