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Operando 7Li Solid State NMR for the Characterization of Battery Anodes

Lorie Lopez, Jose Luis
http://orcid.org/0000-0002-1365-3815
http://rave.ohiolink.edu/etdc/view?acc_num=osu1546475665088431

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Chemistry.
Li-ion batteries are used in many devices, such as in cars, laptop computers, and cell phones. These batteries, however, have a short usable range and a limited life time. Currently, graphite is used as an anode material in most batteries, and even though graphite electrodes have good cycling performance, they have limited specific capacity of 372 mAh/g. Operando spectra of a battery often consists of a strongly overlapping mixture of time dependent and independent resonances due to the compositional complexity. Here I report a new method called Derivative Operando (dOp) that improves the resolution of operando nuclear magnetic resonance (NMR) spectra by removing time independent signals and further distinguishes between time dependent signals associated with formation and removal of species. This approach not only provides better resolution but also more clearly reveals correlations between resonances and the chemical transformations occurring at a specific potential. With the dOp-NMR method we detect the formation of lithium graphite intercalation compounds (GICs), including the signatures of LiC72 and its precursors, which have been previously undetected. We also observe a clear correlation of the dOp 7Li NMR spectra of lithium metal dendrites on the counter electrode to the chemistry of the working electrode. Operando 7Li nuclear magnetic resonance (NMR), ex-situ 7Li magic-angle spinning (MAS) NMR and pair distribution function (PDF) methods are used to investigate the electrochemical lithiation and delithiation of 60 nm particles of tin. While the structural transformation pathways between Li-Sn intermetallics during lithiation and delithiation of Sn nanoparticles are somewhat consistent with the structural evolution of Li{Sn phases expected from the equilibrium binary phase diagram, there are some notable exceptions with the observation of a metastable phase Li2Sn3, and two vacancy rich metastable phases, Li7-zSn3, and Li13-dSn5 during delithiation. The capacity fade of  30 % per cycle is not attributed to particle cracking, but rather to particles losing contact with the carbon/PVDF binder. The disconnecting particles are associated with LixSn phases undergoing large decreases in diameters on delithiation, i.e., Sn, Li2Sn5, LiSn, and Li7Sn3. A peculiar behavior of capacity fade in this system is that it only occurs during delithiation. This is explained by a model of disconnecting-reconnecting LixSn-containing particles which remain in the electrode and become reconnected every cycle by the volume increase of neighboring connected particles during the lithiation process. Similarly, I use operando 7Li NMR and ex-situ 7Li MAS NMR techniques to obtain a better understanding of the lithiation and delithiation mechanisms of Sn oxides. I found that the cycling of SnO behaves similar to b-Sn after the initial reduction reaction, including the formation of vacancy rich phases. The electrochemical reduction of SnO2, however, results in a metallic form of Sn that lithiates differently than b-Sn, with the absence of some intermetallic phases with low lithium content like Li2Sn5, LiSn and thus, resulting in better cyclability. This is somehow contradictory to previous thoughts that SnO2 should cycle identical to -Sn after the first reduction reaction.
Anne Co (Advisor)
Philip Grandinetti (Advisor)
Yiying Wu (Committee Member)
Robert Baker (Committee Member)
173 p.
Analytical Chemistry; Chemistry; Materials Science; Physical Chemistry
lithium-ion batteries; operando NMR; LiSn; lithium; tin; tin oxides; graphite;

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Citations

  • Lorie Lopez, J. L. (2019). Operando 7Li Solid State NMR for the Characterization of Battery Anodes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546475665088431

    APA Style (7th edition)

  • Lorie Lopez, Jose. Operando 7Li Solid State NMR for the Characterization of Battery Anodes. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1546475665088431.

    MLA Style (8th edition)

  • Lorie Lopez, Jose. "Operando 7Li Solid State NMR for the Characterization of Battery Anodes." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546475665088431

    Chicago Manual of Style (17th edition)

osu1546475665088431
52
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This open access ETD is published by The Ohio State University and OhioLINK.