2, Helios Resource Ltd., Saransk, , Russian Federation
Ultracapacitors are widely used in modern power electronics, automotive industry and renewable energy systems. The main component of the ultracapacitor design is the electrode system on the basis of highly-porous carbon materials that have a number of advantages: a large surface area (up to 2000 m2/g), low resistance, reasonable cost.
The aim of the work is to investigate nanoporous material – carbon fabrics, which is used as electrodes in rechargeable energy storage capacitors (ultracapacitors). The performed studies resulted in determination of the investigated carbon material structure, determination of impurities composition of carbon material and change of impurities content depending on thermal treatment in vacuum.
For the investigation of impurities composition of carbon material and change of impurities content the thermal treatment in vacuum was developed. Dimensions and structure of the fibers are tested by JEOL JSM-6610LV scanning electron microscope (SEM). SEM has Oxford Instruments Inca X-Max20 with X-ray spectroscopy energy-dispersive analyzer (EDX) which is used for the elements concentration control.
The samples annealing was carried out at temperatures of 400°C, 600°C, 800°C and 1000°C during 1, 2 and 4 hours in 10-6 Torr vacuum. The main observed impurities are O, Al, Fe, Cr, Na, Si, Cl, Ni. On the fiber surface any modifications were not detected. The oxygen diffusion from the volume to the surface was detected. The microanalysis of the elements concentration along the fiber cross-section was made before and after annealing. The average fiber diameter was 7.5 mm. It was clearly detected than annealing leads to oxygen redistribution in the fiber. After annealing the oxygen concentration decrease in the fiber volume took place.
The carried out research on study of the structure of carbon fabrics and impurities on its surface makes it possible to establish the impurities structure and composition. The main impurity type is oxygen, which is in a bound state throughout the total volume of the material. As a result of carbon fabrics annealing in vacuum, oxygen diffuses to the surface. The regularities of oxygen diffusion in carbon are established. The annealing temperature and time increase result in increase of the ultracapacitor capacity and its parameters stabilization. Obtained results are important for the ultracapacitor use in energy storage devices.