Structural analysis of Li2MnO3 and related Li-Mn-O materials

Structure of Li₂MnO₃ during charge and discharge is studied by x-ray diffraction, Raman spectroscopy and x-ray absorption spectroscopy (XAS). During electrochemical delithiation, development of a local spinel-like structure and an increase in disordering of Mn in Li ₂MnO₃ is observed from Raman spectroscopy and XAS, respectively. However, the charge-discharge curves show a sloping profile, which is associated with Mn atoms in the transition metal layer. Upon cycling, plateaus develop in the 3 and 4 V regions, suggesting transformation of Li ₂MnO₃ to a spinel structure. The formation of spinel phase is linked to Mn re-arrangement in the lattice and lowering of oxygen content, as indicated by results of Li-Mn-O compounds made by varying Li/Mn ratio during synthesis and by chemically (acid treatment) extracting Li from Li ₂MnO₃. Our results suggest the better cycle performance of Li-excess materials with a solid solution of Li₂MnO ₃-LiMnO₂ is due to stabilization of the Li ₂MnO₃ structure by addition of a layered component into the structure. © 2011 The Electrochemical Society.