D.A.B. Iozzo, M. Tong, V. Sukhotskiy, G. Wu, E.P. Furlani
SUNY at Buffalo,
Keywords: Supercapacitors, electric double layer, ion transport, electrochemistry
Summary:Electric double layer capacitors (EDLCs), also known as supercapacitors, contain an electrolyte with positive and negative ions confined between an anode and cathode. When a voltage is applied, the ions separate and accumulate on the surface of oppositely charged electrodes. The formation of closely spaced layers of charge, i.e. ions and the electrode, gives rise to a stored “capacitor” energy. Moreover, the minuscule charge separation, on the order of angstroms, combined with the relatively large surface area that can be obtained using highly porous activated carbon electrodes, enables EDLCs to have a significantly higher capacitance than traditional capacitors. However, despite the potential and growing applications of EDLCs, many fundamental aspects of their behavior are not well understood, and rational design towards optimization is lacking. In this talk, we introduce computational models that can be used to analyze EDLC performance as a function of critical device parameters, including finite ion size and concentration, the field-dependent permittivity of the electrolyte, the specific surface area of the electrodes, and the applied voltage. The models predict the equilibrium and transient charge distribution within the cell. We demonstrate the models by applying them to a practical EDLC device and perform a parametric analysis to quantify the relative impact of various parameters on the gravimetric capacitance. We also compare the capacitance obtained using organic and aqueous electrolytes. The models provide unique insight into the internal physics of an electrochemical cell and are well suited for the rational design of novel EDL supercapacitors.