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Elucidating Chemical and Electrochemical Side-Reaction Mechanisms in Li-ion Batteries
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-0481-5544
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
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 [en]
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: urn:nbn:se:uu:diva-523121ISBN: 978-91-513-2037-3 (print)OAI: oai:DiVA.org:uu-523121DiVA, id: diva2:1837795
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
List of papers
1. Elucidating the Step‐Wise Solid Electrolyte Interphase Formation in Lithium‐Ion Batteries with Operando Raman Spectroscopy
Open this publication in new window or tab >>Elucidating the Step‐Wise Solid Electrolyte Interphase Formation in Lithium‐Ion Batteries with Operando Raman Spectroscopy
2022 (English)In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 9, no 22, article id 2200945Article in journal (Refereed) Published
Abstract [en]

The solid electrolyte interphase (SEI) is arguably one of the most critical components of the Li-ion cell. Despite decades of studies of the SEI, its intrinsic complexity and the lack of suitable characterization tools still prevent a real consensus on the governing mechanisms to be reached. Herein, operando Raman spectroscopy supported by complimentary online electrochemical mass spectrometry is employed to study the SEI formation on Au in a model electrolyte based on LiClO4 in ethylene carbonate (EC). Both the electrolyte itself and cell contaminants, such as O2, CO2, and H2O, contribute in stepwise electro-/chemical processes to the build-up of the SEI. Effects associated with electrode/electrolyte double-layer charging, electrode adsorbate polarization (stark effect), and SEI dissolution are discerned. Lithium carbonate and lithium oxide are identified as major products formed already ≈2 V versus Li+/Li. Although Raman spectroscopy provides deeper insights into the underlying mechanisms, complementary techniques are necessary to support spectral interpretations. Classical challenges in the field of surface science, such as contaminations, have to be systematically addressed if the puzzle of the SEI ever will be completed.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
Keywords
interphases, Li-ion batteries, operando, Raman, solid electrolyte interphase, SERS
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-480332 (URN)10.1002/admi.202200945 (DOI)000823854500001 ()
Funder
Swedish Research Council, 2016‐04069Knut and Alice Wallenberg Foundation, 2017.0204Swedish Foundation for Strategic Research, FFL18-0269StandUp
Available from: 2022-07-09 Created: 2022-07-09 Last updated: 2024-02-14Bibliographically approved
2. Base-driven Ring-Opening Reactions of Vinylene Carbonate
Open this publication in new window or tab >>Base-driven Ring-Opening Reactions of Vinylene Carbonate
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-523096 (URN)
Available from: 2024-02-14 Created: 2024-02-14 Last updated: 2024-02-14
3. Unveiling Reaction Pathways of Ethylene Carbonate and Vinylene Carbonate in Li-ion Batteries
Open this publication in new window or tab >>Unveiling Reaction Pathways of Ethylene Carbonate and Vinylene Carbonate in Li-ion Batteries
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-522072 (URN)
Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-02-14
4. Silyl-Functionalized Electrolyte Additives and Their Reactivity toward Lewis Bases in Li-Ion Cells
Open this publication in new window or tab >>Silyl-Functionalized Electrolyte Additives and Their Reactivity toward Lewis Bases in Li-Ion Cells
Show others...
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
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-474784 (URN)10.1021/acs.chemmater.2c00345 (DOI)000795962300023 ()
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
5. Reactivity of Organosilicon Additives with Water in Li-ion Batteries
Open this publication in new window or tab >>Reactivity of Organosilicon Additives with Water in Li-ion Batteries
Show others...
2024 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 128, no 4, p. 1654-1662Article in journal (Refereed) Published
Abstract [en]

Introducing small volumes of organosilicon-containing additives as part of lithium-ion battery (LIB) electrolyte engineering has been getting a lot of attention owing to these additives’ multifunctional properties. Tris(trimethylsilyl)phosphate (TMSPa) is a prominent member of this class of additives and scavenges Lewis bases such as water, although the rate at which the reaction occurs and the fate of the resultant product in the battery system still remain unknown. Herein, we have employed complementary nuclear magnetic resonance and gas chromatography–mass spectrometry to systematically study the reactivity of TMSPa with water in conventional organic carbonate solvents mimicking the Li-ion cell environment. The reaction products are identified, and a working reaction pathway is proposed by following the chemical evolution of the products over varying time and temperatures. We found that the main reaction products are trimethylsilanol (TMSOH) and phosphoric acid (H3PO4); however, various P–O–Si-containing intermediates were also found. Similar to water, the Lewis base TMSOH can undergo reaction with TMSPa at room temperature to form hexamethyldisiloxane and can also activate ethylene carbonate (EC) ring-opening reactions at elevated temperatures (≥80 °C), yielding a TMS derivative with ethylene glycol (TMS-EG). While the formation of TMS-EG at the expense of EC is in principle an unwanted parasitic reaction, it should be noted that this reaction is only activated at elevated temperatures in comparison to EC ring-opening by H2O, which takes place at ≥40 °C. Thus, the study underlines the advantages of organo-silicon compounds as electrolyte additives. Elucidating the reaction mechanism in model systems like this is important for future studies of similar additives in order to improve the accuracy of additive exploration in LIBs.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2024
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-522242 (URN)10.1021/acs.jpcc.3c07505 (DOI)001156038200001 ()
Funder
Swedish Research Council, 2016-04069Knut and Alice Wallenberg Foundation, 2017.0204Swedish Foundation for Strategic Research, FFL18-0269
Available from: 2024-02-01 Created: 2024-02-01 Last updated: 2024-03-06Bibliographically approved

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