JP2015176888A - Method of manufacturing separator for electrochemical element and separator for electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a separator for electrochemical element capable of manufacturing a precise separator for electrochemical element excellent in the mechanical strength and the paper strength.SOLUTION: In a method of manufacturing a separator for electrochemical element where a fibrous web, formed from fiber slurry containing a solvent spinning cellulose and a synthetic short fiber, produced by beating, by using a wet paper-making machine, a paper strength enhancement agent is sprayed by 0.01-1.00 g/m, in solid content, to the upper surface when the fibrous web is formed on the wire or the felt of the wet paper-making machine.

Description

  The present invention relates to a method for producing an electrochemical element separator and an electrochemical element separator.

  In recent years, further increase in capacity has been demanded for lithium ion batteries and electric double layer capacitors. In order to obtain a higher capacity, it is necessary to reduce the volume of the electrochemical element separator (hereinafter also referred to as “separator”) in the electrochemical element and to increase the volume ratio of the polarization component. There is a need for thin film separators. As a separator for an electrochemical element having a dense structure that is not easily short-circuited even if it is made into a thin film, for example, a paper separator mainly composed of a beaten product of solvent-spun cellulose fiber or regenerated cellulose fiber is used (Patent Documents 1 and 2). reference). However, the separators mainly composed of the beaten cellulose fibers are weak in entanglement between the fibers and are not fused. Therefore, the mechanical strength is low, and the separator breaks when wound together with the electrode. There was a problem that it was easy. Also, these separators are manufactured by drying a fiber web formed using a wet paper machine, but the paper surface strength is also low, and the fiber web is formed on the wire or felt of the wet paper machine. The upper surface (hereinafter sometimes referred to as “fiber web upper surface”) tends to be fluffy, and depending on the process, many fibers fall off, resulting in contamination (contamination). was there.

  Further, as a means for improving the mechanical strength of the separator, a separator containing a water-soluble polymer such as carboxymethyl cellulose has been proposed (see Patent Document 3). However, since these are separators manufactured by an internal addition method in which a water-soluble polymer is added to the papermaking slurry, the effect of adding the water-soluble polymer may be insufficient.

Japanese Patent No. 3661104 JP 2000-3834 A International Publication No. 2012/008559 Pamphlet

  The subject of this invention is providing the manufacturing method of the separator for electrochemical elements which can manufacture the separator for electrochemical elements which was precise | minute and excellent in mechanical strength and paper surface strength.

  As a result of intensive studies to solve the above problems, the following invention has been found.

(1) In a method for producing a separator for an electrochemical element, in which a fiber web formed using a wet paper machine is dried from a fiber slurry containing solvent-spun cellulose fibers and synthetic short fibers formed by beating, the wire of the wet paper machine Electrochemistry characterized by spraying a paper strength enhancer in a solid content of 0.01 to 1.00 g / m ² on the upper surface when the fiber web is formed on the top or felt. A method for manufacturing a separator for an element.
(2) The method for producing a separator for an electrochemical element according to the above (1), wherein the paper strength enhancer is at least one selected from the group of carboxymethyl cellulose and polyacrylamide resins.
(3) The content of the solvent-spun cellulose fiber formed by beating is 10 to 95% by mass of the whole fiber contained in the electrochemical device separator. The electrochemical device separator according to (1) or (2), Production method.
(4) An electrochemical element separator manufactured by the method for manufacturing an electrochemical element separator according to any one of (1) to (3) above.

  The method for producing a separator for an electrochemical element according to the present invention comprises a finely beaten solvent-spun cellulose fiber, so that it is possible to obtain a separator for an electrochemical element that is excellent in denseness. In addition to forming a network by intertwining, the mechanical strength and the paper strength can be increased by fusing the fibers together by spraying and drying a paper strength enhancer on the upper surface of the wet fiber web. An excellent electrochemical element separator can be obtained.

  Hereinafter, the separator for electrochemical devices of the present invention will be described in detail. The electrochemical element in the present invention is a lithium battery, lithium ion battery, lithium polymer battery, polyacene battery, organic radical battery, electric double layer capacitor, lithium ion capacitor, hybrid capacitor, redox capacitor, aluminum electrolytic capacitor, conductive polymer It refers to an electrochemical element that has a power storage function and a rectifying function, such as an aluminum solid electrolytic capacitor.

  The solvent-spun cellulose fiber used in the present invention means a cellulose fiber obtained by spinning by dissolving directly in an organic solvent without passing through a cellulose derivative. The beating of solvent-spun cellulose fibers consists of a refiner, a beater, a mill, an attritor, a rotary blade homogenizer that applies shearing force with a high-speed rotary blade, and a cylindrical inner blade that rotates at high speed and a fixed outer blade. This is done using a double-cylindrical high-speed homogenizer that generates a shearing force, an ultrasonic crusher that is refined by impact by ultrasonic waves, a high-pressure homogenizer, and the like. The degree of beating is preferably a modified freeness of 0 to 250 ml. The modified freeness in the present invention is measured in accordance with JIS P811, 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% by mass. Means freeness.

  In the separator for electrochemical devices of the present invention, the content of the solvent-spun cellulose fiber formed by beating is preferably 10 to 95% by mass, more preferably 30 to 90% by mass, and 50 to 50%. More preferably, it is 85 mass%. If the content is less than 10% by mass, the denseness of the separator becomes insufficient and an internal short circuit may occur. On the other hand, if it exceeds 95% by mass, the paper strength may be low, or the separator may be too dense and the internal resistance may be high.

  Synthetic short fibers constituting the separator for electrochemical devices of the present invention are polyolefin, polyester, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, Examples include short fibers made of resins such as polyether, polyvinyl alcohol, diene, polyurethane, phenol, melamine, furan, urea, aniline, unsaturated polyester, alkyd, fluorine, silicone, polyamideimide, polyphenylene sulfide, polyimide, and derivatives thereof. It is done.

  Acrylic is composed of a polymer of 100% acrylonitrile, and is obtained by copolymerizing acrylonitrile with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl acetate, etc. Etc.

  Polyamides include aliphatic polyamides such as nylon, poly-p-phenylene terephthalamide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide, wholly aromatic polyamides such as poly-m-phenylene isophthalamide, A semi-aromatic polyamide having, for example, a fatty chain as part of the chain can be mentioned.

  The synthetic short fiber may be a fiber (single fiber) made of a single resin or a composite fiber made of two or more kinds of resins. Moreover, the synthetic short fiber contained in the separator for electrochemical elements of the present invention may be one kind or a combination of two or more kinds. Examples of the composite fiber include a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, an orange type, and a multiple bimetal type.

  The fineness of the synthetic short fiber is preferably 0.01 to 1.7 dtex, more preferably 0.03 to 0.6 dtex. When the fineness of the synthetic short fiber exceeds 1.7 dtex, it is difficult to reduce the thickness. When the fineness of the synthetic short fiber is less than 0.01 dtex, stable production of the fiber may be difficult.

  The fiber length of the synthetic short fiber is preferably 1 to 10 mm, and more preferably 1 to 6 mm. If the fiber length exceeds 10 mm, formation may be poor. On the other hand, when the fiber length is less than 1 mm, the entanglement between the fibers becomes insufficient, and the mechanical strength and the paper strength may be lowered.

  The content of the synthetic short fiber is preferably 5 to 90% by mass, more preferably 10 to 70% by mass, and further preferably 15 to 50% by mass based on the entire fiber. If the content is less than 5% by mass, the mechanical strength and the paper surface strength may be insufficient, and if it exceeds 90% by mass, the denseness may be insufficient.

  The separator for electrochemical elements of the present invention may contain fibers other than solvent-spun cellulose fibers and synthetic short fibers formed by beating. Examples thereof include natural cellulose fibers, pulped and fibrillated natural cellulose fibers, solvent-spun cellulose short fibers, regenerated cellulose short fibers and fibrillated products, fibrils made of synthetic resin, pulped products, fibrillated products, and inorganic fibers. The modified freeness of natural cellulose pulp or fibrillation is preferably 0 to 400 ml. Examples of the inorganic fiber include glass, alumina, silica, ceramics, and rock wool.

  Examples of the paper strength enhancer used in the present invention include starches such as corn starch, potato starch, wheat starch and tapioca starch; vegetable gums such as guar gum, locust bean gum and tragacanth gum; dialdehyde starch, cationic starch, methylcellulose, Semi-synthetic polymers such as carboxymethylcellulose, hydroxymethylcellulose, and hydroxyethylcellulose; synthetic polymers such as polyacrylamide resins, polyurethane resins, polyethyleneimine resins, urea resins, polyethylene oxide (PEO), and polyvinyl alcohol (PVA) Can be mentioned. Among them, it is preferable to use carboxymethyl cellulose and polyacrylamide resin from the viewpoint of the effect of fusing fibers together and workability.

  As a method for producing the separator for an electrochemical element of the present invention, wet paper such as a long-mesh type, a short-mesh type, a circular-mesh type, and an inclined type is obtained from a fiber slurry containing solvent-spun cellulose and synthetic short fibers that are beaten. After forming a fiber web using a paper machine and spraying a paper strength enhancer on the upper surface of the wet fiber paper web on the wire or felt of a wet paper machine, a drying part such as a Yankee type or multi-cylinder dryer is used. Dry the fibrous web by passing it through. According to this method, a separator excellent in mechanical strength and paper strength can be obtained.

  In the method for producing a separator for an electrochemical element of the present invention, the paper strength enhancer is spray-coated on a fiber web in a wet paper state. There are cases where sufficient mechanical strength and paper surface strength cannot be obtained by the internal addition method in which a paper strength enhancer is added to the fiber slurry. Further, when a paper strength enhancer is impregnated and applied to a fiber web in a wet paper state, the fiber web may be broken, and when it is impregnated or spray-applied to a dried nonwoven fabric, wrinkles or paper breakage may occur. .

The content of a paper strength agent in the separator for an electrochemical device of the present invention is a 0.01~1.00g / ^{m 2} by solid content, and more preferably 0.03~0.60g / ^{m 2} . When the content of the paper strength enhancer is less than 0.01 g / m ² , the mechanical strength and the paper surface strength are insufficient, and when it exceeds 1.00 g / m ² , the ion permeability is inhibited and the internal resistance is reduced. Get higher.

  In the manufacturing method of the separator for electrochemical elements of the present invention, heat treatment, calendering, thermal calendering, etc. may be performed as necessary.

  The thickness of the electrochemical device separator of the present invention is preferably 4 to 60 μm, more preferably 6 to 50 μm, and still more preferably 8 to 40 μm. If the thickness is less than 4 μm, the mechanical strength of the separator may be insufficient, and if it exceeds 60 μm, the internal resistance of the separator may be increased.

Density of separator for an electrochemical element of the present invention is preferably 0.20~0.80g / cm ^3, more preferably 0.40~0.70g / cm ^3. When the density is less than 0.20 g / cm ^{3, the} density of the separator may be insufficient. When the density exceeds 0.80 g / cm ³ , the porosity of the separator decreases and the amount of electrolyte retained becomes insufficient. The internal resistance may be high.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

  A1 to A3 in Table 1 mean solvent-spun cellulose formed by beating using a refiner, and its modified freeness is as shown in Table 1. B1 is a polyethylene terephthalate fiber having a fineness of 0.03 dtex and a fiber length of 1 mm, B2 is a polyethylene terephthalate fiber having a fineness of 0.1 dtex and a fiber length of 3 mm, B3 is a fineness of 1.1 dtex and a fiber length of 10 mm, and the core is polyethylene terephthalate (melting point 253 C) means a polyester core-sheath type heat-sealing fiber whose sheath is a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.), C1 means a polyacrylonitrile fiber having a fineness of 0.4 dtex and a fiber length of 5 mm. D1 means a fibrillated natural cellulose fiber having a modified freeness of 0 ml, which is obtained by treating a linter with a high-pressure homogenizer.

<Preparation of separator for electrochemical device>
Example 1
Using fiber slurry 1, a fiber web is formed on the wire with an inclined paper machine, and a paper strength enhancer is formed on the upper surface of the fiber web on the inclined wire so that the content after drying is 0.01 g / m ^2. After spray-applying a carboxymethylcellulose aqueous solution as the above, it was dried with a Yankee dryer and calendered to obtain an electrochemical device separator of Example 1 shown in Table 2.

(Example 2)
Using fiber slurry 2, a fiber web is formed on the wire with an inclined paper machine, and a paper strength enhancer is formed on the upper surface of the fiber web on the inclined wire so that the content after drying is 0.10 g / m ^2. After spray-applying a carboxymethylcellulose aqueous solution, it was dried with a Yankee dryer and calendered to obtain an electrochemical device separator of Example 2 shown in Table 2.

(Example 3)
Using the fiber slurry 3, a fiber web is formed on the wire with an inclined paper machine, and as a paper strength enhancer on the upper surface of the fiber web on the inclined wire so that the content after drying is 0.50 g / m ^2. After the polyacrylamide aqueous solution was spray-coated, it was dried with a Yankee dryer and calendered to obtain an electrochemical device separator of Example 3 shown in Table 2.

Example 4
Using the fiber slurry 4, a fiber web is formed on the wire with an inclined paper machine, and a paper strength enhancer is formed on the upper surface of the fiber web on the inclined wire so that the content after drying is 0.30 g / m ^2. After the polyacrylamide aqueous solution was spray-coated, it was dried with a Yankee dryer and calendered to obtain a separator for an electrochemical element of Example 4 shown in Table 2.

(Example 5)
Using the fiber slurry 5, a fiber web is formed on the wire with an inclined paper machine, and a paper strength enhancer is formed on the upper surface of the fiber web on the inclined wire so that the content after drying is 1.00 g / m ^2. After spray application of the polyacrylamide aqueous solution, it was dried with a Yankee dryer and calendered to obtain an electrochemical device separator of Example 5 shown in Table 2.

(Example 6)
Using fiber slurry 6 as a paper strength enhancer on the upper surface of the fiber web on the inclined wire so that the fiber web is formed on the wire with an inclined paper machine and the content after drying is 0.80 g / m ^2. After spray-applying a carboxymethylcellulose aqueous solution, it was dried with a Yankee dryer and calendered to obtain an electrochemical device separator of Example 6 shown in Table 2.

(Example 7)
A separator for an electrochemical element of Example 7 shown in Table 2 was obtained in the same manner as in Example 2 except that the paper strength enhancer was changed from a carboxymethyl cellulose aqueous solution to a polyurethane aqueous solution.

(Example 8)
A separator for an electrochemical element of Example 8 shown in Table 2 was obtained in the same manner as in Example 4 except that the paper strength enhancer was changed from a polyacrylamide aqueous solution to a polyurethane aqueous solution.

Example 9
A separator for an electrochemical element of Example 9 shown in Table 2 was obtained in the same manner as in Example 3 except that the fiber slurry 3 was changed to the fiber slurry 7.

(Example 10)
A separator for an electrochemical element of Example 10 shown in Table 2 was obtained in the same manner as in Example 6 except that the fiber slurry 6 was changed to the fiber slurry 8.

(Comparative Example 1)
A separator for an electrochemical device of Comparative Example 1 shown in Table 2 was obtained in the same manner as in Example 1 except that the content of carboxymethylcellulose after drying was changed to 0.008 g / m ² .

(Comparative Example 2)
A separator for an electrochemical device of Comparative Example 2 shown in Table 2 was obtained in the same manner as in Example 5 except that the content of polyacrylamide after drying was changed to 1.10 g / m ² .

(Comparative Example 3)
A polyacrylamide aqueous solution as a paper strength enhancer was added to the fiber slurry 2 at a solid concentration of 1.00% by mass with respect to the fiber, and mixed and fixed uniformly. Thereafter, a fiber web was formed with an inclined paper machine, dried with a Yankee dryer, and calendered to obtain an electrochemical element separator of Comparative Example 3 shown in Table 2.

(Comparative Example 4)
Using the fiber slurry 2, a fiber web was formed with an inclined paper machine and dried with a Yankee dryer to obtain a wet nonwoven fabric. After applying the carboxymethylcellulose aqueous solution as a paper strength enhancer to the upper surface of the fiber web of the wet nonwoven fabric after drying, the solution was dried again with a Yankee dryer, calendered, and the electrochemical device of Comparative Example 4 shown in Table 2 A separator was obtained. The content of carboxymethyl cellulose after drying was 0.10 g / m ² .

(Comparative Example 5)
A separator for an electrochemical element of Comparative Example 5 shown in Table 2 was obtained in the same manner as in Example 2 except that the fiber slurry 2 was changed to the fiber slurry 9.

(Comparative Example 6)
A separator for an electrochemical element of Comparative Example 6 shown in Table 2 was obtained in the same manner as in Example 2 except that the fiber slurry 2 was changed to the fiber slurry 10.

  In the examples and comparative examples, the occurrence of wrinkles was observed in the process of manufacturing the separator for electrochemical devices. Moreover, the following test was done with respect to the separator for electrochemical devices obtained in Examples and Comparative Examples, and the results are shown in Table 2.

Wrinkle Occurrence Situation About the wrinkle occurrence situation of the separators obtained in the above Examples and Comparative Examples. Evaluation was made according to the following criteria.

○: Wrinkle was not generated.
X: Wrinkles occurred.

Test 1 (thickness)
The thickness was measured according to JIS C2111.

Test 2 (density)
The density was measured according to JIS C2111.

Test 3 (fluff evaluation)
The separators for electrochemical devices obtained in the examples and comparative examples were cut to a width of 20 mm and a length of 50 mm. The test piece is set on a Gakushin type friction fastness tester (trade name: AB-301, manufactured by Tester Sangyo Co., Ltd.), and a 100% cotton black cloth (Birikenmos (registered trademark)) is used as a friction element. After rubbing the upper surface of the fiber web of the test piece for 10 seconds at a speed of 2N, 30 reciprocations per minute, the fibers adhering to the black cloth were visually judged to evaluate fuzz. The fuzz evaluation criteria are as follows.

○: Three or less fibers are visually confirmed. Good with less fiber loss due to fluffing.
Δ: 4 to 10 fibers visually confirmed. There is fiber loss due to fluffing, but the effect is recognized.
X: 11 or more fibers visually confirmed. Many fibers fall off due to fluffing, which is problematic in practice.

Test 4 (winding property evaluation)
A separator, an electric double layer capacitor negative electrode, a separator, and an electric double layer capacitor positive electrode were laminated in this order, wound using a winding machine, and the winding property when a wound element was produced was determined according to the following criteria. As the negative electrode and positive electrode active materials, activated carbon having a BET specific surface area of 2000 m ² / g was used.

○: The separator could be wound without breaking.
X: The separator broke and hindered the winding property.

Test 5 (DC resistance)
The winding element produced by the above-described method for evaluating the winding property was put in a predetermined metal can, and sealed by injecting an electrolytic solution to produce an electric double layer capacitor equipped with the separators obtained in Examples and Comparative Examples. . As the electrolytic solution, a solution obtained by dissolving (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ in propylene carbonate so as to be 1.5 mol / l was used. These electric double layer capacitors are repeated at constant current charge / discharge for 500 cycles at 25 ° C., charge / discharge voltage range of 0-2.7 V, charge / discharge current of 1 A, and the internal resistance is calculated from the voltage drop immediately after the start of the 500th cycle discharge. And the average value of 100 was made into DC resistance.

○: DC resistance of less than 4Ω Δ: DC resistance of 4Ω or more and less than 5Ω ×: DC resistance of 5Ω or more

Test 6 (Internal short-circuit failure rate)
When measuring the DC resistance, the internal short-circuit failure rate was calculated.

○: Internal short circuit defect rate 0%
Δ: Internal short circuit failure rate 1% or more and less than 5% ×: Internal short circuit failure rate 5% or more

As is apparent from Table 2, the separators of Examples 1 to 10 are separators for drying a fiber web formed using a wet paper machine from a fiber slurry containing solvent-spun cellulose fibers and synthetic short fibers formed by beating. In the production method, a paper strength enhancer is applied by spraying in a solid content of 0.01 to 1.00 g / m ² on the upper surface when the fiber web is formed on the wire or felt of a wet paper machine. Therefore, the mechanical strength and the paper surface strength were excellent, and excellent results were obtained in winding property and fluff evaluation. Moreover, the electric double layer capacitor provided with the separators of Examples 1 to 10 was excellent in low internal resistance and internal short circuit failure rate.

  From the comparison of Examples 2, 4, 7, and 8, the separators of Examples 7 and 8 in which polyurethane was applied by spraying as a paper strength enhancer showed slightly inferior results in fluff evaluation. From the comparison of Examples 3 and 9, the separator of Example 9 in which the content of the solvent-spun cellulose fiber formed by beating exceeds 95% by mass showed a slightly inferior result in fluff evaluation, and the electric double layer capacitor provided with the separator Slightly higher internal resistance was shown. From the comparison between Examples 6 and 10, the electric double layer capacitor including the separator of Example 10 in which the content of the solvent-spun cellulose fiber formed by beating is less than 10% by mass shows a slightly inferior result in the measurement of the internal short circuit rate. It was.

Compared to the examples, the separator of Comparative Example 1 having a paper strength enhancer content of less than 0.01 g / m ² shows inferior results in fluff and rollability evaluation, and the electric double layer capacitor provided with the separator is high. The internal short circuit rate was shown.

The electric double layer capacitor including the separator of Comparative Example 2 in which the content of the paper strength enhancer exceeds 1.00 g / m ² showed high internal resistance.

  The separator of Comparative Example 3 prepared by internally adding polyacrylamide as a paper strength enhancer to the fiber slurry resulted in inferior fluff and rollability evaluation, and the electric double layer capacitor equipped with the separator showed a high internal short-circuit rate. It was.

  In the separator of Comparative Example 4 produced by spraying carboxymethyl cellulose as a paper strength enhancer onto a wet nonwoven fabric in a dry state, wrinkles were generated, and the electric double layer capacitor provided with the separator showed high internal resistance.

  The separator of Comparative Example 5 containing no synthetic short fiber resulted in inferior fluff and rollability evaluation, and the electric double layer capacitor equipped with the separator showed a high internal short circuit rate.

  Since the separator of Comparative Example 6 containing no beaten solvent-spun cellulose fiber was inferior in compactness, the electric double layer capacitor provided with the separator exhibited a high internal short-circuit rate.

  The present invention relates to a separator for an electrochemical element. The present invention includes lithium batteries, lithium ion batteries, lithium polymer batteries, polyacene batteries, organic radical batteries, electric double layer capacitors, lithium ion capacitors, hybrid capacitors, redox capacitors, aluminum electrolytic capacitors, conductive polymer aluminum solid electrolytic capacitors, etc. In addition, it can be used as a separator for an electrochemical element having a power storage function, a rectifying function, and the like.

Claims (4)

In a method for producing a separator for an electrochemical device, a fiber web formed with a wet paper machine from a fiber slurry containing solvent-spun cellulose fibers and synthetic short fibers formed by beating, on a wire of a wet paper machine or felt A separator for an electrochemical element, wherein a paper strength enhancer is applied by spraying in a solid content of 0.01 to 1.00 g / m ² on the upper surface when a fiber web is formed on the top. Manufacturing method.   The method for producing a separator for an electrochemical element according to claim 1, wherein the paper strength enhancer is at least one selected from the group consisting of carboxymethylcellulose and polyacrylamide resins.   The method for producing a separator for an electrochemical element according to claim 1 or 2, wherein the content of the solvent-spun cellulose fiber formed by beating is 10 to 95% by mass of the whole fiber contained in the separator for an electrochemical element.   The separator for electrochemical elements manufactured by the manufacturing method of the separator for electrochemical elements in any one of Claims 1-3.