JP2018087400A - Nonwoven fabric and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nonwoven fabric excellent in mechanical strength and its manufacturing method by inhibiting a hydrogen bond in a cellulose fiber.SOLUTION: Nonwoven fabric provided in the present invention comprises an aqueous resin in which breaking elongation of a single film is 50% or more and fine cellulose fibers. In the nonwoven fabric, breaking elongation is 3% or more. Preferably, the aqueous resin is at least one selected from an urethane resin, a polyvinyl alcohol resin, and a maleic acid modified polyethylene and the fine cellulose fiber has an I type crystal structure and its fiber diameter is less than 1μ.SELECTED DRAWING: None

Description

  The present invention relates to a nonwoven fabric such as a separator for a lithium ion secondary battery and a method for producing the same.

  Secondary batteries are used in a wide range of mobile electronic devices, electric vehicles, hybrid vehicles, and the like. In particular, lithium ion secondary batteries have a high energy density, and thus are actively developed.

  At present, polyolefin-based microporous membranes that are inexpensive, chemically stable, and have excellent mechanical properties are mainly used as separators for lithium ion secondary batteries. In order to compensate for this, methods using coating of ceramic particles or chemical cross-linking have been studied. However, these methods have a problem that the cost increases because the number of steps for coating on the microporous film increases.

  Therefore, the use of a material having high heat resistance has been studied. In particular, cellulose is attracting attention because it is a material derived from wood that is thermally stable up to about 300 ° C. and can be reproduced.

  Here, the separator using the cellulose fiber becomes a hard and brittle separator due to the infinite number of hydrogen bonds between the fibers due to the hydroxyl groups present on the surface of the cellulose fiber. There was a problem that it was bad and inferior in handleability.

  Then, the separator aiming at reducing the quantity of the hydrogen bond between cellulose fibers and improving mechanical strength by mixing a cellulose fiber and synthetic fibers, such as a polyester fiber, is disclosed (for example, Patent Document 1).

  Moreover, in order to improve the strength between the cellulose fibers, a separator in which the cellulose surface is crosslinked using a carbodiimide group-containing compound or an oxazoline group-containing compound having a terminal isocyanate group as a crosslinking agent is disclosed (for example, Patent Documents). 2). Similarly, there is disclosed a separator having improved strength by crosslinking cellulose fibers using a reactive crosslinking agent produced by an addition reaction between a polyfunctional isocyanate compound and an active hydrogen-containing compound ( For example, see Patent Document 3).

JP-A-2015-176888 JP 2014-198835 A Japanese Patent Laid-Open No. 2006-72309

  However, in the separator described in Patent Document 1, although the amount of hydrogen bonds between cellulose fibers is reduced, a large number of hydrogen bonds remain, so that there is a problem that the separator is damaged at the time of winding in a minute portion. . Furthermore, since the different types of fibers added have a larger fiber diameter than the fine cellulose fibers, there is a problem that the ionic conductivity is lowered.

  In the separators described in Patent Documents 2 and 3, since a reactive cross-linking agent that does not define elongation is used, the hydrogen bonds of cellulose fibers are bonded more firmly due to the cross-linking agent. As a result, there has been a problem that the separator becomes even harder and more brittle.

  Then, this invention is made | formed in view of this point, and provides the nonwoven fabric, such as a separator for lithium ion secondary batteries which is excellent in mechanical strength, and its manufacturing method by suppressing the hydrogen bond in a cellulose fiber. For the purpose.

  In order to achieve the above object, the nonwoven fabric of the present invention is a nonwoven fabric made of a water-based resin having a single film with a breaking elongation of 50% or more and fine cellulose fibers, and has a breaking elongation of 3% or more. Features.

  The nonwoven fabric production method of the present invention is a nonwoven fabric production method having a breaking elongation of 3% or more, and a water-based resin in which a single film has a breaking elongation of 50% or more in a solution containing fine cellulose fibers. At least a step of preparing a water-based resin mixed solution and a step of preparing a porous film by mixing a water-soluble pore-opening agent in the water-based resin mixed solution.

  ADVANTAGE OF THE INVENTION According to this invention, the mechanical strength is high and the nonwoven fabric which can improve handleability can be provided.

It is an absorption spectrum which shows the result of an infrared total reflection absorption measurement.

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiment.

  The nonwoven fabric of the present invention can be used for applications such as filters such as air conditioners and vacuum cleaners, gas adsorption filters, soundproof materials, vibration proof materials, reinforcing materials, non-aqueous electrochemical separators, etc., but has high mechanical strength, Since it is excellent in handleability, it is particularly suitable for a separator for a lithium ion secondary battery. For example, it is suitable for a separator for a lithium ion secondary battery containing fine cellulose fibers (cellulose nanofibers) and an aqueous resin.

  Hereinafter, the lithium ion secondary battery separator will be described as an example of the nonwoven fabric of the present invention.

(Fine cellulose fiber)
In the present embodiment, fine cellulose fibers are used as a material for forming the separator, and cellulose having an I-type crystal structure is used as the fine cellulose fibers from the viewpoint of preventing strength reduction and dissolution of the cellulose fibers. The

  The cellulose used as the raw material for the fine cellulose fiber is not particularly limited, and for example, natural cellulose isolated and purified from biosynthesis of plants, animals, bacteria-producing gels and the like can be used. More specifically, for example, softwood pulp, hardwood pulp, cotton pulp such as cotton linter, non-wood pulp such as straw pulp and bagasse pulp, cellulose isolated from bacterial cellulose and sea squirt, isolated from seaweed And cellulose to be used.

  The fine cellulose fibers preferably have an average fiber diameter of about 3 nm to 300 nm. When the average fiber diameter is 3 nm or less, cellulose cannot maintain the fiber shape in the I-type crystal structure, which is not preferable. Moreover, it is preferable not to contain fibers having a fiber diameter of 1 μm or more as much as possible. Specifically, the proportion of fibers having a fiber diameter of less than 1 μm is preferably 80% by mass or more, and more preferably 95% by mass or more. Furthermore, it is preferable that the ratio of the fiber of 500 nm or less is 80 mass% or more. By reducing the ratio of fibers having a large fiber diameter, it becomes easy to control the thickness, pore diameter, Gurley air permeability, and the like as a separator during film formation.

  The fiber diameter can be measured by observing with a transmission electron microscope or a scanning electron microscope the state of the separator or a cast film of a dilute solution of cellulose fibers and drying it. The fiber diameter is less than 1 μm by comprehensively evaluating the viscosity (E-type or B-type viscometer), tensile strength, and specific surface area of the porous membrane of an aqueous cellulose fiber dispersion of less than 0.1 to 2% by weight Can be obtained (see, for example, International Publication No. 2013/054884).

(Water-based resin)
In the present embodiment, as a material for forming the separator, an aqueous resin having a single film having a breaking elongation of 50% or more is used together with fine cellulose fibers.

  By using such a water-based resin, it becomes possible to cover the surface of the cellulose fiber with the water-based resin and distort the contact point where hydrogen bonding occurs on the surface of the cellulose fiber. Solid bonding due to hydrogen bonding is suppressed, and the mechanical strength (breaking elongation) of the separator is improved. When the breaking elongation of the single film is less than 50%, the nonwoven fabric may have insufficient flexibility when formed into a nonwoven fabric together with fine cellulose fibers.

  In addition, unlike conventional separators, it does not contain synthetic fibers (polyester fibers, etc.) that have a larger fiber diameter than cellulose fibers, which inhibits the movement of lithium ions between electrodes when using lithium ion secondary batteries. Nothing will happen. As a result, good battery performance (cycle characteristics) can be realized.

  The “single film” as used herein refers to a film in a state where an aqueous resin is cast into a container such as a petri dish and the solvent is dried.

  Further, the “aqueous resin” here refers to a resin that is dissolved and dispersed in water as a solvent.

  Further, the “breaking elongation” here refers to a value measured according to JIS K7127.

  Examples of the water-based resin include urethane resin, acrylic resin, phenol resin, polyester resin, epoxy resin, polystyrene resin, polyvinyl alcohol, maleic acid-modified polyethylene, and polyacrylamide resin, but excellent elongation at break in a single film. In view of the above, it is preferable to use at least one of urethane resin, polyvinyl alcohol, and maleic acid-modified polyethylene.

  As the urethane resin, both reactive and non-reactive types can be used, and both reactive and non-reactive types may be used in combination.

  In addition, from the viewpoint of withstand voltage characteristics when using a lithium ion secondary battery, flexibility of the resin, and complexing with fine cellulose fibers, the urethane resin is at least of a polyester skeleton, a polyether skeleton, and a polycarbonate skeleton. Those containing one skeleton are used. More specifically, for example, Superflex series (Daiichi Kogyo Seiyaku Co., Ltd.), Elastron series (Daiichi Kogyo Seiyaku Co., Ltd.), Hydran series (Dic Corporation), Barnock Series (Dic Corporation), Commercial products such as Evaphanol series (manufactured by Nikka Chemical Co., Ltd.), Bascoal series (manufactured by Meisei Chemical Industry Co., Ltd.), and Adeka Bon titer series (manufactured by Adeka Co., Ltd.) can be used.

(Separator for lithium ion secondary battery)
The separator for a lithium ion secondary battery of the present embodiment has a breaking elongation of 3% or more from the viewpoint of improving the handleability (winding property) at the time of manufacturing the secondary battery.

  And in the separator for lithium ion secondary batteries of this embodiment, as mentioned above, since the breaking elongation of a single film contains 50% or more of an aqueous resin, the mechanical strength (breaking elongation) of the separator is high. In addition to being improved, since it has a breaking elongation of 3% or more, the handleability (winding property) at the time of manufacturing the secondary battery is improved. As a result, it becomes possible to prevent the separator from being damaged when the secondary battery is manufactured.

  Moreover, in the separator for lithium ion secondary batteries of this embodiment, it is preferable that content of the water-based resin with respect to the whole fine cellulose fiber is 0.1 mass% or more and 50 mass% or less.

  This is because when the content of the water-based resin is larger than 50% by mass, the pores of the separator may be blocked and the ionic conductivity may be deteriorated. When the content is smaller than 0.1% by mass, the separator This is because there is a case in which the breaking elongation of the material does not improve and the material becomes brittle.

  The thickness of the lithium ion secondary battery separator of the present embodiment is preferably 5 μm or more and 30 μm or less. This is because when the thickness is smaller than 5 μm, the tensile strength becomes weak and it may not be wound when wound, and when it is larger than 30 μm, the volume occupied by the separator increases inside the battery, and the capacity decreases. This is because the inconvenience of becoming may occur.

  Further, the air permeability of the lithium ion secondary battery separator of the present embodiment is preferably 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less. This is because when the air permeability is smaller than 10 seconds / 100 cc, the pore distribution of the separator becomes larger, which may cause inconvenience that inert lithium is likely to be generated, and when the air permeability is larger than 1000 seconds / 100 cc. This is because the ionic conductivity may decrease.

  Here, “air permeability” refers to a value measured according to JIS P8117.

From the viewpoint of strength required for the separator, the tensile breaking strength of the separator is preferably from 200 kgf / cm ² or more, more preferably 250 kgf / cm ² or more, 300 kgf / cm ² or more is more preferable. The tensile strength can be measured according to JIS K7127, similarly to the above-described breaking elongation.

  Next, a method for manufacturing a separator according to this embodiment will be described. The separator manufacturing method of the present embodiment includes a step of adjusting the aqueous resin mixture, a step of adjusting the coating solution, a step of applying the coating solution on the substrate, and a coating solution applied on the substrate. A step of drying, and a step of peeling the coating film from the substrate after drying. Moreover, the separator can be pressed as necessary. This press is not always necessary.

<Aqueous resin mixture preparation process>
First, an aqueous suspension of fine cellulose fibers having a predetermined concentration is prepared.

  Next, a water-based resin mixed solution is prepared by adding an emulsion of a water-based resin (for example, polyurethane resin or the like) in which the breaking elongation of a single film is 50% or more to an aqueous suspension of fine cellulose fibers.

  Then, as described above, since the surface of the cellulose fiber is covered with the water-based resin, it becomes possible to distort the contact where hydrogen bonding occurs on the surface of the cellulose fiber, and the hydrogen bonding between the fibers due to the hydroxyl group present on the surface of the cellulose fiber. Can be suppressed. Therefore, firm bonding due to innumerable hydrogen bonds existing on the surface of the fine cellulose fiber is suppressed, and the mechanical strength (breaking elongation) of the separator is improved.

  At this time, as described above, the emulsion of the aqueous resin is mixed so that the content of the aqueous resin is 0.1% by mass or more and 50% by mass or less with respect to the entire fine cellulose fiber.

  Further, the concentration of fine cellulose fibers in the solution may be adjusted as appropriate depending on the method of film formation. The solvent of the solution is preferably water from the viewpoint of handling and cost, but a solvent having a higher vapor pressure than water can also be added and used.

<Coating solution preparation process>
Next, a water-soluble pore-opening agent is added to the aqueous resin mixture described above to prepare a coating solution. As this water-soluble pore-opening agent, known ones can be used. For example, higher alcohols such as 1,5-pentanediol and 1-methylamino-2,3-propanediol, lactones such as iprosin caprolactone and α-acetyl-γ-butyllactone, diethylene glycol, 1,3- Glycols such as butylene glycol and propylene glycol, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol Monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol Glycol ethers such as dimethyl monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether, glycerin, propylene carbonate, N-methylpyrrolidone and the like can also be used. Of these, triethylene glycol butyl methyl ether is preferred.

  Further, the amount of the water-soluble pore-opening agent added in the solution can be adjusted according to the required characteristics of the membrane, but from the viewpoint of securing the pores necessary as a separator, 100 parts by mass of fine cellulose fibers 5 parts by mass or more is preferable, 100 parts by mass or more is more preferable, 3000 parts by mass or less is preferable, and 1000 parts by mass or less is more preferable.

<Application process>
Next, the prepared coating solution is applied onto the substrate. More specifically, a comma coater, roll coater, reverse roll coater, direct gravure coater, reverse gravure coater, offset gravure coater, roll kiss coater, reverse kiss coater, micro gravure coater, air doctor coater, knife coater, bar coater, The coating can be performed by any method such as a wire bar coater, die coater, dip coater, blade coater, brush coater, curtain coater, die slot coater, cast coater, or a combination of two or more coating methods. The application method may be a batch method or a continuous method.

  The material for forming the substrate is not particularly limited, but is polyester (polyethylene terephthalate, polyethylene naphthalate, polylactic acid, etc.), polyolefin (polyethylene, polypropylene, etc.), cellulose (cellulose, triacetyl cellulose, etc.) , Polyamide (nylon, etc.), acrylic (polyacrylonitrile, etc.), polystyrene, polyimide, polycarbonate, polyvinyl chloride, polyurethane, polyvinyl alcohol, paper, fluorine compound (Teflon (registered trademark), etc. ), Glass, metal, or derivatives thereof.

  Moreover, the shape of a base material is not specifically limited, When it is a film and a sheet | seat, thickness should just be 10 micrometers or more and 1000 micrometers or less.

  In addition, in consideration of the adhesion of the coating liquid and the coating film after drying to the substrate, surface treatment such as fluorine coating, corona treatment, plasma treatment, UV treatment, anchor coating, etc. may be performed on the substrate. Good.

<Drying process>
Next, the non-woven fabric (porous film) is formed by drying the coating solution applied on the substrate. For example, it can be dried using hot air drying, infrared drying, hot plate drying, vacuum drying and the like.

  Moreover, it is preferable to perform a drying process at 50 degreeC or more from a viewpoint of fully reducing the residual amount of a solvent and a water-soluble pore opening agent, and it is more preferable to carry out at 60 degreeC or more. Moreover, it is preferable to carry out at 200 degrees C or less from a viewpoint of preventing deterioration of a fine cellulose fiber, It is more preferable to carry out at 150 degrees C or less, It is further more preferable to carry out at 120 degrees C or less.

  In addition, after evaporating water and a water-soluble pore-opening agent and forming a porous membrane, the obtained porous membrane can be wash | cleaned using an organic solvent etc. The organic solvent is not particularly limited. For example, organic solvents having a relatively high volatilization rate such as toluene, acetone, methyl ethyl ketone, ethyl acetate, n-hexane, propanol or the like may be used alone or in combination of two or more kinds. Can be used in divided times.

  For the purpose of cleaning the remaining pore-opening agent, a solvent having a high affinity with water such as ethanol and methanol is preferable. However, the moisture in the coated base material is transferred to the solvent, or moisture in the air is absorbed. In order to affect the physical properties of the cellulose microporous membrane and the sheet shape, it is preferable to use the cellulose microporous membrane in a state where the water content is controlled. Highly hydrophobic solvents such as n-hexane and toluene can be suitably used because they are poor in the cleaning effect of the hydrophilic pore-opening agent but hardly absorb moisture.

  For the above reasons, a method of replacing the solvent while repeating washing and changing the type of the solvent so as to gradually increase the hydrophobicity is preferable. For example, washing can be performed in the order of acetone, toluene, and n-hexane.

  After washing, the porous membrane can be obtained by peeling the nonwoven fabric from the substrate.

  And the separator for lithium ion secondary batteries of this invention can be obtained by pressing the obtained porous membrane as needed.

  Hereinafter, the present invention will be described based on examples. In addition, this invention is not limited to these Examples, These Examples can be changed and changed based on the meaning of this invention, and they are excluded from the scope of the present invention. is not.

Example 1
(Preparation of separator)
An aqueous suspension of 2.5% by mass of fine cellulose fibers (number average fiber diameter: 50 nm) and an aqueous polyurethane emulsion of 0.5% by mass as a water-based resin (trade name: Superflex, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 150 HS, non-reactive type having a polyether skeleton, elongation at break of single film: 480%) was added and stirred.

  Next, pure water and triethylene glycol butyl methyl ether (manufactured by Toho Chemical Co., Ltd.) as a water-soluble pore-opening agent were added to this water suspension and stirred to prepare a coating solution.

  In addition, with respect to 100 mass parts of fine cellulose fibers, it added so that water-based polyurethane might be 10 mass parts and a water-soluble pore opening agent might be 250 mass parts, and the final solid content was 0.5 mass%.

  Next, the obtained coating solution was applied to a petri dish, water was dried in an oven at 85 ° C., thoroughly washed with toluene, and peeled from the petri dish to obtain a porous film. And this separator was obtained by pressing this porous membrane at 50 MPa.

<Measurement of thickness>
The thickness of the produced separator was measured using a micrometer (trade name: PG-02J, manufactured by Teclock Corporation). The results are shown in Table 1.

<Measurement of air permeability>
The air permeability of the produced separator was measured. More specifically, using a Gurley air permeability meter (Gurley type densometer, manufactured by Toyo Seiki Co., Ltd.) defined in JIS P8117, about 100 mL of a test piece that is closely fixed to a circular hole having an outer diameter of 28.6 mm The time for the air to pass was measured. The results are shown in Table 1.

<Measurement of tensile strength at break and elongation at break>
Next, based on JIS K-7127, the tensile breaking strength and elongation at break of the produced separator were measured. More specifically, a strip-shaped test piece having a width of 15 mm and a length of 50 mm is produced from the produced separator, and a tensile test apparatus is provided so that the distance between the chucks is 10 mm at both ends in the length direction of the test piece. Then, the tensile strength was measured under the conditions of a temperature of 23 ° C. and a tensile strength of 5 mm / min, and the tensile strength at the time of fracture was defined as tensile fracture strength [kgf / cm ² ]. Moreover, the percentage value when the displacement at the time of breaking was divided by the length of 30 mm excluding the chuck portion was taken as the breaking elongation [%]. The results are shown in Table 1.

<Measurement of infrared absorption spectrum>
Next, an infrared total reflection absorption (ATR) spectrum was measured for the produced separator. For the measurement, Nicolet is10 manufactured by Thermo Scientific was used. Diamond was used for the prism. Absorption intensity was normalized by a peak near 1053 cm ⁻¹ . Then, in the obtained spectrum, the presence or absence of a peak attributed to a urethane bond (a peak near 1700 cm ⁻¹ ) was confirmed. The above results are shown in FIG.

<Measurement of capacity retention>
Next, a test battery was produced using the separator of this example. First, the positive electrode of the test battery was lithium cobaltate, and the negative electrode was artificial graphite. It was formed by charging and discharging (4.35-2.75 V) at a rate of 10 hours in an environment of 25 ° C. Thereafter, the battery was charged for the second time to 4.35 V at a 5-hour rate, and then discharged to 2.75 V to confirm the initial capacity. In addition, the battery is charged for the third time up to 4.35V at a 5-hour rate, discharged from the incubator set at 60 ° C in the charged state, cooled to 25 ° C, and discharged to 2.75V at the 5-hour rate. And the capacity was measured. The ratio of the obtained value to the initial capacity was defined as the capacity maintenance rate [%]. The results are shown in Table 1.

(Example 2)
As an aqueous resin, an emulsion of 0.5% by mass of an aqueous polyurethane (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Superflex E-4800, non-reactive type having a polyether skeleton and a polyester skeleton, elongation at break of a single film: Except for using 720%), a separator was prepared in the same manner as in Example 1 described above, and the thickness was measured, the air permeability was measured, the tensile strength at break, and the elongation at break were measured. The results are shown in Table 1.

(Example 3)
As an aqueous resin, an emulsion of 0.5% by mass of an aqueous polyurethane (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Elastron E-37, reactive type having a polyester skeleton, elongation at break of single film: 500%) is used. The separator was prepared in the same manner as in Example 1 except that the coating solution was applied to a petri dish and water was dried in an oven at 85 ° C., followed by heat treatment at 150 ° C. for 1 hour. The thickness, the air permeability, the tensile strength at break, and the elongation at break were measured. The results are shown in Table 1.

Example 4
Except for using 10% by weight of polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, degree of polymerization 3500, degree of saponification 86 mol%, breaking elongation of single film: 240%) instead of water-based polyurethane as the water-based resin. A separator was prepared in the same manner as in Example 1, and the thickness, the air permeability, the tensile strength at break, and the elongation at break were measured. The results are shown in Table 2.

(Example 5)
The above-mentioned except that an emulsion of 10% by mass of maleic acid-modified polyethylene (manufactured by Toyobo Co., Ltd., trade name: Hardlane AP-03, single film breaking elongation: 400%) was used as the aqueous resin instead of the aqueous polyurethane. A separator was prepared in the same manner as in Example 1, and the thickness was measured, the air permeability was measured, the tensile strength at break, and the elongation at break were measured. The results are shown in Table 2. In Table 2, the breaking elongation on the second line is the breaking elongation of the single film, and the breaking elongation on the second line from the bottom is the breaking elongation of the separator.

(Comparative Example 1)
A separator was prepared in the same manner as in Example 1 except that no water-based polyurethane was used. The thickness was measured, the air permeability was measured, the tensile break strength, the break elongation was measured, and the capacity retention rate was measured. Measurements were made. The results are shown in Table 1.

(Comparative Example 2)
As a water-based resin, an emulsion of 0.5% by weight of a water-based polyurethane (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Elastron H3-DF, breaking elongation of non-reactive single film having a polyester skeleton: 40%) was used. Except for this, a separator was prepared in the same manner as in Example 1 above, and the thickness was measured, the air permeability was measured, the tensile strength at break, and the elongation at break were measured. The results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 3 using a water-based polyurethane having a single film having a breaking elongation of 50% or more, Comparative Example 1 in which a water-based polyurethane was not used and the breaking elongation of the single film were Compared to Comparative Example 2 using less than 50% aqueous polyurethane, the elongation at break is 3% or more, indicating that the mechanical strength is excellent. As shown in Table 2, the elongation at break was also the same as in Examples 1 to 3 in Example 4 using polyvinyl alcohol with a single film having a breaking elongation of 50% or more, and Example 5 using maleic acid-modified polyethylene. Since the degree exceeds 3%, the mechanical strength is excellent.

  Moreover, in the lithium ion secondary battery using the separator of Example 1, compared with the comparative example 1, it turns out that a capacity | capacitance maintenance factor is high and it is excellent in the battery characteristic.

In Examples 1 to 3 containing an aqueous polyurethane in the ATR spectrum shown in FIG. 1, a peak attributed to a urethane bond (a peak near 1700 cm ⁻¹ ) is recognized, and the aqueous polyurethane is present in the separator. You can see that

  Examples of utilization of the present invention include nonwoven fabrics such as separators for lithium ion secondary batteries and methods for producing the same.

Claims (10)

There is a non-woven fabric composed of a water-based resin having a breaking elongation of 50% or more of a single film and fine cellulose fibers,
A nonwoven fabric characterized by having a breaking elongation of 3% or more.   The nonwoven fabric according to claim 1, wherein the water-based resin is at least one of urethane resin, polyvinyl alcohol, and maleic acid-modified polyethylene.   The nonwoven fabric according to claim 1 or 2, wherein the fine cellulose fiber has an I-type crystal structure.   The non-woven fabric according to any one of claims 1 to 3, wherein the fine cellulose fiber has a fiber diameter of 80% by weight or more in a fiber diameter of less than 1 µm.   It is a separator for lithium ion secondary batteries, The nonwoven fabric of any one of Claims 1-4 characterized by the above-mentioned. A method for producing a nonwoven fabric having a breaking elongation of 3% or more,
A step of preparing a water-based resin mixed solution by mixing a water-based resin in which the breaking elongation of a single film is 50% or more with a solution containing fine cellulose fibers;
The manufacturing method of the nonwoven fabric characterized by including the process of mixing a water-soluble pore-opening agent with the said water-system resin liquid mixture, and producing a porous membrane.   The said aqueous resin is at least 1 sort (s) among urethane resin, polyvinyl alcohol, and maleic acid modified polyethylene, The manufacturing method of the nonwoven fabric of Claim 6 characterized by the above-mentioned.   The method for producing a nonwoven fabric according to claim 6 or 7, wherein the fine cellulose fibers have an I-type crystal structure.   The method for producing a nonwoven fabric according to any one of claims 6 to 8, wherein the fine cellulose fiber has a fiber diameter of 80% by weight or more in a fiber diameter of less than 1 µm.   It is a separator for lithium ion secondary batteries, The manufacturing method of the nonwoven fabric of any one of Claims 6-9 characterized by the above-mentioned.

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