A lithiated manganese oxide for use in primary lithium cells is described. The lithiated manganese oxide can be prepared by exposure to a lithium source under conditions that result in the formation of a modified manganese oxide phase. When the modified phase is used in a primary lithium cell, the operating voltage of an electrochemical cell containing the lithiated manganese oxide increases relative to the operating voltage of a cell containing a manganese dioxide that is not exposed to the lithium source.