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Li-O2 Battery Degradation by Lithium Peroxide (Li2O2): A Model Study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-2538-8104
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.
Department of Applied Physics, Chalmers University of Technology.
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2013 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 1, 77-84 p.Article in journal (Refereed) Published
Abstract [en]

The chemical stability of the Li-O2 battery components (cathode and electrolyte) in contact with lithiumperoxide (Li2O2) was investigated using X-ray photoelectron spectroscopy (XPS). XPS is a versatile method to detect amorphous as well as crystalline decomposition products of both salts and solvents. Two strategies were employed. First, cathodes including carbon, α‑MnO2 catalyst, and Kynar binder (PVdF-HFP) were exposed to Li2O2 and LiClO4 in propylenecarbonate (PC) or (tetraethylene glycol dimethyl ether) TEGDME electrolytes. The results indicated that Li2O2 degrades TEGDME to carboxylate containing species and that the decomposition products in turn degraded the Kynar binder. The α‑MnO2 catalyst was unaffected. Second, Li2O2 model surfaces were kept in contact with different electrolytes to investigate the chemical stability, and also the resulting surface layer on Li2O2. Further, the XPS experiments revealed that the Li salts LiPF6, LiBF4, and LiClO4 decomposed to form LiF or LiCl together with P-O or B-O bond containing compounds when exposed to Li2O2. PC decomposed to carbonate and ether based species. The degradation of the electrolytes increased from short to long exposure time indicating that the surface layer on Li2O2 became thicker by increasing time. Overall, it was shown that a mixture of ethylene carbonate and diethyl carbonate (EC/DEC) is more robust in contact with Li2O2 compared to PC.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013. Vol. 25, no 1, 77-84 p.
Keyword [en]
Lithium-air, Li2O2, oxygen battery, X-ray photoelectron spectroscopy, Lithium-Oxygen, XPS
National Category
Physical Chemistry Materials Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Polymer Chemistry; Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-183884DOI: 10.1021/cm303226gISI: 000313303400013OAI: oai:DiVA.org:uu-183884DiVA: diva2:564950
Funder
Swedish Research CouncilStandUp
Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Characterization of Reaction Products in the Li-O2 Battery Using Photoelectron Spectroscopy
Open this publication in new window or tab >>Characterization of Reaction Products in the Li-O2 Battery Using Photoelectron Spectroscopy
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rechargeable Li-O2 battery has attracted interest due to its high theoretical energy density (about 10 times better than today’s Li-ion batteries). In this PhD thesis the cycling instability of the Li-O2 battery has been studied. Degradation of the battery has been followed by studying the interface between the electrodes and electrolyte and determining the chemical composition and quantity of degradation products formed after varied cycling conditions. For this in-house and synchrotron based Photoelectron Spectroscopy (PES) were used as a powerful surface sensitive technique. Using these methods quantitative and qualitative information was obtained of both amorphous and crystalline compounds. To make the most realistic studies the carbon cathode pore structure was optimised by varying the binder to carbon ratio. This was shown to have an effect on improving the discharge capacity. For Li-O2 batteries electrolyte decomposition is a major challenge. The stability of different electrolyte solvents and salts were investigated. Aprotic carbonate and ether based solvents such as PC, EC/DEC, TEGDME, and PEGDME were found to decompose during electrochemical cycling of the cells. The carbonate based electrolytes decompose to form a 5-10 nm thick surface layer on the carbon cathode during discharge which was then removed during battery charging. The degradation products of the ether based electrolytes consisted mainly of ether and carbonate based surface species. It is also shown that Li2O2 as the final discharge product of the cell is chemically reactive and decomposes carbonate and ether based solvents. The stability of lithium electrolyte salts (such as LiPF6, LiBF4, LiB(CN)4, LiBOB, and LiClO4) was also studied. The PES results revealed that all salts are unstable during the cell cycling and in contact with Li2O2. Decomposition layers thinner than 5 nm were observed on Li2O2. Furthermore, it is shown that the stability of the interface on the lithium anode is a chief issue. When compared to Li batteries (where oxygen levels are below 10 ppm) working in the presence of excess oxygen leads to the decomposition of carbonate based electrolytes to a larger degree.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1001
Keyword
Li-O2 Battery, Surface Characterization, Lithium-Air Battery, Photoelectron Spectroscopy, XPS
National Category
Materials Chemistry Physical Chemistry
Research subject
Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-183887 (URN)978-91-554-8544-3 (ISBN)
Public defence
2012-12-19, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-11-27 Created: 2012-11-05 Last updated: 2016-04-26Bibliographically approved

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Publisher's full texthttp://pubs.acs.org/doi/abs/10.1021/cm303226g

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Younesi, RezaHahlin, MariaBjörefors, FredrikEdström, Kristina

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