JP6430839B2 - Battery separator and non-aqueous electrolyte battery - Google Patents

Description

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

  Porous membranes, particularly porous membranes composed mainly of polyolefin resin, are widely used as separators in batteries, capacitors and the like because they exhibit excellent electrical insulation or ion permeability. In recent years, with the increase in functionality and weight of portable devices, lithium ion secondary batteries with high output density or high capacity density are used as the power source. Also in such lithium ion secondary batteries, a porous film mainly composed of a polyolefin resin is used as a separator.

  Here, in the lithium ion secondary battery, an organic solvent is usually used as an electrolytic solution. Therefore, when an abnormal situation such as a short circuit or overcharge occurs in the lithium ion secondary battery, the electrolytic solution may be decomposed, and in the worst case, ignition may occur. In order to prevent such a situation, some safety functions are incorporated in the lithium ion secondary battery. An example is the separator shutdown function.

  The shutdown function means a function of stopping the progress of the electrochemical reaction by suppressing the ionic conduction in the electrolytic solution by blocking the micropores of the separator due to heat melting or the like when the battery is abnormally heated. Generally, the lower the shutdown temperature, the higher the safety. Since polyethylene has an appropriate shutdown temperature, polyethylene is preferably used as a component of the separator.

  However, a battery having high energy may generate a large amount of heat during thermal runaway. If the temperature continues to rise even after the shutdown temperature is exceeded, there is a danger that both electrodes will be short-circuited due to the membrane breakage of the separator (hereinafter sometimes referred to as “short-circuit”), causing further heat generation. Under such circumstances, a method for forming a layer mainly composed of an insulating inorganic filler between a separator and an electrode has been proposed.

  Further, Patent Document 1 includes a porous layer containing an inorganic filler and a resin binder on at least one surface of a polyolefin resin porous membrane, and the heat shrinkage stress of the porous membrane is 10 g or less. There is a description that a multilayer porous membrane excellent in permeability is provided.

  Patent Document 2 describes a microporous membrane having a high tensile strength characterized by containing a polyolefin containing quaternary carbon.

JP 2009-26733 A JP 2009-138159 A

  Here, from the viewpoint of further improving the performance of the battery, it is possible to improve the mechanical stability of the battery, specifically, the ability to maintain safety even when mechanical power is applied to the battery. Desired.

  However, there is still room for study on the mechanical stability of a battery provided with the multilayer porous film described in Patent Document 1 or the microporous film described in Patent Document 2 as a separator.

  Accordingly, an object of the present invention is to provide a battery separator having excellent mechanical stability. Moreover, it aims at providing the nonaqueous electrolyte battery provided with favorable process property, the outstanding charging / discharging characteristic, and high safety | security by using such a battery separator.

The inventor of the present invention has arrived at the present invention as a result of intensive studies to solve the above-mentioned problems. That is, the present invention is as follows.
[1]
A battery separator comprising a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous film,
The battery separator has a thermal shrinkage rate at 150 ° C. of less than 5.0%, and the battery separator has a tensile strength of 120 MPa or more.
The battery separator.
[2]
The battery separator according to [1], wherein the tensile strength is 150 MPa or more.
[3]
The battery separator set on the sample stage of the moisture vaporizer and the moisture content of the battery separator measured after flowing nitrogen gas for 5 minutes in the moisture vaporizer is 50 to 500 ppm. The battery separator according to [1] or [2].
[4]
In the thermal mechanical analysis (TMA) measurement of the battery separator at 135 ° C., the stress relaxation rate in the width (TD) direction of the battery separator is 0.5 mgf / sec to 4.0 mgf / sec. The battery separator according to any one of [1] to [3].
[5]
The battery separator according to any one of [1] to [4], wherein the thickness of the porous film is 3 μm or more and 16 μm or less.
[6]
The battery separator according to any one of [1] to [5], wherein the porous film includes a polyolefin resin.
[7]
The battery separator according to [6], wherein the polyolefin resin is ultra high molecular weight polyethylene.
[8]
The battery separator according to any one of [1] to [7], wherein the dynamic friction coefficient of the porous layer is 0.1 to 0.6.
[9]
The battery separator according to any one of [1] to [8], wherein the inorganic filler has an average particle diameter of 0.5 to 2.5 μm.
[10]
The battery separator according to [9], wherein the inorganic filler has an average particle diameter of 0.5 to 1.5 μm.
[11]
The battery separator according to any one of [1] to [10], wherein the inorganic filler is at least one selected from boehmite, calcined kaolin, alumina, and magnesium oxide.
[12]
The battery separator according to any one of [1] to [11], wherein the resin binder is at least one selected from an acrylic polymer, a fluorine-containing resin, and polyamide.
[13]
[1] A non-aqueous electrolyte battery comprising the battery separator according to any one of [12], a positive electrode, a negative electrode, and a non-aqueous electrolyte.
[14]
A battery separator comprising a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous film,
The dynamic friction coefficient of the porous layer is 0.1 to 0.6,
The battery shrinkage rate at 150 ° C. of the battery separator is less than 5.0%,
The tensile strength of the battery separator is 120 MPa or more, and the battery separator was measured after setting the battery separator on a sample stage of a moisture vaporizer and flowing nitrogen gas into the moisture vaporizer for 5 minutes. The moisture content of the separator is 50 to 500 ppm,
The battery separator.

  According to the present invention, a battery separator having excellent mechanical stability is provided. Further, by using such a battery separator, a non-aqueous electrolyte battery having good processability, excellent charge / discharge characteristics, and high safety is provided.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

<Battery separator>
In the present embodiment, battery separator, the at least one side of the porous membrane, comprising a porous layer containing an inorganic filler and a resin binder, a thermal shrinkage at 1 5 0 ° C. for a battery separator be less than 5.0% The tensile strength of the battery separator is 120 MPa or more.

[Porous membrane]
The porous film is preferably a porous film having low electron conductivity, ionic conductivity, high resistance to organic solvents, and a fine pore size.
Examples of such a porous film include a porous film containing a polyolefin resin, a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene. , A woven fabric of polyolefin fibers (woven fabric), a nonwoven fabric of polyolefin fibers, paper, and an aggregate of insulating substance particles. Among these, when obtaining a multilayer porous membrane, that is, a battery separator through a coating process, the coating liquid is excellent in coating properties, the separator is made thinner, and the active material in an electricity storage device such as a battery. From the viewpoint of increasing the capacity per volume by increasing the ratio, a porous membrane containing a polyolefin resin (hereinafter also referred to as “polyolefin resin porous membrane”) is preferable.

[Polyolefin resin porous membrane]
The polyolefin resin porous membrane is formed from a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous membrane from the viewpoint of improving shutdown performance when used as a battery separator. A porous film is preferable. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

  The polyolefin resin contained in the polyolefin resin composition is not particularly limited. For example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are used as monomers. Examples thereof include a homopolymer, a copolymer, or a multistage polymer. Moreover, these polyolefin resins may be used independently or may be used in mixture of 2 or more types.

  Among these, polyethylene, polypropylene, copolymers thereof, and mixtures thereof are preferable as the polyolefin resin from the viewpoint of shutdown characteristics when used as a battery separator.

Specific examples of polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc.
Specific examples of the copolymer include an ethylene-propylene random copolymer and ethylene propylene rubber.

  Further, from the viewpoint of improving the heat resistance of the porous membrane, it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin. In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

In the present invention, among the above polyolefin resins, it is preferable to use ultrahigh molecular weight polyethylene from the viewpoint of film strength. Ultra high molecular weight polyethylene is polyethylene having an intrinsic viscosity [η] of 10 dL / g or more. Ultra high molecular weight polyethylene is not only an ethylene homopolymer, but also ethylene, an α-olefin having 3 to 20 carbon atoms, a cyclic olefin having 3 to 20 carbon atoms, a formula CH ₂ = CHR ¹ (where R ¹ is the number of carbon atoms) 6-20 aryl groups) and at least one olefin selected from the group consisting of linear, branched or cyclic dienes having 4 to 20 carbon atoms. Also included. The olefin to be copolymerized is preferably propylene from the viewpoint of not increasing the entanglement of the polymer chain. The molar ratio of ethylene in the monomer is typically 50% to 100%, more preferably 80% to 100%.

  Arbitrary additives can be contained in the polyolefin resin composition. Examples of additives include polymers other than polyolefin resins; inorganic fillers; phenol-based, phosphorus-based and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers An antistatic agent, an antifogging agent, a coloring pigment, and the like. The total addition amount of these additives is preferably 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin from the viewpoint of improving the shutdown performance and the like, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass. Or less.

[Details of porous membrane]
The porous membrane has a porous structure in which a large number of very small pores are gathered to form a dense communication hole. Therefore, the porous membrane has excellent ion conductivity as well as good withstand voltage characteristics and high strength. It has the characteristics.

  The porous film may be a single layer film made of the above-described material or a laminated film.

  The thickness of the porous film is preferably 3 μm or more and 16 μm or less, more preferably 4 μm or more and 14 μm or less, and further preferably 5 μm or more and 12 μm or less. 3 μm or more is preferable from the viewpoint of mechanical strength, and 16 μm or less is preferable from the viewpoint of increasing the capacity of the battery. The film thickness of the porous film can be adjusted by controlling the die lip interval and the draw ratio in the drawing step.

  The average pore diameter of the porous membrane is preferably 0.03 μm or more and 0.70 μm or less, more preferably 0.04 μm or more and 0.20 μm or less, further preferably 0.05 μm or more and 0.10 μm or less, and particularly preferably 0.06 μm or more and 0 or less. 0.09 μm or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 to 0.70 μm is preferable. The average pore diameter of the porous membrane can be measured by the measurement method described later.

  The average pore diameter should be adjusted by controlling the composition ratio, the extrusion sheet cooling rate, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat setting, the relaxation rate at the time of heat setting, or a combination thereof. Can do.

  The porosity of the porous film is preferably 25% or more and 95% or less, more preferably 30% or more and 65% or less, and still more preferably 35% or more and 55% or less. 25% or more is preferable from the viewpoint of improving ion conductivity, and 95% or less is preferable from the viewpoint of withstand voltage characteristics. The porosity of the porous film can be measured by the method described later.

  The porosity of the porous film controls the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat fixing, the relaxation rate at the time of heat fixing, or a combination thereof. Can be adjusted.

  When the porous membrane is a polyolefin resin porous membrane, the viscosity average molecular weight of the polyolefin resin porous membrane is preferably from 30,000 to 12,000,000, more preferably from 50,000 to less than 2,000,000. More preferably, it is 100,000 or more and less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferred because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when it is used as a battery separator, it is preferable that the viscosity average molecular weight is less than 1,000,000 because it tends to close a hole when the temperature rises and a good shutdown function tends to be obtained. The viscosity average molecular weight of the polyolefin resin porous membrane can be measured by a method described later.

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

Hereinafter, as an example of a method for producing a porous film, a method for extracting a pore-forming material after melt-kneading a polyolefin resin composition and a pore-forming material to form a sheet will be described.
First, the polyolefin resin composition and the hole forming material are melt-kneaded. As the melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc., while the resin component is heated and melted. A method of introducing and kneading the pore-forming material at an arbitrary ratio is mentioned.

  Examples of the pore forming material include a plasticizer, an inorganic material, or a combination thereof.

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

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

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

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

  Moreover, it is preferable to extend | stretch the said sheet-like molded object or porous film. The stretching may be performed before extracting the hole forming material from the sheet-like molded body. Moreover, you may carry out with respect to the porous film which extracted the hole formation material from the said sheet-like molded object. Furthermore, it may be performed before and after extracting the hole forming material from the sheet-like molded body.

  As the stretching treatment, either uniaxial stretching or biaxial stretching can be used. Biaxial stretching is preferred in order to improve the mechanical safety of the battery including the separator including the porous film by improving the strength of the obtained porous film. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous film is difficult to tear and has a high puncture strength.

  Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. From the viewpoint of improving the mechanical safety of the battery, simultaneous biaxial stretching or sequential biaxial stretching is preferable. More specifically, simultaneous biaxial stretching is preferable from the viewpoints of improvement in puncture strength, uniformity of stretching, and shutdown property. Further, sequential biaxial stretching is preferred from the viewpoint of easy control of plane orientation.

  Here, simultaneous biaxial stretching is a stretching method in which stretching in the MD (machine direction of continuous microporous membrane) stretching and TD (in the direction crossing the MD of the microporous membrane at an angle of 90 °) are performed simultaneously. The stretching ratio in each direction may be different.

  Sequential biaxial stretching refers to a stretching method in which MD and TD are stretched independently. When MD or TD is stretched, the other direction is fixed in an unconstrained state or a constant length. State.

  From the viewpoint of improving the mechanical safety of the battery, the draw ratio is preferably in the range of 20 times to 100 times, more preferably in the range of 25 times to 70 times in terms of surface magnification. The draw ratio in each axial direction is preferably in the range of 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, and 5 to 8 times in TD. More preferably, it is the range. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the obtained porous film. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is prevented and high productivity is achieved. Tends to be obtained.

  In order to suppress the shrinkage of the porous film, a heat treatment can be performed for the purpose of heat setting after the stretching process or after the formation of the porous film. Further, the porous film may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a cross-linking treatment with ionizing radiation.

  It is preferable to heat-treat the porous film for the purpose of heat setting from the viewpoint of suppressing shrinkage. As a heat treatment method, a stretching operation performed at a predetermined temperature atmosphere and a predetermined stretching rate for the purpose of adjusting physical properties and / or a relaxation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of reducing stretching stress. Operation is mentioned. The relaxation operation may be performed after the stretching operation. These heat treatments can be performed using a tenter or a roll stretching machine.

  In the stretching operation, it is preferable to stretch the film MD and / or TD by 1.1 times or more, more preferably 1.2 times or more from the viewpoint of obtaining a porous film having higher strength and high porosity.

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

  The stretching and relaxation operations after this plasticizer extraction are preferably performed at TD. The temperature in the stretching and relaxation operation is preferably lower than the melting point of the polyolefin resin (hereinafter also referred to as “Tm”), and more preferably in the range of 1 ° C. to 25 ° C. lower than Tm. When the temperature in the stretching and relaxation operation is in the above range, it is preferable from the viewpoint of the balance between the reduction in thermal shrinkage and the porosity.

[Porous layer]
A porous layer containing an inorganic filler and a resin binder will be described.

[Inorganic filler]
The inorganic filler used in the porous layer is not particularly limited, but is preferably one that has high heat resistance and electrical insulation and is electrochemically stable within the range of use of the lithium ion secondary battery.

  As an inorganic filler, an aluminum compound, a magnesium compound, and another compound are mentioned, for example.

  Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, and hydrotalcite.

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

  Among these, aluminum oxide, aluminum hydroxide oxide, and aluminum silicate are preferable from the viewpoints of electrochemical stability and heat resistance. A specific example of aluminum oxide is alumina. Specific examples of the aluminum hydroxide oxide include boehmite. Specific examples of aluminum silicate include kaolinite, dickite, nacrite, halloysite, and pyrophyllite.

  As the aluminum oxide, alumina is more preferable from the viewpoint of electrochemical stability. By adopting particles mainly composed of alumina as the inorganic filler that constitutes the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and a porous film with a thinner porous layer thickness. The thermal contraction at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Of these, α-alumina is most preferable because it is thermally and chemically stable.

  As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit due to generation of lithium dendrite. By adopting boehmite-based particles as the inorganic filler that constitutes the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and even with a thinner porous layer thickness, the porous film The thermal contraction at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the electrochemical device is more preferred.

  Among the aluminum silicates, kaolinite (hereinafter, also referred to as kaolin) mainly composed of kaolin mineral is preferable from the viewpoint of lightness and air permeability. Kaolin includes wet kaolin and calcined kaolin, which is calcined. However, calcined kaolin releases crystal water during the calcining process and removes impurities. Particularly preferred. By adopting particles containing calcined kaolin as the main component for the inorganic filler that constitutes the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and it is porous even with a thinner porous layer thickness. Thermal contraction of the film at a high temperature is suppressed, and excellent heat resistance tends to be exhibited.

  The average particle size of the inorganic filler is preferably from 0.5 μm to 2.5 μm, more preferably from 0.5 μm to 2.0 μm, and more preferably from 0.5 μm to 1.5 μm. Further preferred. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of further improving the mechanical stability of the battery.

  As for the particle size distribution of the inorganic filler, the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. The ratio of the maximum particle size / average particle size is preferably 50 or less, more preferably 30 or less, and still more preferably 20 or less. Adjusting the particle size distribution of the inorganic filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures. Moreover, you may have a several particle size peak between the maximum particle size and the minimum particle size. In addition, as a method for adjusting the particle size distribution of the inorganic filler, for example, a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill or the like to adjust to a desired particle size distribution, or a filler having a plurality of particle size distributions is adjusted. Examples thereof include a method of post-blending.

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a polyhedron, a needle shape, a columnar shape, a spherical shape, a spindle shape, and a lump shape. A plurality of inorganic fillers having the above shapes may be used in combination. Among these, a plate shape, a scale shape, and a polyhedron are preferable from the viewpoint of improving permeability.

  The proportion of the inorganic filler in the porous layer can be appropriately determined from the viewpoint of appropriately adjusting the dynamic friction coefficient of the porous layer described later. The proportion is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, particularly preferably 95% by mass or more, and most preferably 97% by mass or more. . Further, the ratio is preferably less than 100% by mass, more preferably 99.99% by mass or less, further preferably 99.9% by mass or less, and particularly preferably 99% by mass or less.

[Resin binder]
The resin binder is a resin that plays the role of binding the inorganic fillers described above. Moreover, it is preferable that it is resin which plays the role which bind | concludes an inorganic filler and a porous film mutually. As the type of the resin binder, it is preferable to use a resin binder that is insoluble in the electrolyte solution of the lithium ion secondary battery when used as a separator and is electrochemically stable within the use range of the lithium ion secondary battery.

Specific examples of the resin binder include the following 1) to 7).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugated diene polymer: for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic polymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer;
4) Polyvinyl alcohol resin: for example, polyvinyl alcohol, polyvinyl acetate;
5) Fluorine-containing resin: For example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer;
6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
7) A resin having a melting point and / or glass transition temperature of 180 ° C. or higher or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher: for example, polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide , Polyamide, polyester.

  From the viewpoint of further improving the mechanical stability of the battery, 3) an acrylic polymer, 5) a fluorine-containing resin, or 7) a polyamide as a polymer is preferable. As the polyamide, a fully aromatic polyamide, particularly polymetaphenylene isophthalamide is preferable from the viewpoint of durability.

  From the viewpoint of compatibility between the resin binder and the electrode, 2) a conjugated diene polymer is preferable, and from the viewpoint of voltage resistance, 3) an acrylic polymer and 5) a fluorine-containing resin are preferable.

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

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

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

  The 2) conjugated diene polymer may be obtained by copolymerizing the (meth) acrylic compound as another monomer.

[Details of porous layer]
The thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulation, more preferably 1.0 μm or more, still more preferably 1.2 μm or more, even more preferably 1.5 μm or more, particularly Preferably it is 1.8 μm or more, and most preferably 2.0 μm or more. In addition, the thickness is preferably 10 μm or less, more preferably 8 μm or less, still more preferably 6 μm or less, and particularly preferably 7 μm or less from the viewpoint of increasing the battery capacity and improving the permeability.

  The filling rate of the inorganic filler in the porous layer is preferably 95% by volume or less, more preferably 80% by volume or less, further preferably 70% by volume or less, and particularly preferably 60% by volume or less, from the viewpoint of lightness and high permeability. preferable. In light of heat shrinkage suppression and dendrite suppression, the lower limit is preferably 20% by volume or more, more preferably 30% by volume or more, and still more preferably 40% by volume or more. The filling rate of the inorganic filler can be calculated from the layer thickness of the porous layer and the weight and specific gravity of the inorganic filler.

  The porous layer may be formed only on one side of the porous film or on both sides.

  Examples of the method for forming the porous layer include a method in which a porous layer is formed by applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a porous film containing a polyolefin resin as a main component.

  The form of the resin binder in the coating solution may be an aqueous solution dissolved or dispersed in water or an organic medium solution dissolved or dispersed in a general organic medium, but a resin latex is preferred. . “Resin latex” refers to a resin dispersed in a medium. When a resin latex is used as a binder, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of a polyolefin porous film, ion permeability is unlikely to decrease and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily obtained.

  When forming the coating solution, the amount of the resin binder used relative to the amount of inorganic filler used is not limited, but as will be described later, the dynamic friction coefficient of the porous layer after the separator is formed is 0.1 to 0. 0. The amount is preferably such that it can be adjusted within the range of 6.

  The average particle diameter of the resin latex binder is preferably 50 to 1,000 nm, more preferably 60 to 500 nm, and still more preferably 80 to 250 nm. When the average particle size is 50 nm or more, when a porous layer containing an inorganic filler and a binder is laminated on at least one surface of the polyolefin porous film, it exhibits good binding properties, and when it is used as a separator, heat shrinkage is good. It tends to be excellent in safety. When the average particle size is 1,000 nm or less, the ion permeability is hardly lowered and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily obtained. The average particle size can be controlled by adjusting a polymerization time, a polymerization temperature, a raw material composition ratio, a raw material charging order, pH, a stirring speed and the like when manufacturing the resin binder.

  As a medium for the coating solution, those capable of uniformly and stably dispersing or dissolving the inorganic filler and the resin binder are preferable. For example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water , Ethanol, toluene, hot xylene, methylene chloride, hexane and the like.

  Various additives such as surfactants, thickeners, wetting agents, antifoaming agents, pH adjusting agents including acids and alkalis are added to the coating solution in order to stabilize dispersion or improve coating properties. May be added. The total addition amount of these additives is preferably 20 parts by weight or less of the active ingredient (the weight of the additive component dissolved when the additive is dissolved in the solvent) with respect to 100 parts by weight of the inorganic filler. More preferably, it is 10 parts by weight or less, and further preferably 5 parts by weight or less.

  The method for dispersing or dissolving the inorganic filler and the resin binder in the medium of the coating liquid is not particularly limited as long as it is a method capable of realizing the dispersion characteristics of the coating liquid necessary for the coating process. Examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade.

  The method for applying the coating solution to the porous film is not particularly limited as long as the required layer thickness or coating area can be realized. For example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll Examples include 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, etc. .

  Furthermore, it is preferable to apply a surface treatment to the surface of the porous film prior to the application of the coating liquid because the coating liquid can be easily applied and the adhesion between the inorganic filler-containing porous layer after coating and the surface of the porous film is improved. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous film. For example, corona discharge treatment method, plasma discharge treatment method, mechanical surface roughening method, solvent treatment method, acid treatment Method, ultraviolet oxidation method and the like.

  The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the porous film, for example, a method of drying at a temperature below the melting point while fixing the porous film, at a low temperature. The method of drying under reduced pressure, extraction drying, etc. are mentioned. Further, a part of the solvent may be left as long as the battery characteristics are not significantly affected. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film in which the porous film and the porous layer are laminated, it is preferable to appropriately adjust the drying temperature, the winding tension, and the like.

[Details of battery separator]
The battery separator of the present invention will be described. The separator is a battery separator including a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous film. The separator is excellent in heat resistance and has a shutdown function, and thus is suitable for a battery separator that separates a positive electrode and a negative electrode in a battery.

  In particular, since the separator is difficult to short-circuit even at high temperatures, it can be safely used as a separator for a high electromotive force battery.

  The final film thickness of the separator of the present invention is preferably 2 μm or more and 20 μm or less, more preferably 4 μm or more and 18 μm or less, and further preferably 6 μm or more and 16 μm or less. If the film thickness is 2 μm or more, the mechanical strength tends to be sufficient, and if it is 20 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the battery capacity.

  From the viewpoint of improving the mechanical stability of the battery, the separator of the present invention preferably has a heat shrinkage rate at 150 ° C. of less than 5.0%, and is further excellent in electrical stability during overcharge. From the viewpoint, it is more preferably 0% or more and 4.5% or less, and further preferably 0% or more and 4.0% or less. Here, as the thermal contraction rate of the separator, the larger value of both the MD thermal contraction rate and the TD thermal contraction rate is used. A method for measuring the thermal shrinkage at 150 ° C. will be described later. The adjustment of the thermal shrinkage rate of the separator can be performed by appropriately combining the above-described stretching operation and heat treatment of the porous membrane.

  From the viewpoint of improving the mechanical stability of the battery, the tensile strength of the separator of the present invention is preferably 120 MPa or more, more preferably 130 MPa or more, and further preferably 150 MPa or more.

  The tensile strength of the separator can be measured by a measurement method described later. The tensile strength of the separator can be adjusted by controlling the magnification of the aforementioned stretching operation.

  In the thermomechanical analysis (TMA) measurement of the separator of the present invention, the stress relaxation rate in the width (TD) direction of the separator when the separator is held at 135 ° C. is 0.5 mgf / sec or more and 4.0 mgf / sec or less. It is preferable from the viewpoint that the electrical stability during overcharging is further excellent.

  The lower limit value of the stress relaxation rate is more preferably 0.7 mgf / sec or more, further preferably 1.0 mgf / sec or more, and the upper limit value is more preferably 4.0 mgf / sec or less. Preferably, it is 3.8 mgf / sec or less.

  The stress relaxation rate can be measured by a measurement method described later. The stress relaxation rate can be adjusted by controlling the draw ratio and relaxation rate of the heat treatment described above.

  The water content of the separator of the present invention is preferably 50 to 500 ppm from the viewpoint of improving the mechanical stability of the battery. It is preferable that the water content of the separator is 50 ppm or more because a sufficient amount of water can be secured in the separator to obtain the effect of preventing the generation of static electricity. On the other hand, when the water content of the separator is 500 ppm or less, it is preferable because the amount of adsorbed water in the separator can be controlled to an amount that can suppress deterioration of battery characteristics.

  The water content of the separator can be measured by a measurement method described later using a Karl Fischer moisture meter. The water content of the separator can be influenced by factors such as the material of the porous film (polyolefin), the basis weight, the type of the resin binder of the porous layer, the ratio of the resin binder to the inorganic filler, the particle size of the inorganic filler, and the like. The amount of moisture adsorbed in the separator can be adjusted by the drying time, drying temperature, etc. of the separator.

  From the viewpoint of suppressing the occurrence of step shift due to impact when the separator of this embodiment is elongated, the dynamic friction coefficient of the porous layer formed in the separator of the present invention (hereinafter simply referred to as “friction coefficient”). Is preferably 0.1 or more, and more preferably 0.2 or more. In addition, from the viewpoint of the feeding resistance of the separator winding body and the initial failure rate of the battery manufactured using the separator, the friction coefficient is preferably 0.6 or less, more preferably 0.5 or less. is there. The coefficient of friction is measured according to the method described in the following examples. In addition, as a method of adjusting the friction coefficient of a separator porous layer in the said range, it can adjust with the kind, content, etc. of an inorganic filler and a resin binder.

  The feeding resistance can be influenced by the coefficient of friction on the polyolefin porous membrane side. The coefficient of friction on the polyolefin porous membrane side depends on the polymer type, the basis weight of the polyolefin porous membrane, and the like.

  In the separator according to the present invention, it is preferable that powder does not fall off. This is to avoid contamination at the time of manufacturing the separator and the battery. Further, such contamination may affect the charge / discharge characteristics of the battery. Although the mechanism for reducing the powder falling is unknown in detail, it is estimated that the ratio of the inorganic filler and the resin binder in the porous layer is correlated.

One aspect of producing the battery separator of the present invention may be a method for producing a battery separator including the following steps:
(I) a step of melt-kneading the ultrahigh molecular weight polyethylene-containing resin composition and the pore-forming material to obtain a melt-kneaded product;
(II) A step of forming the melt-kneaded product into a sheet shape to obtain a sheet body;
(III) extracting the pore-forming material from the sheet body to obtain a porous film;
(IV) stretching the porous membrane by simultaneous biaxial stretching or sequential biaxial stretching to obtain a stretched porous membrane; and (V) an inorganic filler having an average particle size of about 0.5 to 2.5 μm; Applying a coating liquid containing a resin binder to the stretched porous film to form a porous layer on the stretched porous film;

  In step (IV), the thickness of the stretched porous membrane is preferably adjusted to about 3 μm to about 16 μm, and / or the stretch ratio of the porous membrane is adjusted within the range of 20 times to 100 times as the surface magnification. Is preferred. Furthermore, in the step (V), the kind or amount of the inorganic filler or resin binder used is adjusted so that the dynamic friction coefficient of the exposed portion of the porous layer to be formed is in the range of 0.1 to 0.6. It is preferable.

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

[Nonaqueous electrolyte battery]
A preferred embodiment in the case where the electricity storage device is a nonaqueous electrolyte battery will be described below. The nonaqueous electrolyte battery includes the battery separator of the present invention, a positive electrode, a negative electrode, and a nonaqueous electrolyte.

  The battery using the separator according to the present invention is excellent in the battery initial failure rate. Here, the initial failure rate of the battery is an evaluation of the initial charge / discharge efficiency of the battery manufactured using the separator, and the initial charge / discharge efficiency is 85% or less. Of these, the percentage of defective batteries is indicated. This battery failure rate is preferably less than 40%, and more preferably less than 20%.

  Here, although the mechanism by which the evaluation of the initial failure rate of the battery is good / bad is unknown in detail, it is presumed that the proportion of the inorganic filler and the resin binder in the porous layer is correlated. When the ratio of the resin binder is large, it is considered that when the battery is wound, the feeding resistance from the separator roll is increased and the separator is pulled, so that the battery may be wound with the separator deformed.

  A battery using the separator according to the present invention is excellent in capacity retention during high-temperature storage. The capacity maintenance rate is a value obtained by dividing the discharge capacity after charge / discharge by the initial discharge capacity when the battery is stored and charged / discharged at a certain temperature.

  Here, although the mechanism by which this battery initial failure rate becomes good or bad is unknown in detail, it is presumed that the water absorption rate of the separator is correlated. If the water absorption rate is high, moisture may remain in the battery even after the battery is manufactured, and it is considered that the moisture may cause decomposition of the electrolyte, leading to a decrease in discharge capacity.

  The battery using the separator according to the present invention is excellent in the nail penetration test. The nail penetration test is one of battery safety evaluations.

  Here, the mechanism by which this nail penetration test is good or bad is unknown in detail, but the inorganic filler particle size of the porous layer, the thermal shrinkage of the separator at 150 ° C., the tensile strength, and the stress in the TD direction at a high temperature holding state. It has a correlation with the relaxation rate and is considered to be influenced by factors such as the heat resistance of the porous film, mechanical strength, and the rubble (stone wall shape) structure of the porous layer.

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

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

[Method of manufacturing power storage device]
Although the said electrical storage device is not specifically limited, For example, it manufactures as follows. That is, the separator is produced as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). Next, the separator is stacked together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. If necessary, the laminate may be folded ninety-nine. Next, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And an electrical storage device is obtained by passing the process of accommodating the said winding body in an exterior body, and also inject | pouring electrolyte solution.

  In addition, the electricity storage device is formed by forming a separator, a positive electrode, and a negative electrode in a flat plate shape, and then laminating in order of positive electrode-separator-negative electrode-separator-positive electrode or negative electrode-separator-positive electrode-separator-negative electrode. After that, it can be manufactured through a process such as housing in an exterior body and injecting an electrolytic solution therein.

  In addition, a battery can or a bag-like film can be used as the exterior body.

  The present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In addition, the physical property etc. in an Example were measured with the following method.

(1) Film thickness measurement Dial gauge PEACOCKNo. 25 (manufactured by Ozaki Seisakusho). A sample of MD: 10 mm × TD: 10 mm was cut out from the porous film, and the film thickness was measured at nine locations (3 points × 3 points) in a lattice shape. The average value obtained was defined as the film thickness (μm).

(2) Particle size measurement of inorganic filler contained in separator porous layer Field emission scanning of JSM-6700F manufactured by JEOL Ltd., sampled for field emission scanning electron microscope observation of separators according to Examples and Comparative Examples The surface of the porous layer of the separator is observed with an electron microscope, and the particle size of 30 particles is measured using “measurement between two points” in the software of JEOL PC-SEM 6700. It was set as the particle size of the particle | grains contained in. When the particles are not ordinary spherical particles, such as when they are deformed instead of being spherical, the longest diameter and the shortest diameter are measured, and the average of the two points is taken as one particle diameter. Measurement conditions are as shown below.

Acceleration voltage: 1 kV
Objective aperture: 4
Secondary electron detection key: ON
Mode: 2
Emission: 10 μm
Auto reset: OFF
Observation mode: LEM
Scan rotation: 0
Dynamic focus: 0

(3) Measurement of thermal contraction rate of separator The separator was cut to 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 was sandwiched between two sheets of paper so that the hot air did not directly hit the sample. After taking out the sample from the oven and cooling, the length (mm) was measured, and the thermal shrinkage was calculated by the following formula. The measurement was performed in the MD direction and the TD direction, and the larger value was taken as the heat shrinkage rate.
Thermal shrinkage rate (%) = {(100−length after heating) / 100} × 100

(4) Measurement of separator tensile strength MD and TD samples (shape: width 10 mm x length 100 mm) using a tensile tester manufactured by Shimadzu Corporation and Autograph AG-A type (trademark) in accordance with JIS K7127 It was measured. In addition, the sample had a chuck spacing of 50 mm. For the tensile strength at break (MPa), the smaller measured value of MD and TD was adopted. The measurement was performed under conditions of a temperature of 23 ± 2 ° C., a chuck pressure of 0.30 MPa, and a tensile speed of 200 mm / min.

(5) Evaluation of stress relaxation rate at 135 ° C. by TMA measurement with a separator Measurement was performed using Shimadzu Corporation TMA50 (trademark). A sample cut into a width of 3 mm in the MD and TD directions was fixed to a chuck so that the distance between chucks was 10 mm, and set in a dedicated probe. The initial load was 1.0 g, and the probe was heated from 30 ° C. to 135 ° C. at a rate of 10 ° C./min. After reaching 135 ° C., the probe was held for 300 seconds. From the time when the temperature reached 135 ° C. and the contraction force (gf) after holding for 300 seconds, the stress relaxation rate was calculated using the following formula.
Stress relaxation rate (mgf / sec) = [Shrinkage force (when reaching 135 ° C.) − Shrinkage force (after holding for 300 seconds)] / 300 × 1000

  The stress relaxation rate was performed in the MD and TD directions, and the smaller calculated value was adopted as the stress relaxation rate. When the contraction force disappeared during the 300-second holding, the measurement of the stress relaxation rate was impossible.

(6) Water content measurement of separator About the separator concerning an Example and a comparative example, the water content by the coulometric titration method was measured using Karl Fischer moisture meter MKC-160 (made by Kyoto Electronics Industry). Specifically, about 150 mg of each separator is used as a measurement sample weight, and after setting the separator on a sample stage of a moisture vaporizer ADP-611 (manufactured by Kyoto Electronics Industry), nitrogen gas is flowed at 150 ° C. for 5 minutes. After drying, measurement was performed and the water content was calculated from the following formula. As the Karl Fischer reagent, Hydranal Coulomat AK (manufactured by Sigma Aldrich) and Hydranal Coulomat CGK (manufactured by Sigma Aldrich) were used.
Water content (ppm) = measured value (μm) / sample weight (mg) * 10 ⁻³

(7) Measurement of dynamic friction coefficient of separator porous layer About the porous layer of the separator according to Examples and Comparative Examples, using a KES-SE friction tester manufactured by Kato Tech Co., Ltd., load 50 g, contact area 10 × 10 = 100 mm ² (20 mm stainless steel wire made of SUS304 0.5 mmφ wound with no gaps between them and without overlapping), contact feed speed 1 mm / sec, tension 6 kPa, temperature 25 ° C., and humidity 50 The coefficient of dynamic friction was measured under the condition of%. The sample size was width 50 mm × measurement direction 200 mm, and measured three times each in the MD and TD directions to determine the average.

(8) Separation evaluation of separator About the separator concerning an Example and a comparative example, it cuts into strip shape of TD50mm width xMD200mm, the upper end is fixed with a tape, and the black cloth which put the weight of 50g on that is slid. The black cloth and the separator at that time were visually confirmed and evaluated as follows.
○: No adhesion of the porous body to the black cloth and no peeling of the porous body.
X: The porous body is attached to the surface of the black cloth, and peeling is seen in the porous body.

(9) Evaluation of battery initial failure rate a. Production of Battery In this evaluation, a cylindrical lithium ion battery was produced and evaluated as follows.
For the positive electrode, a 15 μm thick aluminum foil current collector was coated with a positive electrode mixture containing a lithium transition metal composite oxide as a positive electrode active material almost evenly, and this was cut into a strip having a width of 51 mm and a length of about 750 mm did. On the other hand, a negative electrode mixture containing a carbon powder material made of graphite or the like capable of reversibly occluding and releasing lithium ions as a negative electrode active material is applied almost uniformly to a copper foil current collector having a thickness of 10 μm on the negative electrode. This was cut into a strip having a width of 54 mm and a length of about 800 mm. These belt-shaped positive electrode and negative electrode are equipped with a conductive lead for passing a current through a current collector not coated with an electrode mixture at the electrode end so that the conductive lead comes to a predetermined position after winding. Attach with. And as a separator, the microporous film concerning an Example and a comparative example was cut | disconnected and used for the strip | belt shape of width 57mm and length about 900mm.

For the winding operation of these members, a winding device having a diameter of about 4 mm and a half-cracked winding shaft was used. Then, the two separators wound in a roll shape are pulled out, sandwiched between half-cracked portions of the winding shaft, wound by rotating the winding shaft several times, and a positive electrode and a negative electrode are inserted between the separator and the separator. Turned. A tension of 0.05 to 0.15 MPa (0.5 to 1.5 kgf / cm ² ) is applied to the positive electrode, the negative electrode, and the separator in the direction opposite to the rotation direction of the winding shaft, Looseness was prevented. After winding the positive electrode and the negative electrode, the separator was further wound several times and cut.

  The electrodes produced as described above were housed in a battery can having a nickel-plated surface with insulating plates attached to the top and bottom with the negative electrode side down and the positive electrode side up. And the electrode rod of the welding resistance machine was inserted in the center hole of the electrode, and the negative electrode lead was welded to the bottom of the battery can. Next, a groove for attaching the battery lid was formed on the upper part of the battery can, a gasket was put on the upper side of the groove, and then the positive electrode lead and the battery lid were welded. What was assembled so far was put into a vacuum dryer and kept in a vacuum atmosphere at 60 ° C. for about 16 hours to remove the adhering moisture.

  Next, it moved in the glove box of argon gas atmosphere, and inject | poured the predetermined amount electrolyte solution. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a mixed solvent such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was used. After injecting the electrolyte, the battery lid was lightly placed in the gasket on the top of the battery can, and the battery can was caulked and sealed with a caulking machine.

b. Evaluation of Initial Battery Failure Rate Five of the above batteries were prepared, and the failure rate was evaluated based on the following criteria from the initial charge / discharge efficiency.
Battery failure rate (%) =
[Number of batteries with initial charge / discharge efficiency of 85% or less] / Evaluation batteries (5) × 100
The defective rate of the battery was evaluated according to the following criteria.
○: Battery failure rate of 0% or more and less than 20% △: Battery failure rate of 20% or more and less than 40% ×: Battery failure rate of 40% or more

(10) Capacity maintenance evaluation during storage of battery at high temperature Using the separators according to Examples and Comparative Examples, a non-aqueous secondary battery was produced according to the following procedure, and the capacity maintenance rate was evaluated using it. .

a. Production of Positive Electrode 89.5 parts by weight of lithium cobalt oxide (LiCoO ₂ , manufactured by Nippon Chemical Industry Co., Ltd.), 4.5 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and polyvinylidene fluoride (Clea Chemical Industries Co., Ltd.) A positive electrode paste was prepared using 6 wt% of an NMP solution of polyvinylidene fluoride so that the dry weight of the product was 6 parts by weight. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

b. Manufacture of Negative Electrode As a negative electrode active material, 6 wt% so that 87 parts by weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.), 3 parts by weight of acetylene black, and 10 parts by weight of polyvinylidene fluoride are dried. A negative electrode paste was prepared using an NMP solution of polyvinylidene fluoride. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.

c. Preparation of Nonaqueous Electrolyte A solution in which LiPF ₆ was dissolved to 1 mol / L in a solution in which ethylene carbonate and ethyl methyl carbonate were mixed at a weight ratio of 3: 7 was used.

d. Production of non-aqueous secondary battery The positive electrode and the negative electrode obtained as described above were opposed to each other through a laminated separator. This was impregnated with a non-aqueous electrolyte and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery.

e. Evaluation of capacity maintenance rate About the non-aqueous secondary battery produced as mentioned above, in a 60 degreeC thermostat, the charge / discharge measuring apparatus (HJ-101SM6 by Hokuto Denko Co., Ltd.) was used, and the charge / discharge characteristic was measured. . Regarding charging / discharging conditions, charging is performed at 0.2 C to 4.2 V for 8 hours, discharging is performed at 0.2 C at 2.75 V, and the capacity maintenance rate is the discharge at the time of 500 cycles with respect to the initial discharging capacity. The capacity ratio was evaluated according to the following criteria.
○: Capacity maintenance rate is 70% or more ×: Capacity maintenance rate is less than 70%

(11) Battery nail penetration test a. Production of positive electrode Lithium nickel manganese cobalt composite oxide powder (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) and lithium manganese composite oxide powder (LiMn ₂ O ₄ ), which are positive electrode active materials, have a mass ratio of 70: Mixed positive electrode active material mechanically mixed at 30: 85 parts by mass, acetylene black as a conductive auxiliary agent: 6 parts by mass, PVdF as a binder: 9 parts by mass, N-methyl-2-pyrrolidone (NMP) as a solvent The mixture was mixed uniformly to prepare a positive electrode mixture-containing paste. This positive electrode mixture-containing paste is uniformly applied to both sides of a 20 μm-thick current collector made of aluminum foil, dried, and then subjected to compression molding with a roll press so that the total thickness becomes 130 μm. The thickness of the positive electrode mixture layer was adjusted. A positive electrode was produced using a rectangular sheet having a short side of 95 mm and a long side of 120 mm, and an active material-uncoated aluminum foil having a length of 20 mm on the short side.

b. Preparation of Negative Electrode Graphite as a negative electrode active material: 91 parts by mass and PVdF as a binder: 9 parts by mass were mixed so as to be uniform using NMP as a solvent to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste is uniformly applied to both sides of a 15 μm-thick current collector made of copper foil, dried, and then subjected to compression molding with a roll press so that the total thickness becomes 130 μm. The thickness of the negative electrode mixture layer was adjusted. A negative electrode using a rectangular sheet having a short side of 95 mm and a long side of 120 mm and an active material uncoated copper foil having a length of 20 mm at the upper part of the short side as a lead tab was prepared.

c. Preparation of non-aqueous electrolyte solution In a mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 1: 1: 1 (volume ratio) as a non-aqueous electrolyte solution, LiPF ₆ as a solute is adjusted to a concentration of 1.0 mol / liter. Prepared by dissolving.

d. Cell Preparation The above-described positive electrode sheet 27 and negative electrode sheet 28 were alternately stacked, and each was separated by a separator according to Examples and Comparative Examples to prepare an electrode plate laminate. The separator was a 125 mm wide strip-shaped separator, which was alternately folded into ninety-nine folds to produce an electrode plate laminate. The electrode plate laminate was pressed into a flat plate shape, then housed in an aluminum laminate film, and heat sealed on three sides. The positive electrode lead tab and the negative electrode lead tab were led out from one side of the laminate film. Further, after drying, the above non-aqueous electrolyte was poured into this container, and the remaining one side was sealed. The lithium ion battery thus manufactured was designed to have a capacity of 10 Ah. Six or more batteries were prepared for each sample of the example and the comparative example.

e. Evaluation of nail penetration Laminate cell charged with constant current and constant voltage (CCCV) for 3 hours under the conditions of current value 3A (0.3C) and end-of-life battery voltage 4.2V is left on the iron plate in the explosion-proof booth and placed in the center of the cell A penetration test was carried out on an iron nail having a diameter of 2.5 mm under an environment of around 25 ° C. at a speed of 10 mm / second and 20 mm / second, with n = 3. The nail was maintained in a penetrating state, and those that ignited or exploded within 15 minutes were rejected, those that did not ignite or explode were accepted, and evaluation was made according to the following criteria.
A: 20 mm / second evaluation; all three passed, 10 mm / second evaluation; all three passed ○: 20 mm / second evaluation; all three passed, 10 mm / second evaluation; one or two passed △: 20 mm / second evaluation; all three passed, 10 mm / second evaluation; all three failed x: 20 mm / second evaluation; one or more failed, 10 mm / second evaluation; all three failed

(12) Viscosity average molecular weight (hereinafter also referred to as “Mv”)
Based on ASRM-D4020, the intrinsic viscosity [η] at 135 ° C. in a decalin solvent was determined, and Mv of polyethylene was calculated by the following equation.
[Η] = 0.00068 × Mv 0.67
The Mv of polypropylene was calculated from the following formula.
[Η] = 1.10 × Mv0.80

[Example 1]
47 parts by mass of polyethylene having an Mv of 700,000, 46 parts by mass of polyethylene having an Mv of 300,000, and 7 parts by mass of polypropylene having an Mv of 400,000 were dry blended using a tumbler blender. To 99 parts by mass of the obtained pure polymer mixture, 1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added, and the tumbler was added again. A dry blend was performed using a blender to obtain a polymer mixture. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78 ° C. 7.59 × 10 −5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

  The feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 65 parts by mass. The melt-kneading conditions were set at a preset temperature of 200 ° C., a screw rotation speed of 240 rpm, and a discharge rate of 12 kg / h.

  Subsequently, the melt-kneaded material was extruded and cast onto a cooling roll controlled at a surface temperature of 25 ° C. through a T-die, to obtain a gel sheet having a thickness of 1200 μm.

  Next, it led to the simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions are an MD magnification of 7.0 times, a TD magnification of 7.0 times, and a set temperature of 123 ° C.

  Next, the solution was introduced into a methylene chloride bath and sufficiently immersed in methylene chloride to extract and remove liquid paraffin, and then methylene chloride was removed by drying.

  Next, it was led to a TD tenter and heat fixed. The stretching temperature and magnification during heat setting were 128 ° C. and 2.0 times, and the temperature and relaxation rate during the subsequent relaxation were set as 133 ° C. and 0.80 to obtain a polyolefin resin porous membrane.

  After the corona discharge treatment (discharge amount 50 W) is performed on the surface of the polyolefin resin porous membrane, 96.0 parts by mass of aluminum hydroxide oxide (boehmite, average particle size 1.0 μm) and acrylic latex are formed on the treated surface side. (Solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0 ° C. or less) 4.0 parts by mass, 100 parts by mass of 1.0 part by mass of an aqueous polycarboxylate ammonium solution (SN Dispersant 5468 manufactured by San Nopco) The coating solution is uniformly dispersed in water and applied to the surface of the polyolefin resin porous membrane using a gravure coater, and then dried at 60 ° C. to remove water, and a porous layer having a thickness of 3 μm is formed on the porous membrane. And a separator having a total film thickness of 12 μm was obtained. The results are also shown in Table 1.

[Example 2]
A separator was obtained according to the method of Example 1 except that the thickness of the melt-kneaded product was 1100 μm, the setting temperature of the simultaneous biaxial tenter stretching machine was 121 ° C., and the thickness of the porous layer was 4 μm. The results are also shown in Table 1.

[Example 3]
A separator was obtained according to the method of Example 2 except that the thickness of the porous layer was 2 μm. The results are also shown in Table 1.

[Example 4]
A separator was obtained according to the method of Example 1 except that the thickness of the melt-kneaded product was 1500 μm, the setting ratio of the simultaneous biaxial tenter stretching machine was TD ratio 8.0 times, and the porous layer thickness was 2 μm. The results are also shown in Table 1.

[Example 5]
A separator was obtained according to the method of Example 4 except that the thickness of the porous layer was 4 μm. The results are also shown in Table 1.

[Example 6]
The thickness of the melt-kneaded product is 1800 μm, the setting magnification of the simultaneous biaxial tenter stretching machine is TD magnification 8.0 times, the setting temperature is 121 ° C., the porous layer thickness is 2 μm, and the total film thickness of the separator is 14 μm. A separator was obtained according to the method of Example 1. The results are also shown in Table 1.

[Example 7]
A separator was obtained according to the method of Example 6 except that the thickness of the melt-kneaded product was 1800 μm and the set temperature of the simultaneous biaxial tenter stretching machine was 119 ° C. The results are also shown in Table 1.

[Example 8]
A separator was obtained according to the method of Example 4 except that aluminum hydroxide oxide (boehmite, average particle size 0.6 μm) was used as the inorganic filler. The results are also shown in Table 1.

[Example 9]
A separator was obtained according to the method of Example 4 except that aluminum hydroxide oxide (boehmite, average particle size 1.4 μm) was used as the inorganic filler. The results are also shown in Table 1.

[Example 10]
A separator was obtained according to the method of Example 4 except that calcined kaolin (average particle size 2.0 μm) was used as the inorganic filler. The results are also shown in Table 1.

[Example 11]
A separator was obtained according to the method of Example 4 except that polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more) was used as the resin binder. The results are also shown in Table 1.

[Example 12]
A separator was obtained according to the method of Example 4 except that aluminum hydroxide oxide (boehmite, average particle size 0.3 μm) was used as the inorganic filler. The results are also shown in Table 1.

[Example 13]
A separator was obtained according to the method of Example 4 except that aluminum hydroxide oxide (boehmite, average particle size 1.7 μm) was used as the inorganic filler. The results are also shown in Table 1.

[Example 14]
Mv 150,000 copolymer polyethylene (comonomer: propylene, propylene monomer unit content 0.6 mol%, density 0.95) 28.5 parts by mass, Mv 300,000 homo high density polyethylene 28.5 parts by mass, Mv 700,000 14.2 parts by weight of homo high-density polyethylene, 23.8 parts by weight of Mv 2 million homo ultrahigh molecular weight polyethylene, and 5 parts by weight of homopolymer polypropylene were dry blended using a tumbler blender.

1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant is added to 99 parts by mass of the obtained polymer mixture, and again A mixture such as a polymer was obtained by dry blending using a tumbler blender. The obtained mixture of polymers and the like was substituted with nitrogen and then fed to the twin-screw extruder with a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump.

  The feeder and pump were adjusted so that the liquid paraffin content ratio in the total mixture melt-kneaded and extruded was 62 mass% (resin composition concentration was 38 mass%). The melt kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 100 rpm, and a discharge rate of 12 kg / h.

  Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled at a surface temperature of 25 ° C. through a T-die, to obtain a gel sheet having a thickness of 1600 μm.

  Next, it led to the simultaneous biaxial tenter stretching machine, and biaxial stretching was performed. The set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 6.1 times, and a preset temperature of 123 ° C. Next, the solution was introduced into a methylene chloride bath and sufficiently immersed in methylene chloride to extract and remove liquid paraffin, and then methylene chloride was removed by drying.

  Next, it was led to a TD tenter and heat fixed. The heat setting temperature was 117 ° C., the maximum TD magnification was 2.0 times, the relaxation rate was 0.90, and a polyolefin resin porous membrane was obtained.

  A separator was obtained by forming the same porous layer as in Example 2 on the surface of the polyolefin resin porous membrane. The results are also shown in Table 1.

[Example 15]
A separator was obtained according to the method of Example 14 except that the thickness of the melt-kneaded product was 1700 μm and the thickness of the porous layer was 9 μm. The results are also shown in Table 1.

[Example 16]
A binder solution in which 5 parts by weight of PVdF-HFP and 5 parts by weight of cyanoethyl polyvinyl alcohol (product name: cyanoresin CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) are dissolved in acetone is mixed with alumina (density: 4.0 g / cm ³⁾ as an inorganic filler. ) After 90 parts by weight were added, a slurry was prepared by dispersing by a ball mill method.

  And the said slurry was coated on the polyolefin resin porous film manufactured in Example 6, and it dried and obtained the separator. The formed coating layer had an average thickness of 3 μm. The results are also shown in Table 1.

[Example 17]
Meta-type wholly aromatic polyamide (hereinafter also referred to as m-aramid) (product name: Conex, manufactured by Teijin Techno Products) and magnesium hydroxide having an average particle size of 0.8 μm as an inorganic filler (manufactured by Kyowa Chemical Industry Co., Ltd.) Kisuma 5P) is mixed at a mass ratio of 25:75, and this mixture is mixed with dimethylacetamide (DMAc) and tripropylene glycol (with a meta-type wholly aromatic polyamide concentration of 5.5% by mass). TPG) was mixed in a mixed solvent having a mass ratio of 50:50. After mixing, the obtained mixed solution was allowed to stand at room temperature under atmospheric pressure for 5 hours to obtain a coating slurry.

  Then, the slurry was coated on the polyolefin resin porous membrane produced in Example 6 and dried to obtain a separator. The formed porous layer had an average thickness of 3 μm. The results are also shown in Table 1.

[Example 18]
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (product name “Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate, The gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ° C.

  On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94.8 parts of butyl acrylate, 2 parts of acrylonitrile, 1 part of methacrylic acid, A monomer mixture was obtained by mixing 1.2 parts of N-methylolacrylamide and 1 part of allyl glycidyl ether (AGE). This monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to produce an aqueous dispersion containing a (meth) acrylic polymer as a binder. The obtained (meth) acrylic polymer had a volume average particle diameter D50 of 0.36 μm and a glass transition temperature of −45 ° C.

  Alumina particles (AKP-3000 manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter D50 = 0.45 μm, tetrapod-like particles) were prepared as inorganic fillers. As the viscosity modifier, an etherification degree of 0.8 to 1.0 carboxymethyl cellulose (manufactured by Daicel Finechem, product name D1200) was used. The viscosity of a 1% aqueous solution of the viscosity modifier was 10 to 20 mPa · s.

  100 parts of the inorganic filler, 1.5 parts of the viscosity modifier, and ion-exchanged water were mixed and dispersed so that the solid content concentration was 40% by weight. Further, an aqueous dispersion containing the above (meth) acrylic polymer as a binder is mixed in an amount of 4 parts by solid content, and 0.2 part of a polyethylene glycol type surfactant (San Nopco SN wet 366) is mixed to form a slurry for coating. Manufactured.

  Then, the slurry was coated on the polyolefin resin porous membrane produced in Example 6 and dried to obtain a separator. The formed coating layer had an average thickness of 3 μm. The results are also shown in Table 1.

[Example 19]
The coating solution of Example 1 was prepared by using 99.0 parts by mass of alumina particles (AA-1.5 manufactured by Sumitomo Chemical Co., Ltd., volume average particle size D50 = 1.6 μm), acrylic latex (solid content concentration 40%, average particle size 145 nm). The minimum coating temperature was 0 ° C. or less) and the coating liquid was produced in the same manner as in Example 1.

  Then, the slurry was coated on the polyolefin resin porous membrane produced in Example 5 and dried to obtain a separator. The formed coating layer had an average thickness of 2 μm. The results are also shown in Table 1.

[Example 20]
The coating solution of Example 1 was prepared by using 60.0 parts by mass of aluminum hydroxide oxide (boehmite, average particle size 1.0 μm), acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0 ° C. or less). The amount was changed to 40.0 parts by mass, and a coating solution was produced in the same manner as in Example 1.

  Then, the slurry was coated on the polyolefin resin porous membrane produced in Example 5 and dried to obtain a separator. The formed coating layer had an average thickness of 4 μm. The results are also shown in Table 1.

[Comparative Example 1]
A separator was obtained according to the method of Example 1 except that the thickness of the melt-kneaded product was 1600 μm and the set temperature of the simultaneous biaxial tenter stretching machine was 125 ° C. The results are also shown in Table 1.

[Comparative Example 2]
A separator was obtained according to the method of Comparative Example 1 except that the thickness of the porous layer was 4 μm. The results are also shown in Table 1.

[Comparative Example 3]
The thickness of the melt-kneaded product is 1100 μm, the setting temperature of the simultaneous biaxial tenter stretching machine is 128 ° C., the stretching temperature and magnification during heat setting are 130 ° C. and 1.6 times, and the temperature and relaxation rate during the subsequent relaxation are 130 ° C. And 0.80 and the separator was obtained according to the method of Example 1 except the thickness of the porous layer having been 5 μm. The results are also shown in Table 1.

[Comparative Example 4]
A separator was obtained according to the method of Example 4 except that the thickness of the porous layer was 1 μm. The results are also shown in Table 1.

[Comparative Example 5]
The polyolefin resin porous membrane used for the substrate in Example 4 was evaluated. The results are also shown in Table 1.

[Comparative Example 6]
The polyolefin resin porous membrane used for the substrate in Example 6 was evaluated. The results are also shown in Table 1.

In addition, Examples 1, 2, 5, 14-18, and 20 are reference examples.

Claims (18)

A battery separator comprising a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous film,
The film thickness of the battery separator is 4 μm or more and 18 μm or less,
The porous layer has a thickness of 2 μm or more and less than 3 μm,
The battery separator has a thermal shrinkage rate at 150 ° C. of less than 5.0%, and the tensile strength value of the smaller of the tensile strengths in the MD direction and the TD direction of the battery separator is 130 MPa or more. ,
The battery separator.   The battery separator according to claim 1, wherein the tensile strength is 150 MPa or more.   The moisture content of the battery separator measured after setting the battery separator on the sample stage of the moisture vaporizer and flowing nitrogen gas into the moisture vaporizer for 5 minutes is 50 to 500 ppm. Item 3. The battery separator according to Item 1 or 2.   In the thermomechanical analysis (TMA) measurement of the battery separator at 135 ° C., the stress relaxation rate in the width (TD) direction of the battery separator is 0.5 mgf / sec or more and 4.0 mgf / sec or less. Item 4. The battery separator according to any one of Items 1 to 3.   The battery separator according to any one of claims 1 to 4, wherein a thickness of the porous film is 3 µm or more and 16 µm or less.   The battery separator according to claim 1, wherein the porous film contains a polyolefin resin. The battery separator according to claim 6, wherein the porous film is a polyolefin resin porous film, and the viscosity average molecular weight of the polyolefin resin porous film is 30,000 or more and 12,000,000 or less. The battery separator according to claim 6 or 7 , wherein the polyolefin resin is ultra high molecular weight polyethylene. The dynamic friction coefficient of the porous layer is 0.1 to 0.6, the battery separator according to any one of claims 1-8. The battery separator according to any one of claims 1 to 9 , wherein the inorganic filler has an average particle diameter of 0.5 to 2.5 µm. The battery separator according to claim 10 , wherein the inorganic filler has an average particle diameter of 0.5 to 1.5 μm. 12. The battery separator according to claim 1, wherein the inorganic filler has a minimum particle size of 0.02 μm or more in a particle size distribution of the inorganic filler. The battery separator according to any one of claims 1 to 12, wherein a maximum particle size of the inorganic filler is 20 µm or less in a particle size distribution of the inorganic filler. 14. The battery separator according to claim 1, wherein in the particle size distribution of the inorganic filler, a ratio of the maximum particle size / average particle size of the inorganic filler is 50 or less. The battery separator according to any one of claims 1 to 14 , wherein the inorganic filler is at least one selected from boehmite, calcined kaolin, alumina, and magnesium oxide. The battery separator according to any one of claims 1 to 15 , wherein the resin binder is at least one selected from an acrylic polymer, a fluorine-containing resin, and polyamide. A battery separator comprising a porous layer containing an inorganic filler and a resin binder on at least one surface of a porous film,
The film thickness of the battery separator is 4 μm or more and 18 μm or less,
The porous layer has a thickness of 2 μm or more and less than 3 μm,
The dynamic friction coefficient of the porous layer is 0.1 to 0.6,
The battery shrinkage rate at 150 ° C. of the battery separator is less than 5.0%,
Of the tensile strengths in the MD direction and TD direction of the battery separator , the smaller tensile strength value is 130 MPa or more, and the battery separator is set on a sample stage of a moisture vaporizer, and the moisture vaporization is performed. The water content of the battery separator measured after flowing nitrogen gas into the apparatus for 5 minutes is 50 to 500 ppm,
The battery separator. A non-aqueous electrolyte battery comprising the battery separator according to any one of claims 1 to 17 , a positive electrode, a negative electrode, and a non-aqueous electrolyte.