Water‐Capture Filter Paper Separator Realizing Ambient Li–Air Battery

Abstract Lithium–air battery (LAB) is regarded as one of the most promising energy storage systems. However, the challenges arising from the lithium metal anode have significantly impeded the progress of LAB development. In this study, cellulose‐based filter paper (FP) is utilized as a separator for ambient Li–air batteries to suppress dendrite growth and prevent H 2 O crossover. Thermogravimetric analysis and molecular spectrum reveal that FP enables ambient Li–air battery operation due to its surface functional groups derived from cellulose. The oxygen‐enriched surface of cellulose not only enhances ion conductivity but also captures water and confines solvent molecules, thereby mitigating anode corrosion and side reactions. Compared with commercial glassfiber (GF) separator, this cellulose‐based FP separator is cheaper, renewable, and environmentally friendly. Moreover, it requires less electrolyte while achieving prolonged and stable cycle life under real air environment conditions. This work presents a novel approach to realizing practical Li–air batteries by capturing water on the separator's surface. It also provides insights into the exploration and design of separators for enabling practical Li–air batteries toward their commercialization.