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Preparation and Anion-doping Modification of LiFePO4/C Cathode Materials for Lithium Ion Batteries

Author: LuFei
Tutor: ZhouYiChun
School: Xiangtan University
Course: Materials Physics and Chemistry
Keywords: Lithium ion battery Cathode material LiFePO4 Anion doping Hydrothermal method
CLC: TM912
Type: Master's thesis
Year: 2011
Downloads: 49
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Abstract


Olivine-type LiFePO 4 materials as environmentally friendly, low-cost, good thermal stability, no moisture absorption, excellent cycling performance and safety performance is a great application potential power lithium-ion battery cathode materials. However, due to the restrictions of the crystal structure, the electronic conductivity and ion diffusion rate is very low, a serious impediment to its commercial application. This article discusses the cathode material progress based on the olivine structure LiFePO 4 study, focusing on the modification of its anion doping. Were used to optimize the process of high-temperature solid-phase method and hydrothermal synthesis method LiFePO 4 F - doped modified system. The use of SEM, TEM characterization of the surface morphology of the material, the XRD analysis of material microstructure, battery test systems research material cycling performance and charge-discharge performance, electrochemical impedance spectroscopy and cyclic voltammetry curve analysis material electrochemical reaction mechanism. Specific work and the results are summarized as follows: the high temperature solid 2 CO 3 of Li the the FeC 2 O 4 · 2H 2 O, NH 4 H 2 PO 4 as raw material, C 6 H 12 O 6 as a carbon source and reducing agent, synthesized LiFePO 4 / C, and the synthesis temperature sintering time on the structure and properties of materials, to determine the optimization of process parameters for the synthesis temperature of 700 oC, synthesis time of 12 h. In this optimization process synthesis the LiFePO 4 / C cathode material has the single olivine type LiFePO structure, the first discharge capacity at 0.1 C to 152.03 mAh / g The charge and discharge efficiency was 98.9%, the capacity retention rate was 97% after 30 cycles. The high-temperature solid-phase method to optimize the process parameters the synthesized F - the ion doped LiFePO 4 / C by XRD, SEM, EIS and other methods to study the electrochemical performance and the microscopic structure of the relationship. Synthesis Life (PO 4 ) 1-x F 3x / C (x = 0, 0.01, 0.03, 0.05) cathode materials have The single, olivine-type LiFePO 4 structure, the initial capacity of the material is 0.1 C, respectively 153.4 mAh / g, 159.74 mAh / g, 165.06 mAh / g and 162.47 mAh / g. Explore other modification methods, synthesized by hydrothermal method F - the ion doped LiFePO 4 / C materials, and studied F - ion doped LiFePO 4 structure and electrochemical performance of the cathode material. By XRD and XPS analysis, evidentiary materials have a single olivine-type LiFePO 4 structure Description F - ion doped into the lattice structure of the material, and there is no changes in the lattice structure of the material, just causing tiny cell expansion. When the doping content x = 0.03, the electrochemical properties of the material (more than the capacity, rate capability and cycle stability) excellent.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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