Electron-outflowing heterostructure hosts for high-voltage aqueous zinc-iodine batteries

Abstract

Enhancing the energy density is an imperative challenge in the advancement of aqueous zinc-iodine (Zn-I2) batteries, which hold great promise for grid energy storage systems. Achieving the reversible conversion reaction of high-valence iodine species, particularly I+/I0 redox chemistry, offers a substantial potential for improved energy density. In this study, we introduce a novel method of employing electron-outflowing heterostructured hosts to stabilize I+ ions in aqueous halide-free ZnSO4 electrolytes. Both experimental analyses and density functional theory (DFT) calculations reveal that the stabilization of thermodynamically unstable I+ cations originates from the charge transfer interaction between I+ ions and copper phthalocyanine (CuPc) within the hosts. The electron-outflowing effect resulting from the π-π conjugation between CuPc and the carbon framework in heterostructured hosts further intensifies the charge transfer interaction, leading to the reversible I+/I5− conversion reaction in Zn-I2 batteries. Consequently, this emerging redox reaction, validated by in-situ Raman and ex-situ ultraviolet-visible spectroscopy, introduces another voltage plateau at ∼1.6 V and enhances the energy density to 233.8 Wh kg–1 at 3.0 A g–1. This work showcases outstanding electrochemical performance for the Zn-I2 battery, providing valuable insights into advancing iodine redox chemistry featuring multiple electrons.