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Low-Cost Iron-Based Cathode Materials for Large-Scale Battery Applications

<p>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)O<sub>2</sub>-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 LiFePO<sub>4</sub>. A second and in some ways even more attractive material - Li<sub>2</sub>FeSiO<sub>4</sub> - has emerged during the course of this work.</p><p>An effort has here been made to understand the Li extraction/insertion mechanism on electrochemical cycling of Li<sub>2</sub>FeSiO<sub>4</sub>. 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 Li<sub>2</sub>FeSiO<sub>4</sub> and LiFeSiO<sub>4</sub>, but with the structure of the original Li<sub>2</sub>FeSiO<sub>4</sub> 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 Li<sub>2</sub>FeSiO<sub>4</sub> and the delithiated on LiFeSiO<sub>4</sub> structure provide an interesting insight into the experimental result.</p><p>Photoelectron spectroscopy was used to study the surface chemistry of both carbon-treated LiFePO<sub>4</sub> and Li<sub>2</sub>FeSiO<sub>4</sub> 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.</p><p>LiFePO<sub>4</sub> and Li<sub>2</sub>FeSiO<sub>4</sub> should both be seen as highly promising candidates as positive-electrode materials for large-scale Li-ion battery applications.</p>

Identiferoai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6842
Date January 2006
CreatorsNytén, Anton
PublisherUppsala University, Department of Materials Chemistry, Uppsala : Acta Universitatis Upsaliensis
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, text
RelationDigital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 179

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