Satisfying both sides: Novel low-cost soluble redox mediator ethoxyquin for high capacity and low overpotential Li-O2 batteries

Abstract

Abstract Due to cathode passivation caused by the insulating discharged products and by-products, Li-O2 batteries sustain some obstacles encompassing poor discharge capacity and high overpotential. Herein, we introduce 6-Ethoxy-2,2,4-trimethylquinoline (EQ) as a bifunctional redox mediator into electrolyte and investigate its influence on the electrochemical performance of Li-O2 batteries. Strikingly, the discharge process is promoted in the solution phase by the solvated Li+ with EQ, and the correlative capacity exhibits more than a 30-fold increase than pristine Li–O2 battery at the current density of 3000\xa0mA g−1carbon. DFT calculations further clarify the working mechanism of oxygen reduction reaction (ORR) induced by EQ. Furthermore, the surface electrostatic potential diagram shows that N and O atoms in EQ are electron-rich, which is prone to donate electrons to get its desirable oxidation state and effectively catalyze the oxidation of Li2O2, resulting in the extremely low charge plateau at 3.08\xa0V and longtime stable cyclability (150 cycles at a current density of 500\xa0mA g−1carbon with a fixed capacity of 1000 mAh g−1carbon).