JPH0722077B2 - Solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a conductive polymer compound obtained by doping a polymer compound having a repeating unit represented by the general formula (I) with a dopant as a solid electrolyte. The present invention relates to a solid electrolytic capacitor.

[Prior Art] A solid electrolytic capacitor has a structure in which a solid electrolyte is attached to a film-forming metal such as aluminum or tantalum having an anodized film.

Manganese dioxide formed by thermal decomposition of manganese nitrate is mainly used as a solid electrolyte of a conventional solid electrolytic capacitor of this type. However, due to the high heat required for the thermal decomposition of manganese nitrate and the oxidizing action of the generated NO _x gas, the metal oxide film of aluminum, tantalum, etc., which is a dielectric, is damaged, and as a result, the withstand voltage of the solid electrolytic capacitor is reduced. Has a very large defect such as a decrease in leakage current, an increase in leakage current, and deterioration of dielectric characteristics.

In order to compensate for these drawbacks, a method of forming a solid electrolyte layer without applying high heat, that is, a method of using a highly conductive organic semiconductor material as a solid electrolyte has been attempted.

As an example thereof, a solid having a conductive high polymer composition containing a 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex salt described in JP-A-52-79255 as a solid electrolyte is used. There is known an electrolytic capacitor, a solid electrolytic capacitor described in JP-A-58-17609, which uses a complex salt of Nn-propylisoquinoline and TCNQ as a solid electrolyte.

However, these TCNQ complex salt compounds are inferior in adhesion to the anodized film even if various measures are taken as described above, and the electric conductivity of TCNQ itself is insufficient as 10 ⁻³ to 10 ⁻² S · cm ^−1. Therefore, the capacitance value of the capacitor is small and the dielectric loss is large. Further, the thermal stability over time was poor and the reliability was poor.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned conventional drawbacks.
It is an object of the present invention to provide a solid electrolytic capacitor which uses a conductive polymer compound having high conductivity and good adhesion to a dielectric film as a solid electrolyte.

[Means for Solving the Problems] The present invention has the general formula The present invention relates to a solid electrolytic capacitor, wherein a conductive polymer compound obtained by doping a polymer compound having a repeating unit represented by the above with a dopant is used as a solid electrolyte.

Typical examples of these polymer compounds include polythiophene and polyfuran.

The method for producing these polymer compounds is not particularly limited, but for polythiophene, for example, J. Polym.
-Sci.Polyn.Lett.Ed., 18, 9 (1980); J. Electroanal.che
m., 135 , 173 (1982) Makromol.chem., Rapid common.2,55
1 (1981), for polyfranc J. Electroanal.che
m., 135 , 173 (1982) and the like.

In the present invention, the polythiophene may be a polymer of a thiophene compound such as thiophene or 3-methylthiophene, or a copolymer or mixture thereof. The polyfuran may be a polymer of furan compound such as furan or 3-methylfuran, or a copolymer or mixture thereof.

In addition, I ₂ and B as dopants are added to these polymer compounds.
By doping using chemical methods to _{r 2, SO 3, AsF 5} , SbF electron acceptor, such as _5, or BF ₄ as a dopant ^{_{-, ClO 4 -, PF 6}} -, ASF 6 - anions such as Electrical conductivity of 10 ^-1 was obtained by doping using an electrochemical method.
It can be increased to ~ 10 ² S · cm ^-1 .

In the present invention, the term "dopant" refers to an electron acceptor and an electron donor additive such as an anion, which are added in a small amount in order to impart conductivity to the polymer compound having the repeating unit represented by the general formula (I). Further, the dopants described in JP-A-58-54553 and JP-A-58-54554 filed by the applicant of the present application can also be appropriately used.

The dope or doping is addition of the above-mentioned dopant to the polymer compound having the repeating unit represented by the above-mentioned general formula, and as a result, the electric conductivity of the conjugated polymer compound is dramatically increased. It is a thing.

The addition of the dopant may be performed by a chemical method after once producing the polymer, or may be performed by using the dopant as an auxiliary electrolyte in the electrolytic polymerization and performing the doping simultaneously with the polymerization.

The outline of the solid electrolytic capacitor to which the present invention is applied is shown in FIG.

A metal sintered body 1 having a valve action, such as tantalum or aluminum, has a surface covered with an oxide film (dielectric layer) 2, and the dielectric layer is covered with a doped conductive polymer compound 3. (In the drawing, the voids formed by the valve metal particles of the sintered body are not shown, but most of the sintered body surface is formed by interparticle voids,
It goes without saying that the oxide film and the conductive polymer compound also exist in the interparticle voids. ). The cathode is taken out by surrounding it with the conductive paste 4, put in a case, and the cathode 7 taken out from the sintered metal body 1 is sealed with a sealing resin 8 to form a solid electrolytic capacitor.

As the metal having a valve action used for the anode, a metal having a valve action such as aluminum, tantalum, niobium, titanium, or an alloy having these metals as a substrate can be used.

The anode is not particularly limited in shape, and may be a porous sintered body of these metals, a plate (including ribbon, foil, etc.) surface-treated by etching or the like, a wire, or the like.

The oxide derivative layer on the surface of the anode substrate is an oxide of the anode substrate itself, and apparently covers the surface of the anode substrate (including the inside of the sintered body).

As a method of providing these oxide dielectric layers, a conventionally known method can be used.

For example, when an aluminum foil is used, the surface of the aluminum foil is electrochemically etched and further electrochemically treated in an aqueous solution of boric acid and ammonium borate. It is possible to form an oxide dielectric layer consisting of

When a sintered body of tantalum powder is used, an oxide film can be formed on the sintered body by anodizing in a phosphoric acid aqueous solution, for example.

The anode lead wire is connected to the anode valve metal substrate before and after forming the oxide dielectric layer.

After providing the oxide dielectric layer on the surface of the anode valve metal substrate in this way, an excellent solid electrolytic capacitor is manufactured by depositing a conductive polymer compound doped as a solid electrolyte on the oxide dielectric layer. The inventors have found that they can be achieved and completed the present invention.

[Operation] The larger the surface area of the pole, the larger the capacitance of the capacitor. It is also natural that the gap between the electrodes must be insulated. Therefore, it is also well known that in a sintered electrolytic capacitor, a surface area is secured by sintering fine powder, and a valve metal is used to oxidize the surface to provide an insulator (dielectric layer). Is. A solid electrolyte is provided on the oxide dielectric layer as the other electrode to form an electrolytic capacitor.

On the other hand, the polymer compound having a repeating unit represented by the general formula (I) is obtained by subjecting a raw material monomer solution containing an auxiliary electrolyte (which can also be used as a dopant) to oxidative electrolysis to obtain a conductive polymer compound doped in the positive electrode. It is known to precipitate.

However, it is known only to deposit on a positive electrode made of a metal plate such as platinum, and an oxide dielectric layer (electrical insulator) provided on a metal surface for manufacturing a solid electrolytic capacitor. It was not known to deposit on top.

In the present invention, although the reason could not be clarified, the conductive polymer compound deposited on the oxide dielectric layer was surprisingly excellent in adhesion and coverage to the valve metal oxide film. It is also clear from the performance of the obtained solid electrolytic capacitor that the solid oxide well covers the oxide dielectric layer.

Therefore, the solid electrolytic capacitor obtained by the present invention has remarkably excellent performances in capacity, dielectric loss, and stability over time, as compared with the conventional solid electrolytic capacitors using inorganic oxide semiconductors and organic semiconductors.

[Examples] Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 A Ta powder sintered body is anodized in a phosphoric acid aqueous solution to form a dielectric film, washed and dried, and then the Ta element is immersed in a polythiophene-chloroform solution and dried. This operation of dipping and drying is repeated to form a polymer compound layer made of polythiophene on the dielectric layer, and then AsF ₅ gas is contacted to dope AsF ₅ to form an electrolyte layer made of a conductive polymer compound. . Then, the silver paste was used to take out the cathode and put it in a case to seal the resin to prepare a solid electrolytic capacitor.

Separately, a polythiophene film prepared under the same conditions was used as AsF ₅
The conductivity when doped with is 10.sup.- ¹ S.cm.sup.- ¹ .

(Example 2) A sintered body of Ta powder is anodized in a phosphoric acid aqueous solution to form a dielectric film, and then the Ta element is used as a positive electrode and platinum is used as a negative electrode, and a thiophene monomer of 0.01 M is added to an electrolytic solution. Dissolved
0.1 M Bu ₄ NBF ₄ performs electrolytic polymerization using -CH ₃ CN, BF ₄ on Ta element which is coated with a dielectric film ^- forming an electrolyte layer of doped polythiophene to prepare a solid electrolytic capacitor .

Under the same conditions, a polythiophene film doped with BF ₄ ⁻ was prepared on a platinum plate, and the conductivity was 10 ² S · cm ⁻¹ when measured by peeling off the film.

(Example 3) In Example 2, a furan monomer was used instead of the thiophene monomer to form an electrolyte layer, and a solid electrolytic capacitor was produced in the same manner.

BF ₄ was separately prepared ^- is the conductivity of the polyfuranes doped with 10
It was S · cm ⁻¹ .

(Example 4) In Example 2, instead of the thiophene monomer, 3-
An electrolyte layer was formed using methylthiophene, and a solid electrolytic capacitor was similarly prepared.

The conductivity of the separately prepared BF ₄ ⁻ -doped poly-3-methylthiophene was 0.8 S · cm ⁻¹ .

(Comparative Example 1) A solid electrolytic capacitor using the conventional manganese dioxide as an electrolyte, which uses the same anodized Ta element as in Example 1, was produced.

Table 1 shows the characteristics of the solid electrolytic capacitors produced in Examples 1 to 4 and Comparative Example 1.

As is clear from Table 1, the solid electrolytic capacitor using the conductive polymer compound doped with the dopant according to the present invention as an electrolyte has a dielectric loss (tan δ) higher than that of a conventional solid electrolytic capacitor using manganese dioxide as an electrolyte. A solid electrolytic capacitor having a small leakage current, a high rated voltage, and a high withstand voltage can be manufactured.

Further, the value of capacity × rated voltage of the solid electrolytic capacitor according to the present invention is larger than that of the solid electrolytic capacitor using manganese dioxide, and a large capacity can be obtained with the same shape.

(Example 5) With the same material and method as in Example 1, a conductor layer was formed in the order of a carbon paste and a silver paste on an element in which a solid electrolyte layer was formed. A solid electrolytic capacitor was prepared by sealing.

This capacitor has a capacity of 1.00μF, tanδ1.00%, ESR100
The value was 0.23Ω at KHz, the rated voltage was 50V, and the leakage current was 50n, less than 10nA.

(Comparative Example 2) Ta device anodized with an NN-dimethylformamide solution containing N-methylacridinium-TCNQ complex salt and poly-2-vinylpyridine in a weight ratio of 85:15 as an electrolyte solution Was repeatedly dipped and dried to form an electrolyte layer. A silver paste was immediately attached to this product without attaching graphite, dried, placed in a case, and sealed with a resin to prepare a solid electrolytic capacitor.

This capacitor has a capacity of 1.1μF, tanδ1.1%, ESR100K
It was 1.32Ω at Hz and 10nA or less at a leak current of 50V.

As is clear from the above Examples and Comparative Examples, when the conductive polymer compound obtained by doping the solid electrolyte layer with the polymer compound having the repeating unit represented by the general formula (I) with a dopant is used, The performance of the solid electrolytic capacitor is almost the same regardless of whether the conductor layer is a silver paste or a carbon paste or a silver paste. However, the solid electrolyte layer may be replaced with N-methylacridinium-TCNQ complex salt and poly-2. -When replacing with vinyl pyridine, it is clear that the performance as a solid electrolytic capacitor is deteriorated even if all other configurations are the same.

In the above embodiments, the metal of the element was the tantalum sintered body, but other metals such as aluminum and niobium may be used, and the shape is not limited to the powder sintered body.

[Effects of the Invention] In a solid electrolytic capacitor, the following effects can be obtained by using a conductive polymer compound obtained by doping a polymer compound having a repeating unit represented by the general formula (I) with a dopant as a solid electrolyte. To be

Since the electrolyte layer can be formed without heating at a high temperature, the oxide film on the anode is less damaged. Therefore, the rated voltage can be made several times higher than the conventional one, and the size can be reduced to obtain a capacitor having the same capacity and the same rated voltage.

Small leakage current.

Capacitors with high withstand voltage can be manufactured.

Since the electric conductivity of the electrolyte is sufficiently high as 10 ^-1 to 10 ² S · cm ^-1 , it is not necessary to provide a conductive layer such as graphite and the process is simplified.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a solid electrolytic capacitor according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Sintered metal such as Ta and Al 2 ... Oxide film 3 ... Conductive polymer compound 4 ... Conductive paste 5 ... Solder 6 ... Case and cathode, 7 ... Anode 8 ... Sealing resin

Claims (1)

[Claims] 1. A general formula A solid electrolytic capacitor comprising a conductive polymer compound obtained by doping a polymer compound having a repeating unit represented by the above with a dopant as a solid electrolyte.