The Decisive Role of Li2O2 Desorption for Oxygen Reduction Reaction in Li–O2 Batteries

Fundamental issues relevant to the oxygen reduction reaction (ORR) mechanism and reaction interface are ambiguous in Li–O2 batteries. Herein, we utilized highly sensitive surface-enhanced Raman spectroscopy (SERS) to reveal the spontaneous desorption behavior of insoluble products of lithium peroxide (Li2O2) from the electrode surface. Furthermore, the electrochemical ORR mechanism is elucidated at the electrode/Li2O2 interface based on a dynamic equilibrium between the generation and desorption of Li2O2. The desorption of adsorbed Li2O2 species (Li2O2*) is crucial to releasing surface sites and maintaining the electrochemical ORR process at the electrode substrate surface instead of the Li2O2/electrolyte interface. The proceeding of Li2O2* desorption can guarantee the stability of Li2O2* concentration and the discharge plateau in the galvanostatic ORR process. The suppression of Li2O2* desorption is proved to induce the termination of Li2O2* generation, which is accompanied by the growth of adsorbed lithium superoxide (LiO2*), leading to rapid potential attenuation.