Surface Properties of Electrode Materials: A Key Factor Affecting the Catalytic Activity of Redox Mediators in Li–O₂ Battery Discharge

Redox mediators (RMs) represent the most promising strategy to address the sluggish kinetics of lithium–oxygen (Li–O₂) batteries. To achieve high-energy and cost-effective Li–O₂ batteries, carbon materials are typically regarded as ideal cathodes in these systems. However, the impact of their surface properties—which often regulate specific discharge pathways—on the RM-mediated oxygen reduction reaction (ORR) remains unclear. In this study, CNTs electrodes with different surface properties are fabricated. Results suggest that CNTs with more surface defects not only promote the unmediated discharge pathway even in RMs-involved battery systems but also exacerbate the corrosion of carbon cathodes. This, in turn, leads to the undesired accumulation of Li₂O₂ and Li₂CO₃ on the cathode surface, which hinders effective and continuous electron transfer between the cathode and RMs, ultimately decreasing the catalytic activity of RMs. As a result, the discharge capacity of the battery is seriously diminished, especially at large current densities. These findings underscore the significance of surface engineering in advancing the performance of RMs-assisted Li–O₂ batteries.