Promoting Li–O ₂ Batteries With Redox Mediators

Li–O ₂ batteries have a high theoretical specific energy, 3500 Wh kg ⁻¹ ; however, its practical capacity is far below this value and limited by the passivation with the insulating discharge product Li ₂ O ₂ . The nonconductive nature of Li ₂ O ₂ also impedes the charging process, leading to a low coulombic efficiency and high overpotential on charge even at a moderate rate. To address these challenges, redox mediators could be used both during discharge and charge to transfer electrons between O ₂ /electrode surface or Li ₂ O ₂ /electrode surface to overcome the passivation of Li ₂ O ₂ , which would facilitate the discharge and charge process. The capacity and current density were significantly improved using the redox mediators, thus representing a promising strategy to achieve a high energy density for Li–O ₂ batteries.