Triazine and Hydroxyl Covalent Organic Framework Modified Separator for Zn-ion Fast and Selective Transport and Dendrite-Free Deposition in Zinc–iodine Battery

Aqueous zinc–iodine (Zn–I) batteries show a great development potential in the field of energy storage due to their advantages of low cost, high safety and ecological friendliness. However, Zn dendrite growth and shuttle effect of polyiodide seriously aggravate the self-discharge behavior and thus decrease the cycle life of batteries. Therefore, controlling the diffusion of zinc ion and inhibiting soluble polyiodide in the separator are the most effective strategy to extend the lifespan of batteries. Herein, we design and prepare a multifunctional Janus separator composed of a covalent organic framework (COF) layer, a commercial glass fiber (GF) substrate and a graphene (Gr) layer to achieve durable Zn–I batteries. The COF layer features abundant polar groups and uniform open-channel mesopores enabling homogeneous Zn2+ flux and simultaneously inhibiting polyiodide species migration. The highly conductive Gr layer can not only load iodide but also effectively activate the redox kinetics of iodine species. The full cell assembled with the TTA-DHTPA-COF@GF@Gr Janus separator demonstrated a recorded energy density of up to 6.4 mA h·cm−2 at a high current density of 20 mA cm−2 in aqueous Zn–I batteries. The design of the multifunctional Janus separator provides a new insight into separator engineering for durable Zn-ion batteries.