Research On Preparation And Property Of Spinel LiMn₂O₄

The principle and development of lithium ion batteries and the survey of cathode materials have been described in this paper. The preparation methods and technical conditions of LiMn₂O₄ were studied. During charge-discharge progress some existing problems of LiMn₂O₄ have been introduced with emphasis, such as the Jahn-Teller distortion, Mn dissolution to electrolyte and the formation of passivating films on the surface, which are the three main factors resulting in fading capacity and poor cyclability. In order to solve these problems, we used two methods such as single ion doping and multiple doping with Fe,Al,Cu cations,and research the modified of spinel LiMn₂O₄ cathode material.The LiMn₂O₄ and Li_1.08Mn₂O₄ samples were prepared by the sol-gel method. The X-ray diffraction and cyclability analysis were used to contrast the two samples. It was found that after 50th charge-discharge cycle, the discharge specific capacity retention of Li_1.08Mn₂O₄ was 80.3%,but that of LiMn₂O₄ only turned to 78.10% compared with the original one.So it can be seen clearly that the scheme of lithium-rich improved the cyclability properties of spinel, but the first discharge specific capacity retention slight decreased simultaneously. We combine the scheme of lithium-rich with doping technology, which is named "lithium-rich+ doping" scheme.Li_1+xMn_2-yM_yO₄,which was synthesized by the aboved scheme, can restrain the loss of the capacity.The spinel compound LiFe_xMn_2-xO₄,LiAl_xMn_2-xO₄,LiCu_xMn_2-xO₄, LiCu_0.025M_0.025Mn_1.95O₄ and LiCu_0.025Fe_0.025Al_0.025Mn_1.925O₄ were prepared by the sol-gel method. The influences of the single cation doping and multiple doping of cations on the structure, morphology and electrochemical performance of LiMn₂O₄ was investigated by X-ray diffraction (XRD), scanning electric microscopy (SEM), charge-discharge at constant current, AC impedance (EIS), cyclic voltammety (CV) as well as various electrochemical analysis methods. The results show that all the samples formed pure spinel structure. As the doping content increased, the first discharge specific capacity of samples were reduces, but the structural stability and cycle performances were improved. The result of cyclic voltammety (CV) indicated that the electrochemical reversibility was improved, for the redox potential difference of the cathode materials was smaller after doping Fe³⁺,Al³⁺,Cu²⁺ ions. Together with the advantages of single ion doping, two and multiple doping was carried out in this thesis. The property of LiFe_0.025Cu_0.025Mn_1.95O₄ cathode material is the best. The first discharge specific capacity is 101.89 mAh·g^-1, and the discharge specific capacity is 97.10 mAh·g^-1 after 50th cycle. The discharge specific capacity retention reaches 95.3%.