INVESTIGATING SOLID-STATE SUPERCAPACITORS CONSTRUCTED WITH PVA/CNT NANOCOMPOSITE ELECTROLYTES A Thesis by Temmuz Coskun Bachelor of Science, Wichita State University, 2012 Submitted to the Department of Mechanical Engineering and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirements for the degree of Master of Science May 2014 © Copyright 2014 by Temmuz Coskun All Rights Reserved INVESTIGATING SOLID-STATE SUPERCAPACITORS CONSTRUCTED WITH PVA/CNT NANOCOMPOSITE ELECTROLYTES The following faculty members have examined the final copy of this thesis for form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Mechanical Engineering. ___________________________________________ Ramazan Asmatulu, Committee Chair ____________________________________________ Hamid Lankarani, Committee Member ____________________________________________ Mehmet Bayram Yildirim, Committee Member iii DEDICATION To my mother, father, and soon-to-be wife iv ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. Ramazan Asmatulu for his everlasting support and mentoring throughout the duration of this work. Also, I would like to extend my sincere gratitude to the members of my committee, Dr. Hamid Lankarani and Dr. Mehmet Bayram Yildirim, for their valuable comments and suggestions on this work. I would like to recognize that this project could not be possible without Dr. Asmatulu and the Department of Mechanical Engineering, Wichita State University proving facilities and resources. I would also like to thank Dr. Anil Mahapatro for providing me with testing equipment, and Department of Chemistry, Wichita State University, for providing me with materials essential for my work. Also, I would like to thank Tom McGuire from the Department of Engineering, Wichita State University, for broadening my knowledge about capacitive behavior and electrical measurement methods. My sincere appreciation goes out to my fellow researchers Aybala Usta, Amir Jabbarnia, Vamsidhar Patolla, and Muhammet Ceylan for their helpful cooperation and encouragement. Finally, I would like to thank my family, without them I would not be here; and my fiancée Emily, for helping me keep my sanity throughout this project. v ABSTRACT The search for alternative energy generation methods requires development for new energy storage methods as well. The ability to use nanotechnology to achieve high surface area, which is correlated to increased energy storage, brought advancements in supercapacitor applications. Supercapacitors have the potential to charge and discharge quickly and hold as much energy as batteries and other chemical storage devices. By having a completely solid-state supercapacitor, problems with leakage and decay could be avoided. Supercapacitors were assembled from electrodes made by reducing graphene oxide in a computer disc drive and adhering two electrodes with composite electrolytes having various concentrations of PVA/CNT. Tests were performed on the completed supercapacitors, as well as the individual components. The analysis of the different concentrations of carbon nanotubes in PVA electrolytes showed the lowest resistivity for 0.5wt% CNT (294 Ωcm) and the highest specific capacitance for 1.0wt% CNT (123.5 F/g). This specific capacitance is a 27% improvement on an electrolyte without CNT. The electrolyte with pure PVA has similar capacitance to other solid-state supercapacitors in the literature. Electrolytes with higher percentages of CNT (0.5%) show higher resistivity because of the decreased carbon solubility or agglomerations. The final product supercapacitors, thin, flexible, and environmentally friendly, can be used in wide temperature ranges, and have a theoretically long lifespan. They can charge more quickly than batteries, and hold more energy than capacitors. This study shows promising enhancements in solid-state supercapacitors, making them an even more plausible replacement for batteries in the near future. The improvements made on the specific capacitance with the different electrolytes could lead to greater efficiency and lower cost in many unique applications requiring absence of liquid components. vi TABLE OF CONTENTS Chapter Page 1. INTRODUCTION ...............................................................................................................1 1.1. Motivation ....................................................................................................................1 1.2. General Background .....................................................................................................3 1.3. Research Objectives ......................................................................................................4 2. LITERATURE REVIEW .....................................................................................................5 2.1. Principles of Supercapacitors ........................................................................................5 2.2. Advantages of Supercapacitors Compared to Batteries ..................................................5 2.3. Supercapacitor Models ..................................................................................................6 2.3.1. Helmholtz ..............................................................................................................7 2.3.2. Gouy-Chapman ......................................................................................................8 2.3.3. Stern ......................................................................................................................9 2.4. Types of Supercapacitors ............................................................................................ 10 2.4.1. Electric Double Layer Supercapacitor .................................................................. 10 2.4.2. Faradaic Supercapacitors...................................................................................... 11 2.5. Electrodes ................................................................................................................... 11 2.5.1. Background.......................................................................................................... 11 2.5.2. Transition Metal Oxides ....................................................................................... 13 2.5.3. Conductive Polymers ........................................................................................... 14 2.5.4. Carbons ............................................................................................................... 15 2.5.5. Graphene Electrodes for Supercapacitors ............................................................. 17 2.6. Electrolytes ................................................................................................................. 20 2.6.1. Aqueous electrolytes ............................................................................................ 20 2.6.2. Organic Electrolytes ............................................................................................. 20 2.6.3. Ionic Liquids ........................................................................................................ 21 2.6.4. Solid Electrolyte .................................................................................................. 21 2.7. Separator ..................................................................................................................... 21 2.8. Applications ................................................................................................................ 22 vii TABLE OF CONTENTS (cont'd) Chapter Page 2.8.1. Backup memory ................................................................................................... 22 2.8.2. Electric / Hybrid Vehicles .................................................................................... 23 2.8.3. Power Quality ...................................................................................................... 24 2.8.4. Battery monitoring ............................................................................................... 24 2.8.5. Portable power supplies ....................................................................................... 25 2.8.6. Electrochemical Actuators ................................................................................... 25 2.8.7. Integrating in Renewable Energy ......................................................................... 26 2.9. Nanomaterials ............................................................................................................. 27 2.9.1. Graphene ............................................................................................................. 27 2.9.2. Carbon Nanotubes ................................................................................................ 27 2.9.3 Nanotechnology Safety Concerns…………………………………………………28 3. EXPERIMENTAL ............................................................................................................. 29 3.1. Materials ..................................................................................................................... 29 3.1.1. Electrode.............................................................................................................. 29 3.1.2. Electrolyte ........................................................................................................... 30 3.2.