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Development of negative electrodes for lithium-ions batteries
Drahokoupil, Petr ; Libich, Jiří (referee) ; Sedlaříková, Marie (advisor)
This thesis deals with lithiation of negative electrode li-ion batteries. In this thesis is used several electrode materials: carbon, FeCl3, lithiated carbon electrodes and silicon carbide. Reduction of irreversible capacity lithium-ion batteries leads to increased capacity and also we can use new materials as a positive electrode. Thesis deals with the differences in the properties of materials using lithiation and their use in practice
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Flame retarders of polymeric materials
Winkler, David ; Poláček, Petr (referee) ; Kučera, František (advisor)
Bachelor thesis focuses on the study of expanded graphite as flame retardant added to low density polyethylene and it´s potential synergistic effect with ammonium polyphosphate. Additive and non-additive dog-bone samples were prepared by compounding and injection. Crystalization, melting point and thermal decomposition of the samples were monitored by TGA and DSC thermal analysis methods. The effect of expanded graphite on the mechanical proporties of the materiál was monitored by a tenssile test. The effect of expanded graphite as a flame retardant and its synergistic effect with ammonium polyphosphate was confirmed by a flame test in the horizontal position of the sample.
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Zinc based negative electrode for alkaline accumulators
Prchal, Jiří ; Svoboda, Vít (referee) ; Špičák, Petr (advisor)
The object of this project is research and preparation of the permanent zinc electrode in a strong alkaline surrounding for the usage in Ni-Zn accumulators. This system is characterized by a low overall ecological impact on environment, higher specific energy and higher electromotive force than nowadays commonly used systems (lead, nickel-cadmium). The goal of this project is to originate a new procedure, which will make possible to steady a zinc electrode. Every research faces a problem shaping changes of zinc electrode during cycling and related low cycle life. This work consists of the theoretical part, in which is explained a basic accumulators mechanism and practical part, in which is described performed research.
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Composite electrode materials for lithium-ion batteries based on LiFePO4 prepared using GAC method
Vilhelm, Ondřej ; Neoral, Jiří (referee) ; Čech, Ondřej (advisor)
Presented work investigates the problem of secondary lithium-ion cells and the different available cathode materials. We have prepared samples of LiFePO4 with the addition of different kinds of carbon materials such as Super P, Vulcan and expanded graphite. We have always created the sample with and without surfactant. Developed samples were compared by measuring electrochemical methods (cyclic voltammetry, charge and discharge cycles and impedance spectroscopy). We also modeled the three-point cell for measuring electrochemical electrode materials.
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Electrical behaviour of polymeric composites with expanded graphite
Šimonek, Michal ; Petruš, Josef (referee) ; Kučera, František (advisor)
Electrically conductive thermoplastic composites made from graphene nanoplatelets or graphene precursors are a promising branch of new functional materials. Graphene nanocomposites were prepared via processing in an internal mixer from four extrusion grade polyethylenes (PE) and expanded graphite (EG). As a method of possible improvement of EG dispersion, compounding in presence of various compatibilizers is examined. Melt compounding was performed for 10 min at 200 °C and 60 rpm. The electrical conductivity of compression-molded samples was determined from a current voltage characteristic or direct resistance measurement. Composite morphology was characterized by scanning electron microscopy. Depending on the PE matrix and compatibilizer structure, different electrical conductivities and morphologies were observed, which corresponded in agreement with either percolation theory or the random-resistor network of Miller and Abrahams models. Substantial reduction of percolation threshold was achieved in compatibilized ultra-low density polyethylene where percolation occurred at 3,92 % vol.
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Expanded and Flake Natural Graphite as Negative Electrode Material in Lithium-ion Cell
Paulovics, Petr ; Kazda, Tomáš (referee) ; Libich, Jiří (advisor)
This diploma thesis deals with an issue of lithium-ion batteries, primarily with negative (anode) electrode materials. Natural graphite in two forms, namely flake and expanded graphite, is used in the thesis as active electrode material. It is concerned with study of their capacity and output characteristics depending on the pressing pressure and discharging current. The first part of thesis consists of theory and describes basic principles and the composition of lithium-ion batteries. Materials, their characteristics used in production and theoretical description of measurement techniques are presented then. The second part of the thesis is focused on production, assembling and measurement of the characteristics of the produced electrodes. The aim of the thesis is finding the effects of changes of pressing pressure on the capacity, stability during cycling and stability at higher loads.
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Porosity increasing agents for supercapacitors
Hovorka, Martin ; Dvořák, Petr (referee) ; Sedlaříková, Marie (advisor)
This work deals with questions connected with ultracapactors and lightening agents of activated carbon used for production of supercapacitors’s electrodes. Our goal was examination of ideal ratio of carbon and lightening agent in surveyed electrode. Materials which were used: expanded graphite, soda saleratus, ammonium bicarbonate and ammonium formate. Specimens were measured by cyclic voltammetry. The best results was reached by using of soda saleratus with ideal ratio 1:0,5. During measurement was found that weight of electrode has basic effect on eventual capacity.
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Inflence of Granulation to Sorption Properties of Expanded Graphite
Hladík, Jakub ; Poláček, Petr (referee) ; Kučera, František (advisor)
Expanded graphite is one of the promising sorption materials, but its disadvantage is difficult handling. This thesis deals with the granulation of expanded graphite and the effect of granulation on oil sorption. Samples with a starch and dextrin binder were prepared. Samples filled with cellulose fibers and wood flour were prepared with a starch binder. The strength of the granulate was determined from the sub-sieve fraction. The sorption capacity was determined gravimetrically after 30 minutes of oil immersion. The granulate filled with a lower amount of wood flour achieved the highest sorption capacity. The addition of cellulose fibers substantially strengthened the granulate. Based on the previous results, a granulate of a defined shape and size was prepared. The morphology of the granulate was observed by scanning electron microscopy.
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Butyl Rubber Modified Using Expanded Graphite
Žůrek, Michal ; Petruš, Josef (referee) ; Kučera, František (advisor)
This work deals with the influence of expanded graphite (EG) as a reinforcing filler on the mechanical and tribological properties of vulcanizates of butyl rubber blends. Tensile strength, elongation at break, moduli (M100, M200, M300 a M500), and Young's modulus of elasticity of the prepared vulcanizates were studied by the tensile test method. In addition to the tensile test results, the dispersion of EG particles was studied on scanning electron microscopy (SEM) images of the fracture surfaces of the prepared vulcanizates. The filler-matrix interaction was evaluated using the Kraus model for filled rubber and the results were subsequently compared with SEM images of the EG particle-matrix interface on the fracture surfaces of the vulcanizates. The effect of EG on the properties of the vulcanizates was compared with the effect of common rubber blacks (N220 and N772). It was found that an important factor affecting the mechanical properties of filled vulcanizates is the dispersion of filler particles. EG dosage higher than 5 phr promotes the agglomeration of filler particles in the butyl rubber matrix, which negatively affects the mechanical properties of the blend. Vulcanizates filled only with EG have lower tensile strength than those filled with N220 or N772 blacks. By choosing an appropriate ratio of EG to blacks, higher mechanical strength was achieved than with the use of only one filler.
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Electrical behaviour of polymeric composites with expanded graphite
Šimonek, Michal ; Petruš, Josef (referee) ; Kučera, František (advisor)
Electrically conductive thermoplastic composites made from graphene nanoplatelets or graphene precursors are a promising branch of new functional materials. Graphene nanocomposites were prepared via processing in an internal mixer from four extrusion grade polyethylenes (PE) and expanded graphite (EG). As a method of possible improvement of EG dispersion, compounding in presence of various compatibilizers is examined. Melt compounding was performed for 10 min at 200 °C and 60 rpm. The electrical conductivity of compression-molded samples was determined from a current voltage characteristic or direct resistance measurement. Composite morphology was characterized by scanning electron microscopy. Depending on the PE matrix and compatibilizer structure, different electrical conductivities and morphologies were observed, which corresponded in agreement with either percolation theory or the random-resistor network of Miller and Abrahams models. Substantial reduction of percolation threshold was achieved in compatibilized ultra-low density polyethylene where percolation occurred at 3,92 % vol.
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