Matériaux d'électrode positive à base de phosphates pour accumulateurs Li-ion et phénomènes aux interfaces (apport de la spectroscopie photoélectronique à rayonnement X (XPS))

Ce travail de thèse est centré sur l étude de matériaux LiMPO4 (M=Fe, Mn, Co) et de leur évolution en cyclage (processus rédox et interfaces électrode / électrolyte) dans des accumulateurs Li-ion. Il a été mené essentiellement sur la base d analyses en spectroscopie photoélectronique à rayonnement X (XPS) couplées à des tests électrochimiques. Une oxydation de surface du phosphate LiFePO4 a été mise en évidence lors d une exposition à l air de ce matériau avec la formation d impuretés de surface type Fe2O3. Au plan structure électronique, l analyse des bandes de valence des matériaux LiMPO4 (M=Fe, Mn, Co) a notamment permis, pour LiFePO4, la visualisation de l électron spin down du niveau Fe 3d amenant la première preuve expérimentale de la configuration électronique particulière (3d )5(3d )1 de Fe2+dans ce matériau. Ce travail a également contribué à mieux comprendre l influence de la température de fonctionnement ainsi que de la nature de l électrode négative sur les mécanismes de vieillissement des accumulateurs Li-ion. Pour les accumulateurs LiFePO4 // Graphite, la comparaison d interfaces solide/électrolyte distribuées spatialement a montré que le vieillissement se caractérisant par la perte de lithium actif pouvait être mis en parallèle avec une hétérogénéité de fonctionnement de l électrode positive. Enfin, l extension des travaux aux matériaux prometteurs d électrode positive Li(FeMn)PO4 a révélé que le potentiel de travail de fin de charge plus élevé pour le phosphate mixte, comparativement à LiFePO4, résultait dans une réactivité accrue vis-à-vis de l électrolyte dont les conséquences ont été analysées.This thesis is focused on the study of LiMPO4 (M = Fe, Mn, Co) materials and on their evolution upon cycling (redox process end electrodes / electrolyte interfaces) in lithium ion cells. It is based on X-Ray Photoelectron Spectroscopy (XPS) analyses coupled with electrochemical tests. During air exposure, a surface oxidation of phosphate LiFePO4 was observed that lead to the formation of surface impurities such as Fe2O3. Concerning electronic structure, the analysis of LiMPO4 (M=Fe, Mn, Co) materials valence spectra allowed for LiFePO4 the visualization of spin down Fe 3d electron which is the first experimental proof of the particular electronic configuration (3d )5(3d )1 of Fe2+ in this material. This work also allowed a better understanding of the effect of the working temperature as well as the nature of the negative electrode on Li-ion cells ageing mechanisms. For LiFePO4 // Graphite cell, the comparison of spatially distributed solid/electrolyte interfaces showed that ageing mechanisms, characterized by a loss of active lithium, could be associated with a heterogeneity of working of the positive electrode. In addition, the extension of these studies on new promising Li(FeMn)PO4 materials for positive electrode showed that higher working potential of mixed phosphate material compared to LiFePO4 material leads to a higher electrolyte reactivity which consequences were analysed.PAU-BU Sciences (644452103) / SudocSudocFranceF

Réactivité de surface d'oxydes lamellaires, matériaux d'électrode positive dans des accumulateurs au lithium approches expérimentale et théorique

L'objectif de ce travail est de contribuer, par le biais d'approches expérimentales (XPS/chimisorption de sondes gazeuses) et théoriques (approches type DFT), à une meilleure compréhension fondamentale de la réactivité de surface de matériaux d'électrode positive et plus spécifiquement d'oxydes lamellaires lithiés LiMO2. La réactivité de surface du matériau LiCoO2 et l influence d une substitution de l atome de cobalt par l atome d aluminium a été étudiée pour avancer dans la compréhension de l effet bénéfique des coatings à base d alumine. L étude expérimentale a été centrée sur l adsorption de SO2 et montre que la présence d atomes d aluminium induit une diminution de réactivité : elle génère des espèces de type sulfite, différentes des sulfates seuls identifiés pour LiCoO2. La modélisation de cette adsorption permet la mise en évidence de deux modes d adsorption distincts : passage d un contrôle rédox pour LiCoO2 à un contrôle acido-basique pour des matériaux contenant des atomes d aluminium (LiAlO2), thermodynamiquement moins favorable. L influence de la nature du métal de transition a été analysée sur la base d études théoriques également menées sur LiMnO2 et LiNiO2. La modélisation de l adsorption de SO2 sur les surfaces des matériaux LiMO2 révèle la présence des deux processus de chimisorption (formation de sulfites et sulfates), avec mise en évidence du rôle important des cations de sous-surface dans les processus de réduction conduisant aux sulfates. Cette étude théorique a permis d interpréter les résultats expérimentaux obtenus pour Li(Ni1/3Mn1/3Co1/3)O2, l identification de sulfites résulterait de la présence des ions Ni2+ alors que celle de sulfates serait liée à la présence des ions Mn4+ et Co3+.This work is devoted to a better fundamental understanding of the surface reactivity of positive electrode materials, and specifically lamellar lithiated oxides LiMO2 through experimental (XPS/chemisorption of gaseous probes) and theoretical (DFT calculations) approaches. The beneficial effect of aluminum-based coatings on electrochemical performances is well known but the exact mechanisms are not totally understood. A detailed study of the surface reactivity of LiCoO2 and of the influence of Al/Co substitution is carried out. The experimental approach is focused on SO2 adsorption and shows that Al/Co substitution induces a decrease of the surface reactivity and a change in the nature of adsorbed species (identification of sulfite species whereas only sulfate species are characterized for LiCoO2). Theoretical calculations highlighs two different adsorption modes controlled by redox properties for LiCoO2 and by acid-base properties for -LiAlO2 (less energetically favorable). The theoretical study is extended to LiMnO2 and LiNiO2 in order to analyse the influence of the nature of the transition metal atom. The modelization of SO2 adsorption reveals two chemisorption processes (sulfite and sulfate formation), and highligths the key role of subsurface cations in the reduction process which leads to sulfates. Thus theoretical approach allows on interpretation of the experimental data obtained for Li(Ni1/3Mn1/3Co1/3)O2. The identification of sulfites may be explained by the presence of Ni2+ ions whereas sulfate species may result from the presence Mn4+ and Co3+ ions.PAU-BU Sciences (644452103) / SudocSudocFranceF

Crystal structure of 4-{2-[4-(di­methyl­amino)­phen­yl]diazen-1-yl}-1-methyl­pyridinium iodide

The molecular geometry of the ionic title compound, C14H17N4 + I or DAZOP+ I , is essentially featureless. Regarding the crystal structure, in addition to the obvious cation–anion Coulombic interactions, the packing is mostly directed by non-covalent interactions involving both ring systems, as well as the iodide anion. It consists of cationic molecules aligned along [101] and disposed in an antiparallel fashion while linked into -bonded dimeric entities by a stacking contact involving symmetry-related phenyl rings, with a centroid–centroid distance of 3.468 (3) A˚ and a slippage of 0.951 A˚ . The dimers are, in addition, sustained by a number of C—HI and I (Icentroid = 3.876 A˚ ) interactions involving the anion. Finally, interdimeric contacts are of the C—HI and C—H types. Keywords: crystal sChulvi, K.; Costero Nieto, AM.; Ochando Gómez, LE.; Gabiña, P. (2015). Crystal structure of 4-{2-[4-(di­methyl­amino)­phen­yl]diazen-1-yl}-1-methyl­pyridinium iodide. Acta Crystallographica Section E: Crystallographic Communications. 71:01069-01070. doi:10.1107/S2056989015023646S01069010707

Physical characteristics of localized surface plasmons resulting from nano-scale structured multi-layer thin films deposited on D-shaped optical fiber

Novel surface plasmonic optical fiber sensors have been fabricated using multiple coatings deposited on a lapped section of a single mode fiber. UV laser irradiation processing with a phase mask produces a nano-scaled surface relief grating structure resembling nano-wires. The resulting individual corrugations produced by material compaction are approximately 20 μm long with an average width at half maximum of 100 nm and generate localized surface plasmons. Experimental data are presented that show changes in the spectral characteristics after UV processing, coupled with an overall increase in the sensitivity of the devices to surrounding refractive index. Evidence is presented that there is an optimum UV dosage (48 joules) over which no significant additional optical change is observed. The devices are characterized with regards to change in refractive index, where significantly high spectral sensitivities in the aqueous index regime are found, ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity

An Auger and XPS survey of cerium active corrosion protection for AA2024-T3 aluminum alloy

XPS evidenced the proximity of the inhibitor with the surface AA2024 alloy.Cerium conversion coatings with [Ce] = 0.1 M offer the best corrosion resistance. SAM shown the migration of Ce + III entities towards the corrosion pits or crevices. High resolution analyses (Auger) connecting the nano-scale order with the chemical distribution

Li 4 Ti 5 O 12 Nanocrystals Synthesized by Carbon Templating from Solution Precursors Yield High Performance Thin Film Li‐Ion Battery Electrodes

Nanocrystals of Li 4 Ti 5 O 12 (LTO) have been prepared by processing an ethanol‐toluene solution of LiOEt and Ti(OiPr) 4 using a carbon black template. The mechanism of crystal growth has been tracked by SEM and TEM microscopies. The resulting nanocrystals grown using the carbon template (C‐LTO) show less aggregation than materials prepared from solution without the template (S‐LTO), which is reflected in higher surface area (27 m 2 /g) and concomitantly smaller particle size (58 nm) for C‐LTO compared to 20 m 2 /g and 201 nm for S‐LTO. Electrochemically, thin‐film electrodes composed of C‐LTO demonstrate reversible cycling, storing ∼160 mAh/g at both 1 C (175 mA/g) and 10 C current. Important is that resistance to charge transfer between the C‐LTO nanocrystals and added conducting carbon is 3 times smaller than that for S‐LTO. Accordingly, C‐LTO shows excellent rate capability, maintaining an energy‐storage capacity >150 mAh/g even at 100 C current. These characteristics solidify C‐LTO a suitable replacement for carbon as a Li‐ion battery anode. High power Li 4 Ti 5 O 12 (LTO) nanocrystals can be synthesized by a carbon‐templating method for Li‐ion battery electrodes . These electrodes demonstrate reversible cycling of 160 mAh/g at both 1 C and 10 C current, and remains above 150 mAh/g even at 100 C.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98313/1/aenm_201200964_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/98313/2/753_ftp.pd