JPH05136007A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PURPOSE:To make the performance and stability of solid electrolytic capacitors higher by using meltable conductive polymer in the case of their manufacture. CONSTITUTION:A solid electrolyte layer 3 having high conductivity and high stability is formed on a dielectric oxide film 2 using, as a solid electrolyte, meltable polymer whose number average molecular weight is controlled to be 50,000 or less by fractionation.

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 having a conductive polymer as a part of an electrode, and particularly to a high capacity, frequency characteristic and heat resistance having a conductive polymer having a controlled molecular weight as a part of the electrode. The present invention relates to an excellent solid electrolytic capacitor and a manufacturing method thereof.

[0002]

2. Description of the Related Art With the progress of electronics, miniaturization and weight saving of devices are required, and miniaturization and chipping of capacitors are also required, and low impedance in a high frequency region, large capacity, etc. Expectations for improved performance are increasing. Conventionally, in solid electrolytic capacitors, an oxide film of a film-forming metal such as tantalum or aluminum is used as a dielectric, and manganese dioxide or 7,7 ′, 8,8′-tetracyanoquinodimethane (TCNQ) complex salt is used as an electrode. Some have been developed, but those with manganese dioxide as part of the electrode have a low conductivity, so the impedance in the high frequency range is large, and those with the TCNQ complex as part of the electrode. However, since the TCNQ complex salt melted, it was insulated in the solder bath and could not be used at high temperature. on the other hand,
Aromatic conductive polymers such as polypyrrole were developed,
It is known that it has higher conductivity and higher heat resistance than manganese dioxide. For example, Japanese Examined Patent Publication No. 60-37114 discloses a solid electrolytic capacitor using a doped five-membered heterocyclic compound polymer as a solid electrolyte. Also,
Japanese Unexamined Patent Publication No. 60-244017 discloses a method for producing a solid electrolytic capacitor in which a polymer of a heterocyclic compound is formed by electrolytic oxidation. However, in principle, electrolytic polymerization on the surface of the dielectric, which is an insulator, cannot be performed. As a method of forming a conductive polymer as a solid electrolyte, Japanese Patent Laid-Open No. 63-80517 discloses a conductive polymer solution containing a repeating five-membered heterocyclic compound, which is made soluble by introducing a substituent. It is disclosed that a solid polymer layer is formed by applying and drying to form a conductive polymer layer on the dielectric film and then vapor-doping. However, since it is difficult for the dielectric oxide film to penetrate sufficiently to the inside only by applying the conductive polymer solution to the expanded metal surface, it is necessary to devise it by impregnating it under reduced pressure.

[0003]

As described above, in the solid electrolytic capacitor having the conductive polymer as a part of the electrode, the conductive polymer has high conductivity and excellent heat resistance. Although it is expected that good characteristics will be exhibited, development has been insufficient, and therefore good characteristics have not been obtained. An object of the present invention is to develop a solid electrolytic capacitor which has a conductive polymer as a part of an electrode and has a high capacity and excellent frequency characteristics and heat resistance.

[0004]

That is, according to the present invention, an oxide film layer formed on the surface of a film-forming metal is used as a dielectric,
A solid electrolytic capacitor having a conductive polymer as a part of an electrode, wherein the conductive polymer is controlled to have a number average molecular weight of 50,000 or less. Further, the manufacturing method is to introduce a solution of a soluble conductive polymer having a number average molecular weight of 50,000 or less and a dopant into a dielectric surface composed of an oxide film layer formed on the surface of a film-forming metal and removing the solvent. To form a solid electrolyte layer.

The solid electrolytic capacitor of the present invention comprises an anode made of a film-forming metal, its dielectric oxide film layer, and a conductive sheet.
It consists of a strike layer. The film-forming metal of the present invention includes aluminum, tantalum, titanium, niobium, zirconium,
It is a metal having a valve action such as magnesium, zinc, bismuth, silicon and hafnium. The type of the conductive polymer in which the number average molecular weight which is a part of the electrode of the solid electrolytic capacitor of the present invention is controlled to 50,000 or less is not particularly limited, but a solvent-soluble one is preferable from the viewpoint of easy control of the molecular weight. In particular, the following formula (1):

[Chemical 2] [In the formula (I), R ¹ and R ² are a hydrogen atom, an alkyl group,
Alkoxyl group or aryl group (R ¹ and R ² may form a cyclic structure), X is —O—, —S—, or NR.
³ (R ³ is a hydrogen atom, an alkyl group, an aryl group or an alkylaryl group). ] A polymer or copolymer containing at least one repeating unit of the monomer represented by

The method of synthesizing the electroconductive polymer used in the present invention is not particularly limited, and it is possible to synthesize the electroconductive polymer by a conventionally known chemical oxidative polymerization, electrochemical polymerization or the like. In the present invention, the conductive polymer thus obtained is used as it is or after adjusting the molecular weight if necessary, as a part of the electrode of the solid electrolytic capacitor. Examples of the method for controlling the molecular weight include, but are not limited to, ultrafiltration and reprecipitation. Further, the number average molecular weight of the present invention is 50,000.
A conductive polymer controlled to be 0 or less means that the number average molecular weight measured by gel permeation chromatography (hereinafter referred to as GPC) is 50,000 or less in terms of polystyrene, and up to 5%. Even if a small amount of a component having a number average molecular weight of 50,000 or more is contained, the substantial effect does not change. In the present invention, since the number average molecular weight of the conductive polymer is controlled to 50,000 or less, the conductive polymer is uniformly and closely adhered to the expanded dielectric surface of the solid electrolytic capacitor to form the conductive polymer. It can be formed as part of the electrode. As a result, a high capacity solid electrolytic capacitor is obtained.

The electroconductive polymer of the present invention is used by being doped with an electron-withdrawing or electron-donating dopant, but the present invention is not particularly limited by the type of dopant.
Known halogens such as iodine, bromine and bromine iodide, iron trichloride, arsenic pentafluoride, antimony pentafluoride, silicon tetrafluoride, phosphorus pentachloride, phosphorus pentafluoride, which are conventionally known as dopants for conductive polymers. Lewis acids such as aluminum chloride and molybdenum chloride, protic acids such as sulfuric acid and nitric acid, benzene sulfonates such as sodium benzenesulfonate and sodium p-toluenesulfonate, and their derivatives can be used.

The method of forming the solid electrolyte layer in the method of the present invention is not particularly limited, and after the soluble conductive polymer solution is applied to the surface of the dielectric formed of the oxide film layer of the film-forming metal, it is contacted with the dopant. And a method of forming a solid electrolyte, or a method of dip-coating a pellet in a mixed solution of a soluble conductive polymer solution and a dopant solution, and particularly a number-average molecular weight of 50,000 or less A method of introducing a solution of a conductive polymer and a dopant and removing the solvent is preferable. In this case, the concentrations and proportions of the soluble conductive polymer and the dopant are not particularly limited, and the method of introducing these solutions is also not limited. The solvent is
It can dissolve or disperse conductive polymers and dopants depending on the type, for example, chlorine-based solvents such as chloroform and dichloromethane, ether-based solvents such as tetrahydrofuran, hexane, benzene, toluene, etc. The hydrocarbon-based solvent and the like. The solid electrolytic capacitor of the present invention, after forming a conductive polymer as a part of the electrode, apply a conductive paste, take out the electrode,
If necessary, carry out molding. As the conductive paste, ordinary silver paste and carbon paste can be used alone or in combination.

[0009]

In the present invention, a soluble conductive polymer layer whose number average molecular weight is controlled to 50,000 or less is used as a solid electrolyte on a metal foil having a valve action, which has a dielectric oxide film formed by chemical conversion treatment. High performance and high stability of electrolytic capacitors are possible.

[0010]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 33 g of iron trichloride (FeCl ₃ ) dried at 100 ° C. under reduced pressure for 1 hour was put in 200 ml of chloroform, 10 g of 3-octylthiophene was slowly added dropwise thereto with stirring, and the mixture was stirred at room temperature for 2 hours. did. When the reaction solution was added to 2000 ml of methanol, a precipitate insoluble in methanol was obtained. This was suction filtered to obtain a crude polymer. Excess FeCl ₃ was removed from this using Soxhlet extractor with methanol and acetone, followed by extraction with chloroform, and then the solvent was distilled off to remove solvent-soluble poly (3-octylthiophene) [hereinafter, It is called P3OT. ] Was obtained. The molecular weight of the P3OT sample determined by GPC measurement is polystyrene equivalent (the same applies hereinafter), the number average molecular weight (Mn) is 13,000, and the weight average molecular weight (Mw).
Was 40,000. 1.0 g of the above P3OT sample
Was dissolved in 50 ml of chloroform, and 10 ml of methanol was slowly added dropwise with vigorous stirring. After vigorously stirring for about 1 hour, two types of P3O separated by filtering off the high molecular weight precipitate and distilling off the filtrate
I got T. Let P3OT of the precipitate be P3OT-5. The filtrate was fractionated by the same operation as described above, changing the amount of methanol added to 15 ml, 20 ml, and 25 ml. As a result, five types of P3OT (P3OT-1, P3OT
3OT-2, P3OT-3, P3OT-4, P3OT-
5) was obtained.

Next, a solid electrolytic capacitor as shown in FIG. 1 was produced using the conductive polymer obtained above.
The manufacturing method will be described below with reference to FIG. The surface was expanded by etching (32μAngstrom / c
m ² ) An aluminum foil to be the anode 1 having a film thickness of 70 μm and an area of 1 cm × 1.2 cm (weld margin 0.2 cm: effective area 1 cm ² ) was formed by oxidation at 40 V in a 10% ammonium adipate aqueous solution at 60 ° C. The film 2 was formed, and then the lead terminals were welded to produce aluminum pellets.
The pellet was dipped and dried in a 1.5 ml chloroform solution of 0.035 g (0.18 mmol) of P3OT-1 several times to form a thin film layer. Further, this anode foil is impregnated with a nitromethane solution of FeCl ₃ for 30 minutes and is doped to form a solid electrolyte layer 3, and a graphite layer 4 and a silver paste layer 5 are formed on the surface of the solid electrolyte layer 3. After forming, the cathode 6 was taken out and molded to prepare a capacitor. P3OT
-2 and P3OT-3 were similarly prepared as capacitors. Various characteristics of these capacitors were measured.

Example 2 The same operation as in Example 1 was carried out except that 3-hexylthiophene was used in place of 3-octylthiophene in Example 1, and 10 ml and 15 ml of methanol were used for separation to obtain 3 types. Solvent-soluble poly (3-hexylthiophene)
(P3HT-1, P3HT-2, P3HT-3) was obtained. The capacitor characteristics were also measured in the same manner as P3OT.

Example 3 0.02 g of P3OT in 1 ml of chloroform and F
A mixed solution of 0.074 g of eCl ₃ and 1 ml of a chloroform solution was prepared, and the aluminum pellets of Example 1 were dipped and dried several times to form a solid electrolyte layer. A conductive paste was applied and molded to prepare a capacitor. The capacitor characteristics were good as in Example 1.

Comparative Example 1 Instead of P3OT-1 of Example 1, a number average molecular weight of 52,
000 P3OT-4, 90,000 P3OT-5,
The same operation as in Example 1 was performed except that P3HT-3 of 80,000 and 80,000 was used to prepare a capacitor, and various characteristics were measured. Table 1 shows the results of Examples 1 and 2 and Comparative Example 1.
As shown in Table 1, a high coverage of 85% or more was obtained at a number average molecular weight of 50,000 or less.

[0015]

[Table 1]

[0016]

As described above, according to the present invention,
By using a conductive polymer controlled to have a number average molecular weight of 50,000 or less as a part of the electrode, it is possible to manufacture a solid electrolytic capacitor having high capacity and excellent frequency characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a solid electrolytic capacitor according to the present invention.

[Explanation of symbols]

1 Anode 2 Dielectric oxide film 3 Solid electrolyte layer 4 Graphite layer 5 Silver paste layer 6 Cathode

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeyoshi Suzuki 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation

Claims (3)

[Claims] 1. A solid electrolytic capacitor having an oxide film layer formed on the surface of a film-forming metal as a dielectric and a conductive polymer as a part of an electrode, wherein the conductive polymer has a number average molecular weight of 50,000 or less. A solid electrolytic capacitor characterized by being controlled to. 2. The conductive polymer has the following general formula: [In the formula, R ¹ and R ² are a hydrogen atom, an alkyl group, an alkoxyl group or an aryl group (R ¹ and R ² may form a cyclic structure), X is —O—, —S—, Or NR ³ (R ³
Represents a hydrogen atom, an alkyl group, an aryl group or an alkylaryl group). ] The solid electrolytic capacitor according to claim 1, which is a polymer containing at least one type of repeating unit represented by the following formula. 3. A solution of a soluble conductive polymer having a number average molecular weight of 50,000 or less and a dopant is introduced to the surface of a dielectric formed of an oxide film layer formed on the surface of a film-forming metal, and the solvent is removed. A method for manufacturing a solid electrolytic capacitor, which comprises forming a solid electrolyte layer by means of the method.