Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Abstract. Vita. Also available via the Internet

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

This thesis studies the feasibility of utilizing Zigbee standard devices to create a shipboard wireless sensor network. Two primary methods were used to demonstrate feasibility. The first method demonstrated initial feasibility with a series of laboratory tests. The tests included range, reliability, and battery life tests. In the second portion, a prototype pressure sensor was created by matching a low power pressure transducer to a Zigbee modem via an integrated DAQ unit. Supporting software was generated using LabVIEW 6.0 to act as a server program and allow a remote Integrated Condition Assessment System (ICAS) workstation to log in via a TCP/IP connection and monitor sensor data. The expected contribution from the research effort would a completely wireless sensor network which would result in a net savings in man hours required to maintain and monitor. The sensor network would be reliable, relatively inexpensive, and entirely COTS available. With an extended battery life of 18 to 24 months, even the battery replacement could be fit into a standard annual or bi-annual PMS cycle, minimizing the workload to maintain. Initial feasibility testing was completed satisfactorily and the prototype sensor was successfully created and integrated to interface with the existing sensor infrastructure.

Liu, Hao = 鋰離子電池納米電極的製備和表徵 / 劉昊. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 99-103). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Liu, Hao = Li li zi dian chi na mi dian ji de zhi bei he biao zheng / Liu Hao.

Batteries are complex, multidisciplinary, electrochemical energy storage systems that are crucial for powering our society. During operation, all battery technologies suffer from voltage losses due to energetic penalties associated with the electrochemical processes (i.e., ohmic resistance, kinetic barriers, and mass transport limitations). A majority of the voltage losses can be attributed to processes occurring on/in the battery electrodes, which are responsible for facilitating the electrochemical reactions. A major challenge in the battery field is developing strategies to mitigate these losses. To accomplish this, researchers must i) identify the processes limiting the performance of the electrode, ii) characterize the main, performance-limiting processes to understand the underlying mechanisms responsible for the poor performance, and iii) mitigate the voltage losses by developing strategies which target these underlying mechanisms. In this thesis, three studies are presented which highlight the role of electrochemical engineers in alleviating the performance limiting processes in battery electrodes. Each study is focused on a different step of the research approach (i.e., identification, characterization, and mitigation) and analyzes an electrode from a different battery system. The first part of the thesis is focused on identifying the processes limiting the capacity in nanocomposite lithium-magnetite electrodes. To accomplish this, the mass transport processes and phase changes occurring within magnetite electrodes during discharge and voltage recovery are investigated using a combined experimental and modeling approach. First, voltage recovery data are analyzed through a comparison of the mass transport time-constants associated with different length-scales in the electrode. The long voltage recovery times are hypothesized to result from the relaxation of concentration profiles on the mesoscale, which consists of the agglomerate and crystallite length-scales. The hypothesis was tested through the development of a multi-scale mathematical model. Using the model, experimental discharge and voltage recovery data are compared to three sets of simulations, which incorporate crystal-only, agglomerate-only, or multi-scale transport effects. The results of the study indicate that, depending on the crystal size, the low utilization of the active material (i.e., low capacity) is caused by transport limitations on the agglomerate and/or crystal length-scales. For electrodes composed of small crystals (6 and 8 nm diameters), it is concluded that the transport limitations in the agglomerate are primarily responsible for the long voltage recovery times and low utilization of the active material. In the electrodes composed of large crystals (32 nm diameter), the slow voltage recovery is attributed to transport limitations on both the agglomerate and crystal length-scales. Next, the multi-scale model is further expanded to study the phase changes occurring in magnetite during lithiation and voltage recovery experiments. Phase changes are described using kinetic expressions based on the Avrami theory for nucleation and growth. Simulated results indicate that the slow, linear voltage change observed at long times during the voltage recovery experiments can be attributed to a slow phase change from α¬-LixFe3O4 to β¬-Li4Fe3O4. In addition, simulations for the lithiation of 6 and 32 nm Fe3O4 suggest the rate of conversion from α¬-LixFe3O4 to γ-(4 Li2O + 3 Fe) decreases with decreasing crystal size. The next part of the thesis presents a study aimed at characterizing the formation of PbSO4 films on Pb in H2SO4, which has been previously identified as a performance-limiting process in lead-acid batteries. Transmission X-ray microscopy (TXM) is utilized to monitor, in real time, the initial formation, the resulting passivation, and the subsequent reduction of the PbSO4 film. It is concluded with support from quartz-crystal-microbalance experiments that the initial formation of PbSO4 crystals occurs as a result of acidic corrosion. Additionally, the film is shown to coalesce during the early stages of galvanostatic oxidation and to passivate as a result of morphological changes in the existing film. Finally, it is observed that the passivation process results in the formation of large PbSO4 crystals with low area-to-volume ratios, which are difficult to reduce under both galvanostatic and potentiostatic conditions. In a further extension of this study, TXM and scanning electron microscopy are combined to investigate the effects of sodium lignosulfonate on the PbSO4 formation and the initial growth of PbSO4 crystals. Sodium lignosulfonate is shown to retard, on average, the growth of the PbSO4 crystals, yielding a film with smaller crystals and higher crystal densities. In addition, an analysis of the growth rates of individual, large crystals showed an initial rapid growth which declined as the PbSO4 surface coverage increased. It was concluded that the increase in PbSO4 provides additional sites for precipitation and reduces the precipitation rate on the existing crystals. Finally, the potential-time transient at the beginning of oxidation is suggested to result from the relaxation of a supersaturated solution and the development of a PbSO4 film with increasing resistance. The final part of the thesis presents a study aimed at mitigating the ohmic losses during pulse-power discharge of a battery by the adding a second electrochemically active material to the electrode. Porous electrode theory is used to conduct case studies for when the addition of a second active material can improve the pulse-power performance. Case studies are conducted for the positive electrode of a sodium metal-halide battery and the graphite negative electrode of a lithium-ion battery. The replacement of a fraction of the nickel chloride capacity with iron chloride in a sodium metal-halide electrode and the replacement of a fraction of the graphite capacity with carbon black in a lithium-ion negative electrode were both predicted to increase the maximum pulse power by up to 40%. In general, whether or not a second electrochemically active material increases the pulse power depends on the relative importance of ohmic-to-charge transfer resistances within the porous structure, the capacity fraction of the second electrochemically active material, and the kinetic and thermodynamic parameters of the two active materials.

Batteries are ubiquitous in modern society, from the portable devices we use daily to the yet-to-be realized integration of batteries into the electrical grid and electrical vehicle markets. One of the primary roles of batteries to date has been to enable portability of devices, and as chemical energy storage becomes more affordable, batteries will play a larger role in how society cares for the environment by enabling technologies that are poised to decrease greenhouse gas emissions. Low cost and environmentally conscious materials are pivotal for the economic feasibility and widespread integration of batteries into new markets. Batteries operate far from equilibrium and may operate under extreme stress and varying loads, therefore, for a material to be successful in an operational battery it must meet multiple design criteria. Here, an in-depth analysis of magnetite, a low cost and abundant iron oxide studied for use as an electrode material in lithium-ion batteries, is presented. In the second Chapter, an in-depth analysis into how magnetite accepts lithium into the solid state at low depths of discharge is examined with density functional theory and a mechanistic understanding of a phase change from the parent spinel to a rocksalt-like material is presented. When magnetite is used as an electrode material in a lithium-ion battery, lithium must enter into and eject from the solid state of the host material, where the direction of lithium movement is a function of the current in the battery. In many electrode materials, magnetite included, large structural rearrangements can occur in the host material as lithium moves into and out of the lattice. These structural rearrangements can be irreversible and can contribute to overpotentials, decreasing efficiency and lifecycle for the battery. The structural rearrangements in bulk magnetite occurring due to lithium insertion are found to be driven primarily by Coulombic interactions. Additionally, the energetics and structural rearrangements for lithium insertion into defective magnetite and maghemite are examined, as these derivative structures commonly co-exist with magnetite, especially when the material is nanostructured. It is found that defective magnetite and maghemite accept lithium by a different mechanism, one that does not initially result in substantial structural rearrangement, as is the case in magnetite. In Chapter three, the effects of nanostructuring magnetite on the reversible potential are examined as a function of nanoparticle size. Due to solid-state mass-transport resistances, active electrode materials in batteries are commonly nanostructured. When a material is nanostructured, the bulk properties are often replaced due to interesting phenomena that can occur as a result of stark differences between the nanostructured material and the bulk counterpart. These differences are often attributed to surface area to volume ratios, the exaggerated role of surface energies, lattice defects, and the variation in electronic behavior, all properties which change between a bulk and nanostructured material. The reversible potential is found to be particle size dependent, and this dependence is explained, in part, by the cationic defective surfaces in the particles and the differences in surface area to volume ratio between varying particle sizes. Evidence for these defects is presented with materials characterization techniques such as XRD and EELS studies. Finally, the reversible potential at low lithiation states is predicted theoretically and found to match well to the experimentally measured potential. A study of the DFT predicted potentials and XRD characterization for multiple metastable pathways is examined in the fourth Chapter. Room temperature and long-time scale persistence of metastable phases is a pervasive phenomenon in nature. Magnetite is known to undergo both phase change and conversion reactions upon lithiation. Due to large mass transport and kinetic resistances, multiple phase changes are often observed in parallel during discharge, resulting in heterogenous phase formation in particles which can have large local lithium concentration variations. Phases which form during discharge can become kinetically trapped and the equilibrium state can therefore follow a metastable pathway. Theoretical potentials and XRD patterns are compared to the experimental patterns taken following 600 hours of relaxation following discharge at the slow rate of C/600. The evidence presented supports a metastable pathway occurring on the first voltage plateau. In the fifth Chapter, the methodologies for the density functional theory calculations are presented in full detail. This includes various studies on the more subtle electronic properties of magnetite and its lithiated derivates studied herein. These studies include examination of the charge and orbital ordering problem related to the Verwey transition in magnetite, the charge and magnetic order in the rocksalt-like lithiated magnetite, and a full theoretical description of the various phases in the Li-Fe-O ternary phase diagram that were calculated to make the relevant conclusions in Chapters 2-4. Finally, corrections to DFT predicted formation energy and volume are presented. The aim of this thesis is to use theoretical techniques to examine the lithiation of magnetite on the atomic scale and make meaningful connections to the experimentally observed electrochemical behavior of the material. To accomplish this, magnetite and the structural derivatives of magnetite that co-exist with the material under physically realistic conditions must be treated theoretically. In this thesis, ties between phenomena occurring on the atomic scale and the measurable properties of the macroscopic system, such as voltage, will be related. It will be illustrated that as a function of nanoparticle size, the magnetite system can vary in its atomic structure and the resultant electrochemistry and phase change characteristics are both affected. The findings indicate the relevance of the atomic properties and nanostructure for magnetite to the observed and measured electrochemical properties of the material.

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.

This thesis presents a study on the design method to optimise the performance for producing green power from multiple renewable energy generators. The design method is presented through PLC (Programmable Logic Controller) theory. All the digital and analogue inputs are connected to the input cards. According to different operations conditions for each generator, the PLC will image all the inputs and outputs, from these images; a software program has been built to create a control method for multiple renewable energy generators to optimise production of green power. A control voltage will supply the output contractor from each generator via an interface relay. Three renewable generators (wind, solar, battery bank) have been used in the model system and the fourth generator is the back up diesel generator. The priority is for the wind generator due to availability of wind 24 hours a day, then solar, battery bank, and LPG or Diesel generators. Interlocking between the operations of the four contractors has been built to prevent interface between them. Change over between contractors, according to the generator's change over has also been built, so that it will delay supplying the main bus bar to prevent sudden supply to the load. Further study for controlling multiple renewable energy generators for different conditions such as controlling the multi-renewable energy generators from remote, or supplying weather forecast data from bureau of meteorology to the PLC directly as recommended. / Master of Electrical Engineering (Hons)

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Julian, Alexander L. Second Reader: Crisiti, Roberto. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Pulsed power, charger, buck converter, field programmable gate array (FPGA), lithium-ion batteries. Includes bibliographical references (p. 77-79). Also available in print.

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