Electron-rich N/S-functionalized covalent organic frameworks for polyiodide immobilization in aqueous zinc-iodine batteries

Aqueous zinc-iodine batteries (AZIBs) are regarded as promising energy storage devices owing to their high theoretical capacity, low cost, and high safety. However, severe capacity fading caused by slow reaction kinetics and the shuttle effect of polyiodides (I 3 − and I 5 − ) greatly limits their practical application. To address these issues, we synthesized two covalent organic frameworks COF-NS1 and COF-NS2 with different densities of electron-rich heteroatoms via a Schiff base reaction. The highly conjugated framework structures and abundant electron-rich heteroatoms (N and S) effectively suppress the polyiodide shuttle effect and promote redox activity. Experimental and theoretical investigations demonstrate that COF-NS2 exhibits more favorable polyiodide confinement and redox kinetics than COF-NS1. These differences arise from the combined effects of the framework structure, including electron-rich heteroatom density, specific surface area, and crystallinity, with the higher density of electron-rich heteroatom sites in COF-NS2 making an important contribution. Consequently, I 2 @COF-NS2 delivers a high specific capacity of 263 mAh g −1 at 1 C and maintains 80% of its capacity after 8000 cycles at 5 C. The excellent polyiodide confinement capability and electrochemical performance of the I 2 @COF-NS2 cathode provide new insights for further exploration of COFs as electrode materials for AZIBs.