A Multifunctional Wood‐Derived Separator Towards the Problems of Semi‐Open System in Lithium‐Oxygen Batteries

Abstract The semi‐open system of lithium‐oxygen batteries (LOBs) results in electrolyte depletion, lithium anode corrosion, and by‐product deposition, and therefore represents a major challenge that hinders their application. Here, the aligned and open microchannel structures of wood are fabricated as separators to provide low‐tortuosity pathways for rapid ionic transport and serve as reservoirs for retaining the electrolyte by capillary forces to improve the electrochemical kinetics. In an open environment, the wood separator can hold 39% of the initial adsorption electrolyte capacity after 40 days, much higher than that of glass fiber (GF, 15%). The cellulose in the wood can confine the crossover effect of water thereby inhibiting the corrosion of lithium anode and reducing the deposition of by‐products. Density functional theory calculations certify that the abundant functional groups and uniform electron distribution in cellulose increase lithium‐ion concentration on the wood surface and promote lithium‐ion migration with a low diffusion barrier. LOBs composed of the wood‐derived separator displayed excellent anodic reversibility (over 1200 h) and effectively improved cathodic lifetime over 300 cycles (1.6 times longer than that of GF separator). These findings illustrate the significant potential of this candidate separator for high‐performance LOBs and are expected to be extended to metal‐air batteries.