JP5909685B2 - Nanofiber sheet, capacitor separator, capacitor, and method of manufacturing capacitor separator - Google Patents

Description

  The present invention relates to a capacitor, a capacitor separator, and a method of manufacturing a capacitor separator, and more particularly to an improvement of a capacitor separator.

  Nanofibers are ultrafine fibers having a fiber diameter of several tens to several hundreds of nanometers, and exhibit physical properties different from those of conventional fibers when the fibers are ultrafine. Therefore, nanofibers themselves or nanofiber products (for example, non-woven fabrics) have attracted attention in various fields such as energy, biotechnology, and healthcare. In particular, nanofiber nonwoven fabrics are expected to be used in a wide range of fields because they can be made smaller in pore diameter than conventional nonwoven fabrics due to the small fiber diameter of nanofibers.

  Nanofiber nonwoven fabrics are attracting attention, for example, as a support for electrolyte membranes in fuel cells and as separators in primary or secondary batteries such as alkaline batteries and lithium batteries in the energy field.

  Patent Document 1 discloses that a separator made of a porous layer containing nanofibers formed by an electrospinning method is joined and integrated with an electrode surface. In Patent Document 1, a porous layer is formed by spraying and spinning a polymer solution constituting a nanofiber on the substrate surface of an electrode. In Patent Document 1, a nanofiber porous layer is formed by directly electrospinning an electrode substrate. In such a method, nanofibers are deposited on the substrate as the polymer solution is jetted.

JP 2010-225809 A

  However, the nanofibers in contact with the surface of the substrate are in a state of being slightly crushed because the shape of the surface of the substrate is transferred as the nanofibers are deposited. Since the crushed nanofiber has a large maximum fiber diameter in the surface direction of the nanofiber nonwoven fabric, the contact area with the surface of the substrate becomes large. As a result, the contact resistance at the contact surface between the substrate and the porous layer is increased. Therefore, even if such a technique is applied to a capacitor separator, the capacitor performance is likely to deteriorate.

  Even when a separately formed nanofiber nonwoven fabric is used as a separator, the nanofiber nonwoven fabric is once formed on a substrate by electrospinning or the like, and then peeled off from the substrate. Therefore, as in the case of Patent Document 1, in the porous layer, the fiber state is different between the surface in contact with the substrate and the surface opposite to the substrate, and as a result, the characteristics are also different. .

  When such a nanofiber nonwoven fabric is used as a capacitor separator, the surface of the electrode in which the nanofiber is slightly crushed and the maximum fiber diameter in the surface direction of the nanofiber nonwoven fabric is increased is in contact with either electrode. As a result, the contact resistance increases, and as a result, the capacitor characteristics are degraded.

  An object of the present invention is to provide a capacitor having reduced contact resistance at the contact surface between the separator and the electrode, a capacitor separator capable of reducing contact resistance with the electrode, and a method for manufacturing the same.

One aspect of the present invention is a nanofiber sheet that includes nanofibers and has a first surface and a second surface opposite thereto, the average of the maximum fiber diameters of the nanofibers in the plane direction of the nanofiber sheet, When comparing the vicinity of the first surface and the vicinity of the second surface with the central portion in the thickness direction of the nanofiber sheet, the average Ds1 of the maximum fiber diameter of the nanofibers near the first surface and the nanofibers near the second surface The present invention relates to a nanofiber sheet in which the average Ds2 of the maximum fiber diameter is smaller than the average Dc of the maximum fiber diameters of the nanofibers in the center portion in the thickness direction of the nanofiber sheet . The nanofiber sheet satisfies the relationship of 1.1 ≦ Dc / Ds1 ≦ 2.5 and 1.1 ≦ Dc / Ds2 ≦ 2.5, or the average fiber diameter Dc is 60 nm to 2 μm. .

Another aspect of the present invention includes a Na Nofaiba, and a capacitor separator sheet shape having a first surface and a second surface opposite thereto, a maximum fiber diameter of the nano fibers in the surface direction of the separators Of the maximum fiber diameter of the nanofibers in the vicinity of the first surface and the nano values in the vicinity of the second surface are compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator. The present invention relates to a capacitor separator in which an average Ds2 of maximum fiber diameters of fibers is smaller than an average Dc of maximum fiber diameters of nanofibers in a central portion of the separator in the thickness direction. The capacitor separator satisfies the relationship of 1.1 ≦ Dc / Ds1 ≦ 2.5 and 1.1 ≦ Dc / Ds2 ≦ 2.5, or the average fiber diameter Dc is 60 nm to 2 μm. .
Still another aspect of the present invention includes a pair of electrodes, a separator interposed between the electrodes, and an electrolyte. The separator includes nanofibers, and the first surface and the second surface opposite to the first surface. When the average of the maximum fiber diameters of the nanofibers in the surface direction of the separator is compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator, An average Ds1 of the maximum fiber diameters of the nanofibers near the surface and an average Ds2 of the maximum fiber diameters of the nanofibers near the second surface are smaller than the average Dc of the maximum fiber diameters of the nanofibers at the central portion in the thickness direction of the separator. The capacitor. The separator satisfies the relationship of 1.1 ≦ Dc / Ds1 ≦ 2.5 and 1.1 ≦ Dc / Ds2 ≦ 2.5, or the average Dc of the maximum fiber diameter is 60 nm to 2 μm.

  Still another aspect of the present invention is that (i) a step of supplying a base material sheet to the nanofiber formation space, and (ii) a static electricity from a raw material liquid containing a solvent and a resin raw material dissolved in the solvent in the nanofiber formation space. Forming nanofibers by force and depositing the produced nanofibers on the main surface of the base sheet to form a porous sheet having a nanofiber matrix structure; and (iii) a pair of porous sheets The surfaces that were in contact with the main surface of the base sheet are joined to face each other, and the surfaces that are not in contact with the main surface of the base sheet of the pair of porous sheets are the first surface and the opposite side, respectively. Forming a capacitor separator as a second surface, and a method for manufacturing the capacitor separator.

  Another aspect of the present invention conveys the long first and second base sheets from upstream to downstream of the first and second lines, respectively, and upstream of the first and second base sheets. A method for manufacturing a capacitor separator, comprising: forming first and second porous sheets on the surfaces and joining the first and second porous sheets facing each other on the downstream side, wherein (i) the first and second A step of transporting the second base sheet to the nanofiber formation space upstream of the first and second lines, and (ii) in the nanofiber formation space, the static electricity from the raw material liquid containing the solvent and the resin raw material dissolved in the solvent. First and second porous materials having a nanofiber matrix structure are formed by generating nanofibers by force and depositing the generated nanofibers on the main surfaces of the first and second substrate sheets to be conveyed, respectively. (Iii) removing the first and second base sheets from the conveyed first and second porous sheets downstream of the first and second lines; and (iv) ) On the further downstream side of the first and second lines, the surfaces of the first and second porous sheets to be conveyed which are in contact with the main surfaces of the first and second base sheets are opposed to each other. And a step of forming a nanofiber sheet.

  According to the present invention, although the separator has a nanofiber matrix structure formed by an electrospinning method, the average of the maximum fiber diameters of the nanofibers in the surface direction of the separator is in the vicinity of both surfaces of the separator. It can be made smaller than the average of the maximum fiber diameters at the center in the thickness direction. Therefore, in the capacitor, the contact resistance at the contact surface between the separator and the electrode can be reduced.

FIG. 1 is a conceptual view of a cross section of a capacitor separator according to an embodiment of the present invention. FIG. 2 is a perspective view showing an electrode group of a capacitor according to an embodiment of the present invention. FIG. 3 is a diagram schematically showing a configuration of a manufacturing system for carrying out a method for manufacturing a capacitor separator according to an embodiment of the present invention. FIG. 4 is a top view schematically showing the configuration of the porous sheet forming apparatus 40 of FIG. FIG. 5 is a diagram schematically showing a configuration of a manufacturing system for carrying out a method for manufacturing a capacitor separator according to an embodiment of the present invention. FIG. 6 is a diagram schematically showing a configuration of a manufacturing system for carrying out a method for manufacturing a capacitor separator according to an embodiment of the present invention.

[Capacitor]
The capacitor includes a pair of electrodes, a separator interposed between the electrodes, and an electrolyte. The separator has a nanofiber matrix structure formed by electrospinning and has a sheet shape having a first surface and a second surface opposite to the first surface (hereinafter also simply referred to as a nanofiber sheet). Is used.

  In the nanofiber sheet, when the average of the maximum fiber diameter in the surface direction of the nanofiber separator is compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator, The average Ds1 of the maximum fiber diameters of the nanofibers and the average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are smaller than the average Dc of the maximum fiber diameters of the nanofibers at the center in the thickness direction of the separator.

(Nanofiber sheet)
A nanofiber nonwoven fabric is conventionally produced by depositing nanofibers on a substrate by electrospinning or the like. Therefore, the nanofibers in contact with the surface of the base material are in a state of being slightly crushed after the shape of the surface of the base material is transferred. Thereby, as for the nonwoven fabric obtained, the fiber of the surface of the side in contact with a base material will be in a flat state. When this non-woven fabric having a flat fiber surface is used as a capacitor separator, the flat fiber surface is in contact with the electrode, and the contact area increases, so that the contact resistance increases. As a result, direct current resistance and alternating current resistance (ESR) are increased, and the capacitor characteristics are deteriorated.

  In the present invention, the nanofiber nonwoven fabric as described above is bonded to the surfaces in which the fibers are crushed to form a nanofiber sheet. Therefore, although the nanofiber sheet is formed by the electrospinning method, the nanofibers in the vicinity of both surfaces of the nanofiber sheet are not in a slightly crushed state as in the conventional case.

  More specifically, the nanofiber sheet of the present invention is a porous sheet (nanofiber nonwoven fabric) having a matrix structure of nanofibers, for example, by depositing nanofibers on the main surface of the base sheet by electrospinning. Forming a pair of porous sheets peeled from the main surface of the base sheet, and joining the pair of porous sheets with the surfaces in contact with the main surface of the base sheet facing each other, Can be obtained. Details of the manufacturing method of the nanofiber sheet will be described later.

FIG. 1 is a conceptual diagram of a cross section of a nanofiber sheet for explaining the fiber structure of the nanofiber sheet.
As shown in FIG. 1, the nanofiber sheet 1 has a first surface 1a and a second surface 2a opposite to the first surface 1a, and the first porous sheet P1 and the second porous sheet 1a. It has a structure in which the quality sheet P2 is bonded. The first porous sheet P1 and the second porous sheet P2 are joined with the surfaces that are in contact with the main surface of the base sheet facing each other. Therefore, in the vicinity 3 (specifically, the central portion in the thickness direction of the nanofiber sheet 1) 3 near the joint surface 3a, the fibers are in a state of being slightly crushed.

  On the other hand, the first surface 1a and the second surface 2a of the nanofiber sheet 1 correspond to the respective surfaces of the porous sheets P1 and P2 on the side not in contact with the base sheet. Therefore, the fibers are not crushed in the first surface vicinity 1b and the second surface vicinity 2b. Therefore, when the average of the maximum fiber diameter in the surface direction of the nanofiber sheet of the nanofiber is compared between the vicinity of the first surface and the vicinity of the second surface, and the central portion in the thickness direction of the nanofiber sheet, the vicinity of the first surface The average Ds1 of the maximum fiber diameters of the nanofibers in 1a and the average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are in the vicinity of the joint surface 3a of the nanofiber sheet 1 (specifically, the central part in the thickness direction). ) 3 is smaller than the average Dc of the maximum fiber diameters of the nanofibers.

  Thus, since the average of the maximum fiber diameter of the nanofiber in the surface direction of the nanofiber sheet is small on the surface of the nanofiber sheet, when the nanofiber sheet is used as a separator and brought into contact with the electrode, the contact area Can be suppressed. Thereby, since the increase in contact resistance is suppressed, the deterioration of capacitor characteristics can be suppressed.

  In addition, since the fibers near both surfaces of the nanofiber sheet are not crushed, in addition to the fact that many gaps are maintained between the fibers, the nanofiber sheet generally has a high porosity, so When used, the electrolyte can be absorbed quickly and a large amount of electrolyte can be retained in the voids.

  Furthermore, since the nonwoven fabric has a high porosity, pinholes are likely to occur. However, the present invention can effectively prevent the generation of pinholes due to the nanofiber matrix structure.

“Nanofiber” refers to a filamentous material having a fiber diameter of 50 to 800 nm made of a polymer material such as a polymer.
The maximum fiber diameter in the surface direction of the nanofiber sheet is the largest fiber width in the surface direction of the nanofiber sheet when the fiber cross section (cross section in the fiber width direction) of one nanofiber is viewed. Means. The average of the maximum fiber diameter means the average value of the maximum fiber diameters of a plurality of arbitrarily selected (for example, 10) nanofibers in the cross section in the thickness direction of the nanofiber sheet. Note that the maximum fiber diameter in the surface direction of the nanofiber sheet may be simply referred to as the maximum fiber diameter.

  The average maximum fiber diameter Dc is the average of the maximum fiber diameters of nanofibers in the vicinity of a plane parallel to the surface of the nanofiber sheet (or the bonding surface of the porous sheet) that passes through the center of the nanofiber sheet in the thickness direction. Mean value.

  The central portion of the nanofiber sheet in the thickness direction is preferably located at the center or near the center in the thickness direction, but is not necessarily located at the center or near the center. The nanofiber sheet of the present invention only needs to have a region where the average of the maximum fiber diameters of the nanofibers is larger inside the nanofiber sheet. For example, in a region having a thickness of 10 to 40% of the thickness of the entire sheet centering on a plane parallel to the surface of the nanofiber sheet (or a bonding surface of the porous sheet), the average of the maximum fiber diameters of the nanofibers May include larger regions.

Note that the vicinity of a plane parallel to the surface of the nanofiber sheet passing through the center in the thickness direction of the nanofiber sheet as indicated by reference numeral 3 in FIG. 1 is, for example, the entire sheet centered on this plane. It means a region having a thickness of 10 to 30% of the thickness.
The average fiber diameter Dc is, for example, 60 nm to 2 μm, preferably 100 nm to 1.2 μm, and more preferably 200 to 1000 nm.

  In the nanofiber sheet, the average Ds1 and Ds2 of the maximum fiber diameter of the nanofiber are relatively small in the vicinity of both surfaces. Therefore, very fine pores are uniformly formed. When the separator is interposed between the pair of electrodes of the capacitor, the electrolyte distribution at the interface becomes extremely uniform. Therefore, contact resistance can be reduced for both electrodes. In other words, since a relatively constant property is easily obtained on both surfaces of the sheet, the capacitor characteristics are stabilized.

  The average maximum fiber diameter Ds1 of the nanofibers in the vicinity of the first surface means an average value of the maximum fiber diameters of the nanofibers in the vicinity of the first surface. Similarly, the average maximum fiber diameter Ds2 of the nanofibers in the vicinity of the second surface means an average value of the maximum fiber diameters of the nanofibers in the vicinity of the second surface.

  Note that the vicinity of the first surface means, for example, a region having a thickness of 10% of the thickness of the entire sheet from the first surface of the nanofiber sheet. Similarly, the vicinity of the second surface means, for example, a region having a thickness of 10% of the thickness of the entire sheet from the second surface of the nanofiber sheet.

  In the nanofiber sheet, the average Ds1 of the maximum fiber diameter and the average Ds2 of the maximum fiber diameter preferably satisfy 0.9 ≦ Ds1 / Ds2 ≦ 1.1, and 0.95 ≦ Ds1 / Ds2 ≦ 1.05. It is more preferable to satisfy When Ds1 and Ds2 satisfy such a relationship, it is advantageous because the physical properties of both surfaces of the nanofiber sheet can be made more uniform.

  The average Ds1 and Ds2 of the maximum fiber diameter are, for example, 50 to 800 nm, preferably 60 to 500 nm, and more preferably 70 to 200 nm, respectively. When the average of the maximum fiber diameters on both surfaces of the nanofiber sheet is in such a range, the contact resistance with the electrode can be more effectively reduced when used as a capacitor separator.

  For example, Ds1 and Dc satisfy the relationship of 1.1 ≦ Dc / Ds1 ≦ 2.5, preferably 1.2 ≦ Dc / Ds1 ≦ 2.2, and more preferably 1.3 ≦ Dc / Ds1 ≦ 2. . Ds2 and Dc have a relationship of, for example, 1.1 ≦ Dc / Ds2 ≦ 2.5, preferably 1.2 ≦ Dc / Ds1 ≦ 2.2, more preferably 1.3 ≦ Dc / Ds1 ≦ 2. Satisfy. When the nanofiber sheet satisfies such a maximum fiber diameter relationship, the contact resistance with the electrode can be more effectively reduced when used as a capacitor separator.

The average porosity P of the nanofiber sheet is, for example, 50 to 95%, preferably 60 to 92%, and more preferably 70 to 90%.
In the nanofiber sheet, the porosity Ps1 in the vicinity of the first surface and the porosity Ps2 in the vicinity of the second surface preferably satisfy 0.9 ≦ Ps1 / Ps2 ≦ 1.1, and 0.95 ≦ Ps1 / Ps2 More preferably, ≦ 1.05 is satisfied. When Ps1 and Ps2 satisfy such a relationship, it is advantageous because the physical properties of both surfaces of the nanofiber sheet can be made more uniform.

  When the thicknesses of the first and second porous sheets are substantially the same, the bonding surface is located at the center in the thickness direction of the nanofiber sheet. The bonding surface is not necessarily located at the center in the thickness direction of the nanofiber sheet, but is preferably located at or near the center.

  The nanofiber sheet does not need to have a symmetric structure with the joint surface of the porous sheet or the central portion in the thickness direction of the nanofiber sheet as a boundary, but preferably has a symmetric structure. Specifically, the nanofiber sheet is placed on the first surface side with the center in the thickness direction of the nanofiber sheet (specifically, a plane passing through the center and parallel to the surface of the nanofiber sheet) as a boundary. When the first region and the second region on the second surface side are divided, it is preferable that the first region and the second region have a symmetric structure with respect to the boundary. In the nanofiber sheet having such a structure, physical properties can be made more uniform on the first surface side and the second surface side.

The nanofiber sheet has a nanofiber matrix structure and is usually in the form of a nonwoven fabric.
In the matrix structure of the nanofiber sheet, the nanofibers may be bonded to each other at the contact points, or may be separated without bonding. The nanofibers may be bonded at random in the matrix structure.

In addition, if necessary, a solution containing a binder such as a polymer is applied to the nanofiber matrix structure by impregnation or coating, or the nanofiber raw material is bonded to the nanofibers with a binder. May be.
In the nanofiber sheet, the adhesion between the nanofibers may be greater in the vicinity of the central portion in the thickness direction than in the vicinity of both surfaces.

  In the electrospinning method, the nanofiber is formed by spinning a polymer solution or a molten polymer. Therefore, the adhesion between the nanofibers may be welding or fusion between the nanofibers.

In electrospinning using a polymer solution, when the nanofibers in a swollen state are deposited in the solvent without the solvent completely evaporating, the nanofibers are compatible with each other by the action of the solvent at the contact point, and the solvent is volatilized. Is a state in which the nanofibers are welded to each other.
In electrospinning using a molten polymer, when nanofibers are deposited, if nanofibers that are not completely solidified are solidified in contact with each other, the nanofibers are fused at the contact points.

  The type of polymer material such as polymer (or resin raw material) constituting the nanofiber is not particularly limited as long as it can be electrospun, and examples include various thermoplastic polymers that can be melted and polymers that can be dissolved in a solvent. it can.

  Examples of such polymers include olefin resins (for example, homopolymers or copolymers containing ethylene and / or propylene as monomer units); vinyl resins (polyvinyl acetate, ethylene-vinyl acetate copolymers, etc.) Vinyl acetate resin or a saponified product thereof (polyvinyl alcohol or a modified product thereof); Aromatic vinyl resin such as a copolymer containing polystyrene or styrene as a monomer unit; Vinyl cyanide resin such as polyacrylonitrile; Homopolymer or copolymer containing acrylic acid ester or methacrylic acid ester as a monomer unit such as methyl methacrylate); Fluororesin; Polyester resin (aliphatic polyester such as polylactic acid or polycaprolactone, aromatic polyester, etc.) Polyamide resins; polyimide resins; cellulose derivatives (cellulose esters, cellulose ethers); and biopolymers such biodegradable polymers. These polymers can be used individually by 1 type or in combination of 2 or more types.

  Of the above polymers, olefin resins, fluororesins, polyamide resins, and polyimide resins are particularly preferable. Such a polymer is advantageous in that the permeability of the electrolyte can be improved when the nanofiber sheet is used as a capacitor separator. Moreover, since polyamide resin, polyimide resin, etc. have high heat resistance, when they are used as capacitor separators, they can more effectively suppress internal short circuit due to low heat shrinkage.

  Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-ethylene copolymer. Examples thereof include homopolymers and copolymers having fluorine-containing monomer units such as polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF).

  Examples of the polyamide resin include aliphatic polyamides such as polyamide 6 and polyamide 6-12; alicyclic polyamides; aromatic polyamides such as polyamide MDX-6 and aramid. From the viewpoint of heat resistance, aromatic polyamides, particularly wholly aromatic polyamides such as aramid are preferred.

Examples of the polyimide resin include thermosetting polyimides such as condensation type polyimides and bismaleimide resins obtained from polyamic acid; and thermoplastic polyimides. Examples of the thermoplastic polyimide include polyimide, polyether imide, polyamide imide, and polyester imide that include benzophenone tetracarboxylic acid and diaminodiphenylmethane as monomer units.
A nanofiber may contain a well-known additive other than a polymer as needed. The content of the additive is, for example, 5% by mass or less of the nanofiber sheet.

  The thickness of the nanofiber sheet can be selected from the range of about 1 to 1000 μm depending on the application, and is, for example, 5 to 200 μm, preferably 10 to 100 μm or 15 to 70 μm.

In the capacitor of the present invention, the nanofiber sheet is interposed between a pair of electrodes as a capacitor separator.
Examples of the capacitor include those using an electrolyte, such as an electrolytic capacitor such as an aluminum electrolytic capacitor, an electric double layer capacitor, a pseudo capacitor, and a lithium ion capacitor. Among these, an electric double layer capacitor and a lithium ion capacitor are particularly preferable. The electrolyte includes a cation, an anion, a non-aqueous solvent that dissolves them, and the like.

The shape of the capacitor is not particularly limited, and may be either a cylindrical shape or a box shape depending on the type of the capacitor.
The electrode of the capacitor, the electrode active material, the electrolyte, and the like can be appropriately selected according to the type of capacitor.

  The electrode usually includes a current collector and a mixture layer attached to the surface of the current collector. As the current collector, a conventional non-porous or porous conductive substrate can be used. Examples of the metal material forming the current collector for the anode include materials known for use in capacitor current collectors, such as aluminum, aluminum alloys, stainless steel, and titanium. Examples of the metal material forming the current collector for the cathode include known materials such as stainless steel, nickel, copper, and copper alloys in the application of the current collector for capacitors. The thickness of the current collector can be selected from a range of 3 to 50 μm, for example.

The mixture layer can be formed by applying an electrode slurry containing an active material, a binder, and a dispersion medium to one or both sides of a current collector and drying. After drying, rolling treatment may be performed as necessary. The mixture layer may further contain a thickener, a conductive material, and the like as necessary. The electrode slurry can be prepared by a method using a conventional mixer or kneader, and can be applied to the surface of the current collector by a conventional coating method using various coaters.
The thickness of the mixture layer is, for example, 50 to 300 μm, more preferably 100 to 200 μm.

The components of the capacitor will be described below by taking an electric double layer capacitor and a lithium ion capacitor as examples.
(Electrode active material)
In the capacitor, it is preferable that at least one of the pair of electrodes includes a carbonaceous material as a polarizable material forming the electric double layer.
In the electric double layer capacitor, activated carbon is used as an active material for both electrodes.
Lithium ion capacitors use materials known for lithium ion capacitor applications such as activated carbon, carbon black, graphite, carbon nanotubes, fullerenes, and polyacene semiconductors (PAS) as active materials for anodes. May be. These can be used individually by 1 type or in combination of 2 or more types. Of these active materials, activated carbon is preferred.

  In a lithium ion capacitor, as an active material of the cathode, for example, a carbonaceous material such as a material having a graphite-type crystal structure, graphitizable carbon, non-graphitizable carbon, pyrolytic carbon, cokes, carbon black, carbon nanotube, fullerene, etc. Material can be used. Examples of the material having a graphite type crystal structure include natural graphite and spherical or fibrous artificial graphite. The cathode active material can be used singly or in combination of two or more. In the lithium ion capacitor, the anode active material and the cathode active material may be different or the same.

  In the lithium ion capacitor, the active material of the cathode may be coated with a water-soluble polymer such as cellulose derivative, polyacrylic acid, or polyvinyl alcohol, if necessary. Further, the mixture layer may be doped with lithium.

As binder, fluororesin such as polyvinylidene fluoride (PVDF); acrylic resin such as polymethyl acrylate and ethylene-methyl methacrylate copolymer; rubber such as styrene-butadiene rubber, acrylic rubber or modified products thereof The material can be exemplified.
The ratio of a binder is 0.1-10 mass parts per 100 mass parts of active materials, Preferably it is 1-5 mass parts.

  Examples of the dispersion medium include water, alcohols such as ethanol, ethers such as tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.

  Examples of the conductive agent include carbon black; conductive fibers such as carbon fibers; and carbon fluoride. The ratio of the conductive agent is, for example, 0.1 to 7 parts by mass per 100 parts by mass of the active material.

Examples of the thickener include cellulose derivatives such as carboxymethyl cellulose (CMC); poly C _2-4 alkylene glycol such as polyethylene glycol. The ratio of the thickener is, for example, 0.1 to 10 parts by mass per 100 parts by mass of the active material.

(Electrolytes)
As an electrolyte used in the electric double layer capacitor, in addition to an aqueous electrolyte containing an acid such as sulfuric acid, a quaternary ammonium borofluoride salt (for example, tetraethylammonium borofluoride, triethylmethylammonium borofluoride) or the like is dissolved in a non-aqueous solvent. Non-aqueous electrolyte can be used.

Non-aqueous solvents include propylene carbonate (PC), cyclic carbonates such as ethylene carbonate (EC); chain carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate, and dimethyl carbonate; γ-butyrolactone, γ-valerolactone Cyclic carboxylic acid esters such as: chain ethers such as diethyl ether and ethyl propyl ether; cyclic ethers such as ethylene oxide and propylene oxide; sulfoxides such as dimethyl sulfoxide; fluorine atom substitution products thereof (containing fluorine atoms such as fluoroethylene carbonate) Cyclic carbonates: fluorine atom-containing chain ethers such as HCF ₂ CH ₂ —O—CF ₂ CF ₂ H and CF ₃ CF ₂ CH ₂ —O—CF ₂ CF ₂ H). These non-aqueous solvents can be used alone or in combination of two or more.

  In the lithium ion capacitor, the electrolyte is a non-aqueous electrolyte having lithium ion conductivity. The non-aqueous electrolyte includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, a non-aqueous solvent similar to the electrolyte of the electric double layer capacitor can be used.

Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF _{3 3} ). A lithium salt can be used individually by 1 type or in combination of 2 or more types.

  The concentration of the solute (the quaternary ammonium borofluoride or lithium salt) in the electrolyte is, for example, 1 to 3 mol / L, preferably 1.2 to 2.5 mol / L.

  A known additive, for example, a vinylene carbonate compound such as vinylene carbonate (VC); a sultone compound such as 1,3-propane sultone (PS) or the like may be added to the electrolyte.

(Other)
The capacitor can be manufactured by a known method according to the type and shape of the capacitor. For example, a capacitor may be manufactured by winding an electrode group by winding a pair of electrodes and a capacitor separator separating them, and housing the electrode group and the electrolyte in a case. The electrode group is not limited to a wound one, but may be a laminated one or a zigzag folded one. The shape of the electrode group may be a cylindrical shape or a flat shape having an oval end surface perpendicular to the winding axis depending on the shape of the capacitor.

  As the case material, aluminum, an aluminum alloy (such as an alloy containing a minute amount of a metal such as manganese or copper), a steel plate, or the like can be used.

  FIG. 2 is a perspective view showing an electrode group of a capacitor according to an embodiment of the present invention. The electrode group 4 is wound with separators 6a and 6b interposed between a pair of electrodes 5a and 5b formed of metal foil. Lead leads 7a and 7b are connected to the electrodes 5a and 5b, respectively. The capacitor can be manufactured, for example, by housing the electrode group 4 and an electrolyte (not shown) in a case (not shown) and sealing the case with a sealing material such as rubber or phenol resin.

(Manufacturing method of nanofiber sheet)
The nanofiber sheet is in contact with the main surface of the base sheet of the pair of porous sheets by the step (A) of forming a porous sheet by depositing nanofibers on the main surface of the base sheet by an electrospinning method. It can manufacture by passing through the process (B) which makes the surfaces which faced face each other and join.
In addition to the step (A), the method for producing a nanofiber sheet further includes the step (a) of arranging or supplying the base sheet in a space (nanofiber formation space) in which nanofibers are formed and / or the step ( You may have the process (C) which collects the completed sheet | seat after B).

  In the step (a), a long base sheet may be conveyed from the upstream side of the line to the nanofiber formation space. In order to form a pair of porous sheets composed of the first and second porous sheets in the step (A), in the step (a), for example, the long first from the upstream to the downstream of the first and second lines, respectively. You may convey the 1st and 2nd base material sheet. In the step (A), the first and second porous sheets are respectively formed on the main surfaces of the first and second base sheets on the upstream side of the line. In the step (B), on the downstream side of the line The first and second porous sheets may be joined to face each other.

  The surface of the porous sheet that has been in contact with the main surface of the base sheet is crushed a little by transferring the shape of the main surface of the base sheet, and the fibers are flat. Moreover, the average Dc of the maximum fiber diameter of the nanofiber in the center part of the thickness direction of the nanofiber sheet obtained by joining a pair of porous sheets so that the surfaces in such a state are opposed to each other. And it can be larger than the average Ds1 and Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface.

  Further, the nanofiber is not crushed on the surface of the porous sheet that is not in contact with the main surface of the base sheet, and the maximum fiber diameter in the surface direction of the porous sheet can be kept small. By joining the surfaces of the porous sheet that have been in contact with the main surface of the base sheet, the surface in a state where the small maximum fiber diameter in the surface direction of the opposite porous sheet is maintained is the nanofiber sheet. It becomes the first and second surfaces. Therefore, when used as a capacitor separator, the contact area with the electrode can be reduced, and the contact resistance can be reduced.

(A) Porous sheet forming step The porous sheet can be formed by an electrospinning method. Specifically, in the step (A) of forming the porous sheet, nanofibers are generated by electrostatic force from a raw material liquid containing a polymer material such as a resin raw material (the exemplified polymer) in a nanofiber formation space. At the same time, it may be a step of depositing the produced nanofibers on the main surface of the base sheet to form a porous sheet having a nanofiber matrix structure.

The raw material liquid may be a melt of a resin raw material or a solution containing a solvent and a resin raw material dissolved in the solvent. You may add a well-known additive to a raw material liquid as needed.
The solvent is not particularly limited as long as it can dissolve the resin raw material and can be removed by volatilization or the like, and can be appropriately selected according to the type of the resin raw material. Examples of the solvent include various organic solvents such as ketones such as acetone, nitriles such as acetonitrile, amides such as N, N-dimethylformamide, ethers such as tetrahydrofuran, sulfoxides such as dimethyl sulfoxide, and N-methyl-2-pyrrolidone. It can be illustrated. Aprotic polar solvents are preferred.

  In the electrospinning method, nanofibers are generated by an electrostatic stretching phenomenon. For example, when a solution containing a resin raw material is used as the raw material liquid, the solvent gradually evaporates from the raw material liquid that has flowed into the charged space while flying through the space. As a result, the volume of the raw material liquid in flight gradually decreases, but the charge imparted to the raw material liquid remains in the raw material liquid. As a result, the charge density of the raw material liquid in flight through the space gradually increases. Then, when the charge density of the raw material liquid increases and the repulsive Coulomb force generated in the raw material liquid exceeds the surface tension of the raw material liquid, a phenomenon occurs in which the raw material liquid is explosively stretched linearly. . This phenomenon is an electrostatic stretching phenomenon. According to the electrostatic stretching phenomenon, nanofibers having a fiber diameter of sub-micron to nano order can be efficiently manufactured.

  In addition, when using the melt of a resin raw material as a raw material liquid, the charge density of a raw material liquid can be raised by applying a high voltage to the raw material liquid which flowed out into nanofiber formation space. The principle of subsequent nanofiber formation is almost the same as described above.

  The fiber diameter of the produced nanofibers changes depending on the state of the raw material liquid, the configuration of the emitter, the magnitude of the electric field formed by the charging means, and the like. Therefore, in the step of forming the porous sheet, a plurality of electrospinning units can be used to generate different nanofibers in each unit. For example, a plurality of types of nanofibers having different fiber diameters may be sequentially deposited on the main surface of the base sheet. Further, the fiber diameters of the nanofibers deposited on the main surface may be sequentially reduced from the base sheet side. Examples of a method for providing such gradation include a method using a plurality of electrospinning units that generate nanofibers having different fiber diameters.

  For example, in the step (A), a nanofiber may be formed using a first electrospinning unit disposed on the upstream side of the line and a second electrospinning unit disposed on the downstream side of the line. In this case, it is possible to form a porous sheet whose fiber diameter changes in the thickness direction.

  Specifically, the fiber diameter of the nanofiber generated by the first electrospinning unit arranged on the upstream side may be intentionally larger than the fiber diameter of the nanofiber generated by the second electrospinning unit. it can. Conversely, the fiber diameter of the nanofiber generated by the first electrospinning unit arranged on the upstream side can be intentionally made smaller than the fiber diameter of the nanofiber generated by the second electrospinning unit. However, the fiber diameter tends to increase in the vicinity of the boundary between the base sheet and the porous layer formed of nanofibers. Therefore, when changing the fiber diameter of the porous layer, it is easier to achieve the intended structure by generating nanofibers having a larger fiber diameter on the upstream side.

After forming the porous sheet, the substrate sheet is removed from the porous sheet. Therefore, the method for producing a nanofiber sheet may include a step (a2) of removing the base sheet in the step (A) or after the step (A).
The kind of base sheet is not limited. The main surface of the base material sheet may be subjected to a known release treatment such as coating with a release agent or roughening so that the porous sheet is easily peeled off.

(B) Porous sheet joining step The formed porous sheet is subjected to a joining step (B). In the bonding step (B), the pair of porous sheets are bonded in a state where the surfaces that have been in contact with the main surface of the base sheet are opposed to each other, thereby forming a nanofiber sheet.

  In the step (B), instead of using a pair of porous sheets, one porous sheet may be folded and bonded so that the surfaces that have been in contact with the main surface of the base sheet face each other. . The end on the bent side may be cut as necessary.

  In the step (B), the first porous sheet and the separately formed second porous sheet may be joined with the surfaces in contact with the main surfaces of the respective base material sheets facing each other.

  Alternatively, the first and second porous sheets may be formed in parallel, and the surfaces that have been in contact with the main surfaces of the respective base material sheets may be opposed to be joined continuously. Specifically, the first and second porous sheets are conveyed from the upstream side in the first and second lines, respectively, and the main surface of the substrate sheet of the first and second porous sheets conveyed The contacting surfaces may be joined to face each other on the downstream side of the line.

  When using a melt of a resin raw material in the step (A), the bonding is performed before the nanofibers are completely solidified in the vicinity of the surface of at least the main surface of the base sheet of the pair of porous sheets. Thus, the nanofibers of one porous sheet and the nanofibers of the other porous sheet may be fused.

When a resin raw material solution is used, bonding is performed in a state where the nanofiber contains a solvent in the vicinity of the surface of at least the main surface of the base sheet of the pair of porous sheets, so that one porous The nanofiber of the sheet and the nanofiber of the other porous sheet may be welded.
Further, the pair of porous sheets may be joined by a known joining method using thermocompression bonding or an adhesive.

Below, the manufacturing method of a nanofiber sheet is demonstrated more concretely, referring drawings.
The manufacturing method of the nanofiber sheet is, for example,
(I) supplying a base sheet to the nanofiber formation space;
(Ii) In the nanofiber formation space, nanofibers are generated by electrostatic force from a raw material solution containing a solvent and a resin raw material dissolved in the solvent, and the generated nanofibers are deposited on the main surface of the base sheet, Forming a porous sheet having a matrix structure of:
(Iii) A pair of porous sheets joined together with the surfaces that were in contact with the main surface of the base sheet facing each other, and the surfaces that were not in contact with the main surface of the base sheet of the pair of porous sheets Forming a nanofiber sheet as a first surface and a second surface opposite to the first surface, respectively.

  In the step (iii), the pair of porous sheets are joined in a state where at least the surface of the pair of porous sheets in contact with the main surface of the base sheet contains a solvent, You may weld a fiber and the nanofiber of the other porous sheet.

FIG. 3 is a diagram schematically showing a configuration of a manufacturing system for carrying out a method for manufacturing a capacitor separator (or nanofiber sheet) according to an embodiment of the present invention.
The manufacturing system 100 in FIG. 3 constitutes a manufacturing line for manufacturing a nanofiber sheet. In the manufacturing system 100, the base sheet S is conveyed from upstream to downstream of the manufacturing line. Formation of the porous sheet P1 is performed on the base sheet S in the middle of conveyance as needed.

  The uppermost stream of the manufacturing system 100 is provided with a base material sheet supply device 20 that accommodates the base material sheet S wound in a roll shape. The base sheet supply apparatus 20 rolls out the roll-shaped base sheet S and supplies the base sheet S to another apparatus adjacent to the downstream side of the base sheet supply apparatus 20. Specifically, the base sheet supply device 20 rotates the supply reel 22 by the motor 24 and supplies the base sheet S wound around the supply reel 22 to the first conveyor 21.

  The rolled-out base sheet S is transferred to the porous sheet forming apparatus 40 by the first transport conveyor 21. The porous sheet forming apparatus 40 includes an electrospinning mechanism. More specifically, the electrospinning mechanism opposes the emitter 42 for discharging the raw material liquid installed above the apparatus, charging means for charging the discharged raw material liquid, and the emitter 42. And a third transport conveyor 41 for transporting the base sheet S from the upstream side to the downstream side. The 2nd conveyance conveyor 41 functions as a collector part which collects nanofiber with the base material sheet S. FIG.

  The charging means includes a voltage applying device 43 that applies a voltage to the emitter 42 and a counter electrode 44 that is installed in parallel with the second transport conveyor 41. The counter electrode 44 is grounded. Thereby, a potential difference (for example, 20 to 200 kV) according to the voltage applied by the voltage application device 43 can be provided between the emitter 42 and the counter electrode 44. The configuration of the charging unit is not particularly limited. For example, the counter electrode 44 may not necessarily be grounded. Moreover, you may comprise the belt part of the 2nd conveyance conveyor 41 from a conductor instead of providing the counter electrode 44. FIG.

  The emitter 42 is made of a conductor, has a long shape, and its inside is hollow. The hollow portion serves as a storage portion that stores the raw material liquid 45. On the side of the emitter 42 facing the base sheet S, a plurality of outlets are provided in a regular array at regular intervals. The raw material liquid 45 is supplied from the raw material liquid tank 45 a to the hollow of the emitter 42 by the pressure of the pump 46 communicating with the hollow portion of the emitter 42. And the raw material liquid 45 is discharge | released toward the main surface Sa of the base material sheet S from a some discharge port with the pressure of the pump 46. FIG. The discharged raw material liquid undergoes electrostatic explosion while moving in the space between the emitter 42 and the third transport conveyor 41 in a charged state, and generates nanofibers. The produced nanofibers are attracted to the main surface Sa of the base sheet S by electrostatic attraction, and are deposited there. Thereby, a porous layer (nonwoven fabric) made of nanofibers is formed.

  A squeegee 47 that contacts the main surface Sa of the base sheet S may be provided on the most upstream side of the second transport conveyor 41. The squeegee 47 can remove irregularities and wrinkles on the main surface Sa of the base sheet S before the nanofibers are deposited. Thereby, the base material sheet S adheres to the surface of the belt portion of the second transport conveyor 41. Therefore, the nanofibers are uniformly deposited on the main surface Sa of the base sheet S without being partially concentrated. Therefore, the surface of the formed porous layer becomes flat and the thickness of the porous layer tends to be uniform.

  The belt portion of the second conveyor 41 may be a dielectric. As described above, when the belt portion is made of a conductor, the nanofibers tend to be concentrated slightly on the collector portion near the discharge port of the emitter 42. From the viewpoint of more uniformly dispersing the nanofibers in the collector portion, it is more desirable to form the belt portion of the second conveyor 41 with a dielectric. When the belt portion is formed of a dielectric, the counter electrode 44 may be brought into contact with the inner peripheral surface of the belt portion (the surface opposite to the surface in contact with the base sheet S). Due to such contact, dielectric polarization occurs inside the belt portion, and a uniform charge is generated on the contact surface with the base sheet S. Thereby, the possibility that nanofibers concentrate and deposit on a part of the main surface Sa of the base sheet S is further reduced.

FIG. 4 is a top view schematically showing the configuration of the porous sheet forming apparatus 40.
In the porous sheet forming apparatus 40, the emitter 42 is installed so as to cross obliquely with respect to the moving direction of the base sheet S (the direction of the white arrow in FIG. 4). Since the emitter 42 is installed obliquely in this manner, the facing area between the second transport conveyor 41 and the emitter 42 is increased, so that the productivity of the porous layer can be increased. The acute angle θ formed by the emitter 42 and the arrow is not particularly limited, but is preferably about 30 to 60 ° in order to sufficiently improve productivity. The emitting body 42 has a longitudinal direction of the base material due to the second support body 49 extending downward from the first support body 48 parallel to the moving direction of the base material sheet S installed above the porous sheet forming apparatus 40. The sheet S is supported so as to be parallel to the main surface Sa.

  On the side of the emitter 42 facing the main surface Sa of the base sheet S, a plurality of raw material liquid outlets 42a are provided. By arranging the emission ports 42a in the emission bodies 42 in a regular pattern, the amount of nanofibers deposited on the main surface Sa of the base sheet S can be made uniform over a wide area of the main surface Sa. . The distance between the discharge port 42a of the emitter 42 and the base sheet S depends on the scale of the nanofiber sheet manufacturing system, but may be, for example, 100 to 600 mm.

  In FIG. 3, only one porous sheet forming apparatus 40 is provided and the number of the emitters 42 included in one porous sheet forming apparatus 40 is two. The number and the number of emitters 42 included in one porous sheet forming apparatus 40 are not particularly limited. For example, as shown in FIG. 5, a manufacturing system 200 in which two porous sheet forming apparatuses 40 are continuously provided may be configured. That is, a set of two porous sheet forming apparatuses 40 may function as one electrospinning mechanism. In this case, the electrospinning mechanism can be considered to have a first electrospinning unit 40A disposed on the upstream side of the line and a second electrospinning unit 40B disposed on the downstream side of the line.

  In addition, the said manufacturing system is comprised so that each apparatus can be isolate | separated. Therefore, it is easy to change the number of devices. Similarly, a device (not shown) having an additional function may be arranged so as to be interposed between any adjacent devices.

  When the electrospinning mechanism has a first electrospinning unit disposed on the upstream side of the line and a second electrospinning unit disposed on the downstream side of the line, each electrospinning unit generates the same nanofiber. Different nanofibers may be generated. When producing the same nanofiber, for example, the thickness of the porous sheet can be increased, or the speed of the base sheet S moving on the production line can be increased to improve the production tact. Moreover, when producing | generating different nanofibers, the porous sheet which consists of a several different fiber layer can be formed by producing | generating nanofibers from which a fiber diameter differs, for example.

  Here, if the fiber diameter of the nanofiber generated by the first electrospinning unit disposed on the upstream side is intentionally larger than the fiber diameter of the nanofiber generated by the second electrospinning unit, the porous structure The base material sheet S side of the sheet can be composed of nanofibers having a large fiber diameter, and the side opposite to the base material sheet S can be composed of nanofibers having a small fiber diameter.

  When the nanofiber sheet is formed by joining the base sheet S side surfaces of the porous sheet having such a structure, the average Dc of the maximum fiber diameters of the nanofibers at the center portion in the thickness direction of the nanofiber sheet is further increased. The average Ds1 and Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the first and second surfaces can be further reduced.

  In addition, when forming the porous sheet which consists of a multiple layer different fiber layer, the number of different fiber layers is although it does not specifically limit, 2-5 layers are preferable and 2-3 layers are more common.

  When the porous sheet P1 is formed on the surface of the base sheet S in the porous sheet forming apparatus 40, the porous sheet P1 is transported to the next step in the direction of the arrow in the figure, and the base sheet S Is peeled from the porous sheet P1 and collected on the supply reel 22 of the base sheet S.

  In FIG. 3, the occurrence of a spark that may occur when the base sheet S and the roll of the second transport conveyor 41 are peeled is suppressed at a position where the base sheet S and the second transport conveyor 41 are separated (peeled). In order to do so, a static eliminator that neutralizes the base sheet S may be provided. In addition, a suction duct that sucks nanofibers in the vicinity of the window between the porous sheet forming device 40 and each device adjacent thereto so that the nanofibers generated in the nanofiber forming space are not released to the outside. May be provided.

  The porous sheet (first porous sheet) P1 carried out from the porous sheet forming apparatus 40 is transferred to the porous sheet joining apparatus 50 disposed on the further downstream side. At this time, the porous sheet P1 is transferred such that the surface on the side not in contact with the base sheet S1 is in contact with the peripheral surface of the pressure roller 51a among the pair of pressure rollers 51a and 51b. At the same time, the porous sheet bonding apparatus 50 moves the second porous sheet P2 in the direction of the arrow in the figure so as to cover the surface of the conveyed porous sheet P1. Supply in between. At this time, the 1st porous sheet P1 and the 2nd porous sheet P2 are supplied so that it may be in the state where the surfaces which were contacting each base material sheet were made to oppose. The first porous sheet P1 is preferably in a state where the surface is dry and the base sheet S side is slightly moistened.

  The porous sheet joining apparatus 50 accommodates the second porous sheet P2 wound in a roll shape on the supply reel 52a with the surface that has been in contact with the base material sheet facing outside. The second porous sheet P2 is rolled out by a conveying roller 52b having a rotation axis that intersects perpendicularly with the moving direction of the first porous sheet P1 and having a peripheral surface parallel to the first porous sheet P1. The rolled-out second porous sheet P2 is supplied so as to be laminated with the first porous sheet P1 between the pair of joining rollers 51a and 51b. And the 1st porous sheet P1 and the 2nd porous sheet P2 pass through the gap between a pair of joining rollers 51a and 51b in the state where it laminated, and the 1st porous sheet P1 and the 2nd porous sheet P2 is pressed and integrated to complete the nanofiber sheet.

  When the porous sheets P1 and P2 are pressure-bonded, when the vicinity of the surface of the first porous sheet P1 contains a solvent, the fibers on the surface of the first porous sheet P1 Two fibers on the surface of the porous sheet P2 are welded. The vicinity of the surface of the second porous sheet P2 may also contain a solvent. The pressure bonding by the joining rollers 51a and 51b can be performed while heating.

  The completed nanofiber sheet F is collected by the collection device 70 via the conveyance roller 71. The collection device 70 has a built-in collection reel 72 that scrapes the conveyed nanofiber sheet F. The collection reel 72 is rotationally driven by a motor 74.

  In the manufacturing system as shown in FIG. 3, the motor 74 that rotates the base material sheet supply device 20 and the recovery device 70 that recovers the nanofiber sheet is used to transport the base material sheet S passing through the manufacturing line, and the porous material. The rotation speed is controlled so that the sheet conveyance speed is constant. Thereby, the base material sheet S and the porous sheet are conveyed while maintaining a predetermined tension. Such control is performed by a control device (not shown) provided in the manufacturing system 100. The control device is configured to control and manage each device constituting the manufacturing system 100 in an integrated manner.

  A preliminary collection unit may be disposed between the porous sheet bonding apparatus 50 and the nanofiber sheet collection apparatus 70. The preliminary collection unit is provided so that the completed nanofiber sheet F can be easily collected by the collection device 70. Specifically, in the preliminary collection unit, the completed nanofiber sheet F transferred from the porous sheet bonding apparatus 50 is collected in a slack state without being scraped by a certain length. Meanwhile, the recovery reel 72 of the recovery device 70 is stopped without rotating. Then, every time the length of the loose nanofiber sheet F collected by the preliminary collection unit becomes a certain length, the collection reel 72 of the collection device 70 is rotated for a predetermined time, and the collection reel 72 makes the nanofiber sheet F rotate. Scatter the fiber sheet F. By providing such a preliminary recovery unit, it is not necessary to control the rotational speeds of the motors 24 and 74 included in the base sheet supply device 20 and the nanofiber sheet recovery device 70 in strict association with each other. The control device can be simplified.

  The above-described nanofiber sheet manufacturing system is merely an example of a manufacturing system that can be used to carry out the method of manufacturing the nanofiber sheet (or capacitor separator) of the present invention. In the nanofiber sheet manufacturing method, a nanofiber is generated in a nanofiber formation space and deposited on a main surface of a base sheet to form a porous sheet having a nanofiber matrix structure; As long as it has the process of making the surface which contacted the base material sheet of the quality sheet face each other, joining, and forming a nanofiber sheet, it is not specifically limited.

  The step of supplying the base sheet to the nanofiber formation space is not limited to the step of rolling out the roll-shaped base sheet S by the base sheet supply device and supplying the base sheet S to the uppermost stream of the production line. For example, a production line integrated with an apparatus for producing the base sheet S can also be used. In that case, you may supply the base material sheet S immediately after manufacture to a porous sheet forming apparatus as it is.

  Also, the step of forming the porous sheet may be a step of generating nanofibers from the raw material liquid by electrostatic force in a predetermined nanofiber formation space and depositing the generated nanofibers on the main surface of the base sheet S. Any electrospinning mechanism may be used. For example, the shape of the emitter is not particularly limited. The shape of the cross section perpendicular to the longitudinal direction of the emitter may be a shape (V-type nozzle) that gradually decreases from the top to the bottom. Moreover, you may comprise a discharge body with a rotary body.

  Specifically, the emitter may be formed into a hollow annular body such as a tube of a bicycle tire, and the raw material liquid may be accommodated in the hollow. If a plurality of discharge ports are provided along the outer peripheral surface of the hollow annular body and the annular body is rotated around the center, the raw material liquid can be discharged from the discharge port by centrifugal force. In that case, if the moving direction of the raw material liquid in the space is controlled by air blowing or the like, nanofibers can be deposited on a predetermined collector portion.

Furthermore, the step of joining the first and second porous sheets may be performed by any method.
The method for producing a nanofiber sheet of the present invention is particularly suitable for producing a capacitor separator, but can also be used for producing a nanofiber sheet used for various other applications.

  Moreover, although the above-mentioned embodiment demonstrated the case where the base material sheet S was elongate, this invention is applicable also when, for example, the rectangular base material sheet S is used. In this case, the base material sheet supply apparatus may be an apparatus that sequentially places rectangular base material sheets on the first transport conveyor, for example. If such a base sheet supply apparatus is provided with a tray feeder that accommodates a plurality of rectangular base sheet S, the base sheet S can be supplied efficiently.

  Further, the nanofiber sheet, for example, conveys the long first and second substrate sheets from the upstream to the downstream of the first and second lines, respectively, and on the upstream side, the main fibers of the first and second substrate sheets It can also be manufactured by a manufacturing method in which the first and second porous sheets are formed on the surfaces and the first and second porous sheets are opposed to each other on the downstream side.

Such a manufacturing method is, for example,
(I) conveying the first and second substrate sheets to the nanofiber formation space upstream of the first and second lines;
(Ii) In the nanofiber formation space, nanofibers are generated by electrostatic force from a raw material solution containing a solvent and a resin raw material dissolved in the solvent, and the main of the first and second base sheet transported the generated nanofibers Forming first and second porous sheets having a matrix structure of nanofibers, each deposited on a surface;
(Iii) removing the first and second substrate sheets from the conveyed first and second porous sheets on the downstream side of the first and second lines;
(Iv) On the further downstream side of the first and second lines, the surfaces of the first and second porous sheets to be conveyed that are in contact with the main surfaces of the first and second substrate sheets are opposed to each other. And forming a nanofiber sheet.

  In the step (iv), the first and second porous sheets are in a state in which at least the surfaces of the first and second porous sheets in contact with the main surfaces of the first and second base sheets contain a solvent. The nanofibers of the first porous sheet and the nanofibers of the second porous sheet may be welded together.

FIG. 6 is a diagram schematically showing a configuration of a manufacturing system for carrying out a method for manufacturing a capacitor separator (or nanofiber sheet) according to an embodiment of the present invention.
In the manufacturing system 300 of FIG. 6, the base sheet supply device 20A is provided in the uppermost stream of the first line, and the base sheet supply device 20B is provided in the uppermost stream of the second line. The manufacturing system 300 does not supply the second porous sheet P2 from the supply reel 52a of the porous sheet joining apparatus 50 in the manufacturing system 100 of FIG. However, it is the same as that of the manufacturing system 100 of FIG. 3 except that it is continuously supplied between the pair of joining rollers 51a and 51b.

  However, in FIG. 6, for the sake of convenience, the reference numeral of the porous sheet joining apparatus is 50A, and the base sheet supply apparatus and its constituent elements are represented by the base sheet supply apparatus 20A, the supply reel 22a, and the first transport conveyor 21a, respectively. . The base sheet supply apparatus 20A rotates the supply reel 22a by the motor 24a, and supplies the first base sheet S1 wound around the supply reel 22a to the first transport conveyor 21a. The first base sheet S1 spun out is transferred to the porous sheet forming apparatus 40 by the first transport conveyor 21a so that the main surface S1a faces the discharge body 42 in the porous sheet forming apparatus 40, The porous sheet forming apparatus 40 forms the first porous sheet P1.

  The second porous sheet P2 is formed in the same manner as the first porous sheet P1. Specifically, it is formed as follows. First, the base sheet supply apparatus 20B supplies the second base sheet S2 wound around the supply reel 22b to the first transport conveyor 21b by the rotation of the supply reel 22b by the motor 24b. The first conveyor 21b transfers the second base sheet S2 that has been spun out to the porous sheet forming apparatus 80 located downstream of the base sheet supplying apparatus 20B in the second line, and the porous sheet forming apparatus In 80, a porous sheet (second porous sheet P2) is formed by the same mechanism as the porous sheet forming apparatus 40.

  In the porous sheet forming apparatuses 40 and 80 located on the downstream side of the first and second lines, respectively, the first and second porous sheets P1 and P2 are respectively formed by the conveyors 41 and 81, respectively. Supplied to the process. Then, the first and second base sheets S1 and S2 are removed from the porous sheets P1 and P2, respectively, and collected on the supply reels 22a and 22b.

  A porous sheet bonding apparatus 50A is disposed further downstream of the first and second lines. The first porous sheet P1 conveyed from the porous sheet forming apparatus 40 in the first line and the second porous sheet P2 conveyed from the porous sheet forming apparatus 80 in the second line are first and second. It is supplied between the pair of joining rollers 51a and 51b so that the surfaces that have been in contact with the main surfaces S1a and S2a of the base sheets S1 and S2 face each other.

  In the porous sheet bonding apparatus 50A, similarly to the bonding mechanism in the porous sheet bonding apparatus 50 in FIG. 3, the first and second porous sheets pass through the gap between the pair of bonding rollers 51a and 51b. P1 and P2 are pressed and integrated to complete a nanofiber sheet.

The completed nanofiber sheet F is recovered by the recovery device 70 in the same manner as in FIG.
Also in the manufacturing system as shown in FIG. 6, according to the case of FIG. 3, the conveying speed of the base sheets S1 and S2, the porous sheets P1 and P2, etc. may be controlled to be constant by a control device (not shown). In addition, a preliminary recovery unit may be disposed between the porous sheet bonding apparatus 50A and the nanofiber sheet recovery apparatus 70 in the same manner as described above.

  In the present invention, while having a nanofiber matrix structure (nanofiber nonwoven fabric structure) formed by electrospinning, the average of the maximum fiber diameters in the vicinity of both surfaces is the maximum fiber diameter at the center in the thickness direction. A nanofiber sheet (nonwoven fabric) smaller than the average is obtained. Such a nanofiber sheet is suitable for a capacitor separator because it has excellent surface properties and there is no significant difference between the properties of both surfaces. In addition to the separator for capacitors, the nanofiber sheet is useful in various fields such as medical materials, sensors, catalysts, and reinforcing materials in addition to filters and ion exchange membranes.

1: nanofiber sheet, 1a: first surface, 1b: near first surface, 2a: second surface, 2b: near second surface, P1: first porous sheet, P2: second porous sheet P2, 3a : Bonding surface, 3: Near central portion of nanofiber sheet in thickness direction 4: Electrode group, 5a, 5b: Electrode, 6a, 6b: Separator, 7a, 7b: Lead lead

100, 200, 300: Nanofiber sheet (capacitor separator) manufacturing system 20, 20A, 20B: base sheet supply device, 21, 21a, 21b: first conveyor, 22, 22a, 22b: supply reel,

  40, 80: porous sheet forming apparatus, 40A: first electrospinning unit, 40B: second electrospinning unit, 41, 81: second transport conveyor, 42, 82: discharge body, 42a: discharge port, 43, 83 : Voltage application device, 44, 84: Counter electrode, 45, 85: Raw material liquid, 45a, 85a: Raw material liquid tank, 46, 86: Pump, 47, 87: Squeegee, 48, 88: First support, 49, 89: Second support,

50, 50A: Porous sheet joining apparatus, 51a, 51b: joining roller, 52a: supply reel, 52b: transport roller,
70: collection device, 71: transport roller, 72: collection reel,

  S: base material sheet, S1: first base material sheet, S2: second base material sheet, Sa: main surface of base material sheet, S1a: main surface of first base material sheet, S2a: first base material sheet Main surface, F: Nanofiber sheet (Separator for capacitors)

Claims (17)

  A nanofiber sheet comprising nanofibers and having a first surface and a second surface opposite thereto,
  When the average of the maximum fiber diameters of the nanofibers in the plane direction of the nanofiber sheet is compared between the vicinity of the first surface and the vicinity of the second surface, and the central portion in the thickness direction of the nanofiber sheet, An average Ds1 of the maximum fiber diameters of the nanofibers in the vicinity of the first surface and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the nanofiber sheets at the center in the thickness direction of the nanofiber sheet. Smaller than the average fiber diameter Dc,
  A nanofiber sheet satisfying the relationship of 1.1 ≦ Dc / Ds1 ≦ 2.5 and 1.1 ≦ Dc / Ds2 ≦ 2.5.   A nanofiber sheet comprising nanofibers and having a first surface and a second surface opposite thereto,
  When the average of the maximum fiber diameters of the nanofibers in the plane direction of the nanofiber sheet is compared between the vicinity of the first surface and the vicinity of the second surface, and the central portion in the thickness direction of the nanofiber sheet, An average Ds1 of the maximum fiber diameters of the nanofibers in the vicinity of the first surface and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the nanofiber sheets at the center in the thickness direction of the nanofiber sheet. Smaller than the average fiber diameter Dc,
  A nanofiber sheet having an average Dc of the maximum fiber diameter of 60 nm to 2 μm.   The average Ds1 of the maximum fiber diameter and the average Ds2 of the maximum fiber diameter satisfy 0.9 ≦ Ds1 / Ds2 ≦ 1.1, and the porosity Ps1 of the nanofiber sheet in the vicinity of the first surface, The nanofiber sheet according to claim 1 or 2, wherein a porosity Ps2 of the nanofiber sheet in the vicinity of the second surface satisfies 0.9 ≦ Ps1 / Ps2 ≦ 1.1.   The nanofiber sheet according to any one of claims 1 to 3, wherein the nanofibers are welded at random in the nanofiber sheet.   The nanofiber sheet according to any one of claims 1 to 4, wherein the nanofiber includes at least one selected from the group consisting of an olefin resin, a fluororesin, a polyamide resin, and a polyimide resin.   The nanofiber sheet according to any one of claims 1 to 5, wherein the nanofiber sheet has a matrix structure of the nanofibers formed by an electrospinning method.   The nanofiber sheet according to any one of claims 1 to 6, wherein an average Dc of the maximum fiber diameter is 200 to 1000 nm.   The nanofiber sheet according to any one of claims 1 to 7, wherein a relationship of 1.3? Dc / Ds1? 2 is satisfied.   A sheet-shaped capacitor separator comprising nanofibers and having a first surface and a second surface opposite to the first surface,
  When the average of the maximum fiber diameters of the nanofibers in the surface direction of the separator is compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator, the vicinity of the first surface An average Ds1 of the maximum fiber diameters of the nanofibers and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the average Dc of the maximum fiber diameters of the nanofibers at the center in the thickness direction of the separator. Smaller,
  A capacitor separator satisfying the relations 1.1 ≦ Dc / Ds1 ≦ 2.5 and 1.1 ≦ Dc / Ds2 ≦ 2.5.   A sheet-shaped capacitor separator comprising nanofibers and having a first surface and a second surface opposite to the first surface,
  When the average of the maximum fiber diameters of the nanofibers in the surface direction of the separator is compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator, the vicinity of the first surface An average Ds1 of the maximum fiber diameters of the nanofibers and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the average Dc of the maximum fiber diameters of the nanofibers at the center in the thickness direction of the separator. Smaller,
  The separator for capacitors whose average Dc of the said largest fiber diameter is 60 nm-2 micrometers. A pair of electrodes, a separator interposed between the electrodes, and an electrolyte;
The separator comprises a Na Nofaiba, and has a sheet shape having a first surface and a second surface on the opposite side,
The average of the maximum fiber diameter of the nanofibers in the plane direction before Symbol separator, wherein the first surface vicinity and the second vicinity of the surface, when compared with the central portion in the thickness direction of the separator, the first surface An average Ds1 of the maximum fiber diameters of the nanofibers in the vicinity and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the averages of the maximum fiber diameters of the nanofibers in the center portion in the thickness direction of the separator. Smaller than Dc ,
1.1 ≦ Dc / Ds1 ≦ 2.5, and 1.1 you satisfy the relationship ≦ Dc / Ds2 ≦ 2.5, capacitors. A pair of electrodes, a separator interposed between the electrodes, and an electrolyte;
The separator includes a nanofiber and has a sheet shape having a first surface and an opposite second surface;
When the average of the maximum fiber diameters of the nanofibers in the surface direction of the separator is compared between the vicinity of the first surface and the vicinity of the second surface and the central portion in the thickness direction of the separator, the vicinity of the first surface An average Ds1 of the maximum fiber diameters of the nanofibers and an average Ds2 of the maximum fiber diameters of the nanofibers in the vicinity of the second surface are the average Dc of the maximum fiber diameters of the nanofibers at the center in the thickness direction of the separator. Smaller,
The average Dc maximum fiber diameter is 60Nm～2myuemu, key Yapashita. At least one of the pair of electrodes includes a carbonaceous material as a polarizable material forming an electric double layer,
The capacitor according to claim 11 or 12 , wherein the electrolyte includes a cation, an anion, and a non-aqueous solvent for dissolving them. (I) supplying a base sheet to the nanofiber formation space;
(Ii) In the nanofiber formation space, nanofibers are generated by electrostatic force from a raw material solution containing a solvent and a resin raw material dissolved in the solvent, and the generated nanofibers are deposited on the main surface of the base sheet. Forming a porous sheet having a nanofiber matrix structure;
(Iii) A pair of the porous sheets are bonded so that the surfaces that have been in contact with the main surface of the base sheet face each other, and are in contact with the main surface of the base sheet of the pair of porous sheets Forming a capacitor separator having the first surface and the second surface on the opposite side as the first surface and the second surface, respectively. In the step (iii), in the state where at least the surface of the pair of porous sheets in contact with the main surface of the base sheet sheet contains the solvent, the pair of porous sheets is joined, The manufacturing method of the separator for capacitors of Claim 14 which welds the nanofiber of the said porous sheet, and the nanofiber of the other said porous sheet. The first and second base sheets that are long are conveyed from the upstream side to the downstream side of the first and second lines, respectively, and on the upstream side, the first and second surfaces are respectively formed on the main surfaces of the first and second base sheet. A method for producing a capacitor separator, comprising forming a porous sheet and joining the first and second porous sheets oppositely on the downstream side,
(I) transporting the first and second base sheets to a nanofiber formation space upstream of the first and second lines;
(Ii) In the nanofiber formation space, nanofibers are generated by electrostatic force from a raw material liquid containing a solvent and a resin raw material dissolved in the solvent, and the first and second groups are transported by the generated nanofibers. Forming first and second porous sheets having a matrix structure of nanofibers, each deposited on a main surface of a material sheet;
(Iii) removing the first and second base material sheets from the first and second porous sheets conveyed on the downstream side of the first and second lines;
(Iv) On the further downstream side of the first and second lines, the surfaces of the first and second porous sheets conveyed that are in contact with the main surfaces of the first and second substrate sheets are opposed to each other. And a step of forming a nanofiber sheet by bonding to form a nanofiber sheet. In the step (iv), in the state where at least the surface vicinity of the first and second porous sheets in contact with the main surfaces of the first and second base sheets contains the solvent, the first and second porous sheets The manufacturing method of the separator for capacitors according to claim 16 which joins the 2nd porous sheet and welds the nanofiber of the 1st porous sheet, and the nanofiber of the 2nd porous sheet.

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