JPH0243716A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To obtain the title capacitor having a large capacitance and an excellent long-term reliability by a method wherein a polarization electrode, consisting of the activated carbon obtained by carbonizing and activating the phenol resin powder having heat-fusing property, is used by combining it with a non-aqueous solvent electrolyte. CONSTITUTION:In an electric double layer capacitor utilizing the electric double layer formed on the interface of polarization electrodes 1 and 2 and an electrolyte, the polarization electrodes 1 and 2, consisting of activated carbon obtained by carbonizing and activating the phenol resin powder having heat-fusing property, and a non-aqueous solvent electrolyte are used in combination. For example, an activated carbon of the specific surface area of 3100m<2>/g can be obtained by having heat-fusing phenol-formaldehyde resin powder heated at 1100 deg.C for three hours in an algon gas atmosphere. The mixture obtained by adding carbon black and PTFE powder to the above-mentioned activated carbon powder, is formed into a sheet, and the polarization electrodes 1 and 2 are formed. Also, the solution formed by having tetrabutylphosphonium tetrafluoroborate dissolved with propylene carbonate in the concentration of 1M/l is used as the electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor using polarizable electrodes made of activated carbon.

(Prior Art, Problems to be Solved by the Invention) Conventionally, as polarizable electrodes used in electric double layer capacitors, thin plates made of metal such as aluminum, net or punched metal, activated carbon, and various other materials have been used. .

As an example of using activated carbon, an electrode that is used by mixing it with an electrolyte to form a paste is proposed in Japanese Patent Publication No. 55-41015. However, the specific surface area of activated carbon used in such paste electrodes is up to 1,500
m/g, and a capacitor using this electrode had insufficient capacity per unit volume.

Further, an electrode using activated carbon fiber as the carbon material is also disclosed in Japanese Patent Publication No. 15138/1983. However, activated carbon fibers have a large porosity, making it difficult to increase the capacity per unit volume.

In order to improve this point, electrodes using pulverized activated carbon fibers or special binders have been proposed (Japanese Patent Application Laid-Open Nos. 61-26207 and 61-26208). However, even in this case, the specific surface area of the activated carbon is still not large enough, so that the effect of improving the volume per unit volume is insufficient, and furthermore, there is the additional disadvantage that the mechanical strength of the activated carbon fibers is impaired.

Furthermore, JP-A-60-27112 and JP-A-60-27
Publication No. 113 discloses an example in which activated carbon, which is obtained by carbonizing and activating a molded phenolic resin having heat-fusible properties, is used for an electrode. However, when phenol resin in the form of a film or sheet is activated carbonized, there are problems with its mechanical strength and current collecting ability as an electrode, and not only does the electrode need to be reinforced with a metal base, but it can also be activated in powder form. The reaction surface area is smaller compared to the case where the reaction surface area is smaller, and therefore the specific surface area is smaller c
) There was a problem that only activated carbon could be obtained.

An object of the present invention is to solve the above-mentioned problems and provide an electric double layer capacitor with a large capacity and excellent long-term reliability.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte. The present invention provides an electric double layer capacitor whose vF characteristic is the use of a polarizable electrode made of activated carbon obtained by carbonizing and activating a phenolic resin powder having a polarity and a non-aqueous electrolyte in combination. .

The raw materials for activated carbon used in the polarizable electrode in the present invention include 0
．． A phenolic resin powder having a particle size of 5 to 100 μm, preferably 1 to 20 μm and having thermal adhesive properties is used. Examples of the phenolic resin include resins produced by a condensation reaction between phenol and aldehydes such as formaldehyde, acetaldehyde, and furfural, and phenol formaldehyde resins are particularly preferably used.

The nophenolic resin powder is carbonized and activated by treating it at 500-1800°C, preferably 600-1,100'C, for 0.5-30 hours in an inert gas atmosphere such as nitrogen or argon. At this time, water vapor may be mixed into the gas atmosphere, or zinc chloride or the like may be used as a catalyst.

Through the above steps, the specific surface area (BET method > 2,000
~3.500 tri/g preferably ~2,500
3.400 i/g1 Bulk density 0.1-1.5 g/ml
Preferably 0.2 to 1.0 g/mj! , total pore volume 0.
5-3.0ml/g preferably 0.8-2.8m
Activated carbon powder with physical properties of l/H is obtained.

As the electrode used in the present invention, it is also possible to use as an electrode a paste obtained by mixing this activated carbon powder with an electrolytic solution. However, an electrode with even better capacity per unit volume and mechanical strength can be created by forming activated carbon powder into a sheet using a binder with excellent chemical resistance such as polytetrafluoroethylene (hereinafter abbreviated as PTFE). There are electrodes that can be used. For such a sheet-like electrode, first, preferably 1 to 50 f is applied to the activated carbon fine powder.
flfffi%, more preferably 5 to 30% of a PTFE dispersion was mixed, and the resulting viscous mixture was formed into a sheet by compression, extrusion or rolling, or a combination of these means. can be used suitably.

This sheet-like molded product can be further processed in one direction as needed.
Or biaxially stretched. This stretching process consists of 2
0 to 380°C, preferably 20 to 200°C, preferably 1.1 to 5.0 times that of steaming, particularly preferably 1.2 to 200°C.
2.0 times by a known method (for example, Japanese Patent Application Laid-open No. 5
9-166541). The stretched product thus obtained can be used as it is, but if necessary, it can be further rolled or compressed using a roll, press, etc., and then fired or semi-baked before use.

The polarizable electrode of the present invention is used in combination with a non-aqueous electrolyte, but such electrolyte is not particularly limited, and any electrolyte that can be used as an electric double layer capacitor may be used as appropriate. Examples of such a non-aqueous electrolytic solution include tetraalkylammonium salts, tetraalkylphosphonium salts of perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, peralkylsulfonic acid, or trifluoromethanesulfonic acid; A solute such as an ammonium salt or an amine salt is dissolved in a polar organic solvent such as propylene carbonate, butylene carbonate, β-butyrolactone, γ-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane, etc. Examples include those dissolved at a concentration of about 1.5 M/l.

The electric double layer according to the present invention is produced by sandwiching a porous separator between electrodes made by processing and molding the sheet-like material described above to match the shape of a capacitor, impregnating or filling it with the electrolytic solution described above, and sealing it in a case. A capacitor is obtained.

As the porous separator, for example, polypropylene fiber nonwoven fabric, glass fiber mixed paper nonwoven fabric, etc. can be suitably used. Further, the thickness of the separator is suitably 50 to 200 μm, and particularly preferably 100 to 150 μm.

(Functions and Effects) Activated carbon obtained by carbonizing and activating conventional activated carbon powder, activated carbon fiber, or phenol resin molded products such as films and sheets has a specific surface area of about 1,500 to 2,000 ml/g, and even more. If an attempt is made to increase the yield to 2,500 m/g or more through activation, the yield will drop significantly, whereas the activated carbon obtained by carbonizing and activating the phenolic resin powder according to the present invention has a pore growth rate that is low during activation. is large, and a high specific surface area of about 3,000 m/g can be easily obtained without a decrease in yield. Therefore, by using a polarizable electrode whose main component is activated carbon, the capacity per unit volume can be increased. A large electric double layer capacitor with excellent long-term reliability can be obtained.

(Example) Examples and comparative examples of the present invention will be specifically described below with reference to the drawings.

Example 1 Heat-fusible phenol-formaldehyde resin powder with a particle size of 15 μm, “Belvar S” (Kanebo Co., Ltd. trade name, weight loss initiation temperature in nitrogen 380 to 400°C, specific gravity 1.25) was heated to 1.100 in an argon gas atmosphere. After carbonization and activation at ℃ for 3 hours, the specific surface area (BET method) was 3,100rr?
/g, bulk density 0.32g/mA, pore volume 1.522
Activated carbon having physical properties of mβ/g was obtained.

200 parts by weight of water was added to 100 parts by weight of this powder mixture consisting of 80% by weight of activated carbon, 10% by weight of carbon black, and 10% by weight of PTFE powder (particle size 0.3 μm), and mixed in a V-shaped blender. did.

The obtained paste-like mixture was rolled using a roll forming machine to form a sheet having a thickness of l and l us. This sheet was preheated to 300° C. and stretched in the uniaxial direction at a magnification of 1.1 to obtain a sheet electrode material having a thickness of 0.6 mm.

Using this sheet-like electrode material, a coin-type electric double layer capacitor unit cell (diameter 2
0mm, thickness 2. Omm) was produced using the following procedure.

Polarizable electrodes 1 and 2 (diameter: 15 fins, thickness: 0.7 mm) are punched out from the sheet-like electrode material into a disk shape, and these polarizable electrodes 1.2 are connected to each other via a separator plate 3 made of a nonwoven polypropylene fiber fabric. They are placed in an exterior container consisting of a stainless steel cap 4 and a stainless steel can 5, facing each other.

Next, a predetermined electrolytic solution (tetrabutylphosphonium tetrafluoroborate dissolved in propylene carbonate at a concentration of IM/β) is injected into the unit cell, and this electrolytic solution is poured into the polarizable electrode 1.2 and the separator 3. After sufficiently impregnating the can, the ends of the cap 4 and the can 5 were caulked and sealed via a polypropylene puffing 6 to integrate them.

Using the unit cell of the electric double layer capacitor produced as described above, constant voltage charging was performed at 2.8V for 30 minutes, and then 1mA constant current discharge was performed until the voltage between the terminals at the time of discharge reached 0■. The time was measured and the initial capacitance per unit volume of a single electrode (F/cn) was calculated.Next, the capacitance was measured in the same manner after 2.8 cm of continuous voltage was applied to the same cell at 70°C for 1000 hours. The capacity deterioration rate was calculated by comparing the values and the results are shown in Table 1.

Example 2 The same phenol formaldehyde resin powder as in Example 1 was carbonized and activated at 700°C for 3 hours in an argon gas atmosphere to give a specific surface area of 2.800 tri/g, bulk density of 0.4 g/mA, and total fineness. Activated carbon powder having physical properties with a pore volume of 1.32 mβ/g was obtained.

A polarizable electrode was prepared using this activated carbon powder in the same manner as in Example 1, and the unit cell of an electric double layer capacitor using this electrode was evaluated in the same manner as in Example 1. The results are shown in Table 1. Ta.

Example 3 The same phenol formaldehyde resin powder as in Example 1 except that the particle size was 100 μm was carbonized and activated at 1,100°C for 3 hours in an argon gas atmosphere to obtain a specific surface area of 2,100 m/g and bulk. Density 0゜38g/m6,
Total pore volume 0.63m7! Activated carbon powder having physical properties of /g was obtained.

Using this activated carbon powder, the same treatment and evaluation as in Example 1 were performed and the results are shown in Table 1.

Comparative Example 1 The same treatment and evaluation as in Example 1 were performed, and the results are shown in Table 1, except that activated carbon made from a heat-fusible phenol formaldehyde resin sheet with a specific surface area of 2.000 m / g was used. Indicated.

Comparative Example 2 The same treatment and evaluation as in Example 1 were performed, except that heat-fusible phenolic resin activated carbon fibers having a specific surface area of 2,000 m/g were used, and the results are shown in Table 1.

Table 1 (Effects of the Invention) As explained above, according to the present invention, by using a polarizable electrode made of activated carbon obtained by carbonizing and activating a phenolic resin powder having heat-fusible properties, unit An electric double layer capacitor having a large capacity per volume and excellent long IU1 reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing one embodiment of an electric double layer capacitor according to the present invention. 1.2... Polarizable electrode, 3... Separator, 4... Cap, 5... Can, 6... Packing. Patent applicant Asahi Glass Co., Ltd.7

Claims (4)

[Claims] (1) In an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, a component made of activated carbon obtained by carbonizing and activating a phenolic resin powder that has thermal adhesive properties An electric double layer capacitor characterized by using a combination of a polar electrode and a non-aqueous electrolyte. (2) The electric double layer capacitor according to claim 1, wherein the phenolic resin is a phenol formaldehyde resin. (3) The particle size of the phenolic resin powder is 0.5 to 10
The electric double layer capacitor according to claim 1 or 2, which has a diameter of 0 μm. (4) The activated carbon has a specific surface area of 2,000 to 3,50
The electric double layer capacitor according to any one of claims 1 to 3, wherein the electric double layer capacitor is 0 m^2/g.