<p>The Li-ion battery has, from its commercialisation in the early 1990's, now become the most widely used power source for portable low-power electronics: laptops, cellular phones and MP3-players are a few examples. To further develop existing and find new electrode materials for these batteries, it is vital to understand the lithium insertion/extraction mechanisms taking place during battery operation. In this thesis, single-crystal X-ray diffraction has been used to investigate lithium insertion/extraction mechanisms in the cathode materials V<sub>6</sub>O<sub>13</sub> and LiFePO<sub>4</sub>. A novel single-crystal electrochemical cell for <i>in situ</i> single-crystal X-ray diffraction studies has also been developed.</p><p>The phases Li<sub>3</sub>V<sub>6</sub>O<sub>13</sub> and Li<sub>3+x</sub>V<sub>6</sub>O<sub>13</sub>, 0<x<1, both contain a disordered lithium ion. A low-temperature study of Li<sub>3.24</sub>V<sub>6</sub>O<sub>13</sub> (at 95 K) shows that this disorder is static rather than dynamic; the lithium ion is equally distributed above and below an inversion centre in the centrosymmetric V<sub>6</sub>O<sub>13</sub> host structure. Short-range-ordering between this disordered lithium ion and the lithium ion inserted into Li<sub>3</sub>V<sub>6</sub>O<sub>13</sub> gives rise to solid-solution behaviour not observed earlier in the Li<sub>x</sub>V<sub>6</sub>O<sub>13</sub> system. A model is proposed for the lithium insertion mechanism up to the end-member composition Li<sub>6</sub>V<sub>6</sub>O<sub>13</sub>.</p><p>Lithium has also been electrochemically extracted from LiFePO<sub>4</sub> single crystals. On the basis of the shapes of the LiFePO<sub>4</sub> and FePO<sub>4</sub> reflections, it is concluded that FePO<sub>4</sub> is formed at the crystal surface and that the LiFePO<sub>4</sub>/FePO<sub>4</sub> interface propagates into the crystal. This is in agreement with an earlier proposed model for lithium extraction from LiFePO<sub>4</sub> particles.</p><p>Initial experiments with the newly developed single-crystal electrochemical cell for <i>in situ</i> single-crystal X-ray diffraction demonstrate that it is possible to insert lithium into a single crystal of V<sub>6</sub>O<sub>13</sub> and then collect single-crystal X-ray diffraction data. The method needs further development but promises to become a powerful tool for studying lithium insertion/extraction mechanisms.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-4055 |
| Date | January 2004 |
| Creators | Höwing, Jonas |
| 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 | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 949 |
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