JP2016072155A - Method of manufacturing separator for power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a separator for power storage device excellent in adhesion to an electrode, and exhibiting excellent cycle characteristics without causing any stickiness.SOLUTION: The method of manufacturing a separator for power storage device includes a step for forming a porous layer by coating a porous substrate layer with a coating liquid which contains an inorganic agent, a resin binder and a solvent and then drying the layer. In the method, the surface softening temperature of the porous layer is 30-60°C, the immobilization time at the average drying temperature of the coating liquid is 10-120 sec, and the resin binder contains a first resin binder exhibiting the glass-transition temperature in a region of 30°C or more, and a second resin binder exhibiting the glass-transition temperature in a region of less than 30°C.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a separator for an electricity storage device. Specifically, for example, a battery such as a primary battery, a secondary battery, or a fuel cell;
The present invention relates to a method for producing a separator suitably used for an electrical energy storage device or the like.

In power storage devices such as lithium ion secondary batteries and electric double layer capacitors, a separator made of a microporous substrate layer is provided between the positive and negative electrodes of the porous substrate layer. As a function of the separator, for example, in order to prevent direct contact between the positive and negative electrodes, permeate ions, etc., from the viewpoint of safety,
"Fuse characteristics" that immediately stop the battery reaction when the storage device is abnormally heated,
"Short characteristics" that maintain the original shape even at high temperatures and prevent dangerous situations where the cathode and anode materials react directly
Etc. are required.
As a material constituting such a separator, for example, non-woven fabric, paper, polyethylene terephthalate, polyolefin and the like are known.

In recent years, there has been a demand for improving the adhesion between an electrode and a separator from the viewpoint of uniform charge / discharge current and suppression of lithium dendrite growth in an electricity storage device. If the close contact between the separator and the electrode is improved, the charge / discharge current is expected to be uniform and the growth of lithium dendrite is expected to be suppressed. As a result, the charge / discharge cycle life of the electricity storage device may be improved. It will be expected.
Under such circumstances, for the purpose of improving the adhesion between the separator and the electrode, an attempt has been made to apply an adhesive resin binder to a microporous substrate layer made of polyolefin ( For example, see Patent Documents 1 and 2).

JP 2007-59271 A JP 2011-54502 A Special table 2009-518809 International Publication No. 2014/017651 JP 2012-38597 A Japanese Patent No. 5114654

According to the techniques of Patent Documents 1 and 2 described above, certain effects are certainly recognized for improving the cycle characteristics of the electricity storage device. However, these techniques are not satisfactory in terms of lithium ion permeability, and also cause a problem that “stickiness” occurs on the surface of the separator and handling properties are lowered.
In this regard, Patent Document 3 discloses a technique in which two or more kinds of resin binders are mixed and used in order to achieve both adhesion to the electrode and suppression of stickiness on the separator surface;
Patent Document 4 discloses a technique for controlling the migration of two or more types of resin binders;
Patent Document 5 discloses a technique in which two types of resin binders are applied in layers;
In Patent Document 6, the concept of the immobilization time of the coating liquid for suppressing the occurrence of streaks,
Each is listed.

However, the attempts in the above Patent Documents 3 to 5 have all been successful as attempts to improve industrially meaningful forms, such as some of which have not achieved the target and some have lost productivity. Not. In addition, the technique of patent document 6 is related with the coating liquid for coating paper, and the component of a coating liquid, solid content, a viscosity, a coating speed, a coating method, etc. differ. Therefore, the above conditions cannot be used for the intended use of the present invention. Therefore, the immobilization time of the coating liquid disclosed in Patent Document 6 cannot be applied to the application of the present invention. Furthermore, even if the technique of Patent Document 6 is forcibly applied to the intended use of the present invention, the adhesion with the electrode, the adhesive strength with the porous substrate layer, the binding strength of the inorganic filler, and the stickiness of the outermost surface of the separator It is not possible to obtain a separator that is excellent in all properties and handling properties.
The present invention has been made in order to overcome the above-described present situation. Accordingly, the object of the present invention is to provide excellent cycle characteristics without causing stickiness on the outermost surface of the separator as well as excellent adhesion to the electrode, adhesion strength to the porous substrate layer, and binding strength of the inorganic filler. It is providing the method for manufacturing the separator which gives the electrical storage device which shows this.

The inventors of the present invention have made extensive studies to achieve the above object. as a result,
When manufacturing a separator having a porous layer composed of an inorganic filler and a resin binder on the porous substrate layer,
As the resin binder, a plurality of types having different glass transition temperatures are mixed and used, and the immobilization time of the coating liquid to be applied to the porous substrate layer is controlled within an appropriate range. It has been found that the migration can be controlled in a desired manner, and the surface softening temperature of the formed porous layer can be controlled within an optimum range, so that the above-mentioned problems can be solved.
That is, the present invention is as follows.

[1] To the porous substrate layer (A),
Applying a coating liquid (B ′) containing an inorganic filler (b-2), a resin binder (b-1), and a solvent, followed by a step of forming a porous layer (B) by drying, A method for producing a separator for an electricity storage device, comprising:
The surface softening temperature of the porous layer (B) is 30 to 60 ° C.,
1st resin whose immobilization time in the average drying temperature of the said coating liquid (B ') is 10 to 120 second, and the said resin binder (b-1) shows a glass transition temperature in the 30 degreeC or more area | region. The manufacturing method of the said separator characterized by containing the 2nd resin binder (b-1-2) which shows a glass transition temperature in the area | region below 30 degreeC with a binder (b-1-1).
[2] The average drying temperature of the coating liquid (B ′) when forming the porous layer (B) is:
It is not more than the minimum film formation temperature of the first resin binder (b-1-1) and not less than the minimum film formation temperature of the second resin binder (b-1-2).
The manufacturing method of the separator as described in [1].
[3] The method for producing a separator according to [1] or [2], wherein the coating liquid (B ′) further contains a water retention agent (b-3).
[4] The method for producing a separator according to any one of [1] to [3], wherein the separator has an air permeability of 10 to 500 seconds / 100 cc.
[5] A separator for an electricity storage device manufactured by the method for manufacturing a separator according to any one of [1] to [4].
[6] A positive electrode, the separator according to [5],
A negative electrode,
A laminated body characterized by being laminated.
[7] An electricity storage device comprising the laminate according to [6].

According to the method of the present invention, a separator having both excellent adhesion with the electrode, adhesive strength with the porous base material layer, binding strength of the inorganic filler, stickiness of the outermost surface, and handling properties is excellent. Can be given in productivity.
An electricity storage device including a separator manufactured by the method of the present invention can maintain a high battery capacity for a long period of time.

The schematic sectional drawing which shows a part of apparatus used in order to measure the immobilization time of a coating liquid (B ') in an Example.

The separator produced by the method of the present invention is
A porous substrate layer (A);
A porous layer (B) containing an inorganic filler (b-2) and a resin binder (b-1);
Have

<Porous substrate layer (A)>
The porous substrate layer (A) in the present invention will be described.
As the porous substrate layer (A), those having a small electron conductivity, an ionic conductivity, a high resistance to an organic solvent, and a fine pore diameter are preferable.
As such a porous substrate layer (A), for example, a porous substrate layer containing a polyolefin resin; polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, Examples thereof include a porous substrate layer containing a resin such as polytetrafluoroethylene; a polyolefin fiber woven (woven fabric); a polyolefin fiber nonwoven fabric; paper; and an aggregate of insulating substance particles. Among these, when a multilayer porous substrate layer, that is, a battery separator, is obtained through a coating process, the coating liquid (B ′) is excellent in coating property, and the separator film thickness is reduced, so that From the viewpoint of increasing the active material ratio in the electricity storage device and increasing the capacity per volume, a porous substrate film containing a polyolefin resin (hereinafter also referred to as “polyolefin resin porous substrate film”) is preferable.

The polyolefin resin porous substrate film will be described.
The polyolefin resin porous substrate membrane is a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous substrate layer from the viewpoint of improving shutdown performance when used as a battery separator. A porous substrate layer formed of a product 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. For example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are used as monomers. Examples thereof include a homopolymer, a copolymer, or a multistage polymer. Moreover, these polyolefin resins may be used independently or may be used in mixture of 2 or more types.
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 invention, high density polyethylene means polyethylene having a density of 0.942 to 0.970 g / cm ³ . In the present invention, the density of polyethylene refers to a value measured according to the D) density gradient tube method described in JIS K7112 (1999).

  Moreover, it is preferable to use the mixture of polyethylene and a polypropylene as polyolefin resin from a viewpoint of improving the heat resistance of a porous base material layer (A). 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% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by 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, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass. Or less.

Since the porous base material layer (A) has a porous structure in which a large number of very small holes are gathered to form a dense communication hole, it has excellent ion conductivity and at the same time withstand voltage characteristics, Moreover, it has a feature of high strength.
The porous substrate layer (A) may be a single layer made of the above-described material or may be a laminated layer.

  The film thickness of the porous substrate layer (A) is preferably from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm, and even 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 porous substrate layer (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 porous substrate layer (A) is preferably 0.03 μm or more and 0.70 μm or less, more preferably 0.04 μm or more and 0.20 μm or less, still more preferably 0.05 μm or more and 0.10 μm or less, 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 porous substrate layer (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 porous substrate layer (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 porous substrate layer (A) can be measured by the method described later.
When the porous substrate layer (A) is composed of a polyolefin resin porous substrate film, the porosity is the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting. It can be adjusted by controlling the relaxation rate during heat setting, or by combining these.

  When the porous substrate layer (A) is a polyolefin resin porous substrate film, the viscosity average molecular weight of the polyolefin resin porous substrate film is preferably 30,000 or more and 12,000,000 or less, more preferably It is 50,000 or more and less than 2,000,000, more preferably 100,000 or more and 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.

There is no restriction | limiting in particular as a method of manufacturing a polyolefin resin porous base material film, 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 then the surface is made porous by peeling the interface between the polyolefin and the inorganic material by stretching,
(4) A method of making the polyolefin resin composition porous by immersing it in a poor solvent for polyolefin to coagulate the polyolefin and simultaneously removing the solvent.

  Hereinafter, as an example of a method for producing a porous substrate layer (A) comprising a polyolefin resin porous substrate film, a polyolefin resin composition and a pore-forming material are melt-kneaded to form a sheet, and then the pore-forming material is extracted. How to do will be described.

  First, the polyolefin resin composition and the hole forming material are melt-kneaded. As the melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc., while the resin component is heated and melted. A method of introducing and kneading the pore-forming material at an arbitrary ratio is 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 a uniform solution above 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. . Note that these plasticizers may be recovered and reused after extraction by an operation such as distillation. Further, preferably, before being put into the resin kneading apparatus, the polyolefin resin, other additives and plasticizer are previously kneaded in advance at a predetermined ratio using a Henschel mixer or the like. More preferably, in pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is appropriately heated in a resin kneader and kneaded while side-feeding. By using such a kneading method, the dispersibility of the plasticizer is increased, and when the sheet-shaped molded body of the melt-kneaded product of the resin composition and the plasticizer is stretched in a later step, a high magnification is obtained without breaking the film. Tend to stretch.

  Among the plasticizers, liquid paraffin is highly compatible with polyolefin resins such as polyethylene and polypropylene, and even when the melt-kneaded product is stretched, the interface between the resin and the plasticizer does not easily peel, and uniform stretching is possible. Is preferable because it tends to be easily implemented.

  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. For example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, nitriding Nitride ceramics such as boron; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite Ceramics such as asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fibers. 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 addition, when the extruded kneaded product is brought into contact with a metal roll, sandwiching it between the rolls further increases the efficiency of heat conduction, and the sheet is oriented to increase the film strength and improve the surface smoothness of the sheet. This is more preferable. 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, and there is little influence on the film quality such as streaks and defects, 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 fast and 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 performing rolling, the orientation of the surface layer portion can be particularly 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 finally obtained porous base material layer (A) tends to increase. On the other hand, when the rolling ratio is 3 times or less, the orientation difference between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

  Next, the pore-forming material is removed from the sheet-like molded body to obtain a porous substrate layer (A). As a method for removing the hole forming material, for example, a method of extracting the hole forming material by immersing the sheet-shaped 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 film constituting the porous base material layer (A), it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Moreover, it is preferable to make the pore formation material residual amount in a porous base material layer less than 1 mass% with respect to the mass of the whole porous base material layer (A).

  As the extraction solvent used when extracting the pore-forming material, it is preferable to use a solvent which is a poor solvent for the polyolefin resin and a good solvent for the pore-forming material and has a boiling point lower than the melting point of the polyolefin resin. . 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. Moreover, when using an inorganic material as a pore formation material, aqueous solution, such as sodium hydroxide and potassium hydroxide, can be used as an extraction solvent.

Moreover, it is preferable to extend | stretch the film | membrane which comprises the said sheet-like molded object or a porous base material layer (A). The stretching may be performed before extracting the hole forming material from the sheet-like molded body. Moreover, you may carry out with respect to the film | membrane which comprises the porous base material layer (A) which extracted the hole formation material from the said sheet-like molded object. 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 preferable from the viewpoint of improving the strength and the like of the obtained porous base material layer (A). When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous base material layer is difficult to tear and has a 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. Further, sequential biaxial stretching is preferred from the viewpoint of easy control of plane orientation.

  Here, simultaneous biaxial stretching means stretching in MD (machine direction (length direction) when continuously forming the porous substrate layer (A)) and TD (MD of the porous substrate layer (A) of 90 °. In the direction crossing at an angle of 2), and the stretching ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD and TD are stretched independently. When MD or TD is stretched, the other direction is fixed in an unconstrained state or a constant length. State.

  The draw ratio is preferably in the range of 20 times to 100 times in terms of surface magnification, and more preferably in the range of 25 times to 70 times. 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 porous base material layer (A). It tends to prevent and achieve high productivity.

  In order to suppress shrinkage of the film constituting the porous substrate layer (A), heat treatment can be performed for the purpose of heat setting after the stretching step or after the film is formed. Further, the membrane constituting the porous substrate layer (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 film constituting the porous base material layer (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 or a roll stretching machine.

The stretching operation is performed by stretching the film MD and / or TD by 1.1 times or more, more preferably 1.2 times or more, so that the porous substrate layer (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 only one of the MD and TD may be performed.
The stretching and relaxation operations after this plasticizer extraction are preferably performed at TD. The temperature in the stretching and relaxation operation is preferably lower than the melting point of the polyolefin resin (hereinafter also referred to as “Tm”), and more preferably in the range of 1 ° C. to 25 ° C. lower than Tm. When the temperature in the stretching and relaxation operation is in the above range, it is preferable from the viewpoint of the balance between the reduction in thermal shrinkage and the porosity.

<Porous layer (B)>
The porous layer (B) containing the inorganic filler (b-2) and the resin binder (b-1) will be described.
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 adopting particles mainly composed of alumina as the inorganic filler (b-2) constituting the porous layer, it is possible to realize a very lightweight porous layer (B) while maintaining high permeability. Even if the thickness of the porous layer (B) is thinner, thermal shrinkage of the porous substrate layer (A) at high temperatures is 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, thermal shrinkage of the porous base material layer (A) at a high temperature is suppressed even with a thinner porous layer thickness, 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 to this, even when the thickness of the porous layer (B) is thinner, the thermal contraction of the porous substrate layer (A) at a high temperature is suppressed, 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 the air permeability and heat shrinkage at 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 thermal shrinkage at high temperatures. 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.

The inorganic filler (b-2) in the porous layer (B) is preferably present uniformly in the porous layer (B). As the index, the amount of inorganic filler in the thickness range of 0 to 50% from the outer surface of the porous layer (B) (b-2U) / the amount of inorganic filler present in the thickness range exceeding 50% to 100% The ratio of (b-2D) is preferably 0.8 to 1.2, more preferably 0.85 to 1.15, and still more preferably 0.9 to 1.1. When the ratio is 0.8 to 1.2, the pore size distribution in the porous layer (B) becomes uniform, and the reproducibility of the cycle characteristics of the battery is improved.
The location of the inorganic filler (b-2) in the porous layer (B) can be known by using a technique combining a cross-sectional photograph of the porous layer (B) and element mapping. As the cross-sectional photograph, for example, an SEM (scanning electron microscope) image;
As the element mapping method, for example, EDX (energy dispersive X-ray spectroscopy) can be employed. In these analyses, it is possible to know the location of the inorganic filler (b-2) by mapping in the cross-sectional direction while focusing on the metal element constituting the main component of the inorganic filler (b-2). . When the inorganic filler (b-2) is boehmite or kaolin, for example, the position of the inorganic filler (b-2) can be known by mapping in the cross-sectional direction of the Al (aluminum) element constituting the main component.

A resin binder (b-1) is resin which plays the role which bind | concludes the inorganic filler (b-2) mentioned above. Moreover, it is preferable that it is resin which plays the role which bind | concludes an inorganic filler (b-2) and a porous base material layer (A) mutually.
The type of the resin binder (b-1) is one that is insoluble in the electrolyte solution of the lithium ion secondary battery when used as a separator and is electrochemically stable within the range of use of the lithium ion secondary battery. It is preferable to use it.

Specific examples of the resin binder (b-1) include the following 1) to 6).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic polymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer;

4) Polyvinyl alcohol resin: for example, polyvinyl alcohol, polyvinyl acetate;
5) Fluorine-containing resin: For example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene Copolymer, hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer;
6) A resin having a melting point and / or glass transition temperature of 180 ° C. or higher or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher: for example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide , Polyamide, polyester. In particular, from the viewpoint of durability, wholly aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred.
Among these, 2) conjugated diene polymers are preferable from the viewpoint of easy compatibility with electrodes, and 3) acrylic polymers and 5) fluorine-containing resins are preferable from the viewpoint of voltage resistance.

The 2) conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit.
Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and substituted linear chains. Examples thereof include conjugated pentadienes, substituted and side chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferable.

The 3) acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The (meth) acrylic compound indicates at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester.
Examples of (meth) acrylic acid used in the above 3) acrylic polymer include acrylic acid and methacrylic acid.
As the (meth) acrylic acid ester used in the above 3) acrylic polymer, for example,
(Meth) acrylic acid alkyl esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl amethacrylate, phenyl acrylate, phenyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate ;
Epoxy group-containing (meth) acrylic acid esters such as glycidyl acrylate and glycidyl methacrylate may be used, and these may be used alone or in combination of two or more.

The above 2) conjugated diene polymer and 3) acrylic polymer may be obtained by copolymerizing other monomers copolymerizable therewith. Examples of other copolymerizable monomers used include unsaturated carboxylic acid alkyl esters, aromatic vinyl monomers, vinyl cyanide monomers, and unsaturated monomers containing a hydroxyalkyl group. , Unsaturated carboxylic acid amide monomer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and the like. These may be used alone or in combination of two or more. Good. Among the above, an unsaturated carboxylic acid alkyl ester monomer is particularly preferable. Examples of unsaturated carboxylic acid alkyl ester monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and the like. It may be used alone or in combination of two or more.
The 2) conjugated diene polymer may be obtained by copolymerizing the (meth) acrylic compound as another monomer.

The resin binder (b-1) is
A first resin binder (b-1-1) exhibiting a glass transition temperature in a region of 30 ° C. or higher;
A second resin binder (b-1-2) exhibiting a glass transition temperature in a region of less than 30 ° C .;
It is a mixture containing.
The glass transition temperature of the 1st resin binder (b-1-1) which shows a high glass transition temperature is 30 degreeC or more, Preferably it is 45 degreeC or more, More preferably, it is 70 degreeC or more. When glass transition temperature is 30 degreeC or more, it is preferable from the viewpoint of the stickiness of a separator outermost surface, and handling property.
The glass transition temperature of the 2nd resin binder (b-1-2) which shows a low glass transition temperature is less than 30 degreeC, Preferably it is 5 degrees C or less, More preferably, it is -10 degrees C or less. When glass transition temperature is less than 30 degreeC, it is preferable from a viewpoint of adhesiveness with an electrode, adhesive strength with a porous base material layer (A), and binding strength of an inorganic filler (b-2).

As the first resin binder (b-1-1) and the second resin binder (b-1-2), binders having the above glass transition temperatures are selected, and the resin binders (b) having different glass transition temperatures are used. -1) can be separated and migrated. As a result, in the resulting porous layer (B), the adhesion to the electrode, the adhesive strength with the porous substrate layer (A), the binding strength of the inorganic filler (b-2), and the stickiness of the outermost surface of the separator Performance and handling performance can be made compatible.
Migration refers to the process of drying the coating layer after the coating liquid (B ′) is applied to the porous layer base material layer (A), in which the resin binder (b-1) such as latex is applied to the porous layer (B). It is a phenomenon that moves to the outer surface side.

  It is preferable that the first resin binder (b-1-1) and the second resin binder (b-1-2) do not exhibit complete compatibility. Since these two types of resin binders do not exhibit complete compatibility, resin binders having different properties are present separately, and each characteristic can be exhibited. Therefore, the adhesiveness with the electrode, the adhesive strength with the porous base material layer (A), the binding strength of the inorganic filler (b-2), the stickiness and handling properties of the outermost surface of the separator are at a high level. It can be compatible. Here, when two types of resins exhibit complete compatibility, the resin binders having different properties behave as if they are one type of polymer. As a result, depending on the glass transition temperature as a whole of the mixture shown after the compatibilization, adhesion with the electrode, adhesion strength with the porous base material layer (A), binding of the inorganic filler (b-2) The strength, the stickiness of the outermost surface of the separator, and the handling properties are not preferable because they only show averaged performance.

The amount of the resin binder (b-1) used is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, based on the total amount of the porous layer (B). It is still more preferable to set it as 5-10 mass%. It is preferably 0.5% by mass or more from the viewpoint of adhesion to the electrode, adhesive strength with the porous base material layer (A), and binding strength of the inorganic filler (b-2), and is 30% by mass. The following is preferable from the viewpoints of stickiness on the outermost surface of the separator and handling properties.
The use ratio of the first resin binder (b-1-1) and the second resin binder (b-1-2) is the first resin binder (b-1) with respect to the total amount of the resin binder (b-1). -1) use ratio {mass ratio of (b-1-1) / (b-1)} is preferably 0.05 to 0.95, more preferably 0.1 to 0.7. More preferably, it is still more preferably 0.15 to 0.5. It is preferably 0.05 or more from the viewpoint of the stickiness of the outermost surface of the separator and handling properties, and 0.95 or less is the adhesion to the electrode and the adhesive strength to the porous substrate layer (A). And from the viewpoint of the binding strength of the inorganic filler (b-2).

<Other ingredients>
The porous layer (B) may consist only of the inorganic filler (b-2) and the resin binder (b-1), 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.
By including the water retention agent (b-3) in the coating liquid (B ′) forming the porous layer (B), the immobilization time (described later) of the coating liquid (B ′) can be extended. As a result, the migration difference between the two types of binders is clearly expressed, and adhesion with the electrode, adhesion strength with the porous base material layer (A), and binding strength of the inorganic filler (b-2) Both the stickiness and handling properties of the separator outermost surface can be achieved.

Examples of the water retention agent (b-3) include methyl cellulose, carboxymethyl cellulose, sodium salt of carboxymethyl cellulose, ammonium salt of carboxymethyl cellulose, hydroxyethyl cellulose, hyperbranched polyester amide, acrylic acrylamide copolymer, acrylic modified polymer, Examples include polyoxyalkylene fatty acid esters and other water-soluble plasticizers.
The multi-branched polyester amide is a copolymer containing an ester group and at least one amide group in the skeleton, and preferably has a molar mass of 800 to 16,000 g / mol from the viewpoint of water retention.
The acrylic acrylamide copolymer is preferable because it has a significantly high swellability upon water absorption, and is prevented from penetrating into the resin binder (b-1) and the porous substrate layer (A).
The sodium salt or ammonium salt of carboxymethyl cellulose can be easily applied with a uniform coating surface. In particular, when the degree of etherification is 0.60 to 1.00 and the degree of polymerization is 600 to 1,200, it is preferable in terms of good handleability.

Other water-soluble plasticizers include, for example, polyhydric alcohols such as ethylene glycol, glycerin, trimethylolpropane, diethylene glycol, triethylene glycol, dipropylene glycol, pentaerythritol, sorbitol, sorbitan, and sucrose; polyethylene having various degrees of polymerization And polyalkylene glycols such as glycol and polypropylene glycol. From the viewpoint of preventing powder falling, glycerin, trimethylolpropane, diethylene glycol, triethylene glycol, or dipropylene glycol is preferable.
A water retention agent (b-3) may be used individually by 1 type, and may use 2 or more types together.

  The amount of the water retention agent (b-3) is preferably 5 parts by mass or less, more preferably 3 parts by mass when the total of the resin binder (b-1) and the inorganic filler (b-2) is 100 parts by mass. Part or less, more preferably 1.5 parts by weight or less. Setting the amount of the water retention agent (b-3) to 5 parts by mass or less means that the adhesion with the electrode, the adhesive strength with the porous base material layer (A), and the binding strength of the inorganic filler (b-2) are reduced. It is preferable from the viewpoint.

<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 filling rate of the inorganic filler (b-2) in the porous layer (B) is preferably 95% by volume or less, more preferably 80% by volume or less, and 70% by volume or less from the viewpoint of lightness and high permeability. More preferred is 60% by volume or less. In light of heat shrinkage suppression and dendrite suppression, the lower limit is preferably 20% by volume or more, more preferably 30% by volume or more, and still more preferably 40% by volume or more. The filling rate of the inorganic filler (b-2) can be calculated from the layer thickness of the porous layer and the mass and specific gravity of the inorganic filler (b-2).

The surface softening temperature of a porous layer (B) is 30-60 degreeC, Preferably it is 30-50 degreeC, More preferably, it is 30-45 degreeC, More preferably, it is 35-45 degreeC. 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 polyolefin polymer generally used as a separator material has a glass transition temperature that 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 porous base material layer (A) or may be formed on both sides.

<Method for forming porous layer (B)>
As a formation method of the porous layer (B) in the present invention, an inorganic filler (b-2) and a resin binder (b-1) are preferably formed on at least one surface of the porous substrate layer (A) mainly composed of a polyolefin resin. ), And a coating liquid containing other components used as necessary, to form a porous layer (B).
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 filler (b-2) and the resin binder (b-1) is at least one side of the porous substrate layer (A). When laminated, 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 average particle size of the resin binder (b-1) particles in the resin latex is preferably 50 to 1,000 nm, more preferably 60 to 500 nm, and still more preferably 80 to 250 nm. When the average particle diameter is 50 nm or more, when the porous layer (B) containing the inorganic filler (b-2) and the resin binder (b-1) is laminated on at least one surface of the porous substrate layer (A), It exhibits good binding properties, and when used as a separator, it tends to have good heat shrinkage and excellent safety. When the average particle size is 1,000 nm or less, the ion permeability is unlikely to decrease 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 average particle diameter can be controlled by adjusting a polymerization time, a polymerization temperature, a raw material composition ratio, a raw material charging order, a pH, a stirring speed, and the like when producing the resin latex.

  As a medium for the coating liquid, one that can uniformly and stably disperse or dissolve the inorganic filler (b-2) and the resin binder (b-1) is preferable. For example, water, N-methylpyrrolidone, N , N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane and the like.

  Various additives such as surfactants, thickeners, wetting agents, antifoaming agents, pH adjusters including acids and alkalis are added to the coating solution in order to stabilize dispersion and improve coating properties. An agent may be added. The total amount of these additives is the amount of the effective component (the mass of the additive component dissolved when the additive is dissolved in the solvent) with respect to 100 parts by mass of the inorganic filler (b-2). As for, 20 mass parts or less are preferable, More preferably, it is 10 mass parts or less, More preferably, it is 5 mass parts or less.

  As for the method of dispersing or dissolving the inorganic filler (b-2) and the resin binder (b-1) in the medium of the coating liquid (B ′), the dispersion characteristics of the coating liquid necessary for the coating process are realized. There is no particular limitation as long as it can be performed. Examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade.

  The upper limit of the solid content of the coating liquid (B ′) used for forming the porous layer (B) is preferably 55% by mass or less, more preferably 45% by mass or less, and further preferably 35% by mass or less. . The lower limit of the solid content of the coating liquid (B ′) is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more. Immobilization of the coating liquid (B ′) can be slowed by setting the upper limit of the solid content of the coating liquid (B ′) to 60% by mass or less, and the lower limit of the solid content of the coating liquid (B ′). By making 5 mass% or more, the immobilization of the coating liquid (B ′) can be accelerated. As a result, the immobilization time of the coating liquid (B ′) can be controlled within the optimum range, and a migration difference between two or more kinds of resin binders in the coating liquid (B ′) can be clearly expressed, Adhesion strength with the porous substrate layer (A), binding strength of the inorganic filler (b-2), stickiness on the outermost surface of the separator, and handling properties can be achieved.

The immobilization time of the coating liquid (B ′) containing the inorganic filler (b-2), the resin binder (b-1), and the solvent is 10 to 120 seconds, preferably 10 to 100 seconds, more preferably. Is 10 to 80 seconds, more preferably 10 to 60 seconds. When the immobilization time is 10 seconds or more, the migration difference between the two types of resin binders (b-1) is clearly expressed, the adhesion with the electrodes, the adhesive strength with the porous substrate layer (A), and the inorganic filling It is preferable from the viewpoint of achieving both the binding strength of the material (b-2), the stickiness of the outermost surface of the separator, and the handling property. When the immobilization time is 120 seconds or less, it is preferable from the viewpoint of productivity.
As a factor for controlling the immobilization time of the coating liquid (B ′),
Factors related to coating liquid (B ') (solid content concentration, water retention, high shear viscosity, type of solvent, etc.)
Factors relating to the porous substrate layer (A) to which the coating liquid (B ′) is applied (air permeability, surface tension, etc.) and factors relating to the drying conditions of the coating liquid (B ′) in the coating process (average) Drying temperature, drying air volume, drying zone length, drying time, drying zone line speed, drying method (hot air, infrared, etc.))
The immobilization time of the coating liquid (B ′) can be controlled in consideration of the balance of the above various factors.

For example, when the solid content of the coating liquid (B ′) is increased, the immobilization time can be shortened. However, there is a disadvantage that streaks tend to occur on the coated surface. Conversely, if the solid content of the coating liquid (B ′) is lowered, the immobilization time can be extended. However, on the other hand, it is necessary to lengthen the drying time, and productivity is lowered.
When the average drying temperature (described later) is increased, the immobilization time can be shortened. However, on the other hand, the coated surface condition after drying is deteriorated. Conversely, if the average drying temperature is lowered, the immobilization time can be lengthened. However, on the other hand, it is necessary to lengthen the drying time, and productivity is lowered.
When water retention is added to the coating liquid (B ′), the water retention in the coating liquid (B ′) is improved, so that the immobilization time can be extended, but the battery performance and the like are adversely affected. There is.

The immobilization time of the coating liquid (B ′) refers to the time required for the viscosity of the coating film to rapidly increase after the coating liquid is applied to form a coating film. The immobilization time can be measured using an apparatus comprising a combination of a rheometer and an immobilization cell in accordance with the description in Patent Document 6 (Japanese Patent No. 5114654). Specifically, a coating film of the coating liquid (B ′) is formed in the apparatus, the coating film is placed under a certain reduced pressure, and the time required for the viscosity increase (until the rapid viscosity increase is completed) ) Is measured, and this time is defined as the immobilization time of the coating liquid (B ′). Specific measurement conditions are as follows:
Decompression degree: 700 hPa
Shear rate: 1 (1 / s)
Initial gap: 0.5mm
Coating substrate: porous substrate layer (A)
Measurement temperature: Average drying temperature

  The method for applying the coating liquid (B ′) to the porous substrate layer (A) is not particularly limited as long as it is a method capable of realizing the required layer thickness and coating area. For example, a gravure coater method , 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.

  Furthermore, when the surface treatment is applied to the surface of the porous substrate layer (A) prior to the application of the coating liquid (B ′), the coating liquid can be easily applied and the porous layer (B ) And the surface of the porous substrate layer (A), the adhesion is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous substrate layer (A). For example, corona discharge treatment method, plasma discharge treatment method, mechanical surface roughening method, solvent Examples thereof include a treatment method, an acid treatment method, and an ultraviolet oxidation method.

  The method for removing the solvent from the coating film after coating the coating liquid (B ′) with the porous substrate layer (A) is not particularly limited as long as it does not adversely affect the porous substrate layer (A). Examples thereof include a method of drying the porous substrate layer (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 porous substrate layer (A) and the separator (porous substrate layer (A) laminated with the porous layer (B)), the drying temperature, the winding tension, etc. are adjusted as appropriate. It is preferable.

The average drying temperature when forming the porous layer (B) is equal to or lower than the lowest film formation temperature of the first resin binder (b-1-1), and the second resin binder (b-1-2). It is preferable that the temperature is equal to or higher than the minimum film formation temperature.
The average drying temperature refers to the set temperature of the dryer in the heating process. When there are a plurality of drying zones, the arithmetic average of the set temperature and the drying zone length in each drying zone is defined as the average drying temperature.
The minimum film-forming temperature of the resin binder is the thickness of the resin binder latex 0 on a substrate made of an aluminum plate placed on a thermal gradient tester (high temperature side: 100 ° C., low temperature side: set to −30 ° C.). The temperature at the boundary between the region where the film was successfully formed and the region where the crack occurred when the coating film was formed by coating at 1 mm. The level of the minimum film forming temperature is generally positively correlated with the level of the glass transition temperature of the resin binder. However, in the case of a resin binder having a hydrogen bonding functional group (for example, an amide group, an imide group, an amino group, an imino group, a carboxyl group, a hydroxyl group, etc.), the minimum film-forming temperature is positive with the glass transition temperature. May be out of correlation.

Therefore, by setting the above average drying temperature within the above temperature range, a film is formed between the first resin binder (b-1-1) and the second resin binder (b-1-2). The following phenomenon occurs due to the difference in the temperature dependence of ease. That is,
Since the second resin binder (b-1-2) having a low minimum film formation temperature is fast immobilized and hardly migrates, it exists in the vicinity of the surface of the porous film (A);
On the other hand, the first resin binder (b-1-1) having a high minimum film-forming temperature is slow to immobilize and thus easily migrates, so that the outer surface of the porous layer (B) far from the porous substrate layer (A) There are many in the vicinity.

<Separator>
The separator obtained by the method of the present invention will be described.
The separator having the porous substrate layer (A) and the porous layer (B) containing the inorganic filler (b-2) and the resin binder (b-1) 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 air permeability of the separator is preferably 10 seconds / 100 cc to 500 seconds / 100 cc, more preferably 20 seconds / 100 cc to 500 seconds / 100 cc, more preferably 30 seconds / 100 cc to 400 seconds / 100 cc. Hereinafter, it is particularly preferably 50 seconds / 100 cc or more and 300 seconds / 100 cc or less. When the air permeability is 10 seconds / 100 cc or more, self-discharge tends to decrease when used as a battery separator, and when it is 500 seconds / 100 cc or less, good charge / discharge characteristics tend to be obtained.

The final film thickness of the separator is preferably 2 μm to 200 μm, more preferably 5 μm to 100 μm, and still more preferably 7 μm to 30 μm. When the film thickness is 2 μm or more, the mechanical strength tends to be sufficient, and when the film thickness is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the battery capacity.
The thermal shrinkage rate at 130 ° C. of the separator is preferably 0% or more and 15% or less, more preferably 0% or more and 10% or less, and particularly preferably 0% or more and 5% or less. By making the heat shrinkage rate 15% or less, it is possible to prevent the separator from being broken even during abnormal heat generation of the battery, and to suppress the contact between the positive and negative electrodes (from the viewpoint of realizing better safety performance). preferable. The heat shrinkage rate is preferably set in the above range in both the MD direction and the TD direction.
The shutdown temperature of the separator (the temperature at which the micropores of the separator are blocked by heat melting or the like when the battery generates abnormal heat) is preferably 120 ° C. or higher. The upper limit is preferably 160 ° C. or lower, preferably 150 ° C. or lower. It is preferable that the shutdown temperature is set to 160 ° C. or lower from the viewpoint of promptly executing current interruption and obtaining better safety performance when the battery generates heat. On the other hand, setting the shutdown temperature to 120 ° C. or higher is preferable from the viewpoint of enabling use at a high temperature of, for example, about 100 ° C., from the viewpoint of performing various heat treatments, and the like.

<Power storage device>
Hereinafter, the electricity storage device will be described. The electricity storage device includes the separator, and other configurations may be the same as those conventionally known. The power storage device is not particularly limited, and examples thereof include batteries such as non-aqueous electrolyte batteries, capacitors, and capacitors. Among these, a non-aqueous electrolyte battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable from the viewpoint of more effectively obtaining the benefits of the operational effects of the present invention. Hereinafter, a suitable aspect in the case where the electricity storage device is a non-aqueous electrolyte battery will be described.

There is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, A well-known thing can be used.
Examples of the positive electrode material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ , and examples of the negative electrode material include graphite, non-graphitizable carbonaceous, and easy graphite. Carbonaceous materials such as carbonaceous carbonaceous and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like.

As the non-aqueous electrolyte, an electrolyte in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples thereof include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

Although the said electrical storage device is not specifically limited, For example, it manufactures as follows. That is, the separator is produced as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). Next, the separator is stacked together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. Next, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And an electrical storage device is obtained by passing the process of accommodating the said winding body in an exterior body, and also inject | pouring electrolyte solution.
The electricity storage device is formed by forming a separator, a positive electrode, and a negative electrode in a flat plate shape, and then laminating in order of positive electrode-separator-negative electrode-separator-positive electrode or negative electrode-separator-positive electrode-separator-negative electrode. After that, it can be manufactured through a process such as housing in an exterior body and injecting an electrolytic solution therein.
In addition, a battery can or a bag-like film can be used as the exterior body.

  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 stated, various measurements and evaluations were performed under conditions of room temperature 23 ° C., 1 atm, and relative humidity 50%.

<Measurement method>
(1) Glass transition temperature (Tg) of resin binder (b-1)
An appropriate amount of the latex containing the resin binder (b-1) was placed in an aluminum dish and dried for 30 minutes with a hot air dryer at 130 ° C. to obtain a film sample. This film-like sample is cut into a size of 10 mm in width and 35 mm in length, and set in a twist type geometry of a dynamic viscoelasticity measuring device “ARES” (trade name, manufactured by TI Instruments Inc.) The measurement was performed under the conditions of an effective measurement length of 25 mm, a strain of 0.5%, and a frequency of 1 Hz from −70 ° C. to 150 ° C. under a temperature increase rate of 3 ° C./min. The tan δ peak temperature was determined from a peak automatically detected by “RSI Orchestrator” (trade name, manufactured by TI Instruments Inc.).

(2) Minimum film formation temperature (° C)
The obtained resin binder (b-1) latex was placed on an aluminum plate placed on a thermal gradient tester (high temperature side: 100 ° C., low temperature side: set to −30 ° C.) with an applicator having a clearance of 0.1 mm. Coated and dried. In the obtained coated film, the temperature at the boundary between the region where the film was formed and the region where the crack was generated was defined as the minimum filming temperature.
The notation “0>” in the “Minimum film formation temperature” column of Table 1 indicates that the minimum film formation temperature was less than 0 ° C.

(3) Thickness (film thickness, μm)
(3) -1 Thickness (μm) of polyolefin resin porous substrate layer (A) and power storage device separator
A 10 cm x 10 cm square sample was cut out from the polyolefin resin porous substrate layer (A) and the electricity storage device separator, respectively, and the film thicknesses at 9 locations (3 points x 3 points) selected in a lattice shape were measured. (Toyo Seiki Seisakusho Co., Ltd. type KBM) was used and 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 substrate layer (A) or the separator for an electricity storage device.
(3) -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 and observed at an acceleration voltage of 1.0 kV and 30,000 times, and the thickness of the porous layer 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 substrate layer was not visible was defined as the porous layer region.

(4) Porosity (volume%) of polyolefin resin porous substrate layer (A)
A 10 cm × 10 cm square sample was cut out from the polyolefin resin porous substrate layer, its volume (cm ³ ) and mass (g) were measured, and the film density was 0.95 (g / cm ³ ). Calculated using mathematical formulas.
Porosity (%) = (volume−mass / membrane density) / volume × 100

(5) Puncture strength (g) of polyolefin resin porous substrate layer (A)
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the polyolefin resin porous substrate layer (A) was fixed with a sample holder having an opening diameter of 11.3 mm. Next, the central portion of the fixed polyolefin resin porous substrate layer (A) was subjected to a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec with a pin having a radius of curvature of the needle tip of 0.5 mm. . The maximum puncture load measured here was defined as the puncture strength (g).

(6) Immobilization time of coating liquid (B ′) According to the description in Japanese Patent No. 5114654, a device was produced by combining Anton Paar's rheometer type MCR101 and the company's immobilization cell. A schematic sectional view showing a part of this apparatus is shown in FIG. In FIG. 1, the lower part including the parallel plate lower part 11b corresponds to an immobilization cell.
Using this device
As a measurement target coating liquid (B ′), a coating liquid (B ′) containing an inorganic filler (b-2) and a resin binder (b-1),
A porous film (A) as a material corresponding to the paper base material 19,
Each was used to measure the immobilization time.
As a measuring jig, a parallel plate upper part 11a having a diameter of 50 mm is used, the initial gap is 0.5 mm, the volume of the coating liquid (B ′) 17 is 2 ml, and the shear rate during measurement by the operation of the rotation control unit 15 is measured. Is a constant value of 1 (1 / s). Intake from the air inlet 13b, the degree of decompression of the decompression chamber 13a is set to 700 hPa, measurement of the viscosity of the coating liquid (B ′) is started after the start of decompression, and the viscosity increases after the viscosity of the coating liquid (B ′) suddenly increases Was the time for immobilization of the coating liquid (B ′). The measurement temperature was the average drying temperature of the coating liquid (B ′).

(7) Surface softening temperature of porous layer (B) The surface of the separator and black lasha paper were put together and pressed using a calender under the conditions of a roll temperature of 20 ° C. and a calender roll linear pressure of 10 kgf / cm. Thereafter, the two were pulled apart, and the presence or absence of the transfer of the black rash paper onto the separator was confirmed. When transfer was not confirmed, the calender roll temperature was raised by 5 ° C. and the same test was performed. Thereafter, the same test was repeated while increasing the roll temperature in increments of 5 ° C., and the temperature when the transfer of the black rush paper to the separator was seen was defined as the surface softening temperature of the porous layer (B).
The notation “20>” in the “Surface softening temperature of porous layer (B)” column of Table 1 indicates that the surface softening temperature was less than 20 ° C.

(8) 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.

(9) Adhesiveness between separator and electrode The adhesiveness between the separator and the electrode (negative electrode) was evaluated by the following procedure.
(Preparation of negative electrode)
Artificial graphite 96.9% by mass as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethyl cellulose as a negative electrode binder, and 1.7% by mass (in terms of solid content) of styrene-butadiene copolymer latex (Production Example 1e described later) ) 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 to obtain a negative electrode. At this time, the active material coating 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 .

(Adhesion test)
The negative electrode obtained by the above method was cut into a width of 20 mm and a length of 40 mm. On this negative electrode, an electrolyte solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate were mixed at a ratio (volume ratio) of 2: 3 was poured to the extent that the negative electrode was immersed, and a separator was laminated to obtain a laminate. It was. This laminate was placed in an aluminum zip and pressed at 80 ° C. and 10 MPa for 2 minutes.
Thereafter, the laminate was taken out, the separator was peeled off from the electrode, observed visually, and evaluated according to the following criteria.
(Evaluation criteria)
◎ (Excellent): When the negative electrode active material adheres to 40% or more of the separator area ○ (Good): When the negative electrode active material adheres to 30% or more and less than 40% of the separator area △ (Yes): 10 of the separator area % When the negative electrode active material adheres to less than 30% x (defect): When the negative electrode active material adheres to less than 10% of the separator area

(10) Stickiness and coating layer peel strength A positive electrode current collector (Ashiji processed paper Co., Ltd., aluminum foil 20 μm) cut as an adherend was cut to 30 mm × 150 mm and overlapped with a separator to obtain a laminate. . The obtained laminate was sandwiched between two Teflon (registered trademark) sheets (Nichias Co., Ltd., Naflon PTFE (polytetrafluoroethylene) sheet TOMBO-No. 9000), and the press conditions were varied as follows. By performing pressing, two types of test samples with different pressing conditions were obtained.
Condition 1) Pressurization at a temperature of 25 ° C. and a pressure of 5 MPa for 3 minutes Condition 2) Pressurization at a temperature of 80 ° C. and a pressure of 10 MPa for 3 minutes

The peel strength of each test sample obtained was measured at a tensile speed of 200 mm / min according to JIS K6854-2. As a measuring device, an autograph AG-IS type (trademark) manufactured by Shimadzu Corporation was used.
Based on the obtained results, the peel strength of the separator was evaluated according to the following evaluation criteria.
[Sticky]
Regarding the sample after pressing under condition 1)
◎ (Excellent): When peel strength is 4 gf / cm or less ○ (Good): When peel strength exceeds 4 gf / cm and 6 gf / cm or less △ (Yes): Peel strength is 6 gf / cm When exceeding 8 gf / cm x (defect): When the peel strength exceeds 8 gf / cm, it was used as an index of stickiness and handling properties.
[Coating layer peel strength]
Regarding the sample after pressing in condition 2)
◎ (excellent): When the peel strength is 15 gf / cm or more ○ (Good): When the peel strength is 10 gf / cm or more and less than 15 gf / cm × (defect): The peel strength is less than 10 gf / cm It was used as an index of the adhesive strength with the porous substrate layer (A) and the binding strength of the inorganic filler (b-2).

(11) Average pore size (μm), curvature, and number of pores of the polyolefin microporous substrate layer (A) The fluid inside the capillary has a Knudsen flow when the mean free path of the fluid is larger than the pore size of the capillary, When small, it is known to follow the flow of Poiseuille. Therefore, it is assumed that the air flow in the air permeability measurement of the porous base material layer (A) follows the Knudsen flow, and the water flow in the water permeability measurement of the porous base material layer (A) follows the Poiseuille flow. .
The average pore diameter d (μm) and the curvature τa (dimensionless) are the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)) and the water permeation rate constant R _liq (m ³ / ( m ² · sec · Pa)), air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure Ps (= 101,325 Pa), porosity ε (%), and film thickness It calculated | required using the following numerical formula from L (micrometer).
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 106
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 mentioned here can be obtained as the air resistance by measuring the polyolefin porous substrate layer (A) according to the description of “(8) Air permeability of separator”.
[Water permeability]
A polyolefin porous substrate layer (A) previously immersed in ethanol was set in a stainless steel liquid-permeable cell having a diameter of 41 mm, and the ethanol in the membrane 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. .
The molecular velocity ν of air is determined from the gas constant R (= 8.314), the absolute temperature T (K), the circumference ratio π, and the average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol). It is calculated | required using the following numerical formula.
ν = {(8R × T) / (π × M)} ^1/2
The number of holes B (pieces / μm ² ) is obtained by the following mathematical formula.
B = 4 × (ε / 100) / (π × d ² × τa)

(12) Battery cycle characteristics (12) -1 Preparation of sample for evaluation [Preparation of electrode]
A negative electrode was prepared in the same manner as “(Preparation of negative electrode)” in “(9) Adhesiveness between separator and electrode”.
The positive electrode was produced as follows.
(Preparation of positive electrode)
92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as the positive electrode active material, 2.3% by mass of flake graphite and acetylene black as the conductive material, and 3.2% by mass of polyvinylidene fluoride as the binder Was dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This 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 to obtain a positive electrode. At this time, the active material coating amount of the positive electrode was 250 g / m ² and the active material bulk density was 3.00 g / cm ³ .

The positive electrode was cut to a width of about 57 mm, and the negative electrode was cut to a width of about 58 mm to form a strip, thereby preparing an evaluation electrode.
[Adjustment of non-aqueous electrolyte]
The non-aqueous electrolyte was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.0 mol / L in a mixed solvent composed of ethylene carbonate / ethyl methyl carbonate = 1/2 (volume ratio).
[Preparation of separator]
The separator for evaluation was produced by cut | disconnecting each separator obtained by the Example and the comparative example into 60 mm, and making it strip | belt shape.

(12) -2 Evaluation of battery cycle characteristics [battery assembly]
The electrode and separator obtained in (12-1) are stacked in the order of negative electrode, separator, positive electrode and separator, wound at a winding speed of 250 gf, and wound at a winding speed of 45 mm / sec. An electrode laminate was prepared. The electrode laminate is housed in a stainless steel container having an outer diameter of 18 mm and a height of 65 mm. An aluminum tab derived from the positive electrode current collector is used as the container lid terminal portion, and a nickel tab derived from the negative electrode current collector is used as the container. Welded to the wall. Then, it dried for 12 hours at 80 degreeC under vacuum. In the argon box, the non-aqueous electrolyte was poured into the assembled battery container and sealed to prepare an evaluation battery.
[Preprocessing]
The battery assembled as described above was charged with a constant current up to a voltage of 4.2 V at a current value of 1/3 C (coulomb), then charged with a constant voltage of 4.2 V for 8 hours, and then 3 with a current of 1/3 C. Discharge was performed to a final voltage of 0V. Next, after constant current charging to a voltage of 4.2 V with a current value of 1 C, 4.2 V constant voltage charging was performed for 3 hours, and then discharging was performed to a final voltage of 3.0 V with a current of 1 C. Finally, after constant current charging to 4.2 V with a current value of 1 C, 4.2 V constant voltage charging was performed for 3 hours, and the pretreatment was completed.
1C represents a current value for discharging the reference capacity of the battery in one hour.

[Cycle test]
About the battery which performed the said pretreatment, after discharging to discharge end voltage 3V with discharge current 1A on the conditions of temperature 25 degreeC, it charged to charge end voltage 4.2V with charge current 1A. Charging / discharging was repeated with this as one cycle, the capacity retention after 200 cycles with respect to the initial capacity was examined, and the cycle characteristics were evaluated according to the following criteria.
(Evaluation criteria)
◎ (Excellent): When the capacity retention is 95% or more and 100% or less ○ (Good): When the capacity retention is 90% or more and less than 95% × (Bad): When the capacity retention is less than 90% If there is

<Production of resin binder (b-1)>
(Production Example 1a) Production of acrylic polymer latex In a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 70.4 parts by mass of ion-exchanged water, “AQUALON KH1025” (trade name, No. 1) Ichi Kogyo Seiyaku Co., Ltd., 25% by weight aqueous solution) 0.085 parts by mass (in terms of solid content) and “Adekaria Soap SR1025” (trade name, manufactured by ADEKA Corporation, 25% by mass aqueous solution) 0.085 parts by mass ( Solid content conversion), and the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature at 80 ° C., 0.15 parts by mass of ammonium persulfate (2% by weight aqueous solution) was added (in terms of solid content). did.
5 minutes after adding the ammonium persulfate aqueous solution, 85 parts by weight of methyl methacrylate, 5.4 parts by weight of n-butyl acrylate, 2 parts by weight of 2-ethylhexyl acrylate, 0.1 part by weight of methacrylic acid, 0.1 parts of acrylic acid Part by mass, 2 parts by mass of 2-hydroxyethyl methacrylate, 5 parts by mass of acrylamide, 0.4 parts by mass of glycidyl methacrylate, 0.7 parts by mass of trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Co., Ltd.) , "AQUALON KH1025" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by weight aqueous solution) 0.75 parts by mass (solid content conversion), "ADEKA rear soap SR1025" (trade name, manufactured by ADEKA Corporation, 25 mass) % Aqueous solution) 0.75 parts by mass (in terms of solid content), 0.05 parts by mass of sodium p-styrenesulfonate, persulfuric acid A mixture of 0.15 parts by weight of ammonia (2% by weight aqueous solution) (in terms of solid content), 0.3 parts by weight of γ-methacryloxypropyltrimethoxysilane, and 52 parts by weight of ion-exchanged water was mixed for 5 minutes using a homomixer. Thus, an emulsion was prepared. The obtained emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes.
After completion of the dropwise addition of the emulsion, the reaction container was maintained at an internal temperature of 80 ° C. for 90 minutes and then cooled to room temperature to obtain an emulsion. A latex containing an acrylic polymer (1a) having a concentration of 40% by mass was obtained by adding ammonium hydroxide aqueous solution (25% by mass aqueous solution) to the obtained emulsion and adjusting the pH to 9.0.
As a result of observation with a transmission electron microscope (TEM), it was found that the acrylic polymer (1a) was spherical and monodispersed with a particle diameter of 161 nm. The obtained acrylic polymer (1a) had a glass transition temperature of 90 ° C. and a minimum film formation temperature of 80 ° C.

(Production Example 1b) Production of Acrylic Polymer Latex Acrylic polymer having a solid content concentration of 40% by mass by operating in the same manner as in Production Example 1a, except that the amounts used of the following components were changed as described below. A latex containing polymer (1b) was obtained.
[Initial preparation]
Aqualon KH1025: 0.45 parts by mass (solid content conversion)
ADEKA rear soap SR1025: 0.45 parts by mass (solid content conversion)
Ammonium persulfate (2% by mass aqueous solution): 0.15 parts by mass (in terms of solid content)
[Monomer in emulsion]
Methyl methacrylate: 30.5 parts by mass n-butyl acrylate: 60.8 parts by mass 2-ethylhexyl acrylate: 2 parts by mass Methacrylic acid: 1 part by mass Acrylic acid: 1.5 parts by mass 2-hydroxyethyl methacrylate: 2 parts by mass Acrylamide: 0.2 parts by mass Glycidyl methacrylate: 2 parts by mass Trimethylolpropane triacrylate: 0.7 parts by mass As a result of observation with a transmission electron microscope (TEM), the acrylic polymer (1b) has a particle size of It was 121 nm spherical and monodisperse. The obtained acrylic polymer (1b) had a glass transition temperature of −20 ° C. and a minimum film forming temperature of 0 ° C. or lower.

(Production Example 1c) Production of Acrylic Polymer Latex Acrylic polymer having a solid content concentration of 40% by mass by operating in the same manner as in Production Example 1a, except that the use amounts of the following components were changed as described below. A latex containing polymer (1c) was obtained.
[Initial preparation]
Aqualon KH1025: 0.45 parts by mass (solid content conversion)
ADEKA rear soap SR1025: 0.45 parts by mass (solid content conversion)
Ammonium persulfate (2% by mass aqueous solution): 0.15 parts by mass (in terms of solid content)
[Monomer in emulsion]
Methyl methacrylate: 44.3 parts by mass n-butyl acrylate: 47.0 parts by mass 2-ethylhexyl acrylate: 2 parts by mass Methacrylic acid: 1 part by mass Acrylic acid: 1.5 parts by mass 2-hydroxyethyl methacrylate: 2 parts by mass Acrylamide: 0.2 parts by mass Glycidyl methacrylate: 2 parts by mass Trimethylolpropane triacrylate: 0.7 parts by mass As a result of observation with a transmission electron microscope (TEM), the acrylic polymer (1c) has a particle size of It was 119 nm spherical and monodisperse. The obtained acrylic polymer (1c) had a glass transition temperature of 5 ° C. and a minimum film formation temperature of 10 ° C.

(Production Example 1d) Method for Producing Styrene-Butadiene Polymer Latex After the inside of a temperature-adjustable reactor equipped with a stirrer was previously replaced with nitrogen, 850 parts by mass of ion-exchanged water, 20 parts by mass of sodium dodecylbenzenesulfonate ( Solid content conversion), 0.1 part by weight of sodium hydroxide, 0.5 part by weight of sodium hydrogen sulfite, and 0.0005 part by weight of ferric sulfate were charged. Thereafter, a total amount of a monomer mixture consisting of 15 parts by mass of styrene, 30 parts by mass of methyl methacrylate, 51 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of 2-hydroxyethyl acrylate, and 2 parts by mass of itaconic acid was added for polymerization. After adjusting the system temperature to 90 ° C., a uniform initiator aqueous solution consisting of 1 part by mass of ammonium persulfate and 50 parts by mass of ion-exchanged water was added all at once. Thereafter, the polymerization system internal temperature was maintained at 90 ° C. for 2 hours, and then the polymerization system internal temperature was lowered to obtain seed latex A. The solid content of the obtained seed latex A was about 10% by mass, the volume average particle size of the polymer was 16 nm, the glass transition temperature was 2 ° C., and the weight average molecular weight (Mw) was 70,000.

Next, 0.05 parts by mass of seed latex A obtained above (in terms of solid content) and 0.3 parts by mass of sodium dodecylbenzenesulfonate (in terms of solid content) were obtained in a pressure-resistant reaction vessel equipped with a stirrer and a temperature control jacket. Then, 200 parts by mass of ion-exchanged water was added and the liquid temperature was adjusted to 60 ° C., and then 1.0 part by mass of ammonium persulfate (in terms of solid content) was added. Here, as a monomer, 70 parts by mass of styrene, 15 parts by mass of butadiene, 7 parts by mass of methyl methacrylate, 3 parts by mass of acrylonitrile, 1 part by mass of acrylic acid, 2 parts by mass of glycidyl methacrylate, and 2 parts by mass of itaconic acid, A mixed liquid consisting of 0.2 parts by mass of α-methylstyrene dimer and 0.5 parts by mass of t-dodecyl mercaptan as a chain transfer agent was added over 6 hours while maintaining the liquid temperature at 70 ° C. The final polymerization rate was 98%. The produced latex was filtered through a 200 mesh wire mesh.
An aqueous ammonium hydroxide solution (25% by mass) was added to the latex after filtration to adjust to pH = 8, and then the unreacted monomer was removed. After further concentration, 0.5 parts by weight of sodium polyacrylate and potassium hydroxide were added to obtain a latex having a solid content concentration of 50% and pH = 8 containing a styrene-butadiene-based polymer (1d). .
As a result of observation with a transmission electron microscope (TEM), the styrene-butadiene polymer (1d) was spherical and monodispersed with a particle diameter of 200 nm. The latex polymer (1d) had a glass transition temperature of 70 ° C. and a minimum film formation temperature of 75 ° C.

(Production Example 1e) Method for Producing Styrene-Butadiene Polymer Latex Using seed latex A obtained in the same manner as in Production Example 1d, the amount of each of the seed latex A, each monomer, and the additives described below was used. Except for the following, a latex containing a styrene-butadiene-based polymer (1e) having a solid concentration of 50% by mass was obtained by operating in the same manner as in the latter stage of Production Example 1d.
[Initial preparation]
Seed latex A: 0.8 part by mass (solid content conversion)
Sodium dodecylbenzenesulfonate: 1 part by mass (solid content conversion)
[Batch added monomer]
Styrene: 40 parts by mass Butadiene: 40 parts by mass Methyl methacrylate: 10 parts by mass Acrylonitrile: 5 parts by mass Acrylic acid: 1 part by mass Glycidyl methacrylate: 2 parts by mass Itaconic acid: 2 parts by mass The final polymerization rate was 98%.
As a result of observation with a transmission electron microscope (TEM), the styrene-butadiene polymer (1e) was spherical and monodispersed with a particle diameter of 80 nm. The latex polymer (1e) had a glass transition temperature of −40 ° C. and a minimum film formation temperature of 0 ° C. or lower.

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) furopionone] as an antioxidant is added to 99 parts by mass of the polymer mixture obtained. Then, a polymer equal mixture was obtained by dry blending again using a tumbler blender.
The obtained polymer equal mixture was purged with nitrogen and then fed to a twin screw extruder by 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 25 ° 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 of these series of treatments, the film thickness is 17 μm, the porosity is 60%, the air permeability is 84 seconds / 100 cc, the average pore diameter d = 0.57 μm, the curvature τa = 1.45, the number of holes B = 165 / μm ^2. A polyolefin resin porous substrate layer (A1) having a puncture strength of 5,679 f in terms of 25 μm was obtained.

[Preparation of coating liquid (B ′)]
Next, as the inorganic filler (b-2), a calcined kaolin (2a) (wet kaolin mainly composed of kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) at high temperature, a volume average particle 93.0 parts by mass of 1.0 μm in diameter)
As resin binder (b-1),
2.0 parts by mass of the acrylic polymer (1a) latex obtained in Production Example 1a in terms of solid content, and 5.0 parts by mass of the acrylic polymer (1b) latex obtained in Production Example 1b in terms of solid content When,
A coating liquid (B ′) was prepared by uniformly dispersing 0.5 parts by mass of an aqueous solution of ammonium polycarboxylate (San Nopco, SN Dispersant 5468) in 180 parts by mass of water. The immobilization time of the obtained coating liquid (B ′) was 80 seconds at 60 ° C.

[Formation of porous layer (B) (manufacture of separator)]
On one side of the polyolefin-based porous substrate layer (A1) obtained in [Manufacture of polyolefin resin porous substrate layer], the coating solution obtained in [Preparation of coating solution] was applied with a microgravure coater. . The obtained coating film was dried at 60 ° C. to remove water, and a porous layer (B) having a thickness of 2 μm was formed on one surface of the porous base material layer (A) to obtain a separator.
The obtained separator was evaluated according to the method described above. The obtained results are shown in Table 1.

Examples 2-7 and Comparative Examples 1-6
In Example 1, a coating liquid was prepared in the same manner as in Example 1 except that a predetermined amount of the resin binder (b-1) shown in Table 1 was used, and a separator was produced.
In Example 7, boehmite (2b) (aluminum hydroxide oxide, average volume particle size 1.0 μm) was used as the inorganic filler (b-2).
The obtained separator was evaluated by the above method. The obtained results are shown in Table 1.

  The abbreviation “CMC” in the water retention agent column means carboxymethylcellulose.

The separator produced by the method of the present invention has adhesion to the electrode, adhesive strength to the porous substrate layer (A), binding strength of the inorganic filler (b-2), and stickiness of the outermost surface of the separator. And handling properties are compatible.
An electricity storage device including a separator manufactured by the method of the present invention can maintain a high capacity for a long period of time and is excellent in productivity.
Therefore, the separator manufactured by the method of the present invention can be suitably used as a separator for a battery such as a non-aqueous electrolyte secondary battery; a capacitor; an electricity storage device such as a capacitor.

11a Parallel plate upper part 11b Parallel plate lower part 13a Pressure chamber 13b Air inlet 15 Rotation control part 17 Coating liquid (B ')
19 Paper base material

Claims (7)

In the porous substrate layer (A),
Applying a coating liquid (B ′) containing an inorganic filler (b-2), a resin binder (b-1), and a solvent, followed by a step of forming a porous layer (B) by drying, A method for producing a separator for an electricity storage device, comprising:
The surface softening temperature of the porous layer (B) is 30 to 60 ° C.,
1st resin whose immobilization time in the average drying temperature of the said coating liquid (B ') is 10 to 120 second, and the said resin binder (b-1) shows a glass transition temperature in the 30 degreeC or more area | region. The manufacturing method of the said separator characterized by containing the 2nd resin binder (b-1-2) which shows a glass transition temperature in the area | region below 30 degreeC with a binder (b-1-1). The average drying temperature of the coating liquid (B ′) when forming the porous layer (B) is:
It is not more than the minimum film formation temperature of the first resin binder (b-1-1) and not less than the minimum film formation temperature of the second resin binder (b-1-2).
The manufacturing method of the separator of Claim 1.   The manufacturing method of the separator of Claim 1 or 2 with which the said coating liquid (B ') contains a water retention agent (b-3) further.   The manufacturing method of the separator as described in any one of Claims 1-3 whose air permeability of the obtained separator is 10-500 second / 100cc.   The separator for electrical storage devices manufactured by the manufacturing method of the separator as described in any one of Claims 1-4. A positive electrode;
A separator according to claim 5;
A negative electrode,
A laminated body characterized by being laminated.   An electrical storage device comprising the laminate according to claim 6.

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