JPH0342696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a method for manufacturing a solid electrolytic capacitor using manganese dioxide and lead dioxide as a solid electrolyte.

[Conventional technology]

Electrolytic capacitors are made of aluminum, tantalum,
A film-forming metal such as niobium or titanium that forms an insulating oxide film, a group of metals also called valve metals, is used as the positive electrode, and the oxide film layer is formed on the surface of this metal by a method such as anodizing. However, this oxide film layer is used as a dielectric.
A capacitor is formed by disposing a cathode-side electrode with an electrolyte layer interposed outside the oxide film layer.

Electrolytes include liquid electrolytes in which inorganic acids, organic acids, or their salts are dissolved in water or various polar solvents, and conductive oxides such as manganese dioxide, lead dioxide, tetracyanoquinodimethane complex salts, etc. There are solid electrolytes using organic substances. Capacitors using the latter are called solid electrolytic capacitors.

Manganese dioxide is a well-known solid electrolyte material. Manganese dioxide is produced by immersing a valve metal anode with an oxide film layer on its surface in liquid manganese nitrate and firing it to convert manganese nitrate into manganese dioxide and use it as an electrolyte. However, with this structure, the required manganese dioxide layer cannot be formed in one go, and immersion and firing must be repeated several to more than ten times.
For this reason, manufacturing is complicated, and heating during firing,
There are drawbacks such as the generation of gas deteriorates the dielectric oxide film and adversely affects the characteristics of the electrolytic capacitor.

On the other hand, devices using lead dioxide as a solid electrolyte are known (for example, Japanese Patent Publication No. 49-29374). Lead dioxide has higher electrical conductivity than manganese dioxide, so it has excellent electrical properties as a capacitor. The lead dioxide layer is formed by immersing the anode body in an aqueous solution containing lead acetate and ammonium persulfate.
Then, if you pull up the anode body and dry it at room temperature,
A thin layer of lead dioxide is formed on the surface of the anode body.

In this way, the lead dioxide layer can be formed in a solution at about room temperature, so unlike the firing of manganese dioxide, there is no adverse effect from heat or firing gas. Further, since the formation of the electrolyte is easily carried out, the desired characteristics can be obtained with a far lower frequency of immersion than in the formation of manganese dioxide.

In this way, when lead dioxide is used as a solid electrolyte, it has excellent aspects as described above.

However, lead dioxide is formed on the surface of the dielectric oxide film layer by reacting lead acetate and ammonium persulfate, but during this formation process, a colloid of lead dioxide is generated, and this colloid is used as a core to form lead dioxide. grows. However, in order to expand the surface area of electrode foils in recent years, strong etching treatment is applied to the surface of the electrode foils, and these etching holes are extremely fine and intricately formed. However, since the electrolyte layer cannot be formed on the inner surface of the etching hole, the desired capacitance cannot be obtained.

FIG. 2 is a sectional view showing a state in which a solid electrolyte layer made of lead dioxide is formed on the etched anode electrode surface.

As shown in the figure, the surface of an anode electrode 1 made of a film-forming metal such as aluminum is etched to increase the surface area, and as a result, fine etched holes 2 are formed. An insulating dielectric oxide film layer 3 is formed on the entire surface of the anode electrode 1 including the inside of the etching hole 2 by anodic oxidation.

A solid electrolyte layer 5 is formed on the surface of this dielectric oxide film layer 3. When lead dioxide is used for the solid electrolyte layer 5, colloidal lead dioxide 7 is first formed by the reaction between lead acetate and persulfate. is formed. However, the colloidal lead dioxide 7 cannot penetrate into the fine etching holes 2, and instead adheres to the vicinity of the opening of the etching hole 2, and from there, the colloidal lead dioxide 7 forms a core and forms the lead dioxide electrolyte layer 5. As a result, a space 6 is formed inside the etching hole 2, and the contact between the dielectric oxide film layer 3 and the lead dioxide layer becomes sufficient.

On the other hand, manganese dioxide does not have this phenomenon and can form a solid electrolyte layer deep into the etching hole.

Traditionally, solid electrolytes include manganese dioxide and
For example, as in (JP-A-54-12447), a manganese dioxide layer is first formed on a sintered porous anode body, and then a lead dioxide layer is used as an electrolyte layer. It is known that the carbon layer is formed between the carbon layer and the carbon layer.

[Problem that the invention seeks to solve]

This invention improves the above-mentioned drawbacks, and includes an anode body consisting of a foil-like anode made of a film-forming metal that has been subjected to etching treatment and dielectric film formation treatment and then wound or laminated. By improving the method of forming the electrolyte layer of the solid electrolytic capacitor used, it is possible to ensure contact between the dielectric film layer and the cathode extraction layer, thereby improving the electrical characteristics of the capacitor.

[Means for solving problems]

In the method of the present invention, a foil anode made of a film-forming metal whose surface has been subjected to an etching treatment and a dielectric oxide film formation treatment is immersed in an aqueous solution of manganese nitrate, and the manganese nitrate is converted into manganese dioxide by baking. After forming a first solid electrolyte layer, the foil anode electrode is wound or laminated together with a cathode electrode to form a capacitor element,
This manufacturing method is characterized by forming a second solid electrolyte layer by immersing this capacitor element in an aqueous solution containing lead ions and drying it. After that, if necessary, the capacitor element is coated with an exterior, etc. A solid electrolytic capacitor was created by applying this method.

[Effect]

According to the method of the present invention, the first stage of electrolyte formation on a foil-shaped anode electrode is first immersed in an aqueous solution of manganese nitrate in a flat state before being rolled or laminated, and then subjected to a baking treatment to form an electrolyte. Forms a manganese layer. Therefore, a sufficient solid electrolyte layer of manganese dioxide is first formed within the etching hole.

The capacitor element is then wound or laminated together with the cathode foil, and in the second step, the capacitor element is immersed in an aqueous solution containing lead ions to form a second electrolyte. A second electrolyte layer of lead dioxide is formed in the gap between the first electrolyte layer made of manganese dioxide and the cathode electrode, and the gap is filled with sufficient electrolyte.

At this time, the gap between the layers where the foil-shaped anode and cathode are wound or laminated is larger than the space of the etching hole on the surface of the anode, so even if colloid is formed, the gap will A sufficient layer of lead dioxide will be formed.

As a result, the capacitance increases due to an increase in the contact area between the dielectric oxide film layer and the cathode electrode. Furthermore, since the voids are filled with electrolyte, loss and leakage current are reduced.

FIG. 1 is a sectional view showing the state of a solid electrolyte layer formed by the method of the present invention.

The figure shows a solid electrolyte layer 5 made of manganese dioxide and lead dioxide formed on the surface of an anode electrode 1 made of a foil-like material of a film-forming metal such as aluminum. The surface of the anode electrode 1 is etched in advance by an electrochemical method or the like in order to enlarge the surface area, and a large number of fine etching holes 2 are provided therein. Further, on the surface of the anode electrode 1 including the inner surface of the etching hole 2, a dielectric oxide film layer 3 of an insulator is formed by anodic oxidation.

First, a first solid electrolyte layer 8 made of manganese dioxide is formed on the anode electrode 1 before being wound or laminated. This first solid electrolyte layer 8 is formed so as to fill the etching hole 2 of the anode electrode 1.

Next, the anode electrode 1 on which the first solid electrolyte layer 8 is formed is overlapped with the cathode electrode 4 inserted for current collection in the cathode part, and is wound or laminated to form a capacitor element. In the space between the solid electrolyte layer 8 and the cathode electrode 4, a second solid electrolyte layer 9 made of lead dioxide is formed.

According to this method, sufficient contact with the dielectric oxide film layer 3 inside the etching hole 2 of the anode electrode 1 is achieved by forming the first solid electrolyte layer 8, and the second solid electrolyte layer 9 By forming the cathode electrode 4
There will be sufficient contact with the

According to the method of the present invention, the formation of the first solid electrolyte layer 8 and the formation of the second solid electrolyte layer 9 may be performed by dipping once each, and depending on the state of formation of the electrolyte layer, , each forming step may be performed multiple times.

〔Example〕

Next, an example will be shown in which solid electrolytic capacitors were manufactured using the method of the present invention and their characteristics were compared.

The prototype solid electrolytic capacitor uses high-purity aluminum foil (99.99% purity, 80μ thick) for the anode electrode.
m), the surface was etched with a direct current using an aqueous hydrochloric acid solution, washed with water, and dried.
The surface was oxidized by anodic oxidation treatment by applying a voltage of 70°C in a boric acid aqueous solution to form a dielectric oxide film layer, which was then cut into pieces of 6 mm in width and 85 mm in length. Note that a 2.5 mm wide aluminum tab, also anodized, was connected to a portion of this electrode foil by ultrasonic welding for electrode extraction.

Similarly, high-purity aluminum foil with a thickness of 50 μm was used for the anode electrode, and was cut into the same dimensions as the anode foil.

These anode electrodes and cathode electrodes are used as examples of the present invention.
Commonly used in comparative examples.

(Example of the present invention) The above anode electrode foil is immersed in an aqueous solution of manganese nitrate (concentration 4.5 mol/) before being wound,
Then, after removing it from the aqueous solution, it is heated at 250℃ in a firing furnace.
Baking was performed for 10 minutes. After repeating this operation three times, the foil was overlapped with the cathode foil and wound from one end, and the end of the winding was fixed with an adhesive resin tape to form a cylindrical capacitor element.

Next, this capacitor element was prepared using lead acetate (concentration 1 m
ol/), ammonium persulfate (concentration 2 mol/)
After repeating the process of immersing it in an aqueous solution and air drying it three times, the outer periphery of the capacitor element was coated with conductive resin, the lead was connected to this conductive resin layer, and the outer surface was further coated with silicone resin to seal it. .

Comparative Example 1 First, the above anode foil and cathode foil were overlapped and wound to create a cylindrical capacitor element. Next, this capacitor element was mixed with lead acetate (concentration 1 mol/
), immersion in an aqueous solution of ammonium persulfate (concentration 2 mol/) and air drying were repeated four times, and then the same exterior packaging as in the example of the present invention was applied.

Comparative Example 2 The above anode foil and cathode foil were overlapped and wound to create a cylindrical capacitor element. Next, this capacitor element was mixed with manganese nitrate (concentration 4.5mol/
) and then removed from the aqueous solution and fired in a firing oven at 250°C for 10 minutes.
This operation was repeated six times. Thereafter, the same exterior as in the example of the present invention was applied.

After applying a voltage of 35 to the capacitors of the present invention example and Comparative Examples 1 and 2 and aging them for 8 hours, their electrical characteristics were compared. The results are shown in the table below.

■■■ Turtle Shell [0012] ■■■ As is clear from the above results, the solid electrolytic capacitor of the present invention has a large capacitance, low loss (tan δ), and has excellent electrical characteristics with little leakage current.

On the other hand, Comparative Example 1 has the same loss as the inventive example, but has extremely low capacitance and high leakage current value. This is thought to be because the solid electrolyte did not penetrate sufficiently into the etching holes and did not make sufficient contact with the dielectric oxide film.

In addition, in Comparative Example 2, the electrolyte penetrates into the etching holes sufficiently and shows a high capacitance value like the inventive example, but since the solid electrolyte is manganese dioxide, the conductivity is low. It can be seen that the internal resistance is high, the loss is large, and the number of firings is large, which indicates that the dielectric oxide film is greatly deteriorated and the leakage current is increased.

〔Effect of the invention〕

As described above, in a solid electrolytic capacitor in which an electrolyte layer is formed using the method of the present invention, an electrolyte made of manganese dioxide that has good permeability is formed on the contact surface with the dielectric film layer inside the etching hole. Since this is used, a sufficient contact area between the dielectric oxide film layer and the electrolyte layer can be obtained, and the capacitance can be increased. In addition, since the manganese dioxide layer was formed in a flat state before the formation of the capacitor element, the number of steps of immersion in a manganese nitrate aqueous solution and firing can be reduced, and the adverse effects of heat and firing gas can be minimized. Deterioration of characteristics such as leakage current can be prevented.

In addition, the gap between the anode electrode surface and the cathode electrode is relatively large, and an electrolyte layer of lead dioxide with good conductivity is formed in the long part of the electrical conduction path.
It is possible to prevent an increase in internal resistance value and reduce capacitor loss.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the state when a solid electrolyte layer is formed using the method of the present invention, and Figure 2 is a cross-sectional view showing a state in which a lead dioxide layer is formed directly on the etched anode electrode surface by a conventional method. FIG. 3 is a cross-sectional view showing the state of the solid electrolyte layer when the solid electrolyte layer is in the state. DESCRIPTION OF SYMBOLS 1...Anode electrode, 2...Etching hole, 3...Dielectric oxide film layer, 4...Cathode electrode, 5...Solid electrolyte layer,
6... Space, 7... Colloidal lead dioxide, 8... First
solid electrolyte layer, 9... second solid electrolyte layer.

Claims (1)

[Claims] 1 A foil anode made of a film-forming metal whose surface has been etched and treated to form a dielectric oxide film is immersed in an aqueous manganese nitrate solution, and fired to convert the manganese nitrate into manganese dioxide. After forming the solid electrolyte layer 1, the foil-like anode electrode is wound or laminated together with the cathode electrode to form a capacitor element, and this capacitor element state is immersed in an aqueous solution containing lead ions and dried to form a lead dioxide layer. A method for manufacturing a solid electrolytic capacitor, comprising forming a second solid electrolyte layer comprising: