Enabling a Reversible Six-Electron Redox Reaction Based on I−/I+ and Br−/Br0 for Aqueous Zinc-Bromine Batteries

Zinc-halogen batteries are usually based on two-electron transfer reactions from X− to X2. However, the halogen is capable of being further oxidized to higher valence states, thereby achieving the higher capacity of zinc- halogen batteries. Here, a six-electron reaction based on I−/I+ and Br−/Br0 is activated successfully by introducing KI into the electrolyte. ZIF-8-derived porous carbon (ZPC), serving as the host of halogen, effectively suppresses polybromide/polyiodide shuttle owing to the chemisorption/physical adsorption. Additionally, the adsorption of I− on the surface of the zinc anode effectively inhibits the growth of dendrites and the formation of by-products. Consequently, zinc-bromine batteries exhibit outstanding electrochemical performance, including a specific capacity of 345 mAh g−1 at 1 A g−1 and an excellent capacity retention of 80% after 3000 cycles at 2 A g−1. This strategy provides a novel way for enhancing the electrochemical performance of zinc-halogen batteries.