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采用基于密度泛函理论的第一性原理研究了含空位和杂质缺陷的LiFePO_4电子结构,通过能带、态密度、布居分布分析,阐明缺陷及阴离子掺杂对材料电化学性能的影响,为LiFePO_4的结构设计和实验研究提供理论基础。结果表明,Li、Fe和O空位型缺陷对LiFePO_4的带型变化影响较小,禁带中无新的导带,禁带宽度有一定程度缩小,有利于电子的传导,但总能量上升,造成结构的不稳定性,在实际高温制备过程中,可能产生少量杂相,影响LiFePO_4正极材料的电化学性能;P空位缺陷对LiFePO_4的带型影响同样较小,但在禁带中产生了两条新的导带,禁带宽度明显变窄,有利于电子的传导,虽然总能量上升,造成结构的不稳定性,但在实际高温制备过程中,可能产生微量有利于电化学性能的杂相;F掺杂LiFePO_4的带型出现了明显的变化,半导体类型由p型转变为n型,极大地促进了电子的导电性,总能量下降,结构稳定,对LiFePO_4正极材料的电化学性能有正面的影响。
The first-principle based on density functional theory (DFT) was used to study the electronic structure of LiFePO 4 with defects of vacancies and impurities. The effects of defects and anion doping on the electrochemical properties of the material were analyzed by energy band, density of states and population distribution. LiFePO_4 structure design and experimental research to provide the theoretical basis. The results show that Li, Fe and O vacancy defects have little effect on the change of the band shape of LiFePO_4. There is no new conduction band in the forbidden band, and the forbidden band width is reduced to a certain extent, which is conducive to the conduction of electrons. However, the total energy is increased, resulting in The instability of the structure may produce a small amount of heterophasic phase during actual high temperature preparation, which may affect the electrochemical performance of the LiFePO 4 cathode material. The P vacancy defects have the same effect on the strip type of LiFePO 4, but two in the forbidden band The new conduction band, the band gap is obviously narrower, is conducive to the conduction of electrons, although the total energy rise, resulting in structural instability, but in the actual high temperature preparation process, may produce a trace of heterogenous phase conducive to electrochemical properties; The band shape of F-doped LiFePO_4 changed obviously. The type of semiconductor changed from p-type to n-type, which greatly promoted the electronic conductivity, decreased the total energy, and stabilized the structure. It had a positive effect on the electrochemical performance of LiFePO 4 cathode material influences.