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Synthesis and Elecrochemical Performance of Li2FeSiO4/C Composite Cathode Mate

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Tutor: ZuoPengJian
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: lithium ion battery,Li2FeSiO4/C,solid-state method,hydrothermalmethod
CLC: TM912
Type: Master's thesis
Year:  2012
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Abstract:
Li2FeSiO4has been attracted more attention as a promising cathode materialfor Li-ion batteries because of its low cost, a wide range of raw materials,environmental friendliness, high safety. However, the application of Li2FeSiO4islimited, because of its low the material¨s electronic conductivity and lithium ionmigration rate. In this paper, Li2FeSiO4/C nanocomposites are prepared bysolid-state method and hydrothermal method. The impact of different preparationconditions to the material morphology and electrochemical performance are studied.The Li2FeSiO4/C nanocomposite prepared under different hydrothermaltemperature and carbon content in the control of hydrothermal methods werestudied by structure analysising and electrochemical testing.The lithium-ion battery cathode material Li2FeSiO4was prepared by asolid-state method with stoichiometric amount of analytical reagents, Li2CO3,FeC2O4,2H2O, SiO2and sucrose. There are a certain number of impurity in thematerial, the particle size is concentrated in the range of several tens of nanometers.At1/16C rate, the first discharge capacity of Li2FeSiO4cathode material is153mAh,g-1. After35cycles, the discharge capacity is55mAh,g-1with the capacityretention ratio of36%. Then put stoichiometric amount of C4H6MnO4,4H2O intothe raw materials and get Li2Fe0.5Mn0.5SiO4/C. At1/16C rate, the first chargecapacity of Li2Fe0.5Mn0.5SiO4/C cathode material is211mAh,g-1, up to308mAh,g-1in the second cycle and approach to the theoretical capacity of Li2MnSiO4.After25cycles, the capacity retention ratio is33%. By comparison, theLi2Fe0.5Mn0.5SiO4/C cathode material has higher discharge capacity and bettercycle performance, which shows that the doping Mn has effectively improved theperformance of the material.The lithium-ion battery cathode materials Li2FeSiO4were prepared byhydrothermal method with stoichiometric amount of analytical reagents,CH3COOLi,2H2O, FeC2O4,2H2O, SiC2H5O4and sucrose. The Li2FeSiO4/Cnanocomposite prepared under different hydrothermal temperature and carboncontent in the control of hydrothermal methods, were in-depth studied by structureand electrochemical methods. The results showed that, when the hydrothermaltemperature is150≧, Material has a smaller particle size, it has higher dischargecapacity and better cycle performance. The Li2FeSiO4of12.5%carbon content,particles smaller and more uniform and electrochemical performance is moresuperior. Above all, at the hydrothermal reaction temperature of150≧, with the carbon content of12.5%, the preparaed Li2FeSiO4/C has uniform particle andconcentrated in a dozen nano. At0.1C rate, the first charge capacity and dischargecapacity of Li2FeSiO4optimized material were140mAh,g-1and144mAh,g-1, thecoulomb¨s efficiency is more than100%. The discharge capacity is160mAh,g-1inthe following cycle, The largest discharge capacity is166mAh,g-1and reach thetheoretical capacity of Li2FeSiO4, and the discharge capacity is151mAh,g-1without decresing the capacity after20cycles. At the same time, material has agood performance rate. At1C rate, the first discharge capacity of Li2FeSiO4cathode material is121mAh,g-1, in30cycles the discharge capacity is110mAh,g-1. At2C rate, the first discharge capacity of Li2FeSiO4cathode material is90mAh g-1, the discharge capacity is100mAh,g-1in the following cycle, and thedischarge capacity is93mAh,g-1after50cycles; At5C rate, the first dischargecapacity of Li2FeSiO4cathode material is84mAh,g-1, the discharge capacity is100mAh,g-1in the following cycle, and after50cycles the discharge capacity is82mAh,g-1.
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