Synthesis And Modification Of Spinel Lithium Manganese Oxide

The spinel LiMn2O4 of the cathode for rechargeable lithium-ion batteries was synthesized by mechanochemical activation way and wet chemical process, respectively. The cobalt-doped, chrome-doped and lithium-doped lithium manganese oxides were prepared by wet chemical process. Based on the experimental study, the influence of technological conditions on the chemical composition and the powder characteristics, such as structure, morphology and electrochemical performance was systematically investigated by modern analytical methods of chemical analysis, X-ray diffraction (XRD), thermogravimetric (TG) and differential thermal analyzer (DTA), scanning electron microscope (SEM), microelectrode cyclic voltammetry, constant-current charge-discharge test and so on.The influence of technological conditions in the mechanochemical activation process such as grinding type, mass ratio of balls to material, grinding time, lithium-source and calcining temperature on the structure, specific surface area, morphology and electrochemical performance of the products was examined. The optimal prepared conditions of shake-type ball mill as grinding instrument, Li2CO3-MnO2 as initial reagents, the mass ratio of balls to material being 40:1, grinding time being 60 minutes and calcined temperature being 720 were obtained. The samples revealed a well-defined cubic spinel structure, a narrow particle size distribution of 0.2 um mean particle size, a large specific surface area of 4.3703 m2/g. The first discharge capacity was 119.659 mAh/g.The precursors of lithium manganese oxides were prepared by wet chemical process with MnO2 and LiOH ?H2O as main starting reagents. The spinel LiMn2O4 with well-defined structure could be obtained after being calcined for 8 h at 720 . The cobalt-doped, chrome-doped and lithium-doped lithium manganese oxides synthesized by above process had the same structure as spinel LiMn2O4 and narrow particle size distribution. The lattice parameters of the samples decreased withincreasing amount of doping cobalt (chrome, lithium). The electrochemical performance tests showed the first discharge capacities decreased with the increase of doping Co (Cr, Li), however, cycleability was improved. According to both the capacity and the cyclic property, Li1.02Mn1.98Co0.02O4 and LiMn1.92Cr0.08O4 had best electrochemical performance in the Cobalt-doped samples and Chrome-doped samples, respectively. The first discharge capacity of Li1.02Mn1.98Co0.02O4 was 118.860mAh/g, the sixth was 113.459 mAh/g. The capacity of Li1.02Mn2O4 obtained by calcined at two different temperatures was 122.478 mAh/g and 109.206 mAh/g in the first circle and the tenth circle. Compared with Li-doped and chrome-doped spinel, Li1.02Mn1.98Co0.02O4 had more stable circling performance.The microelectrode cyclic voltammetry test of Li1.02Mn2O4 suggested that the mechanism of Li+ intercalating and de-intercalating did not change.