Photonic titanium dioxide film obtained from hard template with chiral nematic structure for environmental application

International audienceIn the present work, mesoporous TiO 2 with a photonic structure was elaborated using cellulose nanocrystals (CNCs) as a biotemplate by two-step hard template methods. This strategy enables to replicate the chiral nematic (CN) structure of the photonic films (biotemplate) in TiO 2 films. A series of iridescent CNCs films with different weight ratios of silica/CNCs composite photonic films were prepared via evaporation induced self-assembly (EISA) method. The films showed iridescent color and tuneable Bragg reflection wavelengths by solely changing the ratio between the silica and the CNCs biotemplate. Polarized optical microscopy (POM) performed on hydride SiO 2 /CNCs films showed a birefringence and typical fingerprint of chiral nematic structure. This birefringence was also observed for TiO 2 films obtained using SiO 2 films as a hard template, which suggested the transfer of the chiral nematic structure in TiO 2 materials. Afterwards, their optical, morphological and electronic properties were studied by scanning electron microscope (SEM), POM, energy-dispersive X-ray spectroscope (EDX) and time resolved microwave conductivity (TRMC). The photocatalytic activities were evaluated by following the phenol degradation using high performance liquid chromatography (HPLC). The results showed that the structuration of the TiO 2 film using a chiral nematic SiO 2 film as hard template enhances the photocatalytic performance compared to non-structured mesoporous TiO 2

Étude de nouvelles voies de dépôt du matériau d'électrode positive LiCoO2 pour la réalisation de micro-accumulateurs 3D à haute capacité surfacique

La miniaturisation des systèmes électroniques est aujourd hui l un des enjeux majeurs de la recherche et demande une importante évolution des sources d énergie. Les micro-accumulateurs tout solide sont une réponse parfaitement adaptée à ce besoin. Leur capacité est toutefois actuellement limitée à 50-200 Ah.cm-2 du fait de la difficulté d employer des couches de matériaux actifs d épaisseur supérieure à 5 m. L une des pistes pour augmenter la capacité spécifique des micro-accumulateurs est de déposer les différents matériaux sur un substrat texturé. Les techniques de dépôt sous vide classiques ne permettent pas de déposer des films conformes sur de telles surfaces, principalement à cause d effets d ombrage. L objectif de ce travail de thèse a donc été de développer de nouvelles voies de dépôt pour la réalisation de micro-accumulateurs tout-solide 3D. Deux voies de dépôt chimique ont été explorées : la synthèse sol-gel et l électrodépôt sous conditions hydrothermales. La synthèse sol-gel n a pas permis d aboutir à la réalisation de films denses et conformes. Cependant, elle s est avérée très intéressante pour synthétiser des poudres de LiCoO2 rhomboédrique présentant d importantes surfaces spécifiques, sans étape de broyage, à des températures de synthèse modérées (600-700C). Le dépôt électrolytique en conditions hydrothermales s est quant à lui révélé très prometteur tant pour sa vitesse de dépôt importante, jusqu à 300 nm.mn-1, que pour sa température de synthèse basse, à partir de 125C, sans nécessiter de recuit. Les films synthétisés présentent d excellentes performances électrochimiques en électrolyte liquide et une conformité sur des substrats texturés supérieure à 97 %.The miniaturization of electronic systems is today a main topic of research and requires an important evolution of energy sources. All solid state micro-batteries are a perfectly adapted solution for this need. However, their specific capacity is limited to 50-200 Ah.cm-2 due to the difficulty to use films of active materials thickness over than 5 m. One of the answers to enhance micro-batteries specific capacity is to deposit materials on textured substrate. Nevertheless, classical vacuum deposition techniques are not adapted to deposit conformal thin films on such surfaces because of shadow effects. The aim of this PhD-work was to develop new synthesis routes to realize 3D all solid state micro-batteries. Two chemical synthesis routes were studied: the sol-gel method and the electrodeposition under hydrothermal conditions. The sol-gel synthesis was not efficient to realize conformal and dense films. However, this technique was very effective to obtain rhombohedra LiCoO2 powders with high specific surface, without grinding step, at moderate temperature (600-700C). The electrodeposition under hydrothermal conditions was very promising, both for its high deposition rate (up to 300 nm.mn-1) and its low synthesis temperature (from 125C) without any annealing. The synthesized films exhibited excellent electrochemical performances in liquid electrolyte and a conformity higher than 97 % on textured substrates.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Étude des mécanismes et modélisation du vieillissement des batteries lithium-ion dans le cadre d'un usage automobile

Ce travail vise à modéliser le vieillissement des batteries lithium-ion soumises à des sollicitations de type véhicule (électrique ou hybride). Cette étude a notamment pour but d optimiser le dimensionnement des packs batteries pour véhicule et les stratégies de gestion électrique. Une approche originale, de type fatigue mécanique, a été sélectionnée car potentiellement capable de modéliser des sollicitations complexes et variées. Cette approche a été développée pour une batterie lithium-ion spécifique graphite/NCA. Il apparaît qu un simple cumul de dommage n est pas entièrement pertinent et que deux contributions au vieillissement sont à l œuvre : l une en fonction de la charge échangée et l autre en fonction du temps. De multiples essais de vieillissement ont été effectués et montrent l influence très importante de la température, du courant et de l état de charge sur chacune de ces contributions. Ces essais permettent de mettre en équation l impact de chacun de ces paramètres sur la vitesse de dégradation. Il en découle un modèle informatique de prévision du vieillissement, capable de prendre en compte les périodes d arrêt comme de roulage. Les résultats, sur des sollicitations peu à moyennement complexes, donnent une très faible erreur au niveau de la prévision. Des analyses post-mortem ont également été effectuées sur les batteries étudiées afin de comprendre les mécanismes en jeu. Plusieurs analyses (physico-chimiques et électrochimiques, par spectroscopie d impédance) permettent de relier les principaux mécanismes de vieillissement à chacune des deux contributions : une altération de la structure cristalline du matériau actif d électrode positive pour la contribution fatigue, la passivation du matériau actif d électrode négative pour la contribution temporelle. Ces analyses apportent une vision plus complète du vieillissement et justifient les hypothèses effectuées lors de la mise en place du modèle. Elles permettent également d envisager une généralisation du modèle à d autres technologies de batteries lithium-ion. D ailleurs, un essai de généralisation à une autre batterie commerciale a permis de vérifier la fiabilité et de détecter les limites de notre approche.This scientific piece of work aims at modeling the aging of lithium-ion batteries, depending on the vehicle stress (electric or hybrid type). More specifically, this study intends to optimise the design of battery packs for vehicle and power management strategies. A original mechanical fatigue approach has been selected as potentially able to model complex and varied demands. This approach was developed for a specific graphite / NCA lithium-ion battery. It appears that a simple damage accumulation is not entirely relevant, and that two contributions to aging are ongoing: one based on charge throughput and the other based on time. Multiple aging tests were performed and have shown the important influence of temperature, current power and state of charge for each contribution. They led to the establishment of equations linking each of these parameters to battery degradation rate. Thanks to these equations, a computer model for aging prevision has been built, able to take into account both cycling and calendar ageing. The model gives, for slightly to moderately complex solicitations, a very small predicting error. Postmortem analyses were also performed on the batteries to understand the mechanisms involved. Several analytical techniques (physicochemical and electrochemical, impedance spectroscopy) make possible to connect the main mechanisms of ageing to the contributions: an alteration of the crystalline structure of the positive electrode active material for the fatigue contribution, passivation of the negative electrode active material for the time contribution. These analyses provide a more complete view of aging and justify the hypothesis made during the implementation of the model. These electrochemical results allow us to consider a generalisation to other lithium-ion battery technologies. Indeed, an attempt to generalise the model to another commercial battery has made possible to check the reliability and to detect limits of this approach.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Fatigue des batteries Li-ion dans le cadre d'une utilisation véhicule électrique (impact des conditions d'utilisation sur le vieillissement)

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

SYNTHESE, CARACTERISATION ET ETUDE DES PROPRIETES ELECTROCHIMIQUES DE NOUVEAUX OXYDES DE MANGANESE POUR ELECTRODES POSITIVES D'ACCUMULATEURS AU LITHIUM

PARIS-BIUSJ-Physique recherche (751052113) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocSudocFranceF

Reliable Discrimination of Models Based on EIS Data: I. Calibration on Equivalent Electrical Circuits

International audienc

Synthesis of LiCoO2 thin films by sol/gel process

International audienceLiCoO2 thin films were synthesized by sol/gel process using acrylic acid (AA) as chelating agent. The gel formulation was optimized by varying solvent (ethylene glycol or water) and precursors molar ratios (Li, Co, AA) in order to obtain a dense film for positive electrode of lithium batteries. The gel was deposited by spin-coating technique on an Au/TiO2/SiN/SiO2/Si substrate. Thin films were deposited by either single or multistep process to enhance the density of the thin film and then calcined during 5 h at 800 °C to obtain the R-3m phase (HT-LiCoO2). A chemical characterization of the solution was realized by Fourier Transform Infrared (FTIR) spectroscopy. Thermal decomposition of precursors and gel was studied by Thermo Gravimetric Analyses (TGA). Further investigations were done to characterize rheologic behaviour of the gel and solvents affinity with the substrate. Crystallinity and morphology were analyzed respectively by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The formation of R-3m phase was confirmed by the electrochemical behaviour of the gel derived LiCoO2. Cyclic voltammograms and galvanostatic cycling show typical curve shape of the HT-LiCoO2

A fast constant-voltage technique to determine the rating performance with application to solid-state batteries

International audienceOne of the main characterization necessary to compare different battery technology is the extraction of the rating performance [1]. In Ragone or Ragone-like plot [2], [3] the evolution of the available capacity as a function of the discharge/charge current or power is plotted for different technology in such a way to compare them not only at a particular discharge condition, but on the whole spectrum of available current density. This comparison is of paramount interest because it may lead to unexpected results, as in the case of nanostructured electrode (e.g., Carbon nanofibers based electrode). That kind of electrode usually shows a poor capacity, compared to standard slurry electrode, at low current density, due to the intrinsic loss of active material linked to the 3D porous structure. Notwithstanding, when the comparison spans multiple decades of current density, the former technology will prove far better of the latter due to a superior electrolyte permeation and hence an almost zero loss of capacity with increasing current density[4]. Nowadays, the extraction of the rating performance is accomplished by discharging a cell at multiple current density and the final capacity value correspond to a single point on the rating plot. The corresponding test time is very high (>100h) even if lots of test channel are available. The test time will always be at least the time required to discharge a cell at the lowest probed current density. In the present work, we propose different and faster methods to acquire the same information and compare them to the standard protocol both in terms of quality of results and total test time. Solid state Enfilm [5] has been considered as a test vehicle for this work The first corresponds to start discharging a cell with the highest current under test and each time the voltage limit (e.g., 3V) is reached, to restart the discharge with a lower current, down to the minimum current under test. The resulting discharge profile while be composed by N-current step. This method limits the time at which the cell is discharge at the lowest current and strongly increases the amount of data: each test provides data for all probed current and not only one as in the case of the standard protocol. The second method consists in discharging the cell at constant voltage. The voltage is fixed equal to the limiting voltage (i.e., 3V) and the current is registered. In this case, no previous knowledge of the maximum current is required and the number of points in the final plot are equal to the sampling of the measurement. The rating performance is directly available on the current versus capacity plot. The capacity available for each current density is obtained by integrating the discharge curve up to the desired current. This method can be considered the limit of the N-current step method for N approaching infinity. Theoretical discussion and validity of application of the technique will be further discussed

Minimal architecture lithium batteries: toward high energy density storage solutions

International audienceThe coupling of thick and dense cathodes with anode-free lithium metal configuration is a promising path to enable the next generation of high energy density solid-state batteries. In this work, LiCoO$_2$ (30 µm)/LiPON/Ti is considered as a model system to study the correlation between fundamental electrode properties and cell electrochemical performance, and a physical model is proposed to understand the governing phenomena. The first cycle loss is demonstrated to be constant and independent of both cathode thickness and anode configuration, and only ascribed to the diffusion coefficient's abrupt fall at high lithium contents. Subsequent cycles achieve close to 100% coulombic efficiency. The examination of the effect of cathode thickness demonstrate a nearly linear correlation with areal specific capacity for sub-100 µm LiCoO$_2$ and 0.1 mA cm$^{−2}$ current density. These findings bring new insights to better understand the energy density limiting factors and to suggest potential optimization approaches