JPH02224316A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a large capacitance solid electrolytic capacitor having excellent characteristics as far as to a high frequency region and also having excellent reliability by a method wherein the surface of a porous molded body, made of film-formation metal having an oxide film, is wetted with an electrolyte containing a monomer to be used for electrolytic polymerization, and electrolytic polymerization is conducted using a work electrode provided making contact with said porous molded body. CONSTITUTION:The surface of the porous molded body of a film-forming metal 1, having an oxide film, is wetted with an electrolyte 4 containing a monomer for electrolytic polymerization, an electrolytic polymerization operation is conducted using the work electrode which is provided making contact with the porous molded body, and a resin or reticulate conductive high molecular compound is formed on the surface of the porous molded body. Then, a solid electrolyte is formed by conducting electrolytic polymerization on an aromatic compound using the above-mentioned conductive high molecular compound as the anode. Accordingly, the porous molded body is filled into their fine holes with solid electrolyte having sufficiently high conductivity. As a result, equivalent series resistance is made small, resonance frequency is increased to 1MHz or higher and excellent characteristics are shown as far as to a high frequency region, and a large capacitance solid electrolytic capacitor, having a large maximum allowable current and small leakage current, can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to the production of solid electrolytic capacitors using a conductive polymer compound as a solid electrolyte. The present invention relates to a method for manufacturing a solid electrolytic capacitor that uses a molecular compound as a solid electrolyte and has excellent high frequency characteristics.

〔overview〕

The present invention provides a method for manufacturing a solid electrolytic capacitor in which an oxide of a film-forming metal is used as a dielectric and a conductive polymer compound is used as a solid electrolyte. The porous molded body is wetted with an electrolytic solution containing a monomer for polymerization, and electrolytically polymerized using a working electrode provided in contact with the porous molded body to form a dendritic or network-like conductive polymer compound on the surface of the porous molded body. The conductive polymer compound is then used as an anode to perform electrolytic polymerization of an aromatic compound to form the solid electrolyte, thereby improving the characteristics of the capacitor, especially the high frequency characteristics.

[Conventional technology]

In recent years, with advances in science and technology, electronic devices have become smaller and smaller.
BACKGROUND ART There is a need for improved reliability, and in conjunction with the development of digital equipment, there is an increasing demand in the capacitor field for large-capacity capacitors that have good characteristics even in the high frequency range and are highly reliable. For such requests,
The solid electrolytic capacitors that have been developed so far have a large capacity and are excellent in reliability because the electrolyte is solid, but the conductivity of the solid electrolyte is still insufficient, making it difficult to perform well in the high frequency range. Characteristics not obtained.

Usually, a solid electrolytic capacitor uses a porous molded body of film-forming metal such as tantalum or aluminum as the first electrode (anode), and its surface oxide film is used as a dielectric material, manganese dioxide and 7.7.8.8-tetra. It has a structure in which a solid electrolyte such as a cyanoquinodimethane complex salt is part of the second electrode (cathode). In this case, the solid electrolyte is required to have the function of electrically connecting the entire surface of the dielectric inside the porous molded body and the electrode leads, and the function of repairing electrical short circuits caused by defects in the dielectric film. As a result, metals with high electrical conductivity but without a dielectric repair function cannot be used as solid electrolytes, and manganese dioxide and the like, which transfer to insulators due to heat generated by short-circuit current, etc., have been used. However, the solid electrolyte conventionally used has insufficient electrical conductivity, and the technology for completely filling the pores of a porous molded body with a complicated shape has not yet been perfected.

On the other hand, the development of new materials has progressed in the field of polymers, and as a result, conjugated polymer films such as polyacetylene, polyparaphenylene, and polypyrrole, or films to which electron-donating or electron-withdrawing compounds (dopants) are added ( Conductive polymers (doped) have been developed so far.

Among these, aromatic conductive polymers such as polypyrrole have particularly high conductivity and good stability over time, so solid electrolytic capacitors using them as solid electrolytes have been proposed.

For example, ``Japanese Unexamined Patent Publication No. 60-37114'' discloses a solid electrolytic capacitor using a doped polymer of a five-membered heterocyclic compound as a solid electrolyte.

The electrical conductivity of polypyrrole is 0.163/c compared to conventional solid electrolytes such as manganese dioxide, although it depends on its synthesis method.
For example, M Sato (M, 5a
rSynthoMet by toh) et al., 14.
289 (1986) J, it can reach up to 500 S/cm when synthesized by electrolytic polymerization under selected conditions. In addition to the above-mentioned electrolytic polymerization method, methods for synthesizing polypyrrole include an oxidized cationic polymerization method using an oxidizing agent, and a method using Grignard reaction of dihalide derivatives of pyrrole. Among these methods, electrolytic polymerization is A conductive film with the highest conductivity can be formed if the method is legal.

Since the properties of solid electrolytic capacitors in the high frequency range improve depending on the conductivity of the electrolyte, it is thought that polypyrrole produced by electrolytic polymerization can be advantageously used as the solid electrolyte of capacitors. However, since polypyrrole is insoluble and infusible and has poor processability, it is difficult to directly adhere it onto the dielectric film inside the pores of a porous molded body of film-forming metal.

``Japanese Unexamined Patent Publication No. 60-244017'' discloses a solid electrolytic capacitor in which a polymer film of a five-membered heterocyclic compound is formed on a metallized film by an electrolytic polymerization method. In the manufacturing method described here, the metal oxide film layer is an insulator, and it is impossible to form an electrolytic polymer film on it.
Or very difficult. Further, even if electrolytic polymerization were to occur from a defective portion of the oxide film layer, the structure would be such that the cathode and anode were short-circuited, and the capacitor could not be formed. moreover,"
JP-A-62-118511 discloses a method in which a conductive polymer is formed on a dielectric with exposed metal by electrolytic polymerization, and then the metal is anodized. According to this method, polypyrrole can be attached to the surface of the porous molded body, but the inside of the pores of the porous molded body cannot be completely filled. Furthermore, ``Japanese Unexamined Patent Publication No. 165313/1989'' discloses a method of electrolytic polymerization using a porous dielectric material having an oxide film as an anode and using a conductive material provided on a part of the surface as a starting point. However, even with the method exemplified here, it seems difficult to completely fill the pores of a porous dielectric.

[Problem that the invention seeks to solve]

As mentioned above, polypyrrole produced by electrolytic polymerization is expected to have excellent performance as a solid electrolyte for electrolytic capacitors, but conventional solid electrolytic capacitor manufacturing methods do not sufficiently fill the pores of the porous molded body of film-forming metal. Therefore, there was a problem in that it was not possible to manufacture a large-capacity solid electrolytic capacitor that had good characteristics up to a high frequency range and was excellent in reliability.

The purpose of the present invention is to solve the above-mentioned problems.
An object of the present invention is to provide a large-capacity solid electrolytic capacitor that has good high-frequency characteristics and excellent reliability.

[Means for solving problems]

In order to solve the above problems, the present inventors conducted various studies and found that by adopting a specific method, the conductive polymer compound was sufficiently filled into the pores of the porous molded body of the film-forming metal. We have discovered that this can be done, and have come up with the present invention.

That is, the present invention provides a method for manufacturing a solid electrolytic capacitor using an oxide of a film-forming metal as a dielectric and a conductive polymer compound as a solid electrolyte, in which the surface of a porous molded body of a film-forming metal having an oxide film is electrolyzed. The porous molded body is wetted with an electrolytic solution containing a monomer for polymerization, and electrolytically polymerized using a working electrode provided in contact with the porous molded body to form a dendritic or network-like conductive polymer compound on the surface of the porous molded body. is formed, and then electrolytic polymerization of an aromatic compound is performed using this conductive polymer compound as an anode to form the solid electrolyte.

Film-forming metals in the present invention include tantalum, aluminum, niobium, and the like, with tantalum and aluminum being preferred. In addition, porous molded bodies of these metals are defined as molded bodies of a type in which the specific surface area is increased compared to the area of the outer peripheral surface of the molded body, for example, fine powder sintered bodies in the case of tantalum, and fine powder sintered bodies in the case of aluminum. There are etching foils, etc.

In the present invention, the shape and size of the porous molded body are not particularly limited, but a preferred factor in practice is that all or at least some of the pores constituting the porous body are located on one side of the molded body. One example is that it is connected to other planes.

In the present invention, a dendritic or network-like conductive polymer compound is first formed on the surface of a porous molded body of a film-forming metal having an oxide film, and the aromatic compound is electrolytically polymerized using this as an anode. Characteristically, this dendritic or network-like conductive polymer includes conductive polymers obtained using pyrrole, thiophene, benzene, and their derivatives as monomers, and these monomers are produced by electrolytic polymerization. . These monomers polymerize in various forms depending on the polymerization conditions, but if specific conditions are selected, they will become dendritic or network-like.

Next, a method for forming a dendritic or network-like conductive polymer on the surface of a porous material will be explained using figures.

First, a tankle pellet 1, which is a porous molded body with an oxide film formed on its surface, is wetted in advance with an electrolytic solution containing a monomer, and a gold wire 2 as a working electrode is brought into contact thereon, and a part of the lower part of the tankle pellet is wetted with an electrolytic solution containing a monomer. immersed in electrolyte 4,
A nickel plate 3 is provided below as a counter electrode. In this case, the gold wire 2 and the nickel plate 3 are connected via the electrolytic solution 4 and the electrolytic solution film layer 5 formed on the surface of the tumble pellet 1. Then, by applying a predetermined voltage between both electrodes to perform electrolytic oxidation polymerization, a dendritic or network-like conductive polymer compound grows in the electrolyte film layer 5.

When the working electrode 2 and the tank pellet (1) are completely immersed in the electrolyte 4, the conductive polymer tends to grow in lumps.

The electrolytic solution used here contains an aromatic compound as a monomer and a supporting electrolyte, and the type and composition of the solvent and solute may be particularly selected as long as they can be subjected to normal electrolytic oxidative polymerization as described below. There are no restrictions. Furthermore, the object of the present invention is that the porous molded body does not necessarily have to be completely immersed in an electrolytic solution in advance, but if a part of it is immersed in the electrolytic solution, the liquid penetrates through capillary action and wets the surface. can be achieved.

Examples of the working electrode include all metals, semiconductors, and conductive polymers used in ordinary electrode reactions, and from the viewpoint of preventing damage to the dielectric, it is preferably in the form of a flexible fiber or film, such as , gold wire, stainless steel mesh, carbon fiber, conductive polymer film, etc. can be used. Among these, polypyrrole or polypyrrole having a substituent is preferred as the conductive polymer.

Further, the type of counter electrode is not particularly limited, and all metals, semiconductors, conductive polymers, etc. used in ordinary electrode reactions can be used.

Furthermore, when applying a voltage, the potential gradient in the electrolyte film layer on the surface of the porous molded body may be IV/cm or more, preferably 5 to 100 V/cm. IV
/cm, the resulting polymer does not have a dendritic or network shape and tends to be lumpy.

In the present invention, in the first step, a dendritic or network-like conductive polymer is formed on the porous molded body, and then in the second step, the formed conductive polymer is substantially Electrolytic polymerization is performed as an anode to form a solid electrolyte layer of a solid electrolytic capacitor.

First, the porous molded body and the counter electrode that have undergone the first step are immersed in an electrolytic polymerization solution, and the electrolytic polymerization solution is introduced into the pores of the dielectric. Here, the solution for electrolytic polymerization may be the same as that used in forming the dendritic or network conductive polymer, or may be a different solution. Furthermore, the porous molded body does not have to be entirely immersed in the electrolytic solution, but may be partially immersed.

Next, when electrolytic oxidative polymerization is carried out according to a conventional method, the dendritic or network conductive polymer becomes a substantial working electrode (anode), and the conductive polymer is first formed on the dendritic or network conductive polymer. It is formed to cover the surface of the porous molded body and at the same time invade the inside of the pores. By carrying out the reaction for a certain period of time in this manner, a pellet or foil whose pores are filled with a conductive polymer produced by electrolytic polymerization can be obtained. This is pulled out of the electrolytic solution, washed and dried, and then the counter electrode lead is taken out using conductive carbon or silver paste used for boat fishing, and then covered with epoxy resin or the like to form a solid electrolytic capacitor.

The electrolytic solution for electrolytic polymerization in the present invention is basically a polar solvent to which an aromatic compound as a monomer and a supporting electrolyte salt are added, and may contain other components as necessary. In the present invention, examples of the aromatic compound used in electrolytic polymerization include benzene, pyrrole, thiophene, and furan, which may have a substituent, and preferably pyrrole or pyrrole having a substituent. Examples of polar solvents include water, acetonitrile,
Examples include, but are not limited to, benzonitrile, tetrahydrofuran, nitrobenzene, nitromethane, and propylene carbonate, and two or more types of solvents can also be used in combination. Examples of anions constituting the supporting electrolyte salt include halogen ions such as I-, F-, and C-do, various halogen compounds such as BF, -1C104-, and AsF6-, rutile sulfate ion, substituted benzenesulfonate ion, and polystyrene sulfone. Examples include acid ions. Furthermore, typical cations include alkali metals, alkaline earth metals, and quaternary ammonium.

In the present invention, the electrolytic polymerization voltage is controlled by a method used in commonly performed electrochemical reactions, and is generally 0.1 to 5.
A direct current voltage in the range of 00V is used, which can be superimposed with an alternating current if desired.

However, in the first step, when forming a dendritic or network-like conductive polymer, the above-mentioned restrictions apply.

In the solid electrolytic capacitor obtained as described above, which has a film-forming metal oxide as a dielectric and a conductive polymer compound as a solid electrolyte, the solid electrolyte is a conductive polymer synthesized by an electrolytic polymerization method. Therefore, it has a high electrical conductivity, reaching 500 S/cm in the case of polypyrrole, and therefore has good high frequency characteristics. This conductivity is 0.163/cm of manganese dioxide, a conventional solid electrolyte.
In addition, the LOO3/cm of polypyrrole produced by the oxidized cationic polymerization method, and the Q of polypyrrole produced by the Grignard method, 137 cm 1. : It's big compared to others.

[Effect]

The present invention consists of a two-stage electrolytic polymerization process as described above, but the conductive polymer formed in the first stage has a dendritic or network-like shape that easily penetrates into the pores of the porous molded body. Becomes the property of In the second stage, the conductive polymer compound sufficiently penetrates into the pores, forming an almost complete solid electrolyte at 7'.

Therefore, the inside of the pores of the porous molded potting soil are sufficiently filled with a solid electrolyte with high conductivity, so the equivalent series resistance is small, and the resonance frequency shows good characteristics up to a high frequency range of I MHz or higher. , tlanδ is small,
It becomes possible to obtain a highly reliable, large-capacity solid electrolytic capacitor with a large maximum allowable current, improved characteristics, and low leakage current.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to these Examples.

Example 1 A cylindrical fine tantalum powder sintered pellet (50% porosity) with a diameter of 5 mm and a height of 5 mm was heated at 100 V in an aqueous nitric acid solution.
After anodizing, washing and drying, a gold wire was brought into contact with the top surface of the pellet, and 1.25M pyrrole and 0.3
Once immersed in an acetonitrile solution containing tetraethylammonium paratoluenesulfonate of M and pulled up,
A portion of the lower portion was left immersed in the same solution. In this state, when a voltage of 5.8 V was applied between the metal and the nickel plate placed below the pellet as a cathode, polypyrrole immediately grew from the surface of the gold wire, and dendritic polypyrrole was formed on the pellet surface. After about 2 minutes, the side of the pellet and the opposite side of the pellet were reached. The reaction was stopped at this point, and the entire body including the gold wire was immersed in the same solution, and a voltage of 1.8V was applied to react for 4 hours, resulting in pellets in which the voids were filled with polypyrrole. Ta. The filling rate of polypyrrole into the voids of this pellet, determined from the weight change before and after the reaction, was 80%.

Next, leads were drawn out from the polypyrrole on the surface of the pellet using silver paste, and the capacitor was completed by covering it with epoxy resin. The obtained capacitor is 120H
The tangent of the capacitance 4.8μF1 loss angle (tha
nδ) was 0.008. The capacitance change rate of this capacitor is less than 10% up to l MHz, and t: an
δ was also 0.1 or less up to 600 kHz, and the high frequency characteristics were good with a resonant frequency of IMHz or more.

Example 2 A polypyrrole film with a thickness of 20 μm was obtained by an electrolytic oxidation reaction using a platinum plate as an anode using an aqueous solution containing 0.25 M of virol and 0.2 M of sodium paratoluenesulfonate. Next, this film was made into a width of 1 mm.
When a voltage was applied to the fine tantalum powder sintered pellet of Example 1 by cutting it into a strip with a length of 30n+m and using it as a working electrode in place of the gold wire of Example 1, Example 1 was obtained. Similarly to 1, dendritic polypyrrole was generated on the pellet surface and reached the side surface of the pellet and the opposite surface of the pellet after about 1 minute and 40 seconds. The reaction was stopped here, and then a voltage of 1.8 zo was applied and the reaction was continued for 4 hours, resulting in a sample in which 85% of the pellet voids were filled with polypyrrole.

Leads were drawn out from this sample using the method of Example 1 and packaged to complete a capacitor. The obtained capacitor had a capacitance of 5.0 μF at 120 Hz, and a loss angle tangent (tlan δ) of 0.012. The capacitance change rate of this capacitor is less than 10% up to I MHz, and tAnδ is less than 0.1 up to 600 kHz.
It had good high frequency characteristics with a resonance frequency of z or more.

Example 3 An etched aluminum foil was electrolytically oxidized in ammonium borate at 100 V, washed and dried, and then the top surface of the foil was brought into contact with a strip of polypyrrole film produced by the method of Example 2, and the other surface was exposed to 1. The rectangular polypyrrole film was immersed in an acetonitrile solution containing 25 M pyrrole and 0.3 M tetraethylammonium paratoluenesulfonate, and a voltage of 5.8 V was applied between the nickel plate cathode provided in the same solution and the strip-shaped polypyrrole film. Where the voltage was applied, dendritic polypyrrole was generated on the surface of the aluminum foil and inside the etched portion. After 50 minutes, the reaction was stopped, and then a voltage of 1.8 V was applied to react for 4 hours, yielding a sample in which the surface of the aluminum foil and the inside of the etched portion were filled with polypyrrole.

Next, leads were drawn out from the polypyrrole on the surface of the aluminum foil using silver paste, and the capacitor was completed by covering the capacitor with epoxy resin. The obtained capacitor is 1
At 20Hz, capacitance 1.6μF1 loss angle tangent (
tan δ) was 0.009.

The rate of change of capacitance of this capacitor is 1 up to I MHz.
0% or less, tan δ was also 0.1 or less up to 600 kHz, and the high frequency characteristics were good with a resonance frequency of 1 M)Iz or more.

Example 4 In Example 3, 2.
5M benzene and 0.1M cupric chloride and L
A nitrobenzene solution containing iAsF5 was used and a voltage of 20 V was applied to generate dendritic polyparaphenylene on the surface of the aluminum foil and inside the etched portion. 5
Stop the reaction after 0 minutes and withdraw from the monomer solution,
Subsequently, the aluminum foil was partially immersed in an acetonitrile solution containing 1.25M pyrrole and 0.3M tetraethylammonium paratoluenesulfonate, and a voltage of 1.8V was applied to react for 4 hours. A sample filled with polypyrrole was obtained.

Next, the leads were drawn out from the polypyrrole on the aluminum grown surface using silver paste and then covered with epoxy resin to complete the capacitor. The resulting capacitor is
At 120 Hz, the capacitance was 1.6 μF and the loss angle tangent (tan δ) was 0.019.

The rate of change of capacitance of this capacitor is 1 up to I MHz.
0% or less, tan δ was also 0.1 or less up to 500 kHz, and the high frequency characteristics were good with a resonance frequency of IM)lz or more.

Example 5 A porous aluminum foil having a width of 10 mm and a length of 25 mm was subjected to a chemical conversion treatment in an aqueous ammonium borate solution at 100 V to form an oxide film, and then washed and dried.

Using an aqueous solution containing 0.25M pyrrole and 2M sodium para-toluenesulfonate, a polypyrrole film with a thickness of 20 μm was obtained by electrolytic oxidation reaction using a platinum plate as an anode, and then this was made into a film with a width of 1 mm and a length of 30 mm. Cut out into strips. While fixing one end of the polypyrrole film in contact with 10 mm from the upper end of the chemical aluminum foil that has undergone the chemical conversion treatment, add an electrolytic solution (IM's pyrrole, 0.1 M (acetonitrile solution containing dodecylbenzenesulfonic acid and 0.1M triethylamine). Place a nickel plate as a cathode almost parallel to the aluminum foil and on the opposite side to where the polypyrrole film was attached.
When the polypyrrole film was immersed in an electrolytic solution at a position of 1.5 cm, and a voltage of 20 V was applied between it and the polypyrrole film, the polypyrrole formed a tree on the chemical aluminum foil toward the surface of the electrolytic solution from the polypyrrole film that served as an anode. After approximately 20 minutes, almost the entire surface of one side of the aluminum foil was covered with dendritic polypyrrole. At this time, the potential gradient in the liquid film layer of the electrolytic solution on the surface of the aluminum foil was about 20 V/cm.

Next, this aluminum foil was immersed up to the upper end of the liquid polypyrrole portion with the polypyrrole film still attached, and 2.5V was applied between the polypyrrole film and the nickel plate.
voltage was applied. After about 2 hours, both sides of the aluminum foil were covered with polypyrrole. The filling rate of polypyrrole into the pores of the aluminum foil, determined from the weight change before and after the reaction, was 90%.

Next, leads were drawn out from the polypyrrole on the surface of the aluminum foil using silver paste, and the capacitor was completed by covering the capacitor with epoxy resin. The resulting capacitor is
At 120 Hz, the capacitance was 2.7 μF and the loss angle tangent (tan δ) was 0.01 or less.

The capacitance change rate of this capacitor is less than 10% up to 500 kHz, and tan δ is 0.1 up to 300 kHz.
It had good high frequency characteristics with a resonant frequency higher than IMflz.

Example 6 A gold wire was used as the working electrode in place of the polypyrrole film of Example 5, and the same operation as in Example 5 was performed to form a polypyrrole foil film on the aluminum foil. The filling rate of polypyrrole into the pores was 80%. From this, the lead wires were drawn out and sheathed in the same manner as in Example 5 to complete the capacitor. The obtained capacitor had a capacitance of 2.4 μF at 120H2 and a loss angle tangent (tan δ) of less than o, oog. The capacitance change rate of this capacitor was 10% or less up to 800 kHz, and the tan δ was 0.1 or less up to 500 kHz, and it had good high frequency characteristics with a resonance frequency of I MHz or higher.

Comparative Example In Example 1, a gold wire was brought into contact with the top surface of the pellet, the whole was immersed in the electrolyte, and a voltage of 1.8 V was applied to react for 4 hours. As a result, a polypyrrole film was formed only on the top surface of the pellet. was formed.

When a capacitor was assembled in the same manner as in Example 1 and the capacitance was measured, it was found to be extremely small at 100 nF.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily manufacture a large capacity solid electrolytic capacitor that has good characteristics up to a high frequency range and is excellent in reliability, which has great effects.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing a main part of an example of the configuration of the present invention. 1... Tankle pellet (film-forming metal), 2...
・Gold wire (working electrode), 3...nickel plate (counter electrode)
, 4... Electrolyte solution, 5... Electrolyte solution membrane layer.

Claims (3)

[Claims] 1. In a method for manufacturing a solid electrolytic capacitor using an oxide of a film-forming metal as a dielectric and a conductive polymer compound as a solid electrolyte, the surface of a porous molded body of a film-forming metal having an oxide film is coated with an electrolytic polymer containing a monomer for electrolytic polymerization. Wet the porous molded body with a liquid and perform electrolytic polymerization using a working electrode provided in contact with the porous molded body to form a dendritic or network-like conductive polymer compound on the surface of the porous molded body, and then, A method for manufacturing a solid electrolytic capacitor, which comprises forming the solid electrolyte by electrolytically polymerizing an aromatic compound using the conductive polymer compound as an anode. 2. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the monomer for electrolytic polymerization is pyrrole, thiophene, benzene, or a derivative thereof. 3. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the aromatic compound is pyrrole, thiophene, benzene, or a derivative thereof.