WO2021230037A1 - Separator for secondary batteries - Google Patents

Abstract

The present invention provides a separator for secondary batteries, said separator exhibiting excellent permeability.　A separator for secondary batteries according to the present disclosure comprises a porous base material layer (A) and a heat-resistant layer (B) which is formed of a nonwoven fabric that contains a binder and microfibers having a melting point or decomposition temperature of 200°C or higher; and this separator satisfies at least one of the formulae (a) and (b) described below.　(a): (Y – X)/Z < 12 (b): (Y – X) < 60 In the formulae, X represents the air permeability (sec/100 mL) of the porous base material (A); Y represents the air permeability (sec/100 mL) of the separator; and Z represents the thickness (μm) of the heat-resistant layer (B).

Description

Separator for secondary battery

The present disclosure relates to a separator for a secondary battery, a method for manufacturing a separator for a secondary battery, and a secondary battery provided with a separator for a secondary battery. This application claims the priority of Japanese Patent Application No. 2020-084306 filed in Japan on May 13, 2020, the contents of which are incorporated herein by reference.

In a power storage device such as a lithium ion secondary battery, a separator that insulates a positive electrode and a negative electrode while holding an electrolytic solution is used. Therefore, the separator is required to ensure electrical insulation. In addition, since the battery functions when lithium ions move through this separator, it is also required to ensure transparency.

Furthermore, the lithium-ion secondary battery has a "shutdown function" that stops the flow of lithium ions between the electrodes and safely stops the function of the battery when the inside of the battery becomes abnormally high temperature. Desired. Further, when the temperature inside the battery rises further even after the flow of lithium ions is stopped, if the separator shrinks (shrinks) or melts (melts down), the electrodes may be short-circuited or thermal runaway may occur. Therefore, the separator is required to have heat resistance that can maintain its shape even in an abnormally high temperature environment.

In recent years, lithium-ion secondary batteries have been considered to be installed in hybrid vehicles and electric vehicles in addition to information-related equipment such as smartphones and laptop computers due to their characteristics of light weight, high voltage, and large capacity. High heat resistant separators are required to cope with high energy density.

Patent Document 1 describes that a separator for a secondary battery containing a porous base material and a heat-resistant layer made of a non-woven fabric containing specific fine fibers and a binder has excellent heat resistance.

However, in recent years, there has been an increasing demand for higher performance secondary batteries, and separators are required to have even higher electrolyte permeability while ensuring electrical insulation.

Japanese Unexamined Patent Publication No. 2019-149361

Therefore, an object of the present disclosure is to provide a separator for a secondary battery having excellent permeability.
Another object of the present disclosure is to provide a method for manufacturing a separator for a secondary battery having excellent permeability.
Another object of the present disclosure is to provide a secondary battery provided with a separator for a secondary battery having excellent permeability.

As a result of diligent studies to solve the above problems, the inventors of the present disclosure have formed a heat-resistant layer (B) made of a non-woven fabric containing fine fibers having a melting point or decomposition temperature of 200 ° C. or higher and a binder into a porous substrate layer. It has been found that the specific structure obtained by laminating on the surface of (A) has excellent permeability, and that such a structure can be efficiently produced by a specific method. This disclosure has been completed based on these findings.

That is, the present disclosure includes a porous base material layer (A) and a heat-resistant layer (B) made of a non-woven fabric containing microfibers having a melting point or a decomposition temperature of 200 ° C. or higher and a binder, and the following formula (a). , (B) are satisfied, and a separator for a secondary battery is provided.
(YX) / Z <12 (a)
(YX) <60 (b)
X: Air permeability of the porous substrate (A) (sec / 100 mL)
Y: Air permeability of separator (sec / 100mL)
Z: Thickness (μm) of heat-resistant layer (B)

The present disclosure also provides a separator for a secondary battery in which the microfibers are aramid fibers.

The present disclosure also provides a separator for a secondary battery in which the above binder is a water-based binder.

In the present disclosure, the binder is also selected from a polysaccharide derivative (1), a compound having a structural unit represented by the following formula (2), and a compound having a structural unit represented by the following formula (3). Provided is a separator for a secondary battery, which is at least one kind.

(In the formula, R represents a hydroxyl group, a carboxyl group, a phenyl group, an N-substituted or unsubstituted carbamoyl group, or a 2-oxo-1-pyrrolidinyl group.)

(In the formula, n represents an integer of 2 or more, and L represents an ether bond or a (-NH-) group.)

The present disclosure also provides a separator for a secondary battery in which the binder is at least one selected from cellulose, starch, glycogen, and derivatives thereof.

The present disclosure also provides a separator for a secondary battery having an average thickness of 0.01 to 10 μm and an average length of 0.01 to 2 mm of the fine fibers.

The present disclosure also provides a separator for a secondary battery in which the thickness of the heat-resistant layer (B) is 0.5 to 20 μm and the total thickness of the separator for the secondary battery is 10 to 50 μm.

The present disclosure also provides a separator for a secondary battery in which the basis weight of the heat-resistant layer (B) is 10 g / m ^{2 or less.}

In the present disclosure, a release film is attached to one surface of the porous substrate layer (A), and a dispersion containing fine fibers and a binder is contained on the other surface of the porous substrate layer (A). Manufacture of a separator for a secondary battery, wherein a liquid is applied, the dispersion medium in the dispersion is volatilized, and then the release film is peeled off from the porous substrate layer (A) to obtain a separator for a secondary battery. Provide a method.

In the present disclosure, the surface of the porous base material layer (A) is prepared to a Dine value of 40 to 45 mN / m by surface treatment, and a dispersion liquid containing fine fibers and a binder is applied to the surface, and the dispersion liquid is applied. Provided is a method for manufacturing a separator for a secondary battery, which obtains a separator for a secondary battery by volatilizing the dispersion medium inside.

In the present disclosure, a dispersion liquid containing microfibers and a binder is applied to one surface of the porous substrate layer (A), and low polarity or low polarity or from the other surface of the porous substrate layer (A). Provided is a method for producing a separator for a secondary battery, which obtains a separator for a secondary battery by infiltrating a non-polar organic solvent and then volatilizing the dispersion medium in the dispersion liquid.

The present disclosure also provides a secondary battery provided with the above-mentioned separator for a secondary battery.

The present disclosure also describes a method for manufacturing a secondary battery, which comprises obtaining a separator for a secondary battery by the above method for manufacturing a separator for a secondary battery and manufacturing a secondary battery using the obtained separator for a secondary battery. offer.

The separator for a secondary battery disclosed in the present disclosure has excellent transparency. Therefore, the secondary battery provided with the separator for the secondary battery of the present disclosure can be suitably used for information-related devices such as smartphones and notebook computers, hybrid vehicles, electric vehicles, and the like. Further, according to the manufacturing method of the present disclosure, it becomes possible to efficiently manufacture a separator for a secondary battery having excellent permeability.

[Separator for secondary battery]
The separator for a secondary battery of the present disclosure has a porous base material layer (A) and a heat-resistant layer (B) made of a non-woven fabric containing fine fibers and a binder having a melting point or a decomposition temperature of 200 ° C. or higher.

Since the separator for a secondary battery of the present disclosure satisfies at least one of the following formulas (a) and (b), it is excellent in transparency.
(YX) / Z <12 (a)
(YX) <60 (b)
X: Air permeability of the porous substrate (A) (sec / 100 mL)
Y: Air permeability of separator (sec / 100mL)
Z: Thickness (μm) of heat-resistant layer (B)

The separator for a secondary battery of the present disclosure has excellent permeability because the voids of the porous base material layer (A) are suppressed from being blocked when the heat-resistant layer (B) is formed. The above formula is used in relation to the air permeability of the porous substrate (A) before the heat-resistant layer (B) is formed, the air permeability of the separator after the heat-resistant layer (B) is formed, and the thickness of the heat-resistant layer (B). It satisfies at least one of (a) and (b).

The value of (YX) / Z in (a) above is less than 12, preferably 11 or less, more preferably 10 or less, and the lower limit is usually 0.

The value according to (YX) in (b) above is less than 60, preferably 50 or less, more preferably 40 or less, and the lower limit is usually 0.

The air permeability of the separator for a secondary battery of the present disclosure is, for example, 100 to 650 sec / 100 mL, preferably 100 to 450 sec / 100 mL, particularly preferably 100 to 400 sec / 100 mL, and most preferably 100 to 350 sec / 100 mL. .. When the air permeability is within the above range, it is possible to improve the permeability, that is, the permeability of the electrolytic solution, while maintaining the insulating property of the electrode well. The smaller the value of air permeability, the better the transparency.

Further, the separator for a secondary battery of the present disclosure is very lightweight because the heat-resistant layer (B) is formed of a non-woven fabric. Therefore, the weight of the secondary battery provided with the separator for the secondary battery of the present disclosure can be reduced, and the weight of the electric vehicle or the like using the secondary battery can also be significantly reduced.

Since the separator for a secondary battery of the present disclosure can exhibit sufficient heat resistance even if the heat-resistant layer (B) is thin, the separator for a secondary battery can be thinned, and its total thickness is It is preferably 10 to 50 μm, more preferably 12 to 30 μm. When the total thickness is within the above range, the separator for a secondary battery of the present disclosure can increase the filling density of the battery while maintaining the insulating property, and thus can contribute to the miniaturization of the secondary battery. Become.

<Porous substrate layer (A)>
The porous substrate layer (A) has voids, and the size of the voids is, for example, 0.01 to 1 μm, preferably 0.02 to 0.06 μm. If the size of the void exceeds the above range, the insulating property tends to decrease and a short circuit tends to occur easily. On the other hand, when the size of the void is less than the above range, the electric resistance tends to increase.

The porosity of the porous base material layer (A) is preferably, for example, 20 to 70% by volume, and particularly preferably 30 to 60% by volume. If the porosity exceeds the above range, the strength tends to be insufficient. On the other hand, when the porosity is lower than the above range, the permeability of lithium ions tends to deteriorate and the electrical resistance tends to increase.

The air permeability of the porous substrate layer (A) is, for example, 100 to 600 sec / 100 mL, preferably 100 to 400 sec / 100 mL, and particularly preferably 100 to 350 sec / 100 mL. When the air permeability exceeds the above range, the permeability of lithium ions tends to deteriorate and the electrical resistance tends to increase. On the other hand, when the air permeability is lower than the above range, the strength tends to be insufficient.

It is preferable that the porous base material layer (A) is insoluble in an electrolytic solution and has a function of softening in a high temperature environment to close voids, that is, a shutdown function. Therefore, a thermoplastic polymer is preferable as the material of the porous base material layer (A). Examples of the thermoplastic polymer include polyolefins such as polyethylene and polypropylene; polyester resins such as polyethylene terephthalate; and aliphatic polyamides such as 2,6-nylon. Then, it is preferable to appropriately select and use the thermoplastic polymer according to the desired shutdown temperature. For example, when the shutdown temperature is set to 150 ° C., it is preferable to use a thermoplastic polymer having a melting point or a softening temperature of 140 to 150 ° C.

The thickness of the porous base material layer (A) is, for example, 5 to 40 μm, preferably 10 to 25 μm. If the thickness exceeds the above range, the electric resistance of the battery tends to increase and the volume capacity tends to decrease. On the other hand, when the thickness is lower than the above range, the strength tends to be insufficient.

The porous base material layer (A) is made porous by, for example, heating and melting the material of the porous base material (for example, polyolefin) to form an extruded film, and stretching the obtained coating film. It can be manufactured by a method or the like.

Further, the surface of the porous substrate layer (A) is ozone-treated, roughened, easily adhered, antistatic, sandblasted (sandmatted), corona discharge treated, plasma treated, and chemically etched. The surface treatment can be performed by one or more methods selected from water mat treatment, flame treatment, acid treatment, alkali treatment, ultraviolet irradiation treatment, silane coupling agent treatment and the like.

For example, the surface of the porous substrate layer (A) is surface-treated by a method selected from ozone treatment, corona discharge treatment, plasma treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment, and then surface treatment is performed. When the silane coupling agent treatment is applied, the effect of improving the adhesion between the porous substrate layer (A) and the heat-resistant layer (B) can be obtained as compared with the case where the silane coupling agent treatment is applied alone.

In the present disclosure, it is particularly preferable to impart a polar group (for example, a hydroxyl group, a carbonyl group, a carboxyl group, etc.) to the surface of the porous substrate layer (A) such as a corona discharge treatment and a plasma treatment.

<Heat-resistant layer (B)>
The heat-resistant layer (B) is made of a non-woven fabric containing fine fibers having a melting point or decomposition temperature of 200 ° C. or higher and a binder.

The heat-resistant layer (B) can be formed by applying a dispersion liquid containing at least fine fibers and binder to at least one surface of the porous substrate layer (A) and volatilizing the dispersion medium.

The porosity of the heat-resistant layer (B) is preferably 30 to 60% by volume, more preferably 35 to 55% by volume. If the porosity exceeds the above range, heat resistance (for example, shape retention in a high temperature environment) tends to be insufficient. On the other hand, when the porosity is lower than the above range, the permeability of lithium ions tends to deteriorate and the electrical resistance tends to increase.

The air permeability of the heat-resistant layer (B) is, for example, 1 to 500 sec / 100 mL, preferably 1 to 300 sec / 100 mL, particularly preferably 1 to 100 sec / 100 mL, and most preferably 1 to 70 sec / 100 mL. When the air permeability exceeds the above range, the permeability of lithium ions tends to deteriorate and the electrical resistance tends to increase. On the other hand, when the air permeability is lower than the above range, the heat resistance (for example, the shape retention in a high temperature environment) tends to be insufficient.

The thickness of the heat-resistant layer (B) is, for example, 0.5 to 20 μm, and the lower limit is preferably 1 μm because it is particularly excellent in heat resistance (for example, shrinkage suppressing effect and shape retention in a high temperature environment). It is particularly preferably 2 μm and most preferably 3 μm. Further, the upper limit is preferably 15 μm, more preferably 12 μm, particularly preferably 10 μm, and most preferably 8 μm in that the filling density of the electrodes can be improved and the secondary battery can be further miniaturized. Particularly preferably, it is 5 μm.

The heat-resistant layer (B) is extremely lightweight and has a basis weight of, for example, 10 g / m ² or less, and is preferably 9 g / m ² or less, more preferably 7 g / m ^{2 in terms of contributing to weight reduction of the battery.} Below, it is particularly preferably 6 g / m ² or less, most preferably 5 g / m ² or less, and particularly preferably less than ^{2.5 g / m 2.} The lower limit of the basis weight is, for example, 0.3 g / m ² , and 0.5 g / m ² is preferable, and 0.8 g / m ² is particularly preferable, and 0.8 g / m 2 is particularly preferable. It is 1 g / m ² . The basis weight of the heat-resistant layer (B) can be measured according to JIS P8124.

The content ratio of the fine fibers and the binder in the dispersion liquid is, for example, 1 to 20 parts by weight of the binder with respect to 10 parts by weight of the fine fibers.

The non-volatile content concentration (that is, the total content of the fine fibers and the binder) in the dispersion liquid can be appropriately adjusted according to the thickness of the heat-resistant layer (B) to be formed, for example, 0.5 to 10 weight. %, Preferably 0.7 to 3% by weight.

The dispersion may contain other components (for example, a dispersant, a surfactant, etc.) in addition to the fine fibers, the binder, and the dispersion medium, if necessary. The proportion of the total content of the fine fibers, the binder, and the dispersion medium is, for example, 50% by weight or more, preferably 60% by weight or more, particularly preferably 70% by weight or more, most preferably 80% by weight or more, and particularly preferably 90% by weight. It is more than% by weight. Excessive content of other components tends to make it difficult to obtain the effects of the present application.

In addition, it is preferable to use water as the dispersion medium for the dispersion liquid because it has a small environmental load and is excellent in safety. The dispersion medium may contain an organic solvent in addition to water, but the content of the organic solvent is preferably 30% by weight or less of the total amount of the dispersion medium (= total amount of volatile components) contained in the dispersion liquid. It is particularly preferably 10% by weight or less, most preferably 5% by weight or less, and particularly preferably 2% by weight or less. The content of the organic solvent is preferably, for example, 30% by weight or less, particularly preferably 10% by weight or less, most preferably 5% by weight or less, and particularly preferably 2% by weight or less, based on the total amount of the dispersion liquid.

(Fine fiber)
The melting point or decomposition temperature of the fine fibers, that is, the melting point or the decomposition temperature when there is no melting point, is 200 ° C. or higher, preferably 250 ° C. or higher, and particularly preferably 300 ° C. or higher. The upper limit of the melting point or decomposition temperature of the fine fibers is, for example, 500 ° C.

The average thickness (average diameter D) of the fine fibers is not particularly limited, but is, for example, 0.01 to 10 μm, and has more excellent heat resistance (for example, shape retention in a high temperature environment). Even if the thickness is thinner, a heat-resistant layer having sufficient heat resistance can be formed, which contributes to the thinning of the separator (or the miniaturization of the secondary battery), and the average thickness (average). The upper limit of the diameter D) is preferably 5 μm, particularly preferably 1 μm, and most preferably 0.5 μm. The lower limit of the average thickness (average diameter D) is preferably 0.03 μm, particularly preferably 0.05 μm. For the average thickness of the fine fibers, an electron microscope image was taken for a sufficient number (for example, 100 or more) of fine fibers using an electron microscope (SEM, TEM), and the thickness (diameter) of these fine fibers was taken. ) Is measured and arithmetically averaged.

The average length (average length L) of the fine fibers is not particularly limited, but is, for example, 0.01 to 1 mm, and has more excellent heat resistance (for example, shape retention in a high temperature environment). , Even if it is thinner, it is possible to form a heat-resistant layer with sufficient heat resistance, which contributes to the thinning of the separator (or to the miniaturization of the secondary battery), and the average length (average). The upper limit of the length L) is more preferably 0.8 mm, particularly preferably 0.5 mm, and most preferably 0.4 mm. Further, the lower limit of the average length (average length L) is more preferably 0.03 mm, and particularly preferably 0.07 mm. The average length of the fine fibers is measured by taking an electron microscope image of a sufficient number (for example, 100 or more) of fine fibers using an electron microscope (SEM, TEM) and measuring the length of these fine fibers. However, it is calculated by arithmetic averaging. The length of the microfibers should be measured in a linearly stretched state, but in reality, many of them are bent, so the projected diameter and projection of the microfibers from the electron microscope image using an image analyzer. The area shall be calculated, and it shall be calculated from the following formula assuming a cylindrical body.
Length = projected area / projected diameter

The average aspect ratio (average length / average thickness) of the fine fibers is not particularly limited, but is, for example, 10 to 2000, and among them, more excellent heat resistance (for example, shape retention in a high temperature environment) is obtained. Even if it has a thinner thickness, it can form a heat-resistant layer with sufficient heat resistance, which contributes to the thinning of the separator (or to the miniaturization of the secondary battery), and has an average aspect ratio. The upper limit of is more preferably 1500, and particularly preferably 1000. Further, the lower limit of the average aspect ratio is more preferably 50, particularly preferably 100, most preferably 500, and particularly preferably 800.

Examples of the fine fibers include cellulose fibers, aramid fibers, polyphenylene sulfide fibers, polyimide fibers, fluorine fibers, glass fibers, carbon fibers, polyparaphenylene benzoxazole fibers, polyether ether ketone fibers, liquid crystal polymer fibers and the like. .. These can be used alone or in combination of two or more.

Among the fine fibers, fibers having excellent heat resistance are preferable, and in particular, the 5% weight loss temperature (T _d5 ) measured at a heating rate of 10 ° C./min (in nitrogen) is 200 ° C. or higher (for example, 200). It is preferably a fiber having a temperature of about 1000 ° C.), more preferably 300 ° C. or higher, still more preferably 400 ° C. or higher, and particularly preferably 450 ° C. or higher. The 5% weight loss temperature can be measured by, for example, TG / DTA (differential thermal / thermogravimetric simultaneous measurement).

Among the above-mentioned fine fibers, aramid fibers are preferable in that they have excellent heat resistance and can be easily made into fine fibers. The aramid fiber is a fiber composed of a polymer having a structure in which two or more aromatic rings are bonded via an amide bond (that is, a total aromatic polyamide), and the total aromatic polyamide includes a meta type and a para type. Is done. Examples of the total aromatic polyamide include a polymer having a structural unit represented by the following formula (a).

In the above formula, Ar ¹ and Ar ² indicate the same or different aromatic rings, or groups in which two or more aromatic rings are bonded via a single bond or a linking group. Examples of the aromatic ring include an aromatic hydrocarbon ring having 6 to 10 carbon atoms such as a benzene ring and a naphthalene ring. The linking group includes, for example, a divalent hydrocarbon group (for example, a linear or branched alkylene group having 1 to 18 carbon atoms and a divalent alicyclic hydrocarbon having 3 to 18 carbon atoms. Groups, etc.), carbonyl groups (-CO-), ether bonds (-O-), ester bonds (-COO-), -NH-, -SO _2-, and the like. Further, the aromatic ring has various substituents [for example, halogen atom, alkyl group (for example, C _1-4 alkyl group), oxo group, hydroxyl group, substituted oxy group (for example, C _1-4 alkoxy group, C _{1). -4} acyloxy group, etc.), carboxyl group, substituted oxycarbonyl group (eg, C _1-4 alkoxycarbonyl group), cyano group, nitro group, substituted or unsubstituted amino group (eg, mono or di-C _1-4 alkylamino). Group), sulfo group, etc.] may be possessed. Further, the aromatic ring may be condensed with a heterocyclic ring having an aromatic or non-aromatic attribute.

The above-mentioned aramid fiber can be produced, for example, by reacting a halide of at least one aromatic dicarboxylic acid with at least one aromatic diamine (for example, solution polymerization, surface polymerization, etc.).

Examples of the aromatic dicarboxylic acid include isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 3,3'-biphenyldicarboxylic acid. Examples thereof include 4,4'-diphenyl ether dicarboxylic acid.

Examples of the aromatic diamine include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminobiphenyl, 2,4-diaminodiphenylamine, 4,4'-diaminobenzophenone, and 4,4'-diaminodiphenyl ether. Examples thereof include 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylamine, 4,4'-diaminodiphenylsulfone, 2,4-diaminotoluene, 2,6-naphthalenediamine, 1,5-naphthalenediamine and the like.

The above-mentioned aramid fiber can be produced by spinning the above-mentioned all-aromatic polyamide into a fibrous form by a well-known and conventional method (for example, through steps such as spinning, washing, and drying). Further, after being spun into a fibrous form, a crushing treatment or the like can be performed as needed. In the present disclosure, a heat-resistant layer having sufficient heat resistance (for example, shape retention in a high temperature environment) can be formed even if the thickness is thinner, which further contributes to the thinning of the separator (or is secondary). In terms of contributing to the miniaturization of the battery), it is preferable to apply a strong mechanical shearing force to the microfibril with an ultra-high pressure homogenizer or the like.

As the aramid fiber, for example, a commercially available product such as the fine fibrous aramid "Tiara" (manufactured by Daisel Finechem Co., Ltd.) may be used.

(Binder)
By adding the binder in the present disclosure to the dispersion liquid, the binder exerts an effect of imparting an appropriate viscosity to improve coatability, and further imparts adhesiveness to impart the fine fibers to the porous base material layer. (A) is a compound that exerts an action of adhering to the surface.

It is not essential to use a binder having excellent heat resistance in terms of developing the heat resistance of the heat-resistant layer (B), but it is preferable, and the melting point or decomposition temperature of the binder is, for example, 160 ° C. or higher (preferably 180 ° C. or higher). It is particularly preferable to use a binder having a temperature of 200 ° C. or higher. The upper limit of the melting point or decomposition temperature of the binder is, for example, 400 ° C.

As the binder, the viscosity of the 1 wt% aqueous solution (at 25 ° C. and 60 rpm) is preferably, for example, 100 to 5000 mPa · s, particularly preferably 500 to 3000 mPa · s, and most preferably 1000 to 2000 mPa · s. Is.

Examples of the binder include non-aqueous binders such as fluorine-based binders (for example, polyvinylidene fluoride, etc.), polyester-based binders, epoxy-based binders, acrylic-based binders, vinyl ether-based binders, and water-based binders. In the present disclosure, it is preferable to use a water-based binder because it has a small environmental load and is excellent in safety.

Examples of the aqueous binder include a polysaccharide derivative (1), a compound having a structural unit represented by the following formula (2), a compound having a structural unit represented by the following formula (3), and the like. These can be used alone or in combination of two or more.

(In the formula, R represents a hydroxyl group, a carboxyl group, a phenyl group, an N-substituted or unsubstituted carbamoyl group, or a 2-oxo-1-pyrrolidinyl group.)

(In the formula, n represents an integer of 2 or more, and L represents an ether bond or a (-NH-) group.)

As the N- substituted carbamoyl _{group, -CONHCH (CH 3) 2,} -CON (CH 3) such as ₂ groups include N-C _1-4 alkyl-substituted carbamoyl group.

The above carboxyl group may form a salt with an alkali metal.

The above n is an integer of 2 or more, for example, an integer of 2 to 5, preferably an integer of 2 to 3. _{Therefore, the [C n} H _2n ] group in the formula (3) is an alkylene group having 2 or more carbon atoms, and examples thereof include a dimethylene group, a methylmethylene group, a dimethylmethylene group, and a trimethylene group.

The compound having the structural unit represented by the above formula (2) and the compound having the structural unit represented by the following formula (3) are each represented by the structural unit represented by the formula (2) or the formula (3). It may have a structural unit other than the represented structural unit.

Examples of the compound having a structural unit represented by the above formula (2) include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), and butadiene rubber (BR). Diene-type rubbers such as; acrylic polymers such as polyacrylic acid, sodium polyacrylate, acrylic acid / maleic acid copolymer / sodium salt, acrylic acid / sulfonic acid copolymer / sodium salt; polyacrylamide, poly-N. -Acrylamide-based polymers such as isopropylacrylamide, poly-N, N-dimethylacrylamide; polyvinylpyrrolidone and the like can be mentioned.

Examples of the compound having a structural unit represented by the above formula (3) include polyalkylene glycols such as polyethylene glycol and polypropylene glycol; polyethyleneimine and the like.

The polysaccharide derivative (1) is a compound obtained by polymerizing two or more monosaccharides by glycosidic bonds. In the present disclosure, among them, a compound in which glucose (for example, α-glucose or β-glucose) is polymerized by a glycosidic bond, or a derivative thereof is preferable, and in particular, cellulose, starch, glycogen, or a derivative thereof is used. At least one selected is preferred.

As the polysaccharide derivative (1), it is particularly excellent in heat resistance to use cellulose or a derivative thereof, and by adding a small amount, excellent adhesive strength and viscosity can be imparted to the dispersion liquid. Is preferable.

Examples of the cellulose or its derivatives include compounds having a structural unit represented by the following formula (1-1).

(In the formula, R ¹ to R ³ represent the same or different alkyl groups having hydrogen atoms, hydroxyl groups or carboxyl groups and having 1 to 5 carbon atoms. The hydroxyl groups and carboxyl groups are alkali metals and salts. May be formed.)

Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an s-butyl group, a t-butyl group, a pentyl group and the like.

The hydroxyl group and the carboxyl group may form a salt with an alkali metal, for example, the -OH group may form a salt with sodium to form a -ONa group, and the -COOH group may form a sodium. It may form a salt to form a -COONa group.

Specific examples of the cellulose derivative include hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and alkali metal salts thereof (for example, sodium carboxymethyl cellulose).

From the above, as the binder in the present disclosure, an aqueous binder is preferable, and among them, the effect of imparting viscosity is excellent, the coatability of the dispersion can be improved by adding a small amount, and the fine fibers are made into a porous base material layer (a porous base material layer (). The polysaccharide derivative (1) is preferable, and cellulose or a derivative thereof is particularly preferable, because it can exert an action of adhering to the surface of A) and is excellent in heat resistance.

(Dispersion)
The dispersion contains at least the fine fibers and the binder.

The dispersion liquid is prepared, for example, by mixing fine fibers, a binder and water, and using an ultrahigh pressure homogenizer or the like to apply a mechanical shearing force having a treatment pressure of 30 to 300 MPa to microfibrillate the fine fibers. can do.

The content of the fine fibers in the dispersion is, for example, 0.1 to 3.0% by weight, and in particular, an increase in air permeability can be suppressed and the permeability of the electrolytic solution can be improved. The lower limit of the content of the fine fibers is preferably 0.3% by weight, particularly preferably 0.5% by weight. The upper limit of the content of the fine fibers is preferably 3% by weight, particularly preferably 2.5% by weight, and most preferably 2% by weight.

The content of the binder in the dispersion is, for example, 0.01 to 3.0% by weight, and the lower limit of the content of the binder is preferable from the viewpoint of enabling uniform coating. Is 0.05% by weight, particularly preferably 0.08% by weight, most preferably 0.1% by weight, and particularly preferably 0.15% by weight. Further, the upper limit of the binder content is preferably 1.0% by weight, more preferably 0. In that the increase in air permeability can be suppressed and the permeability of the electrolytic solution can be improved. It is 7% by weight, particularly preferably 0.6% by weight, most preferably 0.4% by weight, and particularly preferably 0.3% by weight.

The content of the binder in the dispersion liquid is, for example, 10 to 200 parts by weight with respect to 100 parts by weight of the fine fibers. Excessive use of binder tends to block the voids in the separator and increase electrical resistance. Therefore, the upper limit of the binder content is preferably 160 parts by weight, particularly preferably 120 parts by weight, and particularly preferably 100 parts by weight. The lower limit of the binder content is preferably 15 parts by weight, particularly preferably 20 parts by weight, in terms of improving the adhesion to the porous base material layer (A). In the present disclosure, since the microfibers and the binder are contained together, the binding property between the microfibers is improved, the strength of the heat-resistant layer (B) is enhanced, and the heat-resistant layer is improved as compared with the case where only the microfibers are used. The adhesion of (B) to the porous base material layer (A) is improved. Therefore, the separator for a secondary battery of the present disclosure is particularly excellent in heat resistance (for example, shape retention in a high temperature environment). On the other hand, when the binder content is less than the above range, the porous base material layer (A) and the heat-resistant layer (B) are easily peeled off, and the shape of the porous base material layer (A) is maintained in a high temperature environment. It tends to be difficult to do. In addition, the strength of the heat-resistant layer (B) tends to decrease.

The dispersion liquid may contain an organic solvent other than water as the dispersion medium, but the content of the organic solvent is preferably 50% by weight or less of the total amount of the dispersion medium contained in the dispersion liquid. Particularly preferably, it is 30% by weight or less, and most preferably 10% by weight or less.

The dispersion may contain other components (for example, a dispersant, a surfactant, a filler, etc.) in addition to the fine fibers and the binder as the non-volatile content, but the non-volatile content contained in the dispersion. The ratio of the total content of the fine fibers and the binder to the total amount is, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, particularly preferably 80% by weight or more, and most preferably. 90% by weight or more, particularly preferably 95% by weight or more.

The non-volatile content concentration in the dispersion liquid can be appropriately adjusted according to the thickness of the non-woven fabric to be formed, and is, for example, 0.5 to 5% by weight.

The viscosity of the dispersion liquid at a temperature of 25 ° C. and a shear rate of 100 (1 / s) is, for example, 10 to 10000 mPa · s, and is particularly preferably 50 to 5000 mPa · s in terms of enabling uniform coating. Particularly preferably, it is 150 to 3000 mPa · s.

[Manufacturing method of separator for secondary battery]
When the binder permeates the porous base material layer (A) together with the dispersion medium when the dispersion liquid is applied to the porous base material layer (A), the binder remaining after the dispersion medium is volatilized. Closes the voids, so that the air permeability of the porous base material layer (A) is lowered, and the air permeability of the separator for a secondary battery tends to be inferior. The method for producing a separator for a secondary battery of the present disclosure is for a secondary battery by suppressing the penetration of the dispersion medium and the binder into the porous base material layer (A) when the dispersion liquid is applied. The air permeability of the separator can be improved.

That is, in the method for producing a separator for a secondary battery of the present disclosure, (I) a release film is attached to one surface of the porous substrate layer (A), and the porous substrate layer (A) is formed. A production method in which the dispersion liquid is applied to the other surface, the dispersion medium in the dispersion liquid is volatilized, and then the release film is peeled off from the porous base material layer (A), (II) the porous group. A production method in which the surface of the material layer (A) is prepared to a dyne value of 40 to 45 mN / m by surface treatment, the dispersion liquid is applied to the surface, and the dispersion medium in the dispersion liquid is volatilized, or (III). After applying the dispersion liquid to one surface of the porous substrate layer (A) and allowing a low-polarity or non-polar organic solvent to permeate from the other surface of the porous substrate layer (A). This is a production method for volatilizing the dispersion medium in the dispersion liquid, and can produce a separator for a secondary battery having excellent permeability.

<Method (I)>
In the production method (I), the release film is attached to one surface of the porous substrate layer (A), and then the release film is attached to the other surface of the porous substrate layer (A). By applying the dispersion liquid, volatilizing the dispersion medium, and then peeling the release film from the porous substrate layer (A), a separator for a secondary battery having excellent permeability can be obtained.

By attaching the release film to one surface of the porous substrate layer (A), one opening of the void communicating with both sides of the porous substrate layer (A) is closed and gas is released. Since it becomes difficult to escape, the permeation of the dispersion medium and the binder into the porous base material layer (A) is suppressed, and the blockage of the voids due to the residue of the binder after the dispersion medium is volatilized is reduced. It is considered to be a thing.

The release film used in the production method (I) is not particularly limited as long as it can be attached to the porous base material layer (A) while the dispersion medium in the dispersion liquid is volatilized. However, for example, resin films (polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polybutylene terephthalate film, polyurethane film, ethylene- Separation having an adhesive layer made of an adhesive (acrylic adhesive, urethane adhesive, silicone adhesive, polyester adhesive, rubber adhesive, etc.) on one surface of a vinyl acetate copolymer film, etc. A mold film can be mentioned.

For the above dispersion, it is preferable to use an aqueous binder as the binder and water as the dispersion medium in terms of low environmental load and excellent safety.

The method for applying the dispersion liquid is not particularly limited, and can be applied by, for example, a printing method, a coating method, or the like. Specific examples thereof include screen printing method, mask printing method, offset printing method, inkjet printing method, flexo printing method, gravure printing method, stamping, dispense, squeegee printing method, silk screen printing method, spraying, and brush coating. .. Further, it may be applied by a film applicator, a bar coater, a die coater, a comma coater, a gravure coater or the like.

The method for volatilizing the dispersion medium is not particularly limited, and examples thereof include heating, depressurization, and ventilation. The heating temperature and heating time, decompression degree and decompression time, air volume, air velocity, air temperature, type and dryness of gas to be blown, area to be blown, direction of air blow, etc. can be arbitrarily selected. ..

The method for peeling the release film is not particularly limited, and a conventionally known method can be used.

Further, in the present disclosure, by volatilizing the dispersion medium and then pressing the dispersion medium, the total thickness of the separator for the secondary battery can be further reduced, the filling density of the battery can be increased, and the secondary battery can be increased. It is preferable in that it contributes to the miniaturization of the battery. The pressure at the time of pressing is, for example, 0.1 MPa or more, preferably 1 to 100 MPa, particularly preferably 5 to 50 MPa, and most preferably 10 to 30 MPa. The pressing time is, for example, about 1 second to 100 minutes.

In the above press treatment, for example, the heat-resistant layer (B) is pressed until the thickness is 15 μm or less (preferably 12 μm or less, more preferably 10 μm, particularly preferably 5 μm or less, most preferably 4 μm or less, particularly preferably 3 μm or less). It is preferable to do. It was

The press process can be performed by using a well-known and commonly used device such as a roll press machine, a hand press machine, an air press machine, and a hydraulic press machine.

<Method (II)>
In the production method (II), the surface of the porous substrate layer (A) is prepared to a dyne value of 40 to 45 mN / m by surface treatment, and then the dispersion liquid is applied to the surface to disperse the medium. By volatilizing the above, a separator for a secondary battery having excellent permeability can be obtained.

The surface treatment preferably imparts a polar group (for example, a hydroxyl group, a carbonyl group, a carboxyl group, etc.) to the surface of the porous substrate layer (A), such as a corona discharge treatment or a plasma treatment.

In the surface treatment, the dyne value of the surface of the porous base material layer (A) is preferably 40 to 45 mN / m, more preferably 41 to 44 mN / m, and further preferably 42 to 43 mN / m. be.

By setting the dyne value within the above range, the affinity of the dispersion liquid with respect to the porous base material layer (A) can be applied to the dispersion liquid, but the dispersion medium and the binder are porous. Since the adjustment is made within the range in which the penetration into the quality base material layer (A) is suppressed, it is considered that the blockage of the voids due to the residue of the binder after the dispersion medium is volatilized is reduced.

The dyne value is a film wetting tension check pen with a dyne number of 36 to 50 mN / m (manufactured by Pacific Chemical Co., Ltd., in increments of 2 mN / m) in a standard test room atmosphere with a temperature of 23 ° C and a relative humidity of 50%. The pen tip of the pen is applied to the porous base material layer (A) and the ink of the pen is applied by moving it in one direction, and the ink is kept wet after 3 seconds. It can be measured by checking the number of dyne.

The surface treatment and the application of the dispersion liquid can be performed on one side or both sides of the porous base material layer (A).

The method of applying the binder, the dispersion medium, the dispersion liquid, and the method of volatilizing the dispersion medium in the above-mentioned production method (II) can be the same as in the case of the above-mentioned production method (I). Further, in the above-mentioned production method (II), the dispersion medium may be volatilized and then pressed, and the pressing process can be the same as in the above-mentioned production method (I).

<Method (III)>
In the production method (III), the dispersion liquid is applied to one surface of the porous substrate layer (A), and low polarity or low polarity or from the other surface of the porous substrate layer (A). By infiltrating a non-polar organic solvent and then volatilizing the dispersion medium, a separator for a secondary battery having excellent permeability can be obtained.

The low-polarity or non-polar organic solvent has a high affinity with the porous substrate layer (A), but has a low affinity with the dispersion medium and the binder. Therefore, from the other aspect, the porous substrate has a low affinity. Since it easily permeates the layer (A) to fill the voids and suppresses the permeation of the dispersion medium and the binder into the porous base material layer (A), the binder after volatilizing the dispersion medium It is considered that the blockage of the voids due to the residue is reduced.

Examples of the above-mentioned low-polarity or non-polar organic solvent include aliphatic hydrocarbons (pentane, hexane, heptane, octane, decane, undecane, dodecane, octadecane, etc.) and alicyclic hydrocarbons (cyclopentane, cyclohexane, cyclo). Octane, etc.), aliphatic unsaturated hydrocarbons (dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene, etc.), aromatic hydrocarbons (toluene, xylene, ethylbenzene, cumene, etc.), halogenated hydrocarbons (chloroform, dichloroethane, etc.) ), Halogenized aromatic hydrocarbons (orthodichlorobenzene, chlorobenzene, chloronaphthalene), ester solvents (ethyl acetate, butyl acetate), paraffinic hydrocarbons (liquid paraffin, etc.) and the like.

The permeation of the low-polarity or non-polar organic solvent into the porous substrate layer (A) is, for example, a known coating method (drop casting method, blade method, edge casting method, spraying method, brush coating method, etc.). ) Is applied to the porous base material layer (A). Further, the porous base material layer (A) is brought into contact with the impregnated material (paper, non-woven fabric, woven fabric, etc.) impregnated with the organic solvent by a single-wafer type or a continuous type using an impregnated roller, or It can also be carried out by spraying the heated steam of the organic solvent onto the porous base material layer (A) to cause dew condensation.

When the low-polarity or non-polar organic solvent is a high-boiling organic solvent such as liquid paraffin and it is difficult to remove it from the separator by volatilization, a low-boiling low-polarity or non-polar organic solvent such as hexane is used. The separator may be removed by washing with a polar organic solvent.

The method of applying the binder, the dispersion medium, and the dispersion liquid in the above-mentioned production method (III) and the method of volatilizing the dispersion medium can be the same as in the case of the above-mentioned production method (I). Further, in the above-mentioned production method (III), the dispersion medium may be volatilized and then pressed, and the pressing process can be the same as in the above-mentioned production method (I).

The method for manufacturing the separator for a secondary battery disclosed in the present disclosure may be a combination of the above (I) to (III).

[Secondary battery]
A secondary battery is a power generation element including a positive electrode in which a positive electrode active material layer is arranged in a positive electrode current collector, a negative electrode in which a negative electrode active material layer is arranged in a negative electrode current collector, a separator, and an electrolytic solution. The secondary battery of the present disclosure is included inside the exterior body, and is characterized in that the separator is the above-mentioned separator for a secondary battery.

The secondary battery of the present disclosure is a wound battery in which a positive electrode, a negative electrode and a separator are laminated and wound, and the battery is enclosed in a container such as a can together with an electrolytic solution, and the positive electrode, the negative electrode and the separator are laminated. A laminated battery in which a sheet-like material is enclosed together with an electrolytic solution inside a relatively flexible exterior body may be used.

The secondary battery of the present disclosure is excellent in safety because it is provided with the above-mentioned separator for a secondary battery having excellent heat resistance (for example, shape retention in a high temperature environment). Further, the separator for the secondary battery is lightweight. Therefore, the secondary battery of the present disclosure is light. Therefore, information-related devices such as smartphones and notebook computers, hybrid vehicles, electric vehicles, and the like equipped with the secondary battery of the present disclosure can be reduced in weight while maintaining high safety. For example, an electric vehicle using the secondary battery of the present disclosure can be significantly reduced in weight, thereby dramatically improving fuel efficiency.

The secondary battery of the present disclosure is manufactured by a method of obtaining a separator for a secondary battery by the manufacturing methods (I) to (III) above and manufacturing a secondary battery using the obtained separator for a secondary battery. can do.

The configurations and combinations thereof in each of the above embodiments are examples, and the configurations can be added, omitted, replaced, and other changes as appropriate without departing from the gist of the present disclosure. The invention according to the present disclosure is not limited by embodiments, but only by the claims.

Also, each aspect disclosed herein can be combined with any other feature disclosed herein.

Hereinafter, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to these examples.

[Example 1]
Add 15.89 g of sodium carboxymethyl cellulose (CMC, dry weight loss: 5.6%, manufactured by Daisel Finechem Co., Ltd., product number: 1380) to 1484 g of water, and add a rotating revolution agitator (manufactured by Shinky Co., Ltd., product name: Awatori Rentaro,). A 1.0 wt% CMC aqueous solution was prepared by stirring at 3000 rpm for 30 minutes using model number: ARE-310).

Next, aramid fine fibers (average diameter D: 0.56 μm, average length L: 0.43 mm, average aspect ratio: 768, decomposition temperature: 400 ° C. or higher, solid content: 20.7%, manufactured by Daisel Finechem Co., Ltd. , Product name: Tiara, Product number: KY400S) 19 parts by weight of water was added to 1 part by weight, and the mixture was stirred at 2000 rpm for 5 minutes using a rotating revolution stirrer. Further, the treatment was performed using a high-pressure homogenizer (50 MPa, 30 passes) to obtain a 1.0 wt% aramid fiber aqueous dispersion.

Mix 100 parts by weight of 1.0% by weight CMC aqueous solution, 300 parts by weight of 1.0% by weight aramid fiber aqueous dispersion (1), and 100 parts by weight of water, and stir at 3000 rpm for 30 minutes using a rotating revolution stirrer. As a result, the dispersion liquid (1) was obtained.

A dispersion liquid (1) on one side of a polyethylene microporous film (dyne value 44 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) as a porous substrate subjected to corona discharge treatment. ) Is applied at a rate of 240 mm / sec (coating thickness: 250 μm) using an automatic coating device (manufactured by Tester Sangyo Co., Ltd., model number: PI-1210), and then dried at 60 ° C. for 20 minutes. A heat-resistant layer, which is a non-woven fabric, was formed to obtain a separator, which is a laminated body (porous base material layer / heat-resistant layer). The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Example 2]
Same as Example 1 except that a polyethylene microporous membrane (dyne value 42 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) subjected to corona discharge treatment having different dyne values was used. And obtained a separator. The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Example 3]
Separator in the same manner as in Example 1 except that a polyethylene microporous membrane (dyne value 44 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) subjected to ozone discharge treatment was used. Got The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Example 4]
Dispersion liquid on one surface of a polyethylene microporous film (dyne value 46 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) as a porous substrate subjected to corona discharge treatment. (1) was applied at a rate of 240 mm / sec (coating thickness: 250 μm) using an automatic coating device (manufactured by Tester Sangyo Co., Ltd., model number: PI-1210), and then hexane was added. A heat-resistant layer, which is a non-woven fabric, is formed by applying paper to the other surface and drying at 60 ° C. for 20 minutes with the paper soaked in hexane, and then using a laminate (porous base material layer / heat-resistant layer). Obtained a separator. The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Example 5]
Dispersion liquid on one surface of a polyethylene microporous film (dyne value 46 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) as a porous substrate subjected to corona discharge treatment. (1) is applied at a rate of 240 mm / sec using an automatic coating device (manufactured by Tester Sangyo Co., Ltd., model number: PI-1210) (coating thickness: 250 μm), and then liquid paraffin is added. A heat-resistant layer, which is a non-woven fabric, was formed by applying the paper to the other surface and drying at 60 ° C. for 20 minutes while applying the paper containing liquid paraffin. Further, the laminate (porous base material layer / heat-resistant layer) was washed with hexane and dried at 60 ° C. for 5 minutes to obtain a separator. The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Example 6]
Slightly adhered to one surface of a polyethylene microporous film (dyne value 46 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) as a porous substrate subjected to corona discharge treatment. After adhering the film (manufactured by Panac Co., Ltd., TS25B), apply the dispersion liquid (1) to the other surface using an automatic coating device (manufactured by Tester Sangyo Co., Ltd., model number: PI-1210), 240 mm. It was applied at a rate of / sec (coating thickness: 250 μm) and dried at 60 ° C. for 20 minutes to form a heat-resistant layer which is a non-woven fabric, and the slightly adhesive film was peeled off to obtain a separator. The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Comparative Example 1]
Example 1 except that a polyethylene microporous membrane (dyne value 46 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) was used as a porous substrate subjected to corona discharge treatment. In the same manner as above, a separator was obtained. The total thickness was 25 μm, the thickness of the heat-resistant layer was 5 μm, and the basis weight of the heat-resistant layer was ^{1.80 g / m 2.}

[Comparative Example 2]
Only polyethylene microporous membrane (dyne value 46 mN / m, thickness 20 μm, air permeability 235 sec / 100 mL, manufactured by Double Scope Co., Ltd.) as a porous substrate subjected to corona discharge treatment (without forming a heat resistant layer) ) Was used as a separator.

For the separators obtained in Examples and Comparative Examples, the air permeability of the separator and the basis weight of the heat-resistant layer (B) were measured by the following methods.

(Air permeability test)
The air permeability was measured according to JIS P8117 using a Garley type densometer B type manufactured by Tester Sangyo Co., Ltd. The number of seconds was measured with a digital auto counter. The smaller the value of air permeability (Garley value), the higher the air permeability.

(Basis weight of heat resistant layer (B))
The basis weight was measured according to JIS P8124.

The above results are summarized in the table below.

Hereinafter, variations of the invention according to the present disclosure will be described.
[Appendix 1] A porous base material layer (A) and a heat-resistant layer (B) made of a non-woven fabric containing microfibers having a melting point or a decomposition temperature of 200 ° C. or higher and a binder are included, and the following formulas (a) and (b) are included. ), A separator for a secondary battery that satisfies at least one of them.
(YX) / Z <12 (a)
(YX) <60 (b)
X: Air permeability of the porous substrate (A) (sec / 100 mL)
Y: Air permeability of separator (sec / 100mL)
Z: Thickness (μm) of heat-resistant layer (B)
[Appendix 2] The separator for a secondary battery according to Annex 1, wherein the value according to (YX) / Z is 0 to 10.
[Supplementary Note 3] The separator for a secondary battery according to Supplementary note 1 or 2, wherein the value according to (YX) is 0 to 40.
[Appendix 4] The separator for a secondary battery according to any one of the appendices 1 to 3, wherein the separator has an air permeability of 100 to 650 sec / 100 mL.
[Appendix 5] The separator for a secondary battery according to any one of the appendices 1 to 3, wherein the separator has an air permeability of 100 to 350 sec / 100 mL.
[Appendix 6] The separator for a secondary battery according to any one of the appendices 1 to 5, wherein the size of the voids of the porous substrate layer (A) is 0.01 to 1 μm.
[Appendix 7] The separator for a secondary battery according to any one of the appendices 1 to 5, wherein the size of the voids of the porous substrate layer (A) is 0.02 to 0.06 μm.
[Appendix 8] The separator for a secondary battery according to any one of the appendices 1 to 7, wherein the porous base material layer (A) has a porosity of 20 to 70% by volume.
[Appendix 9] The separator for a secondary battery according to any one of the appendices 1 to 7, wherein the porous base material layer (A) has a porosity of 30 to 60% by volume.
[Appendix 10] The separator for a secondary battery according to any one of the appendices 1 to 9, wherein the porous substrate layer (A) has an air permeability of 100 to 600 sec / 100 mL.
[Appendix 11] The separator for a secondary battery according to any one of the appendices 1 to 9, wherein the porous substrate layer (A) has an air permeability of 100 to 350 sec / 100 mL.
[Supplementary Note 12] The separator for a secondary battery according to any one of Supplementary note 1 to 11, wherein the material of the porous base material layer (A) is polyolefin, polyester resin or aliphatic polyamide.
[Supplementary Note 13] The separator for a secondary battery according to any one of Supplementary note 1 to 11, wherein the material of the porous base material layer (A) is polyethylene.
[Appendix 14] The separator for a secondary battery according to any one of the appendices 1 to 13, wherein the porous substrate (A) has a thickness of 5 to 40 μm.
[Appendix 15] The separator for a secondary battery according to any one of the appendices 1 to 13, wherein the porous substrate (A) has a thickness of 10 to 25 μm.
[Appendix 16] The separator for a secondary battery according to any one of the appendices 1 to 15, wherein the melting point or decomposition temperature of the microfiber is 300 to 500 ° C.
[Appendix 17] The separator for a secondary battery according to any one of the appendices 1 to 16, wherein the fine fibers have an average aspect ratio (average length / average thickness) of 10 to 2000.
[Appendix 18] The separator for a secondary battery according to any one of the appendices 1 to 16, wherein the average aspect ratio (average length / average thickness) of the fine fibers is 800 to 1000.
[Appendix 19] The microfiber is at least one selected from the group consisting of fluorine fiber, glass fiber, carbon fiber, polyparaphenylene benzoxazole fiber, polyether ether ketone fiber and liquid crystal polymer fiber, Appendix 1 to 18. The separator for a secondary battery according to any one of the above.
[Supplementary Note 20] The separator for a secondary battery according to any one of Supplementary note 1 to 18, wherein the microfibers are aramid fibers.
[Appendix 21] The separator for a secondary battery according to any one of the appendices 1 to 20, wherein the binder has a melting point or a decomposition temperature of 160 to 400 ° C.
[Appendix 22] The separator for a secondary battery according to any one of the appendices 1 to 20, wherein the binder has a melting point or a decomposition temperature of 200 to 400 ° C.
[Supplementary Note 23] The separator for a secondary battery according to any one of Supplementary note 1 to 22, wherein the viscosity of the 1 wt% aqueous solution of the binder (at 25 ° C. and 60 rotations) is 100 to 5000 mPa · s.
[Supplementary Note 24] The separator for a secondary battery according to any one of Supplementary note 1 to 22, wherein the viscosity of the 1 wt% aqueous solution of the binder (at 25 ° C. and 60 rotations) is 1000 to 2000 mPa · s.
[Appendix 25] The binder is at least one selected from the group consisting of a fluorine-based binder, a polyester-based binder, an epoxy-based binder, an acrylic-based binder, a vinyl ether-based binder, and a water-based binder, any one of Supplementary note 1 to 24. The separator for the secondary battery described in 1.
[Supplementary Note 26] The separator for a secondary battery according to any one of Supplementary note 1 to 24, wherein the binder is a water-based binder.
[Appendix 27] At least the binder is selected from a polysaccharide derivative (1), a compound having a structural unit represented by the following formula (2), and a compound having a structural unit represented by the following formula (3). The separator for a secondary battery according to Appendix 26, which is one type.

(In the formula, R represents a hydroxyl group, a carboxyl group, a phenyl group, an N-substituted or unsubstituted carbamoyl group, or a 2-oxo-1-pyrrolidinyl group).

(In the formula, n indicates an integer of 2 or more, and L indicates an ether bond or a (-NH-) group).
[Appendix 28] The separator for a secondary battery according to Annex 27, wherein the binder is a polysaccharide derivative (1) and is at least one selected from cellulose, starch, glycogen, and derivatives thereof.
[Supplementary Note 29] The separator for a secondary battery according to Supplementary note 27, wherein the binder is a polysaccharide derivative (1) and is cellulose or a derivative thereof having a structural unit represented by the following formula (1-1).

(In the formula, R ¹ to R ³ represent the same or different alkyl groups having hydrogen atoms, hydroxyl groups or carboxyl groups and having 1 to 5 carbon atoms. The hydroxyl groups and carboxyl groups are alkali metals and salts. May be formed.)
[Appendix 30] The separator for a secondary battery according to Annex 26, wherein the binder is at least one selected from hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose and alkali metal salts thereof.
[Appendix 31] The separator for a secondary battery according to any one of the appendices 1 to 30, wherein the fine fibers have an average thickness of 0.01 to 10 μm.
[Appendix 32] The separator for a secondary battery according to any one of the appendices 1 to 30, wherein the fine fibers have an average thickness of 0.05 to 0.5 μm.
[Appendix 33] The separator for a secondary battery according to any one of the appendices 1 to 32, wherein the fine fibers have an average length of 0.01 to 1 mm.
[Appendix 34] The separator for a secondary battery according to any one of the appendices 1 to 32, wherein the fine fibers have an average length of 0.07 to 0.4 mm.
[Appendix 35] The separator for a secondary battery according to any one of the appendices 1 to 30, wherein the fine fibers have an average thickness of 0.01 to 10 μm and an average length of 0.01 to 2 mm.
[Appendix 36] The secondary battery according to any one of the appendices 1 to 30, wherein the fine fibers have an average thickness of 0.05 to 0.5 μm and an average length of 0.07 to 0.4 mm. Separator.
[Appendix 37] The separator for a secondary battery according to any one of the appendices 1 to 36, wherein the heat-resistant layer (B) has a thickness of 0.5 to 20 μm.
[Appendix 38] The separator for a secondary battery according to any one of the appendices 1 to 36, wherein the heat-resistant layer (B) has a thickness of 3 to 5 μm.
[Appendix 39] The separator for a secondary battery according to any one of the appendices 1 to 38, wherein the total thickness of the separator for the secondary battery is 10 to 50 μm.
[Appendix 40] The separator for a secondary battery according to any one of the appendices 1 to 38, wherein the total thickness of the separator for the secondary battery is 12 to 30 μm.
[Supplementary Note 41] The secondary battery according to any one of Supplementary note 1 to 36, wherein the heat-resistant layer (B) has a thickness of 0.5 to 20 μm, and the total thickness of the separator for a secondary battery is 10 to 50 μm. Separator for.
[Appendix 42] The separator for a secondary battery according to any one of the appendices 1 to 36, wherein the heat-resistant layer (B) has a thickness of 3 to 5 μm and the total thickness of the separator for a secondary battery is 12 to 30 μm. ..
[Supplementary Note 43] The separator for a secondary battery according to any one of Supplementary note 1 to 42, wherein the heat-resistant layer (B) has a basis weight of 10 g / m ^{2 or less.}
[Appendix 44] The separator for a secondary battery according to any one of the appendices 1 to 42, wherein the heat-resistant layer (B) has a basis weight of 1 to 5 g / m ^2.
[Appendix 45] The separator for a secondary battery according to any one of the appendices 1 to 44, wherein the heat-resistant layer (B) has a porosity of 30 to 60% by volume.
[Supplementary Note 46] The separator for a secondary battery according to any one of Supplementary note 1 to 44, wherein the heat-resistant layer (B) has a porosity of 35 to 55% by volume.
[Appendix 47] The separator for a secondary battery according to any one of the appendices 1 to 46, wherein the heat-resistant layer (B) has an air permeability of 1 to 500 sec / 100 mL.
[Appendix 48] The separator for a secondary battery according to any one of the appendices 1 to 46, wherein the heat-resistant layer (B) has an air permeability of 1 to 70 sec / 100 mL.
[Appendix 49] A release film is attached to one surface of the porous substrate layer (A), and a dispersion liquid containing fine fibers and a binder is applied to the other surface of the porous substrate layer (A). Then, after volatilizing the dispersion medium in the dispersion liquid, the release film is peeled off from the porous base material layer (A), whereby the secondary battery according to any one of Supplementary note 1 to 48 is used. A method for manufacturing a separator for a secondary battery to obtain a separator.
[Appendix 50] After preparing the surface of the porous base material layer (A) to a dyne value of 40 to 45 mN / m by surface treatment, a dispersion liquid containing fine fibers and a binder is applied to the surface, and the dispersion liquid contains the fine fibers and a binder. A method for manufacturing a separator for a secondary battery, wherein the separator for a secondary battery according to any one of Supplementary note 1 to 48 is obtained by volatilizing the dispersion medium of the above.
[Supplementary Note 51] The method for manufacturing a separator for a secondary battery according to Supplementary Note 50, wherein the dyne value is 42 to 43 mN / m.
[Appendix 52] The method for producing a separator for a secondary battery according to Appendix 50 or 51, wherein the dispersion liquid containing the fine fibers and the binder is applied to one side or both sides of the porous base material layer (A).
[Appendix 53] A dispersion liquid containing fine fibers and a binder is applied to one surface of the porous substrate layer (A), and low polarity or non-polarity is applied from the other surface of the porous substrate layer (A). A method for producing a separator for a secondary battery, which comprises permeating the organic solvent of the above and then volatilizing the dispersion medium in the dispersion liquid to obtain a separator for a secondary battery according to any one of Supplementary note 1 to 48. ..
[Appendix 54] The low-polarity or non-polar organic solvent is an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aliphatic unsaturated hydrocarbon, an aromatic hydrocarbon, a halogenated hydrocarbon, a halogenated aromatic hydrocarbon, and the like. The method for producing a separator for a secondary battery according to Appendix 53, which is at least one selected from an ester-based solvent and a paraffin-based hydrocarbon.
[Appendix 55] The method for producing a separator for a secondary battery according to Appendix 53, wherein the low-polarity or non-polar organic solvent is liquid paraffin and / or hexane.
[Appendix 56] The secondary according to any one of the appendices 49 to 55, wherein the content ratio of the fine fibers and the binder in the dispersion liquid is 1 to 20 parts by weight with respect to 10 parts by weight of the fine fibers. Manufacturing method of battery separator.
[Appendix 57] The method for producing a separator for a secondary battery according to any one of the appendices 49 to 56, wherein the total content of the fine fibers and the binder in the dispersion is 0.5 to 10% by weight.
[Appendix 58] The method for producing a separator for a secondary battery according to any one of the appendices 49 to 56, wherein the total content of the fine fibers and the binder in the dispersion is 0.7 to 3% by weight.
[Supplementary Note 59] The separator for a secondary battery according to any one of Supplementary note 49 to 58, wherein the ratio of the total content of the fine fibers, the binder and the dispersion medium in the dispersion liquid is 50% by weight or more. Production method.
[Supplementary Note 60] The separator for a secondary battery according to any one of Supplementary note 49 to 58, wherein the ratio of the total content of the fine fibers, the binder and the dispersion medium in the dispersion liquid is 90% by weight or more. Production method.
[Supplementary Note 61] The method for producing a separator for a secondary battery according to any one of Supplementary note 49 to 60, wherein the dispersion medium contains water.
[Appendix 62] The method for producing a separator for a secondary battery according to Appendix 61, wherein the dispersion medium contains 2% by weight or less of an organic solvent in the total amount of the dispersion medium.
[Supplementary Note 63] A secondary battery provided with the secondary battery separator according to any one of Supplementary note 1 to 48.
[Appendix 64] A secondary battery separator is obtained by the method for manufacturing a secondary battery separator according to any one of the appendices 49 to 62, and a secondary battery is manufactured using the obtained secondary battery separator. How to manufacture a secondary battery.
[Appendix 65] The porous base material layer (A) and the heat-resistant layer (B) made of a non-woven fabric containing microfibers having a melting point or a decomposition temperature of 200 ° C. or higher and a binder are included, and the following formulas (a) and (b) are included. ), A laminate that satisfies at least one of the above, and is used as a separator for a secondary battery.
(YX) / Z <12 (a)
(YX) <60 (b)
X: Air permeability of the porous substrate (A) (sec / 100 mL)
Y: Air permeability of separator (sec / 100mL)
Z: Thickness (μm) of heat-resistant layer (B)

The separator for a secondary battery of the present disclosure has low air permeability, is excellent in moisture permeability, and is also excellent in moisture permeability in a low temperature and low humidity environment, so that it can be particularly preferably used as a total heat exchange sheet. Further, according to the manufacturing method of the present disclosure, it becomes possible to efficiently manufacture a separator for a secondary battery having excellent permeability. Therefore, the present disclosure has industrial applicability.

Claims (13)

1. It contains a porous base material layer (A) and a heat-resistant layer (B) made of a non-woven fabric containing fine fibers and a binder having a melting point or decomposition temperature of 200 ° C. or higher, and at least one of the following formulas (a) and (b). A separator for secondary batteries that meets the requirements.
   (YX) / Z <12 (a)
   (YX) <60 (b)
   X: Air permeability of the porous substrate (A) (sec / 100 mL)
   Y: Air permeability of separator (sec / 100mL)
   Z: Thickness (μm) of heat-resistant layer (B)
2. The separator for a secondary battery according to claim 1, wherein the fine fibers are aramid fibers.
3. The separator for a secondary battery according to claim 1 or 2, wherein the binder is a water-based binder.
4. Claims that the binder is at least one selected from a polysaccharide derivative (1), a compound having a structural unit represented by the following formula (2), and a compound having a structural unit represented by the following formula (3). Item 2. The separator for a secondary battery according to any one of Items 1 to 3.
   

   

   (In the formula, R represents a hydroxyl group, a carboxyl group, a phenyl group, an N-substituted or unsubstituted carbamoyl group, or a 2-oxo-1-pyrrolidinyl group).
   

   

   (In the formula, n indicates an integer of 2 or more, and L indicates an ether bond or a (-NH-) group).
5. The separator for a secondary battery according to any one of claims 1 to 3, wherein the binder is at least one selected from cellulose, starch, glycogen, and derivatives thereof.
6. The separator for a secondary battery according to any one of claims 1 to 5, wherein the fine fibers have an average thickness of 0.01 to 10 μm and an average length of 0.01 to 2 mm.
7. The separator for a secondary battery according to any one of claims 1 to 6, wherein the heat-resistant layer (B) has a thickness of 0.5 to 20 μm, and the total thickness of the separator for a secondary battery is 10 to 50 μm.
8. The separator for a secondary battery according to any one of claims 1 to 7, wherein the heat-resistant layer (B) has a basis weight of 10 g / m ^{2 or less.}
9. A release film is attached to one surface of the porous substrate layer (A), and a dispersion liquid containing fine fibers and a binder is applied to the other surface of the porous substrate layer (A) to disperse the dispersion. The separator for a secondary battery according to any one of claims 1 to 8 is obtained by volatilizing the dispersion medium in the liquid and then peeling the release film from the porous substrate layer (A). , A method for manufacturing a separator for a secondary battery.
10. After preparing the surface of the porous base material layer (A) to a dyne value of 40 to 45 mN / m by surface treatment, a dispersion liquid containing fine fibers and a binder is applied to the surface, and the dispersion medium in the dispersion liquid is applied. A method for manufacturing a separator for a secondary battery, wherein the separator for a secondary battery according to any one of claims 1 to 8 is obtained by volatilizing the separator.
11. A dispersion liquid containing fine fibers and a binder is applied to one surface of the porous substrate layer (A), and a low-polarity or non-polar organic solvent is applied from the other surface of the porous substrate layer (A). A method for producing a separator for a secondary battery, wherein the separator for a secondary battery according to any one of claims 1 to 8 is obtained by infiltrating and then volatilizing the dispersion medium in the dispersion liquid.
12. A secondary battery provided with the separator for the secondary battery according to any one of claims 1 to 8.
13. A secondary battery separator is obtained by the method for manufacturing a secondary battery separator according to any one of claims 9 to 11, and a secondary battery is manufactured using the obtained secondary battery separator. Next battery manufacturing method.