Imidazole-Based Deep Eutectic Solvents as Efficient Leaching Media for Recycling of Spent Lithium-Ion Batteries

Abstract

Accelerated deployment of electric vehicles as a countermeasure against global warming has increased demand for lithium-ion batteries (LIBs). These LIBs contain numerous critical metals, and the importance of recycling technologies for LIBs has grown. In conventional hydrometallurgical LIB recycling, highly concentrated inorganic acids are used in the leaching step, raising environmental concerns associated with the generation of large volumes of acidic wastewater. Here, deep eutectic solvents (DESs) were prepared as alternatives to inorganic acids using a 4,4,4-trifluorobutanedione-functionalized compound as the hydrogen-bond donor and an imidazole-containing compound as the hydrogen-bond acceptor. The prepared DESs were applied as leaching media for spent LIB black mass (i.e., shredded electrode powder), and efficient leaching of Li, Ni, Mn, and Co was achieved. Furthermore, stripping (back-extraction) from the DES phase demonstrated that the recovered metals could be separated into three fractions: a Li solution, a mixed Ni–Mn–Co solution, and a Cu solution. These results suggest that the proposed DES-based separation process can serve as a leaching medium to replace conventional acid leaching in LIB recycling and may contribute to the development of environmentally benign recycling processes.