| With the rapid development of electronic devices and electric vehicles, all have a higher demand for lithium-ion battery. Because of its abundance of raw materials, high discharge voltage and it can charge and discharge in high-current, Spinel-type lithium manganese is considered one of the most promising cathode material of lithium-ion battery. However, the capacity of the LiMn2O4 is fading fast in charge-discharge cycle, especially at high temperature, this shortcomings hinder its commercial production.In this paper, the research status of LiMn2O4 is summarized and we summed up the main reason for the capacity fading of LiMn2O4 which is the Jahn-Teller effect and the disproportionation dissolution of Mn3+. Some measures can be taken to improve its electrochemistry properties. Firstly, doping metal ion.Secondly, coating materials to suppress the dissolution of Mn ion, Like ZnO. Thirdly, changing different synthetic methods and Li/Mn ratio to get a stoichiometric LiMn2O4, especially no oxygen vacancy samples. At last, using an electrolyte with lower content of fluorine. As for doping metal ion, Li+,Ga3+,Zn2+,Al3+,Ni2+,Cu2+,Co3+,Cr3+, Fe3+ are the common metal ion. But the doping microcosmic mechanism is not clear, especially not clear what has happened in the unit cell, let alone the changes of bond, density of states, populations etc. so what we did in this paper is to find the answer, the answer how doping has an effect on improving its electrochemistry properties.Doping Al ion has been discussed in this paper.Unlike other researchers that study it by chemical synthetic method. In this paper, what we did is theoretic research through First Principles which is also called ab initio.Computing platform is the CASTEP package (Cambridge Sequential Total Energy Package). Eight models has been established, which are LiMn2O4, LiMn1.9375Al0.0625O4, LiMn1.875Al0.125O4, LiAl2O4 and their completely delithium models. Then calculate their total energy, unit cell parameter, length and angle of bond, population, density of states etc. Chapter one mainly illustrate the shortcomings and advantages of LiMn2O4, research status, and methods to optimize. Chapter two illustrate the computing theoretical basis (DFT) and CASTEP package. In this paper, four parts have been discussed and the results are as follows:.Firstly, we have built LiMn2O4 standard model by inquiring crystallography database. Then optimize the unit cell with different computing methods. To find the most accurate computing methods, ten variables has been discussed separately by control variable method. The results shows that the most accurate result is 8.2363 A, which is very closely to 8.2383 A. It appears when we use the PW91 correction under GGA function, the value of cutoff and k-point is set to 300 ev and 4 ×4×4.Secondly, After confirming the most accurate computing methods, then we start to calculate other seven models, then we contrast seven models’cell parameters. As doping of Al, The lattice constant and volume of unit cell both have narrowed. As for LiMn1.9375Al0.0625O4, the lattice constant shortens evenly and symmetrically in three-dimensional.Volume of cell shorten about 0.1%.but LiMn1.875Al0.125O4 which is not shortened evenly, it’s a,b axle shrink dramatically (0.31%), c axle only shrink 0.06%.the computing results are consistent with analyses gotten by experiments. Moreover, bond results show that the lengths of O-O and Mn-O are shortened along and the length of Li-O elongates with Al doping. There is no doubt that Al doping will enhance the cycling stability and rate capability of spinel LiMn2O4;Thirdly, density of states, population and bond order will be illustrated after Al doping. It shows that valance of Li is+1 in four models implying that Li ion is pure ionic bond. The valance of Mn and O are 0.72 and -0.64, which is not +3.5 and -2. Because Mn-O is apparently covalent bond, their share electron pair. Besides, from the results of density of states, energy of electrons are lower than pure LiMn2O4 as a whole, especially the amount of electrons with high energy. Meanwhile, bond order become much bigger than pure LiMn2O4 from 2.5 to almost 10.0. So there is no doubt that doping Al will make the structure more stable.At last, the relationship between Al doping and electrochemistry have been discussed.In this part, we find that Al doping will increase the voltage platform during charge/discharge. LiMn2O4, LiMn1.9375Al0.0625O4, LiMn1.875Al0.125O4, LiAl2O4 are 4.02,4.25,4.38 and 5.59V respectively:It is also consistent with experiment results.The innovation of this paper is using the DFT theory instead of traditional valance theory to illustrate the electrochemistry behaviors of cathode materials LiMn2O4, which is more objective to reflect the micro reality. It is conducive to understand and reveal the essentials of electrochemical process and provide a more vivid guidance to synthetic materials by experiment.
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