Revealing the Surface Effect of the Soluble Catalyst on Oxygen Reduction/Evolution in Li-O Batteries.

Understanding catalytic mechanisms at the nanoscale is essential for the advancement of lithium-oxygen (Li-O) batteries. Using in situ electrochemical atomic force microscopy, we explored the interfacial evolution during the Li-O 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 LiO formed in the electrolyte with DBBQ but small toroid without DBBQ. Upon charge, LiO 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-O reactions at the nanoscale, which is critical for the performance optimization of Li-O batteries.