基于同步辐射的X射线吸收谱探讨LiFexMn1-xO2的精细结构

利用共沉淀法合成出了一系列化合物LiFexMn1-xO2 (0≤x≤1)，电化学测试表明LiFe0.25Mn0.75O2可逆容量最高，当倍率为0.1C(1C=140 mA/g)时，可逆容量可达180 mAh/g.通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、X射线吸收谱（XAS）对所制备的材料的组成、形貌和精细结构进行了表征.XRD和XAS的结果显示LiFexMn1-xO2 (0<x<1)含有三重晶体相即尖晶石相(LiMn2O4)、富锂相(Li2MnO3)和层状相(LiFeO2).另外，XAS结果证明材料中的Mn相和Fe相是随机堆叠的.该研究表明Fe的替代影响了晶体相的组成和Mn相的局域结构，进而调节了该正极材料的电化学性能，得到当x=0.25时最优的电化学性能.
Abstract：LiFexMn1-xO2 (0≤x≤1) compounds were synthesized by the co-precipitation method. Electrochemical tests show that the LiFe0.25Mn0.75O2 composite has a maximum reversible capacity of 180 mAh/g at 0.1 C(1 C=140 mA/g). These as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). XRD and XAS results show that the LiFexMn1-xO2 (0<x<1) samples actually have multiple crystal phases， especially the spinel phase (LiMn2O4), Li-rich phase (Li2MnO3) and layered phase (LiFeO2). Moreover, XAS reveals that the Mn-phase and the Fe-phase are randomly stacked in the samples. The work shows the doping of Fe influences the crystal phase and local structure of the Mn-phase upon the samples and then adjusts the electrochemical performances of the cathode materials, giving an optimal proportion (x=0.25) of the spinel and Li-rich and layered phase.