Enhanced Electrochemical Properties of Cobalt by Varying the Ethylene Glycol - Choline Chloride Composition in a Deep Eutectic Solvent Mixture

The increased demand for portable electronic devices and electric vehicles has resulted in an exponential increase in lithium-ion battery (LIB) waste, and becoming in turn an important secondary source for critical metals. Electrowinning is a commonly used method to recover base and precious metals from a solution, which can also be used to recover valuable metals from spent LIBs. This study unveiled the cobalt electrochemical recovery using model Co sources in increasing amounts of ethylene glycol (EG), 67 molar %, 82 molar % and 100 molar %, in a mixture with choline chloride. The electrochemical results show that increasing the amount of EG together with a small concentration of sulfate anions, in conjunction with chloride anions, in the solution mixture favours the reduction of Co²⁺. This improved electrochemistry seems to be related to changes of Co²⁺ speciation easing the reduction process. Additionally, the nature of the Co salt has a significant impact on the recovery efficiency, morphology, and purity of the Co electrodeposit. This work will underpin the science to design safe electrolyte mixtures to enhance the electrochemical recovery of Co²⁺ in solution from secondary sources.