JP7078420B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

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

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

Generally, these conductive polymers are insoluble or sparingly soluble in a solvent, and are insoluble, so that molding and processing are difficult.

A solid electrolytic capacitor is known in which a solid electrolyte layer containing a conductive polymer is formed on a valve acting 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 oxidizing agent are adhered and brought into contact with each other on a valve acting metal on which a dielectric oxide film is formed to polymerize the valve acting metal, resulting in high conductivity on the valve acting metal. A solid electrolyte layer composed of molecules can be formed.

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

Patent Document 1 discloses a solid electrolytic capacitor in which a cathode layer composed of a room 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, ESR, high durability, and high moisture resistance cannot be obtained.

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

Japanese Unexamined Patent Publication No. 2006-024708

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 manufacturing a solid electrolytic capacitor having 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, it is possible to provide a method in which the volume appearance rate, ESR, durability and moisture resistance are remarkably excellent.

That is, the present invention is as shown below.

The first invention relates to a method for manufacturing a solid electrolytic capacitor, which comprises 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. In the step (a) of retaining the electrolyte salt, a pretreatment liquid obtained by diluting the ionic liquid to a predetermined concentration with a solvent is prepared, and the pretreatment liquid is brought into contact with the anode metal to evaporate the solvent. It is a method for manufacturing a solid electrolytic capacitor, which is a step of holding 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 the ionic liquid. It is a manufacturing method of.

The 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. ..

A fourth aspect of the invention is any of the first to third aspects of the invention, wherein the ionic liquid contains a non-polymeric nitrogen onium cation and the cation moiety has at least an imidazolium and / or a pyridinium skeleton. The method for manufacturing a solid electrolytic capacitor according to one of the above.

A fifth aspect of the invention is 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. The method for manufacturing a solid electrolytic capacitor according to the above.

The 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. The method for manufacturing a solid electrolytic capacitor according to any one of the five inventions.

According to the present invention, it is possible to provide a method for manufacturing a solid electrolytic capacitor having excellent electrical characteristics, high durability and high moisture resistance. That is, it is possible to provide a highly reliable method for manufacturing a solid electrolytic capacitor, which can achieve both high capacitance and low ESR, and has extremely little change in electrical characteristics with time in a moisture resistance test.

It is a graph which shows the time-dependent change of the capacity change rate in a heat resistance test. It is a graph which shows the time-dependent change of the capacity 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 a dielectric oxide film formed]
Examples of the anode metal include valve acting metals such as aluminum, tantalum, niobium, and titanium. The shape of the anode metal is a sintered body obtained by sintering fine particles, or a foil-like or plate-like shape that has been roughened by etching or the like. Among these anode metals, a sintered body of at least one metal selected from the group consisting of tantalum, niobium, and titanium is preferable.

By applying a known chemical conversion treatment to the anode metal, a dielectric oxide film can be formed on the surface of the valve acting metal. For example, the anodic oxidation treatment can be performed in an aqueous solution of diammonium adipate or the like to form a dielectric oxide film on the anodic metal.

[Electrolyte salt]
The electrolyte salt used in the present invention can be an ionic liquid. The ionic liquid in the present invention refers to a molten salt (ionic compound) that exhibits a liquid at room temperature (25 ° C.), and is a salt composed of a cationic component and an anionic component.
Examples of the cation component include alkylammonium, alkylphosphonium, alkylpyridinium, and alkylimidazolium, and examples of the anion component include tetrafluoroboric acid, hexafluorophosphate, trifluoromethanesulfonic acid, and perfluoroalkylsulfonylimide. Examples thereof include perfluoroalkylsulfonylmethides, cyclic perfluoroalkylsulfonylimides, hydrofluorides, bistrifluoromethanesulfonylimide anions, and bisfluoromethanesulfonylimide anions.
Among these cation components, those having a non-polymer nitrogen onium cation and having an imidazolium and / or a pyridinium skeleton at the cation moiety are preferable in terms of moisture resistance and heat resistance. Further, among the anion components, it is preferable that the anion has a fluorine-containing organic anion and the anion is a bistrifluoromethanesulfonylimide anion in terms of moisture resistance and heat resistance. Further, as a cation component, it has a non-polymer nitrogen onium cation, the cation moiety has an imidazolium and / or a pyridinium skeleton, and as an anion component, it has a fluorine-containing organic anion, and the anion is bistrifluoro. Those which are methanesulfonylimide anions are preferable in terms of moisture resistance and heat resistance.

[Solvent for 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.

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, 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 thereof include ethylene glycol, ethylene glycol monomethyl ether, glycerin, diethylene glycol, propylene glycol and the like.

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

Esters include ethyl acetoacetate, ethyl benzoate, methyl benzoate, isobutyl nitrate, ethyl lysate, propyl nitrate, methyl isomerate, 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.

Examples of aromatic hydrocarbons include benzene, toluene, xylene and the like.

Examples of the aliphatic hydrocarbons include hexane and cyclohexane.

The solvent can be mixed and used.

Among the above-mentioned solvents, it is preferable that the solvent is at least one selected from the group consisting of methanol, ethanol and isopropyl alcohol.

[Pretreatment liquid obtained by diluting an ionic liquid to a predetermined concentration with a solvent]
The above-mentioned pretreatment liquid 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. It is particularly preferable that the amount of the solvent is 15 to 19 parts by weight with respect to 10 parts by weight of the ionic liquid. Within this range, a solid electrolytic capacitor having particularly excellent capacitance and ESR characteristics can be manufactured.

The above-mentioned pretreatment liquid is preferably 25 to 50% by mass of the ionic liquid and 50 to 75% by mass of the solvent, and more preferably 30 to 45% by mass of the ionic liquid and 55 to 70% by mass of the solvent. More preferably, the ionic liquid is 35 to 40% by mass and the solvent is 60 to 65% by mass. Within this range, a solid electrolytic capacitor having particularly excellent capacitance and ESR characteristics can be manufactured.

[Step to retain electrolyte salt]
The step of retaining the above-mentioned electrolyte salt will be described below. The above-mentioned pretreatment liquid is brought into contact with the valve acting metal having a dielectric oxide film and then dried to produce a capacitor element in which the valve acting metal having a dielectric oxide film holds an electrolyte salt. The method of contacting may be any method, but a method of immersing is preferable.

That is, it is preferable to have a step of immersing the valve acting metal having a dielectric oxide film in the above-mentioned pretreatment liquid, pulling it up, and then drying it to attach an electrolyte salt to the valve acting metal having a dielectric oxide film. ..

The step of immersing the valve acting 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 from natural drying at room temperature to heat drying, but it is preferable to heat to 80 ° C. or higher for drying.

[Solid electrolyte]
The conductive polymer used in the step of forming the solid electrolyte layer is preferably a dopant-doped polymer. The monomer compound used for producing the polymer is not particularly limited, and for example, pyrroles, thiophenes, anilines and the like can be used, but since they are excellent in conductivity, the following general formula ( It is more preferable that it is a thiophene compound represented by 1).

In the above 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, respectively.

Specific examples of the thiophene compound represented by the general formula (1) include 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, and the like. 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 Examples thereof include dithiathiophene, methyl-3,4-propylene dithiathiophene, ethyl-3,4-propylene dithiathiophene, propyl-3,4-propylene dithiathiophene and the like.

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

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

The dopant may have a functional group capable of chemically oxidizing a polymer, and preferred examples thereof include a sulfate ester group, a phosphoric acid ester group, a phosphoric acid group, a carboxyl group, and a sulfo group. Among these, a sulfate ester group, a carboxyl group, and a sulfo group are more preferably mentioned, and a sulfo group is particularly preferable, from the viewpoint of the doping effect.

Examples of the dopant include halogen ions such as iodine, bromine and chlorine, halide ions such as hexafluorolin, hexafluoroarsenic, hexafluoroantimon, tetrafluoroboron and perchloric acid, or methanesulfonic acid and dodecylsulfonic acid. Alkyl-substituted organic sulfonic acid ion, cyclic sulfonic acid ion such as camphor sulfonic acid ion, or alkyl-substituted or unsubstituted benzenemono or disulfonic acid ion such as benzenesulfonic acid, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, benzenedisulfonic acid. , 2-naphthalene sulfonic acid, alkyl-substituted or unsubstituted ion of naphthalene sulfonic acid in which 1 to 4 sulfonic acid groups such as 1,7-naphthalenedi sulfonic acid are substituted, anthracene sulfonic acid ion, anthraquinone sulfonic acid ion, alkyl biphenyl sulfone. Alkyl-substituted or unsubstituted biphenyl sulfonic acid ion such as acid and biphenyl disulfonic acid, high molecular weight sulfonic acid ion such as polystyrene sulfonic acid and naphthalene sulfonic acid formalin condensate, or molybdrine acid, tongue sulphonic acid and tongue tomolib sulphonic acid. Examples thereof include heteropolyacid ions such as, methoxybenzene sulfonic acid, ethoxybenzene sulfonic acid, and xylene sulfonic acid. Among these, at least one selected from polystyrene sulfonic acid, benzene sulfonic acid, paratoluene sulfonic acid, methoxybenzene sulfonic acid, ethoxybenzene sulfonic acid, and xylene sulfonic acid is more preferable, and paratoluene sulfonic acid is particularly preferable. ..

[Step of forming a solid electrolyte layer]
The step of forming the solid electrolytic layer will be described below. The above-mentioned mixed solution containing the monomer compound, the dopant and the oxidizing agent is brought into contact with a valve acting 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 in which a conductive polymer is attached to a valve-acting metal holding a salt is manufactured. The method of contacting may be any method, but a method of immersing is preferable.

That is, the valve acting metal having a dielectric oxide film and holding an electrolyte salt is immersed in the above-mentioned solution containing the monomer compound and the dopant, pulled up, and then dried to be conductive to the valve acting metal having a dielectric oxide film. It is preferable to have a step of adhering a polymer.

The step of immersing the valve acting metal having a dielectric oxide film in a mixed solution containing the above-mentioned monomer compound, dopant and oxidizing agent, 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.

Examples of the step of forming the solid electrolyte include a chemical polymerization method in which an oxidizing agent solution containing a monomer compound and 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 acting metal. ..

Drying may be performed from natural drying at room temperature to heat drying, but when the conductive polymer dispersion contains a high boiling point organic solvent, it is preferably heated to 150 ° C. or higher to dry. Be done.

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

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

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

(Manufacturing of a mixed solution containing a conductive polymer monomer, a dopant and an oxidizing agent)
1.0 part of 2-ethyl-2,3-dihydrothieno [3,4-b] -1,4-
Dioxine (2-ethyl-EDOT) and 3.0 parts of a 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 to retain electrolyte salt)
Next, the step 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 further performed at 150 ° C. for 1 hour to retain the electrolyte salt, and the capacitor was retained. It was an element.

(Step of forming a solid electrolyte layer)
Next, the step 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 was repeated 3 times, and then 150 more. A solid electrolyte layer was formed by heat treatment at ° C. for 1 hour to obtain a capacitor element.

(Making a solid electrolytic capacitor)
After that, 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 to form a solid. The electrolytic capacitor was completed.

(Examples 6 to 10, Comparative Examples 3 to 8 )
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the ratio of the ionic liquid and the solvent was changed so as to correspond to Table 1.

( Comparative Example 9 )
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 Kasei Kogyo 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 Kasei Kogyo Co., Ltd.).

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

(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 according to Example 1 was not performed.

<Evaluation of capacitance and ESR characteristics of solid electrolytic capacitors>
For the solid electrolytic capacitors obtained from Examples 1 , 6 to 10, 14, 15 and Comparative Examples 1 to 9 , the capacitance (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 weight part of the pretreatment liquid is the case where the weight part of the ionic liquid and the electrolytic solution for the 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 the condition of an additional voltage of 2.5 V. The capacitance (μF) at 120 Hz of the solid electrolytic capacitor after the heat resistance 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 capacitors>
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 condition of no voltage addition. Under the conditions, the capacitance (μF) at 120 Hz of the solid electrolytic capacitor after 100 hours, 500 hours, 1000 hours, 1500 hours, and 2000 hours was measured, and the equivalent series resistance (ESR) at 100 kHz was measured. .. The measurement results are shown in FIGS. 2 and 3.

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 (4)

In the method for manufacturing 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 electrolyte salt is held. In step (a), a pretreatment liquid diluted to 10 to 30 parts by weight of a solvent is prepared with respect to 10 parts by weight of the ionic liquid, and the pretreatment liquid is brought into contact with the anode metal to evaporate the solvent. , A step of retaining the electrolyte salt on the dielectric oxide film,
A method for producing a solid electrolytic capacitor, wherein the ionic liquid contains a fluorine-containing organic anion, and the anion has at least a bistrifluoromethanesulfonylimide anion . 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 method for producing a solid electrolytic capacitor according to claim 1 or 2 , wherein the ionic liquid contains a non-polymeric nitrogen onium cation, and the cation moiety has at least an imidazolium and / or a pyridinium skeleton. One of claims 1 to 3 , wherein 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 method for manufacturing a solid electrolytic capacitor according to the description.

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