Synergistic Catalysis by Single-Atom Catalysts and Redox Mediator to Improve Lithium-Oxygen Batteries Performance.

Lithium-oxygen (Li-O2 ) batteries with ultrahigh theoretical energy density have attracted widespread attention while there are still problems with high overpotential and poor cycle stability. Rational design and application of efficient catalysts to improve the performance of Li-O2 batteries is of significant importance. In this work, Co single atoms catalysts are successfully combined with redox mediator (lithium bromide [LiBr]) to synergistically catalyze electrochemical reactions in Li-O2 batteries. Single-atom cobalt anchored in porous N-doped hollow carbon spheres (CoSAs-NHCS) with high specific surface area and high catalytic activity are utilized as cathode material. However, the potential performances of batteries are difficult to adequately achieve with only CoSAs-NHCS, owing to the blocked electrochemical active sites covered by insulating solid-state discharge product Li2 O2 . Combined with LiBr as redox mediator, the enhanced OER catalytic effect extends throughout all formed Li2 O2 during discharge. Meantime, the certain adsorption effect of CoSAs-NHCS on Br2 and Br3 - can reduce the shuttle of RMox . The synergistic effect of Co single atoms and LiBr can not only promote more Li2 O2 decomposition but also reduce the shuttle effect by absorbing the oxidized redox mediator. Li-O2 batteries with Co single atoms and LiBr achieve ultralow overpotential of 0.69 V and longtime stable cyclability.