Cradle-to-cradle recycling of spent NMC batteries with emphasis on novel Co2+/Ni2+ separation from HCl leached solution and synthesis of new ternary precursor

Abstract

Herein, a cradle-to-cradle recycling of post-consumer NMC batteries has been demonstrated with a focused separation of cobalt over nickel by applying the ionic liquid, trihexyl(tetradecyl)phosphonium bis-2,4,4-(trimethylpentyl)phosphinate. At the optimized condition of: 0.8 mol·L−1 ionic liquid, 3.0 mol·L−1 Cl− ions, equilibrium pH value ∼5.0, and organic-to-aqueous ratio 2/3, > 99% cobalt was extracted in the organic phase with a separation factor of 1097. Approximately 99% cobalt from the loaded organic was stripped back in 2.0 mol·L−1 HCl solution, yielding high-pure CoCl2·xH2O crystals after crystallizing the stripped solution. Subsequently, ∼99% of nickel from the Co-depleted raffinate was extracted over lithium using 0.32 mol·L−1 acetophenone at an organic-to-aqueous ratio of 1 and equilibrium pH ∼5.3. Nickel stripped in 2.0 mol·L−1 H2SO4 was crystallized to yield high-pure NiSO4·6H2O crystals. Further, Li-bearing raffinate was subjected to carbonate precipitation at a higher pH (∼12) and CO32−:Li+ ratio of 1.2. All the recycled products were further employed to the stepwise synthesis of a new ternary precursor, exhibiting similar electrochemical behaviour (with 149 mAh·g−1 capacity) and found compatible with the precursor prepared using virgin materials. The sustainable process index value determined to be 0.0006 cap·t−1 for the overall recycling process indicated that the process is suitable for sustainable development.