Pouch film and manufacturing method therefor

Abstract

The present invention relates to a pouch film comprising: a sealant layer; an outer layer; and a barrier layer between the sealant layer and the outer layer, comprising aluminum, wherein the number of air bubbles per unit area on the surface of the sealant layer is 0.1 ea / mm2 to 20 ea / mm2, and the number of air bubbles is reduced such that inflow of an electrolyte solution during battery cell manufacturing or cracking of the sealant layer after molding is prevented, and structural stability can be improved.

Description

Pouch film and method for manufacturing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0160565, filed November 20, 2023, and Korean Patent Application No. 10-2024-0164502, filed November 18, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Technology field

[0005] The present invention relates to a pouch film and a method for manufacturing the same.

[0006]

[0007] Secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries. These batteries are used in small products such as digital cameras, DVD players, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes, as well as larger products requiring high output, such as electric and hybrid vehicles, as well as power storage devices that store surplus power or renewable energy, and as backup power storage devices.

[0008] To manufacture these secondary batteries, first, an electrode active material slurry is applied to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, and these are laminated on both sides of a separator to form an electrode assembly of a predetermined shape. Then, the electrode assembly is housed in a battery case, filled with electrolyte, and sealed.

[0009] Secondary batteries can be classified into pouch, cylindrical, and square types depending on the type of outer material of the case that accommodates the electrode assembly.

[0010] Among these secondary batteries, pouch-type batteries are in the form where the electrode assembly (cell) is built into a pouch made of a metal laminate sheet. They are easy to manufacture, have low manufacturing costs, and are particularly advantageous in that it is easy to manufacture a large-capacity battery pack (battery pack) by connecting multiple unit cells in series or parallel. Therefore, they are mainly used in fields that require large-capacity secondary batteries, such as electric vehicles. The pouch, which is the case of the pouch-type secondary battery, is manufactured by performing press processing on a flexible pouch film laminate to form a cup portion. Then, when the cup portion is formed, the electrode assembly is accommodated in the receiving space of the cup portion, and the sealing portion is sealed to manufacture the secondary battery.

[0011] Meanwhile, conventional pouch film products can generate bubbles at the interface between a sealant layer, for example, a sealant layer including polypropylene, and a barrier layer during the lamination process due to air inflow or differences in the sliding speed of the polypropylene. These bubbles can cause cracks or defects in the sealant layer during the inflow of electrolyte when manufacturing a secondary battery cell or after molding. Therefore, research on process methods for reducing these bubbles is essential.

[0012]

[0013] The problem to be solved by the present invention is to provide a method for manufacturing a pouch film capable of reducing the insulation resistance failure rate by reducing bubbles occurring at the interface of a sealant layer.

[0014] In addition, the problem to be solved by the present invention is to provide a pouch film that can prevent electrolyte from flowing into the pouch film and increase electrical efficiency by controlling the number of bubbles in the sealant layer.

[0015]

[0016] The present invention provides a pouch film and a method for manufacturing the same.

[0017] (1) The present invention comprises a sealant layer, an outer layer, and a barrier layer containing aluminum between the sealant layer and the outer layer, and the number of bubbles per unit area of ​​the surface of the sealant layer is 2.5 ea / mm. 2 More than 20 ea / mm 2 A pouch film is provided as follows.

[0018] (2) The present invention provides a pouch film in which, in the above (1), the ratio of bubbles to the surface unit area of ​​the sealant layer is 0.1% or more and 1.1% or less.

[0019] (3) In the present invention, in the above (1) or (2), the number of bubbles per unit area of ​​the bubbles having a long side of 20 ㎛ or more is 6.0 ea / mm. 2 A pouch film is provided as follows.

[0020] (4) In any one of the above (1) to (3), the number of bubbles having a long side of less than 20 ㎛ among the bubbles is 9 ea / mm. 2 A pouch film is provided as follows.

[0021] (5) The present invention provides a pouch film in which the TD deviation according to the number of bubbles on the surface of the sealant layer measured according to the following measuring method is 5 or less in any one of the above (1) to (4).

[0022] [measurement method]

[0023] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2, the interface between the barrier layer and the sealant layer was photographed using a white LED as a lamp light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of bubbles per unit area was calculated by dividing the measured number by the measured area. The deviation value was calculated by calculating the number of bubbles per unit area at 10 cm intervals based on the entire width of the MR (Mother Roll).

[0024] (6) The present invention provides a pouch film in any one of the above (1) to (5), wherein the sealant layer includes at least one selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber.

[0025] (7) The present invention provides a pouch film according to any one of the above (1) to (6), wherein the sealant layer includes an extrusion coating layer and a non-stretched polypropylene layer.

[0026] (8) The present invention provides a pouch film having an insulation resistance failure rate of less than 0.9% according to the method described below, in any one of the above (1) to (7).

[0027] [Method for Measuring Insulation Resistance Defect Rate]

[0028] 1000 30mm x 40mm dummy cells (small cells) were manufactured, and 250V was applied to the aluminum tab portion and the aluminum layer (barrier layer) of the pouch using an insulation resistance meter to measure the insulation resistance value (GΩ). If it was 100MΩ or less, it was recorded as defective, and the defect rate was calculated.

[0029] (9) The present invention provides a method for manufacturing a pouch film, comprising the steps of introducing a barrier layer and a sealant layer into a roll-to-roll device including a nip roll, a backup roll, and a cooling roll, laminating the sealant layer on one surface of the barrier layer, and attaching an outer layer to the other surface of the barrier layer, wherein the pressure applied to the barrier layer and the sealant layer into which the nip roll has introduced is 5 bar or more and less than 8 bar, and the step difference between the center portion and both ends of the nip roll is more than 0.4 mm and less than 1.2 mm.

[0030] (10) The present invention provides a method for manufacturing a pouch film, wherein, in the above (9), the backup roll is in contact with the nip roll, and the pressure applied by the backup roll to the nip roll is 5 bar or more and less than 8 bar.

[0031] (11) The present invention provides a method for manufacturing a pouch film, wherein in the above (9) or (10), the step of combining is performed by adding an additive including at least one selected from the group consisting of polytetrafluoroethylene, silicone resin, and amide resin.

[0032] (12) The present invention provides a method for manufacturing a pouch film, wherein, in the above (11), the additive is added in an amount of 500 ppm or more and 10,000 ppm or less based on the weight of the entire sealant layer.

[0033] (13) The present invention provides a method for manufacturing a pouch film, wherein the pressure of the nip roll and the pressure applied to the nip roll by the backup roll are the same pressure in any one of the above (9) to (12).

[0034] (14) The present invention provides a method for manufacturing a pouch film, wherein, in any one of the above (9) to (13), the step difference between the central portion and both ends of the nip roll is 0.6 mm or more and 0.8 mm or less.

[0035]

[0036] The pouch film manufacturing method of the present invention can have the effect of reducing the insulation resistance defect rate by controlling the pressure of the nip roll and the backup roll and the crown of the roll and adding an additive during the lamination process to control the number of bubbles in the pouch film.

[0037] The pouch film of the present invention can prevent electrolyte from flowing into the pouch film and increase electrical efficiency by controlling the number of bubbles.

[0038]

[0039] Figure 1 shows the number of bubbles per unit area of ​​the sealant layer according to Example 2.

[0040] Figure 2 shows the number of bubbles per unit area of ​​the sealant layer according to Comparative Example 1.

[0041] Figure 3 shows the number of bubbles per unit area of ​​the sealant layer according to Comparative Example 2.

[0042] Figure 4 is a side view of a nip roll according to the present invention.

[0043]

[0044] Hereinafter, the present invention will be described in more detail to facilitate understanding. The terms and words used in this specification and claims should not be interpreted based on their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concepts of terms to best explain his or her invention, they should be interpreted in a way that aligns with the technical spirit of the present invention.

[0045] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0046] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0047]

[0048] pouch film

[0049] The present invention comprises a sealant layer, an outer layer, and a barrier layer containing aluminum between the sealant layer and the outer layer, wherein the number of bubbles per unit area of ​​the surface of the sealant layer is 0.1 ea / mm. 2 More than 20 ea / mm 2 A pouch film is provided as follows.

[0050] Previously, during the pouch film manufacturing process, problems arose such as air being introduced into the interface of the sealant layer during the lamination process of the sealant layer containing polypropylene, or bubbles being generated due to differences in the sliding speed of the polypropylene, thereby increasing the difficulty of laminating the sealant layer. The bubbles generated above have a high possibility of causing electrolyte to flow into the secondary battery cell when manufacturing the secondary battery cell or causing cracks in the sealant layer after molding, and therefore were problems that absolutely had to be improved in terms of the structural stability and performance of the secondary battery cell.

[0051] Accordingly, the inventor of the present invention controlled various process conditions, such as the nip roll and back roll, used in the process of laminating the sealant layer and the barrier layer, and through this, developed a pouch film in which the number of bubbles generated on the surface of the sealant layer was significantly reduced.

[0052] The number of bubbles per unit area of ​​the surface of the sealant layer of the present invention is 20.0 ea / mm 2 Below 2.5 ea / mm 2 Ideally, the number of bubbles per unit area of ​​the sealant layer surface is 20.0 ea / mm.2 Below, 19.0 ea / mm 2 Below, 18.0 ea / mm 2 Below, 17.0 ea / mm 2 Below, 16.0 ea / mm 2 Below, 15.5 ea / mm 2 Below, 15.0 ea / mm 2 Below, 14.8 ea / mm 2 Below, 14.0 ea / mm 2 Below, 13.8 ea / mm 2 Below, 13.0 ea / mm 2 Below, 12.0 ea / mm 2 Below, 11.0 ea / mm 2 Below, 10.2 ea / mm 2 Below, 10.0 ea / mm 2 Below, 9.0 ea / mm 2 Below, 8.0 ea / mm 2 Below, 0.1 ea / mm 2 Above, 0.5 ea / mm 2 Above, 1.0 ea / mm 2 Above, 1.5 ea / mm 2 Above, 2.0 ea / mm 2 Above, 2.5 ea / mm 2This may be abnormal. If the number of bubbles per unit area of ​​the surface of the sealant layer is outside the upper limit of the above range, a significant number of bubbles may exist on the surface of the sealant layer, which may deteriorate the electrolyte properties, increase the insulation resistance failure rate, deteriorate the insulation properties, and deteriorate the thermal bonding strength and peel strength properties. In addition, if the number of bubbles per unit area of ​​the surface of the sealant layer is outside the lower limit of the above range, theoretically, it is desirable for the number of bubbles to be close to 0, but it is impossible to make the number of bubbles 0 in the actual process, and the manufacturing of a pouch film containing a number of bubbles outside the lower limit range requires very high work and process difficulty, and may be significantly inefficient in terms of cost. In addition, the pressure must be increased to the maximum during the process, but in this case, a problem may arise in which the insulation failure rate rather increases due to resin deterioration. Here, the number of bubbles was measured using the following method. Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed using a white LED as a lamp light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of bubbles per unit area was calculated by dividing the measured area by the measured number.

[0053] In addition, according to one embodiment of the present invention, the number of bubbles per unit area of ​​the bubbles having a long side of 20 ㎛ or more is 6.0 ea / mm 2 It may be as follows. For example, among the above bubbles, the number of bubbles per unit area of ​​the bubbles having a long side of 20 ㎛ or more is 6.0 ea / mm 2 Below, 5.6 ea / mm 2 Below, 5.5 ea / mm 2 Below, 5.0 ea / mm 2 Below, 4.5 ea / mm 2 Below, 4.0 ea / mm 2 Below, 3.5 ea / mm2 Below, 3.3 ea / mm 2 Below, 3.1 ea / mm 2 Below, 3.0 ea / mm 2 Below, 2.9 ea / mm 2 Below, 2.7 ea / mm 2 Below, 2.5 ea / mm 2 It could be as follows:

[0054] In addition, according to one embodiment of the present invention, the number of bubbles per unit area of ​​the bubbles having a long side of less than 20 ㎛ is 9.0 ea / mm 2 It may be as follows. For example, the number of bubbles per unit area of ​​the bubbles having a long side of less than 20 ㎛ among the bubbles is 9.0 ea / mm 2 Below, 8.5 ea / mm 2 Below, 8.4 ea / mm 2 Below, 8.0 ea / mm 2 Below, 7.5 ea / mm 2 Below, 7.0 ea / mm 2 Below, 6.5 ea / mm 2 Below, 6.0 ea / mm 2 Below, 5.5 ea / mm 2 Below, 5.2 ea / mm 2 Below, 5.0 ea / mm 2 Below, 4.5 ea / mm 2 Below, 4.0 ea / mm 2 Below, 3.5 ea / mm 2 Below, 3.0 ea / mm 2 Below, 2.5 ea / mm 2 Below, 2.0 ea / mm 2 Below, 1.9 ea / mm 2 Below, 1.7 ea / mm 2 Below, 1.5 ea / mm 2It may be below. The size of the bubbles existing on the surface of the sealant layer varies, and when classified by bubble size, the bubbles can be classified into small-diameter bubbles having a long side of about 0 ㎛ to less than 20 ㎛ and large-diameter bubbles having a long side of 20 ㎛ or more. Here, in the case of large-diameter bubbles having a size of 20 ㎛ or more, the effect on the deterioration of the physical properties of the pouch film is greater than that of small-diameter bubbles, so it is important to reduce the number of large-diameter bubbles. Accordingly, when the number of bubbles per unit area of ​​the bubbles having a long side of 20 ㎛ or more and the number of bubbles per unit area of ​​the bubbles having a long side of less than 20 ㎛ are controlled within the above ranges, the electrolyte resistance properties, insulation properties, thermal bonding strength, and peel strength properties can be improved. Here, the long side refers to the length of the longest axis when the bubbles have a circular, elliptical, or irregular shape.

[0055] Here, the long side of the bubble is measured using an optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed and measured using a white LED as a lamp light source.

[0056] According to one embodiment of the present invention, the ratio of bubbles to the surface unit area of ​​the sealant layer may be 0.1% or more and 1.1% or less. For example, the ratio of bubbles to the entire surface of the sealant layer may be 1.10% or less, 1.05% or less, 1.00% or less, 0.95% or less, 0.90% or less, 0.85% or less, 0.80% or less, 0.75% or less, 0.70% or less, 0.65% or less, 0.50% or less, 0.45% or less, 0.43% or less, 0.40% or less, 0.35% or less, 0.30% or less, 0.25% or less, 0.24% or less, 0.18% or less, 0.16% or less, 0.15% or less, or 0.13% or less. When the ratio of bubbles to the surface unit area of ​​the sealant layer satisfies the above range, it can have excellent thermal bonding strength and insulation resistance characteristics. Here, the ratio of bubbles can be measured by the following method. Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed using a white LED as a light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. After measurement, the measured area was 1.637 mm by adding the area of ​​bubbles. 2 The number of bubbles per area was calculated by dividing by .

[0057] According to one embodiment of the present invention, the TD deviation according to the number of bubbles on the surface of the sealant layer measured according to the following measuring method may be 5 or less.

[0058] [measurement method]

[0059] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2, the interface between the barrier layer and the sealant layer was photographed using a white LED as a lamp light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of bubbles per unit area was calculated by dividing the measured number by the measured area. The deviation value was calculated by calculating the number of bubbles per unit area at 10 cm intervals based on the entire width of the MR.

[0060] Specifically, the TD deviation according to the number of bubbles on the surface of the sealant layer can be divided into five zones: the first end (OS, operation side), the second end, the center (CEN, center), the third end, and the fourth end (DS, drive side) by dividing the area in the TD direction of the surface of the sealant layer into equal width lengths from the edge of the MR of the sealant layer specimen, and the deviation of the number of bubbles present in each zone is calculated. For example, the TD deviation according to the number of bubbles may be 5.0 or less, 4.5 or less, 4.0 or less, 3.8 or less, 3.5 or less, 3.1 or less, 3.0 or less, 2.5 or less, and 2.0 or less. When the above range is satisfied, the entire sealant layer surface area can have uniform quality, so that quality reliability and structural stability can be improved.

[0061] According to one embodiment of the present invention, the insulation resistance failure rate of the pouch film according to the method described below may be less than 0.9%.

[0062] [Method for Measuring Insulation Resistance Defect Rate]

[0063] Specifically, the insulation resistance measurement method was to manufacture 1,000 30 mm X 40 mm dummy cells (small cells), apply 250 V to the aluminum tab portion and the aluminum layer (barrier layer) of the pouch using an insulation resistance meter, measure the insulation resistance value (GΩ), and record it as defective when it is 100 MΩ or less to calculate the defect rate. For example, the insulation resistance failure rate may be less than 0.90%, 0.87% or less, 0.85% or less, 0.80% or less, 0.75% or less, 0.70% or less, 0.65% or less, 0.60% or less, 0.55% or less, 0.50% or less, 0.45% or less, 0.43% or less, 0.40% or less, 0.35% or less, 0.30% or less, 0.25% or less, 0.21% or less, 0.20% or less, 0.15% or less, or 0.13% or less. When the insulation resistance failure rate satisfies the above range, the insulation property of the pouch film may be improved.

[0064]

[0065] The pouch film of the present invention includes an outer layer, a barrier layer, and a sealant layer.

[0066] The outer layer included in the pouch film is required to have excellent processability and formability because it serves to prevent contact with the outside and seal the electrode assembly contained inside. The processability and formability are affected by the mechanical properties, and in particular, are greatly affected by the mechanical properties of the outer layer.

[0067] The above outer layer may be the outermost layer of the lithium secondary battery outer pouch film, and the outer layer may have an appropriate thickness within a range that can secure sufficient mechanical strength and sufficient formability as an outer material. For example, the thickness of the outer layer may be 15 ㎛ or more, 20 ㎛ or more, 25 ㎛ or more, 27 ㎛ or more, 35 ㎛ or more, 37 ㎛ or more, 70 ㎛ or less, 50 ㎛ or less, or 40 ㎛ or less. When the above range is satisfied, the insulation breakdown voltage can be maintained at a high level.

[0068] The outer layer may include a first outer layer and a second outer layer, and the first outer layer may include one or more compounds selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate.

[0069] In addition, the second outer layer, which is a heat-resistant resin layer having a melting point higher than the heat bonding temperature of the sealant layer, may include one or more compounds selected from the group consisting of polyamide-based compounds, polyester-based compounds, polyolefin-based compounds, and polyacrylic-based compounds.

[0070] According to one embodiment of the present invention, the outer layer may be formed of a laminated film of a first outer layer (polyethylene terephthalate) and a second outer layer (nylon). In this case, the thinner the first outer layer and the thicker the second outer layer, the more advantageous the formability. However, the thinner the first outer layer may be in terms of insulation breakdown voltage. From this point of view, for example, the thickness of the second outer layer may be 10 ㎛ or more, 12 ㎛ or more, 15 ㎛ or more, 20 ㎛ or more, 40 ㎛ or less, 35 ㎛ or less, 30 ㎛ or less, 27 ㎛ or less, or 25 ㎛ or less, and the thickness of the first outer layer may be 5 ㎛ or more, 8 ㎛ or more, 10 ㎛ or more, 12 ㎛ or more, 30 ㎛ or less, 25 ㎛ or less, 20 ㎛ or less, 17 ㎛ or less, or 15 ㎛ or less.

[0071] The sealant layer may be the innermost layer of the pouch film for the external lithium secondary battery. That is, the sealant layer may be in direct contact with the battery main body (e.g., electrode, separator, and / or electrolyte). Therefore, the sealant layer must have excellent electrolyte resistance and excellent insulation. To this end, the sealant layer may include at least a polyolefin-based resin. The polyolefin-based resin has excellent electrolyte resistance and excellent insulation, and accordingly, the sealant layer including the polyolefin-based resin may also have excellent electrolyte resistance and excellent insulation derived from the polyolefin-based resin.

[0072] According to one embodiment of the present invention, the sealant layer provides a pouch film including at least one selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon, and glass fiber.

[0073] The thickness of the above sealant layer may be, for example, 20 ㎛ or more, 30 ㎛ or more, 40 ㎛ or more, 50 ㎛ or more, 100 ㎛ or less, 90 ㎛ or less, 80 ㎛ or less, 70 ㎛ or less, or 60 ㎛ or less, and when the above numerical range is satisfied, excellent electrolyte resistance and insulation may be achieved.

[0074] According to one embodiment of the present invention, the sealant layer may be composed of a laminate of two or more layers in order to diversify functions. As a specific example, the sealant layer may include a first sealant layer disposed on the barrier layer, and a second sealant layer disposed on the first sealant layer. Here, the first sealant layer may be a layer that assists adhesion between the barrier layer and the second sealant layer while further enhancing the function as a sealant layer, and the second sealant layer may be a layer that constitutes the innermost sealant layer of the pouch film, and may be a layer that simultaneously seals and prevents leakage of a secondary battery, particularly a non-aqueous electrolyte. The first sealant layer may be an Extrusion Lamination Coating (abbreviated as EC) layer (mainly an extruded polypropylene layer), and the second sealant layer may be a polypropylene (PP) layer resin, preferably a non-stretched polypropylene (CPP) layer, located under the first sealant layer (inner side based on the pouch film). In this case, for example, the thickness of the non-stretched polypropylene (CPP) layer of the sealant layer may be, for example, 20 ㎛ or more, 30 ㎛ or more, 40 ㎛ or more, 50 ㎛ or more, 80 ㎛ or less, 70 ㎛ or less, or 60 ㎛ or less, and the thickness of the polypropylene (PP) layer of the sealant layer may be, for example, 0 ㎛ or more, 10 ㎛ or more, 20 ㎛ or more, 30 ㎛ or more, 60 ㎛ or less, 50 ㎛ or less, or 40 ㎛ or less.

[0075] Additionally, according to one embodiment of the present invention, the polypropylene (PP) layer of the sealant layer may contain various additives (rubber, elastomer, slip agent, etc.) depending on the required properties.

[0076] The barrier layer may be an intermediate layer of the lithium secondary battery outer pouch film (e.g., a layer disposed between the outer layer and the sealant layer), and may serve to prevent the intrusion of gas and / or moisture. The barrier layer is not particularly limited in type, but may include at least one selected from the group consisting of aluminum, stainless steel, copper, titanium, and alloys thereof, and specifically may include aluminum.

[0077] The above barrier layer may have an appropriate thickness within a range that can effectively prevent the intrusion of the aforementioned gas and / or moisture while ensuring sufficient formability. For example, the thickness of the barrier layer may be 20 ㎛ or more, 30 ㎛ or more, 40 ㎛ or more, 50 ㎛ or more, 55 ㎛ or more, 60 ㎛ or more, 150 ㎛ or less, 140 ㎛ or less, 130 ㎛ or less, 125 ㎛ or less, 120 ㎛ or less, 115 ㎛ or less, 110 ㎛ or less, 105 ㎛ or less, 100 ㎛ or less, 95 ㎛ or less, 90 ㎛ or less, 85 ㎛ or less, or 80 ㎛ or less.

[0078]

[0079] Pouch-type secondary battery case and secondary battery

[0080] The secondary battery of the present invention includes a pouch-type secondary battery case including the battery body part and the pouch film, and the secondary battery case may include the pouch film of the present invention. The battery body part is sealed by the pouch-type secondary battery case. For example, the secondary battery may be a lithium secondary battery, and in this case, the battery body part may include a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and an electrolyte.

[0081] The above lithium secondary battery positive electrode can be used without limitation as long as it is one that is commonly used as a positive electrode of a lithium secondary battery. For example, the above lithium secondary battery positive electrode can be LiCoO2, LiMnO2, LiFeO2, Li(Ni 0.6 Mn 0.2 Co 0.2 ) may contain a positive electrode active material such as O2.

[0082] The above electrolyte may include a lithium salt and a non-aqueous organic solvent. Here, the lithium salt and the non-aqueous organic solvent may be used without limitation as long as they are commonly used as electrolytes and organic solvents for lithium secondary batteries, respectively.

[0083] The above-mentioned negative electrode for a lithium secondary battery may be used without limitation as long as it is one that is commonly used as a negative electrode for a lithium secondary battery. For example, the above-mentioned negative electrode for a lithium secondary battery may include a negative electrode active material such as a carbon-based active material or a silicon-based active material.

[0084] The above pouch-type secondary battery case may have excellent sealing strength characteristics. Accordingly, the problem of the battery body sealed by the pouch-type secondary battery case being exposed to the external environment may not occur.

[0085]

[0086] Pouch film manufacturing method

[0087] Hereinafter, a method for manufacturing a pouch film of the present invention will be described. The method for manufacturing the pouch film is not limited to the manufacturing method described below, and the manufacturing method described below may be one of several methods for manufacturing pouch films.

[0088]

[0089] The present invention provides a method for manufacturing a pouch film, comprising the steps of introducing a barrier layer and a sealant layer into a roll-to-roll device including a nip roll, a backup roll, and a cooling roll, laminating the sealant layer on one surface of the barrier layer, and adhering an outer layer to the other surface of the barrier layer, wherein the pressure applied to the barrier layer and the sealant layer into which the nip roll has introduced is 5 bar or more and less than 8 bar, and the step difference between the center portion and both ends of the nip roll is more than 0.4 mm and less than 1.2 mm.

[0090] In order to bond / lamine a sealant layer on one side of a barrier layer during the pouch film manufacturing process, a roll-to-roll device may be utilized, and the roll-to-roll device may include a nip roll, a backup roll, and a cooling roll. The nip roll is a core component of the roll-to-roll device, and serves to produce a sheet of a desired thickness by directly contacting an object to be rolled or bonded. The backup roll may be installed in contact with the nip roll, and may serve to transmit pressure to the nip roll during rolling or bonding and to structurally support it. The cooling roll may serve to lower the temperature of the sheet during rolling or bonding to prevent thermal deformation. In the pouch film manufacturing method, the barrier layer and the sealant layer may be introduced between the nip roll and the cooling roll to perform a rolling or bonding process. At this time, the pressure applied to the barrier layer and the sealant layer into which the nip roll has entered is 5 bar or more and less than 8 bar. For example, the pressure of the nip roll may be 5.0 bar or more, 5.5 bar or more, 6.0 bar or more, 6.5 bar or more, less than 8.0 bar, 7.5 bar or less, or 7.0 bar or less.

[0091] In addition, the step difference between the center and both ends of the nip roll may be more than 0.4 mm and less than 1.2 mm. Fig. 4 is a side view of the nip roll according to the present invention. The step difference refers to the difference in the radius of the center and both ends of the roll. The radius refers to half the length of the diameter, and refers to the length from the center line passing through the roll in the longitudinal direction to the outer circumference of the roll. The nip roll may also undergo elastic deformation while the workpiece is plastically deformed during the rolling or bonding process. The gap between the rolls during the rolling or bonding process must be completely parallel. If not, the thicknesses of the both edges of the workpiece (joint) may be different, and according to the law of constancy of volume, the lengths of the both edges may also be deformed differently, which may cause a problem of wrinkles. In order to prevent such elastic deformation of the roll, as in the nip roll of the present invention of Fig. 4, the diameter of the center of the roll may be processed to be slightly larger than the diameters of the both ends, thereby preventing elastic deformation of the nip roll. At this time, the nip roll of the present invention may have a step difference between the center and both ends of the nip roll of more than 0.4 mm and less than 1.2 mm. Here, the step difference between the center and both ends of the nip roll may be expressed as a crown. For example, the step difference between the center and both ends of the nip roll may be more than 0.40 mm, 0.45 mm or more, 0.50 mm or more, 0.55 mm or more, 0.60 mm or more, 0.65 mm or more, 0.70 mm or more, less than 1.2 mm, 1.15 mm or less, 1.10 mm or less, 1.05 mm or less, 1.00 mm or less, 0.95 mm or less, 0.90 mm or less, 0.85 mm or less, or 0.80 mm or less. If the pressure applied to the barrier layer or sealant layer into which the nip roll has entered and the step difference between the center and both ends of the nip roll are outside the above-mentioned range, it is difficult to control the number of bubbles per unit area located on the surface of the sealant layer, the TD deviation according to the number of bubbles, and the area ratio occupied by the bubbles, and accordingly, the electrolyte properties, insulation, peel strength, and thermal bonding strength properties may be deteriorated.

[0092] In addition, according to one embodiment of the present invention, the backup roll is in contact with the nip roll, and the pressure that the backup roll applies to the nip roll may be 5 bar or more and less than 8 bar. For example, the pressure that the backup roll applies to the nip roll may be 5.0 bar or more, 5.5 bar or more, 6.0 bar or more, 6.5 bar or more, less than 8.0 bar, 7.5 bar or less, or 7.0 bar or less, and when the above pressure is satisfied, the number of bubbles on the surface of the sealant layer may be reduced, thereby improving the electrolyte resistance properties, insulation properties, peel strength, and thermal bonding strength properties.

[0093] In addition, according to one embodiment of the present invention, the pressure of the nip roll and the pressure applied to the nip roll by the backup roll may be the same pressure. If the pressure of the nip roll is higher than the pressure of the backup roll, the pressure may not be sufficiently transmitted during lamination, which may reduce the improvement effect of the electrolyte resistance, insulation, peel strength, and thermal bonding strength characteristics. In addition, conversely, if the pressure of the nip roll is lower than the pressure of the backup roll, the pressure balance may not be correct, which may cause wrinkles during lamination.

[0094] In addition, according to one embodiment of the present invention, the laminating step may be performed by adding one or more additives selected from the group consisting of polytetrafluoroethylene, silicone-based resins, and amide-based resins. Specifically, the additives may be prepared by polymerizing one or more monomers selected from the group consisting of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, and ethylene. The additives have high inertness against chemical reactions, excellent thermal stability, and low surface energy, and can exist as independent particles without being mixed with other types of polymers in the matrix resin. When prepared by adding the additives, the surface energy between the metal wall surface in the extruder and the molten polymer can be lowered, and the frictional force at the die can be reduced, thereby eliminating melt fracture, which is a surface defect phenomenon that occurs when extruding in a molten state, and obtaining the effects of improving gloss, reducing surface defects, and improving surface roughness.

[0095] The above additive may be added in an amount of 500 ppm or more and 10,000 ppm or less based on the weight of the entire sealant layer. For example, the above additive may be added in an amount of 500 ppm or more, 600 ppm or more, 700 ppm or more, 900 ppm or more, 950 ppm or more, 1000 ppm or more, 10,000 ppm or less, 9,000 ppm or less, 8,000 ppm or less, 7,000 ppm or less, 6,000 ppm or less, 5,000 ppm or less, 4,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, 1,900 ppm or less, 1,700 ppm or less, 1,500 ppm or less, 1,300 ppm or less, or 1,100 ppm or less based on the weight of the entire sealant layer. When the above additive is added within the above range, the surface of the sealant layer is modified to reduce surface contamination and the number of bubbles is reduced, enabling the production of a pouch film with excellent quality.

[0096]

[0097] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0098]

[0099] Example 1

[0100] A pouch film was manufactured by laminating an outer layer, a barrier layer, and a sealant layer, wherein the outer layer is a laminated film of a polyethylene terephthalate (PET) film (thickness 12㎛) as the outermost layer and a nylon (Ny) film (thickness 15㎛) as the inner layer, the barrier layer is made of aluminum (thickness 40㎛), and the sealant layer (thickness 80㎛) includes a polypropylene extrusion coating (EC) layer (thickness 30㎛) and a non-stretched polypropylene film (CPP) (thickness 50㎛) using an extrusion lamination method. In the extrusion lamination method, the barrier layer and the sealant layer were injected and bonded between a nip roll and a cooling furnace. At this time, the pressure of the nip roll was 5 bar, the pressure of the back roll was 5 bar, and the difference (crown) between the diameter of the center of the nip roll and the diameter of both ends was 0.6 mm.

[0101]

[0102] Examples 2 to 6

[0103] A pouch film was manufactured in the same manner as in Example 1, except that the conditions of the pressure of the nip roll, the pressure of the back roll, and the difference in diameter between the center and both ends of the nip roll (crown) were changed as shown in Table 1 below. In addition, in Examples 3 and 6, 1000 ppm of an additive manufactured by copolymerizing VF2, HFP, TFE, and ethylene propylene was added during the extrusion lamination process.

[0104]

[0105] Comparative Examples 1 to 7

[0106] A pouch film was manufactured in the same manner as in Example 1, except that the conditions of the pressure of the nip roll, the pressure of the back roll, and the difference in diameter between the center and both ends of the nip roll (crown) were changed as shown in Table 1 below. In addition, in Comparative Example 4, 1000 ppm of an additive manufactured by copolymerizing VF2, HFP, TFE, and Etylene propylene was added during the extrusion lamination process.

[0107]

[0108] Experimental example

[0109] (1) Number of bubbles per unit area (ea / mm) 2 )

[0110] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed using a white LED as a lamp light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of bubbles per unit area was calculated by dividing the measured area by the measured number.

[0111]

[0112] (2) Ratio of bubble area per unit area of ​​sealant layer surface (%)

[0113] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed using a white LED as a light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. After measurement, the measured area was 1.637 mm by adding the area of ​​bubbles. 2 The bubble ratio per area was calculated by dividing by .

[0114]

[0115] (3) TD deviation

[0116] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, measuring area 1.637 mm 2 , the interface between the barrier layer and the sealant layer was photographed using a white LED as a lamp light source. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of bubbles per unit area was calculated by dividing the measured number by the measured area. The deviation value was calculated by calculating the number of bubbles per unit area at 10 cm intervals based on the entire width of the MR.

[0117]

[0118] (4) Insulation resistance failure rate

[0119] 1000 30 mm x 40 mm dummy cells (small cells) including the pouch films of Examples 1 to 6 and Comparative Examples 1 to 6 were manufactured, and 250 V was applied to the aluminum tab portion and the aluminum layer (barrier layer) portion of the pouch using an insulation resistance meter to measure the insulation resistance value (GΩ). If it was 100 MΩ or less, it was recorded as defective, and the defective rate was calculated.

[0120]

[0121] ClassificationExample 1Example 2Example 3Example 4Example 5Example 6Comparative Example 1Comparative Example 2Comparative Example 3Comparative Example 4Comparative Example 5Comparative Example 6Comparative Example 7AdditiveFluorine polymer--1000ppm---1000ppm---1000ppm---PressureNip roll (bar)5665664566568Backup roll (bar)5665664566568Crown (mm)0.60.60.60.80.80.80.40.40.40.41.21.20.8Number of bubbles per unit area (EA / mm) 2)19.514.813.815.510.28.045.241.439.537.430.222.32.3Number of quenching points per unit area--8.2--5.2---13.8-9.1Number of substitution points per unit area--5.6--2.9---23.5-8.6-Area (%)1.050.650.430.450.240.132.502.231.851.571.451.120.02TD deviation4.53.53.03.83.12.14.24.03.53.315.213.20.2Insulation resistance failure rate (Effect) 0.87% 0.43% 0.30% 0.21% 0.15% 0.13% 2.50% 2.15% 1.87% 1.76% 1.50% 1.12% 0.90%

[0122] Referring to Table 1 and FIGS. 1 to 3 above, in the case of Examples 1 to 6, the number of bubbles per unit area of ​​the sealant layer surface falls within the range of the present invention, and therefore, it can be confirmed that the insulation resistance failure rate is significantly lower than that of the comparative examples. Furthermore, the ratio of bubbles to the surface unit area and the TD deviation also fall within the numerical range of the present invention, which confirms that each component has an organic interrelationship and increases the insulation resistance effect.

[0123] The pouch film of the above embodiment is manufactured by limiting the pressure of the nip roll and back roll to a specific range during manufacturing, and simultaneously controlling the crown to satisfy the specific numerical range of the present invention, thereby satisfying the specific number of bubbles per unit area. However, the manufacturing method may be one of several manufacturing methods for satisfying the specific number of bubbles per unit area.

[0124] In addition, in the case of Examples 3 and 6, it can be confirmed that the number of bubbles per unit area is smaller and the effect of insulation resistance failure rate is also superior compared to Examples 2 and 5 manufactured under the same conditions, in which an additive including a fluorinated polymer was added. In addition, the number of small-diameter bubbles and the number of large-diameter bubbles per unit area of ​​Examples 3 and 6 and Comparative Examples 4 and 6, which have the same nip roll and backup roll pressure, were measured. In this case, the number of small-diameter and large-diameter bubbles is also affected depending on the difference in the crown and the number of bubbles per unit area, and in the case of Comparative Examples 4 and 6, it can be confirmed that the number of small-diameter and large-diameter bubbles per unit area is significantly greater than that of Examples 3 and 6.

[0125] In the case of Comparative Examples 1 to 6, since the number of bubbles per unit area of ​​the present invention is not satisfied, the insulation resistance failure rate is very high, and therefore, it can be confirmed that it is not suitable for use as a pouch film. In addition, in the case of Comparative Example 7, since it exceeds the lower limit of the range of the number of bubbles per unit area of ​​the present invention, it can be confirmed that the insulation failure rate actually increases due to resin deterioration caused by excessive pressure during the manufacturing process.

[0126]

[0127] Acknowledgement

[0128] The present invention is a result of the following task support.

[0129] Assignment Number: 20022450

[0130] Ministry Name: Ministry of Trade, Industry and Energy

[0131] Project Management (Professional) Agency Name: Korea Institute of Industrial Technology Planning and Evaluation

[0132] Research Project Name: Material and Components Technology Development (Leeumsung Corporation)

[0133] Research Project Title: Development of Next-Generation Secondary Battery Pouches Capable of Delivering More Than Double the Bonding Strength (60°C)

[0134] Contribution rate: 1 / 1

[0135] Project implementation organization name: Yulchon Chemical Co., Ltd.

[0136] Research period: January 1, 2024 - December 31, 2024

Claims

1. Sealant layer; Outer layer; and A barrier layer containing aluminum is included between the sealant layer and the outer layer, The number of bubbles per unit area of ​​the sealant layer surface is 2.5 ea / mm 2 More than 20 ea / mm 2 Pouch film as follows.

2. In claim 1, A pouch film wherein the ratio of air bubbles to the surface unit area of ​​the sealant layer is 0.1% or more and 1.1% or less.

3. In claim 1, The number of bubbles per unit area of ​​the bubbles having a long side of 20 ㎛ or more is 6.0 ea / mm 2 Pouch film as follows.

4. In claim 1, The number of bubbles per unit area of ​​the bubbles having a long side of less than 20 ㎛ is 9.0 ea / mm 2 Pouch film as follows.

5. In claim 1, A pouch film having a TD deviation of 5 or less according to the number of bubbles on the surface of the sealant layer measured by the following measuring method. [measurement method] Optical microscope Olympus OLS5100 (3D Laser microscope) Lens x10, Measuring area 1.637 mm 2 , Lamp light source white LED was used to photograph the interface between the barrier layer and the sealant layer. The magnification of the photograph taken above was input to measure the area of ​​bubbles visible at the interface between the barrier layer and the sealant layer. The number of measured bubbles was divided by the measured area to calculate the number of bubbles per unit area. The number of bubbles per unit area was calculated at 10 cm intervals based on the entire width of the MR to calculate the deviation value.

6. In claim 1, A pouch film wherein the sealant layer comprises at least one 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.

7. In claim 1, A pouch film wherein the sealant layer comprises an extrusion coating layer and a non-stretched polypropylene layer.

8. In claim 1, A pouch film having an insulation resistance defect rate of less than 0.9% according to the method described below. [Method for measuring insulation resistance failure rate] 1,000 30 mm x 40 mm dummy cells (small cells) were manufactured, and 250 V was applied to the aluminum tab portion and the aluminum layer (barrier layer) of the pouch using an insulation resistance meter to measure the insulation resistance value (GΩ). A value of 100 MΩ or less was recorded as defective, thereby calculating the defect rate.

9. A step of introducing a barrier layer and a sealant layer into a roll-to-roll device including a nip roll, a backup roll, and a cooling roll and laminating the sealant layer on one side of the barrier layer; and Comprising a step of bonding an outer layer to the other surface of the barrier layer, The pressure applied to the barrier layer and sealant layer into which the above nip roll has entered is 5 bar or more and less than 8 bar, A method for manufacturing a pouch film, wherein the step between the center and both ends of the above-mentioned nip roll is more than 0.4 mm and less than 1.2 mm.

10. In claim 9, A method for manufacturing a pouch film, wherein the backup roll is in contact with the nip roll, and a pressure applied by the backup roll to the nip roll is 5 bar or more and less than 8 bar.

11. In claim 9, A method for manufacturing a pouch film, wherein the above step of combining is performed by adding an additive including at least one selected from the group consisting of polytetrafluoroethylene, silicone-based resin, and amide-based resin.

12. In claim 11, A method for manufacturing a pouch film, wherein the above additive is added in an amount of 500 ppm or more and 10,000 ppm or less based on the weight of the entire sealant layer.

13. In claim 9, A method for manufacturing a pouch film, wherein the pressure of the above-mentioned nip roll and the pressure applied to the nip roll by the above-mentioned backup roll are the same pressure.

14. In claim 9, A method for manufacturing a pouch film, wherein the step between the center and both ends of the above-mentioned nip roll is 0.6 mm or more and 0.8 mm or less.

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