Housing material for battery housing and battery case

Abstract

Battery housing material (1) with: a biaxially stretched polyamide film layer as an outer layer (2), an unstretched thermoplastic resin film layer as an inner layer (3) and an aluminum foil layer (4) arranged between the two film layers (2, 3), wherein the biaxially stretched polyamide film layer has a density of 1.142 to 1.146 kg / m 3 and was achieved by stretching by a simultaneous biaxial stretching process and by setting a heat setting temperature in a range of 200 to 205°C during stretching.

Description

Technical field

[0001] The present invention relates to a battery casing material for, for example, a lithium-ion accumulator battery.

[0002] In this description, the word “aluminum” is used to encompass the meaning of aluminum and its alloys. Technical background

[0003] A lithium-ion secondary battery is widely used as a power source for, for example, notebook computers, video cameras, mobile phones, and electric cars. As such a lithium-ion secondary battery, a lithium-ion secondary battery is used, which has a structure in which the periphery of the battery body is surrounded by a casing. As such a battery casing material, it is generally known that a battery casing material has a structure in which, for example, an outer layer of a stretched polyamide film, an aluminum foil layer, and an inner layer of an unstretched polypropylene film are integrally bonded in this order (see Patent Document 1).

[0004] Such a battery casing material is molded into various battery shapes, and therefore, it is required to have high deep-drawing formability. To impart high deep-drawing formability, a lubrication-imparting component containing fatty acid amide groups is usually coated on a surface of an outer layer film to increase the sliding ability of the battery casing material into the drawing die at the time of molding (see Patent Document 2), or the outer layer film has an increased thickness relative to the thickness of the aluminum foil layer. Patent document 1:JP 2001-006 631 A Patent document 2: JP 2002-216 714 A

[0005] Furthermore, WO 2006 / 126370 A1 and US 2002 / 142178 A1 disclose a material for a battery casing comprising a polyamide film layer, a thermoplastic resin film layer and an aluminum foil layer, JP 2003 053884 A describes a nylon resin film adsorbing a substance consisting of turmeric, and US 4522867 A describes a biaxially oriented, amorphous polyamide film. Disclosure of the inventionProblems to be solved by the invention

[0006] However, in the structure in which a lubricating component composed of fatty acid amide groups is coated on the surface of the outer layer film, a coating process of the lubricating component was required, resulting in a problem that productivity was low. Furthermore, the lubricating component evaporates during the vacuum deaeration and / or battery sealing process, causing the evaporated component to adhere to the processing equipment, requiring a cleaning process to remove the adhered component. This further reduced productivity.

[0007] Furthermore, in the structure in which the outer layer film has a larger thickness compared to the thickness of the aluminum foil layer, the total thickness of the battery case material is increased, and thereby there was a problem that the volume / capacity ratio was reduced.

[0008] The present invention has been made in view of the above-mentioned technical background and aims to provide a battery case material and a battery case which are capable of ensuring excellent formability without the need for coating with a lubricating component and which are also capable of ensuring a sufficient volume / capacity ratio. Means to solve the problems

[0009] To achieve the above-mentioned objects, as a result of intensive studies, the present inventor acquired a new knowledge that the material and density of the stretched film layer constituting the outer layer of the battery case material affect the deformability of the battery case material, and completed the present invention. Thus, the present invention provides the following means. [1] A battery casing material comprising a biaxially stretched polyamide film layer as an outer layer, an unstretched thermoplastic resin film layer as an inner layer, and an aluminum foil layer disposed between the two film layers, wherein the biaxially stretched polyamide film layer has a density of 1.142 to 1.146 kg / m 3 and was achieved by stretching through a simultaneous biaxial stretching process and by setting a heat setting temperature in a range of 200 to 205°C. [2] The battery casing material according to the aforementioned aspect [1], wherein the biaxially stretched polyamide film layer has a thickness of 12 to 50 µm, the unstretched thermoplastic resin film layer has a thickness of 20 to 80 µm, and the aluminum foil layer has a thickness of 5 to 50 µm. [3] The battery casing material according to the aforementioned aspect [1] or [2], wherein the biaxially stretched polyamide film layer and the aluminum foil layer are integrally laminated by means of a urethane group adhesive layer. [4] A battery case formed by subjecting the battery case material according to any one of the aforementioned aspects [1] to [3] to a deep drawing process or a stretching process. Effect of the invention

[0010] When the stretched resin film forming the outer layer is the biaxially stretched polyamide film with a density of 1,130 to 1,160 kg / m 3is used, the battery case material exhibits excellent formability, such as deep drawing or stretch forming, enabling sharp and deep forming. Therefore, excellent formability can be ensured without coating with a lubrication component, and therefore, it is not necessary to add a coating step with a lubrication component as required in conventional technology, and excellent productivity is achieved. Accordingly, unlike conventional technology, it is also not necessary to increase the thickness of the outer layer film relative to the thickness of the aluminum foil layer in particular, thereby making it possible to achieve a sufficient volume / capacity ratio.

[0011] According to the present invention, the biaxially stretched polyamide film layer has a density of 1.142 to 1.146 kg / m 3and therefore, the formability, such as for deep drawing and / or stretch forming, can be further improved, making it possible to form a shape deeper in the mold height.

[0012] In the invention described in the aforementioned aspect [2], the generation of pinhole porosity can be sufficiently prevented, and the production cost can be reduced.

[0013] In the invention described in the aforementioned aspect [3], since the biaxially stretched polyamide film layer and the aluminum foil layer are integrally laminated with each other by means of a urethane adhesive layer, sharp molding can be performed.

[0014] In the invention described in the aforementioned aspect [4], a battery case having a shape which is sharp and deep in shape height can be provided. Brief description of the drawings Fig.1 is a cross-sectional view showing an embodiment of a battery casing material of the invention. Fig. 2 is a view showing an example of a manufacturing method of a battery casing material of the present invention. Description of reference symbols 1 Battery housing material 2 Outer layer (biaxially stretched polyamide film layer) 3 Inner layer (unstretched thermoplastic resin film layer) 4 aluminum foil layer Best mode for carrying out the invention

[0015] An embodiment of a battery casing material according to the present invention is shown in Fig.1. The battery casing material is used as a battery casing material for a lithium-ion secondary battery casing. The battery casing material 1 has a structure in which a biaxially stretched polyamide film layer (outer layer) 2 is integrally bonded to an upper surface of the aluminum foil layer 4 by a first adhesive layer 5, and an unstretched thermoplastic resin film layer (inner layer) 3 is integrally bonded to a lower surface of the aluminum foil layer 4 by a second adhesive layer 6.

[0016] The biaxially stretched polyamide film layer (outer layer) 2 is an element whose main role is to ensure the excellent formability of the battery casing material. In other words, its role is to prevent the aluminum foil from breaking due to constriction during the forming process. If the density is less than 1.130 kg / m 3delamination occurs between the biaxially stretched polyamide film layer 2 and the aluminum foil layer 4 after the forming process. On the other hand, if the density is 1.160 kg / m 3 exceeds, breakage and / or cracking of the battery casing material may occur during forming, such as deep drawing or stretch forming. According to the invention, a biaxially stretched polyamide film having a density of 1.142 to 1.146 kg / m 3 used.

[0017] In this disclosure, the aforementioned "density" means a density measured with a density meter conforming to JIS K7112-1999 D method (density gradient tube method). In other words, the "density" indicates a density measured by placing a test piece of biaxially stretched polyamide film (3 mm x 3 mm) in a density gradient tube and reading the height position of the center of gravity of a density float after 24 hours have passed since the test piece was placed therein.

[0018] The density of the biaxially stretched polyamide film can be controlled, for example, by adjusting the thermal setting temperature during the stretching process. Control can also be achieved by changing the orientation of the resin crystals by selecting the stretching method (for example, a simultaneous biaxial stretching method in which stretching is performed simultaneously in the vertical and horizontal directions, and a sequential biaxial stretching method in which stretching is performed sequentially in the vertical and horizontal directions).

[0019] It is preferable that the thickness of the biaxially stretched polyamide film layer 2 is set to 12 to 50 µm.

[0020] The unstretched thermoplastic resin film layer (inner layer) 3 has the role of imparting excellent chemical resistance to an electrolytic solution with strong corrosiveness, such as that used for lithium-ion storage batteries, and also imparting hot sealing ability to the battery casing material.

[0021] The unstretched thermoplastic resin film layer 3 is not particularly limited to, but is preferably formed of, an unstretched film made of at least one type of thermoplastic resins selected from the group consisting of polyethylene, polypropylene, olefin group copolymer, acid denaturation thereof, and ionomer.

[0022] The thickness of the unstretched thermoplastic resin film layer 3 is preferably set to 20 to 80 μm. Setting the thickness to 20 μm or more sufficiently prevents the generation of pinhole porosity, and setting the thickness to less than 80 μm reduces the amount of resin to be used, resulting in a cost reduction. Overall, it is more preferable that the thickness of the unstretched thermoplastic resin film layer 3 be set to 30 to 50 μm.

[0023] Both the biaxially stretched polyamide film layer 2 and the unstretched thermoplastic resin film layer 3 can be a single layer or a multilayer.

[0024] The aluminum foil layer 4 serves the role of providing a gas barrier property that prevents the penetration of oxygen and / or moisture into the battery casing material. A foil with a thickness of 5 to 50 µm and made of pure aluminum or Al-Fe group alloy can preferably be used as the aluminum foil layer 4.

[0025] Although the first adhesive layer 5 is not specifically limited, it may be a urethane group adhesive layer or an acrylic group adhesive layer. Overall, it is preferable that the first adhesive layer 5 be a urethane group adhesive layer formed by a urethane group two-component reactive adhesive, which allows for sharper molding.

[0026] The second adhesive layer 6 is not particularly limited, and examples thereof include adhesive layers formed from urethane group resin, acrylic group resin, resin containing thermoplastic elastomer, and acid-denatured polyolefin such as maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene. The second adhesive layer 6 is formed, for example, by laminating an adhesive resin film (for example, an acid-denatured polyolefin film) onto one side surface of the unstretched thermoplastic resin film layer 3.

[0027] In the aforementioned embodiment, the structure is provided with the first adhesive layer 5 and the second adhesive layer 6. However, it should be noted that these layers 5 and 6 do not constitute essential structural layers, and that structures without such layers may be provided.

[0028] The battery casing material 1 of the present invention is preferably used as a lithium-ion secondary battery casing material requiring a high volume energy density, but it is not particularly limited to this use.

[0029] A battery case can be obtained by subjecting the battery case material 1 of the present invention to forming and shaping (for example, in the form of deep drawing or stretch forming). Embodiments

[0030] Next, specific embodiments of the present invention will be explained. However, it should be noted that the present invention is not specifically limited to these embodiments. Embodiment 1 (not according to the invention)

[0031] As in Fig.2, a maleic anhydride-modified polyethylene layer 21 having a thickness of 3 µm and an unmodified polypropylene layer 22 having a thickness of 12 µm are co-extruded while an aluminum foil (AA8079-0) 4 having a thickness of 40 µm is fed from the left side of the drawing and while an unstretched film 3 having a thickness of 30 µm and formed of polypropylene is also fed from the right side of the drawing, and the maleic anhydride-modified polyethylene layer 21 and the unmodified polypropylene layer 22 which have been co-extruded are passed between the unstretched film 3 and the aluminum foil 4 and pressed together by means of a pair of heating and pressing rollers, thereby being heat-laminated.

[0032] Next, a urethane resin group adhesive material 5 was applied to the surface of the aluminum foil 4 of the obtained laminated film by using a coating roller. After drying the adhesive to a certain degree by applying heat, the biaxially stretched film 2 with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon laminated to the adhesive surface to achieve a battery casing material.

[0033] The biaxially stretched nylon film 2 with a density of 1.152 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching method and by setting the heat setting temperature to 210°C during stretching. Embodiment 2 (not according to the invention)

[0034] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 20 µm and a density of 1.158 kg / m 3 made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0035] The biaxially stretched nylon film with a density of 1.158 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching method and by setting the heat setting temperature to 220°C during stretching. Embodiment 3 (according to the invention)

[0036] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 15 µm and a density of 1.142 kg / m 3and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0037] The biaxially stretched nylon film with a density of 1.142 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching method and by setting the heat setting temperature to 200°C during stretching. Embodiment 4 (according to the invention)

[0038] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 20 µm and a density of 1.144 kg / m 3 and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0039] The biaxially stretched nylon film with a density of 1.144 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching process and by setting the heat setting temperature to 203°C during stretching. Embodiment 5 (according to the invention)

[0040] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 15 µm and a density of 1.146 kg / m 3 and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0041] The biaxially stretched nylon film with a density of 1.146 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching method and by setting the heat setting temperature to 205°C during stretching. Embodiment 6 (not according to the invention)

[0042] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 15 µm and a density of 1.138 kg / m 3 and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0043] The biaxially stretched nylon film with a density of 1.138 kg / m 3 was a film obtained by stretching by a simultaneous biaxial stretching method and by setting the heat setting temperature to 198°C during stretching. Embodiment 7 (not according to the invention)

[0044] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 15 µm and a density of 1.132 kg / m 3 and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0045] The biaxially stretched nylon film with a density of 1.132 kg / m 3 was a film obtained by stretching via simultaneous biaxial stretching method and setting the heat setting temperature to 195°C during stretching. Comparison example 1

[0046] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 20 µm and a density of 1.128 kg / m 3and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0047] The biaxially stretched nylon film with a density of 1.128 kg / m 3 was a film obtained by stretching by a sequential biaxial stretching method and by setting the heat setting temperature to 190°C during stretching. Comparison example 2

[0048] A battery casing material was obtained in the same manner as in Embodiment 1, except that a biaxially stretched film having a thickness of 25 µm and a density of 1.165 kg / m 3 and made of nylon was used instead of the aforementioned biaxially stretched film with a thickness of 25 µm and a density of 1.152 kg / m 3 and made of nylon.

[0049] The biaxially stretched nylon film with a density of 1.165 kg / m3 was a film obtained by stretching via sequential biaxial stretching method and setting the heat setting temperature to 230°C during stretching. Table 1 Structure of the outer layer (biaxially stretched film) Formability Resin type Thickness (µm) Density (kg / m 3 ) (6 mm process) Delamination Embodiment 1 nylon 25 1,152 ◯ No Embodiment 2 nylon 20 1,158 ◯ No Embodiment 3 nylon 15 1,142 ⊚ No Embodiment 4 nylon 20 1,144 ⊚ No Embodiment 5 nylon 15 1,146 ⊚ No Embodiment 6 nylon 15 1,138 ◯ No Embodiment 7 nylon 15 1,132 ◯ No Comparison example 1 nylon 20 1,128 ◯ Yes Comparison example 2 nylon 25 1,165 × No

[0050] The properties of each of the battery casing materials obtained as above were estimated based on the following estimation method. Property estimation method

[0051] The formability of the battery case material was estimated by preparing the battery case material in a 110 x 180 mm sheet shape and performing a single deep drawing step using a straight die with a die height of 6 mm. The results are shown as "⊚" when no cracks were generated, as "○" when almost no cracks were formed except for a small restricted area, as "Δ" when cracks were formed in significant portions, and as "x" when cracks were formed over almost the entire surface. The punch shape of the drawing die used was 60 mm in long side length, 45 mm in short side length, 1-2 mm in corner radius R, 1-2 mm in punch radius R, and 0.5 mm in die shoulder radius R. Estimation of the occurrence of delamination on the outer surface

[0052] After the molded object obtained by the aforementioned single-step deep drawing molding process was left in the drying machine at 80°C for 3 hours, a visual inspection was conducted to confirm whether delamination (peeling) of the outer layer occurred or not.

[0053] As can be seen from the table, the battery case materials of Embodiments 1 to 5 of the present invention were excellent in formability and could be formed with sharper height shapes in depth, and no delamination of the outer layer occurred. In particular, the battery case materials of Embodiments 3 to 5 were even more excellent in formability.

[0054] On the other hand, in Comparative Example 1, in which the density of the outer layer of the stretched polyamide film was less than 1,130 kg / m 3was delamination of the outer layer. Furthermore, in Comparative Example 2, in which the density of the outer layer of the stretched polyamide film was over 1,160 kg / m 3 was, the deformability was insufficient. Industrial applicability

[0055] The battery casing material of the present invention can be used, for example, as a battery casing material for lithium-ion secondary batteries.

Claims

[1] Battery casing material (1) with: a biaxially stretched polyamide film layer as an outer layer (2), an unstretched thermoplastic resin film layer as an inner layer (3) and an aluminum foil layer (4) arranged between the two film layers (2, 3), wherein the biaxially stretched polyamide film layer has a density of 1.142 to 1.146 kg / m 3 and was achieved by stretching by a simultaneous biaxial stretching process and by setting a heat setting temperature in a range of 200 to 205°C during stretching. [2] The battery casing material (1) according to claim 1, wherein the biaxially stretched polyamide film layer has a thickness of 12 to 50 µm, the unstretched thermoplastic resin film layer has a thickness of 20 to 80 µm, and the aluminum foil layer (4) has a thickness of 5 to 50 µm. [3] The battery casing material (1) according to claim 1, wherein the biaxially stretched polyamide film layer and the aluminum foil layer (4) are integrally laminated by means of a urethane group adhesive layer (5). [4] Battery case, characterized in that the battery case material (1) according to any one of claims 1 to 3 is subjected to deep drawing or stretch forming.

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