Modification Of LiFePO₄/C As Cathode Materials In Lithium Ion Batteries

With the rapid development of the technology of science and the increasing deterioration of the energy problem, the new global energy development strategy put forward higher request for lithium ion secondary battery. Lithium iron phosphate is the first choice of cathode materials for power batteries used in electric vehicles in the future because of its low cost, environmentally benign, high safety performance, relatively high capacity, good cyclic performance and other advantages. Lithium iron phosphate has been hot spot the battery industry all over the world competitively exploit and research. Although lithium iron phosphate has many advantages, the low migration rate of lithium ions in the electrode reaction process led to its low conductivity which effects the electrochemical properties of materials. To improve its electrochemical properties, lithium iron phosphate can be coated with carbon or doped some metal irons in the preparation of materials.The preparation of LiFePO4/C battery anode material in lithium ion battery is used lithium dihydrogen phosphate, ferric oxide and glucose as the main reactants, then LiFePO4/C was modified by Mg2+doping. The preparation process of LiFePO4/C, the modification process of Mg2+doping, the physical and electrochemical characterization of the product and so on were investigated systematically by using XRD, EDX, SEM, PSD, charge-discharge tests, CV and EIS methods.LiFePO4/C powders were prepared through high temperature mechanochemistry technology, the influence factors such as ball milling temperature, time, ball powder weight ratio and lithium ferrum molar ratio on the physical and electrochemical characterization were studied. Results showed that LiFePO4/C powders acquired at600℃for5h with ball powder weight ratio was8:1and lithium ferrum molar ratio was1:0.96exhibited high distribution with the particle size between0.35-1μm, and showed better electrochemical performance with the charging and discharging platform about3.4V. The first discharge specific capacity was 98.5mAh/g at0.1C.Li1-xMgxFePO4/C modified by Mg2+doping was obtained base on the better condition of the preparation of LiFePO4/C. The effects of different Mg2+doping and carbon coating amounts on the physical and electrochemical characterization were investigated. The results showed when the content of Mg2+doping is0.02and the carbon coating is8%, Li1-xMgxFePO4/C powders exhibited high distribution with the particle size between0.5-1μm, and showed better electrochemical performance with the charging and discharging platform about3.4V, and the first discharge specific capacity was123.4mAh/g at0.1C. Li0.98Mg0.02FePO4/C has smaller resistance in the process of electric charge and lithium ion migration, and has higher specific capacity compared with lithium iron phosphate only with carbon coated.