Tightly confined iodine in surface-oxidized carbon matrix toward dual-mechanism zinc-iodine batteries

The dissolution of iodine species into the aqueous electrolyte is an inevitable issue in zinc-iodine (Zn-I2) battery, leading to its fading capacity and inferior cycle life. Herein, the porous oxidized salt-templated carbon (OSTC) with abundant carbonyl groups is prepared by using H2O and ZnCl2 as gasification agent/oxidant and salt-template, respectively. The synergistic effect of oxygen-containing functional group and unique pore structure in OSTC makes it a promising host to confine iodine tightly, resulting in the extraordinary cycling stability (a high capacitance retention of 85.04% after 10,000 cycles) and excellent rate performance for the as-assembled Zn-I2 battery. Experimental ex-situ and in-situ characterizations, and theoretical calculations (density functional theory calculation and COMSOL Multiphysics simulation) are conducted jointly to reveal its dual energy storage mechanisms: (1) only one-step redox reaction between I2 and I− can be observed without any appearance of I3− intermediates that is beneficial to increasing the utilization of iodine; (2) the abundant C=O groups on the OSTC surface can also react with the Zn2+ ions to form C-O-Zn group and provide extra pseudocapacity for Zn-I2 battery. This work not only presents a high-performance cathode for Zn-I2 battery, but also sheds light on possible strategies for other metal-I2 batteries.