Study On The Synthesis And Jahn-Teller Effect Of LiMn₂O₄ Cathode Materials For Lithium Ion Batteries

The spinel LiMn₂O₄ cathode material for lithium-ion battery is prepared by sol-gel. The infuence of synthesis condition on both configuration and electrochemical performance of the product is studied. The results show that the prime craftwork conditions to prepare theLiMn₂O₄ are as follow: Li/Mn =1.05/2;pH=7.5;increase the temperature from room temperature to 450℃ at the rate of 8℃/min;keep this temperature for 5h;then increase the temperature from 450℃to 650℃, 12h at last, cool off.Analysis and discussion of the different samples, namely pure LiMn₂O₄, LiMn_2-xV_xO-4, LiMn_2-xLa_xO₄ and LiMn_2-x-yNi_xCo_yO₄, spinel compounds.From the results of their XRD analysis, SEM analysis and XPS analysis the following conclusions could be gotten, analysis and electrochemical analysis of the samples showed that the LiMn_2-xM_xO)4, (M=V, La, Ni-Co) spinel cathode materials had better performances In particular, the LiMn1.9Nio.05Coo.05O4 spinel cathode material had the best performance of the samples, but its initial discharge-capacity increased by 139mAh/g. Its discharge capacity still remained 133.9mAh/g after the 36 cycles at room temperature and constant charge-discharage current of 0.2C, which capacity retention reach 96.4%.The Mgo-coated LiMn₂O₄ and LiMn_2-x-yNi_xCo_yO₄ spinel cathode materials were compared. Their XRD analysis,SEM analysis, and XPS analysis showed that they had the appearance of full crystal and that their grain distribution was uniform and their average was 2μm. The coated compounds, which was cubic spinel, were Mg-rich in the grains' surfaces, better stability electrochemically and structurally more stable.First,Li-rich spinel Li_1+xMn_2-xO₄ was prepared by sol-gel,Jahn-Teller effect of spinel LiMn₂O₄ has been researched by XRD measurement ,c/a and rate of [Mn⁴⁺]/[Mn³⁺] etc.The results show Jahn-Teller effect is inhibited when 650℃ of calcinatin temperature and x=0.05.Second ,The grains of LiMn₂O₄ and LiM_xMn_2-xO₄(M=Li,Ni-Co) were coated with MgO by using sol-gel process. The Jahn-Teller effect of spinel LiMn₂O₄ has been researched by XRD measurement and rate of [Mn⁴⁺]/[Mn³⁺],etc.The surface treatment is effective improving cyclability of spinel Li_1.05Mn_1.9Co_0.05Ni_0.05O₄ cathode materials and Jahn-Teller effect isinhibited.