Modelling and optimization of electrodes utilization in symmetric electrochemical capacitors for high energy and power

- Expression for getting electrode's optimum thickness, charging current and utilization in symmetric ECs were obtained.
- Electrode's effective thickness and utilization in a given device were determined.
- Maximum materials utilization and cell performance were achieved by using electrode's optimum thickness and current.
- Guideline for getting optimum electrode's thickness, charging current and utilization were studied.
- Charging current and electrode thickness were optimized to maximize energy and power densities.

Expressions and guidelines for determination of electrode's effective thickness, optimum charging current density and electrode utilization in device with certain electrode's and electrolyte's effective conductivity were developed, and systematically used to study the performance of electrochemical capacitors (ECs). Effective thickness of electrode increases along with increase in effective conductivity of electrolyte and decreases as charging current density is increase. It was seen that every current density applied to device of specific electrode's and electrolyte's effective conductivity has corresponding effective thickness of electrode, and when charged at current density higher than its maximum current density, materials (electrodes) utilization was less than 100%. Also, when device with electrode's thickness higher than the effective thickness was charged at its maximum current density, materials (electrodes) utilization reduced below 100%. Materials utilization decreases along with increase in charging current density and electrode thickness, but increases as effective conductivity of electrode and electrolyte are increase. Therefore, optimum/effective thickness of electrode and optimum current density must be employed in charging device of given electrode's and electrolyte's effective conductivity for maximum materials utilization and performance (with minimum or no potential drop). Optimum current density beyond which energy density decays increases along with increase in electrode's and electrolyte's effective conductivity and decrease in electrode thickness. Use of optimum current density and effective electrode's thickness to maximize energy and power densities is inevitable, because increase in current density results in increase in power density and decrease in energy density.