Enhancing the electrochemical properties of LT-LiCoO2 in lithium cells by doping with Mn

Nearly stoichiometric LiCo1-xMnxO2 mixed oxides (x = 0, 0.2) were prepared by using a sol-gel method and their electrochemical properties as lithium cell cathodes were examined. Gels of the two samples fired at 400degreesC exhibited the same structure as LT-LiCoO2, with the transition elements in a tervalent state as revealed by XPS spectroscopy. A modified spinel structure model is proposed to account for the X-ray diffraction data. Substitution of Co by Mn ions has the following favorable effects on the electrochemical properties: (i) a decrease in polarization between the charge and discharge curves; (ii) an increase in capacity delivered by the cell; (iii) a marked improvement in the cycling properties of the cell, particularly when the calcining temperature is raised to 600degreesC. The enhanced cell performance is ascribed to lithium occupying in an orderly manner available positions in the modified spinel structure adopted. The presence of Mn enhances cation ordering, thus increasing the reversibility of the lithium reaction. (C) 2003 Elsevier B.V. All rights reserved.