Controlling Solid–Liquid Conversion Reactions for a Highly Reversible Aqueous Zinc–Iodine Battery

Aqueous rechargeable batteries are desirable for energy storage because of their low cost and high safety. However, low capacity and short cyclic life are significant obstacles to their practical applications. Here, we demonstrate a highly reversible aqueous zinc–iodine battery using encapsulated iodine in microporous carbon as the cathode material by controlling solid–liquid conversion reactions. We identified the factors influencing solid–liquid conversion reactions, e.g., the pore size, surface chemistry of carbon host, and solvent effect. Rational manipulation of the competition between the adsorption in carbon and solvation in electrolytes for iodine species is responsible for the high reversibility and cyclic stability. The zinc–iodine battery delivers a high capacity of 174.4 mAh g–1 at 1C, stable cyclic life over 3000 cycles with ∼90% capacity retention, and negligible self-discharge. We believe that the principles for stabilizing the zinc–iodine system could provide new insight for other conversion systems such as lithium–sulfur systems.