Li–O2 batteries attract extensive attention because they exhibit the highest theoretical energy density among the rechargeable batteries reported so far. However, most studies have focused on improving the cyclability and efficiency of Li–O2 batteries under low-capacity conditions instead of under practical conditions. Here, we increase the capacity range of Li–O2 batteries to a practical condition of 5 mA h cm−2 by introducing CF3(CF2)2I as a dual-functional additive. An electrolyte comprising 1 M LiNO3 in N,N-dimethylacetamide and CF3(CF2)2I provides stable cycle retention and high reversibility even at high areal capacity. Ab initio molecular dynamics simulations demonstrate that the reaction between CF3(CF2)2I and Li metal is spontaneous and leads to the simultaneous formation of LiF as a protective layer on Li metal and LiI as a redox mediator for the oxygen evolution reaction. This study provides new insights for the development of electrolyte additives toward practical Li–O2 batteries.