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Synthesis And Study On The Sohd-State Reaction Process Of Phosphate Material

Posted on:2016-06-24Degree:MasterType:Thesis
Country:ChinaCandidate:S GongFull Text:PDF
GTID:2191330470969507Subject:Metallurgical engineering
Abstract/Summary:PDF Full Text Request
LiMnP04 and LiFeP04 was synthesized by solid-state method, and the thermal behavior, microstructure, phase constitution and carbon content of the raw material. precursor and carbon coated LiMnPO4 and LiFePO4 samples were investigated by means of thermogravimetry-differential scanning calorimetry (TG-DSC), mass spectrometry (MS), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and carbon content test.Experimental results revealed that there were three steps in the solid-state reaction of LiMnP04 and LiFePO4 precursor under argon gas atmosphere, including precursor decomposition, phase formation and growth. The results of TG-DSC and MS tests showed that the precursor decomposed and released H2O, CO and CO2. X-ray diffraction patterns revealed that the LiMnPO4 phase formation has started at 200℃ and the phase formation was slowly, while, the LiFePO4 phase formation has started at 400℃ and the phase formation was fast. The pyrolysis of glucose produced amorphous carbon. The SEM microphotographs reported that with increasing reaction temperature, the primary particles and microstructure of LiMnPo4 changed inconspicuously, and the primary particles were slightly sintered only above 500℃. But, the primary particles of LiFePo4 grew quickly when the reaction temperature was increasing and the particle size reached 250.52nm at 650℃. The SEM microphotographs of LiFePO4 also showed that the amorphous carbon was attached at the surface of and between the particles. TEM image of the prepared carbon-coated LiMnPO4 sample by heat treatment at 600℃ showed that amorphous carbon generated by decomposition of dextrose monohydrate was heterogeneously coated on LiMnP04 primary particles with an average thickness of one to three nanometers. The results of carbon content test of the samples by heat treatment at different temperatures and TG test of dextrose monohydrate indicated that the dextrose monohydrate decomposed mainly below 350℃.In order to investigate the influence of heating rate on the LiFePO4 solid state reaction, the LiFePO4 precursor was characterized by TG-DTA at different heating rates. According to the TG-DTA curve of the precursor pre-processed at 350℃, the pyrolysis of glucose monohydrate was basically finished and the precursor decomposed completely indicated the glucose monohydrate in the precursor barely affect the formation of the LiFePO4. As the heating rate rising in the solid phase reaction, the crystallization temperature of the lithium iron phosphate increased, the intensity of reaction became fiercely and the phase formation processing time was shorten.
Keywords/Search Tags:process analysis, solid-state method, LiMnPO4, LiFePO4
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