High-Energy Density Aqueous Zinc–Iodine Batteries with Ultra-long Cycle Life Enabled by the ZnI2 Additive

Aqueous zinc–iodine batteries, featuring high energy density, safety, and cost-effectiveness, have been regarded as a promising energy storage system. Nevertheless, poor cycling stability and dissolution of iodine/polyiodide have greatly limited the development of zinc–iodine batteries. Here, iodine encapsulated by hierarchical porous carbon is employed as a positive material to assemble high-performance zinc–iodine batteries. Meanwhile, the utilization of the ZnI2 additive in the electrolyte can enhance the capacity and cycling stability of as-assembled devices because the existence of polyiodide (I3– and I5–) can effectively inhibit the dissolution of iodine. Thanks to the high conductivity and interconnected structure of the prepared carbon material, the as-assembled zinc–iodine batteries deliver an excellent specific capacity of 360.6 mA h g–1 at 0.5 C, a superb durability (∼98.4% retention of the initial capacity at a high density of 50 C after 35,000 cycles), and an ultra-high energy/power density of 422.6 W h kg–1/21.6 kW kg–1. Significantly, the mechanism of the constructed device was investigated by ex-situ Raman and ex-situ X-ray diffraction. Besides, when coupling carbon@I2 electrodes with the hydrogel electrolyte to assemble quasi-solid-state zinc–iodine batteries, the as-built device can well service for an electronic clock.