No description available.

<p>This Dissertation aims at establishing an integrated framework of multimodal experiments and multiphysics theory to extend the understanding of the mechanics in electrochemically active materials using organic mixed ionic-electronic conductors (OMIECs) as a model system. </p> <p>OMIECs allow the transport of both ions and electrons, which is accompanied by the (electronic, micro-) structural reorganization. The electronic structural change in OMIECs induces transforms in the electrical conductivity and optical absorbance. The change in molecular packing invites the size change and evolution of mechanical properties. The multiphysics processes render OMIECs a fascinating platform for understanding the multi-physics coupling and advancing organic electrochemical devices. </p> <p>Despite significant progress, there are urgent needs in the experimental techniques and the subsequent mechanical characterization, theoretical understanding of the multiphysics processes, and mechanics-informed design principles for high-performance devices. Specifically, (i) an accurate and straightforward experimental method is in need to better understand the mechanical behaviors and kinetics such as swelling and softening of OMIECs upon electrochemical redox reactions; (ii) a theoretical framework is missing that describes the rich coupled multiphysics processes such as large deformation, charge and mass transport, electrostatics, and phase evolution in OMIECs; (iii) the rational design of the materials and structures based on mechanics principles are required for mechanically reliable, high-performance organic electrochemical devices.</p> <p>In this Dissertation, the mechanics of OMIECs are studied systematically. The basics of OMIECs, knowledge gaps, and the outline are introduced in Chapter 1. The in-situ environmental nanoindentation apparatus and the associating characterization techniques are presented in Chapter 2. In Chapter 3, a theoretical mechanics model is presented that elucidates the interfacial mechanical degradation of thin-film electrodes and outlines the design principles for mechanically reliable electrodes. In Chapter 4, the electrochemical doping kinetics and its stress dependency on conductive polymers are studied via a designed moving front device. Chapter 5 presents a thermodynamically consistent continuum theory of two-phase OMIECs undergoing large deformation, charge and mass transport, electrostatics, and phase separation, which forms the theoretical foundation for such conductive polymer systems. The conclusion and perspectives on future work are presented in Chapter 6. </p>

The purpose of this dissertation was to elucidate my lived experiences as an HBCU band director as I navigated through tensions within HBCU culture, between HBCU culture and the dominant culture, and issues of inequality, and access. I chronicle my early life and influences to bring clarity and meaning to the choices and decisions made as I transitioned to becoming an HBCU student and then band director at an early age. It was my intention to use autoethnographic self-examination and personal narrative to make transparent racial inequality as it: (a) impacts the academic and musical quality of HBCU band programs, (b) raises questions regarding access to resources, and (c) elicits larger and more complex questions related to race and culture. In addition to a thorough review of my personal recollections and historical artifacts, I also sought to interview as many people as possible that had impacted me, my life, and HBCU bands in order to check my memory and perspectives. As the word got out about my project, hundreds in the HBCU community reached out wanting to participate. Of the eighty-seven persons that agreed to an interview, I was able to interview fifty-two. I analyzed my story through the framework of "Double-Consciousness Theory" as articulated by W. E. B. Du Bois, specifically through the concepts of the veil, the color line, and twoness. The guiding question for my inquiry was: Why is the musicianship of HBCU bands praised by one culture and viewed in a mostly deficit view in another, and how did an HBCU band director navigate these tensions to lead two successful programs? The findings demonstrate that there are multiple and conflicting expectations and perceptions of HBCU band programs. By considering HBCU bands through my own experience of double-consciousness it was possible to amplify the voices of marginalized groups and provide more nuanced understandings to those who have a one-dimensional view of such band programs.

No description available.

Yes / Ionic liquids (ILs) are key materials for the development of a wide range of emerging technologies. Protic ionic liquids, an important class of ILs, have long been envisioned as promising anhydrous electrolytes for fuel cells. It is well known that in comparison to all other cations, protons exhibit abnormally high conductivity in water. Such superprotonic dynamics was expected in protic ionic conductors as well. However, many years of extensive studies led to the disappointing conclusion that this is not the case and most protic ionic liquids display subionic behavior. Therefore, the relatively low conductivity seems to be the main obstacle for the application of protic ionic liquids in fuel cells. Using dielectric spectroscopy, herein we report the observation of highly decoupled conductivity in a newly synthesized protic ionic conductor. We show that its proton transport is strongly decoupled from the structural relaxation, in terms of both temperature dependence and characteristic rates. This finding offers a fresh look on the charge transport mechanism in PILs and also provides new ideas for design of anhydrous materials with exceptionally high proton conductivity. / National Science Centre within the framework of the Opus project (Grant No. DEC 2011/03/B/ST3/02072). Financial assistance from FNP START. The LDRD Program of ORNL, managed by UT-Battelle, LLC, for the U.S. DOE. Support from the NSF under grant CHE-1213444.

Functional materials, particularly metal oxides, have been the focus of much attention in solid state chemistry for many years and impact every aspect of modern life. The approach adopted in this thesis to access desirable functionality for enhanced fundamental understanding is via modifying existing materials by deploying reducing synthetic procedures. This work spans several groups of inorganic crystalline materials, but is unified by the development of new properties within host compounds of particular relevance to solid oxide fuel cell technology, which allow interstitial oxide ion conduction at elevated temperatures. The Ca₁₂Al₁₄O₃₂e₂ electride was successfully synthesized by replacing the mobile extra-framework oxygen ions with electrons acting as anions. The high concentration of electrons in the C12A7 electride gives rise to an exceptionally high electronic conductivity of up to 245 S cm⁻¹ at room temperature. Making use of the high density of electrons in Ca₁₂Al₁₄O₃₂e₂ electride, the strong N-N bonds in N₂ was found to be broken when heating Ca₁₂Al₁₄O₃₂e₂ in a N₂ atmosphere. A reaction between silicate apatites and the titanium metal yielded another completely new electride material La₉.₀Sr₁.₀(SiO₄)₆O₂.₄e₀.₂ which was found to be a semiconductor. To fully understand the role of oxygen interstitials in silicate apatites, high-resolution transmission electron microscopy (HRTEM) was employed as the main technique in probing how the oxygen nonstoichiometry is accommodated at the atomic level. Atomic-resolution imaging of interstitial oxygen in La₉.₀Sr₁.₀(SiO₄)₆O₂.₅ proved to be a success in this thesis. Substitution of oxygen in 2a and interstitial sites with fluoride ions in La[subscript(8+y)]Sr[subscript(2- z)](SiO₄)₆O[subscript(2+(3y-2z)/2)] (0<y<2, 0<z<2) could be an approach to enriching the functionalities in the apatite structure. A wide range of fluoride substitution levels was tolerated in La[subscript(10-x)]Sr[subscript(x)](SiO₄)₆O[subscript(3-1.5x)]F[subscript(2x)] (x= 0.67, 1, 1.5, 2) and AC impedance measurements were found in support of a tentative conclusion that fluoride ions could be mobile in fluorinated apatites. The last part of this thesis was focused on a new class of fast oxide ion conductors based on Ge₅P₆O₂₅ whose performance was superior to both La₉.₀Sr₁.₀(SiO₄)₆O₂.₅ and Ca₁₂Al₁₄O₃₃ in the low temperature range.

Fast ionic conductors, i.e. materials in which charge transport mainly occurs through the motion of ions, are an important class of materials with immense scope for industrial applications. There are different classes of fast ionic conductors e.g. polymer electrolytes, glasses, oxide ion conductors etc. and they find applications such as solid electrolytes in batteries, in fuel cells and in electro active sensors. There are mixed conducting materials as well which have both ions and electrons as conducting species that are used as electrode materials. Specifically, polymer electrolytes 1−3 have been in use in lithium polymer batteries, which have much more advantages compared to other secondary batteries. Polymer electrolyte membranes have been in use in direct methanol fuel cells (DMFC). The membranes act as proton conductors and allow the protons produced from the fuel (methanol) to pass through. Oxide ion conductors are used in high temperature solid oxide fuel cells (SOFC) and they conduct via oxygen ion vacancies. Fuel cells are rapidly replacing the internal combustion engines, because they are more energy efficient and environment friendly. The present thesis is concerned with the preparation, characterization and conductivity studies on the following fast ionic conductors: (MPEG)xLiClO4, (MPEG)xLiCF3SO3 where (MPEG) is methoxy poly(ethylene glycol), the hydrotalcite [Mg0.66Al0.33(OH)2][(CO3)0.17.mH2O] and the nanocomposite SPE, (PEG)46 LiClO4 with dispersed nanoparticles of hydrotalcite. We also present our investigations of spin probe electron spin resonance (SPESR) as a possible technique to determine the glass transition temperature (Tg) of polymer electrolytes where the conventional technique of Tg determination, namely, differential scanning calorimetry, (DSC), is not useful due to the high crystallinity of the polymers. In the following we summarize the main contents of the thesis. In Chapter 1 we provide a brief introduction to the phenomenon of fast ionic conduction. A description of the different experimental techniques used as well as the relevant theories is also given in this chapter. In most solid polymer electrolytes (SPE), the usability is limited by the low value of the ionic conductivity. A number of different routes to enhance the electrical, thermal and mechanical properties of these materials is presently under investigation. One such route to enhance the ionic conductivity in polymer electrolytes is by irradiating the polymer electrolyte with gamma rays, electron beam, ion beams etc. In Chapter 2, we describe our work on the effect of electron beam (e-beam) irradiation on the solid polymer electrolytes (MPEG)xLiClO4 and (MPEG)xLiCF3SO3. The polymer used is methoxy poly(ethylene glycol) or poly(ethylene glycol) methyl ether with a molecular weight 2000. Salts used are LiClO4 and LiCF3SO3. ’x’ in the subscript is a measure of the salt concentration; it is the ratio of the number of ether oxygens in the polymer chain to that of the Li+ ion. ’x’ values chosen are 100, 46, 30 and 16. Nearly one order of magnitude increase in the conductivity is observed for samples (MPEG)100LiClO4 and (MPEG)16LiCF3SO3 on irradiation. It was found that the increase in the net ionic conductivity is a function of both the irradiation dose and the salt concentration. The enhanced ionic conductivity remains constant for ∼ 100 hrs, which signifies a possible near permanent change in the polymer electrolyte system due to irradiation. The samples were also characterized using DSC and Fourier transform infrared spectroscopy (FTIR). DSC results could be correlated with conductivity findings, giving low Tg values for samples having high conductivity. It was also found that there is a small increase in the crystalline fraction of the samples on irradiation, which agrees with earlier reports on samples irradiated with low dosage. FTIR results are suggestive of decreased cross linking as the reason for increased ionic conductivity. However, this aspect needs a further confirmatory look before the findings can be termed conclusive. In Chapter 3, we describe the studies we have carried out on Li -doped hydrotalcite. We report the details of preparation and characterization of hydrotalcite as well as NMR and ionic conductivity measurements on both doped (with Li+ ions) and undoped hydrotalcite. Hydrotalcite was prepared by co-precipitation method and the composition of hydrotalcite was chosen as [Mg0.66Al0.33(OH)2][(CO3)0.17.mH2O]. Samples were prepared with salt (LiClO4) concentration 5 %, 10 %, 15 %, 20 % and 25 %. It was found that the highest ionic conductivity occurs for the sample with 20 % doping. 7Li NMR plots for all the samples clearly show an overlap of a Gaussian and a Lorentzian lineshape. The Gaussian line is because of the presence of a less mobile fraction of the 7Li+ ions and the Lorentzian line is because of the presence of a more mobile fraction of 7Li+ ions. The highest ionic conductivity was found for the salt concentration 20 % and from the room temperature 7Li NMR studies we found that for this particular concentration, the mobile fraction of the 7Li ion is also maximum. Without the salt doping, the conductivity of the sample was too small to be measured. Temperature variation of both 1H and 7Li NMR was also done, to compare the ionic conductivities from NMR. Another method to obtain enhanced properties in polymer electrolytes is by forming ’nanocomposite’ polymer electrolytes. Nanocomposites are formed by dispersing nanoparticles of certain materials in the polymer electrolyte matrix. Till now, nanoparticles used are mostly oxides of metals, e.g. Al2O3, TiO2, MgO, SiO2 etc and clays like montmorillonite, liponite, hydrotalcite etc. Chapter 4 describes the preparation and characterization of the nanocomposite polymer electrolyte (PEG)46LiClO4 formed with hydrotalcite nanoparticles. The polymer used is PEG, poly(ethylene glycol) of molecular weight 2000, and salt used is LiClO4. The salt concentration is selected so as to give the highest ionic conductivity for the solid polymer electrolyte. Hydrotalcite belongs to a class of materials called LDH, layered double hydroxides. The composition selected is [Mg0.66Al0.33(OH)2][(CO3)0.17 .mH2O], since this is the most stable composition. These materials are easy to prepare in the nano size and are being used in a number of applications. These are characterized by the presence of layers of positively charged double hydroxides separated by layers of anions and water molecules. The water molecules give stability to the structure. Nanoparticles of hydrotalcite were prepared in the laboratory itself. XRD data of hydrotalcite confirm the crystal structure. TEM data show the particle size to be ∼ 50 nm. The polymer electrolyte (PEG)46LiClO4 was doped with these nanoparticles and the doping levels are 1.8 %, 2.1 %, 2.7 %, 3.6 % and 4.5 % by weight. Impedance spectroscopy was used to find the ionic conductivity. We have found that the sample with a doping of 3.6 % by weight gives the highest ionic conductivity and the increase in ionic conductivity is nearly one order of magnitude. DSC was used for thermal characterization of these nanocomposites. The glass transition temperatures, Tg , found from DSC measurements corroborates the ionic conductivity data, giving the lowest Tg for the sample with highest conductivity. Temperature variation of the ionic conductivity shows Arrhenius behavior. 7Li NMR was done on the pristine SPE (PEG)46LiClO4 and the nanocomposite of (PEG)46LiClO4 with 3.6 % filler. The ionic conductivity was also estimated from the temperature variation of 7Li NMR line widths. Studies on the DSC endotherms of the nanocomposites give the fractional crystallinity of the samples. From these studies it can be concluded that the variation in ionic conductivity can be attributed to the change in fractional crystallinity; the nanocomposite polymer electrolyte having highest ionic conductivity, i.e. the NCPE with filler concentration of 3.6 % also has the lowest fractional crystallinity. Additionally, a possible increase in the segmental motion inferred from a reduction in the glass transition temperature coupled with a lowering of the activation energy may also contribute to the increased ionic conductivity in the nanocomposite polymer electrolyte. Glass transition temperature Tg has a very important role in studying the dynamics of polymer electrolytes. In Chapter 5, we explore the possibility of using spin probe electron spin resonance (SPESR) as a tool to study the glass transition temperature of polymer electrolytes. When the temperature of the polymer is increased across the glass transition, the viscosity of the sample decreases. This corresponds to a transition from a slow tumbling regime with τc = 10−6 s to a fast tumbling regime with τc = 10−9 s where τc is the correlation time for the probe dynamics. Spin probe ESR can be used to probe this transition in polymers. We have used 4-hydroxy tempo (TEMPOL) as the spin probe which is dispersed in the nanocomposite polymer electrolyte based on (PEG)46LiClO4 and hydrotalcite. Below and across the glass transition, this nitroxide probe exhibits a powder pattern showing both Zeeman (g) and hyperfine (hf) interaction anisotropy. When the frequency of the dynamics increases such that the jump frequency f is of the same order of magnitude as the anisotropy of the hf interaction, i.e., ∼ 108 Hz, the anisotropy of the interactions averages out and a spectrum of reduced splitting and increased symmetry in the line shape is observed. This splitting corresponds to the nonvanishing isotropic value of the hyperfine tensor and is observed at a temperature higher than but correlated with Tg. The crossover from the anisotropic to isotropic spectrum is reflected in a sharp reduction in the separation between the two outermost components of the ESR spectrum, which corresponds to twice the value of the z-principal component of the nitrogen hyperfine tensor, 2Azz, from ∼75 G to ∼ 35 G. In our study, we have varied the concentration of the nano-fillers. The Tg for all the samples were estimated from the measurement of T50G and the known correlation between 4 T50G and Tg, where T50G is the temperature at which the extrema separation (2Azz) of the ESR spectra becomes 50 Gauss. The values obtained from this method are compared with the values found from DSC done on the same samples. Within experimental error, these two techniques give reasonably close values. Tg’s were also estimated by a cross over in the correlation time (τc) vs temperature plot. The τc values were calculated using a spectral simulation program. We conclude that spin probe ESR can be an alternative to the DSC technique for polymers with high fraction of crystallinity, for which DSC often does not give any glass transition signature. In Appendix I, ionic conductivity studies on quenched and gamma irradiated polymer electrolytes (PEG)46LiClO4 and (MPEG)16LiClO4 is done. It is observed that, (i) the samples quenched to 77 K after melting show enhancement of ionic conductivity by a factor of 3 & 4; (ii) on irradiation, the ionic conductivity decreases for a dose of 5 kGy and subsequently, keeps on increasing for higher doses of 10 kGy and 15 kGy. In Appendix II, the BASIC language program (eq-res.bas) used for impedance data analysis is given.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung neuer Schichtsysteme für die Realisierung biaxial texturierter hochtemperatursupraleitender Bandleiter. Bisher sind eine Vielzahl von Bandleiterarchitekturen bekannt, die sowohl durch physikalische Depositionsmethoden als auch mittels Abscheidung aus der chemischen Lösung hergestellt werden können. Während die Funktion von YBCO-Bandleitern mit Hilfe physikalischer Depositionsmethoden in den letzten Jahren demonstriert werden konnte, zeigen auf chemischem Wege deponierte Bandleiter schlechtere Eigenschaften. Seitens der Industrie besteht ein starkes Interesse, die hohen Produktionskosten, die im Hinblick auf physikalische Depositionsmethoden mit einem hohen Anlagenaufwand verbunden sind, anhand der kostengünstigen chemischen Synthese von Einzelschichten oder der gesamten Bandleiterarchitektur zu senken. Gelöst wurde diese Aufgabe innerhalb der vorliegenden Arbeit durch die Entwicklung metallorganischer Vorstufenlösungen zur Deposition von CaTiO3-, SrTiO3-Pufferschichten und supraleitender YBa2Cu3O7-Schichten.

The present thesis demonstrates and discusses polymeric ion and mixed ion-electron conductors for rechargeable batteries based on lithium viz. lithium-ion and lithium-sulphur batteries. The proposed polymer ion conductors in the thesis are discussed primarily as potential alternatives to conventional liquid and solid-crystalline electrolytes in lithium-ion batteries. These discussions are part of Chapters 2-4. On the other hand, the polymer based mixed ion-electron conductor is demonstrated as a novel electrode for lithium-Sulphur battery in Chapter 5. Possibility of application of polymer ion conductors is discussed in the context of Li-S battery in Chapter 6. A distinct correlation between the physical properties and electrochemical performance of the proposed conductors is highlighted in detail in this thesis. Systematic investigation of the ion transport mechanism in the polymeric ion conductors has been carried out using various spectroscopic techniques at different time and length scales. Such detailed investigations demonstrate the key structural and physical parameters for design of alternative polymer conductors for rechargeable batteries. Though the thesis discusses the various polymeric conductors in the context of lithium-based batteries, it is strongly felt that the design strategies are equally likely to be beneficial for different battery chemistries as well as for other electrochemical generation and storage devices. A brief discussion of the contents and highlights of the individual chapters are described below: The thesis comprises of six Chapters. Chapter 1 briefly reviews the important developments and materials of lithium-based batteries, with specific focus on Li-ion and Li-S batteries. It starts with discussions on different types of liquid, solid crystalline and solid-like electrolytes. Their materials characteristics, advantages and disadvantages are discussed in the context of secondary batteries such as lithium-ion and lithium-sulphur batteries. As prospective alternative electrolytes polymer based soft matter electrolytes are discussed in detail. Special emphasis is given to the recent developments in polymer electrolytes and their ion conduction mechanism, which are central themes to this thesis. The importance of investigation of charge transport, typically ion, on electrochemical processes is also briefly discussed in Chapter 1. A brief discussion about the characteristics, materials and non-trivialities of the electrochemical storage process in Li-S battery is also reviewed. Chapter 2A demonstrates a binary polymer physical network based gel (PN-x) electrolyte, comprising of an ionic liquid confined inside a binary polymer system for electrochemical devices such as secondary batteries. The synthesis, physical property and electrochemical performances are studied as a function of content of one of the polymers in this Chapter. A physical network of two polymers with different functional groups leads to multiple interesting consequences. The polymer physical network characteristics determine all physical properties including electrochemical property of the ionic liquid integrated PN based GPE. The conductivities of the proposed gel are nearly an order in magnitude higher than the unconfined ionic liquid electrolyte and displays good dimensional stability and electrochemical performance in a separator-free battery configuration. The ac-impedance spectroscopy, steady shear viscosity measurement, dynamic rheology are employed to study physical properties of the proposed gel polymer electrolyte. Chapter 2B discusses the detailed investigations of the ion transport mechanism of the gel polymer electrolyte, as discussed in Chapter 2A. Ion conduction mechanism is investigated in the light of ion diffusion and solvent dynamics of the entrapped ionic liquid inside the polymer. The studies reveal a heavy influence of network characteristics on the ion conduction mechanism. The influence of solvent dynamics on the ion transport is drastically altered by polymer physical network. Consequently, a drastic change in the ion mobility and nature of predominant charge carrier is observed in the polymer physical network based gel electrolyte. A clear transformation from dual ion conductivity to a predominantly anion conductivity is observed on going from single polymer to a dual polymer network. The spectroscopic tools such as pulsed field gradient nuclear magnetic resonance (PFG–NMR), Brillouin light scattering spectroscopy, ac-impedance spectroscopy, FT-Raman and FTIR spectroscopy were used to elucidate the ion transport mechanism in the Chapter. Chapter 3 demonstrates a simple design strategy of gel polymer electrolyte comprising of a lithium salt (lithium bis(trifluoromethanesulfonyl) imide, LiTFSI) solvated by two plastic crystalline solvents, one a solid (succinonitrile, abbreviated as SN) and another a (room temperature) ionic liquid (1-butyl-1-methyl-pyrrolidinium bis(trifluoromethane sulfonyl) imide, (abbreviated as IL) confined inside a linear network of poly(methyl methacrylate) (PMMA). The concentration of the IL component determines the physical properties of the unconfined electrolyte and when confined inside the polymer network in gel polymer electrolyte. Intrinsic dynamics of one plastic crystal influences the conduction mechanism of gel polymer electrolytes. The enhanced disordering in the plastic phase of succinonitrile by IL doping alters both the local ion environment and viscosity. The proposed plastic crystal electrolytes show predominantly anion conduction (tTFSI ≈ 0.5) however, lithium transference number (tLi ≈ 0.2) is nearly an order higher than the ionic liquid electrolyte (IL-LiTFSI) (tLi ≈ 0.02-0.06), discussed in Chapter 2. The gel polymer electrolyte displayed high mechanical compliability, stable Li-electrode | electrolyte interface, low rate of Al corrosion and stable cyclability. The promising electrochemical performance further justifies simple strategy of employing mixed physical state plasticizers to tune the physical properties of polymer electrolytes requisite for application in rechargeable batteries. Chapter 4A proposes a novel liquid dendrimer–based single ion conducting liquid electrolyte as potential alternative to conventional molecular liquid solvent–salt solutions and conventional solid polymer electrolytes for rechargeable batteries, sensors and actuators. The physical properties are investigated as a function of peripheral functionalities in the first generation poly(propyl ether imine) (G1-PETIM)–lithium salt complexes. The change in peripheral group simultaneously affects the effective physical properties viz. viscosity, ionic conductivity, ion diffusion coefficients, transference numbers and also the electrochemical response. The specific change from ester (–COOR) to cyano (–CN) terminated peripheral group resulted in a remarkable switch over from a high cation (tLi+ = 0.9 for –COOR) to a high anion (tPF6- = 0.8 for –CN) transference number. Chapter 4B presents an analysis of the frequency dependent ionic conductivity of single ion dendrimer conductors by using time temperature scaling principles (TTSPs) and dielectric modeling of the electrode polarization. The TTSP provides information on the salt dissociation and number density of mobile charges and hence provides direct insights into the ion conduction mechanism. Summerfield and Baranovskii–Cordes scaling laws, which are well known TTSPs, have been applied to analyze the ion conductivity. The electrode polarization, which quantifies the number density of mobile charges and ionic mobility, is studied using Macdonald-Coelho model of electrode polarization. The combination of these two theoretical investigations of the experimental data emanating from one technique i.e. ac– impedance spectroscopy, predicts independently the contributions of the effect of mobile ion charges and ionic mobility to ion conduction mechanism. In Chapter 5 focus shifts from polymer ion conductors to polymer mixed ion-electron conductor. The polymer mixed ion-electron conductor is demonstrated as a novel electrode material for Li-S battery. A simple strategy to overcome the challenges towards practical realization of a stable high performance Li–S battery is discussed. A soft mixed conducting polymeric network is utilized to configure sulphur nanoparticle. The soft matter network provides efficient and distinct pathways for lithium and electron conduction simultaneously. A lithiated polyethylene glycol (PEG) based surfactant tethered on ultra-small sulphur nanoparticles and wrapped up with polyaniline (PAni) (abbreviated as S-MIEC) is demonstrated here as an exceptional cathode for Li–S batteries. The S-MIEC is characterized by several methods: powder-X-ray diffraction (PXRD), thermo gravimetric analysis (TGA), fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), ac-impedance spectroscopy and dc current-voltage measurements are performed to evaluate conductivity of S-MIEC cathode. Electrochemical studies such as cyclic voltammetry, galvanostatic charge-discharge cycling, galvanostatic intermittent titration (GITT) are performed to demonstrate feasibility of S-MIEC in the Li–S battery performance. Chapter 6 provides a brief summary of the work carried out as part of this thesis and also demonstrates the future perspective of the present work. Potential of the polymer physical network based gel polymer electrolytes, which are discussed in Chapter 2A-B for lithium-ion batteries, are demonstrated in Li-S battery. The proposed polymer physical network confines higher order lithium polysulfides (typically Li2S8) dissolved in tetraethylene glycol dimethyl ether (TEGDME) based electrolyte (TEGDME-1M LiTFSI). The three dimensional polymer network is proposed to be formed by physical blending of the poly(acrylonitrile) (PAN) with the copolymer of AN and poly(ethylene glycol) methyl ether methacrylate (PEGMA), [ P(AN–co–PEGMA)]. We extend here the similar synthetic approaches as described in Chapter 2A. The approach proposed and demonstrated in this concluding Chapter is expected to mitigate some of the major issues of Li-S chemistry. The proposed Li2S8 confined gel electrolyte exhibits moderately high values of ionic conductivity, 2 × 10-3 Ω-1cm-1 and shows a stable capacity of 350 mAhg-1 over 30 days in a separator free Li-S battery.

Electromagnetic effects of lightning currents during a direct hit to tall communication towers, other instrumented towers and chimneys can be hazardous to associated cables, as well as, electrical and electronics systems. The standard practice in telecommunication and other related fields is to bond the cable sheath to the tower and ground connection is made before it enters the base station. However, in some specific cases when power, signal and data logging cables are to be supported on the same tower, isolation of power cables is demanded. In a totally different situation, attempts are also made to have a dedicated isolated down conductor. A critical review of the situation demanded a more quantitative answer to the following questions: (i) whether it is possible to electrically isolate a dedicated down conductor, (ii) is it possible to electrically isolate the cables and their terminal equipment both mounted on towers serving as down conductor and if so, what will be the nature of current induced in the cables and (iii) as per the standard practice, if the cable sheaths are connected to the tower/structure, what will be the nature of the current shared by them. Addressing these important issues formed the scope of the present work. For the tall structures considered in this work, for the critical time periods, wave nature of the current dominates. This called for electromagnetic modeling covering Transverse Magnetic (TM) mode of the wave propagation. Owing to the complex geometrical features involved with the problem, both experiments on electromagnetically scaled laboratory models, as well as, theoretical simulation is attempted. An electromagnetically scaled laboratory model is employed for the time domain experimental investigation. This approach, which has been validated earlier, is further scrutinized to ensure its adequacy. In order to achieve generality and noting the fact that the associated parameters are rather difficult to be varied in the experimentation, theoretical investigation is also employed. For this, both NEC-2, as well as, an in-house thin wire time domain code developed for this work is employed. NEC-2 could handle multi-wire multi-radius junctions, while in-house time domain code could handle proximity and non-cylindrical shapes encountered with tower lattice elements. The investigation of induction to isolated cables on simple down conductors and towers is considered first. The induced current is shown to be bipolar oscillatory with the period of oscillation governed by the length of the cable. It is shown that the level of induction for good earth termination is below 5 – 10 % while that with moderate inductance in the earth termination can enhance the induction to higher levels. The level of induction is shown to be not critically dependent on the length of the cable, gap between cable and down conductor/tower. When multiple cables are mounted, they seem to influence each other and individually carry currents of lower amplitude. Also, the effect of shape and proximity of the tower lattice elements on induction is investigated. If the cable is housed inside a metallic tray, the amplitude of induced current is shown to be quite small. Subsequently, the evaluation of electrical stress between the isolated down conductor on tower and simplified representation of the structure is considered. A suitable definition of the electric stress for the wave regime is evolved and then it is shown that, at present, the voltage difference defined by the path integral of electric field across shortest path between the two entities is the best indicator for the stress. The electrical stress in the case of isolated down conductor on tower, as well as, down conductor with isolated cable is shown to reach very dangerous levels. On the other hand, the stress on the isolated cables on towers also serving as down conductors is shown to be relatively moderate. Interestingly, it is shown that the electrical stress and the voltage difference is dependent on the gap and for the critical time period, can be much lower than that calculated as a product of equivalent tower surge impedance and the stroke current, even before the arrival of ground end reflections. Finally, the current shared by cables connected to the down conductor is investigated. For the case of simple cylindrical down conductor with cable connected to it at the top, it is shown that the amount of current shared by the cable is not dependent on its length and the relative radii (cross section) have only a weak influence. For the case with down conductor formed by L and + angles, it is shown that the placement of cable at their interior corner can reduce the initial current shared by the cable. In order to model best possible situation with towers, experiments are conducted with cable inside an aluminum pipe. Even in this case, cable current builds up with successive reflections to become comparable with the current through the pipe itself. Subsequent investigation with 1:40 and 1:20 tower models lead to several interesting observations. Cables running along leg/face of the tower whether placed inside or outside the tower, always shares good amount of current. Further, frequent bonding of the sheath to the tower increases the current shared by the cable. Cable when housed in a metallic tray shares less than 50% of the current shared without the tray. Even though a complete quantification is not to be achieved in this work, it has made a good beginning with some significant contribution towards lightning protection issues pertaining to tall towers and structures.