An electropolymerized poly(1,10-phenanthroline)–iodine complex as a high-capacity and stable cathode for zinc–iodine batteries

Abstract

Rechargeable zinc–iodine batteries (ZIBs) have emerged as promising energy storage systems due to their high energy density, low cost, and inherent safety. However, the severe dissolution of active iodine and the shuttle effect of polyiodides (I₃⁻ and I₅⁻) significantly hinder the capacity retention and cycling stability of ZIBs. To address this issue, this study utilizes iodide ions (I⁻) as iodine precursors and adopts a one-step electropolymerization method to co-deposit 1,10-phenanthroline (Phen) and zinc iodide (ZnI₂) onto carbon paper (CP), resulting in the PPhen-I/CP-2 composite cathode material with uniformity, high conductivity, and excellent stability. This method in situ forms a conductive polymer matrix that interacts with active iodine species, significantly simplifying the traditional preparation process of the cathode. The developed PPhen-I/CP-2 composite material demonstrates excellent iodine species confinement capability. The extended π-conjugated structure and abundant nitrogen sites in PPhen strongly interact with polyiodides, effectively suppressing iodine dissolution and the shuttle effect, thereby enhancing the cycling stability of zinc–iodine batteries. As a result, compared to the single I/CP, the integrated composite cathode based on PPhen-I/CP-2 exhibits superior electrochemical performance: a high specific capacity of 270 mAh g⁻¹ at 0.2 A g⁻¹ was achieved, combined with a capacity retention of 90%; even at a high current density of 2 A g⁻¹, the capacity remains at 160 mAh g⁻¹ after 3000 cycles, with a coulombic efficiency close to 98%. This study provides a novel strategy for the rational design of polymer-based materials for advanced energy storage applications.