The increased demand for portable electronic devices and electric vehicles has resulted in an exponential increase in the lithium-ion battery (LIB) and waste at the end of their life cycle.^1-3 Spent batteries contain toxic, flammable chemicals, and heavy metals that can create a serious impact on human health and ecosystems.⁴ LIB recycling processes have become vital to protect the environment and recover critical metals. Specially, the recycling of cobalt has attracted much attention because it is expensive, and categorized as a CMR (carcinogenic, mutagenic, or toxic to reproduction) substance.⁴ The current recycling state of the art of cobalt on an industrial scale is based on using concentrated inorganic acids such as HCl, and H₂SO₄ with H₂O₂ as a reducing agent, which leads to the corrosion of equipment, generation of acidic wastewater, and emission of toxic gases (NO_x, SO₂ and Cl₂).^5-8

Greener solvents for recovery of cobalt, deep eutectic solvents (DESs) and ionic liquids (ILs), are drawing much attention due to their unique chemical and physical properties.^{9, 10} Several DESs have been studied to leach cobalt from LiCoO₂ and cobalt oxides (Co₃O₄) in the literature.⁵ However, recovery of leached Co²⁺ using the electrodeposition approach in DES has not been given much attention. Electrodeposition has been considered a more sustainable, cost effective and efficient approach to recover leached Co²⁺ compared to the solvent extraction and chemical precipitation.⁵

This research work is focused on the electrochemical recovery of cobalt using environmentally friendly ethylene glycol based solvent systems at lower temperature (50 °C). Cyclic voltammetry was used to study the effect of anion and chemical composition of the solvent system on the electrochemical behaviour of cobalt. UV- Vis spectrophotometer was used to identify the coordination geometry of Co²⁺ in each solvent system. The surface morphologies of the deposited cobalt samples were examined using scanning electron microscopy (SEM). X-ray photo electron microscopy (XPS) and energy dispersive x-ray spectroscopy (EDX) were conducted to analyse the purity of the electrodeposited cobalt samples.

References

1. Chen, W.-S.; Ho, H.-J., Recovery of Valuable Metals from Lithium-Ion Batteries NMC Cathode Waste Materials by Hydrometallurgical Methods. Metals 2018, 8 (5).
2. Wang, X.; Gaustad, G.; Babbitt, C. W.; Richa, K., Economies of scale for future lithium-ion battery recycling infrastructure. Resources, Conservation and Recycling 2014, 83, 53-62.
3. Scrosati, B.; Garche, J., Lithium batteries: Status, prospects and future. Journal of Power Sources 2010, 195 (9), 2419-2430.
4. Zheng, X.; Zhu, Z.; Lin, X.; Zhang, Y.; He, Y.; Cao, H.; Sun, Z., A Mini-Review on Metal Recycling from Spent Lithium Ion Batteries. Engineering 2018, 4 (3), 361-370.
5. Tran, M. K.; Rodrigues, M.-T. F.; Kato, K.; Babu, G.; Ajayan, P. M., Deep eutectic solvents for cathode recycling of Li-ion batteries. Nature Energy 2019, 4 (4), 339-345.
6. Wang, S.; Zhang, Z.; Lu, Z.; Xu, Z., A novel method for screening deep eutectic solvent to recycle the cathode of Li-ion batteries. Green Chemistry 2020, 22 (14), 4473-4482.
7. Schiavi, P. G.; Altimari, P.; Branchi, M.; Zanoni, R.; Simonetti, G.; Navarra, M. A.; Pagnanelli, F., Selective recovery of cobalt from mixed lithium ion battery wastes using deep eutectic solvent. Chemical Engineering Journal 2021, 417.
8. Golmohammadzadeh, R.; Faraji, F.; Rashchi, F., Recovery of lithium and cobalt from spent lithium ion batteries (LIBs) using organic acids as leaching reagents: A review. Resources, Conservation and Recycling 2018, 136, 418-435.
9. Fan, E.; Li, L.; Wang, Z.; Lin, J.; Huang, Y.; Yao, Y.; Chen, R.; Wu, F., Sustainable Recycling Technology for Li-Ion Batteries and Beyond: Challenges and Future Prospects. Chem Rev 2020, 120 (14), 7020-7063.
10. Golmohammadzadeh, R.; Rashchi, F.; Vahidi, E., Recovery of lithium and cobalt from spent lithium-ion batteries using organic acids: Process optimization and kinetic aspects. Waste Manag 2017, 64, 244-254.