Layered lithium-manganese-oxide electrodes with the general formula Li2-xMnO3-x/2 (0 < x < 2), and structural analogs in which some of the manganese has been substituted by Zr or Al have been prepared and characterized by structural and electrochemical methods. Although the discharge capacity for electrode compositions that contained Zr or Al fades at a slower rate in lithium cells than an unsubstituted compound, Li0.106MnO2.053 (Li2-xMnO3-x/2, where x = 1.894), these materials deliver lower capacities (similar to 90 mA h/g after 20 cycles) than Li2-xMnO3-x/2 when cycled between 3.8 and 2.0 V at a C/8-C/10 rate. Under humid conditions or in contact with carbon, Li2-xMnO3-x/2 compounds transform slowly to gamma-MnO2 on standing at room temperature, whereas the Zr- and Al-substituted materials appear to be more resistant to the conversion to gamma-MnO2.