Measurements of oxygen activities in a matte at high-temperature could be useful to determine and control the repartition of different elements, such as iron, copper, and nickel between the oxidised phase, (the slag) and the sulphide phase, (the matte). Electrochemical measurement of oxygen partial pressure in equilibrium with the melt can be performed by using solid electrolytes such as the zirconia solid electrolyte. The oxygen measurements in Cu-Ni-Fe-S matte were studied experimentally by measuring the partial pressure of oxygen through the EMF, using a silica-saturated slag and either a CO-CO2-SO2 gas mixture or Ar gas, at 1250oC. The calculated equilibrium oxygen partial pressure varied from 1.53x10-8 to 2.64x10-7atm. Oxygen measurements were conducted by using fully stabilized zirconia as solid electrolyte. Two different solid reference electrodes were used: Cr/Cr2O3 and Fe/FeO. EMF measurements obtained with Cr/Cr2O3 solid reference electrode were less stable and accurate compared to those with Fe/FeO solid reference electrode. Therefore, EMF measurements on oxygen concentration point out that the Fe/FeO is more suitable solid reference electrode for this application than Cr/Cr2O3. Analyses were obtained using the SEM, (scanning electron microscope) and the electron probe microanalyser. The measured oxygen concentration was found to be sensitive to the iron content in the matte. / Dissertation (MEng (Metallurgy))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

The main aim of this thesis is to reveal the chemical structures of the solid-liquid interphase in lithium ion batteries by NMR spectroscopy in order to understand the working mechanism of electrolyte additives for achieving stable cycling performance. In the first part, a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization (DNP) are employed to monitor the formation of the solid electrolyte interphase (SEI) on next-generation, high-capacity Si anodes in conventional carbonate electrolytes with and without fluoroethylene carbonate (FEC) additives. A model system of silicon nanowire (SiNW) electrode is used to avoid interference from the polymeric binder. To facilitate characterization via one- and two-dimensional NMR, ^13C-enriched FEC was synthesized and used, ultimately allowing a detailed structural assignment of the organic SEI. FEC is found to first defluorinated to form soluble vinylene carbonate (VC) and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. In the second part, the same methodology is applied to study the decomposition products of pure FEC or VC electrolytes containing 1 M LiPF_6. The pure FEC/VC system simplifies the electrolyte solvent formulation and avoids the interaction between different solvent molecules. Polymeric SEIs formed in pure FEC or VC electrolytes consist mainly of cross-linked PEO and aliphatic chain functionalities along with additional carbonate and carboxylate species. The presence of cross-linked PEO-type polymers in FEC and VC correlates with good capacity retention and high Coulombic efficiencies of the SiNWs anode. Using ^29Si DNP NMR, the interfacial region between SEI and the Si surface was probed for the first time with NMR spectroscopy. Organosiloxanes form upon cycling, confirming that some of the organic SEI is covalently bonded to the Si surface. It is suggested that both the polymeric structure of the SEI and the nature of its adhesion to the redox-active materials are important for electrochemical performance. Finally, the soluble decomposition products of EC formed during electrochemical cycling have been thoroughly analyzed by solution NMR and mass spectrometry, in order to explain the capacity-fading of Si anodes in a conventional EC-based electrolyte and address questions that arose when studying the additive-containing electrolytes. The detailed structures for the EC-degradation products are determined: a linear oligomer consist of ethylene oxide and carbonate units is observed as the major degradation product of EC.

No description available.

Die Röntgenabsorptionsspektroskopie (XAS) ist eine element-spezifische Charakterisierungs-methode, welche es erlaubt die elektronische und chemische Struktur der SEI zu untersuchen. In dieser Arbeit stelle ich ein neues Verfahren vor, das die Transmissions-XAS von Flüssigkeiten und Dünnschicht-Batterieelektroden unter in-situ Bedingungen mit weicher Röntgenstrahlung ermöglicht. Thematisch ist die Arbeit in zwei Teile gegliedert. Das neuartige Verfahren wird zunächst umfangreich vorgestellt und dann zur Untersuchung der Solid Electrolyte Interphase (SEI) auf Silizium angewendet. Das Verfahren basiert auf einer elektrochemischen Halbzelle, die mit einem Stapel aus zwei Siliziumnitrid-Membranfenster ausgestattet ist, um den Elektrolyten einzuschließen. Eines der Membranfenster ist gleichzeitig der Träger für die Dünnschicht-Siliziumanode, die Ladezyklen mit einer Kathode aus metallischem Lithium durchläuft. Nachdem sich die SEI gebildet hat, wird mittels eines Röntgenstrahls von hoher Intensität vorsätzlich eine Blase erzeugt, um überschüssigen Elektrolyten abzudrängen und einen dünnen Elektrolytfilm über der SEI zu stabilisieren. Durch den Elektrolytfilm bleibt die SEI in-situ. Das erzeugte System aus Blase, Elektrolytfilm, SEI und Siliziumanode wird dann mittels Transmissions-XAS untersucht. Im zweiten Teil meiner Arbeit werden dann Silizium Dünnschicht-Anoden mit dem vorgestellten Verfahren am Elektronenspeicherring BESSY II in Berlin untersucht. Bei der elektrochemischen Charakterisierung zeigen die Dünnschicht-anoden alle für die De-/Lithiierung von Silizium üblichen Merkmale. Als Hauptbestandteile der SEI wurden Lithiumacetat, Li Ethylendicarbonat oder -monocarbonat, Li Acetylacetonat, LiOH und LiF ermittelt. Darüber hinaus deuten Anzeichen von Aldehyden auf flüssige Einschlüsse in einer möglich-erweise porösen SEI Struktur hin. / X-ray Absorption Spectroscopy (XAS) is an element-specific technique, which allows to probe the electronic and chemical structure of the SEI. In this work, I introduce a novel approach for transmission XAS on liquids and thin-film battery electrode materials under in-situ conditions in the soft X-ray regime. Thematically, this work is divided into two parts: 1) the introduction of this novel method and 2) its application to investigate the Solid Electrolyte Interphase (SEI) on silicon thin film anodes. The presented technique is based on an electrochemical half-cell equipped with a sandwich of two silicon nitride membrane windows to encapsulate the electrolyte. One of the membranes acts as substrate for the silicon thin-film anode, which is cycled with a metallic lithium counter-electrode. After the SEI has formed, a gas bubble is intentionally introduced through radiolysis by a high intensity X-ray to push out excessive electrolyte and stabilize a thin electrolyte layer on top of the SEI, keeping it in-situ. The obtained stack comprised of bubble, electrolyte thin-layer, SEI and anode, is then probed with transmission XAS. The second part of this work utilizes the presented method to investigate the SEI on amorphous silicon anodes at the BESSY II synchrotron facility in Berlin. The anodes’ electrochemical characterization shows all significant features of silicon’s de-/lithiation. The SEI’s main components are determined as Li acetate, Li ethylene di-carbonate or Li ethylene mono-carbonate, Li acetylacetonate, LiOH, and LiF. Additionally, the evidence for aldehyde species indicates possible liquid inclusions within a presumably porous SEI morphology.

As células eletroquímicas emissoras de luz são dispositivos eletroluminescentes cuja camada ativa é uma mistura de um material eletroluminescente e um eletrólito sólido a base de sais de metais alcalinos, geralmente lítio. A presença dos íons na camada ativa modificam o mecanismo de funcionamento das células quando comparadas ao diodos emissores de luz. Nas células, a concentração de íons nas interfaces eletródicas forma uma dupla camada elétrica que auxilia a injeção de cargas na camada ativa, por sua vez e na presença dos íons, o material eletroluminescente sofre dopagem se tornando condutor, os portadores injetados irão se encontrar numa região da camada ativa recombinando-se e emitindo luz. Compreender as interações dos diversos materiais que formam a camada ativa é fundamental para otimizar o desempenho do dispositivo. Neste trabalho estudamos a interação do ADS108GE, um polímero luminescente, e um eletrólito sólido a base de poli (óxido de etileno) (PEO) e LiCF3SO3 ou LiB(C2O4)2. O LiB(C2O4)2 foi sintetizado neste trabalho para estudar a viabilidade de se substituir o LiCF3SO3 que é o sal tipicamente utilizado nas células. Foram utilizadas técnicas de Análise Dinâmico-Mecânica (DMA), Espectroscopia Vibracional no Infravermelho (FTIR), Microscopia de Força Atômica (AFM), Difração de Raios-X (DRX), Microscopia Óptica de Varredura no Campo Próximo (IR-SNOM), Impedância Elétrica e Voltametria Cíclica. Os resultados de DMA em conjunto com DRX e AFM, permitiram estabelecer que o aumento da concentração de sal contribui para mudanças morfológicas que se relacionam com o aumento da fração de fase amorfa e independem do ânion, demonstrando que estes efeitos estão ligados à interação PEO-Lítio. Por outro lado, os espectros de FTIR e resultados de impedância elétrica mostram que o aumento da concentração de LiCF3SO3 gera agregação do sal diminuindo a condutividade, a mobilidade iônica e o número de portadores efetivos, enquanto para o LiB(C2O4)2 não se observa tal efeito. O IR-SNOM permitiu identificar nas misturas utilizadas como camada ativa que o ADS108GE forma estruturas globulares embebidas numa matriz de PEO. Do ponto de vista operacional, as células a base de LiB(C2O4)2 possuem uma eficiência maior do que as a base LiCF3SO3 e maior estabilidade. / Light-emitting electrochemical cells are electroluminescent devices whose active layer is a mixture of an electroluminescent material and a solid electrolyte based on alkaline salts, usually a lithium salt. The ions within thea ctive layer change the devices working mechanism when compared to light emitting diodes. In the cells, there is an ion build up at electrodic interfaces creating an electric double layer allowing charge injection in the active layer. The electroluminescent material is doped by these injected charges becoming conductive. These injected charges recombine emitting light. In order to optimize devices performance, it is fundamental to study materials interactions when mixed as an active layer. In this work, we studied the interactions between ADS108GE, a luminescent polymer, and a solid electrolyte based on polyethylene oxide and LiCF3SO3 or LiB(C2O4)2. LiB(C2O4)2 was prepared in this work to assess its feasibility as LiCF3SO3 substitution which is the typical choice. We used the following techniques in this work: Dynamical Mechanical Analysis (DMA), Infrared Vibration Spectroscopy (FTIR), Atomic Force Microscopy AFM), X-Ray Diffraction (XRD), Infrared Scanning Near-Field Optical Microscopy (IRSNOM), Electrical Impedance and Cyclic Voltammetry. From DMA, XRD and AFM results, it is possible to conclude that as we increase salt concentration, the active layer has morphological changes related to an increasing fraction of an amorphous phase. These effects are anion independent showing that PEO-Li interactions are the responsible ones. On the other hand, FITR and electrical impedance experiments show that increasing LiCF3SO3 concentration leads to salt aggregation decreasing conductivity, ionic mobility and the effective number of carriers, moreover, we do not see this effect with LiB(C2O4)2. IR-SNOM identified that ADS108GE were organized as globular structures embedded in a PEO matrix. The cells made with LiB(C2O4)2 were more efficient than those based on LiCF3SO3 and were even more stable.

The ionic conductivity of the lithium ionic conductor, Li5La3Ta2O12, is studied in an attempt to better understand the intrinsic bulk ionic conductivity and extrinsic sample dependent contributions to the ionic conductivity, such as grain boundary effects and the electrode-electrolyte interface. To characterize the material, traditional AC impedance spectroscopy studies were performed as well novel in-situ nanoscale transport measurements. To perform the nanoscale measurements, higher quality samples were required and new synthesis techniques developed. The results of these new synthesis techniques was samples with higher densities, up to 96% of theoretical, and slightly higher room temperature ionic conductivity, 2x10^−5 S/cm. By combining the AC impedance spectroscopy results and in-situ nanoscale transport measurements from this study and prior reported results, as well as introducing models traditionally used to analyze supercapacitor systems, a new interpretation of the features seen in the AC impedance spectroscopy studies is presented. This new interpretation challenges the presence of Warburg Diffusion at low frequencies and the offers a new interpretation for the features that have been traditionally associated with grain boundary effects.

abstract: This work investigates in-situ stress evolution of interfacial and bulk processes in electrochemical systems, and is divided into two projects. The first project examines the electrocapillarity of clean and CO-covered electrodes. It also investigates surface stress evolution during electro-oxidation of CO at Pt{111}, Ru/Pt{111} and Ru{0001} electrodes. The second project explores the evolution of bulk stress that occurs during intercalation (extraction) of lithium (Li) and formation of a solid electrolyte interphase during electrochemical reduction (oxidation) of Li at graphitic electrodes. Electrocapillarity measurements have shown that hydrogen and hydroxide adsorption are compressive on Pt{111}, Ru/Pt{111}, and Ru{0001}. The adsorption-induced surface stresses correlate strongly with adsorption charge. Electrocatalytic oxidation of CO on Pt{111} and Ru/Pt{111} gives a tensile surface stress. A numerical method was developed to separate both current and stress into background and active components. Applying this model to the CO oxidation signal on Ru{0001} gives a tensile surface stress and elucidates the rate limiting steps on all three electrodes. The enhanced catalysis of Ru/Pt{111} is confirmed to be bi-functional in nature: Ru provides adsorbed hydroxide to Pt allowing for rapid CO oxidation. The majority of Li-ion batteries have anodes consisting of graphite particles with polyvinylidene fluoride (PVDF) as binder. Intercalation of Li into graphite occurs in stages and produces anisotropic strains. As batteries have a fixed size and shape these strains are converted into mechanical stresses. Conventionally staging phenomena has been observed with X-ray diffraction and collaborated electrochemically with the potential. Work herein shows that staging is also clearly observed in stress. The Li staging potentials as measured by differential chronopotentiometry and stress are nearly identical. Relative peak heights of Li staging, as measured by these two techniques, are similar during reduction, but differ during oxidation due to non-linear stress relaxation phenomena. This stress relaxation appears to be due to homogenization of Li within graphite particles rather than viscous flow of the binder. The first Li reduction wave occurs simultaneously with formation of a passivating layer known as the solid electrolyte interphase (SEI). Preliminary experiments have shown the stress of SEI formation to be tensile (~+1.5 MPa). / Dissertation/Thesis / Deconvolution programm - see Appendix C / ECdata4 program - see Appendix C / Ph.D. Materials Science and Engineering 2011

As células eletroquímicas emissoras de luz são dispositivos eletroluminescentes cuja camada ativa é uma mistura de um material eletroluminescente e um eletrólito sólido a base de sais de metais alcalinos, geralmente lítio. A presença dos íons na camada ativa modificam o mecanismo de funcionamento das células quando comparadas ao diodos emissores de luz. Nas células, a concentração de íons nas interfaces eletródicas forma uma dupla camada elétrica que auxilia a injeção de cargas na camada ativa, por sua vez e na presença dos íons, o material eletroluminescente sofre dopagem se tornando condutor, os portadores injetados irão se encontrar numa região da camada ativa recombinando-se e emitindo luz. Compreender as interações dos diversos materiais que formam a camada ativa é fundamental para otimizar o desempenho do dispositivo. Neste trabalho estudamos a interação do ADS108GE, um polímero luminescente, e um eletrólito sólido a base de poli (óxido de etileno) (PEO) e LiCF3SO3 ou LiB(C2O4)2. O LiB(C2O4)2 foi sintetizado neste trabalho para estudar a viabilidade de se substituir o LiCF3SO3 que é o sal tipicamente utilizado nas células. Foram utilizadas técnicas de Análise Dinâmico-Mecânica (DMA), Espectroscopia Vibracional no Infravermelho (FTIR), Microscopia de Força Atômica (AFM), Difração de Raios-X (DRX), Microscopia Óptica de Varredura no Campo Próximo (IR-SNOM), Impedância Elétrica e Voltametria Cíclica. Os resultados de DMA em conjunto com DRX e AFM, permitiram estabelecer que o aumento da concentração de sal contribui para mudanças morfológicas que se relacionam com o aumento da fração de fase amorfa e independem do ânion, demonstrando que estes efeitos estão ligados à interação PEO-Lítio. Por outro lado, os espectros de FTIR e resultados de impedância elétrica mostram que o aumento da concentração de LiCF3SO3 gera agregação do sal diminuindo a condutividade, a mobilidade iônica e o número de portadores efetivos, enquanto para o LiB(C2O4)2 não se observa tal efeito. O IR-SNOM permitiu identificar nas misturas utilizadas como camada ativa que o ADS108GE forma estruturas globulares embebidas numa matriz de PEO. Do ponto de vista operacional, as células a base de LiB(C2O4)2 possuem uma eficiência maior do que as a base LiCF3SO3 e maior estabilidade. / Light-emitting electrochemical cells are electroluminescent devices whose active layer is a mixture of an electroluminescent material and a solid electrolyte based on alkaline salts, usually a lithium salt. The ions within thea ctive layer change the devices working mechanism when compared to light emitting diodes. In the cells, there is an ion build up at electrodic interfaces creating an electric double layer allowing charge injection in the active layer. The electroluminescent material is doped by these injected charges becoming conductive. These injected charges recombine emitting light. In order to optimize devices performance, it is fundamental to study materials interactions when mixed as an active layer. In this work, we studied the interactions between ADS108GE, a luminescent polymer, and a solid electrolyte based on polyethylene oxide and LiCF3SO3 or LiB(C2O4)2. LiB(C2O4)2 was prepared in this work to assess its feasibility as LiCF3SO3 substitution which is the typical choice. We used the following techniques in this work: Dynamical Mechanical Analysis (DMA), Infrared Vibration Spectroscopy (FTIR), Atomic Force Microscopy AFM), X-Ray Diffraction (XRD), Infrared Scanning Near-Field Optical Microscopy (IRSNOM), Electrical Impedance and Cyclic Voltammetry. From DMA, XRD and AFM results, it is possible to conclude that as we increase salt concentration, the active layer has morphological changes related to an increasing fraction of an amorphous phase. These effects are anion independent showing that PEO-Li interactions are the responsible ones. On the other hand, FITR and electrical impedance experiments show that increasing LiCF3SO3 concentration leads to salt aggregation decreasing conductivity, ionic mobility and the effective number of carriers, moreover, we do not see this effect with LiB(C2O4)2. IR-SNOM identified that ADS108GE were organized as globular structures embedded in a PEO matrix. The cells made with LiB(C2O4)2 were more efficient than those based on LiCF3SO3 and were even more stable.

The goal of this thesis is to generate fundamental understandings of charge transport behaviors of composites consisting of garnet structured Al substituted Li7La3Zr2O12 (LLZO) electrolyte and LiCoO2 electrode. In order to take full advantage of all-solid-state batteries, bulk type composite electrodes should be introduced to increase energy and power density. However, the charge utilization of bulk type composite electrodes is quite low. Understanding ionic conduction behavior is, therefore, important for improving the performance of all-solid-state batteries, because ion conduction within solids depends on effective pathways. Electronic conductivity can be easily compensated by adding carbon black, but ionic conductivity can only depend on composites electrode itself. Here, we show that electronic and ionic conductivities of composites consisting of LiCoO2 and Al doped LLZO can be achieved separately. 3D reconstructed image obtained from focused ion beam-scanning electron microscope (FIB-SEM) demonstrates that porosity, percolation, and grain boundaries often play antagonistic roles in controlling the charge transport behaviors in the composite electrodes, resulting in an overall conductivity dominated by electrons. This work suggests an approach to optimize electronic and ionic conductivities for bulk type composite electrodes, which may eventually be utilized in all-solid-state batteries.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22456号 / 工博第4717号 / 新制||工||1737(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 安部 武志, 教授 作花 哲夫, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM