A soluble phenolic mediator contributing to enhanced discharge capacity and low charge overpotential for lithium-oxygen batteries

In this study, a phenolic antioxidant of 2,6-di-tert-butyl-hydroxytoluene (BHT) is applied in Li-O₂ batteries to simultaneously improve discharge capacity and reduce charge overpotential. BHT exhibits a redox couple at ~ 3.0 V (vs. Li⁺/Li), which is extremely close to the thermodynamic potential of a Li-O₂ battery (2.96 V). The unique chemical and electrochemical behaviors of BHT contribute to the improvement on both oxygen reduction reaction and oxygen evolution reaction performances. These factors lead to the notable enhancement of discharge capacity (capacity increases by 72%) and the reduction of charge plateau (the plateau is 3.2 V and 4.2 V, respectively, with and without BHT) for Li-O₂ batteries. Furthermore, in-situ X-ray diffraction results confirm that the BHT-mediated formation and decomposition of Li₂O₂, rather than parasitic reactions, dominate the discharge and charge processes. The results provide a new approach for exploiting appropriate soluble mediators for rechargeable Li-O₂ batteries.