Halogen-confining host materials for high-performance zinc-halogen batteries

Zinc-halogen batteries hold great promise for grid-scale energy storage owing to their multi-electron transfer capability, abundant halogen resources, low cost and high theoretical voltage and capacity. However, they are still constrained by the sluggish redox kinetics of halogen species and the uncontrollable shuttling of polyhalide intermediates, which compromise energy efficiency and cycling stability. In this regard, the rational design of halogen-confining host materials has emerged as a promising strategy; however, a comprehensive review of this fast-evolving field is still lacking. This tutorial review begins with an overview of configurations and fundamental mechanisms of zinc-halogen batteries, followed by in-depth discussions on their thermodynamic and kinetic characteristics governing halogen reactions. We then critically analyze the key challenges of halogen cathodes and propose a confinement-catalysis-conduction triad to rationalize the design of host materials, elucidating their structure-performance correlations and mechanistic insights across various zinc-halogen battery systems, including Zn-Cl₂, Zn-Br₂, Zn-I₂ and Zn-dual halogen configurations. Furthermore, optimization strategies encompassing rational structural design, surface functionalization, heteroatom doping, engineering of single/dual-atom catalysts and heterostructure engineering are highlighted to promote halogen confinement, accelerate redox kinetics, and facilitate charge transport within halogen-based cathodes. Finally, we provide a concise perspective on existing barriers and emerging opportunities, offering valuable guidance for high-performance zinc-halogen batteries.