Ionic liquids in aqueous zinc metal batteries using mild electrolytes: from electrolyte engineering to interfacial chemistry

Aqueous zinc metal batteries (AZMBs) are considered as promising candidates for grid-scale energy storage systems because of the abundance of zinc reserves, high theoretical capacity of zinc anode, and intrinsic safety of the aqueous electrolytes. However, zinc anodes in aqueous electrolytes suffer from severe issues, such as H$_2$ evolution, dendrite growth, and spontaneous corrosion, resulting in poor reversibility and lifespan. Introducing ionic liquids (ILs) with tunable structures and superior physicochemical properties offers a viable solution. This strategy modulates both the bulk electrolyte and the interfacial environment, thereby addressing these challenges. This review outlines the recent progress in ILs for AZMBs employing mild electrolytes, emphasizing electrolyte design strategies and interfacial chemistry. We begin by introducing the fundamental properties of ILs relevant to AZMBs. Subsequently, we elucidate their specific roles and functions within the electrolyte, followed by an analysis of the modified interfacial chemistry at the anode. Finally, the remaining challenges associated with IL utilization are examined, and a potential future direction for the practical development of IL-based electrolytes in AZMBs is proposed.