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Charge storage in rechargeable lithium batteries is limited by the positive electrode, usually the lithium intercalation compound LiCoO2, which can store 130 mAhgÀ1.[1–3] Intense efforts are underway worldwide to discover new lithium intercalation compounds for use as positive electrodes which, it is hoped, may deliver specific capacities of about 300 mA hg À1. However, increasing the capacity significantly beyond this limit is a major challenge requiring a more radical approach, such as replacement of the intercalation electrode by an O2 electrode, in which Li+ from the electrolyte and eÀ from the external circuit combine reversibly with O2 from the air within a porous matrix containing a catalyst.[4–8] Although it provides higher capacities than intercalation electrodes, much fundamental work is required to understand and optimize the performance of the O2 electrode for lithium batteries before it can be considered …