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Electric potential gradient at the buried interface between Lithium-ion battery electrodes and the SEI observed using 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, 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, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
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2016 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 10, 1775-1780 p.Article in journal (Refereed) Published
Abstract [en]

The buried interface between the bulk electrode material and the solid electrolyte interphase (SEI) in cycled Li-ion battery anodes is suggested to incorporate an electric potential gradient. This suggestion is based on photoelectron spectroscopy (PES) results from different anode materials that all show relative binding energy shifts between the components of the SEI and the active anode. Implications of this electric potential gradient on binding energy reference points in PES as well as on charge-transfer kinetics in Li-ion batteries are discussed. Specifically, we show that the separation of surface layer and bulk material spectral contributions (depth profiling) is crucial for consistent data interpretation. We conclude that previous interpretations of lithiation as cause for changes in PES spectra may need to be revised.

Place, publisher, year, edition, pages
2016. Vol. 7, no 10, 1775-1780 p.
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-281687DOI: 10.1021/acs.jpclett.6b00391ISI: 000376421200004PubMedID: 27104985OAI: oai:DiVA.org:uu-281687DiVA: diva2:915182
Funder
EU, FP7, Seventh Framework Programme, 608575StandUpSwedish Research Council, VR-2012-4681
Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2017-11-30Bibliographically approved
In thesis
1. Si negative electrodes for Li-ion batteries: Aging mechanism studies by electrochemistry and photoelectron spectroscopy
Open this publication in new window or tab >>Si negative electrodes for Li-ion batteries: Aging mechanism studies by electrochemistry and photoelectron spectroscopy
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focusing on the challenges when using Si as a possible new negative electrode material in Li-ion batteries. The overall aim is to contribute to a general understanding of the processes in the Si electrode, to identify aging mechanisms, and to evaluate how they influence the cycling performance. Another objective is to investigate how photoelectron spectroscopy (PES) can be used to analyze these mechanisms.

LiPF6 based electrolytes are aggressive towards the oxide layer present at the surface of the Si particles. With the use of fluoroethylene carbonate (FEC) as an electrolyte additive the cycling performance is improved, but the oxide layer is still affected. A recently developed salt, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), is shown not to have any detrimental effects on the oxide. The SEI with FEC and vinylene carbonate (VC) as contains a high concentration of LiF and polymeric carbonate species and this composition seems to be beneficial for the cycling performance, but the results indicate that additional aging mechanisms occur. Therefore, electrochemical analysis is performed and confirms a continuous SEI formation. However, it also reveals a self-discharge mechanism and that a considerable amount of Li is remaining in the Si material after standard cycling.

PES is used in this work to analyze the SEI-layers as well as the surface and the bulk of the Si material. With this technique it is hence possible to distinguish changes in the Si material as a function of lithiation. To improve the data interpretation of PES spectra, a range of battery electrode model systems are investigated. These results show shifts of the SEI peaks relative to the electrode specific peaks as a result of the SEI thickness and the presence of a dipole layer. Also other electronically insulating composite electrode components show relative peak shifts as a function of the electrochemical potential.

To summarize, these studies investigate a number of well recognized aging mechanisms in detail and also establish additional processes contributing to aging in Si electrodes. Furthermore, this work highlights phenomena that influence data interpretation of PES measurements from battery materials.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1362
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-281694 (URN)978-91-554-9533-6 (ISBN)
Public defence
2016-06-02, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-05-09 Created: 2016-03-29 Last updated: 2016-05-12

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Maibach, JuliaLindgren, FredrikEriksson, HenrikEdström, KristinaHahlin, Maria

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