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Gel polymer electrolyte (GPE) membranes based on two polymers, a copolymer of poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), and the poly(ethylene oxide) (PEO), together with a plasticizer, the dibutylphtalate (DBP), were elaborated in two ways. Firstly, the polymers and the plasticizer were mixed together to obtain a single membrane. Secondly, a bi-layer separator membrane was made by adjunction, through lamination, of a DBP plasticized PVdF-HFP film and a homemade DBP-PEO thin film. We report here a protocol based on a simple galvanostatic polarization of Li/GPE/Li symmetric cells as a way to rapidly screen new viable membranes. Such a procedure enables to quickly discriminate separators by leading experiments that do no not exceed 1 week compared to hundreds of days needed with classical batteries. The validity of such an approach was confirmed by investigating the performances of the membranes in Li/GPE/Li4Ti5O12 flat battery configuration. Besides, through this study we also highlighted the role of the macroscopic PEO-PVdF interface toward dendrite of bi-layered separator, while a single blended membrane does not seem to be suitable for a practical use. Post-mortem pictures and SEM investigation have confirmed this result. © 2005 Elsevier B.V. All rights reserved.

We report on experimental and theoretical studies of dendritic growth in Li/polymer/Li symmetric cells. Potential evolution with time, impedance and in situ microscopy experiments enable to characterise the onset and evolution of dendrites. In particular we observe that dendrites may burn when a high enough current goes through them, a thermo-fusible effect predicted in a previous paper and confirmed by SEM experiments. We present a calculation that gives a quantitative description of this effect: our results enable to understand a series of experimental data published in the literature concerning impedance variations observed while cycling lithium-polymer cells. © 2006 Elsevier Ltd. All rights reserved.

A new effective Gel Polymer Electrolyte membrane based on two polymers, the polyethylene oxide (PEO), a poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) copolymer and a plasticizer, the dibutylphtalate (DBP), was realized. This separator membrane was made by adjunction, through lamination, of an industrially made DBP/PVdF-HFP film and a homemade DBP/PEO thin film. Once the plasticizer was removed and the separator gelled by the electrolyte, the PEO enables the formation of a good interface with the lithium while the PVdF-HFP film brings the mechanical strength to the membrane. The electrochemical behavior of lithium batteries based on this bi-layer separator was investigated versus temperature, cycling potential and cycling rate. Owing to the promising results obtained with laboratory cells, a 1 Ah prototype was successfully assembled, and its cycling and rate performances were reported. © 2005 Elsevier B.V. All rights reserved.

Gel polymer electrolyte (GPE) membranes based on two polymers, the polyethylene oxide (PEO) and a copolymer of polyvinylidene fluoride- hexafluoropropylene (PVdF-HFP), and a plasticizer, the dibutylphthalate (DBP), were elaborated in two ways. First, the polymers and the plasticizer were mixed together to obtain a single membrane. Second, a bilayer separator membrane was made by adjunction, through lamination, of a DBP plasticized PVdF-HFP film and a homemade DBP-PEO thin film. The physicochemical properties of the gels were analyzed. AC impedance spectroscopy was carried out on symmetric Li/GPE/Li cells using either the single layer or bilayer membrane as a function of aging (isothermal at 20 and 70°C), temperature (-40 to 70°C), and finally, galvanostatic cell polarization. Both GPE membranes exhibit high ionic conductivities, but the most spectacular result was the measured decrease in the interface resistance, indicative of a deep modification of the interface Li/GPE when the cells were polarized. Aside from having a good interface with the Li metal electrode, such membranes were also shown to form good interfaces with the cathode because assembled Li/GPE/Li4Ti5O12 flat cells were able to sustain, at room temperature, more than 80% of their initial capacity for more than 300 cycles. © 2004 The Electrochemical Society. All rights reserved.

Although widely used, the most promising Li-based technologies still suffer from a lack of suitable electrodes. There is therefore a need to seek new materials concepts to satisfy the increasing demands for energy storage worldwide. Here we report on a new layered electrode material, Cu2.33V4O11, which shows a sustainable reversible capacity of 270 mA h g-1 at a voltage of about 2.7 V, and electrochemically reacts with Li in an unusual and spectacular way. The reaction entails a reversible Li-driven displacement process leading to the growth and disappearance of Cu dendrites with a concomitant reversible decomposition and recrystallization of the initial electrode material. We show from structural considerations that the uniqueness of Cu2.33V4O11 is rooted in the peculiar flexibility of the stacked [V4O11]n layers, which is due to the presence of pivot oxygen atoms. Fully reversible displacement reactions could provide a new direction for developing an alternative class of higher energy density Li storage electrodes.

We report live observations of lithium polymer batteries upon cycling within the microscope antechamber by means of a scanning electron microscope, equipped with a transfer system that avoids sample air exposure. The well-established direct correlation between current density and dendrite formation is confirmed, and the formation of a mossy or dendritic interface was evidenced to be at the origin of the delaminating between the substrate, where the lithium is plated, and the polymer. These experiments enable a better understanding of the dendrite formation mechanism, like the important finding that they grow tipwise as well as sidewise. © 2002 The Electrochemical Society.

Polymer dispersed liquid crystal (PDLC) films can be switched electrically from a light scattering off-state to a highly transparent on-state. Mixtures including different amounts of a high molecular weight copolymer and the eutectic nematic low molecular weight liquid crystal E7 were prepared in acetone which acts as a common organic solvent. PDLC films were obtained by a solvent induced phase separation (SIPS) initiated by evaporation of the solvent. The optical transmission properties of the obtained PDLC films were investigated as a function of composition, film thickness, and amplitude of the applied AC voltage. The electro-optical curves depend on the liquid crystal content and are highly reproducible. The particular properties of the copolymer allow to obtain a strong physical polymer network which in turn leads to well defined films compared to results obtained for other linear polymer/E7 systems. © 2001 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint. a member of the Taylor & Francis Group,.