JP2019145679A - Manufacturing method of solid electrolytic capacitor - Google Patents

Abstract

To provide a manufacturing method of a solid electrolytic capacitor with high durability and high reliability.SOLUTION: In a manufacturing method of a solid electrolytic capacitor including at least a step (a) of holding an electrolyte salt on an anode metal on which a dielectric oxide film is formed and a step (b) of forming a solid electrolyte layer, the step (a) of holding the electrolyte salt includes a step of holding the electrolyte salt on the dielectric oxide film by preparing a pretreatment liquid obtained by diluting an ionic liquid to a predetermined concentration with a solvent, contacting the pretreatment liquid on the anode metal, and evaporating the solvent.SELECTED DRAWING: None

Description

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

  Conductive polymers such as polyaniline, polypyrrole, and polythiophene have been applied to electrolytes for solid electrolytic capacitors because they have excellent stability and conductivity.

  These conductive polymers are generally insoluble or hardly soluble in a solvent and infusible, so that they are difficult to mold and process.

  A solid electrolytic capacitor is known in which a solid electrolyte layer containing a conductive polymer is formed on a valve metal having a dielectric oxide film.

  As a method for forming a solid electrolyte layer containing a conductive polymer, a chemical oxidative polymerization method is known. In the chemical oxidative polymerization method, for example, a solution containing a monomer compound and an oxidant are adhered and contacted on a valve action metal on which a dielectric oxide film is formed. A solid electrolyte layer made of molecules can be formed.

  However, this chemical oxidative polymerization method has a problem that a desired capacity appearance rate, ESR, durability, and particularly moisture resistance cannot be obtained.

  Patent Document 1 discloses a solid electrolytic capacitor in which a cathode layer made of an ambient temperature molten salt having a decomposition point of at least 300 ° C. and a conductive polymer is formed on the cathode layer. However, the solid electrolytic capacitor has a problem that a desired capacity appearance rate and ESR, high durability, and high moisture resistance cannot be obtained.

  From the above, there has been a demand for a method for producing a solid electrolytic capacitor having excellent electrical characteristics, high durability, and high moisture resistance.

JP 2006-024708 A

  The conventional manufacturing method has a problem that a desired capacity appearance rate, ESR, durability, and moisture resistance cannot be obtained. Therefore, the present invention provides a method for producing a solid electrolytic capacitor having both excellent capacity appearance rate and ESR, and having high durability, particularly high moisture resistance.

  The present invention has found that, by using a pretreatment liquid obtained by diluting an ionic liquid to a predetermined concentration with a solvent, a method that is surprisingly superior in capacity appearance rate, ESR, durability, and moisture resistance can be provided.

  That is, the present invention is as follows.

  A first invention is a method for producing a solid electrolytic capacitor having at least a step (a) of holding an electrolyte salt on an anode metal on which a dielectric oxide film is formed, and a step (b) of forming a solid electrolyte layer. The step (a) of holding the electrolyte salt prepares a pretreatment liquid obtained by diluting an ionic liquid to a predetermined concentration with a solvent, contacts the pretreatment liquid on the anode metal, and evaporates the solvent. A method for producing a solid electrolytic capacitor, comprising a step of retaining an electrolyte salt on a dielectric oxide film.

  The second invention is the solid electrolytic capacitor according to the first invention, wherein the pretreatment liquid is diluted with 10 to 30 parts by weight of a solvent with respect to 10 parts by weight of an ionic liquid. It is a manufacturing method.

  A third invention is the method for producing a solid electrolytic capacitor according to the first or second invention, wherein the solvent is at least one selected from the group consisting of methanol, ethanol and isopropyl alcohol. .

  According to a fourth invention, in any one of the first to third inventions, wherein the ionic liquid contains a non-polymeric nitrogen onium cation, and the cation portion has at least an imidazolium and / or pyridinium skeleton. This is a method for producing a solid electrolytic capacitor according to any one of the above.

  According to a fifth invention, in any one of the first to fourth inventions, wherein the ionic liquid contains a fluorine-containing organic anion, and the anion has at least a bistrifluoromethanesulfonylimide anion. It is a manufacturing method of the described solid electrolytic capacitor.

  A sixth invention is characterized in that the anode metal on which the dielectric oxide film is formed is a sintered body of at least one metal selected from the group consisting of tantalum, titanium and niobium. It is a manufacturing method of the solid electrolytic capacitor as described in any one of 5 invention.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the manufacturing method of the solid electrolytic capacitor which has the outstanding electrical property and comprised high durability and high moisture resistance. That is, it is possible to provide both a high electrostatic capacity and a low ESR, and provide a highly reliable method of manufacturing a solid electrolytic capacitor with very little change in electrical characteristics over time in a moist heat test.

It is a graph which shows the time-dependent change of the capacity | capacitance change rate in a heat resistance test. It is a graph which shows the time-dependent change of the capacity | capacitance change rate in a moisture resistance test. It is a graph which shows the time-dependent change of ESR in a moisture resistance test.

  The present invention will be described below.

  The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor in which an electrolyte salt and a solid electrolyte are formed on an anode metal on which a dielectric oxide film is formed.

[Anode metal with dielectric oxide film]
Examples of the anode metal include valve action metals such as aluminum, tantalum, niobium, and titanium. As the shape of the anode metal, a sintered body obtained by sintering fine particles, a foil-like or plate-like shape roughened by etching or the like is used. Among these anode metals, a sintered body of at least one metal selected from the group consisting of tantalum, niobium and titanium is preferable.

  A dielectric oxide film can be formed on the surface of the valve metal by subjecting the anode metal to a known chemical conversion treatment. For example, an anodizing treatment can be performed in an aqueous solution such as diammonium adipate to form a dielectric oxide film on the anode metal.

[Electrolyte salt]
The electrolyte salt used in the present invention can be an ionic liquid. The ionic liquid as used in the field of this invention refers to the molten salt (ionic compound) which exhibits a liquid state at room temperature (25 degreeC), and is a salt which consists of a cation component and an anion component.
Examples of the cationic component include alkylammonium, alkylphosphonium, alkylpyridinium, alkylimidazolium, and the anionic component includes tetrafluoroboric acid, hexafluorophosphoric acid, trifluoromethanesulfonic acid, perfluoroalkylsulfonylimide, Examples include perfluoroalkylsulfonylmethide, cyclic perfluoroalkylsulfonylimide, hydrofluoride, bistrifluoromethanesulfonylimide anion, bisfluoromethanesulfonylimide anion, and the like.
Among these cation components, those having a non-polymeric nitrogen onium cation and having a imidazolium and / or pyridinium skeleton at the cation site are preferable in terms of heat and moisture resistance. Moreover, it is preferable in terms of heat-and-moisture resistance that it has a fluorine-containing organic anion among anion components, and this anion is a bistrifluoromethanesulfonylimide anion. The cation component has a non-polymeric nitrogen onium cation, the cation moiety has an imidazolium and / or pyridinium skeleton, the anion component has a fluorine-containing organic anion, and the anion is bistrifluoro What is a methanesulfonylimide anion is preferable in terms of heat-and-moisture resistance.

[Solvent of pretreatment liquid]
As the solvent of the pretreatment liquid of the present invention, water or an organic solvent can be used.

  As the organic solvent, alcohols, ketones, esters, ethers, cellosolves, aromatic hydrocarbons, aliphatic hydrocarbons and the like can be used.

  Examples of alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, n-butanol, s-butanol, t-butanol, n-amyl alcohol, s-amyl alcohol, t-amyl alcohol, allyl alcohol, isoamyl alcohol, and isobutyl. Alcohol, 2-ethylbutanol, 2-octanol, n-octanol, cyclohexanol, tetrahydrofurfuryl alcohol, furfuryl alcohol, n-hexanol, n-heptanol, 2-heptanol, 3-heptanol, benzyl alcohol, methylcyclohexanol, Examples include ethylene glycol, ethylene glycol monomethyl ether, glycerin, diethylene glycol, and propylene glycol.

  Examples of ketones include acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, methyl isobutyl ketone, and methyl-n-propyl ketone.

  Esters include ethyl acetoacetate, ethyl benzoate, methyl benzoate, isobutyl formate, ethyl formate, propyl formate, methyl formate, isobutyl acetate, ethyl acetate, propyl acetate, methyl acetate, methyl salicylate, diethyl oxalate, diethyl tartrate , Dibutyl tartrate, ethyl phthalate, methyl phthalate, butyl phthalate, γ-butyrolactone, ethyl malonate, methyl malonate and the like.

  Examples of cellosolves include methyl cellosolve and ethyl cellosolve.

  Aromatic hydrocarbons include benzene, toluene, xylene and the like.

  Examples of aliphatic hydrocarbons include hexane and cyclohexane.

  The said solvent can be mixed and used.

  Among these solvents, at least one selected from the group consisting of methanol, ethanol and isopropyl alcohol is preferred.

[Pretreatment solution obtained by diluting an ionic liquid with a solvent to a predetermined concentration]
The pretreatment liquid described above is preferably diluted with 10 to 30 parts by weight of the solvent with respect to 10 parts by weight of the ionic liquid, and more preferably 12 to 23 parts by weight with respect to 10 parts by weight of the ionic liquid. Particularly preferably, the solvent is 15 to 19 parts by weight with respect to 10 parts by weight of the ionic liquid. By setting it within this range, a solid electrolytic capacitor having particularly excellent electrostatic capacity and ESR characteristics can be produced.

  The pretreatment liquid described above is preferably 25 to 50% by mass of ionic liquid and 50 to 75% by mass of solvent, more preferably 30 to 45% by mass of ionic liquid and 55 to 70% by mass of solvent, More preferably, the ionic liquid is 35 to 40% by mass and the solvent is 60 to 65% by mass. By setting it within this range, a solid electrolytic capacitor having particularly excellent electrostatic capacity and ESR characteristics can be produced.

[Step of retaining electrolyte salt]
The step of retaining the above electrolyte salt will be described next. The pretreatment liquid described above is brought into contact with a valve metal having a dielectric oxide film and then dried, thereby producing a capacitor element in which an electrolyte salt is held in the valve metal having the dielectric oxide film. Although the method to contact may be arbitrary methods, Preferably, the method of immersing is mentioned.

  That is, it is preferable to include a step of attaching the electrolyte salt to the valve action metal having the dielectric oxide film by immersing the valve action metal having the dielectric oxide film in the above-described pretreatment liquid, pulling it up, and drying. .

  The step of immersing the valve action metal having a dielectric oxide film in the pretreatment liquid, pulling it up and then drying it may be repeated a plurality of times. The preferred number of times is preferably 1 to 6 times, more preferably 1 to 3 times, and particularly preferably 1 time.

  The drying may be any of natural drying at room temperature to heat drying, but it is preferable to dry by heating to 80 ° C. or higher.

[Solid electrolyte]
The conductive polymer used in the step of forming the solid electrolyte layer is preferably a polymer doped with a dopant. The monomer compound used for producing the polymer is not particularly limited, and for example, pyrroles, thiophenes, anilines, and the like can be used. The thiophene compound represented by 1) is more preferable.

  In the general formula (1), Ra represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, and X represents an oxygen atom or a sulfur atom which may be the same or different.

  Specific examples of the thiophene compound represented by the general formula (1) include 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, Propyl-3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, methyl-3,4-propylenedioxythiophene, ethyl-3,4-propylenedioxythiophene, propyl-3,4-propylenedi Oxythiophene, 3,4-ethylenedithiathiophene, methyl-3,4-ethylenedithiathiophene, ethyl-3,4-ethylenedithiathiophene, propyl-3,4-ethylenedithiathiophene, 3,4-propylene Dithiathiophene, methyl-3,4-propylene dithiathiophene, ethyl-3,4 Propylene dithiastannolane thiophene, propyl-3,4-propylene di-thia thiophene and the like.

  Among these, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, and ethyl-3,4-ethylenedioxythiophene are particularly preferred because they are particularly excellent in electrical characteristics in solid electrolytic capacitors. .

  The conductive polymer used in the present invention can be obtained by chemical oxidative polymerization of a monomer compound such as the thiophene compound represented by the general formula (1) in the presence of the dopant. As the oxidizing agent for chemical oxidative polymerization, for example, a known oxidizing agent described in JP 2010-31160 A can be used.

  The dopant only needs to have a functional group capable of causing chemical oxidation doping to the polymer, and preferred examples include a sulfate ester group, a phosphate ester group, a phosphate group, a carboxyl group, and a sulfo group. Among these, from the point of the dope effect, a sulfate group, a carboxyl group, and a sulfo group are more preferable, and a sulfo group is particularly preferable.

  Examples of the dopant include halogen ions such as iodine, bromine, and chlorine, halide ions such as hexafluorolin, hexafluoroarsenic, hexafluoroantimony, tetrafluoroboron, and perchloric acid, or methanesulfonic acid and dodecylsulfonic acid. Cyclic sulfonate ions such as alkyl-substituted organic sulfonate ions and camphor sulfonate ions, or alkyl-substituted or unsubstituted benzene mono- or disulfonate ions such as benzene sulfonic acid, para-toluene sulfonic acid, dodecyl benzene sulfonic acid, and benzene disulfonic acid Alkyl substituted or unsubstituted ions of naphthalenesulfonic acid substituted with 1 to 4 sulfonic acid groups such as 2-naphthalenesulfonic acid and 1,7-naphthalenedisulfonic acid, anthracenesulfonic acid ion, anthracene Non-sulfonate ions, alkyl-substituted or unsubstituted biphenyl sulfonate ions such as alkylbiphenyl sulfonate and biphenyl disulfonate, polymer sulfonate ions such as polystyrene sulfonate and naphthalene sulfonate formalin condensate, etc., or molybdophosphate and tongue Examples include heteropolyacid ions such as strinic acid and tungstomolybdophosphoric acid, methoxybenzenesulfonic acid, ethoxybenzenesulfonic acid, and xylenesulfonic acid. Among these, at least one selected from polystyrenesulfonic acid, benzenesulfonic acid, paratoluenesulfonic acid, methoxybenzenesulfonic acid, ethoxybenzenesulfonic acid, and xylenesulfonic acid is more preferable, and paratoluenesulfonic acid is particularly preferable. .

[Step of forming solid electrolyte layer]
The step of forming the solid electrolytic layer will be described next. The mixed solution containing the monomer compound, the dopant, and the oxidant described above is contacted with a valve action metal having a dielectric oxide film and holding an electrolyte salt, and then dried to have a dielectric oxide film and an electrolyte. A capacitor element is produced by attaching a conductive polymer to a valve action metal holding salt. Although the method to contact may be arbitrary methods, Preferably, the method of immersing is mentioned.

  In other words, the valve action metal having a dielectric oxide film and holding the electrolyte salt is immersed in a solution containing the monomer compound and the dopant described above, and then dried, and then dried, and the valve action metal having the dielectric oxide film is electrically conductive. It is preferable to include a step of attaching a polymer.

  The step of drying the valve action metal having a dielectric oxide film after immersing it in the mixed solution containing the monomer compound, the dopant and the oxidant and pulling it up may be repeated a plurality of times. The preferred number of times is preferably 1 to 6 times, more preferably 1 to 3 times, and particularly preferably 1 time.

  Examples of the step of forming a solid electrolyte include a chemical polymerization method in which a monomer compound and an oxidant solution containing a dopant are alternately contacted, an electrolytic polymerization method, and a method in which a conductive polymer dispersion is brought into contact with the valve action metal. .

  Drying may be any of natural drying at room temperature to heat drying, but when the conductive polymer dispersion contains a high-boiling organic solvent, it is preferable to heat to 150 ° C. or higher for drying. It is done.

[Solid electrolytic capacitor]
Depending on the type and shape of the valve metal used, the solid electrolytic capacitor can be a chip type.

(Example 1)
A tantalum sintered body having a size of 1.3 × 2.1 × 1.6 mm ³ was used as the anode, and the tantalum wire was used as the anode wire in a 0.05 wt% phosphoric acid aqueous solution at 80 ° C. and 25 V. Anodized for 150 minutes, washed with running deionized water, dried to obtain a capacitor element.

(Manufacture of pretreatment liquid)
10 parts by weight of 1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylimide (using bistrifluoromethanesulfonylimide anion, manufactured by Tokyo Chemical Industry Co., Ltd.) was diluted with 19 parts of methanol to obtain a pretreatment solution.

(Production of mixed solution containing conductive polymer monomer, dopant and oxidizing agent)
1.0 part of 2-ethyl-2,3-dihydrothieno [3,4-b] -1,4-
Dioxin (2-ethyl-EDOT) and 3.0 parts of 40% ferric paratoluenesulfonic acid / n-butanol solution were mixed to obtain a mixed solution containing a conductive polymer monomer, a dopant and an oxidizing agent.

(Step of retaining electrolyte salt)
Next, the process of immersing the capacitor element in the pretreatment liquid for 5 minutes and drying at 150 ° C. for 5 minutes was repeated three times, and then heat treatment was performed at 150 ° C. for 1 hour to retain the electrolyte salt, and the capacitor It was set as the element.

(Step of forming a solid electrolyte layer)
Next, after repeating the process of immersing the capacitor element in the mixed solution containing the conductive polymer monomer, the dopant and the oxidizing agent obtained above for 5 minutes and drying at 150 ° C. for 5 minutes, further 150 A heat treatment was performed at 1 ° C. for 1 hour to form a solid electrolyte layer to obtain a capacitor element.

(Production of solid electrolytic capacitors)
Thereafter, a graphite layer and a silver paste layer are sequentially formed on the solid electrolyte of the capacitor element obtained above, and a cathode lead is connected to the silver paste layer via a conductive adhesive, and an anode lead is connected to the anode, respectively. An electrolytic capacitor was completed.

(Examples 2 to 12)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the ratio of the ionic liquid to the solvent was changed so as to correspond to Table 1.

(Example 13)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the anion of the ionic liquid was changed to trifluoromethanesulfonic acid.

(Example 14)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the cation of the ionic liquid was changed to pyridinium (1-butyl-pyridinium bistrifluoromethanesulfonylimide, manufactured by Tokyo Chemical Industry Co., Ltd.).

(Example 15)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the cation of the ionic liquid was changed to trimethylpropylammonium bis (trifluoromethanesulfonyl) imide (manufactured by Tokyo Chemical Industry Co., Ltd.).

(Comparative Example 1)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that in the step of retaining the electrolyte salt described in Example 1, the ionic liquid was not diluted with a solvent.

(Comparative Example 2)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the step of retaining the electrolyte salt described in Example 1 was not performed.

<Evaluation of capacitance and ESR characteristics of solid electrolytic capacitor>
For the solid electrolytic capacitors obtained from Examples 1 to 12 and Comparative Examples 1 and 2, the electrostatic capacity (μF) at 120 Hz was measured, and the equivalent series resistance (ESR) at 100 kHz was measured. The measurement results are shown in Table 1. The solvent part by weight of the pretreatment liquid is that when the part by weight of the ionic liquid and the electrolytic solution for electrolytic capacitor is 10.

<Heat resistance test of solid electrolytic capacitor>
The solid electrolytic capacitors obtained from Example 1 and Comparative Example 2 were tested in a constant temperature bath at 125 ° C. under an additional voltage of 2.5V. The capacitance (μF) at 120 Hz of the solid electrolytic capacitor after the heat test after 5 hours, 12 hours, 20 hours, 29 hours, and 37 hours was measured. The result of calculating the capacity change rate from the measurement result is shown in FIG.

<Moisture resistance test of solid electrolytic capacitor>
The solid electrolytic capacitors obtained from Example 1 and Comparative Example 2 were tested in a constant temperature bath at 60 ° C. and 85% RH under the conditions without voltage application. Under the conditions, the capacitance (μF) at 120 Hz of the solid electrolytic capacitor after 100 hours, after 500 hours, after 1000 hours, after 1500 hours, after 2000 hours was measured, and the equivalent series resistance (ESR) at 100 kHz was measured. . The measurement results are shown in FIGS.

  Since the solid electrolytic capacitor of the present invention is excellent in reliability and durability, it can be applied to high frequency digital devices and the like.

Claims (6)

  In the method of manufacturing a solid electrolytic capacitor having at least the step (a) of holding an electrolyte salt on the anode metal on which the dielectric oxide film is formed and the step (b) of forming a solid electrolyte layer, the electrolyte salt is held. The step (a) prepares a pretreatment liquid obtained by diluting an ionic liquid to a predetermined concentration with a solvent, contacts the pretreatment liquid on the anode metal, and evaporates the solvent. A method for producing a solid electrolytic capacitor, which is a step of retaining an electrolyte salt.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the pretreatment liquid is diluted with 10 to 30 parts by weight of a solvent with respect to 10 parts by weight of the ionic liquid.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the solvent is at least one selected from the group consisting of methanol, ethanol, and isopropyl alcohol.   The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the ionic liquid contains a non-polymeric nitrogen onium cation, and the cation portion has at least an imidazolium and / or pyridinium skeleton. Manufacturing method.   The method for producing a solid electrolytic capacitor according to claim 1, wherein the ionic liquid contains a fluorine-containing organic anion, and the anion has at least a bistrifluoromethanesulfonylimide anion.   The anode metal on which the dielectric oxide film is formed is a sintered body of at least one metal selected from the group consisting of tantalum, titanium, and niobium. The manufacturing method of the solid electrolytic capacitor of description.

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