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This dissertation presents studies using high-resolution solid state NMR spectroscopy and a relatively new imaging technique (Stray-Field Imaging, STRAFI) on energy related materials. NMR spectroscopy studies were carried out on three porphyrins, Octaethyl porphyrin (OEP) and its metallated derivatives ZnOEP and NiOEP, which are found in higher boiling fractions during the refining of crude oil and cause clogging of the refining pipes. Although these compounds had been investigated by others via high resolution solid state 13C cross polarization magic angle spinning (CP-MAS) NMR using powders, the peak assignments had been ambiguous because of large line widths. Arguing that a significant cause of broadening might be the anisotropic bulk magnetic susceptibility, we utilized single crystals in our 13C CP-MAS measurements and observed a nearly 2-fold line-narrowing. This enhanced resolution enabled us to assign chemical shifts to each carbon for all the three compounds. The new assignments are now in agreement with X-ray structural data, and allowed us to probe the motional dynamics of the methyl and methylene carbons of the OEP side chains. Magnetic resonance imaging (MRI) of battery materials provides a noninvasive method for in situ monitoring of electrochemical processes involved in charge/discharge cycling. Here we introduce the use of Stray Field Imaging (STRAFI) technique that utilizes a very large field-gradient in the fringe field of a magnet to improve the image resolution particularly for solid materials (generally very difficult to obtain using conventional MRI methods). We got a resolution of ~15µm, about an order-of-magnitude resolution enhancement than that possible by conventional MRI, which enabled us to use and study graphite||Li and LiFePO4||Li half cells in situ. The high resolution 7Li STRAFI profiles allowed us to monitor the in situ Li ions transfer between the electrodes during charge/discharge cycling as well as the formation and changes of the irreversible Li microstructures components.
CP-MAS NMR, high resolution NMR, Li ion batteries, single crystal, STRAFI
Date of Defense
June 27, 2013.
A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Naresh Dalal, Professor Directing Dissertation; Irinel Chiorescu, University Representative; Harold Kroto, Committee Member; Albert Stiegman, Committee Member.
Florida State University
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