슈퍼커패시터용 탄소/니켈 복합에어로젤 전극에 대한 연구

Abstract

Abstract

Research on Carbon/Nickel Composite Aerogel Electrodes for Supercapacitors

A-Rum Jang Dept. of Chemical Engineering The Graduate School Hanyang University

A supercapacitor is different from a battery which is used the chemical reaction to store and generate electric energy from a oxidation/reduction reaction. The principles of electric generation in battery is a chemical reaction and supercapacitors store electrical energy through electrical double layer capacitance (EDLC) generated by physical adsorptions of ions to the surfaces of electrode. The early supercapacitors adopted an inorganic electrolyte to obtain below 1 F capacitance with low consumer current like ㎂ in memory back-up power. Through continuous developments and researches, various materials for supercapcitors were invented. After developing an organic electrolyte, the energy density is improved because usable voltage is increased to 2.5 V. Recently, supercapacitors have been considered as a promising high power energy source for digital communication devices, high power suppliers, memory back-up systems and advanced vehicles, e.g. hybrid electric and fuel cell vehicles. Although they can not store as much energy as batteries, the supercapacitors possess advantages such as higher charge/discharge efficiency, longer cycle life and faster charge capability In this study, carbon aerogels were synthesized from resorcinol and formaldehyde by using magnesium acetate as a catalyst. We changed Resorcinol/Catalyst (R ratio) from 50 to 500. We prepared CA50, CA100, CA200, and CA500, where CA means carbon aerogel and the number is R ratio. To composite CA and nickel, we dipped CA in nickel solution and then heat treated in nitrogen gas flow. We conducted our research to find out the relations between pore structures of CA and supercapacitor properties, and the effects of nickel composition to supercapacitor performances. Magnesium acetate contents are known to be very important to form three dimensional network of carbon particles. The pores and particle sizes became larger when R ratio were increased. Below 200 of R ratio, the particle size increased between 20 and 100 nm and the pore size showed a similar trend. However, For CA500, the particle size was one micron and the pore size more than hundreds nanometer. Surface area increased with decreasing R ratio. Specific capacitance by cyclic voltammetry, galvanostatic charge/discharge cycling is increasing with decreasing R ratio. The surface area and pore size by the composition of CA and nickel decreased by infiltrating nickel into the pores. However, the specific capacitances of nickel composite aerogel is bigger than those of CAs. Therefore, it is thought that nickel has contributed to improve the capacitance. At this time, the reason is not quite clear, but the results of CV and impedance analyses showed that nickel composition results in the lowering of internal resistance and the pseudo-capacitor characteristics by the redox reaction by nickel nanoparticles. Another possible factor for the enhancement of capacitance is the graphitization of CAs by nickel composition which was confirmed by XRD, Raman scattering and TEM. However, at the moment the mechanism is not clear. In conclusion, we can control the pore size and specific surface area and pore volume by varying R ratio. We can obtain very nanoporous carbon aerogel materials by adding magnesium acetate upto 50 of R ratio. CA50 has high specific surface area and pore volume including micropores, mesopores and macropores, so that it has the highest specific capacitance value, 25 F/g for full cell. Nickel composition increases the capacitance value due to the lowering of the internal resistance and the pseudocapacitance effects of nickel oxide, although it decreases the pore volume and the specific surface area.