Binder free vertical aligned (VA) CNT/sulfur composite electrodes with high sulfur loadings up to 70 wt% were synthesized delivering discharge capacities higher than 800 mAh g−1 of the total composite electrode mass. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Les travaux de ce mémoire s’inscrivent dans la continuité des résultats obtenus par C. Marino sur le matériau de conversion TiSnSb. En effet, les bonnes performances électrochimiques du matériau de conversion TiSnSb vs. lithium sont dues à un mélange intime des espèces en fin de décharge. Les interfaces optimisées entre les alliages lithiés d’antimoine (Li3Sb), d’étain (Li7Sn2) et les nanoparticules de titane facilitent le transfert de charges et assurent la reconstruction du matériau TiSnSb en charge. Dans ce contexte, l’objectif était de savoir s’il était possible de créer un mélange intime d’espèces en fin de décharge, de natures et quantités façonnables, à l’origine d’un mécanisme de conversion efficace. Au travers de nombreux essais, il a été démontré que l’empreinte créée par le composé intermétallique défini dans l’électrode de départ, est la clé de l’efficience de la réaction de conversion à l’origine de bonnes performances, et qu’il est difficile de reproduire ces conditions par d’autres moyens. La synthèse des matériaux s’est alors orientée vers le matériau chimiquement le plus proche de TiSnSb, à savoir le binaire SnSb pour évaluer le rôle du titane. Ce dernier a été complètement investigué comme matériau d’électrode négative, de la synthèse jusqu’au mécanisme électrochimique du premier cycle ainsi que son évolution au cours du cyclage, en mettant en évidence son mécanisme de défaillance, à température ambiante et à 60°C. Une nouvelle méthode de synthèse d’intermétalliques comme matériau d’électrode a été développée en utilisant les micro-ondes. La synthèse se déroule sous air, sans formation d’oxydes et ne prend qu’une minute pour produire un gramme de SnSb. Les performances électrochimiques de SnSb issu de la synthèse par micro-ondes ont été comparées à celles de SnSb préparé par mécanosynthèse.Le mécanisme électrochimique du matériau SnSb peu décrit dans la littérature a été ré-investigué. Pour ce faire et compte tenu de la complexité du mécanisme électrochimique, la DRX et la spectroscopie Mössbauer 119Sn en mode operando ont été réalisées sur SnSb ainsi que la DRX operando sur le mélange Sn+Sb. L’analyse électrochimique de l’alliage SnSb, du mélange Sn+Sb ainsi que de Sb vs. Li a permis de totalement identifier le mécanisme et d’en comprendre la défaillance.La dernière partie de la thèse a été axée sur l’étude du vieillissement du mécanisme électrochimique de SnSb en fonction de la température de cyclage. Cette étude a été réalisée sur des batteries ayant cyclé plus de 6 mois à 60°C et un an à température ambiante (25°C) et a mis en évidence des phénomènes originaux non décrits dans la littérature et toujours en cours d’étude étant donnée leur complexité. / This thesis takes place following on from the results obtained by C. Marino on a conversion type material TiSnSb. The interesting electrochemical performance of TiSnSb vs. Li are due to a close mixture of the lithiated species at the end of the discharge. All the interfaces between lithiated antimony phase (Li3Sb), lithiated tin phase (Li7Sn2) and titanium nanoparticles are optimized, leading to a facilitated charge transfer, which assures the rebuilding of TiSnSb on charge. In this context, the main objective was to try to create same type of mixture at the end of the discharge, with an adjustable nature and amount of elements leading to an effective conversion reaction. Through numerous tests, it was proved that the pristine fingerprint material created by the intermetallic crystalline compound play a key role in the conversion mechanism, which is tricky to reproduce by some other ways.The synthesis was oriented toward SnSb to evaluate the role of titanium in the good performance of TiSnSb. Tin antimony alloy was completely investigated as negative electrode material, from the synthesis to the electrochemical mechanism at 25°C and 60°C at the first cycle and its evolution throughout the cycling. Furthermore, failure mechanism was also identified.A new synthetic route for the intermetallic compounds as electrode active materials was developed by using the microwaves. The synthesis takes place directly under air, without oxide formation in a record time of one minute for 1 gram of SnSb. Electrochemical performance of microwave-SnSb were compared with that of SnSb prepared by mecanosynthesis.The electrochemical mechanism of SnSb, poorly described in the literature was reinvestigated. Considering the complexity of the electrochemical mechanism, operando XRD and 119Sn Mossbauer spectroscopy were both performed on SnSb and on the simple mixture of Sn+Sb. Analysis of galvanostatic measurements of SnSb alloy, Sn+Sb mixture and Sb vs. Li was completed to identify the mechanism and understanding failure mechanism.The last part of the thesis was devoted to the ageing mechanism of SnSb depending on the cycling temperature. The cycling duration was 6 months and one year at 60°C and 25°C respectively. These long cycling highlighted some original phenomena, never described in the literature, which are still under investigation.

O objetivo deste trabalho foi estudar o perfil oxidativo de concentrados para bovinos adicionados de óleo de soja, refinado e degomado, em um período de armazenamento de 15 dias, sob as temperaturas de 25ºC e 40ºC. Foram formados cinco grupos de alimentos: controle (C) sem adição de óleo, tratamentos (T) 1, 2, 3 e 4 com adição de 2, 4, 6 e 8%, respectivamente, de óleo de soja refinado ou degomado. Para tal, foram avaliados os índices de peróxidos e de acidez. Com relação à influência da temperatura de estocagem, ao longo do período experimental à 25ºC, não houve alteração com relação aos valores de índice de peróxido quando se adicionou óleo de soja refinado aos concentrados, contudo, à 40ºC, houve aumento observando-se um valor máximo em torno de 0,9 mEq/kg de concentrado. O índice de acidez do óleo refinado extraído dos concentrados armazenados à 25ºC não foi alterado ao longo do período de armazenamento, e à 40ºC resultou em aumento de 19, 25, 44 e 44% para os respectivos T1, T2, T3 e T4 em relação ao controle. Quanto à influência do tipo de óleo processado na oxidação lipídica dos concentrados armazenados à 40ºC, a adição de óleo de soja refinado não alterou os índices de peróxidos dos concentrados ao longo dos 15 dias de experimento, e para o degomado observou-se um aumento no 3º dia de armazenamento em 57%, 44%, 123% e 93% para os respectivos T1, T2, T3 e T4, em relação ao controle. Também, o efeito da adição de óleo de soja degomado resultou em aumento do índice de acidez de 21%, 36%, 43% e 57% a partir do 5º dia de experimento, em relação ao 1º dia. Conclui-se que durante os 15 dias de armazenamento, houve diferença no perfil oxidativo dos concentrados adicionados de óleo de soja quando se comparou as temperaturas de 25ºC e 40ºC, mas se manteve inalterado quando se avaliou os tipos de óleo refinado e degomado em diferentes porcentagens. Assim, a adição de óleo de soja refinado ou degomado não altera o perfil oxidativo do concentrado para bovino sob as condições deste estudo. / The objective of this work was to study the oxidative profile of concentrates for cattle added soybean oil, refined and degummed in a storage period of 15 days, at temperatures of 25ºC and 40ºC. Were formed five food groups: control (C) without addition of oil, treatments (T) 1, 2, 3 and 4 with the addition of 2, 4, 6 and 8%, respectively, of refined or degummed soybean oil. For this purpose ware available index of peroxide and of acidic. Regarding the influence of storage temperature, the addition of refined soybean oil did not alter the values of the peroxide during the trial period at 25ºC, however, at 40ºC of storage of food alter this parameter and was shown a maximum value about 0.9 mEq/kg of concentrate. The acidity of refined oil extracted from concentrates stored at 25ºC was not changed during the storage period, and 40ºC resulted in an increase of 19, 25, 44 and 44% for the respective T1, T2, T3 and T4 compared the control. Regarding the influence of oil processed in lipid oxidation of concentrates stored at 40ºC, the addition of refined soybean oil did not alter the levels of peroxide concentrates over the 15 days of experiment, and the degummed observed an increase in 3rd day of storage in 57%, 44%, 123% and 93% for the respective T1, T2, T3 and T4, compared to control. Also, the effect of addition of crude soybean oil resulted in increased acid value of 21%, 36%, 43% and 57% from the 5th day of experiment, as compared to day 1. Thus, the addition of refined soybean oil or degummed not change profile for bovine oxidative concentrated under the conditions of this study.

The experimental data presented in this thesis demonstrates the preparation and characterization of TiO₂ polymorphs (anatase and TiO₂-(B)) in the form of nanomaterials. The reduced dimension of the nanomaterials amplifies the properties compared to the bulk TiO₂; however, this is often at the cost of the tapped density. The anatase nanomaterials with pseudo-spherical nanoparticles of 5 to 70 nm in size were synthesized and their volumetric capacities compared. Both the gravimetric and volumetric capacity is higher for nanoparticles of less than 10 nm in diameter. The volumetric capacity is also dependent on the agglomerate size. For example at the very lowest rate of 50 mA/g, the agglomerate larger than 50 μm leads to the highest volumetric capacity; while at a rate higher than 600 mA/g the smaller agglomerates are preferred. Following this, we reported the synthesis of mesoporous TiO₂-(B) with the particle size along the [010] direction ranged from 3 to 300 nm, and the pore size increasing from 2.5 to more than 20 nm. By comparing the volumetric capacity of these TiO₂-(B) mesoporous materials, the optimal morphology for an improved volumetric capacity was identified. TiO₂-(B) with a novel microstructure was synthesized via a hydrothermal reaction. The primary particles are brick-like in shape with the shorter dimensions (4 - 10 nm) in parallel to the [100] and [010] directions, facilitating the Li⁺ ion diffusion in the particle. This TiO₂-(B) offers a superior rate capability compared to many other titanate anodes reported in the literature. In addition, it exhibits a great cycleability due to its exceptional structural stability and minimal SEI layer. Surface treatments could reduce its first cycle irreversible capacity to ~10%.

La mise en œuvre de nouvelles formulations d’électrolytes adaptées à des électrodes positives à haut potentiel pour batterie lithium-ion est un défi majeur pour des systèmes à haute densité d’énergie. Afin d’obtenir une stabilité en oxydation supérieure à 5 V vs. Li+/Li, différents solvants (dinitriles, lactones, phosphates) ont été analysés. Nous avons montré par voltampérométrie cyclique que des électrolytes contenant du sébaconitrile sont stables jusqu’à 5,3 V vs. Li+/Li sur LiCoPO4. Toutefois, les résultats obtenus par impédance électrochimique et spectroscopie photoélectronique X ont révélé la présence d’une nouvelle interface à l’électrode positive issue de la dégradation de l’électrolyte. Bien que cette dégradation limite la cyclabilité, une optimisation de l’interface formée pourrait s’avérer un atout du point de vue de la sûreté du système grâce à une protection de l’électrode positive. / Implementation of new electrolyte formulations adapted to high potential positive electrodes for lithium-ion battery is a key challenge for high energy density systems. In order to obtain stability in oxidation greater than 5 V vs. Li+/Li, various solvents (dinitriles, lactones, phosphates) were analyzed. We have shown by cyclic voltammetry that electrolytes containing sebaconitrile are stable up to 5.3 V vs. Li+/Li on LiCoPO4. Nonetheless, the results obtained by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy revealed the presence of a new interface onto the positive electrode due to electrolyte degradation. Even though this degradation limits the cycle ability, optimization of the formed interface could be an asset in view of the system safety through the protection of the positive electrode.

Binder free vertical aligned (VA) CNT/sulfur composite electrodes with high sulfur loadings up to 70 wt% were synthesized delivering discharge capacities higher than 800 mAh g−1 of the total composite electrode mass. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

In this study, quantum chemical methods have been used to study two isomers of the proposed high energy density material N8. It has been suggested as a green substitute for conventional solid rocket fuel. Several techniques were used to study the barrier height towards decomposition along reaction path of four N8 isomers. The potential energy surfaces around the transition states of two of the isomers were further investigated. Results show that the bond length of the isomers may have been overestimated, and one of the isomers has a lower barrier and may have a more complicated reaction route. Furthermore, there is a rather large difference in barrier height between calculations at the CCSD and CCSD(T) levels of theory / I den här studien har kvantkemiska beräkningsmetoder använts för att studera två isomerer av N8. På grund av sitt höga energiinnehåll har N8 föreslagits som ett grönt alternativ till konventionellt fast racketbränsle. Flera tekniker har använts för att studera barriären för nedbrytning utefter reaktionskoordinaten för fyra N8-isomerer. Potentialytan runt aktiveringstillståndet för två av isomererna studerades närmare. Resultaten visar att bindningslängden hos isomererna kan ha överskattats och en av isomererna har en lägre barriär samt kan ha en mer komplicerad reaktionsväg. Vidare är det en tämligen stor skillnad i aktiveringsenergi mellan CCSD- och CCSD(T)- nivåerna.

No description available.

Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current ISO standards, by describing several experimental and analytical results.

Due to climate change, the energy system needs to change from traditional fossil fuels to be dominated by renewable energy sources. Not only the energy system, but the increasing number of vehicles and emissions from the transport sector are a problem for climate change and that need to be solved. Both can be solved with batteries, to handle climate change issue. The lithium-ion batteries (LIBs) have a high energy density which is important due to the less needed materials for the batteries. LIBs can be used in a battery energy storage system (BESS) to store the excess energy for later usage, and as an electric vehicle (EV) battery. For these high energy density batteries, there comes drawbacks such as safety issues by deviating temperatures which have effects on the capacity, lifetime, performance, and in worst case a thermal runaway can occur which may lead to fire and explosions. These temperature issues can be solved with a battery thermal management system (BTMS), which can manage temperature deviation. Cylindrical battery cells with the dimension 18650 with the cell chemistry Lithium-Nickel-Cobalt-Aluminum-Oxide (NCA) will be investigated with different discharge rates, how the heat generation increases, and how it can be handled by cooling systems. A battery pack will be built up in computational fluid dynamics (CFD) software called Ansys Fluent, to be simulated and see how the influence of cooling methods affect the energy density of the 18650 batteries. Air-cooling and liquid-cooling with fan as air-cooling and plate cooling as liquid cooling will be used in this work. 20 cells were investigated with air and liquid cooling, with two different cases with air-cooling. 100 cells with just liquid cooling during 0,5C was investigated on how the number of cells impacted on the energy density. It was seen that the different discharge rates (C-rate) had an impact on the amount of cooling, with air cooling being not as good as liquid cooling for cooling the battery pack and more flow was needed. The energy density in relation to weight showed that 20 cells with less spacing using air-cooling had the best energy density at 196,68 Wh/kg. It was also seen that the number of cells had an impact on the energy density in relation to volume. With the best energy density with 100 cells using liquid cooling at 279,96 Wh/L.