Lithium manganate spinels with the formula Li+xMn2-xO4 undergo lithium -proton ion exchange to forma protonated gimel-MnO2-type phase. The Li1+xMn2-xO4 phases are metastable, and preparation at temperatures in excess of 400 degreesC results in phase separation. By partially substituting the manganese with cobalt, single-phase spinels of formula Li-1.33-x/3CoxMn1.67-2x/3O4 (0 proton ion exchange. Incoherent inelastic neutron scattering (INS) shows that inserted protons are present predominately as structurally ordered hydroxyl, which is reexchangeable with lithium in aqueous solution. (C) 2004 Elsevier B.V All rights reserved.