Nano - Engineering and Simulating Electrostatic Capacitors for Electrical Energy Storage

Title of Dissertation: NANO-ENGINEERING AND SIMULATING ELECTROSTATIC CAPACITORS FOR ELECTRICAL ENERGY STORAGE Lauren Christine Haspert, Doctor of Philosophy, 2012 Dissertation directed by: Professor Gary W. Rubloff Minta Martin Professor of Engineering, Department of Materials Science and Engineering and the Institute for Systems Research Electrical energy storage solutions with significantly higher gravimetric and volumetric energy densities and rapid response rates are needed to balance the highly dynamic, time-variant supply and demand for power. Nanoengineering can provide useful structures for electrical energy storage because it offers the potential to increase efficiency, reduce size/weight, and improve performance. While several nanostructured devices have shown improvements in energy and/or power densities, this dissertation focuses on the nanoengineering of electrostatic capacitors (ESC) and application of these high-power electrostatic capacitors in electrical energy storage systems. A porous nano-template with significant area enhancement per planar unit area coated with ultra-thin metal-insulator-metal (MIM) layers has shown significant improvements in areal capacitance. However, sharp asperities inherent to the initial nano-template localized electric fields and caused premature (low field) breakdown, limiting the possible energy density (E = 1⁄2 CV/m). A nanoengineering strategy was identified for rounding the template asperities, and this showed a significant increase in the electrical breakdown strength of the device, providing rapid charging and discharging and an energy density of 1.5 W-h/kg – which compares favorably with the best state-ofthe-art devices that provide 0.7 W-h/kg. The combination of the high-power ESC with a complementary high-energydensity electrochemical capacitor (ECC) was modeled to evaluate methods resulting in the combined power-energy storage capabilities. While significant improvements in the ESC’s energy density were reported, the nanodevices display nonlinear leakage resistance, which directly relates to charge retention. The ECC has distinctly different nonlinearities, but can retain a greater density of charge for significantly longer, albeit with slower inherent charging and discharging rates than the ESC. The experimentally derived dynamic model simulating the nonlinear performance of the ESC and ECC devices indicated this hybrid-circuit reduces the time required to charge the ECC to nearmaximum capacity by a factor of up to ~ 12. NANO-ENGINEERING AND SIMULATING ELECTROSTATIC CAPACITORS FOR ELECTRICAL ENERGY STORAGE by Lauren Christine Haspert Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment Of the requirements for the degree of Doctor of Philosophy 2012