Suppressing Singlet Oxygen Formation during the Charge Process of Li-O Batteries with a CoO Solid Catalyst Revealed by Operando Electron Paramagnetic Resonance.

Aprotic lithium-oxygen (Li-O) batteries promise high energy, but the cycle life has been plagued by two major obstacles, the insulating products and highly reactive singlet oxygen (O), which cause higher overpotential and parasitic reactions, respectively. A solid-state catalyst is known to reduce overpotential; however, it is unclear whether it affects O generation. Herein, CoO was employed as the representative catalyst in Li-O batteries, and O generation was investigated by ex-situ and operando electron paramagnetic resonance (EPR) spectroscopy. By comparing a carbon nanotube (CNT) cathode with a CoO/CNT cathode, we find that O generation in the charge process can be suppressed by the CoO catalyst. After carefully studying the discharge products on the two electrodes and the corresponding decomposition processes, we conclude that a LiO-like species is responsible for the O generation during the early charge stage. The CoO catalyst reduces the amount of LiO-like species in discharge products, and thus the O formation is suppressed.