Increasing specific capacitance by optimization of the thickness of carbon electrodes

Abstract

Increasing energy density without sacrificing lifetime, power and cyclability of electrochemical capacitors is a very important goal. However, most efforts are directed toward improvement of active charge storing materials, while design of devices and minimization of the wight/volume of passive component have received less attention. We propose here a mathematical model of a carbon supercapacitor in organic electrolyte, which establishes a relationship between the specific capacitance of a device, the thickness of its electrodes, and the weight of its passive components (case, external current leads, current collectors, etc.). The model was built on the basis of experimentally obtained dependences and has been validated using experiments with electrodes made of two porous carbon materials. Regardless of the pore size distribution in the specified range of electrode thicknesses, the functional dependence of the electrode's specific capacitance on the thickness is well described within the linear approximation. The use of the developed model enables optimization of the electrode thickness, thus maximizing specific energy density for a chosen carbon electrode material.