Progress in aluminum-ion battery: Evaluation of deep eutectic solvent as electrolyte

Aluminum-ion battery (AIB) has emerged as a promising technology for both portable and large-scale energy storage applications, owing to its high theoretical specific capacity, safety, abundance and non-toxic nature of aluminum metal. Though ionic liquids are the primary choice as electrolyte for this battery chemistry, the utilization of deep eutectic solvents (DES) as electrolytes is growing due to their low cost, environmentally friendly nature, and biocompatibility. However, AIB consisting of DES electrolytes are still in the early stages of development due to their limited electrochemical stability windows, which open avenues for further exploration of their properties and electrochemical performance. This review focuses on comprehensive understanding of various DES electrolytes in terms of their effective ionic species at different compositions, electrochemical stability as compared to ionic liquid counterparts, and examining aspects such as reversible aluminum electrode- position. Additionally, the review summarizes the development of AIB utilizing DES electrolytes in terms of their overall performance. Finally, it critically discusses the challenges and prospects associated with DES electrolytes for AIB applications. This review aims to provide insights that can guide the development of advanced DES electrolytes for high-performance AIB.