Cobalt Electrochemical Recovery from Lithium Cobalt Oxides in Deep Eutectic Choline Chloride+Urea Solvents.

Electrochemical recovery of the cobalt in deep eutectic solvent shows its promise in recycling and recovery of valuable elements from the spent lithium-ion battery due to its high selectivity and minimal environmental impacts. This work unveiled the roles of the substrates, applied potentials, and operating temperatures on the performance of cobalt electrochemical recovery in a deep eutectic choline chloride+urea solvent. The solvent contains cobalt and lithium ions extracted from lithium cobalt oxides - 3an essential lithium-ion battery cathode material. Our results highlight that the substrate predetermines the cobalt recovery modes via substrate-cobalt interactions, which could be predicted by the cobalt surface segregation energies and crystallographic misfits. We also show that a moderate cathode potential under -1.0 V vs. silver quasi-reference electrode at 94-104 °C is essential to ensure a selective cobalt recovery at an optimal rate. We also found that the stainless-steel mesh is an optimal substrate for cobalt recovery due to its relatively high selectivity, fast recovery rate, and easy cobalt collection. Our work provides new insights on metal recovery in deep eutectic solvents and offers a new avenue to control the metal electrodeposition modes via modulation of substrate compositions and crystal structures.