| Lithium iron phosphate (LiFePO4) has been a promising cathode material for Lithium ion batteries among the simplest, most widely studied and potentially most useful cathode materials. Much attention had been paid to it for its merits: safety, environmental friendliness, low material cost, high energy density, and ease of synthesis and stability in common organic electrolyte systems. However, differing significantly from that in the layered and spinel structures, there is no continuous network of FeO6 edge-shared octahedral that might contribute to electronic conductivity, resulting in a extremely low electronic conductivity, which has been the greatest obstacle for application of lithium iron phosphate. When current density increases, its reversible capacity drops dramatically. The main methods for improving electronic conductivity of LiFePO4 focus on carbon coating and metal particle and ion doping. In 2002, Chiang and co-workers in Massachusetts institute of technology firstly reported that by supervalent ion doping, the electronic conductivity of LiFePO4 could be improved by eight orders of magnitude to 10-2 S/cm. The little dopant doesn't influence the crystal structure and other physico-chemical characters, but enhance the capacity delivery and cyclability. So supervalent ion doping is an effective method to improve LiFePO4 electrochemical property. However, few deeper research results were reported, and there are still lots of problems unsolved. In the paper, LiFePO4 doped with ions was thoroughly studied based on Cu2+ ion doping. The issues systematically studied include the doping ion type, the doping manner and the dopant type of precursor. The optimal technological parameters have been attained. The physico-chemical properties of LiFePO4 doped with Cu2+ ion, Li0.99Cu0.01FePO4, following the optimal route were investigated thoroughly. Furthermore, deep discussion was carried out from the aspects of micro electronic structure and conductive essence, crystalline structure and material electrochemical property. The main contents are given as following.Firstly, the paper retrospects the history and development of cathode materials for lithium ion batteries, focusing on reviewing the research progress on LiFePO4 during the last several years, and pointing out the problems unsolved and the future researching direction. The main working plans and research approaches are given. Then undoping LiFePO4 has been synthesized, and the temperature effects are investigated. The results indicate that LiFePO4 synthesized at 675℃ exhibits the optimal electrochemical property due to its ideal olivine structure and medium particle size.Doping LiFePO4 is thoroughly studied in chapter four. All kinds of synthesis factors including heat-treated manner, dopant content, Li/Fe ratio, decomposing temperature and time, sintering temperature and time are systemically investigated based on Cu2+ ion doping, and the optimal technological parameters have been attained. LiFePO4 doped with 1% Cu2+ ion (Li0.99Cu0.01FePO4) synthesized following the optimal route exhibited excellent electrochemical properties. It can deliver a reversible capacity as high as 157 mAh/g at a discharging rate 0.1C at room temperature, even though the discharging current rate rise to 2C, it is able to deliver a capacity of 124 mAh/g. Temperature effects and overcharge behaviors are studied to versify its super thermodynamic stability. Another two doping manners, co-precipitation doping and spray doping, are also studied in this paper. The former is an effective route used to improve doping effect and near 130 mAh/g reversible capacity of Li0.99Cu0.01FePO4 was achieved when discharge current rate rise to 2C. Spray is a widely used manner to synthesize electrode materials, but it has not expressed the results as expected in our experiments. Much work should be loaded. In chapter five, versatile supervalent ions are investigated for ion doping. The results seemingly indicate that the effects of doping have little concern with dopant precu...
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