JPS63232309A - Electric double-layer capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electric double layer capacitors, and more particularly to electric double layer capacitors with improved internal resistance.

Conventional technology Electric double layer capacitors have a capacitance per unit volume that is several thousand times higher than that of conventional capacitors, so they can function as both a capacitor and a battery; As an example of its application, it is used as a backup power source.

An electric double layer capacitor, for example, as shown in Fig. 4,
A pair of polarizable electrodes 2 made of activated carbon and an electrolyte solution are inserted through a non-electronically conductive and ion-permeable porous separator 1.
．． 2°, and each of these polarizable electrodes is provided with an electron-conductive and ion-impermeable conductive collector electrode 3.3° to form a basic cell, and this basic cell is connected to an insulator 4.4"
It has a sealed structure. As a result, when a voltage is applied to the conductive current collecting electrode 3.3', ions in the electrolyte solution are separated into positive and negative charges through the porous separator l, and between the conductive current collecting electrode 3.3'' Each of these makes it possible to form an electric double layer, maintains operational reliability, and facilitates handling.

The polarizable electrode includes activated carbon made from natural polymeric materials such as coconut shell, sawdust, and coal, and artificial polymeric materials such as phenol, rayon, and polyacrylonitrile;
It consists of a non-aqueous electrolyte solution in which an inorganic acid salt is dissolved in an organic solvent with a high dielectric constant such as propylene carbonate or acetonitrile, and a binder such as acrylic resin, bo-11 amide resin, or phenol resin.

Problems to be Solved by the Invention Such polarizable electrodes are made by kneading activated carbon particles with a resin solution, removing the solvent, and then impregnating them with an electrolyte solution.On the other hand, current collecting electrodes have a roughened surface. Although measures have been taken to increase the surface area of the current collecting electrode and lower the contact resistance between the current collecting electrode and the polarizable electrode, the contact resistance between the current collecting electrode and the polarizable electrode is still high. Electric double layer capacitors have the disadvantage of having a large internal resistance, and the problem is that the amount of current that can be used is small.

An object of the present invention is to provide an electric double layer capacitor with low internal resistance and a large amount of usable current.

Means for Solving the Problems In order to solve the above problems, the present invention provides a porous separator that is non-electronically conductive and ion-permeable, and a polarizable electrode provided on at least one side of the porous separator. An electric double layer capacitor having conductive current collecting electrodes on both sides of the structure, characterized in that a conductive layer containing conductive powder as a product is provided between the polarizable electrode and the conductive current collecting electrode. The purpose of this invention is to provide an electric double layer capacitor.

Next, the present invention will be explained in detail.

The polarizable electrode of the electric double layer capacitor in the present invention contains at least activated carbon, an electrolyte solution, and a resin, but from the viewpoint of suppressing the deterioration of the equal series resistance over time, it is desirable to further contain a conductive substance.

Examples of activated carbon include those in spherical and other shapes manufactured by carbonizing and then activating a thermosetting resin such as a resol type phenolic resin.

Spherical ones are preferable because they can increase the packing density and increase the capacitance.The above resol type phenolic resin can have various degrees of condensation polymerization, but is not limited to these and modified resins modified with other resins. Phenolic resins and other thermosetting resins can also be used.

There are various methods for carbonizing and activating this thermosetting resin, and any of them can be used. For example, the activation method can be broadly classified into two types: a gas activation method and a chemical activation method. The former is a method of activation through a gas phase reaction with various high-temperature oxidizing gases (e.g., water vapor, carbon dioxide, air, etc.), and the latter is a method of activation using dehydrating salts and acids (calcium chloride, magnesium chloride, zinc chloride, phosphorus, etc.). This is a method in which the reaction is carried out at a temperature of 750°C or lower. As an example of these methods, in the pore distribution of activated carbon using water vapor and zinc chloride, the latter has a center of pore radius of several tens of pores, and the former has a center of pore radius of 10 Å or less. These gas activation methods and chemical activation methods can also be used in combination.

In addition to the above-mentioned activated carbon, activated carbon made from natural materials such as conventionally used coconut shell activated carbon, activated carbon made from artificial polymeric materials such as phenol, rayon, and polyacrylonitrile can be used alone or in combination. Amorphous shapes such as fibers and cross shapes are also used.

The above electrolyte solution includes esters such as propylene carbonate and γ-butyrolactone, nitriles such as acetonitrile, halides such as chloroform, ketones such as acetone, amides such as dimethylformamide, amines such as pyridine, and tetrahydrofuran. ethers such as
C102SBF; 5PFi6, AsF6.
Examples include those obtained by melting lithium salts such as AlCl2-, CF35Oi, other metal salts, alkylammonium salts, etc., but are not limited thereto, and electrolyte solutions such as aqueous solutions of acids, alkalis, and salts can also be used.

Furthermore, the resin used in the present invention is, for example, polymethyl (
Acrylic resins consisting of polymers of acrylic monomers such as meth)acrylate, polyethyl(meth)acrylate, poly(meth)acrylate, and polyacrylonitrile, or combinations of these seven polymers with other monomers, such as styrene-acrylonitrile co-mers, etc. resins, vinyl homopolymer resins such as polyvinyl acetate and polyvinyl chloride, vinyl copolymer resins such as polyvinyl chloride and vinyl acetate copolymers, vinylidene chloride-acrylonitrile-vinyl chloride, acetal resins, and polyamide resins such as nylon. Examples include polyurethane resins, polycarbonate resins, polyalkylene oxide resins such as polyethylene oxide, 4M copolymers of vinylidene fluoride and ethylene trifluoride, cellulose derivatives such as ethyl cellulose and cellulose acetate, and rubbers such as butyl rubber and natural rubber. be done.

In addition, the conductive substances used in the present invention include acetylene black produced by a furnace method, carbon black produced by another furnace method or impact method, carbon black produced by a channel method, conductive polymers such as graphite and polyacetylene, carbon fibers, and metal fibers. , metal flakes, metal powder, etc. Note that, for example, a conductive resin may be used as both the conductive substance and the binder, and this case is also included.

In the present invention, the polarizable electrode remains solid in use, and an electric double layer capacitor can be easily manufactured by stacking current collecting electrodes, and a sealing means is provided to prevent electrolyte leakage. It doesn't have to be used. To create such a molded polarizable electrode, the above thermoplastic resin is heated and dissolved in an electrolyte solution containing the above electrolyte, and it is left in a gel-like state (flowing unless force is applied) by heating or cooling it.
Add activated carbon and a conductive substance to the resin electrolyte solution, or add resin, electrolyte solution, activated carbon, and conductive substance simultaneously and knead with a triple roll, etc. Adding a substance is preferable in that the electrolyte is contained uniformly.

By creating polarizable electrodes in this way, the process of removing the solvent can be omitted, compared to the method of applying a solution consisting of activated carbon, resin, and solvent, and then impregnating the electrolyte solution after the solvent has evaporated and removed. If a polarizable electrode is prepared by pre-mixing with a resin or the like, the step of impregnating with an electrolyte solution can be omitted, further shortening the process and improving quality.

Further, examples of the conductive current collecting electrode used in the present invention include metal foil that is stable in the electrolyte, conductive rubber, and flexible graphite treated to be impermeable.

In the present invention, a conductive layer is provided between the polarizable electrode and the conductive current collecting electrode. This conductive layer has a lower electrical resistance than the polarizable electrode, and by providing this layer, the resistance between the polarizable electrode and the conductive current collecting electrode can be made smaller than when the polarizable electrode is directly provided on the conductive current collecting electrode. In addition to stainless steel and aluminum, this conductive layer includes metal powders such as nickel, tungsten, molybdenum, tin, and platinum, as well as highly conductive Ketjen black, acetylene black, and other electrolytes such as organic solvents of the above-mentioned conductive substances. It is preferable that the liquid component has a corrosion-resistant substance as its main component, but its structure is such that the powder of this conductive substance is packed more densely than a polarizable electrode, and the gaps between them are reduced to improve conductivity. Things are exemplified. This conductive layer can also contain the above resin as a binder.

In addition, the material of the porous separator used in the present invention includes cellophane, polymeric materials such as polypropylene and polyethylene, and natural fibers, and the shape includes a microporous film with many minute through holes, a certain degree of Examples include a sponge-like film with a thickness of In addition to these materials, we also use materials that satisfy the following properties: good coexistence with the electrolyte solution, no passage of activated carbon, high ion permeability (or porosity), and sufficient mechanical strength. be able to. From the viewpoint of capacitor characteristics, it is preferable to use a capacitor with a relatively low porosity for a capacitor that requires a small leakage current, and a capacitor that has a relatively high porosity for a capacitor that requires a low series equivalent resistance.

In order to manufacture the electric double layer capacitor of the present invention, when the polarizable electrode is a sheet-like molded body, the polarizable electrode is stacked on both sides of the above-mentioned porous separator, and then a current collecting electrode is attached via a conductive layer. It is completed by stacking and sandwiching these on the surfaces of the polarizable electrodes on both sides.

To provide this conductive layer, it may be formed into a sheet and sandwiched between the polarizable electrode and the current collector electrode, but it may be buried in the main surface of the polarizable electrode and/or the current collector electrode, or It may be formed by coating on the main surface. For example, a conductive layer formed on an unvulcanized conductive rubber sheet plate (which becomes a current collecting electrode) in which the above conductive substance is kneaded into rubber, or an unvulcanized conductive layer is formed, and this is used as a bottom plate. A cylindrical unvulcanized rubber gasket is placed and filled with polarizable electrodes from its open end to its upper end. Thereafter, a porous separator is applied to the filling side, and the gasket filled with polarizable electrodes is further vulcanized in the same manner as above with the filling side being applied to the porous separator. In this way, a basic cell is completed, and when it is fixed in a sealed container with conductive adhesive and connected to lead wires, an electric double layer capacitor is completed.

The electric double layer capacitor of the present invention includes not only a structure having polarizable electrodes on both sides of a porous separator and a current collecting electrode on each polarizable electrode, but also a structure in which a polarizable electrode is provided on one side of the porous separator. It also includes one in which the polarizable electrode and the porous separator are each provided with a current collecting electrode.

The activated carbon used in working polarizable electrodes has an irregular shape;
Although the specific resistance varies depending on its composition and shape, it is about one to two orders of magnitude higher than that of metal, and the contact resistance with the current collecting electrode is high. If a conductive layer made of powder of a conductive material with excellent corrosion resistance against electrolyte solution is provided between the polarizable electrode containing activated carbon and the current collecting electrode, direct contact between the activated carbon and the current collecting electrode can be achieved. is avoided, and the contact resistance between the current collector electrode and the conductive layer becomes small.On the other hand, since the contact between the conductive layer and the polarizable electrode can be made better by penetration of the electrolyte, the overall resistance between the polarizable electrode and the current collector electrode is reduced. It is thought that the resistance can be reduced, but the details of the principle are not clear.

Embodiment Next, an embodiment of the present invention will be explained based on FIGS. 1 to 3.

Example 1 As shown in Fig. 1, a current collector electrode 11.11' made of a stainless steel plate with a 15 fl angle and a thickness of 0.1 m, and a porous separator 12 with a 15 fl angle and a thickness of 0.1 m were prepared. do.

Next, add 0.5 m of tetraethylammonium perchlorate.
5 parts by weight of polymethyl methacrylate (Delpef LP-1 manufactured by Asahi Kasei Co., Ltd.) was added to 1fi253@ parts of propylene carbonate containing the ol concentration, and heated while stirring.
When the temperature reaches 100°C, stirring is continued while keeping the temperature at 100°C to completely melt the polymethyl methacrylate. This solution is cooled to room temperature to obtain a gel-like substance.

Next, activated carbon powder (BP-20 manufactured by Kuraray Chemical Co., Ltd.)
2 parts by weight and 3M parts of carbon black were kneaded together with the gel material in a three-roll mill, formed into a sheet with a thickness of 0.6 fl, and from this was formed two circular polarizable electrodes 10 m in diameter. ” to cut.

Stainless steel powder (manufactured by Wako Kagaku Co., Ltd., passed through a 100 mesh sieve, passed through a 300 mesh sieve) was passed through a 300 mesh sieve on each main surface of the polarizable electrode 13, 13' to the extent that the powder overlapped in 1 to 5 layers. Sprinkle.

This is subjected to a roll press with a roll interval of 0.6 m to embed stainless steel powder in the main surface of the polarizable electrode, thereby forming a polarizable electrode having conductive layers 14 and 14'.

The main surface of the conductive layer 14.14° made of stainless steel powder of this polarizable electrode 13.13° is connected to the current collecting electrode 11.
．． Then, the polarizable electrodes are stacked on both sides of the porous separator 12, and the polarizable electrodes on both sides are sandwiched between current collecting electrodes with the porous separator interposed therebetween to produce a basic cell.

The capacitance of the electric double layer capacitor thus obtained is measured according to the following procedure.

The stainless steel plate (collecting electrode) of the electric double layer capacitor 15 obtained above is attached to the sample terminal 1 in the measurement circuit shown in FIG.
Connect to 6.17. In this state, switch S- is connected to terminal 1.
After the voltage reaches 2.8V, switch to constant voltage charging and charge the sample for 30 minutes.

After that, switch SW is switched to the terminal 19 side, a constant current is discharged at 1 mA as shown in FIG.
Time T1 when it became OV and time T2 when it became 0.5v.
and to measure. The capacitance was determined from these measured values using the following formula, and the results are shown in Table 1. Reference numeral 21 indicates a power supply 22, an ammeter, and 23 and 24, variable resistors.

However, C: Capacitance (Farad) i: Current (Amp) T1, T2: Time (minutes) Next, use a commercially available LCR meter (YHP4274A) to
The resistance value at KHz was measured and shown in Table 1 as the initial resistance value.

Furthermore, the electric double layer capacitor 15 was connected to the test sample terminal I6.17 in the measurement circuit shown in FIG. Switch the switch SW to the terminal 19 side and set it to 0.
One cycle is discharging until the voltage drops to 3V or less. After repeating this 1000 cycles, measure the resistance value of this electric double layer capacitor in the same way as above, and find the rate of change from the initial resistance value obtained above. The results are shown in Table 1 as resistance change rates.

Example 2 Actual M An electric double layer capacitor was produced in the same manner as in Example 1 except that aluminum powder (manufactured by Wako Chemical Co., Ltd., passed through a 100 mesh sieve, did not pass through a 300 mesh sieve) was used instead of stainless steel powder, In this case as well, the capacitance, initial resistance value, and rate of change in resistance were determined in the same manner as in Example I, and the results are shown in Table 1.

Example 3 An electric double layer capacitor was produced in the same manner as in Example 1 except that 1 part by weight of acetylene black (average particle size 0.5μ) was used instead of stainless steel powder,
In this case as well, the capacitance, initial resistance value, and resistance change rate were determined in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 An electric double layer capacitor was produced in the same manner as in Example 1, except that instead of stainless steel powder, powder obtained by plating the surface of spherical phenolic resin powder with electroless nickel and electrolytic nickel was used. Similarly to Example 1, the capacitance, initial resistance value, and rate of change in resistance were determined, and the results are shown in Table 1.

Example 5 In Example 1, titanium powder (
5 parts by weight (passed through Wako Kagaku Corporation's lOO mesh, did not pass through 350 mesh) was added, kneaded, and formed into a sheet with a thickness of 0.1 m. From this, two discs with a diameter of 10 am were punched out. An electric double layer capacitor was produced in the same manner as in Example 1, except that the two sheets were stacked on each side of the polarizable electrode to form a conductive layer, and this was used as the polarizable electrode. The capacitance, initial resistance value, and resistance change rate were determined, and the results are shown in Table 1.

An electric double layer capacitor was manufactured in the same manner as in the comparative example except that the conductive layer using stainless steel powder was not provided and the collector electrode was made of expanded metal (Nunobiki Seisakusho's Luster Metal). was prepared, and its capacitance, initial resistance value, and resistance change rate were determined in the same manner as in Example 1, and the results are shown in Table 1.

From the above results, it can be seen that the initial resistance of the example was 172 or less and the resistance change rate was 173 or less than that of the comparative example.

Effects of the Invention According to the present invention, a conductive layer containing powder of a conductive substance is provided between a current collecting electrode and a polarizable electrode, so that between this conductive layer and the current collecting electrode, this conductive layer and The contact resistance between the polarizable electrodes can be reduced, and the internal resistance of the electric double layer capacitor can be reduced. This makes it possible to increase the amount of current that can be used, improve its performance, and expand its range of use as an electric circuit element.

[Brief explanation of the drawing]

Fig. 1 (A) is a diagram showing the structure of an electric double layer capacitor according to the first embodiment of the present invention, Fig. 1 (B) is a partially enlarged view thereof, Fig. 2 is a measurement circuit diagram thereof, and Fig. 3 is an operation explanatory diagram. , FIG. 4 is a diagram showing the structure of a conventional electric double layer capacitor. In the figure, 1111' is a current collecting electrode, 12 is a porous separator, and 13.13'' is a polarizable electrode. March 20, 1988

Claims (1)

[Claims] 1) In an electric double layer capacitor having conductive current collecting electrodes on both sides of a structure of a non-electronically conductive and ion permeable porous separator and a polarizable electrode provided on at least one side of the porous separator. An electric double layer capacitor characterized in that a conductive layer containing conductive powder as a main component is provided between a polarizable electrode and a conductive current collecting electrode.