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The Lithium-ion Battery Cathode Materials For The Preparation Of Spinel Lithium Manganese Oxide And Modification

Posted on:2008-04-23Degree:MasterType:Thesis
Country:ChinaCandidate:S D MaFull Text:PDF
GTID:2192360215985008Subject:Electrochemical Engineering
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Spinel LiMn2O4 is one of the most promising cathode materials of 21st century because of high working voltage, excellent security, low manufacture cost, and environment friendly. But large-scale application is restricted because of low theoretical specific capacity and poor electrochemical performance. This dissertation emphasized on searching for resultful methods to improve bulk specific energy density and to restrain capacity fading. And the article mainly included preparation of high density manganese oxide, preparation of spinel LiMn2O4, doping effects on spinel LiMn2O4 and discussion about Li deintercalation/intercalation process.High tap density manganese oxide was prepared through low temperature sintering-mechanical activation-high temperature sintering route with electrolytic manganese powder as raw material. The effects of sintering temperature, dwelling time and calefactive velocity on physical-chemistry property of manganese oxide were studied, and showed that the low temperature sintering process is the oxidation of Mn, and the high temperature sintering process actually the crystallization process of manganese oxide prepared in low temperature sintering. And heat treatment system is as follows: low sintering temperature is 700℃and dwelling time is 7h, high temperature sintering 1050℃, respectively, and dwelling time is 7h. X-ray-diffraction spectra indicated that the manganese oxides were the mixture of Mn3O4 and Mn2O3, and its tap density is 2.70g·cm-3(D50≈4.0μm).LiMn2O4 was prepared with high tap density manganese oxides we as precursor and Li2CO3 as Li sources through the mechanical activation-high temperature solid state route. Effect of sintering temperature, sintering time and x(LixMn2O4) on spinel structure, morphology and electrochemical property, and the result showed that Sintering temperature affected Spinel structure, morphology and electrochemical property evidently. Sintering time affected spinel structure, morphology and electrochemical property slightly. Electrochemical property was affected by X(LixMn2O4) remarkably, Li-rich spinel LiMn2O4 exhibited good capacity retention, and Li-poor spinel LiMn2O4 showed poor capacity retention. And the initial discharge specific capacity of Li1.015Mn2O4 is 111.25mAh·g-1(0.1C, 4.2V, vs.C) and is the maximum among the different Li/Mn molar ratio, and has a high capacity retention of 95.03% after 30 cycles.Lithium manganese oxides of Li1.015Mn2-xMxO4(M=Co,Ni,Ti,Zr) were prepared with Co3O4,NiO,TiO2,ZrO2 as dopant. Effects on structure, morphology and electrochemical property were investigated, and the results indicated that Li1.015Mn2-xMxO4(M=Co,Ni,Ti,Zr; x≤0.1) exhibited a cubic pure spinel structure, except Li1.015Mn1.9Zr0.1O4. Cations order was optimized. With the increasing of dopant content, initial specific capacity deceased and electrochemical performance was enhanced. Initial specific capacity deceased unnotably when x≤0.01 but notably when x>0.1. Particle sizes became smaller and tap density decreased in a way with the import of substituted ionic.Li deintercalation/intercalation process from spinel LiMn2O4 was studied by AC impedance measurement. It was found that the exchange current density and structure stability were enhanced through doping, and diffusion coefficient of Li+ was also affected by doping.
Keywords/Search Tags:cathode material, lithium manganese oxide spinel, mechanical activation, electrochemical property, cyclic voltammetry, AC impedance
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