Bifunctional Redox Mediator Supported by an Anionic Surfactant for Long-Cycle Li–O₂ Batteries

Although the soluble redox mediator (RM) has been effectively applied in Li–O 2 batteries, parasitic reactions between the lithium anode and RM + can result in poor cycle performance. Herein, we proposed a nonelectroactive surfactant (sodium dodecyl sulfate, SDS) that could adsorb on the hydrophobic carbon surface and form a stable anionic layer upon charge, which can effectively suppress the diffusion of oxidized RM + and facilitate charge transfer at the electrode–solution interface. To coordinate with SDS, a new RM named 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) was adopted due to its oxidation process following after in situ formation of the anionic layer. Moreover, as a bifunctional mediator, PTIO cannot only get a low charge plateau but also greatly enhance the discharge capacity when applied in Li–O 2 batteries. The electrochemical results demonstrated that the cycling performance, energy efficiency, and discharge capacity were significantly improved owing to the synergistic effect of PTIO and SDS.