First principles studies on the electronics structures of (Li1−x Me x )FePO4 (Me=Na and Be)

Abstract

Based on density functional theory (DFT) of the first-principle for cathode materials of lithium ion battery, the electronic structures of (Li 1-x Me x )FePO 4 (Me=Na and Be, x=0-0.40) are calculated by plane wave pseudo-potential method using Cambridge serial total energy package (CASTEP) program. The calculated results show that Li-site doping can improve the electronic conductivity enormously. Doping with Na has a noticeable effect on improving its electrical conductivity. However, serious structural distortion will occur when its doping density is beyond 0.25. In view of this, the best density of doping Na is less than 0.25. Doping with Be has an inconspicuous effect on increasing its electrical conductivity and has good cyclical stability, but it cannot achieve as good results as when it is doped with Na. Therefore we cannot find a middle ground between the two proposals. Considering cost and environmental protection, it is ideal to choose Na. So this method gives a reasonable prediction to the improvement of electronic conductivity through Li-site doping in LiFePO 4 material. lithium ion battery, LiFePO 4 , first-principle, electronic structure Citation:Hou X H, Hu S J. First principles studies on the electronics structures of (Li 1−x Me x )FePO 4 (Me=Na and Be).

Acoustic Polaron in Cylindrical Quantum Wires

“…To compare with the previous results, 8,9,12,13 we have also expressed the energy in units of mc 2 and the phonon vector in units of mc/ in the calculations. Considering that the radius of the quantum wire is generally about tens of angstrom and the length units of /mc have an order of 100Å, the radius of the quantum wire in this paper will be taken as 0.1 and 0.5.…”

“…The character of the critical coupling constant varying with the cutoff wave vector k 0 is consistent with the previous papers. 8,12,13 It is worth noting that the critical values of the e-p coupling constant increase with the increasing radius of the quantum wire. For example, when the cutoff wave vector k 0 equals to 40, the critical coupling constant, α c , is around 0.00052 for the radius 0.1 (Fig.…”

“…8 Otherwise, the e-p coupling effects will be substantially enhanced in confined structures, such as two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D) systems, so that the self-trapping transition would be easier to be realized. 10,12,13,21 The ground state energies and the numerical derivates of the acoustic polaron in 2D and 1D system have been calculated in our previous works. 12,13 It is determined that the self-trapping of the electrons in AlN as well as the holes in AlN and GaN is expected to be observed in 2D systems 12 and the 1D acoustic polarons in alkali halides and GaN and AlN systems are expected to have the self-trapping transition.…”

“…10,12,13,21 The ground state energies and the numerical derivates of the acoustic polaron in 2D and 1D system have been calculated in our previous works. 12,13 It is determined that the self-trapping of the electrons in AlN as well as the holes in AlN and GaN is expected to be observed in 2D systems 12 and the 1D acoustic polarons in alkali halides and GaN and AlN systems are expected to have the self-trapping transition. 13 In this paper, we study the possibility of the self-trapping transition of the acoustic polaron in the cylindrical quantum wire.…”

“…12,13 It is determined that the self-trapping of the electrons in AlN as well as the holes in AlN and GaN is expected to be observed in 2D systems 12 and the 1D acoustic polarons in alkali halides and GaN and AlN systems are expected to have the self-trapping transition. 13 In this paper, we study the possibility of the self-trapping transition of the acoustic polaron in the cylindrical quantum wire. Since cylindrical quantum wires belong to the confined structures of quasi-1D systems, which can be speculated that the self-trapping transition of the acoustic polarons is most probably to be occurred in this system.…”