Precise Ni/Co separation from spent Li-Ion batteries: Revealing the pivotal role of H2O in deep eutectic solvents

XY Hu and H Shi and YL Zheng and PH Shao and LM Yang and XB Luo, ENERGY STORAGE MATERIALS, 82, 104585 (2025).

DOI: 10.1016/j.ensm.2025.104585

The sustainable recovery of valuable metals from end-of-life lithium-ion batteries (LIBs) has become essential for relieving the supply-demand contradiction of key resources. However, the high similarity in physicochemical properties of transition metals poses a fundamental challenge for the selective recycling. Here we proposed a facile strategy for defining the demarcation line of precipitation/dissolution behavior for precise Ni/Co separation. A malonic acid-based deep eutectic solvent (DES) is developed, emphasizing the H2O-mediated competitive coordination and differentiated solubility. We discovered the distinctive formation of Ni(H2O)(6)(2+) and CoCl4(2-) in the DES-20 % H2O system. Furthermore, the K-sp differences of the Ni-complex and Co-complex in the C3H2O42--rich environment was effectively magnified. These significant differences synergistically enable the generation of C3H2NiO4 center dot 2H(2)O precipitation (similar to 99.9 % purity), achieving a remarkable Ni/Co separation factor of 125, which guarantees sequential separation of all metals. This universal methodology along with indepth mechanism understanding provides a guideline toward value-added recovery of LIBs.

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