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Synthesis And Modification Of The Composite Cathode Material LiFePO_/C

Posted on:2015-05-02Degree:MasterType:Thesis
Country:ChinaCandidate:L LuoFull Text:PDF
GTID:2181330434954191Subject:Metallurgical engineering
Abstract/Summary:PDF Full Text Request
Olivine-structured LiFePO4has become a very promising choice of cathode materials for powering electric vehicles (EVs), hybrid electric vehicles (HEVs), and power tools because of its inexpensive, environment friendly, good thermal stability and excellent circle performance. However, the intrinsic crystal structure of LiFePO4results in poor electronic conductivity, ionic conductivity, and low volume power density, which seriously limited its application in industry. Therefore, this article studied through metal ion doping and the morphology controlling to synthesis LiFePO4composite with good electrochemical properties and specific microstructure and nanostructure.LiFe1-xVxPO4/C、Li1-§FeyTixPO4/C and LiFe1-§TiyVxPO4composites with Vanadium and Titanium doped and carbon coated were prepared by solid-state method synthesis route, using LiH2PO4and low-priced Fe2O3as starting materials and glucose as organic carbon source. The structures, morphologies, and electrochemical performance of materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), and charge-discharge experiment. The results indicated that the doped Vanadium was V5+and would not change the structure of the materials, the optimum LiFe0.95V0.05PO4/C cathode material displayed153mAh·g-1at0.1C,146.5mAh·g-1at1C,135.3mAh·g-1at2C; LiFe0.98Ti0.02PO4cathode using Ti to replace the Fe-sites displayed151.9mAh·g-1at0.1C,142.9mAh·g-1at1C,132.8mAh·g-1at2C that had the better performance than the sample using Ti to replace the Li-sites. V and Ti ions co-doped LiFe1-§TiyVxPO4cathode materials had worse performance than individual doped samples. The LiFe0.98Ti0.02PO4obtained from the scale up test displayed150.7mAh·g-1at0.1C,140.5mAh·g-1at1C.Assisted by the action of surface active agent, LiFePO4composite with specific microstructure and nanostructure was synthesized in ethylene glycol-water system using FeSO4·7H2O and LiH2PO4as starting materials, the influence of the ratio of ethylene glycol, reaction temperature and time were investigated on the structure and morphology of the samples by XRD, SEM, and transmission electron microscopy (TEM). The results indicated that the optimum synthesis process as follows:the volume ratio of ethylene glycol to water is95:5, temperature is230℃and reaction time is12h, the obtained sample displays an interesting spherical structure which was constructed by (010) crystal orientated porous sheet of8μm in length and nanoscale in thickness and reach a discharge capacity of123.4mAh·g-1at0.1C,97.7mAh·g-1at1C.
Keywords/Search Tags:Lithium ion battery, LiFePO4, doping, microstructure andnanostructure
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