Les phosphates de structure olivine LiMPO4 (M=Fe, Mn) comme matériau actif d'électrode positive des accumulateurs Li-ion

Ce mémoire est consacré à la recherche de matériaux d'électrode positive pour batteries Li-ion et plus particulièrement aux phases de type olivine : LiFePO4, LiFe1-yMnyPO4, LiFe1-yCoyPO4 et LiMnyCo1-yPO4 obtenues par voie céramique. Une étude des propriétés physico-chimiques et structurales de ces composés a été réalisée par les techniques classiques de la Chimie du Solide et de la Science des Matériaux : spectrométrie Mössbauer de 57Fe, microscopie MEB et diffraction des rayons X. L'objectif de cette étude est d'identifier et de comprendre les mécanismes de réaction lors du cyclage de la batterie qui peuvent améliorer ou limiter les performances de la batterie.Cette étude a permis de montrer la complémentarité de la spectrométrie Mössbauer et de la diffraction des rayons X pour l'analyse des mécanismes d'oxydo-réduction mis en jeu dans les réactions électrochimiques. A partir du mécanisme biphasé bien connu de LiFePO4, des mécanismes électrochimiques en trois étapes et les phases formées lors du cyclage ont été identifiés pour les phases substituées au manganèse. L'aptitude de ces composés à fonctionner comme matériaux d'électrode positive de batteries Li-Ion de puissance a été démontrée par des cyclages à longue durée à différentes températures et vitesses de cyclage.This thesis is devoted to finding positive electrode materials for Li-ion batteries and more particularlycompounds of olivine type: LiFePO4, LiFe1-yMnyPO4, LiFe1-yCoyPO4 and LiMnyCo1-yPO4. An in-depth study of their physicochemical and structural properties was done combining Solid State Chemistry and Material Sciences techniques: Mössbauer spectrometry of 57Fe, microscopy SEM and X-ray diffraction. The aim of this study is to identify and understand the electrochemical mechanism during the cycling of the battery that can enhance or limit the battery performance. This study has shown the complementarity of Mössbauer spectrometry and X-ray diffraction to analyze the redox mechanisms involved into the electrochemical reactions. From the well-known two-phase mechanism of LiFePO4, electrochemical mechanisms in three steps and phases formed during cycling have been identified for phase substituted manganese. The ability of these compounds to be used as positive electrode materials for powerful Li-Ion batteries was demonstrated by long-term cycling at different temperatures and rates of cycling.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Lithium-induced conversion reaction in wüstite Fe1-xO studied by 57Fe Mössbauer spectroscopy.

International audienceFe1-xO wüstite as negative electrode material for Li-ion batteries has been studied. The aim of this work is to get a better understanding of the insertion mechanism involved during reduction/oxidation processes. Electrochemical tests have been done in SwagelockTM cells and shown a high specific capacity of 800 Ah/kg for the first discharge. X-ray diffraction and 57Fe Mössbauer spectroscopy provide us valuable information on both local and long range order. Hence, Li reaction with wüstite induces formation of highly divided metallic iron (alpha-Fe and nano-Fe) and Li2O with a small amount of Fe2O3 occurring in a diffusion layer at the surface of the primary particles. Based on the X-ray and Mössbauer spectroscopic analyses, a core-shell model is proposed in order to explain the irreversible capacity of about 1 Li observed at the first cycle. It involves cation diffusion induced by lithium acting as an "electronic pressure‟

Mössbauer spectroscopy as a powerful tool to study local electronic structure

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Thermal stability of some glassy compositions of the Ge-As-Te ternary

L. Aldon, M. Leh Deli, P.E. Lippens, J. Olivier-Fourcade, J.-C.JumasInternational audienceTellerium-based chalcogenide glasses have been studied extensively in the recent past not only because of their technological applications, but also due to their interesting physical properties. Tellerium is a good element for far infrared transmission but is a poor glass former. Glass forming domains are very narrow in binary Ge-Te or As-Te system. Better glass forming ability and thermal stability are observed in presence of arsenic and germanium atoms. These glasses possess a wide optical window that is maximal for the Ge10As20Te70 glass (20µm). It made it possible to show that the substitution of germanium by selenium and antimony reduces the physical properties (ρ, Eg, Tg, Tc1, Tc2, Tc1-Tg et Tm). Indeed germanium supports the formation of glasses, contrary to metal antimony

Li deinsertion mechanism and Jahn–Teller distortion in LiFe0.75Mn0.25PO4: an operando x-ray absorption spectroscopy investigation

International audienceThe electrochemical lithiation of the mixed metal olivine LiFe0.75Mn0.25PO4 was followed by operando x-ray absorption spectroscopy (XAS) at both Fe and Mn K edges. XAS data were interpreted using an innovating chemometric approach, allowing the detailed reconstruction of the rather complicated reaction mechanism involving two different metal centres. In this way it was possible to precisely describe the Jahn–Teller effect occurring upon oxidation of the manganese centres. The thorough comprehension of the electrochemical mechanism is of high interest for studying the effect of lithium extraction in the olivine structure in the presence of Mn, which is known to partially hamper the complete lithiation of such mixed metal systems

Combined operando studies of new electrode materials for Li-ion batteries

International audienceThe performances of Li-ion batteries depend on many factors amongst which the important ones are the electrode materials and their structural and electronic evolution upon cycling. For a better understanding of lithium reactivity mechanism of many materials the combination of X-Ray Powder Diffraction (XRPD) and Transmission Mössbauer Spectroscopy (TMS) providing both structural and electronic information during the electrochemical cycling has been carried out. Thanks to the design of a specific electrochemical cell, derived from a conventional Swagelock cell, such measurements have been realised in operando mode. Two examples illustrate the greatness of combining XRPD and TMS for the study of LiFe0.75Mn0.25PO4 as positive electrode and TiSnSb as negative electrode. Different kinds of insertion or conversion reactions have been identified leading to a better optimization and design of performing electrodes

Structural transformation in lithiared Mn2Sb electrodes probed by Mössbauer spectroscopy and X-ray diffraction

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