Enhancing I0/I- Conversion Efficiency by Starch Confinement in Zinc-Iodine Battery

The redox couple of I-0/I- in aqueous rechargeable iodine-zinc (I-2-Zn) batteries is a promising energy storage resource since it is safe and cost-effective, and provides steady output voltage. However, the cycle life and efficiency of these batteries remain unsatisfactory due to the uncontrolled shuttling of polyiodide (I-3(-) and I-5(-)) and side reactions on the Zn anode. Starch is a very low-cost and widely sourced food used daily around the world. "Starch turns blue when it encounters iodine" is a classic chemical reaction, which results from the unique structure of the helix starch molecule-iodine complex. Inspired by this, we employ starch to confine the shuttling of polyiodide, and thus, the I-0/I- conversion efficiency of an I-2-Zn battery is clearly enhanced. According to the detailed characterizations and theoretical DFT calculation results, the enhancement of I-0/I- conversion efficiency is mainly originated from the strong bonding between the charged products of I-3(-) and I-5(-) and the rich hydroxyl groups in starch. This work provides inspiration for the rational design of high-performance and low-cost I-2-Zn in AZIBs.