JP2009130339A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further reduce resistance by electrically and reliably connecting a tab terminal to electrode foil, and to reduce a leakage current and improve a withstand voltage. <P>SOLUTION: In a method of manufacturing a solid electrolytic capacitor for forming a solid electrolyte made of an electroconductive polymer in a capacitor element 6 composed by winding or laminating anode electrode foil 3 and cathode electrode foil 4 to which tab terminals 1, 2 are mounted, respectively, via a separator as shown in Fig. 1, when manufacturing a capacitor element, unformed tab terminals, where no chemical coating films by chemical formation or anodic oxidation are formed on a connection surface with the electrode foil of at least a tab terminal, are mounted to the electrode foils each, and then the unformed tab terminals are subjected to chemical formation treatment during a formation process of the solid electrolytic capacitor to form them as chemical formation tab terminals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a foil wound type or foil laminated type solid electrolytic capacitor using a solid electrolyte made of a conductive polymer, and more specifically, a technique for reducing connection resistance between a tab terminal and an electrode foil. It is about.

  As shown in FIG. 1, a solid electrolytic capacitor using a solid electrolyte made of a conductive polymer has a basic configuration in which both tab terminals 1 and 2 are connected to an anode electrode foil 3 and a cathode electrode foil 4 as lead terminals, respectively. It is attached.

  In the foil-wound solid electrolytic capacitor, a conductive element with an appropriate conductivity selected from polypyrrole, polythiophene, or the like is used for the capacitor element 6 formed by winding the anode electrode foil 3 and the cathode electrode foil 4 with the separator 5 therebetween. It is produced by impregnating and polymerizing molecules to form a solid electrolyte, which is housed in an exterior case (not shown), and the opening is sealed with a sealing body or resin.

  As shown in FIG. 2, the tab terminals 1 and 2 include a terminal main body 11 and a CP wire (solder-plated copper-coated steel wire) 12 attached to the terminal main body 11. In recent years, solder plating of CP wire has been changed from lead to lead-free.

  The terminal body 11 is formed by using a round bar wire of aluminum as a base material, leaving a round bar portion 11a of a predetermined length, and forming one end side of the round bar wire by a press, for example, to form a flat plate portion 11b like a battledore. The CP wire 3 is attached to the other end of the round bar portion 11a by welding.

  The tab terminals 1 and 2 are usually attached to the electrode foils 3 and 4 by caulking, respectively. That is, as shown in FIG. 2, the flat portions 11b of the tab terminals 1 and 2 are respectively arranged on the electrode foils 3 and 4, and usually, for example, two caulking needles 7 and 7 are pierced from the flat portion 11b side. The flat portion 11b and the electrode foils 3 and 4 are penetrated.

  A piercing hole penetrating the flat portion 11b and the electrode foils 3 and 4 is formed by the piercing of the caulking needles 7 and 7, and a petal-like nail piece protruding toward the electrode foils 3 and 4 around the piercing hole. (Both not shown) are formed, and at the same time, the claw pieces are crushed and pressure-bonded to firmly press the electrode foils 3 and 4.

  In an aluminum solid electrolytic capacitor, the separator 5 may be carbonized before impregnating the conductive polymer.

  Usually, polythiophene and polypyrrole are generally used as the conductive polymer used in the aluminum solid electrolytic capacitor. However, since the conductive polymer is poor in formation of a chemical conversion film and restorability, the tab terminals 1 and 2 are previously provided. A chemical conversion film is formed.

  Before forming the aluminum round bar wire into the tab terminal shape from the viewpoint of its productivity, the tab terminals 1 and 2 were immersed in the chemical conversion liquid as a long round bar wire to form a chemical conversion film on the surface. So-called aluminum conversion wires are used.

When the aluminum chemical conversion wire is used, a part of the chemical conversion film on the surface is damaged by an impact when the flat portion 11b is formed by pressing a round bar. Therefore, chemical conversion is performed again before the tab terminal is attached to the electrode foil, or the aluminum conversion film (Al ₂ O ₃ ) is repaired in the process of forming a conversion film on the side surface of the electrode foil or the capacitor aging process. (For example, refer to Patent Document 1).

JP 2001-176753 A

  However, when using a chemical conversion tab terminal to which a chemical conversion film has been applied in advance, there is a problem that the connection resistance with the electrode foil is high, and it is difficult to reduce the leakage current and improve the withstand voltage.

  In order to investigate the cause, the present inventors observed the surface of the chemical conversion tab terminal whose chemical conversion film was repaired by the above-mentioned method with an electron microscope. The electron micrograph is shown in FIG. As can be seen, a non-uniform chemical conversion film including a large number of irregularities is formed on the surface of the tab terminal repaired with the chemical conversion film.

  This non-uniform conversion coating is due to the fact that the conversion coating damaged when pressing the aluminum conversion wire cannot be completely repaired and does not become a uniform coating. It was found that the connection resistance between the electrode foil and the electrode foil was increased, and that the reduction of leakage current and the improvement of the withstand voltage were hindered.

  Therefore, the subject of the present invention is to solidly connect the tab terminal and the electrode foil in a solid electrolytic capacitor using a solid electrolyte made of a conductive polymer to further reduce the resistance, The purpose is to reduce the leakage current and improve the withstand voltage.

  In order to solve the above-described problems, the present invention provides a solid electrolyte made of a conductive polymer on a capacitor element in which an anode electrode foil and a cathode electrode foil each having a tab terminal attached thereto are wound or laminated via a separator. In the method for producing a solid electrolytic capacitor to be formed, at the time of producing the capacitor element, an unformed tab terminal in which a chemical conversion film by chemical conversion or anodic oxidation is not formed at least on the connection surface of the tab terminal with the electrode foil is used as the electrode foil. Each of the non-formed tab terminals is formed into a formed tab terminal by performing a chemical conversion process in the forming step in the solid electrolytic capacitor forming step.

  In the present invention, it is preferable that the unformed tab terminal is subjected to a chemical conversion treatment before the solid electrolyte is formed on the capacitor element.

  Further, as a preferred embodiment of the present invention, after the chemical conversion treatment is performed, before the solid electrolyte is formed on the capacitor element, re-chemical conversion is performed for 1/6 to 1/2 of the time required for the chemical conversion treatment. Processing may be performed.

  Moreover, it is preferable to perform a chemical conversion treatment or a re-chemical conversion treatment with the chemical conversion liquid which has an adipic acid type, a phosphoric acid type, or a boric acid type as a main component.

  In this case, the chemical conversion liquid used for the re-chemical conversion treatment may be the same chemical conversion liquid as that used in the chemical conversion treatment, but preferably a different chemical conversion liquid is used.

  According to the present invention, by attaching an unformed tab terminal having no chemical film formed by chemical conversion or anodic oxidation on the surface of the portion connected to the electrode foil to the electrode foil, the tab terminal is then subjected to chemical conversion treatment. Since a uniform chemical conversion film is formed on the surface of the tab terminal, the connection resistance between the tab terminal and the electrode foil is reduced, the leakage current from the weak part of the chemical conversion film is reduced, and the voltage resistance is improved. .

  Also in the present invention, as shown in FIG. 1, as a basic configuration, an anode electrode foil 3 and a cathode electrode foil 4 to which tab terminals 1 and 2 are attached as charge / discharge electrode terminals are provided via a separator 5. The capacitor element 6 is rolled and impregnated with a conductive polymer to be polymerized to form a solid electrolyte, which is housed in a bottomed cylindrical aluminum metal case (not shown), and the opening is used as a sealing body. Thus, a foil wound type solid electrolytic capacitor using a solid electrolyte made of a conductive polymer is manufactured.

  For the electrode foils 3 and 4, valve metal foils such as aluminum, tantalum, and titanium, alloy foils or vapor deposition foils thereof are used.

  As shown in FIG. 2, the tab terminals 1 and 2 include a terminal main body 11 and a CP wire (solder-plated copper-coated steel wire) 12 attached to the terminal main body 11.

  The terminal body 11 is formed by using a round bar wire made of aluminum as a base material, leaving a round bar portion 11a having a predetermined length, and forming one end side thereof as a flat plate portion 11b by pressing, for example, a CP wire 12 Is attached to the other end of the round bar 11a by welding.

  In the present invention, an unformed aluminum round bar wire is used for the terminal body 11. The unformed aluminum round bar wire refers to a solid aluminum round bar wire that does not have a chemical conversion film intentionally formed on the surface of the round bar wire by chemical conversion or anodizing treatment.

  That is, the tab terminals 1 and 2 used in the present invention are unformed terminals in which a chemical conversion film by chemical conversion or anodic oxidation is not formed at least at a position where they are in contact with the electrode foils 3 and 4. The terminals (unformed tab terminals) 1 and 2 are attached to the electrode foils 3 and 4 as they are.

  When the caulking is adopted as the mounting method, as shown in FIG. 2, the flat portions 11b of the tab terminals 1 and 2 are overlapped on the electrode foils 3 and 4, respectively, and the caulking needles 7 and 7 are attached from the flat portion 11b side. pierce. In the illustrated example, there are two caulking locations, but there may be 3 or more locations. Moreover, depending on the case, one place may be sufficient.

  Note that the method of attaching the tab terminals 1 and 2 to the electrode foils 3 and 4 may be laser welding, ultrasonic welding, cold pressure welding, or the like in addition to caulking.

  In the present invention, 3,4-ethylenedioxythiophene is preferable as the conductive polymer, but various monomers that become conductive polymers by oxidative polymerization such as pyrrole, thiophene, furan, aniline, and derivatives thereof may be used. Good.

Examples of the oxidizing agent applied to the present invention include an aqueous oxidizing agent and an organic solvent oxidizing agent. Examples of the aqueous oxidizing agent include peroxodisulfuric acid and its Na salt, K salt, NH ₄ salt, Examples include cerium (IV) nitrate, ammonium cerium (IV) nitrate, iron (III) sulfate, iron (III) nitrate, and iron (III) chloride.

  Examples of organic solvent-based oxidizing agents include ferric salts of organic sulfonic acids such as ferric paratoluenesulfonate, iron (III) dodecylbenzenesulfonate, and iron (III) p-toluenesulfonate. However, it is not limited to these.

  Examples of the solvent for the oxidant solution include ethers such as tetrahydrofuran (THF), dioxane, and diethyl ether; ketones such as acetone and methyl ethyl ketone, dimethylformamide, acetonitrile, benzonitrile, N-methylpyrrolidone (NMP), dimethyl sulfoxide ( An aprotic solvent such as DMSO), alcohols such as methanol, butanol, and propanol, water, or a mixed solvent thereof can be used. Preferably, water, alcohols or ketones or a mixed system thereof is desirable.

  The chemical conversion treatment time of the unformed tab terminal in the present invention may be arbitrarily selected, but if the liquid temperature is high, the immersion time can be shortened. For example, at a liquid temperature of 85 ° C., the immersion time is about 30 minutes. Can do.

  Examples of the chemical conversion liquid include phosphoric acid and boric acid in addition to adipic acid. The voltage applied during the chemical conversion treatment is preferably applied at least twice the rated voltage of the aluminum solid electrolytic capacitor to increase the withstand voltage of the chemical conversion film.

  Moreover, it is preferable that the unformed tab terminal in the present invention is re-formed as necessary after the chemical conversion treatment step. In this case, assuming that the liquid temperature is the same as the chemical liquid used in the chemical conversion treatment step, the re-chemical conversion treatment time may be about 1/6 to 1/2 of the chemical conversion treatment time. Examples of the re-chemical conversion liquid include adipic acid-based, phosphoric acid-based, boric acid-based and the like, similar to the chemical conversion liquid in the chemical conversion treatment step.

[Example 1]
First, an aluminum round bar wire not subjected to chemical conversion or anodization was pressed to produce an unformed tab terminal having a flat portion having a width of 2.5 mm and a thickness of 190 μm. Using a pair of these unformed tab terminals, an anode foil having a thickness of 100 μm and a width of 2.2 mm is attached to a flat portion of one unformed tab terminal, and a thickness is attached to the flat portion of the other unformed tab terminal. A cathode foil of 60 μm and a width of 2.2 mm was attached in the same manner. And it wound by interposing a separator between anode foil and cathode foil, and produced a capacitor element.

  Next, in order to repair the defects existing in the oxide film of each electrode foil of the anode foil and the cathode foil, and to form a chemical conversion film on the cut surface of the electrode foil side surface and the flat portion of the tab terminal, the main component is ammonium adipate. The solution was immersed in a chemical conversion solution for 20 to 60 minutes, and a voltage was applied to perform chemical conversion. In this embodiment, the applied voltage is set to 32 V or more because the rated voltage is 16 V in order to provide a margin for the withstand voltage.

  Next, after applying heat of 200 ° C. or higher at which the separator carbonized to the capacitor element to carbonize the separator, re-chemical conversion was performed by immersing in a chemical conversion liquid mainly composed of ammonium phosphate for 5 to 20 minutes.

  When the flat part of the tab terminal after this re-chemical conversion was observed with an electron microscope, a substantially uniform chemical conversion film was observed as shown in FIG. This is because the base of the unformed tab terminal does not have an oxide film by chemical conversion or anodization in the first place, and has no irregularities due to defects due to the oxide film.

  Since it is preferable to carbonize the separator of the capacitor element, in Example 1, the separator was carbonized by heat treatment, but it is not necessary to carbonize.

  Next, a thiophene monomer (3,4-ethylenedioxythiophene), which is a conductive polymer, was impregnated into a capacitor element and polymerized, followed by heat treatment to produce a solid electrolyte in the capacitor element.

  After this capacitor element is put in an aluminum outer case and sealed with a rubber sealing body and assembled, it is subjected to an aging treatment for 100 minutes or more by applying a voltage in a heated atmosphere of 130 ° C. or higher to obtain an aluminum solid electrolytic capacitor. Produced.

[Comparative Example 1]
The aluminum solid electrolytic capacitor was subjected to the same process as in Example 1 except that an aluminum conversion wire was used as a tab terminal, a conversion tab terminal that was re-formed after molding, and the conversion treatment time was 5 minutes. Was made. The reason for shortening the chemical conversion treatment time to 5 minutes as compared to 30 minutes in Example 1 is to prevent the chemical conversion film from being formed thicker on the chemical conversion tab terminal.

[Comparative Example 2]
Although the unchemical tab terminal was used like the said Example 1, the chemical conversion treatment time was 10 minutes. Other than that, the aluminum solid electrolytic capacitor was produced through the same steps as in Example 1 above.

  According to Example 1 and Comparative Examples 1 and 2, 600 samples of an aluminum solid electrolytic capacitor equivalent to a rating of 16 V 100 μF were prepared, and a voltage was applied between the capacitor terminals at a sweep speed of 100 V / min for each of the samples. The change in current value at that time was measured. The measurement result (average value) in each example is shown in the graph of FIG.

  According to this, in each of Comparative Examples 1 and 2, the current suddenly increases after the voltage exceeds 15V, while in Example 1, the current increase is suppressed to about 18V, and the withstand voltage is It can be seen that it has improved by about 20%.

  Further, five characteristics after aging of each sample according to Example 1 and Comparative Examples 1 and 2 (formation final current (μA), capacity (μF), tan δ, ESR (mΩ), leakage current (μA); Table 1 shows the measurement results.

  In Example 1, the ESR is low and the leakage current is small as compared with Comparative Example 1. Since Comparative Example 2 uses an unformed tab terminal, the leakage current is large although the ESR is low. This is because the chemical conversion treatment time was shorter than that of Example 1 and the formation of the oxide film was insufficient.

  In addition to the foil wound type, the present invention can also be applied to a stacked solid electrolytic capacitor in which an anode foil and a cathode foil each having a tab terminal attached thereto are stacked via a separator.

The typical disassembled perspective view which shows the structure of a foil winding type solid electrolytic capacitor. The typical perspective view showing the state where a tab terminal is connected to electrode foil by caulking. The electron micrograph which image | photographed the surface of the tab terminal formed by this invention. The graph which shows the voltage-current characteristic of Example 1 and Comparative Examples 1 and 2. FIG. The electron micrograph which image | photographed the surface of the chemical conversion tab terminal used conventionally.

Explanation of symbols

1, 2 Tab terminal 1 Terminal body 11a Round bar portion 11b Flat portion 12 CP wire 3, 4 Electrode foil 5 Separator 6 Capacitor element

Claims (5)

In a method for producing a solid electrolytic capacitor, in which a solid electrolyte made of a conductive polymer is formed on a capacitor element formed by winding or laminating an anode electrode foil and a cathode electrode foil each having a tab terminal attached thereto via a separator,
At the time of making the capacitor element, at least the unformed tab terminal on which the chemical conversion or anodic oxidation conversion film is not formed on the connection surface of the tab terminal with the electrode foil is attached to the electrode foil, and the unformed tab terminal is attached. A method for producing a solid electrolytic capacitor, characterized in that a chemical conversion treatment is performed in a chemical conversion step in the solid electrolytic capacitor forming step to form a chemical conversion tab terminal.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the unformed tab terminal is subjected to a chemical conversion treatment before the solid electrolyte is formed on the capacitor element.   After the chemical conversion treatment is performed, before the solid electrolyte is formed on the capacitor element, the chemical conversion treatment is performed for 1/6 to 1/2 of the time required for the chemical conversion treatment. Item 3. A method for producing a solid electrolytic capacitor according to Item 1 or 2.   4. The solid electrolysis according to any one of claims 1 to 3, wherein the chemical conversion treatment or the re-chemical conversion treatment is performed with a chemical conversion liquid mainly composed of adipic acid, phosphoric acid, or boric acid. Capacitor manufacturing method.   The method for producing a solid electrolytic capacitor according to claim 3 or 4, wherein a chemical conversion liquid used in the re-chemical conversion treatment is different from a chemical conversion liquid used in the chemical conversion treatment.