Towards sustainable battery recycling: investigating ammonium-based deep eutectic solvents for NMC cathode material recovery

The rapid growth of the electric vehicle industry has led to an unprecedented demand for lithium-ion batteries (LIBs), resulting in the accumulation of large quantities of spent batteries that pose significant environmental challenges. This study presents a sustainable recycling approach for nickel-manganese-cobalt (NMC) cathode materials using ammonium-based deep eutectic solvents (DESs) as leaching agents. Two DESs were synthesised using ethylammonium chloride (EAC) and diethylammonium chloride (dEAC) as hydrogen bond donors (HBDs) and ethylene glycol (EG) as a hydrogen bond acceptor (HBA). The structural and thermal characteristics of the DESs were confirmed using Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The leaching process was systematically optimised by varying the DES molar ratio (1:2–1:5), reaction time (8–48 h), and temperature (25–120 °C). The optimal conditions were identified as 100 °C for 24 h, achieving leaching efficiencies of 83.7, 98.2, 98.4, and 50.1 % for Li, Co, Ni, and Mn, respectively. Notably, this method avoids the use of conventional volatile acids and offers a greener and more efficient route for LIB recycling than conventional methods. The high recovery rates of critical metals highlight the promise of DES-based systems in promoting sustainable battery circularity and mitigating both resource depletion and environmental impacts.