Electrolytic capacitor and method for manufacturing the same

Abstract

This electrolytic capacitor is provided with a positive electrode body, a dielectric layer that covers the positive electrode body, a first solid electrolyte layer that covers the dielectric layer, and a second solid electrolyte layer that covers the first solid electrolyte layer. The first solid electrolyte layer contains a first conductive polymer that comprises a polypyrrole as a basic skeleton. The second solid electrolyte layer contains a second conductive polymer that comprises a polythiophene as a basic skeleton. The thickness of the second solid electrolyte layer is 1 μm or more.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor including a solid electrolyte layer and a method for manufacturing the same.

Background Art

[0002] An electrolytic capacitor includes a capacitor element, an electrode terminal electrically connected to the capacitor element, and an exterior body that seals the capacitor element. The capacitor element includes, for example, an anode body, a dielectric layer covering the anode body, and a solid electrolyte layer covering the dielectric layer.

[0003] The solid electrolyte layer contains a conductive polymer. As the conductive polymer, for example, polypyrrole is used (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, improvement of capacitance and reduction of leakage current of electrolytic capacitors have been demanded.

Means for Solving the Problems

[0006] One aspect of the present invention includes 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 contains a first conductive polymer having polypyrrole as a basic skeleton, the second solid electrolyte layer contains a second conductive polymer having polythiophene as a basic skeleton, and the thickness of the second solid electrolyte layer is 1 μm or more. The present invention relates to an electrolytic capacitor.

[0007] Another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, including: a first step of preparing an anode body on which a dielectric layer is formed; a second step of electrochemically polymerizing a precursor of a first conductive polymer having polypyrrole as a basic skeleton on the dielectric layer to form a first solid electrolyte layer containing the first conductive polymer; and a third step of attaching a treatment liquid containing a second conductive polymer having polythiophene as a basic skeleton to the first solid electrolyte layer to form a second solid electrolyte layer containing the second conductive polymer, wherein the thickness of the second solid electrolyte layer is 1 μm or more.

Advantages of the Invention

[0008] According to the present invention, for an electrolytic capacitor, it is possible to improve the capacitance and reduce the leakage current.

[0009] The novel features of the present invention are set forth in the appended claims. The present invention, both as to its construction and its content, will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings and in light of the other objects and features of the present invention.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure can be obtained. In addition, components other than the characteristic parts of the present disclosure may be applied with the components of known electrolytic capacitors. In this specification, when referring to "the range from numerical value A to numerical value B", this range includes numerical value A and numerical value B. When multiple materials are exemplified, one of them may be selected and used alone, or two or more of them may be used in combination.

[0012] An electrolytic capacitor according to an embodiment of the present invention includes 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 (hereinafter also referred to as the first layer) contains a first conductive polymer having polypyrrole as a basic skeleton (hereinafter also referred to as a polypyrrole-based polymer). The second solid electrolyte layer (hereinafter also referred to as the second layer) contains a second conductive polymer having polythiophene as a basic skeleton (hereinafter also referred to as a polythiophene-based polymer). The thickness of the second solid electrolyte layer is 1 μm or more. 90% by mass or more of the first layer penetrates into the pores of the anode body. 90% by mass or more of the second layer exists outside the pores of the anode body. The second layer may have a form of a skin layer formed along the outer shape ignoring the pores of the anode body.

[0013] When the above configuration is satisfied, it is possible to achieve both an improvement in capacitance and a reduction in leakage current.

[0014] The first layer contains a polypyrrole-based polymer and is easy to reduce leakage current, but it is difficult to improve capacitance. On the other hand, by disposing the second layer having a high conductivity on the first layer, the capacitance can be improved.

[0015] In addition, the second layer contains a polythiophene-based polymer and tends to increase the conductivity, but also tends to increase the leakage current. On the other hand, by increasing the thickness of the second layer to 1 μm or more, the increase in leakage current is significantly suppressed.

[0016] Since it is advantageous for the anode body to have a large surface area for forming the dielectric layer and the solid electrolyte layer, it usually has a porous portion at least on the surface (surface layer). The porous portion contains many pores (pits). The dielectric layer covers the outer surface of the porous portion and the inner wall surface of the pores. The first layer only needs to cover at least the inner wall surface of the pores of the porous portion via the dielectric layer. The first layer may cover the outer surface of the porous portion via the dielectric layer. In that case, the thickness of the first layer covering the outer surface of the porous portion may be smaller than the thickness of the first layer covering the inner wall surface of the pores of the porous portion. The second layer covers the outer surface of the porous portion via the dielectric layer (or the dielectric layer and the first layer). The second layer may further cover the inner wall surface of the pores of the porous portion via the dielectric layer and the first layer.

[0017] When the second treatment liquid described later contains a large amount of particles of the polythiophene-based polymer and / or when the particles of the polythiophene-based polymer contained in the second treatment liquid described later are large, it is easy to increase the thickness of the second layer to 1 μm or more. In this case, it is difficult to form the second layer inside the pores of the porous portion. The second layer may be formed on the outer surface of the porous portion so as to cover the openings of the pores of the porous portion. In this case, the second layer may be formed to slightly enter the opening side inside the pores of the porous portion. The second layer may be in direct contact with the first layer partially (near the openings of the pores of the porous portion). A gap may be formed between the first layer covering the inner wall surface of the pores of the porous portion and the second layer covering the outer surface (pore openings) of the porous portion.

[0018] When the thickness of the second layer (the thickness T2 of the second layer 9b in FIG. 2) is 1 μm or more, the leakage current can be reduced. From the viewpoint of reducing the leakage current, the thickness of the second layer is preferably 5 μm or more. The thickness of the second layer may be 1 μm or more and 20 μm or less, or may be 5 μm or more and 20 μm or less. When the thickness of the second layer is 20 μm or less, it is easy to reduce the ESR.

[0019] Note that the thickness of the second layer means the thickness of the second layer (thickness T2 in Fig. 2) that covers the outer surface of the porous portion of the anode body through the dielectric layer and the first layer. The thickness of the second layer can be determined by the following method. First, disassemble the electrolytic capacitor, take out the capacitor element, and obtain an image of the cross section of the capacitor element using a scanning electron microscope (SEM). Using the said image, measure the thicknesses of any 10 points of the second layer that covers the outer surface of the porous portion (outside the line defining the outer shape of the anode body) through the dielectric layer (or the dielectric layer and the first layer). Calculate the average value of the measured values of the said thicknesses. Note that the first layer and the second layer can be confirmed by analysis using SEM-EDX (energy dispersive X-ray spectroscopy).

[0020] The thickness of the first layer (thickness T1 of the first layer 9a in Fig. 2) may be 50 nm or more, or may be 50 nm or more and 100 nm or less. When the thickness of the first layer is 50 nm or more, it is easy to reduce the leakage current. When the thickness of the first layer is 100 nm or less, it is easy to cover the inner wall surface of the pores of the porous portion with the first layer through the dielectric layer. Note that the thickness of the first layer means the thickness of the first layer (thickness T1 in Fig. 2) that covers the inner wall surface of the porous portion through the dielectric layer. The thickness of the first layer can be determined by the same method as the thickness of the second layer. That is, in the cross-sectional image by SEM, measure the thicknesses of any 10 points of the second layer that covers the inner wall surface of the pores of the porous portion through the dielectric layer, and calculate the average value.

[0021] It is preferable that the first layer has a lower conductivity than the second layer. The second layer with a high conductivity is advantageous for improving the capacitance, but on the other hand, the leakage current is likely to increase. By covering the surface of the dielectric layer with the second layer through the first layer, which has a lower conductivity than the second layer and is advantageous for reducing the leakage current, it is easy to achieve both reduction of the leakage current and improvement of the capacitance.

[0022] From the viewpoint of reducing the leakage current, the conductivity of the first layer is preferably 200 S / cm or less, and more preferably 60 S / cm or more and 150 S / cm or less.

[0023] The conductivity of the first layer can be determined by the following method. Disassemble the electrolytic capacitor, take out the capacitor element, and analyze the components of the first layer (polypyrrole-based polymer and the first dopant). When forming the first layer using the first treatment liquid in the second step described later, the first treatment liquid may be analyzed. As the analysis method, the TEM-EELS method (electron energy loss spectroscopy), the NMR method (nuclear magnetic resonance spectroscopy), Raman spectroscopy, etc. can be used. Based on the analysis results, a sample film (for example, 20 to 40 μm thick) containing the same components as the first layer is formed, and the conductivity of the sample film is determined as the conductivity of the first layer.

[0024] The first layer is usually formed by electrochemically polymerizing a precursor of a polypyrrole-based polymer in the presence of the first dopant. Therefore, a sample film containing the same components as the first layer can be formed by preparing a sample liquid containing a precursor of a polypyrrole-based polymer and the first dopant, immersing a metal substrate in the sample liquid, passing an electric current through the metal substrate, and electrochemically polymerizing the precursor. The first treatment liquid may be used to form the sample film. For measuring the conductivity of the sample film, Loresta-GX and PSP probes manufactured by Nitto Seiko Analytic Co., Ltd. can be used.

[0025] From the viewpoint of improving the capacitance, the conductivity of the second layer is preferably 350 S / cm or more, and more preferably 350 S / cm or more and 800 S / cm or less. The conductivity of the second layer can be determined by the same method as that of the first layer. Based on the analysis results, a sample film (for example, 20 to 40 μm thick) containing the same components as the second layer is formed, and the conductivity of the sample film may be determined as the conductivity of the second layer. A sample film containing the same components (polythiophene-based polymer and the second dopant) as the second layer can be formed by preparing a sample liquid containing a polythiophene-based polymer and the second dopant, applying the sample liquid to a substrate, and drying it. When forming the second layer using the second treatment liquid in the third step described later, the second treatment liquid may be analyzed, and the second treatment liquid may be used to form the sample film.

[0026] Hereinafter, the electrolytic capacitor and its manufacturing method will be described more specifically. [Electrolytic Capacitor] (Anode body) The anode body can include valve - acting metals, alloys containing valve - acting metals, compounds containing valve - acting metals, etc. These materials can be used alone or in combination of two or more. As the valve - acting metal, for example, aluminum, tantalum, niobium, and titanium are preferably used. The anode body may have a porous portion on its surface layer. Such an anode body can be obtained, for example, by roughening the surface of a base material (such as a foil - shaped or plate - shaped base material) containing a valve - acting metal by etching or the like. Also, the anode body may be a molded body of particles containing a valve - acting metal or a sintered body thereof. Since the sintered body has a porous structure, the whole of the anode body can become a porous portion.

[0027] (Dielectric layer) The dielectric layer is formed by anodizing the valve - acting metal on the anode body surface by a formation treatment or the like. The dielectric layer only needs to be formed so as to cover at least a part of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the surface of the porous portion of the anode body, it is formed along the inner wall surfaces of the holes and depressions (pits) on the surface of the anode body.

[0028] The dielectric layer contains an oxide of the valve - acting metal. For example, when tantalum is used as the valve - acting metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve - acting metal, the dielectric layer contains Al2O3. Note that the dielectric layer is not limited to this, as long as it functions as a dielectric.

[0029] (Solid electrolyte layer) The solid electrolyte layer is formed so as to cover the dielectric layer. The solid electrolyte layer does not necessarily need to cover the whole (entire surface) of the dielectric layer, and only needs to be formed so as to cover at least a part of the dielectric layer. The solid electrolyte layer includes a first layer containing a polypyrrole - based polymer and a second layer containing a polythiophene - based polymer formed on the first layer. When there is a region on the dielectric layer where the first layer is not formed, in this region, the second layer may be formed on the dielectric layer.

[0030] (First layer) The first layer contains a polypyrrole-based polymer. The polypyrrole-based polymer includes polypyrrole and its derivatives. The weight average molecular weight of the polypyrrole-based polymer is, for example, 100 or more and 100,000 or less. In this specification, the weight average molecular weight is the weight average molecular weight based on polystyrene measured by gel permeation chromatography (GPC).

[0031] The first layer usually contains a non-self-doped type polypyrrole-based polymer. In this case, the first layer contains a polypyrrole-based polymer (non-self-doped type) and a first dopant. In this case, the conductivity of the first layer can be adjusted according to the first dopant.

[0032] Examples of the non-self-doped type polypyrrole-based polymer include conductive polymers having no anionic groups (specifically, sulfonic acid groups, carboxy groups, phosphoric acid groups, phosphonic acid groups, and salts thereof) directly or indirectly bonded to the polypyrrole skeleton of the conductive polymer by covalent bonds.

[0033] The first dopant may be a low molecular weight dopant. The low molecular weight dopant is, for example, a dopant capable of forming anions. Specific examples of the low molecular weight dopant include sulfuric acid, nitric acid, phosphoric acid, boric acid, organic sulfonic acids, etc. Examples of the organic sulfonic acid include aromatic sulfonic acids. Examples of the aromatic sulfonic acid include benzenesulfonic acid, alkylbenzenesulfonic acid (for example, paratoluenesulfonic acid), naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, etc.

[0034] In the first layer, the first dopant may form a polypyrrole-based polymer and a polypyrrole-based polymer composite. In the first layer, the first dopant may be contained in the form of an anion or in the form of a salt.

[0035] The content of the first dopant in the first layer is, for example, 10 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the polypyrrole-based polymer.

[0036] The first layer may contain a conductive polymer other than a polypyrrole-based polymer, but preferably contains a large amount of a polypyrrole-based polymer. The ratio of the polypyrrole-based polymer in the total conductive polymer contained in the first layer is, for example, 90% by mass or more, and may be 100% by mass.

[0037] The first layer may be a single layer or may be composed of a plurality of layers. When the first layer is composed of a plurality of layers, the polypyrrole-based polymers contained in each layer may be the same or different. The first layer may further contain other components as long as the effects of the present invention are not impaired.

[0038] (Second layer) The second layer contains a polythiophene-based polymer. The polythiophene-based polymer includes polythiophene and its derivatives. Examples of the polythiophene-based polymer include poly(3,4-ethylenedioxythiophene) (PEDOT). In this case, the second layer has high conductivity and it is easy to obtain a high capacitance. The weight average molecular weight of the polythiophene-based polymer is, for example, 100 or more and 100,000 or less.

[0039] The second layer may contain a non-self-doped type polythiophene-based polymer. In this case, the second layer contains a polythiophene-based polymer (non-self-doped type) and a second dopant. In this case, the conductivity of the second layer can be adjusted according to the second dopant. When the polythiophene-based polymer is of the non-self-doped type, it is easy to disperse the particles of the polythiophene-based polymer in the second treatment liquid used in the subsequent third step (formation of the second layer), and it is easy to form a second layer with a large thickness.

[0040] Incidentally, examples of the non-self-doped type polythiophene-based polymer include conductive polymers that do not have an anionic group (specifically, a sulfonic acid group, a carboxy group, a phosphoric acid group, a phosphonic acid group, and salts thereof) directly or indirectly bonded to the polythiophene skeleton of the conductive polymer by a covalent bond.

[0041] The second dopant may be a polymer dopant. The polymer dopant is, for example, a dopant capable of forming a polyanion. Specific examples of the polymer dopant include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, and the like.

[0042] In the second layer, the second dopant may form a polythiophene-based polymer and a polythiophene-based polymer composite. In the second layer, the second dopant may be contained in the form of a polyanion or in the form of a salt.

[0043] The content of the second dopant in the second layer is, for example, 0.1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polythiophene-based polymer.

[0044] The second layer may contain a conductive polymer other than the polythiophene-based polymer, but it is preferable that the content of the polythiophene-based polymer is large. The ratio of the polythiophene-based polymer in the total conductive polymer contained in the second layer is, for example, 90% by mass or more, and may be 100% by mass.

[0045] The second layer may be a single layer or may be composed of a plurality of layers. When the second layer is composed of a plurality of layers, the polythiophene-based polymers contained in each layer may be the same or different. The second layer may further contain other components within a range not impairing the effects of the present invention.

[0046] FIG. 1 is a cross-sectional view schematically showing the structure of an electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view schematically showing region II in FIG. 1. The electrolytic capacitor 1 includes a capacitor element 2, a resin sealing material (outer package) 3 that seals the capacitor element 2, and an anode terminal 4 and a cathode terminal 5, at least a part of each of which is exposed outside the resin sealing material 3. The anode terminal 4 and the cathode terminal 5 can be made of, for example, a metal (such as copper or a copper alloy). The resin sealing material 3 has a substantially rectangular parallelepiped outer shape, and the electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape. As the material of the resin sealing material 3, for example, an epoxy resin can be used.

[0047] The capacitor element 2 includes an anode body 6, a dielectric layer 7 covering the anode body 6, and a cathode portion 8 covering the dielectric layer 7. The cathode portion 8 includes a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode lead-out layer 10 covering the solid electrolyte layer 9. The cathode lead-out layer 10 has a carbon layer 11 and a silver paste layer 12.

[0048] The anode body 6 has a porous portion 6a and includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. The porous portion 6a includes a large number of holes P. The holes P may be sponge-like pits or tunnel-like pits. Among the regions of the anode body 6 that do not face the cathode portion 8, an insulating separation layer 13 is formed so as to cover the surface of the anode body 6 in a band shape in a portion adjacent to the cathode portion 8, and the contact between the cathode portion 8 and the anode body 6 is restricted. Among the regions of the anode body 6 that do not face the cathode portion 8, a part of the other regions is electrically connected to the anode terminal 4 by welding. The cathode terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed by a conductive adhesive.

[0049] The main surfaces 4S and 5S of the anode terminal 4 and the cathode terminal 5 are exposed from the same surface of the resin sealing material 3. This exposed surface is used for soldering connection with a substrate (not shown) on which the electrolytic capacitor 1 is to be mounted.

[0050] The carbon layer 11 only needs to have conductivity, and for example, it can be formed using a conductive carbon material (such as graphite). For the silver paste layer 12, for example, a composition containing silver powder and a binder resin (such as an epoxy resin) can be used. Note that the configuration of the cathode lead-out layer 10 is not limited to this, and any configuration having a current collecting function is acceptable.

[0051] The solid electrolyte layer 9 is formed so as to cover the dielectric layer 7. The dielectric layer 7 is formed along the surface of the anode body 6 (the inner wall surface and the outer surface S of the pores P in the porous portion 6a). The surface of the dielectric layer 7 has an uneven shape corresponding to the shape of the surface of the anode body 6. The solid electrolyte layer 9 is preferably formed so as to fill such unevenness of the dielectric layer 7.

[0052] The solid electrolyte layer 9 includes a first layer 9a and a second layer 9b. The first layer 9a is formed so as to cover the inner wall surface of the pores P in the porous portion 6a via the dielectric layer 7. As shown in FIG. 2, the first layer 9a does not necessarily cover the outer surface S of the porous portion 6a. The second layer 9b is formed so as to cover the outer surface S of the porous portion 6a via the dielectric layer 7. As shown in FIG. 2, the second layer 9b does not necessarily enter into the pores P of the porous portion 6a, and may be formed so as to cover the openings of the pores P in the porous portion 6a. In this case, a gap may exist between the first layer 9a and the second layer 9b within the pores P. The first layer 9a contains a polypyrrole-based polymer, and the second layer 9b contains a polythiophene-based polymer. The first layer 9a and the second layer 9b each have a thickness T1 and a thickness T2. The thickness T2 of the second layer 9b is 1 μm or more.

[0053] The first layer may further be formed so as to cover the outer surface S of the porous portion 6a via the dielectric layer 7. In this case, the second layer is formed so as to cover the outer surface S of the porous portion 6a via the dielectric layer and the first layer.

[0054] The electrolytic capacitor according to this embodiment is not limited to the electrolytic capacitor having the above structure, and can be applied to electrolytic capacitors having various structures. Specifically, the present invention can also be applied to an electrolytic capacitor using a sintered body of metal powder as an anode body, a wound-type electrolytic capacitor, and the like.

[0055] [Method for manufacturing an electrolytic capacitor] The method for manufacturing an electrolytic capacitor according to an embodiment of the present invention includes a first step of preparing an anode body on which a dielectric layer is formed, a second step of forming a first layer on the dielectric layer, and a third step of forming a second layer on the first layer. The first layer contains a polypyrrole-based polymer, and the second layer contains a polythiophene-based polymer. Further, the second layer has a thickness of 1 μm or more. By the second step and the third step, a solid electrolyte layer including the first layer and the second layer is formed. Further, the method for manufacturing an electrolytic capacitor may include a step of preparing an anode body prior to the first step. The manufacturing method may further include a step of forming a cathode lead-out layer and / or a step of sealing the capacitor element. Hereinafter, each step will be described in more detail.

[0056] (Step of preparing an anode body) In this step, an anode body is formed by a known method according to the type of the anode body. The anode body can be prepared, for example, by roughening the surface of a foil-shaped or plate-shaped base material containing a valve metal. By roughening, a porous portion is formed on the surface layer of the anode body. The roughening only needs to be able to form irregularities on the surface of the base material, and may be performed, for example, by etching (for example, electrolytic etching) the surface of the base material.

[0057] Further, a powder of a valve metal (for example, tantalum) is prepared, and a molded body molded into a desired shape (for example, a block shape) is obtained in a state where one end side in the longitudinal direction of a rod-shaped anode lead is embedded in this powder. By sintering this molded body, an anode body having a porous structure in which one end of the anode lead is embedded may be formed.

[0058] (First step) In the first step, a dielectric layer is formed on the anode body. The dielectric layer is formed by anodizing the anode body. Anodization can be performed by a known method, such as a chemical conversion treatment. The chemical conversion treatment can be performed, for example, by immersing the anode body in a chemical conversion solution to impregnate the surface of the anode body with the chemical conversion solution, and applying a voltage between the anode body as an anode and a cathode immersed in the chemical conversion solution. As the chemical conversion solution, for example, an aqueous phosphoric acid solution is preferably used.

[0059] (Second step) In the second step, it is preferable to electrochemically polymerize a precursor of a polypyrrole-based polymer on the dielectric layer to form a first layer containing the polypyrrole-based polymer. In the case of electrochemical polymerization, a conductive precoat layer may be formed prior to the electrochemical polymerization. In this case, the first layer may be formed directly on the dielectric layer or may be formed via the precoat layer.

[0060] In the case of electrochemical polymerization, for example, the first layer is formed using a first treatment solution containing a precursor of a polypyrrole-based polymer, a first dopant, and a dispersion medium (or solvent). The first layer may be formed, for example, by immersing the anode body on which the dielectric layer and the precoat layer are formed in the first treatment solution and supplying power from a supply electrode using the precoat layer as an electrode. The precoat layer is formed of, for example, a conductive material (such as a conductive polymer or an inorganic conductive material). The conductive material constituting the precoat layer is not particularly limited, and for example, known ones can be used.

[0061] Also, in the second step, the first layer may be formed by chemically polymerizing a precursor of a polypyrrole-based polymer. In the case of chemical polymerization, for example, the first layer is formed using a treatment solution containing a precursor of a polypyrrole-based polymer, a first dopant, an oxidizing agent, and a dispersion medium (or solvent). After the treatment solution is adhered to the dielectric layer, it may be heated.

[0062] Also, in the second step, a treatment solution containing a polypyrrole-based polymer, a first dopant, and a dispersion medium (or solvent) may be adhered to the dielectric layer to form the first layer.

[0063] As the polypyrrole-based polymer and the first dopant, those exemplified above can be used respectively. Examples of the precursor of the polypyrrole-based polymer include the monomer constituting the polypyrrole-based polymer and / or an oligomer in which several monomers are linked. Examples of the dispersion medium (or solvent) include water, an organic solvent, or a mixture thereof. Examples of the organic solvent include monohydric alcohols (such as methanol, ethanol, and propanol), polyhydric alcohols (such as ethylene glycol and glycerin), or aprotic polar solvents (such as N, N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone, and benzonitrile). The treatment liquid (first treatment liquid) may further contain other components.

[0064] (Third step) In the third step, for example, a second treatment liquid containing a polythiophene-based polymer is attached to the first layer to form a second layer containing the polythiophene-based polymer. For example, after immersing the anode body with the first layer formed on the dielectric layer in the second treatment liquid, it may be dried to form the second layer. After applying or dropping the second treatment liquid onto the anode body with the first layer formed on the dielectric layer, it may be dried to form the second layer.

[0065] The second treatment liquid contains a polythiophene-based polymer, a dispersion medium (or solvent), and, if necessary, a second dopant. As the polythiophene-based polymer and the second dopant, those exemplified above can be used. As the dispersion medium (or solvent), those exemplified in the second step can be used. The second treatment liquid may further contain other components.

[0066] As the second treatment liquid, for example, a dispersion (or solution) of a polythiophene-based polymer, or a dispersion (or solution) of a polythiophene-based polymer composite of a polythiophene-based polymer and a second dopant may be used. The second treatment liquid can be obtained, for example, by oxidatively polymerizing a precursor of a polythiophene-based polymer in a dispersion medium (or solvent). Examples of such a precursor include monomers constituting a polythiophene-based polymer and / or oligomers in which several monomers are linked. The second treatment liquid containing a polythiophene-based polymer composite can be obtained by oxidatively polymerizing a precursor of a polythiophene-based polymer in the presence of a second dopant in a dispersion medium (or solvent). Examples of the polythiophene-based polymer composite include PEDOT doped with PSS (PEDOT / PSS).

[0067] From the viewpoint of forming a second layer with a large thickness, the second treatment liquid may be a dispersion of a polythiophene-based polymer (or a polythiophene-based polymer composite). A non-self-doping type polythiophene-based polymer is less soluble in water than a self-doping type polythiophene-based polymer, and more particles of the polythiophene-based polymer (or the polythiophene-based polymer composite) can be dispersed in the second treatment liquid containing water, making it easier to form a second layer with a large thickness.

[0068] From the viewpoint of facilitating the formation of a second layer with a large thickness, the average particle diameter of the particles of the polythiophene-based polymer (or the polythiophene-based polymer composite) dispersed in the second treatment liquid may be 20 nm or more, 100 nm or more, or 150 nm or more. The upper limit of the average particle diameter is not particularly limited, but is, for example, 1000 nm or less. Here, the average particle diameter means the median diameter (D50) in the volume-based particle size distribution.

[0069] The average particle diameter of the polythiophene-based polymer (or polythiophene-based polymer composite) can be determined from the particle size distribution by the dynamic light scattering method (DLS). Specifically, the particles are dispersed by ultrasonic waves in water (in the second treatment liquid containing water), and the particle size distribution of the particles is measured on a volume basis using a dynamic light scattering type particle size distribution measuring device (LB-550 manufactured by HORIBA, Ltd.), and the median diameter (D50) thereof is taken as the average particle diameter.

[0070] (Step of forming the cathode extraction layer) In this step, a cathode extraction layer is formed by sequentially laminating a carbon layer and a silver paste layer on the second layer formed in the third step. By forming the cathode extraction layer, a capacitor element can be obtained.

[0071] Note that a conductive adhesive layer is disposed on the surface of the cathode extraction layer, and one end of the cathode terminal is electrically connected to the capacitor element through this adhesive layer. As the cathode terminal, an electrode terminal used in an electrolytic capacitor can be used without particular limitation. For example, a so-called lead frame may be used.

[0072] (Step of encapsulating the capacitor element with a resin encapsulant) The formed capacitor element is encapsulated with a resin material together with, for example, a part of each of the anode terminal and the cathode terminal. By this encapsulation, a resin encapsulant is formed. As the resin material, a thermosetting resin (such as an epoxy resin) or a resin composition is preferable. Note that the resin encapsulant includes a cured product of a thermosetting resin or a resin composition.

[0073] [Examples] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0074] 《Example 1》 (Step of forming a dielectric layer on the surface of the anode body) As the anode body, a sintered tantalum body (porous body) with a part of the anode lead embedded therein was prepared. The sintered tantalum body was a rectangular parallelepiped, and the anode lead was implanted from one end face of the rectangular parallelepiped. Anodic oxidation was performed on the anode body in an aqueous phosphoric acid solution to form a dielectric layer containing tantalum oxide (Ta2O5) on the surface of the anode body.

[0075] (Step of forming the first layer) An aqueous dispersion (first treatment solution) containing pyrrole and a first dopant (sulfonate having a naphthalene skeleton) was prepared. The concentration of pyrrole in the first treatment solution can be appropriately selected, for example, in the range of 1 to 6% by mass, and the concentration of the first dopant in the first treatment solution can be appropriately selected, for example, in the range of 3 to 12% by mass.

[0076] The anode body having the dielectric layer formed thereon was immersed in a treatment solution containing a conductive material to form a precoat layer. The anode body having the dielectric layer and the precoat layer formed thereon was immersed in the first treatment solution, and the electrolytic polymerization of pyrrole was allowed to proceed using the precoat layer as an electrode to form a first layer (conductivity: 80 S / cm) containing polypyrrole and the first dopant.

[0077] (Step of forming the second layer) An aqueous dispersion (second treatment solution) containing a polymer composite (PEDOT / PSS) of PEDOT (polythiophene-based polymer) and a second dopant (PSS) was prepared. The concentration of PEDOT / PSS in the second treatment solution can be appropriately selected, for example, in the range of 1 to 2% by mass. The average particle diameter of PEDOT / PSS was 200 nm.

[0078] The anode body having the first layer formed thereon was immersed in the second treatment solution, and then dried at 150 °C for 10 to 30 minutes once to form a second layer (conductivity: 400 S / cm). In this way, a solid electrolyte layer composed of the first layer and the second layer was formed. The thickness T1 of the first layer was 100 nm. The thickness T2 of the second layer was 1 μm.

[0079] (Step of forming the cathode lead-out layer) A carbon layer was formed by applying a dispersion of graphite particles in water to the surface of the solid electrolyte layer and then drying. Subsequently, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer, and then heated to cure the binder resin, thereby forming a silver paste layer. In this way, a cathode lead-out layer composed of a carbon layer and a silver paste layer was formed. In this way, a capacitor element was obtained.

[0080] (Step of encapsulating the capacitor element) An anode terminal (anode lead frame) was welded to the anode lead, a cathode terminal (cathode lead frame) was connected to the cathode lead-out layer with a conductive adhesive, and the capacitor element was encapsulated with a resin encapsulant. In this way, the electrolytic capacitor A1 of Example 1 was manufactured.

[0081] 《Example 2》 In the step of forming the second layer, the step of immersing the anode body on which the first layer was formed in the second treatment liquid was repeated twice, and the electrolytic capacitor A2 of Example 2 was manufactured in the same manner as in Example 1, except that the thickness T2 of the second layer was set to 5 μm.

[0082] 《Example 3》 In the step of forming the second layer, the step of immersing the anode body on which the first layer was formed in the second treatment liquid was repeated four times, and the electrolytic capacitor A3 of Example 3 was manufactured in the same manner as in Example 1, except that the thickness T2 of the second layer was set to 20 μm.

[0083] 《Example 4》 In the step of forming the second layer, the step of immersing the anode body on which the first layer was formed in the second treatment liquid was repeated six times, and the electrolytic capacitor A4 of Example 4 was manufactured in the same manner as in Example 1, except that the thickness T2 of the second layer was set to 30 μm.

[0084] 《Comparative Example 1》 The electrolytic capacitor B1 of Comparative Example 1 was manufactured in the same manner as in Example 1, except that a layer (conductivity: 80 S / cm) containing the same components as the first layer (polypyrrole and the first dopant) was formed as the second layer.

[0085] Comparative Example 2 In the step of forming the second layer, except that the water content in the second treatment liquid was increased (the viscosity of the second treatment liquid was lowered) and the thickness T2 of the second layer was set to 0.6 μm, an electrolytic capacitor B2 of Comparative Example 2 was produced in the same manner as in Example 1.

[0086] [Evaluation] The following evaluations were performed on the electrolytic capacitors of the Examples and Comparative Examples produced above. In an environment of 20°C, using an LCR meter for four-terminal measurement, the initial capacitance (μF) at a frequency of 120 Hz was measured. Also, in an environment of 25°C, the current value flowing after 40 seconds under a predetermined voltage was measured as the leakage current. The leakage current is measured at a voltage corresponding to the model (for example, 2.5V, 16V, 35V, etc.).

[0087] The evaluation results are shown in Table 1. In Table 1, the capacitance and leakage current are shown as relative values when the capacitance and leakage current of the electrolytic capacitor B1 of Comparative Example 1 are set to 100, respectively.

[0088]

Table 1

[0089] For electrolytic capacitors A1 to A4, higher capacitance and smaller leakage current were obtained than those of electrolytic capacitors B1 to B2.

[0090] Furthermore, for electrolytic capacitors A1 to A4, in an environment of 20°C, using an LCR meter for four-terminal measurement, the initial ESR (mΩ) at a frequency of 100 kHz was measured. As a result, all of electrolytic capacitors A1 to A4 showed good ESR. Among them, electrolytic capacitors A1 to A3 with the thickness T2 of the second layer being 1 to 20 μm obtained lower ESR.

Industrial Applicability

[0091] The electrolytic capacitor according to the present invention is suitably used for applications that require a high capacitance and a small leakage current for the electrolytic capacitor.

[0092] Although the present invention has been described with respect to its presently preferred embodiments, such disclosure should not be construed in a limiting sense. Various modifications and alterations will no doubt become apparent to those skilled in the art in the technology field to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims are to be construed to include all modifications and alterations without departing from the true spirit and scope of the present invention.

Description of Symbols

[0093] 1: Electrolytic capacitor, 2: Capacitor element, 3: Resin encapsulant, 4: Anode terminal, 4S: Main surface of anode terminal, 5: Cathode terminal, 5S: Main surface of cathode terminal, 6: Anode body, 7: Dielectric layer, 8: Cathode portion, 9: Solid electrolyte layer, 9a: First layer, 9b: Second layer, 10: Cathode lead-out layer, 11: Carbon layer, 12: Silver paste layer, 13: Separation layer, 14: Adhesive layer

Claims

A first step of preparing an anode body having a porous portion and a dielectric layer covering an inner wall surface and an outer surface of the porous portion; A second step of electrochemically polymerizing a precursor of a first conductive polymer having polypyrrole as a basic skeleton on the dielectric layer to cover the dielectric layer with a first solid electrolyte layer containing the first conductive polymer; A third step of attaching a treatment liquid containing a second conductive polymer having polythiophene as a basic skeleton to the first solid electrolyte layer covering the outer surface through the dielectric layer to form a second solid electrolyte layer containing the second conductive polymer, In the second step, the thickness of the portion of the first solid electrolyte layer covering the inner wall surface through the dielectric layer is set to 50 nm or more and 100 nm or less; In the third step, the thickness of the portion of the second solid electrolyte layer covering the outer surface through the first solid electrolyte layer and the dielectric layer is set to 1 μm or more and 20 μm or less; A method for manufacturing an electrolytic capacitor, wherein there is a region on the dielectric layer where the first solid electrolyte layer is not formed, and in this region, a second solid electrolyte layer is formed on the dielectric layer. Claim 2 The method for manufacturing an electrolytic capacitor according to claim 1, wherein the first solid electrolyte layer contains a non-self-doped type of the first conductive polymer. Claim 3 The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein the second solid electrolyte layer contains a non-self-doped type of the second conductive polymer. Claim 4 The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 3, wherein the thickness of the portion of the second solid electrolyte layer covering the outer surface through the first solid electrolyte layer and the dielectric layer is 5 μm or more.

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