Synergistic and efficient leaching of valuable metals from spent NCM cathodes using a novel chlorine-free acidic deep eutectic solvent

The rapid expansion of electric vehicles has driven a surge in end-of-life lithium-ion batteries (LIBs). Conventional hydrometallurgical recycling, dependent on strong inorganic acids and chloride-containing reagents, induces severe secondary pollution and equipment corrosion. Although deep eutectic solvents (DESs) are extensively explored as green alternatives, mainstream chloride salt-acid systems persistently risk chlorine contamination, necessitating inherently safe chloride-free alternatives. This study developed a novel chloride-free DES with excellent recyclability using trimethylglycine (TMG) and glycolic acid (GA). Response surface methodology (RSM) optimization yielded optimal leaching conditions: 1.95 h, TMG:GA molar ratio of 1:3.2, S/L of 20 g/L, and 99 °C. Under these conditions, unprecedented leaching efficiencies (>99%) for Li, Ni, Co, and Mn from spent LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) were achieved, with demonstrated universality across multiple cathode configurations (>94%). The kinetic study showed that the leaching process is governed by surface chemical reaction, with activation energies of 33.19/42.61/40.50/37.38 kJ mol -1 for Li/Ni/Co/Mn. Density functional theory (DFT) calculations unveiled that the DES disrupts metal–oxygen (M−O) bonds via a synergistic reductive-chelation mechanism, where binding energies followed Mn > Co > Ni. This work offers a promising approach for recycling spent batteries with its environmental friendliness, high efficiency, broad applicability, and in-depth mechanism.