Multimodal electrolyte architecting for static aqueous zinc-halogen batteries

Rechargeable static aqueous zinc-halogen batteries (AZHBs) thrive in energy-storage applications due to their suitable redox potential, abundant reserves and relatively high energy density. This non-flow battery relies on the collaboration of the reversible stripping/plating process of Zn metal and the halogen-participating zincation reactions. However, the corrosion of Zn metal and the shuttling of the halogen species result in serious capacity decay, posing challenges to their reversibility and lifespan. Moreover, the instability of high-valence halides hinders the implementation of multi-electron reactions in AZHBs. This review elaborates on the fundamentals, challenges and recent progress in AZHBs, highlighting the significance of the electrolyte design that is aimed at synchronous optimization for both the halogen cathode and the Zn anode in AZHBs. We discuss the design principles and protocols, along with concerns in the effective testing and evaluation of synchronous electrolytes. Possible approaches towards synchronous electrolytes are proposed - namely, biphasic electrolytes, gradient hydrogel electrolytes and ionic liquid electrolytes. This review may help to guide the research in achieving AZHBs with high energy density and longevity for practical applications.