Lithium-oxygen (Li-O₂) batteries have a great potential in energy storage and conversion due to their ultra-high theoretical specific energy, but their applications are hindered by sluggish redox reaction kinetics in the charge/discharge processes. Redox mediators (RMs), as soluble catalysts, are widely used to facilitate the electrochemical processes in the Li-O₂ batteries. A drawback of RMs is the shuttle effect due to their solubility and mobility, which leads to the corrosion of a Li metal anode and the degradation of the electrochemical performance of the batteries. Herein, we synthesize a polymer-based composite protective separator containing molecular sieves. The nanopores with a diameter of 4 Å in the zeolite powder (4A zeolite) are able to physically block the migration of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) molecules with a larger size; therefore, the shuttle effect of TEMPO is restrained. With the assistance of the zeolite molecular sieves, the cycle life of the Li-O₂ batteries is significantly extended from ~ 20 to 170 cycles at a current density of 250 mA·g⁻¹ and a limited capacity of 500 mAh·g⁻¹. Our work provides a highly effective approach to suppress the shuttle effects of RMs and boost the electrochemical performance of Li-O₂ batteries.