Adhesive film for metal terminals, method for manufacturing an adhesive film for metal terminals, metal terminal with adhesive film for metal terminals, energy storage device using the adhesive film for metal terminals, and method for manufacturing an energy storage device.

Abstract

To provide an adhesive film for metal terminals which has excellent adhesion to metal terminals of an adhesive film when heat-sealed and in which a decrease in the adhesion is suppressed even if an electrolytic solution adheres to the adhesive film tightly adhered to the metal terminals.SOLUTION: There is provided an adhesive film for metal terminals which is interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device exterior material. The adhesive film for metal terminals comprises a laminate including a first polyolefin layer disposed on a metal terminal side, a substrate, and a second polyolefin layer disposed on a power storage device exterior material side, in this order. A sea-island structure is observed in an electron microscope cross-sectional image of a cross-section of the first polyolefin layer in a direction parallel to a TD and in a thickness direction. In the cross-sectional image after the adhesive film for metal terminals is heated for 12 seconds at a temperature of 190°C and a surface pressure of 0.016 MPa, a ratio of the total area of island portions of the sea-island structure is 25.0-35.0%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to an adhesive film for metal terminals, a method for manufacturing an adhesive film for metal terminals, a metal terminal with an adhesive film for metal terminals, a power storage device using an adhesive film for metal terminals, and a method for manufacturing a power storage device.

Background Art

[0002] Conventionally, various types of power storage devices have been developed. In all power storage devices, an exterior material for power storage devices is an essential member for sealing power storage device elements such as electrodes and electrolytes. Conventionally, a metal exterior material for power storage devices has been frequently used as the exterior material for power storage devices. However, in recent years, with the improvement of performance in electric vehicles, hybrid electric vehicles, personal computers, cameras, mobile phones, etc., power storage devices are required to have various shapes, and at the same time, are required to be thinned and lightened. However, the conventionally frequently used metal exterior material for power storage devices has the disadvantages that it is difficult to follow the diversification of shapes and there is also a limit to weight reduction.

[0003] Therefore, in recent years, as an exterior material for power storage devices that can be easily processed into various shapes and can achieve thinning and weight reduction, a laminated sheet in which a base material layer / an adhesive layer / a barrier layer / a heat-sealable resin layer are sequentially laminated has been proposed. When using such a film-shaped exterior material for power storage devices, with the heat-sealable resin layers located in the innermost layer of the exterior material for power storage devices facing each other, the peripheral portion of the exterior material for power storage devices is heat-sealed by heat sealing, whereby the power storage device elements are sealed by the exterior material for power storage devices.

[0004] Metal terminals protrude from the heat-sealed portion of the casing material for energy storage devices. The energy storage device element sealed by the casing material is electrically connected to the outside by the metal terminals, which are electrically connected to the electrodes of the energy storage device element. In other words, in the heat-sealed portion of the casing material for energy storage devices, the portion where the metal terminals are present is heat-sealed with the metal terminals sandwiched between heat-fusible resin layers. Since the metal terminals and the heat-fusible resin layer are composed of dissimilar materials, adhesion tends to decrease at the interface between the metal terminals and the heat-fusible resin layer.

[0005] For this reason, an adhesive film is sometimes placed between the metal terminal and the heat-sealable resin layer to improve their adhesion. An example of such an adhesive film is the one described in Patent Document 1. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-79638 [Overview of the project] [Problems that the invention aims to solve]

[0007] Such adhesive films require excellent adhesion to metal terminals when heat-sealed.

[0008] Furthermore, the adhesive film is required to effectively suppress any decrease in adhesion to the metal terminals even when the electrolyte sealed by the packaging material comes into contact with the adhesive film.

[0009] However, conventional adhesive films have not been adequately considered in terms of their adhesion to metal terminals when in contact with an electrolyte. The inventors of this disclosure sought to suppress the decrease in adhesion to metal terminals when an electrolyte adheres to an adhesive film that is in contact with a metal terminal, in addition to the excellent adhesion of the adhesive film to metal terminals by heat sealing.

[0010] The primary objective of this disclosure is to provide an adhesive film for metal terminals that exhibits excellent adhesion to metal terminals by heat sealing, and furthermore, that effectively suppresses a decrease in adhesion to metal terminals even when an electrolyte adheres to the adhesive film that is in contact with the metal terminals. Furthermore, the primary objective of this disclosure is to provide a method for manufacturing the adhesive film for metal terminals, a metal terminal with an adhesive film for metal terminals using the adhesive film for metal terminals, an energy storage device using the adhesive film for metal terminals, and a method for manufacturing the energy storage device. [Means for solving the problem]

[0011] The inventors of this disclosure have diligently studied to solve the above problems. As a result, they have found that an adhesive film for metal terminals is composed of a laminate comprising a first polyolefin layer arranged on the metal terminal side, a substrate, and a second polyolefin layer arranged on the exterior material side for energy storage devices, in this order, and that when the adhesive film for metal terminals is left to stand for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa, and then left to stand for 1 hour in an environment at a temperature of 25°C (typical heating conditions during heat sealing), the proportion of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the metal terminal side of the first polyolefin layer is within a predetermined range, indicating excellent adhesion of the adhesive film to the metal terminal by heat sealing, and furthermore, even when an electrolyte adheres to the adhesive film that is in close contact with the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is suitably suppressed. This disclosure was completed by further studies based on these findings.

[0012] In other words, this disclosure provides inventions in the following embodiments. An adhesive film for metal terminals, interposed between a metal terminal electrically connected to the electrode of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element, The adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the exterior material side for the energy storage device. A sea-island structure was observed in the cross-sectional image obtained using a field emission scanning electron microscope of the cross-sectional area of ​​the first polyolefin layer in a direction parallel to the TD (Transverse Direction) and in the thickness direction. The aforementioned cross-sectional image is obtained within a range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%. The adhesive film for metal terminals is subjected to a heating and pressurizing environment of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and then subjected to a cross-sectional image taken after 1 hour in an environment of 25°C, wherein the proportion of the total area of ​​the island portion of the sea-island structure is 25.0% or more and 35.0% or less. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide an adhesive film for metal terminals that exhibits excellent adhesion to metal terminals by heat sealing, and furthermore, even when an electrolyte adheres to the adhesive film that has adhered to the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is suitably suppressed. Furthermore, this disclosure also aims to provide a method for manufacturing the adhesive film for metal terminals, a metal terminal with an adhesive film for metal terminals using the adhesive film for metal terminals, an energy storage device using the adhesive film for metal terminals, and a method for manufacturing the energy storage device. [Brief explanation of the drawing]

[0014] [Figure 1]It is a schematic plan view of the power storage device of the present disclosure. [Figure 2] It is a schematic cross-sectional view taken along line A-A' of FIG. 1. [Figure 3] It is a schematic cross-sectional view taken along line B-B' of FIG. 1. [Figure 4] It is a schematic cross-sectional view of the adhesive film for metal terminals of the present disclosure. [Figure 5] It is a schematic cross-sectional view of the adhesive film for metal terminals of the present disclosure. [Figure 6] It is a schematic cross-sectional view of the exterior material for the power storage device of the present disclosure. [Figure 7] In the example, it is a schematic cross-sectional view of a laminate of an adhesive film / metal terminal / adhesive film (metal terminal with an adhesive film for metal terminals) obtained by sandwiching a metal terminal between two adhesive films and heat-sealing them. [Figure 8] It is a cross-sectional image (binarized with image processing software) obtained using a field emission scanning electron microscope for a cross-section in the direction parallel to TD and in the thickness direction of the first polyolefin layer of the adhesive film for metal terminals obtained in Example 1 (the surface portion on the metal terminal side (opposite side to the base material)). It is a cross-sectional image obtained within the range up to 30% of the thickness from the surface on the opposite side to the surface on the base material side of the first polyolefin layer. The left cross-sectional image is before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and the right cross-sectional image is after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 9]This is a cross-sectional image (binarized with image processing software) obtained using a field emission scanning electron microscope for the cross-section in the direction parallel to the TD of the first polyolefin layer of the adhesive film for metal terminals obtained in Example 1 and in the thickness direction (the surface portion on the substrate side). It is a cross-sectional image obtained within the range from the surface on the substrate side of the first polyolefin layer to the portion of 30% of the thickness. The left cross-sectional image is before heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds, and the right cross-sectional image is after heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 10] This is a cross-sectional image (binarized with image processing software) obtained using a field emission scanning electron microscope for the cross-section in the direction parallel to the TD of the first polyolefin layer of the adhesive film for metal terminals obtained in Comparative Example 1 and in the thickness direction (the surface portion on the metal terminal side (opposite side to the substrate)). It is a cross-sectional image obtained within the range from the surface on the side opposite to the surface on the substrate side of the first polyolefin layer to the portion of 30% of the thickness. The left cross-sectional image is before heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds, and the right cross-sectional image is after heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 11] This is a cross-sectional image (binarized with image processing software) obtained using a field emission scanning electron microscope for the cross-section in the direction parallel to the TD of the first polyolefin layer of the adhesive film for metal terminals obtained in Comparative Example 1 and in the thickness direction (the surface portion on the substrate side). It is a cross-sectional image obtained within the range from the surface on the substrate side of the first polyolefin layer to the portion of 30% of the thickness. The left cross-sectional image is before heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds, and the right cross-sectional image is after heating the adhesive film for metal terminals at a temperature of 190 °C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 12]The image shows a cross-sectional view (the surface portion on the metal terminal side (opposite to the substrate)) of the first polyolefin layer of the adhesive film for metal terminals obtained in Comparative Example 2, taken using a field emission scanning electron microscope (binarized using image processing software). The image was taken within a range from the surface opposite to the substrate side of the first polyolefin layer up to 30% of its thickness. The cross-sectional image on the left is before heating the first polyolefin layer at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and the cross-sectional image on the right is after heating the first polyolefin layer at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 13] The image shows a cross-sectional view (surface portion on the substrate side) of the first polyolefin layer of the adhesive film for metal terminals obtained in Comparative Example 2, taken using a field emission scanning electron microscope (binarized using image processing software). The image was taken within the range from the substrate side surface of the first polyolefin layer up to 30% thickness. The cross-sectional image on the left is before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and the cross-sectional image on the right is after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. [Figure 14] This is a schematic diagram showing the MD, TD, and thickness direction (y) in a manufacturing line for adhesive films for metal terminals. [Modes for carrying out the invention]

[0015] The adhesive film for metal terminals of the present disclosure is an adhesive film for metal terminals interposed between a metal terminal electrically connected to an electrode of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element, wherein the adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the outer casing material side for an energy storage device, wherein a sea-island structure is observed in a cross-sectional image obtained using a field emission scanning electron microscope of the cross-section of the first polyolefin layer in a direction parallel to the TD and in the thickness direction, wherein the cross-sectional image is obtained within a range from the surface opposite to the surface on the substrate side to a portion with a thickness of 30%, when the thickness of the first polyolefin layer is set to 100%, and the proportion of the total area of ​​the island portions of the sea-island structure in the cross-sectional image obtained after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds is 25.0% or more and 35.0% or less.

[0016] The adhesive film for metal terminals of this disclosure is a cross-sectional image of the surface portion of the first polyolefin layer arranged on the metal terminal side (specifically, a cross-sectional image obtained within the range from the surface opposite to the substrate side to the portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%), and in the cross-sectional image after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the ratio of the total area of ​​the island portions of the sea-island structure is set to 25.0% or more and 35.0% or less. As a result, the adhesive film has excellent adhesion to the metal terminal by heat sealing, and even when an electrolyte adheres to the adhesive film that is in contact with the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is suitably suppressed.

[0017] Furthermore, the energy storage device of this disclosure comprises at least an energy storage device element having a positive electrode, a negative electrode, and an electrolyte; an outer casing material for the energy storage device that seals the energy storage device element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding to the outside of the outer casing material for the energy storage device, wherein the adhesive film for metal terminals of this disclosure is interposed between the metal terminals and the outer casing material for the energy storage device. The adhesive film for metal terminals of this disclosure, a method for manufacturing the same, an energy storage device using the adhesive film for metal terminals, and a method for manufacturing the same will be described in detail below.

[0018] In this specification, numerical ranges indicated by "~" mean "greater than or equal to" and "less than or equal to." For example, the notation 2~15mm means 2mm or more and 15mm or less.

[0019] Another method for confirming the MD (mass density) of adhesive films for metal terminals involves observing a cross-section of the adhesive film (for example, the first polyolefin layer, the substrate, or the second polyolefin layer) with an electron microscope to confirm the sea-island structure. In this method, the direction parallel to the cross-section where the average diameter of the island shapes perpendicular to the thickness direction of the adhesive film for metal terminals is maximized can be determined as the MD. Specifically, the sea-island structure is confirmed by observing electron microscope images of each of the following cross-sections (a total of 10 cross-sections): the cross-section in the length direction of the adhesive film for metal terminals, and each cross-section from the direction parallel to the cross-section in the length direction, with angles changed by 10 degrees increments, up to the direction perpendicular to the cross-section in the length direction. Next, the shape of each individual island is observed in each cross-section. For each island shape, the diameter y is defined as the straight-line distance connecting the leftmost point perpendicular to the thickness direction of the adhesive film for metal terminals and the rightmost point perpendicular to that direction. In each cross-section, the average of the top 20 diameters y, ordered from largest to smallest, is calculated. The direction parallel to the cross-section where the average of the relevant diameter y of the island's shape was largest is determined to be the MD (Movement Direction).

[0020] 1. Adhesive film for metal terminals The adhesive film for metal terminals of this disclosure is interposed between a metal terminal electrically connected to the electrodes of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element. Specifically, as shown in Figures 1 to 3, for example, the adhesive film 1 for metal terminals of this disclosure is interposed between a metal terminal 2 electrically connected to the electrodes of an energy storage device element 4 and an outer casing material 3 for an energy storage device that seals the energy storage device element 4. The metal terminal 2 protrudes to the outside of the outer casing material 3 and is sandwiched between the outer casing material 3 and the heat-sealed outer casing material 3 via the adhesive film 1. In this disclosure, the heating temperature when heat-sealing the outer casing material for an energy storage device is typically in the range of 160 to 190°C, and the pressure is typically in the range of 1.0 to 2.0 MPa. In the process of bonding metal terminals to the exterior material for energy storage devices via an adhesive film, it is common to perform multiple heating and pressurizing steps, such as a temporary bonding step and a final bonding step. The temporary bonding step is a step to temporarily fix the adhesive film to the metal terminals and remove air bubbles, while the final bonding step is a step to bond the adhesive film to the metal terminals by heating and pressurizing one or more times under higher temperature conditions than the temporary bonding step. For example, the temporary bonding step of the adhesive film for metal terminals to the metal terminals is performed under conditions such as a temperature of approximately 140-160°C, a pressure of approximately 0.01-1.0 MPa, a time of approximately 3-15 seconds, and 3-6 times, while the final bonding step is performed under conditions such as a temperature of approximately 160-240°C, a pressure of approximately 0.01-1.0 MPa, a time of approximately 3-15 seconds, and 1-3 times.

[0021] The adhesive film 1 for metal terminals of this disclosure is provided to improve the adhesion between the metal terminals 2 and the exterior material 3 for the energy storage device. By improving the adhesion between the metal terminals 2 and the exterior material 3 for the energy storage device, the sealing performance of the energy storage device element 4 is improved. As described above, when heat sealing the energy storage device element 4, the metal terminals 2 electrically connected to the electrodes of the energy storage device element 4 protrude to the outside of the exterior material 3 for the energy storage device, thereby sealing the energy storage device element. At this time, since the metal terminals 2, which are made of metal, and the heat-fusible resin layer 35 (a layer made of a heat-fusible resin such as polyolefin) located in the innermost layer of the exterior material 3 for the energy storage device are made of different materials, if such an adhesive film is not used, the sealing performance of the energy storage device element tends to be low at the interface between the metal terminals 2 and the heat-fusible resin layer 35.

[0022] As shown in Figures 4 and 5, the adhesive film 1 for metal terminals of this disclosure includes a configuration in which at least a first polyolefin layer 12a, a substrate 11, and a second polyolefin layer 12b are laminated in this order. The first polyolefin layer 12a is positioned on the metal terminal 2 side. The second polyolefin layer 12b is positioned on the exterior material 3 side for the energy storage device. In the adhesive film 1 for metal terminals of this disclosure, the first polyolefin layer 12a and the second polyolefin layer 12b are located on the surfaces of both sides, respectively.

[0023] In the adhesive film 1 for metal terminals of this disclosure, the first polyolefin layer 12a and the second polyolefin layer 12b are each layers containing a polyolefin resin. Examples of polyolefin resins include polyolefin and acid-modified polyolefin. The first polyolefin layer 12a preferably contains acid-modified polyolefin, and more preferably is a layer formed of acid-modified polyolefin. The second polyolefin layer 12b preferably contains polyolefin or acid-modified polyolefin, more preferably contains polyolefin, and even more preferably is a layer formed of polyolefin. By using the same resin to form the heat-sealable resin layer 35 of the heat-sealable resin layer 35 of the heat-sealable resin layer 3 of the heat-sealable resin layer 3 of this disclosure as the resin to form the second polyolefin layer 12b which is arranged on the exterior material 3 for the energy storage device, the adhesion between the adhesive film 1 for metal terminals of this disclosure and the exterior material for the energy storage device is improved.

[0024] Furthermore, the base material 11 preferably contains a polyolefin resin, preferably contains polyolefin, and more preferably is a layer formed of polyolefin.

[0025] In the first polyolefin layer 12a, the second polyolefin layer 12b, and the substrate 11, the polyolefin resin is preferably a polypropylene resin, the polyolefin is preferably polypropylene, and the acid-modified polyolefin is preferably acid-modified polypropylene. The polyolefin resins, such as polyolefin and acid-modified polyolefin, may contain known additives, fillers, pigments, etc., as described later.

[0026] Specific examples of preferred lamination configurations of the adhesive film 1 for metal terminals of this disclosure include a three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of polypropylene are laminated in this order; and a three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of acid-modified polypropylene are laminated in this order. Among these, the three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of polypropylene are laminated in this order is particularly preferred.

[0027] Details of the materials constituting the first polyolefin layer 12a, the second polyolefin layer 12b, and the substrate 11 will be described later.

[0028] When the adhesive film 1 for metal terminals of this disclosure is placed between the metal terminal 2 of the energy storage device 10 and the exterior material 3 for the energy storage device, the surface of the metal terminal 2, which is made of metal, and the heat-fusible resin layer 35 (a layer formed of a heat-fusible resin such as polyolefin) of the exterior material 3 for the energy storage device are bonded together via the adhesive film 1 for metal terminals. The first polyolefin layer 12a of the adhesive film for metal terminals 1 is positioned on the metal terminal 2 side, and the second polyolefin layer 12b is positioned on the exterior material 3 side for the energy storage device, with the first polyolefin layer 12a in close contact with the metal terminal 2 and the second polyolefin layer 12b in close contact with the heat-fusible resin layer 35 of the exterior material 3 for the energy storage device.

[0029] In the adhesive film 1 for metal terminals of this disclosure, a sea-island structure is observed in a cross-sectional image obtained using a field emission scanning electron microscope of the cross-section of the first polyolefin layer 12a in a direction parallel to the TD and in the thickness direction. The said cross-sectional image is obtained within the range from the surface opposite to the surface on the substrate 11 side to the part with a thickness of 30%, assuming the thickness of the first polyolefin layer 12a is 100%. Furthermore, in the said cross-sectional image obtained after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the ratio of the total area of ​​the island portion of the sea-island structure is 25.0 to 35.0%. The method for heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds is the same as the method for measuring the adhesion strength in the examples described later, using a hot plate heated to 190°C for 12 seconds.

[0030] Furthermore, when the thickness of the first polyolefin layer 12a is set to 100%, the area from the surface opposite to the surface on the substrate 11 side up to 30% thickness may be abbreviated as the surface portion of the first polyolefin layer 12a opposite to the surface on the substrate 11 side (or the surface portion of the first polyolefin layer 12a on the metal terminal 2 side). Similarly, when the thickness of the first polyolefin layer 12a is set to 100%, the area from the surface on the substrate 11 side up to 30% thickness may be abbreviated as the surface portion of the first polyolefin layer 12a on the substrate 11 side.

[0031] The proportion of the total area of ​​the island portion of the sea-island structure may be in the range of 25.0 to 35.0%, but the adhesion of the adhesive film to the metal terminal by heat sealing is particularly excellent, and furthermore, even when the electrolyte adheres to the adhesive film that has adhered to the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is more preferably suppressed. Therefore, the proportion of the total area of ​​the island portion of the sea-island structure is preferably about 26.0% or more, and more preferably about 28.0% or more. Also, the proportion of the total area of ​​the island portion of the sea-island structure is preferably about 32.0% or less, and more preferably about 30.0% or less. Preferred ranges for the proportion of the total area of ​​the island portion of the sea-island structure are about 26.0 to 32.0%, about 26.0 to 30.0%, about 28.0 to 35.0%, about 28.0 to 32.0%, and about 28.0 to 30.0%.

[0032] The observation of the sea-island structure in the cross-sectional image of the first polyolefin layer is performed as follows.

[0033] <Observation of sea-island structure in cross-sectional images> A metal terminal adhesive film is embedded in a thermosetting epoxy resin and cured. A cross-section in the desired direction (a cross-section along the TD) is prepared using a commercially available rotary microtome (e.g., LEICA UC6) and a diamond knife. This cross-section is prepared at -70°C using a cryomicrotome with liquid nitrogen. The embedded resin is stained with ruthenium tetroxide overnight. When stained, the polypropylene expands, so the expanded portion is trimmed with the microtome, and the cutting is advanced in 100nm to 300nm increments in the MD direction, until a total of 1μm to 2μm has been cut. The exposed cross-section is then observed as follows. The stained cross-section is observed using a field emission scanning electron microscope (e.g., Hitachi High-Technologies Corporation S-4800 TYPE1, measurement conditions: 3kV 20mA High WD6mm detector (Upper)) and an image (magnification 10000x) is obtained. The cross-sectional image is obtained for the surface portion of the first polyolefin layer on the metal terminal side (with the thickness of the first polyolefin layer set to 100%, this is the area from the surface opposite to the substrate side up to 30% thickness; see Figure 4). The surface portion of the first polyolefin layer on the substrate side (with the thickness of the first polyolefin layer set to 100%, this is the area from the substrate side up to 30% thickness) can also be obtained in the same manner by changing the observation point. Next, using image processing software capable of binarizing the image (for example, WinROOF (Ver7.4) image analysis software manufactured by Mitani Corporation), the image is binarized into island portions and sea portions of the sea-island structure to determine the number of islands, the ratio of the total area of ​​the islands (total area of ​​islands / area of ​​the measurement range of the image), the average particle diameter of the islands, the particle diameter deviation σ of the islands, and the roundness of the islands.

[0034] Binarized cross-sectional images of Example 1 and Comparative Examples 1 and 2 are shown in Figures 8 to 13, respectively. Figure 8 shows the surface portion of the first polyolefin layer of Example 1 on the metal terminal side, Figure 9 shows the surface portion of the first polyolefin layer of Example 1 on the substrate side, Figure 10 shows the surface portion of the first polyolefin layer of Comparative Example 1 on the metal terminal side, Figure 11 shows the surface portion of the first polyolefin layer of Comparative Example 1 on the substrate side, Figure 12 shows the surface portion of the first polyolefin layer of Comparative Example 2 on the metal terminal side, and Figure 13 shows the surface portion of the first polyolefin layer of Comparative Example 2 on the substrate side. Furthermore, in Figures 8 to 13, the image on the left is before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and the image on the right is after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds (similar to the adhesion strength measurement described later, the adhesive film for metal terminals was heated on a hot plate heated to 190°C under a surface pressure of 0.016 MPa for 12 seconds (heated so that the first polyolefin layer side was facing the hot plate)). In this measurement, the island areas were stained more than the sea areas, so the island areas appeared brighter than the sea areas. [Image processing conditions] Image processing can be performed using the image analysis software ImageJ. Specifically, SEM images are acquired as grayscale digital files (such as JPEG format), and then processed according to the following binarization procedure and parameters. Pixels with a grayscale level above the threshold (bright) are output as 1, and pixels with a grayscale level below the threshold (dark) are output as 0, defining these as island areas and sea areas, respectively. <Binarization> 1. Spike noise reduction (Despeckle) 2. Remove Outliers (remove outliers radius=4 threshold=1 which=Bright) 3. Remove Outliers radius=4 threshold=1 which=Dark 4. Spike noise reduction (Despeckle) 5. Gaussian blur in the X-axis direction (short side of the sample) (threshold = 3 pixels) 6. Contrast enhancement (saturated = 0.2) 7. Remove Outliers (radius=4 threshold=1 which=Bright) 8. Remove Outliers radius=4 threshold=1 which=Dark 9. Otsu's binarization

[0035] The average particle diameter of the island area is calculated from the maximum Ferret diameter of the island area in the binarized image using the image analysis software ImageJ. The particle diameter deviation σ of the island area is calculated from the standard deviation of the average particle diameter. The roundness of the island area is calculated from the difference in radii between two concentric geometric circles when the island area in the binarized image is enclosed by two concentric geometric circles, and the distance between the concentric circles is minimized.

[0036] The aforementioned cross-sectional image is, for example, as shown in the schematic diagram of Figure 4, a cross-sectional image obtained within the range from the surface on the metal terminal side (opposite to the substrate 11) to the part with a thickness of 30% (the area with cross-hatching in Figure 4), assuming that the total thickness of the first polyolefin layer 12a is 100%. The surface of the first polyolefin layer 12a opposite to the substrate 11 has a thickness of 0%. To explain with a specific example, for example, in the adhesive film for metal terminals in which a first polyolefin layer (thickness 50 μm) / substrate (thickness 50 μm) / second polyolefin layer (thickness 50 μm) are laminated in order, as in Example 1 described later, the thickness of the first polyolefin layer of 50 μm is set to 100%. Also, the thickness of the surface of the first polyolefin layer 12a opposite to the substrate 11 is set to 0%. Then, a cross-sectional image is acquired using a field emission scanning electron microscope within the range from the surface (0% thickness) to the 30% thickness position (i.e., with 50 μm as 100%, the 30% thickness position is a position where the thickness is 15 μm from the surface opposite the substrate layer side of the first polyolefin layer toward the substrate side).

[0037] Furthermore, the observation of a sea-island structure in a cross-sectional image means that a sea portion (sea area) and an island portion (island area) are observed in the cross-sectional image. For example, if a small amount of polyethylene is added to acid-modified polypropylene as the resin composition for forming the first polyolefin layer 12a, and the first polyolefin layer 12a is formed by melt extrusion molding, a sea-island structure is formed in which polyethylene island portions are dispersed within the acid-modified polypropylene sea portion. To observe this sea-island structure, as described above, the cross-section of the first polyolefin layer 12a is stained with ruthenium tetroxide or the like, and a cross-sectional image is acquired and observed using a field emission scanning electron microscope.

[0038] In the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal side (specifically, the portion with a thickness of 30% from the surface on the metal terminal side (opposite side from the base material 11)) after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the proportion of the total area of ​​the island portions of the sea-island structure is 25.0 to 35.0%. The adhesive film 1 for metal terminals of this disclosure has such characteristics, resulting in excellent adhesion of the adhesive film to the metal terminal by heat sealing, and furthermore, even when an electrolyte adheres to the adhesive film that is in close contact with the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is suitably suppressed. More specifically, in the first polyolefin layer 12a disposed on the metal terminal side of the adhesive film 1 for metal terminals of this disclosure, the total area of ​​the island portion of the sea-island structure on the surface portion on the metal terminal 2 side (the island portion is mainly formed of polyethylene, for example, which makes the first polyolefin layer 12a flexible and improves adhesion, while being somewhat inferior in electrolyte resistance) is set to an appropriate range of 25.0 to 35.0%, thereby ensuring excellent adhesion to the metal terminal while suitably suppressing the penetration of the electrolyte, and as a result, it is believed that the decrease in adhesion to the metal terminal when the electrolyte adheres is suppressed. The surface portion on the metal terminal side of the adhesive film for metal terminals, after being heated at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, corresponds to the surface portion after the first polyolefin layer 12a has adhered to the metal terminal 2 by heat sealing. In the adhesive film 1 for metal terminals of this disclosure, the ratio of the total area of ​​the island portions of the sea-island structure on the surface portion on the metal terminal 2 side of the first polyolefin layer 12a after heat sealing is set to an appropriate range of 25.0 to 35.0%.

[0039] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, when the thickness of the first polyolefin layer 12a is set to 100%, a sea-island structure is usually observed in the cross-sectional image obtained within the range up to the surface portion on the substrate 11 side (specifically, the portion with a thickness of 30% from the surface on the substrate 11 side), even in the cross-sectional image after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. The ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the substrate 11 side is not particularly limited, but is preferably about 25.0% or more, more preferably about 30.0% or more. Also, the ratio of the total area of ​​the island portions is preferably about 35.0% or less, more preferably about 33.0% or less. Preferred ranges for the ratio of the total area of ​​the island portions are about 25.0~35.0%, about 25.0~33.0%, about 30.0~35.0%, and about 30.0~33.0%. Regarding the method for heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, as described above, the method of heating on a hot plate heated to 190°C for 12 seconds is adopted, similar to the method used for measuring adhesion strength in the examples described later.

[0040] In the adhesive film 1 for metal terminals of this disclosure, for example, after heating the adhesive film 1 for metal terminals 1 at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the metal terminal 2 side may be smaller or larger than the ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the substrate 11 side, but it is desirable that they be about the same. That is, in the adhesive film 1 for metal terminals of this disclosure, the ratio of the total area of ​​the island portions of the sea-island structure in the surface portion on the metal terminal 2 side may be smaller or larger than the ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the substrate 11 side, but it is desirable that they be about the same. Furthermore, it is preferable that the ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the metal terminal 2 side is about the same before and after heating the adhesive film 1 for metal terminals 1 at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and it is also preferable that the ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the substrate 11 side is about the same.

[0041] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, when the thickness of the first polyolefin layer 12a is set to 100%, a sea-island structure is usually observed in a cross-sectional image obtained within the range up to the surface portion on the metal terminal 2 side (specifically, the portion with a thickness of 30% from the surface opposite to the substrate 11), even in the cross-sectional image before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. The ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the metal terminal 2 side of the first polyolefin layer 12a before heating is not particularly limited, but is preferably about 22.0% or more, more preferably about 24.0% or more. Also, the ratio of the total area of ​​the island portions is preferably about 32.0% or less, more preferably about 28.0% or less. The preferred ranges for the proportion of the total area of ​​the island in question are approximately 22.0-32.0%, 22.0-28.0%, 24.0-32.0%, and 24.0-28.0%.

[0042] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, when the thickness of the first polyolefin layer 12a is set to 100%, a sea-island structure is usually observed in a cross-sectional image obtained within the range up to the surface portion on the substrate 11 side (specifically, the portion with a thickness of 30% from the surface on the substrate 11 side), even in the cross-sectional image before heating the first polyolefin layer 12a at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds. The ratio of the total area of ​​the island portions of the sea-island structure in the cross-sectional image of the surface portion on the substrate 11 side of the first polyolefin layer 12a before heating is not particularly limited, but is preferably about 26.0% or more, more preferably about 28.0% or more. Also, the ratio of the total area of ​​the island portions is preferably about 35.0% or less, more preferably about 32.0% or less. The preferred ranges for the proportion of the total area of ​​the island in question are approximately 26.0-35.0%, 26.0-32.0%, 28.0-35.0%, and 28.0-32.0%.

[0043] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the average particle diameter of the island portion of the sea-island structure is preferably about 0.3 μm or more, more preferably about 0.4 μm or more. Also, the average particle diameter of the island portion is preferably about 0.6 μm or less, more preferably about 0.5 μm or less. Furthermore, preferred ranges for the average particle diameter of the island portion include about 0.3 to 0.6 μm, about 0.3 to 0.5 μm, about 0.4 to 0.6 μm, and about 0.4 to 0.5 μm.

[0044] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the average particle diameter of the island portion of the sea-island structure is preferably about 0.3 μm or more, more preferably about 0.4 μm or more. Also, the average particle diameter of the island portion is preferably about 0.6 μm or less, more preferably about 0.5 μm or less. Furthermore, preferred ranges for the average particle diameter of the island portion include about 0.3 to 0.6 μm, about 0.3 to 0.5 μm, about 0.4 to 0.6 μm, and about 0.4 to 0.5 μm.

[0045] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the average particle diameter of the island portion of the sea-island structure is preferably about 0.2 μm or more, more preferably about 0.3 μm or more. Also, the average particle diameter of the island portion is preferably about 0.5 μm or less, more preferably about 0.4 μm or less. Furthermore, preferred ranges for the average particle diameter of the island portion include about 0.2 to 0.5 μm, about 0.2 to 0.4 μm, about 0.3 to 0.5 μm, and about 0.3 to 0.4 μm.

[0046] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the average particle diameter of the island portion of the sea-island structure is preferably about 0.3 μm or more, more preferably about 0.4 μm or more. Furthermore, the average particle diameter of the island portion is preferably about 0.6 μm or less, more preferably about 0.5 μm or less. Furthermore, preferred ranges for the average particle diameter of the island portion include about 0.3 to 0.6 μm, about 0.3 to 0.5 μm, about 0.4 to 0.6 μm, and about 0.4 to 0.5 μm.

[0047] The average particle size of the island areas in the cross-sectional image is calculated using the image analysis software ImageJ.

[0048] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the particle size deviation σ of the island portion of the sea-island structure is preferably 0.4 or less, more preferably about 0.3 or less. Also, the particle size deviation σ of the island portion is, for example, 0.1 or more. Furthermore, a preferred range for the particle size deviation σ of the island portion is approximately 0.1 to 0.4 or approximately 0.1 to 0.3.

[0049] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the particle size deviation σ of the island portion of the sea-island structure is preferably 0.4 or less, more preferably about 0.3 or less. Also, the particle size deviation σ of the island portion is, for example, 0.1 or more. Furthermore, a preferred range for the particle size deviation σ of the island portion is approximately 0.1 to 0.4 or approximately 0.1 to 0.3.

[0050] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the particle size deviation σ of the island portion of the sea-island structure is preferably 0.4 or less, more preferably about 0.3 or less. Also, the particle size deviation σ of the island portion is, for example, 0.1 or more. Furthermore, a preferred range for the particle size deviation σ of the island portion is approximately 0.1 to 0.4 or approximately 0.1 to 0.3.

[0051] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the particle size deviation σ of the island portion of the sea-island structure is preferably 0.5 or less, more preferably about 0.4 or less. Also, the particle size deviation σ of the island portion is, for example, 0.1 or more. Furthermore, a preferred range for the particle size deviation σ of the island portion is about 0.1 to 0.5 or about 0.1 to 0.4.

[0052] The particle size deviation σ in the island areas of the cross-sectional image is a value calculated by the image analysis software ImageJ.

[0053] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the roundness of the island portion of the sea-island structure is preferably 0.75 or higher, more preferably about 0.80 or higher. Also, the roundness of the island portion is, for example, 0.95 or lower. Furthermore, a preferred range for the roundness of the island portion is approximately 0.75 to 0.95 or approximately 0.80 to 0.95.

[0054] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the roundness of the island portion of the sea-island structure is preferably 0.72 or higher, more preferably about 0.75 or higher. Also, the roundness of the island portion is, for example, 0.95 or lower. Furthermore, a preferred range for the roundness of the island portion is approximately 0.72 to 0.95 or approximately 0.75 to 0.95.

[0055] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the metal terminal 2 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the roundness of the island portion of the sea-island structure is preferably 0.55 or higher, more preferably about 0.60 or higher. Also, the roundness of the island portion is, for example, 0.95 or lower. Furthermore, a preferred range for the roundness of the island portion is approximately 0.55 to 0.95 and approximately 0.60 to 0.95.

[0056] Furthermore, in the adhesive film 1 for metal terminals of this disclosure, in the cross-sectional image of the surface portion on the substrate 11 side before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, the roundness of the island portion of the sea-island structure is preferably 0.55 or higher, more preferably about 0.60 or higher. Also, the roundness of the island portion is, for example, 0.95 or lower. Furthermore, a preferred range for the roundness of the island portion is approximately 0.55 to 0.95 and approximately 0.60 to 0.95.

[0057] The roundness of the island portion in the cross-sectional image is calculated using the image analysis software ImageJ.

[0058] The ratio of the total area of ​​the island portions, the average particle diameter of the island portions, the particle diameter deviation σ of the island portions, and the roundness of the island portions in the sea-island structure of the cross-section of the first polyolefin layer of the adhesive film for metal terminals of this disclosure can be adjusted by the composition, backbone, dispersibility, molecular weight, melting point, MFR of the resin constituting the first polyolefin layer, as well as by conditions such as the T-die and inflation in the manufacture of the adhesive film for metal terminals 1 (for example, the extrusion width from the T-die, the stretching ratio, the stretching speed, the heat treatment temperature, and also the line speed, cooling rate, and extrusion temperature during extrusion).

[0059] The total thickness of the adhesive film 1 for metal terminals of this disclosure is, for example, about 60 μm or more, preferably about 80 μm or more, preferably about 100 μm or more, more preferably about 120 μm or more, and even more preferably about 150 μm or more, from the viewpoint of improving adhesion to the aforementioned metal terminals 2 while suitably suppressing the decrease in adhesion due to the electrolyte. Furthermore, the total thickness of the adhesive film 1 for metal terminals of this disclosure is preferably about 200 μm or less, more preferably 180 μm or less. Preferred ranges for the total thickness of the adhesive film 1 for metal terminals of this disclosure include about 60 to 200 μm, about 60 to 180 μm, about 80 to 200 μm, about 80 to 180 μm, about 100 to 200 μm, about 100 to 180 μm, about 120 to 200 μm, about 120 to 180 μm, about 150 to 200 μm, and about 150 to 180 μm. More specifically, when the adhesive film 1 for metal terminals of this disclosure is used in consumer energy storage devices, the total thickness is preferably about 60 to 100 μm, and when it is used in automotive energy storage devices, the total thickness is preferably about 100 to 200 μm.

[0060] The first polyolefin layer 12a, the second polyolefin layer 12b, and the substrate 11 will be described in detail below.

[0061] [First polyolefin layer 12a and second polyolefin layer 12b] As shown in Figures 4 and 5, the adhesive film 1 for metal terminals of this disclosure comprises a first polyolefin layer 12a on one side of the substrate 11 and a second polyolefin layer 12b on the other side. The first polyolefin layer 12a is positioned on the metal terminal 2 side. The second polyolefin layer 12b is positioned on the exterior material 3 side for the energy storage device. In the adhesive film 1 for metal terminals of this disclosure, the first polyolefin layer 12a and the second polyolefin layer 12b are located on the surfaces of both sides, respectively.

[0062] The explanation of the sea-island structure in the cross-sectional image of the first polyolefin layer 12a, which is positioned on the metal terminal 2 side, is as described above.

[0063] In the adhesive film 1 for metal terminals of this disclosure, the first polyolefin layer 12a and the second polyolefin layer 12b are each layers containing a polyolefin resin. Examples of polyolefin resins include polyolefins and acid-modified polyolefins. The first polyolefin layer 12a preferably contains acid-modified polyolefins, and more preferably is a layer formed of acid-modified polyolefins. The second polyolefin layer 12b preferably contains polyolefins or acid-modified polyolefins, more preferably contains polyolefins, and even more preferably is a layer formed of polyolefins. Acid-modified polyolefins have a high affinity for metals. Polyolefins also have a high affinity for heat-fusible resins such as polyolefins. Therefore, in the adhesive film 1 for metal terminals of this disclosure, by arranging the first polyolefin layer 12a, which is formed of acid-modified polyolefin, on the metal terminal 2 side, even better adhesion can be achieved at the interface between the adhesive film 1 for metal terminals and the metal terminal 2. Furthermore, by placing the second polyolefin layer 12b, formed of polyolefin, on the heat-fusible resin layer 35 side of the exterior material 3 for the energy storage device, even better adhesion can be achieved at the interface between the adhesive film 1 for metal terminals and the heat-fusible resin layer 35.

[0064] Specific examples of preferred lamination configurations of the adhesive film 1 for metal terminals of this disclosure include a three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of polypropylene are laminated in this order; and a three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of acid-modified polypropylene are laminated in this order. Among these, the three-layer configuration in which a first polyolefin layer made of acid-modified polypropylene, a substrate made of polypropylene, and a second polyolefin layer made of polypropylene are laminated in this order is particularly preferred.

[0065] The acid-modified polyolefin is not particularly limited as long as it is an acid-modified polyolefin, but preferably it is a polyolefin graft-modified with an unsaturated carboxylic acid or its anhydride.

[0066] Examples of polyolefins that can be acid-modified include polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymer of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymer of propylene and ethylene); and ethylene-butene-propylene terpolymers. Among these polyolefins, polyethylene and polypropylene are preferred, and polypropylene is particularly preferred.

[0067] Furthermore, the polyolefin that is acid-modified may be a cyclic polyolefin. For example, a carboxylic acid-modified cyclic polyolefin is a polymer obtained by copolymerizing a portion of the monomers constituting the cyclic polyolefin with an α,β-unsaturated carboxylic acid or its anhydride, or by block polymerization or graft polymerization of an α,β-unsaturated carboxylic acid or its anhydride to a cyclic polyolefin.

[0068] The acid-modified cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of olefins that are constituent monomers of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of cyclic monomers that are constituent monomers of the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these polyolefins, cyclic alkenes are preferred, and norbornene is more preferred. Styrene can also be used as a constituent monomer.

[0069] Examples of carboxylic acids or their anhydrides used for acid modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride. When the first polyolefin layer 12a is analyzed by infrared spectroscopy, it is preferable that a peak originating from maleic anhydride is detected. For example, when maleic anhydride-modified polyolefin is measured by infrared spectroscopy, a peak at wavenumber 1760 cm⁻¹ is detected. -1 Nearby wave frequency 1780cm -1 A peak derived from maleic anhydride is detected in the vicinity. If the first polyolefin layer 12a or the second polyolefin layer 12b is composed of maleic anhydride-modified polyolefin, a peak derived from maleic anhydride will be detected when measured by infrared spectroscopy. However, if the degree of acid modification is low, the peak may become small and not be detected. In that case, analysis is possible by nuclear magnetic resonance spectroscopy.

[0070] The first polyolefin layer 12a and the second polyolefin layer 12b may each be formed from a single resin component, or from a blended polymer combining two or more resin components. Furthermore, the first polyolefin layer 12a and the second polyolefin layer 12b may each be formed as a single layer, or as two or more layers made from the same or different resin components. From the viewpoint of film-forming properties of the first polyolefin layer 12a and the second polyolefin layer 12b, it is preferable that these layers each be formed from a blended polymer combining two or more resin components. When a blended polymer is used, it is preferable that the first polyolefin layer 12a has acid-modified polypropylene as the main component (50% by mass or more) and 50% by mass or less of other resins (preferably polyethylene). Similarly, it is preferable that the second polyolefin layer 12b has polypropylene as the main component (50% by mass or more) and 50% by mass or less of other resins (preferably polyethylene). On the other hand, from the viewpoint of electrolyte resistance of the first polyolefin layer 12a and the second polyolefin layer 12b, it is preferable that the first polyolefin layer 12a contains acid-modified polypropylene alone as the resin, and it is preferable that the second polyolefin layer 12b contains polypropylene alone as the resin.

[0071] Furthermore, the first polyolefin layer 12a and the second polyolefin layer 12b may each contain a filler as needed. The inclusion of a filler in the first polyolefin layer 12a and the second polyolefin layer 12b allows the filler to function as a spacer, effectively suppressing short circuits between the metal terminal 2 and the barrier layer 33 of the energy storage device exterior material 3. The particle size of the filler can range from approximately 0.1 to 35 μm, preferably 5.0 to 30 μm, and more preferably 10 to 25 μm. The filler content can be approximately 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, per 100 parts by mass of the resin component forming the first polyolefin layer 12a and the second polyolefin layer 12b.

[0072] Both inorganic and organic fillers can be used. Examples of inorganic fillers include carbon (carbon, graphite), silica, aluminum oxide, barium titanate, iron oxide, silicon carbide, zirconium oxide, zirconium silicate, magnesium oxide, titanium oxide, calcium aluminate, calcium hydroxide, aluminum hydroxide, magnesium hydroxide, and calcium carbonate. Examples of organic fillers include fluororesins, phenolic resins, urea resins, epoxy resins, acrylic resins, benzoguanamine-formaldehyde condensates, melamine-formaldehyde condensates, polymethyl methacrylate crosslinked products, and polyethylene crosslinked products. From the viewpoint of shape stability, rigidity, and content resistance, aluminum oxide, silica, fluororesins, acrylic resins, and benzoguanamine-formaldehyde condensates are preferred, and among these, spherical aluminum oxide and silica are particularly preferred. As for the method of mixing the filler into the resin components that form the first polyolefin layer 12a and the second polyolefin layer 12b, methods such as melt-blending the two in advance using a Banbury mixer or the like to create a masterbatch and then mixing it in a predetermined ratio can be employed, or a direct mixing method with the resin components can be employed.

[0073] Furthermore, the first polyolefin layer 12a and the second polyolefin layer 12b may each contain a pigment as needed. Various inorganic pigments can be used as the pigment. Specific examples of the pigment include carbon (carbon, graphite), as exemplified in the filler above. Carbon (carbon, graphite) is a material commonly used inside energy storage devices and does not leach into the electrolyte. In addition, a sufficient coloring effect can be obtained with an amount that does not significantly impede adhesion, and it does not melt with heat, thus increasing the apparent melt viscosity of the added resin. Furthermore, it prevents the pressurized portion from becoming thin during heat bonding (heat sealing), providing excellent sealing between the energy storage device exterior material and the metal terminals.

[0074] When adding pigment to the first polyolefin layer 12a and the second polyolefin layer 12b, the amount added is, for example, about 0.05 to 0.3 parts by mass, preferably about 0.1 to 0.2 parts by mass, per 100 parts by mass of the resin component forming the first polyolefin layer 12a and the second polyolefin layer 12b, when using carbon black with a particle size of about 0.03 μm. By adding pigment to the first polyolefin layer 12a and the second polyolefin layer 12b, the presence or absence of the adhesive film 1 for metal terminals can be detected by a sensor or inspected visually. It is particularly preferable that the first polyolefin layer 12a contains the pigment. When adding a filler and a pigment to the first polyolefin layer 12a and the second polyolefin layer 12b, the filler and pigment may be added to the same first polyolefin layer 12a and the second polyolefin layer 12b. However, from the viewpoint of not hindering the heat-sealing properties of the adhesive film 1 for metal terminals, it is preferable to add the filler and pigment separately to the first polyolefin layer 12a and the second polyolefin layer 12b.

[0075] The thicknesses of the first polyolefin layer 12a and the second polyolefin layer 12b are preferably about 10 μm or more, more preferably about 15 μm or more, even more preferably about 20 μm or more, and even more preferably about 30 μm or more, respectively, from the viewpoint of improving adhesion to the aforementioned metal terminal 2 while suitably suppressing the decrease in adhesion due to the electrolyte. Alternatively, they may be, for example, about 80 μm or less, preferably about 60 μm or less, and even more preferably about 50 μm or less. Preferred ranges for the thickness of the first polyolefin layer 12a and the second polyolefin layer 12b include, respectively, about 10 to 80 μm, about 10 to 60 μm, about 10 to 50 μm, about 15 to 80 μm, about 15 to 60 μm, about 15 to 50 μm, about 20 to 80 μm, about 20 to 60 μm, about 20 to 50 μm, about 30 to 80 μm, about 30 to 60 μm, and about 30 to 50 μm. As a more specific example, when the adhesive film 1 for metal terminals of this disclosure is used in consumer energy storage devices, the thickness of the first polyolefin layer 12a and the second polyolefin layer 12b is preferably about 10 to 30 μm each, and when used in automotive energy storage devices, the thickness is preferably about 30 to 80 μm each.

[0076] The ratio of the thickness of the substrate 11 to the total thickness of the first polyolefin layer 12a and the second polyolefin layer 12b is preferably about 0.3 or more, more preferably about 0.4 or more, even more preferably 0.5 or more, and also preferably about 1.0 or less, more preferably about 0.8 or less, with preferred ranges including about 0.3 to 1.0, about 0.3 to 0.8, about 0.4 to 1.0, about 0.4 to 0.8, about 0.5 to 1.0, and about 0.5 to 0.8.

[0077] Furthermore, with the total thickness of the adhesive film 1 for metal terminals being 100%, the ratio of the total thickness of the first polyolefin layer 12a and the second polyolefin layer 12b is preferably about 30-80%, more preferably about 50-70%.

[0078] [Base material 11] In the adhesive film 1 for metal terminals, the substrate 11 is a layer that functions as a support for the adhesive film 1 for metal terminals.

[0079] The material forming the base material 11 is not particularly limited. Examples of materials for forming the base material 11 include polyolefin resins, polyamide resins, polyester resins, epoxy resins, acrylic resins, fluororesins, silicon resins, phenolic resins, polyetherimides, polyimides, polycarbonates, and mixtures or copolymers thereof, among which polyolefin resins are particularly preferred. In other words, the material forming the base material 11 is preferably a resin containing a polyolefin skeleton, such as polyolefin or acid-modified polyolefin. The presence of a polyolefin skeleton in the resin constituting the base material 11 can be analyzed, for example, by infrared spectroscopy or gas chromatography-mass spectrometry.

[0080] As described above, the base material 11 preferably contains a polyolefin resin, preferably contains a polyolefin, and more preferably is a layer formed of polyolefin. Specifically, examples of polyolefins include polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymer of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymer of propylene and ethylene); and ethylene-butene-propylene terpolymer. Among these polyolefins, polyethylene and polypropylene are preferred, and polypropylene is more preferred. Furthermore, because of its excellent electrolyte resistance, the base material 11 preferably contains homopolypropylene, and is particularly preferably formed of homopolypropylene.

[0081] Specifically, examples of polyamides include aliphatic polyamides such as nylon 6, nylon 66, nylon 610, nylon 12, nylon 46, and copolymers of nylon 6 and nylon 66; hexamethylenediamine-isophthalic acid-terephthalic acid copolymer polyamides such as nylon 6I, nylon 6T, nylon 6IT, and nylon 6I6T (where I represents isophthalic acid and T represents terephthalic acid), which contain constituent units derived from terephthalic acid and / or isophthalic acid; aromatic polyamides such as polymetaxylylene adipamide (MXD6); alicyclic polyamides such as polyaminomethylcyclohexyl adipamide (PACM6); polyamides copolymerized with lactam components or isocyanate components such as 4,4'-diphenylmethane-diisocyanate; polyesteramide copolymers and polyether esteramide copolymers, which are copolymers of copolymerized polyamides with polyester or polyalkylene ether glycol; and copolymers thereof. These polyamides may be used individually or in combination of two or more.

[0082] Specifically, examples of polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, copolymer polyesters with ethylene terephthalate as the main repeating unit, and copolymer polyesters with butylene terephthalate as the main repeating unit. Furthermore, specific examples of copolymer polyesters with ethylene terephthalate as the main repeating unit include copolymer polyesters polymerized with ethylene isophthalate using ethylene terephthalate as the main repeating unit (hereinafter abbreviated as polyethylene (terephthalate / isophthalate)), polyethylene (terephthalate / isophthalate), polyethylene (terephthalate / adipate), polyethylene (terephthalate / sodium sulfoisophthalate), polyethylene (terephthalate / sodium isophthalate), polyethylene (terephthalate / phenyl dicarboxylate), and polyethylene (terephthalate / decanedicarboxylate). Furthermore, specific examples of copolymer polyesters with butylene terephthalate as the main repeating unit include copolymer polyesters polymerized with butylene isophthalate using butylene terephthalate as the main repeating unit (hereinafter abbreviated as polybutylene(terephthalate / isophthalate)), polybutylene(terephthalate / adipate), polybutylene(terephthalate / sebacate), polybutylene(terephthalate / decanedicarboxylate), and polybutylene naphthalate. These polyesters may be used individually or in combination of two or more types.

[0083] Furthermore, the base material 11 may be formed from a nonwoven fabric made of the above-mentioned resin. When the base material 11 is a nonwoven fabric, it is preferable that the base material 11 is made of the aforementioned polyolefin resin, polyamide resin, etc.

[0084] Furthermore, by incorporating a coloring agent into the base material 11, the base material 11 can be made into a layer containing the coloring agent. Light transmittance can also be adjusted by selecting a resin with low transparency. If the base material 11 is a film, a colored film or a film with low transparency can be used. If the base material 11 is a nonwoven fabric, a nonwoven fabric using fibers or binders containing the coloring agent, or a nonwoven fabric with low transparency can be used.

[0085] If the substrate 11 is made of a resin film, the surface of the substrate 11 may be subjected to known easy-adhesion methods such as corona discharge treatment, ozone treatment, or plasma treatment, as needed.

[0086] The thickness of the substrate 11 is, for example, about 100 μm or less, preferably about 60 μm or less, and more preferably about 55 μm or less, from the viewpoint of improving adhesion to the aforementioned metal terminals 2 while suitably suppressing the decrease in adhesion due to the electrolyte. Furthermore, the thickness of the substrate 11 is preferably about 20 μm or more, more preferably about 30 μm or more, and even more preferably about 40 μm or more. Preferred ranges for the thickness of the substrate 11 include about 20 to 100 μm, about 20 to 60 μm, about 20 to 55 μm, about 30 to 100 μm, about 30 to 60 μm, about 30 to 55 μm, about 40 to 100 μm, about 40 to 60 μm, and about 40 to 55 μm. As a more specific example, when the adhesive film 1 for metal terminals of this disclosure is used in consumer energy storage devices, the thickness of the substrate 11 is preferably about 30 to 55 μm, and when it is used in automotive energy storage devices, it is preferably about 40 to 100 μm.

[0087] [Adhesion promoter layer 13] The adhesion promoter layer 13 is a layer provided as needed for the purpose of firmly bonding the substrate 11 to the first polyolefin layer 12a and the second polyolefin layer 12b (see Figure 5). The adhesion promoter layer 13 may be provided on only one side between the substrate 11 and the first polyolefin layer 12a and the second polyolefin layer 12b, or on both sides.

[0088] The adhesion promoter layer 13 can be formed using known adhesion promoters such as isocyanate-based, polyethyleneimine-based, polyester-based, polyurethane-based, and polybutadiene-based promoters. From the viewpoint of further improving electrolyte resistance, it is preferable that the layer be formed using an isocyanate-based adhesion promoter. Among isocyanate-based adhesion promoters, those consisting of an isocyanate component selected from triisocyanate monomer and polymeric MDI exhibit excellent laminate strength and less reduction in laminate strength after immersion in electrolyte. In particular, it is especially preferable to form the adhesion promoter consisting of triphenylmethane-4,4',4"-triisocyanate, which is a triisocyanate monomer, or polymethylene polyphenyl polyisocyanate (NCO content of approximately 30%, viscosity of 200-700 mPa·s), which is a polymeric MDI. It is also preferable to form the adhesion promoter using tris(p-isocyanatephenyl)thiophosphate, which is a triisocyanate monomer, or a two-component curing type adhesion promoter mainly composed of polyethyleneimine and polycarbodiimide as a crosslinking agent.

[0089] The adhesion promoter layer 13 can be formed by applying and drying it using known coating methods such as bar coating, roll coating, or gravure coating. The amount of adhesion promoter to apply is 20-100 mg / m² in the case of an adhesion promoter consisting of triisocyanate. 2 To a degree, preferably 40-60 mg / m² 2 The concentration is approximately 40-150 mg / m², and in the case of adhesion promoters consisting of polymeric MDI, it is approximately 40-150 mg / m². 2 The amount, preferably 60-100 mg / m² 2 In the case of a two-component curing type adhesion promoter that uses polyethyleneimine as the main component and polycarbodiimide as a crosslinking agent, the concentration is approximately 5-50 mg / m². 2 Degree, preferably 10-30 mg / m² 2 It is to that extent. Note that triisocyanate monomer is a monomer having three isocyanate groups in one molecule, and polymeric MDI is a mixture of MDI and MDI oligomers obtained by polymerization of MDI, and is represented by the following formula.

[0090] [ka]

[0091] The adhesive film 1 for metal terminals of this disclosure can be manufactured, for example, by laminating a first polyolefin layer 12a and a second polyolefin layer 12b on both surfaces of a substrate 11, respectively. The lamination of the substrate 11 and the first polyolefin layer 12a and the second polyolefin layer 12b can be carried out by known methods such as extrusion lamination and thermal lamination. Furthermore, when laminating the substrate 11 and the first and second polyolefin layers 12a and 12 via an adhesion promoter layer 13, for example, the adhesion promoter constituting the adhesion promoter layer 13 can be applied to and dried on the substrate 11 using the method described above, and the first polyolefin layer 12a and the second polyolefin layer 12b can be laminated on top of the adhesion promoter layer 13, respectively.

[0092] There are no particular limitations on the method of interposing the adhesive film 1 for metal terminals between the metal terminals 2 and the outer casing material 3 for the energy storage device. For example, as shown in Figures 1 to 3, the adhesive film 1 for metal terminals may be wrapped around the metal terminals 2 in the portion where the metal terminals 2 are sandwiched by the outer casing material 3 for the energy storage device. Although not shown in the figures, the adhesive film 1 for metal terminals may also be placed on both sides of the metal terminals 2 so as to cross both metal terminals 2 in the portion where the metal terminals 2 are sandwiched by the outer casing material 3 for the energy storage device.

[0093] [Metal terminal 2] The adhesive film 1 for metal terminals of this disclosure is used interposed between a metal terminal 2 and an outer casing material 3 for an energy storage device. The metal terminal 2 (tab) is a conductive member electrically connected to the electrode (positive or negative electrode) of an energy storage device element 4, and is made of a metallic material. The metallic material constituting the metal terminal 2 is not particularly limited and includes, for example, aluminum, nickel, and copper. For example, the metal terminal 2 connected to the positive electrode of a lithium-ion energy storage device is usually made of aluminum or the like. Also, the metal terminal 2 connected to the negative electrode of a lithium-ion energy storage device is usually made of copper, nickel, or the like.

[0094] From the viewpoint of improving electrolyte resistance, it is preferable that the surface of the metal terminal 2 be subjected to a chemical conversion treatment. For example, when the metal terminal 2 is made of aluminum, specific examples of chemical conversion treatment include known methods for forming corrosion-resistant coatings such as phosphates, chromates, fluorides, and triazinethiol compounds. Among the methods for forming corrosion-resistant coatings, phosphate chromate treatment using a material composed of three components: phenolic resin, chromium(III) fluoride compound, and phosphoric acid is preferred.

[0095] The size of the metal terminal 2 can be appropriately set according to the size of the energy storage device used. The thickness of the metal terminal 2 is preferably about 50 to 1000 μm, more preferably about 70 to 800 μm. The length of the metal terminal 2 is preferably about 1 to 200 mm, more preferably about 3 to 150 mm. The width of the metal terminal 2 is preferably about 1 to 200 mm, more preferably about 3 to 150 mm.

[0096] [Exterior material for energy storage devices 3] An example of an exterior material 3 for an energy storage device is one having a laminated structure consisting of a base layer 31, a barrier layer 33, and a heat-fusible resin layer 35 in that order. Figure 6 shows an example of the cross-sectional structure of the exterior material 3 for an energy storage device, in which the base layer 31, an adhesive layer 32 (if necessary), a barrier layer 33, an adhesive layer 34 (if necessary), and a heat-fusible resin layer 35 are laminated in that order. In the exterior material 3 for an energy storage device, the base layer 31 is the outer layer, and the heat-fusible resin layer 35 is the innermost layer. When assembling the energy storage device, the heat-fusible resin layers 35 located around the periphery of the energy storage device element 4 are brought into contact and heat-fused to seal the energy storage device element 4, thereby sealing the energy storage device element 4. Figures 1 to 3 show an energy storage device 10 using an embossed type exterior material 3 for an energy storage device formed by embossing, but the exterior material 3 for an energy storage device may be an unformed pouch type. Note that pouch-type packaging includes three-sided seal, four-sided seal, and pillow-type packaging, but any type is acceptable.

[0097] The thickness of the laminate constituting the outer casing material 3 for the energy storage device is not particularly limited, but from the viewpoint of cost reduction and energy density improvement, the upper limit is preferably about 190 μm or less, about 180 μm or less, about 160 μm or less, about 155 μm or less, about 140 μm or less, about 130 μm or less, and about 120 μm or less. From the viewpoint of maintaining the function of the outer casing material 3 for the energy storage device, which is to protect the energy storage device element 4, the lower limit is preferably about 35 μm or more, about 45 μm or more, about 60 μm or more, and about 80 μm or more. For example, a preferred range is about 35 to 190 μm, about 35 to 180 μm, and about 35 to 160 μm. , about 35-155μm, about 35-140μm, about 35-130μm, about 35-120μm, about 45-190μm, about 45-180μm, 45- Approx. 160μm, approx. 45~155μm, approx. 45~140μm, approx. 45~130μm, approx. 45~120μm, approx. 60~190μm, 60~180μm Examples of particle sizes include approximately 60-160 μm, 60-155 μm, 60-140 μm, 60-130 μm, 60-120 μm, 80-190 μm, 80-180 μm, 80-160 μm, 80-155 μm, 80-140 μm, 80-130 μm, and 80-120 μm.

[0098] (Base material layer 31) In the exterior material 3 for the energy storage device, the base layer 31 is a layer that functions as the base material for the exterior material of the energy storage device and is the layer that forms the outermost layer.

[0099] The material forming the base layer 31 is not particularly limited, as long as it possesses insulating properties. Examples of materials for forming the base layer 31 include polyester, polyamide, epoxy, acrylic, fluororesin, polyurethane, silicon resin, phenol, polyetherimide, polyimide, and mixtures or copolymers thereof. Polyesters such as polyethylene terephthalate and polybutylene terephthalate have excellent electrolyte resistance and are less prone to whitening when exposed to electrolyte, making them suitable for use as a material for forming the base layer 31. Polyamide films also have excellent stretchability, which can prevent whitening due to resin cracking of the base layer 31 during molding, making them suitable for use as a material for forming the base layer 31.

[0100] The base layer 31 may be formed from a uniaxially or biaxially stretched resin film, or from an unstretched resin film. Among these, uniaxially or biaxially stretched resin films, and especially biaxially stretched resin films, are suitable for use as the base layer 31 because their heat resistance is improved by oriented crystallization.

[0101] Among these, the resin film forming the base layer 31 is preferably nylon, polyester, and more preferably biaxially oriented nylon and biaxially oriented polyester.

[0102] The base layer 31 can also be constructed by laminating resin films of different materials to improve pinhole resistance and insulation when used as packaging for energy storage devices. Specifically, examples include a multilayer structure in which polyester film and nylon film are laminated, or a multilayer structure in which biaxially oriented polyester and biaxially oriented nylon are laminated. When the base layer 31 is made into a multilayer structure, each resin film may be bonded via an adhesive, or it may be laminated directly without an adhesive. When bonding without an adhesive, examples include bonding in a thermally fused state such as co-extrusion, sand lamination, or thermal lamination.

[0103] Furthermore, the base layer 31 may be made friction-reducing to improve moldability. When the base layer 31 is made friction-reducing, there are no particular restrictions on the coefficient of friction of its surface, but for example, it may be 1.0 or less. Examples of methods for making the base layer 31 friction-reducing include mat treatment, formation of a thin film layer of a slip agent, and combinations thereof.

[0104] The thickness of the substrate layer 31 can be, for example, about 10 to 50 μm, preferably about 15 to 30 μm.

[0105] (Adhesive layer 32) In the exterior material 3 for the energy storage device, the adhesive layer 32 is a layer that is placed on the base material layer 31 as needed in order to provide adhesion to the base material layer 31. That is, the adhesive layer 32 is provided between the base material layer 31 and the barrier layer 33.

[0106] The adhesive layer 32 is formed by an adhesive capable of bonding the base layer 31 and the barrier layer 33. The adhesive used to form the adhesive layer 32 may be a two-component curing adhesive or a one-component curing adhesive. Furthermore, the bonding mechanism of the adhesive used to form the adhesive layer 32 is not particularly limited and may be a chemical reaction type, solvent evaporation type, thermal melting type, hot pressure type, etc.

[0107] As for the resin component of the adhesive that can be used to form the adhesive layer 32, from the viewpoint of having excellent ductility, durability under high humidity conditions, yellowing suppression effect, and heat degradation suppression effect during heat sealing, and effectively suppressing the occurrence of delamination by suppressing the decrease in laminate strength between the base layer 31 and the barrier layer 33, two-component curable polyurethane adhesives; polyamide, polyester, or blended resins of these with modified polyolefins are preferred.

[0108] Furthermore, the adhesive layer 32 may be multilayered with different adhesive components. When the adhesive layer 32 is multilayered with different adhesive components, from the viewpoint of improving the lamination strength between the base material layer 31 and the barrier layer 33, it is preferable to select a resin with excellent adhesion to the base material layer 31 as the adhesive component arranged on the base material layer 31 side, and an adhesive component with excellent adhesion to the barrier layer 33 as the adhesive component arranged on the barrier layer 33 side. Specifically, when the adhesive layer 32 is multilayered with different adhesive components, preferred adhesive components arranged on the barrier layer 33 side include acid-modified polyolefins, metal-modified polyolefins, mixed resins of polyester and acid-modified polyolefins, and resins containing copolymerized polyesters.

[0109] The thickness of the adhesive layer 32 can be, for example, about 2 to 50 μm, preferably about 3 to 25 μm.

[0110] (Barrier layer 33) In an exterior material for an energy storage device, the barrier layer 33 is a layer that not only improves the strength of the exterior material for the energy storage device but also has the function of preventing water vapor, oxygen, light, etc. from entering the inside of the energy storage device. The barrier layer 33 is preferably a metal layer, that is, a layer made of metal. Specifically, examples of metals that make up the barrier layer 33 include aluminum, stainless steel, and titanium, with aluminum being preferred. The barrier layer 33 can be formed, for example, from metal foil, a metal vapor-deposited film, an inorganic oxide vapor-deposited film, a carbon-containing inorganic oxide vapor-deposited film, or a film provided with these vapor-deposited films, and it is preferably formed from metal foil, and even more preferably from aluminum foil. From the viewpoint of preventing wrinkles and pinholes from occurring in the barrier layer 33 during the manufacturing of the exterior material for energy storage devices, it is more preferable that the barrier layer be formed from soft aluminum foil, such as annealed aluminum (JIS H4160:1994 A8021H-O, JIS H4160:1994 A8079H-O, JIS H4000:2014 A8021P-O, JIS H4000:2014 A8079P-O).

[0111] Regarding the thickness of the barrier layer 33, from the viewpoint of making the exterior material for the energy storage device thinner while also making it less likely for pinholes to occur during molding, it is preferably about 10 to 200 μm, and more preferably about 20 to 100 μm.

[0112] Furthermore, it is preferable that at least one surface, preferably both surfaces, of the barrier layer 33 be chemically treated to stabilize adhesion and prevent dissolution and corrosion. Here, chemical treatment refers to a treatment that forms a corrosion-resistant film on the surface of the barrier layer.

[0113] (adhesive layer 34) In the exterior material 3 for the energy storage device, the adhesive layer 34 is a layer provided between the barrier layer 33 and the heat-fusible resin layer 35 as needed, in order to firmly bond the heat-fusible resin layer 35.

[0114] The adhesive layer 34 is formed by an adhesive capable of bonding the barrier layer 33 and the heat-fusible resin layer 35. The composition of the adhesive used to form the adhesive layer is not particularly limited, but examples include resin compositions containing acid-modified polyolefins. Examples of acid-modified polyolefins include those exemplified in the first polyolefin layer 12a and the second polyolefin layer 12b.

[0115] The thickness of the adhesive layer 34 can be, for example, about 1 to 40 μm, preferably about 2 to 30 μm.

[0116] (Thermal adhesive resin layer 35) In the exterior material 3 for the energy storage device, the heat-sealable resin layer 35 is the innermost layer, and during the assembly of the energy storage device, the heat-sealable resin layers heat-seal each other to seal the energy storage device elements.

[0117] The resin component used in the heat-fusible resin layer 35 is not particularly limited, as long as it is heat-fusible, but examples include polyolefins and cyclic polyolefins.

[0118] Specifically, the polyolefins include polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymer of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymer of propylene and ethylene); and ethylene-butene-propylene terpolymers. Among these polyolefins, polyethylene and polypropylene are preferred.

[0119] The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of olefins that are constituent monomers of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, isoprene, and the like. Examples of cyclic monomers that are constituent monomers of the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, norbornadiene, etc. Among these polyolefins, cyclic alkenes are preferred, and norbornene is more preferred. Styrene can also be used as a constituent monomer.

[0120] Among these resin components, preferred are crystalline or amorphous polyolefins, cyclic polyolefins, and blends thereof; more preferably, polyethylene, polypropylene, copolymers of ethylene and norbornene, and blends of two or more of these.

[0121] The heat-fusible resin layer 35 may be formed by a single resin component or by a blended polymer combining two or more resin components. Furthermore, the heat-fusible resin layer 35 may be formed as a single layer or as two or more layers made of the same or different resin components. It is particularly preferable that the resins of the second polyolefin layer 12b and the heat-fusible resin layer 35 are the same, as this improves the adhesion between these layers.

[0122] Furthermore, the thickness of the heat-sealable resin layer 35 is not particularly limited, but is preferably about 2 to 2000 μm, more preferably about 5 to 1000 μm, and more preferably about 10 to 500 μm.

[0123] 2. Energy storage devices The energy storage device 10 of this disclosure comprises at least an energy storage device element 4 having a positive electrode, a negative electrode, and an electrolyte; an outer casing material 3 for the energy storage device that seals the energy storage device element 4; and metal terminals 2 electrically connected to the positive electrode and the negative electrode, respectively, and protruding to the outside of the outer casing material 3 for the energy storage device. The energy storage device 10 of this disclosure is characterized in that the adhesive film 1 for metal terminals of this disclosure is interposed between the metal terminals 2 and the outer casing material 3 for the energy storage device. That is, the energy storage device 10 of this disclosure can be manufactured by a method that includes a step of interposing the adhesive film 1 for metal terminals of this disclosure between the metal terminals 2 and the outer casing material 3 for the energy storage device.

[0124] Specifically, a storage device element 4 comprising at least a positive electrode, a negative electrode, and an electrolyte is covered with a storage device exterior material 3, with the metal terminals 2 connected to the positive and negative electrodes respectively protruding outward. The adhesive film 1 for metal terminals of this disclosure is interposed between the metal terminals 2 and the heat-sealable resin layer 35. A flange portion (the area where the heat-sealable resin layers 35 come into contact, and the peripheral edge portion 3a of the storage device exterior material) of the storage device exterior material is formed around the periphery of the storage device element 4. The heat-sealable resin layers 35 of the flange portion are then heat-sealed to create a sealed storage device 10 using the storage device exterior material 3. When housing the storage device element 4 using the storage device exterior material 3, the heat-sealable resin layer 35 of the storage device exterior material 3 is used so that it faces inward (the surface in contact with the storage device element 4).

[0125] The casing material for energy storage devices disclosed herein can be suitably used in energy storage devices such as batteries (including capacitors, capacitors, etc.). Furthermore, the casing material for energy storage devices disclosed herein can be used in either primary batteries or secondary batteries, but is preferably used in secondary batteries. The type of secondary battery to which the casing material for energy storage devices disclosed herein can be applied is not particularly limited, and examples include lithium-ion batteries, lithium-ion polymer batteries, all-solid-state batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, polyvalent cation batteries, capacitors, capacitors, etc. Among these secondary batteries, lithium-ion batteries and lithium-ion polymer batteries are particularly suitable applications for the casing material for energy storage devices disclosed herein. [Examples]

[0126] The present disclosure will be described in detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the examples.

[0127] <Manufacturing of adhesive films for metal terminals> Example 1 As the polyolefin forming the first polyolefin layer, maleic anhydride-modified polypropylene (PPa) was prepared; as the polyolefin forming the second polyolefin layer, polypropylene (PP) was prepared; and as the substrate, an unstretched polypropylene film (CPP, homopolypropylene, 50 μm thick) was prepared. Maleic anhydride-modified polypropylene (PPa) was extruded onto one side of the substrate (CPP) using a T-die extruder to form the first polyolefin layer (50 μm thick); and polypropylene (PP) was extruded onto the other side of the substrate (CPP) using a T-die extruder to form the second polyolefin layer (50 μm thick). A metal terminal adhesive film was obtained in which the first polyolefin layer (50 μm, PPa layer) / substrate (50 μm, CPP layer) / second polyolefin layer (50 μm, PP layer) were laminated in that order.

[0128] Comparative Example 1 As the polyolefin forming the first polyolefin layer, maleic anhydride-modified polypropylene (PPa) was prepared, as the polyolefin forming the second polyolefin layer, and as the base material, a polypropylene film (PP, 30 μm thick) colored black with carbon black was prepared. Maleic anhydride-modified polypropylene (PPa) was extruded onto one side of the base material (PP) using a T-die extruder to form the first polypropylene layer (50 μm thick), and polypropylene (PP) was extruded onto the other side of the base material (PP) using a T-die extruder to form the second polypropylene layer (50 μm thick), thereby obtaining an adhesive film for metal terminals in which the first polyolefin layer (50 μm, PPa layer) / base material (30 μm, PP layer) / second polyolefin layer (20 μm, PP layer) were laminated in that order.

[0129] Comparative Example 2 As the polyolefin forming the first polyolefin layer, maleic anhydride-modified polypropylene (PPa) was prepared; as the polyolefin forming the second polyolefin layer, maleic anhydride-modified polypropylene (PPa) was prepared; and as the base material, polypropylene (PP) was prepared. Using the resins for each layer, multilayer air-cooled inflation molding was performed to obtain an adhesive film for metal terminals in which the first polyolefin layer (25 μm, PPa layer) / base material (50 μm, PP layer) / second polyolefin layer (25 μm, PPa layer) were laminated in that order.

[0130] The number of islands, the ratio of the total area, the average particle size, the particle size deviation, and the roundness in the sea-island structure of the cross-section of the first polyolefin layer of the adhesive film for metal terminals described in Tables 1 and 2 can be adjusted by the composition, backbone, dispersibility, molecular weight, melting point, MFR of the resin constituting the first polyolefin layer, as well as by conditions such as the T-die and inflation during the manufacture of the adhesive film for metal terminals 1 (e.g., extrusion width from the T-die, stretching ratio, stretching speed, heat treatment temperature, and line speed, cooling rate, and extrusion temperature during extrusion). In Example 1, the film was heated for 12 seconds on a hot plate heated to 190°C (surface pressure of 0.016 MPa) and then naturally cooled at room temperature (25°C). The sea-island structure may also change depending on the cooling conditions after heating.

[0131] <Observation of Islands in Sea-Island Structures> A metal terminal adhesive film was embedded in a thermosetting epoxy resin and cured. A cross-section in the desired direction (parallel to the TD and in the thickness direction) was prepared using a commercially available rotary microtome (LEICA UC6) and a diamond knife. The cross-section was prepared at -70°C using a cryomicrotome with liquid nitrogen. The embedded resin was stained with ruthenium tetroxide overnight. Since the polypropylene expands upon staining, the expanded portion was trimmed with the microtome, and the cutting was advanced in increments of 100 nm to 300 nm in the MD direction, until a total of approximately 1 μm to 2 μm was cut. The exposed cross-section was then observed as follows. The stained cross-section was observed using a field emission scanning electron microscope (Hitachi High-Technologies Corporation S-4800 TYPE1, measurement conditions: 3kV 20mA High WD6mm detector (Upper)) and an image (magnification 10000x) was acquired. Cross-sectional images were obtained for the metal terminal side surface of the first polyolefin layer (the area from the surface opposite to the substrate side to 30% thickness, assuming the thickness of the first polyolefin layer is 100%; see Figure 4) and the substrate side surface of the first polyolefin layer (the area from the substrate side to 30% thickness, assuming the thickness of the first polyolefin layer is 100%). Next, using image processing software capable of binarizing images (WinROOF (Ver7.4) image analysis software manufactured by Mitani Corporation), the image was binarized into island portions and sea portions of the sea-island structure, and the number of island portions, the ratio of the total area of ​​the island portions (total area of ​​island portions / area of ​​the measurement range of the image), the average particle diameter of the island portions, the particle diameter deviation σ of the island portions, and the roundness of the island portions were determined. The results are shown in Tables 1 and 2. Table 1 shows the measurement results for a sample after heating the adhesive film for metal terminals for 12 seconds using a hot plate heated to 190°C, in the same manner as in <Measurement of adhesion strength between adhesive film for metal terminals and metal terminals> described later, and Table 2 shows the measurement results for a sample that was not heated.

[0132] Binarized cross-sectional images of Example 1 and Comparative Examples 1 and 2 are shown in Figures 8 to 13, respectively. Figure 8 shows the surface portion of the first polyolefin layer of Example 1 on the metal terminal side, Figure 9 shows the surface portion of the first polyolefin layer of Example 1 on the substrate side, Figure 10 shows the surface portion of the first polyolefin layer of Comparative Example 1 on the metal terminal side, Figure 11 shows the surface portion of the first polyolefin layer of Comparative Example 1 on the substrate side, Figure 12 shows the surface portion of the first polyolefin layer of Comparative Example 2 on the metal terminal side, and Figure 13 shows the surface portion of the first polyolefin layer of Comparative Example 1 on the substrate side. In each of Figures 8 to 13, the image on the left is before heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and the image on the right is after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds (heated for 12 seconds on a hot plate heated to a temperature of 190°C and a surface pressure of 0.016 MPa, similar to the measurement of adhesion strength described later). In this measurement, the island area was stained more than the sea area, so the island area appeared brighter than the sea area. [Image processing conditions] Image processing was performed using the image analysis software ImageJ. Specifically, SEM images were acquired as grayscale (JPEG) digital files, and processed according to the following binarization procedure and parameters. Pixels with a grayscale level above the threshold (bright) were output as 1, and pixels with a grayscale level below the threshold (dark) were output as 0, defining these as island areas and sea areas, respectively. <Binarization> 1. Spike noise reduction (Despeckle) 2. Remove Outliers (remove outliers radius=4 threshold=1 which=Bright) 3. Remove Outliers radius=4 threshold=1 which=Dark 4. Spike noise reduction (Despeckle) 5. Gaussian blur in the X-axis direction (short side of the sample) (threshold = 3 pixels) 6. Contrast enhancement (saturated = 0.2) 7. Remove Outliers (radius=4 threshold=1 which=Bright) 8. Remove Outliers radius=4 threshold=1 which=Dark 9. Otsu's binarization

[0133] The average particle diameter of the island area is calculated from the maximum Ferret diameter of the island area in the binarized image using the image analysis software ImageJ. The particle diameter deviation σ of the island area is calculated from the standard deviation of the average particle diameter. The roundness of the island area is calculated from the difference in radii between two concentric geometric circles when the island area in the binarized image is enclosed by two concentric geometric circles, and the distance between the concentric circles is minimized.

[0134] <Measurement of adhesion strength between adhesive film for metal terminals and metal terminals> As metal terminals, aluminum (JIS H4160:1994 A8079H-O) with dimensions of 50 mm in length, 22.5 mm in width, and 0.2 mm in thickness was prepared. In addition, each adhesive film for metal terminals obtained in the examples and comparative examples was cut to a length of 45 mm and a width of 15 mm. Next, the adhesive film for metal terminals was placed on the metal terminals to obtain a laminate of metal terminals / adhesive film. At this time, the vertical and horizontal directions of the metal terminals coincided with the length and width directions of the adhesive film for metal terminals, respectively, and the lamination was performed so that the centers of the metal terminals and the adhesive film for metal terminals coincided. Furthermore, the first polyolefin layer of the adhesive film for metal terminals was positioned on the metal terminal side. Next, a tetrafluoroethylene-ethylene copolymer film (ETFE film, 100 μm thick) was placed on top of the adhesive film for metal terminals of the laminate (the surface of the adhesive film for metal terminals was covered with the ETFE film), and the laminate was placed on a hot plate heated to 190°C (with the metal terminals facing the hot plate), and a 500 g weight with a sponge attached was placed on top (surface pressure of 0.016 MPa). The laminate was left undisturbed for 12 seconds to heat-seal the adhesive film to the metal terminals. The laminate was then allowed to cool naturally to 25°C. Next, in an environment of 25°C, the adhesive film for metal terminals was peeled off the metal terminals using a Tensilon universal material tester (RTG-1210, manufactured by A&D Company, Limited). The maximum strength at the time of peeling was defined as the adhesion strength to the metal terminals (N / 15 mm). The peeling speed was 50 mm / min, the peeling angle was 180°, and the distance between chucks was 30 mm. The average value of three measurements was used. The results are shown in Table 1. The process of leaving the material undisturbed for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa is intended to simulate the heat and pressure applied during the preliminary bonding and final bonding processes described above.

[0135] <Adhesion strength after immersion in electrolyte solution> The adhesive film was heat-fused to the metal terminal in the same manner as described in the <Measurement of Adhesion Strength Between Adhesive Film for Metal Terminals and Metal Terminals> above. The laminate was allowed to cool naturally to 25°C after heat fusion. Next, the resulting laminate was immersed for one day in an 85°C electrolyte (prepared by mixing lithium hexafluoride phosphate to a concentration of 1 mol / L in a solution of ethylene carbonate:diethyl carbonate:dimethyl carbonate in a volume ratio of 1:1:1). After immersion, the laminate was rinsed with water until the electrolyte and salt were thoroughly washed away, and then removed. Within one hour, the adhesive film for metal terminals was peeled off the metal terminal in the same manner as described in the <Measurement of Adhesion Strength Between Adhesive Film for Metal Terminals and Metal Terminals> above, and the maximum strength at the time of peeling was taken as the adhesion strength to the metal terminal (N / 15mm). The results are shown in Table 1.

[0136] [Table 1]

[0137] [Table 2]

[0138] The adhesive film for metal terminals in Example 1 is shown in the cross-sectional image of the surface portion of the first polyolefin layer on the metal terminal side, and is a cross-sectional image taken after heating the adhesive film for metal terminals at a temperature of 190°C and a surface pressure of 0.016 MPa for 12 seconds, in which the ratio of the total area of ​​the island portion of the sea-island structure is set to 25.0 to 35.0%. The adhesive film for metal terminals in Example 1 exhibits excellent adhesion of the adhesive film to the metal terminal by heat sealing, and furthermore, even when electrolyte adheres to the adhesive film that is in close contact with the metal terminal by heat sealing, the decrease in adhesion to the metal terminal is suitably suppressed.

[0139] As described above, this disclosure provides inventions in the following embodiments. Item 1. An adhesive film for metal terminals, interposed between a metal terminal electrically connected to the electrodes of a power storage device element and an outer casing material for a power storage device that seals the power storage device element, The adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the exterior material side for the energy storage device. A sea-island structure was observed in the cross-sectional image obtained using a field emission scanning electron microscope of the cross-section of the first polyolefin layer in a direction parallel to the TD and in the thickness direction. The aforementioned cross-sectional image is obtained within a range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%. The adhesive film for metal terminals is subjected to a heating and pressurizing environment of 190°C and a surface pressure of 0.016 MPa for 12 seconds, and then subjected to a cross-sectional image taken after 1 hour in an environment of 25°C, wherein the proportion of the total area of ​​the island portion of the sea-island structure is 25.0% or more and 35.0% or less. Item 2. The adhesive film for metal terminals according to Item 1, wherein in the cross-sectional image, the average particle diameter of the island portion is 0.3 μm or more. Item 3. The adhesive film for metal terminals according to Item 1 or 2, wherein the particle size deviation of the island portion in the cross-sectional image is 0.3 or less. Item 4. The adhesive film for metal terminals according to any one of items 1 to 3, wherein the roundness of the island portion in the cross-sectional image is 0.75 or greater. Item 5. The adhesive film for metal terminals according to any one of items 1 to 4, wherein the thickness of the first polyolefin layer is 60 μm or less. Item 6. The adhesive film for metal terminals according to any one of items 1 to 5, wherein the thickness of the substrate is 60 μm or less. Item 7. The adhesive film for metal terminals according to any one of items 1 to 6, wherein the thickness of the second polyolefin layer is 60 μm or less. Item 8. The adhesive film for metal terminals according to any one of items 1 to 7, wherein the thickness of the adhesive film for metal terminals is 180 μm or less. Item 9. The first polyolefin layer comprises a pigment, and is an adhesive film for metal terminals according to any one of items 1 to 8. Item 10. The substrate is an adhesive film for metal terminals according to any one of items 1 to 9, comprising a polyolefin skeleton. Item 11. A method for manufacturing an adhesive film for metal terminals, which is interposed between a metal terminal electrically connected to the electrodes of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element, The adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the exterior material side for the energy storage device. The process includes a step of obtaining a laminate comprising the first polyolefin layer, the substrate, and the second polyolefin layer in this order. A sea-island structure was observed in the cross-sectional image obtained using a field emission scanning electron microscope of the cross-section of the first polyolefin layer in a direction parallel to the TD and in the thickness direction. The aforementioned cross-sectional image is obtained within a range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%. A method for manufacturing an adhesive film for metal terminals, wherein the adhesive film for metal terminals is left to stand for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa, and then left to stand for 1 hour in an environment at a temperature of 25°C, and in the cross-sectional image obtained therefrom, the proportion of the total area of ​​the island portion of the sea-island structure is 25.0% or more and 35.0% or less. Item 12. A metal terminal with an adhesive film for metal terminals, wherein an adhesive film for metal terminals described in any one of items 1 to 10 is attached to the metal terminal. Item 13. A power storage device comprising at least a positive electrode, a negative electrode, and an electrolyte; an outer casing material for the power storage device that encloses the power storage device element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding from the outer casing material for the power storage device, An energy storage device in which an adhesive film for metal terminals according to any one of items 1 to 10 is interposed between the metal terminal and the exterior material for the energy storage device. Item 14. A method for manufacturing an energy storage device comprising at least a positive electrode, a negative electrode, and an electrolyte; an outer casing material for the energy storage device that seals the energy storage device element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding to the outside of the outer casing material for the energy storage device, A method for manufacturing an energy storage device, comprising the step of interposing an adhesive film for metal terminals described in any one of items 1 to 10 between the metal terminals and the exterior material for the energy storage device, and sealing the energy storage device element with the exterior material for the energy storage device. [Explanation of symbols]

[0140] 1. Adhesive film for metal terminals 2 metal terminals 3. Exterior materials for energy storage devices 3a Peripheral edge of exterior material for energy storage device 4 Energy Storage Device Elements 10 Energy storage devices 11 Base material 12a First polyolefin layer 12b Second polyolefin layer 13. Adhesion promoter layer 31 Base material layer 32 Adhesive layer 33 Barrier layer 34 Adhesive layer 35 Heat-fusible resin layer

Claims

1. An adhesive film for metal terminals, interposed between a metal terminal electrically connected to the electrode of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element, The adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the exterior material side for the energy storage device. A sea-island structure was observed in the cross-sectional image of the first polyolefin layer in a direction parallel to TD and in the thickness direction, obtained using a field emission scanning electron microscope. The aforementioned cross-sectional image is obtained within a range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%. In the cross-sectional image obtained when the adhesive film for metal terminals is left standing for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa, and then left standing for 1 hour in an environment at a temperature of 25°C, the proportion of the total area of ​​the island portion of the sea-island structure is 25.0% or more and 35.0% or less. An adhesive film for metal terminals, wherein the roundness of the island portion in the cross-sectional image is 0.75 or greater.

2. The adhesive film for metal terminals according to claim 1, wherein in the cross-sectional image, the average particle diameter of the island portion is 0.3 μm or more.

3. The adhesive film for metal terminals according to claim 1 or 2, wherein the roundness of the island portion in the cross-sectional image is 0.80 or greater.

4. The adhesive film for metal terminals according to any one of claims 1 to 3, wherein the thickness of the first polyolefin layer is 60 μm or less.

5. The adhesive film for metal terminals according to any one of claims 1 to 4, wherein the thickness of the substrate is 60 μm or less.

6. The adhesive film for metal terminals according to any one of claims 1 to 5, wherein the thickness of the second polyolefin layer is 60 μm or less.

7. The adhesive film for metal terminals according to any one of claims 1 to 6, wherein the thickness of the adhesive film for metal terminals is 180 μm or less.

8. The first polyolefin layer comprises a pigment, wherein the adhesive film for metal terminals is according to any one of claims 1 to 7.

9. The aforementioned substrate is an adhesive film for metal terminals according to any one of claims 1 to 8, comprising a polyolefin skeleton.

10. The aforementioned substrate is an adhesive film for metal terminals according to any one of claims 1 to 9, comprising homopolypropylene.

11. The cross-sectional image obtained within the range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%, wherein the adhesive film for metal terminals is left standing for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa, and then left standing for 1 hour in an environment at a temperature of 25°C, The adhesive film for metal terminals according to any one of claims 1 to 9, wherein the proportion of the total area of ​​the island portion of the aforementioned sea-island structure is 28.0% or more and 35.0% or less.

12. A method for manufacturing an adhesive film for metal terminals, which is interposed between a metal terminal electrically connected to the electrode of an energy storage device element and an outer casing material for an energy storage device that seals the energy storage device element, The adhesive film for metal terminals is composed of a laminate comprising, in this order, a first polyolefin layer disposed on the metal terminal side, a substrate, and a second polyolefin layer disposed on the exterior material side for the energy storage device. The process includes a step of obtaining a laminate comprising the first polyolefin layer, the substrate, and the second polyolefin layer in this order. A sea-island structure was observed in the cross-sectional image of the first polyolefin layer in a direction parallel to TD and in the thickness direction, obtained using a field emission scanning electron microscope. The aforementioned cross-sectional image is obtained within a range from the surface opposite to the substrate side to a portion with a thickness of 30%, assuming the thickness of the first polyolefin layer is 100%. In the cross-sectional image obtained when the adhesive film for metal terminals is left standing for 12 seconds in a heated and pressurized environment at a temperature of 190°C and a surface pressure of 0.016 MPa, and then left standing for 1 hour in an environment at a temperature of 25°C, the proportion of the total area of ​​the island portion of the sea-island structure is 25.0% or more and 35.0% or less. In the aforementioned cross-sectional image, the roundness of the island portion is 0.75 or greater. A method for manufacturing adhesive films for metal terminals.

13. A metal terminal with an adhesive film for metal terminals, wherein the adhesive film for metal terminals described in any one of claims 1 to 11 is attached to the metal terminal.

14. A power storage device comprising, at least, a positive electrode, a negative electrode, and an electrolyte; an outer casing material for the power storage device that seals the power storage device element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding to the outside of the outer casing material for the power storage device, An energy storage device comprising an adhesive film for metal terminals according to any one of claims 1 to 11 interposed between the metal terminal and the exterior material for the energy storage device.

15. A method for manufacturing an energy storage device comprising at least a positive electrode, a negative electrode, and an electrolyte, an outer casing material for the energy storage device that seals the energy storage device element, and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding to the outside of the outer casing material for the energy storage device, A method for manufacturing an energy storage device, comprising the step of interposing an adhesive film for metal terminals according to any one of claims 1 to 11 between the metal terminals and the exterior material for the energy storage device, and sealing the energy storage device element with the exterior material for the energy storage device.

Images