Electrolytic capacitors

Abstract

Disclosed is an electrolytic capacitor (100) including a capacitor element (10). The capacitor element (10) includes a positive electrode, a dielectric layer formed on a surface of the positive electrode, a negative electrode, and an electrolyte layer and a separator that are arranged between the dielectric layer and the negative electrode. The electrolyte layer includes a non-aqueous solvent, electrically conductive particles, and an electrically conductive polymer. The amount of electrically conductive particles present in a dielectric-layer-side first portion of the electrolyte layer differs from the amount of electrically conductive particles present in a negative-electrode-side second portion of the electrolyte layer.

Description

Technical Field

[0001] The present disclosure relates to an electrolytic capacitor.

Background Art

[0002] Capacitors used in electronic devices are required to have a large capacitance and a low equivalent series resistance (ESR) value in the high-frequency region. When the ESR is large, various problems occur. For example, when a ripple current flows, heat generation proportional to the ESR occurs, and the characteristics of the conductive polymer deteriorate due to the heat generation.

[0003] As a capacitor with a large capacitance and a low ESR, an electrolytic capacitor using a conductive polymer such as polypyrrole, polythiophene, polyfuran, or polyaniline is promising. Patent Document 1 (International Publication No. 2012 / 117994) discloses, as a conductive polymer solution for forming a solid electrolyte layer, "a conductive polymer solution containing a conductive polymer, a polysulfonic acid or a salt thereof that functions as a dopant for the conductive polymer, a mixture of a polyacid and a carbon material, and a solvent" (Claim 1 of Patent Document 1). Patent Document 1 also discloses a solid electrolytic capacitor manufactured using the conductive polymer solution.

Prior Art Documents

Patent Documents

[0004] <00​​​​​​​​​​​​​​​​

[0006] One aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes a capacitor element, the capacitor element comprising an anode, a dielectric layer formed on the surface of the anode, a cathode, and an electrolyte layer and a separator disposed between the dielectric layer and the cathode, the electrolyte layer comprising a non-aqueous solvent, conductive particles, and a conductive polymer, wherein the amount of conductive particles present in a first portion of the electrolyte layer on the dielectric layer side is different from the amount of conductive particles present in a second portion of the electrolyte layer on the cathode side. [Effects of the Invention]

[0007] According to this disclosure, an electrolytic capacitor with a low rate of ESR increase over a long period of time can be obtained. 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, along with other objects and features of the present invention. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing an example of an electrolytic capacitor of the present disclosure. [Figure 2] This diagram schematically shows a portion of the electrolytic capacitor shown in Figure 1. [Modes for carrying out the invention]

[0009] The following descriptions illustrate embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. While specific numerical values ​​and materials may be given as examples in the following descriptions, other numerical values ​​and materials may be applied as long as the effects of the present disclosure are achieved. In this specification, when we refer to "numerical values ​​A to B," the range includes numerical values ​​A and B.

[0010] (Electrolytic capacitor) The electrolytic capacitor according to this embodiment includes a capacitor element. The capacitor element includes an anode, a dielectric layer formed on the surface of the anode, a cathode, and an electrolyte layer and separator disposed between the dielectric layer and the cathode. The electrolyte layer includes a non-aqueous solvent, conductive particles, and a conductive polymer. The amount of conductive particles present in the first portion of the electrolyte layer on the dielectric layer side (anode side) is different from the amount of conductive particles in the second portion of the electrolyte layer on the cathode side.

[0011] Conductive particles are virtually immune to thermal degradation. Therefore, by adding conductive particles to the electrolyte layer, the rise in ESR can be suppressed over the long term. On the other hand, increasing the content of conductive particles can make it difficult to position the conductive polymer between the anode and cathode. In the electrolytic capacitor according to this embodiment, there are areas with a low amount of conductive particles, making it possible to easily introduce the conductive polymer from those areas. Therefore, in the electrolytic capacitor according to this embodiment, the packing rate of conductive polymer and conductive particles between the anode and cathode can be increased. As a result, an electrolytic capacitor with a low rate of ESR increase over a long period of time can be obtained.

[0012] The relative amounts of conductive particles present in the first and second parts can be evaluated, for example, by the following method. First, the first and second parts are photographed using equipment (such as an optical microscope or electron microscope) that can identify the shape of particles by photographing them at a magnification of 100x or more. For each of the first and second parts, images are taken of areas of a predetermined size at 10 different locations. Then, the number of particles in the images is counted by image processing. The arithmetic mean of the number of particles in each of the 10 images is taken, and this arithmetic mean is taken as the particle amount in that part. This determines the relative amounts of conductive particles present in the first and second parts. Alternatively, the area of ​​the particles in the images is determined by image processing as described above, and the equivalent diameter of a circle is determined from that area. Then, the volume of the particle with that equivalent diameter as its diameter is determined. Using the volume of the particle thus determined, the ratio of the conductive particle content C1 (volume %) in the first part to the conductive particle content C2 (volume %) in the second part can be determined.

[0013] Alternatively, the first and second portions may be measured using an instrument capable of identifying elemental species, such as energy-dispersive X-ray spectroscopy (EDX) or electron beam microanalyzer (EPMA), and the magnitude of conductive particles present in the first and second portions may be evaluated by calculating the distribution of elements other than those originating from the separator. It is possible to calculate the amount of particles in an image using an optical or electron microscope, and it is also possible to calculate the amount of elements from the intensity obtained in elemental analysis.

[0014] The first part is all or part of the electrolyte layer that lies on the dielectric layer side of the central plane of the electrolyte layer (the plane where the distance to the dielectric layer and the distance to the cathode are equal). The second part is all or part of the electrolyte layer that lies on the cathode side of the central plane of the electrolyte layer. In one example, the first part is all of the electrolyte layer that lies on the dielectric layer side of the central plane of the electrolyte layer, and the second part is all of the electrolyte layer that lies on the cathode side of the central plane of the electrolyte layer.

[0015] The first portion may be a first surface of the electrolyte layer that is in contact with the dielectric layer, and the second portion may be a second surface of the electrolyte layer that is in contact with the cathode. Alternatively, the first and second portions may each be within a certain depth range from the first and second surfaces. For example, when the average thickness of the separator is average thickness T (μm), the certain depth may be in the range of 0.05T to 0.5T (e.g., 0.05T to 0.2T or 0.05T to 0.1T). Alternatively, when the thickness of the electrolyte layer at any position is thickness S (μm), the certain depth may be in the range of 0.05S to 0.5S (e.g., 0.05S to 0.2S or 0.05S to 0.1S). The portion with a certain depth of 0.5S is located on the central surface of the electrolyte layer. The thickness S of the electrolyte layer may be in the range of 10μm to 500μm (e.g., 20μm to 200μm). The separator is typically positioned between the dielectric layer and the cathode in contact with them. Therefore, the thickness of the separator can be considered equivalent to the thickness of the electrolyte layer.

[0016] In an example of an electrolytic capacitor according to this embodiment, the amount of conductive particles present on the dielectric layer side of the electrolyte layer is different from the amount of conductive particles present on the cathode side of the electrolyte layer. For example, the former may be greater than the latter, or the former may be less than the latter.

[0017] A capacitor element may include a foil-shaped anode having a dielectric layer on its surface, a foil-shaped cathode, and a separator and electrolyte layer disposed between the anode (more specifically the dielectric layer) and the cathode. The capacitor element may be of the wound type or the multilayer type. In one example of a wound capacitor element, the foil-shaped anode, foil-shaped cathode and separator are wound together such that a separator is placed between the anode and cathode. In one example of a multilayer capacitor element, the foil-shaped anode, foil-shaped cathode and separator are folded in a zigzag pattern such that a separator is placed between the anode and cathode.

[0018] The electrolytic capacitor of this embodiment may satisfy the following conditions (1) and / or (2). By using these configurations, the effects described below can be obtained. (1) The electrolyte layer contains a dopant of a conductive polymer. By using a dopant, the conductivity of the electrolyte layer can be increased. Examples of the conductive polymer and the dopant will be described later. (2) The dopant is a polymer dopant containing an acidic group, and the electrolyte layer contains an electrolytic solution containing a non-aqueous solvent and a base component dissolved in the non-aqueous solvent. In this case, the content rate of the base component in the electrolytic solution may be 0.1 mass% or more and 20 mass% or less.

[0019] The mass of the conductive particles contained in the electrolyte layer may be larger than the total mass of the conductive polymer and the dopant contained in the electrolyte layer. According to this configuration, an increase in ESR can be particularly suppressed. Alternatively, the mass of the conductive particles contained in the electrolyte layer may be equal to or less than the total mass of the conductive polymer and the dopant contained in the electrolyte layer. According to this configuration, the initial ESR can be reduced. The total content rate M (mass%) of the conductive polymer and the dopant in the electrolyte layer and the content rate N (mass%) of the conductive particles in the electrolyte layer may satisfy M < N. Also, N > 0.1 may hold, and M > 0.05 may hold.

[0020] The electrolytic capacitor according to this embodiment may satisfy the following conditions (3) and / or (4), and may further satisfy the following condition (5). (3) The content rate C1 (volume%) of the conductive particles in the first part is in the range of 0 to 0.5 times (for example, in the range of 0 to 0.3 times or in the range of 0.1 to 0.3 times) of the content rate C2 (volume%) of the conductive particles in the second part. According to this configuration, it becomes particularly easy to impregnate the second part with the conductive polymer. Note that the first and second parts are, for example, the parts described above. (4) The conductive particles are unevenly distributed in the second part. According to this configuration, it becomes particularly easy to impregnate the second part with the conductive polymer. (5) The cathode body is a metal foil, and the conductive particles are metal particles. When the cathode body is a metal foil, the contact resistance between the conductive polymer and the cathode body may increase. According to the configuration of (5), the contact resistance between the cathode body and the conductive particles can be reduced, so that the ESR can be particularly reduced.

[0021] The conductive particles may be conductive inorganic particles. The conductive particles may be particles of a conductive carbon material. For example, the conductive particles may include at least one particle selected from the group consisting of carbon black particles, carbon nanotube particles, graphite particles, and graphene particles. These particles are preferable in that the average particle size, the structure between particles, and the surface properties can be variously controlled. The conductive particles may be composed of only one type of these particles, or may be composed of a plurality of types of these particles.

[0022] The conductive particles may have a spherical or flaky shape. The type of the flaky conductive particles is not particularly limited, and may be flaky particles made of a conductive carbon material. For example, graphite, graphene, etc. are likely to take a flaky form, and it is easy to obtain flaky particles. By using flaky particles, effects such as increasing the conductivity of the electrolyte layer, enhancing the affinity between the electrolyte or separator and the conductive particles, and suppressing the uneven distribution of the conductive particles in the electrolyte or separator can be obtained.

[0023] The average aspect ratio of the flaky carbon particles may be 2 or more, or may be 3 or more. The average aspect ratio of the carbon particles can be obtained as follows. First, an image of the carbon particles is obtained using a scanning electron microscope (SEM). In the obtained SEM image, an arbitrary plurality (for example, 10) of carbon particles are selected. Next, for the selected carbon particles, the maximum diameter D1 is measured, and further, the maximum diameter D2 in the direction orthogonal to the maximum diameter D1 is measured. For each carbon particle, the ratio D1 / D2 of D1 to D2 is obtained as the aspect ratio, and the average aspect ratio is obtained by calculating the arithmetic mean of these.

[0024] The conductive particles may have a whisker-like (rod-like) shape. By using whisker-like particles, effects such as increasing the conductivity of the electrolyte layer, increasing the affinity between the electrolyte or separator and the conductive particles, and suppressing the uneven distribution of conductive particles within the electrolyte or separator can be obtained.

[0025] The type of conductive particles having a whisker-like shape is not particularly limited and may be made of a conductive carbon material or other inorganic material. For example, the conductive particles having a whisker-like shape may be carbon nanotubes or carbon nanofibers. Alternatively, the conductive particles may be made by coating whisker-shaped inorganic particles (e.g., glass fibers) with a conductive metal (e.g., a conductive alloy).

[0026] Except for the parts characteristic of the electrolytic capacitor according to this disclosure, there are no particular limitations on the components of the electrolytic capacitor according to this disclosure, and known components may be used. Examples of components of the electrolytic capacitor according to this disclosure are described below.

[0027] (electrolyte layer) The electrolyte layer is positioned between the dielectric layer and the cathode, and is in contact with them. In other words, the region between the dielectric layer and the cathode constitutes the region of the electrolyte layer. As described above, the electrolyte layer comprises a non-aqueous solvent, conductive particles, and a conductive polymer.

[0028] (conductive polymer) The conductive polymer contained in the electrolyte layer is described below. Note that in this specification, "conductive polymer" may be read as "conductive polymer."

[0029] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and their derivatives. These derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as their basic skeletons. For example, derivatives of polythiophene include poly(3,4-ethylenedioxythiophene). These conductive polymers may be used individually or in combination. Conductive polymers may also be copolymers of two or more monomers. The weight-average molecular weight of conductive polymers is not particularly limited and may be in the range of, for example, 1,000 to 100,000. A preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0030] Preferably, the conductive polymer is doped with a dopant. From the viewpoint of suppressing dedoping from the conductive polymer, it is preferable to use a polymer dopant as the dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually or in combination of two or more. These may also be included in the electrolyte layer in the form of salts. A preferred example of a dopant is polystyrene sulfonic acid (PSS). As in the example above, typically the conductive polymer and the dopant are separate molecules. However, the conductive polymer may also be a self-doped conductive polymer containing an atomic group (e.g., a sulfonic acid group) that functions as a dopant.

[0031] The weight-average molecular weight of the dopant is not particularly limited. From the viewpoint of facilitating the formation of a homogeneous electrolyte layer, the weight-average molecular weight of the dopant may be in the range of 1,000 to 100,000.

[0032] In the electrolytic capacitor of this disclosure, the dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the electrolyte layer may contain poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0033] (Liquid component) The electrolyte layer of the electrolytic capacitor of this disclosure contains a non-aqueous solvent. The electrolyte layer may also contain an electrolyte (non-aqueous electrolyte) comprising a non-aqueous solvent and a basic component dissolved in the non-aqueous solvent. That is, the electrolyte layer of the electrolytic capacitor of this disclosure may contain a liquid component. Hereinafter, the liquid component (non-aqueous solvent or electrolyte) contained in the electrolyte layer may be referred to as "liquid component (L)". In this specification, liquid component (L) may be a component that is liquid at room temperature (25°C) or a component that is liquid at the temperature at which the electrolytic capacitor is used. An electrolytic capacitor having an electrolyte layer containing liquid component (L) may be called a hybrid capacitor.

[0034] The non-aqueous solvent contained in the electrolyte layer may be an organic solvent or an ionic liquid. Examples of non-aqueous solvents include polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (γBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde.

[0035] Furthermore, polymeric solvents may be used as non-aqueous solvents. Examples of polymeric solvents include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group in a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specifically, examples of polymeric solvents include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol. Examples of polymeric solvents further include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. Non-aqueous solvents may be used individually or as a mixture of two or more.

[0036] As described above, the electrolyte layer may contain a non-aqueous solvent and a basic component (base) dissolved in the non-aqueous solvent. Alternatively, the electrolyte layer may contain a non-aqueous solvent and a basic component and / or an acid component (acid) dissolved in the non-aqueous solvent.

[0037] Polycarboxylic acids and monocarboxylic acids can be used as the acid component. Examples of the above polycarboxylic acids include aliphatic polycarboxylic acids ([saturated polycarboxylic acids, e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebatic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids, e.g., maleic acid, fumaric acid, eicotanoic acid]), aromatic polycarboxylic acids (e.g., phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.).

[0038] Examples of the monocarboxylic acids mentioned above include aliphatic monocarboxylic acids (1 to 30 carbon atoms) ([saturated monocarboxylic acids, e.g., formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids, e.g., acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (e.g., benzoic acid, cinnamic acid, naphthoic acid), and oxycarboxylic acids (e.g., salicylic acid, mandelic acid, resorcinic acid).

[0039] Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcinic acid are thermally stable and are therefore preferred.

[0040] Inorganic acids may be used as the acid component. Typical examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, borofluoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. In addition, composite compounds of organic and inorganic acids may be used as the acid component. Examples of such composite compounds include borodiglycolic acid, borodioxalic acid, and borodisalicylic acid.

[0041] The basic component may be a compound having an alkyl-substituted amidine group, for example, an imidazole compound, a benzimidazole compound, or an alicyclic amidine compound (pyrimidine compound, imidazoline compound). Specifically, 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethylimidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole are preferred. By using these, a capacitor with excellent impedance performance can be obtained.

[0042] As the base component, a quaternary salt of a compound having an alkyl-substituted amidine group may be used. Examples of such base components include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) that have been quaternized with an alkyl or arylalkyl group having 1 to 11 carbon atoms. Specifically, 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, and 1,3-dimethylbenzimidazolium are preferred. By using these, a capacitor with excellent impedance performance can be obtained.

[0043] Furthermore, tertiary amines may be used as the base component. Examples of tertiary amines include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.) and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among these, trialkylamines are preferred in that they increase the conductivity of the electrolyte layer, and it is more preferable to include at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Furthermore, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia may be used as the base component.

[0044] The liquid component (L) may contain a salt of an acidic component and a basic component. The salt may be an inorganic salt and / or an organic salt. An organic salt is a salt in which at least one of the anion and cation is an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0045] To suppress dopant dedoping, the pH of the liquid component (L) may be set to less than 7, or to 5 or less (for example, in the range of 2 to 4.5).

[0046] In electrolytic capacitors, a low ESR is important. Low ESR can be achieved by using an electrolyte layer containing a dopant-doped conductive polymer. However, the inventors of this invention have found that when an electrolyte layer containing a dopant-doped conductive polymer and a non-aqueous solvent (liquid component (L)) is used, although the initial ESR is low, there is a significant degradation phenomenon in which the ESR increases over time. Upon investigating the cause, it was found that in electrolyte layers containing a liquid component (L), the dopant may be easily dedoped. This dedoping is thought to cause the ESR to increase over time. Therefore, compared to solid electrolytic capacitors containing a solid electrolyte that does not contain a liquid component (L), it is important to suppress the time-dependent increase in ESR in electrolytic capacitors containing a liquid component (L).

[0047] Conductive polymers are effective in reducing ESR due to their high conductivity. However, the conductivity of conductive polymers decreases over time, leading to an increase in ESR. In particular, the increase in ESR is significant when the electrolyte layer contains a liquid component (L). On the other hand, the conductivity of conductive particles is considered to degrade very little over time. Therefore, the increase in ESR over time can be suppressed by adding conductive particles.

[0048] In the electrolytic capacitor of this disclosure, the dopant may be a dopant containing an acidic group, or a polymer dopant containing an acidic group. Through investigation, the inventors of this application have newly discovered that when a dopant containing an acidic group is used, dedoping may occur significantly as the pH increases. Therefore, when using a dopant containing an acidic group, it is particularly important to suppress the time-dependent increase in ESR.

[0049] In the electrolytic capacitor of this disclosure, the dopant may be a polymer dopant containing an acidic group, and the electrolyte layer may contain an electrolyte solution containing a non-aqueous solvent and a basic component dissolved in the non-aqueous solvent. In this case, since dedopanting is likely to occur due to the basic component, it is particularly important to suppress the rise in ESR over time. As described above, since the electrolytic capacitor of this disclosure contains conductive particles, the rise in ESR over time can be suppressed.

[0050] Examples of acidic groups include sulfonic acid groups and carboxyl groups. A polymer dopant containing an acidic group is a polymer in which at least some of its constituent units contain an acidic group. Examples of such polymer dopants include the polymer dopants mentioned above.

[0051] In the electrolytic capacitor of this disclosure, the amount of basic components in the electrolyte may be 0.1% by mass or more and 20% by mass or less. When the amount of basic components is 0.1% by mass or more, the use of conductive particles becomes particularly important. Furthermore, by setting the amount of basic components to 20% by mass or less, it becomes easier to dissolve the basic components in the electrolyte. The content of the liquid component (L) in the electrolyte layer may be in the range of 10 to 99.85% by mass (e.g., 30 to 95% by mass). The total content of conductive polymers and dopants in the electrolyte layer may be in the range of 0.05 to 20% by mass (e.g., 1 to 10% by mass). The content of conductive particles in the electrolyte layer may be in the range of 0.1 to 80% by mass (e.g., 1 to 30% by mass). These content levels may be outside the ranges described herein, as long as the effects of this disclosure are obtained.

[0052] (Conductive particles) The conductive particles contained in the electrolyte layer are described below. These conductive particles are made of a conductive material. Note that these conductive particles are different from the conductive polymers mentioned above. Typically, these conductive particles are made of materials that are not polymers.

[0053] The conductive particles contained in the electrolyte layer may consist of only one type of conductive particle or may contain multiple types of conductive particles. Conductive particles are conductive particles, and at least one conductive material is present on their surface. Conductive particles may also be particles made of a conductive material. The conductive material may be at least one selected from the group consisting of metals, conductive carbon materials, conductive oxides, and metal plating materials. Examples of metals include gold, silver, copper, nickel, and tin. Examples of conductive carbon materials include carbon black, carbon nanotubes, graphite, and graphene. Examples of conductive oxides include tin oxide, indium oxide, and zinc oxide. Alternatively, the conductive material may be conductive nickel-phosphorus (Ni-P) material, conductive indium-tin (In-Sn) material, conductive tin-silver (Sn-Ag), etc. Conductive particles may be obtained by coating the surface of glass beads, mica powder, glass fibers, and carbon fibers with the above conductive material (for example, by metal plating). The conductive particles may be metal particles, conductive carbon material particles, or conductive oxide particles.

[0054] The average particle size of conductive particles may be in the range of 0.2 μm to 50 μm (for example, in the range of 2 μm to 20 μm). In this specification, the average particle size is the median diameter (D) at which the cumulative volume in the volume-based particle size distribution becomes 50%. 50 The median diameter can be determined, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0055] (Anode) A metal foil with a dielectric layer formed on its surface may be used as the anode. The type of metal constituting the metal foil is not particularly limited. Examples of metals constituting the metal foil include valve-forming metals and alloys of valve-forming metals, such as aluminum, tantalum, niobium, and titanium, because the dielectric layer is easily formed. A preferred example is aluminum and aluminum alloys. Typically, the surface of the anode is roughened (porous). The dielectric layer of the anode is formed in the porous portion (roughened surface). The electrolyte layer is in contact with the dielectric layer of the anode.

[0056] The dielectric layer formed on the surface of the anode can be formed by known methods. For example, it may be formed by oxidizing the surface of the metal foil that will serve as the anode through a chemical conversion treatment.

[0057] (Cathole body) A metal foil may be used for the cathode. The type of metal constituting the metal foil is not particularly limited. Examples of metals constituting the metal foil include valve-forming metals and alloys of valve-forming metals such as aluminum, tantalum, niobium, and titanium. A preferred example is aluminum and aluminum alloys. The surface of the cathode may be provided with a chemical conversion coating, or a coating of a different metal (dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon.

[0058] (Separator) The separator can be a sheet-like material that can be impregnated with an electrolyte; for example, a sheet-like material that is insulating and can be impregnated with an electrolyte may be used. The separator may be a woven fabric, a nonwoven fabric, or a porous membrane. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamide-imide, polyetherimide, rayon, and glass.

[0059] The basis weight of the separator is 10-50 g / m². 2 range (e.g., 10-30 g / m 2 It may be within the range of ). Here, the basis weight is the value measured according to JIS P 8124.

[0060] The separator may be a separator formed by bonding two separators together. For example, it may be a separator formed by bonding a first separator on the dielectric layer side and a second separator on the cathode side. In that case, the air permeability G1 of the first separator and the air permeability G2 of the second separator may be different.

[0061] The average thickness T of the separator may be in the range of 10 μm to 200 μm (for example, in the range of 20 μm to 100 μm). The average thickness of the separator can be measured using a constant-pressure thickness measuring instrument compliant with JIS P 8118.

[0062] (Example of electrolytic capacitor manufacturing method) An example of a manufacturing method for the electrolytic capacitor of this disclosure is described below. The electrolytic capacitor of this disclosure may be manufactured by methods other than those described below. Note that the matters described for the electrolytic capacitor of this disclosure can also be applied to the manufacturing method described below, so redundant explanations may be omitted. For example, the components of the capacitor element have been described above, so redundant explanations may be omitted. In addition, the matters described below regarding the manufacturing method may also be applied to the electrolytic capacitor described above.

[0063] The manufacturing method relating to this disclosure includes steps (i), (ii), and (iii), which are described below.

[0064] (Step (i)) Step (i) is a step (i) of preparing a capacitor element precursor including an anode having a dielectric layer on its surface. Step (i) may also be a step of forming a capacitor element precursor by a known method.

[0065] Step (i) is a step of forming a capacitor element precursor that includes a foil-shaped anode having a dielectric layer on its surface, a foil-shaped cathode, and a separator disposed between the anode and the cathode. In this case, as described above, the capacitor element precursor may be of the wound type or the laminated type. That is, the capacitor element precursor may be a wound body.

[0066] The separator used in step (i) is pre-attached with conductive particles. For example, conductive particles are attached to the separator by bringing it into contact with a dispersion of conductive particles (hereinafter sometimes referred to as "dispersion A") and then drying the separator. There are no particular limitations on the dispersion medium of dispersion A; it may be water, an organic solvent, or a mixture thereof. Conductive particles can be unevenly distributed by coating dispersion A on only one side of the separator (for example, by spray coating). Alternatively, when coating the separator with dispersion A containing conductive particles, multiple dispersions A with different conductive particle content may be used. Specifically, conductive particles can be unevenly distributed by using a higher concentration of dispersion A (a dispersion with a higher conductive particle content) on the side where uneven distribution of conductive particles is desired. Furthermore, conductive particles can be unevenly distributed by immersing a separator consisting of two separators with different air permeability in dispersion A. Alternatively, conductive particles may be attached to one of the two separators before stacking them. Or, the conductive particles may be unevenly distributed by stacking two separators with different amounts of conductive particles attached to them.

[0067] Furthermore, when using dispersion A to unevenly distribute conductive particles, it is preferable that the conductive particles have a particle size that restricts their movement within the separator. By using conductive particles with a particle size that restricts their movement within the separator, it becomes easier to unevenly distribute the conductive particles. Such a particle size can be selected according to the type of separator.

[0068] When a dispersion containing a conductive polymer also contains conductive polymer particles, the average particle size of the conductive polymer particles may be larger than the average particle size of the conductive polymer particles. This configuration can make it easier to achieve a state in which the conductive polymer particles are dispersed throughout the separator and the conductive particles are unevenly distributed.

[0069] (Step (ii)) Step (ii) is a step of forming a polymer layer containing a conductive polymer and conductive particles adjacent to the dielectric layer by impregnation treatment. The conductive polymer may be doped with a dopant. An example of a conductive polymer doped with a dopant is described below.

[0070] The impregnation treatment in step (ii) may be an impregnation treatment (x) in which a dispersion containing a dopant-doped conductive polymer (hereinafter sometimes referred to as "dispersion B") is impregnated into the capacitor element precursor. For example, the capacitor element precursor can be impregnated with dispersion B by immersing it in dispersion B. By removing (drying) the dispersion medium of dispersion B impregnated into the capacitor element precursor, a polymer layer containing a dopant-doped conductive polymer and conductive particles can be arranged adjacent to the dielectric layer. The impregnation treatment (x) may be performed multiple times. In that case, a drying step to remove the dispersion medium of the impregnated dispersion may be performed before the second and subsequent impregnation treatments (x). The dispersion B used in the impregnation treatment (x) may contain trace amounts of conductive particles.

[0071] There are no particular limitations on the dispersion medium of the dispersion, and any known dispersion medium may be used. For example, an aqueous liquid containing water may be used as the dispersion medium, or water may be used.

[0072] By adjusting the mass (content) of conductive particles pre-attached to the separator and the mass (content) of conductive polymers in the dispersion, the ratio of these in the formed electrolyte layer can be adjusted. The conductive particles in the separator are unevenly distributed, with areas containing fewer conductive particles. Therefore, the conductive polymers and dopants are more easily impregnated through these areas with fewer conductive particles. As a result, it becomes possible to increase the content of conductive polymers and dopants in the electrolyte layer containing conductive particles.

[0073] (Step (iii)) Step (iii) is a step of impregnating the layer formed in step (ii) with a non-aqueous solvent. This forms an electrolyte layer containing a dopant-doped conductive polymer, conductive particles, and a non-aqueous solvent. Step (iii) may also be a step of impregnating the polymer layer formed in step (ii) with an electrolyte containing a non-aqueous solvent. That is, step (iii) may also be a step of impregnating the polymer layer formed in step (ii) with a liquid component (L).

[0074] There are no particular limitations on the impregnation method in step (iii), and known methods may be used. For example, the capacitor element precursor that has gone through step (ii) may be immersed in a non-aqueous solvent (or electrolyte). The non-aqueous solvent (or electrolyte) used in step (iii) can be one of those described above.

[0075] In the manufacturing method of the present disclosure, the dopant may be a polymer dopant containing an acidic group, and step (iii) may be a step of impregnating the polymer layer with an electrolyte containing a non-aqueous solvent and a basic component dissolved in the non-aqueous solvent.

[0076] A capacitor element is obtained through step (iii). After step (iii), an electrolytic capacitor can be manufactured using the components obtained in step (iii). There are no particular limitations on this step, and known methods can be used.

[0077] Furthermore, the dispersion A used in step (i) may contain a conductive polymer. By using dispersion A containing a conductive polymer, it is possible to form a conductive polymer layer on the separator in step (i). In that case, step (ii) may or may not be performed.

[0078] One example of a manufacturing method includes an element formation step of forming a capacitor element comprising a foil-shaped anode having a dielectric layer on its surface, a foil-shaped cathode, and a separator disposed between the anode and the cathode, and an impregnation step of impregnating the formed capacitor element with a liquid component (L). The element formation step includes a step of arranging conductive particles and a conductive polymer on the separator. In the element formation step, the conductive particles are arranged to be unevenly distributed. The conductive particles and the conductive polymer can be arranged by the above-described step (i), or by steps (i) and (ii).

[0079] In the following, an example of an electrolytic capacitor relating to this disclosure will be specifically described with reference to the drawings, but the electrolytic capacitor of this disclosure is not limited to the drawings below. The components of the example electrolytic capacitor described below can be the components described above. Furthermore, the components of the example electrolytic capacitor described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiments. Note that the same reference numerals may be used for similar parts, and redundant explanations may be omitted.

[0080] (Embodiment 1) Embodiment 1 describes an example of an electrolytic capacitor according to the present disclosure. This electrolytic capacitor is an electrolytic capacitor that includes capacitor elements. Figure 1 schematically shows a cross-section of an example of the electrolytic capacitor 100 of Embodiment 1. Figure 2 shows a schematic diagram of a part of the capacitor elements 10 included in the electrolytic capacitor 100 shown in Figure 1.

[0081] As shown in Figure 1, the electrolytic capacitor 100 includes a capacitor element 10, a bottomed case 11 housing the capacitor element 10, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, and lead tabs 15A and 15B connecting the lead wires 14A and 14B to the electrodes of the capacitor element 10. The capacitor element 10 is housed in the bottomed case 11. The area near the opening end of the bottomed case 11 is tapered inward, and the opening end of the bottomed case 11 is curled to crimp the sealing member 12.

[0082] Referring to Figure 2, the capacitor element 10 includes a foil-shaped anode 21 having a dielectric layer on its surface, a foil-shaped cathode 22, and a separator 23 and an electrolyte layer (not shown) placed between them. The anode 21 and cathode 22 are wound with the separator 23 placed between them. The outermost circumference of the winding is secured by a winding stopper tape 24. Note that Figure 2 shows the winding in a partially unfolded state before the outermost circumference is secured. [Examples]

[0083] The embodiments of this disclosure will be described in more detail below with reference to examples. In the following embodiments, multiple electrolytic capacitors were fabricated and evaluated.

[0084] [Fabrication of Capacitor A1] Capacitor A1 is a wound-type electrolytic capacitor with a rated voltage of 35V and a rated capacitance of 270μF. Capacitor A1 was fabricated using the following procedure.

[0085] (Preparation of cathode and anode) A 70 μm thick aluminum foil was used as the cathode. The anode, with a dielectric layer formed on its surface, was fabricated using the following procedure. First, a 120 μm thick aluminum foil was prepared. This aluminum foil was subjected to DC etching to roughen its surface. Next, the aluminum foil was subjected to a chemical conversion treatment. Specifically, the aluminum foil was immersed in an aqueous solution of ammonium adipate, and while applying a voltage of 50 V to the aluminum foil, a chemical conversion treatment was performed at 70°C for 30 minutes to form a dielectric layer (thickness: approximately 70 nm) on the surface of the aluminum foil. In this way, an anode with a dielectric layer formed on its surface was obtained. Subsequently, the anode was cut to a predetermined size to prepare the anode for capacitor A1.

[0086] (PEDOT: Preparation of PSS dispersion) A dispersion of a dopant-doped conductive polymer was prepared by the following method. First, a mixed solution of 3,4-ethylenedioxythiophene and polystyrene sulfonic acid (dopant) was prepared by dissolving them in deionized water. While stirring the resulting mixed solution, iron(III) sulfate (oxidizing agent) dissolved in deionized water was added to carry out the polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent. In this way, a dispersion containing poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (approximately 5% by mass relative to poly(3,4-ethylenedioxythiophene)) was obtained. Hereinafter, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid may be referred to as "PEDOT:PSS".

[0087] (PEDOT: Addition of conductive particles to PSS dispersion) Nickel metal particles (spherical, average particle size: 2 μm) were added to a dispersion containing 2% by mass of the above-mentioned PEDOT:PSS. In this way, treatment solution A (dispersion) containing PEDOT:PSS and conductive particles was prepared. In treatment solution A, the ratio of (mass of PEDOT:PSS) to (mass of conductive particles) was set to 40:60 (the same ratio was applied to the treatment solutions used in capacitors A2-A4, C2, and C3).

[0088] (Formation of conductive polymer layer) A nonwoven fabric (50 μm thick) was prepared as the separator. The nonwoven fabric is composed of 50% by mass of synthetic fibers (25% by mass of polyester fibers, 25% by mass of aramid fibers) and 50% by mass of cellulose, and contains polyacrylamide as a paper strength enhancer. The density of the nonwoven fabric is 0.35 g / cm³. 3 That was the case.

[0089] The above-mentioned treatment solution A was applied to one main surface of the separator and dried at 60°C for 30 minutes, followed by drying at 150°C for another 30 minutes. This removed the dispersion medium (water) contained in the applied treatment solution A. In this way, a conductive polymer layer containing conductive particles was formed, unevenly distributed on one main surface of the separator.

[0090] (Preparation of coiled bodies) Anode lead tabs and cathode lead tabs, each connected to anode and cathode bodies, were respectively attached. Then, the separator was placed between the anode and cathode bodies and the coil was wound around them, with the outer surface secured with winding tape. At this time, the separator was positioned between the anode and cathode bodies such that the conductive polymer layer containing conductive particles was located on the cathode side. In other words, the separator was positioned so that the conductive particles were predominantly located on the cathode side. A wound coil was thus fabricated. The fabricated wound coil was immersed in an ammonium adipate solution, and a chemical conversion treatment was performed again at 70°C for 60 minutes while applying a voltage of 50V to the anode body. This chemical conversion treatment mainly formed a dielectric layer on the end face of the anode body. After that, an electrolytic capacitor was fabricated by some of the methods described in the embodiment.

[0091] (Impregnation with electrolyte solution) A wound body with a conductive polymer layer was impregnated with an electrolyte at room temperature under atmospheric pressure. The electrolyte used was a solution prepared by mixing polyethylene glycol, γ-butyrolactone, sulfolane, and mono(ethyldimethylamine) phthalate (solute) in a mass ratio of polyethylene glycol:γ-butyrolactone:sulfolane:mono(ethyldimethylamine) phthalate = 30:30:20:20. In this way, a capacitor element containing the electrolyte layer was obtained. This capacitor element was sealed to complete the electrolytic capacitor. Subsequently, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage. In this way, capacitor A1 was obtained.

[0092] [Fabrication of Capacitor A2] Capacitor A2 was fabricated using the same materials and conditions as capacitor A1, except that the arrangement of the separator was changed. In the winding of capacitor A2, the separator was placed between the anode and cathode so that the conductive polymer layer containing conductive particles was located on the anode side (dielectric layer side). In other words, the separator was positioned so that the conductive particles were unevenly distributed on the anode side (dielectric layer side).

[0093] [Making Capacitor A3] Capacitor A3 was fabricated using the same materials and conditions as capacitor A1, except that the conductive particles used in processing solution A were changed. In processing solution A used to fabricate capacitor A3, graphene particles (flaky, average particle size: 0.4 μm) were used as conductive particles instead of nickel metal particles. In capacitor A3, the separator was placed between the anode and cathode so that the conductive polymer layer containing the conductive particles was located on the cathode side. In other words, the separator was positioned so that the conductive particles were predominantly located on the cathode side.

[0094] [Making Capacitor A4] Capacitor A4 was fabricated using the same materials and conditions as capacitor A3, except that the arrangement of the separator was changed. In the winding of capacitor A4, the separator was placed between the anode and cathode so that the conductive polymer layer containing conductive particles was located on the anode side (dielectric layer side). In other words, the separator was positioned so that the conductive particles were unevenly distributed on the anode side (dielectric layer side).

[0095] [Fabrication of Capacitor C1 (Comparative Example)] Capacitor C1 was fabricated using the same materials and conditions as capacitor A1, except that the method for forming the conductive polymer layer was changed. The conductive polymer layer of capacitor C1 was formed in the same manner as the conductive polymer layer of capacitor A1, except that treatment solution A, which does not contain conductive particles, was used. Therefore, the conductive polymer layer of capacitor C1 contains PEDOT:PSS but does not contain conductive particles.

[0096] [Fabrication of Capacitor C2 (Comparative Example)] Capacitor C2 was fabricated using the same materials and conditions as capacitor A1, except that a conductive polymer layer was uniformly formed on the separator. In other words, in capacitor C2, the conductive particles (nickel particles) are dispersed throughout the separator and are not unevenly distributed.

[0097] [Fabrication of Capacitor C3 (Comparative Example)] Capacitor C3 was fabricated using the same materials and conditions as capacitor A3, except that a conductive polymer layer was uniformly formed on the separator. In other words, in capacitor C3, the conductive particles (graphene particles) are dispersed throughout the separator and are not unevenly distributed.

[0098] (ESR measurement) The equivalent series resistance (ESR) was measured for the electrolytic capacitors fabricated as described above. The ESR was measured using a 4-terminal LCR meter in an environment of 20°C. The ESR was measured both initially after fabrication and after the electrolytic capacitors were left at high temperatures (145°C for 150 hours and 500 hours). The relative value of the initial ESR was calculated using the following formula. The relative value of the initial ESR is the relative value when the initial ESR of capacitor C1 is set to 100%. In addition, as an indicator of long-term characteristics, the ESR change rate for each capacitor was calculated using the following formula. Relative value of initial ESR (%) = 100 × (initial ESR of each capacitor) / (initial ESR of capacitor C1) ESR change rate (%) = 100 × (ESR value of each capacitor after being left at high temperature) / (initial ESR value of each capacitor) - 100

[0099] Table 1 shows the ESR evaluation results for the electrolytic capacitors mentioned above.

[0100] [Table 1]

[0101] As shown in Table 1, capacitors A1 to A4, in which conductive particles were unevenly distributed, showed low ESR both initially and after being left at high temperatures. Capacitors A1 and A3, in which conductive particles were unevenly distributed on the cathode side, showed particularly low ESR. [Industrial applicability]

[0102] This disclosure can be used for electrolytic capacitors and methods for manufacturing the same. 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]

[0103] 10 Capacitor element 21 Anode 22 Cathode Body 23 Separator 100 electrolytic capacitors

Claims

1. An electrolytic capacitor including a capacitor element, The capacitor element includes an anode, a dielectric layer formed on the surface of the anode, a cathode, and an electrolyte layer and a separator disposed between the dielectric layer and the cathode. The electrolyte layer comprises a non-aqueous solvent, conductive particles, and a conductive polymer. The amount of conductive particles present in the first portion of the electrolyte layer on the dielectric layer side is different from the amount of conductive particles present in the second portion of the electrolyte layer on the cathode side. The separator is an electrolytic capacitor made of a single layer of nonwoven fabric.

2. The electrolytic capacitor according to claim 1, wherein the electrolyte layer comprises a dopant of the conductive polymer.

3. The aforementioned dopant is a polymer dopant containing an acidic group, The electrolytic capacitor according to claim 2, wherein the electrolyte layer comprises an electrolyte solution containing the non-aqueous solvent and a basic component dissolved in the non-aqueous solvent.

4. The electrolytic capacitor according to claim 3, wherein the content of the basic component in the electrolyte is 0.1% by mass or more and 20% by mass or less.

5. The electrolytic capacitor according to any one of claims 2 to 4, wherein the mass of the conductive particles contained in the electrolyte layer is greater than the total mass of the conductive polymer and the dopant contained in the electrolyte layer.

6. The electrolytic capacitor according to any one of claims 1 to 5, wherein the content C1 (volume %) of the conductive particles in the first portion is in the range of 0 to 0.5 times the content C2 (volume %) of the conductive particles in the second portion.

7. The first portion has a first surface that contacts the dielectric layer, The second portion has a second surface that contacts the cathode body, When the average thickness of the separator is T (μm), the first portion is the part with a thickness in the range of 0.05T to 0.2T from the first surface, and the second portion is the part with a thickness in the range of 0.05T to 0.2T from the second surface. The electrolytic capacitor according to any one of claims 1 to 5, wherein the content C1 (volume %) of the conductive particles in the first portion is in the range of 0.1 to 0.3 times the content C2 (volume %) of the conductive particles in the second portion.

8. The electrolytic capacitor according to any one of claims 1 to 5, wherein the conductive particles are unevenly distributed in the second portion.

9. The cathode body is a metal foil, The electrolytic capacitor according to claim 7 or 8, wherein the conductive particles are metal particles.

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