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caused by slow oxidation of the electrolyte by the fully charged manganese oxide, corrosion at the current collector interfaces, and/ or mass transfer effects. These phenomena can easily be minimized by lowering the voltage limit upon charge, improving electrolyte compositions and current collector materials, and by judicious use of rest periods between half-cycles. At any rate, these early results demonstrate that the orthorhombic sodium manganese oxide is remarkably stable and undergoes alkali metal intercalation processes readily and reversibly. Conclusions The suitability of the orthorhombic sodium manganese oxide for use as a cathode material in alkali metal secondary batteries has been demonstrated. This material, which has never before been used in a battery, has high specific capacity in both lithium and sodium cells, and discharge characteristics suitable for use with polymer electrolytes. An especially striking feature is the excellent reversibility and stability upon cycling in lithium cells.

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.

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