JP2005197309A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor having good electrostatic capacitance characteristics. <P>SOLUTION: The solid electrolytic capacitor includes a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator and a conductive polymer is held by the separator. Since an aluminum foil, such as an etching foil, a plane foil, etc. having a film made of an ITO formed on the front surface is used as the cathode electrode foil, the electrostatic capacity, the ESR characteristics are good by the good conductivity of the ITO. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

  An electrolytic capacitor is made of a valve action metal such as tantalum or aluminum, and has a structure in which an oxide film layer serving as a dielectric is formed on the surface of an anode electrode having fine holes and etching pits, and an electrode is drawn from the oxide film layer. Become. And extraction of the electrode from an oxide film layer is performed by the electrolyte layer which has electroconductivity. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. Such an electrolyte layer functioning as a true cathode is required to have adhesion, denseness, and uniformity with the oxide film layer. In particular, the adhesion within the fine holes of the anode electrode and the etching pits has a great influence on the electrical characteristics, and a number of electrolyte layers have been proposed in the past.

  By the way, in recent years, with the digitization and high frequency of electronic equipment, a capacitor having a small size and a large capacity and a low impedance in a high frequency region is required.

In response to these requirements, a capacitor element in which a cathode foil and an anode foil are wound through a separator is housed in a metal case, and a small and large capacity is realized by a wound type electrolytic capacitor that is sealed with a sealing rubber. Can do. And it can respond to low impedance by using a solid electrolyte as an electrolyte. As such a solid electrolyte, conductive polymers having high conductivity such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex, polypyrrole, polythiophene and the like are known. Attention is now focused on polyethylenedioxythiophene (PEDT), which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode (see Patent Document 1), and as a result, the anode electrode foil and the cathode electrode Capacitor element wound with foil through a separator is impregnated with monomer and oxidant, and then polyethylenedioxythiophene, which is a solid electrolyte, is generated by a chemical polymerization reaction between the monomer and oxidant that occurs slowly. (See Patent Document 2).
JP-A-2-15611 Japanese Patent Laid-Open No. 10-340829

By the way, in recent years, electronic information devices have been digitized, and the driving frequency of the microprocessor which is the heart of these electronic information devices has been increased. Along with this, the power consumption has been increasing and the problem of reliability due to heat generation has become obvious. Therefore, the drive voltage has been reduced as a countermeasure.

In order to reduce the drive voltage, a large number of capacitors having low ESR are used as output-side capacitors of a power supply that supplies highly accurate power to the microprocessor. As the capacitor having such a low ESR characteristic, the solid electrolytic capacitor as described above is used.

However, the increase in the driving frequency of the microprocessor is remarkable, and accordingly, the power consumption further increases, and further increase in the power supplied from the capacitor is required. For this reason, the solid electrolytic capacitor is required to have a large capacity. ing.

Accordingly, an object of the present invention is to provide a solid electrolytic capacitor having a high capacitance in order to solve the above-described problems.

    The present invention relates to a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator and a conductive polymer is held by the separator. The aluminum foil which formed is used.

ITO (Indium Tin Oxide) is an indium tin oxide in which indium oxide In ₂ O ₃ is doped with tin oxide SnO ₂ and has high conductivity and high transmittance.

  The solid electrolytic capacitor of the present invention will be described. An anode electrode foil made of a valve action metal such as aluminum and having an oxide film layer formed on the surface thereof and a cathode electrode foil are wound through a separator to form a capacitor element. The conductive polymer is held in the separator of the capacitor element.

  The anode electrode foil is made of a valve action metal such as aluminum, and an oxide film layer serving as a dielectric is formed on the surface of the anode electrode foil by applying a voltage in an aqueous solution of ammonium adipate or the like. The cathode electrode foil is made of aluminum or the like like the anode electrode foil, and the surface is subjected to etching treatment.

  Anode extraction means and cathode extraction means for connecting the respective electrodes to the outside are connected to the anode electrode foil and the cathode electrode foil by known means such as stitching and ultrasonic welding. These electrode lead-out means are led out from the end face of the wound capacitor element.

  The capacitor element is formed by winding the anode electrode foil and the cathode electrode foil with a separator interposed therebetween. The dimensions of the bipolar electrode foil are arbitrary depending on the specifications of the solid electrolytic capacitor to be manufactured, and the separator having a slightly larger width may be used depending on the dimensions of the bipolar electrode foil.

  A conductive polymer is formed in this capacitor element. When polyethylenedioxythiophene (PEDT) is used as the conductive polymer, a solid electrolytic capacitor having a large capacity and low ESR characteristics can be obtained. This PEDT can be obtained by polymerizing 3,4-ethylenedioxythiophene (EDT) as a monomer with ferric p-toluenesulfonate as an oxidizing agent. Polymerization can be performed by injecting EDT or an EDT solution and an oxidant solution into a capacitor element and heating, or by injecting a mixed liquid of EDT and an oxidant into the capacitor element, or immersing the capacitor element in a mixed solution. It can also be performed by heating.

  Then, the capacitor element in which the conductive polymer is formed is housed in a bottomed cylindrical metal case, and is swaged and sealed with a sealing rubber to form a solid electrolytic capacitor.

  Here, in this invention, the aluminum foil which formed the film | membrane which consists of ITO on the surface is used as a cathode electrode foil. Examples of the method for forming a film made of ITO include chemical film formation methods such as spray pyrolysis and CVD, and physical film formation methods such as electron beam evaporation and sputtering. Among these, the sputtering method is preferable because it is a film forming method that can easily increase the area and obtain a high-performance film.

When a film made of ITO is formed by a sputtering method, an alloy target made of metal indium and metal tin or a composite oxide target made of indium oxide and tin oxide can be used as a sputtering target, and can be formed by an ordinary sputtering method.

As the aluminum foil, an etching foil or a plain foil, an etching foil having a chemical conversion film formed on the surface, or a plain foil having a chemical conversion film formed on the surface can be used. In particular, when a plain foil is used, the thickness of the foil can be reduced because there is no etched portion compared to the etching foil, and the capacitance can be increased by increasing the foil area. Moreover, although it seems that when a chemical conversion film is formed on these aluminum foils, the adhesiveness of the conductive polymer to the aluminum foil is improved, ESR is reduced.

  In the above solid electrolytic capacitor, the specific electric resistance of ITO formed on the surface of the cathode foil is low, so that the conductive polymer and the cathode foil are in a conductive state, the combined capacity of the capacitor is maximized, and the capacitance is increased. It becomes. Furthermore, since the adhesion between ITO and the conductive polymer is good, ESR is reduced.

    The present invention relates to a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator and a conductive polymer is held by the separator. Since the aluminum foil formed is used, the capacitance characteristics and the ESR characteristics are good.

Next, the solid electrolytic capacitor of the present invention will be specifically described.
The anode electrode foil and the cathode electrode foil are made of a valve metal, such as aluminum or tantalum, and the surface thereof is preliminarily etched to increase the surface area. The anode electrode foil is further subjected to chemical conversion treatment, and an oxide film layer made of aluminum oxide is formed on the surface. The anode electrode foil and the cathode electrode foil are wound through a separator to obtain a capacitor element.

  Next, the capacitor element is impregnated with EDT and an oxidizing agent. As the oxidizing agent, a butanol solution of ferric p-toluenesulfonate is used and polymerized by heating at 150 ° C. for 1 hour to produce PEDT which is a conductive polymer.

  Thus, the capacitor element in which the conductive polymer layer is formed on the separator interposed between the anode electrode foil and the cathode electrode foil is housed in a bottomed cylindrical case and sealed with a sealing rubber made of butyl rubber. A solid electrolytic capacitor is formed. The rating is 2.5 WV-820 μF.

  Here, as Example 1, a 50 μm etching foil having a 0.5 μm ITO film formed thereon, a 30 μm plain foil having a 0.5 μm ITO film formed as Example 2, and a 0.5 μm ITO film as Example 3 were used. As a cathode foil, a 50 μm 2V conversion etching foil having a film formed thereon and a 30 μm 2V conversion plain foil having a 0.5 μm ITO film formed thereon as Example 4 were used.

  Further, as Comparative Example 1, a 50 μm etching foil formed with a 0.3 μm titanium nitride film was used, and as Comparative Example 2, a 50 μm 2V chemical conversion etching foil formed with a 0.3 μm titanium nitride film was used.

  Next, initial characteristics of these solid electrolytic capacitors are shown in (Table 1).

(Table 1)
┌────────┬────────┬────────┐
│ │Capacitance (μF) │ ESR (mΩ) │
├────────┼────────┼────────┤
│ Example 1 │ 854 │ 7.3 │
├────────┼────────┼────────┤
│ Example 2 │ 927 │ 6.6 │
├────────┼────────┼────────┤
│ Example 3 │ 853 │ 5.3 │
├────────┼────────┼────────┤
│ Example 4 │ 923 │ 6.5 │
├────────┼────────┼────────┤
│ Comparative Example 1 │ 849 │ 10.8 │
├────────┼────────┼────────┤
│ Comparative Example 2 │ 849 │ 8 │
└────────┴────────┴────────┘

As described above, the example has better electrostatic capacity and ESR than the comparative example.

Claims (4)

In a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator and a conductive polymer is held by the separator, an aluminum having a film made of ITO formed on the surface as a cathode electrode foil Solid electrolytic capacitor using foil. 2. The solid electrolytic capacitor according to claim 1, wherein the aluminum foil is an etching foil or a plain foil. 2. The solid electrolytic capacitor according to claim 1, wherein the aluminum foil is an etching foil having a chemical conversion film formed on a surface thereof, or a plain foil having a chemical conversion film formed on a surface thereof. 4. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer is polyethylene dioxythiophene formed by chemical polymerization of 3,4-ethylenedioxythiophene and an oxidizing agent.