A Study on the Cause of Deterioration in Float-Charged Lithium-Ion Batteries Using LiMn2O4 as a Cathode Active Material

The deterioration mechanism of float-charged lithium-ion batteries with lithium manganese oxide spinel as the cathode active material was investigated in order to improve battery lifetime, which is especially important for Li-ion batteries used in backup applications. After lengthy charging at a constant voltage, the cathodes and anodes of deteriorated batteries were tested electro-chemically and analyzed. The capacity deterioration of the anode was 18.4%, and that of the cathode was 5.7%, although the reduction in the cell capacity was 41.9%. Electron probe microanalysis revealed the manganese deposition on the anode, suggesting that the reduction in battery capacity was caused by a decrease in the number of mobile lithium ions because the manganese deposition may occur instead of lithium insertion into the anode during charging. However, a precise comparison of the decrease in the number of mobile lithium ions caused by the manganese deposition and the battery capacity reduction showed that the capacity reduction cannot be explained by the manganese deposition alone. Side reactions related to the deposited manganese that accompanies the loss of electric charge may be occurring at the anode as well. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3543651] All rights reserved.