Lithium ion batteries (LIBs) are widely used for storing and converting chemical energy into electrical energy. During battery operation, lithium ions move between electrode materials, enabling energy storage. However, aging mechanisms like lithium plating can negatively impact battery performance and lifetime. Lithium plating occurs when lithium ions are reduced to metallic lithium on the graphite electrode. The undesired Li plating in LIBs leads to dendrite formation that may puncture the separator, causing internal short-circuit and ultimately thermal runaway. This study aims to investigate the internal processes of LIBs during charge and discharge. Two analysis methods are employed: online electrochemical mass spectrometry (OEMS) and acoustic emission monitoring (AEM). OEMS is a gas analysis technique that combines electrochemical measurements with mass spectrometry to provide real-time testing of cells. OEMS allows identifying and quantifying gas evolution/consumption of chemical species. AE is a diagnostic tool, offering monitoring the health of LIBs through detection and characterisation of stress waves produced by parasitic mechano-electrochemical events. The results indicates that the formation of SEI thin film layer, generated gases like hydrogen and ethylene, while consuming carbon dioxide. During induced lithium plating, hydrogen and carbon dioxide were consumed, and ethylene gas was produced, due to new SEI film formation process. The acoustic emission analysis indicated that lithium plating was an active process, whereas SEI formation was less AE active. Further research is needed to understand the relationships and significance of these processes for battery performance and safety. Overall, this study highlighted the importance of investigating aging mechanisms in LIBs to enhance their performance and longevity. By combining OEMS and AE, it was possible to analyse the batteries behaviour during cycling. The evolution of gas and acoustic signals provided insights into the reactions and processes occurring inside the battery during cycling.

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It is known that organic monolayers on solid surfaces can enable electronic properties that are absent in the bulk of the solid materials. Often, once the organic film come into the contact with a solid surface, the established electronic interaction at their interface remains undisturbed. However, using a redox-active organic monolayer creates the possibility for modulating the extent and the direction of the interfacial charge transfer, establishing a switch at the interface. The theme of this thesis is investigation of the interfacial interaction of different redox states of a molecular switch, phenyl-capped aniline tetramer (PCAT) with iron oxide and graphite surfaces and their potential application in electronic devices. The nucleation and growth of submonolayer films of different oxidation states of PCAT on iron oxide surface was studied. Using atomic force microscopy and scaling island size distribution method the surface diffusion parameters of these islands were evaluated. Using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy the changes in these organic monolayers before and after interaction with iron oxide were demonstrated. However, these techniques were unable to provide similar data from the solid surface side of the interface. Instead, we were able to demonstrate the changes in the iron oxide film as a result of interfacial charge transfer using electrical conductivity measurement techniques. Based on this information a microfluidic chemical sensor based on the interface of pencil film and PCAT for quantification of free chlorine in drinking water was constructed. Using XPS and UV-vis spectroscopy it was shown that the interaction the organic monolayer with sodium hypochlorite solution leads to the development of positive charges on the backbone of PCAT. This electrostatic charge can affect the charge transport in the pencil film causing the modulation of electrical conductivity of the film. The presented work demonstrates alternative pathways for the design of novel hybrid electronic devices based on thin molecular film and solid surfaces. / Thesis / Doctor of Philosophy (PhD)

Le revêtement d'une cuve d'électrolyse est constitué en grande partie de matériaux à base de carbone. La caractérisation thermomécanique de ces matériaux est essentielle afin de modéliser leur comportement lors du préchauffage et en phase de production d'aluminium. Une vaste étude expérimentale a ainsi été élaborée afin de caractériser les cathodes de carbone et se veut une collaboration entre l'Université Laval et Carbone Savoie. Cette étude porte sur la détermination du module d'Young et de l'en-dommagemciit et ce, pour des températures allant de 25°C à 1000'C. Les échantillons cylindriques utilisés ont un diamètre de 50 mm, soit des échantillons de très grandes tailles considérant les contraintes techniques dans un contexte de caractérisation à haute température. Ce mémoire présente donc les résultats obtenus sur des échantillons de cathode de type graphitique pour des températures allant de la température ambiante jusqu'à la température d'opération.

Graphene is a two-dimensional carbon structure that exhibits remarkable structure-property relations. Consequently, there has been immense effort undertaken towards developing methods for graphene synthesis. Chemical vapor deposition (CVD) and chemical exfoliation from colloidal suspensions are two common methods used for obtaining graphene films. However, the underlying experimental conditions have to be carefully optimized in order to obtain graphene films of controllable thickness and morphology. In this context, a significant part of this dissertation was devoted towards developing and improving current CVD-based and chemical exfoliation based methods for synthesizing high quality graphene films. Specifically, in the CVD based procedure for growing graphene on copper, the effect of surface pretreatment of copper was investigated and the quality of graphene grown using two different pretreatment procedures was compared and analyzed. In particular, graphene grown on electropolished copper (EP-Cu) was analyzed with respect to its surface morphology, surface roughness and thickness, and compared with graphene grown on as cold-rolled acetic acid cleaned copper (AA-Cu). It was shown that electropolishing of the Cu substrates prior to graphene growth greatly enhanced the ability to obtain flat, uniform, predominantly single layer graphene surface coverage on copper. The reported surface roughness of the graphene on EP-Cu was found to be much lower than for previously reported systems, suggesting that the electropolishing procedure adopted in this work has great promise as a pretreatment step for Cu substrates used in CVD growth of graphene. Obtaining graphene from colloidal suspensions of graphitic systems was also examined. In this work, an acid (H₂SO₄ + HNO₃) treatment process for intercalating natural graphite flakes was examined and the ability to reversibly intercalate and deintercalate acid ions within graphitic galleries was investigated. More importantly, a rapid-thermal expansion (RTP) processing was developed to thermally expand the acid-treated graphite, followed by exfoliation of predominantly bilayer graphene as well as few layer graphene flakes in an organic solvent (N, N-Dimethylformamide - DMF). The developed method was shown to provide bilayer and few layer graphene flakes in a reliable fashion. Fullerene is another carbon nanostructure that has garnered attention due to unique structure and chemical properties. Recently, there has been increased focus towards harnessing the properties of fullerenes by synthesizing fullerene self-assemblies in the form of extended rods, tubes and more complex shapes. Current methods to synthesize these self-assemblies are either cumbersome, time consuming or expensive. In this context, an alternate, straightforward dip-coating procedure technique to self-assemble equal-sized, faceted, polymerized fullerene nanorods on graphene-based substrates in a rapid fashion was developed. By suitably modifying the kinetics of self-assembly, the ability to reliably control the spatial distribution, size, shape, morphology and chemistry of fullerene nanorods was achieved.

Cette thèse a été effectuée dans le cadre des projets DISTOR (Européen) et HTPSTOCK (Français) qui visent à concevoir et étudier de nouveaux composites graphite/sel destinés au stockage de l'énergie thermique à haute température (>200°C). Elle est scindée en deux parties distinctes. <br />La première partie détaille les travaux relatifs à l'élaboration et la caractérisation thermique de ces nouveaux composites. On y présente les différentes voies d'élaboration des composites (dispersion, compression uniaxiale, isostatique) associées aux différents types de graphite (graphite naturel expansé (GNE), graphite synthétique) investigués au cours de cette thèse. On y retrouve également les résultats liés à la campagne de caractérisation thermique de ces composites permettant de mettre en exergue l'impact du graphite sur les propriétés conductrices des matériaux étudiés. A partir de ces résultats, des études de modélisation de l'évolution de la conductivité thermique ont pu être entrepris afin d'approfondir la compréhension de l'effet du graphite (quantité, taille de particules) sur la conductivité effective des composites.<br />La deuxième partie présente essentiellement les dispositifs de caractérisation thermique et les modèles thermocinétiques associés qui ont du être développés et adaptés aux spécificités des matériaux nouvellement élaborés. Cela concerne principalement les matériaux élaborés par compression, matériaux difficilement reproductible et possédant des propriétés orthotropes. La caractérisation de ce type de matériaux s'avère très délicate et pour le moins fastidieuse. C'est pourquoi nous nous sommes attachés à développer et adapter les moyens de caractérisation existants afin de permettre la caractérisation thermique complète d'un matériau conducteur orthotrope à partir d'une seule mesure sur un seul échantillon

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Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

The thesis deals with a study of the various carbon materials for negative electrode of lithium ion accumulators. The object of the work is to gain the most knowledge about these materials and to project their possible improvements. In the first part of the work is described the latest knowledge about carbon materials and their application. In the following parts of the work is handled about manufacture,optimization of composition of electrode and the choice of carbon material for liquid and gel electrolyte.