Identification of battery products and intermediates through NMR spectroscopy

Huff, Laura

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https://hdl.handle.net/2142/50463 Copy

Description

Title

Identification of battery products and intermediates through NMR spectroscopy

Author(s)

Huff, Laura

Issue Date

2014-09-16

Director of Research (if dissertation) or Advisor (if thesis)

Gewirth, Andrew A.

Doctoral Committee Chair(s)

Gewirth, Andrew A.

Committee Member(s)

• Girolami, Gregory S.
• Moore, Jeffrey S.
• Bailey, Ryan C.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Lithium-oxygen (Li-O2) battery
• Lithium-sulfur (Li-S) battery
• lithium-ion (Li-ion) battery
• Nuclear magnetic resonance (NMR)
• Nuclear magnetic resonance (NMR) spectroscopy
• solid-state Nuclear magnetic resonance (NMR)
• Lithium-7 (7Li)
• Lithium-6 (6Li)
• Sulfur-33 (33S)
• Carbon-13 (13C)
• products
• intermediates
• secondary electrolyte interphase (SEI)
• 2-D Nuclear magnetic resonance (NMR) spectroscopy
• identification of battery products

Abstract

This dissertation focuses on identification of products and intermediates formed in the lithium-oxygen, lithium-sulfur, and lithium-ion battery systems. Interest in the species formed in cycled batteries is motivated by incomplete knowledge of the discharge mechanisms and products formed, where knowledge of these species can allow the design of more efficient batteries with greater specific energy density. The greater interest in batteries with high energy storage capabilities is motivated by the current social and economic goal of creating a sustainable energy future that is powered by renewable energy sources and energy storage devices. The first section focuses on identification of species formed in lithium-oxygen (Li-O2) batteries. Discharged lithium–O2 battery cathodes are investigated with different catalysts present including Pd, α-MnO2 and CuO, and containing two different electrolyte solvents, 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC) and tetraethylene glycol dimethyl ether (TEGDME). Solid-state 6Li magic angle spinning (MAS) NMR spectroscopy is used identify lithium products that are formed in the cathodes and differences between products formed with different catalysts and solvents present. Significant differences in the products formed in Li–O2 cathodes with the two different solvents, EC/DMC and TEGDME, are described. Due to the small chemical shift range of lithium, the exact speciation is difficult to obtain from 6Li MAS NMR data alone. Fitting of the 6Li NMR peaks with tested Li-oxide powder standards indicates that Li–O2 cathodes discharged in EC/DMC produce primarily Li2CO3 as a lithium product and those discharged in TEGDME produce primarily Li2O2. Solution 2-D correlation 1H–13C NMR spectroscopy techniques allow for determination of side-products produced in Li–O2 cathodes, which are presented. The second section focuses on identification of products and intermediates formed in lithium-sulfur (Li-S) battery cathodes using solid-state 6Li and 33S MAS NMR spectroscopy. Cathodes are stopped and measured ex-situ at three different potentials during battery discharge to obtain chemical shifts and T2 relaxation times of the products formed, which are discussed. The chemical shifts in the spectra of both 6Li and 33S NMR demonstrate that long-chain, soluble lithium polysulfide species formed at the beginning of discharge are indistinguishable from each other (similar chemical shifts), while short-chain, insoluble polysulfide species that form at the end of discharge (presumably Li2S2 and Li2S) have a different chemical shift, thus distinguishing them from the soluble long-chain products. Spin-spin T2 relaxation measurements of discharged cathodes are also presented, which demonstrate that T2 relaxation rates form two groupings and support previous conclusions that long-chain polysulfide species are converted to shorter chain species during discharge. Through the complementary techniques of 1-D 6Li and 33S solid-state MAS NMR spectroscopy, solution 7Li and 1H NMR spectroscopy, and T2 measurements, structural information about the discharge products of Li-S batteries is obtained and discussed. The final section focuses on identification of compounds formed in the secondary electrolyte interphase (SEI) layer of lithium-ion (Li-ion) battery anodes using solid-state NMR spectroscopy matrix assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS). Solid-state 7Li and 13C MAS NMR spectra of cycled Li-ion anodes demonstrate SEI compound formation that occurs upon lithiation of Li-ion anodes and changes that occur in the SEI compounds upon de-lithiation of the anodes. Solid-state 13C DPMAS NMR shows changes in organic peaks associated with the solvent compounds (ethylene carbonate and dimethyl carbonate, EC/DMC) upon battery cycling, which are due to formation and subsequent changes in SEI compounds. Solid-state 13C NMR spin-lattice (T1) relaxation rate measurements of lithiated Li-ion anodes and standard polyethylene oxide (PEO) powders and MALDI-TOF mass spectrometry results indicate that large molecular-weight polymers are formed in the SEI layers of discharged anodes. MALDI-TOF MS and NMR spectroscopy results additionally both indicate that greater amounts of different products are present in de-lithiated anodes compared with lithiated anodes.

Graduation Semester

2014-08

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Permission to use copyrighted material was obtained from the Journal of Power Sources.

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