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Framework for the characterization and performance projection of electrochemical capacitor electrodes Fok, Chi Wah Eddie

Abstract

The objective of this thesis is to develop a framework for the characterization and performance projection of new electrochemical capacitor electrode materials. This framework was demonstrated on a new commercial electrode, called EXCELLERATOR®, from W.L. Gore & Associates, Inc. The electrode was tested in a Schlenk-type apparatus using cyclic voltammetry in a 0.5M tetrabutylammonium hexafluorophosphate in propylene carbonate solution. A macroscopic homogeneous volume averaged model was used to simulate the cyclic voltammetry response of the electrode. Subsequent fitting of the simulated response to the experimental data gave estimates of the volumetric capacitance and time constant of the electrode to be 40F/cm³ and 133.4s, respectively. Analytical solutions for the terminal voltage, energy density and power density were derived for the constant current discharging of a complete electrochemical capacitor. The evolution of the terminal voltage during discharge was explained. The energy and power densities for discharging the capacitor of different electrode thicknesses and at different current densities were investigated. The observed trends were explained by comparing the relative utilization of the electrode. The maximum energy density that can be extracted from an electrochemical capacitor during different lengths of time was simulated. It was shown that the thinner electrodes have higher energy and power densities at short times because of the lower unused active material mass. For long times, the thicker electrodes are superior because their active material mass is a larger fraction of the total mass. It was shown that the ultimate electrode geometry would involve thin electrodes with negligible non-active material masses. In this case, the thinnest electrodes would have higher energy and power densities than thicker ones even at long times.

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