Molecular dynamic (MD) simulation and density function theory (DFT) calculation relevant to green leaching of metals from spent lithium-ion battery cathode materials using glucose-based deep eutectic solvent (DES)

Abstract

Deep eutectic solvents (DES), as environmentally-friendly solvents, have shown potential for recovering metals in the cathodes of spent lithium-ion batteries (LIBs). This study employed a glucose-based DES of choline chloride to recover cobalt, manganese, nickel, and lithium from LIB cathode materials, optimizing temperature and time parameters in the range of 60–110 °C and 2–24 h for leaching the cathode materials. The highest metal recoveries were observed between 60 and 110 °C, with 82.4% for Ni, 94.2% for Co, 97.6% for Ni, and 93.7% for Li after 24 h of leaching at 100 °C. The Co, Mn, Ni, and Li recoveries in the DES solution increased with time at 100 °C. UV–visible spectroscopy analysis investigated the leaching mechanisms for cathode metals, confirming that the spent LIBs leaching in DES (ChCl:G) is not completely associated with the reduction of cobalt. It appears that other metal ions, such as Li, Mn, and Ni, form complexes with chloride ions originating from the choline chloride agent. The results of the MD simulation show that hydrogen of the OH in choline chloride has a very strong attractive interaction with the Cl⁻ ion. Also, H atoms of OH groups in glucose molecules interact considerably with the chloride ion of choline chloride. In addition, all H atoms of OH groups in glucose form hydrogen bonds with O5 of the glucose. All metal ions, including Co³⁺, Li⁺, Mn²⁺, and Ni²⁺, have very strong electrostatic interactions with the Cl⁻ of the choline chloride molecule. The MD calculations show that metal ions are complexed with some oxygen atoms of the glucose molecule. Results show that the choline chloride molecule (via Cl⁻ ion) and glucose molecule (via oxygen atoms) play a significant role in the leaching of metal ions from LIBs via electronegative atoms. Another finding is that the molecules of choline chloride and glucose have no selectivity towards the leaching of ions, which agrees with the experimental results, so all ions are almost 100% extracted.