Topic Metal-Air Batteries: Singlet Oxygen Formation during the Charging Process of an Aprotic Lithium–Oxygen Battery

Aprotic lithium-oxygen (Li–O₂) batteries have attracted considerable attention in recent years owing to their outstanding theoretical ener-gy density. A major challenge, however, is their poor reversibility caused by unwanted degradation reactions, which mainly occur dur-ing battery charge and are still poorly understood. Herein, we show that singlet oxygen (¹D_g) is formed upon Li₂O₂ oxidation at potentials above 3.5 V. Singlet oxygen was detected through a reaction with a spin-trap to form a stable radical that was observed by time- and voltage resolved in-operando EPR spectroscopy in a purpose-built spectro-electrochemical cell. According to our estimate, a lower limit of approximately 0.5 % of the evolved oxygen is singlet oxygen. The occurrence of highly reactive singlet oxygen might be the long-overlooked missing link in the understanding of the electrolyte deg-radation and carbon corrosion reactions that occur during the charg-ing of Li–O2 cells.

J. Wandt, P. Jakes, J. Granwehr, H.A. Gasteiger, R.-A. Eichel, Angew. Chem. Int. Ed. 55 (2016) 6892-6895