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A Mössbauer spectroscopy study of polyol synthesized tavorite LiFeSO4F.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
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.
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2014 (English)In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, ISSN 0304-3843, Vol. 226, no 1-3, 229-236 p.Article in journal (Refereed) Published
Abstract [en]

The tavorite polymorph of LiFeSO4F has attracted considerable attention as a cathode material for lithium ion batteries due to interesting structural and electrochemical characteristics. For the analysis of such iron-based electrode materials, Mössbauer spectroscopy has become an important and highly useful tool. In this work, we perform a detailed Mössbauer study of pristine tavoriteLiFeSO4F prepared by an optimized synthesis in tetraethylene glycol as reaction media. In contrast to many reported results, we demonstrate the use of an asymmetric fitting model for the inner doublet of the spectrum, which is coupled to the structural properties of the compound. Moreover, we discuss a new approach of ascribing the Fe2 + -doublets to the two distinct crystallographic iron sites of tavorite LiFeSO4F by comparing the Mössbauer signal intensities with the expected f-factors for the corresponding iron atom.

Place, publisher, year, edition, pages
2014. Vol. 226, no 1-3, 229-236 p.
Keyword [en]
lithium ion battery, tavorite LiFeSO4F, Mössbauer spectroscopy
National Category
Materials Chemistry
Research subject
Physics with specialization in Nuclear Physics; Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-241039DOI: 10.1007/s10751-013-0935-1OAI: oai:DiVA.org:uu-241039DiVA: diva2:777546
Conference
Proceedings of the 32nd International Conference on the Applications of the Mössbauer Effect (ICAME 2013) held in Opatija, Croatia, 1–6 September 2013.
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2017-12-05
In thesis
1. LiFeSO4F as a Cathode Material for Lithium-Ion Batteries: Synthesis, Structure, and Function
Open this publication in new window or tab >>LiFeSO4F as a Cathode Material for Lithium-Ion Batteries: Synthesis, Structure, and Function
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, two recently discovered polymorphs of LiFeSO4F, adopting a tavorite- and triplite-type structure, were investigated as potential candidates for use as cathode materials in Li-ion batteries. The studies aimed at enriching the fundamental understanding of the synthetic preparations, structural properties, and electrochemical functionality of these materials.

By in situ synchrotron X-ray diffraction (XRD), the formation mechanism of the tavorite-type LiFeSO4F was followed starting from two different sets of precursors, FeSO4∙H2O + LiF, and Li2SO4 + FeF2. The results indicated that the formation of LiFeSO4F is possible only through the structurally related FeSO4∙H2O, in line with the generally recognized topotactic reaction mechanism. Moreover, an in-house solvothermal preparation of this polymorph was optimized with the combined use of XRD and Mössbauer spectroscopy (MS) to render phase pure and well-ordered samples. Additionally, the triplite-type LiFeSO4F was prepared using a facile high-energy ball milling procedure.

The electrochemical performance of as-prepared tavorite LiFeSO4F was found to be severely restricted due to residual traces of the reaction medium (tetraethylene glycol (TEG)) on the surface of the synthesized particles. A significantly enhanced performance could be achieved by removing the TEG residues by thorough washing, and a subsequent application of an electronically conducting surface coating of p-doped PEDOT. The conducting polymer layer assisted the formation of a percolating network for efficient electron transport throughout the electrode, resulting in optimal redox behavior with low polarization and high capacity. In the preparation of cast electrodes suitable for use in commercial cells, reducing the electrode porosity was found to be a key parameter to obtain high-quality electrochemical performance. The triplite-type LiFeSO4F showed similar improvements upon PEDOT coating as the tavorite-type polymorph, but with lower capacity and less stable long-term cycling due to intrinsically sluggish kinetics and unfavorable particle morphology.

Finally, the Li+-insertion/extraction process in tavorite LiFeSO4F was investigated. By thorough ex situ characterization of chemically and electrochemically prepared LixFeSO4F compositions (0≤x≤1), the formation of an intermediate phase, Li1/2FeSO4F, was identified for the first time. These findings helped redefine the (de)lithiation mechanism which occurs through two subsequent biphasic reactions, in contrast to a previously established single biphasic process.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1291
Keyword
Li-ion battery, cathode, LiFeSO4F, tavorite, triplite, synthesis, performance, structure, coating, PEDOT, XRD, Mössbauer spectrocopy, SEM, TEM, electrochemistry
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-262715 (URN)978-91-554-9344-8 (ISBN)
Public defence
2015-11-05, Häggsalen, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-10-14 Created: 2015-09-18 Last updated: 2015-10-27

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Sobkowiak, AdamEricsson, ToreEdström, KristinaGustafsson, TorbjörnBjörefors, FredrikHäggström, Lennart

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