Investigation Of Preparation And Performance Of Lithium-manganese-cobalt-nickel Oxides Cathode Material For High-capacity Lithium-ion Battery

The cathode materials xLi[Li1/3Mn2/3]O2·(1-x)LiMO2 are becoming appealing recently because of their high capacitie, safety, mild character with electrolyte when charged to higher potential, low cost and environmental-friendly. And xLi [Li1/3Mn2/3]O2·(1-x)Li[Ni1/3Mn1/3Co1/3]O2 in these materials is considered to be one of the best candidates for lithium ion power battery In this paper, we optimized the composition of xLi[Li1/3Mn2/3]O2·(1-x)Li[Ni1/3Mn1/3Co1/3]O2 system firstly, and Li[Li0.2Mn0.54Ni0.13Co0.13]O2 was selected to be the object of ours reseach. The influence of the raw materials on the properties of this cathode material was investigated, and LiOH·H2O,Ni(OH),Mn3O4,Co3O4 were chosen as the raw materials.Li[Li0.2Mn0.54Ni0.13Co0.13]O2 was synthesized by solid state reaction and mechanical activation, and the synthesizing conditions such as activation time, calcinating temperature and time were optimized. The optimal technological conditions for prepared Li[Li0.2Mn0.54Ni0.13Co0.13]O2 were obtained, after activated for 4h, the mixture powders were sintered at 900℃for 10h. The investigations of SEM, XRD, galvanostatic charge-discharge, cycle voltammetry and electrochemical impedance spectroscopy were introduced to characterizes the micro-morphology, structure and electrochemical properties of the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 obtained under optimum conditions. The results of electrochemical performance tests show that the first specific discharge capacity of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 can reach 286.2mAh/g at 60mA/g in voltages of 2-4.8V at 55℃, and the capacity manitenance rate is 99.79% after 30 charge-discharge circles, and at 150mA/g, the discharge capacity has no fading. The specific discharge capacity at 40℃and 25℃is a little lower than 55℃, but the cycle performance is also good. Though the cycle performance is good at 10℃and 0℃, the specific discharge capacity is very low, so the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material is sensitive to temperature.xLi[Li1/3Mn2/3]O2·(1-x)Li[Ni0.4Co0.2Mn0.4]O2 and xLi[Li1/3Mn2/3]O2· (1-x)Li[Ni0.5Mn0.5]O2 cathode materials synthesized by solid state reaction and mechanical activation were preliminarily studied. The investigations of ICP, SEM, XRD, galvanostatic charge-discharge and electrochemical impedance spectroscopy were introduced to characterizes the micro-morphology, structure and electrochemical properties of these cathode materials, and the results showed that these two series cathode materials were synthesized successfully by solid state reaction with mechanical activation. The electrochemical performance of these materials were studied when x value was 0.2,0.4,0.6 and 0.8 respecticely. The results showed that the cathode material 0.2Li[Li1/3Mn2/3]O2·0.8Li[Ni0.4Co0.2Mn0.4]O2 had higher capacity and better cycle performance at 60mA/g and 150 mA/g with a voltage window of 2-4.8V at 55℃, the electrochemical performance of 0.4Li[Li1/3Mn2/3]O2·0.6Li[Ni0.5Mn0.5]O2 is better than the other cathode materials of xLi[Li1/3Mn2/3]O2·(1-x)Li[Ni0.5Mn0.5]O2.The preparation of these composite cathode materials by mechanical activation and solid state reaction was not only characterized by its simplicity and relative lower costs, but also by higher purity and homogenous in morphology and perfect electrochemical performance.