Optimisation d'électrodes composites pour accumulateurs Li-ion de puissance élaborées en milieux aqueux

Ces travaux portent sur l'optimisation d'électrodes composites positives et négatives, respectivement à base de LiFePO4 et de Li4Ti5O12, pour accumulateurs Li-ion de puissance. Dans le cadre de l'élaboration d'électrodes par voie aqueuse, des formulations optimisées ont été définies pour les deux matériaux d'électrodes LiFePO4 (thèse W. Porcher 2007) et Li4Ti5O12 par étude couplée des dispersions d'encre, des morphologies d'électrodes et des performances finales. A partir de ces électrodes, dont les performances électrochimiques sont évaluées en configuration demi-pile par rapport à du lithium métal, une étude systématique est menée sur les courbes de décharge qui caractérisent l'insertion du lithium dans la structure cristalline des matériaux d'électrodes. La réponse électrochimique du système est étudiée précisément suivant les paramètres de formulation (modification de l'agent conducteur et/ou des additifs polymères), de mise en oeuvre (épaisseur, grammage) et de structure des électrodes (porosité, tortuosité). Il en résulte une discrimination des différentes contributions résistives et des différentes limitations cinétiques de l'électrode (matériau d'électrode et son environnement) selon le grammage, la porosité et le régime de fonctionnement. Par l'identification de ces limitations, un début de diagnostic peut alors être avancé quant aux paramètres sur lesquels agir (conduction électronique, conduction ionique, architecture d'électrode, morphologie du matériau d'électrode) pour optimiser les performances des électrodes considéréesThis work focuses on the optimization of composite positive and negative electrodes, respectively based on LiFePO4 and Li4Ti5O12 materials, for Li-ion power accumulators. In the framework of electrodes elaboration via aqueous route, optimized formulations were defined for both LiFePO4 (W. Porcher's PhD - 2007) and Li4Ti5O12 electrode materials by coupling studies of ink dispersions, electrode morphologies and final performance. From these electrodes, electrochemically tested in coin cells vs. a lithium foil electrode, a systematic study is carried out on the discharge curves that characterize the lithium insertion in the electrode materials crystalline structure. The electrochemical response of the system is studied precisely as a function of the electrode formulation (modification of the conductive agent and/or polymer additives), the electrode processing (thickness, loading) and the electrode structure (porosity, tortuosity). This thorough analysis leads to a discrimination of the electrode different resistive contributions and kinetics limitations (electrode material and its environment) as a function of the electrode loading and porosity, and of the discharge rate. By identifying these limitations, a diagnosis can be propounded regarding the electrodes parameters on which one could play (electronic conduction, ionic conduction, electrode architecture, electrode material morphology) so as to optimize the electrode performanceNANTES-BU Sciences (441092104) / SudocSudocFranceF

A hybrid method using the widely-used WIEN2k and VASP codes to calculate the complete set of XAS/EELS edges in a hundred-atoms system

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NMR quantitative analysis of solid electrolyte interphase on aged Li-ion battery electrodes

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Degradation diagnosis of aged Li4Ti5O12/LiFePO4 batteries

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High voltage spinel oxides for Li-ion batteries: From the material research to the application

International audienceLi-ion batteries are already used in many nomad applications, but improvement of this technology is still necessary to be durably introduced on new markets such as electric vehicles (EVs), hybrid electric vehicles (HEVs) or eventually photovoltaic solar cells. Modification of the nature of the active materials of electrodes is the most challenging and innovative aspect. High voltage spinel oxides for Li-ion batteries, with general composition LiMn2−xMxO4 (M a transition metal element), may be used to face increasing power source demand. It should be possible to obtain up to 240 Wh kg−1 at cell level when combining a nickel manganese spinel oxide with graphite (even more with silicon/carbon nanocomposites at the anode). Specific composition and material processing have to be selected with care, as discussed in this paper. It is demonstrated that ‘LiNi0.5Mn1.5O4' and LiNi0.4Mn1.6O4 have remarkable properties such as high potential, high energy density, good cycle life and high rate capability. Choice of the electrolyte is also of primary importance in order to prevent its degradation at high voltage in contact with active surfaces. We showed that a few percents of additive in the electrolyte were suitable for protecting the positive electrode/electrolyte interface, and reducing the self-discharge. High voltage materials are also possibly interesting to be used in safe and high power Li-ion cells. In this case, the negative electrode may be made of Li4Ti5O12 or TiO2 to give a ‘3 V' system

High voltage nickel manganese spinel oxides for Li-ion batteries

International audienceHigh voltage spinel oxides with composition LiMn2 − xMxO4 (M, a transition metal element) have remarkable properties such as high potential, high energy density and high rate capability. We believe that these positive electrode materials could replace the widespread commercial layered nickel cobalt oxides in some applications. The present assessment highlights electrochemical performance of optimized LiNi0.5Mn1.5O4 and substituted counterparts, all having a spinel structure (cubic close-packed oxygen array) similar to the relative LiMn2O4. To fully emphasize the benefit from high potential spinel oxides, tests have been performed versus lithium metal, Li4Ti5O12 and graphite, using various electrode loadings (0.3-4.5 mAh cm−2) and cycling rates (from C/20 to 60C rate). Steady capacity retention (130-140 mAh g−1 for nearly 500 cycles) and flat voltage (4.7 V vs. Li+/Li) have been obtained at C/5 rate at room temperature. Effect of cycling at high temperature has been shown to be less critical than for LiMn2O4. High voltage spinel oxides still sustain 100 mAh g−1 and over after 400 cycles at 55 °C at 1C rate. Rate capability is also excellent, with only 4% loss of capacity when comparing C/8 and 8C rates (thin electrodes)

Laser pyrolysis for the one-step synthesis of core-shell silicon-carbon nanoparticles: interest as anode material in Li-ion batteries

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One Step Core-Shell Silicon/Carbon Nanoparticle Synthesis By Laser Pyrolysis: Application to Anode Material in Lithium-Ion Batteries

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Core shell amorphous silicon-carbon nanoparticles synthesis by double stage laser pyrolysis, application to anode material

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Core shell amorphous silicon-carbon nanoparticles synthesis by double stage laser pyrolysis, application to anode material

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