Lithium-metal oxides with a high formal Li2O content, such as Li5FeO4 (5Li2O center dot Fe2O3) and a Li2MnO3 center dot LiFeO2 composite ({Li2O center dot MnO2}center dot{Li2O center dot Fe(2)O(3)g) have been explored as electrocatalysts for primary and rechargeable Li-O-2 cells. Activation occurs predominantly by Li2O removal, either electrochemically or chemically by acid-treatment. Superior electrochemical behavior is obtained if activation occurs by acid-treatment; Li2MnO3 center dot LiFeO2 catalysts provide 2516 mAh/g (carbon) corresponding to 931 mAh/g (electrocatalyst + carbon) during the initial discharge. The reaction is reasonably reversible during the early cycles. The approach has implications for designing electrocatalysts that participate through electrochemical Li2O extraction/reformation reactions, offering exceptionally high capacities. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3555366] All rights reserved.