JP2015095616A - Solid electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor excellent in moisture resistance, in which the change of electric capacity is small even under high temperature and high humidity, and low ESR is maintained.SOLUTION: A capacitor element 4 formed by winding an anode foil 1, on which a dielectric oxide membrane is formed, and a cathode foil 3 via a separator 2 has a first conductive polymer layer formed by impregnating and drying a solution dissolving a first conductive polymer on the dielectric oxide membrane, and a second conductive polymer layer formed by impregnating and drying a fluid dispersion containing a second conductive polymer, different from the first conductive polymer, on the first conductive polymer layer, and is impregnated with a non-ion conductive organic solvent having a boiling point of 150°C or more.

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

  Solid electrolytic capacitors are known in which a conductive polymer layer is formed on an anode foil of a capacitor element in which an anode foil with a dielectric oxide film formed on the surface and a cathode foil are wound through a separator. ing.

  In general, the anode electrode of a solid electrolytic capacitor forms a dielectric oxide film on a metal foil having a valve action such as aluminum, tantalum, niobium, etc. whose surface area is increased by etching, and is electrically conductive on this dielectric oxide film. A polymer layer is formed and an electrode is drawn out. This conductive polymer layer plays a role as a true cathode in the electrolytic capacitor, and greatly affects the electrical characteristics of the electrolytic capacitor.

  A conductive polymer layer is a layer containing a solid electrolyte that is electronically conductive, and a conductive polymer such as polythiophene derivatives such as polyethylenedioxythiophene (PEDOT), polythiophene, polyaniline, and polypyrrole is used as a solid electrolyte. It is known to use as (patent document 1).

As a method for forming such a conductive polymer layer, a mixed solution of an oxidant and a monomer is prepared in advance, and a capacitor element is immersed in this mixed solution and impregnated. There is a method of sequentially impregnating capacitor elements. For example, in the solid electrolytic capacitor described in Patent Document 2, a capacitor element is immersed in a mixed solution in which a polymerizable monomer and an oxidizing agent are mixed, and a polymerization reaction of a conductive polymer is generated in the capacitor element. Then, after forming the solid electrolyte layer, the capacitor element is immersed in a predetermined ion conductive material, and the void portion in the capacitor element is filled with the ion conductive material. Prevents deterioration.
Each of the above methods forms a conductive polymer layer while a polymerization reaction proceeds on a capacitor element. These methods include changes in solution viscosity accompanying the progress of polymerization, It has also been known that there are difficulties in process control such as insufficient mixing with monomers.

  On the other hand, a method of forming a conductive polymer layer by impregnating and drying a dispersion liquid containing a conductive polymer that has been polymerized in advance to form a coating film is also known. Since this method does not require a polymerization reaction on the dielectric oxide film, the process is relatively easy to control and is advantageous in terms of mass productivity. (Patent Document 3).

  In the invention of Patent Document 3, Baytron-P (trade name, manufactured by Starck, Germany), which is an aqueous dispersion of polyethylenedioxythiophene (PEDOT), which is a conductive polymer, and polystyrenesulfonic acid (PSS), is electrically conductive. It is used to form a polymer layer, and aims to improve conductivity (avoidance of ESR increase) in the conductive polymer layer and improve long-term reliability of electrical characteristics. In the invention of Patent Document 3, an anodic oxide film is first formed, and a precoat layer (layer obtained by applying and drying polystyrene sulfonic acid) and an internal conductive polymer layer (formed by chemical oxidative polymerization, having a relatively molecular weight formed on the surface thereof. An anode body having a small conductive polymer film) is prepared. Next, a solution containing naphthalene sulfonic acids, high molecular weight PSS, boric acid, mannitol, glycols and water is mixed with an aqueous dispersion containing PEDOT and PSS, thereby preparing a polymer polymerization solution. The polymer solution is applied or impregnated into the anode body and dried to provide a conductive polymer layer.

JP-A-2-15611 Japanese Patent No. 4779277 JP 2008-311582 A

  By the way, as the use of solid electrolytic capacitors expands, there is a demand for capacitors that can be used without problems even in harsher environments. Specifically, 85 ° C.-85% R.I. H. Capacitors with little change in electrical characteristics even under high temperature and high humidity conditions are demanded. However, a conventional solid electrolytic capacitor has not been known that has sufficient moisture resistance, even when it is placed under high temperature and high humidity, with little change in electric capacity and little increase in ESR. In view of such circumstances, it is an object of the present invention to provide a solid electrolytic capacitor excellent in moisture resistance in which a change in electric capacity is small even under high temperature and high humidity, and low ESR is maintained.

  The inventors immerse the capacitor element in a dispersion containing a conductive polymer composed of polyethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS), which has been polymerized in advance, thereby increasing the conductivity of the capacitor element. In the process of removing moisture by impregnating molecules and then drying, attention was paid to the following problems. That is, the inventors swell a layer composed of polyethylene dioxythiophene and polystyrene sulfonic acid (hereinafter sometimes referred to as PEDOT / PSS) due to moisture, so that the characteristic change is large in a short time in a high humidity atmosphere. Focused on the problem of becoming.

And as a result of inventors' earnestly examining with respect to the said subject, it discovered that it could solve by the two points shown below.
i) impregnating a capacitor element with a non-ion conductive organic solvent having a boiling point of 150 ° C. or higher.
By including an organic solvent in the conductive polymer, the influence of moisture can be reduced. Here, the organic solvent can be classified into a solution having ion conductivity (ion conductive solution) and a non-ion conductive solution not having ion conductivity. When an ion conductive solution is used, the capacitance change in a low temperature region becomes large, which is not preferable. On the other hand, even when a non-ion conductive solution is used, the capacitance change becomes slightly large. However, by applying the following point (ii), the influence of the non-ion conductive solution can be reduced. Furthermore, by adopting a high boiling point solvent having a boiling point of 150 ° C. or higher as the non-ion conductive organic solvent, it is possible to prevent the expansion of the product during reflow, which is a practical problem, in addition to alleviating the adverse effects of moisture.
ii) A conductive polymer (first conductive polymer layer) different from the conductive polymer layer (second conductive polymer layer) made of polyethylenedioxythiophene (PEDOT) and polystyrenesulfonic acid (PSS) ) On the dielectric oxide film.
With the above configuration, the influence of the non-ion conductive solution at the point (i) can be reduced. That is, the first conductive polymer layer formed on the dielectric oxide film can suppress the second conductive polymer layer from swelling due to moisture, and can improve the moisture resistance of the solid electrolytic capacitor. . As the first conductive polymer layer, polythiophene, polypyrrole, polyaniline or a derivative thereof is preferable.

That is, the solid electrolytic capacitor according to the present invention is a capacitor element in which an anode foil having a dielectric oxide film formed thereon and a cathode foil are wound through a separator.
A first conductive polymer layer formed by impregnating and drying a solution in which the first conductive polymer is dissolved on the dielectric oxide film;
A second conductive material formed by impregnating and drying a dispersion liquid containing a second conductive polymer different from the first conductive polymer on the first conductive polymer layer. A polymer layer,
The capacitor element is impregnated with a non-ion conductive organic solvent having a boiling point of 150 ° C. or higher.

  Since the above solid electrolytic capacitor is impregnated with an organic solvent, it is not easily affected by moisture in a high humidity atmosphere. Since this organic solvent is a non-ion conductive organic solvent, the change in capacitance in the low temperature region is smaller than when the organic solvent is an ion conductive organic solvent. Further, impregnation with a non-ion conductive organic solvent can suppress the occurrence of a leakage current failure after aging. Since the first conductive polymer layer is provided on the anode film, it is possible to obtain a solid electrolytic capacitor with high moisture resistance by further suppressing the influence of moisture. Moreover, since the boiling point of the organic solvent to be impregnated is 150 ° C. or higher, the product expansion during reflow is suppressed, and a solid electrolytic capacitor with stable quality can be obtained.

  The second conductive polymer layer preferably includes a layer composed of polyethylene dioxythiophene and polystyrene sulfonic acid, and the first conductive polymer layer includes polythiophene, polypyrrole, polyaniline or a derivative thereof. preferable. The nonionic conductive organic solvent having a boiling point of 150 ° C. or higher is preferably one or more organic solvents selected from the group consisting of γ-butyrolactone, polyethylene glycol, sulfolane, dimethyl sulfoxide, and dimethylformamide.

  By configuring the second conductive polymer layer with a layer (PEDOT / PSS) made of polyethylene dioxythiophene and polystyrene sulfonic acid, a solid electrolytic capacitor with high conductivity can be obtained. In addition, by configuring the first conductive polymer layer with the above-described substance, it is possible to reduce the influence of the impregnating nonionic conductive organic solvent and improve the electrical characteristics.

  The separator for the solid electrolytic capacitor is preferably a separator having no hydrolyzability. In particular, in a high temperature / high humidity region, a solid electrolytic capacitor having higher durability can be obtained by using a separator having no hydrolyzability.

  The present invention also relates to a method for producing a solid electrolytic capacitor, in which a conductive polymer is dissolved in a capacitor element in which an anode foil on which a dielectric oxide film is formed and a cathode foil are wound through a separator. Impregnating and drying the solution to form a first conductive polymer layer on the dielectric oxide film, impregnating and drying a dispersion containing polyethylenedioxythiophene and polystyrenesulfonic acid, It has the process of forming a 2nd conductive polymer layer on one conductive polymer layer, and the process of impregnating the nonionic conductive organic solvent whose boiling point is 150 degreeC or more.

  According to the production method of the present invention, by using a dispersion of polyethylene dioxythiophene and polystyrene sulfonic acid, the oxidant and monomer components are less likely to remain in the capacitor element, particularly at high temperatures and high humidity. Deterioration of the dielectric film in the is suppressed. Therefore, it is possible to obtain a solid electrolytic capacitor excellent in moisture resistance, in which the change in capacitance in the low temperature region is small, and the change in capacitor characteristics is small even under high temperature and high humidity.

  In the production method of the present invention, the solution in which the conductive polymer is dissolved is preferably a solution in which any of polythiophene, polypyrrole, polyaniline, or a derivative thereof is dissolved. The nonionic conductive organic solvent having a boiling point of 150 ° C. or higher is preferably γ-butyrolactone, polyethylene glycol, sulfolane, dimethyl sulfoxide, dimethylformamide, or the like. The separator of the solid electrolytic capacitor is preferably a separator that does not have hydrolyzability.

  By using the above-mentioned solution in which the conductive polymer is dissolved, it is possible to form a single layer of the conductive polymer layer on the surface of the anode foil by a general method. Also, by using a conductive polymer solution, it is possible to form a conductive polymer layer more uniformly than when a polymerization reaction is carried out on the anodized film, and unreacted monomers in the capacitor element. Since unnecessary substances such as oxidants and oxidants do not remain, it is possible to improve the moisture resistance of the solid electrolytic capacitor and improve the electrical characteristics.

  According to the present invention, it is possible to obtain a solid electrolytic capacitor with little change in capacitance in a low temperature region and little change in characteristics even under high temperature and high humidity.

It is a disassembled perspective view which shows the outline | summary of a capacitor | condenser element.

  FIG. 1 is an exploded perspective view showing an outline of a capacitor element. In the capacitor element 4, an anode foil 1 and a cathode foil 3 are wound and accommodated via a separator 2, and an anode lead wire 5 connected to the anode foil and a cathode lead wire 6 connected to the cathode foil. Has been pulled out.

  The anode foil of the solid electrolytic capacitor of the present invention was formed by subjecting the surface of the valve action metal on a flat plate having a predetermined width to a rough surface by etching, followed by chemical oxidation treatment to form a dielectric oxide film on the surface. Use things. As the valve metal action, a metal containing at least one selected from aluminum, tantalum, niobium, and titanium is preferable, and aluminum is particularly preferable.

  Etching treatment and chemical oxidation treatment can be performed by a known method, and the treatment may be carried out using known materials and conditions generally used for solid electrolytic capacitors, or purchased products may be used. For example, the chemical conversion liquid used for the chemical conversion treatment may be a chemical conversion liquid in which a solute of an organic acid salt having a carboxylic acid group or an inorganic acid salt such as phosphoric acid is dissolved in an organic solvent or an inorganic solvent.

  As described above, the anode foil is wound together with the separator and the cathode foil. After the winding, in order to repair the dielectric oxide film that has been lost when the anode foil is cut or the external lead electrode is attached, according to known conditions and methods. Perform restoration formation. As a chemical conversion liquid for restoration chemical conversion, a chemical conversion liquid in which a solute of an organic acid salt having a carboxylic acid group or an inorganic acid salt such as phosphoric acid is dissolved in an organic solvent or an inorganic solvent can be used.

  In the solid electrolytic capacitor of the present invention, the first conductive polymer layer is formed on the dielectric oxide film. The first conductive polymer layer is preferably formed by impregnating and drying a solution type conductive polymer solution. The first conductive polymer layer is formed using a solution mainly composed of polythiophene, polypyrrole, polyaniline or a derivative thereof, that is, a conductive polymer layer mainly composed of polythiophene, polypyrrole, polyaniline or a derivative thereof. It is preferable that The concentration of the conductive polymer in the solution is 0.1 to 2.0 wt%, regardless of whether the solvent is alcohol, ethers, or aromatic, the conductive polymer is dissolved and the drying temperature is less than 250 ° C. A solvent that can be evaporated can be used. The drying conditions are not limited as long as the solvent can be removed and the capacitor element is not adversely affected. For example, the drying can be performed at 100 to 250 ° C. for 30 to 120 minutes. Particularly preferably, the solution for forming the first conductive polymer layer can be formed by using a polyaniline / isopropyl alcohol solution of 0.5 to 1.5 wt% and drying at 150 ° C. for 30 minutes. As the polyaniline dopant, for example, a sulfosuccinate can be used.

  A second conductive polymer layer is formed on the first conductive polymer layer. The second conductive polymer layer is formed by immersing and impregnating the capacitor element in a polymer dispersion containing polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS), and then removing moisture by drying. Preferably it is formed. As a PEDOT / PSS dispersion liquid, what uses water as a solvent is preferable, and what was produced as the density | concentration of PEDOT / PSS in a dispersion liquid 0.5-3.0 wt% may be used. The step of forming the second conductive polymer layer can be performed under known conditions, and it is also preferable to perform the impregnation and immersion under reduced pressure. The impregnation and drying can be repeated once or twice or more. The drying conditions are not limited as long as the solvent can be removed and the capacitor element is not adversely affected. For example, drying can be performed at 85 to 150 ° C. for 30 to 120 minutes. Particularly preferably, by repeating the step of immersing and impregnating for 15 minutes under a reduced pressure of 10 kPa using a polymer dispersion solution containing 1.0 wt% PEDOT / PSS and drying at 100 ° C. for 60 minutes, A second conductive polymer layer can be formed.

In the solid electrolytic capacitor of the present invention, the capacitor element is further impregnated with a non-ion conductive organic solvent having a boiling point of 150 ° C. or higher. Examples of the non-ion conductive organic solvent having a boiling point of 150 ° C. or higher include γ-butyrolactone, polyethylene glycol, sulfolane, dimethyl sulfoxide, dimethylformamide and the like. These non-ion conductive organic solvents are preferably impregnated so as to have a ratio of 30% to 100% with respect to the voids after the formation of the conductive polymer. When the nonionic conductive solvent is less than 30%, the moisture absorption amount of the capacitor element increases, and 85 ° C.-85% R.D. H. In the moisture resistance test, the characteristics change greatly after 1000 hours, which is not preferable.
By impregnating such a solvent into the capacitor element having the conductive polymer layer described above, the solid electrolytic capacitor becomes less susceptible to moisture, improving moisture resistance and suppressing product expansion during reflow. Thus, a solid electrolytic capacitor having both high moisture resistance and electrical characteristics and excellent product stability can be obtained.

  As the separator, a separator having no hydrolyzability is preferable. For example, a separator mainly composed of polyacrylonitrile or aramid is preferable.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[Example 1]
A tab terminal for an external lead electrode was connected to the anode foil and the cathode foil cut to a predetermined width. As the anode foil, an aluminum foil was used as a valve metal, and the surface of the valve metal was subjected to an etching treatment and a chemical conversion treatment to form a dielectric oxide film.
The anode foil and the cathode foil were wound through a separator mainly composed of polyacrylonitrile to complete a wound element.
Subsequently, a so-called chemical conversion treatment was performed to repair the dielectric oxide film that was missing when the anode foil was cut or the external lead electrode was attached. Using a 0.5 wt% to 3 wt% chemical conversion solution in which ammonium adipate was dissolved in an aqueous solvent, a voltage approximate to the chemical conversion voltage value of the dielectric oxide film was applied to perform chemical conversion treatment.

Next, a conductive polymer layer that is a cathode layer of the solid electrolytic capacitor was formed.
First, the wound element was impregnated with a 1.0 wt% polyaniline / isopropyl alcohol solution and dried at 150 ° C. for 30 minutes to form a first conductive polymer layer.
Thereafter, a polymer dispersion solution containing 2.0 wt% PEDOT / PSS was immersed and impregnated for 15 minutes under a reduced pressure of 10 kPa, and the water was removed by heating at 100 ° C. for 60 minutes. This impregnation and drying were repeated three times to form a second conductive polymer layer.
Furthermore, the element was impregnated by impregnating with polyethylene glycol (molecular weight 600) under a reduced pressure of 10 kPa for 30 minutes.

  The capacitor element on which the conductive polymer layer was formed by the above method was housed in a metal case, and the opening of the metal case was curled. Subsequently, an aging treatment was performed by applying a rated voltage to the capacitor under a temperature condition of about 150 ° C. to complete a solid electrolytic capacitor.

[Example 2]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that γ-butyrolactone was used instead of polyethylene glycol (molecular weight 600) as the solution impregnating the capacitor element.

[Comparative Example 1]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that polyethylene glycol (molecular weight 600) containing 25 wt% triethylamine hydrogen phthalate was used as the solution impregnating the capacitor element instead of polyethylene glycol (molecular weight 600). .

[Comparative Example 2]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the polyaniline / isopropyl alcohol solution was not impregnated and dried (the first conductive polymer layer was not formed).

[Comparative Example 3]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the polyaniline / isopropyl alcohol solution was not impregnated and dried, and the polyethylene glycol (molecular weight 600) was not impregnated.

[Comparative Example 4]
As the separator, a hemp 100% type separator was used instead of the one mainly composed of polyacrylonitrile. Further, a chemical conversion treatment was performed in the same manner as in Example 1, followed by carbonization of the separator (280 ° C. × 60 minutes).
Subsequently, a conductive polymer was formed by the following method.
By impregnating the oxidizing agent solution by immersing the oxidizing agent solution (p-toluenesulfonic acid / butanol solution, concentration 40%) for 1 minute in the capacitor element that has been subjected to chemical conversion treatment, by heating at 200 ° C. for 5 minutes, The solvent was evaporated.
After impregnating the ethylenedioxythiophene (monomer) / isopropanol solution for 5 seconds, the solution is heated in a polymerization tank at a predetermined temperature for a certain time (200 ° C./30 minutes) to chemically polymerize the oxidant and the monomer to obtain a solid electrolyte. (Polyethylenedioxythiophene) was formed.
Then, the element was impregnated by impregnating with polyethylene glycol (molecular weight 600) under a reduced pressure of 10 kPa for 30 minutes.
The capacitor element on which the conductive polymer layer was formed by the above method was stored in a metal case, and the opening of the metal case was curled. Subsequently, a rated voltage was applied to the capacitor at a temperature of about 150 ° C. to perform an aging treatment, thereby completing a solid electrolytic capacitor.

[Comparative Example 5]
A solid electrolytic capacitor was produced in the same manner as in Comparative Example 4 except that it was not impregnated with polyethylene glycol (molecular weight 600).

[Evaluation of Solid Electrolytic Capacitors of Examples and Comparative Examples]
About the solid electrolytic capacitor of an Example and a comparative example, 85 degreeC-85% R. H. The electrical characteristics after 2000 hours when the rated voltage of 16 V was applied and the capacitance change of -55 ° C / 20 ° C were measured. The results are shown in Table 1.

  As shown in the above table, the Examples are stable in that the characteristic change before and after the test is significantly smaller than those of Comparative Examples 3 to 5. In addition, the capacity change of −55 ° C./20° C. is remarkably small in Examples compared with Comparative Examples 1 to 4. Furthermore, compared with Comparative Examples 3-5, an Example has a remarkably low leakage current defect rate after aging. That is, the solid electrolytic capacitor of the example has a low leakage current failure rate after aging and excellent productivity, and is 85 ° C.-85% R.D. H. Even under high temperature and high humidity conditions, there is little change in characteristics and excellent moisture resistance, and even in a low temperature region (-55 ° C.), there is little change in capacity and excellent stability.

1 Anode foil 2 Separator 3 Cathode foil 4 Capacitor element 5 Anode lead wire 6 Cathode lead wire

Claims (6)

In a capacitor element in which an anode foil on which a dielectric oxide film is formed and a cathode foil are wound through a separator, the dielectric oxide film is impregnated with a solution in which a first conductive polymer is dissolved. A first conductive polymer layer formed by drying and a second conductive polymer different from the first conductive polymer are included on the first conductive polymer layer. A solid electrolytic capacitor having a second conductive polymer layer formed by impregnating and drying the dispersion, wherein the capacitor element is impregnated with a nonionic conductive organic solvent having a boiling point of 150 ° C. or higher . The solid electrolytic capacitor according to claim 1, wherein the second conductive polymer layer includes a layer made of polyethylene dioxythiophene and polystyrene sulfonic acid. The solid electrolytic capacitor according to claim 1, wherein the first conductive polymer layer includes polythiophene, polypyrrole, polyaniline, or a derivative thereof. The nonionic conductive organic solvent having a boiling point of 150 ° C or higher is one or more organic solvents selected from the group consisting of γ-butyrolactone, polyethylene glycol, sulfolane, dimethyl sulfoxide, and dimethylformamide. A solid electrolytic capacitor according to any one of the above. The solid electrolytic capacitor according to claim 1, wherein the separator is a separator having no hydrolyzability. A capacitor element in which an anode foil formed with a dielectric oxide film and a cathode foil are wound through a separator,
Impregnating and drying a solution in which a conductive polymer is dissolved to form a first conductive polymer layer on the dielectric oxide film;
A step of impregnating and drying a dispersion containing polyethylene dioxythiophene and polystyrene sulfonic acid to form a second conductive polymer layer on the first conductive polymer layer, and a boiling point of 150 ° C. or higher A method for producing a solid electrolytic capacitor, comprising a step of impregnating a nonionic conductive organic solvent.

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