Effects of yttrium ion doping on electrochemical performance of LiFePO4/C cathodes for lithium-ion battery

The olivine-type LiFe1-x Y (x) PO4/C (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) products were prepared through liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectroscopy (EDS), galvanostatic charge-discharge, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). We found that the small amount of Y3+ ion-doped can keep the microstructure of LiFePO4, modify the particle morphology, decrease charge transfer resistance, and enhance exchange current density, thus enhance the electrochemical performance of the LiFePO4/C. However, the large doping content of Y3+ ion cannot be completely doped into LiFePO4 lattice, but existing partly in the form of YPO4. The electrochemical performance of LiFePO4/C was restricted owing to YPO4. Among all the doped samples, LiFe0.98Y0.02PO4/C showed the best electrochemical performance. The LiFe0.98Y0.02PO4/C sample exhibited the initial discharge capacity of 166.7, 155.8, 148.2, 139.8, and 121.1 mAh g(-1) at a rate of 0.2, 0.5, 1, 2, and 5 C, respectively. And, the discharge capacity of the material was 119.6 mAh g(-1) after 100 cycles at 5 C rates.