Die vorliegende Dissertation beschäftigt sich mit der Synthese, den Li+-Transporteigenschaften und der Thermodynamik von Olivin-Typ LiFePO4. Es werden verschiedene Solvothermalsynthesen untersucht. Neben der Einstellung von Partikelgröße und Partikelmorphologie steht die Analyse der Hydrothermalsynthese aus Li3PO4 und Vivianit durch in situ Messung der elektrolytischen Leitfähigkeit im Vordergrund. Die Untersuchung des Li+-Transportes geschieht auf Basis von Redoxreaktionen. Die formalkinetische Auswertung von Lithiierungs- und Delithiierungsreaktionen und eine Nukleationsanalyse wird durch ein Modell zur Auswirkung von antisite-Defekten auf die Kapazität des Elektrodenmaterials ergänzt. Die Ramanspektroskopie wird in Verbindung mit Lösungsenthalpien zur Identifizierung reaktiver Spezies herangezogen. Schwerpunkt der thermodynamischen Charakterisierung ist die experimentelle Ermittlung der Wärmekapazität. Diese wurde unter Berücksichtigung einer magnetischen Phasenumwandlung im Bereich von 2 K bis 773 K ermittelt. Die Daten erlauben die Berechnung wichtiger thermodynamischer Funktionen.

New iron phosphate and borophosphate compounds were synthesized and characterized by single crystal/powder X-ray diffraction, infrared spectroscopy, raman spectroscopy, thermogravimetric analysis, electron microscopy and elemental analysis. Using several compositions, Fey B(PO4)x type of compounds were attempted to be prepared by solid state reactions. The solid state reactions of boron compounds with a phosphating agent has been completed at 950oC. A new product Fe2BP3O12 is synthesized and indexed in this work which is isostructural with Cr2 BP3O12 A single crystal of iron ammonium phosphate, (NH4)3-xHxFeP3O12, was synthesized by a hydrothermal method and characterized. Its X-ray powder diffraction pattern was indexed in orthorhombic system. The unit cell parameters were found to be as a = 7.775 (&Aring / ), b = 7.445(&Aring / ), c = 14.331(&Aring / ) The compound with the formula NH4FeBP2O8OH was synthesized by hydrothermal method. Its X-ray powder diffraction pattern was indexed in monoclinic system. The unit cell parameters were found to be a = 9.336, b = 8.278, c =9.642&Aring / , and &amp / #946 / = 101.60o, which are good agreement with the literature values. Ferro-axinite type of compound was discovered as single crystals resembling the axinite mineral. The compound was indexed in triclinic system with the unit cell parameters of a = 7.167, b = 8.840 , c = 9.455&Aring / , &amp / #945 / = 64.83o, &amp / #946 / = 64.83o, &amp / #947 / = 69.42o. A zeotype Fe(H2O)2BP2O8.H2O, which was obtained by hydrothermal methods before, was synthesized by a precipitation method using different initial reactant. In this case, instead of Fe+2, Fe+3 compound was used as a reactant. All the compounds have been investigated by FTIR spectroscopy and the assignments of the functional BO3, BO4 and PO4 groups have been done.

Li-ion batteries are not only a technology for the future, they are indeed already the technology of choice for today’s mobile phones, laptops and cordless power tools. Their ability to provide high energy densities inexpensively and in a way which conforms to modern environmental standards is constantly opening up new markets for these batteries. To be able to maintain this trend, it is imperative that all issues which relate safety to performance be studied in the greatest detail. The surface chemistry of the electrode-electrolyte interfaces is intrinsically crucial to Li-ion battery performance and safety. Unfortunately, the reactions occurring at these interfaces are still poorly understood. The aim of this thesis is therefore to increase our understanding of the surface chemistries and stability phenomena at the electrode-electrolyte interfaces for three novel Li-ion battery electrode materials. Photoelectron spectroscopy has been used to study the surface chemistry of the anode material AlSb and the cathode materials LiFePO4 and Li2FeSiO4. The cathode materials were both carbon-coated to improve inter-particle contact. The surface chemistry of these electrodes has been investigated in relation to their electrochemical performance and X-ray diffraction obtained structural results. Surface film formation and degradation reactions are also discussed. For AlSb, it has been shown that most of the surface layer deposition occurs between 0.50 and 0.01 V vs. Li°/Li+ and that cycling performance improves when the lower cut-off potential of 0.50 V is used instead of 0.01 V. For both LiFePO4 and Li2FeSiO4, the surface layer has been found to be very thin and does not provide complete surface coverage. Li2CO3 was also found on the surface of Li2FeSiO4 on exposure to air; this was found to disappear from the surface in a PC-based electrolyte. These results combine to give the promise of good long-term cycling with increased performance and safety for all three electrode materials studied.

Made available in DSpace on 2014-10-09T12:52:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:11Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Ce mémoire est consacré à l'étude théorique des matériaux de cathode pour batteries Li-ion de structure olivine LiMPO4 (M=Mn, Fe, Co, Ni), des phases délithiées MPO4 et des phases mixtes LiFexMn1-xPO4, FexMn1-xPO4 et LiFexCo1-xPO4. La stabilité des phases magnétiques et les paramètres de maille théoriques ont été déterminés par la méthode des pseudopotentiels et comparés aux données expérimentales. Les structures électroniques ont été calculées par une méthode « tout électron » et analysées en termes d'hybridation des orbitales atomiques Ces résultats ont permis d'interpréter les spectres de photoélectrons X et d'absorption des rayons X, en particulier les modifications réversibles associées aux cycles de lithiation/délithiation. Les effets de la polarisation de spin et de la corrélation électronique ont été discutés. Enfin, le calcul des paramètres Mössbauer du 57Fe a montré qu'un accord quantitatif entre les résultats théoriques et les données expérimentales nécessitait la prise en compte de ces deux effets. Ce type de calcul a permis de prédire et d'expliquer que la transformation LiFePO4FePO4 s'accompagnait de la variation du gradient de champ électrique Vzz d'une extrémité à l'autre de l'échelle Mössbauer pour 57Fe. / This thesis is devoted to the theoretical study of the cathode materials for Li-ion batteries with olivine structure LiMPO4 (M=Mn, Fe, Co, Ni), the delithiated phases MPO4 and the mixed phases LiFexMn1-xPO4, FexMn1-xPO4 and LiFexCo1-xPO4. The magnetic phase stability and lattice parameters were theoretically determined from pseudopotential calculations and the results have been compared with experiments. Electronic structures were obtained from all electron calculations and analyzed in terms of orbital hybridization. The results have been used for the interpretation of X-ray photoemission and X-ray absorption spectra, especially changes due to lithiation/delithiation cycles. Effects of spin polarization and electronic correlation on the electronic structures have been also discussed. It has been shown that ab initio calculations of the 57Fe Mössbauer parameters also require these two effects in order to obtain a quantitative agreement with experiments. Finally, it was found that LiFePO4FePO4 transformation involves a dramatic change of the electric field gradient VZZ from one end to the other of the 57Fe Mössbauer scale.

<p>Surface film formation at the electrode/electrolyte interface in lithium-ion batteries has a crucial impact on battery performance and safety. This thesis describes the characterisation and treatment of electrode interfaces in lithium-ion batteries. The focus is on interface modification to improve battery safety, in particular to enhance the onset temperature for thermally activated reactions, which also can have a negative influence on battery performance. </p><p>Photoelectron Spectroscopy (PES) and Differential Scanning Calorimetry (DSC) are used to investigate the surface chemistry of electrodes in relation to their electrochemical performance. Surface film formation and decomposition reactions are discussed.</p><p>The upper temperature limit for lithium-ion battery operation is restricted by exothermic reactions at the graphite anode; the onset temperature is shown to be governed by the composition of the surface film on the anode. Several electrolyte salts, additives and an anion receptor have been exploited to modify the surface film composition. The most promising thermal behaviour is found for graphite anodes cycled with the anion receptor, tris(pentafluorophenyl)borane, which reduces salt reactions and increases the onset temperature from ~80 °C to ~150 °C.</p><p>The electrochemical performance and surface chemistry of Swedish natural graphite, carbon-treated LiFePO₄ and anodes from high-power lithium-ion batteries are also investigated. Jet-milled Swedish natural graphite exhibits a high capacity and rate capability, together with a decreased susceptibility to solvent co-intercalation. Carbon-treated LiFePO₄ shows promising results: no solvent reaction products are detected. The amount of salt compounds increases, with power fade occurring for anodes from high-power lithium-ion batteries; the solvent reduction products comprise mainly Li-carboxylate type compounds.</p>

<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 V₆O₁₃ and LiFePO₄. 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 Li₃V₆O₁₃ and Li_3+xV₆O₁₃, 0<x<1, both contain a disordered lithium ion. A low-temperature study of Li_3.24V₆O₁₃ (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 V₆O₁₃ host structure. Short-range-ordering between this disordered lithium ion and the lithium ion inserted into Li₃V₆O₁₃ gives rise to solid-solution behaviour not observed earlier in the Li_xV₆O₁₃ system. A model is proposed for the lithium insertion mechanism up to the end-member composition Li₆V₆O₁₃.</p><p>Lithium has also been electrochemically extracted from LiFePO₄ single crystals. On the basis of the shapes of the LiFePO₄ and FePO₄ reflections, it is concluded that FePO₄ is formed at the crystal surface and that the LiFePO₄/FePO₄ interface propagates into the crystal. This is in agreement with an earlier proposed model for lithium extraction from LiFePO₄ 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 V₆O₁₃ 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>

<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)O₂-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 LiFePO₄. A second and in some ways even more attractive material - Li₂FeSiO₄ - 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 Li₂FeSiO₄. 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 Li₂FeSiO₄ and LiFeSiO₄, but with the structure of the original Li₂FeSiO₄ 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 Li₂FeSiO₄ and the delithiated on LiFeSiO₄ structure provide an interesting insight into the experimental result.</p><p>Photoelectron spectroscopy was used to study the surface chemistry of both carbon-treated LiFePO₄ and Li₂FeSiO₄ 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>LiFePO₄ and Li₂FeSiO₄ should both be seen as highly promising candidates as positive-electrode materials for large-scale Li-ion battery applications.</p>

Surface film formation at the electrode/electrolyte interface in lithium-ion batteries has a crucial impact on battery performance and safety. This thesis describes the characterisation and treatment of electrode interfaces in lithium-ion batteries. The focus is on interface modification to improve battery safety, in particular to enhance the onset temperature for thermally activated reactions, which also can have a negative influence on battery performance. Photoelectron Spectroscopy (PES) and Differential Scanning Calorimetry (DSC) are used to investigate the surface chemistry of electrodes in relation to their electrochemical performance. Surface film formation and decomposition reactions are discussed. The upper temperature limit for lithium-ion battery operation is restricted by exothermic reactions at the graphite anode; the onset temperature is shown to be governed by the composition of the surface film on the anode. Several electrolyte salts, additives and an anion receptor have been exploited to modify the surface film composition. The most promising thermal behaviour is found for graphite anodes cycled with the anion receptor, tris(pentafluorophenyl)borane, which reduces salt reactions and increases the onset temperature from ~80 °C to ~150 °C. The electrochemical performance and surface chemistry of Swedish natural graphite, carbon-treated LiFePO4 and anodes from high-power lithium-ion batteries are also investigated. Jet-milled Swedish natural graphite exhibits a high capacity and rate capability, together with a decreased susceptibility to solvent co-intercalation. Carbon-treated LiFePO4 shows promising results: no solvent reaction products are detected. The amount of salt compounds increases, with power fade occurring for anodes from high-power lithium-ion batteries; the solvent reduction products comprise mainly Li-carboxylate type compounds.

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 V6O13 and LiFePO4. A novel single-crystal electrochemical cell for in situ single-crystal X-ray diffraction studies has also been developed. The phases Li3V6O13 and Li3+xV6O13, 0&lt;x&lt;1, both contain a disordered lithium ion. A low-temperature study of Li3.24V6O13 (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 V6O13 host structure. Short-range-ordering between this disordered lithium ion and the lithium ion inserted into Li3V6O13 gives rise to solid-solution behaviour not observed earlier in the LixV6O13 system. A model is proposed for the lithium insertion mechanism up to the end-member composition Li6V6O13. Lithium has also been electrochemically extracted from LiFePO4 single crystals. On the basis of the shapes of the LiFePO4 and FePO4 reflections, it is concluded that FePO4 is formed at the crystal surface and that the LiFePO4/FePO4 interface propagates into the crystal. This is in agreement with an earlier proposed model for lithium extraction from LiFePO4 particles. Initial experiments with the newly developed single-crystal electrochemical cell for in situ single-crystal X-ray diffraction demonstrate that it is possible to insert lithium into a single crystal of V6O13 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.