High-Energy Density Aqueous Zinc–Iodine Batteries with Ultra-long Cycle Life Enabled by the ZnI 2 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 ZnI 2 additive in the electrolyte can enhance the capacity and cycling stability of as-assembled devices because the existence of polyiodide (I 3 – and I 5 – ) 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@I 2 electrodes with the hydrogel electrolyte to assemble quasi-solid-state zinc–iodine batteries, the as-built device can well service for an electronic clock.