Mo 掺杂 LiFePO4正极材料的第一性原理研究(英文)

First-Principle Calculation of LiFe_(1-x)Mo_xPO_4 as Cathode Material for Rechargeable Lithium Batteries

基于第一性原理密度泛函理论计算了LiFePO4和LiFe1-xMoxPO4(x=0.005,0.01,0.015,0.02,和0.025)的电子结构和锂离子扩散能垒。结果显示掺杂后的LiFe0.99Mo0.01PO4样品具有最大的(101)晶面间距,由此可知LiFe0.99Mo0.01PO4沿[101]晶向具有最宽的锂离子扩散通道。未掺杂的LiFePO4的锂离子扩散能垒为4.289 eV,而掺杂后LiFe0.99Mo0.01PO4降为4.274 eV,经过计算得出掺杂样品LiFe0.99Mo0.01PO4的锂离子扩散系数增为未掺杂LiFePO4的1.79倍,表明Mo掺杂有利于改善LiFePO4的锂离子扩散能力。态密度图显示,掺杂Mo后导带底附近的峰强度增强,对LiFePO4电子导电性能的提高是有利的。因此,掺杂Mo有益于提高LiFePO4的锂离子扩散能力和电子导电能力。结合我们的实验结果比较得知,在磷酸铁锂性能的改善上,相比电子导电能力,锂离子扩散能力的提高起到了更重要的作用。

The electronic structure and diffusion barriers of lithium ions in pure LiFePO4 and doped LiFe1-xMoxPO4（x=0.005, 0.01, 0.015, 0.02, and 0.025） have been calculated based on the first-principle density functional theory （DFT）. The calculated results show that the LiFe0.99Mo0.01PO4 has the largest interplanar distance of （101） crystal plane, suggesting the widest Li ion diffusion pathway in [010] direction. Pure LiFePO4 has diffusion energy barrier of 4.289 eV for lithium ions, while the LiFe0.99Mo0.01PO4 has lower diffusion energy barrier of 4.274 eV. The calculated diffusion coefficient of LiFe0.99Mo0.01PO4 is 1.79 times as large as that of pure LiFePO4, indicating that Mo doping is beneficial to lithium ion diffusivity of LiFePO4. The intensity of the partial density of states （PDOS） near the bottom of conduction bands （CBs） becomes stronger after doping with Mo. According to the analysis above, Mo doping is beneficial to improve the electronic conductivity and lithium ion diffusivity of LiFePO4. Lithium ion diffusivity plays more important roles than electronic conductivity on improving the electrochemical performance of LiFePO4 by doping with Mo.