Designing Low-Cost, Green, and Recyclable Deep Eutectic Solvents for Selective Separation and Recovery of Valuable Metals from Spent Li-Ion Batteries

Deep eutectic solvents (DESs) have significant selective leaching efficiency in the recycling of spent lithium-ion batteries (LIBs). Here, a new type of DES, consisting of caprolactam (CPL), urea (UR), and formic acid (FA), was designed for extracting valuable metal lithium cobalt oxide (LiCoO2, LCO) from cathode active materials of spent LIBs. Results illustrate that Li+ ions can be selectively leached in the supernatant of DESs, with leaching efficiencies >99% under optimized conditions (20 g/L, 120 °C, 150 min), and cycle extraction times without electrodeposition can be more than 20 times. Meanwhile, Co3+ ions were reduced to form a purple NH4Co(HCOO)3 precipitation located at the bottom of DESs, which can be directly recovered. Moreover, Li+ leaching kinetics was controlled by the interfacial chemical reaction, and the apparent activation energy was about 50.05 kJ/mol. Noteworthily, the FA with strong reducing capacity is the nucleus of efficient leaching, UR is an ideal carrier for Co ion coordination, and the CPL with almost no consumption is the key to multiple cyclic leaching. This research offers a feasible path for the application of DESs in the field of recycling of spent LIBs.