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

The uncontrolled Zn²⁺ 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 (─SO₃H) 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 ─SO₃H 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/V₂O₅ 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.