No description available.

Thesis (Ph. D.)--Columbia University, 1931. / Vita. Bibliography: p. [40].

Thesis (Ph. D.)--Florida State University, 2006. / Advisor: Srinivas Palanki, Florida State University, FAMU-FSU College of Engineering, Dept. of Chemical Engineering. Title and description from dissertation home page (viewed June 8, 2006). Document formatted into pages; contains xi, 145 pages. Includes bibliographical references.

As baterias automotivas de chumbo-ácido são componentes, que em grande parte dos fabricantes de automóveis nacionais, estão garantidas (ou dentro do período de garantia) por um ano. Mesmo sendo um período considerado curto para garantia de um veículo nos dias atuais, a bateria tem uma contribuição expressiva para os custos de garantia nas empresas por este período. Com o intuito de conhecer a confiabilidade deste componente e verificar a influência do período de armazenagem do veículo produzido na confiabilidade da bateria, foi elaborado um estudo com dados coletados em campo por um determinado fabricante de automóveis de passeio. Os parâmetros de entrada destes dados são o tempo de pátio do veículo, o tempo em que uma falha na bateria foi detectada no período de um ano de garantia e a quantidade de falhas observadas no período. Os dados permitiram análises em função do tempo, de forma que pelo método de análise paramétrica foram traçadas as curvas de confiabilidade do produto representadas por uma distribuição de Weibull de dois parâmetros, bem como, da densidade de probabilidade de falha e ainda da taxa de falha. As análises forneceram uma estimativa da confiabilidade da bateria em função do tempo, da qual foi possível extrair algumas conclusões que serão descritas neste trabalho, tais como: o comportamento de falha por desgaste das baterias automotivas e a diminuição da confiabilidade de baterias de acordo com o tempo de pátio. / The guarantee for the automotive batteries at the majority of the national vehicle manufactures is given for 1 year. Even considering this as a short period actually, this component has an expressive contribution to the guarantee costs of the companies. With the intention to know the reliability of the automotive batteries and to evaluate the vehicle storage time influence, it was carried out a study case, which had as inputs collected data from a particular vehicle manufacturer. The selected input parameters for the analysis were the vehicle storage time, time to failure and the failures amount detected in a period of 1 year. This data provided information to analyze the time domain and, supported by the reliability parametric methods, estimate the reliability of the automotive batteries. The two parameter Weibull distribution is used to model the probability density function, the failure rate analysis and reliability providing information for the conclusion of this study, like the batteries behavior of failure by wear and the reliability decrease according to the storage time.

Li-ion batteries have become one of the chosen energy storage devices that are used in applications such as power tools, cellular phones and electric vehicles (EV). With the demand for portable high energy density devices, the rechargeable Li-ion battery has become one of the more viable energy storage systems for large scale commercial EVs because of their higher energy density to weight or volume ratio when compared to other current commercial battery energy storage systems. Various safety procedures for the use of Li-ion batteries in both consumer and EV applications have been developed by the international associations. The test procedures studied in this dissertation demonstrated the importance of determining the true capacity of a cell at various discharge rates. For this, the well known Peukert test was demonstrated. The study also showed that cells with different battery geometries and chemistries would demonstrate different thermal heating during discharge and slightly different Ragone results if different test methods were used as reported in the literature. Accelerated ageing tests were done on different cells at different Depth-of-Discharge (DoD) regions. The different DoD regions were determined according to expected stresses the electrode material in a cell would experience when discharged to specific DoD that follows the discharge voltage profile. Electrochemical Impedance Spectroscopy (EIS) was used to measure various electrochemical changes within these cells. The EIS results showed that certain observed modelled parameters would change similarly to the ageing of the cell as it aged due to the accelerated testing. EIS was also done on cells at different State-of-Charge (SoC) and temperatures. The results showed that EIS can be used as an effective technique to observe changes within a Li-ion cell as the SoC or temperature changed. For automotive vehicles that are powered by a fuel cell or battery, a supercapacitor can be coupled to a battery in order to increase and optimize the energy and power densities of the drive systems. A test procedure in the literature that evaluated the use of capacitors with Pb-acid batteries was applied to Li-ion type cells in order to quantify the increased power due to the use of a supercapacitor with a Li-ion cell. Both a cylindrical LiCoO2 cell and a VRLA Pb-acid cell showed some additional charge acceptance and delivery when connected to the supercapacitors. A LiMn2O4 pouch cell showed significant charge acceptance and delivery when connected to supercapacitors. The amount of additional charge acceptance and delivery of the different combinations could be explained by EIS, in particular, the resistance and capacitance of the cell in comparison to the combination of the cell and supercapacitor. A large capacity LiCoO2 cell showed high charge acceptance and delivery without connection with a supercapacitor. The study proved that EIS can be used to model the changes within cells under the different conditions and using different test procedures.

Abstract not available

Porous carbons are versatile materials with applications in different fields. They are used in filtration, separation and sequestration of fluids and gases, as conductive additives in many energy storage materials, as coloring agents, as pharmaceutical and food additives, and in many other vital technologies. Porous carbons produced by pyrolysis and activation of organic precursors commonly suffer from poorly controlled morphology, microstructure, chemistry, and pore structure. In addition, the poorly controlled parameters of porous carbons make it challenging to elucidate the underlying key physical parameters controlling their performance in energy storage devices, including electrochemical capacitors (ECs) and lead-acid batteries (LABs). Zeolite-templated carbons (ZTCs) are a novel class of porous carbon materials with uniform and controllable pore size, microstructure, morphology, and chemistry. In spite of their attractive properties, they have never been explored for use in LABs and their studies for ECs have been very limited. Here I report a systematic study of ZTCs applications in ECs operating at temperatures as low as - 70 C and in LABs. Greatly improved power and energy performance, compared to state of the art devices, has been demonstrated in the investigated ECs. Moreover, the application of ZTCs in LABs has resulted in a dramatic enhancement of their cycle life and power and energy densities.

With increasing interest in energy storage and conversion devices for automobile applications, the necessity to understand and predict life behavior of rechargeable batteries, PEM fuel cells and super capacitors is paramount. These electrochemical devices are most beneficial when used in hybrid configurations rather than as individual components because no single device can meet both range and power requirements to effectively replace internal combustion engines for automobile applications. A system model helps us to understand the interactions between components and enables us to determine the response of the system as a whole. However, system models that are available predict just the performance and neglect degradation. In the first part of the thesis, a framework is provided to account for the durability phenomena that are prevalent in fuel cells and batteries in a hybrid system. Toward this end, the methodology for development of surrogate models is provided, and Pt catalyst dissolution in PEMFCs is used as an example to demonstrate the approach. Surrogate models are more easily integrated into higher level system models than the detailed physics-based models. As an illustration, the effects of changes in control strategies and power management approaches in mitigating platinum instability in fuel cells are reported. A system model that includes a fuel cell stack, a storage battery, power-sharing algorithm, and dc/dc converter has been developed; and preliminary results have been presented. These results show that platinum stability can be improved with only a small impact on system efficiency. Thus, this research will elucidate the importance of degradation issues in system design and optimization as opposed to just initial performance metrics. In the second part of the thesis, modeling of silicon negative electrodes for lithium ion batteries is done at both particle level and cell level. The dependence of the open-circuit potential curve on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. Firstly, for modeling of lithium-silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs. composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/de-insertion in single silicon electrode particle under potentiodynamic control are modeled and compared with experimental data to provide justification for the same. This work stresses the need for experiments for accurate determination of transfer coefficients and the exchange current density before reasoning kinetic hysteresis for the potential gap in Li-Si system. The silicon electrode particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the silicon electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. Need for accurate determination of exchange current density for lithium insertion in silicon nanoparticles is discussed. This model and knowledge thereof can be used in cell-sandwich model for the design of practical lithium ion cells with composite silicon negative electrodes. Secondly, galvanostatic charge and discharge of a silicon composite electrode/separator/ lithium foil is modeled using porous electrode theory and concentrated solution theory. Porosity changes arising due to large volume changes in the silicon electrode with lithium insertion and de-insertion are included and analyzed. The concept of reservoir is introduced for lithium ion cells to accommodate the displaced electrolyte. Influence of initial porosity and thickness of the electrode on utilization at different rates is quantitatively discussed. Knowledge from these studies will guide design of better silicon negative electrodes to be used in dual lithium insertion cells for practical applications.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 178-184). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--State University of New York at Binghamton, Materials Science and Engineering Program, 2009. / Includes bibliographical references.