Rechargeable lithium batteries represent one of the most important developments in energy storage for 100 years, with the potential to address the key problem of global warming. However, their ability to store energy is limited by the quantity of lithium that may be removed from and reinserted into the positive intercalation electrode, Li(x)CoO(2), 0.5 < x < 1 (corresponding to 140 mA.h g(-1) of charge storage). Abandoning the intercalation electrode and allowing Li to react directly with O(2) from the air at a porous electrode increases the theoretical charge storage by a remarkable 5-10 times! Here we demonstrate two essential prerequisites for the successful operation of a rechargeable Li/O(2) battery; that the Li(2)O(2) formed on discharging such an O(2) electrode is decomposed to Li and O(2) on charging (shown here by in situ mass spectrometry), with or without a catalyst, and that charge/discharge cycling is sustainable for many cycles.

Higher‐capacity lithium batteries can be fabricated by using α‐MnO2 nanowires as the catalyst in a porous, composite oxygen cathode. In the depicted scanning electron micrograph of a composite positive electrode, deposits of Li2O2, which accumulates during discharge, can be seen within a porous matrix consisting of α‐MnO2 and carbon.

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The electrochemical reactivity of tailor-made CuO powders prepared according to a new low-temperature synthesis method was studied by a combination of transmission electron microscopy (TEM) and electrochemical techniques. All the processes involved during cycling were successfully identified. We show that the reduction mechanism of CuO by lithium involves the formation of a solid solution of Cu1−xIICuxIO1−x/2 0⩽x⩽0.4, a phase transition into Cu2O, then the formation of Cu nanograins dispersed into a lithia matrix false(Li2Ofalse) followed by the growth of an organic-type coating. This one is responsible for the extra capacity observed on the voltage vs. composition curve. During the subsequent charge, the organic layer vanishes first, and then the Cu grains are partially or fully oxidized with a concomitant decomposition of Li2O. The formation of Li2O and Cu nanograins and then the one of Cu, CuO, and Cu2O nanograins on the first discharge and subsequent charge, respectively, were identified by high-resolution TEM studies. These results enabled a better understanding of the processes governing the reactivity of 3d metal oxides vs. lithium down to 0.02 V. © 2001 The Electrochemical Society. All rights reserved.