Abstract
Based on the structural characteristics of the anodes of lithium-ion batteries, an improved Hummers’ method is proposed to recycle the anode materials of spent lithium-ion batteries into graphene. In order to effectively separate the active material from the copper foil, water was selected as an ultrasonic solvent in this experiment. In order to further verify whether lithium ions exist in the active material, carbon powder, it was digested by microwave digestion. ICP-AES was then used to analyse the solution. It was found that lithium ions were almost non-existent in the carbon powder. In order to further increase the added value of the active material, graphene oxide was obtained by an improved Hummers’ method using the carbon powder. The graphene material was also reduced by adding vitamin C as a reducing agent through a chemical reduction method using graphene oxide. Meanwhile, the negative graphite, graphite oxide and graphene samples were characterized by XRD, SEM, FTIR and TEM. The conductivity of the negative graphite, graphite oxide and graphene was tested. The results show that graphene prepared by a redox method has a better layered structure, less impurities and oxygen groups in its molecular structure, wider interlayer spacing and smaller resistivity.
Highlights
Lithium-ion batteries have become ideal energy sources in the 21st century due to their lightweight, small volume, high specific energy, small self-discharge and long cycle life[1,2,3,4]
In order to obtain the optimal conditions for the separation of anode materials, NMP, H2O, acetone and ethaneiol were used as ultrasonic solvents, which could be used to separate the anode materials efficiently during the course of the experiment
Water was chosen as the ultrasonic solvent, and the active material of the anode material could be separated from the copper foil by ultrasound at room temperature for 2 min
Summary
Optimum separation conditions of active material and copper foil. In order to obtain the optimal conditions for the separation of anode materials, NMP, H2O, acetone and ethaneiol were used as ultrasonic solvents, which could be used to separate the anode materials efficiently during the course of the experiment. The absorption peak at 1720 cm−1 belongs to the stretching vibration peak of C=O, and the peak at 1265 cm−1 belongs to the vibration absorption peak of C-O-C (Fig. 2(c)) This shows that graphite oxide under this experimental condition contains at least three functional groups: OH, C=O and C-O-C. Compared with the FTIR spectra ofgraphite oxide (Fig. 2(c)), the absorption peaks of graphene (Fig. 2(d)) are reduced by vitamin C, and the absorption peaks caused by the vibration of surface functional groups almost disappear, indicating that the oxygen-containing groups were essentially removed (Fig. 2(d)). When graphite oxide is reduced to graphene, the diffraction peak of graphene appears near 2θ of ~26° (Fig. 3(d)), which is similar to the position of the diffraction peak of anode graphite (Fig. 3(b)), but the diffraction peak broadens and the intensity decreases This is due to the reduction of graphite lamellae, the decrease of crystal structure integrity and the increase of disorder. With the increase of magnification factor, the thin yarn layered structure of graphite becomes more and more obvious
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