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The Cathode Surface Composition of a Cycled Li–O2 Battery: A Photoelectron Spectroscopy 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.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 39, 20673-20680 p.Article in journal (Refereed) Published
Abstract [en]

A layer of reaction products, dominantly built up of C and O in the form of ethers and lithium alkyl carbonates, is formed on the surface of the carbon cathode during discharge of a Li–O2 battery in an electrolyte of 1 M LiPF6 in PC. The results are based on a detailed surface analysis combining the use of in house X-ray photoelectron spectroscopy (XPS) and synchrotron based hard X-ray photoelectron spectroscopy (HAXPES). The Li–O2 batteries were investigated at uncycled state (stored), after the first discharge, after the first charge, and at the end of life (discharge state). The results showed little to no Li2O2 and/or Li2O among the discharge products. The surface layers on the cathode were dominantly removed during charging of the battery. At the end of battery life, no complete discharge product layer is formed. The cathodes showed a strong indication of binder decomposition during cycling of the Li–O2 cell. Overall, the results obtained in this investigation show that the whole cathode formulation as well as the electrolyte composition need a completely new approach for the realization of a recyclable Li–O2 battery.

Place, publisher, year, edition, pages
2012. Vol. 116, no 39, 20673-20680 p.
Keyword [en]
Litihum-air, Li-O2, battery, Metal-air, XPS, PES, Photoelectron Spectroscopy
National Category
Physical Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-182604DOI: 10.1021/jp302168hISI: 000309375700003OAI: oai:DiVA.org:uu-182604DiVA: diva2:560149
Funder
StandUp
Available from: 2012-10-11 Created: 2012-10-11 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/jp302168h

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Younesi, RezaEdström, KristinaHahlin, Maria

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