Electrodes based on the layered compounds Li-x[Mn1-yLiy]O-2, y less than or equal to 0.2, have been charged in the electrolyte, 1 m LiPF6 in ethylene carbonate/diethyl carbonate (1:2 v/v). Initially Li+ removal is accompanied by oxidation of Mn3+ to Mn4+. Once all Mn is in the 4+ oxidation state further Li+ removal occurs by two unconventional mechanisms, one involving oxidation of O2- with subsequent O loss (effective removal of Li2O) and the other electrolyte oxidation generating H+ which exchanges for Li+ in the electrode. Although both mechanisms appear to occur at 30 and 55degreesC, the former dominates at both temperatures in contrast to Li2MnO3. (C) 2003 The Electrochemical Society.