Interfacial Engineering of Ion‐Sieving Sodium Alginate/Halloysite Nanotubes Modified Cellulose Separator for Ultra‐Stable Aqueous Zinc‐Ion Batteries

Abstract Aqueous zinc‐ion batteries (AZIBs) attract growing attention as promising alternatives for large‐scale energy storage. However, the Zn dendrite growth and parasitic side reactions, caused by inhomogeneous Zn 2+ ion flux and anion shuttling, severely hinder the practical application of AZIBs. Herein, a sustainable, low‐cost Janus separator is reported by anchoring sodium alginate (SA)‐composited halloysite nanotubes (HNTs) onto one side of cellulose filter paper. The oppositely charged architecture of HNTs with ion‐sieving function facilitates rapid Zn 2+ transport while effectively restricting anion shuttling. The SA matrix with abundant hydrophilic functional groups and strong Zn 2+ affinity captures free water molecules through hydrogen bonding, and homogenizes Zn 2+ ion flux at the interface, thereby mitigating side reactions. Moreover, the interlocked structure between SA and HNTs regulates the pore structure of cellulose fibers, ensuring efficient Zn 2+ desolvation and enhanced Zn 2+ transport kinetics. This synergistic ion regulation mechanism enables exceptional cycling stability in Zn||Zn symmetric cells, achieving over 2000 h at room temperature and 1800 h at a low temperature of −10 °C. This work provides a practical, cost‐effective, and environmentally friendly solution for suppressing Zn dendrite growth and side reactions, thereby advancing the development of multi‐functional separators toward sustainable AZIBs.