Effect of graphitic structure on electrochemical ion intercalation into positive and negative electrodes

Commercially activated carbons are known for their high specific surface areas and low pack densities, thus giving a poor volumetric capacitance for supercapacitors. Here, nonporous pyrolyzed graphite oxides with high pack densities and controllable graphitic structures were prepared through a facile oxidation-heat treatment. XRD, Raman, SEM, and TEM were used to characterize the textural properties and morphologies of these materials. Galvanostatic charge–discharge and cyclic voltammetry revealed that the voltage-driven electrochemical ion intercalation process is, in fact, highly dependent on the graphitic structure. Less graphitized materials with larger interlayer spacings are more easily electrochemically activated, while a more rigid graphitic structure proves to be more difficult. After adequate electrochemical activation, abundant ion-accessible sites were created for charge storage, and the cell-specific capacitance dramatically increased from 3.5 to 23 F/g. The intercalation behaviors of TEA⁺ and BF₄ ^? were separately studied. The results revealed that, due to its smaller anion size, BF₄ ^? displayed superior intercalation capability as well as higher specific capacitance on the positively polarized electrode after electrochemical activation. Therefore, through optimizing the graphitic structure and the EA conditions, a high volumetric capacitance can be achieved.