NMR studies of intercalation materials for lithium ion batteries.
Item
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Title
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NMR studies of intercalation materials for lithium ion batteries.
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Identifier
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AAI3083669
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identifier
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3083669
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Creator
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Guo, Xiaodong.
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Contributor
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Adviser: Steven G. Greenbaum
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Date
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2003
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Energy | Physics, Electricity and Magnetism
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Abstract
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Although lithium ion batteries have been commercially available products, there are still a lot of unsolved questions stimulating basic materials research with the aim of further improving their properties. The goals include: higher capacity for lithium uptake; higher lithium diffusivity for higher discharge current; greater chemical and electrochemical stability and structural stability over a wider range of lithiation. Understanding the correlation between the structural and electrochemical properties of electrode materials is a key step to improve the performance of the batteries. These studies are often hampered by the lack of long-range order found only in well-defined crystalline phase. Nuclear magnetic resonance (NMR) spectroscopy is an ideal method and one of a few very powerful tools for exploring local structural and electronic environment of ions such as Li+ ions in lithium ion battery electrode materials due to the high NMR sensitivity of the naturally abundant 7Li nucleus.;Both pristine and partially oxidized graphite exhibit three 7 Li resonances corresponding to different reversible Li sites associated with high and low lithiation levels. The population of Li bonded to edge sites is enhanced in the partially oxidized graphite, and increasing lithiation results in host structural rearrangement converting the edge-site Li into intercalated Li.;One of the primary failure mechanics believed to occur in the cells is the formation of a passivating layer on the positive electrode that eventually leads to a loss of electrical contact between active cathode particles. The 7Li NMR spectra demonstrate the presence of a solid electrolyte interface (SEI), characterized by a relatively featureless absorption centered at 0 ppm. The SEI growth has been quantitatively monitored by integrating the spectral intensities of the SEI feature.;7Li NMR spectra show at least two local phases that cannot be distinguished by X-ray diffraction (XRD) measurement for cation-substituted (Fe,Co) LiNiO2. Substituting Fe for Ni creates larger local structure distortion.;Two sets of LiCoxNil1-xVO4 samples prepared via two different methods are studied by 7Li and 51V NMR. The cation distribution is obtained by analyzing the 51V NMR spectra; the results are different from the XRD data result. Deviation from ideal inverse spinel structure is observed.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
