The extensive use of lithium-ion batteries (LIBs) in new electric vehicles has brought the pile of battery waste, while the current commercial recycling model still has some problems, such as environmental pollution, high energy consumption and low comprehensive economic benefits and so on. In recent years, to solve these problems, some new recycling processes have appeared frequently. Among these new technologies, green and inexpensive deep eutectic solvents (DESs) have attracted much attention due to their excellent selectivity and leaching efficiency. Here, a new type of DESs, consisting of caprolactam (CPL), urea (UR) and organic acids (RCOOH), were designed for extracting valuable metals lithium cobalt (iii) oxide (LiCoO₂) from cathode active materials of spent LIBs. The as-prepared DES possessed strong dissolving, reducing and coordination ability, low viscosity, and low cost, which were suitable for metal extraction. Under the optimal conditions (leaching temperatures: 120 °C, leaching time: 2 h, solid/liquid ratio: 1/20), the Li and Co can achieve efficient leaching and recovery. Results illustrate that Li⁺ ions located in the interlayer of layered LiCoO₂ can be selectively leached in the supernatant of DESs, leaching efficiencies >99%. While Co³⁺ ions in the skeleton structure were reduced and coordinated by RCOOH to form Co²⁺− RCOOH complexes, as a purple precipitation located at the bottom of DESs (Scheme 1). Noteworthy, CPL-UR-DESs has two functions in the leaching system: (1) as an ideal green solvent to provide a reaction site for organic acids with almost no consumption and easy recycling for more than one extraction, (2) as an extractant of Co used for the direct separation and recovery of Co from the DESs system, thus avoiding the addition of precipitant. This strategy can realize the selective leaching of Li and the direct recovery of Co by one step method, thus boosting recycling process sustainability.

Jiajun Wang

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