| Because of increasingly serious energy and environmental problems, and the traditional fossil energy will be used exhaustively in the future, electric vehicles and hybrid electric vehicles, and its power supply are paid more and more attention, and rapidly develop. Currently, lead-acid and nickel-hydrogen batteries are mainly used in the electric vehicle or hybrid electric vehicles, their life is short and easy to pollute the environment. Because of its excellent performance, lithium-ion batteries has been widespread since it was found, and it has the absolute advantage of replacing the lead-acid and nickel-hydrogen batteries to be used in electric vehicle or hybrid electric vehicle. Now one of the bottlenecks restricting the development of the lithium-ion battery is cathode materials, lithium-ion battery requires cathode materials possess not only a high specific capacity, good charge-discharge performance and cycle, but also the price is an important factor which can not be ignored. Since Goodenough found that lithium iron phosphate material can be reversibly embedded and deintercalation of lithium ions, can act as a lithium ion battery cathode material, lithium iron phosphate cathode material has attracted a lot of attention. Compared with the conventional positive electrode materials of lithium-ion secondary power supply lithium cobaltate of LiCoO2, lithium nickel oxide LiNiC2, lithium manganate LiMn2O4, olivine structure of lithium iron phosphate (LiFePO4) cathode material has a relatively high specific capacity (170mAh/g), stable working voltage (3.5V) and a better cycle life (2000cycles), low price, good thermal and chemical stability, environmental friendly and is rich in raw materials, which is greatly promising green energy.The advantages and disadvantages of several commonly used cathode materials of lithium ion battery, the structure of LiFePO4, as well as its existing problems and modification research. In addition, for the problem of higher cost of preparation of lithium iron phosphate, It was proposed a method to effectively reduce the cost of synthesis, while effectively reducing the pollution of the environment compared with the conventional synthetic method. Iron powder as a source of iron, the precursor FePO4of cathode material LiFePO4of lithium-ion battery was prepared by excessive inorganic acid cycle auxiliary. The experimental results show that:reaction of the iron powder with phosphoric acid can be promoted to complete using excess of phosphoric acid and sulfuric acid, and the excess of phosphoric acid and sulfuric acid can be reused in the reaction system, as the result,the entire reaction system has no liquid waste. XRD and SEM analysis showed that their structure, morphology and size of the first synthesis of FePO4and after30cycles FePO4are the same. The yields of three batches which were obtained by the above reaction were all about99.10%, showed a higher product yield. And, Fe/P ratio is measured by inductively coupled plasma mass spectrometer (ICP-MS) method substantially equal to1. LiFePO4/C composites are synthesized by mixing as-prepared FePO4and stoichiometric proportion of LiOH and sucrose which are sintered at350℃for5h and700℃for15h under the atmosphere of5%H2-95%N2. Electrical properties show that all the samples prepared from FePO4obtained at different cycles not only have high specific capacity which the discharge capacity of0.2C,0.5C,1C and5C is155.1,144.0,134.4and101.7mAhg-1respectively, but also exhibit the excellent cyclic stability and high-rate capability.Meanwhile, the use of excess hydrochloric acid and nitric acid can also induce complete reaction of iron powder with phosphoric acid, but because of their volatility and decomposition resistance, so that the cycle of the reaction is restricted. Further study based on the optimized different concentrations and adding a surfactant to the influence of the particle size of the sample. Try to take advantage of organic acids-citric acid instead of an excess of phosphoric acid to provide an acidic environment. In addition, the use of spray drying-carbothermal reduction method has been long and short spherical spherical of LiFePO4found to have excellent performance by the electrical properties. |
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