Cathode Design via Iron-Coordinated Covalent Organic Frameworks Facilitating Four-Electron Transfer to Achieve High-Capacity Aqueous zinc–iodine Batteries
Songde Guo, Sanlue Hu, Senlin Li, Dun Wang, Siqi Zhang, Lian‐Wei Luo, Hong Guo, Yagang Yao, Cuiping Han
Abstract
The variable valence states of iodine(I) render Zn–I 2 batteries an intriguing area of research. However, current Zn–I 2 batteries are mostly based on I – /I 0 redox chemistry. Effective strategies for activating the high-voltage I 0 /I + redox couple in iodine-based cathode materials remain relatively scarce. Herein, an iron (Fe)-coordinated porphyrin bipyridine covalent organic framework (PPBY-Fe-COF) is designed as a host material featuring Fe and conjugated C═N active sites to enable consecutive I – /I 0 /I + redox chemistry. I – migrate to cationic Fe sites for oxidation to I 0, followed by its immobilization on anionic C═N groups. Assisted by OTF –, the formation of N–I + –O bonds suppresses the I + hydrolysis tendency, enabling reversible redox reactions. Consequently, the four-electron transfer Zn||I@PPBY-Fe-COF battery exhibited a specific capacity of 240 mAh g I –1 (based on iodine loading) at 1 A g –1 and a capacity retention of 90.9% after 8000 cycles. This work presents an effective methodology for developing high-energy-density aqueous Zn–I 2 battery systems.