Stage-Specific Roles of Deep Eutectic Solvents in Recycling of Spent Lithium-Ion Batteries

The exponential growth of lithium-ion batteries (LIBs) market driven by electric vehicles has intensified the demand for sustainable and efficient recycling technologies. Among emerging solutions, deep eutectic solvents (DESs) have attracted increasing attention due to their tunable properties, low toxicity, and environmental compatibility. While DESs have been widely applied in the leaching of spent cathodes, their functions and mechanisms remain underexplored. In this review, we critically examine the stage-specific roles of DESs in the recovery of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) from spent cathodes. DES applications are systematically classified into metal co-dissolution, single-metal selectivity (Li-first, Ni-first), and two-metal pairwise separations. We discuss key DES design principles for achieving metal-specific selectivity, highlighting emerging hydrophobic DESs and redox-active systems, and expanding roles beyond leaching (binder removal, graphite pre-concentration, direct regeneration, and hydrophobic DESs for liquid-liquid extraction). Finally, this review identifies major challenges limiting DES scalability, including viscosity, component stability, recyclability, impurity tolerance, and limited techno-economic and life cycle analyses. We also propose future directions to fully integrated, closed-loop, and sustainable DES-based recycling processes for critical metals. This review provides solvent design and mechanistic insight guidance toward green, selective, and scalable LIB recycling technologies. © 2026 The Author(s). Advanced Energy Materials published by Wiley-VCH GmbH.