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Characterization of Reaction Products in the Li-O2 Battery Using Photoelectron Spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.ORCID iD: 0000-0003-2538-8104
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 [en]
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: urn:nbn:se:uu:diva-183887ISBN: 978-91-554-8544-3 (print)OAI: oai:DiVA.org:uu-183887DiVA: diva2:564991
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
List of papers
1. Influence of the Cathode Porosity on the Discharge Performance of the Lithium-Oxygen Battery
Open this publication in new window or tab >>Influence of the Cathode Porosity on the Discharge Performance of the Lithium-Oxygen Battery
2011 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, no 22, 9835-9838 p.Article in journal (Refereed) Published
Abstract [en]

By varying the ratio between the amount of carbon and Kynar binder in the cathode of a lithium-oxygen battery, it could be shown that an increasing amount of binder resulted in a decrease in the discharge capacity, mainly as a result of the decrease in the cathode porosity. It was shown that the Kynar binder blocked the majority of the pores with a width below 300 angstrom as determined by studying the pore volume and pore size distribution by nitrogen adsorption. Three carbonate based electrolytes (PC, PC:DEC (1:1), and EC:DEC (2:1) with 1 M LiPF(6)) were tested with the various cathode film compositions. Generally, the PC:DEC and EC:DEC based electrolytes provided higher capacities than PC. The results indicated that the air electrode composition and its effect on the porosity of the cathode, as well as electrolyte properties, are important when optimizing the discharge capacity.

Keyword
Lithium-oxygen, Air electrode, Porosity, Cathode formulation
National Category
Chemical Sciences Inorganic Chemistry Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-160711 (URN)10.1016/j.jpowsour.2011.07.062 (DOI)000295602400099 ()
Available from: 2011-11-02 Created: 2011-10-31 Last updated: 2017-12-08Bibliographically approved
2. Ether Based Electrolyte, LiB(CN)4 Salt and Binder Degradation in the Li-€“O2 Battery Studied by Hard X-ray Photoelectron Spectroscopy (HAXPES)
Open this publication in new window or tab >>Ether Based Electrolyte, LiB(CN)4 Salt and Binder Degradation in the Li-€“O2 Battery Studied by Hard X-ray Photoelectron Spectroscopy (HAXPES)
Show others...
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 35, 18597-18604 p.Article in journal (Refereed) Published
Abstract [en]

Li-O2 cells composed of a carbon cathode containing an α-MnO2 nanowire catalyst and a Kynar (PVDF-HFP) binder were cycled with different electrolytes containing 0.5 M LiB(CN)4 salt in polyethylene glycol dimethyl ether (PEGDME) or tetraethylene glycol dimethyl ether (Tetraglyme) solvents. All cells exhibited fast capacity fading. To explain this, the surface chemistry of the carbon electrodes were investigated by synchrotron based hard X-ray photoelectron spectroscopy (HAXPES) using two photon energies of 2300 and 6900 eV. It is shown that the LiB(CN)4 salt and Kynar binder were degraded during cycling, forming a layer composed of salt and binder residues on the cathode surface. The degradation mechanism of the salt differed in the two tested solvents and, consequently, different types of boron compounds were formed during cycling. Larger amounts of the degraded salt was observed using Tetraglyme as the solvent. With a nonfluorined Li-salt, the observed formation of LiF, which might be a reason for the observed blockage of pores in the cathode and for the observed capacity fading, must be due to Kynar binder decomposition. The amount of LiF formed in the PEGDME cell was larger than that formed in the Tetraglyme cell. The results indicate that not only the electrolyte solvent, but also electrolyte salt as well as the binder used for the porous cathode must be carefully considered when building a successful rechargeable Li-O2 battery.

Keyword
Lithium-air, Li-O2, battery, metal/air, Hard X-ray Photoelectron Spectroscopy, XPS, LiB(CN)4, Ether electrolyte, Kynar, binder decomposition
National Category
Physical Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-182045 (URN)10.1021/jp303691m (DOI)000308339600004 ()
Funder
StandUp
Available from: 2012-10-02 Created: 2012-10-02 Last updated: 2017-12-07Bibliographically approved
3. Li-O2 Battery Degradation by Lithium Peroxide (Li2O2): A Model Study
Open this publication in new window or tab >>Li-O2 Battery Degradation by Lithium Peroxide (Li2O2): A Model Study
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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
Keyword
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:nbn:se:uu:diva-183884 (URN)10.1021/cm303226g (DOI)000313303400013 ()
Funder
Swedish Research CouncilStandUp
Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2017-12-07Bibliographically approved
4. The Cathode Surface Composition of a Cycled Li–O2 Battery: A Photoelectron Spectroscopy Study
Open this publication in new window or tab >>The Cathode Surface Composition of a Cycled Li–O2 Battery: A Photoelectron Spectroscopy Study
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.

Keyword
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:nbn:se:uu:diva-182604 (URN)10.1021/jp302168h (DOI)000309375700003 ()
Funder
StandUp
Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2017-12-07Bibliographically approved
5. Surface Characterization of the Carbon Cathode and the Lithium Anode of Li-O2 Batteries using LiClO4 or LiBOB salts
Open this publication in new window or tab >>Surface Characterization of the Carbon Cathode and the Lithium Anode of Li-O2 Batteries using LiClO4 or LiBOB salts
2013 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 4, 1333-1341 p.Article in journal (Refereed) Published
Abstract [en]

The surface compositions of a MnO2 catalyst containing carbon cathode and a Li anode in a Li–O2 battery were investigated using synchrotron-based photoelectron spectroscopy (PES). Electrolytes comprising LiClO4 or LiBOB salts in PC or EC:DEC (1:1) solvents were used for this study. Decomposition products from LiClO4 or LiBOB were observed on the cathode surface when using PC. However, no degradation of LiClO4 was detected when using EC/DEC. We have demonstrated that both PC and EC/DEC solvents decompose during the cell cycling to form carbonate and ether containing compounds on the surface of the carbon cathode. However, EC/DEC decomposed to a lesser degree compared to PC. PES revealed that a surface layer with a thickness of at least 1–2 nm remained on the MnO2 catalyst at the end of the charged state. It was shown that the detachment of Kynar binder influences the surface composition of both the carbon cathode and the Li anode of Li–O2 cells. The PES results indicated that in the charged state the SEI on the Li anode is composed of PEO, carboxylates, carbonates, and LiClO4 salt.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
Keyword
Li-O2 battery, XPS, Carbon Cathode, Lithium Anode, Perchlorate, Lithium/Air, Photoelectron Spectroscopy, lithium bis(oxalato)borate
National Category
Materials Chemistry Physical Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-183885 (URN)10.1021/am3026129 (DOI)000315619100022 ()
Funder
StandUp
Available from: 2012-11-05 Created: 2012-11-05 Last updated: 2017-12-07Bibliographically approved
6. The SEI Layer Formed on Lithium Metal in the Presence of Oxygen: A Seldom Considered Component in the Development of the Li-O2 battery
Open this publication in new window or tab >>The SEI Layer Formed on Lithium Metal in the Presence of Oxygen: A Seldom Considered Component in the Development of the Li-O2 battery
2013 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 225, 40-45 p.Article in journal (Refereed) Published
Abstract [en]

The SEI layer formed on metallic Li which has been used as an anode in a Li-O2 battery is studied for the first time. We have used XPS to monitor the surface composition of the lithium electrode and have identified the various chemical species present. The XPS results indicated that the composition of the SEI layer is affected by the presence of oxygen and is unstable during cycling. We also observed decomposition products from the binder material used in the cathode on the surface of the lithium anode. This new SEI layer has an increased resistance affecting the lithium deposition which is essential for battery operation.

Keyword
Litihum-air, SEI, solid electrolyte interphase, Li-O2, Battery, Lithium anode, XPS, Photoelectron Spectroscopy
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-183344 (URN)10.1016/j.jpowsour.2012.10.011 (DOI)000313923400007 ()
Available from: 2012-10-24 Created: 2012-10-24 Last updated: 2017-12-07Bibliographically approved

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