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Doping And Surface Coating Of Spinel LiMn2O4Cathode Material For Lithium-ion Battery

Posted on:2013-01-10Degree:MasterType:Thesis
Country:ChinaCandidate:X F FanFull Text:PDF
GTID:2231330392958451Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
Spinel LiMn2O4is regarded as the most potential cathode material for Li-ionbatteries due to its abundance, low cost, easy manufacture, and nontoxicity.However, there are still some problems that should be solved prior to its commercialuse: the poor cycling performance,the severe capacity fading, and the dissolution ofMn2+ions especially at elevated temperature(55oC). In this paper, we use Co-S andNi-F anion-cation co-doping, optimize the synthetic methode and surfacemodification of spinel LiMn2O4to stabilize the sturcture during the cycling andimprove the electrochemical performance both at room temperature and elevatedtemperature.Our work focus on the following four directions:1.Li1.05Co0.1Mn1.9O4-xSxand Li1.05Ni0.1Mn1.9O3.98F0.02cathode material of Co-S and Ni-F anion-cationco-doping were synthesized by the solid-state reaction method respectively.2.Thenano SiO2coated Li1.05Co0.1Mn1.9O4xSxspinels were synthesized by the Sol-gelcoating process.3.Doped spinel Li1.05Ni0.1Mn1.9O3.98F0.02with2~3μm particle sizeand good crystallinity was synthesized using a easy two-step process: The solid-statereaction method combines molten salt method.4. Li1.05Ni0.1Mn1.9O3.98F0.02was coatedby solid electrolyte Li-La-Ti-O.Fabricate the coin cells and measure the cycleperformance at elevated temperature.The samples were characterized in terms of their phase formation, surfacemorphology, charge-discharge capacity, rate capability, and electrochemicalimpedance. The results demonstrate that Co-S and Ni-F co-doping can enhance thecrystal structure stability and overcomes the Jahn-Teller distortion, but cannot resolvethe elevated temperature cycling issue of the spinel cathode materials. The capacityloss of Li1.05Co0.1Mn1.9O3.98S0.02without SiO2coating gets to15.6%after50cycles,whereas the2.0wt.%SiO2-coated Li1.02Co0.1Mn1.9O3.98S0.02cathode material has only8.7%capacity loss after50cycles at elevated temperature (55oC).Our approach,based on high-quality crystalline Li1.05Ni0.1Mn1.9O3.98F0.02coated by solid electrolyteLLTO, is a very effective way in improving the electrochemical performance of lithium manganese spinel electrodes in lithium-ion cells. The cathode material deliverinitial discharge capacity of108.3mAh/g in range of3.0~4.3V with a retention of94.6%over50cycles at55oC. Electrochemical impedance spectroscopy(EIS) wasused to study the materials and impedance of LLTO-coated Li1.05Ni0.1Mn1.9O3.98F0.02is decreased greatly compared to the pristine Li1.05Ni0.1Mn1.9O3.98F0.02.It indicates thatthe high-quality crystalline can enhance the LMO structural stability and LLTOcoating can suppress Mn2+dissolution in the electrolyte during cycling. They cansignificantly improve the cycling performances at elevated temperature.
Keywords/Search Tags:Cathode materials, LiMn2O4, High-quality crystalline, Electrochemistry, LLTO coating
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