WO2025028069A1 - Electrolytic capacitor and production method for electrolytic capacitor - Google Patents

Abstract

An electrolytic capacitor according to the present invention includes a laminate and a liquid component impregnated into the laminate. The laminate includes: a positive electrode foil that has a dielectric layer on the surface thereof; a negative electrode foil; a separator; a first conductive polymer layer that is retained on the separator; and a second conductive polymer layer that is formed on the dielectric layer. The first conductive polymer layer contains a first conductive polymer, a polyvinyl alcohol polymer, and a boric acid compound. The second conductive polymer layer contains a second conductive polymer. The boric acid compound is at least one boric acid compound selected from the group consisting of boric acid and borate compounds. The polyvinyl alcohol polymer in the first conductive polymer layer is at least partially crosslinked.

Description

Electrolytic capacitor and method for manufacturing the same

This disclosure relates to electrolytic capacitors and methods for manufacturing electrolytic capacitors.

A known electrolytic capacitor is one that includes a wound body of an anode foil, a separator, and a cathode foil. One example of such an electrolytic capacitor includes a conductive polymer layer disposed in the wound body. The conductive polymer layer can be formed by impregnating the wound body with a dispersion liquid that contains a conductive polymer. Various proposals have been made in the past regarding electrolytic capacitors that include a conductive polymer layer.

Patent Document 1 (Patent No. 6911910) states in claim 1 that "an electrolytic capacitor is characterized in that a capacitor element is formed by winding an anode electrode foil and a cathode electrode foil with a separator interposed therebetween, and a solid electrolyte layer is formed using a conductive polymer compound dispersion containing conductive polymer particles and sorbitol or sorbitol and a polyhydric alcohol, the solid electrolyte layer containing 60 to 92 wt % of the sorbitol or sorbitol and a polyhydric alcohol, and the voids in the capacitor element in which the solid electrolyte layer is formed are filled with an electrolyte solution containing 10 wt % or more of ethylene glycol in a solvent."

Claim 1 of Patent Document 2 (JP Patent Publication No. 2019-516241) describes a "capacitor including a processing element, the processing element including: an anode including a dielectric on a surface and an anode conductive polymer layer on the surface of the dielectric; a cathode including a cathode conductive polymer layer; a conductive separator between the anode and the cathode; an anode lead in electrical contact with the anode; and a cathode lead in electrical contact with the cathode."

Claim 1 of Patent Document 3 (WO 2021/125182) describes a hybrid electrolytic capacitor comprising: a cathode having a cathode substrate made of a valve metal, an oxide layer made of an oxide of the valve metal provided on the surface of the cathode substrate, an inorganic conductive layer containing an inorganic conductive material provided on the surface of the oxide layer, and an organic conductive layer containing a conductive polymer provided on the surface of the inorganic conductive layer; an anode having an anode substrate made of a valve metal, and a dielectric layer made of an oxide of the valve metal constituting the anode substrate provided on the surface of the anode substrate; a solid electrolyte layer provided between the organic conductive layer of the cathode and the dielectric layer of the anode and containing conductive polymer particles in contact with them, and an electrolyte filled between the conductive polymer particles in the solid electrolyte layer.

Patent No. 6911910 Special Publication No. 2019-516241 International Publication No. 2021/125182

One aspect of the present disclosure relates to an electrolytic capacitor including a laminate and a liquid component impregnated in the laminate. The laminate includes an anode foil having a dielectric layer on a surface thereof, a cathode foil, a separator, a first conductive polymer layer held by the separator, and a second conductive polymer layer formed on the dielectric layer. The first conductive polymer layer contains a first conductive polymer, a polyvinyl alcohol-based polymer, and a boric acid-based compound. The second conductive polymer layer contains a second conductive polymer. The boric acid-based compound is at least one boric acid-based compound selected from the group consisting of boric acid and boric acid compounds. At least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked.

Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor. The manufacturing method includes a preparation step of preparing an anode foil having a dielectric layer on its surface, a first polymer layer formation step of forming a first conductive polymer layer containing a first conductive polymer and a polyvinyl alcohol-based polymer in the voids of a separator, a second polymer layer formation step of forming a second conductive polymer layer on the surface of the dielectric layer, a laminate formation step of forming a laminate containing the first conductive polymer layer and the second conductive polymer layer by stacking the anode foil, the cathode foil, and the separator so that the separator is disposed between the anode foil and the cathode foil, an impregnation step of impregnating the laminate with a liquid component containing at least one boric acid-based compound selected from the group consisting of boric acid and boric acid compounds, and a crosslinking step of heating the laminate impregnated with the liquid component to a temperature of 85° C. or higher. In the crosslinking step, at least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked by the at least one boric acid-based compound.

According to the present disclosure, an electrolytic capacitor containing a liquid component and a conductive polymer layer and having a low ESR can be obtained.

FIG. 1 is a side view illustrating a schematic diagram of an example of an electrolytic capacitor according to an embodiment of the present disclosure. FIG. 2 is an exploded perspective view illustrating a schematic diagram of an example of a capacitor element according to an embodiment of the present disclosure.

The following is a brief explanation of the problems with the conventional technology.

Since the dispersion liquid containing the conductive polymer has a high viscosity, even if the dispersion liquid is impregnated into the wound body, it may not be possible to form a sufficient conductive polymer layer inside the wound body. Insufficient formation of the conductive polymer layer can cause an increase in equivalent series resistance (ESR).

There has long been a need to reduce the ESR of electrolytic capacitors. This disclosure provides an electrolytic capacitor that contains a liquid component and a conductive polymer layer and can reduce the ESR.

Below, examples of embodiments according to the present invention are described, but the present invention is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and other materials may be applied as long as the invention according to this disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when numerical values for specific physical properties or conditions are exemplified as lower and upper limits, any of the exemplified lower limits can be arbitrarily combined with any of the exemplified upper limits, as long as the lower limit is not equal to or greater than the upper limit.

(Method of manufacturing electrolytic capacitor)
The manufacturing method according to this embodiment may be referred to as "manufacturing method (M)" below. The manufacturing method (M) includes a preparation step, a polymer layer forming step (a first polymer layer forming step, a second polymer layer forming step), a laminate forming step, an impregnation step, and a crosslinking step, in this order. The first polymer layer forming step and the second polymer layer forming step may be performed in any order, and either may be performed first. These steps will be described later.

As described below, in manufacturing method (M), the polyvinyl alcohol polymer contained in the conductive polymer layer is cross-linked with a boric acid compound. This improves the adhesion between the anode foil and the separator and between the cathode foil and the separator, thereby reducing the ESR of the electrolytic capacitor. Furthermore, the retention of electrolyte in the conductive polymer layer is improved, improving the repairability of the dielectric layer and increasing the voltage resistance of the electrolytic capacitor. Furthermore, loss of electrolyte due to volatilization can be suppressed during long-term use, making it possible to extend the life of the electrolytic capacitor.

(Preparation process)
The preparation step is a step of preparing an anode foil having a dielectric layer on its surface. The anode foil having a dielectric layer on its surface may be a commercially available product, or may be formed by forming a dielectric layer on the surface of a metal foil (anode foil). The dielectric layer may be formed by a known method. For example, the dielectric layer may be formed by oxidizing the surface of the metal foil (anode foil).

(First polymer layer formation step)
The first polymer layer forming step is a step of forming a first conductive polymer layer containing a first conductive polymer and a polyvinyl alcohol-based polymer in the voids of the separator. The first polymer layer forming step may include a first coating liquid applying step of applying a first coating liquid containing the first conductive polymer, a polyvinyl alcohol-based polymer, and a first liquid medium to the voids of the separator, and a first liquid medium removing step of removing at least a part of the first liquid medium from the first coating liquid to form a first conductive polymer layer in the voids of the separator.

A polyvinyl alcohol polymer is a polymer containing -CH ₂ CH(OH)- (hereinafter sometimes referred to as "vinyl alcohol unit") as a constituent unit. The proportion of vinyl alcohol units in all constituent units may be 40 mol % or more, 60 mol % or more, or 80 mol % or more. Examples of constituent units other than vinyl alcohol units include vinyl acetate units. The total of vinyl alcohol units and vinyl acetate units in all constituent units may be 60 mol % or more, or 80 mol % or more.

Examples of polyvinyl alcohol-based polymers include polyvinyl alcohol and derivatives of polyvinyl alcohol. The polyvinyl alcohol-based polymer may be a polymer obtained by saponifying a vinyl acetate polymer. Alternatively, the polyvinyl alcohol-based polymer may be a polymer obtained by saponifying a copolymer of vinyl acetate and another monomer.

The weight average molecular weight of the polyvinyl alcohol polymer may be in the range of 500 to 3500 (e.g., in the range of 1000 to 2000).

The concentration of the polyvinyl alcohol-based polymer in the first coating liquid may be in the range of 0.01% by mass to 3.0% by mass (e.g., in the range of 0.05% by mass to 0.5% by mass). In the first coating liquid, the ratio Wp/Wc of the mass Wp of the polyvinyl alcohol-based polymer to the mass Wc of the first conductive polymer may be 0.01 or more, and may be in the range of 0.01 to 3.0 (e.g., in the range of 0.05 to 0.5). That is, in the first conductive polymer layer, the ratio (Wp/Wc) of the mass Wp of the polyvinyl alcohol-based polymer to the mass Wc of the first conductive polymer may be 0.01 or more, and may be in the range of 0.01 to 3.0 (e.g., in the range of 0.05 to 0.5).

(Second polymer layer formation step)
The second polymer layer forming step is a step of forming a second conductive polymer layer on the surface of the dielectric layer. The second polymer layer forming step may include a second coating liquid applying step of applying a second coating liquid containing a second conductive polymer and a second liquid medium to the surface of the dielectric layer (the dielectric layer on the surface of the anode foil), and a second liquid medium removing step of removing at least a part of the second liquid medium from the second coating liquid to form a second conductive polymer layer on the surface of the dielectric layer.

The second coating liquid may or may not contain a polyvinyl alcohol-based polymer. The first conductive polymer and the second conductive polymer may be the same or different. The first liquid medium and the second liquid medium may be the same or different. The first coating liquid and the second coating liquid may be the same or different.

The conductive polymers (first conductive polymer, second conductive polymer) may be dispersed in the coating liquid (first coating liquid, second coating liquid) in the form of particles. Examples of conductive polymers will be described later.

In the first coating liquid, the ratio (Wp/Wc) of the mass Wp of the polyvinyl alcohol-based polymer to the mass Wc of the first conductive polymer may be 0.01 or more, 0.05 or more, or 0.1 or more, and may be 3.0 or less, or 0.5 or less. By making the ratio Wp/Wc 0.01 or more, it is possible to obtain a sufficient amount of polyvinyl alcohol-based polymer crosslinked by reaction with the boric acid compound while maintaining the stability of the coating liquid.

The liquid medium (first liquid medium, second liquid medium) is not particularly limited, and any liquid medium that can be used to form a polymer layer can be used. Examples of liquid media include water, organic solvents (e.g., alcohol), and mixtures thereof.

The liquid medium may contain water and an organic compound that does not boil at 100°C at 1 atmosphere (101,325 Pa). Hereinafter, the organic compound may be referred to as "organic compound (C)." Organic compound (C) may be one type of compound or may be composed of multiple types of compounds.

The method of applying the coating liquid (first coating liquid, second coating liquid) is not limited, and may be applied by a known method. For example, a method using a coater may be used, the coating liquid may be sprayed, or the object to be coated may be immersed in the coating liquid. Examples of methods using a coater include gravure coating and die coating. In one example of the gravure coating method, the coating liquid is first applied to a transfer member (gravure roll, etc.), and then excess coating liquid is removed from the transfer member. Next, the coating liquid applied to the transfer member is transferred to a specified member (anode foil, cathode foil, or separator), so that a layer of coating liquid with a uniform thickness can be applied to the member. The viscosity of the coating liquid may be, for example, 10 mPa·s or more (for example, 100 mPa·s or more) and 200 mPa·s or less. In this case, the coating liquid is easy to apply to the anode foil, cathode foil, and separator, and is easy to impregnate the separator. The viscosity of the coating liquid is measured at room temperature (20°C) using a vibration viscometer (e.g., VM-100A, manufactured by Sekonic Corporation).

The method of removing at least a part of the liquid medium from the coating liquid is not particularly limited, and can be performed by heating or the like. When the coating liquid contains an organic compound (C), heating may be performed so that the organic compound (C) remains in the polymer layer. For example, when the coating liquid contains an organic compound (C) and water (liquid medium), it is possible to remove water from the coating liquid while leaving the organic compound (C) in the polymer layer by heating the coating liquid at a temperature at which the organic compound (C) does not boil or decompose and at a temperature of 100°C or higher. The heating temperature may be 100°C or higher, 120°C or higher, or 140°C or higher, and may be 200°C or lower, or 160°C or lower. The heating temperature may be in the range of 100°C to 200°C. There is no particular limit to the heating time, and it may be a time that allows a part of the liquid medium to be appropriately removed. An example of the heating time is in the range of 5 to 60 minutes.

By leaving the organic compound (C) in the conductive polymer layer (first conductive polymer layer, second conductive polymer layer), it is possible to reduce the shrinkage of the conductive polymer layer when the liquid medium is removed from the coating liquid. As a result, in the subsequent impregnation step, the liquid component (e.g., electrolyte) can easily penetrate into the conductive polymer layer. As a result, the liquid component's function of forming a dielectric layer (oxide film) can be fully exerted, and leakage current is reduced.

In a preferred example of manufacturing method (M), the water content in the coating liquid is 40 mass % or more (e.g., 50 mass % or more), and the liquid medium of the applied coating liquid is removed so that the mass of the organic compound (C) in the conductive polymer layer is greater than the mass of water in the conductive polymer layer. If the water content in the coating liquid is high, the conductive polymer layer is more easily impregnated with the electrolyte after the conductive polymer layer is formed.

(Laminate Forming Process)
The laminate formation step is a step of forming a laminate including a first conductive polymer layer and a second conductive polymer layer by laminating an anode foil, a cathode foil, and a separator such that the separator is disposed between the anode foil and the cathode foil.

The method for forming the laminate is not particularly limited, and the laminate may be formed by a known method. The laminate may be a wound body. In this case, in the laminate formation process, the wound body may be formed by winding the anode foil, the cathode foil, and the separator so that the separator is disposed between the anode foil and the cathode foil. In the wound body, the anode foil, the cathode foil, and the separator are stacked in the radial direction of the wound body.

The laminate may be formed by stacking flat anode foils, flat cathode foils, and flat separators in one direction. For example, a laminate may be formed by stacking multiple anode foils, multiple cathode foils, and multiple separators in one direction. In a typical example of such a laminate, the anode foils and cathode foils are arranged alternately, and the separator is arranged between the anode foils and the cathode foils.

(Impregnation process)
The impregnation step is a step of impregnating the laminate with a liquid component containing at least one boric acid compound selected from the group consisting of boric acid and boric acid compounds. Hereinafter, the liquid component may be referred to as a "liquid component (LC)". The method of impregnating the laminate with the liquid component (LC) is not limited. For example, the laminate may be impregnated with the liquid component (LC) by immersing at least a part of the laminate in the liquid component (LC). The liquid component (LC) may be an electrolyte solution.

Examples of boric acid compounds include boric acid and borate salts. Examples of borate salts include ammonium salts of boric acid (such as ammonium borate), sodium salts of boric acid (such as sodium tetraborate), and potassium salts of boric acid. The boric acid compound may be at least one selected from the group consisting of boric acid, ammonium salts of boric acid, sodium salts of boric acid, and potassium salts of boric acid.

The concentration of the boric acid compound in the liquid component (LC) may be in the range of 0.5% by mass to 5.0% by mass (e.g., in the range of 1.5% by mass to 3.5% by mass).

The liquid component (LC) may further contain at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane. By containing these compounds in the liquid component (LC), the withstand voltage of the capacitor can be increased. Furthermore, loss of the electrolyte due to volatilization during long-term use can be suppressed, enabling the life of the electrolytic capacitor to be extended.

(Crosslinking process)
The crosslinking step is a step of heating the laminate impregnated with the liquid component (LC) to a temperature of 85° C. or higher. In the crosslinking step, at least a part of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked by the at least one boric acid compound. That is, the crosslinking step is a step of crosslinking the polyvinyl alcohol-based polymer in the first conductive polymer layer by the boric acid compound by heating the laminate impregnated with the liquid component (LC) to a temperature of 85° C. or higher. When the second conductive polymer layer contains a polyvinyl alcohol-based polymer, the polyvinyl alcohol-based polymer in the second conductive polymer layer is also crosslinked by the boric acid compound. By crosslinking the polyvinyl alcohol-based polymer in the conductive polymer layer, the above-mentioned effects can be obtained.

The heating temperature of the laminate in the crosslinking step is 85°C or higher, and may be 100°C or higher, or 105°C or higher. The heating temperature may be 180°C or lower, 160°C or lower, or 135°C or lower. The heating time of the laminate in the crosslinking step varies depending on the heating temperature, but may be in the range of 30 to 180 minutes (for example, in the range of 60 to 90 minutes).

By heating the laminate in the cross-linking process, it is possible to promote re-oxidation of the anode foil surface. In other words, it is possible to oxidize the areas of the anode foil surface where the oxide film is insufficient. As a result, leakage currents and the like can be reduced. In addition, in the cross-linking process, the anode foil may be re-chemically formed by applying a voltage between the anode foil and the cathode foil. Alternatively, the anode foil may be re-chemically formed separately from the cross-linking process.

In this manner, a capacitor element is obtained. Thereafter, other processes are carried out as necessary. For example, a process of encapsulating the capacitor element impregnated with the liquid component (LC) in an exterior body may be carried out. Note that a crosslinking process may be carried out after the process of encapsulating the capacitor element impregnated with the liquid component (LC) in an exterior body.

The manufacturing method (M) may include a liquid application step and a removal step in this order after the laminate formation step and before the impregnation step. The liquid application step is a step of impregnating the laminate with a liquid (hereinafter, sometimes referred to as "liquid (L)"). The removal step is a step of removing at least a part of the liquid (L) impregnated in the laminate. The liquid (L) may be a liquid containing water as a main component and an organic compound (C) that does not boil at 100°C under 1 atmosphere. In that case, the removal step may be a step of removing a part of the liquid (L) impregnated in the laminate such that the mass of the organic compound (C) in the laminate is greater than the mass of water in the laminate. The liquid (L) may be a liquid containing an organic solvent.

The liquid (L) used in the liquid application step may be a liquid obtained by removing the conductive polymer component from the second coating liquid used in the second polymer layer formation step. The impregnation of the liquid in the liquid application step may be performed by the method exemplified for the coating liquid application step in the polymer layer formation step. The removal of the liquid in the removal step may be performed by the method exemplified for the liquid medium removal step in the polymer layer formation step. By performing the liquid application step and the removal step, the adhesion between the first conductive polymer layer and the second conductive polymer layer, and the adhesion between the first conductive polymer layer and the cathode foil can be improved. In addition, since the conductive polymer layer containing the polyvinyl alcohol-based polymer crosslinked in the crosslinking step has sufficient adhesiveness, the adhesion between the first conductive polymer layer and the second conductive polymer layer, and the adhesion between the first conductive polymer layer and the cathode foil can be improved. Therefore, the liquid application step is not essential.

In the electrolytic capacitor manufactured by manufacturing method (M), the cathode foil may have an inorganic layer on its surface, and the conductive polymer layer may be in close contact with the inorganic layer.

If the cathode foil is made of only a metal foil (e.g., aluminum foil), an oxide layer forms on the surface of the metal foil, and capacitance also occurs in the cathode foil. As a result, the capacitance of the anode foil and the capacitance of the cathode foil are combined, which can cause a problem of a decrease in the capacitance of the entire capacitor. By covering the surface of the metal foil with an inorganic layer, etc., it is possible to prevent such a problem from occurring. In other words, by forming an inorganic layer, it is possible to draw out only the capacitance of the anode foil. On the other hand, if the adhesion between the conductive polymer layer and the inorganic layer is low, the ESR will be high. By performing the above liquid application process, it is possible to increase the adhesion between the first conductive polymer layer and the inorganic layer.

Inorganic layers tend to repel water, so in the conventional method of forming a conductive polymer layer by impregnating a laminate (capacitor element) with an aqueous dispersion of a conductive polymer, the conductive polymer has difficulty entering between the inorganic layer of the cathode foil and the anode foil in the laminate, making it impossible to form a uniform conductive polymer layer on the separator placed between the cathode foil and anode foil, resulting in an increase in ESR. In manufacturing method (M), a laminate (capacitor element) is formed using a separator on which a first conductive polymer layer has already been formed. This makes it possible to prevent the first conductive polymer from becoming unevenly distributed within the separator.

The surface density of the conductive polymer layer (first conductive polymer layer, second conductive polymer layer) may be 0.05 mg/cm ² or more, 0.1 mg/cm ² or more, or 0.3 mg/cm ² or more, and may be 1.0 mg/cm ² or less, or 0.5 mg/cm ² or less. For example, the surface density of the conductive polymer layer may be 0.05 mg/cm ² or more and 1.0 mg/cm ² or less. According to this configuration, an electrolytic capacitor with a particularly low ESR is obtained. The surface density means mass per unit area. In addition, when the second conductive polymer layer is formed on both sides of the anode foil, the surface density of the second conductive polymer layer means the surface density of one second conductive polymer layer formed on one side of the anode foil. The surface density of the conductive polymer layer can be controlled by the concentration of the conductive polymer in the coating liquid or the amount of the coating liquid applied.

The areal density of the first conductive polymer layer can be determined by the following method. First, five samples are prepared by cutting out a specified area from the separator before the first conductive polymer layer is formed, and the mass of the five samples is measured. In addition, five samples are prepared by cutting out the separator on which the first conductive polymer layer is formed, and the mass of the samples is measured. The areal density of the first conductive polymer layer is determined using the specified area and the difference between the total mass of the five samples after the first conductive polymer layer is formed and the total mass of the five samples before the first conductive polymer layer is formed. The areal density of the second conductive polymer layer can also be determined by a similar method.

(Electrolytic capacitor)
The electrolytic capacitor according to this embodiment may be referred to as "electrolytic capacitor (E)" below. The electrolytic capacitor (E) may be manufactured by the manufacturing method (M) described above. The matters described for the manufacturing method (M) may be applied to the electrolytic capacitor (E), and therefore, duplicated explanations may be omitted. The matters described for the electrolytic capacitor (E) may also be applied to the manufacturing method (M).

The electrolytic capacitor (E) includes a laminate and a liquid component impregnated in the laminate. The laminate includes an anode foil having a dielectric layer on its surface, a cathode foil, a separator, a first conductive polymer layer held by the separator, and a second conductive polymer layer formed on the dielectric layer. The first conductive polymer layer contains a first conductive polymer, a polyvinyl alcohol-based polymer, and a boric acid-based compound. The second conductive polymer layer contains a second conductive polymer. The boric acid-based compound is at least one boric acid-based compound selected from the group consisting of boric acid and boric acid compounds. At least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked.

The electrolytic capacitor (E) provides the effects described in the manufacturing method (M). For example, the configuration of the electrolytic capacitor (E) makes it possible to reduce the ESR.

In the first conductive polymer layer of the electrolytic capacitor (E), the ratio (Wp/Wc) of the mass Wp of the polyvinyl alcohol polymer to the mass Wc of the first conductive polymer may be within the range described above. For example, the ratio (Wp/Wc) may be 0.2 or more.

In the electrolytic capacitor (E), the cathode foil may have an inorganic layer on its surface. In that case, it is preferable that the first conductive polymer layer is in close contact with the inorganic layer.

The liquid component (LC) of the electrolytic capacitor (E) may further contain at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

As mentioned above, the laminate may be a wound body, or it may be a laminate other than a wound body.

Below, examples of materials and components used in the manufacturing method (M) and electrolytic capacitor (E) are described. However, the materials and components used in the manufacturing method (M) and electrolytic capacitor (E) are not limited to the examples described below.

In this specification, the term "conductive polymer component" may be used. When the conductive polymer is not doped with a dopant, the conductive polymer component is made of a conductive polymer. When the conductive polymer is doped with a dopant, the conductive polymer component is made of a conductive polymer and a dopant.

(Coating Fluids (First Coating Fluid, Second Coating Fluid))
The coating liquids (first coating liquid, second coating liquid) used in the polymer layer forming step may contain a conductive polymer and water. The conductive polymer (conductive polymer component) may be contained in the coating liquid in the form of particles. The coating liquid may be an aqueous dispersion of the conductive polymer (conductive polymer component).

The coating liquid may contain other components (e.g., organic compound (C)). The organic compound (C) may contain at least one selected from the group consisting of polyhydric alcohols, sulfolane, γ-butyrolactone, and boric acid esters, or may be at least one of the above. The organic compound (C) may contain at least one selected from the group consisting of glycols, glycerins, sugar alcohols, sulfolane, γ-butyrolactone, and boric acid esters, or may be at least one of the above.

Examples of polyhydric alcohols include glycols, glycerins, and sugar alcohols. Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycols (e.g., polyethylene glycol), polyoxyethylene polyoxypropylene glycol (ethylene oxide-propylene oxide copolymer), and the like. Examples of glycerins include glycerin and polyglycerin. Examples of sugar alcohols include mannitol, xylitol, sorbitol, erythritol, and pentaerythritol, and the like.

Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and derivatives thereof. The derivatives include polymers having polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as the basic skeleton. For example, a derivative of polythiophene includes poly(3,4-ethylenedioxythiophene). These conductive polymers may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. The weight-average molecular weight of the conductive polymer is not particularly limited and may be in the range of 1,000 to 100,000, for example. A preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

The conductive polymer may be doped with a dopant. From the viewpoint of suppressing dedoping from the conductive polymer, it is preferable to use a polymer dopant as the dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacryl sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, and the like. These may be used alone or in combination of two or more. At least a portion of these may be added in the form of a salt. A preferred example of a dopant is polystyrene sulfonic acid (PSS).

The dopant may be polystyrenesulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the conductive polymer component may be poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

When using a conductive polymer doped with a dopant, the pH of the coating liquid is preferably less than 7.0 in order to suppress dedoping of the dopant, and may be 6.0 or less or 5.0 or less. The pH of the coating liquid may be 1.0 or more, or 2.0 or more.

The water content in the coating liquid may be 40% by mass or more, 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. The water content may be 98% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less.

The content of the organic compound (C) in the coating liquid may be 1.0 mass% or more, 3.0 mass% or more, 5.0 mass% or more, or 10 mass% or more. It may be 30 mass% or less, 20 mass% or less, 15 mass% or less, or 10 mass% or less. The content of the conductive polymer component in the coating liquid may be 0.5 mass% or more, or 1.0 mass% or more, and may be 4.0 mass% or less, 3.0 mass% or less, or 2.0 mass% or less. The content may be in the range of 0.5 to 4.0 mass% or 1.0 to 4.0 mass%. In any of these ranges, the upper limit may be 3.0 mass% or 2.0 mass%. In terms of excellent physical properties and their stability over time of the coating liquid, and a good balance between the ESR of the electrolytic capacitor and the cost, the content is preferably in the range of 1.0 to 3.0%. In addition, when the coating liquid contains a dopant, the mass of the dopant is included in the mass of the conductive polymer component.

There are no particular limitations on the mass of the dopant contained in the coating liquid, and it may be in the range of 0.1 to 5 times (e.g., 0.5 to 3 times) the mass of the conductive polymer contained in the coating liquid.

There are no particular limitations on the mass of the dopant contained in the coating liquid, and it may be in the range of 0.1 to 5 times (e.g., 0.5 to 3 times) the mass of the conductive polymer contained in the coating liquid.

In the coating liquid, the water content: organic compound (C) content: conductive polymer component content may be 40-98:1.0-59.5:0.5-4.0, or the water content: organic compound (C) content: conductive polymer component content may be 69.5-98:1.0-30:0.5-4.0.

(Liquid component (LC))
Examples of the liquid component (LC) used in the impregnation step include a non-aqueous solvent and an electrolytic solution. The electrolytic solution may be an electrolytic solution containing a non-aqueous solvent and a solute dissolved in the non-aqueous solvent. In this specification, the liquid component (LC) may be a component that is liquid at room temperature (25° C.) or a component that is liquid at the temperature when the electrolytic capacitor is used.

The non-aqueous solvent used in the liquid component (LC) may be an organic solvent, an ionic liquid, or a protic solvent. Examples of non-aqueous solvents include polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (γBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde.

Furthermore, a polymer solvent may be used as the non-aqueous solvent. Examples of polymer solvents include polyalkylene glycol, derivatives of polyalkylene glycol, and compounds in which at least one hydroxyl group in a polyhydric alcohol is replaced with polyalkylene glycol (including derivatives). Specifically, examples of polymer solvents include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol. Examples of polymer solvents further include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. The non-aqueous solvent may be used alone or in a mixture of two or more.

The liquid component (LC) may include a non-aqueous solvent and a base component (base) dissolved in the non-aqueous solvent. The liquid component (LC) may also include a non-aqueous solvent and a base component and/or an acid component (acid) dissolved in the non-aqueous solvent.

As the acid component, polycarboxylic acids and monocarboxylic acids can be used. Examples of the polycarboxylic acids include aliphatic polycarboxylic acids (saturated polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid), aromatic polycarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.).

Examples of the monocarboxylic acids include aliphatic monocarboxylic acids (1 to 30 carbon atoms) ([saturated monocarboxylic acids, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids, such as acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, naphthoic acid), and oxycarboxylic acids (such as salicylic acid, mandelic acid, resorcylic acid).

Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcylic acid are thermally stable and are preferably used.

Inorganic acids may be used as the acid component. Representative examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, boric fluoride, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. In addition, composite compounds of organic acids and inorganic acids may be used as the acid component. Examples of such composite compounds include borodiglycolic acid, borodioxalic acid, and borodisalicylic acid.

The base component may be a compound having an alkyl-substituted amidine group, such as an imidazole compound, a benzimidazole compound, or an alicyclic amidine compound (pyrimidine compound, imidazoline compound). Specifically, 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptyl imidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecyl imidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, or 1-methylbenzimidazole is preferred. By using these, a capacitor with excellent impedance performance can be obtained.

The base component may be a quaternary salt of a compound having an alkyl-substituted amidine group. Examples of such base components include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) that are quaternized with an alkyl group or arylalkyl group having 1 to 11 carbon atoms. Specifically, 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethyl-imidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, and 1,3-dimethylbenzimidazolium are preferred. By using these, a capacitor with excellent impedance performance can be obtained.

Also, a tertiary amine may be used as the base component. Examples of tertiary amines include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.), and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among these, trialkylamines are preferred in terms of increasing electrical conductivity, and it is more preferred to include at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Also, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia may be used as the base component.

The liquid component (LC) may contain a salt of an acid component and a base component. The salt may be an inorganic salt and/or an organic salt. An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of organic salts that may be used include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono 1,2,3,4-tetramethylimidazolinium phthalate, and mono 1,3-dimethyl-2-ethylimidazolinium phthalate.

To suppress de-doping of the dopant, the pH of the liquid component (LC) may be less than 7.0 or less than 5.0, or may be greater than 1.0, or greater than 2.0. The pH may be greater than 1.0 and less than 7.0 (e.g., in the range of 2.0 to 5.0).

The liquid component (LC) preferably contains a protic solvent. By using a protic solvent, it is possible to increase the adhesion of the conductive polymer layer. In addition to the protic solvent, the liquid component (LC) may contain a solvent other than the protic solvent.

The protic solvent may include at least one selected from the group consisting of glycols, glycerin, polyglycerin, and sugar alcohols, or may be at least one of the above. The protic solvent may be composed of only one type of compound, or may include multiple types of compounds.

The organic compound (C) and the liquid component (LC) may contain the same compound. For example, they may contain the same polyhydric alcohol, the same glycols (such as ethylene glycol), or the same sugar alcohol.

(Liquid (L))
The liquid (L) may be a liquid containing the organic compound (C) and water. In this case, it is preferable to impregnate the laminate with the liquid (L) and then remove water from the laminate under conditions in which the organic compound (C) remains in the laminate. The organic compound (C) may be at least one selected from the group consisting of mannitol, mannitol derivatives, xylitol, and xylitol derivatives.

The liquid (L) may contain at least one substance (hereinafter, sometimes referred to as "substance X") selected from the group consisting of sugar, sugar alcohol, epoxy resin, and polyvinyl alcohol. By containing substance X in the liquid (L), the adhesion between the conductive polymer layer and the cathode foil can be improved. The content of substance X in the liquid (L) may be in the range of 10% by mass to 70% by mass (for example, in the range of 30% by mass to 50% by mass).

The sugar alcohol may include at least one selected from the group consisting of mannitol, mannitol derivatives, xylitol, and xylitol derivatives, or may be at least one of the above. The substance X may be at least one selected from the group consisting of mannitol, mannitol derivatives, xylitol, and xylitol derivatives. Mannitol, mannitol derivatives, xylitol, and xylitol derivatives have the effect of adhering the conductive polymer layer and the cathode foil. Examples of mannitol derivatives include compounds in which some of the hydroxyl groups of mannitol are esterified, compounds in which some of the hydroxyl groups of mannitol are etherified, and compounds in which some of the hydroxyl groups of mannitol are anionized to form a salt. Examples of xylitol derivatives include compounds in which some of the hydroxyl groups of xylitol are esterified, compounds in which some of the hydroxyl groups of xylitol are etherified, and compounds in which some of the hydroxyl groups of xylitol are anionized to form a salt.

The organic solvent contained in the liquid (L) may contain at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol, or may be at least one of the organic solvents. By containing these in the liquid (L), the electrical conductivity of the conductive polymer layer can be increased.

A preferred example of the liquid (L) is a liquid containing xylitol in at least one organic solvent selected from the group consisting of triethylene glycol and polyethylene glycol.

(anode foil)
Examples of the anode foil include metal foils containing at least one of valve metals such as titanium, tantalum, aluminum, and niobium, and may be metal foils of valve metals (e.g., aluminum foils). The anode foil may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. The thickness of the anode foil may be 15 μm or more and 300 μm or less. The surface of the anode foil may be roughened by etching or the like.

A dielectric layer is formed on the surface of the anode foil. The dielectric layer may be formed by subjecting the anode foil to a chemical conversion treatment. In this case, the dielectric layer may contain an oxide of a valve metal (e.g., aluminum oxide). Note that the dielectric layer may be formed of any dielectric other than an oxide of a valve metal as long as it functions as a dielectric.

In an electrolytic capacitor, a conductive polymer layer does not need to be formed on the end surface of the anode foil. However, it is preferable that a dielectric layer is formed on the end surface of the anode foil.

(cathode foil)
The cathode foil includes a metal foil (e.g., aluminum foil). The metal constituting the metal foil may be a valve metal or an alloy containing a valve metal. The surface of the metal foil may be roughened by etching or the like. The thickness of the cathode foil may be 15 μm or more and 300 μm or less. A conductive polymer layer may be formed on the surface of the cathode foil by the above-mentioned method.

As described above, the cathode foil may have an inorganic layer on its surface. The cathode foil having an inorganic layer on its surface may be a commercially available product, or may be formed by forming an inorganic layer on the surface of a metal foil (cathode foil). The inorganic layer may be formed by a known method. For example, the inorganic layer may be formed by a vacuum deposition method or the like. Alternatively, the inorganic layer may be formed by applying a paste containing one selected from the group consisting of carbon (particularly a conductive carbon material), titanium, and nickel onto the metal foil (cathode foil) and then drying it. The amount of the inorganic layer may be in the range of 50 mg/m ² to 300 mg/m ² (for example, in the range of 70 mg/m ² to 200 mg/m ² ). Examples of carbon (particularly a conductive carbon material) contained in the inorganic layer include graphite, hard carbon, soft carbon, carbon black, and the like. In addition, when the inorganic layer contains titanium, it may be a layer formed by depositing titanium or a layer formed by particles of titanium oxide. The inorganic layer may be a carbon layer. The carbon layer may be a layer containing carbon, and may have a carbon content of 50 mass% or more. In this specification, the term "inorganic layer" may be replaced with "carbon layer."

The cathode foil may include a metal foil, an inorganic layer, and a titanium-containing layer disposed between the inorganic layer and the metal foil. An example of the cathode foil has a laminated structure of inorganic layer/titanium-containing layer/metal foil (e.g., aluminum foil)/titanium-containing layer/inorganic layer. The titanium-containing layer may contain at least one selected from the group consisting of titanium and titanium compounds. Examples of titanium compounds include titanium nitride, titanium oxide, titanium aluminum alloy, titanium carbonate, and the like. The method of forming the titanium-containing layer is not limited, and the layer may be formed by a known method. For example, the titanium-containing layer may be formed by a physical vapor deposition method such as a vacuum deposition method or a sputtering method. The deposition amount of the titanium-containing layer may be in the range of 200 mg/m ² to 500 mg/m ² (e.g., in the range of 250 mg/m ² to 400 mg/m ² ).

(Separator)
A porous sheet can be used for the separator. Examples of the porous sheet include woven fabric, nonwoven fabric, and microporous membrane. The thickness of the separator is not particularly limited and may be in the range of 10 to 300 μm. Examples of the material of the separator include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, glass, and the like.

(Exterior body)
The laminate and the liquid component (LC) are housed in an exterior body. The exterior body includes a case and/or a sealing resin. There is no limitation thereto, and a known case and sealing resin may be used. The sealing resin may include a thermosetting resin. Examples of the thermosetting resin include an epoxy resin, a phenolic resin, a silicone resin, a melamine resin, a urea resin, an alkyd resin, a polyurethane, a polyimide, an unsaturated polyester, and the like. The sealing resin may include a filler, a curing agent, a polymerization initiator, and/or a catalyst, and the like.

Below, an example of the present disclosure will be specifically described with reference to the drawings. The components described above can be applied to the components of the example described below. Furthermore, the components of the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Furthermore, in the example described below, components that are not essential to the electrolytic capacitor of the present disclosure may be omitted.

FIG. 1 is a cross-sectional view showing an example of an electrolytic capacitor 100 according to this embodiment. FIG. 2 is a schematic diagram showing an exploded view of a portion of a capacitor element 10 included in the electrolytic capacitor 100.

The electrolytic capacitor 100 comprises a capacitor element 10, a bottomed case 101 that houses the capacitor element 10, a sealing member 102 that closes the opening of the bottomed case 101, a seat plate 103 that covers the sealing member 102, lead wires 104A, 104B that extend from the sealing member 102 and pass through the seat plate 103, and lead tabs 105A, 105B that connect the lead wires to the electrodes of the capacitor element 10. The area near the open end of the bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to the sealing member 102.

Capacitor element 10 is, for example, a wound body as shown in FIG. 1. The wound body includes an anode foil 11 connected to lead tab 105A, a cathode foil 12 connected to lead tab 105B, and a separator 13. Capacitor element 10 (wound body) includes a conductive polymer layer (not shown). The conductive polymer layer may include an organic compound (C). Electrolytic capacitor 100 includes a liquid component (LC) (e.g., an electrolyte) impregnated in capacitor element 10.

The anode foil 11 and the cathode foil 12 are wound with a separator 13 between them. The outermost circumference of the wound body is fixed with a stop tape 14. Note that Figure 2 shows the wound body in a partially unfolded state before the outermost circumference is fixed.

An electrolytic capacitor may have at least one capacitor element, but may also have multiple capacitor elements. The number of capacitor elements included in an electrolytic capacitor may be determined according to the application.

(Additional Note)
Based on the above description, the following techniques are disclosed.

(Technique 1)
An electrolytic capacitor comprising a laminate and a liquid component impregnated in the laminate,
The laminate comprises:
an anode foil having a dielectric layer on a surface thereof;
A cathode foil;
A separator;
a first conductive polymer layer supported by the separator;
a second conductive polymer layer formed on the dielectric layer;
the first conductive polymer layer contains a first conductive polymer, a polyvinyl alcohol-based polymer, and a boric acid-based compound;
the second conductive polymer layer contains a second conductive polymer,
The boric acid compound is at least one boric acid compound selected from the group consisting of boric acid and boric acid compounds,
At least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked.

(Technique 2)
The electrolytic capacitor according to claim 1, wherein in the first conductive polymer layer, a ratio (Wp/Wc) of a mass Wp of the polyvinyl alcohol-based polymer to a mass Wc of the first conductive polymer is 0.01 or more.

(Technique 3)
The cathode foil has an inorganic layer on a surface thereof,
The electrolytic capacitor according to claim 1 or 2, wherein the first conductive polymer layer is in close contact with the inorganic layer.

(Technique 4)
The electrolytic capacitor according to any one of techniques 1 to 3, wherein the liquid component further contains at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, an ethylene glycol condensate having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

(Technique 5)
The electrolytic capacitor according to any one of Techniques 1 to 4, wherein the laminate is a wound body.

(Technique 6)
A method for manufacturing an electrolytic capacitor, comprising the steps of:
A preparation step of preparing an anode foil having a dielectric layer on a surface thereof;
a first polymer layer forming step of forming a first conductive polymer layer containing a first conductive polymer and a polyvinyl alcohol-based polymer in voids of the separator;
a second polymer layer forming step of forming a second conductive polymer layer on a surface of the dielectric layer;
a laminate formation step of forming a laminate including the first conductive polymer layer and the second conductive polymer layer by stacking the anode foil, the cathode foil, and the separator such that the separator is disposed between the anode foil and the cathode foil;
an impregnation step of impregnating the laminate with a liquid component containing at least one boric acid compound selected from the group consisting of boric acid and boric acid compounds;
A crosslinking step of heating the laminate impregnated with the liquid component to a temperature of 85° C. or higher,
In the crosslinking step, at least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked with the at least one boric acid-based compound.

(Technique 7)
7. The method for producing an electrolytic capacitor according to claim 6, wherein in the first conductive polymer layer, a ratio (Wp/Wc) of a mass Wp of the polyvinyl alcohol-based polymer to a mass Wc of the first conductive polymer is 0.01 or more.

(Technique 8)
The cathode foil has an inorganic layer on a surface thereof,
8. The method for producing an electrolytic capacitor according to claim 6 or 7, wherein the first conductive polymer layer is in close contact with the inorganic layer.

(Technique 9)
The method for producing an electrolytic capacitor according to any one of techniques 6 to 8, wherein the liquid component further contains at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, an ethylene glycol condensate having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

(Technique 10)
The method for producing an electrolytic capacitor according to any one of Techniques 6 to 9, wherein the laminate is a wound body.

Below, the present disclosure will be described in more detail based on examples, but the present disclosure is not limited to the examples. In these examples, multiple electrolytic capacitors were produced and evaluated by the following method.

(Capacitor A1)
An electrolytic capacitor (capacitor A1) was produced by the following method.

(a) Preparation of components An aluminum foil (thickness: 100 μm) was etched to roughen the surface of the aluminum foil. The roughened surface of the aluminum foil was chemically treated to form a dielectric layer. In this way, an anode foil with a dielectric layer formed on both sides was obtained. A carbon layer was formed on both sides of an aluminum foil (thickness: 50 μm) that would become a cathode foil. The carbon layer was formed by vacuum deposition.

A nonwoven fabric (thickness 50 μm) was prepared as a separator. The nonwoven fabric used was made of polyester fiber, aramid fiber, and cellulose.

(b) Formation of a conductive polymer layer A dispersion (commercially available) in which particles of polyethylenedioxythiophene (PEDOT) doped with polystyrene sulfonic acid (PSS) were dispersed in water was prepared. Polyvinyl alcohol and water were added to this dispersion to obtain a coating liquid. The concentration of the conductive polymer component in the coating liquid was 1.8% by mass, and the concentration of polyvinyl alcohol in the coating liquid was 0.6% by mass.

Next, the coating liquid was applied to one side of the anode foil (surface of the dielectric layer) using a gravure coater. A drying process was then performed to form a second conductive polymer layer on one side of the anode foil (surface of the dielectric layer). The drying process was performed by heating the anode foil with the coating liquid applied at 125°C for 5 minutes. Next, a second conductive polymer layer was formed on the other side of the anode foil (surface of the dielectric layer) in the same manner. A first conductive polymer layer was formed on the separator by applying the coating liquid to the separator and then performing a drying process.

(c) Formation of a wound body (laminate) The anode foil, cathode foil, and separator were each cut to a predetermined size. The anode lead tab and cathode lead tab were connected to the anode foil and cathode foil, respectively. Next, the anode foil and cathode foil were wound with the separator interposed therebetween. At that time, the ends of the outer surface of the wound body were fixed with a winding stop tape. The anode lead wire and cathode lead wire were connected to the ends of each lead tab protruding from the wound body, respectively. The obtained wound body was again subjected to a chemical conversion treatment to form a dielectric layer on the end surface of the anode foil. In this manner, a capacitor element was obtained.

(d) Impregnation of liquid component o-phthalic acid and triethylamine (base component) were dissolved in ethylene glycol (solvent) at a total concentration of 25 mass%, and ammonium borate was further added to prepare an electrolyte (liquid component). The concentration of ammonium borate in the electrolyte was set to 2.5 mass%. The capacitor element was immersed in the electrolyte for 5 minutes in a reduced pressure atmosphere (40 kPa). This allowed the capacitor element (laminate) to be impregnated with the electrolyte.

(e) Capacitor Element Sealing and Crosslinking Process The capacitor element impregnated with the electrolytic solution was sealed to assemble an electrolytic capacitor as shown in FIG. 1. Then, the electrolytic capacitor including the capacitor element (laminate) was heated at 105° C. for 60 minutes while applying a voltage between the anode foil and the cathode foil. This process crosslinked the polyvinyl alcohol in the conductive polymer layer with ammonium borate. This process also reconstituted the anode foil. In this way, an electrolytic capacitor (capacitor A1) was produced.

(Capacitor C1)
An electrolytic capacitor (capacitor C1) was produced in the same manner and under the same conditions as those for producing capacitor A1, except that polyvinyl alcohol was not added to the coating liquid for forming the conductive polymer layer.

(Capacitor C2)
An electrolytic capacitor (capacitor C2) was produced in the same manner and under the same conditions as those for producing capacitor A1, except that ammonium borate was not added to the electrolyte.

(Capacitor C3)
An electrolytic capacitor (capacitor C3) was produced in the same manner and under the same conditions as those for producing capacitor A1, except that polyvinyl alcohol was not added to the coating liquid for forming the conductive polymer layer, and ammonium borate was not added to the electrolytic solution.

(evaluation)
The equivalent series resistance (ESR) and withstand voltage of the produced electrolytic capacitor were measured. The evaluation results are shown in Table 1. It is preferable that the ESR is low and the withstand voltage is high.

Capacitor A1 is an electrolytic capacitor (E) according to the present disclosure manufactured by manufacturing method (M). Capacitors C1 to C3 are comparative examples. As shown in Table 1, capacitor A1 had a low ESR and a high withstand voltage.

This disclosure can be used in electrolytic capacitors.

10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 100: Electrolytic capacitor

Claims (10)

An electrolytic capacitor comprising a laminate and a liquid component impregnated in the laminate,
The laminate comprises:
an anode foil having a dielectric layer on a surface thereof;
A cathode foil;
A separator;
a first conductive polymer layer supported by the separator;
a second conductive polymer layer formed on the dielectric layer;
the first conductive polymer layer contains a first conductive polymer, a polyvinyl alcohol-based polymer, and a boric acid-based compound;
the second conductive polymer layer contains a second conductive polymer,
The boric acid compound is at least one boric acid compound selected from the group consisting of boric acid and boric acid compounds,
At least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked. The electrolytic capacitor of claim 1, wherein in the first conductive polymer layer, the ratio (Wp/Wc) of the mass Wp of the polyvinyl alcohol-based polymer to the mass Wc of the first conductive polymer is 0.01 or more. The cathode foil has an inorganic layer on a surface thereof,
The electrolytic capacitor of claim 1 , wherein the first conductive polymer layer is in close contact with the inorganic layer. The electrolytic capacitor of claim 1, wherein the liquid component further contains at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane. The electrolytic capacitor of claim 1, wherein the laminate is a wound body. A method for manufacturing an electrolytic capacitor, comprising the steps of:
A preparation step of preparing an anode foil having a dielectric layer on a surface thereof;
a first polymer layer forming step of forming a first conductive polymer layer containing a first conductive polymer and a polyvinyl alcohol-based polymer in voids of the separator;
a second polymer layer forming step of forming a second conductive polymer layer on a surface of the dielectric layer;
a laminate formation step of forming a laminate including the first conductive polymer layer and the second conductive polymer layer by stacking the anode foil, the cathode foil, and the separator such that the separator is disposed between the anode foil and the cathode foil;
an impregnation step of impregnating the laminate with a liquid component containing at least one boric acid compound selected from the group consisting of boric acid and boric acid compounds;
A crosslinking step of heating the laminate impregnated with the liquid component to a temperature of 85° C. or higher,
In the crosslinking step, at least a portion of the polyvinyl alcohol-based polymer in the first conductive polymer layer is crosslinked with the at least one boric acid-based compound. The method for manufacturing an electrolytic capacitor according to claim 6, wherein in the first conductive polymer layer, the ratio (Wp/Wc) of the mass Wp of the polyvinyl alcohol-based polymer to the mass Wc of the first conductive polymer is 0.01 or more. The cathode foil has an inorganic layer on a surface thereof,
The method for producing an electrolytic capacitor according to claim 6 , wherein the first conductive polymer layer is in close contact with the inorganic layer. The method for manufacturing an electrolytic capacitor according to claim 6, wherein the liquid component further contains at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane. The method for manufacturing an electrolytic capacitor according to claim 6, wherein the laminate is a wound body.

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