Pouch film laminate and secondary battery

Abstract

The pouch film laminate according to the present invention comprises a base layer, a sealant layer, and a gas barrier layer disposed between the base layer and the sealant layer, wherein the gas barrier layer comprises stainless steel, and the tensile breaking strength of the pouch film laminate is 130% to 250% of the tensile breaking strength of the gas barrier layer.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182364, filed December 22, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a pouch film laminate and a secondary battery produced by molding the same. [Background technology]

[0003] Generally, types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, lithium-ion polymer batteries, etc. These secondary batteries are used not only in small products such as digital cameras, DVD players, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products requiring high output such as electric vehicles and hybrid vehicles, power storage devices for storing surplus generated power and new renewable energy, and backup power storage devices.

[0004] To manufacture such a secondary battery, first, an electrode active material slurry is applied to a positive electrode current collector and a negative electrode current collector to form a positive electrode and a negative electrode, which are then stacked on both sides of a separator to form an electrode assembly of a predetermined shape.The electrode assembly is then placed in a battery case, an electrolyte is injected, and the battery case is sealed.

[0005] Secondary batteries are divided into pouch type and can type depending on the material of the case that houses the electrode assembly. Pouch type secondary batteries house the electrode assembly in a pouch made of flexible polymer material, while can type secondary batteries house the electrode assembly in a case made of metal or plastic.

[0006] The pouch, which is the case of a pouch-type secondary battery, is manufactured by pressing a flexible pouch film laminate to form a cup portion. Once the cup portion is formed, an electrode assembly is placed in the receiving space of the cup portion, and the seal portion is sealed to manufacture a secondary battery.

[0007] Generally, a pouch film laminate is formed of multiple layers, with a substrate layer laminated on one side of a metal gas barrier layer and a sealant layer laminated on the other side. Aluminum pouches, which use aluminum for the gas barrier layer, have the advantages of ensuring a certain level of mechanical strength, being lightweight, and providing support for the electrochemical properties of the electrode assembly and electrolyte, as well as heat dissipation. However, aluminum pouches can suffer from problems such as melting or deformation when the internal pressure and temperature of the cell increase due to a fire or other causes.

[0008] To address these issues, a technology has been developed that uses high-strength materials, such as stainless steel, instead of aluminum for the gas barrier layer to prevent deformation due to high temperatures and pressures. However, pouch film laminates using high-strength materials as gas barrier layers have poor formability, which can lead to problems such as insufficient forming depth during cup formation, resulting in breakage of the pouch film laminate. If the pouch film laminate does not have sufficient forming depth, the number of electrode assemblies that can be housed inside is limited, making it difficult to improve cell energy density.

[0009] Therefore, there is a need to develop a pouch film that can be durable under high temperature and pressure conditions and has sufficient processing depth. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a pouch film laminate and a pouch-type secondary battery that can improve the formability of the pouch. [Means for solving the problem]

[0011] According to one embodiment of the present invention, there is provided a pouch film laminate. The pouch film laminate may include a substrate layer, a gas barrier layer, and a sealant layer. The gas barrier layer may be disposed between the substrate layer and the sealant layer. The gas barrier layer may include stainless steel. The tensile break strength of the pouch film laminate may be 130% to 250% of the tensile break strength of the gas barrier layer.

[0012] Next, according to one embodiment of the present invention, the difference between the tensile breaking strength of the pouch film laminate and the tensile breaking strength of the gas barrier layer may be 30% to 150% of the tensile breaking strength of the gas barrier layer.

[0013] Next, according to one embodiment of the present invention, the tensile breaking strength of the pouch film laminate may be 400N / 15mm or more.

[0014] Next, according to the embodiment of the present invention, the tensile breaking strength of the gas barrier layer may be 300N / 15mm to 700N / 15mm.

[0015] Next, according to one embodiment of the present invention, the sum of the thickness of the base layer and the thickness of the sealant layer may be 200% to 500% of the thickness of the gas barrier layer.

[0016] Next, according to one embodiment of the present invention, the thickness of the pouch film laminate may be 80 μm to 300 μm.

[0017] Next, according to one embodiment of the present invention, the thickness of the gas barrier layer may be 40 μm to 100 μm.

[0018] Next, according to one embodiment of the present invention, the melting point of the gas barrier layer may be 1000° C. or more.

[0019] Next, according to one embodiment of the present invention, the stainless steel may contain 10% to 20% by weight of chromium.

[0020] Next, according to one embodiment of the present invention, the stainless steel may contain 5% to 20% by weight of nickel.

[0021] According to another embodiment of the present invention, a pouch-type secondary battery is provided. The pouch-type secondary battery may include a pouch-type battery case in which an electrode assembly is housed. The pouch-type battery case may include a pouch film laminate. The pouch-type battery case may be defined by the pouch film laminate. The pouch film laminate may include a substrate layer, a gas barrier layer, and a sealant layer. The gas barrier layer may be disposed between the substrate layer and the sealant layer. The gas barrier layer may include stainless steel. The tensile break strength of the pouch film laminate may be 130% to 250% of the tensile break strength of the gas barrier layer.

[0022] According to yet another embodiment of the present invention, there is provided a pouch film laminate. The pouch film laminate may include a substrate layer, a gas barrier layer, and a sealant layer. The gas barrier layer may be disposed between the substrate layer and the sealant layer. The gas barrier layer may include stainless steel. The tensile breaking strength of the gas barrier layer may be 40% to 80% of the tensile breaking strength of the pouch film laminate. Next, according to yet another embodiment of the present invention, the tensile breaking strength of the gas barrier layer may be 50% to 65% of the tensile breaking strength of the pouch film laminate.

[0023] According to yet another embodiment of the present invention, the tensile breaking strength of the gas barrier layer may be 62% to 65% of the tensile breaking strength of the pouch film laminate.

[0024] According to yet another embodiment of the present invention, the thickness of the pouch film laminate may be 80 μm to 300 μm.

[0025] According to yet another embodiment of the present invention, the sum of the thickness of the base layer and the thickness of the sealant layer may be 200% to 500% of the thickness of the gas barrier layer.

[0026] According to yet another embodiment of the present invention, the gas barrier layer may have a thickness of 40 μm to 100 μm.

[0027] According to yet another embodiment of the present invention, the melting point of the gas barrier layer may be 1000° C. or higher.

[0028] According to yet another embodiment of the present invention, the stainless steel may contain 10% to 20% by weight of chromium.

[0029] According to yet another embodiment of the present invention, the stainless steel may contain 5% to 20% by weight of nickel. [Effects of the Invention]

[0030] The pouch film laminate according to the present invention includes a gas barrier layer containing stainless steel, and is characterized in that the tensile breaking strength of the pouch film laminate is 130% to 250% of the tensile breaking strength of the gas barrier layer. A pouch film laminate that satisfies these conditions has excellent durability at high temperatures and high pressures, and the formability of the pouch film laminate is improved, ensuring sufficient forming depth. [Brief explanation of the drawings]

[0031] [Figure 1]1 is a cross-sectional view of a pouch film laminate according to the present invention. [Figure 2] 1 is an exploded view of a pouch-type secondary battery according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0032] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be embodied in various different forms. However, the present embodiments are provided to fully disclose the present invention and fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined only by the claims. The same reference symbols refer to the same elements throughout the specification.

[0033] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0034] In this specification, when a part is said to include a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary.

[0035] In this specification, the phrase "A and / or B" means A, or B, or A and B.

[0036] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0037] Pouch film laminate The pouch film laminate according to the present invention comprises a base layer, a gas barrier layer, and a sealant layer laminated in this order. The gas barrier layer comprises stainless steel. The tensile breaking strength of the pouch film laminate is 130% to 250% of the tensile breaking strength of the gas barrier layer.

[0038] The present invention solves the problem of reduced formability that has been a problem when using stainless steel, a high-strength material, as a component of the gas barrier layer by adjusting the ratio of the tensile breaking strength of the pouch film laminate and the gas barrier layer. Despite using stainless steel as a component of the gas barrier layer, the present invention increases the extensibility of the gas barrier layer, resulting in excellent formability and ensuring sufficient processing depth for the cup portion, thereby realizing a pouch-type battery case with excellent durability and high formability. Therefore, the present invention makes it possible to realize a pouch-type secondary battery that can accommodate a large number of electrode assemblies, improves cell energy density, and has excellent durability against high heat and high pressure.

[0039] Fig. 1 is a cross-sectional view of a pouch film laminate 100 according to the present invention. As shown in Fig. 1, the pouch film laminate 100 may include a substrate layer 110, a gas barrier layer 120, and a sealant layer 130 laminated in this order.

[0040] According to the present invention, the tensile breaking strength of the pouch film laminate 100 can be 130% to 250%, specifically 130% to 220%, specifically 130% to 200%, and more specifically 150% to 200% of the tensile breaking strength of the gas barrier layer 120. When this numerical range is satisfied, the pouch cup can be easily formed and sufficient mechanical strength to withstand the internal pressure of the pouch can be ensured. If the tensile breaking strength of the pouch film laminate 100 is less than 130% of the tensile breaking strength of the gas barrier layer 120, the gas barrier layer 120 will not be stretched uniformly, resulting in reduced pouch formability and an inability to ensure sufficient forming depth. If the tensile breaking strength of the pouch film laminate 100 exceeds 250% of the tensile breaking strength of the gas barrier layer 120, the total thickness of the pouch film laminate will be too thick, reducing the cell energy density, and heat will not be transferred efficiently within the limited sealing time, which may result in reduced sealing quality and make handling and cutting difficult.

[0041] According to the present invention, the difference between the tensile breaking strength of the pouch film laminate 100 and the tensile breaking strength of the gas barrier layer 120 (tensile breaking strength of the pouch film laminate - tensile breaking strength of the gas barrier layer) can be 30% to 150%, specifically 50% to 150%, more specifically 50% to 100%, even more specifically 50% to 80%, and even more specifically 50% to 60% of the tensile breaking strength of the gas barrier layer 120. When this numerical range is satisfied, the pouch cup portion can be easily formed, and sufficient mechanical strength to withstand the internal pressure of the pouch can be ensured.

[0042] The tensile breaking strength of the pouch film laminate can be 400 N / 15 mm or more, specifically 700 N / 15 mm or more, more specifically 700 N / 15 mm to 1500 N / 15 mm, even more specifically 700 N / 15 mm to 1200 N / 15 mm, still more specifically 740 N / 15 mm to 1020 N / 15 mm, and still more specifically 750 N / 15 mm to 1000 N / 15 mm.

[0043] On the other hand, the difference between the tensile breaking strength of the pouch film laminate 100 and the tensile breaking strength of the gas barrier layer 120 can be 150N / 15mm to 600N / 15mm, specifically 200N / 15mm to 500N / 15mm, and more specifically 250N / 15mm to 400N / 15mm.

[0044] The sum of the thickness of the base layer 110 and the thickness of the sealant layer 130 can be 200% to 500%, specifically 200% to 400%, and more specifically 200% to 350% of the thickness of the gas barrier layer 120. When this numerical range is satisfied, the pouch cup portion can be easily formed and sufficient mechanical strength to withstand the internal pressure of the pouch can be ensured. Stress can be distributed so that the gas barrier layer 120 is uniformly stretched, increasing the stretch rate of the pouch film laminate and improving formability.

[0045] The thickness of the pouch film laminate may be specifically 80 μm to 300 μm, more specifically 100 μm to 280 μm, and even more specifically 120 μm to 250 μm. This range is preferable in that it makes it easy to form the pouch cup portion, ensures sufficient mechanical strength to withstand the internal pressure of the pouch, allows a sufficient number of electrode assemblies to be accommodated for the same thickness of the cell, and improves the cell energy density.

[0046] Hereinafter, each component of the pouch film laminate of the present invention will be described in more detail.

[0047] (1) Base material layer The substrate layer 110 is formed as the outermost layer of the pouch film laminate 100 to protect the secondary battery from external friction and impact. The substrate layer 110 is made of a polymer and can electrically insulate the electrode assembly from the outside.

[0048] The thickness of the base layer 110 can be 10 μm to 150 μm, specifically 35 μm to 130 μm, and more specifically 40 μm to 120 μm. When the thickness of the base layer 110 satisfies this range, the insulation properties of the pouch can be ensured, and the formability of the pouch film laminate using a gas barrier layer with high tensile strength at break can be improved, which is preferable in that problems of reduced heat transfer efficiency and reduced sealing quality caused by an excessively thick pouch film laminate can be prevented.

[0049] The substrate layer 110 may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. Preferably, the substrate layer is made of polyethylene terephthalate (PET), nylon, or a combination thereof, which are abrasion-resistant and heat-resistant. More preferably, the substrate layer may include polyethylene terephthalate; or polyethylene terephthalate and nylon.

[0050] The substrate layer 110 may have a single film structure.

[0051] The substrate layer 110 may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber. The substrate layer may preferably include at least one polyester film, such as polyethylene terephthalate or polybutylene terephthalate, which has abrasion resistance and heat resistance, specifically, but is not limited to, polyethylene terephthalate.

[0052] In the present invention, the pouch film laminate may further include an adhesive layer interposed between the substrate layer 110 and a gas barrier layer 120 described below. The adhesive layer may be introduced for bonding or adhering the substrate layer and the gas barrier layer, and any adhesive layer known in the art may be used without limitation.

[0053] Meanwhile, the substrate layer 110 may have a composite film structure in which two or more materials are formed into layers.

[0054] Specifically, the substrate layer 110 according to the present invention may include a first substrate layer, a second substrate layer, and / or an adhesive layer. Here, the thickness of the substrate layer 110 refers to the total thickness of the first substrate layer, the second substrate layer, and / or the adhesive layer. The first substrate layer may be disposed as the outermost layer of the pouch film laminate, and the second substrate layer may be disposed between the first substrate layer and the gas barrier layer. The adhesive layer may be disposed between the first substrate layer and the second substrate layer, or between the second substrate layer and the gas barrier layer. The first substrate layer, the second substrate layer, and the adhesive layer may be made of materials with different materials and / or physical properties. An interface may exist between the first substrate layer, the second substrate layer, and the adhesive layer. This means that the first substrate layer, the second substrate layer, and the adhesive layer are different layers and may be formed separately.

[0055] The first substrate layer may be the outermost layer of the pouch film laminate. In this case, the first substrate layer may serve to prevent moisture from penetrating from outside the pouch. The first substrate layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. Preferably, the first substrate layer may include at least one polyester film such as polyethylene terephthalate or polybutylene terephthalate, which has abrasion resistance and heat resistance, but is not limited thereto.

[0056] As described above, the second substrate layer may be a layer disposed between the first substrate layer and the gas barrier layer 120. In this case, the second substrate layer may improve the formability of the pouch. The second substrate layer may include at least one of polyamide films such as, but not limited to, nylon 6, nylon 6,6, nylon MXD6, and nylon 4,10. Preferably, the second substrate layer may include nylon 6, which has the advantage of improving the formability of the pouch due to the excellent stretchability of nylon 6.

[0057] (2) Gas barrier layer The gas barrier layer 120 is laminated between the base layer 110 and the sealant layer 130 to ensure the mechanical strength of the pouch, block the entry and exit of gases or moisture outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type battery case.

[0058] The tensile breaking strength of the gas barrier layer 120 can be 300 N / 15 mm to 700 N / 15 mm, specifically 350 N / 15 mm to 700 N / 15 mm, and more specifically 400 N / 15 mm to 650 N / 15 mm. When the tensile breaking strength of the gas barrier layer 120 satisfies this range, sufficient mechanical strength to withstand the internal pressure of the pouch can be ensured.

[0059] The thickness of the gas barrier layer 120 can be 40 μm to 100 μm, specifically 50 μm to 90 μm, and more specifically 55 μm to 85 μm. When the thickness of the gas barrier layer 120 satisfies this range, excellent moldability and gas barrier performance can be obtained when molding the cup portion.

[0060] As described below, the gas barrier layer according to the present invention contains stainless steel, and therefore there may be little or no change in the thickness of the gas barrier layer due to the process of forming or stretching the cup portion of the pouch film laminate.

[0061] The melting point of the gas barrier layer 120 can be 1000° C. or higher, specifically 1200° C. to 1500° C., and more specifically 1300° C. to 1450° C. When the melting point of the gas barrier layer 120 is within the above range, structural collapse of the pouch can be prevented even when the temperature of the pouch cell rises suddenly due to thermal runaway.

[0062] The gas barrier layer 120 according to the present invention includes stainless steel. Specifically, the gas barrier layer 120 may be manufactured by molding and / or processing a stainless steel thin film. A gas barrier layer 120 including stainless steel has relatively low thermal conductivity, which is effective in preventing or delaying heat diffusion to other cells during thermal runaway. It also has relatively high toughness, which can prevent cracks from occurring in the pouch during use of the pouch battery. While the inclusion of stainless steel in the gas barrier layer can reduce the formability of the pouch film laminate, as described above, the present invention can achieve a pouch film that has improved durability at high temperatures and pressures and also improved formability by adjusting the ratio of the tensile breaking strengths of the substrate layer, gas barrier layer, and sealant layer that make up the pouch film laminate to a specific level.

[0063] The stainless steel may contain one or more metal elements other than iron (Fe), such as copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), zinc (Zn), phosphorus (P), carbon (C), sulfur (S), and molybdenum (Mo).

[0064] Specifically, the stainless steel may contain 10 to 20% by weight of chromium, more specifically 16 to 20% by weight, and more specifically 18 to 20% by weight. When the above numerical range is satisfied, the stainless steel has excellent corrosion resistance.

[0065] Furthermore, the stainless steel may contain 5 to 20% by weight, specifically 6 to 15% by weight, and more specifically 8 to 14% by weight of nickel. When the content of nickel is within this range, there is an effect of further improving corrosion resistance against neutral / weak acidic conditions.

[0066] On the other hand, as long as the ratio of the tensile breaking strength of the pouch film laminate to the tensile breaking strength of the gas barrier layer is satisfied, the standard and type of stainless steel are not limited. For example, the SUS grade of the stainless steel may be at least one of SUS304, SUS304I, SUS304L, and SUS316L, and more specifically, at least one of SUS304I, SUS304L, and SUS316L.

[0067] In the present invention, the percentage or ratio R of the thickness of the gas barrier layer to the thickness of the pouch film laminate calculated by the following formula 1 is t can be 13% to 40%, specifically 15% to 25%. Within this range, it is possible to realize a pouch film laminate that has sufficient gas barrier performance, excellent durability against high temperatures and high pressures, and excellent formability.

[0068] [Formula 1] R t (%) = (gas barrier layer thickness / pouch film laminate thickness) x 100

[0069] (3) Sealant layer The sealant layer 130 is intended to completely seal the interior of the pouch-type battery case by being thermally bonded to each other at the seal portion when the pouch-type battery case accommodating the electrode assembly inside is sealed. To this end, the sealant layer 130 may be made of a material having excellent thermal adhesive strength.

[0070] The sealant layer 130 may be formed of a material having insulating properties, corrosion resistance, and sealing properties. Specifically, since the sealant layer 130 is in direct contact with the electrode assembly and / or electrolyte inside the pouch-type battery case, it may be formed of a material having insulating properties and corrosion resistance. Furthermore, since the sealant layer 130 must completely seal the interior of the pouch-type battery case and prevent the transfer of materials between the inside and outside, it may be formed of a material having high sealing properties (e.g., excellent thermal adhesive strength). To ensure such insulating properties, corrosion resistance, and sealing properties, the sealant layer 130 may be formed of a polymer material.

[0071] The sealant layer 130 may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon®, and glass fiber, and is preferably made of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be cast polypropylene (CPP), acid-modified polypropylene (PPa), polypropylene-ethylene copolymer, and / or polypropylene-butylene-ethylene terpolymer.

[0072] The thickness of the sealant layer 130 can be 30 μm to 130 μm, specifically 50 μm to 120 μm, more specifically 70 μm to 100 μm. When the thickness of the sealant layer satisfies the above range, it is possible to ensure the seal strength of the sealed portion and the formability of the pouch film laminate.

[0073] Meanwhile, the sealant layer 130 according to the present invention may have a single film structure made of any one material. Alternatively, the sealant layer 130 may have a composite film structure formed by layers of two or more materials. Specifically, the sealant layer 130 may include a first sealant layer and a second sealant layer. In this case, the first sealant layer may be a layer disposed adjacent to the gas barrier layer, and the second sealant layer may be a layer disposed on the first sealant layer. The first sealant layer and the second sealant layer may be made of materials having different materials and / or physical properties. An interface may exist between the first sealant layer and the second sealant layer. This means that the first sealant layer and the second sealant layer are different layers and may be formed separately.

[0074] In order to ensure long-term adhesion between the gas barrier layer and the first sealant layer, it is particularly preferable that the first sealant layer is made of acid-modified polypropylene (PPa), which may be maleic anhydride polypropylene (MAH PP).

[0075] The second sealant layer may be formed of a material having insulating, corrosion-resistant, and sealing properties. Specifically, since the second sealant layer is in direct contact with the electrode assembly (260 in FIG. 2) and / or the electrolyte inside the housing (224 in FIG. 2), it may be formed of a material having insulating and corrosion-resistant properties. Furthermore, since the second sealant layer must completely seal the interior of the battery case and prevent the transfer of materials between the interior and exterior, it may be formed of a material having high sealing properties. To ensure such insulating, corrosion-resistant, and sealing properties, the second sealant layer may be formed of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber. Preferably, the second sealant layer may be formed of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be composed of unstretched polypropylene, acid-modified polypropylene, polypropylene-ethylene copolymer, and / or polypropylene-butylene-ethylene terpolymer. Here, the acid-modified polypropylene may be maleic anhydride polypropylene (MAH PP). More preferably, the second sealant layer may include cast polypropylene (CPP), which has heat-sealing properties and high tensile strength.

[0076] Pouch-type secondary battery Next, the pouch-type secondary battery according to the present invention will be described.

[0077] The pouch-type secondary battery according to the present invention includes a pouch-type battery case in which an electrode assembly is housed, the pouch-type battery case including a pouch film laminate, the pouch film laminate including a base layer, a gas barrier layer, and a sealant layer laminated in that order, the gas barrier layer including stainless steel, and the tensile breaking strength of the pouch film laminate being 130% to 250% of the tensile breaking strength of the gas barrier layer.

[0078] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to FIG.

[0079] 2 is an exploded view of a pouch-type secondary battery 200 according to the present invention. As shown in FIG. 2, the pouch-type secondary battery 200 according to the present invention may include a pouch-type battery case 210, an electrode assembly 260, an electrode lead 280, an insulating portion 290, and an electrolyte (not shown).

[0080] (1) Pouch-type battery case The pouch-type battery case 210 can house the electrode assembly 260 inside. The pouch-type battery case 210 can be manufactured by molding the pouch film laminate of the present invention described above. The detailed structure and physical properties of the pouch film laminate are as described above, and a detailed description thereof will be omitted.

[0081] The pouch film laminate may be drawn and stretched using a punch or the like to manufacture the pouch-type battery case 210. As a result, the pouch-type battery case 210 may include a cup portion 222 and a receiving portion 224. The receiving portion 224 is a portion that receives the electrode assembly, and may refer to a bag-shaped receiving space formed inside the cup portion 222 as the cup portion 222 is formed.

[0082] According to one embodiment of the present invention, the pouch-type battery case 210 may include a first case 220 and a second case 230, as shown in Fig. 2. The first case 220 includes a receiving portion 224 that can receive the electrode assembly 260, and the second case 230 may cover the receiving portion 224 from above to prevent the electrode assembly 260 from falling out of the battery case 210. The first case 220 and the second case 230 may be manufactured with one side connected to each other as shown in Fig. 2, but are not limited to this and may be manufactured in various ways, such as being separately manufactured.

[0083] According to another embodiment of the present invention, when forming cup portions in a pouch film laminate, two symmetrical cup portions 222, 232 may be formed adjacent to each other by drawing one pouch film laminate. In this case, as shown in FIG. 2, the first case 220 and the second case 230 may be formed with the cup portions 222, 232, respectively. After the electrode assembly 260 is accommodated in the accommodating portion 224 of the cup portion 222 of the first case 220, the bridge portion 240 formed between the two cup portions 222, 232 may be folded so that the two cup portions 222, 232 face each other. In this case, the cup portion 232 of the second case 230 may accommodate the electrode assembly 260 from above. Therefore, since two cup portions 222, 232 accommodate one electrode assembly 260, an electrode assembly 260 that is thicker than when there is only one cup portion 222 can be accommodated. In addition, folding the pouch-type battery case 210 forms one corner of the secondary battery 200, and the number of corners to be sealed during the subsequent sealing process can be reduced, thereby improving the processing speed of the pouch-type secondary battery 200 and reducing the number of sealing processes.

[0084] The pouch-type battery case 210 may be sealed with the electrode assembly 260 housed therein so that a portion of the electrode lead 280, i.e., a terminal portion, described below, is exposed. Specifically, after the electrode lead 280 is connected to the electrode tab 270 of the electrode assembly 260 and an insulating portion 290 is formed on a portion of the electrode lead 280, the electrode assembly 260 may be housed in the housing portion 224 provided in the cup portion 222 of the first case 220, and the second case 230 may cover the housing portion 224 from above. Next, an electrolyte may be injected into the housing portion 224, and the sealing portion 250 formed on the periphery of the first case 220 and the second case 230 may be sealed.

[0085] The sealing portion 250 may serve to seal the receiving portion 224. Specifically, the sealing portion 250 may be formed along the periphery of the receiving portion 224 to seal the receiving portion 224. The temperature at which the sealing portion 250 is sealed may be 180°C to 250°C, specifically 200°C to 250°C, and more specifically 210°C to 240°C. When the sealing temperature is within this range, the pouch-type battery case 210 can ensure sufficient seal strength through thermal bonding.

[0086] According to the present invention, when the sealant layers of the first case 220 and the second case 230 are laminated and abutted against each other and then sealed for 1.6 seconds under conditions of 210°C and 1.2 MPa, the thickness of the sealant layer of the seal portion 250 formed in the pouch-type battery case 210 can be 54% to 86%, specifically 55% to 85%, and more specifically 60% to 85%, of the thickness of the sealant layer of the pouch film laminate. When the thickness of the sealant layer of the seal portion 250 satisfies this numerical range relative to the thickness of the sealant layer of the pouch film laminate, there is an effect of ensuring sufficient seal strength and maintaining insulation properties.

[0087] (2) Electrode assembly The electrode assembly 260 can be inserted into the pouch-type battery case 210 and sealed by the pouch-type battery case 210 after the electrolyte is injected.

[0088] The electrode assembly 260 may be formed by sequentially stacking a positive electrode, a separator, and a negative electrode. Specifically, the electrode assembly 260 may include two electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other.

[0089] The positive and negative electrodes may each have a structure in which an active material slurry is applied to an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper. The slurry may be formed by stirring a granular active material, auxiliary conductor, binder, conductive material, etc., in a solvent. The solvent may be removed in a subsequent process.

[0090] A slurry containing a mixture of an electrode active material, a binder, and / or a conductive material is applied to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, which are then stacked on both sides of a separator to manufacture a predetermined shape of the electrode assembly 260. The electrode assembly 260 may be of a stack type, a jelly roll type, a stack and folding type, or the like, but is not limited thereto.

[0091] The electrode assembly 260 may include an electrode tab 270 .

[0092] The electrode tabs 270 are connected to the positive and negative electrodes of the electrode assembly 260, respectively, and protrude from the electrode assembly 260 to serve as paths for electrons to move between the inside and outside of the electrode assembly 260. The electrode current collector included in the electrode assembly 260 may be composed of a portion coated with an electrode active material and an end portion, i.e., a plain portion, where the electrode active material is not coated. The electrode tabs 270 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion by ultrasonic welding, for example. As shown in FIG. 2, the electrode tabs 270 may protrude in different directions from the electrode assembly 260, but are not limited thereto. They may protrude in various directions, such as protruding in parallel from one side in the same direction.

[0093] (3) Electrode lead The electrode lead 280 may supply electricity to the outside of the secondary battery 200. The electrode lead 280 may be connected to the electrode tab 270 of the electrode assembly 260 by spot welding or the like.

[0094] The electrode lead 280 may be connected to the electrode assembly 260 and may protrude to the outside of the pouch-type battery case 210 through the sealing portion 250. Specifically, one end of the electrode lead 280 may be connected to the electrode assembly 260, particularly the electrode tab 270, and the other end of the electrode lead 280 may protrude to the outside of the pouch-type battery case 210.

[0095] The electrode lead 280 may include a positive electrode lead 282 having one end connected to the positive electrode tab 272 and extending in the direction in which the positive electrode tab 272 protrudes, and a negative electrode lead 284 having one end connected to the negative electrode tab 274 and extending in the direction in which the negative electrode tab 274 protrudes. The other ends of the positive electrode lead 282 and the negative electrode lead 284 may protrude to the outside of the battery case 210. This allows electricity generated inside the electrode assembly 260 to be supplied to the outside. In addition, because the positive electrode tab 272 and the negative electrode tab 274 protrude in different directions, the positive electrode lead 282 and the negative electrode lead 284 may also extend in different directions. The positive electrode lead 282 and the negative electrode lead 284 may be made of different materials. That is, the positive electrode lead 282 may be made of the same aluminum (Al) material as the positive electrode current collector, and the negative electrode lead 284 may be made of the same copper (Cu) material as the negative electrode current collector or a copper material coated with nickel (Ni). A portion of the electrode lead 280 protruding outside the battery case 210 serves as a terminal portion and may be electrically connected to an external terminal.

[0096] (4) Insulation section The insulating portion 290 prevents electricity generated from the electrode assembly 260 from flowing to the battery case 210 via the electrode lead 280, thereby maintaining the seal of the battery case 210. To this end, the insulating portion 290 may be formed of an insulator that is electrically non-conductive and does not easily pass electricity. Generally, the insulating portion 290 is formed of an insulating tape or film that is easily attached to the electrode lead 280 and has a relatively thin thickness, but is not limited thereto, and any material that can insulate the electrode lead 280 may be used.

[0097] The insulating part 290 may be disposed to surround the outer circumferential surface of the electrode lead 280. Specifically, at least a portion of the electrode lead 280 may be surrounded by the insulating part 290. In this case, the insulating part 290 may be disposed between the electrode lead 280 and the pouch-type battery case 210. The insulating part 290 may be located only in the seal part 250 where the first case 220 and the second case 230 of the pouch-type battery case 210 are heat-sealed, and may bond the electrode lead 280 to the battery case 210.

[0098] (5) Electrolyte The pouch-type secondary battery 200 according to the present invention may further include an electrolyte (not shown) injected into the pouch-type battery case 210. The electrolyte is used to move lithium ions generated by an electrochemical reaction of the electrodes during charging / discharging of the secondary battery 200, and may include a non-aqueous organic electrolyte solution that is a mixture of a lithium salt and an organic solvent, or a polymer using a polymer electrolyte. Furthermore, the electrolyte may include a sulfide-based, oxide-based, or polymer-based solid electrolyte, and such a solid electrolyte may have flexibility that makes it easily deformable under external force.

[0099] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present description, and it goes without saying that such changes and modifications are within the scope of the appended claims.

[0100] Examples and Comparative Examples Example 1: Manufacturing of a pouch film laminate On one side of a 266 mm wide, 50 mm long, 60 μm thick stainless steel thin film, a 266 mm wide, 50 mm long, 3 μm thick first adhesive film, a 266 mm wide, 50 mm long, 50 μm thick nylon film, a 266 mm wide, 50 mm long, 50 μm thick second adhesive film, and a 266 mm wide, 50 mm long, 50 μm thick polyethylene terephthalate (PET) film were laminated in this order. A 266 mm wide, 50 mm long, 80 μm thick polypropylene (PP) film was laminated on the other side of the stainless steel thin film. As a result, a pouch film laminate was produced with a structure in which polypropylene film / stainless steel thin film / first adhesive film / nylon film / second adhesive film / polyethylene terephthalate film were laminated in this order.

[0101] Here, the SUS grade of the stainless steel contained in the stainless steel thin film was SUS304L.

[0102] Here, the polypropylene film is a sealant layer, the stainless steel thin film is a gas barrier layer, and the first adhesive film, nylon film, second adhesive film and polyethylene terephthalate film are base layers.

[0103] Example 2: Manufacturing of a pouch film laminate A pouch film laminate was produced in the same manner as in Example 1, except that a stainless steel thin film having a thickness of 40 μm was used.

[0104] The SUS grade of the stainless steel contained in the stainless steel thin film of Example 2 was SUS304L.

[0105] Example 3: Preparation of a pouch film laminate On one side of a 266 mm wide, 50 mm long, and 60 μm thick stainless steel thin film, a 266 mm wide, 50 mm long, and 3 μm thick adhesive film and a 266 mm wide, 50 mm long, and 40 μm thick polyethylene terephthalate (PET) film were laminated in that order. On the other side of the stainless steel thin film, a 266 mm wide, 50 mm long, and 80 μm thick polypropylene (PP) film was laminated. As a result, a pouch film laminate was produced with a structure in which polypropylene film / stainless steel thin film / adhesive film / polyethylene terephthalate film were laminated in that order.

[0106] Here, the SUS grade of the stainless steel contained in the stainless steel thin film was SUS304L.

[0107] Here, the polypropylene film is a sealant layer, the stainless steel thin film is a gas barrier layer, and the adhesive film and polyethylene terephthalate film are base layers.

[0108] Example 4: Preparation of a pouch film laminate On one side of a 266 mm wide, 50 mm long, and 60 μm thick stainless steel thin film, a 266 mm wide, 50 mm long, and 3 μm thick adhesive film and a 266 mm wide, 50 mm long, and 40 μm thick polyethylene terephthalate (PET) film were laminated in that order. On the other side of the stainless steel thin film, a 266 mm wide, 50 mm long, and 80 μm thick polypropylene (PP) film was laminated. As a result, a pouch film laminate was produced with a structure in which polypropylene film / stainless steel thin film / adhesive film / polyethylene terephthalate film were laminated in that order.

[0109] Here, the SUS grade of the stainless steel contained in the stainless steel thin film was SUS304I.

[0110] Here, the polypropylene film is a sealant layer, the stainless steel thin film is a gas barrier layer, and the adhesive film and polyethylene terephthalate film are base layers.

[0111] Example 5: Preparation of a pouch film laminate On one side of a 266 mm wide, 50 mm long, and 60 μm thick stainless steel thin film, a 266 mm wide, 50 mm long, and 3 μm thick adhesive film and a 266 mm wide, 50 mm long, and 40 μm thick polyethylene terephthalate (PET) film were laminated in that order. On the other side of the stainless steel thin film, a 266 mm wide, 50 mm long, and 80 μm thick polypropylene (PP) film was laminated. As a result, a pouch film laminate was produced with a structure in which polypropylene film / stainless steel thin film / adhesive film / polyethylene terephthalate film were laminated in that order.

[0112] The SUS grade of the stainless steel contained in the stainless steel thin film was SUS316L.

[0113] Here, the polypropylene film is a sealant layer, the stainless steel thin film is a gas barrier layer, and the adhesive film and polyethylene terephthalate film are base layers.

[0114] Comparative Example 1: Production of pouch film laminate A pouch film laminate was produced in the same manner as in Example 1, except that a polyethylene terephthalate (PET) film having a thickness of 12 μm and a nylon film having a thickness of 15 μm were used.

[0115] Comparative Example 2: Production of pouch film laminate A pouch film laminate was manufactured in the same manner as in Example 1, except that a polyethylene terephthalate (PET) film having a thickness of 12 μm, a nylon film having a thickness of 15 μm, and a stainless steel thin film having a thickness of 40 μm were used.

[0116] The SUS grade of the stainless steel contained in the stainless steel thin film of Comparative Example 2 was SUS304L.

[0117] A pouch-type battery case was manufactured in the same manner as in Example 1, except that the pouch film laminate manufactured by the above method was used.

[0118] Comparative Example 3: Production of pouch film laminate A pouch film laminate was manufactured in the same manner as in Example 1, except that a polyethylene terephthalate (PET) film having a thickness of 100 μm, a nylon film having a thickness of 100 μm, and a stainless steel thin film having a thickness of 40 μm were used.

[0119] The SUS grade of the stainless steel contained in the stainless steel thin film of Comparative Example 3 was SUS304L.

[0120] Experimental Example 1: Measurement of the tensile strength of a pouch film laminate and each layer The tensile breaking strength of each layer of the pouch film laminates produced in Examples 1 to 5 and Comparative Examples 1 to 3 was measured and is shown in Table 1 below.

[0121] Specifically, a pouch film laminate or each film was cut into a 15 mm wide and 100 mm long test specimen, and both longitudinal ends of the test specimen were fastened to the upper and lower fixtures of a universal testing machine (UTM) (here, the distance between the end fastened to the upper fixture and the end fastened to the lower fixture was 50 mm). The specimen was then pulled in a 180° direction at a rate of 5 mm / min at room temperature (25°C). The tensile strength was defined as the maximum load applied until the specimen broke, divided by the cross-sectional area of ​​the specimen before pulling. The results are shown in Table 1 below.

[0122] Experimental Example 2: Evaluation of Maximum Forming Depth The maximum forming depth was measured for each of the pouch film laminates produced in Examples 1 to 5 and Comparative Examples 1 to 3. Specifically, the pouch film laminate was cut to a size of 266 mm wide and 200 mm long, and then the cut pouch film laminate was processed and stretched using a pouch-forming device manufactured by Gwangshin Hi-Tech to form a cup portion measuring 90 cm wide and 160 cm long. The maximum forming depth was defined as the forming depth (unit: mm) just before the pouch film laminate broke. Ten pouch film laminates were prepared in Examples 1 to 5 and Comparative Examples 1 to 3, and the above maximum forming depth measurement experiment was performed 10 times. The average values ​​are shown in Table 1 below.

[0123] [Table 1]

[0124] According to Table 1, in Examples 1 to 5, in which the tensile breaking strength of the pouch film laminate was 130% to 250% of the tensile breaking strength of the gas barrier layer, the processing depth of the cup portion was deeper than in Comparative Examples 1 to 3, confirming the excellent formability of the pouch film laminates manufactured in Examples 1 to 5. On the other hand, in Comparative Example 3, in which the tensile breaking strength of the pouch film laminate was more than 150% of the tensile breaking strength of the gas barrier layer, formability was at the same level as in Example 2, but while the processing depth did not increase any further, the pouch film laminate was thick, resulting in reduced heat transfer required for sealing and an inability to accommodate a sufficient number of electrode assemblies within the thickness of the pouch-type secondary battery under consideration, resulting in reduced cell energy density. [Explanation of symbols]

[0125] 100 Pouch film laminate 110 Base material layer 120 Gas barrier layer 130 Sealant Layer 200 Pouch-type secondary battery 210 Pouch-type case 220 Case 1 222 Cup section 224 Storage Unit 230 Case 2 232 Cup section 240 Bridge section 250 Seal part 260 Electrode assembly 270 Electrode Tab 272 Positive electrode tab 274 Negative electrode tab 280 Electrode Lead 282 Positive lead 284 Negative lead 290 Insulation

Claims

1. A pouch film laminate comprising a base layer, a sealant layer, and a gas barrier layer disposed between the base layer and the sealant layer, the gas barrier layer comprises stainless steel; A pouch film laminate, wherein the tensile breaking strength of the pouch film laminate is 130% to 250% of the tensile breaking strength of the gas barrier layer.

2. 2. The pouch film laminate according to claim 1, wherein a difference between the tensile breaking strength of the pouch film laminate and the tensile breaking strength of the gas barrier layer is 30% to 150% of the tensile breaking strength of the gas barrier layer.

3. The pouch film laminate according to claim 1 , wherein the pouch film laminate has a tensile breaking strength of 400 N / 15 mm or more.

4. 2. The pouch film laminate according to claim 1, wherein the gas barrier layer has a tensile breaking strength of 300 N / 15 mm to 700 N / 15 mm.

5. 2. The pouch film laminate according to claim 1, wherein the sum of the thickness of the base layer and the thickness of the sealant layer is 200% to 500% of the thickness of the gas barrier layer.

6. The pouch film laminate according to claim 1, wherein the thickness of the pouch film laminate is 80 μm to 300 μm.

7. 2. The pouch film laminate according to claim 1, wherein the gas barrier layer has a thickness of 40 μm to 100 μm.

8. The pouch film laminate according to claim 1 , wherein the gas barrier layer has a melting point of 1000° C. or higher.

9. 2. The pouch film laminate according to claim 1, wherein the stainless steel contains 10% to 20% by weight of chromium.

10. 2. The pouch film laminate according to claim 1, wherein the stainless steel contains 5% to 20% by weight of nickel.

11. A pouch-type secondary battery including a pouch-type battery case in which an electrode assembly is housed, the pouch-type battery case includes a pouch film laminate; the pouch film laminate includes a base layer, a sealant layer, and a gas barrier layer disposed between the base layer and the gas barrier layer, the gas barrier layer comprises stainless steel; The pouch-type secondary battery has a tensile breaking strength of the pouch film laminate that is 130% to 250% of the tensile breaking strength of the gas barrier layer.

12. A pouch film laminate comprising a base layer, a sealant layer, and a gas barrier layer disposed between the base layer and the sealant layer, the gas barrier layer comprises stainless steel; A pouch film laminate, wherein the tensile breaking strength of the gas barrier layer is 40% to 80% of the tensile breaking strength of the pouch film laminate.

13. The pouch film laminate according to claim 12, wherein the tensile breaking strength of the gas barrier layer is 50% to 65% of the tensile breaking strength of the pouch film laminate.

14. The pouch film laminate according to claim 12, wherein the tensile breaking strength of the gas barrier layer is 62% to 65% of the tensile breaking strength of the pouch film laminate.

15. The pouch film laminate according to claim 12, wherein the thickness of the pouch film laminate is 80 μm to 300 μm.

16. The pouch film laminate according to claim 12, wherein the sum of the thickness of the base layer and the thickness of the sealant layer is 200% to 500% of the thickness of the gas barrier layer.

17. The pouch film laminate according to claim 12, wherein the gas barrier layer has a thickness of 40 μm to 100 μm.

18. The pouch film laminate according to claim 12, wherein the gas barrier layer has a melting point of 1000°C or higher.

19. The pouch film laminate according to claim 12, wherein the stainless steel contains 10% to 20% by weight of chromium.

20. The pouch film laminate according to claim 12, wherein the stainless steel contains 5% to 20% by weight of nickel.

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