(677h) Towards Sustainable Lithium-Ion Battery Recycling: Electrochemical Recovery of Metals from Cathode Materials

The growing demand for lithium-ion batteries (LIBs) in electric vehicles and energy storage systems has increased LIB wastes and is expected to produce 7.5 Mt of LIBs by 2030.¹ Spent LIB cathode materials contain significant amounts of valuable metal elements, such as cobalt (Co), nickel (Ni), and manganese (Mn). Currently, most of the spent LIBs are disposed of in landfills, and the toxicity of these metals released into landfills represents a series of threats to human health and the environment.² Hence, efficient metal recovery from LIB waste is essential to meet the growing demand sustainably. The traditional LIB recycling methods, such as pyrometallurgy and hydrometallurgy, have limitations regarding energy consumption and environmental impact. A significant challenge in this field is the selective recovery of metals such as Ni, Co, and Mn due to their similar chemical properties, often co-precipitating in the same pH range, necessitating multiple purification steps.

Although electrodeposition is an efficient method for separating metals in high purity, current inorganic acid-based leaching agents have a narrow electrochemical stability window (0.4-1 V vs. Ag), leading to reduced faradaic efficiency due to side reactions such as the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, we address these challenges by exploring the potential of Deep Eutectic Solvents (DESes) as an alternative. DESes are compounds formed by mixing hydrogen bond donors and acceptors and exhibit a high capability for metal dissolution.³ DES has a wide electrochemical stability window (2-3 V vs. Ag), making it ideal for electrodeposition. While DES holds promise for sustainable LIB recycling, current applications are hindered by high leaching temperatures (140-220°C) and prolonged durations, extending even to days.

In this study, we investigate the physical properties of a novel ternary DES (T-DES) and assess its leaching capabilities alongside electrodeposition studies. Remarkably, using the T-DES significantly reduces leaching time to 4 hours and lowers the temperature to 90°C, achieving nearly 100 % leaching efficiency. We further investigate the leaching kinetics, comparing them with those of conventional binary DES (B-DES). The electrochemical properties of the T-DES are explored, revealing an electrochemical window of 2-3V vs Ag. Furthermore, we perform potentiostatic electrodeposition of metals from the leach liquor on different substrates (copper and carbon) at various potentials (-0.7 to -1.6 V vs. Ag), different temperatures (45-115⁰C), and time (10-90 min). The electrodeposited metals are characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy. Our findings indicate that the proposed T-DES holds significant promise for efficient and environmentally friendly metal recovery from LIB waste, paving the way for advancements in sustainable battery recycling technologies.

References

1. Jia, G. Yang, Y. He, Z. Cao, J. Gao, H. Zhao, Z. Piao, J. Wang, A. M. Abdelkader, Z. Liang, R. Vasant Kumar, G. Zhou, S. Ding, and K. Xi, Adv. Mater., 2024, 2313273
2. Harper, R. Sommerville, E.a Kendrick, L. Driscoll, P. Slater, R. Stolkin, A. Walton, P. Christensen, O. Heidrich, S. Lambert, A. Abbott, K. Ryder, L. Gaines and P. Anderson Nature, 2019, 575, 75–86
3. K. Tran, M.-T.F. Rodrigues, K. Kato, G. Babu, and P.M. Ajayan, Nat. Energy, 2019, 4, 339-345