Aşkar, Yasemin
The increasing energy demand requires battery systems with high volumetric energy density, therefore one of the current aims is to maximize the amount of active material that can be loaded per unit volume. This situation is directly related to the particle agglomeration state and dispersible particles are required to achieve high volumetric energy density. Carbon coating, which is used to increase the electrical conductivity of active materials, also plays a significant role in the agglomeration of the particles. For this reason, in this thesis, it was aimed to develop a suitable carbon coating procedure in such a way that individual electroactive materials maintain their dispersibility. Herein, as a novel approach, colloidal principles and a proceeding pyrolysis step were used to synthesize dispersible particles with full carbon coverage. LiFePO4 (LFP) electroactive material was chosen as the model system. Individually dispersible LFP particles were produced with the polyol method. After zeta potential analyses on pristine LFP particles, CTAB (cetyltrimethylammonium bromide) was chosen as the surfactant and used as a carbon source for pyrolysis. The critical ratio of CTAB to LFP at which zeta potential reverses sign and stabilizes were determined and a two-stage pyrolysis procedure was designed. The optimal carbon-coated individual particles produced in this process and bare LFP were compared in terms of their dispersibility, tap density, and electrochemical performance. The tap density of the pristine LFP (1.11 g∙cm-3) and carbon-coated LFP particles (1.16 g∙cm-3) was obtained quite similar. Results demonstrate the applicability of the zeta potential analysis-based approach utilized herein producing homogeneous carbon coating without any loses in tap density and dispersibility.


Synthesis of dispersible LiFePO4 particles with controlled size and morphology via polyol route
Coşkun, Elif; Çınar, Simge; Maviş, Bora; Department of Metallurgical and Materials Engineering (2022-8-22)
Despite their widespread use in energy storage, high cost and safety are two major concerns for lithium-ion batteries (LIBs). The lack of safe, scalable, robust, and energy-efficient methods enabling high yield synthesis is one of the main reasons for the high cost of electroactive materials. This need has driven an interest in polyol synthesis technique due to simplicity and scalability. As applied in the synthesis of LiFePO4 (LFP) nanoparticles, polyol methods have generally been performed at high tempera...
Modeling of reaction and degradation mechanisms in lithium-sulfur batteries
Erişen, Nisa; Külah, Görkem; Department of Chemical Engineering (2019)
Lithium-sulfur batteries are promising alternatives for the energy storage systems beyond Li-ion batteries due to their high theoretical specific energy (2567 Wh/kg) in addition to the natural abundancy, non-toxicity and low cost of sulfur. The reaction and degradation mechanisms in a Li-S battery include various electrochemical and precipitation/dissolution reactions of sulfur and polysulfides; however, the exact mechanism is still unclear. In this study, the effect of critical cathode design parameters su...
Synthesis and thermoelectric characterization of Ca3Co4O9 particles
Ertuğrul, Hediye Merve; Özenbaş, Ahmet Macit; Department of Metallurgical and Materials Engineering (2018)
Thermoelectric materials can convert waste heat to electrical energy as well as thermal energy to electrical energy. Thermoelectric technology can aid to solve the energy problem which causes global environmental problems as an alternative energy source and provide long-lasting power sources which can be used for space missions. Ca3Co4O9 is environment friendly, nontoxic, humidity resistant at high temperatures, oxidation resistant, abundant, chemically and thermally stable in air and light. Also, this mate...
Hierarchical multi-component nanofiber separators for lithium polysulfide capture in lithium-sulfur batteries: an experimental and molecular modeling study
Zhu, Jiadeng; Yıldırım, Erol; Aly, Karim; Shen, Jialong; Chen, Chen; Lu, Yao; Jiang, Mengjin; Kim, David; Tonelli, Alan E.; Pasquinelli, Melissa A.; Bradford, Philip D.; Zhang, Xiangwu (2016-01-01)
Sulfur (S) has been considered as a promising cathode candidate for lithium batteries due to its high theoretical specific capacity and energy density. However, the low active material utilization, severe capacity fading, and short lifespan of the resultant lithium-sulfur (Li-S) batteries have greatly hindered their practicality. In this work, a multi-functional polyacrylonitrile/silica nanofiber membrane with an integral ultralight and thin multi-walled carbon nanotube sheet is presented and it provides a ...
Design and implementation of all-SiC MPPT boost converter for grid connected photovoltaic systems
Koç, Elif Tuğçe; Ermiş, Muammer; Department of Electrical and Electronics Engineering (2019)
Output power generated by a photovoltaic array is prone to fluctuations during utilization due to varying solar irradiance exposure throughout the day and changes in cell temperature; therefore, maximum power point tracking is essential for overall system efficiency. For this purpose, DC-DC Maximum Power Point Tracker (MPPT) Converters are used in photovoltaic systems connected to the grid in order to extract the available power. SiC semiconductors are favorable new devices that enable greater power convers...
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