Covalent Organic Frameworks Coupled with Redox Center and Adsorption Site for Efficient Shuttle-Free Zn-Iodine Batteries.

Aqueous zinc-iodine (Zn-I) batteries exhibit significant potential for next-generation energy storage system, but the polyiodide shuttle effect severely impairs their performance and stability. Herein, a series of woven covalent organic frameworks (COFs), namely COF-RuNCS-X (X = 1-6), with pre-designed ruthenium(II) redox center and sulfur adsorption sites were constructed for shuttle-free cathode material in Zn-I batteries. The porous COF-RuNCS-X with abundant sulfur adsorption sites showed a selective adsorption of I species for effectively mitigating the shuttle effect. Meanwhile, the incorporation of ruthenium(II) center into the COFs skeleton enhanced the redox kinetics of iodine species. Remarkably, COF-RuNCS-6 featuring the large pore size and high degree of conjugation demonstrated a discharge specific capacity as high as 395.8 mAh g in Zn-I batteries and exhibited cycle stability up to 5000 cycles. This work provides a new understanding of the design of COF-based materials as efficient shuttle-free cathode materials for Zn-I batteries.