<p dir="ltr">This dissertation addresses the significant challenge of enhancing the performance of lithium-ion batteries (LIBs) in extremely low-temperature environments, which is critical for applications in defense and space exploration. By innovating both electrolyte formulations and electrode materials, this research extends the operational boundaries of LIBs to temperatures below -100 ℃. </p>

The chemical element carbon plays a key role in the 21st century. “The new carbon age” is associated with the global warming due to increasing carbon dioxide emissions. The latter are a major consequence of the continued combustion of fossil fuels for energy generation. However, carbon is also one key component to overcome these problems. Especially porous carbon materials are highly attractive for many environmentally relevant applications. These materials provide high specific surface area, high pore volume, thermal/chemical stability, and high electrical conductivity. They are promising candidates for the removal of carbon dioxide or other environmentally relevant gases from exhaust gas mixtures. Furthermore, porous carbons are used in electrochemical energy storage devices (e.g. batteries or electrochemical capacitors). The performance of the materials in these applications depends on their pore structure. Hence, precise control over the pore size and the pore geometry is important to achieve. Besides a high specific surface area (SSA) and a well-defined pore size, pore accessibility must be ensured because the surface must be completely available. If the porous carbons exhibit ink-bottle pores, the high surface area is useless because the guest species do not reach the pore interior. Therefore, carbon materials with hierarchical pore structure are attractive. They combine at least two different pore systems of different size which contribute with their individual advantages. While smaller pores provide large specific surface area, larger pores ensure efficient mass transport. Numerous methods for the targeted synthesis of carbide-derived carbon materials (CDCs) with hierarchical pore architectures were developed within this thesis (Figure 1). CDCs are produced by the extraction of metal- or semi-metal atoms from carbide precursors leading to the formation of a microporous carbon network with high specific surface area. PolyHIPE-CDCs with porosity on three hierarchy levels and total pore volumes as high as 8.5 cm3/g were prepared by a high internal phase emulsion technique. CO2 activation increases the SSA to values above 3100 m2/g. These materials are promising for the filtration of non-polar organic compounds from gas mixtures. CDC nanospheres with diameters below 200 nm were obtained from polycarbosilane-based miniemulsions. They show high capacitance of up to 175 F/g in symmetrical EDLCs in 1 M H2SO4 aqueous electrolyte. Besides such emulsion techniques, the hard-templating concept (also referred to as nanocasting) was presented as an efficient approach for the synthesis of CDC mesofoam powders and meso-macroporous CDC monoliths starting from silica templates and polycarbosilane precursors. As a wide range of pore sizes is approachable, the resulting materials are highly versatile in terms of application. Due to their high nanopore volume, well-defined mesopores and large SSA, they show outstanding properties as electrode materials in EDLCs or in Li-S batteries as well as high and rapid uptake in gas adsorption processes. CDC aerogels were produced by pyrolysis and high-temperature chlorine treatment of cross-linked polycarbosilane aerogels. These materials can be tailored for efficient CO2 adsorption and show outstanding performance in EDLC electrodes at high current densities of up to 100 A/g due to the very short electron diffusion pathways within the aerogel-type pore system. It was further shown that CDCs can be combined with mesopores by the sacrificial template method starting from PMMA particles as the pore-forming material. The use of highly toxic hydrofluoric acid for template removal and large amounts of organic solvents as typical for hard- and soft-templating approaches can be overcome. SSAs and total pore volumes of 2434 m2/g and 2.64 cm3/g are achieved ensuring good performance of PMMA-CDCs in Li-S batteries cathodes. Besides the characterization of CDCs in real energy storage devices and adsorption processes, their use as model substances in energy- and environmentally relevant applications was part of this thesis. The questions “How does it work?” and “What do we need?” must be clearly answered before any material can be tailored under the consideration of economic and ecological perspectives. The high potential of CDCs for this purpose was shown in this thesis. These carbons were used as model substances in combination with nuclear magnetic resonance (NMR) techniques to get a detailed understanding of the adsorption processes on porous carbon surfaces. However, such investigations require the use of model substances with a tailored and well-defined pore structure to clearly differentiate physical states of adsorbed species and to understand fundamental mechanisms. The characterization of the interaction of electrolyte molecules with the carbon surface was performed with solid-state NMR experiments. The materials were also studied in the high-pressure adsorption of 129Xe using an in-situ NMR technique. Both NMR studies enable the analysis of ions or gas atoms adsorbed on the carbon surface on an atomic level and experimentally demonstrate different strength of interaction with pores of variable size and connectivity. In addition, the novel InfraSORP technology was used for the investigation of the thermal response of CDCs and templated carbon and carbide materials during n-butane adsorption. These model systems lead to a more profound understanding of this technique for the rapid characterization of porous materials. The Kroll-Carbon (KC) concept is a highly attractive alternative for the synthesis of well-defined carbons on the large scale. In this technique, the porous materials are produced by the reductive carbochlorination reaction between oxidic nanoparticles and a surrounding carbon matrix. First KC materials were produced with high SSA close to 2000 m2/g and total pore volumes exceeding 3 cm3/g. This method was established with template particles of various dimensions as well as by using various types of oxides (silica, alumina, titania). Hence, porous carbon materials with various textural parameters are approachable. The first generation of KCs is promising for the use in Li-S battery cathodes and as electrode materials in EDLCs.

Les supercondensateurs sont des dispositifs de stockage électrochimique de l’énergie ayant été récemment mis au point et possédant des performances intermédiaires entre les condensateurs diélectriques et les batteries. Leurs intéressantes valeurs de densité d’énergie et de puissance, conjuguées à leur excellente durée de vie et à leur miniaturisation facilité rendent ces composants prometteurs pour des micro-dispositifs électroniques, tels des micro-capteurs autonomes ou des implants médicaux.Le silicium nanostructuré par CVD a prouvé être un remarquable matériau d’électrode de supercondensateur, pour des applications miniaturisées, lors de récents travaux. L’excellent contrôle de la morphologie et des propriétés électroniques permis par la synthèse montante de nano-fils et nano-arbres de silicium, ainsi que la grande stabilité électrochimique et thermique de ce matériau font des nanostructures de silicium obtenues par synthèse montante une excellente plate-forme pour des micro-supercondensateurs.La présente thèse s’attache à explorer plusieurs voies d’amélioration et d’utilisation des nano-fils et nano-arbres de silicium. Une étude systématique de l’optimisation des nanostructures a été conduite, permettant d’améliorer largement les performances précédemment établies. Ensuite, une fonctionnalisation par des couches minces d’alumines utilisant la technique d’ALD a permis d’accroitre largement la plage de tensions d’utilisation des supercondensateurs, et d’augmenter leur stabilité électrochimique. Enfin, la croissance « sur-puce », ainsi que l’étude de la stabilité en température des dispositifs ont été effectuées, laissant entrevoir d’importantes perspectives d’applications. / Supercapacitors are electrochemical energy storage devices which have been recently developed, and possess intermediate performances between dielectric capacitors and batteries. These components exhibit interesting power and energy densities, combined with an exceptional cycle life and an easy miniaturization. Supercapacitors are thus envisioned as energy storage solutions for electronic micro-devices, such as autonomous micro-sensors or implantable medical devices.In recent studies, CVD nanostructured silicon proved to be an excellent electrode material candidate for micro-supercapacitor applications. Bottom-up synthesis allows an exceptional control of the morphology and electrical properties of the obtained silicon nano-wires and nano-trees. Moreover, the nanostructured electrodes possess superior electrochemical and temperature stability. These arguments lead to consider silicon as an excellent platform for micro-supercapacitors applications.This PhD thesis details various ways to improve and use silicon nano-wires and nano-trees. The nanostructures have been subjected to a systematic optimization study, yielding a significant increase of the electrochemical performances of the electrodes, compared to previously published studies. In addition, surface functionalization using thin ALD alumina layers permitted a considerable increase of the supercapacitor voltage window and an improved electrochemical stability. Finally, “on-chip” nanostructure growth, and temperature stability studies of the device were conducted, opening a broad field of improvements and potential uses for these silicon nanostructures.

The chemical element carbon plays a key role in the 21st century. “The new carbon age” is associated with the global warming due to increasing carbon dioxide emissions. The latter are a major consequence of the continued combustion of fossil fuels for energy generation. However, carbon is also one key component to overcome these problems. Especially porous carbon materials are highly attractive for many environmentally relevant applications. These materials provide high specific surface area, high pore volume, thermal/chemical stability, and high electrical conductivity. They are promising candidates for the removal of carbon dioxide or other environmentally relevant gases from exhaust gas mixtures. Furthermore, porous carbons are used in electrochemical energy storage devices (e.g. batteries or electrochemical capacitors). The performance of the materials in these applications depends on their pore structure. Hence, precise control over the pore size and the pore geometry is important to achieve. Besides a high specific surface area (SSA) and a well-defined pore size, pore accessibility must be ensured because the surface must be completely available. If the porous carbons exhibit ink-bottle pores, the high surface area is useless because the guest species do not reach the pore interior. Therefore, carbon materials with hierarchical pore structure are attractive. They combine at least two different pore systems of different size which contribute with their individual advantages. While smaller pores provide large specific surface area, larger pores ensure efficient mass transport. Numerous methods for the targeted synthesis of carbide-derived carbon materials (CDCs) with hierarchical pore architectures were developed within this thesis (Figure 1). CDCs are produced by the extraction of metal- or semi-metal atoms from carbide precursors leading to the formation of a microporous carbon network with high specific surface area. PolyHIPE-CDCs with porosity on three hierarchy levels and total pore volumes as high as 8.5 cm3/g were prepared by a high internal phase emulsion technique. CO2 activation increases the SSA to values above 3100 m2/g. These materials are promising for the filtration of non-polar organic compounds from gas mixtures. CDC nanospheres with diameters below 200 nm were obtained from polycarbosilane-based miniemulsions. They show high capacitance of up to 175 F/g in symmetrical EDLCs in 1 M H2SO4 aqueous electrolyte. Besides such emulsion techniques, the hard-templating concept (also referred to as nanocasting) was presented as an efficient approach for the synthesis of CDC mesofoam powders and meso-macroporous CDC monoliths starting from silica templates and polycarbosilane precursors. As a wide range of pore sizes is approachable, the resulting materials are highly versatile in terms of application. Due to their high nanopore volume, well-defined mesopores and large SSA, they show outstanding properties as electrode materials in EDLCs or in Li-S batteries as well as high and rapid uptake in gas adsorption processes. CDC aerogels were produced by pyrolysis and high-temperature chlorine treatment of cross-linked polycarbosilane aerogels. These materials can be tailored for efficient CO2 adsorption and show outstanding performance in EDLC electrodes at high current densities of up to 100 A/g due to the very short electron diffusion pathways within the aerogel-type pore system. It was further shown that CDCs can be combined with mesopores by the sacrificial template method starting from PMMA particles as the pore-forming material. The use of highly toxic hydrofluoric acid for template removal and large amounts of organic solvents as typical for hard- and soft-templating approaches can be overcome. SSAs and total pore volumes of 2434 m2/g and 2.64 cm3/g are achieved ensuring good performance of PMMA-CDCs in Li-S batteries cathodes. Besides the characterization of CDCs in real energy storage devices and adsorption processes, their use as model substances in energy- and environmentally relevant applications was part of this thesis. The questions “How does it work?” and “What do we need?” must be clearly answered before any material can be tailored under the consideration of economic and ecological perspectives. The high potential of CDCs for this purpose was shown in this thesis. These carbons were used as model substances in combination with nuclear magnetic resonance (NMR) techniques to get a detailed understanding of the adsorption processes on porous carbon surfaces. However, such investigations require the use of model substances with a tailored and well-defined pore structure to clearly differentiate physical states of adsorbed species and to understand fundamental mechanisms. The characterization of the interaction of electrolyte molecules with the carbon surface was performed with solid-state NMR experiments. The materials were also studied in the high-pressure adsorption of 129Xe using an in-situ NMR technique. Both NMR studies enable the analysis of ions or gas atoms adsorbed on the carbon surface on an atomic level and experimentally demonstrate different strength of interaction with pores of variable size and connectivity. In addition, the novel InfraSORP technology was used for the investigation of the thermal response of CDCs and templated carbon and carbide materials during n-butane adsorption. These model systems lead to a more profound understanding of this technique for the rapid characterization of porous materials. The Kroll-Carbon (KC) concept is a highly attractive alternative for the synthesis of well-defined carbons on the large scale. In this technique, the porous materials are produced by the reductive carbochlorination reaction between oxidic nanoparticles and a surrounding carbon matrix. First KC materials were produced with high SSA close to 2000 m2/g and total pore volumes exceeding 3 cm3/g. This method was established with template particles of various dimensions as well as by using various types of oxides (silica, alumina, titania). Hence, porous carbon materials with various textural parameters are approachable. The first generation of KCs is promising for the use in Li-S battery cathodes and as electrode materials in EDLCs.

<p>Energy storage devices have become an integral part of the digital infrastructure of the 21st century. Li-ion batteries are a widely used chemical form of energy storage devices comprising components with varied chemical, mechanical and electrochemical properties. Over long-term usage, the anode and cathode experience spatially heterogeneous Li reaction, mechanical degradation, and reversible capacity loss. The small particle size and environmental sensitivity of materials used in Li-ion battery materials make investigating electrodes' electrochemical and mechanical properties an arduous task. Nevertheless, understanding the effect of electrochemical fatigue load (during the battery's charging and discharging process) on composite electrodes' mechanical stability is imperative to design and manufacture long-lasting energy storage devices.</p><p>Due to the low-symmetry lattice, Lithium Nickel Manganese Cobalt Oxide (NMC) cathode materials exhibit direction-dependent (anisotropic) mechanical properties. In this Dissertation, we first measure the anisotropic elastic stiffness of NMC cathode material using nano-indentation. We also determine the effect of Ni stoichiometry on the indentation modulus, hardness, and fracture toughness of NMC materials. The complete information on the mechanical properties of cathode materials will enable accurate computational results and the design of robust cathodes.</p><p>Further, using operando optical experiments, we report that NMC porous composite cathode experiences asynchronous reactions only during the 1st charging process. Non-uniform carbon binder network coverage across the cathode and Li concentration-dependent material properties of NMC results in the initial asynchronous phenomenon. The information on the degree of electrochemical conditioning of Li-ion battery cathode obtained from optical microscopy can test the consistency of product quality in the industrial manufacturing process. We also investigate the effects of non-uniform reactions on active material’s local morphology change and study the evolution of particle network over long-term cycling. Reported data from experiments depicts that in the early cycles, individual particles’ characteristics significantly influence the degree of damage across the cathode.</p><p>However, the interaction with neighboring particles becomes more influential in later cycles. Computational modeling uses a multiphysics-based theoretical framework to explain the interplay between electrochemical activity and mechanical damage. The methodology, theoretical framework, and experimental procedure detailed here will enable the design of efficient composite electrodes for long-lasting batteries.</p>

The fast pyrolysis plant at RISE – ETC, Piteå produces carbon rich chars in bulk from various sources of biomass as feedstock. These in-house manufactured carbon rich chars were upgraded via pyrolysis as well as chemical activation using KOH to enhance their potential as an electrode material for supercapacitors. Commercial activated charcoal (Merck) was also studied and used as a yardstick for comparing performance of our materials. Investigations using EDX show enrichment in carbon content and very low amounts of impurities in the materials prepared from wood char after specific treatments for upgrading. Two-electrode coin cell apparatus with an aqueous electrolyte was used to determine the electrochemical performance of these materials. Wood char after KOH activation shows a high specific capacitance of ~105 Fg-1 at 2 Ag-1 in galvanostatic charge discharge measurements which outperformed activated charcoal used in this study (~68 Fg-1 at 2 Ag-1). This material was tested in a wide range of conditions (current density ranging from 0.1 Ag-1 to 10 Ag-1) and showed specific capacitance from ~90 Fg-1 (for 10 Ag-1) up to ~118 Fg-1 (for 0.1 Ag-1). Fatigue testing for &gt;20000 cycles showed a remarkably high retention (&gt;96%) of capacitance. Currently, most commercial supercapacitors use activated carbon materials prepared from coconut shells as the active electrode material which are not native to Sweden. In this study, we upgrade wood chars produced at RISE – ETC from biomass sources obtained locally (Sweden and Scandinavia) and demonstrate their applicability as supercapacitor electrode materials. / Den snabba pyrolysanläggningen vid RISE - ETC, Piteå, producerar kolrika kol i bulk från olika källor till biomassa som råvara. Dessa interna tillverkade kolrika karaktärer uppgraderades via pyrolys samt kemisk aktivering med hjälp av KOH för att förbättra deras potential som ett elektrodmaterial för superkondensatorer. Kommersiellt aktivt kol (Merck) studerades och användes som en måttstock för att jämföra våra materials prestanda. Undersökningar med EDX visar berikning av kolinnehåll och mycket låga mängder föroreningar i material som framställts av träkol efter specifika behandlingar för uppgradering. Tvåelektrodmyntcellapparater med en vattenhaltig elektrolyt användes för att bestämma den elektrokemiska prestandan hos dessa material. Träkol efter KOH-aktivering visar en hög specifik kapacitans på ~ 105 Fg-1 vid 2 Ag-1 i galvanostatiska laddningsurladdningsmätningar som överträffade aktivt kol som användes i denna studie (~ 68 Fg-1 vid 2 Ag-1). Detta material testades under ett stort antal betingelser (strömtäthet från 0,1 Ag-1 till 10 Ag-1) och visade specifik kapacitans från ~ 90 Fg-1 (för 10 Ag-1) upp till ~ 118 Fg-1 (för 0,1 Ag-1). Trötthetstestning för &gt; 20000 cykler visade en anmärkningsvärt hög retention (&gt; 96%) av kapacitansen. För närvarande använder de flesta kommersiella superkondensatorer aktivt kolmaterial framställt av kokosnötskal som det aktiva elektrodmaterialet som inte är hemma i Sverige. I den här studien uppgraderar vi träkolor som produceras vid RISE - ETC från biomassakällor erhållna lokalt (Sverige och Skandinavien) och visar deras användbarhet som superkapacitorelektrodmaterial.

Rechargeable Li-ion batteries and supercapacitors are the most promising electrochemical energy storage devices in terms of energy density and power density, respectively. Recently, nanostructured materials have gained enormous interest in the field of energy technology as they have special properties compared to the bulk. Commercially available Li-ion batteries, which are the most advanced among the rechargeable batteries, utilize microcrystalline transition metal oxides as cathode materials which act as lithium insertion hosts. To explore better electrochemical performance the use of nanomaterials instead of conventional materials would be an excellent alternative. High Li-ion insertion at high discharge rates causes slow Li+ transport which in turn results in concentration polarization of lithium ions within the electrode material, causing a drop in cell voltage. This eventually, leads in termination of the discharge process before realizing the maximum capacity of the electrode material being used. This problem can be addressed by decreasing the average particle size which leads to an increase in surface area of the electrode material. Nanostructured materials, because of their high surface area and large surface to volume ratio, to some extent can overcome the problem of slow diffusion of ions. Supercapacitors are electrical energy storage devices which can deliver large energy in a short time. A supercapacitor can be used as an auxiliary energy device along with a primary source such as a battery or a fuel cell to achieve power enhancement in short pulse applications. Active materials for supercapacitors are classified into three categories: (i) carbonaceous materials, (ii) conducting polymers and (iii) metal oxides. Among the materials studied over the years, metal oxides have been considered as attractive electrode materials for supercapacitors due to the following merits: variable oxidation state, good chemical and electrochemical stability, ease of preparation and handling. The performance of supercapacitors can be enhanced by moving from bulk to nanostructured materials. The theme of the thesis is to explore novel routes to synthesize nanostructured materials for Li-ion batteries and supercapacitors, and to investigate their physical and electrochemical characteristics. Chapter I is an introduction of various types of electrochemical energy systems such as battery, fuel cell and supercapacitor. A brief review is made on electrode materials for Li-ion batteries and supercapacitors, and nanostructured materials. Chapter II deals with the study of nanostrip orthorhombic V2O5 synthesized by a two-step procedure, with the formation of a vanadyl ethylene glycolate precursor and post-calcination treatment. The precursor and the final product are characterized for phase and composition by powder X-ray diffraction (XRD), infrared (IR) spectroscopy, thermal analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The morphological changes are investigated using field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). It is found that the individual strips have the following dimensions, length: 1.3 μm, width: 332 nm and thickness: 45 nm. The electrochemical lithium intercalation and de-intercalation of nanostrip V2O5 is investigated by cyclic voltammetry (CV), galvanostatic charge-discharge cycling, galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy. Chapter III describes the synthesis of nanoparticels of LiMn2O4 by microwave assisted hydrothermal method. The phase and purity of spinel LiMn2O4 are confirmed by powder XRD analysis. The morphological studies are carried out using FE-SEM and HRTEM. The electrochemical performance of spinel LiMn2O4 is studied by using CV and galvanostatic charge-discharge cycling. The initial discharge capacity is found to be about 89 mAh g-1 at a current density of 21 mA g-1 with reasonably good cyclability. Chapter IV deals with synthesis of MoO2 nanoparticles through ethylene glycol medium and its electrochemical characterization. XRD data confirms the formation MoO2 on monoclinic phase, space group P21/c. Polygon shape of MoO2 is observed in HRTEM. MoO2 facilitates reversible insertion-extraction of Li+ ions between 0.25 to 3.0 V vs. Li/Li+. CV and galvanostatic charge-discharge cycling are conducted on this anode material to complement the electrochemical data. Chapter V reports the synthesis of nanostructured MnO2 at ambient conditions by reduction of potassium permanganate with aniline. Physical characterization is carried out to identify the phase and morphology. The as prepared MnO2 is amorphous and it contains particles of 5 to 10 nm in diameter. On annealing at a temperature > 400 °C, the amorphous MnO2 attains crystalline α-phase with a concomitant change in morphology. A gradual conversion of nanoparticles to nanorods (length 500-750 nm and diameter 50-100 nm) is evident from SEM and TEM studies. High resolution TEM images suggest that nanoparticles and nanorods grow in different crystallographic planes. The electrochemical lithium intercalation and de-intercalation of nanorods was performed by (CV) and galvanostatic charge-discharge cycling. The initial discharge capacity of nanorod α-MnO2 is found to be about 197 mAh g-1 at a current density of 13.0 mA g-1. Capacitance behavior of amorphous MnO2 is studied by CV and galvanostatic charge-discharge cycling in a potential range from -0.2 to 1.0 V vs. SCE in 0.1 M sodium sulphate solution. The effect of annealing on specific capacitance is also investigated. Specific capacitance of about 250 F g-1 is obtained for as prepared MnO2 at a current density of 0.5 mA cm-2 (0.8 A g-1). Chapter VI pertains to electrochemical supercapacitor studies on nanostructured MnO2 synthesized by polyol method. Although X-ray diffraction (XRD) pattern of the as synthesized nano-MnO2 shows poor crystallinity, it is found that it is locally arranged in δ-MnO2 type layered structure composed of edge-shared network of MnO6 octahedra by Mn K-edge X-ray Absorption Near Edge Structure (XANES) measurement. Annealed MnO2 shows high crystalline tunneled based α-MnO2 as confirmed by powder XRD pattern and XANES. As synthesized MnO2 exhibits good cyclability as an electrode material for supercapacitor. In Chapter VII, capacitance behavior of nanostrip V2O5, TiO2 coated V2O5 and nanocomposites of PEDOT/V2O5 are presented. Structural and morphological studies are carried out by powder XRD, IR, TGA, SEM and TEM. Cyclic voltammogram of pristine V2O5 shows the regular rectangular shape indicating the ideal capacitance behavior in aqueous 0.1 M K2SO4. The SC value of pristine V2O5 is found to be about 100 F g-1. Nanostrip V2O5 is modified with TiO2 using titanium isobutoxide to enhance the capacitance retention upon cycling. Only 48 % of the initial capacitance remains in the case of pristine V2O5 after 100 cycles, while TiO2 coated V2O5 exhibits better cyclability with capacitance of 70 % of the initial capacitance. The capacitance retention is attributed to the presence of TiO2 on the surface of V2O5 which prevents the vanadium dissolution into the electrolyte. Microwave assisted hydrothermally synthesized PEDOT/V2O5 nanocomposites are utilized as capacitor materials. The initial SC of PEDOT/V2O5 (237 F g-1) is higher than that of either pristine V2O5 or PEDOT. The enhanced electrochemical performance is attributed to synergic effect and an enhanced bi-dimensionality. Details of the above studies are described in the thesis with a conclusion at the end of each Chapter.

Die Menschheit steht vor der großen Herausforderung der Energieversorgung des 21. Jahrhundert. Nirgendwo ist diese noch dringlicher geworden als im Bereich der Energiespeicherung und Umwandlung. Konventionelle Energie kommt hauptsächlich aus fossilen Brennstoffen, die auf der Erde nur begrenzt vorhanden sind, und hat zu einer starken Belastung der Umwelt geführt. Zusätzlich nimmt der Energieverbrauch weiter zu, insbesondere durch die rasante Verbreitung von Fahrzeugen und verschiedener Kundenelektronik wie PCs und Mobiltelefone. Alternative Energiequellen sollten vor einer Energiekrise entwickelt werden. Die Gewinnung erneuerbarer Energie aus Sonne und Wind sind auf jeden Fall sehr wichtig, aber diese Energien sind oft nicht gleichmäßig und andauernd vorhanden. Energiespeichervorrichtungen sind daher von großer Bedeutung, weil sie für eine Stabilisierung der umgewandelten Energie sorgen. Darüber hinaus ist es eine enttäuschende Tatsache, dass der Akku eines Smartphones jeglichen Herstellers heute gerade einen Tag lang ausreicht, und die Nutzer einen zusätzlichen Akku zur Hand haben müssen. Die tragbare Elektronik benötigt dringend Hochleistungsenergiespeicher mit höherer Energiedichte. Der erste Teil der vorliegenden Arbeit beinhaltet Lithium-Ionen-Batterien unter Verwendung von einzelnen aufgerollten Siliziumstrukturen als Anoden, die durch nanotechnologische Methoden hergestellt werden. Eine Lab-on-Chip-Plattform wird für die Untersuchung der elektrochemischen Kinetik, der elektrischen Eigenschaften und die von dem Lithium verursachten strukturellen Veränderungen von einzelnen Siliziumrohrchen als Anoden in einer Lithium-Ionen-Batterie vorgestellt. In dem zweiten Teil wird ein neues Design und die Herstellung von flexiblen on-Chip, Festkörper Mikrosuperkondensatoren auf Basis von MnOx/Au-Multischichten vorgestellt, die mit aktueller Mikroelektronik kompatibel sind. Der Mikrosuperkondensator erzielt eine maximale Energiedichte von 1,75 mW h cm-3 und eine maximale Leistungsdichte von 3,44 W cm-3. Weiterhin wird ein flexibler und faserartig verwebter Superkondensator mit einem Cu-Draht als Substrat vorgestellt. Diese Dissertation wurde im Rahmen des Forschungsprojekts GRK 1215 "Rolled-up Nanotechnologie für on-Chip Energiespeicherung" 2010-2013, finanziell unterstützt von der International Research Training Group (IRTG), und dem PAKT Projekt "Elektrochemische Energiespeicherung in autonomen Systemen, no. 49004401" 2013-2014, angefertigt. Das Ziel der Projekte war die Entwicklung von fortschrittlichen Energiespeichermaterialien für die nächste Generation von Akkus und von flexiblen Superkondensatoren, um das Problem der Energiespeicherung zu addressieren. Hier bedanke ich mich sehr, dass IRTG mir die Möglichkeit angebotet hat, die Forschung in Deutschland stattzufinden. / Human beings are facing the grand energy challenge in the 21st century. Nowhere has this become more urgent than in the area of energy storage and conversion. Conventional energy is based on fossil fuels which are limited on the earth, and has caused extensive environmental pollutions. Additionally, the consumptions of energy are still increasing, especially with the rapid proliferation of vehicles and various consumer electronics like PCs and cell phones. We cannot rely on the earth’s limited legacy forever. Alternative energy resources should be developed before an energy crisis. The developments of renewable conversion energy from solar and wind are very important but these energies are often not even and continuous. Therefore, energy storage devices are of significant importance since they are the one stabilizing the converted energy. In addition, it is a disappointing fact that nowadays a smart phone, no matter of which brand, runs out of power in one day, and users have to carry an extra mobile power pack. Portable electronics demands urgently high-performance energy storage devices with higher energy density. The first part of this work involves lithium-ion micro-batteries utilizing single silicon rolled-up tubes as anodes, which are fabricated by the rolled-up nanotechnology approach. A lab-on-chip electrochemical device platform is presented for probing the electrochemical kinetics, electrical properties and lithium-driven structural changes of a single silicon rolled-up tube as an anode in lithium ion batteries. The second part introduces the new design and fabrication of on chip, all solid-state and flexible micro-supercapacitors based on MnOx/Au multilayers, which are compatible with current microelectronics. The micro-supercapacitor exhibits a maximum energy density of 1.75 mW h cm-3 and a maximum power density of 3.44 W cm-3. Furthermore, a flexible and weavable fiber-like supercapacitor is also demonstrated using Cu wire as substrate. This dissertation was written based on the research project supported by the International Research Training Group (IRTG) GRK 1215 "Rolled-up nanotech for on-chip energy storage" from the year 2010 to 2013 and PAKT project "Electrochemical energy storage in autonomous systems, no. 49004401" from 2013 to 2014. The aim of the projects was to design advanced energy storage materials for next-generation rechargeable batteries and flexible supercapacitors in order to address the energy issue. Here, I am deeply indebted to IRTG for giving me an opportunity to carry out the research project in Germany. September 2014, IFW Dresden, Germany Wenping Si

L'objectif de ce travail est de développer et d’étudier une nouvelle classe de fluidesintelligents à base de dispersions colloïdales de carbone, sensibles à un stimulus externe pour desapplications de conversion et stockage d’énergie. Ces stimuli sont de différentes natures : vibrationmécanique, mouvement humain, variation de pression ou écoulement d'un solvant, et peuventaltérer les structures de tels systèmes. Ceci induit une modification de la structure locale desparticules et par conséquent des propriétés diélectriques et électriques. Habituellement, lessuspensions de matériaux carbonés sont étudiées au repos ou séchées. Toutefois, comprendre leurcomportement en flux est essentiel pour de nouvelles applications où ces matériaux sont exploitésdans des conditions dynamiques telle que le stockage d'énergie électrochimique assisté par flux(FAES). Par exemple, les matériaux à base de graphène jouent désormais un rôle important dans lesnouvelles technologies énergétiques. Ils sont utilisés comme additifs conducteurs dans lesassemblages d'électrodes, mais en raison de leur forme anisotrope spécifique, ils permettentégalement d’obtenir des fluides diélectriques sous écoulement.Les cristaux liquides d'oxyde de graphène, en tant que matériau souple électrostrictif, sont étudiéspour la récupération d'énergie mécanique, ainsi que des dispersions de noir de carbone pour lestockage d'énergie.Les propriétés diélectriques et électriques de ces dispersions fluides dans des conditions statiques etdynamiques sont mesurées et analysées. Enfin, l’effet de l’écoulement sur l’orientation et laréorganisation locale des particules et leur comportement diélectrique et électrique sont examinés. / The aim of this work is to develop and study a new class of smart fluids made of colloidalcarbon-based dispersions, which are sensitive to an external stimulus for energy storage orconversion applications. The effect of an external input, such as mechanical vibration, humanmotion, variable pressure, flowing of a solvent, can alter the structures of such systems.Consequently these changes induce modifications of the dielectric and electrical properties. Usually,the suspensions of carbon materials are investigated at rest or dried. However, their flow behavior iscritical when new technologies, which exploit these materials in dynamic conditions such as FAES(Flow-Assisted Electrochemical Energy Storage) are considered. For example, graphene-basedmaterials are now playing a significant role in energy materials. They act as conductive additives inelectrode assemblies, but due to their specific anisotropic shape they also provide a new route toachieve dielectric liquid media.In details, Graphene Oxide liquid crystals as electrostrictive soft material for mechanical energyharvesting and Carbon black dispersions as percolated flowable electrodes for capacitive energystorage are investigated.In particular, the dielectric and electrical properties of these flowable dispersions are studied understatic and dynamic conditions. The effect of the flow-rate on the local orientation and reorganizationof the particles and their related dielectric and electrical behavior are examined.

Lack of energy storage is a key issue in the development of renewable energy sources. Most renewables, especially solar and wind, when used alone, cannot sustain a reliably constant power output over an extended period of time. These sources generally generate variable amounts of power intermittently, therefore, an efficient electrical energy storage (EES) method is required to better temporally balance power generation to power consumption. One of the more promising methods of electrical energy storage is the unitized regenerative fuel cell (UFRC.) UFRCs are fuel cells that can operate in a charge-discharge cycle, similar to a battery, to store and then to subsequently release power. Power is stored by means of electrolysis while the products of this electrolysis reaction can be recombined as in a normal fuel cell to release the stored power. A major advantage of UFRCs over batteries is that storage capacity can be decoupled from cell power, thus reducing the potential cost and weight of the cell unit. Here we investigate UFRCs based on hydrogen-halogen systems, specifically hydrogen-bromine, which has potential for improved electrode reaction kinetics and hence cheaper catalysts and higher efficiency and energy density. A mathematical model has been developed to analyze this system and determine cell behavior and cycle efficiency under various conditions. The conventional H2-Br2 URFCs, however also so far have utilized Pt catalysts and Nafion membranes. Consequently, a goal of this work was to explore alternate schemes and materials for the H2-Br2 URFC. Thus, three generations of test cells have been created. The first two cells were designed to use a molten bromide salt, ionic liquid or anion exchange membrane as the ion exchange electrolyte with the liquids supported on a porous membrane. This type of system provides the potential to reduce the amount of precious metal catalyst required, or possibly eliminate it altogether. Each cell showed improvement over the previous generation, although the results are preliminary. The final set of results are promising for anion exchange membranes on a cost basis compared Nafion. Another promising energy storage solution involves liquid methanol as an intermediate or as a hydrogen carrier. An alternative to storing high-pressure hydrogen is to produce it on-board/on-site on demand via a methanol electrocatalytic reformer (eCRef), a PEM electrolyzer in which methanol-water coelectrolysis takes place. Methanol handling, storage, and transportation is much easier than that for hydrogen. The hydrogen produced via methanol eCref may then be used in any number of applications, including for energy storage and generation in a standard H2-O2 PEM fuel cell. The mathematical modeling and analysis for an eCref is very similar to that of the HBr URFC. In this work, a comprehensive model for the coelectrolysis of methanol and water into hydrogen is created and compared with experimental data. The performance of the methanol electrolyzer coupled with a H2-O2 fuel cell is then compared for efficiency to that of a direct methanol fuel cell data and was found to be superior. The results suggest that an efficient and small paired eCRef-fuel cell system is potentially be a cheaper and more viable alternative to the standard direct methanol fuel cell. Both the H2-Br2 URFC and the methanol eCref in combination with a H2-O2 fuel cell have significant potential to provide higher energy efficiency and energy density for EES purposes.