JPH04206917A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To reduce an internal resistance, to contrive to make a capacity higher and to improve a withstand voltage by constituting an apparatus of polarizable electrodes using an activated carbon block formed by carbonization and activation of a resin foam and of an organic electrolytic solution coming in contact with the electrodes. CONSTITUTION:An activated carbon block is formed by carbonization and activation of a phenol formalin resin foam, substantially has an open-cell structure and has 0.1g/cm<3> or more bulk density and 500m<2>/g or more specific surface area. A pair of polarizable electrodes 1, 1 using the block and separator 3 arranged between are housed in a case 5 and impregnated with an organic electrolytic solution. A preferred organic electrolytic solution is formed by dissolution of a quaternary -onium salt represented by formula [I] in an organic solvent. In the formula, n is an integer of 1-3, A is nitrogen or phosphorus, R<1>, R<2>, R<3> and R<4> are any of hydrogen, carbon, alkyl group with carbon number of 1-18 and aryl group with carbon number of 6-18 and may be identical or different except that all of them are hydrogen atoms, and X<n-> is a negative ion having a valence number corresponding to n.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an electric double layer capacitor using carbon-based electrodes.

Technical Background of the Invention In recent years, electric double layer capacitors, which have a long life and can be charged and discharged at high speed, have been used as backup power sources for electronic devices. An electric double layer capacitor is a capacitor that consists of a polarizable electrode and an electrolyte in contact with the polarizable electrode, and at the interface between these electrodes, positive and negative electrodes are arranged and distributed to accumulate charge in the electric double layer. , the capacitance of the electric double layer increases depending on the area of the electrode interface.

Activated carbon, which has a large specific surface area and excellent conductivity, is attracting attention as a polarizable electrode used in such electric double layer capacitors.

Polarizable electrodes using activated carbon include, for example, electrodes in which activated carbon powder paste is pressed onto a conductive rubber electrode, electrodes in which a metal collecting electrode is formed on one side of a bundle of activated carbon fibers or a cloth made of carbon fibers by thermal spraying, Electrodes made of textiles made of activated carbon fibers and conductive glands, electrodes made by molding, carbonizing, and activating powdered phenolic resin with thermal fusibility on a base made of fiber metal, etc. can be made. Publication No. 63-10574, Japanese Patent Publication No. 110416, Japanese Patent Publication No. 63-14492, Japanese Patent Publication No. 63-14492, Japanese Patent Publication No. 63-5
5205, JP-A-63-194319).

However, in polarizable electrodes in which activated carbon powder paste is pressed onto conductive rubber electrodes, since the paste or activated carbon powder is prepared with a suitable binder, the activated carbon content in the polarizable electrode is small and the conductivity is reduced. However, the advantages of activated carbon, such as excellent properties and large specific surface area, cannot be fully utilized, and the resulting electric double layer capacitor has the drawbacks of high internal resistance and low capacity.

Polarizable electrodes made by thermally spraying metal onto activated carbon fibers or cloth using activated carbon fibers have a large contact resistance because the contact surface between the fibers is small, and this contact surface is deformed by external pressure applied during the manufacturing process. However, the disadvantage is that the internal resistance of the electric double layer capacitor using this is large and unstable.

In addition, when manufacturing large-capacity polarizable electrodes using activated carbon fiber cloth, the cloth must be laminated, which results in high resistance in addition to the contact resistance between the fibers and the high resistance between the cloths in surface contact. As a result, the electrical resistance becomes even more unstable.

Polarizable electrode consisting of a fabric of activated carbon fibers and conductive glands,
Polarizable electrodes are made by molding, carbonizing, and activating powdered phenolic resin with heat-adhesive properties onto a base made of metal fibers. Although these electrodes are effective in lowering internal resistance, the amount of activated carbon in the polarizable electrodes is low. Because of the small amount of conductive metal, it is not suitable for increasing capacity, and the problem that it is difficult to process conductive metal into fibers cannot be ignored.

As described above, each of the conventional polarizable electrodes has its own drawbacks.

On the other hand, the characteristics of an electric double layer capacitor are greatly influenced by the electrolyte; for example, the capacity is affected not only by the ion concentration and the properties of the electrolyte itself, but also by the relationship between the ion diameter of the solute and the pore diameter of the polarizable electrode. be done. Therefore, in an electric double layer capacitor, in addition to the characteristics of the polarizable electrode, an optimal material combination of the polarizable electrode and the electrolytic solution is required.

Furthermore, the withstand voltage of an electric double layer capacitor varies depending on the type of electrolyte, so selecting the type of electrolyte is important in order to obtain a high voltage electric double layer capacitor.

OBJECTS OF THE INVENTION The present invention aims to solve the problems associated with the prior art, and aims to provide an electric double layer capacitor that is easy to manufacture and has good characteristics.

Summary of the Invention The electric double layer capacitor according to the present invention is characterized by having a polarizable electrode using an activated carbon block made by carbonizing and activating a resin foam, and an organic electrolyte in contact with the polarizable electrode. It is said that

According to the electric double layer capacitor according to the present invention, the activated carbon block constituting the polarizable electrode has low electrical resistance;
Since the bulk density and specific surface area are large, internal resistance can be reduced and capacity can be increased, and since an organic electrolyte is used, an electric double layer capacitor with high withstand voltage can be provided.

DETAILED DESCRIPTION OF THE INVENTION The electric double layer capacitor according to the present invention will be specifically described below.

The electric double layer capacitor according to the present invention uses an activated carbon block obtained by carbonizing and activating a resin foam as a polarizable electrode. The resin foam used in the present invention is a resin porous body having a cellular structure obtained by mixing a resin prepolymer with a foaming agent, a curing agent, etc., and foaming and curing the mixture.

Specifically, such resins include polyurethane,
Thermosetting resins such as phenol resin, furfural resin, epoxy resin, furan resin, polyisocyanurate resin, polyimide resin, and urea resin are mainly used.

Among these resin foams, phenolic resins are preferred because they have uniform cell shapes, are easy to manufacture, and can be expected to have good yields when carbonized and activated. Foam is preferred.

Resoles can be obtained by reacting phenols and aldehydes in the presence of an alkali catalyst according to known methods.

Specific examples of such phenols include phenol, cresol, xylenol, and resorcinol, with phenol being particularly preferred.

Specific examples of the aldehydes include formaldehyde, trioxane, acetaldehyde, and furfural, with formaldehyde being particularly preferred.

Further, as the alkali catalyst, specifically, L i O
HS KOH, NaOH, NH3, NH40H.

Mention may be made of ethanolamine, ethylenediamine, triethylamine and the like.

As the blowing agent for obtaining the resin foam, conventionally known decomposition-type, reaction-type and evaporation-type blowing agents can be used, but among these, it is preferable to use an evaporation-type blowing agent that operates at relatively low temperatures. Specifically, butane, pentane, hexane,
Examples include paraffinic hydrocarbons such as heptane, alcohols such as methanol, ethanol and butanol, halogenated hydrocarbons such as dichlorotrifluoroethane (Freon 123), ethers and mixtures thereof.

For foaming and curing, a curing agent is used together with a foaming agent. As this curing agent, a conventionally known curing agent is selected and used depending on the type of prepolymer. When the prepolymer is a resol-type phenol-formalin resin, specifically, inorganic acids such as sulfuric acid, phosphoric acid, and hydrochloric acid, and organic acids such as para-toluenesulfonic acid and cresolsulfonic acid are used.

Resin foams can be obtained by mixing, for example, the above-mentioned resol-type phenolic resin prepolymer with a blowing agent, a curing agent, and if necessary, additives such as a foam stabilizer, filler, and stabilizer, either all at once or sequentially. The creamy material is heated and supplied into a heated mold, wooden mold, or cardboard, or between a double belt conveyor, and foamed and hardened.
It can be obtained by trimming if necessary. Among these methods, the method of supplying a creamy material into a mold and gradually foaming it at a slow speed is preferred in order to obtain a uniform foamed product. On the contrary, the cellular structure of rapidly foamed and hardened foam tends to be non-uniform and the direction and location of the foaming is not uniform, so there is a problem that the internal resistance value varies. It is desirable to make the foam as uniform as possible. Further, it is desirable that the bubbles have a large number of open cells in consideration of contact with the electrolytic solution and ion mobility.

The activated carbon block used in the present invention is produced by processing such a molded resin foam as it is, or by cutting or cutting it into a desired shape such as a plate, followed by carbonization and activation treatment.

The carbonization treatment is performed by firing the resin foam in a non-oxidizing atmosphere. That is, the resin foam is prepared under reduced pressure or in Ar.
Among gases, He gas, N2 gas, CO2 gas, halogen gas, ammonia gas, N2 gas, mixed gases thereof, etc., preferably 500 to 1200 °C1, especially 600 °C
It is fired at a temperature of ~900°C. In this way, the foam is carbonized and a porous carbon body is obtained. Although there is no particular restriction on the rate of temperature increase during firing, it is preferable to increase the temperature gradually around 200 to 600°C, where decomposition of the resin generally begins.

The activation treatment is performed by heating the obtained porous carbon material in the presence of an oxidizing gas. Processing temperature is usually 800-1200'C
I will do it. If the treatment temperature is too low, activation will not proceed sufficiently,
Only small specific surface areas can be obtained. On the other hand, if the treatment temperature is too high, cracks will easily form in the carbide foam.

The oxidizing gas in the present invention refers to an oxygen-containing gas such as water vapor, carbon dioxide, air, oxygen, etc., but it is usually replaced with an inert gas such as combustion gas, N2 gas, etc. for ease of operation. Used as a mixed gas. The exposure time to the oxidizing gas depends on the concentration of the oxidizing gas and the treatment temperature, but as a guide, it should be within a range that does not damage the shape of the carbide foam.

Further, the activation treatment may be a chemical activation method other than the above-mentioned gas activation, or a method using both of them in combination. The chemical activation method is a method in which chemicals such as zinc chloride, phosphoric acid, potassium sulfide, etc. are added to the resin foam and then heated in an inert gas atmosphere to simultaneously carbonize and activate the foam.

The activated carbon block that can be used in the present invention has a substantially open cell structure as a whole, and has a bulk density of 0.1 g/Cm.
3 or more, preferably 0.15 g/cm3 to 0.7
0 g/cm'', specific surface area of 500 nz/g or more, preferably 700 d/g or more, more preferably 700 to 2000 d/g, which increases contact with the electrolyte and has a large capacity. It is preferable to use a capacitor.

In the present invention, a substantially open cell structure means that the volume of the electrolyte impregnated into the activated carbon block under vacuum (less than 1 O-' torr) is smaller than the theoretically calculated spatial volume of the activated carbon block. This refers to a case where the volume ratio is 60% or more, preferably 80% or more, and more preferably 90% or more.

In the present invention, the open cell ratio was determined as follows.

Examples of the types of electrolytes used during measurement include 3
0% by weight sulfuric acid (density 1.215g/cc (25°C))
Alternatively, an electrolytic solution (density 1.088 g/cc (25°C)) containing 10% by weight of tetraethylammonium tetrafluoroborate in propylene carbonate is used.

The theoretical space volume (V,) is the body of activated carbon block VT =
(1-AD/Do)xV Here, the 1-eight measurement of activated carbon was carried out by crushing the sample in a mortar and drying it, and then using toluene as the immersion liquid and using a pycnometer with a Gehrsack thermometer.

The volume (VL) of the electrolyte impregnated into the activated carbon block is
Weight of activated carbon block before impregnation (W, ) and shape after impregnation ff
i (W2) and the density of the electrolytic solution (D, ).

VL-(W2-W,')/DL Therefore, the open cell ratio is VL/VTX100 [%] Calculated by

Since such an activated carbon block has a substantially open cell structure, it has a large specific surface area and is easily infiltrated with an electrolyte. In addition, this activated carbon block has a continuous skeleton, so it exhibits high strength, has a large specific surface area, and can be used to manufacture self-supporting polarizable electrodes that are difficult to break. It also has low electrical resistance compared to electrodes using activated carbon fibers. and stable. Furthermore, the activated carbon block can be trimmed to a desired thickness and shape to form polarizable electrodes of any shape, making it easy to manufacture large, thick, and high-capacity electric double layer capacitors from a planar size. In addition to this, it is also possible to reduce the volume of the polarizable electrode, thereby reducing the overall size of the capacitor.

Since the activated carbon block used in the present invention has a suitable average pore diameter, ions can freely move in and out of the organic electrolyte, making it possible to obtain a polarizable electrode with a substantially large surface area. .

A current collector made of a conductive material is formed on one surface of the polarizable electrode made of such an activated carbon block. This current collector can be formed extremely easily by directly plasma spraying metal onto an activated carbon block, or by surface-contacting or bonding a conductive plate such as a metal plate, graphite plate, or conductive resin plate. It can be installed in

The electric double layer capacitor according to the present invention uses an organic electrolyte solution together with a polarizable electrode using such an activated carbon block.

As the electrolyte for such an organic electrolyte solution, an onium salt, particularly a quaternary onium salt represented by the following general formula [I] is preferable.

However, in the above formula [I], n is an integer of 1 to 3, and A
is nitrogen or phosphorus.

R1, R2, R3 and R4 are hydrogen, carbon number 1-18
an alkyl group or an aryl group having 6 to 18 carbon atoms, which may be the same or different except that all of them are hydrogen.

Among these, at least one of R1, R2, R3 and R4 is a quaternary onium salt which is a lower alkyl group having 1 to 4 carbon atoms, and at least one of R1, R2, R3 and R4 is a lower alkyl group having 6 to 18 carbon atoms. A quaternary onium salt which is an aryl group having one or two benzene nuclei is preferred.

The lower alkyl group having 1 to 4 carbon atoms may be linear or branched.

In addition, X゛- is an anion having a valence corresponding to the above n, and specifically,
1ASFs-1SbF6-1AβCn 4-1Rf S
O3- (Rf is a fluoroalkyl group having 1 to 8 carbon atoms), F-1CZ-, Br-, NO3-1HCO3-1
It may be any of -valent anions such as H3○4-, divalent anions such as so4''-, and trivalent anions such as PO43-.

In particular, Xn- is BF4-1P F 6-, Cl
Quaternary onium salts that are either O4- and RfSO,- are preferred. The electrolyte may be used alone or in combination of two or more types.

Specifically, such onium salts include tetraethylammonium tetrafluoroborate (Et4N"BF4
-), tetrabutylammonium tetrafluoroborate (B
IJ4N"BF4-), tetramethylammonium tetrafluoroborate (M84N"BF4-), lithium tetrafluoroborate (Ll"BF4-), ammonium tetrafluoroborate, benzyltrimethylammonium tetrafluoroborate, etc. tetrafluoroborate, tetraethylammonium hexafluorophosphate (Et4N” PF, -), 6
Tetrabutylammonium fluoride phosphate (BLI4N”
PF6-), tetramethylammonium hexafluoride phosphate (M84N+pps-), lithium hexafluoride phosphate (L+" PF6-), ammonium hexafluoride phosphate (NH4", PF6-), benzyl hexafluoride phosphate Examples include trimethylammonium and 67-fluorophosphate.

In the electrolytic solution used in the present invention, the electrolyte is preferably used in an amount of 0.1 to 3 equivalents, particularly 0.5 to 2 equivalents.

In the present invention, an organic solvent is used as a solvent for such an electrolyte. The organic solvent may be any organic substance that is thermally and electrically stable and capable of dissolving the electrolyte.

Specific examples of such organic solvents include propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethoxyethane, acetonitrile hydrofuran, dimethylformamide, dimethylsulfoxide, methylformate, 2. 4-1
-Umethyl-1,3-dioxolane, nitromethane, etc. can be mentioned.

By using such an organic solvent, even if a high voltage is applied, the solvent does not undergo electrolysis, so a high voltage electric double layer capacitor can be obtained.

Further, in the present invention, the electrolytic solution may contain additives such as an electrolyte decomposition inhibitor, a solvent viscosity reducing agent, a surfactant, and a stabilizer.

Specific examples of such decomposition inhibitors include triethylphosphine, l-butylphosphine, and triphenylphosphine.

Specifically, the viscosity reducing agent includes dimethyl ether,
Mention may be made of diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, acetone, and 1,3-dioxolane.

Here, a specific structure of an electric double layer capacitor using polarizable electrodes and an organic electrolyte as described above will be explained with reference to the accompanying drawings.

Attached FIG. 1 shows an example of an electric double layer capacitor according to the present invention, and as shown in the figure, this electric double layer capacitor includes a pair of polarizable electrodes 1, 1, and a structure between them. The disposed separator 3 is housed in a case 5. In addition, in the figure, 6 is a lead wire.

The case 5 is made of plastic case halves 5a, 5.
)) and an insulating packing 4 interposed therebetween.

To make an electric double layer capacitor equipped with such a member, first, the polarizable electrodes 1 and 1 and the separator 3 are degassed, and then they are impregnated with an electrolytic solution, and then the separator 3 is placed in between. With the current collector 2 such as a graphite plate on the outside, the polarizable electrodes are arranged so that ±1 and ■ are facing each other, and this is then attached to the case half 5a. 5b, and tightening the two halves 5a and 5b together with screws 7 through gaskets 4.

Note that the electric double layer capacitor according to the present invention has no particular structural limitations other than using the polarizable electrode and organic electrolyte, for example, without providing a current collector on the polarizable electrode,
It is also possible to adopt a structure in which the metal case also serves as a current collector.

Effects of the Invention According to the electric double layer capacitor according to the present invention, the activated carbon block constituting the polarizable electrode has low electrical resistance;
Moreover, since the bulk density and specific surface area are large, it is possible to reduce internal resistance and increase capacity, and since an organic electrolyte is used, it is possible to provide an electric double layer capacitor with high withstand voltage.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 First, 100 parts by weight of resol (phenol-formalin resin prepolymer), 10 parts by weight of para-toluenesulfonic acid as a hardening agent, and 1.5 parts by weight of dichlorotrifluoroethane as a blowing agent were sufficiently stirred with a high-speed mixer. rear,
Pour this mixture into a mold, cover it, and leave it in an air oven at 80°C for 30 minutes.
A plate-shaped phenolic resin foam having a width of 30 cm, a thickness of 3 cm, and a bulk density of 0.3 g/c was obtained.

This molded plate is 20cm long, 10cm wide, and 1.0cm thick.
After cutting into pieces, they were placed in a Matsufuru furnace and heated under a nitrogen atmosphere at a heating rate of 60°C/hour to a temperature of 600°C, held at this temperature for 1 hour, and then cooled to a length of 16 cm.
, width 8cm, thickness 0.8cm, bulk density 0.29g/c
A plate-like porous carbon material of nr was obtained.

Further, this plate-shaped porous carbon material was heated to 950° C., steam was introduced into the combustion gas, and the material was maintained for 16 hours and then cooled.

The bulk density, strength, and specific surface area of the obtained activated carbon block were examined. Further, the open cell rate of this block was measured by the method described above and was found to be 99%.

The results are shown in Table 1.

Table 1 The above activated carbon block was band sawed to a length of 7.5 cm and a width of 2 cm.
It was cut to a thickness of 0.5 cm, degassed under reduced pressure, and then impregnated with an electrolytic solution containing 90% by weight of propylene carbonate and 10% by weight of tetrafunctional tylammonium tetrafluoroborate.
An electric double layer capacitor having the structure shown in FIG. 1 was prepared by sandwiching a polypropylene non-woven fabric as a separator and facing each other with a pair of polarizable electrodes each having a graphite plate with a thickness of 1 mm applied from the outside.

For the obtained capacitor, at a constant current of 50 mA, 3
The battery was charged and discharged to v and the capacity was measured.

The results are shown in Table 2.

Example 2 In Example 1, the bulk density was reduced to 0.13 g by increasing the amount of dichlorotrifluoroethane added as a blowing agent.
/cm? Activated carbon blocks were obtained. An electric double layer capacitor was produced in exactly the same manner as in Example 1.

The obtained performance is also shown in Table 2.

Example 3 In Example 1, an electric double layer capacitor was produced using the same shape and electrolyte as in Example I except that the separator was replaced with natural cellulose having a thickness of 50 μm.

The obtained results are also shown in Table 2.

Table 2 Example 4 Same shape as Example 1, 90% by weight of acetonitrile,
An electric double layer capacitor was produced in the same manner as in Example 1, except that it was impregnated with an electrolytic solution containing 10% by weight of tetrafunctional tylammonium tetrafluoroborate and the charge/discharge rate was up to 2.7 µ.

The obtained performance is shown in Table 3.

Example 5 Same shape as Example 1, propylene carbonate 45
An electric double layer was prepared in the same manner as in Example 1, except that the electrolyte solution was impregnated with an electrolytic solution containing 45% by weight of dimethoxyethane and 10% by weight of tetrafluoroborate tetrafluoroborate, and the charging and discharging was limited to 2.4 V. Created a capacitor.

The obtained performance is also shown in Table 3.

Example 6 Using an activated carbon block with the same bulk density as in Example 2, in the same shape as in Example 1, 43% by weight of propylene carbonate, 43% by weight of γ-butyrolactone, 4% by weight of 1,3-dioxolane, 96.4% by weight. An electric double layer capacitor similar to that of Example 1 was prepared except that it was impregnated with an electrolytic solution containing 10% by weight of tetratechylammonium fluoroborate.

The obtained performance is also shown in Table 3.

Table 3

[Brief explanation of the drawing]

FIG. 1 attached is a cross-sectional view showing a preferred embodiment of the electric double layer canister according to the present invention. In the figure, 1 is a polarizable electrode, 2 is a current collector, 3 is a separator, 4 is an insulating packing, and 5 is a case.

Claims (9)

[Claims] (1) An electric double layer capacitor characterized by having a polarizable electrode using an activated carbon block obtained by carbonizing and activating a resin foam, and an organic electrolyte in contact with the polarizable electrode. (2) The electric double layer capacitor according to claim 1, wherein the activated carbon block has a bulk density of 0.1 g/cm^3 or more and a specific surface area of 500 m^2/g or more. (3) The activated carbon block is made by carbonizing and activating a phenol-formalin resin foam and has a substantially open cell structure. double layer capacitor. (4) The organic electrolyte is formed by dissolving a quaternary onium salt represented by the following general formula [I] in an organic solvent. Electric double layer capacitor. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the above formula [I], n is an integer from 1 to 3, A is nitrogen or phosphorus, and R^1, R^2, R^3 and R
^4 is hydrogen, an alkyl group having 1 to 18 carbon atoms, and 6 carbon atoms.
~18 aryl groups, each of which may be the same or different except that all are hydrogen, and X
^n^- is an anion with a valence corresponding to n above] (5) The above quaternary onium salt is represented by R^ in the above formula [I].
1, R^2, R^3 and R^4 are hydrogen, carbon number 1-
4 or an aryl group having 6 to 18 carbon atoms, each of which may be the same or different, and at least one is the lower alkyl group described above. 4. The electric double layer capacitor according to 4. (6) The above quaternary onium salt is represented by R^ in the above formula [I].
1, R^2, R^3 and R^4 are hydrogen, carbon number 1-
18 lower alkyl groups, 1 or 2 with 6 to 18 carbon atoms
any aryl group having benzene nuclei,
5. The electric double layer capacitor according to claim 4, each of which may be the same or different, and at least one of which is the aryl group. (7) The above quaternary onium salt is represented by X^ in the above formula [I].
n^- is BF_4^-, PF_6^-, ClO_4^
-, AsF_6^-, SbF_6^-, AlCl_4^
-, RfSO_3^- (Rf is a fluoroalkyl group having 1 to 8 carbon atoms), F^-, Cl^-, Br^-, N
O_3^-, SO_4^2^- and PO_4^3^-
The electric double layer capacitor according to claim 4, wherein the electric double layer capacitor is any one of the following. (8) The above quaternary onium salt is represented by X^ in the above formula [I].
n^- is BF_4^-, PF_6^-, ClO_4^
- and RfSO_3^-, the electric double layer capacitor according to claim 7. (9) The organic solvent according to any one of claims 1 to 8, wherein the organic solvent comprises at least one selected from propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethoxyethane, acetonitrile, and sulfolane. double layer capacitor.