Non-aqueous metal–oxygen batteries depend critically on the reversible formation/decomposition of metal oxides on cycling. Irreversible parasitic reactions cause poor rechargeability, efficiency, and cycle life, and have predominantly been ascribed to the reactivity of reduced oxygen species with cell components. These species, however, cannot fully explain the side reactions. Here we show that singlet oxygen forms at the cathode of a lithium–oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products. The amount increases during discharge, early stages of charge, and charging at higher voltages, and is enhanced by the presence of trace water. Superoxide and peroxide appear to be involved in singlet oxygen generation. Singlet oxygen traps and quenchers can reduce parasitic reactions effectively. Awareness of the highly reactive singlet oxygen in non-aqueous metal–oxygen batteries gives a rationale for future research towards achieving highly reversible cell operation.
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S.A.F. is indebted to the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 636069). We further gratefully acknowledge funding from the Austrian Federal Ministry of Economy, Family and Youth and the Austrian National Foundation for Research, Technology and Development and initial funding from the Austrian Science Fund (FWF, Project No. P26870-N19). The authors thank R. Saf for help with the MS, R. Breinbauer for discussions about the reaction mechanism, S. Landgraf for help with the NIR measurement, and J. Schlegl for manufacturing instrumentation for the methods used.
The authors declare no competing financial interests.
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Mahne, N., Schafzahl, B., Leypold, C. et al. Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium–oxygen batteries. Nat Energy 2, 17036 (2017). https://doi.org/10.1038/nenergy.2017.36
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