Advanced Zinc–Iodine Batteries with Ultrahigh Capacity and Superior Rate Performance Based on Reduced Graphene Oxide and Water‐in‐Salt Electrolyte

Abstract Aqueous rechargeable zinc–iodine batteries have received increasing attention in the field of portable electronics due to their high safety, low‐cost, and great electrochemical performance. However, the insulated nature of iodine and the unrestricted shuttle effect of soluble triiodide seriously limit the lifespan and Coulombic efficiency (CE) of the batteries. Herein, a high‐performance zinc–iodine energy storage system based on the hydrothermal reduced graphene oxide (rGO) and a high concentration zinc chloride water‐in‐salt electrolyte are promoted. The 3D microporous structures and outstanding electrical conductivity of rGO make it an excellent host for iodine, while the water‐in‐salt electrolyte effectively suppresses the shuttle effect of triiodide and improves the CE of the system. As a result, an ultra‐high I 2 mass loading of 25.33 mg cm −2 (loading ratio of 71.69 wt.%) is realized during the continuous charging/discharging process. The batteries deliver a high capacity of 6.5 mAh cm −2 at 2 mA cm −2 with a much‐improved CE of 95% and a prominent rate performance with capacity of 1 mAh cm −2 at 80 mA cm −2 . A stable long‐term cycling performance is also achieved with capacity retention of 2 mAh cm −2 after 2000 cycles at 50 mA cm −2 .