JP7070565B2 - Separator manufacturing method - Google Patents

Description

The present invention relates to a separator, and more particularly to a battery separator preferably used for a non-aqueous electrolyte battery such as a lithium ion battery.

Microporous membranes mainly containing thermoplastic resins are widely used as substance separation membranes, selective permeation membranes, isolation membranes and the like. As an example of such an application, a battery separator used for a lithium ion secondary battery, a nickel-hydrogen secondary battery, a nickel-cadmium secondary battery, a polymer secondary battery, etc., a separator for an electric double layer capacitor, a back-penetration filtration membrane, etc. , Ultrafiltration membranes, various filters such as precision filtration membranes, moisture permeable and waterproof clothing, medical materials, and the like can be mentioned.

In particular, as a separator for a lithium ion secondary battery, it has ion permeability due to impregnation with an electrolytic solution, has excellent electrical insulation, and cuts off current at a temperature of about 120 to 150 ° C. when the temperature inside the battery rises abnormally, resulting in excessive A microporous film made of polyolefin having a pore closing function for suppressing the temperature rise is preferably used.

Lithium-ion secondary battery separators are deeply involved in battery characteristics, battery productivity and battery safety, and have excellent mechanical characteristics, heat resistance, electrode adhesion, dimensional stability, hole closure characteristics (shutdown characteristics), etc. Is required. So far, for example, it has been studied to use a microporous polyolefin membrane as a porous substrate and provide a porous layer on the surface thereof to impart functions such as heat resistance and electrode adhesion to a battery separator. Coating in which polyamide-imide resin, polyimide resin, polyamide resin, etc., and fluororesin, acrylic resin, etc. are dispersed and dissolved in an organic solvent, water, etc. to impart heat resistance. A product in which a porous layer is formed by applying a liquid to the surface of a porous substrate has been proposed and put into practical use (see, for example, Patent Document 1).

In recent years, there has been a demand for thinner separators in order to increase the capacity energy density of secondary batteries, and along with this, the porous layer is also becoming thinner. Further, in order to increase the productivity of the secondary battery, the transfer speed exceeding 40 m / min is being increased. If any defect occurs in the porous layer existing on the surface of the separator in the manufacturing process of the secondary battery, the resistance between the electrodes of the positive electrode and the negative electrode becomes non-uniform, which causes poor insulation of the battery cell.

In the process of assembling the flat winding cell, specifically, referring to FIG. 1, the negative electrode active material is applied to both sides of the current collector made of copper foil, and the negative electrode material winding body 11 wound up and the negative electrode material winding body 11 The positive electrode active material is applied to both sides of the current collector made of aluminum foil, and the wound positive electrode material winding body 31 and the two separator winding bodies 21 and 41 pass through their respective movement paths and the two nip rolls 51. The four materials are aggregated at and 52, and the flat winding cell 71 is created by winding the material in an elliptical shape around the first pin 65 arranged in the first winder 61 (FIG. 2). To. When a predetermined amount is wound, the turret 60 is swiveled (FIG. 3), the aggregated negative electrode material 1, the positive electrode material 3 and the two separators 2 and the separator 4 are cut, and the second winder 62 is arranged in the second winder 62. It is connected to the pin 66 of the above and is wound again in an elliptical shape, and the production of the flat winding cell 72 is started (FIG. 4). By repeating this continuously, a flat winding cell is produced. At this time, since the flat winding cell rotates around the center of gravity of the ellipse or turns the turret 60 to switch from the first winder 61 to the second winder 62. , The positive electrode material 3, the negative electrode material 1, and the two separators 2, the separator 4, are wound while repeatedly accelerating, decelerating, and stopping the moving path.

Here, if minute solids or protrusions such as fallen objects and dust of the positive electrode material 3 and the negative electrode material 1 are present in any of the moving paths, there is a problem that insulation failure occurs and the yield of the secondary battery is lowered. It has become.

Japanese Patent No. 6054001

In view of the background of the prior art, it is an object of the present invention to provide a separator having a low insulation failure rate of a battery cell even if minute solids such as dust and protrusions are present in any of the moving paths of the separator. And.

As a result of diligent studies to solve this problem, the present inventor moves at high speed when minute solids or protrusions such as fallen substances and dust of the positive electrode material and the negative electrode material are present in the cell assembly process. It was found that the solid matter or the protrusion comes into contact with the surface of the separator, and the film of the porous layer is linearly peeled off along the mechanical direction (MD) of the separator (FIG. 5), and the present invention was conceived. bottom.

That is, the present invention comprises a film-like porous substrate having a plurality of pores and a porous layer containing an adhesive resin formed on at least one surface of the porous substrate, and is in the mechanical direction (MD). A separator having a Young's modulus of 500 MPa or more and a critical damage load of 3 mN or more. The preferred embodiment of the present invention is
(1) The porous layer contains a filler, and the proportion of the filler in the porous layer is 10% by volume or more and 99% by volume or less.
(2) The pressure was continuously applied for 1 hour or more at a pressure of 0.1 MPa or more and 2 MPa or less in an environment of 10 ° C to 30 ° C from the direction perpendicular to the porous layer.
(3) The breaking elongation in the mechanical direction (MD) is 10% or more and 150% or less.
(4) The thickness of the porous layer is 0.05 μm or more and 3 μm or less.
(5) The adhesive resin contained in the porous layer contains a resin containing a fluorine atom.
(6) The adhesive resin contained in the porous layer contains an acrylic resin.
Is.

According to the present invention, even if minute solids or protrusions such as dust are present in any of the moving paths of the separator, the film peeling of the porous layer that occurs linearly along the mechanical direction (MD) of the separator is suppressed. However, it is possible to provide a separator having a low insulation defect rate of the battery cell.

It is a schematic diagram which shows the assembly process of a flat winding cell. It is a schematic diagram of the state where the first winder 61 of FIG. 1 is rotated by 90 °. It is a schematic diagram which shows the state which the turret 60 is turning. It is a schematic diagram which shows the state which the 2nd winder 62 is wound flat. It is an electron microscope image of the film peeling part of a porous layer. It is a schematic diagram of a scratch test. It is an optical microscope image of Example 1 in the critical damage load measurement. It is an optical microscope image of Example 2 in the critical damage load measurement. It is an optical microscope image of the comparative example 1 in the critical damage load measurement. It is an optical microscope image of Example 3 in the critical damage load measurement.

The present invention has earnestly studied the above-mentioned problem, that is, providing a separator having a low insulation defect rate of a battery cell, and has a film-like porous substrate having a plurality of pores and at least one surface of the porous substrate. It has been clarified that such a problem can be solved by providing a formed porous layer containing an adhesive resin, a Young's modulus in the mechanical direction (MD) of 500 MPa or more, and a critical damage load of 3 mN or more. Is.

Hereinafter, an embodiment of the separator of the present invention will be described, but the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the present invention. It should be noted that the terms and words used in the present specification and the scope of patent claims should not be construed in a normal or lexical sense, and the inventor shall explain his invention in the best possible way. In accordance with the principle that the concept of terms can be properly defined, it must be interpreted as a meaning and concept consistent with the technical idea of the present invention.

(Porosity substrate)
The porous substrate is a porous film-like substrate having a three-dimensionally irregularly connected network structure, and is one of the elements constituting the separator. Examples of the porous substrate include a membrane and a non-woven fabric, and the type thereof is not particularly limited, but a porous substrate made of a polyolefin resin is preferably exemplified. Examples of the polyolefin resin include polyethylene, polypropylene, polybutylene, and polypentene.

The mass average molecular weight (Mw) of the polyolefin resin is not particularly limited, but is usually in the range of 1 × 10 ⁴ to 1 × 10 ⁷ , preferably in the range of 1 × 10 ⁴ to 5 × 10 ⁶ , and more preferably. Is in the range of 1 × 10 ⁵ to 5 × 10 ⁶ . The mass average molecular weight (Mw) referred to here is obtained from a calibration curve obtained by using a monodisperse polystyrene standard sample by a gel permeation chromatography (GPC) method.

The polyolefin resin preferably contains polyethylene, but the polyethylene is ultra-high molecular weight polyethylene, high-density polyethylene having a density of 0.942 or more, medium-density polyethylene having a density of 0.925 or more and less than 0.942, and a density of 0.925. Less than low density polyethylene and the like. The polymerization catalyst is also not particularly limited, and examples thereof include polyethylene produced by a polymerization catalyst such as a Ziegler-Natta catalyst, a Phillips catalyst, and a metallocene catalyst. These polyethylenes may be not only ethylene homopolymers but also copolymers containing a small amount of other α-olefins. Examples of α-olefins other than ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, (meth) acrylic acid ester, and styrene. Can be preferably used.

The polyethylene may be a single material, but is preferably a mixture of two or more types of polyethylene. As the polyethylene mixture, a mixture of two or more kinds of ultra-high molecular weight polyethylene having different Mw, a similar high-density polyethylene mixture, a similar medium-density polyethylene mixture and a low-density polyethylene mixture may be used, or ultra-high molecular weight polyethylene may be used. , A mixture of two or more polyethylenes selected from the group consisting of high density polyethylene, medium density polyethylene and low density polyethylene may be used.

Among them, as a polyethylene mixture, Mw is selected from the viewpoints of responsiveness to the temperature rise of the shutdown phenomenon (shutdown speed) and maintaining the shape of the polyolefin porous film in the high temperature region above the shutdown temperature and maintaining the insulation between the electrodes. A mixture consisting of 5 × 10 ⁵ or more ultra-high molecular weight polyethylene and polyethylene having an Mw of 1 × 10 ⁴ or more and less than ⁵ × 105 is preferable. The Mw of the ultra-high molecular weight polyethylene is preferably in the range of 5 × 10 ⁵ to 1 × 10 ⁷ , and more preferably in the range of 1 × 10 ⁶ to 5 × 10 ⁶ . As the polyethylene having an Mw of 1 × 10 ⁴ or more and less than ⁵ × 105, any of high-density polyethylene, medium-density polyethylene and low-density polyethylene can be used, but it is particularly preferable to use high-density polyethylene. As the polyethylene having Mw of 1 × 10 ⁴ or more and less than ⁵ × 105, two or more kinds of polyethylene having different Mw may be used, or two or more kinds of polyethylene having different densities may be used. Melt extrusion can be facilitated by setting the upper limit of Mw of the polyethylene mixture to 5 × ¹⁰⁶ . The content of ultra-high molecular weight polyethylene in the polyethylene mixture is preferably 1% by weight or more, more preferably in the range of 10 to 80% by weight, based on the total polyethylene mixture.

The polyolefin resin may contain polypropylene together with polyethylene for the purpose of improving the meltdown resistance and the high temperature storage property of the battery. The Mw of polypropylene is preferably in the range of 1 × 10 ⁴ to 4 × 10 ⁶ . As polypropylene, block copolymers containing homopolymers or other α-olefins and / or random copolymers can also be used. Ethylene is preferred as the other α-olefin. The polypropylene content is preferably 80% by weight or less with the entire polyolefin mixture (mixture of polyethylene and polypropylene) as 100% by weight.

The polyolefin resin may contain a polyolefin that imparts shutdown characteristics in order to improve the characteristics as a battery separator. As the polyolefin that imparts shutdown characteristics, for example, low-density polyethylene can be used. The low-density polyethylene is preferably at least one selected from the group consisting of branched, linear, and single-site catalyst-produced ethylene / α-olefin copolymers. The amount of low-density polyethylene added is preferably 20% by weight or less with 100% by weight of the entire polyolefin. If the amount of low-density polyethylene added exceeds 20% by weight, film breakage is likely to occur during stretching, which is not preferable.

In the polyethylene composition containing the ultra-high molecular weight polyethylene, poly-1-butene having Mw in the range of 1 × 10 ⁴ to 4 × 10 ⁶ and Mw in the range of 1 × 10 ³ to 4 × 10 ⁴ are optional components. Polyethylene wax and at least one polyolefin selected from the group consisting of ethylene / α-olefin copolymers having an Mw in the range of 1 × 10 ⁴ to 4 × 10 ⁶ may be added. The amount of these optional components added is preferably 20% by weight or less with the polyolefin composition as 100% by weight.

When a film-like porous base material is produced from a resin such as polyolefin, the resin is melted together with a plasticizer such as liquid paraffin and then extruded from a T-die to form a sheet. Examples thereof include, but are not limited to, a method of extracting the plasticizer contained in the sheet after stretching. As will be described later, the separator of the present invention is characterized by having a predetermined Young's modulus, and in order to realize this Young's modulus, the degree of stretching of the porous substrate is adjusted to form a porous group. It is preferable that the material itself has a predetermined Young's modulus (that is, 500 MPa or more in the mechanical direction (MD) of the separator) described later.

As described above, the porous substrate has a three-dimensionally irregularly connected network structure, and the porosity is preferably 20 to 80%. When the porosity of the porous substrate is 20% or more, good air permeability of the separator can be realized, and an increase in electrical resistance due to the membrane can be suppressed to allow a large current to flow, which is preferable. Further, when the porosity of the porous substrate is 80% or less, sufficient mechanical strength of the separator can be obtained, which is preferable. The porosity is more preferably 25 to 65%, particularly preferably 30 to 55%. The porosity is the ratio (volume%) of the pores to the porous substrate, and the following formula is used from the results obtained by measuring the sample volume (cm ³ ) and mass (g). The porosity (%) was calculated.
Porosity (%) = (1-mass / (resin density x sample volume)) x 100

(Poor layer)
The porous layer is a layer formed on at least one surface of the porous substrate, and may be formed on only one surface of the porous substrate or on both sides.

The thickness of the porous layer is preferably 0.05 μm or more and 3 μm or less, and more preferably 0.1 μm or more and 2.5 μm or less. When the thickness of the porous layer is 0.05 μm or more, good adhesion to the electrode can be obtained and mechanical strength can be maintained, which is preferable. When the thickness of the porous layer is 3 μm or less, it is preferable. It is preferable because the film resistance of the separator can be suppressed to a small value.

(Adhesive resin)
The porous layer comprises an adhesive resin. Examples of the adhesive resin include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer, polyimide, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, and polyvinylacetate. , Ethylene vinyl acetate copolymer, polyethylene oxide, polyamideimide, polyimide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pulllan, carboxy Examples thereof include methyl cellulose. Among these, a resin containing a fluorine atom and / or an acrylic resin is preferable, and polyvinylidene fluoride (PVDF) can be particularly preferably mentioned. These resins can be used alone or in combination of two or more.

(Filler)
The porous layer may contain a filler in addition to the adhesive resin. Examples of the filler include inorganic particles and organic particles, and inorganic particles are more preferable. The inorganic particles are not particularly limited, but for example, calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, boehmite, silica-alumina composite oxide particles, and the like. Examples thereof include barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, and mica. Further, heat-resistant crosslinked polymer particles may be added as needed. Examples of the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic particles, and crosslinked methyl methacrylate particles. The shape of the inorganic particles includes a true sphere shape, a substantially spherical shape, a plate shape, a needle shape, and a polyhedral shape, but is not particularly limited.

The inclusion of the filler in the porous layer suppresses the internal short circuit caused by the growth of dendrites of the electrode, and when the secondary battery is internally short-circuited and thermal runaway occurs, the porous substrate made of polyolefin Can be suppressed from contracting. These fillers can be used alone or in combination of two or more. The content of the filler in the porous layer is preferably 10 to 99% by volume, more preferably 20 to 90% by volume, still more preferably 30 to 80% by volume. When the heat resistance content in the porous layer is within these ranges, it is possible to effectively suppress the generation of dendrites and suppress the shrinkage of the porous polyolefin substrate when thermal runaway occurs. can.

(Young's modulus)
The separator of the present invention is characterized by having a Young's modulus in the mechanical direction (MD) of 500 MPa or more. According to the study by the present inventors, when the Young's modulus in the mechanical direction (MD) of the separator is 500 MPa or more, a minute solid such as dust is used in one of the transfer paths of the separator in the manufacturing process of the secondary battery. Even if an object or a protrusion is present, it is possible to suppress the peeling of the linear porous layer along the mechanical direction of the separator. The reason for obtaining such an effect is not always clear, but the following can be considered in general. First, when minute solids or protrusions existing on the separator transport line come into contact with the separator, it is considered that the surface layer of the separator is slightly deformed (strained) by the solids, but the degree of deformation is large. In that case, it is considered that the porous layer cannot follow the deformation, and the porous layer itself is damaged such as cracks, cracks, and tears. If such cracks, cracks, and tears occur continuously in the separator transported at high speed, it is considered that the film of the porous layer is peeled off. On the other hand, when the Young's modulus in the mechanical direction (MD) of the separator is high and the deformation of the surface layer portion of the separator is suppressed even if a minute solid substance comes into contact with the separator, such defects, that is, cracks, cracks, and tears. It is considered that the occurrence of such factors is suppressed. The upper limit of the Young's modulus in the mechanical direction (MD) is not particularly specified, but about 3000 MPa can be mentioned for the purpose of reducing the defective rate due to wrinkles or breaks in the battery cell assembly process.

In order to make the Young's modulus in the mechanical direction (MD) of the separator as described above, the Young's modulus in the mechanical direction (MD) of the porous substrate may be increased, or the Young's modulus in the mechanical direction (MD) of the porous layer may be increased. May be increased, or both may be used. Among these, it is convenient to set the Young's modulus in the mechanical direction (MD) of the porous substrate to 500 MPa or more. In this case, the Young's modulus in the mechanical direction (MD) of the porous substrate may be adjusted by a known method such as the molecular weight of the resin, the processing temperature, and the stretching ratio so as to satisfy the above conditions.
Young's modulus is measured by the method described in Examples described later.

(Elongation at break)
The separator of the present invention has a breaking elongation in the mechanical direction (MD) of 10% or more and 150% or less. It is preferably 20% or more and 110% or less, and more preferably 30% or more and 100% or less. If the breaking elongation is less than 10%, the separator itself may be torn when a minute solid substance or protrusion existing in the transfer line of the separator comes into contact with the separator. If it is larger than 150%, the degree of deformation (strain) of the separator due to the solid substance may increase and the film of the porous layer may peel off. When the content is in the range of 10% or more and 150% or less, the separator is not torn and the peeling of the film of the porous layer can be suppressed.
The elongation at break is calculated by the method described in Examples described later.

(Critical damage load)
In the scratch test, the separator of the present invention preferably has a critical damage load of 3 mN or more that causes peeling of the porous layer existing on the surface thereof. When the separator of the present invention satisfies such a condition, it is possible to suppress the occurrence of linear defects along the mechanical direction (MD) in the manufacturing process of the secondary battery. The critical damage load is more preferably 3 mN or more. The upper limit of the critical damage load is not particularly limited, but is preferably 500 mN, more preferably 300 mN. When the separator of the present invention satisfies such a condition, it is possible to suppress the occurrence of linear defects along the mechanical direction (MD) in the manufacturing process of the secondary battery. The critical damage load is more preferably 20 mN or more. Such a critical damage load can be obtained by, for example, an ultrathin film scratch tester sold by Anton Pearl Co., Ltd. or the like. Specifically, the scratch test referred to in the present application is a vertical load by pressing a 90 ° diamond conical indenter 9 having a radius of curvature of 10 μm shown in FIG. 6 against the separator surface 8 at 0.3 mN according to the ASTM D7187-15 test. At a speed of 4 mm / min while increasing at 100 mN / min (25 mN / mm). The film surface is scratched with a metal, and the vertical load when the porous membrane is damaged, that is, the critical damage load is measured.
The critical damage load is measured by the method described in Examples described below.

(Pressure in the direction perpendicular to the porous layer)
The separator of the present invention is characterized in that it is continuously pressurized at a pressure of 0.1 MPa or more and 2 MPa or less in an environment of 10 ° C. to 30 ° C. for 1 hour or more from a direction perpendicular to the porous layer. The lower limit of the pressure is 0.1 MPa, preferably 0.3 MPa. When it is at least this lower limit value, sufficient pressure can be applied between the layers of the porous layer and the base material, so that film peeling can be suppressed. The upper limit of the pressure is 2 MPa, preferably 1.5 MPa in order to prevent the porous structure of the porous substrate and the porous layer from being deformed. The pressurizing temperature is preferably in the range of 10 ° C to 30 ° C. If the pressurizing time is short, the effect of suppressing the peeling of the film may not be sufficient, and it is preferably 1 hour or more. The upper limit is not particularly limited, but is preferably 1 × ¹⁰⁴ hours or less in order to prevent the porosity of the porous film itself from decreasing if the pressurizing time is too long. .. As a method of pressurizing, for example, a flat plate pressing device can be used. Alternatively, when forming the porous layer, the reel-shaped winding body is wound so that the pressure of the winding core portion and / or the intermediate portion of the reel-shaped winding body is within the above range, and the temperature environment is described. A method of applying pressure over the entire length of the wound body may be used by rewinding the reel after 1 hour or more. As a method of winding the reel-shaped winding body so that the pressure of the winding core portion is within the above range, for example, on the surface of the winding core and / or on the intermediate portion of the reel-shaped winding body. , A pressure measurement film (manufactured by Fujifilm Co., Ltd., Prescale (registered trademark)) is placed, and conditions within the pressure range are found in advance by known methods such as separator tension, touch roll pressure, and winding speed. It can be obtained by winding under the conditions.

(Method of forming a porous layer)
The porous layer is formed by applying a coating liquid containing a resin to the surface of a porous substrate. The coating liquid is prepared by dissolving or dispersing the resin or the like in a solvent that can dissolve the resin used for forming the porous layer and is miscible with water. Examples of the method of applying the coating liquid to the surface of the porous substrate include ordinary coating methods known in the art, and examples of such methods include a dip coating method, a wire bar method, and a gravure method. Examples include a coating method, a kiss method, a die coating method, a roll coating method, and a comma coating method.

After applying the coating liquid to one or both sides of the porous substrate, the porous substrate is immersed in an aqueous solvent. Then, the coated resin solidifies into a three-dimensional network. As a result, a porous layer is formed. The aqueous solvent is a solvent containing water, which is a poor solvent for the resin. Examples of the solvent that can coexist with water include alcohols, acetone, N-methyl-2-pyrrolidone and the like. After forming a porous layer on the surface of the porous substrate, it is dried with hot air at 100 ° C. or lower.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited to the examples.

[Evaluation method]
Each evaluation was performed as follows.

(Young's modulus, elongation at break, tensile strength)
A porous base material or a separator was cut into a rectangle having a length of 150 mm and a width of 10 mm and used as a sample. A tensile test was conducted using a tensile tester (Tensilon UCT-100 manufactured by Orientec Co., Ltd.) at an initial chuck distance of 50 mm, a tensile speed of 300 mm / min, and a tensile test at 25 ° C. and a 65% HR environment. Young's modulus was calculated from the strain and stress slope of the sample according to JIS K 7161-1 (2014), and the fracture elongation and tensile strength when the sample broke were measured. In the tensile test of each Example / Comparative Example, it was confirmed that the linear elastic region had an elongation rate of at least 2%. The measurement was performed 5 times for each sample, the average value was used for evaluation, and the results are shown in Table 1.

(Puncture strength)
The maximum load measured when a porous substrate or separator is pierced at a speed of 2 mm / sec using a needle having a spherical tip surface (radius of curvature: 0.5 mm) and a diameter of 1 mm is used as the puncture strength. Was performed 5 times for each sample, evaluated by the average value, and the results are shown in Table 1.

(Critical damage load measurement)
Apply UV curable epoxy acrylate adhesive (Unisolar Hard Co., Ltd.) on a slide glass to a thickness of 20 μm, fix the separator, and use Anton Pearl Nano Scratch Tester NST3. The indenter was scanned in the mechanical direction (MD) to measure the critical damage load of the porous coating film. The test conditions were as follows.
Indenter: 10 μm 90 ° diamond cone Initial load: 0.3 mN
Final load: 50mN
Load rate: 100 mN / min (25 mN / mm)
Scanning speed: 4 mm / min

As a result of the above critical damage load measurement, the load when the porous layer starts to peel off from the porous substrate is defined as the critical damage load, and the measurement is performed 5 times for each sample, and the average value is used for evaluation. The result is described. Further, the optical microscope images after the critical damage load measurement are shown in FIGS. 7 to 10.

(Electrical insulation of battery cells)
Preparation of Positive Electrode An NMP solution containing 1.2 parts by mass of PVDF was added to 97 parts by mass of lithium cobalt oxide and 1.8 parts by mass of carbon black and mixed to obtain a positive electrode mixture-containing slurry. This positive electrode mixture-containing slurry is uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm and dried to form a positive electrode layer, and then compression-molded by a roll press machine to form a current collector. A positive electrode was prepared by setting the density of the positive electrode layer excluding the above to 3.6 g / cm ³ .

Preparation of Negative Electrode An aqueous solution containing 1.0 part by mass of carboxymethyl cellulose was mixed by adding 98 parts by mass of artificial graphite and 1.0 part by mass of styrene butadiene latex to prepare a slurry containing a negative electrode mixture. This negative electrode mixture-containing slurry is uniformly applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm and dried to form a negative electrode layer, and then compression-molded by a roll press to collect electricity. A negative electrode was prepared by setting the density of the negative electrode layer excluding the body to 1.45 g / cm ³ .

Flat winding cell assembly A flat winding body was prepared by using a battery cell winding device for the separators tabbed on the positive electrode and the negative electrode and the separators produced by the method described later. After that, the flat winding body was placed in an aluminum laminated bag, and this was used as a test flat winding cell.

Insulation defect inspection method Using a withstand voltage tester (TOS5051A, manufactured by Kikusui Electronics Co., Ltd.), a voltage of 50 V was applied to the positive and negative terminals of the flat winding cell for 10 seconds, and no current flowed. Was passed, and the one with current flowing was rejected.

Judgment method In the inspection for insulation defects, "◎" is used when the number of rejected cells is 5 or less per 1000 flat wound cells, "○" is used when 6 or more and 15 or less are used, and 16 or more are used. Was set to "x".

(Preparation of sample)
Preparation of coating liquid 50 parts by volume of vinylidene fluoride-hexafluoropropylene copolymer resin (manufactured by Kureha Co., Ltd., product name KF polymer W # 9300) and 50 parts by volume of alumina particles having a particle size (D50) of 1.0 μm. Was added to N-methyl-2-pyrrolidone so that the active ingredient was 10% by mass, mixed and dispersed to prepare a coating liquid.

[Examples 1 and 2, Comparative Example 1]
For each of the three types of polyethylene porous substrate (thickness 7 μm, manufactured by Toray Battery Separator Film Co., Ltd., trade name Setira (registered trademark)) with different Young's modulus, apply the above coating liquid on both sides using a die coater. Applied. Then, it was immersed in an aqueous solvent for phase separation, washed with water and dried to form a laminated film having a film thickness of 1.5 μm per surface. Then, using a precision press device (manufactured by Shinto Kogyo Co., Ltd .; CYPT10), pressure was applied in the vertical direction of the separator at 25 ° C. under the condition of 0.3 MPa for 1 hour. These were used as separators of Example 1, Example 2, and Comparative Example 1. The results are shown in Table 1.

[Example 3]
A test piece was prepared in the same manner as in Example 1 except that the press time of Example 2 was changed to 10 minutes, the same evaluation was performed, and the results are shown in Table 1.

As is clear from Table 1 and FIGS. 7 to 10, the separator of the present invention having a young ratio of 500 MPa or more in the mechanical direction (MD) of Examples 1 to 3 has high scratch resistance and manufacture of a secondary battery or the like. It can be seen that even if there are minute solids or protrusions on the separator transport line in the process, the peeling of the porous film can be suppressed and the manufacturing yield of the secondary battery or the like can be improved. Further, it can be seen that further improvement can be achieved by applying pressure in the direction perpendicular to the porous layer.

This application is based on a Japanese patent application filed on May 30, 2017 (Japanese Patent Application No. 2017-106635), the contents of which are incorporated herein by reference.

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.

Claims (7)

A film-like porous substrate having a plurality of pores and a porous layer containing an adhesive resin formed on at least one surface of the porous substrate are provided, and the Young's modulus in the mechanical direction (MD) is 500 MPa or more. It is a method for manufacturing a separator characterized by having a critical damage load of 3 mN or more, and is 0.1 MPa or more and 2 MPa or less in an environment of 10 ° C. to 30 ° C. from a direction perpendicular to the porous layer. A method for producing a separator, which comprises a step of continuously pressurizing with pressure for 1 hour or more. The method for producing a separator according to claim 1, wherein the porous layer contains a filler, and the ratio of the filler in the porous layer is 10% by volume or more and 99% by volume or less. The method for manufacturing a separator according to claim 1 or 2, wherein the separator has a breaking elongation in the mechanical direction (MD) of 10% or more and 150% or less . The method for producing a separator according to any one of claims 1 to 3 , wherein the thickness of the porous layer is 0.05 μm or more and 3 μm or less. The method for producing a separator according to any one of claims 1 to 4 , wherein the adhesive resin contained in the porous layer contains a resin containing a fluorine atom. The method for producing a separator according to any one of claims 1 to 5 , wherein the adhesive resin contained in the porous layer contains an acrylic resin. The method for manufacturing a separator according to any one of claims 1 to 6 , wherein the separator is for a secondary battery .

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