This work deals with electrolytic conductivity of gel polymer electrolytes. In the theoretical part of the work the methacrylates, the polymerization and the basic outlines of gel polymer electrolytes conductivity are described. The preparation and electrical conductivity of gels based on PMMA are described in the experimental part.

The demand for electric vehicles is increasing rapidly as the world is preparing for a fossil fuel-free future in the automotive field. Lithium battery technologies are the most effective options to replace fossil fuels due to their higher energy densities. However, safety remains a major concern in using lithium as the anode, and the development of non-volatile, non-flammable, high conductivity electrolytes is of great importance. In this dissertation, a gel polymer electrolyte (GPE) consisting of ionic liquid, lithium salt, and a polymer has been developed for their application in lithium batteries. A comparative study between GPE and ionic liquid electrolyte (ILE) containing batteries shows a superior cyclic performance up to 5C rate and a better rate capability for 40 cycles for cells with GPE at room temperature. The improvement is attributed to GPE’s improved stability voltage window against lithium as well as higher lithium transference number. The performance of the GPE in lithium-sulfur battery system using sulfur-CNT cathodes shows superior rate capability for the GPE versus ILE for up to 1C rates. Also, GPE containing batteries had higher capacity retention versus ILE when cycled for 500 cycles vii at C/2 rate. Electrochemical impedance spectroscopy (EIS) studies reveal interfacial impedances for ILE containing batteries grew faster than in GPE batteries. The accumulation of insoluble Li2S2/Li2S on the electrodes decreases the active material thus contributes to capacity fading. SEM imaging of cycled cathodes reveals cracks on the surface of cathode recovered from ILE batteries. On the other hand, the improved electrochemical performance of GPE batteries indicates better and more stable passivation layer formation on the surface of the electrodes. Composite GPE (cGPE) containing micro glass fillers were studied to determine their electrochemical performance in Li batteries. GPE with 1 wt% micro fillers show superior rate capability for up to 7C and also cyclic stability for 300 cycles at C/2 rate. In situ, EIS also reveals a rapid increase in charge transfer resistance in GPE batteries, responsible for lowering the capacity during cycling. Improved ion transport properties due to ion-complex formations in the presence of the micro fillers, is evidenced by improved lithium transference number, ionic conduction, and ion-pair dissociation detected using Raman spectroscopy.

No description available.

This graduate work deals with the study and preparation of gel polymer electrolytes with flame retardants for lithium-ion batteries. The theoretical part describes the types of electrolytes, their features, benefits, how they differ and where they are used in detail. The basis of this section is gel electrolytes with flame retardants, to measure their electrical and electrochemical properties. The experimental part deals with the preparation of samples of gel electrolytes with different percentages of flame retardant, where varied species of flame retardants and measuring their electrical conductivity and potential windows. Impedance spectroscopy, cyclic voltammetry and dynamic-analytical thermal analysis were selected as measuring methods.

This work deals with preparation of PMMA based gel polymer electrolytes with high fire safety and high ionic conductivity. In the theoretical part of the work GPEs for Li – ion accumulators, fire safety tests, fire retardants are mentioned. Preparation of GPEs, electrical and other properties are described in the experimental part. Furthermore, new possible methods of gel preparation are discussed.

The present work deals with the research and development of gel polymer electrolytes and their applications. Thesis talks about the mechanisms that take place in gel electro-lytes. It also discusses the electroanalytical methods used in assessing the gel electro-lytes. The main focus of the work is the preparation of gel polymer electrolytes and compared their properties using methods of impedance spectroscopy, cyclic voltam-metry and methods of measurement of transference numbers. KEYWORDS

Dans le but d’améliorer les performances des micro-accumulateurs au lithium, de nouvelles voies de dépôt, compatibles avec des géométries texturées, sont actuellement explorées. Au cours de ce travail de thèse, un nouvel électrolyte solide déposé par voie « humide » a été développé. Ce matériau, composé d’un liquide ionique et d’un sel de lithium confinés dans une matrice solide, a été synthétisé par polymérisation in-situ d’un oligomère diméthacrylate. Afin de définir leurs caractéristiques de conduction ionique, de nouvelles méthodes, comme le suivi de la photo-polymérisation par impédance in-situ ou encore la réalisation d’un nouveau design de cellules à base de peignes interdigités, ont été développées. De plus, le transfert du lithium a été mesuré par RMN diffusionnelle. Une diminution significative de la vitesse de diffusion des ions Li+ après la photo-polymérisation a ainsi été mise en évidence. La spectroscopie Raman a permis de démontrer que celle-ci est due à la complexation des ions par les chaines de poly(oxyde d’éthylène) de la matrice solide. En outre, grâce aux observations de différentes compositions, un mécanisme de diffusion mixte des ions Li+ par migration dans le liquide et par sauts dans le solide a été identifié. Par conséquent, ces résultats nous ont permis de définir une stratégie pour améliorer la diffusion des ions Li+ : l’ajout d’un copolymère monofonctionnel a permis de diminuer la densité de réticulation de la matrice solide et ainsi d’optimiser la mobilité des chaines polymères. En effet, les performances de cyclage dans des empilements de micro-accumulateurs complets ont été améliorées. A température ambiante, ces résultats se sont révélés très proches de ceux obtenus avec l’électrolyte solide standard LiPON. En conclusion, l’analyse établie a permis de comprendre les liens entre structure et performances électrochimiques, ce qui a permis de dégager les voies d’amélioration les plus prometteuses pour ce type d’électrolytes. / New deposition techniques compatible with making tridimensional geometries are currently being investigated with the aim of improving the performances of lithium microbatteries. This work focuses on the development of a new quasi-solid electrolyte deposited by a “wet process”. An ionic liquid-based membrane containing a lithium salt was prepared by the photo-induced polymerization of a dimethacrylate oligomer. New methods such as a new type of conductivity cell based on planar interdigitated electrodes to measure ionic conductivity as well as in-situ monitoring of photo-polymerization using impedance spectroscopy were used. Transport properties of lithium ion were measured by PGSE-NMR. Interestingly, a significant reduction of lithium ion mobility was observed after UV-curing while the total ionic conductivity only decreased slightly. This phenomenon is due to the formation of lithium ion complexes with ethylene oxide moieties of the solid matrix, evidenced by Raman spectroscopy measurements. Additionally, we have shown that the structures of the complexes depend on the salt concentration and a dual solid/liquid transport mechanism was suggested. Hence, in order to improve lithium ion diffusion, a co-polymer was added in an attempt to decrease the cross-linking density of the solid matrix thus improving its segmental motion. The cyclability of the all solid state micro batteries was indeed improved. Comparable performances with the standard solid electrolyte LiPON were obtained at room temperature. In summary, it was established that electrochemical performances of the solid state microbatteries depend to a certain extent on the structure of the polymer electrolyte. Therefore it is possible to find new ways in designing these types of electrolytes for further improvement.

Au cours de cette thèse, un nouvel électrolyte polymère gel pour la réalisation de microbatteries au lithium a été développé. Le gel a été préparé par « confinement » d’une phase de N-propyl-N-méthylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) et de LiTFSI dans un réseau semi-interpénétré (sRip) de polymère (PVdFHFP/ réseau de POE). L’électrolyte gel a tout d’abord été optimisé et étudié en termes de propriétés physicochimiques et de transport ionique en fonction de sa composition. Ensuite, des batteries Li/LiNi1/3Mn1/3Co1/3O2 ont été assemblées en utilisant l’électrolyte sRip. Les performances ont par ailleurs été comparées aux systèmes de références utilisant l’électrolyte à base de POE ou de PVdF-HFP. Outre ses propriétés améliorées par rapport au PVdF-HFP et au réseau de POE (propriétés mécaniques, confinement), l’électrolyte sRip est compatible avec le procédé de dépôt de l’électrode négative en lithium par évaporation sous vide. L’électrolyte sRip optimisé a donc été utilisé pour fabriquer une nouvelle génération de microbatteries en s’affranchissant de l’électrolyte céramique, le LiPON, afin d’abaisser la résistance interne. Les microbatteries Li/sRip gel/LiCoO2 délivrent une capacité nominale stable de 850 μAh à C sur 100 cycles à 25°C. / In this thesis, a new polymer gel electrolyte was prepared and optimized for Li based microbatteries. The gel consisted of an ionic liquid based phase (P13FSI/LiTFSI) confined in a semi-interpenetrating polymers (sIPN) network (PVdF-HFP/crosslinked PEO). sIPN electrolytes were prepared and optimized according to the PVdFHFP/ crosslinked PEO ratio and the liquid phase fraction. Furthermore, the sIPN electrolyte was used as an electrolyte in Li/LiNi1/3Mn1/3Co1/3O2 battery. The performances of the battery (specific capacity, efficiency, cyclability) were determined and compared to batteries using a crosslinked PEO or PVdF-HFP based gel. Such a thin and stable sIPN electrolyte film enabled the preparation of Li based microbatteries using thermal evaporation deposition of lithium directly conducted on the sIPN electrolyte film. This assembly (Li/sIPN) was therefore used to prepare a LiCoO2/sIPN gel/Li quasi solid-state microbattery. This microbattery showed a stable nominal capacity of 850 μAh for over 100 cycles of charge and discharge under 1 C rate at 25°C.

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.

This master‘s thesis concerns gel polymer electrolytes formed on a methyl methacrylate base with selected types of nanoparticles. In the thesis are also analyzed the methods for measuring electrochemical properties. The practical portion deals with sample preparations of gel polymer electrolytes with different contents of alkaline salt in a solvent, creating gels with different nanoparticle content and comparing gel polymer electrolytes polymerized with heat and UV radiation. The thesis deals with the evaluation of these samples from the viewpoint of electrical conductivity and potential windows as well as thermal analysis of selected samples.