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While the process of electrifying transportation is already underway, competing with fossil fuels in applications such as long-range vehicles and aircrafts will require energy densities that are beyond what is achievable using conventional Li-ion battery chemistries. Li metal batteries are promising candidates for such applications, yet meeting cycle life, power density, and safety demands while utilizing the unmatched specific capacity of Li metal anodes is a formidable challenge. It is well known that the interfacial layer of electrolyte decomposition products which forms on the Li surface during electrochemical cycling (i.e. the solid electrolyte interphase (SEI)) is critical in dictating Li deposit morphology and subsequent performance. However, both the composition and arrangement of the SEI are difficult to study because the SEI is just nanometers-thin, air-sensitive, and evolves as a function of electrochemical cycling protocol. Thus, it is important to develop in situ and operando techniques which are capable of characterizing the SEI in its native environment. Here, we study interphase formation in carbonate, ether, solid ceramic, and highly concentrated electrolytes to develop a framework for the general design of electrolytes and SEIs for Li metal batteries. In the first chapter, we broadly motivate electrochemical energy storage devices and define the metrics which make them attractive compared to alternative forms of energy storage. We then describe Li-based batteries, outline the differences between Li-ion and Li metal batteries, and present some of the key advantages and challenges that Li metal chemistries face. After, we provide a classical description of electrodeposition frameworks, focusing on the effects of charge-transfer kinetics and ion transport on deposition morphology. Then, we present the SEI as a factor which convolutes this process in Li metal anodes and describe how the SEI is formed and arranged on the electrode surface. Finally, we describe common tools used to characterize the SEI and how these may be used to design future electrolytes. The second chapter focuses on the effect of potassium additives on conventional carbonate electrolytes. Recent work has shown that alkali metal additives can lead to smooth Li deposits, yet the underlying mechanisms are not well understood. In this work, we demonstrate that alkali metal additives (here, K+) alter SEI composition, thickness, and solubility. Through post-mortem elemental analyses, we find that K+ ions do not deposit, but instead modify the reactivity of the electrode-electrolyte interface. Using quantitative nuclear magnetic resonance (NMR) and density functional theory (DFT), we show that K+ mitigates solvent decomposition at the Li metal surface. These findings suggest that alkali metal additives can be leveraged to suppress the formation of undesired SEI components (e.g., Li2CO3, soluble organic species), serving as an alternative approach for SEI modification compared to sacrificial additives. We believe that our work will spur further interest in the underexplored area of cation engineering. In the third chapter, we examine both chemical structure and ion dynamics in the SEI, correlating these properties to electrochemical performance to guide the design of new electrolytes. We use a combination of NMR spectroscopy and X-ray photoelectron spectroscopy (XPS) to show that fast Li transport, well-ordered SEI architectures, and low solubility at the electrode/SEI interface in 0.5 M LiNO3 + 0.5 M LiTFSI electrolyte bi-salt in 1,3-dioxolane:dimethoxyethane (DOL:DME, 1:1, v/v) are responsible for the formation of low-surface-area Li deposits and high Coulombic efficiency (CE). This improved performance in the presence of LiNO3 is observed despite the fact that there are higher quantities and more types of compounds in the SEI than in LiTFSI alone, suggesting that the identity of the electrolyte decomposition products, rather than the amount, alters plating. SEI design strategies that increase SEI stability and Li interfacial exchange rate are thus expected to lead to more even current distribution, ultimately providing a new framework to generate smooth Li morphologies during plating/stripping. The fourth chapter describes the dynamic behavior of the interface between a lithium metal electrode and a solid-state electrolyte, lithium lanthanum zirconium oxide (Li7La3Zr2O12 or LLZO). The evolution of this interface throughout cycling involves multiscale mechanical and chemical heterogeneity at the micro- and nano-scale and plays a critical role in all-solid-state battery performance. These features are dependent on operating conditions such as current density and stack pressure. Here we report the coupling of operando acoustic transmission measurements with NMR and magnetic resonance imaging (MRI) to correlate changes in interfacial mechanics (such as contact loss and crack formation) with the growth of lithium microstructures during cell cycling. Together, the techniques reveal the chemo-mechanical behavior that governs lithium metal and LLZO interfacial dynamics at various stack pressure regimes and with voltage polarization. In the fifth chapter, we redefine the premise of a class of Li metal battery electrolytes known as localized high concentration electrolytes (LHCE). LHCEs operate on the assumption that high concentration electrolytes (HCEs) may be augmented using a “diluent,” which interacts scarcely with both the ionic species and the Li metal surface, forming pockets of localized high concentration Li+ which have advantageous bulk and interfacial properties. We report on the use of operando NMR spectroscopy to observe electrolyte decomposition during Li stripping/plating and identify the influence of individual components in LHCEs on Li metal battery performance. Data from operando 19F solution NMR indicates that both bis(fluorosulfonyl)imide (FSI–) salt and bis(2,2,2-trifluoroethyl)ether (BTFE) diluent molecules play a key role in SEI formation, in contrast to prior reports that suggest diluents are inert. Using solution 17O NMR, we assess differences in solvation between LHCEs and low concentration electrolytes (LCEs). We find that BTFE diluents are reduced during Li metal battery operation, which can be detected with operando NMR, but not conventional electrochemical methods. Solid-state NMR (SSNMR) and XPS measurements confirm that LHCEs decompose to form an SEI on Li metal that contains organic BTFE reduction products (CF2, CF3), trapped BTFE, and high quantities of lithium fluoride, likely due to both BTFE and FSI– reduction. These chemical characterizations are correlated with changes in interfacial impedance measured separately at the anode and cathode using three-electrode electrochemical impedance spectroscopy (EIS). Insight into the mechanisms of SEI and CEI formation in LHCEs suggests that fluorinated ethers exhibit tunable reactivity that can be leveraged to control Li deposition behavior. To conclude, we reflect on some of the broad guidelines for electrolyte and SEI engineering that we gleaned from the previous chapters. Finally, we highlight recent notable works which we think will enable major advances in interfacial characterization of Li metal batteries (focusing on in situ and operando techniques which can be applied to study both structure and dynamics in commercial setups).

<p>The protonation for several classes of weak bases has been studied by n.m.r. techniques and the structure of the conjugate acids determined. The rates of proton transfer and the activation energies for some of the processes have been calculated and in the cases of the methylbenzene-HSO₃F systems the mechanism of the proton transfer process has been elucidated.</p> <p>The acidity function (H₀) for the HSO₃F/SbF₅ system has been redetermined and extended to higher concentrations of SbF₅• The application of some n.m.r. methods to the measurement of H₀ is discussed.</p> <p>The behaviour of the n.m.r. spectra of sulphuric and fluorosulphuric acids upon the addition of electrolytes has been studied and the results interpreted.</p> / Thesis / Doctor of Philosophy (PhD)

<P> A study has been made of the transformation of deoxidation products in the Fe-V-0 system in the temperature range 1545 -1640°C, using galvanic cells with solid electrolytes. The cells used were in the form of Zr02 (caO) immersion probes and Th02(Y2o2) crucible assemblies. The fields of study of Fev2o4(spinel) and v2o3 were established with respect to oxygen activity and temperature. </p> / Thesis / Master of Engineering (MEngr)

This thesis describes direct measurements of equilibrium adsorption of ions in thin (< 100 nm) aqueous films. Adsorption in thin films is important because it is through adsorption that the stability of colloidal suspensions is frequently tuned. The vast majority of measurements of adsorption to date have been to a single interfaces, whereas the subject of this thesis is adsorption in a thin film between two interfaces. There are two isolated interfaces when particles in a suspension are far apart, but during the collision, a thin film forms between the particles, and the properties of the thin film determines the stability of the colloid. Thus, adsorption in the thin film determines the stability of the colloidal dispersion. There is a distinct gap in the scientific literature concerning adsorption in thin films mainly because there is no technique for measuring such adsorption. To fill this gap in knowledge, I first developed of a technique to directly measure adsorption in thin films, and then applied this technique to explore the behavior of co-ions near charged interfaces as a function of bulk solution composition and the thickness of the film. The adsorption behavior of fluorescein, a di-anion, to negatively charged silica interfaces was studied in dilute electrolytes. The focus was on the effect of the electrostatic screening length, or Debye-length. The separation was measured using interference microscopy and the adsorption of fluorescein was measured using fluorescence microscopy. The Debye-length was altered by variation of the background salt (NaCl) concentration in dilute (<1 M) solution. The surface excess of adsorption for fluorescein was shown to depend on both the Debye-length and the separation distance between two interfaces. Increasing the Debye-length from 4 nm to 21 nm increased the plateau surface excess at large separations, and decreasing the separation lead to a monotonically decreasing surface excess. The surface excess varied over a range that scaled with the Debye-length. The results were compared to solution of the Poisson-Boltzmann model and good agreement was found between the model and the experiment. The effect of background salt concentration on fluorescein adsorption was also studied in concentrated electrolytes (2.5 – 10 M) for various monovalent salts (LiCl, NaCl and CsCl). The results showed that the fitted electrostatic screening length showed an opposite trend to predictions from Poisson-Boltzmann, with the screening-length increasing with increasing salt concentration. That is, the Debye-length prediction was quantitatively incorrect and predicts the incorrect trend. For example, in 10 M LiCl where the Debye-length is 0.1 nm, and therefore colloidal chemists would traditionally predict that double-layer forces are negligible, my results show that the actual decay length is about 10 nm, which is about the same as in 10-3 M LiCl solution. The rate of increase of screening-length as a function of concentration was also an ion specific effect. In addition, the results show that there is an inversion of the surface charge in concentrated salt solution. The original device on which all the above measurements were made had two limitations: (1) the maximum film thickness was 50 nm and (2) the film was asymmetric, which hampered calculation of the surface excess and increased the number of degrees of freedom in modeling of the adsorption. In the last part of my thesis, I describe development of a symmetric sample which (1) enables measurement of films up to 1 µm, (2) simplifies modeling of the optics by eliminating optical interference of the fluorescence excitation, and reduces the number of parameters when comparing to models. / Doctor of Philosophy / This thesis aims to understand the behavior of electrically charged molecules and atoms in thin nanometer scale (< 100 nm) liquid films subject to confinement between two charged interfaces. This situation frequently arises in colloidal suspensions, which consist of tiny sub-microscopic particles (colloid), droplets and large molecules dispersed in a second continuous medium. The stability of these suspensions, i.e. whether the colloidal materials agglomerate and sediment out of the suspension or remain stably suspended, depends on the surface forces between their interfaces during collision events, which frequently arise due to Brownian motion. As the fluid between particles thins as they approach each other during these collision events, the behavior of the dissolved molecules can be significantly different than when they are far apart due to the presence two interacting interfaces. Typically the dissolved molecules are used to tune the surface forces and understanding their behavior in confinement is relevant to a colloid scientist whose aim is to tune the behavior of the suspension. In the first part of this work, a technique is developed that serves as the static analogue to colloidal objects colliding with each other. The equilibrium behavior of a negatively charged fluorescent ion is measured as a function of film thickness and background salt concentration between two negatively charged interfaces. The Poisson-Boltzmann model predicts that with decreased salt concentration, there is a greater magnitude of depletion of the fluorescent ion at large separations and the characteristic length over which there is a change in the magnitude of depletion increases. Good agreement is found between the model and the experiment validating the technique developed and providing the first direct observation of molecular behavior subject to confinement as a function of solution composition. This effect of background salt type and concentration was tested for concentrated electrolytes as well. The experimental results showed an opposite trend to predictions from the Poisson-Boltzmann model. The fluorescent ion was now adsorbed to negatively charged interfaces indicating that the negatively charged interfaces were now positively charged. The magnitude of adsorption at large separations and characteristic length over which the magnitude of adsorption changes was a function of the salt concentration and the ion type. Finally, improvements were made to the original device to overcome limitations with the original device. The limitations were that (1) the maximum film thickness was 50 nm and (2) the interfaces were asymmetric which complicated theoretical calculations of the equilibrium behavior of the ions. In the last part of my thesis, I develop a sample which (1) enables measurements of films up to 1 µm and (2) simplifies the optical modeling necessary in the first two sections of this thesis.

Polymer electrolytes are indispensable in numerous electrochemical systems. Existing polymer electrolytes rarely meet all technical demands by their applications (e.g., high ionic conductivity and good mechanical strength), and new types of polymer electrolytes continue to be developed. In this dissertation, the molecular structure and dynamics of three emerging types of polymer electrolytes featuring Coulombic liquids, i.e., polymerized ionic liquids (polyILs), nanoscale ionic materials (NIMs), and polymeric ion gels, were investigated using molecular dynamics (MD) simulations to help guide their rational design. First, the molecular structure and dynamics of a prototypical polyILs, i.e., poly(1-butyl-3-vinylimidazolium hexafluorophosphate), supported on neutral and charged quartz substrates were investigated. It was found that the structure of the interfacial polyILs is affected by the surface charge on the substrate and deviates greatly from that in bulk. The mobile anions at the polyIL-substrate interfaces diffuse mainly by intra-chain hopping, similar to that in bulk polyILs. However, the diffusion rate of the interfacial mobile anions is much slower than that in bulk due to the slower decay of their association with neighboring polymerized cations. Second, the structure and dynamics of polymeric canopies in the modeling NIMs where the canopy thickness is much smaller than their host nanoparticle were studied. Without added electrolyte ions, the polymeric canopies are strongly adsorbed on the solid substrate but maintain modest in-plane mobility. When electrolyte ion pairs are added, the added counter-ions exchange with the polymeric canopies adsorbed on the charged substrate. However, the number of the adsorbed electrolyte counter-ions exceeds the number of desorbed polymeric canopies, which leads to an overscreening of the substrate's charge. The desorbed polymers can rapidly exchange with the polymers grafted electrostatically on the substrate. Finally, the molecular structure and dynamics of an ion gel consisting of PBDT polyanions and room-temperature ionic liquids (RTIL) were studied. First, a semi-coarse-grained model was developed to investigate the packing and dynamics of the ions in this ion gel. Ions in the interstitial space between polyanions exhibit distinct ordering, which suggests the formation of a long-range electrostatic network in the ion gel. The dynamics of ions slow down compared to that in bulk due to the association of the counter-ions with the polyanions' sulfonate groups. Next, the RTIL-mediated interactions between charged nanorods were studied. It was discovered that effective rod-rod interaction energy oscillates with rod-rod spacing due to the interference between the space charge near each rod as the two rods approach each other. To separate two rods initially positioned at the principal free energy minimum, a significant energy barrier (~several kBT per nanometer of the nanorod) must be overcome, which helps explain the large mechanical modulus of the PBDT ion gel reported experimentally. / Ph. D. / Polymer electrolytes are an indispensable component in numerous electrochemical devices. However, despite decades of research and development, few existing polymer electrolytes can offer the electrochemical, transport, mechanical, and thermal properties demanded by practical devices and new polymer electrolytes are continuously being developed to address this issue. In this dissertation, the molecular structure and dynamics of three emerging novel polymer electrolytes, i.e., polymerized ionic liquids (polyILs), nanoscale ionic materials (NIMs), and polymeric ion gels, are investigated to understand how their transport and mechanical properties are affected by their molecular design. The study of polyILs focused on the interfacial behavior of a prototypical polyILs supported on neutral and charged quartz substrates. It was shown that the structure and diffusion mechanism of the interfacial polyILs are sensitive to the surface charges of the substrate and can deviate strongly from that in bulk polyILs. The study of NIMs focused on how the transport properties of the dynamically grafted polymers are affected by electrolyte ion pairs. It was discovered that the contaminated ions can affect the conformation the polymeric canopies and the exchange between the “free” and “grafted” polymers. The study of polymeric ion gels focused on the molecular and mesoscopic structure of the ionic liquids in the gel and the mechanisms of ion transport in these gels. It was discovered that the ions exhibit distinct structure at the intermolecular and the interrod scales, suggesting the formation of extensive electrostatic networks in the gel. The dynamics of ions captured in simulations is qualitatively consistent with experimental observations.

Photovoltaic (PV) technologies are a promising approach to achieve clean, renewable energy production on a global scale. However, the widespread implementation of this technology is limited due to the intricate challenges associated with its complex electrochemical processes. One such challenge is the formation of long-lived charge-separated states (CSSs), a process that directly influences device efficiencies. Viable strategies for increasing CSS lifetimes involve the inhibition of parasitic back-electron transfer pathways. In liquid-junction PVs, electronic recombination is prevented by utilizing redox electrolytes that promote directional electron transfer at the electrode/electrolyte interface, where forward electron transfer (i.e. to the electrode) is favored and the corresponding electronic recombination reaction is impeded. To meet this criterion, researchers seek to employ redox electrolytes that undergo a spin-exchange reaction induced by electron transfer. This event, known as charge transfer-induced spin crossover (CTISC), significantly increases the reorganization energy associated with electronic recombination, producing long-lived CSSs and elevated device efficiency. This dissertation describes a suite of manganese-based redox mediators that exhibit CTISC across a tunable range (1.5 V) of formal potentials (E1/2). These complexes are utilized as redox electrolytes in liquid-junction PVs and result in a two-fold enhancement in the device efficiency relative to other CTISC redox species. Photosensitizer regeneration rates are monitored using transient absorption spectroscopy (TAS) to discern the optimal E1/2 values in this class of complexes while density functional theory is employed to calculate the reorganization energy of each species. By implementing these promising electrolytes into PV devices, scientists and engineers are armed with new tools to increase the accessibility and efficiency of next-generation PVs, thereby transforming past promises into progress. / Doctor of Philosophy / To realize next-generation renewable fuels, scientists must understand how electron transfer at an interface is controlled. This dissertation highlights one method of forming a chemically useful and long-lived charge separated state. The formation of this charge separated state is achieved through an electronic reorganization that occurs at a metal center after electron transfer. Chapters 2, 3, and 4 investigate the synthesis and characterization of new metal species that possess this electronic reorganization process and provide an advanced understanding of how this process facilitates the formation of long-lived charge separated states. This work is intended to motivate new schools of thought that aid the design of next-generation catalytic materials for light-driven chemical reactions.

The immediate goal of this thesis was the analysis of a three-component system whose major component was water. This analysis was to be the result of a procedure which could be readily extended to more complex systems.

In the last decade new materials appeared that are candidates to be used as an electrolyte in a Solid Oxide Fuel Cell, SOFC. Some materials show high ionic conductivity but lack in important properties, such as mechanical stability or chemical compatibility with other materials in the fuel cell. Scandia Stabilised Zirconia, SSZ, became a possibility when the scandia price dropped with the opening of the Chinese and Russian markets. In the starting system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2), scandia is introduced to improve conductivity and stabilise the cubic phase; yttria is introduced to fully stabilise the cubic phase and ceria to enhance conductivity lost with the introduction of yttria. The aim of this project is to develop a reliable new method to produce quality ceramics that are not strongly composition dependent, then to prepare a range of compositions and compare intrinsic properties without having to be concerned that poor sintering dominates conduction properties. This project can be divided in two sections, the first section the powder production method, the characteristics of the powders and its final products are in focus. In the second section the relation between electric characteristics and microstructure of the material is reported. In the first section, the effect of different compositions of the system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2) is studied, in terms of structure, phase and microstructure. The nature, size and shape of the powders are discussed, and their effect on the final product. The sol-gel and combustion method gives the formation of hard agglomerates (shells), during the combustion, a wide range of grain sizes, between less than 1µm and 200 µm, and the formation of grains with non spherical shape. In this project, the sol-gel and combustion process and solid state method are also compared. In the second section of this project, AC Impedance measurements, as a function of temperature, oxygen partial pressure and time are discussed. The Arrhenius plot for all compositions shows two regions (high and low temperature) and the change of region occurs at 580 °C. At low temperatures there is a slight difference between compositions but this difference is less at high temperatures. The obtained ionic conductivity, at 350 °C, varies from 3.84×10⁻⁶ to 5.53×10⁻⁵ S/cm; at 700 °C, ionic conductivity from 0.013 to 0.044 S/cm. At low temperatures, the activation energy associated with bulk process is generally lower than grain boundary process; for example, the composition Ce₀.₁Y₀.₁Sc₀.₆Zr₃.₂O₇.₆₅ has an activation energy, for the bulk process, of 1.05 eV and an activation energy, for the grain boundary process, of 1.17 eV. For compositions with higher ceria content, activation energy, for bulk and grain boundary, have similar values. The AC impedance as function of oxygen partial pressure show that the amount of ceria introduced as an effect on the conductivity at low oxygen partial pressure. For the sample with no ceria in its composition, Y₀.₂Sc₀.₆Zr₃.₂O₇.₆₀, the conductivity does not vary significantly as the oxygen partial pressure is decreased; for oxygen partial of 0.21 atm, conductivity is 0.018 S/cm and when oxygen partial pressure is approximately 10⁻²⁴ atm conductivity is 0.018 S/cm. For the sample with a higher content of ceria, Ce₀.₁₂Y₀.₀₈Sc₀.₆Zr₃.₂O₇.₆₆, there is a decrease in conductivity while oxygen partial pressure decreases; and there is also the appearance of a semi-circle for lower oxygen partial pressures. For oxygen partial pressure approximately 0.21 atm, conductivity is 0.019 S/cm, but when oxygen partial pressure is decreased to 10⁻²⁴ atm conductivity decreases to 0.011 S/cm. AC impedance measurements as a function of annealing time at 600 °C were performed. Total conductivity is fairly stable, for all compositions, until 1800 hours but after this time, conductivity slowly decreases. Some compositions show a second semi-circle in the AC impedance spectra, either from the beginning, time equals 0 hours, or after some working hours. Here, the changes in conduction and conduction processes with time are discussed.