The purpose of this research project was to determine the processing conditions necessary for preparing flexible carbon nanofiber electrodes by electrospinning and to explore various applications for those electrodes. It was found that by varying only the relative humidity while electrospinning a poly(acrylonitrile) precursor, fragile or flexible freestanding carbon nanofiber electrodes were prepared. The relative humidity during electrospinning controlled the fiber diameter, the bulk porosity of the material, and flexibility of the final carbon electrode. Higher porosity mats electrospun in a high relative humidity environment prevented fiber sintering, which if not minimized, resulted in non-flexible carbon electrodes. Both flexible and fragile electrodes were freestanding, binderless, and collectorless. Additionally, they required no further processing before use and were 100 wt.% active material. When cycled galvanostatically as a lithium ion battery anode, the flexible electrode exhibited a specific capacity of 379 mAH g-1 at the 100th cycle and capacity retention was 97.4% relative to the fifth cycle. When applied as an active material support electrode for lithium ion battery cathodes, the carbon support was successfully utilized with both micron and nano structured active material and cycled for 100 cycles with limited capacity loss. The same electrodes were also found to be a viable replacement for Pt electrode based actuators/artificial muscles. However, this application requires much further research to understand better the required processing and effects of the physical properties of the electrode on actuator performance. In addition to this, the flexible electrodes have a wide variety of other potential applications including, electrochemical storage and conversion devices, chemical sensing, and filtration. The focus of this work was electrochemical storage and conversion devices in the form of lithium ion battery anodes and cathodes as well as ionic polymer composite actuators. / PHD / In this research, the processing conditions required to prepare flexible carbon nanofiber electrodes by electrospinning was determined. These carbon electrodes were then applied as the anode for lithium ion battery applications, as a support material for the cathode active material for lithium ion battery applications and as an electrode for electrically stimulated actuators, also known as artificial muscles. In addition to these applications, the carbon nanofibers developed here have potential uses for fuel cells, chemical sensors, and filtration. The method used to develop these electrodes was electrospinning, an industrially scalable manufacturing technique that produces nanofibers with diameters ranging from 100 nm to a few microns in diameter. To produce the flexible carbon nanofibers, it was found the precise control of all electrospinning variables had to be maintained. Specifically, the relative humidity of the electrospinning environment was found to be the most crucial. When the electrode was applied as a lithium ion battery anode, it was used without additional processing which made it 100 wt.% active material. When the performance of the battery was tested, a specific capacity, or the energy stored, was found to be 379 mAH/g on the 100th cycle. Relative to the 5th cycle, after the electrode had stabilized, this was a capacity retention of 97.4%. In addition to its successful use as an anode, the carbon nanofiber electrode was also applied as a support material for a flexible lithium ion battery cathode. For this application, two cathode types were examined, micron and nanostructured. Both were prepared by vacuum filtering a dispersion of the active material through the carbon nanofiber electrode support material. Both the micron and nano structured active material were successfully cycled for 100 cycles with limited capacity loss using this novel cathode support material. The same electrodes were also found to be a viable replacement for Pt electrode based actuators/artificial muscles. However, this application requires much further research to understand better the required processing and effects of the physical properties of the electrode on actuator performance.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/89627 |
| Date | 04 December 2017 |
| Creators | Beach, Jeremy |
| Contributors | Chemistry, Moore, Robert Bowen, Ellis, Michael W., Esker, Alan R., Long, Timothy E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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