钛离子掺杂对LiFePO_4结构和性能的影响

Effect of Ti^(4+) Ion Doping on the Performance and Structure of Lithium Iron Phosphate

为提高LiFePO4的充放电性能,用Ti(Ⅳ)对LiFePO4进行掺杂．用电化学方法测量了Li1-xTixFePO4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．固相反应可以制备单相Li1-xTixFePO4(x=0．00、0．01、0．02、0．03,0．05和0．07, 摩尔分数),其中Li0．98Ti0．02FePO4具有更好的电化学性能,在80mA／g的充放电电流下,第2 次的放电比容量为136．606mAh／g,循环20次后为128．388mAh／g．研究表明,少量钛离子掺杂不仅改变了原子间距和位置、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,从而能有效地提高LiFePO4的比容量和循环性能．

In order to improve the performance of LiFePO4, Li1-xTixFePO4（x=0.00, 0.01, 0.02, 0.03, 0.05 and 0.07,mol fraction） with Ti（Ⅳ） dopant was prepared. Crystal structure and charge/discharge performance of Ti（Ⅳ） doped LiFePO4 were investigated by X-ray diffraction using the Rietveld method and electrochemical measurement, respectively. Single phase Li1-xTixFePO4 can be prepared by solid state reaction. Li0.98Ti 0.02FePO4 shows higher capacity than LiFePO4 through the research on Li1-xMxFePO4. As Li0.98Ti0.02PO4 is charged and discharged at 80mA/g, its 2nd and 20th discharge capacity is 136.606 and 128.388mAh/g, respectively. The results show that low concentration Ti（Ⅳ） dopant can increase the capacity and cycle performances of LiFePO4. because it 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.