Revealing the Surface Effect of the Soluble Catalyst on Oxygen Reduction/Evolution in Li–O2 Batteries

Understanding catalytic mechanisms at the nanoscale is essential for the advancement of lithium–oxygen (Li–O2) batteries. Using in situ electrochemical atomic force microscopy, we explored the interfacial evolution during the Li–O2 electrochemical reactions in dimethyl sulfoxide-based electrolyte, further revealing the surface catalytic mechanism of the soluble catalyst 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ). The real-time views showed that during discharge flower-like Li2O2 formed in the electrolyte with DBBQ but small toroid without DBBQ. Upon charge, Li2O2 decomposes at a slow rate from bottom to top in the absence of DBBQ, yet with an outside-in approach in the presence of DBBQ. Bigger discharge products and more efficient decomposition pathways in the DBBQ-containing system reveal the catalytic activity of DBBQ straightforwardly. Our work provides a direct insight into the surface effect of soluble catalyst DBBQ on Li–O2 reactions at the nanoscale, which is critical for the performance optimization of Li–O2 batteries.