A Multiscale Ion‐Sieving Separator Toward Long‐Cycling Aqueous Zinc‐Based Batteries

Abstract A sandwich‐structured composite separator integrating ion selectivity and multi‐size sieving capabilities has been developed. Aqueous zinc‐ion batteries benefit from this ion modulation strategy, which effectively prevents the migration of undesired ions, non‐uniform Zn 2+ transport, and passivation/corrosion reactions caused by SO 4 2− /H 2 O. These issues typically lead to capacity degradation and shortened cycle life. By sequentially modifying a glass fiber separator with bacterial cellulose and Ti 0.87 O 2 nanosheets, the Zn 2+ flux is effectively homogenized, while the migration of harmful ions to the zinc anode surface is suppressed. Negatively charged Ti 0.87 O 2 nanosheets with Ti vacancies contribute to a high Zn 2+ transference number, accelerated desolvation, and provide atomic‐scale ion‐sieving capabilities. Notably, Zn||Zn symmetric cells equipped with this novel separator exhibit an extended cycling life at 1 mA cm −2 /1 mAh cm −2 and enable dense, dendrite‐free zinc deposition at 4 mA cm −2 /8 mAh cm −2 . Furthermore, Zn||V 2 O 5 full cells deliver a high specific capacity of 278.9 mAh g −1 at 1 A g −1 , while high‐mass‐loading Zn/I 2 full cells retain 97.1% of their capacity after 1600 cycles at 2 A g −1 . This ion modulation strategy offers valuable insights for the rational design and modification of separators toward dendrite‐free metal batteries.