Study On The Preparation, Electrochemical Performance And Surface Modified Of LiMn₂O₄

With the energy becoming less and less and the pollution of the environment becomingmore and more serious, people are looking for new energy to add or replace the normalenergy. Because lithium-ion batteries have excellent properties such as high voltage, highcapacity, high energy and good cycle performance, they have been developed rapidly inrecent years and have become a new kind of power source.The properties of cathode materials are very important for the whole lithium-ion batteries,so the research and development of new cathode materials with high electrochemicalperformance and low cost are necessary. In all kinds of lithium-ion battery cathode materialssuch as LiCoO₂, LiNiO₂, LiMn₂O₄and LiFePO₄, LiMn₂O₄with spinel structure has alwaysbeen focused just because of its high voltage, low cost, good cycle performance, safety and noharm. However, LiMn₂O₄has the obvious capacity fading phenomena in repeated charge anddischarge process, and this drawback seriously affects the battery life and restricts LiMn₂O₄commercialized.In this thesis, the powders of LiMn₂O₄have been prepared by using lithium carbonateand electrolytic manganese dioxide as starting materials and by high temperature solid statereaction method. The thermal effect characterisitics of the solid state reaction and the contentevolution of reaction products have been studied with thermal gravimetric analysis （TG） anddifferential scanning calorimetry （DSC）. Phase transformation was investigated by X-raydiffraction （XRD）. The morphological features of LiMn₂O₄powders were examined byscanning electron microscope （SEM）. The effected factors on preparation of LiMn₂O₄powders were tested and analysed by Orthogonal experiment. The optimal synthetic conditionare following: n（Li）﹕n（Mn）=0.525﹕1.000, the sintering temperature is820℃, constanttemperature time is8¹0h. Electrochemical performances of LiMn₂O₄powders weremeasured by various electrochemical measuring methods. The results show that it coulddeliver125.0mAh/g initial discharge capacity at0.1C rate, and discharge capacity remain81.2%of initial capacity after20cycles.LiMn₂O₄cycle property was improved through the surface coating. The results ofexperiments show that the initial discharge capacity of covering1.12%carbon,3%Al₂O₃,2%SrF₂and3%FePO₄of LiMn₂O₄anode materials the initial discharge capacity is126.8,120.4,121.2and122.8mAh/g respectively, and after cycle20weeks the capacity retention is95.8%,90.2%,94.1%and93.2%respectively. Although the first discharge capacity is slightlyreduced, its circulation performance has been significantly improved.