Enhanced Cycling Stability of Lithium–Oxygen Batteries through a Bilayer Solid Polymer Electrolyte with Independent Anode Protection and Cathode Activation

Lithium–oxygen batteries (LOBs) are promising next-generation energy storage systems owing to their high theoretical energy density (~3500 Wh kg^-1). However, their practical use is limited by electrolyte instability, reactive oxygen species (ROS)-induced degradation, and redox mediator (RM) shuttle effects at the lithium metal anode. Here, we report a bilayer solid polymer electrolyte (SPE) based on poly(arylene ether sulfone)-graft-poly(ethylene glycol) (PAES-g-PEG) with layer-specific interfacial functions. The SPE was fabricated using succinonitrile (SN), tetraethylene glycol dimethyl ether (TEGDME), LiTFSI, LiI, and fluoroethylene carbonate (FEC), enabling self-assembled microphase separation with high ionic conductivity and mechanical stability. The optimized 7:3 SN@TEGDME composition provided balanced ion transport and oxygen diffusion for stable LOB operation. In the bilayer structure, the cathode-facing layer contained LiI to facilitate Li₂O₂ decomposition, while the anode-facing layer protected the lithium metal by suppressing iodide shuttle and dendrite growth. As a result, the bilayer SPE enabled stable lithium plating/stripping for over 2000 h in symmetric Li|SPE|Li cells. In Li|SPE|RuO₂@graphene/Ni foam cells, it maintained reversible cycling for over 200 cycles at 0.5 A g^-1, significantly outperforming the single-layer SPE. These results demonstrate that layer-specific interfacial engineering of SPEs is an effective strategy for improving the stability and cycling durability of lithium–oxygen batteries.