Sheet, method for manufacturing sheet, electrolytic capacitor, and method for manufacturing electrolytic capacitor

Abstract

This sheet is used in an electrolytic capacitor, and includes a porous layer exposed on a surface thereof. The porous layer is composed of fibers including mixed fibers. The mixed fibers contain a conductive material and an insulating material, and has irregularities on a surface thereof.

Description

Sheet, method for producing sheet, electrolytic capacitor, and method for producing electrolytic capacitor

[0001] The present disclosure relates to a sheet, a method for producing a sheet, an electrolytic capacitor, and a method for producing an electrolytic capacitor.

[0002] Various electrolytic capacitors and separators have been conventionally proposed. Claim 1 of Patent Document 1 (Japanese Patent No. 7444561) recites "a method for producing an aluminum electrolytic capacitor, comprising: an anode having a first metal layer containing aluminum and a dielectric layer formed on a surface of the first metal layer; a cathode having a second metal layer containing aluminum; and a fiber film provided between the anode and the cathode, the method comprising: a forming step of forming the fiber film on one of the anode and the cathode by an electrospinning method; and a fixing step performed after the forming step, wherein the fiber film is fixed to the one member by pressurizing the one member on which the fiber film is formed, wherein in the fixing step, the one member on which the fiber film is formed is pressurized with a press pressure of 15 N / mm or more and less than 60 N / mm using a roller having a diameter of 250 mm or less, and wherein in the forming step, after first fibers having a first diameter are deposited on the anode to form a first layer, second fibers having a second diameter smaller than the first diameter are deposited on the first layer to form a second layer", which is a method for producing an aluminum electrolytic capacitor.

[0003] Claim 1 of Patent Document 2 (Japanese Patent No. 6012932) recites "a method for producing a separator for producing a separator comprising, as at least one layer among layers constituting the separator, a nanofiber composite having a structure in which a base material layer and a nanofiber layer formed on the base material layer by an electrospinning method using a polymer solution, wherein the nanofiber layer is in a state where nanofibers and bead-shaped structures are mixed, and the base material layer and the nanofiber layer are laminated, the method comprising forming the nanofiber layer by performing an electrospinning step under electrospinning conditions that form the nanofiber layer in a state where nanofibers and bead-shaped structures are mixed", which is a method for producing a separator.

[0004] Japanese Patent No. 7444561 Publication, Japanese Patent No. 6012932 Publication

[0005] One method to improve the capacitance characteristics of electrolytic capacitors is to thin the separator to increase the capacitance per unit volume. However, thinning conventional separators makes them difficult to handle, increases the likelihood of short circuits between the anode and cathode foils, and makes the manufacturing of electrolytic capacitors more difficult. Therefore, methods such as electrospinning to directly form a porous layer on the electrode foil are being considered. However, with conventional porous layers, it is difficult to improve adhesion to the electrode foil, which may prevent improvements in productivity and ensure long-term reliability. In this context, one of the objectives of this disclosure is to provide a sheet that can improve adhesion to the electrode foil, and an electrolytic capacitor using the same.

[0006] One aspect of the present disclosure relates to a sheet used in an electrolytic capacitor, comprising a porous layer exposed on its surface, wherein the porous layer is composed of fibers including a mixed fiber, the mixed fiber comprising a conductive material and an insulating material, and having irregularities on its surface.

[0007] Another aspect of this disclosure relates to a method for manufacturing a sheet, comprising the steps of (i) preparing a raw material liquid containing a conductive material and an insulating material, and (ii) forming a porous layer composed of fibers containing mixed fibers by an electrospinning method using the raw material liquid, wherein the mixed fibers contain the conductive material and the insulating material and have irregularities on their surface.

[0008] Another aspect of the present disclosure relates to an electrolytic capacitor comprising an anode having a dielectric layer on its surface, a cathode, a porous layer disposed between the anode and the cathode, and an electrolyte disposed in the voids of the porous layer, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers comprising a conductive material and an insulating material, and having irregularities on its surface.

[0009] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor having an anode and a cathode having a dielectric layer on their surfaces, comprising: (I) forming a porous layer on at least one electrode selected from the group consisting of the anode and the cathode; (II) stacking the anode and the cathode such that the porous layer is positioned between the anode and the cathode; and (a) arranging an electrolyte in the voids of the porous layer, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers include a conductive material and an insulating material, and have irregularities on their surface.

[0010] According to this disclosure, a sheet with high adhesion to electrode foil and an electrolytic capacitor using the same 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.

[0011] This figure schematically shows an example of the electrospinning method. This is a schematic cross-sectional view showing an example of an electrolytic capacitor according to this embodiment. This is an electron microscope image showing an example of mixed fibers (mixed fiber A) formed in the embodiment.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0013] (Sheet) The sheet according to this embodiment may be referred to as "sheet (S)" below. Sheet (S) includes a porous layer exposed on its surface. The porous layer may be referred to as "porous layer (L)" below. The porous layer (L) is composed of fibers including mixed fibers. The mixed fibers include a conductive material and an insulating material and have irregularities on their surface. The mixed fibers may be referred to as "mixed fiber A" below. The irregularities of mixed fiber A may be formed by aggregation of the conductive material and / or the insulating material. The conductive material and the insulating material may be a conductive polymer and an insulating polymer, respectively. The fibers constituting the porous layer (L) may include fibers other than mixed fiber A.

[0014] The porous layer (L) of the sheet (S) is composed of fibers including mixed fibers A, which have an uneven surface. Therefore, the porous layer (L) has high adhesion to other components. In other words, the sheet (S) has high adhesion to other components. Furthermore, since the mixed fibers A contain a conductive material, static charge can be suppressed. In this respect as well, there is a possibility of improving adhesion to other components.

[0015] The mixed fiber A includes a conductive material and an insulating material. The conductive materials can aggregate with each other, and / or the insulating materials can aggregate with each other, thereby forming an uneven surface on the mixed fiber A.

[0016] The mixed fiber A has an uneven surface. For example, the mixed fiber A may have recesses on its surface in which the length in the direction D in which the fiber extends is in the range of 0.1 μm to 5 μm, the length (width) in the direction perpendicular to direction D is in the range of 0.005 μm to 0.1 μm, and the maximum depth is in the range of 0.001 μm to 0.1 μm.

[0017] The sheet (S) may further include a base layer. In that case, the porous layer (L) may be directly laminated to the base layer. Because the porous layer (L) has high adhesion to other layers, the porous layer (L) and the base layer can be firmly bonded together.

[0018] The substrate layer is selected according to the application. Examples of substrate layers include substrates, sheets, and porous materials. Examples of substrate layer materials include metals, ceramics, and resins. Examples of substrate layers include metal foils, dielectric layers formed on the surface of electrode foils (anode foil, cathode foil, etc.), metal layers formed on the dielectric layer, ceramic substrates, resin substrates, and separators (insulating porous materials). When a sheet (S) is used as a separator in an electrolytic capacitor, the sheet (S) may be placed on the dielectric layer on the surface of the anode (e.g., anode foil). Alternatively, the sheet (S) may be placed on the cathode (e.g., cathode foil) of the electrolytic capacitor.

[0019] The insulating material is not particularly limited. Examples of insulating materials include insulating inorganic oxides (SiO₂). ２ Al ２ O ３ This includes ), and insulating polymers, etc.

[0020] Examples of insulating polymers include polyacrylonitrile, fluoropolymers (such as polyvinylidene fluoride), polyurethane, polyethylene oxide, polyvinyl alcohol, poly-L-lactic acid, nylon 6, polyethylene terephthalate, polystyrene, polymethyl methacrylate, polypropylene, polysulfone, polyethersulfone, polycaprolactone, polyimide, and cellulosic polymers. Examples of cellulosic polymers include cellulose and cellulose derivatives. Examples of cellulose derivatives include alkylcellulose and cellulose acetate.

[0021] The insulating material may include at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. These insulating polymers are preferred because they are easily spun by electrospinning.

[0022] The conductive material is not particularly limited, but it is preferably a material that dissolves in the liquid medium of the raw material solution for spinning. Examples of conductive materials include carbon materials and metal oxides (e.g., ZnO, TiO). ２Examples of carbon materials include conductive polymers, etc. Examples of carbon materials include reduced graphene oxide (rGO) and carbon nanotubes.

[0023] Examples of conductive polymers include poly(3,4-ethylenedioxythiophene) (PEDOT), polythiophene, polypyrrole, polyaniline, polyacetylene, poly(p-phenylene), and poly(p-phenylenevinylene). Among these, PEDOT is preferred due to its high conductivity and pressure resistance. PEDOT may be doped with a dopant (e.g., polystyrene sulfonic acid). Examples of preferred combinations of conductive and insulating polymers include combinations of polyacrylonitrile and PEDOT, and combinations of polyvinylidene fluoride and PEDOT.

[0024] The content of conductive material in mixed fiber A may be 0.5% by mass or more, or 7.0% by mass or more, or 50.0% by mass or less, or 12.0% by mass or less. The content of insulating material in mixed fiber A may be 50.0% by mass or more, or 88.0% by mass or more, or 99.5% by mass or less, or 93.0% by mass or less.

[0025] Other components may be arranged on the surface of the fibers constituting the porous layer (L). Examples of other components include nanoparticles (e.g., metals, metal oxides, carbon). The fibers constituting the porous layer (L) may consist only of mixed fiber A. Alternatively, the fibers constituting the porous layer (L) may include fibers other than mixed fiber A. The proportion of mixed fiber A in the fibers constituting the porous layer (L) may be 50% by mass or more, 70% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more. When calculating the proportion of components constituting the porous layer (L), substances present in the voids of the porous layer (L) (e.g., electrolyte) are not considered. Examples of fibers other than mixed fiber A that constitute the porous layer (L) include insulating fibers (e.g., polyolefin fibers) and conductive fibers.

[0026] The average diameter of mixed fiber A may be 0.05 μm or more, or 0.1 μm or more, and may be 2.0 μm or less, or 1.5 μm or less. For example, the average diameter of mixed fiber A may be 0.05 μm or more and 2.0 μm or less. The average diameter of mixed fiber A is determined by the following method. First, the diameters of 30 arbitrarily selected mixed fiber A are measured. The diameter of each mixed fiber A is determined using an image of the cross-section of the sheet (S). Specifically, first, the sheet to be measured is embedded in resin to prepare a sample for measurement. Next, the cross-section of the sample is exposed with an ion beam. Next, the exposed cross-section is photographed with a scanning electron microscope. The diameter of the fiber is determined using the obtained image. If the cross-section of the fiber is not circular, the equivalent diameter of the circle calculated from the area of ​​the cross-section of the fiber is taken as the diameter of the fiber. The arithmetic mean of the 30 measured diameters is taken as the average diameter of mixed fiber A.

[0027] The thickness of the porous layer (L) and the thickness of the sheet (S) may be independently 0.5 μm or more, or 3.0 μm or more, or 50 μm or less, or 30 μm or less. For example, the thickness of the sheet (S) may be 0.5 μm or more and 50 μm or less. However, if the sheet (S) includes a base layer, the thickness of the sheet (S) will be in proportion to the thickness of the base layer.

[0028] If the sheet (S) is thin (for example, less than 200 μm), the thickness of the sheet (S) can be measured by the following method. First, the sheet to be measured is embedded in resin to prepare a sample for measurement. Next, the cross-section of the sample is exposed using an ion beam. Then, the exposed cross-section is photographed with a scanning electron microscope. The thickness of the sheet can be determined by measuring the thickness of the sheet portion using the obtained electron microscope image.

[0029] (Method for Manufacturing the Sheet) The method according to this embodiment for manufacturing the sheet may be referred to as "manufacturing method (M1)" below. According to manufacturing method (M1), a sheet (S) can be manufactured. The matters described for the sheet (S) can be applied to manufacturing method (M1). The matters described for manufacturing method (M1) may also be applied to the sheet (S).

[0030] The manufacturing method (M1) includes steps (i) and (ii). Each step is described below.

[0031] (Step (i)) Step (i) is a step of preparing a raw material solution containing a conductive material and an insulating material. An example of step (i) is a step of dissolving the conductive material and the insulating material in a solvent (liquid medium). The conductive material and the insulating material may be a conductive polymer and an insulating polymer, respectively. The solvent is not particularly limited and may be selected considering the type of material, etc. Examples of solvents include dimethylformamide, dimethyl sulfoxide, ethylene glycol, tetrahydrafuran, N-methyl-2-pyrrolidone, and acetone. The concentration of the components in the raw material solution is not particularly limited and may be determined considering the diameter of the fiber to be formed and the diameter of the nozzle used in the electrospinning method, etc. The concentration of the conductive material in the raw material solution may be 0.1% by mass or more, or 1.0% by mass or more, or 10.0% by mass or less, or 3.0% by mass or less. The concentration of the insulating material in the raw material liquid may be 1.0% by mass or more, or 4.0% by mass or more, or 50.0% by mass or less, or 10.0% by mass or less. By changing the ratio of components (conductive polymer, insulating polymer, etc.) in the raw material liquid, the ratio of components constituting the mixed fiber A can be changed.

[0032] (Step (ii)) Step (ii) is a step of forming a porous layer composed of fibers including mixed fibers (mixed fiber A) by an electrospinning method using a raw material liquid. As described above, the mixed fiber A contains a conductive material and an insulating material and has irregularities on its surface. The irregularities may be formed by the aggregation of the conductive material and / or the aggregation of the insulating material.

[0033] By spinning using the above raw material liquid, the above-described mixed fiber A is obtained. By depositing the mixed fiber A onto a predetermined member, a porous layer composed of the mixed fiber A can be formed. By peeling the porous layer from the member, a sheet (S) is obtained. When forming a sheet (S) by peeling off the porous layer, a member that facilitates the peeling of the porous layer is used. Examples of such members include release paper, release paper, and release film.

[0034] The conditions for electrospinning and the equipment used for electrospinning are not particularly limited and should be selected according to the type of raw material liquid and the physical properties of the mixed fiber A to be formed. The physical properties of the mixed fiber A can be changed by changing the conditions of the electrospinning method (nozzle diameter, applied voltage, type of solvent, concentration of components, etc.).

[0035] The apparatus for carrying out the electrospinning method is not particularly limited. An example of an apparatus 200 for carrying out the electrospinning method is schematically shown in Figure 1. The apparatus 200 includes a syringe 201 having a conductive nozzle 201a and a power supply 202. An example of the electrospinning method is described below. A solution 211 in which conductive material and insulating material are dissolved is placed in the syringe 201. A high voltage is applied between the nozzle 201a and the electrode 221 (anode or cathode) by the power supply 202. Fibers 212 are formed by ejecting the solution 211 containing the conductive material and insulating material from the nozzle 201a. The formed fibers 212 are deposited on the electrode 221, forming a porous insulating layer. By increasing the number of nozzles 201a, it is possible to deposit a large number of fibers 212 simultaneously.

[0036] In step (ii), a porous layer may be formed on the substrate layer. The porous layer may be laminated directly onto the substrate layer. The laminate comprising the substrate layer and the porous layer can be used for a predetermined application. The substrate layer may be the substrate layer described above.

[0037] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment may be referred to as "electrolytic capacitor (C)" below. The electrolytic capacitor (C) includes an anode having a dielectric layer on its surface, a cathode, a porous layer disposed between the anode and the cathode, and an electrolyte disposed in the voids of the porous layer. The porous layer is a porous layer (L). That is, the porous layer is composed of fibers including mixed fibers A. The mixed fibers A include a conductive material and an insulating material and have irregularities on their surface. These irregularities may be formed by aggregation of the conductive material and / or the insulating material.

[0038] By placing a porous layer (L) between the anode and cathode, direct short circuits between the anode and cathode can be suppressed. By forming the porous layer (L) directly on the electrodes (anode and / or cathode), a strong bond can be established between the electrodes and the porous layer (L). As a result, improvements in capacitance characteristics, productivity, and long-term reliability can be achieved. When the porous layer (L) is formed on the anode, more specifically, the porous layer (L) is formed on the dielectric layer on the surface of the anode.

[0039] The porous layer (L) may be in contact with at least one selected from the group consisting of a dielectric layer and a cathode. For example, the porous layer (L) may be in contact with both the dielectric layer and the cathode.

[0040] As described above, the insulating material may include at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

[0041] An outer edge of at least a portion of the anode and / or cathode may be positioned inward of an outer edge of the porous layer (L) adjacent to said portion. According to this configuration, short-circuiting between the anode and the cathode can be suppressed. In a case where the electrode group is a wound-type electrode group and the porous layer (L) is formed on the anode (more specifically, on a dielectric layer on a surface of the anode), a long side of the cathode may be positioned inward of a long side of the porous layer (L). In a case where the electrode group is a wound-type electrode group and the porous layer (L) is formed on the cathode, a long side of the anode may be positioned inward of a long side of the porous layer (L).

[0042] (Method for Manufacturing Electrolytic Capacitor) Hereinafter, the method of the present embodiment for manufacturing an electrolytic capacitor may sometimes be referred to as "manufacturing method (M2)". Manufacturing method (M2) is a method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on a surface thereof and a cathode. Manufacturing method (M2) includes step (I), step (II), and step (a).

[0043] Step (II) and step (a) are performed after step (I). Step (a) is normally performed after step (II). These steps are described below.

[0044] (Step (I)) Step (I) is a step of forming a porous layer on at least one electrode selected from the group consisting of an anode and a cathode. Said porous layer is the porous layer (L). That is, said porous layer is constituted of fibers including mixed fibers (mixed fiber A). Said mixed fiber A contains a conductive material and an insulating material, and has irregularities on a surface thereof. Said irregularities may be formed by aggregation of the conductive material and / or aggregation of the insulating material.

[0045] Step (I) can be performed by the method described in the method for producing the sheet (S). In a case where the porous layer (L) is formed on the anode, the porous layer (L) is formed on the dielectric layer present on the surface of the anode.

[0046] In step (I), the porous layer (L) may be formed by depositing fibers on the at least one electrode. For example, in step (I), fibers may be deposited on the at least one electrode by an electrospinning method.

[0047] Before step (II), the anode and / or cathode are cut into a predetermined size as necessary. For example, after forming the porous layer (L) on a large-format sheet (anode sheet or cathode sheet), the sheet may be cut into a predetermined size.

[0048] (Step (II)) Step (II) is a step of laminating an anode and a cathode such that the porous layer (L) is disposed between the anode and the cathode. An electrode assembly is formed by laminating the anode and the cathode. The electrode assembly may be of a stacked type or a wound type. When the electrode assembly is of a stacked type, the electrode assembly is formed by stacking at least one anode and at least one cathode in one direction. The anodes and cathodes may be stacked alternately.

[0049] When the electrode assembly is of a wound type, the electrode assembly is formed by winding the anode and the cathode. That is, in step (II), the anode and the cathode may be laminated by winding the anode and the cathode.

[0050] The porous layer (L) may be formed on both surfaces of the anode, may be formed on both surfaces of the cathode, or may be formed on one surface of the anode and one surface of the cathode. In any case, the porous layer (L) is disposed between the anode and the cathode.

[0051] (Step (a)) Step (a) is a step of disposing an electrolyte in voids of the porous layer (L). The method for carrying out step (a) is not particularly limited. For example, the electrolyte may be disposed in the voids of the porous layer (L) by immersing the electrode assembly in the electrolyte or a liquid containing the electrolyte. Examples of the liquid containing an electrolyte include a solution of a conductive polymer and a dispersion of a conductive polymer. The electrolyte may contain an electrolytic solution or may be an electrolytic solution. The electrolyte may contain an electrolytic solution and a conductive polymer.

[0052] Examples of components used in electrolytic capacitors (C) are described below. However, the components used in electrolytic capacitors (C) are not limited to the examples described below. Components other than those specific to electrolytic capacitors (C) are not particularly limited, and known components may be used.

[0053] (Anode) Examples of anodes (typically anode foil) include metal foil containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode may also be a metal foil of valve metal (e.g., aluminum foil). The anode may contain valve metal in the form of an alloy containing valve metal or a compound containing valve metal. The surface of the anode may be roughened by etching or the like. That is, the surface of the anode may be porous. The thickness of the anode may be 15 μm or more, or 50 μm or more, or 300 μm or less, or 100 μm or less. When the electrode group is a wound electrode group, the anode has a strip shape.

[0054] A dielectric layer is formed on the surface of the anode. The dielectric layer may be formed by chemical treatment of the anode. In this case, the dielectric layer may contain an oxide of the valve metal (e.g., aluminum oxide).

[0055] (Cathode) A conductive sheet can be used for the cathode (typically a cathode foil), or a metal foil (e.g., aluminum foil) may be used. The metal constituting the metal foil may be valve metal or an alloy containing valve metal. The surface of the cathode may be roughened by etching or the like. That is, the surface of the cathode may be porous. The thickness of the cathode may be 15 μm or more, or 50 μm or more, or 300 μm or less, or 100 μm or less. If the electrode group is a wound electrode group, the cathode has a strip shape.

[0056] (Electrolyte) The electrolyte is placed between the anode and the cathode (for example, in the voids of the porous layer (L)). A solid electrolyte (e.g., a conductive polymer) and / or an electrolyte solution may be used as the electrolyte. The electrolytic capacitor (C) may contain a conductive polymer and a liquid component placed between the anode and the cathode. The liquid component may be an electrolyte solution or a non-aqueous solvent used in the electrolyte solution. Using a conductive polymer and an electrolyte solution as the electrolyte is preferable because it is easier to achieve high reliability and high voltage resistance while reducing ESR.

[0057] 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 the basic skeleton. For example, derivatives of polythiophene include poly(3,4-ethylenedioxythiophene). These conductive polymers may be used individually or in combination of multiple types. Furthermore, the conductive polymer may be a copolymer of two or more monomers. The weight-average molecular weight of the conductive polymer 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).

[0058] Conductive polymers may be doped with dopants. From the viewpoint of suppressing dedoping from conductive polymers, polymer dopants may be used as dopants. 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. At least some of these may be added in the form of salts. A preferred example of a dopant is polystyrene sulfonic acid (PSS).

[0059] The dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0060] When a conductive polymer is placed between the anode and cathode, a liquid containing the conductive polymer may be used. The liquid medium is not particularly limited. Examples of liquid mediums include water, organic solvents (alcohols, ethylene glycol), and mixed solvents thereof. The liquid containing the conductive polymer may be a dispersion in which particles of the conductive polymer are dispersed in a liquid mainly composed of water (content: 50% by mass or more).

[0061] The content of the conductive polymer in a liquid containing a conductive polymer may be 0.5% by mass or more, or 1.0% by mass or more, and may also be 4.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less.

[0062] The electrolyte is not particularly limited, and any known electrolyte used in electrolytic capacitors may be used. The electrolyte may contain a non-aqueous solvent and a solute (e.g., an organic salt) dissolved in the non-aqueous solvent.

[0063] 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.

[0064] The non-aqueous solvent may include polymeric 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. The non-aqueous solvent may be used alone or as a mixture of two or more.

[0065] Examples of solutes include inorganic and organic salts. Organic salts are salts 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.

[0066] (Enclosure) The capacitor element is housed in an enclosure. The enclosure is not particularly limited, and known enclosures may be used.

[0067] Hereinafter, an example of this disclosure will be specifically described with reference to the drawings. The components of the example described below can be the components described above. Furthermore, the components of the example described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiments. Furthermore, in the example described below, components that are not essential to the electrolytic capacitor according to this disclosure may be omitted.

[0068] (Embodiment 1) Embodiment 1 describes an example of an electrolytic capacitor (C). A cross-sectional view of the electrolytic capacitor 100 of Embodiment 1 is shown in Figure 2. The electrolytic capacitor 100 includes an anode 11 having a dielectric layer 11b on its surface, a cathode 12, a porous layer 13, and an electrolyte. The anode 11 includes a valve metal foil 11a and a dielectric layer 11b formed on the surface of the valve metal foil 11a. The porous layer 13 is disposed between the anode 11 and the cathode 12. The electrolyte is disposed in at least the voids of the porous layer 13. The porous layer 13 is the porous layer (L) described above. In one view, the porous layer 13 is a sheet (S). When the porous layer 13 is formed on the anode 11, the laminate of the anode 11 and the porous layer 13 can be considered as a sheet (S). When the porous layer 13 is formed on the cathode 12, the laminate of the cathode 12 and the porous layer 13 can be considered as a sheet (S).

[0069] (Note) The above description discloses the following technologies: (Technology 1) A sheet used in an electrolytic capacitor, comprising a porous layer exposed on its surface, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers comprising a conductive material and an insulating material, and having irregularities on its surface. (Technology 2) The sheet according to Technology 1, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material. (Technology 3) The sheet according to Technology 1 or 2, wherein the average diameter of the mixed fibers is 0.05 μm or more and 2.0 μm or less. (Technology 4) The sheet according to any one of Technology 1 to 3, further comprising a base layer, wherein the porous layer is directly laminated on the base layer. (Technology 5) The sheet according to any one of Technology 1 to 4, wherein the insulating material comprises at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. (Technology 6) A sheet according to any one of Technologies 1 to 5, having a thickness of 0.5 μm or more and 50 μm or less. (Technology 7) A method for manufacturing a sheet, comprising the steps of (i) preparing a raw material liquid containing a conductive material and an insulating material, and (ii) forming a porous layer composed of fibers containing mixed fibers by an electrospinning method using the raw material liquid, wherein the mixed fibers contain the conductive material and the insulating material and have irregularities on their surface. (Technology 8) The manufacturing method according to Technology 7, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material. (Technology 9) An electrolytic capacitor comprising an anode having a dielectric layer on its surface, a cathode, a porous layer disposed between the anode and the cathode, and an electrolyte disposed in the voids of the porous layer, wherein the porous layer is composed of fibers containing mixed fibers, and the mixed fibers contain a conductive material and an insulating material and have irregularities on their surface. (Technical 10) The electrolytic capacitor according to Technical 9, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material.(Technical 11) The electrolytic capacitor according to Technical 9 or 10, wherein the porous layer is in contact with at least one selected from the group consisting of the dielectric layer and the cathode. (Technical 12) The electrolytic capacitor according to any one of Technical 9 to 11, wherein the insulating material includes at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. (Technical 13) The electrolytic capacitor according to any one of Technical 9 to 12, wherein the outer edge of at least a portion of the anode and / or the cathode is located inward from the outer edge of the porous layer adjacent to that portion. (Technical 14) A method for manufacturing an electrolytic capacitor comprising an anode and a cathode having a dielectric layer on their surfaces, comprising: (I) forming a porous layer on at least one electrode selected from the group consisting of the anode and the cathode; (II) stacking the anode and the cathode such that the porous layer is positioned between the anode and the cathode; and (a) arranging an electrolyte in the voids of the porous layer, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers include a conductive material and an insulating material, and have irregularities on their surface. (Technical 15) The manufacturing method according to Technical 14, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material. (Technical 16) The manufacturing method according to Technical 14 or 15, wherein in step (I), the porous layer is formed by depositing the fibers on the at least one electrode. (Technical 17) The manufacturing method according to Technical 16, wherein in step (I), the fibers are deposited on the at least one electrode by an electrospinning method. (Technical 18) A manufacturing method according to any one of Technical 14 to 17, wherein in step (II), the anode and the cathode are stacked by winding them together.

[0070] The present disclosure will be described in more detail below based on the examples. In these examples, different sheets were formed on a substrate and evaluated.

[0071] (Sheet A1) First, the raw material solution used in the electrospinning method was prepared. Specifically, the raw material solution was prepared by dissolving a conductive polymer and an insulating polymer in an organic solvent. For the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS) was used. For the insulating polymer, polyacrylonitrile was used. For the organic solvent, a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a mass ratio of 9:1 was used. The content of the conductive polymer (PEDOT and PSS) in the raw material solution was 1.0% by mass. The content of polyacrylonitrile in the raw material solution was 11.0% by mass.

[0072] Next, a porous layer (porous layer (L)) was formed on the aluminum foil. In this way, a sheet A1 was prepared, which included the aluminum foil and the porous layer formed on the aluminum foil.

[0073] The porous layer was formed by depositing mixed fibers A, containing a conductive polymer and an insulating polymer, onto aluminum foil using an electrospinning method with the above-mentioned raw material liquid. The average fiber diameter of mixed fibers A was 0.6 μm. A scanning electron microscope image of mixed fibers A is shown in Figure 3. As shown in Figure 3, irregularities were formed on the surface of mixed fibers A, which are thought to be due to the aggregation of the conductive polymer and / or the insulating polymer.

[0074] The peel strength between the aluminum foil and the porous layer was measured for the fabricated laminate (a laminate of aluminum foil and a porous layer). Specifically, first, adhesive tape was attached to the tip of a probe. A cylindrical probe was used. Next, the probe was lowered and the adhesive tape was pressed against the porous layer with a constant pressure. Then, the probe was raised and the peak load was measured. The same evaluation was performed for three sheets A1. The average peel strength was then obtained by arithmetic mean of the measured peak loads.

[0075] (Sheet C1) First, the raw material solution used in the electrospinning method was prepared. Specifically, the raw material solution was prepared by dissolving an insulating polymer in an organic solvent. Polyacrylonitrile was used as the insulating polymer. Dimethylformamide (DMF) was used as the organic solvent. The polyacrylonitrile content in the raw material solution was 12% by mass.

[0076] Next, a porous layer was formed on the aluminum foil. In this way, a sheet C1 was fabricated, comprising the aluminum foil and the porous layer formed on the aluminum foil. The porous layer was formed by electrospinning, similar to the porous layer of sheet A1. The fabricated sheet C1 was evaluated in the same manner as sheet A1, and the average peel strength was determined.

[0077] Sheet A1 is the sheet (S) according to this disclosure. Sheet C1 is a comparative example. The average peel strength of Sheet A1 was 9.3 times that of Sheet C1. A higher peel strength indicates better adhesion between the aluminum foil and the porous layer. The porous layer of Sheet A1 had high adhesion to the aluminum foil.

[0078] This disclosure can be applied to sheets containing a porous layer and to electrolytic capacitors. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be constrained. 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 construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0079] 11: Anode 11b: Dielectric layer 12: Cathode 13: Porous layer 100: Electrolytic capacitor 212: Fiber 221: Electrode

Claims

1. A sheet used in an electrolytic capacitor, comprising a porous layer exposed on its surface, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers comprising a conductive material and an insulating material, and having irregularities on its surface.

2. The sheet according to claim 1, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material.

3. The sheet according to claim 1, wherein the average diameter of the mixed fibers is 0.05 μm or more and 2.0 μm or less.

4. The sheet according to claim 1 or 2, further comprising a base layer, wherein the porous layer is directly laminated to the base layer.

5. The sheet according to claim 1 or 2, wherein the insulating material comprises at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

6. The sheet according to claim 1 or 2, wherein the thickness is 0.5 μm or more and 50 μm or less.

7. A method for manufacturing a sheet, comprising the steps of (i) preparing a raw material liquid containing a conductive material and an insulating material, and (ii) forming a porous layer composed of fibers containing mixed fibers by an electrospinning method using the raw material liquid, wherein the mixed fibers contain the conductive material and the insulating material and have irregularities on their surface.

8. The manufacturing method according to claim 7, wherein the irregularities are formed by aggregation of the conductive material and / or the insulating material.

9. An electrolytic capacitor comprising an anode having a dielectric layer on its surface, a cathode, a porous layer disposed between the anode and the cathode, and an electrolyte disposed in the voids of the porous layer, wherein the porous layer is composed of fibers including mixed fibers, and the mixed fibers include a conductive material and an insulating material, and have irregularities on their surface.

10. The electrolytic capacitor according to claim 9, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material.

11. The electrolytic capacitor according to claim 9, wherein the porous layer is in contact with at least one selected from the group consisting of the dielectric layer and the cathode.

12. The electrolytic capacitor according to claim 9 or 10, wherein the insulating material comprises at least one selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

13. The electrolytic capacitor according to claim 9 or 10, wherein the outer edge of at least a portion of the anode and / or cathode is located inward from the outer edge of the porous layer adjacent to the portion.

14. A method for manufacturing an electrolytic capacitor comprising an anode and a cathode having a dielectric layer on their surfaces, comprising: (I) forming a porous layer on at least one electrode selected from the group consisting of the anode and the cathode; (II) stacking the anode and the cathode such that the porous layer is positioned between the anode and the cathode; and (a) arranging an electrolyte in the voids of the porous layer, wherein the porous layer is composed of fibers including mixed fibers, the mixed fibers include a conductive material and an insulating material, and have irregularities on their surface.

15. The manufacturing method according to claim 14, wherein the irregularities are formed by the aggregation of the conductive material and / or the aggregation of the insulating material.

16. The manufacturing method according to claim 14 or 15, wherein the porous layer is formed in step (I) by depositing the fibers on the at least one electrode.

17. The manufacturing method according to claim 16, wherein in step (I), the fibers are deposited on the at least one electrode by an electrospinning method.

18. The manufacturing method according to claim 14 or 15, wherein in step (II), the anode and the cathode are stacked by winding them together.

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