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- ItemComprehensive Study of Rapid Capacity Fade in Prismatic Li-ion Cells with flexible packaging(Nature Research, 2024-11-18) Stravová, Zuzana; Klvač, Ondřej; Báňa, Jiří; Anothumakkool, Bihag; Zikmund, Tomáš; Blažek, Pavel; Kaiser, Jozef; Kazda, TomášPrismatic lithium-ion batteries (LIBs) are considered promising electric energy sources in electromobility applications due to their efficient space utilization. However, their sensitivity to external and internal influences and reduced durability lead to inflation risk and potential explosions throughout their lifecycle. These critical processes are strongly influenced by the inner construction of the cell, especially concerning the coating and mechanical fixation. This study subjects a commercially available prismatic LIB cell to comprehensive, correlative analysis employing various imaging techniques. The inner structure of the entire cell is visualized non-destructively by X-ray computed tomography (CT), enabling the identification of critical design flaws prior to electrochemical cycling. Electrochemical cycling simulates the battery lifecycle, and the cell is subsequently disassembled in the fully charged state. The usage of the inert-gas transfer system allowed the preparation of Broad Ion Beam (BIB) electrodes cross-sections in a fully native state and for the first time to observe the tearing of graphite particles due to over-lithiation. Established region labeling system allowed to use CT and scanning electron microscopy (SEM) correlatively to identify critical regions. After 100 cycles, a 40% capacity loss was observed and event diagram describing deagradation mechanisms, related both to the cell design and to the processes occurring at high load, was created.
- ItemCFD Analyses of Density Gradients under Conditions of Supersonic Flow at Low Pressures(MDPI, 2024-09-14) Bayer, Robert; Bača, Petr; Maxa, Jiří; Šabacká, Pavla; Binar, Tomáš; Vyroubal, PetrThis paper deals with CFD analyses of the difference in the nature of the shock waves in supersonic flow under atmospheric pressure and pressure conditions at the boundary of continuum mechanics for electron microscopy. The first part describes the verification of the CFD analyses in combination with the experimental chamber results and the initial analyses using optical methods at low pressures on the boundary of continuum mechanics that were performed. The second part describes the analyses on an underexpanded nozzle performed to analyze the characteristics of normal shock waves in a pressure range from atmospheric pressure to pressures at the boundary of continuum mechanics. The results obtained by CFD modeling are prepared as a basis for the design of the planned experimental sensing of density gradients using optical methods, and for validation, the expected pressure and temperature courses from selected locations suitable for the placement of temperature and pressure sensors are prepared from the CFD analyses.
- ItemAssessing the Carbon Footprint of Viticultural Production in Central European Conditions(MDPI, 2024-07-31) Bača, Petr; Mašán, Vladimír; Vanýsek, Petr; Burg, Patrik; Binar, Tomáš; Burgová, Jana; Abrham, ZdeněkA number of factors will increasingly play a role in the sustainability of wine production in the coming period. The current situation suggests that the analysis of energy consumption and greenhouse gas (GHG) emissions will play a particularly important role. The so-called carbon footprint, expressed in CO2 equivalents, is used to express the sum of GHG emissions. This study presents an analysis of vine cultivation in a particular Central European region, with the main focus on quantifying the inputs, yield, fuel consumption, and GHG emissions. The emphasis was placed on conventional, integrated, and ecological production systems of growing, evaluated with the help of the developed AGROTEKIS version 5 software. A total of 30 wine-grower entities in the Morava wine-growing region, the subregion Velk & eacute; Pavlovice, in the Czech Republic weather climate, were included in the input data survey. By analyzing the aggregated values, the real savings in energy and curbing of CO2 emissions of vineyards could be observed, relating to individual work procedures with lower energy demand used in the vineyard treatment as well as the amounts and doses of agrochemicals used. The average values of the total impacts did not show any statistically significant differences between the conventional (971 +/- 78 kg CO2eqha-1year-1) and integrated production systems (930 +/- 62 kg CO2eqha-1year-1), whereas the values for the ecological production system were significantly higher (1479 +/- 40 kg CO2eqha-1year-1). The results show that growing vines under ecological production conditions generates a higher proportion of the carbon footprint than under conventional production conditions. Overall, the best results can be achieved in an integrated production system.
- ItemNovel Cu(II)-based metal-organic framework STAM-1 as a sulfur host for Li-S batteries(NATURE PORTFOLIO, 2024-04-22) Niščáková, V.; Almáši, Miroslav; Capková, Dominika; Kazda, Tomáš; Čech, Ondřej; Čudek, Pavel; Petruš, Ondrej; Volavka, D.; Orinaková, Renáta; Straková Fedorková, AndreaDue to the increasing demand for energy storage devices, the development of high-energy density batteries is very necessary. Lithium-sulfur (Li-S) batteries have gained wide interest due to their particularly high-energy density. However, even this type of battery still needs to be improved. Novel Cu(II)-based metal-organic framework STAM-1 was synthesized and applied as a composite cathode material as a sulfur host in the lithium-sulfur battery with the aim of regulating the redox kinetics of sulfur cathodes. Prepared STAM-1 was characterized by infrared spectroscopy at ambient temperature and after in-situ heating, elemental analysis, X-ray photoelectron spectroscopy and textural properties by nitrogen and carbon dioxide adsorption at - 196 and 0 degrees C, respectively. Results of the SEM showed that crystals of STAM-1 created a flake-like structure, the surface was uniform and porous enough for electrolyte and sulfur infiltration. Subsequently, STAM-1 was used as a sulfur carrier in the cathode construction of a Li-S battery. The charge/discharge measurements of the novel S/STAM-1/Super P/PVDF cathode demonstrated the initial discharge capacity of 452 mAh g-1 at 0.5 C and after 100 cycles of 430 mAh g-1, with Coulombic efficiency of 97% during the whole cycling procedure at 0.5 C. It was confirmed that novel Cu-based STAM-1 flakes could accelerate the conversion of sulfur species in the cathode material.
- ItemHeat Effects during the Operation of Lead-Acid Batteries(MDPI, 2024-04-27) Bača, Petr; Vanýsek, Petr; Langer, Martin; Zimáková, Jana; Chladil, LadislavThermal events in lead-acid batteries during their operation play an important role; they affect not only the reaction rate of ongoing electrochemical reactions, but also the rate of discharge and self-discharge, length of service life and, in critical cases, can even cause a fatal failure of the battery, known as “thermal runaway.” This contribution discusses the parameters affecting the thermal state of the lead-acid battery. It was found by calculations and measurements that there is a cooling component in the lead-acid battery system which is caused by the endothermic discharge reactions and electrolysis of water during charging, related to entropy change contribution. Thus, under certain circumstances, it is possible to lower the temperature of the lead-acid battery during its discharging. The Joule heat generated on the internal resistance of the cell due to current flow, the exothermic charging reaction, and above all, the gradual increase in polarization as the cell voltage increases during charging all contribute to the heating of the cell, overtaking the cooling effect. Of these three sources of thermal energy, Joule heating in polarization resistance contributes the most to the temperature rise in the lead-acid battery. Thus, the maximum voltage reached determines the slope of the temperature rise in the lead-acid battery cell, and by a suitably chosen limiting voltage, it is possible to limit the danger of the “thermal runaway” effect. The overall thermal conditions of the experimental cell are significantly affected by the ambient temperature of the external environment and the rate of heat transfer through the walls of the calorimeter. A series of experiments with direct temperature measurement of individual locations within a lead-acid battery uses a calorimeter made of expanded polystyrene to minimize external influences. A hitherto unpublished phenomenon is discussed whereby the temperature of the positive electrode was lower than that of the negative electrode throughout the discharge, while during charging, the order was reversed and the temperature of the positive electrode was higher than that of the negative electrode throughout the charge. The authors relate this phenomenon to the higher reaction entropy change of the active mass of the positive electrode than that of the negative electrode.