Nanomaterials have attracted great interest in recent years, and are now also being considered for battery applications. Reducing the particle size of some electrode materials can increase battery performance considerably, especially with regard to capacity, power and rate capability. This thesis presents a study focused on the performance of such a material, vanadium oxide nanotubes, as cathode material for rechargeable lithium batteries. These nanotubes were synthesized by a sol-gel process followed by hydrothermal treatment. They consist of vanadium oxide layers separated by structure-directing agents, normally amines or metal ions, e.g., Na+, Ca2+, Mn2+ and Cu2+. The layers are arranged in a scroll-like manner, allowing the interlayer structure to expand and contract, depending on the size of the embedded guest. This tubular form of vanadium oxide was able to insert lithium ions reversibly, making it a candidate cathode material. The structural and electrochemical response to lithium ion insertion was carefully studied to define optimal performance criteria and probe the lithium insertion mechanism. This was done using several characterization techniques, including X-ray diffraction, a variety of spectroscopic methods and electrochemical testing. Galvanostatic measurements show that the material can be charged and discharged reversibly for >100 cycles with a capacity of 150-200 mAh/g. The electrochemical performance is, however, dependent on the electrode film preparation technique, the choice of salt in the electrolyte and the nature of the embedded guest. Results from photoelectron spectroscopy, and soft X-ray emission and absorption spectroscopy confirm that vanadium is reduced during lithium insertion and that three oxidation states (V5+, V4+ and V3+) co-exist at potentials below 2.0 V. In situ X-ray diffraction, performed during potential stepping, identifies two separate processes during lithium insertion: a fast decrease of the interlayer distance followed by a slow two-dimensional relaxation of the vanadium oxide layers.

Layered crystals with magnetic elements as Co and Fe have been studied. In TlCo2Se2, where Co atoms in one sheet are separated by Tl and Se from the next Co sheet, magnetic interaction within and between the sheets have been studied. Samples doped with 4% 57Fe replaced Co, show a magnetic spiral character with hyperfine fields in a flower shape in the ab-plane. The magnetic moment of 0.46 μB per Co atom derived from the average field is in good agreement with the result from neutron diffraction. In TlCu1.73Fe0.27Se2 the easy axis of magnetisation is the c-axis. The magnetic moment calculated from the Mössbauer data and SQUID magnetrometry is 0.97 μB per Fe atom with TC = 55(5) K. Multilayers of different elements have been studied. The effect of vanadium atoms on iron atoms at the interface of FeNi/V multilayers has been determined and the intermixing at the interface has been calculated to be 2-3 monolayers. For FeNi/Co 1/1 monolayer the magnetic hyperfine field (Bhf) is 45° out-of-plane, while for superlattices containing 2 to 5 monolayers it is in the plane. An study on Fe/Co superlattice were done by experimental, theoretical and simulational methods. The Bhf is highest for the Fe at the second layer next to the interface and gets the bulk value in the centre of thicker Fe layers. Studied magnetic nanoparticles coated with a lipid bilayer (magnetoliposomes) are found to have the magnetite structure but being non-stoichiometric as a result of the manufacturing process. The composition was approximately 32% γ-Fe2O3 and 68% Fe3O4. The oxidation evolution and its effect on magnetic properties of Fe clusters were also studied by means of different techniques. The extraction and insertion mechanism of lithium in the cathode material Li2FeSiO4 has been monitored by in situ x-ray diffraction and Mössbauer spectroscopy during the first two cycles. The relative amount of Fe+3/ Fe+2 at each end state was in good agreement with the results obtained from electrochemical measurements. A possible explanation to the observed lowering of the potential plateau from 3.10 to 2.80 V occurring during the first cycle, involves a structural rearrangement process in which some of the Li ions and the Fe ions are interchanged. The behaviour of small amounts of Fe in brass is investigated using Mössbauer spectroscopy. It was shown that a heat treatment can increase the amount of the precipitates of γ-Fe and ~650° C is the optimal treatment for having the highest amount of this phase.

The role of nanohybrid materials in the fields of polymer composites and electrochemical energy systems is significant since they affect the enhanced physical properties and improved electrochemical performance, respectively. As basic nanomaterials, carbon nanotubes and graphene were utilized due to their outstanding physical properties. With these materials, hybrid nanostructures were generated through a novel synthesis method, modified sol-gel process; namely, carbon nanotubes (CNTs)-maghemite and reduced graphene oxide (rGO)-maghemite nanohybrid materials were developed. In the study on polymer composities, developed CNTs-maghemite (magnetic carbon nanotbues (m-CNTs)) were readily aligned under an externally applied magnetic field, and due to the aligned features of m-CNTs in polymer matrices, it showed much enhanced anisotropic electrical and mechanical properties. In the study on electrochemical energy system (Li-ion batteries), rGO-maghemite were used as anode materials; as a result, they showed improved electrochemical performance for Li-ion batteries due to their specific morphology and characteristics.

Les premières observations de l'émission d'électrons Auger au cours du bombardement ionique d'une cible solide remontent à 1965 (Snoek et al. 11) dans le cas d'électrons caractéristiques des particules projectiles, et à 1967 (Hennequin et al. 12) dans le cas d'électrons caractéristiques des atomes cibles. Il existe actuellement une soixantaine de publications sur le sujet, mais les publications étrangères n'apparaissent qu'à partir de 1974, certains auteurs semblant même avoir incidenment redécouvert le phénomène. L'émission Auger lors de collisions en phase gazeuse a fait aussi l'objet de nombreuses études durant la même période. La connaissance précise des conditions mécaniques de la collision et l'existence d'états électroniques bien définis, tant avant qu'après la désexcitation par effet Auger, facilitent considérablement l'interprétation des expériences. La théorie de Fano et Lichten 1960 est maintenant bien établie : certaines des orbitales moléculaires formées lors de la collision de deux particules sont promues vers des niveaux moins liés et, après interaction avec une orbitale incomplète, peuvent conduire à la formation d'un trou électronique interne dans l'un ou l'autre des partenaires. Plus généralement, ce sont les progrès récents de la physique des collisions qui permettent maintenant de comprendre l'ensemble du mécanisme de l'émission Auger à partir des solides. Il existe naturellement un lien entre -l'émission d'électrons Auger et l'émission d'ions secondaires durant le bombardement ionique d'un solide. Ce lien est même direct dans le cas des ions rapides ou multichargés qui sont formés par désexcitation Auger, à l'extérieur de la cible, d'atomes éjectés ayant conservé un trou électronique interne : c'est le modèle de l'émission cinétique de Joyes 1975. C'est d'ailleurs à la suite d'une suggestion de Castaing, et pour interpréter l'émission d'ions secondaires, que l'étude de ce lien a été entreprise tant sur le plan expérimental que théorique. L'émission Auger permet en outre d'atteindre une meilleure connaissance des collisions les plus violentes à l'intérieur d'un solide, et c'est dans cet esprit que le présent travail a été réalisé. Plus précisément, nous avons cherché à mieux déterminer dans quelle mesure les conclusions théoriques de la physique des collisions peuvent être utilisées pour rendre compte des résultats expérimentaux relatifs à l'émission Auger des solides et prévoir l'influence de la nature de la cible et du projectile sur les caractéristiques de cette émission. D'abord un rappel théorique nécessaire à l'interprétation des résultats expérimentaux, nous suivrons les étapes conduisant à l'émission d'un électron Auger à la suite de l'impact de l'ion primaire sur les atomes de la cible : la création d'une cascade de collisions dans le solide, l'excitation d'un niveau électronique interne au cours d'une collision violente, la désexcitation par effet Auger au cours de la migration de la particule excitée et enfin la sortie de l'électron à l'extérieur de la cible. Puis la description des propriétés des dispositifs expérimentaux que nous avons réalisés pour cette étude. Ensuite, dans les deux chapitres suivants, nous étudierons les collisions responsables de l'émission des électrons Auger caractéristiques soit du projectile, soit de la cible. Dans le premier cas (chapitre III), nous nous intéresserons essentiellement à l'émission des électrons Auger de l'argon lors du bombardement de diverses cibles par des ions Ar d'énergie comprise entre 2 et 16 keV et pourrons montrer ainsi le bon accord entre les expériences sur les solides et les interprétations théoriques fondées sur les collisions atomiques et la promotion des orbitales moléculaires. Une fois établi cet accord, il nous sera possible (chapitre IV) d'étendre cette interprétation à l'émission des électrons Auger caractéristiques de la cible, pour lesquels la situation est compliquée par le fait que l'énergie de collision est mal connue et qu'un doute peut subsister sur la nature de la collision responsable de l'excitation : collision symétrique entre deux atomes identiques de la cible ou collision asymétrique entre l'ion incident et l'un des atomes de la cible. Dans le cas des métaux légers, magnésium et aluminium, nous montrerons que la proportion des collisions asymétriques est une fonction croissante de l'énergie des ions incidents, mais reste faible dans notre domaine d'énergie (2 - 16 keV). Les résultats que nous présentons ont pour la plupart fait l'objet de publications antérieures.

An alternate family of “high” voltage (where the equilibrium voltage lies between 3.6 V and 4.2 V) polyanion cathode materials is reported in this thesis with the objective of improving specific energy density (Wh/kg) and developing a better understanding of polyanion electrochemistry. The electrochemical properties, synthesis and the structure of novel fluorosulfate materials crystallizing in the tavorite and the triplite type mineral structures are described. These materials display highest discharge voltages reported for any Fe2+/Fe3+ redox couple. LiFeSO4F was prepared in both the tavorite and the triplite polymorphs using inexpensive and scalable methods. Complete structural characterization was performed using X-ray and neutron based diffraction methods. A rapid synthesis of fluorosulfates can be achieved by using microwave heating. The local rapid heating created by the microwaves generates nanocrystalline LiFeSO4F tavorite with defects that induce significant microstrain. To date, this is unique to the microwave synthesis method. Phase transformation to the more stable triplite framework, facilitated by the lattice defects which include hydroxyl groups, is therefore easily triggered. The formation of nanocrystalline tavorite leads to nanocrystalline triplite, which greatly favors its electrochemical performance because of the inherently disordered nature of the triplite structure. Direct synthesis of the electrochemically active triplite type compound can be carried out either by extending the duration of the solvothermal reactions or by the partial substitution of Fe by Mn to produce LiFe1-xMnxSO4F. This study, overall, has led to a better understanding of the transformation of tavorite to the triplite phase. To examine Li and the Na ion conduction and their correlation with the electrochemical performance of 3-D, 2-D and 1-D ion conductors, atomistic scale simulations have been used to investigate tavorite type LiFeSO4F, NaFeSO4F, olivine type NaMPO4 (M= Fe, Mn, Fe0.5Mn0.5) and layered Na2FePO4F. These calculations predict high mobility of the Li-ion in the tavorite type LiFeSO4F but sluggish Na-ion transport in iso-structural NaFeSO4F. High mobility of the Na-ion is predicted for phosphate layered and olivine structures. Finally, the synthesis and structural details of NaMSO4F (M=Fe, Mn) and NH4MSO4F (M=Fe, Mn) are presented in the last chapter to show the structural diversity present in the fluorosulfate family.

The batteries used in plug-in hybrid electric vehicles (PHEVs) need to overcome significant technical challenges in order for PHEVs to become economically viable and have a large market penetration. The internship at Argonne National Laboratory (ANL) involved two experiments which looked at a vehicle systems approach to analyze two such technical challenges: Battery life and low battery power at cold (-7 ⁰C) temperature. The first experiment, concerning battery life and its impact on gasoline savings due to a PHEV, evaluates different vehicle control strategies over a pre-defined vehicle drive cycle, in order to identify the control strategy which yields the maximum dollar savings (operating cost) over the life of the vehicle, when compared to a charge sustaining hybrid. Battery life degradation over the life of the vehicle, and fuel economy savings on every trip (daily) are taken into account when calculating the net present value of the gasoline dollars saved. The second experiment evaluates the impact of different vehicle control strategies in heating up the PHEV battery (due to internal ohmic losses) for cold ambient conditions. The impact of low battery power (available to the vehicle powertrain) due to low battery and ambient temperatures has been well documented in literature. The trade-off between the benefits of heating up the battery versus heating up the internal combustion engine are evaluated, using different control strategies, and the control strategy, which provided optimum temperature rise of each component, is identified.

Die umfangreichen Untersuchungen ausgewählter Mg2Si-basierter Materialien innerhalb dieser Arbeit zeigen neue Wege für die Anwendung der SPS-Technik in der Grundlagen- als auch angewandten Forschung und liefern entscheidendes, neues Material für die Charakterisierung der Li-Verbindungen Li2xMg2-xX (X = Si, Ge, Sn, Pb). Aufbauend auf vorangegangenen Arbeiten und den hier dargestellten Resultaten ergeben sich sowohl neue Möglichkeiten der Synthese, basierend auf dem SPS-Prozess (in Verbindung mit der Pulverherstellung, ‑verarbeitung und einem entsprechenden Werkzeugdesign), als auch eine Optimierung der Materialeigenschaften von Verbundwerkstoffen durch Nutzung dieser Technik. Die ternären Phasen Mg2Si1−xXx (X = Ge, Sn, Pb) und Mg2−x/2Si1−xSbx Die pulvermetallurgische Herstellung der Phasen Mg2Si1-xXx (X = Ge, Sn und Pb) und der Phase Mg2‑x/2Si1-xSbx gelang in dieser Arbeit erstmals mit Hilfe der SPS-Technik aus kugelgemahlenen Pulvergemischen (MgH2, Si, X). Die ternären Phasen Li2xMg2−xX (X = Si, Ge, Sn, Pb) Der Einbau von Li in Mg2Si wurde in dieser Arbeit erstmalig durch die SPS-Festkörperreaktion aus LiH, MgH2 und Si untersucht. Die Synthese der Li-armen Li2xMg2−xSi-Phasen gelingt schon bei Temperaturen von max. 700 °C. Die Schmelzsynthese dieser extrem luft- und feuchtigkeitsempfindlichen Proben wurde unter Argon-Schutzgas aus den Elementen mit anschließender Wärmebehandlung bei 200 °C angewendet. Dabei lassen sich drei unterschiedliche kubische Li2xMg2−xSi-Phasen mit 0 < x < 0,8 auf der Mg2Si-reichen Seite des ternären Systems finden. Mit steigendem Li-Gehalt können röntgenographisch zwei strukturelle Umwandlungen, ausgehend von der Raumgruppe Fm-3m für Mg2Si zu P-43m und P-43m mit der Bildung einer Überstruktur mit a′ = 2a bestimmt werden. Mit steigendem Li-Gehalt in Li2xMg2−xSi ändern sich die Eigenschaften. Der Übergang vom halbleitenden zum metallischen Zustand konnte in dieser Arbeit erstmalig gezeigt werden. In Analogie zu Li2xMg2−xSi konnten die Phasen Li2xMg2−xX (X = Ge, Sn, Pb) charakterisiert werden. Eine Intercalation für Li in Mg2X ist nicht möglich. Die Verbundwerkstoffe basierend auf Mg2Si Das spröde Materialverhalten vonMg2Si-Proben kann durch einen pulvermetallurgisch erzeugten Verbundwerkstoff mit Mg reduziert werden. Die SPS-Technik Basierend auf vorangegangenen Arbeiten konnte innerhalb dieser Arbeit durch die Verwendung von MgH2 die Strom-, Dichte- und Temperaturverteilung während des SPS-Prozesses innerhalb der Probe und des Werkzeuges beurteilt werden. / Extensive investigation on selected Mg2Si based materials demonstrate new routes for the application of the SPS technique in respect to basic as well as applied research and provide decisive new material on the characterisation of the Li compounds Li2xMg2-xX (X = Si, Ge, Sn, Pb). Based on prior activities and the results shown in this work new ways of the synthesis using the SPS process (in combination with powder making and processing and suitable tool design) as well as the optimization of material properties of composite materials can be achieved using the SPS technique. The Ternary Phases Mg2Si1−xXx (X = Ge, Sn, Pb) and Mg2−x/2Si1−xSbx For the first the powder metallurgic manufacturing route of the phases Mg2Si1-xXx (X = Ge, Sn und Pb) and the phase Mg2‑x/2Si1-xSbx is shown using the SPS technique and a ball milled powder mixture (MgH2, Si, X). The Ternary Phases Li2xMg2−xX (X = Si, Ge, Sn, Pb) The intercalation of Li into Mg2Si is investigated for the first time by using the SPS solid state reaction based on LiH, MgH2 and Si. The synthesis of the Li poor phase Li2xMg2−xSi could be obtained at temperatures of max. 700 °C. The melting technique made of the elements of these extremely air and moisture sensitive samples could be performed under Argon protective atmosphere followed by a heat treatment at 200 °C. Three different cubic phases of Li2xMg2−xSi can be found on the Mg2Si rich side of the ternary System with the composition in the range of 0 < x < 0,8. With increasing Li content two structural conversions can be found using the x-ray analysis. A change from the space group Fm-3m for Mg2Si via P-43m to P-43m with a superstructure of a′ = 2a could be detected. Linked with the increasing Li content is a change of the properties. The change from the semiconducting behaviour to a metallic characteristic could be shown for the first time. Analogous to Li2xMg2−xSi the phase Li2xMg2−xX (X = Ge, Sn, Pb) could be synthesised and analysed. An intercalation of Li in to Mg2X ist not possible. Composite Materials Based on Mg2Si The brittle behaviour of Mg2Si samples can be reduced by composite material with Mg using the powder metallurgical route. The SPS-Technique Using MgH2 the distribution of the current, the density and the temperature in the sample and tool could be judged.

Dans le cadre des travaux du LCS, du LEMME et du GRL sur les "smart windows" (vitrage a transmission contrôlée de la lumière) faisant intervenir deux films électrochrômes complémentaires insérant réversiblement les ions Li+, nous avons étudie les propriétés de films minces déposés par pulvérisation cathodique: les électrodes transparentes (ET) d'une part, et les films électrochimichromes (EC) d'autre part. Les performances des ET à base d'oxyde d' indium et (ou) d' étain, ont été améliorés par des dopages appropries. C'est ainsi que les oxydes SnO2:F (FTO), In2O3-SnF2 (FITO), In2O3-x(IO) allient, lorsqu'ils sont déposés en couches minces, une excellente transparence à une conductivité très élevée. Les EC étudies, Li2x-yNi1-xO et Li1-xCrO2. Ces nouveaux matériaux présentent des performances inéégalées a ce jour ; elles sont a l'état amorphe de bonnes caractéristiques électrochromes, complémentaires de celles de WO3. Ces nouveaux matériaux présentent des performances inégalées à ce jour; elles sont liées à la présence de liaisons pendantes. Les mécanismes de conduction mixte (ionique-électronique) s'expliquent sur la base du modèle des petits polarons.

Thesis (Ph. D.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.

Energy harvesting and energy storage are two most important technologies in today's green and renewable energy science. As for energy harvesting, the fundamental science and practically applicable technologies are not only essential in realizing the self-powered electronic devices and systems, but also tremendously helpful in meeting the rapid-growing world-wide energy consumptions. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. Owing to the limitations of the traditional technologies for mechanical energy harvesting, it is highly desirable to develop new technology that can efficiently convert different types of mechanical energy into electricity. On the other hand, the electricity generated from environmental energy often needs to be stored before used to drive electronic devices. For the energy storage units such as Li-ion batteries as the power sources, the limited lifetime is the prominent problem. Hybridizing energy harvesting devices with energy storage units could not only provide new solution for this, but also lead to the realization of sustainable power sources. In this dissertation, the research efforts have led to several critical advances in a new technology for mechanical energy harvesting—triboelectric nanogenerators (TENGs). Previous to the research of this dissertation, the TENG only has one basic mode—the contact mode. Through rational structural design, we largely improved the output performance of the contact-mode TENG and systematically studied their characteristics as a power source. Beyond this, we have also established the second basic mode for TENG—the lateral sliding mode, and demonstrated sliding-based disk TENGs for harvesting rotational energy and wind-cup-based TENGs for harvesting wind energy. In order to expand the application and versatility of TENG by avoid the connection of the electrode on the moving part, we further developed another basic mode—freestanding-layer mode, which is capable of working with supreme stability in non-contact mode and harvesting energy from any free-moving object. Both the grating structured and disk-structured TENGs based on this mode also display much improved long-term stability and very high energy conversion efficiency. For the further improvement of the TENG’s output performance from the material aspect, we introduced the ion-injection method to study the maximum surface charge density of the TENG, and for the first time unraveled its dependence on the structural parameter—the thickness of the dielectric film. The above researches have largely propelled the development of TENGs for mechanical energy harvesting and brought a big potential of impacting people’s everyday life. Targeted at developing sustainable and independent power sources for electronic devices, efforts have been made in this dissertation to develop new fundamental science and new devices that hybridize the nanogenerator-based mechanical energy harvesting and the Li-ion-battery-based energy storage process into a single-step process or in a single device. Through hybridizing a piezoelectric nanogenerator with a Li-ion battery, a self-charging power cell has been demonstrated based on a fundamentally-new mechanical-to-electrochemcial process. The triboelectric nanogenerator as a powerful technology for mechanical energy harvesting has also been hybridized with a Li-ion battery into a self-charging power unit. This new concept of device can sustainably provide a constant voltage for the non-stop operation of electronic devices.