The development and commercialization of alkali ion secondary batteries has played a critical role in the development of personal electronics and electric vehicles. The recent increase in demand for electric vehicles has pushed for lighter batteries with a higher energy density to reduce the weight of the vehicle while with an emphasis on improving the mile range. A resurgence has occurred in lithium, and sodium, metal anode research due to their high theoretical capacities, low densities, and low redox potentials. However, Li and Na metal anodes suffer from major safety issues and long-term cycling stability. This dissertation focuses on the investigation of the interfacial chemistries between alkali metal-carbon host interactions and the electrode-electrolyte interactions of the cathode and anode with boron-based electrolytes to establish design rules for "lean" alkali metal composite anodes and improve long-term stability to enable alkali metal batteries for practical electrochemical applications. Chapter 2 of this thesis focuses on the design and preliminary investigation of "lean" lithium-carbon nanofiber (<5 mAh cm-2) composite anodes in full cell testing using a LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode. We used the electrodeposition method to synthesize the Li-CNF composite anodes with a range of electrodeposition capacities and current densities and electrolyte formulations. Increasing the electrodeposition capacity improved the cycle life with 3 mAh cm-2 areal capacity and 2% vinylene carbonate (VC) electrolyte additive gave the best cycle life before reaching a state of "rapid cell failure". Increasing the electrodeposition rate reduced cycling stability and had a faster fade in capacity. The electrodeposition of lithium metal into a 2D graphite anode significantly improved cycle life, implying the increased crystallinity of the carbon substrate promotes improved anode stability and cycling capabilities. As the increased crystallinity of the carbon anode was shown to improve the "lean" composite anode's performance, Chapter 3 focuses on utilizing a CNF electrode designed with a higher degree of graphitization and probing the interacting mechanism of Li and Na with the CNF host. Characterization of the CNF properties found the material to be more reminiscent of hard carbon materials. Electrochemical analysis showed better long-term performance for Na-CNF symmetric cells. Kinetic analysis, using cyclic voltammetry (CV), revealed that Na ions successfully (de)intercalated within the CNF crystalline interlayers, while Li ions were limited to surface adsorption. A change in mechanism was quickly observed in the Na-CNF symmetric cycling from metal stripping/plating to ion intercalation/deintercalation, enabling the superior cycling stability of the composite anode. Improving the Na metal stability is necessary for enabling Na-CNF improved long-term performance. Sodium batteries have begun to garner more attention for grid storage applications due to their overall lower cost and less volumetric constraint required. However, sodium cathodes have poor electrode-electrolyte stability, leading to nanocracks in the cathode particles and transition metal dissolution. Chapter 4 focuses on electrolyte engineering with the boron salts sodium difluoro(oxolato)borate (NaDFOB) and sodium tetrafluoroborate (NaBF4) mixed together with sodium hexafluorophosphate (NaPF6) to improve the electrode-electrolyte compatibility and cathode particle stability. The electrolytes containing NaDFOB showed improved electrochemical stability at various temperatures, the formation of a more robust electrode-electrolyte interphase, and suppression in transition metal (TM) reduction and dissolution of the cathode particles measured after cycling. In Chapter 5, we focus on the electrochemical properties and the anode-electrolyte interfacial chemistry properties of the sodium borate salt electrolytes. Similar to Chapter 4, the NaDFOB containing electrolytes have improved electrochemical performance and stability. Following the same electrodeposition parameters as Chapter 2, we find the NaDFOB electrolytes improves the stability of electrodeposited Na metal and the "lean" composite anode's cyclability. This study suggests the great potential for the NaDFOB electrolytes for Na ion battery applications. / Doctor of Philosophy / The ever-increasing demand for high energy storage in personal electronics, electric vehicles, and grid energy storage has driven for research to safely enable alkali metal (Li and Na) anodes for practical energy storage applications. Key research efforts have focused on developing alkali metal composite anodes, as well as improving the electrode-electrolyte interfacial chemistries. A fundamental understanding of the electrode interactions with the electrolyte or host materials is necessary to progress towards safer batteries and better battery material design for long-term applications. Improving the interfacial interactions between the host-guest or electrode-electrolyte interfaces allows for more efficient charge transfer processes to occur, reduces interfacial resistance, and improves overall stability within the battery. As a result, there is great potential in understanding the host-guest and electrode-electrolyte interactions for the design of longer-lasting and safer batteries. This dissertation focuses on probing the interfacial chemistries of the battery materials to enable "lean" alkali metal composite anodes and improve electrode stability through electrolyte interactions. The anode-host interactions are first explored through preliminary design development for "lean" alkali composite anodes using carbon nanofiber (CNF) electrodes. The effect on increasing the crystallinity of the CNF host on the Li- and Na-CNF interactions for enhanced electrochemical performance and stability is then investigated. In an effort to improve the capabilities of Na batteries, the electrode-electrolyte interactions of the cathode- and anode-electrolyte interfacial chemistries using sodium borate salts are probed using electrochemical and X-ray analysis. Overall, this dissertation explores how the interfacial interactions affect, and improve, battery performance and stability. This work provides insights for understanding alkali metal-host and electrode-electrolyte properties and guidance for potential future research of the stabilization for Li- and Na-metal batteries.

Li-ion battery technologies have transformed the consumer electronics and electric vehicles landscape over the last few decades. Single-crystal cathode materials with controllable physical properties including size, morphology, and crystal facets can aid researchers in developing relationships between physical characteristics, chemical properties, and electrochemical performance. High-voltage LiNi_0.5Mn_1.5O₄ (LNMO) materials are desirable as cathodes due to their low cost, low toxicity, and high capacity and energy density making them promising to meet increasing consumer demands for battery materials. However, transition metal dissolution, interfacial instability, and capacity fading plague these materials when paired with graphite, limiting their commercial capability. Furthermore, variation in Ni/Mn ordering can lead to complex multiphase co-existence and changes in Mn oxidation state and electrochemical performance. These properties can be adjusted during synthesis using a facile and tunable molten salt synthesis method. This dissertation focuses on the investigation of chemical and structural heterogeneities of LNMO prepared under different synthetic conditions at different length scales. In Chapter 2, the influences of molten salt synthesis parameters on LNMO particle size, morphology, bulk uniformity, and performance are evaluated revealing the difficulty of reproducible cathode synthesis. We utilize the X-ray nanodiffraction technique throughout this work, which provides high-resolution structural information. We develop a method to measure and relate lattice strain to phase distribution at the tens of nanometers scale. In Chapter 3, mapping lattice distortions of LNMO particles with varying global Mn oxidation states reveals inherent structural defects and distortion heterogeneities. In Chapter 4, we examine lattice distortion evolution upon chemical delithiation, Mn dissolution behaviors, and evaluate the chemical delithiation method as a means to replicate electrochemical cycling conditions. We further investigate lattice distortion spatially via in situ nanodiffraction during battery cycling in Chapter 5, illustrating the capabilities of the measurement to provide practical understanding of cathode transformations. From intra-particle to electrode materials level, heterogeneities that arise in cathode materials can dictate performance properties and degradation mechanisms and are necessary for researchers to understand for the improvement of Li-ion battery systems. The development of the nanodiffraction measurements aids in our understanding of inherent and dynamic materials chemical and structural heterogeneities. / Doctor of Philosophy / The invention of rechargeable Li-ion batteries in the 1990s has undeniably revolutionized modern civilization. Cell phones, laptops, grid energy storage, and electric vehicles have become fundamental fixtures of the 21st century. As technologies improve and requirements for advanced renewable energy storage have increased, researchers have sought to design longer lasting, faster charging, and more lightweight batteries. Modifying and finding new positive electrode materials is one way to improve the capabilities of modern batteries as their properties are governed by fundamental chemistry. High-voltage LiNi_0.5Mn_1.5O₄ (LNMO) is one such material that can allow for fast charging and high energy storage capacity, but its commercialization is hindered by complex physical and chemical properties, which can limit its lifetime in batteries. Large, particles with well-defined shapes are desirable to improve the stability of the materials; however, understanding their defects and structural heterogeneities is vital to continued optimization and requires advanced characterization techniques. In this dissertation, we characterize the physical phases and chemical properties of LNMO samples prepared under different conditions resulting in different particle shapes, sizes, and chemical distributions. An advanced X-ray nanodiffraction technique is used to measure phase distributions within individual particles while lab-based analytical techniques and electrochemical testing can determine bulk properties and battery performance of materials. Overall, the aim of this work is to develop techniques to measure structural and chemical heterogeneities of cathode materials at different length scales and to understand how they influence properties and performance in batteries. This work provides valuable insights into the inherent and dynamic properties of high-voltage electrode materials useful to advance our understanding of how these materials fail and to aid researchers in creating design principles to develop stable, high-performing future generations of rechargeable batteries.

The commercialization of lithium-ion batteries has played a pivotal role in the development of consumer electronics and electric vehicles. In recent years, much research has focused on the development and modification of the active materials of electrodes to obtain higher energies for a broader range of applications. High voltage spinel materials including LiNi_0.5Mn_1.5O_4-δ (LNMO) have been considered as promising cathode materials to address the increasing demands for improved battery performance due to their high operating potential, high energy density, and stable cycling lifetimes. In an effort to elucidate fundamental structure-property relationships, this thesis explores the tunable properties of single-crystal LNMO. Utilizing facile molten salt synthesis methods, the structural and electronic properties of LNMO can be well controlled. Chapter 2 of this thesis focuses on uncovering the effect of molten salt synthesis parameters including molten salt composition and synthetic temperature on the materials properties. A range of imaging, microscopic, and spectroscopic techniques are used to characterize structural and electronic properties which are investigated in tandem with electrochemical performance. Results indicate the Mn oxidation state is highly dependent on synthesis temperature and can dictate performance, while the molten salt composition strongly influences the particle morphology. In Chapter 3, we explore the concept of utilizing LNMO as a tunable support for heterogeneous metal nanocatalysts, where alteration of the support structure and electronics can have an influence on catalytic properties due to unique support effects. Ultimately, this work illustrates the tunable nature of single-crystal LNMO and can inform the rational design of LNMO materials for energy applications. / M.S. / The development of lithium-ion batteries has been fundamental to the expansion and prevalence of consumer electronics and electric vehicles in the twenty-first century. Despite their ubiquity, there is an ongoing drive by researchers to address the limitations and improve the quality and performance of lithium ion batteries. Much research has focused on altering the composition, structure, or properties of electrodes at the materials level to design higher achieving batteries. A fundamental understanding of how composition and structure effect battery performance is necessary to progress toward better materials. This thesis focuses on investigating the properties of LiNi_0.5Mn_1.5O_4-δ (LNMO). LNMO material is considered a promising cathode material to meet the increasing consumer demands for improved battery performance. Through the synthesis methods, the shape of individual particles and the global electronic properties of LNMO can be tuned. In this work, specific synthesis parameters are systematically tuned and the properties of the resultant LNMO materials are explored. Electrochemical testing also evaluates the performance of the materials and offers insights into how they may fair in real battery systems. In an effort to potentially recycle spent battery materials, LNMO is also utilized as a catalyst support. Alteration of shape and electronic properties of the LNMO support can influence the catalytic properties, or the ability of the material to enhance the rate of a chemical reaction. Overall, this thesis explores how LNMO can be tuned and utilized for different applications. This work provides insights for understanding LNMO properties and direction for the development of future battery materials.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24853号 / エネ博第462号 / 新制||エネ||87(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 野平, 俊之, 教授 萩原, 理加, 教授 佐川, 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第25387号 / 人博第1129号 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 吉田 鉄平, 教授 雨澤 浩史 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

Research into the processing conditions and parameters of polymeric nanocomposites has always been challenging to scientists and engineers alike. Many have developed tools and procedures to allow materials to be exploited and their properties improved with the addition of nanofillers to achieve the desired end material for various applications. Initial trials are mostly conducted using conventional small scale experiments using specialised equipment within the laboratory that can replicate the larger industrial equipment. This is a logical approach as it could save time and costs as many nanocomposites are relatively expensive to produce. Experiments have previously been done using the likes of the Haake twin screw extruder to manufacture nanocomposites within the laboratory but this research project has used a novel minimixer specifically developed to replicate mixing like large twin screw extrusion machines. The minimixer uses a twin paddle system for high shear mixing in conjunction with a single screw thus theoretically allowing an infinitely long recirculation. It is this ability to mix intensely whilst allowing for as long as desired recirculation which enables the replication in this very small mixer (10-30g capacity) of the mixing conditions in a large twin screw extruder. An added feature of the minimixer is that it can undertake inline data analysis in real time. The main experiments were conducted using a comprehensive DOE approach with several different factors being used including the temperature, screw speed, residence time, clay and compatibiliser loading and two polymer MFI¿s. The materials used included PP, Cloisite 20A, Polybond 3200, PET, Somasif MTE, Polyurethane 80A and Single / Multi-walled Carbon nanotubes. Detailed experimental results highlighted that rheological analysis of the nanocomposite materials as an initial testing tool were accurate in determining the Elastic and Loss modulus values together with the Creep and Recovery, Viscosity and Phase Angle properties in the molten state. This approach was also used in an additional set of experiments whereby the temperature, speed, residence time and compatibiliser were kept constant but the clay loading was increased in 1% wt. increments. These results showed that the G¿ & G¿¿ values increased with clay loading. Another important finding was the bi-axial stretching step introduced after the processing stage of the nanocomposite materials which highlighted a further improvement in the modulus values using rheological testing. Other tests included using inline monitoring to look into both the viscosity and ultrasound measurements in real time of the molten polymer nanocomposite through a slit die attachment to the minimixer. / EPSRC

Dans cette thèse, nous avons exploré les possibilités de réaliser des structures hybrides à base graphène (GBHS) par la fonctionnalisation bilatérale du graphène. Le premier chapitre donne une introduction générale sur le graphène et sur la littérature concernant les différentes méthodes d’intercalations de métaux dans le graphène. Le chapitre 2 décrit les techniques expérimentales utilisées. Le chapitre 3 concerne la fonctionnalisation du graphène épitaxié sur SiC (0001) par intercalation d'atome d’or. Les différents modes d'intercalation de l’or ont été mis en évidence par microscopie tunnelle (formation d'agrégats d'atomes d'or individuels et formation d'une couche d'or continue). La nature de ces atomes d'or intercalées a été examinée par des calculs d’image de densité de charge, et par Spectroscopie de Photoélectrons X (XPS). La modification de la structure de bande du graphène a aussi été mise en évidence par Spectroscopie de Photoélectrons UV Résolue Angulairement (ARPES) par des expériences sur synchrotron. Ces études ont révélé une forte extension de la singularité de Van Hove et une augmentation de la vitesse de Fermi. Afin d’agir sur cette extension de la singularité de Van Hove, des molécules fortement donneuses d'électrons, telle que la molécule de TetraThioFulvalene (TTF) ont été déposée sur graphène intercalé or et sur graphite (chapitre 4). La dépendance du transfert de charge de ces molécules avec leur conformation et la réactivité photochromique de ces molécules conjuguées sur le graphène ont également été abordés. Pour comprendre les propriétés structurales de ces molécules, des mesures photophysiques ont été effectuées qui apparaissant dans le chapitre 5. / In this thesis, we have explored the possibilities to realize a Graphene Based Hybrid structures (GBHs) by the functionalization of a graphene layer on both sides. The first chapter gives a general introduction about graphene and a literature review of different metal intercalations on graphene. The second chapter explains the experimental techniques used in this work. In chapter 3, we studied the functionalization of epitaxial graphene on SiC(0001) by gold intercalation. With the help of Scanning Tunneling Microscopy, we have evidenced and characterized different intercalation modes such as the formation of aggregates of individual gold atoms and the formation of a continuous gold layer between the top graphene and the buffer layer. The free standing nature of the intercalated gold atoms was examined by differential charge density plot, projected density of states calculations and further by X-ray photoelectron spectroscopy. The band structure modification of graphene due to these intercalated gold atoms was evidenced by Angle-resolved photoemission spectroscopy, which reveals a strong Van Hove extension and an increase of the Fermi velocity. Extend to this research, to obtain an extended Van Hove singularity usually observed in highly doped graphene; we studied highly electron donor molecules, TetraThioFullvalene (TTF) on pristine and gold intercalated graphene and on graphite (chapter 4). The dependence of charge transfer of these molecules with their conformation and the reactivity of photochromic with conjugated molecules on graphene were also discussed. To understand the structural properties of these molecules photophysical measurements were performed in chapter 5.

Le premier chapitre de cette thèse présente l’intérêt et la problématique de la fonctionnalisation du graphène. L’état de l’art actuel de cette thématique est présenté. Dans un deuxième chapitre, nous discutons de façon détaillée des techniques expérimentales. Le chapitre 3 est centré sur la modification du graphène par réaction de cycloaddition par molécules dérivées de maleimides. Dans cette étude, nous démontrons le greffage covalent de molécules sur graphène épitaxié sans défaut sur SiC, ainsi qu’une tendance d’ouverture de bande interdite à l’aide de caractérisations par spectroscopie Raman, XPS, ARPS et STM. L’augmentation du rapport ID /IG des pics Raman et des liaisons sp3 sur l’échantillon en fonction de la durée de réaction chimique confirme le greffage. Par analogie avec les bords de marche de type « zigzag » ou « armchair », l’étude des ondes de densité de charge générées sur le graphène par les molécules permet de déterminer la nature des sous-réseaux mis en jeu lors du greffage. Dans le chapitre 4, nous étudions l’intercalation du terbium dans le graphène épitaxié. Après intercalation, l’ARPES montre une structure de bande complexe dont une composante correspond à une monocouche de graphène fortement dopée n. Nous avons pu isoler cette composante et montrer qu’elle provient du découplage de la couche tampon du substrat par le Terbium. Ces résultats sont confirmés par les données XPS. Le graphène avec Terbium intercalé produit également un réseau de lignes visibles par imagerie STM, qui a l’échelle atomique à basse tension montrent les 6 atomes de carbone de la structure en nid d’abeille, confirmant ainsi la transformation de la couche tampon en graphène. / The first chapter of this thesis explains the general motivation and problematic of graphene functionalization. It presents the state of the art of current research in this field. In the second chapter we discuss the experimental techniques in detail. Chapter 3 of this thesis work focuses on covalent modification of graphene by cycloaddition reaction of maleimide derivative molecules. In these studies we have confirmed the grafting of molecules on epitaxial defect free graphene on SiC and a tendency to open a gap with the help of Raman spectroscopy, XPS, ARPES and STM studies. An increase in the ID /IG ratio for Raman signature and sp3 bonding on the sample with increasing reaction time confirmed the reaction of molecules. By drawing an analogy with the standing waves obtained on armchair step edges of graphene and standing waves generated by molecules it was possible to determine the location of grafted molecules on the graphene lattice. In chapter 4, studies on terbium intercalation of epitaxial graphene are discussed. After intercalation a complex band structure was observed by ARPES with one spectra corresponding to highly n-doped graphene monolayer. We were able to isolate this highly n-doped graphene and confirmed its origin from decoupling of buffer layer and making it graphene like. These results are also supported by the XPS data. STM images on Terbium intercalated on buffer layer samples showed an interesting pattern of lines, atomic resolution scans at low bias voltage on these lines showed 6 atoms of hexagon confirming the transformation of buffer layer into graphene layer.

The use of kaolinite for preparing functionalized materials for specialized applications is still a relatively niche research subject. This is in spite of its low cost, high availability, and the potential for covalently grafting organic functional groups to its inner and outer surfaces. These grafted compounds have been shown to be highly resistant to heat and solvents, making them very useful for certain applications, for example in polymer nanocomposite materials that require high thermal resistance during polymer processing. Solid state NMR has been shown to play an essential role in solving the structure of functionalized kaolinite materials, however the current knowledge base for these functionalized kaolinites is notably lacking for some nuclei such as 1H, 27Al and 17O. Research was undertaken to address these concerns by developing new synthetic strategies for preparing kaolinite based materials for use as nanocomposites and to examine commonly prepared modified kaolinite precursors materials by 1H and 27Al MAS NMR in an attempt to demonstrate their utility for characterizing kaolinite intercalated and grafted complexes. Solid state 1H NMR of a natural kaolinite, kGa-1b, identified two main proton signals attributed to inner and inner surface hydroxyl protons. The different affinity of these two types of hydroxyl groups towards exchange with deuterium was used to differentiate between the two. The 1H NMR spectra of a DMSO intercalated kaolinite, kDMSO, and a methanol grafted kaolinite, kmethoxy, were fitted with high accuracy using models consistent with the known structures of these materials. The 27Al MAS NMR spectra of a natural kaolinite, kGa-1b, a DMSO intercalated kaolinite, kDMSO, and a methanol grafted kaolinite, kmethoxy measured at 21.1T showed little difference between one another, while noticeable differences could be seen at 4.7T. 27Al MQMAS experiments found almost no difference between these materials in the multiple quantum dimension, suggesting the differences that were observed are a result of differences in quadrupolar parameters rather than chemical shifts. The 27Al NMR spectra of kGa-1b, kDMSO and kmethoxy were fitted with good accuracy using models consistent with known structures of these materials. Different Al(III) sites with CQ values varying by up to 0.6MHz were found. The 27Al NMR spectra of two different methanol grafted kaolinites were also compared and it was found that the intensities of the sites with lower values of CQ were dependent on the quantity of grafted aluminum sites. The interlayer space of kaolinite was functionalized with a block copolymer: poly(ethylene)-block-poly(ethylene glycol) using a kaolinite pre-intercalated with DMSO, kDMSO, and with a biodegradable polymer: poly(lactide) using a kaolinite pre-intercalated with urea, kurea, both by using melts of the polymer. The polymers were found to completely displace their precursors from the interlayer space giving a monolayer type arrangement of the polymer. Attempts were made to graft compounds containing polymerizable functional groups: 3-allyloxy-1,2-propanediol and ethylene glycol vinyl ether to kaolinite’s inner surfaces using a kaolinite pre-intercalated and grafted with methanol, kmethoxy, and a kaolinite pre-intercalated with DMSO, kDMSO, respectively. Both compounds were found to displace their precursors from the interlayer space, adopting a monolayer type arrangement. 13C and 29Si NMR results suggest 3-allyloxy-1,2-propanediol’s allyl group remains intact and partially keys into the clay mineral’s siloxane rings. Ethylene glycol vinyl ether was found to undergo intramolecular cyclization to form an acetal product, consuming its vinyl group in the process. This reaction was observed using an unmodified kaolinite, kGa-1b, suggesting that the clay mineral’s surfaces, both inner and outer, act as an acid catalyst.

Die Strukturen der Erdalkalimetall-Subnitride (EA2N) von Calcium, Strontium und Barium ermöglichen mit ihrem schichtartigen Aufbau aus EA6N-Oktaedern Intercalationsreaktionen. Die Redox-Intercalation von Stickstoff in Sr2N wurde an Einkristallen untersucht. Nur durch eine drastische Erhöhung des Reaktionsgasdruckes im Vergleich zu den Reaktionen an mikrokristallinen Proben wurde die Intercalation der Diazenidionen in die Kristalle zu Sr4N3 und SrN möglich. Für eine analoge Intercalation von Wasserstoff in Sr2N konnten die Reaktionsbedingungen dahingehend optimiert werden, dass erstmals phasenreines Strontiumnitridhydrid (Sr2N)H bzw. deuterid (Sr2N)D erhalten wurde. Anhand von Intercalationsreaktionen mit Sr2N Kristallen konnte gezeigt werden, dass der Intercalationsprozess, erkennbar an der deutlichen Farbänderung von schwarz nach bersteinfarben, von außen nach innen fortschreitet. Als Methode zur räumlich aufgelösten Analyse wurde die Laserablation, in Kombination mit einem ICP - Massenspektrometer (LA-ICP-MS) verwendet. In der Literatur beschriebene Quantifizierungsstrategien wurden auf die Anwendbarkeit für die gegebene Fragestellung untersucht. Mit der ortsaufgelösten Analyse von Einkristallen konnte gezeigt werden, dass die Intercalation von Stickstoff in die Kristalle kontinuierlich von den Kanten zur Kristallmitte fortschreitet.