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The electrochemical and structural properties of spinel phases in the Li-Mn-O system are discussed as insertion electrodes for rechargeable lithium batteries. The performance of button-type cells containing electrodes from the Li20 9 yMnOz system, e.g., the stoichiometric spinel Li4Mn5012 (y = 2.5) and the defect spinel Li2Mn,O9 (y = 4.0), is highlighted and compared with a cell containing a standard LiMn204 spinel electrode.

The electrochemical properties of 0.5 Li 2 MnO 3 •0.5 LiNi 0.44 Co 0.25 Mn 0.31 O 2 electrodes, when preconditioned and activated with acid for 2-24 h, have been studied in lithium cells. Powder X-ray diffraction data and electrochemical measurements provide supporting evidence for an intergrown, composite electrode structure from which Li 2 O can be leached from the Li 2 MnO 3 ͑Li 2 O•MnO 2 ͒ component with acid, thereby mimicking the electrochemical charge process at high potentials ͑Ͼ4.5 V͒. The MnO 2 -rich domains generated by acid treatment are reduced during electrochemical discharge at a lower potential than electrochemically generated MnO 2 -rich domains. With prolonged cycling between 4.6 and 2.0 V, dQ/dV plots of untreated and acidtreated electrodes develop similar, but not identical, character, suggesting a coalescence and redox interaction of the manganese ions in MnO 2 -rich and Ni 0.44 Co 0.25 Mn 0.31 O 2 regions of the structure. Acid treatment eliminates the first-cycle capacity loss of the electrodes, consistent with earlier reports for related systems, but it damages their cycling stability and rate capability.