Storage battery exterior material, storage battery case using said storage battery exterior material, and storage battery using said storage battery case

Abstract

[Problem] To provide: a storage battery exterior material which has excellent heat resistance, long-term durability, and cold formability; a storage battery case using said storage battery exterior material; and a storage battery. [Solution] Provided are: a storage battery exterior material formed by laminating a base material layer, a barrier layer and a sealant layer in this order from the outside, wherein the sealant layer comprises a biaxially stretched polybutylene terephthalate film; a storage battery case which uses said storage battery exterior material; and a storage battery.

Description

Exterior material for storage batteries, storage battery case using said exterior material for storage batteries, and storage battery using said storage battery case

[0001] The present invention relates to a packaging material for a storage battery that has excellent heat resistance, long-term durability, and cold formability. More specifically, the present invention relates to a packaging material for a storage battery that is used in severe environments such as high temperature and high temperature and humidity.

[0002] Conventionally, laminated exterior materials constructed by sequentially laminating a base material layer, a barrier layer, and a sealant layer have been used in many applications, such as packaging bags for food, medicine, etc., vacuum insulation materials, and exterior materials for storage batteries such as electric double layer capacitors and lithium-ion batteries, because they can be easily processed into a variety of shapes and can be made thin and lightweight. Among these applications, in recent years, there has been a movement to change the electrolyte of lithium-ion batteries, which are the main storage batteries used in mobile terminals such as smartphones, IoT devices, electric vehicles, unmanned aerial vehicles, etc., from liquid electrolytes to solid electrolytes in order to improve safety, reliability, and charging speed.

[0003] On the other hand, all-solid-state batteries using solid electrolytes are expected to be storage batteries that can be used for long periods of time in harsh environments such as low temperature and low humidity, and high temperature and high humidity, due to their characteristics. However, sealant layers using polyethylene and polypropylene films, which are used in conventional battery casing materials, do not have the sealing strength to withstand use over a wider temperature range, especially at high temperatures, making it difficult for them to meet the requirements for use as casing materials for all-solid-state batteries.

[0004] Under these circumstances, with the aim of providing an exterior material for an electricity storage device that can exhibit high sealing strength in a wide range of temperature environments from low to high, a exterior material for an electricity storage device has been proposed that is composed of a laminate having at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order, the heat-sealable resin layer including a film that has a glass transition temperature of 67°C or lower, and the resin forming the film has at least Polyester Structure A (Patent Document 1). Also, with the aim of providing an exterior material for an electricity storage device that can be heat-sealed at low temperatures and that maintains excellent heat-sealability even when exposed to a high-temperature environment after heat-sealing, a exterior material for an electricity storage device has been proposed that has a structure in which at least a base material layer, an adhesive layer, a metal foil layer, a sealant adhesive layer, and a sealant layer are laminated in this order, and the sealant layer contains amorphous polyethylene terephthalate (Patent Document 2).

[0005] Japanese Patent No. 7311073 Japanese Patent Application Laid-Open No. 2020-113368

[0006] However, the film contained in the heat-sealable resin layer in the electrical storage device packaging material proposed in Patent Document 1 has a glass transition temperature of 67°C or lower, and the resin forming the film contains polyester structure A, so that the electrical storage device packaging material exhibits high sealing strength in a wide range of temperature environments from low to high (for example, a range of -30°C to 150°C). However, there is a risk that the strength and elongation will decrease over long-term durability in high-temperature environments, raising concerns about its reliability as a film for packaging all-solid-state batteries that undergo repeated expansion and contraction during charging and discharging. Furthermore, the electrical storage device packaging material proposed in Patent Document 2 has a sealant layer containing amorphous polyethylene terephthalate, so that it can be heat-sealed at low temperatures (specifically, 190°C) compared to electrical storage device packaging materials whose sealant layer contains crystalline polyethylene terephthalate, and can maintain excellent heat-sealability even in high-temperature environments due to crystallization after heat-sealing. However, the use of a sealant layer containing amorphous polyethylene terephthalate raised concerns about its strength as an electrical storage device packaging material. Furthermore, if the storage battery is an all-solid-state battery, there is a risk that the temperature may rise to nearly 180°C to 200°C if an abnormality occurs, and the exterior material of such a storage battery is now required to have sealing properties in this temperature range.

[0007] An object of the present invention is to provide a storage battery packaging material that is excellent in heat resistance, long-term durability, and cold formability, and a storage battery case and storage battery that use the storage battery packaging material.

[0008] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a storage battery casing material including a base material layer, a barrier layer, and a sealant layer laminated in this order from the outside, in which the sealant layer contains a biaxially stretched polybutylene terephthalate film, can be suitably used particularly as a casing material for all-solid-state batteries, and have completed the present invention.

[0009] That is, the present invention provides the following [1] to [8]. [1] A storage battery packaging material comprising a base layer, a barrier layer, and a sealant layer laminated in this order from the outside, wherein the sealant layer contains a biaxially oriented polybutylene terephthalate film. [2] The storage battery packaging material according to [1], wherein the biaxially oriented polybutylene terephthalate film has a tensile breaking strength of 170 MPa or more in all four directions (0° (MD), 45°, 90° (TD), 135°), a ratio of the maximum to the minimum tensile breaking strengths in the four directions (maximum / minimum) of 1.5 or less, and a tensile breaking elongation in all four directions of 50% or more and 200% or less. [3] The biaxially oriented polybutylene terephthalate film according to [2], wherein the biaxially oriented polybutylene terephthalate film has a tensile breaking strength of 140 MPa or more in two directions (0° (MD) and 90° (TD)) and a tensile breaking elongation of 50% or more and 200% or less, measured after being left at 135°C for 500 hours or at 80°C and a relative humidity of 85% for 500 hours. [4] The biaxially oriented polybutylene terephthalate film according to [2], wherein the base material layer is a multilayer film, and the outermost film on the barrier layer side of the base material layer is a biaxially oriented film having a tensile breaking strength of 170 MPa or more in all four directions (0° (MD), 45°, 90° (TD), 135°), a ratio of the maximum to the minimum tensile breaking strengths in the four directions (maximum / minimum) of 1.5 or less, and a tensile breaking elongation of 50% or more and 200% or less. [5] The battery casing material according to [4], wherein the biaxially stretched film is a biaxially stretched polyamide film or a biaxially stretched polybutylene terephthalate film. [6] A battery case having a battery storage compartment formed using the battery casing material according to any one of [1] to [5]. [7] A battery in which a battery main body is enclosed in the battery storage compartment of the battery case according to [6]. [8] The battery according to [7], wherein the battery is an all-solid-state battery.

[0010] The present invention can provide a storage battery packaging material that is excellent in heat resistance, long-term durability, and cold formability, and a storage battery case and a storage battery that use the storage battery packaging material.

[0011] Fig. 1 is a schematic cross-sectional view of an exterior packaging material for a storage battery of the present invention. Fig. 2 is a schematic cross-sectional view of an exterior packaging material for a storage battery of the present invention. Fig. 3 is a schematic cross-sectional view of a storage battery of the present invention. Fig. 4 is a schematic plan view of a storage battery of the present invention.

[0012]

[0023] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 shows a battery packaging material 5 formed by laminating a base material layer 1, a barrier layer 2, and a sealant layer 3 in this order from the outside. The surface of the sealant layer 3 opposite to the surface on the barrier layer side is a sealing surface 4.

[0013] <Sealant Layer> In the exterior packaging material for a storage battery of the present invention, the sealant layer 3 is a single layer or multilayer, and contains a biaxially stretched polybutylene terephthalate film.

[0014] (Raw Materials for Biaxially Stretched Polybutylene Terephthalate Film) The raw materials used for biaxially stretched polybutylene terephthalate films are not particularly limited as long as they are polyesters containing butylene terephthalate as the main repeating unit. Specifically, they are homo-type polybutylene terephthalates obtained by condensing 1,4-butanediol or its ester-forming derivatives as the glycol component and terephthalic acid or its ester-forming derivatives as the dibasic acid component as the main components, or copolymer-type polyesters mainly composed of polybutylene terephthalate. To impart optimal mechanical strength characteristics to biaxially stretched polybutylene terephthalate films, polybutylene terephthalates having a melting point of 200 to 250°C and an intrinsic viscosity (IV value) of 1.10 to 1.35 dL / g are preferred, with those having a melting point of 215 to 225°C and an intrinsic viscosity (IV value) of 1.15 to 1.30 dL / g being particularly preferred. The intrinsic viscosity is measured in accordance with JIS K7367 by pulverizing polybutylene terephthalate pellets, dissolving them in a solvent (tetrachloroethane:phenol=1:1 volume ratio).

[0015] The copolymer-type polyester mainly composed of polybutylene terephthalate as described above is a polyester obtained by condensing a dibasic acid component in which a portion of the terephthalic acid component has been replaced with another dibasic acid component such as isophthalic acid, phthalic acid, adipic acid, or sebacic acid, and / or a glycol component in which a portion of the 1,4-butanediol component has been replaced with another glycol component such as ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, or cyclohexanedimethanol, and preferably contains 70% or more butylene terephthalate units.

[0016] The polybutylene terephthalate used in the present invention may be mixed with or laminated with other polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyhexamethylene terephthalate, and poly(ethylene terephthalate / ethylene isophthalate), or other resins such as polycarbonate and polyamide, to the extent that the physical properties are not adversely affected. Furthermore, if necessary, additives such as lubricants, antiblocking agents, inorganic fillers, antioxidants, UV absorbers, antistatic agents, flame retardants, plasticizers, colorants, crystallization inhibitors, and crystallization accelerators may be added to the polybutylene terephthalate used in the present invention (or, in some cases, the above-mentioned polyester resins and other resins). Furthermore, to avoid a decrease in viscosity due to hydrolysis during heat melting, it is preferable to thoroughly pre-dry the polybutylene terephthalate pellets before heat melting so that the moisture content is 0.05% by mass or less, preferably 0.02% by mass or less.

[0017] (Method for manufacturing unstretched polybutylene terephthalate raw sheet) In order to stably biaxially stretch unstretched polybutylene terephthalate raw sheet, it is necessary to minimize crystallization of the unstretched raw sheet. When cooling the extruded polybutylene terephthalate melt to form a film, the melt must be cooled at a rate above the crystallization temperature range, i.e., the raw sheet cooling rate is an important factor. The raw sheet cooling rate is 200°C / sec or higher, preferably 250°C / sec or higher, and particularly preferably 350°C / sec or higher. Unstretched raw sheets formed into films at high cooling rates maintain an extremely low crystalline state, dramatically improving bubble stability during stretching. Furthermore, high-speed film formation is possible, thereby improving productivity. If the cooling rate is less than 200°C / sec, the resulting unstretched raw sheet will have high crystallinity and poor stretchability. As a result, in extreme cases, the stretching bubble may burst, making it impossible to continue stretching. The raw web film production method is not particularly limited as long as it satisfies the raw web cooling rate. However, in terms of rapid film production, the internal and external direct water cooling method is most suitable. An outline of the raw web film production method using the internal and external direct water cooling method is described below. First, polybutylene terephthalate pellets are melt-kneaded in an extruder set at a temperature of 210 to 270°C. In the case of T-die film production, the sheet-shaped molten resin is directly water-cooled both inside and outside by immersing it in a water tank. On the other hand, in the case of annular film production, the molten resin is extruded downward through an annular die attached downward to the extruder to form a molten tubular thin film. Next, the molten tubular thin film is introduced into a cooling mandrel connected to the annular die, and cooling water introduced from each nozzle of the cooling mandrel directly contacts the inside of the molten tubular thin film to cool it. Simultaneously, cooling water is also flowed from an external cooling tank used in combination with the cooling mandrel, and cooling water also directly contacts the outside of the molten tubular thin film to cool it. The temperatures of the internal water and external water are preferably 30° C. or less, and from the viewpoint of rapid cooling film formation, particularly preferably 20° C. or less. If the temperature is higher than 30° C., whitening of the raw sheet or poor appearance of the raw sheet due to boiling of the cooling water may occur, and stretching may gradually become difficult.

[0018] (Method for producing biaxially oriented polybutylene terephthalate film) Unstretched polybutylene terephthalate raw material must be transported to the stretching zone while maintaining an ambient temperature of 25°C or less, preferably 20°C or less. Under this temperature control, the crystallinity of the unstretched raw material immediately after film formation can be maintained regardless of the residence time. This crystallization control up to the start of stretching, along with the film formation technology for the unstretched raw material, is important for stably performing biaxial stretching of the unstretched polybutylene terephthalate raw material. The biaxial stretching method is not particularly limited and can be appropriately selected from, for example, a tubular system, a tenter system, simultaneous longitudinal and transverse biaxial stretching, or a sequential biaxial stretching system. In terms of the balance of physical properties in the circumferential direction of the resulting biaxially oriented polybutylene terephthalate film, simultaneous biaxial stretching by the tubular system is particularly preferred. The unstretched raw fabric introduced into the stretching zone is passed through a pair of low-speed nip rolls and heated by a stretching heater while pressurized air is injected between them. Simultaneously, air is blown from a cooling shoulder air ring at the end point of stretching. This results in a simultaneous biaxially stretched film in the machine direction (hereinafter also referred to as MD) and the direction perpendicular to the machine direction (hereinafter also referred to as TD) by the tubular method. Considering the stretching stability and the strength properties, transparency, and thickness uniformity of the resulting biaxially stretched polybutylene terephthalate film, the stretching ratio is preferably in the range of 2.7 to 4.0 times in both MD and TD. A stretching ratio less than 2.7 times is undesirable because the resulting biaxially stretched polybutylene terephthalate film will have insufficient tensile strength and impact strength. Furthermore, a stretching ratio greater than 4.0 times causes excessive molecular chain distortion due to stretching, resulting in frequent breakages and punctures during stretching, potentially hindering stable production. Furthermore, entanglement of molecular chains during heat sealing may be reduced, resulting in a risk of reduced seal strength. The stretching temperature is preferably in the range of 40 to 80°C, and particularly preferably 45 to 65°C. The unstretched raw film produced at the above-mentioned high cooling rate has low crystallinity and can therefore be stably stretched at a relatively low stretching temperature range. High-temperature stretching above 80°C may cause the stretching bubble to sway violently, resulting in significant stretching unevenness and the risk of not being able to obtain a film with good thickness precision.On the other hand, at a stretching temperature of less than 40°C, excessive stretch-oriented crystallization occurs due to low-temperature stretching, leading to whitening of the film and, in some cases, the stretching bubbles may burst, making it difficult to continue stretching. By performing biaxial stretching in this way, it is possible to obtain a biaxially stretched polybutylene terephthalate film with significantly improved strength properties and little anisotropy.

[0019] The obtained biaxially stretched polybutylene terephthalate film can be placed in a heat treatment facility using a hot roll system, a tenter system, or a combination of these for a desired period of time and heat-treated at 180 to 240°C, particularly preferably 190 to 210°C, to obtain a biaxially stretched polybutylene terephthalate film with excellent thermal dimensional stability. If the heat treatment temperature is higher than 240°C, the bowing phenomenon may become too large, increasing anisotropy in the width direction, or the crystallinity may become too high, resulting in a decrease in strength properties. On the other hand, if the heat treatment temperature is lower than 180°C, the thermal dimensional stability of the film may be significantly reduced, making the film prone to shrinkage during lamination, printing, and heat sealing, which may cause practical problems.

[0020] The total thickness of the sealant layer 3 containing a biaxially oriented polybutylene terephthalate film is preferably 5 to 50 μm, more preferably 15 to 40 μm, and even more preferably 25 to 35 μm. When the sealant layer 3 is a single layer and is made of a biaxially oriented polybutylene terephthalate film, its thickness is preferably 5 to 50 μm, more preferably 15 to 40 μm, and even more preferably 25 to 35 μm. If the total thickness of the sealant layer 3 (including when the sealant layer 3 is a single layer) is less than 5 μm, the impact resistance of the battery packaging material may be reduced, cold formability may be insufficient, and heat seal strength may be reduced. On the other hand, if the total thickness of the sealant layer 3 (including when the sealant layer 3 is a single layer) exceeds 50 μm, although the shape retention strength and heat seal strength are improved, the effects on improving breakage prevention and formability are small, and it simply reduces the mass and volumetric energy density, which is undesirable.

[0021] The tensile strength of the biaxially stretched polybutylene terephthalate film in all four directions (0° (MD), 45°, 90° (TD), 135°) is preferably 170 MPa or more, more preferably 180 MPa or more, even more preferably 190 MPa or more, particularly preferably 200 MPa or more, and even more particularly preferably 205 MPa or more. In addition, to reduce anisotropy, the ratio of the maximum to the minimum tensile strength (maximum / minimum) in the four directions (0° (MD), 45°, 90° (TD), 135°) is preferably adjusted to 1.5 or less, more preferably adjusted to 1.4 or less, even more preferably adjusted to 1.3 or less, particularly preferably adjusted to 1.2 or less, and even more particularly preferably adjusted to 1.1 or less. Furthermore, in order to prevent breakage or elongation of the film due to tension when laminating it to a barrier layer (e.g., a metal foil), the tensile breaking elongation in all four directions is preferably 50% or more and 200% or less, more preferably 70% or more and 190% or less, even more preferably 80% or more and 180% or less, particularly preferably 90% or more and 175% or less, and even particularly preferably 100% or more and 170% or less. By having the tensile breaking strength, the ratio of the maximum to the minimum of the tensile breaking strengths in the four directions, and the tensile breaking elongation in all four directions all fall within the above ranges, regardless of the shape or forming depth, even if a metal foil or the like is used as a barrier layer during cold forming, the metal foil or the like is less likely to break, and stable formability can be ensured. If the tensile strength at break in any one direction is less than 170 MPa, or if the ratio of the maximum to the minimum of the tensile strengths in the four directions (maximum / minimum) is greater than 1.5, or if the tensile elongation at break in all four directions is greater than 200% or less than 50%, the barrier layer (e.g., metal foil) or the biaxially oriented polybutylene terephthalate film itself may easily break during cold forming, making it difficult to obtain stable formability. Furthermore, the 50% modulus values ​​in all four directions are preferably 90 MPa or more. If the 50% modulus values ​​in all four directions are 90 MPa or more, more stable formability can be ensured.The tensile strength and elongation at break and 50% modulus value in four directions (0° (MD), 45°, 90° (TD), 135°) of the biaxially stretched polybutylene terephthalate film used in the present invention are determined from a stress-strain curve obtained by a tensile test (sample width 15 mm, chuck distance 100 mm, tensile speed 200 mm / min).

[0022] Furthermore, it is preferable that the biaxially stretched polybutylene terephthalate film exhibits little deterioration in strength and elongation properties under the high temperatures and high humidity conditions expected for the use of storage batteries such as all-solid-state batteries. The biaxially stretched polybutylene terephthalate film preferably has a tensile break strength of 140 MPa or more in two directions (0° (MD) and 90° (TD)) when measured after being left at 135°C for 500 hours or at 80°C and 85% relative humidity (RH) for 500 hours. The tensile break elongation in the two directions is preferably 50% to 200%, more preferably 70% to 195%, even more preferably 80% to 190%, particularly preferably 90% to 185%, and even more preferably 100% to 180%. Because the biaxially stretched polybutylene terephthalate film has a tensile strength at break and a tensile elongation at break in these ranges, it is less likely to break or stretch even when used for a long period of time at high temperatures and high humidity, and has excellent durability. This makes it a suitable exterior material for all-solid-state batteries, whose thickness changes due to expansion and contraction during charging and discharging. A film with such properties can be stably obtained by the above-mentioned manufacturing method. In a more preferred embodiment, the biaxially stretched polybutylene terephthalate film has a tensile strength at break in both directions (0° (MD) and 90° (TD)) of preferably 140 MPa or more, more preferably 145 MPa or more, even more preferably 150 MPa or more, particularly preferably 155 MPa or more, and even particularly preferably 160 MPa or more, measured after being left at 135°C for 500 hours and at 80°C and a relative humidity (RH) of 85% for 500 hours. Furthermore, the tensile elongation at break in the two directions is preferably 50% or more and 200% or less, more preferably 70% or more and 195% or less, even more preferably 80% or more and 190% or less, particularly preferably 90% or more and 185% or less, and even more particularly preferably 100% or more and 180% or less.

[0023] (Sealing Surface) In the sealant layer 3 of the present invention, the sealing surface 4 located on the surface opposite to the barrier layer side may be treated with corona, plasma, ultraviolet light, or heat, or may be coated with a heat-resistant polyester-based sealing agent by in-line or off-line treatment in order to improve the sealing strength.

[0024] <Substrate Layer> The substrate layer 1 of the present invention is composed of a single-layer or multi-layer film. Biaxially oriented films are preferred as the film, and examples thereof include films made of polyester, polyamide, polyphenyl sulfide, polyether ether ketone, etc. Examples of the polyester film include films made of polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, polytrimethylene terephthalate, polyhexamethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, etc., which may be used alone or in combination of two or more. Examples of the polyamide film include films made of nylon (polyamide) 6, nylon 6 / 6, nylon 11, nylon 12, nylon 6 / 10, nylon 6 / 12, nylon 6 / 6 / 12 copolymer, other polyamide copolymers, polymetaxylylene adipamide (nylon MXD6), aramid, etc., which may be used alone or in combination of two or more. Among these films, biaxially oriented polyethylene terephthalate film, biaxially oriented polyamide film, and biaxially oriented polybutylene terephthalate film are particularly preferred. When the base layer 1 is multilayered, a combination of a biaxially oriented polyethylene terephthalate film and a biaxially oriented polyamide film is preferred, and a combination of a biaxially oriented polyethylene terephthalate film and a biaxially oriented polybutylene terephthalate film is preferred.

[0025] When the base layer 1 is a single layer, the film constituting the base layer 1 is preferably a biaxially stretched film, as described above. When the base layer 1 is a multilayer (two or more layers), it is particularly preferable that the film of the outermost layer on the barrier layer side of the base layer 1 is a biaxially stretched film, as described above. For example, when the base layer 1 is two layers as shown in FIG. 2 , the film of the outermost layer on the barrier layer side of the base layer 1 corresponds to base layer 1b. The biaxially stretched film preferably has a tensile breaking strength of 170 MPa or more in all four directions (0° (MD), 45°, 90° (TD), 135°) of 170 MPa or more, more preferably 180 MPa or more, even more preferably 190 MPa or more, particularly preferably 200 MPa or more, and even particularly preferably 205 MPa or more. Furthermore, the biaxially stretched film preferably has a ratio of the maximum to the minimum (maximum / minimum) of the tensile breaking strengths in all four directions of 1.5 or less, more preferably 1.4 or less, even more preferably 1.3 or less, particularly preferably 1.2 or less, and even particularly preferably 1.1 or less. For the outermost film on the barrier layer side of the substrate layer 1, the tensile breaking strengths in all four directions and the ratio of the maximum to the minimum (maximum / minimum) of the tensile breaking strengths in the four directions are within these ranges, so that the barrier layer (e.g., metal foil) is less likely to break during cold forming, regardless of the shape or forming depth, and stable formability can be ensured. If the tensile breaking strength in any one direction of the biaxially stretched film is less than 170 MPa, or if the ratio of the maximum to the minimum (maximum / minimum) of the tensile breaking strengths in the four directions is greater than 1.5, the barrier layer (e.g., metal foil) or the biaxially stretched film itself may easily break during cold forming, resulting in unstable formability. On the other hand, the tensile elongation at break in all four directions is preferably 50% or more and 200% or less, more preferably 70% or more and 190% or less, even more preferably 80% or more and 180% or less, particularly preferably 90% or more and 175% or less, and even more particularly preferably 100% or more and 170% or less.If the tensile elongation at break in all four directions is greater than 200% or less than 50%, the film is likely to break or elongate due to the tension when it is laminated to a barrier layer (e.g., a metal foil), which is undesirable. Furthermore, the 50% modulus values ​​in all four directions are preferably 90 MPa or more. When the 50% modulus values ​​in all four directions are 90 MPa or more, more stable formability can be ensured.

[0026] When the substrate layer 1 is a single layer, by constructing the film constituting the substrate layer 1 from a biaxially oriented film having the same tensile breaking strength and tensile breaking elongation as those of the sealant layer 3, and when the substrate layer 1 is a multilayer, by constructing the outermost film on the barrier layer side of the substrate layer 1 from a biaxially oriented film having the same tensile breaking strength and tensile breaking elongation as those of the sealant layer 3, stress during cold forming is applied uniformly from both sides of the barrier layer 2 (e.g., metal foil) described below, making it less likely that cracks or pinholes will occur, allowing for deeper forming, and improving cold formability. When the substrate layer 1 is a single layer, the film constituting the substrate layer 1 is particularly preferably a biaxially oriented polyethylene terephthalate film, a biaxially oriented polyamide film, or a biaxially oriented polybutylene terephthalate film. When the substrate layer 1 is a multilayer, the outermost film on the barrier layer side of the substrate layer 1 is particularly preferably a biaxially oriented polyamide film or a biaxially oriented polybutylene terephthalate film.

[0027] When the base layer 1 is multilayered, the outermost film on the surface side is preferably a film for protecting the outermost film on the barrier layer side. For example, when the base layer 1 is two-layered as shown in Fig. 2, the outermost film on the surface side corresponds to the base layer 1a laminated on the base layer 1b on the barrier layer side. When the base layer 1 is multilayered, the outermost film on the surface side is preferably a polyester-based stretched film that has higher heat resistance than the biaxially stretched polybutylene terephthalate film contained in the sealant layer 3, has excellent abrasion resistance in various storage battery processing steps, and long-term durability in environments ranging from low temperature and low humidity to high temperature and high humidity, and does not impair cold formability, and is more preferably a biaxially stretched polyethylene terephthalate film.

[0028] The thickness of the substrate layer 1 (including the case where the substrate layer 1 is two or more layers) is preferably 5 to 50 μm, more preferably 10 to 30 μm. If the thickness is less than 5 μm, the impact resistance of the battery packaging material may be reduced, and cold formability may be insufficient. On the other hand, if the thickness exceeds 50 μm, although the strength for maintaining the shape is improved, the effects on preventing breakage and improving formability are small, and the volume and weight energy density are simply reduced, which is undesirable.

[0029] For example, when the substrate layer 1 has two layers as shown in FIG. 2 , a preferred embodiment is one in which the substrate layer 1a on the surface side of the substrate layer 1 is a biaxially oriented polyethylene terephthalate film, the substrate layer 1b on the barrier layer side is a biaxially oriented polyamide film or a biaxially oriented polybutylene terephthalate film, and the sealant layer 3 is a biaxially oriented polybutylene terephthalate film. In this embodiment, the thickness of the biaxially oriented polyethylene terephthalate film of the substrate layer 1a on the surface side is 5 to 20 μm, more preferably 10 to 15 μm. If the thickness of the substrate layer 1a on the surface side is less than 5 μm, wrinkles are likely to occur when laminating the substrate layer 1b on the barrier layer side with an adhesive described below, which may cause problems in the lamination process and may reduce the protective function for the substrate layer 1b on the barrier layer side. If the thickness of the substrate layer 1a on the surface side is greater than 20 μm, the protective function is improved, but cold formability may be reduced.

[0030] <Base layer: biaxially stretched polyamide film> When the base layer 1 is a biaxially stretched polyamide film, the biaxially stretched polyamide film is preferably produced using the following materials and production method.

[0031] (Raw Materials for Polyamide Film) The raw materials for the polyamide film that can be used in the present invention are not particularly limited as long as they are polyamide-based resins. Examples include nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, nylon 612, nylon 6,66,12 copolymers, other polyamide-based copolymers, polymetaxylylene adipamide (nylon MXD6), aramid, polyamideimide (PAI), aromatic polyimide, polyetherimide (PEI), polymaleimide amine (PMIA), and polyaminobismaleimide (PABM). However, nylon 6 is most preferred from the viewpoint of film properties, primarily productivity, cold formability, and strength. Furthermore, when nylon 6 is used as the raw material, its number average molecular weight is preferably 10,000 to 30,000, and particularly preferably 22,000 to 24,000. If the number average molecular weight is less than 10,000, the impact strength and tensile strength of the resulting polyamide film may be insufficient. Furthermore, if the number average molecular weight is greater than 30,000, the molecular chains will be significantly entangled, and excessive strain will occur during stretching, resulting in frequent breakages and punctures during stretching, which may hinder stable production. The number average molecular weight is the polystyrene-equivalent number average molecular weight determined by gel permeation chromatography (GPC) measurement.

[0032] (Method for Producing Biaxially Stretched Polyamide Film) The polyamide film that can be used in the present invention is obtained by biaxially stretching an unstretched raw film made of any of the polyamide resins described above under conditions that result in a stretch ratio of 2.8 to 4.0 in each of the MD and TD, followed by heat treatment at a temperature of 180 to 220°C. The stretch ratio is preferably in the range of 2.8 to 4.0 in each of the MD and TD, and particularly preferably in the range of 3.0 to 3.4. If the stretch ratio is less than 2.8 in each of the MD and TD, the impact strength and tensile strength of the resulting biaxially oriented polyamide film may be insufficient. Furthermore, if the stretch ratio is 4.0 or more in each of the MD and TD, excessive molecular chain strain occurs due to stretching, which may frequently cause breakage or punctures during stretching, resulting in the risk of unstable production. Examples of biaxial stretching methods include simultaneous biaxial stretching by a tubular method or a tenter method, and sequential biaxial stretching, but simultaneous biaxial stretching by the tubular method is preferred in terms of the balance of strength in the longitudinal and transverse directions. By performing such biaxial stretching processing, it is possible to obtain a biaxially stretched polyamide film that is excellent in cold formability and in particular in strength properties.

[0033] The resulting stretched film can be placed in a heat treatment facility using a hot roll system, a tenter system, or a combination of these for a desired period of time and heat-treated at 180 to 220°C, preferably 190 to 210°C, to obtain a biaxially stretched polyamide film that can be used in the present invention. Heat treatment temperatures higher than 220°C can result in excessive bowing, increasing anisotropy in the width direction, or excessively high crystallinity, potentially resulting in reduced strength. Heat treatment temperatures lower than 180°C can significantly reduce the thermal dimensional stability of the film, potentially leading to shrinkage during lamination or delamination during the heat-sealing process after cold forming, potentially causing practical problems.

[0034] The thickness of the biaxially oriented polyamide film is preferably 5 to 50 μm, more preferably 10 to 30 μm. If the thickness of the biaxially oriented polyamide film is less than 5 μm, the impact resistance of the battery packaging material may be reduced, and cold formability may be insufficient. On the other hand, if the thickness of the biaxially oriented polyamide film exceeds 50 μm, although the strength for maintaining the shape is improved, the effects on preventing breakage and improving formability are small, and the volume and weight energy density are simply reduced, which is undesirable.

[0035] The maximum value of the heat shrinkage stress of the biaxially oriented polyamide film at 170 to 210°C is preferably 5.0 MPa or less in both MD and TD. When the maximum value of the heat shrinkage stress of the biaxially oriented polyamide film in both MD and TD is 5.0 MPa or less, stable quality can be maintained even during secondary processing such as heat sealing after molding. If the maximum value of the heat shrinkage stress in either MD or TD exceeds 5.0 MPa, the heat shrinkage stress of the base layer increases, which is undesirable because delamination (peeling) easily occurs between the barrier layer and the base layer, particularly during heat sealing in which heat of around 200°C is applied to the base layer. The heat shrinkage stress of a biaxially stretched polyamide film is measured after conditioning the biaxially stretched polyamide film in an environment of 23°C x 50% humidity for 2 hours, using an EXSTAR-TMA / SS6100 manufactured by SII Nano Technology Co., Ltd., with a sample width of 3 mm, a chuck distance of 15 mm, and a temperature program of 30 to 245°C (heating rate: 10°C / min).

[0036] <Base layer: biaxially stretched polybutylene terephthalate film> When the base layer 1 is a biaxially stretched polybutylene terephthalate film, the biaxially stretched polybutylene terephthalate film is preferably produced using the same material and by the same production method as the biaxially stretched polybutylene terephthalate film contained in the sealant layer.

[0037] <Barrier Layer> Examples of the barrier layer 2 include various metal foils such as aluminum and stainless steel. From the viewpoints of moisture resistance, processability (e.g., ductility), and cost, aluminum foil is preferred as the metal foil. Furthermore, aluminum foil made of a soft aluminum-iron alloy is more preferred because of its excellent pinhole resistance and ductility during molding. Furthermore, to prevent dissolution and corrosion, the barrier layer 2 may be subjected to a hydrothermal modification treatment, a chemical conversion treatment, or a plating treatment. Furthermore, a corrosion-resistant coating may be provided on one or both sides of the barrier layer 2 by coating. Furthermore, to improve adhesion during lamination, one or both sides of the aluminum foil may be subjected to a surface treatment such as an undercoat treatment with a coupling agent such as a silane coupling agent or a titanium coupling agent, or a corona discharge treatment. The thickness of the barrier layer 2 (e.g., metal foil) is preferably 6 μm to 200 μm, more preferably 15 μm to 150 μm, and even more preferably 20 μm to 100 μm. If the thickness of the barrier layer 2 is less than 6 μm, the layer is likely to break when stress is applied during molding. On the other hand, if the thickness of the barrier layer 2 exceeds 200 μm, molding becomes difficult, the volume and mass of the battery packaging material increase, and the volume and weight energy density of the battery decrease.

[0038] <Storage Battery Exterior Material> The storage battery exterior material 5, which is formed by laminating a substrate layer 1, a barrier layer 2, and a sealant layer 3, can be produced by a dry lamination method in which the substrate layer 1, the barrier layer 2, and the sealant layer 3 are laminated together via an adhesive. The resin used as the adhesive is not particularly limited, but examples include adhesives that use a resin such as a polyester resin, an epoxy resin, a polyurethane resin, a polyester-epoxy copolymer resin, or a polyesterurethane-epoxy copolymer as a main agent and one or more of an isocyanate resin, a melamine resin, an oxazoline resin, or a phenolic resin as a curing agent. An adhesive layer formed using such an adhesive is suitable for cold forming. In the present invention, the dry application amount of the adhesive for the storage battery exterior material is 1 g / m ２ ~10g / m ２ is preferred, and 2 g / m ２ ~9g / m ２More preferably, 3 g / m ２ ~8g / m ２ More preferably, 4 g / m ２ ~7g / m ２ Here, the dry coating amount refers to the amount of solid content of the adhesive after application and drying. Furthermore, the total thickness of the battery packaging material 5 of the present invention is preferably 600 μm or less, more preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, particularly preferably 200 μm or less, and even more particularly preferably 150 μm or less. When the dry coating amount of the adhesive is 1 g / m ２ If the dry adhesive application amount is less than 10 g / m, cracks and pinholes are likely to occur at the corners when cold forming is performed deeply. ２ If the thickness exceeds 100 μm, or if the total thickness of the exterior packaging material 5 for a storage battery of the present invention exceeds 600 μm, it becomes difficult to design corners by cold forming, making it impossible to obtain a molded product with a sharp shape, and there is a risk that the volume and weight energy efficiency will also deteriorate.

[0039] [Battery Case] ​​The present invention includes a battery case 6 in which a battery storage section 7 is formed using the battery exterior material 5 described above, with the sealant layer 3 serving as the innermost layer. The battery case 6 of the present invention is particularly suitable for use as a battery case for an all-solid-state battery. Furthermore, since the battery exterior material 5 of the present invention has excellent formability, the battery case 6 of the present invention can be easily obtained by molding it according to a known method. While the molding method is not particularly limited, cold (room temperature) molding (stretch molding or deep drawing) can be used to produce battery cases with complex shapes and high dimensional accuracy. It is also possible to produce a battery case with a cold-formed recess and a flat portion that serves as a lid when a battery is placed in the recess and sealed.

[0040] [Storage Battery] For example, Figures 3 and 4 are schematic cross-sectional and plan views showing a storage battery 12 manufactured using the storage battery exterior material 5 of the present invention. As shown in both figures, the storage battery 12 of the present invention has the following configuration. A storage battery body 8 of an all-solid-state battery, with tab leads 9 connected to the positive and negative electrodes, is placed in a storage battery storage section 7 of a storage battery case 6 obtained by molding the storage battery exterior material 5. Furthermore, a lid member 10 made of the planar (sheet-like) storage battery exterior material 5 is placed on the storage battery body 8 with its sealant layer 3 side facing inward (lower). The sealant layer 3 on the outer peripheral edge 10a of the lid member and the sealant layer 3 on the flange portion (sealing peripheral portion) 6a of the storage battery case are sealed by heat sealing or ultrasonic sealing. The inner surface of the storage battery storage section 7 is made of the sealant layer 3. In FIG. 3 , the reference numeral "11" denotes a seal formed by joining (welding) the outer peripheral edge 10a of the lid member and the flange (sealing peripheral edge) 6a of the battery case. Furthermore, the process of enclosing the battery body 8 in the battery housing portion 7 of the battery case 6 preferably comprises the following steps, from the viewpoint of suppressing thickness changes due to charging and discharging of the all-solid-state battery. This process comprises seal-joining the tab lead 9 except for one side protruding from the battery body 8, and then seal-joining the remaining side while evacuating the interior of the battery, including the battery housing portion 7, to seal the battery body 8. The battery 12 is not particularly limited, but examples thereof include a lithium-ion secondary battery and a sodium-ion secondary battery. The solid electrolyte may be any solid electrolyte, such as a sulfide-based or oxide-based solid electrolyte.

[0041] The present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to these examples. The substrate layer, sealant layer, barrier layer (metal foil), and adhesive used in the examples are shown below. <Substrate Layer> (1) OPBT1: Biaxially Stretched Polybutylene Terephthalate Film Polybutylene terephthalate pellets (homotype, melting point = 224°C, IV value = 1.26 dl / g) dried in a hot air dryer at 140°C for 5 hours were melt-kneaded in an extruder at cylinder and die temperatures of 210 to 260°C, and a molten tubular thin film was extruded downward from an annular die. Subsequently, the film was passed through the outer diameter of a cooling mandrel and folded by a carapace roll, and then taken up by a take-up nip roll at a speed of 1.2 m / min. The unstretched film produced under these conditions was transported to a low-speed nip roll in an atmosphere of 20°C and subjected to simultaneous longitudinal and transverse biaxial stretching using a tubular method. The stretching ratios were 3.1 times in MD and 3.2 times in TD, and the stretching temperature was 60°C. Next, this biaxially stretched film was placed in a hot roll type heat treatment facility, and then in a tenter type heat treatment facility, where it was heat-treated at 205°C to obtain a biaxially stretched polybutylene terephthalate film (OPBT1). The thickness of OPBT1 was 15 μm. (2) OPBT4: Biaxially stretched polybutylene terephthalate film (manufactured by Toyobo Co., Ltd., Toughstar (registered trademark), thickness 25 μm) (3) CPBT: Unstretched polybutylene terephthalate film (manufactured by OG Film Co., Ltd., Ultra Soft PBT, thickness 25 μm)

[0042] (4) ONY: Biaxially oriented polyamide film. Nylon (polyamide) 6 pellets (relative viscosity 3.48) were melt-kneaded at 255°C in an extruder by adjusting the cylinder and die temperatures. The melt was then extruded downward through a circular die. Subsequently, the pellets were passed through the outer diameter of a cooling mandrel, folded by a carapace roll, and then taken up by a take-up nip roll at a speed of 1.2 m / min. The unstretched film produced under these conditions was transported to a low-speed nip roll in an atmosphere of 20°C and subjected to simultaneous longitudinal and transverse biaxial stretching using a tubular system. The stretch ratios were 3.0 times in the MD and 3.2 times in the TD. The stretched film was then placed in a hot roll heat treatment facility, then placed in a tenter heat treatment facility, and heat-treated at 210°C to obtain a biaxially oriented polyamide film. The thickness of this biaxially oriented polyamide film was 25 μm.

[0043] (5) OPET: Biaxially stretched polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., Toyobo Ester (registered trademark) Film E5001, thickness 12 μm, 25 μm)

[0044] <Sealant layer> (1) OPBT2 and 3: Biaxially stretched polybutylene terephthalate films A biaxially stretched polybutylene terephthalate film (OPBT2) having a thickness of 25 μm and a biaxially stretched polybutylene terephthalate film (OPBT3) having a thickness of 30 μm were obtained in the same manner as the biaxially stretched polybutylene terephthalate film of the base layer, except that the thickness of the obtained film was changed. (2) CPP: Unstretched polypropylene film (ET200, manufactured by Okamoto Corporation, thickness 80 μm)

[0045] <Barrier Layer (Metal Foil)> Aluminum A: Aluminum foil (manufactured by Toyo Aluminum K.K., thickness 40 μm)

[0046] <Adhesives> Adhesive A: Two-component reactive polyurethane adhesive (manufactured by Toyo-Morton Co., Ltd., base grade: TM-K55, hardener grade: CAT-10L, blending ratio (base / hardener): 100 / 10.5)

[0047] <Example 1> In FIG. 2, the base material layer 1a is OPET having a thickness of 12 μm, the base material layer 1b is ONY having a thickness of 15 μm, the barrier layer 2 is aluminum A having a thickness of 40 μm, and the sealant layer 3 is OPBT2 having a thickness of 25 μm. ２ ) and then aging was performed at 60°C for 72 hours to obtain an outer casing material for a storage battery of Example 1. <Example 2> Except for using OPBT3 having a thickness of 30 µm for the sealant layer 3, processing was performed in the same manner as in Example 1 to obtain an outer casing material for a storage battery of Example 2. <Example 3> Except for using OPBT1 having a thickness of 15 µm for the base material layer 1b, processing was performed in the same manner as in Example 1 to obtain an outer casing material for a storage battery of Example 3. <Example 4> In Fig. 1, the base material layer 1 was made of OPET having a thickness of 25 µm, the barrier layer 2 was made of aluminum A having a thickness of 40 µm, and the sealant layer 3 was made of OPBT2 having a thickness of 25 µm, and each was coated with adhesive A (dry coating amount 4.0 g / m ２ ) and then aging was performed at 60°C for 72 hours to obtain an outer casing material for a storage battery of Example 4. <Comparative Example 1> Except for using CPP with a thickness of 80 µm for the sealant layer 3, processing was performed in the same manner as in Example 1 to obtain an outer casing material for a storage battery of Comparative Example 1. <Comparative Example 2> Except for using OPBT4 with a thickness of 25 µm for the sealant layer 3, processing was performed in the same manner as in Example 4 to obtain an outer casing material for a storage battery of Comparative Example 2. <Comparative Example 3> Except for using CPBT with a thickness of 25 µm for the sealant layer 3, processing was performed in the same manner as in Example 1 to obtain an outer casing material for a storage battery of Comparative Example 3.

[0048] <Evaluation Items> (1) Tensile Breaking Strength and Elongation and 50% Modulus Value of OPBT1 to 4, CPBT, and ONY The tensile breaking strength and elongation of OPBT1 to 4, CPBT, and ONY were measured in all four directions, namely, 0°C (MD), 45°, 90° (TD), and 135°, using a Tensilon universal testing machine (model: RTC-1210-A) manufactured by Orientec Co., Ltd., under the conditions of a sample width of 15 mm, a chuck distance of 100 mm, and a pulling rate of 200 mm / min. The measurements were carried out after OPBT1 to 4, CPBT, and ONY were conditioned for 2 hours in an environment of 23°C and a relative humidity (RH) of 50%. The tensile strength at break, tensile elongation at break, and 50% modulus values ​​(excluding CPBT) in each direction, as well as the ratio of the maximum to minimum tensile strengths in the four directions, were determined based on the obtained stress-strain curves and are shown in Table 1. (2) Long-Term Durability of OPBT2 (2-1) Heat-Resistant Long-Term Durability Test of OPBT2 OPBT2 was left in a sheet-like condition at 135°C for 500 hours without load. The OPBT2 was then left in an environment of 23°C and 50% relative humidity (RH) for 24 hours, after which measurements were performed in both the MD and TD directions using a Tensilon universal testing machine (model: RTC-1210-A) manufactured by Orientec Co., Ltd., under conditions of a sample width of 15 mm, a chuck distance of 100 mm, and a tensile speed of 200 mm / min. Based on the obtained stress-strain curves, the tensile strength and tensile elongation at break after the heat-resistant long-term durability test were determined. The results are shown in Table 2. (2-2) Long-term wet heat durability test of OPBT2 OPBT2 was left in a sheet-like state without load at 80°C and a relative humidity of 85% for 500 hours. The OPBT2 was then left in an environment of 23°C and a relative humidity (RH) of 50% for 24 hours, after which measurements were performed in both the MD and TD directions using a Tensilon universal testing machine (model: RTC-1210-A) manufactured by Orientec Co., Ltd., under conditions of a sample width of 15 mm, a chuck distance of 100 mm, and a tensile speed of 200 mm / min. Based on the obtained stress-strain curve, the tensile strength and tensile elongation at break after the long-term wet heat durability test were determined. The results are shown in Table 2. (3) Cold Formability The battery packaging materials of Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to humidity control for 2 hours in an environment of 23°C and 50% RH, and then cold-molded (at room temperature) from the sealant layer side using a compression mold (38 mm x 38 mm) at a maximum load of 10 MPa.Cold formability was evaluated based on the maximum forming depth at which defects such as pinholes and cracks did not occur. The forming depth was evaluated in increments of 0.5 mm. The results are shown in Table 3. (4) Heat Sealability (4-1) Heat Sealability Evaluation Test at 23°C The battery packaging materials of Examples 1 to 4 and Comparative Examples 1 to 3 were folded in half and overlapped so that the sealing surfaces of the sealant layers faced each other. Then, heat sealing was performed approximately 10 mm inward from the fold under the following conditions to obtain heat-sealed samples of Examples 1 to 4 and Comparative Examples 1 to 3. The heat-sealed samples of Examples 1 to 4 and Comparative Examples 1 to 3 were then cut to a width of 15 mm and left in an environment of 23°C for 2 minutes. Thereafter, the heat-sealable samples of Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to T-peel using a Tensilon universal testing machine (model: RTC-1210-A) manufactured by Orientec Co., Ltd., with a chuck distance of 100 mm and a tensile speed of 300 mm / min, to measure the heat-seal strength (N / 15 mm) at 23°C, and the heat-sealability was evaluated according to the following evaluation criteria. The results are shown in Table 3. <Heat-sealing conditions for obtaining heat-sealed samples> Apparatus: Heat seal tester [manufactured by Tester Sangyo Co., Ltd. (model number: TP-701-B)] (for the battery exterior materials of Examples 1 to 4 and Comparative Examples 2 and 3 in which the sealant layer 3 is a polybutylene terephthalate film) Sealing temperature: 240°C Sealing width: 10 mm Pressure: 0.5 MPa Time: 4 seconds (for the battery exterior material of Comparative Example 1 in which the sealant layer 3 is CPP) Sealing temperature: 200°C Sealing width: 10 mm Pressure: 0.5 MPa Time: 4 seconds (4-2) Heat-sealability evaluation test at 150°C The same operation as in the heat-sealability evaluation test at 23°C was performed, except that the heat-sealed samples of Examples 1 to 4 and Comparative Examples 1 to 3 were left in an environment of 150°C for 2 minutes. The results are shown in Table 3. (4-3) Evaluation test of heat sealability at 190°C The same operation as in the evaluation test of heat sealability at 23°C was carried out, except that the heat-sealed samples of Examples 1 to 4 and Comparative Examples 1 to 3 were left in an environment of 190°C for 2 minutes. The results are shown in Table 3.(Evaluation criteria) A: Heat seal strength is 10N / 15mm or more B: Heat seal strength is 6N / 15mm or more and less than 10N / 15mm C: Heat seal strength is 3N / 15mm or more and less than 6N / 15mm D: Heat seal strength is less than 3N / 15mm.

[0049]

[0050]

[0051]

[0052] The results shown in Tables 1 to 3 show that the battery packaging materials of Examples 1 to 4, which contained OPBT 2 or 3 in the sealant layer 3 (OPBT 2 and 3 are biaxially oriented polybutylene terephthalate films that had a tensile breaking strength of 170 MPa or more in all four directions, a ratio of the maximum to the minimum tensile breaking strength in the four directions of 1.5 or less, and a tensile breaking elongation of 50% or more and 200% or less), had a heat seal strength of 10 N / 15 mm or more at 150°C, and even at 190°C, this was in the range of 6 N / 15 mm or more and less than 10 N / 15 mm, and there was no significant decrease in heat seal strength in a high-temperature environment. Furthermore, the battery casing materials of Examples 1 to 3, in which the base material layer 1b on the barrier layer side was a biaxially oriented polybutylene terephthalate film (OPBT1) or a biaxially oriented polyamide film, were evaluated for cold formability, with a maximum forming depth of 9 mm at which defects such as pinholes and cracks did not occur, demonstrating high formability. On the other hand, the battery casing material of Comparative Example 1, in which an unstretched polypropylene film was used for the sealant layer 3, had a heat seal strength of 10 N / 15 mm or more at 150°C but less than 3 N / 15 mm at 190°C, demonstrating inferior heat seal strength in high-temperature environments compared to the battery casing materials of Examples 1 to 4. Furthermore, the maximum forming depth at which defects such as pinholes and cracks did not occur was 6 mm at which cold formability was inferior to the battery casing materials of Examples 1 to 3. Furthermore, the battery casing material of Comparative Example 2, which used OPBT4 (OPBT4 is a biaxially oriented polybutylene terephthalate film with an MD tensile breaking strength of less than 170 MPa and a ratio of the maximum to minimum tensile breaking strength in four directions of more than 1.5) for the sealant layer 3, was found to have inferior cold formability, although the evaluation of heat seal strength was the same, compared to the battery casing material of Example 4, which had the same configuration except for using OPBT2 for the sealant layer 3.Furthermore, the battery packaging material of Comparative Example 3, which used an unstretched polybutylene terephthalate film for the sealant layer 3, had a heat seal strength of less than 6 N / 15 mm at 150°C and less than 6 N / 15 mm even at 190°C, indicating that the heat seal strength in a high-temperature environment was inferior to the battery packaging materials of Examples 1 to 4. In addition, the battery packaging material of Comparative Example 3 was also inferior in cold formability to the battery packaging material of Example 1, which had the same configuration except that OPBT2 was used for the sealant layer 3.

[0053] The present invention can provide a storage battery packaging material that is excellent in heat resistance, long-term durability, and cold formability, and a storage battery case and a storage battery that use the storage battery packaging material.

[0054] REFERENCE SIGNS LIST 1 substrate layer 1a surface-side substrate layer 1b barrier layer-side substrate layer 2 barrier layer 3 sealant layer 4 sealing surface 5 storage battery packaging material 6 storage battery case 6a flange portion (sealing peripheral edge portion) of storage battery case 7 storage battery storage portion 8 storage battery main body 9 tab lead 10 lid member 10a outer peripheral edge portion of lid member 11 sealing portion 12 storage battery

Claims

1. A casing material for a storage battery, which is formed by laminating a base layer, a barrier layer, and a sealant layer in this order from the outside, and which is characterized in that the sealant layer contains a biaxially oriented polybutylene terephthalate film.

2. The battery packaging material according to claim 1, characterized in that the biaxially stretched polybutylene terephthalate film has a tensile breaking strength of 170 MPa or more in all four directions (0° (MD), 45°, 90° (TD), 135°), a ratio of the maximum to the minimum tensile breaking strength in the four directions (maximum / minimum) of 1.5 or less, and a tensile breaking elongation of 50% or more and 200% or less in all four directions.

3. The battery packaging material according to claim 2, characterized in that the biaxially stretched polybutylene terephthalate film has a tensile breaking strength of 140 MPa or more in two directions (0° (MD), 90° (TD)) and a tensile breaking elongation of 50% or more and 200% or less, when measured after being left at 135°C for 500 hours or at 80°C and a relative humidity of 85% for 500 hours.

4. The battery packaging material according to claim 2, wherein the base layer is made of a multilayer film, and the outermost film on the barrier layer side of the base layer is a biaxially oriented film having a tensile breaking strength of 170 MPa or more in all four directions (0° (MD), 45°, 90° (TD), 135°), a ratio of the maximum to the minimum tensile breaking strengths in the four directions (maximum / minimum) of 1.5 or less, and a tensile breaking elongation of 50% or more and 200% or less in all four directions.

5. The battery packaging material according to claim 4, wherein the biaxially oriented film is a biaxially oriented polyamide film or a biaxially oriented polybutylene terephthalate film.

6. A battery case in which a battery storage section is formed using the battery packaging material according to any one of claims 1 to 5.

7. A storage battery in which a storage battery body is enclosed in the storage battery storage section of the storage battery case according to claim 6.

8. The storage battery according to claim 7, wherein the storage battery is an all-solid-state battery.