Paving the way toward highly reversible aluminum metal anodes: the core role of ionic liquid electrolyte systems.

Rechargeable aluminum-ion batteries (AIBs) are promising candidates for next-generation energy storage, yet their practical deployment is hampered by the intrinsic limitations of conventional ionic liquid (IL) electrolytes, such as high viscosity, corrosivity, and moisture sensitivity. This review focuses on the core role of IL electrolyte design in enabling highly reversible aluminum metal anodes. First, the fundamental requirements and working mechanisms of ILs are systematically elucidated. Furthermore, recent optimization strategies are critically summarized and discussed in terms of four aspects: (1) cation-anion pair engineering to regulate active aluminum species, tailor physicochemical properties, and reduce reliance on costly imidazolium-based components, (2) functional additives to enhance ion transport and regulate solid electrolyte interphase (SEI) formation, (3) deep eutectic solvent formulations as potentially lower-cost and more sustainable alternatives, and (4) gel and quasi-solid-state architecture construction to improve safety and mechanical strength. Finally, the performance-sustainability trade-offs of current IL electrolyte systems are discussed, and design guidelines are provided for developing safer and more sustainable electrolytes with high ionic conductivity, wide electrochemical windows, and robust interfacial compatibility. These advancements are expected to facilitate the realization of highly reversible aluminum metal anodes and high-energy-density AIBs, thereby propelling the development of next-generation aluminum-based energy storage technologies.