Oxygen Reduction Reaction Promotes Li + Desorption from Cathode Surface in Li‐O 2 Batteries

Li‐O 2 batteries are claimed to be one of the future energy storage technologies. Great number of scientific and technological challenges should be solved first to transform Li‐O 2 battery from a promise to real practical devices. Proposed mechanisms for oxygen reduction assume a reservoir of solved Li + ions in the electrolyte. However, the role that adsorbed Li + on the electrode surface might have on the overall oxygen reduction reaction (ORR) has not deserved much attention. Adsorbed Li + consumption is monitored here using impedance measurements from extended electrochemical double layer capacitance, which depends on the carbon matrix surface area. The presence of O 2 drastically reduces the amount of adsorbed Li + , signaling the kinetic competition between Li + surface adsorption and its consumption, only for potentials corresponding to the oxygen reduction reaction. Noticeably double layer capacitance remains unaltered after cycling. This fact suggests that the ORR products (Li 2 O 2 and Li 2 CO 3 ) are not covering the internal electrode surface, but deposited on the outer electrode‐contact interface, hindering thereby the subsequent reaction. Current results show new insights into the discharge mechanism of Li‐O 2 batteries and reveal the evidence of Li + desorption from the C surface when the ORR starts.