Köln, Universiẗat, Diss., 2005.

This thesis examines parts of the kinetics and performance in Li-battery cells using lithium titanate anodes and lithium manganese oxide cathodes. Lithium titanate (Li4Ti5O12) is a candidate for battery applications in automotive vehicles due to its long lifetime and its suggested zero-strain ability. The zero-strain ability, meaning no volume changes in the material during cycling, would allow for the high charge/discharge rates required in electric vehicles. Two approaches of analysis have been performed. In situ XRD-analysis was used to verify the zero-strain ability of lithium titanate and XPS studies were used to analyze the surface chemistry of lithium titanate after cycling. It is known that lithium titanate/lithium manganeseoxide battery cells suffer from abnormal gas evolution and power degradation, and it is therefore of interest to find ways to prevent this. To be able to find methods of preventing the performance degradation deeper understanding of the kinetics are needed, since the mechanism behind this is not fully understood. The results in this thesis strengthen the understanding of lithium titanate as a zero-strain material. Furthermore, it is seen that the performance degradation possibly can be avoided or postponed by ALD deposition of aluminium oxide on the surface of the lithium manganese oxide electrode.

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Thesis (Ph. D.)--Oregon Graduate Center, 1980.

The extent of BiInO3 substitution in the perovskite system xBiInO3-(1-x)PbTiO3 and the corresponding raise in the Curie temperature were investigated using thermal analysis, X-ray diffraction and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x=0.20, with a corresponding Curie temperature of 582C. Phase-pure tetragonal perovskite was obtained for x less than 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD) by crushing after calcining, dry pressing and firing. Sol-gel fabrication resulted in nano-sized tetragonal or pseudo-cubic perovskite particles, which after two-step firing, resulted in a tetragonal perovskite microstructure at as high as (x=0.25) 98.2% of TD.

Dislocation loops in pressureless-sintered undoped BaTiO3 ceramics have been analysed via transmission electron microscopy (TEM). The Burgers vector b = [100] of the loops was initially determined by the contrast analysis of the g•b = 0 criteria combining with the inside-outside contrast method by which the sense of the Burgers vector was concluded. The vacancy nature were determined by adopting the inside-outside contrast analysis using the criteria of (g•b)sg being positive or negative when the loops were imaged under kinematical diffraction conditions of sg ¡Ú 0. High-resolution imaging of such loops has enabled us to confirm its vacancy nature, consistent with the contrast analysis. Further, the loops¡¦ Burgers vector was determined to be b = 1/2[100] and the loops were therefore negative partial dislocation loops lying in {200} where part of the TiO2-deficiency existed locally in the grains of sintered BaTiO3 ceramics was accommodated by the presence of vacancy loops. It is suggested that the extrinsic defects of both titanium and oxygen vacancies ( and ,) generated by the non-stoichiometry which gave clustered during sintering in air are responsible for the formation of the dislocation loops.

Thèse de doctorat : Physique et Chimie des surfaces : Strasbourg 1 : 2008. Thèse de doctorat : Physique et Chimie des surfaces : Université d'Antananarivo, Madagascar : 2008. / Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Notes bibliogr.

The ever increasing awareness of the environment and sustainability drives research to find new solutions in every part of society. In the transport sector, this has led to a goal of replacing the internal combustion engine (ICE) with an electrical engine that can be powered by renewable electricity. As a battery for vehicles, the Li-ion chemistries have become dominant due to their superior volumetric and gravimetric energy densities. While promising, electric vehicles require further improvements in terms of capacity and power output before they can truly replace their ICE counterparts. Another aspect is the CO2 emissions over lifetime, since the electric vehicle itself presently outlives its battery, making battery replacement necessary. If the lifetime of the battery could be increased, the life-cycle emissions would be significantly lowered, making the electric vehicle an even more suitable candidate for a sustainable society. In this context, lithium titanium oxide (LTO) has been suggested as a new anode material in heavy electric vehicles applications due to intrinsic properties regarding safety, lifetime and availability. The LTO battery chemistry is, however, not fully understood and fundamental research is necessary for future improvements. The scope of this project is to investigate degradation mechanisms in LTO-based batteries to be able to mitigate these and prolong the device lifetime so that, in the end, a suitable chemistry for large scale applications can be suggested. The work presented in this licentiate thesis is focused on the LTO electrode/electrolyte interface. Photoelectron spectroscopy (PES) was applied to determine whether the usage of LTO would prevent anode-side electrolyte decomposition, as suggested from the intercalation potential being inside the electrochemical stability window of common electrolytes. It has been found that electrolyte decomposition indeed occurs, with mostly hydrocarbons of ethers, carboxylates, and some inorganic lithium fluoride as decomposition products, and that this decomposition to some extent ensued irrespective of electrochemical battery operation activity. Second, an investigation into how crossover of manganese ions from Mn-based cathodes influences this interfacial layer has been conducted. It was found, using a combination of high-energy x-ray photoelectron spectroscopy (HAXPES) and near-edge x-ray absorption fine structure (NEXAFS) that although manganese is present on the LTO anode surface when paired with a common manganese oxide spinel cathode, the manganese does little to alter the surface chemistry of the LTO electrode.

Thesis (Ph. D.)Oregon Graduate Center, 1986.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / A new approach to synthesize nanosized strontium titanate (SrTiO3) and barium titanate (BaTiO3) has been developed. Nanocrystals of mixed metal oxide were synthesized by a modified aerogel procedure from alkoxides. The textural and surface characteristic properties were studied by nitrogen BET analysis, transmission electron microscopy, and powder XRD. The crystallite sizes of aerogel prepared powders can vary from 6 to 25 nm by the use of different solvents. A mixture of ethanol and toluene was found to be the best binary solvent for supercritical drying, which produced a SrTiO3 sample with a surface area of 159 m2/g and an average crystallite size of 8 nm, and a BaTiO3 sample with a surface area of 175 m2/g and an average crystallite size of 6 nm. These titanates have been studied for photocatalytic oxidation of volatile organic compounds and acetaldehyde (CH3CHO) in particular. The big band gaps of the bulk (3.2 eV for SrTiO3 and 3.1 eV for BaTiO3) limit their application to a UV light region only. The modification of titanates by doping with transition metal ions (partial substitution of Ti ions with metal ions) creates a valence band or electron donor level inside of the band gap, narrows it, and increases the visible light absorption. The enhanced adsorption of visible light was achieved by the synthesis of nanosized SrTiO3 and BaTiO3 by incorporating Cr ions during the modified aerogel procedure. Gaseous acetaldehyde photooxidation has been studied on pure SrTiO3 and BaTiO3, and on chromium doped Cr-SrTiO3 and Cr-BaTiO3 under UV and visible light irradiation, and compared with the photoactivity of P25 TiO2. SrTiO3 doped with antimony/chromium shows absorption in visible light and show photocatalytic activity for CH3CHO oxidation. The reason for the codoping of SrTiO3 with Sb/Cr was to maintain the charge balance and to suppress oxygen defects in the lattice. This photocatalyst shows high photoactivity under visible light irradiation even after several continuous runs. The photoactivity under visible and UV light irradiation was almost identical for the Sb/Cr-SrTiO3 photocatalyst. Dielectric properties of aerogel prepared barium titanate samples have being studied and the bulk resistance values of AP-BaTiO3 were significantly lower than that of commercial BaTiO3, by several orders of magnitude.