Preparation And Electrochemical Performance Characterization Of Olivine-Type Cathode Material Of Lithium Ion Battery

Compared with the traditional secondary batteries, lithium ion battery shows greater advantages at the aspects of energy density, rate capability and charge-discharge performance.Moreover, lithium ion batterys also have the advantages of low self-discharge rate, long cycle-life and eco-friendliness. Recently, lithium ion batterys have been widely used in all aspects of our life.Commercial LiCoO2is the best choice of the cathode materials due to its perfect capability, however, it meets the obstacles on the developmental way of lithium ion battery, especially for electric vehicle applications because of its high cost and toxicity. LiFePO4has the advantages of abundant raw material, high capacity, nontoicity, high safety and the excellent abuse tolerance. So it has been investigated intensively as attractive cathode materials for rechargeable lithium batteries. LiMnP04is another promising cathode material for lithium-ion batteries because of its higher redox voltage of4.2V versus Li/Li+. However, both materials show poor rate capability. Recently, many efforts have been made to further improve the power performance of LiFePO4through low-temperature route to obtain tailored particles and carbon supporting to improve the conductivity of solid phase. Various kinds of carbon materials have been suggested as conductivity supporters (or additives) for LiFePO4, However, up to date, the comparative investigation about the effect of carbon supporters on the electrochemical performance is still rarely reported. In the present work, we expiore various synthesis process using different carbon sources to improve its electrochemical performance. The main contents of this thesis are shown as follows:1. Acetylene black, carbon nanotube and graphene were employed as carbon supporter to prepare LiFePO4/acetylene black composite, LiFePO4/carbon nanotube composite and LiFePO4/grapheme composite by a facile solvothermal route followed by heat treatment.The LiFePO4/grapheme shows the best electrochemical performance.2. A spherical LiFePO/C composite was prepared from the spherical FePO4in reaction with lithium salts with carbon black or glucose as carbon source for synthesis. It was found that LiFePO4/C shows good electrochemical performance with carbon content of10%.3. The pure phase lithium manganese phosphate was prepared by different synthesis methods, including solvothermal route and chemical precipitation method. Finally, a Ni doped LiMn1-x NixPO4was prepared by a solid state reaction process. The Ni-doped Materials exhibits good charge/discharge performance.