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As global energy consumption moves away from fossil fuel sources to alternative energy, the concern for energy storage is paramount. Through lithium ion batteries (LIBs), secondary battery storage has been secured for both large applications of electric vehicles, solar storage, and smaller items like personal cell phones and laptops. However, LIBs use flammable liquid electrolytes and due to engineering defects or dendritic short-circuits have the potential to swell, catch on fire, or even explode because of the volatile organic solvents within the battery. In the pursuit of new commercial lithium ion battery technologies that are safe, nonflammable, and highly conductive, solid-state electrolytes (SSE) are promising candidates for these critical innovations. To achieve SSEs with electrochemically and functionally desirable properties such as ease of manufacturing, good adherence to electrodes, and high ionic conductivities, continued efforts are devoted to improving electrolyte materials. The two main electrolyte types of interest are polymer electrolytes and ceramic electrolytes. Although polymer electrolytes have desirable physical flexibility to form good contact with electrode surfaces, they continually suffer from low ionic conductivities comparatively. Meanwhile ceramic electrolytes have high ionic conductivities (especially high cationic conductivities) but suffer from both poor electrode contact and brittleness. Single-ion conductive materials (like most ceramic conductors) are necessary to increase lifetime performance of batteries. An avenue to access these necessary attributes in LIB-SSEs is explored through novel boron-containing polymers and polymer-ceramic hybrids with the focus to synthesize a material with a high lithium transference number. By exploiting the Lewis basic nature of borane centers to form negatively charged polymer backbones, novel solid-state electrolytes were synthesized with the goal of creating only cation-conductive polymer networks by incorporating the anionic component within the polymer matrix. The synthesis, chemical and electrochemical characterization of these types of polymers and polymer-ceramic hybrids are analyzed by various techniques including x-ray diffraction, thermal gravimetric analysis, nuclear magnetic spectroscopy, gel permeation chromatography, electrochemical impedance spectroscopy and lithium transference number characterization. / Chemistry

A novel ionic liquid crystal (ILC) system (C18IMCNBr) with a liquid crystal alignment used as an electrolyte for a dye-sensitized solar cell (DSSC) showed the higher short-circuit current density (Jsc) and the higher light-to-electricity conversion efficiency than the system using the non- alignment liquid crystalline ionic liquid (C18IMCNBr),due to the higher conductivity of liquid crystal alignment. The larger Jsc and efficiency value of liquid crystal alignment supported that the higher conductivity of liquid crystal alignment is attributed to the enhancement of the exchange reaction between iodide species. As a result of formation of the two-dimensional electron conductive pathways organized by the localized I3- and I- at liquid crystal alignment layers, the concentration of polyiodide species exemplified by Im- (m =5,7, ...) was higher in alignment C18IMCNBr. However, in the two-dimensional electron conductive pathways of C18IMCNBr, more collision frequencies between iodide species (I-,I3-, and Im-) could be achieved than that in the three-dimensional space of C18IMCNBr, which could lead to the promotion of the exchange reaction between iodide species, the contribution of a two-dimensional structure of the conductive pathway through the increase of collision frequency between iodide species was proposed.

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

Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Perovskite-structured LLT is a promising solid electrolyte with high lithium ion conductivity. LLT also serves as a good model system to understand lithium ion diffusion behaviors in solids. In this thesis, molecular dynamics and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism in bulk crystal and grain boundary in lithium lanthanum titanate (LLT) solid state electrolytes. The effects of defect concentration on the structure and lithium ion diffusion behaviors in LLT were systematically studied and the lithium ion self-diffusion and diffusion energy barrier were investigated by both dynamic simulations and static calculations using the nudged elastic band (NEB) method. The simulation results show that there exist an optimal vacancy concentration at around x=0.067 at which lithium ions have the highest diffusion coefficient and the lowest diffusion energy barrier. The lowest energy barrier from dynamics simulations was found to be around 0.22 eV, which compared favorably with 0.19 eV from static NEB calculations. It was also found that lithium ions diffuse through bottleneck structures made of oxygen ions, which expand in dimension by 8-10% when lithium ions pass through. By designing perovskite structures with large bottleneck sizes can lead to materials with higher lithium ion conductivities. The structure and diffusion behavior of lithium silicate glasses and their interfaces, due to their importance as a grain boundary phase, with LLT crystals were also investigated by using molecular dynamics simulations. The short and medium range structures of the lithium silicate glasses were characterized and the ceramic/glass interface models were obtained using MD simulations. Lithium ion diffusion behaviors in the glass and across the glass/ceramic interfaces were investigated. It was found that there existed a minor segregation of lithium ions at the glass/crystal interface. Lithium ion diffusion energy barrier at the interface was found to be dominated by the glass phase.

Le couplage de la spectroscopie d’impédance électrochimique(EIS) et de la spectroscopie photoélectronique à rayonnement X(XPS) a permis d’étudier en profondeur le lien entre la structure etles propriétés électrochimiques d’électrolytes solides en couchesminces, ainsi que de l’interface formée avec le matériau d’électrodepositive LiCoO2. L’incorporation d’azote dans la structure duLiPON, électrolyte solide de référence dans les microbatteries, estcaractérisée par la formation de lacunes de lithium et d’oxygènesfavorables au transport des ions lithium. Un électrolyte solideLiPOS a été développé par pulvérisation cathodique radiofréquencevia l’incorporation de soufre dans la structure initiale Li3PO4. Laprésence d’une interface solide/solide entre le LiPON et LiCoO2 estcaractérisée par une réduction partielle du cobalt et une oxydationdu LiPON à son voisinage, vraisemblablement responsable del’augmentation de la résistance de transfert de charges entre lesdeux matériaux. / The link between the structure and the electrochemicalproperties of thin-film electrolytes and the interface formed withthe cathode material LiCoO2 has been intensively studied bycoupling Electrochemical Impedance Spectroscopy (EIS) and X-rayPhotoelectron Spectroscopy (XPS). Nitrogen incorporation intoLiPON, reference solid-state electrolyte for microbatteries, ischaracterized by the formation of lithium and oxygen vacancies,increasing the lithium ions transport. A sulfide based thin filmelectrolyte called LiPOS has been developed by radiofrequencysputtering, with the incorporation of sulfur into the initial Li3PO4structure. The solid/solid interface between LiPON and LiCoO2 ischaracterized by a partial reduction of cobalt and oxidation ofLiPON, which is in all probability responsible of the increase of thecharge transfer resistance between the two materials.

The direct epitaxial growth of multilayer BN by atomic layer deposition is of critical significance forfo two-dimensional device applications. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) demonstrate layer-by-layer BN epitaxy on two different substrates. One substrate was a monolayer of RuO2(110) formed on a Ru(0001) substrate, the other was an atomically clean Ni(111) single crystal. Growth was accomplished atomic layer deposition (ALD) cycles of BCl3/NH3 at 600 K substrate temperature and subsequent annealing in ultrahigh vacuum (UHV). This yielded stoichiometric BN layers, and an average BN film thickness linearly proportional to the number of BCl3/NH3 cycles. The BN(0001)/RuO2(110) interface had negligible charge transfer or band bending as indicated by XPS and LEED data indicate a 30° rotation between the coincident BN and oxide lattices. The atomic layer epitaxy of BN on an oxide surface suggests new routes to the direct growth and integration of graphene and BN with industrially important substrates, including Si(100). XPS and LEED indicated epitaxial deposition of h-BN(0001) on the Ni(111) single crystal by ALD, and subsequent epitaxially aligned graphene was deposited by chemical vapor deposition (CVD) of ethylene at 1000 K. Direct multilayer, in situ growth of h-BN on magnetic substrates such as Ni is important for spintronic device applications. Solid-state electrolytes (SSEs) are of significant interest for their promise as lithium-ion conducting materials but are prone to degradation due to lithium carbonate formation on the surface upon exposure to atmosphere, adversely impacting Li ion conduction. In situ XPS monitored changes in the composition of the SSE Li garnet (Li6.5La3Zr1.5Ta0.5O12, LLZTaO) upon annealing in UHV and upon Ar+ ion sputtering. Trends in core level spectra demonstrate that binding energy (BE) calibration of the Li 1s at 56.4 eV, yields a more consistent interpretation of results than the more commonly used standard of the adventitious C 1s at 284.8 eV. Annealing one ambient-exposed sample to >1000 K in UHV effectively reduced surface carbonate and oxygen, leaving significant amounts of carbon in lower oxidation states. A second ambient-exposed sample was subjected to 3 keV Ar+ ion sputtering at 500 K in UHV, which eliminated all surface carbon, and reduced the O 1s intensity and BE. These methods present alternative approaches to lithium carbonate removal than heating or polishing in inert atmospheres and are compatible with fundamental surface science studies. In particular, the data show that sputtering at mildly elevated temperatures yields facile elimination of carbonate and other forms of surface carbon. This is in contrast to annealing in either UHV or in noble gas environments, which result in carbonate reduction, but with significant remnant coverages of other forms of carbon.