JP2004247433A - Raw-material coal composition of carbon material for electrodes of electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a raw-material coal composition to form an electric double-layer capacitor which simultaneously attain high level electrostatic capacitance and internal resistance by sufficiently increasing a specific area of an electrode material after the activation process. <P>SOLUTION: The raw-material coal composition includes the volatile matter of 6.0 to 15 mass% and shows an average interlayer distance d<SB>002</SB>of the plumbago crystal obtained through the X-ray diffraction is 0.3445 nm or less. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a raw coal composition suitable as an electrode material of an electric double layer capacitor, a carbon material for an electrode using the same, and an electric double layer capacitor provided with an electrode containing the carbon material for an electrode.
[0002]
[Prior art]
Conventionally, it has been considered that the capacitance of an electric double layer capacitor is substantially proportional to the surface area of a polarizable electrode (such as a carbon electrode) provided as an anode and a cathode constituting the electric double layer capacitor. Therefore, when a carbon electrode is used as the polarizable electrode, various studies have been made to increase the surface area of the carbon material for the carbon electrode to increase the capacitance.
[0003]
For example, conventionally, activated carbon has been mainly used as a carbon material for a carbon electrode, and such activated carbon is used for so-called non-graphitizable carbon obtained by carbonizing coconut shell, wood flour, coal, and phenol resin. It is generally manufactured by performing gas activation using steam or the like or chemical activation using an alkali metal hydroxide or the like. However, in the case of activated carbon produced from such non-graphitizable carbon, there is a problem that the capacitance per unit volume does not increase for the increase in specific surface area. That is, since the activation reaction of non-graphitizable carbon is caused by the formation of pores by the oxidation reaction from the particle surface in both the gas activation method and the chemical activation method, the loss due to oxidation increases as the activation proceeds, and The activated carbon had a low density. When such activated carbon is used for the electrode material, the bulk density of the electrode also decreases, so even if the capacitance per unit mass of the electrode increases, the increase in the capacitance density per unit volume of the electrode is limited. was there. Furthermore, such activated carbon has poor electrical conductivity due to its non-graphitizing property, which has caused the internal resistance of the electrode to be high.
[0004]
In contrast, mesophase pitch and mesophase pitch-based carbon fiber obtained by spinning the same are obtained by infusibilizing and carbonizing, and further, the easily graphitizable raw material obtained by carbonizing petroleum coke, coal pitch coke, etc. Activated carbon activated with metal hydroxide has been proposed. When such an easily graphitizable material is activated with an alkali metal hydroxide, an activated carbon with a high bulk density can be obtained with a high yield of activated carbon. The capacitance density per volume could be increased. In addition, activated carbon produced from graphitizable carbon generally has higher electrical conductivity than that produced from non-graphitizable carbon, and thus has the advantage that the internal resistance of the electrode can be easily reduced.
[0005]
However, mesophase pitch and mesophase pitch-based carbon fiber obtained by spinning it are expensive raw materials themselves, and must be subjected to infusibilization and carbonization prior to activation. There was a problem of increasing costs. Furthermore, since oxygen is introduced by the infusibilization reaction, the graphitization property is reduced, and as a result, there is a problem that the internal resistance of the electrode is not so reduced.
[0006]
[Problems to be solved by the invention]
On the other hand, JP-A-10-199767 discloses that petroleum coke or coal pitch coke is carbonized to have a volatile content of 1.0 to 5.0% by mass and an H / C atomic ratio of 0.05 to 0. After satisfying the condition of No. 30, a method of activating with an alkali metal hydroxide has been proposed.
[0007]
However, the capacitance per unit volume of the electrode material using the carbon material obtained as described above is not yet sufficient, and there is a demand for a higher performance such that the capacitance in recent years exceeds 30 F / cc. Further improvements were needed to meet the requirements. The present inventors have conducted intensive studies on the cause and the like, and as a result, as described in the above-mentioned publication, carbonization of the volatile matter and the H / C atomic ratio of petroleum coke or coal pitch coke has already progressed too much. Therefore, it has been found that the expression of the specific surface area by the activation treatment is insufficient.
[0008]
The present invention has been made in view of the above-mentioned problems of the related art, and has been made to sufficiently increase the specific surface area of the electrode material after the activation treatment, and achieve a high level of capacitance and internal resistance at the same time. It is an object of the present invention to provide a raw coal composition capable of manufacturing a double-layer capacitor.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have determined that the volatile matter of the raw coal composition which is a substance in a state before the activation treatment of the carbon material which is a constituent material of the carbon electrode of the electric double layer capacitor is obtained. And the graphite crystal interlayer distance are defined so as to satisfy a predetermined condition, whereby the specific surface area of the carbon material obtained by activating the raw carbon composition is sufficiently increased, and the electrode manufactured using the carbon material is provided. The present inventors have found that the capacitance of the electric double layer capacitor is improved and the internal resistance is reduced, and arrived at the present invention.
[0010]
That is, according to the present invention, the volatile content is 6.0 to 15% by mass, and the average interlayer distance d of graphite crystals determined by X-ray diffraction ₀₀₂ Is not more than 0.3445 nm. The raw material carbon composition for a carbon material for an electrode of an electric double layer capacitor.
[0011]
Further, the present invention has a specific surface area of 1800 m obtained by activating the raw coal composition of the present invention. ² / G or more in the carbon material for an electrode of an electric double layer capacitor, wherein the activation treatment is preferably an activation treatment using an alkali metal compound.
[0012]
Further, the present invention resides in an electric double layer capacitor comprising an electrode including the carbon material for an electrode of the present invention.
[0013]
The volatile matter according to the present invention is measured according to the method described in JIS M8812 “Coals and cokes—Industrial analysis method”.
[0014]
Further, the average interlayer distance d of graphite crystals determined by X-ray diffraction according to the present invention ₀₀₂ Means the average interlayer distance (d) of the layer corresponding to the lattice plane (002) of microcrystalline carbon, measured by the X-ray diffraction method as described below. ₀₀₂ ). That is, a sample (raw coal composition) was mixed with 15% silicon powder and filled in a measurement cell, and a wide angle X-ray diffraction line was measured by a reflection diffractometer method using CuKα radiation as a radiation source. The average interlayer distance (d) of the (002) plane based on the Gakushin method ₀₀₂ ).
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0016]
The raw coal composition of the present invention has a volatile content of 6.0 to 15% by mass and an average interlayer distance d of graphite crystals determined by X-ray diffraction. ₀₀₂ Is 0.3445 nm or less.
[0017]
The lower limit of the volatile content in the raw coal composition of the present invention is 6.0% by mass, preferably 6.5% by mass, and more preferably 7.0% by mass. When the volatile matter content is less than 6.0% by mass, the carbonization of the raw coal composition is excessively advanced, so that the reactivity of the activation treatment decreases (for example, the reactivity with an activator such as an alkali metal hydroxide). ), A large specific surface area cannot be obtained, and the capacitance when this is used as a carbon material for a capacitor also becomes small. On the other hand, the upper limit of the volatile content is 15% by mass, preferably 12% by mass. When the volatile content exceeds 15% by mass, the average interlayer distance d of graphite crystals ₀₀₂ Cannot satisfy the specific range.
[0018]
Further, the average interlayer distance d of graphite crystals obtained by X-ray diffraction in the raw coal composition of the present invention. ₀₀₂ Has an upper limit of 0.3445 nm, preferably 0.3440 nm, and more preferably 0.3435 nm. Average interlayer distance d ₀₀₂ Exceeds 0.3445 nm, a large specific surface area cannot be obtained in the activation treatment because the graphite crystals are not sufficiently developed. In particular, when the activation treatment is performed using an alkali metal compound, it is difficult for the alkali metal generated in the activation process to enter between the layers of the graphite crystal, so that a large specific surface area cannot be obtained. On the other hand, from the viewpoint of obtaining a higher specific surface area, the average interlayer distance d ₀₀₂ Is preferably as low as possible, but generally the average interlayer distance d ₀₀₂ Does not fall below the theoretical value of graphite crystals (0.3354 nm).
[0019]
The raw coal composition of the present invention has the specific properties described above, and the raw material is not particularly limited, but is preferably a petroleum-based coke-based material, which usually exhibits properties as easily graphitizable carbon. is there. A carbon material produced from such graphitizable carbon has higher electric conductivity than that produced from non-graphitizable carbon, and the internal resistance of the obtained electrode tends to be lower.
[0020]
Next, a method for producing the raw coal composition of the present invention will be described. In general, as the carbonization temperature increases, the volatile content decreases, and accordingly, the average interlayer distance d ₀₀₂ Also decreases. On the other hand, the volatile content and the average interlayer distance d ₀₀₂ The relationship also depends on the characteristics of the raw material oil and the carbonization conditions. The raw coal composition of the present invention has a characteristic such that graphite crystals are formed in the initial stage of carbonization having a high volatile content and carbonization conditions. Can be manufactured for the first time by the following method with strictly set.
[0021]
That is, a feedstock (for example, petroleum oil) having a sulfur content of 0.4% by mass or less, preferably 0.3% by mass or less, and an asphaltene amount of 2.0% by mass or less, preferably 1.7% by mass or less. The raw material oil of the present invention is obtained by carbonizing the raw material oil at a temperature of 400 to 500 ° C., preferably 430 to 480 ° C., usually for about 3 to 100 hours under an inert atmosphere. A composition is obtained. If the sulfur content exceeds 0.4% by mass or the asphaltene amount exceeds 2.0% by mass, a three-dimensional structure develops due to a cross-linking reaction in the carbonization process, and No composition can be obtained. Also, when carbonization is performed at a temperature exceeding 500 ° C., the carbonization proceeds rapidly, so that a three-dimensional structure is generated and the raw coal composition of the present invention cannot be obtained. On the other hand, when carbonization is performed at a temperature lower than 400 ° C., carbonization does not proceed, and it is difficult to reduce the volatile matter content to 15% by mass or less, and the raw coal composition of the present invention cannot be obtained. If the carbonization time is less than 3 hours, carbonization does not proceed and it is difficult to reduce the volatile content to 15% by mass or less, and the raw coal composition of the present invention cannot be obtained.
[0022]
Next, the carbon material for an electrode of the electric double layer capacitor of the present invention will be described. The carbon material for an electrode of the present invention is obtained by activating the raw coal composition of the present invention, and has a specific surface area of 1800 m ² / G or more.
[0023]
Examples of such an activation treatment include an activation reaction with a drug and an activation reaction with a gas. An activation reaction with a drug is more preferable, and an activation reaction using an alkali metal compound is particularly preferable. According to the activation treatment using such an alkali metal compound, the specific surface area of the obtained carbon material tends to be further improved by the alkali metal penetrating between the layers of the graphite crystal and reacting.
[0024]
In the activation treatment, various carbonates and hydroxides can be used as the alkali metal compound. Specifically, sodium carbonate, potassium carbonate, potassium hydroxide, sodium hydroxide, lithium hydroxide, rubidium hydroxide, Cesium hydroxide is exemplified, and among them, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are particularly preferred. Further, two or more of these alkali metal compounds may be used in combination (for example, a combination of potassium hydroxide and sodium hydroxide).
[0025]
The activation method is usually performed by mixing an activator such as an alkali metal compound and the raw carbon composition and heating the mixture. The mixing ratio between the raw coal composition and the activator such as an alkali metal hydroxide is not particularly limited, but usually the mass ratio of both (raw coal composition: activator) is 1: 0.5 to 1:10. Is preferable, and the range of 1: 1 to 1: 5 is more preferable. In general, if the activator such as an alkali metal compound is too small, the activation reaction does not proceed sufficiently and a required specific surface area tends to be unable to be obtained.On the other hand, if the activator such as an alkali metal compound is too large, the specific surface area increases. However, the activation cost increases, the activation yield decreases, the bulk density of the obtained carbon material tends to decrease, and the capacitance per unit volume tends to decrease.
[0026]
The heating temperature during the activation treatment is not particularly limited, but the lower limit is usually 500 ° C., preferably 600 ° C., and the upper limit is usually 1000 ° C., preferably 900 ° C., and more preferably 800 ° C. In general, when the temperature at the time of the activation treatment is low, the activation reaction does not proceed, and there is a tendency that a sufficient specific surface area cannot be obtained. On the other hand, when the temperature at the time of the activation treatment is too high, the specific surface area also tends to decrease, leading to a decrease in the capacitance per unit volume. The heating time in the activation treatment is not particularly limited, but is usually about 10 minutes to 10 hours, preferably about 30 minutes to 5 hours. In the activation treatment, it is desirable to heat the raw coal composition together with the activator under a non-oxidizing atmosphere.
[0027]
When the activation treatment is performed using a gas, for example, the raw coal composition is heated in an atmosphere of a weakly oxidizing activation gas such as carbon dioxide (combustion gas), oxygen, hydrogen chloride, chlorine, or steam. Method. The temperature at this time is usually desirably about 500 to 1000 ° C. The activation method using a gas and the activation method using a chemical may be combined. Further, such an activation reaction can be performed in any form such as an electric furnace, a fixed bed, a fluidized bed, a moving bed, and a rotary kiln.
[0028]
By activating the raw coal composition of the present invention in this way, the specific surface area by the BET method is 1800 m. ² / G or more, preferably 1900 m ² / G or more of electrode carbon material can be obtained. The specific surface area of the carbon material for an electrode of the present invention is 1800 m. ² If it is less than / g, the specific surface area is small, so that the electrostatic capacity of the electrode material obtained by using it is not sufficiently improved. The upper limit of the specific surface area is not particularly limited, but is usually 2500 m ² / G is desirable.
[0029]
The mechanism of the specific surface area when easily graphitizable carbon is used as the raw material carbon composition of the present invention and the activated carbon is activated with an alkali metal hydroxide, for example, is hardly graphitizable carbon such as coconut shell charcoal. Not only due to pore formation due to oxidation reaction from the particle surface as in the case of gas activation, but also because the decomposed alkali metal penetrates between graphite crystal layers and reacts directly with carbon, It is formed to increase the specific surface area. It is important that the carbon graphite crystal is sufficiently developed for the alkali metal to enter the inside of the carbon. Therefore, in order to express a sufficient specific surface area in such activation treatment with an alkali metal hydroxide, the raw coal composition has sufficient crystallinity to penetrate into the interior of the raw coal composition, and It is necessary to have sufficient reactivity with an alkali metal, and the raw coal composition of the present invention satisfies this condition. That is, the raw coal composition of the present invention contains a predetermined amount of a high volatile content having good reactivity with the alkali metal, and the alkali metal easily penetrates between the graphite crystal layers to form the alkali inside the particles. It has a crystal structure that facilitates the reaction with the metal, and together with these actions, a carbon material having a very high specific surface area can be obtained.
[0030]
The carbon material for an electrode of the present invention thus obtained preferably has the following various physical properties. That is, for example, the pore volume is preferably 0.60 to 1.30 cm. ³ / G, more preferably 0.70 to 1.20 cm ³ / G, and the average pore diameter is preferably 1.5 to 2.5 nm, more preferably 1.7 to 2.3 nm. Further, as the carbon material for an electrode, the lower the sulfur content, the better, and the sulfur content is particularly preferably 500 ppm or less.
[0031]
After being activated as described above, the raw coal composition of the present invention is usually subjected to an alkali washing, an acid washing, a water washing, a drying and a pulverizing process to become a carbon material for an electrode for an electric double layer capacitor. In the case of the activation reaction using an alkali metal compound, the amount of the alkali metal in the carbon material is not particularly limited as long as the amount is lower than a level that may adversely affect the electric double layer capacitor (preferably 1000 ppm or less). However, usually, it is desirable to wash so as to have a pH of about 7 to 8 and to wash out as much alkali metal as possible. In addition, the pulverization step is performed by a known method, and it is usually desirable to form fine powder having an average particle diameter of 0.5 to 50 μm, preferably about 1 to 20 μm.
[0032]
Next, the electric double layer capacitor of the present invention will be described. An electric double layer capacitor according to the present invention includes an electrode including the carbon material for an electrode according to the present invention.
[0033]
Such an electrode may be, for example, an electrode formed by adding a carbon material for an electrode and a binder, more preferably a conductive material, and further integrated with a current collector.
[0034]
Known binders can be used as such a binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, a fluoroolefin / vinyl ether copolymer crosslinked polymer, carboxymethylcellulose, polyvinylpyrrolidone, and polyvinyl alcohol. And polyacrylic acid. The content of the binder in the electrode is not particularly limited, but is appropriately selected usually in the range of about 0.1 to 30% by mass based on the total amount of the carbon material for the electrode and the binder.
[0035]
Further, as the conductive material, powder such as carbon black, powdered graphite, titanium oxide, ruthenium oxide and the like are used. The compounding amount of the conductive material in the electrode is appropriately selected depending on the purpose of the compounding, but is usually appropriately selected within the range of about 1 to 50% by mass, preferably about 2 to 30% by mass.
[0036]
In addition, as a method of mixing the carbon material for the electrode, the binder, and the conductive material, a known method is appropriately applied. For example, a solvent having a property of dissolving the binder is added to the above components to form a slurry. A method of uniformly applying the composition on a current collector, or a method of kneading the above components without adding a solvent and then press-molding the mixture at room temperature or under heating is adopted.
[0037]
Known materials and shapes can be used as such a current collector, and for example, alloys such as aluminum, titanium, tantalum, nickel, and stainless steel can be used.
[0038]
The unit cell of the electric double layer capacitor of the present invention is generally formed by using a pair of the above electrodes, facing each other via a separator (a nonwoven fabric of polypropylene fiber, a nonwoven fabric of glass fiber, synthetic cellulose paper, etc.), and immersing in an electrolytic solution. You.
[0039]
As an electrolytic solution used for the electric double layer capacitor of the present invention, a known aqueous electrolytic solution and an organic electrolytic solution can be used, but an organic electrolytic solution is more preferably used. As such an organic electrolyte, those used as a solvent for an electrochemical electrolyte can be used. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, a sulfolane derivative, -Methylsulfolane, 1,2-dimethoxyethane, acetonitrile, glutaronitrile, valeronitrile, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dimethoxyethane, methyl formate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. . In addition, these electrolytes may be mixed and used.
[0040]
Further, the supporting electrolyte in the organic electrolyte is not particularly limited, and various salts such as salts, acids, and alkalis commonly used in the field of electrochemistry or the field of batteries can be used. And inorganic ion salts such as alkaline earth metal salts, quaternary ammonium salts, cyclic quaternary ammonium salts, and quaternary phosphonium salts. 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 And the like are preferred. The concentration of these salts in the electrolytic solution is appropriately selected usually in the range of about 0.1 to 5 mol / l, preferably about 0.5 to 3 mol / l.
[0041]
Although a more specific configuration of the electric double layer capacitor of the present invention is not particularly limited, for example, a metal is disposed between a pair of thin sheet or disk-shaped electrodes (positive electrode and negative electrode) having a thickness of 10 to 500 μm via a separator. Examples include a coin type housed in a case, a wound type in which a pair of electrodes are wound via a separator, and a stacked type in which a large number of electrode groups are stacked via a separator.
[0042]
【Example】
Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. The physical properties of the raw oil, raw coal composition and carbon material obtained in the examples and comparative examples were measured as follows.
(1) Sulfur content
It was measured according to the method described in JIS M8813 “Coals and cokes—elemental analysis method”.
(2) Asphaltene content
It measured based on the method of IP143 / 90 "Determination of Asphaltenes (HeptaneInsolubles)."
(3) volatile matter
It was measured according to the method described in JIS M8812 “Coals and cokes—Industrial analysis method”.
(4) Average interlayer distance of graphite crystal
A sample (a raw coal composition) was mixed with 15% silicon powder and filled in a measuring cell. Using a CuKα ray as a radiation source, an X-ray diffractometer (trade name: RINT1400VX, manufactured by Rigaku Corporation) was used. And a wide-angle X-ray diffraction line was measured by a reflection type diffractometer method. ₀₀₂ ).
[0043]
(Example 1)
(I) Production of raw coal composition
A petroleum heavy oil having a sulfur content of 0.25% by mass and an asphaltene amount of 1.5% by mass is carbonized at 470 ° C. for 6 hours in an inert gas atmosphere by a batch process to obtain a volatile content of 7.2% by mass and graphite. Average interlayer distance d of crystal ₀₀₂ Was 0.3435 nm. The raw coal composition thus obtained exhibited properties as easily graphitizable carbon.
(Ii) Production of carbon material
100 parts by mass of the above raw coal composition was mixed with 200 parts by mass of potassium hydroxide, the activation reaction was allowed to proceed at 750 ° C. for 1 hour in a nitrogen gas atmosphere, and after the reaction, washing with water and acid washing (HCl) Was used to remove metallic potassium remaining in the carbon material, followed by drying to obtain a carbon material for an electrode of an electric double layer capacitor. The specific surface area of this carbon material is 1980 m ² / G. The pore volume is 0.91 cm ³ / G, pore diameter was 0.18 nm. (Iii) Preparation of electrode
10 parts by mass of carbon black and 10 parts by mass of polytetrafluoroethylene powder were added to 80 parts by mass of the carbon material pulverized to an average particle size of 40 μm, and kneaded in a mortar until it became a paste. Next, the obtained paste was rolled with a roller press of 180 kPa to produce an electrode sheet having a thickness of 200 μm.
(Iv) Cell assembly
After punching out two discs each having a diameter of 16 mm from the above-mentioned electrode sheet and vacuum drying them at 120 ° C. and 0.1 Torr for 2 hours, the organic electrolyte solution (triethylmethyl Ammonium tetrafluoroborate in propylene carbonate (concentration: 1 mol / l) was vacuum impregnated. Next, the two electrodes were used as a positive electrode and a negative electrode, respectively. A glass fiber separator (manufactured by ADVANTEC, trade name: GA-200, thickness: 200 μm) was attached between the two electrodes, and a collector of aluminum foil was attached to both ends. An electric double-layer capacitor (coin-type cell) was fabricated by incorporating the battery into a two-electrode cell manufactured by Hosen.
(V) Measurement of capacitance
The coin cell was charged to 2.7 V at a constant current of 10 mA per F. After maintaining the voltage at 2.7 V for 12 hours after the end of charging, a constant current discharge of 10 mA was performed. Then, from the energy amount at the time of discharge, the following equation:
Total discharge energy W [W · s] = ｛Capacitance C [F] × (discharge start voltage V [V]) ² ｝ / 2
Was calculated according to the following equation.
[0044]
As a result, the capacitance per unit mass (F / g) obtained by dividing this capacitance by the mass of the carbon material in the electrode was 44.3 F / g. The capacitance per unit volume (F / cc) multiplied by the density was 32.1 F / cc. The internal resistance was 21Ω. From the above results, it was confirmed that the electric double layer capacitor of the present invention can achieve a very high level of capacitance of 30 F / cc or more.
[0045]
(Comparative Example 1)
The raw coal composition obtained by carbonizing a petroleum heavy oil having a sulfur content of 4.5% by mass and an asphaltene amount of 9.5% by mass in an inert gas atmosphere at 480 ° C. for 4 hours has a volatile content of 6. 8% by mass, but the average interlayer distance d of graphite crystals ₀₀₂ Was 0.3450 nm, which was beyond the range of the present invention.
[0046]
The alkali activation treatment was performed under the same conditions as in Example 1 except that this raw coal composition was used. As a result, the specific surface area of the carbon material after the activation treatment was 1340 m. ² / G. The capacitance (F / g) per unit mass of the electric double layer capacitor assembled in the same manner as in Example 1 except that this carbon material was used was 30.9 F / g, and the capacitance per unit volume. The capacity was also reduced to 22.0 F / cc. Further, the internal resistance was 36Ω.
[0047]
(Comparative Example 2)
When the heavy petroleum oil used in Example 1 was carbonized at 550 ° C. for 4 hours in a nitrogen gas atmosphere, the obtained raw coal composition was found to have an average interlayer distance d of graphite crystals. ₀₀₂ Was 0.3425 nm, and the volatile matter content was 5.5% by mass.
[0048]
As a result of performing the alkali activation treatment under the same conditions as in Example 1 except that this raw coal composition was used, the specific surface area of the carbon material after the activation treatment was 1590 m. ² / G. Also, the capacitance per unit mass (F / g) of the electric double layer capacitor assembled in the same manner as in Example 1 except that this carbon material was used was 35.6 F / g, and the capacitance per unit volume. The capacity was also reduced to 25.5 F / cc. Further, the internal resistance was 31Ω.
[0049]
(Comparative Example 3)
When the petroleum heavy oil used in Example 1 was carbonized in a nitrogen gas atmosphere at 750 ° C. for 4 hours, the obtained raw coal composition showed an average interlayer distance d of graphite crystals. ₀₀₂ Was 0.3415 nm, and the volatile matter was 2.2% by mass.
[0050]
The alkali activation treatment was performed under the same conditions as in Example 1 except that this raw coal composition was used. As a result, the specific surface area of the carbon material after the activation treatment was 350 m ² / G. The capacitance per unit mass (F / g) of the electric double layer capacitor assembled in the same manner as in Example 1 except that this carbon material was used was 18.2 F / g, and the capacitance per unit volume. The capacity was also reduced to 13.4 F / cc. Further, the internal resistance was 40Ω.
[0051]
【The invention's effect】
As described above, by using the raw coal composition of the present invention, it is possible to improve the bulk density of the electrode material for the electrode after the activation treatment, to sufficiently increase the specific surface area, and to achieve a high level of static electricity. An electric double layer capacitor in which the capacitance and the internal resistance are simultaneously achieved can be manufactured. Further, the temperature of the activation treatment for obtaining the electrode carbon material can be made relatively low, and the yield of the electrode carbon material can be improved.
[0052]
As described above, by using an electrode containing the carbon material for an electrode of the present invention obtained from the raw coal composition of the present invention, an electric double layer capacitor having a large capacitance and a low internal resistance can be obtained. Are very useful for various applications such as power sources for automobiles, standby power sources for various home appliances, and power sources for various portable devices.

Claims (4)

A carbon material for an electrode of an electric double layer capacitor, characterized by having a volatile content of 6.0 to 15% by mass and an average interlayer distance d ₀₀₂ of graphite crystals determined by X-ray diffraction of 0.3445 nm or less. Coking coal composition. A carbon material for an electrode of an electric double layer capacitor, which has a specific surface area of 1800 m ² / g or more, obtained by activating the raw coal composition according to claim 1. The carbon material for an electrode of an electric double layer capacitor according to claim 2, wherein the activation treatment is an activation treatment using an alkali metal compound. An electric double layer capacitor comprising an electrode containing the carbon material for an electrode according to claim 2.