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Dissertation/Thesis Abstract

Solid state nuclear magnetic resonance investigations of advanced energy materials
by Bennett, George D., Ph.D., City University of New York, 2009, 115; 3369199
Abstract (Summary)

In order to better understand the physical electrochemical changes that take place in lithium ion batteries and asymmetric hybrid supercapacitors solid state nuclear magnetic resonance (NMR) spectroscopy has been useful to probe and identify changes on the atomic and molecular level. NMR is used to characterize the local environment and investigate the dynamical properties of materials used in electrochemical storage devices (ESD). NMR investigations was used to better understand the chemical composition of the solid electrolyte interphase which form on the negative and positive electrodes of lithium batteries as well as identify the breakdown products that occur in the operation of the asymmetric hybrid supercapacitors. The use of nano-structured particles in the development of new materials causes changes in the electrical, structural and other material properties. NMR was used to investigate the affects of fluorinated and non fluorinated single wall nanotubes (SWNT). In this thesis three experiments were performed using solid state NMR samples to better characterize them.

The electrochemical reactions of a lithium ion battery determine its operational profile. Numerous means have been employed to enhance battery cycle life and operating temperature range. One primary means is the choice and makeup of the electrolyte. This study focuses on the characteristics of the solid electrolyte interphase (SEI) that is formed on the electrodes surface during the charge discharge cycle. The electrolyte in this study was altered with several additives in order to determine the influence of the additives on SEI formation as well as the intercalation and de-intercalation of lithium ions in the electrodes. 7Li NMR studies where used to characterize the SEI and its composition.

Solid state NMR studies of the carbon enriched acetonitrile electrolyte in a nonaqueous asymmetric hybrid supercapacitor were performed. Magic angle spinning (MAS) coupled with cross polarization NMR techniques were used to determine what effects 200 ppm of intentionally added water would have on the decomposition of the acetonitrile. The resultant NMR spectra yielded several prominent peaks which were assigned to acetamide, glycolonitrile, formaldehyde and other lithium carbon derivatives. The aforementioned decomposition products are a believed to be a result of the acetonitrile being hydrolyzed as well as its interaction with the lithium salt. The decomposition products are deposited on electrode surface leading to operation changes in the life of the supercapacitors. The information gained from the NMR studies may be beneficial understanding the supercapacitor operation and aid in future design.

Carbon nanotubes are used to enhance structural stability and performance. In this experiment NMR is used to determine if the addition of nanotubes to two types of polymer matrix changes the structural stiffness and motional dynamics. The polymers studied by direct 1H NMR observations are Polybutadiene (PB) and Polyisobutylene (PIB). PB and PIB with single walled carbon nanotubes (SWNT) as well as functionalized with fluorine (F) produce significantly stronger composites as compared to composites without SWNT.

Indexing (document details)
Advisor: Greenbaum, Steve G.
Commitee: Amatucci, Glen G., Boutis, Gregory S., Catto, Sultan, Chen, Ying Chih
School: City University of New York
Department: Physics
School Location: United States -- New York
Source: DAI-B 70/08, Dissertation Abstracts International
Subjects: Condensed matter physics
Keywords: Carbon nanotubes, Lithium ion batteries, Supercapacitors
Publication Number: 3369199
ISBN: 978-1-109-31042-9
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