Deep eutectic solvent of tetraethylammonium chloride and citric acid for sustainable recycling of spent ternary cathode materials

Deep eutectic solvents have emerged as promising media for the sustainable recycling of spent lithium-ion batteries (LIBs). In this work, a tetraethylammonium chloride citric acid (TEAC–CA) based deep eutectic solvent (DES) system was developed for the recovery and regeneration of valuable metals from spent ternary cathode material (NCM) cathodes. Under optimized conditions, the TEAC–CA DES achieved high and relatively balanced leaching efficiencies of 99.9% for Li, 99.9% for Ni, 97.6% for Co, and 96.4% for Mn. Kinetic analysis indicated that the leaching process was governed mainly by surface chemical reactions, with possible diffusion contribution under some conditions, while spectroscopic and Density Functional Theory (DFT) results supported a cooperative mechanism in which citric acid promotes proton-assisted lattice activation and chloride/carboxylate coordination environments stabilize dissolved transition-metal species. The recovered metals were converted into a ternary precursor and subsequently regenerated as LiNi 0.5 Co 0.2 Mn 0.3 O 2 , which delivered an initial discharge capacity of 171.7 mAh g −1 at 0.1C, together with stable cycling and competitive rate performance. The regenerated cathode exhibited a layered structure closely comparable to that of commercial NCM523, and the recovered TEAC–CA-based working solvent was reused for five consecutive leaching cycles after solvent reconditioning. These results demonstrate that the DES provides an efficient, mechanistically supported, and practically promising route for balanced multimetal extraction and cathode-material regeneration from spent LIB cathodes.