ИСТИНА

In this work carbon nanowalls were grown on titanium foil by direct current plasma enhanced chemical vapor deposition (DC PECVD) process in a H2/CH4 gas mixture without use of any catalysts. A typical SEM image of as-grown carbon film (Figure 1a) reveals that it is mainly composed of nanowalls oriented perpendicular to the substrate. An average height of the nanowalls is about 1 μm, their width seems to be in range of 0.5 – 1 μm. TEM study reveals that nanowall thickness doesn’t exceed 15 nm. Gravimetric measurements of titanium foils before and after nanowall growth revealed that total specific mass of the grown carbon film is order of 5×10-6 g/cm2. Presented work may be divided on two parts. In the first part we have used carbon nanowalls as an electrode material for supercapacitors. For electrochemical measurement test cells of capacitors were assembled and sealed in an argon-filled glovebox. A supercapacitor unit cell comprised two titanium foils covered by carbon nanowalls as electrodes and separated by porous membrane. Electrochemical properties of fabricated supercapacitors were studied in the aqueous solution of 0.5 M H2SO4 and the ionic liquid EMIMBF4. Capacitances of the unit cells were measured using charge/discharge curves in accordance with the following expression: , where I is the current of discharge and is the slope of the linear portion of the voltage profile. It was shown that supercapacitors based on DC PECVD grown carbon nanowalls possess specific capacitance up to 350 Fg-1 and specific energy density more than 110 Whkg-1. In the second part of the presented work carbon nanowalls were used for engineering of 3D anodes for lithium-ion batteries. Composite material based on carbon nanowalls and nanostructured silicon has been developed for these purposes. DC PECVD grown nanowalls were homogeneously covered by silicon with use of magnetron sputtering method. SEM image of such composite is show in Figure 1b. Total mass of the silicon film and its structural properties have been controlled by parameters of deposition. TEM, SEM, XPS and Raman spectroscopy methods were used for characterization of morphology and structural properties of the developed composite material. In order to probe electrochemical performance Si/nanowalls anodes were charged/discharged in a galvanostatic mode versus a metallic lithium foil. Preliminary discharge cycle was performed in order to form SEI layer on the silicon surface. Specific capacity obtained while cycling in the range of 0.05 – 2.00 V at the C/2 rate was estimated to be about 3000 mAh per 1 g of silicon. Effect of structural properties of the silicon film and carbide interface between silicon and nanowall on lithium storage capacity and cycling performance have been investigated as well. It was shown that silicon/carbon nanowalls based composite may be used as an effective anode material with high lithium capacity and low rate of structural degradation during process of cycling.