This dissertation focuses on three major advances on multiple-input multiple-output (MIMO) systems. The first studies and compares decoding algorithms for multi-layered space time coded (MLSTC) systems. These are single user systems that combine spatial multiplexing and transmit diversity. Each layer consists of a space time code. The detection algorithms are based on multi-user detection theory. We consider joint, interference nulling and cancellation, and spatial sequence estimation algorithms. As part of joint detection algorithms, the sphere decoder is studied and its complexity is evaluated over MIMO channels. The second part contributes to the field of space frequency time (SFT) coding for MIMO-OFDM systems. It proposes a full spatial and frequency diversity codes at much lower number of trellis states. The third part proposes and compares uplink scheduling algorithms for multiuser systems with spatial multiplexing. Several scheduling criteria are examined and compared. The capacity and error rate study of MLSTBC reveals the performance of the detection algorithms and their advantage over other open loop MIMO schemes. The results show that the nulling and cancellation operations limit the diversity of the system to the first detected layer in serial algorithms. For parallel algorithms, the diversity of the system is dominated by the performance after parallel nulling. Theoretically, parallel cancellation should provide full receive diversity per layer but error propagations as a result of cancellation prevent the system from reaching this goal. However, parallel cancellation provides some gains but it doesn't increase the diversity. On the other hand, joint detection provides full receive diversity per layer. It could be practically implemented with sphere decoding which has a cubic complexity at high SNR. The results of the SFT coding show the superiority of the IQ-SFT codes over other codes at the same number of sates. The IQ-SFT codes achieve full spatial and frequency diversity at much lower number of trellis states compared to conventional codes. For V-BLAST scheduling, we propose V-BLAST capacity maximizing scheduler and we show that scheduling based on optimal MIMO capacity doesn't work well for V-BLAST. The results also show that maximum minimum singularvalue (MaxMinSV) scheduling performs very close to the V-BLAST capacity maximizing scheduler since it takes into account both the channel power and the orthogonality of the channel. / Ph. D.

Ni-rich layered oxide materials have gained significant attention due to the ongoing advances and demands in energy storage. The energy revolution continues to catapult the need for improved battery materials, especially for applications in portable electronic devices and electric vehicles. Lithium batteries are at the frontier of energy storage. Due to geopolitical concerns, there is a growing need to understand the chemistries of Co-free, Ni-rich layered oxide materials which are cost-efficient and possess increased practical capacity. The challenge to studying this class of materials is their inherent electronic and structural fragility. The fragility of these materials is facilitated by a cooperation of metal cation migration, lattice oxygen loss, and undesirable oxide cathode-electrolyte interfacial reactions. Each of these phenomena contribute to complex electrolyte decomposition pathways and oxide cathode structural distortions. Structural instability leads to poor battery performance metrics including specific capacity fading and decreased Coulombic efficiency. Electrolyte decomposition occurs at the oxide cathode surface, but it can lead to bulk electronic and structural changes, chemomechanical breakdown, and irreversible phase transformations in the material. The work in this dissertation focuses on understanding some of the chemistries associated with degradation of representative Ni-rich layered oxides, specifically LiNiO2 (LNO) and LiNixMnyCozO2 (NMC) (where x+y+z =1) materials. Chapter 1 provides a comprehensive review of the interfacial chemistries of fragile, Ni-rich layered oxide materials with carbonate-based liquid electrolytes. These reactions are key in deducing mechanistic pathways that promote thermal runaway. Uncontrollable oxygen loss and electrolyte oxidation leads to catastrophic battery fires and explosions. The chapter highlights the material properties that become perturbed during high states-of-charge which complicate the materials chemistry associated with Ni-rich layered oxides. Lastly, a few strategies to mitigate undesired, structurally detrimental reactions at the Ni-rich layered oxide cathode surface are provided in Chapter 1. To obtain the technical data detailed in this dissertation, a variety of analytical methods are employed. Chapter 2 introduces the working principles of the X-ray techniques, electron microscopy, and other quantification methods. X-ray techniques including synchrotron X-ray absorption spectroscopy (XAS), and its components XANES and EXAFS are discussed. Other X-ray techniques, including X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are additionally included. Electron microscopy techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) are provided. Quantification methods, such as gas chromatography – flame ionization detection (GC-FID) and other electrochemical testing methods are also described. Detailed experimental information obtained using the analytical methods is provided in the technical chapters. In understanding the chemistry of Ni-rich layered oxides, exploring surface reconstruction is key. Surface reconstruction, a phenomenon caused by a collaboration between Li/Ni cation intermixing and lattice oxygen loss, is one of the major explanations for structural degradation in Ni-rich layered oxide materials. Chapter 3 explores surface reconstruction and deduces a mechanism by which lattice oxygen is loss in LiNi0.6Mn0.2Co0.2O2 (NMC622). By exploiting Li+ intercalation chemistry, the work emulates various states-of-charge to explore how delithiation impacts small, organic molecule oxidation. Benzyl alcohol serves as a good probing molecule. It is similar to an oxidizable, nonaqueous electrolytic species that undergoes oxidation at the oxide cathode surface. Structure-reactivity trends are defined to correlate electronic and structural changes, lattice oxygen loss, and small molecule oxidation. After studying a proxy molecule, a practical system is required to grasp the complexity of the cathode-electrolyte interfacial reactions that promote Ni-rich layered oxide degradation. In Chapter 4, an electrolyte stirring experiment is described. Stirring experiments provide an accelerated testing method which helps to deduce the influences of chemical electrolyte decomposition on structural degradation of LiNiO2 (LNO). X-ray techniques are used to illustrate electronic perturbations and structural distortions in the material after probing with EC/DMC w/w 3:7 LiPF6. Additionally, this dissertation chapter features a novel voltage oscillation experiment that is employed to quantify Ni-rich oxide cathode degradation at the phase transition regions. LNO has three charging plateaus – H1  M, M  H2, and H2  H3. The latter two plateaus have been largely associated with irreversible structural fragility in Ni-rich layered oxides. Cation intermixing and oxygen loss are two phenomena that are largely associated with decreased Li+ intercalation kinetics and increased undesired side reactions. Although researchers debate the chemical phenomenon that occur at each of the phase transitions, most agree that the H2  H3 transition is highly influenced by irreversible lattice oxygen loss. This dissertation chapter describes the studies used to explore the electronic changes and structural distortions that accompany the voltage oscillation electrochemical testing. While Ni-rich layered oxides are largely employed as lithium battery cathodes, this class of material is unique in that it is a reducible and electronically tunable. Electronically modifiable metal oxide materials provide a unique platform to lend information to other applications, such as catalysis. There is much debate surrounding the role of metal oxides on metal nanocatalyst performance for catalytically reductive pathways. Chapter 5 discusses the method of employing LiNiO2 and other NMC materials as electronically tunable metal oxides to determine the role of the reducible metal oxide support on the gold (Au) nanocatalyst for p-nitrophenol reduction to p-aminophenol. By obtaining a continuum of nickel (Ni) oxidation states using delithiation strategies, structural-activity relationship trends are provided. Conversion rates for each of the delithiated materials was calculated using pseudo first-order kinetics. Lastly, a detailed discussion on metal oxide reducibility and its influences on key mechanistic factors, such as the induction period is included. Chapter 6 in this dissertation provides conclusions for the technical work provided. It bridges the works together and describes the overarching findings associated with the chemistries of Ni-rich layered oxide materials. This dissertation lays the foundation for future experimentation and innovation in understanding the surface chemistry of Ni-rich layered oxides. Chapter 7 provides future perspectives for each of the technical works included herein. Additionally, the final chapter includes insights toward the future of lithium batteries and other cathode chemistries. As the world navigates the energy revolution, it is important to provide global perspectives expected to catapult a sustainable future with batteries towards a greener world. / Doctor of Philosophy / Rechargeable lithium batteries have gained a significant surge of interest due to the ongoing demands for portable electronic devices, as well as the global trend towards electric vehicles to decrease the carbon footprint. Lithium batteries reside at the pinnacle of the energy transition. Layered oxide materials are typically employed as the cathode in Li-ion batteries. Ni-rich layered oxides have gained much interest due to their low cost and good charge/discharge capabilities. As consumers want increased charging rates and longer lifetimes, researchers struggle to optimize the balance between incorporating Ni-rich cathodes and increased safety concerns caused by cathode structural fragility. The lack of structural robustness is largely due to the surface reactivity of Ni-rich layered oxide materials. Bonding arrangements and electron transfer pathways intrinsic to this class of material increases the complexity in understanding the surface chemistry and the associated degradation pathways. Oxygen loss is the major cause of the safety issues in lithium batteries such as battery fires and explosions. To mitigate the safety concerns, it is imperative to understand the chemistries that promote organic, liquid electrolyte decomposition, electronic and structural changes, chemomechanical breakdown, and irreversible phase transformations. Each of these components leads to decreased battery performance. The work in this dissertation describes model and practical platforms to probe and understand the chemistries associated with battery performance degradation. A variety of analytical methods were utilized to determine overall structure-activity relationship trends and are highlighted in Chapter 2. Chapters 3-5 is technical research providing insight on Ni-rich layered oxide degradation pathways and behaviors. The work advances the understanding of battery surface chemistry which will lead to improved cathode design. As batteries continue to grow, it is important to know other applications that benefit from the unique chemistry of Ni-rich layered oxide materials. By exploiting the lithium battery cathode chemistry, this dissertation highlights a method to utilize these materials to understand the role of metal oxides on Au nanocatalysts. Conclusions to the findings in this dissertation are provided in Chapter 6. Future perspectives on the technical research provided herein this dissertation is included in Chapter 7. Additionally, Chapter 7 details future perspectives for lithium batteries and how they can facilitate the global transition toward a sustainable future.

Alkali-ion batteries have revolutionized modern life through enabling the widespread application of portable electronic devices. The call for adapting renewable energy in many applications will also see an increase in the demand of alkali-ion batteries, specially to account for the intermittent nature of the renewable energy sources. However, the advancement of such technologies will require innovation on the forefront of materials development as well as fundamental understanding on the physical and chemical processes from atomic to device length scales. Herein, we focus on advancing energy storage devices such as alkali-ion batteries through cathode materials development and discovery as well as fundamental understanding through multiscale advanced synchrotron spectroscopic and microscopic characterizations. Multiscale electrochemical properties of cathode materials are unraveled through complementary characterizations and design principles are developed for stable cathode materials for alkali-ion batteries. In Chapter 1, we provide a comprehensive background on alkali-ion batteries and cathode materials. The future prospect of Li-ion and beyond Li-ion batteries are summarized. Surface to bulk chemistry of alkali-ion cathode materials is introduced. The prospect of combined cationic and anionic redox processes to enhance the energy density of cathode materials is discussed. Structural and chemical complexities in cathode materials during electrochemical cycling as well as due to anionic redox are summarized. In Chapter 2, we explain an inaugural effort on tuning the 3D nano/mesoscale elemental distribution of cathode materials to positively impact the electrochemical performance of cathode materials. We show that engineering the elemental distribution can take advantage of depth dependent redox reactions and curtail harmful side reactions at cathode-electrolyte interface which can stabilize the electrochemical performance. In Chapter 3, we show that the surface to bulk chemistry of cathode particles is distinct under applied electrochemical potential. We show that the severe surface degradation at the beginning stages of cycling can impact the long-term cycling performance of cathode materials in alkali-ion batteries. In Chapter 4, we utilize the structural and chemical complexities of sodium layered oxide materials to synthesize stable cathode materials for half cell and full cell sodium-ion batteries. Meanwhile, challenges with enabling long term cycling (more than 1000 cycles) are deciphered to be transition metal dissolution and local and global structural transformations. In Chapter 5, we utilize anionic redox in conjunction with conventional cationic redox of cathode materials for alkali-ion batteries to enhance the energy density. We show that the stability of anionic redox is closely related to the local transition metal environment. We also show that a reversible evolution of local transition metal environment during cycling can lead to stable anionic redox. In Chapter 6, we provide design principles for cathode materials for advanced alkali-ion batteries for application under extreme environments (e.g., outer space and nuclear power industries). For the first time, we systematically study the microstructural evolution of cathode materials under extreme irradiation and temperature to unravel the key factors affecting the stability of battery cathodes. Our experimental and computational studies show that a cathode material with smaller cationic antisite defect formation energy than another is more resilient under extreme environments. / Doctor of Philosophy / Alkali-ion batteries are finding many applications in our life, ranging from portable electronic devices, electric vehicles, grid energy storage, space exploration and so on. Cathode materials play a crucial role in the overall performance of alkali-ion batteries. Reliable application of alkali-ion batteries requires stable and high-energy cathode materials. Hence, design principles must be developed for high-performance cathode materials. Such design principles can be benefited from advanced characterizations that can reveal the surface-to-bulk properties of cathode materials. Herein, we focus on formulating design principles for cathode materials for alkali-ion batteries. Aided by advanced synchrotron characterizations, we reveal the surface-to-bulk properties of cathodes and their role on the long-term stability of alkali-ion batteries. We present tuning structural and chemical complexities as a method of designing advanced cathode materials. We show that energy density of cathode materials can be enhanced by taking advantage of a combined cationic and anionic redox. Lastly, we show design principles for stable cathode materials under extreme conditions in outer space and nuclear power industries (under extreme irradiation and temperature). Our study shows that structurally resilient cathode materials under extreme irradiation and temperature can be designed if the size of positively charged cations in cathode materials are almost similar. Our study provides valuable insights on the development of advanced cathode materials for alkali-ion batteries which can aid the future development of energy storage devices.

Li-ion batteries (LIBs) have achieved remarkable success in electric vehicles (EVs), consumer electronics, grid energy storage, and other applications thanks to a wide range of electrode materials that meet the performance requirements of different application scenarios. Cathodes are an essential component of LIBs, which governs the performance of commercial LIBs. Layered transition metal oxide, i.e., LiNixCoyMn1-x-yO2 (NMC), is one family of cathodes that are widely applied in the prevailing commercial LIBs. With increasing demand for high energy density, the development of layered oxide cathodes is towards high Ni content because Ni redox couples majorly contribute to the battery capacity. Meanwhile, the battery community has been making tremendous efforts to eliminate Co in layered cathodes due to its high cost, high toxicity, and child labor issues during Co mining. However, these Ni-rich Co-free cathodes usually suffer from low electrochemical and structural stability. Several strategies are adopted to enhance the stability of Ni-rich Co-free cathodes, such as doping, coating, and synthesizing single crystal particles. However, the design principles and synthesis mechanisms of these approaches have not been fully understood. Herein, we design and synthesize stable Ni-rich and low/no-Co layered oxide cathodes by manipulating the chemical and structural properties of cathode particles. Our studies reveal the cathode formation mechanisms and shed light on the cathode design through complementary synchrotron microscopic and spectroscopic characterization methods. In Chapter 1, the motivation for LIB research is introduced from the perspective of its indispensable role in achieving carbon neutrality. We then comprehensively introduce the status of LIBs at present, including assessing their sustainability, worldwide supply chain and manufacturing, and cathode materials. Subsequently, we focus on the Co-free layered oxide cathodes and discuss their structure, limitations, and strategies to address the challenges. Finally, we discuss single crystal Ni-rich layered oxide cathodes and the challenges and strategies associated with their synthesis. In Chapter 2, we investigate the dopant redistribution, phase propagation, and local chemical changes of layered oxides at multiple length scales using a multielement-doped LiNi0.96Mg0.02Ti0.02O2 (Mg/Ti-LNO) as a model platform. We observed that dopants Mg and Ti diffuse from the surface to the bulk of cathode particles below 300 °C long before the formation of any layered phase, using a range of synchrotron spectroscopic and imaging diagnostic tools. After calcination, Ti is still enriched at the cathode particle surface, while Mg has a relatively uniform distribution throughout cathode particles. Our findings provide experimental guidance for manipulating the dopant distribution upon cathode synthesis. In Chapter 3, we synthesized Mn(OH)2-coated single crystal LiNiO2 (LNO) and used it as the platform to monitor the Mn redistribution and the structural and chemical evolution of the LNO cathode. We use in situ transmission X-ray microscopy (TXM) to track the Mn tomography inside the LNO particle and Ni oxidation state evolution at various temperatures below 700 °C. We further reveal chemical and structural changes induced by different extents of Mn diffusion at ensemble-averaged scale, which validates the results at the single particle scale. The ion diffusion behavior in the cathode is highly temperature dependent. Our study provides guidance for ion distribution manipulation during cathode modification. In Chapter 4, we successfully fabricated a surface passivation layer for NMC particles via a feasible quenching approach. A combination of bulk and surface structural characterization methods show the correlation of surface layer with bulk chemistry including valence state and charge distribution. Our design enables high interfacial stability and homogeneous charge distribution, impelling superior electrochemical performance of NMC cathode materials. This study provides insights into the cathode surface layer design for modifying other high-capacity cathodes in LIBs. In Chapter 5, we use statistical tools to identify the significance of multiple synthetic parameters in the molten salt synthesis of single crystal Ni-rich NMC cathodes. We also create a prediction model to forecast the performance of synthesized single crystal Ni-rich NMC cathodes from the input of synthetic parameters with relatively high prediction accuracy. Guided by the models, we synthesize single crystal LiNi0.9Co0.05Mn0.05O2 (SC-N90) with different particle sizes. We find large single crystals show worse capacity and cycle life than small single crystals especially at high current rates due to slower Li kinetics. However, large single crystal has higher thermal stability potentially because of smaller specific surface area. The findings of particle size effect on the performance provide insights into size engineering while developing next-generation single crystal Ni-rich NMC cathodes. The statistical and prediction models developed in this study can guide the molten salt synthesis of Ni rich cathodes and simplify the optimization process of synthetic parameters. Chapter 6 summarizes our efforts on the novel design and fundamental understanding of the state-of-the-art cathodes. We also provide our future perspectives for the development of LIBs. / Doctor of Philosophy / Lithium-ion batteries (LIBs) have been studied for decades and are widely applied in electronics and vehicles because of their high energy density and long lifetime. With the increasing demand for higher energy density, particularly in electric vehicles, the development of Ni-based layered oxide cathode materials has been focused on increasing the Ni content. Meanwhile, decreasing or eliminating Co has become a consensus due to its high cost, toxicity, and human rights issues during mining. Enhancing the stability of these Ni-rich and low/no-Co layered oxide cathodes is challenging yet crucial to their practical applications. Herein, we design and synthesize multiple Ni-rich and low/no-Co layered cathodes through ion distribution engineering and structure modification at various length scales. We also investigate the dopant redistribution, phase propagation, and local chemical changes during layered oxides cathode formation through a combination of complementary characterization methods at different length scales. In addition, we provide guidance for synthesis optimization by statistical correlations and performance prediction models with the input of synthetic conditions. Overall, this dissertation provides insights into the design and synthesis principles of Ni-rich low/no-Co layered oxide cathode, which can facilitate the transition to a sustainable future with next-generation LIBs.

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.

One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is vinyl ester resin. Vinyl ester resin is comprised of low molecular weight poly(hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate endgroups cure with styrene via free radical copolymerization to yield thermoset networks. The copolymerization behavior of these networks was monitored by Fourier Transform Infrared Spectroscopy (FTIR) at various cure conditions. Reactions of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1) were followed independently. Oligomers possessing number average molecular weights of 700 g/mole were studied with systematically increasing levels of styrene. The Mortimer-Tidwell reactivity ratios indicated that at low conversion more styrene was incorporated into the network at lower cure temperatures. The experimental vinyl ester-styrene network compositions deviated significantly from those predicted by the Meyer-Lowry integrated copolymer equation at higher conversion, implying that the reactivity ratios for these networks may change with conversion. The kinetic data were used to provide additional insight into the physical and mechanical properties of these materials. In addition to establishing the copolymerization kinetics of these materials, the development of halogen free fiber reinforced vinyl ester composites exhibiting good flame properties was of interest. Flame retardant vinyl ester resins are used by many industries for applications requiring good thermal resistance. The current flame-retardant technology is dependent on brominated vinyl esters, which generate high levels of smoke and carbon monoxide. A series of halogen free binder systems has been developed and dispersed in the vinyl ester to improve flame retardance. The binder approach enables the vinyl ester resin to maintain its low temperature viscosity so that fabrication of composites via Vacuum Assisted Resin Transfer Molding (VARTM) is possible. The first binder system investigated was a polycaprolactone layered silicate nanocomposite, which was prepared via intercalative polymerization. Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) data indicated a mixed morphology of exfoliated and intercalated structures. The mechanical properties and the normalized peak heat release rates were comparable to the neat vinyl ester resin. Alternative binder systems possessing inherent flame retardance were also investigated. A series of binders comprised of novolac, bisphenol A diphosphate, and montmorillonite clay were developed and dispersed into the vinyl ester matrix. Cone calorimetry showed reductions in the peak heat release rate comparable to the brominated resin. / Ph. D.

The optimal conditions for deposition of nickel coating and Ni-layered double hydroxide metal matrix composite coatings onto stainless steel discs in a modified all-sulfate solutions have been examined. Nickel films provide good general corrosion resistance and mechanical properties as a protective layer on many metallic substrates. In recent years, there has been interest in incorporation nano-dimensional ceramic materials, such as montemorillonite, into the metal matrices to improve upon the corrosion and mechanical properties. Layered double hydroxides have been used as corrosion enhancer in polymer coatings by increasing mechanical strength and lowering the corrosion rate but until now, have not been incorporated in a metal matrix by any means. Layered double hydroxides can be easily synthesized in a variety of elemental compositions and sizes but typically require the use of non-polar solvents to delaminate into nanodimensional colloidal suspensions. The synthesis of a Zn-Al LDH has been studied and characterized. The effects of the non-polar solvents dimethylformamide and n-butanol on the deposition and corrosion resistance of nickel coatings from a borate electrolyte bath have been studied, a nickel-LDH nanocomposite coating has been synthesized by electrochemical deposition and the corrosion resistance has been studied. Results indicate an improvement in corrosion resistance for the coatings with minimal change in the nickel matrix's internal strain and crystallite size.

Consumers use batteries daily, and the lithium-ion battery has undergone a lot of engineering advances in the last few decades. There is a need to understand and improve the cathode chemistry to adapt to the rapidly growing electronics and electric vehicle market that is continually demanding more energy from batteries. Nickel-rich layered LiNi_1-x-yMn_xCo_yO₂ (1-x-y ≥ 0.6, NMC) cathodes could potentially provide the necessary energy to meet the demand of the high energy applications. Overcoming the stability issues from oxygen activation in nickel-rich materials is one of the largest challenges facing the commercial incorporation of NMCs. This thesis focuses on, LiNi_0.8Mn_0.1Co_0.1 (NMC811). Using surface sensitive techniques, such as Xray Absorption (XAS), our research reveals that degradation of NMC811 occurs during cycling, regardless of temperature, and that oxygen activation plays a role in the overall surface changes and degradation observed in NMC811. The thesis then explores the role of substituting a transition metal in the NMC811. Then we used a gradient addition of titanium to the NMC811 material to stabilize the battery performance. Theoretical techniques, such as Finite Difference Method Near Edge Structure, and experimental techniques, such as XAS, revealed how transition metal substitution, specifically titanium, stabilized the lattice. The results indicated that titanium deactivates oxygen by limiting the nickel and oxygen covalency that typically leads to oxygen activation upon charging. We observed that the titanium substitution increases cycling reversibility after hundreds of cycles. Overall, the work indicates that a more stable nickel-rich material is possible. It identifies the reasons why substitution can work in cathode materials. Additionally, the methods described can provide a guideline to further studies of stabilization of the cathode. / Master of Science / Consumers across the world use lithium-ion batteries in some fashion in their everyday life. The growing demand for energy has led to batteries dying quicker than consumers want. Thus, there are calls for researchers to develop batteries that are longer lasting. However, the initial increase in battery life over the years has been from better engineering and not necessarily from making a better material for a battery. This thesis focuses on the understanding of the chemistry of the materials of a battery. Throughout the chapters, the research delves into the how and why materials with extra nickel degrade quickly. Then, it investigates a method of making these nickel-rich materials last longer and how the chemistry within these materials are affected by the addition of a different metal. Overall, the findings indicate that the addition of titanium creates a more stable material because it mitigates the release of oxygen and prevents irreversible changes within the structure of the material. It determines that the chemistry behind the failings of nickel-rich lithium-ion batteries and a potential method for allowing the batteries to last longer. It also provides insight and guidance for potential future research of stabilization of lithium-ion materials.

Supercritical carbon dioxide (scCO2) was used as a processing aid to improve the level of exfoliation achievable in a PET-layered silicate nanocomposite produced from melt compounding. Layered silicate and scCO2 were allowed to mix for a period of time before being released into the second stage of a single screw extruder. The rapid expansion forced silicate particles into a modified hopper containing neat PET pellets. The mixture of layered silicate and PET was immediately melt mixed in a single screw extruder, cooled in a water bath and pelletized. Two sets of samples each containing layered silicate with different surface chemistries were produced with this method at 1, 3 and 5 wt% silicate. For comparison, samples of the same weight fraction and type of silicate were produced from a traditional melt compounding method. Wide angle x-ray diffraction (WAXD), mechanical testing and rheological analysis were used in order to characterize the silicate morphology, the composite mechanical properties and the relative amount of degradation between the various samples. Results show that scCO2 processed samples contain a higher degree of layered silicate exfoliation than samples produced with traditional melt compounding. Mechanical property improvements are shown to be dependent on the type of silicate surface modification employed. Finally, degradation of the PET matrix appears to be far less extensive in the scCO2 processed samples as shown from rheological data. / Master of Science

O presente trabalho trata da preparação e da caracterização de sistemas contendo tetrassulfoftalocianinas de Co(II) (CoPcTs) e Fe(III) (FePcTs) intercaladas ou somente adsorvidas externamente em matrizes de hidróxidos duplos lamelares (HDLs). Foram sintetizados materiais com composições variadas e empregando-se diferentes métodos de síntese visando, principalmente, o isolamento de materiais com microporosidade intracristalina e/ou com um baixo grau de agregação da ftalocianina. Técnicas de caracterização textural (difração de raios-X e medidas de área superficial) e espectroscópicas (vibracional na região do infravermelho, eletrônica no UV/visível, ressonância paramagnética eletrônica e absorção de raios-X), além das análises elementar (C, H, N e metais) e termogravimétrica foram utilizadas para a caracterização dos sólidos sintetizados. Avaliaram-se os materiais como catalisadores na reação de oxidação do 2,6-di-terc-butilfenol e do catecol, utilizando O2ou H2O2 como oxidantes. Nos materiais isolados contendo a CoPcTs intercalada em HDLs com composição MgxAl (x = 2, 3 e 4) e ZnxAl (x = 4 e 5), a ftalocianina está orientada perpendicularmente às lamelas do HDL, independentemente do método de síntese e da composição dos HDLs utilizados. Adicionalmente, constatou-se que a CoPcTs intercalada está altamente agregada e que os materiais não possuem microporosidade. Porém, a diminuição da densidade de carga do HDL provoca uma pequena diminuição na agregação da CoPcTs. Sob determinada condição sintética, a CoPcTs intercalada nos HDLs ZnxAl sofre o processo de enxertia através dos grupos sulfônicos. Quando testados como catalisadores na oxidação do 2,6-di-terc-butilfenol, os materiais contendo a CoPcTs intercalada e enxertada apresentaram reatividade inexpressiva, que pode ser devida ao acesso restrito do substrato ao sítio ativo na região interlamelar. Estudos de adsorção da FePcTs em HDLs MgxAl na forma carbonato, investigados por espectroscopia eletrônica UV/Visível in situ, mostraram uma elevada tendência de agregação da ftalocianina na superfície dos HDLs. Os espectros eletrônicos indicaram também que diferentes espécies derivadas da FePcTs são formadas durante o processo de adsorção nos HDLs e que a densidade de carga influencia o tipo de espécie adsorvida: há predominância de um dímero do tipo µ-oxo nos HDLs Mg2Al e Mg3Al e do dímero (FePcTs)2 no HDL Mg4Al. Os espectros de absorção de raios-X (XANES) da FePcTs adsorvida nos HDLs MgxAl mostraram que as espécies adsorvidas apresentam geometria piramidal de base quadrada (C4v) e/ou octaédrica (Oh), corroborando com os dados de espectroscopia no UV/Visível. Já os espectros de ressonância paramagnética eletrônica mostraram que a ftalocianina de Fe(III) quando adsorvida nos HDLs gera uma mistura de espécies com configuração de baixo spin e alto spin e, também, elevada distorção rômbica. A FePcTs adsorvida nos HDLs MgxAl apresentou estabilidade e reatividade catalítica superior quando comparada com a ftalocianina livre na oxidação dos fenóis. A ftalocianina adsorvida na superfície externa do HDL deve favorecer o acesso do substrato ao sítio ativo. Uma correlação entre os estudos de adsorção e os resultados dos testes catalíticos mostrou que a espécie dimérica do tipo µ-oxo pode ser a espécie mais ativa na oxidação dos fenóis. Nestes sistemas, as camadas positivas do HDL devem provocar um enfraquecimento da ligação O-H do fenol, facilitando a sua desprotonação (uma das etapas do mecanismo de oxidação). Este último efeito pareceu atuante, pois foram observadas reatividades crescentes dos catalisadores à medida que se aumentava a densidade de carga do HDL. Estes resultados indicaram que existe um efeito cooperativo nos HDLs MgxAl contendo a FePcTs adsorvida, mostrando que o HDL não atua como um suporte inerte nos processos estudados. / The present work describes the preparation and characterization of materials containing Co(II) and Fe(III) tetrasulfonated phthalocyanines (CoPcTs and FePcTs, respectively) intercalated or adsorbed on layered double hydroxides (LDHs). Different compositions and synthetic methods were used to isolate materials with microporosity and/or the phthalocyanine in a low aggregation degree. X-ray diffraction analysis, surface area measurements, spectroscopic techniques (infrared, UV/visible and X-ray absorption), elemental analysis and thermogravimetry were used to characterize the solids. The materials were tested as catalysts in the 2,6-di-terc-butilfenol and catechol oxidation, using O2 or H2O2 as oxidants. In the materials prepared by intercalation of the CoPcTs in MgxAl (x = 2, 3 and 4) and ZnxAl (x = 4 and 5) LDHs, the phthalocyanine is perpendicularly orientated related to the LDH layers, regardless of synthetic method or LDH composition used. In addition, it was observed that the intercalated phthalocyanine is aggregated and the solids do not have microporous. However, the aggregation degree of the phthalocyanine is slightly lower when the LDH charge density decreases. Under a particular synthetic conditions the CoPcTs intercalated in the LDH ZnxAl is grafted through the sulfonic groups. Catalytic tests uisng this material in the 2,6-di-terc-butilfenol oxidation showed a neglectful reactivity, which confirms the aggregation of the intercalated CoPcTs, thus avoiding that the substrate accesses the reactive center. In an adsorption study carried by monitoring in situ the FePcTs UV/Vis electronic spectra during its addition to LDH suspensions, a strong tendency of aggregation was observed for the FePcTs. In addition, different FePcTs species are formed during the adsorption process on the LDHs, which is influenced by the LDH charge density: the µ-oxo complex is the main species adsorbed on the Mg2Al and Mg3Al LDHs, whereas for Mg4Al the non oxo-bridged dimeric complex prevailed. X-ray absorption spectra (XANES) of the adsorbed FePcTs on the MgxAl LDHs showed that the species present a square-pyramidal (C4v) and/or an octahedral (Oh) symmetry, in agreement with the UV/visible spectroscopic data. EPR spectra of these samples showed that the FePcTs adsorbed on the LDHs leads to a mixture of Fe(III) high and low spin species along with a strong rhombic distortion. The FePcTs adsorbed on the MgxAl LDHs showed an enhanced catalytic activity and longevity in the phenols oxidation compared to the homogeneous counterpart. The phthalocyanine on the LDH external surfaces allows the access of the substrate to the reactive metal center. A correlation between the adsorption study and the catalytic tests pointed that the FePcTs µ-oxo complex may be the active species in the oxidation of phenols. Furthermore, the positive charge of LDH layers may weaken the O-H bonding in the phenol molecules making them more easily ionized (one step of the phenol oxidation mechanism). This feature seems to be effective because higher activities of the catalysts were observed along with increasing charge density of the LDHs. These results indicated that a cooperative effect takes place in the materials containing the FePcTs adsorbed on the MgxAl LDHs, showing that LDH do not act as an inert support in the studied catalytic reactions.