JP5065856B2 - Electrode material for electric double layer capacitor, electrode and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an add-in material for electrode materials which enlarges capacitance per unit mass of an electrode material for an electric double layer capacitor and which reduces the internal resistance of the capacitor, an electrode material containing the add-in material, an electrode for an electric double layer capacitor manufactured using the electrode material, and the electric double layer capacitor. <P>SOLUTION: An add-in material with a specific surface area of 750-1100 m<SP>2</SP>/g and an acidic surface functional group amount of 0.26 meq/g or more which is obtained by carrying out alkali activation of carbon black is used as an add-in material for electrode materials. The specific surface area of the add-in material is desirably 820 m<SP>2</SP>/g or more. An acidic surface functional group is desirably set to 0.32 meq/g or more and 0.35 meq/g or less. The used amount of the add-in material is preferably 25 parts by mass or less relative to 100 parts by mass of active carbon. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an additive used for an electrode material of an electric double layer capacitor mixed with activated carbon, an electrode material for an electric double layer capacitor containing the additive, and an electric double layer capacitor manufactured using the electrode material The present invention relates to a manufacturing method of an electrode and an electric double layer capacitor, and an additive for an electrode material.

  An electric double layer capacitor is known as a large-capacity capacitor based on the principle of power storage that an electric double layer is generated at the interface between an electrolyte and an electrode. In order to use the electric double layer capacitor as a general-purpose power source for information equipment memory backup, motor drive, etc., it is desired to further improve its capacitance and internal resistance. In order to cope with this, as disclosed in, for example, the following Patent Documents 1 to 3, technical development relating to electrodes such as electrode materials and electrode manufacturing methods has been advanced.

  In Patent Document 1, as a technique for reducing resistance between electrodes of an electric double layer capacitor and improving capacitance, activated carbon powder, a conductivity imparting material (carbon black) having a smaller particle diameter than the activated carbon powder is disclosed. And a step of kneading a small amount of a water-soluble binder solution in which a resin is dissolved or dispersed, a step of adding a dispersion solvent little by little to the kneaded product to prepare a paste having a predetermined viscosity, and a current collecting metal foil A method for producing an electrode for an electric double layer capacitor comprising the step of applying to the substrate and removing the dispersion solvent is disclosed.

  In Patent Document 2, in order to realize an electric double layer capacitor having a low internal resistance and a large capacitance, an electrode material containing activated carbon and a carbonaceous material obtained by heat treatment or activation treatment is used. It is disclosed that it may be used as. The activation target is fullerene-containing soot or an extraction residue obtained by substantially extracting at least a part of fullerene from the fullerene-containing soot using a solvent, and activates chemical activation, gas activation, etc. It is described that the process can be selected. A carbonaceous material obtained by gas activation treatment or heat treatment is disclosed as a specific carbonaceous material.

Patent Document 3 discloses the use of an electrode material in which carbonaceous conductive powders having different average particle diameters are mixed in order to improve capacitance characteristics. Activated carbon, acetylene black, ketjen black and the like are disclosed as the carbonaceous conductive powder, and it is said that the surface activity can be increased by treating the carbonaceous conductive powder with an alkali. In addition, neither the specific example which carried out the alkali process of carbonaceous electroconductive powder nor the conditions for the alkali process is disclosed by patent document 3. FIG.
JP 2002-222741 A JP 2006-294817 A Japanese Patent Laid-Open No. 2003-272961

  As described above, it is desired to provide a technique for improving the capacitance and internal resistance of the electric double layer capacitor. In view of such circumstances, the present invention is capable of increasing the capacitance per unit mass of an electrode material for an electric double layer capacitor and adding the electrode material that can reduce the internal resistance of the capacitor. The purpose is to provide materials.

  The inventors have a specific surface area and an acidic surface functional group amount within a predetermined range, and if a carbon material obtained by alkali activation of carbon black is used as an additive for an electrode material, the mass in the electric double layer capacitor It has been found that the reference capacity ("mass reference capacity" is an electrostatic capacity developed by an electrode material having a predetermined mass containing the additive according to the present invention) can be improved and the internal resistance of the capacitor can be reduced. The present invention has been completed.

That is, the additive for an electrode material according to the present invention used for an electrode material of an electric double layer capacitor is obtained by alkali activation of carbon black, and has a specific surface area of 750 to 1100 m ² / g, an acidic surface functional group. The amount is 0.26 meq / g or more.

The upper limit of the acidic surface functional group in the additive is preferably 0.35 meq / g from the viewpoint of production cost. Further, the lower limit of the specific surface area and the acidic surface functional group in the additive is not limited to the mass standard capacity of the electric double layer capacitor but also to increase the volume standard capacity, the specific surface area is 820 m ² / g, acidic surface The functional group is preferably 0.32 meq / g. Here, the “volume reference capacity” is an electrostatic capacity developed by a predetermined volume of electrode material containing the additive according to the present invention.

The electrode material for electric double layer capacitors according to the present invention comprises the additive for electrode material according to the present invention and activated carbon. The activated carbon in this electrode material lacks any of alkali-activated carbon black, specific surface area of 750 to 1100 m ² / g, and acidic surface functional group content of 0.26 meq / g or more. Clearly distinguished from additives. The content of the additive in the electrode material according to the present invention is not particularly limited, but is preferably 25 parts by mass or less with respect to 100 parts by mass of the activated carbon.

  If the electrode material for electric double layer capacitors according to the present invention is used, an electrode for electric double layer capacitor can be manufactured, and an electric double layer capacitor can be manufactured using the electrode.

  Moreover, the manufacturing method of the additive for electrode materials which concerns on this invention is a manufacturing method of the additive for electrode materials which concerns on the said invention, Comprising: It has the process of activating carbon black alkali.

  The additive for electrode material according to the present invention has a specific surface area and an acidic surface functional group amount within a predetermined range, and is obtained by alkali activation of carbon black, thus realizing improvement in mass reference capacity and reduction in internal resistance. can do.

  The additive according to the present invention will be described in detail below. In the following, “electric double layer capacitor” is simply referred to as “capacitor”, “electrode for electric double layer capacitor” is simply referred to as “electrode”, and “electrode material for electric double layer capacitor” is simply referred to as “electrode material”. May be called.

  The additive of the present invention is obtained by alkali activation of carbon black and is used as an additive for electrode materials. And the specific surface area and acidic surface functional group amount of this additive are a predetermined range value.

The specific surface area of the additive is less than 750 m ² / g, which is not preferable because the mass reference capacity becomes small, and is 750 m ² / g or more. Preferably, it is 820 m ² / g or more which improves the volume capacity. On the other hand, the larger the specific surface area, the larger the mass reference capacity, but the manufacturing cost of the additive increases, so the specific surface area is preferably 1100 m ² / g or less. Here, a specific surface area is calculated | required by BET method which measures a nitrogen adsorption isotherm.

  The amount of the acidic surface functional group of the additive according to the present invention is 0.26 to 0.35 meq / g. If it is less than 0.26 meq / g, the mass reference capacity cannot be improved, which is not preferable. If it exceeds 0.35 meq / g, the additive becomes expensive and is not preferable. A preferable amount of the acidic surface functional group is 0.32 to 0.35 meq / g capable of improving the volume capacity.

  By the way, in the conventionally known activated carbon obtained by the activation treatment, depending on the presence of carboxyl groups, phenolic hydroxyl groups, carbonyl groups, etc. as surface functional groups, the activation method and the conditions of the method, the types of surface functional groups and the surface It is known that the amount of functional groups varies. Similarly, the carbon material obtained by activating carbon black also varies in the type and amount of surface functional groups if the type of activation treatment or the conditions differ. In the carbon material (additive) obtained by subjecting the carbon black of the present invention to an alkali treatment, it is considered that the acidic surface functional group affects the capacitance and internal resistance of the capacitor. Therefore, the acidic surface functional group amount of the additive of the present invention is set to 0.26 meq / g or more.

  The Boehm method (the details thereof are described in the document “H.P. Boehm, Adzan. Catal, 16, 179 (1966)”) is used to determine the amount of the acidic surface functional group. That is, after putting it into a conical stoppered Erlenmeyer flask (capacity 100 ml) containing 2 g of additive, 50 ml of 1/10 normal sodium ethoxide was added to the flask and left for 30 minutes after shaking for 30 minutes. This shaking and leaving was repeated three times. Next, the mixture was further left for 24 hours, and 25 ml of the filtrate obtained by filtration and separation was neutralized and titrated with 1/10 N hydrochloric acid. A blank test was also conducted. And the value computed by following Formula is the amount of acidic surface functional groups.

  Although the average particle diameter of an additive is not specifically limited, Usually, it is 3-20 micrometers.

  As described above, the additive of the present invention is produced by alkali activation of carbon black.

  The carbon black used as a raw material for the additive is a nanoparticle having an amorphous carbon content of 95% by mass or more obtained by incomplete combustion or thermal decomposition of natural gas, liquid hydrocarbon or the like. It is known that carbon black can be obtained by manufacturing methods such as the furnace method and impact method. For physical and chemical properties, see, for example, “Carbon Black (Author: JBDonnet, A.Voet” published by Kodansha. Translators: Hiroshi Takahashi, Shinzo Yamashita, Kazuo Tsutsumi. Date of issue: May 1978).

Carbon black may contain crystals, but if it contains many crystals, an additive having a specific surface area of 750 m ² / g or more and an acidic surface functional group content of 0.26 meq / g or more is obtained. It can't be done or it becomes difficult. Therefore, the crystal thickness (Lc) in the c-axis direction by XRD may be used as an index for selecting carbon black, Lc may be 2.5 nm or less, preferably 2.0 nm or less, and further 1.5 nm or less. preferable.

Moreover, the specific surface area of carbon black is not particularly limited, but is preferably 70 to 120 m ² / g. This specific surface area is determined by the BET method that measures the nitrogen adsorption isotherm.

  Examples of carbon black that can be used as a raw material include furnace black, lamp black, thermal black, acetylene black, channel black, roller black, and disk black. Carbon black satisfying the above Lc range and specific surface area range is commercially available. For example, carbon black “Toka Black # 7360SB” manufactured by Tokai Carbon Co., Ltd. is available.

  Alkali activation for producing the additive is a process of heating a mixture of an alkali metal compound and carbon black. Examples of the alkali metal compound used here include hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide; carbonates such as sodium carbonate, potassium carbonate and lithium carbonate. One or more of these may be selected, and potassium hydroxide is preferably selected. As the amount of the alkali metal compound used increases, the specific surface area of the additive increases and the amount of acidic surface functional groups also increases. Although it depends on the type of carbon black, (mass of alkali metal compound) / (mass of carbon black) is preferably approximately 2.8 or more, and preferably 3.7 or more. On the other hand, the upper limit of the usage-amount of an alkali metal compound is not limited. However, if the amount of the alkali metal compound to be used increases, the production cost increases. Therefore, the (mass of alkali metal) / (mass of carbon black) is preferably 7.0 or less, and more preferably 6.0 or less. Preferably it is 5.5 or less.

  In alkali activation, water may be mixed with carbon black and an alkali metal compound in order to facilitate melting of the alkali metal compound. The amount of water mixed at this time is preferably 0.05 to 10 times the mass of the alkali metal compound.

  In heating in alkali activation, the heating temperature at that time is preferably about 400 to 900 ° C, and is usually about 800 ° C. When the heating temperature is low, the specific surface area tends to decrease, and when the heating temperature is high, the specific surface area tends to increase. The heating in the alkali activation is performed under an inert gas atmosphere such as argon or nitrogen; or under reduced pressure (in a vacuum);

  Impurities derived from carbon black and / or alkali metal compounds may be adsorbed on the surface of the additive obtained by alkali activation. The impurities are metal elements (iron, copper, nickel, alkali metals, etc.) and metal element compounds (hereinafter “metal elements and metal element compounds” are referred to as “metal elements”), and a large amount of such metal elements adsorb. The capacitor manufactured using the added material may induce a decrease in durability (shortening of the capacitor life). For this reason, the obtained additive is usually washed.

  Metal elements and the like can be removed from the additive by a known cleaning method. The known cleaning methods include, for example, (1) a method in which only water is used as a cleaning solution to clean the additive, and (2) a strong acid aqueous solution in which one or more strong acids such as hydrochloric acid and sulfuric acid are mixed. And a method of washing the additive with water.

  When it is necessary to adjust the average particle size of the additive, the average particle size of the additive is adjusted by a known particle size adjusting means appropriately selected. For example, the average particle diameter of the additive may be adjusted using a pulverizer such as a ball mill, a vibration mill, or a jet mill.

  The additive is used by mixing with activated carbon which is a main material of the electrode material. The greater the amount of additive added to the activated carbon, the better the mass reference capacity and internal resistance. The amount of the additive is usually 25 parts by mass or less with respect to 100 parts by mass of the activated carbon.

The activated carbon preferably has a specific surface area exceeding 1100 m ² / g. The lower limit of the specific surface area of the activated carbon is preferably 1500 m ² / g, more preferably 2000 m ² / g, and even more preferably 2100 m ² / g. On the other hand, the upper limit value may be 3000 m ² / g, or 2500 m ² / g. In order to obtain the specific surface area, a BET method for measuring a nitrogen adsorption isotherm is used. The physical characteristics of the activated carbon other than the specific surface area such as the average pore diameter and the average particle diameter are not particularly limited.

  In order to produce the activated carbon, a carbonaceous material which is a known activated carbon raw material may be activated.

  The carbonaceous material for producing activated carbon is not particularly limited. For example, non-graphitizable carbon such as wood, sawdust, charcoal, coconut shell, cellulosic fiber, synthetic resin (eg, phenol resin, furan resin); pitch (eg, mesophase pitch), coke (eg, pitch coke, needle coke) ), Graphitizable carbon such as polyvinyl chloride, polyimide, and PAN; and mixtures thereof. If necessary, a carbonaceous material that has been carbonized before the activation treatment is used as the activated carbon raw material. Here, the carbonization treatment is a treatment in which a carbonaceous material is placed in an inert gas such as nitrogen at a high temperature (for example, 900 to 1000 ° C.) and carbonization of the carbonaceous material proceeds.

  The activation treatment for producing activated carbon is a treatment for forming pores on the surface of the carbonaceous material and increasing the specific surface area and pore volume. Unlike the method for producing an additive according to the present invention, (1) gas activation for producing activated carbon by heating a carbonaceous material in the presence of gas, and (2) heating a mixture of the activation material and the carbonaceous material. Any of the chemical activation processes for producing activated carbon can be used as the activation process.

  When gas activation is selected, one or two or more oxidizing gases selected from water vapor, air, carbon dioxide, combustion gas, and the like are brought into contact with a carbonaceous material in a temperature atmosphere of 700 to 1000 ° C. And good. By this contact, the pore diameter, specific surface area, and pore volume of the carbonaceous material are increased, and activated carbon is produced.

  It is preferable to select a chemical activation that can easily produce activated carbon having a large specific surface area compared to the gas activation. As described above, this drug activation is performed by heating a mixture of an activator and a carbonaceous substance. In this case, it is preferable to use one or more selected from known activators such as phosphoric acid, sulfuric acid, calcium chloride, zinc chloride, potassium sulfide, and alkali metal compounds. Examples of the activator that can be easily activated for the production of activated carbon include hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide; carbonates of alkali metals such as potassium carbonate and sodium carbonate; potassium sulfate and sodium sulfate Alkali metal sulfates such as alkali metal hydroxides are preferred, alkali metal hydroxides are more preferred, and potassium hydroxide is more preferred. The amount of the activator used is preferably 0.5 to 10 times the mass of the carbonaceous material when, for example, an alkali metal hydroxide is used as the activator. Activated carbon with a large specific surface area and average pore diameter can be produced as the amount used is larger, and activated carbon with a smaller specific surface area and average pore diameter can be produced as the amount is smaller.

  In addition, also in the chemical activation for activated carbon manufacture, in order to make an activator easy to melt | dissolve, you may mix water with a carbonaceous material and an activator. The amount of water mixed at this time is preferably 0.05 to 10 times the mass of the activator when an alkali metal hydroxide is used as the activator.

  In heating in drug activation, the heating temperature at that time is preferably about 400 to 900 ° C. When the heating temperature is low, the specific surface area and the average pore diameter tend to decrease, and when the heating temperature is high, the specific surface area and the average pore diameter tend to increase. In addition, the heating in chemical | medical agent activation is performed by inert gas atmosphere, such as argon and nitrogen; or under reduced pressure (in a vacuum);

  As with the additive according to the present invention, the activated carbon obtained by the activation treatment may be washed to remove metal elements and the like on the surface. Moreover, when it is necessary to adjust the average particle diameter of activated carbon, it is good to use a well-known particle diameter adjustment means. It is possible to adjust the average particle size to be small with a known pulverizer (for example, ball mill, vibration mill, jet mill). For example, the average particle diameter of the activated carbon is adjusted to 6 μm or less.

  An electrode for an electric double layer capacitor can be produced using an electrode material obtained by mixing the additive of the present invention and activated carbon. In manufacturing the electrode, a known manufacturing method may be used. For example, a mixture of an additive and activated carbon according to the present invention, a conductivity imparting material, and a binder solution are kneaded, a solvent is added to prepare a paste, and this paste is applied to a current collector plate such as an aluminum foil Then, the electrode can be manufactured by removing the solvent by drying.

  Examples of the binder used when manufacturing the electrode include fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, and phenol resin. Examples of the conductivity-imparting material include carbon-based conductivity imparting materials such as carbon black, acetylene black, and ketjen black; metal oxide-based conductivity imparting materials such as ruthenium oxide. In addition, since the internal resistance of the capacitor can be reduced by using the additive according to the present invention, the use of the conductivity imparting material is preferably used only when the internal resistance can be further improved.

  There are known electric double layer capacitors such as a coin type, a wound type, and a multilayer type, and the capacitor generally has an electrode, an electrolytic solution, and a separator, and a structure in which a separator is disposed between a pair of electrodes. It is.

  As the electrolytic solution, it is preferable to select a nonaqueous electrolytic solution having a nonaqueous polar solvent having a high decomposition voltage as a main solvent. As the solvent for the non-aqueous electrolyte solution, it is preferable to use one or two or more kinds selected from non-aqueous polar solvents such as propylene carbonate, ethylene carbonate, and methyl ethyl carbonate as the main solvent. Examples of the electrolyte of the electrolytic solution include salts of amidine or quaternary ammonium with perchloric acid, boron tetrafluoride or phosphorus hexafluoride. Moreover, if a separator is illustrated, the nonwoven fabric, cloth, and microporous film which have cellulose, glass fiber, or polyolefins, such as polyethylene and a polypropylene, as a main component are mentioned.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately modified and implemented within a range that can meet the purpose described above and below. All of which are within the scope of the present invention.

  Means for determining the average particle size and the like in the following are as follows.

Crystal thickness in the c-axis direction (Lc):
Using XRD, Lc was determined under the following analysis conditions.
XRD analyzer: X-ray diffractometer manufactured by Spectris "PaNalytical X 'Pert PRO (detector: X'Celerator)"
X-ray source: Cu-Kα ray (wavelength 1.54 mm)
Tube voltage: 45KV
Tube current: 40 mA
Scanning axis: θ / 2θ
Scanning range: 2θ = 15-35 °
Scanning speed: 2.0 ° / min.
Capture width: 0.004 °
Measurement mode: Continuous
2θ correction: Internal standard method (mixing 10% by mass of standard Si)

Average particle size:
Put the sample in water, add a small amount of surfactant, ultrasonically disperse the sample, and calculate the median diameter determined using a laser diffraction particle size distribution analyzer “SALD-2000” manufactured by Shimadzu Corporation as the average particle size. did.

Specific surface area:
The specific surface area was calculated | required by BET method which measures an nitrogen isotherm using the ASAP-2400 nitrogen adsorption apparatus by a micromeritics company.

Acid surface functional groups:
The amount of acidic surface functional groups was calculated by the Boehm method.

  Additives of Examples and Comparative Examples having a predetermined particle diameter were prepared, and the average particle diameter, specific surface area, and acidic surface functional group amount of the additive were determined. A capacitor was fabricated using an electrode material obtained by mixing activated carbon and an additive. The details are as follows.

(Additives)
Carbon black “Toka Black # 7360SB (soft bead product)” manufactured by Tokai Carbon Co., Ltd. or acetylene black “Denka Black (powder product)” manufactured by Denki Kagaku Kogyo Co., Ltd. was used as the raw material carbon black. As a result of analysis of Lc of these carbon blacks, Lc of Toka Black # 7360SB was 1.5 nm other than that used in Example 5, 3.7 nm was used in Example 5, and Lc of Denka Black was 3.7 nm.

Additives of Examples 1a-1d, Examples 2-5, Comparative Examples 2, 3, and 5:
An alkali activation treatment is carried out by heating a mixture of carbon black and KOH (special grade reagent manufactured by Kishida Chemical Co., Ltd.) in an amount of 0.0 to 5.0 times the carbon black in a nitrogen atmosphere at 800 ° C. Or the activation processed material containing the additive of a comparative example was obtained. Thereafter, the activation treatment product at room temperature was washed with deionized water, and then the additive was separated by filtration. Next, the additive to which dilute hydrochloric acid was added was boiled, washed with deionized water and neutralized, and then dried. And it grind | pulverized with the planetary ball mill (Fritsch Japan company "P-5 type"), and the additive of the Example or the comparative example was obtained.

Comparative Example 1:
The additive prepared in the same manner as in Example 2 was heat-treated in a nitrogen atmosphere at 800 ° C. This heat treatment is for reducing the amount of surface functional groups of the additive.

Additive of Comparative Example 4:
Carbon black itself was used as an additive.

(Electrode material)
Examples 1a-1d, Examples 2-5, Comparative Examples 1-5:
A mixture of 2 to 5 parts by mass of the additive and 100 parts by mass of a phenol resin activated carbon “Maxsorb” manufactured by Carbontec Co., Ltd. was used as the electrode material. The activated carbon used here has an average particle diameter of 3 μm in Examples 1a to 1d, Examples 2 to 4 and Comparative Examples 1 to 5, and Example 5 has an average particle diameter of 6 μm. did.

Comparative Examples 6-7:
Only carbon resin phenolic activated carbon “Maxsorb” was used as an electrode material. In Comparative Example 6, activated carbon having an average particle diameter of 3 μm was used, and in Comparative Example 7, activated carbon having an average particle diameter of 6 μm was used.

(Capacitor production)
1. Production of electrode 9 parts by mass of electrode material of Example or Comparative Example, 0.7 part by mass of 2.0% by mass of carboxymethyl cellulose, 1.2 parts by mass of acetylene black, 4.0 parts by mass of 5% by mass of styrene butadiene A mixture comprising an aqueous rubber solution and 43 parts by mass of ion exchange water was prepared. After this mixture was applied to an aluminum foil, the aluminum foil was dried at 100 ° C. The thickness of the electrode material layer after drying (a layer applied on the surface of the aluminum foil) was 80 μm. Next, the aluminum was punched into a circle with a diameter of 25.4 mm, and this was pressed at 77 MPa to produce an electrode.

2. Assembling the capacitor After drying the electrode under vacuum conditions at 200 ° C. for 1 hour, the electrode was charged with an electrolyte (a propylene carbonate solution containing 1 mol / L of tetraethylammonium tetrafluoroborate) in a glove box in which nitrogen gas was circulated. Was vacuum impregnated. This electrode was sandwiched between polypropylene separators impregnated with electrolytic solution (Celgard “Celguard # 3501”), and further sandwiched between aluminum plates to assemble a capacitor.

  Using the produced capacitor, the mass standard capacity, volume standard capacity, and internal resistivity were determined as follows.

(Mass-based capacity, volume-based capacity)
Connect the charge / discharge terminal of the charge / discharge device ("ACD-01" manufactured by Asuka Electronics Co., Ltd.) to the aluminum plate of the capacitor, and charge at 20mA at -30 ° C until the voltage between the current collector plates reaches 2.5V. Then, the battery was charged with a constant voltage of 2.5 V for 5 minutes. After charging, the capacitor was discharged with a constant current (discharge current = 0.015 A). The capacitance of the capacitor was determined from the slope between 2.0 and 1.0 V of the obtained discharge curve. Then, the mass reference capacity (unit: F / g) is calculated by dividing the capacitance of the capacitor by the working mass of the electrode material, and the capacitance of the capacitor is divided by the total volume of the electrode material layer in the electrode. The volume reference capacity (unit: F / cm ³ ) was calculated.

(Internal resistivity of capacitor)
After charging the capacitor under the same conditions as the evaluation of the capacitance, the capacitor was discharged with a constant current (discharge current = 0.015 A). The internal resistivity was determined from the voltage drop immediately after the start of discharge. That is, a voltage gradient is derived from each measured voltage between 0.5 and 2.0 seconds after the start of discharge, a voltage at the start of discharge is obtained from this voltage gradient, and the voltage, charge voltage (2.5 V), and voltage difference Was divided by the discharge current to determine the resistance, and this resistance was divided by the thickness of the electrode material layer to determine the internal resistivity.

  The above results are shown in Table 1.

Claims (6)

Contains an additive for electrode material and activated carbon,
Electrical the electrode material for the additive material is obtained a carbon black and an alkali activation and a specific surface area 750~1100m ² / g, an acidic surface functional group amount is equal to or is 0.26 meq / g or more Electrode material for double layer capacitors . The electrode material for an electric double layer capacitor according to claim 1, wherein the additive amount for the electrode material has an acidic surface functional group amount of 0.35 meq / g or less. 2. The electrode material for an electric double layer capacitor according to claim 1, wherein the additive for electrode material has a specific surface area of 820 m ² / g or more, and the amount of the acidic surface functional group is 0.32 meq / g or more. The electrode material for an electric double layer capacitor according to any one of claims 1 to 3, wherein a content of the additive for electrode material is 25 parts by mass or less with respect to 100 parts by mass of activated carbon. The electrode for electric double layer capacitors manufactured using the electrode material for electric double layer capacitors of any one of Claims 1-4 . The electric double layer capacitor manufactured using the electrode for electric double layer capacitors of Claim 5 .