Date of Award

Spring 2015

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

N. M. Ravindra

Second Advisor

Michael Jaffe

Third Advisor

Halina Opyrchal

Fourth Advisor

Balraj Subra Mani

Fifth Advisor

Willis B. Hammond

Abstract

Graphene has been identified as a promising material for energy storage, especially for high performance ultracapacitors. Graphene-based ultracapacitors show high stability, significantly-improved capacitance and energy density with fast charging and discharging time at a high current density, due to enhanced ionic electrolyte accessibility in deeper regions. The surface area of a single graphene sheet is 2630 m2/g, substantially higher than values derived from Brunauer Emmett Teller (BET) surface area measurements of activated carbons used in the current electrochemical double layer capacitors.

In an ultracapacitor cell, chemically modified graphene (CMG) materials demonstrate high specific capacitances of 135 and 99 F/g in aqueous and organic electrolytes, respectively. In addition, high electrical conductivity gives these materials consistently good performance over a wide range of voltage scan rates.

This paper reports a modeling methodology to predict the electrical behavior of a 2.7 V/650 F ultracapacitor cell. The ultracapacitor cell is subject to the charge/discharge cycling with constant-current between 1.35 V and 2.7 V. The charge/discharge current values examined are 50, 100, 150, and 200 A. A three resistor-capacitor (RC) parallel branch model is employed to calculate the electrical behavior of the ultracapacitor. The simulation results for the variations of the cell voltage as a function of time for various charge/discharge currents are in good agreement with the experimental measurements.

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