Doped Lithium Manganese Oxide Synthesis And Properties Of The Study

Spinel LiMn₂O₄ has attracted particular attention due to its high safety, low cost and non-toxicity. However, the bad cycle ability at high temperture is the main barrier limiting its application. So the research must be carried out to improve its cycle ability at high temperture.The spinel LiMn₂O₄ was synthesized by sol-gel method. The effects of Li/Mn ratio, calcining temperature on structure and performance of spinel LiMn₂O₄ was investigated by XRD,SEM and electrochemical methods. The results show that the structure and electrochemical performance of Li_1.08Mn₂O₄ is good when it was synthesized at 700℃.The effects of doped with Na⁺ and SO₄^2- on structure and electrochemical performance of spinel LiMn₂O₄ was studied detailed. The XRD results show that the synthesized material doped with Na⁺ was pure spinel, but there is a little of Mn₂O₃ exist in the spinel phase when the material was doped with SO₄^2-. The structure of LiMn₂O₄ doped with Na⁺ was studied by rietveld refinement with fullprof program. Refinement results show that the Na⁺ substitute some Li⁺ which was located in the 8a sites of spinel structure, and then a part of Li⁺ substitute some Mn³⁺ which was located in the 16d sites. The results of electrochemical test show that the cycle performance of LiMn₂O₄ at room and high temperture was improved by Na⁺ doping, but it decrease the capacity of LiMn₂O₄ at some degree. As there are some Mn₂O₃ appeared in the phase, the capacity of LiMn₂O₄ decreased qucikly with the the doped amounts of SO₄^2- increasing, when the doped amonts is less than 0.04, it can improved the cycle performance of LiMn₂O₄ at room and high temperature.Spinel LiMn₂O₄ doped with F^- was synthesized by sol-gel method. The structure of the synthesized material was pure spinel phase. The Li_1.05Mn₂O_4-xF_x cathode materials increased the capacity, enhanced the stability and improved the cycle ability at 55℃. As the amount of F^- increases from 0 to 0.1, the capacity of the materials increases from 119.7mAh·g^-1 to 124.9mAh·g^-1, and the capacity retention after 30 cycles at 55℃increases from 79.4% to 84.4%. The kinetics behavior of part synethesized materials has characterized by Cyclic voltammetry (CV) and Electrochemical impedance spectrosocpy (EIS). The process of deintercalation-intercalation of Li⁺ was analyzed and a suited equivalent circuit diagram was found. The difference of the doping materials and the pure LiMn₂O₄ was further proved in electrochemical performance kinetically.