Rational design of redox mediators for advanced Li-O₂ batteries

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 Li 2 O₂ 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.