Influence of nitrogen gas flow rate on the physical properties of corncob activated carbon for lithium-ion capacitor electrodes

To address the disadvantages of both lithium-ion batteries (low power density) and supercapacitors (low energy density), lithium-ion capacitors (LICs) were created as a hybrid energy storage system. In this study, the biomass-derived activated carbon from corncob (CACN) was prepared by adopting physical and chemical activation processes under different nitrogen gas flow rates (N2). The material was activated with KOH and then pyrolyzed at 700 ℃ under varying N2 flow rates from 200 to 400 standard cubic centimeters per minute (sccm). Scanning electron microscopy (SEM) images revealed that the surface morphology appears to have a highly porous structure. The highest specific surface area (SSA) (1936 m2 g-1) was achieved following activation at 300 sccm, confirmed by the Brunauer–Emmett–Teller (BET) results. X-ray diffraction (XRD) and Raman spectroscopy indicated that the crystal structure was amorphous. Through electrochemical tests, the quasi-rectangular cyclic-voltammogram (CV) graph of the LIC coin-cell constructed by CACN (LICN) has similar characteristics to capacitors and batteries. The best coulombic stability was found for LIC with CACN activated at 300 sccm, presenting the highest energy and power density (10.79 Wh kg-1 and 526.39 W kg-1) by charge-discharge (CD) tests. This optimization of carbon activation enables us to achieve the optimum physical characteristics and electrochemical performance of activated carbon and LIC, respectively.