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Functional Data Models for Raman Spectral Data and Degradation AnalysisDo, Quyen Ngoc 16 August 2022 (has links)
Functional data analysis (FDA) studies data in the form of measurements over a domain as whole entities. Our first focus is on the post-hoc analysis with pairwise and contrast comparisons of the popular functional ANOVA model comparing groups of functional data. Existing contrast tests assume independent functional observations within group. In reality, this assumption may not be satisfactory since functional data are often collected continually overtime on a subject. In this work, we introduce a new linear contrast test that accounts for time dependency among functional group members. For a significant contrast test, it can be beneficial to identify the region of significant difference. In the second part, we propose a non-parametric regression procedure to obtain a locally sparse estimate of functional contrast. Our work is motivated by a biomedical study using Raman spectroscopy to monitor hemodialysis treatment near real-time. With contrast test and sparse estimation, practitioners can monitor the progress of the hemodialysis within session and identify important chemicals for dialysis adequacy monitoring. In the third part, we propose a functional data model for degradation analysis of functional data. Motivated by degradation analysis application of rechargeable Li-ion batteries, we combine state-of-the-art functional linear models to produce fully functional prediction for curves on heterogenous domains. Simulation studies and data analysis demonstrate the advantage of the proposed method in predicting degradation measure than existing method using aggregation method. / Doctor of Philosophy / Functional data analysis (FDA) studies complex data structure in the form of curves and shapes. Our work is motivated by two applications concerning data from Raman spectroscopy and battery degradation study. Raman spectra of a liquid sample are curves with measurements over a domain of wavelengths that can identify chemical composition and whose values signify the constituent concentrations in the sample. We first propose a statistical procedure to test the significance of a functional contrast formed by spectra collected at beginning and at later time points during a dialysis session. Then a follow-up procedure is developed to produce a sparse representation of the contrast functional contrast with clearly identified zero and nonzero regions. The use of this method on contrast formed by Raman spectra of used dialysate collected at different time points during hemodialysis sessions can be adapted for evaluating the treatment efficacy in real time. In a third project, we apply state-of-the-art methodologies from FDA to a degradation study of rechargeable Li-ion batteries. Our proposed methods produce fully functional prediction of voltage discharge curves allowing flexibility in monitoring battery health.
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Heterogeneous Redox Chemistries in Layered Oxide Materials for Lithium-Ion BatteriesXu, Zhengrui 05 January 2022 (has links)
The invention of the lithium-ion battery has revolutionized the passenger transportation field in recent years, and it has emerged as one of the state-of-the-art solutions to address greenhouse gases emission and air pollution issues. Layered oxide lithium-ion battery cathode materials have become commercially successful in the past few decades due to their high energy density, high power density, long cycle life, and low cost. Yet, with the increasing demand for battery performance, it is crucial to understand the material fading mechanisms further to improve layered oxide materials' performance. A heterogeneous redox reaction is a dominant fading mechanism, which limits the utilization percentage of a battery materials' redox capability and leads to adverse effects such as detrimental interfacial reactions, lattice oxygen release, and chemomechanical breakdown. Crystallographic defects, such as dislocations and grain boundaries, are rich in battery materials. These crystallographic defects change the local lithium-ion diffusivity and have a dramatic effect on the redox reactions. To date, there is still a knowledge gap on how various crystallographic defects affect electrochemistry at the microscopic scale. Herein, we adopted synchrotron-based diffraction, imaging, and spectroscopic techniques to systematically study the correlation between crystallographic defects and redox chemistries in the nanodomain. Our studies shed light on design principles of next-generation battery materials.
In Chapter 1, we first provide a comprehensive background introduction on the battery chemistry at various length scales. We then introduce the heterogeneous redox reactions in layered oxide cathode materials, including a discussion on the impacts of heterogeneous redox reactions. Finally, we present the different categories of crystallographic defects in layered oxide materials and how these crystallographic defects affect electrochemical performance.
In Chapter 2, we use LiCoO2, a representative layered oxide cathode material, as the material platform to quantify the categories and densities of various crystallographic defects. We then focus on geometrically necessary dislocations as they represent a major class of crystallographic defects in LiCoO2. Combining synchrotron-based X-ray fluorescence mapping, micro-diffraction, and spectroscopic techniques, we reveal that geometrically necessary dislocations can facilitate the charging reactions in LiCoO2 grains. Our study illustrates that the heterogeneous redox chemistries can be potentially mitigated by precisely controlling the defects.
In Chapter 3, we systematically investigated how grain boundaries affect redox reactions. We reveal that grain boundaries can guide redox reactions in LiNixMnyCo1-x-yO2 (NMC) materials. Specifically, NMC materials with radially aligned grains have a more uniform charge distribution, less stress mismatch, and better cycling performance. NMC materials with randomly orientated grains have a more heterogeneous redox reaction. These heterogeneous redox reactions are related to the lattice strain mismatch and worse cycling performance. Our study emphasizes the importance of tuning grain orientations to achieve improved performance.
Chapter 4 systematically investigated how the grain boundaries and crystallographic orientations affect the thermal stability of layered oxide cathode materials. Combining diffraction, spectroscopic, and imaging techniques, we reveal that a cathode materials' microstructure plays a significant role in determining the lattice oxygen release behavior and, therefore, determines cathode materials' thermal stability. Our study provides a fundamental understanding of how the grain boundaries and crystallographic orientations can be tuned to develop better cathode materials for the next-generation Li-ion batteries.
Chapter 5 summarizes the contributions of our work and provides our perspective on future research directions. / Doctor of Philosophy / Lithium-ion battery technology has revolutionized the portable electronic device and electric vehicle markets in recent years. Yet, the performance of current lithium-ion batteries still cannot satisfy customer demands. To further improve battery performance, we need a deeper understanding of why battery materials degrade over long-term cycling. One of the fading mechanisms in lithium-ion batteries is heterogeneous redox reactions, i.e., charge or discharge reactions do not proceed at the same pace at different locations in the electrode materials. Herein, we utilize layered oxide cathode materials as an example to systematically investigate how crystallographic defects in the cathode materials lead to heterogeneous redox reactions. Our study indicates that crystallographic defects, such as geometrically necessary dislocations, contribute positively to the charging reaction of the cathode materials. We also unveil that the grain crystallographic orientations of the primary particles affect the redox reactions directly. By aligning the single grains in the radial direction, the volumetric-change-induced stress can be effectively mitigated to ensure prolonged cycling performance. Our study also points out that the single grain orientations are related to the thermal stability of the battery materials. To summarize, our studies provide new insights into the heterogeneous redox reactions in battery materials and offer critical material design criteria to improve battery performance further.
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Model-Based Design of an Electric Powertrain Vehicle; Focus on Physical Modeling of Lithium-ion BatteriesGirard, Alex Thomas 19 August 2016 (has links)
Formula SAE (FSAE) vehicle systems are very complex. Understanding how subsystems effect the overall vehicle is essential for making design trade-offs. FSAE is a competitive environment. Teams need to have reliable and high performing vehicles to do well in competition. The Virginia Tech (VT) FSAE team has produced a prototype electric powertrain (EPT) vehicle, VTM16e, and will take their first EPT vehicle, VTM17e, to competition in 2017.
The use of model-based design (MBD) for an EPT FSAE vehicle is investigated through this thesis. The goal of the research is to build the framework of a full vehicle simulation to take knowledge gained from the VTM16e prototype vehicle, and apply it to the VTM17e competition vehicle.
A top-down, bottom-up approach is taken to build a full vehicle model of an EPT FSAE vehicle. A full vehicle simulation is built with subsystems to establish an overall structure and subsystem interactions. Individual subsystems are then focused on for testing and validation. Breaking the vehicle down into subsystems allows the overall model to be incrementally improved. The battery subsystem is focused on in this thesis. Extensive testing is performed on the batteries to characterize their performance. Computer models are generated from empirical data through parameter estimation techniques. Validation of the battery models is performed and the resulting model is incorporated into the overall vehicle model. Performance limits of the vehicle are determined through model exploration, and design modifications to increase the reliability and performance for the VTM17e vehicle are proposed. / Master of Science
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Synthèse et caractérisation de poly[5-alkyl-thieno-[3,4-c]-pyrrole-4,6-dione]s pour la fabrication d’électrodes de batteries lithium-ionRobitaille, Amélie 23 April 2018 (has links)
Le potentiel d’oxydoréduction des anodes utilisée dans un pile lithium-ion doit se trouver au-dessus de 0,75V vs Li/Li+ pour rester sécuritaire et ne doit pas excéder 2V vs Li/Li+ pour conserver une puissance adéquate. Suite aux travaux effectués les polythienopyrroledione (PTPD) ont démontré des potentiels d'oxydo-réduction de 1,6V vs Li/Li+ ce qui correspond aux critères établis ci-haut. De plus, ils ont une capacité théorique de 215 mAh/g, ont obtenu une capacité expérimentale de 209 mAh/g. Cette capacité est toutefois inférieure à celle des matériaux d'anodes actuellement sur le marché. Par contre, étant donné que la capacité d'une pile est limitée par la capacité de l'électrode la plus faible, et qu'actuellement les piles lithium-ion sur le marché sont basées sur le LiFePO₄ qui possède une capacité de 170 mAh/g, il serait envisageable que les PTPD puissent potentiellement être des anodes commercialisables.
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<b>Lithium storage mechanisms and Electrochemical behavior of Molybdenum disulfide</b>Xintong Li (18431580) 03 June 2024 (has links)
<p dir="ltr">This study investigates the electrochemical behavior of molybdenum disulfide (MoS<sub>2</sub>) when utilized as an anode material in Li-ion batteries, particularly focusing on the intriguing phenomenon of extra capacity observed beyond theoretical expectations and the unique discharge curve of the first cycle. Employing a robust suite of advanced characterization methods such as in situ and ex situ X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), the research unravels the complex structural and chemical evolution of MoS<sub>2</sub> throughout its cycling process. A pivotal discovery of the research is the identification of a distinct lithium intercalation mechanism in MoS<sub>2</sub>, which leads to the formation of reversible Li<sub>x</sub>MoS<sub>2</sub>. These phases play a crucial role in contributing to the extra capacity observed in the MoS<sub>2</sub> electrode. Additionally, density functional theory (DFT) calculations have been utilized to explore the potential for overlithiation within MoS<sub>2</sub>, suggesting that Li<sub>5</sub>MoS<sub>2</sub> could be the most energetically favorable phase during the lithiation-delithiation process. This study also explores the energetics of a Li-rich phase forming on the surface of Li<sub>4</sub>MoS2, indicating that this configuration is energetically advantageous and could contribute further to the extra capacity. The incorporation of reduced graphene oxide (RGO) as a conductive additive in MoS<sub>2</sub> electrodes, demonstrating that RGO notably improves the electrochemical performance, rate capability, and durability of the electrodes. These findings are supported by experimental observations and are crucial for advancing the understanding of MoS<sub>2</sub> as a high-capacity anode material. The implications of this research are significant, offering a pathway to optimize the design and composition of electrode materials to exceed traditional performance and longevity limits in Li-ion batteries.</p>
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Advancing Sustainable Resource Management through Circular Economy: The Case of Graphite in Lithium-Ion BatteriesFadyl, Said January 2023 (has links)
This case study investigates the potential graphite circular economy within the lithium-ion battery industry, intending to create sustainable management of graphite waste streams. The improper handling of graphite as waste amplifies the carbon footprint and incurs additional costs for battery recyclers. Unlike cathode materials in batteries, graphite regeneration into battery-grade material has not beenindustrialized. Therefore, the study investigates recycling and other alternative approaches to obtain the circularity of graphite. The research explores downcycling, recycling, and upcycling business modelsfor graphite from lithium batteries. With the aim to maximize value and minimize efforts and associated costs. As per methods, an exploratory qualitative method was employed with the data mainly collected through interviews with actors in the graphite sector and recycling technologies. The findings showeconomic viability, feasibility, market dynamic, and regulatory aspects as crucial considerations for the decision-making of battery recyclers. Given the novelty of the material, evaluating technical feasibility through research and development requires coordination with potential partners. Several potential customer options, including graphene applications, steel and refineries, and refractory products, are proposed, each involving a respective business model. Furthermore, the study suggests diversifying partners and establishing partnerships with material receivers as a short-term strategy while awaiting advancements in recycling and upcycling technologies.
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Materials Design for Lithium Batteries with High Energy DensityJin, Tianwei January 2024 (has links)
Lithium-ion batteries (LIBs) play a pivotal role in advancing transportation electrification, offering a crucial solution to address climate change and fossil fuel depletion, but the current energy density of LIBs remains unsatisfying, limiting electric transportation range. To address this limitation, extensive efforts focus on developing novel electrode materials, including high-voltage cathodes and high-specific-capacity electrodes. However, the pursuit of higher energy densities introduces safety concerns due to the higher possibility of thermal runaway and flammable nature of conventional liquid electrolytes. In this doctoral thesis, I will present several innovative strategies for high-performance lithium battery systems aimed at enhancing the mileage of electric transportation without compromising or even enhancing safety.
The first part (Chapter 3) discusses a novel design for structural batteries. Structural batteries are the energy storage devices with enhanced mechanical properties integrated as structural components in vehicles to reduce vehicle weights and increase mileage. Through the development of a scalable and feasible tree-root-like lamination at the electrode/separator interface, an 11-fold enhancement in the flexural modulus of pouch cells is achieved, and the underlying mechanism is revealed by finite element simulations. This lamination has a minimal impact on the electrochemical performance of LIBs and the smallest reported specific energy reduction of ~3% in structural batteries. The prototype "electric wings" showcases stable flight for an aircraft model, highlighting the effectiveness and scalability of engineering interfacial adhesion in developing structural batteries with superior mechanical and electrochemical properties.
The second part (Chapter 4) presents a design rule for polymer electrolytes to enhance lithium metal battery safety. Lithium metal batteries are attractive for electric transportation due to their high energy densities, but their application is hindered by the safety concerns from dendrite growth. In this work, we observe that if the compositions of polyethylene oxide (PEO) electrolytes are near the boundary between amorphous and polymer-rich regions, concentration polarization in electrolytes will induce a phase transformation and create a PEO-rich phase at the electrode surface. This new phase is mechanically rigid with a Young’s modulus of ∼1-3 GPa so that it can suppress lithium dendrites, which allows Li/PEO/LiFePO₄ cells with such a phase transformation demonstrate superior lithium reversibility without dendrites for 100 cycles.
The third part (Chapter 5) proposes an innovative cathode design for all-solid-state Li-S batteries (ASSLSBs) which have ultra-high energy densities and enhanced battery safety. However, conventional cathode designs of filling sulfur in carbon hosts suffer from accelerated decomposition of electrolytes and sulfur detachment, leading to significant capacity loss. As a solution, I propose that nonconductive polar hosts allow long cycling life of ASSLSBs via stabilizing the adjacent electrolytes and bonding sulfur/Li₂S steadily to avoid detachment. By using a mesoporous SiO₂host filled with 70 wt.% sulfur as the cathode, we demonstrate steady cycling in ASSLSBs with a capacity reversibility of 95.1% in the initial cycle and a discharge capacity of 1446 mAh g-1 after 500 cycles at C/5.
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A detailed study of the lithiation of iron phosphate as well as the development of a novel synthesis of lithium iron silicate as cathode material for lithium-ion batteriesGaloustov, Karen 03 1900 (has links)
Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources.
Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau. / In this thesis, we demonstrate work on two different cathode materials for lithium-ion batteries. First, the synthesis of lithium iron phosphate (LiFePO4) is reproduced from literature using two lithiation methods starting with amorphous iron phosphate (FePO4). For both reactions, the product at each step of the synthesis was analyzed using Mössbauer Spectroscopy and X-ray diffraction in order to gain further insight of the reaction mechanism. The results of this work were published in Journal of Power Sources.
The second cathode material of interest was lithium iron silicate (Li2FeSiO4). A novel synthetic method was developed to produce lithium iron silicate cost effectively starting with low cost precursors and basic laboratory equipment. The material was synthesized using a solid- state synthesis after milling and carbon coating, electrochemical performance was evaluated. An attempt was made to synthesize off-stoichiometric lithium iron silicate in order to increase the electrochemical performance of the material.
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Novel approaches to the synthesis and treatment of cathode materials for lithium-ion batteriesRodrigues, Isadora R. 07 1900 (has links)
Nous avons mis au point une approche novatrice pour la synthèse d’un
matériau de cathode pour les piles lithium-ion basée sur la décomposition
thermique de l’urée. Les hydroxydes de métal mixte (NixMnxCo(1-2x)(OH)2) ont
été préparés (x = 0.00 à 0.50) et subséquemment utilisés comme précurseurs à la
préparation de l’oxyde de métal mixte (LiNixMnxCo(1-2x)O2). Ces matériaux,
ainsi que le phosphate de fer lithié (LiFePO4), sont pressentis comme matériaux
de cathode commerciaux pour la prochaine génération de piles lithium-ion. Nous
avons également développé un nouveau traitement post-synthèse afin
d’améliorer la morphologie des hydroxydes.
L’originalité de l’approche basée sur la décomposition thermique de
l’urée réside dans l’utilisation inédite des hydroxydes comme précurseurs à la
préparation d’oxydes de lithium mixtes par l’intermédiaire d’une technique de
précipitation uniforme. De plus, nous proposons de nouvelles techniques de
traitement s’adressant aux méthodes de synthèses traditionnelles. Les résultats
obtenus par ces deux méthodes sont résumés dans deux articles soumis à des
revues scientifiques.
Tous les matériaux produits lors de cette recherche ont été analysés par
diffraction des rayons X (DRX), microscope électronique à balayage (MEB),
analyse thermique gravimétrique (ATG) et ont été caractérisés
électrochimiquement. La performance électrochimique (nombre de cycles vs
capacité) des matériaux de cathode a été conduite en mode galvanostatique. / We have developed a novel approach to the synthesis of cathode
materials for lithium-ion batteries, based on the thermal decomposition of urea.
Mixed metal hydroxides (NixMnxCo(1-2x)(OH)2), x = 0.00 to 0.50, were prepared
and subsequently used as precursor for lithiated mixed metal oxide
(LiNixMnxCo(1-2x)O2). These materials along with lithium iron phosphate
(LiFePO4) are being considered as cathode materials for the next generation of
lithium-ion batteries. We have also developed new post-synthetic treatments on
the hydroxides in order to enhance the morphology, which would result in
improved electrode properties.
The novelty of this thesis is that for the first time mixed metal
hydroxides for use as precursors for lithium mixed oxides have been prepared
via a uniform precipitation technique from solution. In addition, we have
proposed new treatments techniques towards the more traditional synthesis
method for mixed metal hydroxides. The results obtained from these two
methods are summarized within two articles that were recently submitted to
peer-reviewed journals.
Within this thesis, all materials were analyzed with X-ray diffraction
(XRD), scanning electron microscopy (SEM), thermal gravimetric analysis
(TGA) and electrochemical measurements. The electrochemical performance
(capacity vs cycle number) of the cathode materials were tested
galvanostatically.
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Low cost synthesis of cathode and anode materials for lithium-ion batteriesCheng, Lifeng 04 1900 (has links)
Dans cette thèse, nous démontrons des travaux sur la synthèse à faible coût des matériaux de cathode et l'anode pour les piles lithium-ion.
Pour les cathodes, nous avons utilisé des précurseurs à faible coût pour préparer LiFePO4 et LiFe0.3Mn0.7PO4 en utilisant une méthode hydrothermale. Tout d'abord, des matériaux composites (LiFePO4/C) ont été synthétisés à partir d'un précurseur de Fe2O3 par une procédé hydrothermique pour faire LiFePO4(OH) dans une première étape suivie d'une calcination rapide pour le revêtement de carbone. Deuxièmement, LiFePO4 avec une bonne cristallinité et une grande pureté a été synthétisé en une seule étape, avec Fe2O3 par voie hydrothermale. Troisièmement, LiFe0.3Mn0.7PO4 a été préparé en utilisant Fe2O3 et MnO comme des précurseurs de bas coûts au sein d'une méthode hydrothermale synthétique.
Pour les matériaux d'anode, nous avons nos efforts concentré sur un matériau d'anode à faible coût α-Fe2O3 avec deux types de synthèse hydrothermales, une a base de micro-ondes (MAH) l’autre plus conventionnelles (CH).
La nouveauté de cette thèse est que pour la première fois le LiFePO4 a été préparé par une méthode hydrothermale en utilisant un précurseur Fe3+ (Fe2O3). Le Fe2O3 est un précurseur à faible coût et en combinant ses coûts avec les conditions de synthèse à basse température nous avons réalisé une réduction considérable des coûts de production pour le LiFePO4, menant ainsi à une meilleure commercialisation du LiFePO4 comme matériaux de cathode dans les piles lithium-ion. Par cette méthode de préparation, le LiFePO4/C procure une capacité de décharge et une stabilité de cycle accrue par rapport une synthétisation par la méthode à l'état solide pour les mêmes précurseurs Les résultats sont résumés dans deux articles qui ont été récemment soumis dans des revues scientifiques. / In this thesis, low cost syntheses of cathode and anode materials for lithium ion batteries will be presented.
For cathode materials, low cost precursors were used to prepare LiFePO4 and LiFe0.3Mn0.7PO4 using low temperature hydrothermal method. Initially, a LiFePO4/C composite material was synthesized from a Fe2O3 precursor using a hydrothermal method to prepare LiFePO4(OH) in a first step followed by a fast calcination and carbon coating. Secondly, LiFePO4 with good crystallinity and high purity was synthesized, in one step, with nanometric sized Fe2O3 by a hydrothermal method. Thirdly, LiFe0.3Mn0.7PO4 was prepared using low cost Fe2O3 and MnO as precursors within a hydrothermal synthetic method.
For anode materials, a low cost anode material α-Fe2O3 was prepared using two hydrothermal synthetic methods, microwave assisted (MAH) and conventional hydrothermal (CH).
The novelty of the thesis is for the first time LiFePO4 has been prepared using a low cost Fe3+ precursor (Fe2O3) by a hydrothermal method. Low cost precursors and low temperature synthesis conditions will greatly reduce the synthetic cost of LiFePO4, leading to greater commercialization of LiFePO4 as a cathode materials for lithium-ion batteries. The as-prepared LiFePO4/C product provided enhanced discharge capacity and cycling stability compared to that synthesized using a solid state method with the same precursors. The results were summarized within two articles that were recently submitted to peer reviewed scientific journals.
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