Recent Advances in Leaching of Lithium-Ion Battery Cathode Materials Using Deep Eutectic Solvents and Ionic Liquids: Efficiency, Mechanisms, and Challenges

The escalating production and use of lithium-ion batteries (LIBs) have led to a pressing need for efficient and sustainable methods for recycling valuable metals such as cobalt, nickel, manganese, and lithium from spent cathode materials. Traditional hydrometallurgical leaching approaches, based on mineral acids, face significant limitations, including high reagent consumption, secondary pollution, and poor selectivity. In recent years, deep eutectic solvents (DESs) and ionic liquids (ILs) have emerged as innovative, environmentally benign alternatives, offering tunable physicochemical properties, enhanced metal selectivity, and potential for reagent recycling. This review provides a comprehensive analysis of the current state and prospects of leaching LIB cathode materials using DES and ILs. We summarize the structural diversity and composition of common LIB cathodes, highlighting their implications for leaching strategies. The mechanisms, efficiency, and selectivity of metal dissolution in various DES- and IL-based systems are critically discussed, drawing on recent advances in both laboratory and real-sample studies. Special attention is given to the unique extraction mechanisms facilitated by complexation, acid–base, and redox interactions in DES and ILs, as well as to the effects of key operational parameters. A comparative analysis of DES- and IL-based leaching is presented, with discussion of their advantages, challenges, and industrial potential. While DES offers low toxicity, biodegradability, and cost-effectiveness, it may suffer from limited solubility or viscosity issues. Conversely, ILs provide remarkable tunability and metal selectivity but are often hampered by higher costs, viscosity, and environmental concerns. Finally, the review identifies critical bottlenecks in upscaling DES and IL leaching technologies, including long-term solvent stability, metal recovery purity, and economic viability. We also highlight research priorities that emphasize applying circular hydrometallurgy and life-cycle assessment to improve the sustainability of battery recycling.