Electrochemically Generated KO2 as a Phase-Transfer Mediator for Na–O2 Batteries

Superoxide-based Na–O 2 batteries have attracted much attention as promising alternatives to peroxide-based Li–O 2 batteries because of their small polarization for oxygen evolution reactions. However, the limited solubility of their discharge product, NaO 2, leads to the surface-confined mechanism at high current densities, resulting in the poor energy density of Na–O 2 batteries. In this connection, a few protic phase-transfer catalysts, such as water and benzoic acid, have been examined to improve reversible capacity because they promote the solution-mediated mechanism. Herein, KO 2, which is electrochemically generated from potassium trifluoromethanesulfonate dissolved in electrolytes during discharge, is introduced as a phase-transfer mediator for Na–O 2 batteries. The reaction mechanism of Na–O 2 batteries containing a KO 2 mediator is clarified through ex situ XRD, cross-sectional…