Solid electrolytic capacitor

Abstract

A capacitor element included in this solid electrolytic capacitor includes: an anode body which has a porous portion and has a first section including a first end part and a second section including a second end part; a dielectric layer; a cathode section which covers at least a part of the dielectric layer in the second section; and a separation section which is positioned between the first end part and the second end part of the anode body and insulates the first section and the cathode section from each other. The cathode section includes at least a conductive polymer layer. The conductive polymer layer has an inner layer filling voids of the porous portion and an outer layer protruding from a main surface of the anode body having the dielectric layer. The separation section has an end part A located on the first end part side and an end part B located on the second end part side. When the length from the end part B to an end part of the cathode section located on the second end part side is defined as L, the porous portion has a filling rate of 46% or higher in a region C included within 0.05 L from the end part B.

Description

Technical Field

[0001] The present disclosure relates to a solid electrolytic capacitor.

Background Art

[0002] A solid electrolytic capacitor includes a capacitor element, a resin exterior or a case that seals the capacitor element, and an external electrode electrically connected to the capacitor element. The capacitor element includes, for example, an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion that covers at least a part of the dielectric layer. The cathode portion includes a conductive polymer (for example, a conjugated polymer and a dopant) that covers at least a part of the dielectric layer. The conductive polymer is also referred to as a solid electrolyte. In the capacitor element, the anode body is divided into a portion covered by the cathode portion (which may also be referred to as a cathode formation portion, more specifically, the conductive polymer) and a portion not covered by the cathode portion.

[0003] Patent Document 1 discloses a solid electrolytic capacitor including an anode, a dielectric layer provided on the surface of the anode, a first conductive polymer layer provided on the dielectric layer, a second conductive polymer layer provided on the first conductive polymer layer, a third conductive polymer layer provided on the second conductive polymer layer, and a cathode layer provided on the third conductive polymer layer, wherein the first conductive polymer layer is made of a conductive polymer film formed by polymerizing pyrrole or a derivative thereof, the second conductive polymer layer is made of a conductive polymer film formed by polymerizing thiophene or a derivative thereof, and the third conductive polymer layer is made of a conductive polymer film formed by polymerizing pyrrole or a derivative thereof.

[0004] Patent Document 2 discloses a capacitor element including an anode body having a porous portion on its surface, a dielectric layer covering at least a part of the anode body, and a cathode portion covering at least a part of the dielectric layer, wherein the cathode portion includes a solid electrolyte layer covering at least a part of the dielectric layer. The anode body includes a first anode body portion on which the solid electrolyte layer is formed and a second anode body portion on which the solid electrolyte layer is not formed. The solid electrolyte layer includes a first solid electrolyte layer disposed within the porous portion and a second solid electrolyte layer disposed outside the porous portion. When the length of the first anode body portion in the longitudinal direction is defined as length L, A solid electrolytic capacitor element is proposed in which, in a region between an interface between the first anode body portion and the second anode body portion and a position at a length of 0.05L from the interface toward the first anode body portion, the layer thickness of the second solid electrolyte layer is 1 μm or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] For solid electrolytic capacitors, excellent durability is required to obtain a high capacitance even when used for a long time or in a high-temperature environment.

Means for Solving the Problems

[0007] One aspect of the present disclosure is a solid electrolytic capacitor including at least one capacitor element, wherein the capacitor element has a porous portion at least on the surface layer, and an anode body having a first portion including a first end portion and a second portion including a second end portion opposite to the first end portion, a dielectric layer covering at least a part of the anode body, and a cathode portion covering at least a part of the dielectric layer in the second portion. A separation part that is located between the first end part and the second end part of the anode body and insulates the first part and the cathode part. including The cathode part includes at least a conductive polymer layer that covers at least a part of the dielectric layer. The conductive polymer layer includes a conductive polymer, and has an inner layer filled in the voids of the porous part and an outer layer protruding from the main surface of the anode body having the dielectric layer. The separation part has an end part A on the first end part side and an end part B on the second end part side. When the length from the end part B to the end part on the second end part side of the cathode part is L, the filling rate in the region C included in the part within 0.05L from the end part B of the porous part is 46% or more. Regarding the solid electrolytic capacitor, the filling rate is the area ratio of the part other than the voids in the region C.

Advantages of the Invention

[0008] A solid electrolytic capacitor excellent in durability can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] The novel features of the present invention are described in the appended claims, but the present invention will be better understood from the following detailed description in conjunction with the drawings, with respect to both the configuration and the content, together with other objects and features of the present invention.

[0011] In a capacitor element, the anode body can be divided into a second part where a cathode part (especially a conductive polymer layer) is formed and a first part where no cathode part (especially a conductive polymer layer) is formed. The anode body includes a first end portion and a second end portion on the side opposite to the first end portion. The first part includes the first end portion, and the second part includes the second end portion. In the capacitor element, in order to ensure the insulation between the first part and the cathode part, an insulating separation part may be provided at an appropriate position between the first end portion and the second end portion of the anode body (for example, at the boundary between the first part and the cathode part and in the vicinity thereof).

[0012] In a solid electrolytic capacitor, from the viewpoint of ensuring a high capacitance, a porous part is provided at least on the surface layer of the anode body to increase the surface area. The voids in the porous part are filled with a conductive polymer via a dielectric layer. From the viewpoint of ensuring a large surface area, it is preferable that the size of the voids is small. However, it is difficult to highly fill the conductive polymer in the voids of a small size. In particular, in the vicinity of the separation part in the second part of the anode body, the filling rate of the conductive polymer tends to be low. This is considered to be because the treatment liquid used for forming the conductive polymer is repelled by the insulating separation part, and it is difficult for the treatment liquid to enter the voids in the vicinity of the separation part.

[0013] In a solid electrolytic capacitor, when the filling rate of the conductive polymer in the voids is low (in other words, the porosity is high) in the vicinity of the separation part, air may enter from the first part side to the second part side through the remaining space of the porous part of this part, or air may enter the second part from the vicinity of the boundary between the separation part and the second part. Further, when the filling rate of the conductive polymer is low, the mechanical strength of the porous part is also low. Therefore, in a solid electrolytic capacitor, when stress is applied to the capacitor element due to deformation by molding or voltage application, or thermal stress is applied, stress concentrates on the part near the separation part of the cathode part and the porous part is broken, and an air intrusion path may be formed. Also due to this, air enters from the first part side to the second part side. When air enters the second part of the anode body, the conductive polymer covering the second part may be oxidized and deteriorated, or dedoping (or decomposition of the dopant, etc.) may occur, and the conductivity of the conductive polymer decreases. Oxidation deterioration and dedoping, etc. of the conductive polymer are particularly prominent when the solid electrolytic capacitor is used for a long period of time or used at a high temperature (especially when the voltage application state continues for a long time or is repeated), and the decrease in capacitance also becomes prominent. Capacitance can be measured experimentally even at the stage of the capacitor element before sealing by the exterior body. However, at the stage of the capacitor element, the stress applied to the vicinity of the separation part of the cathode part is extremely small compared to the case of the solid electrolytic capacitor after sealing. Therefore, even when excellent results are obtained in the evaluation of capacitance using the capacitor element, when actually evaluating using the solid electrolytic capacitor, the decrease in capacitance may become prominent compared to the case of the capacitor element.

[0014] In view of the above, (1) the solid electrolytic capacitor according to the present disclosure includes at least one capacitor element. The capacitor element has a porous portion at least on the surface layer, and an anode body having a first portion including a first end and a second portion including a second end opposite to the first end, a dielectric layer covering at least a part of the anode body, a cathode portion covering at least a part of the dielectric layer in the second portion, and a separation portion located between the first end and the second end of the anode body and insulating the first portion and the cathode portion. The cathode portion includes at least a conductive polymer layer covering at least a part of the dielectric layer. The conductive polymer layer includes a conductive polymer and has an inner layer filled in the voids of the porous portion and an outer layer protruding from the main surface of the anode body having the dielectric layer. The separation portion has an end A on the first end side and an end B on the second end side. When the length from the end B to the end on the second end side of the cathode portion is L, the filling rate in the region C included in the portion within 0.05L from the end B of the porous portion is 46% or more. The filling rate is the area ratio of the portion other than the voids in the region C.

[0015] By setting the filling rate in the region C near the separation portion to 46% or more, in addition to reducing the remaining space in the region C, the mechanical strength is increased. The high-filling-rate portion near the separation portion in the second portion serves as a barrier, reducing the intrusion of air from the first portion side to the second portion side of the anode body. In addition, the diffusion of air in the second portion and the diffusion of air from the second portion to the conductive polymer layer are suppressed. Therefore, even when the solid electrolytic capacitor is used for a long time or at a high temperature (especially when the voltage application state continues or repeats for a long time), the deterioration of the conductive polymer is suppressed, and the high conductivity of the conductive polymer is maintained, suppressing the decrease in capacitance. Thus, excellent durability can be ensured. In other words, high reliability of the solid electrolytic capacitor when used for a long time or at a high temperature can be obtained. In the present disclosure, since the decrease in the capacitance of the solid electrolytic capacitor is suppressed even when the voltage application state continues or repeats for a long time at a high temperature, high heat resistance (specifically, high durability against heat) of the solid electrolytic capacitor can also be ensured.

[0016] In this specification, the direction parallel to the direction from the first end portion to the second end portion of the anode body is referred to as the length direction of the anode body. More specifically, the length direction of the anode body is the direction connecting the center of the end face of the first end portion and the center of the end face of the second end portion. The length direction of the cathode portion and the length direction of the capacitor element are each a direction parallel to the length direction of the anode body. Further, the direction perpendicular to the length direction and the thickness direction of the capacitor element is referred to as the width direction of the capacitor element. When comparing the lengths of the capacitor element in two directions perpendicular to the length direction of the capacitor element, the direction with the shorter length is taken as the thickness direction, and the direction with the longer length is taken as the width direction. When the lengths of the capacitor element in two directions perpendicular to the length direction of the capacitor element are the same, either direction may be the width direction or the thickness direction. The length L from the end portion B of the separation portion to the end portion on the second end portion side of the cathode portion is the length in the direction parallel to the length direction of the cathode.

[0017] The filling ratio is determined for a region C of a predetermined size in the vicinity of the separation part of a cross-section parallel to the length direction and the thickness direction in the vicinity of the center in the width direction of the capacitor element (specifically, a portion with a length of 0.05L from the end B of the separation part). The vicinity of the center in the width direction refers to a region of ±0.1W from the center in the width direction of the capacitor element, where W is the maximum width of the portion where the cathode part of the capacitor element is formed. When parallel to the length direction of the capacitor element, cases where the angle (acute angle) formed with the length direction is in the range of ±5° are included. Similarly, when parallel to the thickness direction of the capacitor element, cases where the angle (acute angle) formed with the thickness direction is in the range of ±5° are also included. A sample for measuring the filling ratio is prepared by cutting a solid electrolytic capacitor and exposing the above-mentioned cross-section by ion milling. An image of the exposed cross-section is taken with an optical microscope, this image is binarized, and the area ratio occupied by the portion other than the voids in region C is obtained, and this area ratio is taken as the filling ratio (%). The binarization process is performed by the Otsu binarization method, and the threshold value that gives the largest difference when the color distribution in region C of the cross-section image is divided into white and black is determined. The color distribution in region C is divided into white and black with this threshold value, and the ratio (%) of the white pixels to the total pixels in region C is obtained. This ratio is obtained for region C of the porous part on both main surface sides of the anode body in the above-mentioned cross-section and averaged. The obtained average value is taken as the filling ratio (%). The ratio (%) of the black pixels to the total pixels in region C corresponds to the porosity. The sum of the porosity and the filling ratio is 100%. Note that the length L from the end B of the separation part to the end on the second end side of the cathode part is obtained from the above-mentioned cross-section image. The magnification of the cross-section image by the optical microscope is set to 10 to 30 times (for example, 20 times). As the optical microscope, for example, the digital microscope "VHX-6000" series manufactured by Keyence Corporation is used.

[0018] (2) In the above (1), region C is preferably a rectangular region where the length of the first side is 15 μm or more and 20 μm or less, and the length of the second side orthogonal to the first side is 20 μm or more and 25 μm or less in the horizontal direction. In this case, the filling ratio can be accurately obtained.

[0019] The first side of region C may or may not be parallel to the length direction or the thickness direction of the capacitor element. The second side of region C may or may not be parallel to the thickness direction or the length direction of the capacitor element.

[0020] (3) In the above (1) or (2), the anode body may have a core portion and a porous portion integrally formed with both surfaces of the core portion, and the shortest distance between region C and the surface of the core portion is preferably 0 μm or more and 5 μm or less. In this case, it is advantageous in reducing the variation in the measured value of the filling rate. The shortest distance between region C and the surface of the core portion is the shortest distance between the average surface of the core portion (in other words, the average bottom surface of the porous portion) determined in the above cross-sectional image and region C. The filling rate is measured for each region C of the porous portions formed on both surface sides of the core portion as described above, and is obtained by averaging. It is preferable that both the shortest distance between each such region C and the average bottom surface of the porous portion including each region C satisfy the above range.

[0021] (4) In any one of the above (1) to (3), the conductive polymer layer may contain a conjugated polymer including a monomer unit corresponding to at least one selected from the group consisting of a pyrrole compound, a thiophene compound, and an aniline compound.

[0022] Hereinafter, the solid electrolytic capacitor of the present disclosure will be described more specifically with reference to the drawings as necessary. At least one selected from the components described below can be arbitrarily combined with at least one of the above (1) to (4) according to the solid electrolytic capacitor of the present disclosure as long as the technical combination is possible.

[0023] [Solid electrolytic capacitor] (Capacitor element) The capacitor element includes an anode body, a dielectric layer covering at least a part of the anode body, a cathode portion covering at least a part of the dielectric layer in a second portion, and a separation portion insulating the first portion and the cathode portion.

[0024] (Anode body) The anode body can include a valve-acting metal, an alloy containing a valve-acting metal, and a compound containing a valve-acting metal, etc. The anode body may contain one of these materials or may contain a combination of two or more of them. As the valve-acting metal, for example, aluminum, tantalum, niobium, and titanium are preferably used.

[0025] The anode body has a porous portion at least on the surface layer.

[0026] An anode body with a porous surface layer can be obtained, for example, by roughening the surface of a base material (such as a sheet-shaped (e.g., foil-shaped, plate-shaped) base material) containing a valve-acting metal by etching or the like. The roughening can be performed, for example, by an etching treatment or the like. Such an anode body may have a core portion and a porous portion integrally formed with both surfaces of the core portion. For one surface of the base material, the thickness of the porous portion may be, for example, 30 μm or more. When the thickness of the porous portion for one surface of the base material is 40 μm or more, it tends to be difficult to highly fill the conductive polymer in the vicinity of the separation portion of the porous portion. In the present disclosure, even when the thickness of the porous portion is 40 μm or more, the conductive polymer can be highly filled in the vicinity of the separation portion, and a high filling rate can be ensured. The thickness of the porous portion may be 70 μm or less for one surface of the base material, although it also depends on the thickness of the base material.

[0027] The anode body may be a porous molded body of particles containing a valve-acting metal or a porous sintered body thereof. Note that each of the porous molded body and the sintered body usually has a porous structure throughout the anode body. Each of the molded body and the sintered body may have a sheet-like shape or may have a rectangular parallelepiped, cubic, or similar shape.

[0028] The anode body has a first portion including a first end portion and a second portion including a second end portion opposite to the first end portion. The first end portion and the second end portion are both end portions in the longitudinal direction of the anode body. In the second portion, a cathode portion (especially a conductive polymer layer) is formed via a dielectric layer. Therefore, the second portion may be referred to as a cathode forming portion. Among the first portions where the cathode portion is not formed, the portion where the separation portion is not formed may be referred to as an anode portion (or an anode lead-out portion). An anode lead terminal may be connected to the anode portion.

[0029] (Dielectric layer) The dielectric layer is formed so as to cover at least a part of the anode body. The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing the valve action metal on the surface of the anode body by a forming process or the like. In the dielectric layer formed on the surface of the anode body having a porous portion, the surface of the dielectric layer has a fine uneven shape according to the shape of the surface of the porous portion.

[0030] The dielectric layer may be formed of a material that functions as a dielectric layer. As such a material, the dielectric layer includes, for example, an oxide of a valve action metal. For example, when tantalum is used as the valve action metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve action metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these specific examples.

[0031] (Cathode portion) The cathode portion is formed so as to cover at least a part of the dielectric layer in the second portion. The cathode portion includes at least a conductive polymer layer (solid electrolyte layer) that covers at least a part of the dielectric layer. The cathode portion may include a conductive polymer layer and a cathode lead-out layer that covers at least a part of the conductive polymer layer. Hereinafter, the conductive polymer layer and the cathode lead-out layer will be described.

[0032] (Conductive polymer layer) The conductive polymer layer includes a conductive polymer layer. The conductive polymer layer has an inner layer filled in the voids of the porous portion and an outer layer protruding from the main surface of the anode body having a dielectric layer. Note that a dielectric layer is formed on at least a part of the inner wall of the void. The inner layer may be formed so as to adhere to the inner wall of the void via the dielectric layer. The main surface of the anode body having a dielectric layer is an average surface located at each of both ends in the thickness direction of the anode body (in other words, a direction parallel to the stacking direction of each layer in the capacitor element) in the cross-sectional image for measuring the filling rate. Note that in the second portion, the conductive polymer layer may also have an inner layer filled in the void and an outer layer protruding from the side surface (an average surface located at both ends in the width direction of the anode body) or the end surface (an average surface located at the end in the length direction of the anode body) other than the above main surface.

[0033] In the present disclosure, the filling rate in region C included in the portion within 0.05 L from the end B of the separation portion of the porous portion is 46% or more. In other words, in the porous portion near the separation portion where it is difficult to achieve high filling originally, the filling rate is as high as 46% or more. As a result, the intrusion of air from the anode portion side into the second portion is suppressed, and even when the solid electrolytic capacitor is used for a long time or at a high temperature with a voltage applied, the deterioration of the conductive polymer is suppressed, and a high conductivity is maintained, so that a high capacitance can be maintained. The filling rate may be 47% or more, or may be 47.4% or more. In these cases, the effect of maintaining a high capacitance is further enhanced, and higher durability can be ensured. The filling rate corresponds to the ratio of white pixels binarized by the Otsu binarization method as described above. The white pixels mainly correspond to the anode body, the conductive polymer layer (inner layer), and the dielectric layer. Therefore, the filling rate tends to be high when there are few voids. However, in the porous portion of the second portion, a high capacitance can be obtained by forming many voids to increase the specific surface area. Therefore, in region C included in the porous portion of the second portion, a relatively high porosity is provided at the stage before forming the conductive polymer layer. Therefore, the fact that region C in the solid electrolytic capacitor exhibits a high filling rate of 46% or more means that region C is highly filled with the conductive polymer. The upper limit value of the filling rate is not particularly limited, but it is difficult to set it to 100%, and usually it is 70% or less.

[0034] The conductive polymer constituting the conductive polymer layer includes, for example, a conjugated polymer and a dopant. The conductive polymer may further contain an additive as necessary.

[0035] Examples of the conjugated polymer include known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. Examples of the conjugated polymer include polymers having a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. Among these, polymers having a basic skeleton of polypyrrole, polythiophene, or polyaniline are preferable. The above polymers only need to contain at least one kind of monomer unit constituting the basic skeleton. The monomer unit also includes a monomer unit having a substituent. The above polymers include homopolymers and copolymers of two or more kinds of monomers. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) and the like.

[0036] Among the conjugated polymers, conjugated polymers containing monomer units corresponding to at least one selected from the group consisting of pyrrole compounds, thiophene compounds, and aniline compounds are preferable. Examples of the pyrrole compound include compounds having a pyrrole ring and capable of forming a repeating structure of the corresponding monomer unit. Examples of the thiophene compound include compounds having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit. These compounds can be linked at the 2-position and 5-position of the pyrrole ring or thiophene ring to form a repeating structure of the monomer unit. Examples of the aniline compound include compounds having a benzene ring and at least one (preferably one) amino group bonded to the benzene ring and capable of forming a repeating structure of the corresponding monomer unit. The aniline compound can be linked, for example, at the amino group and the part of the p-position CH group (CH group constituting the benzene ring) with respect to the amino group to form a repeating structure of the monomer unit.

[0037] The pyrrole compound may have a substituent at at least one of the 3-position and the 4-position of the pyrrole ring, for example. The thiophene compound may have a substituent at at least one of the 3-position and the 4-position of the thiophene ring, for example. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring condensed with the pyrrole ring or the thiophene ring. Examples of the pyrrole compound include pyrrole which may have a substituent at at least one of the 3-position and the 4-position. Examples of the thiophene compound include thiophene which may have a substituent at at least one of the 3-position and the 4-position, an alkylenedioxythiophene compound (such as an ethylenedioxythiophene compound). The alkylenedioxythiophene compound includes those having a substituent at the alkylidene group part. Examples of the aniline compound include aniline which may have a substituent at at least one of the o-position and the p-position with respect to the amino group. 2-4 Examples of the alkylenedioxythiophene compound include those having a substituent at the alkylidene group part. Examples of the aniline compound include aniline which may have a substituent at at least one of the o-position and the p-position with respect to the amino group.

[0038] Examples of the substituent include an alkyl group (a C alkyl group such as a methyl group, an ethyl group), an alkoxy group (a C alkoxy group such as a methoxy group, an ethoxy group), a hydroxy group, a hydroxyalkyl group (a hydroxy C alkyl group such as a hydroxymethyl group), etc., but are not limited thereto. When each of the pyrrole compound, the thiophene compound, and the aniline compound has two or more substituents, the respective substituents may be the same or different. 1-4 Examples of the substituent include an alkyl group (a C alkyl group such as a methyl group, an ethyl group), an alkoxy group (a C alkoxy group such as a methoxy group, an ethoxy group), a hydroxy group, a hydroxyalkyl group (a hydroxy C alkyl group such as a hydroxymethyl group), etc., but are not limited thereto. When each of the pyrrole compound, the thiophene compound, and the aniline compound has two or more substituents, the respective substituents may be the same or different. 1-4 Examples of the substituent include an alkyl group (a C alkyl group such as a methyl group, an ethyl group), an alkoxy group (a C alkoxy group such as a methoxy group, an ethoxy group), a hydroxy group, a hydroxyalkyl group (a hydroxy C alkyl group such as a hydroxymethyl group), etc., but are not limited thereto. When each of the pyrrole compound, the thiophene compound, and the aniline compound has two or more substituents, the respective substituents may be the same or different. 1-4 Examples of the substituent include an alkyl group (a C alkyl group such as a methyl group, an ethyl group), an alkoxy group (a C alkoxy group such as a methoxy group, an ethoxy group), a hydroxy group, a hydroxyalkyl group (a hydroxy C alkyl group such as a hydroxymethyl group), etc., but are not limited thereto. When each of the pyrrole compound, the thiophene compound, and the aniline compound has two or more substituents, the respective substituents may be the same or different.

[0039] A conjugated polymer containing at least a monomer unit corresponding to pyrrole, or a conjugated polymer (such as PEDOT) containing at least a monomer unit corresponding to at least a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)) may be used. The conjugated polymer containing at least a monomer unit corresponding to pyrrole may contain only the monomer unit corresponding to pyrrole, or in addition to the monomer unit, may contain a monomer unit corresponding to a pyrrole compound other than pyrrole (such as pyrrole having a substituent). The conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only the monomer unit corresponding to EDOT, or in addition to the monomer unit, may contain a monomer unit corresponding to a thiophene compound other than EDOT.

[0040] The conductive polymer layer may contain one kind of conjugated polymer or may contain a combination of two or more kinds.

[0041] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0042] In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values in terms of polystyrene measured by gel permeation chromatography (GPC). Note that GPC is usually measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0043] Examples of the dopant include at least one selected from the group consisting of anions and polyanions.

[0044] Examples of the anion include sulfate ion, nitrate ion, phosphate ion, borate ion, organic sulfonate ion, carboxylate ion, etc., but are not particularly limited. Examples of the dopant that generates sulfonate ion include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid.

[0045] Examples of the polyanion include polymer anions. The conductive polymer layer may contain, for example, a conjugated polymer containing a monomer unit corresponding to a thiophene compound and a polymer anion.

[0046] Examples of the polymer anion include polymers having a plurality of anionic groups. Examples of such polymers include polymers containing monomer units having anionic groups. Examples of the anionic group include a sulfo group and a carboxy group. The polymer anion preferably has at least a sulfo group.

[0047] In the conductive polymer layer, the anionic group of the dopant may be contained in a free form, an anion form, or a salt form, or may be contained in a form bonded or interacting with the conjugated polymer. In this specification, all of these forms may be simply referred to as "anionic group", "sulfo group", or "carboxy group".

[0048] Examples of the polymer anion having a sulfo group include polymeric type polysulfonic acids. Specific examples of the polymer anion include polyvinylsulfonic acid, polystyrenesulfonic acid (including copolymers and substituents having substituents), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolak resin. However, the polymer anion is not limited to these specific examples.

[0049] The amount of the dopant contained in the conductive polymer layer is, for example, 10 parts by mass or more and 1000 parts by mass or less, 20 parts by mass or more and 500 parts by mass or less, or 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the conjugated polymer.

[0050] In the conductive polymer layer, the inner layer and the outer layer may be single layers or layers with different compositions. Each of the conductive polymer layer, the inner layer, and the outer layer may be a single layer or may be composed of a plurality of layers. When the conductive polymer layer, the inner layer, or the outer layer is composed of a plurality of layers, the conductive polymers contained in each layer may be the same or different. Also, the dopants contained in each layer may be the same or different.

[0051] A layer for enhancing adhesion or the like may be interposed between the dielectric layer and the conductive polymer layer.

[0052] Examples of the additive include known additives added to the conductive polymer layer (for example, coupling agents, silane compounds), known conductive materials other than the conductive polymer, and water-soluble polymers. The conductive polymer layer (or each layer constituting the conductive polymer layer) may contain one of these additives or may contain a combination of two or more of them. When the conductive polymer layer, the inner layer, or the outer layer is composed of a plurality of layers, the additives contained in each layer may be the same or different.

[0053] Examples of the conductive material as the additive include at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0054] The conductive polymer layer is generally formed by using a liquid composition (such as a solution or a liquid dispersion) containing a conductive polymer, or by performing in-situ polymerization (such as chemical polymerization or electrolytic polymerization) using a liquid composition (polymerization solution) containing a precursor of a conjugated polymer and a dopant. In the present disclosure, from the viewpoint of highly filling the conductive polymer in the region near the separation part of the second part and forming a dense inner layer, at least a part of the inner layer (when the inner layer is formed of a plurality of layers, at least the innermost layer) is preferably formed by electrolytic polymerization. By controlling the polymerization conditions and the like by electrolytic polymerization, the porous part can be highly filled with the conductive polymer even in the vicinity of the separation part, and the filling rate can be increased. The entire conductive polymer layer may be formed by electrolytic polymerization. Further, the part other than the outer layer or the innermost layer of the conductive polymer layer may be formed by chemical polymerization, formed using a liquid composition containing a conductive polymer, or formed by combining these.

[0055] Electrolytic polymerization can be carried out in a three-electrode system. For example, at least a part of the inner layer may be formed by electrolytically polymerizing a precursor of a conjugated polymer in the presence of a dopant in a three-electrode system on the surface of the dielectric layer. For example, electrolytic polymerization is carried out in a state where the second part of the anode body having a dielectric layer formed on its surface is immersed in a liquid composition (polymerization solution) containing a precursor of a conjugated polymer and a dopant. In the three-electrode system, electrolytic polymerization is carried out using the anode body, the counter electrode, and the reference electrode. In the three-electrode system, compared with the two-electrode system using the anode body and the counter electrode, the polymerization reaction can be controlled with high precision, so a dense conductive polymer layer is easily formed, and the filling rate of the porous part can be increased even in the vicinity of the separation part. Further, not only in the vicinity of the separation part, but also in the entire second part, the filling rate of the porous part is increased, and the intrusion of air into the entire cathode part can be reduced compared with the conventional case. Therefore, in the entire conductive polymer layer, the deterioration of the conductive polymer is suppressed, and the durability of the solid electrolytic capacitor can be improved.

[0056] Examples of the precursor of the conjugated polymer include a raw material monomer of the conjugated polymer, an oligomer in which a plurality of molecular chains of the raw material monomer are connected, and a prepolymer. One type of precursor may be used, or two or more types may be used in combination. From the viewpoint of easily obtaining higher orientation of the conjugated polymer, it is preferable to use at least one type (particularly, a monomer) selected from the group consisting of a monomer and an oligomer as the precursor.

[0057] The liquid composition used for electrolytic polymerization usually contains a solvent. Examples of the solvent include water, an organic solvent, and a mixed solvent of water and an organic solvent (such as a water-soluble organic solvent). When other conductive materials, additives, etc. are used, they may be added to the liquid composition.

[0058] The liquid composition (polymerization solution) may contain an oxidizing agent as necessary. Further, the oxidizing agent may be applied to the anode body on which the dielectric layer is formed before or after bringing the liquid composition into contact with the anode body. Examples of such an oxidizing agent include a compound capable of generating Fe 3+ (such as ferric sulfate), a persulfate (such as sodium persulfate, ammonium persulfate), and hydrogen peroxide. The oxidizing agent may be used alone or in combination of two or more.

[0059] Three-electrode electrolytic polymerization is carried out in a state where an anode body on which a dielectric layer is formed, a counter electrode, and a reference electrode are immersed in the liquid composition (polymerization solution). As the counter electrode, for example, a Ti electrode is used, but it is not limited thereto. As the reference electrode, it is preferable to use a silver / silver chloride electrode (Ag / Ag + )

[0060] In electrolytic polymerization, the polymerization voltage is, for example, 0.6 V or more and 1.5 V or less. From the viewpoint of easily achieving high filling of the conductive polymer in the voids of the porous portion, the polymerization voltage is preferably 0.6 V or more and less than 1 V, more preferably 0.7 V or more and 0.95 V or less, and may be 0.75 V or more and 0.9 V or less. By performing electrolytic polymerization in a three-electrode system at such a polymerization voltage, the polymerization reaction in the voids can be precisely controlled. Therefore, in the voids, in the presence of a dopant, the polymer chains of the conjugated polymer can be grown, and the conductive polymer can be highly filled in the voids. Further, since the polymerization can proceed slowly, the orientation and crystallinity of the conjugated polymer can be further enhanced, a relatively high doping rate can be obtained, and relatively high conductivity can be easily ensured. The polymerization voltage is the potential of the anode with respect to the reference electrode (silver / silver chloride electrode (Ag / Ag + ))

[0061] The temperature at which electrolytic polymerization is carried out is, for example, 5°C or more and 60°C or less, and may be 15°C or more and 35°C or less.

[0062] From the viewpoint of highly filling the conductive polymer in the voids, it is preferable to form a precoat layer containing a conductive material on the surface of the dielectric layer prior to electrolytic polymerization. The precoat layer may be formed using a liquid composition containing a conductive polymer. However, in the liquid composition used for forming the precoat layer, it is preferable that the particle size of the conductive polymer is small or the conductive polymer is dissolved. Further, the concentration of the conductive polymer in the liquid composition is preferably a relatively low concentration. The dry solid content concentration of the liquid composition used for electrolytic polymerization is, for example, 1.2 mass% or less.

[0063] When the liquid composition is a liquid dispersion containing a conductive polymer (such as a conductive polymer and a dopant), the average primary particle diameter of the particles of the conductive polymer contained in the liquid dispersion is, for example, 100 nm or less, and may be 60 nm or less. In the case of a liquid composition (such as a liquid dispersion) containing a conductive polymer used to form the conductive polymer layer constituting the cathode portion, the average primary particle diameter of the particles of the conductive polymer is usually 200 nm or more, and the dry solid content concentration is 2% by mass or more.

[0064] Also, it is preferable when the liquid composition is a solution. The liquid composition in solution form contains, for example, a self-doped type conductive polymer as the conductive polymer. In the self-doped type conductive polymer, an acid group such as a sulfo group is introduced into the polymer chain, and it is easily dissolved in a solvent, and a liquid composition in solution form is easily obtained. Therefore, the liquid composition easily penetrates into the voids, and polymerization is more likely to occur uniformly in the voids. For example, a precoat layer may be formed using a polyaniline compound (such as a soluble polyaniline compound) into which an acid group such as a sulfo group is introduced.

[0065] The conjugated polymer of the precoat layer (or the polymer chain of the conductive polymer) and the conjugated polymer formed by electrolytic polymerization may be of the same type or different types. The dopant of the precoat layer and the dopant used for electrolytic polymerization may be the same or different.

[0066] From the viewpoint of easily ensuring a higher filling rate, the weight average molecular weight (Mw) of the conductive polymer (or conjugated polymer) forming the precoat layer is preferably 1,000 or more and 1,000,000 or less, and may be 1,000 or more and 850,000 or less.

[0067] From the viewpoint of easily ensuring a higher filling rate, the molecular weight distribution (= weight average molecular weight / number average molecular weight = Mw / Mn) of the conductive polymer (or conjugated polymer) forming the precoat layer is preferably 3.2 or less, may be 3 or less, 2.9 or less, or 2.85 or less. Mw / Mn is 1 or more.

[0068] (Cathode extraction layer) The cathode extraction layer may at least include a first layer that contacts the conductive polymer layer and covers at least a part of the conductive polymer layer, and may further include a second layer that covers the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, a cathode extraction layer may be constituted by a layer containing conductive carbon (also referred to as a carbon layer) as the first layer and a layer containing metal powder or a metal foil as the second layer. When using a metal foil as the first layer, the cathode extraction layer may be constituted by this metal foil.

[0069] Examples of the conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0070] The layer containing metal powder as the second layer can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such a second layer include a metal particle-containing layer (for example, a metal paste layer such as a silver paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). As the resin, a thermoplastic resin can be used, but it is preferable to use a thermosetting resin such as an imide-based resin or an epoxy resin.

[0071] When using a metal foil as the first layer, the type of metal is not particularly limited. It is preferable to use a valve metal (aluminum, tantalum, niobium, etc.) or an alloy containing a valve metal for the metal foil. If necessary, the surface of the metal foil may be roughened. A formation film may be provided on the surface of the metal foil, or a coating of a metal (dissimilar metal) or a non-metal different from the metal constituting the metal foil may be provided. Examples of the dissimilar metal or non-metal include a metal such as titanium and a non-metal such as carbon (conductive carbon, etc.).

[0072] A coating of the above-mentioned dissimilar metal or non-metal (for example, conductive carbon) may be used as the first layer, and the above-mentioned metal foil may be used as the second layer.

[0073] (Separator) When a metal foil is used for the cathode lead-out layer, a separator may be disposed between the metal foil and the anode body (such as an anode foil). The separator is not particularly limited, and for example, a non-woven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, polyamide (such as aliphatic polyamide, aromatic polyamide such as aramid), etc. may be used.

[0074] (Separation portion) The separation portion is located between the first end portion and the second end portion. The separation portion is provided so as to insulate the first portion (more specifically, the anode portion) and the cathode portion. The separation portion is provided, for example, with a predetermined width in a portion where a porous portion is formed between the first end portion and the second end portion of the anode body. The separation portion may be formed, for example, at an end portion on the second portion side of the first portion. However, there may be a case where the cathode portion is formed at an end portion on the second end side of the surface of the separation portion. In other words, the insulating region may be provided from the end portion on the second portion side of the first portion to the end portion on the first portion side of the second portion. From the viewpoint of more surely ensuring the insulation between the first portion and the cathode portion, it is preferable that the separation portion is not provided in the second portion.

[0075] In a region where the separation portion of the anode body is formed, the porous portion may be compressed in the thickness direction of the anode body. Also, in a region where the separation portion of the anode body is formed, the porous portion may be removed as necessary. In these cases, the intrusion of air from the anode portion side to the second portion side through the voids near the separation portion can be further suppressed.

[0076] The separation part includes an insulating material, for example, an insulating resin material or a cured product thereof. Examples of the resin material include thermoplastic resins (or compositions thereof), curable resin materials (such as curable resin compositions), and the like. The separation part may include an insulating material filled in the voids of the porous part, may include an insulating material disposed on the surface of the porous part, or may include both of these. For example, the separation part may include a cured product of an insulating material formed in the voids of the porous part and a cured product of an insulating material formed on the main surface of the anode body via a dielectric layer. Further, the separation part may include a sheet-like insulating material such as an insulating tape attached to the main surface of the anode body. The separation part may include a cured product of an insulating material formed in the voids of the porous part and a sheet-like insulating material such as an insulating tape attached to the main surface of the anode body.

[0077] Examples of the resin material include curable resins (such as polyimide-based resins, silicone resins, phenolic resins, urea resins, melamine resins, unsaturated polyesters, furan resins, polyurethanes, silicone resins (silicones), curable acrylic resins, epoxy resins, etc.), photoresists, thermoplastic resins (e.g., polyamides, polyamide-imides, thermoplastic polyimides, polyphenylene sulfone-based resins, polyether sulfone-based resins, cyanate ester resins, fluorine resins), and the like. The resin material may include one of these resins or a combination of two or more of them. Note that the resin material includes, depending on the type of resin, in addition to the resin that is a polymer, also precursors of the resin (such as monomers, oligomers, or prepolymers). The curable resin material may be of a one-component curing type or a two-component curing type. The resin composition may include at least one selected from the group consisting of a curing agent, a curing accelerator, a polymerization initiator, a catalyst, and a coupling agent, in addition to the above resins. Further, the resin composition may include, if necessary, known additives used for forming the separation part of the capacitor element. Examples of such additives include flame retardants, fillers, colorants, mold release agents, and inorganic ion scavengers.

[0078] The separation part can be formed by a process including a sub-step of filling a treatment liquid containing a resin composition and a solvent into the pores of the porous part and curing the resin composition. In the manufacture of the capacitor element, prior to the step of forming the separation part (the third step), a first step of preparing an anode body having a porous part at least on the surface layer and a second step of forming a dielectric layer on the surface of the porous part are performed. For the first step and the second step, reference can be made to the description of the anode body and the dielectric layer. Then, after forming the separation part, a cathode part including a conductive polymer layer or the like is formed on the second part of the anode body with the dielectric layer interposed therebetween (the fourth step).

[0079] The separation part is formed of an insulating material and is easy to squeeze out the liquid composition for electrolytic polymerization (polymerization liquid). Therefore, in the porous part near the separation part, it is difficult to highly fill the voids with the conductive polymer. In the present disclosure, by adjusting the polymerization conditions of electrolytic polymerization (particularly, the polymerization voltage), the conditions of precoating, etc., it is possible to highly fill the voids with the conductive polymer even in the vicinity of the separation part, and the filling rate of region C can be increased. Thus, the intrusion of air into the capacitor element is suppressed, and the deterioration of the conductive polymer is suppressed, so that the decrease in capacitance when used for a long time or at a high temperature with a voltage applied can be suppressed. Therefore, excellent durability of the solid electrolytic capacitor can be ensured.

[0080] (Others) The solid electrolytic capacitor includes at least one capacitor element. The solid electrolytic capacitor may be of a wound type, or may be either a chip type or a multilayer type. For example, the solid electrolytic capacitor may include two or more laminated capacitor elements. Also, the solid electrolytic capacitor may include two or more wound capacitor elements. The configuration of the capacitor element may be selected according to the type of the solid electrolytic capacitor.

[0081] In a capacitor element, one end of a cathode lead terminal is electrically connected to the cathode extraction layer, for example. The cathode lead terminal is joined to the cathode extraction layer through, for example, applying a conductive adhesive to the cathode extraction layer. One end of an anode lead terminal is electrically connected to the anode portion of the anode body, for example. The other ends of the anode lead terminal and the cathode lead terminal are each drawn out from a resin exterior or a case. The other ends of the respective terminals exposed from the resin exterior or the case are used for soldering connection to a substrate on which the solid electrolytic capacitor is to be mounted, etc.

[0082] The capacitor element is sealed using a resin exterior or a case. For example, the capacitor element and the material resin of the exterior (for example, uncured thermosetting resin and filler) may be housed in a mold, and the capacitor element may be sealed with the resin exterior by a transfer molding method, a compression molding method, or the like. At this time, the portions on the other end sides of the anode lead terminal and the cathode lead terminal connected to the anode lead drawn out from the capacitor element are each exposed from the mold. Further, the capacitor element may be housed in a bottomed case such that the portions on the other end sides of the anode lead terminal and the cathode lead terminal are located on the opening side of the bottomed case, and a solid electrolytic capacitor may be formed by sealing the opening of the bottomed case with a sealing body.

[0083] FIG. 1 is a cross-sectional view schematically showing the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure. However, the solid electrolytic capacitor of the present disclosure is not limited only to the following embodiments. Further, the components of the following embodiments may be arbitrarily combined with at least any one of the above (1) to (4) related to the solid electrolytic capacitor of the present disclosure.

[0084] As shown in FIG. 1, the solid electrolytic capacitor 1 includes a capacitor element 2, a resin exterior 3 that seals the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a part of each of which is exposed outside the resin exterior 3. The anode lead terminal 4 and the cathode lead terminal 5 can be made of a metal such as copper or a copper alloy. The resin exterior 3 has a substantially rectangular parallelepiped outer shape, and the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0085] The capacitor element 2 includes an anode foil 6 formed of an Al foil, a dielectric layer 7 that covers the anode foil 6, and a cathode portion 8 that covers the dielectric layer 7. The cathode portion 8 includes a conductive polymer layer 9 that covers the dielectric layer 7 and a cathode lead-out layer 10 that covers the conductive polymer layer 9. The anode foil 6 has a porous portion formed by etching or the like on both surface layers. The conductive polymer layer 9 has an inner layer filled in the voids of the porous portion and an outer layer protruding from the main surface of the anode foil 6 in the anode foil 6 having the dielectric layer 7.

[0086] The anode foil 6 includes a region (second portion) facing the cathode portion 8 and a region (first portion) not facing it. The first portion includes one end portion (first end portion) in the length direction of the anode foil 6, and the second portion includes a second end portion on the side opposite to the first end portion. A separation portion 13 that insulates the first portion and the cathode portion 8 is formed between the first end portion and the second end portion of the anode foil 6. In the illustrated example, the separation portion 13 is formed so as to cover the surface of the anode foil 6 in a band shape, and regulates the contact between the cathode portion 8 and the first portion of the anode foil 6. In the vicinity of the end portion B on the second end side of the separation portion 13, the filling rate in a predetermined region of the porous portion is 46% or more.

[0087] Among the region (first portion) of the anode foil 6 that does not face the cathode portion 8, the portion on the first end side (anode portion) is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0088] [Example] Hereinafter, the solid electrolytic capacitor according to the present disclosure will be specifically described based on examples and comparative examples. However, the solid electrolytic capacitor according to the present disclosure is not limited only to the following examples.

[0089] 《Solid electrolytic capacitors A1 to A3 and B1 to B2》 Solid electrolytic capacitors were fabricated and evaluated in the following manner.

[0090] (1) Preparation of anode foil Both surfaces of an aluminum foil (thickness: 130 μm) were roughened by etching to produce an anode foil having porous portions on both surface layers. The obtained anode foil had porous portions formed on the surface layers on both main surface sides and a core portion sandwiched between these porous portions. The thickness of the porous portion on each main surface side was 50 μm, and the thickness of the core portion was 30 μm.

[0091] (2) Formation of dielectric layer A second portion (cathode forming portion) including the second end portion of the anode foil was immersed in a formation solution, and a DC voltage of 70 V was applied for 20 minutes to form a dielectric layer containing aluminum oxide.

[0092] (3) Formation of conductive polymer layer In a predetermined region between the first end portion and the second end portion of the anode foil on which the dielectric layer was formed (more specifically, a predetermined region including the end portion on the second portion side of the first portion), a separation portion was formed. The anode foil on which the separation portion was formed was immersed in a liquid composition containing polyaniline sulfonic acid as a conductive material, taken out, and dried to be pre-coated. The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polyaniline sulfonic acid used for the pre-coating are shown in Table 1.

[0093] A polymerization solution containing pyrrole (a monomer of a conjugated polymer), naphthalenesulfonic acid (a dopant), and water was prepared. Electrolytic polymerization was carried out in a three-electrode system using the obtained polymerization solution. More specifically, a pre-coated anode foil, a counter electrode, and a reference electrode (silver / silver chloride reference electrode) were immersed in the polymerization solution. A voltage was applied to the anode foil so that the potential of the anode foil with respect to the reference electrode became the value of the polymerization voltage shown in Table 1, and electrolytic polymerization was carried out at 25 °C to form a conductive polymer layer.

[0094] (4) Formation of the cathode lead-out layer The anode foil obtained in the above (3) was immersed in a dispersion liquid in which graphite particles were dispersed in water, taken out from the dispersion liquid, and dried to form a first layer (carbon layer) on the surface of the conductive polymer layer. Drying was carried out at 130 to 180 °C for 10 to 30 minutes.

[0095] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the first layer and heated at 150 to 200 °C for 10 to 60 minutes to cure the binder resin, thereby forming a second layer (metal particle-containing layer). In this way, a cathode lead-out layer composed of the first layer (carbon layer) and the second layer (metal particle-containing layer) was formed, and a cathode portion composed of the conductive polymer layer and the cathode lead-out layer was formed. A capacitor element was fabricated as described above.

[0096] (5) Assembly of the solid electrolytic capacitor One end of the cathode portion of the capacitor element obtained in the above (4) and one end of the cathode lead terminal were joined via an adhesive layer formed of a conductive adhesive. One end of the anode lead terminal was joined to a region on the first end side of the first portion of the anode foil protruding from the capacitor element by laser welding. Next, a resin outer package formed of an insulating resin was formed around the capacitor element by mold molding. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal 5 were in a state of being drawn out from the resin outer package. In this way, the solid electrolytic capacitor was completed. Twenty solid electrolytic capacitors were fabricated in total in the same manner as above.

[0097] [Evaluation] The following evaluations were performed using solid electrolytic capacitors.

[0098] (a) Durability (reliability) test In an environment of 20°C, using an LCR meter for four-terminal measurement, measure the initial capacitance (μF) at a frequency of 120 Hz for each solid electrolytic capacitor. Then, obtain the average value (C0) among 20 solid electrolytic capacitors.

[0099] Next, leave the solid electrolytic capacitor standing for 400 hours with a voltage of 2 V applied at 145°C. After standing, measure the capacitance in the same procedure as in the case of the initial capacitance in a 20°C environment, and obtain the average value (C1) among 20 solid electrolytic capacitors. Obtain the ratio of C1 / C0, and regard the solid electrolytic capacitor with C1 / C0 < 0.8 as a defective product with low durability (reliability), and evaluate the durability (reliability) based on the ratio (%) of the number of defective products among 20.

[0100] (b) Filling rate in region C Using a solid electrolytic capacitor, by the above-described procedure, binarize the optical microscope image (magnification: 20 times) of the cross section parallel to the length direction and the thickness direction near the center in the width direction of the capacitor element by the Otsu binarization method, and obtain the area ratio (filling rate (%)) occupied by the region other than the voids in region C.

[0101] The evaluation results are shown in Table 1. A1 to A3 are examples, and B1 to B2 are comparative examples.

[0102] [Table 1]

[0103] As shown in Table 1, when the filling rate of region C is 46% or more, the defect rate is 0%, and excellent durability (reliability) can be obtained (A1 to A3). On the other hand, when the filling rate of region C is less than 46%, the defect rate becomes significantly higher compared to A1 to A3 (comparison between A1 to A3 and B1 to B2). As the filling rate decreases, the defect rate tends to increase (comparison between A1 to A3 and B1 to B2).

[0104] Although the present invention has been described with respect to the preferred embodiments at the present time, such disclosure should not be construed in a limiting sense. Various modifications and alterations will undoubtedly become apparent to those skilled in the art within the technical field to which the present invention pertains upon reading the above disclosure. Therefore, the appended claims should be construed to encompass all modifications and alterations without departing from the true spirit and scope of the present invention.

Industrial Applicability

[0105] According to the present disclosure, high heat resistance of the solid electrolytic capacitor can be ensured. The solid electrolytic capacitor of the present disclosure can be used in various applications where excellent durability (reliability) or high heat resistance is required. However, the applications of the solid electrolytic capacitor are not limited to these only.

Explanation of Signs

[0106] 1: Solid electrolytic capacitor 2: Capacitor element 3: Resin exterior body 4: Anode lead terminal 5: Cathode lead terminal 6: Anode foil 7: Dielectric layer 8: Cathode portion 9: Conductive polymer layer (solid electrolyte layer) 10: Cathode lead-out layer 11: First layer (carbon layer) 12: Second layer (metal particle-containing layer) 13: Separation portion 14: Adhesive layer

Claims

1. A solid electrolytic capacitor including at least one capacitor element, wherein the capacitor element comprises: an anode body having a porous portion at least on a surface layer, and having a first portion including a first end portion and a second portion including a second end portion opposite to the first end portion; a dielectric layer covering at least a part of the anode body; a cathode portion covering at least a part of the dielectric layer in the second portion; a separation portion located between the first end portion and the second end portion of the anode body and insulating the first portion from the cathode portion; and includes the cathode portion includes at least a conductive polymer layer covering at least a part of the dielectric layer, the conductive polymer layer includes a conductive polymer and has an inner layer filled in voids of the porous portion and an outer layer protruding from a main surface of the anode body having the dielectric layer, the separation portion has an end portion A on the first end portion side and an end portion B on the second end portion side, when the length from the end portion B to an end portion on the second end portion side of the cathode portion is L, a filling rate in a region C included in a portion within 0.05L from the end portion B of the porous portion is 46% or more, the filling rate is an area ratio of a portion other than the voids in the region C, a solid electrolytic capacitor.

2. The solid electrolytic capacitor according to claim 1, wherein the region C is a rectangular region having a length of a first side of 15 μm or more and 20 μm or less and a length of a second side orthogonal to the first side of 20 μm or more and 25 μm or less.

3. The anode body has a core portion and the porous portion, the porous portion is integrally formed with both surfaces of the core portion, the solid electrolytic capacitor according to claim 1 or 2, wherein a shortest distance between the region C and a surface of the core portion is 0 μm or more and 5 μm or less.

4. The solid electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer includes a conjugated polymer including a monomer unit corresponding to at least one selected from the group consisting of a pyrrole compound, a thiophene compound, and an aniline compound.

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