JP2005239450A - Manufacturing method of porous carbon, porous carbon, and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon material capable of providing an electric double layer capacitor having a sufficiently high energy density. <P>SOLUTION: In this manufacturing method of a porous carbon, a colloidal crystal comprising colloidal particles is prepared, then a carbon source is introduced among the colloidal particles forming the colloidal crystal. Then, by heat treatment, the carbon source is carbonized, and, at the same time, the colloidal crystal is dissolved and removed, and a porous material comprising carbon is formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing porous carbon, porous carbon, and an electric double layer capacitor.

  Electrochemical capacitors are expected to be used as backup power sources for semiconductor memories, auxiliary power sources for electric vehicles, power storage materials for load leveling of power systems and measures against instantaneous voltage drop. As such an electrochemical capacitor, an electric double layer capacitor, a supercapacitor and the like have been developed. In particular, an electric double layer capacitor using a carbon fiber material or a carbon porous material is practically used as a backup power source for a semiconductor memory. .

However, the electric double layer capacitor using the carbon fiber material or the carbon porous material does not have sufficient energy density and power density, and as a result, the electric double layer capacity (F / g) or per surface area. The electric double layer capacity (F / cm ² ) and the like are not sufficient, and cannot be applied to other practical uses such as a power supply excluding the backup power supply.

  An object of the present invention is to provide a carbon material capable of providing an electric double layer capacitor having sufficiently high energy density and power density, and to provide the electric double layer capacitor.

In order to achieve the above object, the present invention provides:
Preparing a colloidal crystal composed of colloidal particles;
Introducing a carbon source between the colloidal particles constituting the colloidal crystal;
Heat treating the carbon source and carbonizing;
Dissolving and removing the colloidal crystal to form a porous body made of carbon;
It is related with the preparation method of porous carbon characterized by comprising.

In the conventional carbon porous material, the energy density and power density of the electric double layer capacitor, that is, the electric double layer capacity (F / g) and per surface area are increased by increasing the surface area in consideration of the pores formed therein. It was thought that the electric double layer capacity (F / cm ² ) could be increased. However, actually, even if the substantial surface area of the electric double layer capacitor is increased by the conventional method, the electric double layer capacity cannot be sufficiently improved.

  In view of this point, the present inventors have intensively studied, and in the porous electric double layer capacitor as described above, it is not the surface area of the electric double layer capacitor that greatly contributes to the electric double layer capacitance, It was found that the pores were formed inside. That is, when the electrolyte or ions penetrate into the pores, the pores themselves function as electric double layer capacitors, and the surface of the pores has a high electric double layer capacity. I found out that Therefore, the electric double layer capacity of the electric double layer capacitor varies greatly depending on how many pores exist as described above.

  A conventional electric double layer capacitor has a high generation ratio of micropores having a pore diameter of 2 nm or less, and electrolytes and ions cannot sufficiently penetrate into the micropores. Therefore, even if the surface area of the electric double layer capacitor is increased by forming a large number of micropores, the pore hardly functions as a capacitor, and as a result, the electric double layer capacitance of the electric double layer capacitor is reduced. Could not be improved sufficiently.

  In view of such points, the present inventors used colloidal crystals as templates and synthesized carbon between colloidal particles of the templates, whereby mesopores having a pore diameter of 2 nm or more and 50 nm or less and / or pore diameters in the carbon. It has been found that macropores of 50 nm or more are generated. And it discovered that electrolyte solution, ion, etc. osmose | permeated fully in the said mesopore and the said macropore, and the said mesopore itself fully functions as an electric double layer capacitor. Therefore, it has been found that by forming an electric double layer capacitor from the porous carbon of the present invention, the electric double layer capacity can be sufficiently increased due to the mesopores.

  As described above, according to the present invention, it is possible to provide a carbon material capable of providing an electric double layer capacitor having sufficiently high energy density and power density, and to provide the electric double layer capacitor. .

  The details of the present invention and other features and advantages will be described in detail below based on the best mode.

  In the method for producing porous carbon of the present invention, a colloidal crystal to be used as a template is first prepared. This colloidal crystal can be formed from, for example, a predetermined aqueous colloidal solution by using a centrifugal separation method, a solvent evaporation method, a precipitation method, an electrodeposition method, or the like. In particular, it is preferable to use a centrifugal separation method.

The colloidal crystal can be composed of SiO ₂ , Al ₂ O ₃ , Fe ₂ O _3, polystyrene, and the like, and is composed of SiO _{2 in} particular from the viewpoint of easy availability and pore diameter controllability. It is preferable.

  Next, a carbon source is introduced between the colloidal particles constituting the colloidal crystal. As the carbon source, it can be composed of phenol resin, resorcinol, furfuryl alcohol, scroll, divinylbenzene, polyimide, polyacrylonitrile, etc., but the target porous carbon can be easily simplified by comprising especially phenol resin. Can be formed.

  In order to introduce a phenol resin between the colloidal particles of the colloidal crystal, a mixed solution of phenol / formaldehyde / hydrochloric acid is prepared, and the colloidal crystal is immersed in the mixed solution, and the temperature is set to 60 ° C. to 200 ° C. This is done by heating.

  Next, the carbon source is carbonized by subjecting the carbon source to a heat treatment. For example, when a phenol resin is used as the carbon source, the phenol resin is carbonized by heating to a temperature of, for example, 550 ° C. or higher by the heat treatment.

  Next, the colloidal crystal is dissolved and removed by immersing it in, for example, an HF aqueous solution to obtain a porous body made of carbon in which, for example, the phenol resin is converted. The pores in the porous body are formed when the colloidal particles constituting the colloidal crystal fall out by the dissolution and removal operation.

  The obtained porous body contains at least one of mesopores having a pore diameter of 50 nm or less and 2 nm or more and macropores having a pore diameter of 50 nm or more, preferably 100 nm or less. As described above, electrolytes and ions do not penetrate into the micropores, and as a result, the micropores themselves do not function as much as an electric double layer capacitor. On the other hand, since the electrolyte, ions, and the like sufficiently permeate into the mesopores, the mesopores themselves function as electric double layer capacitors. The inner surface has a relatively large electric double layer capacity.

Therefore, when the carbon porous body is used as an electric double layer capacitor, the electric double layer capacitor has high energy density and power density. For example, it exhibits an electric double layer capacity of 100 F / g or more and an electric double layer capacity of 10 F / cm ² or more per surface area.

  In order to improve the electric double layer capacity of the electric double layer capacitor by forming the mesopores, at least one of the mesopores and the macropores with respect to the total surface area of the porous carbon. The area ratio is preferably 55% or more. Since the pores are formed by the colloidal particles falling off when the colloidal crystals are dissolved and removed, the ratio can be adjusted by controlling the size of the colloidal particles.

  Specifically, it is important to form colloidal crystals having a close-packed colloidal particle array with colloidal particles of the smallest possible size, but if the colloidal particle size becomes too small, the size of the pores also decreases. turn into. Therefore, in order to form the above-mentioned mesopores and / or macropores, the colloidal particle size is set to 5 nm or more and 100 nm or less.

(Preparation of porous carbon)
To form a SiO ₂ colloidal crystals by centrifugation of SiO ₂ colloid solution. Next, the SiO ₂ colloidal crystal is immersed in a mixed solution of phenol / formaldehyde / hydrochloric acid, and then subjected to a heat treatment at 128 ° C. in an argon gas atmosphere, whereby the phenol resin is placed between the colloidal particles of the colloidal crystal. Generated. Subsequently, the said colloidal crystal containing the said phenol resin was heat-processed at 1000 degreeC, and the said phenol resin was carbonized. Next, the colloidal crystal was removed by immersing it in an HF aqueous solution to obtain porous carbon.

At this time, the following three types of porous carbon were obtained by controlling the size of the SiO ₂ colloidal particles constituting the SiO ₂ colloidal crystal.
(A) Porous carbon having micropores having a pore size of 0.7 nm or less (B) Porous carbon having micropores having a pore size of 0.7 nm or less and macropores having an average pore size of 120 nm (area of macropores) Of about 40% of the total surface area)
(C) Porous carbon having micropores having a pore size of 0.7 nm or less and mesopores having an average pore size of 45 nm (ratio of mesopore area to total surface area is about 65%)
(D) Porous carbon having micropores having a pore size of 0.7 nm or less and mesopores having an average pore size of 16 nm (ratio of mesopore area to total surface area is about 70%)

(Evaluation of porous carbon)
The electric double layer capacity was evaluated from the cyclic voltammogram for the porous carbons (A) to (D). FIG. 1 is a graph showing cyclic voltammograms of porous carbons (A) to (D). The potential sweep rate was 1 mV / sec. As is clear from FIG. 1, any porous carbon exhibited a rectangular cyclic voltammogram, and it was confirmed that charging and discharging were performed on the electric double layer.

  From the graph shown in FIG. 1, the electric double layer capacities of the porous carbons (A), (B), (C) and (D) are 10 F / g, 64 F / g, 127 F / g and 190 F / g, respectively. It turned out to be. Therefore, according to the present invention, when mesopores are present in porous carbon, it is compared with porous carbon (A) having only micropores and porous carbon (B) including micropores and macropores. Thus, it has been found that the electric double layer capacity is sufficiently high.

  FIG. 2 is a graph showing the relationship between the electric double layer capacity of porous carbon (A) to (D) and the total surface area. Each point of (A) to (D) is on one straight line, that is, the electric double layer capacity is increased in proportion to the increase in the total surface area.

Further, since the value of the intersection of the straight line and the horizontal axis substantially coincides with the surface area value of the micropore, it was found that the contribution of the micropore surface to the electric double layer capacity is negligibly small. That is, the surface of mesopores and macropores substantially contributes to the electric double layer capacity, and from this, a value obtained by subtracting the micropore surface area value from the total surface area value, That is, when the electric double layer capacity per mesopore and macropore surface area was determined from the slope of the straight line, it was found to be about 20 μF / cm ² .

  As described above, the present invention has been described in detail based on the embodiments of the present invention with specific examples. However, the present invention is not limited to the above contents, and all modifications and changes are made without departing from the scope of the present invention. It can be changed.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used as a backup power source for semiconductor memories, an auxiliary power source for electric vehicles, and a power storage material for load leveling of power systems and countermeasures against instantaneous voltage drops.

It is a graph which shows the cyclic voltammogram of porous carbon. It is the graph which showed the relationship between the electric double layer capacity | capacitance of porous carbon, and the total surface area.

Claims (14)

Preparing a colloidal crystal composed of colloidal particles;
Introducing a carbon source between the colloidal particles constituting the colloidal crystal;
Heat treating the carbon source and carbonizing;
Dissolving and removing the colloidal crystal to form a porous body made of carbon;
A method for producing porous carbon, comprising:   The method for producing porous carbon according to claim 1, wherein the colloidal crystal is formed from a predetermined colloidal solution by a centrifugal separation method. The method for producing porous carbon according to claim 1, wherein the colloidal crystal is a SiO ₂ colloidal crystal.   The said carbon source is a phenol resin, The preparation method of the porous carbon as described in any one of Claims 1-3 characterized by the above-mentioned.   5. The porous body according to claim 4, wherein the phenol resin is produced by immersing the colloidal crystal in a mixed solution of phenol / formaldehyde / hydrochloric acid and heating to a temperature of 60 ° C. to 200 ° C. 6. Carbon production method.   The method for producing porous carbon according to claim 4 or 5, wherein the heat treatment for the carbon source is performed at a temperature of 550 ° C or higher.   The porous carbon according to any one of claims 1 to 6, wherein the porous carbon includes at least one of mesopores having a pore diameter of 50 nm or less, 2 nm or more, and macropores having a pore diameter of 50 nm or more. Manufacturing method.   8. The porous body according to claim 1, wherein the ratio of the area of at least one of the mesopores and the macropores to the total surface area of the porous carbon is 55% or more. 9. Carbon production method.   A porous carbon comprising at least one of mesopores having a pore diameter of 50 nm or less, 2 nm or more and macropores having a pore diameter of 50 nm or more.   The porous carbon according to claim 9, wherein a ratio of an area of at least one of the mesopores and the macropores to the total surface area of the porous carbon is 55% or more.   The porous carbon according to claim 9 or 10, wherein the mesopores function as an electric double layer capacitor.   An electric double layer capacitor comprising the porous carbon according to any one of claims 9 to 11.   The electric double layer capacitor according to claim 12, wherein the electric double layer capacity per weight is 100 F / g or more. The electric double layer capacitor according to claim 12 or 13, wherein the electric double layer capacity per surface area is 10 µF / cm ² or more.

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