Preparation And Study Of Layered LiMnO₂ As Cathode Materials For Lithium Batteries

In contrast of lithium cobalt oxide, layered lithium manganese oxide is a promising cathode material of lithium batteries because of the abundance of raw material, cheapness, safety and high theoretic capacity. It has been a hotspot for studying at the present time. Owing to the complicated technics and high cost of manufacture, LiMnO2 can not satisfy the applications. The cycle stability is very poor, which is a result of the Jahn-Teller distortion effect causing by tervalent manganese ion. Thus, exploiting the feasible technics of preparation and seeking the method to enhance the cycle stability of layered lithium manganese oxide are the targets of many research groups.In this thesis, solid state synthesis method was employed to prepare the orthorhombic layered LiMnO2, with homogeneous structure. SEM pictures showed that the thickness of flake was about 150nm, the size of flake was about 5~10μm, the grains were uniform. After the test of charge-discharge at 0.1C, layered LiMnO2 which was synthesized by solid state method reached 126.6mAh/g of the initial discharge specific capacity, and had two obvious slopes at 4.5~2.5V. The results indicated that the layered structure transferred to the spinel structure. After 80 cycles the discharge capacity was 82.0mAh/g, the capacity loss was about 35.2%.In order to solve the problem of stability fading, sol-gel method and hydrothermal synthesis method, called as soft chemical methods, were employed to prepare the materials and improve the performance by the body-doping. The LiMnO2 synthesized by sol-gel method was orthorhombic phase and Pmnm space group, with farthing impurity of Mn2O3。The result of SEM showed that the size of flake was about 1~2μm, the thickness of flake was about 50~100nm. The highest discharge capacity is 170.7mAh/g. After 80 cycles, the discharge capacity fell to 100mAh/g, the capacity loss was about 40.9%. Afterwards, sol-gel method was employed to form 2% Al3+ doping. The doped material performed well electrochemical property for cycling. The initial discharge capacity of doped material was 165mAh/g. After 80 cycles, the capacity loss was about 20%.