JP6357395B2 - Battery separator - Google Patents

Description

  The present invention relates to a battery separator.

Polyolefin resin porous membranes are widely used as separators in batteries, capacitors and the like because they exhibit excellent electrical insulation and ion permeability. In recent years, in particular, with the increase in functionality and weight of portable devices, lithium-ion secondary batteries with high output density and high capacity density have been used as power sources. A polyolefin porous membrane is mainly used.
Lithium ion secondary batteries use an organic solvent as the electrolyte. Therefore, the electrolyte solution decomposes due to heat generated due to an abnormal situation such as a short circuit or overcharge, and in the worst case, ignition may occur.

  In order to prevent such a situation, some safety functions are incorporated in the lithium ion secondary battery. One of them is the separator shutdown function. The shutdown function is a function that stops the progress of the electrochemical reaction by blocking the ionic conduction in the electrolytic solution by blocking the micropores of the separator due to heat melting or the like when the battery is abnormally heated. Generally, the lower the shutdown temperature, the higher the safety. One of the reasons why polyethylene is used as a component of the separator is that it has an appropriate shutdown temperature.

However, in a battery having high energy, the temperature in the battery continues to rise even if the progress of the electrochemical reaction is stopped by the shutdown. As a result, there may be a problem that the separator is thermally contracted to break the film, and both electrodes are short-circuited.
For the purpose of providing a battery with higher safety, Patent Document 1 describes a technique for forming a separator by laminating a heat-resistant layer on a first porous layer mainly composed of a thermoplastic resin. Yes. In recent years, the capacity of batteries has been further increased, and even in such high capacity batteries, a separator having a small thickness and high heat resistance has been demanded, and studies thereof are underway.
For example, Patent Document 1 discloses a battery separator in which a porous layer containing an inorganic filler and an acrylic polymer and a porous film mainly composed of a polyolefin resin are integrated in order to improve heat resistance. Yes.

JP 2011-5670 A

Since the separator of Patent Document 1 is certainly higher in heat resistance when compared to a normal separator having no heat-resistant layer, it is considered that the safety of the battery is improved. However, since the separator has low resistance to the electrolytic solution, there is still room for improvement from the viewpoint that the binding strength of the heat-resistant layer is reduced in the electrolytic solution and the safety of the battery is reduced when the battery is operated for a long time. It is what you have.
An object of this invention is to provide the battery separator which has the outstanding heat resistance also in electrolyte solution, and can maintain high battery stability for a long time.

As a result of intensive studies in view of the above circumstances, the present inventors,
On the polyolefin resin porous membrane,
It has been found that by providing a porous layer containing an inorganic filler and a resin binder having specific physical properties, a battery separator having high resistance in an electrolytic solution can be obtained, thereby solving the above problems. Thus, the present invention has been completed.
That is, the present invention is as follows:

[1] On at least one surface of the polyolefin resin porous membrane (A),
An inorganic filler (b-2);
The gel fraction in the toluene solution is 90 to 99% by mass, the glass transition temperature is shown in the region below 30 ° C., and the swelling degree with respect to the ethylene carbonate / diethyl carbonate mixture (volume ratio: 2/3) is 105 to 200. % Resin binder (b-1),
A battery separator comprising a porous layer (B) containing
The residual rate of the porous layer (B) when the battery separator is subjected to ultrasonic treatment for 10 minutes in an ethylene carbonate / diethyl carbonate mixed solution (volume ratio: 2/3) at 25 ° C. is 60% or more. The battery separator according to the present invention.

[2] The battery separator according to [1], wherein the resin binder (b-1) exhibits a glass transition temperature in a region of 0 ° C. or lower.
[3] The battery separator according to [1] or [2], wherein the resin binder (b-1) is an acrylic polymer.
[4] The battery separator according to any one of [1] to [3], which is a non-aqueous electrolyte battery separator.
[5] A non-aqueous electrolyte battery comprising the separator for a non-aqueous electrolyte battery according to [4], a positive electrode, a negative electrode, and an electrolytic solution.

  ADVANTAGE OF THE INVENTION According to this invention, even if a battery is operated for a long time, the battery separator which has high battery safety is provided.

Hereinafter, the best mode for carrying out the present invention (hereinafter abbreviated as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.
The battery separator of this embodiment includes a porous layer (B) on at least one surface of the polyolefin resin porous membrane (A).

The separator of the present embodiment includes a resin binder having the above gel fraction, glass transition temperature, and swelling degree, and exceeds 10 minutes in an ethylene carbonate / diethyl carbonate mixed liquid (volume ratio: 2/3) at 25 ° C. By having a porous layer having a residual rate of 60% or more when sonicated, a lithium ion secondary battery having high safety in a nail penetration test can be realized.
The nail penetration test is a test for observing the behavior of a battery when it is forcibly short-circuited by artificially penetrating a nail from the side of the battery as one of safety evaluation methods against an internal short circuit. In the nail penetration test, when the separator breaks at the nail penetration site, the positive electrode and the negative electrode react directly to generate heat. Due to the heat generated at this time, the separator is melted, and then the hole is further expanded, the short-circuit area is expanded, and eventually, thermal runaway may be reached. At this time, if the positive electrode active material is decomposed and oxygen is released, the battery with low safety may lead to ignition. Therefore, it is considered important to suppress the expansion of the hole in the ruptured part due to the penetration in order to suppress the heat generation.

  The reason why the separator of this embodiment is excellent in the nail penetration test is not clear, but the adhesive strength between the porous layer and the polyolefin resin porous film in the electrolytic solution, the resin binder and the inorganic filler in the porous layer in the electrolytic solution, When the external short circuit occurs in the battery due to the binding strength of the polyolefin resin and the isotropic nature of the polyolefin resin porous membrane and the separator, the expansion of the pores of the separator is suppressed, and thus the rate of heat generation is slowed down. It is estimated that the safety at the time has increased.

Next, the polyolefin resin porous membrane in the separator will be described.
As the polyolefin resin porous membrane in the separator, those having a small electron conductivity, an ionic conductivity, a high resistance to an organic solvent, and a fine pore diameter are preferable.
Examples of such a resin porous membrane include a porous membrane containing a polyolefin resin (this porous membrane does not include a woven fabric and a non-woven fabric); a porous membrane made of woven polyolefin fibers (woven fabric); a polyolefin Examples thereof include a porous film made of a nonwoven fabric of fibers. Among these, it is excellent in the coating property of the coating liquid when the battery separator is obtained through the coating process, the separator film thickness is reduced, and the active material ratio in the electricity storage device such as the battery is increased to increase the volume. From the viewpoint of increasing the hit capacity, a porous film containing a polyolefin resin (this woven film does not include a woven fabric or a non-woven fabric; hereinafter, also referred to as “polyolefin resin porous film”) is preferable.
The battery separator of the present embodiment uses the preferred polyolefin resin porous membrane (A) as described above as the resin porous membrane.

<Polyolefin resin porous membrane (A)>
The polyolefin resin porous membrane (A) will be described.
The polyolefin resin porous membrane (A) is formed from a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the constituent resin component from the viewpoint of improving shutdown performance when used as a battery separator. It is preferable. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.
The polyolefin resin contained in the polyolefin resin composition is not particularly limited, and can be obtained using, for example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene or the like as a monomer. And homopolymers, copolymers, multistage polymers and the like. These polyolefin resins may be used alone or in admixture of two or more.

Among these, polyethylene, polypropylene, copolymers thereof, and mixtures thereof are preferable as the polyolefin resin from the viewpoint of shutdown characteristics when used as a battery separator.
Specific examples of polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, and the like;
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene and the like;
Specific examples of the copolymer include ethylene-propylene random copolymer, ethylene-propylene rubber, ethylene-butylene copolymer, ethylene-octene copolymer, etc.
Each is listed.

Among these, polyethylene, particularly high-density polyethylene, is preferably used as the polyolefin resin from the viewpoint of satisfying the required performance of a low melting point and high strength when used as a battery separator. In the present specification, high density polyethylene refers to polyethylene having a density of 0.942 to 0.970 g / cm ³ . In the present specification, the density of polyethylene refers to a value measured according to D) density gradient tube method described in JIS K7112 (1999).
From the viewpoint of improving the heat resistance of the polyolefin resin porous membrane (A), it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin. In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20%, from the viewpoint of achieving both heat resistance and a good shutdown function. It is 4 mass%, More preferably, it is 4-10 mass%.

Arbitrary additives can be contained in the polyolefin resin composition. Examples of additives include polymers other than polyolefin resins; inorganic materials; antioxidants such as phenols, phosphorus and sulfur; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers An antistatic agent, an antifogging agent, a coloring pigment, and the like. The total addition amount of these additives is preferably 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin from the viewpoint of improving the shutdown performance and the like, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass. Or less.
Since the polyolefin resin porous membrane (A) has a porous structure in which a large number of very small holes are gathered to form dense communication holes, it has excellent ion conductivity and at the same time withstand voltage characteristics, Moreover, it has a feature of high strength.
The polyolefin resin porous membrane (A) may be a single layer made of the above-described material or may be a laminated layer.

The film thickness of the polyolefin resin porous membrane (A) is preferably from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm, still more preferably from 3 μm to 25 μm. From the viewpoint of mechanical strength, 0.1 μm or more is preferable, and from the viewpoint of increasing the capacity of the battery, 100 μm or less is preferable. The film thickness of the polyolefin resin porous membrane (A) can be adjusted by controlling the die lip interval, the draw ratio in the drawing step, and the like.
The average pore diameter of the polyolefin resin porous membrane (A) is preferably from 0.03 μm to 0.70 μm, more preferably from 0.04 μm to 0.20 μm, still more preferably from 0.05 μm to 0.10 μm, particularly preferably. It is 0.06 μm or more and 0.09 μm or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 to 0.70 μm is preferable. The average pore diameter of the polyolefin resin porous membrane (A) can be measured by a measurement method described later. The average pore diameter should be adjusted by controlling the composition ratio, the extrusion sheet cooling rate, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat setting, the relaxation rate at the time of heat setting, or a combination thereof. Can do.

  The porosity of the polyolefin resin porous membrane (A) is preferably 25% to 95%, more preferably 30% to 65%, and still more preferably 35% to 55%. 25% or more is preferable from the viewpoint of improving ion conductivity, and 95% or less is preferable from the viewpoint of withstand voltage characteristics. The porosity of the polyolefin resin porous membrane (A) can be measured by the method described later. The porosity of the polyolefin resin porous membrane (A) controls the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat fixing, or the relaxation rate at the time of heat fixing. It can be adjusted by combining these two kinds of sulfur controls.

  The viscosity average molecular weight of the polyolefin resin porous membrane (A) is preferably from 30,000 to 12,000,000, more preferably from 50,000 to less than 2,000,000, still more preferably 100,000 or more. Less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension at the time of melt molding becomes large, the moldability becomes good, and the strength tends to become high due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when it is used as a battery separator, it is preferable that the viscosity average molecular weight is less than 1,000,000 because it tends to close a hole when the temperature rises and a good shutdown function tends to be obtained.

  The puncture strength of the polyolefin resin porous membrane (A) is preferably 400 to 2,000 gf, more preferably 420 to 1,800 gf, and more preferably 450 to 1,500 gf in terms of a film thickness of 25 μm. Is more preferable, and 500 to 1,200 gf is particularly preferable. Here, the puncture strength of the polyolefin resin porous membrane (A) is the type and composition ratio of the polyolefin resin, the cooling rate of the extruded sheet, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat fixing, and the time of heat fixing. It can be adjusted by controlling the relaxation rate of these and a combination thereof.

There is no restriction | limiting in particular as a method of manufacturing a polyolefin resin porous membrane (A), A well-known manufacturing method is employable. For example;
(1) A method in which a polyolefin resin composition and a pore-forming material are melt-kneaded and formed into a sheet, and then stretched as necessary, and then the pore-forming material is extracted to make it porous.
(2) A method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio and then made porous by peeling off the polyolefin crystal interface by heat treatment and stretching,
(3) A method in which a polyolefin resin composition and an inorganic material are melt-kneaded and formed on a sheet, and thereafter the surface is made porous by peeling the interface between the polyolefin resin and the inorganic material by stretching,
(4) After dissolving the polyolefin resin composition, it is immersed in a poor solvent for the polyolefin resin to solidify the polyolefin resin and at the same time remove the solvent to make it porous.

Hereinafter, as an example of the method for producing the polyolefin resin porous membrane (A), a method for extracting the pore-forming material after melt-kneading the polyolefin resin composition and the pore-forming material into a sheet shape will be described.
First, the polyolefin resin composition and the hole forming material are melt-kneaded. As a melt-kneading method, for example, polyolefin resin and other additives as necessary, by introducing into an appropriate resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, and kneading, A method of introducing and kneading the hole forming material at an arbitrary ratio while heating and melting the resin component can be mentioned.

Examples of the pore forming material include a plasticizer, an inorganic material, or a combination thereof.
Although it does not specifically limit as a plasticizer, It is preferable to use the non-volatile solvent which can form the uniform solution of this polyolefin resin in the temperature more than melting | fusing point of polyolefin. Specific examples of such a non-volatile solvent include, for example, hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. . These plasticizers may be recovered and reused by an operation such as distillation after extraction.

More preferably, the polyolefin resin, other additives, and the plasticizer are previously kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being put into the resin kneading apparatus. More preferably, in this preliminary kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while being side-feeded by appropriately heating the resin kneader. By using such a kneading method, the dispersibility of the plasticizer is increased, and when stretching a sheet-like molded body composed of a melt-kneaded product of the resin composition and the plasticizer in the subsequent step, without film breakage. It becomes possible to stretch at a high magnification.
Among the plasticizers, liquid paraffin is highly compatible with polyolefin resins (especially polyethylene, polypropylene, etc.), and therefore, when the melt-kneaded product is stretched, the interface peeling between the resin and the plasticizer hardly occurs and is uniform. It tends to be easy to carry out stretching, which is preferable.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 20 to 90 mass%, more preferably 30 to 80 mass%. When the mass fraction of the plasticizer is 90% by mass or less, the melt tension at the time of melt molding tends to be sufficient for improving moldability. On the other hand, when the mass fraction of the plasticizer is 20% by mass or more, even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin molecular chain is not broken, and the pore structure is uniform and fine. Are easily formed, and the strength is also easily increased.

  The inorganic material is not particularly limited, and examples thereof include oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, Nitride ceramics such as boron nitride; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, Ceramics such as bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fiber. These may be used alone or in combination of two or more. Among these, silica, alumina, and titania are preferable from the viewpoint of electrochemical stability, and silica is particularly preferable from the viewpoint of easy extraction.

  The ratio between the polyolefin resin composition and the inorganic material is preferably 5% by mass or more, more preferably 10% by mass or more with respect to the total mass from the viewpoint of obtaining good separability. From the viewpoint of ensuring strength, the content is preferably 99% by mass or less, and more preferably 95% by mass or less.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. Examples of the heat conductor used for cooling and solidifying include metals, water, air, and plasticizers. Among these, it is preferable to use a metal roll because of its high heat conduction efficiency. In particular, when the extruded kneaded product is brought into contact with a metal roll, sandwiching it between the gaps of the plurality of rolls further increases the heat conduction efficiency, and the sheet is oriented to increase the film strength, thereby improving the surface smoothness of the sheet. Therefore, this is a more preferable embodiment. The die lip interval when the melt-kneaded product is extruded from the T die into a sheet is preferably 200 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2,500 μm or less. When the die lip interval is 200 μm or more, the mess and the like are reduced, adverse effects on the film quality such as streaks and defects are reduced, and the risk of film breakage and the like in the subsequent stretching process can be reduced. On the other hand, when the die lip interval is 3,000 μm or less, the cooling rate is increased, cooling unevenness can be prevented, and the thickness stability of the sheet can be maintained.

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. By rolling the sheet, particularly the orientation of the surface layer portion can be increased. The rolling surface magnification is preferably more than 1 and 3 or less, more preferably more than 1 and 2 or less. When the rolling ratio exceeds 1, the plane orientation increases, and the film strength of the polyolefin resin porous film (A) finally obtained increases. On the other hand, when the rolling ratio is 3 times or less, there is an advantage that a uniform porous structure can be formed in the thickness direction of the film by reducing the orientation difference between the surface layer portion and the center inside.

  Next, the pore-forming material is removed from the sheet-like molded body to obtain a polyolefin resin porous film (A). As a method for removing the hole forming material, for example, a method of extracting the hole forming material by immersing the sheet-like molded body in an extraction solvent and sufficiently drying it may be mentioned. The method for extracting the hole forming material may be either a batch type or a continuous type. In order to suppress shrinkage of the polyolefin resin porous membrane (A) membrane, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. The pore forming material remaining amount in the polyolefin resin porous membrane (A) is preferably less than 1% by mass with respect to the mass of the entire polyolefin resin porous membrane (A).

  The extraction solvent used when extracting the pore-forming material is a poor solvent for the polyolefin resin and a good solvent for the pore-forming material and having a boiling point lower than the melting point of the polyolefin resin. preferable. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation. When an inorganic material is used as the pore forming material, an aqueous solution containing an alkali such as sodium hydroxide or potassium hydroxide can be used as the extraction solvent.

It is preferable to stretch | stretch the film | membrane which comprises the said sheet-like molded object or polyolefin resin porous membrane (A). Stretching may be performed before extracting the hole forming material from the sheet-shaped molded body, or the film constituting the polyolefin resin porous film (A) after extracting the hole forming material from the sheet-shaped molded body. You may do it for. Furthermore, it may be performed before and after extracting the hole forming material from the sheet-like molded body.
As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferred from the viewpoint of improving the film strength and the like of the resulting polyolefin resin porous membrane (A). By stretching the sheet-like molded body at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, the polyolefin resin porous film (A) finally obtained is difficult to tear, and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferable from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property. From the viewpoint of controllability of plane orientation, sequential biaxial stretching is preferable.

Here, simultaneous biaxial stretching means stretching of MD (machine direction (length direction) of continuous molding of polyolefin resin porous membrane (A)) and TD (MD of polyolefin resin porous membrane (A) membrane of 90 °). It refers to a stretching method in which stretching in a direction crossing at an angle is performed simultaneously. The draw ratio in each direction may be the same or different. Sequential biaxial stretching refers to a stretching method in which MD and TD stretching are performed independently. When the MD or TD is stretched, the other direction is preferably in an unconstrained state or a fixed state.
The draw ratio is preferably in the range of 20 times to 100 times, and more preferably in the range of 25 times to 70 times, as the surface magnification. The draw ratio in each axial direction is preferably in the range of 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, and 5 to 8 times in TD. More preferably, it is the range. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the resulting polyolefin resin porous membrane (A). On the other hand, when the total area magnification is 100 times or less, the film in the stretching step Breaking is prevented and high productivity tends to be obtained.

  In order to suppress shrinkage of the membrane constituting the polyolefin resin porous membrane (A), heat treatment can be performed for the purpose of heat setting after the stretching step or after the membrane is formed. Further, the membrane constituting the polyolefin resin porous membrane (A) may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

The membrane constituting the polyolefin resin porous membrane (A) is preferably subjected to heat treatment for the purpose of heat setting from the viewpoint of suppressing shrinkage. As a heat treatment method, a stretching operation performed at a predetermined temperature atmosphere and a predetermined stretching rate for the purpose of adjusting physical properties and / or a relaxation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of reducing stretching stress. Operation is mentioned. The relaxation operation may be performed after the stretching operation. These heat treatments can be performed using a tenter, a roll stretching machine or the like.
The stretching operation is performed by subjecting the membrane MD and / or TD to stretching 1.1 times or more, more preferably 1.2 times or more, so that the polyolefin resin porous membrane (A) having higher strength and high porosity can be obtained. It is preferable from a viewpoint obtained.

  The relaxation operation is an operation for reducing the film to MD and / or TD. The relaxation rate is a value obtained by dividing the dimension of the film after the relaxation operation by the dimension of the film before the relaxation operation. When both MD and TD are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate. The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and still more preferably 0.95 or less. The relaxation rate is preferably 0.5 or more from the viewpoint of film quality. The relaxation operation may be performed in both the MD and TD directions, but may be performed in only one of the MD and TD.

  The stretching and relaxation operations after extraction of the pore forming material are preferably performed in the TD direction. The treatment temperature during the stretching and relaxation operations is preferably lower than the melting point (hereinafter also referred to as “Tm”) of the polyolefin resin, and more preferably 1 to 25 ° C. lower than Tm. The temperature during the stretching and relaxation operation is preferably in the above-mentioned range from the viewpoint of the balance between the thermal shrinkage reduction and the porosity.

  The ratio of MD tensile strength / TD tensile strength of the polyolefin microporous membrane (A) is related to the orientation of the polymer chain formed by pulling or stretching by extrusion molding. The polyolefin porous membrane (A) in the present embodiment has a ratio of MD / TD tensile strength of 1.0 to 1.0 from the viewpoint of suppressing the expansion of the hole in the ruptured portion during penetration and being excellent in a nail penetration test. 5.5 is preferable, 1.0 to 3.5 is more preferable, and 1.0 to 2.5 is still more preferable. When the ratio of MD / TD tensile strength deviates from 1.0 to 5.5, the orientation anisotropy of the polymer chain becomes excessively strong. As a result, once the hole is drilled, the crack expands along the direction of stronger orientation. On the other hand, if the ratio of MD / TD tensile strength is within the above range, the orientation of the polymer chain is isotropic, and the expansion of the pores is suppressed. When the ratio of MD / TD tensile strength is within the above range, even when the separator of this embodiment is supplied as a wound body, the fluttering of the film is suppressed during feeding from the separator reel, and high speed winding is performed. It is also preferable from the viewpoint of suppressing poor ear standing.

  The air permeability of the polyolefin resin porous membrane (A) in this embodiment is preferably 10 sec / 100 cc or more from the viewpoint of safety and suppression of self-discharge, and is 500 sec / 100 cc or less from the viewpoint of ion permeability. It is preferable. The air permeability of the polyolefin resin porous membrane is more preferably 100 to 220 sec / 100 cc.

<Resin binder (b-1)>
The resin binder (b-1) used in this embodiment is
The gel fraction in the toluene solution is 90 to 99% by mass,
The glass transition temperature is exhibited in the region below 30 ° C., and the degree of swelling with respect to the ethylene carbonate / diethyl carbonate mixture (volume ratio: 2/3) is 105 to 200%.

(Gel fraction of resin binder (b-1))
The gel fraction of the resin binder (b-1) is an insoluble content ratio of the resin binder (b-1) to toluene, and corresponds to the degree of crosslinking in the resin binder (b-1).
The gel fraction of the resin binder (b-1) in this embodiment is 90 to 99%, preferably 95 to 98%, more preferably 96 to 98%. When the gel fraction is 90% by mass or more, dissolution and swelling in an organic solvent (particularly a non-aqueous solvent contained in the electrolytic solution) can be suppressed, and the strength of the resin binder (b-1) inside the battery can be maintained. When the gel fraction in toluene is 99% or less, the binding property with the electrode is excellent.
The gel fraction of the resin binder (b-1) is adjusted by adjusting the polymerization conditions such as the type and ratio of the monomer used when producing the resin binder (b-1), the polymerization temperature, and the monomer addition time. It is possible to adjust to the range.

(Glass transition temperature Tg of resin binder (b-1))
Resin binder in the present embodiment (b-1 shows a glass transition temperature Tg in a region below 30 ° C. The glass transition temperature of the resin binder (b-1) is preferably 10 ° C. or less, more preferably 0. The resin binder (b-1) having a glass transition temperature of less than 30 ° C. has adhesiveness with the electrode and adhesive strength with the polyolefin resin porous membrane (A). And from the viewpoint of the binding strength with the inorganic filler (b-2).

(Swelling degree of resin binder (b-1))
The degree of swelling of the resin binder (b-1) is the degree of swelling with respect to an ethylene carbonate / diethyl carbonate mixed liquid (volume ratio: 2/3), which is a typical example of the solvent contained in the electrolytic solution. The degree of swelling of the resin binder (b-1) is 105 to 200%, preferably 105 to 180%, more preferably 105 to 150%.
By setting the degree of swelling of the resin binder (b-1) within the above range, the resin binder (b-1) swells with respect to the electrolytic solution while maintaining the binding property of the resin binder (b-1) in the electrolytic solution. Can be suppressed. Therefore, a separator having excellent heat resistance can be obtained, and the safety of the nail penetration test of the secondary battery can be improved.

When the swelling degree of the resin binder (b-1) with respect to the electrolytic solution is 105% or more, the resin binder (b-1) in the porous layer in the secondary battery can sufficiently contain the electrolytic solution. The resistance can be reduced, and the deterioration of cycle life and output characteristics can be suppressed. On the other hand, when the swelling degree of the resin binder (b-1) with respect to the electrolytic solution is 200% or less, the swelling of the resin binder (b-1) in the electrolytic solution can be suppressed, and the binding property can be expressed. Therefore, the heat resistance of the separator and the safety of nail penetration of the secondary battery can be maintained.
The degree of swelling of the resin binder (b-1) with respect to the electrolytic solution is determined based on the type and ratio of the crosslinkable monomer used when producing the resin binder (b-1), the type and ratio of other monomers, the polymerization temperature, and the addition of the monomer. By adjusting the polymerization conditions such as the addition time and the particle size, the above range can be adjusted.

(Constituent monomer unit of resin binder (b-1))
The resin binder (b-1) in the present embodiment is preferably an acrylic copolymer containing a (meth) acrylic compound as a monomer unit. Here, examples of the monomer include a non-crosslinkable monomer and a crosslinkable monomer.

Examples of non-crosslinkable monomers include unsaturated acid monomers, (meth) acrylic acid esters, epoxy group-containing vinyl monomers, methylol group-containing vinyl monomers, alkoxymethyl group-containing vinyl monomers, vinyl monomers having hydrolyzable silyl groups, Examples include unsaturated carboxylic acid alkyl esters, unsaturated polar compounds, unsaturated aromatic compounds, and vinyl cyanide. Specific examples of these are:
Examples of the unsaturated acid monomer include acrylic acid, methacrylic acid, fumaric acid, and itaconic acid; examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth). Acrylate, 2-ethylhexyl (meth) acrylate, phenyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, etc .; as the epoxy group-containing vinyl monomer, for example, glycidyl acrylate, glycidyl methacrylate, allyl Glycidyl ether, methyl glycidyl acrylate, methyl glycidyl methacrylate, etc .; as the methylol group-containing vinyl monomer, for example, N-methylol acrylamide, N-methylol methacrylate De, dimethylol acrylamide, dimethylol methacrylamide, and the like;

Examples of the alkoxymethyl group-containing vinyl monomer include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, etc .; as the vinyl monomer having a hydrolyzable silyl group For example, vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, etc .; the unsaturated carboxylic acid alkyl ester For example, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and the like; As polar compounds, for example, (meth) acrylamide or the like; as the unsaturated aromatic compound, e.g., styrene, alpha-methyl styrene, 4-hydroxystyrene;
Examples of the vinyl cyanide include (meth) acrylonitrile and the like.

  From the viewpoint of reducing the degree of swelling with respect to the electrolytic solution, methyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate are preferable among the non-crosslinkable monomers, and cyclohexyl (meth) acrylate is more preferable. The proportion of cyclohexyl (meth) acrylate used relative to all monomers is preferably 5% by mass or more, and most preferably 15% by mass or more.

Examples of the crosslinkable monomer include monomer monomers having two or more radical polymerizable double bonds.
As a monomer having two or more radical polymerizable double bonds, examples of the monomer having two radical polymerizable double bonds include divinylbenzene, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, Polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc .; monomers having three radical polymerizable double bonds such as trimethylolpropane triacrylate, trimethylol group Bread trimethacrylate and the like; as monomers having four radically polymerizable double bond, for example, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate and the like, can be exemplified respectively.

  As the crosslinkable monomer having two or more radical polymerizable double bonds used for the resin binder (b-1), it is preferable to select a crosslinkable monomer having a large number of radical polymerizable double bonds. The gel fraction of the binder (b-1) can be increased and the degree of swelling with respect to the electrolytic solution can be decreased.

  The use amount of the crosslinkable monomer having two or more radical polymerizable double bonds is 0.1% by mass or more as a ratio with respect to 100 parts by mass in total of all monomers used for the resin binder (b-1). Is preferably 0.5% by mass or more, and more preferably 1% by mass or more. When this value is 0.1% by mass or more, the gel fraction of the resin binder (b-1) can be increased, and the swelling degree of the electrolytic solution can be decreased. Further, the ratio of the use amount of the crosslinkable monomer having two or more radical polymerizable double bonds to the total 100 parts by mass of all monomers is preferably 10% by mass or less, and 7% by mass. More preferably, it is more preferably 5% by mass or less. By setting this value to 10% by mass or less, the resin binder (b-1) can contain an electrolytic solution, so that better battery performance can be exhibited.

(Manufacturing method of resin binder (b-1))
The resin binder (b-1) used in the present embodiment is preferably obtained as a latex by a known emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, It can carry out by a conventionally well-known method. For example, in an aqueous medium, preferably in a dispersion system comprising a chain transfer agent, a surfactant, and a radical polymerization initiator, and other additive components used as necessary, as basic components, the monomers described above This is a method for producing a latex by polymerization. In the polymerization, a method of making the monomer composition uniform throughout the entire polymerization process,
Various methods can be used as desired, such as a method of giving a morphological composition change of latex particles produced by sequentially or continuously changing in the polymerization process.

The solid content concentration in the latex of the resin binder (b-1) is preferably selected in the range of 30 to 60% by weight.
The average particle diameter of the resin binder (b-1) is preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, and most preferably 100 nm or less. When the average particle diameter of the resin binder (b-1) is 300 nm or less, the reaction rate can be increased when polymerizing particles of 300 nm or less. Accordingly, the gel fraction of the resin binder (b-1) is increased and the molecular weight between cross-linking points is decreased, so that the degree of swelling with respect to the electrolytic solution can be decreased.
The average particle diameter of the resin binder (b-1) can be measured by the method described later when it is dispersed in the latex and when it is granular in the porous layer (B) constituting the separator.
The average particle diameter of the resin binder (b-1) can be adjusted by using the seed latex, the surfactant, the use ratio of the polymerization initiator, and the like. In general, the higher the proportion of these used, the smaller the average particle size of the copolymer latex produced. The seed latex may be polymerized in the same reaction vessel prior to the polymerization of the latex of the present invention, or seed latex separately polymerized in a different reaction vessel may be used.

A chain transfer agent is generally used to adjust the molecular weight and gel generation amount of a synthetic resin. For example, mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-methylstyrene dimer that can be used in usual emulsion polymerization are used. it can.
About the polymerization temperature at the time of manufacturing a resin binder (b-1), it is preferable that it is 65 degreeC or more as average polymerization temperature, It is more preferable that it is 75 degreeC or more, It is further more preferable that it is 85 degreeC or more. . The average polymerization temperature is determined by the polymerization rate and the polymerization temperature. When the average polymerization temperature is 65 ° C. or higher, the polymerization rate is increased, and in particular, the crosslinking reaction is faster than the growth reaction. Therefore, the gel fraction of the resin binder (b-1) can be increased. By reducing the molecular weight between the crosslinking points, the degree of swelling with respect to the electrolytic solution can be controlled.

  The monomer for producing the resin binder (b-1) may be added all at once, or a part of the monomer may be added before the start of the reaction, and the remaining monomer may be additionally added as the polymerization proceeds. Also good. In the present embodiment, in order to obtain the above-described preferred resin binder (b-1), polymerization according to an aspect in which a monomer is added is preferable. The monomer addition time is preferably 2 hours or more, more preferably 3.5 hours or more, and even more preferably 5.5 hours or more. By setting the monomer addition time to 2 hours or longer, the monomer / polymer ratio in the reaction system can be kept low. As a result, since the crosslinking reaction is faster than the growth reaction, the gel fraction of the resin binder (b-1) is increased, and hence the molecular weight between the crosslinking points is decreased, so that the degree of swelling with respect to the electrolytic solution can be decreased. .

In producing the binder resin (b-1) of this embodiment, an anionic emulsifier is preferably used.
Regarding the amount of the emulsifier in the initial state (state of polymerization rate of 10% by mass or less) when the resin binder (b-1) is produced, the amount of the anionic emulsifier is 0.05 parts by mass or more with respect to 100 parts by mass of the monomer. It is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and most preferably 0.5 parts by mass or more. By setting the amount of the anionic emulsifier to 0.05 parts by mass or more, the number of particles generated in the initial stage can be increased, and the final particle size of the resin binder (b-1) can be reduced. This makes the crosslinking reaction faster than the growth reaction. Accordingly, the gel fraction of the resin binder (b-1) is increased and the molecular weight between cross-linking points is decreased, so that the degree of swelling with respect to the electrolytic solution can be decreased.

In producing the binder resin (b-1) of this embodiment, it is preferable to use a radical polymerization initiator.
The amount of radical polymerization initiator in the initial state (state of polymerization rate of 10% by mass or less) when producing the resin binder (b-1) is 0.05 parts by mass or more with respect to 100 parts by mass of the monomer. It is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and most preferably 0.3 parts by mass or more. By setting the radical polymerization initiator amount to 0.05 parts by mass or more, the number of particles generated in the initial stage can be increased, so that the final particle size of the resin binder (b-1) can be reduced. This makes the crosslinking reaction faster than the growth reaction. Accordingly, the gel fraction of the resin binder (b-1) is increased and the molecular weight between cross-linking points is decreased, so that the degree of swelling with respect to the electrolytic solution can be decreased.

<Inorganic filler (b-2)>
Although it does not specifically limit as an inorganic filler (b-2) used for the said porous layer (B), Heat resistance and electrical insulation are high, and it is electrochemically stable in the use range of a lithium ion secondary battery. Some are preferred.
Examples of the inorganic filler (b-2) include an aluminum compound, a magnesium compound, and other compounds.

Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, and hydrotalcite.
Examples of the magnesium compound include magnesium sulfate and magnesium hydroxide.
Other compounds include oxide ceramics, nitride ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fiber, etc. Is mentioned. Examples of the oxide ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide and the like. Examples of nitride ceramics include silicon nitride, titanium nitride, boron nitride and the like. Examples of the clay mineral include talc, montmorillonite, sericite, mica, amicite, bentonite and the like.
These may be used alone or in combination.

Among these, aluminum oxide, aluminum hydroxide oxide, and aluminum silicate are preferable from the viewpoints of electrochemical stability and heat resistance. A specific example of aluminum oxide is alumina. Specific examples of the aluminum hydroxide oxide include boehmite. Specific examples of aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite.
As the aluminum oxide, alumina is more preferable from the viewpoint of electrochemical stability. By using particles mainly composed of alumina as the inorganic filler (b-2) constituting the porous layer (B), a very lightweight porous layer (B) is realized while maintaining high permeability. In addition, even when the thickness of the porous layer (B) is thinner, thermal shrinkage of the polyolefin resin porous membrane (A) at a high temperature tends to be suppressed, and excellent heat resistance tends to be exhibited. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Of these, α-alumina is most preferable because it is thermally and chemically stable.

  As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit due to generation of lithium dendrite. Realizing a very lightweight porous layer (B) while maintaining high permeability by adopting particles mainly composed of boehmite as the inorganic filler (b-2) constituting the porous layer (B) In addition, even when the thickness of the porous layer (B) is thinner, thermal shrinkage of the polyolefin porous membrane (A) at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the electrochemical device is more preferred.

  Among the aluminum silicates, kaolinite (hereinafter, also referred to as kaolin) mainly composed of kaolin mineral is preferable from the viewpoint of lightness and air permeability. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities. Particularly preferred. As the inorganic filler (b-2) constituting the porous layer (B), by adopting particles containing calcined kaolin as a main component, a very lightweight porous layer (B) is maintained while maintaining high permeability. In addition, the thermal shrinkage of the polyolefin resin porous membrane (A) at a high temperature is suppressed even when the thickness of the porous layer (B) is thinner, and excellent heat resistance tends to be exhibited.

  The average particle diameter of the inorganic filler (b-2) is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.2 μm or more and 5.0 μm or less, and 0.4 μm or more and 3. More preferably, it is 0 μm or less. It is preferable to adjust the average particle diameter of the inorganic filler (b-2) to the above range from the viewpoint of suppressing air shrinkage and thermal contraction of the separator at a high temperature.

As a particle size distribution of the inorganic filler (b-2), the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. The ratio of the maximum particle size / average particle size is preferably 50 or less, more preferably 30 or less, and still more preferably 20 or less. Adjusting the particle size distribution of the inorganic filler (b-2) to the above range is preferable from the viewpoint of suppressing the thermal contraction of the separator at a high temperature. Moreover, you may have a several particle size peak between the maximum particle size and the minimum particle size. In addition, as a method of adjusting the particle size distribution of the inorganic filler (b-2), for example, the inorganic filler (b-2) is pulverized using a ball mill, a bead mill, a jet mill or the like, and adjusted to a desired particle size distribution. And a method of blending the fillers (b-2) having a plurality of particle size distributions after adjustment.
Examples of the shape of the inorganic filler (b-2) include a plate shape, a scale shape, a polyhedron, a needle shape, a columnar shape, a spherical shape, a spindle shape, a lump shape, and the like. The inorganic filler (b-2) having the above shape is used. You may use in combination of multiple types. Among these, a plate shape, a scale shape, and a polyhedron are preferable from the viewpoint of improving permeability.

  The ratio of the inorganic filler (b-2) in the porous layer (B) is the permeability and heat resistance of the separator, and the inorganic filler (b-2) is bound in the porous layer (B). It can determine suitably from viewpoints, such as the required amount of the resin binder (b-1) to make. The proportion of the inorganic filler (b-2) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, from the viewpoint of the permeability and heat resistance of the separator. Especially preferably, it is 93 mass% or more, Most preferably, it is 96 mass% or more. Moreover, from the viewpoint of the required amount of the resin binder (b-1) for binding the inorganic filler (b-2) in the porous layer (B), the ratio of the inorganic filler (b-2) is 100 masses. % Is preferable, more preferably 99.5% by mass or less, still more preferably 99% by mass or less, and particularly preferably 98% by mass or less.

<Other ingredients>
The porous layer (B) may consist only of the resin binder (b-1) and the inorganic filler (b-2), or may contain other components besides these. Examples of other components used here include water retention agents, dispersants, thickeners, stabilizers, pH adjusters, and the like.

<Other characteristics of porous layer (B)>
From the viewpoint of improving heat resistance and insulation, the layer thickness of the porous layer (B) is preferably 1 μm or more, more preferably 1.0 μm or more, still more preferably 1.2 μm or more, and particularly preferably 1. It is 5 μm or more, particularly preferably 1.8 μm or more, and most preferably 2.0 μm or more. Further, from the viewpoint of increasing the capacity of the battery and improving the permeability, it is preferably 50 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less, and particularly preferably 7 μm or less.

The surface softening temperature of the porous layer (B) is preferably 30 to 60 ° C, more preferably 30 to 50 ° C, still more preferably 30 to 45 ° C, and particularly preferably 35 to 45 ° C. . When the surface softening temperature is 30 ° C. or higher, when the separator is rolled into a roll at the time of manufacture, when the separator is unwound at the time of pressure bonding with the electrode, the separators are not closely contacted and the separator is unwrinkled. It is preferable in that it can be performed. When the surface softening temperature is 60 ° C. or less, it is preferable in that wrinkles are not generated in a laminate obtained by pressure-bonding the electrode and the separator using a high-temperature press. The glass transition temperature of a polyolefin resin generally used as a separator material is not so high. However, according to the structure of the separator manufactured by the method of the present invention, there is an advantage that wrinkles are not generated in the obtained laminate even after pressure bonding at a high temperature.
The porous layer (B) may be formed only on one side of the polyolefin resin porous membrane (A) or may be formed on both sides.

<Method for forming porous layer (B)>
As a formation method of the porous layer (B) in this embodiment, Preferably a resin binder (b-1) and an inorganic filler (b-) are provided on at least one surface of the polyolefin resin porous membrane (A) mainly composed of a polyolefin resin. 2) and a method of forming a porous layer (B) by applying a coating solution containing other components used as necessary.
The form of the resin binder (b-1) in the coating liquid may be an aqueous solution dissolved or dispersed in water or an organic medium solution dissolved or dispersed in a general organic medium. Resin latex is preferred. “Resin latex” refers to a resin dispersed in a solvent. When the resin latex is used as the resin binder (b-1), the porous layer (B) containing the inorganic resin binder (b-1) and the inorganic filler (b-2) is added to at least the polyolefin resin porous film (A). When laminated on one side, the ion permeability is not easily lowered and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily obtained.

The method for coating the coating liquid on the polyolefin resin porous membrane (A) is not particularly limited as long as the required layer thickness and coating area can be realized. For example, a gravure coater method, a small-diameter gravure coater Method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing Method, spray coating method and the like.
The method of removing the solvent from the coating film after coating the coating liquid on the polyolefin resin porous membrane (A) is not particularly limited as long as it does not adversely affect the polyolefin resin porous membrane (A). Examples thereof include a method of drying the polyolefin resin porous membrane (A) at a temperature below its melting point, a method of drying under reduced pressure at a low temperature, and a method of extraction drying. Further, a part of the solvent may be left as long as the battery characteristics are not significantly affected. From the viewpoint of controlling the shrinkage stress in the MD direction of the polyolefin resin porous membrane (A) and the separator (polyolefin resin porous membrane (A) laminated with the porous layer (B)), the drying temperature, the winding tension, etc. are adjusted as appropriate. It is preferable.

<Separator>
The separator obtained by the method of this embodiment will be described.
The separator having a polyolefin resin porous membrane (A) and a porous layer (B) containing a resin binder (b-1) and an inorganic filler (b-2) is excellent in heat resistance and has a shutdown function. Therefore, it is suitable for a battery separator that separates the positive electrode and the negative electrode in the battery.
In particular, since the separator is difficult to short-circuit even at high temperatures, it can be safely used as a separator for a high electromotive force battery.
The residual rate of the porous layer (B) when the separator in this embodiment is subjected to ultrasonic treatment for 10 minutes in an ethylene carbonate / diethyl carbonate mixed solution (volume ratio: 2/3) at 25 ° C. is 60% or more. . This residual ratio is determined by appropriately selecting the gel fraction of the resin binder (b-1), the glass transition temperature, the degree of swelling of the electrolyte, the amount used, the type and amount of the inorganic filler (b-2), and the like. Can be adjusted.

In the separator of the present embodiment, the residual rate of the porous layer (B) after ultrasonic treatment under the above conditions is 60% by mass or more, preferably 70% by mass or more, and preferably 80% by mass or more. More preferably, it is more preferably 90% by mass or more. When the remaining rate is 60% by mass or more, the number of defects in the nail penetration test related to the safety of the battery can be reduced.
Both the MD heat shrinkage and the TD heat shrinkage at 130 ° C. of the separator are preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less. When the heat shrinkage rate is 15% or less, deformation under a high temperature environment can be suppressed. Moreover, even if the separator has a hole, since the expansion of the crack can be suppressed, it is excellent in the nail penetration test, which is preferable in terms of safety.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to an Example. The measurement methods and evaluation methods for various physical properties in the following production examples, examples, and comparative examples are as follows. Unless otherwise specified, various measurements and evaluations were performed under conditions of a room temperature of 23 ° C., 1 atm, and a relative humidity of 50%.

<Measurement method>
(1) Porosity (volume%) of polyolefin resin porous membrane (A)
A sample of 10 cm × 10 cm square is cut from the polyolefin resin porous membrane (A), its volume (cm ³ ) and mass (g) are measured, and the membrane density is 0.95 (g / cm ³ ), and the following formula is used. Calculated.
Porosity (%) = (volume−mass / membrane density) / volume × 100
(2) Air permeability of the separator (sec / 100cc)
In accordance with JIS P-8117, the air resistance measured by a Gurley type densometer G-B2 (trademark) manufactured by Toyo Seiki Seisakusho was used as the air permeability.

(3) Puncture strength (g) of polyolefin resin porous membrane (A)
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the polyolefin resin porous membrane (A) membrane was fixed by a sample holder having an opening diameter of 11.3 mm. Under an atmosphere of 25 ° C., a puncture test was performed on the central portion of the fixed polyolefin resin porous membrane (A) using a needle having a radius of curvature of 0.5 mm at the tip at a puncture speed of 2 mm / sec. The maximum puncture load at this time was defined as the puncture strength (g).

(4) Polyolefin resin porous membrane (A) average pore diameter (μm), curvature, and number of pores When the mean free path of the fluid is larger than the capillary pore diameter, the fluid inside the capillary is small in Knudsen's flow Is known to follow the flow of Poiseuille. Therefore, it is assumed that the air flow in the air permeability measurement of the polyolefin resin porous membrane (A) follows the Knudsen flow, and the water flow in the water permeability measurement of the polyolefin resin porous membrane (A) follows the Poiseuille flow. .

The pore diameter d (μm) and the curvature τa (dimensionless) are determined by the air transmission rate constant R _gas (m ³ / (m ² · sec · Pa)) and the water transmission rate constant R _liq (m ³ / (m ² · sec · Pa)), molecular velocity of air ν (m / sec), water viscosity η (Pa · sec), standard pressure Ps (= 101,325 Pa), porosity ε (%), and film thickness L It calculated | required from the (micrometer) using the following numerical formula.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
τa = (d × (ε / 100) × ν / (3L × Ps × P _gas )) ^1/2
Here, R _gas and R _liq are respectively obtained using the following mathematical expressions.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101,325))
R _liq = water permeability / 100

The air permeability and the water permeability are obtained as follows.
[Air permeability]
The air permeability referred to here can be obtained as the air resistance by measuring the polyolefin resin porous membrane (A) in accordance with the description of “(2) Air permeability of separator”.
[Water permeability]
A polyolefin resin porous membrane (A) previously immersed in ethanol was set in a stainless steel liquid-permeable cell having a diameter of 41 mm, and the ethanol in this layer was washed with water. Thereafter, water was permeated at a differential pressure of about 50,000 Pa, and the water permeation amount per unit time, unit pressure, unit area was calculated from the water permeation amount (cm ³ ) when 120 seconds had elapsed, and this was regarded as the water permeability. .
In addition, the molecular velocity ν of air is a gas constant R (= 8.314), an absolute temperature T (K), a circumference π, and an average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol). From the above, it is obtained using the following mathematical formula.
ν = {(8R × T) / (π × M)} ^1/2
Further, the number of holes B (pieces / μm ² ) was obtained from the following equation.
B = 4 × (ε / 100) / (π × d ² × τa)

(5) Thickness (film thickness, μm)
(5) -1 Polyolefin resin porous membrane (A) membrane and battery separator thickness (μm)
Samples of 10 cm x 10 cm square were cut out from the polyolefin resin porous membrane (A) membrane and battery separator, respectively, and the film thicknesses at 9 locations (3 points x 3 points) selected in a lattice shape were measured using a microthickness meter (Toyo Using a Seiki Seisakusho Co., Ltd. type KBM), it was measured at room temperature 23 ± 2 ° C. The average value of the measured values at nine locations was taken as the thickness (μm) of the polyolefin resin porous membrane (A) or the separator for an electricity storage device.

(5) -2 Thickness (μm) of porous layer (B)
The thickness of the porous layer (B) was measured by observing the cross section of the separator using a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI”. A sample separator was cut to about 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule and frozen with liquid nitrogen, and then the sample was cleaved with a hammer. The sample was subjected to osmium vapor deposition, observed at an acceleration voltage of 1.0 kV and 30,000 times, and the thickness of the porous layer (B) was calculated. At this time, in the SEM image, the outermost surface region where the porous structure of the cross section of the polyolefin resin porous membrane (A) was not visible was defined as the region of the porous layer (B).

(6) Glass transition temperature (Tg) of resin binder (b-1)
An appropriate amount of the resin binder (b-1) -containing latex was taken in an aluminum dish and dried with a hot air dryer at 130 ° C. for 30 minutes to obtain a dry film. About 17 mg of the obtained dried film was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained using a DSC measuring apparatus (manufactured by Shimadzu Corporation, DSC 6220). The measurement conditions were as follows.

(First stage temperature rise program)
Start at 70 ° C and heat up at a rate of 15 ° C per minute. Maintained for 5 minutes after reaching 110 ° C.
(Second stage temperature drop program)
The temperature drops from 110 ° C at a rate of 40 ° C per minute. Maintain for 5 minutes after reaching -70 ° C.
(Third-stage temperature rising program)
The temperature was raised from -70 ° C to 300 ° C at a rate of 15 ° C per minute. DSC and DDSC (DSC derivative) data are acquired at the third stage of temperature increase. The peak top temperature of DDSC was taken as the glass transition temperature.

(7) Toluene gel fraction of resin binder (b-1) A latex containing the resin binder (b-1) was coated on a Teflon (registered trademark) plate, and the conditions were 23 ° C./50% RH for 24 hours. Left to stand. Next, it was left still in an oven set at 90 ° C. for 15 minutes. The film made of the resin binder (b-1) formed by this operation was peeled off from the Teflon (registered trademark) plate.
About 0.5 g of the obtained resin binder (b-1) film was precisely weighed, and this value was defined as (a) g. The precisely weighed film was immersed in 30 ml of toluene and shaken for 3 hours. The film after shaking was filtered with a 325 mesh having a known mass and dried at 140 ° C. for 1 hour, and the total mass of the mesh and insoluble matter was weighed. By subtracting the mesh mass from this value, a dry weight (b) g of toluene-insoluble matter was obtained. The toluene gel fraction was calculated by the following formula.
Toluene gel fraction of resin binder (b-1) = (b) / (a) × 100 [%]

(8) Swelling degree of electrolyte solution of resin binder (b-1) After leaving the latex containing the resin binder (b-1) in an oven at 80 ° C for 9 hours, vacuum drying was further performed at 80 ° C for 12 hours, A dried product of the resin binder (b-1) was obtained. The mass of about 0.5 g of the dried product of the obtained resin binder (b-1) was weighed and used as the mass before immersion (W _A ). This resin binder (b-1) dried product was placed in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (volume ratio) at 25 ° C. and immersed for 24 hours. It was taken out and wiped off with a towel paper, and the mass was immediately measured to obtain the mass after immersion (W _B ).
The degree of swelling of the resin binder (b-1) was calculated from the following formula.
Swelling degree (%) = W _B / W _A × 100
In the above formula, when the resin binder (b-1) sample does not swell or dissolve in the mixed solvent, the degree of swelling is 100%.

(9) Average particle diameter of resin binder (b-1) (9-1) Average particle diameter in latex The average particle diameter of the resin binder (b-1) in latex is determined by a particle diameter measuring device (manufactured by Nikkiso Co., Ltd.). , Microtrac UPA150). As measurement conditions, loading index = 0.15 to 0.3, measurement time 300 seconds, and in the obtained data, a numerical value of 50% volume particle diameter was defined as an average particle diameter.
(9-2) Average Particle Diameter in Separator The average particle diameter of the granular resin binder (b-1) in the porous layer (B) constituting the separator is the scanning electron microscope (SEM) of the ruthenium-stained separator. Using “Model S-4800, manufactured by HITACHI”, the measurement was performed by observing at an acceleration voltage of 1.0 kV and 30,000 times. The part with the largest diameter of the resin binder (b-1) was defined as the particle diameter, and the average value of 20 particles was defined as the average particle diameter.

(10) Residual rate after ultrasonic treatment of porous layer (B) in electrolyte solution The mass of a sample obtained by cutting the separator into 76 mm × 26 mm was measured, and the mass before ultrasonic treatment was D. This separator sample was placed in a 50 mL vial containing 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (volume ratio) at 25 ° C., and an ultrasonic cleaner (model US-102 manufactured by SND Corporation). ) For 10 minutes at an oscillation frequency of 38 kHz. Then, after taking out a sample and wash | cleaning with ethanol, it was made to dry at room temperature, the sample mass was measured, and it was set as mass after ultrasonic treatment: E. As a sample mass of 76 mm × 26 mm square of the polyolefin resin porous membrane used as the base material: F, the residual ratio of the porous layer in the electrolytic solution after ultrasonic treatment was calculated from the following equation.
Residual rate (%) = (E−F) / (D−F) × 100

(11) MD / TD heat shrinkage rate (%)
The Zeparator was cut into 100 mm squares so that each side was parallel to the MD and TD of the polyolefin resin porous membrane (A) as a base material layer, and left in an oven adjusted to 130 ° C. for 1 hour. The MD / TD heat shrinkage rate of the separator was measured.

(12) Battery safety test (nail penetration test)
a. Battery production
(A-1) Preparation of positive electrode plate
92.2% by mass of lithium cobalt composite oxide LiCoO ₂ as an active material, 2.3% by mass of flake graphite and acetylene black as a conductive agent, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a binder (Solid content conversion) was dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. The slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the positive electrode was 250 g / m ₂ , and the active material bulk density was 3.00 g / cm ³ . This was cut into a width of about 40 mm to form a strip.

(A-2) Production of negative electrode plate
Artificial graphite 96.9% by mass as an active material, ammonium salt of carboxymethyl cellulose 1.4% by mass (in terms of solid content) as a binder, and styrene-butadiene copolymer (Tg = −40 ° C., particle size 80 nm) 1.7% by mass (Solid content conversion) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ . This was cut into a width of about 40 mm to form a strip.

(A-3) Preparation of non-aqueous electrolyte
An electrolyte solution was prepared by dissolving LiPF ₆ as a solute to a concentration of 1.0 mol / liter in a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (volume ratio) as a nonaqueous electrolyte solution.
(A-4) Winding and assembly
The separator, strip-shaped positive electrode, and strip-shaped negative electrode were stacked in the order of the strip-shaped negative electrode, the separator, the strip-shaped positive electrode, and the separator and wound in a plurality of times to form an electrode plate laminate. After pressing this electrode plate laminate into a flat plate, it is housed in an aluminum container, the aluminum lead led out from the positive electrode current collector is used as the container wall, and the nickel lead derived from the negative electrode current collector is used as the container lid terminal part. Connected. Furthermore, after injecting the non-aqueous electrolyte described above into this container, the rectangular lithium ion battery was produced by sealing. The square lithium ion battery thus manufactured is designed to have a vertical (thickness) of 6.3 mm, a width of 30 mm, and a height of 48 mm, and a nominal discharge capacity of 620 mAh.

b. Capacity measurement (mAh)
The prismatic lithium ion battery assembled as described above was charged with a constant current and constant voltage (CCCV) for 6 hours under the conditions of a current value of 310 mA (0.5 C) and a final battery voltage of 4.2 V. At this time, the current value immediately before the end of charging was almost zero. Then, it was left for 1 week (aging) in an atmosphere at 25 ° C. Next, after charging with a constant current constant voltage (CCCV) for 3 hours under the conditions of a current value of 620 mA (1.0 C) and a termination battery voltage of 4.2 V, the battery is discharged to a battery voltage of 3.0 V with a constant current value (CC) of 620 mA. I went through the cycle. The discharge capacity at this time was defined as the initial discharge capacity. A battery having an initial discharge capacity within ± 10 mA was used for safety evaluation.

c. Safety evaluation (nail penetration test)
For a battery charged with a constant current and constant voltage (CCCV) for 3 hours under the conditions of a current value of 620 mA (1.0 C) and a final battery voltage of 4.2 V, an iron round nail having a diameter of 2.7 mm is placed at 20 ° C. Under the environment, it penetrated at a speed of 5 mm / sec, and the heat generation state at that time was observed.
The case where the maximum temperature reached on the battery surface in the vicinity of the battery penetration point was less than 100 ° C was accepted, and the case where it was 100 ° C or more was rejected. 20 samples were evaluated per sample, and the number of rejects was defined as the number of defective products.

<Synthesis Example of Resin Binder (b-1)>
[Synthesis Example 1]
Into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 74 parts by mass of water and Aqualon KH1025 (polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt: 25 as an initial charge: 25 0.125 parts by mass (aqueous solution / Daiichi Kogyo Seiyaku Co., Ltd.) 0.125 parts by mass (in terms of solid content) and Adekaria soap SR1025 (25% by mass aqueous solution / product by ADEKA) 0.125 parts by mass (in terms of solids) ), The temperature in the reaction vessel was kept at 75 ° C. (polymerization temperature (1)), and 0.15 part by mass of ammonium peroxodisulfate (10 mass aqueous solution) (in terms of solid content) was added. 5 minutes after the addition, as a non-crosslinkable monomer, 11.8 parts by weight of methyl methacrylate, 5 parts by weight of cyclohexyl methacrylate, 1 part by weight of butyl methacrylate, 33 parts by weight of butyl acrylate, 42 parts by weight of 2-ethylhexyl methacrylate, 0.1 part of methacrylic acid Parts by weight, acrylic acid 0.1 parts by weight, glycidyl methacrylate 0.8 parts by weight, 2-hydroxyethyl methacrylate 5 parts by weight, and γ-methacryloxypropyltrimethoxysilane 0.2 parts by weight;
As a crosslinkable monomer, 1 part by mass of trimethylolpropane triacrylate;
As emulsifiers, Aqualon KH1025: 0.15 parts by mass (in terms of solid content) and Adekaria soap SR1025 (25% by mass aqueous solution): 0.15 parts by mass (in terms of solid content);
As an initiator, an emulsified mixed solution composed of 10% aqueous solution of ammonium peroxodisulfate: 0.15 parts by mass (in terms of solid content) and 65 parts by mass of water was added to the reaction vessel over 2.5 hours. Meanwhile, the reaction solution temperature was controlled to 75 ° C. (polymerization temperature (1), polymerization time (1)). After completion of the addition of the emulsified mixture, the mixture is stirred at 75 ° C. for 1 hour (polymerization temperature (2), polymerization time (2)), and then heated from 75 ° C. to 85 ° C. over 1 hour (polymerization temperature (3). Time (3)) and further stirring at 85 ° C. for 1 hour (polymerization temperature (4), polymerization time (4)) to complete the reaction. From the start of the reaction to completion, the pH of the reaction solution was maintained at 4 or less.
After completion of the reaction, the reaction solution was cooled to room temperature. After cooling, the reaction solution was filtered through a 200-mesh wire mesh to remove aggregates and the like, and then the pH was adjusted to 8 with 25% by mass of ammonia water, and water was added so that the solid content was 40% by mass. . Subsequently, the resin binder latex (LTX1) was obtained by filtering with a 325 mesh metal-mesh. The obtained resin binder-containing latex (LTX1) had a glass transition temperature of −40 ° C. and a volume average particle size of 141 nm.

[Synthesis Examples 2 to 20]
In Synthesis Example 1, the amount of the initial emulsifier, the kind and amount of the crosslinkable monomer, the kind and amount of the non-crosslinkable monomer, the polymerization temperature, and the polymerization time were changed as shown in Table 1, respectively. Similarly, resin binder-containing latexes (LTX2) to (LTX20) were obtained.
In Synthesis Examples 2, 4, 19 and 20, the temperature shown in Table 1 was maintained without increasing the temperature at the polymerization temperature (3).

Abbreviations of emulsifiers, initiators, and monomers in Table 1 above have the following meanings, respectively.
[emulsifier]
KH1025: Aqualon KH1025 (polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt: 25% by mass aqueous solution / Daiichi Kogyo Seiyaku Co., Ltd.)
SR1025: Adekaria soap SR1025 (25% by weight aqueous solution / manufactured by ADEKA Corporation)
[Initiator]
APS: ammonium peroxodisulfate

[Non-crosslinking monomer]
CHMA: cyclohexyl methacrylate MAA: methacrylic acid AA: acrylic acid AM: acrylamide HEMA: 2-hydroxyethyl methacrylate MMA: methyl methacrylate BMA: butyl methacrylate BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate GMA: glycidyl methacrylate MTMS: γ-methacryloxy Propyltrimethoxysilane

[Crosslinking monomer]
A-TMPT: Trimethylolpropane triacrylate P-TA: Pentaerythritol tetraacrylate

<Manufacture of polyolefin resin porous membrane (A)>
Production Example 1
47.5 parts by mass of homopolymer polyethylene having a volume average molecular weight of 700,000, 47.5 parts by mass of homopolymer polyethylene having a volume average molecular weight of 250,000, and 5 parts by mass of polypyrene pyrene having a volume average molecular weight of 400,000 Dry blended using a tumbler-blender. 1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant is added to 99 parts by mass of the obtained polymer mixture. Then, again by dry blending using a tumbler blender, an equal polymer mixture was obtained.

The resulting polymer equal mixture was purged with nitrogen and then fed to a twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump. The feeder and pump were adjusted so that the ratio of the amount of liquid paraffin in the total mixture extruded by melt kneading was 67% by mass (the concentration of the mixture such as polymer was 33% by mass). The melt kneading conditions were as follows: a preset temperature of 200 ° C., a screw rotation speed of 100 rpm, and a discharge rate of 12 kg / h.

The obtained melt-kneaded product was extruded and cast via a T-die on a cooling roll controlled at a surface temperature of 250 ° C. to obtain a gel sheet having a thickness of 1,600 μm. Next, this gel sheet was guided to a simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 6.1 times, and a preset temperature of 121 ° C. The stretched gel sheet was introduced into a methyl ethyl ketone bath and sufficiently immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was removed by drying. Next, the processed sheet was guided to a TD tenter and heat-set. The heat setting temperature was 120 ° C., the TD maximum magnification was 2.0 times, and the relaxation rate was 0.90.
As a result, the film thickness was 17 μm, the porosity was 60%, the air permeability was 84 seconds / 100 cc, the average pore diameter calculated by the gas-liquid method was d = 0.057 μm, the curvature τa = 1.45, the number of holes B = 165 / A polyolefin resin porous membrane (A1) having a μm ² and a pin puncture strength of 5,679 f in terms of 25 μm was obtained.

Example 1
[Formation of porous layer (B) and production of separator]
95.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm) as the inorganic filler (b-2), acrylic latex (solid content concentration 40%, swelling degree 168%) as the resin binder (b-1) 4.0 parts by mass (in terms of solid content) and 1.0 part by mass (in terms of solid content) of an aqueous polycarboxylate aqueous solution (manufactured by San Nopco, SN Dispersant 5468) as a dispersant are uniformly added to 100 parts by mass of water. A coating solution was prepared by dispersing.
Next, the surface of the polyolefin resin porous membrane (A1) obtained in Production Example 1 was subjected to corona discharge treatment (discharge amount 50 W), and then the above-mentioned coating solution was applied to the treated surface using a micro gravure coater. did. After coating, by drying at 60 ° C., a porous layer (B) having a thickness of 4 μm was formed on the polyolefin resin porous membrane (A1) to obtain a separator.
Table 2 shows the evaluation results of this separator according to the method described above.

Examples 2-16 and Comparative Examples 1-7
In Example 1, the coating liquid was prepared in the same manner as in Example 1 except that the latexes shown in Table 2 were used as the resin binder (b-1) and the inorganic filler (b-2). A separator was manufactured.
Table 2 shows the evaluation results of these separators according to the method described above.

Abbreviations of the inorganic filler and the dispersant in Table 2 have the following meanings.
[Inorganic filler (b-2)]
b-2a: Aluminum hydroxide oxide (average particle diameter: 1.0 μm)
b-2b: calcined kaolin (average particle size 1.0 μm)
b-2c: Alumina (average particle size 1.0 μm)
Each of the inorganic fillers (b-2) was used after being pulverized using a bead mill and adjusted to have an average particle size of 1.0 μm.
[Dispersant]
PCA: Ammonium polycarboxylate aqueous solution (manufactured by San Nopco, SN Dispersant 5468)

Claims (5)

On at least one side of the polyolefin resin porous membrane (A),
An inorganic filler (b-2);
The gel fraction in the toluene solution is 90 to 99% by mass, the glass transition temperature is shown in the region below 30 ° C., and the swelling degree with respect to the ethylene carbonate / diethyl carbonate mixture (volume ratio: 2/3) is 105 to 200. % Resin binder (b-1),
A battery separator comprising a porous layer (B) containing
The residual rate of the porous layer (B) when the battery separator is subjected to ultrasonic treatment for 10 minutes in an ethylene carbonate / diethyl carbonate mixed solution (volume ratio: 2/3) at 25 ° C. is 60% or more. The battery separator according to the present invention.   The battery separator according to claim 1, wherein the resin binder (b-1) exhibits a glass transition temperature in a region of 0 ° C. or lower.   The battery separator according to claim 1 or 2, wherein the resin binder (b-1) is an acrylic polymer.   The battery separator according to any one of claims 1 to 3, which is a nonaqueous electrolyte battery separator.   A nonaqueous electrolyte battery comprising the separator for a nonaqueous electrolyte battery according to claim 4, a positive electrode, a negative electrode, and an electrolytic solution.