Bag film, bag-type battery case, and secondary battery including the same, and method of manufacturing the same

Abstract

The present invention relates to a bag film including a sealing layer, a barrier layer, a second outer layer, and a first outer layer which are sequentially stacked, wherein the second outer layer contains a nylon-based resin, the thickness of the second outer layer is 35 to 60 μm, and the ratio of the tensile strength of the barrier layer to that of the second outer layer is 0.9 to 1.2 as measured according to the following measurement conditions. [Measurement conditions]: The barrier layer and the second outer layer of the bag film are peeled off to make test pieces each having a width of 15 mm, and then the test pieces are fixed between two grips of a tensile testing machine (UTM) at room temperature (initial grip separation: 50 mm), and then while each test piece is pulled in the MD direction at a measurement speed of 50 mm / min, the travel (mm) and the strength (N) of the test piece are measured. In a graph obtained from the measured values, the x-axis is the travel (mm), the y-axis is the tensile strength (N), and the tensile strength of the barrier layer and the second outer layer at a travel of 5 mm is measured.

Description

Cross-references to related applications

[0001] This application claims priority to Korean Patent Application No. 10-2023-0143316, filed with the Korean Intellectual Property Office on October 24, 2023, pursuant to 35 USC §119, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] This application relates to a pouch film for a secondary battery, a pouch-type battery casing, and a secondary battery including the pouch film, as well as a method for manufacturing the same. Background Technology

[0003] Rechargeable batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries. These batteries are used not only in small products such as digital cameras, P-DVD players, MP3 players, mobile phones, PDAs, portable gaming devices, power tools, and electric bicycles, but also in large products requiring high output, such as electric vehicles and hybrid vehicles, as well as in energy storage devices and backup energy storage devices used to store surplus generated electricity or renewable energy.

[0004] To manufacture this type of secondary battery, firstly, an electrode active material slurry is coated onto a positive electrode current collector and a negative electrode current collector to create the positive and negative electrodes. Then, the positive and negative electrodes are stacked on both sides of a separator to form an electrode assembly with a predetermined shape. Additionally, the electrode assembly is housed in a battery casing, injected with electrolyte, and then sealed.

[0005] Based on the type of external material of the housing that houses the electrode components, secondary batteries can be classified into pouch type, cylindrical type, and square type.

[0006] Among these secondary batteries, pouch batteries are those in which electrode assemblies (cells) are embedded in a pouch of stacked metal sheets. Pouch batteries are easy to manufacture and have low manufacturing costs, especially since large-capacity battery packs can be easily manufactured by connecting multiple individual cells in series or parallel. Therefore, pouch batteries are mainly used in fields such as electric vehicles that require high-capacity secondary batteries. The pouch serving as the casing of the pouch secondary battery is manufactured by stamping a flexible pouch film to form a cup-shaped portion. Furthermore, during the formation of the cup-shaped portion, the electrode assembly is housed within the receiving space of the cup-shaped portion, and the sealing portion is sealed, thereby manufacturing the secondary battery. In this text, the cup-shaped portion refers to the part that houses the electrode assembly, and the sealing portion refers to the sealed edge portion of the pouch film within the cup-shaped portion.

[0007] Meanwhile, in the case of high-energy-density secondary batteries using pouch films, the ideal approach is to increase formability to insert as much active material as possible into a single package. Secondary batteries using pouch films require methods to improve the formability of the pouch film to insert as much battery active material as possible into the pouch, thereby increasing energy density, and for this purpose, the pouch film needs to ensure higher formability. However, in existing pouch films, when exhibiting high formability, the remaining thickness of the barrier layer decreases due to stretching during the molding process, which may lead to moisture penetration and electrolyte leakage, thus compromising stability.

[0008] Currently commercially available bag films are 183 μm products and include PP80 / Al60 / Nylon25 / PET12. These highly formable bags only ensure approximately 12 mm to 15 mm of formability. Furthermore, because the remaining Al thickness after molding is only about 30 μm, it is difficult to adequately protect battery materials sensitive to air and moisture. Therefore, research is being conducted to ensure high formability and the remaining thickness of the Al barrier layer after molding. Summary of the Invention

[0009] [Technical Issues] The problem to be solved by this application is to provide a bag film with high formability, a bag-type battery casing including the bag film, a secondary battery, and a method for manufacturing the same.

[0010] [Technical Solution] This application provides a pouch membrane, a pouch-type battery casing including the pouch membrane, a secondary battery, and a method for manufacturing the same.

[0011] (1) This application provides a bag film comprising a sealing layer, a barrier layer, a second outer layer and a first outer layer stacked sequentially, wherein the second outer layer comprises a nylon-based resin, the thickness of the second outer layer is in the range of 35 μm to 60 μm, and the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer, measured according to the measurement conditions, satisfies the following formula 1.

[0012] [Formula 1] 0.9 ≤ tensile strength of the barrier layer / tensile strength of the second outer layer ≤ 1.2 [Measurement Conditions] After preparing a 15 mm wide specimen by peeling off the barrier layer and second outer layer of the bag film, the specimen was fixed between two clamps of a UTM tensile testing machine at room temperature (initial clamp gap 50 mm). The specimen was then stretched along the MD direction at a measuring speed of 50 mm / min, while the stroke (mm) and strength (N) were measured. In the graph obtained from the measurements, the X-axis represents the stroke (mm), the Y-axis represents the tensile strength (N), and the tensile strength of the barrier layer and the second outer layer was measured at a stroke of 5 mm.

[0013] (2) This application provides the bag film of (1), wherein the ratio of the thickness of the barrier layer to the thickness of the second outer layer can be in the range of 1:0.5 to 1:07.

[0014] (3) This application provides the bag film of (1) or (2), wherein the thickness of the barrier layer can be in the range of 40 μm to 100 μm.

[0015] (4) This application provides a bag film according to any one of (1) to (3), wherein the sum of the thickness of the first outer layer and the thickness of the second outer layer may be in the range of 40 μm to 100 μm.

[0016] (5) This application provides a bag film according to any one of (1) to (4), wherein the ratio of the thickness of the barrier layer to the sum of the thickness of the first outer layer and the thickness of the second outer layer may be in the range of 1:0.65 to 1:0.9.

[0017] (6) This application provides a bag film according to any one of (1) to (5), wherein the MD elongation and TD elongation of the second outer layer can be independently in the range of 50% to 300%.

[0018] (7) This application provides a bag film according to any one of (1) to (6), wherein the tensile strength of the second outer layer along the MD direction is in the range of 200 N / 15 mm to 300 N / 15 mm.

[0019] (8) This application provides a bag film according to any one of (1) to (7), wherein, according to Formula 2, the thickness retention rate of the barrier layer can be 55% or higher: [Equation 2] Thickness retention rate (%) = (Thickness of the barrier layer after molding / Thickness of the barrier layer before molding) × 100 In Equation 2, After cutting the bag film excluding the sealing portion, a sample with dimensions of 266 mm (TD) × 240 mm (MD) × 15 mm (width) was prepared. Low-density polyethylene (LDPE) was added to both sides of the sample. The sample was then pressed at 0.3 MPa using a 30 mm × 75 mm test mold, and the test was molded to a molding depth of 17 mm. The thickness of the barrier layer after molding was measured. In this case, the average thickness of the barrier layer was calculated by measuring six times at each of the four corners of the rectangular molded shape.

[0020] (9) This application provides a bag film according to any one of (1) to (8), wherein the second outer layer may comprise a single layer or a stack of two or more layers.

[0021] (10) This application provides a bag film as described in any one of (1) to (9), wherein the thickness of the bag film may be in the range of 205 μm to 250 μm.

[0022] (11) This application provides a bag film according to any one of (1) to (10), wherein the first outer layer may comprise one or more materials selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylenebenzodioxazole), polyarylate, Teflon and glass fiber.

[0023] (12) This application provides a bag film according to any one of (1) to (11), wherein the thickness of the first outer layer may be in the range of 5 μm to 40 μm.

[0024] (13) This application provides a bag film according to any one of (1) to (11), wherein the barrier layer may comprise one or more materials selected from the group consisting of aluminum, stainless steel, copper, titanium and alloys thereof.

[0025] (14) This application provides a pouch-type battery casing, which includes the pouch membrane described in any one of (1) to (13).

[0026] (15) This application provides a secondary battery comprising: an electrode assembly in which a positive electrode, a separator and a negative electrode are stacked and formed; and a pouch-type battery housing as claimed in claim 14, wherein the electrode assembly is housed.

[0027] (16) This application provides a method for manufacturing a bag film, the method comprising: stacking a sealing film on one surface of a barrier film; and sequentially stacking a second outer layer and a first outer layer on another surface of the barrier film, wherein the second outer layer comprises a nylon-based resin and the second outer layer is manufactured by blow molding.

[0028] [Beneficial Effects] The bag film of this application can have excellent tensile strength and excellent elongation, and therefore can have high formability.

[0029] Furthermore, the bag film of this application can have excellent barrier layer thickness retention rate after molding, thereby preventing moisture penetration and electrolyte leakage.

[0030] Furthermore, the bag membrane of this application can accommodate a large number of electrode components due to its high formability, and therefore can have high capacitance and efficiency. Attached Figure Description

[0031] Figure 1 This is a schematic diagram showing the structure of the bag film according to this application.

[0032] Figure 2 This is a graph showing the stroke (mm) of the barrier layer and the tensile strength (N) of the second outer layer.

[0033] Figure 3 This shows an SEM image of the remaining thickness of the formed barrier layer according to Example 1.

[0034] Figure 4 The image shown is an SEM image of the remaining thickness of the barrier layer after molding, according to Comparative Example 2. Detailed Implementation

[0035] The present application will be described in more detail below to aid in understanding it. In this context, the terms or words used in the specification and appended claims should not be construed as limited to their ordinary or dictionary meanings, but rather as meanings and concepts corresponding to the technical spirit of the present application, based on the principle that the inventors may appropriately define the concepts of the terms in order to best describe their own disclosure.

[0036] The terminology used herein is for describing exemplary embodiments only and is not intended to limit this application. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0037] It should be understood in the specification that terms such as “comprising,” “having,” and “having” are intended to indicate the presence of features, quantities, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, components, or combinations thereof.

[0038] In this application, when the secondary battery bag includes various layers, the secondary battery bag may not necessarily include only the corresponding layers, but may also include additional layers.

[0039] In this application, the term "formation" in "specific layer" includes not only the case of "formed directly on the corresponding layer," but also the case of "formed after the insertion of additional layers."

[0040] In this specification, an extruded coating (EC) layer refers to an extruded layer of resin, such as a polyolefin-based resin, preferably a polypropylene-based resin, wherein the resin is extruded to be laminated with a barrier layer as part of or entirely of a sealing layer. When unstretched polypropylene (CPP) and an EC layer are both present in the sealing layer, the EC layer is located on the barrier layer side.

[0041] In this application, the polypropylene (PP) layer of the sealing layer can be used as the core resin layer constituting the sealing layer, which can perform a sealing function, and may include one or more layers made of polypropylene-based resin. Compared with the EC layer used for lamination with the barrier layer, the PP layer is located on the inside of the bag film based on the EC layer (i.e., the side opposite to the barrier layer).

[0042] Bag film This application provides a bag film comprising a sealing layer, a barrier layer, a second outer layer and a first outer layer stacked sequentially, wherein the second outer layer comprises a nylon-based resin, the thickness of the second outer layer is in the range of 35 μm to 60 μm, and the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer, measured according to measurement conditions, satisfies the following formula 1.

[0043] [Formula 1] 0.9 ≤ tensile strength of the barrier layer / tensile strength of the second outer layer ≤ 1.2 [Measurement Conditions] After preparing a 15 mm wide specimen by peeling off the barrier layer and second outer layer of the bag film, the specimen was fixed between two clamps of a tensile testing machine (UTM) at room temperature (initial clamp gap 50 mm). The specimen was then stretched along the MD direction at a measuring speed of 50 mm / min, while the stroke (mm) and strength (N) were measured. In the graph obtained from the measurements, the X-axis represents the stroke (mm), the Y-axis represents the tensile strength (N), and the tensile strength of the barrier layer and the second outer layer was measured at a stroke of 5 mm.

[0044] The outer layer contained in the bag membrane serves to block contact with the outside and seal the electrode assembly housed therein. Therefore, it needs to have excellent processability and moldability, which are affected by mechanical properties, particularly the mechanical properties of the outer layer. The inventors of this application have discovered that in the case of prior art bag membranes, the molding process is performed according to the size of the electrode assembly to accommodate an electrode assembly of the required size. However, the remaining thickness of the barrier layer (metal layer) is reduced due to stretching during molding, which may lead to moisture penetration and electrolyte leakage.

[0045] To address these issues, the inventors have provided a bag film with high formability by: defining the thickness of a second outer layer comprising a nylon-based resin, controlling the tensile strength ratio of the barrier layer to the second outer layer within a specific range, while maintaining excellent tensile strength and elongation, improving thickness retention after molding, and preventing moisture penetration and electrolyte leakage.

[0046] Figure 1The structure of a bag film according to this application is shown. The bag film of this application includes a sealing layer located on its inner side, an outer layer, and an aluminum-containing barrier layer between the inner sealing layer and the outer layer. Furthermore, the outer layer includes a first outer layer and a second outer layer. Specifically, the outer layer may be formed by laminating the first outer layer and the second outer layer. The second outer layer may contain a heat-resistant resin with a melting point higher than the heat-bonding temperature of the sealing layer, and the second outer layer may contain a nylon-based resin.

[0047] Furthermore, the outer layer can be the outermost layer of the pouch film used for packaging lithium secondary batteries, and the thickness of the outer layer can be limited to ensure sufficient mechanical strength and formability as the packaging material. In particular, when further considering the thickness retention rate of the barrier layer, the second outer layer of the outer layer in this application can have a greater thickness than the second outer layer according to the prior art.

[0048] The thickness of the second outer layer in this application is in the range of 35 μm to 60 μm. For example, the thickness of the second outer layer can be 35 μm or greater, 37 μm or greater, 39 μm or greater, 40 μm or greater, 43 μm or greater, 45 μm or greater, 47 μm or greater, 50 μm or greater, 60 μm or less, 59 μm or less, 57 μm or less, 55 μm or less, 53 μm or less, and 51 μm or less. Specifically, the thickness of the second outer layer can be in the range of 40 μm to 55 μm. When the thickness of the second outer layer deviates from the thickness range, the tensile strength may decrease, and the formability of the bag film may deteriorate.

[0049] Furthermore, the second outer layer may comprise a single layer or a stack of two or more layers. To increase the thickness of the second outer layer and achieve a balance with the physical properties of the barrier layer, the second outer layer may be formed as a single layer or by stacking two or more separate layers.

[0050] Furthermore, in the bag film of this application, the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer according to Formula 1 is in the range of 0.9 to 1.2. For example, the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer according to Formula 1 is 0.90 or greater, 0.91 or greater, 0.93 or greater, 0.95 or greater, 0.97 or greater, 1.00 or greater, 1.01 or greater, 1.03 or greater, 1.05 or greater, 1.07 or greater, 1.09 or greater, 1.20 or less, 1.19 or less, 1.17 or less, 1.15 or less, 1.13 or less, 1.11 or less, or 1.10 or less, and specifically, this value is in the range of 0.95 to 1.17. The tensile strength and elongation of the barrier layer and the outer layer are among the main properties that may be related to the formability of the bag film. For example, as tensile strength increases, toughness can increase, and as elongation increases, the limit of formability may increase.

[0051] Figure 2 This is a diagram showing the tensile strength of the barrier layer and the outer layer. In Figure 2 In the diagram, the dashed lines represent the tensile strength curves of the barrier layer Al with thicknesses of 60 μm and 80 μm, while the solid lines represent the tensile strength curves of the second outer layer Ny corresponding to each thickness. When the ratio of the tensile strength of the second outer layer to that of the barrier layer is too low, the formability will be significantly reduced. Therefore, by increasing the thickness of the second outer layer, the ratio of the tensile strength of the barrier layer to that of the second outer layer is controlled to be close to 1.

[0052] In other words, by controlling the bag film of this application to simultaneously satisfy the thickness range of the second outer layer and the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer, optimal tensile strength and elongation characteristics are simultaneously achieved. Therefore, this application can provide a bag film with excellent formability, which can increase the thickness retention rate of the barrier layer and can be finely and accurately formed to the desired dimensions.

[0053] According to embodiments of this application, the thickness of the first outer layer can be in the range of 5 μm to 40 μm. As the thickness of the first outer layer decreases while the thickness of the second outer layer increases, moldability becomes more favorable. However, as the thickness of the first outer layer becomes thinner, the insulation breakdown voltage may become more unfavorable. From this perspective, the thickness of the first outer layer can be 5 μm or greater, 8 μm or greater, 10 μm or greater, 12 μm or greater, 40 μm or less, 39 μm or less, 37 μm or less, 35 μm or less, 33 μm or less, 31 μm or less, 30 μm or less, 29 μm or less, 27 μm or less, 25 μm or less, 23 μm or less, 21 μm or less, 20 μm or less, 19 μm or less, 17 μm or less, 15 μm or less, or 13 μm or less.

[0054] According to embodiments of this application, the thickness of the barrier layer can be in the range of 40 μm to 100 μm. The barrier layer can be an intermediate layer (a layer disposed between the outer layer and the sealing layer) of a pouch membrane for the exterior of a lithium secondary battery, and can be used to block the intrusion of gas and / or moisture.

[0055] There are no particular restrictions on the type of barrier layer, but the barrier layer may include one or more materials selected from the group consisting of aluminum, stainless steel, copper, titanium and their alloys, and may specifically include aluminum.

[0056] Furthermore, as an example, the thickness of the barrier layer can be 40 μm or greater, 42 μm or greater, 44 μm or greater, 46 μm or greater, 48 μm or greater, 50 μm or greater, 52 μm or greater, 54 μm or greater, 56 μm or greater, 58 μm or greater, 60 μm or greater, 62 μm or greater, 64 μm or greater, 66 μm or greater, 68 μm or greater, 70 μm or greater, 72 μm or greater, 74 μm or greater, 75 μm or greater, 100 μm or less, 99 μm or less, 98 μm or less, 96 μm or less, 94 μm or less, 92 μm or less, 90 μm or less, 88 μm or less, 86 μm or less, 84 μm or less, 82 μm or less, 80 μm or less, 78 μm or less, or 76 μm. The thickness is μm or smaller, specifically in the range of 70 μm to 90 μm. When the thickness range of the barrier layer is met, the intrusion of gas and / or moisture can be effectively blocked, while the tensile strength ratio with the second outer layer can be maintained within a specific range, thus ensuring excellent formability.

[0057] According to embodiments of this application, the ratio of the thickness of the barrier layer to the thickness of the second outer layer can be in the range of 1:0.5 to 1:0.7. For example, the thickness ratio of the barrier layer to the second outer layer can be 1:0.50 or greater, 1:0.51 or greater, 1:0.53 or greater, 1:0.55 or greater, 1:0.57 or greater, 1:0.59 or greater, 1:0.60 or greater, 1:0.61 or greater, 1:0.63 or greater, 1:0.70 or less, 1:0.69 or less, 1:0.67 or less, or 1:0.65 or less, and specifically, the thickness ratio of the barrier layer to the second outer layer can be in the range of 1:0.5 to 1:0.69.

[0058] Furthermore, according to embodiments of this application, the sum of the thicknesses of the first outer layer and the second outer layer can be in the range of 50 μm to 80 μm. For example, the sum of the thicknesses of the first outer layer and the second outer layer can be 50 μm or greater, 52 μm or greater, 55 μm or greater, 57 μm or greater, 60 μm or greater, 62 μm or greater, 80 μm or less, 78 μm or less, 76 μm or less, 74 μm or less, 72 μm or less, 70 μm or less, 69 μm or less, 67 μm or less, or 65 μm or less, and specifically, the sum of the thicknesses of the first outer layer and the second outer layer can be in the range of 52 μm to 67 μm.

[0059] Furthermore, according to embodiments of this application, the ratio of the thickness of the barrier layer to the sum of the thicknesses of the first outer layer and the second outer layer can be in the range of 1:0.65 to 1:0.9. For example, the ratio of the thickness of the barrier layer to the sum of the thicknesses of the first and second outer layers can be 1:0.65 or greater, 1:0.67 or greater, 1:0.69 or greater, 1:0.70 or greater, 1:0.71 or greater, 1:0.73 or greater, 1:0.75 or greater, 1:0.77 or greater, 1:0.78 or greater, 1:0.90 or less, 1:0.89 or less, 1:0.87 or less, 1:0.85 or less, 1:0.84 or less, 1:0.83 or less, 1:0.81 or less, or 1:0.80 or less. Specifically, the ratio of the thickness of the barrier layer to the sum of the thicknesses of the first and second outer layers can be in the range of 1:0.65 to 1:0.84.

[0060] The ratio of the thickness of the barrier layer to the thickness of the second outer layer, the sum of the thicknesses of the first and second outer layers, and the ratio of the thickness of the barrier layer to the sum of the thicknesses of the first and second outer layers are designed to simultaneously maintain high levels of tensile strength and elongation, while reducing the thickness retention rate of the barrier layer after molding to ensure excellent formability, and to control the balance between the physical properties of the outer layers and the barrier layer. In other words, by satisfying the thickness range between the barrier layer, the first outer layer, and the second outer layer, the thickness retention rate of the barrier layer can be improved, while maintaining excellent formability.

[0061] According to an embodiment of this application, the MD elongation and TD elongation of the second outer layer can be independently within the range of 50% to 300%. For example, the MD elongation and TD elongation of the second outer layer can be 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 300% or less, 290% or less, 280% or less, 270% or less, 260% or less, 250% or less, 240% or less, 230% or less, 220% or less, 210% or less, 200% or less, 190% or less, 180% or less, 170% or less, 160% or less, 150% or less, 140% or less, 130% or less, 120% or less, 110% or less, 100% or less, 95% or less, 90% or less, 85% or less, or 80% or less.

[0062] Furthermore, according to embodiments of this application, the tensile strength of the second outer layer along the MD direction can be in the range of 200N / 15mm to 300N / 15mm. For example, the tensile strength of the second outer layer along the MD direction can be 200 N / 15 mm or greater, 205 N / 15 mm or greater, 210 N / 15 mm or greater, 213 N / 15 mm or greater, 215 N / 15 mm or greater, 220 N / 15 mm or greater, 225 N / 15 mm or greater, 230 N / 15 mm or greater, 235 N / 15 mm or greater, 240 N / 15 mm or greater, 245 N / 15 mm or greater, 250 N / 15 mm or greater, 255 N / 15 mm or greater, 300 N / 15 mm or less, 295 N / 15 mm or less, 290 N / 15 mm or less, 285 N / 15 mm or less, 280 N / 15 mm or less, 276 N / 15 mm or less, 275 N / 15 mm or less, 270 N / 15 mm or less, 270 N / 15 mm or less. mm or smaller, 269 N / 15 mm or smaller, 265 N / 15 mm or smaller, or 260 N / 15 mm or smaller.

[0063] When the elongation and tensile strength of the second outer layer are within the specified range, the balance with the physical properties of the barrier layer can be optimally maintained, and the thickness retention rate of the barrier layer after molding can be increased.

[0064] According to an embodiment of this application, according to Formula 2, the thickness retention rate of the barrier layer can be 55% or greater.

[0065] [Equation 2] Thickness retention rate (%) = (Thickness of the barrier layer after molding / Thickness of the barrier layer before molding) × 100 In Equation 2, After cutting the bag film excluding the sealing portion, a sample with dimensions of 266 mm (TD) × 240 mm (MD) × 15 mm (width) was prepared. Low-density polyethylene (LDPE) was added to both sides of the sample. The sample was then pressed using a 30 mm × 75 mm test mold at 0.3 MPa until it reached a molding depth of 17 mm. The thickness of the formed barrier layer was then measured. In this case, the average thickness of the barrier layer was calculated by measuring six times at each of the four corners of the rectangular molded shape.

[0066] The thickness retention rate of the barrier layer corresponds to a very important criterion determining the formability of the bag film. Due to the stretching of the barrier layer, shrinkage may occur even after forming to the desired depth, potentially leading to moisture penetration and electrolyte leakage. Therefore, it is important to maintain the thickness of the formed barrier layer at a high level, and for example, the thickness retention rate can be 55% or greater, 57% or greater, 59% or greater, 60% or greater, 61% or greater, 63% or greater, or 65% or greater. Meeting the barrier layer thickness retention rate ensures formability of 17 mm or greater based on 1 cup and 30 mm or greater based on 2 cups. Here, low-density polyethylene (LDPE) can be a laminated film laminated to one surface of the barrier layer to replace CPP film for formability testing, and may also contain polyethylene (PE), and the thickness of the LDPE can be in the range of 40 μm to 60 μm, preferably 50 μm. Additionally, the coefficient of friction of LDPE can be in the range of 0.05 to 0.5, preferably 0.1.

[0067] According to embodiments of this application, the thickness of the bag film can be in the range of 205 μm to 250 μm. For example, the total thickness of the bag film can be 205 μm or greater, 210 μm or greater, 212 μm or greater, 215 μm or greater, 220 μm or greater, 222 μm or greater, 225 μm or greater, 227 μm or greater, 250 μm or less, 245 μm or less, 240 μm or less, or 235 μm or less, or 230 μm or less. When the total thickness of the bag film is too thick, the balance of physical properties between tensile strength and elongation may be biased to one side; therefore, it is preferable to keep the thickness of the bag film within the above-mentioned range.

[0068] According to embodiments of this application, the first outer layer may include one or more materials selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylenebenzodioxazole), polyarylate, Teflon, and glass fiber. For example, the first outer layer may include polyethylene terephthalate.

[0069] The sealing layer can be the innermost layer of a pouch membrane used on the exterior of a lithium secondary battery. That is, the sealing layer can be in direct contact with the battery body (e.g., electrodes, separator, and / or electrolyte). Therefore, the sealing layer should have excellent electrolyte resistance and excellent insulation properties. For this purpose, the sealing layer can comprise at least a polyolefin-based resin. Polyolefin-based resins can have excellent electrolyte resistance and excellent insulation properties; therefore, a sealing layer comprising a polyolefin-based resin can also possess the excellent electrolyte resistance and excellent insulation properties derived from polyolefin-based resins.

[0070] Polyolefin-based resins may comprise, for example, polyolefins derived from olefins or their derivatives, copolymers thereof, or blends comprising at least one of them. For example, polyolefin-based resins may comprise one or more copolymers and blends thereof selected from the group consisting of polyethylene, polypropylene, polybutene, monomers derived from ethylene and / or propylene, and monomers derived from α-olefins.

[0071] For example, the thickness of the sealing layer can be 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less, and when the above numerical range is met, the sealing layer can have excellent electrolyte resistance and insulation.

[0072] According to embodiments of this application, the sealing layer can be configured as a laminate comprising two or more layers to diversify its functions. Specifically, the sealing layer may include a first sealing layer disposed on a barrier layer and a second sealing layer disposed on the first sealing layer. Here, the first sealing layer may be a layer that assists in the adhesion between the barrier layer and the second sealing layer and further enhances its function as a sealing layer, and the second sealing layer may be a sealing layer constituting the innermost side of the bag film and used for sealing and preventing leakage of the secondary battery, particularly the non-aqueous electrolyte. The first sealing layer may be an EC layer (mainly an extruded polypropylene layer), and the second sealing layer may be a PP resin layer located below the first sealing layer (relative to the inner side of the bag film), preferably a CPP layer. In this case, for example, the thickness of the CPP layer of the sealing layer can be, for example, 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, 80 μm or less, 70 μm or less, or 60 μm or less, and the thickness of the PP layer of the sealing layer can be, for example, 0 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 60 μm or less, 50 μm or less, or 40 μm or less.

[0073] In addition, according to the embodiments of this application, the PP layer of the sealing layer may contain various additives (rubber, elastomer, lubricant, etc.) depending on the required physical properties.

[0074] pouch-type secondary battery casing and secondary battery The secondary battery of this application includes a battery body and a pouch-type secondary battery casing including a diaphragm, and the secondary battery casing may include the diaphragm of this application. The battery body is sealed by the pouch-type secondary battery casing. For example, the secondary battery may be a lithium secondary battery, and in this case, the battery body may include a negative electrode for the lithium secondary battery, a positive electrode for the lithium secondary battery, and an electrolyte.

[0075] The positive electrode used in lithium secondary batteries can be any commonly used positive electrode for lithium secondary batteries, without particular limitation. For example, the positive electrode for lithium secondary batteries can contain positive electrode active materials such as LiCoO2, LiMnO2, LiFePO4, LiFeO2, or Li(Ni) 0.6 Mn 0.2 Co 0.2 )O2.

[0076] The electrolyte may include lithium salts and non-aqueous organic solvents. Here, lithium salts and non-aqueous organic solvents commonly used as electrolytes and organic solvents in lithium secondary batteries can be used without particular limitation.

[0077] The negative electrode used in lithium secondary batteries can be any negative electrode commonly used in lithium secondary batteries, without particular limitations. For example, the negative electrode used in lithium secondary batteries can contain negative electrode active materials, such as carbon-based active materials and silicon-based active materials.

[0078] Pouch-type secondary battery casings offer excellent sealing strength characteristics. Therefore, the battery body sealed by the pouch-type secondary battery casing is not exposed to the external environment.

[0079] Methods for manufacturing bag films The method for manufacturing the bag film according to the present invention will be described below. The method for manufacturing the bag film is not limited to the method described below; the method described below can be one of various methods for manufacturing bag films.

[0080] This application provides a method for manufacturing a bag film, the method comprising: stacking a sealing film on one surface of a barrier film; and sequentially stacking a second outer layer and a first outer layer on another surface of the barrier film, wherein the second outer layer comprises a nylon-based resin and is manufactured by blow molding.

[0081] Blow molding is a method of melting and extruding a polymer, injecting air, and then inflating the film like a balloon. It is mainly used in the production of high-strength films such as nylon. Specifically, blow molding can include operations such as extrusion, tube forming, blowing, cooling, flattening, and winding. Extrusion refers to the operation of heating polymer granules and then converting them into a molten state through an extruder, and tube forming refers to the operation of extruding molten polymer into a cylindrical tube shape through a die. Blowing is the operation of injecting air into the center of the tube and inflating it, and the film thickness can also be adjusted during the blow molding operation. Then, a second outer layer is produced by a cooling operation to cool the expanded tube, a flattening operation to pass the cooled tube between pressure rollers and form the tube into a film shape, and a winding operation to wind the film into a roll shape.

[0082] Furthermore, based on the direction of air injection during the blowing operation, blow molding can be divided into upward blowing and downward blowing. Upward blowing is advantageous for manufacturing films with a thickness of 25 μm or less, but it is difficult to increase the thickness to 25 μm or greater, and quality control may be challenging due to cooling uniformity issues. As the thickness increases, uneven cooling easily occurs, affecting the mechanical properties or quality of the film, thus presenting current technological limitations in increasing nylon thickness and applying it to secondary batteries. Conversely, downward blowing, utilizing gravity, is advantageous for manufacturing films with a thickness of 40 μm or less and can maintain a relatively stable thickness between 25 μm and 40 μm. However, when the thickness is excessively increased, cooling efficiency may decrease, potentially leading to quality problems.

[0083] The second outer layer, manufactured by blow molding, can elongate together with the barrier layer during molding, thus the formability of the bag film can be excellent.

[0084] When biaxial stretching is used in addition to blow molding, tensile strength and durability may be improved, but flexibility and elongation may be significantly reduced, thus potentially resulting in a low level of formability.

[0085] The embodiments of this application will be described in detail below to enable those skilled in the art to readily implement this application. However, this application can be implemented in various different forms and is not limited to the embodiments described herein.

[0086] <Examples and Comparative Examples> Example 1 The bag film is a laminate comprising an outer layer, a barrier layer, and a sealing layer. The outer layer consists of an outermost polyethylene terephthalate (PET) film (12 μm thick) and innermost first nylon Ny film (25 μm thick) and second nylon Ny film (25 μm thick). The bag film is manufactured using aluminum as a barrier layer (80 μm thick) and a sealing layer (80 μm thick) comprising a polypropylene EC layer (30 μm thick) and a CPP layer (50 μm thick), produced using an extrusion lamination method. The first and second nylon laminates are manufactured by an upward blowing process, and the elongation, extrusion speed, temperature, and pressure conditions of the barrier layer and the first nylon film are adjusted during manufacturing. In this case, the ratio of the thickness of the second outer layer Ny1+Ny2 to the thickness of the barrier layer Al is 0.63, the ratio of the thickness of the entire outer layer PET+Ny1+Ny2 to the thickness of the barrier layer Al is 0.78, and the ratio of the tensile strength of the barrier layer Al to the tensile strength of the second outer layer Ny1+Ny2 is 1.00.

[0087] Example 2 The bag film is a laminate comprising an outer layer, a barrier layer, and a sealing layer. The outer layer consists of an outermost polyethylene terephthalate (PET) film (12 μm thick) and innermost first nylon Ny film (15 μm thick) and second nylon Ny film (25 μm thick). The bag film is manufactured using aluminum as a barrier layer (80 μm thick) and a sealing layer (80 μm thick) comprising a polypropylene EC layer (30 μm thick) and a CPP layer (50 μm thick) produced by an extrusion lamination method. The first and second nylon laminates are manufactured by an up-blown process, and the elongation, extrusion speed, temperature, and pressure conditions of the barrier layer and the first nylon film are adjusted during manufacturing. In this case, the ratio of the thickness of the second outer layer Ny1+Ny2 to the thickness of the barrier layer Al is 0.50, the ratio of the thickness of the entire outer layer PET+Ny1+Ny2 to the thickness of the barrier layer Al is 0.65, and the ratio of the tensile strength of the barrier layer Al to the tensile strength of the second outer layer Ny1+Ny2 is 1.17.

[0088] Example 3 The bag film is a laminate comprising an outer layer, a barrier layer, and a sealing layer. The outer layer consists of an outermost polyethylene terephthalate (PET) film (12 μm thick) and innermost first nylon Ny film (25 μm thick) and second nylon Ny film (30 μm thick). The outer layer uses aluminum as a barrier layer (80 μm thick) and a sealing layer (80 μm thick) comprising a polypropylene EC layer (30 μm thick) and a CPP layer (50 μm thick), manufactured using an extrusion lamination method. The first and second nylon laminates are manufactured by an up-blown process, and the elongation, extrusion speed, temperature, and pressure conditions of the barrier layer and the first nylon film are adjusted during manufacturing. In this case, the ratio of the thickness of the second outer layer Ny1+Ny2 to the thickness of the barrier layer Al is 0.69, the ratio of the thickness of the entire outer layer PET+Ny1+Ny2 to the thickness of the barrier layer Al is 0.84, and the ratio of the tensile strength of the barrier layer Al to the tensile strength of the second outer layer Ny1+Ny2 is 0.95.

[0089] Example 4 The bag film is constructed as a laminate comprising an outer layer, a barrier layer, and a sealing layer, wherein an outermost PET film (12 μm thick) and an innermost nylon Ny film (40 μm thick) are used as the outer layer. An 80 μm thick sealing layer is constructed using aluminum as the barrier layer and an 80 μm thick sealing layer comprising a 30 μm thick polypropylene EC layer and a 50 μm thick CPP layer, produced using an extrusion lamination method. The nylon layer is manufactured by a down-blown process, and the elongation, extrusion speed, temperature, and pressure conditions of the barrier layer and the nylon film are adjusted during manufacturing. In this case, the ratio of the thickness of the second outer Ny layer to the thickness of the barrier layer A1 is 0.50, the ratio of the total thickness of the outer PET+Ny layer to the thickness of the barrier layer A1 is 0.65, and the ratio of the tensile strength of the barrier layer A1 to the tensile strength of the second outer Ny layer is 0.99.

[0090] Comparative Example 1 The bag film was manufactured in the same manner as in Example 1, except that a laminated film using a nylon (Ny) film (25 μm thick) and a second nylon Ny film (25 μm thick) was used instead of a laminated film using a first nylon Ny film (25 μm thick) and a second nylon Ny film (25 μm thick) and an aluminum barrier layer (80 μm thick) was used.

[0091] Comparative Example 2 The bag film was manufactured in the same manner as in Example 1, except that a nylon (Ny) film (25 μm thick) was used instead of a laminated film consisting of a first nylon (Ny) film (25 μm thick) and a second nylon (Ny) film (25 μm thick).

[0092] Comparative Example 3 The bag film was manufactured in the same manner as in Example 1, except that a nylon (Ny) film (thickness of 30 μm) was used instead of a laminated film consisting of a first nylon (Ny) film (thickness of 25 μm) and a second nylon (Ny) film (thickness of 25 μm).

[0093] Experimental Example (1) Evaluation of tensile strength and elongation For tensile strength, according to the examples and comparative examples, after preparing a 15 mm wide specimen by peeling off the barrier layer and the second outer layer of the bag film, the specimen was fixed between the two clamps of the tensile testing machine UTM at room temperature (initial clamp gap of 50 mm), and then the specimen was stretched along the MD direction at a measuring speed of 50 mm / min while the stroke (mm) and strength (N) of the specimen were measured. The measured tensile strength values ​​are shown in Table 1 below.

[0094] In addition, the elongation in this application is measured by the following method: Two parallel lines are drawn at the center of the specimen, and the initial spacing between the lines is set to 30 mm. Then, the specimen is mounted on a tensile testing machine for a tensile strength test, and the actual length between the lines elongated due to tension is measured.

[0095] The elongation is calculated according to Formula 1 below, and the elongation is shown in Table 1.

[0096] [Formula 1] Elongation = ((elongated length - 30mm) / 30mm) x 100 In Equation 1, The elongation is the final distance between the two lines after the tensile test.

[0097] Then, in the graph obtained from the measurements, the X-axis represents the stroke (mm) and the Y-axis represents the tensile strength (N). The tensile strength of the barrier layer and the second outer layer was measured when the stroke was 5mm, and the tensile strength ratio of the tensile strength of the barrier layer Al to the tensile strength of the second outer layer Ny1+Ny2 is shown in Table 1 below.

[0098] (2) Evaluation of thickness retention rate after molding The bag film according to the examples and comparative examples was cut into specimens excluding the sealing portion, with dimensions of 266 mm (TD) × 240 mm (MD) × 15 mm (width). LDPE was added to both sides of the specimen, and the specimen was pressed at 0.3 MPa using a test mold with dimensions of 30 mm × 75 mm, and then the specimen was molded to a molding depth of 17 mm. The thickness of the barrier layer after molding was measured. In this case, the average thickness of the barrier layer was calculated by measuring six times at each of the four corners of the rectangular molded shape. The measured remaining thickness and the measured thickness retention rate of the barrier layer after molding are then shown in Table 1 below.

[0099] (3) Maximum molding measurement evaluation In addition, for the bag films manufactured in the examples and comparative examples, 1-cup molding was evaluated, and the average value of the maximum molding length was measured using vernier calipers.

[0100] [Table 1]

[0101] Refer to Table 1 and Figure 3 and Figure 4 In the cases of Examples 1 to 4, which satisfy the thickness of the second outer layer and the ratio of the tensile strength of the second outer layer to the tensile strength of the barrier layer according to the present application, it can be determined that the thickness during cup molding is greater than that of the comparative example, and the thickness retention rate of the barrier layer after molding is high, thus achieving excellent moldability.

[0102] Furthermore, even in the case of Example 4, since a single-layer film is used instead of a laminated film as the second outer layer, it can be determined that the same formability as in Examples 1 to 3 is achieved.

[0103] On the other hand, in the case of Comparative Examples 1 to 3 where the ratio of the thickness to tensile strength of the second outer layer is not satisfied, it can be determined that the thickness during cup molding is less than that of the embodiment, and the thickness retention rate after molding is also low. Therefore, the moldability is worse than that of the embodiment.

[0104] (4) Evaluate the thickness retention rate after molding based on the manufacturing method of nylon. As described below, a bag film containing the nylon laminate was manufactured after forming the nylon laminate using a biaxial stretching method instead of a blow molding method. For Comparative Examples a and b below Example 1, measurements were similarly performed according to the thickness retention rate evaluation after molding (2). The remaining thickness and thickness retention rate of the barrier layer after molding are shown in Table 2 below.

[0105] <Comparative Example a> The bag film was manufactured in the same manner as in Example 1, except that the biaxial stretching method was used instead of the blow molding method to manufacture the nylon laminated film.

[0106] <Comparative Example b> The bag film was manufactured in the same manner as in Example 1, except that a nylon (Ny) film (45 μm thick) manufactured by biaxial stretching (instead of blow molding) was used instead of a laminated film of a first nylon (Ny) film (25 μm thick) and a second nylon (Ny) film (25 μm thick) to manufacture the nylon laminate.

[0107] [Table 2]

[0108] Referring to Table 2, it can be determined that, compared with Comparative Examples a and b manufactured by biaxial stretching according to the related art, Examples 1 and 4 manufactured by top blowing and bottom blowing according to this application exhibit significantly superior formability.

[0109] Acknowledgments This application was the result of support from the following projects.

[0110] Project Number: 20022450 Department Name: Trade, Industry and Resources Department Project Management (Professional) Organization Name: Korea Institute for Industrial Technology Evaluation Research Project Title: Materials and Component Technology Development (Leading Enterprise) Research Project Title: Development of Next-Generation Rechargeable Battery Bags Capable of Achieving High Adhesion Strength (60°C) More Than Two Blows Contribution rate: 1 / 1 Project implementing organization: Youlchon Chemical Co., Ltd. Research period: January 1, 2024 to December 31, 2024.

Claims

1. A bag film, comprising: The sealing layer, the barrier layer, the second outer layer, and the first outer layer are stacked in sequence. The second outer layer comprises a nylon-based resin. The thickness of the second outer layer is in the range of 35 μm to 60 μm, and Wherein, the ratio of the tensile strength of the barrier layer to the tensile strength of the second outer layer, as measured according to the measurement conditions, satisfies Equation 1. [Equation 1], 0.9 ≤ tensile strength of the barrier layer / tensile strength of the second outer layer ≤ 1.2, and [Measurement Conditions] After peeling off the barrier layer and the second outer layer of the bag film to prepare a corresponding specimen with a width of 15 mm, the specimen is fixed between two clamps of a tensile testing machine (UTM) at room temperature (initial clamp gap of 50 mm). The specimen is then stretched along the MD direction at a measuring speed of 50 mm / min while the stroke (mm) and strength (N) of the specimen are measured. In the graph derived from the measurements, the X-axis is the stroke (mm) and the Y-axis is the tensile strength (N). The tensile strength of the barrier layer and the second outer layer is measured when the stroke is 5 mm.

2. The bag film according to claim 1, wherein, The ratio of the thickness of the barrier layer to the thickness of the second outer layer is in the range of 1:0.5 to 1:0.

7.

3. The bag film according to claim 1, wherein, The thickness of the barrier layer is in the range of 40 μm to 100 μm.

4. The bag film according to claim 1, wherein, The sum of the thickness of the first outer layer and the thickness of the second outer layer is in the range of 40 μm to 100 μm.

5. The bag film according to claim 1, wherein, The ratio of the thickness of the barrier layer to the sum of the thicknesses of the first outer layer and the second outer layer is in the range of 1:0.65 to 1:0.

9.

6. The bag film according to claim 1, wherein, The MD elongation and TD elongation of the second outer layer are independently in the range of 50% to 300%.

7. The bag film according to claim 1, wherein, The tensile strength of the second outer layer along the MD direction is in the range of 200 N / 15 mm to 300 N / 15 mm.

8. The bag film according to claim 1, wherein, According to Equation 2, the thickness retention rate of the barrier layer is 55% or higher. [Equation 2], Thickness retention rate (%) = (thickness of the barrier layer after molding / thickness of the barrier layer before molding) × 100, In Equation 2, After cutting the bag film excluding the sealing part, a sample with dimensions of 266mm (TD) × 240mm (MD) × 15mm (width) was prepared. Low-density polyethylene (LDPE) was added to both sides of the sample. The sample was pressed at 0.3 MPa using a test mold with dimensions of 30mm × 75mm, and then the sample was molded to a molding depth of 17mm. The thickness of the barrier layer after molding was measured. In this case, the average thickness of the barrier layer was calculated by measuring six times at each of the four corners of the rectangular molded shape.

9. The bag film according to claim 1, wherein, The second outer layer comprises a single layer or a stack of two or more layers.

10. The bag film according to claim 1, wherein, The thickness of the bag film is in the range of 205 μm to 250 μm.

11. The bag film according to claim 1, wherein, The first outer layer comprises one or more materials selected from the group consisting of: polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, poly(p-phenylenebenzodioxazole), polyarylate, Teflon, and glass fiber.

12. The bag film according to claim 1, wherein, The thickness of the first outer layer is in the range of 5 μm to 40 μm.

13. The bag film according to claim 1, wherein, The barrier layer comprises one or more materials selected from the group consisting of aluminum, stainless steel, copper, titanium, and alloys thereof.

14. A pouch-type battery casing, comprising the pouch membrane according to claim 1.

15. A secondary battery, comprising: An electrode assembly in which a positive electrode, a separator, and a negative electrode are stacked and formed. and The electrode assembly is housed within the pouch-type battery housing according to claim 14.

16. A method for manufacturing a bag film, the method comprising: A sealing film is stacked on one surface of the barrier film; and A second outer layer and a first outer layer are sequentially stacked on the other surface of the barrier film. The second outer layer comprises a nylon-based resin, and The second outer layer is manufactured by blow molding.

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