Capacity fading of graphite electrodes due to the deposition of manganese ions on them in Li-ion batteries

The capacity fading of lithiated and delithiated graphite electrodes has been studied using lithium manganese oxide as a counter electrode. Higher storage temperatures and longer storage periods give larger capacity losses and larger amounts of manganese (Mn) deposition on the graphite. The capacity losses appear to be related to the amount of deposited Mn in storage experiments in dry electrolyte solutions containing various concentrations of Mn2+ ions, but definite evidence has not been found that the Mn deposit is a simple and direct cause of the capacity fading. The capacity losses estimated from quantities of Mn deposition on the graphite, assuming a Mn2+ -Li+ exchange process, appear negligible when compared with the experimental findings. Scanning electron microscope and transmission electron microscope observations show the presence of some amounts of fluoride compounds accompanying some Mn contents on the graphite. The capacities of the graphites are recovered to some extent during the cycles. (C) 2002 The Electrochemical Society.