Size confinement strategy effect enables advanced aqueous zinc-iodine batteries

Aqueous Zn-I${}_2$ batteries have considerable potential owing to their environmental friendliness and high safety. However, the slow iodine conversion kinetics and shuttle effect prevent their practical applicability. In this study, a series of Zn-MOF-74 rods with controllable diameters of 40-500 nm are facilely prepared, denoted as P1-P5. A size confinement strategy effect of Zn-MOF-74 derived porous carbon as iodine hosts is proposed to suppress the formation of undesirable iodine species, such as I${}_3$${}^{-}$ and I${}_5$${}^{-}$. Moreover, the graphitization degree of porous carbon samples, including P2-900, P2-1000, and P2-1100, play a critical effect on the iodine conversion kinetics. The P2-1000 sample possesses a high conductive skeleton and abundant mesopores, which improve the adsorption ability toward iodine species. The electrochemical tests and the in situ technology reveal the size confinement strategy effect and the conversion mechanism of iodine. As a result, the I${}_2$@P2-1000 cathode exhibits a superior discharge capacity of 179.9 mA h g${}^{-1}$ at 100 mA g${}^{-1}$ and exceptional long-term cycle ability after 5000 cycles. Furthermore, the soft batteries and the flexible quasi-solid-state batteries are capable of powering devices, promising to exhibit tremendous adaptability and realize flexible electronic devices in various scenarios. (© 2024 Wiley‐VCH GmbH)