LiFeSO4F as a Cathode Material for Lithium-Ion Batteries: Synthesis, Structure, and Function

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LiFeSO4F as a Cathode Material for Lithium-Ion Batteries : Synthesis, Structure, and Function

Sobkowiak, Adam, 1985- (author): Uppsala universitet,Institutionen för kemi - Ångström,Structural Chemistry

Björefors, Fredrik, Docent (thesis advisor): Uppsala universitet,Institutionen för kemi - Ångström

Edström, Kristina (thesis advisor)

Andersson, Anna, PhD (thesis advisor): ABB Corporate Research

Palacin, M. Rosa, Prof. (opponent): Institut de Ciència de Materials de Barcelona

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ISBN 9789155493448
Uppsala : Acta Universitatis Upsaliensis, 2015
English 79 s.
Series: Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 1291

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Doctoral thesis (other academic/artistic)

Abstract Subject headings

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.

Subject headings

NATURVETENSKAP -- Kemi -- Materialkemi (hsv//swe)
NATURAL SCIENCES -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Keyword

Li-ion battery
cathode
LiFeSO4F
tavorite
triplite
synthesis
performance
structure
coating
PEDOT
XRD
Mössbauer spectrocopy
SEM
TEM
electrochemistry
Kemi med inriktning mot materialkemi
Chemistry with specialization in Materials Chemistry

Publication and Content Type

vet (subject category)
dok (subject category)

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