Boosting Reversible Four-Electron Redox in Aqueous Zn-Iodine Batteries with Two Halogen Ionic Additives and a N, F Codoped Carbon Cathode

Recent interest has focused on aqueous zinc–iodine batteries (AZIBs), yet their practical application is hampered by their limited capacity and energy density. To overcome these limitations, we report herein AZIBs with improved electrochemical performance by incorporating two halogen-containing ionic additives (0.1 M ZnI2 and 0.1 M ZnBr2) into the ZnSO4 electrolyte. Importantly, unlike previously reported approaches, nitrogen and fluorine codoped porous carbon (N/F-PC) can be directly utilized as the cathode material for AZIBs without the need for preloading iodine. This allows the full utilization of its rich porous structure, thereby promoting the four-electron redox reaction (based on the iodine molecule) and facilitating the conversion between I– and I+. Besides, bromide (Br–) is introduced to activate iodine species by stabilizing I+ through the formation of interhalogen bonds. The resulting AZIBs display two distinct discharge plateaus at 1.55 and 1.15 V, corresponding to reversible redox reactions among I–/I0/I+. In contrast, the control electrolyte without ZnBr2 additive exhibits only a single plateau at 1.15 V. Consequently, the N/F-PC-based AZIBs demonstrate a large specific capacity of 452.6 mAh g–1 and a huge energy density of 584.1 Wh kg–1, significantly outperforming conventional Zn-iodine batteries based on I–/I0. The strategy presented in this study may pave the way for the development of high-energy-density aqueous electrochemical storage devices.