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

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 Zn²⁺ transport, and passivation/corrosion reactions caused by SO₄ ^2-/H₂O. These issues typically lead to capacity degradation and shortened cycle life. By sequentially modifying a glass fiber separator with bacterial cellulose and Ti_0.87O₂ nanosheets, the Zn²⁺ flux is effectively homogenized, while the migration of harmful ions to the zinc anode surface is suppressed. Negatively charged Ti_0.87O₂ nanosheets with Ti vacancies contribute to a high Zn²⁺ 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||V₂O₅ full cells deliver a high specific capacity of 278.9 mAh g^-1 at 1 A g^-1, while high-mass-loading Zn/I₂ 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.