JP2004059387A - Production method for activated carbon, polarizable electrode and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an activated carbon which is highly densified without lowering the capacitance per unit weight and has a high capacitance per unit volume. <P>SOLUTION: This method for producing the activated carbon comprises performing a primary mixing treatment of a carbonaceous material and an alkali metal hydroxide, carbonizing the primary mixture, secondarily mixing the carbonized material with the alkali metal hydroxide, and activating the secondary mixture. The amount of the alkali metal hydroxide used in the primary mixing treatment is 0.01-0.5 times the weight of the carbonaceous material, and that in the secondary mixing is 0.5-4 times the weight of the carbonized material. <P>COPYRIGHT: (C)2004,JPO

Description

【００５６】
表１の結果から、本発明の製造方法により得られた活性炭は、細孔容積及び比表面積は低下するが、静電容量は向上していることがわかる。従って、本発明の製造方法によれば、単位重量あたりの静電容量を低下させることなく、通常の熱処理を施した活性炭よりも単位体積あたりの静電容量の向上した活性炭を得ることができる。
【００５７】
【発明の効果】
本発明の製造方法によれば、単位重量あたりの静電容量を低下させること無く、単位体積あたりの静電容量の高い活性炭が得られる。
【図面の簡単な説明】
【図１】電気二重層キャパシタの一例を示す断面概略図である。
【符号の説明】
１，２　集電部材、３，４　分極性電極、５　セパレータ、６　ガスケット、７　ケース[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing activated carbon, a polarizable electrode, and an electric double layer capacitor. Since the activated carbon of the present invention has a high density and a large capacitance per volume, it is formed into a polarizable electrode and is suitably used for an electric double layer capacitor.
[0002]
[Prior art]
In recent years, new electronic devices such as mobile phones and notebook computers have rapidly spread, and electric double-layer capacitors have attracted attention as memory backup devices and auxiliary power sources for motors and the like. In particular, many electric double layer capacitors using activated carbon having a high specific surface area as an electrode material have been developed. Heretofore, as activated carbon for electric double layer capacitors, activated carbon obtained by activating coconut shell, resin, coal, pitch and the like in an acidic gas atmosphere such as water vapor or carbon dioxide gas has been widely used. Further, activation (alkali activation) of a carbonaceous material using an alkali metal hydroxide such as KOH is also performed. Among them, activated carbon obtained by alkali activation has a relatively large specific surface area and high capacitance, and is therefore expected as a polarizable electrode of an electric double layer capacitor (for example, WO91 / 12203, JP-A-10-199767). No.).
[0003]
By the way, with the recent trend toward smaller and lighter electronic devices, the electric double-layer capacitors used tend to require smaller and larger capacities. It is required to exhibit a high capacitance as described above. For this reason, it is conceivable that the activated carbon is made more porous by the same method as in the past to increase the specific surface area. However, although an improvement in the capacitance per weight can be expected, the static carbon per unit volume is reduced due to a decrease in the activated carbon density. No improvement in capacity is expected. In addition, it is possible to increase the activated carbon density by controlling the amount of alkali metal hydroxide used and the reaction temperature to suppress the progress of alkali activation, but as a result, the capacitance per unit weight decreases. Therefore, improvement in the capacitance per unit volume cannot be expected.
[0004]
As a solution to this problem, it has been proposed to produce an activated carbon by activating the carbonaceous raw material with an alkali, removing an alkali metal compound, and performing a heat treatment (Japanese Patent Application Laid-Open No. 9-21590).
[0005]
[Problems to be solved by the invention]
However, according to the method described in Japanese Patent Application Laid-Open No. 9-213590, when heat treatment is performed on a product obtained by removing an alkali metal compound from an alkali activated treatment of a carbonaceous raw material in order to increase the density of activated carbon, static electricity per unit weight is reduced. There is a problem that the capacitance is reduced, and as a result, the capacitance per unit volume is improved by only about several percent at most.
[0006]
An object of the present invention is to increase the density and increase the capacitance per unit volume without decreasing the capacitance per unit weight, regardless of the method of changing the degree of activation or applying a normal heat treatment. It is to provide a method for obtaining activated carbon.
[0007]
[Means for Solving the Problems]
The present inventors have studied diligently, and instead of simply performing a heat treatment on a product obtained by removing an alkali metal compound from an alkali activation treatment product of a carbonaceous raw material, a carbonaceous material and an alkali metal hydroxide are mixed and temporarily mixed. The present inventors have found that the above object can be achieved by performing a carbonization treatment and further activating an alkali by adding an alkali metal hydroxide, and have accomplished the present invention.
[0008]
That is, the present invention provides a primary mixing process of a carbonaceous material and an alkali metal hydroxide, a carbonizing process of the obtained primary mixture, and a secondary mixing process of the obtained carbonized product and the alkali metal hydroxide. And a method for producing activated carbon, characterized in that activated carbon is obtained by activating the obtained secondary mixture.
[0009]
The present invention also provides a polarizable electrode formed by mixing the activated carbon thus obtained, at least a binder and a conductive material, and provides an electric double layer capacitor incorporating such a polarizable electrode. .
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The production method of the present invention comprises a primary mixing treatment of a carbonaceous material and an alkali metal hydroxide, a carbonization treatment of the obtained primary mixture, and a secondary mixing of the obtained carbonized treatment product and an alkali metal hydroxide. The activated carbon is obtained by activating the obtained secondary mixture. Activated carbon obtained by the production method of the present invention exhibits high capacitance. Although the reason cannot be clearly explained, the alkali metal hydroxide used in the primary mixing process contributes to carbonization (strong oxidation) of the carbonaceous material during the carbonization process, and the alkali metal hydroxide used in the secondary mixing process. It is presumed that the contribution of the hydroxide to the activation treatment is to increase the effective surface of the electric double layer while increasing the crystallinity of the activated carbon.
[0011]
First, the raw materials used in the present invention will be described.
[0012]
The carbonaceous material used in the present invention is not particularly limited as long as it can be activated to form activated carbon, and examples thereof include coal, coconut shell, resin, petroleum coke, and coal pitch coke. As the carbonaceous material, a carbonaceous material that has not been subjected to a heat treatment at 1000 ° C. or higher, more preferably 600 ° C. or higher is preferable. The shape of the carbonaceous material is not particularly limited, and various shapes such as granules, powders, fibers, and sheets can be used.
[0013]
Further, the state of the carbonaceous material can be used regardless of whether it is solid or liquid. Here, when the carbonaceous material is solid, it is preferable to use a pulverized material in order to make the mixing with the alkali metal hydroxide uniform. The ground particle size is preferably 2 mm or less, more preferably 0.2 mm or less. When the carbonaceous material is a liquid such as a liquid resol resin, it can be used as it is.
[0014]
Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, cesium hydroxide, and rubidium hydroxide. These may be used alone or in combination of two or more. Among them, preferred alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and mixtures thereof.
[0015]
Further, the alkali metal hydroxide can be used not only in the form of powder or liquid, but also in that the mixing with the carbonaceous material is uniform. When making the alkali metal hydroxide liquid, there is no particular limitation as long as the alkali metal hydroxide is in a liquid state. The alkali metal hydroxide may be used in an alkali metal hydroxide solution dissolved in water, alcohol, or the like.
[0016]
Next, the method for producing activated carbon of the present invention will be described for each treatment.
[0017]
In the method for producing activated carbon of the present invention, first, a carbonaceous material and an alkali metal hydroxide are subjected to a primary mixing treatment to obtain a primary mixture. The mixer used in this treatment is not particularly limited, and a known rotary container type mixer or a fixed container type mixer is used, but the rotary container type mixer is used in that uniform mixing is obtained. It is better to use a machine. As a material of these devices, an alkali-resistant material, particularly a material mainly containing nickel is preferable.
[0018]
In the primary mixing treatment, the use amount of the alkali metal hydroxide is too small, the progress of crystallization is slow, and if too large, the activation proceeds earlier than the progress of crystallization. It is preferably 0.5 times by weight, more preferably 0.05 to 0.3 times by weight.
[0019]
The processing temperature during the primary mixing is usually sufficient at room temperature.
[0020]
The primary mixture obtained by the primary mixing treatment (when the carbonaceous material is in a liquid state, uniformly mixed with the alkali metal hydroxide and subjected to infusibilization treatment) may be subjected to the carbonization treatment as it is. It may be formed into a sphere, granule, pellet, plate or the like. At the time of molding, a known binder such as pitch and tar may be mixed as needed to improve moldability.
[0021]
Next, the primary mixed product is carbonized to obtain a carbonized product. This carbonization treatment is a treatment in which an organic substance contained in the carbonaceous material is oxidized and carbonized by heating with a carbonaceous material and a relatively small amount of an alkali metal hydroxide. If a mixture of a carbonaceous material and a relatively large amount of an alkali metal hydroxide is activated without performing the carbonization treatment, it becomes difficult to improve the capacitance per volume of the active material.
[0022]
If the treatment temperature during the carbonization treatment is too low, the effect of promoting crystallization is small, and if it is too high, the crystallization proceeds too much and inhibits the progress of activation, so it is preferably 300 ° C to 1000 ° C, more preferably 300 ° C. C. to 800C.
[0023]
The rate of temperature rise to the treatment temperature during the carbonization treatment is not particularly limited, but if it is too slow, it takes too much time to reach the intended treatment temperature, thereby lowering industrial productivity. Since generation or rapid gas generation occurs and is dangerous, the operation is preferably performed at about 0.1 to 4.0 ° C./min, more preferably about 0.5 to 3.0 ° C./min. The carbonization time (heat treatment time) is not limited, but is usually 1 to 24 hours.
[0024]
In addition, since the carbonization treatment is a high-temperature heat treatment, the carbonization treatment is preferably performed in an atmosphere of an inert gas such as nitrogen, carbon dioxide, argon gas, combustion gas, or a mixed gas thereof.
[0025]
The primary mixing process and the carbonization process may be performed separately, but the carbonization process may be performed while performing the primary mixing process.
[0026]
Next, an alkali metal hydroxide is secondarily mixed with the carbonized product obtained by the carbonizing process to obtain a secondary mixture. In this case, for example, a carbonized product that has been allowed to cool to room temperature may be used, or the carbonization may be performed without cooling. As the mixer used in this process, the mixer exemplified in the primary mixing process can be used.
[0027]
In the secondary mixing treatment, the use amount of the alkali metal hydroxide is too small, the progress of activation is slow, and if too large, it is overactivated, so that the carbonaceous material is preferably 0.5 to 10 times by weight, It is preferably 0.5 to 4 times by weight in consideration of operability and safety.
[0028]
The processing temperature at the time of the secondary mixing process can be usually performed in the range of room temperature to 80 ° C., but when the secondary mixing process is performed continuously to the carbonization process, the temperature may be the same as the carbonization temperature. .
[0029]
When the secondary mixing is performed at room temperature, the secondary mixing may be performed in an air atmosphere.However, when the secondary mixing is performed at substantially the same temperature as the carbonization, nitrogen, carbon dioxide, argon, combustion gas, It is preferable to carry out in an atmosphere of an inert gas such as a mixed gas of the above.
[0030]
Next, the secondary mixture obtained by the secondary mixing treatment is subjected to an activation treatment to obtain an activation treatment product, and then activated carbon is obtained. Here, the secondary mixing process and the activation process may be performed separately, but the activation process may be performed while performing the secondary mixing process. In particular, after the carbonization treatment, without lowering the temperature of the reaction system, an alkali metal hydroxide may be added to the carbonization treatment product to perform the secondary mixing treatment and at the same time to proceed with the activation treatment.
[0031]
The activation treatment includes carbon, 177 (1997) p. Known alkali activation methods described in 76-79 and the like can be applied. For example, the secondary mixture obtained by the secondary mixing treatment is performed by heating in a batch or continuous manner under an atmosphere of nitrogen, carbon dioxide gas, argon gas, combustion gas, or an inert gas of these mixed gases. Can be. Here, when the activation treatment temperature is too high, the surface area of the activated carbon increases, but the capacitance of the electric double layer capacitor decreases, and the danger of metal potassium generated in the activation treatment evaporates. Significantly higher. On the other hand, if the activation treatment temperature is too low, a fine structure which is gasified by the activation treatment and which should be removed from the system is not removed, so that, for example, the electric resistance when used as an electrode material increases. Therefore, the activation treatment temperature is preferably 500 to 1000C, more preferably 600 to 800C.
[0032]
The activated material obtained by the activation treatment is cooled under a stream of an inert gas such as nitrogen or argon in order to suppress the combustion of the treated material. Then, by a conventional method, the activation treatment product is washed with water, and if necessary, pickled, washed with water to remove alkali metal components and impurities, and heated at room temperature or under atmospheric pressure or reduced pressure, and dried to obtain the desired product. Get activated carbon.
[0033]
The activated carbon obtained by the production method of the present invention described above is useful as a material of a polarizable electrode particularly suitable for an electric double layer capacitor.
[0034]
Such a polarizable electrode is obtained by mixing at least a binder such as polyvinylidene fluoride and polytetrafluoroethylene and a conductive material such as carbon black with activated carbon obtained by the production method of the present invention, and molding the mixture. It is. Mixing a conductive material can reduce the resistance of the electrode, which is effective in reducing the internal resistance of the polarizable electrode and reducing the volume of the electrode.
[0035]
In order to manufacture a polarizable electrode suitable for such an electric double layer capacitor, a generally known method can be applied. For example, a commercially available material known as a binder such as polyvinylidene fluoride or polytetrafluoroethylene or a conductive material such as carbon black may be added to a few percent if necessary, and the mixture may be kneaded. And press-molded, or rolled into a sheet, and punched into a required shape to form an electrode. Alternatively, the kneaded material may be applied to a current collector to form an application electrode. When forming an electrode, an organic compound such as alcohol or N-methylpyrrolidone, a solvent such as water, a dispersant, or various additives may be used as necessary. It is also possible to apply heat within a range that does not impair the effects of the invention.
[0036]
The polarizable electrode described above is useful as an electrode of an electric double layer capacitor as shown in FIG. 1 (schematic sectional view). Each component constituting the capacitor of FIG. 1 can have the same configuration as a known electric double layer capacitor except that the polarizable electrode according to the present invention is used. , 3 and 4 are polarizable electrodes made of the activated carbon of the present invention, 5 is a separator made of polypropylene non-woven fabric and the like, 6 is a gasket made of polypropylene, polyethylene, polyamide, polyamide imide, polybutylene, etc. And 7 indicate a case made of a material such as stainless steel.
[0037]
In order to function as an electric double layer capacitor, a known electrolyte such as tetraethylammonium tetrafluoroborate or tetramethylammonium tetrafluoroborate is placed in the case 7 with a carbonate such as ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate. , Acetonitrile and other nitriles, α-methyl-γ-butyrolactone and other lactones, dimethylsulfoxide and other sulphoxides, and dimethylformamide and other amides and the like must be filled with an electrolytic solution.
[0038]
Since the electric double layer capacitor having the configuration shown in FIG. 1 uses the activated carbon of the present invention, it has a small size and a high capacitance.
[0039]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples.
[0040]
Example 1
In a nickel cylinder having a diameter of 10 cm and a height of 90 cm, 50 g of semi-anthracite and 20 g of a 50% by weight aqueous potassium hydroxide solution pulverized with a ball mill to a center particle size of about 50 μm were added and kneaded. After kneading, the mixture was pelletized, dried at 120 ° C., and then carbonized at 730 ° C. under an air flow of 0.6 liter (L) / min of nitrogen. 86.4 g of 85% potassium hydroxide was mixed with 43.2 g of the obtained carbide, and the temperature was increased to 730 ° C. at a rate of 200 ° C./hour under a gas flow of 0.6 L / min. After reaching 730 ° C., it was kept for 3 hours for activation treatment, and then allowed to cool to room temperature. The obtained activated product was repeatedly pickled and washed with water to remove potassium, and then dried at 120 ° C. to obtain 26.7 g of activated carbon.
[0041]
Example 2
Into the same apparatus as in Example 1, 33 g of semi-anthracite and 10 g of a 50% by weight aqueous potassium hydroxide solution pulverized with a ball mill to a central particle size of about 50 μm were added. 10 g was added and kneaded. After kneading, the mixture was pelletized, dried at 120 ° C., and then carbonized at 730 ° C. under an air flow of 0.6 L / min of nitrogen. 85.0 g of 85% potassium hydroxide was mixed with 42.5 g of the obtained carbonized product, and the temperature was raised to 730 ° C. at a rate of 200 ° C./hour under a gas flow of 0.6 L / min. After reaching 730 ° C., it was kept for 3 hours for activation treatment, and then allowed to cool to room temperature. The obtained activated product was subjected to repeated acid washing and water washing to remove potassium, and then dried at 120 ° C. to obtain 26.6 g of activated carbon.
[0042]
Comparative Example 1
Activated carbon was obtained by mixing 50 g of semi-anthracite and 100 g of 85% KOH pulverized to a center particle size of about 50 μm with a ball mill, activating it in the same manner as in Example 1, removing potassium, and drying.
[0043]
Comparative Example 2
50 g of semi-anthracite was pulverized with a ball mill to a median particle size of about 50 μm, and carbonized at 730 ° C. under an air flow of 0.6 L / min of nitrogen. 95.6 g of 85% KOH was mixed with 45.6 g of the obtained carbonized product, activated in the same manner as in Example 1, potassium was removed, and dried to obtain activated carbon.
[0044]
Comparative Example 3
100 g of semi-anthracite was pulverized with a ball mill to a center particle size of about 50 μm, and carbonized at 830 ° C. under an air flow of 0.6 L / min of nitrogen. 162.4 g of 85% KOH was mixed with 81.2 g of the obtained carbonized product, activated as in Example 1, potassium was removed, and dried to obtain activated carbon.
[0045]
Example 3
Into the same apparatus as in Example 1, 50 g of petroleum coke and 10 g of a 50% by weight aqueous solution of potassium hydroxide pulverized with a ball mill to a center particle size of about 50 μm were added, and 10 g of water was further added and kneaded. After kneading, the mixture was pelletized, dried at 120 ° C., and then carbonized at 730 ° C. under an air flow of 0.6 L / min of nitrogen. 85.0 g of 85% potassium hydroxide was mixed with 42.5 g of the obtained carbonized product, and the temperature was raised to 730 ° C. at a rate of 200 ° C./hour under a gas flow of 0.6 L / min. After reaching 730 ° C., it was kept for 3 hours for activation treatment, and then allowed to cool to room temperature. The obtained activated product was repeatedly pickled and washed with water to remove potassium, and then dried at 120 ° C. to obtain 29.5 g of activated carbon.
[0046]
Example 4
Into the same apparatus as in Example 3, 50 g of petroleum coke and 10 g of a 50% by weight aqueous potassium hydroxide solution pulverized by a ball mill to have a center particle diameter of about 50 μm were added, and 10 g of water was further added and kneaded. After kneading, the mixture was pelletized, dried at 120 ° C., and then carbonized at 730 ° C. under an air flow of 0.6 L / min of nitrogen. 42.5 g of the carbonized product was washed with warm water to remove alkali, and then dried at 120 ° C. 80.0 g of 85% potassium hydroxide was mixed with 40 g of the alkali-removed carbide, and the temperature was increased to 730 ° C. at a rate of 200 ° C./hour under an air flow of 0.6 L / min of nitrogen. After reaching 730 ° C., it was kept for 3 hours for activation treatment, and then allowed to cool to room temperature. The obtained activated product was repeatedly pickled and washed with water to remove potassium, and then dried at 120 ° C. to obtain 28.1 g of activated carbon.
[0047]
Example 5
Into the same apparatus as in Example 3, 50 g of petroleum coke and 10 g of a 50% by weight potassium hydroxide aqueous solution pulverized by a ball mill to a center particle size of about 50 μm were added, and 10 g of water was further added and kneaded. After kneading, the mixture was pelletized, dried at 120 ° C., and carbonized at 630 ° C. under an air flow of 0.6 L / min of nitrogen. 53.0 g of the obtained carbonized product is washed with warm water, 40 g of the carbonized product after washing is mixed with 80.0 g of 85% potassium hydroxide, and 200 ° C./hour up to 730 ° C. under an air flow of 0.6 L / min of nitrogen. The temperature rose. After reaching 730 ° C., it was kept for 3 hours for activation treatment, and then allowed to cool to room temperature. The obtained activated product was repeatedly pickled and washed with water to remove potassium, and then dried at 120 ° C. to obtain 26.2 g of activated carbon.
[0048]
Comparative Example 4
50 g of petroleum coke and 100.0 g of 85% KOH mixed with a ball mill to a center particle size of about 50 μm were mixed, activated in the same manner as in Example 1, potassium was removed, and dried to obtain activated carbon.
[0049]
Comparative Example 5
70 g of petroleum coke was ground with a ball mill to a center particle diameter of about 50 μm, and carbonized at 730 ° C. under an air flow of 0.6 L / min of nitrogen. 121.0 g of 85% KOH was mixed with 61.0 g of the obtained carbonized product, and activated in the same manner as in Example 1 to remove potassium and obtain activated carbon.
[0050]
Comparative Example 6
100 g of petroleum coke was ground with a ball mill to a center particle size of about 50 μm, and carbonized at 630 ° C. under an air flow of 0.6 L / min of nitrogen. 100.0 g of 85% KOH was mixed with 50.0 g of the obtained carbonized product, and activated in the same manner as in Example 1 to remove potassium and obtain activated carbon.
[0051]
Comparative Example 7
50 g of petroleum coke was ground with a ball mill to a center particle diameter of about 50 μm, mixed with 125.0 g of 85% KOH, activated as in Example 1, and potassium was removed to obtain activated carbon.
[0052]
(Evaluation)
In addition, in order to evaluate the pore volume and specific surface area of the activated carbon obtained in the above Examples and Comparative Examples, the benzene (Bz) adsorption amount and the iodine adsorption amount were measured according to JIS 1474. Table 1 shows the measurement results.
[0053]
The activated carbon obtained in each of the examples and comparative examples was pulverized by a vibration mill to an average particle size of 5 to 30 μm to obtain powdered activated carbon, and 80 parts by weight of the activated carbon powder, 10 parts by weight of conductive carbon and polytetrafluorocarbon were added. Oleethylene (PTFE) (10 parts by weight) was added and kneaded in an agate mortar. Next, the obtained kneaded material was formed into a sheet having a thickness of about 200 μm by roll rolling, punched into a circular shape having a diameter of 2 cm, and dried at 150 ° C. for 4 hours under reduced pressure to produce a polarizable electrode.
[0054]
The fabricated polarizable electrode was assembled in a cell using a stainless steel case and an aluminum collecting electrode and a glass separator in a clove box having a dew point of −50 ° C. or less, and propylene containing tetraethylammonium tetrafluoroborate was used. It was impregnated with a carbonate solution and swaged and sealed in a glove box. The electrostatic capacity was measured using a power system electric double layer capacitor evaluation device at room temperature, 2.7 V constant current and 5 charge / discharge cycles. Table 1 shows the capacitance obtained by the energy conversion method from the fifth charge / discharge cycle.
[0055]
[Table 1]

[0056]
From the results shown in Table 1, it can be seen that the activated carbon obtained by the production method of the present invention has reduced pore volume and specific surface area, but improved capacitance. Therefore, according to the production method of the present invention, it is possible to obtain an activated carbon having an improved capacitance per unit volume as compared with activated carbon subjected to ordinary heat treatment, without lowering the capacitance per unit weight.
[0057]
【The invention's effect】
According to the production method of the present invention, activated carbon having a high capacitance per unit volume can be obtained without lowering the capacitance per unit weight.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of an electric double layer capacitor.
[Explanation of symbols]
1,2 current collecting member, 3,4 polarity electrode, 5 separator, 6 gasket, 7 case

Claims (8)

The carbonaceous material and the alkali metal hydroxide are subjected to a primary mixing treatment, the obtained primary mixture is subjected to a carbonization treatment, and the obtained carbonized treatment product and the alkali metal hydroxide are subjected to a secondary mixing treatment. A method for producing activated carbon, characterized in that activated carbon is obtained by activating the next mixture. The method for producing activated carbon according to claim 1, wherein the amount of the alkali metal hydroxide used in the primary mixing treatment is 0.01 to 0.5 times the weight of the carbonaceous material. The method for producing activated carbon according to claim 1 or 2, wherein the amount of the alkali metal hydroxide used in the secondary mixing treatment is 0.5 to 4 times the weight of the carbonized product. The method for producing activated carbon according to any one of claims 1 to 3, wherein the alkali metal hydroxide is sodium hydroxide, potassium hydroxide or a mixture thereof. The method for producing activated carbon according to any one of claims 1 to 4, wherein a treatment temperature in the carbonization treatment is 300C to 1000C. Activated carbon obtained by the production method according to claim 1. A polarizable electrode formed by mixing the activated carbon of claim 6 with at least a binder and a conductive material. An electric double layer capacitor using the polarizable electrode according to claim 7.

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