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Synthesis and Performance of LiFePO4 by Mechanical/Chemical-in Situ Polymerization Reaction

Author: ZuoXiangLi
Tutor: WangChaoYang
School: South China University of Technology
Course: Materials Science
Keywords: LiFePO4 The mechanical chemical - in situ polymerization Situ polymerization - carbothermal reduction F-doped PANi coated
CLC: TM912
Type: Master's thesis
Year: 2011
Downloads: 103
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Abstract


Olivine-type lithium iron phosphate (LiFePO 4 ) as a cathode material for lithium ion secondary battery with high capacity, structural stability, cyclic reversibility, rich in raw materials and easy to get, cheap, and safe and nontoxic and other prominent advantages, the most promising development in lithium ion battery cathode material one. The proposed low-carbon, electric vehicles and smart grid development to the study of lithium iron phosphate bring greater opportunity, but large-scale industrial production of lithium iron phosphate is needed to solve three problems: 1. Substantial increase in iron phosphate lithium conductivity, to improve the material rate performance; find a method for the preparation of a low-cost, large-scale production; 3. improve the tap density of the material, in order to increase the volume of material than the capacity. In this paper, on the basis of the traditional solid-phase method using mechanochemical method and in situ polymerization combined preparation the LiFePO 4 / C composites. The trivalent iron source (the FeCl 3 , Fe (NO 3 ) 3 and FePO ), compare Both synthetic chemical mechanical - situ polymerization and in situ polymerization - carbothermal reduction method LiFePO 4 / C substrate crystal structure, morphology and electrochemical properties. Also studied in the F-doped and in situ polymerization of PANi coated on LiFePO 4 / C composite surface morphology and electrochemical properties. Study different trivalent iron salts (the FeCl 3 the the Fe (NO 3 ) 3 and FePO 4 ) for source of iron, mechanical and chemical - in situ polymerization and in situ polymerization - carbothermic reduction the Preparation LiFePO 4 / C composites. XRD, SEM and charge-discharge tester on the crystal structure of the material, morphology and electrochemical performance characterization. The results show that: relative to the situ polymerization - carbothermal reduction method using mechanical and chemical - situ polymerization the LiFePO 4 / C electrochemical performance is excellent, three kinds of iron sources 1C discharge capacity were : 132.05 mAh / g, 130.18 mAh / g and 125.8 mAh / g, while the use of in situ polymerization - carbothermal reduction synthesis of LiFePO 4 / C electrochemical performance is relatively poor, three kinds of iron source 1C discharge capacity: 109.07 mAh / g, 105.2 mAh / g and 102.65 mAh / g; Raman spectra show that, relative to sucrose as a carbon source carbothermal reduction Prepared LiFePO 4 / C mechanochemical - C graphite samples in situ polymerization significantly improve; SEM morphology analysis showed, the mechanical chemical - in situ polymerization synthesis the LiFePO 4 / C particle size - carbon thermal reduction the synthesized LiFePO 4 / C particle size (greater than 500 nm) and smaller (less than 200 nm), and the use of in-situ polymerization. F-doped and in situ polymerization PANi coated LiFePO 4 / C composite surface morphology and electrochemical performance. The results show that the F-doped and in situ polymerization PANi coated to improve the the LiFePO 4 / C materials rate capability and cycle performance, F-doped sample 1C rate discharge capacity of 142.03 mAh / g with undoped sample (132.05 mAh / g) compared to its high g capacity of 10 mAh / g after 20 cycles, the capacity retention rate was 98.3%; situ polymerization PANi coated sample to the discharge capacity at 1C rate 135.7 mAh / g, and the undoped sample (132.05 mAh / g), compared grams increase the capacity, the capacity retention rate was 99.25%, after 20 cycles; SEM analysis showed that the in situ polymerization PANi, LiFePO < sub> 4 / C the surface of the base material coated with a layer of material; confirmed by infrared spectroscopy and surface spectroscopy tests, that the cladding layer of the surface of the base body for the PANi polymer.

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