A Hydrophilic Sulfonated Polyethersulfone Separator Enables Highly Reversible Zn Anode in Aqueous Zinc‐Ion Batteries

ABSTRACT The uncontrolled Zn 2+ deposition on the surface of Zn metal anode remains a critical challenge in the development of zinc‐ion batteries (ZIBs). Here, a novel separator featuring negatively charged sulfonic acid groups (─SO 3 H) and strong hydrophilicity is reported to promote ion conduction and solvation stability. Through systematic experimental investigations and density functional theory, it is demonstrated that the water‐retaining effect of the ─SO 3 H group effectively suppresses side reactions and reduces the desolvation energy barrier, thereby establishing a hydrogen‐bond‐mediated ion transport channel. As a result, the Zn/Zn symmetric cells with sulfonated polyethersulfone (SPES) nanofiber separator demonstrate a long‐term stability over 4400 h under stepwise current densities of 0.5/2.5/4 mA cm −2 . Meanwhile, the Zn/V 2 O 5 cells exhibit excellent long‐cycle life, maintaining 96.2% capacity retention after 2250 cycles at 1 A g −1 . This work offers a new way to further reduce the cost and promote the industrial application of ZIBs.