JPH07201657A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

(57) [Summary] [Purpose] To realize a solid electrolytic capacitor in which manganese dioxide is formed even in the inside of fine pores to enable miniaturization and large capacity while improving tan δ, leakage current, and high frequency characteristics. [Structure] After impregnating an aqueous solution of manganese nitrate to which a nonionic surfactant is added alone or in a mixture with another surfactant, an anodized film formed on a porous electrode body of a valve metal is impregnated, Manganese dioxide layer 3 by thermal decomposition
As a result of the formation of manganese dioxide, the manganese dioxide adheres to the entire surface of the anodic oxide film, the coverage is improved and the capacity becomes large, and the amount of manganese dioxide that has the ability to repair the oxide film at the interface between the oxide film 2 and the manganese dioxide increases, causing leakage. The current is reduced. In addition, since the clogging inside the pores is improved, the conductive path is widened and the resistance is reduced, so that tan δ and impedance at high frequencies are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a capacitor, especially a solid electrolytic capacitor.

[0002]

2. Description of the Related Art Generally, a method for producing a solid electrolytic capacitor includes a step of growing a chemical conversion film on a porous body made of so-called valve metal such as tantalum, aluminum and titanium by anodic oxidation, and a step of growing manganese dioxide on the chemical conversion film. And a step of forming a semiconductor layer of The step of forming the manganese dioxide layer is performed by repeating a step of impregnating and adhering a manganese nitrate aqueous solution into a porous body having a chemical conversion film and thermally decomposing the porous body several times to ten or more times. At this time, in the tantalum electrolytic capacitor and the aluminum electrolytic capacitor, since the oxide film is thin and has a large area, there is a possibility that the leakage current may increase due to the damage of the oxide film. The specific resistance of manganese dioxide is 10Ω.
The value is about cm, which is not so low, and since it is difficult to form a homogeneous manganese dioxide layer inside the pores, the impedance in the high frequency region is higher than that of the monolithic ceramic capacitor by one order or more.

[0003]

However, these electrolytic capacitors are also required to be smaller and have a larger capacity. For example, in the case of aluminum electrolytic capacitors, the etching rate is increased and they are being used even in the fine holes.
In tantalum electrolytic capacitors, efforts are being made to increase the specific surface area by using a fine powder sintered body and to extract the capacitance from the pores. However, for example, 30000 CV / g
When a tantalum electrolytic capacitor with a fine powder sintered body of 50000 CV / g and a manganese dioxide as an electrolyte is manufactured in the same manner as the conventional one with the same size as the fine powder sintered tantalum electrolytic capacitor of It had the drawbacks of lowering, tan δ, impedance and leakage current.
The present invention solves the above-mentioned conventional problems. By forming manganese dioxide even in the inside of fine pores, a small size and a large capacity can be realized, and tan δ, leakage current, and high frequency characteristics have been improved. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor.

[0004]

In order to achieve the above object, the present invention provides a nonionic surfactant alone or another interface on an anodized film formed on a porous electrode body of a valve metal. The method for producing a solid electrolytic capacitor is characterized in that a manganese dioxide layer is formed by impregnating an aqueous solution of manganese nitrate added by mixing with an activator and then thermally decomposing it.

[0005]

According to the present invention, therefore, by adding a surfactant containing at least a nonionic surfactant to an aqueous solution of manganese nitrate and thermally decomposing it, dense manganese dioxide inside fine pores of various pore diameters can be obtained. Even if the porous electrode body is formed on the entire surface of the anodic oxide film and has different pore diameters, it is pyrolyzed using a mixed surfactant in which one or more different surfactants are mixed with a nonionic surfactant. By doing so, the particle size of the manganese dioxide particles can be controlled and optimized according to the pores of the porous electrode body, and the clogging inside the pores can be improved. As a result, the coating rate is improved, resulting in a large capacity, and the amount of manganese dioxide having the ability to repair the oxide film at the interface between the oxide film and the manganese dioxide is increased and the leakage current is reduced. Further, since the conductive path is widened and has low resistance, tan δ and impedance at high frequency are reduced.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In FIG. 1, the two kinds of tantalum electrode bodies 1 used are the sintered bodies of fine powders of 29000 CV / g and 50000 CV / g, respectively, which are formed at 50 V in a phosphoric acid solution at 80 ° C.
The oxide film 2 is formed. Further, the manganese dioxide layer 3 was impregnated with a 3 mol / 1 manganese nitrate aqueous solution containing 0.1% by weight of a surfactant polyoxyethylene alkylamine and thermally decomposed at 260 ° C. This was repeated 5 times, followed by 5.9 mol / 1. It was formed by impregnating an aqueous solution of manganese nitrate and thermally decomposing it at 240 ° C., and repeating this three times. After that, a cathode extraction electrode 4 composed of a carbon layer and a silver conductive resin layer was provided. Furthermore, a capacitor was manufactured by using a mixed surfactant in which the weight ratio of polyoxyethylene alkylamine and polyoxyethylene nonylphenyl ether was changed as the surfactant to be added.

The capacitance, tan δ, impedance, and leakage current of the tantalum solid electrolytic capacitor according to this embodiment are
The characteristics are shown in Table 1 in comparison with the characteristics of the tantalum solid electrolytic capacitor in which the manganese dioxide layer 3 was formed by using the manganese nitrate solution without adding the surfactant.

[0008]

[Table 1]

The capacitance and tan δ were measured at 120 Hz, the impedance was measured at 1 MHz, the leakage current was applied with a voltage of 20 V, and the current value after 1 minute was measured. Also, the theoretical capacity of this capacitor was compared with the actual electrostatic capacity to obtain the coverage. The pore diameter of the tantalum electrode body 1 used in Table 2 is
Table 3 shows the specific surface area of manganese dioxide obtained by thermal decomposition at 260 ° C.

[0010]

[Table 2]

[0011]

[Table 3]

According to the present example from Table 1, a surfactant was added to the manganese nitrate aqueous solution to reduce the interfacial tension with the anodized film, so that the manganese nitrate aqueous solution was impregnated into the fine pores. , Manganese dioxide adheres to the entire surface of the anodized film, improving the coverage and increasing the capacitance. Moreover, in the thermal decomposition step, even if manganese dioxide adheres to the vicinity of the entrance of the pores and closes the entrance to the inside of the pores, the next manganese nitrate solution easily gets wet and penetrates into the pores, and the manganese dioxide enters the pores. Since manganese is formed, that is, the condition is improved, the conductive path is widened to have low resistance, and tan δ and impedance at high frequencies are reduced. The amount of manganese dioxide, which has the ability to repair the oxide film at the interface between the anodized film and manganese dioxide, increases, and the leakage current decreases.

Further, as is clear from (Table 2) and (Table 3), the specific surface area of manganese dioxide, that is, the primary particle diameter is optimized in accordance with the size of the average pore diameter, so that various characteristics of the capacitor can be obtained. The characteristics are improved. Surfactants, whether cationic, anionic, amphoteric or nonionic, are soluble in manganese nitrate solution, which is a strong acid, and reduce the interfacial tension with the oxide of the valve metal to improve wettability. Needless to say, as long as it improves, since two or more kinds of surfactants are mixed, at least one of them does not react with an acid or an alkali in order to avoid mutual reaction, and has high stability. It is desirable to include a nonionic surfactant. The present invention limits the method for forming manganese dioxide on the solid electrolytic capacitor, and does not limit the structure of the manganese dioxide-conductive polymer composite solid electrolyte or the like.

[0014]

As is apparent from the above description, in the solid electrolytic capacitor of the present invention, a nonionic surfactant alone is added to a manganese nitrate aqueous solution on an anodized film formed on a valve metal porous electrode body. Alternatively, by mixing with other surfactants and thermally decomposing, dense manganese dioxide is formed inside the minute pores of various pore diameters over the entire surface of the anodic oxide film, and the pores with different pore diameters are formed. Even if it is a porous electrode body, the particle size of the manganese dioxide particles can be controlled by pyrolyzing the mixed surface active agent in which one or more different surface active agents are mixed with the nonionic surface active agent to control the particle size of the manganese dioxide particles. It can be optimized depending on the pores of the electrode body, and the clogging inside the pores can be improved. Manganese dioxide adheres to the entire surface of the anodized film, improving the coverage and increasing the capacity.
The amount of manganese dioxide that has the ability to repair the oxide film at the interface between the oxide film and manganese dioxide increases, and the leakage current decreases. Further, since the clogging inside the pores is improved, the conductive path is widened and the resistance is reduced, so that tan δ and impedance at high frequency are reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which a solid electrolyte layer is formed in an example of the present invention.

[Explanation of symbols]

1 ... Tantalum electrode body, 2 ... Oxide film, 3 ... Manganese dioxide layer, 4 ... Cathode extraction electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Ida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. An anodized film formed on a porous metal electrode body of a valve metal is impregnated with an aqueous solution of manganese nitrate containing a nonionic surfactant alone or mixed with another surfactant. After that, a manganese dioxide layer is formed by pyrolyzing the solid electrolytic capacitor.