| Summary: | 碩士 === 國立交通大學 === 理學院應用科技學程 === 103 === In recent years, there has been increasing interest to develop cathode materials for lithium-ion batteries with high energy density. Most of the commercial lithium batteries use layered LiCoO2 as the cathode material, but it has a limited practical capacity of 140 mAhg-1 because of chemical and structural instabilities at deep charge state. The spinel LiMn2O4 and olivine LiFePO4 have been proposed as an alternative to LiCoO2. However, their poor capacities and low conductivity of electron and/or lithium diffusivity hamper the possibility of commercial cell application. Solid solution cathode materials which can be denoted as a composite xLi[Li1/3Mn2/3]O2•(1-x)LiMO2 (M = Ni, Co, Mn, etc.), though it alternatively can be expressed as a layered form Li1+xM1-xO2, are of great potential as a generation of positive electrode materials for high energy density lithium-ion batteries. This series of materials can deliver around 270 mAhg-1 at a low charge-discharge current with good cycle performance. However, there are several problems such as the lower initial efficiency during the first charge-discharge process and the poor rate capability which should be overcome so as to put them into application as soon as possible.
The goal of this dissertation was to study a literature review for the composite cathode material xLi [Li1 / 3Mn2 / 3] O2 • (1-x) LiMO2 (M = Ni, Co, Mn, etc.), and then detailing the experimental methods of this material (co-precipitation method). We also study the effect of the parameters including the calcination temperature、sintering time and stoichiometry on the electrochemical properties. The Cr-doped composite cathode delivered a first discharge capacity of 268 mAh/g at a 0.2 C-rate between 2.0-4.8 V, and the capacity remains 90 % after 200 cycles. X-ray diffraction and electron diffraction pattern investigations demonstrated that all the composite cathode products are a layer phase crystal. TEM micrographs show the prepared products are highly crystalline with an average particle size of 20-50 nm. Finally, these findings make a brief of conclusions for future research in this high-capacity composite cathode material development of reference.
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