Enhanced Redox Capacity and Hydrogen Bonding Interactions for Efficient Metal Recovery from Spent Batteries

Abstract

Green and efficient recycling of critical metals from spent lithium-ion batteries is of great importance. Deep eutectic solvents (DESs) show great potential to replace conventional inorganic acids due to their eco-friendly, low-cost, and superior leaching performance. However, the low solid–liquid ratio, high leaching temperature, and complex stepwise recovery processes may lead to large solvent and energy consumption. Herein, a selection principle is proposed according to the enhanced redox capacity and abundant hydrogen bonding interactions, which help to design novel ternary DESs. The results demonstrate that the DESs could disrupt metal–oxygen bonds efficiently and reduce high-valent metals to form low-valent metal complexes in solution. Besides, water as a dilutant can reduce the viscosity of DESs and benefit to form abundant hydrogen bonds. As a result, the DESs can achieve high-metal leaching efficiency of 98.65% (Li), 96.92% (Ni), 96.94% (Co), and 95.53% (Mn) at relatively low temperature (60 °C) and high solid–liquid ratio (RS/L = 10), respectively. The regenerated cathodes via co-precipitation methods exhibit excellent electrochemical performance similar to that of commercial ternary cathodes. Finally, the economic and environmental evaluation of the entire process shows high profitability and low environmental impact.