Subcritical water electrolysis for cobalt recovery from spent lithium-ion batteries in an acidic environment

Precious metal recovery was realized in this study using the electrowinning technique under subcritical water conditions. The experiments were performed in a batch system at temperatures of 110–200 °C with reaction times of 60–300 min. Electric currents of 1–3 A were applied to an electrolyte solution containing Co and Li as target elements via stainless steel (SUS) electrodes. SEM/EDS and XRD analyses indicated that the metallic elements in the deposited metal on the cathode cell surface comprised Co as the primary element. Inductively coupled plasma atomic emission spectroscopy suggested that the Co yield independently increased with increases in operating parameters such as reaction time, reaction temperature, and applied electric current. The Co yield approached 56.2% when the experiment was conducted at 200 °C with an applied electric current of 1.0 A for 300 min. The technique described herein is innovative and practical for advanced precious-metal recovery based on the use of electric current in a one-step process.