Papers by Abdelbast Guerfi
ECS Meeting Abstracts, 2005
Proceedings, annual meeting, Electron Microscopy Society of America, 1992
Many transition metal oxides have been studied in the last two decades. By an appropriate chemica... more Many transition metal oxides have been studied in the last two decades. By an appropriate chemical or electrical means, ions can be inserted into the structure of these oxides with minimal structural changes. This process known as coloration can easily be reversed. This reversible mechanism is of particular interest in applications such as battery and fuel cell electrodes, chemical sensors, electrochromic displays and catalysts.In this study, films of three transition metal oxides (WO3, MoO3, V2O5) were prepared by electrodeposition. The morphology and the structure of these films were analyzed by transmission electron microscopy (TEM) in their as-deposited states and after heat treatment in ambient air up to 500°C. Previous measurements made by differential scanning calorimetry (DSC) showed exothermic peaks corresponding to phase changes. The temperature values determined at those peaks were then chosen as specific treatment temperatures.
ECS Meeting Abstracts, 2012
Introduction: Silicon is an attractive anode material due to its high gravimetric and volumetric ... more Introduction: Silicon is an attractive anode material due to its high gravimetric and volumetric capacity density of 4200 mAh/g and 9800 mAh/mL, respectively, when the Li4.4Si phase is formed. In spite of this advantage, Si-based anodes show numerous problems that limits their use in commercial in Li-ion batteries. A significant capacity fade occurs during cycling, and low coulombic efficiency is obtained. The performance degrades during the first few cycles due to the large volume change from alloying/de-alloying (chargedischarge) that induces cracks in the micro-size particles and then a failure of electrical contacts. To reduce this effect, we have selected carboncoated SiOx mixed with graphite, nano structured Si particles and carbon-coated nano Si. The characteristic features of SiOx electrodes are they exhibit less volume change than Si during chargedischarge cycling. Lithium metal is very attractive anode material because it does not require a binder, is an electronic conductor and current collector. The aim of this paper is to present the results on the effect of new binders and carbon additives on the electrochemical performance of carbon-coated nano Si and carbon-coated SiOx-graphite electrodes compared to lithium metal electrodes. The morphology changes to nano Si, carbon-coated nano Si and C-SiOx particles using in situ and ex situ scanning electron microscopy will be presented The physicochemical properties and the electrochemical performance of active materials are intimately connected, therefore both must be considered in selecting an alternative material to graphite in negative electrodes for Li-ion batteries. An analysis of this relationship is discussed in this paper. Results: The charge-discharge potential curves at C/24 for C-SiOx-graphite electrodes are shown in Fig. 1. The reversible capacity with SiOx-graphite is 980 mAh/g), but the columbic efficiency is only about 84%. The presence of graphite decreases the capacity and increases the conductivity of the electrode. The capacity of the SiOx-graphite also accounts for the weight of graphite; consequently a lower capacity is expected. Six electrodes at different voltage (Fig. 1) were analyzed. The irreversible capacity loss is due to the formation of the SEI layer on carbon-coated SiOx and graphite surfaces, and the formation of Li2O is evident from EDX and SEM analyses.
Sustainable Energy & Fuels, 2017
In liithium–sulfur battery the lithium metal surface was analyzed by in situ Raman spectroscopy.
ECS Transactions, 2014
In addition of the poor intrinsic conductivity of LiFePO4 particle, surface effects become increa... more In addition of the poor intrinsic conductivity of LiFePO4 particle, surface effects become increasingly important, and can eventually dominate the physical and the chemical properties when the size decreases below 100 nm. Carbon coating appeared to overcome the drawback of highly resistive LiFePO4 powders and to cure the disordered surface layer that reduces the electrochemical performance of non-coated sample. Here, we analyze the effect of the carbon coating on the LiFePO4 particles that meets a worldwide success as a positive electrode for commercial Li-ion batteries.
ECS Transactions, 2014
We report that the rotation speed of the stirring in the hydrothermal reactor process is an impor... more We report that the rotation speed of the stirring in the hydrothermal reactor process is an important parameter that affects the structural properties and the electrochemical performance of LiFePO4. The best results are obtained for a rotation speed of 280 revolutions per minute. It is argued that this improved performance is related to the optimized morphology of the particles, and a smaller agglomeration of the particles. Since this material meets a worldwide success as a positive electrode for commercial Li-ion batteries.
ECS Transactions, 2007
Hybrid supercapacitor that contain high-surface-area carbon and metal oxide electrodes are attrac... more Hybrid supercapacitor that contain high-surface-area carbon and metal oxide electrodes are attracting interest for use in electrochemical devices. Metal oxide electrodes containing Li4Ti5O12 in liquid electrolytes (ionic liquid or nonaqueous liquid) were investigated. A new procedure developed at Hydro Quebec produced Li4Ti5O12 powders with diameters in the range of 100 nm. At high-rate (1 minute) charge-discharge, the hybrid supercapacitor had an average voltage of about 2.21 V, with 85% nominal capacity. These hybrid supercapacitors also exhibited a very long cycle life of >20,000 cycles at high- rate charge-discharge. The results of this study demonstrate that the Li4Ti5O12-based electrochemical system has attractive characteristics for high-power application such as in portable devices and HEVs
Electrochimica Acta, 2004
The interface microstructure of the state-of-the-art cathode material for solid oxide fuel cells,... more The interface microstructure of the state-of-the-art cathode material for solid oxide fuel cells, SrLa1_1MnO3 (SLM), was investigated with respect to its electrochemical performance. The interface microstructure was characterized by grain size and coverage of SLM on the electrolyte surface. Variation of the grain size was obtained by using three differ-ent sintering temperatures, whereas variation of the coverage was obtained by using two powders with a different mor-
Journal of Power Sources, 1997
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Papers by Abdelbast Guerfi