Synthesization And Performance Of LiFePO₄ Cathode Materials For Lithium Ion Battery

Lithium Iron Phosphate (LiFePO₄) has become more and more concerned for its so many obvious characters such as nontoxic, environmental friendly, low raw material cost, high specific capacity, excellent cycle performance and safety, and it is considered to be the most promising cathode material for Lithium Iron battery. However, because of the low electronic conductivity, the poor high rate performance should be improved. In order to decreasing the production cost and enhancing the high rate performance of this material, this paper adopted liquid-phase carbothermal reduction method to improve LiFePO₄'s behavior by mainly using carbon coated and M doped method.It is found that we can more easily obtain the good behavior material under the conditions of 20%carbon coating, 700℃sintering temperature, after testing the influence of carbon coating capacity and the different sintering temperature.Single and binary ion doping was carried out to improve performace of LiFePO₄/C composite synthesized by liquid-phase carbothermal reduction method. It is shown by XRD test that the prepared materials were single olive structure, no impurity is observed in them and the doping ion entered into inside of crystal lattice by substituting some of Fe²⁺; SEM figures indicated that the particle shape and size was better than that of the materials which were not doped; In this study, the cyclic property of LiFe_0.95Co_0.05PO₄ single doping material is best, it could export 128.84 mAh·g^-1 of the specific capacity at initial cycle and remain 93.37% of initial capacity after 40 cycles.At the same time, the radius of the doped Ni²⁺, Mn³⁺, Mg²⁺ are closed to Fe²⁺,so the ions were used to substitute Fe²⁺.The result told that the Ni-doping can excellently improve the electronic conductivity of samples, stabilize crystal structure and result in perfect electrochemical performance.Among the binary doping materials, the cyclic property of LiCo_0.025Ni_0.025Fe_0.95PO₄ cathode material was best, and the discharge specific capacity at initial cycle could reach 120.42mAh·g^-1,after 40 cycles,it still kept 113.44mAh·g^-1.