JP4795331B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor using a conductive polymer as an electrolyte and a method for manufacturing the same.

  The electrolytic capacitor includes an anode foil made of a valve metal such as aluminum, tantalum, or niobium, or an anode body made of a valve metal powder. The surface of the anode foil or anode body is oxidized as a dielectric. A film is formed. Electrical extraction from the oxide film is performed by an electrolyte having conductivity between the anode foil and the cathode foil or between the anode body and the cathode terminal, and this electrolyte is responsible for the true cathode in the electrolytic capacitor. ing. Since the electrolyte functioning as the true cathode has a great influence on the electrical characteristics of the electrolytic capacitor, electrolytic capacitors employing various types of electrolytes have been proposed.

  Among such electrolytic capacitors, a solid electrolytic capacitor uses a conductive polymer such as polyethylenedioxythiophene (PEDOT) as an electrolyte, and has an impedance in a high frequency region as compared with an electrolytic capacitor using a liquid electrolyte. Excellent characteristics.

In recent years, digitalization of various electronic devices has progressed, and solid electrolytic capacitors are required to have a large capacity and a small size. As a solid electrolytic capacitor satisfying such requirements, there is a wound type solid electrolytic capacitor.
In a winding type solid electrolytic capacitor, an anode foil and a cathode foil on which an oxide film is formed are wound through a separator made of one or more of paper fibers such as Manila paper, glass fibers, and resin fibers. In addition, the separator has a structure in which a solid electrolyte layer made of a conductive polymer is held (see, for example, Patent Document 1). With this structure, a large electrode area can be secured.

  Such a solid electrolytic capacitor is provided with a winding element or an anode lead by winding an anode foil and a cathode foil on which an oxide film is formed via a separator, and after forming an anode body on which an oxide film is formed, These elements are manufactured by impregnating a polymerization solution composed of a monomer or an oxidizing agent and performing chemical polymerization.

JP 2001-189242 A

  However, when the above-described solid electrolytic capacitor is used under a high temperature condition or a high current or a high voltage is applied, the oxide film which is a dielectric material may cause a chemical reaction, and the oxide film may be defective. As a result, the withstand voltage decreases and the leakage current increases. Moreover, when defects occur in the oxide film, the adhesion between the oxide film and the solid electrolyte layer decreases, and ESR increases.

In addition, for the purpose of reducing ESR (equivalent series resistance) of a solid electrolytic capacitor using a winding element, after forming a winding element using a separator containing paper fibers, a heat treatment may be performed in which the winding element is heated. is there. This heat treatment carbonizes the paper fibers of the separator and lowers the density of the separator, so that ESR (equivalent series resistance) is reduced.
However, when such heat treatment is performed, the ESR can be reduced, but the separator becomes thin, so that the winding element is loosened, the withstand voltage is lowered, and the leakage current may be increased.

  Therefore, an object of the present invention is to provide a solid electrolytic capacitor having a low ESR and leakage current and a high withstand voltage, and a method for manufacturing the same.

  The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor in which a solid electrolyte layer made of a conductive polymer composition is formed, and the conductive polymer composition contains a compound represented by the following chemical formula 1. It is characterized by doing.

  However, in formula, OA represents a C2-C4 oxyalkylene group, n represents the number of 1-50, a and b represent the number of 1-10.

  Furthermore, in the solid electrolytic capacitor of the present invention, it is preferable that the conductive polymer is any one of polythiophene, polyaniline, polypyrrole, and derivatives thereof.

  In the method for producing a solid electrolytic capacitor of the present invention, a capacitor element having an oxide film formed on a surface thereof is impregnated with a monomer that becomes a conductive polymer by polymerization, a dopant, an oxidizing agent, and a compound represented by the above chemical formula 1. And a polymerization step of forming a solid electrolyte layer made of a conductive polymer composition on the surface of the oxide film by polymerization.

According to the solid electrolytic capacitor of the present invention, since the compound represented by the chemical formula 1 contained in the conductive polymer composition constituting the solid electrolyte layer has an ether bond in the main chain, the oxygen atom of the ether bond is oxidized. A protective film is formed on the surface of the oxide film by coordination with the film.
Thereby, even if the solid electrolytic capacitor is used under a high temperature condition or a high voltage or high current is applied, the oxide film is less likely to cause a chemical reaction, and the generation of defects in the oxide film can be suppressed.
Therefore, the withstand voltage of the solid electrolytic capacitor can be improved and the leakage current can be reduced. Further, since defects are hardly generated in the oxide film, the adhesion between the oxide film and the solid electrolyte layer is maintained, and the ESR of the solid electrolytic capacitor can be kept low.

  In the solid electrolytic capacitor of the present invention, when the conductive polymer is any one of polythiophene, polyaniline, polypyrrole, and derivatives thereof, the conductivity and heat resistance of the solid electrolyte layer are increased.

According to the method for producing a solid electrolytic capacitor of the present invention, the conductive polymer composition formed by the polymerization step contains the compound represented by Chemical Formula 1. Since the compound represented by Chemical Formula 1 has an ether bond in the main chain, the oxygen atom of the ether bond coordinates with the oxide film, and a protective film is formed on the surface of the oxide film.
As a result, even if the solid electrolytic capacitor is used under high temperature conditions, or when a high voltage or high current is applied to the solid electrolytic capacitor, the oxide film is less likely to cause a chemical reaction, resulting in the generation of defects in the oxide film. Can be suppressed.
Therefore, the withstand voltage of the solid electrolytic capacitor can be improved and the leakage current can be reduced. Further, since defects are hardly generated in the oxide film, the adhesion between the oxide film and the solid electrolyte layer is maintained, and the ESR of the solid electrolytic capacitor can be kept low.

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a solid electrolytic capacitor 1 according to this embodiment includes a winding element having a structure in which an anode foil 2 having an oxide film 2a formed on a surface thereof and a cathode foil 3 are wound through a separator 4. 11.
Further, as shown in FIG. 2, a solid electrolyte layer 5 made of a conductive polymer composition held by a separator 4 is formed between the anode foil 2 and the cathode foil 3.
The winding element 11 and the solid electrolyte layer 5 constitute a capacitor element 10.

The anode foil 2 is made of a valve metal such as aluminum, tantalum, or niobium. As shown in FIG. 2, the surface of the anode foil 2 is roughened by an etching process, and an oxide film 2a is formed. The cathode foil 3 is made of aluminum or the like, like the anode foil 2, and the surface thereof is roughened.
As shown in FIG. 1, lead tabs (not shown) are connected to the anode foil 2 and the cathode foil 3, respectively, and lead wires 6 and 7 are respectively connected from the anode foil 2 and the cathode foil 3 through the lead tabs. Has been pulled out.

  As the separator 4, paper fibers such as manila paper, hemp paper, and craft paper are used, but glass fibers and resin fibers may be mixed.

As shown in FIG. 2, a solid electrolyte layer 5 made of a conductive polymer composition is held on both surfaces of the separator 4.
As the conductive polymer of the solid electrolyte layer 5, any of polythiophene, polyaniline, polypyrrole, and derivatives thereof having excellent conductivity and heat resistance can be used.

  The conductive polymer composition contains a compound represented by Chemical Formula 1.

  However, in formula, OA represents a C2-C4 oxyalkylene group, n represents the number of 1-50, a and b represent the number of 1-10.

  In the manufacturing process of the solid electrolytic capacitor 1, the compound represented by the chemical formula 1 and the winding element 11, for example, a monomer that becomes the conductive polymer described above by polymerization, a dopant having an oxidizing action (or a dopant and an oxidizing agent), and the like. Then, the solid electrolyte layer 5 is formed by chemical polymerization after impregnating the mixed solution.

Specifically, thiophene, aniline, pyrrole, and derivatives thereof are used as the monomer.
As the thiophene derivative, a thiophene derivative having at least one of a hydroxyl group, an acetyl group, a carboxyl group, an alkyl group, and an alkoxy group as a substituent at the 3-position, 3-position, 4-position or S-position of the thiophene skeleton, or 3, 4 -Alkylenedioxythiophenes can be mentioned.
Examples of the aniline derivative include an aniline derivative having an aniline skeleton and having at least one substituent selected from an alkyl group, a phenyl group, an alkoxy group, an ester group, and a thioether group.
Examples of the pyrrole derivative include a pyrrole derivative having at least one of a hydroxyl group, an acetyl group, a carboxyl group, an alkyl group, and an alkoxy group as a substituent at the 3-position, 3-position, 4-position or N-position of the pyrrole skeleton. it can.

  Although a dopant is not specifically limited, In order to obtain the solid electrolytic capacitor 1 with a favorable characteristic, a sulfonic acid compound is preferable. For example, 1,5-naphthalenedisulfonic acid, 1,6-naphthalenedisulfonic acid, 1-octanesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid and the like can be mentioned.

  Moreover, as an oxidizing agent, an organic sulfonic acid type metal salt can be used, for example. For example, iron salt of iron methoxybenzenesulfonate, iron salt of iron dodecylbenzenesulfonate, and the like can be mentioned.

  Moreover, what combined the dopant mentioned above and iron (III) can be used for the dopant which has an oxidation effect | action. Examples thereof include iron (III) p-toluenesulfonate, iron (III) ethanesulfonate, and iron (III) p-dodecylbenzenesulfonate.

  Moreover, methanol, butanol, methylene glycol, water, or the like can be used as a solvent for dissolving monomers, dopants, and the like.

  Moreover, the compound represented by Chemical formula 1 has a C2-C4 oxyalkylene group in the structure. Examples of the oxyalkylene group having 2 to 4 carbon atoms include oxyethylene group, oxypropylene group, oxybutylene group, and oxytetramethylene group. The compound represented by Chemical Formula 1 may contain only one kind of these oxyalkylene groups or may contain two or more kinds.

Since the compound represented by the chemical formula 1 has an ether bond in the main chain, the oxygen atom of the ether bond is coordinated with the oxide film 2a of the anode foil 2, and the protective film is formed on the surface of the oxide film 2a. Is formed.
As a result, even when the solid electrolytic capacitor 1 is used under high temperature conditions or when a high voltage or high current is applied, the oxide film 2a is less likely to cause a chemical reaction, resulting in defects in the oxide film 2a. Can be suppressed.
Therefore, since the withstand voltage of the solid electrolytic capacitor 1 can be improved, the leakage current can be reduced. In addition, since defects are hardly generated in the oxide film 2a, the adhesion between the oxide film 2a and the solid electrolyte layer 5 is maintained, and the ESR of the solid electrolytic capacitor 1 can be suppressed low.

  Furthermore, since the compound represented by Chemical Formula 1 has an ether bond in the main chain, it has high solubility in a solvent such as methanol. Therefore, the above-described protective film can be formed uniformly on the surface of the oxide film 2a.

  N in Chemical Formula 1 is the number of repeating oxyalkylene groups. If n is too large, the conductivity of the solid electrolyte is lowered, and thus the ESR of the solid electrolytic capacitor 1 is increased. By appropriately setting n, it is possible to prevent a decrease in conductivity. Specifically, the range of n is 1-50.

  Moreover, a and b in Chemical Formula 1 are the number of repeating methylene groups. a and b may be the same or different. When a or b is too large, solubility in a solvent such as methanol is poor. By appropriately setting a and b, solubility in a solvent can be increased. The specific range of a and b is 1-10.

  In the solid electrolytic capacitor 1 according to the present embodiment, the capacitor element 10 is housed in a bottomed cylindrical outer case (not shown) formed of aluminum or the like, and the opening of the outer case has lead wires 6 and 7. In the drawn-out state, it has a structure sealed with a sealing material (not shown) such as resin or rubber.

  Next, a method for manufacturing the solid electrolytic capacitor 1 according to this embodiment will be described.

  First, the surface of the metal foil for forming the anode foil 2 and the surface of the metal foil for forming the cathode foil 3 are each roughened by etching. Next, an oxide film 2a is formed on the surface of the metal foil for forming the anode foil 2 by chemical conversion (anodic oxidation), and then cut into a predetermined dimension to obtain the anode foil 2. Moreover, the metal foil for forming the cathode foil 3 is cut into a predetermined size to obtain the cathode foil 3.

  The lead wires 6 and 7 are connected to the anode foil 2 and the cathode foil 3 on which the oxide film 2a is formed via lead tabs (not shown), respectively, and the anode foil 2 and the cathode foil 3 are connected to each other via the separator 4. To form a cylindrical winding element 11 (winding step).

  Next, chemical conversion is performed on the anode foil 2 in the state of the winding element 11 (restoration chemical conversion step). Thereby, the oxide film 2a damaged during the winding process is repaired, and the oxide film 2a is formed on the cut surface (cut edge) of the anode foil 2.

  Subsequently, the winding element 11 is heated to carbonize the separator 4 (heat treatment step). This heat treatment is performed in order to reduce the density of the separator 4 and reduce ESR. The heating temperature is, for example, 100 to 300 ° C. Note that this heat treatment may not be performed.

  Next, after impregnating the winding element 11 with a mixed solution of the monomer and the dopant having an oxidizing action (or dopant and oxidizing agent) and the compound represented by the chemical formula 1 (impregnation step), winding is performed by chemical polymerization. A solid electrolyte layer 5 made of a conductive polymer composition is formed between the anode foil 2 and the cathode foil 3 of the rotating element 11 (polymerization step).

  During this polymerization process, ether-bonded oxygen atoms present in the structure of the compound represented by Chemical Formula 1 are coordinated with the oxide film 2a of the anode foil 2 to form a protective film on the oxide film 2a. Is done.

  The capacitor element 10 formed as described above is housed in an outer case (not shown), and the opening of the outer case is sealed with a sealing material (not shown), and then an aging process is performed. Thereby, the solid electrolytic capacitor 1 is manufactured. The aging process is a process of applying a predetermined voltage in an environment where the solid electrolytic capacitor 1 is used at the highest temperature (or higher temperature), and is performed to reduce the leakage current of the solid electrolytic capacitor 1.

  In the embodiment, in the impregnation step, the winding element 11 is impregnated with the mixed solution of the monomer and the dopant solution having an oxidizing action (or the mixed solution of the dopant and the oxidizing agent) and the compound represented by the chemical formula 1. However, the impregnation treatment may be performed by the following methods (1) to (4).

(1) After impregnating the winding element 11 with a mixed solution of the monomer and the compound represented by the chemical formula 1, the winding element 11 is added with a dopant solution having an oxidizing action (or a mixed solution of a dopant and an oxidizing agent). To impregnate.
In addition, you may add the compound represented by Chemical formula 1 only to the solution finally impregnated to the winding element 11, ie, the dopant solution (or mixed solution of a dopant and an oxidizing agent) which has an oxidizing action.

(2) After impregnating the winding element 11 with the mixed solution of the monomer, the dopant and the compound represented by the chemical formula 1, the winding element 11 is impregnated with the mixed solution of the monomer and the oxidizing agent.
The compound represented by Chemical Formula 1 may be added only to the solution that is finally impregnated into the winding element 11, that is, the mixed solution of the monomer and the oxidizing agent.

(3) After impregnating the winding element 11 with a mixed solution of a dopant having an oxidizing action (or a dopant and an oxidizing agent) and the compound represented by the chemical formula 1, the winding element 11 is impregnated with a monomer solution.
The compound represented by Chemical Formula 1 may be added only to the solution that is finally impregnated into the winding element 11, that is, the monomer solution.

(4) After impregnating the winding element 11 with the mixed solution of the dopant and the compound represented by the chemical formula 1, the winding element 11 is impregnated with the monomer solution, and finally, the oxidizing agent solution is added to the winding element 11. To impregnate.
The compound represented by Chemical Formula 1 may be added only to the monomer solution or only to the oxidant solution.

  Note that, as described in the above embodiment, a method of forming a conductive polymer by chemical polymerization after impregnating the winding element 11 with one solution is called a one-liquid method. In addition, as described in (2) to (3) above, a method in which the winding element 11 is impregnated with two solutions in order and then a conductive polymer is generated by chemical polymerization is called a two-liquid method. Further, as described in (4) above, a method in which the winding element 11 is impregnated with three solutions in order and then a conductive polymer is generated by chemical polymerization is referred to as a three-liquid method.

  Moreover, in the said embodiment, although a conductive polymer is produced | generated only by chemical polymerization, you may produce | generate a conductive polymer combining a chemical polymerization and electrolytic polymerization.

  Next, specific examples of the present invention will be described together with comparative examples.

The solid electrolytic capacitors of Examples 1 to 4 were produced by the following procedure.
First, aluminum foil was used as the anode foil and the cathode foil. The aluminum foil for the anode foil was subjected to anodization with an applied voltage of 47 V to form an oxide film. After winding this anode foil and cathode foil through a separator made of manila paper to produce a winding element, this winding element was immersed in an aqueous solution of diammonium adipate and a voltage of 47 V was applied for 60 minutes. Then, restoration conversion was performed.

  Next, the wound elements of Examples 1 and 2 were immersed in the solutions shown in Table 1 containing the compounds A and B represented by Chemical Formulas 2 and 3, respectively, and then heated under the conditions shown in Table 1. Polyethylenedioxythiophene (PEDOT) was formed by chemical polymerization.

  In addition, the winding elements of Examples 3 and 4 were immersed in the first solution shown in Table 2, respectively, and then heated under the conditions shown in Table 2 to evaporate the solvent. Then, after immersing a winding element in the 2nd solution shown in Table 2 containing each of compounds C and D represented by Chemical Formulas 4 and 5, the PEDOT is heated by chemical polymerization and heated under the conditions shown in Table 2. Formed.

  The capacitor element of the example produced as described above was housed in a bottomed cylindrical outer case, and the opening was sealed with rubber packing or the like to produce solid electrolytic capacitors.

Moreover, the solid electrolytic capacitor of the comparative example was produced according to the following procedure.
PEDOT was formed by chemical polymerization by heating under the conditions shown in Table 1 in the same manner as in Example 1 except that the winding element was immersed in the solution shown in Table 1 not containing the compound of Chemical Formula 1.
A solid electrolytic capacitor was produced in the same manner as in the example using the capacitor element thus produced.

  For the solid electrolytic capacitors of Examples 1 to 4 and Comparative Example above, the compounds added and the results of the measured electrical properties are shown in Table 3. As the electrical characteristics, capacitance (measurement frequency 120 Hz), tan δ (measurement frequency 100 kHz), ESR (measurement frequency 100 kHz), leakage current (rated voltage application), and short-circuit occurrence rate during aging were measured. Aging was performed by applying a rated voltage at 100 ° C. for 60 minutes. Note that the number of each test is 50, and the capacitance, tan δ, ESR, and leakage current are average values of those excluding the shorted product.

As shown in Table 3, in Examples 1 to 4, the leakage current is reduced as compared with the comparative example. Moreover, since Examples 1-4 have also reduced the incidence rate of a short circuit compared with a comparative example, it turns out that the withstand voltage is improving.
Moreover, although the comparative example is performing the heat processing for reducing ESR, the ESR of Examples 1-4 is more reduced than this comparative example.

  In the above embodiment, PEDOT is used as the conductive polymer. However, it is confirmed that the same effect can be obtained when a known conductive polymer other than PEDOT (for example, polyaniline or polypyrrole) is used. Has been.

  In the above embodiment, the conductive polymer is generated by the one-liquid method or the two-liquid method, but the same effect can be obtained when the two-liquid method and the three-liquid method other than the examples are used. It has been confirmed.

  Furthermore, in the above embodiment, aluminum is used as the material of the anode foil, but it has been confirmed that the same effect can be obtained when tantalum or niobium is used.

  In the above embodiment, the winding element is used, but the solid electrolyte of the solid electrolytic capacitor that forms the solid electrolyte on the anode body formed by forming and sintering the valve action metal powder and forming the oxide film is used. It has been confirmed that similar effects can be obtained when used.

It is a disassembled perspective view of the capacitor | condenser element in the solid electrolytic capacitor which concerns on this invention. It is a conceptual diagram which shows the structure of the solid electrolytic capacitor which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid electrolytic capacitor 2 Anode foil 2a Oxide film 3 Cathode foil 4 Separator 5 Solid electrolyte layer 6, 7 Lead wire 10 Capacitor element 11 Winding element

Claims (3)

A solid electrolytic capacitor in which a solid electrolyte layer made of a conductive polymer composition is formed,
The said conductive polymer composition contains the compound represented by following Chemical formula 1, The solid electrolytic capacitor characterized by the above-mentioned.

However, in formula, OA represents a C2-C4 oxyalkylene group, n represents the number of 1-50, a and b represent the number of 1-10.   The solid electrolytic capacitor according to claim 1, wherein the conductive polymer is any one of polythiophene, polyaniline, polypyrrole, and derivatives thereof. An impregnation step of impregnating a capacitor element having an oxide film formed on its surface with a monomer, a dopant, an oxidant, and a compound represented by the following chemical formula 1 that become a conductive polymer by polymerization;
A polymerization step of forming a solid electrolyte layer comprising a conductive polymer composition on the surface of the oxide film by polymerization;
A method for producing a solid electrolytic capacitor, comprising:

However, in formula, OA represents a C2-C4 oxyalkylene group, n represents the number of 1-50, a and b represent the number of 1-10.

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