Designing principles of deep eutectic solvents for sustainable recycling of spent lithium-ion batteries

The exponential growth of lithium-ion batteries (LIBs) waste, coupled with the severe environmental and economic limitations of conventional pyrometallurgical and hydrometallurgical recycling, necessitates sustainable alternatives. Deep eutectic solvents (DESs) have emerged as promising green solvents for spent LIBs recycling due to their tunability, low cost, low volatility, and potential biodegradability. This review elucidates the fundamental chemical principles governing DESs, particularly their hydrogen-bond-driven self-assembly and structure-property-performance relationships. We critically analyze recent advances in the rational design of DESs for efficient and selective metal leaching, separation, and direct cathode regeneration from spent LIBs. Key design strategies include component engineering (e.g., binary/ternary HBA/HBD combinations, water/additive modulation), coordination environment regulation, and reducibility modulation targeting specific cathode chemistries (LCO, NCM, LFP). Furthermore, we evaluate the greenness and technoeconomic viability of DESs processes, highlighting their potential for lower energy consumption, reduced emissions, and high-value product regeneration. Despite impressive lab-scale achievements, challenges in scalability, DESs regeneration, and complex waste stream handling persist. Future research must bridge fundamental understanding with industrial implementation to realize the full potential of DESs for securing the critical materials supply chain essential for an electrified future.