JP3114337B2 - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To enable an electrolytic double-layer capacitor to be enhanced in both productivity and reliability by a method wherein electrolytic solution is made to contain surface-active agent as a second component. CONSTITUTION:A polypropylene case 4a is evacuated, and two polarizable electrodes 1 are inserted into the case 4a as electrolytic solution is filled into the case 4a, whereby the polarizable electrodes 1 are impregnated with electrolytic solution. For instance, 0.01wt.% nonylphenol/ethylene oxide as (7mol) adduct dissolved uniformly into sulfuric acid water solution is used as electrolytic solution. By this setup, the impregnation of a polarizable electrode with electrolytic solution can be sharply shortened in time. An electric double-layer capacitor can be lessened in electrostatic capacity change with time due to the separation of electrolytic solution from the impregnated surface of activated carbon, and gas is restrained from being generated when a voltage is applied to a capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor is a large-capacity capacitor utilizing an electric double layer generated at an interface between an electrode and an electrolytic solution, and is mainly used for backing up a microcomputer or memory of a VTR, a camera, a telephone, or the like. In recent years, there has been a strong demand for miniaturization of electronic components, and in order to reduce the size of electric double-layer capacitors, it is necessary to develop an electrode material having a large capacity per unit weight and to improve the packing density of the electrode material. There is a need. Activated carbon powder or activated carbon fiber has been used as a polarizable electrode of a conventional electric double layer capacitor. These polarizable electrodes must be pressurized and compressed in order to make electrical connection between powders or fibers, so there are limits to miniaturization and low resistance of the electric double layer capacitor. In addition, there is a limit in improving the capacity per unit volume.

[0003] Therefore, a polarizable electrode that solves these problems has recently been developed. For example, Japanese Patent Application No. 3-8
As disclosed in No. 1262, an activated carbon / polyacene-based material composite obtained by molding a mixture of activated carbon powder and phenol resin powder under heat and pressure and further heat treatment is a polarizable electrode suitable for this. It has been found that Further, as disclosed in JP-A-64-2314, activated carbon powder or activated carbon fiber obtained by mixing activated carbon powder or activated carbon fiber with coal tar or pitch and heat-treating in a non-oxidizing atmosphere is mixed with activated carbon powder or activated carbon fiber. Some electrodes are composed of carbonaceous materials. Further, solid activated carbon obtained by putting coal having caking properties as disclosed in Japanese Patent Application Laid-Open No. 62-292612 into a mold, sintering at a solidification temperature or higher, and steam activation is also used. It can be used as a polarizable electrode of a multilayer capacitor. Further, as disclosed in JP-A-3-78221, solid activated carbon obtained by sintering activated carbon powder by applying a pulsed voltage to the activated carbon powder under high temperature and pressure is also used as an electric double layer capacitor. It can be used as a polarizing electrode. It is well known that solid activated carbon can be obtained by any of these methods.

[0004] Further, from the viewpoint of miniaturization and thinning of the capacitor, as disclosed in Japanese Patent Application No. 3-81262,
Activated carbon thick-film electrodes having a thickness of several tens to several hundreds of microns, which are obtained by forming a paste obtained by adding a solvent to activated carbon powder and a phenol resin and mixing them on a substrate and subjecting the paste to heat treatment, have been developed. Also, as disclosed in JP-A-61-110416 and JP-A-2-266509, in the case of a pasty polarizable electrode using a conventional activated carbon powder, an interface between the electrolyte and the electrolyte is used to improve the pasteability. Methods for adding activators have been developed.

[0005]

However, when the above-mentioned solid activated carbon or activated carbon thick film is used as a polarizable electrode, it takes a very long time to impregnate the electrolytic solution because the activated carbon as the polarizable electrode is hydrophobic. In particular, in the case of block-shaped solid activated carbon, it took 6 hours or more to impregnate the electrolyte into the inside of the pores of the electrode. Even after impregnation once, the surface of the activated carbon separates from the electrolytic solution with the lapse of time, so that the capacitance changes over time.If the electrolytic solution is not sufficiently impregnated, the capacitance of the capacitor decreases. In addition, there is a problem that gas remaining in the pores of the activated carbon electrode is generated when a voltage is applied to the capacitor. An object of the present invention is to solve such a conventional problem and to provide an electric double layer capacitor in which an electrolytic solution is sufficiently impregnated inside a polarizable electrode in a short time.

[0006]

Means for Solving the Problems A first aspect of the present invention is an electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein the polarizable electrode is made of activated carbon and a polyacene-based material.
An electric double layer capacitor comprising a composite material and a surfactant as a second component in an electrolytic solution. A second aspect of the present invention is an electric double layer capacitor using an activated carbon thick film as a polarizable electrode, wherein the polarizable electrode is
An electric double layer capacitor comprising a composite of activated carbon and a polyacene-based material, wherein the electrolyte contains a surfactant as a second component.

As the surfactant, a nonionic surfactant or a sulfonate type surfactant is desirable. Among them, the nonionic surfactant is a polyoxyethylene alkylphenol represented by the following general formula in which ethylene oxide is added to an alkylphenol,

Embedded image (Wherein, R ¹ is a hydrocarbon group having 5 to 20 carbon atoms, and n is 1
Is an integer of up to 20. Alternatively, a polyethylene glycol type surfactant such as a polyoxyethylene higher alcohol represented by the following general formula in which ethylene oxide is added to a higher alcohol is preferable. R ² —O (CH ₂ CH ₂ O) _n H ( _where R ² is a hydrocarbon group having 8 to 22 carbon atoms, and n is 1
Is an integer of up to 20. In addition, the sulfonate type surfactant is a surfactant represented by the following general formula, or R ³ SO ₃ M (wherein, R ³ represents a hydrocarbon group and M represents an alkali metal.) Alternatively, a surfactant represented by the following general formula is preferable.

Embedded image (In the formula, R ⁴ represents a hydrocarbon group having 5 to 20 carbon atoms, and M represents an alkali metal.) The amount of the surfactant to be added in the electrolyte is preferably in the range of 0.001 to 0.5% by weight. is there.

[0008]

In an electric double layer capacitor using a solid activated carbon or an activated carbon thick film as a polarizable electrode, a nonionic surfactant or a sulfonate type surfactant which does not decompose even in an aqueous sulfuric acid solution is contained as an electrolytic solution as a second component. By doing so, the electrolyte can be impregnated in a short time,
Also, since the electrolyte is sufficiently impregnated inside the polarizable electrode, the capacitance as a capacitor is improved, generation of gas at the time of applying a voltage can be prevented, and the change with time of the capacitance can be reduced. it can.

[0009]

Next, an embodiment of the present invention will be described. Example 1 A phenol-based activated carbon powder and a phenol resin powder (trade name: Bellpearl (registered trademark), manufactured by Kanebo Co., Ltd.) were weighed so as to have a weight ratio of 70/30, and were dry-mixed with a ball mill. 10 g of this mixed powder is placed at 150 ° C. and 100 k
mold at a pressure of g / cm ² for 10 minutes, 50 × 35
An activated carbon-containing phenol resin plate having a thickness of ² mm and a thickness of 6 mm was obtained. This was subjected to a heat treatment at 900 ° C. for 2 hours in an N ₂ atmosphere in an electric furnace. The temperature rise / fall rate was 10 ° C./h. The size of the obtained solid activated carbon is a rectangular parallelepiped of 47 × 33 × 6 mm ³ , which becomes a polarizable electrode. The current collector made of glassy carbon has a cylindrical projection in part, and a screw hole is provided in the cylindrical projection. These were integrated with a carbon-based conductive adhesive. A conductive adhesive is applied to the current collector made of glassy carbon and adhered to the polarizable electrode.
Heat cured for minutes. After that, 8 hours in an electric furnace under N ₂ atmosphere.
Heat treatment was performed at 00 ° C. for 30 minutes to carbonize the conductive adhesive.

Next, the structure of the electric double layer capacitor manufactured in this embodiment will be described with reference to FIG. Current collector 2 described above
Another one-sided electrode having the same configuration was prepared using the polarizable electrode 1 in which the above was integrated as one-sided electrode, and faced each other with a polypropylene separator 3 having a thickness of 25 μm interposed therebetween. These were bonded and sealed to a polypropylene container lid 4b using an epoxy resin as a sealing agent. In order to impregnate the polarizable electrode 1 with the electrolytic solution, the whole was evacuated, and then the above-mentioned two polarizable electrodes 1 were inserted while pouring the electrolytic solution into the polypropylene container 4a. As an electrolytic solution, 0.01% by weight of a 7 mol nonylphenol ethylene oxide adduct was dissolved in a 30% by weight aqueous sulfuric acid solution to form a uniform solution, which was impregnated with a vacuum for 30 minutes. The four corners of the sealing cross section of the polypropylene container 4a and the lid 4b are also rounded to a radius of 4 mm on the outer periphery so as to facilitate sealing. The lid 4b and the container 4a were sealed with an ultrasonic welding machine having an output of 1200 W and a frequency of 21 kHz. The conditions of the ultrasonic fusion are as follows: a pressure of 1.0 kg / cm ² before and during fusion, oscillation after pressure, and a fusion time of 0.1 kg / cm ² .
5 seconds. A stainless steel terminal 5 threaded from the outside of the lid 4b of the sealed container 4a was connected. Thus, an electric double-layer capacitor of the present invention was experimentally manufactured.

The capacitance and equivalent series resistance of the ten electric double layer capacitors thus obtained were measured. 0.9V is applied between both electrodes of the electric double layer capacitor, constant voltage charging is performed for 6 hours, constant current discharge is performed at 100mA and 10A , and time required for the voltage to drop from 0.54V to 0.45V , The capacity of the electric double layer capacitor was determined. The impedance of these electric double layer capacitors was measured by the AC four-terminal method. The input signal voltage was 10 mV _rms, and the real part of the impedance at 1 kHz was the equivalent series resistance. In addition, an electric double layer capacitor having exactly the same contents as described above was prepared except that no 7 mol adduct of nonylphenol ethylene oxide was added to the electrolytic solution. Table 1 below summarizes the average values of the capacitance and the equivalent series resistance measured for each of the ten electric double layer capacitors of the present invention and the conventional example.

[0012]

[Table 1] ―――――――――――――――――――――――――――――― Electrolyte impregnation time Capacitance Capacitance equivalent series resistance ( (Time) (100mA discharge) (10A discharge) (mΩ) (F) (F) ――――――――――――――――――――――――――――――― -Example of the present invention 0.5 1004 951 39.0 6.0 1008 949 38.2 ―――――――――――――――――――――――――――――― ―― Conventional example 0.5 296 54 50.1 6.0 984 627 38.0 ―――――――――――――――――――――――――――― -

As described above, conventionally, it took 6 hours or more to impregnate the solid activated carbon polarizable electrode with the electrolytic solution. 30 minutes was enough. No gas was generated when voltage was applied. In addition to the solid activated carbon shown here, solid activated carbon obtained by mixing activated carbon powder or activated carbon fiber with coal tar or pitch and heat-treating in a non-oxidizing atmosphere, coal having caking properties is used in a mold. The same results were obtained for solid activated carbon obtained by steam activation after dry distillation and firing at a temperature equal to or higher than the solidification temperature, or solid activated carbon obtained by sintering activated carbon powder by applying pulsed voltage to activated carbon powder under high temperature and pressure. was gotten.

Example 2 The same procedure as in Example 1 was carried out except that 0.01% by weight of a 7 mol adduct of nonylphenolethylene sacoxide and 0.01% by weight of an adduct of 10 mol of ethylene oxide reduced alcohol ethylene oxide were used in Example 1. To produce an electric double layer capacitor. The capacitance and the equivalent series resistance of the obtained electric double layer capacitor at an electrolyte impregnation time of 0.5 (hour) were 991 (F) and 48.3 (mΩ), respectively.

Embodiment 3 FIG. 2 shows a sectional view of the basic structure of an electric double layer capacitor of this embodiment. First, a method for manufacturing the polarizable electrode (activated carbon thick film) 13 will be described with reference to FIGS. A phenol-based activated carbon powder, a phenol resin powder (trade name: Bellpearl (registered trademark), manufactured by Kanebo Co., Ltd.) and methyl cellosolve were mixed in a paste so that the weight ratio was 70/30/82.
As shown in FIG. 3, the paste-like mixture was applied to a 50 × 5 area using a 200-mesh stainless steel screen.
0 mm ² , 0.2 mm thick glassy carbon substrate 11
Was printed in an area of 40 × 40 mm ^{2 on} one side and heat-cured in an oven at 150 ° C. for 30 minutes. In FIG. 4, a thermosetting film similar to that of FIG. 3 was formed on both surfaces of a glassy carbon substrate 12 having an area of 50 × 50 mm ² and a thickness of 0.2 mm.
These were heat-treated at 900 ° C. for 2 hours in an N ₂ atmosphere in an electric furnace to produce an activated carbon thick film electrode 13. The temperature rise / fall rate was 100 ° C./h. 30w for these activated carbon thick films
A uniform solution obtained by dissolving 0.02% by weight of sodium dodecylbenzenesulfonate in a t% aqueous sulfuric acid solution was added dropwise, followed by vacuum impregnation for 30 minutes to impregnate the active carbon thick film with the electrolyte solution.

Next, the glassy carbon substrate 11 on which the activated carbon thick film 13 having the structure shown in FIG.
Gasket 10 obtained by cutting a central portion of 40 × 40 mm ² from a butyl rubber sheet having a thickness of 0 × 50 mm ² and a thickness of 0.2 mm.
Butyl rubber gasket 10
One without was prepared. Activated carbon thick film 1 having the structure of FIG.
A glassy carbon substrate 12 on which one of the above 3 is formed and a butyl rubber gasket 10 similarly bonded to one side
I prepared a pair. Next, as shown in FIG. 2, the polarizable electrodes 13 on the glassy carbon substrate 11 having the structure of FIG. 3 are arranged at both ends such that they are inside, and the polarizable electrodes 13 on the glassy carbon substrate 12 having the structure of FIG. The electrode 13 and the 110 μm-thick polyethylene separator 9 immersed in a 30 wt% sulfuric acid aqueous solution are alternately sandwiched, and the whole is heated and pressurized, so that the butyl rubber gasket 10 and the glassy carbon substrate 7 are bonded to each other. Sealing was performed by applying a sulfuric epoxy resin. Next, as shown in FIG. 5, a stainless steel plate 15 having a thickness of 0.3 mm and having terminal protruding portions is bonded to the outer glassy carbon substrate side using a conductive adhesive, and the whole is formed of an insulating film. After being insulated, it was stored in a stainless steel case 16 having a thickness of 0.2 mm.

The ten electric double-layer capacitors thus produced and the conventional electric double-layer capacitors exactly the same as those described above, except that sodium dodecylbenzenesulfonate was not added to the electrolytic solution, were used. After applying 0 V and performing constant-voltage charging for 1 hour, the battery was discharged at a constant current of 1 mA, and the capacitance was determined from the time required for the voltage to drop from 3.0 V to 2.5 V. The equivalent series resistance was determined from the voltage appearing at both ends when a constant current of 1 kHz and 10 mA was passed through this electric double layer capacitor. Table 2 shows the respective average values.

[0018]

[Table 2]

A high-temperature load test was performed for 72 hours at a temperature of 70 ° C. with a DC 5.5 V applied to each of the ten electric double layer capacitors of the present invention and the conventional example. After implementation, the capacitance of each capacitor was measured. Table 3 below shows the rate of change in the capacitance after the test with respect to the initial value before the test.

[0020]

[Table 3]

As described above, it has been found that the electric double layer capacitor of the present invention has a smaller change in capacitance with time than the conventional electric double layer capacitor.

[0022]

As described above, according to the present invention, the impregnation time of the polarizable electrode with the electrolytic solution can be remarkably reduced by adding the surfactant to the electrolytic solution as the second component. In addition, there is an effect that a change in capacitance with time due to separation of the electrolytic solution from the activated carbon surface after impregnation is reduced, and generation of gas when voltage is applied to the capacitor is suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of an electric double layer capacitor using solid activated carbon according to the present invention for a polarizable electrode.

FIG. 2 is a cross-sectional view of an example of an electric double layer capacitor using a thick activated carbon film as a polarizable electrode according to the present invention.

FIG. 3 is a sectional view of an activated carbon thick film polarizable electrode formed on one surface of a current collector substrate.

FIG. 4 is a cross-sectional view of an activated carbon thick film polarizable electrode formed on both surfaces of a current collector substrate.

FIG. 5 is an external view illustrating an example of an electric double-layer capacitor using the activated carbon thick film of the present invention as a polarizable electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid activated carbon polarizable electrode 2 Current collector made of glassy carbon 3 Separator 4a Container 4b Container lid 5 Terminal 9 Separator 10 Gasket made of butyl rubber 11, 12 Glassy carbon substrate 13 Activated carbon thick film 14 Electric double layer capacitor 15 Stainless steel plate 16 Stainless steel Case

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-266509 (JP, A) JP-A-61-110416 (JP, A) JP-A-4-288361 (JP, A) JP-A 63-110 226019 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01G 9/058 H01G 9/038

Claims (9)

(57) [Claims] 1. An electric double-layer capacitor using solid activated carbon as a polarizable electrode, wherein the polarizable electrode is activated carbon.
An electric double layer capacitor comprising : a polyacene-based material composite, wherein a surfactant is contained as a second component in an electrolytic solution. 2. An electric double layer capacitor using an activated carbon thick film as a polarizable electrode, wherein the polarizable electrode is an activated carbon.
An electric double layer capacitor comprising : a polyacene-based material composite, wherein a surfactant is contained as a second component in an electrolytic solution. 3. The electric double layer capacitor according to claim 1, wherein the surfactant is a nonionic surfactant. 4. The electric double layer capacitor according to claim 3, wherein the nonionic surfactant is a polyethylene glycol type surfactant. 5. The electric double layer capacitor according to claim 4, wherein the nonionic surfactant is a polyoxyethylene alkylphenol represented by the following general formula obtained by adding ethylene oxide to an alkylphenol. Embedded image (Wherein, R ¹ is a hydrocarbon group having 5 to 20 carbon atoms, and n is 1
Is an integer of up to 20. ) 6. The non-ionic surfactant is a polyoxyethylene higher alcohol represented by the following general formula in which ethylene oxide is added to a higher alcohol.
The electric double-layer capacitor as described. R ² —O (CH ₂ CH ₂ O) _n H (wherein, R 2 is a hydrocarbon group having 8 to 22 carbon atoms, and n is 1
Is an integer of up to 20. ) 7. The electric double layer capacitor according to claim 1, wherein the surfactant is a sulfonate type surfactant. 8. The electric double layer capacitor according to claim 7, wherein the sulfonate type surfactant is a surfactant represented by the following general formula. R ³ SO ₃ M (wherein, R ³ represents a hydrocarbon group and M represents an alkali metal.) 9. The electric double layer capacitor according to claim 7, wherein the sulfonate type surfactant is a surfactant represented by the following general formula. Embedded image (In the formula, R ⁴ represents a hydrocarbon group having 5 to 20 carbon atoms, and M represents an alkali metal.)