V.A. Nalimova

Mechanical Energy Storage in Carbon Nanotube Springs

Compression of purified, unoriented, highly crystalline single-wall carbon nanotube material reveals an exceptionally large and reversible volume reduction. Density increases rapidly with increasing pressure, approaching that of graphite, and recovers completely upon pressure release. The reversible work done in compressing to 29thinspthinspkbar is 0.18 eV/C atom. We attribute this effect to crushing, or flattening the tube cross section from circular to elliptical. {copyright} {ital 1999} {ital The American Physical Society}

Lithium interaction with carbon nanotubes

Abstract Lithium interaction with catalytic carbon nanotubes under high-pressure conditions was studied. A large amount of Li (2Li/C) reacted with the carbon nanotubes forming an intercalation compound (Ic~4.1 A) which follows from X-ray diffraction and IR spectroscopy data. We cannot exclude also the possibility of insertion of a part of Li into the channel of the nanotubes.

The alkali metals in graphite matrixes-new aspects of metallic state chemistry

Abstract Graphite-alkaline metal systems (lithium, potassium, rubidium, cesium) have been investigated under high-pressure conditions. New graphite intercalation compounds of C4M composition with alkali metal contents twice as high as in those obtained with traditional methods without applying high pressure have been produced. The solid-phase postintercalation reactions of potassium and rubidium in C8 M under 0.2–0.3 GPa pressure have been investigated. The compressibility of different composition intercalation compounds obtained was determined under 2.5 GPa pressure by the volume method. The increase in metal content in layers has been shown to lead to reduced compound compressibility. The phase transformation in C8 K under −1.2 GPa pressure, associated with the metal compaction in the intervals between graphite layers, has been investigated.

X-ray investigation of highly saturated Li-graphite intercalation compound

Abstract Highly saturated lithium-graphite intercalation compounds (of a composition LiC2LiC4) synthesized under high-pressure conditions were investigated using X-ray diffraction. It was shown that these compounds present the structure with hexagonal unit cell with a parameter 8.63 A , c = 3I c = 3 · 3.7 = 11.1 A . The most probable stoichiometry for this unit cell is LiC2.67, as deduced from the comparison of the calculated and observed intensities of (hkl) reflections. It is supposed that this structure is the most “stable” step in decomposition of LiC2 compound obtained under pressure.

NMR Study of LICX Graphite Intercalation Compounds Prepared Under High Pressure

Abstract A highly saturated Li graphite intercalation compound synthesized under high pressure, was investigated after pressure relaxation by Li NMR spectroscopy. At low temperature the sample exhibits a doublet at 256 ppm downfield from Li+. The lineshape agrees with the simulation of an island of 7 Li atoms with nearest neighbours at 2.46° distances, in good agreement with a local LiC2 structure. This confirms short metal-metal bondlengths and possible Li-Li covalent bonds which were shown by IR Spectroscopy.

Super Dense LiC2 as a High Capacity Li Intercalation Anode

LiC 2 , the super dense high-pressure phase of lithium-intercalated graphite, has been tested in a two-electrode cell vs. Li with an organic electrolyte. A primary capacity of 910 mAh/g per carbon atom was observed during the first deintercalation cycle at constant current, almost three times greater than the ideal 372 mAh/g value for the normal saturated-phase LiC 6 . LiC 2 also exhibited the desirable characteristic of a low and flat working voltage profile, and most of the Li was removed at ∼18 mV. The first deintercalation cycle also showed weak anomalies which coincide with previously identified phase transitions between high order Li in-plane superlattices. Repeated cycling yielded a reversible capacity close to 372 mAh/g, with Li removed at ∼100 mV. The high initial capacity and near ideal reversible secondary capacity suggests that this material could be useful in rechargeable batteries requiring a very large first deintercalation capacity.

SODIUM GRAPHITE SYSTEM AT HIGH-PRESSURES

Abstract Sodium intercalation into graphite is investigated ‘ in situ ’ at high pressures, the volumetric and DTA techniques being used. Synthesis conditions of the highly saturated compounds (composition close to C 2.5–3.0 Na) are determined. It is shown that sodium intercalation into graphite at 40-kbar pressure takes place after metal melting, the reaction being complete within several minutes. In addition, the volumetric method establishes the possibility of this reaction at lower pressures (∼ 20 kbar) and heating for 5–10 h.

Intercalation in the graphite-rubidium system under high pressure

Abstract Results of investigations on the graphite-rubidium system under high pressure (up to 25 kbar) are presented. In this system new graphite intercalation compounds of C 4.3−6.0 Rb compositions have been obtained. These compounds have been shown to be unstable under normal conditions and to decompose to rubidium and less metal-saturated compounds when the pressure is reduced. The reaction is reversible - rubidium can be again intercalated into C 8 Rb under high pressure at room temperature.

IR Study of Ozone Modified Graphite Matrix

Abstract The oxidation of graphite powder was reported to enhance the capacity of graphite anodes in Li-ion batteries. Here we present IR-spectroscopic study of the graphite powder modified via oxidation by ozone with the subsequent LiOH or butyl-Li treatment compared to the results obtained by “wet” acid oxidation. Ozone treatment leads to the formation of ozonides, C-O-O-C, carboxylic and epoxy groups on graphite surface. Subsequent treatment of ozone modified graphite with LiOH eliminates the majority of C-O containing groups and yields only a few COOLi surface groups. Treatment of ozonated graphite with butyllithium appears to be more efficient.

Vibrational spectra of superdense lithium graphite intercalation compounds

IR investigations of lithium graphite intercalation compounds with different lithium in-plane density (LiC6, LiC4, LiC2) were carried out. The spectra interpretation was done on the basis of normal coordinate analysis for model structures. LiC2 and LiC4 spectra exhibit the bands corresponding to a complex skeleton stretching in Li7 or LiC6 clusters including equilateral triangles of metal atoms at short distances which shows that covalence exists between Li atoms in the intercalated layer and that LiC2 decomposition proceeds keeping these clusters in LiCx structure for x < 4 at least.