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http://hdl.handle.net/11375/20793
Title: | NMR of Cathodes for Lithium Ion Batteries |
Authors: | Tessaro, Matteo |
Advisor: | Goward, Gillian |
Department: | Chemistry and Chemical Biology |
Publication Date: | 2016 |
Abstract: | Polyanionic and layered oxide cathodes for lithium ion batteries (LIBs) have been studied using a combination of nuclear magnetic resonance (NMR) spectroscopy and galvanostatic cycling. The pyrophosphate series of 6Li-enriched and 7Li Li2Mn1-yFeyP2O7 were synthesized, and characterized by magic angle spinning (MAS) NMR. The four crystallographic sites in Li2MnP2O7 are resolved in its 6Li MAS spectrum, but as iron content increases across the series the resonances broaden, and in Li2FeP2O7 only one resonance is partially resolvable from the other overlapped resonances. Li2FeP2O7 shows the highest capacity in the series. Super-fast MAS rates of 60 kHz were obtainable using a 1.3 mm NMR probe, which enabled the effective analysis of electrochemical samples of Li2FeP2O7 using NMR. Spectra of cycled samples of Li2FeP2O7 reveal that one particular lithium site (Li4) is fully extracted by full charge (4.6 V). The layered oxide cathodes studied here, Li(Ni1/3Mn1/3Co1/3)O2 and Li1+x(Ni0.5Mn0.5)1-xO2, possess large chemical shift anisotropies and wide isotropic regions such that, in the 7Li spectra, spinning sidebands overlap with the isotropic region even at high spinning rates (60 kHz). The pj-MATPASS experiment effectively removes all spinning sidebands, revealing the full isotropic region in 7Li spectra. NMR of cycled samples of NMC show that lithium in the transition metal layer and in the lithium layer is extracted upon charge, and a change of paramagnetic Ni2+ toward diamagnetic Ni4+ is reflected by resonances of the remaining lithium in the lithium layer at full charge. Lastly, the pj-MATPASS spectra of the Li1+x(Ni0.5Mn0.5)1-xO2 series reveals an increase in intensity in the transition metal layer region of the spectra as the amount of lithium (x) increases. Spectra of cycled lithium-rich Li1.2Ni0.4Mn0.4O2 show that structure is unaffected by reversible cycling between 2.5-4.4 V, whereas cycling between 2.5-4.8 V gives rise to irreversible loss in signal intensity. |
URI: | http://hdl.handle.net/11375/20793 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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tessaro_matteo_z_finalsubmission2016September_M.Sc..pdf | 4.07 MB | Adobe PDF | View/Open |
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