镁离子掺杂对磷酸铁锂结构和性能的影响

为提高LiFePO4的充放电性能,用化学沉淀法制备了镁离子掺杂的磷酸铁锂,用电化学方法测量了Li1-xMgxFePO4(x=0.00、0.02、0.05、0.07、0.10和0.20,摩尔分数)的充放电性能,用X射线衍射(XRD)和里特沃尔特(Rietveld)方法表征了掺杂对LiFePO4的晶体结构的影响.结果表明少量镁离子掺杂能有效地提高LiFePO4的比容量和循环性能,其中Li0.95Mg0.05FePO4具有更好的电化学性能,放电比容量高出LiFePO4约20mAh/g,镁离子掺杂提高了LiFePO4中Fe3 /Fe2 共存态的浓度,使材料具有更好的导电能力.

Performance and structure of Mg2+ doped lithium iron phosphate prepared by chemical precipitation methode

In order to improve the performance of LiFePO_4,Li_(1-x)Mg_xFePO_4 was prepared by co-precipitation method,where x,the mol fraction of Mg~(2+),is 0.00,0.02,0.05,0.07,0.10 and 0.20.Crystal structure and charge/discharge performance of doped LiFePO_4 were investigated by X-ray diffraction with the Rietveld method and electrochemical measurement,respectively.The results show that Mg~(2+) doping with low concentration can increase the capacity and cycle performances of LiFePO_4,and Li_(0.95)Mg_(0.05)FePO_4 has better performance than the others,which discharge capacity is higher 20mAh/g than LiFePO_4.Rietveld refinement indicates that doped metal atoms randomly substitute for Li atom in the LiFePO_4 structure.Because Mg~(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 LiFePO_4,which increases the electrical conductivity of LiFePO_4.