JP2000306784A - Electrode for capacitor, method for manufacturing the same, and capacitor - Google Patents

Abstract

(57) [Problem] To provide a thin and flexible electrode having a polarizable electrode material layer, a manufacturing method thereof, and a capacitor using such an electrode and having excellent large current characteristics. SOLUTION: In an electrode in which a polarizable electrode material layer composed of a mixture containing activated carbon powder, a conductive auxiliary agent and a binder is supported on a current collector, hydroxyalkyl cellulose and polytetrafluoroethylene are used as a binder. . When producing this electrode, a paint for forming a polarizable electrode material layer is prepared by dispersing activated carbon powder and a conductive auxiliary in an aqueous solvent containing hydroxyalkylcellulose and a polytetrafluoroethylene dispersion. Is applied on a current collector and dried. Further, a capacitor is formed by using the above-mentioned electrodes for the positive electrode and the negative electrode, respectively. In this case, in a state where the separator is arranged between the pair of positive and negative electrodes, both electrodes are wound, for example, in a spiral shape to form a wound electrode body, which is housed in a cylindrical container or the like, and then the organic electrolytic solution And then seal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-capacity capacitor having excellent large-current characteristics.

[0002]

2. Description of the Related Art One of those used as large-capacity capacitors is, for example, an electric double layer capacitor. An electric double layer capacitor utilizes the electric storage action of an electric double layer formed at the interface between a polarizable electrode and an electrolyte. Generally, a pair of polarizable electrodes (a positive electrode and a negative electrode) and a pair of these electrodes are used. An electrolytic solution to be impregnated, a porous separator impregnated with an electrolyte and having an ion-permeable and electrically insulating property, and a current collector and the like coupled to each electrode in order to separate the electrodes from each other and prevent a short circuit therebetween. Be composed.

In recent years, attention has been paid to the large-current charge / discharge characteristics of the large-capacity capacitor as described above, and the
Attempts have been made to use it as a load-leveling power source for secondary batteries for (electric vehicles). When such a large-capacity capacitor is used as a load-leveling power supply, it is said that the voltage fluctuation of the secondary battery at the time of starting, sudden acceleration, or recovery of braking energy is reduced, and the life of the secondary battery is dramatically improved. .

When a large-capacity capacitor is used as a load-leveling power supply, a large-capacity capacitor is required to drive the motor.
A voltage of 0 to 300 V must be secured. Therefore, it is necessary to connect 80 to 120 or more basic cells in a capacitor using an organic electrolytic solution, and 300 to 380 or more basic cells in a capacitor using an aqueous electrolytic solution in series. Therefore, in the point that the number of basic cells connected in series is small, the former organic electrolyte system is more advantageous than the latter aqueous solution system. However, due to the necessity of passing a current of 50 to 200 A, in an organic electrolyte system having a higher electric resistance than an aqueous system, a film having a high current collection efficiency such as an aluminum foil is used as a current collector, In addition, it is necessary to increase the facing area of the electrodes by forming a thin layer of a polarizable electrode material (polarizable electrode material layer) on such a film.

[0005] In producing such an electrode for a capacitor, conventionally, for example, a metal foil, a conductive polymer film, a carbon film or the like is used as a current collector, on which activated carbon and a conductive auxiliary agent are added. Forming a polarizable electrode material layer composed of a mixture of a binder and a binder. The following techniques are specifically known as techniques relating to the formation of the polarizable electrode material layer in this case. Using polytetrafluoroethylene (PTFE) as a binder, kneading the binder, activated carbon powder, and a conductive additive to form a rubber-like kneaded product, and extruding this into a wire-mesh-shaped current collector (Al expand). ,
What was molded. Using polyvinylidene difluoride (PVdF) as a binder, this binder, activated carbon powder, and a conductive additive are kneaded to prepare a paint for forming a polarizable electrode material layer, and this is used as a film-like current collector (aluminum). (Foil). Using a water-soluble binder such as hydroxymethylcellulose, hydroxyethylcellulose, carboxycellulose, and hydroxypropylcellulose, mixing the water-soluble binder, the activated carbon fiber, and the conductive additive to prepare a paint for forming a polarizable electrode material layer, Paints coated on a current collector (aluminum foil) (JP-A-4-14209).

[0006]

As the electrode used for the large-capacity capacitor, it is preferable to form a thin and uniform layer of a polarizable electrode material on a current collector. In forming such a polarizable electrode material layer, it is preferable to use PTFE having excellent heat resistance and electrochemical stability as described above as a binder in the polarizable electrode material. In addition, in that a thin and uniform polarizable electrode material layer can be efficiently and relatively easily formed, as described above, a paint for forming a polarizable electrode material layer is prepared in advance,
It is desirable to apply this paint on the current collector. That is, PTFE is used as a binder, a paint for forming a polarizable electrode material layer containing the binder is prepared, and the paint is applied on a current collector to form a thin and uniform polarizable electrode material layer. If it is possible, it becomes possible to efficiently form a polarizable electrode material layer having excellent characteristics.

[0007] However, PTFE is poor in viscosity and adhesion, and it is not possible to obtain the physical stability or chemical stability required for a coating even if an attempt is made to produce the coating using the PTFE. It was difficult to make the mixture containing a paint. For this reason, in the above, a rubber-like kneaded material is used instead of a paint, but in this case, it is necessary to use a wire mesh current collector such as Al-expand, and the layer of the polarizable electrode material is thick. Therefore, there is a problem that the internal resistance of the capacitor tends to be high, and it is difficult to obtain a large current.

On the other hand, PVdF
(In the case of) and a water-soluble binder such as hydroxymethylcellulose (in the case of), there is no problem as in the case of using PTFE, but on the contrary, the excellent heat resistance of PTFE Etc. cannot be used. In this case, although a thin polarizable electrode material layer supported on the current collector can be produced, PVd
Since it is difficult to completely remove the N-methylpyrrolidone (NMP) solvent used for dissolving F and remains in the electrolytic solution, the withstand voltage is likely to be low, and PVdF is easily decomposed during drying, and is coated and dried. There is a problem that the life of the device is easily shortened.

It is an object of the present invention to provide a thin, flexible, and small-diameter wound electrode as a polarizable electrode suitable for a large-capacity capacitor. Further, an object of the present invention is to use a paint that is physically or chemically stable, has a long pot life, and is excellent in heat resistance as a means for forming a polarizable electrode material layer, so that the above-mentioned thin and thin material is used. It is an object of the present invention to provide a method capable of efficiently producing an electrode capable of being wound to a flexible and small diameter. Further, an object of the present invention is to realize a capacitor excellent in large current characteristics by using the thin and flexible electrode thus obtained.

[0010]

Means for Solving the Problems The present inventors have set forth the following requirements in order to realize an electrode for a capacitor suitable for a high-current application such as a load-leveling power supply for an EV secondary battery or a power supply for a hybrid vehicle. The satisfying binder system was discussed. That is, first, a thin coating film of the polarizable electrode material can be formed on the current collector, second, the coating film can be wound to a small diameter, and third, the pot life of the coating material is long. thing.

In view of the above, an investigation was made on a case where PTFE, which is supple when used as a binder for a polarizable electrode material and is stable up to a high temperature, is combined with a water-soluble binder also having high heat resistance. At that time, PTF
As a water-soluble binder used with E, carboxycellulose, polyvinylpyrrolidone (PVP), hydroxyalkylcellulose and the like were examined. However, when a material other than hydroxyalkylcellulose was used, the coating viscosity increased as the dispersing time and standing time became longer. It was found that no coatable paint could be obtained. Through such studies, the present inventors have obtained the knowledge that the use of polytetrafluoroethylene and hydroxyalkyl cellulose as a binder can provide an electrode for a capacitor that satisfies the above-mentioned requirements, and obtained the present invention. Was completed.

That is, in the capacitor electrode according to the present invention, a polarizable electrode material layer composed of a mixture containing activated carbon powder, a conductive additive and a binder is carried on a current collector, and the binder is formed of It is characterized by containing hydroxyalkylcellulose and polytetrafluoroethylene. Here, the polarizable electrode material layer may be supported on only one surface of the current collector, or may be supported on both surfaces. In any case, the polarizable electrode material layer is required to improve large current characteristics. Is preferably 200 μm or less (excluding 0 μm), more preferably 50 to 100 μm. Further, it is preferable to use an aluminum foil for the current collector because the internal resistance can be reduced and the electrodes become more flexible.

Specific examples of the hydroxyalkyl cellulose include hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose. The content of these hydroxyalkylcelluloses is 1 to activated carbon powder.
It is 50% by weight, more preferably 2 to 20% by weight. If this value is less than 1% by weight, the adhesiveness is reduced, and if it exceeds 50% by weight, the content of the activated carbon powder is correspondingly reduced, so that the capacity is reduced.

In the electrode of the present invention, the polarizable electrode material layer carried on the current collector is composed of a mixture containing activated carbon powder, a conductive auxiliary and a binder. An electrode containing a conductive aid together with activated carbon powder in a layer has a particularly low internal resistance and is effective for a capacitor used for a large current.

Examples of the conductive additive include carbon black such as acetylene black, natural graphite, artificial graphite, and the like.
Ketjen black, carbon fiber, metal powder, metal fiber and the like can be used.

In the method of the present invention, when producing such an electrode, the activated carbon powder and the conductive additive are dispersed in an aqueous solvent containing hydroxyalkylcellulose and a polytetrafluoroethylene dispersion to form a polarizable electrode material. A paint for forming a layer is prepared, and the paint is applied on a current collector and dried. Here, it is preferable to add a small amount of alcohol to the water solvent during the production of the paint, since the fluidity of the paint will be appropriately increased. If the amount of the alcohol is too small, the fluidity of the paint cannot be increased. If the amount is too large, the fluidity of the paint will be too high, causing problems such as sagging during application. Specifically, the addition amount of the alcohol is 1 to 50% by weight, more preferably 1 to 10% by weight, based on the dispersion of the hydroxyalkyl cellulose and the polytetrafluoroethylene.

The present invention can be applied to a capacitor of the type in which ordinary plate-shaped electrodes are stacked. However, since the electrodes are flexible, this type of electrode is wound into a small diameter and accommodated in a metal can. Especially effective. Further, the paint used in the method of the present invention has a high fluidity and can be applied thinly on the current collector.
It is particularly advantageous when preparing the following polarizable electrode material layer.

A capacitor according to the present invention uses the above-mentioned electrode. That is, a pair of electrodes formed by carrying a polarizable electrode material layer composed of a mixture containing activated carbon powder, a conductive auxiliary agent, and a binder on a current collector, and a separator disposed between these electrodes, A capacitor comprising: an organic electrolyte solution impregnated in each electrode and a separator; and a container for accommodating the organic electrolyte solution, wherein the binder contains hydroxyalkylcellulose and polytetrafluoroethylene. . In this case, since the pair of electrodes used is supple as described above, it is suitable to be wound into a small diameter, and thus has a structure in which this pair of electrodes is wound via a separate. Is preferred. In this way, a large electrode area can be secured, so that a capacitor having a large capacity can be obtained in unit volume.

As the separator, a thin film made of cellulose, polypropylene, polyethylene or the like can be used.

Examples of the electrolytic solution include solvents such as propylene carbonate, γ-butyrolactone, and trimethyl phosphate, in which quaternary ammonium and quaternary phosphonium are used as cations, and tetrafluoroborate and hexafluorophosphate are used as anions. What melt | dissolved the electrolyte which has can be used.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applied to, for example, an electric double layer capacitor as shown in FIG. This electric double layer capacitor has a sheet-like positive electrode 1 and negative electrode 2 constituted by the electrodes of the present invention. In FIG. 1, in order to avoid complication, the positive electrode 1 and the negative electrode 2 are not illustrated separately from the polarizable electrode material layer and the current collector, which are constituent members thereof, but the current collector serving as a conductive portion is not illustrated. The exposed portion 1a of the current collector of the positive electrode 1 protrudes from the upper end of the separator and its tip is in contact with the positive electrode current collector plate 9, and the exposed portion of the current collector of the negative electrode 2 is exposed. Reference numeral 2a protrudes from the lower end of the separator 3 and the front end thereof is in contact with the negative electrode current collector plate 6. The positive electrode 1 and the negative electrode 2 are spirally wound via a separator 3 and housed in a container 5 together with an electrolyte 4 as an electrode body having a spirally wound structure. Sign R
Indicates the innermost diameter of the spirally wound electrode body. According to the present invention, even when the innermost diameter is 5 mm or less, it is possible to manufacture a wound electrode body without peeling of the polarizable electrode material layer.

The container 5 is made of iron with its surface plated with nickel, and also serves as a negative electrode terminal. A negative electrode current collector plate 6 made of nickel mesh is fixed to the bottom of the container 5 by welding before the electrode body is inserted. Reference numeral 6a is the welded portion. A metal ring 8 is arranged at the bottom of the container 5 to prevent the negative electrode current collector plate 6 from being thickened. A nickel lead 7 of the negative electrode 2 is fixed to the negative electrode current collector plate 6 by welding.

On the upper part of the spirally wound electrode body,
A positive electrode current collector 9 made of an aluminum net is placed. An aluminum lead body 10 of the positive electrode 1 is welded to the positive electrode current collector plate 9. Reference numeral 10a is the welded portion. Although the lead body 10 is shown in a linear shape, it is actually bent into a U-shape after being ultrasonically connected to the sealing plate 12.

An insulating plate 11 made of polypropylene is arranged on the upper part of the positive electrode current collector plate 9, and a hole for injecting an electrolyte and a hole for taking out a lead body are provided substantially near the center thereof.

The sealing lid includes a sealing plate 12, a terminal plate 13, an explosion-proof valve 14, a welded portion 15, an insulating packing 16, and the like. The sealing plate 12 is made of aluminum and is formed in a disk shape. A thin portion 12a is provided at the center of the sealing plate 12, and an internal pressure is applied around the thin portion 12a.
A hole is provided as a pressure introduction port 12b for acting on the pressure. The projection 14a of the explosion-proof valve 14 is welded to the upper surface of the thin portion 12a of the sealing plate 12 to form a welded portion 15.

The terminal plate 13 is made of rolled steel, the surface of which is plated with nickel, and provided with a gas discharge hole 13a. The explosion-proof valve 14 is made of aluminum and is formed in a disk shape. The lower surface of the projection 14a projecting downward in the state of FIG. It is welded to the upper surface to form a welded portion 15.

The insulating packing 16 is made of polypropylene, is formed in an annular shape, and is disposed above the peripheral portion of the sealing plate 12. The insulating packing 16 insulates the sealing plate 12 and the explosion-proof valve 14 and seals a gap between the two so that the electrolyte 4 does not leak from between the two. The annular gasket 17 is made of polypropylene, and insulates the container 5 also serving as the negative electrode terminal from the terminal plate 13 of the sealing lid, the sealing plate 12, the explosion-proof valve 14, and the like, which function as the positive electrode terminal.

[0028]

Next, examples of the present invention and comparative examples will be described. These are examples in which the present invention is applied to an electrode double-layer capacitor.

Example 1 Activated carbon powder, acetylene black as a conductive additive, polytetrafluoroethylene and hydroxypropylcellulose as binders, and water as a solvent were mixed and mixed in the following proportions. Then, a paint for forming a polarizable electrode material layer was prepared. Activated carbon powder 32 parts by weight Acetylene black 8 parts by weight Polytetrafluoroethylene 3 parts by weight Hydroxypropyl cellulose 3 parts by weight Water 150 parts by weight

Next, this paint was uniformly applied in a film form on both surfaces of a current collector made of aluminum foil having a thickness of 20 μm. The coating amount in this case was 5.5 mg / cm ² per side. Next, the applied material was dried on a plate heated to 120 ° C. for 30 minutes to remove water as a solvent. Further, the coated material from which the solvent had been removed was compressed by a roll press and then cut to produce an electrode having a predetermined size (500 mm × 55 mm). In this way, an electrode is obtained in which a polarizable electrode material layer comprising a mixture of activated carbon, a conductive additive (acetylene black) and a binder (polytetrafluoroethylene and hydroxypropylcellulose) is supported on both surfaces of the current collector. However, the thickness of the polarizable electrode material layer in this electrode was 80 μm on one side.

The electrodes obtained as described above were used as a positive electrode and a negative electrode, respectively (therefore, two electrodes were used). An aluminum lead (so-called Al ribbon) was used for the positive electrode, and nickel was used for the negative electrode. Each of the lead bodies (so-called Ni ribbon) was welded. Next, the positive electrode and the negative electrode were spirally wound by a winding machine with a paper separator interposed therebetween to obtain an electrode body having a spirally wound structure. This is then placed in a negative electrode can (here, an iron bottomed cylindrical can with nickel plating on the surface).
After being inserted and accommodated in the container, an organic electrolyte solution (here, a solution in which propylene carbonate is used as a solvent and tetraethylammonium tetrafluoroborate is used as an electrolyte) is injected, and the container is sealed. Obtained.

(Example 2) A capacitor was produced in the same manner as in Example 1 except that hydroxypropylmethylcellulose was used instead of hydroxypropylcellulose used in Example 1.

Comparative Example 1 A capacitor according to Comparative Example 1 was produced in the same manner as in Example 1 except that carboxymethyl cellulose was used in place of hydroxypropyl cellulose used in Example 1.

Comparative Example 2 A capacitor according to Comparative Example 2 was produced in the same manner as in Example 1, except that polyvinylpyrrolidone was used instead of hydroxypropylcellulose used in Example 1.

(Evaluation) In each of Examples 1 and 2 and Comparative Examples 1 and 2, the physical properties of the coating material for forming the polarizable electrode material layer and the physical properties of the electrodes were examined. Items examined were the presence or absence of splices (solids present in the paint) for paint, and the condition after storage of the paint for 3 days. The presence or absence of peeling of the polarizable electrode material layer on the electrode surface when compressed by a roll press, and the presence or absence of peeling of the polarizable electrode material layer on the electrode surface when spirally wound by a winding machine. .
Table 1 shows the results.

[0036]

[Table 1]

As shown in Table 1, in the case of Comparative Example 1 using polytetrafluoroethylene and carboxymethylcellulose as the binder, a step was generated in the paint prepared for forming the polarizable electrode material layer. In the electrode manufactured using the generated paint, the polarizable electrode material layer on the electrode surface was peeled off during the above-described compression and winding.

In the case of Comparative Example 2 in which polytetrafluoroethylene and polyvinylpyrrolidone were used as the binder, the paint prepared for forming the polarizable electrode material layer was separated after storage for 3 days and lacked stability. , Pot life of paint was short.

On the other hand, in Example 1 using polytetrafluoroethylene and hydroxypropylcellulose as the binder and Example 2 using polytetrafluoroethylene and hydroxypropylmethylcellulose as the binder, the physical properties of the paint and the electrode Physical properties were all good. As described above, according to the first and second embodiments of the present invention, a thin and flexible electrode is obtained in which the polarizable electrode material layer carried on the current collector does not peel off when compressed or wound. The capacitors according to Examples 1 and 2 manufactured by winding such a thin and flexible electrode are capable of charging and discharging a large current. In this way, for example, a capacitor excellent in large current characteristics that can be used as a load level power supply for EV is obtained.

[0040]

As described above, according to the present invention, since a binder containing polytetrafluoroethylene and hydroxyalkylcellulose is used as a binder for a polarizable electrode material, a polarizable electrode material layer is formed on a current collector. Can be realized as a thin electrode that can be wound as an electrode for a capacitor on which is carried. In that case, a paint for forming a polarizable electrode material is prepared by dispersing the activated carbon powder and the conductive additive in an aqueous solvent containing the binder as described above or a solvent containing water and alcohol, and this paint is prepared. According to the method of the present invention in which is coated on a current collector and dried, a thin and uniform polarizable electrode material layer can be efficiently and relatively easily formed. Further, by using such an electrode, it is possible to obtain a capacitor excellent in a large current characteristic and usable as, for example, a load level power supply for an EV.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a capacitor (electric double layer capacitor) to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode (electrode) 2 Negative electrode (electrode) 3 Separator 4 Electrolyte 5 Container

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Edamoto 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Jun Sato 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Hitachi Maxell, Ltd.

Claims (8)

[Claims] A polarizable electrode material layer composed of a mixture containing activated carbon powder, a conductive additive, and a binder is supported on a current collector, and the binder comprises hydroxyalkyl cellulose and polytetrafluoroethylene. An electrode for a capacitor, comprising: 2. The electrode for a capacitor according to claim 1, wherein the thickness of one side of the polarizable electrode material layer carried on the current collector is 200 μm or less (excluding 0 μm). 3. The hydroxyalkyl cellulose is any one of hydroxypropylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose, and has a content of 1 to 50% by weight based on the activated carbon powder. The electrode for a capacitor according to claim 1 or 2. 4. The electrode for a capacitor according to claim 3, wherein the current collector is made of an aluminum foil. 5. A polarizable electrode material comprising: dispersing an activated carbon powder and a conductive additive in an aqueous solvent containing hydroxyalkylcellulose and a polytetrafluoroethylene dispersion to produce the capacitor electrode according to claim 1. A method for producing an electrode for a capacitor, comprising preparing a coating for forming a layer, applying the coating on a current collector, and drying the coating. 6. A method for producing an electrode for a capacitor according to claim 1, wherein water containing a hydroxyalkylcellulose and a polytetrafluoroethylene dispersion, and water containing the hydroxyalkylcellulose and the polytetrafluoroethylene dispersion are added in an amount of 1: 1. Activated carbon powder and a conductive auxiliary are dispersed in a solvent containing ５０50% by weight of alcohol to prepare a coating for forming a polarizable electrode material layer, and this coating is applied on a current collector. And producing the electrode for a capacitor. 7. A pair of electrodes having a polarizable electrode material layer composed of a mixture containing activated carbon powder, a conductive auxiliary agent and a binder supported on a current collector, and disposed between the electrodes. A capacitor comprising a separator, an organic electrolyte solution impregnated in each electrode and the separator, and a container for accommodating them, wherein the binder contains hydroxyalkylcellulose and polytetrafluoroethylene. Characteristic capacitor. 8. The capacitor according to claim 7, wherein the pair of electrodes are wound via a separator.