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Synthesis and Properties of Spinel Limn2 O4 as Cathode Material

Author: LiShuang
Tutor: LvWenZhong；ZhangWuXing
School: Huazhong University of Science and Technology
Course: Microelectronics and Solid State Electronics
Keywords: Lithium ion battery Cathode material Spinel LiMn2O4 Solid state reaction FePO4 surface coating Electrochemical performance
CLC: TM912
Type: Master's thesis
Year: 2011
Downloads: 148
Quote: 1
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Abstract


Lithium ion batteries have attracted much attention in recent years because of the growing demand for energy. Intensive studies have been focused on the cathode materials, especially LiMn2O4. LiMn2O4 is a promising candidate as cathode material for lithium ion batteries, owing to its high voltage, high energy density, safety, high abundance, low-cost, non-toxicity and environmental friendlkiness. Unfortunately, its severe capacity loss during cycling, especially at elevated temperature, is still a tough task. Some methods such as optimization of synthesis methods, surface modification or doping have been adopted to reduce the capacity loss of LiMn2O4 in previous studies.In this thesis, hydrothermal method was used to synthesize MnO2 nanomaterials under different temperature for 12 h. Then, the MnO2 nanomaterials were mixed with Li2CO3 to synthesize the spinel LiMn2O4 cathode materials using solid state method. The influence of MnO2 precursors, calcination temperature and calcination time on the electrochemical performance of LiMn2O4 were investigated systematically. Under the optimum condition, the as-prepared LiMn2O4 was modified by FePO4 surface coating. The thermal analysis was conducted by TG/DTA. The structure, morphology and element of materials were characterized by XRD, SEM, HRTEM and EDAX. The electrochemical performance was tested by charge-discharge, cycling volt-ampere （CV） and Electrochemical Impedance Spectroscopy （EIS）.The results show that MnO2 nanomaterials with different crystallographic types and morphologies can be synthesized via tunable hydrothermal method.β-MnO2 sphere which was assembled by nanorods are obtained at 120℃for 12 h. Using it as the precursor, spherical LiMn2O4 with good crystallinity and small particle size can be obtained and presents good electrochemical performance. During the synthesis process of LiMn2O4 by solid state method, calcination temperature and calcination time are important factors influcing the the electrochemical performance of LiMn2O4. When reacted at 750℃for 20 h, LiMn2O4 has the best electrochemical performance.FePO4 surface coating can effectively enhance the electrochemical performance of LiMn2O4. LiMn2O4 coated with 1wt.% FePO4 has the best electrochemical performance. The initial discharge capacity is 117.2 mAh/g at 1 C, and still remains 98.4 mAh/g after 100 cycles with the rention of 84.0%.

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