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Surface characterization and stability phenomena in Li2FeSiO4 studied by PES/XPS
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2006 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 16, no 34, 3483-3488 p.Article in journal (Refereed) Published
Abstract [en]

Photoelectron spectroscopy (PES) has been used to characterise the surface of Li2FeSiO4 cathodes extracted from lithium-ion batteries. Pristine, uncycled, air-exposed electrodes were first analysed and found to carry significantly greater amounts of Li2CO3 on their surfaces than electrodes stored under inert atmosphere. The surface film formed on electrochemical cycling of Li2FeSiO4 electrodes at 60 degrees C using a LiN(SO2CF3)(2) salt based electrolyte revealed high salt stability and only small amounts of solvent reaction products. These were mainly of Li-carboxylate type; neither carbonates nor LiF were found. The excellent capacity retention (<3% over 120 cycles) and minimal irreversible capacity during the first cycle are probably a direct result of this very thin surface film. Li2FeSiO4 must therefore be seen as a most promising ( and potentially cheap) positive electrode material for future large-scale Li-ion battery applications.

Place, publisher, year, edition, pages
2006. Vol. 16, no 34, 3483-3488 p.
National Category
Chemical Sciences Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94468DOI: 10.1039/b605578hISI: 000239937400008OAI: oai:DiVA.org:uu-94468DiVA: diva2:168317
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2011-06-23Bibliographically approved
In thesis
1. Low-Cost Iron-Based Cathode Materials for Large-Scale Battery Applications
Open this publication in new window or tab >>Low-Cost Iron-Based Cathode Materials for Large-Scale Battery Applications
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There are today clear indications that the Li-ion battery of the type currently used worldwide in mobile-phones and lap-tops is also destined to soon become the battery of choice in more energy-demanding concepts such as electric and electric hybrid vehicles (EVs and EHVs). Since the currently used cathode materials (typically of the Li(Ni,Co)O2-type) are too expensive in large-scale applications, these new batteries will have to exploit some much cheaper transition-metal. Ideally, this should be the very cheapest - iron(Fe) - in combination with a graphite(C)-based anode. In this context, the obvious Fe-based active cathode of choice appears to be LiFePO4. A second and in some ways even more attractive material - Li2FeSiO4 - has emerged during the course of this work.

An effort has here been made to understand the Li extraction/insertion mechanism on electrochemical cycling of Li2FeSiO4. A fascinating picture has emerged (following a complex combination of Mössbauer, X-ray diffraction and electrochemical studies) in which the material is seen to cycle between Li2FeSiO4 and LiFeSiO4, but with the structure of the original Li2FeSiO4 transforming from a metastable short-range ordered solid-solution into a more stable long-range ordered structure during the first cycle. Density Functional Theory calculations on Li2FeSiO4 and the delithiated on LiFeSiO4 structure provide an interesting insight into the experimental result.

Photoelectron spectroscopy was used to study the surface chemistry of both carbon-treated LiFePO4 and Li2FeSiO4 after electrochemical cycling. The surface-layer on both materials was concluded to be very thin and with incomplete coverage, giving the promise of good long-term cycling.

LiFePO4 and Li2FeSiO4 should both be seen as highly promising candidates as positive-electrode materials for large-scale Li-ion battery applications.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 54 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 179
Keyword
Inorganic chemistry, Li-ion battery, cathode material, lithium iron phosphate, lithium iron silicate, X-ray powder diffraction, Mössbauer spectroscopy, photoelectron spectroscopy, Oorganisk kemi
Identifiers
urn:nbn:se:uu:diva-6842 (URN)91-554-6559-5 (ISBN)
Public defence
2006-05-12, Häggsalen, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2013-05-17Bibliographically approved
2. Stability Phenomena in Novel Electrode Materials for Lithium-ion Batteries
Open this publication in new window or tab >>Stability Phenomena in Novel Electrode Materials for Lithium-ion Batteries
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Li-ion batteries are not only a technology for the future, they are indeed already the technology of choice for today’s mobile phones, laptops and cordless power tools. Their ability to provide high energy densities inexpensively and in a way which conforms to modern environmental standards is constantly opening up new markets for these batteries. To be able to maintain this trend, it is imperative that all issues which relate safety to performance be studied in the greatest detail. The surface chemistry of the electrode-electrolyte interfaces is intrinsically crucial to Li-ion battery performance and safety. Unfortunately, the reactions occurring at these interfaces are still poorly understood. The aim of this thesis is therefore to increase our understanding of the surface chemistries and stability phenomena at the electrode-electrolyte interfaces for three novel Li-ion battery electrode materials.

Photoelectron spectroscopy has been used to study the surface chemistry of the anode material AlSb and the cathode materials LiFePO4 and Li2FeSiO4. The cathode materials were both carbon-coated to improve inter-particle contact. The surface chemistry of these electrodes has been investigated in relation to their electrochemical performance and X-ray diffraction obtained structural results. Surface film formation and degradation reactions are also discussed.

For AlSb, it has been shown that most of the surface layer deposition occurs between 0.50 and 0.01 V vs. Li°/Li+ and that cycling performance improves when the lower cut-off potential of 0.50 V is used instead of 0.01 V. For both LiFePO4 and Li2FeSiO4, the surface layer has been found to be very thin and does not provide complete surface coverage. Li2CO3 was also found on the surface of Li2FeSiO4 on exposure to air; this was found to disappear from the surface in a PC-based electrolyte. These results combine to give the promise of good long-term cycling with increased performance and safety for all three electrode materials studied.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 49 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 343
Keyword
Inorganic chemistry, Li-ion battery, electrode material, intermetallic, AlSb, lithium iron phosphate, lithium iron silicate, photoelectron spectroscopy, Oorganisk kemi
Identifiers
urn:nbn:se:uu:diva-8214 (URN)978-91-554-6969-6 (ISBN)
Public defence
2007-09-28, 4101, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-09-07 Created: 2007-09-07 Last updated: 2011-06-23Bibliographically approved

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Nytén, AntonStjerndahl, MårtenRensmo, HåkanSiegbahn, HansArmand, MichelGustafsson, TorbjörnEdström, Kristina

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