KR20230031205A - Battery Separator - Google Patents

Abstract

(Problem) An object of this invention is to provide the separator which is excellent in heat resistance and improved injectability of electrolyte solution in battery manufacture.
(Solution) The present invention is a battery separator comprising a polyolefin porous film and a heat-resistant porous layer formed on at least one surface of the porous film, wherein the heat-resistant porous layer contains inorganic particles and an organic synthetic resin component, and particles among the inorganic particles It is characterized in that the number of particles (B) with a particle diameter of 100 nm or less adhering to the surface of the inorganic particles (A) with a diameter of 0.3 μm or more is 5.0 or less.

Description

Battery Separator

The present invention relates to a battery separator comprising a polyolefin porous film and a heat-resistant porous layer on at least one surface of the porous film. The battery separator according to the embodiment of the present invention can be usefully used as a separator for a lithium ion secondary battery.

BACKGROUND OF THE INVENTION [0002] Thermoplastic resin porous membranes are widely used as material separation, selective permeation, and isolation materials. For example, various filters such as separators for lithium ion secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, polymer batteries, etc., separators for electric double layer capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes. , moisture-permeable waterproof medical, and medical materials.

In particular, as a separator for a lithium ion secondary battery, it has ion permeability by being impregnated with an electrolyte solution, has excellent electrical insulation properties, electrolyte resistance and oxidation resistance, cuts off current at a temperature of about 120 to 150 ° C. when the battery temperature rises abnormally, and excessive temperature rise A polyolefin porous film having a hole-blocking effect that suppresses the film is suitably used.

However, if the temperature rise continues even after the pores are closed for some reason, the polyolefin porous film may break. This phenomenon is not limited to the case where polyolefin is used, and is unavoidable above the melting point of the resin constituting the porous film.

In contrast, a heat-resistant separator coated with a heat-resistant porous layer mainly composed of inorganic particles and a binder resin is employed for a polyolefin porous film. By using this heat-resistant separator, shrinkage of the polyolefin porous film due to temperature rise is suppressed by the heat-resistant porous layer.

In such a separator, in order to improve the electrolyte solution injection performance of the injection step in battery manufacturing, for example,

A separator with a heat-resistant porous layer using inorganic particles and resins such as specific polyamide, polyimide, and polyamideimide as a resin binder (Patent Document 1);

A separator having a heat-resistant porous layer formed of a porous film composition comprising a specific water-soluble thickener, a carbodiimide compound crosslinking agent having monomer units derived from dihydric or higher alcohol, and a particulate polymer (Patent Document 2, paragraph [0034]);

A separator that satisfies a specific expression in the relationship between the critical surface tension of the outermost surface of the heat-resistant porous layer and the critical surface tension on the side of the porous film when the heat-resistant porous layer is peeled at the interface with the porous film (Patent Document 3)

has been proposed, but it cannot be said to be sufficient yet, and a separator with good additional electrolyte pourability is required.

Japanese Unexamined Patent Publication No. 2009-87562 Publication No. WO2014/024991 Japanese Unexamined Patent Publication No. 2016-49774

An object of the present invention is to provide a separator having excellent heat resistance and improved electrolyte pourability in battery production.

In view of the prior art, the present inventors studied intensively,

A battery separator having a polyolefin porous film and a heat-resistant porous layer formed on at least one side of the porous film,

The heat-resistant porous layer includes inorganic particles and an organic synthetic resin component,

The battery separator characterized in that the average number of particles (B) having a particle diameter of 100 nm or less adhering to the surface of the inorganic particles (A) having a particle diameter of 0.3 μm or more among the inorganic particles is 5.0 or less, this subject found what solves it.

A more preferred aspect is

(1) The inorganic particles are precipitated barium sulfate;

(2) that the precipitated barium sulfate is a particle synthesized by the sulphate method;

(3) When the total of the inorganic particle component and the organic synthetic resin component contained in the heat-resistant porous layer is 100% by weight,

The inorganic particles are contained in a ratio of 50% by weight or more and 99% by weight,

(4) the organic synthetic resin component,

At least one selected from the group consisting of (meth)acrylic acid copolymer resins, polyacrylamide resins, polyvinylidene fluoride resins, polyvinyl alcohol resins, polyimide resins, polyamideimide resins, polyamide resins, and poly(meth)aramid resins. is to contain

According to the embodiment of the present invention, it is possible to provide a separator having excellent heat resistance and excellent electrolyte pourability in battery production.

1 is a scanning electron microscope image of the surface of a heat-resistant porous layer of a separator produced in Example 1 of the present invention.
2 is a scanning electron microscope image of the surface of the heat-resistant porous layer of the separator produced in Comparative Example 1 of the present invention.
3 is a scanning electron microscope image of the surface of the heat-resistant porous layer of the separator produced in Comparative Example 2 of the present invention.
4 is a photograph of evaluating the wet spreadability of the electrolyte solution of the separator manufactured in Example 1 of the present invention.
5 is a photograph of evaluating the wet spreadability of the electrolyte solution of the separator manufactured in Comparative Example 1 of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail. In addition, this invention is not limited to the embodiment described below.

A battery separator according to an embodiment of the present invention includes a polyolefin porous film and a heat-resistant porous layer formed on at least one side of the porous film.

[Polyolefin Porous Film]

The thickness of the polyolefin porous film in the embodiment of the present invention is not particularly limited as long as it has a function of a battery separator, but is preferably 25 μm or less. More preferably, they are 7 μm or more and 20 μm or less, and still more preferably 9 μm or more and 16 μm or less. If the thickness of the polyolefin porous film is 25 μm or less, both practical film strength and hole blocking function can be achieved, and the area per unit volume of the battery case is not restricted, and it is suitable for increasing the capacity of the battery.

The air permeability resistance of the polyolefin porous film is preferably 30 sec/100 cm 3 Air or more and 200 sec/100 cm 3 Air or less. More preferably, it is 40 sec/100 cm<3>Air or more and 150 sec/100 cm<3>Air or less, More preferably, it is 50 sec/100 cm<3>Air or more and 100 sec/100 cm<3>Air or less. If the air permeability resistance is 30 sec/100 cm 3 Air or more, sufficient mechanical strength and insulation are obtained, so that the possibility of short circuit occurring during charging and discharging of the battery is reduced. If it is 200 sec/100 cm3Air or less, it is sufficient in terms of sufficient charge and discharge characteristics of the battery, particularly ion permeability (charge and discharge operating voltage) and life of the battery (closely related to the amount of retention of the electrolyte solution), and can sufficiently exhibit the function as a battery. can

The porosity of the polyolefin porous film is preferably 20% or more and 70% or less. More preferably, it is 30% or more and 60% or less, and still more preferably 55% or less. When the porosity is 30% or more and 70% or less, it is sufficient in terms of sufficient charge and discharge characteristics of the battery, particularly ion permeability (charge and discharge operating voltage) and life of the battery (closely related to the retention amount of the electrolyte solution), and as a battery Functions can be sufficiently exhibited, and the possibility of short circuit occurring during charging and discharging is lowered by obtaining sufficient mechanical strength and insulation.

Since the average pore diameter of the polyolefin porous film greatly affects the pore blocking performance, it is preferably 0.01 μm or more and 1.0 μm or less. More preferably, they are 0.02 μm or more and 0.5 μm or less, and still more preferably 0.03 μm or more and 0.3 μm or less. When the average pore diameter of the polyolefin porous film is less than 0.01 μm, when the heat-resistant porous layer is deposited, clogging of the pores by organic synthetic components may occur, and air resistance and electrical resistance may deteriorate. When it is 1 µm or more, clogging of pores by the heat-resistant porous layer composition may occur, deterioration in air permeability and electrical resistance, or deterioration in battery safety due to occurrence of non-short circuits.

When the average pore diameter of the polyolefin porous film is 0.01 μm or more and 1.0 μm or less, due to the anchor effect of the binder, sufficient adhesion strength of the heat-resistant porous layer to the polyolefin porous film is obtained, and air permeability resistance when the heat-resistant porous layer is laminated And the electrical resistance does not significantly deteriorate, the response to the temperature of the hole blocking phenomenon does not become sluggish, and the hole blocking temperature shifts to a higher temperature side due to a change in the temperature increase rate is less. The average particle diameter as used in the present invention is a measured value obtained by the bubble point method specified in JIS K 3832:1990.

The polyolefin resin constituting the polyolefin porous film is not particularly limited, but is preferably polyethylene or polypropylene. This is because, in addition to basic characteristics such as electrical insulating properties and ion permeability, it has a hole blocking effect of suppressing excessive temperature rise by cutting off current when the battery temperature rises abnormally.

Moreover, it may be a single substance or a mixture of two or more types of different polyolefin resins, for example, a mixture of polyethylene and polypropylene, or a copolymer of other olefins.

Among them, polyethylene is particularly preferred from the viewpoint of excellent pore closing performance. Hereinafter, polyethylene is described in detail as an example of the polyolefin resin used in the present invention, but the embodiment of the present invention is not limited thereto.

As polyethylene, ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, etc. are mentioned, for example. In addition, the polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. These polyethylenes may be not only ethylene homopolymers, but also copolymers containing small amounts of other α-olefins. Suitable α-olefins other than ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth)acrylic acid, esters of (meth)acrylic acid, and styrene. .

Although polyethylene may be a single substance, it is preferable that it is a mixture consisting of 2 or more types of polyethylene. As the polyethylene mixture, a mixture of two or more types of ultra-high molecular weight polyethylene having different weight average molecular weight (Mw), or a mixture of the same high-density polyethylene, medium-density polyethylene, and low-density polyethylene may be used, and ultra-high molecular weight polyethylene, high-density polyethylene, medium-density polyethylene, and low-density polyethylene may be used. A mixture of two or more types of polyethylene selected from the group consisting of polyethylene may be used.

The polyolefin porous membrane is required to have a function of closing pores in the event of an abnormal charge/discharge reaction. Therefore, the melting point (softening point) of the constituting resin is preferably 70°C or higher and 150°C or lower. It is more preferably 80°C or higher and 140°C or lower, and even more preferably 100°C or higher and 130°C or lower. If the melting point of the constituting resin is 70 ° C. or more and 150 ° C. or less, the battery will not become unusable due to the expression of the pore blocking function during normal use, and safety is ensured by the expression of the pore blocking function during abnormal reactions. can do.

[Heat resistant porous layer]

In the battery separator according to an embodiment of the present invention, a heat-resistant porous layer is formed on at least one side of the polyolefin porous film, and contains inorganic particles and an organic synthetic resin component.

The heat-resistant porous layer may be formed on only one side of the polyolefin porous film, or may be formed on both sides. When formed on only one side, the number of steps for forming the heat-resistant porous layer is reduced, and the production cost can be more suppressed. shrinkage can be reduced.

[Inorganic Particles]

In the inorganic particles in the present invention, the inorganic particles (A) and particles (B) defined below have a specific relationship in the heat resistance layer. The number of particles (B) having a particle diameter of 100 nm or less adhering to the surface of the inorganic particles (A) having a particle diameter of 0.3 µm or more is 5.0 or less. Preferably it is 3.0 or less, More preferably, it is 1.0 or less. Here, the inorganic particle (A) of the present invention is a reflection electron image (BEI) obtained by observing inorganic particles of a heat-resistant porous layer formed on the surface of a battery separator with a scanning electron microscope (hereinafter referred to as SEM) at a magnification of 30,000, Particles with a diameter of 0.3 μm or more. The particle (B) is a particle having a minor axis diameter of 100 nm or less adhering to the surface of the inorganic particle (A).

The number of particles (B) attached to inorganic particles (A) is the average number of attachments per inorganic particle (A) by counting the number of particles (B) attached to 20 randomly selected inorganic particles (A). . When the number of particles (B) adhering to the surface of the inorganic particles (A) is larger than 5.0, the electrolyte solution injectability in battery production may deteriorate. This is similar to the fact that special microparticles are scattered and inserted on the surface of a lotus leaf or rose petal, forming a concave-convex structure at the microscopic nano level to create super-water repellency (the so-called lotus effect), as well as microscopic nanoparticles on the surface of inorganic particles (A). It is thought that this is because the wettability of the electrolytic solution to the surface of the inorganic particle (A) may be deteriorated because the concavo-convex structure in the level is formed by adhesion of the particle (B). When the average number of the particles (B) attached to the surface of the inorganic particle (A) is 5.0 or less, a concavo-convex structure at the fine nanolevel is not formed on the surface of the inorganic particle (A), and the surface of the inorganic particle (A) The wettability of the electrolyte solution is good, and as a result, the electrolyte solution pourability in battery production is good.

In the average particle diameter of the inorganic particles of the present invention, the number of particles (B) having a particle diameter of 100 nm or less adhering to the surface of the inorganic particles (A) having a particle diameter of 0.3 µm or more, which is one of the constituent elements of the present invention, is 5.0 or less. To achieve this, the volume-average particle diameter of the inorganic particles in the heat-resistant layer determined by a particle size distribution analyzer using a laser diffraction scattering method is preferably 0.4 μm or more, more preferably 0.5 μm or more. If the volume-based average particle diameter determined by the particle size distribution analyzer by the laser diffraction scattering method is 0.4 µm or more, this is not a sufficient condition, but particles with a particle diameter of 100 nm or less adhering to the surface of inorganic particles (A) having a particle diameter of 0.3 µm or more ( The number of B) can be controlled to 5.0 or less. The upper limit of the average particle diameter of an inorganic particle is 2.0 micrometer or less. When the average particle diameter of the inorganic particles is larger than 2.0 μm, the number of contact points between the individual inorganic particles in the heat-resistant porous layer decreases, and the structure of the heat-resistant porous layer becomes brittle, making it difficult to suppress shrinkage of the polyolefin porous film at high temperatures. Coarse particles increase, unevenness occurs on the surface of the heat-resistant porous layer, and streaks may occur in the manufacturing method of the heat-resistant porous layer described later.

The material of the inorganic particle of the present invention is not particularly limited as long as it is electrochemically stable. Specifically, sodium oxide, potassium oxide, magnesium oxide, calcium oxide, barium oxide, lanthanum oxide, cerium oxide, strontium oxide, vanadium oxide, SiO ₂ -MgO (magnesium silicate), SiO ₂ -CaO (calcium silicate), hydrotal Site, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, basic titanate, basic silica titanate, basic copper acetate, basic lead sulfate, layered double hydroxide (Mg-Al type, Mg -Fe type, Ni-Fe type, Li-Al type), layered double oxide-alumina silica gel composite, boehmite, alumina, zinc oxide, lead oxide, iron oxide, iron oxyhydroxide, hematite, bismuth oxide, tin oxide, titanium oxide , anion adsorbents such as zirconium oxide, cation adsorbents such as zirconium phosphate, titanium phosphate, apatite, non-basic titanate, niobate, niobium titanate, zeolite, calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, barium sulfate, alumina Oxide-based ceramics such as trihydride (ATH), fumed silica, precipitated silica, zirconia, and yttria, nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride, silicon carbide, kaolinite, talc, decite, and nac layered silicates such as light, halloysite, phyllophylite, montmorillonite, sericite, amethyst, bentonite, asbestos, diatomaceous earth, fiberglass, synthetic layered silicates such as mica or fluoromica, and zinc borate; is selected from the group consisting of These may be used individually by 1 type, and may use 2 or more types together. Among these, barium sulfate is particularly preferred, and precipitated barium sulfate is more preferred. Specifically, barium sulfate particles obtained by a method for obtaining barium sulfate by adding sulfuric acid to barium carbonate or barium sulfide (sulfuric acid method) and a method for obtaining barium sulfate by adding sodium sulfate to barium chloride (sulfuric acid method). By using the barium sulfate particles produced by the synthetic method, the particle diameter of the inorganic particles can be controlled with high accuracy, and the particle diameter, which is one of the constituent elements of the present invention, is adhered to the surface of the inorganic particles (A) of 0.3 μm or more. The number of particles (B) having a particle diameter of 100 nm or less can be controlled to 5.0 or less.

Particles (B) of the present invention are not particularly limited, and may be organic particles or inorganic particles. It is preferably an inorganic particle, and it is more preferable that it is the same material as the inorganic particle (A).

As the barium sulfate particles used in the present invention, it is preferable to use precipitated barium sulfate particles obtained by a synthesis method, in particular, barium sulfate particles synthesized by a method in which barium chloride is used as a starting material and reacted with sodium sulfate. . The reason for this is that, in the process of examining barium sulfate particles, the barium sulfate particles synthesized by the sulphate method produce very little hydrogen sulfide, and the generation of corrosive gas can be suppressed.

[Organic synthetic resin component]

The organic synthetic resin component in the embodiment of the present invention has both an effect of binding the inorganic particles constituting the heat-resistant porous layer and an effect of adhering the heat-resistant porous layer to the polyolefin porous film.

Specifically, (meth) acrylic acid copolymer resins, polyacrylamide resins, polyvinylidene fluoride resins, polyvinyl alcohol resins, polyimide resins, polyamideimide resins, polyamide resins, poly (meth) aramid resins selected from the group One or more can be used, and commercially available aqueous solutions or aqueous dispersions can be used. Specifically as the acrylic resin, "Polysol" series manufactured by Showa Denko Co., Ltd., "BM" series manufactured by Nippon Zeon Co., Ltd., and "Julimer" manufactured by Toagosei Co., Ltd. (registered trademark) AT-210, ET- 410, "Aaron" (registered trademark) A-104, AS-2000, NW-7060, "LIOACCUM" (registered trademark) series manufactured by Toyochem Co., Ltd., TRD202A, TRD102A manufactured by JSR Co., Ltd., Arakawa Chemical Co., Ltd. ) "Polystron" (registered trademark) 117, 705, 1280, "Kogum" (registered trademark) series manufactured by Showa Denko Co., Ltd., WEM-200U and WEM-3000 manufactured by Daisei Fine Chemical Co., Ltd. can be heard Specifically as polyvinyl alcohol, "Kurabepoval" (registered trademark) 3-98, 3-88 manufactured by Kuraray Co., Ltd., "Gosenol" (registered trademark) N-300, GH- manufactured by Mitsubishi Chemical Co., Ltd. 20 and the like. Among them, an acrylic resin having high versatility and easy binding of barium sulfate particles to each other is preferable. In the case of forming a heat-resistant porous layer by applying and drying a particulate dispersion among organic synthetic resin components, the particle shape is not maintained after the heat-resistant porous layer is formed, or the particle shape is not maintained even after the heat-resistant porous layer is formed. In the case of holding, it is preferable that the average primary particle diameter of the particles made of the organic synthetic resin component after forming the heat-resistant porous layer is 100 nm or more. If it is 100 nm or more, the number of particles (B) having a particle size of 100 nm or less adhering to the surface of inorganic particles (A) having a particle size of 0.3 μm or more, which is one of the components of the present invention, can be controlled to 5.0 or less, Injectability of the electrolyte solution in battery production becomes good.

The heat-resistant porous layer may appropriately contain a dispersant for the purpose of improving the dispersion stability of inorganic particles, a thickener and a wetting agent for the purpose of improving coatability, and a thermosetting resin and a crosslinking agent for the purpose of improving heat resistance.

[Weight Composition Ratio of Heat Resistant Porous Layer]

The content of the inorganic particles contained in the heat-resistant porous layer in the embodiment of the present invention is 50% by mass or more and 99% by mass or less based on 100% by mass of the total of the inorganic particles and the organic synthetic resin component.

More preferably, they are 77 mass % or more and 95 mass % or less, More preferably, they are 80 mass % or more and 93 mass % or less.

When the content of the inorganic particles is less than 50% by mass, the gaps between the inorganic particles in the heat-resistant porous layer are clogged with the organic synthetic resin component, so that the ion movement path is narrowed or lengthened, thereby increasing the electrical resistance and air permeability resistance. .

When the content of the inorganic particles is greater than 99% by mass, the organic synthetic resin component that connects and fixes the inorganic particles becomes insufficient, and the structure as a heat-resistant porous layer cannot be maintained.

When the content of the inorganic particles is 50% by mass or more and 99% by mass or less, the gaps between the inorganic particles in the heat-resistant porous layer are less likely to be clogged with the organic synthetic resin component, and good electrical resistance and air permeability resistance can be obtained, In addition, since there is no shortage of a binder that connects and fixes the inorganic particles, shrinkage of the porous polyolefin film due to heat can be suppressed.

[Average Thickness of Heat Resistant Porous Layer]

It is preferable that the average thickness of the heat-resistant porous layer in the embodiment of the present invention is 2.0 μm or more and 10 μm or less. More preferably, they are 2.5 μm or more and 6 μm or less, and still more preferably 3.0 μm or more and 4.0 μm or less. When the thickness of the heat-resistant porous layer is less than 2.0 μm, it may become impossible to suppress shrinkage of the porous polyolefin film due to heat. When the average thickness of the heat-resistant porous layer is greater than 10 μm, the ion movement path becomes longer, so the air permeability resistance increases or the distance between the positive electrode and the negative electrode of the battery cell increases, so the ratio of the battery separator to the battery cell capacity increases. , the electrical resistance may increase. When the average thickness of the heat-resistant porous layer is 2.0 µm or more and 10 µm or less, air permeability resistance or electrical resistance does not increase.

[Formation method of heat-resistant porous layer]

The heat-resistant porous layer for obtaining the present invention can be obtained in the following steps.

(a) Preparation of coating dispersion for heat-resistant porous layer.

(b) A step of coating the slurry on at least one side or both sides of a polyolefin porous film.

(c) After the coating, drying the solvent with a dryer to form a heat-resistant porous layer.

In the step (a), it is preferable to use water as a dispersion medium. A mixture of water and a hydrophilic solvent such as methanol, ethanol, or N-methylpyrrolidone may be used as a dispersion medium as long as the dispersion stability of the coating dispersion for the heat-resistant porous layer is not impaired. A known method can be used as a method for producing a coating dispersion for a heat-resistant porous layer containing at least inorganic particles and an organic synthetic resin. For example, ball mills, bead mills, planetary ball mills, vibratory ball mills, sand mills, colloid mills, roll mills, high-speed impeller dispersion, dispersers, homogenizers, planetary mixers and planetary kneaders, ultrasonic dispersion , mechanical stirring with stirring blades, and the like. Among the inorganic particles, which are one of the components of the present invention, in order to reduce the number of particles (B) having a particle size of 100 nm or less attached to the surface of the inorganic particles (A) having a particle size of 0.3 μm or more to 5.0 or less, in this step, the number of inorganic particles It is preferable that it is a mild dispersion in which cracking and cracking do not occur as long as possible. If the dispersion is excessive, the inorganic particles (A) are cracked, so that many active surfaces are newly exposed, or a large number of newly formed particles (B) of 100 nm or less are formed, and the inorganic particles (B) are formed on the active surface generated by the cracking. There are cases where it is attracted and attached to the active surface of (A). Mild dispersion can reduce the generation of new active surfaces generated by cracking of inorganic particles (A) and the number of newly formed particles (B) by cracking, and the surface of inorganic particles (A) having a particle diameter of 0.3 µm or more. The number of particles (B) with a particle diameter of 100 nm or less adhering to may be 5.0 or less.

Mild dispersion as used herein means that in the process of dispersing inorganic particles in an agglomerated state into a dispersion medium, excessive energy is not applied to the particles, and the size, shape, crystal structure, surface state, etc. of the primary particles of the inorganic particles are maintained. A mild dispersion state can be obtained by using beads having a smaller bead diameter or using beads having a smaller specific gravity of the beads when using a bead mill dispersing device.

In the step (b), a known method can be used for coating at least one side or both sides of the polyolefin porous film with the coating dispersion for the heat-resistant porous layer. Examples include reverse roll coating method, gravure coating method, small diameter gravure coating method, kiss coating method, roll brush method, air knife coating method, Meyerba coating method, pipe doctor method, blade coating method, and die coating method. These methods can be used alone or in combination.

The battery separator according to an embodiment of the present invention is a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium-sulfur battery, etc. It can be used as a separator for batteries of In particular, it is preferable to use as a separator of a lithium ion secondary battery.

Example

Hereinafter, examples are shown and specifically described, but the present invention is not limited in any way by these examples. In addition, the measured value in an Example is the value obtained by the following method.

1. Particle diameter of inorganic particles (μm)

The particle diameter of the inorganic particles measured the following physical property values using a laser diffraction type particle size distribution analyzer (LA-960V2 manufactured by Horiba Seisakusho Co., Ltd.) according to JISZ8825 (2013).

1) Particle diameter D50 (μm) when volume-based integration rate is 50%

2. The number of particles (B) attached to the surface of inorganic particles (A)

Using a scanning electron microscope (manufactured by Nippon Electronics Co., Ltd., model JSM-6700F, hereinafter referred to as SEM), at an accelerating voltage of 2.0 kV, the inorganic particles of the heat-resistant porous layer formed on the surface of the battery separator were observed at a magnification of 30,000 The resulting reflection electron image (BEI) was photographed, and particles having a short axis diameter of 0.3 μm or more were used as inorganic particles (A), and particles having a short axis diameter of 100 nm or less adhering to the surface of the inorganic particle (A) were used as particles (B). Twenty inorganic particles (A) were arbitrarily selected, and the number of particles (B) adhering to the surface was counted, and the average value was rounded to one decimal place.

3. Thickness (㎛)

The thickness was determined by averaging the measured values of 5 points using a contact type film thickness meter ("Light Matching" (registered trademark) series 18 manufactured by Mitutoyo Co., Ltd.) for the polyolefin porous film and the battery separator. It was measured under conditions of a weight of 0.01 N using an ultra-hard spherical measuring ruler φ9.5 mm. In addition, the thickness (μm) of the heat-resistant porous layer was obtained by washing the battery separator with a liquid such as the solvent contained in the slurry, and measuring the polyolefin porous film from which the heat-resistant porous layer was removed with the contact type thickness meter, and obtained by the following calculation formula.

The thickness of the heat-resistant porous layer (μm) = the thickness of the battery separator (μm) - the thickness of the polyolefin porous film (μm).

4. Thermal contraction rate (%) of battery separator (heat resistance)

The heat resistance of the battery separator was measured in the MD direction (longitudinal direction) and TD direction (lateral direction) of the battery separator by the following method. A detailed procedure is described below.

1) Cut three battery separators with a size of 100 mm × 100 mm, put on a transparent glass scale (measurement accuracy of 0.1 mm), and measure the distance between the midpoints of the two facing sides of the battery separator as the length in the MD direction and the length in the TD direction, respectively. It is measured and used as the initial dimension (mm).

2) A battery separator was sandwiched between two sheets of A3 size paper, put in an oven at 130°C, and left to stand for 1 hour. Then, the separator for batteries was taken out and left to cool for 30 minutes.

3) The distance between the midpoints of the two facing sides of the battery separator was again measured with the glass scale described above, and was taken as the dimension (mm) after shrinkage. The measurement position at this time is the same position as the position where the initial dimension was measured, and when the edge part of the battery separator was curled, it spread and measured. Using the obtained initial dimension and the dimension after shrinkage, the length in the MD direction and the length in the TD direction and the respective heat shrinkage rates (%) were obtained by the following calculation formula.

Heat shrinkage rate (%) = {initial size (mm) - size after shrinkage (mm)}/initial size (mm) x 100.

5. Wet spreadability of the electrolyte of the battery separator

The wet spreadability of the electrolyte solution of the battery separator was measured by the following method. A detailed procedure is described below.

1) A battery separator MD was cut out to a size of 100 mm x 100 mm, and this was used as a measurement sample.

2) It was left in a dry room with a temperature of 23°C and a dew point temperature of -50°C for 24 hours.

3) In the dry room, with the heat-resistant porous film facing up, 5 mm from both ends of the separator in the MD direction were held horizontally with clips so as not to enter wrinkles.

4) Using a polycarbonate liquid as a measurement liquid, 0.5 µL of the measurement liquid was collected using a micro syringe and slowly dripped onto the measurement sample.

5) The measurement sample was photographed 8 minutes after the measurement liquid was dropped, and the area (cm 2 ) of the droplet wetted and spread was measured from the photographed image.

(Example 1)

[Production of Battery Separator]

100 parts by weight of the particles A shown in Table 1 (barium sulfate (forget-me-not method), D50 = 1.2 μm), 0.5 parts by weight of a polyacrylic acid-based dispersant (SA/HAPS = 85/15 mol% copolymer, Mw = 6000) active ingredient), and water were added, followed by bead mill dispersion using 0.1 mm diameter alumina beads (TB-1, specific gravity of beads 3.9 g/cm 3 , manufactured by Daimei Chemical Industry Co., Ltd.), and the active ingredient ratio was 60 weight % dispersion was obtained.

To the obtained dispersion, as a thickener, 1.5 parts by weight of sodium partially neutralized polyacrylic acid having a degree of neutralization of 50% (Biscomate NP-700, manufactured by Showa Denko Co., Ltd.), as a binder, an acrylic emulsion (Showa Denko Co., Ltd.) Polyzol AP-4735) 3.0 weight (active ingredient), wetting agent (manufactured by Sanofco, trade name "SN Wet 366") 0.5 weight part (active ingredient), and water were added and stirred, and the solid content was 50 weight % coating solution was produced.

The obtained coating solution was applied to one side (one side) of a polyethylene porous film a (thickness 10 μm, “SETELA” (registered trademark) manufactured by Toray Co., Ltd.) shown in Table 2 by the microgravure method, and dried to obtain a thickness of 4 μm. A battery separator having a heat-resistant porous layer was produced.

For the prepared battery separator, the thickness of the heat-resistant porous layer, the number of particles (B) adhering to the surface of the inorganic particles (A), the thermal contraction rate (%) of the separator, and the wet spreadability of the electrolyte were evaluated, and the results are shown in Table 3. shown in

(Examples 2 and 3, Comparative Examples 1 to 4)

A battery separator was produced and evaluated in the same manner as in Example 1 except that the particle A of Example 1 was replaced with the particles B to G shown in Table 1, and the results were shown in Table 3.

(Example 4)

A battery separator was prepared and evaluated in the same manner as in Example 1, except that the bead mill dispersion of Example 1 was changed to dispersion by an ultrasonic homogenizer (24 kHz, 14 mm Φ), and the results were shown in Table 3.

(Comparative Example 5)

Particles A of Example 1 were replaced with Particles D shown in Table 1, and battery separators were prepared and evaluated in the same manner as in Example 4, and the results were shown in Table 3.

(Comparative Example 6)

A battery separator was prepared in the same manner as in Example 1 except that the 0.1 mm diameter alumina beads of Example 1 were replaced with 1.0 mm diameter zirconia beads (Toray Serum (registered trademark) beads, specific gravity of beads: 6.0 g/cm 3 manufactured by Toray Corp.) It was produced, evaluated, and the results are shown in Table 3.

(Examples 5 to 7)

A battery separator was produced and evaluated in the same manner as in Example 1, except that the polyethylene porous film a of Example 1 was replaced with the polyethylene porous films b to d shown in Table 2, and the results were shown in Table 3.

(Example 8)

100 parts by weight of the particles H shown in Table 1, 1.5 parts by weight (active ingredient) of polyvinyl alcohol (K-17C, manufactured by Denka Co., Ltd.) and water were added, and dispersed in a bead mill in the same manner as in Example 1, A dispersion liquid having an active ingredient ratio of 40% by weight was obtained. Next, in the same manner as in Example 1, battery separators were produced and evaluated, and the results are shown in Table 3.

As is clear from Table 3, the battery separators of Examples 1 to 8 had good thermal shrinkage (%) of the separator and good wet spreadability of the electrolyte solution.

The separator of the present invention can be suitably used as a battery separator preferably used for non-aqueous electrolyte batteries such as lithium ion batteries.

1 Inorganic Particles (A)
Particle 2 (B)

Claims (5)

A battery separator having a polyolefin porous film and a heat-resistant porous layer formed on at least one side of the porous film,
The heat-resistant porous layer includes inorganic particles and an organic synthetic resin component,
A battery separator in which the number of particles (B) having a particle size of 100 nm or less adhering to the surface of inorganic particles (A) having a particle size of 0.3 μm or more among the inorganic particles is 5.0 or less.
Here, the number of particles (B) adhering to the inorganic particles (A) is the image obtained by observing the inorganic particles of the heat-resistant porous layer formed on the surface of the battery separator at a magnification of 30,000 times with a scanning electron microscope, 2 μm in length and 2 μm in width. It is the average number of attachments per inorganic particle (A) by counting the number of particles (B) adhering to 20 inorganic particles (A) arbitrarily selected from the range. According to claim 1,
A battery separator in which the inorganic particles are precipitated barium sulfate. According to claim 2,
A separator for a battery in which the precipitated barium sulfate is a particle synthesized by the sulphate method. According to any one of claims 1 to 3,
When the total of the inorganic particle component and the organic synthetic resin component contained in the heat-resistant porous layer is 100% by weight,
A battery separator in which the inorganic particles are contained in an amount of 50% by weight or more and 99% by weight. According to any one of claims 1 to 4,
The organic synthetic component,
At least one selected from the group consisting of (meth)acrylic acid copolymer resins, polyacrylamide resins, polyvinylidene fluoride resins, polyvinyl alcohol resins, polyimide resins, polyamideimide resins, polyamide resins, and poly(meth)aramid resins. A battery separator containing a.

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