Resin film for terminals, and energy 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 terminals and a power storage device using the same.

Background Art

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

[0003] As such a power storage device, a laminated lithium-ion secondary battery in which a battery body is housed inside a bag-shaped exterior material is known. Such a power storage device generally includes a metal terminal called a tab for extracting current from the battery body, and a part of the outer peripheral surface of the metal terminal is covered with a resin film for terminals (sometimes called a "tab sealant").

[0004] As such a resin film for terminals, conventionally, for example, the one described in Patent Document 1 below is known. The document describes a three-layer resin film for terminals in which a core layer using polypropylene with a melting point of 160°C is sandwiched between two skin layers using acid-modified polypropylene with a melting point of 140°C.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, in energy storage devices such as lithium-ion secondary batteries, the device itself generates heat and reaches high temperatures. This causes the electrolyte to volatilize, increasing the internal pressure of the casing, which can eventually cause the device to swell. If this condition persists, the internal pressure will continue to rise, eventually leading to rupture. Therefore, it is desirable to open the energy storage device before the internal pressure reaches its limit.

[0007] However, in the terminal resin film described in Patent Document 1, both the skin layer and the core layer have high melting points, making it impossible to open the energy storage device until the terminal resin film reaches a high temperature. In other words, the terminal resin film described in Patent Document 1 had room for improvement in terms of early opening when the energy storage device generates heat.

[0008] This disclosure has been made in view of the problems of the above-mentioned prior art, and aims to provide a resin film for terminals that allows an energy storage device to be opened early when the energy storage device generates heat, and an energy storage device using the same. [Means for solving the problem]

[0009] To achieve the above objective, the present disclosure provides a terminal resin film disposed to cover a portion of the outer circumferential surface of a metal terminal electrically connected to a main body of an energy storage device, wherein the terminal resin film comprises, in this order, a first sealant layer adhered to the metal terminal, a core layer containing a polyolefin resin, and a second sealant layer, wherein 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, 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] According to the above-described terminal resin film, in an energy storage device obtained by adhering the first sealant layer of the terminal resin film to the outer surface of a portion of the metal terminals electrically connected to the energy storage device body, housing the energy storage device body and electrolyte in an outer casing, and adhering the second sealant layer of the terminal resin film to the outer casing, the following effects can be obtained. That is, in the terminal resin film, 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 point of the polyolefin resin or acid-modified polyolefin resin contained in the first sealant layer, core layer, and second sealant layer. Therefore, even if the energy storage device body becomes hot due to its own heat generation, the adhesive layer can be melted 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 outer casing increases due to the evaporation of the electrolyte and the energy storage device expands excessively. In this case, since the first sealant layer and the second sealant layer contain acid-modified polyolefin resin, sufficient adhesion between the first sealant layer and the metal terminal, and between the second sealant layer and the exterior material are ensured. Therefore, with the terminal resin film, when the internal pressure of the exterior material increases further, it becomes possible to open the energy storage device earlier, 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 material. Thus, the terminal resin film of this disclosure can enhance the safety of the energy storage device.

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

[0012] In this case, among the multiple melting peaks in the adhesive layer, the melting peak furthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer is located at a temperature between 70°C and 110°C, thereby further improving the heat resistance of the energy storage device.

[0013] 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.

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

[0015] In the above-mentioned resin film for terminals, it is preferable that the melt flow rate of the acid-modified polyolefin resin contained in the first sealant layer is 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 adheres to the metal terminal is 2.0 g / 10 min or higher, 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 heat-sealing the terminal resin film to the metal terminal of the energy storage device. Furthermore, if the melt flow rate of the acid-modified polyolefin resin contained in the first sealant layer is less than 35 g / 10 min, the outflow of the first sealant layer can be suppressed when heat-sealing the terminal resin film to the metal terminal of the energy storage device.

[0017] In the above-mentioned resin film for terminals, it is preferable that the melt flow rate of the polyolefin resin contained in the insulating layer is 0.1 g / 10 min or more and less than 5 g / 10 min.

[0018] In this case, if the melt flow rate of the polyolefin resin contained in the insulating layer is 0.1 g / 10 min or higher, the processability of the insulating layer can be improved, and the elongation at break of the terminal resin film can be improved. Furthermore, if the melt flow rate of the polyolefin resin contained in the insulating layer is less than 5 g / 10 min, the insulating layer becomes less likely to melt. Therefore, when heat sealing is performed with the terminal resin film sandwiched between the metal terminal of the energy storage device and the outer material containing the metal layer, thinning of the insulating layer (seal shrinkage) can be suppressed, making it easier to ensure insulation between the metal terminal and the metal layer of the outer material.

[0019] In the above-mentioned resin film for terminals, it is preferable that 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 less than 160°C.

[0020] In this case, if the melting point of the acid-modified polyolefin resin contained in the first and second sealant layers is 120°C or higher, the first and second sealant layers will not melt easily even when the terminal resin film is at a high temperature, making it easier to maintain the sealing properties between the first sealant layer and the metal terminal, and between the second sealant layer and the exterior material. Furthermore, if the melting point of the acid-modified polyolefin resin contained in the first and second sealant layers is less than 160°C, the acid-modified polyolefin resin will melt more easily during heat sealing, further improving the heat seal strength.

[0021] In the above-mentioned resin film for terminals, it is preferable that the melting point of the polyolefin resin contained in the insulating layer is 130°C or higher and less 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. Therefore, when heat-sealing the resin film for terminals while sandwiching it between the metal terminals of the power storage device and the exterior material including the metal layer, thinning (seal slimming) of the insulating layer can be suppressed, and it becomes easier to ensure the insulation between the metal terminals 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, so the followability to the metal terminals is improved and the embedding property is improved.

[0023] In the above resin film for terminals, it is preferable that the adhesive layer is a layer formed using an adhesive composition containing an acid-modified polyolefin and a curing agent.

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

[0025] In the above resin film for terminals, 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 it is preferable that the resin layer contains an acid-modified polyolefin resin.

[0026] In this case, since the first sealant layer or the second sealant layer, the adhesive composition used for the adhesive layer, and the resin layer of the core layer all contain an acid-modified polyolefin resin, the adhesion between the first sealant layer or the second sealant layer and the adhesive layer is further improved, and the adhesion between the resin layer and the adhesive layer is further improved. For this reason, it becomes difficult for the first sealant layer or the second sealant layer to peel off from the core layer.

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

[0028] In this case, the first sealant layer becomes more difficult to peel from the core layer.

[0029] In the resin film for terminals, it is preferable 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.

[0030] In this case, the first sealant layer becomes particularly difficult to peel from the core layer.

[0031] In the resin film for terminals, it is preferable that the polyfunctional isocyanate compound is composed of at least one selected from the group consisting of nurate forms, adduct forms, burette forms, and derivatives thereof.

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

[0033] In the resin film for terminals, it is preferable that the thickness of the first sealant layer is larger than the thickness of the second sealant layer.

[0034] When the thicknesses of the resin films for terminals are the same, when the resin film for terminals is heat-sealed to the metal terminal of the power storage device with the first sealant layer facing the metal terminal side, since the amount of resin filling the gap between the first sealant layer and the metal terminal can be made larger than that of the second sealant layer, the gap can be filled more easily.

[0035] In the above-mentioned resin film for terminals, it is preferable that the adhesive layer contains a coloring agent.

[0036] The adhesive layer can be made thinner than the first sealant layer, the core layer, and the second sealant layer, and thickness uniformity can be improved. Therefore, when the adhesive layer contains a coloring agent, color unevenness in the terminal resin film can be suppressed.

[0037] Furthermore, the present disclosure may also provide an energy storage device comprising: an energy storage device body; a metal terminal electrically connected to the energy storage device body; an outer casing material that clamps the metal terminal and houses the energy storage device body; an electrolyte contained within the outer casing material; and a terminal resin film that covers a portion of the outer circumferential surface of the metal terminal and is disposed between the metal terminal and the outer casing material, wherein the terminal resin film is made of the above-described terminal resin film, the first sealant layer of the terminal resin film is bonded to the metal terminal, and the second sealant layer is bonded to the outer casing material.

[0038] In this energy storage device, the adhesive layer in the terminal resin film has a melting peak at a temperature of 110°C or lower, and the temperature at this melting peak is lower than the melting point of the polyolefin resin or acid-modified polyolefin resin contained in the first sealant layer, core layer, and second sealant layer. Therefore, even if the energy storage device body becomes hot due to its own heat generation, the adhesive layer can be melted before the first sealant layer, core layer, and second sealant layer, reducing the adhesive strength of the adhesive layer, before the pressure inside the outer material increases due to the evaporation of the electrolyte and the energy storage device expands excessively. At this time, since the first sealant layer and the second sealant layer contain acid-modified polyolefin resin, sufficient adhesion between the first sealant layer and the metal terminal, and between the second sealant layer and the outer material is ensured. Therefore, with this energy storage device, when the pressure inside the outer material increases further, it is possible to open the energy storage device early, starting from the adhesive layer, rather than between the first sealant layer and the metal terminal, or between the second sealant layer and the outer material. Therefore, energy storage devices can be made safer.

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

[0040] Furthermore, in this disclosure, "melting point" means the temperature at the melting peak if there is one melting peak, and the temperature at the lowest melting peak if there are multiple melting peaks.

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

[0042] According to this disclosure, it is possible to provide a resin film for terminals that allows an energy storage device to be opened early when the energy storage device generates heat, and an energy storage device using the same. [Brief explanation of the drawing]

[0043] [Figure 1] This is a perspective view showing the energy storage device according to this embodiment. [Figure 2] Figure 1 is a cross-sectional view of the resin film for the terminal and the metal terminal in the direction of line AA. [Figure 3] Figure 1 is a schematic cross-sectional view showing the resin film for the terminals. [Figure 4] Figure 1 is a cross-sectional view showing an example of exterior material. [Figure 5] This is a schematic cross-sectional view showing a first modified example of a resin film for terminals. [Figure 6] This is a schematic cross-sectional view showing a second modified example of the resin film for terminals. [Figure 7] This is a schematic diagram illustrating the method for preparing samples for measuring heat seal strength in the examples. [Modes for carrying out the invention]

[0044] Preferred embodiments of this disclosure will be described below 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. Furthermore, the dimensional ratios in the drawings are not limited to those shown.

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

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

[0047] The energy storage device body 11 is the battery body that performs charging and discharging. The outer casing material 13 houses the energy storage device body 11 and the electrolyte, and also holds a pair of metal terminals 14 via a terminal resin film 16. The pair of metal terminals 14 are electrically connected to the energy storage device body 11, with one end of each metal terminal 14 positioned inside the outer casing material 13 and the other end positioned outside the outer casing material 13. A portion of the outer circumferential surface of each metal terminal 14 is covered by the terminal resin film 16 (see Figure 2), and the terminal resin film 16 is bonded to the outer casing material 13. As shown in Figures 1 to 3, the terminal resin film 16 has, in this order, a first sealant layer 1 bonded to the metal terminals 14, a core layer 2 containing polyolefin resin, and a second sealant layer 3 bonded to the outer casing material 13. The core layer 2 has an insulating layer 2B containing polyolefin resin, and the first sealant layer 1 and the second sealant layer 3 contain acid-modified polyolefin resin. The first sealant layer 1 is bonded to the insulating layer 2B via an adhesive layer 4, and the second sealant layer 3 is bonded to the insulating layer 2B of the core layer 2. The adhesive layer 4 has a melting peak at temperatures below 110°C, and the temperature at this melting peak (hereinafter referred to as the "melting peak temperature") is lower than the melting point 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 energy 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, and the melting peak temperature is lower than the melting point 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 energy storage device body 11 becomes hot due to its own heat generation, the adhesive layer 4 can be melted before the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3, thereby reducing the adhesive strength of the adhesive layer 4, before the pressure inside the exterior material 13 increases due to the evaporation of the electrolyte and the energy storage device 10 expands excessively. At this time, since the first sealant layer 1 and the second sealant layer 3 contain acid-modified polyolefin resin, 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 are ensured. Therefore, with the energy storage device 10, when the internal pressure of the outer casing material 13 increases further, it is possible to open the energy storage device 10 earlier, starting from the adhesive layer 4, rather than from between the first sealant layer 1 and the metal terminal 14, or between the second sealant layer 3 and the outer casing material 13. Thus, the safety of the energy storage device 10 can be enhanced.

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

[0050] [Exterior materials] Figure 4 is a cross-sectional view showing an example of the exterior material shown in Figure 1.

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

[0052] The inner layer 21 is a sealant layer that provides heat sealing properties to the outer material 13, and is placed on the inside of the energy storage device 10 during assembly and heat-sealed (heat-fused). As the base material of the inner layer (sealant layer) 21, for example, a polyolefin resin or an acid-modified polyolefin resin obtained by grafting maleic anhydride or the like onto a polyolefin resin can be used. As the above polyolefin resin, low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; homo, block, or random polypropylene; propylene-α-olefin copolymer, etc. can be used. Among these, it is preferable that the above polyolefin resin contains polypropylene. These polyolefin resins can be used individually or in combination of two or more types.

[0053] The inner layer 21 may be a single-layer film or a multilayer film formed by laminating multiple layers, depending on the required function. Specifically, it may be a multilayer film with a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene interposed to provide moisture resistance. The inner layer 21 may contain various additives (flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, tackifiers, etc.).

[0054] The thickness of the inner layer 21 is preferably 10 to 150 μm, and more preferably 30 to 80 μm. A thickness of 10 μm or more for the inner layer 21 allows the outer material 13 to have sufficient adhesion to the outer material 13 or the terminal resin film 16. Furthermore, a thickness of 150 μm or less for the inner layer 21 can reduce the cost of the outer material 13.

[0055] As the inner adhesive layer 22, any known adhesive such as a dry lamination adhesive or an acid-modified heat-sealable resin can be appropriately selected and used.

[0056] As shown in Figure 4, it is preferable from a performance standpoint to form the corrosion-preventive treatment layers 23-1 and 23-2 on both sides of the barrier layer 24. However, from the viewpoint of reducing costs, the corrosion-preventive treatment layer 23-1 may be placed only on the side of the barrier layer 24 that is located on the inner layer 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, and aluminum is preferred from the viewpoint of cost, mass (density), etc.

[0058] As the outer adhesive layer 25, a polyurethane-based adhesive mainly composed of polyester polyol, polyether polyol, acrylic polyol, etc., can be used.

[0059] The outer layer 26 may be a single-layer film or a multi-layer film of nylon, polyethylene terephthalate (PET), etc. The outer layer 26 may contain various additives (flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, tackifiers, etc.) similar to the inner layer 21. The outer layer 26 may have a protective layer formed by laminating it with a resin insoluble in the electrolyte or coating it with a resin component insoluble in the electrolyte to prevent electrolyte leakage.

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

[0061] The material used for the metal terminal body 14-1 can be metal. This metal can be determined by considering the structure of the energy storage device body 11 and the materials of each component of the energy storage device body 11.

[0062] When the energy 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 energy 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 energy 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 energy storage device body 11 is more preferably aluminum material with a purity of 97% or higher, such as 1N30. In addition, when the metal terminal body 14-1 is bent, it is preferable to use O material that has been sufficiently annealed to add flexibility. The material of the metal terminal body 14-1 connected to the negative electrode of the energy 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 according to the size and capacity of the lithium-ion secondary battery. For small lithium-ion secondary batteries, the thickness of the metal terminal body 14-1 may be 50 μm or more. For large lithium-ion secondary batteries used in energy storage, automotive applications, 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 positioned to cover the surface of the metal terminal body 14-1. In the case of lithium-ion secondary batteries, the electrolyte contains corrosive components such as LiPF6. The corrosion prevention layer 14-2 is a layer that suppresses corrosion of the metal terminal body 14-1 by corrosive components such as LiPF6 contained in the electrolyte.

[0065] [Resin film for terminals] As shown in Figure 3, the terminal resin film 16 has, in this order, a first sealant layer 1 that is bonded to the metal terminal 14, a core layer 2, and a second sealant layer 3 that is bonded to the exterior material 13. The core layer 2 has an insulating layer 2B containing polyolefin resin, the first sealant layer 1 is bonded to the insulating layer 2B via an adhesive layer 4, and the second sealant layer 3 is bonded to the insulating layer 2B of the core layer 2. The first sealant layer 1, 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 imparts heat-sealing properties to the first sealant layer 1 and the second sealant layer 3. In this case, since the first sealant layer 1 and the second sealant layer 3 contain an acid-modified polyolefin resin, 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 are ensured. Examples of acid-modified polyolefin resins include resins obtained by graft-modifying a polyolefin resin with maleic anhydride, carboxylic acid, sulfonic acid, and their derivatives. It is preferable that the acid-modified polyolefin resin is modified with maleic anhydride because it tends to improve heat seal strength compared to other modification groups. Examples of the above 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, it is preferable that the above polyolefin resin contains polypropylene from the viewpoint of heat seal strength and processability. The above-mentioned acid-modified polyolefin resin may be used alone or in combination of two or more types. Furthermore, the first sealant layer 1 and the second sealant layer 3 may or may not contain other resins other than the acid-modified polyolefin resin.

[0067] The acid modification rate 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% by mass, and more preferably 0.3 to 5% by 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, and nucleating agents. These additives may be blended in multiple types.

[0069] The melting point of the acid-modified polyolefin resin contained in the first sealant layer 1 and the second sealant layer 3 should be higher than the melting peak temperature of the adhesive layer 4 at 110°C, but is preferably 120°C or higher and less than 160°C, more preferably 125 to 155°C, and even more preferably 130 to 150°C. Having a melting point of 120°C or higher for the acid-modified polyolefin resin makes it less likely for the first sealant layer 1 and the second sealant layer 3 to melt even when the terminal resin film 16 is at a high temperature, thus making it easier to maintain the sealing properties between the first sealant layer 1 and the metal terminal 14, and between the second sealant layer 3 and the exterior material 13. Furthermore, having a melting point of less than 160°C for the acid-modified polyolefin resin makes it easier for the acid-modified polyolefin resin to melt during heat sealing, further improving the 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 MFR of the acid-modified polyolefin resin contained in the first sealant layer 1 is 2.0 g / 10 min or more, the fluidity of the first sealant layer 1 at high temperatures is increased, making 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 energy storage device 10. Furthermore, when the MFR of the acid-modified polyolefin resin contained in the first sealant layer 1 is less than 35 g / 10 min, when the terminal resin film 16 is heat-sealed to the metal terminal 14 of the energy storage device 10, the outflow of the resin contained in the first sealant layer 1 can be suppressed, and the outflow of the resin from the first sealant layer 1 can be suppressed from adhering (temporarily adhering) to the metal terminal 14.

[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. A thickness of 10 μm or more for the first sealant layer 1 and the second sealant layer 3 can further improve the adhesion between the metal terminal 14 or exterior material 13 and the terminal resin film 16. Furthermore, a thickness of 200 μm or less for the first sealant layer 1 and the second sealant layer 3 can further improve the processability and tensile strength of the first sealant layer 1 and the second sealant layer 3.

[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 it is preferable that it be greater than the thickness of the second sealant layer 3. When the thickness of the terminal resin film 16 is the same, if the thickness of the first sealant layer 1 is greater than the thickness of the second sealant layer 3, then when the terminal resin film 16 is heat-sealed to the metal terminal 14 of the energy storage device 10, the amount of resin used to fill the gap between the first sealant layer 1 and the metal terminal 14 can be increased compared to 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 each contain the same resin or different resins. Furthermore, 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 terminal resin film 16, it is preferable that all of the above-described components of the first sealant layer 1 and the second sealant layer 3 are identical.

[0074] (Core layer) The insulating layer 2B contained 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 copolymers; homo, block, or random polypropylene; propylene-α-olefin copolymers; polybutene; polymethylpentene; and polynorbornene. Among these, the polyolefin resin preferably contains polypropylene from the viewpoint of heat seal strength and processability.

[0075] The insulating layer 2B may further contain resin additives such as antioxidants, slip agents, flame retardants, light stabilizers, dehydrators, tackifiers, fillers, and 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 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 it is preferable that it 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. In this case, when heat-sealing the exterior material 13, which includes a barrier layer 24 made of a metal layer, to the terminal resin film 16, the shrinkage (thinning) of the insulating layer 2B can be suppressed, making it easier to ensure insulation between the barrier layer 24 of the exterior material 13 and the metal terminal 14.

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

[0078] The MFR of the polyolefin resin contained in the insulating layer 2B may be smaller than or equal to the MFR of the first sealant layer 1 and the second sealant layer 3, but it is preferable that it be 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 heat-sealing the exterior material 13, which includes a barrier layer 24 made of a metal layer, to the terminal resin film 16, the thinning of the insulating layer 2B can be suppressed, making it easier to ensure insulation between the barrier layer 24 of the exterior 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. Having an MFR of 0.1 g / 10 min or more for the polyolefin resin contained in the insulating layer 2B improves the processability of the insulating layer 2B and improves the break elongation of the terminal resin film 16. Furthermore, having an MFR of less than 5 g / 10 min for the polyolefin resin contained in the insulating layer 2B makes the insulating layer 2B less likely to melt. Therefore, when heat sealing is performed with the terminal resin film 16 sandwiched between the metal terminal 14 of the energy storage device 10 and the exterior material 13 containing a barrier layer 24 made of a metal layer, thinning of the insulating layer 2B (seal shrinkage) can be suppressed, making it easier to ensure insulation between the metal terminal 14 and the barrier layer 24 made of a metal layer of the exterior material 13.

[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. A thickness of 10 μm or more for the insulating layer 2B can further improve the adhesion between the exterior material 13 and the terminal resin film 16 under high-temperature conditions. Furthermore, a thickness of 300 μm or less for the insulating layer 2B can further improve processability and the film's elongation at break.

[0081] (adhesive layer) The adhesive layer 4 has a melting peak at temperatures below 110°C.

[0082] The adhesive layer 4 may have multiple melting peaks at temperatures below 110°C. In this case, all of the melting peaks may be at temperatures below 110°C, but this is not necessarily required; some of the melting peak temperatures may be below 110°C, while the remaining melting peak temperatures are above 110°C.

[0083] In the adhesive layer 4, if there are multiple melting peaks at temperatures below 110°C, it is preferable that the melting peak furthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer 4 (hereinafter sometimes referred to as the "main melting peak") is located at a temperature between 70°C and 110°C. Here, the "melting peak furthest from the baseline of the DSC curve" refers to the melting peak where the shortest distance between the melting peak (the point indicating the maximum value of heat flow) and the baseline is the largest. It is more preferable that the main melting peak is located at a temperature of 75°C or higher, and particularly preferable that it is located at a temperature of 80°C or higher. By having the main melting peak located at 70°C or higher, the heat resistance of the energy storage device 10 can be further improved.

[0084] In the adhesive layer 4, the melting peak temperature at temperatures below 110°C is lower than the melting points of the first sealant layer 1, core layer 2, and second sealant layer 3. Here, if the melting peak temperature of the adhesive layer 4 is T (°C) and the lowest melting point among the melting points of the first sealant layer 1, core layer 2, and 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. However, from the viewpoint of improving processability, it is preferable to be 5°C or higher, and from the viewpoint of more reliably opening the energy storage device 10 with the adhesive layer 4 and further improving processability, it is preferable to be 10°C or higher, and more preferably 20°C or higher.

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

[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. If 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 curing agents include polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group. These can be used individually or in combination of two or more. Among these, it is preferable that the curing agent consists of at least one selected from the group consisting of polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group. In this case, the first sealant layer 1 becomes less likely to peel off from the core layer 2.

[0088] The curing agent consists of a polyfunctional isocyanate compound, and it is particularly preferable that 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. In this case, the first sealant layer 1 becomes particularly difficult to peel off from the core layer 2.

[0089] Here, it is preferable that the polyfunctional isocyanate compound consists of at least one selected from the group consisting of a nurate, an adduct, and a biuret. In this case, peeling of the first sealant layer 1 from the core layer 2 is effectively suppressed.

[0090] The terminal resin film 16 may contain a coloring agent from the viewpoint of improving visibility. In this case, the coloring agent may be included in any of the layers of the first sealant layer 1, core layer 2, second sealant layer 3, or adhesive layer 4, but it is preferable that it be included in the adhesive layer 4. The adhesive layer 4 can be made thinner than the other layers (i.e., the first sealant layer 1, the insulating layer 2B of the core layer 2, and the second sealant layer 3), and it is possible to improve the uniformity of thickness. Therefore, when the adhesive layer 4 contains a coloring agent, color unevenness in the terminal resin film 16 can be suppressed.

[0091] Colorants include coloring pigments and dyes. Examples of coloring pigments include 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 1x or less, and more preferably 0.5x or less, 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 heat-sealing the terminal resin film 16 with the metal terminal 14 or exterior material 13, the flow of 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 or the like.

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

[0095] The total thickness of the terminal resin film 16 is preferably 200 μm or more, and more preferably 250 μm or more. A total thickness of 200 μm or more of the terminal resin film 16 makes it easier to fill the gap between the metal terminal 14 and the terminal resin film 16 when the terminal resin film 16 is bonded to the thicker 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 for 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] If 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 manufactured 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 for forming the adhesive layer 4.

[0098] The two-layer film to be prepared in advance can be manufactured using co-extrusion methods such as T-die extrusion or inflation method, but from the viewpoint of film thickness stability, it is preferable to manufacture it using the inflation method.

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

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

[0101] Then, while the cylindrical, inflated two-layer film is being transported, it is deformed into a flat shape by a guide section, and then the two-layer film is folded into a sheet shape by a pair of pinch rolls. The ends of the folded tube are slit, and a pair (two strips) of film is wound onto a winding core in a roll shape to produce a roll of two-layer film.

[0102] The extrusion temperature is preferably in the range of 130 to 300°C, and more preferably in the range of 130 to 250°C. When the extrusion temperature is 130°C or higher, the resin constituting each layer melts sufficiently, resulting in a lower melt viscosity and stable extrusion from the screw. When the extrusion temperature is 300°C or lower, oxidation and degradation of the resin constituting each layer are suppressed, preventing a decrease in the quality of the two-layer film.

[0103] The screw rotation speed, blow ratio, and take-up speed can be set appropriately considering 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 a dry lamination method using an adhesive composition for forming the adhesive layer 4.

[0105] Specifically, a resin film 16 for terminals can be obtained by applying an adhesive composition to a two-layer film, drying it, then supplying a second sealant layer 3 on top and heat-pressing it, followed by aging. Drying can be performed at 80-140°C for 30 seconds to 5 minutes. Aging can be performed after heat-pressing at 30-80°C for 24 hours to 240 hours. Through aging, the adhesive composition hardens and an adhesive layer 4 is formed.

[0106] [Method for fusion bonding of resin films for terminals] The fusion bonding process for melt-bonding the terminal resin film 16 and the exterior material 13 shown in Figure 3 will be described below. In the following description, we will explain the case where the first sealant layer 1 of the terminal resin film 16 shown in Figure 3 is facing the metal terminal 14 side and the second sealant layer 3 is facing the exterior material 13 side.

[0107] In the fusion process, the terminal resin film 16 and the exterior material 13 are heat-fused together by simultaneously melting the second sealant layer 3 by heating and ensuring close adhesion between the second sealant layer 3 and the exterior material 13 by applying pressure.

[0108] In the fusion bonding process, it is preferable to heat the second sealant layer 3 to a temperature above the melting point of the acid-modified polyolefin resin, from the viewpoint of obtaining sufficient adhesion and sealing performance between the terminal resin film 16 and the exterior material 13.

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

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

[0111] Furthermore, with reference to Figure 2, a fusion bonding process for melting and bonding the terminal resin film 16 and the metal terminal 14 according to this embodiment will be described. In the fusion bonding process, the terminal resin film 16 and the metal terminal 14 are heat-fused together by simultaneously melting the first sealant layer 1 by heating and ensuring close contact between the first sealant layer 1 and the metal terminal 14 by pressurizing.

[0112] In the fusion bonding process, it is preferable to heat the acid-modified polyolefin resin contained in the first sealant layer 1 to a temperature above its melting point, from the viewpoint of obtaining sufficient adhesion and sealing performance between the terminal resin film 16 and the metal terminal 14.

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

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

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

[0116] For example, in Figure 4, the core layer 2 is composed only of an insulating layer 2B, but as shown in Figure 5, the core layer 2 may be composed of a laminate of an insulating layer 2B and a resin layer 2A. The resin included 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, it is preferable that the resin layer 2A contains an acid-modified polyolefin as the resin. In this case, by including an acid-modified polyolefin in the adhesive composition used in the first sealant layer 1 and the adhesive layer 4, and in the resin layer 2A of the core layer 2, the adhesion between the first sealant layer 1 and the adhesive layer 4 is further improved, as is the adhesion between the resin layer 2A and the adhesive layer 4. As a result, the first sealant layer 1 becomes less likely to peel off from the core layer 2.

[0117] Furthermore, in the case where the core layer 2 and the second sealant layer 3 are bonded via an adhesive layer 4, as in the terminal resin film 216 shown in Figure 6, it is preferable that the resin layer 2A contains acid-modified polyolefin. In this case, the inclusion of acid-modified polyolefin in the second sealant layer 3, the adhesive layer 4, and the resin layer 2A of the core layer 2 further improves the adhesion between the second sealant layer 3 and the adhesive layer 4, as well as the adhesion between the resin layer 2A of the core layer 2 and the adhesive layer 4. As a result, the second sealant layer 3 becomes less likely to peel off the core layer 2. Similarly, the first sealant layer 1 becomes less likely to peel off the core layer 2. Note that, as in the terminal resin film 216, when there are multiple adhesive layers 4, the multiple adhesive layers 4 may each be formed using the same adhesive composition, or they may be formed using different adhesive compositions. Furthermore, the thicknesses of the multiple adhesive layers 4 may be the same or different. From the viewpoint of processability and curl suppression of the terminal resin film 16, it is preferable that all of the above-described configurations of the multiple adhesive layers 4 are the same.

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

[0119] The present disclosure will be described in detail below 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> The 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. Specifically, 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 (product name "Admer", manufactured by Mitsui Chemicals, Inc.), which consists of maleic anhydride-modified PP.

[0121] The melting point of the acid-modified PP in this acid-modified PP resin composition was determined by the melting peak temperature appearing in the DSC curve, which was measured by DSC at a heating rate of 10°C / min. The melting point was 140°C, as shown in "Resin Properties" in Table 1. Furthermore, the MFR of the acid-modified PP in the acid-modified PP resin composition was measured using an MFR measuring instrument (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a measurement temperature of 230°C in accordance with JIS K7210. The MFR was 7.0 g / 10 min, as shown in "Resin Properties" in Table 1.

[0122] <Preparation of polypropylene resin composition> The polypropylene (PP) resin composition used for the insulating layer of the core layer was prepared as follows. Specifically, a PP resin composition was obtained by blending 1 part by mass of a coloring agent with 100 parts by mass of PP (product 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 "Resin Properties" in Table 1. Furthermore, the MFR (Metal Fluid Ratio) of the PP in the PP resin composition was 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 "Resin Properties" in Table 1.

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

[0125] When the DSC curve for 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 temperature of the melting peak furthest from the baseline of the DSC curve (main melting peak) was 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 added to 100 parts by mass of acid-modified PP.

[0127] When the DSC curve for adhesive composition 2 was measured in the same manner as for adhesive composition 1, one melting peak appeared in the DSC curve. 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 hexamethylene diisocyanate (HDI) nurate was blended with 100 parts by mass of acid-modified PP.

[0129] When the DSC curve of adhesive composition 3 was measured in the same manner as that of 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 added to 100 parts by mass of PP.

[0131] When the DSC curve of adhesive composition 4 was measured in the same manner as that of adhesive composition 1, one melting peak appeared in the DSC curve. 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-mentioned toluene diisocyanate (TDI) adduct (product name "CAT10L", manufactured by Toyo Morton Co., Ltd.) was added to 100 parts by mass of acid-modified PP.

[0133] When the DSC curve for 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 furthest 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 toluene diisocyanate (TDI) adduct (product name "CAT10L" manufactured by Toyo Morton Co., Ltd.) with a polyester polyol (product name "TMK55" manufactured by Toyo Morton Co., Ltd.) so that the NCO / OH (molar ratio) was 20.

[0135] When the DSC curve for 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 hexamethylene diisocyanate (HDI) nurate was blended with 100 parts by mass of acid-modified PP.

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

[0138] (Example 1) A three-layer film was prepared by co-extruding three layers in this order using the inflation method: a resin layer as a core layer made of the above acid-modified PP resin composition, an insulating layer as a core layer made of the above PP resin composition, and a second sealant layer made of the above acid-modified PP resin composition. The thickness of each layer is shown in Table 1.

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

[0140] Then, the adhesive composition 1 was applied onto the first sealant layer by direct gravure printing and dried. After drying, the first sealant layer was laminated to the three-layer film via the adhesive composition 1. Subsequently, aging was performed 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. In this way, a resin film for terminals was 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 only of 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 the first sealant layer, the insulating layer of the core layer, and the second sealant layer were co-extruded without using an adhesive layer.

[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 the adhesive composition 7 described above was used as the adhesive composition.

[0150] [Early opening] (1) Creating tabs For the metal terminals, we used ones with a width of 5 mm, a length of 30 mm, and a thickness of 100 μm. The material of the metal terminals was 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. For the terminal resin film, we used pieces cut to a width of 15 mm and a length of 10 mm. The terminal resin film / metal terminal / terminal resin film were laminated in that order, and fusion was performed at a fusion temperature of 150°C for a fusion time of 10 seconds. This resulted in obtaining the positive electrode tab and the negative electrode tab.

[0151] (2) Manufacturing of the battery pack The outer packaging material used had a laminated structure consisting 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-chromium surface treatment. The outer packaging material was sized 50 mm x 90 mm, folded in half along the longer side, and heat-sealed one side of the 45 mm wide edge with the positive and negative electrode tabs sandwiched inside. The heat sealing was performed at 190°C for 5 seconds. The remaining two sides without tabs were heat-sealed at 190°C for 3 seconds. First, the opposite side of the folded edge was heat-sealed, then 2 ml of an electrolyte solution containing a mixture of diethyl carbonate and ethylene carbonate with LiPF6 (lithium hexafluoride phosphate) added was filled in, and finally the opposite side of the tabs was heat-sealed. This allowed us to create a battery pack for evaluating tabs, which did not contain battery elements such as current collectors. The manufacturing conditions for the aforementioned battery pack were more stringent in terms of heating temperature and heat sealing time than those used in actual battery production processes.

[0152] (3) Evaluation The battery packs prepared as described above were heated in an oven, and their condition was visually observed until the temperature reached 120°C. The ease of opening the terminal resin film was then evaluated according to the evaluation criteria below. An evaluation of "◎" was considered a pass, and an evaluation of "×" was considered a fail. The results are shown in Table 1. An evaluation of "◎" indicates that the battery pack was opened early by the terminal resin film after the internal pressure of the battery pack had risen. (Evaluation Criteria) ◎: After the battery pack expands, it will contract before the temperature reaches 120°C. ×: The battery pack remains swollen even after reaching a temperature of 120°C.

[0153] [Adhesion] A sample of terminal resin film cut to a size of 50 mm (TD) x 100 mm (MD) was folded in half, sandwiching a chemically treated aluminum foil cut to a size of 50 mm x 50 mm. The end opposite the fold was heat-sealed with a sealing bar at 165°C / 0.6 MPa / 10 seconds over a width of 10 mm. Subsequently, a 15 mm wide section was cut from the center along the longitudinal direction of the heat-sealed area (see Figure 7) to prepare a sample for heat seal strength measurement. This heat seal strength measurement sample was immersed in an electrolyte solution containing 1500 ppm water at an environment of 85°C for one week. The electrolyte solution 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 LiPF6 (lithium hexafluoride phosphate) was added to a concentration of 1.0 M. Subsequently, a T-shaped peel test was performed using a tensile testing machine (manufactured by Shimadzu Corporation) at 25°C and a tensile speed of 50 mm / min to peel the resin film for the terminals from the aluminum foil. Based on the results obtained, the heat seal strength (burst strength) against the aluminum foil was evaluated according to the evaluation criteria below. The results are shown in Table 1. (Evaluation Criteria) ◎: Heat seal strength of 20N / 15mm or more ○: Heat seal strength of 15N / 15mm or more, and less than 20N / 15mm. ×: Heat seal strength less than 15N / 15mm

[0154] [Implantable] Three samples were prepared by sandwiching a surface-treated aluminum metal terminal, 5 cm long, 6 mm wide, and 200 μm thick, between two identical terminal resin films and heat-sealing them at 165°C / 0.6 MPa. The sealing times for the three samples were 2 seconds, 3 seconds, or 4 seconds, respectively. The samples were then examined to determine if the gap between the outer surface of the metal terminal and the terminal resin film was filled using a red checker solution (product name "NEW Microcheck Penetrant," manufactured by Ichinen Chemicals Co., Ltd.) as a penetrant. Specifically, after immersing the samples in the red checker solution for 10 minutes, the gap between the outer surface of the metal terminal and the terminal resin film was visually inspected to see if it had turned red. Based on the results, the embedding ability of the terminal resin film was evaluated according to the following evaluation criteria. The results are shown in Table 1. (Evaluation Criteria) ◎: Can fill gaps in 2 seconds. ○: Can fill gaps in 3 seconds. ×: The gap cannot be filled unless the sealing time is 4 seconds.

[0155] [Table 1]

[0156] As shown in Table 1, the terminal resin films of Examples 1 to 7 passed the test in terms of early opening in high-temperature environments, while the terminal resin films of Comparative Examples 1 to 3 failed in terms of early opening in high-temperature environments. Therefore, it has been confirmed that the terminal resin film of this disclosure allows the energy storage device to be opened early when it overheats. [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...Energy storage device, 11...Energy storage device body, 14...Metal terminals, 16,116,216...Resin films for terminals.

Claims

1. A resin film for terminals, which is positioned to cover a portion of the outer surface of a metal terminal that is electrically connected to the main body of an energy storage device, The aforementioned resin film for the terminals A first sealant layer is bonded to the metal terminal, A core layer containing polyolefin resin, It has the second sealant layer and the 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 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. The thickness of the first sealant layer is greater than the thickness of the second sealant layer. A resin film for terminals, wherein 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 point of the polyolefin resin or acid-modified polyolefin resin contained in the first sealant layer, the core layer, and the second sealant layer.

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 furthest from the baseline of the DSC curve measured for the adhesive constituting the adhesive layer is located at a temperature of 70°C to 110°C.

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

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

5. A 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 less than 160°C.

6. The terminal resin film 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 less than 175°C.

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

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

9. The terminal resin film according to claim 7 or 8, wherein the curing agent comprises at least one selected from the group consisting of polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group.

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

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

12. The resin film for terminals according to any one of claims 1 to 11, wherein the adhesive layer contains a coloring agent.

13. The main unit of the energy storage device, The main body of the energy storage device and the metal terminals electrically connected thereto An outer casing material that clamps the metal terminals and houses the main body of the energy storage device, The electrolyte contained within the exterior material, The terminal includes a resin film that covers a portion of the outer surface of the metal terminal and is positioned between the metal terminal and the exterior material, The aforementioned resin film for the terminal is made of the resin film for the terminal according to any one of claims 1 to 12. The first sealant layer of the resin film for the terminal is bonded to the metal terminal. An energy storage device in which the second sealant layer is bonded to the exterior material.

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