Lithium Ion Battery Cathode Material Limn < Sub > 2 < / Sub > O < Sub > 4 < / Sub > Synthetic Conditions Optimization And Surface Coating Modification

As one of the lithium-ion battery cothode materials, spinel lithium manganese (LiMn2O4) has the advantages such as high voltage platform, low raw material costs, no environmental pollution. Because of these advantages, LiMn2O4had been considered as the cathode material which could replace lithium cobalt oxide (LiCoO2) in conventional lithium-ion battery and lithium iron phosphate (LiFePO4) in power rechargeable batteries. Presently, which prevent LiMn2O4from large-scale commercial production were mainly these two problems:the profit is not enough, and materials had bad electrochemical performance under the temperature above50℃.In order to solve these two problems, in this paper, the inexpensive sources of manganese were used to reduce the cost, and surface coating was used to improve the electrochemical performance of LiMn2O4under high temperature. The samples prepared were characterized and analyzed by TG-DTG, XRD, SEM, PSD and the electrochemical testing methods, and the crystal structure, surface morphology, particle size and electrochemical performance had been studied. The main contents of the research include:(1) Precipitation method:using ammonium carbonate as the precipitant, Mn(NO3)2was turned into MnCCO3precursor with uniform particle size distribution. LiMn2O4was prepared by using MnCO3precursor as the manganese source, Li2CO3as the lithium source. The samples synthesized with different pretreatment temperature were studied by analyzing their electrochemical performance, crystal structure and compositions, then a better synthesis condition was confirmed under precipitation method.(2) Melt-impregnation method:LiMn2O4samples were synthesized with melt-impregnation method by using industrial EMD as manganese source and LiOH as lithium source. The influences of crystal structure, morphology and electrochemical performance on LiMn2O4samples with different ball-milling pretreatment time of EMD were studied. Research results showed that, when the ball-milling pretreatment time was8h, the LiMn2O4prepared had the best electrochemical performance. (3) High-temperature solid-state method:LiMn2O4samples were synthesized with high-temperature heat treatment by using industrial EMD and Li2CO3as manganese/lithium source. The ptimal calcination condition was confirmed by comparing calcination ways, final heat treatment temperature and holding time, annealing speed and lithium contents. With constant total ball-milling time, the influences of EMD ball-milling pretreatment time on LiMn2O4were also studied. Research results showed that, in the best calcination conditions, when the ball-milling pretreatment time was8h, mixing ball-milling time was6h, the LiMn2O4sample had the best electrochemical performance.(4) LiMn2O4samples prepared were coated by Al2O3, MgO, ZnO and Li4Ti5O12. Reasearch results showed that surface coating had little effect on the crystal structure of LiMn2O4. Compared with other coating materials, samples coated by Al2O3had significant specific capacity decrease. And all the coated samples showed improvement on electrochemical cycling stability under both room temperature and high temperature.