How to develop a homogeneous redox mediator (RM) towards both ORR and OER and how to prevent the shuttle effect are two main issues for Li-O₂ batteries thus far. Here, we firstly report 1,2-dimethyl-3-propylimidazolium iodide (DMPII), which serves multiple functions as a RM for discharge capacity promotion, a RM for charge potential reduction, and a Li anode protector for shuttling suppression by in situ generating a “self-defensed” SEI layer. Benefiting from these advantages, a cell with DMPII displays a stable cyclability with a low terminal charge potential of ∼ 3.6 V till the cell death, a considerable rate performance, and a good reversibility associated with Li₂O₂ formation and degradation. Based on the experimental and density functional theory (DFT) calculation results, a working mechanism for a cell operation is also proposed. These results represent a promising progress in the development of multiple-functional RM for Li-O₂ batteries. Moreover, we expect that this work gives an insight into the in situ protection of Li metal anode for board applications (e.g., Li-S batteries, all-solid-state Li-ion batteries, etc.).