JP2001284185A - Polarizable electrode for electric double-layer capacitor, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizable electrode, that has a low internal resistance value per prescribed projection area of an electric double-layer capacitor, a large capacitance per a prescribed volume and superior fracture strength, and to provide method of manufacturing the same. SOLUTION: The polarizable electrode of the present invention is manufactured, through the formation of a mixed power by dry-blending of activated carbon powder, conductive auxilary power and polymer resin powder containing fluorine with a lamellar structure and then compressing and molding this mixed powder into a sheet. In this plarizable electrode manufactured using this method, activated carbon is connected, so as to be held by three-dimensional structure composed of microfilaments of the polymer resin, containing fluorine formed by fracture of lamellar structure. Therefore, a polarizable electrode having superior fracture strength can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizable electrode for an electric double layer capacitor and a method for manufacturing the same, and more particularly to a polarizable electrode having a low internal resistance per predetermined projected area, a large capacity per predetermined volume, and excellent breaking strength. The present invention relates to a polarizable electrode.

[0002]

2. Description of the Related Art It is expected that an electric double layer capacitor having a large capacity and a low internal resistance will be used for load leveling of a large electric power supply or as a high power density storage power supply for a hybrid car or the like.

However, since the conventional electric double layer capacitor has a high internal resistance and cannot take out a large current, a high voltage electric double layer capacitor bank is formed by series connection, and a high output is obtained by a peripheral circuit technology using a converter or the like. However, it is costly.

In a conventional electric double layer capacitor using an organic electrolyte, the polarizable electrode has a high resistance per projected unit area, and a current density of 1 to 20 mA / cm ² is used. In this case, the voltage drop becomes large, and the output remarkably decreases. Therefore, attempts have been made to reduce the resistance by reducing the coating thickness of the polarizable electrode in order to increase the electrode area, but in this case, the filling amount of the polarizable electrode per package of the electric double layer capacitor is reduced, The capacity per package of the electric double layer capacitor is reduced, and a sufficient energy density cannot be obtained.

[0005] With such conventional organic electrolytes and polarizable electrodes, it is difficult to obtain a high output density while maintaining the required energy density due to the limitation of the resistance per unit area of projection of the polarizable electrode. there were.

A method for producing a polarizable electrode of an electric double layer capacitor includes applying a slurry containing activated carbon powder, a conductive auxiliary agent, and a binder resin onto a current collector plate, drying the slurry, and using activated carbon powder, a conductive auxiliary agent. In addition, there is a product in which a mixture of a fluorine-containing polymer resin is molded, stretched, and then formed into a sheet.

[0007] A polarizable electrode formed by a coating method has a weak binding property of activated carbon powder and is easily detached, and has a large contact resistance between activated carbon particles because it enters between activated carbon particles. The internal resistance of the capacitor is increased. Further, only by coating, the density of activated carbon does not increase and the capacity per unit volume tends to be small.

In view of this, it has been practiced to increase the mechanical strength by forming the sheet into a sheet by stretching, thereby suppressing the desorption of particles and increasing the density. For example, Japanese Patent Publication No. 7-105316 discloses a method in which an admixture composed of carbon fine powder, a fluoropolymer resin and a liquid lubricant is formed into a sheet and further subjected to a stretching treatment.

[0009]

SUMMARY OF THE INVENTION
In the polarizable electrode formed into a sheet by the conventional stretching treatment described in Japanese Patent Publication No. 316, since the liquid lubricant is present, sufficient pressure is not applied to the admixture, and the fluoropolymer resin is not sufficiently formed during sheet formation. In order to exhibit good binding properties, the resin must be added in a large amount.

[0010] Further, the carbon fine powder is contained in the fluoropolymer resin, so that the contact resistance between the carbon fine powder increases and the capacity is insufficient due to the limitation of the filling amount of the carbon fine powder. It is difficult to apply for low electric double layer capacitor applications. For this reason, a secondary process in which the sheet is further stretched after being formed into a sheet and the carbon fine powder is included in the fine nodules of the fluoropolymer resin has been indispensable.

The present invention provides a polarizable electrode of an electric double layer capacitor having a low internal resistance per predetermined projected area, a large capacity per predetermined volume, and a high breaking strength, and a method of manufacturing the same. The purpose is to:
In particular, the discharge current density per projected area of the polarizable electrode is 2
It is an object of the present invention to provide a high-power-density polarizable electrode for an electric double-layer capacitor in which a decrease in output at a large current density exceeding 0 mA / cm ² is reduced, and a method for manufacturing the same.

[0012]

According to the present invention, there is provided a method of manufacturing a polarizable electrode for an electric double layer capacitor, comprising dry-mixing activated carbon powder, conductive auxiliary powder and fluoropolymer resin powder having a lamellar structure. After forming the mixed powder, the mixed powder is compressed and molded into a sheet.

[0013] Further, the activated carbon powder, the conductive auxiliary powder and the fluoropolymer resin powder having a lamellar structure are wet-mixed by adding a dispersion solvent containing at least one of water and a liquid hydrocarbon, and then dispersed. May be removed and pulverized to form a mixed powder, and the mixed powder may be compressed and formed into a sheet.

Further, in any of the above manufacturing methods,
A fluoropolymer having a lamellar structure, characterized in that 0.1 to 30% by weight of a fluoropolymer resin having a lamellar structure and 1 to 20% by weight of a conductive auxiliary powder are mixed with activated carbon powder. The resin is polytetrafluoroethylene, and the mixed powder is pulverized and / or classified to have a secondary particle diameter of 0.1 to 2.0 mm.

Further, the mixed powder is heated from room temperature to 200 ° C.
At 50 ° C. to 100 ° C.

Further, the present invention provides a polarizable electrode for an electric double layer capacitor, comprising an activated carbon, a conductive auxiliary and a fluoropolymer resin having a lamellar structure, wherein the activated carbon is formed by destruction of the lamellar structure. It is characterized in that it is bonded so as to be held by a three-dimensional network structure made of fine fibers of a fluoropolymer resin.

The polarizable electrode for an electric double-layer capacitor is a polarizable electrode containing activated carbon, a conductive auxiliary agent and a fluoropolymer resin having a lamellar structure.
The volume occupied by the above pores is determined to be 0.
3-0.6cc / cc, density 0.5-0.8g / cc
It is characterized by being.

The activated carbon has a particle size of 0.5 to 200 μm.
m, or the particle size of the conductive auxiliary agent is 0.1 μm or less, and the diameter of the fine fibers of the fluoropolymer resin formed by destruction of the lamellar structure is 0.3 μm or less.

Further, in the polarizable electrode for an electric double layer capacitor according to the present invention, the fluorine-containing polymer resin is polytetrafluoroethylene and has a thickness of 10 to 2 times.
It is characterized in that it is a sheet-shaped molded product of 000 μm.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The polarizable electrode of the present invention is obtained by compressing a powdery dry mixture comprising activated carbon powder, a conductive auxiliary agent, and a fluoropolymer resin having a lamellar structure, and heating as necessary. Thus, it is formed into a sheet shape, and more specifically, manufactured as follows.

1) Preparation of powdery mixture 1 to 20% by weight, preferably 5 to 15% by weight, of a conductive auxiliary agent to activated carbon powder, and 0.1 to 30% by weight of a fluoropolymer resin powder having a lamellar structure. %, Preferably 1 to 10% by weight, and dry-mixed uniformly with a rotary mixer to prepare a mixed powder. Further, at the time of mixing, 50 to 200% by weight of a dispersion solvent containing at least one of water and liquid hydrocarbons may be added to the activated carbon powder and wet-mixed,
In this case, after uniform mixing, the dispersion solvent is removed by drying, and the mixture is pulverized again to obtain a mixed powder.

2) Classification of mixed powder The mixed powder is classified, and if necessary, pulverized, and the diameter of the aggregated secondary particles is set to a range of 0.1 to 2 mm.

3) Sheet Forming The classified mixed powder is compressed and, if necessary, heated to form a sheet-like molded product. The heating is performed at room temperature to 200 ° C., preferably at 50 ° C. to 100 ° C., to form a sheet. At least below room temperature, it is difficult to form a sheet, and even if heated above this temperature, the fluororesin will thermally decompose at about 260 ° C., which will also make the sheet brittle. .

In the compression step of the mixed powder and the heating step to be carried out as required, a pressing machine can be used or a heated roll can be used. In this case, by continuously supplying the mixed powder to the gap between the rolls, the sheet can be continuously formed. When a roll is used, the thickness of the sheet-shaped polarizable electrode can be any thickness between 10 μm and 2000 μm by adjusting the diameter and spacing. Thereafter, the film can be made thinner by passing it through a calender roll or the like, and an arbitrary thickness can be obtained.

In the polarizable electrode manufactured by the above-described manufacturing method, as shown in the electron micrograph of FIG. 1, the fluoropolymer resin having a lamellar structure is compressed or applied as necessary in the manufacturing method. The conductive auxiliary particles having a smaller particle diameter than the fibers adhere, coagulate, contact or become continuous with the fine fibrous fluoropolymer resin. Further, the fine fibrous fluoropolymer resin is mutually bonded so as to come into contact with activated carbon having a larger particle diameter than the fiber, and as a result, the activated carbon becomes fine fibrous fluoropolymer resin, and Activated carbon is formed by the destruction of the lamellar structure because activated carbon is bonded to each other so as to be in contact or continuity with the conductive auxiliary particles adhered and agglomerated to the fine fibrous fluoropolymer resin. Are bonded so as to be held by the three-dimensional network structure made of fine fibers of the above.

The structure of the polarizable electrode will be described with reference to the schematic diagram shown in FIG. FIG. 2 is a schematic diagram based on FIG. 1 of the electron micrograph shown above. The fibrous lamellar structure fluoropolymer resin is indicated by a broken line 3 and the aggregate of conductive auxiliary particles is shown. Is an ellipse 2 and activated carbon is represented by a shaded polygon 1.

That is, the polarizable electrode according to the present invention comprises:
The conductive auxiliary particles 2 having a smaller particle diameter than the fiber 3 adhere to, coagulate, contact, or become continuous with the fiber 3 of the fluoropolymer resin, and the fiber 3 is activated carbon having a larger particle diameter than the fiber 3. 1 so that the activated carbon 1 is held together by the three-dimensional network of fibers 3.

In the sheet-shaped polarizable electrode having the above structural characteristics, the volume occupied by pores of 36 ° or more is 0.3 to 0.6 cc / cc as measured by a mercury intrusion method, and the density is 0.5.
0.8 g / cc, and the tensile strength is 0.1 MPa or more.

The activated carbon has a particle size of 0.5 to 200 μm, preferably 1 to 100 μm, and the conductive auxiliary powder preferably has a particle size of 0.1 μm or less.

Thus, the activated carbon and the conductive auxiliary are
Since the packing density of activated carbon is increased by binding with a minimum amount of the fluoropolymer resin and forming a continuous sheet-like structure by the capturing effect of the resin fibers, the sheet-like polarizable electrode As the capacity per volume increases, the breaking strength increases, and furthermore, the minimum amount of the fluoropolymer resin maintains the amount of voids between the particles, so that the ion migration resistance decreases and the polarizable electrode decreases. , The internal resistance per predetermined projected area is reduced.

[0031]

Next, an embodiment of the present invention will be described. (Example 1) Average particle diameter is 27 μm and specific surface area is 1300
Water and isopropyl alcohol (IPA) 9 with respect to a powder mixture containing 10% by weight of carbon black having a primary particle size of 0.1 μm or less based on m ² / g of activated carbon.
170 wt% of the mixed dispersion solvent of No. 1 was added to a rotary mixer and mixed, and then polytetrafluoroethylene having a lamellar structure having an average diameter of 0.15 to 0.3 μm (PT
13% by weight of a dispersion in which FE) is dispersed in water at 60% by weight (7.8% by weight in terms of PTFE solid content)
Was added and mixed on a rotary mixer.

Next, the mixture was taken out and dried in a vacuum dryer.
After heating to 5 ° C. to remove the dispersing solvent, the powder pulverized by a cutting mixer and classified to a particle size of 0.1 to 2 mm was heated to 60 ° C. in advance to a diameter of 120 mm.
The two rolls were continuously charged into a gap set at 0.18 mm and heated and compressed to continuously obtain a sheet-shaped polarizable electrode having a thickness of 0.2 mm.

This sheet-shaped polarizable electrode is 20 mm in diameter.
Punched out into a disc shape, opposed to each other with a 50 μm-thick cellulose fiber nonwoven fabric separator interposed therebetween, and further placed a platinum plate outside the element as a current collecting plate, and further sandwiched and fixed with a Teflon (registered trademark) plate from the outside. Thus, an electric double layer capacitor cell was obtained. This cell was immersed in an electrolytic solution in which tetraethylammonium and tetrafluoroborate were dissolved in propylene carbonate so as to be 1 mol, and impregnated under reduced pressure.

Next, after charging the cell at a constant voltage of 2.5 V for 30 minutes, the discharge current density was 20 mA /
was measured capacity by a constant current discharge at cm ^2, 50mA / cm ^2. The internal resistance was calculated from the voltage drop at the beginning of discharge at a discharge current density of 50 mA / cm ² .

(Example 2) 2-1) The same operation as in Example 1 was performed except that the roll heating temperature was changed to 80 ° C.

2-2) In Example 1, the roll diameter was set to 1
The procedure was the same as in Example 1, except that the gap was 60 mm and the gap between the rolls was 0.1 mm.

2-3) Example 1 was repeated except that the amount of PTFE was changed to 5% by weight in terms of solid content in Example 1.
The same was done.

Example 3 The procedure of Example 1 was repeated except that activated carbon having an average particle diameter of 8 μm and a specific surface area of 2400 m ² / g was used.

(Comparative Example 1) The mixture taken out of the rotary mixer in Example 1 was rolled by a roll forming machine without drying to form a sheet having a thickness of 1 mm, and then heated and stretched with a calender roll to continuously produce the sheet. Except that a sheet-shaped polarizable electrode having a thickness of 0.2 mm was obtained, the same procedure was performed as in Example 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the powder crushed by the cutting mixer was not classified.

Comparative Example 3 The procedure of Example 1 was repeated except that the amount of PTFE was changed to 40% by weight in terms of solid content.

Comparative Example 4 The procedure of Example 1 was repeated, except that a phenol carbide having an average particle diameter of 3 μm and a carbonization temperature of 1200 ° C. or higher was used as the conductive additive. Table 1 shows the characteristic values of the sheet-shaped polarizable electrodes of the above Examples and Comparative Examples.

[0043]

[Table 1]

As is clear from Table 1, according to the present invention, a continuous sheet-like structure can be prepared with a minimum amount of the fluoropolymer resin, so that a large amount of the activated carbon is filled and the above-mentioned sheet-like part is formed. As the capacity per volume of the polar electrode increases, the breaking strength increases, and the interparticle void volume (pore volume) is maintained, so that the ion migration resistance decreases,
It can be seen that the internal resistance per predetermined projected area of the polarizing electrode has been reduced.

In Comparative Example 2, since the powder was not classified, a material having a size that could not be wound on a roll was included, and a large number of holes were formed in the sheet-like molded product to obtain a sample as a continuous structure. Did not.

[0046]

As described above, according to the present invention, the mixed powder is compressed as it is without using a liquid lubricant or the like as in the prior art, and heat-treated as necessary to form a sheet. A sufficient pressure can be applied to the mixture, and when the mixture is formed into a sheet, the fluoropolymer resin can exhibit sufficient binding properties, and a polarizable electrode having excellent breaking strength can be obtained. it can.

Further, since the contact resistance between the activated carbon powders is reduced, an electric double layer capacitor having a large capacity and a low internal resistance can be realized.

Further, after the sheet is formed into a sheet, a secondary process such as stretching the sheet is not required, and the output of the high power density with a large current density exceeding 20 mA / cm ² is reduced. Double layer capacitors can be made.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing the structure of a polarizable electrode according to the present invention.

FIG. 2 is a schematic view showing the structure of a polarizable electrode according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Activated carbon 2 Conductive auxiliary agent 3 Fiber

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideki Shibuya 8 Fujikurasawa, Fujisawa-shi, Kanagawa CRF Fujisawa Center Co., Ltd.

Claims (14)

[Claims] 1. An electric device for forming a mixed powder by dry-mixing an activated carbon powder, a conductive auxiliary powder and a fluoropolymer resin powder having a lamellar structure, and then compressing the mixed powder to form a sheet. A method for producing a polarizable electrode for a multilayer capacitor. 2. A method of adding a dispersion solvent containing at least one of water and a liquid hydrocarbon to an activated carbon powder, a conductive auxiliary powder, and a fluoropolymer resin powder having a lamellar structure, and wet-mixing the dispersion. And pulverizing the mixture to form a mixed powder, and compressing the mixed powder into a sheet to produce a polarizable electrode for an electric double layer capacitor. 3. The activated carbon powder is mixed with 0.1 to 30% by weight of a fluoropolymer resin having a lamellar structure and 1 to 20% by weight of a conductive auxiliary powder.
Manufacturing method. 4. The method according to claim 1, wherein the fluoropolymer resin having a lamellar structure is polytetrafluoroethylene. 5. The secondary particle diameter obtained by pulverizing and / or classifying the mixed powder is 0.1 to 2.0 mm.
Alternatively, the method according to claim 2. 6. The method according to claim 1, wherein the mixed powder is compressed at room temperature to 200 ° C. 7. The method according to claim 1, wherein the mixed powder is heated and compressed at 50 ° C. to 100 ° C. 8. A three-dimensional network structure comprising activated carbon, a conductive auxiliary agent and a fluoropolymer resin having a lamellar structure, wherein the activated carbon is made of fine fibers of a fluoropolymer resin formed by destruction of the lamellar structure. Polarizable electrode for electric double layer capacitor coupled to be held by a. 9. A polarizable electrode comprising activated carbon, a conductive auxiliary agent and a fluoropolymer resin having a lamellar structure,
The volume occupied by pores of 6 mm or more is 0.3 to 0.6 cc / cc as measured by a mercury intrusion method, and the density is 0.5 to 0.8 g /
9. The polarizable electrode for an electric double layer capacitor according to claim 8, which is cc. 10. The activated carbon has a particle size of 0.5 to 200 μm.
9. The polarizable electrode for an electric double layer capacitor according to claim 8, wherein 11. The polarizable electrode for an electric double layer capacitor according to claim 8, wherein the particle size of the conductive auxiliary agent is 0.1 μm or less. 12. The polarizable electrode for an electric double layer capacitor according to claim 8, wherein the fine fibers of the fluoropolymer resin formed by the destruction of the lamellar structure have a diameter of 0.3 μm or less. 13. The polarizable electrode for an electric double layer capacitor according to claim 8, wherein the fluoropolymer resin is polytetrafluoroethylene. 14. A polarizable electrode comprising activated carbon, a conductive auxiliary and a fluoropolymer resin having a lamellar structure, having a thickness of 1
The polarizable electrode for an electric double layer capacitor according to claim 8, which is a sheet-like molded product having a thickness of 0 to 2000 µm.