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Unveiling Reaction Pathways of Ethylene Carbonate and Vinylene Carbonate in Li-ion Batteries
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: 0000-0001-5653-0383
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.ORCID iD: 0000-0001-6691-6706
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-522072OAI: oai:DiVA.org:uu-522072DiVA, id: diva2:1833281
Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-02-14
In thesis
1. Exploring Reaction Pathways in Li-ion Batteries with Operando Gas Analysis
Open this publication in new window or tab >>Exploring Reaction Pathways in Li-ion Batteries with Operando Gas Analysis
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reliance on Li-ion batteries is increasing as we transition from fossil fuels to renewable energy sources. Despite their widespread use, a gap remains in understanding certain processes within these batteries, especially regarding the solid electrolyte interphase (SEI) and the impact of side reactions on Li-ion batteries. A custom-made Online Electrochemical Mass Spectrometry (OEMS) instrument was designed to explore these aspects. The OEMS instrument was validated through the study of gas-evolving reactions in the classic LiCoO2 | Graphite system. In-depth studies focusing on the reaction pathways of ethylene carbonate, the archetype Li-ion battery electrolyte solvent, identified the specific reaction pathways contributing to SEI formation. Moreover, ethylene carbonate’s interaction with residual contaminants like OH from H2O reduction was explored. It was revealed that the integrity of the SEI can be compromised by minor amounts of contaminants, establishing a competitive dynamic at the negative electrode surface between ethylene carbonate and residual contaminants such as H2O and HF. Additionally, the roles of additives like vinylene carbonate and lithium bis(oxolato) borate in SEI formation were explored. Vinylene carbonate was shown to form a layer on the negative electrode, but also scavenge protons and H2O, revealing that it is a multi-functional additive. Lithium bis(oxolato) borate on the other hand formed an SEI layer before H2O reduction, blocking the residual contaminant and ethylene carbonate from reaching the electrode surface. By providing insights into the negative electrode’s interphase and SEI formation through a custom-made OEMS instrument, this research underscores the complexity of reaction pathways and the necessity of considering both major and minor, as well as, primary and secondary reactions for a holistic understanding of Li-ion batteries.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2024. p. 80
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2363
Keywords
Online electrochemical mass spectrometry; Li-ion batteries; Solid electrolyte interphase; Reaction pathways;
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-522294 (URN)978-91-513-2034-2 (ISBN)
Public defence
2024-03-22, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2024-02-29 Created: 2024-02-02 Last updated: 2024-02-29
2. 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)
Opponent
Supervisors
Available from: 2024-03-13 Created: 2024-02-14 Last updated: 2024-03-13

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Lundström, RobinBerg, ErikGogoi, NeehaMelin, Tim

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