The Potential of Choline Chloride-Based Deep Eutectic Solvents for Recycling Spent Batteries: A Comprehensive Review of Sustainable Strategies for a Circular Economy

The exponential proliferation of electric vehicles, portable electronics, and renewable energy storage devices has led to a huge rise in battery waste, encompassing lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), zinc–carbon and alkaline batteries, nickel–metal hydride (NiMH), nickel–cadmium batteries (NiCBs), and lead–acid batteries (LABs). Improper disposal of these spent batteries poses a high risk to human health and the ecosystem owing to the presence of toxic and critical metals, including lithium (Li), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), lead (Pb), and cadmium (Cd). Traditional recycling approaches, including pyrometallurgy and hydrometallurgy, are costly, high-power-consuming, and environmentally hazardous owing to the utilization of toxic chemicals and complex operational conditions. In response, choline chloride-based deep eutectic solvents (ChCl-DESs), which have low volatility, excellent metal selectivity, and minimal environmental impacts, have emerged as an appealing green alternative for all types of battery waste. This review comprehensively examines the fundamentals of ChCl-DESs, their classification, and the distinctive benefits they offer in the selective leaching of valuable metals, such as Ni, Co, Mn, and Li. It highlights recent developments in ChCl-DES-based leaching approaches, including key leaching parameters that influence recovery efficiency, the mechanisms involved in binder dissolution, and the mechanisms underlying the reclamation of graphite and valuable metals from various types of battery waste. The review also addresses techno-economic analysis, environmental assessment, and the current challenges to industrial scalability. Finally, future directions are outlined to address present challenges and improve the practicality of ChCl-DESs in sustainable battery recycling.