Polyiodide Confinement by Starch Enables Shuttle-Free Zn-Iodine Batteries.

Aqueous Zn-iodine (Zn-I 2 ) batteries have been regarded as a promising energy-storage system owing to their high energy/power density, safety, and cost-effectiveness. However, the polyiodide shuttling results in serious active mass loss and Zn corrosion, which limits the cycling life of Zn-I 2 batteries. Inspired by the chromogenic reaction between starch and iodine, a structure confinement strategy is proposed to suppress polyiodide shuttling in Zn-I 2 batteries by hiring starch, due to its unique double-helix structure. In situ Raman spectroscopy demonstrates an I 5 - -dominated I - /I 2 conversion mechanism when using starch. The I 5 - presents a much stronger bonding with starch than I 3 - , inhibiting the polyiodide shuttling in Zn-I 2 batteries, which is confirmed by in situ ultraviolet-visible spectra. Consequently, a highly reversible Zn-I 2 battery with high Coulombic efficiency (≈100% at 0.2 A g -1 ) and ultralong cycling stability (>50 000 cycles) is realized. Simultaneously, the Zn corrosion triggered by polyiodide is effectively inhibited owing to the desirable shuttling-suppression by the starch, as evidenced by X-ray photoelectron spectroscopy analysis. This work provides a new understanding of the failure mechanism of Zn-I 2 batteries and proposes a cheap but effective strategy to realize high-cyclability Zn-I 2 batteries.