Method for manufacturing electrolytic capacitor and electrolytic capacitor

Abstract

To reduce variation in an ESR when an electrolytic capacitor is exposed to a high-humidity environment.SOLUTION: A manufacturing method of an electrolytic capacitor includes: a step of preparing an anode body having a dielectric layer on a surface thereof; and a step of forming a solid electrolyte. The step of forming the solid electrolyte includes a sub-step A of bringing a treatment liquid containing a conjugated polymer and a polymer dopant into contact with the anode body, and at least one of the following (i) and (ii) is satisfied that (i) after the sub-step A, the method further includes a sub-step B of bringing an aqueous solution containing a chemical compound that generates an organic anion and a divalent metal ion (excluding a transition metal ion) into contact with the anode body, and (ii) before the sub-step A, the method further includes a sub-step C of preparing the treatment liquid by mixing the aqueous solution containing the chemical compound with a liquid composition containing the conjugated polymer and the polymer dopant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrolytic capacitor and an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor includes, for example, an anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte (conductive polymer) covering at least a portion of the dielectric layer. The solid electrolyte is formed on the dielectric layer by in-situ polymerization such as chemical polymerization. Alternatively, the solid electrolyte may be formed by applying a liquid composition containing a conductive polymer (such as a conjugated polymer and a dopant) onto the dielectric layer and drying it.

[0003] Patent Document 1 proposes a conductive polymer characterized in that at least one organic sulfonate salt composed of an anion of an organic sulfonic acid and a cation other than a transition metal is coated on a matrix of a conductive polymer obtained by oxidative polymerization, or at least one organic sulfonate salt composed of an anion of an organic sulfonic acid and a cation other than a transition metal is contained in the matrix of the conductive polymer obtained by the above oxidative polymerization. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 014692 Summary of the Invention [Problem to be solved by the invention]

[0005] Reduces the variation in equivalent series resistance (ESR) when electrolytic capacitors are exposed to high humidity environments. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a method for manufacturing an electrolytic capacitor including a capacitor element including a solid electrolyte, the method comprising: providing an anode body having a dielectric layer on a surface thereof; forming a solid electrolyte covering at least a portion of the dielectric layer; The step of forming the solid electrolyte includes: a sub-step A of contacting the anode body with a treatment solution containing a conjugated polymer and a polymer dopant; (i) and (ii) below: (i) after the sub-step A, further comprising a sub-step B of contacting the anode body with an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion); (ii) before the sub-step A, a sub-step C of mixing an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion) with a liquid composition containing the conjugated polymer and the polymer dopant to prepare the treatment liquid; The present invention relates to a method for manufacturing an electrolytic capacitor that satisfies at least one of the above requirements.

[0007] A second aspect of the present disclosure is an electrolytic capacitor including a capacitor element including a solid electrolyte, an anode body having a dielectric layer on a surface thereof; and a solid electrolyte covering at least a portion of the dielectric layer and containing a metal element corresponding to a divalent metal ion (excluding a divalent transition metal ion), the solid electrolyte includes a first conductive polymer layer containing a conjugated polymer, a polymer dopant, and the metal element; The electrolytic capacitor relates to the metal element being dispersed throughout the first conductive polymer layer. [Effects of the Invention]

[0008] This reduces ESR fluctuations when electrolytic capacitors are exposed to high humidity environments. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] In high humidity environments (e.g., 70% RH or higher), moisture penetrates into the electrolytic capacitor, causing the dopant components to dissolve into the moisture. The dissolved dopant components diffuse throughout the electrolytic capacitor (especially in the solid electrolyte), lowering the pH. If the pH drops locally within the electrolytic capacitor, dedoping will proceed further, reducing the conductivity of the solid electrolyte. If the conductivity of the solid electrolyte decreases, the ESR will fluctuate significantly. The ESR fluctuations are most noticeable at relatively high temperatures (e.g., temperatures between 60°C and 120°C).

[0011] (Technical 1) In view of the above, a method for manufacturing an electrolytic capacitor according to a first aspect of the present disclosure is a method for manufacturing an electrolytic capacitor including a capacitor element containing a solid electrolyte. The method for manufacturing an electrolytic capacitor includes the steps of preparing an anode body having a dielectric layer on its surface, and forming a solid electrolyte that covers at least a portion of the dielectric layer. The step of forming the solid electrolyte includes a sub-step A of contacting the anode body with a treatment liquid containing a conjugated polymer and a polymer dopant. The step of forming the solid electrolyte includes the steps of (i) and (ii) below: (i) after the sub-step A, further comprising a sub-step B of contacting the anode body with an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion); (ii) before the sub-step A, a sub-step C of mixing an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion) with a liquid composition containing the conjugated polymer and the polymer dopant to prepare the treatment liquid; At least one of the following is satisfied.

[0012] According to the present disclosure, the process for forming a solid electrolyte includes the above-described substep A and at least one of substeps B and C. Specific examples of compounds that generate organic anions and divalent metal ions include salts of organic anions and divalent metal ions. Using such compounds in the process for forming a solid electrolyte using a treatment solution containing a conjugated polymer and a polymer dopant can reduce ESR fluctuations when the electrolytic capacitor is exposed to a high-humidity environment. This is believed to be because the divalent metal ions derived from the compounds capture the dopant dissolved in the water, thereby suppressing a decrease in pH in the solid electrolyte. The suppression of the decrease in pH in the solid electrolyte suppresses further undoping. These effects are believed to suppress a decrease in the conductivity of the solid electrolyte and a change in ESR. These effects are also observed when the electrolytic capacitor is exposed to a relatively high-temperature, high-humidity environment, and are more pronounced than when both (i) and (ii) are not satisfied.

[0013] (Technology 2) In the above (Technology 1), the organic anion may include an aromatic sulfonate anion. Aromatic sulfonate anions are easily dissociated in an aqueous solution or a treatment solution, and therefore divalent metal ions are easily generated from the compound. This can enhance the effect of capturing dopants.

[0014] (Technology 3) In the above (Technology 1) or (Technology 2), the divalent metal ion may be at least one selected from the group consisting of barium ions, calcium ions, and magnesium ions. Salts of these divalent metal ions and organic anions are easily dissociated in aqueous solutions or treatment solutions. In addition, they are less likely to degrade capacitor performance and are easy to capture dopants.

[0015] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the step of forming the solid electrolyte may further include Substep D, in which a polymerization solution containing a conjugated polymer precursor and a dopant is brought into contact with the anode body and the precursor is polymerized in the presence of the dopant. In this case, Substep A is performed after Substep D. A second conductive polymer layer is formed from the polymerization solution by in-situ polymerization so as to cover at least a portion of the dielectric layer of the anode body. Then, a first conductive polymer layer containing a conjugated polymer and a polymer dopant is formed so as to cover at least a portion of the second conductive polymer layer. Divalent metal ions (or metal elements corresponding to divalent metal ions) are dispersed in the first conductive polymer layer. This reduces leakage current and suppresses undoping. This further reduces ESR fluctuations when the electrolytic capacitor is exposed to a high-humidity environment.

[0016] (Technology 5) In any one of the above (Technology 1) to (Technology 4), the concentration of the organic anion and the compound that generates the divalent metal ion contained in the aqueous solution in (i) may be 1% by mass or more and 10% by mass or less. In this case, the divalent metal ion can be more uniformly dispersed in the solid electrolyte, the dopant capturing effect is enhanced, and leakage current can be suppressed.

[0017] (Technology 6) In any one of the above (Technology 1) to (Technology 5), the concentration of the compound that generates the organic anion and the divalent metal ion contained in the treatment solution in (ii) may be 0.2 mass % or more and 3.0 mass % or less. In this case, the divalent metal ions can be more uniformly dispersed in the solid electrolyte, the dopant capturing effect is enhanced, and leakage current can be suppressed.

[0018] (Technology 7) Any one of the above (Technology 1) to (Technology 6) may further include a step of heat-treating the anode body after sub-step A, or after sub-step B if sub-step B is performed. In the step of heat-treating the anode body, the heat treatment may be performed at a temperature of 80°C or higher and 150°C or lower for 5 minutes or longer. Such a heat treatment step makes it possible to fix divalent metal ions in a more uniformly dispersed state in the solid electrolyte, and even if the dopant is eluted due to the penetration of moisture, it can be efficiently captured by the divalent metal ions.

[0019] (Technology 8) An electrolytic capacitor according to a second aspect of the present disclosure includes a capacitor element containing a solid electrolyte. The electrolytic capacitor includes an anode body having a dielectric layer on its surface, and a solid electrolyte covering at least a portion of the dielectric layer and containing a metal element corresponding to a divalent metal ion (excluding divalent transition metal ions). The solid electrolyte includes a conjugated polymer, a polymer dopant, and a first conductive polymer layer containing the metal element. The metal element is dispersed throughout the first conductive polymer layer. Hereinafter, the metal element corresponding to the divalent metal ion (excluding divalent transition metal ions) may be referred to as the first metal element.

[0020] Because the first metal element is dispersed throughout the first conductive polymer layer, even if moisture penetrates the first conductive polymer layer and the dopant dissolves, the divalent metal ions corresponding to the first metal element capture the dopant throughout the first conductive polymer layer. This prevents a decrease in pH in the first conductive polymer layer and further dedoping. Therefore, fluctuations in ESR can be suppressed when the electrolytic capacitor is exposed to a high-humidity environment (especially a relatively high-temperature, high-humidity environment).

[0021] (Technology 9) In the above (Technology 8), the metal element may be at least one selected from the group consisting of barium, calcium, and magnesium. Divalent metal ions corresponding to these metal elements are moderately likely to dissociate in an aqueous solution or treatment solution and easily diffuse into the first conductive polymer layer. In addition, they are unlikely to degrade capacitor performance and are likely to capture dopants.

[0022] (Technology 10) In the above (Technology 8) or (Technology 9), the solid electrolyte may include a second conductive polymer layer covering at least a portion of the dielectric layer, and the first conductive polymer layer covering at least a portion of the second conductive polymer layer. The second conductive polymer layer may include a conjugated polymer and a dopant. The content of the metal element (first metal element) in the first conductive polymer layer is higher than the content of the metal element (first metal element) in the second conductive polymer layer. The first conductive polymer layer contains a polymer dopant and is typically formed using a treatment solution containing at least a conjugated polymer and a polymer dopant. Such a first conductive polymer layer typically occupies a large portion of the solid electrolyte. The dispersion of a large amount of the first metal element throughout such a first conductive polymer layer makes it easier to capture eluted dopant, thereby suppressing a decrease in pH of the first conductive polymer layer and further reducing ESR fluctuations.

[0023] (Technology 11) In any one of (Technology 8) to (Technology 10) above, the electrolytic capacitor may include a carbon layer covering at least a portion of the surface of the first conductive polymer layer. After the electrolytic capacitor is left standing for 1000 hours at 85°C and 85% RH while applying a voltage 0.8 times the rated voltage, the metal element (first metal element) in the first conductive polymer layer may segregate at the interface between the first conductive polymer layer and the carbon layer. When the electrolytic capacitor is left standing under the above conditions, the first metal element contained in the first conductive polymer layer becomes ionized and more mobile due to the influence of moisture and applied voltage, and segregates at the interface. As the first metal element (or divalent metal ion) moves, it captures the dopant dissolved in the moisture in the first conductive polymer layer, thereby suppressing a decrease in the conductivity of the first conductive polymer layer and suppressing fluctuations in ESR, even when a voltage is applied for a long period of time under high temperature and high humidity as described above.

[0024] The electrolytic capacitor manufacturing method and electrolytic capacitor of the present disclosure will be described in more detail below, including the above-mentioned (Technology 1) to (Technology 11), with reference to the drawings as necessary. At least one of the above-mentioned (Technology 1) to (Technology 11) may be combined with at least one of the elements described below, provided that there is no technical contradiction.

[0025] [Manufacturing method of electrolytic capacitors] The capacitor element included in the electrolytic capacitor of the present disclosure includes, for example, an anode portion and a cathode portion. The anode portion includes an anode body. The anode portion may include an anode body and an anode wire. The cathode portion may include a solid electrolyte, or may include a solid electrolyte and a cathode extraction layer.

[0026] The method for manufacturing an electrolytic capacitor according to the present disclosure includes the steps of preparing an anode body having a dielectric layer on its surface (first step) and forming a solid electrolyte that covers at least a portion of the dielectric layer (second step). The manufacturing method may further include the step of forming a cathode extraction layer that covers at least a portion of the solid electrolyte (third step). A capacitor element included in an electrolytic capacitor is formed by performing steps one to three. The manufacturing method may further include the steps of connecting an anode lead terminal and a cathode lead terminal to the capacitor element, and sealing the capacitor element in a case or with an exterior body (such as a resin exterior body).

[0027] (1st step) The first step may include, for example, a sub-step of preparing an anode body and a sub-step of forming a dielectric layer on the surface of the anode body. Through these sub-steps, an anode body having a dielectric layer on its surface is prepared.

[0028] The anode body may contain a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. These materials may be used alone or in combination. Preferred examples of the valve metal include aluminum, tantalum, niobium, and titanium.

[0029] The anode body may be an anode foil, or may be a porous sintered body or a porous molded body of particles containing a valve metal. Each of the porous sintered body or molded body and the porous sintered body may be in the form of a sheet, a rectangular parallelepiped, a cube, or a similar shape.

[0030] From the viewpoint of obtaining a high capacity, the anode body preferably has a porous portion at least in the surface layer. The anode body has a large number of fine voids in the porous portion. Such a porous portion gives the anode body a finely uneven shape. The sintered body or molded body may be entirely porous. Each of the porous molded body and the porous sintered body may have a sheet-like shape, or may be a rectangular parallelepiped, a cube, or a shape similar thereto.

[0031] An anode body having a porous portion on its surface layer can be obtained, for example, by roughening the surface of a substrate (such as a sheet-like (e.g., foil-like, plate-like) substrate) containing a valve metal. The roughening may be performed, for example, by etching (electrolytic etching, chemical etching, etc.). Such an anode body has, for example, a core portion and porous portions formed on the surface of both the core portion and the core portion so as to be integrated with the core portion. A porous sintered body containing Ta element is preferred as the anode body.

[0032] The anode body may have an anode lead portion including a first end and a cathode forming portion including a second end opposite the first end. A cathode portion including a solid electrolyte is formed on the surface of the cathode forming portion of the anode body. The anode lead portion is used, for example, for electrical connection with an external electrode on the anode side. An anode lead terminal may be connected to the anode lead portion.

[0033] When the anode body is a porous sintered body or a porous molded body, the anode part may include an anode wire. In this case, the first step may include a step of preparing the anode wire and a step of embedding the anode wire in the anode body. By embedding one end of the anode wire in the anode body, an anode part including the anode body and the anode wire is formed.

[0034] The anode wire may be a wire made of metal. Examples of materials for the anode wire include the valve metals mentioned above, copper, or copper alloys. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from the end face of the anode body. The end of the anode wire that protrudes outward corresponds to the first end, and the end of the anode body opposite the first end corresponds to the second end.

[0035] In the first step, a dielectric layer is further formed on the surface of the anode body. The dielectric layer is formed by anodizing the valve metal on the surface of the anode body. Anodization is performed, for example, by chemical conversion treatment. The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body.

[0036] The dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these and may be any material that functions as a dielectric.

[0037] The dielectric layer is usually formed on the surface of the anode body. When the dielectric layer is formed on the surface of the porous portion of the anode body, the dielectric layer is formed along the inner wall surfaces of the pores in the porous portion and the depressions (pits) on the surface of the anode body.

[0038] (2nd process) In the second step, a solid electrolyte is formed so as to cover at least a portion of the dielectric layer. The second step includes a sub-step A in which a treatment liquid containing a conjugated polymer and a polymer dopant is brought into contact with the anode element having the dielectric layer. The treatment liquid may be a liquid dispersion or a solution. Examples of liquid media contained in the treatment liquid include water, organic liquid media (such as water-soluble organic liquid media), and mixtures thereof.

[0039] In the present disclosure, it is important to satisfy at least one of the following conditions (i) and (ii). This allows the solid electrolyte to contain a first metal element corresponding to a divalent metal ion. Even if moisture penetrates the solid electrolyte in a high-humidity environment and the dopant dissolves in the moisture in the solid electrolyte, it is captured by the divalent metal ion, which prevents a decrease in the surrounding pH and reduces fluctuations in ESR.

[0040] (i) The second step further includes, after the sub-step A, a sub-step B of contacting an aqueous solution containing an organic anion and a compound that generates a divalent metal ion (excluding a divalent transition metal ion) with the anode body having a dielectric layer. (ii) The second step further includes, before the sub-step A, a sub-step C of preparing a treatment liquid by mixing an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion) with a liquid composition containing a conjugated polymer and a polymer dopant.

[0041] Examples of organic anions include organic sulfonate anions, organic phosphonate anions, organic phosphinate anions, and organic carboxylate anions. The organic anions may be aliphatic, alicyclic, or aromatic. The organic anions may contain a heteroatom (such as a nitrogen atom, a sulfur atom, or an oxygen atom) in the organic moiety. The compound may contain one type of organic anion, or two or more types of organic anions. From the viewpoint of ease of dissociation of divalent metal ions in an aqueous solution or treatment solution, the organic anion preferably contains an organic sulfonate anion, and more preferably contains an aromatic sulfonate anion.

[0042] The divalent metal ion preferably includes a metal ion of Group 2 of the periodic table, and is preferably at least one selected from the group consisting of barium ion, calcium ion, and magnesium ion.

[0043] A compound capable of generating an organic anion and a divalent metal ion is added to the aqueous solution or treatment solution, and the organic anion and the divalent metal ion are generated in the aqueous solution or treatment solution. The aqueous solution or treatment solution containing these ions is used in substep B or substep C of the second process. Such a compound may be a salt of the organic anion and the divalent metal ion.

[0044] The concentration of the compound that generates organic anions and divalent metal ions contained in the aqueous solution in (i) above may be 10% by mass or less, or may be 7% by mass or less. The concentration of the compound in the aqueous solution may be 1% by mass or more. When the concentration of the compound in the aqueous solution is within this range, the divalent metal ions can be more uniformly dispersed in the solid electrolyte, thereby enhancing the effect of capturing the dopant.

[0045] The concentration of the compound that generates organic anions and divalent metal ions contained in the treatment solution in (ii) above may be 0.2% by mass to 3.0% by mass, or 0.3% by mass to 2.5% by mass. When the concentration of the compound in the treatment solution is in this range, the divalent metal ions can be more uniformly dispersed in the solid electrolyte, and the dopant capturing effect is enhanced.

[0046] The second step may further include a step of heat-treating the anode element to which the treatment liquid has been applied after sub-step A. When the second step includes sub-step B, the second step may further include a step of heat-treating the anode element to which the aqueous solution has been applied after sub-step B. These heat treatment steps dry the liquid medium contained in the applied treatment liquid or aqueous solution.

[0047] The temperature in the heat treatment step can be selected depending on the type of liquid medium, and may be 80°C or higher and 150°C or lower, or 95°C or higher and 120°C or lower.

[0048] The heating time in the heat treatment step may be 1 minute or more, 5 minutes or more, or 10 minutes or more. Heat treatment for 5 minutes or more can effectively remove the liquid medium (especially moisture). The heating time may be 60 minutes or less.

[0049] The second step may include a substep D prior to the substep A. In the substep D, a polymerization solution containing a conjugated polymer precursor and a dopant is brought into contact with an anode element having a dielectric layer, and the precursor is polymerized in the presence of the dopant. In the substep D, polymerization of the precursor proceeds on the dielectric layer to form a second conductive polymer layer containing the conjugated polymer and the dopant. The second conductive polymer layer is formed so as to cover at least a portion of the dielectric layer. Then, in the substep A, a first conductive polymer layer is formed so as to cover at least a portion of the second conductive polymer layer, thereby forming a solid electrolyte (in other words, a solid electrolyte layer) containing the second conductive polymer layer and the first conductive polymer layer. By satisfying at least one of the above (i) and (ii), divalent metal ions (or a first metal element corresponding to the divalent metal ions) can be dispersed and present in the first conductive polymer layer. This suppresses undoping. Therefore, fluctuations in ESR when the electrolytic capacitor is exposed to a high-humidity environment can be further reduced.

[0050] In the solid electrolyte, the anionic group of the organic anion (such as a sulfo group or a carboxy group) may be contained in a free form, an anionic form, or a salt form, or may be contained in a form bound to or interacting with other components such as a conjugated polymer. In this specification, all of these forms may be simply referred to as an "anionic group," "sulfo group," or "carboxy group."

[0051] Conjugated polymers contained in the solid electrolyte (each of the first and second conductive polymer layers) include π-conjugated polymers. Examples of such conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The monomer unit may also include a monomer unit having a substituent. The above polymers may also include homopolymers and copolymers of two or more monomers. For example, polythiophenes include PEDOT (poly(3,4-ethylenedioxythiophene)).

[0052] The polymer dopant contained in the solid electrolyte or the first conductive polymer layer may be a polymer anion. The polymer dopant may be a polymer having multiple sulfo groups. The polymer dopant may have other anionic groups (e.g., carboxy groups) in addition to the sulfo groups.

[0053] An example of a polymer dopant having a sulfo group is polymeric polysulfonic acid. Specific examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products having substituents), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolac resin. However, the polymer dopant is not limited to these specific examples. The solid electrolyte or the first conductive polymer layer may contain one type of polymer dopant or a combination of two or more types.

[0054] The total concentration of the conjugated polymer and the polymer dopant in the treatment liquid may be 1% by mass or more and 6% by mass or less, or may be 2% by mass or more and 4% by mass or less.

[0055] When forming the second conductive polymer layer, for example, a polymerization liquid containing a precursor of the conjugated polymer and a dopant is used. Examples of the dopant include aromatic sulfonic acids (naphthalenesulfonic acid, p-toluenesulfonic acid, etc.). However, the dopant is not limited to these.

[0056] The polymerization liquid may contain an oxidizing agent, which may also function as a dopant. The oxidizing agent is Fe 3+ Examples of the oxidizing agent include compounds capable of generating oxidizing agent (such as ferric sulfate and iron p-toluenesulfonate), persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. The oxidizing agent can be used alone or in combination of two or more.

[0057] Examples of precursors of conjugated polymers include raw material monomers of conjugated polymers, oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together, etc. One type of precursor may be used, or two or more types may be used in combination.

[0058] The polymerization liquid usually contains a solvent, such as water, an organic solvent, or a mixed solvent of water and an organic solvent (such as a water-soluble organic solvent).

[0059] In the solid electrolyte, the polymer dopant or the anionic group of the dopant (such as a sulfo group or a carboxy group) may be contained in a free form, an anion form, or a salt form, or may be contained in a form bonded to or interacting with the conjugated polymer. In this specification, all of these forms may be simply referred to as an "anionic group," "sulfo group," "carboxy group," or the like.

[0060] In the present disclosure, the second step satisfies at least one of the above conditions (i) and (ii), so that the content of the first metal element in the first conductive polymer layer can be made higher than the content of the first metal element in the second conductive polymer layer, which makes it easier to obtain a low initial ESR and further suppresses fluctuations in ESR when the electrolytic capacitor is exposed to a high-humidity environment for a long period of time.

[0061] (3rd step) In the third step, a cathode extraction layer may be formed so as to cover at least a portion of the solid electrolyte.

[0062] The cathode extraction layer may include at least a first layer that is in contact with the solid electrolyte and covers at least a portion of the solid electrolyte, and may include a first layer and a second layer that covers the first layer. The first layer may be formed so as to cover at least a portion of the solid electrolyte. A second layer may be further laminated so as to cover the formed first layer. In this manner, the cathode extraction layer is formed. Each layer is formed according to the type of each layer.

[0063] Examples of the first layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be composed of a first layer containing conductive carbon (also referred to as a carbon layer) and a second layer containing metal powder or metal foil. When metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil.

[0064] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer is formed, for example, by applying a composition (slurry or paste, etc.) containing conductive carbon so as to cover at least a portion of the solid electrolyte and drying it. The composition may contain a resin (binder resin). The resin may be a thermoplastic resin, or a thermosetting resin such as an imide resin or an epoxy resin.

[0065] The second layer containing metal powder can be formed, for example, by laminating a composition (such as a paste) containing metal powder on the surface of the first layer. Examples of such second layers include metal particle-containing layers (such as a metal paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). While thermoplastic resins can be used as the resin, it is preferable to use thermosetting resins such as imide resins and epoxy resins.

[0066] The metal foil is disposed so as to be laminated on a base layer (for example, a solid electrolyte). When a metal foil is used as the first layer, the type of metal is not particularly limited. It is preferable to use a valve metal (aluminum, tantalum, niobium, etc.) or an alloy containing a valve metal for the metal foil. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0067] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0068] (others) The manufacturing method can further include steps of connecting an anode lead terminal and a cathode lead terminal to the capacitor element, and sealing the capacitor element in a case or with an exterior body (such as a resin exterior body).

[0069] In the capacitor element, one end of a cathode lead terminal may be electrically connected to the cathode extraction layer. The cathode lead terminal is bonded to the cathode extraction layer via a conductive adhesive applied to the cathode extraction layer, for example. One end of an anode lead terminal may be electrically connected to the anode extraction portion of the anode body. The other end of the anode lead terminal and the other end of the cathode lead terminal are each extracted from the resin exterior body or the case. The other end of each terminal exposed from the resin exterior body or the case is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted, for example. Furthermore, instead of extracting a lead terminal, at least one end face of the anode portion and the cathode portion may be exposed from the outer surface of the sealing body and electrically connected to an external electrode.

[0070] The capacitor element is sealed using a resin outer package or case. For example, the capacitor element and the resin material of the outer package (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin outer package by transfer molding, compression molding, or the like. At this time, the other end portions of the anode lead terminal and the cathode lead terminal connected to the anode lead drawn from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case so that the other end portions of the anode lead terminal and the cathode lead terminal are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor. The leads may be wire-shaped or frame-shaped (e.g., lead frame).

[0071] [Electrolytic capacitor] An electrolytic capacitor according to a second aspect of the present disclosure includes a capacitor element containing a solid electrolyte. Such an electrolytic capacitor is formed, for example, by the above-described method for manufacturing an electrolytic capacitor. For the components of the electrolytic capacitor, the description of the method for manufacturing an electrolytic capacitor can be referred to.

[0072] The electrolytic capacitor of the present disclosure includes an anode body having a dielectric layer on its surface, and a solid electrolyte covering at least a portion of the dielectric layer and including a metal element (first metal element) corresponding to a divalent metal ion (excluding a divalent transition metal ion). In the electrolytic capacitor, the solid electrolyte may form a solid electrolyte layer.

[0073] The solid electrolyte includes a first conductive polymer layer containing a conjugated polymer (first conjugated polymer), a polymer dopant (first dopant), and a first metal element. The solid electrolyte may include a second conductive polymer layer covering at least a portion of the dielectric layer, and a first conductive polymer layer covering at least a portion of the second conductive polymer layer. The second conductive polymer layer may include a conjugated polymer (second conjugated polymer) and a dopant (second dopant).

[0074] As described above, the content of the first metal element in the first conductive polymer layer may be higher than the content of the first metal element in the second conductive polymer layer, which can be achieved by forming the solid electrolyte (particularly the first conductive polymer layer) in the second step of the production method so as to satisfy at least one of (i) and (ii).

[0075] The form of the first metal element in each of the solid electrolyte, the first conductive polymer layer, and the second conductive polymer layer is not particularly limited. For example, at least one element selected from the group consisting of barium, calcium, and magnesium may be dispersed throughout the first conductive polymer layer. In each of the solid electrolyte, the first conductive polymer layer, and the second conductive polymer layer, the first metal element may be contained in the form of metal ions, or may be contained in a state in which the metal ions interact with or are bonded to other components such as a dopant or polymer dopant, or may be contained in the form of a compound containing a salt.

[0076] The first metal element may be dispersed throughout the first conductive polymer layer. By having the first metal element dispersed throughout the first conductive polymer layer, the eluted dopant can be captured, the decrease in pH can be suppressed, and further dedoping can be suppressed. Therefore, fluctuations in ESR when the electrolytic capacitor is exposed to a high-humidity environment can be suppressed.

[0077] For example, when the thickness of the first conductive polymer layer is T, the presence probability Pb of the first metal element present in the region from the surface of the dielectric layer of the first conductive polymer layer to 0.5T, and the presence probability Pt of the first metal element present in the region from the position of 0.5T from the surface of the dielectric layer of the first conductive polymer layer to the outermost surface may satisfy 0.8 < Pb / Pt < 1.2.

[0078] When the electrolytic capacitor is left standing for 1000 hours while applying a voltage 0.8 times the rated voltage at 85°C and 85% RH, after standing, in the first conductive polymer layer, the first metal element segregates on the surface opposite to the dielectric layer. In the first conductive polymer layer, when at least a part of the first conductive polymer layer is covered by the cathode lead-out layer (such as the first layer like a carbon layer) on the side opposite to the dielectric layer, it corresponds to the interface between the first conductive polymer layer and the cathode lead-out layer (such as the first layer like a carbon layer). Therefore, the first metal element may segregate at this interface. Even in such a case, a decrease in the conductivity of the first conductive polymer layer can be suppressed, and fluctuations in ESR can be suppressed.

[0079] The distribution state of elements in the electrolytic capacitor or capacitor element is analyzed by elemental mapping using an electron probe microanalyzer (EPMA) on the cross-section of the electrolytic capacitor or capacitor element.

[0080] EPMA analysis is performed on samples of exposed cross sections of electrolytic capacitors or capacitor elements, including the anode body and the cathode portion containing a solid electrolyte, coated with a platinum film. In the cross-sectional image of the anode body with the cathode portion formed, elemental mapping is performed using EPMA to measure the net intensity of the elements contained in the region from the anode body to the outermost surface of the cathode extraction layer, based on differences in the wavelength of characteristic X-rays. The net intensity is the measured value for each element, subtracting background (noise). The net intensity of the target element (e.g., the first metal element, the S element contained in the conductive polymer) is determined in specific regions of the solid electrolyte layer (e.g., the first conductive polymer layer, the second conductive polymer layer, the surface portion of the solid electrolyte opposite the dielectric layer, the interface between the first conductive polymer layer and the first layer of the cathode extraction layer, the surface of the second layer of the cathode extraction layer, and its vicinity). For each region, the net intensity of the target element is determined in multiple regions (e.g., five regions), and the average value is calculated to determine the relative abundance ratio of the target element in each region. The conditions for the EPMA analysis are as follows: Measurement equipment: JEOL JSM-7900F (field emission scanning electron microscope) Detector: JEOL XM-86030 Measurement environment: 25°C, atmospheric pressure Accelerating voltage: 15.0 kV Beam current: 50.4nA Integration time: 50.0 ms / point (12 min mode) Spectroscopic crystal: AP / CH1, PbST / CH2, PET / CH3, LiF / CH4, LSA80 / CH5

[0081] An analytical sample can be prepared, for example, by the following procedure. First, a solid electrolytic capacitor or capacitor element is embedded in a curable resin, and the curable resin is cured. The anode body has a first end and a second end opposite the first end, and a solid electrolyte is formed on the second end of the anode body. The cured product obtained above is wet- or dry-polished at a predetermined position in the direction from the first end to the second end of the anode body (i.e., the longitudinal direction of the anode body or capacitor element) so as to expose a cross section perpendicular to the longitudinal direction of the capacitor element and parallel to the thickness direction. The exposed cross section is smoothed by ion milling. A platinum film with a thickness of 1 nm to 2 nm is formed on the smoothed cross section by sputtering platinum (Pt) using a sputtering device. In this way, an analytical sample is obtained. Note that the cross section is measured at a position greater than 0 and not greater than 0.05 from the end of the region where the solid electrolyte is formed on the second end side, where the length of the region where the solid electrolyte is formed in the direction parallel to the longitudinal direction of the capacitor element is 1. Pb and Pt are also determined in a similar manner.

[0082] In the first conductive polymer layer, the amount of the polymer dopant contained in the solid electrolyte may be 10 parts by mass or more and 1000 parts by mass or less, or 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0083] (others) An electrolytic capacitor includes at least one capacitor element. The electrolytic capacitor may be a wound type, and may be either a chip type or a stacked type. For example, the electrolytic capacitor may include multiple stacked capacitor elements. Alternatively, the electrolytic capacitor may include two or more wound capacitor elements. The configuration of the capacitor element may be selected depending on the type of electrolytic capacitor.

[0084] FIG. 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure. Electrolytic capacitor 20 includes a capacitor element 10 including an anode portion 6 and a cathode portion 7, an exterior body 11 that seals capacitor element 10, an anode lead frame 13 electrically connected to anode portion 6, and a cathode lead frame 14 electrically connected to cathode portion 7.

[0085] The anode part 6 has an anode body 1 and an anode wire 2. A portion of the anode wire 2 is embedded in the anode body 1, and the remainder protrudes outward from the outer surface of the anode body 1. A portion of the first portion of the anode lead frame 13 is joined to the protruding portion of the anode wire 2 by welding or the like, and is electrically connected to it.

[0086] A dielectric layer 3 is formed on the surface of the anode body 1. The cathode portion 7 has a solid electrolyte layer 4 covering at least a portion of the dielectric layer 3, and a cathode extraction layer 5 covering at least a portion of the surface of the solid electrolyte layer 4. The cathode extraction layer 5 has a carbon layer (first layer) formed so as to cover at least a portion of the surface of the solid electrolyte layer 4, and a metal particle-containing layer (second layer) formed so as to cover at least a portion of the carbon layer. A portion of the first portion of the cathode lead frame 14 is adhered to and electrically connected to the cathode extraction layer 5 via a conductive adhesive layer 8.

[0087] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0088] Examples 1 to 3 (1) Fabrication of electrolytic capacitors An electrolytic capacitor was fabricated as follows. (1st step) Tantalum metal particles were used as the valve metal. The tantalum metal particles were molded into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and the molded body was then sintered in a vacuum. This resulted in an anode part including an anode body made of a porous tantalum sintered body and an anode wire with one end embedded in the anode body and the remaining portion embedded in one surface of the anode body.

[0089] Next, the anode body and a portion of the anode wire embedded in the anode body were immersed in an electrolytic bath filled with an aqueous phosphoric acid solution, and the other end of the anode wire was connected to the anode body in the electrolytic bath. Anodization was then performed to form a uniform dielectric layer of tantalum oxide (Ta2O5) on the surface of the anode body (the surface of the porous sintered body, including the inner wall surfaces of the pores) and on the surface of part of the anode wire.

[0090] (2nd process) Next, 3,4-ethylenedioxythiophene (monomer), iron(III) p-toluenesulfonate, and 1-butanol were mixed to prepare a dispersion (polymerization solution). The anode body was immersed in this polymerization solution, then removed from the dispersion, and heat-treated in air. In this case, iron(III) p-toluenesulfonate served as both an oxidizing agent and a dopant. In this way, the monomer was polymerized on the dielectric layer, forming a second conductive polymer layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) through chemical polymerization. The anode body with the second conductive polymer layer formed was then washed.

[0091] Next, the anode body with the washed second conductive polymer layer formed was immersed in an aqueous dispersion containing PEDOT as a conjugated polymer and polystyrene sulfonic acid (PSS, Mw = 160,000) as a polymer dopant at a total concentration of 2 to 4 mass%. After immersion, the anode body was removed and dried under atmospheric pressure. In this way, a first conductive polymer layer containing PEDOT and PSS was formed to cover the second conductive polymer layer.

[0092] Next, an aqueous solution was prepared containing the salts shown in Table 1 at the concentrations shown in Table 1. The anode body having the first conductive polymer layer obtained above was immersed in this aqueous solution, removed, and dried for 10 minutes at 105° C. In this manner, an anode body having a solid electrolyte layer containing components derived from the salts shown in Table 1 was obtained.

[0093] (3rd step) A carbon paste and a metal paste were applied in this order to a predetermined area on the surface of the second conductive polymer layer, forming a cathode extraction layer consisting of a carbon layer (first layer) and a silver paste layer (second layer).In this way, a capacitor element was obtained.

[0094] The anode lead frame and cathode lead frame were placed on the capacitor element and sealed with an epoxy resin sealant to form an exterior housing, and then the anode lead frame and cathode lead frame protruding from the exterior housing were bent along the exterior housing to obtain electrolytic capacitors E1 to E3. A total of 20 electrolytic capacitors of each type were produced.

[0095] (2) Evaluation (a) ESR The initial ESR (R0) (mΩ) of the electrolytic capacitors was measured at a frequency of 100 kHz using a four-terminal LCR meter in an environment of 20°C. The initial ESR was then calculated as the arithmetic average value of 10 electrolytic capacitors.

[0096] Ten electrolytic capacitors whose initial ESR had been measured were subjected to a high-humidity test by being left in a high-temperature, high-humidity environment (85°C and 85% RH) for 1,000 hours while a voltage 0.8 times the rated voltage was continuously applied. After the high-humidity test, the electrolytic capacitors were cooled to 20°C. The ESR (R1) (μΩ) of the electrolytic capacitors after cooling was measured under the same conditions as for the initial ESR measurement. For each electrolytic capacitor, the ESR change was calculated by dividing the initial ESR (R0) by the ESR (R1) after cooling after the high-humidity test. The arithmetic mean (relative value) and standard deviation were calculated from the ESR change of the 10 electrolytic capacitors.

[0097] (b) Initial leakage current (LC) A 1 kΩ resistor was connected in series to the remaining 10 electrolytic capacitors used in the ESR measurement, and the leakage current (μA) was measured after applying a rated voltage of 10 V for 20 seconds using a DC power supply, and the median value (μA) of the leakage current for the 10 electrolytic capacitors was calculated.

[0098] Comparative Example 1 In the second step, the anode element having the first conductive polymer layer was not immersed in an aqueous solution containing a salt and dried. Except for this, an anode element having a solid electrolyte layer was prepared in the same manner as in Example 1, and an electrolytic capacitor was prepared using this anode element and evaluated.

[0099] Comparative Example 2 In the second step, an aqueous solution containing phenolsulfonic acid was used instead of the aqueous solution containing a salt. Except for this, an anode body including a solid electrolyte layer was produced in the same manner as in Example 1, and an electrolytic capacitor was produced using this anode body and evaluated.

[0100] Comparative Example 3 In the second step, a solid electrolyte layer composed only of a second conductive polymer layer was formed by chemical polymerization. A first conductive polymer layer was not formed using an aqueous dispersion. The polymerization time was adjusted so that the average thickness of the solid electrolyte layer was approximately the same as that of the solid electrolyte layer in Example 1. Except for these, an anode body including a solid electrolyte layer was fabricated in the same manner as in Example 1, and an electrolytic capacitor was fabricated using this anode body and evaluated.

[0101] The evaluation results are shown in Table 1. In Table 1, E1 to E3 are Examples 1 to 3, and C1 to C3 are Comparative Examples 1 to 3.

[0102] [Table 1]

[0103] As shown in Table 1, electrolytic capacitors with a first conductive polymer layer containing a component (particularly a first metal element) derived from an aqueous solution containing a compound (e.g., salt) that generates organic anions and divalent metal ions exhibited suppressed ESR fluctuations even after prolonged exposure to high-temperature, high-humidity environments (E1 to E3). They also exhibited low initial leakage currents (E1 to E3). In contrast, C1, whose first conductive polymer layer did not contain the first metal element, exhibited a low initial ESR, but exhibited significantly greater ESR fluctuations and ESR value variability after prolonged exposure to high-temperature, high-humidity environments. C2, which used phenolsulfonic acid, exhibited a relatively low initial ESR, but exhibited significant initial leakage current. Therefore, high-humidity testing was not possible. C3, which had a solid electrolyte layer formed solely from a chemically polymerized film, exhibited a higher initial ESR, a larger ESR fluctuation after high-humidity testing, and greater ESR variability compared to E1 to E3, even though the above-mentioned compound (e.g., salt) was used.

[0104] Furthermore, elemental mapping of the cross section of the electrolytic capacitor of Example 2 was performed using an EPMA according to the procedure described above. In the electrolytic capacitor immediately after fabrication, Ca and S elements were relatively uniformly dispersed in the first conductive polymer layer. Elemental mapping was performed in the same manner as above on the electrolytic capacitor after it was subjected to a high humidity test for ESR measurement. The results showed that S elements were distributed throughout the first conductive polymer layer, and Ca elements were segregated at the interface between the solid electrolyte layer and the carbon layer (first layer) of the cathode extraction layer. [Industrial Applicability]

[0105] The electrolytic capacitor and manufacturing method thereof disclosed herein can reduce the increase in ESR when the electrolytic capacitor is exposed to relatively high temperatures (or a relatively high-temperature, high-humidity environment). Because the solid electrolytic capacitor disclosed herein can maintain a stable low ESR even when exposed to relatively high temperatures for long periods of time, it can be used in a variety of applications requiring heat resistance, moisture resistance, or reliability. However, the applications of the electrolytic capacitor are not limited to these. [Explanation of symbols]

[0106] 20: Electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode extraction layer 6: Anode part 7: Cathode 8: Conductive adhesive layer 11: Exterior body 13: Anode lead frame 14: Cathode lead frame

Claims

1. 1. A method for manufacturing an electrolytic capacitor including a capacitor element including a solid electrolyte, comprising: providing an anode body having a dielectric layer on a surface thereof; forming a solid electrolyte covering at least a portion of the dielectric layer; The step of forming the solid electrolyte includes: a sub-step A of contacting the anode body with a treatment solution containing a conjugated polymer and a polymer dopant; The following (i) and (ii): (i) after the sub-step A, further comprising a sub-step B of contacting the anode body with an aqueous solution containing a compound that generates an organic anion and a divalent metal ion (excluding a divalent transition metal ion); (ii) before the sub-step A, a sub-step C of preparing the treatment liquid by mixing an aqueous solution containing an organic anion and a compound that generates a divalent metal ion (excluding a divalent transition metal ion) with a liquid composition containing the conjugated polymer and the polymer dopant; A method for manufacturing an electrolytic capacitor that satisfies at least one of the above requirements.

2. The method for producing an electrolytic capacitor according to claim 1 , wherein the organic anion includes an aromatic sulfonate anion.

3. 3. The method for producing an electrolytic capacitor according to claim 1, wherein the divalent metal ion is at least one selected from the group consisting of barium ions, calcium ions, and magnesium ions.

4. The step of forming the solid electrolyte includes: a sub-step D of polymerizing the precursor in the presence of the dopant while a polymerization solution containing a conjugated polymer precursor and a dopant is in contact with the anode body; The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein the sub-step A is performed after the sub-step D.

5. 3. The method for producing an electrolytic capacitor according to claim 1, wherein a total concentration of the compound that generates the organic anion and the divalent metal ion contained in the aqueous solution in (i) is 1% by mass or more and 10% by mass or less.

6. 3. The method for manufacturing an electrolytic capacitor according to claim 1, wherein a total concentration of the compound that generates the organic anion and the divalent metal ion contained in the treatment solution in (ii) is 0.2 mass % or more and 3.0 mass % or less.

7. further comprising a step of heat-treating the anode body after the sub-step A, or after the sub-step B if the sub-step B is performed, 3. The method for manufacturing an electrolytic capacitor according to claim 1, wherein the step of heat-treating the anode body comprises heat-treating the anode body at a temperature of 80° C. to 150° C. for 5 minutes or longer.

8. An electrolytic capacitor including a capacitor element including a solid electrolyte, an anode body having a dielectric layer on a surface thereof; and a solid electrolyte covering at least a portion of the dielectric layer and containing a metal element corresponding to a divalent metal ion (excluding a divalent transition metal ion), the solid electrolyte includes a first conductive polymer layer containing a conjugated polymer, a polymer dopant, and the metal element; The metal element is dispersed throughout the first conductive polymer layer.

9. 9. The electrolytic capacitor according to claim 8, wherein the metal element is at least one selected from the group consisting of barium, calcium, and magnesium.

10. the solid electrolyte includes a second conductive polymer layer covering at least a portion of the dielectric layer, and the first conductive polymer layer covering at least a portion of the second conductive polymer layer, the second conductive polymer layer contains a conjugated polymer and a dopant, 10. The electrolytic capacitor according to claim 8, wherein the content of the metal element in the first conductive polymer layer is higher than the content of the metal element in the second conductive polymer layer.

11. the electrolytic capacitor includes a carbon layer covering at least a portion of a surface of the first conductive polymer layer; 10. The electrolytic capacitor according to claim 8, wherein after the electrolytic capacitor is left to stand for 1000 hours at 85°C and 85% RH while a voltage that is 0.8 times the rated voltage is applied, the metal element in the first conductive polymer layer segregates at the interface between the first conductive polymer layer and the carbon layer.

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