Dual‐Mechanism Aqueous Battery with I − /I 2 Redox and Bi/BiOI Conversion

Abstract Aqueous zinc–iodine batteries are considered as promising energy storage device, but the severe shuttle effect of polyiodide species limits their cycling life. The conventional physical adsorption has a limited effect in preventing polyiodide shuttling. Herein, a dual strategy of physical adsorption and chemical confinement is performed through nitrogen/boron dual‐doped carbon nanofiber‐encapsulated bismuth nanoparticles. In situ characterizations and theoretical calculations confirm that the nitrogen and boron co‐doping endows carbon nanofibers with strong physical adsorption for iodine species, hindering polyiodide shuttling. A robust chemical confinement is realized by Bi/BiOI conversion, proved by ex situ tests and suppressing the formation of polyiodide. Moreover, Bi nanoparticles are restricted to carbon nanofibers, the charge transfer and structural stability of electrode are improved with the help of 3D conductive network. Therefore, the elaborate dual‐mechanism aqueous batteries deliver a high reversible capacity of 275 mA h g −1 at 0.5 A g −1 , an excellent rate performance with 207 mA h g −1 at 10 A g −1 , and a long‐term cycle life over 2000 cycles. Remarkably, high mass loading electrode (10 mg cm −2 ) and flexible pouch cell still display satisfactory performances. This work provides a new idea to design host with strong physicochemical confinement for iodine species.