tab

Abstract

To provide a resin film for terminals that can achieve sufficiently high levels of both seal strength at high temperatures and initial seal strength. [Solution] A resin film for terminals, comprising a main body of an energy storage device and terminals electrically connected to the main body of the energy storage device, for covering a portion of the outer surface of the terminals, the resin film for terminals comprising a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent.

Description

Technical Field

[0001] The present disclosure relates to a resin film for a terminal that is disposed to cover a part of the outer peripheral surface of a terminal in a power storage device including a power storage device main body and a terminal electrically connected to the power storage device main body. The present disclosure also relates to a power storage device using the resin film for a terminal.

Background Art

[0002] As power storage devices, for example, secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and lead-acid batteries, and electrochemical capacitors such as electric double layer capacitors are known. Further miniaturization of the power storage device is required due to miniaturization of portable devices or limitation of installation space, and lithium-ion batteries with high energy density have attracted attention. Conventionally, a metal can has been used as an exterior material for lithium-ion batteries, but a multilayer film that is lightweight, has high heat dissipation, and can be manufactured at low cost is now being used.

[0003] A lithium-ion battery using the above multilayer film as an exterior material is called a laminated lithium-ion battery. The exterior material covers the battery contents (positive electrode, separator, negative electrode, electrolyte, etc.) and prevents intrusion of moisture into the interior. A laminated lithium-ion battery is manufactured, for example, by forming a concave portion by cold forming in a part of the exterior material, accommodating the battery contents in the concave portion, and folding back the remaining portion of the exterior material and sealing the edge portion by heat sealing (see, for example, Patent Document 1).

[0004] A laminated lithium-ion battery includes a current extraction terminal (sometimes referred to as a "tab lead"). For the purpose of improving the adhesion between the current extraction terminal and the exterior material, a resin film for a terminal (sometimes referred to as a "tab sealant") may be disposed to cover a part of the outer periphery of the current extraction terminal (see, for example, Patent Documents 2 to 4).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-101765 [Patent Document 2] Japanese Patent Publication No. 2008-4316 [Patent Document 3] Japanese Patent Publication No. 2010-218766 [Patent Document 4] Japanese Patent Publication No. 2009-259739 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, research and development is underway on a next-generation battery called a solid-state battery, which is considered the successor to lithium-ion batteries. Solid-state batteries are characterized by using a solid electrolyte instead of an organic electrolyte. While lithium-ion batteries cannot be used at temperatures higher than the boiling point of the electrolyte (around 80°C), solid-state batteries can be used at temperatures exceeding 100°C, and their lithium-ion conductivity can be increased by operating them at high temperatures (for example, 100-150°C).

[0007] However, when using the above-mentioned laminate as the outer material to manufacture a laminate-type all-solid-state battery, there is a risk that the sealing of the all-solid-state battery package may be insufficient due to the insufficient heat resistance of the terminal resin film.

[0008] This disclosure aims to provide a resin film for terminals that can achieve sufficiently high levels of both sealing strength at high temperatures and initial sealing strength. Furthermore, this disclosure aims to provide an energy storage device using the above-mentioned resin film for terminals. [Means for solving the problem]

[0009] A terminal resin film relating to one aspect of this disclosure is a film for covering a portion of the outer surface of a terminal in an energy storage device comprising an energy storage device body and a terminal electrically connected to the energy storage device body. This terminal resin film includes a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent.

[0010] Polypropylene is known to exist in four crystalline structures: α, β, γ, and smectic. While most structures formed under typical conditions are α-type, the inventors deliberately used an additive (crystal nucleating agent) to induce the formation of a β-type structure during heat sealing, successfully achieving both high temperature resistance and initial seal strength. The inventors speculate on the following reasons for this superior effect: Initial seal strength: Seal strength measured at room temperature (25°C). • Stress relaxation ability is important (if it is hard and brittle, it is difficult to develop strength). In the β type, stress relaxation capacity is improved, and strength is achieved. High-temperature seal strength: The seal strength measured at high temperatures (150°C). It is important that the resin is not easily heated, and that even when heated, the resin does not easily melt. The β-type melts (endothermally) at around 150°C, making it difficult to heat the resin. Also, the β-type quickly transforms into the α-type after melting, making the resin less likely to melt even when exposed to high temperatures.

[0011] In one embodiment of a resin film for terminals, the content of the β-nucleating agent may be 0.001 to 15% by mass, based on the total amount of the resin composition.

[0012] In one embodiment of a resin film for terminals, the β-nucleating agent may be an amide compound.

[0013] One embodiment of a resin film for terminals includes three or more polypropylene layers, of which at least one layer may be a polypropylene layer P.

[0014] One aspect of the resin film for terminals includes three or more polypropylene layers, and at least one of the outermost layers may be a polypropylene layer P.

[0015] In one aspect of the resin film for terminals, the polypropylene layer P may contain acid-modified polypropylene.

[0016] One aspect of the resin film for terminals includes three or more polypropylene layers, and at least one of the outermost layers may contain long-chain branched polypropylene.

[0017] The power storage device according to one aspect of the present disclosure includes a power storage device main body, a terminal electrically connected to the power storage device main body, and an exterior material that sandwiches the terminal and houses the power storage device main body. In this power storage device, between the terminal and the exterior material, a part of the outer peripheral surface of the terminal is covered with the above resin film for terminals by heat sealing.

[0018] In one aspect of the power storage device, the crystallinity of the β crystal of the polypropylene layer P in the heat-sealed portion of the resin film for terminals may be 3 to 90%.

[0019] In one aspect of the power storage device, the crystallinity ratio (β / α) of the polypropylene layer P in the heat-sealed portion of the resin film for terminals may be 0.01 to 50.

[0020] In one aspect of the power storage device, when the power storage device is left standing at 150°C for one week and then cooled to 25°C, the crystallinity of the α crystal of the polypropylene layer P in the heat-sealed portion of the resin film for terminals may be 25% or more, and the crystallinity ratio (β / α) may be 0 to 1.

Advantages of the Invention

[0021] According to the present disclosure, there is provided a resin film for terminals that can achieve both a sufficient seal strength at high temperatures and an initial seal strength at a sufficiently high level. Further, according to the present disclosure, there is provided a power storage device using the resin film for terminals. Although not particularly limited, the resin film for terminals (tab sealant for a power storage device) of the present disclosure can be suitably used in all-solid-state batteries that may be exposed to a high-temperature environment.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a perspective view showing an example of a power storage device. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of an exterior material for a power storage device. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III shown in FIG. 1, and is a cross-sectional view schematically showing the configuration of tabs (resin film for terminals and metal terminals) of an all-solid-state battery. [Figure 4] FIG. 4 is a plan view schematically showing evaluation samples prepared in Examples and Comparative Examples.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are not limited to the ratios shown.

[0024] <Power Storage Device> The power storage device includes a power storage device main body, terminals electrically connected to the power storage device main body, and an exterior material that sandwiches the terminals and houses the power storage device main body. The terminals extend from the power storage device main body. Between the terminals and the exterior material in the power storage device, a part of the outer peripheral surface of the terminals is covered with a resin film for terminals described later by heat sealing.

[0025] Figure 1 is a perspective view showing the schematic configuration of the energy storage device according to this embodiment. In Figure 1, an all-solid-state battery is shown as an example of the energy storage device 100, and the following explanation will be given. Note that the energy storage device with the configuration shown in Figure 1 is sometimes called a battery pack or battery cell.

[0026] The energy storage device 100 is an all-solid-state battery and comprises an energy storage device body 50, an outer casing material 10, a pair of metal terminals 30, and a terminal resin film 40 (tab sealant). The energy storage device body 50 is the battery body that performs charging and discharging. The outer casing material 10 covers the surface of the energy storage device body 50 and is positioned to be in contact with a portion of the terminal resin film 40.

[0027] [Exterior materials] Figure 2 is a cross-sectional view showing an example of a cross-section of the exterior material 10. The exterior material 10 has a multilayer structure comprising, from the outside to the inside (towards the main body 50 of the energy storage device), a base material layer 11, a first adhesive layer 12, a barrier layer 13, a corrosion prevention treatment layer 14, a second adhesive layer 17, and a sealant layer 16 in this order.

[0028] (Sealant layer) The sealant layer 16 is a layer that provides heat sealing properties to the exterior material 10, and is placed on the inside and heat-sealed (heat-fused) during the assembly of the energy storage device.

[0029] As the sealant layer 16, thermoplastic resins such as polyolefin, polyamide, polyester, polycarbonate, polyphenylene ether, polyacetal, polystyrene, polyvinyl chloride, and polyvinyl acetate can be used, and from the viewpoint of heat resistance and sealing suitability, polyolefin, polyamide, and polyester can be used. When directly laminating to the barrier layer without an adhesive, it is preferable to use a material in which at least one layer in contact with the barrier layer has been modified with an acid or glycidyl.

[0030] Examples of polyolefin resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymers; polypropylene; and propylene-α-olefin copolymers. When polyolefin resins are copolymers, they may be block copolymers or random copolymers.

[0031] Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). These polyester resins may be used individually or in combination of two or more. Alternatively, a copolymer of any acid and glycol may be used.

[0032] Examples of polyamide resins include nylon 6 and nylon 6,6.

[0033] To impart sealing properties, heat resistance, and other functionalities, for example, antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, nucleating agents, plasticizers, etc., may be added to the sealant layer. For example, zinc oxide or cupric oxide may be added to the sealant layer to impart hydrogen sulfide resistance, and zeolites may be added to impart moisture barrier properties.

[0034] The peak melting temperature of the sealant layer varies depending on the application, but for exterior materials for all-solid-state batteries, it is preferably between 160 and 280°C because it improves heat resistance.

[0035] The sealant layer 16 may be a single layer or a multilayer structure of two or more layers. If the sealant layer is a single layer, its thickness can be 10 to 300 μm, or 20 to 100 μm. A thickness of 10 μm or more of the sealant layer 16 makes it easier to ensure airtightness and insulation, while a thickness of 300 μm or less allows for sufficient cell volume.

[0036] (base material layer) The base layer 11 provides heat resistance during the sealing process when manufacturing energy storage devices and plays a role in suppressing the occurrence of pinholes that may occur during molding and distribution. In particular, for exterior materials of large-scale energy storage devices, it can also provide scratch resistance, chemical resistance, and insulation.

[0037] The base layer 11 is preferably a layer made of a resin film formed from an insulating resin. Examples of resin films include stretched or unstretched films such as polyester film, polyamide film, polypropylene film, and polyphenylene sulfide film. The base layer 11 may be a single-layer film made of any of these resin films, or it may be a laminated film made of two or more of these resin films.

[0038] Among these, polyester film and polyamide film are preferred as the base layer 11 due to their excellent moldability, and polyamide film is more preferred. These films are preferably biaxially oriented films. Examples of polyester resins constituting the polyester film include polyethylene terephthalate. Examples of polyamide resins constituting the polyamide film include nylon 6, nylon 6,6, copolymers of nylon 6 and nylon 6,6, nylon 6,10, polymetaxylylene adipamide (MXD6), nylon 11, nylon 12, etc. Among these, nylon 6 (ONy) is preferred from the viewpoint of excellent heat resistance, puncture strength, and impact strength.

[0039] Examples of stretching methods for biaxially oriented films include sequential biaxial stretching, tubular biaxial stretching, and simultaneous biaxial stretching. From the viewpoint of obtaining better deep-drawing properties, it is preferable that the biaxially oriented film is stretched by the tubular biaxial stretching method.

[0040] The thickness of the base layer 11 is preferably 6 to 40 μm, and more preferably 10 to 30 μm. A base layer thickness of 6 μm or more tends to improve the pinhole resistance and insulation properties of the exterior material 10. When the thickness of the base layer 11 exceeds 40 μm, the total thickness of the exterior material 10 tends to increase.

[0041] (First adhesive layer) The first adhesive layer 12 is a layer that adheres the base layer 11 and the barrier layer 13. Specific examples of materials constituting the first adhesive layer 12 include polyurethane resins obtained by reacting a bifunctional or more isocyanate compound with a main component such as polyester polyol, polyether polyol, acrylic polyol, or carbonate polyol. The various polyols mentioned above can be used individually or in combination of two or more, depending on the functions and performance required for the exterior material. In addition, various other additives and stabilizers may be added to the polyurethane resin, depending on the performance required for the adhesive.

[0042] The thickness of the first adhesive layer 12 is not particularly limited, but from the viewpoint of obtaining desired adhesive strength, conformability, and processability, for example, 1 to 10 μm is preferred, and 3 to 7 μm is more preferred.

[0043] (Barrier layer) The barrier layer 13 has water vapor barrier properties that prevent moisture from entering the inside of the energy storage device. Furthermore, the barrier layer 13 is ductile for deep drawing. As the barrier layer 13, various metal foils such as aluminum, stainless steel, and copper, as well as metal vapor-deposited films, inorganic oxide vapor-deposited films, carbon-containing inorganic oxide vapor-deposited films, and films with these vapor-deposited films can be used. From the viewpoints of mass (specific gravity), moisture resistance, processability, and cost, metal foil is preferred, and aluminum foil is more preferred.

[0044] As for the aluminum foil, soft aluminum foil that has undergone annealing treatment is particularly preferred because it can provide the desired ductility during molding. However, it is even more preferable to use aluminum foil containing iron in order to provide further pinhole resistance and ductility during molding. The iron content in the aluminum foil is preferably 0.1 to 9.0% by mass, and more preferably 0.5 to 2.0% by mass, of 100% by mass of aluminum foil. By having an iron content of 0.1% by mass or more, an exterior material 10 with better pinhole resistance and ductility can be obtained. By having an iron content of 9.0% by mass or less, an exterior material 10 with better flexibility can be obtained. Untreated aluminum foil may be used, but it is preferable to use degreased aluminum foil. When degreasing the aluminum foil, the degreasing treatment may be applied to only one side of the aluminum foil, or to both sides.

[0045] The thickness of the barrier layer 13 is not particularly limited, but it is preferably 9 to 200 μm, and more preferably 15 to 100 μm, considering barrier properties, pinhole resistance, and processability.

[0046] (Corrosion-resistant treatment layer) The corrosion-preventive treatment layer 14 is a layer provided to prevent corrosion of the barrier layer 13. The corrosion-preventive treatment layer 14 can be formed, for example, by degreasing, hot water modification, anodizing, chemical conversion, or a combination of these treatments.

[0047] Degreasing methods include acid degreasing and alkaline degreasing. Acid degreasing methods include using inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid individually, or mixtures thereof. Alkaline degreasing methods include using sodium hydroxide, etc.

[0048] Examples of hydrothermal alteration treatments include the boehmite treatment, which involves immersing aluminum foil in boiling water to which triethanolamine has been added. Examples of anodizing treatments include the anodizing treatment.

[0049] Chemical treatments can be immersion-type or coating-type. Immersion-type chemical treatments include, for example, chromate treatment, zirconium treatment, titanium treatment, vanadium treatment, molybdenum treatment, calcium phosphate treatment, strontium hydroxide treatment, cerium treatment, ruthenium treatment, or various chemical treatments consisting of mixed phases of these. On the other hand, a coating-type chemical treatment is a method of applying a coating agent having corrosion-preventive properties onto the barrier layer 13.

[0050] Of these corrosion prevention treatments, if at least a portion of the corrosion prevention treatment layer is formed by hot water modification, anodizing, or chemical conversion, it is preferable to perform the degreasing treatment described above beforehand. Furthermore, if a degreased metal foil, such as a metal foil that has undergone an annealing process, is used as the barrier layer 13, it is not necessary to perform degreasing treatment again when forming the corrosion prevention treatment layer 14.

[0051] The coating agent used in the coating-type chemical conversion treatment preferably contains trivalent chromium. The coating agent may also contain at least one polymer selected from the group consisting of cationic polymers and anionic polymers, as described later.

[0052] In particular, in the hydrothermal alteration treatment and anodic oxidation treatment described above, the surface of the aluminum foil is dissolved by the treatment agent, forming aluminum compounds (boehmite, anodized aluminum) with excellent corrosion resistance. As a result, a co-continuous structure is formed from the barrier layer 13 using aluminum foil to the corrosion-preventive treatment layer 14, and therefore the above treatment is included in the definition of chemical conversion treatment. On the other hand, as will be described later, it is also possible to form the corrosion-preventive treatment layer 14 using only a pure coating method, which is not included in the definition of chemical conversion treatment. One example of this method is to use a sol of a rare earth element oxide such as cerium oxide with an average particle size of 100 nm or less, as it has a corrosion-preventive effect on aluminum (inhibitor effect) and is also environmentally suitable. By using this method, it is possible to impart a corrosion-preventive effect to metal foils such as aluminum foil even with a general coating method.

[0053] Examples of sols for the rare earth element oxides mentioned above include sols using various solvents such as aqueous, alcohol, hydrocarbon, ketone, ester, and ether systems. Among these, aqueous sols are preferred. In order to stabilize the dispersion of the rare earth element oxide sols, inorganic acids or their salts, such as nitric acid, hydrochloric acid, and phosphoric acid, or organic acids such as acetic acid, malic acid, ascorbic acid, and lactic acid are usually used as dispersion stabilizers. Of these dispersion stabilizers, phosphoric acid in particular is expected to provide the following benefits in the exterior material 10: (1) stabilization of sol dispersion, (2) improved adhesion with the barrier layer 13 by utilizing the aluminum chelating ability of phosphoric acid, and (3) improved cohesive force of the corrosion prevention treatment layer 14 (oxide layer) due to the ease with which dehydration condensation of phosphoric acid occurs even at low temperatures.

[0054] The corrosion-preventive treatment layer 14 formed by the above-mentioned rare earth element oxide sol is an aggregate of inorganic particles, and therefore, even after the drying and curing process, the cohesive force of the layer itself may decrease. Therefore, in this case, it is preferable that the corrosion-preventive treatment layer is compounded with the following anionic polymer or cationic polymer to compensate for the cohesive force.

[0055] The corrosion-preventive treatment layer is not limited to the layer described above. For example, it may be formed using a treatment agent that combines a resin binder (such as aminophenol) with phosphoric acid and a chromium compound, as is known from the field of coating chromate. Using this treatment agent, a layer can be formed that possesses both corrosion-preventive properties and adhesion. Furthermore, although it is necessary to consider the stability of the coating liquid, a layer can be formed that possesses both corrosion-preventive properties and adhesion by using a coating agent that pre-mixes a rare earth element oxide sol with a polycationic polymer or a polyanionic polymer into a single liquefaction.

[0056] The mass per unit area of ​​the corrosion-preventive treatment layer is 0.005 to 0.200 g / m², regardless of whether it is a multilayer or single-layer structure. 2 Preferably, 0.010 to 0.100 g / m 2 A more preferable mass per unit area is 0.005 g / m². 2If the above is true, it is easier to impart corrosion prevention functionality to the barrier layer 13. Also, the above mass per unit area is 0.200 g / m². 2 Even if the thickness exceeds a certain limit, the corrosion prevention function does not change significantly. On the other hand, when using rare earth element oxide sols, if the coating film is thick, the heat during drying may result in insufficient curing, potentially leading to a decrease in cohesive force. The thickness of the corrosion prevention treatment layer 14 can be calculated from its specific gravity.

[0057] The corrosion-preventive treatment layer may, from the viewpoint of adhesion between the sealant layer and the barrier layer, for example, contain cerium oxide, 1 to 100 parts by mass of phosphoric acid or phosphate per 100 parts by mass of cerium oxide, and a cationic polymer; it may be formed by applying a chemical conversion treatment to the barrier layer 13; or it may be formed by applying a chemical conversion treatment to the barrier layer and also contain a cationic polymer.

[0058] (Second adhesive layer) The second adhesive layer 17 is a layer that bonds the barrier layer 13, on which the corrosion-preventive treatment layer 14 is formed, to the sealant layer 16. A general adhesive for bonding the barrier layer 13 and the sealant layer 16 can be used for the second adhesive layer 17.

[0059] If the corrosion-preventive treatment layer 14 has a layer containing at least one polymer selected from the group consisting of cationic polymers and anionic polymers described above, it is preferable that the second adhesive layer 17 is a layer containing a compound that is reactive with the polymer contained in the corrosion-preventive treatment layer 14 (hereinafter also referred to as "reactive compound").

[0060] For example, if the corrosion-preventive treatment layer 14 contains a cationic polymer, the second adhesive layer 17 contains a compound that is reactive with the cationic polymer. If the corrosion-preventive treatment layer 14 contains an anionic polymer, the second adhesive layer 17 contains a compound that is reactive with the anionic polymer. Furthermore, if the corrosion-preventive treatment layer 14 contains both a cationic polymer and an anionic polymer, the second adhesive layer 17 contains a compound that is reactive with the cationic polymer and a compound that is reactive with the anionic polymer. However, the second adhesive layer 17 does not necessarily have to contain the above two types of compounds, and may contain a compound that is reactive with both the cationic polymer and the anionic polymer. Here, "reactive" means forming a covalent bond with the cationic polymer or the anionic polymer. The second adhesive layer 17 may further contain an acid-modified polyolefin resin.

[0061] Compounds that react with cationic polymers include at least one compound selected from the group consisting of polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group.

[0062] Examples of these polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group include the polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group that were previously exemplified as crosslinking agents for creating a crosslinked structure of cationic polymers. Among these, polyfunctional isocyanate compounds are preferred because they have high reactivity with cationic polymers and readily form crosslinked structures.

[0063] Compounds that react with anionic polymers include at least one compound selected from the group consisting of glycidyl compounds and compounds having an oxazoline group. Examples of these glycidyl compounds and compounds having an oxazoline group include the glycidyl compounds and compounds having an oxazoline group that were previously exemplified as crosslinking agents for creating a crosslinked structure of cationic polymers. Among these, glycidyl compounds are preferred due to their high reactivity with anionic polymers.

[0064] When the second adhesive layer 17 contains an acid-modified polyolefin resin, it is preferable that the reactive compound is also reactive with the acidic groups in the acid-modified polyolefin resin (i.e., forms a covalent bond with the acidic groups). This further improves adhesion to the corrosion-preventive treatment layer 14. In addition, the acid-modified polyolefin resin becomes a cross-linked structure, further improving the solvent resistance of the exterior material 10.

[0065] The content of the reactive compound is preferably equal to or 10 times the amount of the acidic groups in the acid-modified polyolefin resin. If the amount is equal to or greater than the amount, the reactive compound will react sufficiently with the acidic groups in the acid-modified polyolefin resin. On the other hand, if the amount exceeds 10 times the amount, the crosslinking reaction with the acid-modified polyolefin resin will be sufficiently saturated, and unreacted material will be present, raising concerns about a decrease in various performance characteristics. Therefore, for example, the content of the reactive compound is preferably 5 to 20 parts by mass (solid content ratio) per 100 parts by mass of the acid-modified polyolefin resin.

[0066] Acid-modified polyolefin resins are polyolefin resins into which acidic groups have been introduced. Examples of acidic groups include carboxyl groups, sulfonic acid groups, and acid anhydride groups, with maleic anhydride groups and (meth)acrylic acid groups being particularly preferred. As an acid-modified polyolefin resin, for example, the same type as the modified polyolefin resin used in the sealant layer 16 can be used.

[0067] The second adhesive layer 17 may contain various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, and tackifiers.

[0068] Examples of adhesives that form the second adhesive layer 17 include polyurethane resins obtained by reacting a difunctional or more isocyanate compound with a main component such as polyester polyol, polyether polyol, acrylic polyol, or carbonate polyol, and epoxy resins obtained by reacting an amine compound with a main component having epoxy groups, which are preferred from the viewpoint of heat resistance.

[0069] The thickness of the second adhesive layer 17 is not particularly limited, but from the viewpoint of obtaining the desired adhesive strength and processability, it is preferably 1 to 10 μm, and more preferably 2 to 7 μm.

[0070] [Metal terminal (terminal)] Figure 3 is a cross-sectional view of the resin film and metal terminals for the terminals shown in Figure 1, taken along the line III-III. Of the pair of metal terminals 30, 30, one metal terminal 30 is electrically connected to the positive terminal of the energy storage device body 50, and the other metal terminal 30 is electrically connected to the negative terminal of the energy storage device body 50. The pair of metal terminals 30, 30 extend from the energy storage device body 50 to the outside of the exterior material 10. The shape of the pair of metal terminals 30, 30 can be, for example, a flat plate shape.

[0071] The material for the metal terminal 30 can be any metal. The metal used for the metal terminal 30 should be determined by considering the structure of the energy storage device body 50 and the materials of its components. For example, if the energy storage device 100 is an all-solid-state battery, aluminum can be used as the material for the metal terminal 30 connected to the positive electrode of the energy storage device body 50. For the metal terminal 30 connected to the negative electrode of the energy storage device body 50, copper with a nickel plating layer formed on its surface, or nickel can be used.

[0072] The thickness of the metal terminals 30 depends on the size and capacity of the battery. For small batteries, the thickness of the metal terminals 30 can be, for example, 50 μm or more. For large batteries such as those used for energy storage and automotive applications, the thickness of the metal terminals 30 can be appropriately set within a range of, for example, 100 to 500 μm.

[0073] [Resin film for terminals] The terminal resin film is a film used to cover a portion of the outer surface of a terminal in a power storage device that comprises a power storage device body and terminals electrically connected to the power storage device body.

[0074] As shown in Figures 1 and 3, the terminal resin film 40 is positioned to cover a portion of the outer circumferential surface of the metal terminal 30. Specifically, between the metal terminal 30 and the outer circumferential material 10, a portion of the outer circumferential surface of the metal terminal 30 is covered with the terminal resin film 40 by heat sealing. In Figure 3, the symbol H indicates the heat-sealed portion. By positioning the terminal resin film 40 between the metal terminal 30 and the outer circumferential material 10, the sealing and insulating properties of the energy storage device 100 can be further enhanced. The terminal resin film 40 has heat resistance equivalent to or exceeding that of the sealant layer 16 and the base material layer 11 described above. From the viewpoint of achieving both initial sealing strength and high-temperature sealing strength, heat sealing is preferably performed at 250 to 300°C, more preferably 270 to 290°C, and after heat sealing, cooling is preferably performed at a cooling rate of 1 to 100°C / minute.

[0075] The terminal resin film 40 includes a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent. The polypropylene layer P is obtained by adding a β-nucleating agent to a polypropylene base resin and kneading (dry blending), and then molding it by a T-die method or an inflation method. Alternatively, a masterbatch may be prepared by kneading a nucleating agent at a high concentration into the base resin, and this may be diluted and used as a raw material for layer formation.

[0076] Polypropylene may be a homopolymer of propylene (homopolypropylene), a copolymer of ethylene, butene, octene, etc. with propylene (random polypropylene), or a polypropylene in which polyethylene (preferably polyethylene coated with ethylene propylene rubber (EPR)) is dispersed in homopolypropylene (block polypropylene). From the viewpoint of achieving both initial and high-temperature seal strength, the melting point of the base resin, polypropylene, can be 150 to 175°C, or 160 to 170°C. From this viewpoint, a homopolymer of propylene is preferably used as the polypropylene.

[0077] Polypropylene may be acid-modified polypropylene. Acid-modified polypropylene is polypropylene into which acidic groups have been introduced. Specifically, examples include polypropylene copolymerized or graft polymerized with maleic anhydride, carboxylic acid, sulfonic acid, or their derivatives. From the viewpoint of adhesion to exterior materials and terminals, acid-modified polypropylene may be maleic anhydride-modified polypropylene, and from the viewpoint of adhesion and melting point, the polymerization method may be graft polymerization. In the crystallization of polypropylene, a crystal nucleus is formed as a starting point, and the crystal grows while these form a chemical three-dimensional network. At that time, it is presumed that the acid-modified component in the polypropylene assists in network formation, thereby promoting the formation of β crystals. Furthermore, acid-modified polypropylene also has excellent adhesion to terminals.

[0078] Polypropylene may contain long-chain branched polypropylene. This strengthens the entanglement of the resin, further improving the seal strength (heat resistance). The content of long-chain branched polypropylene in polypropylene can be 2 to 30% by mass, or 5 to 20% by mass, from the viewpoint of flexibility and heat resistance.

[0079] Based on the total amount of the resin composition, the content of the β-nucleating agent can be 0.001 to 15% by mass, may be 0.005 to 5% by mass, may be 0.005 to 1% by mass, or may be 0.02 to 0.5% by mass. If the content of the β-nucleating agent is above the lower limit, it is easier to suppress the decrease in initial and high-temperature seal strength due to insufficient β-crystal formation, and if it is below the upper limit, it is easier to suppress the decrease in initial and high-temperature seal strength due to a decrease in cohesive force.

[0080] Examples of β-crystal nucleating agents from the viewpoint of β-crystal formation include amide compounds, tetraoxaspiro compounds, and quinacridone compounds. The amide compound may be an amide compound having a naphthalene skeleton, a compound having a naphthalene skeleton and two amide bonds, or an amide compound having a cyclohexyl group and a naphthalene skeleton. The amide compound may be N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide or a derivative thereof, or N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide. The above β-crystal nucleating agents may be used individually or as a blend of two or more.

[0081] The β-nucleating agent can be analyzed using known analytical methods such as IR, NMR, various mass (mass) spectroscopy methods, X-ray analysis, and Raman spectroscopy.

[0082] The terminal resin film 40 may contain two or more polypropylene layers, and in particular, three or more polypropylene layers, from the viewpoint of easily adjusting the physical properties of the film. The number of polypropylene layers may be 3 to 10, or 3 to 5, from the viewpoint of processability. However, at least one of these layers is the polypropylene layer P. The polypropylene layers other than polypropylene layer P are formed from a resin composition containing polypropylene. The polypropylene used as the base resin for each layer may be the same or different.

[0083] From the viewpoint of suppressing curling, the outermost layer of the terminal resin film 40 can be formed from the same resin composition. Here, the outermost layer refers to the side that contacts the exterior material of the energy storage device (outer layer side) and the side that contacts the terminal (inner layer side). From the viewpoint of achieving both embedding and insulating properties, the melt flow rate (MFR) can be set such that the outermost layer > intermediate layer, specifically the outermost layer: 1 g / 10 min or more and less than 25 g / 10 min, and the intermediate layer: 0.05 g / 10 min or more and less than 1 g / 10 min.

[0084] When the terminal resin film 40 includes three or more polypropylene layers, at least one of the outermost layers may be a polypropylene layer P, and all layers may be polypropylene layers P. In the terminal resin film 40, the layer that is most susceptible to load (and therefore most prone to cracking), and is in contact with the exterior material or terminal, greatly affects the seal strength. Therefore, by arranging the polypropylene layer P to be in contact with at least the exterior material or terminal, it is easier to improve the seal strength both initially and at high temperatures.

[0085] If the terminal resin film 40 includes three or more polypropylene layers, from the viewpoint of adhesion to the terminal and cost, at least one of the outermost layers may be made of acid-modified polypropylene, but all layers may be made of acid-modified polypropylene.

[0086] If the terminal resin film 40 includes three or more polypropylene layers, from the viewpoint of flexibility and heat resistance, at least one of the outermost layers may contain long-chain branched polypropylene, but all layers may also contain long-chain branched polypropylene.

[0087] The resin composition forming the polypropylene layer may contain other components such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, hydrogen sulfide adsorbents, and tackifiers. The resin composition forming the polypropylene layer may also contain, for example, zinc oxide or cupric oxide to provide hydrogen sulfide resistance, and zeolites to provide moisture barrier properties.

[0088] The thickness of the resin film for the terminal can be 25 μm or more from the viewpoint of sealing performance, and 500 μm or less from the viewpoint of productivity. From this viewpoint, the thickness of the resin film for the terminal may be 50 to 300 μm, or 80 to 200 μm.

[0089] When the terminal resin film includes three polypropylene layers, the thickness ratio of each layer can be, for example, 1:2:1 in the ratio of outer layer:inner layer:outer layer, but the thickness may also be asymmetrical, such as 2:4:4, 2:3:5, 4:4:2, 5:3:2, etc.

[0090] When the terminal resin film contains three polypropylene layers, multiple resin compositions may be prepared and laminated by the T-die method or the inflation method, or two layers may be formed and then another layer may be extruded onto them, or each layer may be made by the inflation method and then bonded together with an adhesive. As for the adhesive to be used, an agent containing acid-modified polypropylene and a curing agent (e.g., isocyanate) can be used from the viewpoint of interfacial adhesion.

[0091] The degree of crystallinity of the β-crystals in the polypropylene layer P (polypropylene layer P after heat sealing) at room temperature (25°C) in the heat-sealed portion of the terminal resin film produced by heat sealing can be 3 to 90%, may be 15 to 80%, or may be 30 to 70%. A degree of crystallinity of β-crystals above the lower limit makes it easier to ensure initial seal strength. A degree of crystallinity of β-crystals below the upper limit makes it easier to ensure seal strength at high temperatures (if a large amount of β-crystals remain, the seal strength at high temperatures tends to decrease). The degree of crystallinity and the degree of crystallinity ratio can be measured by wide-angle X-ray diffraction.

[0092] The crystallinity ratio (β / α: ratio of β crystals to α crystals) of the polypropylene layer P at room temperature (25°C) in the heat-sealed portion of the terminal resin film produced by heat sealing can be 0.01 to 50, may be 0.5 to 30, or 1 to 25. A crystallinity ratio above the lower limit makes it easier to ensure initial seal strength. A crystallinity ratio below the upper limit makes it easier to ensure seal strength at high temperatures (high-temperature seal strength tends to decrease if a large amount of β crystals remain).

[0093] When the energy storage device is left standing at 150°C for one week and then cooled to 25°C, the degree of crystallinity of the α-crystals in the polypropylene layer P at room temperature (25°C) in the heat-sealed portion of the terminal resin film formed by heat sealing can be 25% or more, and the degree of crystallinity ratio (β / α) can be 0 to 1. The degree of crystallinity and the degree of crystallinity ratio (β / α) may be 35% or more and 0 to 0.8, respectively, and 50% or more and 0 to 0.5. A sufficiently large proportion of α-crystals (a small proportion of β-crystals) after standing at 150°C for one week means that a sufficient transition from β-crystals to α-crystals has occurred, which means that the seal strength at high temperatures is excellent.

[0094] Whether a resin film can be suitably used as the above-mentioned resin film for terminals can be determined by the following method. DSC measurements are performed on the polypropylene layer of the resin film under the following conditions to confirm whether the layer has a melting main peak at 160-170°C in the 1st run and a melting main peak at 140-160°C in the 2nd run. A resin film having such a layer (polypropylene layer P) can be determined to be suitable for use as the above-mentioned terminal resin film. The 1st run profile is intended to form an α-crystal by gradually heating and then transition to a β-crystal by gradually cooling. The 2nd run profile is intended to prevent the transition to an α-crystal by rapidly heating. <Measurement conditions> 1st run: Heating from 25℃ to 290℃ (rate: 1.5℃ / min, hold: 290℃-10min), cooling from 290℃ to 25℃ (1.5℃ / min, 25℃-10min) 2nd run: Heating from 25℃ to 290℃ (150℃ / min, 290℃-10min)

[0095] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. In the above embodiment, an example was given in which the corrosion-preventive treatment layer 14 is provided only on one surface of the barrier layer 13 (the side with the second adhesive layer 17). However, the corrosion-preventive treatment layer 14 may also be provided on the other surface of the barrier layer 13 (the side with the first adhesive layer 12). If the sealant layer 16 is attached to the barrier layer 13 by thermal lamination instead of dry lamination, the second adhesive layer 17 does not need to be provided. If the base material layer 11 is provided by coating, the first adhesive layer 12 does not need to be provided. In the above embodiment, a solid-state battery was exemplified as the energy storage device to which the exterior material 10 is applied, but the exterior material 10 may also be applied to other energy storage devices (for example, lithium-ion batteries). [Examples]

[0096] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0097] [Materials used] The base resin and nucleating agent shown in Table 1 were prepared.

[0098] [Table 1]

[0099] [Manufacturing of resin film] According to Tables 2 and 3, a nucleating agent was added to the base resin and kneaded by dry blending (the blending ratios in the tables are in "mass %"). A film was prepared using the inflation method while applying a temperature of 270°C to this mixture. If the resin film had multiple layers, layer (1) was designated as the terminal side.

[0100] [Crystallization] In Tables 2 and 3, the degree of crystallinity was measured as follows. A battery pack as shown in Figure 1 was fabricated using a resin film as the terminal resin film. The heat sealing conditions for the terminal resin film were 290°C, 0.5 MPa, 15 seconds, with a sealing width of 5 mm, and the cooling conditions to 25°C (room temperature) after heat sealing were 50°C / min. A cross-section of the terminal portion was cut out, and the degree of crystallinity of the polypropylene layer of the heat-sealed portion of the terminal resin film was measured using wide-angle X-ray diffraction. The conditions for wide-angle X-ray diffraction were as follows: Filter: Ni (under Cu-Kα line) Output: 40kV, 40mA Analysis: Calculated from diffraction peaks on the α-crystal (040, 060, 110, 130) plane and the β-crystal (300) plane. The measurement conditions for each degree of crystallinity in the table were as follows. • "β-crystallinity": Measured at 25°C after heat sealing. • "β / α": Measured at 25°C after heat sealing. • "α-crystallinity, β / α": Measured at 25°C after being left to stand for one week in a 150°C environment after heat sealing.

[0101] [Table 2]

[0102] [Table 3]

[0103] <Rating> The following evaluation tests were performed on the resin films obtained in each example. The results are shown in Table 4. In Table 4, those without a "D" in the evaluation results can be said to have excellent overall quality.

[0104] [Initial seal strength] A chemically treated aluminum plate (50 mm x 50 mm) was prepared. On the other hand, a resin film was cut to 50 mm (TD) x 100 mm (MD) to obtain a test specimen. This test specimen was folded in half, and the aluminum plate was placed in between. One side of the laminate (test specimen / aluminum plate / test specimen) was heat-sealed with a 10 mm wide sealing bar at 290°C, 0.5 MPa, and for 15 seconds. After that, the sealed portion was cut to a width of 15 mm to obtain a measurement sample (see Figure 4). The seal strength (burst strength) was measured at room temperature (25°C) with a peeling speed of 50 mm / min. Based on the results, the following criteria were used for evaluation. A: Seal strength of 35N / 15mm or more B: Seal strength of 30N / 15mm or more, and less than 35N / 15mm C: Seal strength of 25N / 15mm or more, and less than 30N / 15mm. D: Seal strength less than 25N / 15mm

[0105] [Seal strength under high temperature] A chemically treated aluminum plate (50 mm x 50 mm) was prepared. On the other hand, a resin film was cut to 50 mm (TD) x 100 mm (MD) to obtain a test specimen. This test specimen was folded in half, and the aluminum plate was placed in between. One side of the laminate (test specimen / aluminum plate / test specimen) was heat-sealed with a 10 mm wide sealing bar at 290°C, 0.5 MPa, and for 15 seconds. After that, the sealed portion was cut to a width of 15 mm, left to stand in a 150°C environment for 5 minutes, and then the seal strength (burst strength) was measured in a 150°C environment at a peeling speed of 50 mm / min. Based on the results, the following criteria were used for evaluation. A: Seal strength of 20N / 15mm or more B: Seal strength of 15N / 15mm or more, and less than 20N / 15mm C: Seal strength of 10N / 15mm or more, and less than 15N / 15mm D: Seal strength less than 10N / 15mm

[0106] [Insulation Test] A battery pack, as shown in Figure 1, was fabricated using a resin film as the terminal resin film. The insulation between the negative lead of this battery pack and the outer casing material with exposed metal foil (barrier layer) was measured using a tester. When 25V was applied, a short circuit was determined if the resistance value was less than 30MΩ. The insulation performance was evaluated based on the number of samples that showed a short circuit out of 200 samples, according to the following evaluation criteria. A: Less than 2 short samples B: Two or more short samples, but less than four. C: Short samples: 4 or more, but less than 6 D: Six or more short samples

[0107] [Carl's rating] Samples of resin film cut to a size of 50 mm (TD) x 100 mm (MD) were placed on a smooth surface, and the height from the smooth surface was measured at four points. The curlability was evaluated from the average of the four heights based on the following evaluation criteria. A: Curl height less than 15mm B: Curl height 15mm or more, less than 20mm C: Curl height 20mm or more, less than 25mm D: Curl height of 25mm or more

[0108] [Table 4]

[0109] [Determining the suitability of resin film for use] DSC measurements were performed on the layers of some resin films under the following conditions to confirm whether the layers had a melting main peak at 160-170°C in the 1st run and a melting main peak at 140-160°C in the 2nd run. The melting main peaks are shown in Table 5. In light of the results in Table 4, it can be seen that resin films having such layers can be suitably used as resin films for terminals. <Measurement conditions> 1st run: Heating from 25℃ to 290℃ (rate: 1.5℃ / min, hold: 290℃-10min), cooling from 290℃ to 25℃ (1.5℃ / min, 25℃-10min) 2nd run: Heating from 25℃ to 290℃ (150℃ / min, 290℃-10min)

[0110] [Table 5] [Explanation of Symbols]

[0111] 10...Exterior material, 11...Base material layer, 12...First adhesive layer, 13...Barrier layer, 14...Corrosion prevention treatment layer, 16...Sealant layer, 17...Second adhesive layer, 30...Metal terminal, 40...Resin film for terminal, 50...Energy storage device body, 100...Energy storage device, H...Heat seal section.

Claims

1. A resin film for a terminal, comprising a main body of the energy storage device and terminals electrically connected to the main body of the energy storage device, for covering a portion of the outer surface of the terminals, A resin film for terminals comprising a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent.

2. The terminal resin film according to claim 1, wherein the content of the β-nucleating agent is 0.001 to 15% by mass, based on the total amount of the resin composition.

3. The terminal resin film according to claim 1 or 2, wherein the β-nucleating agent is an amide compound.

4. A resin film for terminals according to any one of claims 1 to 3, comprising three or more polypropylene layers, wherein at least one of the layers is the polypropylene layer P.

5. A resin film for terminals according to any one of claims 1 to 4, comprising three or more polypropylene layers, wherein at least one of the outermost layers is the polypropylene layer P.

6. The terminal resin film according to any one of claims 1 to 5, wherein the polypropylene layer P comprises acid-modified polypropylene.

7. A resin film for terminals according to any one of claims 1 to 6, comprising three or more polypropylene layers, wherein at least one of the outermost layers comprises long-chain branched polypropylene.

8. The main unit of the energy storage device, The terminals electrically connected to the main body of the energy storage device, The device comprises an exterior material that clamps the terminals and houses the main body of the energy storage device, A power storage device in which, between the terminal and the exterior material, a portion of the outer surface of the terminal is covered with a terminal resin film according to any one of claims 1 to 7 by heat sealing.

9. The energy storage device according to claim 8, wherein the degree of crystallinity of the β crystals of the polypropylene layer P in the heat-sealed portion of the resin film for the terminal is 3 to 90%.

10. The energy storage device according to claim 8 or 9, wherein the degree of crystallinity ratio (β / α) of the polypropylene layer P in the heat-sealed portion of the resin film for the terminal is 0.01 to 50.

11. The energy storage device according to any one of claims 8 to 10, wherein when the energy storage device is left standing at 150°C for one week and then cooled to 25°C, the degree of crystallinity of the α crystal of the polypropylene layer P in the heat-sealed portion of the terminal resin film is 25% or more, and the degree of crystallinity ratio (β / α) is 0 to 1.

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