Closed-loop cathode recycling of spent lithium batteries via green deep eutectic solvents and oxalic acid.

The eco-friendly recovery of strategic metals from spent lithium-ion batteries is pivotal for realizing circular economy goals. This study introduces a low-viscosity hydrated deep eutectic solvent (DES) composed of citric acid (CA) and choline chloride (ChCl) for the efficient extraction of crucial metals from spent LiNiCoMnO (NCM) cathodes. The leaching parameters were optimized within response surface methodology (RSM), and maximum extraction efficiencies of 97.75 % Li, 99.57 % Co, 99.91 % Ni, and 99.56 % Mn were achieved under the optimal conditions. Kinetic analysis revealed extraction mechanisms controlled by surface reactions. The DES maintained high leaching efficiency over multiple recycling cycles, confirming its excellent reusability. A sequential separation strategy was developed to integrate the co-precipitation of Ni-Co-Mn oxalates followed by selective Li oxalate recovery, enabling the regeneration of high-purity ternary cathode precursors via oxalate-mediated crystallization. Density functional theory (DFT) calculations provided atomic-scale insights into the coordination interactions between the multivalent metal ions and DES functional groups. This process significantly reduces hazardous chemical consumption while maintaining cost-effectiveness throughout the recovery workflow. These findings validate the potential of this DES system for scalable, sustainable industrial applications in critical metal recycling from spent LIB cathodes.