Dynamic Bifunctional Sites on a COF Enable Efficient Immobilization and Conversion of Iodine Species Toward Li‐Iodine Batteries

ABSTRACT

The thermodynamic instability of iodine cation (I ⁺ ) and shuttle effect of polyiodide in the two‐electron Li‐iodine (Li‐I ₂ ) batteries remain an unresolved bottleneck. The design and preparation of an advanced cathode capable of effectively anchoring and activating iodine species is a desirable but highly challenging target to overcome these issues. In this study, we strategically synthesized a pyridine‐functionalized COF (BPY‐COF‐HI) cathode that enables highly reversible multivalent transition of iodine (I ⁻ /I ⁰ /I ⁺ ) within Li‐I ₂ batteries. The pyridine sites reversibly switch between protonated state (NH ⁺ ) and neutral state (N), allowing them to anchor I ₃ ⁻ via electrostatic interactions and activate I ⁺ via halogen bonding, respectively. Benefiting from this dynamic bifunctional regulation driven by the single pyridine site, a carbon‐nanotube‐integrated composite cathode (BPY‐COF@CNT‐HI) delivers a high‐voltage discharge plateau at 3.58 V corresponding to the reversible I ⁺ /I ⁰ redox and achieves a gravimetric energy density of 642 Wh kg _I ⁻¹ at 0.3 A g ⁻¹ . Remarkably, the cathode maintains ultralong cycling stability over 8000 cycles at 2.0 A g ⁻¹ with an exceptionally low capacity fade of 0.0055% per cycle. This result widens perspectives for designing high‐performance cathodes for Li‐I ₂ batteries with two‐electron redox chemistry.