X-ray absorption spectroscopy of Li ion battery and electronic materials

Layered lithium manganese oxides are of interest as potential cathode materials for Li ion secondary batteries. The manganese analogues of the widely used and well studied LiCoO2 and are substantially cheaper and more environmentally friendly, but most formulations suffer from poor discharge characteristics and short cycle life due to capacity fade. This is attributed to alteration of the cathode to phases such as the spinel structured LiMn2O4. Monoclinic LiMnO2 is a layered structure, isomorphous with LiCoO2, however this monoclinic polymorph is only stable with structure regulating dopants such as Cr or A] in some of the manganese sites. In this study A] and Cr doped LiMnO2 and a number of related compounds, have been prepared and examined by XPS, and XANES measurements of the transition metal Ledges. In conjunction with XRD and Reitveld analysis, the high resolution Ledge spectra reveal detail of the electronic structure of these materials, and provide substantially better definition of both manganese oxidation states, and the role of the dopant, in these compounds, than does conventional XPS. The absence of Mn3+ in the highly Cr doped materials means these are less prone to problematic Jahn-Teller effects.