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 Li2MnO3 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 Li2MnO3 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 Li2MnO3. Our results suggest the better cycle performance of Li-excess materials with a solid solution of Li2MnO3-LiMnO2 is due to stabilization of the Li2MnO3 structure by addition of a layered component into the structure. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3609849] All rights reserved.