| Lithium iron phosphate (LiFePO4) is a new type of lithium-ion battery cathode material; the material is non-toxic, environmentally benign, abundant supply, has high capacity, cycling performance and excellent thermal stability, particularly in the large-scale lithium ion batteries. However, LiFePO4 has very low conductivity, which hinders its practical application.On the base of reviewing the development of lithium ion battery and its cathode materials in detail, olivine LiFePO4 was chosen as cathode material and its synthesis and modification was studied,but there are some major shortcomings, as well as important factors that effect its electrochemical properties. Our research focus on changes and improvements in costs, synthesis conditions, as well as improve the electrochemical properties of this material, its main contents are as follows:1. Study on the impact of the typical structure of organic carbon on the electrochemical performance of synthetic product. the major organic carbon sources were polyethylene glycol (PEG1000), soluble starch, lauric acid, adipic acid, 8 - hydroxyquinoline. The results showed that the effect of PEG was the best, when the iron source and PEG molar ratio was 1:2, the highest discharge capacity was140.13 mAh/g; when the organic carbon sources were adipic acid,8 - hydroxyquinoline,soluble starch and lauric acid, the initial discharge capacities of 132.87 mAh/g,120 mAh/g,90.6 mAh/g and 106.76 mAh/g (0.1C), respectively. The results showed that the selection of conductive agent affected the performance of the product obviously.2. The impact of PEG and glucose as compound carbon source on the electrochemical performance of product was studied. When the molar ratio of PEG and glucose was 1:1, the molecular weight of PEG changes between 400 and 6000, the PEG of short chain demonstrated excellent fast charging and discharging abilities.PEG400 was the best: discharge capacity was 163 mAh/g at 0.15C, 0.3 C for 150 mAh/g. when PEG1000: glucose was 2:1, the sample had the best electrochemical performance, reversible capacity was 139.9 mAh / g, and retained over 138.7 mAh/g after 20cycles, it is 99.14% of initial capacity.3. With water as the solvent and different trivalent iron as iron source, LiFePO4 was synthesized through sol - gel method. The influence of Fe3+source on the structure and electrochemical properties of material LiFePO4 was studied. When the iron sources were (NH4)3Fe(C6H5O7)2, Fe(C6H5O7)?H2O, and Fe(NO3)3?9H2O, the initial discharge capacities was 76.82 mAhg-1, 119.08 mAhg-1 and136.51 mAh / g, respectively. The better water-soluble source of inorganic trivalent iron was more effective to reaction.4. Using the precursor with Li, P, Fe, C molecular complex and glucose and citric acid as a reducing agent synthesized LiFePO4 through rheological phase method. It showed good electrochemical performance, the first discharge capacity was 133.19 mAh / g and 136.58 mAh / g, and attenuated only 0.51 percent and 3.83 percent after 20 cycles.The LiFePO4 was characterized by XRD,SEM and EIS . The results showed that the grain size was nano-scale, electronic microscope photograph displayed the sample was gathered with LiFePO4 particles.
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