Reversible multielectron transfer I−/IO3− cathode enabled by a hetero-halogen electrolyte for high-energy-density aqueous batteries

The ever-increasing need for energy-dense batteries with high safety is fuelling global research and innovations in new redox chemistry and device design. Here we show an aqueous battery employing highly concentrated hetero-halogen electrolytes that contain I− and Br-, resulting in a multielectron transfer process of I−/IO3−. The intermediate bromide species IBr and Br2, generated during the electrochemical process, enhances the reaction kinetics and alleviates the potential gap between oxidation and reduction. When using a 6 M I− electrolyte to achieve over 30 M electron transfers, the I−/IO3− cathode displayed a high specific capacity of over 840 Ah lcatholyte−1. A battery with Cd/Cd2+ as the anode demonstrated a high energy density of over 1,200 Wh lcatholyte−1. Even at an exceptionally high current density of 120 mA cm−2, an energy efficiency of 72% was obtained. Our work demonstrates that safe aqueous batteries with high energy density are possible, offering a development option for grid-scale energy storage and even electric vehicles. Aqueous batteries, such as iodide/iodate-based ones, confront challenges due to their low energy densities. Here the authors utilize hetero-halogen electrolytes to enable fast multielectron transfer, yielding high-energy-density aqueous batteries.