JP2018181546A - Nonaqueous electrolyte secondary battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery separator which has an adequate heat resistance although it is thin, and which allows the battery safety to be ensured by suppressing the degradation of the heat resistance with time.SOLUTION: A nonaqueous electrolyte secondary battery separator comprises: a fine porous film base; and a heat-resistant layer laminated on the film base. The fine porous film base is 40% or more in cross linking degree. In a 160°C-thrusting test which is performed with a needle having a curvature radius of 0.5 mm at its tip end at a thrusting rate of 2 mm/sec under a 160°C-atmosphere, the nonaqueous electrolyte secondary battery separator is 30 g or larger in 160°C-thrusting strength.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte secondary battery separator.

In recent years, development of non-aqueous electrolyte secondary batteries has been actively conducted. Usually, in the non-aqueous electrolyte secondary battery, a separator including a microporous film is provided between the positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes, and transmitting ions through the electrolytic solution held in the fine pores.
The microporous polyolefin membrane is an electronic insulator, but is widely used as a separator for non-aqueous electrolyte secondary batteries because it exhibits ion permeability due to its porous structure. A microporous polyolefin membrane is a shut-down function that blocks the conduction of ions in the electrolytic solution and stops the progress of the electrochemical reaction by closing the pores by heat melting when the non-aqueous electrolyte secondary battery causes abnormal heat generation. Also have.

Thus, although it is a polyolefin microporous membrane having an excellent shutdown function, it may shrink significantly during heat melting. For example, when the separator is broken due to the inclusion of metallic foreign matter or the like and a short circuit occurs between the electrodes, the battery temperature rises due to the generation of Joule heat, which causes heat shrinkage of the microporous polyolefin membrane. The short circuit progresses and the battery temperature also rises.
On the other hand, according to Patent Document 1, by subjecting the microporous polyethylene membrane subjected to the crosslinking treatment to heat treatment, it is possible to eliminate the temporal strength deterioration without lowering the mechanical strength and the permeability. It has been disclosed that as a microporous polyethylene film having high strength and excellent heat resistance, it has a crosslinked structure, a porosity of 20 to 80%, an average pore diameter of 0.001 to 0.2 .mu.m, and a melt piercing strength Of 0.01 N or more, and the retention of molten piercing strength is 40% or more.
Patent Document 2 discloses a method for producing a separator excellent in reliability and safety under high temperature, specifically, a composition for forming a separator that can be polymerized by irradiation of energy rays, particularly ultraviolet rays. It describes about the process of applying to the base material which consists of PET nonwoven fabric, and the process of irradiating a energy beam to the coat of the composition for separator formation applied to the base material, and forming resin which has a crosslinked structure. It is said that shrinkage and melt deformation of the separator can be suppressed by the coating film having a crosslinked structure and the heat resistant layer, and battery short circuit suppression and safety under high temperature can be ensured.

Further, Patent Document 3 discloses an electron beam crosslinked separator in which a microporous film made of polyethylene is crosslinked by electron beam irradiation, and the separator has a film breaking temperature compared to a non-crosslinked polyethylene separator. Although the temperature rises, the other physical properties of the separator (for example, the shutdown temperature and the like) do not change at all, and thus it is possible to suppress the rupture of the separator while fully exhibiting the shutdown function. Furthermore, it is described that by using a separator in which a microporous film having a melting point of 200 ° C. or more is laminated on the separator, the rupture temperature of the separator is further raised to further suppress the rupture of the separator.
Furthermore, Patent Document 4 discloses a separator for a non-aqueous electrolyte secondary battery having a synthetic resin microporous film and a coated inorganic layer, which are excellent in ion permeability and heat resistance, and micropores are disclosed therein. A radically polymerizable compound is coated on the surface of a microporous film made of polypropylene having a part and then irradiated with active energy rays to obtain a separator having a polymer film layer, and the high hardness and appropriate elasticity of the separator It is described that heat resistance is improved by suppressing reduction in mechanical strength such as puncture strength and elongation.
However, in the documents 1 to 4 above, in order to secure the safety, the film thickness including the functional layer is increased to cope with the problem, but as the thickness increases, the number of electrodes packed in a certain volume decreases, and the battery capacity is increased. There was a problem that it could not be raised. Moreover, in patent document 4, since polypropylene is used as a suitable base material, there existed a problem that the time-lapse deterioration of the mechanical strength and heat resistance of a separator can not be suppressed by combined use with an active energy ray.

Unexamined-Japanese-Patent No. 2004-123791 JP, 2013-080691, A JP, 2017-012441, A International Publication No. 2015/166949

Recently, it is desirable for lithium secondary batteries to have high capacity and high output as well as to ensure excellent safety as described above, but especially for separators, it is thinner and the high capacity and high output of the battery It has been strongly hoped that it is possible to be used, which is more heat resistant and less likely to deteriorate with time.
On the other hand, the separators described in Patent Documents 1 to 4 still leave room for improvement in heat resistance and time-lapse deterioration from the viewpoint of a thin film as desired.

  Therefore, it is an object of the present invention to provide a separator for a non-aqueous electrolyte secondary battery, which is thin but sufficiently heat resistant, and in which the heat resistant deterioration with time is suppressed and the safety of the battery is secured. Do.

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said subject could be solved with the following technical means, as a result of earnest examination.
[1] A separator having a heat-resistant layer laminated on a microporous membrane substrate, wherein the microporous membrane substrate has a degree of crosslinking of 40% or more and a needle having a curvature radius of 0.5 mm at the tip, A separator for a non-aqueous electrolyte secondary battery characterized in that 160 ° C. piercing strength in a 160 ° C. piercing test performed at a piercing speed of 2 mm / sec under an atmosphere of 160 ° C. is 20 g or more.
[2] The microporous membrane base material for which the piercing strength is measured at 160 ° C. is placed in a pressure-resistant autoclave, pressurized to 9.8 MPa with compressed air, and measured before and after storage for 10 days at 25 ° C. The separator for a non-aqueous electrolyte secondary battery according to [1], wherein the retention of molten piercing strength of the membrane substrate is 50% or more.
[3] The separator for a non-aqueous electrolyte secondary battery according to [1] or [2], wherein the microporous membrane base has a crosslinked structure.
[4] The separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [3], wherein the thickness of the microporous membrane base is 12 μm or less.
[5] The separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the thickness of the heat-resistant layer is 3 μm or less.
[6] The separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein the microporous membrane substrate is made of polyethylene.
[7] The non-aqueous electrolyte secondary battery separator according to any one of [1] to [6], wherein the heat-resistant layer contains inorganic particles.
[8] A secondary battery including the separator for a non-aqueous electrolyte secondary battery according to any one of the above [1] to [7].
[9] The method for producing a separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [8], including the step of irradiating the non-aqueous electrolyte secondary battery separator with an electron beam.

  According to the present invention, a separator for a non-aqueous electrolyte secondary battery is provided which has sufficient heat resistance even if it is thin, and further suppresses heat deterioration due to aging and secures battery safety.

  Hereinafter, modes for carrying out the present invention (hereinafter abbreviated as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can variously deform and implement within the range of the summary.

<Separator for non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery separator (hereinafter, also simply referred to as "separator") of the present invention comprises a porous substrate and a heat-resistant layer disposed on at least one side of the porous substrate. This separator may consist only of a porous substrate and a heat-resistant layer, and may have other layers. The other layers can be disposed on one side or both sides of the porous substrate or as an intermediate layer of the laminated porous substrate layer to such an extent that the thickness of the separator of the present invention is not too large. When the heat-resistant layer is disposed on the surface having the other layers, their mutual positional relationship is optional.

  The preferred embodiments of the members constituting the non-aqueous electrolyte secondary battery separator of the present invention and the method of manufacturing the non-aqueous electrolyte secondary battery separator will be described below.

[Microporous membrane substrate]
The base material used in the present embodiment may itself be one conventionally used as a separator. The substrate is preferably a porous film having no electron conductivity, ion conductivity, high resistance to an organic solvent, and a fine pore diameter.

  As the microporous film, for example, a microporous film containing a resin such as a polyolefin (for example, polyethylene, polypropylene, polybutene and polyvinyl chloride) and a mixture or copolymer thereof as a main component; polyethylene terephthalate, polycycloolefin, poly A microporous film comprising a resin such as ether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene or the like as a main component; woven fabric of polyolefin fiber (woven fabric); nonwoven fabric of polyolefin fiber; Paper; and aggregates of particles of insulating material. Among these, when obtaining a polymer layer through a coating process, it is excellent in the coating property of a coating liquid, thickness of a separator is made thinner, the active material ratio in electrical storage devices, such as a battery, is raised, and per volume From the viewpoint of increasing the volume of the film, a microporous polyolefin membrane containing a polyolefin resin as a main component is preferable. In the present specification, "containing as a main component" means that the content of the specific component or member exceeds 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

  In the present embodiment, the content of the polyolefin resin in the microporous polyolefin membrane is not particularly limited, but from the viewpoint of the shutdown performance when used as a separator, 50% by mass or more and 100% by mass of all components constituting the porous substrate It is preferable that it is a porous film which consists of a polyolefin resin composition which polyolefin resin occupies by% or less. The proportion of the polyolefin resin is more preferably 60% by mass to 100% by mass, and still more preferably 70% by mass to 100% by mass.

  The polyolefin resin is not particularly limited, but may be a polyolefin resin used for ordinary extrusion, injection, inflation and blow molding, and ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1 Homo- and copolymers such as octene, multistage polymers etc. can be used. Polyolefins selected from the group consisting of these homopolymers, copolymers and multistage polymers can be used alone or in combination.

  Representative examples of polyolefin resin include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, ethylene propylene Rubber etc. are mentioned.

  As a material of the polyolefin microporous membrane base used as a separator, it is preferable to use a resin mainly composed of high density polyethylene, because it has a low melting point and high strength. Two or more of these polyethylenes may be mixed to impart flexibility. The polymerization catalyst used in the production of these polyethylenes is also not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts and metallocene catalysts.

In order to improve the heat resistance of the polyolefin microporous membrane base, it is more preferable to use a porous membrane made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene. The steric structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene.
The proportion of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but 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.
Further, the polymerization catalyst is also not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts.
In this case, polyolefin resins other than polypropylene are not particularly limited, and, for example, homopolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene Or copolymers. Specifically, as polyolefin resins other than polypropylene, polyethylene, polybutene, ethylene-propylene random copolymer and the like can be mentioned.

Low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high-molecular-weight polyethylene, etc. as polyolefin resins other than polypropylene from the viewpoint of shutdown characteristics in which the pores of the polyolefin microporous membrane base are closed by heat melting. It is preferable to use the following polyethylene. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density of 0.93 g / cm ³ or more measured according to JIS K7112.

  The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane base is not particularly limited, but is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or more and 2,000,000. It is less than, more preferably 100,000 or more and less than 1,000,000. When the viscosity average molecular weight is 30,000 or more, the melt tension at the time of melt molding is increased, the moldability is improved, and entanglement between polymers tends to result in high strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12,000,000 or less, it becomes easy to melt and knead uniformly, which is preferable because it tends to be excellent in sheet formability, particularly thickness stability. Furthermore, a viscosity average molecular weight of less than 1,000,000 is more preferable because the pores tend to be clogged when the temperature rises and a good shutdown function tends to be obtained.

The viscosity-average molecular weight (Mv) is determined according to ASTM-D4020 from the limiting viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent, and the following formula:
Polyethylene: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 (Chiang's formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80
Calculated by

  For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1,000,000 alone, it is a mixture of a polyolefin having a viscosity average molecular weight of 2,000,000 and a polyolefin having a viscosity average molecular weight of 270,000, A mixture having a viscosity average molecular weight of less than 1,000,000 may be used.

The polyolefin microporous membrane substrate in the present embodiment can contain any additive. The additive is not particularly limited. For example, polymers other than polyolefins; inorganic particles; antioxidants such as phenol type, phosphorus type and sulfur type; metal soaps such as calcium stearate and zinc stearate; UV absorbers; Light stabilizers; antistatic agents; antifogging agents; color pigments etc. may be mentioned.
The total content of these additives is preferably 0.001 parts by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5 parts by mass with respect to 100 parts by mass of the polyolefin resin composition. Part or less.

The porosity of the microporous polyolefin membrane substrate in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, and preferably 90% or less, preferably 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing the ion permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of securing the piercing strength. In the present specification, the porosity can be determined, for example, from the volume (cm ³ ), mass (g), and film density (g / cm ³ ) of the polyolefin microporous membrane substrate,
Porosity = (volume-mass / film density) / volume x 100
It can be determined by For example, in the case of a polyolefin microporous membrane base composed of polyethylene, the porosity can be calculated assuming a membrane density of 0.95 (g / cm ³ ). The porosity can be adjusted by, for example, changing the draw ratio of the polyolefin microporous membrane substrate.

  The air permeability of the polyolefin microporous membrane substrate in the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, and preferably 1,000 seconds / 100 cc or less. More preferably, it is 500 seconds / 100 cc or less. Setting the air permeability to 10 seconds / 100 cc or more is preferable from the viewpoint of suppressing the self-discharge of the non-aqueous electrolyte secondary battery. On the other hand, setting the air permeability to 1,000 seconds / 100 cc or less is preferable from the viewpoint of obtaining good charge and discharge characteristics. As used herein, air permeability is air permeability measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or the stretching ratio of the porous substrate.

  The average pore diameter of the polyolefin microporous membrane substrate in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. Setting the average pore diameter to 0.15 μm or less is preferable from the viewpoint of suppressing the self-discharge of the non-aqueous electrolyte secondary battery and suppressing the capacity decrease. The average pore size can be adjusted by, for example, changing the draw ratio at the time of producing the microporous polyolefin membrane substrate.

  The puncture strength of the microporous polyolefin membrane substrate in the present embodiment is not particularly limited, but is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2,000 g / 20 μm or less, more preferably 1 Or less. The piercing strength of 200 g / 20 μm or more is preferable from the viewpoint of suppressing membrane breakage due to the dropped active material or the like during battery winding and from the viewpoint of suppressing short circuit due to expansion and contraction of the electrode accompanying charge and discharge. On the other hand, a piercing strength of 2,000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation at the time of heating. The puncture strength is measured by the method described in the examples. The puncture strength can be adjusted by adjusting the stretching ratio and / or stretching temperature of the polyolefin porous substrate.

  The film thickness of the polyolefin microporous membrane substrate in the present embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 50 μm or less, more preferably 30 μm or less, still more preferably 12 μm or less is there. It is preferable from the viewpoint of improving the mechanical strength that the film thickness be 2 μm or more. On the other hand, setting the film thickness to 50 μm or less is preferable because the occupied volume of the separator in the battery is reduced, which tends to be advantageous for increasing the capacity of the battery.

The polyolefin microporous membrane base according to the present embodiment is preferably produced by the following production method, but is not limited thereto.
The method for producing a microporous polyolefin membrane substrate comprises the steps of (1) forming a gel-like stretched film (hereinafter referred to as a gel-like stretched film forming step) (2) crosslinking the gel-like stretched film at least once (Hereinafter referred to as a crosslinking step), (3) a step of heat treating the crosslinked film at a temperature of 110 ° C. or more (hereinafter referred to as a radical deactivation step), (4) the heat treated film Can be divided into the step of extracting and removing the plasticizer contained in (hereinafter referred to as the extraction step).
After the above process (1), proceed to the process of (4) without going through the processes of (2) and (3), and then carry out the crosslinking treatment, and then carry out the heat treatment of (3) I do not care.
Here, gel-like refers to a composition comprising a polyolefin and at least one plasticizer. The gel-like stretched film refers to a gel-like composition in which the molecular chains of the polyolefin are oriented in at least one axial direction.

(Gel-like stretched film preparation)
The method of forming a gel-like stretched film is not particularly limited. For example, a method of stretching a sheet solidified by cooling and solidifying after melt-kneading a polyolefin and a plasticizer in at least one uniaxial direction, or stretching a polyolefin sheet in at least one uniaxial direction After that, a method of swelling the stretched film with a plasticizer can be used.
The plasticizer used when preparing the gel-like composition is a liquid which is swellable with respect to the polyolefin, and examples thereof include hydrocarbons such as liquid paraffin, lower aliphatic alcohols, lower aliphatic ketones, and nitrogen-containing organic compounds. And ethers, glycols, lower aliphatic esters, silicone oils, etc., which may be used alone or in combination.

[Heat resistant layer]
In the present embodiment, the heat-resistant layer is disposed on at least one side of the microporous membrane substrate.
The thickness of the heat-resistant layer disposed on the microporous membrane substrate is more preferably 0.1 μm or more per side of the substrate. The thickness is preferably 5 μm or less, more preferably 4 μm or less, and still more preferably 3 μm or less. It is preferable to adjust the thickness of the heat-resistant layer to 0.1 μm or more in order to secure the heat resistance. It is preferable to adjust the thickness of the heat-resistant layer to 5 μm or less from the viewpoint of suppressing the decrease in ion permeability of the separator.

  In the present embodiment, the thickness of the heat-resistant layer disposed on the microporous membrane substrate is measured according to the method described in the following examples. For example, it can adjust by changing the application quantity of the coating liquid apply | coated to a base material, the coating method, and coating conditions.

(Inorganic filler and resin particle filler)
Although the inorganic filler contained in the heat-resistant layer is not limited, it has a melting point of 200 ° C. or higher, has high electrical insulation, and is electrochemically stable in the use range of the lithium ion secondary battery Is preferred.
The inorganic filler is not particularly limited, but, for example, oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide and iron oxide; nitrides such as silicon nitride, titanium nitride and boron nitride Based ceramics; Silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dicite, nacrite, halloysite, pyrophyllite, montmorillonite, cericite, mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, glass fibers, etc. may be mentioned. These may be used alone or in combination of two or more.
Among them, from the viewpoint of improving the electrochemical stability and the heat resistance of the separator, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; and ion exchange such as kaolinite, dicite, nacrite, halloysite and pyrophyllite Aluminum silicate compounds having no function are preferred.

  As the aluminum oxide compound, aluminum hydroxide oxide (AlO (OH)) is particularly preferable. As a specific example of aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuit caused by generation of lithium dendrite. A heat-resistant layer containing an inorganic filler containing boehmite as a main component suppresses heat shrinkage of the microporous membrane substrate at high temperature even if it is reduced in weight and thickness while maintaining high ion permeability, and is excellent It tends to develop heat resistance. Synthetic boehmite is more preferable from the viewpoint of reducing ionic impurities that adversely affect the characteristics of the non-aqueous electrolyte secondary battery.

  As the aluminum silicate compound having no ion exchange ability, kaolin composed mainly of kaolin mineral is more preferable since it is inexpensive and easily available. As kaolin, wet kaolin and calcined kaolin obtained by calcining the same are known. In the present embodiment, calcined kaolin is particularly preferable from the viewpoint of electrochemical stability because crystal water is released during the calcination treatment and impurities are further removed.

A resin fine particle filler can be included as a filler which comprises a heat-resistant layer.
The resin filler is composed of an electrochemically stable resin which has heat resistance and electrical insulation, is stable to the non-aqueous electrolyte in the battery, and is difficult to be reduced and reduced in the operating voltage range of the battery. Is preferred. As a resin for forming such resin fine particles, styrene resin (polystyrene etc.), styrene butadiene rubber, acrylic resin (polymethyl methacrylate etc.), polyalkylene oxide (polyethylene oxide etc.), fluorine resin (polyvinylidene fluoride etc.) And crosslinked products of at least one resin selected from the group consisting of these derivatives; urea resins; polyurethanes; and the like.
Further, polyamide fine particles, polyimide fine particles and the like, which are particularly excellent in heat resistance and electrical insulation, can also be used.
As the resin fine particle filler, the resins exemplified above may be used alone or in combination of two or more. The fine resin particle filler may contain, if necessary, known additives which can be added to the resin, such as an antioxidant.

  The average particle diameter of the inorganic filler and the resin fine particle filler is preferably more than 0.1 μm, and more preferably more than 0.3 μm. The upper limit of the average particle diameter of the inorganic filler and the fine resin particle filler is preferably 4.0 μm or less, more preferably 3.5 μm or less, and still more preferably 3.0 μm or less. Adjusting the average particle diameter of the inorganic filler and the resin fine particle filler to the above range tends to further suppress the thermal contraction at high temperature even when the thickness of the heat-resistant layer is thin.

  With respect to the particle size distribution of the inorganic filler and the resin fine particle filler, the minimum particle size is preferably 0.001 μm or more, more preferably 0.005 μm or more, still more preferably 0.01 μm or more, and the maximum particle size is 20 μm or less Is preferably 10 μm or less, more preferably 7 μm or less. Furthermore, the ratio of the maximum particle diameter / average particle diameter is preferably 50 or less, more preferably 30 or less, and still more preferably 20 or less. Thus, adjusting the particle size distribution of the inorganic filler and the resin fine particle filler is preferable from the viewpoint of suppressing the thermal contraction of the separator at high temperature.

  As a method of adjusting the particle size of the inorganic filler and the resin fine particle filler and the distribution thereof, for example, a method of grinding the inorganic filler and the resin fine particle filler with a grinding device such as a ball mill, bead mill or jet mill can be mentioned.

  Examples of the shape of the inorganic filler and the resin fine particle filler include plate, scale, needle, column, sphere, polyhedron, and mass. A plurality of types of inorganic fillers having these shapes or a plurality of types of resin fine particle fillers may be used, or one or more types of inorganic fillers or resin fine particles may be used in combination.

  The content of the inorganic particles in the heat-resistant layer of the inorganic filler and the resin fine particle filler is preferably 40% by mass to less than 100% by mass, and more preferably 50 to 99.99% by mass with respect to 100% by mass of the porous layer. More preferably, it is 60 to 99.9% by mass, and particularly preferably 70 to 99% by mass. When the content of the inorganic filler and the resin particle filler is in the above range, the binding properties of the inorganic filler and the resin particle filler, the permeability of the separator, the heat resistance, and the like tend to be further improved.

(Binder)
The heat-resistant layer in the present embodiment preferably contains a binder in order to bind the inorganic fillers described later, or in order to bind the layer containing the inorganic filler and the microporous membrane substrate.
In the present embodiment, when the heat-resistant layer contains a binder, it contributes to at least one of the adhesion between the heat-resistant layer and the microporous membrane base and the adhesion between the inorganic fillers in the heat-resistant layer.

  The binder is not particularly limited. For example, when using a separator, it is preferable that the binder be insoluble or poorly soluble in an electrolytic solution and electrochemically stable. Such a binder is not particularly limited. For example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as vinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer Fluorine-containing rubbers such as ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, Rubber such as methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; melting point and / or glass transition temperature of polyphenylene ether, polysulfone, polyether sulfone, polyphenyl sulfone, polyphenylene sulfide, polyetherimide, polyamide imide, polyester etc. Resin etc. more than ° C are mentioned.

  Among these, resin-made latex binders are preferable. In the present specification, “resin latex” indicates a resin in a state of being dispersed in a medium. A separator having a layer containing an adsorbent and a resin-made latex binder is less likely to have reduced ion permeability and tends to have high output characteristics. In addition, even when the temperature rise at the time of abnormal heat generation is fast, smooth shutdown performance is exhibited, the heat shrink resistance is high, and high safety tends to be easily obtained.

  The resin-made latex binder is not particularly limited, and can be obtained, for example, by emulsion polymerization of an aliphatic conjugated diene monomer or an unsaturated carboxylic acid monomer, and another monomer copolymerizable therewith. The thing is mentioned. The use of such a resin latex binder tends to further improve the electrochemical stability and the binding property. The emulsion polymerization method is not particularly limited, and a conventionally known method can be used. Moreover, it does not specifically limit about the addition method of a monomer and another component, either of the batch addition method, the division | segmentation addition method, or the continuous addition method is employable. In addition, any of single-stage polymerization, two-stage polymerization or multi-stage polymerization can be employed.

  The aliphatic conjugated diene-based monomer is not particularly limited. For example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1 And 3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. Among these, 1,3-butadiene is preferable. The aliphatic conjugated diene-based monomer may be used alone or in combination of two or more.

  The unsaturated carboxylic acid monomer is not particularly limited, and examples thereof include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. Among these, acrylic acid and / or methacrylic acid are preferable. The unsaturated carboxylic acid monomers may be used alone or in combination of two or more.

  The aliphatic conjugated diene monomer or other monomer copolymerizable with the unsaturated carboxylic acid monomer is not particularly limited, and, for example, aromatic vinyl monomer, vinyl cyanide monomer amount And unsaturated carboxylic acid alkyl ester monomers, unsaturated monomers containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomers, and the like. Among these, unsaturated carboxylic acid alkyl ester monomers are preferable. These may be used alone or in combination of two or more.

The unsaturated carboxylic acid alkyl ester monomer is not particularly limited, and, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl malate, diethyl Malate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like can be mentioned. Among these, methyl methacrylate is preferred. These may be used alone or in combination of two or more.
In addition to the monomers described above, monomer components other than the above can also be used to improve various qualities and properties.

The average particle diameter of the resin latex binder is preferably 50 nm to 500 nm, more preferably 60 nm to 460 nm, and still more preferably 70 nm to 420 nm. When the average particle diameter is 50 nm or more, the ion permeability of the separator having a layer containing the adsorbent and the resin-made latex binder does not easily decrease, and high output characteristics tend to be easily obtained. In addition, even when the temperature rise at the time of abnormal heat generation is fast, the separator exhibits smooth shutdown performance, and also tends to have high heat shrinkage resistance and be more excellent in safety. In addition, when the average particle diameter is 500 nm or less, good binding property is exhibited, and when the separator is formed as a multilayer porous film, heat shrinkability becomes good, and it tends to be more excellent in safety.
Control of the average particle size of the resin-made latex binder is possible by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material feeding order, pH and the like.

  The content of the binder in the heat-resistant layer is preferably 0.01% by mass or more and less than 60% by mass, more preferably 0.1 to 50% by mass, and further preferably 0 with respect to 100% by mass of the heat-resistant layer. It is 0.5 to 40% by mass, particularly preferably 1 to 30% by mass. When the content of the binder is in the above range, the binding property of the inorganic filler or the resin fine particle filler, the permeability of the separator, the heat resistance, and the like tend to be further improved.

In the present invention, in order to further improve the heat resistance of the heat resistant layer, the following heat resistant resin can be used as a binder.
The heat resistant resin is a polymer containing a nitrogen atom in the main chain, and in particular, one containing an aromatic ring is preferable from the viewpoint of heat resistance. For example, aromatic polyamide (hereinafter sometimes referred to as "aramid"), aromatic polyimide (hereinafter sometimes referred to as "polyimide"), aromatic polyamideimide and the like can be mentioned.
Examples of the aramid include meta-oriented aromatic polyamide (hereinafter sometimes referred to as "meta-aramid") and para-oriented aromatic polyamide (hereinafter sometimes referred to as "para-aramid"). Among these, para-aramid is preferable because it is easy to form a porous heat-resistant resin layer (R) having a uniform film thickness and excellent air permeability.

(Para-aramid)
The above-mentioned para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is at the para position of the aromatic ring or an orientation position according to it (for example, 4, 4 ′ -Consisting essentially of repeat units linked in oppositely oriented coaxial or parallel orientations, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene and the like. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide, poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylene dicarboxylic acid amide), poly (para Para-orientation type or para-orientation type such as phenylene-2,6-naphthalene dicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), para-phenylene terephthalamide / 2, 6-dichloro-para-phenylene terephthalamide copolymer, etc. The para-aramid which has a structure according to is illustrated.

In the present invention, para-aramid is dissolved in a polar organic solvent and used as a coating solution.
Examples of the polar organic solvent include, but are not limited to, polar amide solvents or polar urea solvents described later.
From the viewpoint of coatability, para-aramid is preferably para-aramid having an intrinsic viscosity of 1.0 dl / g to 2.8 dl / g, and more preferably an intrinsic viscosity of 1.7 dl / g to 2.5 dl / g . If the intrinsic viscosity is less than 1.0 dl / g, the strength of the formed heat-resistant layer may be insufficient. When the intrinsic viscosity exceeds 2.8 dl / g, it may be difficult to obtain a stable para-aramid-containing coating solution. Intrinsic viscosity here is a value which melt | dissolved the para-aramid which once precipitated and was measured as a para-aramid sulfuric acid solution, and is a value used as the index of what is called molecular weight.
From the viewpoint of coatability, the para-aramid concentration in the coating liquid is preferably 0.5 to 10 parts by mass.

In order to improve the solubility of the resulting para-aramid in a solvent, it is preferable to add an alkali metal or alkaline earth metal chloride during para-aramid polymerization. Specific examples include, but are not limited to, lithium chloride or calcium chloride.
The amount of the chloride added to the polymerization system is preferably in the range of 0.5 to 6.0 mol, more preferably in the range of 1.0 to 4.0 mol, per 1.0 mol of the amide group formed by condensation polymerization. . If the chloride is 0.5 mol or more, the generated para-aramid is easily dissolved, and if it is 6.0 mol or less, the chloride is easily dissolved in the solvent. Generally, if the amount of chloride of alkali metal or alkaline earth metal is less than 2 parts by mass, the solubility of para-aramid may be insufficient, and if it exceeds 10 parts by mass, chloride of alkali metal or alkaline earth metal may be used. However, it may not dissolve in polar organic solvents such as polar amide solvents or polar urea solvents.

(Polyimide)
As a polyimide used for the heat-resistant-resin layer (R) of the lamination | stacking porous film (RG) of this invention, the wholly aromatic polyimide manufactured by condensation polymerization of an aromatic acid dianhydride and diamine is preferable.
Specific examples of the acid dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenyl sulfone tetracarboxylic acid dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid Examples include acid dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic acid dianhydride, and the like.
Specific examples of the diamine include oxydianiline, paraphenylene diamine, benzophenone diamine, 3,3'-methylenedianiline, 3,3'-diaminobenzophenone, 3,3'-diaminodiphenylsulfone, 1,5 Although the '-naphthalene diamine etc. are mentioned, this invention is not limited to these.

  As the polyimide, a solvent-soluble polyimide can be suitably used. As such a polyimide, the polyimide of the polycondensate of 3,3 ', 4,4'- diphenyl sulfone tetracarboxylic dianhydride and aromatic diamine is mentioned, for example. As the polar organic solvent for dissolving the polyimide, dimethyl sulfoxide, cresol, o-chlorophenol and the like can be suitably used in addition to those exemplified as the solvent for dissolving the aramid.

[Placement method of heat-resistant layer]
One embodiment of the method of disposing the heat-resistant layer on the microporous membrane substrate includes, for example, a method of forming a heat-resistant layer by applying a coating liquid containing a filler and a binder on at least one surface of the microporous membrane substrate. be able to.

  The solvent for the coating solution is preferably one capable of uniformly and stably dispersing the filler and the binder, and examples thereof include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, Thermal xylene, methylene chloride, hexane and the like can be mentioned.

When a binder other than the heat-resistant resin is used as the binder, water, which is a poor solvent for the binder, or ethanol, methanol, which is a mixed solvent of water and a water-soluble organic medium, is preferable among the above solvents. Among these, water is more preferable. Generally, when the coating liquid is applied to the substrate when the coating liquid penetrates into the inside of the substrate, the binder clogs the surface and the inside of the pores of the substrate, and the permeability is easily lowered. On the other hand, when water is used as the solvent or dispersion medium of the coating solution, the coating solution is less likely to enter the interior of the substrate, and the binder is more likely to be present on the outer surface of the substrate. Is preferable because it can more effectively suppress the reduction of
On the other hand, when a heat-resistant resin is used as the binder, it is preferable to use a good solvent for the heat-resistant resin as described above such as N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide.

  In the coating solution, a dispersing agent such as a surfactant, a thickener, a wetting agent, an antifoamer, and various additives such as a pH adjusting agent containing an acid and an alkali for improving the dispersion stability and the coating property. May be added. These additives are preferably those which can be removed at the time of solvent removal, but are electrochemically stable in the use range of the lithium ion secondary battery, porous if they do not inhibit the battery reaction and are stable up to about 200 ° C. It may remain in the layer.

  The method of dispersing the filler and the binder in the solvent of the coating solution is not particularly limited as long as the method can realize the dispersion characteristics of the coating solution necessary for the coating process. For example, ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high speed impeller dispersions, dispersers, homogenizers, high speed impact mills, ultrasonic dispersions, mechanical stirring by sales promotion blades, etc. may be mentioned.

  The method for applying the coating liquid on the microporous membrane substrate is not particularly limited as long as it can realize a desired coating pattern, coating thickness, and coating area, but, for example, a gravure coater method, a small diameter gravure coater method Reverse roll coater method transfer roll coater method kiss coater method dip coater method knife coater method air doctor coater method blade coater method rod coater method squeeze coater method cast coater method die coater method screen printing method , Spray coating method, ink jet coating method and the like. Among them, a gravure coater method or a spray coating method is preferable from the viewpoint of easily obtaining a preferable area ratio.

  It is preferable to apply a surface treatment to the surface of the microporous membrane substrate prior to coating, as it facilitates application of the coating solution and improves the adhesion between the microporous membrane substrate and the heat-resistant layer. Examples of the surface treatment method include corona discharge treatment, plasma treatment, mechanical surface roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as the microporous membrane substrate or the heat-resistant layer is not adversely affected. For example, a method of drying at a temperature lower than the melting point while fixing the microporous membrane substrate, a method of drying under reduced pressure at a low temperature, particularly when a heat resistant resin is used as a binder, it is immersed in a poor solvent for the heat resistant resin. And the method of extracting the solvent at the same time as coagulating the binder into particles.

Nonaqueous Electrolyte Secondary Battery Separator
The non-aqueous electrolyte secondary battery separator according to the present embodiment includes the specific heat-resistant layer on the microporous membrane substrate, and can improve the ion permeability and the heat resistance of the secondary battery.
The air permeability of the nonaqueous electrolyte secondary battery separator according to the present embodiment is preferably 10 to 10,000 seconds / 100 cc, more preferably 10 to 1,000 seconds / 100 cc, and still more preferably 50 to 50 seconds. It is 500 seconds / 100 cc. Thereby, when a separator is applied to a lithium ion secondary battery, it shows large ion permeability. This air permeability is the air resistance measured in accordance with JIS P-8117, similarly to the air permeability of the porous substrate.

(Ionizing radiation to the separator)
A crosslinked structure is introduced into the separator for a non-aqueous electrolyte secondary battery according to this embodiment by ionizing radiation.
As a specific crosslinking treatment method, the separator can be subjected to at least one crosslinking treatment. Examples of the crosslinking method include ultraviolet light, electron beam, and ionizing radiation irradiation represented by gamma rays. Among them, the method by electron beam irradiation is preferable.

In the microporous polyolefin membrane substrate and the heat resistant layer constituting the non-aqueous electrolyte secondary battery separator, the ionizable radiation may be directly irradiated to the microporous polyolefin membrane substrate, or as a separator provided with the heat resistant layer. It may be irradiated.
When the microporous polyolefin membrane is directly irradiated, as described above, the microporous polyolefin membrane substrate can be irradiated during the production process.
That is, as one method, irradiation can be performed in the step of (2) in the steps shown below, and as the other method, (2) and (2) (after the step of (1) below) It is a method of proceeding to the step of (4) without passing through the step of 3), then performing the crosslinking treatment, and subsequently performing the heat treatment of (3).
Here, the method for producing a polyolefin includes (1) a step of forming a gel-like stretched film, (2) a step of subjecting the gel-like stretched film to at least one cross-linking treatment, (3) the cross-linked treated film 110 It is the process of heat-processing at the temperature more than ° C, and (4) the process of extracting and removing the plasticizer contained in the heat treatment film.

  The dose for electron beam irradiation is preferably 1 to 300 kGy, more preferably 2 to 200 kGy, and particularly preferably 5 to 150 kGy. When the dose is too small, a sufficient crosslinking density can not be obtained, and when the dose is too large, the microporous membrane substrate and the heat-resistant layer may be deteriorated to lower the mechanical strength.

Although the temperature at the time of irradiation is not particularly limited, for example, room temperature or higher is preferable, 80 ° C. or higher is more preferable, 130 ° C. or lower is preferable, and 110 ° C. or lower is more preferable.
Although the irradiation atmosphere is not particularly limited, it is preferable to carry out, for example, in a nitrogen atmosphere having an oxygen concentration of 100 ppm or less in order to reduce an instantaneous strength reduction. In addition, since the gel-like stretched film of the present invention has pores (or a precursor structure thereof) filled with a plasticizer or the like, even in the same irradiation atmosphere as in the prior art in which the polyethylene microporous film is irradiated, oxygen It has the advantage that the contact probability with is significantly lower.
The acceleration voltage at the time of irradiation is also not particularly limited, but in the case of irradiating a microporous film with a film thickness of about 30 μm, for example, the crosslinking treatment can be satisfactorily performed with an acceleration voltage of about 200 kV.

(Radical inactivation process)
In order to deactivate radicals remaining in the separator after the crosslinking treatment, the gel-like stretched film after the crosslinking treatment is heat-treated while being restrained in at least one axial direction. Similar to the crosslinking step, for example, when the microporous polyethylene membrane is subjected to heat treatment at a high temperature in the prior art, the permeability and mechanical strength may be impaired due to the melting of the microporous polyethylene membrane. On the other hand, in one aspect of the present invention, since the gel-like stretched film is subjected to the heat treatment, the heat treatment at a sufficiently high temperature can be carried out without fear of the decrease in permeability and the like. However, although the present invention effectively prevents the reduction in permeability due to melting, the reduction in mechanical strength due to orientation relaxation at high temperatures is not limited to this, so the upper limit temperature and time of heat treatment are mechanical strength and It is desirable to adjust with reference to the melt penetration strength retention rate.

The temperature of the heat treatment is 110 ° C. or higher, preferably 120 ° C. or higher, more preferably 125 ° C. or higher, and still more preferably 130 ° C. or higher. More specifically, the temperature range of the heat treatment is preferably 120 ° C. or more and 200 ° C. or less, more preferably 125 ° C. or more and 160 ° C. or less. It is also possible to carry out a radical deactivation step during the crosslinking step of the gel-like stretched film.
The heat treatment time is preferably 1 second to 10 minutes, more preferably 5 seconds to 5 minutes, still more preferably 10 seconds to 3 minutes, and still more preferably 20 seconds to 1 minute. Even if the heating temperature is less than 110 ° C., the radical may be inactivated by performing the heat treatment for 10 minutes or more, but the heat treatment time of 10 minutes or more is not preferable from the viewpoint of productivity.

Although the crosslinked structure is introduced into the separator for a non-aqueous electrolyte secondary battery according to the present embodiment by the above ionizing radiation irradiation, a preferable range as a degree of crosslinking represented as a gel fraction of a substrate constituting the separator Is 40% or more. The piercing strength at 160 ° C. of the separator to be described later is dramatically improved when the crosslinking degree is 40% or more as described above, and the retention of molten piercing strength is excellent, and the nail of the non-aqueous electrolyte secondary battery provided with the separator No smoke or fire occurs in the stabbing test.
In addition, about the measuring method of the gel fraction of a base material, it mentions later.

The piercing strength at room temperature of the separator for a non-aqueous electrolyte secondary battery according to the present embodiment, which is indicated by the above ionizing radiation, is preferably 250 g or more. The upper limit of the room temperature puncture strength is not particularly limited, but is substantially 500 g.
The method for measuring the room temperature puncture strength will be described later.

Furthermore, the 160 ° C. piercing strength of the separator for a non-aqueous electrolyte secondary battery according to this embodiment, which is shown by the above-mentioned ionizing radiation, is preferably 20 g or more, more preferably 30 g or more. The upper limit of the 160 ° C. piercing strength is not particularly limited, but is substantially 200 g.
The method of measuring the piercing strength at 160 ° C. will be described later.

The retention of molten piercing strength of the separator for a non-aqueous electrolyte secondary battery according to this embodiment, which is indicated by the above ionizing radiation, is preferably 50% to 100%, and more preferably 70% to 100%. is there.
In the nail penetration test of the non-aqueous electrolyte secondary battery, when the molten puncture strength retention ratio is 50% or more and 100% or less, the battery does not emit smoke or ignition.
The method of measuring the gel fraction of the substrate will be described later.

<Non-aqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery including the separator for the nonaqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and examples thereof include batteries such as nonaqueous electrolyte secondary batteries, capacitors, and capacitors. Among them, from the viewpoint of obtaining the benefits of the effects of the present invention more effectively, batteries are preferable, non-aqueous electrolyte secondary batteries are more preferable, and lithium ion secondary batteries are more preferable.

  The configuration of the non-aqueous electrolyte secondary battery according to the present embodiment may be as conventionally known except for including the non-aqueous electrolyte secondary battery separator described above. The preferable aspect about the case where non-aqueous electrolyte secondary batteries are non-aqueous electrolyte solution secondary batteries, such as a lithium ion secondary battery, is demonstrated below.

When manufacturing a lithium ion secondary battery using the separator which concerns on this embodiment, there is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, and each can use a well-known thing.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include aluminum foil and the like; and examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , spinel LiMnO ₄ , olivine LiFePO _4, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ containing lithium-containing composite oxides etc. can be mentioned respectively. The positive electrode active material layer may contain, in addition to the positive electrode active material, a binder, a conductive material, and the like.

  As the negative electrode, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. As the negative electrode current collector, for example, a copper foil or the like; as the negative electrode active material, for example, a graphite powder, graphitic, non-graphitizable carbonaceous matter, graphitizable carbonaceous matter, carbon material such as composite carbon body; silicon, tin , Metallic lithium, various alloy materials, etc. can be mentioned respectively.

The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution 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, ethyl methyl carbonate and the like. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ and LiPF ₆ .

The method of manufacturing a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator which concerns on this embodiment is illustrated below.
The separator according to the present embodiment is manufactured as an elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4,000 m (preferably 1,000 to 4,000 m). The positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are laminated in this order and wound into a circular or flat spiral shape to obtain a wound body, and the wound body is housed in a battery can, An electric storage device can be manufactured by injecting an electrolytic solution. Alternatively, a laminate comprising a sheet-like separator and an electrode (for example, positive electrode-separator-negative electrode-separator-positive electrode, or negative electrode-separator-positive electrode-separator-negative electrode laminated in the order of plate), or electrode and The separator may be folded to form a wound body, and the resultant may be put into a battery container (for example, a film made of aluminum), and then manufactured by a method of injecting an electrolytic solution.

Hereinafter, the present invention will be described in detail based on examples and comparative examples, but the present invention is not limited to the examples. The measuring method and evaluation method of the various physical properties in the following manufacture example, an Example, and a comparative example are as follows, respectively.
<< Measurement method >>
<Base material evaluation>
(1) Weight of base material (g / m ² )
The sample was cut into a 10 cm × 10 cm square, and the mass was measured using an electronic balance AEL-200 (trade name) manufactured by Shimadzu Corporation. Is multiplied by the resulting mass 100 was calculated 1 m ² per layer of basis weight (g / ^{m 2)} in.
(2) Substrate film thickness (μm)
Cut a sample of 10 cm × 10 cm from the base material, select 9 places (3 points × 3 points) in a grid, and use a micro thickness gauge (Type Toyo Seiki Co., Ltd. Type KBM) at room temperature 23 ± 2 ° C The film thickness was measured. The average value of the obtained nine measured values was calculated as the film thickness of the substrate.
(3) Porosity A 10 cm × 10 cm square sample was cut out of the base material, and its volume (cm ³ ) and mass (g) were determined. Using these values, assuming that the density of the substrate is 0.95 (g / cm ³ ), the porosity can be expressed by the following formula:
Porosity (%) = (1-mass / (volume x 0.95)) x 100
Calculated by

(4) Air permeability (second / 100 cc)
The air permeability was measured according to JIS P-8117 using a Gurley-type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. as the air permeability.
(5) Piercing strength (g)
The substrate was fixed with a sample holder with a diameter of 11.3 mm at the opening using a Kato Tech handy compression tester KES-G5 (trademark). Next, the central part of the fixed base material is punctured under a 25 ° C. atmosphere at a piercing speed of 2 mm / sec using a needle with a curvature radius of 0.5 mm at the tip to achieve a maximum puncture load. The strength (g) was obtained.
(6) Average pore size (μm)
Assuming that the air flow in the air permeability measurement of the microporous membrane substrate follows the Knudsen flow, and the water flow in the water permeability measurement of the microporous membrane substrate follows the Poiseuille flow, the following equation:
d = 2ν × (R _liq / R _gas ) × (16/3/3 P _s ) × 10 ⁶
{Wherein ν: molecular velocity of air (m / sec), R _liq : permeation rate constant of water (m ³ / (m ² · sec · Pa)), R _gas : permeation rate constant of air (m ³ / (M ² · sec · Pa)), η: viscosity of water (Pa · sec), P _s : standard pressure (= 101325 Pa). }
The average pore diameter d (μm) was determined from the above.

<Separator evaluation>
(1) Heat resistant layer thickness (μm)
The thickness of the heat-resistant layer is a separator for a non-aqueous electrolyte secondary battery in which the heat-resistant layer is laminated on the microporous film base by the same method as measuring the thickness of the microporous film base described in (2) above. The film thickness of the microporous film substrate was subtracted from the film thickness of the microporous film.
(2) Electron beam dose (kGy)
At the irradiation position in the electron beam irradiation apparatus, the dose measured by the film dosimeter is taken as the absorbed dose of the sample to be irradiated as the electron beam irradiation dose.
(3) Crosslinking degree (base gel fraction (%))
Based on ASTM D2765, based on the weight change of the microporous membrane substrate constituting the separator after extraction of the solubles for 12 hours in boiling paraxylene, the ratio of the remaining mass after extraction to the mass of the sample before extraction is :
Degree of crosslinking (gel fraction (%)) = 100 x remaining mass (g) / sample mass (g)
Determined by

(4) TD heat shrinkage (130 ° C heat shrinkage (%))
The separator is cut into 100 mm in the MD direction and 100 mm in the TD direction, and left in an oven at 150 ° C. for 1 hour. At this time, the sample is put on two sheets of paper so that the warm air does not directly contact the sample. After the sample is removed from the oven and cooled, the length (mm) is measured and the following equation:
MD heat shrinkage (%) = (100-length of MD after heating) / 100 × 100
TD thermal contraction rate (%) = (100-length of TD after heating) / 100 x 100
The thermal contraction rate of MD and TD is calculated with.
(5) Room temperature piercing strength (g)
Using a Kato Tech KES-G5 Handy Compression Tester at a measurement temperature of 25 ° C, perform a piercing test under the conditions of a needle tip curvature radius of 0.5 mm and a piercing speed of 2 mm / sec. ). The piercing strength was multiplied by 25 (film thickness (μm)) to obtain a 25 μm converted room temperature piercing strength.
(6) 160 ° C puncture strength (g)
A microporous polyethylene membrane is sandwiched between two SUS washers with an inner diameter of 13 mm and an outer diameter of 25 mm, and the periphery is clipped, and then it is in silicone oil (Shin-Etsu Chemical: KF-96-10CS) preheated to 160 ° C. The sample was immersed for 1 minute and melted for 1 minute, and then the piercing strength (melt piercing strength) (g) was measured on the sample in silicone oil by the same method as (5) of <Separator evaluation>. .

(7) Melt piercing strength retention rate (%)
Under the assumption that the contact probability between oxygen and radicals at 100 atmospheric pressure is 100 times that of atmospheric pressure, this is used as an indicator of aging of the separator in air after 1000 days (high pressure air acceleration test). Specifically, the separator was put in a pressure resistant autoclave, pressurized to 9.8 (MPa) with compressed air, and stored at 25 ° C. for 10 days, and then the melt puncture strength of the separator was measured.
(8) Nail penetration test The battery after initial charge and discharge was charged to 4.20 V with a constant current of 1.0 C, then charged for 3 hours with a constant voltage of 4.20 V, and charged to 100% SOC (charge depth) . Subsequently, additional charge was performed at a constant current of 1.0 C to charge up to SOC 150%.
The battery charged to SOC 150% is left in an atmosphere of 60 ° C. for 30 minutes, and after the battery temperature is set to 60 ° C., a nail with a diameter of 2.5 φmm and a tip angle of 60 ° in the center of the battery, piercing speed 10 mm I stabbed at / sec. At that time, the battery state was observed and the temperature change of the nail bite portion was measured, and the heat generation rate was determined from the temperature change per second.
○: No smoke or ignition occurred in the laminate element after the test.
Fair: Smoke was generated in the laminate element after the test.
X: Ignition occurred in the laminate element after the test.
(9) Maximum heating rate at nailing (° C / sec)
In the nail penetration test above, a nail with a thickness of 2.5 mm and a tip angle of 60 ° is pierced at a piercing speed of 10 mm / sec at the central part of the battery charged to SOC 150%, and the temperature per second of the nail penetration area The maximum value of the heat generation rate was determined from the change. The nail has a hollow of 1.0 mm, and by inserting a sheath type thermocouple into the hollow part, the temperature of the nail penetration part can be measured. The sheath type thermocouple used a K type thermocouple with a sheath diameter of 0.15 mm.

<Electron beam irradiation>
A polyethylene (PE) microporous membrane substrate or a separator provided with a heat-resistant layer on the substrate is fixed to a metal frame and placed under an atmosphere of oxygen concentration 100 ppm and 110 ° C. for 10 minutes. Electron beam irradiation was performed at an accelerating voltage of 150 kV. After the irradiation treatment, it was put into an oven thermostated at 130 ° C. and heated for 1 minute to carry out a radical deactivation treatment.

<Battery assembly>
(Production of positive electrode)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (made by Nippon Chemical Industrial Co., Ltd.) as a positive electrode active material, powder of acetylene black (made by Denki Kagaku Kogyo Co., Ltd.) as a conduction aid, and polyvinylidene fluoride solution as a binder (Kureha Co., Ltd.) is mixed at a solid content mass ratio of 90: 6: 4, N-methyl-2-pyrrolidone is added as a dispersion solvent so as to have a solid content of 40 mass%, and further mixed, A slurry-like solution was prepared. The slurry-like solution was applied to both sides of a 20-μm thick aluminum foil, the solvent was removed by drying, and then rolled by a roll press to obtain a positive electrode. The rolled sheet was punched into a 30 mm × 50 mm rectangular shape except for the tab portion to obtain a positive electrode.
The coated basis weight of the positive electrode active material layer at this time was 48 mg / cm ² , and the packing density was 2.89 g / cm ³ .

(Fabrication of negative electrode)
Graphite powder (Osaka Gas Chemical Co., Ltd., trade name "OMAC1.2H / SS") and another graphite powder (TIMCAL, trade name "SFG6") as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, It mixed with carboxymethylcellulose aqueous solution by solid content mass ratio of 90: 10: 1.5: 1.8. The resulting mixture was added to water as a dispersion solvent so that the solid content concentration was 45% by mass, to prepare a slurry-like solution. The slurry-like solution was applied to both sides of a copper foil having a thickness of 18 μm, the solvent was removed by drying, and rolling was performed by a roll press. The rolled sheet was punched into a 32 mm × 52 mm rectangular shape except for the tab portion to obtain a negative electrode. The coated basis weight of the negative electrode active material layer at this time was 21.2 mg / cm ² , and the packing density was 1.50 g / cm ³ .
(Preparation of non-aqueous electrolyte)
A non-aqueous electrolytic solution was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / L.

(Production of battery)
Eight positive electrode plates and nine negative electrode plates were laminated via a separator in the direction in which the positive electrode tab and the negative electrode tab were disposed on the same side. At this time, the positive electrode plate and the negative electrode plate were alternately laminated such that the outermost layers on both sides become negative electrode plates. The negative electrode which became the outermost layer peeled off the negative electrode active material layer of the surface which is not facing the positive electrode, and made one side unpainted. An insulating tape was wound around the obtained laminate to maintain its shape, to obtain an electrode laminate.
A positive electrode lead terminal made of aluminum was connected by ultrasonic welding to eight tab portions of a positive electrode plate of the electrode laminate. Similarly, a nickel negative electrode lead terminal of the same size as the positive electrode lead terminal was connected to nine negative electrode plate tab portions by ultrasonic welding.
The three sides of two aluminum laminate films were bonded by heat fusion to prepare a bag-like laminate outer package. The above electrode laminate was inserted into the laminate outer package. The electrolytic solution was injected and vacuum impregnated, and then the opening was sealed by heat fusion under reduced pressure to obtain a laminate type lithium ion battery.
The stacked lithium ion battery was charged to 4.2 V with a constant current of 250 mA, and then charged for 8 hours with a constant voltage of 4.2 V to perform initial charging. When the battery was discharged to 3.0 V with a constant current of 750 mA after the initial charge, the discharge capacity was 750 mAh.

<Production example of polyolefin microporous membrane base material>
<Production example 1 (Production of polyethylene microporous membrane substrate 1)>
45 parts by mass of homopolymer high-density polyethylene having an Mv of 700,000
45 parts by mass of homopolymer high-density polyethylene having an Mv of 300,000
5 parts by mass of homopolymer polypropylene having an Mv of 400,000
Were dry blended using a tumbler blender.
To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane is added as an antioxidant, and this is again the tumbler blender The mixture was obtained by dry blending using
The resulting mixture was fed by a feeder to a twin screw extruder under a nitrogen atmosphere.
Also, liquid paraffin (kinetic viscosity 7.59 × 10 ⁻⁵ m ² / s at 37.78 ° C.) was injected into the extruder cylinder by a plunger pump.
The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin was 65 parts by mass and the polymer concentration was 35 parts by mass in the total mixture extruded.

Then, they are melt-kneaded while heating to 230 ° C. in a twin-screw extruder, and the resulting melt-kneaded product is extruded through a T-die onto a cooling roll controlled to a surface temperature of 80 ° C. By contacting with a cooling roll, casting, and cooling and solidifying, a sheet-like molding having a thickness of 1200 μm was obtained.
This sheet was stretched at a temperature of 112 ° C. in a simultaneous biaxial stretching machine at a magnification of 7 × 6.4. Thereafter, the drawn material is immersed in methylene chloride, and after removing liquid paraffin, it is dried, and further drawn twice in the transverse direction at a temperature of 130 ° C. using a tenter drawing machine.
Thereafter, the stretched sheet was relaxed by about 10% in the width direction to perform a heat treatment, to obtain a microporous polyethylene membrane substrate 1. Physical properties of the obtained base material 1 are shown in Table 1.

[Production of Polyolefin Microporous Membrane Substrates 2 to 6]
<Production Example 2>
A microporous polyethylene membrane 2 of 9 μm was obtained in the same manner as in Production Example 1 except that the thickness of the sheet-like molding was changed to 1250 μm.
<Production Example 3>
A microporous polyethylene membrane 3 of 12 μm was obtained in the same manner as in Production Example 1 except that the thickness of the sheet-like molding was changed to 1600 μm.
Production Example 4
A microporous polyethylene membrane 4 of 6 μm was obtained in the same manner as in Production Example 1 except that the thickness of the sheet-like molding was 800 μm.
<Production Example 5>
A 1200 μm sheet-like molded product of Production Example 1 was stretched at a temperature of 112 ° C. at a magnification of 7 × 6.4 times with a simultaneous biaxial stretching machine to produce a stretched film. Next, the sheet-like stretched film is restrained to a metal frame, and an accelerating voltage of 150 kV and an absorbed dose of 20 kGy are applied at a total of 100 kGy under a nitrogen atmosphere of 110 ppm and an oxygen concentration of 100 ppm using a batch type electron beam irradiation apparatus. , Electron beam crosslinking treatment was performed. After the crosslinking treatment, it was placed in an oven adjusted to 130 ° C. and heated for 1 minute to conduct radical deactivation treatment. Next, the membrane was confined with a metal frame and after removing the paraffin oil with methylene chloride, it was dried to obtain a microporous polyethylene membrane 5.
<Production Example 6>
According to the method described in Example 18 in the specification of WO 2015/166949, a homopolypropylene microporous film is produced, and then a coating layer and a ceramic coating layer composed of alumina particles are formed to obtain a heat resistant homo. A polypropylene microporous film 6 was obtained.

Example 1
According to the production example of the above-mentioned substrate, a polyethylene microporous film substrate 1 is prepared as a polyolefin microporous film substrate, and then a heat-resistant layer is laminated by the following procedure to obtain a separator for a non-aqueous electrolyte secondary battery. The
<Formation of heat-resistant layer>
4. 96.0 parts by mass of aluminum hydroxide oxide (average particle diameter 1.0 μm), acrylic latex (solid content concentration 40%, average particle diameter 145 nm, minimum film forming temperature 0 ° C. or less) as a heat-resistant layer-forming coating solution A coating liquid was prepared by uniformly dispersing 0 parts by mass and 1.0 parts by mass of an aqueous solution of ammonium polycarboxylate (SN Disperse 5468 manufactured by San Nopco) in 100 parts by mass of water. Subsequently, the coating solution was coated on the surface of the polyolefin resin porous membrane base using a gravure coater. Thereafter, the resultant was dried at 60 ° C. to remove water, to obtain a separator having a porous layer of aluminum hydroxide oxide (boehmite), which is an inorganic filler, formed with a thickness of 2 μm on the porous polyolefin resin film.
The obtained separator is confined in a metal frame, and an electron beam is applied at a total absorbed dose of 100 kGy at an accelerating voltage of 150 kV and an absorbed dose of 20 kGy at 110 ° C. and a nitrogen atmosphere of 100 ppm oxygen concentration using a batch type electron beam irradiation apparatus. Crosslinking treatment was performed. After crosslinking treatment, it was placed in an oven adjusted to a temperature of 130 ° C. and heated for 1 minute to conduct radical deactivation treatment to obtain a separator after electron beam irradiation. And the nonaqueous electrolyte secondary battery was obtained according to the method described in the item of the above-mentioned <assembly of a battery> using the separator after this electron beam irradiation. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Examples 2 to 5
A separator for a non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the heat-resistant layer shown in Table 2 was laminated using the PE microporous membrane base shown in Table 1 (Table 2). Next, electron beam irradiation was performed to the obtained separator on conditions shown in Table 2, and the separator after electron beam irradiation was obtained. And the nonaqueous electrolyte secondary battery was obtained according to the method described in the item of the above-mentioned <assembly of a battery> using the separator after this electron beam irradiation. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Example 6
In accordance with the above production example of the base material, a polyethylene microporous membrane base 1 was prepared as a polyolefin microporous membrane base. Next, after electron beam irradiation was performed on this base material under the conditions shown in Table 2, a separator for a non-aqueous electrolyte secondary battery in which a heat resistant layer (2 μm) was laminated was obtained in the same manner as Example 1. . Then, a non-aqueous electrolyte secondary battery was manufactured according to the method described in the above-mentioned <Assembly of Battery>. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Example 7
According to the production example of the above-mentioned base material, polyethylene microporous membrane base 5 was created as polyolefin microporous membrane base. In the same manner as in Example 1, a separator for a non-aqueous electrolyte secondary battery in which a heat-resistant layer (2 μm) was laminated was obtained. Then, a non-aqueous electrolyte secondary battery was manufactured according to the method described in the above-mentioned <Assembly of Battery>. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Comparative Example 1
In this comparative example, using only the PE microporous membrane base 1 shown in Table 1 (Table 2), a separator for a non-aqueous electrolyte secondary battery was prepared without providing a heat-resistant layer. Next, a non-aqueous electrolyte secondary battery was obtained according to the method described in the above-mentioned <Assembly of battery> without using electron beam irradiation with this separator. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 2
A non-aqueous electrolyte secondary battery was obtained in the same manner as in Comparative Example 1, except that the non-aqueous electrolyte secondary battery separator in Comparative Example 1 was subjected to electron beam irradiation under the above-described electron beam irradiation conditions. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 3
In this comparative example, the heat-resistant layer shown in Table 2 was provided using the PE microporous membrane base 1 shown in Table 1 (Table 2) to prepare a separator for a non-aqueous electrolyte secondary battery. Next, a non-aqueous electrolyte secondary battery was obtained according to the method described in the above-mentioned <Battery Assembly>, without irradiating the separator with an electron beam. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Comparative Example 4
In this comparative example, using only the PE microporous membrane base 3 shown in Table 1 (Table 2), a separator for a non-aqueous electrolyte secondary battery was prepared without providing a heat-resistant layer. Next, the separator was subjected to electron beam irradiation under the above-described electron beam irradiation conditions, and then a non-aqueous electrolyte secondary battery was obtained according to the method described in the above-mentioned <Battery assembly>. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 5
In this comparative example, using the PE microporous membrane base 3 shown in Table 1 (Table 2), a heat-resistant layer shown in Table 2 was provided to prepare a separator for a non-aqueous electrolyte secondary battery. Next, a non-aqueous electrolyte secondary battery was obtained according to the method described in the above-mentioned <Battery Assembly>, without irradiating the separator with an electron beam. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 6
In this comparative example, the heat-resistant layer shown in Table 2 was provided using the PE microporous membrane base 1 shown in Table 1 (Table 2) to prepare a separator for a non-aqueous electrolyte secondary battery. Next, this separator was subjected to electron beam crosslinking treatment and radical deactivation treatment under the same conditions as in Example 1 except that the absorbed dose was changed to 20 kGy, to obtain a separator. A non-aqueous electrolyte secondary battery was obtained according to the method described in <Battery assembly> described above. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

Comparative Example 7
In this comparative example, a non-aqueous electrolyte secondary battery was obtained in the same manner as in Comparative Example 6 except that the electron beam irradiation condition in Comparative Example 6 was changed to the absorbed dose of 180 kGy. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 8
In this comparative example, when manufacturing the PE microporous membrane base 5 shown in Table 1 (Table 2), a separator in a state before being made porous without extracting liquid paraffin was created. Next, after subjecting this separator to electron beam irradiation under the above-mentioned electron beam irradiation conditions, as shown in Table 2, without providing a heat-resistant layer, according to the method described in the above-mentioned <Battery assembly>, A non-aqueous electrolyte secondary battery was obtained. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.
Comparative Example 9
In the present comparative example, the separator obtained using only the PP dry microporous membrane base 6 shown in Table 1 (Table 2) was subjected to the electron beam irradiation under the lower irradiation condition than the electron beam irradiation condition described above. Next, a heat-resistant layer containing alumina instead of aluminum hydroxide was provided on the substrate in the same manner as in Example 1 to prepare a separator for a non-aqueous electrolyte secondary battery. Then, using this separator, a non-aqueous electrolyte secondary battery was obtained according to the method described in <Battery assembly> described above. Table 2 shows the performance results of the separator and the battery after the electron beam irradiation.

<Summary of Performance of Separator for Nonaqueous Electrolyte Secondary Battery of the Present Invention and Nonaqueous Electrolyte Secondary Battery>
As shown in Table 2, the separator for a non-aqueous electrolyte secondary battery in which the heat-resistant layer was laminated on the PE microporous membrane base obtained in Examples 1 to 5 was appropriately irradiated with electron beam, Has a good degree of crosslinking, so it has excellent puncture strength and retention of molten puncture strength, and also in the nailing test of a battery made using this separator, the maximum heating rate of nailing is suppressed, and Neither smoke nor fire occurs.
Next, in the separator for non-aqueous electrolyte secondary battery (Examples 6, 7) obtained by inorganic coating after electron beam irradiation and the battery made using the separator, similarly excellent piercing at 160 ° C. In the nail penetration test of the battery having the strength and the fusion penetration strength retention rate and further made of the battery using the separator, the nail penetration maximum heat generation rate is suppressed, and neither smoke nor ignition occurs.
On the other hand, as in Comparative Example 1 shown in Table 2, in the separator for a non-aqueous electrolyte secondary battery in which the polyethylene microporous membrane substrate 1 was used as a substrate and no heat-resistant layer and no electron beam irradiation were applied. Since the crosslinked structure is not introduced into the substrate, the puncture strength is inferior at 160 ° C., and the maximum heat generation rate of nails is large even in the nail penetration test of the non-aqueous electrolyte secondary battery prepared using the separator. , Ignition phenomenon was seen.
Next, in the separator for a non-aqueous electrolyte secondary battery (comparative example 2) in which the polyethylene microporous membrane substrate 1 was used as a substrate and electron beam irradiation was applied to the substrate but the heat-resistant layer was not provided, Although it has an adequate degree of cross-linking, the piercing strength at 160 ° C. is not sufficient because there is no heat-resistant layer, and in the nailing test of a battery prepared using the separator, the maximum heating rate is high and ignition is also excessive. Happened.

As in Comparative Example 3, in the separator for a non-aqueous electrolyte secondary battery obtained by using the polyethylene microporous membrane substrate 1 as the substrate and providing the heat-resistant layer thereon but not applying the electron beam irradiation However, since the heat resistance layer is not introduced, the puncture strength is inferior at 160 ° C. because the crosslinked structure is not introduced, and also in the nail penetration test of the non-aqueous electrolyte secondary battery prepared using the separator, the nail heating maximum heating rate There was a big fire and fire.
As in Comparative Example 4, a relatively thick film of the microporous polyethylene membrane substrate 3 is used as a substrate, and a non-aqueous electrolyte secondary obtained by electron beam irradiation without providing a heat-resistant layer thereon In the battery separator, although a crosslinked structure is introduced, the piercing strength at 160 ° C. is not sufficient because it does not have a heat-resistant layer, and the nonaqueous electrolyte secondary battery fabricated using the separator Also in the nail sticking test, the maximum nail sticking heat generation rate was large, and ignition occurred.
In addition, as in Comparative Example 5, a relatively thick film of the microporous polyethylene membrane substrate 3 was used as a substrate, and a non-irradiated non-irradiated heat resistant layer was deposited thereon. In the separator for water electrolyte secondary batteries, no crosslinked structure is introduced, and therefore the puncture strength is inferior at 160 ° C., and also in the nail penetration test of the non-aqueous electrolyte secondary battery produced using the separator, The maximum heat generation rate was relatively high, and smoke was observed.
Furthermore, as in Comparative Example 6, the microporous polyethylene membrane substrate 1 is used as the substrate, and the heat-resistant layer is laminated thereon, and as shown in Table 2, electron beam irradiation is performed under low electron beam irradiation conditions. In the separator for a non-aqueous electrolyte secondary battery obtained by applying the present invention, the 160.degree. C. piercing strength is not sufficient because a sufficient crosslinked structure is not introduced, and the non-aqueous electrolyte prepared using the separator Also in the nailing test of the secondary battery, the maximum heating rate of the nailing was relatively large, and smoke was observed.
Furthermore, as in Comparative Example 7, the microporous polyethylene membrane substrate 1 was used as the substrate, and the heat-resistant layer was laminated thereon, and then electron beam irradiation was performed under high electron beam irradiation conditions as shown in Table 2. In the separator for a non-aqueous electrolyte secondary battery obtained by applying the above method, although the piercing strength is excellent at 160 ° C. because the crosslinked structure is excessively introduced, the non-aqueous electrolyte 2 prepared using the separator is preferable. In the nail penetration test of the secondary battery, the result that the retention of the fusion penetration strength was inferior was obtained. The inferiority of the strength retention as described above is considered to be due to insufficient radical deactivation in the separator.
Furthermore, as in Comparative Example 8, the base before producing the microporous polyethylene membrane base 5 and using the base before extracting the liquid paraffin which is a plasticizer for forming pores is used for the base As shown in Table 2, in the separator for a non-aqueous electrolyte secondary battery obtained by electron beam irradiation under electron beam irradiation conditions, a sufficient cross-linked structure is introduced, so that the piercing strength at 160 ° C. is sufficient. Although the heat-resistant layer was not provided, the non-aqueous electrolyte secondary battery produced using the separator had a relatively high nail sticking maximum heat generation rate, and ignition was observed because of the absence of the heat-resistant layer.
Then, as in Comparative Example 9, electron beam irradiation was performed on the thick-film polypropylene dry microporous membrane base 6 under the electron beam irradiation conditions shown in Table 2, and thereafter, a 3 μm-thick heat-resistant layer containing alumina was laminated. In the separator for a non-aqueous electrolyte secondary battery obtained as described above, although a sufficient crosslinked structure is not introduced, the piercing strength at 160.degree. C. is sufficient, and a non-aqueous electrolyte secondary battery fabricated using the separator No fire was observed in the nail penetration test of No. 1, but the result was that the melt penetration strength retention rate was inferior.

Claims (9)

  A separator in which a heat-resistant layer is laminated on a microporous membrane substrate, and the microporous film substrate has a degree of crosslinking of 40% or more, and a needle having a curvature radius of 0.5 mm at the tip, a piercing speed of 2 mm A separator for a non-aqueous electrolyte secondary battery, characterized in that 160 ° C. piercing strength in a 160 ° C. piercing test performed in an atmosphere at 160 ° C./sec.   The microporous membrane substrate measured after inserting the microporous membrane substrate whose puncture strength at 160 ° C. was measured in a pressure-resistant autoclave, pressurized to 9.8 MPa with compressed air, and stored at 25 ° C. for 10 days The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the retention of molten piercing strength is at least 50%.   The separator for non-aqueous electrolyte secondary batteries according to claim 1 or 2, wherein the microporous membrane base has a crosslinked structure.   The separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 3, wherein the microporous membrane substrate has a thickness of 12 μm or less.   The separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 4, wherein the heat-resistant layer has a thickness of 3 μm or less.   The separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 5, wherein the microporous membrane substrate is made of polyethylene.   The separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 6, wherein the heat-resistant layer contains inorganic particles.   The secondary battery containing the separator for non-aqueous electrolyte secondary batteries as described in any one of Claims 1-7.   The manufacturing method of the separator for non-aqueous electrolyte secondary batteries as described in any one of Claims 1-8 including the process of electron beam irradiation to the separator for non-aqueous electrolyte secondary batteries.