Tab sealant and power storage device using the same

Abstract

To provide a tab sealant having safety performance for reducing internal pressure when the internal pressure of a power storage device reaches a certain level due to heat generation of a power storage device body, and capable of stably exhibiting sealing performance during manufacturing of the power storage device.SOLUTION: A tab sealant disposed so as to cover an outer peripheral surface of a part of a metal terminal of a power storage device, the tab sealant comprising a first sealant layer disposed so as to face the metal terminal, a high melting point layer containing a polyolefin resin, and a second sealant layer in this order, wherein each of the first sealant layer and the second sealant layer comprises a low-melting-point layer comprising an acid-modified polyolefin resin and a medium-melting-point layer disposed between the low-melting-point layer and the high-melting-point layer, the low-melting-point layer has a melting point of 100 to 135 °C, the high-melting-point layer has a melting point of 140 to 170 °C, and the medium-melting-point layer has a melting point that is higher than the melting point of the low-melting-point layer by 10 °C or more and lower than the melting point of the high-melting-point layer by 10 °C or more.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a tab sealant and an electricity storage device using the same. [Background technology]

[0002] In recent years, there has been an increasing demand for miniaturization of portable devices and effective utilization of naturally generated energy. Electricity storage devices such as lithium-ion secondary batteries can produce high voltages and have high energy densities. Research and development of electricity storage devices with even better performance is being conducted. As one form of electricity storage device, a laminate-type electricity storage device in which the electricity storage device main body is housed inside a bag-shaped exterior material is known. This form of electricity storage device generally includes a metal terminal (also called a "tab") for extracting current from the electricity storage device main body. A portion of the outer periphery of the metal terminal is covered with a resin film called a tab sealant.

[0003] Patent Document 1 discloses an invention related to a resin film (sealant) covering metal terminals for secondary batteries that has excellent shape stability and adhesiveness when heated and also ensures insulation. The sealant 24 shown in Figure 2 of Patent Document 1 includes a core layer 22 and two skin layers 21 and 23 sandwiching the core layer 22. Patent Document 1 describes that the melt flow rate (MFR) of the core layer 22 should be in the range of 0.1 g / 10 min to 2.5 g / 10 min, and that the difference in MFR between the core layer 22 and the skin layers 21 and 23 should be in the range of 5 g / 10 min to 30 g / 10 min (see paragraph

[0025] of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-132538 Summary of the Invention [Problem to be solved by the invention]

[0005] In energy storage devices such as lithium-ion secondary batteries, the device body may suddenly heat up and reach a high temperature due to some reason. This increases the internal pressure of the device, causing the exterior material encasing the device body to expand. If the internal pressure continues to increase, the exterior material will eventually burst. The present inventors have investigated ways to impart a safety feature to a tab sealant, which would reduce the pressure by losing its sealing properties when the internal pressure of the device reaches a certain level. For example, if the tab sealant has a multilayer structure and includes a layer with a lower melting point than the other layers, the layer with the lower melting point will melt due to the heat from the device body, releasing the internal gas and reducing the internal pressure.

[0006] However, simply providing a low-melting-point layer on the tab sealant as described above requires strict temperature control of the tab sealant during the manufacturing process of the energy storage device. That is, if the temperature when fusing the tab sealant is too high, the low-melting-point layer melts and flows, resulting in insufficient adhesion of the outer surface of the tab sealant (the surface closer to the heat source of the heat seal) to the inner surface of the exterior material. On the other hand, if the temperature when fusing the tab sealant is too low, the low-melting-point layer does not melt sufficiently, resulting in insufficient adhesion of the inner surface of the tab sealant (the surface farther from the heat source of the heat seal) to the surface of the metal terminal.

[0007] The present disclosure provides a tab sealant that has safety performance of reducing the internal pressure of an electricity storage device when the internal pressure reaches a certain level due to heat generation in the main body of the electricity storage device, and that can exhibit stable sealing properties during the manufacture of the electricity storage device, and an electricity storage device using the same. [Means for solving the problem]

[0008] One aspect of the present disclosure relates to a tab sealant arranged to cover the outer peripheral surface of a portion of a metal terminal of an electric storage device. The tab sealant includes, in this order, a first sealant layer arranged to face the metal terminal, a high-melting-point layer containing a polyolefin resin, and a second sealant layer, each of which includes a low-melting-point layer containing an acid-modified polyolefin resin and a mid-melting-point layer arranged between the low-melting-point layer and the high-melting-point layer, the low-melting-point layer having a melting point of 100 to 135°C, the high-melting-point layer having a melting point of 140 to 170°C, and the mid-melting-point layer having a melting point at least 10°C higher than that of the low-melting-point layer and at least 10°C lower than that of the high-melting-point layer.

[0009] According to the above-mentioned tab sealant, when the internal pressure of the electricity storage device reaches a certain level due to heat generation in the electricity storage device, the low-melting-point layer of the first sealant layer melts, establishing electrical conductivity between the inside and outside of the packaging material. This releases gas from the packaging material to the outside, reducing the internal pressure. Meanwhile, the tab sealant can stably exhibit sealing properties during the manufacturing process of the electricity storage device. That is, even if the temperature used to fuse the tab sealant is slightly too high, causing the low-melting-point layer of the second sealant layer to melt and flow, the medium-melting-point layer of the second sealant layer can adequately melt to exhibit sealing properties.

[0010] In the above tab sealant, both the first sealant layer and the second sealant layer have a mid-melting point layer and a low-melting point layer arranged in this order from the high-melting point layer toward the surface. The tab sealant of the present disclosure may also have a low-melting point layer and a mid-melting point layer arranged in this order from the high-melting point layer toward the surface. That is, the tab sealant of the present disclosure may include a first sealant layer arranged to face the metal terminal, a high-melting point layer containing a polyolefin resin, and a second sealant layer, in this order, wherein both the first sealant layer and the second sealant layer include a mid-melting point layer containing an acid-modified polyolefin resin and a low-melting point layer arranged between the mid-melting point layer and the high-melting point layer, wherein the melting point of the low-melting point layer is 100 to 135°C, the melting point of the high-melting point layer is 140 to 170°C, and the melting point of the mid-melting point layer is 10°C or more higher than that of the low-melting point layer and 10°C or more lower than that of the high-melting point layer.

[0011] The melting point referred to in this disclosure is measured by a differential scanning calorimeter (DSC) at a heating rate of 10°C / min in accordance with ASTM D2117, and refers to the temperature at the top of the main peak, which is the peak with the greatest heat of dissolution.

[0012] One aspect of the present disclosure relates to an electricity storage device using the above-mentioned tab sealant, which includes an electricity storage device main body, metal terminals electrically connected to the electricity storage device main body, an exterior material that houses the electricity storage device main body and sandwiches the metal terminals, and the above-mentioned tab sealant disposed between the metal terminals and the exterior material, with a first sealant layer of the tab sealant adhering the metal terminals and a second sealant layer adhering the exterior material. [Effects of the Invention]

[0013] According to the present disclosure, there are provided a tab sealant that has safety performance of reducing the internal pressure of an electricity storage device when the internal pressure reaches a certain level due to heat generation in the main body of the electricity storage device, and that can exhibit stable sealing properties during the manufacture of the electricity storage device, and an electricity storage device using the same. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a schematic configuration of an electricity storage device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a cut surface of the exterior packaging material shown in FIG. [Figure 3] 2 is a cross-sectional view of the tab sealant and the metal terminal shown in FIG. 1 taken along line AA. [Figure 4] FIG. 2 is a cross-sectional view showing an example of a cross section of the tab sealant shown in FIG. [Figure 5] 1 is an SEM image showing an example of a sea-island structure of a low melting point layer. [Figure 6] 1 is an SEM image showing an example of the sea-island structure of a mid-melting point layer. [Figure 7] FIG. 2 is a schematic diagram illustrating a method for preparing a sample for measuring heat seal strength to aluminum foil in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] [Energy storage devices] The electricity storage device 10 shown in FIG. 1 is a lithium ion secondary battery, and includes an electricity storage device body 11, an electrolyte (not shown), an exterior material 13, a pair of metal terminals 14 (tab leads), and a tab sealant 16.

[0017] The electricity storage device main body 11 is a battery main body that charges and discharges. The exterior material 13 accommodates the electricity storage device main body 11 and an electrolyte, and sandwiches a pair of metal terminals 14 via a tab sealant 16. The pair of metal terminals 14 are electrically connected to the electricity storage device main body 11, with one end of each metal terminal 14 located inside the exterior material 13 and the other end located outside the exterior material 13. A portion of the outer circumferential surface of each metal terminal 14 is covered with a tab sealant 16 (see FIG. 1), and the tab sealant 16 is bonded to the exterior material 13. As shown in FIG. 4, the tab sealant 16 has, in this order, a first sealant layer 3 bonded to the metal terminal 14, a high-melting-point layer 4 containing a polyolefin resin, and a second sealant layer 8 bonded to the exterior material 13.

[0018] [Exterior materials] 2, the exterior material 13 has a multilayer structure including, from the electricity storage device main body 11 side, an inner layer 21, an inner layer side adhesive layer 22, a barrier layer 24, an outer layer side adhesive layer 25, and an outer layer 26. On the surface of the barrier layer 24, corrosion prevention treatment layers 23-1 and 23-2 are formed.

[0019] The inner layer 21 is a sealant layer that provides heat-sealing properties to the exterior material 13, and is a layer that is placed on the inside and heat-sealed (thermally fused) when assembling the electricity storage device 10. Examples of the base material for the inner layer (sealant layer) 21 include polyolefin resins and acid-modified polyolefin resins obtained by graft-modifying polyolefin resins with maleic anhydride or the like. Examples of the polyolefin 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, the polyolefin resin may contain polypropylene. These polyolefin resins may be used alone or in combination of two or more.

[0020] The inner layer 21 may be a single-layer film or a multilayer film in which multiple layers are laminated, depending on the required function. Specifically, it may be a multilayer film in which a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene is interposed to impart moisture resistance. The inner layer 21 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier).

[0021] The thickness of the inner layer 21 may be 10 to 150 μm or 30 to 80 μm. When the thickness of the inner layer 21 is 10 μm or more, the exterior packaging material 13 tends to have sufficient adhesion between the exterior packaging material 13 and the tab sealant 16. Furthermore, when the thickness of the inner layer 21 is 150 μm or less, the cost of the exterior packaging material 13 can be reduced.

[0022] The inner adhesive layer 22 can be appropriately selected from known adhesives such as dry lamination adhesives and acid-modified heat-fusible resins.

[0023] As shown in Figure 2, the corrosion prevention treatment layers 23-1 and 23-2 may be formed on both sides of the barrier layer 24, or from the standpoint of reducing costs, the corrosion prevention treatment layer 23-1 may be formed only on the surface of the barrier layer 24 located on the inner layer side adhesive layer 22 side.

[0024] The barrier layer 24 may be a conductive metal layer. Examples of materials for the barrier layer 24 include aluminum and stainless steel, and aluminum is preferred from the standpoints of cost, mass (density), and the like.

[0025] The outer adhesive layer 25 may be a polyurethane adhesive containing polyester polyol, polyether polyol, acrylic polyol, or the like as a main component.

[0026] The outer layer 26 may be a single layer or a multilayer film made of nylon, polyethylene terephthalate (PET), or the like. Like the inner layer 21, the outer layer 26 may contain various additives (such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier). The outer layer 26 may have a protective layer formed by laminating a resin insoluble in the electrolyte solution or coating the outer layer with a resin component insoluble in the electrolyte solution to prevent leakage of the electrolyte solution.

[0027] [Metal terminal] 1 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 electricity storage device body 11, and the other metal terminal body 14-1 is electrically connected to the negative electrode of the electricity storage device body 11. The pair of metal terminal bodies 14-1 extend in a direction away from the electricity storage device body 11, and a portion thereof is exposed from the exterior material 13. The shape of the pair of metal terminal bodies 14-1 may be, for example, a flat plate shape.

[0028] The material of the metal terminal body 14-1 can be a metal, which can be determined in consideration of the structure of the electricity storage device body 11, the materials of each component of the electricity storage device body 11, and the like.

[0029] When the electricity storage device 10 is a lithium-ion secondary battery, aluminum can be used as the positive electrode current collector, and copper can be used as the negative electrode current collector. From the viewpoint of corrosion resistance to the electrolyte, the material of the metal terminal body 14-1 connected to the positive electrode of the electricity storage device body 11 may be an aluminum material with a purity of 97% or more, such as 1N30. Furthermore, when the metal terminal body 14-1 is to be bent, 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 electricity storage device body 11 may be copper with a nickel plating layer formed on its surface, or nickel.

[0030] The thickness of the metal terminal body 14-1 can be determined depending on the size and capacity of the lithium ion secondary battery. In the case of a small lithium ion secondary battery, the thickness of the metal terminal body 14-1 may be 50 μm or more. In the case of a large lithium ion secondary battery for power storage, vehicle use, etc., the thickness of the metal terminal body 14-1 can be appropriately set within the range of 100 to 500 μm.

[0031] The corrosion prevention layer 14-2 is disposed so as to cover the surface of the metal terminal body 14-1. In the case of a lithium-ion secondary battery, the electrolyte contains a corrosive component such as LiPF6. The corrosion prevention layer 14-2 is a layer for preventing corrosion of the metal terminal body 14-1 due to the corrosive component such as LiPF6 contained in the electrolyte.

[0032] [Tab Sealant] Tab sealant 16 is arranged to cover part of the outer peripheral surface of metal terminal 14 (see FIGS. 1 and 3). Tab sealant 16 is a resin film with a multilayer structure (see FIG. 4). Tab sealant 16 is formed by laminating, in this order, a first sealant layer 3 consisting of two layers, a low melting point layer 1 and a medium melting point layer 2, and a second sealant layer 8 consisting of two layers, a high melting point layer 4 and a medium melting point layer 6 and a low melting point layer 7. In other words, tab sealant 16 has a structure in which low melting point layer 1, medium melting point layer 2, high melting point layer 4, medium melting point layer 6, and low melting point layer 7 are laminated in this order.

[0033] During use, when the internal pressure of the electricity storage device 10 reaches a certain level due to, for example, heat generation from the metal terminals 14, the low-melting-point layer 1 of the first sealant layer 3 melts due to the heat generated by the metal terminals 14, establishing electrical continuity between the interior of the exterior of the sheath 13. This releases gas from the exterior of the sheath 13, reducing the internal pressure. During the manufacture of the electricity storage device 10, the tab sealant 16 is fused to the exterior 13 and the metal terminals 14 by pressing a heat seal bar against the exterior 13. Even if the temperature during heat sealing of the tab sealant 16 is slightly too high, causing the low-melting-point layer 7 of the second sealant layer 8 to melt and flow, the intermediate-melting-point layer 6, which has a higher melting point than the low-melting-point layer 7, will melt appropriately, thereby achieving sealing with the exterior 13.

[0034] The low-melting-point layer is formed using a resin composition containing an acid-modified polyolefin resin, such as a graft-modified resin obtained by graft-modifying a polyolefin resin with maleic anhydride, carboxylic acid, sulfonic acid, or a derivative thereof, or a copolymer resin obtained by copolymerizing an olefin with maleic anhydride, carboxylic acid, sulfonic acid, or a derivative thereof.

[0035] Examples of polyolefin resins include low-density, medium-density, and high-density polyethylenes, ethylene-α-olefin copolymers, homo-, block-, or random polypropylenes, propylene-α-olefin copolymers, polybutene, polymethylpentene, and polynorbornene. The polyolefin resin may contain polypropylene from the viewpoint of improving heat resistance, processability, and adhesion to the exterior material.

[0036] The acid-modified polyolefin resin may be a graft-modified polyolefin resin from the viewpoint of adhesiveness to a metal terminal, or may be a maleic anhydride-modified polyolefin resin or an acid-modified random polypropylene copolymer from the viewpoint of improving heat seal strength. The acid-modified polyolefin resin may be used alone or in combination of two or more.

[0037] The resin composition used to form the low-melting-point layer may contain an acid-modified polyolefin resin other than an acid-modified random polypropylene copolymer as the acid-modified polyolefin resin, or may contain an unmodified resin (e.g., polyethylene). The resin composition used to form the low-melting-point layer may contain, for example, an acid-modified polyolefin resin other than an acid-modified random polypropylene copolymer or an unmodified polyolefin resin. When the low-melting-point layer contains these resins, a sea-island structure is formed, making it easier to open the electricity storage device before the internal pressure of the exterior material becomes too high when the electricity storage device generates heat. Of these resins, acid-modified polyethylene is preferred. Acid-modified polyethylene easily ensures adhesion to the metal terminal even when a relatively large amount is added.

[0038] The degree of modification with acid of the polyolefin resin (for example, the mass of the portion derived from maleic anhydride relative to the total mass of maleic anhydride-modified polypropylene) may be 0.1 to 20 mass % or 0.3 to 5 mass % from the viewpoint of improving heat seal strength.

[0039] The resin composition used to form the low-melting-point layer may contain resin additives such as a compatibilizer, antioxidant, slip agent, flame retardant, light stabilizer, dehydrating agent, color pigment, tackifier, filler, and crystal nucleating agent. These additives may be used alone or in combination of two or more. The resin composition may contain a compatibilizer to easily improve adhesion to a metal terminal or an exterior material. The resin composition may contain a color pigment and a filler to improve the visibility of the tab sealant.

[0040] Examples of the compatibilizer include ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), block copolymers, and graft copolymers.

[0041] Examples of block copolymers include block copolymers composed of crystalline polyethylene units and ethylene-butylene copolymer units, block copolymers composed of polyethylene units and ethylene-1-octene copolymer units, and block copolymers composed of polypropylene units and polyethylene units.

[0042] An example of the graft copolymer is a graft copolymer in which a polyethylene unit is grafted onto a polypropylene. Each unit constituting the copolymer may be a crystalline unit or a non-crystalline unit.

[0043] The compatibilizer may be a block copolymer or a graft copolymer, which facilitates improving adhesion to the metal terminal or the exterior material. When the resin composition used to form the low-melting-point layer contains polyethylene, the compatibilizer may have a portion compatible with polyethylene and a portion compatible with the acid-modified polyolefin resin. The compatibilizer may be used alone or in combination of two or more.

[0044] Examples of color pigments include carbon black, quinacridone pigments, polyazo pigments, and isoindolinone pigments.

[0045] Examples of the filler include inorganic fillers such as aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, calcium carbonate, zirconium silicate, zinc oxide, barium sulfate, copper oxide, cobalt oxide, titanium oxide, tin oxide, iron oxide, antimony oxide, boron nitride, aluminum nitride, and silicon nitride.

[0046] The melting point of the low melting point layer is 100 to 135°C, and may be 110 to 135°C, 120 to 135°C, or 120 to 130°C.

[0047] The thickness of the low-melting point layer (thickness per layer) may be 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more. By having the thickness within this range, it is possible to sufficiently fill the space created by the thickness of the metal terminal. The thickness of the low-melting point layer may be 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, or 20 μm or less. By having the thickness within this range, it is easy to open the electricity storage device when the internal pressure of the electricity storage device increases due to heat generation.

[0048] The melt flow rate (MFR) of the low-melting-point layer at 230°C and a load of 2.16 kg may be 1.0 to 10.0 g / 10 min or 4.0 to 9.0 g / 10 min. When the MFR of the low-melting-point layer is 1.0 g / 10 min or more, the breaking elongation of the tab sealant can be improved. Furthermore, when the MFR of the low-melting-point layer is 10.0 g / 10 min or less, the breaking strength of the tab sealant can be improved. In the present disclosure, MFR refers to a value measured using a melt flow rate measuring device in accordance with JIS K7210 under conditions of a measuring temperature of 230°C and a load of 2.16 kg. For example, a measuring device manufactured by Toyo Seiki Seisakusho, Ltd. can be used.

[0049] The low-melting-point layer may have a sea-island structure as shown in Fig. 5, from the viewpoint of making it easier to open the electricity storage device before the internal pressure of the exterior material becomes too high when the electricity storage device generates heat. The area ratio of the island portions in the low-melting-point layer may be 5 to 90%, 10 to 80%, or 20 to 60%. The area ratio of the island portions in the low-melting-point layer can be measured by observing a cross-section of the low-melting-point layer with a scanning electron microscope (SEM), binarizing the observed image, and calculating the area of ​​each of the island portions and the sea portion; specifically, it can be measured by the method described in the Examples below.

[0050] The Vicat softening point of the low-melting-point layer may be 80 to 130°C, 85 to 125°C, or 90 to 125°C. The Vicat softening point of the low-melting-point layer may be at least 10°C lower than the Vicat softening point of the mid-melting-point layer, from the viewpoint of improving adhesion with the metal terminal. The Vicat softening point of the low-melting-point layer can be measured according to ASTM D1525 (standard test method for Vicat softening temperature of plastics), specifically, according to the method described in the Examples below. The Vicat softening point may be measured using, for example, a No. 533 HDT testing device (manufactured by Toyo Seiki Seisakusho, Ltd.).

[0051] The mid-melting point layer is formed using a resin composition containing an acid-modified polyolefin resin, such as a graft-modified resin obtained by graft-modifying a polyolefin resin with maleic anhydride, carboxylic acid, sulfonic acid, or a derivative thereof, or a copolymer resin obtained by copolymerizing an olefin with maleic anhydride, carboxylic acid, sulfonic acid, or a derivative thereof.

[0052] Examples of polyolefin resins include low-density, medium-density, and high-density polyethylenes, ethylene-α-olefin copolymers, homo-, block-, or random polypropylenes, propylene-α-olefin copolymers, polybutene, polymethylpentene, and polynorbornene. The polyolefin resin may contain polypropylene from the viewpoint of improving heat resistance, processability, and adhesion to the exterior material.

[0053] The acid-modified polyolefin resin may be a graft-modified polyolefin resin from the viewpoint of adhesiveness to a metal terminal, or may be a maleic anhydride-modified polyolefin resin or an acid-modified random polypropylene copolymer from the viewpoint of improving heat seal strength. The acid-modified polyolefin resin may be used alone or in combination of two or more.

[0054] The resin composition used to form the mid-fusing layer may contain a resin component (e.g., a rubber component) other than the acid-modified random polypropylene copolymer as the acid-modified polyolefin resin, or may contain an unmodified resin (e.g., polyethylene), from the viewpoint of preventing excessive resin outflow during heat sealing and easily improving adhesion to the packaging material. The resin composition used to form the mid-fusing layer may contain, for example, an acid-modified polyolefin resin other than the acid-modified random polypropylene copolymer or an unmodified polyolefin resin. The mid-fusing layer may have a sea-island structure due to these resins.

[0055] The resin composition used to form the mid-melting point layer may contain additives such as antioxidants, slip agents, flame retardants, light stabilizers, dehydrating agents, coloring pigments, tackifiers, fillers, and crystal nucleating agents. A plurality of types of these additives may be used in combination. To improve the visibility of the tab sealant, the resin composition may contain coloring pigments and fillers. The coloring pigments and fillers may be the same as those used in the low-melting point layer.

[0056] The thickness of the mid-melting point layer (thickness per layer) may be 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 15 μm or more from the viewpoint of easily improving adhesion to the metal terminal or the exterior material, and may be 150 μm or less, 100 μm or less, 50 μm or less, 30 μm or less, or 20 μm or less from the viewpoint of easily improving processability and the breaking strength of the film.

[0057] The ratio of the thickness of the low-melting-point layer to the thickness of the mid-melting-point layer (thickness of the low-melting-point layer / thickness of the mid-melting-point layer) may be 0.1 or more, 0.5 or more, 1 or more, 2 or more, or 3 or more. When the ratio is within this range, the tab sealant is likely to exhibit excellent adhesion to the exterior material. This ratio may be 10 or less, 8 or less, 6 or less, 4 or less, or 3 or less. When the ratio is within this range, the electricity storage device is easy to open when the internal pressure of the electricity storage device increases due to heat generation.

[0058] From the viewpoint of easily improving adhesion to the exterior material, when the thickness of the mid-melting point layer is taken as 1, the thickness of the low-melting point layer may be 1 or more, and when the first sealant layer of the tab sealant is heat-sealed to an aluminum plate under conditions of 170°C, 0.5 MPa, and 5 seconds, the thickness of the mid-melting point layer of the second sealant layer may be 0.1 or more, 0.3 or more, 0.5 or more, or 0.7 or more.

[0059] The melting point of the mid-melting layer is at least 10° C. higher than that of the low-melting layer and at least 10° C. lower than that of the high-melting layer. The melting point of the mid-melting layer may be 130 to 150° C., 135 to 150° C., or 135 to 145° C., from the viewpoints of preventing excessive resin outflow during heat sealing and easily improving adhesion to the packaging material.

[0060] The MFR of the mid-melting layer at 230°C and a load of 2.16 kg may be 1.0 to 10.0 g / 10 min or 4.0 to 9.0 g / 10 min. When the mid-melting layer has an MFR of 1.0 g / 10 min or more, the breaking elongation of the tab sealant can be improved. When the mid-melting layer has an MFR of 10.0 g / 10 min or less, the breaking strength of the tab sealant can be improved.

[0061] The mid-melting point layer may have a sea-island structure as shown in Fig. 6, from the viewpoint of making it easier to open the electricity storage device before the internal pressure of the exterior material becomes too high when the electricity storage device generates heat. The area ratio of the islands in the mid-melting point layer may be 1 to 50%, 5 to 40%, or 10 to 30%. The area ratio of the islands in the mid-melting point layer can be measured by the same method as for the area ratio of the islands in the low-melting point layer.

[0062] The area ratio of the island portion of the low melting point layer may be 1.5 to 100 times, 2 to 50 times, or 3 to 20 times the area ratio of the island portion of the medium melting point layer, from the viewpoint of making it easier to open the electricity storage device when the internal pressure of the electricity storage device increases due to heat generation in the electricity storage device body.

[0063] The Vicat softening point of the mid-melting point layer may be 80 to 130° C., 85 to 125° C., or 90 to 125° C. The Vicat softening point of the mid-melting point layer can be measured by the same method as for the Vicat softening point of the low-melting point layer.

[0064] The high-melting-point layer is formed using a resin composition containing a polyolefin resin. Examples of polyolefin resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymers; homo-, block-, or random polypropylenes; propylene-α-olefin copolymers; polybutene; polymethylpentene; and polynorbornene. Among these, the polyolefin resin may be polypropylene or block polypropylene from the viewpoint of improving heat seal strength and processability. The polyolefin resin used in the high-melting-point layer may be an unmodified polyolefin resin from the viewpoint of improving insulation properties. The polyolefin resin may be used alone or in combination of two or more types. The resin composition used to form the high-melting-point layer may contain resins other than polyolefin resins.

[0065] The resin composition used to form the high melting point layer may contain additives such as antioxidants, slip agents, flame retardants, light stabilizers, dehydrating agents, color pigments, tackifiers, fillers, and crystal nucleating agents. A plurality of types of additives may be used in combination. From the viewpoint of improving the visibility of the tab sealant, the resin composition may contain color pigments and fillers. The color pigments and fillers may be the same as those used in the low melting point layer.

[0066] The thickness of the high-melting-point layer (thickness per layer) may be 2 μm or more, 10 μm or more, or 20 μm or more from the viewpoint of improving the insulation between the metal foil used in the exterior packaging material and the metal terminal, and the thickness of the intermediate-melting-point layer may be 100 μm or less, 50 μm or less, or 20 μm or less from the viewpoint of easily improving the processability and the breaking strength of the film.

[0067] The melting point of the high melting point layer is 140 to 170°C, and may be 150 to 170°C, 150 to 165°C, or 155 to 165°C.

[0068] The MFR of the high-melting-point layer at 230°C and a load of 2.16 kg may be 0.05 to 3.0 g / 10 min, 0.05 to 2.0 g / 10 min, or 0.05 to 1.0 g / 10 min. By making the MFR of the high-melting-point layer 0.05 g / 10 min or more, the breaking elongation of the tab sealant can be improved. Furthermore, by making the MFR of the low-melting-point layer 3.0 g / 10 min or less, the breaking strength of the tab sealant can be improved.

[0069] The thickness of the first sealant layer and the second sealant layer may be 10 to 300 μm, 10 to 200 μm, 10 to 100 μm, 10 to 50 μm, 10 to 30 μm, or 10 to 20 μm. The thickness of the first sealant layer and the second sealant layer may be the same or different.

[0070] The total thickness of the tab sealant 16 may be 40 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, or 200 μm or more. The total thickness of the tab sealant may be, for example, 1000 μm or less, 500 μm or less, 300 μm or less, 200 μm or less, or 100 μm or less.

[0071] In the tab sealant 16, the plurality of low melting point layers may all be layers formed using the same resin. The plurality of low melting point layers may all be layers formed using the same resin composition. Furthermore, the thickness, melting point, and MFR of the plurality of low melting point layers may all be the same.

[0072] In the tab sealant 16, the multiple mid-melting point layers may all be layers formed using the same resin. The multiple mid-melting point layers may all be layers formed using the same resin composition. Furthermore, the multiple mid-melting point layers may all have the same thickness, melting point, and MFR.

[0073] The tab sealant 16 may include layers other than the low-melting point layer, the medium-melting point layer, and the high-melting point layer (layers that do not fall into the category of low-melting point layer, medium-melting point layer, or high-melting point layer), or may consist only of the low-melting point layer, the medium-melting point layer, and the high-melting point layer.

[0074] When the plane along the surface of tab sealant 16 is defined as the XY plane and the direction perpendicular to the XY plane (the thickness direction of tab sealant 16) is defined as the Z direction, a cross section of tab sealant 16 along the Z direction may have a layer structure that is symmetrical in the Z direction with the high melting point layer at the center. That is, in tab sealant 16 shown in FIG. 4, low melting point layers 1 and 7 have the same structure (composition, thickness, etc.), and mid melting point layers 2 and 6 have the same structure, and the layer structure may be symmetrical in the thickness direction of tab sealant 16 with high melting point layer 4 at the center. This structure has the advantage that the user of tab sealant 16 does not need to worry about the front and back of the tab sealant 16.

[0075] Another embodiment of the tab sealant includes a first sealant layer facing the metal terminal, a high-melting-point layer containing a polyolefin resin, and a second sealant layer, in that order. Both the first and second sealant layers include a mid-melting-point layer containing an acid-modified polyolefin resin and a low-melting-point layer disposed between the mid-melting-point layer and the high-melting-point layer. The low-melting-point layer has a melting point of 100 to 135°C, the high-melting-point layer has a melting point of 140 to 170°C, and the mid-melting-point layer has a melting point at least 10°C higher than that of the low-melting-point layer and at least 10°C lower than that of the high-melting-point layer. This tab sealant also provides safety by reducing the internal pressure of an electrical storage device when the internal pressure reaches a certain level due to heat generation in the device body, and can provide stable sealing properties during the manufacture of the electrical storage device. The low-melting-point layer, mid-melting-point layer, and high-melting-point layer of the tab sealant may be the same as the low-melting-point layer, mid-melting-point layer, and high-melting-point layer described above.

[0076] [Production method of tab sealant] Next, a description will be given of a method for manufacturing the tab sealant 16. The method for manufacturing the tab sealant 16 is not limited to the following.

[0077] When the tab sealant 16 has a five-layer structure of low-melting-point layer / mid-melting-point layer / high-melting-point layer / mid-melting-point layer / low-melting-point layer, the five layers may be laminated by coextrusion, or some of the layers may be pre-formed and then laminated by sandwich lamination. For example, a three-layer film consisting of a low-melting-point layer / mid-melting-point layer / high-melting-point layer and the low-melting-point layer may be pre-formed, and then the three-layer film and the low-melting-point layer may be laminated by sandwich lamination using a resin composition that constitutes the mid-melting-point layer. Alternatively, a three-layer film consisting of a low-melting-point layer / mid-melting-point layer / high-melting-point layer may be pre-formed, and then a two-layer film consisting of a mid-melting-point layer / low-melting-point layer may be extruded onto the three-layer film.

[0078] Even when the number of layers constituting the tab sealant 16 is six or more, it can be produced by appropriately using the above-mentioned production method.

[0079] As an example of a method for producing the tab sealant 16, a method for producing a five-layer film by an inflation method will be described.

[0080] First, base materials for a low-melting-point layer, a mid-melting-point layer, a high-melting-point layer, a mid-melting-point layer, and a low-melting-point layer are prepared. Next, the base materials for the low-melting-point layer, the mid-melting-point layer, the high-melting-point layer, the mid-melting-point layer, and the low-melting-point layer are fed into an inflation molding machine. Next, the five base materials are extruded from the extrusion section of the inflation molding machine to form a five-layer structure (a structure in which the low-melting-point layer, the mid-melting-point layer, the high-melting-point layer, the mid-melting-point layer, and the low-melting-point layer are laminated in this order), while air is supplied from inside the extruded five-layer laminate.

[0081] The cylindrically inflated five-layer film is then conveyed and flattened by a guide, after which the five-layer film is folded into a sheet by a pair of pinch rolls. Both ends of the folded tube are slit, and the pair of films (two strips) are wound into a roll around a winding core, producing a roll of five-layer tab sealant 16.

[0082] The extrusion temperature may be 130 to 300°C or 130 to 250°C. When the extrusion temperature is 130°C or higher, the resins constituting each layer are sufficiently melted, reducing the melt viscosity and tending to stabilize extrusion from the screw. When the extrusion temperature is 300°C or lower, oxidation and deterioration of the resins constituting each layer are suppressed, preventing deterioration in the quality of the five-layer film.

[0083] The screw rotation speed, blow ratio, take-up speed, etc. can be set appropriately taking into account the film thickness. The film thickness ratio of each layer in a five-layer film can be adjusted by changing the rotation speed of each screw.

[0084] [How to fuse tab sealant] A fusion process for melt-bonding the tab sealant 16 and the exterior material 13 shown in Fig. 4 will be described below. The case where the low melting point layer 1 of the tab sealant 16 shown in Fig. 4 is arranged facing the metal terminal side and the low melting point layer 7 facing the exterior material side will be described below.

[0085] In the fusion process, the low melting point layer 7 is melted by heating and the low melting point layer 7 and the exterior material 13 are adhered to each other by applying pressure, thereby thermally fusing the tab sealant 16 and the exterior material 13 together.

[0086] In the fusion treatment, from the viewpoint of obtaining sufficient adhesion and sealing properties between the tab sealant 16 and the exterior material 13, heating may be performed to a temperature equal to or higher than the melting point of the resin constituting the low melting point layer 7.

[0087] The heating temperature of the tab sealant 16 may be, for example, 140 to 170°C. The treatment time (total time of heating time and pressurizing time) can be determined taking into consideration the adhesion to the exterior material and productivity. The treatment time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0088] From the viewpoint of improving the production takt time (productivity) of the tab sealant 16, heat fusion may be performed by shortening the pressurizing time at a temperature exceeding 170° C. In this case, the heating temperature may be, for example, higher than 170° C. and not higher than 230° C., and the pressurizing time may be, for example, 3 to 20 seconds.

[0089] 3, a fusion process for melt-bonding the tab sealant 16 and the metal terminal 14 will be described. In the fusion process, the tab sealant 16 and the metal terminal 14 are thermally fused together while simultaneously melting the low melting point layer 1 by heating and bonding the low melting point layer 1 and the metal terminal 14 together by applying pressure.

[0090] In the fusion process, the tab sealant 16 and the metal terminal 14 may be heated to a temperature equal to or higher than the melting point of the resin that constitutes the low melting point layer 1 in order to obtain sufficient adhesion and sealing properties between the tab sealant 16 and the metal terminal 14 .

[0091] The heating temperature of the tab sealant 16 may be, for example, 140 to 170°C. The treatment time (total time of heating and pressing) can be determined taking into consideration the adhesion to the metal terminal and productivity. The treatment time can be set appropriately within the range of, for example, 1 to 60 seconds.

[0092] From the viewpoint of improving the production takt time (productivity) of the tab sealant 16, heat fusion may be performed at a temperature exceeding 170° C. for a short pressurizing time. In this case, the heating temperature may be, for example, higher than 170° C. and not higher than 230° C., and the pressurizing time may be, for example, 3 to 20 seconds.

[0093] In the above embodiment, the tab sealant 16 is applied to a lithium ion secondary battery, but it can also be applied to electricity storage devices other than lithium ion secondary batteries (for example, all-solid-state batteries, lithium-air batteries, etc.). [Example]

[0094] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to the following examples.

[0095] [Preparation of tab sealant] A masterbatch resin was prepared by dry blending acid-modified random polypropylene resin (acid-modified random PP) as a base, with acid-modified polyethylene resin (acid-modified PE) and / or compatibilizer added as needed. The melting points and MFRs of the acid-modified random polypropylene resin, acid-modified polyethylene resin, and compatibilizer used are shown in Table 1. The melting points and MFRs in Table 1 were measured using the methods described below. [Table 1]

[0096] The masterbatch resins thus prepared were used to form films by inflation film extrusion or T-die extrusion to produce single layers of the masterbatch resin, thereby producing base materials for the low-melting-point layer, the mid-melting-point layer, and the high-melting-point layer. The base materials thus prepared are shown in Table 2. Note that base material F differs from base material G in that it contains a compatibilizer, whereas base material G does not. The melting point, MFR, and Vicat softening point in Table 2 were measured using the methods described below.

[0097] [Table 2]

[0098] [Melting point] The resin compositions used to form each layer were formed into a film to obtain a single layer, and then the melting peak was measured at a heating rate of 10°C / min using a differential scanning calorimeter (DSC) in accordance with ASTM D2117. The peak with the greatest heat of dissolution was defined as the main peak, and the melting point was measured by reading the temperature at the peak top.

[0099] [MFR] The resin compositions used to form each layer were formed into a film to obtain a single layer, and then the MFR was measured at a measurement temperature of 230°C and a load of 2.16 kg using a melt flow rate measuring device (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K7210.

[0100] [Vicat softening point] The resin composition used to form each layer was formed into a film to obtain a single layer, and then the Vicat softening temperature was measured by the A50 method of ASTM D1525 (standard test method for determining the Vicat softening temperature of plastics).

[0101] (Examples 1 to 12, Comparative Examples 1 to 4) Five layers, namely, low melting point layer / mid melting point layer / high melting point layer / mid melting point layer / low melting point layer, were co-extruded and laminated at an extrusion temperature of 220°C using an inflation method to obtain a five-layer tab sealant with the thickness of each layer shown in Table 3. For Comparative Example 1, the mid melting point layer was omitted, and a three-layer tab sealant, namely, low melting point layer / high melting point layer / low melting point layer, was obtained. The "sea-island ratio" in Table 3 refers to the ratio of the area ratio of the island portions of the low melting point layer to the area ratio of the island portions of the mid melting point layer (area ratio of island portions of low melting point layer / area ratio of island portions of mid melting point layer), and the area ratios of the island portions of the low melting point layer and mid melting point layer were measured using the method described below. The "thickness ratio" in Table 3 refers to the ratio of the thickness of the low melting point layer to the thickness of the mid melting point layer (thickness of low melting point layer / thickness of mid melting point layer). The "remaining rate of mid-melting point layer" in Table 3 means the thickness of the mid-melting point layer of the second sealant layer after heat sealing when the first sealant layer of the prepared tab sealant is heat-sealed to an aluminum plate under conditions of 170°C, 0.5 MPa, and 5 seconds, assuming the thickness of the mid-melting point layer of the second sealant layer before heat sealing to be 1.

[0102] [Table 3]

[0103] [Island area ratio] As a pretreatment, the prepared resin film for terminals was embedded in epoxy resin and cured. The epoxy-embedded film was sliced ​​using a diamond knife on a microtome so that the cross sections of the low-melting-point layer and mid-melting-point layer of the resin film for terminals were visible. The resulting slice was stained with ruthenium tetroxide, and the expanded portion after staining was trimmed using the same microtome. The stained slice was placed in a scanning electron microscope (SEM) to observe the cross sections of the low-melting-point layer and mid-melting-point layer of the resin film for terminals. The observed image was binarized, and the area ratio of the island portion was calculated from the area of ​​the island portion and the sea portion of the sea-island structure of the low-melting-point layer and mid-melting-point layer. The ratio was calculated from the area ratio of the island portion of the low-melting-point layer and mid-melting-point layer.

[0104] [Safety] Batteries were fabricated using the prepared resin film for terminals, and the temperature of the fabricated batteries was raised stepwise up to 140°C. After the internal pressure increased, the joint between the resin film for terminals and the metal terminals was opened to release the internal pressure, and the battery was visually evaluated. The evaluation results are shown in Table 3. A: The internal pressure is released before the temperature reaches 130°C. B: The internal pressure is released before the temperature reaches 140°C. C: The internal pressure is not released even when the temperature reaches 140°C.

[0105] [Adhesion to exterior materials] A 50mm (TD) x 100mm (MD) sample of tab sealant was folded in half, sandwiching a 50mm x 50mm piece of chemically treated aluminum foil. The edge opposite the fold was heat-sealed at 165°C / 0.6MPa / 10s over a 10mm width. The sealant layer of the exterior packaging material, which had a laminated structure of nylon film (25μm thick), adhesive, aluminum foil (40μm thick), and a polypropylene sealant layer (80μm thick), was then folded over the tab sealant. The edge opposite the fold (where the tab sealant and aluminum foil were heat-sealed) was heat-sealed over a 10mm width at 190°C / 0.5MPa / 5s to produce a laminate consisting of exterior packaging material / tab sealant / aluminum foil / tab sealant / exterior packaging material. A 15mm wide sample was cut from the longitudinal center of the heat-sealed portion (see Figure 7) to prepare a sample for heat-seal strength measurement. A T-peel test was performed on the heat-sealed portion of this sample at room temperature (25°C) at a tensile speed of 50 mm / min using a tensile tester (Shimadzu Corporation). The heat-seal strength (burst strength) of the sample relative to the outer casing was evaluated based on the following criteria. The results are shown in Table 3. A: Heat seal strength is 100N / 15mm or more B: Heat seal strength is 80N / 15mm or more and less than 90N / 15mm C: Heat seal strength is less than 80N / 15mm

[0106] [Overdressed] In the above-mentioned test for adhesion to the packaging material, the heat-sealed portion of the sample cut into a width of 15 mm for measuring heat-seal strength was visually inspected to evaluate whether or not there was any fusion (excessive adhesion) in areas that should not have been heat-sealed. The evaluation results are shown in Table 3. A: Only the area where the heat seal bar was applied was fused. B: The film is fused within 1 mm of the point where the heat seal bar was applied. C: The film is fused within a range of more than 1 mm from the point where the heat seal bar was applied.

[0107] [Embeddability] The tab sealant was placed so as to sandwich a 6 mm wide, 100 μm thick metal terminal, and heat sealing was performed at 165°C / 0.6 MPa every second. After each second of heat sealing, the embeddability of the side of the metal terminal was evaluated by visually checking for penetration using Red Checker liquid (penetration liquid). The evaluation results are shown in Table 3. A: A heat seal time of 2 seconds provides good embeddability. B: The heat sealing time is 3 seconds, and embeddability is good. C: Heat sealing time of 4 seconds or more provides good embeddability. [Explanation of symbols]

[0108] 1,7...low melting point layer, 2,6...mid-melting point layer, 3...first sealant layer, 4...high melting point layer, 8...second sealant layer, 10...electricity storage device, 11...electricity storage device main body, 13...exterior material, 14...metal terminal, 14-1...metal terminal main body, 14-2...corrosion prevention layer, 16...tab sealant, 21...inner layer, 22...inner layer side adhesive layer, 23-1, 23-2...corrosion prevention treatment layer, 24...barrier layer, 25...outer layer side adhesive layer, 26...outer layer.

Claims

1. A tab sealant arranged to cover a part of an outer peripheral surface of a metal terminal of an electricity storage device, a first sealant layer disposed to face the metal terminal; a high melting point layer containing a polyolefin resin; a second sealant layer; and In this order, each of the first sealant layer and the second sealant layer includes a low-melting-point layer containing an acid-modified polyolefin resin, and a mid-melting-point layer disposed between the low-melting-point layer and the high-melting-point layer; The melting point of the low-melting-point layer is 100 to 135°C, The melting point of the high melting point layer is 140 to 170°C, A tab sealant, wherein the melting point of the medium melting point layer is 10°C or more higher than the melting point of the low melting point layer and 10°C or more lower than the melting point of the high melting point layer.

2. each of the first sealant layer and the second sealant layer has a two-layer structure including the low-melting point layer and the mid-melting point layer; the mid-melting point layer contains an acid-modified polyolefin resin, 2. The tab sealant according to claim 1, wherein the mid-melting point layer has a melting point of 130 to 150°C.

3. the thickness of each of the first sealant layer and the second sealant layer is 10 to 300 μm; 3. The tab sealant according to claim 1, wherein the low melting point layer and the intermediate melting point layer each have a thickness of 3 μm or more.

4. the low-melting-point layer and the intermediate-melting-point layer each have an MFR of 1.0 to 10.0 g / 10 min at 230°C and a load of 2.16 kg; The tab sealant according to any one of claims 1 to 3, wherein the high melting point layer has an MFR of 0.05 to 3.0 g / 10 min at 230°C and a load of 2.16 kg.

5. the low melting point layer and the intermediate melting point layer both have a sea-island structure, 5. The tab sealant according to claim 1, wherein the area ratio of the island portions of the low melting point layer is 1.5 to 100 times the area ratio of the island portions of the medium melting point layer.

6. the thickness of the low-melting-point layer is 1 or more when the thickness of the mid-melting-point layer of the second sealant layer is 1; The tab sealant according to any one of claims 1 to 5, wherein when the first sealant layer of the tab sealant is heat-sealed to an aluminum plate under conditions of 170°C, 0.5 MPa, and 5 seconds, the thickness of the mid-melting point layer in the second sealant layer is 0.1 mm or more.

7. The tab sealant according to any one of claims 1 to 6, wherein in the second sealant layer, the Vicat softening point of the low melting point layer is 10°C or more lower than the Vicat softening point of the medium melting point layer.

8. the low-melting-point layer contains acid-modified polypropylene and polyethylene, The tab sealant according to any one of claims 1 to 7, wherein the low melting point layer further contains a compatibilizer having a portion compatible with the acid-modified polypropylene and a portion compatible with the polyethylene.

9. A tab sealant arranged to cover a part of an outer peripheral surface of a metal terminal of an electricity storage device, a first sealant layer disposed to face the metal terminal; a high melting point layer containing a polyolefin resin; a second sealant layer; and In this order, each of the first sealant layer and the second sealant layer includes a mid-melting point layer containing an acid-modified polyolefin resin, and a low-melting point layer disposed between the mid-melting point layer and the high-melting point layer; The melting point of the low-melting-point layer is 100 to 135°C, The melting point of the high melting point layer is 140 to 170°C, A tab sealant, wherein the melting point of the medium melting point layer is 10°C or more higher than the melting point of the low melting point layer and 10°C or more lower than the melting point of the high melting point layer.

10. a power storage device body; a metal terminal electrically connected to the power storage device body; an exterior material that houses the power storage device main body and sandwiches the metal terminals; The tab sealant according to any one of claims 1 to 9, which is disposed between the metal terminal and the exterior material; Equipped with the first sealant layer of the tab sealant adheres to the metal terminal; The second sealant layer adheres the exterior material to the electricity storage device.

Images