A manganese-based solid solution with the composition of Li1.95Mn0.9Co0.15O3 was synthesized by a simplified coprecipitation method, followed by a combustion technique, and its electrochemical characteristics as a lithium-battery cathode were investigated. Rietveld refinement based on neutron diffraction data revealed that the material is assigned to an Li2MnO3-type structure model with a monoclinic cell due to the space group symmetry of C2/m. In cycling of the Li/Li+/Li1.95Mn0.9Co0.15O3 cell in the potential range of 2.0-4.8 V at current densities of 30 mAg(-1), the discharge capacity characteristically increases from 46.3 to 196.5mAhg(-1) as the cycle increases from 1 to 11, and a discharge capacity of > 175.5 mAhg(-1) is obtained between the 23rd and 58th cycles with small capacity fading of 2.41%. The results of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) measurements showed that the manganese redox reaction (Mn3+/Mn4+) in the Li1.95Mn0.9Co0.15O3 system is progressively activated during the first ten-odd cycles, following continuous occurrence of the extraction of oxygen molecules from the electrode material over these charge processes. It could be assumed that such behaviors significantly influence the electrochemical characteristics of the Li1.95Mn0.9Co0.15O3 system. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.079203jes] All rights reserved.