JPH06267794A - Manufacture of polarizable electrode material - Google Patents

Abstract

PURPOSE:To provide an electrode which is large in a specific surface and also large in capacitance by hardening and baking a sheet which is mainly composed of a cellulosic fiber including an activated carbon power and pulp and a phenol resin and then performing steam-activation. CONSTITUTION:A sheet which is mainly composed of an activated carbon power, a cellulosic fiber and a phenol resin is hardened and baked, and then steam- activated. At that time, the activated carbon powder is preferably not less than 30% by weight (hereinafter, % represents % by weight) to increase the surface of an electrode. The upper limit is preferably not more than 50% because of the conditions for maintaining the quantities of the other components. A cellulosic fiber facilitates paper making and is preferably not less than 30% to keep the strength of the sheet and the electrode and also preferably up to about 70% because of the conditions for containing the other components. A phenol resin is preferably not less than 10% to maintain the strength of the sheet and the electrode and also is preferably not more than 30%, because it closes the fine hole of the activated carbon powder when it is too much.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polarizable electrode material, and more specifically to a polarizable electrode material using an electric double layer formed at the interface between the electrode surface and the electrolytic solution. It relates to a manufacturing method. This electrode is used for an electric double layer capacitor, a secondary battery, an electrochromic display 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, 1 is 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 of the polarizable electrode 1 is sealed with a sealing material 3, and a conductive sheet 4 serving as a collecting electrode is arranged outside the polarizable electrode 1.

A polarizable electrode (hereinafter simply referred to as "electrode") requires a large surface area in order to increase the electrostatic capacity, and therefore, activated carbon powder, activated carbon fiber, etc. are often used. The form of the electrode is (1) a paste-like electrode in which activated carbon powder is pasted with an electrolytic solution such as an aqueous solution of sulfuric acid (Japanese Patent Laid-Open Nos. 62-130506 and 63-244609,
(JP-A-2-174210), (2) A porous carbon molded body is used by being impregnated with an electrolytic solution, and a phenol resin molded body is foamed, carbonized, and activated as the carbon molded body (JP-A-2-174210). 2-297915), a mesopitched activated, shaped and carbonized porous electrode (Japanese Patent Laid-Open No. 2-18500).
8) and (3) there is a carbon fiber electrode (Japanese Patent Laid-Open No. 64-82514) in which a woven cloth of activated carbon fiber or the like is used to impregnate an electrolytic solution.

[0004]

The electrode is required to have a large surface area in order to increase the electrostatic capacity, as well as a small electric resistance, a good corrosion resistance, and a large withstand voltage. In the above-mentioned paste-like electrode (1), the large specific surface area of the activated carbon powder is directly utilized in the surface area of the electrode, so that there is an advantage that the surface area is large, but the electric resistance is large and the assembling work of the capacitor is troublesome. Since the porous electrode (2) formed into a molded 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 molded body. Further, the activated carbon fiber itself is expensive, and the electrode (3) using the activated carbon fiber is not only expensive, but also has insufficient electric resistance and surface area. Therefore, it is an object of the present invention to provide a method for manufacturing an electrode which has a large surface area and thus a large electrostatic capacity, is excellent in electric resistance, corrosion resistance and strength, and is easy to manufacture and handle.

[0005]

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

[0006] As the activated carbon, ordinary activated carbon such as activated carbon obtained by carbonizing coconut chips, sawdust, coal, phenol resin, etc. is used. It is preferable to use this activated carbon after pulverizing it to about 50 μm or less.

As the cellulosic fiber, pulp normally used for paper is suitable, but other short fiber such as rayon and cotton can be used. The fibers are formed into a sheet together with the activated carbon powder and the phenol resin. At that time, the papermaking method is easy in manufacturing, and the length of the papermaking fibers is preferably 5 mm or less. The phenol resin is preferably a resol type. The uncured liquid phenol resin can uniformly impregnate the cellulose fiber sheet, and this method is the most advantageous resin impregnation method. At this time, the viscosity can be adjusted by adding an organic solvent such as acetone to the phenol resin to facilitate the impregnation.

The activated carbon powder as a component of the sheet, which is the starting material of the electrode according to the present invention, is preferably 30% by weight (hereinafter% means "% by weight") or more in order to increase the surface area of the electrode. The upper limit is 50 because of the constraint of securing the amount for other components.
% Or less is preferable.

The cellulosic fiber is preferably 30% or more for facilitating papermaking and for maintaining the strength of the sheet and the electrode, and is preferably about 70% due to the restriction of containing 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 if it is too much, the pores of the activated carbon powder are blocked. In this case, the amount of resin is in terms of solid content excluding solvent, water and the like.

The sheet contains the above-mentioned components as main components, but it is possible to add fibers such as polyacrylonitrile, polyvinyl alcohol, etc., and fine graphite powder, etc. in a total amount of about 20% or less in order to improve conductivity.

When a papermaking cellulose fiber is impregnated with a phenol resin (hereinafter abbreviated as "resin"), the activated carbon powder is preferably contained in pulp or the like at the time of papermaking. It is also possible to mix it with the above and to add it to the sheet simultaneously with the impregnation of the resin. Further, commercially available paper such as filter paper may be used and may contain activated carbon powder and resin, and the sheet in the present invention includes such paper. The impregnated sheet of the resin is immersed in a solution of the resin, then pulled up, and if necessary, the impregnated amount is adjusted by passing between rolls. The impregnated amount can also be adjusted by changing the concentration of the resin solid content with a solvent.

The sheet containing the resin and activated carbon powder is then dried, preferably at about 120 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 that a plurality of thin sheets are laminated and pressure-bonded, and then cured and baked. If the sheet is thick, it is difficult to make a paper, and it is difficult to uniformly impregnate the resin and the activated carbon powder, so a thickness of 0.1 to 1 mm is preferable.

The prepreg sheet is preferably 150-2.
The resin is heated to a curing temperature of about 00 ° C. and cured. At this time, sandwich the prepreg sheet between graphite plates etc.
Compressing to about 10 kg / cm2 will prevent the generation of large pores, and in the case of lamination, the adhesion between sheets will be improved, and the adhesion of the electrode material will increase, resulting in a larger surface area. It is possible to make the electrode material that has.

The cured sheet is then fired under an inert atmosphere. The firing is preferably carried out, for example, by sandwiching it 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 and fibers will be rapid, and large pores will be generated, so it is preferable to heat up to about 800 ° C. for 20 to 100 hours. The final temperature of calcination is not particularly limited, and can be up to 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.

The fired sheet is then activated. There are various activation methods such as ultraviolet irradiation activation, glow discharge activation fluorine activation, steam activation, etc., but only steam activation is a method showing preferable electrode characteristics. The conditions for steam activation are preferably temperature: 750 to 1000 ° C. and time: 20 minutes to 180 minutes. When the temperature is 750 ° C or less and the time is 20 minutes or less, the treatment time is too long to be practical, and when the temperature is 1000 ° C or more and the time is 180 minutes or more, non-uniformity and deterioration of physical properties such as strength and electrical resistivity Is expressed.

[0017]

In the sheet of the present invention, the activated carbon powder is mixed with the phenol resin, but since the amount of the resin is reduced by the amount of the cellulose powder, the pores of the activated carbon powder are less likely to be blocked by the resin. Further, pores are newly formed by activating steam after firing, so that an electrode material having a large surface area can be easily manufactured. Cellulosic fibers enhance their handling by reinforcing the sheet prior to carbonization. Cellulosic fibers are partially decomposed during the carbonization process, but a significant portion remains in the form of carbonized fibers. Fine pores are generated along with partial decomposition and volatilization of the fiber, which leads to an increase in surface area. Carbonized fibers also help improve strength. As described above, it is considered that specific carbon among the carbons obtained by carbonizing each raw material component is selectively activated by steam, but the details are not clear.

[0018]

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 used in a circular net paper machine (Co., Ltd.).
Papermaking was performed using a TSS type sheet machine manufactured by Toyo Seiki Seisakusho, Ltd. to obtain a mixed sheet. The sheet was 0.25 mm thick and weighed 110 g.

This sheet was dipped in a phenol resin (BRL-120Z manufactured by Showa Highpolymer Co., Ltd.) and then at 1
It was dried for a minute to obtain a prepreg sheet. The resin impregnation amount (solid content) was 24%. Six sheets were laminated, sandwiched between graphite plates, and pressurized at 5 kg / cm @ 2, and heat-cured at 260 DEG C. for 10 minutes. The produced sheets were joined together when observed with the naked eye. Four sheets were stacked and sandwiched between graphite plates, and the temperature was raised to 1000 ° C. for 4 days in a non-oxidizing atmosphere. Next, the four carbon plates taken out from the graphite plate after spontaneous cooling were independent without adhesion and each had a good appearance.

40 ° C. saturated steam bubbling with N 2 gas was introduced into a furnace whose temperature was adjusted to 850 ° C., and two of the above four sheets were steam activated for 20 minutes. The remaining two fired plates are comparative materials. Table 1 shows the physical properties of the above carbon plate.

[0021]

[Table 1] Calcined Plate Calcined / Steam Activated Plate Bulk Density (g / cm3) 0.52 0.51 0.43 0.41 Bending Strength (kg / cm2) 200 190 190 190 Specific Surface Area (m2 / g) 760 890 1,370 1,350 Electrical Resistivity ( μΩ-cm) 16,000 17,000 15,000 16,000 Compressive strength (kg / cm2) 91 83 85 88 Ash (%) 0.41 0.38 0.37 0.38 Corrosion current (μA / cm2) 12 13 15 14

Specific surface area: BET method, N2 gas electrical resistivity: four-terminal method, current 1Amp Bending strength: three-point bending method, load speed 0.5 mm / min Compressive strength: 10 mm square samples are laminated five layers above and below The whole is pressed and the strength at break is measured. Load speed 0.5m
m / min Corrosion current: Measured in 100% sulfuric acid. Use hydrogen standard electrode Ash content: 850 ℃, burn 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 (1, 2, 4) were stacked, and Al plates 5 were arranged at the upper and lower ends to make conductive terminals.
Here, the carbon plate was processed into a circular plate having a diameter of 18 mm and a thickness of 0.4 mm, and this was impregnated with 40% sulfuric acid to form the electrode 1. The conductive sheet 4 serving as the collector electrode was processed into a dense glassy carbon (Showa Denko KK, SG carbon, thickness 0.4 mm) disk having a diameter of 23 mm and used. A sheet 2 made of polyethylene non-woven fabric (made by Japan Vilene Co., Ltd.) having a porosity of 18% (area ratio) is 20 mm in diameter and 0.11 in thickness.
Used in mm.

For sealing the periphery of the electrode, a Teflon packing sheet 3 (PFA manufactured by Daikin Industries, Ltd.) having an outer diameter of 23 m is used.
It was used after being processed to m and an inner diameter of 18 mm.

The bakelite plates 6 are arranged above and below the electric double layer capacitor thus assembled, and the bakelite plates 6 are arranged from above and below.
The performance was examined under a load of 0 kg / cm 2. Electrode 1
The electrode 1 was obtained by impregnating propylene carbonate (PC) under vacuum instead of the sulfuric acid impregnated in the above, and the performance was examined with the other configurations being the same. The results are shown in Table 2.

[0026]

[Table 2] Sulfuric acid impregnation P. In case of C impregnation Electrode content Capacitor capacity Internal resistance Capacitor content Internal resistance Farad / gm Ω Farad / gm Ω Firing plate 32 10 3 11 Firing / steam activation plate 51 12 21 14

[0027]

According to the present invention, an electrode having a large specific surface area and a large electrostatic capacity can be obtained only by performing steam activation after firing. 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 thin and easy to handle, 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.

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

[Explanation of symbols]

 1 Electrode Impregnated with Electrolyte 2 Porous Electrical Insulating Separator 3 Sealing Material 4 Conductive Sheet 5 Aluminum Plate 6 Bakelite Plate

Front page continued (72) Inventor Shigeru Murakami 6850 Omachi, Omachi City, Nagano Prefecture Showa Denko Co., Ltd. Omachi Plant (72) Inventor Keigo Sasabayashi 6850, Omachi City, Nagano Prefecture Showa Denko Co. Ltd. Omachi Plant (72) Invention Hisahara Shinohara 1080 Inaka-cho, Inari-cho, Nagano-shi, Nagano Inside the dormitory of Kawanakajima (72) Inventor Shigeru Kobayashi 151-1, Tsumashina-cho, Nagano-shi, Nagano Prefecture

Claims (3)

[Claims] 1. A process for producing a polarizable electrode material, which comprises activating steam after curing and firing a sheet mainly composed of activated carbon powder, cellulosic fibers and phenol resin. 2. The activated carbon powder of the sheet 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.
A method for producing the polarizable electrode material described. 3. The method for producing a polarizable electrode material according to claim 1, wherein a plurality of the laminated sheets of claim 1 are pressure-bonded and cured and baked.