JP7355178B2 - Solid electrolytic capacitor and solid electrolytic capacitor manufacturing method - Google Patents

Description

The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and particularly to a solid electrolytic capacitor suitable for high voltage applications of 80 WV or higher and a method for manufacturing the same.

In recent years, solid electrolytic capacitors used to supply power to digitalized electrical equipment are strongly desired to be smaller and have larger capacities. Solid electrolytic capacitors that use valve-acting metals such as aluminum can obtain large capacitance in a small size by making the valve-acting metal as an anode foil into a shape such as etching foil and enlarging the surface of the dielectric. It is widely used because of its ability to

Solid electrolytic capacitors for small-sized, large-capacity applications generally have a capacitor element formed by winding an anode foil and a cathode foil made of a valve metal such as aluminum with a separator interposed therebetween. A solid electrolytic capacitor has a structure in which a capacitor element is impregnated with a driving electrolyte, and the capacitor element is housed in a metal case such as aluminum or a synthetic resin case, and the capacitor element is sealed. Note that as the anode material, aluminum, tantalum, niobium, titanium, etc. are used, and as the cathode material, the same kind of metal as the anode material is used.

In addition, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known as solid electrolytes used in solid electrolytic capacitors, but in recent years, the reaction rate is slow and the anode There is a technology (Patent Document 1) that focuses on conductive polymers such as polyethylene dioxythiophene (hereinafter referred to as PEDOT) that have excellent adhesion to the oxide film layer of foil.

Japanese Unexamined Patent Publication No. 2-15611

By the way, as solid electrolytic capacitors for vehicles and general power supply circuits, those for low voltage applications of about 25 WV and 63 WV are used. However, in recent years, there has been a demand for solid electrolytic capacitors with good ESR characteristics at high temperatures for use in high voltage applications of 80 WV or higher.

The present invention was proposed to solve the above problems, and its purpose is to provide a solid electrolytic capacitor with excellent characteristics for high voltage applications of 80 WV or higher, and a method for manufacturing the same.

In order to solve the above problems, the present inventors have conducted various studies and found that in the high voltage region exceeding 80 WV, by using an aliphatic carboxylic acid as a solute in the electrolyte filled in the capacitor element, the ESR characteristics can be improved. Based on this knowledge, we have completed the present invention.

That is, the solid electrolytic capacitor of the present invention has a capacitor element in which an anode foil and a cathode foil are wound with a separator in between, and the capacitor element has a solid electrolyte layer containing a conductive polymer, The void in the capacitor element is filled with an electrolytic solution, and the electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent, and the electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent. The amount of the group carboxylic acid added is 0.6 mol/kg or less, and the solute contains an ammonium salt of an aliphatic carboxylic acid having a molecular weight of 150 or more at 50 wt% or more based on the total solute .

The polyhydric alcohol may be ethylene glycol. The amount of the aliphatic carboxylic acid, which is the solute, added to the solvent may be 0.37 mol/kg or less. The amount of ammonium ion of the solute added to the solvent may be 0.6 mol/kg or less. The amount of the aliphatic carboxylic acid having a molecular weight of 150 or more, which is the solute, added to the solvent may be 0.6 mol/kg or less.

Further, a method for manufacturing the solid electrolytic capacitor as described above is also one embodiment of the present invention.

According to the present invention, it is possible to provide a solid electrolytic capacitor with excellent characteristics in high voltage applications of 80 WV or higher and a method for manufacturing the solid electrolytic capacitor.

FIG. 1 is a perspective view showing an example of the configuration of a solid electrolytic capacitor according to a first embodiment.

[1. composition]
Hereinafter, the solid electrolytic capacitor of this embodiment will be described in detail with reference to FIG. 1. As shown in FIG. 1, the solid electrolytic capacitor includes a capacitor element 10 in which an anode foil 1 and a cathode foil 2 are wound with a separator 3 in between. The solid electrolytic capacitor is manufactured by housing the capacitor element 10 together with an electrolyte in a bottomed cylindrical case (not shown) and sealing the case.

The anode foil 1 is made of a valve metal foil having a dielectric film on its surface. Aluminum, tantalum, niobium, titanium, etc. can be used as the valve metal foil. The surface area of the valve metal foil may be expanded by roughening the surface by performing electrochemical etching treatment in an aqueous chloride solution. Further, the dielectric film can be formed by performing a chemical conversion treatment using, for example, ammonium oxide, ammonium borate, or the like. The cathode foil 2 is made of valve metal foil similar to the anode foil 1. The surface of the cathode foil may also be roughened by etching treatment. Further, a thin dielectric film (approximately 1 to 10 V) may be formed on the cathode foil 2 by chemical conversion treatment if necessary. Hereinafter, the anode foil 1 and the cathode foil 2 may be collectively referred to as electrode foil. The dimensions of the electrode foil can be arbitrarily set according to the specifications of the solid electrolytic capacitor to be manufactured.

As shown in FIG. 1, lead wires 4 and 5 for connecting the respective electrodes to the outside are connected to the anode foil 1 and the cathode foil 2 by, for example, stitching or ultrasonic welding. The lead wires 4 and 5 are made of aluminum or the like. The lead wires 4 and 5 are electrode lead-out means for electrically connecting the anode foil 1 and the cathode foil 2 to the outside, and are led out from the end face of the wound capacitor element.

As the separator 3, a nonwoven fabric mainly composed of synthetic fibers or glass fiber can be used. Examples of synthetic fibers include polyester fibers, nylon fibers, rayon fibers, and the like, and these fibers may be used alone or in combination. Alternatively, a separator made of natural fibers may be used. The separator 3 may have a slightly larger width depending on the dimensions of the anode foil 1 and the cathode foil 2.

The capacitor element 10 formed as described above may be subjected to repair chemical formation. Mechanical stress is applied to the electrode foil during winding of the capacitor element, which may cause damage such as cracks to the dielectric film. In the repair chemical conversion process, the capacitor element 10 is immersed in a chemical liquid for chemical conversion, thereby forming a dielectric film on the portion where the crack has occurred, thereby making it possible to repair the damage. As the chemical solution, use a phosphoric acid-based chemical solution such as ammonium dihydrogen phosphate or diammonium hydrogen phosphate, a boric acid-based chemical solution such as ammonium borate, or an adipic acid-based chemical solution such as ammonium adipate. be able to. Among these, it is particularly preferable to use ammonium dihydrogen phosphate.

A solid electrolyte layer is formed in the capacitor element 10. Specifically, the solid electrolyte layer is formed on the separator 3 and the electrode foil. The solid electrolyte layer can be formed by dipping the capacitor element 10 in a conductive polymer dispersion and then drying it. The immersion and drying steps in the conductive polymer dispersion may be repeated multiple times. A conductive polymer dispersion is a solution in which conductive polymer particles are dispersed in a solvent. As the conductive polymer, for example, PEDOT powder can be used. Further, the solvent may contain a solid content of polystyrene sulfonic acid as a dopant.

The solvent for the conductive polymer dispersion may be any solvent that can dissolve the conductive polymer particles or powder, and water is mainly used. However, if necessary, ethylene glycol may be used alone or in combination as a solvent for the dispersion. It has been found that when ethylene glycol is used as a solvent for the dispersion, it is possible to reduce the electrical properties of the product, particularly the ESR. In order to improve the impregnating properties and conductivity of the conductive polymer dispersion, various additives may be added to the conductive polymer dispersion, or neutralization may be performed by adding cations. In particular, when sorbitol or sorbitol and a polyhydric alcohol are used as additives, ESR can be reduced and deterioration of voltage resistance characteristics due to lead-free reflow or the like can be prevented.

Further, the concentration of the conductive polymer can be 1 to 10 wt% relative to the aqueous solution. The conductive polymer particles include primary conductive polymer particles, aggregates (secondary particles) of conductive polymer compounds and dopants, and powders thereof.

Specifically, as the conductive polymer, it is preferable to use a mixture of particles of thiophene or its derivative and a solid content of a dopant consisting of a polymeric sulfonic acid. The conductive polymer dispersion is obtained by oxidative polymerization of thiophene or its derivative as a polymerizable monomer in water or an aqueous liquid in the presence of a polymeric sulfonic acid as a dopant. Examples of thiophene derivatives in the conductive polymer thiophene or its derivatives include 3,4-ethylenedioxythiophene, 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4 -alkylthiophene, 3,4-alkoxythiophene and the like. Suitably, the alkyl group or alkoxy group has 1 to 16 carbon atoms, and 3,4-ethylenedioxythiophene is particularly preferred. Moreover, not only thiophene but also pyrrole and its derivatives may be used. Particularly preferable conductive polymers obtained from these polymerizable monomers include polythiophene, polyethylenedioxythiophene, and polypyrrole.

The capacitor element 10 on which the solid electrolyte layer is formed is immersed in an electrolytic solution, and the void inside the capacitor element 10 is filled with the electrolytic solution. When filling the electrolytic solution into the capacitor element 10, the amount of filling is arbitrary as long as the electrolytic solution can fill the voids within the capacitor element 10, but it is preferably 3 to 100% of the voids within the capacitor element 10.

The electrolytic solution of this embodiment is a non-aqueous electrolytic solution that does not contain water as a solvent. In this specification, a non-aqueous electrolytic solution is an electrolytic solution to which water is not added during the preparation of the electrolytic solution. When a non-aqueous electrolyte is used, an increase in ESR can be suppressed compared to when an aqueous electrolyte containing water as a solvent is used. However, during the manufacturing process, moisture contained in the air or in the separator mixes into the solid electrolytic capacitor, but if the amount of moisture contained in the solid electrolytic capacitor can be controlled to 3 wt% or less, there is no risk of an increase in ESR.

As the solvent that can be used in the electrolytic solution, it is preferable to use a solvent whose boiling point is 120° C. or higher because the electrolytic solution is difficult to volatilize. Examples of solvents include γ-butyrolactone, polyhydric alcohols such as ethylene glycol, sulfolane, dimethylformamide, and the like. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, dipropylene glycol, 1,2-propanediol, glycerin, 1,3-propanediol, 1,3-butanediol, 2-methyl-2,4-pentanediol, etc. Low molecular weight polyhydric alcohols are preferred. In particular, if a solvent containing ethylene glycol is used, the initial ESR characteristics will be good, and the high temperature characteristics will also be good. Further, the amount of ethylene glycol added in the mixed solvent is preferably 5 wt% or more, more preferably 40 wt% or more, and most preferably 60 wt% or more.

Furthermore, by adding a predetermined amount of γ-butyrolactone as a solvent, the impregnation of the electrolyte into the capacitor element 10 can be improved. By using ethylene glycol, which has a relatively high viscosity, and γ-butyrolactone, which has a relatively low viscosity, the impregnation into the capacitor element 10 can be enhanced. Therefore, good initial characteristics and good characteristics during long-term use are maintained, and charge/discharge characteristics at low temperatures are improved. The amount of γ-butyrolactone added in the mixed solvent is preferably 40 wt% or less.

Furthermore, at least one solvent selected from sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane may be additionally used in addition to the ethylene glycol solvent of the ion-conductive substance. Since these sulfolane-based solvents have a high boiling point, they suppress volatilization of the electrolytic solution and have good high-temperature characteristics. The amount of these sulfolane solvents added in the mixed solvent is preferably 40 wt% or less.

The electrolytic solution contains ammonium salts of aliphatic carboxylic acids as solutes. It is preferable to use an ammonium salt of an aliphatic carboxylic acid because pressure resistance characteristics are improved. Examples of the aliphatic carboxylic acids include azelaic acid, adipic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, 7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid, and 7,9-decanedicarboxylic acid. -Aliphatic dicarboxylic acids such as dimethyl-7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid, 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid, and other aliphatic dicarboxylic acids. Monocarboxylic acids and aliphatic polycarboxylic acids such as aliphatic tricarboxylic acids can be used. These aliphatic carboxylic acids may be used alone or in combination. Moreover, it is preferable to use an aliphatic carboxylic acid having a molecular weight of 150 or more. When the molecular weight of the aliphatic carboxylic acid increases, the voltage resistance characteristics of the solid electrolytic capacitor are further improved. Although the solute may contain something other than the ammonium salt of aliphatic carboxylic acid, it is preferable to use the ammonium salt of aliphatic carboxylic acid as the main solute. Here, the term "main solute" refers to 50 wt% or more of the total solute.

In the above electrolytic solution, as is clear from the results of Examples described later, the amount of solute acid added to the solvent is preferably 0.6 mol/kg or less. By controlling the amount of solute acid added to the solvent to be 0.6 mol/kg or less, changes in capacitance and ESR in a load test can be suppressed at high pressures of 80 WV or higher.

Furthermore, as additives for the electrolyte solution, polyoxyethylene glycol, complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, nitro compounds (o-nitrobenzoic acid, etc.) , m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, etc.), phosphoric acid esters, and the like. Among these, it is particularly preferable to add boric acid and mannitol because changes in capacitance and ESR can be further suppressed in a load test.

[2. Manufacturing method of solid electrolytic capacitor]
The method for manufacturing a solid electrolytic capacitor according to the present embodiment as described above includes the following steps.
(1) Step of forming a capacitor element (2) Step of forming a solid electrolyte layer on the capacitor element (3) Step of filling the void in the capacitor element with electrolyte (4) Step of forming a solid electrolytic capacitor

Each step will be explained in detail below.
(1) Step of forming capacitor element In the step of forming capacitor element 10, capacitor element 10 is formed by winding anode foil 1 and cathode foil 2 with separator 3 in between. The anode foil 1 is formed, for example, by etching a flat valve metal foil such as aluminum, and then forming a dielectric film by chemical conversion treatment. The cathode foil 2 is formed of, for example, an etched foil obtained by etching a flat metal foil similarly to the anode foil 1. Lead wires 4 and 5 are connected to the anode foil 1 and the cathode foil 2, respectively. Capacitor element 10 is formed by winding up anode foil 1 and cathode foil 2 as described above with separator 3 interposed therebetween. Note that the formed capacitor element 10 may be immersed in a repair liquid to undergo repair chemical conversion. The immersion time is preferably 5 to 120 minutes.

(2) Step of forming a solid electrolyte layer on a capacitor element After immersing the capacitor element 10 in a conductive polymer dispersion, it is dried to form a solid electrolyte layer 7. The time for immersing the capacitor element 10 in the conductive polymer dispersion is determined by the size of the capacitor element 10, but it is 5 seconds or more for a capacitor element of about 5 mm in diameter x 3 mm in height, and for a capacitor of about 9 mm in diameter x 5 mm in height. It is desirable for the device to be immersed for 10 seconds or more, and it is necessary to immerse the device for at least 5 seconds. Note that there is no adverse effect on the characteristics even if the product is immersed for a long time. Further, after being immersed in this manner, it is preferable to maintain the product under reduced pressure. The reason for this is thought to be that the amount of residual volatile solvent decreases. Impregnation and drying of the conductive polymer dispersion may be performed multiple times as necessary.

After the capacitor element 10 is immersed in the conductive polymer dispersion, the capacitor element 10 is dried at a predetermined temperature. The drying temperature is preferably 100 to 160°C and the drying time is preferably 0.5 to 3 hours. Through this drying process, a solid electrolyte layer containing a conductive polymer is formed in the capacitor element 10, particularly on the dielectric film in the etching pits of the etching foil.

(3) Step of filling the void within the capacitor element with an electrolyte The capacitor element 10 on which the solid electrolyte layer 7 is formed is immersed in an electrolyte, and the void within the capacitor element 10 is filled with the electrolyte.

(4) Step of forming a solid electrolytic capacitor The capacitor element 10 is inserted into an exterior case together with an electrolyte, a sealing rubber is attached to the open end, and the capacitor element 10 is sealed by crimping. Thereafter, aging is performed to produce a solid electrolytic capacitor. In addition to the exterior case, a solid electrolytic capacitor can also be produced by covering the exterior of the capacitor element 10 with an insulating resin such as an epoxy resin and aging the capacitor element 10.

[3. Effect】
(1) The solid electrolytic capacitor of this embodiment has a capacitor element 10 in which an anode foil 1 and a cathode foil 2 are wound with a separator 3 in between, and the capacitor element 10 has a solid electrolyte layer, The void in the capacitor element 10 is filled with an electrolytic solution, and the electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent, and the amount of the solute acid added to the solvent is It is 0.6 mol/kg or less.

As mentioned above, the electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent. When an ammonium salt of an aliphatic carboxylic acid is used as a solute, pressure resistance characteristics are improved at high pressures of 80 WV or higher. Further, by setting the amount of solute acid added to the solvent to be 0.6 mol/kg or less, changes in capacitance and ESR can be suppressed at high pressures of 80 WV or higher.

When a solvent containing a polyhydric alcohol such as ethylene glycol is used, the initial ESR is lower than when a solvent containing no ethylene glycol is used, and the rate of change in capacitance ( ΔCap) is found to be small. The reason for this is thought to be that polyhydric alcohols such as ethylene glycol have the effect of promoting the extension of the polymer chains of the conductive polymer, thereby improving the conductivity and reducing the ESR.

In particular, in electrolytes that use ammonium salts of aliphatic carboxylic acids as solutes and polyhydric alcohols such as ethylene glycol as solvents, solid electrolytic capacitors are exposed to a hot atmosphere, causing esterification reactions in the electrolytes. esters of polyhydric alcohols and carboxylic acids are produced. In the case of amine salts, aminium ions lose protons and gasify through this esterification reaction, but because of their high boiling point, they remain in the capacitor case, resulting in excessive changes in the pH of the electrolyte. , deterioration of the conductive polymer is likely to occur. However, in the ammonium salt of aliphatic carboxylic acid used as a solute as in the present invention, ammonium ions lose protons through esterification, gasify, and evaporate. It is thought that excessive changes in the pH of the conductive polymer are less likely to occur, and deterioration of the conductive polymer is reduced.

Additionally, as a result of evaluating various solutes, we found that ammonium salts of aliphatic carboxylic acids not only have improved chemical formation properties as electrolytes, but also have good compatibility with conductive polymers and do not cause deterioration of the solid electrolyte layer in high-temperature durability tests. This is thought to be because the lower the solute concentration, the more suppressed is the deterioration of the solid electrolyte layer. As described above, according to the present embodiment, it is possible to provide a solid electrolytic capacitor with excellent characteristics in high voltage applications of 80 WV or higher and a method for manufacturing the solid electrolytic capacitor.

(2) The polyhydric alcohol may be ethylene glycol.
A protic solvent having a hydroxyl group such as ethylene glycol has a higher affinity with separators, electrode foils, and conductive polymers than γ-butyrolactone or sulfolane. Therefore, during the process of electrolyte volatilization when using a solid electrolytic capacitor, charge is easily transferred between the separator, electrode foil, conductive polymer, and electrolyte, resulting in a small capacitance change rate (ΔCap). It is considered to be.

(3) The electrolytic solution may be a non-aqueous electrolytic solution that does not contain water as a solvent.
If an aqueous electrolytic solution containing water is used as a solvent, there is a risk that the conductive polymer of the electrode foil and the solid electrolyte layer will deteriorate and the ESR will increase. In this embodiment, since a non-aqueous electrolytic solution containing no water is used as a solvent, an increase in ESR can be suppressed compared to the case where an aqueous electrolytic solution is used.

(4) The electrolytic solution may further contain boric acid and mannitol.
By adding boric acid and mannitol to the electrolytic solution, changes in capacitance and ESR can be further suppressed in a load test.

(5) The molecular weight of the aliphatic carboxylic acid may be 150 or more.
By using an aliphatic carboxylic acid having a molecular weight of 150 or more, the pressure resistance characteristics at high pressures exceeding 80 WV can be further improved.

Hereinafter, the present invention will be explained in more detail based on Examples. Note that the present invention is not limited to the following examples.

(1) Withstand voltage test of solid electrolytic capacitor (rated voltage 80WV)
First, in order to conduct a withstand voltage test on a solid electrolytic capacitor with a rated voltage of 80 WV, the following solid electrolytic capacitor was manufactured.

<Production of solid electrolytic capacitor of Example 1>
A lead wire, which is an electrode extraction means, is connected to the anode foil with a dielectric film layer formed on the surface and the cathode foil, and both electrode foils are wound through a manila separator, so that the element shape is 8 mm in diameter x height. A capacitor element with a diameter of 10 mm was formed. Then, this capacitor element was immersed in an aqueous ammonium dihydrogen phosphate solution for 40 minutes to perform repair chemical conversion.

Thereafter, a conductive polymer dispersion was prepared by dispersing PEDOT particles and polystyrene sulfonic acid in an aqueous solution. The capacitor element was immersed in the conductive polymer dispersion, and the capacitor element was pulled out and dried at 150° C. for 30 minutes. The capacitor element was immersed in a conductive polymer dispersion and dried multiple times to form a solid electrolyte layer made of a conductive polymer on the capacitor element.

Next, ammonium azelate salt was added to ethylene glycol to prepare an electrolytic solution. The breakdown of the amount of azelaic acid ammonium salt added was 0.09 mol/kg of azelaic acid and 0.09 mol/kg of ammonium ion relative to the solvent. Further, as additives, a total of 2 wt % of phosphoric acid ester and p-nitrobenzoic acid were added to the electrolyte. After immersing the capacitor element in the prepared electrolytic solution, it was inserted into a cylindrical outer case with a bottom, a sealing rubber was attached to the open end, and the capacitor element was sealed by crimping. Thereafter, aging was performed by applying a voltage to form a solid electrolytic capacitor. Note that the rated capacity of this solid electrolytic capacitor is 39 μF.

<Production of solid electrolytic capacitor of Example 2>
It was produced in the same manner as in Example 1, except that the details of the amounts of azelaic acid ammonium salt added were 0.26 mol/kg for azelaic acid and 0.26 mol/kg for ammonium ions.

<Production of solid electrolytic capacitor of Example 3>
It was produced in the same manner as in Example 1, except that the contents of the azelaic acid ammonium salt added were 0.37 mol/kg for azelaic acid and 0.37 mol/kg for ammonium ion.

<Production of solid electrolytic capacitor of Example 4>
It was produced in the same manner as in Example 1, except that the details of the amounts of azelaic acid ammonium salt added were 0.60 mol/kg for azelaic acid and 0.60 mol/kg for ammonium ions.

<Production of solid electrolytic capacitor of Example 5>
It was produced in the same manner as in Example 1, except that a total of 2.8 wt% of phosphate ester, p-nitrobenzoic acid, boric acid, and mannitol were added as additives to the electrolytic solution.

<Production of solid electrolytic capacitor of Example 6>
Azelaic acid ammonium salt was converted into adipic acid ammonium salt. The details of the amount of ammonium adipic acid added were 0.06 mol/kg for adipic acid and 0.06 mol/kg for ammonium ion. Other than that, it was produced in the same manner as in Example 1.

<Production of solid electrolytic capacitor of Example 7>
It was produced in the same manner as in Example 6, except that the amounts of ammonium adipic acid added were 0.10 mol/kg for adipic acid and 0.10 mol/kg for ammonium ions.

<Production of solid electrolytic capacitor of Example 8>
It was produced in the same manner as in Example 6, except that the amounts of ammonium adipic acid added were 0.16 mol/kg for adipic acid and 0.16 mol/kg for ammonium ions.

<Production of solid electrolytic capacitor of Example 9>
It was produced in the same manner as in Example 6, except that the amounts of ammonium adipic acid added were 0.20 mol/kg for adipic acid and 0.20 mol/kg for ammonium ions.

<Production of solid electrolytic capacitor of Example 10>
Azelaic acid ammonium salt was changed to 1,6-decanedicarboxylic acid ammonium salt. The details of the amount of 1,6-decanedicarboxylic acid ammonium salt added were 0.09 mol/kg for 1,6-decanedicarboxylic acid and 0.09 mol/kg for ammonium ion. Other than that, it was produced in the same manner as in Example 1. Note that the rated capacity of this solid electrolytic capacitor is 22 μF.

<Production of solid electrolytic capacitor of Example 11>
Azelaic acid ammonium salt, 1,7-octanedicarboxylic acid ammonium salt, 7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid ammonium salt, 7,9-dimethyl-7,9-dimethoxycarbonyl-1, 11-dodecanedicarboxylic acid ammonium salt and 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid ammonium salt. The breakdown of the amount of solutes added is as follows: 1,7-octanedicarboxylic acid 0.05 mol/kg, 7-methyl-7-methoxycarbonyl-1,9-decanedicarboxylic acid 0.01 mol/kg, 7,9-dimethyl -7,9-dimethoxycarbonyl-1,11-dodecanedicarboxylic acid 0.01 mol/kg, 7,8-dimethyl-7,8-dimethoxycarbonyl-1,14-tetradecanedicarboxylic acid 0.02 mol/kg, ammonium The ion was set at 0.09 mol/kg. Other than that, it was produced in the same manner as in Example 1. Note that the rated capacity of this solid electrolytic capacitor is 22 μF.

<Production of solid electrolytic capacitor of Comparative Example 1>
Azelaic acid ammonium salt was converted into phthalic acid triethylamine salt. The breakdown of the amount of triethylamine phthalate added was 0.60 mol/kg for phthalic acid and 0.47 mol/kg for triethylamine. Other than that, it was produced in the same manner as in Example 1.

<Production of solid electrolytic capacitor of Comparative Example 2>
Azelaic acid ammonium salt was made into azelaic acid triethylamine salt. The breakdown of the amount of azelaic acid triethylamine salt added was 0.60 mol/kg for azelaic acid and 0.47 mol/kg for triethylamine. Other than that, it was produced in the same manner as in Example 1.

<Production of solid electrolytic capacitor of Comparative Example 3>
It was produced in the same manner as in Example 1, except that the details of the amounts of azelaic acid ammonium salt added were 0.81 mol/kg for azelaic acid and 0.81 mol/kg for ammonium ions.

Table 1 shows the results of applying a voltage to the solid electrolytic capacitor produced as described above and checking whether the voltage rose to the withstand voltage of the dielectric film required for an 80 WV solid electrolytic capacitor. In Table 1, the circles are solid electrolytic capacitors whose voltage has increased to the film breakdown voltage of the electrode foil. In addition, the cross mark indicates a solid electrolytic capacitor that was short-circuited without the voltage rising to the film breakdown voltage of the electrode foil.

As is clear from Table 1, Examples 1 to 5 using azelaic acid, Examples 6 to 9 using adipic acid, Example 10 using 1,6-decanedicarboxylic acid, and multiple aliphatic carboxylic acids. In all of Example 11 using a mixed acid solute, the voltage increased to the withstand voltage of the electrode foil film. Further, as in Examples 1 to 11, in Comparative Examples 2 and 3 using aliphatic carboxylic acids, the voltage increased to the withstand voltage of the electrode foil film. However, in Comparative Example 1 using phthalic acid, which is an aromatic carboxylic acid, the voltage did not rise to the withstand voltage of the electrode foil film and a short circuit occurred.

(2) Withstand voltage test of solid electrolytic capacitor (rated voltage 100WV)
Next, in order to perform a voltage resistance test on a solid electrolytic capacitor with a rated voltage of 100 WV, the following solid electrolytic capacitor was further produced.

<Production of solid electrolytic capacitor of Example 12>
A solid electrolytic capacitor was produced in the same manner as in Example 4 except that the rated capacity of the solid electrolytic capacitor was 18 μF.

<Production of solid electrolytic capacitor of Example 13>
Azelaic acid ammonium salt was converted into adipic acid ammonium salt. The details of the amount of ammonium adipic acid added were 0.60 mol/kg for adipic acid and 0.60 mol/kg for ammonium ion. Other than that, it was produced in the same manner as in Example 12.

A voltage was applied to the solid electrolytic capacitor produced as described above, and it was confirmed whether the voltage rose to the withstand voltage of the dielectric film required for a 100 WV solid electrolytic capacitor. Table 2 shows the results. In Table 2, the circles are solid electrolytic capacitors whose voltage has increased to the film breakdown voltage of the electrode foil. In addition, the cross mark indicates a solid electrolytic capacitor that was short-circuited without the voltage rising to the film breakdown voltage of the electrode foil.

As is clear from Table 2, in the 100 WV withstand voltage test, in Example 12 using azelaic acid, the voltage increased to the film withstand voltage of the electrode foil. On the other hand, in Example 13 using adipic acid, a short circuit occurred without the voltage rising to the film breakdown voltage of the electrode foil. In a solid electrolytic capacitor using adipic acid, the voltage increased to the film withstand voltage in an 80 WV withstand voltage test, but the voltage did not increase and a short circuit occurred at 100 WV. This is considered to be due to the fact that the molecular weight of adipic acid is 146.1. The molecular weight of azelaic acid, which gave good results in the 100 WV pressure test, is 188.22. Therefore, it can be seen that as the molecular weight of the aliphatic carboxylic acid increases, the withstand voltage characteristics of the solid electrolytic capacitor improve. In particular, it has been found that pressure resistance characteristics are improved when the molecular weight is 150 or more.

(3) Capacitor characteristics at initial stage and after load test The initial ESR and dielectric loss (tan δ) of the solid electrolytic capacitors of Examples 1 to 11 and Comparative Examples 2 and 3 were measured. Note that the dielectric loss shows the value at 120 kHz (20°C), and the ESR characteristic shows the value at 100 kHz (20°C). Further, as described above, the capacitance of Examples 1 to 9 and Comparative Examples 2 and 3 is 39 μF, and the capacitance of Examples 10 and 11 is 22 μF.

Further, each solid electrolytic capacitor was subjected to a high temperature load test at 125° C. and a rated voltage of 80 WV, and the ESR change rate (ΔESR) and dielectric loss change rate (Δtanδ) after 500 hours and 1500 hours were calculated. Table 3 shows the results after 500 hours.

As is clear from Table 3, in the results after 500 hours of the load test, the ESR change rate and dielectric loss change rate were the lowest in Example 5 in which boric acid and mannitol were added. From Examples 1 to 4, it was found that as the amount of solute acid added increased, the dielectric loss change rate and ESR change rate increased. Furthermore, in Comparative Example 3 in which 0.81 mol/kg of azelaic acid was added, the rate of change in ESR was high. On the other hand, in Examples 1 to 11 and Comparative Example 2 in which the amount of solute acid added was 0.6 mol/kg or less, the ESR change rate was smaller than that in Comparative Example 3.

Next, Table 4 shows the results after 1500 hours.

As is clear from Table 4, in the results after 1500 hours of the load test, the ESR change rate and dielectric loss were higher in Example 5, in which boric acid and mannitol were added, compared to other examples and comparative examples. The rate of change was the lowest value. Furthermore, from Examples 1 to 4, it was found that as the amount of solute acid added increased, the dielectric loss change rate and the ESR change rate increased. Furthermore, in Comparative Example 2 in which the ammonium salt of aliphatic carboxylic acid was not used but the triethylamine salt was used, the values of the dielectric loss change rate and the ESR change rate increased significantly. On the other hand, in Examples 1 to 9 using ammonium salts of aliphatic carboxylic acids, the ESR change rate and dielectric loss change rate were smaller than those in Comparative Example 2.

Furthermore, in Comparative Example 3 in which 0.81 mol/kg of azelaic acid was added, not only the ESR change rate but also the dielectric loss change rate was high. On the other hand, in Examples 1 to 9 in which the ammonium salt of aliphatic carboxylic acid was added and the amount of solute acid added was 0.6 mol/kg or less, the ESR change rate and dielectric loss change rate were higher than those in Comparative Example 3. It became a small value.

1 Anode foil 2 Cathode foil 3 Separators 4, 5 Lead wire 10 Capacitor element

Claims (6)

It has a capacitor element in which an anode foil and a cathode foil are wound through a separator,
The capacitor element has a solid electrolyte layer containing a conductive polymer,
The void within the capacitor element is filled with an electrolyte,
The electrolytic solution contains an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent,
The amount of the aliphatic carboxylic acid as the solute added to the solvent is 0.6 mol/kg or less,
A solid electrolytic capacitor , wherein the solute contains an ammonium salt of an aliphatic carboxylic acid having a molecular weight of 150 or more in an amount of 50 wt % or more based on the total solute . The solid electrolytic capacitor according to claim 1, wherein the polyhydric alcohol is ethylene glycol. 3. The solid electrolytic capacitor according to claim 1, wherein the amount of the aliphatic carboxylic acid as the solute added to the solvent is 0.37 mol/kg or less . 4. The solid electrolytic capacitor according to claim 1 , wherein the amount of ammonium ions of the solute added to the solvent is 0.6 mol/kg or less . 5. The solid electrolytic capacitor according to claim 1, wherein the amount of the aliphatic carboxylic acid having a molecular weight of 150 or more, which is the solute, added to the solvent is 0.6 mol/kg or less. a step of forming a capacitor element by winding an anode foil and a cathode foil with a separator interposed therebetween;
immersing the capacitor element in a conductive polymer dispersion and then drying it to form a solid electrolyte layer containing the conductive polymer;
The capacitor element on which the solid electrolyte layer is formed is immersed in an electrolytic solution containing an ammonium salt of an aliphatic carboxylic acid as a solute and a polyhydric alcohol as a solvent, and the voids in the capacitor element are filled with the electrolytic solution. The process of
including;
The amount of the aliphatic carboxylic acid as the solute added to the solvent is 0.6 mol/kg or less,
A method for producing a solid electrolytic capacitor , wherein the solute contains an ammonium salt of an aliphatic carboxylic acid having a molecular weight of 150 or more at 50 wt % or more based on the total solute .

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