The discovery of effective catalysts is an important step towards achieving Li–O₂ batteries with long cycle life and high round-trip efficiency. Soluble-type catalysts or redox mediators (RMs) possess great advantages over conventional solid catalysts, generally exhibiting much higher efficiency. Here, we select a series of organic RM candidates as a model system to identify the key descriptor in determining the catalytic activities and stabilities in Li–O₂ cells. It is revealed that the level of ionization energies, readily available parameters from a database of the molecules, can serve such a role when comparing with the formation energy of Li₂O₂ and the highest occupied molecular orbital energy of the electrolyte. It is demonstrated that they are critical in reducing the overpotential and improving the stability of Li–O₂ cells, respectively. Accordingly, we propose a general principle for designing feasible catalysts and report a RM, dimethylphenazine, with a remarkably low overpotential and high stability.

Nature Energy 1, Article number: 16066 (2016)
doi:10.1038/nenergy.2016.66

http://www.nature.com/articles/nenergy201666