Aqueous Aluminium-Ion Batteries: Cathode Material Design, Anode Engineering and Electrolyte Innovation

Aqueous aluminium-ion batteries (AAIBs) have emerged as a promising post-lithium energy storage technology due to their low cost, abundant resources, and inherent safety. This review provides a comprehensive summary of recent advances in AAIBs, focusing on three key aspects: cathode materials, anode engineering, and electrolyte innovation. Among cathode materials, manganese-based oxides, Prussian blue analogues, and organic compounds have shown notable capacities and cycling performance, with manganese dioxides standing out for its rich polymorphs and high electrochemical activity. However, structural instability remains a challenge, prompting the development of in situ electrochemical transformation, heteroatom doping, and electrolyte additive strategies. On the anode side, aluminium (Al) metal suffers from passivation and irreversible reactions in aqueous media, limiting its cycling life. Strategies such as surface pretreatment, amorphization, and alloying have been employed to improve reversibility and interfacial stability. Electrolyte development has progressed from traditional Al salt solutions to highly concentrated Al(OTF)₃ systems, deep eutectic solvents, and gel-based formulations, effectively widening the electrochemical stability window and enhancing overall battery performance. Despite significant progress, challenges such as cathode structural degradation and Al anode instability persist. Continued advancements in interfacial engineering and electrolyte design will be crucial to realizing the practical deployment of AAIBs.