3 years ago

Singlet Oxygen during Cycling of the Aprotic Na-O2 Battery

Christian Slugovc, Stefan A. Freunberger, Sergey M Borisov, Lukas Schafzahl, Nika Mahne, Martin Wilkening, Bettina Schafzahl
Aprotic sodium-O2 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. Here we show that singlet oxygen (1O2) 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 1O2 trap that selectively and rapidly forms a stable adduct with 1O2. The 1O2 formation mechanism involves proton mediated superoxide disproportionation on discharge, rest, and charge below ~3.3 V, and direct electrochemical 1O2 evolution above ~3.3 V. Trace water, which is needed for high capacities drives at the same time parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201709351

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