Design and Performance Studies of Supercapacitor Coin Cells from Hierarchical Activated Carbon Acquired from Stems of Musa Acuminata

The ever-escalating urge for green and clean energy necessitates the development of economical and efficient energy storage materials and devices, especially for supercapacitors. In this regard, activated carbons derived from agricultural (bio) waste have been explored as EDLC (Electric double layer capacitor) materials due to their abundance, low cost, and easy availability. Herein we report the carbonization of stems from the banana plant (Musa acuminata) and its activation using KOH and further characterization by P-XRD, BET, SEM, and TEM techniques. BET analysis of KOH-activated carbon from the banana stem (KCB) indicated large surface properties such as surface area (3059 m2/g), pore volume (1.66 cm3/g), and average pore diameter (2.17 nm). KCB was checked for its electrochemical performance in three-electrode systems and two electrode system-symmetric coin cells (CR-2032). KCB exhibited specific capacitance (Cs) of 326 F/g at a scan rate of 2 mV/s in Cyclic voltammetry—CV (−1.6 to 0.4 V) and 95.98 F/g in Chronopotentiometry—CP (−1.3 to 0.4 V) at a current density of 2.5 A/g and 57.8 F/g in Electrochemical Impedance Spectroscopy—EIS studied from 10–2 to 105 Hz in a three-electrode system. A symmetric coin cell using 6 mg of KCB exhibited a Cs of 98 F/g in CV at 2 mV/s in the potential window of 0–2 V, 29 F/g in CP at 1 A/g (0–1.8 V). Further, the coin cell was subjected to 25,000 cycles at a high current density of 20 A/g and it had a Cs of 67% (at the 10,000th cycle) and 56% at the end of 25,000 cycles with 100% coulombic efficiency. Two such coin cells were connected in series and checked for their practical application to power a 1-W white LED.