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–O 2 batteries. Herein, we utilized highly sensitive surface-enhanced Raman spectroscopy (SERS) to reveal the spontaneous desorption behavior of insoluble products of lithium peroxide (Li 2 O 2 ) from the electrode surface. Furthermore, the electrochemical ORR mechanism is elucidated at the electrode/Li 2 O 2 interface based on a dynamic equilibrium between the generation and desorption of Li 2 O 2 . The desorption of adsorbed Li 2 O 2 species (Li 2 O 2 *) is crucial to releasing surface sites and maintaining the electrochemical ORR process at the electrode substrate surface instead of the Li 2 O 2 /electrolyte interface. The proceeding of Li 2 O 2 * desorption can guarantee the stability of Li 2 O 2 * concentration and the discharge plateau in the galvanostatic ORR process. The suppression of Li 2 O 2 * desorption is proved to induce the termination of Li 2 O 2 * generation, which is accompanied by the growth of adsorbed lithium superoxide (LiO 2 *), leading to rapid potential attenuation.