Resin film for terminals and energy storage devices

Abstract

To provide a resin film for terminals that can achieve both excellent embedding properties and insulation properties even when the cycle time of the energy storage device manufacturing process is shortened. [Solution] A resin film for terminals for covering a portion of the outer surface of a metal terminal in an energy storage device comprising an energy storage device body and a metal terminal electrically connected to the energy storage device body, comprising a first sealant layer, an insulating layer, and a second sealant layer on the outer surface side in this order, wherein the first sealant layer, the insulating layer, and the second sealant layer contain a polyolefin resin, the MFR (melt flow rate) of the first and second sealant layers is 6 to 20 g / 10 min, and the MFR of the insulating layer is 5.5 g / 10 min or more and 0.5 to 5.5 g / 10 min lower than the MFR of the first and second sealant layers.

Description

Technical Field

[0005] , , ,

[0001] The present invention relates to a resin film for terminals and an energy storage device.

Background Art

[0002] In recent years, in soft-pack type batteries, mass production and cost reduction have been demanded, and as part of this, shortening the tact time of the battery manufacturing process has been proposed.

[0003] A soft-pack type battery generally includes an outer bag that houses a battery body such as an electrolyte and an electrode, and a metal terminal (tab lead) called a tab for extracting current from the battery body. A part of the outer peripheral surface of the metal terminal is covered with a resin film for terminals (tab sealant). In the processing of the tab lead, a tab sealant is required that enables shortening of the seal time in the heat seal process of fusing the tab lead and the tab sealant, and shortening of the seal time in the heat seal process of fusing the tab lead and the outer packaging material of the outer bag, respectively. As functions required for the tab sealant, (1) the embedding property of voids caused by the thickness of the tab lead, (2) the adhesion to the tab lead and the outer packaging material, and (3) the insulation between the outer packaging material and the tab lead can be mentioned. It is not easy to satisfy all of these functions with a single-layer tab sealant, and therefore, a method of forming the tab sealant into a multi-layer structure has been adopted (for example, see Patent Document 1).

Prior Art Documents

[0006] This disclosure has been made in view of the above-mentioned problems, and aims to provide a resin film for terminals that can achieve both excellent embedding properties and insulating properties even when the cycle time of the energy storage device manufacturing process is shortened. This disclosure also aims to provide an energy storage device obtained using the said terminal resin film. [Means for solving the problem]

[0007] As described above, the inventors investigated a method for achieving both embedding properties and insulating properties in a resin film for terminals, particularly using a resin film for terminals having a three-layer structure consisting of a skin layer (first sealant layer), a core layer (insulating layer), and a skin layer (second sealant layer). Shortening the cycle time also shortens the time it takes for the outermost skin layer to melt and flow. If the resin's fluidity (MFR) is low, its ability to fill voids may decrease, so it is necessary to maintain a certain level of fluidity. On the other hand, if the MFR of the skin layer is increased too much to improve filling ability, the resin's fluidity may become too high. In that case, the excess flowing resin may adhere to unintended areas, or in some cases, the resin in the skin layer may completely flow out, leaving only the core layer. Because the core layer has a high melting point, it is difficult to properly fuse the core layer with the sealant layer of the exterior material. Given these circumstances, the inventors determined that simply improving the skin layer alone would not be easy, and therefore considered it important to re-examine the overall structure of the film, including both the skin and core layers. After diligent research, the inventors discovered that the above problems could be solved by the following disclosure.

[0008] In other words, the terminal resin film of this disclosure is a terminal resin film for covering a portion of the outer surface of a metal terminal that is electrically connected to the main body of an energy storage device constituting an energy storage device, The structure comprises a first sealant layer, an insulating layer, and a second sealant layer on the outer surface side, in this order. The first sealant layer, the insulating layer, and the second sealant layer contain a polyolefin resin. This is a resin film for terminals in which the MFR (melt flow rate) of the first and second sealant layers is 6 to 20 g / 10 min, and the MFR of the insulating layer is 5.5 g / 10 min or more and 0.5 to 5.5 g / 10 min lower than the MFR of the first and second sealant layers.

[0009] According to the above-described terminal resin film, when the terminal resin film is heat-sealed to a portion of the outer surface of a metal terminal, the terminal resin film can exhibit good void-filling and insulating properties. Therefore, it can be said that such a terminal resin film is suitable for shortening cycle time.

[0010] The inventors have considered the following regarding the structure of the resin film for the terminals: Specifically, they believe that by setting the MFR difference between the skin layer (sealant layer) and the core layer (insulating layer) to a smaller range than conventional methods, while setting the MFR of the core layer to a higher level, they were able to improve embedding while maintaining insulation and shorten the cycle time. Generally, core layers are designed with a low MFR (Metal Fiber Rate) and a high melting point to maintain thickness during heat sealing and ensure insulation. Thus, typical core layers contribute almost nothing to embedding, while maintaining a thickness more than sufficient for insulation. Therefore, by deliberately setting a small difference in MFR between the skin layer and the core layer, and deliberately setting a higher MFR for the core layer, we believe we were able to give the core layer a certain degree of fluidity and improve overall embedding. In addition, because the core layer also flows, the skin layer does not flow alone, and we believe that this resulted in better fusion with the sealant layer of the exterior material. Thus, we believe that the above-mentioned resin film for terminals is a film that can shorten cycle time while satisfying various required characteristics.

[0011] In one embodiment, it is preferable that the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin. Since both the first and second sealant layers are layers containing an acid-modified polyolefin resin, the film can be used without worrying about which side is facing up or down.

[0012] In one embodiment, it is preferable that the thickness of the insulating layer is 1.1 times or more the thickness of the first sealant layer. This makes it easier to maintain the thickness of the insulating layer during heat sealing and to ensure insulation.

[0013] In one embodiment, it is preferable that the melting point of the insulating layer is 150 to 165°C, and the melting points of the first and second sealant layers are 10°C or more lower than the melting point of the insulating layer. This makes it easier to achieve both fluidity and insulating properties.

[0014] In one embodiment, it is preferable that the loop stiffness value measured under the following conditions is 570 mN or less. Such a film has excellent conformability to the shape of the metal terminal, making it easier to improve embedding. (Conditions) Sample size: 15mm wide x 200mm long, Loop length: 85mm, Compression speed: 3.3mm / min, Compression time: 3sec, Compression distance: 20mm, Maximum load value was used for measurement.

[0015] Furthermore, the energy storage device of this disclosure comprises an energy storage device body, metal terminals electrically connected to the energy storage device body, an outer bag that holds the metal terminals and houses the energy storage device body, and a terminal resin film between the metal terminals and the outer bag that covers a portion of the outer surface of the metal terminals by heat sealing, wherein the terminal resin film is the aforementioned terminal resin film.

[0016] In this power storage device, a resin film for terminals is fused (adhered) to a part of the outer peripheral surface of a metal terminal by heat sealing. Here, according to the resin film for terminals described above, when heat sealing is performed on the metal terminal, good embedding property and insulation property can be exhibited. Since such a resin film for terminals can suitably cope with shortening of the tact time, it can be said that even when the above power storage device is manufactured with a shortened tact time, it has good reliability.

[0017] In the present disclosure, "melting point" means "melting peak temperature" obtained in accordance with the method described in JIS K7121-1987. When two or more melting peaks appear independently, among the plurality of observed melting peaks, the peak showing the largest enthalpy change (ΔH) is adopted as the melting peak temperature.

[0018] In the present disclosure, "melt flow rate (MFR)" is an index representing the fluidity of a resin, measured in accordance with JIS K 7210 (temperature 230°C, load 2.16 kg).

Advantages of the Invention

[0019] According to the present disclosure, there is provided a resin film for terminals capable of achieving both excellent embedding property and insulation property even when the tact time of the power storage device manufacturing process is shortened. Further, according to the present disclosure, there is provided a power storage device obtained by using the resin film for terminals. [[ID=Z19]]

Brief Description of the Drawings

[0020] [Figure 1] It is a cross-sectional view schematically showing a resin film for terminals according to an embodiment of the present disclosure. [Figure 2] It is a perspective view showing a power storage device according to an embodiment of the present disclosure. [Figure 3] It is a partial cross-sectional view in the A-A line direction of the resin film for terminals and the metal terminal shown in FIG. 2. <Z [Figure 4] It is a cross-sectional view schematically showing an example of an exterior material shown in FIG. 2.

Best Mode for Carrying Out the Invention

[0021] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0022] [Resin Film for Terminals] The resin film for terminals is a film for covering a part of the outer peripheral surface of a metal terminal electrically connected to a power storage device body constituting a power storage device. FIG. 1 is a cross-sectional view schematically showing a resin film for terminals according to an embodiment of the present disclosure. As shown in FIG. 1, the resin film for terminals (hereinafter, also simply referred to as "resin film for terminals") 10 of the present embodiment includes a first sealant layer 1, an insulating layer 2, and a second sealant layer 3 in this order. That is, the resin film for terminals 10 is a multilayer film. The resin film for terminals 10 may have an adhesive layer for adhering the first sealant layer 1 and the insulating layer 2. Also, the resin film for terminals 10 may have an adhesive layer for adhering the second sealant layer 3 and the insulating layer 2.

[0023] The resin film for terminals 10 can achieve both excellent embedding property and insulation property even when the tact time of the power storage device manufacturing process is shortened as compared with the case where the MFR (melt flow rate) of the first sealant layer 1, the insulating layer 2, and the second sealant layer 3 is out of the range defined above. The resin film for terminals 10 is composed of a multilayer film including the insulating layer 2 and sealant layers (the first sealant layer 1 and the second sealant layer 3) provided on both sides of the insulating layer 2, and the functions as the resin film for terminals 10 are separated into each layer as follows. The first sealant layer 1 enables the resin film for terminals 10 and the outer packaging bag of the power storage device to be heat-sealed (heat-fused). The second sealant layer 3 enables the resin film for terminals 10 and the metal terminal to be heat-sealed and fills the gap between the two. The insulating layer 2 ensures the thickness of the terminal resin film 10, thereby ensuring insulation during heat sealing. For example, even if variations occur in the insulation performance of the second sealant layer 3 due to the flow of the second sealant layer 3, the insulating layer 2 ensures the thickness of the terminal resin film 10, thus ensuring stable insulation. Furthermore, the insulating layer 2, which is more fluid than conventional insulating layers, can compensate for the ability of the second sealant layer 3 to fill gaps around the metal terminals.

[0024] Furthermore, since the first sealant layer 1, the insulating layer 2, and the second sealant layer 3 are all made of polyolefin film, the terminal resin film 10 can be manufactured as a laminated film consisting of each layer by co-extrusion, and such a film has excellent interlayer adhesion strength.

[0025] The thickness of the terminal resin film 10 is not particularly limited, but is preferably 50 to 400 μm, more preferably 55 to 300 μm, and even more preferably 80 to 200 μm. A thickness of 50 μm or more for the terminal resin film 10 makes it easier to achieve both embedding properties and insulating properties. A thickness of 400 μm or less for the terminal resin film 10 makes it easier to obtain moisture barrier properties from the terminal resin film 10.

[0026] The terminal resin film 10 preferably has a loop stiffness value of 570 mN or less, as measured under the following conditions. Such a film has superior conformability to the shape of the metal terminal compared to a film with a loop stiffness value exceeding 570 mN, making it easier to improve embedding. From this viewpoint, the loop stiffness value may be 300 mN or less, or 250 mN or less. There is no particular limit to the lower limit of the loop stiffness value, but it can be set to 20 mN from the viewpoint of making the protruding portion after bonding with the tab lead more flexible. (Conditions) Sample size: 15mm wide x 200mm long, Loop length: 85mm, Compression speed: 3.3mm / min, Compression time: 3sec, Compression distance: 20mm, Measurement environment: 10~30℃. The maximum load value was used as the measured value.

[0027] The following describes in detail each layer that makes up the terminal resin film 10.

[0028] <First sealant layer (first skin layer)> In this embodiment, the first sealant layer 1 is a layer that is heat-sealed (heat-fused) to the outer bag of the energy storage device.

[0029] As the first sealant layer 1, a film containing a polyolefin resin (polyolefin film) is used. The polyolefin film has good sealing properties for the outer bag. In addition, since the polyolefin film has heat resistance, the terminal resin film 10 can improve the heat resistance of the energy storage device.

[0030] Examples of polyolefin resins include low-density, medium-density, or high-density polyethylene; ethylene-α-olefin copolymers; polypropylene; block or random copolymers containing propylene as a copolymer component; and polyolefin resins such as propylene-α-olefin copolymers. The polyolefin resin may also 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 are layers containing an acid-modified polyolefin resin, the terminal resin film 10 can be used without worrying about the front or back side.

[0031] Furthermore, the first sealant layer 1 may optionally contain additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, crystal nucleating agents, and plasticizers to provide sealing properties, heat resistance, and other functionalities.

[0032] 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. A melting point of 120°C or higher for the first sealant layer 1 makes it easier to suppress the decrease in the sealing strength of the terminal resin film 10 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 below 120°C.

[0033] The melting point of the first sealant layer 1 is preferably 165°C or lower, and more preferably 155°C or lower. Having a melting point of 165°C or lower allows for a lower heat seal temperature compared to when the melting point is above 165°C. However, the melting point of the first sealant layer 1 is preferably 10°C or more lower than the melting point of the insulating layer 2, and more preferably 15°C or more lower. Even if the MFRs of both layers are close together, a difference of 10°C or more in their melting points makes it easier for the film thickness to be maintained by the insulating layer 2 during heat sealing, thus ensuring insulation. There is no particular upper limit to the difference in melting points between the two layers, but it can be set to 50°C from the viewpoint of embedding.

[0034] The melt flow rate (MFR) of the first sealant layer 1 is 6 to 20 g / 10 min, preferably 7 to 15 g / 10 min, and more preferably 8 to 10 g / 10 min. A melt flow rate of 6 g / 10 min or higher ensures better embedding properties compared to a melt flow rate of less than 6 g / 10 min. Furthermore, a melt flow rate of 20 g / 10 min or lower suppresses excessive flow of the resin in the first sealant layer 1 compared to a melt flow rate exceeding 20 g / 10 min.

[0035] The thickness of the first sealant layer 1 is not particularly limited, but is preferably 10 to 200 μm, and more preferably 20 to 150 μm. A thickness of 10 μm or more of the first sealant layer 1 provides sufficient sealing strength with the outer bag. A thickness of 200 μm or less of the first sealant layer 1 reduces the amount of heat required to melt the first sealant layer 1, allowing the terminal resin film 10 to be sealed to the outer bag in a shorter time (shorter cycle time), thereby improving productivity.

[0036] <Second sealant layer (second skin layer)> In this embodiment, the second sealant layer 3 is a layer that is fused to a portion of the outer surface of the metal terminal 14 by heat sealing.

[0037] As the second sealant layer 3, a film containing a polyolefin resin is used. Polyolefin films have good sealing properties for metal terminals. In addition, since polyolefin films have heat resistance, the terminal resin film 10 can improve the heat resistance of the energy storage device.

[0038] Examples of polyolefin resins include low-density, medium-density, or high-density polyethylene; ethylene-α-olefin copolymers; polypropylene; block or random copolymers containing propylene as a copolymer component; and propylene-α-olefin copolymers. The polyolefin resin may also be an acid-modified polyolefin resin obtained by modifying a polyolefin resin with an acid (such as maleic anhydride) or glycidyl. In particular, the second sealant layer 3 is preferably an acid-modified polyolefin resin layer containing an acid-modified polyolefin resin. Since the acid-modified polyolefin resin layer has excellent adhesion to metal, the adhesion between the terminal resin film 10 and the metal terminal 14 can be further improved.

[0039] The second sealant layer 3 may further contain, as needed, additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, crystal nucleating agents, and plasticizers to provide sealing properties, heat resistance, and other functionalities.

[0040] 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. By having a melting point of 120°C or higher for the second sealant layer 3, it is possible to suppress the decrease in the sealing strength of the terminal resin film 10 against metal terminals, even when the terminal resin film 10 is used in a high-temperature environment, compared to when the melting point is below 120°C.

[0041] The melting point of the second sealant layer 3 is preferably 165°C or lower, and more preferably 155°C or lower. Having a melting point of 165°C or lower allows for a lower heat seal temperature compared to when the melting point is above 165°C. However, the melting point of the second sealant layer 3 is preferably 10°C or more lower than the melting point of the insulating layer 2, and more preferably 15°C or more lower. Even if the MFRs of both layers are close together, a difference of 10°C or more in their melting points makes it easier for the film thickness to be maintained by the insulating layer 2 during heat sealing, thus ensuring insulation. There is no particular upper limit to the difference in melting points between the two layers, but it can be set to 50°C from the viewpoint of embedding.

[0042] The melting point of the second sealant layer 3 may be the same as or different from that of the first sealant layer 1, but it is preferable that they be the same, for example, from the viewpoint that the terminal resin film 10 can be used without worrying about the front or back side.

[0043] The melt flow rate (MFR) of the second sealant layer 3 is 6 to 20 g / 10 min, preferably 7 to 15 g / 10 min, and more preferably 8 to 10 g / 10 min. An MFR of 6 g / 10 min or higher ensures better embedding properties compared to a MFR of less than 6 g / 10 min. Furthermore, an MFR of 20 g / 10 min or lower suppresses excessive flow of the resin in the second sealant layer 3 compared to a MFR greater than 20 g / 10 min.

[0044] The MFR of the second sealant layer 3 may be the same as or different from the MFR of the first sealant layer 1, but it is preferable that they be the same, for example, from the viewpoint that the terminal resin film 10 can be used without worrying about the front or back side.

[0045] The thickness of the second sealant layer 3 is not particularly limited, but is preferably 10 to 200 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 terminal resin film 10 is more easily filled by 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 terminal resin film 10 can be sealed to the metal terminal in a short time (the cycle time can be shortened), and productivity can be further improved.

[0046] The thickness of the second sealant layer 3 may be greater than the thickness of the first sealant layer 1, the same as the thickness of the first sealant layer 1, 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, then, when the thickness of the terminal resin film 10 is the same, a larger amount of resin can be secured to fill the gap between the second sealant layer 3 and the metal terminal when the terminal resin film 10 is heat-sealed to the metal terminal. If the thickness of the second sealant layer 3 and the first sealant layer 1 are the same, then, for example, the terminal resin film 10 can be used without worrying about which side is facing up or down. 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, eliminating the need to distinguish between the first sealant layer 1 and the second sealant layer 3 when fusing the terminal resin film 10 to metal terminals, and allowing the fusing process to be carried out more efficiently.

[0047] <Insulating layer 2 (core layer)> The insulating layer 2 is a layer that suppresses thinning of the terminal resin film 10 (seal shrinkage) during heat sealing and ensures insulation between the metal terminal and the metal layer of the outer casing material.

[0048] As the insulating layer 2, a film containing a polyolefin resin is used. Since the polyolefin film has heat resistance, the terminal resin film 10 can further improve the heat resistance of the energy storage device.

[0049] Examples of polyolefin resins include low-density, medium-density, or high-density polyethylene; ethylene-α-olefin copolymers; polypropylene or homopolypropylene; block or random copolymers containing propylene as a copolymer component (for example, block polypropylene in which polyethylene components are dispersed in homopolypropylene components); and propylene-α-olefin copolymers. Furthermore, MFR may be adjusted by blending these resins.

[0050] Furthermore, the insulating layer 2 may optionally contain additives such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, nucleating agents, colorants, and plasticizers to provide sealing properties, heat resistance, and other functionalities.

[0051] The melting point of the insulating layer 2 is not particularly limited, but is preferably 150°C or higher, more preferably 155°C or higher, and even more preferably 160°C or higher. By having a melting point of 150°C or higher for the insulating layer 2, the decrease in insulation between the barrier layer of the exterior material and the metal terminal can be suppressed even when the terminal resin film 10 is used in a high-temperature environment, compared to when the melting point is below 150°C.

[0052] The melting point of the insulating layer 2 is preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 230°C or lower.

[0053] 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, as described above. In this case, when the terminal resin film 10 is heat-sealed with the exterior material which includes a barrier layer made of a metal layer, the shrinkage (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.

[0054] The MFR of insulating layer 2 is 5.5 g / 10 min or more, preferably 5.7 g / 10 min or more, and more preferably 6.0 g / 10 min or more. Having an MFR of 5.5 g / 10 min or more for insulating layer 2 allows for better embedding properties compared to cases where it is less than 5.5 g / 10 min. The upper limit of the MFR of insulating layer 2 is 19.5 g / 10 min, based on its relationship to the MFRs of the first sealant layer 1 and the second sealant layer 3.

[0055] The MFR of the insulating layer 2 is 0.5 to 5.5 g / 10min lower than the MFR of the first sealant layer 1 and the second sealant layer 3, but preferably 0.75 to 4.0 g / 10min lower, and more preferably 1.0 to 3.0 g / 10min lower. A difference of 0.5 g / 10min or more in MFR ensures the insulating properties of the insulating layer 2. A difference of 5.5 g / 10min or less in MFR allows for a certain degree of fluidity in the insulating layer 2, resulting in an insulating layer 2 with excellent embeddability.

[0056] 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. A thickness of 10 μm or more for the insulating layer 2 makes it easier to obtain sufficient insulation. A thickness of 200 μm or less for the insulating layer 2 makes it possible to reduce the amount of water vapor that penetrates from the periphery of the terminal resin film 10. The thickness of the insulating layer 2 is preferably 1.1 times or more the thickness of the first sealant layer 1, and more preferably 1.2 times or more. Even if the MFRs of both layers are in close proximity, having a thickness ratio of above a certain level makes it easier to maintain the film thickness by the insulating layer 2 during heat sealing, thus ensuring insulation. There is no particular upper limit to the thickness ratio of the two layers, but it can be set to 2.0 times from the viewpoint of embedding.

[0057] [Method for manufacturing resin film for terminals] Next, a method for manufacturing the terminal resin film 10 will be described. However, the method for manufacturing the terminal resin film 10 is not limited to the method described below.

[0058] The terminal resin film 10 can be obtained, for example, by co-extruding a first sealant layer 1, an insulating layer 2, and a second sealant layer 3.

[0059] The terminal resin film 10 can also be obtained by preparing a first sealant layer 1, an insulating layer 2, and a second sealant layer 3 in advance, and then laminating them together using heat lamination. The temperature during thermal lamination should be higher than the melting point of the first sealant layer 1 and the melting point of the second sealant layer 3.

[0060] If the terminal resin film 10 has a first sealant layer 1, an adhesive layer, an insulating layer 2, and a second sealant layer 3, for example, a two-layer film consisting of the insulating layer 2 and the second sealant layer 3 may be manufactured in advance, and then the two-layer film and the first sealant layer 1 may be laminated using an adhesive dry lamination method with an adhesive such as an acid-modified polyolefin.

[0061] [Method for fusion bonding of resin films for terminals] The fusion bonding process for melt-bonding (fusion-sealing) the terminal resin film 10 and the outer bag shown in Figure 1 will be explained below.

[0062] First, a fusion bonding process is performed to melt and bond the terminal resin film 10 and the metal terminal 14. At this time, the second sealant layer 3 of the terminal resin film 10 shown in Figure 1 is oriented toward the metal terminal 14, and the terminal resin film 10 and the metal terminal 14 are heat-fused together by simultaneously melting the second sealant layer 3 by heating and ensuring close contact between the second sealant layer 3 and the metal terminal 14 by pressurizing.

[0063] In the fusion bonding process, it is preferable to heat the second sealant layer 3 to a temperature of 20°C or higher than the melting point of the second sealant layer 3, from the viewpoint of obtaining sufficient adhesion and sealing between the terminal resin film 10 and the metal terminal 14.

[0064] The heating temperature of the terminal resin film 10 may be, for example, 155 to 285°C. The heat fusion time can be determined considering the adhesion to the metal terminal 14 and productivity, and can be set appropriately within the range of, for example, 1 to 60 seconds.

[0065] Next, a fusion bonding process is performed to melt and bond the terminal resin film 10 and the exterior material 13. Specifically, the terminal resin film 10 and the exterior material 13 are heat-fused together by simultaneously melting the first sealant layer 1 by heating and ensuring close adhesion between the first sealant layer 1 and the exterior material by applying pressure.

[0066] In the fusion process, the first sealant layer 1 of the terminal resin film 10 and the sealant layer of the exterior material 13 are heated and melted. At this time, the heating temperature should be such that both the first sealant layer 1 of the terminal resin film 10 and the sealant layer of the exterior material 13 melt. However, from the viewpoint of obtaining sufficient adhesion and sealing performance between the first sealant layer 1 of the terminal resin film 10 and the sealant layer of the exterior material 13, it is preferable to set the temperature to the melting point of the sealant layer with the higher melting point of the first sealant layer 1 of the terminal resin film 10 and the sealant layer of the exterior material 13 to a temperature of 20°C or higher.

[0067] The heating temperature of the terminal resin film 10 may be, for example, 155 to 285°C. The heat fusion time can be determined considering the adhesion to the exterior material 13 and productivity, and can be set appropriately within the range of, for example, 1 to 60 seconds.

[0068] [Energy storage devices] The energy storage device comprises an energy storage device body, metal terminals electrically connected to the energy storage device body, an outer bag that holds the metal terminals and houses the energy storage device body, and a terminal resin film between the metal terminals and the outer bag that covers a portion of the outer surface of the metal terminals by heat sealing. The terminal resin film used here is the terminal resin film described above.

[0069] Figure 2 is a perspective view showing an energy storage device according to one embodiment of the present disclosure, fabricated using the aforementioned terminal resin film. As shown in Figure 2, the energy 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 terminal resin film 10, and an outer bag 54 for housing the battery body 11 in an airtight state. The outer bag 54 is used as a container for housing the battery body 11. The terminal resin film 10 is fused to a portion of the outer surface of the metal terminals 14, and the metal terminals 14 are sandwiched by the outer bag 54 via the terminal resin film 10. In the terminal resin film 10, a second sealant layer 3 is fused to the metal terminals 14, and a first sealant layer 1 is fused to the outer material 13 (outer bag 54).

[0070] In the energy storage device 50, the terminal resin film 10 is fused to a portion of the outer surface of the metal terminal 14 by heat sealing. The terminal resin film 10 exhibits good embedding and insulating properties when heat-sealed to the metal terminal. Since such a terminal resin film can suitably accommodate a shortened cycle time, it can be said that the energy storage device will have good reliability even if it is manufactured with a shortened cycle time.

[0071] The battery body 11, metal terminals 14, and outer packaging bag 54 will be described in detail below.

[0072] <Battery body> The battery body 11 has at least one power generation element consisting of a positive electrode, an electrolyte, and a negative electrode. Examples of electrolytes include organic solvent-based electrolytes, sulfide-based solid electrolytes, oxide-based solid electrolytes, and the like.

[0073] <Metal terminal> As shown in Figures 2 and 3, the pair of metal terminals 14 have a metal terminal body 14-1 and a corrosion-preventive layer 14-2. Figure 3 is a partial cross-sectional view of the terminal resin film and metal terminals shown in Figure 2 in the direction of line AA. 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 part of them is exposed from the outer casing material 13. The shape of the pair of metal terminal bodies 14-1 can be, for example, a flat plate shape.

[0074] The material used for the metal terminal body 14-1 can be metal. This metal can be determined by considering the structure of the battery body 11 and the materials of each component of the battery body 11.

[0075] When the energy 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 energy 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. Alternatively, the material of the metal terminal body 14-1 connected to the positive electrode of the battery body 11 may be an aluminum material with a purity of 97% or higher, such as 1N30. Furthermore, when the metal terminal body 14-1 is bent, O material that has been sufficiently annealed to temper it may be used to add flexibility. The material of the metal terminal body 14-1 connected to the negative electrode of the battery body 11 can be, for example, copper with a nickel plating layer formed on its surface, or nickel. The energy storage device 50 may be an all-solid-state battery.

[0076] The thickness of the metal terminal body 14-1 can be determined according to the size and capacity of the energy storage device 50. If the energy storage device 50 is small, the thickness of the metal terminal body 14-1 may be 50 μm or more. For large batteries such as those used in automobiles, the thickness of the metal terminal body 14-1 can be appropriately set within the range of 100 to 1000 μm.

[0077] The corrosion-preventive layer 14-2 is positioned to cover the surface of the metal terminal body 14-1. In the energy storage device 50, the corrosion-preventive layer 14-2 is formed by a corrosion-preventive treatment using chromate, and is a layer that suppresses corrosion of the metal terminal body 14-1 by corrosive components such as hydrogen fluoride and hydrogen sulfide.

[0078] <Outer bag> As shown in Figure 2, the outer bag 54 is obtained by overlapping two outer materials 13 and heat-sealing the overlapping edges. The outer bag 54 can also be obtained by folding the outer material 13 in half and heat-sealing the overlapping edges. The outer material 13 comprises, 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 base material layer 26 in this order. Figure 4 is a schematic cross-sectional view showing an example of the outer material shown in Figure 2.

[0079] The sealant layer 21 is a layer that provides heat sealing properties to the exterior material 13, and is placed on the inside of the energy storage device 50 during assembly and heat-sealed (heat-fused). As the base material of the sealant layer 21, for example, a polyolefin resin or an acid-modified polyolefin resin obtained by grafting maleic anhydride or the like onto a polyolefin resin can be used. As the polyolefin resin, low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; homo, block, or random polypropylene; propylene-α-olefin copolymer, etc. can be used. Among these, it is preferable that the polyolefin resin contains polypropylene. These polyolefin resins can be used individually or in combination of two or more types.

[0080] The sealant layer 21 may be a single-layer film or a multilayer film formed by laminating multiple layers, depending on the required function. Specifically, it may be a multilayer film with a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene interposed to provide moisture resistance. The sealant layer 21 may contain various additives (flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, tackifiers, etc.).

[0081] The thickness of the sealant layer 21 is preferably 10 to 150 μm, and more preferably 30 to 80 μm. A sealant layer thickness of 10 μm or more allows the exterior material 13 to have sufficient adhesion to the opposing exterior material 13 or to the terminal resin film 10. Furthermore, a sealant layer thickness of 150 μm or less reduces the cost of the exterior material 13.

[0082] As the first adhesive layer 22, any known adhesive such as a dry lamination adhesive or an acid-modified heat-fusible resin can be appropriately selected and used.

[0083] As shown in Figure 4, it is preferable from a performance standpoint to form the corrosion-preventive treatment layers 23-1 and 23-2 on both sides of the barrier layer 24. However, from the viewpoint of reducing costs, the corrosion-preventive treatment layer 23-1 may be placed only on the side of the barrier layer 24 that is located on the side of the first adhesive layer 22.

[0084] The barrier layer 24 may be a metal layer having water vapor barrier properties. Examples of materials for the barrier layer 24 include aluminum and stainless steel, and aluminum is preferred from the viewpoint of cost, mass (density), etc.

[0085] As the second adhesive layer 25, a polyurethane-based adhesive mainly composed of polyester polyol, polyether polyol, acrylic polyol, etc., can be used.

[0086] The base layer 26 may be a single-layer film or a multi-layer film of nylon, polyethylene terephthalate (PET), etc. The base layer 26 may contain various additives (flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, tackifiers, etc.) similar to the sealant layer 21.

[0087] Furthermore, the exterior material 13 may further include a protective layer (not shown) on the surface of the base material layer 26 opposite to the sealant layer 21, to protect the base material layer 26.

[0088] Furthermore, in the exterior material 13, an adhesive resin layer may be used instead of the first adhesive layer 22.

[0089] While preferred embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above.

[0090] One aspect of this disclosure is as follows: [1] A resin film for a terminal, comprising a main body of an energy storage device and a metal terminal electrically connected to the main body of the energy storage device, for covering a part of the outer surface of the metal terminal, The first sealant layer, the insulating layer, and the second sealant layer on the outer circumferential surface are provided in this order. The first sealant layer, the insulating layer, and the second sealant layer each contain a polyolefin resin. The MFR (melt flow rate) of the first sealant layer and the second sealant layer is 6 to 20 g / 10 min. A resin film for terminals, wherein the MFR of the insulating layer is 5.5 g / 10 min or more and is 0.5 to 5.5 g / 10 min lower than the MFR of the first sealant layer and the second sealant layer. [2] The terminal resin film according to [1], wherein the first sealant layer and the second sealant layer each contain an acid-modified polyolefin resin. [3] The terminal resin film according to [1] or [2], wherein the thickness of the insulating layer is 1.1 times or more the thickness of the first sealant layer. [4] A resin film for terminals according to any one of [1] to [3], wherein the melting point of the insulating layer is 150 to 165°C, and the melting points of the first sealant layer and the second sealant layer are 10°C or more lower than the melting point of the insulating layer. [5] A terminal resin film according to any one of [1] to [4], wherein the loop stiffness value measured under the following conditions is 570 mN or less. (Conditions) Sample size: 15mm wide x 200mm long, Loop length: 85mm, Compression speed: 3.3mm / min, Compression time: 3sec, Compression distance: 20mm, Maximum load value was used for measurement. [6] The main unit of the energy storage device, The main body of the energy storage device and the metal terminals electrically connected thereto An outer bag that holds the metal terminals and houses the main body of the energy storage device, Between the metal terminal and the outer bag, there is a resin film for terminals that covers a portion of the outer surface of the metal terminal by heat sealing, An energy storage device wherein the terminal resin film is the terminal resin film described in any one of [1] to [5]. [Examples]

[0091] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0092] <Manufacturing of resin film for terminals> Multiple types of films were prepared, as shown in Table 1, for the first sealant layer, a film for the insulating layer, made of block polypropylene (a homopolypropylene component with a polyethylene component dispersed in it), and a film for the second sealant layer, also made of acid-modified polypropylene. These were then co-extruded using a T-die film formation method to obtain the terminal resin films (polyolefin films) for each example and comparative example.

[0093] [Table 1]

[0094] <Evaluation of resin film for terminals> [Loop stepness value] The loop stiffness values ​​of the terminal resin films in each example were measured using a loop stiffness tester (model: DA-S) manufactured by Toyo Seiki Seisakusho Co., Ltd. under the following conditions. The results are shown in Table 2. (conditions) Sample size: 15mm wide x 200mm long, loop length: 85mm, compression speed: 3.3mm / min, compression time: 3sec, compression distance: 20mm, measurement environment: 10~30℃. The maximum load value was used as the measured value.

[0095] [Implantability assessment] A sample for evaluating embedding properties was prepared as follows: an 8 mm wide terminal resin film was set above and below a 5 mm wide aluminum tab lead material, perpendicular to each other. Using this evaluation sample, the embedding properties of the gap between the terminal resin film and the tab lead were evaluated according to the following criteria when heat sealing was performed with a shorter sealing time than the standard sealing conditions. The results are shown in Table 2. The standard sealing conditions were temperature: 165°C, pressure: 0.6 MPa, and time: 10 sec. (standard) A: The gap could be filled in less than 5 seconds. B: The void could be filled in less than 8 seconds of sealing time. C: If the sealing time was less than 8 seconds, it was impossible to fill the gap.

[0096] [Insulation evaluation] A sample for insulation evaluation was prepared as follows: an 8mm wide terminal resin film was set above and below a 5mm wide aluminum tab lead material, perpendicular to each other. Using this evaluation sample, the insulation between the outer material and the tab lead was evaluated according to the following criteria when heat sealing was performed under the conditions of temperature: 165°C, pressure: 0.6MPa, and time: 8sec. The results are shown in Table 2. • Withstand voltage tester: Insulation resistance tester TOS9201 (manufactured by Kikusui Electronics Co., Ltd.) • Evaluation conditions: Measurement mode DCW. The threshold current for dielectric breakdown is set to 10mA at 1kV or 2kV DC. Dielectric breakdown is considered to have occurred if the current exceeds the threshold current. (standard) A: No insulation breakdown occurred under the condition of 2kV DC. B: No insulation breakdown occurred under the condition of 1kV DC. C: Insulation breakdown occurred under the condition of 1kV DC.

[0097] [Table 2]

[0098] As shown in Tables 1 and 2, the example's terminal resin film, in which the MFR of the first and second sealant layers was 6-20 g / 10 min and the MFR of the insulating layer was 5.5 g / 10 min or higher and 0.5-5.5 g / 10 min lower than the MFR of the sealant layers (first and second sealant layers), was confirmed to achieve both excellent embedding and insulating properties compared to the comparative example's terminal resin film, even when the cycle time of the energy storage device manufacturing process was shortened. [Explanation of symbols]

[0099] 1...First sealant layer, 2...Insulating layer, 3...Second sealant layer, 10...Resin film for terminals, 11...Battery body, 14...Metal terminals, 50...Energy storage device.

Claims

1. A resin film for terminals, which covers the outer surface of a portion of a metal terminal electrically connected to the main body of an energy storage device, The first sealant layer, the insulating layer, and the second sealant layer on the outer circumferential surface are provided in this order. The first sealant layer, the insulating layer, and the second sealant layer each contain a polyolefin resin. The MFR (melt flow rate) of the first sealant layer and the second sealant layer is 6 to 20 g / 10 min. A resin film for terminals, wherein the MFR of the insulating layer is 5.5 g / 10 min or more and is 0.5 to 5.5 g / 10 min lower than the MFR of the first sealant layer and the second sealant layer.

2. The terminal resin film according to claim 1, wherein the first sealant layer and the second sealant layer contain an acid-modified polyolefin resin.

3. The terminal resin film according to claim 1 or 2, wherein the thickness of the insulating layer is 1.1 times or more the thickness of the first sealant layer.

4. The terminal resin film according to claim 1 or 2, wherein the melting point of the insulating layer is 150 to 165°C, and the melting points of the first sealant layer and the second sealant layer are 10°C or more lower than the melting point of the insulating layer.

5. The terminal resin film according to claim 1 or 2, wherein the loop stiffness value measured under the following conditions is 570 mN or less. (Conditions) Sample size: 15 mm wide x 200 mm long, Loop length: 85 mm, Compression speed: 3.3 mm / min, Compression time: 3 seconds, Compression distance: 20 mm, Maximum load value was used for measurement.

6. The main unit of the energy storage device, The main body of the energy storage device and the metal terminals electrically connected thereto An outer bag that holds the metal terminals and houses the main body of the energy storage device, Between the metal terminal and the outer bag, there is a resin film for terminals that covers a portion of the outer surface of the metal terminal by heat sealing, An energy storage device wherein the terminal resin film is the terminal resin film according to claim 1 or 2.

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