镍离子掺杂对LiFePO_4结构和性能的影响

Effect of Ni^(2+) ion doping on performance and structure of lithium iron phosphate

为提高LiFePO4的充放电性能,用Ni2+对LiFePO4进行掺杂。采用电化学方法测量了Li1-xNixFePO4的充放电性能,用X射线衍射和里特沃尔特方法表征了掺杂LiFePO4的晶体结构。固相反应可制备单相Li1-xNixFePO4(x=0.00、0.01、0.02、0.03、0.05和0.07,摩尔分数)。研究表明:少量镍离子掺杂能有效地提高LiFePO4的比容量和循环性能,其中Li0.97Ni0.03FePO4具有更好的电化学性能,放电比容量高出LiFePO4约30mA.h/g,其主要原因是镍离子掺杂不仅改变了晶体中原子间距离和位置,引起晶胞收缩;而且增加了LiFePO4中Fe3+/Fe2+共存态的浓度,提高了材料的导电能力。

To improve the performance of LiFePO4 , single phase Li1-xNix FePO4 was prepared by solid state reaction （x=0.00, 0.01, 0.02, 0.03, 0.05 and 0.07, mole fraction）. Crystal structure and charge/discharge performance of doped LiFePO4 were investigated by X-ray diffractrometry with the Rietveld method and electrochemical measurement, respectively. The results show that Ni^2＋ doping with low concentration can increase the capacity and cycle performances of LiFePO4 , and Li0.97 Ni0.03 FePO4 has better performance than the others, whose discharge capacity is 30 mA · h/g higher than LiFePO4. Because Ni^2＋ doping not only causes the change of atomic position and distance and the shrinkage of crystal cell, but also increases the concentration of coexisted Fe^3＋/Fe^2＋ in LiFePO4, which increases the electrical conductivity of LiFePO4.