Research On The Preparation Of O-LiMnO₂ Cathode Materials For Lithium Ion Battery And Its Electrochemical Properties

With the development of electronic information technology, demands for portable electronic devices increase quickly. Li-ion secondary batteries as one kind of portable power sources are considered potential candidates in this field, since they own some advantages over the other energy source, such as long cycle life, light weight, low cost and environmental compatibility. However, there're plenty of unsolved problems in the field of electric capacity and cyclability of cathode materials. Recently, research interests are focused on how to prepare pure phase LiMnO2 with high capacity and stable cyclability as cathode materials. In this paper, we studied synthesis methods of orthorhombic LiMnO2 cathode material, how to improve its electrochemical performance by doping and the direction of research and application of cathode materials.This paper reported a simple one step hydrothermal routine to prepare o-LiMnO2 powder for Li-ion battery application. The investigation showed that the LiOH concentration and the hydrothermal temperature were the main parameters influencing the phase purity of the final product. o-LiMnO2 prepared with optimized parameters showed advantage over the commonly hydrothermal prepared o-LiMnO2 powder on the electrochemical performance, showing potential application in lithium ion secondary batteries.A hydrothermal conversion of MnOOH needles into o-LiMnO2 nanorods for Li-ion battery application has been further studied. Phase conversion during the Li-ion incorporation, and several intermediate phases were formed during the hydrothermal reaction. The morphological changes during the process showed that LiOH, not only worked as the Li-ion source during the incorporation, but also served as the corrosive media to create nanorod like shape. The single crystalline nature of the nanorods was revealed and a preferred growth direction along b axis direction was also determined.In order to prepare pure phased o-LiMnO2 with the unoptimized parameters, we discovered a brand new method using hydrazine to reduce the hydrothermal process. The result showed a better electrochemical performance than the one without reductant during reaction, indicating this facile method a potential application in the Li-ion battery field.Some preliminary research on improving the electrochemical performance of o-LiMnO2 by doping had been done in this paper. We doped some amount of Co and Ni by means of co-deposition to prepare pure phased o-LiMnO2 solid solution, indicating the prevention from spinel phased transformation and an improved electrochemical properties. Furthermore, the Ni doping was more likely to prepare pure phased o-LiMnO2 solid solution rather than Co doping, so was the improvement of electrochemical properties, especially the electric capacity, from the result of our research.From the researches above, we introduced some innovative methods to prepare pure phased o-LiMnO2 as cathode material for Li-ion secondary batteries, indicating potential industrial application in large scale.