KR102498466B1 - separator - Google Patents

Abstract

Provided is a separator that suppresses peeling of a film of a porous layer even when a fine solid substance such as dust or a protrusion exists in any one of the movement paths of the separator and has a low insulation failure rate of a battery cell. A film-shaped 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, a Young's modulus in the machine direction (MD) of 500 MPa or more, and a critical damage load A separator characterized in that it is 3 mN or more.

Description

separator

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

A microporous membrane mainly composed of a thermoplastic resin is widely used as a material separation membrane, a permselective membrane, or a separation membrane. Examples of such uses include battery separators used in lithium ion secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, polymer secondary batteries, etc., separators for electric double layer capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, and microfiltration membranes. Various filters such as back, moisture-permeable and waterproof clothing, medical materials, and the like are exemplified.

In particular, as a separator for a lithium ion secondary battery, it has ion permeability by being impregnated with an electrolyte and has excellent electrical insulation, so that it cuts off current at a temperature of about 120 to 150 ° C when the temperature inside the battery rises abnormally, and suppresses excessive temperature rise. A polyolefin microporous membrane having a closing function is suitably used.

A separator for a lithium ion secondary battery is closely related to battery characteristics, battery productivity, and battery safety, and requires excellent mechanical properties, heat resistance, electrode adhesion, dimensional stability, hole blocking characteristics (shutdown characteristics), and the like. Until now, it has been studied to impart functions such as heat resistance and electrode adhesiveness to a battery separator by using, for example, a polyolefin microporous film as a porous substrate and forming a porous layer on the surface thereof. To impart heat resistance, polyamide-imide resin, polyimide resin, polyamide resin, etc., or to impart electrode adhesiveness, fluororesin, acrylic resin, etc. are dispersed and dissolved in an organic solvent or water, and a coating solution is applied to the surface of the porous substrate. What formed a porous layer by application|coating was proposed and put into practical use (for example, refer patent document 1).

In recent years, in order to raise the capacity energy density in a secondary battery, thickness reduction of a separator is requested|required, and thickness reduction of a porous layer is also progressing with it. Moreover, in order to raise the productivity of a secondary battery, the speeding-up of the conveyance speed exceeding 40 m/min is progressing. In the manufacturing process of the secondary battery, if any defect occurs in the porous layer present on the surface of the separator, the resistance between the electrodes of the positive electrode and the negative electrode becomes non-uniform, causing poor insulation of the battery cell.

In the assembly process of the flat winding cell, specifically, referring to FIG. 1, the negative electrode active material is applied to both sides of a current collector made of copper foil, and both sides of the wound negative electrode material winding body 11 and the current collector made of aluminum foil The positive electrode active material is applied to the positive electrode material, and the wound positive electrode material winding body 31 and the two separator winding bodies 21 and 41 pass through each moving path, and the four materials are concentrated in the two nip rolls 51 and 52 and winding in an elliptical shape around the first pin 65 arranged in the first winder 61 as an axis (FIG. 2), thereby creating a flat winding cell 71. When a predetermined amount is wound, the turret 60 turns (FIG. 3), and the aggregated negative electrode material 1, positive electrode material 3, and two separators 2 and 4 are cut to form a second winder ( It is connected to the second pin 66 disposed at 62), and is wound into an elliptical shape again, and creation of the flat winding cell 72 is started (FIG. 4). By continuously repeating this, a flat type winding cell is produced. At this time, since the flat winding cell rotates around the center of the ellipse or rotates the turret 60 to switch from the first winder 61 to the second winder 62, the positive electrode material 3 ), negative electrode material 1, and two separators 2 and 4 are wound while repeating acceleration, deceleration, and stop of the movement path.

Here, if minute solids or protrusions such as dust or debris from the positive electrode material 3 and negative electrode material 1 are present in any one of the moving paths, insulation failure occurs and the yield of the secondary battery is lowered. has become

Japanese Patent No. 6054001

In view of the background of the prior art, an object of the present invention is to provide a separator with a low insulation failure rate of a battery cell even if a fine solid substance such as dust or a protrusion is present in any one of the separator movement paths.

As a result of repeated intensive studies to solve these problems, the inventors of the present invention have found that in the cell assembling process, if minute solids or projections such as dust or dust are present in the cell assembly process, the solids are present on the surface of the separator moving at high speed. The present invention was conceived upon discovering that the membrane of the porous layer occurred in a linear fashion along the machine direction (MD) of the separator (FIG. 5).

That is, the present invention includes a film-like porous substrate having a plurality of pores, and a porous layer including an adhesive resin formed on at least one surface of the porous substrate, and has a Young's modulus in the machine direction (MD) of 500 MPa or more , It is a separator characterized in that the critical damage load is 3 mN or more. A preferred embodiment of the present invention is

(1) that the said porous layer contains a filler, and the ratio of the said filler in the said porous layer is 10 volume% or more and 99 volume% or less,

(2) What was continuously pressurized 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 a direction perpendicular to the porous layer,

(3) Elongation at break in the machine direction (MD) is 10% or more and 150% or less;

(4) that the thickness of the porous layer is 0.05 μm or more and 3 μm or less;

(5) that the adhesive resin contained in the porous layer contains a resin containing a fluorine atom;

(6) The adhesive resin contained in the said porous layer contains an acrylic resin.

(Effects of the Invention)

According to the present invention, even if minute solids such as dust or protrusions are present in any one of the movement paths of the separator, peeling of the membrane of the porous layer that occurs linearly along the machine direction (MD) of the separator is suppressed, and the battery cell A separator having a low insulation defect rate can be provided.

1 is a schematic view showing an assembly process of a flat type winding cell.
FIG. 2 is a schematic view of a state in which the first winder 61 of FIG. 1 is rotated by 90°.
3 is a schematic diagram showing a state in which the turret 60 is turning.
Fig. 4 is a schematic diagram showing a state in which the second winder 62 is wound in a flat shape.
Fig. 5 is an electron microscope image of a film separation site in a porous layer.
6 is a schematic diagram of a scratch test.
7 is an optical microscope image of Example 1 in measuring the critical damage load.
8 is an optical microscope image of Example 2 in measuring the critical damage load.
9 is an optical microscope image of Comparative Example 1 in measuring the critical damage load.
10 is an optical microscope image of Example 3 in measuring the critical damage load.

The present invention intensively examines the above problem, that is, to provide a separator with a low insulation failure rate of a battery cell, and includes a film-like porous substrate having a plurality of pores and an adhesive resin formed on at least one surface of the porous substrate. It has been found that such a subject can be solved by providing a porous layer which does, 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, although one embodiment of the separator of this invention is described, this invention can be implemented by adding a change suitably in the scope of the present invention, without being limited in any way to the following embodiment. In addition, the terms or words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

(porous substrate)

The porous substrate is a substrate in the form of a porous film having a three-dimensionally irregularly connected network structure, and is one of the elements constituting the separator. Examples of the porous substrate include membranes, nonwoven fabrics, and the like, and the type is not particularly limited, but a porous substrate made of 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 within the range of 1×10 ⁴ to 1×10 ⁷ , preferably within the range of 1×10 ⁴ to 5×10 ⁶ , more preferably Is within the range of 1×10 ⁵ to 5×10 ⁶ . Incidentally, the mass average molecular weight (Mw) referred to herein is obtained from a calibration curve obtained using a monodisperse polystyrene standard sample by a gel permeation chromatography (GPC) method.

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

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 with different Mws, a mixture of similar high-density polyethylene, a mixture of similar medium-density polyethylene, and a mixture of low-density polyethylene may be used, and ultra-high molecular weight polyethylene, high-density polyethylene, medium-density polyethylene, and A mixture of two or more types of polyethylene selected from the group consisting of low-density polyethylene may be used.

Among them, as a polyethylene mixture, from the viewpoint of the response to the temperature rise of the shutdown phenomenon (shutdown speed) and the shape of the polyolefin porous film in a high-temperature region equal to or higher than the shutdown temperature to maintain the insulation between electrodes, an ultra-high Mw of 5 × 10 ⁵ or more A mixture of molecular weight polyethylene and polyethylene having a Mw of 1×10 ⁴ or more and less than 5×10 ⁵ is preferable. Mw of the ultra-high molecular weight polyethylene is preferably in the range of 5×10 ⁵ to 1×10 ⁷ , 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, but it is particularly preferable to use high-density polyethylene. As polyethylene having a Mw of 1×10 ⁴ or more and less than 5×10 ⁵ , two or more types of polyethylene having different Mws may be used, and two or more types 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 5×10 ⁶ . 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 weight of the polyethylene mixture.

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

The polyolefin resin may contain a polyolefin imparting shutdown characteristics in order to improve characteristics as a battery separator. As the polyolefin imparting shutdown characteristics, low density polyethylene can be used, for example. 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 addition amount of low density polyethylene is preferably 20% by weight or less based on 100% by weight of the total polyolefin. If the addition amount of the low-density polyethylene exceeds 20% by weight, it is not preferable because film breakage easily occurs during stretching.

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

When a film-like porous substrate is produced using a resin such as polyolefin as a raw material, the resin is melted together with a plasticizer such as liquid paraffin, and then extruded from a T-die to form a sheet. A method of extracting the plasticizer can be exemplified, but is not limited thereto. As will be described later, the separator of the present invention is characterized by having a predetermined Young's modulus, but in order to realize this Young's modulus, the degree of stretching of the porous substrate is adjusted, and the porous substrate itself 500 MPa or more in the machine direction (MD) of) is preferably provided.

As described above, the porous substrate has a three-dimensionally irregularly connected network structure, but the porosity is preferably 20 to 80%. When the porosity of the porous substrate is 20% or more, it is possible to realize good air permeability of the separator, suppress an increase in electrical resistance due to the membrane, and allow a large current to flow, which is preferable. In addition, sufficient mechanical strength of the separator is obtained when the porosity of the porous substrate is 80% or less, which is preferable. The porosity is more preferably 25 to 65%, and particularly preferably 30 to 55%. In addition, the porosity is the ratio (volume%) of the voids occupied in the porous substrate, and the porosity (%) was calculated using the following formula from the results obtained by measuring the sample volume (cm 3 ) and mass (g).

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

(porous layer)

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

As thickness of a porous layer, 0.05 micrometer or more and 3 micrometers or less are preferable, and 0.1 micrometer or more and 2.5 micrometer or less are more preferable. When the thickness of the porous layer is 0.05 μm or more, it is preferable because good adhesion is obtained between the electrodes and mechanical strength can be maintained, and when the thickness of the porous layer is 3 μm or less, the film resistance of the separator can be suppressed to a small desirable.

(adhesive resin)

The porous layer is equipped with an adhesive resin. Examples of the adhesive resin include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trichloroethylene copolymer, polyimide, polymethyl methacrylate, polybutyl acrylate, and polyacrylic acid. Ronitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, polyamideimide, polyimide, polyarylate, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, cyano Ethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc. are mentioned. Among these, resins containing fluorine atoms and/or acrylic resins are preferable, and polyvinylidene fluoride (PVDF) is particularly preferable. These resins can be used individually or in combination of 2 or more types.

(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. Examples of inorganic particles include, but are not particularly limited to, calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, boehmite, silica alumina composite oxide particles, barium sulfate, and calcium fluoride. , lithium fluoride, zeolite, molybdenum sulfide, mica, and the like. 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. Examples of the shape of the inorganic particles include spherical, substantially spherical, plate, needle, and polyhedral shapes, but are not particularly limited.

By including a filler in the porous layer, it is possible to suppress internal short-circuit caused by the growth of dendrites (dendrites) in the electrode, and to suppress shrinkage of the polyolefin porous substrate when thermal runaway occurs due to internal short-circuit in the secondary battery. there is. These fillers can be used singly or in combination of two or more. 10-99 volume% is preferable, as for content of the filler in a porous layer, 20-90 volume% is more preferable, and its 30-80 volume% is still more preferable. When the heat resistant content in the porous layer is within these ranges, generation of dendrites can be effectively suppressed, or shrinkage of the polyolefin porous substrate can be suppressed when thermal runaway occurs.

(Young's modulus)

The separator of the present invention is characterized in that the Young's modulus in the machine direction (MD) is 500 MPa or more. According to the study of the present inventors, since the Young's modulus of the separator in the machine direction (MD) is 500 MPa or more, even if minute solids such as dust or protrusions exist in any one of the separator conveyance paths in the manufacturing process of the secondary battery, the separator Film peeling of the linear porous layer along the machine direction can be suppressed. The reason why such an effect is obtained is not necessarily clear, but generally the following is considered. First of all, it is thought that when minute solids or projections present in the separator conveyance line come into contact with the separator, fine deformation (distortion) occurs in the surface layer of the separator due to the solids. It is considered that the porous layer cannot follow, and damage such as cracks, cracks, and cracks occurs in the porous layer itself. And in the separator conveyed at high speed, when such cracks, cracks, and cracks continuously occur, it is considered that the membrane of the porous layer is peeled off. On the other hand, when the separator has a high Young's modulus in the machine direction (MD) and the deformation of the surface layer portion of the separator is suppressed even when fine solids come in contact with it, the occurrence of such defects, that is, cracks, cracks, cracks, etc., is thought to be suppressed. The upper limit of the Young's modulus in the machine direction (MD) is not particularly specified, but may be about 3000 MPa for the purpose of reducing the defect rate due to wrinkling or bending in the battery cell assembly process.

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

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

(break elongation)

The separator of the present invention has a breaking elongation of 10% or more and 150% or less in the machine direction (MD). Preferably they are 20% or more and 110% or less, More preferably, they are 30% or more and 100% or less. If the elongation at break is less than 10%, cracks may occur in the separator itself when fine solid matter or projections present in the separator conveyance line come into contact with the separator. When it is larger than 150%, the degree of deformation (distortion) of the separator by the solid material increases, and film separation of the porous layer may occur. By being in the range of 10% or more and 150% or less, film separation of the porous layer can be suppressed without cracking of the separator.

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

(critical damage load)

The separator of the present invention preferably has a critical damage load of 3 mN or more that causes peeling of the porous layer present on the surface in the scratch test. When the separator of the present invention satisfies these conditions, generation of linear defects along the machine direction (MD) in the manufacturing process of the secondary battery can be suppressed. More preferably, the critical damage load is 3 mN or more. In addition, 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 these conditions, generation of linear defects along the machine direction (MD) in the manufacturing process of the secondary battery can be suppressed. More preferably, the critical damage load is 20 mN or more. In addition, this critical damage load is, for example, Anton Paar Japan K.K. It can be obtained by an ultra-thin film scratch tester sold by et al. The scratch test as used herein is specifically, in accordance with the ASTM D7187-15 test, a 90° diamond cone indenter 9 with a radius of curvature of 10 μm shown in FIG. 6 is pressed against the separator surface 8 with a load of 0.3 mN in the vertical direction. While increasing to 100 mN / min (25 mN / mm), scraping the membrane surface at a speed of 4 mm / min, and measuring the load in the vertical direction when damage to the porous membrane occurs, that is, the critical damage load.

The critical damage load is measured by the method described in the examples described later.

(Pressure in the direction perpendicular to the porous layer)

The separator of the present invention is characterized in that it is continuously pressed at a pressure of 0.1 MPa or more and 2 MPa or less for 1 hour or more in 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, preferably 0.3 MPa. Since sufficient pressure can be applied between the layers of a porous layer and a base material by being more than this lower limit, film|membrane peeling can be suppressed. The upper limit of the pressure is 2 MPa, preferably 1.5 MPa, to prevent deformation of the porous structure of the porous substrate and the porous layer. The pressurizing temperature is preferably in the range of 10°C to 30°C. If the pressurization time is short, the effect of suppressing film peeling may not be sufficient, and it is preferably 1 hour or more. The upper limit is not particularly limited, but is preferably 1×10 ⁴ hours or less in order to prevent the porosity of the porous film itself from decreasing if the pressurization time is too long. As a method of pressurization, for example, a flat press device can be used. Alternatively, when forming the porous layer, the reel-shaped winding body is wound so that the pressure of the core portion and / or the middle portion of the reel-shaped winding body is within the above range, and after 1 hour or more in the temperature environment, rewinding A method of applying pressure over the entire length of the winding object by performing the method may be used. In addition, as a method of winding a reel-shaped winding object so that the pressure at the core portion is within the above range, for example, a pressure measuring film (manufactured by FUJIFILM Corporation, PRESCALE) is applied to the surface of the winding core and/or the middle portion of the reel-shaped winding object (registered trademark)), find in advance a condition within the range of the pressure by a known method such as separator tension, touch roll pressure, and winding speed, and wind under that condition.

(Method of forming porous layer)

The porous layer is formed by applying a coating liquid containing a resin to the surface of the 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. As a method of applying the coating liquid to the surface of the porous substrate, a conventional coating method known in the art may be mentioned, and examples of such methods include a dip coating method, a wire bar method, a gravure coating method, a kiss method, a die coating method, and a roll coating method. method, comma coating method.

After the application liquid is applied to one side or both sides of the porous substrate, the porous substrate is immersed in an aqueous solvent. Then, the applied resin is solidified in a three-dimensional network shape. As a result, a porous layer is formed. An aqueous solvent is a solvent containing water used as a poor solvent in resin. Alcohols, acetone, N-methyl-2-pyrrolidone, etc. can be illustrated as a solvent which can coexist with water. After forming a porous layer on the surface of the porous substrate, it is dried by hot air at 100 ° C or less.

Example

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 substrate or separator was cut into a rectangle having a length of 150 mm and a width of 10 mm, and was referred to as a sample. A tensile test was conducted using a tensile tester (TENSILON UCT-100 manufactured by ORIENTEC CORPORATION) in an environment of 25° C. and 65% HR with an initial distance between chucks of 50 mm and a tensile speed of 300 mm/min. From the slope of strain and stress of the sample, the Young's modulus was calculated according to JIS K 7161-1 (2014), and the elongation at break and tensile strength when the sample broke were measured. In addition, in the tensile test of each Example and Comparative Example, it was confirmed that at least up to 2% of the elongation was in the linear elastic region. The measurement was performed 5 times for each sample, the average value was evaluated, and the result was described in Table 1.

(Rolling robbery)

The maximum load measured when a porous substrate or separator is pierced at a speed of 2 mm/sec using a needle having a diameter of 1 mm and having a spherical tip surface (radius of curvature: 0.5 mm) is referred to as spin strength, and the measurement is 5 for each sample. Each evaluation was carried out and evaluated based on the average value, and the results are shown in Table 1.

(critical damage load measurement)

The separator was applied on a slide glass with UV curable epoxy acrylate adhesive (Uniq Co., Ltd., Uni Solar Hard) to a thickness of 20 μm and fixed, using a nano scratch tester NST3 manufactured by Anton Paar Japan K.K. in the machine direction ( MD) to scan the indenter 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: 0.3mN

Final load: 50 mN

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

Scanning speed: 4 mm/min

As a result of the critical damage load measurement, the load at which the porous layer begins to peel off from the porous substrate is referred to as the critical damage load, and the measurement is performed 5 times for each sample, and the average value is evaluated, and the results are shown in Table 1. listed. In addition, optical microscope images after measuring the critical damage load are shown in FIGS. 7 to 10 .

(Electrical Insulation of Battery Cell)

fabrication of the positive electrode

An NMP solution containing 1.2 parts by mass of PVDF was added to and mixed with 97 parts by mass of lithium cobaltate and 1.8 parts by mass of carbon black to obtain a slurry containing positive electrode mixture. This positive electrode mixture-containing slurry was uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm, dried to form a positive electrode layer, and then compression-molded by a roll press to obtain the density of the positive electrode layer excluding the current collector A positive electrode was produced with 3.6 g/cm 3 .

Fabrication of negative electrode

An aqueous solution containing 1.0 parts by mass of carboxymethylcellulose was mixed with 98 parts by mass of artificial graphite and 1.0 parts by mass of styrene-butadiene latex to obtain a negative electrode mixture-containing slurry. This negative electrode mixture-containing slurry was uniformly applied to both sides of a negative electrode current collector made of copper foil having a thickness of 10 μm, dried to form a negative electrode layer, and then compression-molded by a roll press to determine the density of the negative electrode layer excluding the current collector. A negative electrode was produced as 1.45 g/cm 3 .

Assemble the flat winding cell

A flat wound object was produced using a battery cell winding device for the positive electrode and the negative electrode with tabs attached and a separator produced by the method described later. After that, the flat winding body was installed in an aluminum laminate bag, and this was referred to as a flat winding cell for testing.

Insulation defect inspection method

Using a withstand voltage tester (manufactured by KIKUSUI ELECTRONICS CORP., TOS5051A), a voltage of 50 V was loaded for 10 seconds to the positive electrode terminal and the negative electrode terminal of the flat wound cell, and a case in which current did not flow was regarded as pass, and a case in which current flow was regarded as disqualified.

judging method

In the above insulation defect inspection, a case where the number of disqualifications was 5 or less per 1000 flat wound cells was rated as "◎", a case of 6 or more and 15 or less as "○", and a case of 16 or more as "x".

(production of sample)

Preparation of coating liquid

50 parts by volume of vinylidene fluoride-hexafluoropropylene copolymer resin (manufactured by KUREHA CORPORATION, product name KF polymer W# 9300) and 50 parts by volume of alumina particles having a particle size (D50) of 1.0 μm so that the active ingredient is 10% by mass of N-methyl It was added to -2-pyrrolidone, mixed and dispersed, and was called a coating solution.

[Examples 1 and 2, Comparative Example 1]

For each of 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 moduli, the coating solution was applied to both surfaces using a die coater. Thereafter, the laminate was immersed in an aqueous solvent, subjected to phase separation, washed with water and dried to form a laminated film having a film thickness of 1.5 µm per side. Subsequently, pressure was applied in the vertical direction of the separator for 1 hour under conditions of 0.3 MPa at 25°C using a precision press device (manufactured by SINTOKOGIO, LTD.; CYPT10). These were referred to as the separators of Example 1, Example 2, and Comparative Example 1. The results are shown in Table 1.

[Example 3]

Test pieces were prepared in the same manner as in Example 1 except that the press time in Example 2 was changed to 10 minutes, and 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 separators of the present invention having a Young's modulus in the machine direction (MD) of Examples 1 to 3 of 500 MPa or more have high resistance to scraping, and manufacturing processes such as secondary batteries It turns out that peeling of a porous film can be suppressed and the manufacturing yield of a secondary battery etc. can be improved even if there exists a fine solid substance or a protrusion etc. on the conveyance line of a separator in this. Moreover, it turns out that it can further improve by applying the pressure of a porous layer and a perpendicular direction.

This application is based on the Japanese Patent Application (Japanese Patent Application No. 2017-106635) filed on May 30, 2017, the contents of which are incorporated herein as a 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 (8)

A film-shaped 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, a Young's modulus in the machine direction (MD) of 500 MPa or more, and a critical damage load A method for producing a separator characterized by being 3 mN or more, wherein the separator having a step of being continuously pressurized at a pressure of 0.1 MPa or more and 2 MPa or less for 1 hour or more in an environment of 10 ° C. to 30 ° C. from a direction perpendicular to the porous layer manufacturing method. According to claim 1,
The manufacturing method of the separator characterized by the above-mentioned porous layer containing a filler, and the ratio of the said filler in the said porous layer being 10 volume% or more and 99 volume% or less. According to claim 1 or 2,
A method for producing a separator characterized in that the elongation at break in the machine direction (MD) is 10% or more and 150% or less. According to claim 1 or 2,
A method for producing a separator, characterized in that the thickness of the porous layer is 0.05 μm or more and 3 μm or less. According to claim 1 or 2,
A method for producing a separator characterized in that the adhesive resin contained in the porous layer contains a resin containing a fluorine atom. According to claim 1 or 2,
A method for producing a separator characterized in that the adhesive resin contained in the porous layer contains an acrylic resin. According to claim 1 or 2,
A method for manufacturing a separator in which the separator is for a secondary battery. delete

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