A bifunctional MnxCo3-xO4-decorated separator for efficient Li-LiI-O2 batteries: A novel strategy to promote redox coupling and inhibit redox shuttling

Although redox mediator (RM) strategy can decrease the overpotential in Li-O 2 batteries by tuning the electrochemical formation/degradation of Li 2 O 2 from the circumscribed surface pathway to the solution one, the redox shuttling causes an unexpected RM degradation and a continuous deterioration of Li anode, finally leading to a poor cyclability. This work presents the first report detailing the development of a novel Mn x Co 3-x O 4 -decorated separator for Li-LiI-O 2 batteries. Benefiting from the promotion effect of Mn x Co 3-x O 4 nanocages on I − /I 3 − and I 3 − /I 2 redox coupling, the cell with as-prepared separator maintains a low charge potential of ~3.3 V till the death of cell cycling. In addition, as-prepared separator can efficiently restrain the redox shuttling, leading to an obvious improvement on cycling stability for the cell. Moreover, the contributions of LiI to the battery performance and the operation mechanism are systematically investigated. These results present a promising progress in the development of multi-functional separator materials for RM-involved Li-O 2 batteries and the new design of hybrid energy storage device.