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The Study Of Electrochemistry Performance For Synthesize Spinel Li-Mn-O Materials On The Lithium-ion Battery

Posted on:2006-01-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H LuFull Text:PDF
GTID:1102360212489317Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
The lithium-ion batteries have been widely used in portable electronic products such as, cell phones, notebook computers and cameras because of its high-capacity (2.5 times as large as the Ni-Cd batteries and 1.5 times as large as the Ni-MH batteries) and high average open voltage, that is, 3.7 V in contrast with the 1.2V of Ni-MH batteries. In the near future, the lithium-ion battery will used in the motive-batteries. As key parts of the battery,the anode and cathode have become one of the hottest topics which was studied. Compared with the anode materials and other parts of the battery, the cathode materials play an important role in the charge/discharge capacity, discharge voltage, cycle life and even the safety of the battery. Further more, if we take the electrochemical performance (stability, safety, elevated temperature performance and specific capacity), the environment protection and cost into consideration, cathode materials have become really crucial and the development of new cathode materials with better performance has become an urgent task. Due to the abundance of MnO2 or Mn3O4, low costs, high safety and no pollution, the spinel LiMn2O4 material has become the material that is being studied and researched widely and the most prospective cathode material.The spinel LiMn2O4 belongs to the Fd3m space group. This material is apt to change its structure, which leads to the damage to cycle performance, especially in high temperature (over 55℃). Therefore, its commercialization was limited. After ten years'research, we now have a deep knowledge of the reasons for the capacity decrease of this material, such as the Jahn-Teller deformation effect, the dissolving of the Mn2+ in electrolyte, the form of the less-stable spinel structure and the decomposition of the electrolyte. It is reported that the doping modification to the LiMn2O4 and the surface modification can improve the electrochemical performance such as, cycle stability, safety, high temperature performance and high current charge/discharge. In order to accelerate the speed of the industrialization and commercialization of the spinel LiMn2O4, studies were carried out on the synthesis of the spinel LiMn2O4 as the Li-ion battery cathode material and its electrochemical performance.Combined with the researching results, this study includes the effect of the respective and cooperated doping of anion and cation on the electrochemical performance, high temperature(55℃)charge and discharge performance of the cathode material Li0.2MxMn2-xQyO4-y, the effect of surface modification on the cathode material spinel LiMn2O4, the effect of electrolyte and its composition on the cathode material spinel LiMn2O4 and the effect of particle size on the performance. This paper also studied the particle size distribution of the cathode material spinel LiMn2O4 and apparent pattern, and discussed the related theories of the insertion and escape of the lithium-ion in anode & cathode materials.Improvement of elevated-temperature performance of LiCoxCryMn2-x-yO4 cathode material by SiO2-Al2O3 surface modification was studied. The LiCoxCryMn2-x-yO4 cathode material was treated by SiO2-Al2O3 then heated on certain temperature to get rid of organic material. The structures of the modified and unmodified LiCoxCryMn2-x-yO4 were characterized by XRD, SEM and SpectraPlus. The results showed that the surface layer of LiCoxCryMn2-x-yO4 materials was composed of silicious-aluminium compound. X-ray diffraction showed that all the samples had perfect spinel structure. The electrochemical characterization of modified LiCoxCryMn2-x-yO4 cathode material was tested. The cycle stability of charge & discharge at 55℃was improved. The results of the charge/discharge curves showed that the modified LiCoxCryMn2-x-yO4 had better performance than those unmodified according to the inhibition of decline of reversible capacity of spinel LiCoxCryMn2-x-yO4. Therefore, cycle performance was improved so obviously that 84.84 % of the initial capacity were preserved respectively after 100 cycles.To improve the electrochemical capability of Li-Mn-O spinel materials, the materials LiMxMn2-xFyO4-y doped with several ions (anion-cation) was prepared by solid-state reaction method. X-ray diffraction showed that all the samples have perfect spinel structure. The results of the charge & discharge curves showed that multiple doping spinel LiCraCobLacMn2-a-b-cFyO4-y had better performance than those undoped or cation-doped materials according to the inhibition of decline of reversible capacity of spinel at 25℃. Besides that, the multiple doping spinel has also ideal discharge capacity. And the cycle performance had been improved so obviously that 94.5% of the initial capacity were preserved respectively after 80 cycles. Meanwhile, the elevated temperature(55℃) performance of the material has been improved.The spinel material Li1.02LaxMn2-xO4 doped with lanthanum ions was prepared by solid-state reaction method. X-ray diffraction showed that the samples had perfect spinel structure with x≤0.01, and that new material LaMnO3 was formed in the case of x≥0.02. The results of the charge/discharge curves showed that Li1.02LaxMn2-xO4 had better performance than the undoped materials according to the inhibition of decline of reversible capacity of spinel Li1.02LaxMn2-xO4. Therefore, cycle performance had been improved so obviously that 95% of the initial capacity were preserved respectively after 65 cycles.
Keywords/Search Tags:lithium-ion battery, cathode material, spinel LiMn2O4, doping, surface modification, electrochemical performance, elevated temperature performance
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