Resin film for terminal and power storage device using the same

Abstract

To provide a resin film for terminal and the like which allow a power storage device to be opened at an early stage in heat generation of the power storage device.SOLUTION: There is provided a resin film for terminal which is arranged so as to cover a partial outer peripheral surface of a metal terminal electrically connected to a power storage device body constituting a power storage device and which comprises a first sealant layer that is bonded to the metal terminal, a core layer that includes a polyolefin resin, and a second sealant layer in this order. At least one of the first sealant layer and the second sealant layer is bonded to the core layer via the adhesive layer. The core layer includes an insulation layer including the polyolefin resin. The first sealant layer and the second sealant layer include an acid modified polyolefin resin. The adhesive layer has a fusion peak at the temperature equal to or less than 110°C. The temperature in the fusion peak is lower than a fusion point of the polyolefin resin or acid modified polyolefin resin included in the first sealant layer, the core layer and the second sealant layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a resin film for a terminal and an electricity storage device using the same. [Background technology]

[0002] In recent years, there has been an increasing demand for miniaturization of portable devices and effective utilization of natural energy sources, leading to research and development of energy storage devices such as lithium-ion secondary batteries that can provide higher voltages and have higher energy densities.

[0003] A known example of such an energy storage device is a laminated lithium-ion secondary battery, which contains a battery body housed inside a bag-shaped exterior material. Such energy storage devices generally include metal terminals called tabs for extracting current from the battery body, and a portion of the outer periphery of the metal terminals is covered with a terminal resin film (sometimes called a "tab sealant").

[0004] A known example of such a resin film for terminals is the one described in Patent Document 1. This document describes a three-layer resin film for terminals in which a core layer made of polypropylene with a melting point of 160°C is sandwiched between two skin layers made of acid-modified polypropylene with a melting point of 140°C. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6281176 Summary of the Invention [Problem to be solved by the invention]

[0006] In electricity storage devices such as lithium-ion secondary batteries, the electricity storage device itself generates heat and reaches a high temperature. This causes the electrolyte to volatilize, increasing the internal pressure of the exterior material, which can eventually cause the electricity storage device to swell. If this condition continues, the internal pressure will continue to increase, eventually resulting in rupture. Therefore, it is desirable to open the electricity storage device before the internal pressure reaches its maximum.

[0007] However, in the resin film for terminals described in Patent Document 1, both the two skin layers and the core layer have high melting points, so the electricity storage device cannot be opened until the resin film for terminals reaches a high temperature. In other words, the resin film for terminals described in Patent Document 1 has room for improvement in terms of early opening properties when the electricity storage device generates heat.

[0008] The present disclosure has been made in consideration of the problems associated with the above-described conventional technologies, and aims to provide a terminal resin film that allows an electricity storage device to be opened early when the electricity storage device generates heat, and an electricity storage device using the same. [Means for solving the problem]

[0009] In order to achieve the above object, the present disclosure provides a resin film for terminals that is arranged to cover the outer peripheral surface of a portion of a metal terminal that is electrically connected to a main body of an electricity storage device that constitutes an electricity storage device, the resin film for terminals having, in this order, a first sealant layer that is adhered to the metal terminal, a core layer containing a polyolefin resin, and a second sealant layer, at least one of the first sealant layer and the second sealant layer is adhered to the core layer via an adhesive layer, the core layer includes an insulating layer containing the polyolefin resin, the first sealant layer and the second sealant layer include an acid-modified polyolefin resin, the adhesive layer has a melting peak at a temperature of 110°C or less, and the temperature at the melting peak is lower than the melting point of the polyolefin resin or the acid-modified polyolefin resin contained in the first sealant layer, the core layer, and the second sealant layer.

[0010] The above-described resin film for terminals provides the following advantages in an electricity storage device obtained by adhering a first sealant layer of the resin film for terminals to the outer peripheral surface of a portion of a metal terminal electrically connected to the electricity storage device main body, housing the electricity storage device main body and an electrolyte solution in an exterior packaging material, and adhering a second sealant layer of the resin film for terminals to the exterior packaging material. Specifically, in the resin film for terminals, the adhesive layer has a melting peak at a temperature of 110°C or lower, and the temperature at the melting peak is lower than the melting points of the polyolefin resins or acid-modified polyolefin resins contained in the first sealant layer, core layer, and second sealant layer. Therefore, even if the electricity storage device main body reaches a high temperature due to its own heat generation or the like, the adhesive layer can be melted before the pressure inside the exterior packaging material increases due to the evaporation of the electrolyte solution, causing the electricity storage device to expand excessively. This can reduce the adhesive strength of the adhesive layer. In this case, because the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin, sufficient adhesion is ensured between the first sealant layer and the metal terminal, and between the second sealant layer and the exterior packaging material. Therefore, when the pressure inside the exterior packaging material increases further, the resin film for terminals allows the electricity storage device to be opened quickly, starting from the adhesive layer rather than between the first sealant layer and the metal terminal or between the second sealant layer and the exterior packaging material. Therefore, the resin film for terminals of the present disclosure can improve the safety of electricity storage devices.

[0011] In the above-mentioned resin film for terminals, it is preferable that the adhesive layer has multiple melting peaks, and that among the multiple melting peaks, the melting peak farthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer exists at a temperature of 70°C or higher and 110°C or lower.

[0012] In this case, if the melting peak farthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer among the multiple melting peaks in the adhesive layer is present at a temperature of 70°C or higher and 110°C or lower, the heat resistance of the electricity storage device can be further improved.

[0013] In the resin film for a terminal, the first sealant layer and the second sealant layer preferably contain an acid-modified polyolefin resin.

[0014] In this case, since the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin, the adhesion between the first sealant layer and the metal terminal is excellent, and the adhesion between the second sealant layer and the exterior material is also excellent.

[0015] In the resin film for a terminal, the acid-modified polyolefin resin contained in the first sealant layer preferably has a melt flow rate of 2.0 g / 10 min or more and less than 35 g / 10 min.

[0016] In this case, if the melt flow rate of the acid-modified polyolefin resin contained in the first sealant layer that is adhered to the metal terminal is 2.0 g / 10 min or more, the fluidity of the first sealant layer at high temperatures is increased, making it easier to fill the gap between the first sealant layer and the metal terminal when the resin film for terminals is heat-sealed to the metal terminal of the electricity storage device. Also, if the melt flow rate of the acid-modified polyolefin resin contained in the first sealant layer is less than 35 g / 10 min, outflow of the first sealant layer can be suppressed when the resin film for terminals is heat-sealed to the metal terminal of the electricity storage device.

[0017] In the resin film for a terminal, the polyolefin resin contained in the insulating layer preferably has a melt flow rate of 0.1 g / 10 min or more and less than 5 g / 10 min.

[0018] In this case, the polyolefin resin contained in the insulating layer has a melt flow rate of 0.1 g / 10 min or more, which improves the processability of the insulating layer and the breaking elongation of the resin film for terminals. Furthermore, the polyolefin resin contained in the insulating layer has a melt flow rate of less than 5 g / 10 min, which makes the insulating layer less likely to melt. Therefore, when the resin film for terminals is sandwiched between a metal terminal of an electricity storage device and an exterior material containing a metal layer and heat-sealed, thinning of the insulating layer (seal thinning) can be suppressed, making it easier to ensure insulation between the metal terminal and the metal layer of the exterior material.

[0019] In the resin film for a terminal, the melting point of the acid-modified polyolefin resin contained in the first sealant layer and the second sealant layer is preferably 120°C or higher and lower than 160°C.

[0020] In this case, if the melting point of the acid-modified polyolefin resin contained in the first sealant layer and the second sealant layer is 120°C or higher, the first sealant layer and the second sealant layer are less likely to melt even when the resin film for terminals is in a high temperature state, making it easier to maintain the seal between the first sealant layer and the metal terminal and the seal between the second sealant layer and the exterior material. Also, if the melting point of the acid-modified polyolefin resin contained in the first sealant layer and the second sealant layer is less than 160°C, the acid-modified polyolefin resin is more likely to melt during heat sealing, further improving the heat seal strength.

[0021] In the resin film for a terminal, the polyolefin resin contained in the insulating layer preferably has a melting point of 130°C or higher and lower than 175°C.

[0022] In this case, since the melting point of the polyolefin resin contained in the insulating layer is 130°C or higher, the insulating layer is less likely to melt, and therefore when the terminal resin film is sandwiched between the metal terminal of the electricity storage device and an exterior material containing a metal layer and heat-sealed, thinning of the insulating layer (seal thinning) can be suppressed, making it easier to ensure insulation between the metal terminal and the metal layer of the exterior material. Also, since the melting point of the polyolefin resin contained in the insulating layer is less than 175°C, the insulating layer softens during sealing, improving its conformability to the metal terminal and embeddability.

[0023] In the resin film for a terminal, the adhesive layer is preferably a layer formed using an adhesive composition containing an acid-modified polyolefin and a curing agent.

[0024] In this case, the first sealant layer and the adhesive layer contain an acid-modified polyolefin, which further improves the adhesion between the first sealant layer and the adhesive layer.

[0025] In the above-mentioned resin film for terminals, it is preferable that the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin, the adhesive layer is a layer formed using an adhesive composition containing an acid-modified polyolefin and a curing agent, the core layer further has a resin layer provided between the adhesive layer and the insulating layer, and the resin layer contains an acid-modified polyolefin resin.

[0026] In this case, the first or second sealant layer, the adhesive composition used in the adhesive layer, and the resin layer of the core layer all contain an acid-modified polyolefin resin, which further improves adhesion between the first or second sealant layer and the adhesive layer, as well as between the resin layer and the adhesive layer, making the first or second sealant layer less likely to peel from the core layer.

[0027] In the above-mentioned resin film for terminals, it is preferable that the curing agent comprises at least one selected from the group consisting of a polyfunctional isocyanate compound, a glycidyl compound, a compound having a carboxy group, and a compound having an oxazoline group.

[0028] In this case, the first sealant layer is less likely to peel off from the core layer.

[0029] In the above-mentioned resin film for terminals, it is preferable that the curing agent is composed of the polyfunctional isocyanate compound, and that the polyfunctional isocyanate compound is composed of at least one compound selected from the group consisting of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and derivatives thereof.

[0030] In this case, the first sealant layer is particularly unlikely to peel off from the core layer.

[0031] In the resin film for a terminal, the polyfunctional isocyanate compound is preferably composed of at least one type selected from the group consisting of nurates, adducts, biurets, and derivatives thereof.

[0032] In this case, peeling of the first sealant layer from the core layer is effectively suppressed.

[0033] In the resin film for a terminal, the thickness of the first sealant layer is preferably greater than the thickness of the second sealant layer.

[0034] When the thickness of the resin film for the terminal is the same, the thickness of the first sealant layer is greater than the thickness of the second sealant layer. Therefore, when the resin film for the terminal is heat-sealed to the metal terminal of the energy storage device, if the first sealant layer is facing the metal terminal, the amount of resin filling the gap between the first sealant layer and the metal terminal can be greater than that of the second sealant layer, making it easier to fill the gap.

[0035] In the resin film for a terminal, the adhesive layer preferably contains a colorant.

[0036] The adhesive layer can be made thinner than the first sealant layer, the core layer, and the second sealant layer, and the thickness uniformity can be improved, so that when the adhesive layer contains a colorant, color unevenness in the resin film for terminals can be suppressed.

[0037] The present disclosure may also provide an electricity storage device comprising: an electricity storage device main body; a metal terminal electrically connected to the electricity storage device main body; an exterior material that sandwiches the metal terminal and houses the electricity storage device main body; an electrolyte solution housed within the exterior material; and a terminal resin film that covers a portion of the outer circumferential surface of the metal terminal and is arranged between the metal terminal and the exterior material, wherein the terminal resin film is made of the above-mentioned terminal resin film, and the first sealant layer of the terminal resin film is adhered to the metal terminal and the second sealant layer is adhered to the exterior material.

[0038] According to this electricity storage device, the adhesive layer in the resin film for terminals has a melting peak at a temperature of 110°C or lower, and the temperature at the melting peak is lower than the melting points of the polyolefin resins or acid-modified polyolefin resins contained in the first sealant layer, core layer, and second sealant layer. Therefore, even if the electricity storage device body becomes hot due to its own heat generation or other reasons, the adhesive layer can melt before the first sealant layer, core layer, and second sealant layer, thereby reducing the adhesive strength of the adhesive layer, before the pressure inside the exterior material increases due to the evaporation of the electrolyte solution and the electricity storage device expands excessively. Since the first sealant layer and the second sealant layer contain acid-modified polyolefin resins, sufficient adhesion is ensured between the first sealant layer and the metal terminals and between the second sealant layer and the exterior material. Therefore, according to this electricity storage device, when the pressure inside the exterior material further increases, the electricity storage device can be opened early, starting from the adhesive layer, rather than between the first sealant layer and the metal terminals or between the second sealant layer and the exterior material. Therefore, the safety of the power storage device can be improved.

[0039] In the present disclosure, the term "melting peak" refers to the point showing the maximum value of heat flow that appears on a DSC curve measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0040] In addition, in the present disclosure, "melting point" refers to the temperature at the melting peak when there is one melting peak, and refers to the temperature at the lowest melting peak when there are multiple melting peaks.

[0041] Furthermore, in the present disclosure, "melt flow rate" (hereinafter referred to as "MFR") refers to a value measured at a measurement temperature of 230°C in accordance with JIS K7210. [Effects of the Invention]

[0042] According to the present disclosure, it is possible to provide a terminal resin film that allows an electricity storage device to be opened early when the electricity storage device generates heat, and an electricity storage device using the same. [Brief explanation of the drawings]

[0043] [Figure 1] 1 is a perspective view showing an electricity storage device according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view of the resin film for terminal and the metal terminal shown in FIG. 1 taken along the line AA. [Figure 3] FIG. 2 is a schematic cross-sectional view showing the resin film for terminal of FIG. 1. [Figure 4] FIG. 2 is a cross-sectional view showing an example of the exterior packaging material shown in FIG. [Figure 5] FIG. 10 is a schematic cross-sectional view showing a first modified example of a resin film for a terminal. [Figure 6] FIG. 10 is a schematic cross-sectional view showing a second modified example of the resin film for terminal. [Figure 7] FIG. 2 is a schematic diagram illustrating a method for preparing a sample for measuring heat seal strength in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0044] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0045] [Energy storage devices] FIG. 1 is a perspective view showing the electricity storage device according to this embodiment, FIG. 2 is a cross-sectional view of the terminal resin film and metal terminal shown in FIG. 1 along line AA, and FIG. 3 is a schematic cross-sectional view showing the terminal resin film of FIG. 1.

[0046] The electricity storage device 10 shown in FIG. 1 is a lithium ion secondary battery, and includes an electricity storage device body 11, an electrolyte (not shown), an exterior material 13, a pair of metal terminals 14 (tab leads), and a terminal resin film 16 (tab sealant).

[0047] The electricity storage device main body 11 is a battery main body that charges and discharges. The exterior material 13 accommodates the electricity storage device main body 11 and an electrolyte solution, and sandwiches a pair of metal terminals 14 via a terminal resin film 16. The pair of metal terminals 14 are electrically connected to the electricity storage device main body 11, with one end of each metal terminal 14 located inside the exterior material 13 and the other end located outside the exterior material 13. A portion of the outer periphery of each metal terminal 14 is covered with a terminal resin film 16 (see FIG. 2), and the terminal resin film 16 is bonded to the exterior material 13. As shown in FIGS. 1 to 3, the terminal resin film 16 has, in this order, a first sealant layer 1 bonded to the metal terminal 14, a core layer 2 containing a polyolefin resin, and a second sealant layer 3 bonded to the exterior material 13. The core layer 2 has an insulating layer 2B containing a polyolefin resin, and the first sealant layer 1 and the second sealant layer 3 contain an acid-modified polyolefin resin. The first sealant layer 1 is adhered to the insulating layer 2B via the adhesive layer 4, and the second sealant layer 3 is adhered to the insulating layer 2B of the core layer 2. The adhesive layer 4 has a melting peak at a temperature of 110°C or lower, and the temperature at the melting peak (hereinafter referred to as the "melting peak temperature") is lower than the melting points of the polyolefin resin or acid-modified polyolefin resin contained in the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3.

[0048] In this electricity storage device 10, the adhesive layer 4 in the terminal resin film 16 has a melting peak at a temperature of 110°C or lower, which is lower than the melting points of the polyolefin resin or acid-modified polyolefin resin contained in the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3. Therefore, even if the electricity storage device main body 11 reaches a high temperature due to its own heat generation or the like, the adhesive layer 4 can be melted before the pressure inside the packaging material 13 increases due to volatilization of the electrolyte solution and the electricity storage device 10 excessively expands, thereby reducing the adhesive strength of the adhesive layer 4. At this time, because the first sealant layer 1 and the second sealant layer 3 contain the acid-modified polyolefin resin, sufficient adhesion is ensured between the first sealant layer 1 and the metal terminal 14 and between the second sealant layer 3 and the packaging material 13. Therefore, according to the electricity storage device 10, when the pressure inside the exterior material 13 further increases, it becomes possible to open the electricity storage device 10 early, starting from the adhesive layer 4, rather than between the first sealant layer 1 and the metal terminal 14 or between the second sealant layer 3 and the exterior material 13. Therefore, the safety of the electricity storage device 10 can be improved.

[0049] The exterior material 13, the metal terminal 14, and the resin film for terminal 16 will be described in detail below.

[0050] [Exterior materials] FIG. 4 is a cross-sectional view showing an example of the exterior packaging material shown in FIG.

[0051] As shown in Figure 4, the exterior material 13 has a seven-layer structure in which, from the side of the energy storage device main body 11, an inner layer 21, an inner layer side adhesive layer 22, a corrosion prevention treatment layer 23-1, a barrier layer 24, a corrosion prevention treatment layer 23-2, an outer layer side adhesive layer 25, and an outer layer 26 are laminated in this order.

[0052] The inner layer 21 is a sealant layer that provides heat-sealing properties to the exterior material 13, and is a layer that is placed on the inside and heat-sealed (thermally fused) when assembling the electricity storage device 10. Examples of the base material for the inner layer (sealant layer) 21 include polyolefin resins and acid-modified polyolefin resins obtained by graft-modifying polyolefin resins with maleic anhydride or the like. Examples of the polyolefin resin that can be used include low-density, medium-density, and high-density polyethylenes; ethylene-α-olefin copolymers; homo-, block-, or random polypropylenes; and propylene-α-olefin copolymers. Among these, it is preferable that the polyolefin resin contains polypropylene. These polyolefin resins can be used alone or in combination of two or more.

[0053] The inner layer 21 may be a single-layer film or a multilayer film in which multiple layers are laminated, depending on the required function. Specifically, it may be a multilayer film in which a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene is interposed to impart moisture resistance. The inner layer 21 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier).

[0054] The thickness of the inner layer 21 is preferably 10 to 150 μm, and more preferably 30 to 80 μm. When the thickness of the inner layer 21 is 10 μm or more, the outer casing 13 can have sufficient adhesion to the outer casing 13 or the terminal resin film 16. Furthermore, when the thickness of the inner layer 21 is 150 μm or less, the cost of the outer casing 13 can be reduced.

[0055] The inner adhesive layer 22 can be appropriately selected from known adhesives such as dry lamination adhesives and acid-modified heat-fusible resins.

[0056] As shown in Figure 4, it is preferable from a performance standpoint that the corrosion prevention treatment layers 23-1 and 23-2 are formed on both sides of the barrier layer 24, but from the standpoint of reducing costs, the corrosion prevention treatment layer 23-1 may be placed only on the surface of the barrier layer 24 located on the inner layer side adhesive layer 22 side.

[0057] The barrier layer 24 may be a conductive metal layer. Examples of materials for the barrier layer 24 include aluminum and stainless steel, with aluminum being preferred from the standpoints of cost, mass (density), and the like.

[0058] The outer adhesive layer 25 may be a polyurethane adhesive containing polyester polyol, polyether polyol, acrylic polyol, or the like as a main component.

[0059] The outer layer 26 may be a single layer or a multilayer film made of nylon, polyethylene terephthalate (PET), or the like. Like the inner layer 21, the outer layer 26 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier). The outer layer 26 may have a protective layer formed by laminating a resin insoluble in the electrolyte solution or coating the outer layer with a resin component insoluble in the electrolyte solution to prevent leakage of the electrolyte solution.

[0060] [Metal terminal] 1 and 2, the pair of metal terminals 14 includes a metal terminal body 14-1 and a corrosion prevention layer 14-2. Of the pair of metal terminal bodies 14-1, one metal terminal body 14-1 is electrically connected to the positive electrode of the electricity storage device body 11, and the other metal terminal body 14-1 is electrically connected to the negative electrode of the electricity storage device body 11. The pair of metal terminal bodies 14-1 extend in a direction away from the electricity storage device body 11, and a portion thereof is exposed from the exterior material 13. The shape of the pair of metal terminal bodies 14-1 may be, for example, a flat plate shape.

[0061] The material of the metal terminal body 14-1 can be a metal, which can be determined in consideration of the structure of the electricity storage device body 11, the materials of each component of the electricity storage device body 11, and the like.

[0062] When the electricity storage device 10 is a lithium ion secondary battery, aluminum can be used as the positive electrode current collector, and copper can be used as the negative electrode current collector. When the electricity storage device 10 is a lithium ion secondary battery, the material of the metal terminal body 14-1 connected to the positive electrode of the electricity storage device body 11 is preferably aluminum. Furthermore, from the viewpoint of corrosion resistance to the electrolyte, the material of the metal terminal body 14-1 connected to the positive electrode of the electricity storage device body 11 is more preferably an aluminum material with a purity of 97% or more, such as 1N30. Furthermore, when the metal terminal body 14-1 is to be bent, it is preferable to use an O material that has been tempered by sufficient annealing in order to add flexibility. The material of the metal terminal body 14-1 connected to the negative electrode of the electricity storage device body 11 is preferably copper with a nickel plating layer formed on its surface, or nickel.

[0063] The thickness of the metal terminal body 14-1 can be determined depending on the size and capacity of the lithium ion secondary battery. In the case of a small lithium ion secondary battery, the thickness of the metal terminal body 14-1 may be 50 μm or more. In the case of a large lithium ion secondary battery for power storage, vehicle use, etc., the thickness of the metal terminal body 14-1 can be appropriately set within the range of 100 to 500 μm.

[0064] The corrosion prevention layer 14-2 is disposed so as to cover the surface of the metal terminal body 14-1. In the case of a lithium-ion secondary battery, the electrolyte contains a corrosive component such as LiPF6. The corrosion prevention layer 14-2 is a layer for preventing corrosion of the metal terminal body 14-1 due to the corrosive component such as LiPF6 contained in the electrolyte.

[0065] [Resin film for terminals] As shown in Fig. 3, the resin film for terminal 16 has, in this order, a first sealant layer 1 adhered to the metal terminal 14, a core layer 2, and a second sealant layer 3 adhered to the exterior packaging material 13. The core layer 2 has an insulating layer 2B containing a polyolefin resin, and the first sealant layer 1 is adhered to the insulating layer 2B via an adhesive layer 4, and the second sealant layer 3 is adhered to the insulating layer 2B of the core layer 2. The first sealant layer 1 and the second sealant layer 3, the core layer 2, and the adhesive layer 4 will be described in detail below.

[0066] (First sealant layer and second sealant layer) The first sealant layer 1 and the second sealant layer 3 may contain an acid-modified polyolefin resin that provides heat-sealing properties to the first sealant layer 1 and the second sealant layer 3. In this case, the first sealant layer 1 and the second sealant layer 3 contain an acid-modified polyolefin resin, which ensures sufficient adhesion between the first sealant layer 1 and the metal terminal 14 and between the second sealant layer 3 and the exterior material 13. Examples of acid-modified polyolefin resins include polyolefin resins graft-modified with maleic anhydride, carboxylic acid, sulfonic acid, and derivatives thereof. Acid-modified polyolefin resins that are maleic anhydride-modified tend to have improved heat-sealing strength compared to resins modified with other groups. Examples of the polyolefin resin include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymers; homo-, block-, or random-polypropylene; propylene-α-olefin copolymers; polybutene; polymethylpentene; and polynorbornene. Among these, the polyolefin resin preferably contains polypropylene from the viewpoints of heat-sealing strength and processability. The acid-modified polyolefin resins may be used alone or in combination of two or more. The first sealant layer 1 and the second sealant layer 3 may or may not further contain a resin other than the acid-modified polyolefin resin.

[0067] The degree of modification with acid of the polyolefin resin (for example, the mass of the portion derived from maleic anhydride relative to the total mass of maleic anhydride-modified polypropylene) is preferably 0.1 to 20 mass%, more preferably 0.3 to 5 mass%, from the viewpoint of improving heat seal strength.

[0068] The first sealant layer 1 and the second sealant layer 3 may contain resin additives such as antioxidants, slip agents, flame retardants, light stabilizers, dehydrating agents, tackifiers, fillers, crystal nucleating agents, etc. A plurality of types of these additives may be blended.

[0069] The melting points of the acid-modified polyolefin resins contained in the first sealant layer 1 and the second sealant layer 3 need only be higher than the peak melting temperature of the adhesive layer 4 at 110°C, but are preferably 120°C or higher but lower than 160°C, more preferably 125 to 155°C, and even more preferably 130 to 150°C. When the melting point of the acid-modified polyolefin resin contained in the acid-modified polyolefin resin is 120°C or higher, the first sealant layer 1 and the second sealant layer 3 are less likely to melt even when the terminal resin film 16 is in a high-temperature state, making it easier to maintain the sealability between the first sealant layer 1 and the metal terminal 14 and between the second sealant layer 3 and the exterior material 13. When the melting point of the acid-modified polyolefin resin contained in the acid-modified polyolefin resin is lower than 160°C, the acid-modified polyolefin resin is more likely to melt during heat sealing, thereby further improving heat seal strength.

[0070] The MFR of the acid-modified polyolefin resin contained in the first sealant layer 1 is preferably 2.0 g / 10 min or more and less than 35 g / 10 min, more preferably 3 to 20 g / 10 min, and particularly preferably 4 to 10 g / 10 min. When the acid-modified polyolefin resin contained in the first sealant layer 1 has an MFR of 2.0 g / 10 min or more, the fluidity of the first sealant layer 1 at high temperatures is increased, which makes it easier to fill the gap between the first sealant layer 1 and the metal terminal 14 when the terminal resin film 16 is heat-sealed to the metal terminal 14 of the electricity storage device 10. When the acid-modified polyolefin resin contained in the first sealant layer 1 has an MFR of less than 35 g / 10 min, it is possible to prevent the resin contained in the first sealant layer 1 from flowing out when the terminal resin film 16 is heat-sealed to the metal terminal 14 of the electricity storage device 10, and to prevent the flowing resin of the first sealant layer 1 from adhering (temporarily bonding) to the metal terminal 14, etc.

[0071] The thickness of the first sealant layer 1 and the second sealant layer 3 is preferably 10 to 200 μm, and more preferably 20 to 150 μm. When the thickness of the first sealant layer 1 and the second sealant layer 3 is 10 μm or more, the adhesion between the metal terminal 14 or the exterior material 13 and the terminal resin film 16 can be further improved. Furthermore, when the thickness of the first sealant layer 1 and the second sealant layer 3 is 200 μm or less, the processability and breaking strength of the first sealant layer 1 and the second sealant layer 3 can be further improved.

[0072] The thickness of the first sealant layer 1 may be greater than or equal to the thickness of the second sealant layer 3, but is preferably greater than the thickness of the second sealant layer 3. If the thickness of the terminal resin film 16 is the same, a thickness of the first sealant layer 1 greater than the thickness of the second sealant layer 3 allows a greater amount of resin to fill the gap between the first sealant layer 1 and the metal terminal 14 when the terminal resin film 16 is heat-sealed to the metal terminal 14 of the electricity storage device 10 than with the second sealant layer 3, making it easier to fill the gap.

[0073] The first sealant layer 1 and the second sealant layer 3 may contain the same resin or different resins. The melting points and MFRs of the first sealant layer 1 and the second sealant layer 3 may be the same or different. From the viewpoint of processability and curl suppression of the resin film for terminal 16, it is preferable that the above-mentioned components of the first sealant layer 1 and the second sealant layer 3 are all the same.

[0074] (core layer) The insulating layer 2B included in the core layer 2 contains a polyolefin resin. Examples of polyolefin resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; homo-, block-, or random polypropylene; propylene-α-olefin copolymer; polybutene; polymethylpentene; and polynorbornene. Among these, the polyolefin resin preferably contains polypropylene from the viewpoints of heat-sealing strength and processability.

[0075] The insulating layer 2B may further contain resin additives such as antioxidants, slip agents, flame retardants, light stabilizers, dehydrating agents, tackifiers, fillers, and crystal nucleating agents, as needed.

[0076] The melting point of the polyolefin resin contained in the insulating layer 2B may be higher than the melting point of the acid-modified polyolefin resin contained in the first sealant layer 1 and the second sealant layer 3, or may be lower than the melting point of the acid-modified polyolefin resin contained in the first sealant layer 1 and the second sealant layer 3, but is preferably higher than the melting point of the acid-modified polyolefin resin 3 contained in the first sealant layer 1 and the second sealant layer. In this case, when the exterior packaging material 13 including the barrier layer 24 made of a metal layer is heat-sealed to the resin film for terminal 16, seal thinning (thinning) of the insulating layer 2B can be suppressed, making it easier to ensure insulation between the barrier layer 24 of the exterior packaging material 13 and the metal terminal 14.

[0077] The melting point of the polyolefin resin contained in the insulating layer 2B may be higher than the peak melting temperature of the adhesive layer 4 at 110°C, but is preferably 130°C or higher but lower than 175°C, more preferably 135 to 170°C, and even more preferably 140 to 165°C. Having a melting point of 130°C or higher makes the insulating layer 2B less likely to melt. Therefore, when heat-sealing is performed while the terminal resin film 16 is sandwiched between the metal terminal 14 of the electricity storage device 10 and the exterior packaging material 13 including the barrier layer 24 made of a metal layer, thinning of the insulating layer 2B (sealing thinning) can be suppressed, and insulation between the metal terminal 14 and the barrier layer 24 of the exterior packaging material 13 can be more easily ensured. Furthermore, having a melting point of the insulating layer 2B lower than 175°C makes it easier for the insulating resin to melt during heat-sealing, further improving heat-seal strength.

[0078] The MFR of the polyolefin resin contained in the insulating layer 2B may be smaller than the MFR of the first sealant layer 1 and the second sealant layer 3 or may be equal to or larger than the MFR of the first sealant layer 1 and the second sealant layer 3, but is preferably smaller than the MFR of the polyolefin resin contained in the first sealant layer 1 and the second sealant layer 3. In this case, when the exterior packaging material 13 including the barrier layer 24 made of a metal layer is heat-sealed to the resin film for terminal 16, seal thinning (thinning) of the insulating layer 2B can be suppressed, making it easier to ensure insulation between the barrier layer 24 of the exterior packaging material 13 and the metal terminal 14.

[0079] The MFR of the polyolefin resin contained in the insulating layer 2B is preferably 0.1 g / 10 min or more and less than 5 g / 10 min, more preferably 0.2 to 4 g / 10 min, and particularly preferably 0.4 to 3 g / 10 min. When the MFR of the polyolefin resin contained in the insulating layer 2B is 0.1 g / 10 min or more, the processability of the insulating layer 2B can be improved, and the breaking elongation of the terminal resin film 16 can be improved. Furthermore, when the MFR of the polyolefin resin contained in the insulating layer 2B is less than 5 g / 10 min, the insulating layer 2B is less likely to melt. Therefore, when the terminal resin film 16 is heat-sealed while sandwiched between the metal terminal 14 of the electricity storage device 10 and the exterior packaging material 13 including the barrier layer 24 made of a metal layer, thinning of the insulating layer 2B (seal thinning) can be suppressed, and insulation between the metal terminal 14 and the barrier layer 24 made of a metal layer of the exterior packaging material 13 can be more easily ensured.

[0080] The thickness of the insulating layer 2B is preferably 10 to 300 μm, more preferably 20 to 250 μm, and even more preferably 30 to 200 μm. When the thickness of the insulating layer 2B is 10 μm or more, the adhesion between the packaging material 13 and the resin film for terminal 16 under high temperature conditions can be further improved. Furthermore, when the thickness of the insulating layer 2B is 300 μm or less, the processability and the breaking elongation of the film can be further improved.

[0081] (adhesive layer) The adhesive layer 4 has a melting peak at a temperature of 110°C or less.

[0082] The adhesive layer 4 may have multiple melting peaks at temperatures equal to or lower than 110° C. In this case, all of the multiple melting peaks may be at temperatures equal to or lower than 110° C., but this is not necessarily required; only some of the melting peak temperatures may be at temperatures equal to or lower than 110° C., and the remaining melting peak temperatures may be at temperatures above 110° C.

[0083] When the adhesive layer 4 has multiple melting peaks at temperatures of 110°C or less, it is preferable that the melting peak farthest from the baseline of a DSC curve measured for the adhesive constituting the adhesive layer 4 (hereinafter, sometimes referred to as the "main melting peak") among the multiple melting peaks exists at a temperature of 70°C or more and 110°C or less. Here, the "melting peak farthest from the baseline of the DSC curve" refers to the melting peak with the greatest shortest distance between the melting peak (the point showing the maximum value of heat flow) and the baseline. The main melting peak more preferably exists at a temperature of 75°C or more, and particularly preferably exists at a temperature of 80°C or more. Having the main melting peak exist at 70°C or more can further improve the heat resistance of the electricity storage device 10.

[0084] The peak melting temperature of the adhesive layer 4 at temperatures of 110°C or less is lower than the melting points of the first sealant layer 1, the core layer 2, and the second sealant layer 3. Here, when the peak melting temperature of the adhesive layer 4 is T (°C) and the lowest melting point among the melting points of the first sealant layer 1, the core layer 2, and the second sealant layer 3 is Tmin (°C), the value of Tmin-T is not particularly limited as long as it is greater than 0°C, but from the viewpoint of improving processability, it is preferably 5°C or higher, and from the viewpoint of more reliably opening the electricity storage device 10 with the adhesive layer 4 and further improving processability, it is preferably 10°C or higher, and more preferably 20°C or higher.

[0085] The adhesive layer 4 is usually formed using an adhesive composition containing a resin and a curing agent. Examples of the resin include acrylic resin, epoxy resin, phenolic resin, urea resin, melamine resin, polyurethane resin, polyolefin resin, and acid-modified polyolefin resin.

[0086] Among these, the resin used in the resin composition of the adhesive layer 4 is preferably a polyolefin resin or an acid-modified polyolefin resin. In this case, the adhesion between the first sealant layer 1 and the adhesive layer 4 is further improved. When the first sealant layer 1 contains an acid-modified polyolefin resin, the resin used in the adhesive layer 4 is preferably an acid-modified polyolefin resin. In this case, the adhesion between the adhesive layer 4 and the first sealant layer 1 is further improved.

[0087] Examples of the curing agent include a polyfunctional isocyanate compound, a glycidyl compound, a compound having a carboxy group, and a compound having an oxazoline group. These can be used alone or in combination of two or more. Among these, it is preferable that the curing agent is at least one selected from the group consisting of a polyfunctional isocyanate compound, a glycidyl compound, a compound having a carboxy group, and a compound having an oxazoline group. In this case, the first sealant layer 1 is more unlikely to peel from the core layer 2.

[0088] The curing agent is preferably a polyfunctional isocyanate compound selected from the group consisting of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and derivatives thereof, which makes the first sealant layer 1 particularly resistant to peeling from the core layer 2.

[0089] Here, the polyfunctional isocyanate compound is preferably at least one selected from the group consisting of nurate compounds, adduct compounds, and biuret compounds, which effectively prevents the first sealant layer 1 from peeling off from the core layer 2.

[0090] The resin film for terminals 16 may contain a colorant to improve visibility. In this case, the colorant may be contained in any of the first sealant layer 1, core layer 2, second sealant layer 3, and adhesive layer 4, but is preferably contained in the adhesive layer 4. The adhesive layer 4 can be made thinner than the layers other than the adhesive layer 4 (i.e., the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3), making it possible to improve thickness uniformity. Therefore, when the adhesive layer 4 contains a colorant, color unevenness in the resin film for terminals 16 can be suppressed.

[0091] The coloring agent may include color pigments and dyes, such as carbon black, quinacridone pigments, polyazo pigments, and isoindolinone pigments.

[0092] Examples of dyes include azo dyes and anthraquinone dyes.

[0093] The thickness of the adhesive layer 4 is preferably no more than 1 time, and more preferably no more than 0.5 times, the thickness of the thinnest layer among the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3. In this case, the adhesive layer 4 is sufficiently thinner than the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3. Therefore, even when the terminal resin film 16 is heat-sealed to the metal terminal 14 or the exterior material 13, the outflow of the resin used in the adhesive layer 4 is sufficiently suppressed compared to the resin contained in the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3, and the resin used in the adhesive layer 4 can be prevented from adhering (temporarily bonding) to the metal terminal 14, etc.

[0094] From the viewpoint of the heat seal strength of the resin film for terminal 16, the thickness of the adhesive layer 4 is preferably 1 to 5 μm, and more preferably 2 to 4 μm.

[0095] The total thickness of the terminal resin film 16 is preferably 200 μm or more, and more preferably 250 μm or more. When the terminal resin film 16 has a total thickness of 200 μm or more, it becomes easier to fill the gap between the metal terminal 14 and the terminal resin film 16 when the terminal resin film 16 is adhered to a thick metal terminal 14 by heat sealing. There is no particular upper limit to the total thickness of the terminal resin film 16, but it may be, for example, 1000 μm or less.

[0096] [Method of manufacturing resin film for terminals] Next, a method for manufacturing the terminal resin film 16 according to this embodiment will be described. The method for manufacturing the terminal resin film 16 is not limited to the following.

[0097] When the terminal resin film 16 has a four-layer structure consisting of a first sealant layer 1, an adhesive layer 4, an insulating layer 2B, and a second sealant layer 3, a two-layer film consisting of the insulating layer 2B and the second sealant layer 3 may be formed in advance, and then the two-layer film and the first sealant layer 1 may be laminated by a dry lamination method using an adhesive composition to form the adhesive layer 4.

[0098] The two-layer film to be formed in advance can be produced by a co-extrusion method such as a T-die extrusion method or an inflation method, but from the viewpoint of film thickness stability, it is preferably produced by an inflation method.

[0099] As an example of a method for manufacturing the terminal resin film 16, a method is described in which a two-layer film is first formed by an inflation method, and then the two-layer film and the first sealant layer 1 are laminated using an adhesive composition to form the adhesive layer 4.

[0100] First, base materials for the insulating layer 2B and the second sealant layer 3 are prepared. Next, the base materials for the insulating layer 2B and the second sealant layer 3 are supplied to an inflation molding machine. Next, the two base materials are extruded from the extrusion section of the inflation molding machine to form a two-layer structure (a structure in which the insulating layer 2B and the second sealant layer 3 are laminated), while air is supplied from inside the extruded two-layer laminate.

[0101] The cylindrically inflated bilayer film is then conveyed and flattened by a guide, after which the bilayer film is folded into a sheet by a pair of pinch rolls. Both ends of the folded tube are slit, and the pair of films (two strips) are wound into a roll around a winding core, producing a roll of bilayer film.

[0102] The extrusion temperature is preferably in the range of 130 to 300°C, more preferably 130 to 250°C. When the extrusion temperature is 130°C or higher, the resins constituting each layer are sufficiently melted, reducing the melt viscosity and stabilizing extrusion from the screw. When the extrusion temperature is 300°C or lower, oxidation and deterioration of the resins constituting each layer are suppressed, preventing deterioration in the quality of the two-layer film.

[0103] The screw rotation speed, blow ratio, take-up speed, etc. can be appropriately set taking into account the film thickness. The film thickness ratio of each layer in a two-layer film can be adjusted by changing the rotation speed of each screw.

[0104] Next, the first sealant layer 1 is laminated onto the obtained two-layer film by dry lamination using an adhesive composition for forming the adhesive layer 4.

[0105] Specifically, the adhesive composition is applied to the two-layer film, dried, and then the second sealant layer 3 is provided thereon and thermocompression-bonded, followed by aging, to obtain the resin film for terminal 16. Drying can be performed at 80 to 140°C for 30 seconds to 5 minutes. After thermocompression bonding, aging can be performed at 30 to 80°C for 24 to 240 hours. The aging hardens the adhesive composition, forming the adhesive layer 4.

[0106] [Method for fusing resin film for terminals] A fusion process for melt-bonding the terminal resin film 16 and the exterior packaging material 13 shown in Fig. 3 will be described below. The case where the first sealant layer 1 of the terminal resin film 16 shown in Fig. 3 is disposed facing the metal terminal 14 side and the second sealant layer 3 facing the exterior packaging material 13 side will be described below.

[0107] In the fusion treatment, the second sealant layer 3 is melted by heating and the second sealant layer 3 and the exterior material 13 are adhered to each other by applying pressure, thereby thermally fusing the terminal resin film 16 and the exterior material 13 together.

[0108] In the fusion treatment, it is preferable to heat the terminal resin film 16 to a temperature equal to or higher than the melting point of the acid-modified polyolefin resin contained in the second sealant layer 3 in order to obtain sufficient adhesion and sealing properties between the terminal resin film 16 and the exterior material 13.

[0109] The heating temperature of the resin film for terminal 16 may be, for example, 140 to 170° C. The treatment time (total time of heating time and pressurizing time) can be determined in consideration of the adhesion to the exterior material 13 and productivity. The treatment time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0110] From the viewpoint of improving the production takt time (productivity) of the terminal resin film 16, heat fusion may be performed by shortening the pressurizing time at a temperature exceeding 170° C. In this case, the heating temperature may be, for example, higher than 170° C. and 230° C. or less, and the pressurizing time may be, for example, 3 to 20 seconds.

[0111] 2, a fusion process for melt-bonding the resin film for terminal 16 and the metal terminal 14 according to this embodiment will be described. In the fusion process, the resin film for terminal 16 and the metal terminal 14 are thermally fused together while simultaneously melting the first sealant layer 1 by heating and bonding the first sealant layer 1 and the metal terminal 14 by applying pressure.

[0112] In the fusion treatment, heating is preferably performed to a temperature equal to or higher than the melting point of the acid-modified polyolefin resin contained in the first sealant layer 1, from the viewpoint of obtaining sufficient adhesion and sealing properties between the resin film for terminal 16 and the metal terminal .

[0113] The heating temperature of the terminal resin film 16 may be, for example, 140 to 170° C. The treatment time (total time of heating time and pressure application time) can be determined in consideration of the adhesion to the metal terminal 14 and productivity. The treatment time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0114] From the viewpoint of improving the production takt time (productivity) of the terminal resin film 16, heat fusion may be performed at a temperature exceeding 170° C. for a short pressurizing time. In this case, the heating temperature may be, for example, higher than 170° C. and 230° C. or less, and the pressurizing time may be, for example, 3 to 20 seconds.

[0115] Although the preferred embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure as set forth in the claims.

[0116] For example, while the core layer 2 in FIG. 4 is composed only of an insulating layer 2B, the core layer 2 may be composed of a laminate of an insulating layer 2B and a resin layer 2A, as in the terminal resin film 116 shown in FIG. 5. The resin contained in the resin layer 2A can be the same as the resin used in the first sealant layer 1 and the second sealant layer 3. When the first sealant layer 1 contains an acid-modified polyolefin resin and the adhesive layer 4 is formed using an adhesive composition containing an acid-modified polyolefin resin, the resin layer 2A preferably contains an acid-modified polyolefin as a resin. In this case, the adhesive composition used in the first sealant layer 1 and the adhesive layer 4, and the resin layer 2A of the core layer 2, contain an acid-modified polyolefin, thereby further improving adhesion between the first sealant layer 1 and the adhesive layer 4 and further improving adhesion between the resin layer 2A and the adhesive layer 4. This makes the first sealant layer 1 less likely to peel from the core layer 2.

[0117] Furthermore, when the core layer 2 and the second sealant layer 3 are bonded via an adhesive layer 4, as in the resin film 216 for terminals shown in FIG. 6 , the resin layer 2A preferably contains an acid-modified polyolefin. In this case, the second sealant layer 3, the adhesive layer 4, and the resin layer 2A of the core layer 2 contain an acid-modified polyolefin, which further improves adhesion between the second sealant layer 3 and the adhesive layer 4, as well as between the resin layer 2A of the core layer 2 and the adhesive layer 4. This makes the second sealant layer 3 less likely to peel from the core layer 2. Similarly, the first sealant layer 1 less likely to peel from the core layer 2. Note that, when multiple adhesive layers 4 are present, as in the resin film 216 for terminals, the multiple adhesive layers 4 may each be formed using the same adhesive composition or different adhesive compositions. Furthermore, the thicknesses of the multiple adhesive layers 4 may be the same or different. From the viewpoints of processability and curl suppression of the resin film 16 for terminals, it is preferable that the above-described configurations of the multiple adhesive layers 4 are all the same.

[0118] Furthermore, in the above embodiment, the terminal resin film 16 is applied to a lithium ion secondary battery, but it can also be applied to electricity storage devices other than lithium ion secondary batteries (for example, all-solid-state batteries, lithium-air batteries, etc.). [Example]

[0119] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0120] <Preparation of Acid-Modified Polypropylene Resin Composition> An acid-modified polypropylene (acid-modified PP) resin composition used in the first sealant layer, the resin layer of the core layer, and the second sealant layer was prepared as follows. That is, an acid-modified PP resin composition was obtained by blending 2 parts by mass of an antiblocking agent with 100 parts by mass of acid-modified PP (trade name "Admer", manufactured by Mitsui Chemicals, Inc.) made of maleic anhydride-modified PP.

[0121] The melting point of the acid-modified PP in this acid-modified PP resin composition was determined by DSC at a heating rate of 10°C / min, and the melting peak temperature appearing in the DSC curve was found to be 140°C, as shown in the "Physical properties of resin" section of Table 1. The MFR of the acid-modified PP in the acid-modified PP resin composition was also measured in accordance with JIS K7210 using an MFR measuring device (manufactured by Toyo Seiki Seisaku-sho, Ltd.) at a measurement temperature of 230°C, and the MFR was 7.0 g / 10 min, as shown in the "Physical properties of resin" section of Table 1.

[0122] <Preparation of Polypropylene Resin Composition> A polypropylene (PP) resin composition used in the insulating layer of the core layer was prepared as follows. That is, a PP resin composition was obtained by blending 1 part by mass of a colorant with 100 parts by mass of PP (trade name "Sumitomo Noblen", manufactured by Sumitomo Chemical Co., Ltd.).

[0123] The melting point of the PP in this PP resin composition was determined in the same manner as for the acid-modified PP resin composition, and was found to be 165°C, as shown in "Physical properties of resin" in Table 1. The MFR of the PP in the PP resin composition was also measured in the same manner as for the acid-modified PP resin composition, and was found to be 0.5 g / 10 min, as shown in "Physical properties of resin" in Table 1.

[0124] <Preparation of Adhesive Composition> (Adhesive composition 1) Acid-modified PP (trade name "Auroren", manufactured by Nippon Paper Industries Co., Ltd.) was dissolved in toluene, and 10 parts by mass of hexamethylene diisocyanate (HDI) nurate (trade name "D-204EA-1", manufactured by Mitsui Chemicals, Inc.) was blended with 100 parts by mass of the acid-modified PP to obtain adhesive composition 1.

[0125] When the DSC curve of this adhesive composition 1 was measured in the same manner as for the acid-modified PP resin composition, two melting peaks appeared in the DSC curve. The melting peak temperatures of the two melting peaks were 57°C and 82°C, respectively. Of these, the melting peak farthest from the baseline of the DSC curve (main melting peak) had a melting peak temperature of 82°C.

[0126] (Adhesive composition 2) Adhesive composition 2 was obtained in the same manner as adhesive composition 1, except that 10 parts by mass of hexamethylene diisocyanate (HDI) nurate was blended with 100 parts by mass of acid-modified PP.

[0127] When the DSC curve of this adhesive composition 2 was measured in the same manner as for adhesive composition 1, one melting peak appeared in the DSC curve, and the melting peak temperature was 75°C.

[0128] (Adhesive composition 3) Adhesive composition 3 was obtained in the same manner as adhesive composition 1, except that 10 parts by mass of the nurate form of hexamethylene diisocyanate (HDI) was blended with 100 parts by mass of the acid-modified PP.

[0129] When the DSC curve of this adhesive composition 3 was measured in the same manner as for adhesive composition 1, one melting peak appeared in the DSC curve. The melting peak temperature was 100°C.

[0130] (Adhesive Composition 4) Adhesive composition 4 was obtained in the same manner as adhesive composition 1, except that 10 parts by mass of hexamethylene diisocyanate (HDI) nurate was blended with 100 parts by mass of PP.

[0131] When the DSC curve of this adhesive composition 4 was measured in the same manner as for adhesive composition 1, one melting peak appeared in the DSC curve, and the melting peak temperature was 82°C.

[0132] (Adhesive Composition 5) Adhesive composition 5 was obtained in the same manner as adhesive composition 1, except that 10 parts by mass of the above toluene diisocyanate (TDI) adduct (product name "CAT10L", manufactured by Toyo Morton Co., Ltd.) was blended with 100 parts by mass of acid-modified PP.

[0133] When the DSC curve of this adhesive composition 5 was measured in the same manner as for adhesive composition 1, two melting peaks appeared in the DSC curve. The melting peak temperatures of the two melting peaks were 57°C and 82°C, respectively. Of these, the melting peak farthest from the baseline of the DSC curve (main melting peak) had a melting peak temperature of 82°C.

[0134] (Adhesive Composition 6) Adhesive composition 6 was obtained by blending a polyester polyol (trade name "TMK55", manufactured by Toyo-Morton) with an adduct of toluene diisocyanate (TDI) (trade name "CAT10L", manufactured by Toyo-Morton) so that the NCO / OH (molar ratio) was 20.

[0135] When the DSC curve of this adhesive composition 6 was measured in the same manner as for adhesive composition 1, no melting peak was observed in the DSC curve.

[0136] (Adhesive Composition 7) Adhesive composition 7 was obtained in the same manner as adhesive composition 1, except that 10 parts by mass of the nurate form of hexamethylene diisocyanate (HDI) was blended with 100 parts by mass of the acid-modified PP.

[0137] When the DSC curve of this adhesive composition 7 was measured in the same manner as for adhesive composition 1, one melting peak appeared in the DSC curve, and the melting peak temperature was 115°C.

[0138] Example 1 A three-layer film was produced by co-extrusion in this order using an inflation method: a resin layer serving as a core layer made of the acid-modified PP resin composition, an insulating layer serving as a core layer made of the PP resin composition, and a second sealant layer made of the acid-modified PP resin composition. The thicknesses of each layer are shown in Table 1.

[0139] On the other hand, a first sealant layer made of an acid-modified PP resin composition was produced by the T-die method. The thickness of the first sealant layer is shown in Table 1.

[0140] The adhesive composition 1 was then applied onto the first sealant layer by a direct gravure method, dried, and then the first sealant layer was laminated onto the three-layer film via the adhesive composition 1. The film was then aged at 40°C for 120 hours to cure the adhesive composition 1 and obtain an adhesive layer. The thickness of the obtained adhesive layer was 3 μm, as shown in Table 1. A resin film for terminals was thus obtained.

[0141] Example 2 A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 2 was used as the adhesive composition.

[0142] Example 3 A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 3 was used as the adhesive composition.

[0143] Example 4 A resin film for terminals was obtained in the same manner as in Example 1, except that the core layer was composed of only an insulating layer and the thickness of the first sealant layer was changed as shown in Table 1.

[0144] Example 5 A resin film for terminals was obtained in the same manner as in Example 1, except that the thicknesses of the first sealant layer, the resin layer of the core layer, the insulating layer of the core layer, and the second sealant layer were changed as shown in Table 1.

[0145] Example 6 A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 4 was used as the adhesive composition.

[0146] Example 7 A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 5 was used as the adhesive composition.

[0147] (Comparative Example 1) A resin film for terminals was obtained in the same manner as in Example 1, except that the core layer was composed only of an insulating layer, and no adhesive layer was used, and the first sealant layer, the insulating layer of the core layer, and the second sealant layer were co-extruded.

[0148] (Comparative Example 2) A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 6 was used as the adhesive composition.

[0149] (Comparative Example 3) A resin film for terminals was obtained in the same manner as in Example 1, except that adhesive composition 7 was used as the adhesive composition.

[0150] [Early opening] (1) Preparation of tabs The metal terminals used were 5 mm wide, 30 mm long, and 100 μm thick. The metal terminals were made of aluminum for the positive electrode and nickel for the negative electrode. Both the positive and negative electrodes were subjected to a non-chromium surface treatment. The resin film for the terminals was cut to a width of 15 mm and a length of 10 mm. The resin film for the terminals, metal terminal, and resin film for the terminals were laminated in this order, and fusion was performed at a fusion temperature of 150°C for a fusion time of 10 seconds. This resulted in the production of a positive electrode tab and a negative electrode tab.

[0151] (2) Battery pack construction The exterior material used had a laminated structure of nylon film (25 μm thick), polyester polyol adhesive (5 μm thick), aluminum foil (40 μm thick, A8079-O material), acid-modified polypropylene (30 μm thick), and polypropylene (40 μm thick). Both sides of the aluminum foil were treated with a non-chrome surface. The exterior material measured 50 mm × 90 mm, and the long edge was folded in half. One side of the 45 mm width was heat-sealed with the positive and negative electrode tabs sandwiched between them. Heat sealing was performed at 190°C for 5 seconds. The remaining two tab-free edges were heat-sealed at 190°C for 3 seconds. First, the opposite side of the folded edge was heat-sealed, followed by filling with 2 ml of electrolyte solution containing LiPF6 (lithium hexafluorophosphate) in a mixture of diethyl carbonate and ethylene carbonate. Finally, the opposite side of the tab was heat-sealed. This resulted in the production of a battery pack for evaluation of the tab, which did not contain battery elements such as a current collector. Note that the conditions for producing the battery pack described above were more severe than those in the actual battery production process in terms of heating temperature and heat sealing time.

[0152] (3) Evaluation The battery packs prepared as described above were placed in an oven and heated, and the state of the battery packs was visually observed until the temperature reached 120°C. The early opening property of the terminal resin film was evaluated according to the following evaluation criteria. A rating of "◎" was considered to be acceptable, and a rating of "×" was considered to be unacceptable. The results are shown in Table 1. Note that a rating of "◎" was determined to indicate that the battery pack was opened early by the terminal resin film after the internal pressure of the battery pack increased. (Evaluation criteria) ◎: After the battery pack expands, it shrinks before the temperature reaches 120°C. ×: After the battery pack expands, it remains in this state even when the temperature reaches 120°C.

[0153] [Adhesion] A sample of the terminal resin film was cut to a size of 50 mm (TD) x 100 mm (MD), and folded in half to sandwich a 50 mm x 50 mm piece of chemically treated aluminum foil. The edge opposite the fold was heat-sealed with a sealing bar at 165°C / 0.6 MPa / 10 seconds across a 10 mm width. A 15 mm-wide sample was then cut out from the center of the heat-sealed area (see Figure 7) to prepare a sample for heat-seal strength measurement. This sample was immersed in an electrolyte containing 1500 ppm water at 85°C for one week. The electrolyte used was a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a 1:1:1 (volume ratio) ratio, to which lithium hexafluorophosphate (LiPF6) was added to achieve a concentration of 1.0 M. Then, a T-peel test was performed to peel the resin film for terminals from the aluminum foil using a tensile tester (manufactured by Shimadzu Corporation) at a temperature of 25°C and a tensile speed of 50 mm / min. The heat-resistant heat seal strength (burst strength) to the aluminum foil was evaluated based on the results obtained and the following criteria. The results are shown in Table 1. (Evaluation criteria) ◎: Heat seal strength is 20N / 15mm or more 〇: Heat seal strength is 15N / 15mm or more and less than 20N / 15mm ×: Heat seal strength is less than 15N / 15mm

[0154] [Embeddability] Three samples were prepared by sandwiching a 5 cm long, 6 mm wide, and 200 μm thick metal terminal made of surface-treated aluminum between two identical sheets of terminal resin film and heat-sealing the terminal resin film at 165°C / 0.6 MPa. The sealing times for the three samples were 2, 3, or 4 seconds. The samples were then examined for the filling of the gap between the outer surface of the metal terminal and the terminal resin film using Red Checker Liquid (trade name "NEW Micro Check Penetration Liquid" manufactured by Ichinen Chemicals Co., Ltd.). Specifically, the samples were immersed in Red Checker Liquid for 10 minutes, and then visually inspected for redness in the gap between the outer surface of the metal terminal and the terminal resin film. The embeddability of the terminal resin film was evaluated based on the following criteria. The results are shown in Table 1. (Evaluation criteria) ◎: Sealing time is 2 seconds and gaps can be filled 〇: Seals in 3 seconds and can fill gaps ×: The gap cannot be filled unless the sealing time is 4 seconds.

[0155] [Table 1]

[0156] From the results shown in Table 1, the resin films for terminals of Examples 1 to 7 passed the test in terms of early opening properties in a high-temperature environment, whereas the resin films for terminals of Comparative Examples 1 to 3 failed the test in terms of early opening properties in a high-temperature environment. Therefore, it was confirmed that the resin film for a terminal according to the present disclosure allows the electricity storage device to be opened early when the electricity storage device generates heat. [Explanation of symbols]

[0157] 1...first sealant layer, 2...core layer, 2A...resin layer, 2B...insulating layer, 3...second sealant layer, 4...adhesive layer, 10...electricity storage device, 11...electricity storage device main body, 14...metal terminal, 16,116,216...resin film for terminal.

Claims

1. A terminal resin film that is arranged to cover a part of an outer peripheral surface of a metal terminal that is electrically connected to an electricity storage device main body that constitutes an electricity storage device, The resin film for terminals is a first sealant layer adhered to the metal terminal; a core layer containing a polyolefin resin; a second sealant layer, in this order; At least one of the first sealant layer and the second sealant layer is adhered to the core layer via an adhesive layer; the core layer includes an insulating layer containing the polyolefin resin, the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin, A resin film for terminals, wherein the adhesive layer has a melting peak at a temperature of 110°C or less, and the temperature at the melting peak is lower than the melting point of the polyolefin resin or the acid-modified polyolefin resin contained in the first sealant layer, the core layer, and the second sealant layer.

2. 2. The resin film for terminals according to claim 1, wherein the adhesive layer has a plurality of melting peaks, and among the plurality of melting peaks, the melting peak farthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer is present at a temperature of 70°C or higher and 110°C or lower.

3. The resin film for a terminal according to claim 1 or 2, wherein the acid-modified polyolefin resin contained in the first sealant layer has a melt flow rate of 2.0 g / 10 min or more and less than 35 g / 10 min.

4. The resin film for a terminal according to any one of claims 1 to 3, wherein the polyolefin resin contained in the insulating layer has a melt flow rate of 0.1 g / 10 min or more and less than 5 g / 10 min.

5. The resin film for terminals according to any one of claims 1 to 4, wherein the melting point of the acid-modified polyolefin resin contained in the first sealant layer and the second sealant layer is 120 ° C or higher and lower than 160 ° C.

6. The resin film for terminals according to any one of claims 1 to 5, wherein the melting point of the polyolefin resin contained in the insulating layer is 130°C or higher and lower than 175°C.

7. The resin film for terminals according to any one of claims 1 to 6, wherein the adhesive layer is a layer formed using an adhesive composition containing an acid-modified polyolefin resin and a curing agent.

8. the core layer further includes a resin layer provided between the adhesive layer and the insulating layer, The resin film for a terminal according to claim 7 , wherein the resin layer contains an acid-modified polyolefin resin.

9. The resin film for terminals according to claim 7 or 8, wherein the curing agent is at least one selected from the group consisting of a polyfunctional isocyanate compound, a glycidyl compound, a compound having a carboxy group, and a compound having an oxazoline group.

10. The resin film for terminals according to claim 9, characterized in that the curing agent is composed of the polyfunctional isocyanate compound, and the polyfunctional isocyanate compound is composed of at least one selected from the group consisting of hexamethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and derivatives thereof.

11. The resin film for a terminal according to claim 10, wherein the polyfunctional isocyanate compound is at least one selected from the group consisting of a nurate compound, an adduct compound, a biuret compound, and derivatives thereof.

12. The resin film for a terminal according to any one of claims 1 to 11, wherein the thickness of the first sealant layer is greater than the thickness of the second sealant layer.

13. The resin film for a terminal according to any one of claims 1 to 12, wherein the adhesive layer contains a colorant.

14. a power storage device body; a metal terminal electrically connected to the electricity storage device body; an exterior material that holds the metal terminals and houses the electricity storage device main body; an electrolyte solution contained in the exterior packaging; a terminal resin film that covers a part of an outer peripheral surface of the metal terminal and is disposed between the metal terminal and the exterior material; The resin film for a terminal is made of the resin film for a terminal according to any one of claims 1 to 13, the first sealant layer of the resin film for terminal is adhered to the metal terminal; The second sealant layer is adhered to the exterior material.

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