| Lithium-ion battery with the benefits of high energy, long life and low pollution and so on has been widely used in many fields. Lithium-ion battery has become the main power of portable electronic products in current market and is also considered to be the promising power of EV, HEV and PHEV. LiMn2O4, LiFePO4and Li[NixCoyMn1-x-y]O2are three attractive anode materials for lithium-ion battery in recent years. In addition, Li-rich cathode material is also an attractive lithium-ion battery material owing to its high theoretical specific capacity of (250mAh·g-1). Considering the actual utilization of the electric discharge, life, environmental pollution, and price-cost perspective, the lithium iron phosphate LiFePO4of olivine structure with low cost, rich resource, environment friendly, voltage platform moderate (as opposed to the lithium metal3.4V), and has a high theoretical specific capacity170mAh·g-1and other advantages, is considered the most promising power of lithium-ion battery. But it also has some disadvantages, such as low electronic and ionic conductivity constraints battery current performance, while LiFePO4doped hydrothermal is a viable method in order to improve this problem.This paper carried out a systematic study of LiFePO4preparation, structure and electrochemical performance with modern testing means of XRD, SEM, infrared spectrum (FTIR) and electrochemical properties tests. At the same time, the preliminary exploration of Li1.2Mn0.54Ni0.13Co0.13O2solid-state synthesis is also preceded.The first part of the experiment began with hydrothermal method synthesis of LiFePO4by using LiOH·H2O, H3PO4, and FeSO4·7H2O as reactants, and explored the ratio of the reactants to find a better raw material ratio2.7:1:1by changing the content of Li. Investigated the influence of the hydrothermal reaction temperature, reaction time, and the amount of anti-oxidant to the electrochemical performance, structure and appearance of the product. Using the single factor of temperature230℃, the antioxidant content0.4g, the different time of hydrothermal reaction to synthesize LiFePO4and applying the analysis methods of infrared spectrum (FTIR), SEM, XRD to inspect the changing of the structure and the particle size of LiFePO4hydrothermal synthesis as time went by.The optimum conditions for preparing anode material LiFePO4powder through orthogonal experiment is hydrothermal reaction temperature240℃, reaction time3h and the antioxidant content0.3g. The LiFePO4material synthesized under the optimum conditions, after doped by carbon and calcined, LiFePO4/C have favorable electrochemical properties. The discharge capacity is157.6mAh·g-1under0.1C, the discharge capacity is142.6mAh·g-1under1C, the discharge capacity is63.5mAh·g-1under10C. After cycled40times, the damping decrement of the capacities are6.4%and8.4%respectively at1C and10C.The second part of the experiment is to further improve the electrochemical properties of LiFePO4/C material, prepared a series of LiFe1-xMgxPO4/C(x=0.01,0.02,0.03) materials, and studied the influences of the doped Mg and the quantities to the electrochemical properties. The results shows the doped quantities x=0.02, the performance of the material is the best. The first discharge capacities is respectively150.8mAh·g-1,125.6mAh·g-1and84.5mAh·g-1under0.1C,1C and10C. After cycled40times, the damping decrement of the capacities are3.0%and5.7%respectively under1C and10C. Circulation performance is improved.The third part of the experiment syntheses Li1.2Mn0.54Ni0.13Co0.13O2by using solid-state method and studied the influence of adding H2C2O4to the capacity of materials during the synthesis process. And the experimental results show that the charge and discharge capacities of the synthetic material which are added H2C2O4are increased obviously. |
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