Recycling of graphite and metals from spent Li-ion batteries aiming the production of graphene/CoO-based electrochemical sensors

This work describes the synthesis of hybrid materials based on reduced graphene oxide (rGO) and cobalt oxide (CoO) from recycled Li-ion batteries. A hydrometallurgical route was employed in the recycling process, with citric acid and nitric acid used as the leaching agents for the cathode and anode materials, respectively. Graphene oxide (GO) was prepared from the recycled graphite by a modified Hummers method; the hybrid material was produced by mixing GO and the recycled metal oxides (mostly CoO) using a sol-gel route followed by heat treatment at 450 °C during 2 h. The physicochemical characterization of the hybrid material was conducted by X-ray diffraction, scanning electron microscopy and solid-state 7Li and 13C nuclear magnetic resonance (NMR) spectroscopy; the results indicated the formation of crystalline CoO (with face centered cubic structure) and rGO (with turbostratic structure), whereas lithium and manganese were also identified as minor components. The performance of this product as electrochemical sensor was evaluated by cyclic voltammetry. The study of the electrocatalytic oxidation of ascorbic acid using the hybrid material as electrode showed good linearity in the relationship between the oxidation current and the acid concentration. These results showed that the hybrid material produced from the recycled batteries is promising for applications as an enzyme-free electrochemical sensor.