Electrolyte Effects on Chemical Stability of NaO2 in Na-O2 Batteries
Here we show NaO2 as the only discharge product from Na-O2 cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Immediately after discharge, no Na2O2 · 2H2O was found in the discharged electrode, even with H2O present in the electrolyte up to 6000 ppm. However, Na2O2 · 2H2O was detected upon ageing the electrode in the electrolyte, and the amount of Na2O2 · 2H2O was seen to increase with increasing rest time in the electrolyte. More importantly, the reversibility of the reaction is affected by the presence of Na2O2 · 2H2O, where the cells charged immediately after discharge show a reversible reaction , and the cells charged after resting the electrode in the electrolyte for several hours showed poor reversibility.
The rechargeable nature of a Na-O2 cell is governed by the formation and oxidation of NaO2, making it vital to study the stability of the electrolyte in the presence of NaO2, and also to prevent the formation of irreversible side products.
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