High-performance and low-cost coin-cell supercapacitors based on waste graphite from spent dry-cell batteries

Graphite rods extracted from spent dry-cell batteries were ground into powder and subjected to chemical activation using potassium hydroxide. The activated carbon (AC) powder showed no visible pore formation but instead appeared to have been exfoliated into thin flakes. The elemental and chemical compositions of the AC are observed to be similar to those of graphene oxide, in agreement with its surface morphology. The AC was then modified with nickel oxide (NiO) and reduced graphene oxide (rGO) and was utilized for the fabrication of supercapacitor electrodes and coin-cell supercapacitors. Increased potential window and higher overall current readings were observed in the sample with a 2:1 NiO-rGO ratio due to the redox reaction capability of NiO and fast ion transport of rGO. The electrochemical performance of the supercapacitor electrode and the coin-cell supercapacitor displayed excellent electric-double layer capacitance behavior and fast ion transfer kinetics between the electrode and electrolyte surface. The specific capacitances of the supercapacitor electrode and the coin-cell supercapacitor were determined to be 27.84 F g−1 and 20.10 F g−1, respectively, at a current density of 0.1 A g−1. The highest energy density was found to be 40.20 Wh kg−1 at a power density of 1440 W kg−1.