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First-Principle Studies of Cathode Materials LiFePO4 and Its Doped Systems for Lithium Ion Batteries

Author: ZhangHua
Tutor: ShiSiQi
School: Zhejiang University of Technology
Course: Applied Chemistry
Keywords: LiFePO4 Antiste defect Mg-doping Lattice dynamics First-principles calculations
CLC: TM912
Type: Master's thesis
Year: 2011
Downloads: 80
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Abstract


Lattice dynamical properties of LiFePO4 are studied using first-principles density functional theory taking into account the on-site Coulomb interaction within the GGA+U scheme. Born effective charge tensors, phonon frequencies at the Brillouin zone center and phonon dispersion curves are calculated and analyzed. The Born effective charge tensors exhibit anisotropy, which gives an indirect evidence for the one-dimensional Li migration tunnel along the [010] direction in LiFePO4, which has been proposed by other theoretical calculations and experimental observation. The calculated phonon frequencies at theГpoint of the Brillouin zone agree well with the available experimental results.Antisite defect, electronic conductivity and ionic dynamic properties of LiFePO4 have been investigated using first-principles density functional theory taking into account the on-site Coulomb interaction within the GGA+U scheme. Results indicate the Li/Fe exchange defect is the most preferred to occur in LiFePO4, which causes the Fe-O bond length to change in the direction favors the formation of Li+ diffusion channels, hence improving the ionic dynamic properties of the olivine LiFePO4.Atomic and electronic structures of LiFePO4 with Mg doping at Li and Fe sites have been investigated using the first-principles density functional theory with the on-site Coulomb interaction taken into account. It is demonstrated that Mg is preferentially doped at Fe site instead of Li site to form a new LiFe1-yMgyPO4 solid solution, leading to a higher ionic conductivity. Besides, it is found that formation energies and the cell volumes decreased gradually with the increase of Mg concentration in LiFe1-yMgyPO4, which agrees well with the available experimental data.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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