JPH03114213A - Solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To increase conductivity and adhesion to a dielectric film by applying conductive polymeric compound obtained by doping specified polymeric compound with dopant to solid electrolyte. CONSTITUTION:Conductive polymeric compound obtained by doping polymeric compound having repetition unit shown by formula I (R, R' show alkyl radical or hydrogen atom, and X shows O or S) with dopant is applied to solid electrolyte. As representative examples of the polymeric compound, polythiophene and polyfran can be quoted. By using chemical method, these polymeric compounds are doped with electron acceptor like I2, Br2, SO3, AsF2, SbF6, etc. as dopant. In another case, anion like BF4, ClO4, PF6, AsF6, etc., is used as dopant, and doping is performed by electrochemical method. Thereby electric conductivity can be increased up to 10<-1->10<2>S.cm<-1>.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention uses a conductive polymer compound obtained by doping a dopant into a polymer compound having a repeating unit represented by the general formula (T) as a solid electrolyte. Regarding solid electrolytic capacitors.

[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, which is formed by thermal decomposition of manganese nitrate, is mainly used as the solid electrolyte in conventional solid electrolytic capacitors of this type. However, due to the high heat required during thermal decomposition of manganese nitrate and the oxidizing effect of the NO gas generated, the metal oxide film of dielectric materials such as aluminum and tantalum can be damaged, and as a result, solid electrolytic capacitors withstand voltage There were extremely serious drawbacks such as a decrease in the leakage current, an increase in leakage current, and a deterioration of the dielectric properties.

In order to compensate for these drawbacks, attempts have been made to form a solid electrolyte layer without applying high heat, that is, to use a highly conductive organic semiconductor material as the solid electrolyte.

As an example, a conductive polymer composition containing 7゜7.8.8-tetracyanoquinodimethane (TCNQ) + 11 salt described in JP-A-52-79255 is used as a solid electrolyte. solid electrolytic capacitor, JP-A-58-17
A solid electrolytic capacitor using a complex salt of Nn-propylisoquinoline and TCNQ as a solid electrolyte, which is described in Japanese Patent No. 609, is known.

However, these TCNQm salt compounds have poor adhesion to the anodic oxide film even if various measures are taken as described above, and the electrical conductivity of TCNQ itself is 10-3~I O-''S.
-cm-', which is insufficient, the capacitance value of the capacitor is small and the dielectric loss is large, and the thermal stability over time is also poor, resulting in poor reliability.

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

Means for Solving Problems J The present invention is characterized in that a conductive polymer compound obtained by doping a dopant into a polymer compound having a repeating unit represented by the general formula is used as a solid electrolyte. Regarding solid electrolytic capacitors.

Typical examples of these polymer compounds include polythiophene and polyfuran.

The manufacturing method of these polymer compounds is not particularly limited, but for example, for polythiophene, J, Po
lym, -3ci, Polyn, Left, Ed
, 18.9 (1980): J. Electr.
oanal, che+++,, +35.173(
19821Makro*o1. chere,, Ra
pid comtmon, 2,551+19δl),
J, Electroanal for polyfurans.

Chew, 135.173 (1982) and the like.

In the present invention, polythiophene may be a polymer of thiophene compounds such as thiophene or 3-methyldiophene, or a copolymer or mixture thereof, and polyfuran may be a polymer of furan compounds such as furan or 3-methylfuran. It may be a combination, a copolymer thereof, or a mixture thereof.

In addition, as a dopant to these polymer compounds, ■2, B
By doping electron acceptors such as rz, sol, AsF5.5bFs using chemical methods or BP, - as a dopant.

By doping with anions such as cgo4-, pp, -5ASF, -, etc. using an electrochemical method, the electrical conductivity can be increased to 10-1 to 10''S-am-'.

In the present invention, the dopant refers to an electron donor additive such as an electron acceptor and anion that is added in a small amount to a polymer compound having a repeating unit represented by the general formula (I) in order to impart conductivity.

and Japanese Patent Application Laid-Open No. 58-54553 filed by the applicant.
Dopants described in Japanese Patent Application Laid-Open No. 58-54554 can also be used as appropriate.

In addition, doping or doping refers to adding the above-mentioned dopant to a polymer compound having repeating units as shown in the above general formula, and as a result, the electrical conductivity of the conjugated polymer compound is dramatically increased. It is something.

The dopant may be added by a chemical method after producing the fixed-type composite, but it may also be done by using the dopant as an auxiliary electrolyte during electrolytic polymerization and doping at the same time as the polymerization.

FIG. 1 schematically shows a solid electrolytic capacitor to which the present invention is applied.

A metal sintered body l having valve action such as tantalum or aluminum has its surface covered with an oxide film (dielectric layer) 2, and the dielectric layer is covered with a doped conductive polymer compound 3. (Although the drawing does not show the voids formed by the valve metal particles of the sintered body, most of the surface of the sintered body is formed by interparticle voids,
Of course, the oxide film and the conductive polymer compound also exist in the interparticle voids. ). The cathode is taken out by surrounding it with a conductive paste 4, placed in a case, and the anode 7 taken out from the metal sintered body 1 is sealed with a sealing resin 8 to form a solid electrolytic capacitor.

As the metal having a valve action to be used for the anode, metals having a valve action such as aluminum, tantalum, niobium, titanium, or alloys using these metals as substrates can be used.

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

The oxide dielectric layer on the surface of the anode substrate is an oxide of the anode substrate itself, and a method of providing an oxide dielectric layer that apparently covers the surface of the anode substrate (including the inside of the sintered body) For this purpose, a conventionally known method can be used.

For example, when using aluminum foil, if the surface of the aluminum foil is electrochemically etched and further electrochemically treated in an aqueous solution of boric acid and ammonium borate, alumina can be etched onto the aluminum foil that is the anode substrate. It is possible to form an oxide dielectric layer consisting of:

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

Note that an anode lead wire is connected to the anode valve metal base before and after forming the oxide dielectric layer.

After providing an oxide dielectric layer on the surface of the anode valve metal base in this way, an excellent solid electrolytic capacitor is manufactured by depositing a doped conductive polymer compound as a solid electrolyte on the oxide dielectric layer. They discovered that it is possible to do this, and completed the present invention.

[Function] The larger the surface area of a capacitor's poles, the larger the capacitance. It is also a matter of course that the electrodes must be insulated. Therefore, it is well known that in sintered electrolytic capacitors, the surface area is secured by sintering fine powder, and an insulator (dielectric layer) is provided by using valve metal and oxidizing its surface. It is. A solid electrolyte is provided as the other electrode on this oxide dielectric layer to form a 1M capacitor.

On the other hand, a polymer compound having a repeating unit represented by the general formula (I) can be prepared by oxidizing and electrolyzing a raw material monomer solution containing an auxiliary electrolyte (which can also be used as a dopant) to form a conductive polymer compound doped into a positive electrode. It is known that it precipitates.

However, it is only known to be deposited on a positive electrode made of a metal plate such as platinum, and is used as an oxide dielectric layer (electrical insulator) provided on a metal surface for manufacturing solid electrolytic capacitors. It was not known at all that it would precipitate on the surface.

In the present invention, although the reason could not be clarified, the conductive polymer compound deposited on the oxide dielectric layer surprisingly had a lower V: adhesion and coverage rate with respect to the valve metal oxide film. It is clear from the performance of the obtained solid electrolytic capacitor that it is excellent, and it can be seen that the oxide dielectric layer is well covered as a solid electrolyte.

Therefore, the solid electrolytic capacitor obtained by the present invention has significantly superior performance in terms of capacity, dielectric Ti loss, and stability over time compared to conventional solid electrolytic capacitors using inorganic oxide semiconductors or organic semiconductors.

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

(Example 1) A sintered body of Ta powder is anodized in an aqueous phosphoric acid solution to form a dielectric film, washed and dried, and then the Ta element is immersed in a polythiophene-chloroform solution and dried.

This dipping and drying operation is repeated to form a polymer compound layer made of polythiophene on the dielectric layer, and then A
An electrolyte layer made of a conductive polymer compound is formed by contacting with sFs gas and doping with AsFs. Next, the cathode was removed using silver paste, placed in a case, and sealed with resin to create a solid electrolytic capacitor.

A polythiophene film separately produced under the same conditions was
The conductive layer when doped with sFs is 10-'S-
cm-'.

(Example 2) After a sintered body of Ta powder was anodized in an aqueous phosphoric acid solution to form a dielectric film, the Ta element was used as a positive electrode, platinum was used as a negative electrode, and 0% thiophene monomer was added to the electrolyte. .01M dissolved 0, IM Bu 4NBF, -C:
Electropolymerization is performed using H3CN, and BF is deposited on a Ta element coated with a dielectric film.

A solid electrolytic capacitor was fabricated by forming an electrolyte layer of polythiophene doped with .

A polythiophene film doped with BF and - was prepared on a platinum plate under the same conditions, and when this was peeled off and measured, the conductive layer was l O''S-c+w-'.

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

The conductive layer of polyfuran doped with BF, -, which was prepared separately, was l 05-c layer-1.

(Example 4) In Example 2, 3-
An electrolyte layer was formed using methylthiophene, and a solid electrolytic capacitor was similarly produced.

A conductive layer of poly-3-methylthiophene doped with BF, which was prepared separately, had a conductivity of 0.8 S-cm-'.

(Comparative Example 1) A solid electrolytic capacitor using a conventional manganese dioxide as an electrolyte and using an anodized Ta element similar to that in Example 1 was manufactured.

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

(Hereinafter in the margin) Table 1 (Hereinafter in the margin) As is clear from Table 1, the solid electrolytic capacitor using a conductive polymer compound doped with a dopant as an electrolyte according to the present invention is different from the conventional solid electrolytic capacitor using a manganese dioxide as an electrolyte. It is possible to produce a solid electrolytic capacitor that has lower dielectric loss (tan δ) and leakage current than a capacitor, has a higher rated voltage, and has a high withstand voltage.

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

(Example 5) Using the same materials and method as in Example 1, a conductor layer was formed in the order of carbon paste and silver paste on the element that had been formed up to the solid electrolyte layer. A solid electrolytic capacitor was created by sealing the cap.

This capacitor has a capacitance i of 11.00 μF and a jan δ1.
00%, ESRloooKHz, 0°23Ω, rated voltage 50V, leakage current 50V, 1 OnA or less 8 (Comparative Example 2) Poly-2- on N-methylacridinium-TCNQCN
An NN-dimethylformamide solution containing vinylpyridine in a weight ratio of 85:15 was used as an electrolyte solution, and an anodized Ta element was immersed in the electrolyte solution and dried (repeatedly to form an electrolyte layer).

Silver paste was immediately applied to this product without graphite, dried, placed in a case, and sealed with resin to create a solid electrolytic capacitor.

This capacitor has a capacitance of ff11.1μF and a jan61.
1%, ESR of 100KHz, 1.32Ω, and leakage current of 50V, 10nA or less.

As is clear from the above examples and comparative examples, when a conductive polymer compound obtained by doping a dopant into a polymer compound having a repeating unit represented by general formula (I) is used as the solid electrolyte layer, The performance of solid electrolytic capacitors is almost the same whether the conductor layer is silver paste, carbon paste, or silver paste.
It is clear that when replacing with poly-2-vinylpyridine on N, the performance as a solid electrolytic capacitor deteriorates even if all other configurations are the same.

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

[Effects of the invention] In a solid electrolytic capacitor, if a conductive polymer compound obtained by doping a dopant into a polymer compound having a repeating unit represented by the general formula (N) is used as a solid electrolyte, the following effects can be obtained. .

■ Since the electrolyte layer can be formed without high-temperature heating, there is less damage to the oxide film on the anode. Therefore, the rated voltage can be increased several times compared to conventional ones, and the shape can be made smaller to obtain a capacitor with the same capacity and rated voltage. can be converted into

■Low leakage current.

■Capacitors with high withstand voltage can be manufactured.

■ Electrolyte conductivity is 10-' to 10'' S-ctm
-', which is sufficiently high, there is no need to provide a conductive layer such as graphite, which simplifies the process.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a solid electrolytic capacitor according to the present invention. 1. = Metal sintered body such as Ta or A42 2... - Oxide film 3 - Conductive polymer compound 4... Conductive paste 5 - Solder 6... Case and cathode 7... Anode 8・・－Sealing resin

Claims (1)

[Claims] General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (R, R' are alkyl groups or hydrogen atoms, X is O or S
shows. ) A solid electrolytic capacitor characterized in that a conductive polymer compound obtained by doping a dopant into a polymer compound having a repeating unit represented by the following formula is used as a solid electrolyte.