JPH0574659A - Polarizable electrode, electric double layer capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an electric double layer capacitor in which an equivalent series resistance is reduced by decreasing intrinsic resistances of a current collector and polarizable electrodes by incorporating a specified amount of nickel in the electrode made of an active charcoal/carbon/nickel composite material. CONSTITUTION:A polarizable electrode 1 made of an active charcoal/carbon/ nickel composite material contains 0.1-20wt.% of nickel. In an electric double layer capacitor in which solid active charcoal is used as the electrode 1, nickel or nickel based alloy is used as a current collector 2. Or, in the electric double layer capacitor in which solid active charcoal is used as the electrode 1, either the electrode 1 or the collector 2 or both are covered on predetermined surface parts with nickel or nickel based alloy. Or, in the case of manufacturing the electric double layer capacitor in which the solid active charcoal is used as the electrode 1, the collector 2 is connected to the electrode 2 by conductive adhesive containing nickel power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizable electrode used in an electric double layer capacitor, an electric double layer capacitor and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for miniaturization of electronic parts, and in order to miniaturize electric double layer capacitors, it is necessary to develop an electrode material having a large capacity per unit weight and It is necessary to improve the packing density.
Activated carbon powder or activated carbon fibers have been used as the polarizable electrodes of conventional electric double layer capacitors. These polarizable electrodes have to be pressed and compressed in order to establish electrical connection between powders or fibers, so that there is a limit to increase in size and reduction in resistance of the electric double layer capacitor. Moreover, there is a limit to the improvement of the capacity per unit volume. In recent years, a polarizable electrode that solves these problems has been developed. For example, as disclosed in Japanese Patent Application No. 3-81262, 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. The body has been found to be a suitable polarizable electrode for this. Further, as disclosed in Japanese Patent Laid-Open No. 64-2314, activated carbon powder or activated carbon obtained by mixing activated carbon powder or activated carbon fiber with a corn or pitch and heat-treating in a non-oxidizing atmosphere. Some electrodes are composed of fibers and carbonaceous materials. In addition, solid activated carbon obtained by steam-activating carbon having a caking property as disclosed in JP-A-62-292612 in a mold and firing at a solidification temperature or higher and then steam activation is also an electric double layer. It can be used as a polarizable electrode of a capacitor. Furthermore, JP-A-3-78
As disclosed in Japanese Patent No. 221, the solid activated carbon obtained by sintering the activated carbon powder by applying a pulsed voltage to the activated carbon powder under high temperature and pressure is also used as the polarizable electrode of the electric double layer capacitor. be able to. It is well known that solid activated carbon can be obtained by any of these methods.

[0003]

An electric double layer capacitor using solid activated carbon as a polarizable electrode is expected to be used as an auxiliary power source for supplying a momentary large current. In order to be able to supply a large current, it is desired that the electric double layer capacitor has a low equivalent series resistance. Although the equivalent series resistance of conventional electric double layer capacitors using solid activated carbon as a polarizable electrode is sufficiently low, further reduction of the equivalent series resistance is required, and current collection is one of the factors of the equivalent series resistance. There was a specific resistance of the body and polarizable electrodes. An object of the present invention is to provide an electric double layer capacitor having a reduced equivalent series resistance by reducing the specific resistance of the current collector and the polarizable electrode.

[0004]

The first aspect of the present invention is a polarizable electrode comprising an activated carbon / carbon / nickel composite, which contains 0.1 to 20% by weight of nickel. Is a polarizable electrode. A second aspect of the present invention is an electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein nickel or a nickel-based alloy is used as a current collector. A third aspect of the present invention is an electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein a predetermined surface portion of either or both of the polarizable electrode and the current collector is coated with nickel or a nickel-based alloy. This is an electric double layer capacitor. A fourth aspect of the present invention is a method for producing an electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein the current collector and the polarizable electrode are connected by a conductive adhesive containing nickel powder. It is a manufacturing method of a double layer capacitor.

[0005]

EXAMPLES Examples of the present invention will be described below. Example 1 Phenol-based activated carbon powder and powdered phenol resin were weighed so that the weight ratio was 70/30 and 60/40, and dry-mixed with a ball mill. Nickel powder was added to 100 g of each of the mixed powders at a ratio shown in Table 1 and mixed by a dry type V-type mixer. 10 g of each of these mixed powders was die-molded at 150 ° C. and a pressure of 100 kg / cm ² for 10 minutes, 50 × 35 mm ² , and a thickness of 6 m.
m phenolic resin plate containing activated carbon and nickel was obtained. This was heat-treated in an electric furnace in an N ₂ atmosphere at 900 ° C. for 2 hours. The temperature raising / lowering rate was 10 ° C./h.

The structure of the electric double layer capacitor manufactured in this embodiment will be described with reference to FIG. In FIG. 1, (a)
Is a horizontal sectional view, and (b) is a vertical sectional view. The nickel / activated carbon / carbon composite thus obtained becomes the polarizable electrode 1. The carbon-made current collector 2 has a cylindrical protrusion on a part of it.
The cylindrical protrusion has a screw hole. These were integrated with a conductive adhesive composed of a glassy carbon powder having a central particle size of 5 μm, which was heat-treated at 2000 ° C. from a phenolic resin as a starting material, a phenolic resin powder and a solvent, methyl cellosolve. .. Glassy carbon powder and phenol
Resin resin powder and methyl cellosolve in a weight ratio of 70/30 /
82, which were mixed with a homogenizer. This conductive adhesive was applied to a carbon-made current collector 2, adhered to the polarizable electrode 1, and thermally cured at 150 ° C. for 30 minutes.

Another one-sided electrode having the same structure was prepared by using the polarizable electrode 1 in which the current collector 2 was integrated as one sided electrode, and they were opposed to each other with a polypropylene separator 3 having a thickness of 25 μm interposed therebetween. These were adhered and sealed to an ABS (acrylonitrile butadiene styrene) 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 injecting the electrolytic solution into the polypropylene container 4a. As the electrolytic solution, a 27 wt% potassium hydroxide (KOH) aqueous solution was used. ABS container 4
The corners are rounded to a radius of 4 mm on the outer circumference so that the four corners of the sealing cross section of a and the lid 4b can be easily sealed. The lid 4b and the container 4a were sealed with an ultrasonic fusion machine having an output of 1200 W and a frequency of 21 kHz. The conditions of ultrasonic fusion were as follows: pressure of 1.0 kg / cm ² before and during fusion, oscillation after pressurization, and fusion time of 0.5 seconds. From the outside of the lid 4b of the sealed container 4a, a threaded stainless steel terminal 5 was connected. Thus, the electric double layer capacitor of the present invention was manufactured as a prototype.

Comparative Example 1 An electric double layer capacitor was manufactured in exactly the same manner as in Example 1 except that the polarizable electrode 1 prepared in Example 1 without adding nickel at a mixing ratio of activated carbon / resin of 70/30 was used. Was prototyped. The capacitance and equivalent series resistance of the electric double layer capacitors obtained in Example 1 and Comparative Example 1 were measured. 0.9 V 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 100 mA, and from the time required for the voltage to drop from 0.54 V to 0.45 V, The capacitance of the electric double layer capacitor was calculated. Moreover, 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. The measurement results of the electrostatic capacitance and equivalent series resistance of these electric double layer capacitors are summarized in Table 1 below.

[0009]

[Table 1] ─────────────────────────────────── Nickel equivalent weight (%) Capacitance ESR addition Quantity ──────────────── (1kHz) (g) Nickel activated carbon resin (F) (mΩ) ────────────────── ───────────────── 0 0 70 30 1015 150 0.1 0.1 69.9 30 1005 116 1 1 69.3 29.7 1003 110 5 ^* 4.8 57.1 38.1 982 98 10 9.1 63.6 27.3 856 65 20 ^* 16.7 50 33.3 723 37 25 20 56 24 736 31 ─────────────────────────────────── ^* is nickel addition The previous activated carbon / resin mixing ratio is 60/40, and the others are 70/30. In Example 1 and Comparative Example 1, the capacitance decreases because the content of activated carbon decreases as the added amount of nickel increases. Equivalent series resistance of electric double layer capacitor is reduced Less.
This has a carbon resistivity of about 10 ^-2 Ω · c at room temperature.
While the resistivity of nickel is about 10 ⁻⁵ Ω · cm at room temperature, it is considered that the resistance of the polarizable electrode was lowered by the addition of nickel. 20 nickel
When the content is more than weight%, the capacity becomes small and the amount of resin decreases, so that molding becomes difficult.

Example 2 Using the same polarizable electrode 1 as in Comparative Example 1, an electric double layer capacitor was prototyped with a nickel current collector 2 having the same shape as in Example 1. The polarizable electrode 1 and the current collector 2 were connected using the same carbon conductive adhesive as in Example 1. An electric double layer capacitor was manufactured as a prototype in the same manner as in Example 1 in the subsequent assembling steps.

Example 3 The same polarizable electrode 1 as in Comparative Example 1 was prepared. Central particle size 0.
It was integrated with a conductive adhesive composed of 6 μm nickel fine powder, phenolic resin powder and methyl cellosolve as a solvent. The fine nickel powder, the phenol resin powder, and the methyl cellosolve had a weight ratio of 70/30/82, and these were mixed by a homogenizer. This conductive adhesive is applied to the carbon-made current collector 2 and adhered to the polarizable electrode 1,
The polarizable electrode 1 and the current collector 2 were integrated by thermosetting at 50 ° C. for 30 minutes. An electric double layer capacitor was manufactured as a prototype in the same manner as in Example 1 in the subsequent assembling steps.

Example 4 A polarizable electrode 1 was prepared in exactly the same manner as in Comparative Example 1, and the
Connection with the Bon collector 2 was also performed in the same manner as in Comparative Example 1. The polarizable electrode 1 and the carbon-made current collector 2 were integrated, and the other portions were masked with polyester tape so that only one surface was plated. This is a nickel watt bath (bath composition: NiSO ₄ 7H ₂ O, NiCl ₂ 6H ₂ O,
H ₃ BO ₃ , bath temperature: 50 ° C.), apparent electrode area (5
× 3.5 cm ² ) standardized current density is 0.1 A / c
Constant-current electrolysis was carried out for 10 minutes so as to obtain m ² . Then, after removing the masking tape, vacuum drying was performed at 150 ° C. When the cross section was observed with a scanning electron microscope (SEM), the thickness of the nickel plating film was 10 μm. Two polarizable electrodes 1 were opposed to each other with the non-plated surface facing inward, and an electric double layer capacitor was manufactured in the same manner as in Example 1.

Example 5 A polarizable electrode 1 was prepared in exactly the same manner as in Comparative Example 1, and the
Connection with the Bon collector 2 was also performed in the same manner as in Comparative Example 1. The polarizable electrode 1 and the carbon-made current collector 2 were integrated, and the other portions were masked with polyester tape so that only one surface was plated. This is an acidic bath (bath composition:
Electroless plating was performed in NiSO ₄ .6H ₂ O, sodium acetate, sodium hypophosphite, bath temperature: 60 ° C.) for 10 minutes. The coating composition was a Ni-P alloy containing phosphorus. After removing the masking tape, 15
Vacuum drying was performed at 0 ° C. Scanning electron microscope (S
When observed by EM), the thickness of the nickel plating film was 10 μm. Two polarizable electrodes 1 were opposed to each other with the non-plated surface facing inward, and an electric double layer capacitor was manufactured in the same manner as in Example 1.

Example 6 A polarizable electrode 1 was prepared in the same manner as in Comparative Example 1, and the
Connection with the Bon collector 2 was also performed in the same manner as in Comparative Example 1. The polarizable electrode 1 and the carbon-made current collector 2 were integrated into one and housed in a jig in which a nickel film was formed on only one surface. Ni was deposited to a thickness of about 10 μm on this using an ion plating apparatus of the Holocades type electron beam evaporation system. The film forming conditions are as follows: Argon gas, pressure 1 × 10 ⁻³ T
The purity of Ni of the orr and the vapor deposition source is 99% or more. The film formation rate was about 1 μm / min, and the film thickness was determined by observing a cross section of a separately prepared sample with an SEM. An electric double layer capacitor was manufactured in the same manner as in Example 1, with the side on which the nickel film was not formed facing inside with a polypropylene separator 4 having a thickness of 25 μm sandwiched therebetween.

Example 7 Ni was formed into a film by a flat plate magnetron sputtering method on the same polarizable electrode 2 and carbon-made collecting electrode 3 as those produced in Example 1 which were integrated. Metal Ni as a target
I used. As film forming conditions, a pressure of 1 × 10 ^-2 Torr,
The sputtering gas is argon gas. The film formation rate is about 0.
1 μm / min, which is considerably slower than ion plating. Approximately 5 μm Ni by increasing the film formation time
Formed. After that, an electric double layer capacitor was produced in exactly the same manner as in Example 1. In the same manner as in Example 1, the capacitance and equivalent series resistance of the electric double layer capacitors manufactured in Examples 2 to 7 were measured. These results and the results of Comparative Example 1 are summarized in Table 2 below.

[0016]

[Table 2] ────────────────────────────── Capacitance / F Equivalent series resistance / mΩ ────── Example 2 1053 58 Example 3 1022 77 Example 4 1012 55 Example 5 956 75 Example 6 985 45 Example 7 973 85 Comparative Example 1 1015 121 ───────────────────────────────

From the results of Examples 2 to 7 and Comparative Example 1, nickel was used for the current collector, the polarizable electrode and the current collector were connected with a conductive adhesive containing nickel, and the nickel film was electrolyzed. It can be seen that the equivalent series resistance of the electric double layer capacitor can be reduced by forming it by plating, electroless plating, ion plating or sputtering. Although the solid activated carbon used in this example is an activated carbon / polyacene-based material composite, the effects of the present invention were also obtained with other solid activated carbons described in the section of the prior art. Further, the formation of the coating film made of nickel or a nickel-based alloy had the effect of the present invention on either the polarizable electrode or the current collector.

[0018]

As described above, according to the present invention,
An electric double layer capacitor with reduced equivalent series resistance can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of an electric double layer capacitor according to the present invention.

[Explanation of symbols]

 1 Solid activated carbon polarizable electrode 2 Current collector 3 Separator 4a Container 4b Container lid 5 Terminal

Claims (4)

[Claims] 1. A polarizable electrode comprising an activated carbon / carbon / nickel composite, wherein the polarizable electrode contains nickel in an amount of 0.1 to 20% by weight. 2. An electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein nickel or a nickel-based alloy is used as a current collector. 3. An electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein a predetermined surface portion of one or both of the polarizable electrode and the current collector is coated with nickel or a nickel-based alloy. Characteristic electric double layer capacitor. 4. A method for producing an electric double layer capacitor using solid activated carbon as a polarizable electrode, wherein the current collector and the polarizable electrode are connected by a conductive adhesive containing nickel powder. Capacitor manufacturing method.