JP2002110465A - Solid-state electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor having superior characteristics, which comprises a good dielectric film indispensable to obtain a good leakage current (LC) characteristic of the capacitor and a conductive high molecular electrolyte with which the capacitor is impregnated efficiently with reliability, and also to provide a method of manufacturing the same. SOLUTION: As for a separator which comprises a wound element, one which is formed of such a material whose surface characteristic can be converted from hydrophilic to hydrophobic depending on the capacitor manufacturing processes is used. The separator is controlled so as to have a hydrophilic surface when the dielectric film is formed and to have a hydrophobic surface at the time of polymerization or filling of the solid-state electrolyte. Preferably, the separator includes polyacrylamide or polyvinyl alcohol in the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the digitization of electronic devices,
The demand for capacitors having good frequency characteristics is increasing.
That is, there is a demand for a capacitor having low impedance and exhibiting stable characteristics over a wide temperature range. But,
In the case of an electrolytic capacitor using a general electrolytic solution, since the resistance component depends on ion conduction, there is a problem that the capacity is significantly reduced at a high frequency and the impedance cannot be reduced because the resistance is large. Therefore, recently, a solid electrolytic capacitor using a conductive polymer, which is an electronic conductor, as an electrolyte has attracted attention and has been studied.

A solid electrolytic capacitor using a conductive polymer is roughly classified into two types. One is to form a conductive polymer layer directly on the surface of the anode body, coat the surface with a conductive paste and connect the cathode, and the other is the two electrodes, anode and cathode. The conductive polymer is filled in the gap of the wound element composed of the foil and the separator located therebetween.

[0004] When a conductive polymer is filled in a wound element, a method of impregnating with a monomer and then additionally impregnating with an oxidizing agent to chemically polymerize and fill the wound element, and a method of rapidly mixing a mixed solution of the monomer and the oxidizing agent are used. A method of impregnating the wound element, polymerizing and filling the wound element is general. Known separators of solid electrolytic capacitors using wound elements include carbonized cellulose separators, synthetic fibers, and glass fibers.

[0005]

The monomer used as the raw material of the conductive polymer has a strong hydrophobic property, and the separator must be hydrophobic like the monomer in order to sufficiently impregnate the monomer into the wound element. This is an important requirement. On the other hand, the wound element wound with a separator sandwiched between the anode foil and the cathode foil is immersed in an electrolyte solution called a chemical conversion solution before the step of polymerizing the conductive polymer, that is, before the impregnation of the monomer. It is necessary to perform a chemical conversion treatment for applying a voltage of This is for the following reason. That is, the anode foil is cut into a large sheet-like material having a dielectric oxide film on its surface, and is cut by a winding device. In this winding step, the wound element is manufactured by winding the anode foil, the cathode foil, and the separator between these foils. Of the series of steps, in the cutting step, a portion of the anode foil where no dielectric film is present is exposed. In the winding step, a defect occurs in the dielectric film due to stress at the time of winding. If the winding element is filled with a conductive polymer in this state, a short circuit occurs and the final product does not function as a capacitor.
Therefore, it is necessary to form or repair the dielectric film of the anode foil before polymerizing and filling the conductive polymer. For this purpose, it is necessary to perform a chemical conversion treatment by immersing the wound element in a chemical conversion liquid. In this chemical conversion treatment, a high quality dielectric film can be formed most efficiently when the chemical conversion solution is composed of an aqueous solution.

In the case of a normal electrolytic capacitor using an electrolytic solution, the chemical conversion treatment of the winding element is performed by impregnating the winding element with the electrolytic solution, placing the container in a container, sealing the container, and then performing an aging treatment (using the electrolytic solution as a chemical conversion solution to a high temperature). (Applying a predetermined voltage to the capacitor underneath). However, in a solid electrolytic capacitor, a dielectric film cannot be sufficiently formed and repaired in an aging process such as an aluminum electrolytic capacitor. This is because, in the case of a solid electrolytic capacitor, since the electrolyte is solid and hydrophobic, a film cannot be formed using water in the electrolytic solution as in a conventional electrolytic capacitor using an electrolytic solution. It is difficult to supply water important for film restoration from
This is because a high-quality oxide film serving as a dielectric cannot be formed.

Therefore, in the case of manufacturing a solid electrolytic capacitor using the wound element, before filling the solid element with the solid electrolyte, a film defect portion generated at the time of winding and a film not formed at the time of cutting the anode foil are formed. The portion is immersed in an aqueous electrolyte solution called a chemical conversion solution by applying a predetermined voltage by applying the same operation as the formation of the chemical conversion film (dielectric film) of the anode foil to form an oxide film serving as a dielectric. It is necessary to keep.

The cellulose separator used in the winding element of a conventional electrolytic capacitor using an electrolytic solution is very well-suited to an aqueous electrolytic solution such as a chemical conversion solution, but is a solution of a conductive polymer monomer. Hardly wet with the non-aqueous solvent used in the above. For this reason, the diffusion and penetration of the monomer become insufficient, and it is difficult to obtain a solid electrolyte as desired.

As a solution to such inconvenience,
Carbonized cellulose separator (JP-A-58-123)
715, JP-A-1-86514 and JP-A-1
No. 1-345749) is known. This carbonized cellulose separator has good diffusion and permeation of the monomer, but the heat applied during the carbonization of the cellulose melts the tin or lead plating on the lead wire, so it is excellent in heat resistance but expensive. A lead wire made of a material such as a suitable metal, for example, silver, must be employed. In addition, if the device is processed at a high temperature required for carbonization, the heat destroys the anodic oxide film, so that a further chemical conversion treatment must be performed after carbonization.

Use of a glass fiber separator (Japanese Patent Application Laid-Open Nos. 2-186616 and 2-1866)
No. 17) has also attracted attention, but glass fibers are fragile as a separator material for capacitors, and have the problem of being difficult to handle.

It is also known to use a nonwoven fabric mainly composed of synthetic fibers in order to prevent the separator material from reacting with an oxidizing agent necessary for the polymerization of the monomer (Japanese Patent Application Laid-Open No. Hei 10-340829). Has a winding element of 80 ~
The binder in the separator is dissolved and removed by immersion in water at 100 ° C. However, in this immersion, the film defective portion generated at the time of winding is also repaired, and the film-unformed portion generated at the time of cutting the anode foil is removed. No formation of a chemical conversion film is carried out. Also, even if a chemical conversion treatment step is introduced after winding the element, the synthetic fiber separator, which emphasizes hydrophobic properties, has poor compatibility with the chemical solution, which is an aqueous solution. Therefore, it is difficult to form a high-quality dielectric film because it does not penetrate into the whole, including.

In manufacturing a solid electrolytic capacitor,
The formation of a high-quality dielectric film is indispensable to ensure a good leakage current (LC) characteristic of the capacitor, and the monomer for the conductive polymer is efficiently and reliably incorporated into the wound element during the production of the capacitor. It is essential to impregnate and polymerize. However, it has been difficult to manufacture a solid electrolytic capacitor using a wound element and satisfying and satisfying these two conditions.

Accordingly, an object of the present invention is to provide a solid electrolytic capacitor employing a new separator capable of satisfying both of the above two conditions, and a method of manufacturing the same.

[0014]

Means for Solving the Problems A solid electrolytic capacitor of the present invention, the solid electrolyte is filled in the element wound with a separator which is sandwiched an anode foil and a cathode foil having a lead wire therebetween A solid electrolytic capacitor, wherein the separator is made of a material whose surface characteristics can be controlled from hydrophilic to hydrophobic according to the capacitor manufacturing process. That is, the separator is
The surface is characterized in that it can be made hydrophilic in the process of forming the dielectric film and hydrophobic in the process of filling the fixed electrolyte.

Preferably, a separator having a property that the surface is hydrophilic when a dielectric film is formed and the surface is hydrophobic when a solid electrolyte is polymerized and filled in a capacitor manufacturing process is used. As an example of a separator having such characteristics, polyacrylamide (PAAm) or polyvinyl alcohol (PVA)
Having on the surface. Both polyacrylamide and polyvinyl alcohol can be changed from hydrophilic to hydrophobic by heat treatment, and the heat treatment of polyvinyl alcohol is not particularly limited and can be performed in an atmosphere containing formaldehyde.

A method for manufacturing a solid electrolytic capacitor according to the present invention is a solid electrolytic capacitor in which a solid electrolyte is filled in an element in which an anode foil and a cathode foil each having a lead wire are wound together with a separator sandwiched therebetween. The method of manufacturing, using a separator having a hydrophilic surface characteristics to produce a capacitor winding element, subjected to heat treatment to make the surface characteristics of the separator hydrophobic, and using the element after heat treatment It is characterized in that the solid electrolyte is polymerized and filled.

Preferably, a separator having polyacrylamide or polyvinyl alcohol on its surface as described above is used,
The surface properties are changed from hydrophilic to hydrophobic by performing the reaction at 10 ° C. for 10 to 120 minutes. The heat treatment in the case of polyvinyl alcohol is not particularly limited, and may be performed in an atmosphere containing formaldehyde.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An important point in the production of a solid electrolytic capacitor is the power of a separator of a wound element to suck up a solution, that is, the impregnating ability. Specifically, the following two conditions are required. (1) The separator of the wound element quickly becomes capable of absorbing a chemical conversion solution using water as a solvent to apply a voltage, and forms a highly efficient and good anodic oxide film (chemical conversion film) on the anode foil inside the element. What can be formed. (2) The separator inside the wound element is impregnated with the monomer and polymerized under the condition that the non-aqueous monomer and the absence of water, that is, the so-called “water-free” are required. High-density conductive polymer can be filled.

When a winding element of an ordinary electrolytic capacitor using an electrolytic solution is used for a solid electrolytic capacitor, the winding element is composed of an anode foil, a cathode foil, and a separator. The surface of both the anode and cathode electrode foils is etched and very roughened (there are fine irregularities on the surface), so when impregnated with a solution, etc., physical adsorption on the surface and capillary action Penetration and adsorption are likely to occur. on the other hand,
The separator, depending on the material constituting its surface,
Shows various wettability (familiarity) with various impregnation liquids,
Satisfactory impregnation of both an aqueous chemical solution and a hydrophobic (non-aqueous) monomer solution is required, that is, both hydrophilic and hydrophobic capabilities are required.

In the present invention, a separator composed of a material whose surface characteristics can be controlled from hydrophilic to hydrophobic is used. More specifically, in the capacitor manufacturing process, a capacitor whose surface is hydrophilic when a dielectric film is formed and whose surface is hydrophobic when a solid electrolyte is polymerized and filled is used. The wound element used in the present invention may be the same as that used in an ordinary electrolytic capacitor using an electrolytic solution, except that the separator is as described above.

The wound element manufactured by winding the anode foil and the cathode foil together with the separator is used to repair the aluminum portion generated at the time of cutting the anode foil and the defective portion of the dielectric film caused by the stress at the time of winding the element. Is then subjected to a chemical conversion treatment by immersion in a chemical conversion solution. As mentioned above, in the case of an electrolytic capacitor using an electrolytic solution, the chemical conversion treatment is easily performed by aging after impregnating the wound element with the electrolytic solution, storing the wound element in a case and sealing the case. be able to. However, such an aging process cannot be applied to a solid electrolytic capacitor. This is because, in the case of a solid electrolytic capacitor using a conductive polymer as an electrolyte, the monomer forming the conductive polymer is hydrophobic and does not contain water, so that a chemical conversion film is formed like an electrolytic solution or This is because water required for restoration cannot be supplied efficiently.

Therefore, when a solid electrolytic capacitor is manufactured, before the solid electrolyte monomer is filled in the wound element, the wound element is immersed in an aqueous electrolyte solution called a chemical conversion solution to impregnate the separator in the element with the chemical liquid. Then, it is necessary to form a dielectric oxide film by applying a voltage. Since an aqueous solution is used at this time, in order to sufficiently impregnate the chemical conversion liquid into the separator in the wound element,
The separator surface must be hydrophilic.

The separator of the wound element which has been subjected to the chemical conversion treatment needs to be impregnated with an organic solvent solution containing a monomer for forming a solid electrolyte. At this time, the surface of the separator must be hydrophobic. In the present invention,
The separator surface that was hydrophilic at the time of treatment with the chemical conversion solution,
Before the impregnation of the monomer solution, it should be made hydrophobic.

As an example of such a separator made of a material whose surface characteristics can be controlled from hydrophilic to hydrophobic, those having polyacrylamide (PAAm) or polyvinyl alcohol (PVA) on the surface can be mentioned. Polyacrylamide can be changed from hydrophilic to hydrophobic by heating at a temperature of 130 to 200 ° C. Also in the case where polyvinyl alcohol is changed from hydrophilic to hydrophobic, a heat treatment at 130 to 200 ° C. is performed. The polyvinyl alcohol may be subjected to a heat treatment in an atmosphere containing formaldehyde as needed. Regardless of which material is used, if the heating temperature exceeds 200 ° C., melting of tin, lead, etc., which are constituent metals of the lead wires of the capacitor element (winding element), is not preferable. Also,
The heating time may be generally about 10 to 120 minutes, and varies depending on the heating temperature to be used and the size of the capacitor element.
mm and 10 mm elements for 10 minutes each.
Heat treatment for about 60 minutes and about 120 minutes is preferable.

As the separator in the present invention, the surface of a cellulose separator such as Manila hemp used in an ordinary electrolytic capacitor using an electrolytic solution is changed from hydrophilic to hydrophobic like the above-mentioned polyacrylamide or polyvinyl alcohol. A material to which a changeable material is attached can be preferably used. of course,
The material is not limited to cellulose, and any material having a polyacrylamide or the like on the surface and usable as a separator may be used.

After the surface of the separator is made hydrophobic, a solution containing a monomer of the polymer electrolyte is impregnated into the separator of the spirally wound element and polymerized to form a polymer electrolyte.
In the present invention, any polymer electrolyte may be used,
As an example, there can be cited one that produces a high molecular weight substance by activating and polymerizing a monomer serving as a basic skeleton with an oxidizing agent (oxidative polymerization). Such a method of polymerizing a conductive polymer includes (1) a method in which a monomer and an oxidizing agent are each separately and sequentially impregnated into a wound element and then polymerized (for example,
A series of steps of impregnation of the monomer and drying of the solvent, followed by impregnation of the oxidizing agent, and heating (polymerization))
And (2) a method in which a wound element is impregnated with a mixture of a monomer and an oxidizing agent at a low temperature, and is heated and polymerized. Representative examples of the conductive polymer generated by such oxidative polymerization include polymers such as pyrrole, which is a heterocyclic compound, a derivative thereof, and thiophene, and derivatives thereof.

[0027]

EXAMPLES Next, the present invention will be further described with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

Example 1 A wound element (10 WV-47 μF φ6 mm capacitor) similar to that used in the manufacture of a normal aluminum electrolytic capacitor using an aluminum electrode foil and a separator having polyacrylamide adhered to the surface. One). This winding element is 10w
immersed in an aqueous solution of t% ammonium adipate, subjected to a chemical conversion treatment at 80 ° C. and an applied voltage of 20 V for 10 minutes,
After washing with water, it was dried.

Subsequently, the wound element was subjected to a heat treatment in air at 190 ° C. for 1 hour, and then 3,4-ethylenedioxythiophene (monomer) and iron p-toluenesulfonate (I
II) Solution containing (oxidizing agent) in isopropyl alcohol diluent (mass ratio of monomer: oxidizing agent: diluent = 1: 4:
4) and allowed to stand at 60 ° C. for 2 hours to polymerize the monomer and fill the wound element with the solid electrolyte. Next, this winding element is housed in an aluminum case,
After sealing with an elastic sealing body, aging was performed by applying a rated voltage at 105 ° C. for 2 hours to produce a solid electrolytic capacitor.

(Example 2) Except that polyvinyl alcohol having a polymerization degree of 1700 was used instead of polyacrylamide, and that the wound element after the chemical conversion treatment was heat-treated at 190 ° C. for 1 hour in formaldehyde vapor. A solid electrolytic capacitor was manufactured in the same manner as in Example 1.

Comparative Example 1 A solid electrolytic capacitor was produced in the same manner as in Example 1, except that a separator made of cellulose fiber not coated with polyacrylamide was used, and the monomer solution was impregnated without performing a heat treatment after the chemical conversion treatment. Was prepared.

(Comparative Example 2) A cellulose fiber separator not coated with polyacrylamide was used for 250
Use what was carbonized by heating at ℃ 20 minutes,
Then, a solid electrolytic capacitor was produced in the same manner as in Example 1, except that the monomer solution was impregnated without performing the heat treatment after the chemical conversion treatment.

Comparative Example 3 A solid electrolytic capacitor was manufactured in the same manner as in Example 1 except that a polyester fiber separator not coated with polyacrylamide was used, and the monomer solution was impregnated without performing a heat treatment after the chemical conversion treatment. Was prepared.

The initial characteristics of the solid electrolytic capacitor obtained in each example include a capacity at 120 Hz and a leakage current (LC).
The amount and the equivalent series resistance (ESR) at 100 kHz were measured, and the results shown in Table 1 were obtained.

[0035]

[Table 1]

As is clear from the results, Example 1,
It was shown that the solid electrolytic capacitor of No. 2 was good in any of the characteristics, whereas those of Comparative Examples 1 to 3 were inadequate in any of the characteristics.

[0037]

As described above, according to the present invention,
At first, the hydrophilic surface of the separator of the capacitor winding element allows sufficient absorption of the aqueous chemical conversion solution during the chemical conversion treatment and efficient formation of the oxide film, and the surface that has been rendered hydrophobic by the subsequent heat treatment becomes conductive. The organic solvent solution containing the monomer for a conductive polymer can be sufficiently absorbed, thereby facilitating the filling of the conductive polymer generated by polymerization. Thus, the present invention makes it possible to provide a solid electrolytic capacitor having excellent characteristics manufactured using a wound element.

Claims (6)

[Claims] 1. A solid electrolytic capacitor in which a solid electrolyte is filled in an element in which an anode foil and a cathode foil provided with a lead wire are wound together with a separator sandwiched between the anode foil and the cathode foil. A solid electrolytic capacitor comprising a material whose surface characteristics can be controlled from hydrophilic to hydrophobic depending on the process. 2. The separator according to claim 1, wherein the surface of the separator is hydrophilic when a dielectric film is formed and the surface is hydrophobic when a solid electrolyte is polymerized and filled in a capacitor manufacturing process. Solid electrolytic capacitors. 3. A solid electrolytic capacitor in which an element obtained by winding an anode foil and a cathode foil provided with a lead wire and a separator sandwiched therebetween is filled with a solid electrolyte, wherein the separator is made of polyacrylamide. Alternatively, a solid electrolytic capacitor having polyvinyl alcohol on its surface. 4. A method for manufacturing a solid electrolytic capacitor in which a solid electrolyte is filled in an element in which an anode foil and a cathode foil provided with a lead wire are wound together with a separator sandwiched between the anode foil and the cathode foil. A capacitor wound element is manufactured using a separator having the surface characteristics described above, heat treatment is performed on the element to make the surface characteristics of the separator hydrophobic, and the solid electrolyte is polymerized and filled using the element after the heat treatment. A method for manufacturing a solid electrolytic capacitor, comprising: 5. The separator according to claim 4, wherein said separator has polyacrylamide or polyvinyl alcohol on its surface.
A method for producing the solid electrolyte according to the above. 6. The heat treatment is performed at 130 to 200 ° C. for 10 to 10.
The method for producing a solid electrolyte according to claim 4, wherein the method is performed for 120 minutes.