Physicochemical and functional peculiarities of metal oxide whiskers

Practical aspects of preparation and prospects for practical use of a series of the metal oxide whiskers were studied. The procedures for the synthesis were proposed, and the phase composition, micromorphology, and electrochemical and sensor characteristics of the macroscopic (up to 5–10 mm long) whiskers in the Ba-V-O, Ba-Mn-O, and Sn-O systems were analyzed. The electroconducting BaV₈O_21-δ whiskers were prepared by the hydrothermal treatment. These whiskers possess stable electrochemical characteristics appropriate for the development of novel secondary current sources. The protonated form of the Ba₆Mn₂₄O₄₈ whiskers produced by the isothermal vaporization of chloride fluxes is a mixed conductor with the proton and electron conductivity at a level of mS units at 25 °C. A new procedure by the thermal disproportionation of tin(ii) oxide under nitrogen was proposed for the growth of SnO₂ whiskers of various morphology. The produced whiskers have substantial sensor sensitivity toward a series of toxic components of the gaseous medium, such as nitrogen dioxide. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1023–1034, May, 2008.     

The structure and properties of a new type of nanostructured composite Si/C electrodes for lithium ion accumulators

The results obtained in studies of the structure and electrochemical properties of film electrodes prepared by magnetron plasma sputtering of silicon and graphite and working under the conditions of lithium injection and extraction are generalized. Composite silicon-carbon electrodes synthesized by depositing silicon and carbon nanolayers with the use of a magnetron plasma were films 100–500 nm thick. Part of them exhibited highly uniform nanogranular structure based on a carbon matrix with inserted silicon clusters of size below 6 nm. The nanogranular structure of Si/C composites was observed for the first time; such a morphology was not characteristic of not structured silicon layers deposited under equal conditions. The factors that determined the electrochemical charging-discharging behavior of new composites were the degree of uniformity of the nanogranular structure, the ratio between the silicon and carbon components, and film thickness. For two thin films, the initial composite capacitance was higher than that corresponding to the Li_4.4Si stoichiometry for the silicon component and LiC₆ stoichiometry for the carbon component, which was related to the special nanostructured state of silicon and carbon. The effects (luminescence band and absorption bands in the visible range) characteristic of nanosized silicon particles were observed.     

New type of the nanostructured composite Si/C electrodes

The silicon-carbon composite films, with the silicon and carbon relative content from 39.5: 60.5 to 87: 13 and thickness 100–480 nm, are prepared by magnetron sputtering with layer-by-layer deposition of the components. The film structure is studied by using X-ray diffraction analysis and atomic-force microscopy. All studied films were found to be roentgen-amorphous. Despite the films were deposited in a layer-by-layer mode, they have granular structure, with the granules sized 10–80 nm. The lithium incorporation from LiClO₄ solution in propylene carbonate-dimethoxyethane mixture is studied. All studied films reversibly incorporate lithium; thus, they can serve as the basis for negative electrodes of lithium-ion batteries. The initial capacity of the composite-film electrodes is 1.5 to 2.8 A h/g. As the films are submerged to cycling, the capacity decreases, mainly due to the films’ insufficiently strong adhesion to the substrate, which results in the film defoliation. The most cycling-resistant are the thinnest films containing no less than 30% carbon. The capacity of the best samples is as high as 1 A h/g after 200 cycles.