JP2015060930A - Separator for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a capacitor having high electrolyte retaining property, low internal resistance and low internal short circuit failure occurrence ratio in the separator for the capacitor made of a wet-laid nonwoven fabric containing a fibrillated solvent-spun cellulose fiber and a synthetic short fiber.SOLUTION: In a separator for a capacitor made of a wet-laid nonwoven fabric containing a fibrillated solvent-spun cellulose fiber and a synthetic short fiber as an essential component, the synthetic short fiber having crimps is contained.

Description

  The present invention relates to a capacitor separator. The capacitor in the present invention refers to an electric double layer capacitor, a lithium ion capacitor, a hybrid capacitor, a redox capacitor and the like.

  A capacitor, which is a kind of electrochemical element, has a large electric capacity and has high stability against repeated charge and discharge, and is therefore widely used in applications such as a power supply used in vehicles and electrical equipment. Conventionally, as a capacitor separator (hereinafter, sometimes referred to as “separator”), a paper separator mainly composed of a beaten product of solvent-spun cellulose fiber or regenerated cellulose fiber has been used (for example, Patent Document 1). ~ 2). In recent years, attention has been focused on the volume and weight energy density, and the application has been expanded to flashing road lamps and guide lights combined with solar cells, regenerative energy systems for automobiles and electric cars, and the like. Accordingly, the separator is required to have uniformity and denseness for preventing internal short circuit, electrolyte impregnation and liquid retention, high ion permeability, low internal resistance, strength to withstand capacitor manufacturing, and the like. . In order to improve these requirements, a separator using a solvent-spun cellulose fiber and a synthetic short fiber together with a paper separator has been proposed. (For example, refer to Patent Document 2). However, the separator using the solvent-spun cellulose fiber and the synthetic short fiber improves the strength and denseness, but has a problem that the internal resistance tends to increase.

JP-A-11-168033 JP 2000-3834 A

  The object of the present invention is to provide a capacitor separator made of a wet nonwoven fabric containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, having a high electrolyte solution retention ratio, low internal resistance, and poor internal short circuit The object is to provide a capacitor separator having a low rate.

  As a result of intensive studies to solve the above problems, the following means have been found and the present invention has been achieved.

  A capacitor separator made of a wet nonwoven fabric containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, wherein the capacitor separator contains crimped synthetic short fibers.

  According to the present invention, in a capacitor separator made of a wet nonwoven fabric containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, the electrolytic solution retaining liquid is obtained by containing the synthetic short fibers having crimps. Thus, a capacitor separator having a low internal resistance and a low internal short-circuit failure rate can be obtained.

  The solvent-spun cellulose fiber means a cellulose fiber obtained by dissolving and spinning directly in an organic solvent without passing through a cellulose derivative. In the present invention, solvent-spun cellulose fibers fibrillated by beating treatment are used. In the present invention, the beating degree of solvent-spun cellulose fiber is expressed by modified freeness.

  The modified freeness is a value measured in accordance with JIS P8121, except that an 80 mesh wire net having a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as a sieve plate, and the sample concentration is 0.1 mass%. That is.

  The fibrillated solvent-spun cellulose fiber preferably has a modified freeness of 0 to 400 ml. The modified drainage degree of the fibrillated solvent-spun cellulose fiber is more preferably 0 to 300 ml, and further preferably 0 to 250 ml. If the modified drainage is more than 400 ml, the capacitor separator may be insufficiently dense and the internal short circuit defect rate may be increased.

  In order to obtain fibrillated solvent-spun cellulose fibers, solvent-spun cellulose short fibers are dispersed in water at an appropriate concentration, and this is subjected to shear force by a refiner, beater, mill, milling device, and high-speed rotary blade. Rotating blade type homogenizer, double cylindrical high speed homogenizer that generates shearing force between a cylindrical inner blade that rotates at high speed and a fixed outer blade, ultrasonic crusher that is refined by ultrasonic impact, high pressure It may be beaten by adjusting the conditions such as the shape of the blade, the flow rate, the number of treatments, the treatment speed, and the treatment concentration through a homogenizer.

  The length-weighted average fiber length of the fibrillated solvent-spun cellulose fiber is preferably 0.2 to 2.0 mm, more preferably 0.4 to 1.8 mm, and even more preferably 0.5 to 1.5 mm. When the length-weighted average fiber length is shorter than 0.2 mm, there are cases where the ratio of falling out of the screen and outflowing into the drainage during wet papermaking increases, or fluffing may occur due to rubbing. The fibers may be twisted and become lumps.

  In the present invention, the average fiber length (length-weighted average fiber length) of the fibrillated solvent-spun cellulose fibers is the JAPAN TAPPI paper pulp test method No. According to No. 52 “Paper and Pulp Fiber Length Test Method (Optical Automatic Measurement Method)”, measurement was performed using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation).

  In Kajaani Fiber Lab V3.5 (manufactured by Metso Automation), for each fiber passing through the detection unit, the total true length (L) of the bent fiber and the shortest length (l) of both ends of the bent fiber are determined. Can be measured. The “length-weighted average fiber length” is an average fiber length obtained by measuring and calculating the shortest length (l) of both ends of the bent fiber.

  In the present invention, the capacitor separator contains fibrillated solvent-spun cellulose and synthetic short fibers as essential components, and preferably contains 50-90% by mass of fibrillated solvent-spun cellulose fiber, 60-80% by mass. Is more preferable. If the content of the fibrillated solvent-spun cellulose fiber is less than 50% by mass, the density of the separator may be insufficient and the internal short circuit defect rate may be high. Papermaking properties may be deteriorated.

  As the synthetic short fiber having crimps in the present invention, polyolefin, polyester, acrylic, wholly aromatic polyester, wholly aromatic polyester amide, polyamide, semi-aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyether, wholly aromatic Polycarbonate, polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole (PBI), polytetrafluoroethylene (PTFE) Examples thereof include single fibers and composite fibers made of a resin such as an ethylene-vinyl alcohol copolymer, and they may be contained in combinations of two or more. Among these, polyolefin, polyester, acrylic, wholly aromatic polyester, wholly aromatic polyester amide, polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable, and polyester and acrylic are more preferable.

  The number of crimps and the crimp rate of the synthetic short fiber having crimps in the present invention are not particularly limited, but the number of crimps is preferably 3 to 50, more preferably 10 to 25. Moreover, about a crimp rate, 3 to 30% is preferable and 5 to 20% is more preferable. The “crimp number” and “crimp rate” used in the present invention represent “crimp number” and “crimp rate” defined by JIS L 1015.

  Synthetic short fibers that can be used in combination with the synthetic short fibers having crimps in the present invention include polyolefins, polyesters, acrylics, wholly aromatic polyesters, wholly aromatic polyester amides, polyamides, semi-aromatic polyamides, wholly aromatics. Polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole (PBI), polytetrafluoroethylene (PTFE), a single fiber or a composite fiber made of a resin such as an ethylene-vinyl alcohol copolymer, or a fibrillated product of these may be contained alone in an appropriate amount, or two or more types Even if contained in a combination of There. Moreover, you may contain what divided | segmented various split type composite fibers. Among these, polyolefin, polyester, acrylic, wholly aromatic polyester, wholly aromatic polyester amide, polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable, and polyester and acrylic are more preferable.

  The average fiber diameter of the synthetic short fiber in the present invention is preferably from 0.1 to 20 μm, more preferably from 0.1 to 15 μm, further preferably from 0.1 to 10 μm. If the average fiber diameter is less than 0.1 μm, the fibers may be too thin and fall off from the separator. If the average fiber diameter is greater than 20 μm, it may be difficult to reduce the thickness of the separator.

  The average fiber diameter in the present invention is an average value of 100 fibers randomly selected by measuring the fiber diameter of fibers forming the separator from a scanning electron micrograph of the separator.

  1-15 mm is preferable, as for the fiber length of the synthetic short fiber in this invention, 2-10 mm is more preferable, and 3-5 mm is further more preferable. If the fiber length is shorter than 1 mm, it may fall off from the separator, and if it is longer than 15 mm, the fiber may be tangled and become lumpy, resulting in uneven thickness.

  In the present invention, the capacitor separator contains fibrillated solvent-spun cellulose and synthetic short fibers as essential components, and preferably contains 10 to 50% by mass of synthetic short fibers. Is more preferable. When the content of the synthetic short fiber is less than 10% by mass, the wet paper strength is weakened and the papermaking property may be deteriorated. When the content is more than 50% by mass, the denseness is insufficient and the internal short circuit defect rate is increased. There is.

  In the present invention, the content of the crimped synthetic short fiber is preferably 50 to 100% by mass, and more preferably 70 to 100% by mass of the synthetic short fiber contained in the capacitor separator. If it is less than 50% by mass, the porosity may be insufficient, and the liquid retention of the electrolytic solution may not be sufficiently improved.

The basis weight of the separator for the capacitor in the present invention is preferably 5.0~25.0g / ^{m 2,} more preferably ^{7.0~20.0g / m 2, 7.0~18.0g / m} 2 and more preferable. If it is less than 5.0 g / m ² , sufficient mechanical strength may not be obtained, or the insulation between the positive electrode and the negative electrode may be insufficient and the internal short-circuit failure rate may increase. m and greater than ^2, there is a case where thinning of the separator for the capacitor becomes difficult.

  The thickness of the capacitor separator in the present invention is preferably 10.0 to 50.0 μm, more preferably 12.0 to 45.0 μm, and further preferably 15.0 to 40.0 μm. If the thickness is less than 10.0 μm, sufficient mechanical strength may not be obtained, or the insulation between the positive electrode and the negative electrode may be insufficient and the internal short circuit defect rate may be increased. If it is thicker than 50.0 μm, it may be difficult to reduce the thickness of the capacitor separator.

  In the present invention, as a wet papermaking method for forming a fiber web, a conventionally known method, for example, a paper machine using a papermaking system such as a circular net, a long net, a short net, an inclined short net, or the same type or One example is a method using a combination paper machine in which different types of paper machines are combined. In the present invention, when a wet nonwoven fabric is used as a capacitor separator, in order to reduce pinholes and defects, a combination paper machine combining a circular net and a circular net or an inclined type and a circular net is preferable. The fiber web formed in this manner is dried by a drying method such as a multi-cylinder dryer, a Yankee dryer, a combination of a Yankee dryer and a hot air hood, and a capacitor separator made of a wet nonwoven fabric is obtained. In addition to the fiber raw material, if necessary, a dispersing agent, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like are added to the papermaking slurry, and the solid content is about 5 to 0.001% by mass. A papermaking slurry is prepared to a concentration. The papermaking slurry is further diluted to a predetermined concentration for papermaking. The separator for capacitors obtained by papermaking is subjected to calendering, thermal calendering, heat treatment and the like as necessary.

  The capacitor in the present invention means an electric double layer capacitor, a lithium ion capacitor, a hybrid capacitor, or a redox capacitor. In the electric double layer capacitor, an electric double layer is formed at the interface between the electrode and the electrolytic solution to store electricity. As the electrode active material, carbon materials such as activated carbon, carbon black, carbon aerogel, carbon nanotube, and non-porous carbon are mainly used. As an electrolytic solution, an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, Examples include, but are not limited to, those obtained by dissolving an ion dissociable salt in an organic solvent such as ethylene glycol, propylene glycol, methyl cellosolve, and mixed solvents thereof, and ionic liquids (solid molten salts). is not.

In the lithium ion capacitor, the negative electrode active material is a material capable of reversibly supporting lithium ions, and the positive electrode active material is a material capable of reversibly supporting lithium ions and / or anions. This is a capacitor in which lithium ions are supported. Examples of the negative electrode active material include graphite, non-graphitizable carbon, polyacene organic semiconductor, lithium titanate, and the like. Examples of the positive electrode active material include conductive polymers such as polypyrrole, polythiophene, polyaniline, and polyacetylene, activated carbon, and polyacene organic semiconductor. As the electrolytic solution, an aprotic organic solvent of a lithium salt is used. Examples of the lithium salt include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , and Li (C ₂ F ₅ SO ₂ ) N. Examples of the aprotic organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, ethylene glycol, propylene glycol, and methyl. Cellsolve and mixed solvents thereof may be mentioned.

A hybrid capacitor is a capacitor in which the reaction mechanism or electrode material of the positive electrode and the negative electrode are different. For example, the negative electrode is an oxidation-reduction reaction, and the positive electrode is an electric double layer reaction. Examples of the negative electrode active material of the hybrid capacitor include activated carbon, graphite, hard carbon, polyacene, metal oxides such as Li ₄ Ti ₅ O ₁₂ , and n-type conductive polymers. Examples of the positive electrode active material include activated carbon, MnO ₂ , LiCoO ₂ , metal oxides such as ruthenium oxide, graphite, and a p-type conductive polymer.

A redox capacitor has a storage and discharge mechanism that uses all or part of oxidation / reduction of an electrode active material, adsorption / desorption of ions on the electrode surface, and charge / discharge in an electric double layer. Examples of electrode active materials for redox capacitors include metal oxides such as ruthenium oxide, iridium oxide, titanium oxide, zirconium oxide, nickel oxide, vanadium oxide, tungsten oxide, manganese oxide, and cobalt oxide, and composites of these metal oxides. Hydrates of these metal oxides, composites of these metal oxides and carbon materials, molybdenum nitride, composites of molybdenum nitride and metal oxides, graphite or Li ₄ Ti ₅ O capable of intercalating lithium ions ₁₂ , lithium metal oxides such as LiFePO ₄ , polypyrrole, polyaniline, polythiophene, polyacene, derivatives thereof, polyfluorene derivatives, polyquinoxaline derivatives, polyindoles, cyclic indole polymers, 1,5-diaminoanthraquinone, 1,4- Benzoki Non-, graphite and a complex of these quinone compounds, and metal complex polymers are exemplified. As an electrolytic solution, an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, Examples include, but are not limited to, those obtained by dissolving an ion dissociable salt in an organic solvent such as ethylene glycol, propylene glycol, methyl cellosolve, and mixed solvents thereof, and ionic liquids (solid molten salts). is not.

<Fiber A1>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 0.55 mm and a modified freeness of 0 ml. A1.

<Fiber A2>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 1.25 mm and a modified freeness of 250 ml. A2.

<Fiber A3>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 1.55 mm and a modified freeness of 300 ml. A3.

<Fiber A4>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 1.85 mm and a modified freeness of 400 ml. A4.

<Fiber B1>
Polyethylene terephthalate fiber having an average fiber diameter of 2.4 μm, a fiber length of 3 mm, a crimp number of 10 and a crimp rate of 6% was designated as fiber B1.

<Fiber B2>
Polyethylene terephthalate fiber having an average fiber diameter of 3.0 μm, fiber length of 3 mm, number of crimps of 15 and crimp rate of 10% was designated as fiber B2.

<Fiber B3>
Polyethylene terephthalate fiber having an average fiber diameter of 4.3 μm, a fiber length of 3 mm, a crimp number of 10 and a crimp rate of 6% was designated as fiber B3.

<Fiber B4>
Polyethylene terephthalate fiber having an average fiber diameter of 3.0 μm, fiber length of 3 mm, number of crimps of 6, and crimp rate of 4% was designated as fiber B4.

<Fiber B5>
Polyethylene terephthalate fiber having an average fiber diameter of 4.3 μm, fiber length of 3 mm, crimp number of 27, and crimp rate of 25% was designated as fiber B5.

<Fiber B6>
Polyethylene terephthalate fiber having an average fiber diameter of 3.0 μm and a fiber length of 3 mm and having no crimp was designated as fiber B6.

<Fiber C1>
An acrylic fiber having an average fiber diameter of 3.3 μm, a fiber length of 3 mm, a number of crimps of 15, and a crimp rate of 10% was designated as fiber C1.

<Fiber C2>
An acrylic fiber having an average fiber diameter of 4.7 μm, a fiber length of 3 mm, a crimp number of 10, and a crimp rate of 6% was designated as fiber C2.

<Fiber C3>
An acrylic fiber having an average fiber diameter of 3.3 μm, a fiber length of 3 mm, a crimp number of 6, and a crimp rate of 4% was designated as fiber C3.

<Fiber C4>
An acrylic fiber having an average fiber diameter of 3.3 μm and a fiber length of 3 mm and having no crimp was designated as fiber C4.

<Fiber C5>
An acrylic fiber having an average fiber diameter of 4.7 μm and a fiber length of 3 mm and having no crimp was designated as fiber C5.

<Fiber D1>
Polypropylene fiber having an average fiber diameter of 5.3 μm, fiber length of 4 mm, crimp number of 6 and crimp rate of 4% was designated as fiber D1.

<Fiber D2>
Polypropylene fiber having an average fiber diameter of 5.3 μm and a fiber length of 4 mm and having no crimp was designated as fiber D2.

<Fiber E1>
The linter was treated using a high-pressure homogenizer to produce microfibrillated natural cellulose fiber E1 having a modified freeness of 0 ml.

<Separator>
Example 1
A papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B1, and 5 parts by mass of fiber E1 is set to a basis weight ratio of 50% on the slant side and on the net side by using a slant / circular net combination paper machine. : 50, a wet fiber web was formed, and dried with a Yankee dryer set at 130 ° C and a hot air hood set at 135 ° C to obtain a wet nonwoven fabric. A separator was produced by subjecting the wet nonwoven fabric thus obtained to a supercalender treatment at room temperature.

(Example 2)
A separator was prepared in the same manner as in Example 1 except that the papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B2, and 5 parts by mass of fiber E1 was used.

(Example 3)
A separator was produced in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B3, and 5 parts by mass of fiber E1 was used.

Example 4
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B4, and 5 parts by mass of fiber E1 was used.

(Example 5)
A separator was prepared in the same manner as in Example 1 except that the papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B5, and 5 parts by mass of fiber E1 was used.

(Example 6)
A separator was produced in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A2 and 25 parts by mass of fiber B2 was used.

(Example 7)
A separator was produced in the same manner as in Example 1 except that a papermaking slurry containing 55 parts by mass of fiber A2 and 45 parts by mass of fiber B2 was used.

(Example 8)
A separator was produced in the same manner as in Example 1 except that the papermaking slurry containing 85 parts by mass of fiber A2 and 15 parts by mass of fiber B2 was used.

Example 9
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A2, 15 parts by mass of fiber B2, 5 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Example 10)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A2, 10 parts by mass of fiber B2, 10 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Example 11)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A2, 8 parts by mass of fiber B2, 12 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Example 12)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A3, 8 parts by mass of fiber B2, 12 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Example 13)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 75 parts by mass of fiber A4, 8 parts by mass of fiber B2, 12 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Example 14)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 20 parts by mass of fiber C1, 5 parts by mass of fiber C4, and 5 parts by mass of fiber E1 was used.

(Example 15)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 20 parts by mass of fiber C2, 5 parts by mass of fiber C5, and 5 parts by mass of fiber E1 was used.

(Example 16)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 20 parts by mass of fiber C3, 5 parts by mass of fiber C4, and 5 parts by mass of fiber E1 was used.

(Example 17)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 20 parts by mass of fiber D1, 5 parts by mass of fiber D2, and 5 parts by mass of fiber E1 was used.

(Comparative Example 1)
A separator was prepared in the same manner as in Example 1 except that the papermaking slurry containing 75 parts by mass of fiber A1, 20 parts by mass of fiber B6, and 5 parts by mass of fiber E1 was used.

(Comparative Example 2)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 25 parts by mass of fiber C5, and 5 parts by mass of fiber E1 was used.

(Comparative Example 3)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber A1, 25 parts by mass of fiber D2, and 5 parts by mass of fiber E1 was used.

(Comparative Example 4)
A separator was prepared in the same manner as in Example 1 except that a papermaking slurry containing 70 parts by mass of fiber C1 and 30 parts by mass of fiber E1 was used.

<Electric double layer capacitor>
[Production of electrode for electric double layer capacitor]
10 parts by mass of polyvinylidene fluoride is dissolved in 90 parts by mass of N-methyl-2-pyrrolidone, and 80 parts by mass of powdered activated carbon having an average particle size of 5.0 μm and a specific surface area of 2000 m ² / g starting from a phenol resin. Then, 10 parts by mass of acetylene black having an average particle diameter of 200 nm and 300 parts by mass of N-methyl-2-pyrrolidone were added and mixed sufficiently with a mixing stirrer to obtain an electrode slurry. After applying the electrode slurry to an aluminum foil current collector having a thickness of 30 μm whose surface has been etched with hydrochloric acid using an applicator and drying, press treatment is performed using a roll press apparatus, and an electric current having a thickness of 150 μm is obtained. An electrode for a double layer capacitor was produced.

[Production of electric double layer capacitor]
After a pair of polarizable electrodes produced as described above are wound through the separators of Examples 1 to 17 and Comparative Examples 1 to 4, they are housed in an aluminum case, and heated at 150 ° C. for 10 hours under vacuum. Then, the electrolytic solution was injected into the aluminum case, and the injection port was sealed to produce the electric double layer capacitors of Examples 1 to 17 and Comparative Examples 1 to 4. As the electrolytic solution, a solution obtained by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate so as to be 1.5 mol / l was used.

[Separator basis weight]
The basis weight of the capacitor separator was measured according to JIS P 8124, and the results are shown in Table 1.

[Separator thickness]
The thickness of the capacitor separator was measured according to JIS P 8118, and the results are shown in Table 1.

[Electrolytic solution retention ratio]
A sheet having a size of 10 cm × 10 cm was cut out from the capacitor separators of Examples and Comparative Examples, and the mass (W ₁ ) of the sheet was measured. After immersing this sheet in an electrolytic solution in which tetraethylammonium tetrafluoroborate was dissolved in propylene carbonate so as to be 1.5 mol / l for 5 minutes, the sheet was taken out with tweezers and suspended for 10 minutes. (W ₂ ) was measured, and the electrolyte solution retention rate (%) of the separator was measured by the following formula (1). When the electrolyte solution retention rate is 250% or more, “◎”, when it is 200% or more and less than 250%, “◯”, when it is 150% or more and less than 200%, “△”, when it is less than 150%, “「 ”. × ”. The results are shown in Table 1.

Electrolytic solution retention ratio (%) = (W ₂ −W ₁ ) / W ₁ × 100 (1)

[Internal resistance]
A direct current was applied to the electric double layer capacitors of Examples and Comparative Examples to charge to 2.5V. Subsequently, the voltage of the electric double layer capacitor immediately after starting the discharge with a direct current of 20 mA is measured, and a difference from 2.5 V, that is, a voltage drop is obtained, and a value obtained by dividing this by the discharge current is used as an internal resistance. It was shown in 1.

[Internal short-circuit failure rate]
Using the electric double layer capacitors of Examples and Comparative Examples, the internal short-circuit failure rate when the constant current charge / discharge was repeated 500 cycles at a charge / discharge voltage range of 0 to 2.7 V and a charge / discharge current of 200 mA was calculated. It was shown to.

  From the results of Examples 1 to 17 shown in Table 1, in a capacitor separator made of a wet nonwoven fabric containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, synthetic short fibers having crimps are included. As a result, a capacitor separator having a high electrolyte solution retention ratio, a low internal resistance, and a low internal short-circuit failure rate can be obtained.

  When Examples 1 to 5 are compared, Examples 1 to 3 in which the number of crimps and the crimp rate of the synthetic short fibers having crimps are in a more preferable range are superior to Examples 4 to 5. In Example 4, the number of crimps and the crimp rate are lower than the more preferable ranges, the electrolyte solution retention rate is inferior, and the internal resistance is slightly high. In Example 5, the number of crimps and the crimp rate are higher than the more preferable ranges, and the internal short circuit defect rate is slightly high.

  When Examples 6 to 8 are compared, Example 6 in which the content of fibrillated solvent-spun cellulose and synthetic short fibers is in a more preferable range has a higher electrolyte solution retention rate than Examples 7 to 8, Internal resistance is low and excellent.

  When Examples 9 to 13 are compared, Example 9 in which the content of the synthetic staple fibers having crimps in the synthetic staple fibers is in a more preferable range is the most excellent, and then Example 10 in the preferable range is excellent. Yes. Moreover, when Examples 11-13 are compared, internal resistance falls and it is preferable in the order with preferable modified freeness of solvent-spun cellulose.

  When Examples 14 to 17 are compared, Examples 14 to 15 in which the types of the synthetic short fibers, the number of crimps, and the crimp rate are in a more preferable range are the most excellent. Further, when Examples 16 to 17 are compared, Example 16 which is a more preferable fiber is superior to Example 17.

  Examples of synthetic short fibers are polyethylene terephthalate fibers that are more preferable as types of synthetic short fibers, and examples 1 to 3 in which the number of crimps and the crimp ratio are in a more preferable range, and acrylic fibers that are more preferable as types of synthetic short fibers. Examples 14 to 15 in which the number and crimp rate are in a more preferable range are excellent in that the electrolyte solution retention rate is high, the internal resistance is low, and the internal short circuit defect rate is also low.

  On the other hand, from the results of Comparative Examples 1 to 4, when the fibrillated solvent-spun cellulose and the synthetic staple fiber having crimps were not contained at the same time, the electrolyte solution retention rate was low and the internal resistance was high. Moreover, about Example 3-4, it was a result that the internal short circuit defect rate also became high.

  As an application example of the present invention, a capacitor separator is suitable.

Claims (1)

  A capacitor separator made of a wet nonwoven fabric containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, wherein the capacitor separator contains crimped synthetic short fibers.