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

Abstract

Although the soluble redox mediator (RM) has been effectively applied in Li–O2 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–O2 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.