TW202102595A - Separator film for electricity storage devices and lithium ion battery provided with same - Google Patents

Abstract

The purpose of the present invention is to provide: a separator film for electricity storage devices, which is not susceptible to increase in the ionic resistance even in comparison to single layer porous films, and which exhibits high adhesion of a coating film to a resin porous film; and a lithium ion battery which is provided with this separator film for electricity storage devices. A separator film for electricity storage devices, which comprises a resin porous film and a coating film that is formed on one surface or both surfaces of the resin porous film, wherein: the coating film is composed of the solid content of an aqueous composition for coating, which contains a binder and a filler; and the binder contains 50% by weight or more of a water-soluble acrylic resin that contains 40-45% by weight of a hydroxyl group-containing monomer unit and 8-12% by weight of an acetyl group-containing monomer.

Description

Isolation film for power storage device and lithium ion battery including the same

The present invention relates to a separator for an electrical storage device and a lithium ion battery including the separator.

In recent years, batteries with high energy density, high output, durability, or high safety, suitable for vehicles or portable terminals, are required. Lithium-ion batteries are widely used due to their characteristics, and research and development are being actively carried out.

Lithium-ion batteries have the following structures: a dielectric electrolyte layer, a separator film for electrical storage devices containing a polyolefin-based microporous film (polyolefin porous film) (hereinafter, abbreviated as separator) The case) and the sheet-shaped electrode are arranged inside the main body in a state of being laminated or spiraled inside the main body of the battery. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing the electrolyte held in the porous base material to pass through to allow ions to permeate. The ion permeability of a separator is a property directly related to its charge and discharge capabilities.

If the temperature inside the battery becomes higher, the ion permeability (ion resistance) may deteriorate at a temperature lower than the melting temperature of the polyolefin that is shut down. The separator has been expected to be excellent since the beginning The heat resistance.

In recent years, in order to further improve the heat resistance of the battery, the development of a multilayer heat-resistant separator material coated with an inorganic particle layer on the separator is underway. The multilayer heat-resistant separator material can be manufactured by coating a heat-resistant layer material containing inorganic particles and a binder on a base film such as a polyolefin microporous film and drying it.

Patent Document 1 describes that by including a porous layer containing an inorganic filler and a resin binder on at least one side of a polyolefin resin porous film, the maximum value of the thermal shrinkage stress of the polyolefin resin porous film is set as 10 g or less, a multilayer porous film with excellent heat resistance and permeability can be produced.

In addition, Patent Document 2 and Patent Document 3 describe that the mechanical stability of the battery is improved by using at least one selected from acrylic polymers, fluorine-containing resins, and polyamides as a resin binder. In Patent Document 2 and Patent Document 3, as the form of the resin binder, latex (emulsion type) made of resin is preferred. However, in emulsion-type resins, the adhesion of particles is the main component, and compared with the state where the molecular chains are entangled, the adhesiveness is low, which becomes a problem. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2009-026733 [Patent Document 2] Japanese Patent Laid-Open No. 2016-139490 [Patent Document 3] Japanese Patent Laid-Open No. 2016-139489

[The problem to be solved by the invention] In view of the above-mentioned problems, the object is to provide a separator for electrical storage devices that is less likely to increase in ion resistance than in the case of a single-layer porous film, and has high adhesion of the coated film to the resin-made porous film, and a lithium ion battery including the separator . [Means to solve the problem]

The inventors of the present invention have repeatedly studied hard in order to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention includes the following contents. [1] A separator film for an electrical storage device, comprising: a resin porous film, and a coating film formed on one or both sides of the resin porous film, the coating film including a coating containing a binder and a filler Using the solid content of the aqueous composition, the binder contains 50% by weight or more of a water-soluble acrylic resin, the water-soluble acrylic resin contains 40% to 45% by weight of hydroxyl-containing monomer units, and contains 8% by weight %～12% by weight of monomer containing acetyl group. [2] The separator for a power storage device according to [1], wherein D90 of the filler is 1 μm or less. [3] The separator for an electrical storage device according to [1] or [2], wherein 80% or more of the particles of the filler are 50 nm or more and 700 nm or less. [4] The separator for a power storage device according to any one of [1] to [3], wherein the binder does not substantially contain a water-insoluble resin. [5] The separator for an electricity storage device according to any one of [1] to [4], wherein the resin-made porous film is a polyolefin-made porous film. [6] The separator for an electricity storage device according to [5], wherein the porous film made of polyolefin is a porous film made of polypropylene. [7] The separator for an electrical storage device according to any one of [1] to [6], wherein the interfacial peel strength of the resin porous film and the coating film formed on the resin porous film is 1000 Above gf. [8] A lithium ion battery including the separator for a power storage device as described in any one of [1] to [7]. [Effects of the invention]

According to the present invention, it is possible to provide a separator for an electrical storage device that includes a coated film, has low film resistance, and has high adhesion of the coated film to a resin-made porous film.

Hereinafter, the present invention will be described, but the present invention is not limited to the specific examples or examples described in the embodiment as long as it does not depart from the gist of the present invention.

The separator film for an electrical storage device of the present invention includes a resin porous film and a coating film formed on one or both sides of the resin porous film, the coating film including a water-based coating containing a binder and a filler The solid content of the composition, the binder contains 50% by weight or more of a water-soluble acrylic resin, and the water-soluble acrylic resin contains 40% to 45% by weight of hydroxyl-containing monomer units, and contains 8% to 8% by weight. 12% by weight of acetyl-containing monomer.

＜Coating film＞ (Water-based composition for coating) The coating film included in the isolation film of the electrical storage device contains the solid content of the coating water-based composition. The aqueous composition for coating contains a binder and a filler, the binder contains 50% by weight or more of a water-soluble acrylic resin, and the water-soluble acrylic resin contains 40% to 45% by weight of hydroxyl-containing monomer units, And it contains 8% to 12% by weight of the acetyl group-containing monomer.

(Adhesive) The binder contained in the aqueous composition for coating can bind the filler, and contains a water-soluble acrylic resin that contains 40% to 45% by weight of hydroxyl-containing monomer units and contains 8% by weight %～12% by weight of monomer containing acetyl group. The water-soluble acrylic resin is characterized by being a water-soluble acrylic resin. By using a water-soluble acrylic resin in the water-based composition for coating, the adhesion of the coating film containing the solid content of the water-based composition for coating to the porous film made of resin improves.

Regarding the water-soluble acrylic resin that can be used in the present invention, the pH value in a 1% by weight aqueous solution of the water-soluble acrylic resin is preferably 6-9. If it is the said range, the dispersibility of a filler in a solvent will improve.

Regarding the water-soluble acrylic resin, the viscosity in a 15% by weight aqueous solution of the water-soluble acrylic resin is preferably 4 Pa·s to 8 Pa·s. If it is the said range, the water-based composition for coating can be stored stably.

The water-soluble acrylic resin contains 40% to 45% by weight of hydroxyl-containing monomer units. If it is this range, the adhesiveness of the coating film containing the solid content of a water-based composition for coating with respect to a resin porous film will improve.

In addition, the water-soluble acrylic resin contains 8% by weight to 12% by weight of an acetyl group-containing monomer. If it is this range, the adhesiveness of the coating film containing the solid content of a water-based composition for coating with respect to a resin porous film will improve.

Furthermore, after the polymerization, in order to adjust the solubility with respect to water, the water-soluble acrylic resin may be neutralized.

The adhesive contains 50% by weight or more of water-soluble acrylic resin with respect to the entire resin constituting the adhesive. By containing 50% by weight or more, the effect of improving the adhesiveness is easily expressed. The water-soluble acrylic resin is preferably 60% by weight or more with respect to the entire resin constituting the adhesive. The upper limit of the content of the water-soluble acrylic resin relative to the entire resin constituting the adhesive is not particularly limited, but is preferably 90% by weight or less.

The adhesive may include resins other than water-soluble acrylic resins. Examples of resins that can be included include polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and emulsion acrylic resins.

As the coating film, especially the coating film used in the separator for electrical storage devices, an emulsion type acrylic resin has been used since the beginning. Emulsion-type acrylic resin is a water-insoluble resin when it is a simple substance, so it can be dispersed in water by using a surfactant. From the viewpoint of the adhesiveness with the resin-made porous membrane, it is preferable to reduce the amount of water-insoluble resin used in the water-insoluble resin like emulsion acrylic resin in the adhesive for coating the aqueous composition used in the present invention. The water-insoluble resin contained in the adhesive is preferably 20% by weight or less, more preferably 10% by weight or less, still more preferably 5% by weight or less, and particularly preferably 0% by weight. That is, the binder contained in the aqueous coating composition used in the present invention preferably contains substantially no water-insoluble resin. Here, the "substantially free of water-insoluble resin" means that the water-insoluble resin is not actively contained, and an inevitable impurity level is allowed (relative to the entire resin constituting the binder, the resin is, for example, The content of 0.1% by weight or less) contains the resin.

(filler) The water-based composition for coating used in the present invention is mainly used to improve the heat resistance of the resin porous membrane to be coated. In order to solve the above-mentioned problems, fillers are used in the aqueous composition for coating. The filler is not particularly limited as long as it can achieve the above-mentioned purpose.

Examples of fillers that can be used in the aqueous composition for coating include oxide ceramics such as silica, alumina, titania, zirconia, magnesia, and barium titanate, or hydrogen such as aluminum hydroxide and magnesium hydroxide. Oxide-based ceramics, nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride, or boehmite, talc, kaolin, zeolite, apatite, halogenite, Pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, calcium silicate, magnesium silicate and other substances derived from mineral resources. From the viewpoint of heat resistance, chemical stability, etc., alumina is preferred.

The filler used in the water-based composition for coating can be a filler that has been convenient for use in coating since the beginning, and it is preferably one having a particle diameter smaller than the previous particle diameter. Specifically, the D90 of the filler is preferably 1 μm or less, more preferably 0.6 μm or less, and still more preferably 0.4 μm or less. Furthermore, it is preferable that 80% or more of the particles of the filler is in the range of 50 nm to 700 nm.

In more detail, the average particle diameter of the particles constituting the filler is preferably 50 nm to 500 nm, more preferably 100 nm to 400 nm, and still more preferably 150 nm to 250 nm. In addition, by setting the D90 of the filler, the distribution of the particle diameter of the filler, and the average particle diameter within the above-mentioned ranges, blocking of the separator can be suppressed, air permeability can be maintained, and a coating film having excellent adhesion to the separator can be obtained.

(Other ingredients) The aqueous composition for coating used in the present invention may contain a dispersant. By including the dispersant, the dispersibility of the filler in the solvent can be improved, the water-based composition for coating can be stored stably, and a uniform and uniform coating film can be formed.

The dispersing agent that can be used in the aqueous composition for coating is not particularly limited as long as it can exert the effect of the dispersing agent. Specific examples of the dispersing agent include: polyalkylether, ammonium polyacrylate, and carboxymethyl Cellulose and so on.

The water-based composition for coating used in the present invention may contain water from the viewpoint of easy coating on the porous resin membrane. Regarding the water used in the present invention, although other components are not prevented from being mixed in, the other components contained in the water are preferably 10% or less, more preferably 3% or less, further preferably 1% or less, particularly preferably 0.1% or less .

The water-based coating composition used in the present invention may contain other components in the water-based coating composition according to the application. Examples of components that may be included in the aqueous composition for coating include antibacterial agents, antifungal agents, wetting agents, thickeners, wetting agents, or pH adjusters.

(Component ratio) The water-based composition for coating used in the present invention contains a binder and a filler, and the component ratio will be described. With respect to the total solid content of the aqueous composition for coating (when the total solid content of the aqueous composition for coating is 100%), the lower limit of the binder is preferably 2.5% by weight or more, and more preferably contains It is 2.7% by weight or more, and more preferably 3.0% by weight or more is contained. The upper limit of the binder relative to the entire solid content of the aqueous composition for coating is preferably 5.0% by weight or less, more preferably 4.5% by weight or less, and still more preferably 4.0% by weight or less.

The lower limit of the filler relative to the entire solid content of the aqueous composition for coating is preferably 92% by weight or more, more preferably 93% by weight or more, and still more preferably 94% by weight or more. In addition, the upper limit of the filler relative to the entire solid content of the aqueous composition for coating is preferably 97% by weight or less, more preferably 96% by weight or less, and still more preferably 95% by weight or less.

When the aqueous composition for coating used in the present invention contains a dispersant, the lower limit of the dispersant relative to the solid content of the aqueous composition for coating is preferably 1.0% by weight or more, more preferably 1.5 % By weight or more, more preferably 2.0% by weight or more. In addition, the upper limit of the dispersant is preferably 4.0% by weight or less, more preferably 3.0% by weight or less, and still more preferably 2.5% by weight or less. By setting the content (composition) of the binder, filler, and dispersant in the solid content of the aqueous composition for coating within the above range, it is possible to obtain the adhesiveness of the coating film and the resin porous film, and A coating film that balances the air permeability of the coating film. In addition, the term “solid content” refers to a component obtained by removing solvents such as water from the aqueous composition for coating.

The solid content of the aqueous composition for coating used in the present invention is preferably 20% by weight to 50% by weight, more preferably 25% by weight to 35% by weight.

When the aqueous composition for coating used in the present invention contains other components such as defoamers, antibacterial agents, and antifungal agents, the upper limit of the other components relative to the entire solid content is preferably 1.0% by weight or less , More preferably 0.5% by weight or less, and still more preferably 0% by weight.

(Sticky) The viscosity of the aqueous composition for coating used in the present invention is preferably 0.01 Pa·s to 0.1 Pa·s at 25°C.

(Manufacturing method of water-based composition for coating) The aqueous composition for coating used in the present invention can be prepared by dispersing a binder, a filler, and a dispersant or other components such as water containing 50% by weight or more of a water-soluble acrylic resin. Dispersion can be performed by an existing method, and examples of dispersion devices include planetary stirring devices, propeller stirrers, homogeneous dispersers, bead mills, ultrasonic dispersion devices, and the like.

From the viewpoint of the uniformity of the water-based coating composition, it is preferable to perform the secondary dispersion treatment after the water-based coating composition is dispersed. As an example of a device for performing the dispersion treatment, a wet jet mill and the like can be cited.

(Manufacturing method of coating film) The aqueous composition for coating used in the present invention can be applied to the surface of a porous resin film to form a coating film. Examples of coating methods include: gravure coater method, micro gravure coater method, die coater method, knife coater method, screen printing method, Meyer bar method, reverse roll Coater method, inkjet method, spray method, roll coater method, etc. Furthermore, after coating, it is dried to remove moisture. The drying temperature is preferably 50°C or higher, more preferably 60°C or higher, and still more preferably 70°C or higher.

The coating film is not particularly limited as long as it is a film thickness that can exhibit the characteristics of the coating film. For example, it may be 0.5 μm to 10 μm, and preferably 1.5 μm to 5 μm.

From the viewpoint of storage capacity, the weight per unit area of the coating film can be set to 0.1 g/m ² to 50 g/m ² , preferably 0.1 g/m ² to 30 g/m ² , and more preferably It can be set to 0.1 g/m ² ～10 g/m ² .

Regarding the air permeability per unit thickness of the coating film, in the case of being used as an isolation film for an electrical storage device, from the viewpoint of allowing ions to pass through, the air permeability can be set to 1 sec/μm to 100 sec/μm, preferably It can be set to 1 sec/μm to 70 sec/μm, and more preferably can be set to 1 sec/μm to 30 sec/μm.

＜Porous resin membrane＞ The separator for a power storage device uses a resin porous film as a base material. The resin-made porous membrane is not particularly limited, and since it is necessary to transmit ions, it is preferably a microporous membrane. As the material of the resin porous membrane, polyolefin is preferred. The pore size distribution of the resin porous membrane was measured using BELSORP-max manufactured by Microtrac-bel. The type of adsorbed gas used is calculated by analyzing the Barrett-Joyner-Halenda (BJH) method using high-purity nitrogen (over 99.999%) and nitrogen adsorption behavior. The pore size distribution of the resin porous membrane is preferably 10 nm to 500 nm, more preferably 20 nm to 200 nm. The average pore diameter of the resin porous membrane is preferably 300 nm or less, more preferably 100 nm or less.

The material of the porous film made of polyolefin is not particularly limited, and examples thereof include polyethylene, polypropylene, and polybutene.

The porous film made of polyolefin may be surface-treated if necessary. Examples of surface treatments include corona treatment, plasma treatment, electron beam treatment, radiation treatment, fluorine treatment, ultraviolet method, crosslinking treatment method, acid treatment method, and the like. By performing the above-mentioned treatment, the uniform penetration of the aqueous composition for coating can be promoted, and the adhesion between the coating film and the separator can be improved.

The manufacturing method of the resin porous film is not specifically limited, For example, when the material is polypropylene, it is manufactured through the following steps 1 to 6. That is, first, the raw material polypropylene is melt-kneaded (step 1). Next, a single-screw extruder is used to extrude from a T-die to produce a raw film with a predetermined thickness (step 2). Next, heat treatment of the original film at a predetermined temperature (100°C to 170°C) (step 3). The original film after step 3 is cold stretched along the length direction at a predetermined temperature (15°C to 30°C) (step 4). The stretched film after step 4 is warmly stretched along the length direction at a predetermined temperature (100°C to 170°C) (step 5). Relaxation is performed at a predetermined temperature (100°C to 150°C) so that the length of the stretched film that has passed through step 5 becomes a predetermined length (step 6). In this way, a polypropylene porous film having a final thickness of a predetermined thickness can be obtained.

<Separation film for power storage devices (Separation film for lithium ion batteries)> Specifically, the isolation film of the power storage device of the present invention can be used as the isolation film of a lithium ion battery.

One of the characteristics of the separator for an electrical storage device (separator for a lithium ion battery) of the present invention is low in membrane resistivity. The film resistance increase rate (Rr) after coating is preferably 1.5 or less, more preferably 1.4 or less, and particularly preferably 1.3 or less. Rising rate of film resistance (Rr)=(film resistance after coating)/(film resistance before coating)

One of the characteristics of the separator for an electricity storage device of the present invention is that the coating film has high adhesion to the resin-made porous film. Adhesion is measured as tape peel strength. Regarding the peeling strength of the tape, a resin porous film cut into 2 cm (TD (transverse direction)) × 7 cm (MD (machine dirction)) is applied to a single-sided coated film with a width of 10 mm. × Double-sided adhesive tape with a length of 20 mm (manufactured by Japan 3M Co., Ltd., Scotch PREMIER GOLD (trade name)), attached to one side of the double-sided adhesive tape and cut into width 2 cm×7 cm long kraft paper, clamp the coated film and the ends of the kraft paper with a chuck, and peel off the interface between the coated layer and the resin porous film at a stretching speed of 500 mm/min. It is measured as the interface peeling strength (gf) of the resin-made porous film and the coating film formed in the resin-made porous film. The value when measured using a tensile tester is preferably 1000 gf or more, more preferably 1500 gf or more, and still more preferably 2000 gf or more. [Example]

Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples.

(Type of filler) Table 1 shows the particle characteristics of filler 1, filler 2, and filler 3 (all of which are alumina) contained in the aqueous composition for coating produced as a synthesis example.

(Type of adhesive) The adhesive 1 described in the table is a water-soluble acrylic resin manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., which contains 40% to 45% by weight of hydroxyl-containing monomer units and 8% to 12% by weight of ethyl acetate. The single body of the base. (Adhesive 1 is used as an adhesive for Marpolib AQ-2C manufactured by Matsumoto Oil Pharmaceutical Co., Ltd.) The adhesive 2 described in the table is an acrylic emulsion type adhesive, and is a water-insoluble acrylic resin, and has an average particle diameter of 1 μm or less.

(Synthesis example) (1) Preparation of water-based composition for coating In a predetermined amount of beaker, each solid component (binder, filler, dispersant (polyalkyl ether)) is put in such that the solid content is about 30% by weight with respect to the entire aqueous composition for coating, and Table 2 to Table 7 describe the ratio of solid content) and water, which were stirred with a stirrer (stirrer). After the appearance becomes roughly uniform, use the planetary stirring device mazerustar (trade name, manufactured by Kurabo company, rotation 1340 rpm, revolution 1340 rpm, stirring time 10 minutes) to stir the warp The raw materials are mixed. Secondly, the obtained mixture was dispersed and processed using a wet jet milling device Nanovater (trade name, manufactured by Yoshida Machinery Industrial Co., Ltd., processing pressure of 100 MPa, and processing times of 3 times). The obtained mixture is used as an aqueous composition for coating.

(2) Manufacture of polypropylene porous membrane As the raw material polypropylene, a melt mass-flow rate (MFR) (measured in accordance with Japanese Industrial Standards K6758 (230°C, 21.18 N)) was used as 0.50 g/10 minutes, Mw/ A propylene polymer with a Mn of 8.1 and a melting point of 163°C. The raw material polypropylene was melt-kneaded and extruded from the T-shaped film using a single-screw extruder to produce a raw film with a thickness of 17 μm. Secondly, the original film is heat-treated at 145°C, and the original film is cold stretched to 1.02 times in the length direction at 25°C. Furthermore, the temperature of the stretched film was stretched to 3.31 times in the longitudinal direction at 150°C, and the stretched film was relaxed at 150°C so that the length of the stretched film became 0.75 times, thereby obtaining a polypropylene porous film with a final thickness of 14 μm .

(Example 1 to Example 17, Comparative Example 1) (3) Manufacturing of separators for lithium ion batteries Use the water-based coating composition obtained in (1) above, and use the polypropylene porous membrane of (2), the coating device μ coater (manufactured by Yasui Seiki Co., Ltd.) at a linear speed of 2 m The water-based coating composition is applied to one side under the conditions of 80°C drying temperature and 80°C to form a coating film. The characteristics of the obtained lithium ion separators (Example 1 to Example 17, Comparative Example 1) are shown in Tables 2 to 7. In addition, Reference Example 1, Reference Example 2, and Reference Example 3 in Table 6 are the measured values in the state where the coating film is not formed in Example 12, Example 13, and Example 14, respectively.

[Table 1] filler Packing 1 Packing 2 Packing 3 Product name SAO-020B SAO-035EQ APA-3AF Average particle diameter (μm) 0.20 1.49 1.15 D10 (μm) 0.08 0.16 0.26 D50 (μm) 0.15 0.98 0.84 D90 (μm) 0.37 3.42 2.32

[Table 2] Example 1 Comparative example 1 Coating film filler Packing 1 Packing 1 Adhesive Adhesive 1 Adhesive 2 Composition ratio (filler/binder/dispersant) 93.7/2.3/4.0 93.7/2.3/4.0 Substrate (porous membrane) Material Polypropylene Polypropylene Processing method / extension method Corona treatment/dry one shaft Corona treatment/dry one shaft Physical properties thickness μm 17.7 17 Coating film thickness μm 2.3 1.6 Unit area weight g/m ² 11.9 10.3 Coating film weight per unit area g/m ² 4.9 3.3 Ventilation sec 166 143 Coating membrane air permeability sec 34 11 sec/μm 15 7 Rise rate of membrane resistance - 1.11 1.07 Heat shrink % MD/TD 0.7/0 1.9/0 Tape peel strength gf 857 656

[table 3] Example 2 Example 3 Example 4 Example 5 Coating film filler Packing 1 Packing 1 Packing 1 Packing 1 Adhesive Adhesive 1 Adhesive 1 Adhesive 1 Adhesive 1 Composition ratio (filler/binder/dispersant) 94.4/1.6/3.9 93.8/2.3/3.9 94.1/3.9/2.0 93.5/4.5/1.9 Substrate (porous membrane) Material Polypropylene Polypropylene Polypropylene Polypropylene Processing and extension methods Corona treatment/dry one shaft Corona treatment/dry one shaft Corona treatment/dry one shaft Corona treatment/dry one shaft Physical properties thickness μm 18.2 18.1 18.1 17.6 Coating film thickness μm 2.8 2.7 2.7 2.2 Unit area weight g/m ² 12.6 12.3 11.9 12 Coating film weight per unit area g/m ² 5.6 5.3 4.9 5 Ventilation sec 163 172 179 177 Coating membrane air permeability sec 31 40 47 45 sec/μm 11 15 17 twenty one Rise rate of membrane resistance - 1.09 1.15 1.19 1.18 Heat shrink % MD/TD 0.8/0 0.8/0 0.7/0 0.7/0 Tape peel strength gf 801 919 1058 1315

[Table 4] Example 6 Example 7 Example 8 Coating film filler Packing 1 Packing 1 Packing 1 Adhesive Adhesive 1 Adhesive 1 Adhesive 1 Composition ratio (filler/binder/dispersant) 94.4/2.3/3.3 92.9/2.3/4.8 93.5/3.9/2.6 Substrate (porous membrane) Material Polypropylene Polypropylene Polypropylene Processing and extension methods Corona treatment/dry one shaft Corona treatment/dry one shaft Corona treatment/dry one shaft Physical properties thickness μm 17.8 18.2 18.4 Coating film thickness μm 2.4 2.8 3 Unit area weight g/m ² 12.1 12.2 12.6 Coating film weight per unit area g/m ² 5.1 5.2 5.6 Ventilation sec 162 167 177 Coating membrane air permeability sec 30 35 45 sec/μm 13 13 15 Rise rate of membrane resistance - 1.08 1.11 1.18 Heat shrink % MD/TD 0.7/0 1.0/0 0.7/0 Tape peel strength gf 927 886 1164

[table 5] Example 9 Example 10 Example 11 Coating film filler Packing 1 Packing 1 Packing 1 Adhesive Adhesive 1 Adhesive 1 Adhesive 1 Composition ratio (filler/binder/dispersant) 92.9/3.9/3.2 92.0/6.4/1.6 90.6/6.3/3.1 Substrate (porous membrane) Material Polypropylene Polypropylene Polypropylene Processing and extension methods Corona treatment/dry one shaft Corona treatment/dry one shaft Corona treatment/dry one shaft Physical properties thickness μm 17.8 17.7 18.2 Coating film thickness μm 2.4 2.3 2.8 Unit area weight g/m ² 12.2 12.2 13.8 Coating film weight per unit area g/m ² 5.2 5.2 6.8 Ventilation sec 178 224 304 Coating membrane air permeability sec 46 92 172 sec/μm 19 39 62 Rise rate of membrane resistance - 1.19 1.49 2.03 Heat shrink % MD/TD 0.9/0 0.9/0 0.7/0 Tape peel strength gf 1126 1768 1203

[Table 6] Example 12 Reference example 1 Example 13 Reference example 2 Example 14 Reference example 3 Coating film filler Packing 1 Packing 1 Packing 1 Adhesive Adhesive 1 Adhesive 1 - Adhesive 1 - Composition ratio (filler/binder/dispersant) 94.7/3.3/2.0 94.7/3.3/2.0 94.7/3.3/2.0 Substrate (porous membrane) Material Polypropylene Polypropylene Polyethylene Polyethylene Polyethylene Polyethylene species Corona treatment/dry one shaft Corona treatment/dry one shaft Wet two-axis Wet two-axis Dry one shaft Dry one shaft Physical properties thickness μm 22.6 19.7 22.2 19.1 22.4 20 Coating film thickness μm 2.9 - 3.1 - 2.5 - Unit area weight g/m ² 15.1 9.1 17.6 11.9 15 9.6 Coating film weight per unit area g/m ² 6 - 5.7 - 5.5 - Ventilation sec 200 173 341 305 296 255 Coating membrane air permeability sec 27 - 36 - 41 - sec/μm 9 - 12 - 17 - Rise rate of membrane resistance - 1.23 - 1.18 - 1.26 - Heat shrink % MD/TD 1/0.6 28/0 2.3/3.4 72/68 0.9/1.0 Unable to determine Tape peel strength gf 2359 - 3145 - 2217 -

[Table 7] Example 15 Example 16 Example 17 Coating film filler Packing 1 Packing 2 Packing 3 Adhesive Adhesive 1 Adhesive 1 Adhesive 1 Composition ratio (filler/binder/dispersant) 94.7/3.3/2.0 94.7/3.3/2.0 94.7/3.3/2.0 Substrate (porous membrane) Material Polypropylene Polypropylene Polypropylene species Corona treatment/dry one shaft Corona treatment/dry one shaft Corona treatment/dry one shaft Physical properties thickness μm 18.3 18.5 18.4 Coating film thickness μm 2.9 3.1 3.0 Unit area weight g/m ² 12.5 12.7 12.8 Coating film weight per unit area g/m ² 5.5 5.7 5.8 Ventilation sec 166 201 228 Coating membrane air permeability sec 34 69 96 sec/μm 12 twenty two 32 Rise rate of membrane resistance - 1.11 1.34 1.52 Heat shrink % MD/TD 0.8/0 0.7/0 0.7/0 Tape peel strength gf 1887 1542 2067

(4) Evaluation conditions The characteristics of the water-based coating composition, the polypropylene porous membrane, and the lithium ion separator were evaluated under the following conditions.

A. Particle size distribution (average particle diameter, D10, D50, D90) Regarding the particle size distribution of the filler after the dispersion treatment, the aqueous composition for coating was diluted 1000 times with pure water and measured with LA-950V2 manufactured by HORIBA.

B. Film thickness Cut the obtained coating film and lithium ion battery separator into a circle with a diameter of 72 mm, and use the HKT-1240 (R30 spherical super-hard gauge head manufactured by FUJI WORK) Co., Ltd., and the measurement load is 0.14 N), the thickness is measured at 15 arbitrary places of the coating film, and the average value of the 15 places is regarded as the film thickness.

C. Weight per unit area Cut the obtained coating film and lithium ion battery separator into a circle with a diameter of 72 mm to obtain a sample. For this sample, the weight is measured with an electronic balance to obtain the value of weight per unit area (g/m ² ).

D. Ventilation For the obtained separator for lithium ion batteries, a Gurley-type densityometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used, and the time (sec) for 100 mL of air to pass through was measured in accordance with JIS P 8117. In addition, the difference between the air permeability after coating and the air permeability of the film before coating was calculated as the air permeability of the coating film. Furthermore, the air permeability per unit thickness of the coating film (sec/μm) was calculated by dividing the air permeability of the coating film by the thickness of the coating film.

E. The membrane resistor is prepared in an electrolyte solution prepared by _{dissolving LiPF 6} in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate at a ratio of 1 mol/L. Arrange aluminum positive/negative electrodes in the electrolyte and arrange the obtained coating film and lithium ion battery separator between the positive/negative electrodes. Use an inductance-capacitance-resistance (LCR) meter and use The Cole-Cole plot is measured by the complex impedance method, and the real part of the impedance at 100,000 Hz is obtained and used as an index of the membrane resistance. The measurement is performed in a constant temperature bath at 30°C. The film resistance increase rate was calculated from the film resistance obtained by the measurement method, and the film resistance increase rate was described in the table.

F. Heat shrink The obtained separator for a lithium ion battery was marked with 5 cm intervals in the MD direction, and it was heated at 150° C. for 2 hours in a constant temperature bath (oven) under no load. The length between the marks after heating was measured and calculated as the shrinkage rate. Expressed in the table as thermal shrinkage.

G. Tape peel strength This will be explained with reference to FIG. 4. The resin porous film 1 (the obtained separator for lithium ion batteries) including the coating film 2 was cut into 2 cm (TD) × 7 cm (MD), and the same was cut into a double-sided adhesive tape 3 with a length of 2 cm (Manufactured by Japan 3M Co., Ltd., Scotch PREMIER GOLD (trade name)) is attached to the coating film 2. After that, a kraft paper 4 cut into a width of 2 cm × a length of 7 cm was attached to one side of the double-sided adhesive tape 3, and the ends of the coating film 2 and the paper 4 were clamped at 500 mm/min. The tensile speed of the coating layer 2 / resin porous membrane 1 interface peel strength (gf) was measured. Expressed in the table as the tape peel strength.

1: Resin porous membrane 2: Coating film 3: Double-sided adhesive tape 4: Kraft paper

FIG. 1 is a scanning electron microscope (Scanning Electron Microscope, SEM) image of the surface of the coating film included in the isolation film of Example 15. FIG. 2 is an SEM image of the surface of the coating film included in the isolation film of Example 16. FIG. 3 is an SEM image of the surface of the coating film included in the isolation film of Example 17. FIG. Fig. 4 is a schematic diagram of a method for measuring the peel strength of a tape.

Claims (8)

A separator for an electricity storage device, comprising: a resin-made porous film and a coating film formed on one or both sides of the resin-made porous film, The coating film contains solid components of an aqueous coating composition containing a binder and a filler, The adhesive includes 50% by weight or more of a water-soluble acrylic resin, the water-soluble acrylic resin includes 40% to 45% by weight of hydroxyl-containing monomer units, and 8% to 12% by weight of ethyl-containing The single body of the base. The isolation film for a power storage device according to claim 1, wherein D90 of the filler is 1 μm or less. The isolation film for an electrical storage device according to claim 1 or claim 2, wherein 80% or more of the particles of the filler are 50 nm or more and 700 nm or less. The isolation film for a power storage device according to any one of claims 1 to 3, wherein the binder does not substantially contain a water-insoluble resin. The separator for an electrical storage device according to any one of claims 1 to 4, wherein the resin-made porous film is a polyolefin porous film. The separator for an electricity storage device according to claim 5, wherein the polyolefin-based substrate is a porous film made of polypropylene. The separator for an electrical storage device according to any one of claims 1 to 6, wherein the interface peel strength of the resin porous film and the coating film formed on the resin porous film is 1000 gf the above. A lithium ion battery includes the isolation film for a power storage device according to any one of claim 1 to claim 7.

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