Battery Packaging Materials

Abstract

To provide a packaging material for a battery in which seal strength is lowered at a temperature at which combustible gas caused by an electrolyte is generated, and a case is opened.SOLUTION: A packaging material 1 for a battery includes a base material layer 13 as an outside layer, a sealant layer 20 as an inside layer, and a barrier layer 11 arranged between both of the layers. The sealant layer 20 is composed of a single layer or a plurality of layers, a first sealant layer 21 as the innermost layer is composed of a propylene-based resin containing an ethylene-propylene copolymer, and as for the ethylene-propylene copolymer, a ratio Mw / Mn of a weight average molecular weight Mw to a number average molecular weight Mn, which is measured by gel permeation chromatography (GPC), is 1 to 7, a melt flow rate measured at 230°C and a load of 2.16 kg on the basis of JIS K 7210 is 5 g / 10 min to 30 g / 10 min, and a melting point calculated by differential scanning calorimetry is 120°C to 135°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery packaging material suitably used as a case for, for example, secondary batteries for vehicles, stationary use, notebook computers, mobile phones, and cameras, particularly lithium ion secondary batteries for small portable use, and related technologies thereof. [Background Art]

[0002] Power storage devices represented by lithium ion batteries can be processed into various shapes by using a laminate-type packaging material obtained by bonding resin layers to both sides of aluminum from a can or case, and can also be made thinner and lighter. In a power storage device using a laminate material as a packaging material, when the internal temperature of the battery rises as the capacity of the device increases, gas is generated due to volatilization of the electrolyte and the like, the internal pressure rises, and the case expands or bursts. In addition, there is a risk of ignition if the gas is flammable. For this reason, measures have been taken to prevent bursting and gently release gas from the device case (see Patent Documents 1 and 2).

[0003] Patent Document 1 describes a preventive measure based on the structure of a case, and discloses a valve mechanism that reduces the pressure when the internal pressure of the case rises, and an air passage that guides the gas in the case to the valve mechanism.

[0004] Patent Document 2 describes a preventive measure based on a case material, in which the heat-fusible resin layer (sealant layer) of a laminate material is formed of a resin having a melting peak temperature of 130°C or lower, and a technology is disclosed that suppresses expansion of the battery and gently opens the battery when exposed to a high temperature environment. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent No. 6540871 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2019-29300 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the preventative measures described in Patent Document 1 require additional components such as valve mechanisms and ventilation channels, which increases both material and manufacturing costs. Furthermore, the laminate material described in Patent Document 2 controls the opening temperature using the melting peak temperature of the sealant layer, so in order to ensure opening before rupture, it needs to be designed to open at a low temperature range. This means that it may open even at the practical operating temperature of a battery where no gas is generated. [Means for solving the problem]

[0007] In view of the above-mentioned technical background, the present invention provides a battery packaging material in which the seal strength decreases and the case opens at temperatures in which flammable gases originating from the electrolyte are generated.

[0008] That is, the present invention has the configuration described in [1] to [8] below.

[0009] [1] A battery packaging material comprising a base layer as an outer layer, a sealant layer as an inner layer, and a barrier layer disposed between these two layers, The sealant layer consists of a single layer or multiple layers, and the innermost layer, the first sealant layer, is composed of a propylene resin containing an ethylene-propylene copolymer. The ethylene-propylene copolymer is characterized by having a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio (Mw / Mn) of 1 to 7, measured by gel permeation chromatography (GPC), a melt flow rate of 5 g / 10 min to 30 g / 10 min measured at 230°C and a 2.16 kg load according to JIS K7210, and a melting point of 120°C to 135°C calculated by differential scanning calorimetry.

[0010] [2] The battery packaging material according to item 1, wherein the ethylene-propylene copolymer is a copolymer derived from a metaceron catalyst.

[0011] [3] The battery packaging material according to paragraph 1 or 2, wherein the propylene resin is a mixture of ethylene-propylene copolymer and polyethylene, and the polyethylene content in the mixture is 7% by mass to 20% by mass.

[0012] [4] The battery packaging material according to item 3 above, wherein 70% by mass or more of the polyethylene is polyethylene derived from a metallocene catalyst.

[0013] [5] The sealant layer is a multilayer in which the first sealant layer, one or more second sealant layers, and a third sealant layer are sequentially laminated from the inside of the battery packaging material toward the barrier layer side. The third sealant layer is made of an ethylene-propylene random copolymer. The battery packaging material according to any one of items 1 to 4 above, wherein the melt flow rate of the resin constituting at least one layer of the second sealant layer is smaller than the melt flow rate of the ethylene-propylene copolymer of the first sealant layer.

[0014] [6] A battery case characterized in that a battery element chamber for housing a battery element is formed by joining the battery packaging material described in any of paragraphs 1 to 5 above with the sealant layers facing inward and heat-sealing the edges.

[0015] [7] The battery case according to paragraph 6, wherein the sealing strength of the edge of the battery element chamber is 60 N / 15 mm or more at room temperature, 25 N / 15 mm or more at 100 °C, and 6 N / 15 mm to 12 N / 15 mm at 130 °C.

[0016] [8] A battery characterized in that a battery element is housed in a battery element chamber of the battery case described in paragraph 6 or 7 above. [Effects of the Invention]

[0017] The battery packaging material described in [1] above is configured such that the first sealant layer of the sealant layer, which is the innermost layer, is formed of a propylene-based resin containing an ethylene-propylene copolymer having specified properties, so the sealing strength sharply decreases at 110°C to 130°C. When the battery temperature rises, gas is generated due to volatilization of the electrolyte and the like, and the pressure inside the case rises at around 130°C to start expansion. In a battery using a case produced from the battery packaging material described above, the sealing strength decreases at 110°C to 130°C, which is lower than the temperature at which the case starts expansion, causing the seal to detach and open, so gas is gently released and rupture or ignition of the case is prevented.

[0018] In the battery packaging material described in [2] above, since the ethylene-propylene copolymer in the sealant layer is a copolymer derived from a metallocene catalyst, the sealing strength can be reduced at an intended temperature.

[0019] In the battery packaging material described in [3] above, since the sealant layer is formed of a propylene-based resin containing a predetermined amount of polyethylene, the effect of reducing the sealing strength at an intended temperature is significant.

[0020] In the battery packaging material described in [4] above, since 70% by mass or more of the polyethylene in the propylene-based resin that constitutes the sealant layer is derived from a metallocene catalyst, the polyethylene is easily dispersed in polypropylene, and the effect of controlling the temperature at which sealing strength decreases to the intended temperature is improved.

[0021] In the battery packaging material described in [5] above, the sealant layer is a multilayer including a first sealant layer, a second sealant layer, and a third sealant layer. By forming the third sealant layer from an ethylene-propylene random copolymer, strong bonding strength to a barrier layer can be obtained. By forming the second sealant layer from a resin having a lower melt flow rate and a higher melting point than the ethylene-propylene copolymer of the first sealant layer, opening can be achieved at the seal portion between the first sealant layers.

[0022] According to the battery case described in [6] above, the effects provided by the above-described battery packaging material can be obtained.

[0023] The battery case described in [7] above is unsealed and opened by the seal at the edge of the battery element chamber coming off at 110°C to 130°C.

[0024] According to the battery described in [8] above, the effect of the aforementioned battery packaging material can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] [Figure 1] It is a cross-sectional view of one example of the battery packaging material of the present invention. [Figure 2] It is a cross-sectional view of a battery including a battery case produced from the battery packaging material of Fig. 1. MODES FOR CARRYING OUT THE INVENTION

[0026] Fig. 1 shows one embodiment of the battery packaging material of the present invention. [Battery Packaging Material] In the battery packaging material 1, a base material layer 13 is laminated on one surface of a barrier layer 11 via a first adhesive layer 12, and a multi-layer sealant layer 20 is laminated on the other surface via a second adhesive layer 14. The battery packaging material 1 is arranged with the sealant layers 20 facing each other, and a battery case is produced by heat-sealing the periphery of the battery packaging material 1. In the produced battery case, the base material layer serves as an outer layer, and the sealant layer 20 serves as an inner layer. [Sealant Layer of Battery Packaging Material] The battery packaging material of the present invention is characterized by the material of the sealant layer serving as the inner layer. The sealant layer not only has excellent chemical resistance even against highly corrosive electrolytes and the like, but also plays a role of imparting heat-sealability to the laminate material. The sealant layer may be either a single layer or a multi-layer, and the material of the first sealant layer which is the innermost layer, that is, the layers that contact each other when heat-sealing battery packaging materials arranged facing each other, is specified as follows.

[0027] The sealant layer 20 in the illustrated example has a three-layer structure in which the first sealant layer 21, the second sealant layer 22, and the third sealant layer 23 are stacked in order from the inside of the battery packaging material 1 toward the barrier layer 11. The third sealant layer 23 is in contact with the second adhesive layer 14, and the second sealant layer 22 is an intermediate layer between the first sealant layer 21 and the third sealant layer 33.

[0028] The first sealant layer 21 is composed of a propylene-based resin, which includes at least an ethylene-propylene copolymer containing ethylene and propylene as copolymer components.

[0029] The ethylene-propylene copolymer may be a random copolymer, a block copolymer, or any other type of block copolymer, but it must satisfy the following three essential properties. (1) The ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) Mw / Mn, measured by gel permeation chromatography (GPC), is 1 to 7. A preferred Mw / Mn is 1.2 to 3.5, and even more preferred is 1.5 to 2.8. (2) The melt flow rate (MFR) measured at 230°C and a 2.16 kg load according to JIS K7210 is 5 g / 10 min to 30 g / 10 min. The preferred melt flow rate (MFR) is 5 g / 10 min to 10 g / min. (3) The melting point calculated by differential scanning calorimetry is 120°C to 135°C. The preferred melting point is 122°C to 133°C.

[0030] Ethylene-propylene copolymers that meet the three conditions above experience a decrease in seal strength between 110°C and 130°C, making them prone to seal detachment, while maintaining seal strength at temperatures below this range. As the battery temperature rises, gas is generated due to the volatilization of the electrolyte, and around 130°C, the internal pressure of the battery increases, causing the case to begin expanding. The temperature range at which the seal strength decreases, as described above, is higher than the expected operating temperature range of the battery, but lower than the temperature at which expansion begins. Therefore, if the battery temperature rises rapidly and the internal pressure begins to increase due to gas generation, the seal will detach and the case will open. Once the case opens, the gas is released gradually, preventing the case from rupturing or igniting.

[0031] Ethylene-propylene copolymers that satisfy the three conditions described above can be obtained, for example, by copolymerizing ethylene and propylene, which are copolymer components, with a metallocene catalyst. Ethylene-propylene copolymers derived from metacelon catalysts tend to have high molecular weight uniformity and satisfy the three conditions described above, and are highly effective in reducing seal strength at the desired temperature.

[0032] Furthermore, the propylene-based resin is a mixture of ethylene-propylene copolymer and polyethylene, and it is preferable that the polyethylene content in the mixture is 7% to 20% by mass. Setting the polyethylene content within the above range greatly enhances the effect of reducing the seal strength at the desired temperature. A particularly preferred ethylene content is 10% to 15% by mass. Moreover, it is preferable that 70% or more by mass of the polyethylene is metallocene catalyst-derived polyethylene polymerized with a metallocene catalyst. Metallocene catalyst-derived polyethylene disperses easily in polypropylene, improving the effect of controlling the temperature at which the seal strength decreases to the desired temperature. A particularly preferred content of metacelon catalyst-derived polyethylene is 85% by mass or more.

[0033] It is preferable to add a lubricant or antiblocking agent to the first sealant layer 21.

[0034] Lubricants are not particularly limited, but examples include saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, aromatic bisamides, etc.

[0035] The saturated fatty acid amides mentioned above are not particularly limited, but examples include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide.

[0036] The aforementioned unsaturated fatty acid amides are not particularly limited, but examples include oleic acid amide and erucic acid amide.

[0037] The substituted amides are not particularly limited, but examples include N-oleyl palmitate amide, N-stearyl stearate amide, N-stearyl oleate amide, N-oleyl stearate amide, and N-stearyl erucate amide.

[0038] The methylolamide mentioned above is not particularly limited, but examples include methylol stearate amide.

[0039] The saturated fatty acid bisamides mentioned above are not particularly limited, but examples include methylenebisstearate, ethylenebiscaprate, ethylenebislaurate, ethylenebisstearate, ethylenebishydroxystearate, ethylenebisbehenamide, hexamethylenebisstearate, hexamethylenebisbehenamide, hexamethylenehydroxystearate, N,N'-distearyladipamide, N,N'-distearylsebacinamide, and the like.

[0040] The aforementioned unsaturated fatty acid bisamides are not particularly limited, but examples include ethylenebisoleamide, ethylenebiserucamide, hexamethylenebisoleamide, and N,N'-dioleylsebacinamide.

[0041] The aforementioned fatty acid ester amide is not particularly limited, but examples include stearamidoethyl stearate.

[0042] The aforementioned aromatic bisamides are not particularly limited, but examples include m-xylylenebisstearate, m-xylylenebishydroxystearate, and N,N'-distearyl isophthalamide.

[0043] The lubricant concentration in the first sealant layer 21 is preferably in the range of 100 ppm to 3000 ppm. If the lubricant concentration is less than 100 ppm, the moldability is insufficient, and adding 3000 ppm sufficiently improves the moldability, so adding a large amount exceeding that is undesirable from a cost perspective. A particularly preferred lubricant concentration is 500 ppm to 2000 ppm.

[0044] The antiblocking agent is not particularly limited, but examples include particles of silica, acrylic resin, aluminum silicate, calcium carbonate, barium carbonate, titanium dioxide, talc, kaolin, etc. The particle size of the antiblocking agent is preferably in the range of 0.1 μm to 10 μm in average particle size, and more preferably in the range of 1 μm to 5 μm in average particle size. The concentration of the antiblocking agent is preferably set to 100 ppm to 5000 ppm, and a particularly preferred concentration is 500 ppm to 4000 ppm.

[0045] By incorporating the antiblocking agent (particles) into the first sealant layer 21 of the sealant layer 20 of the battery packaging material 1, minute protrusions are formed on the surface of the first sealant layer 21, reducing the contact area between the films and suppressing blocking between the sealant films. Furthermore, by incorporating the antiblocking agent (particles) together with the lubricant, the slipperiness during molding can be further improved.

[0046] If the sealant layer is a single layer, it will be a single layer of the first sealant layer 21 described above.

[0047] When the sealant layer 20 is a multilayer, preferred materials for the layers other than the first sealant layer 21 are as follows. Note that the present invention does not limit the materials for the layers other than the first sealant layer 21.

[0048] The third sealant layer 23 can be an ethylene-propylene copolymer or an ethylene-propylene random copolymer having the same composition as the first sealant layer 21. Furthermore, since the third sealant layer 23, together with the second adhesive layer 14, is a layer for increasing the bonding strength between the barrier layer 11 and the sealant layer 20, it is preferable that no lubricants or antiblocking agents are added. However, from the viewpoint of ensuring the stability of the sealant layer 20 during film formation and preventing blocking after winding the sealant layer 20, erucic acid amide in an amount of 1000 ppm or less and silica particles in an amount of 2000 ppm or less as an antiblocking agent may be added.

[0049] The second sealant layer 22 is an intermediate layer between the first sealant layer 21 and the third sealant layer 23, and may be a homopolymer of propylene, a copolymer containing propylene and copolymer components other than propylene, or a mixture of multiple polymers. Furthermore, if the same propylene-based resin as the first sealant layer 21 is present, the adhesion between the second sealant layer 22 and the first sealant layer 21 will improve. The second sealant layer 22 may be a single layer or a multi-layer layer.

[0050] The sealant layer 20 in the illustrated example has a three-layer structure and is obtained by producing a multilayer film by co-extrusion or the like from the materials of each layer. Furthermore, it is preferable that the sealant layer 20 is an unstretched film.

[0051] The thickness of the sealant layer 20 is preferably in the range of 20 μm to 100 μm, and even more preferably in the range of 25 μm to 85 μm. In addition, in the three-layer structure of the sealant layer 20 shown in the illustrated example (including the case where the second sealant layer is multi-layered), the preferred ratio of the thicknesses of each layer is first sealant layer 21: second sealant layer 22: third sealant layer 23 = 1 to 3: 4 to 8: 1 to 3.

[0052] If the sealant layer 20 is multilayered, it is preferable to design the sealant layer 20 so that the case can be opened at the seal between the first sealant layers 21 of the two heat-sealed battery packaging materials 1, and to prevent delamination within the sealant layer 20 before the seal between the first sealant layers 21 is broken. If delamination occurs within the sealant layer 20, gas generated inside the battery may have difficulty escaping in a high-temperature environment. Specifically, it is preferable that the third sealant layer 23 is made of ethylene-propylene random copolymer, and the second sealant layer 22 (or at least one of the layers if the second sealant layer is multilayered) is made of a resin with a melt flow rate lower than that of the ethylene-propylene copolymer of the first sealant layer 21 and a high melting point. By making the third sealant layer 23 of ethylene-propylene random copolymer, a strong bonding force to the barrier layer 11 can be obtained. Furthermore, the preferred properties of the material constituting the second sealant layer 22 are a melt flow rate of 2 g / 10 min to 7 g / 10 min measured at 230°C and a 2.16 kg load according to JIS K7210, and a melting point of 120°C to 165°C calculated by differential scanning calorimetry. Particularly preferred melt flow rates are 2 g / 10 min to 5 g / 10 min, and particularly preferred melting points are 140°C to 165°C. By setting the three layers of material in this way, the case is opened between the first sealant layer 21 of the sealant layer 20 of the two battery packaging materials 1. [Layers other than the sealant layer of battery packaging material] In the battery packaging material of the present invention, the layers other than the sealant layer can be made of any known material as appropriate, and the bonding method is not particularly limited. Preferred materials for the layers other than the sealant layer are described below. (base material layer) The base layer 13 uses a heat-resistant resin film that does not melt at the heat-sealing temperature when heat-sealing the battery packaging material 1. The heat-resistant resin used has a melting point that is 10°C or more, preferably 20°C or more, higher than the melting point of the resin constituting the sealant layer 20. Examples of resins that satisfy this condition include polyamide films such as nylon film and polyester films, and stretched films of these are preferably used. In particular, the base layer 13 is preferably a biaxially oriented polyamide film such as biaxially oriented nylon film, a biaxially oriented polybutylene terephthalate (PBT) film, a biaxially oriented polyethylene terephthalate (PET) film, or a biaxially oriented polyethylene naphthalate (PEN) film. The nylon film is not particularly limited, but examples include nylon 6 film, nylon 6,6 film, and MXD nylon film. The base layer 13 may be formed as a single layer, or it may be formed as a multilayer, for example, a polyester film / polyamide film (or a multilayer, such as a PET film / nylon film).

[0053] The thickness of the base material layer 13 is preferably 7 μm to 50 μm, which ensures sufficient strength as a packaging material and reduces stress during molding such as stretch molding and deep drawing, thereby improving moldability. A more preferable thickness for the base material layer 13 is 9 μm to 30 μm. (Barrier layer) The barrier layer 11 plays a role in providing gas barrier properties to the battery packaging material 1, preventing the intrusion of oxygen and moisture. The barrier layer 11 is not particularly limited, but examples include metal foils such as aluminum foil, SUS foil (stainless steel foil), copper foil, nickel foil, titanium foil, and clad foil. The thickness of the barrier layer 11 is preferably 20 μm to 100 μm. A thickness of 20 μm or more prevents the occurrence of pinholes during rolling when manufacturing metal foil, while a thickness of 100 μm or less reduces stress during molding such as stretch molding and deep drawing, thereby improving moldability. A particularly preferred thickness of the barrier layer 11 is 25 μm to 85 μm.

[0054] Furthermore, it is preferable that the barrier layer 11 has undergone a surface treatment such as chemical conversion treatment on at least the surface of the metal foil facing the sealant layer 20. Such chemical conversion treatment can sufficiently prevent corrosion of the metal foil surface by the contents (such as the electrolyte of the battery). (First adhesive layer) The first adhesive layer 12 is not particularly limited, but examples include an adhesive layer formed by a two-component curing adhesive. Examples of the two-component curing adhesive include a two-component curing adhesive composed of a first liquid (main component) consisting of one or more polyols selected from the group consisting of polyurethane polyols, polyester polyols, polyether polyols, and polyester urethane polyols, and a second liquid (curing agent) consisting of isocyanate. In particular, it is preferable to use a two-component curing adhesive composed of a first liquid consisting of one or more polyols selected from the group consisting of polyester polyols and polyester urethane polyols, and a second liquid (curing agent) consisting of isocyanate. The preferred thickness of the first adhesive layer 12 is 2 μm to 5 μm. (Second adhesive layer) The second adhesive layer 14 is not particularly limited, but for example, an adhesive containing one or more of the following is recommended: polyurethane resin, acrylic resin, epoxy resin, polyolefin resin, elastomer resin, fluororesin, and acid-modified polypropylene resin. Among these, an adhesive made of a polyurethane composite resin with acid-modified polyolefin as the main component is preferred. The preferred thickness of the second adhesive layer 14 is 2 μm to 5 μm. (Other lamination forms of battery packaging materials) In the battery packaging material of the present invention, the first adhesive layer and the second adhesive are not essential layers; the base layer may be directly bonded to the barrier layer, or the sealant layer may be directly bonded to the barrier layer.

[0055] Furthermore, the battery packaging material of the present invention can also be configured such that the outer layer consists of multiple layers, including the base layer, by forming another layer on the outside and / or inside (barrier layer side) of the base layer.

[0056] Examples of layers formed on the outside of the base material layer include a protective layer and a matte coating layer. These layers serve as the outermost layer of the battery packaging material, protecting the base material layer and providing good slipperiness to the surface, thereby improving moldability.

[0057] Recommended materials for the protective layer include phenoxy resins, urethane resins, epoxy resins, acrylic resins, polyolefin resins, fluororesins, and the like. The matte coat layer consists of a resin composition in which a matting agent is blended with the resin. Recommended materials for the matting agent include the above-mentioned resin and inorganic fine particles such as silica, alumina, calcium oxide, calcium carbonate, calcium sulfate, and calcium silicate, as well as resin beads such as acrylic beads.

[0058] The protective layer and matte coat layer can be formed by applying a liquid whose fluidity has been adjusted with a solvent to the substrate layer and drying it, or by laminating them to the substrate layer as a film.

[0059] A colored layer can be exemplified as a layer formed on the inside of the base material layer, that is, a layer formed between the base material layer and the first adhesive layer (or between the base material layer and the barrier layer if the first adhesive layer is absent). If the base material layer is transparent, the layer formed behind it can be seen through the base material layer, so by forming a colored layer on the inside of the base material layer, the appearance of the battery packaging material can be given color (including achromatic colors). In the case of battery packaging material in which the colored layer is not formed, the color of the metal foil constituting the barrier layer will be the appearance color.

[0060] As the colored layer, a cured film of a colored ink composition in which a colored pigment is blended into a resin binder can be recommended. As the resin binder, an example is a two-component curable polyester urethane resin binder consisting of a polyester resin as the main component and a polyfunctional isocyanate compound as the curing agent. As the colored pigment, examples include inorganic pigments such as carbon black, calcium carbonate, titanium dioxide, zinc oxide, iron oxide, and aluminum powder, and organic pigments such as azo compounds, phthalocyanine compounds, and condensed polycyclic compounds. [Battery case and batteries] The battery 2 in Figure 2 is equipped with a battery case 30 made of the battery packaging material of the present invention.

[0061] The battery case 30 is manufactured by aligning the sealant layers 20 of the battery packaging material 1 with the inside facing inward and heat-sealing the edges to form a battery element chamber 31 with the sealant layer 20 as the inner surface. Note that the partial enlargement view in Figure 2 omits the illustration of the first adhesive layer and the second adhesive layer of the battery packaging material 1.

[0062] Furthermore, the battery 2 is manufactured by housing battery elements, including a positive electrode, a negative electrode, a separator placed between the positive and negative electrodes, and an electrolyte, in the battery element chamber 31 of the battery case 30. The battery 2 is designed so that the sealing strength of the seal between the layers of sealant 20 deteriorates and the battery opens before it reaches a temperature at which gas is generated due to the battery elements, and the gas is safely released to the outside of the case without increasing the internal pressure, thus preventing the battery from rupturing or igniting.

[0063] The battery case 30 must maintain a seal strength that prevents it from opening even when the battery temperature rises, until a predetermined opening temperature is reached. When the opening temperature is 110°C to 130°C, the desirable seal strength of the edge of the battery element chamber 31 is 60 N / 15 mm or more at room temperature, 25 N / 15 mm or more at 100°C, and 6 N / 15 mm to 12 N / 15 mm at 130°C. A seal strength of 6 N / 15 mm to 10 N / 15 mm at 130°C is even more preferable. [Examples]

[0064] As Examples 1-7 and Comparative Examples 1-5, a three-layer sealant layer 20 and a battery packaging material 1, as shown in Figure 1, were prepared.

[0065] Examples 1-7 and Comparative Examples 1-5 differ only in the material of the first sealant layer 21 of the sealant layer 20; all other materials are the same. The materials of the barrier layer 11, substrate layer 13, first adhesive layer 12, and second adhesive layer 14 are as follows.

[0066] As the barrier layer 11, a chemical conversion treatment solution consisting of polyacrylic acid (acrylic resin), chromium(III) salt compound, water, and alcohol was applied to both sides of an aluminum foil made of A8079 with a thickness of 35 μm, and then dried at 150°C to form a chemical conversion film. The amount of chromium deposited on this chemical conversion film was 5 mg / m2 per side.

[0067] A biaxially oriented nylon 6 film with a thickness of 25 μm was used as the base layer 13.

[0068] A two-component curing urethane-based adhesive was used as the first adhesive layer 12.

[0069] A two-component maleic acid-modified propylene adhesive was used as the second adhesive layer 14. (Preparation of a 3-layer film for sealant layer) A sealant layer 20, consisting of a first sealant layer 21, a second sealant layer 22, and a third sealant layer 23, was fabricated by co-extrusion.

[0070] The first sealant layer 21 consists of a resin composition obtained by adding 1000 ppm erucic acid amide as a lubricant and 2000 ppm silica particles as an antiblocking agent to a mixture of ethylene-propylene random copolymer and polyethylene. The use or non-use of a metaceron catalyst in the polymerization process of the ethylene-propylene random copolymer is shown in Table 1. Also shown in Table 1 are the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (Mw / Mn) of the ethylene-propylene copolymer used in each example, the melt flow rate (MFR) measured according to JIS K7210 (230°C / 2.16 kg load), and the melting point (°C) calculated by differential scanning calorimetry. Furthermore, the polyethylene content relative to the total of ethylene-propylene random copolymer and polyethylene, and the polyethylene content derived from the metallocene catalyst within that polyethylene, are shown in Table 1.

[0071] The second sealant layer 22 is made of a resin composition obtained by adding 2500 ppm of erucic acid amide as a lubricant to an ethylene-propylene block copolymer.

[0072] The third sealant layer 23 is made of a resin composition obtained by adding 1000 ppm of erucic acid amide as a lubricant and 2000 ppm of silica particles as an antiblocking agent to an ethylene-propylene random copolymer.

[0073] The resin compositions constituting the first sealant layer 21, the second sealant layer 22, and the third sealant layer 23 described above were co-extruded to extrude a three-layer film. The thickness of each layer was 6 μm for the first sealant layer 21, 28 μm for the second sealant layer 22, and 6 μm for the third sealant layer 23, producing a sealant film with a total thickness of 40 μm. Each of the sealant layers 20 is an unoriented film.

[0074] Then, an adhesive was applied to one side of the barrier layer 11 to form a first adhesive layer 12 with a thickness of 3 μm, and the base layer 13 was dry laminated with it. At the same time, an adhesive was applied to the other side of the barrier layer 11 to form a second adhesive layer 14 with a thickness of 2 μm, and the third sealant layer 23 of the sealant layer 20 was dry laminated together with it. Furthermore, this laminated sheet was dry laminated by sandwiching it between a rubber nip roll and a laminating roll heated to 100°C and pressing them together, and then aging (heating) it at 40°C for 10 days to obtain the battery packaging material 1 (see Figure 1).

[0075] The seal strength of the prepared battery packaging material was evaluated at three different temperatures: room temperature (25°C), 130°C, and 100°C, using the following method.

[0076] Test specimens for measuring seal strength were prepared by cutting battery packaging material 1 to a width of 15 mm x length of 150 mm, placing the two test pieces with the sealant layers 20 facing inward, and heat-sealing them using a heat sealing device (Tester Industries Co., Ltd., TP-701-A) under the following conditions: heat sealing temperature: 200°C, sealing pressure: 0.2 MPa (gauge indicated pressure), and sealing time: 2 seconds, by heating one side. (Strength at room temperature) The seal strength was measured using a Shimadzu Access Strograph (AGS-5kNX) in accordance with JIS Z0238-1998, by tensilely peeling the sealant layers 20 of the test material in a T-shape at a tensile speed of 100 mm / min. This was defined as the seal strength (N / 15 mm width).

[0077] For the room temperature sealing temperature, the peel strength was measured using the method described above on the test material at room temperature. For the 130°C and 100°C sealing temperatures, the test material was left to stand for 24 hours in each temperature environment, and then the peel strength was measured using the method described above in each temperature environment. The sealing strengths at each temperature are shown in Table 1.

[0078] [Table 1]

[0079] Table 1 confirms that the seal strength can be reduced at the desired temperature by defining the characteristics of the outermost layer of the sealant layer. [Industrial applicability]

[0080] The battery packaging material of the present invention can be suitably used as a case material for rechargeable batteries for vehicles, stationary devices, laptop computers, mobile phones, and cameras, and especially for small portable lithium-ion rechargeable batteries. [Explanation of Symbols]

[0081] 1...Battery packaging material 11… Barrier layer 12…First adhesive layer 13...Base material layer 14…Second adhesive layer 20...Sealant layer 21...First sealant layer 22...Second sealant layer 23…Third sealant layer

Claims

1. A battery packaging material comprising a base layer as an outer layer, a sealant layer as an inner layer, and a barrier layer disposed between these two layers, The sealant layer consists of a single layer or multiple layers, and the innermost layer, the first sealant layer, is composed of a propylene-based resin containing an ethylene-propylene copolymer. The propylene-based resin is a mixture of ethylene-propylene copolymer and polyethylene. The polyethylene content in the aforementioned mixture is 7% by mass to 20% by mass. A battery packaging material characterized in that 65% to 95% by mass of the polyethylene is polyethylene derived from a metallocene catalyst.

2. The battery packaging material according to Claim 1, characterized in that the ethylene-propylene copolymer has a ratio Mw / Mn of weight-average molecular weight Mw to number-average molecular weight Mn, measured by gel permeation chromatography (GPC), which is 1 to 7.

3. The battery packaging material according to claim 1 or 2, characterized in that the melt flow rate measured at 230°C and a 2.16 kg load based on JIS K7210 is 5 g / 10 min to 30 g / 10 min.

4. The battery packaging material according to any one of claims 1 to 3, characterized in that the melting point calculated by differential scanning calorimetry is 120°C to 135°C.

5. The battery packaging material according to any one of claims 1 to 4, characterized in that the ethylene-propylene copolymer is a copolymer derived from a metaceron catalyst.

6. A battery packaging material according to any one of claims 1 to 5 is formed by joining the sealant layers with the inside facing each other and heat-sealing the edges to create a battery element chamber for housing a battery element, A battery case characterized in that the sealing strength of the edge of the battery element chamber is 60 N / 15 mm or more at room temperature, 25 N / 15 mm or more at 100°C, and 6 N / 15 mm to 12 N / 15 mm at 130°C.

7. A battery in which a battery element is housed in a battery element chamber of the battery case according to claim 6, A battery characterized by a decrease in seal strength at 110°C to 130°C, which causes the seal to detach and the battery to open.

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