JPH026209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and particularly to an improvement in a method for forming a solid electrolyte layer made of an organic semiconductor.

Solid electrolytic capacitors use a film-forming metal such as aluminum or tantalum for the anode, and in order to enlarge the area of the anode, it is made porous by etching or sintering, and an oxide film layer that serves as a dielectric is applied to the surface of the anode. , a solid electrolyte layer is formed on the surface of the solid electrolyte layer, and a conductive cathode extraction layer is further formed on the outside of the solid electrolyte layer.

Conventionally, manganese dioxide has been used as this solid electrolyte layer. The method for forming this manganese dioxide on the dielectric oxide film layer is to impregnate the anode electrode in liquid manganese nitrate, and then
Manganese nitrate was thermally decomposed at a temperature of around 300°C and denatured into manganese dioxide.

However, according to this method, only a small amount of manganese dioxide is deposited in one process, so it is necessary to repeat the same process several to more than ten times.

This makes the manufacturing process extremely complicated, and has the disadvantage that the dielectric oxide film deteriorates due to the high temperature and gas generated during thermal decomposition.

Therefore, recently, instead of this manganese dioxide,
It has been proposed to use conductive organic materials in this electrolyte layer.

Known organic electrolytes are those using various complex salts of tetracyanoquinodimethane (hereinafter referred to as TCNQ).

Since TCNQ complex salt is a solid substance at room temperature, the conventional method of attaching it to capacitor elements using it as an electrolyte is to impregnate the anode body in a solution of TCNQ complex salt dissolved in an organic solvent. After that, the anode is pulled out of the solution, the organic solvent is evaporated, and a TCNQ complex layer is formed on the surface of the anode. However, in this method, the concentration of TCNQ complex salt in the solvent is low, so
It was not possible to deposit enough TCNQ complex salt in one impregnation, and it was necessary to repeat this process several to ten times, similar to the formation of the manganese dioxide layer, making the manufacturing process unavoidable.

In addition, after the solvent evaporates, the TCNQ complex salt crystallizes, making it impossible to obtain sufficient contact with the dielectric oxide film on the surface of the anode body, which has been enlarged and has complex asperities. There was a drawback that I couldn't get it.

Recently, a method has been proposed in which only the TCNQ complex salt is heated above its melting point and melted, an anode body is impregnated therein, and then the anode body is pulled up and cooled to adhere the TCNQ complex salt. According to this method, since the highly concentrated TCNQ complex salt itself is deposited on the anode body, sufficient TCNQ complex salt can be deposited in one impregnation step. However, TCNQ complex salts are sensitive to heat, and if kept in a molten state, they decompose in an extremely short period of time, turning into an insulator. For this reason, the above impregnation process can be completed in an extremely short time.
After that, it must be rapidly cooled down,
Rapid processing requires complicated equipment, and productivity is also low. Furthermore, after cooling, the TCNQ complex crystallized, resulting in poor contact with the dielectric oxide film, which resulted in the drawback that sufficient capacitance could not be extracted.

This invention improves on these conventional drawbacks, and simplifies the work process of impregnating a solid electrolyte layer made of TCNQ complex salt onto the dielectric oxide film of the anode body of a solid electrolytic capacitor, and also improves the impregnation rate. The purpose is to improve the characteristics of solid electrolytic capacitors.

This invention relates to isopropyl-isoquinolinium
A mixture obtained by adding a lactone compound to a TCNQ complex salt is used as a solid electrolyte, and the solid electrolyte layer is formed by heating to a temperature lower than the melting point or decomposition temperature of the isopropyl-isoquinolinium TCNQ complex salt to liquefy it. This method is characterized by impregnating a capacitor element in a mixture and cooling and solidifying it after impregnation. Focusing on the phenomenon that the melting point (freezing point) of a mixture is lower than that of a pure substance, we developed a mixture of TCNQ complex salt and additives. The material is heated and melted to impregnate the anode body. This invention will be explained in detail based on the following examples.

First, the manufacturing procedure of the solid electrolytic capacitor according to the present invention will be explained.

FIG. 1 shows the anode body, ie, the capacitor element, used in this example.

This capacitor element 1 is formed by winding a band-shaped electrode body, and the anode 2 is made of high-purity aluminum foil. The anode 2 is first subjected to an etching process to enlarge its surface, and a dielectric oxide film is formed on its surface by anodizing process.

This strip-shaped anode 2 is arranged with collector electrodes 3 having approximately the same area facing each other, and the anode 2 and the collector electrode 3 are arranged opposite each other.
A separator paper 4, which is slightly wider than the electrodes 2 and 3, is sandwiched between the electrodes 2 and 3 and wound from one end to form a cylindrical capacitor element 1. Note that tabs 5 and 6 for obtaining electrical connection with the outside are connected to each of the anode 2 and the collector electrode 3 by means such as welding, and protrude in parallel from one end surface. Further, external leads 7 and 8 are connected to the tips of these tabs by welding.

FIG. 2 shows a method of impregnating the capacitor element 1 with a solid electrolyte layer, and a preheating block 10 is placed on the left side of the figure. This preheating block 10 has a heating heater embedded inside and a recess 11 on the top surface.
The capacitor element 1 is placed in the recess 11, and the capacitor element 1 is heated in advance to maintain a high temperature state.

Next, an impregnating block 12 is placed on the right side of the figure, and this impregnating block 12 also has a heater embedded therein and a recess 13 formed in its upper surface. Then, a powder mixture 14 consisting of a TCNQ complex salt and an additive is injected into the recess 13, and the mixture 14 is melted by heating. The capacitor element 1, which has been kept on standby in the preheating block 10, is then moved here and impregnated for a predetermined period of time. After that, the capacitor element 1 is pulled up from the recess 13, and the liquid mixture 14 is solidified by natural cooling to form a solid electrolyte. form a layer.

As shown in FIG. 3, the capacitor element 1 with the solid electrolyte layer formed thereon is housed in a cylindrical outer case 20 with a bottom, and the open end of the outer case 20 is sealed with an elastic sealing member 21. Closed, outer case 2
Tighten the open end of 0 to seal it. Note that the external leads 7 and 8 drawn out from the capacitor element 1 protrude to the outside from the through hole provided in the elastic sealing body 21, so that an electrical connection between the capacitor element 1 and the outside can be established.

Next, we will show the results of fabricating an actual solid electrolytic capacitor using the procedure described above and determining its characteristics. As a conventional example, a normal dry electrolytic capacitor using a liquid electrolyte and a solid electrolytic capacitor made by melting and impregnating only isopropyl-isoquinolinium TCNQ complex salt are shown in comparison with the present invention.

Conventional example 1 First, as a capacitor element, a width of 2.2 mm and a length of
10mm, 80μm thick high purity aluminum (purity
99.99%) was prepared as an anode, and after enlarging the surface of this anode by electrolytic etching using alternating current, a dielectric oxide film with a withstand voltage of 9 V was formed on the surface by anodizing treatment. Aluminum (purity 99.94%) of the same size as the anode is placed oppositely as a current collecting electrode, and an aluminum tab for external extraction is connected approximately at the center of both electrodes by cold welding. A cylindrical capacitor element was obtained by winding the capacitor with a separator paper interposed therebetween. (The same capacitor element is used in both the conventional example and the inventive example below.) Next, this capacitor element is impregnated with an ethylene glycol-ammonium adipate electrolyte and placed inside an aluminum exterior case. The element is housed in the case, the opening is closed with a sealing material, and the opening end of the outer case is wrapped tightly and sealed to achieve a rated voltage of 6.3V and a rated capacity of 6.3V.
Completed a 10μF electrolytic capacitor. At this time, the external dimensions of the main body were 3 mm in diameter and 5 mm in length.

When this electrolytic capacitor was aged by applying the rated voltage for 15 minutes and its electrical characteristics were investigated, the following results were obtained.

Capacitance 9.2μF Tangent of loss angle 0.30 Equivalent series resistance value (100KHz) 25Ω Leakage current (2-minute value) 0.10μA Conventional example 2 The same capacitor element as in Conventional example 1 is used, and this capacitor element is placed in a preheating block. It was preheated to 250°C in a chamber and kept on standby. Next, only the isopropyl-isoquinolinium TCNQ complex salt was injected into the heat-impregnating block and when heated, it melted at 240°C and became liquid.

Therefore, the capacitor element that was waiting in the preheating block was quickly moved, and the main body of the capacitor element, except for the upper end surface where the tab protruded, was immersed in the molten TCNQ complex salt, held for 10 seconds, and then pulled out. The isopropyl-isoquinolinium TCNQ complex salt was solidified by natural cooling.

Next, this capacitor element was housed in an exterior case of the same size as in Conventional Example 1, and the opening was sealed using the same means to complete a solid electrolytic capacitor.

The characteristics of this solid electrolytic capacitor after aging by applying the rated voltage for one hour were as follows.

Capacitance 5.0μF Tangent of loss angle 0.10 Equivalent series resistance value (100KHz) 2.8Ω Leakage current (2-minute value) 0.13μA Example of the present invention 1 The capacitor element used is the same as the conventional example, and the preheating block is used. The mixture was heated and maintained at 200° C., and a mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.5 part by weight of γ-butyrolactone was poured into the impregnation block and heated. This mixture melted at 150°C.
Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 10.0μF Tangent of loss angle 0.040 Equivalent series resistance value (100KHz) 0.55Ω Leakage current (2-minute value) 0.14μA Example 2 The capacitor element used is the same as the conventional example, and the preheating block is 200μF. A mixture of 1 part by weight of isoprepyl-isoquinolinium TCNQ complex salt and 0.3 part by weight of γ-valerolactone was injected into the impregnating block heated and maintained at .degree. C. and heated. This mixture melted at 200°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.1μF Tangent of loss angle 0.065 Equivalent series resistance value (100KHz) 1.0Ω Leakage current (2-minute value) 0.22μA Invention example 3 The capacitor element used is the same as the conventional example, and the preheating block is A mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.4 part by weight of δ-valerolactone was injected into the impregnating block heated and maintained at 200°C and heated. This mixture melted at 185°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.4μF Tangent of loss angle 0.060 Equivalent series resistance value (100KHz) 0.92Ω Leakage current (2-minute value) 0.15μA Invention example 4 The capacitor element used is the same as the conventional example, and the preheating block is It was heated and maintained at 200°C.
A mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.3 part by weight of ε-caprolactone was poured into the impregnation block and heated. This mixture melted at 200°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.0μF Tangent of loss angle 0.055 Equivalent series resistance value (100KHz) 0.91Ω Leakage current (2-minute value) 0.25μA Invention example 5 The capacitor element used is the same as the conventional example, and the preheating block is It was heated and maintained at 200°C.
Into the impregnation block, a mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.3 part by weight of γ-heptalactone was injected.
Heated. This mixture melted at 190°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.5μF Tangent of loss angle 0.050 Equivalent series resistance value (100KHz) 0.87Ω Leakage current (2-minute value) 0.30μA Present invention example 6 The capacitor element used is the same as the conventional example, and the preheating block is It was heated and maintained at 200°C.
A mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.3 part by weight of δ-nonalactone was poured into the impregnation block and heated. This mixture melted at 200°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.3μF Tangent of loss angle 0.045 Equivalent series resistance value (100KHz) 0.59Ω Leakage current (2-minute value) 0.20μA Invention example 7 The capacitor element used is the same as the conventional example, and the preheating block is It was heated and maintained at 200°C.
Into the impregnation block, a mixture of 1 part by weight of isopropyl-isoquinolinium TCNQ complex salt and 0.5 part by weight of DL-pantoyllactone was injected.
Heated. This mixture melted at 160°C. Therefore, the capacitor element was removed from the preheating block, immersed in the melting bath for 10 seconds, and then taken out and allowed to cool naturally.

Regarding the exterior treatment after solid electrolyte impregnation,
The test was carried out under exactly the same conditions as the conventional example.

The characteristics of this solid electrolytic capacitor were as follows.

Capacitance 9.9μF Tangent of loss angle 0.060 Equivalent series resistance value (100KHz) 1.0Ω Leakage current (2-minute value) 0.35μA Looking at the results of these examples, it is clear that the normal In electrolytic capacitors, the electrolyte is held in a liquid state in the electrolytic capacitor element, so the electrolyte penetrates into the deepest part of the fine etching holes (pits) created by etching to enlarge the anode surface. It has sufficient contact with the body oxide film and exhibits a high capacitance value.

However, the specific resistance value of the electrolyte is
While the specific resistance value of isoquinolinium TCNQ complex salt is less than several tens of Ω·cm, it is high at around 200-300 Ω·cm, which results in a high product loss or equivalent series resistance value.

In addition, in the solid electrolytic capacitor manufactured by heating and melting only the isopropyl-isoquinolinium TCNQ complex salt and impregnating it into the capacitor element, as shown in Conventional Example 2, the specific resistance value of the isopropyl-isoquinolinium TCNQ complex salt is lower than that of the conventional electrolytic solution. It has excellent electrical properties such as loss and equivalent series resistance value, but its capacitance is extremely low.

The reason for this is not clear, but although the molten isopropyl-isoquinolinium TCNQ complex permeates into the etching pit of the anode, during subsequent cooling and solidification, the isopropyl-isoquinolinium TCNQ complex crystallizes into needle-like crystals and is removed from the etching pit. This is thought to be because contact with the dielectric oxide film is only partially made.

On the other hand, the solid electrolytic capacitors manufactured by the method of the present invention have a high impregnation rate and exhibit sufficient capacitance values in all of Examples 1 to 7 of the present invention.
This is because the solid electrolyte of this invention is isopropyl-
Since it is a mixture of isoquinolinium TCNQ complex salt and lactone compound, crystallization of the isopropyl-isoquinolinium TCNQ complex salt is prevented during cooling after melting and impregnation, and it remains in the etching pit in an amorphous state, so it does not interact with the dielectric oxide film. This is thought to be because sufficient contact is maintained. Furthermore, even if some isopropyl-isoquinolium TCNQ complex salts crystallize, it is thought that the presence of lactone compounds between the crystals provides intercrystalline conductivity and ensures electrostatic capacity. .

To confirm this, differential thermal analysis was performed on the isopropyl-isoquinolium TCNQ complex salt after melting and cooling. FIG. 4 shows a solidified product (A) of only the isopropyl-isoquinolium TCNQ complex salt shown in Conventional Example 2 after melting, and a solidified product of the mixture of the isopropyl-isoquinolium TCNQ complex salt and γ-butyrolactone of the present invention 1 after melting. This is a graph showing the results of differential thermal analysis with (B). The TCNQ complex salt of (A) alone has an endothermic peak with a melting point around 225℃, but the mixture of (B) , no endothermic peak indicating the melting point appeared, indicating that the mixture used in this invention was solidified in an amorphous state. The exothermic peak appearing around 250°C in both (A) and (B) indicates the decomposition point. Although not shown in this graph, a similar tendency was observed for mixtures containing other lactone compounds.

According to this invention, in order to melt the mixture of the isopropyl-isoquinolium TCNQ complex salt and the lactone compound, the melting point is lowered, and the mixture is melted and liquefied at a temperature lower than the melting point of the isopropyl-isoquinolium TCNQ complex salt itself. This indicates that the time until pyrolysis can be extended and the impregnation operation can be facilitated.

Specifically, isopropyl-isoquinolium TCNQ complex salt has a melting point of 240°C or higher in pure form, and the thermal decomposition time at this temperature is about 2 minutes. Therefore, impregnation and cooling must be completed within this time, and it is best to repeat this process two cycles, and the remaining TCNQ complex salt has lost its conductivity and must be discarded. However, according to this invention, the melting temperature varies depending on the type of additive and the mixing ratio, but in any case, it can be melted at 200°C or less, and for example, at 200°C, it takes less time to decompose. over 10 minutes, 170
It can maintain a stable state for more than an hour if the temperature is around ℃, and can perform much more cycles of impregnation, allowing expensive TCNQ complex salts to be impregnated without waste.

This example uses a capacitor element in which foil-shaped aluminum is used as the anode, the surface of which is enlarged and then a dielectric oxide film is formed, and a current collecting electrode is wound with a separator paper interposed. However, the capacitor element is not limited to such a structure, and the metal constituting the anode may be other film-forming metals such as tantalum or alloys thereof. Further, the structure is not limited to such a wound structure, but may be a porous body obtained by sintering film-forming metal powder. Moreover, even if it is a wound structure, the separator paper may be omitted, the collecting electrode may be made of a metal other than aluminum, or a heat-resistant conductive resin film may be used.

Regarding the exterior structure, in this example, the case is housed in a metal exterior case, but the exterior body may be a resin case, a resin dip or mold, a laminate film exterior, etc. However, this does not deviate from the scope of this invention.

Note that similar results are obtained even if the lactone compound is other than those exemplified in the examples. Further, in the examples, only one type of lactone compound was added, but the same effect can be expected even if two or more types of lactone compounds are added in a mixture.

As described above, according to the present invention, it is possible to obtain a solid electrolytic capacitor with a high impregnation rate, that is, a high capacitance per unit volume. Moreover, since sufficient characteristics can be obtained in a single impregnation step, the electrolyte layer forming step can be simplified. In addition, since the TCNQ complex salt can be heated and melted at a lower temperature than before, sufficient time for thermal decomposition can be secured, and the impregnation process can be easily performed and a large amount can be impregnated. Furthermore, a simple manufacturing device is sufficient. In addition, it has the effect of allowing expensive TCNQ complex salt to be used without wasting it, which is extremely beneficial for improving the characteristics of solid electrolytic capacitors and improving workability.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the structure of a capacitor element used in an embodiment of the present invention, FIG. 2 is a sectional view showing a solid electrolyte impregnation device of the present invention, and FIG. FIG. 2 is a cross-sectional view showing a completed state of the solid electrolytic capacitor. FIG. 4 is a graph showing the results of differential thermal analysis of a mixture of TCNQ complex salt alone and γ-butyrolactone, which was melted and solidified by cooling. 1... Capacitor element, 2... Anode, 3... Collector electrode, 4... Separator paper, 5, 6... Tab,
7, 8... External lead, 10... Preheating block, 11, 13... Recess, 12... Impregnation block, 14... Mixture, 20... Exterior case, 21
...Elastic sealant.

Claims (1)

[Scope of Claims] 1. A solid electrolytic capacitor in which a dielectric oxide film is formed on the surface of a metal anode, and a solid electrolyte layer is further formed on the upper surface of the solid electrolyte layer, the solid electrolyte layer comprising tetracyanoquinodimethane, isopropyl- A solid electrolytic capacitor comprising a mixture of a complex salt with isoquinolinium and a lactone compound added thereto, which is melted and then solidified. 2 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone. 3. In a solid electrolytic capacitor formed by forming a dielectric oxide film on the surface of the anode metal and further forming a solid electrolyte layer on the upper surface, the solid electrolyte layer is formed by combining tetracyanoquinodimethane and isopropyl-isoquinolinium. A mixture obtained by adding a lactone compound to a complex salt is liquefied by heating to a temperature lower than the melting point or thermal decomposition temperature of the complex salt of tetracyanoquinodimethane and isopropyl-isoquinolinium, and a capacitor is placed in this liquid mixture. A method for producing a solid electrolytic capacitor, which comprises impregnating an element and cooling and solidifying the impregnation. 4 The lactone compound is γ-butyrolactone,
γ-valerolactone, δ-valerolactone, ε-
The method for producing a solid electrolytic capacitor according to claim 3, wherein the solid electrolytic capacitor is one or more selected from the group of caprolactone, γ-heptalactone, δ-nonalactone, and DL-pantoyllactone.