JPH05121271A - Manufacture of polarized electrode material - Google Patents

Abstract

PURPOSE:To manufacture a title material of large surface area, small electric resistance, excellent in corrosion resistance and strength with favorable productivity by curing and baking a sheet consisting mainly of an active carbon powder, cellulosic fibers, and a phenol resin. CONSTITUTION:A slurry solution that is a mixture of a beat lumber pulp 30-70%, PVA fibers, and an active carbon powder 30-50% is made into a sheet to obtain a mixture sheet. This sheet is dipped in a phenol resin and dried to make a prepreg sheet with a resin impregnation amount (solid component) 10-30%. Six sheets are piled up, sandwiched between graphite boards, and pressurized to heat-cured; then, its temperature is raised up to 100 deg.C in four days under a nonoxidative atmosphere. This process can provide an electrode of large surface area and large electrostatic capacitance. This electrode has excellent effects such as small electric resistance, large corrosion resistance, and large strength, and its manufacture is favorable in productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizable electrode material utilizing an electric double layer formed at the interface between the electrode surface and an electrolytic solution. This electrode is used in electric double layer capacitors, secondary batteries, electrochromic displays and the like.

[0002]

2. Description of the Related Art A basic structure of an electric double layer capacitor is shown in FIG. In the figure, reference numeral 1 denotes a polarizable electrode containing an electrolytic solution, and the central portion of the electrode is partitioned by a separator 2 made of an electrically insulating material so as to be ion-permeable. Then, the periphery is sealed with the sealing material 3. A conductive sheet 4 serving as a collecting electrode is arranged outside the electrode 1. Since a polarizable electrode (hereinafter simply referred to as an electrode) needs to have a large surface area, activated carbon powder, activated carbon fibers, etc. are often used. The form of the electrode is as follows: (1) A paste made up of an electrolytic solution such as an aqueous solution of sulfuric acid and activated carbon powder (Japanese Patent Laid-Open No. 62-62160).
-130506, 63-244609, JP-A 2-1
74210), (2) used by impregnating a porous carbon molded body with an electrolytic solution, and as the carbon molded body, a phenol resin molded body is foamed, carbonized, and activated (Japanese Patent Laid-Open No. HEI-2).
-297915), activated mesopitches, molded and carbonized (JP-A-2-185008), and (3) woven cloth of activated carbon fiber, etc., impregnated with an electrolytic solution (JP-A-64).
-82514) and the like.

[0003]

The electrode is required to have a large surface area in order to increase the electrostatic capacity, a small electric resistance, a good corrosion resistance, and a large withstand voltage. The above-mentioned paste-like electrode has an advantage that it has a large surface area because the activated carbon powder is used as it is, but it has a large electric resistance and the assembly work of the capacitor is troublesome. Since the formed body has carbon as a skeleton and is continuously connected, the electric resistance is low, but it is difficult to increase the surface area by activating the formed body. In addition, activated carbon fibers are expensive, and the use of such activated carbon fibers not only increases the cost, but also has insufficient electric resistance and surface area. It is an object of the present invention to provide a method for producing an electrode which has a large surface area and therefore can have a large electrostatic capacity, is excellent in electrical resistance, corrosion resistance and strength and is easy to produce and handle.

[0004]

Means for Solving the Problems The present invention has been devised to achieve the above object, and its gist is to cure and fire a sheet mainly composed of activated carbon powder, cellulosic fiber such as pulp and phenol resin. And a method for producing a polarizable electrode material.

As the activated carbon, usual activated carbon such as coconut wood, sawdust, coal, carbonized and activated phenol resin is used. This activated carbon is crushed to about 50 μm or less before use. As the cellulosic fibers, pulp normally used for paper is suitable, but other cellulose fibers such as rayon and cotton can be used. The fibers are then used in sheets, where the papermaking process is easy to produce,
In that case, the fiber length is preferably 5 mm or less. The phenol resin is preferably of the resol type, and the most advantageous method is to impregnate a fibrous sheet in an uncured liquid form. At this time, the viscosity can be adjusted by adding an organic solvent such as acetone to the phenol resin in order to facilitate impregnation.

In order to increase the surface area, the activated carbon powder as a component of the sheet in the present invention is preferably 30% by weight (hereinafter% means% by weight) or more. The upper limit is preferably 50% or less due to restrictions due to other components. Cellulosic fiber facilitates papermaking and keeps strength of sheet and electrode.
It is preferably 0% or more, and is preferably up to about 70% due to restrictions of other components. The phenol resin is preferably 10% or more in order to maintain the strength of the sheet and the electrode, and is preferably 30% or less because too large an amount blocks the pores of the activated carbon powder. In this case, the amount of resin is in terms of solid content excluding solvent, water and the like.
The sheet mainly contains the above components, but it is possible to add fibers such as polyacrylonitrile, polyvinyl alcohol, etc., and graphite fine powder etc. in a total amount of about 20% or less in order to improve conductivity.

A preferred method for producing a sheet is to make paper in the same way as paper is made from pulp or the like, and impregnate it with an uncured, liquid phenol resin. The activated carbon powder is preferably contained together with pulp and the like in the papermaking process, but particularly in the case of fine powder, it is possible to mix it with a phenol resin and to incorporate it into the sheet simultaneously with impregnation of the resin. Further, commercially available paper such as filter paper may be used, and the sheet in the present invention includes such paper. Resin impregnation involves immersing the sheet in a solution of resin, then pulling it up,
If necessary, the impregnation amount is adjusted by passing it between rolls. The impregnated amount can also be adjusted by changing the concentration of the resin solid content with a solvent.

The sheet containing resin and activated carbon powder is then
Dry at about 20 to 180 ° C to obtain a prepreg sheet. When the prepreg sheet is thick, it can be cured and baked as it is to be a product, but it is preferable to laminate a plurality of thin sheets and press-bond them, and then cure and fire. If the sheet is thick, it is difficult to make paper, and it is difficult to uniformly impregnate the resin and the activated carbon powder. 150-2 for prepreg sheets
Heat to about 00 ° C. to cure. At this time, it is preferable to sandwich it with a graphite plate or the like and compress it to about 0.5 to 10 kg / cm ² . Generation of large pores is prevented by the compression, and in the case of lamination, the adhesion between the sheets is improved, and the bulk density of the electrode material is increased, so that the surface area is increased.

The cured sheet is then fired under an inert atmosphere. The firing is preferably performed by sandwiching the sheet between graphite plates so that the sheet does not warp. At this time, pressure can be applied to adjust the porosity. If the temperature rise during firing is too fast, the decomposition and volatilization of the resin or fiber will be rapid and large pores will be generated, so it is preferable that the temperature be up to about 800 ° C. for 20 to 100 hours. The final temperature of calcination is not particularly limited, and it is possible to reach a temperature close to 3000 ° C. as in ordinary graphitization of carbon. In particular, baking at a high temperature removes impurities by evaporation, which is preferable as an electrode.

[0010]

In the electrode of the present invention, the activated carbon powder is mixed with the phenol resin, but since the amount of the resin is not so large, the pores of the activated carbon powder are less likely to be blocked, and therefore the surface area is large. Cellulosic fibers are partially decomposed during the carbonization process, but a significant portion remains in the form of carbonized fibers. Partial decomposition and volatilization of the fibers generate fine pores, leading to an increase in the surface area. Carbonized fibers also help improve strength. Since the sheet before carbonization is also reinforced with fibers, it has high strength and is easy to handle. In addition, since phenol resin is used, the pores of activated carbon are less blocked than other resins such as furan resin (resin can be hardened in a short time and the amount of permeation into the pores can be suppressed), and mass production is possible. It is excellent in terms of efficiency and cost.

[0011]

Example: 40% beaten wood pulp (Canadian freeness), PVA fiber (Kuraray Co., Ltd., VPB10)
5, 1 denier, length 4 mm) 10%, activated carbon powder (manufactured by Takeda Pharmaceutical Co., Ltd., LPK-436, average particle size 8 μm)
A 50% mixed slurry aqueous solution was paper-made by a round net paper machine Toyo Seiki Seisakusho Co., Ltd. TSS type sheet machine to obtain a mixed paper sheet. The sheet was 0.25 mm thick and weighed 110 g / m ² . This sheet was dipped in a phenol resin (BRL-120Z manufactured by Showa Highpolymer Co., Ltd.) and then dried at 150 ° C. for 1 minute to obtain a prepreg sheet. The resin impregnation amount (solid content) was 24%. Six pieces of this are laminated, sandwiched between graphite plates, and pressurized at 5 kg / cm ² to 260
It was cured by heating at ℃ for 10 minutes. The produced sheets were joined together. Four sheets of this were piled up and sandwiched between graphite plates, and the temperature was raised to 1000 ° C. for 4 days in a non-oxidizing atmosphere. The four carbon plates taken out from the graphite plate after being naturally cooled were not bonded,
They were independent and each had a good appearance. Two of the above four carbons were heated to 2800 ° C. at a temperature rising rate of 10 ° C./min for the purpose of removing impurities and improving the physical properties by an Atchison type graphitization furnace.
Processed. Table 1 shows the physical properties of the above carbon plate.

[0012]

[Table 1] Specific surface area: BET method, N ₂ gas Electrical resistivity: Four-terminal method, current 1 Amp Bending strength: Three-point bending method, load speed 0.5 mm / min Compressive strength: Five 10 mm square samples are laminated, and the whole is placed from above and below Pressurize and measure the strength at break. Load speed 0.5mm
/ Min Corrosion current: Measured in 100% sulfuric acid. Use hydrogen standard electrode Ash content: Burn at 850 ° C for 5 hours in air and measure residue

In order to examine the performance as a capacitor, as shown in FIG. 1, five basic structures were stacked, and Al plates 5 were arranged at the upper and lower ends to make conductive terminals. The carbon plate was processed into a disk having a diameter of 18 mm and a thickness of 0.4 mm and impregnated with 40% sulfuric acid to obtain an electrode 1. As the conductive sheet 4 serving as the collecting electrode, a disc made of dense glassy carbon (SG carbon, manufactured by Showa Denko KK, 0.4 mm in thickness) having a diameter of 23 mm was used. A sheet 2 made of a non-woven polyethylene (made by Japan Vilene Co., Ltd.) having a porosity of 18% (area ratio) is used as the ion-permeable sheet 2 made of an electrically insulating material for partitioning the central portion of the electrode to have a diameter of 20.
mm, thickness 0.11 mm. Teflon packing sheet 3 (manufactured by Daikin Industries, Ltd.,
PFA was used after being processed to have an outer diameter of 23 mm and an inner diameter of 18 mm. The bakelite plates 6 are arranged above and below the electric double layer capacitor assembled in this way, and 20 kg / cm from above and below.
^The performance was examined under a load of ² . The results are shown in Table 2.

[0014]

[Table 2] (Note) Capacitor capacity: Capacity per electrode plate / unit volume (cc)

[0015]

According to the present invention, an electrode having a large surface area and therefore a large capacitance can be obtained. Further, this electrode has low electric resistance and high corrosion resistance. Moreover, since it is reinforced with carbonized fibers, it has excellent effects such as high strength. Since the paper making method is used as the manufacturing method, the sheet is easy to handle even though it is thin, and the productivity is good.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic configuration of an electric double layer capacitor according to the present invention.

FIG. 2 is a cross-sectional view showing a state in which the capacitors of FIG. 1 are laminated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode impregnated with electrolytic solution 2 Porous electrically insulating separator 3 Encapsulating material 4 Conductive sheet 5 Aluminum plate 6 Bakelite plate

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[Procedure amendment]

[Submission date] December 5, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

[Table 1] Specific surface area: BET method, N ₂ gas Electrical resistivity: Four terminal method, current 1 Amp Bending strength: Three-point bending method, load speed 0.5 mm / min Compressive strength: Five 10 mm square samples are laminated, and the whole is placed from above and below Pressurize and measure the strength at break. Load speed 0.5mm
/ Min Corrosion current: Measured in 100% sulfuric acid. Use hydrogen standard electrode Ash content: Burn at 850 ° C for 5 hours in air and measure residue

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takayuki Fukai 6850 Omachi, Omachi-shi, Nagano Showa Denko Co., Ltd. Omachi factory

Claims (3)

[Claims] 1. A method for producing a polarizable electrode material, which comprises curing and firing a sheet mainly composed of activated carbon powder, a cellulosic fiber and a phenol resin. 2. The method for producing a polarizable electrode material according to claim 1, wherein the activated carbon powder is 30 to 50% by weight, the cellulosic fiber is 30 to 70% by weight, and the phenol resin is 10 to 30% by weight as a solid content. 3. The method for producing a polarizable electrode material according to claim 1, wherein a plurality of the sheets according to claim 1 are laminated and pressure-bonded, cured, and fired.