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Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. ENSTA ParisTech, 828 Blvd Marechaux, F-91120 Palaiseau, France.
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: 0000-0003-2538-8104
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 1, p. 347-355Article in journal (Refereed) Published
Abstract [en]

X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2019. Vol. 123, no 1, p. 347-355
National Category
Physical Chemistry Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-375877DOI: 10.1021/acs.jpcc.8b07679ISI: 000455561100036OAI: oai:DiVA.org:uu-375877DiVA, id: diva2:1285498
Funder
Swedish Energy Agency, 39036-1Swedish Research CouncilStandUpCarl Tryggers foundation Available from: 2019-02-04 Created: 2019-02-04 Last updated: 2019-08-05Bibliographically approved
In thesis
1. Modelling the Molecular World of Electrolytes and Interfaces: Delving into Li-Metal Batteries
Open this publication in new window or tab >>Modelling the Molecular World of Electrolytes and Interfaces: Delving into Li-Metal Batteries
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium metal batteries (LMBs) are potential candidates for powering portable electronic devices and for electromobility. However, utilizing the reactive Li metal electrode means tackling serious challenges in terms of safety risks. A better understanding of electrolytes and solid electrolyte interphase (SEI) formation are highly important in order to improve these issues.

In this thesis, density functional theory (DFT) and molecular dynamics (MD) are used to explore novel electrolyte systems and the interfacial chemistry of electrolyte/Li metal surfaces. In the first part, the electronic structure and possible decompositions pathways of organic carbonates at the Li metal surface are investigated, which provide information about initial SEI formation. Computed X-ray photoelectron spectroscopy (XPS) for these interfacial compounds is used as a tool to find likely electrolyte decomposition pathways and are supported by direct comparison with the experimental results. The electronic structure and computed XPS spectra of electrolyte solvents and the LiNO3 additive on Li metal by DFT provide atomistic insights into the interphase layer.

Solid polymer electrolytes (SPEs) are promising electrolytes to be used with the Li metal electrode. In the second part of the thesis, MD simulations of poly(ethylene oxide) (PEO) doped with LiTFSI salt/Li metal interface demonstrate the impact of the surface on the structure and dynamics of the electrolyte. A new interfacial potential model for MD simulations is also developed for the interactions at the SPE/metal interface, which can better capture this chemical interplay. Moreover, the approach to improve the ionic conductivity of SPEs by adding side-chains to the backbone of polymers is scrutinized through MD simulations of the poly(trimethylene carbonate) (PTMC) system. While providing polymer flexibility, a hindering effects of the side-chains on Li+ ion diffusions through reduced coordination site connectivity is observed.

In the final part, different polymer hosts interacting with Li metal are explored, and rapid decomposition of polycarbonates and polyester on the surface is seen. The complexes of these polymers with LiTFSI and LiFSI showed significant changes in the computed electrochemical stability window and salt degradations. Lastly, Li2O was obtained by DFT calculations as a thermodynamically stable layer on the surface of the Li metal oxidized by PEO.

The modelling studies performed in this thesis highlight the applicability of these techniques in order to probe the SEI and electrolyte properties in LMBs at the atomistic level.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 81
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1830
Keywords
Li-metal battery, solid polymer electrolyte, density functional theory, molecular dynamics simulation, solid electrolyte interphase
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-390066 (URN)978-91-513-0703-9 (ISBN)
Public defence
2019-09-20, Polhemsalen, 10134, Ångstrom Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-08-30 Created: 2019-08-05 Last updated: 2019-09-17

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Ebadi, MahsaCarboni, MarcoYounesi, RezaMarchiori, CleberBrandell, DanielAraujo, Carlos Moyses

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