Doctor of Philosophy
School of Chemistry
Jeong, Hyeon Taek, Fabrication of stretchable and flexible supercapacitor using nanocarbon based materials, Doctor of Philosophy thesis, School of Chemistry, University of Wollongong, 2015. https://ro.uow.edu.au/theses/4410
Stretchable and/or flexible electronic devices have emerged as a new generation technologies for wearable and implantable including high performance sportswear, wearable displays and bio-integrated devices. Stretchable and rechargeable energy storage devices are essential component of fully stretchable and flexible electronic devices. The stretchable and flexible supercapacitors are promising candidates due to their high power density, long life, durability and safety.
In this thesis, we have demonstrated stretchable and flexible supercapacitors base on nanocarbon materials such as, carbon nanotubes (CNTs) and reduced graphene oxide (rGO). Nanocarbon material based supercapacitors have been extensively investigated. However, to date nanocarbon material based supercapacitors have not been investigated for use as stretchable and flexible energy storage devices. Therefore, the theme of this thesis is to successfully design and develop novel nanocarbon material based stretchable and flexible supercapacitors with high durability and performance. Chapter 1 introduces nanocarbon-based materials such as, carbon nanotubes (CNTs) and graphene with literature review of nanocarbon-based electrode and supercapacitor for investigation of nanocarbon material based energy storage devices.
Chapter 2 also introduces general experimental including chemical, reagents, characterization methodology, instrumentation and fundamental of the electrochemistry. Chapter 3 investigates the development of stretchable electrode by incorporating acid-treated single-wall nanotubes (SWCNTs) onto latex (natural rubber) substrate using spray coating technique. The use of acid-treated single-wall carbon nanotubes (SWCNTs) improves capacitance due to increased functional groups on the SWCNTs. Electrochemical properties of the electrode are determined using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Galvanostatic charge/discharge tests are also carried out. The impedance and charge/discharge curves of the latex/SWCNTs electrode show good capacitive behaviour even after repetitive stretching to 100% strain. The highest capacitance value obtained for the unstretched SWCNTs electrode is 119 F g-1 in 1 M Na2SO4 at 5 mV s-1. After 100 stretches approximately 80% of the original capacitance was retained.
In chapter 4, a novel reduced graphene oxide (rGO)/single-wall carbon nanotubes (SWCNTs) composite electrode on stretchable polyurethane substrate was developed. The ratio between rGO and SWCNTs is optimized in order to obtain the best performance. The electrochemical properties of the rGO/SWCNTs composite electrodes were compared to rGO and SWCNTs electrodes. All of the electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge test. The highest capacitance value obtained for the unstretched rGO/SWCNTs electrode is 265 F g-1 in 1 M H2SO4 at 5 mV s-1. This performance decreased to 219 and 162 F g-1 after 50 and 100 stretching cycles, respectively. The rGO/SWCNTs composite electrode maintained 75% of its initial capacitance with an applied strain of 100%. The rGO/SWCNTs composite electrode shows enhanced electrochemical properties in comparison to rGO and SWCNTs electrodes. Approximately 70% of the initial capacitance for the rGO/SWCNTs composite electrode was retained after 100 stretching cycles and through 1000 CV cycles, making the electrodes a potential option for stretchable energy storage.
Chapter 5 extends and develops previous studies (chapter 3 and 4) of a stretchable electrochemical latex and polyurethane (PU) electrode to the highly durable and fully stretchable supercapacitor device with electrochemical behaviour determined as a function of strain (0 to 100%) and stretch/release cycles (up to 100). The stretchable v latex supercapacitor (unstretched) showed a specific capacitance of 61.3 F g-1, which decreased to 41.7 F g-1 after 100 stretching cycles at 100% strain. The PU supercapacitor (unstretched) gave a specific capacitance of 42.9 F g-1 which decreased to 31.1 F g-1 after 100 stretches. The stretchable latex and PU supercapacitor retained 74 % and 89 % of the initial capacitance at 100% elongation, respectively.
In chapter 6, a flexible supercapacitor composed of the rGO/SWCNTs composite electrode on a degradable polycaprolactone (PCL) substrate was developed. All of the electrochemical properties for the PCL supercapacitor were investigated under fixed 180o, 120o, 60o and 30o of bending angle and 0 to 500 bending/releasing cycles using a Shimadzu EZ mechanical tester to assess practical and realistic performance of the biocompatible/flexible PCL supercapacitor. The highest capacitance value obtained for the PCL supercapacitor is 52.5 F g-1. 70% of capacitance value of the PCL supercapacitor was retained after bending 500 times and 10,000.
The high stability, durability and stretchability of these supercapacitors demonstrate that nanocarbon based stretchable energy storage devices as supercapacitors have potential application for wearable and biocompatible devices.