The Preparation And Modification Of Spinel Limn2o4

As the best choice of cathode materials, commercial LiCoO2has perfect capability, however, it meets the obstacles on the developmental way of lithium ion battery, especially for electric vehicle applications because of its high cost and toxicity. To be the substitution of LiCoO2, LiMnO2has the advantages of abundant raw material, low cost, high safety, environmental acceptability. As the key cathode materials for lithium batteries, intensive attentions have been focused on it. But its poor cycle life at high temperature need to be improved. Several reasons have been suggested to explain the degradation mechanism including structure instability, Jahn-Teller distortion and Mn dissolution into electrolyte.This dissertation is intending to investigate the modification spinel lithium manganese cathode material for lithium ion battery by ion doping, coating and shape control, so as to improve its electrochemical performance.Mono-cation doping and binary-cation doping methods were adopted to modify the spinel LiMn2O4cathode materials. Their effects on the electrochemical properties were studied respectively. The Li, Ni and Mg dopants result in significantly positive effects on the electrochemical properties in the mono-cation doping. After100cycles the capacity keeps90%. While the Li/Mg and Li/Ni showed the best electrochemical properties in the binary-cation doping, the loss of capacity was only5%after100cycles at room temperature, the spinel LiMn2O4doped with Li/Ni showed the most excellent cycle performance at55℃.The resulting coating layer is not uniform and continues with the traditional sol-gel method. Instead, there are isolated nano-sized metal oxide particles attached on the surface of spinel particles. The improvement in the cycling performance of the obtained spinel is not satisfactory. In this dissertation P2O5was used as a chemical reagent to react with spinel LiMn2O4for forming a uniform and continues layer on the surface of the spinel LiMn2O4. This method can reduce the contact area of the spinel and electrolyte to protect Mn3+dissolution in the electrolyte.We also prepared and studied single crystal spherical spinel LiMn2O4. As everyone knows, the Mn dissolution happens at the (111) face. The area of (111) face is greatly reduced in the spherical spinel compared to the traditional octahedral spinel. As a result, the dissolution of Mn is restrained effectively. And this spherical has a greater tap density. Furthermore, The industrialization prospect of this spherical spinel is good for its simple and controllable preparation with low cost.