改进高温固相法制备磷酸锰铁锂正极材料

LiMn_1-xFe_xPO₄ with the advantages of low cost, environmental amity, high energy density, good thermal stability as well as superior cycling stability, has a good application prospect for lithium-ion batteries. Among various methods for preparing LiMn_1-xFe_xPO₄, the high-temperature solid-state method has been widely used because of its simple process, low cost and high yield. However, the particle size of LiMn_1-x-Fe_xPO₄ is not well-distributed by the high-temperature solid-state method and the particles are easy to aggregate. To solve these problems, the sucrose was used as carbon source to obtain secondary carbon-coated LiMn_0.5Fe_0.5PO₄ material by an improved high-temperature solid-state method in this paper. The structure and the morphologies of the as-prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM). The results showed that the secondary carbon-coated LiMn_0.5Fe_0.5-PO₄ had a single olivine phase and an average particle size of 260 nm. The electrochemical properties of the secondary carbon-coated LiMn_0.5-Fe_0.5PO₄ were studied by galvanostatic charge-discharge method. The LiMn_0.5Fe_0.5PO₄/C could deliver discharge capacities of 165 mAh/g, 132 mAh/g and 92 mAh/g at 0.1C, 1C, and 10C rate, respectively. The capacity retention was more than 90% after 100 cycles at 1C, showing the excellent rate capability and cyclability. In addition, the reason for the improved electrochemical properties of the secondary carbon-coated LiMn_0.5Fe_0.5PO₄ had also been investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements.