Showing papers by "Christian M. Julien published in 2002"

Study of structural defects in γ‐MnO2 by Raman spectroscopy

Abstract: The structural arrangement of γ-MnO2 is currently explained by a random intergrowth of pyrolusite layers in a ramsdellite matrix. The structures of a large variety of γ-MnO2 samples with various structural parameters Pr were studied by x-ray powder diffraction and Raman scattering spectroscopy. We show that elucidation of the quantitative determination of the structural disorder present in γ-MnO2 is accurate by Raman scattering spectroscopy. The Raman data for manganese dioxides with the γ-type structure are treated by a local environment model, which allows one to consider the relationship between the band wavenumber and the pyrolusite intergrowth that corresponds to the structural De Wolff defects. Copyright © 2002 John Wiley & Sons, Ltd.

Layered LiNi 1-y Co y O 2 compounds synthesized by a glycine-assisted combustion method for lithium batteries.

Abstract: The lithiated nickel-cobalt oxide cathode materials were prepared at low temperature using the aqueous glycine-nitrate combustion method. Physicochemical and electrochemical properties of LiNi1−y Co y O2 (0.3 ≤ y ≤ 0.7) calcined at 400–600°C were extensively investigated. It has been found that powders of submicron-sized particles with a layered structure (RR $$\bar 3$$ m space group) were obtained at temperatures below 400°C by the acidification reaction of the aqueous nitrate solution. The method involves the mixing of nitrates of Li, Ni and Co, with a combustion agent, glycine in an aqueous medium. Glycine functioned such as a fuel, decomposed the homogeneous precipitate of metal complexes at low temperature, and yielded the free impurity LiNi1−y Co y O2 compounds. The synthesized products were characterized by structural (XRD, SEM), spectroscopic (FTIR) and thermal (DTA/TG) analyses. The electrochemical properties of the synthesized products in rechargeable Li cells were evaluated using a non-aqueous organic electrolyte mixture of 1M LiPF6 in EC + DMC. The electrodes fired at low temperature exhibed a good cycling behavior.

Intercalation Compounds for Energy Storage

Abstract: As society becomes increasingly more dependent on electricity, the development of systems capable of storing directly or indirectly this secondary energy form will be a crucial issue for the 21st century. Batteries, which are devices converting the energy released by spontaneous chemical reactions to electricity work, have some extraordinary properties in these regards. They store and release electrical energy; they are portable and can be used flexibly with a short lead time in manufacture. In this brief introduction, we show the important functions of intercalation compounds used in advanced systems for energy storage.

Physical Chemistry of Lithium Intercalation Compounds

Abstract: Lithium intercalation compounds are known to form complexes as electron donor systems. A charge transfer which can strongly affect the electronic properties of the host lattice, and a change of preferential crystallographic parameters without destruction of the original structure are the main effects occurring during intercalation. Optical spectroscopies such as Raman scattering, far-infrared reflectivity, absorption measurements, and photoluminescence have been carried out for the study of electronic and structural modification. In this paper, lattice dynamics and physico-chemical properties of various two-dimensional intercalated compounds, i.e. transition metal dichalcogenides, non-transition metal chalcogenides and layered oxides, are presented. Results are discussed with the aim of a better understanding of the intercalation process. Some guide lines are established for improving the performances of these materials in their most eminent applications.