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 LiNi_xCo_yMn_1-x-yO₂ (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.