JP4420381B2 - Activated carbon, manufacturing method thereof and polarizable electrode - Google Patents

Description

  The present invention relates to activated carbon, and particularly to activated carbon useful as an electric double layer capacitor (also referred to as an electric double layer capacitor). More specifically, activated carbon that can be suitably used as a capacitor electrode material having high electric capacity and high durability, a method for producing the same, an electrode for an electric double layer capacitor (polarizable electrode) using the activated carbon, and an electric having the electrode The present invention relates to a double layer capacitor.

Electric double layer capacitors are capable of rapid charge / discharge, are resistant to overcharge / discharge, have a long life because they do not involve chemical reactions, can be used in a wide temperature range, and do not contain heavy metals. It has been used for memory backup power supplies. Furthermore, in recent years, the development of large capacity has progressed rapidly, the development of applications for high-performance energy devices has been promoted, and the use for power storage systems combined with solar cells and fuel cells, engine assistance for hybrid cars, etc. has been considered. Yes.
The electric double layer capacitor has a structure in which a pair of positive and negative polarizable electrodes made of activated carbon or the like are opposed to each other via a separator in a solution containing electrolyte ions. When a DC voltage is applied to the electrode, the anion in the solution is attracted to the electrode polarized to the positive (+) side, and the cation in the solution is attracted to the electrode polarized to the negative (−) side. The electric double layer formed at the interface is used as electric energy.

The conventional electric double layer capacitor is excellent in power density, but has a disadvantage that the energy density is inferior, and further development of larger capacity is required for use in energy device applications. In order to increase the capacity of an electric double layer capacitor, it is indispensable to develop an electrode material that forms many electric double layers between solutions.
Accordingly, in order to form more electric double layers, the use of activated carbon having a large specific surface area has been studied, but such activated carbon is excellent in electric capacity per mass (F / g), but the electrode density is lowered. Therefore, the electric capacity per volume (F / ml) does not increase so much.

  In recent years, it has been proposed to produce activated carbon having graphite-like microcrystals as a raw material for a polarizable electrode (for example, JP-A-11-317333: Patent Document 1). An electric double layer capacitor using activated carbon as a raw material for a polarizable electrode can be said to be an excellent raw material in that it has a large electric capacity (F / ml).

  An activated carbon obtained by heating a pitch-derived carbon material in the presence of an alkali metal hydroxide and activating (alkali activation) has been proposed (for example, Japanese Patent Laid-Open No. 5-258996: Patent Document 2). In addition, an electric double layer capacitor having a high electrode density obtained by alkali activation of a so-called mesophase pitch, which has a relatively developed crystallinity of a carbon material, and a high electric capacity per unit volume has been proposed (for example, Japanese Patent Laid-Open No. 10-121336: Patent Document 3).

However, these activated carbons have problems and are not satisfactory. That is, the activated carbon disclosed in Japanese Patent Application Laid-Open No. 11-317333 expands when a voltage is applied, which may cause damage to the cell due to the expansion. In order to suppress the expansion, a size limiting structure is required, which is a major problem in the capacitor assembly operation. There is a problem. In addition, since the electric capacity is not expressed unless a voltage of about 4 V is applied in advance, there is a possibility that the electrolytic solution is decomposed.
The activated carbons of Japanese Patent Application Laid-Open Nos. 5-258996 and 10-121336 have a large electric capacity (F / g), but since the pores are developed too much, the electrode density is reduced, resulting in an electric capacity ( (F / ml) is small.

JP 11-317333 A JP-A-5-258996 JP-A-10-121336

  The present invention provides an activated carbon capable of increasing the electric capacity per electrode without applying an excessive voltage in an electric double layer capacitor and a method for producing the same, and a high-capacitance capacitor using the activated carbon as an electrode material An object of the present invention is to provide a highly reliable electric double layer capacitor in which electrode expansion is suppressed.

The present invention has been made as a result of intensive studies in order to solve the above problems, and comprises the inventions of the following items.
(1) Activated carbon containing an alkaline earth metal compound inside the particle and having a BET specific surface area of 10 to 2000 m ² / g determined by a nitrogen adsorption method.
(2) The activated carbon according to (1), wherein the alkaline earth metal compound is at least one alkaline earth metal compound selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and radium.
(3) Alkaline earth metal compounds are alkaline earth metals, alkaline earth metal oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates And activated carbon according to (1) or (2), which is at least one selected from the group consisting of nitrates.
(4) The activated carbon according to (3), wherein the alkaline earth metal compound is a calcium compound.
(5) Activated carbon as described in said (1) whose alkaline-earth metal compound is a particle | grain with a particle size of 10 micrometers or less.
(6) Activated carbon as described in said (1) whose content of an alkaline-earth metal compound is 30-100,000 mass ppm.
(7) activated carbon according to the ratio of the peak height of D peak to peak height of the Raman spectrum of the G peak (1580 cm ^-1) (1360 cm ^-1) is 0.8 to 1.2 (1).
(8) The activated carbon according to (1), wherein the pore volume of 20 to 50 angstroms determined by the nitrogen adsorption method is in the range of 0.02 ml / g or more.
(9) Activated carbon obtained by coating the activated carbon according to (1) with a porous carbon layer made of non-graphitizable carbon.
(10) Activated carbon as described in said (9) whose pore volume calculated | required by the nitrogen adsorption method is 0.01 ml / g-1.55 ml / g.
(11) Activated carbon as described in said (9) whose average particle diameter is 3-70 micrometers.
(12) The activated carbon according to (1), which does not substantially contain particles having an average particle diameter of 1 μm or less and / or 100 μm or more.
(13) The activated carbon according to (1) or (9), which is for a polarizable electrode of an electric double layer capacitor.
(14) A polarizable electrode comprising the activated carbon according to any one of (1) to (13).
(15) A polarizable electrode comprising the activated carbon according to any one of (1) to (13) and a vapor grown carbon fiber.
(16) The polarizable electrode according to (15), wherein the vapor grown carbon fiber has a hollow structure, has an outer diameter of 2 to 500 nm, and an aspect ratio of 10 to 15000.
(17) The component according to (15), wherein the vapor grown carbon fiber has a pore volume of 0.01 to 0.4 ml / g, and a BET specific surface area determined by a nitrogen adsorption method is 30 to 1000 m ² / g. Polar electrode.
(18) vapor-phase process polarizable electrode surface spacing d ₀₀₂ of (002) plane of the carbon fiber according to the at most 0.3395nm (15).
(19) The polarizable electrode according to (15), wherein the vapor-grown carbon fiber is a branched fiber and the hollow structure of the branched portion is in communication.
(20) The polarizable electrode according to (15), wherein 0.1 to 20% by mass of vapor grown carbon fiber is mixed with respect to the carbonaceous powder.
(21) The polarizable electrode according to (15), wherein vapor grown carbon fiber is fused to the activated carbon surface.
(22) An electric double layer capacitor using the polarizable electrode according to any one of (14) to (21).
(23) The electric double layer capacitor according to (22), wherein an organic electrolytic solution in which an electrolyte is dissolved in an organic solvent is used.
(24) A slurry containing the activated carbon according to (1) to (13).
(25) A paste containing the activated carbon according to any one of (1) to (13).
(26) An electrode sheet on which the activated carbon according to any one of (1) to (13) is applied.
(27) An energy device including the electric double layer capacitor according to (22).
(28) A method for producing activated carbon, comprising a step of adding an alkaline earth metal compound to a raw material of activated carbon and performing a heat treatment, and then a step of activating by mixing and heating the carbonized product generated by the heat treatment with the alkali metal compound.
(29) A step of adding an alkaline earth metal compound to a raw material of activated carbon and heat-treating it in the vapor of the alkali metal compound, followed by a step of activating by mixing and heating the carbonized product generated by the heat treatment with the alkali metal compound A method for producing activated carbon.
(30) The method for producing activated carbon according to (28) or (29), wherein the heat treatment step is performed in a temperature range of 400 to 600 ° C and 600 to 900 ° C.
(31) The method for producing activated carbon according to (28), wherein the alkali metal compound is an alkali metal hydroxide.
(32) The method for producing activated carbon according to (28) or (29), wherein the alkali metal compound is a compound containing at least one selected from the group consisting of potassium, sodium and cesium.
(33) The method for producing activated carbon according to (28) or (29), wherein the carbonized product is graphitizable carbon.

The activated carbon of the present invention is produced by activating a carbonized material such as coke obtained by heat-treating (calcining) a synthetic resin, coal-based pitch, petroleum-based pitch or the like (raw material).
The electrical characteristics of activated carbon depend greatly on the structural properties such as specific surface area, pore distribution, and crystal structure of activated carbon. In order to obtain activated carbon useful as an electrode material, it is necessary to optimize the structure of carbonized material, carbonization conditions, and activation conditions. In the present invention, what is used as a raw material for activated carbon is a general thermoplastic resin such as vinyl chloride resin, polyacrylonitrile, polybutyral, polyacetal, polyethylene, polycarbonate, polyvinyl acetate, etc., petroleum pitch, coal pitch, etc. It is a pitch-based material. In addition, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, and pyrene, and condensed heterocyclic compounds such as indole, quinoline, carbazole, and acridine can be used. Among the above, pitch-based materials such as petroleum-based and coal-based materials can be suitably used in terms of low cost and high carbonization yield.

  Graphitizable carbon that can be converted into graphite by high-temperature treatment at around 3300 K (about 3000 ° C.), such as petroleum coke, coal-based pitch coke, polyvinyl chloride charcoal, and 3,5-dimethylphenol formaldehyde resin charcoal can be used.

  In addition, when selecting a coal-based pitch, the coal-based pitch has fewer side chains and a higher ratio of aromatic compounds compared to petroleum-based carbon raw materials, and polycyclic aromatic compounds of various molecular structures are mixed. Therefore, it is considered that the activated carbon using this as a raw material is derived from this compound, forms various complex microcrystalline structures, and exhibits excellent electrical characteristics. The coal-based pitch to be selected is not particularly limited, but those having a softening point of 100 ° C. or lower, more preferably 60 ° C. to 90 ° C. can be used.

The activated carbon of the present invention contains an alkaline earth metal compound.
The alkaline earth metal compound may be a compound containing at least one alkaline earth metal element selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and radium. Metal oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates or nitrates.

  Preferred is an oxide, carbonate or sulfide of at least one alkaline earth metal element selected from beryllium, magnesium, calcium, strontium, barium and radium. Specific examples include magnesium oxide, calcium oxide, magnesium fluoride, calcium fluoride, magnesium phosphate, calcium phosphate, magnesium carbonate, calcium carbonate, magnesium sulfide, calcium sulfide, and barium sulfate. Two or more alkaline earth metal compounds may be contained in the activated carbon. Among these, preferred are calcium compounds, particularly calcium oxide, or calcium hydroxide, carbonate, sulfide and the like which are converted to calcium oxide by heating.

  The alkaline earth metal compound contained in the activated carbon particles has a particle diameter of 10 μm or less, preferably 5 μm or less, more preferably 1 μm or less, depending on the particle diameter of the activated carbon. Further, if necessary, the compound particle size is preferably 1 μm or less, preferably 0.1 μm or less, more preferably 0.01 μm or less.

  Further, the content of the alkaline earth metal compound in the activated carbon is preferably 30 to 100000 ppm by mass, more preferably 40 to 5000 ppm by mass, and still more preferably 50 to 1000 ppm by mass with respect to the total amount of activated carbon.

Said alkaline-earth metal compound is added to a raw material when manufacturing activated carbon. For example, an alkaline earth metal compound powder is added to the raw material powder. An alkaline earth metal compound can also be added to the raw material melt.
There are a carbonization step and an activation step to obtain activated carbon from raw materials, but those in which alkaline earth metal compounds decompose during heating in these steps, for example, those in which hydroxides and carbonates decompose into oxides It may be. The type, particle size and amount of the alkaline earth metal compound are determined in consideration of changes in particle size and mass accompanying decomposition, or the carbonization rate of the raw material.

  After adding an alkaline earth metal compound to the raw material, it is carbonized by heat treatment. This carbonization step may be a general method of heating to a temperature of up to about 1000 ° C., but preferably a temperature increase rate of 3 to 10 ° C./hr, more preferably 4 to 6 ° C./hr at 400 ° C. or more and less than 600 ° C. Temperature, preferably 450 ° C. or more and 550 ° C. or less, held at a constant temperature within that range for 5 to 20 hours, more preferably 8 to 12 hours, and then 600 ° C. or more and 900 ° C. or less, preferably at the same temperature increase rate. Is preferably held at a constant temperature in the range of 650 ° C. to 850 ° C. for 1 to 20 hours, more preferably 1 to 12 hours.

The heat treatment method is not limited, but industrially, it is economical and highly productive to carry out using a rotary kiln or tunnel kiln.
When the activated carbon raw material is heated between 400 and 900 ° C., a pyrolysis reaction occurs, gas and light fractions are desorbed, and the residue undergoes polycondensation and finally solidifies. In the first stage of this carbonization process, the microscopic bonding state between carbon atoms is almost determined, and the structure of carbon determined in this process is considered to determine the basis of the structure of the activated carbon that is the final product.

  Although the role (action mechanism) played by the alkaline earth metal compound in the activated carbon of the present invention is not clear, by being involved in the structure of the carbonized product, it is ultimately involved in determining the structure of the activated carbon. It is considered that the characteristics are improved, or that the characteristics are improved by acting during charging and discharging of the electric double layer capacitor.

  It is also effective to perform the heat treatment (carbonization) step in the vapor of an alkali metal compound. The alkali metal acts as a catalyst in the carbonization process. That is, the cross-linking between aromatics in the pitch is promoted, and the carbonization reaction proceeds. Examples of the alkali metal compound include sodium, potassium, cesium and the like.

  The heat treatment can be performed in an alkali metal vapor by, for example, heating while introducing an alkali metal compound vapor volatilized from an alkali activation reaction system described later into the system of the carbonization step. In addition, a heat treatment (carbonization) step and an alkali activation step are performed in parallel by placing raw materials around the reaction vessel for the alkali activation reaction, exposing the vapor to the vapor of the alkali metal compound volatilized from the alkali activation reaction system, and simultaneously heating it. Can be done. Thereby, the processing time as a whole can be shortened, and the cost of energy for heating can be reduced.

  Next, the carbonized product is coarsely pulverized to about 1 to 30 mm and / or pulverized to a particle size of about 1 to 100 μm, mixed with an alkali metal compound as an activator, heated, and finely divided into the carbonized product. Pores are formed into porous activated carbon.

  The alkali activator is not particularly limited as long as it is a compound containing an alkali metal, but a compound that melts during activation is more effective. Potassium, sodium and cesium hydroxides, carbonates, sulfides and sulfates are preferred. For example, potassium hydroxide, sodium hydroxide, cesium hydroxide, potassium carbonate, sodium carbonate, potassium sulfide, sodium sulfide, potassium thiocyanate, potassium sulfate, and sodium sulfate can be used. Preferred are potassium hydroxide and sodium hydroxide, and more preferred is potassium hydroxide. For example, sodium hydroxide / potassium hydroxide, sodium hydroxide / potassium hydroxide / cesium hydroxide, or the like may be used by mixing one or more of these.

  The mixing amount of the alkali metal compound with respect to the raw material of the activated carbon is about 0.5 to 7, more preferably about 1 to 5, more preferably about 2 to 4 with respect to the raw material 1 in mass ratio. Pore development is poor when the mass ratio of the alkali metal compound is less than 0.5, and when it is 7 or more, the surface area tends to decrease because the pores are reduced due to excessive activation and destruction of the pore walls. It is in.

  The activation treatment temperature varies depending on the type and shape of the raw material and the activation reaction rate (activation reaction rate), but is performed at 250 to 1000 ° C., more preferably 500 to 900 ° C., further preferably 600 to 800 ° C. Done in When the activation temperature is 250 ° C. or less, the activation is not sufficiently progressed, and there are few pores in the activated carbon, and the electric capacity is lowered when used as a polarizable electrode material of an electric double layer capacitor. Above 1000 ° C, problems such as shrinkage of the pores of the activated carbon, remarkably deteriorated charging characteristics at high current density, and severe corrosion of the activation device occur.

  The activated carbon after the completion of alkali activation is preferably washed with water to wash the alkali component, neutralized with hydrochloric acid, sulfuric acid, nitric acid, etc., and washed again with water to wash the acid. The activated carbon that has undergone the washing step can be used after sufficiently dried.

  The apparatus for performing the activation is not particularly limited, and an apparatus similar to that used in the heat treatment step can be used. For example, a fixed bed heating furnace, a fluidized bed heating furnace, a moving bed heating furnace, an internal heating type or Any of an external heating type rotary kiln, an electric furnace, etc. is suitably employed.

  The activated carbon after the activation step and the washing step is preferably pulverized to be a fine powder having an average particle size of 0.1 to 100 μm, preferably about 1 to 100 μm, and more preferably about 5 to 30 μm. The pulverizer used in this pulverization step is not particularly limited, but a ball mill, a vibration mill, an attrition mill, a jet mill and the like can be preferably used.

  The activated carbon thus obtained has characteristics that it exhibits a high electric capacity from the first cycle without applying an excessive voltage, has a high retention of the electric capacity, and has little electrode expansion. .

When activated activated carbon of one embodiment was observed with a transmission microscope, it was confirmed that the activated carbon had a turbostratic structure having almost no graphite or graphite-like crystals. Further, in XPS (X-ray photoelectron spectroscopy) analysis, alkaline earth metal compounds hardly exist on the activated carbon surface (about 10 nm depth from the surface) and diffuse as submicron particles inside the particles. It was shown that. Furthermore, the ratio of the D peak (1360 cm ⁻¹ ) height to the G peak (1580 cm ⁻¹ ) height of the Raman spectrum (the height from the baseline to the peak point in the actual measurement curve) was 0.8 to 1.2.

  Here, the intensity ratio of the D peak to the G peak of the Raman spectrum is used as an index indicating the graphitization degree of the carbon material. When this intensity ratio is shown as the peak height ratio, the graphitization degree is high. The smaller the value. In the case of activated carbon having graphitic crystals, the value is approximately around 0.6, but in the case of the activated carbon of the present invention having almost no graphite crystals, the value is 0.8 to 1.2.

Activated carbon of the present invention, the BET specific surface area determined by a nitrogen adsorption method 10~2000m ² / g, preferably 100~1200m ² / g, less than the BET specific surface area of the activated carbon obtained by conventional methods ( Usually 2000 to 3000 m ² / g). Further, the activated carbon used as the electrode for the capacitor needs to have a certain amount or more of 20 to 50 angstrom pores that are considered to contribute to capacity development and electrolyte diffusion, and the activated carbon according to one embodiment of the present invention. The pore volume of 20-50 angstrom (2-5 nm) by BJH (Barrett, Joyner and Halenda) method was 0.02 ml / g or more.

Due to the structure and pores as described above, the activated activated carbon can exhibit a high electric capacity from the first cycle without passing an excessive voltage to insert ions between the graphite layers. Furthermore, since sufficient carbonization process is passed, it is thought that the amount of functional groups on the carbon surface is reduced, and deterioration of electric capacity due to repeated charge / discharge is suppressed.
Moreover, when the activated carbon measured the tap density with the tap density meter (made by Kuramochi Scientific Instruments), it was 0.35-0.70g / ml by 50 times of taps, and powder resistance is 0.4 at 1.0 MPa. It was below Ωcm.

  The activated carbon of the present invention can also be coated with a porous carbon layer made of non-graphitizable carbon on the surface. By covering the surface of the activated carbon with a porous carbon layer made of non-graphitizable carbon, it becomes possible to further suppress the expansion and contraction of the activated carbon during charging and discharging. The covering state may be a full surface covering or an island-like covering, but a state in which approximately 30 to 70% of the surface is covered is preferable.

The method for producing the porous carbon layer-coated activated carbon is not particularly limited, but the carbonized product after the first heat treatment step (400 to 600 ° C.) is coated with the adhesive polymer, and then the second step ( It is preferable to perform heat treatment and activation treatment at 600 to 900 ° C.).
For example, the surface of coke-based carbon powder or the like (hereinafter referred to as “base material” or “base material carbon material”) as a base material is coated with a coating material, heat treatment (heat curing, firing, etc.), activation treatment (gas activation, chemicals) It is preferable to carry out activation.

  As the coating material, it is preferable to use a non-graphitizable raw material that can generate so-called hard carbon by heat treatment and suppress shrinkage during charging and discharging of the base material carbon. Examples of the non-graphitizable raw material include at least one selected from the group consisting of phenol resin, polyvinyl alcohol resin, furan resin, cellulose resin, polystyrene resin, polyimide resin, and epoxy resin, but are not particularly limited thereto. .

  In particular, a dense carbon material can be obtained by using a dry resin or a phenol resin mixed with a fatty acid thereof. This is presumed to be due to a chemical reaction between the phenolic resin and the unsaturated fat bond part in the drying oil, resulting in a so-called drying oil-modified phenolic resin, which eases decomposition and prevents foaming during the heat treatment (or firing) process. Is done. In addition, drying oil does not just have double bonds, but has rather long alkyl groups and ester bonds, which are considered to be involved in terms of ease of gas release during the firing process. It is done.

As the phenol resin, unmodified phenol resins such as novolak and resol produced by the reaction of phenols and aldehydes, and partially modified phenol resins can be used. Moreover, rubbers, such as a nitrile rubber, can be mixed and used for a phenol resin as needed. Examples of phenols include phenol, cresol, xylenol, and alkylphenol having a C20 or lower alkyl group.
For phenolic resin mixed with drying oil or its fatty acid, phenols and drying oil were first added in the presence of a strong acid catalyst, then basic catalyst was added to make the system basic, and formalin addition reaction was performed. Or a product obtained by reacting phenols with formalin and then adding a drying oil.

Dry oils are vegetable oils commonly known as paulownia oil, linseed oil, dehydrated castor oil, soybean oil, cashew nut oil, etc., and these fatty acids may be used, and if they are made into a thin film and left in the air for a relatively short time. It has the property of solidifying and drying.
The ratio of the drying oil or its fatty acid to the phenol resin is suitably 5 to 50 parts by mass (drying oil or its fatty acid), for example, with respect to 100 parts by mass of (condensation product of phenol and formalin). When it exceeds 50 mass parts, there exists a tendency for adhesiveness to fall, and it is unpreferable.
When the base material is coated with this polymer, it is easy to coat the polymer by diluting the polymer with acetone, ethanol, toluene or the like to adjust the viscosity.

The atmosphere at the time of coating may be any of atmospheric pressure, increased pressure, and reduced pressure, but is preferably a reduced pressure coating that improves the affinity between the carbonaceous powder and the polymer.
The covering of the base material is preferably performed by stirring and mixing the base material carbon material and the polymer. Although the stirring method is not particularly limited, for example, apparatuses such as a ribbon mixer, a screw type kneader, a spartan luzer, a redige mixer, a planetary mixer, and a universal mixer can be used.
The temperature and time during the stirring treatment are appropriately selected according to the carbonaceous powder of the base material, the components of the polymer, the viscosity, and the like, but are usually about 0 ° C to 50 ° C, preferably about 10 ° C to 30 ° C. Range.

  The mixture of the base carbon material and the polymer preferably uses a diluting solvent and adjusts the mixing time so that the viscosity is 500 Pa · s or less at the mixing temperature. As the dilution solvent in this case, a solvent having good affinity with the polymer can be used. For example, alcohols, ketones, aromatic hydrocarbons, esters and the like can be mentioned, and methanol, ethanol, butanol, acetone, methyl ethyl ketone, toluene, ethyl acetate, butyl acetate and the like are preferable.

After stirring, it is preferable to remove part or all of the solvent. The removal of the solvent is performed by a known method such as hot air drying or vacuum drying.
The drying temperature depends on the boiling point, vapor pressure, etc. of the solvent used, but is specifically 50 ° C. or higher, preferably 100 ° C. or higher and 1000 ° C. or lower, more preferably 150 ° C. or higher and 500 ° C. or lower.

Most of the known heating devices can be used for heat curing. However, as a manufacturing process, a rotary kiln capable of continuous processing or a belt-type continuous furnace is preferable in terms of productivity.
For example, the phenol resin addition amount is preferably 2% by mass to 30% by mass, more preferably 4% by mass to 25% by mass, and further preferably 6% by mass to 18% by mass.

The heat treatment is performed at 1200 ° C. or less, preferably 400 to 1000 ° C., more preferably 500 to 800 ° C.
If the heat treatment temperature is too high, the subsequent activation reaction will not proceed, and if the heat treatment temperature is too low, the carbonization reaction will not proceed.

The average particle size of the raw material is preferably 1 to 70 μm, preferably 3 to 30 μm, more preferably 3 to 15 μm. The average particle diameter can be determined by a laser diffraction scattering method. When the average particle size is smaller than 1 μm, falling from the electrode sheet and short circuit are likely to occur.
When particles having an average particle diameter exceeding 70 μm are mixed, the surface of the electrode becomes uneven, which may cause damage to the separator used in the battery.

Next, the activated carbon added with vapor grown carbon fiber will be described.
By adding carbon fiber to the activated carbon of the present invention, further improvement in characteristics can be achieved.
As the carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, and the like can be used, but vapor-grown carbon fibers in which crystals grow in the fiber axis direction and the fibers are branched are preferable.
Vapor-grown carbon fiber can be produced by heating an organic compound (for example, benzene) and catalytic metal catalyst particles at a high temperature (for example, about 1000 ° C.) in a hydrogen stream.
Vapor-grown carbon fibers can be used as manufactured, those manufactured by firing at 1000-1500 ° C, or further graphitized, but can be used as manufactured or at 1500 ° C. What was heat-processed by the grade is more suitable.

Moreover, there exists a branched fiber as a preferable form of a vapor growth carbon fiber. The branched fiber has a hollow structure in which the entire fiber including the branched portion communicates with each other. Therefore, the carbon layer which comprises the cylindrical part of a fiber is continuing. A hollow structure is a structure in which a carbon layer is wound in a cylindrical shape, and is not a complete cylinder, a part having a partial cut portion, a structure in which two laminated carbon layers are combined into one layer, etc. Including. Further, the cross section of the cylinder is not limited to a perfect circle, but includes an ellipse or a polygon.
In addition, regarding the crystallinity of the carbon layer, the interplanar spacing _d002 of the carbon layer is not particularly limited. Incidentally, preferred d ₀₀₂ by X-ray diffraction method is 0.3395nm or less, and more preferably equal to or less than 0.3380Nm, thickness Lc in the C-axis direction of the crystal is of 40nm or less.

The vapor growth carbon fiber is a carbon fiber having a fiber outer diameter of 500 nm or less and an aspect ratio of 10 or more, preferably a fiber outer diameter of 50 to 500 nm, a fiber length of 1 to 100 μm (aspect ratio of 2 to 2000), or a fiber outer diameter. The length is 2 to 50 nm and the fiber length is 0.5 to 50 μm (aspect ratio 10 to 25000).
By mixing this vapor growth carbon fiber with activated carbon, the contact resistance between particles is reduced, the electrode strength is improved, and the durability as a polarizable electrode is improved.

It is also possible to use gas-activated or chemical-activated vapor-grown carbon fibers. In this case, micropores (pores of 20 angstroms or less) volume of 0.01 to 0.4 ml / g, BET specific surface area of 30 to It is better to use the one whose surface structure is controlled to be 1000 m ² / g. Mixing carbon fibers with many micropores is not preferable because ion diffusion resistance inside the electrode increases.
In addition, when the base material and the polymer are agitated in order to coat the base material with non-graphitizable carbon, it is possible to produce activated carbon in which carbon fibers are fused by mixing carbon fibers. Is possible. In the carbon fiber fused activated carbon produced in this way, expansion and contraction during charging and discharging are further suppressed. It is also effective because the mechanical strength of the polarizable electrode itself may be improved.

  The mixing amount of the vapor-grown carbon fiber with respect to the activated carbon of the present invention is preferably 0.02 to 50% by mass, more preferably 0.05 to 30% by mass, and further preferably 0.5 to 20% by mass. If it is less than 0.02% by mass, a sufficient effect cannot be obtained because the effect of increasing the contact point with the activated carbon particles is small. If it exceeds 50% by mass, the activated carbon content in the polarizable electrode is lowered and the electric capacity is lowered.

  From the activated carbon of the present invention, polarizable electrodes and electric double layer capacitors can be produced according to known methods. That is, the polarizable electrode is a method of kneading and rolling by adding a conductive agent and a binder to activated carbon, adding a conductive agent, a binder, and, if necessary, a solvent to activated carbon to form a slurry and forming a predetermined thickness on the conductive substrate. It is produced by a method of applying and evaporating the solvent at room temperature or heating, a method of mixing activated carbon with a resin and sintering. In this case, as the conductive base material, foil having a thickness of about 10 μm to 0.5 mm, carbon-coated aluminum, stainless steel, titanium, or other foil, or a plate-like material is used.

  For example, if necessary, a powder of carbon black (Ketjen black, acetylene black, etc.), natural graphite, artificial graphite, titanium oxide, ruthenium oxide or the like as a conductive agent is added to activated carbon powder having an average particle size of about 5 to 100 μm. Add a binder such as fluoroethylene (PTFE), polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer cross-linked polymer, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, or polyacrylic acid to a sheet with a thickness of about 0.1 to 0.5 mm. It shape | molds and vacuum-drys at the temperature of about 100-200 degreeC. This sheet is punched into a predetermined shape and used as an electrode. A metal plate as a current collector is laminated on this electrode, and two metal plates are stacked with a separator interposed therebetween, and immersed in an electrolyte solution to form an electric double layer capacitor.

As an electrolytic solution of the electric double layer capacitor, any of known nonaqueous solvent electrolyte solution and water-soluble electrolyte solution can be used. In addition to the electrolyte solution, a polymer solid electrolyte and a polymer gel electrolyte which are nonaqueous electrolytes Ionic liquids can also be used.
Examples of the aqueous (water-soluble electrolyte solution) include sulfuric acid aqueous solution, sodium sulfate aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonium hydroxide aqueous solution, potassium chloride aqueous solution, potassium carbonate aqueous solution and the like.

As non-aqueous (non-aqueous solvent electrolyte solution), cations represented by R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺ (R ¹ , R ² , R ³ and R ⁴ are each independently an alkyl group or an allyl group having 1 to 10 carbon atoms) and an anion such as BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ or the like. Phosphonium salts are, for example, (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ PBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄ or the like as an electrolyte, diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether Ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, ethylene glycol phenyl ether, etc. ether; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, Amides such as N-dimethylacetamide, N-ethylacetamide, N, N-diethylacetamide, N, N-dimethylpropionamide and hexamethylphosphorylamide; sulfur-containing compounds such as dimethylsulfoxide and sulfolane; methyl ethyl ketone, methyl isobutyl ketone and the like Dialkyl ketones; ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2-dimethoxyethane Cyclic ethers such as 1,3-dioxolane, ethylene carbonate, carbonates such as propylene carbonate; .gamma.-butyrolactone; N- methylpyrrolidone; acetonitrile, a solution of an organic solvent such as nitromethane are preferred. Further, carbonate-based nonaqueous solvents such as ethylene carbonate and propylene carbonate can be preferably used. Two or more electrolytes or solvents can be used.

  Examples of the polymer used in the solid polymer electrolyte or polymer gel electrolyte that are non-aqueous electrolytes include polyethylene oxide derivatives and polymers containing the derivatives, polypropylene oxide derivatives and polymers containing the derivatives, phosphate ester polymers, Examples include polycarbonate derivatives and polymers containing the derivatives. Even though these solutes are not dissolved in a solvent, the ionic liquid is liquid, for example, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluorosulfonate Is mentioned.

  As the separator interposed between the electrodes as necessary, any porous separator that transmits ions may be used. Microporous polyethylene film, microporous polypropylene film, polyethylene nonwoven fabric, polypropylene nonwoven fabric, glass fiber mixed nonwoven fabric, glass mat A filter or the like can be preferably used.

  The electric double layer capacitor of the present invention is a coin type housed in a metal case together with an electrolytic solution through a separator between a pair of sheet-like electrodes, a winding type formed by winding a pair of positive and negative electrodes through a separator, Any structure such as a stacked type in which a large number of sheet-like electrodes are stacked via a separator can be used.

  The present invention will be described in more detail below with typical examples. Note that these are merely illustrative examples, and the present invention is not limited thereto. The measuring method of each characteristic in the following example is as follows.

(1) BET specific surface area and pore volume
Using NOVA1200, manufactured by Quantachrome, from the adsorption isotherm of nitrogen at liquid nitrogen temperature, the BET method and the BJH method were used. The nitrogen adsorption amount was measured at a relative pressure (P / P ₀ ) of 0.01 to 1.0.
(2) Raman spectrum An Ar laser 514.5 nm was used as excitation light, a CCD (Charge Coupled Device) was used as a detector, and a Raman spectrum of activated carbon was measured with a slit of 500 μm and an exposure time of 60 seconds.

で求められる。
充放電測定は北斗電工（株）製充放電試験装置HJ-101SM6を使用し、充放電電流５ｍＡ（1.6ｍＡ／ｃｍ²）、５０ｍＡ（１６ｍＡ／ｃｍ²）、１５０ｍＡ（４８ｍＡ／ｃｍ²）にて０〜2.5Ｖあるいは０〜3.0Ｖで充放電を行い、２回目の定電流放電によって得られた放電曲線から、電気二重層キャパシタの両極活性炭の質量当たりの電気容量（Ｆ／ｇ）と体積当たりの電気容量（Ｆ／ｍｌ）を算出した。
耐久性は、２回目の充放電後の電気容量に対する２０回の充放電サイクル試験後の電気容量の割合として評価した。 (3) Electric capacity 10 parts by mass of PTFE (polytetrafluoroethylene) and 10 parts by mass of carbon black are added to 80 parts by mass of activated carbon having an average particle size of 30 μm, kneaded in an agate mortar and 0.2 mm thick with a rolling roller. The sheet rolled into a shape was punched into a disk with a diameter of 20 mm and vacuum-dried at 200 ° C. all day and night to be used as a polarizable electrode.
The electrode was assembled and used in an evaluation cell whose sectional view is shown in FIG. 1 in a glove box in which high-purity argon was circulated. In FIG. 1, 1 is an aluminum top cover, 2 is a fluororubber O-ring, 3 is a current collector made of aluminum, 4 is an insulating material made of Teflon (registered trademark), 5 is an aluminum container, and 6 is aluminum. A leaf spring, 7 is a polarizable electrode, and 8 is a 1 mm thick separator made of glass fiber. The electrolytic solution used was a product name LIPASTE-P / EAFIN (1 mol / liter) manufactured by Toyama Pharmaceutical Co., Ltd. using PC (propylene carbonate) as a solvent and (C ₂ H ₅ ) ₄ NBF ₄ as an electrolyte. .
The electrode expansion coefficient during charging and discharging was measured using an evaluation cell as shown in FIG. 2 and the displacement in the electrode thickness direction was measured using an indicator. The electrode pressing coil spring (9) in FIG. 2 can be used which requires a load of about 0.1 to 1.0 kgf to compress 1 cm, but this measurement requires a load of 0.3 kgf. I used what to do. The measurement temperature was room temperature (20-30 ° C.). Here, for example, the electrode expansion rate (%) when a 2.5 V voltage is applied is

Is required.
The charge / discharge measurement uses a charge / discharge test apparatus HJ-101SM6 manufactured by Hokuto Denko Co., Ltd., at a charge / discharge current of 5 mA (1.6 mA / cm ² ), 50 mA (16 mA / cm ² ), 150 mA (48 mA / cm ² ). Charge / discharge at 0 to 2.5 V or 0 to 3.0 V, and from the discharge curve obtained by the second constant current discharge, the electric capacity (F / g) per mass of the bipolar activated carbon of the electric double layer capacitor and per volume The electric capacity (F / ml) was calculated.
Durability was evaluated as a ratio of electric capacity after 20 charge / discharge cycle tests to electric capacity after the second charge / discharge.

Example 1:
Add 10g of calcium carbonate to 100g of coal pitch with softening point of 86 ° C, fill into crucible, keep temperature at 500 ° C at 5 ° C / hr, and hold at that temperature for 10 hours (first stage), then the same rate of temperature increase And kept at that temperature for 5 hours (second stage). The obtained carbonized product was mixed with 2.5 times the amount of KOH in a mass ratio and filled in a crucible. This was heated up to 750 ° C. at 3 ° C./hr, and then kept at 750 ° C. for 60 minutes for activation. The activated carbonized product was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum dried at 200 ° C. to obtain activated carbon.
The specific surface area of this activated carbon was 930 m ² / g. The pore volume of 20 to 50 angstroms by the BJH method was 0.0416 ml / g, and the ratio of the D peak height to the G peak height calculated from the Raman spectrum was 0.92.
The electric capacity was 5 mA (1.6 mA / cm ² ) charging / discharging current, 36.5 F / g and 31.0 F / ml at 2.5 V charging / discharging, and the capacity retention after 20 cycles charging / discharging was 98.4%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the charge was 37.7 F / g and 32.0 F / ml at 3.0 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 96.9%. The average expansion coefficient of the positive and negative electrodes was 15%.

Example 2:
Activated carbon was produced in the same manner as in Example 1 except that 10 g of calcium hydroxide was used instead of 10 g of calcium carbonate in Example 1.
The specific surface area of this activated carbon was 892 m ² / g, the pore volume of 20 to 50 Å by the BJH method was 0.0398 ml / g, and the ratio of the D peak height to the G peak height calculated from the Raman spectrum was 0.93.
The electric capacity was 36.8 F / g and 31.3 F / ml at a charge / discharge current of 5 mA and 2.5 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 98.3%. The charge / discharge current was 5 mA, 3.0V, and the charge retention was 37.5 F / g and 31.9 F / ml. The capacity retention after 20 cycles of charge / discharge was 96.8%.
Moreover, the average electrode expansion coefficient after charge was 14%.

Example 3:
The activated carbon obtained by the method of Example 1 was mixed with 5% by mass of vapor grown carbon fiber (average diameter 180 nm, average length 10 μm) to obtain a polarizable electrode material. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 2.5 V charge / discharge was 36.4 F / g, 32.4 F / ml, and the capacity retention after 20 cycles of charge / discharge was 98.9%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 3.0 V charge / discharge was 39.5 F / g, 35.2 F / ml, and the 20-cycle capacity retention was 97.7%. The average expansion coefficient of the positive and negative electrodes was 10%.

Example 4:
Activated carbon was produced in the same manner as in Example 1 except that 10 g of calcium sulfide was added to 10 g of calcium carbonate of Example 1 and heat treatment was performed at a second stage holding temperature of 800 ° C. to obtain a polarizable electrode material.
The specific surface area of this activated carbon was 173 m ² / g, and the pore volume of 20 to 50 Å by the BJH method was 0.0271 ml / g. The ratio of the D peak height to the G peak height in the Raman spectrum was 0.93.
The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 2.5 V charge / discharge was 32.6 F / g, 31.9 F / ml, and the capacity retention after 20 cycles of charge / discharge was 98.7%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 3.0 V charge / discharge was 35.5 F / g, 34.8 F / ml, and the 20-cycle capacity retention was 97.2%. The average expansion coefficient of the positive and negative electrodes was 30%.

Example 5:
The same vapor-phase-processed carbon fiber as used in Example 3, 50 g of potassium hydroxide, and heat-treated at 750 ° C. (micropore volume: 0.3 ml, BET specific surface area of 530 m ² / g) Method of Example 4 A polarizable electrode material was prepared by mixing 5% by mass with respect to the activated carbon produced in (1). The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 2.5 V charge / discharge was 33.5 F / g, 33.5 F / ml, and the capacity retention after 20 cycles of charge / discharge was 99.0%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 3.0 V charge / discharge was 34.5 F / g, 34.5 F / ml, and the 20-cycle capacity retention was 98.0%. The average expansion coefficient of the positive and negative electrodes was 5%.

Comparative Example 1:
Activated carbon was produced in the same manner as in Example 1 except that calcium carbonate in Example 1 was not added. The calcium compound contained in the activated carbon was 25 mass ppm in terms of calcium element.
The specific surface area of this activated carbon was 800 m ² / g. The pore volume of 20 to 50 angstroms by BJH method was 0.038 ml / g, and the ratio of the D peak height to the G peak height calculated from the Raman spectrum was 0.89.
The electric capacity was 36.0 F / g and 30.6 F / ml at a charge / discharge current of 5 mA and 2.5 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 98.0%. The charge / discharge current was 5 mA, the charge was 33.0 F / g and 31.5 F / ml at 3.0 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 96.5%.
Moreover, the average electrode expansion coefficient after charge was 50%.

Comparative Example 2:
Petroleum coke was used as a carbon material, and 2.5 times the amount of KOH was mixed in a mass ratio and filled in a crucible. This was held at 750 ° C. for 60 minutes for activation. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon. The specific surface area of this activated carbon was 1905 m ² / g, and the ratio of the D peak height to the G peak height in the Raman spectrum was 0.98. The calcium compound contained in the activated carbon was 23 mass ppm in terms of calcium element.
The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 2.5 V charge / discharge was 44.5 F / g, 24.0 F / ml, and the capacity retention after 20 cycles of charge / discharge was 96.3%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 3.0 V charge / discharge was 45.0 F / g, 24.3 F / ml, and the 20-cycle capacity retention was 94.0%. The average expansion coefficient of the positive and negative electrodes was 20%.

Comparative Example 3:
MCMB (Mesocarbon microbeads manufactured by Osaka Gas Co., Ltd.) was used as a carbon material, and 5 times the amount of KOH was mixed in a mass ratio and filled in a crucible. This was held at 750 ° C. for 60 minutes for activation. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon. The activated carbon had a specific surface area of 127 m ² / g, a pore volume of 20-50 angstroms of 0.013 ml / g, and a ratio of D peak height to G peak height of the Raman spectrum of 0.92. Moreover, the calcium compound contained in activated carbon was 14 mass ppm in terms of calcium element.
The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 2.5 V charge / discharge was 10.2 F / g, 9.4 F / ml, and the capacity retention after 20 cycles of charge / discharge was 99.1%. The charge / discharge current was 5 mA (1.6 mA / cm ² ), the electric capacity at 3.0 V charge / discharge was 11.5 F / g, 10.6 F / ml, and the 20-cycle capacity retention was 98.5%. The average expansion coefficient of the positive and negative electrodes was 70%.

Example 6:
As the adhering material, a phenol resin partially modified with tung oil prepared by the following method was used. That is, 100 parts by mass of tung oil, 150 parts by mass of phenol, and 150 parts by mass of nonylphenol are mixed and maintained at 50 ° C. 0.5 parts by mass of sulfuric acid was added and stirred, and the temperature was gradually raised and maintained at 120 ° C. for 1 hour to carry out an addition reaction between tung oil and phenols. Thereafter, the temperature was lowered to 60 ° C. or less, 6 parts by weight of hexamethylenetetramine and 100 parts by weight of 37% by weight formalin were added, and the reaction was carried out at 90 ° C. for about 2 hours, followed by vacuum dehydration, 100 parts by weight of methanol, 100 parts by weight of acetone. A varnish having a viscosity of 20 mPa · s (20 ° C.) (hereinafter referred to as “varnish A”) was obtained.
10 g of calcium carbonate was added to 100 g of a coal pitch having a softening point of 86 ° C., and the mixture was charged in a crucible. After that, pulverize and add 12.6 parts by mass of ethanol to 5.4 parts by mass in terms of resin solids of varnish A to carbonaceous powder (19.8 g) adjusted to an average particle size (D50 = 8 μm). The dissolved solution was added so that the solid content of the modified phenol resin was 1.3% by mass and kneaded for 30 minutes with a planetary mixer. The kneaded product was dried in a vacuum dryer at 80 ° C. for 2 hours to remove ethanol. Next, this kneaded material was kept at 700 ° C. for 1 hour in a heating furnace and then cooled. After cooling to room temperature, the obtained heat-treated product was mixed with 2.5 times the amount of potassium hydroxide in a mass ratio, and an activation reaction was carried out in the same manner as in Example 1. The average polarizability of the positive and negative electrodes of the obtained polarizable electrode was 5%.

Example 7:
Activated carbon was produced in the same manner as in Example 6 except that 10% by mass of vapor growth carbon fiber was added and kneaded at the time of kneading. The average polarizability of the obtained polarizable electrode was 4%.

The present invention provides an activated carbon containing an alkaline earth metal compound inside a particle and having a specific surface area of 10 to 2000 m ² / g, a production method thereof, and a polarizable electrode. The activated carbon of the present invention can be suitably used as an electrode for a capacitor having high electric capacity (F / ml), low electrode expansion coefficient during charge / discharge, and good durability without applying an excessive voltage.
Furthermore, it is possible to produce a polarizable electrode and an electric double layer capacitor having more excellent characteristics by mixing vapor grown carbon fiber with the activated carbon.

It is sectional drawing of the cell for electric double layer capacitor evaluation used in the Example. It is sectional drawing of the cell for evaluation used for the measurement of the change of the electrode expansion coefficient at the time of charging / discharging.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper lid 2 O-ring 3 Current collector 4 Insulator 5 Container 6 Leaf spring 7 Electrode 8 Separator 9 Electrode holding coil spring

Claims (24)

Comprises an alkali earth metal compound inside the particles, BET specific surface area as determined by nitrogen adsorption method is 10~2000m ² / g, D peak to peak height of G peak of the Raman spectrum (1580cm ^-1) (1360cm ^{- 1)} Ri ratio 0.8-1.2 der peak height of 20 to 50 angstrom pore volume by the BJH method determined by the nitrogen adsorption method is in the range of more than 0.02 ml / g, the alkaline earth metal compound is Activated carbon having a particle size of 1 μm or less and an alkaline earth metal compound content of 30 to 100,000 mass ppm.   The activated carbon according to claim 1, wherein the alkaline earth metal compound is at least one alkaline earth metal compound selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and radium.   Alkaline earth metal compounds from alkaline earth metals, alkaline earth metal oxides, hydroxides, chlorides, bromides, iodides, fluorides, phosphates, carbonates, sulfides, sulfates and nitrates The activated carbon according to claim 1 or 2, which is at least one selected from the group consisting of:   The activated carbon according to claim 3, wherein the alkaline earth metal compound is a calcium compound.   Activated carbon obtained by coating the activated carbon according to claim 1 with a porous carbon layer made of non-graphitizable carbon. The activated carbon according to claim 1 or 5 , which is used for a polarizable electrode of an electric double layer capacitor. A polarizable electrode comprising the activated carbon according to any one of claims 1 to 6 . Polarizable electrode containing activated carbon and vapor grown carbon fiber according to any one of claims 1 to 6. The polarizable electrode according to claim 8 , wherein the vapor grown carbon fiber has a hollow structure, has an outer diameter of 2 to 500 nm, and an aspect ratio of 10 to 15000. The polarizable electrode according to claim 8 , wherein the vapor grown carbon fiber has a micropore volume of 0.01 to 0.4 ml / g, and a BET specific surface area determined by a nitrogen adsorption method is 30 to 1000 m ² / g. The polarizable electrode according to claim 8 plane spacing d ₀₀₂ of (002) plane of the vapor-grown carbon fiber is less than 0.3395Nm. The polarizable electrode according to claim 8 , wherein the vapor-grown carbon fiber is a branched fiber, and the hollow structure of the branched portion is in communication. The polarizable electrode according to claim 8 , wherein vapor grown carbon fiber is mixed in an amount of 0.1 to 20% by mass with respect to the carbonaceous powder. The polarizable electrode according to claim 8 , wherein the vapor grown carbon fiber is fused to the activated carbon surface. The electric double layer capacitor using the polarizable electrode as described in any one of Claims 7 thru | or 14 . The electric double layer capacitor according to claim 15 , wherein an organic electrolytic solution in which an electrolyte is dissolved in an organic solvent is used. Slurry containing activated carbon according to claims 1 to 6. Claims 1 to paste containing activated carbon according to 6. Electrode sheet Activated carbon according coated on the surface thereof to claims 1 to 6. An energy device comprising the electric double layer capacitor according to claim 15 . A step of adding an alkaline earth metal compound to a pitch having a softening point of 100 ° C. or less, and heat-treating it at a temperature range of 400 to 600 ° C. and 600 to 900 ° C., and then subjecting the graphitizable carbon produced by the heat treatment to an alkali metal compound A process for producing activated carbon, comprising a step of activating by mixing and heating. It includes a step of adding an alkaline earth metal compound to the graphitizable raw material and heat-treating it in the vapor of the alkali metal compound, and then a step of activating the graphitizable carbon generated by the heat treatment by mixing and heating with the alkali metal compound. A method for producing activated carbon. The method for producing activated carbon according to claim 21 , wherein the alkali metal compound is an alkali metal hydroxide. The method for producing activated carbon according to claim 21 or 22 , wherein the alkali metal compound is a compound containing at least one selected from the group consisting of potassium, sodium and cesium.

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