Physical characterization of carbonaceous materials prepared by mechanical grinding

By means of mechanical grinding, we recently reported the ability to prepare tailor-made carbon materials able to reversibly intercalate two lithiums per six carbons (e.g., Li2C6) while having irreversible capacities of 320 mA h/g. A schematic model involving two different types of surface area was previously proposed to account for the reversible and irreversible capacities measured vs. Li with these powders. We experimentally verified this model by means of differential scanning calorimetry (DSC) measurements. Transmission Electronic Microscopy (TEM), which is a powerful tool for the direct imaging of poorly organized materials at the atomic scale has been used, together with Raman Spectroscopy, to follow the disorganization generated by mechanical grinding. © 1999 Elsevier Science S.A. All rights reserved

Raman study on carbonaceous materials prepared by mechanical milling

Through Raman spectroscopy studies, we show that mechanical grinding generates an increasing amount of unorganized carbon at a rate depending on the type of grinding mode used (Shear and Shock-type grinding). The first-order Raman spectrum for pure unground graphite has a well-known G sharp band at 1579 cm -1, which corresponds to the E 2g vibration while the ground samples present a broadened G band accompanied by new components at about 1610 cm -1 (D′), 1510 cm -1 (D″) and 1348 cm -1 (D), usually explained as arising from disorder and defects 1. Shock-type grinding produces a faster disorder increase than shear-type grinding. The latter preserves part of the graphitic character. The general effect of mechanical milling remains however opposite to that of Thermal Treatment (Graphitization). © 1998 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint

Mechanisms of the Reversible Electrochemical Insertion of Lithium Occurring With NCIMs (Nano-Crystallite-Insertion-Materials)

A new family of insertion-compound electrodes, so called NCIMs (Nano-Crystallite-Insertion-Materials), has been proposed: the major requirement is that the electrode materials have to be polycrystalline with a crystallite and particle size as small as possible (the accepted definition being that many crystallites make a particle). Indeed, by minimizing the size of the crystallites, the formation of defects bonds is favored, particularly at the.crystallite surface, acting as reversible (de)grafting sites of Li+. Also, the cation-anion bonding is weakened not only in the grain boundary region but also within the crystallite close to its surface: then the electrochemical insertion of Li+ takes place through easy bonding rearrangements