The Quantum Chemical DV-Xα Study On The Electronic Structure Of Lithium-Manganese-Oxides Electrode Material For Lithium Ion Battery

The investigation and developing of lithium-ion batteries have attracted worldwide attention due to their excellent properties such as high cell voltage and specific capacity, and so on. Remarking progress has been made on researching carbon anode materials. An increasing interest has been focused on lithium-manganese oxides as a cathode material for lithium-ion batteries, because of its low cost, abundant material source and nontoxcity, however, large capacity fade on cycling make it difficult to commercialize. Hence, considerable efforts were made to study the doping of LixMn2O4.In the paper, Li5Mn4O83+ Li5Mn12O24-, Li5Mn16O32+, Li17Mn16O329+ clusters selected by "seed atoms" were calculated theoretically by means of the quantum chemical DV-Xa calculation method. Form the angle of electronic structure, the status of lithium ion and the electrochemical properties of LixMn2O4 were discussed preliminarily according to different conditions (x=l , 2).Based on calculation results, it's found that the Jahn-Teller distortion, which was thought to lead to poor cyclability, occurred during the discharge of LixMn204, and we also confirmed the formation of a novel phase with low energy after overdischarge (x=2). It's around the Fermi energy grade that the state densities were the greatest in y-MnO2, LiMn2O4 and Li2Mn2O4, indicating that three kinds of materials were suitable to intercalation and deintercalation of lithium ion. When x=l, the net charge of lithium ion is +0.7, on the other hand, that of lithium ion changes between maximum of+0.9 and minimum of +0.5 when x=2. Compared with LiMn2O4, Li2Mn2O4 has lower reversible capacity, in that the net charge of lithium ion increases, accordingly interactions between lithium ion and oxygen one strengthen, leading to difficulty for lithium ion to deintercalate. Partial substitution of manganese in LixMn204 by cobalt or lithium can reduce the Fermi energy, increase the. net charge of lithium ion, and diminish the value band width, corresponding to the drop of the discharge voltage, the loss of the reversible capacity, and the improvement of the cycling performance due to increasing structural stability, respectively.