Determining the Facile Routes for Oxygen Evolution Reaction by <i>In Situ</i> Probing of Li–O₂ Cells with Conformal Li₂O₂ Films

An ongoing challenge with lithium–oxygen (Li–O₂) batteries is in deciphering the oxygen evolution reaction (OER) process related to the slow decomposition of the insulating lithium peroxide (Li₂O₂). Herein, we shed light on the behavior of Li₂O₂ oxidation by exploiting various <i>in situ</i> imaging, gas analysis, and electrochemical methods. At the low potentials 3.2–3.7 V (vs Li/Li⁺), OER is exclusive to the thinner parts of the Li₂O₂ deposits, which leads to O₂ gas evolution, followed by the concomitant release of superoxide species. At higher potentials, OER initiates at the sidewalls of the thicker Li₂O₂. The succeeding lateral decomposition of Li₂O₂ indicates the preferential Li⁺ and charge transport occurring at the sidewalls of Li₂O₂. To ameliorate the OER rate, we also investigate an alternative approach of rerouting charge carriers by using soluble redox mediators. Our <i>in situ</i> probes provide insights into the favorable charge-transport routes that can aid in promoting Li₂O₂ decomposition