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LiFePO4/C Composite Cathode Materials Prepared and Characterization

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Tutor: WangDianLong
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: Lithium-ion battery,LiFePO4/C,high-energy ball-milling,rheologicalphase,dope,ele
CLC: TM912
Type: Master's thesis
Year:  2012
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Olivine LiFePO4has been considered as a promising lithium-ion batterycathode material because of the advantage of its safety, stable charge-dischargevoltage, high chemical stability, long cycling period and environmental friendly.However, its low electronic conductivity and low ion diffusion lead to its lowinitial capacity retention rate and discharge capacity under high magnification.These factors have restricted the commercialization of LiFePO4cathodematerials.LiFePO4/C was prepared by high-energy ball-milling methods. Differentsintering temperatures, the lithium source, carbon source and iron source havebeen studied for the influence of LiFePO4/C. The result is: lithium carbonate:ferrous oxalate: lauric acid: ammonium dihydrogen phosphate equals1.05:1:1:1,sucrose equals the60%mass of the final product quality. The rate of frequencyof the high-energy ball mill reaction is2000r/min and the reaction time is1hour.The precursor was sintered in the H2/Ar atmosphere at260¡æfor2h, and thesintered at550¡æfor12h. This LiFePO4/C could reach to122mAh/g at0.1Cand40.91mAh/g at20C.LiFePO4/C was prepared by rheological phase methods. Different sinteringtemperatures, different sintering time, socruse amount and the doped amount ofMg2+have been studied for the influence of LiFePO4/C. The result is: Lithiumnitrate: nitric acid iron: magnesium acetate: ammonium dihydrogen phosphatemolar ratio1.05:0.98:0.2:1, sucrose equals the60%mass of the final productquality. The rate of frequency of the high-energy ball mill reaction is2000r/minand the reaction time is1hour. The precursor was sintered in the H2/Aratmosphere at260¡æfor2h, and the sintered at600¡æfor16hours. ThisLiFePO4/C was homogeneous and its particles were uniform with roughnesssurface. It could reach to159.53mAh/g at0.1C,138.77mAh/g at1C,109.14mAh/g at5C,94.17mAh/g at10C and71.66mAh/g at20C and its capacityretention rate could keep more than90%after500cycles.The LiFePO4/C cathode materials prepared by rheological phase methodshas generally better performance than the one prepared by high-energy ball-milling methods.The LiFePO4/C materials prepared by high-energy ball-millingmethods had an obvious phenomenon of agglomeration. It could be improved bydoping with the right amoubt of Mg2+.
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