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How dynamic is the SEI?
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2007 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 174, no 2, 970-975 p.Article in journal (Refereed) Published
Abstract [en]

The surface chemistry of graphite and intermetallic AlSb has been studied by XPS (X-ray photoelectron spectroscopy) in a Li-ion battery context using LiPF6 in EC/DEC as electrolyte. The main results for graphite are as follows: the SEI (solid electrolyte interphase) is different for the lithiated state after 3 cycles (0.01 V) compared to the delithiated state (1.5 V); after 50 cycles the SEI is thicker; there are more Li2CO3 or semi-carbonates on the surface of the delithiated sample (1.5 V) than on the lithiated sample (0.01 V); LiF is continuously formed during the first cycles but a steady state is reached after 50 cycles; a new peak in the C 1s spectra indicating a fluorine-containing compound is found at high photon energies (292 eV). The main results for AlSb are as follows: the SEI is different for the lithiated state (0.01 V) compared to the delithiated state (1.2 V) after 3 cycles; after 50 cycles the surface layer thickness is slightly larger but significantly thinner than for graphite; contrary to graphite, more Li2CO3 or semi-carbonates are found on the surface of the lithiated sample; also here a new peak indicating a fluorine-containing compound is found in the C 1s spectra at 292 eV. The general result is that the SEI has many similar features between graphite and AlSb but also important differences. The carbonaceous layer is dynamically shifting in chemical composition during cycling for both samples.

Place, publisher, year, edition, pages
2007. Vol. 174, no 2, 970-975 p.
Keyword [en]
Li-ion battery, Intermetallic anode, SEI, Graphite, XPS, AlSb
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96220DOI: 10.1016/j.jpowsour.2007.06.050ISI: 000252020500118OAI: oai:DiVA.org:uu-96220DiVA: diva2:170720
Available from: 2007-09-07 Created: 2007-09-07 Last updated: 2017-12-14Bibliographically approved
In thesis
1. 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
2. Insights into Stability Aspects of Novel Negative Electrodes for Li-ion Batteries
Open this publication in new window or tab >>Insights into Stability Aspects of Novel Negative Electrodes for Li-ion Batteries
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Demands for high energy-density batteries have sharpened with the increased use of portable electronic devices, as has the focus global warming is now placing on the need for electric and electric-hybrid vehicles. Li-ion battery technology is superior to other rechargeable battery technologies in both energy- and power-density. A remaining challenge, however, is to find an alternative candidate to graphite as the commercial anode. Several metals can store more lithium than graphite, e.g., Al, Sn, Si and Sb. The main problem is the large volume changes that these metals undergo during the lithiation process, leading to degradation and pulverization of the anode with resulting limitations in cycle-life.

The Li-ion battery is studied in this thesis with the goal of better understanding the critical parameters determining high and stable electrochemical performance when using a metal or a metal-alloy anode. Various antimony-containing systems will be presented. These represent different routes to circumvent the problems caused by volume change. Sb-compounds exhibit a high lithium storage capability. At most, three Li-ions can be stored per Sb atom, leading to a theoretical gravimetric capacity of 660 mAh/g. Model systems with stepwise increasing complexity have been designed to better understand the factors influencing lithium insertion/extraction.

It is demonstrated that the microstructure of the anode material is crucial to stable cycling performance and high reversibility. The relative importance of the various factors controlling stability, such as particle-size, oxide content and morphology, varies strongly with the type of system studied. The cycling performance of pure Sb is improved dramatically by incorporating a second component, Sb2O3. With a critical oxide concentration of ~25%, a stable capacity close to the theoretical value of 770 mAh/g is obtained for over 50 cycles. Cu2Sb shows stable cycling performance in the absence of oxide. Cu9Sb2 has been presented for the first time as an anode material in a Li-ion battery context. Studies of the Solid Electrolyte Interphase (SEI) formed on AlSb composite electrodes show an SEI layer thinner than graphite, and with a clearly dynamic character.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 405
Keyword
Inorganic chemistry, Li-ion batteries, anode materials, Sb, Cu2Sb, electrodeposition, Oorganisk kemi
Identifiers
urn:nbn:se:uu:diva-8537 (URN)978-91-554-7124-8 (ISBN)
Public defence
2008-04-11, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2008-03-19 Created: 2008-03-19 Last updated: 2010-03-05Bibliographically approved

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Bryngelsson, HannaGustafsson, TorbjörnEdström, Kristina

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