<p>Open questions remain on the influence of various conditions and ion behavior on the hydration-shell of oily molecules. My research uses Raman spectroscopy and Raman multivariate curve resolution to study the hydration-shell of oily molecules as tools to help answer some of these open questions.</p><p>More specifically, I present results on the effect of molecular crowding on the structure of water around various oily molecules, and report the effect of molecular crowding on hydrophobic crossover. These results are important, as crowding has the potential to influence several fields, such as biology and environmental sciences. This work shows that increasing molecular concentration results in oil-oil crowding, decreases the tetrahedrality of the water structure around the oily molecules, and subsequently, the crossover temperature.</p><p>In addition to studying the hydration-shell under crowded conditions, I also present work on ion affiliation for the hydration-shell of an oily molecule. Ion affiliation for oil/water interfaces has been an ongoing topic of research since the Hoffmeister experiments because of their effect on biological processes. This study focuses on hydroxide and its affiliation for tert-butyl alcohol in comparison to other electrolytes. These results show iodide is less repelled by the oil/water interface in comparison to hydroxide.</p><p>Finally, I present findings on the influence of hydrogen peroxide in comparison to other small molecules on the water structure of an oily molecule. Hydrogen peroxide has been shown to reach supercooled temperatures, which may be useful in future studies of liquid phase transitions or studies on solute behavior at supercooled conditions. It is found that hydrogen peroxide does not significantly influence the water structure around tert-butyl alcohol, while other small molecules display significant water structure changes.</p><p>All these projects aim to contribute results to heated debates, as well as share information for future experiments.</p>

Owing to the increased anthropogenic CO₂ emissions over the last several decades, there have been tremendous global efforts in the deployment of renewable energy technologies. However, due to intermittency issues of renewable energy generation and a current lack of reliable long-term energy storage solutions, the development of innovative electrolytes for sustainable energy storage and chemical reactions is an emerging research area. In particular, materials that can host multiple reactions and separations, such as the integrated capture and conversion of CO₂, are highly desired. The direct coupling of renewable energy generation with electrochemical CO₂ conversion to chemicals and fuels is one of the transformative pathways that can aid the global transition to carbon-neutrality, depending on the source of CO₂. However, the current solubility of CO₂ in aqueous electrolytes is quite low (34 mM), thus limiting overall reaction performance. Liquid-like Nanoscale Organic Hybrid Materials (NOHMs) consist of a polymer tethered to a nanoparticle surface and possess a number of favorable properties which are highly desirable in electrochemical applications, including negligible vapor pressure, chemical tunability, oxidative thermal stability and high conductivity. To date, NOHMs have been successfully demonstrated for use as water-lean CO₂ capture solvents, as the polymer canopy can be tuned to capture CO₂ under various sets of operating conditions. Thus, in this dissertation, we have explored the thermal, transport and structural properties of NOHMs in their application as electrolytes enabling the integrated capture and conversion of CO₂. Liquid-like NOHMs functionalized with an ionic bond have been shown to display greatly enhanced oxidative thermal stability compared to the untethered polymer. However, our previous studies were limited in terms of reaction conditions and the detailed mechanisms of the oxidative thermal degradation were not reported. In this study, a kinetic thermal degradation analysis was performed on NOHM-I-HPE and the neat polymer, Jeffamine M2070 (HPE), in both non-oxidative and oxidative conditions. NOHM-I-HPE displayed similar thermal stability to the untethered polymer in a nitrogen environment, but interestingly, the thermal stability of the ionically tethered polymer was significantly enhanced in the presence of air. This observed enhancement of oxidative thermal stability is attributed to the orders of magnitude larger viscosity of the liquid-like NOHMs compared to untethered polymer and the bond stabilization of the ionically tethered polymer in the NOHMs canopy. This study illustrated that NOHMs can serve as functional materials for sustainable energy storage applications because of their excellent oxidative thermal stability, when compared to the untethered polymer. Though NOHMs composed of an ionic bond have demonstrated a high conductivity and an enhanced oxidative thermal stability, their practical application in the neat state is limited by an inherently high viscosity. Thus, when incorporating NOHMs in electrolytes for CO₂ capture and conversion applications, it will be necessary to mix them with a secondary fluid. In this study, a series of binary mixtures of NOHM-I-HPE with five different secondary fluids – water, chloroform, toluene, acetonitrile, and ethyl acetate – were prepared to reduce the fluid viscosity and investigate the effects of secondary fluid properties (i.e., hydrogen bonding ability, polarity, and molar volume) on their transport behaviors including viscosity and diffusivity. Our results revealed that the molecular ratio of secondary fluid to the ether groups of Jeffamine M2070 (λSF) was able to describe the effect that secondary fluid has on transport properties. Our findings also suggest that in solution, the Jeffamine M2070 molecules exist in different nano-scale environments, where some are more strongly associated with the nanoparticle surface than others, and the conformation of the polymer canopy was dependent on the secondary fluid. This understanding of the polymer conformation in NOHMs can allow for the better design of an electrolyte capable of capturing and releasing small gaseous or ionic species. To further investigate the effect of the bond type on the thermal stability as well as the structural and transport properties of the tethered HPE, NOHMs were synthesized by tethering HPE to SiO₂ nanocores via ionic (NOHM-I-HPE) and covalent (NOHM-C-HPE) bonding at two grafting densities. In the neat state, NOHM-C-HPE displayed the highest thermal stability in a nitrogen atmosphere, while NOHM-I-HPE was the most thermally stable under oxidative conditions. Small-angle neutron scattering (SANS) revealed the presence of multiple types of Jeffamine M2070 (HPE) polymers in aqueous solutions of NOHM-I-HPE (i.e., tethered, interacting and free), whereas only tethered HPE chains were observed in NOHM-C-HPE systems. Moreover, the SANS profiles identified clustering of NOHM-C-HPE in dilute aqueous solutions, but not in the corresponding NOHM-I-HPE samples, suggesting that the different types of HPE chains in solutions of NOHM-I-HPE may be crucial to the uniform NOHMs dispersion. Additionally, our investigation of the viscosity and conductivity of different NOHM-based electrolytes revealed that in response to ionic stimulus, the covalently tethered HPE remained fixed at the nanoparticle surface, whereas there was a partial disassociation of HPE chains from the nanoparticle in NOHM-I-HPE. Overall, the results of this study highlight that NOHMs are highly tunable materials whose properties can be strategically altered by changing the bond type linking the polymer to the nanoparticle, as well as grafting density. Finally, two types of aqueous NOHM-based electrolytes were prepared to study the effect of CO₂ Though NOHMs composed of an ionic binding energy (i.e., chemisorption vs. physisorption) on the CO₂ reduction reaction (CO₂RR) over a silver nanoparticle catalyst for the production of syngas, a mixture of H₂ and CO, at various ratios. Poly(ethylenimine) (PEI) and Jeffamine M2070 (HPE) were ionically tethered to SiO₂ nanoparticles to form the amine-containing NOHM-I-PEI and ether containing NOHM-I-HPE, respectively. At less negative applied potentials, PEI and NOHM-I-PEI based electrolytes produced CO at higher rates than 0.1 molal. KHCO₃ due to their enhanced conductivity, while at more negative applied potentials, H₂ production was significantly favored because of the electrochemical inactivity of carbamates and catalyst-electrolyte interactions affecting the selectivity of CO₂RR. Conversely, due to their lower ionic conductivity, HPE and NOHM-I-HPE electrolytes displayed poor CO₂RR performance at less negative applied potentials. At more negative applied potentials, their performance approached that of 0.1 molal. KHCO₃, highlighting how the polymer functional groups of NOHMs are critical to the tunable production of syngas. The results of this study illustrate that more conductive polymer canopies with intermediate binding energies for CO₂ should be explored to improve the performance of NOHM-mediated CO₂ reduction. Altogether, the results of this dissertation demonstrate the ability of NOHM-based electrolytes to be used for systems enabling the integrated capture and electrochemical conversion of CO₂. The polymer grafting density, polymer canopy functionalities, bond type linking the polymer to the nanoparticle, secondary fluid selection and ionic stimulus were all found to play an important role in determining the thermal stability of NOHMs and/or the structural and transport properties of the corresponding NOHM-based fluids/electrolytes, thus highlighting the tunable nature of this class of materials. Additionally, the findings from this dissertation can be applicable to a wide range of energy and environmental applications that require the design and development of novel electrolytes.

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The pursuit of reliable and high-performance batteries has fueled extensive research into new battery chemistries and materials, aiming to enhance the current lithium-ion battery technologies in terms of energy density and safety. Among the potential advancements, solid-state batteries (SSBs) have captured significant attention as the next-generation energy storage technology. One key factor contributing to their appeal is the utilization of solid-state electrolytes (SSEs) with a wide electrochemical stability window (ESW), making SSBs compatible with high-voltage cathodes. The energy density of SSBs can be further improved by employing the “holy-grail” anode, Li-metal, which boasts the lowest working voltage (-3.04 V vs. Li+/Li) and an ultrahigh theoretical capacity (3860 mAh g−1). Consequently, these batteries are referred to as lithium metal batteries (LMBs). However, realizing the full potential of LMBs presents formidable challenge, including the low ionic conductivity of current SSEs, large interfacial resistance between SSE and electrodes, uncontrollable interfacial reactions, and the growth of Li dendrites.  Typically, SSEs can be categorized into three types. Among these, solid composite electrolytes (SCEs) are considered the most promising choice for solid-state LMBs due to their combination of high ionic conductivity and excellent mechanical strength from inorganic solid electrolytes (ISEs) and the flexibility and good interface compatibility provided by solid polymer electrolytes (SPEs). Polymeric ionic liquids (PolyILs), which contain both ionic liquid-like moieties and polymer frameworks, have emerged as highly attractive alternatives to traditional polymers in SCEs.  The overall objective of this thesis was to develop PolyIL-based SCEs with enhanced ionic conductivity, wide ESW, high Li+ transference number, and reduced electrodes/electrolyte interface resistance. The main progress achieved in this thesis is as follows: 1. We selected three F-based Li-salts to prepare SPEs using poly(ethylene oxide) and polyimide. The investigation focused on assessing the impact of molecular size, F content, and chemical structures (F-connecting bonds) of these Li-salts. Additionally, we aimed to uncover the formation process of LiF in the solid electrolyte interphase (SEI). The result revealed that the F-connecting bond plays a more significant role than the molecular size and F element content, resulting in slightly better cell performance using LiPFSI compared to LiTFSI and substantially better performance compared to LiFSI. The preferential breakage of bonds in LiPFSI was found to be related to its position to Li anode. Consequently, we proposed the LiPFSI reduction mechanism based on these findings. 2. Using the template method, we synthesized a monolayer SCE with enhanced Li+ transference number and high ionic conductivity. In this study, boron nitride (BN) nanosheets with a high specific surface area and richly porous structure were employed as inert inorganic filler. These BN nanosheets played a crucial role in homogenizing the Li+ flux and facilitating the Li+ transmission to suppress Li dendrite growth. When integrated into a LiFePO4//Li cell with the optimized SCE, the assembled battery demonstrated remarkable cycling performance.  3. A monolayer GSCE with multifunctionality was synthesized via a natural sedimentation and subsequent UV-curing polymerization technique. This innovative method capitalizes on intrinsic gravity, allowing for the integration of multiple functions within a single layer, thereby eliminating the additional interlayer resistance. The developed GSCE provides an optimum Li+ transportation path and enhanced Li+ transference number, leading to an enhanced ionic conductivity and a long cycle life of Li//Li cells and SSLMBs. Compared with the monolayer uniform SCEs, the gradient structure also alleviates the uncoordinated thermal expansion between fillers and PolyIL, avoiding increased stress during the cycle and battery capacity fade.

The research described here encompasses several different aspects of lithium ion battery operation including deep eutectic electrolytes, manganese trapping evaluation, silicon monoxide anodes, and in-situ NMR development under both static and spinning conditions. Individually, the results of these investigations as contained within the corresponding chapters contribute valuable insight. Collectively, they represent a snapshot into the numerous different ways in which nuclear magnetic resonance spectroscopy is applicable to lithium ion battery characterization. For instance, the deep eutectic electrolytes thus studied were amenable to diffusion coefficient characterization via the 1H, 7Li and 19F nuclei. This provided dynamical information on the anion, cation and neutral component and lent itself well towards parameterization of molecular dynamics simulations. The results thus obtained were useful in describing this relatively understudied class of electrolytes. Another example is that of the evaluation of manganese trapping. In this context 7Li NMR measurements were used to investigate the competitive inhibition of manganese trapping in crown ethers by lithium. Candidate crown ethers were thus evaluated for their ability to trap Mn2+ and Mn3+ in a lithium rich environment. Given the detrimental effects that manganese dissolution from cathode materials has on cycle life performance, the NMR enabled assessment of the appropriate chelating agents had identifiable importance. Additionally described was the progress made with silicon monoxide anodes supported on cellulosic substrates. The high active material loadings achieved, while also intriguing from a performance perspective, enabled 29Si MAS-NMR and 7Li static in-situ NMR measurements. For the in-situ measurements in particular, a novel cell design was constructed to utilize the advantages of a cellulosic substrate in this context. This has also enabled preliminary work on a spinning in-situ design. / Thesis / Doctor of Philosophy (PhD)

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24235号 / 工博第5063号 / 新制||工||1790(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 陰山 洋, 教授 藤田 晃司, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Since their introduction by Sony in 1990, lithium-ion batteries (LIBs) have acquired a sizable market share. They have the best energy densities, a high open circuit voltage, a low self-discharge rate, no memory effect, and a slow loss of charge when not in use. These properties make them the most popular rechargeable batteries for portable gadgets, electric vehicles and aerospace applications.  They do, however, pose major safety issues since the electrolytes are made up of fluorinated salts dissolved in volatile organic solvents, the former being meta-stable at ambient temperature and the latter being flammable a with high vapour pressure. Thus, there is an urge to develop thermally and electrochemically stable non-fluorinated electrolytes to improve the safety and performance of batteries. Electrolytes based on ionic liquids (ILs) in general offer a range of suitable advantages including low volatility and high thermal and electrochemical stabilities,and can additionally be made fluorine-free. In general, their physicochemical properties are determined by the interactions between the cations and anions, which are controlled by the chemical functionalities present, with vast freedom in structural design to reduce these interactions and enhance also the ion mobilities.  In this study, favoring from of “structural design” three different families of fluorine-free ionic liquids-based electrolytes are designed and created. These families of ILs comprising n- tetrabutylphosphonium, imidazolium, pyridinium based cations and pyridine, pyrazine and ether functionalized salicylate-based anions. The structures and purity of these new ILs are characterized by using multinuclear NMR, FTIR and mass spectrometry. Several features and properties of the novel electrolytes are investigated; thermogravimetric analysis, differential scanning calorimetry, ionic conductivity and electrochemical stability. These studies are further complemented by using PFG NMR diffusometry to understand the possible interaction mechanisms between the oppositely charged ions within the electrolytes, and especially, the influence of Li+ addition in the IL-based electrolytes.