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Study On Electrochemical Properties Of LiFePO4 For Lithium Ion Battery Cathode Material

Posted on:2017-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:H Q ZhangFull Text:PDF
GTID:2271330488461087Subject:Materials science
Abstract/Summary:PDF Full Text Request
Poly-anionic olivine structure lithium iron phosphate (LiFePO4) material have a series of advantages, such as high specific capacity (170mAh/g), environmentally friendly, a large charge/discharge platform and high security, which was known as one of the most promising lithium ion battery cathode materials. However, its electrical conductivity is rather poor because of its intrinsic crystalline structure, which worsens the high-rate charge/discharge behavior. Thus, we pay great attention to improving the electrical conductivity of LiFePO4, and one of the common but effective modifications is carbon coating.In this essay, LiFePO4 cathode material were prepared by hydrothermal method with the optimization of reaction parameters, and its electrochemical properties have also been modified by carbon coating and single-walled carbon nanotubes (SWCNTs) doping. The phase, morphology and the electrochemical properties of LiFePO4 were studied by XRD, SEM, galvanostatic charge-discharge and cyclic voltammetry test, respectively.(1) The LiFePO4 cathode material were prepared by the hydrothermal reaction using LiOH·H2O, H3PO4 and FeSO4-7H2O as raw materials, sodium dodecyl benzene sulfonate (SDBS) as surfactant, and ascorbic acid as reductant. The effects of hydrothermal reaction temperature, reaction time and concentration of surfactant on the phase, morphology and electrochemical properties of LiFePO4 have been studied, and the results showed that under the condition of 180℃,6 hours and 16mM SDBS, LiFePO4 exhibited a single phase, platy structure and better electrochemical properties with the first discharge specific capacity 101.9mAh/g at 0.1 C rate.(2) In order to further improve the electrochemical performance of LiFePO4 electrode materials, polystyrene (PS) and polystyrene acrylonitrile (PSAN) have been used as carbon source to improve the electrochemical properties of LiFePO4. The experimental results showed that the phase of LiFePO4 prepared by the two kinds of carbon sources has not been changed while the electrochemical performance has been improved. The composite material exhibited better electrochemical performance with 4% (relative to LiFePO4) PSAN as carbon source, that is, the first discharge specific capacity 146mAh/g at 0.1C rate, and 98.5mAh/g at 1C rate.(3) The after-coated LiFePO4 were combined with single wall carbon nanotubes, and discuss the effects of carbon nanotubes contents on electrochemical properties of LiFePO4 electrode materials haved been discussed. The experimental results showed that when carbon nanotubes content reach 6%, a good three dimensional conductive network structure is formed among active particles and the excellent electrochemical performance is obtained. The first discharge specific capacity reached about 166.7mAh/g at 0.1C rate, and 157.2mAh/g at 1C rate and the specific discharge capacity could also reached 107.2mAh/g even at 10C; the specific discharge capacity of electrode materials retains 158.4mAh/g after 70 cycles at 0.5C rate, and the capacity retention reached 96.6%.
Keywords/Search Tags:Cathode material, LiFePO4, Hydrothermal method, Carbon coating, Carbon nanotubes
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