Electrolytic capacitors

Abstract

An electrolytic capacitor according to the present invention is provided with: a porous positive electrode body; a dielectric layer which is formed on the surface of the positive electrode body; and a conductive polymer and a salt compound, which are filled into the pores of the positive electrode body. If L is the shortest distance from the center of the positive electrode body to a first main surface of the positive electrode body, the first main surface being closest to the center, the region wherein the minimum value of the distances therefrom to main surfaces of the positive electrode body is L / 3 or less is taken as a surface layer part and the region wherein the minimum value of the distances therefrom to main surfaces of the positive electrode body is 2L / 3 or more is taken as a central part within the positive electrode body. In a cross-section that is perpendicular to the first main surface and passes through the center, the ratio B / A of the ion intensity B derived from the salt compound to the sum A of all ion densities as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is taken as the ion intensity ratio. The ratio R2 / R1 of the ion intensity ratio R2 in the central part to the ion intensity ratio R1 in the surface layer part of the positive electrode body is 0.15 or more.

Description

Technical Field

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[0003]

[0001] The present invention relates to an electrolytic capacitor, and more particularly to an electrolytic capacitor provided with a solid electrolyte layer containing a conductive polymer.

Background Art

[0002] Electrolytic capacitors are mounted in various electronic devices because they have a small equivalent series resistance (ESR) and excellent frequency characteristics. An electrolytic capacitor usually includes a capacitor element having an anode portion and a cathode portion. The anode portion includes a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with an electrolyte. There is an electrolytic capacitor that uses a solid electrolyte such as a conductive polymer as the electrolyte (see, for example, Patent Document 1).

[0003] Patent Document 2 describes a method for manufacturing a solid electrolytic capacitor including a capacitor element having an anode body with a dielectric film formed on its surface and a conductive polymer layer formed on the anode body, the method including a step of forming a dielectric film on the surface of the anode body, a step of forming a first conductive polymer layer on the dielectric film, a step of impregnating the anode body on which the first conductive polymer layer is formed with an ionic liquid, and a step of forming a second conductive polymer layer on the first conductive polymer layer after impregnating with the ionic liquid. It is stated that this can enhance the withstand voltage performance because it has the effect of repairing damage to the dielectric film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in electrolytic capacitors using a porous material as the anode, it is difficult to impregnate the anode with ionic liquid deep inside. In the technology described in Patent Document 2, there were no guidelines on how high the distribution of ionic liquid inside the anode should be to impregnate it, leaving room for further investigation. [Means for solving the problem]

[0006] In view of the above, one aspect of the present disclosure comprises a porous anode, a dielectric layer formed on the surface of the anode, and a conductive polymer and a salt compound filled in the pores of the anode, wherein the salt compound is a salt of a cation and anion, and L is the shortest distance from the center of the anode to the first main surface of the anode closest to the center, and within the anode, the region where the minimum distance to each of the main surfaces of the anode is L / 3 or less is defined as the surface layer, and within the anode, the region where the minimum distance to each of the main surfaces of the anode is 2L / 3 or more is defined as The present invention relates to an electrolytic capacitor in which, in a cross section perpendicular to the first main surface and passing through the center of the surface layer, the ratio of the ionic intensity B1 derived from the salt compound to the sum of all ionic intensities A1 measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is R1 (= B1 / A1), and in the cross section of the center, the ratio of the ionic intensity B2 derived from the salt compound to the sum of all ionic intensities A2 measured by time-of-flight secondary ion mass spectrometry is R2 (= B2 / A2), and R2 / R1 is 0.15 or greater. [Effects of the Invention]

[0007] This enables the creation of highly reliable electrolytic capacitors.

[0008] While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, in conjunction with other objects and features of the present invention. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of an anode body for illustrating the surface and central portion of the anode body in an electrolytic capacitor according to one embodiment of the present disclosure. [Figure 2] This is a schematic cross-sectional view showing an example of a capacitor element of an electrolytic capacitor according to one embodiment of the present disclosure. [Figure 3] This is a schematic cross-sectional view showing an electrolytic capacitor according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0011] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0012] An electrolytic capacitor according to one embodiment of the present disclosure comprises a porous anode and a dielectric layer formed on the surface of the anode. Typically, at least a portion of the dielectric layer is covered with a solid electrolyte layer, and at least a portion of the solid electrolyte layer is covered with a cathode layer. Here, since the anode is a porous body, the dielectric layer is formed along the inner walls of the pores of the porous anode, and the solid electrolyte layer is formed to block the pores of the anode. The pores of the anode are filled with a conductive polymer and a salt compound. The salt compound is a salt of a cation and anion. The cation may be an organic cation.

[0013] Electrolytic capacitors are susceptible to damage to their dielectric layer when subjected to prolonged conditions such as high temperatures and high voltages. Damage to the dielectric layer reduces the insulating properties of the damaged area, making it easier for large leakage currents to concentrate and flow through that area. The flow of large currents degrades the conductive polymers along the leakage current path near the damaged area of ​​the dielectric layer, making them more resistant. As a result, the capacitance of electrolytic capacitors tends to decrease in environments with high temperatures and high voltages.

[0014] By incorporating a salt compound into the solid electrolyte layer, the salt compound can be given the ability to repair damage to the dielectric layer, thereby suppressing the degradation of the conductive polymer and the decrease in capacitance of the electrolytic capacitor. The salt compound is fluid in the expected operating environment. The salt compound may also be an ionic liquid that is liquid in the expected operating environment. The salt compound, being an ionic liquid, flows through the gaps in the conductive polymer, and a portion of it reaches the vicinity of the surface of the dielectric layer, and if the dielectric layer is damaged, it has the function of repairing the damage.

[0015] Salt compounds can be dispersed within a solid electrolyte layer composed of conductive polymers by immersing an anode body, which has a conductive polymer layer covering a dielectric layer, in a liquid salt compound, thereby impregnating the conductive polymer layer with the salt compound. In this case, it is more difficult to impregnate the salt compound towards the center of the anode body, resulting in a distribution of salt compound concentration between the surface and the center of the anode body. To suppress the degradation of the conductive polymer and prevent a decrease in the capacitance of the electrolytic capacitor, it is important that a sufficient amount of salt compound is distributed even in the center of the anode body, which is located deep within the pores of the porous material.

[0016] However, the deeper the salt compound is impregnated into the pores of the anode, the greater the manufacturing time and other costs. On the other hand, there are no clear guidelines on how much salt compound should be present in the center of the anode, and impregnating the anode with more salt compound than necessary may increase manufacturing costs and degrade the characteristics of the electrolytic capacitor, such as increasing ESR. This disclosure provides guidance on the salt compound content in the center of the anode to address this problem.

[0017] The distribution of salt compounds in the anode can be evaluated by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0018] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a method for detecting the structure of a solid surface with high precision by irradiating the solid surface with a primary ion beam and detecting secondary ions generated by collisions between the primary ions and the solid surface at the molecular and atomic level using a mass spectrometer. Secondary ions are accelerated by an electric field to reach the detector. Since the time it takes for the ions to reach the detector (time of flight) depends on the mass and valency of the secondary ions, by measuring the distribution of the time of flight of secondary ions, it is possible to obtain information about elements and compounds present on the solid surface with high precision.

[0019] In any region of the cross-section of the anode body, let A be the sum of all ion intensities measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Among the total ion intensity A, let B be the ion intensity derived from the salt compound. The total ion intensity A is obtained by integrating the peaks of all ions with respect to the flight time in the mass spectrometry spectrum. The ion intensity B derived from the salt compound is obtained by integrating the peaks of the ions derived from the salt compound with respect to the flight time in the mass spectrometry spectrum. It can be said that the ratio B / A of the ion intensity B derived from the salt compound to the total ion intensity A represents the content rate of the salt compound in that region.

[0020] The ion intensity may be the anion intensity or the cation intensity. That is, the ion intensity derived from the anion contained in the salt compound may be measured, or the ion intensity derived from the corresponding cation may be measured. In the following embodiments, the case where the ion intensity is the anion intensity will be described as an example, but the present invention is not limited thereto.

[0021] Let L be the distance (shortest distance) from the center of the anode body to a predetermined first main surface of the anode body. The center of the anode body means the center of gravity. However, the center of gravity of the anode body here is obtained by considering only the shape of the outer contour of the anode body, assuming that the density is constant within the anode body without considering the density distribution within the anode body.

[0022] The anode body has one or more main surfaces. In the anode body, a region where the minimum value of the distance to each of the one or more main surfaces is L / 3 or less (in other words, a region where the distance to at least one main surface is L / 3 or less) is defined as the surface layer portion, and a region where the minimum value of the distance to each of the one or more main surfaces is 2L / 3 or more (in other words, a region where the distance to all main surfaces is 2L / 3 or more) is defined as the central portion.

[0023] Consider a cross-section of the anode body passing through the center of the anode body and perpendicular to the first main surface. In the cross-section, let the anion intensity ratio B / A measured in the surface layer part be R1, and the anion intensity ratio B / A measured in the central part be R2. Since it is difficult to impregnate the central part of the anode body with the salt compound compared to the surface layer part, usually R2 < R1, and the closer R2 / R1 is to 1, the more it means that the salt compound is uniformly distributed from the surface layer part to the central part.

[0024] According to the findings of the present disclosure, if R2 / R1 is 0.15 or more, the salt compound sufficiently penetrates to the center of the anode body, and a sufficient effect of repairing the damage to the dielectric layer can be obtained at the center of the anode body. As a result, deterioration of the conductive polymer constituting the solid electrolyte layer can be suppressed, and a decrease in the capacitance of the electrolytic capacitor can be suppressed. R2 / R1 is more preferably 0.4 or more, and the effects of suppressing deterioration of the conductive polymer constituting the solid electrolyte layer and suppressing a decrease in the capacitance of the electrolytic capacitor are remarkable. From the viewpoint of reducing the time for impregnating the anode body with the salt compound and suppressing an increase in manufacturing cost, R2 / R1 may be 0.9 or less, and more preferably 0.8 or less.

[0025] The anode body usually has a plurality of main surfaces (surfaces). For example, when the anode body has a substantially rectangular parallelepiped shape, it has six main surfaces (surfaces) corresponding to each surface of the rectangular parallelepiped. When at least any one of the plurality of main surfaces is defined as the first main surface and the surface layer part and the central part are defined as above, it is sufficient if R2 / R1 satisfies the above relationship. When the main surface with the shortest distance from the center of the anode body among the plurality of main surfaces is defined as the first main surface, if R2 / R1 satisfies the above relationship, a sufficient effect can be obtained. When the main surface with the longest distance from the center of the anode body among the plurality of main surfaces is defined as the first main surface, R2 / R1 may satisfy the above relationship. In all of the plurality of main surfaces, R2 / R1 may satisfy the above relationship when each main surface is defined as the first main surface.

[0026] The larger the size of the anode, the more likely it is that a difference in the distribution of salt compounds will occur between the surface and the center, making it difficult to sufficiently repair damage to the dielectric layer in the center. In particular, when the above-mentioned distance L is 0.1 mm or more, the difference in the distribution of salt compounds between the surface and the center tends to widen, and the deterioration of the conductive polymer and the decrease in capacitance of the electrolytic capacitor due to damage to the dielectric layer become significant. However, in the electrolytic capacitor according to one embodiment of this disclosure, by setting R2 / R1 to 0.15 or more, even when the distance L is 0.1 mm or more, a sufficient effect of repairing damage to the dielectric layer can be obtained even in the center of the anode, thereby suppressing the deterioration of the conductive polymer due to damage to the dielectric layer and suppressing the decrease in capacitance of the electrolytic capacitor.

[0027] Electrolytic capacitors may be provided with an anode wire (lead conductor) that extends from the anode body to electrically connect the anode body to an external anode terminal. Inside the anode body, the anode wire usually extends toward the center of the anode body in a direction perpendicular to a second main surface, which is the mounting surface. Alternatively, the anode wire extends toward the center of the anode body in a direction perpendicular to the second main surface, which is the mounting surface, and then extends further away from the mounting surface after passing through the center. In this case, the first main surface, which defines the surface and the center, may be the mounting surface of the anode wire, or it may be a different surface. The first main surface may be a different surface from the mounting surface of the anode wire and may be a surface that aligns with the direction in which the anode wire extends within the anode body. The anode wire may extend within the anode body in a direction inclined at 0° to 30° with respect to the first main surface.

[0028] Figure 1 shows an example of a cross-section of the anode body of an electrolytic capacitor in this embodiment, illustrating the surface and central regions. The surface of the anode body 1 is covered with a dielectric layer, and at least a portion of the surface of the dielectric layer is covered with a solid electrolyte layer. Since the anode body 1 is porous, the dielectric layer is formed to cover the inner walls of the pores of the porous anode body 1, and the solid electrolyte layer may be formed to block the pores of the anode body 1, extending deep into the porous anode body 1 (for example, to the region near the anode wire 2). However, Figure 1 omits the depiction of the dielectric layer and solid electrolyte layer formed inside the anode body.

[0029] The anode wire 2 is embedded in the anode body 1. A portion of the anode wire 2 is embedded in the main surface S2 of the anode body and exposed to the outside, while the remaining portion of the anode wire 2 is embedded within the anode body 1. Within the anode body 1, the anode wire 2 extends toward the center G of the anode body 1. The anode wire 2 extends toward the center G in a direction substantially parallel to the main surface S1 of the anode body 1, and then passes through the center G and moves away from the surface S2 toward the surface S3 opposite the surface S2, similarly extending toward the surface S1 in a direction substantially parallel to the surface S1.

[0030] Let L be the shortest distance from the center G of the anode 1 to the main surface S1. The surface region X is the area where the minimum distance to each of the main surfaces of the anode is L / 3 or less. The central region Y is the area where the minimum distance to each of the main surfaces of the anode is 2L / 3 or more. In Figure 1, the anode wire 2 is included in the area where the distance to main surfaces S1 to S3 is 2L / 3 or more, but the area where the anode wire 2 exists is not included in the central region Y.

[0031] R2 / R1 can be calculated, for example, as follows:

[0032] First, the anode body, on which the solid electrolyte layer is formed, is cut so as to form a cross-section perpendicular to the main surface S1 and containing the center G of the anode body. A cross-section polisher (CP) may be used to form the cross-section. In the cross-section, the distance (shortest distance) from the center G of the anode body to the main surface S1 is L. In the cross-section, the region where the distance to the outer contour of the anode body is L / 3 or less is the surface layer X, and the region where the distance to the outer contour of the anode body is 2L / 3 or more is the center Y. If the anode wire is visible in the cross-section, the region where the anode wire is visible is not included in the center. The cross-section may be a plane along the direction in which the anode wire extends, or a plane perpendicular to the direction in which the anode wire extends.

[0033] Next, the anion intensity is measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) while scanning the measurement site along the cross-section. The measurement site is scanned within the surface layer X, and the ratio R1 = B1 / A1 of the intensity (number) of secondary anions derived from the salt compound (B1) to the sum of the intensities (number) of all detected secondary anions (A1) is calculated. Similarly, the measurement site is scanned within the central area Y, and the ratio R2 = B2 / A2 of the intensity (number) of secondary anions derived from the salt compound (B2) to the sum of the intensities (number) of all detected secondary anions (A2) is calculated. From this, R2 / R1 can be determined.

[0034] Below is an example of detailed measurement conditions for time-of-flight secondary ion mass spectrometry (TOF-SIMS). Primary ion: Au Acceleration voltage: 30kV Measurement mode: Bunching mode (high mass resolution measurement) Measurement area: 100μm x 100μm Measurement device: PHI TRIFT V nanoTOF (manufactured by ULVAC-PHI)

[0035] Examples of cations constituting salt compounds include imidazolium, pyrrolidinium, piperidinium, pyridinium, morpholinium, ammonium, phosphonium, sulfonium, and their derivatives. The cations may also be organic cations. Examples of anions include anions of acids such as bisulfate ions, acetic acid, sulfuric acid, lactic acid, nitric acid, benzoic acid, methylsulfuric acid, methanesulfonic acid, diethylphosphonic acid, trifluoromethaneacetic acid, and trifluoromethanesulfonic acid, and their derivatives. The anions may contain fluorine. Examples of fluorine-containing anions include the anions of trifluoromethaneacetic acid and trifluoromethanesulfonic acid mentioned above, as well as bis(trifluoromethylsulfonyl)imide anions and their derivatives.

[0036] Salt compounds may also be ionic liquids. An ionic liquid is synonymous with a molten salt, and is, for example, an ionic substance that is liquid at 25°C. Examples of ionic liquids include 1-butyl-3-methylimidazolium bisulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoromethanesulfonic acid, and 1-ethyl-3-methylimidazolium diethylphosphonic acid.

[0037] Hydrophilic ionic liquids are preferred. Hydrophilic ionic liquids readily retain moisture, and the moisture contained in the ionic liquid easily improves the repairability of damage to the dielectric layer. Here, ionic liquids in which the amount of moisture measured by the Karl Fischer method is 0.2% by mass or more relative to the total mass of the ionic liquid are defined as hydrophilic ionic liquids, and ionic liquids in which the amount is less than 0.2% by mass are defined as hydrophobic ionic liquids. Among the ionic liquids listed above, 1-butyl-3-methylimidazolium bisulfate, 1-butyl-3-methylimidazolium trifluoromethanesulfonic acid, and 1-ethyl-3-methylimidazolium diethylphosphonic acid are hydrophilic ionic liquids.

[0038] ≪Electrolytic Capacitors≫ The electrolytic capacitor and its manufacturing method according to this embodiment will be described below with reference to the drawings as appropriate. However, the present invention is not limited thereto. Figure 2 is a schematic cross-sectional view showing an example of a capacitor element of the electrolytic capacitor according to this embodiment. Figure 3 is a schematic cross-sectional view of the electrolytic capacitor according to this embodiment.

[0039] The electrolytic capacitor 20 comprises a capacitor element 10 having an anode portion 6 and a cathode portion 7, an outer casing 11 that encloses the capacitor element 10, an anode lead terminal 13 electrically connected to the anode portion 6 and partially exposed from the outer casing 11, and a cathode lead terminal 14 electrically connected to the cathode portion 7 and partially exposed from the outer casing 11. The anode portion 6 has an anode body 1 and an anode wire 2. A dielectric layer 3 is formed on the surface of the anode body. The cathode portion 7 has a solid electrolyte layer 4 that covers at least a portion of the dielectric layer 3 and a cathode layer 5 that covers at least a portion of the surface of the solid electrolyte layer 4.

[0040] <Capacitor element> The following will provide a detailed explanation of the capacitor element 10, using the case where a solid electrolyte layer is provided as the electrolyte as an example.

[0041] The anode section 6 comprises an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connected to an anode lead terminal 13. The anode 1 is, for example, a rectangular porous sintered body obtained by sintering metal particles. As the metal particles, valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used. One or more types of metal particles are used in the anode 1. The metal particles may be an alloy composed of two or more metals. For example, an alloy containing a valve metal with silicon, vanadium, boron, etc. can be used. Alternatively, a compound containing a valve metal with a typical element such as nitrogen may be used. The valve metal alloy has a valve metal as its main component, for example, containing 50 atomic percent or more of the valve metal.

[0042] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited, and examples include copper, aluminum, aluminum alloy, etc., in addition to the valve metal mentioned above. The materials constituting the anode body 1 and the anode wire 2 may be the same or different. The anode wire 2 has a first portion 2a embedded in the interior of the anode body 1 from one surface of the anode body 1, and a second portion 2b extending from the aforementioned surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited, and examples include circular, track-shaped (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), elliptical, rectangular, polygonal, etc.

[0043] The anode portion 6 is manufactured, for example, by pressure molding a rectangular parallelepiped shape with the first portion 2a embedded in the powder of the first metal particles, and then sintering it. As a result, the second portion 2b of the anode wire 2 is drawn out from one side of the anode body 1 so as to be embedded. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, so that the anode wire 2 and the anode lead terminal 13 are electrically connected. The welding method is not particularly limited and can include resistance welding, laser welding, etc.

[0044] A dielectric layer 3 is formed on the surface of the anode 1. The dielectric layer 3 is composed of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode 1 include, for example, immersing the anode 1 in a chemical conversion solution to anodize the surface of the anode 1, or heating the anode 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to the layer containing the metal oxide described above, and only needs to have insulating properties.

[0045] Furthermore, the anode body 1 is not limited to a porous sintered body, but may also be a metal foil of a valve-acting metal such as aluminum foil.

[0046] (Cathode part) The cathode portion 7 has a solid electrolyte layer 4 and a cathode layer 5 that covers the solid electrolyte layer 4. The solid electrolyte layer 4 is formed to cover at least a portion of the dielectric layer 3.

[0047] For the solid electrolyte layer 4, for example, a manganese compound or a conductive polymer can be used. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used individually or in combination. The conductive polymer may also be a copolymer of two or more monomers. Polythiophene, polyaniline, and polypyrrole may be used because of their excellent conductivity. Polypyrrole may be used in particular because of its excellent water repellency.

[0048] The solid electrolyte layer 4 containing the conductive polymer described above may be composed of two or more solid electrolyte layers. For example, the solid electrolyte layer 4 includes a first conductive polymer layer covering the dielectric layer 3 and a second conductive polymer layer covering the first conductive polymer layer. When the solid electrolyte layer 4 is composed of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may differ. For example, the first conductive polymer layer may be formed by polymerizing raw material monomers on the dielectric layer 3. Alternatively, the second conductive polymer layer may be formed by applying a liquid containing the conductive polymer to the dielectric layer 3.

[0049] In this specification, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, and polyaniline as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0050] Various dopants may be added to polymerization solutions, solutions, or dispersions of conductive polymers to improve the conductivity of the conductive polymer. The dopants are not particularly limited, but examples include naphthalene sulfonic acid, p-toluenesulfonic acid, and polystyrene sulfonic acid.

[0051] When conductive polymers are dispersed in a dispersion medium in the form of particles, the average particle size D50 is, for example, between 0.01 μm and 0.5 μm. If the average particle size D50 is within this range, the particles can easily penetrate into the interior of the anode 1.

[0052] The solid electrolyte layer contains a salt compound. Although not shown in Figures 2 and 3, since the anode 1 is porous, the dielectric layer 3 is formed to cover the inner walls of the pores of the porous anode 1, and the solid electrolyte layer 4 penetrates deep into the porous anode 1 (for example, to the region near the anode wire 2) so as to block the pores of the anode 1. Within the solid electrolyte layer, the salt compound content may differ between the surface side of the anode 1 and the central side closer to the anode wire 2. In the electrolytic capacitor of this embodiment, the difference between the salt compound content on the surface side of the anode 1 and the salt compound content on the central side closer to the anode wire 2 is reduced. Specifically, the salt compound is distributed within the solid electrolyte layer such that the ratio R2 / R1 of the anion intensity ratio R2 derived from the salt compound in the central part to the anion intensity ratio R1 derived from the salt compound in the surface part is 0.15 or more.

[0053] The cathode layer 5 includes, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. However, the configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 is acceptable as long as it has a current collecting function.

[0054] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 may be a metal such as copper, or a nonmetal. Its shape is not particularly limited as long as it is flat. The thickness of the anode lead terminal 13 (distance between the main surfaces of the anode lead terminal 13) may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less, from the viewpoint of reducing the profile.

[0055] One end of the anode lead terminal 13 may be joined to the anode wire 2 by conductive adhesive or solder, or by resistance welding or laser welding. The other end of the anode lead terminal 13 is led out to the outside of the housing 11 and is exposed from the housing 11. The conductive adhesive is, for example, a mixture of a thermosetting resin and carbon particles or metal particles, as described later.

[0056] <Cathode lead terminals> The cathode lead terminal 14 is electrically connected to the cathode portion 7 at the junction 14a. The junction 14a is the portion of the cathode lead terminal 14 that overlaps with the cathode layer 5 when viewed from the direction normal to the cathode layer 5.

[0057] The cathode lead terminal 14 is joined to the cathode layer 5, for example, via a conductive adhesive 8. One end of the cathode lead terminal 14 forms part of the joint 14a, for example, and is located inside the casing 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a portion of the cathode lead terminal 14, including the other end, is exposed from the casing 11.

[0058] The material of the cathode lead terminal 14 is not particularly limited, as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 may be a metal such as copper, or a nonmetal. Its shape is also not particularly limited, and for example, it may be long and flat. From the viewpoint of reducing the profile, the thickness of the cathode lead terminal 14 may be 25 μm to 200 μm, or 25 μm to 100 μm.

[0059] <Exterior> The outer casing 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is made of an insulating material (outer casing material). The outer casing material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0060] ≪Manufacturing Method for Electrolytic Capacitors≫ An example of a method for manufacturing an electrolytic capacitor according to this embodiment is described below.

[0061] (1) Preparation process for capacitor elements First, the capacitor element is prepared. The steps for preparing the capacitor element include, for example, preparing the anode, covering at least a portion of the anode with a dielectric layer, covering at least a portion of the dielectric layer with a solid electrolyte layer, and covering at least a portion of the solid electrolyte layer with a carbon layer. The steps for preparing the capacitor element may further include covering at least a portion of the carbon layer with a conductive resin layer (conductive paste layer).

[0062] (1a) Preparation of the anode A porous sintered body can be used as the anode 1. Valve metal particles and an anode wire 2 are placed in a mold such that the first portion 2a is embedded in the valve metal particles, and after pressure molding, an anode portion 6 including the anode 1, which is a porous body of valve metal, is obtained by sintering. The first portion 2a of the anode wire is embedded in the interior of the porous sintered body from one side. The pressure during pressure molding is not particularly limited. Sintering is preferably carried out under reduced pressure. A binder such as polyacrylic carbonate may be mixed with the valve metal particles as needed.

[0063] Valve-acting metal particles are typically pressure-molded and sintered using a mold with a rectangular internal space. In this case, the shape of the anode body 1 after sintering is also a rectangular parallelepiped and has multiple main surfaces.

[0064] (1b) Dielectric layer formation process Next, the anode 1 is subjected to a chemical treatment to cover at least a portion of the anode 1 with a dielectric layer 3. Specifically, the anode 1 is immersed in a chemical treatment tank filled with an electrolytic aqueous solution (for example, an aqueous phosphoric acid solution), and the second portion 2b of the anode wire 2 is connected to the anode in the chemical treatment tank to perform anodic oxidation, thereby forming a dielectric layer 3 consisting of an oxide film of a valve-acting metal on the surface of the porous portion. As the electrolytic aqueous solution, not only an aqueous phosphoric acid solution but also nitric acid, acetic acid, sulfuric acid, etc., can be used.

[0065] (1c) Process for forming a solid electrolyte layer Next, at least a portion of the dielectric layer 3 is covered with a solid electrolyte layer 4. This gives a capacitor element 10 comprising an anode 1, a dielectric layer 3, and a solid electrolyte layer 4. The solid electrolyte layer 4 may also include multiple conductive polymer layers.

[0066] As an example of forming a solid electrolyte layer 4 containing multiple conductive polymer layers, the solid electrolyte layer formation step may include: (i) impregnating the anode body with a first solution containing a first monomer, which is a raw material for the first conductive polymer, and polymerizing the first monomer on the surface of the dielectric layer to form a first conductive polymer layer covering the dielectric layer; and (ii) impregnating the anode body with a solution or dispersion containing a second conductive polymer to form a second conductive polymer layer covering the first conductive polymer layer.

[0067] In step (i), a first conductive polymer layer is formed on the anode body 1 on which the dielectric layer 3 is formed by impregnating it with monomers or oligomers, and then polymerizing the monomers or oligomers by chemical polymerization or electrolytic polymerization. The first conductive polymer may contain a dopant. The conductive polymer and dopant can be selected from those exemplified for the solid electrolyte layer 4, respectively.

[0068] In step (i) for forming the first conductive polymer layer, the raw material monomers for the first conductive polymer are oxidatively polymerized (so-called "in-situ polymerization") above the dielectric layer 3 to form the first conductive polymer layer on the dielectric layer 3. As a result, fine irregularities may occur on the surface of the first conductive polymer layer due to non-uniform polymerization reactions and non-uniform layer growth.

[0069] In step (ii), a solution or dispersion containing the second conductive polymer is impregnated into the anode body to cover the surface of the first conductive polymer layer with the second conductive polymer layer. The second conductive polymer layer is formed so as to fit into the recesses on the surface of the first conductive polymer layer, thereby improving the adhesion between the first conductive polymer layer and the second conductive polymer layer.

[0070] Prior to step (ii), the anode body on which the first conductive polymer layer is formed may be cleaned to remove any unreacted monomers, dopants, and other unwanted components such as oxidizing agents contained in the first conductive polymer layer.

[0071] Following step (ii), the anode body may be impregnated with a solution or dispersion containing the third conductive polymer to form a third conductive polymer layer covering the second conductive polymer layer.

[0072] The second conductive polymer may contain a dopant. The conductive polymer and dopant may be selected from those exemplified for the solid electrolyte layer 4. A known binder can be used. The dispersion may contain known additives used when forming the solid electrolyte layer.

[0073] After the conductive polymer layer is formed, a step is taken to impregnate the solid electrolyte layer 4 with a salt compound. If the salt compound is an ionic liquid, the impregnation of the salt compound can be performed by immersing the anode 1, on which the conductive polymer layer is formed, in the ionic liquid which is the salt compound. Alternatively, the anode 1, on which the conductive polymer layer is formed, may be immersed in a liquid mixture of the ionic liquid and another solvent. The salt compound may also be impregnated into the solid electrolyte layer under reduced pressure.

[0074] When forming a solid electrolyte layer 4 containing multiple conductive polymer layers, the salt compound impregnation step may be performed after the formation of any of the conductive polymer layers. The closer the conductive polymer layer to which the salt compound is impregnated is to the dielectric layer and the earlier it is formed, the easier it is to distribute the salt compound near the dielectric layer, thereby enhancing the repair effect on damage to the dielectric layer. On the other hand, the later the conductive polymer layer to which the salt compound is impregnated is formed, the more salt compound can be contained within the solid electrolyte layer. In addition, it is easier to control the ratio of ionic strengths R2 / R1 derived from the salt compound to be 0.15 or higher.

[0075] Since the salt compound is introduced into the solid electrolyte layer by immersing the anode body 1, on which a conductive polymer layer is formed, in an ionic liquid, there is a difference in the salt compound content between the surface of the anode body, which is close to the surface of the solid electrolyte layer 4, and the center of the anode body, which is close to the anode wire. Typically, the salt compound content in the surface of the anode body is higher than the salt compound content in the center of the anode body. In an electrolytic capacitor according to one embodiment of this disclosure, the difference in salt compound content between the surface and center of the anode body is reduced so that the ratio R2 / R1 of the ionic intensity ratio R2 derived from the salt compound in the center to the ionic intensity ratio R1 derived from the salt compound in the surface is 0.15 or more within the solid electrolyte layer. This suppresses the degradation of the conductive polymer due to damage to the dielectric layer and reduces the capacitance reduction of the electrolytic capacitor without unnecessarily increasing manufacturing costs.

[0076] Furthermore, the above ratio R2 / R1 can be controlled to be 0.15 or higher by adjusting conditions such as the immersion time, temperature, atmospheric pressure, and mixing ratio of the ionic liquid when immersing the anode in an ionic liquid or a mixture of an ionic liquid and another solvent.

[0077] (1d) Process for forming the carbon layer and the conductive resin layer Next, a cathode layer 5 is formed by sequentially applying carbon paste and metal paste to the surface of the solid electrolyte layer 4, comprising a carbon layer 5a and a conductive resin layer (metal paste layer) 5b. The configuration of the cathode layer 5 is not limited to this, and any configuration that has a current collection function is acceptable.

[0078] (2) Electrical connection process between the capacitor element and the lead terminals Next, the anode lead terminal 13 and cathode lead terminal 14 are prepared. The second portion 2b of the anode wire 2, which is planted from the anode body 1, is joined to the anode lead terminal 13 by laser welding or resistance welding. After applying conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode part 7 via the conductive adhesive 8.

[0079] Next, the capacitor element 10 and the materials for the outer casing 11 (for example, uncured thermosetting resin and filler) are placed in a mold, and the capacitor element 10 is sealed by a transfer molding method, compression molding method, or the like. At this time, a portion of the anode lead terminal 13 and cathode lead terminal 14 are exposed from the mold. The molding conditions are not particularly limited, and the time and temperature conditions should be set appropriately considering the curing temperature of the thermosetting resin used.

[0080] Finally, the exposed portions of the anode lead terminal 13 and cathode lead terminal 14 are bent along the outer casing 11 to form a bent portion. This positions parts of the anode lead terminal 13 and cathode lead terminal 14 on the mounting surface of the outer casing 11. By the method described above, the electrolytic capacitor 20 is manufactured.

[0081] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0082] <Example 1> Electrolytic capacitors were manufactured according to the following procedure. (Formation of anode) Tantalum metal particles were used as the valve metal. The tantalum metal particles were formed into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and then the formed body was sintered in a vacuum. This resulted in an anode section containing an anode body made of a porous sintered tantalum body and an anode wire, one end of which was embedded in the anode body and the remaining part which was planted from one side of the anode body. The size of the anode body after sintering was approximately 5.0 mm × 4.0 mm × 1.0 mm, roughly a rectangular parallelepiped, and the anode wire was planted from a 4.0 mm × 1.0 mm surface.

[0083] Next, the anode body and a portion of the anode wire planted from the anode body were immersed in a chemical conversion tank filled with an electrolytic phosphoric acid solution, and the other end of the anode wire was connected to the anode body in the chemical conversion tank. Then, by performing anodic oxidation, a uniform dielectric layer of tantalum oxide (Ta2O5) was formed on the surface of the anode body (the surface of the porous sintered body including the inner wall surface of the pores) and on the surface of a portion of the anode wire.

[0084] Next, 3,4-ethylenedioxythiophene, the raw material for the first conductive polymer, along with p-iron(III) toluenesulfonate and 1-butanol were mixed to prepare a dispersion (reaction solution) containing the first monomer. After immersing the anode in the dispersion, the anode was removed from the dispersion and heat-treated in the air. In this case, p-iron(III) toluenesulfonate functions as an oxidizing agent. In this manner, the first monomer was polymerized on the dielectric layer, forming a solid electrolyte layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) as the first conductive polymer layer.

[0085] Next, after washing the anode on which the first conductive polymer layer had formed, a second dispersion was prepared by mixing poly(3,4-ethylenedioxythiophene) as the second conductive polymer with p-toluenesulfonate. After immersing the anode in the second dispersion, the anode was removed from the second dispersion, allowing the second dispersion to permeate the anode. Subsequently, a drying treatment was performed at 80°C for 20 minutes under atmospheric pressure to form the second conductive polymer layer.

[0086] Next, the anode body, on which the first and second conductive polymer layers were formed, was immersed in an aqueous solution containing 1-butyl-3-methylimidazolium bisulfate, an ionic liquid, at 25°C. The solid electrolyte layer was impregnated with the salt compound by reducing the pressure to -95 kPa relative to atmospheric pressure in a vacuum desiccator, then returning to atmospheric pressure and holding for 10 minutes. Subsequently, a drying treatment was performed at 130°C for 10 minutes to obtain anode body A1.

[0087] Anode A1 was cut through its center by planes perpendicular to a 5.0 × 4.0 mm plane and a 4.0 mm × 1.0 mm plane to form a cross-section. Anion intensity was measured along the cross-section by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The measurement site was scanned within the surface layer of the cross-section, and the ratio R1 = B1 / A1 of the intensity (number) of secondary anions derived from the salt compound (B1) to the sum of the intensities (number) of all detected secondary anions (A1) was determined. Similarly, the measurement site was scanned within the center of the cross-section, and the ratio R2 = B2 / A2 of the intensity (number) of secondary anions derived from the salt compound (B2) to the sum of the intensities (number) of all detected secondary anions (A2) was determined. The ratio R2 / R1 was 0.4.

[0088] Using anode A1, a cathode layer consisting of a carbon layer and a silver paste layer was formed by sequentially applying carbon paste and metal paste to a predetermined area on the surface of the solid electrolyte layer, thereby obtaining a capacitor element.

[0089] Anode and cathode lead terminals were further arranged on the capacitor element, and an outer casing was formed using a resin containing silica particles as a filler. Subsequently, the anode and cathode lead terminals protruding from the outer casing were bent along the casing to fabricate an electrolytic capacitor C1 with the structure shown in Figure 3.

[0090] <Example 2> In Example 1, the pressure during immersion of the anode in an aqueous solution containing the ionic liquid 1-butyl-3-methylimidazolium bisulfate was changed, and the pressure in the vacuum desiccator was set to -50 kPa relative to atmospheric pressure. Otherwise, anode A2 was obtained in the same manner as in Example 1. An electrolytic capacitor C2 was fabricated using anode A2.

[0091] A cross-section of anode A2 was formed in the same manner as in Example 1, and the ratio R2 / R1 was determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The ratio R2 / R1 was 0.15.

[0092] <Comparative Example 1> In Example 1, the pressure used when immersing the anode in an aqueous solution containing the ionic liquid 1-butyl-3-methylimidazolium bisulfate was changed. No depressurization was performed, and the anode was immersed at atmospheric pressure for 10 minutes. Otherwise, anode B1 was obtained in the same manner as in Example 1. An electrolytic capacitor C3 was fabricated using anode B1.

[0093] A cross-section of anode body B1 was formed in the same manner as in Example 1, and the ratio R2 / R1 was determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The ratio R2 / R1 was 0.03.

[0094] <Comparative Example 2> In Example 1, the anode was not immersed in the ionic liquid. Otherwise, anode B2 was obtained in the same manner as in Example 1. An electrolytic capacitor C4 was fabricated using anode B2.

[0095] The following evaluations were performed on the electrolytic capacitors C1 to C4 of the examples and comparative examples prepared above. [evaluation] Under 20°C conditions, the capacitance C0(F) of the electrolytic capacitor was measured using a 4-terminal LCR meter and evaluated as the initial capacitance.

[0096] Next, a voltage of 50V was applied at a temperature of 105°C for 750 hours. Afterward, the capacitance C1(F) was measured using the same method as described above. The capacitance retention rate was then evaluated as X = (C1 / C0) × 100. The evaluation results are shown in Table 1. Table 1 also shows the values ​​of the anode ratio R2 / R1 used in the evaluation.

[0097] [Table 1]

[0098] Table 1 shows that when using anodes A1 or A2 with a ratio R2 / R1 of 0.15 or higher, the decrease in capacitance of the electrolytic capacitor is suppressed even when high voltage is applied at high temperatures for extended periods, thus maintaining high reliability of the electrolytic capacitor. In anode B1, the ionic liquid is unevenly distributed on the surface of the anode, resulting in a lower capacitance retention rate compared to anode B2, which is not impregnated with ionic liquid. Therefore, immersion under atmospheric pressure alone is considered insufficient as a process for impregnating with ionic liquid. [Industrial applicability]

[0099] The present invention can be used in electrolytic capacitors, and preferably in electrolytic capacitors that use a porous material as the anode.

[0100] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of symbols]

[0101] 20: Electrolytic capacitors 10: Capacitor element 1: Anode 2: Anode wire 2a:First part 2b:Second part 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Conductive resin layer 6: Anode section 7: Cathode 8: Conductive adhesive 11: Exterior 13: Anode lead terminal 14: Cathode lead terminals 14a: Joint

Claims

1. The device comprises a porous anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer containing a conductive polymer covering at least a portion of the dielectric layer, and a salt compound dispersed within the solid electrolyte layer. The aforementioned salt compound is a salt of a cation and anion, Let L be the shortest distance from the center of the anode to the first main surface of the anode closest to the center. Within the anode body, the region where the minimum distance to each of the main surfaces of the anode body is L / 3 or less is defined as the surface layer. Within the anode body, the region where the minimum distance to each of the main surfaces of the anode body is 2L / 3 or more is defined as the central region. In a cross-section passing through the center of the surface layer and perpendicular to the first main surface, the ratio of the ionic intensity B1 derived from the salt compound to the sum of all ionic intensities A1 measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is defined as R1 (= B1 / A1). In the cross-section of the central part, when the ratio of the ionic intensity B2 derived from the salt compound to the sum A2 of all ionic intensities measured by the time-of-flight secondary ion mass spectrometry is R2 (= B2 / A2), An electrolytic capacitor where R2 / R1 is between 0.15 and 0.

4.

2. The system further comprises an anode wire that is planted from the anode body, The electrolytic capacitor according to claim 1, wherein the first main surface is a surface within the anode body that is aligned with the direction in which the anode wire extends.

3. The electrolytic capacitor according to claim 2, wherein the cross-section is a plane along the direction in which the anode wire extends.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the salt compound is an ionic liquid.

5. The electrolytic capacitor according to any one of claims 1 to 3, wherein the salt compound is a hydrophilic ionic liquid.

6. The electrolytic capacitor according to claim 4, wherein the anion constituting the ionic liquid includes a hydrogen sulfate ion.

7. The electrolytic capacitor according to any one of claims 1 to 3, wherein the distance L is 0.1 mm or more.

8. The electrolytic capacitor according to any one of claims 1 to 3, wherein the ionic strength is an anionic strength.

9. The electrolytic capacitor according to any one of claims 1 to 3, wherein the ionic strength is the cation strength.

10. The process of preparing the anode, A step of covering at least a portion of the anode body with a dielectric layer, A step of forming a solid electrolyte layer including a conductive polymer layer so as to cover at least a portion of the dielectric layer, The process includes impregnating the anode body on which the conductive polymer layer is formed with a salt compound, Let L be the shortest distance from the center of the anode to the first main surface of the anode closest to the center. Within the anode body, the region where the minimum distance to each of the main surfaces of the anode body is L / 3 or less is defined as the surface layer. Within the anode body, the region where the minimum distance to each of the main surfaces of the anode body is 2L / 3 or more is defined as the central region. In a cross-section passing through the center of the surface layer and perpendicular to the first main surface, the ratio of the ionic intensity B1 derived from the salt compound to the sum of all ionic intensities A1 measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) is defined as R1 (= B1 / A1). In the cross-section of the central part, when the ratio of the ionic intensity B2 derived from the salt compound to the sum A2 of all ionic intensities measured by the time-of-flight secondary ion mass spectrometry is R2 (= B2 / A2), A method for manufacturing an electrolytic capacitor, comprising the step of impregnating with the salt compound, wherein the salt compound is impregnated such that R2 / R1 is 0.15 or more and 0.4 or less.

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