Preparation And Properties Of Carbon Airgel Electrode Material Of The Storage Capacitor

Supercapacitors named electrochemical capacitors are new electrochemical energy storage devices compared to traditional capacitors and batteries due to their high specific power density, quick charge/discharge rate and long circle lifetime. These particular characteristics make them widely used in many fields, such as hybrid electric vehicles (HEVs), camera flash bulbs, pulsed lasers or any other device that requires a great deal of charges delivered in a very short time. Carbon aerogels are ideal supercapacitor electrode materials due to their sufficient specific surface area, high ratio of mesopore volume, good conductivity and stable physicochemical properties. In this article, in order to develop and prepare high performance supercapacitors, great efforts have been devoted to systematic research of preparation techniques and electrochemical properties of high specific surface area carbon aerogels and electrochemical properties of surface modified carbon aerogels. In order to predigest preparation technology of carbon aerogels, we adopt ambient pressure dryer technology and review its influence to electrochemical properties of carbon aerogels. The main conclusions and results are summarized as follows:(1) As a base of carbon aerogels applying in ICF, a series of different theoretical density carbon aerogels have been prepared by adding resorcinol-formaldehyde as carbon precursor. With the increase of theoretical density, the specific surface area of carbon aerogels decrease, pore size distribution becomes identical, such as micropore mainly focus at 1.39nm, and mesopore mainly focus at about 3nm. 100mg/cc carbon aerogels has higher specific surface area and mesopore volume ratio. Thus prepared carbon aerogel has stable working voltage window, ideal electrochemical performance and specific capacitance of 50F/g in 1mol/L (C2H5)4NBF4/PC electrolytes.(2) In order to improve specific surface area of carbon aerogels, physical activated technology has been investigated because of its simple operation and no pollution to the sample. Using CO2 activated technology, a series of carbon aerogels have been prepared with grads of specific surface area and pore size distribution. It has been concluded that with the increase of activated temperature and time,specific surface area of carbon aerogels increase. The specific capacitance of carbon aerogels are determined by surface area and ratio of mesopore volume. The highe ratio of mesopore volume could effectively improve the surface area utilize quotiety for carbon aerogels. The optima of preparation parameters have been determined to be activated temperature of 950℃and the duration of 8h in CO2 atmosphere. Thus prepared activated carbon aerogels demonstrates the specific surface of 2876 m2/g, mesopore porosity of 65.86% and specific capacitance of 131.29 with nonaqueous electrolyte.(3) Instead of increasing the specific capacitantance by increasing specific surface area and adjusting poresize and distribution,one could also utilize surface functionlization to achieve this aim. Boron doped porous carbon aerogels were synthesized through a facile procedure by adding resorcinol-formaldehyde as carbon precursor and boric acid as boron source. By adding different masses of carbon precursor, sample with different pore structures were obtained. It is thought that boron dose aid in graphitization, so it is not surprising that an increase in crystallite size should occur with a dose of boron. The increase of graphitization for carbon aerogel could decrease resistance of supercapacitor, accordingly, the specific capacitance increased. Cyclic voltammetric and galvanostatic charge/discharge were employed to investigate the electrochemical behavior of the materials. All of the B-doped samples had near rectangular shape I-Vcurves with slightly distorted, which is characteristic of electrochemical capacitor. The charge/discharge curves of all B-doped samples have near triangular shapes, reflecting their good capacitive performance. B:Cl-5 has the largest specific capacitance and result is 212 F/g with the current of 1mA/s. Thus, B:Cl-5 may be an ideal electrode material in supercapacitors. In summary, boron doping can enhance the specific capacitance because of pseudocapacitive and graphitization effect. The results are helpful to understand the effect of heteroatoms doped into carbon matrix on the capacitive behaviors and design different types of supercapacitors apply in any fields.(4) Nitrogen doped in carbon aerogel could increase the alkalescence of materials and increase the surface supply of electron to improve the power and energy density of supercapacitor. Nitrogen doped carbon aerogels with different surface area and pore size distribition have been successfully prepared by compounding with melamine. The capacitance performance are investigated in 6 M KOH electrolyte. The results shows that in spite of its small specific surface area and pore volume, nitrogen doped carbon aerogels has good capacitive behavior and power performance. By the result of charge-discharge curve at identical electric current, MRF 0.1 sample has the highest specific capacitance of 195.5F/g. But with the decrease of surface area, the specific capacitance of carbon aerogels decrease rapidly, however, with the increase of containing nitrogen, its specific capacitance increase, MRF0.9 sample has achieved 173F/g.Nitrogendoped carbon aerogels by adding melamine-resorcinol-formaldehyde as carbon precursor have little surface area but large specific capacitance, it is an promising electrode materials for its in favor of small and practicality of supercapacitor.(5) In order to resolve the complex preparation technology and high cost of carbon aerogels, P123 are added to carbon precursor to decrease the interfacial tension in process of solvent volatilization. Carbon aerogels with whole shape and lesser shrinkage are successfully prepared by dried in ambient pressure. CO2 activation technics are investigated to adjust specific surface area and pore structure of carbon materials. The results shows that carbon aerogels dried in ambient pressure have high specific capacitance and good power performance. CO2 activation could improve surface area and specific capacitance of carbon aerogels.The optima of preparation parameters have been determined to be activated temperature of 950℃and duration 4h in CO2 atmosphere.Thus prepared activated carbon aerogels demonstrates the specific surface of 3560 m2/g, mesopore porosity of 23.52% and specific capacitance of 258.3 with6 M KOH electrolyte.