Direct Observation of Redox Mediator-Assisted Solution-Phase Discharging of Li–O 2 Battery by Liquid-Phase Transmission Electron Microscopy

Li–O 2 battery is one of the important next-generation energy storage systems, as it can potentially offer the highest theoretical energy density among battery chemistries reported thus far. However, realization of its high discharge capacity still remains challenging and is hampered by the nature of how the discharge products are formed, causing premature passivation of the air electrode. Redox mediators are exploited to solve this problem, as they can promote the charge transfer from electrodes to the solution phase. The mechanistic understanding of the fundamental electrochemical reaction involving the redox mediators would aid in the further development of Li–O 2 batteries along with rational design of new redox mediators. Herein, we attempt to monitor the discharge reaction of a Li–O 2 battery in real time by liquid-phase transmission electron microscopy (TEM). Direct in situ TEM ob…