Electrolytic capacitors

Abstract

Disclosed is an electrolytic capacitor (100) which comprises a capacitor element (10). The capacitor element comprises: a positive electrode body; a dielectric layer which is formed on the surface of the positive electrode body; a negative electrode body; and an electrolyte layer and a separator, which are arranged between the dielectric layer and the negative electrode body. The electrolyte layer contains a nonaqueous solvent and conductive particles. The ratio of the average maximum diameter D of the conductive particles to the average thickness T of the separator, namely D / T is within the range of from 0.01 to 0.9.

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). Further, Patent Document 1 discloses a solid electrolytic capacitor manufactured using the conductive polymer solution.

Prior Art Documents

Patent Documents

[0004] [[ID=二十五]] [[ID=二十六]] [[ID=二十七]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] [[ID=三十八]] [[ID=三十九]]Currently, there is a need for an electrolytic capacitor with a low ESR increase rate over a long period. In such a situation, one of the objectives of the present disclosure is to provide an electrolytic capacitor with a low ESR increase rate over a long period. [[ID=四十]] [[ID=四十一]]

Means for Solving the Problems

[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 and conductive particles, the ratio D / T of the average maximum diameter D of the conductive particles to the average thickness T of the separator being in the range of 0.01 to 0.9. [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. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings. [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 and conductive particles. The ratio D / T of the average maximum diameter D (μm) of the conductive particles to the average thickness T (μm) of the separator is in the range of 0.01 to 0.9.

[0011] Conductive particles are virtually immune to thermal degradation. Therefore, adding conductive particles to the electrolyte layer can suppress the increase in ESR over the long term. By setting the D / T ratio to 0.9 or less, short circuits involving conductive particles can be suppressed. By setting the D / T ratio to 0.01 or higher, ESR can be significantly reduced.

[0012] The average thickness T of the separator can be measured using a constant-pressure thickness measuring instrument compliant with JIS P 8118.

[0013] The average maximum diameter D of conductive particles can be measured by the following methods. First, images of the electrolyte layer or on the separator are taken using an instrument capable of identifying the particle shape at a magnification of 100x or more (such as an optical microscope or electron microscope). The maximum diameter of the particles is measured by image processing of the obtained images. The maximum diameter is measured for any 10 particles, and the arithmetic mean is taken as the average maximum diameter D. Unless there are any particular problems, the average maximum diameter D is measured by this method. Alternatively, the volume-based particle size distribution is measured using a sieve, light scattering method, or sedimentation method, and the D at which the cumulative volume reaches 90% is determined. 90 The diameter may also be defined as the average maximum diameter D.

[0014] The electrolytic capacitor of this embodiment may satisfy condition (1) below, and may also satisfy conditions (2) and / or (3). By satisfying conditions (1), (2) and (3), the rise in ESR can be particularly suppressed over a long period of time. (1) The above ratio D / T is in the range of 0.01 to 0.9. The ratio D / T may also be in the range of 0.01 to 0.5 (for example, in the range of 0.01 to 0.33). If the aspect ratio of the conductive particles is 3 or more, the ratio D / T may also be in the range of 0.1 to 1.0. (2) The average thickness T of the separator is in the range of 10 μm to 200 μm (for example, in the range of 20 μm to 100 μm). (3) The average maximum diameter D of the conductive particles is in the range of 0.1 μm to 180 μm (for example, in the range of 0.2 μm to 90 μm).

[0015] 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.

[0016] The electrolytic capacitor of this embodiment may satisfy condition (4) below, and may also satisfy condition (5). By using these configurations, the effects described later can be obtained. (4) The electrolyte layer further contains a conductive polymer. (5) The electrolyte layer contains a conductive polymer dopant. The dopant may be a polymer dopant containing an acidic group. In this case, 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, the content of the basic component in the electrolyte solution may be 0.1% by mass or more and 20% by mass or less.

[0017] The conductivity of the electrolyte layer can be increased by using conductive polymers containing dopants. Examples of conductive polymers and dopants will be described later.

[0018] The mass of the conductive particles contained in the electrolyte layer may be greater 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. 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, 0.1 < N may be satisfied, and 0.05 < M may be satisfied.

[0019] The ratio of the content rate N of the conductive particles to the total content rate M of the conductive polymer and the dopant, N / M, may be in the range of 25 / 75 to 75 / 25. By setting it within this range, an electrolytic capacitor with good characteristics can be obtained.

[0020] 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 contain at least one particle selected from the group consisting of particles of carbon black, particles of carbon nanotubes, particles of graphite, and particles of graphene. These particles are preferable in that the average particle diameter, 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.

[0021] The conductive particles may have a spherical or flaky shape. The type of the conductive particles having a flaky shape 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.

[0022] The average aspect ratio of flaky carbon particles may be 2 or greater, or 3 or greater. The average aspect ratio of carbon particles can be determined as follows: First, an image of the carbon particles is obtained using a scanning electron microscope (SEM). A number of carbon particles (e.g., 10) are selected from the obtained SEM image. Next, the maximum diameter D1 is measured for the selected carbon particles, and the maximum diameter D2 in the direction perpendicular to the maximum diameter D1 is also measured. For each carbon particle, the ratio of D1 to D2, D1 / D2, is calculated as the aspect ratio, and the average aspect ratio is obtained by taking the arithmetic mean of these ratios.

[0023] 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.

[0024] 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).

[0025] In a preferred example, the cathode is a conductive foil and the conductive particles are metal particles. When the cathode is a conductive foil (e.g., metal foil), the contact resistance between the conductive polymer and the cathode may be high. However, by using a conductive foil (e.g., metal foil) for the cathode and metal particles for the conductive particles, the contact resistance between the two can be reduced. Therefore, the ESR of the electrolytic capacitor can be particularly reduced.

[0026] Except for the parts characteristic of the electrolytic capacitor relating to this disclosure, there are no particular limitations on the components of the electrolytic capacitor relating to this disclosure, and known components may be used. Examples of components of the electrolytic capacitor relating 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. That is, the region between the dielectric layer and the cathode becomes the region of the electrolyte layer. As described above, the electrolyte layer contains a non-aqueous solvent and conductive particles, and may further contain 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.

[0052] 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.

[0053] (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.

[0054] 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.

[0055] 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.

[0056] (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.

[0057] 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.

[0058] (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.

[0059] (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.

[0060] The basis weight of the separator is 10-50 g / m². 2 range (e.g., 10-30 g / m 2 It may also be within the range of ). Here, the basis weight is a value measured in accordance with JIS P 8124.

[0061] (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.

[0062] The manufacturing method relating to this disclosure includes steps (i), (ii), and (iii), which are described below. An example of a manufacturing method in which the electrolyte layer contains a conductive polymer is described below. If the electrolyte layer does not contain a conductive polymer, the conductive particles may be attached to the separator beforehand, or attached to the separator in the capacitor element precursor by impregnation treatment. Alternatively, the conductive particles may be dispersed in a non-aqueous solvent, and the non-aqueous solvent and conductive particles may be impregnated into the capacitor element precursor simultaneously.

[0063] (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.

[0064] 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.

[0065] (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.

[0066] The impregnation treatment in step (ii) may be an impregnation treatment (x) in which a dispersion containing a dopant-doped conductive polymer and conductive particles is impregnated into the capacitor element precursor. For example, the capacitor element precursor can be impregnated by immersing it in the dispersion. By removing (drying) the dispersion medium of the dispersion impregnated into the capacitor element precursor, the polymer layer containing the dopant-doped conductive polymer and conductive particles can be positioned 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).

[0067] 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.

[0068] By adjusting the mass (content) of conductive polymers and conductive particles in the dispersion, their ratio in the formed electrolyte layer can be adjusted. For example, by making the mass (content) of conductive polymers in the dispersion greater than the mass (content) of conductive particles in the dispersion, the mass of conductive polymers in the electrolyte layer can be made greater than the mass of conductive particles in the electrolyte layer.

[0069] Furthermore, at least a portion of the conductive particles may be pre-supported on the separator used when forming the capacitor element precursor in step (i). For example, a capacitor element precursor may be formed using a separator on which conductive particles are supported, and in the impregnation treatment (x), a dispersion containing a dopant-doped conductive polymer may be impregnated into the capacitor element precursor. This dispersion may or may not contain conductive particles. There are no limitations on the method of supporting the conductive particles on the separator. For example, the separator may be brought into contact with a liquid in which conductive particles are dispersed, and then the separator may be dried.

[0070] (Step (iii)) Step (iii) is a step of impregnating the polymer 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).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] (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.

[0076] 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.

[0077] 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]

[0078] The embodiments of this disclosure will be described in more detail below with reference to examples.

[0079] (Examples) [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.

[0080] (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.

[0081] (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".

[0082] (PEDOT: Addition of conductive particles to PSS dispersion) Graphene particles (flaky, average maximum diameter D: 0.4 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. The mass ratio of PEDOT:PSS to conductive particles was 75:25.

[0083] (Separator) As a separator, a nonwoven fabric (average thickness: 40 μm) was prepared. 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.

[0084] (Preparation of coiled bodies) Anode lead tabs and cathode lead tabs, each with a lead wire attached, were connected to the anode and cathode bodies described above. Then, the separator described above was placed between the anode and cathode bodies and the coil was wound, and the outer surface was secured with winding tape. A nonwoven fabric made of cellulose was used for the separator. In this way, a wound coil (capacitor element precursor) was 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.

[0085] (Formation of conductive polymer layer) First, the above-mentioned treatment solution A was placed in a container. Next, the wound material was immersed in the treatment solution A in the container for 15 minutes in a reduced-pressure atmosphere (40 kPa) at room temperature, and then the wound material was removed from the treatment solution A. In this way, the treatment solution A was impregnated into the wound material. Next, the wound material was dried in a drying oven at 60°C for 30 minutes, and then at 150°C for 30 minutes. This removed the dispersion medium (water) contained in the impregnated treatment solution A. In this way, a conductive polymer layer containing conductive particles was formed.

[0086] (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 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.

[0087] [Fabrication of Capacitor A2] Capacitor A2 was fabricated using the same materials and conditions as capacitor A1, except that the mass ratio of PEDOT:PSS to conductive particles was set to 25:75.

[0088] [Making Capacitor A3] Capacitor A3 was fabricated using the same materials and conditions as capacitor A1, except that nickel particles (spherical, average maximum diameter D: 2 μm) were used as conductive particles in processing solution A.

[0089] [Making Capacitor A4] Capacitor A4 was fabricated using the same materials and conditions as capacitor A3, except that the mass ratio of PEDOT:PSS to conductive particles was set to 25:75.

[0090] [Making Capacitor A5] Capacitor A5 was manufactured using the same materials and conditions as capacitor A3, except that nickel particles (spherical, average maximum diameter D: 10 μm) were used as conductive particles in processing solution A, and the average thickness of the separator was set to 30 μm.

[0091] [Making Capacitor A6] Capacitor A6 was fabricated using the same materials and conditions as capacitor A5, except that the mass ratio of PEDOT:PSS to conductive particles was set to 25:75.

[0092] [Fabrication of Capacitor C1 (Comparative Example)] Capacitor C1 was fabricated using the same materials and conditions as capacitor A1, except that it did not use conductive particles. Therefore, the conductive polymer layer of capacitor C1 contains PEDOT:PSS but does not contain conductive particles.

[0093] (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. In addition, as an indicator of long-term characteristics, the ESR change rate for each capacitor was calculated using the following formula. The relative value of the initial ESR and the ESR change rate are relative values ​​based on the initial ESR value of capacitor C1. 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 capacitor C1)

[0094] (Measurement of leakage current) Under conditions of 20°C, the rated voltage was applied to an electrolytic capacitor, and the leakage current (LC) was measured after 2 minutes. The leakage current was measured both initially after the electrolytic capacitor was manufactured and after it had been left at high temperatures (145°C for 150 hours and 500 hours). The relative value of the initial leakage current was calculated using the following formula. Furthermore, the rate of change of the leakage current was calculated using the following formula as an indicator of long-term characteristics. The initial value of the leakage current and the rate of change of the leakage current are relative values ​​based on the initial value of the leakage current of capacitor C1. Relative value (%) of the initial leakage current (LC) = 100 × (initial leakage current of each capacitor) / (initial leakage current of capacitor C1) Leakage current change rate (%) = 100 × (Value of leakage current of each capacitor after being left at high temperature) / (Initial value of leakage current of capacitor C1)

[0095] Table 1 shows some of the conditions for forming the electrolyte layer of the electrolytic capacitor described above. The mass ratio (or content ratio) of conductive particles to PEDOT:PSS in the formed electrolyte layer can be considered equal to the content ratio of those particles in the processing solution. Therefore, the mass ratio in the electrolyte layer was calculated from their content in the processing solution. Table 2 shows the evaluation results for the ESR and leakage current of the electrolytic capacitor described above. Lower ESR and leakage current are preferable.

[0096] [Table 1]

[0097] [Table 2]

[0098] As shown in Table 2, the ESRs of capacitors A1 to A6 were significantly lower than those of capacitor C1 in the comparative example.

[0099] Adding conductive particles to a conductive polymer layer generally increases leakage current. However, increasing the value of (average maximum diameter D / average thickness T) reduced the leakage current. Furthermore, the effect of increasing the value of (average maximum diameter D / average thickness T) on reducing leakage current was particularly pronounced when the amount of conductive particles was greater than the amount of conductive polymer. [Industrial applicability]

[0100] 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]

[0101] 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 conductive particles are arranged within the electrolyte layer, extending from the dielectric layer to the cathode. The ratio D / T of the average maximum diameter D of the conductive particles to the average thickness T of the separator is in the range of 0.05 to 0.

5. The electrolyte layer contains the conductive polymer dopant, An electrolytic capacitor 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.

2. The aforementioned dopant is a polymer dopant containing an acidic group, The electrolytic capacitor according to claim 1, wherein the electrolyte layer comprises an electrolyte solution containing the non-aqueous solvent and a basic component dissolved in the non-aqueous solvent.

3. The electrolytic capacitor according to claim 2, wherein the content of the basic component in the electrolyte is 0.1% by mass or more and 20% by mass or less.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the conductive particles are particles of a conductive carbon material.

5. The cathode body is a conductive foil, The electrolytic capacitor according to any one of claims 1 to 3, wherein the conductive particles are metal particles.

6. The electrolytic capacitor according to any one of claims 1 to 5, wherein the separator is made of a single layer of nonwoven fabric.

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