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<p>Reliable ways of storing energy are crucial to support our modern way of life; lithium-ion batteries provide an attractive solution. The constant demand for higher energy density, thinner, lighter and even more mechanically flexible batteries has motivated research into new battery materials. Some of these will be explored in this thesis.</p><p>The main focus is placed on the development of new anode materials for lithium-ion batteries and the assessment of their electrochemical and structural characteristics. The materials investigated are: natural Swedish graphite, SnB₂O₄ glass and intermetallics such as: Cu₆Sn₅, InSb, Cu₂Sb, MnSb and Mn₂Sb. Their performances are investigated by a combination of electrochemical, <i>in si</i>tu X-ray diffraction and Mössbauer spectroscopy techniques, with an emphasis on the structural transformations that occur during lithiation.</p><p>The intermetallic materials exhibit a lithium insertion/metal extrusion mechanism. The reversibility of these reactions is facilitated by the strong structural relationships between the parent compounds and their lithiated counterparts. Lithiation of a majority of the intermetallics in this work proceeds via an intermediate ternary phase. The intermetallic electrodes provide high volumetric capacities and operate at slightly higher voltages vs. Li/Li⁺ than graphite. This latter feature forms the basis for a safer system.</p><p>Jet-milling of natural Swedish graphite results in decreased particle and crystallite size, leading to improved performance; the capacity is close to the theoretical capacity of graphite. Jet-milled graphite also shows an enhanced ability to withstand high charging rates.</p>

Reliable ways of storing energy are crucial to support our modern way of life; lithium-ion batteries provide an attractive solution. The constant demand for higher energy density, thinner, lighter and even more mechanically flexible batteries has motivated research into new battery materials. Some of these will be explored in this thesis. The main focus is placed on the development of new anode materials for lithium-ion batteries and the assessment of their electrochemical and structural characteristics. The materials investigated are: natural Swedish graphite, SnB2O4 glass and intermetallics such as: Cu6Sn5, InSb, Cu2Sb, MnSb and Mn2Sb. Their performances are investigated by a combination of electrochemical, in situ X-ray diffraction and Mössbauer spectroscopy techniques, with an emphasis on the structural transformations that occur during lithiation. The intermetallic materials exhibit a lithium insertion/metal extrusion mechanism. The reversibility of these reactions is facilitated by the strong structural relationships between the parent compounds and their lithiated counterparts. Lithiation of a majority of the intermetallics in this work proceeds via an intermediate ternary phase. The intermetallic electrodes provide high volumetric capacities and operate at slightly higher voltages vs. Li/Li+ than graphite. This latter feature forms the basis for a safer system. Jet-milling of natural Swedish graphite results in decreased particle and crystallite size, leading to improved performance; the capacity is close to the theoretical capacity of graphite. Jet-milled graphite also shows an enhanced ability to withstand high charging rates.

This thesis is concerned with kinetic characterisation of theinsertion compound LiMn2O4, which is used as positive electrodematerial in rechargeable lithium batteries. Three different typesof electrode configurations have been investigated, namely singleparticles, thin films and composite electrodes. Differentelectrochemical techniques, i.e. linear sweep voltammetry (LSV),electrochemical impedance spectroscopy (EIS), potential step, andgalvanostatic experiments were applied under various experimentalconditions. The majority of the experimental data were analysedby relevant mathematical models used for describing the reactionsteps of insertion compounds. It was concluded that a model based on interfacialcharge-transfer, solid-phase diffusion and an external iR-dropcould be fairly well fitted to LSV data measured on a singleelectrode system over a narrow range of sweep rates. However, itwas also found that the fitted parameter values vary greatly withthe characteristic length and the sweep rate. This indicates thatthe physical description used is too simple for explaining theelectrochemical responses measured over a large range of chargeand discharge rates. EIS was found to be a well-suited technique for separatingtime constants for different physical processes in the insertionand extraction reaction. It was demonstrated that the impedanceresponse is strongly dependent on the current collector used.According to the literature, reasonable values of theexchange-current density and solid-phase diffusion coefficientwere determined for various states-of-discharge, temperatures andelectrolyte compositions. Experiments were carried out in bothliquid and gel electrolytes. A method which improves thedistinction between the time constants related to thematerial’s intrinsic properties and possible porous effectsis presented. The method was applied to composite electrodes.This method utilises, in addition to the impedance responsemeasured in front of the electrode, also the impedance measuredat the backside of the electrode. Finally, the kinetics of a composite electrode was alsoinvestigated by in situ X-ray diffraction (in situ XRD) incombination with galvanostatic and potentiostatic experiments. Noevidence of lithium concentration gradients could be observedfrom XRD data, even at the highest rate applied (i.e. ~6C), thusexcluding solid-phase diffusion and also phase-boundary movement,as described by Fick’s law, as the ratelimiting step. <b>Key words:</b>linear sweep voltammetry, electrochemicalimpedance spectroscopy, potential step, in situ X-raydiffraction, microelectrodes, electrode kinetics, LiMn2O4cathode, rechargeable lithium batteries

<p>This thesis is concerned with kinetic characterisation of theinsertion compound LiMn2O4, which is used as positive electrodematerial in rechargeable lithium batteries. Three different typesof electrode configurations have been investigated, namely singleparticles, thin films and composite electrodes. Differentelectrochemical techniques, i.e. linear sweep voltammetry (LSV),electrochemical impedance spectroscopy (EIS), potential step, andgalvanostatic experiments were applied under various experimentalconditions. The majority of the experimental data were analysedby relevant mathematical models used for describing the reactionsteps of insertion compounds.</p><p>It was concluded that a model based on interfacialcharge-transfer, solid-phase diffusion and an external iR-dropcould be fairly well fitted to LSV data measured on a singleelectrode system over a narrow range of sweep rates. However, itwas also found that the fitted parameter values vary greatly withthe characteristic length and the sweep rate. This indicates thatthe physical description used is too simple for explaining theelectrochemical responses measured over a large range of chargeand discharge rates.</p><p>EIS was found to be a well-suited technique for separatingtime constants for different physical processes in the insertionand extraction reaction. It was demonstrated that the impedanceresponse is strongly dependent on the current collector used.According to the literature, reasonable values of theexchange-current density and solid-phase diffusion coefficientwere determined for various states-of-discharge, temperatures andelectrolyte compositions. Experiments were carried out in bothliquid and gel electrolytes. A method which improves thedistinction between the time constants related to thematerial’s intrinsic properties and possible porous effectsis presented. The method was applied to composite electrodes.This method utilises, in addition to the impedance responsemeasured in front of the electrode, also the impedance measuredat the backside of the electrode.</p><p>Finally, the kinetics of a composite electrode was alsoinvestigated by in situ X-ray diffraction (in situ XRD) incombination with galvanostatic and potentiostatic experiments. Noevidence of lithium concentration gradients could be observedfrom XRD data, even at the highest rate applied (i.e. ~6C), thusexcluding solid-phase diffusion and also phase-boundary movement,as described by Fick’s law, as the ratelimiting step.</p><p><b>Key words:</b>linear sweep voltammetry, electrochemicalimpedance spectroscopy, potential step, in situ X-raydiffraction, microelectrodes, electrode kinetics, LiMn2O4cathode, rechargeable lithium batteries</p>

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第18340号 / 農博第2065号 / 新制||農||1024(附属図書館) / 学位論文||H26||N4847(農学部図書室) / 31198 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 木村 恒久, 教授 西尾 嘉之, 教授 髙野 俊幸 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Quasi one-dimensional (1D) nanostructures show great promise for many applications, including in solar cells, nanogenerators and chemical sensors, due to the high surface-to-volume ratio and unique properties of nanostructures. The growth of these nanostructures is commonly catalyzed by metal nanoparticles and generally attributed to the vapor-liquid-solid (VLS) mechanism. The purpose of this research is to better understand the role of the catalyst nanoparticles in the growth of 1D nanostructures, in order to allow improved control of the synthesis process. To this end, nanostructures were grown with a variety of compositions, including Au- and Sn-catalyzed ZnO, Au-catalyzed FexOy and Au-catalyzed Si nanostructures. The morphology of the nanostructures was characterized with electron microscopy, and the crystallographic orientation with X-ray texture analysis. The catalyst particles were further characterized with both in-situ and post-growth X-ray diffraction. The types of bonding in the source material and catalyst play a significant role in the diffusion path of the source material to the growth front and in the catalyst particle state during growth. Dissimilar bonding types in the source material and catalyst prevent bulk diffusion of the source material through the catalyst, thereby preventing eutectic melting of the catalyst. These results bring new insight into the catalyzed growth of 1D nanostructures and assist in the informed choice of appropriate catalyst materials, which may aid the utilization of 1D nanostructures in energy-related and other applications.

Nos efforts se sont portés sur des fluorophosphates de structure TAVORITE de formule LiMPO4F (M = V, Fe, Ti) et LiVPO4O qui, comparés à d’autres familles structurales de phosphates tels que Li3M2(PO4)3 (NASICON) ou LiFePO4(OH) (Tavorite) possèdent d’excellentes densités d’énergie théorique comme matériaux d’électrodes dans des accumulateurs au Li. Des méthodes de synthèse reproductibles, par voie céramique en tubes scellés et/ou ionothermale (synthèse à basse température), ont été mises au point dans ce travail. Les matériaux ainsi préparés ont été caractérisés en détail par magnétométrie, par RMN et surtout par diffraction des rayons X et des neutrons. Les structures cristallines ont ainsi pu être déterminées ainsi que les mécanismes d’insertion/extraction du Li+, via de nombreuses études par diffraction X insitu lors de la charge/décharge des accumulateurs. / This work focused on TAVORITE-based fluorophosphates LiMPO4F (M = V, Fe, Ti) and LiVPO4O which, when compared with other phosphate structural families such as Li3V2(PO4)3 (NASICON) or LiFePO4(OH) (Tavorite), possess superior energy density as electrode materials for Li batteries. Reproducible synthesis procedures were developed through “classical” ceramic routes in sealed containers and/or low temperature ionothermal reaction. The obtained materials were characterized by magnetometry, solid state NMR and heavily by X-Ray and Neutron diffraction. The crystal structures of all the materials were determined, as well as the mechanisms of Li+ insertion/extraction through insitu X-Ray diffraction during electrochemical charge/discharge of the batteries.

Les mécanismes de formation de phases dans des films minces du système ternaire Al-Cu-Fe et des systèmes binaires Al-Cu, Al-Fe et Cu-Fe ont été étudiés. Dans chacun des systèmes, plusieurs échantillons avec des compositions distinctes ont été préparés par pulvérisation cathodique. Des couches d’aluminium, de cuivre et de fer ont été déposées séquentiellement sur des substrats de silicium oxydé et ont été traités thermiquement par différentes méthodes puis caractérisés. Des mesures de diffraction de rayons X et de résistivité in-situ ont été effectuées pour suivre la formation des phases. Des recuits thermiques suivis de trempe ont été réalisés et les échantillons ont été caractérisés par diffraction des rayons X. L’analyse enthalpique différentielle a également été utilisée ainsi que des mesures simultanées in-situ de résistivité et de diffraction des rayons X. L’ensemble des résultats obtenus nous a permis de proposer des mécanismes de formation de phases pour chacun des échantillons étudiés et en utilisant des modèles théoriques de croissance de phases nous avons pu déterminer des données cinétiques sur la formation de phases dans ces films. / The mechanisms of phase formation in thin films have been studied in the Al-Cu, Al-Fe, Fe-Cu and Al-Cu-Fe systems. Several samples with different compositions have been prepared by sputtering. Aluminium, copper and iron layers were deposited onto oxidized silicon substrates, they were heat treated and characterized by using several techniques. In situ X-ray diffraction and resistivity measurements were used to follow the phase formation. Thermal annealings followed by quenching have also been carried out to get additional information.Differential Scanning Calorimetry and coupled in-situ resistivity and X-ray diffractionmeasurements were performed. The whole results allowed us to suggest a mechanism of phase formation for each sample and by using theoretical models of growth we determined kinetic data on the phase formation.

Ce travail s’inscrit dans un cadre de recherche qui a pour objectif essentiel l’étude de l’influence de la vapeur d’eau sur l’oxydation à haute température d’un alliage formeur de Cr2O3 à base de nickel. L’alliage étudié pour cette étude est le SY 625. L’originalité de cette étude repose sur l’utilisation d’un montage expérimental, mis en oeuvre au laboratoire. Ce montage appelé « montage vapeur d’eau » permet de réaliser l’oxydation du SY 625 à haute température (900-1100°C) en présence de vapeur d’eau (7,5 et 33% de vapeur d’eau) avec différents gaz vecteurs (oxygène, air, argon et azote) en conditions isotherme ou cyclique. Les résultats cinétiques obtenus sous air, ne montrent pas de différences notables que l’oxydation soit réalisée en conditions sèche ou humide (quelque soit le taux de vapeur d’eau). Les résultats n’ont pas montré de breakaway pour les durées d’oxydation allant jusqu’à 48 heures. Ceci est attribué au fait qu’il n’y a pas formation d’oxydes de fer sachant que l’alliage contient seulement 0,23% en masse de fer. Les résultats de DRX montrent la formation des mêmes phases quel-que-soit le gaz vecteur utilisé (en atmosphère sèche ou humide). A 900 et 1000°C, l’oxyde Cr2O3 est détecté ainsi que deux composés intermétalliques : Ni3Mo et NbNi4. En revanche à 1100°C, l’oxyde Cr2O3 est toujours présent mais les composés intermétalliques sont oxydés pour donner un oxyde mixte CrNbO4. L’oxydation du molybdène au dessus de 1000°C conduit à la formation de MoO3 qui est un oxyde volatil. Les analyses morphologiques, ont montré la présence de couches de chromine plus plastiques avec une porosité répartie sur toute l’épaisseur de la couche pour les essais réalisés en présence de vapeur d’eau. Les couches d’oxyde sont alors plus adhérentes. Ceci a été confirmé par des essais d’oxydation en conditions cycliques, qui ont montré notamment à 1100°C, une meilleure tenue mécanique de la couche d’oxyde en présence de vapeur d’eau. Les tests d’oxydation en présence d’un marquage à l’or a aussi permis de mettre en évidence un mécanisme d’oxydation mixte pour les oxydations réalisées en atmosphères riche en oxygène que l’on soit sous atmosphère sèche ou humide. En revanche, le marquage à l’or a montré la présence d’un mécanisme d’oxydation interne pour les atmosphères pauvres en oxygène, avec des couches d’oxydes présentant une adhérence parfaite. Le fait d’ajouter de la vapeur d’eau à ces atmosphères pauvres en oxygène, entraine la réapparition d’un mécanisme de diffusion mixte. / This work is a part of a research project which has for essential objective the study of water vapor influence in high temperature oxidation for a chromia forming nickel base alloy. Alloy studied for this study is the SY 625. Originality of this study is based on an experimental assembly use, create in the laboratory. This assembly called “water vapor assembly” is used for realized SY 625 high temperature oxidation (900-1100°C) in presence of water vapor (7,5 and 33 vol. % water vapor) with various carriers gas (oxygen, air, argon and nitrogen) in isothermal and cyclic conditions. The kinetic results obtained under air, do not show considerable differences that the oxidation is realized in dry or wet conditions (with the various water vapor rate). The results do not show breakaway for the oxidation durations going to 48 hours. This is attributed to the fact that there is no formation of oxides iron knowing that the alloy contains only 0,23 mass % of iron. The XRD results show the formation of the same phases which is the carrier gas used (in dry or wet atmosphere). At 900 and 1000°C, the Cr2O3oxide is detected with two intermetallic compounds : Ni3Mo and NbNi4. On the other hand at 1100°C, the oxide Cr2O3 is always present but the intermetallic compounds are oxidized to give a mixed oxide CrNbO4. The oxidation of the molybdenum above 1000°C leads to the formation of MoO3 which is a volatile oxide. The morphological analyses, showed the presence of more plastic chromia layers with a distributed porosity on all the thickness of the layer for the test realized in water vapor presence. The oxide layers are then more adherents. This was confirmed by oxidation test in cyclic conditions, which showed in particular at 1100°C, a better mechanical behavior of oxide layer in water vapor presence. The oxidation tests with gold marker experiments are also showed a mixed oxidation mechanism for the oxidations realized in rich oxygen atmospheres under dry or wet atmosphere. On the other hand, gold marker experiments showed the presence of a internal oxidation mechanism for poor oxygen atmospheres, with oxides layers showing a perfect adhesion. The fact of adding water vapor to these poor oxygen atmospheres, lead to the reappearance of a mixed diffusion mechanism.