JP2010021419A - Solid-state electrolytic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor, which little deteriorates with time, and its manufacturing method. <P>SOLUTION: The electrolytic capacitor 1 includes a capacitor element 2 in which an anode foil 21 with an anodic oxidation film 21a formed thereon and a cathode foil 22 are wound through a separator 23 and a solid-state electrolytic layer 24 consisting of conductive polymer is retained by the separator 23, while sodium hydrogencarbonate 21b is dispersed between the anodic oxidation film 21a and the solid-state electrolytic layer 24. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 or an anode body made of a valve metal such as aluminum, tantalum, or niobium, and an oxide film serving as a dielectric is formed on the surface of the anode foil or anode body. Electrical extraction from the oxide film is performed by a conductive electrolyte that is in contact with the oxide film, and the electrolyte serves as a true cathode in the electrolytic capacitor. 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, the solid electrolytic capacitor uses, for example, a conductive polymer such as polyethylenedioxythiophene (PEDOT) as an electrolyte, and has a higher frequency range than an electrolytic capacitor using a liquid electrolyte. Is excellent in impedance characteristics (see, for example, Patent Document 1).
An electron-accepting substance (dopant such as p-toluenesulfonic acid or p-styrenesulfonic acid) is added to the solid electrolyte layer made of such a conductive polymer, and this dopant is removed from the polymer chain. The polymer has conductivity by extracting electrons and generating holes (carriers) in the polymer.

In recent years, various electronic devices have been digitized, and solid electrolytic capacitors are required to have a large capacity and a small size. As a solid electrolytic capacitor satisfying such a requirement, there is a wound type solid electrolytic capacitor.
A winding type solid electrolytic capacitor includes a capacitor element in which an anode foil and a cathode foil on which an oxide film is formed are wound through a separator, and a solid electrolyte layer made of a conductive polymer is held on the separator. The capacitor element is housed in a bottomed cylindrical case, and the opening is sealed with a rubber sealing material through which a lead wire connected to the electrode foil is penetrated (for example, a patent Reference 1).

JP 2001-102254 A

  Further, in recent years, since solid electrolytic capacitors are often used in a high frequency region, there is a demand for solid electrolytic capacitors to improve electrical characteristics. However, in the solid electrolytic capacitor, the strongly acidic dopant (for example, p-toluenesulfonic acid) contained in the solid electrolyte deteriorates the oxide film of the anode foil, so that the electrical characteristics deteriorate with time.

  Accordingly, an object of the present invention is to provide a solid electrolytic capacitor with small deterioration of electrical characteristics with time and a method for manufacturing the same.

  The solid electrolytic capacitor of the present invention is a capacitor in which an anode foil having an oxide film formed on its surface and a cathode foil are wound through a separator, and a solid electrolyte layer made of a conductive polymer is held on the separator. A solid electrolytic capacitor including an element and a case in which the capacitor element is accommodated, wherein sodium hydrogen carbonate is dispersed between the anode foil and the solid electrolyte layer.

  Further, in the method for producing a solid electrolytic capacitor of the present invention, an anode foil having an oxide film formed on a surface thereof and a cathode foil are wound through a separator, and the separator is made of a solid electrolyte layer made of a conductive polymer. A solid electrolytic capacitor comprising a capacitor element holding the capacitor element and a case in which the capacitor element is accommodated, the capacitor element forming step for forming the capacitor element, and the capacitor element in a sodium hydrogen carbonate solution A sodium bicarbonate dispersion step of dispersing sodium bicarbonate between the anode foil and the solid electrolyte layer.

  According to the present invention, since sodium hydrogen carbonate is dispersed between the anode foil and the solid electrolyte layer, the dopant contained in the solid electrolyte in the capacitor element (for example, p-toluenesulfonic acid, p-styrenesulfonic acid) ) Is neutralized. As a result, it is possible to provide a solid electrolytic capacitor that suppresses deterioration of the anodized film and has little deterioration in electrical characteristics with time.

  In the present invention, the conductive polymer is preferably any of polyaniline, polypyrrole, polythiophene, and polyethylenedioxythiophene. Thereby, the electroconductivity and heat resistance of a solid electrolyte layer improve.

  Moreover, in this invention, it is preferable that the density | concentration of the said sodium hydrogencarbonate solution exists in the range of 5% to a saturated state. By taking such a range, the neutralization reaction with the dopant contained in the solid electrolyte in the capacitor element proceeds favorably, it is possible to suppress the deterioration of the anodic oxide film and to suppress the deterioration of the electrical characteristics over time.

  According to the present invention, since sodium hydrogencarbonate is dispersed between the anode foil and the solid electrolyte layer, the dopant contained in the solid electrolyte in the capacitor element is neutralized. As a result, it is possible to provide a solid electrolytic capacitor that suppresses deterioration of the anodized film and has little deterioration in electrical characteristics with time.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing the appearance and internal structure of a solid electrolytic capacitor 1 of the present invention. FIG. 2 is an exploded perspective view of the capacitor element 2. FIG. 3 is a conceptual diagram showing the configuration of the solid electrolytic capacitor 1.
As shown in FIG. 1, the solid electrolytic capacitor 1 of the present embodiment includes a capacitor element 2, an outer case 4, and a sealing material 5.

As shown in FIG. 2, the capacitor element 2 has a structure in which an anode foil 21 and a cathode foil 22 are wound via a separator 23.
Further, lead tabs (not shown) are connected to the anode foil 21 and the cathode foil 22, respectively, and lead wires 25a and 25b are drawn from the anode foil 21 and the cathode foil 22 through the lead tabs, respectively.

The anode foil 21 is made of a valve metal such as aluminum, tantalum, or niobium. As shown in FIG. 3, the surface of the anode foil 21 is roughened by an etching process, and an anodized film 21a is formed by anodic oxidation (chemical conversion). Further, sodium hydrogen carbonate 21b is dispersed on the surface of the anodized film 21a.
The cathode foil 22 is also formed of aluminum or the like, like the anode foil 21, and the surface thereof is roughened and a natural oxide film 22a is formed.

The separator 23 holds a solid electrolyte layer 24 made of a conductive polymer. That is, the solid electrolyte layer 24 is formed between the anode foil 21 and the separator 23 and between the cathode foil 22 and the separator 23. Further, sodium hydrogen carbonate 21 b is dispersed in the anodic oxide film 21 a and the solid electrolyte layer 24.
As the conductive polymer of the solid electrolyte layer 24, polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene (PEDOT), or the like excellent in conductivity and heat resistance can be used. Such a conductive polymer is produced by chemical polymerization of monomers. The solid electrolyte layer 24 contains p-toluenesulfonic acid as a dopant. In addition, p-styrene sulfonic acid may be contained as a dopant.

  The outer case 4 is made of aluminum or the like and is formed in a bottomed cylindrical shape. The outer case 4 houses the capacitor element 2.

  The sealing material 5 seals the opening of the outer case 4 and is formed of resin, rubber, or the like. The lead wires 25 a and 25 b of the capacitor element 2 are drawn from the outer case 4 through the through holes formed in the sealing material 5.

Next, a method for manufacturing the solid electrolytic capacitor 1 will be described with reference to FIG. FIG. 4 is a process flow diagram showing a method for manufacturing the solid electrolytic capacitor 1. First, in order to increase the effective surface area of the electrode, the anode foil 21 and the cathode foil 22 are subjected to etching treatment to roughen the surface (etching). Further, the surface of the roughened anode foil 21 is subjected to chemical conversion treatment to form an anodized film 21a. A natural oxide film 22a is formed on the roughened surface of the cathode foil 22 (oxide film formation).
Next, the anode foil 21 on which the anodized film 21a is formed and the cathode foil 22 on which the natural oxide film 22a is formed are cut into predetermined dimensions, and the lead wires 25a and 25b are connected to each through lead tabs, These anode foil 21 and cathode foil 22 are wound through a separator 23 (electrode foil winding). Thereafter, a device is formed by applying a voltage in an aqueous solution of ammonium adipate, and further, the separator 23 is carbonized to produce a cylindrical capacitor device 2 (cut formation).

  The produced capacitor element 2 is immersed in an oxidant containing a dopant to impregnate the capacitor element 2 with an oxidant (oxidant impregnation). Next, the capacitor solution 2 impregnated with the oxidizing agent is dropped and impregnated with a monomer solution in a cooling atmosphere of −80 to 0 ° C. (monomer impregnation).

  Thereafter, by heating the capacitor element 2, the oxidant and the monomer are further chemically polymerized, and the conductive polymer is formed between the anodic oxide film 21 a of the anode foil 21 and the natural oxide film 22 a of the cathode foil 22 and the separator 23. The resulting solid electrolyte layer 24 is formed (solid electrolyte formation).

  Next, by immersing the capacitor element 2 in a sodium hydrogen carbonate aqueous solution having the concentration shown in Table 1 for 3 minutes at room temperature, sodium hydrogen carbonate is interposed between the anodized film 21a of the anode foil 21 and the solid electrolyte layer 24. 21b was dispersed. Thereafter, drying was performed at 100 ° C. for 10 minutes.

  Then, the cylindrical capacitor element 2 is housed in a bottomed cylindrical outer case 4 and the opening is sealed with a sealing material 5 to assemble the solid electrolytic capacitor 1 (assembly). Finally, aging treatment was performed (aging) to complete the solid electrolytic capacitor 1.

According to the solid electrolytic capacitor 1 as described above, since the sodium hydrogen carbonate 21b is dispersed between the anodic oxide film 21a and the solid electrolyte layer 24, the dopant contained in the solid electrolyte layer 24 (p-toluenesulfonic acid) ) Is neutralized.
Thereby, since the deterioration of the anodic oxide film 21a is suppressed, it is possible to suppress the deterioration of the solid electrolytic capacitor 1 with time, such as a decrease in the capacitance of the solid electrolytic capacitor and an increase in equivalent series resistance (ESR).

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

[Examples 1 to 3] Immersion in sodium hydrogen carbonate aqueous solution and comparison of concentration In Examples 1 to 3, the capacitor element was immersed in an aqueous sodium hydrogen carbonate solution having sodium bicarbonate concentrations of 3, 5, and 10 wt%, respectively. Then, sodium hydrogen carbonate was dispersed between the oxide film of the anode foil and the solid electrolyte layer to prepare a capacitor sample. In addition, what made the sodium hydrogencarbonate density | concentration of Example 3 10 wt% is in a saturated state at 30 degreeC.

(Conventional example)
In the conventional example, a capacitor sample was produced in the same manner as in Examples 1 to 3, except that sodium hydrogen carbonate was not dispersed between the oxide film of the anode foil and the solid electrolyte layer.

  The ratings of the above-described solid electrolytic capacitors of Examples 1 to 3 and the conventional example were set to a voltage of 2.5 V and a capacitance of 1200 μF.

For the solid electrolytic capacitors of Examples 1 to 3 above and the conventional example, initial electrical characteristics (capacitance, tan δ, equivalent series resistance (ESR), and leakage current) were measured and placed in a constant temperature bath at 125 ° C. After applying the rated voltage for 2000 hours, the electrical characteristics were measured again. The results are shown in Table 1.

As can be seen from Table 1, the solid electrolytic capacitors of Examples 1 to 3 have a lower rate of decrease in capacitance, tan δ, and ESR after voltage application, compared with the conventional example, and particularly the leakage current. It can be seen that the increase is suppressed and the electrical characteristics are stable. In addition, it is particularly preferable to use an aqueous solution having a sodium bicarbonate concentration of 5 wt% or more and 10 wt% (30 ° C. saturated state) or less.
Thus, by dispersing sodium hydrogencarbonate between the oxide film of the anode foil and the solid electrolyte layer, deterioration of the anodized film due to p-toluenesulfonic acid contained in the solid electrolyte in the capacitor element is suppressed, It was confirmed that the deterioration over time of the electrical characteristics of the solid electrolytic capacitor was reduced.

  In the above examples, PEDOT is used as the conductive polymer of the solid electrolyte layer, but it has been confirmed that the same effect can be obtained when polyaniline, polypyrrole or polythiophene is used.

It is the schematic which shows the external appearance and internal structure of the solid electrolytic capacitor of this invention. It is a disassembled perspective view of the capacitor | condenser element in the solid electrolytic capacitor of this invention. It is a conceptual diagram which shows the structure of the solid electrolytic capacitor of this invention. It is process drawing which shows the manufacturing method of the solid electrolytic capacitor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid electrolytic capacitor 2 Capacitor element 4 Exterior case 5 Sealing material 21 Anode foil 21a Oxide film 21b Sodium hydrogen carbonate 22 Cathode foil 23 Separator 24 Solid electrolyte layer 25a, 25b Lead wire

Claims (4)

An anode foil having an oxide film formed on the surface and a cathode foil are wound through a separator, and a capacitor element in which a solid electrolyte layer made of a conductive polymer is held in the separator is housed in the capacitor element A solid electrolytic capacitor with a case to be
A solid electrolytic capacitor, wherein sodium hydrogen carbonate is dispersed between the anode foil and the solid electrolyte layer.   2. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer is any one of polyaniline, polypyrrole, polythiophene, and polyethylenedioxythiophene. An anode foil having an oxide film formed on the surface and a cathode foil are wound through a separator, and a capacitor element in which a solid electrolyte layer made of a conductive polymer is held in the separator is housed in the capacitor element A method of manufacturing a solid electrolytic capacitor comprising a case to be manufactured,
A capacitor element forming step of forming the capacitor element;
A solid electrolytic capacitor comprising a sodium hydrogen carbonate dispersion step for dispersing sodium hydrogen carbonate between the anode foil and the solid electrolyte layer by immersing the capacitor element in a sodium hydrogen carbonate solution Manufacturing method.   4. The method for producing a solid electrolytic capacitor according to claim 3, wherein the concentration of the sodium hydrogen carbonate solution is in a range from 5% to a saturated state.

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