Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Qu, Jianmin; Committee Co-Chair: Garmestani, Hamid; Committee Member: Haynes, Comas; Committee Member: Klaus-Hermann Dahmen; Committee Member: Liu, Meilin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 98-100).

Thesis (Ph. D.)--State University of New York at Binghamton, Materials Science, 2005. / Numerals in chemical formula in title are "subscript" in t.p. of printed version. Includes bibliographical references.

Submitted by Márcio Maia (marciokjmaia@gmail.com) on 2016-08-08T12:30:12Z No. of bitstreams: 1 arquivototal.pdf: 1568585 bytes, checksum: a2238a4716a4526680dc4b1d96c2e0b7 (MD5) / Made available in DSpace on 2016-08-08T12:30:12Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1568585 bytes, checksum: a2238a4716a4526680dc4b1d96c2e0b7 (MD5) Previous issue date: 2016-04-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Fuel cells (FC) are electrochemical devices that convert chemical energy from certain fuels into electrical energy, through oxidation-reduction reactions. They have a basic structure consisting of an electrolyte layer intercalating two electrodes: the cathode (positive electrode) and anode (negative electrode). In this work, cathode materials for solid oxide fuel cells (SOFC) were developed, such as lanthanum cobaltite doped with strontium and iron (La0,6Sr0,4Co0,2Fe0,8O3-8-LSCF6428) was synthesized by the modified polymeric precursors method, also known as modified Pechini method and compared the performance with the composite electrodes La0,6Sr0,4Co0,2Fe0,8O3-8/Ce0,9 Gd0,1O2-8 (LSCF6428/ CGO) and La0,6Sr0,4Co0,2Fe0,8O3-8/Ce0,9Gd0,1O2-8/Prox (LSCF6428/CGO/PROX). The method of synthesis consists in the use of commercial gelatin as polymerizing agent for metal ions. The powder obtained at 350 ° C / 2h was calcined at 800 and 1000 ° C / 4h and characterized by thermal gravimetric analysis (TG), particle size distribution, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The films of (LSCF6428), (LSCF6428 / CGO) and (LSCF6428 / CGO / PROX) were obtained by serigraph of calcined powders at 1000 ° C. The films were deposited on ceria substrates doped with gadolinia Ce0,9Gd0,1O2-8(CGO), sintered at 1150°C and characterized by impedance spectroscopy (in pure oxygen) between 600 and 800°C. The obtained results indicated that the method used was efficient in the formation of porous powders and with the perovskite crystalline structure. The crystallite size for the composite of LSCF6428 / CGO was of 336 (nm) for the LSCF6428 and 98 (nm) for the CGO, being also the expected for a powder calcined at 1000 ° C. The value of the area specific resistance (ASR) for the electrode of pure LSCF6428 at 750 ° C was of 0.25 ohms.cm2 quite plausible, especially because it was not made use of platinum, for the LSCF/CGO/ Prox was obtained an ASR of 0.02 ohms.cm2 at 750 ° C. / As células a combustível (CaC) são dispositivos eletroquímicos que transformam a energia química de determinados combustíveis em energia elétrica, por meio de reações de oxirredução. Possuem uma estrutura básica que consiste em uma camada de eletrólito intercalando dois eletrodos: cátodo (eletrodo positivo) e anodo (eletrodo negativo). Neste trabalho, foram desenvolvidos materiais catódicos para células a combustíveis de óxidos sólidos (SOFC), tais como, a cobaltita de lantânio dopada com estrôncio e ferro (La0,6Sr0,4Co0,2Fe0,8O3-δ – LSCF6428) foi sintetizado pelo método dos precursores poliméricos modificado, também conhecido como Pechini modificado e comparado o desempenho com o de eletrodos compósitos La0,6Sr0,4Co0,2Fe0,8O3-δ/Ce0,9Gd0,1O2-δ (LSCF6428/CGO) e La0,6Sr0,4Co0,2Fe0,8O3-δ/ Ce0,9Gd0,1O2-δ/PrOx (LSCF6428/CGO/PrOx). O método de síntese consiste na utilização da gelatina comercial como agente polimerizante para íons metálicos. O pó obtido a 350 °C/ 2h foi calcinado a 800 e 1000 °C/ 4h e caracterizados por analise termogravimétrica (TG), distribuição de tamanho de partícula, difração de raio X (DRX) e microscopia eletrônica de varredura (MEV). Os filmes de (LSCF6428), (LSCF6428/CGO) e (LSCF6428/CGO/PrOx), foram obtidos por serigrafia de pós calcinados a 1000 °C. Os filmes foram depositados sobre substratos de céria dopada com gadolínia Ce0,9Gd0,1O2-δ (CGO), sinterizados a 1150 °C e caracterizados por espectroscopia de impedância (em oxigênio puro) entre 600 e 800 °C. Os resultados obtidos indicaram que o método utilizado foi eficiente na formação de pós porosos e com a estrutura cristalina perovskita. O tamanho de cristalito para o compósito de LSCF6428/CGO foi de 336 (nm) para o LSCF6428 e 98 (nm) para o CGO, sendo, também o esperado para um pó calcinado a 1000 °C. O valor da resistência específica de área (REA) para o eletrodo de LSCF6428 puro a 750 °C foi de 0,25 ohms.cm2 bastante plausível, principalmente por não ter sido feito uso de platina, para o LSCF/CGO/PrOx foi obtido uma REA de 0,02 ohms.cm2 a 750 °C.

This thesis reports exploratory studies on the synthesis and characterisation of new compounds as cathode materials for second generation sodium batteries, with a particular emphasis on preparing new iron-phosphite and molybdenum oxyfluoride cathode materials. Seven different compounds are hereby reported: the sodium iron fluoro-phosphite of formula NaFe₃(HPO₃)₂[(H,F)PO₂OH)₆], the iron-phosphite Fe₂(HPO₃)₃, the sodium iron-phosphite NaFe(H₂PO₃)₄, the sodium iron phosphate NaFe(HPO₄)(H₂PO₄)₂·H₂O and three molybdenum oxyfluoride compounds of formula Na₂MoO₂F₄, KNaMoO₂F₄ and KMoO₂F₃. The synthesis of these compounds was performed by hydrothermal and solvothermal methods at temperatures ranging from 100 °C to 160 °C. The compounds were then fully characterised using the following techniques: single crystal X-ray diffraction (SXD), powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and electrochemical testing. Magnetic properties have also been studied where appropriate.

T* based La₀.₉Ln₀.₉Sr₀.₂CuO₄ (Ln = Sm & Gd) has been investigated as cathode material for intermediate temperature solid oxide fuel cell using Ce₀.₉Gd₀.₁O₁.₉₅ (GDC) and La₀.₉Sr₀.₁Ga₀.₈Mg₀.₂O₃-δ (LSGM-9182) as the electrolyte material. Both oxides crystallize in tetragonal P4/nmm symmetry. The structural and phase stability has been confirmed up to 800 °C by High temperature XRD studies. The coefficient of thermal expansion (CTE) and oxygen content decrease with decreasing size of the Ln³+ ions from Ln = Sm to Gd. While the decrease in CTE is due to the increasing co-valence of the Ln–O bond, the decrease in electrical conductivity at high temperature is due to the increasing oxide ion vacancies and a bending of the O–Cu–O bonds. The highest value of DC conductivity has been observed for the LSSCu, which showed a metal like temperature dependence. LGSCu showed a semiconductor to metallic temperature dependence of conductivity with a maximum of 25 Scm-¹. From the microstructural characterization and the polarisation resistance measurement of the symmetric cells at temperature ranges from 700 - 800 °C, 900 °C has been chosen as the most suitable sintering temperature and LGSCu has shown the minimum polarization resistance of 0.35 Ωcm² and 0.09 Ωcm² at 800 °C using GDC and LSGM-9182 electrolytes respectively under OCV condition. To improve the ASR of LGSCu, the composite of LGSCu and GDC with varying wt. % of GDC has been optimised and it shows the ASR of 0.12 Ωcm² using GDC as the electrolyte because it enhance the triple phase boundary region. The maximum power density of single-cell SOFCs fabricated with the La₀.₉Ln₀.₉Sr₀.₂CuO₄ (Ln= Sm & Gd) cathodes, La₀.₉Sr₀.₁Ga₀.₈Mg₀.₂O₃-δ (LSGM-9182) electrolyte, and Ni–Ce₀.₉Gd₀.₁O₁.₉₅ cermet anode exhibit 720 and 824 mWcm-² at 800 °C respectively. The phase pure T* Nd₁.₃₂Ce₀.27Sr₀.₄₁CuO₄-δ (NCSCu) has been synthesized by combustion method and its crystal chemistry, thermal and electrochemical properties, and catalytic activity in SOFC were evaluated using LSGM-9182 as the electrolyte. It shows promising performance and can be used as potential cathode materials for IT-SOFC. The effect of B-site Ni and Co substitution for Cu on the structural and electrochemical properties of the T* La₀.₉Gd₀.₉Sr₀.₂CuO₄ has been investigated as cathode materials for intermediate temperature solid oxide fuel cells using LSGM-9182 as the electrolyte. At a given temperature, the electrical conductivity gradually increases with increasing Ni content and the CTE gradually decreases. Ni doping has also improved the electrochemical performance. Sr doped A /A //B₂O₅+δ (A / = Rare Earth, A // = Ba or Sr and B = Transition Metals) layered perovskites improves the electrochemical performance due to the increase in electrical conductivity and smaller size difference between Ln+³ and Sr+². However these layered perovskites suffer from high thermal expansion coefficient (20-23 x 10-6 K-1) which does not match with the state of the art electrolyte materials. B-site transition metal doped layered perovskites of compositions SmBa₀.₅Sr₀.₅Co₂-ₓO₅+δ (M = Cu, Ni, Fe) have been investigated as cathode material for intermediate temperature solid oxide fuel cell using LSGM-9182 as the electrolyte material. Phase purity has been confirmed by XRD technique. The crystal cell parameters have been found out using Rietveld refinement by FULLPROF software. The substitution of Cu, Ni and Fe for Co lowers the CTE of Co-based materials by suppression of the spin state transition of Co³+ which will be highly advantageous for long term SOFC application. The introduction of transition metals exhibit inferior electrochemical performance to pristine cathode using LSGM-9182 as the electrolyte but still shows reasonable power density with advantage of lower CTE value thereby can be explored as promising cathode material for IT-SOFCs.

The increased demand for electric vehicles in recent years has driven the development of Li ion battery technology, yielding interesting trends in cathode materials. The layered cathode material Li(Ni1/3Mn1/3Co1/3)O2 gives 30% more reversible lithium extraction than the earlier LiCoO2 and the “overlithiated” material Li(Li0.2Mn0.54Ni0.13Co0.13)O2 gives a semi-reversible capacity 25% higher than Li(Ni1/3Mn1/3Co1/3)O2.1,2 6,7Li MAS NMR and 7Li MATPASS NMR were used to investigate the relation between the lithium ion and metal positions within these materials. It was found that Li(Ni1/3Mn1/3Co1/3)O2 showed a preference for Li ions to associate with Co at high voltages, that Mn4+ and Ni2+ showed some association and that the metals were not highly ordered. Li(Li0.2Mn0.5Ni0.13Co0.13)O2 showed a decrease in transition metal layer lithium upon cycling, in agreement with previous models, an ordering of the metal ions with the reinsertion of the lithium ions and a significant change in structure on deep discharge.3 These results will hopefully lead to more accurate modelling of the materials, understanding of reversibility and to increased reversible capacities in future cathode materials. Additionally work was done to enable high rate in-situ NMR spectra in which spectra are obtained from a cell while cycling in the bore of an NMR spectrometer. A Teflon Swagelok-style cell was designed and the effectiveness of solenoid and saddle coils were tested. It was found that for a 6 mm diameter cathode with a Li metal anode, at least half of the signal intensity could be obtained with a saddle coil whereas the signal was not detected when using a solenoid coil. / Thesis / Master of Science (MSc)

No description available.

The increasing demand for Li-ion batteries requires moving away from cobalt-containing cathode materials because Co is scarce, expensive, and geographically strongly localized. Co-free Ni-rich cathodes and their derivatives are, in principle, an excellent alternative, as Ni is more abundant, less expensive, and environmentally friendlier than Co. LiNiO₂, the parent of Ni-rich cathode materials, is structurally identical and chemically similar to LiCoO₂, offering almost the same theoretical capacity. However, LiNiO₂ and related materials often degrade rapidly during electrochemical cycling, with degradation modes including Li/Ni mixing, stacking faults, and surface reconstructions, making them unsuitable for battery applications. In this thesis, we used first-principles calculations to investigate the origin of Li/Ni mixing and stacking-fault formation, and we explored if entropy stabilization can be exploited to stabilize cobalt-free cathode materials. At half Li concentration, layered Li₀.₅NiO₂ is metastable, and the ground state is the spinel phase. The phase transformation from the layered to the spinel structure involves Ni migration and leads to Li/Ni mixing but only occurs at high temperatures. To better understand Li/Ni mixing in LiNiO₂, we determined the layered-to-spinel transformation in Li₀.₅NiO₂. We found the mechanism determined by electronic-structure symmetries, leading to a different route and intermediates from other well-studied lithium transition-metal oxides, such as Li₀.₅MnO₂. One important complication in LiNiO₂ is that it forms stoichiometry defects in which Ni atoms replace Li atoms, yielding off-stoichiometric Li₁₋zNi₁₊zO₂. Li/Ni mixing, a process in which Li and Ni interchange sites, can occur during synthesis or electrochemical cycling, and it reduces the capacity by impeding the intercalation of Li ions during battery operation. We unraveled the Li/Ni-mixing mechanism and explained the impact of off-stoichiometry on Li/Ni mixing from an electronic and geometric perspective. We also determined the role of the Li concentration and the Ni oxidation state on the driving force for Li/Ni cation mixing. At low Li contents, stacking faults can form in LiNiO₂, a process in which Ni layers glide relative to each other. These planar glides can alter the particle morphology, create new surfaces, and accelerate degradation. Stacking faults form unfavorable sites for Li, which impedes intercalation and lowers the capacity. We investigated the role of off-stoichiometry in planar glides and Ni migration in the presence of stacking faults. We determined how the distribution of Ni across the Li layers affects planar glides and explained how Li/Ni mixing may prevent the formation of stacking faults. Finally, to provide alternatives to the Ni-rich family of Co-free cathodes, we investigated if entropic stabilization can be exploited to stabilize layered cathode materials and prevent their degradation. We computationally assessed equimolar layered high-entropy oxides, a new class of layered materials that exhibits substitutional disorder in the transition-metal layer. We found that the general strategy of entropic stabilization is viable and identified four candidate compositions with good predicted energy density as a starting point for further studies. The research conducted as part of this thesis advances the understanding of degradation in Co-free cathode materials and identifies a direction for developing stable Co-free layered cathode materials with high energy density.

Le stockage de l'énergie est l'un des enjeux les plus cruciaux du 21e siècle. Le développement de matériaux abordables qui possèdent une grande densité d'énergie et qui affichent une grande stabilité est recherché. Une demande croissante venant du domaine de l'électronique portative fait pression sur la recherche de matériaux toujours plus performants. L'émergence des ordinateurs et téléphones portatifs ainsi que des véhicules électriques est la pièce maitresse de cette révolution. Par ailleurs, le stockage de l'énergie dans des batteries géantes, mais stationnaires, permettra au cours des prochaines années de pallier à la réalité de production d'énergie fluctuante du solaire et de l'éolien au cours d'une journée. La batterie Li-ion est présentement la technologie la plus mature pour mener à ce type de réalisation. L'atome de lithium est pourvu d'une petite masse molaire et l'ion lithium possède un petit rayon ionique. Utilisé à l'anode, le lithium permet d'y avoir une grande densité d'énergie, puis une faible résistance ionique dans l'électrolyte une fois oxydé. Par contre, les batteries Li-ion d'aujourd'hui reposent sur des matériaux de cathode dispendieux comme le cobalt, le nickel et le manganèse, dont l'exploitation soulève de grandes questions environnementales et éthiques. Avec une demande croissante pour des batteries de haute performance, des matériaux de cathode abordables, renouvelables et avec un impact environnemental faible doivent être développés. Dans ce contexte, les molécules organiques qui ont une activité redox ont attiré l'attention avec un faible cout de production, une faible toxicité et une abondance naturelle élevée. Parmi les différents groupements fonctionnels démontrant une activité rédox, les groupements carbonylés se démarquent par leur grande diversité, et leur stabilité à l'état réduit. Les matériaux redox typiques contenant des carbonyles sont les quinones, les 1,2-diones et les imides qui reposent sur un mécanisme d'énolisation lors du processus de réduction. La principale limitation que présentent ces molécules est la dissolution dans l'électrolyte. La formation d'un sel organique ou l'incorporation de la molécule électroactive au sein d'un polymère inerte sont des stratégies qui ont été apportées pour pallier à ce problème. La versatilité des molécules possédant des fonctions imides rend possible l'étude de plusieurs polymères π-conjugués qui ont l'avantage de pouvoir conduire davantage les charges injectées. Dans le cadre de ces travaux de doctorat, l'objectif général était de synthétiser de nouveaux polymères π-conjugués contenant des fonctions imides et d'analyser leurs performances en tant que matériau actif de cathode en batterie Li-ion. Les molécules qui ont été étudiées sont le maléimide, le pyromellitique diimide et le pyrène diimide. Des polymères π-conjugués ont été synthétisés avec ces unités en utilisant les techniques d'Ullmann, de Stille, de Suzuki ou d'arylation directe.