TW201902004A - Separator - Google Patents

Abstract

Provided is a separator with which, even if minute solid matter, such as dust, or a projection exist in any of transport paths of the separator, film peeling of a pore layer can be suppressed and a low battery cell insulation defect ratio can be achieved. The separator is provided with a film of porous base material having a plurality of pores, and a pore layer which is formed on at least one surface of the porous base material and includes an adhesive resin. The separator is characterized in that a machine direction (MD) Young's modulus is not less than 500 MPa, and a critical damage load is not less than 3 mN.

Description

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The present invention relates to a separator, and more particularly to a separator for a battery suitable 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 transmission membranes, and separation membranes. Examples of such applications include separators for batteries used in lithium ion secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, and polymer secondary batteries, and separators for electric double-layer capacitors. , Reverse osmosis filtration membrane, ultrafiltration membrane, microfiltration membrane and other filters, moisture-permeable waterproof clothing, medical materials, etc.

Especially for lithium ion secondary battery separators, it is suitable for: ion penetration through the impregnation of the electrolyte, excellent electrical insulation, and at a temperature of about 120 to 150 ° C during abnormal temperature rise inside the battery Polyolefin microporous membrane that interrupts the current and has a pore blocking function that suppresses excessive temperature rise.

Lithium-ion secondary battery separators are closely related to battery characteristics, battery productivity, and battery safety, and require excellent mechanical characteristics, heat resistance, electrode adhesion, dimensional stability, and pore blocking characteristics (shutdown) Characteristics) and so on. For example, the use of a polyolefin microporous membrane as a porous substrate has been discussed so far, and functions such as heat resistance and electrode adhesion are provided to a battery separator by providing a porous layer on its surface. A porous layer is formed by applying the following coating liquid to the surface of a porous substrate, and has been proposed and put into practical use (for example, refer to Patent Document 1): polyimide, imine resin, polyimide, etc. in order to impart heat resistance. A coating solution in which an imine resin, a polyamide resin, or the like is dispersed and dissolved in an organic solvent or water; or a coating solution in which a fluororesin, an acrylic resin, or the like is dispersed or dissolved in an organic solvent or water in order to impart electrode adhesion.

In recent years, in order to increase the capacity and energy density of secondary batteries, the thickness of the separator has been pursued, and the thickness of the porous layer has also been reduced accordingly. Moreover, in order to improve the productivity of a secondary battery, the conveyance speed is made higher than 40 m / min. In the manufacturing process of the secondary battery, if any defect occurs in the porous layer on the surface of the separator, the resistance between the electrodes of the positive electrode and the negative electrode becomes non-uniform, causing a poor insulation of the battery cell.

In the assembly steps of the flat-type wound battery, specifically referring to FIG. 1, a negative electrode material wound body 11 coated with a negative electrode active material on both sides of a current collector made of copper foil and wound, and an aluminum foil The positive electrode material wound body 31 and the two separator material wound bodies 21 and 41 coated with the positive electrode active material on both sides of the formed current collector are collected by the two rolls 51 and 52 through the respective moving paths. A flat winding battery 71 is produced by winding the first winding needle 65 disposed on the first winder 61 as an axis and winding it into an oval shape (FIG. 2). When it is wound to a predetermined amount, the turntable 60 (FIG. 3) is turned to cut off the collected negative electrode material 1, the positive electrode material 3 and the two separators 2, and the separator 4, and is connected to the second winding device 62. The second winding pin 66 is again wound into an oval shape, and production of the flat-type wound battery 72 is started (FIG. 4). A flat-type wound battery is produced by continuously repeating the above steps. At this time, the flat-type wound-type battery rotates around the center of gravity of the ellipse and rotates the turntable 60 to switch from the first winder 61 to the second winder 62. Therefore, the positive electrode material 3 and the negative electrode Material 1, and 2 separators 2 and 4 can be wound while repeating acceleration, deceleration, and stop of the moving path.

Here, if there are very few solids and protrusions such as falling off and dust of the positive electrode material 3 and the negative electrode material 1 in any place of the moving path, insulation failure occurs, and the yield of the secondary battery becomes a problem.

    [Prior technical literature]         [Patent Literature]    

[Patent Document 1] Japanese Patent No. 605401

The present invention has been made in view of the background of the foregoing prior art, and it is an object of the present invention to provide a separator having a low insulation failure rate of a battery cell even if there are few solids and protrusions such as dust in any place on the moving path of the separator.

The inventors repeatedly studied in order to solve this problem. As a result, they found that if there are very few solids and protrusions such as the falling off of the positive electrode material and the negative electrode material and dust in the assembly process of the battery cell, the solid materials and the protrusions will contact The surface of the separator moving at a high speed, and the film peeling of the porous layer occurred linearly along the mechanical direction (MD) of the separator (FIG. 5), and then the present invention was considered.

That is, the present invention is a separator comprising a thin film-shaped porous substrate having a plurality of pores, and a porous layer containing an adhesive resin formed on at least one side of the porous substrate, in a mechanical direction ( MD) has a Young's modulus of 500 MPa or more and a critical damage load of 3 mN or more. A preferred aspect 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) from a direction perpendicular to the porous layer, Continuously pressurize at a temperature of 10 ℃ to 30 ℃ for more than 1 hour at a pressure of 0.1 MPa to 2 MPa; (3) the elongation at break in the machine direction (MD) is 10% to 150%; (4) the aforementioned porous layer The thickness 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.

According to the present invention, it is possible to provide a separator which can suppress the occurrence of linear formation along the mechanical direction (MD) of the separator even if there are few solids and protrusions such as dust in any place on the moving path of the separator. The film of the porous layer is peeled off, and the poor insulation rate of the battery cell is low.

1‧‧‧Negative electrode material

2‧‧‧ Insulation

3‧‧‧ cathode

4‧‧‧ Insulation

8‧‧‧ Surface of insulation material

9‧‧‧90 ° Diamond Conical Indenter

11‧‧‧ Negative electrode wound body

21‧‧‧Insulation roll

31‧‧‧Polymer wound body

41‧‧‧Insulation roll

51‧‧‧roller

52‧‧‧Roller

60‧‧‧Turntable

61‧‧‧The first winder

62‧‧‧Second Winder

65‧‧‧Volume 1

66‧‧‧Volume 2

71‧‧‧ wound battery

72‧‧‧Flat-type winding battery

[Fig. 1] A schematic diagram showing the steps for assembling a flat-type wound battery.

[Fig. 2] A schematic view of a state where the first winder 61 of Fig. 1 is rotated 90 degrees.

3 is a schematic view showing a state where the turntable 60 is rotating.

4 is a schematic view showing a state where the second winder 62 is being wound into a flat shape.

[Fig. 5] An electron microscope image of the peeling position of the film of the porous layer.

Fig. 6 is a schematic diagram of a scratch test.

[Fig. 7] Optical microscope image of Example 1 in measurement of critical damage load.

[Fig. 8] Optical microscope image of Example 2 in measurement of critical damage load.

[Fig. 9] Optical microscope image of Comparative Example 1 in measurement of critical damage load.

[Fig. 10] An optical microscope image of Example 3 in the measurement of critical damage load.

The present invention is directed to the aforementioned problem, that is, to provide a separator with a low insulation failure rate of a battery cell, and to find out that the problem can be solved by: a thin film-shaped porous substrate having a plurality of pores, With respect to the porous layer containing an adhesive resin formed on at least one side of the porous substrate, the Young's modulus in the machine direction (MD) is 500 MPa or more, and the critical damage load is 3 mN or more.

Hereinafter, one 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 implemented by adding appropriate changes to the scope of the present invention. In addition, the terms or words used in this specification and the scope of the patent application cannot be defined and interpreted as ordinary or dictionary meanings, and must follow the principle that the inventor can properly define the concept of the term in order to explain his invention in the best way , Interpreted as technically consistent with the meaning and concept of the present invention.

(Porous substrate)

The porous base material is a porous thin film-like base material having a network structure irregularly connected in three dimensions, and is one of the elements constituting the separator. Examples of the porous substrate include a film, a nonwoven fabric, and the like, and the type thereof is not particularly limited, but a porous substrate including a polyolefin resin is preferably exemplified. Examples of the polyolefin resin include polyethylene, polypropylene, polybutene, 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 Within the range of 1 × 10 ⁵ to 5 × 10 ⁶ . The mass average molecular weight (Mw) used herein is determined from a calibration curve obtained by using a monodisperse polystyrene standard sample by a gel permeation chromatography (GPC) method.

Polyolefin resins preferably contain polyethylene, and examples of polyethylene include 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 those having a density of less than 0.925. Low density polyethylene, etc. In addition, the polymerization catalyst is not particularly limited, and examples include polymerization produced by polymerization catalysts such as Ziegler-Natta catalyst, Phillips catalyst, and metallocene catalyst. Ethylene. These polyethylenes are not only homopolymers of ethylene, but also copolymers containing a small amount of other α-olefins. As the α-olefin other than ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (meth) acrylic acid, (methyl ) Acrylic esters, styrene, etc.

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

Among them, as a mixture of polyethylene, from the viewpoint of the responsiveness to the temperature rise (closed cell speed) of the closed cell phenomenon, maintaining the shape of the polyolefin porous film in a high temperature region above the closed cell temperature, and maintaining the insulation between the electrodes In view of this, a mixture containing an ultra-high molecular weight polyethylene having a Mw of 5 × 10 ⁵ or more and a polyethylene having a Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ 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 a Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , any of high-density polyethylene, medium-density polyethylene, and low-density polyethylene can be used, and in particular, high-density polyethylene is preferably used. As the polyethylene having a Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , two or more different Mw may be used, or two or more different densities may be used. By setting the upper limit of the Mw of the polyethylene mixture to 5 × 10 ⁶ , the melt extrusion can be easily performed. The content of the ultra-high molecular weight polyethylene in the polyethylene mixture is preferably 1% by weight or more, and more preferably in the range of 10 to 80% by weight, relative to the entire polyethylene mixture.

In order to improve the melting resistance and high-temperature storage characteristics of the battery, the polyolefin resin may also include polypropylene as well as polyethylene. The Mw of polypropylene is preferably in the range of 1 × 10 ⁴ to 4 × 10 ⁶ . Homopolymers or block copolymers and / or random copolymers containing other alpha-olefins can also be used as polypropylene. For other α-olefins, ethylene is preferred. The entire polyolefin mixture (a mixture of polyethylene and polypropylene) is taken as 100% by weight, and the content of polypropylene is preferably 80% by weight or less.

The polyolefin resin may contain a polyolefin that provides closed-cell characteristics in order to improve the characteristics as a battery separator. As the polyolefin that imparts closed-cell characteristics, for example, low-density polyethylene can be used. As the low-density polyethylene, at least one selected from the group consisting of branched, linear, and ethylene / α-olefin copolymers produced by a single-site catalyst is preferred. . The whole polyolefin is taken as 100% by weight, and the addition amount of the low-density polyethylene is preferably 20% by weight or less. If the addition amount of the low-density polyethylene is more than 20% by weight, film breakage is liable to occur during stretching, which is undesirable.

The above-mentioned polyethylene composition containing ultra-high molecular weight polyethylene may also be selected from poly1-butene containing 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 Polyethylene waxes within the range and at least one kind of polyolefin of the group of ethylene / α-olefin copolymers having Mw in the range of 1 × 10 ⁴ to 4 × 10 ^{6 are} used as optional components. The polyolefin composition is 100% by weight, and the amount of these optional components added is preferably 20% by weight or less.

When a film-like porous substrate is produced using a resin such as polyolefin as a raw material, the resin can be melted together with a plasticizer such as liquid paraffin, and then extruded from a T-die to form a sheet. After the sheet is stretched, the method of extracting the plasticizer contained in the sheet is not limited thereto. As described later, the separator of the present invention is characterized by having a predetermined Young's modulus, and in order to realize the Young's modulus, the degree of extension of the porous substrate is adjusted so that the porous substrate itself has It is preferable that the prescribed Young's modulus (that is, the mechanical direction (MD) of the separator is 500 MPa or more) described later.

As described above, the porous substrate has a three-dimensional irregularly connected network structure, and the porosity thereof is preferably 20 to 80%. Since the porosity of the porous base material is more than 20%, it is possible to achieve good air permeability of the separator, suppress the increase in resistance caused by the film, and allow a large current to flow, which is preferable. Moreover, since the porosity of the porous substrate is 80% or less, it is preferable to obtain sufficient mechanical strength of the separator. The porosity is more preferably 25 to 65%, and particularly preferably 30 to 55%. The porosity refers to the proportion (volume%) of the porosity portion occupied by the porous substrate. The porosity (%) was calculated from the results obtained by measuring the volume (cm ³ ) and the mass (g) of the sample, using the following formula.

Porosity (%) = (1-mass / (resin density × sample volume)) × 100

(Porous 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 surfaces.

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, it is preferable to obtain good adhesion with the electrode and maintain mechanical strength. Therefore, it is preferable to suppress the film resistance of the separator to be small by the thickness of the porous layer being 3 μm or less. , So better.

(Adhesive resin)

The porous layer is provided with an adhesive resin. Examples of the adhesive resin include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer, polyimide, polymethyl methacrylate, and polyacrylic acid. Butyl ester, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyimide, imine, polyimide, polyarylate, acetate fiber Cellulose, cellulose acetate butyrate, cellulose acetate propionate, nitrile ethyl polyglucose, nitrile ethyl polyvinyl alcohol, nitrile ethyl cellulose, nitrile ethyl sucrose, polytriglucose, carboxymethyl Cellulose and so on. Among these, a fluorine atom-containing resin and / or an acrylic resin are preferred, and polyvinylidene fluoride (PVDF) is particularly preferred. These resins can be used alone or in combination of two or more kinds.

(Filler)

The porous layer may contain a filler in addition to the aforementioned adhesive resin. Examples of the filler include inorganic particles and organic particles, and inorganic particles are more preferred. The inorganic particles are not particularly limited, and examples thereof include calcium carbonate, calcium phosphate, amorphous silicon dioxide, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, gibbsite, and silica-oxidation. Aluminum composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, etc. Moreover, you may add a heat-resistant crosslinked polymer particle as needed. Examples of the heat-resistant crosslinked polymer particles include crosslinked polystyrene particles, crosslinked acrylic particles, and crosslinked methyl methacrylate particles. Examples of the shape of the inorganic particles include a spherical shape, a spherical shape, a plate shape, a needle shape, and a polyhedron shape, but are not particularly limited.

By including a filler in the porous layer, an internal short circuit due to the growth of dendrites of the electrode can be suppressed. When a thermal runaway occurs in the internal short circuit of the secondary battery, a porous substrate made of polyolefin can be suppressed. Of contraction. These fillers can be used singly or in combination of two or more kinds. The content of the filler in the porous layer is preferably 10 to 99% by volume, more preferably 20 to 90% by volume, and even more preferably 30 to 80% by volume. When the content of the heat resistance in the porous layer is within these ranges, the occurrence of dendritic crystals can be effectively suppressed; when thermal runaway occurs, shrinkage of the porous substrate made of polyolefin can be suppressed.

(Young's modulus)

The separator of the present invention is characterized in that the Young's modulus of the machine direction (MD) is 500 MPa or more. According to discussions by the present inventors, since the Young's modulus of the mechanical direction (MD) of the separator is 500 MPa or more, even in the manufacturing process of the secondary battery, even if there is dust or the like in any place on the transportation path of the separator. Very few solids and protrusions can also suppress peeling of the linear porous layer along the mechanical direction of the separator. The reason why such an effect is obtained may not be clear, but it is considered as follows. First of all, I believe that if there are very few solids and protrusions in the transportation route of the insulation material contacting the insulation material, a slight deformation (strain) caused by the solid will occur in the surface portion of the insulation material. When the degree is large, the porous layer cannot follow the deformation, and damage to the porous layer itself such as cracking, cracking, and breakage occurs. In addition, it is considered that the continuous occurrence of such cracks, cracks, and breakage in a separator that is transported at a high speed may cause the film of the porous layer to peel off. On the other hand, it is believed that the Young's modulus of the mechanical direction (MD) of the separator is high, and even if there is little solid contact, deformation of the surface layer portion of the separator can be suppressed, and such defects (i.e. cracks, cracks) can be suppressed. , Damage, etc.). The upper limit of the Young's modulus in the machine direction (MD) is not particularly limited, and it is about 3000 MPa for the purpose of reducing the defect caused by wrinkles, bending, and the like in the battery cell assembly step.

In order to make the Young's modulus of the mechanical direction (MD) of the separator as described above, the Young's modulus of the mechanical direction (MD) of the porous substrate can be increased, or the Young's modulus of the mechanical direction (MD) of the porous layer can be increased. Modulus can also increase both. Among these, it is simpler to set the Young's modulus of the porous substrate in the machine direction (MD) to 500 MPa or more. At this time, the molecular weight of the resin, the processing temperature, and the elongation ratio may be adjusted by a known method so that the Young's modulus of the mechanical direction (MD) of the porous substrate satisfies the above conditions.

The Young's modulus is measured by a method described in Examples described later.

(Elongation at break)

The separator in the present invention has a mechanical elongation (MD) with an elongation at break of 10% to 150%. It is preferably 20% or more and 110% or less, and more preferably 30% or more and 100% or less. If the elongation at break is less than 10%, there may be a case where the separator itself is damaged when there are very few solids and protrusions in the transportation route of the separator. If it is more than 150%, the degree of deformation (strain) of the separator due to the aforementioned solid may increase, and the film of the porous layer may peel. When it is in the range of 10% to 150%, there is no damage to the separator, and peeling of the porous layer film can be suppressed.

The elongation at break is calculated by a method described in Examples described later.

(Critical Damage Load)

In the separator of the present invention, the critical damage load of the porous layer existing on the surface in the scratch test is preferably 3 mN or more. By satisfying such conditions, the separator of the present invention can suppress the occurrence of linear defects along the machine 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 500 mN is preferred, and 300 mN is further preferred. By satisfying such conditions, the separator of the present invention can suppress the occurrence of linear defects along the machine direction (MD) in the manufacturing process of the secondary battery. The critical damage load is more preferably 20 mN or more. In addition, such a critical damage load can be calculated | required by the ultra-thin film scratch tester marketed by Anton Paar, etc., for example. The so-called scratch test in this case specifically refers to: according to the ASTM D7187-15 test, the 90 ° diamond conical indenter 9 with a radius of curvature of 10 μm shown in FIG. 6 is pressed against the surface 8 of the separator at 0.3 mN, and at 100 mN. / min (25mN / mm) While increasing the load in the vertical direction, the film surface was scratched at a speed of 4mm / min. to measure the load in the vertical direction (that is, the critical damage load) when the porous film was damaged.

The critical damage load is measured by a method described in Examples described later.

(Pressure in a 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 to 2 MPa for 1 hour or more under an environment of 10 ° C to 30 ° C from a direction perpendicular to the porous layer. The lower limit of the pressure is 0.1 MPa, and preferably 0.3 MPa. When the pressure is equal to or higher than the lower limit, sufficient pressure can be applied between the porous layer and the substrate, so that peeling of the film can be suppressed. From the viewpoint of preventing deformation of the porous structure of the porous substrate and the porous layer, the upper limit of the pressure is 2 MPa, and preferably 1.5 MPa. The temperature of the pressure is preferably within a range of 10 ° C to 30 ° C. If the pressurizing time is short, the effect of suppressing film peeling may be insufficient, but it is preferably 1 hour or more. The upper limit is not particularly limited, but from the viewpoint of preventing the porosity of the porous film itself from decreasing if the time for which the pressure is applied is too long, it is preferably 1 × 10 ⁴ hours or less. As a method of pressing, for example, a flat plate pressing device can be used. Alternatively, when the porous layer is formed, the pressure may be such that the pressure at the core portion of the roll-shaped wound body and / or the middle portion of the roll-shaped wound body falls within the aforementioned range, and is wound at the aforementioned temperature. After more than 1 hour has passed in the environment, rewinding is performed again to apply pressure over the entire length of the wound body. In addition, in the method of winding such that the pressure of the core portion of the roll-shaped wound body falls within the aforementioned range, for example, the surface of the roll core and / or the roll-shaped wound body can be wound. A pressure measurement film (Prescale (registered trademark), manufactured by Fujifilm Corporation) is placed in the middle part, and conditions for the pressure range are known in advance by well-known methods such as the tension of the separator, the contact roll pressure, and the winding speed. , Obtained by winding under these conditions.

(Formation method of porous layer)

The porous layer is formed by coating a coating liquid containing a resin on the surface of a porous substrate. The coating liquid can dissolve the resin used to form the porous layer, and can be prepared by dissolving or dispersing the resin or the like using a solvent mixed with water. Examples of the method for applying the coating solution 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 bar coating method, a gravure coating method, Dye-coating method, die coating method, roll coating method, notch wheel coating method.

After the coating liquid is applied to one or both sides of the porous substrate, the porous substrate is immersed in an aqueous solvent. In this way, the coated resin is solidified into a three-dimensional network. Thereby, a porous layer is formed. Aqueous solvent refers to a solvent containing water that is a poor solvent for the resin. Examples of the solvent that can coexist with water include alcohols, acetone, and N-methyl-2-pyrrolidone. After forming a porous layer on the surface of the porous substrate, it is dried by hot air at 100 ° C or lower.

    [Example]    

The present invention is described below based on examples, but the present invention is not limited to the examples.

    [Method of evaluation]    

Each evaluation system was performed as follows.

(Young's modulus, elongation at break, tensile strength)

A porous substrate or a separator was cut out into a rectangle having a length of 150 mm and a width of 10 mm as a sample. A tensile tester (Tensilon UCT-100 manufactured by Orientec Co., Ltd.) was used to perform a tensile test in a 25 ° C, 65% HR environment with an initial inter-chuck distance of 50 mm and a tensile speed of 300 mm / min. The Young's modulus was calculated from the slope of the strain and stress of the sample in accordance with JIS K 7161-1 (2014), and the elongation at break and tensile strength when the sample was broken were measured. Moreover, in the tensile test of each Example and comparative example, it was confirmed that it was a linear elastic area up to at least 2% of elongation. Each sample of the measurement system was performed five times, and the average value was evaluated. The results are shown in Table 1.

(Jack strength)

The maximum load measured when a porous substrate or a separator was punctured at a rate of 2 mm / second using a needle with a diameter of 1 mm having a spherical tip surface (curvature radius: 0.5 mm) was used as the puncture strength to measure each sample. The evaluation was performed five times, and the average value was evaluated. The results are shown in Table 1.

(Critical damage load measurement)

A UV-curable epoxy acrylate adhesive (Unisolar-Hard) was applied on a glass slide to have a thickness of 20 μm to fix the spacer. A nano-scratch tester NST3 manufactured by Anton Paar was used to mechanically The indenter was scanned in the direction (MD) to measure the critical damage load of the porous coating film. The test conditions are shown below.

Indenter: 10 μm 90 ° diamond cone

Initial load: 0.3mN

Final load: 50mN

Load rate: 100mN / min (25mN / mm)

Scanning speed: 4mm / min

As a result of the above-mentioned critical damage load measurement, the load at the time when peeling of the porous layer from the porous base material started was taken as the critical damage load. The measurement was performed 5 times for each sample, and the average value was used for evaluation. The results are described in the table. 1. The optical microscope images after the critical damage load is measured are shown in FIGS. 7 to 10.

(Electrical insulation of battery cells)

Making 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 form a slurry containing a positive electrode mixture. The slurry containing the positive electrode mixture was uniformly coated on 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. Thereafter, the positive electrode layer was removed by compression molding using a roller press. The density became 3.6 g / cm ^{3 to} produce a positive electrode.

Production of negative electrode

To an aqueous solution containing 1.0 part by mass of carboxymethyl cellulose, 98 parts by mass of synthetic graphite and 1.0 part by mass of styrene butadiene latex were added and mixed to form a slurry containing a negative electrode mixture. This slurry containing the negative electrode mixture was uniformly applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm and dried to form a negative electrode layer. Thereafter, the negative electrode layer was compressed and formed by a roller press to remove the current collector. The density of the negative electrode layer was 1.45 g / cm ^{3 to} prepare a negative electrode.

Flat wound battery assembly

A flat wound body was produced by using a battery cell winding device between the above-mentioned positive electrode and negative electrode with ear tabs and a separator made by a method described later. Thereafter, the above-mentioned flat wound body was provided in a laminated aluminum foil bag, and this was used as a flat rolled battery for testing.

Inspection method for poor insulation

Using a withstand voltage tester (TOS5051A, manufactured by Kikusui Electronics Co., Ltd.), a voltage of 50 V was applied to the positive terminal and the negative terminal of the flat-wound battery for 10 seconds. It is set to fail.

Measure to judge

In the aforementioned inspection of poor insulation, the case where the number of unqualified items is 5 or less per 1,000 flat wound batteries is set to "◎", the number of 6 or more and 15 or less is set to "○", and the case of 16 or more Set it to "×".

(Production of samples)

Preparation of coating liquid

50 parts by volume of a 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 diameter (D50) of 1.0 μm, The active ingredient was added to N-methyl-2-pyrrolidone so as to be 10% by mass, mixed and dispersed, and used as a coating liquid.

    [Examples 1 to 2 and Comparative Example 1]    

Each of the three types of polyethylene porous substrates (thickness: 7 μm, manufactured by Toray Battery Separator Film Co., Ltd., trade name: Setela (registered trademark)) having different Young's modules was coated with the coating solution on both sides using a die coater. Thereafter, it was immersed in an aqueous solvent to separate the phases, washed with water, and dried, thereby forming a laminated film having a film thickness of 1.5 μm per one side. Next, using a precision pressurizing device (made by Shinto Industry Co., Ltd .; CYPT10), the pressure was applied to the separator in the vertical direction at 25 ° C and 0.3 MPa for 1 hour. These were used as the separators of Example 1, Example 2, and Comparative Example 1. The results are shown in Table 1.

    [Example 3]    

A test piece was produced in the same manner as in Example 1 except that the pressing time of Example 2 was changed to 10 minutes, and the same evaluation was performed. The results are shown in Table 1.

As clearly shown in Table 1 and FIGS. 7 to 10, it can be seen that the separator of the present invention having a Young's modulus of 500 MPa or more in the mechanical direction (MD) of Examples 1 to 3 has high resistance to scratching and is excellent in secondary batteries. During the manufacturing process, even if there are very few solids and protrusions on the transportation route of the separator, peeling of the porous film can be suppressed, and the manufacturing yield of secondary batteries can be improved. In addition, it can be seen that the pressure can be further improved by applying a pressure in a direction perpendicular to the porous layer.

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

    [Industrial availability]    

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

Claims (8)

    A separator comprising a thin film-shaped porous substrate having a plurality of pores, a porous layer containing an adhesive resin formed on at least one side of the porous substrate, and a Young's mold in a machine direction (MD). The number is 500 MPa or more, and the critical damage load is 3 mN or more.         The separator according to claim 1, wherein 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.         For example, the insulation material of claim 1 or 2, wherein, in a direction perpendicular to the porous layer, under a pressure of 0.1 MPa to 2 MPa in an environment of 10 ° C to 30 ° C for more than 1 hour.         The separator according to any one of claims 1 to 3, wherein the elongation at break in the machine direction (MD) is 10% to 150%.         The separator according to any one of claims 1 to 4, wherein the thickness of the porous layer is 0.05 μm or more and 3 μm or less.         The separator according to any one of claims 1 to 5, wherein the adhesive resin contained in the porous layer contains a resin containing a fluorine atom.         The separator according to any one of claims 1 to 6, wherein the adhesive resin contained in the porous layer contains an acrylic resin.         The separator according to any one of claims 1 to 7, which is for a secondary battery.