Importance of Electrode Preparation Methodologies in Supercapacitor Applications

The work reported here aims toward the optimization of electrode preparation methodologies for superior performance of supercapacitors through a rigorous understanding of underlying physical parameters. Oxygen-functionalized few-layer graphene was employed as an active material while binders [Nafion, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene], solvents for active material dispersion [ethylene glycol and N-methyl-2-pyrrolidone (NMP)], and electrode-drying temperatures (100, 170, and 190 degrees C) were varied. Maximum specific capacitances at different electrode preparation conditions ranged from 240 to 318 F g(-1) at 1 mV s(-1) scan rate of cyclic voltammetry for the same active material. The study revealed that the electrodes prepared using the PVDF binder, the NMP solvent for active material dispersion, 170 degrees C electrode- drying temperature (slightly below the boiling temperature of the solvent) provided the best electrochemical performance. Electrochemical impedance spectroscopy revealed that the resistance for electron transfer at the electrode/electrolyte interface can be minimized while mass transport and pseudocapacitive charging can be improved significantly by tuning electrode preparation methodologies which resulted in smaller time constants and hence better capacitor performances. Scanning electron microscopy images revealed that graphene layers were properly stacked much similar to the synthesized nanomaterial wherein better electrochemical performances were achieved, avoiding the agglomeration of nanomaterials on the electrode surface. Low viscosity of the solvent for active material dispersion and better solubility of the binder in the solvent helped to reduce the agglomeration of nanomaterials by minimizing the strong van der Waals interaction which causes agglomeration.