Showing papers by "Christian M. Julien published in 1994"

Solid State Batteries: Materials Design and Optimization

Abstract: Preface. 1. Design and Optimization of Solid-State Batteries. 2. Materials for Electrolyte: Crystalline Compounds. 3. Materials for Electrolyte: Fast-Ion-Conducting Glasses. 4. Materials for Electrolyte: Thin Films. 5. Polymer Electrolytes. 6. Materials for Electrodes: Crystalline Compounds. 7. Materials for Electrodes: Amorphous and Thin-Films. 8. Applications of Solid-State Ionic Materials. Subject Index.

Lithium insertion in indium selenide films: application to microbatteries

Abstract: Indium selenide films are formed on silica slides and silicon wafers using a flash evaporation technique in which the material source stoichiometry is modified to obtain InpSeq films with various compositions. The structural and optical properties of indium selenide films are reported. These characterizations have shown that, using different growth conditions, either single phases, such as InSe, In4Se3 or In2Se3, are formed or a mixture of these compounds is present in the film structure. The products are examined by X-ray diffraction, and Raman and IR spectroscopies. The electrochemical properties of lithium-intercalated films are presented. It is observed that the morphology and stoichiometry play an important role in the lithium insertion process. The thermodynamics and kinetics of the insertion reaction are reported. Li/Li+ -borate glass/InSe microbatteries have been built, and their characteristics are reported and discussed using a Butler-Volmer relationship.

Optical and Electrical Properties of Ga2Te3 Crystals

Abstract: Optical and electrical properties of the gallium telluride Ga2Te3 are reported. Lattice modes are investigated using far-infrared spectroscopy and polarized Raman scattering experiments. The farinfrared reflectivity spectrum which is analyzed using a Lorentzian-oscillator model and the Raman spectrum shows that this compound has a defect structure with disordered vacancies. Modes with A-symmetry are observed at 86 and 112 cm−1. The semiconducting character is evidenced by electrical studies and the sensitive behavior to normal atmosphere is observed in the electrical conductivity of a sample maintained in air.

Growth and characterizations of Cd-doped InSe films

Abstract: Conditions for the growth of Cd-doped InSe films are developed using the flash evaporation technique. Identifications of these films are carried out using X-ray photoelectron spectroscopy and X-ray diffraction measurements. Optical absorption and photoresponse are investigated in the vicinity of fundamental transitions. Electrical properties of InSeCd0.01 thin films are reported and the conduction mechanism of polycrystalline films is investigated.

Fabrication of V2O5 Thin Films and their Electrochemical Properties in Lithium Microbatteries

Abstract: Thin films of V2O5 were prepared using the flash-evaporation technique. Amorphous and polycrystalline samples were characterized by X-ray diffraction, Raman spectroscopy and XPS analysis. The electrical properties of the samples were determined. The effect of either deposition parameters or post-deposition treatments, i.e., annealing in various atmospheres and at different temperatures, on transport properties are presented. Electrochemical characteristics are evaluated in V2O5/LiCIO4-PC/Li microbatteries. The discharge curves present several voltage plateaus, similar to those already observed in cells with bulk V2O5 cathodes. Kinetics of lithium intercalation have been investigated as a function of the growth conditions of V2O5 films. Chemical diffusion coefficient and enhancement factor are calculated as a function of the degree of lithium intercalation. All the results are compared with previous reported results for bulk vanadium oxides. The relationship between the crystallinity of the films and their electrochemical features is also discussed.

Applications of solid-state ionic materials

Abstract: Solid-state ionic materials have been extensively developed and applications of solid electrolytes as well as insertion compounds have begun to converge into a coherent field during the last 10 years. Various designs of working devices are outlined in this chapter with the emphasis on all solid-state configurations. The large number of references reflects the great interest of researchers in energy storage devices, sensors, and optical and other electrochemical applications of solid-state ionics. For most types it is mentioned whether they are commercially available, items of intense current development, or one of the hot new research items.

Materials for electrodes: Amorphous and thin-films

Abstract: Until now, the materials investigated with a view to finding suitable intercalation host structures for the positive electrode of electrochemical generators with an alkali metal or silver anode have been essentially crystalline (transition metal didialcogenides and oxides). Yet the discovery of the semiconducting properties of phosphorus pentoxide-based glasses, a quarter of a century ago [1], associated with the synthesis of phosphate-based glasses with high ionic conductivity [2, 3] allows us to consider the possibility of employing glasses as positive electrode materials. These materials could offer significant technological advantages due to their vitreous structure: 1. Easy to synthesize; 2. Easy to implement, in particular in the form of micronic powders; 3. Isotropic structure, implying a larger electrochemically active surface than in the case of low dimensionality crystalline structures; 4. The good conductivities observed in glasses suggest a high diffusion coefficient of the mobile ion; 5. The low density of glasses infers a large number of available sites for the intercalants and, consequently, independence of the volume of the material with respect to the intercalation ratio. The use of glasses for the positive electrode of solid state secondary batteries should ensure that good contacts are maintained throughout the discharge-charge cycles; 6. The use of the same forming oxide in the electrolyte and the electrode should avoid a clear-cut localization of their interface since the macromolecular chains of the forming oxide will extend without interruption from the electrolyte to the electrode.

Materials for electrolyte: Fast-ion-conducting glasses

Abstract: Apart from crystalline materials, the second class of solid electrolytes is the family of amorphous conductors which in contrast more closely resemble liquid electrolytes than crystalline solids. It is easier to define an amorphous state by saying what it is not than by precisely specifying what it is. Amorphous materials are noncrystalline substances. They lack long-range periodic ordering of their constituent atoms. That is not to say that amorphous materials are completely disordered on the atomic scale. Local chemistry provides almost rigorous bond-length, and to a lesser extent, bond-angle constraints on the nearest-neighbor environment. For instance, unlike amorphous metals, amorphous semiconductors do not consist of close-packed atoms, but rather they contain covalently bonded atoms arranged in an open network with correlations in ordering up to the third- or fourth-nearest neighbors. The short-range order is directly responsible for observable semiconductor properties such as optical absorption edges and activated electrical conductivities.

Effect of the Heat Treatment on the Lithium Insertion Process in MoO3

Abstract: We have studied the electrochemical characteristics of Li/MoO 3 -based batteries in relation with the morphology of the cathode-active material. The oxides and oxide-hydrates of molybdenum have been prepared with various degrees of heat treatement. The samples were characterized by X-ray diffraction, Raman spectroscopy, and conductivity measurements. The effect of the heat treatment on structural, optical and electrochemical properties are presented in this work. Thermodynamics and kinetics of lithium insertion were studied in MoO 3 cathodes. Diffusion coefficients and enhancement factors were calculated as functions of the degree of lithium intercalation in the domain of the galvanic cell reversibility.

Design and optimization of solid-state microbatteries

Abstract: A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an electrochemical oxidation-reduction reaction, also called redox reaction. This type of reaction involves the transfer of electrons from one material to another through an internal circuit.

Materials for Electrodes: Crystalline Compounds

Abstract: The purpose of this chapter is to give a general overview of the properties of compounds such as electrode materials in lithium batteries, particularly those in which there is an appreciable amount of ionic transport within solid components.

Materials for electrolyte: Thin-films

Abstract: The purpose of this chapter is to introduce the area of solid-electrolyte thin-films and to discuss the various process/property/applications relationships which have been developed in this field. Thin-film technology is examined from the interrelated viewpoints of product application, materials structure/properties relationships, and manufacturing-deposition methods. Special emphasis is given to the thin-film materials properties of lithium-borate glasses, which are likely to have an impact on electrochemical device performance, coupled with the various techniques employed to control those properties.

Materials for electrolyte: Crystalline compounds

Abstract: Superionic conductors are solid compound materials that present an anomalously high ionic conductivity, comparable, in order of magnitude, to that of liquid electrolytes. They also present effective atomic diffusion coefficients of the same order as in liquids or gases. These phenomena are observed in such a variety of substances including crystals, glasses, and polymers. In general the conductivity increases with temperature T according to the Arrhenius law. Systems with ionic conductivity of order of 1 S cm-1 at room temperature are ideal for practical applications but many useful materials show results which are several orders of magnitude lower than this. For comparison, the ionic conductivity of the ordinary ionic conductor NaCl is about 10-15 S cm-1 at room temperature. The common structural feature of these materials is the existence of conduction paths connecting fractionally occupied sites.

Roughness Effect on the Lithium Diffusivity in WO3 Thin Films

Abstract: In this work, we investigate the influence of surface roughness on the kinetics of Li+ during the insertion process in the well-known electrochromic material WO3. Thin films 500 A thick have been grown by rf-sputtering and annealed in therange of 25-350oC. Grazing angle X-ray reflectometry shows that the film roughnessincreases considerably with thermal treatment. These measurements are correlated with chemical diffusion investigations obtained by electrochemical titration in Li/WO3 cells.