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

Abstract

The redox couple of I0/I− in aqueous rechargeable iodine–zinc (I2-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 (I3− and I5−) 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 I0/I− conversion efficiency of an I2-Zn battery is clearly enhanced. According to the detailed characterizations and theoretical DFT calculation results, the enhancement of I0/I− conversion efficiency is mainly originated from the strong bonding between the charged products of I3− and I5− and the rich hydroxyl groups in starch. This work provides inspiration for the rational design of high-performance and low-cost I2-Zn in AZIBs.