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Microstructure and Transport Properties of Porous Li-ion ElectrodesStephenson, David E. 06 June 2011 (has links) (PDF)
The goal of this work is to understand the relationships between electrode microstructure and mass transport resistances. One can use this information to predict cell performance from fundamental principles. This work includes new types of particle-scale 3D models for correlating and predicting the effects of electrode microstructure on both ionic and electronic transport. The 3D models imitate the sub-micrometer-scale arrangement of active material particles, carbon, binder, and pores and use FIB/SEM images as a basis for parameterization. The 3D models are based respectively on the statistical mechanics techniques of molecular dynamics and Monte Carlo. The approach closely related to molecular dynamics, named the dynamic particle packing (DPP) model, uses aggregates of spheres to recreate electrode microstructures. The other approach, named the stochastic grid (SG) model, is closely related to Monte Carlo techniques in which a small set of fundamental interdomain and bulk energy parameters are used to generate structures.In order to predict electrode microstructures we correlated the fundamental interdomain and bulk energy parameters for the SG model to electrode mass composition and porosity. We used the revised computer program, known as predict SG, to estimate structures of which there are no experimental measurements of electrode structure. From these predicted electrode structures we obtained electronic and ionic transport properties. This allowed us to estimate the trade-offs between ionic and electronic transport for different porosities and carbon fractions. We found from experimental measurements of electrode structure that carbon and binder formed distinct agglomerates. From the 3D models we determined at commercial fractions of carbon and binder that the conductivity of these carbon agglomerates plays a large role in determining both the electronic and ionic pathways. So in order to better understand the role that these carbon/binder agglomerates play, we explored and developed several experimental methods to find the electronic and ionic conductivity of both simulated carbon domains and complete electrode films. The goal was not only to elucidate the role carbon agglomerates play, but also to develop a non-destructive method of determining overall film properties. Although we found that a non-destructive method is extremely challenging due to probe contact resistances, we did find success in determining carbon domain properties using a delamination method.
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An Improved Dynamic Particle Packing Model for Prediction of the Microstructure in Porous ElectrodesChao, Chien-Wei 01 September 2015 (has links) (PDF)
The goal of this work is to develop a model to predict the microstructure of Li-ion batteries, specifically focusing on the cathode component of the batteries. This kind of model has the potential to assist researchers and battery manufacturers who are trying to optimize the capacity, cycle life, and safety of batteries. Two dynamic particle packing (DPP) microstructure models were developed in this work. The first is the DPP1 model, which simulates the final or dried electrode structure by moving spherical particles under periodic boundaries using Newton's laws of motion. The experience derived from developing DPP1 model was beneficial in making the final model, called DPP2. DPP2 is an improved version of DPP1 that includes solvent effects and is used to simulate the slurry-coating, drying, and calendering processes. Two type of properties were used to validate the DPP1 and DPP2 models in this work, although not every property was used with the DPP1 model. First are the structural properties, which include volume fraction, and electronic and ionic conductivities. Experimental structural properties were determined by analyzing 2D cross sectional images of the battery cathodes. These images were taken through focused ion beam (FIB) planarization and scanning electron microscopy (SEM). The second category are the mechanical properties, which include film elasticity and slurry viscosity. These properties were measured through experiments executed by our group. The DPP2 model was divided into two submodels : active-free and active-composite. The 2D cross sectional images of the simulated structure of the models have a similar particle arrangements as the experimental structures. The submodels show reasonable agreement with the experimental values for liquid and solid mass density, shrink ratio, and elasticity. For the viscosity, both models show shear-thinning behavior, which is a characteristic of slurries. The volume fractions of the simulated structures of the active-free and active-composite models have better agreement with the experimental values, which is also reflected in the 2D cross sectional images of the structure.
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Revitalizace objektu tkalcovny - Jaroměř / Revitalization of the building -JaroměřKopecký, Marek January 2013 (has links)
The project prepares reconstruction of old factory hall for new elementary music school in Jaroměř. The building is located in the city center with good transport links. Maintaining existing supporting steel structure and masonry perimeter walls allows generous use of space and innovative internal structure. Building equipment includes all fields of art and is designed for a capacity Jaroměř city and vicinity. Thanks jednopodlažnímu solution is an object conceived as partially disabled. Documentation is prepared on the documentation for building permit.
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Impact of anthropogenic activities on the vegetation structure of mangrove forests in Kribi, the Nyong river mouth and Cameroon estuary / Impacts des activités anthropiques sur la structure de la végétation des mangroves de Kribi, de l'embouchure du fleuve Nyong et de l'estuaire du CamerounNfotabong Atheull, Adolphe 13 September 2011 (has links)
Mangroves are intertidal ecosystems found along the tropical and subtropical coastlines.<p>Though globally recognised as ecosystems of ecological, biological and economical<p>remarkable importance, these ecotone formations are characterised by a continuously<p>increasing anthropization. However, very little studies have been focused on the impact of<p>various anthropogenic activities on the mangrove vegetation structure.<p>We have firstly (a) assessed the commercial and subsistence utilization of mangrove<p>wood products in the Littoral region (Cameroon estuary). Then, we have confronted the<p>subsistence usages of mangrove wood products in the Southern region (close to the mouth of<p>the Nyong River and Mpalla village (Kribi)) in comparison with the Littoral region. By doing,<p>we have compared the local residents‟ perceptions on environmental changes that occurred<p>within the two regional mangrove forests. Also, we have (c) studied the structural dynamic of<p>mangrove vegetation neighbouring the Douala city (Cameroon). Always in the vicinity of this<p>town, we have (d) reconstructed the original structure of largely disturbed mangrove forests.<p>Moreover, we have (e) map the mangrove structure in a non peri-urban setting located within<p>the Cameroon estuary. Here, we have finally (f) analysed the spatial distribution of a black<p>mangrove namely Avicennia germinans (L.) Stearn.<p>Our results underlined an excessive utilization of mangrove wood products in the<p>Cameroon estuary. We have showed that the frequency of mangrove harvesting was relatively<p>fewer in Kribi (Mpalla) and the mouth of the Nyong River. The local people inhabiting these<p>two localities perceived mangroves as less degraded areas. In contrast, those established<p>within the Cameroon estuary stated that mangroves were largely disturbed. When combining<p>the local people statements with our field observations, we recorded that it a complex mix of<p>causes (e.i. clear-felled corridors, agriculture, sand and gravel extraction, over-harvesting and<p>anarchic urbanization) that have led to the largely degradation (vegetation and sediment) of<p>the peri-urban mangroves in Cameroon. A diachronic analysis (1974, 2003, 2009) of their<p>coverage revealed that over the 35-year period, mangrove had decreases in cover of 53.16%<p>around Douala. We have also showed that in the peri-urban settings, wood harvesting was<p>commonly applied on the structurally more complex (highly dense stands neighbouring the<p>habitations) mangrove forests (Mboussa Essengue) and, in a lesser extent, on the structurally<p>more developed mangrove stands (fewer dense stands faraway from Douala). On the other<p>hand, the mapping analysis of the non peri-urban mangroves (distant from Douala) has<p>revealed that the structure of these intertidal forests was relatively less impacted. In the<p>Cameroon estuary, we also showed that A. germinans trees were randomly distributed on<p>almost one-half of the sampling plots and clumped at some scales on the remaining plots.<p>Accordingly, this species might play a significant role in the recovery process of artificial<p>gaps found in the non peri-urban areas.<p>The multi-disciplinary approach employed in this study has allowed a better<p>understanding of the direct and indirect impacts of anthropogenic activities on the mangrove<p>vegetation structure in Cameroon. These results constitute a fundamental data base quite<p>useful for the multi-temporal monitoring of these littoral ecosystems perpetually disturbed.<p>The application of similar approach in other mangroves facing high anthropogenic pressures<p>appears important. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
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Structural Color Production in Melanin-based Amorphous Colloidal AssembliesPatil, Anvay 05 June 2022 (has links)
No description available.
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