Insight into fine structures of LiFexMn1-xO2 by synchrotron radiation-based X-ray absorption spectroscopy

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.