Preparation And Characterization Of Lithium Manganese Oxides As Cathode Materials For Li-ion Batteries By Low Heating Solid State Method

In this paper, precursors were prepared by low heating solid state reaction method using different lithium salt (lithium acetate, lithium carbonate), different manganese salt (manganese acetate, manganese carbonate), cobalt acetate, tartaric acid and oxalic acid as starting materials, then the precursors were calcinated to obtained spinel LiMn2O4 and LiCoxMn2-xO4 cathode materials for li-ion batteries in different temperature. The composition, crystal structure and thermo-decomposing process of the precursors have been studied using XRD and TG/DTA analysis. The size and micromorphology of grain were investigated by TEM. The effects of the fabrication conditions on the crystal structure, size, and electrochemical performance of these materials have been studied in depth. The precursors of LiMn2O4 and LiCoxMn2-xO4 have nearly decomposed completely at 350℃, the products are all spinel structure. Different reactants can't affect the crystal structure of product, but they can affect the agglomeration of the grain. The diameters of the grains are nanometer-scale, and reunite rod-like or irregular spherical form. The crystal structure become more perfect and the grain become bigger with increasing temperature. When the calcinate time is too long, the LiMn2O4 was decomposed and Mn2O3 appears, which can affect the electrochemical performance of LiMn2O4.The results of electrochemical properties showed that the first discharge capacity of LiMn2O4 is bigger, the first discharge capacity of powders calcinated at 550℃ can be up to 124.4mAh/g. But the charge-discharge cycle performance is worse. After 10 cycles, the discharge capacity is 74.8 mAh/g, the loss of capacity is 39.8%. Though the first discharge capacity of LiCoxMn2-xO4 powders obtained in different proportion are lower, their cycle performance is better. The LiCo0.16Mn1.84O4 which calcinated at 450℃ has the best cycle performance. The first discharge capacity of Li0.16Mn1.84O4 is 101.5mAh/g. After 50 cycles, the discharge capacity is 76.2mAh/g, the loss of capacity is 25%.The electrochemical properties of LiMn2O4 and LiCo0.16Mn1.84O4 were tested in low temperature. The results showed that the electrochemical properties of LiMn2O4 are abnormal, the first discharge capacity is small, but the discharge capacity increase as the cycle time increasing. The electrochemical properties of LiCo0.16Mn1.84O4 are similar to that in normal temperature. The discharge capacity is decreased gradually as the cycle time increasing. The stability of charge-discharge of LiCo0.16Mn1.84O4 in low temperature even precede to that in normal temperature. So we think that nanoparticles may possess better electrochemical properties in low temperature. The LiMn2O4 prepared and bought were built in various proportions to study their electrochemical properties. The results showed that the electrochemical properties of the built samples are better than that of merely prepared or bought, when the proportion is 1: 9, the electrochemical properties are the best, the first discharge capacity is 122.9mAh/g, after 50 cycles, the discharge capacity is 114.5 mAh/g, the loss of capacity is only 6.8%.