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Silyl-Functionalized Electrolyte Additives and Their Reactivity toward Lewis Bases in Li-Ion Cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-0481-5544
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0001-9070-9264
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0001-6798-9704
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2022 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 34, no 8, p. 3831-3838Article in journal (Refereed) Published
Abstract [en]

Silyl groups are included in a wide range of electrolyte additives to enhance the performance of state-of-the-art Li-ion batteries. A recognized representative thereof is tris-(trimethylsilyl)phosphate (TMSPa) which, along with the similarly structured phosphite, has been at the center of numerous electrolyte studies. Even though the silyl group has already been widely reported to be specifically reactive towards fluorides, herein, a reactivity towards several Lewis bases typically found in Li-ion cells is postulated and investigated with the aim to establish a more simplified and generally applicable reaction mechanism thereof. Both gaseous and electrolyte soluble reactants and products are monitored by combining nuclear magnetic resonance and injection cell-coupled mass spectrometry. Experimental observations are supported by computational models. The results clearly demonstrate that the silyl groups react with water, hydroxide, and methoxide and thereby detach in a stepwise fashion from the central phosphate in TMSPa. Intermolecular interaction between TMSPa and the reactants likely facilitates dissolution and lowers the free energy of reaction. Lewis bases are well known to trigger side reactions involving both the Li-ion electrode and electrolyte. By effectively scavenging these, the silyl group can be explained to lower cell impedance and prolong the lifetime of modern Li-ion batteries.

Place, publisher, year, edition, pages
American Chemical Society (ACS) American Chemical Society (ACS), 2022. Vol. 34, no 8, p. 3831-3838
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-474784DOI: 10.1021/acs.chemmater.2c00345ISI: 000795962300023OAI: oai:DiVA.org:uu-474784DiVA, id: diva2:1660020
Funder
Swedish Research Council, 2016-04069Knut and Alice Wallenberg Foundation, 2017.0204Swedish Foundation for Strategic Research, FFL18-0269StandUpeSSENCE - An eScience CollaborationSwedish National Infrastructure for Computing (SNIC)Available from: 2022-05-23 Created: 2022-05-23 Last updated: 2024-02-14Bibliographically approved
In thesis
1. Elucidating Chemical and Electrochemical Side-Reaction Mechanisms in Li-ion Batteries
Open this publication in new window or tab >>Elucidating Chemical and Electrochemical Side-Reaction Mechanisms in Li-ion Batteries
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries constitute a leading technology that plays a major role in the transition towards sustainable transportation and power generation. The stability of modern batteries relies on a passivation layer formed on the negative electrode known as the solid electrolyte interphase (SEI). Despite concerted efforts to comprehend the various processes taking place during SEI formation, monitoring the reaction pathways in real-time is still very challenging. This is due to the complex interactions within the multicomponent electrochemical system, aggravated by the wide range of electrolyte compositions, electrode materials, and operating conditions.

In this thesis, operando surface enhanced Raman spectroscopy is explored to elucidate the progressive formation of the SEI on the negative electrode surface when the electrode is negatively polarised in a spectro-electrochemical cell. Complementary online-electrochemical mass spectrometry is employed to identify the associated gaseous products formed during the process. The work illustrates that the electrolyte as well as contaminants, such as O2, CO2, and H2O, contribute in electro-/chemical processes that build up the SEI. The thesis then explores reaction pathways involving a SEI-forming electrolyte additive, namely vinylene carbonate (VC), emphasizing its role as a H2O scavenging agent. In comparison to the conventional electrolyte solvent ethylene carbonate, VC exhibits a faster reaction with water impurities, particularly in presence of hydroxide ions. This results in the formation of products that are less likely to impact cell performance.

In the later part, the thesis delves into understanding the stability of electrolyte in an environment of Lewis bases (LB) typically found in the SEI. For that, individual LB (e.g., OH- and OCH3-) are mixed with typical carbonate-based solvents and the products formed as a result of the reaction are analysed. Furthermore, tris(trimethylsilyl)phosphate (TMSPa), a representative of the silyl-functionalised electrolyte additive and known for its reactivity, especially towards fluorides, is used as a means to chemically probe its reactivity towards several LB residues. This investigation aims to establish a more simplified and generally applicable reaction mechanism thereof. The products that are soluble in the electrolyte have been investigated by nuclear magnetic resonance spectroscopy and those in the gas phase is characterised by mass spectrometry. The work highlights that the residues that remain active even after the SEI formation may lead to unwanted side-reactions.

The thesis contributes to a deeper fundamental understanding of the myriad of processes that take place in batteries during SEI formation providing insights crucial for designing next-generation battery materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2365
Keywords
Lithium-ion battery, solid electrolyte interphase, electrolyte additives, reaction mechanism, ethylene carbonate, vinylene carbonate, tris(trimethylsilyl)phosphate, surface enhanced Raman spectroscopy
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-523121 (URN)978-91-513-2037-3 (ISBN)
Public defence
2024-04-05, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Supervisors
Available from: 2024-03-13 Created: 2024-02-14 Last updated: 2024-03-13

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Gogoi, NeehaBowall, ErikLundström, RobinMozhzhukhina, NataliiaHernández, GuiomarBroqvist, PeterBerg, Erik J.

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