| Lithium ion batteries are widely used for their favorable advantages of high voltage, big specific capacity, long cycling life and non-pollution. Intensive research and development work is being conducted to further improve the performance of lithium ion batteries and reduce the cost of electrode materials. The technology of cathode materials is one of the core technologies. Transitional metal oxides with high inserted potential are usually used as cathode material of Lithium-ion batteries. At present, layered compounds LiCoO2, spinel LiMn2O4, olivine-type LiFePO4 and LiNiO2 are extensively studied. As a potential cathode material of large scale moveable Li-ion batteries, Olivine LiFePO4 has become a very attractive cathode material for rechargeable lithium ion batteries due to its high theoretical capacity (170mAh/g) and voltage (about 3. 4V versus Li/Li+), abundant resource, low raw materials cost, environmental friendliness and safe characteristic, but it had low electronic conductivity and the reversible capacity loss at higher current density. Based on summarizing Li-ion Batteries, some correlative materials, extraction-insertion mechanisms of Li-ion, preparation methods, the structure, existy mostly problem, excellent electrochemical characteristics, reseach progess in the world of the cathode LiFePO4 were further introduced.FeC2O4·2H2O, Li3PO4, (NH4)2HPO4 which were activated by ball-milling as raw materials, the cathode material of LiFePO4 for lithium ion battery was synthesized by high temperature solid-state reaction method under the protection of the inert gases.The effects of synthesis temperature, reaction time were discussed and the crystalline structure, morphology of particles, crystalline size of the samples were analysed by means of X-ray diffraction (XRD), scanning electromicroscope (SEM) and electrochemical techniques. The results show that synthesis temperature, calcinations time are main factors affecting the structure andperformance of LiFeP04 cathode materials. Large amount of compounds formed as impurities at lower sintering temperatures, which decreased the charge-discharge capacity. The capacity loss at higher sintering temperatures was caused by the utilization of large particles being constrained by their small surface area. In this work, LiFeP04 is simple pure olive-type phase with small particles, and uniformly distribution of gain size. With the increasement of synthesis temperature and time, the structure and crystal of products are getting to perfect. The products sintered at 600 °C for 24h possessed excellent electrochemical performance.The LiFePd/C composite was also synthesized by solid-state method. The carbon-coated samples with perfect olivine-type structure were characterized by XRD analysis. Both cation doping and carbon coating could enhance the electrochemical performance of LiFeP04. By comparison, cation doping affected greater Rate capability of samples doped with a series of different valent state cation. Lit-s MxFePO4(LiM!,Fei.-s POO was synthesized by Mn> Mg> Cr> Ti doping. The Ti-doped LiFeP04 showed a higher charge and and excellent cycling behavior than other M-doped, the discharge capacity can be increased 34mAh/g after Ti doping. Compared with pristine LiFePO.), the electrochemical performances of the M~doped sample were greatly improved.The composition and production technique of Li-ion batteries were discussed, the influence of important working procedures (including slurrying, coating etc.) on battery performance were analysed. |
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