A Multifunctional Mesoporous Janus Separator With Optimized Mass Transport Regulation Enabling 800‐Cycle Lithium‐Oxygen Batteries

ABSTRACT Lithium‐oxygen batteries (LOBs) deliver ultrahigh theoretical specific energy but suffer from limited cycle life caused by lithium dendrite growth, anode corrosion, and cathode passivation. Developing interfacially compatible functional separators is an effective solution, yet coordinating fast ion conduction and multi‐species mass transport regulation remains challenging. We design an asymmetric multifunctional mesoporous Janus separator (mGP), consisting of a ∼ 3.16 nm mesoporous silica (mSiO 2 ) layer and dense, hydrophobic, mechanically tough polyurethane (PU). Via steric confinement, the mSiO 2 nanochannels optimize mass transport behavior: they homogenize Li + flux and accelerate ion transport, suppress intermediate crossover to alleviate the shuttle effect and cathode passivation. The PU layer prevents dendrite piercing, buffers lithium volume variation, and suppresses water‐ and intermediate‐triggered anode corrosion via hydrophobicity. Li||Li symmetric cells with mGP run stably for 1300 h at 0.1 mA cm −2 . LOBs based on mGP achieve exceptional cycling stability: over 800 cycles at 1000 mAh g −1 and 100 cycles at 3000 mAh g −1 , outperforming traditional glass fiber (GF) separators. This work provides a feasible strategy for constructing high‐performance long‐cycle LOBs through deliberate mass transport optimization.