Preparation and Properties of Li-Mn-O-F Compounds as Cathode in Li-Ion Batteries
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Preparation and Properties of Li-Mn-O-F Compounds as Cathode in Li-Ion Batteries Hanxing Liu Chen Hu Junlei Xia Shixi Zhao and Shixi Ouyang State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, P.R. China ABSTRACT In present study LiMn2O4-xFx were prepared by the sol-gel method . X-ray diffraction (XRD) and scanning electron microscope (SEM ) were employed to detect the microstructure of the reaction products. It were found perfect crystal particles were obtained, and its’ size were uniform in 1~2 m. The specific capacity and cycleability were measured basing on battery program control test system. The results shown the substitution of F for O increased the specific capacity of the material at the cost of the cycleability due to more Mn3+ and less Mn4+ existed in the material. The exist of Mn3+ would reduce cycleability of cathode material due to the Jahn-Teller effect which were caused by the deformation of the crystal structure.
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INTRODUCTION The energy produced by a renewable source will not only be produced at moments that it is needed. Therefore one will have to store the energy to make it available. Energy could be stored in many ways. One of the most convenient and easiest ways is to store electrical energy in rechargeable batteries, and lithium-ion batteries is one of the most attractive way. Favorable characteristics of lithium-ion batteries include a high energy density, a high voltage and a low weight. Due to the high cost and toxicity of cobalt, an search for new cathode materials has been underway for several years[1-5]. One of the most attractive cathode materials is the spinel LiMn2O4 due to their low cost, abundance, and non-toxicity. However, the spinel LiMn2O4 and its derivatives demonstrate lower discharge capacity than layer structured materials and a slow capacity loss at elevated temperature in the range of 50-80 oC. Therefore, researchers have paid more attention on other choice such as layered LiMnO2 with a-NaFeO2 structure. To overcome the shortcomings, the substitution of manganese was adopted widely[6-10]. The traditional theories explain that to keep the charge balance, with the Li+ being inserted or removed, the valence of transition metal Mn have to change between +3 and +4, the cation play a most critical role in the electrochemical properties. With the guide of the theory , Co, Cr, Ni, Zn, Cu, Mg et. al. were substituted for Mn. The results of the cation substitution were that the cycleability has been improved to some extant, but the initial capacity has been decreased instead of being elevated. Therefore, some new measures must be adopted to improve the simple substitution with cations to obtain good cycleability and keep the initial capacity not being decreased. The first-principal calculation results indicate that the anion has a very strong influence on the electrochemical properties[11-12], such as voltage ,because the significant charge transfer to the anion upon intercalation of lithium. I
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