Philosophiae Doctor - PhD (Chemistry) / Supercapacitors, also known as ultracapacitors or electrochemical capacitors, are considered one of the most important subjects concerning electricity or energy storage which has proven to be problematic for South Africa. In this work, graphene oxide (GO) was supported with platinum, silver and copper nanoparticles anchored with dodecylbenzenesulphonic acid (DBSA) doped polyaniline (PANI) to form nanocomposites. Their properties were investigated with different characterization techniques. The high resolution transmission electron microscopy (HRTEM) revealed GO's nanosheets to be light, flat, transparent and appeared to be larger than 1.5 ?m in thickness. This was also confirmed by high resolution scanning electron microscopy (HRSEM) with smooth surfaces and wrinkled edges observed with the energy dispersive X-ray analysis (EDX) confirming the presence of the functional groups such as carbon and oxygen. The HRTEM analysis of decorated GO with platinum, silver and copper nanoparticles (NPs) revealed small and uniformly dispersed NPs on the surface of GO with mean particle sizes of 2.3 ± 0.2 nm, 2.6 ± 0.3 nm and 3.5 ± 0.5 nm respectively and the surface of GO showed increasing roughness as observed in HRSEM micrographs. The X-ray fluorescence microscopy (XRF) and EDX confirmed the presence of the nanoparticles on the surface of GO as platinum, silver and copper which appeared in abundance in each spectra. Anchoring the GO with DBSA doped PANI revealed that single GO sheets were embedded into the polymer latex, which caused the DBSA-PANI particles to become adsorbed on their surfaces. This process then appeared as dark regions in the HRTEM images. Morphological studies by HRSEM also supported that single GO sheets were embedded into the polymer latex as composite formation appeared aggregated and as bounded particles with smooth and toothed edges.

Batteries based on lithium-sulfur technology have the potential to increase the amount of stored energy in comparison with current lithium-ion systems while maintaining the same weight. Achieving this goal is possible due to the high theoretical energy density of sulfur, which exceeds the values of other materials used in batteries. However, these batteries suffer from several failing, which still hinder the practical use. The use of amorphous sulfur instead of its crystalline form might lead to increasing of durability and charge efficiency. Inverse vulcanization of sulfur seems to be the perspective method for the preparation of polymer sulfur because it prevents its recrystallization and stabilizes amorphous sulfur. The aim of this thesis is the preparation and study of properties of materials made of inverse vulcanized sulfur.

This diploma thesis deals with problematics of electrochemical power sources with focus on lithium accumulators, their construction and functioning priciple. It also discusses the safety of li-ion batteries with respect to their flammability. In addition, the flame retarders, which help to lower the flammability, are listed. The thesis describes Cyclic Voltammetry and Galvanostatic Cycling with Potencial which are lithium-ion cell measuring methods. In the last part, the influence of various flame retarders on negative electrode is compared based on the conducted tests.

Das Ziel der Arbeit bestand darin, die aus der Literatur bekannten Zusammenhänge zwischen Korrosionsaktivität von Stahl im Beton und einer galvanostatischen Pulsmessung, welche unter Laborbedingungen gute Ergebnisse liefern, auf Messungen an realen Bauwerken anzuwenden. Dazu wurden zunächst Untersuchungen an 13 Jahre alten Prüfkörpern durchgeführt und ausgewertet. Die abgeleiteten Zusammenhänge konnten anschließend an realen Bauteilen verifiziert werden. Somit stellt die galvanostatische Pulsmessung eine hilfreiche zerstörungsfreie Prüfmethode zur Interpretation des Korrosionszustandes dar. Die neuen Erkenntnisse lassen eine bessere Einschätzung des Korrosionsverhaltens in Stahlbetonbauwerken zu, als es die Potentialmessung erlaubt.

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Depuis la mise en évidence des potentialités du phosphate LiFePO4 comme électrode positive de batteries lithium-ion, un très fort regain d’intérêt pour les phosphates de fer est actuellement observé. Dans cette optique de recherche de nouveaux matériaux, notre intérêt s’est porté sur la phase Na3Fe3(PO4)4 et sur des monophosphates de fer et de manganèse de type alluaudite LiXNa1-XMnFe2(PO4)3. Leurs structures, respectivement en couche et en chaines, en font de bons candidats pour des applications en tant que matériau d’électrode pour des batteries au lithium ou au sodium. Notre étude porte donc, d’une part, sur la synthèse et la caractérisation structurale de ces phases, et d’autre part sur leurs propriétés physiques et électrochimiques. / Since the discovery of highly interesting properties for LiFePO4 as a positive electrode material in lithium ion batteries, the search for novel polyanion-based insertion hosts is intense. Actually, cathodic materials based on iron phosphates exhibit high stability and economical and environmental interests. In this context, we were interested in Na3Fe3(PO4)4 with a lamellar structure and in alluaudite-like iron and manganese phosphates LiXNa1-XMnFe2(PO4)3 which structure exhibits tunnels. This work deals, in one hand, on the synthesis and the structural characterisation of these materials and in the other hand on their physical and electrochemical properties as positive electrode for lithium and sodium batteries.

En remplaçant l’électrolyte liquide par un solide, les batteries tout-solide massivessont souvent considérées comme une solution aux problèmes de sécurité desbatteries Li-ion actuelles. La récente découverte du matériau Li10GeP2S12 destructure dite LGPS présentant une conductivité ionique équivalente à celles desélectrolytes liquides a réactivé ce domaine de recherche.Dans cette optique, nous avons étudié les matériaux Li10MP2S12 (M=Sn, Si) destructure LGPS, au moyen de diverses caractérisations structurales (DRX,RMN du 31P, spectroscopie Mössbauer …), de propriétés de mobilité/conductionionique (RMN du 7Li, spectroscopie d’impédance) et de propriétés électrochimiques(voltammétrie cyclique, cyclage galvanostatique).Les échantillons commerciaux de Li10SnP2S12 contiennent des impuretés et uneincertitude subsiste sur la composition de la phase de structure LGPS. Lamodélisation des déplacements de RMN du 31P a notamment permis de mettre enévidence l’influence des lithium en site octaédrique adjacents. Les mesuresd’impédance suggèrent une réactivité avec le Li métallique et la voltammétrieconfirme que cette phase est très instable à bas potentiel, excluant son utilisation entant que simple électrolyte dans une batterie tout-solide. Nous proposons qu’il puisseêtre utilisé à la fois comme électrolyte et comme matériau de négative.L’étude préliminaire des matériaux au silicium souligne la difficulté d’obtention dematériau pur de structure LGPS, et conduit à la mise en cause du modèle structuraldit thio-LiSICON. Par ailleurs, elle montre là encore l’instabilité de ces matériauxface au lithium métal. / By replacing the liquid electrolyte by a solid one, solid state batteries are oftenconsidered as a solution to safety issues in current Li-ion batteries. The recentdiscovery of Li10GeP2S12 with so-called LGPS structure, which exhibits an ionicconductivity equivalent to that of liquid electrolytes, has boosted related researchactivities.In this perspective, we studied the Li10MP2S12 (M=Sn, Si) materials with LGPSstructure, using various methods to characterize the structure (XRD, 31P NMR,Mössbauer spectroscopy …), the ionic mobility/conductivity (7Li NMR, Impedancespectroscopy), and the electrochemical properties (cycling voltammetry,galvanostatic cycling) of the material.Commercially available Li10SnP2S12 batches contain impurities and there remains anambiguity in the actual composition of the LGPS type phase. Modelling of the 31PNMR shifts reveals the effect of lithium in neighboring octahedral sites. Impedencemeasurements suggest reactivity with Li metal, and cyclic voltammetry confirms thatthe material is highly unstable at low potential, which excludes its use as a simpleelectrolyte in solid state batteries. We propose that it might be used both as anelectrolyte and as a negative electrode.The preliminary study on silicon based materials highlights difficulties in obtaining apure LGPS-type compound and questions the real nature of the so-calledthio-LiSICON structural model. Besides, it also shows the instability of thesematerials versus lithium metal.

Magister Scientiae - MSc (Chemistry) / Blending polymers together offers researchers the ability to create novel materials that have a combination of desired properties of the individual polymers for a variety of functions as well as improving specific properties. The behaviour of the resulting blended polymer or blend is determined by the interactions between the two polymers. The resultant synergy from blending an intrinsically conducting polymer like polyaniline (PANI), is that it possesses the electrical, electronic, magnetic and optical properties of a metal while retaining the poor mechanical properties, solubility and processibility commonly associated with a conventional polymer. Aromatic polyamic acid has outstanding thermal, mechanical, electrical, and solvent resistance properties that can overcome the poor mechanical properties and instability of the conventional conducting polymers, such as polyaniline.

The purpose of this diploma thesis is to describe the impact of compaction pressure on the electrochemical parameters of lithium-sulfur batteries. Theoretical part of this thesis contains briefly described terminology and general issues of batteries and their division. Every kind of battery is provided with a closer description of a specific battery type. A separate chapter is dedicated to lithium cells, mainly lithium-ion batteries. Considering various composition of lithium-ion batteries, this chapter deeply analyzes mostly used active materials of electrodes, used electrolytes and separators. Considering that the electrochemical principle of Li-S and Li-O batteries is different to Li-ion batteries, these accumulators of new generation are included in individual subhead. In the experimental part of this thesis are described methods used to measure electrochemical parameters of Li-S batteries. Next chapter contains description of preparing individual electrodes and their composition. Rest of the experimental part of my thesis is dedicated to the description of individual experiments and achieved results.