Ultrathin, Tough Asymmetric MOF‐Based Separator Enabling Rapid Selective Ion Transport and Stable Aqueous Zn‐Ion Batteries

ABSTRACT For traditional thick and brittle separator in aqueous zinc‐based batteries, it fails to effectively regulate the electrochemical transport and reaction behaviors at the electrode–electrolyte interface, especially for uncontrolled dendrite growth and side reactions. To address these issues, we heterostructurally engineered a flexible, ultrathin and tough Asymmetric separator, featuring a uniform, densely‐integrated micropore layer of conductive Ni‐based metal organic framework (c‐MOF) in situ grown on a hydrophilic bacterial cellulose membrane (BCM) with typical macropore distribution. The substrate of BCM provides superior mechanical strength, flexibility and electrolyte absorption capacity, and the microporous c‐MOF layer regulates Zn ^{2 +} transport and disfavors the migration of bulky hydrated or anion‐associated species through confined ion channels. Additionally, the continuous c‐MOF layer ensures a uniform electric field distribution across the separator, which promotes homogeneous zinc plating at the anode. The Zn//VO ₂ batteries equipped with Asymmetric BCM@c‐MOF separator deliver superior rate performance and capacity retention, together with an enhanced energy density compared with cells using conventional separators. Moreover, the separator markedly enhances electrochemical stability, enabling stable operation over 1200 h at 10 mA cm ⁻² and 2 mAh cm ⁻² with low voltage polarization. This research unlocks a conceptual innovation for advanced separator design to enabling high‐performance aqueous zinc‐based batteries.