Stability of superoxide radicals in glymesolvents for non-aqueous Li–O2 battery electrolytes

Abstract

Glyme-based electrolytes were studied for the use in lithium–air batteries because of their greater stability towards oxygen reduction reaction intermediates (e.g., superoxide anion radicals (O₂˙⁻)) produced upon discharge at the cathode compared to previously employed carbonate-based electrolytes. However, contradictory results of glyme stability tests employing KO₂ as an O₂˙⁻ source were reported in the literature. For clarification, we investigated the reaction of KO₂ with glymes of various chain lengths qualitatively using ¹H NMR and FTIR spectroscopy as well as more quantitatively using UV-Vis spectroscopy. During our experiments we found a huge impact of small quantities of impurities on the stability of the solvents. Therefore, we studied further the influence of impurities in the glymes on the cycling behavior of Li–O₂ cells, demonstrating the large effect of electrolyte impurities on Li–O₂ cell performance.