Solid electrolytic capacitor element and method for manufacturing solid electrolytic capacitor element

Abstract

This solid electrolytic capacitor element 20 includes: a valve action metal base body 4 having a dielectric layer 5 on at least one main surface thereof; a solid electrolyte layer 7a provided on the dielectric layer 5; and a cathode foil 7c in direct contact with the solid electrolyte layer 7a. A joint surface 7c1 in direct contact with the solid electrolyte layer 7a of the cathode foil 7c is roughened. The solid electrolyte layer 87a includes an inner layer 7a1 formed on the surface of the dielectric layer 5 and an outer layer 7a2 formed on the surface of the inner layer 7a1. The outer layer 7a2 includes PEDOT-PSS fine particles and a binder.

Description

Solid electrolytic capacitor element and method for manufacturing the same

[0001] The present invention relates to a solid electrolytic capacitor element and a method for manufacturing a solid electrolytic capacitor element.

[0002] Patent Document 1 describes a method of forming a conductive polymer layer (solid electrolyte layer) by introducing a solution containing a monomer onto a dielectric film and polymerizing the monomer by chemical oxidation or electrolytic oxidation, and then describes a method of physically bonding the surface of a cathode current collector, which is a roughened metal sheet, directly to the conductive polymer layer.

[0003] Patent Document 2 describes a method of forming a cathode conductive layer by immersing an anodized film in a dispersion containing PEDOT and PVNA, applying carbon paint and silver paint, and bonding a cathode lead to the silver paint to obtain a solid electrolytic capacitor.

[0004] Patent Document 3 describes that PEDOT:PSS is used as a conductive polymer liquid, and a solid electrolyte layer is formed by immersing the entire valve action metal substrate having a dielectric layer in the conductive polymer blend liquid, and then bringing the solid electrolyte layer into contact with a metal foil having a carbon layer formed thereon or a metal foil that has been roughened.

[0005] JP 11-219861 A JP 2012-153867 A International Publication No. 2018 / 074408

[0006] The present inventors have found that when a metal foil having a roughened surface is used as the cathode foil to obtain a solid electrolytic capacitor element having a configuration in which the metal foil and the solid electrolyte layer are in direct contact with each other, the contact between the solid electrolyte layer and the metal foil is poor, and when a thermal load or the like is applied during use of the solid electrolytic capacitor element, damage may occur between the metal foil and the solid electrolyte layer, leading to problems such as an increase in ESR.

[0007] Furthermore, it was found that when a solid electrolyte layer containing PEDOT-PSS is brought into contact with a roughened surface of a metal foil and heated and pressurized during the manufacture of a solid electrolytic capacitor element, the adhesion of the solid electrolyte layer to the roughened surface may be insufficient, resulting in a weakened bond strength between the metal foil and the solid electrolyte layer.

[0008] The present invention has been made to solve the above problems, and has an object to provide a solid electrolytic capacitor element in which a solid electrolyte layer and a cathode foil are in direct contact with each other, and in which sufficient bonding strength is provided between the solid electrolyte layer and the cathode foil.

[0009] The solid electrolytic capacitor element of the present invention comprises a valve action metal substrate having a dielectric layer on at least one main surface thereof, a solid electrolyte layer provided on the dielectric layer, and a cathode foil in direct contact with the solid electrolyte layer, wherein the bonding surface of the cathode foil in direct contact with the solid electrolyte layer is roughened, and the solid electrolyte layer comprises an inner layer formed on the surface of the dielectric layer and an outer layer formed on the surface of the inner layer, and the outer layer comprises PEDOT-PSS fine particles and a binder.

[0010] The method for manufacturing a solid electrolytic capacitor element of the present invention includes the steps of: preparing a cathode foil having one surface, i.e., a bonding surface, roughened; preparing a valve action metal substrate having a dielectric layer formed on its surface; applying a dispersion liquid containing PEDOT-PSS fine particles and a binder onto the dielectric layer to form a solid electrolyte layer; and bringing the solid electrolyte layer into contact with the bonding surface of the cathode foil and applying heat and pressure.

[0011] According to the present invention, it is possible to provide a solid electrolytic capacitor element in which a solid electrolyte layer and a cathode foil are in direct contact with each other, and which has sufficient bonding strength between the solid electrolyte layer and the cathode foil.

[0012] FIG. 1 is a perspective view schematically illustrating an example of a solid electrolytic capacitor. FIG. 2 is a cross-sectional view of the solid electrolytic capacitor shown in FIG. 1 taken along line A-A. FIG. 3 is a side cross-sectional view showing an example of a solid electrolytic capacitor element included in the solid electrolytic capacitor. FIG. 4 is an enlarged side cross-sectional view schematically illustrating a partial structure of a solid electrolytic capacitor element. FIG. 5 is an enlarged perspective view schematically illustrating a bonding surface of a cathode foil. FIG. 6 is a perspective view schematically illustrating a state in which a capacitor element sheet and a cathode foil sheet are laminated. FIG. 7A is a schematic view schematically illustrating a process for forming a capacitor element sheet. FIG. 7B is a schematic view schematically illustrating a process for forming a capacitor element sheet. FIG. 7C is a schematic view schematically illustrating a process for forming a capacitor element sheet. FIG. 7D is a schematic view schematically illustrating a process for forming a capacitor element sheet. FIG. 8A is a perspective view schematically illustrating an example of a capacitor element sheet before singulation. FIG. 8B is a top view schematically illustrating an example of a capacitor element sheet before singulation. FIG. 9 is a perspective view schematically illustrating an example of a cathode foil sheet after singulation. Fig. 10 is a perspective view schematically showing an example of a cathode foil sheet before singulation, Fig. 11 is an exploded perspective view schematically showing a structure in which capacitor element sheets and cathode foil sheets are stacked after singulation, and Fig. 12 is an exploded perspective view schematically showing a state in which capacitor element sheets and cathode foil sheets are stacked.

[0013] The solid electrolytic capacitor element and the method for manufacturing the solid electrolytic capacitor element of the present invention will be described below. However, the present invention is not limited to the following configurations, and can be appropriately modified and applied within the scope of the present invention. Note that the present invention also includes a combination of two or more of the preferred configurations of each embodiment of the present invention described below.

[0014] [Solid Electrolytic Capacitor Element] The solid electrolytic capacitor element of the present invention comprises a valve action metal substrate having a dielectric layer on at least one main surface thereof, a solid electrolyte layer provided on the dielectric layer, and a cathode foil in direct contact with the solid electrolyte layer, wherein the bonding surface of the cathode foil in direct contact with the solid electrolyte layer is roughened, and the solid electrolyte layer comprises an inner layer formed on the surface of the dielectric layer and an outer layer formed on the surface of the inner layer, and the outer layer comprises PEDOT-PSS fine particles and a binder.

[0015] Solid electrolytic capacitor elements are included in solid electrolytic capacitors. FIG. 1 is a perspective view schematically showing an example of a solid electrolytic capacitor. FIG. 1 shows a resin molded body 9 that constitutes a solid electrolytic capacitor 1. The shape of the resin molded body that constitutes a solid electrolytic capacitor is not particularly limited, and any three-dimensional shape can be adopted. The shape of the resin molded body is preferably a rectangular parallelepiped. Furthermore, the term "rectangular parallelepiped" does not mean a perfect rectangular parallelepiped, and the surfaces that form the resin molded body may be tapered and not perpendicular to other surfaces, or the shape may have chamfered corners.

[0016] FIG. 1 shows a rectangular parallelepiped resin molded body 9. The resin molded body 9 has a length direction (L direction), a width direction (W direction), and a thickness direction (T direction). The resin molded body 9 has, as its outer surfaces, a first end face 9a and a second end face 9b that face each other in the length direction. An anode external electrode 11 is formed on the first end face 9a, and a cathode external electrode 13 is formed on the second end face 9b. The resin molded body 9 has, as its outer surfaces, a bottom face 9c and a top face 9d that face each other in the thickness direction. The resin molded body 9 also has, as its outer surfaces, a first side face 9e and a second side face 9f that face each other in the width direction.

[0017] In this specification, the surface extending along the length direction (L direction) and thickness direction (T direction) of the solid electrolytic capacitor or resin molding is referred to as the LT surface, the surface extending along the length direction (L direction) and width direction (W direction) is referred to as the LW surface, and the surface extending along the width direction (W direction) and thickness direction (T direction) is referred to as the WT surface.

[0018] FIG. 2 is a cross-sectional view of the solid electrolytic capacitor shown in FIG. 1 taken along line A-A. FIG. 3 is a side cross-sectional view showing an example of a solid electrolytic capacitor element included in the solid electrolytic capacitor. The solid electrolytic capacitor element 20 includes an anode 3 having a dielectric layer 5 on its surface, and a cathode 7 facing the anode 3. In the solid electrolytic capacitor 1, a plurality of solid electrolytic capacitor elements 20 are stacked to form a laminate 30, and the periphery of the laminate 30 is sealed with an exterior resin 8 to form a resin molded body 9. In the laminate 30, the stacked solid electrolytic capacitor elements 20 may be bonded to each other via a conductive adhesive (not shown). The laminate 30 may include only one solid electrolytic capacitor element 20.

[0019] The anode 3 includes a valve metal substrate 4 having a core and a porous portion formed along the surface of the core. A dielectric layer 5 is formed on the surface of the porous portion. The anode-side end face of the valve metal substrate 4 is connected to an anode external electrode 11 formed on a first end face 9 a (surface of the exterior resin) of the resin molded body 9 at the anode-side end face of the solid electrolytic capacitor element 20.

[0020] Examples of the valve metal constituting the valve metal substrate include simple metals such as aluminum, tantalum, niobium, titanium, zirconium, magnesium, and silicon, as well as alloys containing these metals. Among these, aluminum and aluminum alloys are preferred.

[0021] The shape of the valve metal substrate is not particularly limited, but is preferably flat, and more preferably foil-like. The porous portion is preferably an etching layer obtained by etching with hydrochloric acid or the like. The thickness of the valve metal substrate before etching is preferably 60 μm or more and 180 μm or less. The thickness of the unetched valve metal substrate (core portion) after etching is preferably 10 μm or more and 70 μm or less. The thickness of the porous portion is designed according to the withstand voltage and capacitance required for the electrolytic capacitor, and the combined thickness of the porous portions on both sides of the valve metal substrate is preferably 10 μm or more and 120 μm or less.

[0022] The dielectric layer is preferably made of an oxide film of the valve metal. For example, when aluminum foil is used as the valve metal substrate, an oxide film that serves as the dielectric layer can be formed by anodizing in an aqueous solution containing boric acid, phosphoric acid, adipic acid, or their sodium salts, ammonium salts, or the like. The dielectric layer is formed along the surface of the porous portion, thereby forming pores (recesses). The thickness of the dielectric layer is designed according to the withstand voltage and capacitance required for the electrolytic capacitor, but is preferably 3 nm or more and 200 nm or less.

[0023] The cathode 7 includes a solid electrolyte layer 7a formed on the dielectric layer 5 and a cathode foil 7c in direct contact with the solid electrolyte layer 7a. The cathode foil 7c is connected to a cathode external electrode 13 formed on the second end surface 9b (surface of the exterior resin) of the resin molded body 9 at the cathode side end surface of the solid electrolytic capacitor element 20. The cathode foil is preferably an aluminum foil or an aluminum alloy foil. A frame-shaped dam 6 is formed on the outer periphery of the solid electrolyte layer 7a. The dam 6 has insulating properties. The dam 6 limits the formation area of ​​the solid electrolyte layer 7a.

[0024] The exterior resin 8 constituting the resin molded body 9 contains at least a resin, preferably a resin and a filler. The resin is preferably an insulating resin such as an epoxy resin, a phenolic resin, a polyimide resin, a silicone resin, a polyamide resin, or a liquid crystal polymer. The resin molded body 9 may also be composed of two or more types of insulating resin. The exterior resin 8 can be in the form of either a solid or liquid resin. The filler is preferably inorganic particles such as ceramic particles (e.g., silica particles, alumina particles), or metal particles with an insulating surface. It is more preferable to use a material containing silica particles in a solid epoxy resin and a phenolic resin. When a solid sealant is used, a resin mold such as a compression mold or a transfer mold is preferably used to mold the resin molded body. Compression molding is more preferable. When a liquid sealant is used, a molding method such as a dispensing method or a printing method is preferably used.

[0025] An example of the anode external electrode 11 is a configuration including a conductive resin electrode layer 11b containing a conductive component and a resin component, and an outer plating layer 11c. The outer plating layer 11c is preferably a Ni plating layer or a Sn plating layer.

[0026] An example of the cathode external electrode 13 is a configuration including a conductive resin electrode layer 13b containing a conductive component and a resin component, and an outer plating layer 13c. The outer plating layer 13c is preferably a Ni plating layer or a Sn plating layer.

[0027] Figure 4 is an enlarged side cross-sectional view schematically illustrating a partial structure of a solid electrolytic capacitor element. In Figure 4, the solid electrolyte layer 7a is shown divided into an inner layer 7a1 and an outer layer 7a2. The inner layer 7a1 is formed on the surface of the dielectric layer 5, and the outer layer 7a2 is formed on the surface of the inner layer 7a1. The cathode foil 7c has bonding surfaces 7c1 and 7c2 on both sides. In Figure 4, the bonding surface 7c1 of the cathode foil 7c is in direct contact with the outer layer 7a2 of the solid electrolyte layer 7a. The bonding surface 7c1 of the cathode foil 7c is roughened (the opposite bonding surface 7c2 is also roughened).

[0028] The outer layer of the solid electrolyte layer contains PEDOT-PSS microparticles and a binder. The PEDOT-PSS microparticles are microparticles formed by combining PEDOT [poly(3,4-ethylenedioxythiophene)] and polystyrene sulfonic acid (PSS) as a dopant. The average particle diameter of the PEDOT-PSS microparticles is preferably 0.001 μm or more and less than 1 μm. The average particle diameter of the PEDOT-PSS microparticles in the outer layer can be measured by collecting a portion of the outer layer of the solid electrolyte layer of the solid electrolytic capacitor element, dissolving it in an organic solvent (DMSO (dimethyl sulfoxide), NMP (N-methyl-2-pyrrolidone), etc.), and measuring the solution with a particle size distribution analyzer. For example, a particle size distribution analyzer based on dynamic light scattering (DLS) or laser diffraction scattering (LD) can be used as the particle size distribution analyzer.

[0029] The binder contained in the outer layer is not particularly limited, but examples thereof include CMC (carboxymethyl cellulose), MC (methyl cellulose), PVA (polyvinyl alcohol), PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), SBR (styrene butadiene rubber), PMMA (methyl methacrylate), and starch.

[0030] The inner layer of the solid electrolyte layer is not limited to the composition containing the PEDOT-PSS fine particles and binder used as the outer layer of the solid electrolyte layer, and other solid electrolyte materials can be used. As the solid electrolyte layer material for the inner layer, PEDOT-PSS may be used, or conductive polymers having a skeleton of pyrroles, thiophenes, anilines, or the like other than PEDOT may also be used. In addition, the inner layer basically does not contain a binder.

[0031] The solid electrolyte layer can be provided on the dielectric layer by forming an inner solid electrolyte layer that fills the pores (recesses) of the dielectric layer, and then forming an outer solid electrolyte layer that covers the entire dielectric layer. The inner solid electrolyte layer can be formed, for example, by a method of forming a polymer film of poly(3,4-ethylenedioxythiophene) or the like on the surface of the dielectric layer using a treatment liquid containing a monomer such as 3,4-ethylenedioxythiophene, or by applying a dispersion of a polymer such as poly(3,4-ethylenedioxythiophene) to the surface of the dielectric layer and drying it. The outer solid electrolyte layer can be formed, for example, by applying a dispersion containing PEDOT-PSS fine particles and a binder to the surface of the inner layer and drying it.

[0032] The thickness of the inner layer of the solid electrolyte layer is preferably 1 nm or more, and the thickness of the outer layer of the solid electrolyte layer is preferably 0.5 μm or more and 20 μm or less.

[0033] The cathode foil has a roughened bonding surface. The structure of the roughened bonding surface will be described in detail. FIG. 5 is an enlarged perspective view of the bonding surface of the cathode foil. As shown in FIG. 5, numerous openings 7c3 are formed in the bonding surface 7c1 of the cathode foil 7c, making the bonding surface 7c1 a roughened surface rather than a smooth surface. In FIG. 5, the bonding surface 7c1 of the cathode foil 7c is shown as the top surface, and is shown in the opposite orientation to the bonding surface 7c1 of the cathode foil 7c shown in FIG. 4. The openings 7c3 are formed by locally recessing the bonding surface 7c1 and by roughening the bonding surface 7c1. In this case, the maximum width of the openings 7c3 on the same plane as the bonding surface 7c1 is defined as the opening width w, and the depth of the openings 7c3 in the thickness direction of the cathode foil is defined as the opening depth dp.

[0034] The ratio of the opening depth perpendicular to the bonding surface of the opening to the opening width when viewed in plan (opening depth / opening width) is preferably 1 or more. The opening depth ratio is preferably 5 or less. The opening width w is preferably 10 μm or less. For example, if the opening width w is 10 μm, the opening depth dp is preferably 10 μm or more and 50 μm or less. The sizes of the multiple openings when viewed in plan may be the same or different. The opening width w and opening depth dp can be determined from a cross-sectional microscope photograph including the bonding surface of the cathode foil.

[0035] The cathode foil is preferably an etched foil whose bonding surface is roughened by etching, for example, by electrolytic etching or chemical etching, which involves grinding the cathode foil in the depth direction.

[0036] In the solid electrolytic capacitor element of the present invention, the outer layer of the solid electrolyte layer is in direct contact with the roughened bonding surface of the cathode foil. The outer layer of the solid electrolyte layer contains PEDOT-PSS microparticles and a binder, and the PEDOT-PSS microparticles penetrate into the openings of the cathode foil, thereby enabling a strong bond between the solid electrolyte layer and the cathode foil. Furthermore, since the outer layer of the solid electrolyte layer is an aggregate of PEDOT-PSS microparticles bound by the binder, the microparticles are separated from each other, forming a malleable film. From the perspective of film properties, malleable film properties are also suitable for the outer layer of the solid electrolyte layer to fully penetrate into the openings of the cathode foil. By combining the properties of such an outer layer with the roughened bonding surface of the cathode foil, a solid electrolytic capacitor element can be obtained in which the solid electrolyte layer and the cathode foil are in direct contact, and which has sufficient bonding strength between the solid electrolyte layer and the cathode foil.

[0037] Furthermore, because the outer layer of the solid electrolyte layer is malleable, when pressure is applied by heating and pressing during the manufacture of the solid electrolytic capacitor element, the fine particles can move within the range where the binder is bonded. Therefore, the outer layer film is not rigid but is capable of micro-deformation during heating and pressing. This prevents cracking of the outer layer film during heating and pressing. In other words, the solid electrolytic capacitor element of the present invention is suitable for manufacture through a process in which the solid electrolyte layer and the bonding surface of the cathode foil are brought into contact with each other and then heated and pressed, preventing cracking of the outer layer of the solid electrolyte layer due to heating and pressing, and resulting in a solid electrolytic capacitor element in which the solid electrolyte layer and the cathode foil are firmly bonded together.

[0038] [Method for manufacturing a solid electrolytic capacitor element] The method for manufacturing a solid electrolytic capacitor element of the present invention includes the steps of: preparing a cathode foil having one surface, which is the bonding surface, roughened; preparing a valve action metal substrate having a dielectric layer provided on its surface; applying a dispersion liquid in which PEDOT-PSS fine particles and a binder are dispersed onto the dielectric layer to form a solid electrolyte layer; and bringing the solid electrolyte layer into contact with the bonding surface of the cathode foil and applying heat and pressure.

[0039] (Cathode foil preparation process) At least the bonding surface of the cathode foil is roughened. Electrolytic etching or chemical etching can be used as the roughening method. An opening is formed by roughening the bonding surface of the cathode foil. In this case, the cathode layer is etched in the depth direction by electrolytic etching or chemical etching to form an opening with an opening width w and opening depth dp. The method of roughening the bonding surface of the cathode foil is not limited to etching, and wet plating or dry plating may also be used to add thickness to the cathode foil, thereby forming multiple irregularities on the bonding surface of the cathode foil.

[0040] (Step of Preparing a Valve Metal Substrate) A valve metal substrate having a dielectric layer formed on its surface is prepared. A valve metal substrate having a foil shape and a dielectric layer formed thereon is prepared by chemical conversion treatment. At this time, a large number of holes are formed on the surface of the valve metal substrate by etching, and the surface of the valve metal substrate is porous. The dielectric layer covers the surface of the valve metal substrate, including the inner surfaces of the holes.

[0041] (Step of forming a solid electrolyte layer) A dispersion liquid containing PEDOT-PSS fine particles and a binder is prepared for use in forming the outer layer of the solid electrolyte layer. Also, a composition containing a solid electrolyte material (composition for inner layer) is prepared for use in forming the inner layer of the solid electrolyte layer.

[0042] The inner layer composition is applied to a dielectric layer provided on the surface of a valve metal substrate to form an inner layer of a solid electrolyte layer. The dispersion is then applied to form an outer layer of a solid electrolyte layer. The inner layer composition and dispersion can be applied to the dielectric layer by sponge transfer, screen printing, spray coating, a dispenser, inkjet printing, or the like. The dispersion may also be used as the inner layer composition.

[0043] In this specification, the "step of applying a dispersion liquid in which PEDOT-PSS fine particles and a binder are dispersed onto a dielectric layer to form a solid electrolyte layer" also includes a step of applying an inner layer composition onto a dielectric layer to form an inner layer, and then applying a dispersion liquid to cover the inner layer to form an outer layer, thereby forming a solid electrolyte layer consisting of an inner layer and an outer layer. In other words, the method is not limited to forming an outer layer by directly applying a dispersion liquid onto a dielectric layer, and there may be another layer (inner layer) between the dielectric layer and the outer layer formed by applying a dispersion liquid.

[0044] (Heating and Pressuring Step) The joining surface of the solid electrolyte layer and the joining surface of the cathode foil are brought into contact with each other and heated and pressed. The joining surface of the cathode foil is a roughened surface, and the joining surface of the cathode foil is brought into direct contact with the outer layer of the solid electrolyte layer, and heating and pressing are performed. The heating and pressing conditions are preferably a temperature of 80°C or higher and 250°C or lower, and a pressure of 0.1 kPa or higher and 40 kPa or lower.

[0045] The outer layer of the solid electrolyte layer is an aggregate of PEDOT-PSS fine particles bound together by a binder, so the particles are separated from each other, making the outer layer a malleable film. Because the outer layer of the solid electrolyte layer is malleable, when pressure is applied by heating and pressurizing during the production of the solid electrolytic capacitor element, the fine particles can move within the range where the binder can bind them together. Therefore, when heated and pressurized, the outer layer film is not rigid but is capable of micro-deformation. This prevents the outer layer film from cracking when heated and pressurized.

[0046] In contrast, the following describes a case in which the outer layer of the solid electrolyte layer is a polymerized film formed by a method of forming a polymerized film of poly(3,4-ethylenedioxythiophene) or the like on the dielectric layer using a treatment liquid containing a monomer such as 3,4-ethylenedioxythiophene. The polymerized film is formed by densely bundling rigid polymer chains, making it hard and brittle when heated or pressurized, which can lead to cracking of the outer polymerized film. Cracking of the outer polymerized film can cause problems such as an increase (deterioration) in ESR and a deterioration in humidity load resistance.

[0047] For these reasons, the method for manufacturing a solid electrolytic capacitor element of the present invention specifies that the outer layer of the solid electrolyte layer contains PEDOT-PSS fine particles and a binder, and specifies that a step of contacting the outer layer of the solid electrolyte layer with the bonding surface of the cathode foil and applying heat and pressure is performed. This specification makes it possible to manufacture a solid electrolytic capacitor element having sufficient bonding strength between the solid electrolyte layer and the cathode foil.

[0048] An example of a method for manufacturing a solid electrolytic capacitor, including a method for manufacturing a solid electrolytic capacitor element according to the present invention, will now be described with reference to the drawings. Fig. 6 is a perspective view schematically showing a state in which a capacitor element sheet and a cathode foil sheet are laminated.

[0049] As shown in FIG. 6, a capacitor element sheet 110 and a cathode foil sheet 120 are laminated to form a sheet laminate 130 .

[0050] The capacitor element sheet 110 is formed with an arrangement of components other than the cathode foil and exterior resin of a plurality of solid electrolytic capacitor elements that form different solid electrolytic capacitors (see FIGS. 8A and 8B described below). The cathode foil sheet 120 is formed with an arrangement of components of the cathode foil of a plurality of solid electrolytic capacitor elements that form different solid electrolytic capacitors (see FIG. 10 described below). This forms a structure in which a plurality of cathode and anode laminates are arranged in a plane. In other words, the sheet laminate is a planar arrangement of cathode and anode laminates of solid electrolytic capacitor elements.

[0051] Next, the sheet stack is sealed with insulating resin. As will be described in detail later, at this time, through holes that penetrate from the top surface to the bottom surface of the sheet stack are provided in the sheet stack, and the resin sealing is performed by compression molding.

[0052] This sealing with insulating resin is performed in a multi-state (state in which a plurality of solid electrolytic capacitors are arranged) before the solid electrolytic capacitors are separated into individual pieces.

[0053] Next, the sheet laminate sealed with insulating resin is cut into individual pieces, specifically along cutting lines S11, S12, E11, and E12 shown in Fig. 6. This forms a plurality of resin molded bodies without external electrodes.

[0054] Next, an external anode electrode and an external cathode electrode are formed on the first end surface and the second end surface of the resin molded body, respectively, to form a solid electrolytic capacitor.

[0055] Next, each step will be described in more detail. Figures 7A, 7B, 7C, and 7D are schematic diagrams showing steps of forming a capacitor element sheet. Figure 8A is a perspective view showing an example of a capacitor element sheet before singulation, and Figure 8B is a top view showing an example of a capacitor element sheet before singulation.

[0056] As shown in Fig. 7A, a metal foil serving as a valve metal substrate is subjected to chemical conversion treatment to form a dielectric layer 5. At this time, numerous holes are formed on the surface of the valve metal substrate by etching, making the surface of the valve metal substrate porous. The dielectric layer 5 covers the surface of the valve metal substrate, including the inner surfaces of the holes.

[0057] Next, a dam and a solid electrolyte layer are formed on the surface of the dielectric layer 5. More specifically, as shown in Fig. 7B, a dam 6 having a frame-shaped opening is formed. Then, as shown in Fig. 7C, a solid electrolyte layer 7a (a laminated structure of an inner layer 7a1 and an outer layer 7a2) is formed within the opening of the dam 6.

[0058] In this process, a composition containing a solid electrolyte material (inner layer composition) for use in forming the inner layer and a dispersion of PEDOT-PSS microparticles and a binder for use in forming the outer layer are prepared. The inner layer composition and dispersion are then applied to the surface of the dielectric layer to form a solid electrolyte layer. The inner layer composition and dispersion can be applied by sponge transfer, screen printing, spray coating, a dispenser, inkjet printing, or the like.

[0059] Next, as shown in FIG. 7D , anode through holes are formed in the valve metal substrate and the dam. More specifically, as shown in FIGS. 7D , 8A , and 8B , a plurality of cylindrical anode through holes 19C and groove-shaped anode through holes 19L are formed in the valve metal substrate and the dam. In this case, the cylindrical anode through holes 19C and groove-shaped anode through holes 19L penetrate not only the valve metal substrate but also the dam 6. The cylindrical anode through holes 19C and groove-shaped anode through holes 19L are alternately arranged along the direction of the second cutting line along which the portions that will become solid electrolytic capacitor elements are aligned. The cylindrical anode through holes 19C are formed at positions that will realize the anode end of the solid electrolytic capacitor element. The groove-shaped anode through holes 19L are formed at positions that will realize the cathode end of the solid electrolytic capacitor element. FIG. 7D shows the direction of the second cutting lines and the direction of the first cutting lines perpendicular to the second cutting lines as the directions of the cutting lines used when singulating into solid electrolytic capacitor elements.

[0060] As shown in Figures 8A and 8B, this structure is formed in a multi-layer structure in which structures each consisting of a valve metal substrate, a dielectric layer, a solid electrolyte layer (inner layer and outer layer), and a dam are arranged two-dimensionally. In the above-described configuration, the step of forming the anode through-hole is shown after the dam is formed. However, a step of forming the anode through-hole in the valve metal substrate and then forming the dam so as not to block the anode through-hole may also be used.

[0061] Fig. 9 is a perspective view schematically showing an example of a cathode foil sheet after being divided into individual pieces. Fig. 10 is a perspective view schematically showing an example of a cathode foil sheet before being divided into individual pieces. The cathode foil sheet is a metal foil whose bonding surface with the solid electrolyte layer is roughened. The roughening method and the degree of roughening are as described above.

[0062] 9 and 10 , a plurality of cylindrical cathode through holes 29C and groove-shaped cathode through holes 29L are formed in the cathode foil sheet 120. The cylindrical cathode through holes 29C and the groove-shaped cathode through holes 29L are alternately arranged along the direction of the second cutting line along which the portions that will become solid electrolytic capacitor elements are aligned.

[0063] A plurality of cylindrical cathode through holes 29C are formed at positions where cathode ends of the solid electrolytic capacitor elements will be realized, and groove-shaped cathode through holes 29L are formed at positions where anode ends of the solid electrolytic capacitor elements will be realized.

[0064] Fig. 11 is an exploded perspective view schematically illustrating a structure in which a capacitor element sheet and a cathode foil sheet are stacked, and Fig. 12 is an exploded perspective view schematically illustrating a state in which the capacitor element sheet and the cathode foil sheet are stacked.

[0065] 11 and 12, the capacitor element sheets and the cathode foil sheets are alternately stacked. More specifically, the capacitor element sheets and the cathode foil sheets are stacked so as to satisfy the following conditions.

[0066] When viewed in the stacking direction, the plurality of cylindrical anode through holes 19C in the capacitor element sheet and the groove-shaped cathode through holes 29L in the cathode foil sheet overlap (see FIG. 11 ). When viewed in the stacking direction, the groove-shaped anode through holes 19L in the capacitor element sheet and the plurality of cylindrical cathode through holes 29C in the cathode foil sheet overlap (see FIG. 11 ).

[0067] Therefore, a plurality of through holes are formed in the sheet laminate, penetrating from the top surface to the bottom surface of the sheet laminate. This sheet laminate is filled with insulating resin. As a result, the plurality of cylindrical anode through holes 19C and groove-shaped anode through holes 19L in the capacitor element sheet are filled with insulating resin. Similarly, the plurality of cylindrical cathode through holes 29C and groove-shaped cathode through holes 29L in the cathode foil sheet are filled with insulating resin.

[0068] After the insulating resin is applied to each through hole and the portions that will become the side surfaces of the capacitor elements, the sheet laminate filled with the insulating resin is divided into individual pieces. The method of applying the insulating resin to the portions that will become the side surfaces of the capacitor elements is not particularly limited.

[0069] The width of the groove-shaped anode through hole 19L and the groove-shaped cathode through hole 29L may be any size, more specifically, may be determined as long as it is possible to prevent short circuits between adjacent solid electrolytic capacitor elements before singulation.

[0070] Example 1 A dam was formed on an aluminum chemically formed foil (a dielectric layer formed on a valve metal substrate), and a dispersion liquid containing PEDOT-PSS fine particles and a binder was printed onto the foil to form an inner layer of the solid electrolyte layer. Furthermore, a dispersion liquid containing PEDOT-PSS fine particles and a binder was printed onto the foil to form an outer layer of the solid electrolyte layer, forming a solid electrolyte layer consisting of an inner layer and an outer layer. The resulting product was dried at 150°C to remove the solvent contained in the solid electrolyte layer. A capacitor element sheet was produced using the above process. Note that no anode through-holes were formed in the above process.

[0071] An aluminum foil having a roughened surface (metal foil having a roughened surface to be bonded to the solid electrolyte layer) was prepared as a cathode layer sheet. The aluminum foil was laminated so that the roughened surface was in contact with the solid electrolyte layer, and then subjected to a heating and pressurizing treatment at a temperature of 150°C or higher and 190°C or lower (pressure of 5 MPa, pressing time of 5 minutes) to obtain a solid electrolytic capacitor element.

[0072] In the solid electrolytic capacitor element obtained in Example 1, no cracks were generated in the solid electrolyte layer, and the roughened surface of the aluminum foil and the solid electrolyte layer were firmly bonded. The solid electrolytic capacitor element maintained a low ESR.

[0073] Comparative Example 1 A solid electrolytic capacitor element was obtained in the same manner as in Example 1, except that an electrolytically polymerized polypyrrole film was formed as the outer layer of the solid electrolyte layer. In the solid electrolytic capacitor element obtained in Comparative Example 1, delamination (cracks) occurred between the solid electrolyte layer that had penetrated into the irregularities on the roughened surface of the aluminum foil and the solid electrolyte layer near the interface between the solid electrolyte layer and the aluminum foil. In the electrolytically polymerized polypyrrole film, the polypyrrole softens upon heating and pressurizing, allowing it to flow into the irregularities on the roughened surface of the aluminum foil. However, when the solid electrolyte layer contracts and deforms upon cooling after heating and pressurizing, the electrolytically polymerized film cannot flow to relieve internal stress, resulting in cracks near the interface where the most stress is applied. Such cracks in the solid electrolyte layer weakened the adhesion between the roughened surface of the aluminum foil and the solid electrolyte layer, resulting in a high ESR for the solid electrolytic capacitor element.

[0074] The present specification discloses the following:

[0075] The present disclosure (1) provides a solid electrolytic capacitor element comprising: a valve action metal substrate having a dielectric layer on at least one main surface thereof; a solid electrolyte layer provided on the dielectric layer; and a cathode foil in direct contact with the solid electrolyte layer, wherein the bonding surface of the cathode foil in direct contact with the solid electrolyte layer is roughened; the solid electrolyte layer includes an inner layer formed on the surface of the dielectric layer and an outer layer formed on the surface of the inner layer; and the outer layer includes PEDOT-PSS fine particles and a binder.

[0076] The present disclosure (2) is a solid electrolytic capacitor element according to the present disclosure (1), in which an opening is formed in the bonding surface, and the ratio of the opening depth perpendicular to the bonding surface in the opening to the opening width when viewed in a plane (opening depth / opening width) is 1 or more.

[0077] The present disclosure (3) is the solid electrolytic capacitor element according to the present disclosure (1) or (2), wherein the cathode foil is an etched foil whose bonding surface is roughened by etching.

[0078] The present disclosure (4) is the solid electrolytic capacitor element according to any one of the present disclosures (1) to (3), in which the average particle diameter of the fine particles is 0.001 μm or more and less than 1 μm.

[0079] The present disclosure (5) is a method for manufacturing a solid electrolytic capacitor element, which includes the steps of: preparing a cathode foil having one surface, which is a bonding surface, roughened; preparing a valve action metal substrate having a dielectric layer provided on its surface; applying a dispersion liquid in which PEDOT-PSS fine particles and a binder are dispersed onto the dielectric layer to form a solid electrolyte layer; and bringing the solid electrolyte layer into contact with the bonding surface of the cathode foil and applying heat and pressure.

[0080] The present disclosure (6) is the method for producing a solid electrolytic capacitor element according to the present disclosure (5), wherein the heating and pressurizing conditions are a temperature of 80° C. or higher and 250° C. or lower and a pressure of 0.1 kPa or higher and 40 kPa or lower.

[0081] LIST OF SYMBOLS 1 Solid electrolytic capacitor 3 Anode 4 Valve action metal substrate 5 Dielectric layer 6 Dam 7 Cathode 7a Solid electrolyte layer 7a1 Inner layer 7a2 Outer layer 7c Cathode foil 7c1, 7c2 Cathode foil bonding surface 7c3 Opening 8 Exterior resin 9 Resin molded body 9a First end face of resin molded body 9b Second end face of resin molded body 9c Bottom face of resin molded body 9d Top face of resin molded body 9e First side face of resin molded body 9f Second side face of resin molded body 11 Anode external electrode 11b Conductive resin electrode layer 11c Outer layer plating layer 13 Cathode external electrode 13b Conductive resin electrode layer 13c Outer layer plating layer 19C Cylindrical anode through hole 19L Groove-shaped anode through hole 20 Solid electrolytic capacitor element 29C Cylindrical cathode through-hole 29L Groove-shaped cathode through-hole 30 Laminate 110 Capacitor element sheet 120 Cathode foil sheet 130 Sheet laminate

Claims

1. A solid electrolytic capacitor element comprising: a valve metal substrate having a dielectric layer on at least one principal surface; a solid electrolyte layer provided on the dielectric layer; and a cathode foil in direct contact with the solid electrolyte layer, wherein the bonding surface of the cathode foil in direct contact with the solid electrolyte layer is roughened, the solid electrolyte layer includes an inner layer formed on the surface of the dielectric layer and an outer layer formed on the surface of the inner layer, and the outer layer contains PEDOT-PSS fine particles and a binder.

2. A solid electrolytic capacitor element as described in claim 1, wherein an opening is formed in the bonding surface, and the ratio of the opening depth perpendicular to the bonding surface in the opening to the opening width when viewed in a plane (opening depth / opening width) is 1 or more.

3. The solid electrolytic capacitor element according to claim 1 or 2, wherein the cathode foil is an etched foil whose bonding surface is roughened by etching.

4. A solid electrolytic capacitor element according to any one of claims 1 to 3, wherein the average particle size of the fine particles is 0.001 µm or more and less than 1 µm.

5. A method for manufacturing a solid electrolytic capacitor element, comprising the steps of: preparing a cathode foil having one surface, i.e., a roughened bonding surface; preparing a valve metal substrate having a dielectric layer formed on its surface; applying a dispersion liquid containing PEDOT-PSS fine particles and a binder onto the dielectric layer to form a solid electrolyte layer; and bringing the solid electrolyte layer into contact with the bonding surface of the cathode foil and applying heat and pressure.

6. The method for producing a solid electrolytic capacitor element according to claim 5, wherein the heating and pressurizing conditions are a temperature of 80° C. or higher and 250° C. or lower and a pressure of 0.1 kPa or higher and 40 kPa or lower.

Images