JP2728001B2 - Solid electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor using a conductive polymer as an electrolyte and, more particularly, to a capacity controllable solid electrolytic capacitor using at least two kinds of conductive polymers having different conductivity as electrolytes. .

[0002]

2. Description of the Related Art A solid electrolytic capacitor uses a porous molded body of a film-forming metal such as tantalum or aluminum as a first electrode (anode), and uses a surface oxide film as a dielectric, manganese dioxide, 7,7,8,8. -Has a structure in which a tetracyanoquinodimethane complex salt, a conductive polymer, or the like is used as the second electrode (cathode), that is, a solid electrolyte. Among them, since the conductivity of the solid electrolyte has a large effect on the internal resistance and leakage current of the capacitor, loss in the high frequency region, etc., the development of a capacitor using a conductive polymer, which is a highly conductive material, as the electrolyte has been developed. I'm advancing. For example, Japanese Patent Publication No. 4-56445 discloses a solid electrolytic capacitor in which doped polypyrrole or an alkyl-substituted product thereof is used as an electrolyte. The solid electrolytic capacitor is formed by electrolytic polymerization of pyrrole and immersion of a metal having a dielectric film formed in a polypyrrole solution. An electrolyte formation method is described. In general, the conductivity of polypyrrole is
Manganese dioxide (0.16 S / cm), 7, 7, 8, 8-
It is significantly higher than the tetracyanoquinodimethane complex salt (1 S / cm), for example, Synthetic Metals (Synth. Met., 14, 289 (198) by the present inventors.
As shown in 6)), the value obtained by synthesizing under selected conditions reaches 500 S / cm. However, it is difficult to form a conductive polymer on the surface of a dielectric material that is electrically insulative, and the electrolytic polymerization as disclosed in Japanese Patent Publication No. 4-56445 does not have any defect in the dielectric film. In an ideal case, it cannot be implemented in principle. In addition, a conductive polymer is generally insoluble in a solvent and does not melt, so that an electrolyte layer cannot be formed using a polypyrrole solution having a high molecular weight and high conductivity. For this reason, various methods have been proposed for forming an electrolyte made of a conductive polymer. For example, a method has been proposed in which a conductive precoat layer is formed on a dielectric surface, electrolytic polymerization is performed using the precoat layer as an electrode, and a conductive polymer is laminated. JP-A-63-173313 discloses a method in which a conductive polymer synthesized by a chemical polymerization method is used as a precoat layer. JP-A-1-253226 discloses a method in which a conductive or semiconductive metal oxide is used as a precoat layer. Is disclosed. Further, Japanese Patent Application Laid-Open No. H2-222431
No. 6 discloses a method in which a mesh-like conductive polymer is formed from an electrode provided in contact with a dielectric, and this is used as a nucleus to cover the entire surface of the dielectric.

The electrolytic capacitors described in these publications are fixed capacitors having a fixed capacity, and are not variable capacitors whose capacity can be arbitrarily controlled.

Japanese Patent Laid-Open Publication No. 2-74019 discloses that a conductive polymer composite film is formed by coating a dielectric surface with a polymer film in which an oxidizing agent for polymerization is dispersed, and then contacting the polymerizable monomer. A method is disclosed. In this case, the electrolyte is a uniform composite membrane of a conductive polymer and a non-conductive polymer.

[0005]

The solid electrolytic capacitor using a conductive polymer as an electrolyte disclosed in the prior art as described above has high capacitance up to a high frequency region and exhibits good characteristics of low impedance. However, there is a problem that the capacity cannot be controlled.

[0006]

Means for Solving the Problems The present inventors have conducted various studies to solve the above-mentioned problems. As a result, in a solid electrolytic capacitor using a conductive polymer as an electrolyte, the electrolyte layer in close contact with the dielectric has at least two layers having different conductivity.
When the conductive polymer region having high conductivity is made of a continuous phase, and the region of the conductive polymer having low conductivity is dispersed in an island shape, The inventors have found that the object can be achieved, and have reached the present invention.

In the present invention, the conductive polymer is a conjugated polymer compound, and examples thereof include polypyrrole, polyaniline, polythiophene, polyfuran, polyparaphenylene, polyacetylene, polyparaphenylenevinylene, polyazulene, and derivatives thereof. In general, a conjugated polymer compound itself is insulative, and when doped with an electron-accepting compound or an electron-donating compound (dopant), the conductivity increases greatly from the semiconductor region to the metal region.
In the present invention, a conjugated polymer compound is used as a conductive polymer regardless of the conductivity.

In the solid electrolytic capacitor of the present invention, the electrolyte is composed of at least two kinds of conductive polymers having different electric conductivity, and the low conductive polymer is contained in the continuous phase composed of the high conductive polymer. Although dispersed in an island shape, from the viewpoint of the effect of the invention, a highly conductive conductive polymer is doped,
It is preferable that the low-conductivity conductive polymer is a conjugated polymer in a low-concentration doping state or a undoped state. As a material satisfying these conditions, for example, the highly conductive conductive polymer is polypyrrole or polyaniline using an aromatic sulfonic acid compound as a dopant, and the low-conductive conductive polymer compound is undoped poly. Alkylthiophene and the like. In general, it is known that the conductivity of a conjugated polymer compound rapidly increases by several orders of magnitude or more when the dopant concentration becomes 6 mol% or more per repeating unit of the polymer. Therefore, in the present invention, those having a dopant concentration exceeding 6 mol% per repeating unit of the polymer are in a doping state, and those having a dopant concentration of less than 6 mol% are in a low concentration doping state or an undoping state.

The method for producing an electrolyte of the present invention in which a region of a conductive polymer having a low conductivity is dispersed in an island shape in a continuous phase made of a conductive polymer having a high conductivity is not particularly limited. After forming the conductive polymer compound of, a method of introducing a soluble undoped conjugated polymer compound solution,
First, an island-shaped conductive polymer is formed on the surface of the dielectric using an oxidizing agent or the like, and the island-shaped conductive polymer is then de-doped to form a conductive polymer in another doping state. Further, the order of forming the two types of conductive polymers is not particularly limited, and either the conductive polymer having high conductivity or the conductive polymer having low conductivity may be used first or simultaneously. In the present invention, the method of forming the conductive polymer is not limited, either. The method of electrochemically or oxidatively polymerizing the monomer using an oxidizing agent, or the method of forming a conductive polymer such as applying a conductive polymer solution. A conventionally known method can be used.

The electrolytic capacitor of the present invention has an electrolyte in which regions of a conductive polymer having a low conductivity are dispersed in an island shape in a continuous phase formed of a conductive polymer having a high conductivity. A capacitor with low loss and constant capacity up to a high frequency range according to the area of the conductive polymer and a capacitor with a relatively large internal resistance according to the area of the conductive polymer are connected in parallel. Structure. Furthermore, in the electrolytic capacitor of the present invention, since the low-conductive conductive polymer separates charges under an electric field and becomes conductive, when a DC bias is applied, the low-conductive conductive polymer is added to the capacity of the high-conductive region. The capacity of the polymer region is added. For this reason, the capacity of the electrolytic capacitor of the present invention can be controlled by the DC bias. Such an effect is peculiar to a lightly doped or undoped conductive polymer, and is not found in ordinary non-conductive polymers. In the present invention, the DC bias that increases the conductivity of the low-conductive conductive polymer, that is, the DC bias that increases the capacity, can be controlled by the molecular structure, molecular weight, dopant concentration, and the like of the low-conductive conductive polymer.

As a capacitor whose capacitance changes with a DC bias, a ceramic capacitor is also known. However, in this capacitor, the capacitance changes continuously in response to the DC bias, and the capacitance changes as in the electrolytic capacitor of the present invention. Does not show a continuous change. Further, the electrolytic capacitor of the present invention is different from the electrolytic capacitor of the present invention in that the capacitance changes depending on the temperature and the like.

The electrolytic capacitor of the present invention is characterized in that the low-conductivity region is dispersed in an island shape in a continuous phase in which the electrolyte is made of a high-conductivity conductive polymer. The type is not limited, and a conventionally known base metal of an electrolytic capacitor such as tantalum or aluminum can be used. The shape and the method of forming the dielectric film are not particularly limited, and conventionally known materials such as fine powder sintered pellets and etching foil can be used.

[0013] The electrolytic capacitor of the present invention is completed as a conventional solid electrolytic capacitor by using a conductive paste such as a carbon paste or a silver paste to draw out lead electrodes and sealing it with a resin or metal case.

[0014]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

(Example 1) 2 m in diameter with anode lead
m, a columnar tantalum fine powder pellet having a height of 2 mm is immersed in a 0.05% by weight aqueous solution of phosphoric acid, anodized at 48 V with a stainless steel plate as a counter electrode, washed and dried to remove the metal oxide film. A sintered tantalum pellet having a dielectric film was obtained. The pellet was immersed in a 0.1 N aqueous sulfuric acid solution, and the capacitance was measured.

Next, 75 g of a methyl alcohol solution of ferric dodecylbenzenesulfonate having a concentration of 26.7% by weight was placed in a glass container, 5 g of distilled water was added dropwise, and the mixture was stirred.
Cooled to -70 ° C. Add 1.92 g of pyrrole to this
A solution dissolved in 6.16 g of methyl alcohol was added dropwise, and the mixture was sufficiently stirred to prepare a polymerization solution in which pyrrole and ferric dodecylbenzenesulfonate were uniformly dissolved. The pellet on which the dielectric film was formed was immersed in this solution, pulled up after 60 seconds, and kept at room temperature for 30 minutes to polymerize polypyrrole. Furthermore, the pellet was immersed in methyl alcohol for washing, and dried at 85 ° C. to obtain a pellet in which 80% of the dielectric film surface was covered with a polypyrrole continuous phase.

The pellets obtained by the above operation were immersed in a 3% by weight polyoctylthiophene xylene solution under reduced pressure, then returned to normal pressure and dried at 80 ° C., and 80% of the dielectric surface was high. A capacitor element was obtained which was coated with a conductive polypyrrole continuous phase and 20% of undoped polyoctylthiophene.

A cathode lead was attached to the pellet using silver paste to complete a capacitor. The obtained capacitor has a capacitance of 8 μF measured at 120 Hz at a DC bias of 0 to 25 V, and exhibits a good property of little change in capacitance up to the resonance frequency range. The capacity could be controlled.

Example 2 A gold wire was brought into contact with the upper surface of the tantalum sintered compact having a dielectric film obtained in Example 1, and 1.25M pyrrole and 0.25M tetraethylammonium paratoluenesulfonate were used. Was once immersed in an electropolymerization solution consisting of an acetonitrile solution containing and lifted up, and a part of the lower portion was kept immersed in the same solution. In this state, when a voltage of 5.8 V was ignited between the gold wire and the nickel plate disposed below the pellet as the cathode, polypyrrole grew immediately from the gold wire, and polypyrrole on the tree was formed on the upper surface of the pellet. After 2 minutes, the side and bottom surfaces of the pellet were reached. Next, the whole including the gold wire was immersed in the electrolytic polymerization solution, and a voltage of 1.8 V was applied to react for 30 minutes. The pellet was immersed in methyl alcohol, washed, and dried at 85 ° C. to obtain a pellet in which 70% of the surface of the dielectric film was coated with a polypyrrole continuous phase. The pellets obtained by the above operation were immersed in a 3 wt% polyoctylthiophene xylene solution under reduced pressure, returned to normal pressure and dried at 80 ° C., and 70% of the dielectric surface was highly conductive. A capacitor element was obtained which was coated with the polypyrrole continuous phase and with 30% of the undoped polyoctylthiophene.

A cathode lead was attached to the pellet using a silver paste to complete a capacitor. The obtained capacitor has a capacitance of 7 μF measured at 120 Hz at a DC bias of 0 to 25 V, and exhibits a good property of a small capacitance change up to the resonance frequency range. The capacity could be controlled.

Example 3 The tantalum sintered body pellet having a dielectric film obtained in Example 1 was immersed in an aqueous solution of 0.53 M aniline and 0.53 M paratoluenesulfonic acid, and after 30 seconds, Pulled up and dried for 5 minutes. Next, it was immersed in an aqueous solution of 0.8 M ammonium bichromate and 2.4 M paratoluenesulfonic acid maintained at 0 ° C., immediately pulled up, and polymerized for aniline in air for 10 minutes. Further, the pellet was immersed in methyl alcohol for washing and dried at 85 ° C. to obtain a pellet in which 80% of the surface of the dielectric film was coated with a polyaniline continuous phase.

The pellets obtained by the above operation were immersed in a 3% by weight polyoctylthiophene xylene solution under reduced pressure, then returned to normal pressure and dried at 80 ° C., and 80% of the dielectric surface was high. A capacitor element coated with a conductive polyaniline continuous phase and with 20% of undoped polyoctylthiophene was obtained.

A cathode lead was attached to the pellet using a silver paste to complete a capacitor. The obtained capacitor has a capacitance of 8 μF measured at 120 Hz at a DC bias of 0 to 25 V, and exhibits a good property of little change in capacitance up to the resonance frequency range. The capacity could be controlled.

Example 4 The tantalum sintered body pellet having a dielectric film obtained in Example 1 was immersed in a chloroform solution containing 2% by weight of polyhexylthiophene and dried at 80 ° C. Island-like polyhexylthiophene was formed on 40% of the surface.

Next, 75 g of a methyl alcohol solution of ferric dodecylbenzenesulfonate having a concentration of 26.7% by weight was placed in a glass container, and 5 g of distilled water was added dropwise and stirred.
Cooled to -70 ° C. Add 1.92 g of pyrrole to this
A solution dissolved in 6.16 g of methyl alcohol was added dropwise, and the mixture was sufficiently stirred to prepare a polymerization solution in which pyrrole and ferric dodecylbenzenesulfonate were uniformly dissolved. The pellet in which the island-shaped polyhexylthiophene was formed was immersed in this solution, pulled up after 60 seconds, and raised at room temperature for 30 minutes.
The polymerization was carried out by holding for one minute. Further, the pellet was washed by immersing it in methyl alcohol.
After drying at ℃, pellets were obtained in which 40% of the dielectric film surface was coated with polyhexylthiophene in the undoped state and 60% with the continuous phase of polypyrrole.

A cathode lead was attached to the pellet using a silver paste to complete a capacitor. The obtained capacitor has a capacity of 6 μF measured at 120 Hz at a DC bias of 0 to 25 V, and exhibits a good property of little change in capacitance up to the resonance frequency range. The capacity could be controlled.

[0027]

As described above, according to the present invention, the electrolyte is formed by dispersing the regions of the conductive polymer having low conductivity in the continuous phase comprising the conductive polymer having high conductivity in an island shape. By doing so, a solid electrolytic capacitor that can control the capacity during use while maintaining the good performance of a solid electrolytic capacitor using a conductive polymer as an electrolyte, that is, the capacity of high capacity up to the high frequency region and low impedance is maintained. Can be provided, the effect is great.

Claims (2)

(57) [Claims] In a solid electrolytic capacitor using a conductive polymer as an electrolyte, an electrolyte layer in close contact with a dielectric comprises at least two or more types of conductive polymer regions having different conductivity, and a conductive material having a high conductivity. A solid electrolytic capacitor comprising a polymer as a continuous phase in which regions of a conductive polymer having a low conductivity are dispersed in an island shape. 2. The high-conductivity conductive polymer is a conjugated polymer in a doping state, and the low-conductivity conductive polymer is a conjugated polymer in a low-concentration doping state or an undoped state. Solid electrolytic capacitors.