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Electrolyte decomposition on Li-metal surfaces from first-principles theory
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.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 20, article id 204701Article in journal (Refereed) Published
Abstract [en]

Animportant feature in Li batteries is the formation of a solid electrolyte interphase (SEI) on the surface of the anode. This film can have a profound effect on the stability and the performance of the device. In this work, we have employed density functional theory combined with implicit solvation models to study the inner layer of SEI formation from the reduction of common organic carbonate electrolyte solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate) on a Li metal anode surface. Their stability and electronic structure on the Li surface have been investigated. It is found that the CO producing route is energetically more favorable for ethylene and propylene carbonate decomposition. For the two linear solvents, dimethyl and diethyl carbonates, no significant differences are observed between the two considered reduction pathways. Bader charge analyses indicate that 2 e(-) reductions take place in the decomposition of all studied solvents. The density of states calculations demonstrate correlations between the degrees of hybridization between the oxygen of adsorbed solvents and the upper Li atoms on the surface with the trend of the solvent adsorption energies.

Place, publisher, year, edition, pages
2016. Vol. 145, no 20, article id 204701
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-313407DOI: 10.1063/1.4967810ISI: 000390118200037OAI: oai:DiVA.org:uu-313407DiVA, id: diva2:1066999
Funder
Swedish Energy Agency, 39036-1Swedish Research CouncilAvailable from: 2017-01-19 Created: 2017-01-19 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, MahsaBrandell, DanielAraujo, Carlos Moyses

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