LiFePO4论文：锂离子电池正极材料LiFePO_4及其掺杂改性的第一性原理研究

LiFePO4论文：锂离子电池正极材料LiFePO_4及其掺杂改性的第一性原理研究

【中文摘要】基于考虑了Fe-3d电子间的库仑作用U和交换作用J的GGA+U方案,应用第一性原理计算系统研究了LiFePO4的晶格动力学性质。我们计算并分析了玻恩有效电荷张量、布里渊区中心的声子频率和声子色散曲线。玻恩有效电荷张量显示各向异性,佐证了LiFePO4中锂离子沿一维通道方向迁移的机理。布里渊区中心点声子频率的计算值和相应的实验结果符合得比较好。应用第一性原理计算系统研究了LiFePO4的对位缺陷,以及对位缺陷的形成对材料的电导率和离子扩散速率的影响。结果表明,Li/Fe交换缺陷是最容易形成的,形成缺陷后的Fe-O键变长,扩宽了锂离子传输通道,有利于锂离

子在通道中的扩散,对材料电化学性能的改善起到了一定的作用。应用第一性原理计算系统研究了具有Mg掺杂Li和Fe位的LiFePO4材料的原子和电子结构。结果显示,Mg更容易掺杂到LiFePO4的Fe位,进而形成新的LiFe1-yMgyPO4固溶体,可以很好地提高LiFePO4的离子电导率和电子电导率,并由此提出可能的微观导电机理。同时,我们发现随着Mg含量的增加,杂质的形成能和LiFe1-yMgyPO4的体积呈现降低和减小的趋势,这与实验结果符合得比较好。

【英文摘要】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.

【关键词】LiFePO4 对位缺陷 Mg掺杂晶格动力学第一性原理计算

【英文关键词】LiFePO4 Antiste defect

Mg-doping Lattice dynamics First-principles calculations

【目录】锂离子电池正极材料LiFePO_4及其掺杂改性的第一性原理研究

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摘要4-5Abstract5第一章绪论8-29 1.1 锂离子电池发展的历史及其工作原理9-12 1.2 锂离子电池正极材料的类型和结构12-16 1.2.1 锂离子电池正极材料的类

型12 1.2.2 锂离子电池正极材料的结构12-16 1.3 LiFePO_4 材料16-22 1.3.1 LiFePO_4 的结构特点

16-17 1.3.2 LiFePO_4 的优缺点17 1.3.3 LiFePO_4 的制备方法17-19 1.3.4 LiFePO_4 的改性研究

19-22 1.4 本论文的研究目的及意义22-23参考文献