2. Experimental
2.1. Electrodeposition solution preparation
Li-ion batteries were manually dismantled and physically separated into their different parts, including the anode, cathode, steel,separators, and current collectors. Electrodes were dried at 80 ◦C for 24 h and then washed in distilled water at 40◦C for 1 h under agitation to eliminate organic solvents, propylene carbonate (PC), and ethylene carbonate (EC). This procedure also facilitates the detachment of active material from the respective current collectors. Active material was filtered, washed with distilled water at 40 ◦C to remove potential lithium salts (e.g., LiPF6 and LiCl4) and Cu (from anode current collector), and then dried in air for 24 h. A total of 9.17 g of positive electrodematerialwas dissolved in a solution containing 470.00ml of HCl 3.00mol l −1 and 30.00ml of H2O2 (30%, v/v). This system was maintained under constant magnetic agitation at 80 ◦C for 2 h. Cathode dissolution efficiency increases with increasing acid concentration and temperature. The addition of H2O2 was necessary to increase cathode dissolution efficiency [22].H2O2 reduces cobalt froma +III oxidation state,which is insoluble in aqueous systems, to a +II oxidation state, which is soluble in aqueous systems. For an activematerial consisting of LiCoO2, the cathode dissolution reaction is represented by Eq. (10):
The cathode compositionwas found to be LiCoO2,Co3O4, Al, and carbon [8]. The cathode can be contaminated with electrolyte or anode material. Therefore, the leaching solutions used were characterized by atomic absorption spectroscopy (AAS) to detect the presence of lithium, copper, and cobalt. The cobalt and lithium concentrations were both equal to 0.10mol l−1. The ionic copper concentration was not detected. The ionic lithium does not influence the cobalt electrodeposition because its reduction occurs at a more cathodic potential (−3.02V). Solutions were buffered using H3BO3 at 0.10mol l−1 to maintain the electrodeposition bath pH.