JP2000150310A - Solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the capacity of a solid electric field capacitor and to reduce the impedance in high frequency region, by forming a solid electrolyte layer where the high polymer comprising a specific heterocycle is doped with an anion, on a dielectrics film formed on an anode by anodizing before jointed to a cathode. SOLUTION: The solid electric field capacitor A1 comprises an anode 1, dielectrics film 2, solid electrolyte layer 3, carbon paste layer 4, silver paste layer 5, jacket resin 7, anode terminal 8, and cathode terminal 9, etc. The solid electrolyte layer is provided by electrolytic polymerization using, as an electrolytic polymerization liquid, a water solution comprising heterocyclic monomer such as pyrrole thiophene, etc., which comprise a heterocycle monomer unit represented by a formula as a repeated unit and a dopant such as dodecylbenzensulfonic acid ion and sulphate ion, etc. As an anode material, aluminum or tantalum is preferred since the dielectric constant of a dielectrics acquired by anodization is high with high electrical insulation.

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 in which a solid electrolyte layer made of a conductive polymer is formed on a dielectric film, and in particular, has a large capacitance and a small impedance in a high frequency region. The present invention relates to an improvement of the solid electrolyte layer for the purpose of providing a solid electrolytic capacitor.

[0002]

2. Description of the Related Art In recent years,
2. Description of the Related Art As electronic devices have become smaller and lighter, there has been an increasing demand for small-sized and large-capacity capacitors having low impedance in a high frequency region.

Conventionally, capacitors used in a high frequency region include a plastic capacitor, a mica capacitor, a multilayer ceramic capacitor, and the like. However, all of these capacitors are large and it is difficult to increase the capacitance.

As a large-capacity capacitor, an electrolytic capacitor is well known. Examples of the electrolytic capacitor include an electrolytic capacitor using an electrolytic solution (such as an aluminum electrolytic capacitor) and a solid electrolytic capacitor using manganese dioxide (such as an aluminum solid electrolytic capacitor and a tantalum solid electrolytic capacitor).

However, the above electrolytic capacitors have a large impedance in a high frequency region because the electrolytic solution or the solid electrolyte has a large electric resistance.

Recently, as a solid electrolyte in place of the manganese dioxide, pyrrole, polypyrrole heterocyclic monomers thiophene, etc. obtained by electrolytic polymerization, a polymer such as polythiophene, BF ₄ ^- (tetrafluoroborate ion) or ClO ₄ ^-
A conductive polymer doped with (perchlorate ion) has been proposed (see JP-A-60-37114).

However, a conductive polymer using the above-mentioned halogen-based anion as a dopant easily deteriorates a dielectric film. In addition, the thermal stability is low and the conductivity is liable to be reduced due to easy undoping. Particularly when the electrode is heated to a high temperature of about 200 ° C., undoping is easy.

[0008] Such deterioration of the dielectric film and decrease in the conductivity of the conductive polymer increase the leakage current of the capacitor, which causes a decrease in capacitance and an increase in impedance.

As a conductive polymer which has solved the above-mentioned drawbacks, there has been proposed a polymer using an arylsulfonic acid ion such as dodecylbenzenesulfonic acid ion or naphthalenesulfonic acid ion as a dopant (Japanese Patent Application Laid-Open No. Sho 64).
-49211).

However, a conductive polymer using an aryl sulfonate ion as a dopant has a small electrical resistance as compared with a conductive polymer using BF ₄ ^- and ClO ₄ ^- as a dopant, but is still considerably large. Even when used as a solid electrolyte, it is difficult to obtain a solid electrolytic capacitor having a small impedance in a high frequency region.

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a solid electrolytic capacitor having a large capacity and a small impedance in a high frequency region.

[0012]

According to the present invention, there is provided a solid electrolytic capacitor (the capacitor of the present invention) comprising: an anode; a dielectric film formed on the anode by anodic oxidation; A solid electrolyte layer formed on the dielectric film, comprising a conductive polymer obtained by doping dodecylbenzenesulfonate ion and sulfate ion into a polymer having a unit as a repeating unit; and bonding to the solid electrolyte layer And a cathode.

[0013]

Embedded image

Wherein R ¹ and R ² are each independently an alkyl group or H, and X is S or NR ³ (provided that R ³
Is an alkyl group or H. ). ]

The solid electrolyte layer was formed by electrolytic polymerization using an aqueous solution containing a heterocyclic monomer such as pyrrole or thiophene and an ionic dopant such as dodecylbenzenesulfonate ion as an electrolytic polymerization solution. Are preferred because they allow the dopant to be uniformly doped into the polymer.

As the conductive polymer, a polymer obtained by doping a dopant at a ratio of one to every two to five heterocyclic monomer units represented by Chemical Formula 2 is preferable. When the sulfate ion and the dodecylbenzenesulfonate ion are doped by electrolytic polymerization, the molar ratio of both ions is not particularly limited.
0: 1 to 0.1: 10 is preferred. Experiments have shown that sulfate ions cannot be doped in excess of the upper molar ratio of 10: 1. On the other hand, it is possible to dope the sulfate ion with a lower molar ratio of less than 0.1: 10, but this is not preferable because it causes an increase in impedance in a high frequency region.

As the anode material, aluminum or tantalum is preferable because the dielectric obtained by anodic oxidation has a high dielectric constant and a high electric insulation. Since the dielectric film is formed by anodic oxidation, when the anode material is aluminum or tantalum, the dielectric film is formed of aluminum or tantalum oxide.

In the conductive polymer used in the capacitor of the present invention, the dopant is not a halogen-based anion such as BF ₄ ⁻ and ClO ₄ ⁻ but a non-halogen-based anion.
It is difficult to deteriorate the dielectric film. In addition, dodecylbenzenesulfonate ions and sulfate ions have higher thermal stability than BF ₄ ⁻ and ClO ₄ ⁻ even when exposed to high temperatures such as when attaching electrodes, and are hard to be undoped. The conductivity of the polymer is not easily reduced. For this reason, the capacitor of the present invention has a small leakage current and has a small deterioration in characteristics even when exposed to high temperatures. Furthermore, the electric resistance of the conductive polymer in which dodecylbenzenesulfonate ion and sulfate ion coexist as dopants is smaller than that of the conductive polymer in which dodecylbenzenesulfonate ion alone is used as a dopant. As compared with the solid electrolytic capacitor disclosed in Japanese Patent Application Laid-Open No. 64-49211, the impedance in a high frequency region is small and the frequency characteristics are excellent.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

Example 1 A porous tantalum sintered body was anodized to form a dielectric film of tantalum oxide on the surface. Next, a tantalum sintered body having a dielectric film formed on the surface thereof was subjected to hydrogen peroxide (oxidizing agent) 20% by weight, sulfuric acid 1
Immersed in a 30% by weight aqueous solution for 30 minutes, taken out, dried at room temperature for 5 minutes, exposed to pyrrole vapor for 30 minutes,
A polypyrrole film (gas phase polymerized film) was formed on the dielectric film. The polypyrrole film is doped with sulfate ions, thereby imparting conductivity to the polypyrrole film. Next, a tantalum sintered body having a polypyrrole film formed on the dielectric film was subjected to electrolytic polymerization (pyrrole 0.2
M, sodium dodecylbenzenesulfonate 0.06M
And a sulfuric acid 0.0003M aqueous solution), and a stainless steel lead (anode) is attached to the polypyrrole film.
Electrolytic polymerization (electrolytic oxidation polymerization) was performed at a constant current to form a solid electrolyte layer made of a conductive polymer obtained by doping polypyrrole with dodecylbenzenesulfonate ions and sulfate ions on the polypyrrole film. Note that a stainless steel electrode was also used as a counter electrode (cathode). Next, the tantalum sintered body having the solid electrolyte layer formed on the polypyrrole film is washed with water and dried, and then a carbon paste and a silver paste are applied in this order on the solid electrolyte layer, and an aluminum cathode is applied to the silver paste. Attach the terminal, attach the aluminum anode terminal to the terminal attachment part (bare part) of the tantalum sintered body, and further cover the capacitor body with epoxy resin except the electric energy extraction part of the cathode terminal and anode terminal, A solid electrolytic capacitor A1 (the capacitor of the present invention) was produced.

FIG. 1 is a sectional view schematically showing the solid electrolytic capacitor A1 manufactured here (hatching is omitted). The illustrated solid electrolytic capacitor A1 includes an anode (sintered tantalum) 1, a dielectric film (tantalum oxide) 2, a solid electrolyte layer 3, a carbon paste layer 4, a silver paste layer 5, a silver paste layer 6, an exterior resin (epoxy). Resin) 7, anode terminal 8,
It comprises a cathode terminal 9 and the like. The surface of the anode 1 is roughened by electrolytic polishing, and the dielectric film 2 is formed on the roughened surface by anodic oxidation. A solid electrolyte layer 3 is formed on the dielectric film 2 by electrolytic polymerization, and a cathode composed of a carbon paste layer 4, a silver paste layer 5, and a silver paste layer 6 is joined to the solid electrolyte layer 3. . The anode 1 has an anode terminal 8 and a silver paste layer 6.
Are connected to a cathode terminal 9, respectively, from which electric energy stored in the solid electrolytic capacitor A1 by charging can be extracted to the outside. With the anode terminal 8 and the cathode terminal 9 partially exposed, the entire body of the solid electrolytic capacitor A1
It is exterior.

(Example 2) As an electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A solid electrolytic capacitor was prepared in the same manner as in Example 1 except that an aqueous solution of pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.06M and nickel sulfate 0.003M was used instead of the aqueous solution of 06M and sulfuric acid 0.0003M. A2 (the capacitor of the present invention) was produced.

(Example 3) As an electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A solid electrolytic capacitor was prepared in the same manner as in Example 1 except that an aqueous solution of 0.2M pyrrole, 0.06M of sodium dodecylbenzenesulfonate and 0.003M of zinc sulfate was used instead of the aqueous solution of 06M and 0.0003M of sulfuric acid. A3 (the capacitor of the present invention) was produced.

Example 4 As an electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
Instead of an aqueous solution of 0.6M and sulfuric acid of 0.0003M, N-
A solid electrolytic capacitor A4 (the capacitor of the present invention) was produced in the same manner as in Example 1, except that an aqueous solution of methylpyrrole 0.2M, sodium dodecylbenzenesulfonate 0.06M and sulfuric acid 0.0003M was used.

(Example 5) As an electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A solid electrolytic capacitor A5 was prepared in the same manner as in Example 1 except that an aqueous solution of thiophene 0.2M, sodium dodecylbenzenesulfonate 0.06M and sulfuric acid 0.0003M was used instead of the aqueous solution of 06M and sulfuric acid 0.0003M. (A capacitor of the present invention) was produced.

(Example 6) As the electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
Instead of an aqueous solution of 0.6M and sulfuric acid of 0.0003M, N-
A solid electrolytic capacitor A6 (the capacitor of the present invention) was produced in the same manner as in Example 1, except that an aqueous solution of methylthiophene 0.2M, sodium dodecylbenzenesulfonate 0.06M and sulfuric acid 0.0003M was used.

(Comparative Example 1) As the electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A comparative capacitor B1 was produced in the same manner as in Example 1 except that an aqueous solution of pyrrole 0.2M and sodium borofluoride 0.06M was used instead of the aqueous solution of 06M and sulfuric acid 0.0003M.

(Comparative Example 2) As the electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A comparative capacitor B2 was produced in the same manner as in Example 1 except that an aqueous solution of pyrrole 0.2M and sodium perchlorate 0.06M was used instead of the aqueous solution of 06M and sulfuric acid 0.0003M.

(Comparative Example 3) As an electrolytic polymerization solution, pyrrole 0.2M, sodium dodecylbenzenesulfonate 0.1M were used.
A comparative capacitor B3 was produced in the same manner as in Example 1 except that an aqueous solution of pyrrole 0.2M and sodium dodecylbenzenesulfonate 0.06M was used instead of the aqueous solution of 06M and sulfuric acid 0.0003M.

(Comparative Example 4) As an electrolytic polymerization solution, instead of an aqueous solution of pyrrole 0.2M, sodium dodecylsulfonate 0.06M and sulfuric acid 0.0003M, pyrrole 0.1% was used.
2M and sodium butylnaphthalenesulfonate 0.0
A comparative capacitor B4 was produced in the same manner as in Example 1 except that a 6M aqueous solution was used.

The compositions of the electrolytic polymerization solutions used in Examples 1 to 6 and Comparative Examples 1 to 4 are summarized in Table 1.

[0032]

[Table 1]

[Capacity after Aging, Capacitance Reduction Rate and Impedance] The capacitances of the capacitors A1 to A6 of the present invention and the comparative capacitors B1 to B4 at 120 Hz were measured and then kept at 200 ° C. for 3 hours. After aging, the capacitance at 120 Hz and the impedance at 100 kHz were measured. Table 2 shows the capacitance of each capacitor at 120 Hz after aging, the capacitance reduction rate defined by the following equation (1), and the impedance at 100 kHz after aging.

Capacity reduction rate (%) = {(C1−C2) / C1} × 100 (1) [C1: capacitance at 120 Hz before aging, C
2: capacitance at 120 Hz after aging]

[0035]

[Table 2]

As shown in Table 2, the capacitor A1 of the present invention
A6 to A6 have a larger capacitance, a smaller capacity reduction rate, and a smaller impedance than the comparison capacitors B1 to B4.

In the first to sixth embodiments, tantalum is used as the anode material. However, even when aluminum is used as the anode material, a solid electrolytic capacitor having a large capacity and a small impedance in a high frequency region can be obtained. Is possible.

In the above Examples 1 to 6, sodium dodecylbenzenesulfonate was used. However, metal salts other than sodium salts may be used, and ammonium salts (quaternary ammonium salts) may be used instead of metal salts. Etc.) may be used.

In the above Examples 1 to 6, water was used as the solvent for the electrolytic polymerization solution. However, any solvent can be used without particular limitation as long as it can dissolve the heterocyclic monomer and the dopant.

[0040]

According to the present invention, there is provided a solid electrolytic capacitor having a large capacitance and a low impedance in a high frequency region.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a solid electrolytic capacitor manufactured in an example.

[Explanation of symbols]

 A1 Solid electrolytic capacitor 1 Anode 2 Dielectric film 3 Solid electrolyte layer 4 Carbon paste layer 5 Silver paste layer 6 Silver paste layer 7 Outer resin 8 Anode terminal 9 Cathode terminal

Claims (2)

[Claims] 1. A solid electrolyte comprising an anode, a dielectric film formed on the anode by anodic oxidation, a solid electrolyte layer formed on the dielectric film, and a cathode bonded to the solid electrolyte layer. In the capacitor, the solid electrolyte layer is made of a conductive polymer obtained by doping dodecylbenzenesulfonate ion and sulfate ion into a polymer having a heterocyclic monomer unit represented by Chemical Formula 1 as a repeating unit. And a solid electrolytic capacitor. Embedded image Wherein R ¹ and R ² are each independently an alkyl group or H
And X is S or NR ³ (where R ³ is an alkyl group or H). ] 2. The solid electrolytic capacitor according to claim 1, wherein said anode and said cathode are made of aluminum or tantalum.