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 I2 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.