Solvometallurgy: design of ternary deep eutectic solvents for the electrochemical recovery of nickel from lithium-ion cathode materials

Abstract

Recovering critical metals from lithium-ion batteries (LIBs) is crucial for resource conservation and waste management. Current LIB recycling methods, such as pyrometallurgy and hydrometallurgy, have limitations in the selective recovery of pure metals, waste management, etc. Deep Eutectic Solvents (DESs) show potential for recycling critical metals from the cathode materials due to their non-toxic components and low cost. However, they are often limited by high leaching temperatures (140–220 °C) and insufficient recovery methods for leachate solutions. Here, we present the design of a ternary DES (T-DES) of choline chloride (ChCl), ethylene glycol (EG), and citric acid (CA), optimized for both metal leaching and electrochemical recovery. This T-DES achieved high leaching efficiencies (LEs) of 99 ± 2% and 98 ± 4% for Li and Ni at 70 °C. Nickel was successfully recovered from the leachate using electrodeposition, with performance enhanced by optimizing the substrate material, temperature, time, and viscosity. Notably, viscosity reduction, achieved by modifying T-DES molar components, improved faradaic efficiency (FE) by up to 65% (−0.8 V vs. Ag). The T-DES achieved high LE for the NMC cathode material, with 94 ± 8% for Li, 99 ± 6% for Mn, 85 ± 6% for Ni, and 99 ± 3% for Co at 90 °C, demonstrating broader applicability to other LIB cathode materials. Scanning electron microscopy-energy dispersive X-ray spectroscopy validation revealed pure metal deposition. Additionally, our findings indicate that the T-DES design is promising for efficient and environmentally friendly metal recovery from LIB waste, advancing sustainable battery recycling technologies.