Research on low temperature performance of the F-doped LiFePO₄/C cathode materials

F-doped LiFePO₄/C cathode materials were synthesized by two-step solid-state reaction route. The F-doped LiFePO₄/C increases the intrinsic conductivity, the diffusion of lithium ions, also improves the high-rate and low-temperature performances of LiFePO₄. The SEM images reveal some small morphology changes of the two kinds of the materials, so the improved properties may not due to grain size changes but crystal structure changes. The F-doped material has a higher capability at low temperature. At -20°C, with the rate of 0.5C, the discharge capacity was 82mAhg ^-1, higher than that of undoped material(65mAhg^-1) and the result is better than the previous study[17](65mAhg^-1 at the rate of 0.3C), and the disparity would enlarge with the rate increased. The CV plots indicate that the doped material reveals less degree of polarization. F-doping sample improves the electrical conductivity of material, accelerating the process of Li+ deintercalation, therefore, improving the electrochemical performances at low temperature.