Cycle Performance in Each State-of-Charge in LiMn[sub 2]O[sub 4]

Abstract

Cycle performances at 55°C were examined for a cell using a spinel-type of lithium manganese oxide as a positive electrode in each of five regions of the state-of-charge. The results demonstrate that larger capacity losses are found in two of the lowest voltage regions of 0-20% and 20-40% states-of-charge and a smaller capacity loss is observed in a higher voltage region of 60-80% state-of-charge. By the addition of the conductive material to the positive electrode after the cycle, the capacities recover in any regions. The results of our present work imply that the capacity losses can be divided into two major parts; one caused by deterioration of the active material itself and another by poor conduction between the active material and collector. The ratio of the former to the latter is estimated to be about 1:2. A distinct correlation is found between the capacity loss in the storage experiment at each constant potential and that arising from the active material itself, and only a weaker correlation is admitted between the capacity loss in the storage and that resulting from the poor conduction. The poor conduction in the positive electrode would be derived from insulating substances formed by the reaction of a protonated lithium manganese oxide with Li and Mn ions, as found in the storage experiment. However, there is no evidence connecting a cause of these capacity losses with lattice expansion of the lithium manganese oxide. © 2002 The Electrochemical Society. All rights reserved.