Study On Improving The Properties Of LiMn₂O₄ Cathode Material By Doping And Coating

Spinel LiMn2O4 is regarded as the most promising cathode material for lithium-ion cells because of its low cost and environmental friendly nature over LiCoO2. However its poor cyclabiliry greatly prevented it from wide application, especially at high temperature. In this paper, recent development in lithium ion battery materials including cathodes, anodes and electrolytes was summarized and the charge-discharge mechanism of lithium-ion batteries and main influencing factors on properties of LiMn204 positive electrode were discussed in detail. At present, although many researchers studied on the improvement of the performance of LiMn2O4 spinel, they only aimed at one of its structures and properties whose results were dissatisfied. In the paper, the improvement of properties of LiMn2O4 spinel cathode material was studied by the doping-coating method.In this paper, the LiMn204 spinel .compound was prepared by the sol-gel method. XRD qualitative analysis and SEM analysis were employed and the following conclusions from the discussion could be gotten. The performance of the sample which was prepared by heating for 48h at 750 was the best in the three samples.The LiCoO2-coated LiMmO4 and LiNiO2-oated LiMn2O4 spinel cathode materials were compared. Their XRD analysis , SEM analysis, AAS analysis and XPS analysis showed that they had the appearance of full crystal and that their grain distribution was uniform and their average was less than 2um. But differently, LiCoO2-coated LiMn2O4 spinel compound had less parameter of unit cell, better stability electrochemically and structurally more stable suface of its grains .Analysis and discussion of the six different samples, namely pure LiMn2O4, Li1.1Mn1.9O4, Li0.1Mn1.9O4, LiCoO2-coated LiMn2O4, LiCoO2-coated Li0.1Mn1.9O4, LiCoO2-coated Li0.1Mn1.9O4 spinel compounds, was the important part of the paper. From the results of their XRD analysis, SEM analysis and XPS analysis the following conclusions could be gotten.The coated compounds, which was cubic spinel Li1+xM0.1CoxMn1.9-xO4(M:=Li or Ni), were Co-rich in the grains' surfaces; the results of XPS analysis and electrochemical analysis of the six samples also showed that the LiCoO2-coated LiMo.iMni.gO4(M=Li or Ni) spinel cathode materials had better performances and could effectively suppress Jahn-Teller distortion, decrease the amount of Mn2+ dissolved in the electrolyte and improve the structural stability of the cathode materials. In particular, the LiCoO2-coated LiNi0.1Mn1.9O4 spinel cathode material had the best performance of the six samples, though its initial discharge-capacity decreased by 112mAh/g. Its discharge capacity still remained 109.6 mAh/g after the 30 cycles at room temperature and constant charge-discharge current of 1mA, which capacity retention reach 97.9%. Moreover electrochemically it exhibited the good stability at high temperature of 60.