Sealing film for battery cell

Abstract

To provide a sealing film for a battery cell which can be made thinner than a conventional one, has good slipperiness, can suppress blocking, and has good adhesiveness between heat seal layers.SOLUTION: The sealing film for a battery cell has a base material 10 and a heat seal layer 20, the heat seal layer 20 has fine particles 22, and the fine particles 22 protrude from the surface of the heat seal layer 20.SELECTED DRAWING: Figure 6

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 (11) battery cell sealing films. (1) A sealing film for a battery cell, comprising a substrate and a heat seal layer, the heat seal layer containing fine particles, the fine particles protruding from the surface of the heat seal layer. (2) The sealing film for battery cells according to (1) above, wherein 50% or more of the particles contained in the heat seal layer protrude from the surface of the heat seal layer. (3) The microparticles protruding from the surface of the heat seal layer have, on average, 1 / 4 or more of their surface area exposed from the surface of the heat seal layer, or protrude 0.5 μm or more in the height direction from the surface of the heat seal layer, in the sealing film for battery cells described in (1) or (2) above. (4) A sealing film for a battery cell, comprising a substrate and a heat seal layer, the heat seal layer having a multilayer structure, and of the multiple layers constituting the heat seal layer, the surface layer located on the opposite side from the substrate contains a water-dispersible polyolefin resin and fine particles. (5) The sealing film for a battery cell according to (4), wherein the heat seal layer has a layer that does not contain the fine particles below the surface layer. (6) The battery cell sealing film according to any one of (1) to (5) above, wherein the fine particles are crosslinked polymethyl methacrylate particles. (7) The sealing film for a battery cell according to any one of (1) to (6) above, wherein the content of the fine particles in the heat seal layer is less than 10% by weight. (8) The sealing film for a battery cell according to any one of the above (1) to (7), wherein the fine particles have an average primary particle diameter of 0.5 to 10.0 μm. (9) A sealing film for a battery cell according to any one of (1) to (8) above, wherein the thickness A (μm) of the entire 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) (10) The sealing film for a battery cell according to any one of (1) to (9) above, wherein the fine particles are monodisperse fine particles. (11) The sealing film for a battery cell according to any one of (1) to (10) 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 (12) to (20). (12) The sealing film for battery cells according to any one of (1) to (11), wherein the heat seal layer is formed by applying a coating material constituting the heat seal layer onto the substrate. (13) The sealing film for battery cells according to any one of (1) to (12) 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. (14) The sealing film for a battery cell according to any one of (1) to (13) above, wherein the fine particles are spherical or ellipsoidal. (15) The battery cell sealing film according to any one of (1) to (14) above, wherein the fine particles are organic fine particles. (16) The sealing film for a battery cell according to (15) above, wherein the organic fine particles are crosslinked organic fine particles. (17) The sealing film for a battery cell according to any one of (1) to (16) above, wherein the content of the fine particles in the heat seal layer is less than 30% by weight. (18) The sealing film for a battery cell according to any one of (1) to (17) above, wherein the heat seal layer is a thin film having a thickness of 10 μm or less. (19) The sealing film for a battery cell according to any one of (1) to (18) above, 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. (20) The heat seal layer is composed of an intermediate layer containing only the water-dispersible polyolefin resin and a surface layer laminated on the intermediate layer containing the water-dispersible polyolefin 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. In addition, the present invention can be summarized as the following roll film (21). (21) A roll film of the sealing film for battery cells according to any one of (1) to (20) above, wherein the sealing film for battery cells is wound so that the surface layer of the heat seal layer is in contact with the base material. [Effects of the Invention]

[0011] In the present invention, the heat seal layer contains fine particles, and the fine particles protrude from the heat seal layer, which improves the slipperiness of the battery cell sealing film, thereby suppressing blocking of the battery cell sealing film. Furthermore, in the present invention, even if the heat seal layer contains fine particles, the adhesion between the heat seal layers can be improved. Furthermore, in the present invention, the heat seal layer contains a water-dispersible polyolefin resin, which allows the battery cell sealing film to be thinner than conventional films. [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] FIG. 2 is a diagram showing an electron microscope photograph of the battery cell sealing film in the present example. [Figure 7] FIG. 10 is a diagram showing an electron microscope photograph of battery cell sealing films adhered to each other in this example. [Figure 8] 1 is a table summarizing the results of the adhesiveness test and the slippage test of the heat seal layer in this example. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described. The present invention relates to a battery cell sealing film constituting a battery cell, and 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. Here, Fig. 4 is a cross-sectional view showing the battery cell sealing film 1 according to this embodiment. As shown in Fig. 4, the heat seal layer 20 according to this embodiment can have a multilayer structure having an intermediate layer 210 and a surface layer 220 laminated on the intermediate layer 210.

[0024] The intermediate layer 210 is a layer laminated on the substrate 10, and has a matrix 21 made of a water-dispersible polyolefin resin, but does not contain fine particles 22. On the other hand, the surface layer 220 contains the matrix 21 made of a water-dispersible polyolefin resin and fine particles 22, and is configured such that the fine particles 22 are dispersed in the matrix 21 made of a water-dispersible polyolefin resin.

[0025] FIG. 5 is a cross-sectional view of battery cell sealing films 1a and 1b according to other embodiments. In the battery cell sealing film 1 shown in FIG. 4, the heat seal layer 20 has been described as having a two-layer structure consisting of an intermediate layer 210 and a surface layer 220. However, the battery cell sealing film according to the present invention is not limited to a two-layer structure and may have a three-layer structure as shown in FIGS. 5(A) and 5(B). For example, as shown in FIG. 5(A), a layer 230 containing fine particles 22 may be formed on an intermediate layer 210 not containing fine particles 22, and a surface layer 220 containing fine particles 22 may be formed on the layer 230. Alternatively, as shown in FIG. 5(B), a layer 240 not containing fine particles 22 may be formed on an intermediate layer 210 not containing fine particles 22, and a surface layer 220 containing fine particles 22 may be formed on the layer 230. The heat seal layer 20 may also have a multilayer structure of four or more layers.

[0026] Furthermore, 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The viscosity of the water-dispersible polyolefin resin is not particularly limited, but is preferably 100 mPa·s or more at 25°C.

[0034] Here, a battery cell seal film having a heat seal layer formed solely from a water-dispersible polyolefin resin has poor slipperiness of the heat seal layer. When the battery cell seal film is rolled up, the heat seal layer of the lower battery cell seal film may adhere to the substrate of the upper battery cell seal film, causing blocking of the roll film and resulting in poor appearance, such as wrinkles. A roll film with blocking cannot be smoothly unwound, preventing continuous sealing of unit cell assemblies, reducing productivity. Furthermore, a battery cell seal film with poor appearance, such as wrinkles, may cause gaps between the battery cell seal films or between the battery cell seal films and the current collectors 201, 301 when sealing the unit cell assemblies 5, potentially preventing the unit cell assemblies 5 from being sealed. Therefore, the heat seal layer 20 according to this embodiment contains fine particles 22 in the surface layer 220 of the heat seal layer 20 to enhance the slipperiness of the battery cell seal film 1. From another point of view, the heat seal layer 20 according to this embodiment contains the fine particles 22, and the fine particles 22 protrude from the surface layer 220, thereby improving the slipperiness of the battery cell sealing film 1.

[0035] 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.

[0036] 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.

[0037] Furthermore, 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. In this embodiment, the heat seal layer 20 contains the microparticles 22 in the surface layer 220, and the content of the microparticles 22 in the entire surface layer 220 is also preferably less than 15% by weight, more preferably 10% by weight or less. This is because, by setting the content of the microparticles 22 within the above range, the adhesiveness between the heat seal layers 20 and the adhesiveness of the heat seal layer 20 to the current collectors 201, 301 can be improved.

[0038] 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. Therefore, 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. 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. 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.

[0039] 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.

[0040] The thickness of the heat-seal layer 20 can be adjusted by adjusting the number of times the coating material constituting the heat-seal layer 20 is applied or by adjusting the amount of coating material per application. The surface layer 220 and the intermediate layer 210 can be made to have different thicknesses, and the thickness of the heat-seal layer 20 can be adjusted by adjusting the thickness of the surface layer 220. However, from an economical viewpoint such as cost, it is preferable to adjust the thickness of the heat-seal layer 20 by adjusting the thickness of the intermediate layer 210.

[0041] As described above, in this embodiment, the heat seal layer 20 has a multilayer structure, and the surface layer 220 of the heat seal layer 20 opposite the substrate 10 contains the fine particles 22. As shown in Fig. 4, this allows some of the fine particles 22 to protrude from the surface layer 220, thereby improving the slipperiness of the battery cell sealing film 1. In particular, in this embodiment, the fine particles 22 are dispersed in the matrix 21 made of a water-dispersible polyolefin resin, and the relationship between the size of the fine particles 22, the content of the fine particles 22 in the heat seal layer 20, the thickness of the heat seal layer 20, and the thickness of the entire heat seal layer 20 (A) and the average primary particle diameter B of the fine particles 22 is adjusted to fall within the preferred ranges described above. This makes it possible to improve the slipperiness of the battery cell sealing film 1 while improving the adhesion of the heat seal layer 20 to other heat seal layers 20 and to the current collectors 201 and 301.

[0042] Furthermore, in this embodiment, the heat seal layer 20 has an intermediate layer 210 below the surface layer 220 containing the microparticles 22, which does not contain the microparticles 22 or has a lower content of the microparticles 22 than the surface layer 220. Therefore, when the heat seal layers 20 are heat sealed together or when the heat seal layer 20 is heat sealed with the current collectors 201, 301, the matrix 21 softens due to high temperature, and the microparticles 22 are pushed and moved toward the intermediate layer 210. This prevents the microparticles 22 from interfering with the heat seal between the heat seal layers 20 or the heat seal between the heat seal layer 20 and the current collectors 201, 301. As a result, the battery cell sealing film 1 of this embodiment can more effectively heat seal the heat seal layers 20 together or the heat seal layer 20 with the current collectors 201, 301.

[0043] Furthermore, in this embodiment, as described above, the microparticles 22 protrude from the surface layer 220. For example, 80% or more of the microparticles 22 contained in the surface layer 220, more preferably 90% or more of the microparticles 22 contained in the surface layer 220, or 99% or more of the microparticles 22 contained in the surface layer 220 can be in a state where they protrude from the surface layer 220. Furthermore, in the heat seal layer 20 as a whole, 50% or more of the microparticles 22, preferably 80% or more of the microparticles 22, and more preferably 90% or more of the microparticles 22 can be in a state where they protrude from the surface layer 220. Furthermore, it is preferable that ¼ or more of the surface area of ​​the protruding microparticles 22 is exposed from the surface layer 220, and it is also possible that ½ or more of the surface area of ​​the microparticles 22 is exposed from the surface layer 220. Alternatively, the protruding microparticles 22 may protrude from the surface layer 220 by 0.5 μm or more, 0.8 μm or more, or 1.0 μm or more in the protruding direction. From another perspective, the protruding microparticles 22 may protrude from the surface layer 220 by ¼ or more, ⅓ or more, or ½ or more of their diameter in the protruding direction. Note that at least a portion (e.g., half or more) of the protruding microparticles 22 may be configured so that ¼ or more or ½ or more of the surface area of ​​the microparticles 22 is exposed from the surface layer 220, or may protrude from the surface layer 220 by 0.5 μm or more, 0.8 μm or more, or 1.0 μm or more in the protruding direction, or may protrude from the surface layer 220 by ¼ or more, ⅓ or more, or ½ or more of their diameter in the protruding direction.

[0044] In addition, the particle size distribution of the microparticles 22 according to this embodiment is not particularly limited, and any of polydisperse, medium-disperse, and monodisperse microparticles 22 can be used, but of these, medium-disperse or monodisperse microparticles 22 are preferred, and monodisperse is more preferred. In this embodiment, polydisperse microparticles 22 refer to microparticles 22 having a coefficient of variation (CV) value indicating particle size variation of 30% or more and less than 45%, medium-disperse microparticles 22 refer to microparticles 22 having a coefficient of variation (CV) value indicating particle size variation of 15% or more and less than 30%, and monodisperse microparticles 22 refer to microparticles 22 having a coefficient of variation (CV) value indicating particle size variation of 5% or more and less than 15%.

[0045] Furthermore, the battery cell sealing film 1 may be provided with other functional layers as needed, as long as the effects of the present invention are not impaired. 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]

[0046] An example of the present invention will be described below. In this example, a battery cell sealing film 1 was produced having a heat seal layer 20 in which fine particles 22 protruded from a surface layer 220. Specifically, Arrowbase SD-1205J2 manufactured by Unitika Ltd. was used as the matrix 21 constituting the heat seal layer 20. Furthermore, Techpolymer MBX-2H manufactured by Sekisui Plastics Co., Ltd. (crosslinked PMMA with a particle size coefficient of variation CV of approximately 20.9%, hereinafter referred to as medium-dispersion crosslinked PMMA), Techpolymer SSX-102 manufactured by Sekisui Plastics Co., Ltd. (crosslinked PMMA with a particle size coefficient of variation CV of approximately 7.9%, hereinafter referred to as monodispersion crosslinked PMMA), and Seahoster KE-P250 manufactured by Nippon Shokubai Co., Ltd. (hereinafter simply referred to as amorphous silica) were used as the fine particles 22 constituting the heat seal layer 20.

[0047] In addition, in the battery cell sealing film 1 according to this example, the thickness of each layer constituting the heat seal layer 20 was set to 1 μm, which is smaller than the particle diameter of the microparticles 22, so that the microparticles 22 protrude from the surface of the surface layer 220 containing the microparticles 22. Specifically, in this example, an emulsion containing only the matrix 21 or an emulsion containing the matrix 21 and the microparticles 22 was applied to the adhesive layer surface of the 50 μm-thick PET film (Cosmoshine A4160, manufactured by Toyobo Co., Ltd.) serving as the substrate 10 by gravure coating to a thickness of 1 μm, and then dried at 100°C for approximately 30 seconds to form each layer constituting the heat seal layer (intermediate layer in the case of a multilayer structure, surface layer in the case of a single-layer structure). In addition, in the case of a multilayer heat seal layer, when a surface layer is formed on an intermediate layer, or when another intermediate layer is formed on an intermediate layer, the surface layer or another intermediate layer is formed on the formed intermediate layer using the same method as described above.

[0048] Fig. 6 is a diagram showing electron microscope photographs of the produced battery cell seal film 1. Specifically, Fig. 6(A) is an image of the battery cell seal film 1 according to this example (the battery cell seal film 1 of Example 8 described later) taken at a magnification of 1000x, and Fig. 6(B) is an image of the battery cell seal film 1 shown in Fig. 6(A) (the battery cell seal film 1 of Example 8 described later) taken at a magnification of 10,000x. Furthermore, Fig. 6(C) is an image of the battery cell seal film 1 according to this example (the battery cell seal film 1 of Example 9 described later) taken at a magnification of 1000x, and Fig. 6(D) is an image of the battery cell seal film 1 shown in Fig. 6(C) (the battery cell seal film 1 of Example 9 described later) taken at a magnification of 10,000x. As shown in Figures 6(A) to 6(D), in the battery cell sealing film 1 according to this example, it can be seen that some of the microparticles 22 contained in the heat seal layer 20 protrude from the surface layer 220 of the heat seal layer 20. In particular, as shown in Figures 6(A) and 6(C), it can be seen that most of the microparticles 22 contained in the heat seal layer 20 are dispersed in the surface layer 220 and protrude from the surface layer 220. Furthermore, as shown in Figures 6(B) and 6(D), it was also confirmed that for some of the microparticles 22, more than ¼ of the volume of the microparticles 22 protrudes from the surface layer 220. Note that in Figure 6(B), what appears to be a layer of a different color can be seen on the substrate side of the heat seal layer 20, but this is due to the angle at which the cross section was observed, and does not represent the layers of the multilayer structure of the heat seal layer 20.

[0049] 7 is an electron microscope photograph of a cross section of the heat-sealable layers 20 according to this example after they have been heat-sealed and bonded together. The heat-sealable layers 20 according to this example soften when heat is applied to bond the heat-sealable layers 20 together, and as shown in FIG. 7, the microparticles 22 contained in the heat-sealable layers 20 are pushed and moved within the heat-sealable layers 20. Therefore, even when the heat-sealable layers 20 contain microparticles 22 that would normally inhibit the bonding between the heat-sealable layers 20, the heat-sealable layers 20 according to this example can improve the bonding between the heat-sealable layers 20. Similarly, when the heat-sealable layers 20 are heat-sealed and bonded to the current collectors 201 and 301, it is believed that the microparticles 22 move within the heat-sealable layers 20, improving the adhesion to the current collectors 201 and 301.

[0050] In this example, tests were also conducted on the adhesion between the heat seal layers 20, the adhesion of the heat seal layers 20 to the current collectors 201 and 301, and the slipperiness of the heat seal layers 20. Fig. 8 is a table showing the test results of this example, and summarizes the test results for the adhesion between the heat seal layers 20, the slipperiness of the heat seal layers 20 to the substrate 10, and the adhesion of the heat seal layers 20 to the current collectors 201 and 301.

[0051] In the present examples, tests were conducted by varying the number of layers in the heat-seal layer 20, the presence or absence of microparticles 22 in each layer, and the amount of microparticles 22 added. Specifically, in Examples 1 and 10 and Comparative Example 1, the heat-seal layer had a single-layer structure, while in Examples 2, 4 to 8, and 11 and Comparative Examples 2, 4, and 7, the heat-seal layer had a multilayer structure having two layers. Furthermore, in Examples 3, 9, and 12 and Comparative Examples 3, 5 to 6, and 8, the heat-seal layer had a multilayer structure having three layers. Furthermore, as shown in FIG. 8 , among Examples 2 to 9, 11 to 12 and Comparative Examples 2 to 8, which have multilayer heat-seal layers, Examples 2 to 9, 11 to 12 contain microparticles 22 in the surface layer, while Comparative Examples 2 to 9 do not contain microparticles 22 in the surface layer. In the present examples, the heat-seal layer has up to three layers, which are referred to as the first, second, and third layers in order from the side closest to the substrate 10.

[0052] In addition, in Examples 1 to 7 and Comparative Examples 4 to 6, medium-dispersion crosslinked PMMA was used as the microparticles 22, in Examples 8 to 9 and Comparative Examples 7 and 8, monodispersion crosslinked PMMA was used as the microparticles 22, and in Examples 10 to 12, amorphous silica was used as the microparticles 22. The amorphous silica used in these Examples has less variation (lower CV value) than monodispersion crosslinked PMMA. In Comparative Examples 1 to 3, the heat seal layer 20 was configured not to contain microparticles 22.

[0053] Then, as described below, the heat seal layers according to Examples 1 to 12 and Comparative Examples 1 to 8 were measured for adhesion between the heat seal layers, adhesion to the current collectors 201 and 301, and slippage of the heat seal layer relative to the substrate 10. In this example, the number of samples for each of Examples 1 to 12 and Comparative Examples 1 to 8 was three, and the adhesion between the heat seal layers, adhesion to the current collectors 201 and 301, and slippage were calculated as the average values ​​of the three samples.

[0054] Specifically, in this example, the adhesiveness between heat seal layers was tested as follows: For the heat seal layers according to Examples 1 to 12 and Comparative Examples 1 to 8, a pair of battery cell sealing films was tested using a heat seal tester (manufactured by Tester Sangyo Co., Ltd., product name "TP701-B") under the following conditions: seal width 10 mm, temperature 170°C, pressure 4.2 kg / cm, so that the heat seal layers of the same composition were bonded to each other. 2 The adhesive strength of the heat-sealable layers was measured using an autograph (Shimadzu Corporation, Autograph AGS-500NX) at a peeling speed of 40 mm / min. In the example shown in Figure 8, the adhesive strength of the heat-sealable layers was evaluated as good (good) when the peel strength was 2.0 (N / 15 mm) or higher, which satisfies the practical level of adhesiveness.

[0055] In this example, the adhesion of the heat seal layer to the current collectors 201 and 301 was tested as follows. Specifically, the battery cell sealing films having the heat seal layers according to Examples 1 to 11 and Comparative Examples 1 to 10 were overlapped with aluminum foil (Toyo Aluminum Co., Ltd., Aluminum Haku C, 70 μm thick) 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 (Tester Sangyo Co., Ltd., product name "SA-1010") at 100°C and a speed of 1 mm / min. Then, 15 mm-wide test pieces were cut out. The test pieces were then peeled at a peel rate of 40 mm / min using an autograph (Shimadzu Corporation, Autograph AGS-500NX), and the peel strength was measured. In the example shown in FIG. 8, the adhesion of the heat seal layer to the current collectors 201 and 301 was evaluated based on the peel strength of Comparative Examples 1 to 3, which did not contain the microparticles 22. Specifically, for Examples 1 and 10, in which the heat seal layer consisted of one layer, if the peel strength was equal to or greater than the current collectors 201 and 301 of Comparative Example 1, which also consisted of one layer, it was evaluated as "Good," and if it was less than the peel strength of Comparative Example 1, it was evaluated as "Fair." Similarly, for Examples 2, 4 to 8, and 11 and Comparative Examples 4 and 7, in which the heat seal layer consisted of two layers, if the peel strength was equal to or greater than the current collectors 201 and 301 of Comparative Example 2, which also consisted of two layers, it was evaluated as "Good," and if it was less than the peel strength of Comparative Example 2, it was evaluated as "Fair." For Examples 3, 9, and 12 and Comparative Examples 5 to 6, and 8, in which the heat seal layer consisted of three layers, if the peel strength was equal to or greater than the current collectors 201 and 301 of Comparative Example 3, which also consisted of three layers, it was evaluated as "Good," and if it was less than the peel strength of Comparative Example 3, it was evaluated as "Fair." This is because it is known that the battery cell sealing films of Comparative Examples 1 to 3 can adequately support the current collectors 201, 301. In addition, in all Examples 1 to 12 and Comparative Examples 1 to 8, when the peel strength of the heat seal layer to the current collectors 201, 301 was 0 (N / 15 mm), it was evaluated as "X".

[0056] Furthermore, in this example, the slipperiness (blocking suppression) of the heat seal layer relative to the substrate 10 was tested as follows. That is, a pair of battery cell sealing films having heat seal layers according to Examples 1 to 12 and Comparative Examples 1 to 8 were 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 film slipped. The evaluator was a person 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 slipped, the slipperiness of the heat seal layer was evaluated as "good," and if the battery cell sealing film did not slip, the slipperiness of the heat seal layer was evaluated as "poor."

[0057] As shown in FIG. 8, the battery cell sealing films according to Comparative Examples 1 to 3 have a configuration in which none of the heat seal layers contain fine particles 22. In the battery cell sealing films according to Comparative Examples 1 to 3, the adhesiveness (peel strength) between the heat seal layers is high, at 2.2 (N / 15 mm) or more, and it was found that the adhesiveness between the heat seal layers is at a practical level. Furthermore, in the battery cell sealing films according to Comparative Examples 1 to 3, the adhesiveness (peel strength) of the heat seal layer to the current collector is 0.6 (N / 15 mm) or more, and it was also found that the heat seal layer supports the current collectors 201 and 301, improving the handleability of the current collectors 201 and 301. On the other hand, the battery cell sealing films according to Comparative Examples 1 to 3 were evaluated as "poor" for slipperiness. Thus, it was found that when the heat seal layer does not contain fine particles 22, the slipperiness of the heat seal layer is low, and blocking may occur.

[0058] Examples 1 to 3 and Comparative Examples 4 to 6 have in common the addition of 5% of medium-dispersion crosslinked PMMA with an average primary particle diameter of 2.5 μm to one of the heat-seal layers. In Example 1, the heat-seal layer has a single-layer structure, and only this single heat-seal layer 20 contains fine particles 22. In Example 1, the adhesion (peel strength) between the heat-seal layers 20 was high at 2.2 (N / 15 mm), and the slipperiness was also evaluated as good, with a rating of "Good." However, the adhesion (peel strength) of the heat-seal layer 20 to the current collector was 0.0 (N / 15 mm), indicating that the heat-seal layer 20 was unable to support the current collectors 201 and 301. The adhesion (peel strength) of the heat seal layer 20 to the current collector was 0.0 (N / 15 mm). This is thought to be because, when the average primary particle diameter (μm) of the microparticles 22 is B and the thickness of the heat seal layer 20 is A, B / A, i.e., the size B of the microparticles relative to the thickness A of the heat seal layer, was high at 2.5, exceeding the range of 0.3≦(B / A)<1.7, and the microparticles 22 inhibited the adhesion of the heat seal layer 20 to the current collector.

[0059] Furthermore, Example 2 and Comparative Example 4 have a multilayer heat seal layer consisting of two layers. In Example 2, the surface layer 220 (second layer) of the two layers constituting the heat seal layer 20, which is on the side opposite the substrate 10, contains the fine particles 22. In Comparative Example 4, the middle layer (first layer) of the two layers constituting the heat seal layer, which is on the side closer to the substrate 10, contains the fine particles 22. As shown in FIG. 8 , in Example 2, the adhesion (peel strength) between the heat seal layers was high and good at 3.3 (N / 15 mm), and the two-layer structure also resulted in a high and good adhesion (peel strength) of 0.9 (N / 15 mm) between the heat seal layer 20 and the current collector. In addition, in Example 2, the surface layer 220 of the heat seal layer 20 contains the fine particles 22, and therefore the slipperiness was also evaluated as good, being "good." On the other hand, in Comparative Example 4, the adhesion (peel strength) between the heat seal layers was high and good at 2.7 (N / 15 mm), and by using a two-layer structure, the adhesion (peel strength) of the heat seal layer to the collector was also high and good at 1.2 (N / 15 mm). However, since the surface layer of the heat seal layer did not have microparticles 22, the slipperiness was low and the result was rated as "△".

[0060] Furthermore, Example 3 and Comparative Examples 5 and 6 each have a multilayer heat seal layer consisting of three layers. In Example 3, the microparticles 22 are contained in the surface layer 220 (the third layer) of the three layers constituting the heat seal layer 20, which is the farthest from the substrate 10. In Comparative Example 5, the microparticles 22 are contained in the middle layer (the first layer) of the three layers constituting the heat seal layer, which is the closest to the substrate 10. In Comparative Example 6, the microparticles 22 are contained in the middle layer (the second layer) between the first and third layers of the three layers constituting the heat seal layer. As shown in FIG. 8 , in Example 3, the adhesion (peel strength) between the heat seal layers is high and good at 4.7 (N / 15 mm). Furthermore, the three-layer structure also results in a high and good adhesion (peel strength) of the heat seal layer 20 to the current collector at 1.0 (N / 15 mm). Furthermore, in Example 3, the microparticles 22 are contained in the surface layer 220 of the heat seal layer 20, and therefore the slipperiness was evaluated as "good." On the other hand, in Comparative Examples 5 and 6, the adhesion (peel strength) between the heat seal layers was high and good at 4.2 or 4.7 (N / 15 mm), and the adhesion (peel strength) of the heat seal layer 20 to the current collector was also high and good at 1.2 or 1.0 (N / 15 mm). However, since the surface layer 220 of the heat seal layer 20 did not have microparticles 22, the slipperiness was low and was rated as "△".

[0061] From the test results of Examples 1 to 3 and Comparative Examples 4 to 6, it was found that by incorporating the fine particles 22 in the surface layer 220 of the heat seal layer 20 as in Examples 1 to 3, it is possible to improve the slipperiness of the battery cell sealing film 1 and suppress blocking of the battery cell sealing film 1. Furthermore, it was also found that by making the heat seal layer 20 have a multilayer structure, it is possible to improve not only the adhesion between the heat seal layers 20 but also the adhesion of the heat seal layer 20 to the current collector.

[0062] Examples 4 to 7 are common in that they have a heat seal layer 20 with a multilayer structure consisting of two layers, and the surface layer 220 of the heat seal layer 20 contains medium-dispersion crosslinked PMMA as the fine particles 22. The content of the fine particles 22 in the surface layer 220 was varied in Examples 4 to 7, with the content of the fine particles 22 in the surface layer 220 being 1 wt % in Example 4, 3 wt % in Example 5, 7 wt % in Example 6, and 10 wt % in Example 7. As shown in FIG. 8 , the battery cell sealing films 1 of Examples 4 to 7 had good adhesion (peel strength) between the heat seal layers 20, reaching 3.3 (N / 15 mm) or more. It was also found that the slipperiness of the heat seal layer 20 in the battery cell sealing films 1 of Examples 4 to 7 was also good, effectively suppressing blocking of the battery cell sealing films 1. On the other hand, the adhesiveness of the heat seal layer 20 to the current collectors 201, 301 was good, at 0.7 (N / 15 mm) or more when the amount of microparticles 22 added was 1 to 7 wt % as in Examples 4 to 6, but was slightly lower at 0.5 (N / 15 mm) when the amount of microparticles 22 added was 10 wt % as in Example 7. This shows that the adhesiveness of the heat seal layer 20 to the current collectors 201, 301 can be effectively obtained even when the amount of microparticles 22 added is 10 wt %, but it is more preferable to add less than 10 wt %.

[0063] Furthermore, Examples 8-9 and Comparative Examples 7-8 have in common the fact that they have a multilayer heat-seal layer that contains monodisperse crosslinked PMMA as the fine particles 22. Specifically, Example 8 and Comparative Example 7 have a multilayer heat-seal layer consisting of two layers, and in Example 8, the surface layer 220 (second layer) of the two layers that make up the heat-seal layer 20 contains monodisperse crosslinked PMMA, while in Comparative Example 7, the middle layer (first layer) of the two layers that make up the heat-seal layer contains monodisperse crosslinked PMMA. Furthermore, Example 9 and Comparative Example 8 have a multilayer heat-seal layer consisting of three layers, and in Example 9, the surface layer 220 (third layer) of the three layers that make up the heat-seal layer 20 contains monodisperse crosslinked PMMA, while in Comparative Example 8, the middle layer (second layer) of the three layers that make up the heat-seal layer contains monodisperse crosslinked PMMA. The figures shown in (A) and (B) of Figure 6 are images of the battery cell sealing film 1 according to Example 8, and the figures shown in (C) and (D) of Figure 6 are images of the battery cell sealing film 1 according to Example 9.

[0064] As shown in FIG. 8 , in Examples 8 to 9 and Comparative Examples 7 and 8, the adhesion (peel strength) between the heat-seal layers was good, at 3.1 (N / 15 mm) or more, and the adhesion of the heat-seal layer to the current collector was also good, at 0.7 (N / 15 mm) or more. Meanwhile, in Examples 8 and 9, the slipperiness of the heat-seal layer was evaluated as "good," whereas in Comparative Examples 7 and 8, the slipperiness of the heat-seal layer was evaluated as "poor." This indicates that even when monodisperse crosslinked PMMA is used as the fine particles 22, the slipperiness of the battery cell sealing film 1 can be improved and blocking can be suppressed by including monodisperse crosslinked PMMA in the surface layer 220. Furthermore, even when monodisperse crosslinked PMMA is used as the fine particles 22, the multilayer structure of the heat-seal layer 20 can improve the adhesion between the heat-seal layers 20 and the adhesion of the heat-seal layer to the current collector. Furthermore, it was found that in Examples 8 and 9, in which monodisperse crosslinked PMMA was used as the microparticles, the adhesion between the heat seal layers 20 and the adhesion of the heat seal layer to the current collector tended to be better than in Examples 2 and 3, which were the same conditions except that medium-disperse crosslinked PMMA was used as the microparticles.

[0065] Examples 10 to 12 have in common the heat-seal layer 20 containing amorphous silica as fine particles 22. Specifically, Example 10 has a single-layer heat-seal layer 20, and amorphous silica is contained in the single-layer heat-seal layer 20. Example 11 has a multilayer heat-seal layer 20 consisting of two layers, and amorphous silica is contained in the surface layer 220 (second layer). Example 12 has a multilayer heat-seal layer 20 consisting of three layers, and amorphous silica is contained in the surface layer 220 (third layer). As shown in FIG. 8, in Examples 10 to 12, the adhesion (peel strength) between the heat-seal layers was good, at 2.6 (N / 15 mm) or more, and the slipperiness of the heat-seal layer 20 was also good. However, in Example 10, which had a single-layer heat-seal layer 20, the adhesion of the heat-seal layer 20 to the current collector was low at 0.0 (N / 15 mm), while in Examples 11 and 12, which had a multilayer heat-seal layer 20, the adhesion of the heat-seal layer 20 to the current collector was good at 1.3 (N / 15 mm) or more. This shows that even when the fine particles 22 are amorphous silica, the inclusion of the fine particles 22 in the surface layer 220 of the heat-seal layer 20 can improve the slipperiness and improve the adhesion between the heat-seal layers 20. Furthermore, even when the fine particles 22 are amorphous silica, it was found that the adhesion of the heat-seal layer 20 to the current collectors 201, 301 can be improved by making the heat-seal layer 20 have a multilayer structure. Furthermore, it was found that in Examples 10 to 12, in which amorphous silica was used as the microparticles 22, the adhesion between the heat seal layers and the adhesion of the heat seal layer to the current collector tended to be better than in Examples 1 to 3 and 8 to 9, in which medium-dispersion crosslinked PMMA or monodispersion crosslinked PMMA was used as the microparticles 22.

[0066] As described above, the battery cell sealing film 1 according to this embodiment contains microparticles 22 in the surface layer 220 of the heat seal layer 20, and the microparticles 22 protrude from the surface layer 220, thereby improving 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 made into a roll film can be suppressed.

[0067] On the other hand, in the battery cell sealing film 1 according to the present embodiment, the heat seal layer 20 contains microparticles 22, and there was concern that the microparticles 22 would reduce the adhesiveness between the heat seal layers 20. However, in the battery cell sealing film 1 according to the present embodiment, even when the microparticles 22 are added to the heat seal layer 20, the adhesiveness between the heat seal layers 20 can be improved without being impaired. In fact, in the battery cell sealing film 1 according to the present embodiment, by adding the microparticles 22 to the heat seal layer 20, the adhesiveness between the heat seal layers 20 can be improved compared to when the heat seal layer does not contain the microparticles 22 (for example, Comparative Examples 1 to 3 shown in FIG. 8). Furthermore, in the heat seal layer 20 according to the present embodiment, the surface layer 220 has a multilayer structure in which a layer not containing the microparticles 22 is provided below the surface layer 220. This allows the microparticles 22 to be pushed and move toward the lower layer when the heat seal layers 20 are bonded together, thereby improving the adhesiveness between the heat seal layers 20.

[0068] Furthermore, in conventional battery cell manufacturing, since the current collectors 201, 301 are thin films, 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, and in order to prevent such damage to the current collectors, the battery cell sealing film 1 is adhered to the current collectors 201, 301 to physically support the current collectors 201, 301, thereby improving the handleability of the current collectors 201, 301. Therefore, the battery cell sealing film 1 according to this embodiment is required to have good adhesion between the heat seal layers 20, as well as good adhesion between the heat seal layers 20 and the current collectors 201, 301. In this regard, the battery cell sealing film 1 according to this embodiment has a multilayer structure for the heat seal layer 20, and has a layer below the surface layer 220 that does not contain the fine particles 22. This allows the fine particles 22 to be pushed and moved downward when the heat seal layer 20 is bonded to the current collectors 201, 301, thereby improving the adhesion of the heat seal layer 20 to the current collectors 201, 301. Furthermore, in the battery cell sealing film 1 according to this embodiment, the thickness A (μm) of the heat seal layer 20 and the average primary particle diameter B (μm) of the fine particles are adjusted so as to satisfy the relationship (B / A)<2.5, more preferably the relationship (0.3≦(B / A)<1.7), and further preferably the relationship (0.3≦(B / A)≦1.5), thereby improving the adhesion of the heat seal layer 20 to the current collectors 201, 301. In addition, by making the content of microparticles 22 in the entire heat seal layer 20 less than 15% by weight, more preferably 10% by weight or less, and even more preferably less than 10% by weight, the adhesion of the heat seal layer 20 to the current collectors 201, 301 can be further improved.

[0069] In addition, in the battery cell sealing film 1 according to this embodiment, the heat seal layer 20 can be formed by coating by using a matrix 21 made of a water-dispersible polyolefin resin. Therefore, compared to the case where a conventional thermoplastic polyolefin resin is formed by extrusion lamination, the battery cell sealing film 1 can be made thinner, and the fine particles 22 can be properly dispersed in the heat seal layer 20.

[0070] 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.

[0071] For example, in the above-described embodiment, when forming the multilayer heat seal layer 20, the coating material for constituting the heat seal layer 20 (an emulsion containing the matrix 21, or an emulsion containing the matrix 21 and the microparticles 22) is applied to the substrate 10 in equal amounts, and each layer constituting the heat seal layer 20 has the same thickness. However, the present invention is not limited to this configuration, and the thickness of each layer constituting the heat seal layer 20 can be varied. In this case, layers of different thicknesses can be formed by varying the amount of coating material applied for each layer. [Explanation of symbols]

[0072] 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, 1a, 1b...Sealing film for battery cells 10...Base material 20...Heat seal layer 210...middle class 21...The Matrix 220…surface layer 21...The Matrix 22...Fine particles 230,240…layer 110...Tab connection 120...External tab

Claims

1. It has a substrate and a heat seal layer, the heat seal layer contains fine particles, The fine particles protrude from the surface of the heat seal layer.

2. The sealing film for battery cells according to claim 1 , wherein 50% or more of the particles contained in the heat seal layer protrude from the surface of the heat seal layer.

3. 2. The sealing film for battery cells according to claim 1, wherein the fine particles protruding from the surface of the heat seal layer have, on average, ¼ or more of their surface area exposed from the surface of the heat seal layer, or protrude 0.5 μm or more in a height direction from the surface of the heat seal layer.

4. It has a substrate and a heat seal layer, The heat seal layer has a multi-layer structure, The sealing film for battery cells, wherein the surface layer of the plurality of layers constituting the heat seal layer, which is located on the opposite side from the substrate, contains a water-dispersible polyolefin resin and fine particles.

5. The sealing film for battery cells according to claim 4 , wherein the heat seal layer has a layer that does not contain the fine particles below the surface layer.

6. The battery cell sealing film according to claim 1 or 4, wherein the fine particles are crosslinked polymethyl methacrylate particles.

7. The sealing film for a battery cell according to claim 1 or 4, wherein the content of the fine particles in the heat seal layer is less than 10% by weight.

8. 5. 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.

9. 5. The sealing film for battery cells according to claim 1, wherein a thickness A (μm) of the entire 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)

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

11. The sealing film for battery cells according to claim 1 or 4, for sealing a semi-solid battery cell or an all-solid battery cell.

Images