Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 56, Issue 49, Pages 15728-15732Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201709351
Keywords
electrochemistry; Na-O-2 batteries; parasitic reactions; reaction mechanisms; singlet oxygen
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Funding
- European Research Council (ERC) under the European Union's Horizon research and innovation programme [636069]
- Austrian Federal Ministry of Science, Research and Economy
- Austrian Research Promotion Agency [845364]
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Aprotic sodium-O-2 batteries require the reversible formation/dissolution of sodium superoxide (NaO2) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO2, a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Herein we show that singlet oxygen (O-1(2)) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in- and ex-situ via a O-1(2) trap that selectively and rapidly forms a stable adduct with O-1(2). The O-1(2) formation mechanism involves proton-mediated superoxide disproportionation on discharge, rest, and charge below ca. 3.3V, and direct electrochemical O-1(2) evolution above ca. 3.3V. Trace water, which is needed for high capacities also drives parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.
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