This thesis addresses the electronic structure of vanadium and copper oxides using soft X-ray absorption (SXA) spectroscopy and resonant inelastic X-ray scattering (RIXS) at high brightness synchrotron radiation sources. In RIXS incident photons, tuned to the energy of specific absorption resonances, are inelastically scattered leaving behind a low energy valence excitation in the system studied. Effects of electron localization are reflected by the occurrence of low-energy excitations in form of dd- and charge-transfer excitations that are modelled by cluster calculations. Band-like states are dominating when the intermediate core excited state is delocalized. RIXS at V 2p and O 1s resonances has been used to study the electronic structure of the monovalent vanadium oxides VO2 and V2O3, and of the mixed valence compounds, NaV2O5 and V6O13. For NaV2O5 and V6O13 significant contributions from localized low-energy excitations reflect the partly localized character of their valence band electronic structure, whereas VO2 and V2O3 appear mostly as band-like. Effects of carrier doping are addressed for the case of Mo doping into VO2 and reveal a quasi-rigid band behavior. In the cases of VO2 and V6O13 the temperature dependent metal-insulator transition could be monitored by following the spectral evolution of bands originating from V 3d and V 3d - O2p hybridized states. For Na2V3O7 nanotubes it was possible to selectively probe states from the apical and the basal oxygen sites of VO5 pyramids that constitute these nanotubes. Furthermore, the RIXS technique has been demonstrated to be highly valuable in characterizing the charge transfer processes that accompany lithium insertion into vanadium oxide battery cathodes. Finally, for insulating cuprates RIXS at O 1s, Cu 3p and Cu 3s resonances has been recorded at high-resolution for the detailed investigation of crystal field excitations.

Proton exchange membrane fuel cells and lithium polymer batteries are important as future power sources in electronic devices, vehicles and stationary applications. The development of these power sources involves finding and characterising materials that are well suited r the application. The materials investigated in this thesis are the perfluorosulphonic ionomer NafionTM (DuPont) and metal oxides incorporated into the membrane form of this material. The ionomer is used as polymer electrolyte in proton exchange membrane fuel cells (PEMFC) and the metal oxides are used as cathode materials in lithium polymer batters (LPB). Crystallinity in cast Nafion films can be introduced by ion beam exposure or aging. Spectroscopic investigations of the crystallinity of the ionomer indicate that the crystalline regions contain less water than amorphous regions and this could in part explain the drying out of the polymer electrolyte membrane in a PEMFC. Spectroscopic results on the equilibrated water uptake and the state of water in thin cast ionomer films indicate that there is a full proton transfer from the sulphonic acid group in the ionomer when there is one water molecule per sulphonate group. The LPB cathode materials, lithium manganese oxide and lithium cobalt oxide, were incorporated in situ in Nafion membranes. Other manganese oxides and cobalt oxides were incorporated in situ inside the membrane. Ion-exchange experiments from HcoO2 to LiCoO2 within the membrane were also successful. Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction were used for the characterisation of the incorporated species and the Nafion film/membrane.

The Li-ion battery has, from its commercialisation in the early 1990's, now become the most widely used power source for portable low-power electronics: laptops, cellular phones and MP3-players are a few examples. To further develop existing and find new electrode materials for these batteries, it is vital to understand the lithium insertion/extraction mechanisms taking place during battery operation. In this thesis, single-crystal X-ray diffraction has been used to investigate lithium insertion/extraction mechanisms in the cathode materials V6O13 and LiFePO4. A novel single-crystal electrochemical cell for in situ single-crystal X-ray diffraction studies has also been developed. The phases Li3V6O13 and Li3+xV6O13, 0<x<1, both contain a disordered lithium ion. A low-temperature study of Li3.24V6O13 (at 95 K) shows that this disorder is static rather than dynamic; the lithium ion is equally distributed above and below an inversion centre in the centrosymmetric V6O13 host structure. Short-range-ordering between this disordered lithium ion and the lithium ion inserted into Li3V6O13 gives rise to solid-solution behaviour not observed earlier in the LixV6O13 system. A model is proposed for the lithium insertion mechanism up to the end-member composition Li6V6O13. Lithium has also been electrochemically extracted from LiFePO4 single crystals. On the basis of the shapes of the LiFePO4 and FePO4 reflections, it is concluded that FePO4 is formed at the crystal surface and that the LiFePO4/FePO4 interface propagates into the crystal. This is in agreement with an earlier proposed model for lithium extraction from LiFePO4 particles. Initial experiments with the newly developed single-crystal electrochemical cell for in situ single-crystal X-ray diffraction demonstrate that it is possible to insert lithium into a single crystal of V6O13 and then collect single-crystal X-ray diffraction data. The method needs further development but promises to become a powerful tool for studying lithium insertion/extraction mechanisms.

In the early 1970s, research carried out on rechargeable lithium batteries at the Exxon Laboratories in the US established that lithium ions can be intercalated electrochemically into certain layered transition-metal sulphides, the most promising being titanium disulphide. Stemming from this discovery for titanium disulphide, there has been increased interest on lithium-ion intercalation compounds for application in rechargeable batteries. The first rechargeable lithium cell was commercialized in late 1980s by Moli Energy Corporation in Canada. The cell comprised a spirally wound lithium foil as the anode, a separator and MoS2 as the cathode. The cell had a nominal voltage of 1.8 V and an attractive value of specific energy, which was 2 to 3 times greater than either lead-acid or nickel-cadmium cells. However, the battery was withdrawn from the market after safety problems were experienced. This paved way for the discovery of lithium-ion battery. The origin of lithium-ion battery lies in the discovery that Li+-ions can be reversibly intercalated within or deintercalated from the van der Walls gap between graphene sheets of carbon materials at a potential close to the Li/Li+ electrode. Thus, lithium metal is replaced by carbon as the anode material for rechargeable lithium-ion batteries, and the problems associated with metallic lithium mitigated. Complimentary investigations on intercalation compounds based on transition metals resulted in establishing LiCoO2 and LiNiO2 as promising cathode materials. By employing aforesaid intercalation materials, namely carbon and LiCoO2 respectively, as negative and positive electrodes in a non-aqueous lithium-salt electrolyte, a Li-ion cell with a voltage value of about 3.5 V resulted. These findings led to a novel rechargeable battery technology. Lithium-ion batteries were first introduced commercially in 1991 by the Sony Corporation in Japan. Other Japanese manufacturers soon entered the market, followed closely by American and European companies. The subsequent growth in sales of the batteries was truly phenomenal. Beginning from 1991, the lithium-ion battery market has grown from an R&D interest to sales of over 400 million units in 1999. The global market value for lithium-ion batteries at original equipment manufacturer level was estimated to be $1.86 billion in 2000. By 2006, the market is expected to grow to over 1.2 billion units with value of over $4 billion, while the average unit price is expected to fall. Initially, realizable specific energy of commercial Li-ion battery was only about 120 Wh kg-1. However, with continuing improvements in various cell components, present day Li-ion batteries can provide a specific energy density of about 200 Wh kg-1. With the ‘holy grail’ far to be realized, the current R&D efforts are focussed on furthering the specific energy of lithium-ion batteries in conjunction with safety, environmental compatibility, and cost effectiveness. In the Li-ion cell, all of its electrochemical constituents, namely anode, cathode and electrolyte are central to its performance. This thesis describes some novel studies on cathode and anode materials for lithium-ion Batteries.

Made available in DSpace on 2014-12-17T14:07:09Z (GMT). No. of bitstreams: 1 FlaviaMA_TESE_partes_autorizadas.pdf: 1059426 bytes, checksum: e2aa7ae9084b3b21cbc8a9c274f271a1 (MD5) Previous issue date: 2012-11-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Alternative and clean energy generation research has been intensified in last decades. Among the alternatives, fuel cells are one of the most important. There are different types of fuel cells, among which stands out intermediate temperature solid oxide fuel cell (IT-SOFC) matter of the present work. For application as cathode on this type of devices, the ceramic Ba0.5Sr0.5C0.8Fe0.2O3-? doped with rare earth ions (Nd, Sm) have been quite promising because they show good ionic conductivity and operate at relatively low temperatures (500 - 800?C). In this work, Ba0.5Sr0.5Co0.8Fe0.2O3-?, (BaSr)0.5Sm0.5Co0.8Fe0.2O3-? and (BaSr)0.5Nd0.5C0.8Fe0.2O3-? were obtained by modified Pechini method, making use of gelatin as polymerizing agent. The powders were characterized by X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). The perovskite phase was observed in all X-ray patterns for the materials Ba0.5Sr0.5C0.8Fe0.2O3-? doped with rare earth ions (Nd, Sm). The SEM images showed that the materials have a characteristics porous, with very uniform pore distribution, which are favorable for application as cathodes. Subsequently, screen-printed assymmetrical cells were studied by impedance spectroscopy, to assess the kinetics of the cathode for the reduction reaction of oxygen. The best resistance to the specific area was found for the cathode BSSCF sintered at 1050 ?C for 4 hours with around 0.15 ?.cm2 at 750 ?C as well as cathodes BSNCF and BSCF obtained resistances specific area of 0.2 and 0.73 ?.cm2, respectively, for the same conditions. The polarization curves showed similar behavior to the best cathodes BSSCF and BSNCF, such combination of properties indicates that the film potentially depict good performance as IT-SOFC cathodes / Pesquisas voltadas para formas alternativas e n?o poluentes de gera??o de energia que v?m se intensificando. Entre essas, destacam-se as c?lulas a combust?vel de ?xido s?lido de temperatura intermedi?ria (IT-SOFC). Para aplica??o como catodo deste tipo de dispositivo, os ?xidos cer?micos Ba0,5Sr0,5C0,8Fe0,2O3-? dopadas com ?ons de terras raras (Nd, Sm) t?m se mostrado bastante promissores pelo fato de possu?rem boa condutividade i?nica e operarem em temperaturas relativamente baixas (500-800?C). Neste trabalho, Ba0,5Sr0,5C0,8Fe0,2O3-? (BSCF), (BaSr)0,5Sm0,5C0,8Fe0,2O3-? (BSSCF) e (BaSr)0,5 Nd0,5C0,8Fe0,2O3-? (BSNCF) foram obtidos pelo m?todo Pechini modificado, fazendo uso de gelatina que atua como agente polimerizante e coordenante. Os p?s obtidos foram caracterizados por Difra??o de Raios X (DRX), Redu??o ? Temperatura Programada (RTP) e Microscopia Eletr?nica de Varredura (MEV) e Microscopia Eletr?nica de Transmiss?o (MET). A fase perovsquita foi evidenciada em todos os difratogramas de raios X nos ?xidos Ba0,5Sr0,5C0,8Fe0,2O3-? dopados com ?ons de terras raras (Nd, Sm). As imagens de MEV evidenciaram que o p? obtido ? poroso, o que favorece seu uso como c?todos. Posteriormente, foram preparadas c?lulas assim?tricas por screen-pritting para estudos de microestrutura e de espectroscopia de imped?ncia, a fim de avaliar a cin?tica de c?todo da rea??o de redu??o do oxig?nio no c?todo. A melhor resist?ncia ? ?rea espec?fica foi encontrada para o c?todo BSSCF sinterizado a 1050 ?C durante 4 horas com 0,15 ?.cm2 na temperatura de 750?C, bem como os c?todos BSNCF e BSCF obtiveram resist?ncias ? ?rea espec?fica de 0,20 e 0,73 ?.cm2 , respectivamente, para as mesmas condi??es. As curvas de polariza??o demonstraram comportamentos semelhantes aos melhores c?todos BSSCF e BSNCF, sendo assim, adequados para aplica??o como material cat?dico nas SOFC

Li-O2 batteries have attracted world-wide research interest as an appealing candidate for future energy supplies because they possess the highest energy density of any battery technology. However, such system still face some challenges for the practical application. One of the key issues is exploring highly efficient cathode materials for Li-O2 batteries. Here, a rolled-up technology associated with other physical or chemical methods are applied to prepare architectural nanomembranes for the cathode materials in Li-O2 batteries. The strain-release technology has recently proven to be an efficient approach on the micro/nanoscale to fabricate composite nanomembranes with controlled thickness, versatile chemical composition and stacking sequence. This dissertation first focuses on the synthesis of trilayered Pd/MnOx/Pd nanomembranes. The incorporation of active Pd layers on both sides of the poor conductive MnOx layer commonly used in energy storage systems greatly enhances the conductivity and catalytic activity. Encouraged by this design, Pd nanoparticles functionalized MnOx-GeOy nanomembranes are also fabricated, which not only improve the conductivity but also facilitate the transport of Li+ and oxygen-containing species, thus greatly enhancing the performance of Li-O2 batteries. Similarly, Au and Pd arrays decorated MnOx nanomembranes act as bifunctional catalysts for both oxygen reduction reaction and oxygen evolution reaction in Li-O2 batteries. Moreover, by introducing hierarchical pores on the nanomembranes, the performance of Li-O2 batteries is further promoted by porous Pd/NiO nanomembranes. The macropores created by standard photolithography facilitate the rolling process and the nanopores in the nanomembranes induced by a novel template-free method supply fast channels for the reactants diffusion. In addition, a facile thermal treatment method is developed to fabricate Ag/NiO-Fe2O3/Ag hybrid nanomembranes as carbon-free cathode materials in Li-O2 batteries. A competing scheme between the intrinsic strain built in the oxide nanomembranes and an external driving force provided by the metal nanoparticles is introduced to tune the morphology of the 3D tubular architectures which greatly improve the performance by providing continuous tunnels for O2 and electrolyte diffusion and mitigating the side reactions produced by carbonaceous materials.

Na-ion batteries (NIBs) are expected to revolutionise the battery sector by promising an affordable technology while capitalising on sustainable development. To compete with Li-ion batteries, however, electrode materials with higher capacities need to be developed. Transition metal nitroprussides (TM-NPs), NaxM[Fe(CN)5NO]1-y ·zH2O, is a material class derived from one of the most popular positive electrode materials for NIBs, Prussian blue analogues (PBAs), where one of the cyano ligands have been replaced by an electroactive nitrosyl (NO) ligand. Thus, in theory TM-NPs should be able to reach higher capacities than PBAs and therefore be attractive candidates for high-capacity electrodes. However, if the nitrosyl is redox active in NIBs and how the cycling behaviour may be affected by the M cation is unknown. The focus in this thesis is therefore to explore the charge-discharge behaviour of four different TM-NPs (M=Fe, Ni, Mn, and Cu) in Na-ion half-cell batteries to gain an initial understanding of their electrochemical behaviour and to set up research questions to be pursued in the future. Based on our observations and previous studies, we propose that the nitrosyl is electrochemically active in all four TM-NPs, and that it contributes with a considerable amount of capacity, although with a large voltage hysteresis. It is further concluded that all M cations apart from Ni were redox active, but to varying degrees on charging and discharging. We argue that both the redox and the voltage hysteresis is caused by anisotropic charge transfer within the materials, and that it needs to be understood before commercialisation of TM-NPs can be realised. Though there are challenges to overcome, the many interesting attributes of TM-NPs, including anionic redox, anisotropic charge transfer and structural diversity, makes them promising as a new type of cheap and sustainable electrode material for NIBs.

The need for highly efficient energy storage devices has been steadily increasing due to growing energy demands. Research in electrochemical energy storage in the form of batteries has consequently become crucial. Currently, the most commercialized battery technology is the lithium ion battery (LIB). Concerns over the relatively limited global lithium supply, however, have led to the development of sodium ion batteries (SIBs). Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is an ideal technique for analyzing battery materials as it can potentially distinguish between different ions within the material. The most typical cathode for commercial LIBs are the family of NMC layered oxides with the general form Li[NixMnyCo1-x-y]O2, which consist of Li layers between sheets of transition metals (TMs). The pj-MATPASS NMR technique, in conjunction with Monte Carlo simulations, was applied to investigate the ionic arrangement within TM layers of NMC622 (Li[Ni0.6Mn0.2Co0.2]O2), which revealed the presence of ion clustering in the pristine form of this material. This thesis also investigated the promising SIB cathode, Na3V2(PO4)2F3 (NVPF). NVPF has the capability to produce energy densities comparable to those of LIBs and is well understood from a structural standpoint, however ion dynamics within the material are still undetermined. A series of materials have, therefore, been synthesized with the general form, Na3V2-xGax(PO4)2F3 (where x = 0, 1, and 2), where diamagnetic Ga3+ was introduced into the structure to enable the establishment of a structural correlation with observed Na-ion dynamics. It, therefore, became possible to explore ionic site exchange using 23Na ssNMR. Density functional theory (DFT) calculations have also been performed alongside ssNMR to confirm chemical shift assignments and provide structural insight. Additionally, electron paramagnetic resonance (EPR) spectroscopy was also used to investigate the paramagnetic nature of NVPF and its variants. Insights into the ionic arrangement and very fast Na-ion dynamics within these materials were revealed. / Thesis / Master of Science (MSc) / The need for highly efficient energy storage devices, especially in the form of batteries, has been steadily increasing due to growing energy demands. Presently, the most commercialized types of batteries are lithium ion batteries (LIBs). Concerns over the relatively limited global lithium supply, however, have led to the development of sodium ion battery (SIB) alternatives. Various solid-state nuclear magnetic resonance (ssNMR) techniques have been employed in this thesis to investigate both LIB and SIB cathode materials. The LIB cathode Li[Ni0.6Mn0.2Co0.2]O2 was examined with a combination of ssNMR and Monte Carlo simulations, and it was found that ion clustering occurs in the pristine form of these materials. The promising family of SIB cathodes, Na3V2-xGax(PO4)2F3, was studied by a combination of ssNMR, ab initio calculations, and EPR, which allowed for a correlation to be established between the crystal structure and the fast ion dynamics within these materials.

Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources. Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau. / In this thesis, we demonstrate work on two different cathode materials for lithium-ion batteries. First, the synthesis of lithium iron phosphate (LiFePO4) is reproduced from literature using two lithiation methods starting with amorphous iron phosphate (FePO4). For both reactions, the product at each step of the synthesis was analyzed using Mössbauer Spectroscopy and X-ray diffraction in order to gain further insight of the reaction mechanism. The results of this work were published in Journal of Power Sources. The second cathode material of interest was lithium iron silicate (Li2FeSiO4). A novel synthetic method was developed to produce lithium iron silicate cost effectively starting with low cost precursors and basic laboratory equipment. The material was synthesized using a solid- state synthesis after milling and carbon coating, electrochemical performance was evaluated. An attempt was made to synthesize off-stoichiometric lithium iron silicate in order to increase the electrochemical performance of the material.

Dans cette thèse nous démontrons le travail fait sur deux matériaux de cathodes pour les piles lithium-ion. Dans la première partie, nous avons préparé du phosphate de fer lithié (LiFePO4) par deux méthodes de lithiation présentées dans la littérature qui utilisent du phosphate de fer (FePO4) amorphe comme précurseur. Pour les deux méthodes, le produit obtenu à chaque étape de la synthèse a été analysé par la spectroscopie Mössbauer ainsi que par diffraction des rayons X (DRX) pour mieux comprendre le mécanisme de la réaction. Les résultats de ces analyses ont été publiés dans Journal of Power Sources. Le deuxième matériau de cathode qui a été étudié est le silicate de fer lithié (Li2FeSiO4). Une nouvelle méthode de synthèse a été développée pour obtenir le silicate de fer lithié en utilisant des produits chimiques peu couteux ainsi que de l’équipement de laboratoire de base. Le matériau a été obtenu par une synthèse à l’état solide. Les performances électrochimiques ont été obtenues après une étape de broyage et un dépôt d’une couche de carbone. Un essai a été fait pour synthétiser une version substituée du silicate de fer lithié dans le but d’augmenter les performances électrochimiques de ce matériau. / In this thesis, we demonstrate work on two different cathode materials for lithium-ion batteries. First, the synthesis of lithium iron phosphate (LiFePO4) is reproduced from literature using two lithiation methods starting with amorphous iron phosphate (FePO4). For both reactions, the product at each step of the synthesis was analyzed using Mössbauer Spectroscopy and X-ray diffraction in order to gain further insight of the reaction mechanism. The results of this work were published in Journal of Power Sources. The second cathode material of interest was lithium iron silicate (Li2FeSiO4). A novel synthetic method was developed to produce lithium iron silicate cost effectively starting with low cost precursors and basic laboratory equipment. The material was synthesized using a solid- state synthesis after milling and carbon coating, electrochemical performance was evaluated. An attempt was made to synthesize off-stoichiometric lithium iron silicate in order to increase the electrochemical performance of the material.