Battery cell sealing film

Abstract

To provide a battery cell sealing film that can be thinner than conventional films, has excellent slidability, can prevent blocking, and has excellent adhesiveness between heat seal layers.SOLUTION: There is provided a battery cell sealing film including a base material 10 and a heat seal layer 20, the heat seal layer 20 containing a water dispersible polyolefin resin and fine particles 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealing film for sealing an object, and more particularly to a sealing film for a battery cell for sealing a unit cell assembly to manufacture a battery cell. [Background technology]

[0002] Lithium-ion batteries are used in many products due to their high energy density and ability to charge and discharge rapidly, but they pose a high risk of fire due to the use of a flammable electrolyte. To solve this problem, semi-solid lithium-ion batteries that use semi-solid materials such as gel, clay, and resin as the electrolyte have been developed in recent years. Semi-solid lithium-ion batteries consist of battery cells in which unit cell assemblies (one stack) combining an anode and a cathode with a separator that separates them are pouched in a battery cell sealing film, and multiple battery cells are connected to form a battery module to achieve the desired output and capacity (see, for example, Patent Document 1).

[0003] Also, as a method for manufacturing such a battery cell, a method has been proposed in which a semi-solid electrode slurry is continuously dispensed onto a current collector, and then the current collector is cut to form a first electrode, which is then adjacent to a second electrode interposed by a separator to form a unit cell assembly, which is then pouched in a sealing film and packaged (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-12891 [Patent Document 2] Japanese Patent Application Publication No. 2023-123439 Summary of the Invention [Problem to be solved by the invention]

[0005] A battery module of a lithium-ion semi-solid battery is generally constructed by stacking multiple battery cells. In order to increase the electrical capacity and reduce the weight of such a battery module, it is desirable to reduce the thickness of each battery cell and stack and connect more battery cells, and it is also desirable to reduce the thickness of the sealing film that seals the unit cell assemblies and constitutes the battery cells.

[0006] Furthermore, since the battery cell sealing film seals the unit cell assembly by bonding the battery cell sealing films together, the heat seal layer is required to have high adhesiveness (heat sealability) between the battery cell sealing films.

[0007] In addition, because battery cell sealing films are manufactured in the form of long films, they are typically stored and transported in rolled-up form, and when manufacturing battery cells, the battery cell sealing film is pulled out from the roll for use. When forming the battery cell sealing film into a roll film, the heat seal layer of the lower battery cell sealing film may adhere (block) to the substrate of the upper battery cell sealing film, resulting in wrinkles and other defects in the appearance of the roll film. Battery cell sealing films with wrinkles or other defects in appearance cannot seal between battery cell sealing films or between the battery cell sealing film and the current collector without gaps, which may lead to defects in lithium-ion semi-solid batteries. Therefore, battery cell sealing films are also required to have high slip properties that prevent wrinkles from forming even when formed into a roll film.

[0008] An object of the present invention is to provide a sealing film for battery cells that can be made thinner than conventional films, has good slip properties, can suppress blocking, and also has good adhesion between heat-sealable layers. [Means for solving the problem]

[0009] The present invention is summarized as follows: (1) to (9) sealing films for battery cells. (1) A sealing film for a battery cell, comprising a substrate and a heat seal layer, the heat seal layer containing a water-dispersible polyolefin resin and fine particles. (2) The battery cell sealing film according to (1) above, wherein the fine particles are organic fine particles. (3) The sealing film for a battery cell according to (2) above, wherein the organic fine particles are crosslinked polymethyl methacrylate. (4) The sealing film for a battery cell according to any one of (1) to (3) above, wherein the heat seal layer is a thin film having a thickness of 10 μm or less. (5) The sealing film for a battery cell according to any one of (1) to (4) above, wherein the fine particles have an average primary particle diameter of 0.5 to 10.0 μm. (6) The sealing film for a battery cell according to any one of (1) to (5) above, wherein the thickness of the heat seal layer is greater than 2 μm, and the average primary particle diameter of the fine particles is less than 6 μm. (7) The sealing film for battery cells according to any one of (1) to (5) above, wherein the thickness A (μm) of the heat seal layer and the average primary particle diameter B (μm) of the fine particles satisfy the following formula (1): 0.3≦(B / A)<1.7 (1) (8) In the sealing film for battery cells, the heat seal layer is composed of an intermediate layer containing only the water-dispersible polyolefin-based resin and a surface layer laminated on the intermediate layer containing the water-dispersible polyolefin-based resin and the fine particles, or is composed of only the surface layer, and the content of the fine particles in the heat seal layer is less than 10% by weight. The sealing film for battery cells according to any one of (1) to (7) above. (9) The sealing film for a battery cell according to any one of (1) to (8) above, which is a film for sealing a semi-solid battery cell or an all-solid battery cell.

[0010] Furthermore, the present invention can be summarized as the following battery cell sealing films (10) to (14). (10) The heat seal layer is formed by applying a coating material constituting the heat seal layer onto the substrate, a sealing film for a battery cell according to any one of (1) to (9) above. (11) The sealing film for battery cells according to any one of (1) to (10) above, wherein the substrate contains a resin selected from the group consisting of polyester-based resins, polyamide-based resins, and polyolefin-based resins, or has a thickness of 5 to 100 μm. (12) The sealing film for a battery cell according to any one of (1) to (11) above, wherein the fine particles are spherical or ellipsoidal. (13) The sealing film for a battery cell according to any one of (1) to (12) above, wherein the organic fine particles are crosslinked organic fine particles. (14) The sealing film for a battery cell according to any one of (1) to (13) above, wherein the content of the fine particles in the heat seal layer is less than 30% by weight. [Effects of the Invention]

[0011] In the present invention, the heat-sealing layer contains a water-dispersible polyolefin resin, which allows the layer to be thinner than conventional layers, and the heat-sealing layer contains fine particles, which improves the slipperiness and suppresses blocking. Furthermore, in the present invention, even if the heat-sealing layer contains fine particles, the adhesion between the heat-sealing layers can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a battery module according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing a battery cell according to an embodiment of the present invention. [Figure 3] 1 is a schematic diagram for explaining the configuration of a battery cell according to an embodiment of the present invention; [Figure 4]1 is a cross-sectional view showing a sealing film for a battery cell according to an embodiment of the present invention. [Figure 5] FIG. 10 is a cross-sectional view showing a sealing film for a battery cell according to another embodiment. [Figure 6] 1 is a table summarizing test results in this example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the present invention will be described below. The present invention relates to a battery cell sealing film constituting a battery cell, particularly to a battery cell sealing film for manufacturing a single-type battery cell or a battery cell sealing film for manufacturing a bi-cell battery cell. The single-type battery cell is a battery cell manufactured by sealing a unit cell assembly including a single anode, a single cathode, and a single separator. The bi-cell battery cell is a battery cell manufactured by sealing a unit cell assembly including a double-sided anode (including an anode current collector and an anode electrolyte disposed on both sides of the anode current collector) and two single-sided cathodes (including a first cathode current collector and a first cathode electrolyte disposed on the first cathode current collector, and a second cathode current collector and a second cathode electrolyte disposed on the second cathode current collector) disposed on each side of the double-sided anode, or a unit cell assembly including a double-sided cathode and two single-sided anodes disposed on each side of the double-sided cathode. In the following, the present invention will be described by taking as an example a battery module 100 of a lithium ion semi-solid battery made up of a single battery cell.

[0014] Fig. 1 is a configuration diagram showing a battery module 100 according to this embodiment. As shown in Fig. 1, the battery module 100 according to this embodiment has a configuration in which a plurality of battery cells 200 are stacked in order to increase electrical capacity, reduce weight, and reduce size. As shown in Fig. 1, the battery module 100 includes tab connection parts 110 that connect the tabs of each battery cell 200 to external tabs 120, and these external tabs 120 electrically connect the battery module 100 to an external circuit.

[0015] FIG. 2 is a cross-sectional view of a battery cell 200 according to this embodiment. FIG. 3 is a schematic diagram for explaining the configuration of the battery cell 200 according to this embodiment, and is an enlarged view showing the same cross section as FIG. 2. As shown in FIGS. 2 and 3, the battery cell 200 has an anode 2, a cathode 3, a separator 4, and a pair of battery cell sealing films 1. In this embodiment, as shown in FIG. 2, a combination of a single anode 2, a single cathode 3, and a single separator 4 is referred to as a unit cell assembly 5, and the battery cell 200 is configured by sealing the unit cell assembly 5 with a pair of battery cell sealing films 1.

[0016] The configuration of the unit cell assembly 5 can be similar to known unit cell assemblies for lithium-ion semi-solid batteries. That is, the anode 2 comprises an anode current collector 201 and an anode electrolyte 202, and transmits electricity generated in the anode electrolyte 202 to the anode-side tab (electrode) through the anode current collector 201. The cathode 3 also comprises a cathode current collector 301 and a cathode electrolyte 302, and transmits electricity generated in the cathode electrolyte 302 to the cathode-side tab (electrode) through the cathode current collector 301.

[0017] The anode current collector 201 and the cathode current collector 301 may have a known configuration. For example, the anode current collector 201 and the cathode current collector 301 may be in the form of a substrate, a sheet, or a foil. The anode current collector 201 and the cathode current collector 301 may include a conductive material. For example, the anode current collector 201 and the cathode current collector 301 may include aluminum, copper, lithium, nickel, stainless steel, tantalum, titanium, tungsten, vanadium, or a mixture, combination, or alloy thereof. The anode current collector 201 and the cathode current collector 301 may also include a non-metallic material such as carbon, carbon nanotubes, or a metal oxide (e.g., TiN, TiB2, MoSi2, n-BaTiO3, Ti2O3, ReO3, RuO2, IrO2, etc.). Additionally, the anode current collector 201 and the cathode current collector 301 can be constructed with conductive coatings, including carbon-based materials such as composites or layered materials, conductive metals, and / or non-metallic materials.

[0018] The anode electrolyte 202 can be of known construction, including, for example, carbon-based materials such as hard carbon, carbon nanotubes, carbon nanofibers, porous carbon, and graphene. In some embodiments, the anode electrolyte 202 is made of spinel Li4Ti5O 12The materials may include titanium-based oxides such as titanium dioxide (TiO, titania), silicon monoxide (LTO), and titanium dioxide (TiO, titania). Some embodiments include alloyed or dealloyed materials such as silicon, silicon monoxide (SiO), germanium, and tin oxide (SnO). Some embodiments include transition metal compounds (e.g., oxides, phosphides, sulfides, nitrides, etc.). Some embodiments may include amorphous carbon, disordered carbon, graphitic carbon, or metal-coated or metal-decorated carbon, graphite, non-graphitic carbon, mesocarbon microbeads, boron-carbon alloys, hard or disordered carbon, lithium titanium spinel, or solid metals or metalloids or metalloid alloys that react with lithium to form electron compounds, such as, for example, Si, Ge, Sn, Bi, Zn, Ag, Al, any other suitable metal alloy, metalloid alloy, or combinations thereof, or lithiated metals or metal alloys, or lithiated or non-lithiated compositions, or amorphous metal alloys of any other material or alloy thereof. In some embodiments, the anode material can include intermetallic compounds (based on the formula MM', where M is one metal element and M' is a different metal element), such as CuSb, LiCuSb, and LiSb. In some embodiments, the anode material can be made porous to increase the surface area and enhance the lithium intercalation rate of the resulting electrode.

[0019] The cathode electrolyte 302 can be any known material, such as nickel cobalt aluminum (NCA), core-shell gradient (CSG), spinel-based lithium ion (LMO), lithium iron phosphate (LFP), cobalt-based lithium ion (LCO), and nickel cobalt manganese (NCM). In some embodiments, it can include solid-state compounds such as nickel metal hydride (NiMH) batteries and nickel cadmium (NiCd). In some embodiments, it can include solid-state compounds such as D-NaFeO and Li(Ni, Mn, Co)O, LiMnO and its derivatives, which have a spinel structure, so-called "layered spinel nanocomposites" whose structures include nanoscopic domains with ordered rock salt and spinel order, olivine LiMPO (where M includes one or more of Mn, Fe, Co, or Ni) and its derivatives, partially fluorinated compounds such as LiVPOF, other "polyanionic" compounds discussed below, and VO and VO. 11 In some embodiments, the lithium transition metal phosphate material has an overall composition of Li1-x-zM1+zPO4, where M is at least one first-row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, and Ni, x is between 0 and 1, and z can be positive or negative. In some embodiments, the material includes a metal salt that stores alkali ions by undergoing a substitution or conversion reaction. In some embodiments, the material includes a solid, such as an organic redox compound. In some embodiments, the material includes a solid selected from the group consisting of ordered rock salt compounds, LiMO2, such as those having the α-NaFeO2 and orthorhombic LiMnO2 structure types, or derivatives thereof with different crystal symmetries, atomic ordering, or partial substitution of the metal or oxygen.

[0020] Separator 4 can be a thin, microporous membrane that electrically separates cathode 3 from anode 2 but allows ions to pass through its pores between the two electrodes during discharge and charge. In some embodiments, separator 4 comprises a thermoplastic polymer, such as polyolefin, polyvinyl chloride, nylon, fluorocarbon, and polystyrene, among others. In some embodiments, separator 4 comprises a polyolefin material, including, for example, polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutene, polymethylpentene, polyisoprene, copolymers thereof, and combinations thereof. Exemplary combinations can include, but are not limited to, blends comprising two or more of polyethylene, ultra-high molecular weight polyethylene, and polypropylene, as well as blends of the above with copolymers such as ethylene butene copolymers and ethylene hexene copolymers.

[0021] FIG. 4 is a diagram showing a cross-sectional view of a battery cell sealing film 1. As shown in FIG. 4, the battery cell sealing film 1 is composed of a substrate 10 and a heat seal layer 20. More specifically, the battery cell sealing film 1 is formed by applying a coating material that constitutes the heat seal layer 20 onto the substrate 10 and drying the coating material. Note that a series of steps for producing the battery cell sealing film 1 can be performed by coating processes such as wire bar coating, dipping, spraying, spin coating, roll coating, gravure coating, air knife coating, curtain coating, slide coating, and extrusion coating. The battery cell sealing film 1 according to this embodiment will be described in detail below.

[0022] The substrate 10 can be made of a material such as a resin commonly used in sealing films for battery cells. For example, polyester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyamide-based resins such as nylon 6, nylon 6,6, and nylon 12, and polyolefin-based resins such as polypropylene and polyethylene can be used. In this embodiment, PET resin is used. The substrate may be a uniaxially or biaxially stretched film. The thickness of the substrate can be appropriately designed depending on the application, and is not particularly limited, but is, for example, 5 to 100 μm, preferably 7 to 50 μm, and more preferably 10 to 30 μm.

[0023] The heat seal layer 20 softens when heated, and has the property of bonding not only the heat seal layers 20 together but also the current collectors 201, 301. In this embodiment, as shown in Fig. 4, the heat seal layer 20 contains a matrix 21 made of a water-dispersible polyolefin resin and fine particles 22, and has a configuration in which the fine particles 22 are dispersed in the matrix 21 made of the water-dispersible polyolefin resin. Fig. 4 is a cross-sectional view showing a sealing film 1 for a battery cell according to this embodiment.

[0024] As shown in FIG. 5, the heat seal layer 20 may also have a configuration including an intermediate layer 210 and a surface layer 220 laminated on the intermediate layer 210. FIG. 5 is a cross-sectional view showing a battery cell sealing film 1 according to another embodiment. The intermediate layer 210 is a layer laminated on the substrate 10, has a matrix 21 made of a water-dispersible polyolefin-based resin, and does not contain microparticles 22. Similarly to the heat seal layer 20 shown in FIG. 4, the surface layer 220 contains the matrix 21 made of a water-dispersible polyolefin-based resin and microparticles 22, with the microparticles 22 dispersed in the matrix 21 made of the water-dispersible polyolefin-based resin. Although not shown, in yet another embodiment, the intermediate layer 210 may contain microparticles 22, or the intermediate layer 210 may be a multilayer structure of two or more layers. Furthermore, since the heat seal layer 20 shown in FIG. 4 has a configuration in which the intermediate layer 210 has been removed from the heat seal layer 20 shown in FIG. 5, the heat seal layer 20 according to this embodiment can also be regarded as the surface layer 220, as shown in FIG.

[0025] In the heat seal layer 20 according to this embodiment, the water-dispersible polyolefin resin is used as the matrix 21, so that the heat seal layer 20 can be formed by coating. This allows the thickness of the heat seal layer 20 to be thinner than when a conventional thermoplastic polyolefin resin is formed by extrusion lamination.

[0026] Water-dispersible polyolefin resins are polyolefin resins that have been modified with components derived from unsaturated carboxylic acids and / or their anhydrides to introduce hydrophilic functional groups such as carboxyl groups, making them water-soluble. The olefin component in the polyolefin resin is not particularly limited, and known olefins can be used. Typical basic units include ethylene, propylene, butene, etc., and polymers of these or copolymers of multiple components form the main skeleton of the olefin component.

[0027] The water-dispersible polyolefin resin is preferably a polyethylene polymer containing an ethylene component and a component derived from an unsaturated carboxylic acid and / or its anhydride, or a polypropylene polymer containing a propylene component and a component derived from an unsaturated carboxylic acid and / or its anhydride. When the water-dispersible polyolefin resin is the polyethylene polymer or the polypropylene polymer, the proportion of the component derived from the unsaturated carboxylic acid and / or its anhydride is preferably 0.01% by weight or more and 5% by weight or less of the total water-dispersible polyolefin resin.

[0028] The ethylene content of the polyethylene polymer is preferably 50% by mass to 95% by mass, more preferably 55% by mass to 94.5% by mass, and the propylene content of the polypropylene polymer is preferably 50% by mass to 95% by mass, more preferably 55% by mass to 94.5% by mass.

[0029] Examples of unsaturated carboxylic acids contained in polyethylene polymers and polypropylene polymers include (meth)acrylic acid, maleic acid, itaconic acid, fumaric acid, and crotonic acid. Polyethylene polymers and polypropylene polymers can contain two or more components derived from unsaturated carboxylic acids and / or their acid anhydrides.

[0030] The polyethylene polymer and polypropylene polymer may contain components (other components) other than the ethylene component, the propylene component, and the unsaturated carboxylic acid component. Examples of the other components include 1-butene, isobutene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-hexene, 1-octene, butadiene, isoprene, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, dimethyl maleate, diethyl maleate, dibutyl maleate, methyl vinyl ether, ethyl vinyl ether, vinyl formate, vinyl acetate, and vinyl propionate.

[0031] The acid value of the polyethylene polymer and polypropylene polymer is preferably 5 mgKOH / g or more and 50 mgKOH / g or less, and more preferably 7 mgKOH / g or more and 40 mgKOH / g or less, which can improve aqueous dispersibility.

[0032] The viscosity of the water-dispersible polyolefin resin is not particularly limited, but is preferably 100 mPa·s or more at 25°C.

[0033] Here, in a battery cell sealing film in which a heat seal layer is formed only from a water-dispersible polyolefin resin, the heat seal layer has low slipperiness, and when the battery cell sealing film is rolled up, the heat seal layer of the lower battery cell sealing film may come into close contact with the base material of the upper battery cell sealing film, causing blocking of the roll film and resulting in poor appearance such as wrinkles. A roll film in which blocking has occurred cannot be smoothly unwound, making it impossible to continuously seal unit cell assemblies, resulting in reduced productivity. In addition, a battery cell sealing film in which poor appearance such as wrinkles has occurred may cause gaps to form between the battery cell sealing films or between the battery cell sealing film and the current collectors 201, 301 when sealing the unit cell assemblies 5 with the battery cell sealing film, making it impossible to seal the unit cell assemblies 5. Therefore, in order to improve the slipperiness of the battery cell sealing film 1, the heat seal layer 20 of this embodiment contains fine particles 22 in the heat seal layer 20 (in the case where the heat seal layer 20 is composed of a surface layer 220 and an intermediate layer 210 as shown in Figure 5, the surface layer 220).

[0034] In this embodiment, the microparticles 22 are preferably spherical, but may also be ellipsoidal or other shapes. Furthermore, the microparticles 22 are preferably water-dispersible. The microparticles 22 may be inorganic or organic. Examples of inorganic microparticles include inorganic oxides such as amorphous silica, titanium, alumina, and zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Examples of organic microparticles include silicone-based resins, fluorine-based resins, (meth)acrylic resins, and (meth)acrylonitrile-based resins. For example, when preventing metal contamination is important, organic microparticles are preferably used. Furthermore, crosslinked organic microparticles are preferred because they have excellent blocking suppression, excellent adhesiveness, and improved heat seal strength. Examples of crosslinked organic microparticles include crosslinked polymethyl methacrylate (PMMA), crosslinked polybutyl methacrylate, crosslinked acrylic esters, and crosslinked methyl methacrylate-styrene copolymers. In addition to the above organic particles, organic particles of crosslinked polystyrene, silicone, polystyrene, polycarbonate, acrylic styrene, benzoguanamine, melamine, polyolefin, polyester, polyamide, polyimide, polyethylene fluoride, etc. can also be used.

[0035] Furthermore, in the heat seal layer 20 according to this embodiment, the size of the fine particles 22 is preferably 0.5 to 10.0 μm, more preferably 1.0 to 8.0 μm, even more preferably 1.5 to 6.0 μm, and particularly preferably 2.0 to 5.0 μm, in terms of average primary particle diameter. When the average primary particle diameter of the fine particles 22 is within the above range, the sealing film 1 for a battery cell has an excellent ability to suppress blocking between the particles. Furthermore, during the production of the battery cell 200, when the semi-solid electrode slurry is dispensed onto the current collector, the current collector may be damaged (wrinkled, folded, torn, etc.) because the current collector is a thin film. Therefore, the sealing film 1 for a battery cell may be required to improve the handleability of the current collector 201, 301 by adhering to the current collector 201, 301 and physically supporting the current collector 201, 301. By setting the average primary particle diameter of the fine particles 22 in the above range, the heat seal layer 20 according to this embodiment can also improve adhesion to the current collectors 201, 301. In particular, the smaller the average primary particle diameter of the fine particles 22, the better the adhesion of the heat seal layer 20 to the current collectors 201, 301 can be.

[0036] The content of the microparticles 22 in the heat seal layer 20 is preferably less than 30% by weight of the entire heat seal layer 20, more preferably 20% by weight or less, even more preferably 15% by weight or less, and particularly preferably 10% by weight or less. When the heat seal layer 20 is composed of a surface layer 220 and an intermediate layer 210 as shown in FIG. 5 , the content of the microparticles in the surface layer 220 is preferably less than 15% by weight of the entire surface layer 220, more preferably 10% by weight or less. By setting the content of the microparticles 22 within the above range, the adhesion between the heat seal layers 20 and the adhesion of the heat seal layer 20 to the current collectors 201 and 301 can be improved. The content of the microparticles 22 in the intermediate layer 210 may be the same as the content of the microparticles in the surface layer 220, but the content of the microparticles 22 in the intermediate layer 210 is preferably less than that in the surface layer 220.

[0037] Furthermore, the adhesiveness between the heat-seal layers 20 and the adhesiveness of the heat-seal layers 20 to the current collectors 201 and 301 are affected not only by the size of the microparticles 22 but also by the thickness of the heat-seal layers 20, so the thickness of the heat-seal layers 20 is preferably 0.5 to 10.0 μm, more preferably 1.0 to 8.0 μm, even more preferably 1.5 to 6.0 μm, and particularly preferably 1.5 to 4.5 μm. Furthermore, from the viewpoint of the adhesiveness of the heat-seal layers 20 to the current collectors 201 and 301, the thickness of the heat-seal layers 20 is preferably greater than 1 μm, and more preferably greater than 2 μm. 5, when the heat seal layer 20 is composed of a surface layer 220 and an intermediate layer 210, the overall thickness of the heat seal layer 20 is preferably 0.5 to 10.0 μm, more preferably 1.0 to 8.0 μm, even more preferably 1.5 to 6 μm, and particularly preferably 1.5 to 4.5 μm. In this case, the thicknesses of the surface layer 220 and the intermediate layer 210 are each preferably 0.5 to 5.0 μm, more preferably 0.7 to 4.0 μm, even more preferably 0.8 to 3.0 μm, and particularly preferably 1.0 to 2.5 μm.

[0038] In particular, from the viewpoint of the adhesion of the heat seal layer 20 to the current collectors 201 and 301, it is preferable to adjust the thickness A of the heat seal layer 20 and the average primary particle diameter B of the fine particles 22 so as to satisfy the relationship (B / A)<2.5, more preferably so as to satisfy the relationship 0.1≦(B / A)<1.7, and even more preferably so as to satisfy the relationship 0.3≦(B / A)≦1.5, where A is the total thickness of the heat seal layer 20 and B is the average primary particle diameter of the fine particles 22. If the thickness of the heat seal layer 20 and the average primary particle diameter of the fine particles 22 are within the above ranges, blocking occurring in the roll film can be effectively suppressed, and a battery cell sealing film 1 free from appearance defects such as wrinkles can be obtained. In addition, the heat sealability between the heat seal layers 20 of the battery cell sealing film 1 and the heat sealability between the heat seal layers 20 of the battery cell sealing film 1 and the current collectors 201 and 301 can also be excellent.

[0039] The thickness of the heat-seal layer 20 can be adjusted by adjusting the number of applications of the coating material that constitutes the heat-seal layer 20, or by adjusting the amount of coating material per application. When the heat-seal layer 20 is composed of a surface layer 220 and an intermediate layer 210, as shown in Fig. 5, the thickness of the heat-seal layer 20 can be adjusted by adjusting the thickness of the surface layer 220, but from an economical viewpoint such as cost, it is preferable to adjust the thickness of the intermediate layer 210.

[0040] The battery cell sealing film 1 may have other functional layers, if necessary, within the scope that does not impair the effects of the present invention. For example, a gas barrier layer such as a vapor deposition layer or a printed layer may be provided on either side of the substrate 10, or a metal layer or the like may be provided between the substrate 10 and the heat seal layer 20. [Example]

[0041] Examples of the present invention are described below. In these examples, a battery cell sealing film 1 was prepared having a heat seal layer 20 containing a matrix 21 made of a water-dispersible polyolefin resin and fine particles 22, and tests were conducted on the adhesion between the heat seal layers 20, the slipperiness of the heat seal layer 20, and the adhesion between the heat seal layer 20 and the current collectors 201 and 301. Note that Fig. 6 is a table showing the test results of this example, summarizing the test results for the adhesion between the heat seal layers 20, the slipperiness of the heat seal layer 20 relative to the substrate 10, and the adhesion of the heat seal layer 20 to the current collectors 201 and 301.

[0042] In this example, Arrowbase SD-1205J2 manufactured by Unitika Ltd. was used as the matrix 21 constituting the heat-seal layer 20. Furthermore, Techpolymer MB30X-5 manufactured by Sekisui Plastics Co., Ltd. (hereinafter referred to as cross-linked PMMA having an average primary particle diameter of 5 μm), Techpolymer MBX-2H manufactured by Sekisui Plastics Co., Ltd. (hereinafter referred to as cross-linked PMMA having an average primary particle diameter of 2.5 μm), or Seahoster KE-P250 manufactured by Nippon Shokubai Co., Ltd. (hereinafter referred to as amorphous silica having an average primary particle diameter of 2.5 μm) were used as the microparticles 22 constituting the heat-seal layer 20. Specifically, cross-linked PMMA having an average primary particle diameter of 5 μm was used as the microparticles 22 in Examples 1 to 5, cross-linked PMMA having an average primary particle diameter of 2.5 μm was used in Examples 6 to 10 and 14 to 18, and amorphous silica having an average primary particle diameter of 2.5 μm was used in Examples 11 to 13.

[0043] In this example, tests were conducted by changing the thickness of the heat-seal layer 20 and the amount of microparticles 22 added. When the thickness of the heat-seal layer 20 was 2 μm or more, a heat-seal layer 20 having an intermediate layer 210 and a surface layer 220 was formed, as shown in FIG. 5 . Specifically, when the thickness of the heat-seal layer 20 was 2 μm or more, an emulsion containing only the matrix 21 was applied by gravure coating to the adhesive layer surface of a 50 μm-thick PET film (Cosmoshine A4160, manufactured by Toyobo Co., Ltd.) serving as the substrate 10, and then dried at 100°C for a time period (30 to 120 seconds) depending on the thickness, thereby forming the intermediate layer 210. Then, an emulsion containing the matrix 21 and microparticles 22 was applied to the formed intermediate layer 210 to a thickness of 1 μm and dried at 100°C for 30 seconds to form the surface layer 220, thereby forming the heat-seal layer 20. Furthermore, when forming a 5 μm thick heat seal layer 20, first a 4 μm thick intermediate layer 210 was formed, and then a 1 μm thick surface layer 220 was laminated on top to form a 5 μm thick heat seal layer 20 overall. Similarly, when forming an 8 μm thick heat seal layer 20, first a 7 μm thick intermediate layer 210 was formed, and then a 1 μm thick surface layer 220 was laminated on top to form a 8 μm thick heat seal layer 20 overall. Note that when forming a 1 μm thick heat seal layer 20, the intermediate layer 210 was not formed, and only the 1 μm thick surface layer 220 was formed, thereby forming a 1 μm thick heat seal layer 20 overall.

[0044] In this example, heat seal layers not containing the fine particles 22 were prepared as Comparative Examples 1 to 5. In Comparative Example 1, the thickness of the heat seal layer was 1 μm, in Comparative Example 2, the thickness of the heat seal layer was 2 μm, in Comparative Example 3, the thickness of the heat seal layer was 3 μm, in Comparative Example 4, the thickness of the heat seal layer was 5 μm, and in Comparative Example 1, the thickness of the heat seal layer was 8 μm.

[0045] Meanwhile, in Examples 1 to 5, crosslinked PMMA having an average primary particle size of 5 μm was added in an amount of 5 wt % of the entire surface layer 220, and the heat-seal layer 20 was formed to have a thickness of 1 μm, 2 μm, 3 μm, 5 μm, or 8 μm. Furthermore, in Examples 6 to 10, crosslinked PMMA having an average primary particle size of 2.5 μm was added in an amount of 5 wt % of the entire surface layer 220, and the heat-seal layer 20 was formed to have a thickness of 1 μm, 2 μm, 3 μm, 5 μm, or 8 μm. Furthermore, in Examples 11 to 13, amorphous silica having an average primary particle size of 2.5 μm was added in an amount of 5 wt % of the entire surface layer 220, and the heat-seal layer 20 was formed to have a thickness of 1 μm, 3 μm, or 5 μm. In addition, in Examples 14 to 18, cross-linked PMMA with an average primary particle size of 2.5 μm was added in amounts of 1 wt%, 3 wt%, 5 wt%, 7 wt%, and 10 wt%, respectively, relative to the entire surface layer 220, and the heat seal layer 20 was formed to a thickness of 2 μm.

[0046] In this example, the number of samples in each of Comparative Examples 1 to 5 and Examples 1 to 18 was three, and the adhesion between the heat seal layers 20, the slipperiness, and the adhesion to the current collectors 201 and 301 were calculated as the average values ​​of the three samples. In this example, although the conditions were the same for Examples 7 and 16, three samples were separately produced and the adhesion between the heat seal layers 20, the slipperiness, and the adhesion to the current collectors 201 and 301 were measured, so there are slight differences in the values ​​of the adhesion between the heat seal layers 20, the slipperiness, and the adhesion to the current collectors 201 and 301.

[0047] (Adhesion between heat seal layers) 6, the column "Adhesion (to heat seal layer)" shows the test results of the adhesion between the heat seal layers of Comparative Examples 1 to 5 and Examples 1 to 18. In these examples, a pair of battery cell sealing films was tested using a heat seal tester (manufactured by Tester Sangyo Co., Ltd., product name "TP701-B") at a seal width of 10 mm, a temperature of 170°C, and a pressure of 4.2 kg / cm so that the heat seal layers of Comparative Examples 1 to 5 and Examples 1 to 18 would adhere to each other. 2The pair of sealed battery cell sealing films was cut into 15 mm wide test pieces, and the peel strength of the test pieces was measured as the adhesion between the heat seal layers at a peel rate of 40 mm / min using an autograph (Shimadzu Corporation, Autograph AGS-500NX).

[0048] As shown in Fig. 6, in all of Comparative Examples 1 to 5 and Examples 1 to 18, the peel strength was high, at 2.2 (N / 15 mm) or more, and it was found that the adhesiveness between the heat-seal layers was at a practical level. Also, as shown in Fig. 6, it was found that the peel strength between the heat-seal layers 20 tended to be higher in Examples 1 to 18, which contained microparticles 22, compared to Comparative Examples 1 to 5, which did not contain microparticles 22. Furthermore, it was found that even when the same amount of microparticles 22 was added, the thicker the heat-seal layer 20 was and the greater the amount of microparticles 22 added, the higher the peel strength between the heat-seal layers 20 was. Initially, there was concern that the inclusion of microparticles 22 would reduce the adhesiveness between the heat-seal layers 20, but it was found that even when the content of microparticles 22 was increased, the adhesiveness between the heat-seal layers 20 was not impaired.

[0049] (About slipperiness) In this example, the slipperiness (blocking suppression) of the heat seal layer 20 relative to the substrate 10 was also tested. Specifically, a pair of battery cell sealing films was overlapped so that one heat seal layer contacted the other substrate 10, and the battery cell sealing films were rubbed together. An evaluator then sensorily evaluated whether the battery cell sealing films slipped. The evaluator was involved in the development of battery cell sealing films and had specialized knowledge about battery cell sealing films. Specifically, the battery cell sealing films were rubbed together, and if the battery cell sealing film 1 slipped, the slipperiness of the heat seal layer was evaluated as "good." If the battery cell sealing film 1 did not slip, the slipperiness of the heat seal layer was evaluated as "poor." As shown in FIG. 6, in Comparative Examples 1 to 5 in which the heat seal layer did not contain the fine particles 22, the slipperiness of the heat seal layer was evaluated as "poor." In addition, in Example 14, which contained 1% by weight of crosslinked PMMA with an average primary particle size of 2.5 μm, the battery cell sealing film was not slippery, and the slipperiness of the heat seal layer was evaluated as "△", which was relatively poor. In contrast, in the other Examples 1 to 13 and 15 to 18, the battery cell sealing film was slippery, and the slipperiness of the heat seal layer was evaluated as "○", which was good.

[0050] (Adhesion to current collector) Furthermore, in this example, the adhesiveness of the heat seal layer 20 to the current collectors 201 and 301 was tested. Specifically, the battery cell sealing films according to Comparative Examples 1 to 5 and Examples 1 to 18 were overlapped with aluminum foil (Aluminum Haku C, 70 μm thick, manufactured by Toyo Aluminum K.K.) as a current collector so that the heat seal layer and the glossy side of the aluminum foil were adhered, and then laminated using a desktop laminator (product name "SA-1010" manufactured by Tester Sangyo Co., Ltd.) at 100°C and a speed of 1 mm / min, and then 15 mm wide test pieces were cut out. The test pieces were then peeled at a peel speed of 40 mm / min using an autograph (Autograph AGS-500NX manufactured by Shimadzu Corporation), and the peel strength was measured.

[0051] 6, in Comparative Examples 1 to 5, the heat seal layer not containing the fine particles 22 had high peel strength to the aluminum foil, indicating that the heat seal layer had adhesiveness to the aluminum foil. On the other hand, in Examples 1, 2, 6, and 11, the peel strength to the aluminum foil serving as the current collector was 0 (N / 15 mm), indicating that no adhesiveness was obtained. Also, in Example 3, the peel strength to the aluminum foil serving as the current collector was low at 0.4 (N / 15 mm).

[0052] On the other hand, in Examples 4 to 5, 7 to 10, and 12 to 17, the adhesiveness (peel strength) of the heat seal layer 20 to the current collector was 0.9 (N / 15 mm) or more, and it was found that the adhesiveness could support the current collectors 201, 301 and improve the handleability of the current collectors 201, 301. In particular, as shown in Fig. 6, the adhesiveness of the heat seal layer 20 to the current collectors 201, 301 tended to be better as the fine particles 22 were smaller and also tended to be better as the heat seal layer 20 was thicker.

[0053] Therefore, as shown in FIG. 6, the average primary particle diameter (μm) of the fine particles 22 was defined as B, and the thickness of the heat-seal layer 20 as A. B / A was calculated, and the correlation with the evaluation of the adhesiveness (peel strength) of the heat-seal layer 20 to the current collector was examined. As a result, when B / A, which indicates the relationship between the average primary particle diameter (μm) B of the fine particles 22 and the thickness A of the heat-seal layer 20, was 2.5 or more, the adhesiveness of the heat-seal layer 20 to the current collector was evaluated as "×". When B / A was less than 2.5 and 1.7 or more, the adhesiveness of the heat-seal layer 20 to the current collector was evaluated as "△". When B / A was less than 1.7, the adhesiveness of the heat-seal layer 20 to the current collector was evaluated as "○". Thus, it was found that the adhesion of the heat seal layer 20 to the current collector 201, 301 is better as the size of the microparticles 22 is smaller and as the thickness of the heat seal layer 20 is thicker, and is particularly good when the average primary particle diameter B of the microparticles 22 / thickness A of the heat seal layer 20 is less than 2.5, more preferably less than 1.7.

[0054] In Example 18, although B / A was "1.3" less than 1.7, the adhesion (peel strength) of the heat seal layer 20 to the current collector was relatively low at 0.5 (N / 15 mm). This is thought to be because in Example 18, the amount of fine particles 22 added to the entire heat seal layer 20 was as high as 10 wt%. Therefore, it is thought that the adhesion of the heat seal layer 20 to the current collector can be improved by setting the content of the fine particles 22 to less than 15 wt%, preferably 10 wt% or less, of the entire heat seal layer 20.

[0055] As described above, the battery cell sealing film 1 according to this embodiment includes the substrate 10 and the heat seal layer 20. The heat seal layer 20 includes the matrix 21 made of a water-dispersible polyolefin resin and the microparticles 22. In this manner, in this embodiment, the use of the matrix 21 made of a water-dispersible polyolefin resin allows the heat seal layer 20 to be formed by coating. This makes it possible to reduce the thickness of the battery cell sealing film 1 compared to conventional cases where a thermoplastic polyolefin resin is formed by extrusion lamination, and also allows the microparticles 22 to be appropriately dispersed in the heat seal layer 20. Furthermore, the battery cell sealing film 1 according to this embodiment contains the microparticles 22, which can enhance the slipperiness of the heat seal layer 20. As a result, blocking of the battery cell sealing film 1 can be suppressed, and the occurrence of wrinkles when the battery cell sealing film 1 is rolled can be suppressed.

[0056] On the other hand, in the battery cell sealing film 1 according to this embodiment, the heat seal layer 20 contains the fine particles 22, and therefore there is a concern that the fine particles 22 may reduce the adhesiveness between the heat seal layers 20. However, in the battery cell sealing film 1 according to this embodiment, even when the fine particles 22 are added to the heat seal layer 20, the adhesiveness between the heat seal layers 20 is not impaired and can be improved.

[0057] Furthermore, in conventional battery cell manufacturing, the current collectors 201 and 301 are thin films, and thus there is a risk that the current collectors may be damaged (wrinkled, folded, torn, etc.) when a semi-solid electrode slurry is distributed onto the current collectors. To prevent such damage to the current collectors, the battery cell sealing film 1 is adhered to the current collectors 201 and 301 to physically support the current collectors 201 and 301, thereby improving the handleability of the current collectors 201 and 301. Therefore, the battery cell sealing film 1 according to this embodiment is required to have good adhesion between the heat seal layers 20 and also good adhesion between the heat seal layers 20 and the current collectors 201 and 301. In this regard, the battery cell sealing film 1 according to this embodiment can improve the adhesion of the heat seal layer 20 to the current collectors 201 and 301 by setting the average primary particle diameter of the fine particles 22 to less than 6 μm or by setting the thickness of the heat seal layer 20 to more than 2 μm. Furthermore, by adjusting the thickness A (μm) of the heat seal layer 20 and the average primary particle diameter B (μm) of the fine particles so that the relationship (B / A) < 2.5, more preferably the relationship 0.3 ≦ (B / A) < 1.7, and even more preferably the relationship 0.3 ≦ (B / A) ≦ 1.5, the adhesion of the heat seal layer 20 to the current collectors 201, 301 can be further improved. In addition, by setting the content of the fine particles 22 in the entire heat seal layer 20 to less than 15 wt %, more preferably 10 wt % or less, and even more preferably less than 10 wt %, the adhesion of the heat seal layer 20 to the current collectors 201, 301 can be further improved.

[0058] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the above-described embodiments. Various modifications and improvements can be made to the above-described embodiments, and such modifications and improvements are also included in the technical scope of the present invention.

[0059] For example, in the above-described embodiment, the heat-seal layer 20 is formed by applying a coating material (an emulsion containing the matrix 21, or an emulsion containing the matrix 21 and the microparticles 22) for forming the heat-seal layer 20 onto the substrate 10 and drying it, but in this case, the heat-seal layer 20 may be formed by applying the coating material only once, or the heat-seal layer 20 may be formed to a desired thickness by overlapping multiple coating materials. Furthermore, an adhesive layer may be provided between the heat-seal layer 20 and the substrate 10.

[0060] In the above-described embodiment, the heat seal layer 20 consisting only of the surface layer 220 as shown in Fig. 4 has been described as an example, but when the heat seal layer 20 is composed of the surface layer 220 and the intermediate layer 210 as shown in Fig. 5, the surface layer 220 shown in Fig. 5 can be composed of the same composition and blend as the surface layer 220 shown in Fig. 4. Also, when the heat seal layer 20 is composed of the surface layer 220 and the intermediate layer 210 as shown in Fig. 5, the same substrate 10 as in the case of having the heat seal layer 20 consisting only of the surface layer 220 as shown in Fig. 4 can be used.

[0061] Furthermore, in the above-described embodiment, the heat seal layer 20 consisting only of the surface layer 220 as shown in FIG. 4 has been described as an example. However, even when the heat seal layer 20 is composed of the surface layer 220 and the intermediate layer 210 as shown in FIG. 5, it is preferable to adjust the thickness A of the heat seal layer 20 and the average primary particle diameter B of the fine particles 22 so that the thickness A of the entire heat seal layer 20 (the thickness of the surface layer 220 + the thickness of the intermediate layer 210) and the average primary particle diameter B of the fine particles contained in the surface layer 220 satisfy the relationship (B / A)<2.5, more preferably so that the relationship 0.1≦(B / A)<1.7, and even more preferably so that the relationship 0.3≦(B / A)≦1.5 is satisfied. [Explanation of symbols]

[0062] 100...Battery module 200...Battery cells 2...Anode 201...Anode current collector 202...Anode electrolyte 3...Cathode 301...Cathode current collector 302...Cathode electrolyte 4...Separator 5...Unit cell assembly 1...Battery cell sealing film 10...Base material 20...Heat seal layer 210...middle class 21...The Matrix 220…surface layer 21...The Matrix 22...Fine particles 110...Tab connection 120...External tab

Claims

1. It has a substrate and a heat seal layer, The heat seal layer includes a water-dispersible polyolefin resin and fine particles.

2. The battery cell sealing film according to claim 1 , wherein the fine particles are organic fine particles.

3. The battery cell sealing film according to claim 2 , wherein the organic fine particles are crosslinked polymethyl methacrylate.

4. The sealing film for battery cells according to claim 1 , wherein the heat seal layer is a thin film having a thickness of 10 μm or less.

5. 2. The battery cell sealing film according to claim 1, wherein the fine particles have an average primary particle diameter of 0.5 to 10.0 μm.

6. The sealing film for battery cells according to claim 1 , wherein the heat seal layer has a thickness of more than 2 μm, and the fine particles have an average primary particle diameter of less than 6 μm.

7. 2. The sealing film for a battery cell according to claim 1, wherein a thickness A (μm) of the heat seal layer and an average primary particle diameter B (μm) of the fine particles satisfy the following formula (1): 0.3≦(B / A)<1.7...(1)

8. The heat seal layer is The film is composed of an intermediate layer containing only the water-dispersible polyolefin resin, and a surface layer laminated on the intermediate layer and containing the water-dispersible polyolefin resin and the fine particles, or It is composed of only the surface layer, The sealing film for a battery cell according to claim 1 , wherein the content of the fine particles in the heat seal layer is less than 10% by weight.

9. The battery cell sealing film according to claim 1 , which is for sealing a semi-solid battery cell or an all-solid battery cell.

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