Nb掺杂LiFePO_4电子结构的第一性原理研究

First-Principles Study of Electronic Structure of Nb-Doped LiFePO_4

采用基于DFT的第一性原理方法,研究Nb掺杂LiFePO4锂离子电池正极材料的电子结构,并进行能带结构、电子态密度、布居和差分电荷密度性质等分析。结果表明:Nb掺杂后体系结构稳定,带隙降低,由于Nbd轨道电子的作用,使费米面附近能带数增加,更有利于电子传递,使电子电导率增加,充放电速率提高;Li-O键键长明显变大,有利于Li离子的扩散。虽然掺杂量大,带隙下降多,但会影响Li离子的扩散,尤其是在Li位掺杂时。综合考虑掺杂量不需要太大。

The electronic structure of LiFePO4, including the energy band, PDOS and popularity analysis was determined by the first-principles based on the density functional theory （DFT）, via Nb substituting for Fe or Li with Nb in LiFePO4 supercell. Results show that after Nb doping, the structure is stable and the band gap decreases resulting in the increase of the electronic conductivity and the rate of discharge/recharge, and this can be attributed to the electrons in orbital d, which leads to the increasing of the band near the Fermi level. The bond length of Li-O increases, which benefits the diffusivity of lithium ion. The band gap decreases with more doping amount, and it can influence the diffusivity of lithium ion, especially at Li site. Therefore, it is concluded that the doping content should not be too much.