Multistep sintering preparation and electrochemical performances of LiFe0.7 V0.2PO4/C cathode material for lithium-ion batteries

Abstract

Cathode material LiFe0.7 V0.2PO4/C is successfully synthesized by multistep sintering through carbon thermal reaction including 650 °C for 10 h and 750 °C for 6 h. The crystal structure and surface morphology of the synthesized materials are characterized by X-ray diffractometer and scanning electron microscope, respectively. Cycle voltammetry, electrochemical impedance spectroscopy, and charge–discharge test are used to investigate the electrochemical performances of these samples. The results revealed that the synthesized LiFe0.7 V0.2PO4/C material simultaneously contains olivine structure LiFePO4 and monoclinic structure Li3V2(PO4)3. It shows improved conductivity, Li-ion diffusion coefficient, excellent charge/discharge performance, and reversibility due to both the incorporation of Li3V2(PO4)3 fast ion conductor and the employed multistep sintering. The initial discharge specific capacities of LiFe0.7 V0.2PO4/C by multistep sintering are 167.8, 154.7, and 140.8 mAh g−1 at 0.5, 1, and 2 C, respectively. After a total of 230 cycles at different rates, the sample still shows good performances. After 100 cycles at 2 C, the capacity retention is 99.1 %, and the capacity is 139.6 mAh g−1. The LiFe0.7 V0.2PO4/C material synthesized by this method can be used as a cathode material for advanced lithium-ion batteries.