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Preparation and Research Electrochemical Properties of LiFePO4 for Cathode Material of Lithium-ion Batteries

Author: QiZuoZuo
Tutor: JiangYuanRu
School: Xi'an University of Architecture and Technology
Course: Applied Chemistry
Keywords: LiFePO4 Cathode material Coprecipitation Modified Lithium ion battery
CLC: TM912
Type: Master's thesis
Year: 2011
Downloads: 44
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Abstract


High capacity lithium-ion battery charge and discharge cycle performance, self-discharge rate is very low, and environment-friendly advantages are widely used in all kinds of electronic products. Lithium iron phosphate has a wide range of sources of raw materials, low prices, good thermal stability, good cycle performance, outstanding safety performance advantages to become one of the most promising cathode material for lithium-ion battery. However, the low conductivity of the lithium ion battery and the ion diffusion coefficient is low, and a bulk density of the material small limit their large-scale use. Improve the chemical properties of the lithium iron phosphate methods are mainly the improved synthesis method the particles are small and uniform distribution of the product and improve the conductivity of the material by the doping element. The papers by liquid phase coprecipitation prepared lithium iron phosphate cathode material for lithium-ion batteries, the use of X-ray diffraction analysis (XRD), scanning electron microscopy microscope (SEM), electrochemical workstations and other means of samples for analysis. Explore the use of a different source of iron, doped with different carbon source, the amount of carbon, and the synthesis conditions of the sintering temperature and time on the electrochemical properties, and obtained the following test results. FeSO 4 , Fe (NH 4 ) 2 (SO 4 ) 2 , FeC 2 O 4 the prepared LiFePO three different iron source under suitable conditions 4 are high purity, crystallinity characterization results Description Fe (NH the 4 ) 2 (the SO 4 ) 2 is an ideal source of iron, the first discharge capacity 68mAh · g -1 . Comparative effect of different carbon precursor doped to give more uniform distribution of the particles of the sample can be, to increase the ratio of surface area of ??the sample, to improve the electrochemical properties of the sample to add a small amount of carbon. With the increase in the amount of carbon-doped, the charge and discharge capacity of the sample will experience first rose and then dropped in the process. The experimental results show that the glucose is the preferred carbon source, having a high specific capacity and more excellent charge-discharge performance. Sintering temperature and time have a large effect on the morphology and electrochemical properties of the material, the sintering temperature is too low, the smaller particles of the sample and some impurities; sintering temperature, the sample particle agglomeration and charge-discharge capacity reduced. The sintering time is too short, the particle shape of the sample will have no rules; sintering time is too long, crystal grains of the complete re fused together, so that the particle size of the samples has been increased. On different carbon sources (glucose, sucrose, and acetylene black), the amount of carbon doped and the sintering time and temperature conditions of the study found that the use of glucose as a carbon source, doped with 5% of the sample of 10 h was obtained was sintered at 650 ℃ better overall performance. Normal temperature and under atmospheric pressure, to the magnification of the 0.1C charging and discharging test, sample the first charge and discharge capacity of 160.2mAh · g -1 , after 20 cycles, the capacity can still reach 150mAh · g -1 . The experimental results obtained indicate that a different source of iron, carbon, and sintering conditions prepared lithium iron phosphate samples have a discharge voltage of about 3.4V platform, and the high working voltage of the lithium-ion battery, has a good prospect in the electronic component applications.

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