Achieving High Solid–Liquid Ratio through Competitive Coordination towards Efficient Recovery of Metals from Spent Batteries

The recycling of critical metals from spent lithium-ion batteries represents a significant step towards meeting the enhancing resource requirements in the new energy industry. Nevertheless, achieving effective leaching of metals from the stable metal-oxygen (MO₆) structure of spent ternary cathodes and separation of metal products simultaneously still remained a huge challenge towards industrial applications. Herein, a competitive coordination strategy was proposed to design a novel deep eutectic solvent (DESs), which improved both leaching and selective metal recycling capacity even at high solid-liquid ratio (1 : 10). The results demonstrated that the number of hydrogen bonds in designed ternary DESs was 16.5 % higher compared to those in the binary DESs, resulting in efficient reaction kinetics to break the metals-oxygen bond. More importantly, the competing-ligand (p-toluenesulfonic acid) could preferentially enter into the first nanostructure sheath and reduce the proportion of solvated oxalic acid (OxA) from 28.36 % to 17.76 % within the nanostructure, which enable OxA molecules to enhance the coordination interaction with metal for precipitating NiC₂O₄ ⋅ 2H₂O product (~95.7 % purity) from spent cathodes. This work achieved impressive profitability ($16.05 per kg feedstock) and effectively reduction of GHG emissions during the recycling process, making it applicable to critical sustainability initiatives.