Abstract: Stabilized lithiated manganese oxide (LMO) is prepared by reacting cubic spinel lithium manganese oxide particles and particles of an alkali metal compound in air for a time and at a temperature sufficient to decompose at least a portion of the alkali metal compound, providing a treated lithium manganese oxide. The reaction product is characterized as particles having a core or bulk structure of cubic spinel lithium manganese oxide and a surface region which is enriched in Mn+4 relative to the bulk. X-ray diffraction data and x-ray photoelectron spectroscopy data are consistent with the structure of the stabilized LMO being a central bulk of cubic spinel lithium manganese oxide with a surface layer or region comprising A2MnO3, where A is an alkali metal. Electrochemical cells containing the stabilized LMO of the invention have improved charging and discharging characteristics and maintain integrity over a prolonged life cycle.