WO2024143419A1

WO2024143419A1 - Solid electrolytic capacitor and method for producing same

Info

Publication number: WO2024143419A1
Application number: PCT/JP2023/046795
Authority: WO
Inventors: 隆則村中
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2022-12-28
Filing date: 2023-12-26
Publication date: 2024-07-04

Abstract

Disclosed is a solid electrolytic capacitor (100) that comprises: a positive electrode-side member (11) which comprises a positive electrode body (11a) that has a porous surface, and a dielectric layer (11b) that is formed on the porous surface; and a solid electrolyte layer (15). The positive electrode-side member (11) has a porous part (11p) in the surface. The solid electrolyte layer (15) comprises: a first solid electrolyte layer (15a) which is formed on the dielectric layer (11b) and contains a first conductive polymer; and a second solid electrolyte layer (15b) which is formed on the first solid electrolyte layer (15a) and contains a second conductive polymer. The first solid electrolyte layer (15a) is formed using a dispersion liquid in which particles of the first conductive polymer are dispersed. The second solid electrolyte layer (15b) contains an oxidant and/or a residue of an oxidant. The average particle diameter of the above-described particles is smaller than the average pore diameter of the porous part (11p). The ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer (15a) to the conductivity σ2 of the second solid electrolyte layer (15b) is 0.1 or less.

Description

Solid electrolytic capacitor and method of manufacturing same

This disclosure relates to a solid electrolytic capacitor and a method for manufacturing the same.

A solid electrolytic capacitor includes a solid electrolyte layer formed on a dielectric layer. Various solid electrolyte layers and methods for forming them have been proposed.

Patent document 1 (JP Patent Publication 2001-102255 A) describes claim 1 of a tantalum solid electrolytic capacitor in which "an anode body is formed by sintering a compact of tantalum powder in which an anode lead wire is embedded with one end exposed, and is laminated with a dielectric oxide film layer, a layer containing a conductive polymer made of polystyrene sulfonic acid and its derivatives, and a chemically polymerizable conductive polymer layer formed by impregnating the anode body with a solution containing a heterocyclic monomer and a solution containing an oxidizer individually, or with a mixed liquid containing a heterocyclic monomer and an oxidizer."

Patent document 2 (JP Patent Publication 2003-100561 A) describes claim 1 of a solid electrolytic capacitor comprising the steps of: forming a capacitor element by winding an anode foil having a dielectric oxide film layer formed thereon and a cathode foil that has been etched or chemically treated after etching, with a separator between them; forming a first solid electrolyte layer by impregnating the capacitor element with an aqueous solution of a conductive polymer in which fine particles of a conductive polymer are dispersed; and forming a second solid electrolyte layer by impregnating the surface of the first solid electrolyte layer with a solution containing a heterocyclic monomer and a solution containing an oxidizer individually, or with a mixed solution containing a heterocyclic monomer and an oxidizer.

Claim 1 of Patent Document 3 (JP 2008-258307 A) describes an electrolytic capacitor including a capacitor element having an anode body having a plurality of holes on its surface, a dielectric film formed on the surface of the anode body, and a cathode body formed on the dielectric film, the cathode body including a conductive solid layer, the conductive solid layer being a layer including conductive solid particles and/or aggregates thereof formed using a dispersion including conductive solid particles and/or aggregates thereof and a solvent, the conductive solid particles and/or aggregates thereof contained in the dispersion having a first particle size distribution peak and a second particle size distribution peak satisfying the following formula (1) in particle size distribution measurement by a dynamic laser light scattering method.
μ1>μ2 (1)
[In formula (1), μ1 and μ2 represent the average particle diameters of the first and second particle diameter distribution peaks, respectively.]" is described.

Claim 1 of Patent Document 4 (WO 2022/220235) describes an "electrolytic capacitor comprising an anode body, a dielectric layer covering the anode body, a first solid electrolyte layer covering the dielectric layer, and a second solid electrolyte layer covering the first solid electrolyte layer, the first solid electrolyte layer including a first conductive polymer having a polythiophene skeleton, the second solid electrolyte layer including a second conductive polymer having a polypyrrole skeleton, and the conductivity of the first solid electrolyte layer being 2 S/cm or less."

JP 2001-102255 A JP 2003-100561 A JP 2008-258307 A International Publication No. 2022/220235

The porous portion of the surface of the anode body has minute pores (pits). With conventional manufacturing methods, it has been difficult to form a solid electrolyte layer deep within the pores. One of the purposes of this disclosure is to improve the problems with conventional solid electrolytic capacitors and their manufacturing methods, and to provide a solid electrolytic capacitor with superior characteristics.

One aspect of the present disclosure relates to a solid electrolytic capacitor. The electrolytic capacitor includes an anode-side member including an anode body having a porous surface and a dielectric layer formed on the porous surface, and a solid electrolyte layer, the anode-side member having a porous portion formed on the surface by the anode body and the dielectric layer, the solid electrolyte layer includes a first solid electrolyte layer formed on the dielectric layer and containing a first conductive polymer, and a second solid electrolyte layer formed on the first solid electrolyte layer and containing a second conductive polymer, the first solid electrolyte layer is a layer formed using a dispersion liquid in which particles of the first conductive polymer are dispersed, the second solid electrolyte layer contains an oxidizing agent and/or a residue of the oxidizing agent, the average particle size of the particles is smaller than the average pore size of the porous portion, and the ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 or less.

Another aspect of the present disclosure relates to a method for manufacturing a solid electrolytic capacitor. The manufacturing method is a method for manufacturing a solid electrolytic capacitor having an anode side member including an anode body having a porous surface and a dielectric layer formed on the porous surface, the anode side member having a porous portion formed by the anode body and the dielectric layer on the surface, the manufacturing method includes a step (i) of forming a first solid electrolyte layer including the first conductive polymer on the dielectric layer by disposing a dispersion liquid in which particles of a first conductive polymer are dispersed in the porous portion and drying the disposed dispersion liquid, and a step (ii) of forming a second conductive polymer on the first solid electrolyte layer by chemical polymerization using a polymerization liquid including an oxidizing agent, thereby forming a second solid electrolyte layer including the second conductive polymer, the average particle size of the particles being smaller than the average pore size of the porous portion, and the ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer being 0.1 or less.

According to the present disclosure, it is possible to obtain a solid electrolytic capacitor having excellent characteristics.
The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

FIG. 1 is a cross-sectional view illustrating an example of the solid electrolytic capacitor according to the first embodiment. FIG. 2 is a perspective view that typically illustrates a capacitor element included in the solid electrolytic capacitor shown in FIG. FIG. 3 is a cross-sectional view that typically illustrates the state near the surface of the anode member of the solid electrolytic capacitor of the first embodiment.

Below, the embodiments of the present disclosure are described using examples, but the present disclosure 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 effects of the present disclosure are obtained. 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 a lower limit and an upper limit of a numerical value related to a specific physical property or condition are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. In the following description, when examples of components are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

(Electrolytic capacitor)
The solid electrolytic capacitor according to the present embodiment may be referred to as a solid electrolytic capacitor (S) below. The solid electrolytic capacitor (S) includes an anode-side member including an anode body having a porous surface and a dielectric layer formed on the porous surface, and a solid electrolyte layer. The anode-side member has a porous portion formed by the anode body and the dielectric layer on its surface. The solid electrolyte layer includes a first solid electrolyte layer formed on the dielectric layer and containing a first conductive polymer, and a second solid electrolyte layer formed on the first solid electrolyte layer and containing a second conductive polymer. The first solid electrolyte layer is a layer formed using a dispersion liquid in which particles of the first conductive polymer are dispersed. The particles may be referred to as "particles (P)" below. The second solid electrolyte layer includes an oxidizing agent and/or a residue of the oxidizing agent. That is, the second solid electrolyte layer includes at least one of an oxidizing agent and a residue of the oxidizing agent. The average particle diameter Dp of the particles (P) is smaller than the average pore diameter Sp of the porous portion. The ratio σ1/σ2 of the electrical conductivity σ1 of the first solid electrolyte layer to the electrical conductivity σ2 of the second solid electrolyte layer is 0.1 or less.

In order to improve the characteristics of the solid electrolytic capacitor (low ESR, high reliability, etc.), if the concentration of the oxidizing agent in the polymerization solution is increased, the viscosity of the polymerization solution will increase. Therefore, it is difficult to form a sufficient solid electrolyte deep in the pores of the porous part by chemical polymerization. The first solid electrolyte layer of the solid electrolytic capacitor (S) is formed using a dispersion of particles (P) whose average particle size Dp is smaller than the average pore size Sp of the porous part, so that a sufficient solid electrolyte layer can be formed in the pores of the porous part. The electrolyte layer can then be formed by chemical polymerization using a polymerization solution with a high concentration of oxidizing agent. As a result, the capacity extraction property is improved and a low equivalent series resistance (ESR) can be achieved. Furthermore, in the solid electrolytic capacitor (S), the first solid electrolyte layer is formed and then the second solid electrolyte layer is formed by chemical polymerization. Therefore, it is possible to prevent the polymerization solution used in forming the second solid electrolyte layer from coming into contact with the dielectric layer. As a result, it is possible to prevent the dielectric layer from being damaged by substances (high boiling point solvent, oxidizing agent, oxidizing agent residue, etc.) contained in the polymerization solution of the chemical polymerization. As a result, it is possible to suppress the deterioration of initial and long-term properties due to the oxidizing agent or oxidizing agent residue. A polymerization liquid using an oxidizing agent that is solid at room temperature (25°C) may have an increased viscosity. Therefore, the effects of the present disclosure are particularly expected when chemical polymerization is performed using an oxidizing agent that is solid at room temperature.

Furthermore, in the solid electrolytic capacitor (S), the ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 or less. With this configuration, even when a defect occurs in the dielectric layer, the first solid electrolyte layer in the portion where the defect occurs is likely to be insulated first. Therefore, it is possible to reduce leakage current. As a result, a highly reliable solid electrolytic capacitor (S) is obtained. Because the solid electrolytic capacitor (S) does not contain an electrolytic solution, the self-repairing ability of the dielectric layer is low. Therefore, measures against defects in the dielectric layer are particularly important.

Compared to forming a solid electrolyte layer using only a dispersion liquid, forming a second solid electrolyte layer on a first solid electrolyte layer by chemical polymerization is preferable because it allows more solid electrolyte to be formed with fewer treatments.

The average particle size Dp of the particles (P) is the median diameter (D50) at which the cumulative volume is 50% in the volume-based particle size distribution. The average particle size Dp is determined using a laser diffraction/scattering particle size distribution measuring device.

The average pore diameter Sp of the porous portion is determined by measuring the pore diameter distribution of the porous portion using a mercury porosimeter. Specifically, the pore diameter (mode diameter) corresponding to the apex of the peak (maximum peak if multiple peaks exist) that appears on the pore distribution curve (vertical axis: log differential pore volume, horizontal axis: pore diameter) obtained by measurement is determined as the average pore diameter Sp. For example, the AutoPore V series manufactured by Micromeritics is used as the measuring device.

The ratio Dp/Sp of the average particle size Dp of the particles (P) to the average pore size Sp of the porous portion may be 0.1 or more, 0.14 or more, or 0.2 or more. The ratio Dp/Sp may be less than 1, 0.9 or less, or 0.8 or less.

The average pore diameter Sp of the porous portion after chemical conversion may be 50 nm or more, 100 nm or more, or 150 nm or more, and may be 300 nm or less, or 200 nm or less.

The average particle size Dp of the particles (P) can be controlled by the conditions for synthesizing the first conductive polymer. Currently, particles (P) having various average particle sizes Dp are available on the market, so they can be used.

The average pore diameter Sp of the porous portion can be controlled by the etching conditions of the metal foil before forming the dielectric layer, and the conditions of the chemical conversion treatment when forming the dielectric layer. For example, by using an AC etching method, it is possible to reduce the diameter of the pores formed by etching. In addition, by increasing the chemical conversion voltage, the dielectric layer can be made thicker, and as a result, the average pore diameter Sp can be reduced.

The first solid electrolyte layer may be formed so as to fill the pores of the porous portion. Alternatively, the second solid electrolyte layer may penetrate into the pores of the porous portion. However, the first solid electrolyte layer is disposed between the dielectric layer and the second solid electrolyte layer.

The ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 (3/30) or less, and may be 1/30 or less (0.03 or less). The ratio σ1/σ2 may be 0.001/30 or more, 0.001/60 or more, or 0.01/30 or more. The ratio σ1/σ2 may be in the range of 0.001/60 to 1/30 (e.g., in the range of 0.001/60 to 1/30).

The solid electrolytic capacitor (S) may include a separator and a cathode foil. The anode side member (anode foil with a dielectric layer formed thereon), the separator, and the cathode foil may be wound such that the separator is disposed between the anode side member and the cathode foil. That is, the solid electrolytic capacitor (S) may include a wound body of the anode side member, the separator, and the cathode foil.

When the rated voltage is lower, the Joule heat for insulating the conductive polymer is smaller. Therefore, when the rated voltage used is lower (for example, when the rated voltage is 50 V or less), the conductivity σ1 of the first solid electrolyte layer may be 1 S/cm or less. With this configuration, the function of suppressing leakage current is improved. The conductivity σ1 of the first solid electrolyte layer may be 0.8 S/cm or less. Since the thickness of the first solid electrolyte layer is very thin and does not affect the ESR, the conductivity σ1 of the first solid electrolyte layer may be 0.001 S/cm or more. Since the second solid electrolyte layer does not need to have the function of insulating the conductive polymer, the conductivity σ2 is preferably 1 S/cm or more, or 10 S/cm or more, and more preferably 30 S/cm. may be. The conductivity σ2 may be 200 S/cm or less, or 150 S/cm or less.

The ratio σ1/σ2 may be controlled by changing the compounding ratio of the oxidizing agent and the monomer in the chemical polymerization when forming the second solid electrolyte layer, or by changing the amount of the components in the polymerization solution. Alternatively, the ratio σ1/σ2 may be controlled by changing the amount of conductive polymer in each solid electrolyte layer. For example, the conductivity of the solid electrolyte layer can be increased by increasing the amount of conductive polymer contained in the solid electrolyte layer. Also, the conductivity of the solid electrolyte layer can be increased by adding an additive that increases the conductivity when forming the solid electrolyte layer. Examples of such additives include alcohols (particularly polyhydric alcohols and sugar alcohols), base components, etc.

The electrical conductivity σ1 is determined by forming a solid electrolyte layer on a flat insulating substrate under the same conditions as those for forming the first solid electrolyte layer, and measuring the electrical conductivity of the solid electrolyte layer. Similarly, the electrical conductivity σ2 is determined by forming a solid electrolyte layer on a flat insulating substrate under the same conditions as those for forming the second solid electrolyte layer, and measuring the electrical conductivity of the solid electrolyte layer.

The ratio T2/T1 of the average thickness T2 of the second solid electrolyte layer to the average thickness T1 of the first solid electrolyte layer may be 10 or more, or 20 or more, and may be 400 or less, or 600 or less. The ratio T2/T1 is preferably in the range of 20 to 400. With this configuration, the first solid electrolyte layer is more likely to be insulated. In addition, when the conductivity of the first solid electrolyte layer is reduced, an increase in the ESR of the solid electrolytic capacitor (S) can be suppressed. The average thickness T1 of the first solid electrolyte layer may be 50 nm or more, or 100 nm or more, and may be 2000 nm or less, or 4000 nm or less.

The average thickness T1 can be measured by the following procedure (the same applies to the average thickness T2). First, the target capacitor is solidified with resin. Next, the surface of the resin-solidified capacitor is uniformly polished by ion milling or the like. Next, an image of the exposed surface is obtained by a scanning electron microscope (SEM) or the like. Next, 10 arbitrary points of the first solid electrolyte layer are selected in the image, and the thickness of each part is obtained. The average thickness T1 is obtained by arithmetically averaging the thicknesses of the 10 points obtained. The average thickness T2 is also obtained by a similar method. Note that the boundary between the first solid electrolyte layer and the second solid electrolyte layer can be determined from the image. For example, the surface of the first solid electrolyte layer is usually relatively smooth, whereas the second solid electrolyte layer formed by chemical polymerization is a relatively rough layer. Therefore, it is possible to determine the boundary between the first solid electrolyte layer and the second solid electrolyte layer by observing the cross section of the solid electrolyte layer. Also, by observing the above-mentioned image, it is possible to know the state of filling the pores with the solid electrolyte layer.

(Method of manufacturing a solid electrolytic capacitor)
The manufacturing method according to this embodiment will be described below. This manufacturing method may be referred to as "manufacturing method (M)" below. According to the manufacturing method (M), the solid electrolytic capacitor (S) can be manufactured. The matters described for the solid electrolytic capacitor (S) may be applied to the manufacturing method (M), and therefore, duplicated descriptions may be omitted. The matters described for the manufacturing method (M) may be applied to the solid electrolytic capacitor (S).

The manufacturing method (M) is a method for manufacturing a solid electrolytic capacitor having an anode side member including an anode body having a porous surface and a dielectric layer formed on the porous surface. The anode side member has a porous portion formed by the anode body and the dielectric layer on its surface. The manufacturing method (M) includes a step (i) of forming a first solid electrolyte layer including the first conductive polymer on the dielectric layer by disposing a dispersion liquid in which particles (P) of a first conductive polymer are dispersed in the porous portion and drying the disposed dispersion liquid, and a step (ii) of forming a second conductive polymer on the first solid electrolyte layer by chemical polymerization using a polymerization liquid including an oxidizing agent, thereby forming a second solid electrolyte layer including the second conductive polymer. The average particle diameter Dp of the particles (P) is smaller than the average pore diameter Sp of the porous portion. The ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 or less.

(Step (i))
In step (i), the first solid electrolyte layer is formed using a dispersion liquid in which the first conductive polymer particles (P) are dispersed. The dispersion medium of the dispersion liquid includes water, an organic solvent (e.g., a lower alcohol, etc.), and a mixture thereof.

The first solid electrolyte layer can be formed by placing a dispersion of particles (P) in the porous portion and then drying the placed dispersion. By repeating the process of placing and drying the dispersion, it is possible to increase the amount of the first conductive polymer filled in the porous portion and to thicken the first solid electrolyte layer.

Examples of the first conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The first conductive polymer may also be a copolymer of two or more types of monomers. Note that a derivative of the first conductive polymer refers to a polymer that has the first conductive polymer as its basic skeleton. For example, an example of a derivative of polythiophene includes poly(3,4-ethylenedioxythiophene).

The first conductive polymer may include a dopant. The dopant may be selected depending on the first conductive polymer, and known dopants may be used. Examples of dopants include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, and salts thereof. One example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS).

The concentration of the dispersion of the first conductive polymer may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more, and may be 5% by mass or less, 3% by mass or less, or 2% by mass or less. By setting the concentration in the range of 0.1 to 2% by mass, it becomes easier to place the first conductive polymer deep in the pores of the porous portion.

(Step (ii))
In step (ii), the second conductive polymer is formed by chemical polymerization. The conditions of the chemical polymerization (components of the polymerization liquid, temperature, etc.) are not particularly limited, and known chemical polymerization conditions may be used. Step (ii) can be performed by disposing a polymerization liquid for chemical polymerization on the first solid electrolyte layer and allowing polymerization to proceed in the polymerization liquid. The polymerization liquid includes a precursor of the second conductive polymer, an oxidizing agent, and a liquid medium. The polymerization liquid may include a dopant. The polymerization liquid may include other additives.

In addition, the liquid containing the precursor of the second conductive polymer and the oxidizing agent may be supplied separately onto the first solid electrolyte layer. Even in this case, the polymerization liquid for chemical polymerization is placed on the first solid electrolyte layer.

The precursor of the second conductive polymer is selected according to the second conductive polymer to be formed. Examples of the precursor include a monomer, oligomer, prepolymer, etc. of the second conductive polymer. The precursor may be used alone or in combination of two or more types. Examples of the second conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. Examples of the monomer of the second conductive polymer include pyrrole, thiophene, aniline, and derivatives thereof.

The oxidizing agent is used to polymerize the precursor of the second conductive polymer. Examples of the oxidizing agent include sulfates, sulfonic acids, and their salts. The oxidizing agent may be used alone or in combination of two or more kinds.

Examples of sulfates include salts of sulfates (such as sulfuric acid and persulfuric acid) with metals, such as ferric sulfate and sodium persulfate. Examples of metals that make up the salts include alkali metals (sodium, potassium, etc.), iron, copper, chromium, and zinc. Sulfonic acids or their salts function as dopants in addition to functioning as oxidizing agents. Examples of sulfonic acids or their salts include low molecular weight sulfonic acids or their salts. Examples of these will be described later as examples of dopants.

Examples of liquid media used in the polymerization liquid include water, organic media, and mixtures thereof. Examples of organic media include aliphatic alcohols having 1 to 5 carbon atoms, aliphatic ketones (e.g., acetone), nitriles (e.g., acetonitrile, benzonitrile), amides (e.g., N,N-dimethylformamide), and sulfoxides (e.g., dimethyl sulfoxide). Examples of aliphatic alcohols having 1 to 5 carbon atoms include aliphatic monools (e.g., methanol, ethanol, propanol, butanol), and aliphatic polyols (e.g., ethylene glycol, glycerin).

In order to improve the conductivity of the second conductive polymer, a dopant may be added to the polymerization liquid. Examples of dopants include polymeric sulfonic acids, low molecular weight sulfonic acids, and salts thereof. Examples of polymeric sulfonic acids include polystyrene sulfonic acid, polyvinyl sulfonic acid, and the like. Examples of low molecular weight sulfonic acids include aliphatic sulfonic acids (alkanesulfonic acids, etc.), aromatic sulfonic acids (benzenesulfonic acid, toluenesulfonic acid, naphthalenedisulfonic acid, etc.). Examples of salts include metal salts, ammonium salts, piperidium salts, pyrrolidium salts, pyrrolinium salts, and the like. Examples of metal salts include alkali metal salts (sodium salts, potassium salts, etc.), iron salts, copper salts, chromium salts, zinc salts, and the like. The dopants may be used alone or in combination of two or more.

In order to promote chemical polymerization, the polymerization liquid may be placed on the first solid electrolyte and then heated. For example, the liquid may be heated at a temperature in the range of 30 to 95°C for about 5 to 180 minutes.

The first conductive polymer and the second conductive polymer may be the same type of polymer or different types of polymer. When chemical polymerization is used to form the first solid electrolyte layer, the viscosity of the polymerization liquid increases rapidly over time, which causes differences in the way the polymerization liquid enters the pores, resulting in large variations in characteristics, and damage to the dielectric layer due to residual components of the oxidizing agent. These problems can be suppressed by forming the first solid electrolyte layer from a dispersion liquid of particles (P). By forming the second solid electrolyte layer by chemical polymerization, a sufficient solid electrolyte layer can be formed with a single treatment. From the viewpoint of forming the first solid electrolyte layer from a dispersion liquid and forming the second solid electrolyte layer by chemical polymerization, it is preferable that the first conductive polymer and the second conductive polymer are different. In a preferred example, the first conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS), and the second conductive polymer is polythiophene. By using thiophene-based polymers for both the first conductive polymer and the second conductive polymer, it is expected that the interfacial resistance between the solid electrolyte layers will be extremely low. Because thiophene-based polymers have higher heat resistance than pyrrole-based polymers, solid electrolytic capacitors (S) using thiophene-based polymers can be used in products with a wide operating temperature range.

When the second conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS), an example polymerization liquid contains 3,4-ethylenedioxythiophene (monomer), polystyrenesulfonic acid, and an oxidizer (e.g., ferric p-toluenesulfonate).

After the formation of the second solid electrolyte layer by chemical polymerization is completed, a drying process or the like is performed as necessary. The second solid electrolyte layer contains an oxidizing agent and/or oxidizing agent residues (sulfate ions, iron ions, etc.). In the absence of the first solid electrolyte layer, the oxidizing agent, etc. may come into contact with the dielectric layer and damage the dielectric layer. However, in manufacturing method (M), the presence of the first solid electrolyte layer makes it possible to prevent the oxidizing agent, etc. from damaging the dielectric layer.

The manufacturing method (M) may include a step (a) of forming a wound body by winding the anode side member, the separator, and the cathode foil such that the separator is disposed between the anode side member and the cathode foil, prior to the step (i). In this case, in the step (i), the wound body is impregnated with the dispersion liquid, so that the dispersion liquid is disposed in the porous portion. Also, the step (ii) may be performed by disposing a polymerization liquid in the wound body. In this case, the first solid electrolyte layer and the second solid electrolyte layer are laminated in this order on the separator and the cathode foil as well.

As described above, the conductivity of the first solid electrolyte layer may be 1 S/cm or less. As described above, the ratio T2/T1 of the average thickness T2 of the second solid electrolyte layer to the average thickness T1 of the first solid electrolyte layer may be in the range of 20 to 400.

The steps following step (ii) are not particularly limited, and any known steps may be applied. For example, a solid electrolytic capacitor can be obtained by enclosing the above-mentioned wound body in an outer casing.

The following describes examples of the configuration and components of the solid electrolytic capacitor (S) according to this embodiment. Note that the configuration and components of the solid electrolytic capacitor (S) are not limited to the following examples.

The solid electrolytic capacitor (S) includes a capacitor element. An example of a capacitor element includes an anode side member (anode foil with a dielectric layer formed thereon), a cathode foil, a separator, and a solid electrolyte layer (first and second solid electrolyte layers). The separator is disposed between the anode side member and the cathode foil. The anode side member, the cathode foil, and the separator form a laminate. An example of a laminate is the wound body described above.

Another example of a capacitor element includes an anode side member, a solid electrolyte layer (first and second solid electrolyte layers) formed on the dielectric layer of the anode side member, and a cathode lead layer formed on the solid electrolyte layer.

(Anode body)
The anode body may be a metal foil (anode foil). The metal constituting the anode foil is preferably a valve metal or an alloy containing a valve metal. Examples of the valve metal include aluminum, tantalum, niobium, titanium, and the like. The anode foil may be an aluminum foil. The surface of the anode foil is preferably roughened. The surface of the anode foil can be roughened by a known method (e.g., etching treatment). The thickness of the anode foil may be in the range of 15 μm to 300 μm (e.g., 50 μm to 200 μm). Usually, both sides of the anode foil are roughened, and a dielectric layer is formed on both sides of the anode foil.

The anode body may be a porous sintered body. The anode side member may include a porous sintered body (anode body) and an anode wire. A part of the anode wire is embedded in the porous sintered body, and another part protrudes from the porous sintered body. The porous sintered body is formed by sintering material particles. Examples of material particles include particles of the valve metals mentioned above (e.g., titanium, tantalum, niobium, etc.). Only one type of these particles may be used, or two or more types may be mixed and used.

(Dielectric Layer)
The dielectric layer is formed on the porous surface (roughened surface) of the anode body. The method of forming the dielectric layer is not particularly limited, and the dielectric layer may be formed by oxidizing the surface of the anode body. In this case, the dielectric layer may contain an oxide of a valve metal. For example, the dielectric layer may be formed by chemically treating the anode body. When the anode body is an aluminum foil, the aluminum oxide layer (dielectric layer) is formed by oxidizing the surface.

(cathode foil)
The cathode foil is not particularly limited. A metal foil can be used for the cathode foil. A valve metal or an alloy containing a valve metal can be used as the metal constituting the metal foil (cathode foil). Examples of the valve metal include the metals mentioned above. The cathode foil can be an aluminum foil. The surface of the cathode foil can be roughened. The thickness of the cathode foil can be in the range of 15 μm to 300 μm (for example, in the range of 50 μm to 200 μm).

The cathode foil may include a conductive coating layer. When the metal foil includes a valve metal, the coating layer may include carbon, or at least one metal having a lower ionization tendency than the valve metal. This makes it easier to improve the acid resistance of the metal foil. When the metal foil includes aluminum, the coating layer may include at least one selected from the group consisting of carbon, nickel, titanium, tantalum, and zirconium. The thickness of the coating layer may be 5 nm or more, or 10 nm or more, or may be 200 nm or less.

(Separator)
A porous sheet can be used as the separator. Examples of the separator 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.

(Cathode extraction layer)
The cathode extraction layer is a conductive layer laminated on the solid electrolyte layer. The cathode extraction layer is formed of a material having electrical conductivity. The cathode extraction layer may include a carbon layer and a metal particle layer. The carbon layer is a layer containing a conductive carbonaceous material. The metal particle layer is a layer containing metal particles (e.g., silver particles). The carbon layer and the metal particle layer can be formed by a known method. For example, the metal particle layer can be formed using a metal paste containing metal particles (e.g., silver paste).

(others)
The solid electrolytic capacitor (S) may include other components (leads, exterior body, etc.) as necessary. The leads and exterior body are not particularly limited, and known leads and exterior bodies may be used.

Below, examples of the solid electrolytic capacitor (S) are specifically described with reference to the drawings. The above description can be applied to the examples described below. Furthermore, the examples 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 examples described below, matters that are not essential to the solid electrolytic capacitor (S) of the present disclosure may be omitted.

(Embodiment 1)
In the embodiment 1, an example of a solid electrolytic capacitor (S) will be described. A cross-sectional view of a solid electrolytic capacitor 100 of the embodiment 1 is shown typically in Fig. 1. Fig. 2 is a schematic diagram showing a state in which a part of a capacitor element 10 (wound body) included in the solid electrolytic capacitor 100 is developed.

The solid electrolytic capacitor 100 includes a capacitor element 10, a bottomed case 101, a sealing member 102, a seat plate 103,

lead wires

104A and 104B, and lead

tabs

105A and 105B. The bottomed case 101 houses the capacitor element 10. The sealing member 102 covers the opening of the bottomed case 101. The seat plate 103 covers the sealing member 102. The

lead wires

104A and 104B pass through the seat plate 103. The lead tab 105A connects the lead wire 104A to the anode foil of the capacitor element 10. The lead tab 105B connects the lead wire 104B to the cathode foil of the capacitor element 10. The vicinity of the open end of the bottomed case 101 is drawn inward. The open end of the bottomed case 101 is curled to crimp the sealing member 102.

The capacitor element 10 is a wound body. The capacitor element 10 is formed by winding the anode side member 11, the cathode foil 12, and the separator 13 so that the separator 13 is disposed between the anode side member 11 and the cathode foil 12. The outermost circumference of the wound body is fixed with tape 14. The anode side member 11 includes an anode foil and a dielectric layer formed on the surface of the anode foil. The anode side member 11 has a porous portion on its surface. A first solid electrolyte layer and a second solid electrolyte layer are laminated on the anode side member 11 (on the dielectric layer). Note that the solid electrolyte layers are not shown in FIG. 2.

A cross-sectional view of the surface of the anode side member 11 is shown in FIG. 3. As shown in FIG. 3, the anode side member 11 includes an anode body (anode foil) 11a having a porous surface and a dielectric layer 11b formed on the porous surface. The anode side member 11 has a porous portion 11p formed by the anode body 11a and the dielectric layer 11b on its surface. Note that the shape of the porous portion 11p is simplified in FIG. 3, but in reality, the porous portion 11p has a more complicated shape. A solid electrolyte layer 15 consisting of a first solid electrolyte layer 15a and a second solid electrolyte layer 15b is formed on the dielectric layer 11b. The pores of the porous portion 11p are filled with the first solid electrolyte layer 15a. The second solid electrolyte layer 15b is formed on the first solid electrolyte layer 15a.

(Additional Note)
Based on the above description, the following techniques are disclosed.
(Technique 1)
A solid electrolytic capacitor comprising:
an anode side member including an anode body having a porous surface and a dielectric layer formed on the porous surface;
a solid electrolyte layer;
the anode side member has a porous portion on a surface thereof formed by the anode body and the dielectric layer,
the solid electrolyte layer includes a first solid electrolyte layer formed on the dielectric layer and containing a first conductive polymer, and a second solid electrolyte layer formed on the first solid electrolyte layer and containing a second conductive polymer,
the first solid electrolyte layer is a layer formed using a dispersion liquid in which particles of the first conductive polymer are dispersed,
the second solid electrolyte layer comprises an oxidizing agent and/or a residue of the oxidizing agent;
The average particle size of the particles is smaller than the average pore size of the porous portion,
a ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 or less.
(Technique 2)
A separator and a cathode foil,
The solid electrolytic capacitor according to claim 1, wherein the anode side member, the separator, and the cathode foil are wound such that the separator is disposed between the anode side member and the cathode foil.
(Technique 3)
The solid electrolytic capacitor according to claim 1 or 2, wherein the electrical conductivity of the first solid electrolyte layer is 1 S/cm or less.
(Technique 4)
The solid electrolytic capacitor according to any one of the first to third aspects, wherein a ratio T2/T1 of an average thickness T2 of the second solid electrolyte layer to an average thickness T1 of the first solid electrolyte layer is in a range of 20 to 400.
(Technique 5)
A method for manufacturing a solid electrolytic capacitor having an anode-side member including an anode body having a porous surface and a dielectric layer formed on the porous surface, comprising:
the anode side member has a porous portion on a surface thereof formed by the anode body and the dielectric layer,
The manufacturing method includes:
(i) forming a first solid electrolyte layer containing the first conductive polymer on the dielectric layer by disposing a dispersion liquid in which particles of a first conductive polymer are dispersed in the porous portion and drying the disposed dispersion liquid;
and (ii) forming a second conductive polymer on the first solid electrolyte layer by chemical polymerization using a polymerization liquid containing an oxidizing agent, thereby forming a second solid electrolyte layer containing the second conductive polymer;
The average particle size of the particles is smaller than the average pore size of the porous portion,
a ratio σ1/σ2 of the electrical conductivity σ1 of the first solid electrolyte layer to the electrical conductivity σ2 of the second solid electrolyte layer is 0.1 or less.
(Technique 6)
a step (a) of winding the anode-side member, a separator, and a cathode foil such that the separator is disposed between the anode-side member and the cathode foil, before the step (i);
The manufacturing method according to Art 5, wherein in the step (i), the dispersion is disposed in the porous portion by impregnating the wound body with the dispersion.
(Technique 7)
The manufacturing method according to claim 5 or 6, wherein the electrical conductivity of the first solid electrolyte layer is 1 S/cm or less.
(Technique 8)
The manufacturing method according to any one of Techniques 5 to 7, wherein a ratio T2/T1 of an average thickness T2 of the second solid electrolyte layer to an average thickness T1 of the first solid electrolyte layer is in the range of 20 to 400.

The solid electrolytic capacitor according to the present disclosure will be explained in more detail using examples.

(Experimental Example 1)
In Experimental Example 1, a plurality of solid electrolytic capacitors having different average pore diameters Sp of the porous portion and different solid electrolyte layers were produced and evaluated.

(Capacitor A1)
The capacitor A1 was produced by the following method. First, an aluminum etched foil was subjected to a chemical conversion treatment to form a dielectric layer on the surface of the aluminum foil. This resulted in an anode-side member including an anode body having a porous surface and a dielectric layer formed on the porous surface. The average pore diameter of the porous portion present on the surface of the anode-side member was measured and found to be 145 nm. Next, leads were connected to each of the anode-side member and the cathode foil (aluminum foil). Next, the anode-side member, the cathode foil, and the separator were wound to form a wound body.

Then, the wound body was immersed in a dispersion liquid containing particles (P) of a first conductive polymer and then dried. This formed a first solid electrolyte layer on the dielectric layer of the porous portion of the anode side member. For the particles (P), particles of a first conductive polymer with an average particle size of 100 nm were used. For the first conductive polymer, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PSS) was used. Water was used as the dispersion medium. The conductivity of the formed first solid electrolyte layer was 1 S/cm.

Next, the wound body was immersed in a polymerization liquid for chemical polymerization, and then thiophene was polymerized to form a second solid electrolyte layer on the first solid electrolyte layer. The polymerization liquid used contained a monomer, an oxidizing agent, and a liquid medium. Thiophene was used as the monomer. Aromatic sulfonic acid was used as the oxidizing agent. Butanol was used as the liquid medium. Polythiophene (a second conductive polymer) was synthesized by chemical polymerization. The conductivity of the formed second solid electrolyte layer was 30 S/cm. In other words, σ1/σ2 = 1/30. As described above, the conductivity of the solid electrolyte layer was calculated from the conductivity of a solid electrolyte layer formed on an insulating substrate under the same conditions as those for forming the solid electrolyte layer.

Next, the wound body (capacitor element) was housed in an outer casing to obtain a capacitor A1 (solid electrolytic capacitor).
(other capacitors)
Capacitors A2 to A3 and C1 to C6 were produced in the same manner and under the same conditions as those for the production of capacitor A1, except that the average pore diameter Sp of the porous portion and the conditions for forming the solid electrolyte layer were changed as shown in Table 1. The average pore diameter Sp of the porous portion was changed by changing the chemical formation voltage when forming the dielectric layer. Specifically, when the average pore diameter Sp was to be reduced, the chemical formation voltage was increased. The solid electrolyte layers of capacitors C1 to C3 were formed only by chemical polymerization. The conditions for chemical polymerization were the same as those for the production of capacitor A1. In the dispersion liquid used for the production of capacitors C4 to C6, conductive polymer particles with an average particle diameter Dp of 200 nm were used. In addition, σ1/σ2=1/30 was also true for capacitors A2 and A3.

The initial capacitance Ca of each capacitor was measured. In addition, the capacitance Cb of each capacitor was measured after it was left in an environment of 145° C. for 1000 hours. The capacitance reduction rate was calculated using the following formula.
Capacity decrease rate (%) = 100 × (Ca - Cb) / Ca

Table 1 shows some of the manufacturing conditions for each capacitor and the evaluation results for each capacitor. Note that the initial capacitances shown in Table 1 are relative values when comparing capacitors with the same average pore diameter. Specifically, the initial capacitances of capacitors A1, C1, and C4 are relative values when the initial capacitance of capacitor C1 is set to 100%. The initial capacitances of capacitors A2, C2, and C5 are relative values when the initial capacitance of capacitor C2 is set to 100%. The initial capacitances of capacitors A3, C3, and C6 are relative values when the initial capacitance of capacitor C3 is set to 100%.

The higher the initial capacitance, the better. Also, the smaller the rate of capacitance decrease is, the better. Capacitors A1 to A3 are solid electrolytic capacitors (S) according to the present disclosure. Capacitors C1 to C6 are comparative examples.

As shown in Table 1, capacitor A1 had a higher initial capacitance than capacitor C1, which had the same average pore diameter Sp. Similarly, capacitors A2 and A3 showed no decrease in initial capacitance compared to capacitors C2 and C3, which had the same average pore diameter Sp. This is believed to be because the first solid electrolyte layer was sufficiently present within the pores of the porous portion of capacitors A1 to A3, and the first solid electrolyte layer was disposed between the dielectric layer and the second solid electrolyte layer. As shown in Table 1, capacitors C4 to C6 had a low initial capacitance. This is believed to be because the conductive polymer was not sufficiently disposed inside the pores of the porous portion.

As shown in Table 1, capacitors A1 to A3 had a smaller rate of capacitance degradation than capacitors C1 to C6.

(Experimental Example 2)
In Experimental Example 2, a plurality of solid electrolytic capacitors having different solid electrolyte layers were fabricated and evaluated.

(Capacitor A2)
Capacitor A2 was fabricated in the same manner and under the same conditions as capacitor A2 fabricated in experimental example 1.

(other capacitors)
Capacitors A4 to A6 and C7 to C9 were produced in the same manner and under the same conditions as those for producing capacitor A2, except that the conductivity of the solid electrolyte layer was changed as shown in Table 2. The conductivity σ1 of the first solid electrolyte layer was changed by changing the amount of conductive polymer contained in the first solid electrolyte layer and the amount of additive that improves conductivity. As described above, the conductivity of the solid electrolyte layer was determined from the conductivity of a solid electrolyte layer formed on an insulating substrate under the same conditions as those for forming the solid electrolyte layer.

The capacitance loss rate (%) of the produced capacitor was determined using the same method and conditions as in Experimental Example 1. Some of the conditions for forming the solid electrolyte layer and the evaluation results are shown in Table 2.

Capacitors A2, A4 to A6 are solid electrolytic capacitors (S) according to the present disclosure. Capacitors C7 to C9 are comparative examples. As shown in Table 2, capacitors A2, A4 to A6 had a small rate of capacitance decrease. On the other hand, capacitor C7 was short-circuited in the early stages. Capacitors C8 and C9 were short-circuited after 1000 hours had passed. It is believed that the short-circuits occurred because the leakage current suppression function of insulation was not working sufficiently.

The present disclosure can be used for solid electrolytic capacitors.
Although the present invention has been described with respect to the presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be interpreted to cover all variations and modifications without departing from the true spirit and scope of the present invention.

10: Capacitor element 11: Anode side member 11a: Anode body 11b: Dielectric layer 11p: Porous portion 12: Cathode foil 13: Separator 15: Solid electrolyte layer 15a: First solid electrolyte layer 15b: Second solid electrolyte layer 100: Solid electrolytic capacitor

Claims

A solid electrolytic capacitor comprising:
an anode side member including an anode body having a porous surface and a dielectric layer formed on the porous surface;
a solid electrolyte layer;
the anode side member has a porous portion on a surface thereof formed by the anode body and the dielectric layer,
the solid electrolyte layer includes a first solid electrolyte layer formed on the dielectric layer and containing a first conductive polymer, and a second solid electrolyte layer formed on the first solid electrolyte layer and containing a second conductive polymer,
the first solid electrolyte layer is a layer formed using a dispersion liquid in which particles of the first conductive polymer are dispersed,
the second solid electrolyte layer comprises an oxidizing agent and/or a residue of the oxidizing agent;
The average particle size of the particles is smaller than the average pore size of the porous portion,
a ratio σ1/σ2 of the conductivity σ1 of the first solid electrolyte layer to the conductivity σ2 of the second solid electrolyte layer is 0.1 or less.
A separator and a cathode foil,
2 . The solid electrolytic capacitor according to claim 1 , wherein the anode side member, the separator, and the cathode foil are wound such that the separator is disposed between the anode side member and the cathode foil.
The solid electrolytic capacitor according to claim 1 or 2, wherein the electrical conductivity of the first solid electrolyte layer is 1 S/cm or less.
The solid electrolytic capacitor according to claim 1 or 2, wherein the ratio T2/T1 of the average thickness T2 of the second solid electrolyte layer to the average thickness T1 of the first solid electrolyte layer is in the range of 20 to 400.
A method for manufacturing a solid electrolytic capacitor having an anode-side member including an anode body having a porous surface and a dielectric layer formed on the porous surface, comprising:
the anode side member has a porous portion on a surface thereof formed by the anode body and the dielectric layer,
The manufacturing method includes:
(i) forming a first solid electrolyte layer containing the first conductive polymer on the dielectric layer by disposing a dispersion liquid in which particles of a first conductive polymer are dispersed in the porous portion and drying the disposed dispersion liquid;
and (ii) forming a second conductive polymer on the first solid electrolyte layer by chemical polymerization using a polymerization liquid containing an oxidizing agent, thereby forming a second solid electrolyte layer containing the second conductive polymer;
The average particle size of the particles is smaller than the average pore size of the porous portion,
a ratio σ1/σ2 of the electrical conductivity σ1 of the first solid electrolyte layer to the electrical conductivity σ2 of the second solid electrolyte layer is 0.1 or less.
a step (a) of winding the anode-side member, a separator, and a cathode foil such that the separator is disposed between the anode-side member and the cathode foil, before the step (i);
The method according to claim 5 , wherein in the step (i), the dispersion is disposed in the porous portion by impregnating the wound body with the dispersion.
The manufacturing method according to claim 5 or 6, wherein the electrical conductivity of the first solid electrolyte layer is 1 S/cm or less.
The manufacturing method according to claim 5 or 6, wherein the ratio T2/T1 of the average thickness T2 of the second solid electrolyte layer to the average thickness T1 of the first solid electrolyte layer is in the range of 20 to 400.