Research Progress on Iodine Host Materials for Zinc‒Iodine Batteries

Zinc‒iodine (Zn‒I₂) batteries have been extensively explored, owing to the merits including high specific capacity (211 mAh•g⁻¹), ideal redox potential (~0.54 V vs. H⁺/H), high safety, reserve abundance in earth for zinc and iodine and low costs. However, Zn‒I₂ batteries also suffer from several drawbacks, such as low electrical conductivity of iodine and polyiodides, easy dissolution of intermediates in electrolyte, slow conversions of polyiodides and shuttle effect. Currently, the most efficient strategy for resolving these issues is constructing iodine hosts with unique structures. The recent progress on host materials of iodine cathode in Zn‒I₂ batteries was systematically reviewed from the aspects of design concept, constructing approaches, working principles and electrochemical performance, and the inside performance-structure relationships between the compositions, structure and morphology of iodine hosts and the electrochemical performance of Zn‒I₂ batteries was investigated, and the synergistic effects between the physical confinements and chemical adsorption/catalytic effect of host materials to the enhancement of electrochemical performance was revealed. Lastly, based on the remaining existed issues for iodine hosts, the possible development directions in the future were pointed out, such as exploring reaction mechanisms, promoting intermediate conversions, assemble and testing of soft-package batteries, and so on.