Resin film for terminal, method for manufacturing resin film for terminal, and power storage device

Abstract

This resin film for a terminal covers, by heat sealing, the outer peripheral surface of part of a metal terminal electrically connected to a power storage device body constituting a power storage device. The resin film has a thickness of 100-200 μm and a loop stiffness value of 20-200 mN / 15 mm.

Description

Resin film for terminal, method for manufacturing resin film for terminal, and electricity storage device

[0001] The present invention relates to a resin film for a terminal, a method for manufacturing a resin film for a terminal, and an electricity storage device.

[0002] In soft-pack type batteries, an insulating tab sealant (a resin film for terminals) is used to cover the tab lead in order to ensure insulation between the exterior bag and the tab lead (metal terminal). For example, Patent Document 1 describes a tab sealant that includes an innermost layer (second sealant layer) that is arranged in contact with the outer surface of the tab lead, an outermost layer (first sealant layer) that is arranged in contact with the inner surface of the packaging bag and on the surface opposite the innermost layer, and an intermediate layer (insulating layer) that is provided between the two layers.

[0003] International Publication No. 2015 / 008826

[0004] In automotive batteries and other applications requiring high current, the tab leads have become thicker, and as a result, there has been a demand for thicker tab sealants to fill the gaps between the outer packaging and the tab leads. However, it has been found that thicker tab sealants tend to be prone to warping, and attempts to suppress warping tend to result in drooping after metal terminal coating. These warping and drooping tab sealants affect heat sealing processability.

[0005] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a resin film for terminals that exhibits excellent heat-sealing processability for metal terminals when producing an electricity storage device having thick metal terminals, and a method for producing the same. The present disclosure also aims to provide an electricity storage device obtained using the resin film for terminals.

[0006] As a result of extensive research, the inventors discovered that when a resin film for terminals is thickened, the stiffness of the film, among various film properties, significantly affects phenomena such as warping and drooping of the film. They then considered that in order to improve the heat-sealing processability of metal terminals, it is important that the loop stiffness value, which represents stiffness, be within an appropriate range, and developed the resin film for terminals of the present disclosure.

[0007] That is, the resin film for a terminal according to the present disclosure is a resin film for a terminal for covering, by heat sealing, the outer peripheral surface of a part of a metal terminal that is electrically connected to an electricity storage device main body and that constitutes an electricity storage device, and has a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm.

[0008] The above-described terminal resin film allows for satisfactory heat-sealing of metal terminals when fabricating an electric storage device having thick metal terminals. The inventors have considered the following reasons for setting the stiffness, i.e., loop stiffness, of the terminal resin film to a predetermined thickness as described above. For example, if the terminal resin film is too stiff, the edges of the film are likely to be pushed by the slit blade and warp when a thick terminal resin film is obtained from a raw film roll using a microslit. Using a terminal resin film with such warped edges makes alignment during heat sealing difficult, potentially causing problems such as misalignment of the heat seal when adhering to the metal terminal. On the other hand, if the terminal resin film is too weak in stiffness, the edges of the film are likely to droop (loop) after covering the metal terminal. This drooping easily causes problems such as misalignment of the heat seal when adhering to the exterior material. In contrast, the resin film for terminals disclosed herein has a predetermined thickness while also having an appropriate loop stiffness value, making it less likely for warping or sagging to occur at the ends of the film, and allowing for good alignment during heat sealing processing.

[0009] In one embodiment, the resin film for a terminal may be a multilayer film having an insulating layer and a sealant layer provided on at least one side of the insulating layer. When the resin film for a terminal is a multilayer film including an insulating layer and a first sealant layer and a second sealant layer provided on both sides of the insulating layer, it becomes possible to separate the functions of the resin film for a terminal.

[0010] In one embodiment, the sealant layer may be an acid-modified polyolefin resin layer provided on both sides of the insulating layer, and the acid-modified polyolefin resin layer has excellent adhesion to metal, thereby further improving the adhesion between the resin film for terminal and the metal terminal.

[0011] In one embodiment, the thickness of the resin film for terminals may be 125 to 185 μm, which makes it easier to fill gaps that occur between the outer packaging bag and the thick metal terminals and also makes it easier to prevent the resin film for terminals from becoming too stiff.

[0012] In one embodiment, the loop stiffness value may be 25 to 180 mN / 15 mm, which can further prevent the film edges from sagging even when the film has the above thickness, and can further prevent warping of the film edges due to microslit processing.

[0013] In one embodiment, the insulating layer may have a tensile modulus of elasticity of 1,400 MPa or less at 23° C. This makes it easy to prevent the resin film for a terminal from becoming too stiff.

[0014] In one embodiment, the insulating layer may have a tensile modulus of elasticity of 500 to 1200 MPa at 23° C. This makes it easy to prevent the stiffness of the resin film for a terminal from becoming too strong or too weak.

[0015] In one embodiment, the thickness of the resin film for a terminal may be 150 to 200 μm, and the tensile modulus of the insulating layer may be 500 to 1320 MPa at 23° C. This makes it easy to obtain a resin film for a terminal with the desired stiffness.

[0016] In one embodiment, the thickness of the resin film for a terminal may be 100 μm or more and less than 150 μm, and the insulating layer may have a tensile modulus of elasticity of 850 to 1400 MPa at 23° C. This makes it easy to obtain a resin film for a terminal with the desired stiffness.

[0017] In one embodiment, the thickness of the insulating layer may be 20 to 70% of the thickness of the multilayer film, which makes it easier to ensure insulation and obtain good heat sealing properties because the film thickness is maintained by the insulating layer during heat sealing.

[0018] The resin film for a terminal of the present disclosure is a resin film for a terminal for covering, by heat sealing, the outer peripheral surface of a portion of a metal terminal electrically connected to an electricity storage device main body that constitutes an electricity storage device, the resin film comprising a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer, the sealant layers containing maleic anhydride-modified polypropylene, the thickness of the insulating layer being 25 to 65% of the thickness of the multilayer film, the insulating layer having a tensile modulus of elasticity at 23°C of 850 to 1400 MPa, the thickness being 100 μm or more and less than 150 μm, and the loop stiffness value being 35 to 130 mN / 15 mm. Such a resin film for a terminal enables better heat sealing of thick metal terminals when producing an electricity storage device having such a metal terminal.

[0019] The electricity storage device of the present disclosure also includes an electricity storage device main body, a metal terminal electrically connected to the electricity storage device main body, an outer bag that holds the metal terminal and houses the electricity storage device main body, and a terminal resin film that covers a portion of the outer surface of the metal terminal by heat sealing between the metal terminal and the outer bag, and the terminal resin film is the above-mentioned terminal resin film.

[0020] In this electricity storage device, the terminal resin film is fused (adhered) to a part of the outer peripheral surface of the metal terminal by heat sealing, and the metal terminal is covered with the terminal resin film. The above-mentioned terminal resin film has excellent heat sealing processability for the metal terminal when producing an electricity storage device having a thick metal terminal. For this reason, the above-mentioned electricity storage device may be for vehicle use.

[0021] A method for producing a resin film for a terminal according to the present disclosure includes a step of obtaining a resin film for a terminal by an extrusion method. The resin film for a terminal is a film for covering, by heat sealing, the outer peripheral surface of a part of a metal terminal electrically connected to an electricity storage device main body that constitutes an electricity storage device, and has a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm.

[0022] In one aspect, the step of obtaining a resin film for a terminal by an extrusion method may include a co-extrusion step of obtaining a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer by a co-extrusion method, and a cooling step of cooling the multilayer film to obtain the resin film for a terminal.

[0023] In the present disclosure, "melting point" means the "melting peak temperature" determined in accordance with the method described in JIS K7121-1987, and when two or more melting peaks appear independently, the lowest melting peak temperature is adopted.

[0024] According to the present disclosure, a resin film for terminals and a method for producing the same are provided, which exhibit excellent heat-sealing processability for metal terminals when producing an electricity storage device having thick metal terminals. The resin film for terminals of the present disclosure can be said to exhibit excellent heat-sealing processability for metal terminals despite its thickness. Furthermore, according to the present disclosure, an electricity storage device obtained using the resin film for terminals is provided.

[0025] Fig. 2 is a cross-sectional view schematically showing a resin film for a terminal according to an embodiment of the present disclosure. Fig. 3 is a perspective view showing an electricity storage device according to an embodiment of the present disclosure. Fig. 4 is a partial cross-sectional view taken along line AA of the resin film for a terminal and the metal terminal shown in Fig. 2. Fig. 5 is a cross-sectional view schematically showing an example of an exterior packaging material shown in Fig. 2.

[0026] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0027] [Resin Film for Terminal] Fig. 1 is a cross-sectional view schematically illustrating a resin film for terminal according to an embodiment of the present disclosure. As shown in Fig. 1, the resin film for terminal according to this embodiment (hereinafter also simply referred to as "resin film for terminal") 10 may include a first sealant layer 1, an insulating layer 2, and a second sealant layer 3, in this order. That is, the resin film for terminal 10 may be a multilayer film. The resin film for terminal 10 may have an adhesive layer that bonds the first sealant layer 1 and the insulating layer 2. The resin film for terminal 10 may also have an adhesive layer that bonds the second sealant layer 3 and the insulating layer 2.

[0028] When the resin film for terminals 10 is a multilayer film including an insulating layer 2 and a first sealant layer 1 and a second sealant layer 3 provided on both sides of the insulating layer 2, the resin film for terminals 10 can be functionally separated. That is, the insulating layer 2 ensures the thickness of the resin film for terminals 10, thereby ensuring insulation during heat sealing. Meanwhile, the first sealant layer 1 can be heat-sealed (thermally fused) to an outer bag. Meanwhile, the second sealant layer 3 can fill the gap between the resin film for terminals 10 and the metal terminal. Furthermore, even if the first sealant layer 1 is fluidized during heat sealing of the resin film for terminals 10 to the metal terminal, causing variations in the insulation properties of the first sealant layer 1, the insulating layer 2 ensures the thickness of the resin film for terminals 10, thereby ensuring stable insulation. However, the resin film for terminals may be a single-layer film with heat-sealability as long as it has a predetermined loop stiffness value.

[0029] The loop stiffness value, which indicates the stiffness of the resin film for terminals 10, is 20 to 200 mN / 15 mm. When the loop stiffness value of the resin film for terminals 10 is 20 mN / 15 mm or more, the stiffness of the film is not too weak compared to when the value is less than 20 mN / 15 mm, and the tendency for the film edges to sag can be suppressed even when the film has the above-mentioned thickness. When the loop stiffness value of the resin film for terminals 10 is 200 mN / 15 mm or less, the stiffness of the film is not too strong compared to when the value is greater than 200 mN / 15 mm, and the warping of the film edges due to microslit processing can be suppressed even when the film has the above-mentioned thickness. Because the resin film for terminals 10 is thus less likely to warp or sag at its edges, it is easier to align it during heat sealing processing, and the heat sealing position is less likely to shift when it is bonded to a metal terminal.

[0030] From the above viewpoints, the loop stiffness value of the resin film for terminal 10 can be set to 25 to 180 mN / 15 mm, and may be set to 35 to 130 mN / 15 mm.

[0031] The loop stiffness value is measured as follows. Three samples are prepared: one cut to a length of 200 mm in the MD direction and 15 mm in the TD direction, and the other cut to a length of 200 mm in the TD direction and 15 mm in the MD direction. These samples are set in a loop stiffness tester (model DA) manufactured by Toyo Seiki Seisakusho, and measured at a temperature of 23°C under the following conditions. The average of the measured values ​​for six samples is used as the loop stiffness value for that sample. (Conditions) Loop length: 85 mm, compression speed: 3.3 mm / min, compression time: 3 sec, compression distance: 20 mm, measurement value: maximum load value.

[0032] The loop stiffness value can be adjusted by the thickness of the film, the type and physical properties of the materials used as described below, the method of producing the film (adjusting the crystallinity, etc.), and the like.

[0033] The thickness of the resin film 10 for terminals is 100 to 200 μm. A thickness of 100 μm or more makes it easier to fill gaps that occur between the outer packaging bag and the thick metal terminal. From this perspective, the thickness can be 100 μm or more, 125 μm or more, or 150 μm or more. A thickness of 200 μm or less makes it easier to prevent the resin film 10 for terminals from becoming too stiff. From this perspective, the thickness can be 200 μm or less, 185 μm or less, 175 μm or less, or less than 150 μm. From these perspectives, the thickness of the resin film 10 for terminals may be, for example, 100 μm or more but less than 150 μm, 125 to 185 μm, 150 to 175 μm, etc. Note that a thickness of 100 μm or more, 125 μm or more, or 150 μm or more can be considered a thick resin film for terminals 10.

[0034] Each layer constituting the resin film for terminal 10 will be described in detail below.

[0035] <First Sealant Layer (First Skin Layer)> In this embodiment, the first sealant layer 1 is a layer that is heat-sealed (thermally fused) to the exterior bag of the electricity storage device.

[0036] A layer containing a polyolefin resin (a polyolefin layer or a polyolefin film) is used as the first sealant layer 1. The polyolefin layer has good sealing properties for the outer packaging bag. In addition, since the polyolefin layer has heat resistance, the terminal resin film 10 can improve the heat resistance of the electricity storage device.

[0037] Examples of polyolefin-based resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; polypropylene; block or random copolymers containing propylene as a copolymerization component; and propylene-α-olefin copolymers. The polyolefin-based resin may be an acid-modified polyolefin resin obtained by modifying a polyolefin resin with an acid (such as maleic anhydride) or glycidyl. In particular, the first sealant layer 1 may be an acid-modified polyolefin resin layer containing an acid-modified polyolefin resin. For example, if both the first sealant layer 1 and the second sealant layer 3 contain an acid-modified polyolefin resin, the terminal resin film 10 can be used without regard to the front or back. Furthermore, the first sealant layer 1 preferably contains polypropylene from the viewpoints of water vapor barrier properties, the fact that polypropylene is used on the heat-sealed surface of the outer layer bag of many electricity storage devices, and ease of adjusting the loop stiffness value.

[0038] The polyolefin resin contained in the first sealant layer 1 can have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 4 to 20 g / 10 min. The melt flow rate is a parameter that indicates the fluidity of a polymeric material when melted and also a parameter that indicates the molecular weight. The melt flow rate can be used to adjust the loop stiffness value of the resin film for terminal 10. When the melt flow rate of the polyolefin resin contained in the first sealant layer 1 is within the above range, the loop stiffness value can be easily adjusted to an appropriate range. From this perspective, the melt flow rate of the polyolefin resin contained in the first sealant layer 1 can be 5 to 15 g / 10 min, or may be 7 to 12 g / 10 min.

[0039] The first sealant layer 1 may further contain additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, crystal nucleating agents, and plasticizers as needed to impart sealing properties, heat resistance, and other functionalities.

[0040] The melting point of the first sealant layer 1 is not particularly limited, but is preferably 120° C. or higher, and more preferably 130° C. or higher. When the melting point of the first sealant layer 1 is 120° C. or higher, it is easier to prevent a decrease in the seal strength of the terminal resin film 10 with respect to the outer bag, even when the terminal resin film 10 is used in a high-temperature environment, compared to when the melting point is lower than 120° C.

[0041] The melting point of the first sealant layer 1 is preferably 160° C. or lower, more preferably 150° C. or lower, from the viewpoint of low-temperature sealing properties.

[0042] The thickness of the first sealant layer 1 is not particularly limited, but is preferably 10 to 175 μm, and more preferably 20 to 150 μm. When the thickness of the first sealant layer 1 is 10 μm or more, sufficient seal strength with the outer packaging bag can be obtained. When the thickness of the first sealant layer 1 is 200 μm or less, the amount of heat required to melt the first sealant layer 1 is reduced, allowing the terminal resin film 10 to be sealed to the outer packaging bag in a short time (reducing the takt time), thereby further improving productivity.

[0043] <Second Sealant Layer (Second Skin Layer)> In this embodiment, the second sealant layer 3 is a layer that is fused to a part of the outer peripheral surface of the metal terminal 14 by heat sealing.

[0044] A layer containing a polyolefin resin (a polyolefin layer or a polyolefin film) is used as the second sealant layer 3. The polyolefin layer has good sealing properties for metal terminals. In addition, since the polyolefin layer has heat resistance, the terminal resin film 10 can improve the heat resistance of the electricity storage device.

[0045] Examples of polyolefin-based resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; polypropylene; block or random copolymers containing propylene as a copolymerization component; and propylene-α-olefin copolymers. The polyolefin-based resin may be an acid-modified polyolefin resin obtained by modifying a polyolefin resin with an acid (such as maleic anhydride) or glycidyl. Among these, the second sealant layer 3 is preferably an acid-modified polyolefin resin layer containing an acid-modified polyolefin resin. Because the acid-modified polyolefin resin layer has excellent adhesion to metals, it can further improve the adhesion between the terminal resin film 10 and the metal terminal 14. Furthermore, the second sealant layer 3 preferably contains polypropylene from the viewpoint of water vapor barrier properties, as described above.

[0046] The polyolefin resin contained in the second sealant layer 3 may have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 4 to 20 g / 10 min. When the melt flow rate of the polyolefin resin contained in the second sealant layer 3 is within the above range, it is easy to adjust the loop stiffness value to an appropriate range. From this perspective, the melt flow rate of the polyolefin resin contained in the second sealant layer 3 may be 5 to 15 g / 10 min, or may be 7 to 12 g / 10 min.

[0047] The second sealant layer 3 may further contain additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, crystal nucleating agents, and plasticizers as needed to impart sealing properties, heat resistance, and other functionalities.

[0048] The melting point of the second sealant layer 3 is not particularly limited, but is preferably 120° C. or higher, and more preferably 130° C. or higher. When the melting point of the second sealant layer 3 is 120° C. or higher, it is easier to prevent a decrease in the seal strength of the terminal resin film 10 with respect to the outer bag, even when the terminal resin film 10 is used in a high-temperature environment, compared to when the melting point is lower than 120° C.

[0049] From the viewpoint of low-temperature sealing properties, the melting point of the second sealant layer 3 is preferably 160° C. or lower, and more preferably 150° C. or lower.

[0050] The melting point of the second sealant layer 3 may be the same as or different from the melting point of the first sealant layer 1, but is preferably the same from the viewpoint of being able to use the resin film for terminal 10 without worrying about the front and back.

[0051] The thickness of the second sealant layer 3 is not particularly limited, but is preferably 10 to 175 μm, and more preferably 20 to 150 μm. When the thickness of the second sealant layer 3 is 10 μm or more, the gap between the metal terminal and the resin film for terminal 10 is easily filled with the resin constituting the second sealant layer 3. Furthermore, when the thickness of the second sealant layer 3 is 200 μm or less, the amount of heat required to melt the second sealant layer 3 is reduced, so that the resin film for terminal 10 can be sealed to the metal terminal in a short time (the takt time can be shortened), thereby further improving productivity.

[0052] The thickness of the second sealant layer 3 may be greater than, equal to, or less than the thickness of the first sealant layer 1. If the thickness of the second sealant layer 3 is greater than the thickness of the first sealant layer 1, a larger amount of resin can be secured to fill the gap between the second sealant layer 3 and the metal terminal when the resin film for terminal 10 is heat-sealed to the metal terminal. If the second sealant layer 3 and the first sealant layer 1 have the same thickness, the resin film for terminal 10 can be used without regard to the front and back sides. In other words, the first sealant layer 1 can be used as the second sealant layer 3, and the second sealant layer 3 can be used as the first sealant layer 1. This eliminates the need to distinguish between the first sealant layer 1 and the second sealant layer 3 when fusing the resin film for terminal 10 to the metal terminal, allowing for efficient fusing.

[0053] <Insulating Layer 2 (Core Layer)> The insulating layer 2 is a layer that prevents the resin film for terminal 10 from becoming thin (sealing thinning) during heat sealing and ensures insulation between the metal terminal and the metal layer of the exterior material.

[0054] A layer containing a polyolefin resin (a polyolefin layer, a polyolefin film) is used as the insulating layer 2. Because the polyolefin layer has heat resistance, the resin film for terminal 10 can further improve the heat resistance of the electricity storage device.

[0055] Examples of polyolefin resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; polypropylene; block or random copolymers containing propylene as a copolymerization component; and propylene-α-olefin copolymer. The polyolefin resin may be an acid-modified polyolefin resin obtained by modifying a polyolefin resin with an acid (such as maleic anhydride) or glycidyl. From the viewpoints of adhesion to the sealant layer and ease of adjusting the loop stiffness value, the insulating layer 2 preferably contains the same resin as the sealant layer, and preferably contains polypropylene.

[0056] The polyolefin-based resin contained in the insulating layer 2 may have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 1.0 to 10.0 g / 10 min. When the melt flow rate of the polyolefin-based resin contained in the insulating layer 2 is within the above range, it is easy to adjust the loop stiffness value to an appropriate range. From this perspective, the melt flow rate of the polyolefin-based resin contained in the insulating layer 2 may be 1.5 to 7.0 g / 10 min, or may be 1.5 to 4.0 g / 10 min.

[0057] The insulating layer 2 may further contain additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, crystal nucleating agents, colorants, and plasticizers as needed to impart sealing properties, heat resistance, and other functionalities.

[0058] The melting point of the insulating layer 2 is not particularly limited, but is preferably 130° C. or higher, 140° C. or higher, 150° C. or higher, 155° C. or higher, or 160° C. or higher. When the melting point of the insulating layer 2 is 130° C. or higher, deterioration of the insulation between the barrier layer of the exterior material and the metal terminal can be suppressed, compared to when the melting point is lower than 130° C., even when the resin film for terminal 10 is used in a high-temperature environment.

[0059] The melting point of the insulating layer 2 is preferably 250° C. or less, more preferably 240° C. or less, and even more preferably 230° C. or less.

[0060] The melting point of the insulating layer 2 is preferably higher than the melting points of the resins contained in the first sealant layer 1 and the second sealant layer 3, and more preferably 10° C. or more higher than the melting points of the resins contained in the first sealant layer 1 and the second sealant layer 3. In this case, when the resin film for terminal 10 is heat-sealed to an exterior material including a barrier layer made of a metal layer, seal thinning (thinning) of the insulating layer 2 can be suppressed, making it easier to ensure insulation between the barrier layer of the exterior material and the metal terminal.

[0061] The tensile modulus of the insulating layer 2 at 23°C is preferably 1400 MPa or less. This makes it easier to prevent the resin film for terminal 10 from becoming too stiff, compared to when the tensile modulus exceeds 1400 MPa. From this viewpoint, the tensile modulus is more preferably 1200 MPa or less, and even more preferably 1150 MPa or less.

[0062] The tensile modulus of the insulating layer 2 at 23°C is preferably 500 MPa or more. This makes it easier to prevent the stiffness of the resin film for terminal 10 from becoming too weak, compared to when the tensile modulus is less than 500 MPa. From this viewpoint, the tensile modulus is more preferably 550 MPa or more, and even more preferably 600 MPa or more.

[0063] The tensile modulus of elasticity of the insulating layer 2 at 23°C can be adjusted in accordance with the thickness of the resin film for terminals 10, from the viewpoint of obtaining the desired stiffness. When the thickness of the resin film for terminals 10 is 150 to 200 μm, in terms of suppressing warping, the tensile modulus of elasticity of the insulating layer 2 at 23°C is preferably 500 to 1,320 MPa, more preferably 550 to 1,150 MPa, and even more preferably 600 to 1,100 MPa. When the thickness of the resin film for terminals 10 is 100 μm or more but less than 150 μm, in terms of suppressing warping, the tensile modulus of elasticity of the insulating layer 2 at 23°C is preferably 850 to 1,400 MPa, more preferably 900 to 1,300 MPa, and even more preferably 950 to 1,250 MPa.

[0064] The tensile modulus of the insulating layer 2 (film) is measured as follows: In accordance with JIS K 6921-2, a tensile test is performed on a film having a size of 15 mm width x 5 cm length (the length direction is the MD direction) using, for example, an Orientec Tensilon universal testing machine RTC-1250, with a chuck distance of 5 cm and a tensile speed of 200 mm / min at 23°C. The slope of the stress / strain curve corresponding to the two strain points where the tensile elongation is from 0.05% to 0.25% is taken as the tensile modulus of the film.

[0065] The thickness of the insulating layer 2 is not particularly limited, but is preferably 10 to 200 μm, and more preferably 20 to 150 μm. When the thickness of the insulating layer 2 is 10 μm or more, sufficient insulation properties are easily obtained. When the thickness of the insulating layer 2 is 200 μm or less, the amount of water vapor penetrating from the peripheral edge of the resin film for terminal 10 can be reduced.

[0066] The thickness of the insulating layer 2 is preferably 20 to 70%, and more preferably 25 to 65%, of the thickness of the resin film for terminal 10 (multilayer film). This makes it easier to ensure insulation and obtain good heat sealing properties because the film thickness is maintained by the insulating layer 2 during heat sealing.

[0067] [Method for Manufacturing Terminal Resin Film] Next, a description will be given of a method for manufacturing the terminal resin film 10. However, the method for manufacturing the terminal resin film 10 is not limited to the manufacturing method described below.

[0068] The manufacturing method of the resin film for terminal 10 includes a step of obtaining the resin film for terminal by extrusion. That is, the resin film for terminal 10 can be obtained by extruding a raw material for the resin film for terminal containing a polyolefin-based resin. The step of obtaining the resin film for terminal by extrusion can include a co-extrusion step of obtaining a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer by co-extrusion, and a cooling step of cooling the multilayer film to obtain the resin film for terminal. That is, the resin film for terminal 10 can be obtained by co-extruding a raw material for the first sealant layer 1, a raw material for the insulating layer 2, and a raw material for the second sealant layer 3, each of which contains a polyolefin-based resin, and then cooling the obtained multilayer film.

[0069] Examples of extrusion or co-extrusion methods include the T-die method and the inflation method (ring die method). These methods allow the loop stiffness value of the resin film for terminals 10 to be adjusted. Specifically, using an extruder, a resin melted and kneaded at a temperature of, for example, 160 to 250°C is extruded from a T-die or ring die. The extruded resin is cooled with air or cooling water, or nipped and cooled by a temperature-adjustable cooling roll. The cooling roll is installed directly below the extrusion section and includes a metal roll capable of controlling the cooling temperature between 0 and 60°C and a rubber roll capable of similarly controlling the cooling temperature. The crystallinity of the resin changes depending on the cooling rate of the extruded resin. This allows the loop stiffness value of the resin film for terminals 10 to be adjusted.

[0070] [Method of fusing a resin film for terminals] A fusing process for melt-bonding (fusing) the resin film for terminals 10 shown in FIG. 1 to an outer packaging bag will be described.

[0071] First, a fusion process is performed to melt and bond the resin film for terminal 10 to the metal terminal 14. At this time, the second sealant layer 3 of the resin film for terminal 10 shown in Fig. 1 is faced toward the metal terminal 14, and the resin film for terminal 10 and the metal terminal 14 are thermally fused together while simultaneously melting the second sealant layer 3 by heating and bonding the second sealant layer 3 to the metal terminal 14 by applying pressure.

[0072] In the fusion treatment, from the viewpoint of obtaining sufficient adhesion and sealing properties between the resin film for terminal 10 and the metal terminal 14, it is preferable to heat to a temperature of the melting point of the second sealant layer 3 +20° C. or more.

[0073] The heating temperature of the resin film for terminal 10 may be, for example, 155 to 285° C. The heat-sealing time can be determined in consideration of the adhesion to the metal terminal 14 and productivity. The heat-sealing time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0074] Next, a fusion process is performed to melt and bond the resin film for terminal 10 and the exterior material 13. Specifically, the resin film for terminal 10 and the exterior material 13 are heat-fused together while simultaneously melting the first sealant layer 1 by heating and bonding the first sealant layer 1 to the exterior material by applying pressure.

[0075] In the fusion treatment, the first sealant layer 1 of the resin film for terminals 10 and the sealant layer of the exterior material 13 are heated and melted. At this time, the heating temperature may be any temperature at which both the first sealant layer 1 of the resin film for terminals 10 and the sealant layer of the exterior material 13 melt; however, from the viewpoint of obtaining sufficient adhesion and sealing properties of the first sealant layer 1 of the resin film for terminals 10 and the sealant layer of the exterior material 13, the heating temperature is preferably set to a temperature that is 20° C. or higher than the melting point of the sealant layer with the higher melting point, either the first sealant layer 1 of the resin film for terminals 10 or the sealant layer of the exterior material 13.

[0076] The heating temperature of the resin film for terminal 10 may be, for example, 155 to 285° C. The heat-sealing time can be determined in consideration of the adhesion to the exterior material 13 and productivity. The heat-sealing time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0077] [Electricity storage device] The electricity storage device includes an electricity storage device main body, a metal terminal electrically connected to the electricity storage device main body, an outer bag that holds the metal terminal and accommodates the electricity storage device main body, and a resin film for terminals that is disposed between the metal terminals and the outer bag and that covers a part of the outer peripheral surface of the metal terminal by heat sealing. The resin film for terminals is the resin film for terminals described above.

[0078] Fig. 2 is a perspective view showing one embodiment of an electricity storage device fabricated using the above-described resin film for terminal. As shown in Fig. 2, the electricity storage device 50 includes a battery body 11 having an electrolyte, two metal terminals (current extraction terminals) 14 for extracting current from the battery body 11 to the outside, a resin film for terminal 10, and an outer bag 54 for airtightly housing the battery body 11. The outer bag 54 is used as a container for housing the battery body 11. The resin film for terminal 10 is fused to a portion of the outer peripheral surface of the metal terminal 14, and the metal terminal 14 is sandwiched between the outer bag 54 and the resin film for terminal 10. In the resin film for terminal 10, the second sealant layer 3 is fused to the metal terminal 14, and the first sealant layer 1 is fused to the outer packaging material 13 (the outer bag 54).

[0079] In the electricity storage device 50, the terminal resin film 10 is fused to the outer peripheral surface of a portion of the metal terminal 14 by heat sealing, and the metal terminal 14 is covered with the terminal resin film 10. The terminal resin film 10 has excellent heat sealing processability for the metal terminal when producing an electricity storage device having a thick metal terminal.

[0080] The power storage device 50 is not particularly limited as long as it is a device that requires a large current, and examples thereof include an in-vehicle or stationary storage battery.

[0081] The battery body 11, the metal terminals 14, and the outer bag 54 will be described in detail below.

[0082] <Battery Body> The battery body 11 has at least one power generating element consisting of a positive electrode, an electrolyte, and a negative electrode. Examples of the electrolyte include sulfide-based solid electrolytes and oxide-based solid electrolytes.

[0083] 2 and 3, the pair of metal terminals 14 includes a metal terminal body 14-1 and a corrosion prevention layer 14-2. Of the pair of metal terminal bodies 14-1, one metal terminal body 14-1 is electrically connected to the positive electrode of the battery body 11, and the other metal terminal body 14-1 is electrically connected to the negative electrode of the battery body 11. The pair of metal terminal bodies 14-1 extend in a direction away from the battery body 11, and a portion thereof is exposed from the exterior material 13. The shape of the pair of metal terminal bodies 14-1 may be, for example, a flat plate shape.

[0084] The material of the metal terminal body 14-1 can be a metal, which can be determined in consideration of the structure of the battery body 11 and the materials of each component of the battery body 11.

[0085] When the power storage device 50 is a lithium-ion secondary battery, aluminum can be used as the positive electrode current collector, and copper can be used as the negative electrode current collector. When the power storage device 50 is a lithium-ion secondary battery, the material of the metal terminal body 14-1 connected to the positive electrode of the battery body 11 is preferably aluminum. The material of the metal terminal body 14-1 connected to the positive electrode of the battery body 11 may also be an aluminum material with a purity of 97% or higher, such as 1N30. Furthermore, when the metal terminal body 14-1 is to be bent, an O material that has been tempered by sufficient annealing to add flexibility may be used. The material of the metal terminal body 14-1 connected to the negative electrode of the battery body 11 may be, for example, copper with a nickel-plated layer formed on its surface, or nickel. The power storage device 50 may be an all-solid-state battery.

[0086] The thickness of the metal terminal body 14-1 can be determined depending on the size and capacity of the electricity storage device 50. In the case of an automobile-mounted electricity storage device that requires a large current, the thickness of the metal terminal body 14-1 can be set appropriately within the range of 50 to 1000 μm, 100 to 600 μm, or 150 to 500 μm.

[0087] The corrosion prevention layer 14-2 is disposed so as to cover the surface of the metal terminal body 14-1. In the electricity storage device 50, the corrosion prevention layer 14-2 is formed by a corrosion prevention treatment using chromate, and is a layer for suppressing corrosion of the metal terminal body 14-1 due to corrosive components such as hydrogen sulfide.

[0088] <Outer Bag> As shown in Fig. 2, the outer bag 54 is obtained by overlapping two outer packaging materials 13 and heat-sealing the overlapping peripheral portions. The outer bag 54 can also be obtained by folding the outer packaging material 13 in half and heat-sealing the overlapping peripheral portions. The outer packaging material 13 includes, from the battery body 11 side, a sealant layer 21, a first adhesive layer 22, a corrosion prevention treatment layer 23-1, a barrier layer 24, a corrosion prevention treatment layer 23-2, a second adhesive layer 25, and a substrate layer 26, in this order (see Fig. 4).

[0089] The sealant layer 21 is a layer that provides heat-sealing properties to the exterior material 13, and is placed on the inside and heat-sealed (thermal fusion) when assembling the electricity storage device 50. Examples of the base material for the sealant layer 21 include polyolefin resins and acid-modified polyolefin resins obtained by graft-modifying polyolefin resins with maleic anhydride or the like. Examples of the polyolefin resins that can be used include low-density, medium-density, and high-density polyethylenes; ethylene-α-olefin copolymers; homo-, block-, or random polypropylenes; and propylene-α-olefin copolymers. Among these, it is preferable that the polyolefin resin contains polypropylene. These polyolefin resins can be used alone or in combination of two or more.

[0090] The sealant layer 21 may be a single-layer film or a multilayer film in which multiple layers are laminated, depending on the required function. Specifically, it may be a multilayer film in which a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene is interposed to impart moisture resistance. The sealant layer 21 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier).

[0091] The thickness of the sealant layer 21 is preferably 10 to 150 μm, and more preferably 30 to 80 μm. When the thickness of the sealant layer 21 is 10 μm or more, the exterior material 13 can have sufficient adhesion to the opposing exterior material 13 or to the terminal resin film 10. Furthermore, when the thickness of the sealant layer 21 is 150 μm or less, the cost of the exterior material 13 can be reduced.

[0092] The first adhesive layer 22 can be appropriately selected from known adhesives such as dry lamination adhesives and acid-modified heat-fusible resins.

[0093] As shown in Figure 4, it is preferable from a performance standpoint to form the corrosion prevention treatment layers 23-1 and 23-2 on both sides of the barrier layer 24, but from the perspective of reducing costs, the corrosion prevention treatment layer 23-1 may be placed only on the surface of the barrier layer 24 located on the first adhesive layer 22 side.

[0094] The barrier layer 24 may be a conductive metal layer. Examples of materials for the barrier layer 24 include aluminum and stainless steel, with aluminum being preferred from the standpoints of cost, mass (density), and the like.

[0095] The second adhesive layer 25 may be a polyurethane adhesive containing polyester polyol, polyether polyol, acrylic polyol, or the like as a main component.

[0096] The substrate layer 26 may be a single-layer film or a multi-layer film made of nylon, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. Similar to the sealant layer 21, the substrate layer 26 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier).

[0097] Moreover, the exterior material 13 may further include a protective layer (not shown) for protecting the base material layer 26 on the surface of the base material layer 26 opposite to the sealant layer 21 .

[0098] In addition, in the exterior material 13, an adhesive resin layer may be used instead of the first adhesive layer 22.

[0099] Although the preferred embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above-described embodiments.

[0100] One aspect of the present disclosure is as follows. [1] A resin film for a terminal for covering, by heat sealing, the outer peripheral surface of a portion of a metal terminal electrically connected to an electricity storage device main body that constitutes an electricity storage device, the resin film for a terminal having a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm. [2] The resin film for a terminal according to [1], which is made of a multilayer film having an insulating layer and a sealant layer provided on at least one side of the insulating layer. [3] The resin film for a terminal according to [2], wherein the sealant layer is provided on both sides of the insulating layer, and the sealant layer is an acid-modified polyolefin resin layer. [4] The resin film for a terminal according to any one of [1] to [3], which has a thickness of 125 to 185 μm. [5] The resin film for a terminal according to any one of [1] to [4], which has a loop stiffness value of 25 to 180 mN / 15 mm. [6] The resin film for a terminal according to [2] or [3], wherein the insulating layer has a tensile modulus of elasticity of 1,400 MPa or less at 23°C. [7] The resin film for a terminal according to any one of [2], [3], and [6], wherein the insulating layer has a tensile modulus of elasticity of 500 to 1,200 MPa at 23°C. [8] The resin film for a terminal according to any one of [2], [3], [6], and [7], wherein the thickness is 150 to 200 μm and the insulating layer has a tensile modulus of elasticity of 500 to 1,320 MPa at 23°C. [9] The resin film for a terminal according to any one of [2], [3], [6], and [7], wherein the thickness is 100 μm or more and less than 150 μm and the insulating layer has a tensile modulus of elasticity of 850 to 1,400 MPa at 23°C.

[10] The resin film for a terminal according to any one of [2], [3], and [6] to [9], wherein the insulating layer has a thickness of 20 to 70% of the thickness of the multilayer film.

[11] A resin film for a terminal for covering, by heat sealing, the outer peripheral surface of a part of a metal terminal electrically connected to a main body of an electricity storage device that constitutes an electricity storage device, the resin film for a terminal being made of a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer, the sealant layers containing maleic anhydride-modified polypropylene, the thickness of the insulating layer being 25 to 65% of the thickness of the multilayer film, the tensile modulus of the insulating layer at 23°C being 850 to 1400 MPa, the thickness being 100 μm or more and less than 150 μm, and the loop stiffness value being 35 to 130 mN / 15 mm.

[12] An electricity storage device comprising: an electricity storage device main body; a metal terminal electrically connected to the electricity storage device main body; an outer bag that sandwiches the metal terminal and houses the electricity storage device main body; and a terminal resin film that covers, by heat sealing, a portion of the outer peripheral surface of the metal terminal between the metal terminal and the outer bag, wherein the terminal resin film is the terminal resin film according to any one of [1] to

[11] .

[13] The electricity storage device according to

[12] , which is for in-vehicle use.

[14] A method for producing a terminal resin film, comprising: a step of obtaining a terminal resin film by an extrusion method, wherein the terminal resin film is a film for heat sealing a portion of the outer peripheral surface of a metal terminal electrically connected to the electricity storage device main body that constitutes the electricity storage device, the film having a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm.

[15] The manufacturing method according to

[14] , wherein the step of obtaining a resin film for a terminal by an extrusion method comprises: a co-extrusion step of obtaining a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer by a co-extrusion method; and a cooling step of cooling the multilayer film to obtain the resin film for a terminal.

[0101] Hereinafter, the present disclosure will be described more specifically based on examples, but the present disclosure is not limited to the following examples.

[0102] <Preparation of Resin Film for Terminal> Maleic anhydride-modified polypropylene was prepared for the first and second skin layers (first and second sealant layers), and polypropylene resins A to D were prepared for the core layer (insulating layer). (Skin layer) Maleic anhydride-modified polypropylene (P546V, manufactured by Mitsubishi Chemical Corporation, MFR 10.0, melting point 142°C) (Core layer) Polypropylene resin A (PL500A, manufactured by SunAllomer, MFR 3.0, melting point 164°C) Polypropylene resin B (S131, manufactured by Sumitomo Chemical Co., Ltd., MFR 1.5, melting point 132°C) Polypropylene resin C (PF621S, manufactured by SunAllomer, MFR 6.5, melting point 147°C) Polypropylene resin D (PC412A, manufactured by SunAllomer, MFR 2.3, melting point 164°C)

[0103] The tensile modulus of the core layer (film) was measured as follows. Films of polypropylene resins A to D (length direction: MD) measuring 15 mm wide and 5 cm long were prepared. Then, in accordance with JIS K 6921-2, a tensile test was performed on the film using an Orientec Tensilon universal testing machine RTC-1250, with a chuck distance of 5 cm and a tensile speed of 200 mm / min at 23°C. The slope of the stress / strain curve corresponding to the two strain points between 0.05% and 0.25% tensile elongation was taken as the tensile modulus of the film.

[0104] According to Table 1, these resins were co-extruded by the T-die method or the inflation method to obtain polypropylene films that served as the base sheets of the resin film for terminals in each Example and Comparative Example. (T-die method) Using an extruder, the resins of each layer were melt-kneaded at a temperature of 230°C and co-extruded from a T-die. The co-extruded resins were nipped and cooled by cooling rolls whose temperature was adjusted to 20°C. (Inflation method) Using an extruder, the resins of each layer were melt-kneaded at a temperature of 230°C and co-extruded from a ring die by the inflation method. The co-extruded resins were immediately cooled by air.

[0105] From the raw sheet of resin film for terminals of each example, a resin film for terminals having a width of 12 mm was obtained by micro-slitting.

[0106] <Evaluation of Resin Film for Terminal> [Loop Stiffness Value] Three samples were prepared from each example of the original resin film for terminal, each cut to a length of 200 mm in the MD and 15 mm in the TD. Another sample was cut to a length of 200 mm in the TD and 15 mm in the MD. These samples were placed in a loop stiffness tester (model DA) manufactured by Toyo Seiki Seisakusho, and measured at a temperature of 23°C under the following conditions. The average of the measured values ​​for the six samples was used as the loop stiffness value for that sample. The results are shown in Table 1. (Conditions) Loop length: 85 mm, compression speed: 3.3 mm / min, compression time: 3 sec, compression distance: 20 mm, measurement value: maximum load value.

[0107] [Warpage evaluation] Each resin film for terminals was placed on a horizontal surface, and the height of the warpage from the horizontal surface at both ends of the film (the slit portions) was measured with a ruler. Evaluation was then performed according to the following evaluation criteria. The results are shown in Table 1. ×: The height of the warpage at one of both ends was 1 mm or more. ○: The height of the warpage at both ends was 0.5 mm or more but less than 1 mm. ⊚: The height of the warpage at both ends was less than 0.5 mm.

[0108] [Evaluation of ear droop] Using the resin film for terminal of each example, the outer surface of a 200 μm thick metal terminal was heat-sealed (heat-sealing conditions: 165°C, 0.6 MPa, 10 seconds). The heat-sealing was performed so that the resin film for terminal protruded 10 mm from both ends of the metal terminal (forming ears). The obtained sample was held horizontally, and the amount of droop at both ends was measured with a metal ruler. Evaluation was then performed using the following evaluation criteria. The results are shown in Table 1. ×: The amount of droop at one of both ends was 1 mm or more. ○: The amount of droop at both ends was 0.5 mm or more but less than 1 mm. ⊚: The amount of droop at both ends was less than 0.5 mm.

[0109]

[0110] The results shown in Table 1 confirm that resin films for terminals with a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm are less likely to warp or sag at the edges. Such resin films for terminals allow for good alignment during heat sealing of metal terminals.

[0111] REFERENCE SIGNS LIST 1...first sealant layer, 2...insulating layer, 3...second sealant layer, 10...terminal resin film, 11...battery body, 14...metal terminal, 50...electricity storage device

Claims

1. A resin film for terminals, which is used to cover by heat sealing the outer periphery of a portion of a metal terminal electrically connected to the main body of an electric storage device, and which has a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm.

2. The resin film for terminals according to claim 1, which is a multilayer film having an insulating layer and a sealant layer provided on at least one side of said insulating layer.

3. The resin film for terminals according to claim 2, wherein the sealant layer is provided on both sides of the insulating layer, and the sealant layer is an acid-modified polyolefin resin layer.

4. The resin film for a terminal according to claim 1, wherein the thickness is 125 to 185 μm.

5. The resin film for a terminal according to claim 1, wherein the loop stiffness value is 25 to 180 mN / 15 mm.

6. The resin film for terminals according to claim 2, wherein the insulating layer has a tensile modulus of elasticity of 1,400 MPa or less at 23°C.

7. The resin film for terminals according to claim 2, wherein the insulating layer has a tensile modulus of elasticity at 23°C of 500 to 1200 MPa.

8. The resin film for terminals according to claim 2, wherein the thickness is 150 to 200 μm and the insulating layer has a tensile modulus of elasticity at 23° C. of 500 to 1320 MPa.

9. A resin film for terminals according to claim 2, wherein the thickness is 100 μm or more but less than 150 μm, and the insulating layer has a tensile modulus of elasticity at 23° C. of 850 to 1400 MPa.

10. The resin film for a terminal according to claim 2, wherein the thickness of the insulating layer is 20 to 70% of the thickness of the multilayer film.

11. A resin film for terminals used to cover by heat sealing the outer periphery of a portion of a metal terminal electrically connected to a main body of an electric storage device, the resin film for terminals comprising a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer, the sealant layers containing maleic anhydride-modified polypropylene, the thickness of the insulating layer being 25 to 65% of the thickness of the multilayer film, the tensile modulus of the insulating layer at 23°C being 850 to 1400 MPa, the thickness being 100 μm or more but less than 150 μm, and the loop stiffness value being 35 to 130 mN / 15 mm.

12. An electricity storage device comprising: an electricity storage device main body; a metal terminal electrically connected to the electricity storage device main body; an outer bag that holds the metal terminal and contains the electricity storage device main body; and a terminal resin film that covers a part of the outer surface of the metal terminal by heat sealing between the metal terminal and the outer bag, wherein the terminal resin film is the terminal resin film described in any one of claims 1 to 11.

13. The electricity storage device according to claim 12, which is for use in a vehicle.

14. A method for producing a resin film for terminals, comprising the step of obtaining a resin film for terminals by an extrusion method, wherein the resin film for terminals is a film for covering by heat sealing the outer peripheral surface of a portion of a metal terminal that is electrically connected to an electricity storage device main body and that constitutes an electricity storage device, and has a thickness of 100 to 200 μm and a loop stiffness value of 20 to 200 mN / 15 mm.

15. The manufacturing method according to claim 14, wherein the step of obtaining a resin film for terminals by an extrusion method comprises: a co-extrusion step of obtaining a multilayer film having an insulating layer and sealant layers provided on both sides of the insulating layer by a co-extrusion method; and a cooling step of cooling the multilayer film to obtain a resin film for terminals.

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