Preparation And Performance Of Manganese Oxide Electrode Materials For Li-ion Batteries

The development of electrode materials with high performance and low cost is the key to improve the performance of Li-ion batteries, which will promote its application areas such as renewable energy and electric car. As the manganese compounds have the advantages of high specific capacity, earth-abundance, low cost and environmental benign, they have attracted great interest as electrode materials for Li-ion batteries. Among them, cathode material orthorhombic phase LiMnO2 (o-LiMnO2), anode materials Mn2O3 and MnO have received special attention due to their high specific capacity or low electromotive force. The main research work of this thesis is as follows:o-LiMnO2 was prepared under hydrothermal conditions using Mn2O3 and LiOH as reactants and the effects of hydrothermal reaction parameters such as reaction temperature, LiOH and Mn2O3 concentrations on the phase purity of o-LiMnO2 were studied. It was found that high LiOH concentration facilitated the synthesis of pure phase o-LiMnO2. A reaction temperature lower than 140? did not lead to pure phase o-LiMnO2 and the product was the mixed phases of o-LiMnO2 with Li2MnO3. Pure phase o-LiMnO2 had larger discharge capacity than the mixed phases of o-LiMnO2 with Li2MnO3. However, the cycling stability of the latter was better.MnCO3 precursors with different morphologies were prepared using three kinds of surfactants, i.e., cation surfactant cetyl trimethyl ammonium bromide (CTAB), anion surfactant sodium dodecyl sulfate (SDS) and neutral poly(vinyl pyrrolidone) (PVP) as soft templates by room temperature precipitation method. When PVP was used, the reaction manner was changed from precipitation method to hydrothermal method, ethanol/water volume ratios and sources of CO32-(NaHCO3 and urea) were also changed. Porous cubic, regular spherical and nut-like spherical Mn2O3 samples were obtained by calcinating MnCO3. The correlation between the morphology of Mn2O3 and its performance as anode material for Li-ion batteries was systematically evaluated. The Mn2O3 sample with nut-like spherical morphology had the best cycling performance, with the specific discharge capacity of 925 mAh g-1 at current density of 100 mA g-1 after 180 cycles. The Mn2O3 sample composed of cube and sphere had superior rate performance. Its specific discharge capacity decreased with increasing current density from ?872 mAh g-1 at 100 mA g-1 to ?361 mAh g-1 at 2000 mA g-1.4 precursor was prepared by a precipitation method, and then MnO@C samples were obtained by dipping MnC2O4 precursor with different amounts of glucose and sintering at different temperatures. The influences of the amount of glucose and sintering temperature on the electrochemical performance of MnO@C were investigated. The results showed that appropriate carbon content and crystallinity had great effect on the electrochemical performance of MnO@C. The MnO@C sample which was prepared when the molar ratio of glucose and MnC2O4 was 1:5 and the sintering temperature was 700? has the largest specific capacity, which exhibits a high specific discharge capacity of 1587 mAh g-1 at a current density of 100 mA g-1 after 160 cycles. Even at a high current density of 1600 mA g-1, a remarkable discharge capacity of ?630 mAh g-1 could still be delivered, demonstrating a good rate capability. This facile method can be used to the large-scale synthesis of high performance transition metal oxide@carbon composite electrode materials.