<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>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6842 |
| Date | January 2006 |
| Creators | Nytén, Anton |
| Publisher | Uppsala University, Department of Materials Chemistry, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 179 |
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