Pouch film, pouch-type secondary battery case including same, and secondary battery

Abstract

The present invention relates to a pouch film comprising a sealant layer, a barrier layer, a second outer layer, and a first outer layer, which are sequentially laminated, wherein the crystallinity of the first outer layer, the thickness ratio between the barrier layer and the first outer layer, and the thickness ratio between the first outer layer and the second outer layer are specified so that the barrier layer exhibits excellent post-molding thickness retention, and thus the pouch film can prevent moisture penetration and electrolyte leakage and can accommodate a large number of electrode assemblies due to having a high degree of moldability, thus making it possible to achieve high electrical capacity and efficiency.

Description

Pouch film, pouch-type secondary battery case and secondary battery including the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0008741, filed January 19, 2024, and Korean Patent Application No. 10-2024-0196146, filed December 24, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Technology field

[0005] The present invention relates to a secondary battery pouch film, a pouch-type secondary battery case including the same, and a secondary battery.

[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, in the case of secondary batteries with high energy density using pouch films, the most ideal method is to increase the formability and insert the maximum amount of active material into a single packaging. In order to increase the energy density of secondary batteries using the pouch film, it is necessary to improve the formability of the pouch film to insert the maximum amount of battery active material into the pouch, and for this purpose, the pouch film needs to ensure higher formability. However, the current pouch film has a problem in that the residual thickness of the barrier layer is stretched and reduced during forming, which can cause problems such as moisture infiltration and electrolyte leakage, and thus stability is not guaranteed.

[0012] The currently commercialized pouch film is a 183 ㎛ product composed of PP80 / Al60 / Nylon25 / PET12. However, the high-molding pouch only has a formability of about 12 to 15 mm, and the remaining thickness of Al after forming is thin at about 30 ㎛, making it difficult to completely protect battery materials that are sensitive to air and moisture, and problems such as moisture penetration and electrolyte leakage may occur. Therefore, in order to include an electrode assembly that includes the largest possible amount of positive electrode active material while completely protecting battery materials that are sensitive to air and moisture, a pouch film that has high formability and a thick remaining thickness is required.

[0013]

[0014] The problem to be solved by the present invention is to provide a pouch film having high formability and a pouch-type secondary battery case and secondary battery including the same.

[0015]

[0016] The present invention provides a pouch film, a pouch-type secondary battery case including the same, and a secondary battery.

[0017] (1) The present invention provides a pouch film comprising a sealant layer, a barrier layer, a second outer layer, and a first outer layer sequentially laminated, wherein the first outer layer comprises a resin composition having a crystallinity of 5.0% or more and 27.0% or less, and a thickness ratio of the first outer layer to the barrier layer (thickness of the first outer layer (㎛) / thickness of the barrier layer (㎛)) is 0.25 or more and 0.6 or less, and a thickness ratio of the first outer layer to the second outer layer (thickness of the first outer layer (㎛) / thickness of the second outer layer (㎛)) is 0.5 or more and 1.8 or less.

[0018] (2) The present invention provides a pouch film in the above (1) in which the thickness of the first outer layer is 20 ㎛ or more and 40 ㎛ or less.

[0019] (3) The present invention provides a pouch film having an elongation of 200% or more and 600% or less according to the following measurement method in (1) or (2).

[0020] [measurement method]

[0021] According to ASTM D882, a specimen with a width of 15 mm of a pouch film is manufactured, and then the specimen is fixed between two jigs of a tensile testing machine (UTM) with an initial jig gap of 50 mm at room temperature, and the stroke (mm) and strength (N) of the specimen are measured while pulling at a measurement speed of 50 mm / min in the TD and MD directions, and then the length of the crosshead (jig gap) extended by the tension is measured based on the length extended, and then calculated according to the following mathematical equation 1.

[0022] [Mathematical Formula 1]

[0023] Elongation = (length of jig gap increased (movement distance) / initial gauge length) x 100

[0024] (4) The present invention provides a pouch film in which the thickness of the barrier layer is 70 ㎛ or more and 100 ㎛ or less in any one of the above (1) to (3).

[0025] (5) The present invention provides a pouch film according to any one of the above (1) to (4), wherein the total thickness of the pouch film is 200 ㎛ or more and 250 ㎛ or less.

[0026] (6) The present invention provides a pouch film in any one of the above (1) to (5), wherein the first outer layer comprises at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber.

[0027] (7) The present invention provides a pouch film according to any one of the above (1) to (6), wherein the first outer layer further comprises at least one polymer selected from the group consisting of a polyester polymer and a polyolefin polymer.

[0028] (8) The present invention provides a pouch film in the above (7), wherein the polyolefin polymer comprises at least one material selected from the group consisting of ethylene-propylene copolymer (EPR), ethylene-butene copolymer (EBR), ethylene-hexene copolymer (EHR), ethylene-octene copolymer (EOR), propylene-butene copolymer (PBR), propylene-hexene copolymer (PHR), propylene-octene copolymer (POR), LLDPE resin, thermoplastic polyurethane (TPU) resin, and ethylene vinyl acetate (EVA) resin.

[0029] (9) The present invention provides a pouch film comprising a pouch film in which, in the above (7) or (8), the polyester polymer includes at least one material selected from the group consisting of isophthalic acid (IPA), naphthalene dicarboxylic acid, and cyclohexanedimethanol (CHDM).

[0030] (10) The present invention provides a pouch film in any one of the above (1) to (9), wherein the second outer layer includes at least one compound selected from the group consisting of a polyamide-based compound, a polyester-based compound, a polyolefin-based compound, and a polyacrylic-based compound.

[0031] (11) The present invention provides a pouch film in which, in any one of the above (1) to (10), the angle between the X-axis and the slope of the increasing section between the yield strength and the breaking strength in the graph derived according to the following measuring method of the first outer layer is 35 degrees or more and 80 degrees or less.

[0032] [measurement method]

[0033] After cutting the pouch film to produce a specimen with a width of 15 mm, the specimen is fixed between two jigs with an initial jig gap of 50 mm of a tensile testing machine (UTM) at a measurement temperature of 25°C, and the yield strength and breaking strength of the specimen are measured while pulling at a measurement speed of 50 mm / min. The X-axis of the resulting graph represents stroke (mm), and the Y-axis represents strength (N).

[0034] (12) The present invention provides a pouch film comprising an adhesive layer between the second outer layer and the barrier layer in any one of the above (1) to (11), and the thickness of the adhesive layer is 5 ㎛ or more and 8 ㎛ or less.

[0035] (13) The present invention provides a pouch film in which the thickness remaining ratio of the barrier layer according to the following formula 1 is 60% or more in any one of the above (1) to (12).

[0036] [Formula 1]

[0037] Thickness Retention Rate = (Thickness of barrier layer after molding / Thickness of barrier layer before molding) x 100

[0038] In the above equation 1,

[0039] The thickness of the barrier layer after the above molding is measured by cutting the edge portion of the manufactured pouch film using a Microtome (cross-section cutting machine, manufacturer: Leica microsystems, model name: Ultracut UC7) to create a specimen of 266 mm (TD) x 240 mm (MD) x 15 mm (width), and then using a test mold machine with a specification of 30 mm x 75 mm, applying pressure of 0.3 Mpa to mold it to a molding depth of 17 mm, and then measuring the thickness of the barrier layer using an SEM (manufacturer: Hitachi, model name: SU3500).

[0040] (14) The present invention provides a pouch-type secondary battery case including a pouch film according to any one of (1) to (13).

[0041] (15) The present invention provides a secondary battery including an electrode assembly formed by laminating a positive electrode, a separator, and a negative electrode; and a pouch-shaped battery case according to claim 14 for storing the electrode assembly.

[0042]

[0043] The pouch film of the present invention has an excellent thickness retention rate after forming a barrier layer, thereby preventing moisture penetration and electrolyte leakage, and has high formability, thereby being able to accommodate a large amount of electrode assemblies, thereby having high electric capacity and efficiency.

[0044]

[0045] Figure 1 is a schematic diagram showing the structure of the pouch film of the present invention.

[0046]

[0047] 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.

[0048] 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.

[0049] 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.

[0050]

[0051] pouch film

[0052] The present invention provides a pouch film comprising a sealant layer, a barrier layer, a second outer layer, and a first outer layer sequentially laminated, wherein the first outer layer comprises a resin composition having a crystallinity of 5.0% or more and 27.0% or less, a thickness ratio of the first outer layer to the barrier layer (thickness (㎛) of the first outer layer / thickness (㎛) of the barrier layer) is 0.25 or more and 0.6 or less, and a thickness ratio of the first outer layer to the second outer layer (thickness (㎛) of the first outer layer / thickness (㎛) of the second outer layer) is 0.5 or more and 1.8 or less.

[0053] According to one embodiment of the present invention, the pouch film of the present invention includes a sealant layer on an inner side, an outer layer, and a barrier layer comprising aluminum between the inner sealant layer and the outer layer. In addition, the outer layer includes a first outer layer and a second outer layer, which will be described later.

[0054] The first outer layer may include a resin composition having a crystallinity of 5.0% or more and 27.0% or less. For example, the crystallinity of the resin composition included in the first outer layer may be 5.0% or more, 6.0% or more, 7.0% or more, 8.0% or more, 9.0% or more, 10.0% or more, 11.0% or more, 12.0% or more, 13.0% or more, 14.0% or more, 15.0% or more, 16.0% or more, 17.0% or more, 18.0% or more, 27.0% or less, 26.0% or less, 25.0% or less, 24.0% or less, 23.0% or less, 22.0% or less, 21.0% or less, 20.0% or less, or 19.0% or less. The crystallinity of the first outer layer can be controlled according to the heat treatment time, cooling rate, and composition and content of the resin composition during the first outer layer manufacturing process. For example, if the cooling rate is increased, the crystallinity can decrease. If the crystallinity of the resin composition included in the first outer layer is lower than the lower limit of the above range, the amorphous region may increase, which may lower the mechanical properties of the film, such as strength, and may lower the gas and moisture barrier performance. The glass transition temperature may be low, which may cause thermal deformation. In addition, if the crystallinity of the resin composition included in the first outer layer is higher than the upper limit of the above range, the flexibility may be reduced, which may cause it to be easily broken or damaged, the transparency may be reduced, and the formability may be reduced. Here, the crystallinity can be calculated by the following method.

[0055] 2 to 5 g of the resin composition of the first outer layer is placed in a differential scanning calorimeter, and the temperature is increased from 30°C to 300°C at a heating rate of 10°C / min. Then, the heat of melting (△Hf) at the melting peak is checked, and the degree of crystallinity is calculated using the following equation 1.

[0056] [Formula 1]

[0057] Crystallinity (%) = (△Hf / △Hf°) x 100

[0058] In the above equation 1,

[0059] △Hf is the heat of melting at the melting peak,

[0060] △Hf° is the theoretical heat of melting in a 100% crystalline state.

[0061]

[0062] In addition, the thickness ratio of the first outer layer to the barrier layer (thickness of the first outer layer (㎛) / thickness of the barrier layer (㎛)) is 0.25 or more and 0.6 or less, and the thickness ratio of the first outer layer to the second outer layer (thickness of the first outer layer (㎛) / thickness of the second outer layer (㎛)) is 0.5 or more and 1.8 or less. The pouch film of the present invention improves the formability of the pouch film and the thickness residual rate of the barrier layer after forming by controlling the thickness ratio of the barrier layer to the first outer layer and the thickness ratio of the second outer layer to the first outer layer within a specific range. The thickness ratio of the first outer layer to the barrier layer (thickness of the first outer layer (㎛) / thickness of the barrier layer (㎛)) may be, for example, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, 0.30 or more, 0.31 or more, 0.32 or more, 0.33 or more, 0.34 or more, 0.35 or more, 0.60 or less, 0.59 or less, 0.58 or less, 0.57 or less, 0.56 or less, 0.55 or less, 0.54 or less, 0.53 or less, 0.52 or less, 0.51 or less, or 0.50 or less. In addition, the thickness ratio of the first outer layer to the second outer layer (thickness of the first outer layer (㎛) / thickness of the second outer layer (㎛)) is 0.50 or more, 0.51 or more, 0.53 or more, 0.55 or more, 0.57 or more, 0.59 or more, 0.60 or more, 0.61 or more, 0.63 or more, 0.65 or more, 0.67 or more, 0.69 or more, 0.70 or more, 0.71 or more, 0.73 or more, 0.75 or more, 0.77 or more, 0.79 or more, 0.80 or more, 0.81 or more, 0.83 or more, 0.85 or more, 0.87 or more, 0.89 or more, 0.90 or more, 0.91 or more, 0.93 or more, 0.95 or more, 0.97 or more, 0.99 It can be 1.00 or more, 1.80 or less, 1.79 or less, 1.77 or less, 1.75 or less, 1.73 or less, 1.71 or less, 1.70 or less, 1.69 or less, 1.67 or less, 1.65 or less, 1.63 or less, 1.61 or less, or 1.60 or less.When the pouch film is outside the range of the thickness ratio of the barrier layer and the first outer layer and the thickness ratio of the second outer layer and the first outer layer, for example, when the thickness of the first outer layer (PET) is too thick and exceeds the upper limit of the thickness ratio range, the thermal conductivity of the pouch film becomes very low, making it difficult to release the heat generated inside to the outside, which may increase the risk of thermal runaway, and the possibility of thermal deformation in a high-temperature environment may increase, which may lower the durability and reliability of the secondary battery cell. In addition, the drawing properties may deteriorate, which may not withstand stress during the molding process and may cause breakage, and the energy density may decrease, which may cause a deterioration in the performance of the secondary battery.

[0063] On the other hand, if the thickness of the first outer layer (PET) is too thin and falls outside the lower limit of the thickness ratio range, the tensile strength may be reduced, making it difficult to withstand the mechanical stress generated during molding, and rupture and tearing may occur. In addition, durability may be reduced, and there is a risk that the heat blocking performance from the outside may be reduced. In addition, since the first outer layer is a layer with insulating performance, the problem of an increased insulation failure rate may occur.

[0064] That is, the pouch film of the present invention satisfies the ranges of the thickness ratios of the barrier layer and the first outer layer and the thickness ratios of the second outer layer and the first outer layer, thereby having high tensile strength and durability, being able to withstand stress well during molding, minimizing the thermal shrinkage phenomenon, increasing heat blocking performance, and having excellent levels in terms of insulation properties and energy density.

[0065]

[0066] According to one embodiment of the present invention, the thickness of the first outer layer may be 20 μm or more and 40 μm or less. The outer layer of the pouch film according to the present invention includes a first outer layer and a second outer layer, and may be the outermost layer of the pouch film for the outer packaging of a lithium secondary battery. The outer layer may have an appropriate thickness within a range that can secure sufficient mechanical strength and sufficient formability as an outer packaging material. For example, the thickness of the outer layer may be 15 μm or more, 20 μm or more, 25 μm or more, 27 μm or more, 35 μm or more, 37 μm or more, 70 μm or less, 50 μm or less, or 40 μm or less. When the above range is satisfied, the insulation breakdown voltage can be maintained at a high level.

[0067] The first outer layer may include at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber.

[0068] 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.

[0069] 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 first outer layer may be 20 ㎛ or more, 21 ㎛ or more, 23 ㎛ or more, 25 ㎛ or more, 27 ㎛ or more, 29 ㎛ or more, 40 ㎛ or less, 39 ㎛ or less, 37 ㎛ or less, 35 ㎛ or less, 33 ㎛ or less, 31 ㎛ or less, or 30 ㎛ or less. When the first outer layer satisfies the above thickness range, the coating layer described above can effectively prevent external contamination while maintaining an excellent level of formability.

[0070] Additionally, the thickness of the second outer layer may be 10 µm or more, 12 µm or more, 15 µm or more, 17 µm or more, 20 µm or more, 40 µm or less, 37 µm or less, 35 µm or less, 30 µm or less, 27 µm or less, or 25 µm or less.

[0071] According to one embodiment of the present invention, the first outer layer may further include a pouch film further comprising one or more polymers selected from the group consisting of polyester-based polymers and polyolefin-based polymers.

[0072] Here, the polyolefin polymer may include at least one material selected from the group consisting of ethylene-propylene copolymer (EPR), ethylene-butene copolymer (EBR), ethylene-hexene copolymer (EHR), ethylene-octene copolymer (EOR), propylene-butene copolymer (PBR), propylene-hexene copolymer (PHR), propylene-octene copolymer (POR), LLDPE resin, thermoplastic polyurethane (TPU) resin, and ethylene vinyl acetate (EVA) resin. In addition, the polyester polymer may include at least one material selected from the group consisting of isophthalic acid (IPA), naphthalene dicarboxylic acid, and cyclohexanedimethanol (CHDM).

[0073] The first outer layer of the present invention comprises a polyester polymer, thereby ensuring durability and thermal stability of the film, and increasing elongation to prevent cracks and breakage that may occur during film forming. In addition, the first outer layer comprises a polyolefin polymer, thereby achieving excellent flexibility and a low modulus of elasticity, thereby achieving high formability, and also having high thermal stability and minimizing heat shrinkage. In addition, the isophthalic acid is preferably included because it lowers the crystallinity of the film resin composition, thereby improving the formability of the film, and is also cost-effective.

[0074] According to one embodiment of the present invention, the polyester polymer and the polyolefin polymer may be included in an amount of 5 wt% or more and 15 wt%, respectively, relative to the entire resin of the first outer layer. For example, the content of the polyester polymer and the polyolefin polymer may be 5.0 wt% or more, 6.0 wt% or more, 7.0 wt% or more, 8.0 wt% or more, 9.0 wt% or more, 10.0 wt% or more, 15.0 wt% or less, 14.0 wt% or less, 13.0 wt% or less, 12.0 wt% or less, or 11.0 wt% or less relative to the entire resin of the first outer layer. When the polyester polymer and polyolefin polymer are each included in the first outer layer in an amount within the above range, formability can be improved, heat resistance and heat shrinkage stability can be increased, mechanical strength and chemical durability can be improved, durability against contact with electrolyte and chemicals can be increased, film deterioration can be prevented, battery life can be increased, and excellent interfacial adhesion can be secured.

[0075]

[0076] In addition, according to one embodiment of the present invention, the thickness of the barrier layer may be 70 ㎛ or more and 100 ㎛ or less. The barrier layer may be an intermediate layer of the lithium secondary battery external 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 type of the barrier layer is not particularly limited, 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 70 ㎛ or more, 72 ㎛ or more, 74 ㎛ or more, 75 ㎛ or more, 100 ㎛ or less, 99 ㎛ or less, 98 ㎛ or less, 96 ㎛ or less, 94 ㎛ or less, 92 ㎛ or less, 90 ㎛ or less, 88 ㎛ or less, 86 ㎛ or less, 84 ㎛ or less, 82 ㎛ or less, 80 ㎛ or less, 78 ㎛ or less, or 76 ㎛ or less.

[0078]

[0079] According to one embodiment of the present invention, an adhesive layer may be included between the second outer layer and the barrier layer, and the thickness of the adhesive layer may be 5 ㎛ or more and 8 ㎛ or less. For example, the thickness of the adhesive layer may be 4.5 ㎛ or more, 5.0 ㎛ or more, 5.5 ㎛ or more, 6.0 ㎛ or more, 6.5 ㎛ or more, 8 ㎛ or less, 7.5 ㎛ or less, or 7.0 ㎛ or less. When the thickness of the adhesive layer between the second outer layer and the barrier layer satisfies the above range, the formability and mechanical strength can be increased compared to the conventional pouch film of 3 to 4 ㎛, thereby improving the thickness retention rate.

[0080]

[0081] According to one embodiment of the present invention, the sealant layer may be the innermost layer of the pouch film for the external use of the 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.

[0082] The polyolefin-based resin may include, for example, a polyolefin derived from an olefin or a derivative thereof, a copolymer thereof, or a blend comprising at least one of the foregoing. For example, the polyolefin-based resin may include at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, a copolymer derived from a monomer derived from ethylene and / or propylene and a monomer derived from an alpha-olefin, or a blend thereof.

[0083] 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.

[0084] 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 (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 below 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.

[0085] Additionally, according to one embodiment of the present invention, the polypropylene (PP) layer of the sealant layer may contain various additives (rubber, elastomer, lubricant, etc.) depending on the required properties.

[0086]

[0087] According to one embodiment of the present invention, the overall thickness of the pouch film may be 200 ㎛ or more and 250 ㎛ or less. For example, the overall thickness of the pouch film may be 200 ㎛ or more, 205 ㎛ or more, 210 ㎛ or more, 215 ㎛ or more, 220 ㎛ or more, 225 ㎛ or more, 250 ㎛ or less, 245 ㎛ or less, 240 ㎛ or less, 235 ㎛ or less, or 230 ㎛ or less. If the overall thickness of the pouch film becomes excessively thick, the physical property balance between tensile strength and elongation may be biased to one side, so it is preferable to maintain the thickness of the pouch film within the above range.

[0088]

[0089] According to one embodiment of the present invention, the pouch film may have an elongation of 200% or more and 600% or less according to the following measurement method.

[0090] [measurement method]

[0091] According to ASTM D882, a specimen with a width of 15 mm of a pouch film is manufactured, and then the specimen is fixed between two jigs of a tensile testing machine (UTM) with an initial jig gap of 50 mm at room temperature, and the stroke (mm) and strength (N) of the specimen are measured while pulling at a measurement speed of 50 mm / min in the TD and MD directions, and then the length of the crosshead (jig gap) extended by the tension is measured based on the length extended, and then calculated according to the following mathematical equation 1.

[0092] [Mathematical Formula 1]

[0093] Elongation = (length of jig gap increased (movement distance) / initial gauge length) x 100

[0094] The elongation of the above pouch film may be affected by the crystallinity of the first outer layer. For example, the higher the crystallinity of the first outer layer, the lower the elongation. For example, the elongation of the pouch film may be 200% or more, 250% or more, 300% or more, 350% or more, 400% or more, 450% or more, 600% or less, 550% or less, or 500% or less. When the elongation of the pouch film satisfies the above range, it may have optimal formability, and may improve the thickness retention rate and maximum forming depth.

[0095]

[0096] According to one embodiment of the present invention, in a graph derived according to the following measuring method of the first outer layer, the angle between the X-axis and the slope of the increasing section between the yield strength and the fracture strength may be 20 degrees or more and 80 degrees or less.

[0097] [measurement method]

[0098] After cutting the pouch film to produce a specimen with a width of 15 mm, the specimen is fixed between two jigs with an initial jig gap of 50 mm of a tensile testing machine (UTM) at a measurement temperature of 25°C, and the yield strength and breaking strength of the specimen are measured while pulling at a measurement speed of 50 mm / min. The X-axis of the resulting graph represents stroke (mm), and the Y-axis represents strength (N).

[0099] In the graph derived according to the above measurement method of the first outer layer, the angle of the average slope of the increasing section between the yield strength and the fracture strength may be 20 degrees or more, 25 degrees or more, 30 degrees or more, 35 degrees or more, 40 degrees or more, 45 degrees or more, 50 degrees or more, 55 degrees or more, 60 degrees or more, 65 degrees or more, 80 degrees or less, 75 degrees or less, or 70 degrees or less.

[0100] In addition, according to one embodiment of the present invention, a pouch film is provided in which the maximum stroke when measuring the breaking strength of the first outer layer is 20 mm or more. For example, the maximum stroke when measuring the breaking strength of the first outer layer may be 20 mm or more, 25 mm or more, 30 mm or more, 35 mm or more, 40 mm or more, 45 mm or more, 50 mm or more, 55 mm or more, 60 mm or more, 65 mm or more, 70 mm or more, 75 mm or more, or 80 mm or more.

[0101] When the angle of inclination between the yield strength and the fracture strength of the first outer layer satisfies the above range, the formability can be further improved, thereby improving the thickness retention rate and maximum forming depth.

[0102]

[0103] According to one embodiment of the present invention, the thickness retention ratio of the barrier layer according to the following equation 1 may be 60% or more.

[0104] [Formula 1]

[0105] Thickness Retention Rate = (Thickness of barrier layer after molding / Thickness of barrier layer before molding) x 100

[0106] In the above equation 1,

[0107] The thickness of the barrier layer after the above molding is measured by cutting the edge portion of the manufactured pouch film using a Microtome (cross-section cutting machine, manufacturer: Leica microsystems, model name: Ultracut UC7) to create a specimen of 266 mm (TD) x 240 mm (MD) x 15 mm (width), and then using a test mold machine with a specification of 30 mm x 75 mm, applying pressure of 0.3 Mpa to mold it to a molding depth of 17 mm, and then measuring the thickness of the barrier layer using an SEM (manufacturer: Hitachi, model name: SU3500).

[0108] The thickness retention ratio of the above barrier layer is a very important criterion for determining the formability of the pouch film. Even after the forming process of the desired depth due to stretching of the barrier layer, it may shrink, which may cause problems of moisture penetration and electrolyte leakage. Therefore, it is important that the thickness of the barrier layer be maintained at a high level after forming. For example, the thickness retention ratio of the barrier layer according to the above formula 1 may be 60% or more, 61% or more, 63% or more, 65% or more, 67% or more, 70% or more, 71% or more, 73% or more, 75% or more, 77% or more, or 80% or more. When the thickness retention ratio of the above barrier layer is satisfied, a formability of 17 mm or more per 1 cup can be secured, and a formability of 30 mm or more per 2 cups can be secured. Here, the LDPE (low-density polyethylene) may also include PE (polyethylene) as a film to be laminated instead of the CPP (non-stretched polypropylene) film laminated to one side of the barrier layer in order to conduct a formability test, and the thickness of the LDPE (low-density polyethylene) may be 40 ㎛ or more and 60 ㎛ or less, and preferably 50 ㎛. In addition, the friction coefficient of the LDPE may be 0.05 or more and 0.5 or less, and preferably 0.1.

[0109]

[0110] According to one embodiment of the present invention, the maximum formable deformation length of the pouch film of the present invention may be 17 mm or more. For example, the maximum deformation length may be 17.0 mm or more, 17.3 mm or more, 17.5 mm or more, 17.7 mm or more, 17.9 mm or more, 18.0 mm or more, 18.3 mm or more, 18.5 mm or more, 18.7 mm or more, 18.9 mm or more, 19.0 mm or more, 19.3 mm or more, 19.5 mm or more, 19.7 mm or more, 20.0 mm or more, and the upper side may not be significantly limited. The maximum forming length refers to the maximum height of the space in which the electrode assembly can be accommodated in the pouch film, and the present invention can implement an accurate deformation length by reducing the recovery force, and at the same time, implement a maximum deformation length compared to a conventional pouch film. If the maximum deformation length satisfies the above range, more electrode assemblies can be accommodated, which can have a superior level in terms of electrical capacity.

[0111]

[0112] Pouch-type secondary battery case and secondary battery

[0113] The secondary battery of the present invention includes a pouch-type secondary battery case including the electrode assembly (battery main body) and the pouch film laminate, and the electrode assembly (battery main body) 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 main body may include a lithium secondary battery negative electrode, a lithium secondary battery positive electrode, a separator, a current collector, and a liquid electrolyte and a solid electrolyte.

[0114] 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, LiFePO4, Li(Ni x Mn yCo z )O2(X+Y+Z=1), LiNiCoAlO2, etc. may be included as positive active materials.

[0115] 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.

[0116] 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.

[0117] 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.

[0118]

[0119] 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.

[0120]

[0121] Example 1

[0122] The outer layer, barrier layer, and sealant layer were laminated, and the outer layer used a polyethylene terephthalate (PET) film (first outer layer, thickness 25 ㎛) as the outermost layer, and a nylon (Ny) film (second outer layer, thickness 25 ㎛) as the inner layer. The barrier layer used aluminum (thickness 80 ㎛), and the sealant layer (thickness 80 ㎛) was manufactured by extrusion lamination to include a polypropylene extrusion coating (EC) layer (thickness 30 ㎛) and a non-stretched polypropylene film (CPP) (thickness 50 ㎛). The first outer layer used a polyethylene terephthalate (PET) film having a crystallinity of 10% by increasing the cooling rate after heat treatment during film manufacturing by more than twice compared to the conventional 10 to 50 ℃ / s. As shown in Table 1 below, the thickness ratio of the first outer layer and the barrier layer (PET / Al) was 0.31, the thickness ratio of the first outer layer and the second outer layer (PET / Ny) was 1.00, and the elongation of the pouch film was 400%, so that the pouch film was manufactured by adjusting the draw ratio, extrusion speed, temperature, pressure conditions, etc.

[0123]

[0124] Example 2

[0125] A pouch film was manufactured in the same manner as in Example 1, except that the thickness ratio of the first outer layer and the barrier layer (PET / Al) was 0.50, the thickness ratio of the first outer layer and the second outer layer (PET / Ny) was 1.60, and the draw ratio, extrusion speed, temperature, pressure conditions, etc. were adjusted so that the elongation of the pouch film satisfied 400%, according to Table 1 below.

[0126]

[0127] Example 3

[0128] A pouch film was manufactured in the same manner as in Example 1, except that a polyethylene terephthalate film with a crystallinity of 18% was used, which was manufactured by adding isophthalic acid (IPA, 10 wt%), naphthalene dicarboxylic acid (Naphthalene dicarboxylic acid, 15 wt%), and cyclohexanedimethanol (15 wt%) to polyethylene terephthalate (PET), polymerizing the mixture at a reaction temperature of 270°C for 6 hours, manufacturing it into a pellet form, and then forming it into a film.

[0129]

[0130] Example 4

[0131] A pouch film was manufactured in the same manner as in Example 1, except that a polyethylene terephthalate film with a crystallinity of 25% was used, which was prepared by mixing thermoplastic polyurethane (10 wt%) and ethylene vinyle acetate (10 wt%) in the same polyethylene terephthalate (PET) in pellet form at 260°C for 7 minutes, uniformly dispersing the mixture, and then extruding the mixture into a film.

[0132]

[0133] Examples 5 to 8

[0134] A pouch film was manufactured in the same manner as in Example 3, except that the composition ratio, cooling rate, and film elongation ratio were adjusted to have an elongation as shown in Table 1 in Example 3.

[0135]

[0136] Comparative Examples 1 and 2

[0137] A pouch film was manufactured in the same manner as in Example 1, except that the thicknesses of the first outer layer and the second outer layer were adjusted to satisfy the thickness ratios of the first outer layer and the barrier layer (PET / Al) and the thickness ratios of the first outer layer and the second outer layer (PET / Ny), as shown in Table 1 below.

[0138]

[0139] Comparative Example 3

[0140] A pouch film was manufactured in the same manner as in Example 1, except that polyethylene terephthalate having a crystallinity of 30% was used for the first outer layer.

[0141]

[0142] Comparative Example 4

[0143] A pouch film was manufactured in the same manner as in Example 2, except that polyethylene terephthalate having a crystallinity of 30% was used for the first outer layer.

[0144]

[0145] Experimental Example 1

[0146] (1) Elongation evaluation

[0147] According to ASTM D882, a 15 mm wide pouch film specimen is manufactured, and then the specimen is fixed between two jigs of a tensile testing machine (UTM) with an initial jig gap of 50 mm at room temperature, and the stroke (mm) and strength (N) of the specimen are measured while pulling at a measurement speed of 50 mm / min in the TD and MD directions, respectively, and the actual length between lines extended by the tension is measured based on the crosshead displacement, and then calculated according to the following mathematical equation 1. The results are shown in Table 1 below.

[0148] [Mathematical Formula 1]

[0149] Elongation = (Crosshead displacement (movement distance) / Initial gauge length) x 100

[0150]

[0151] (2) Evaluation of residual thickness after molding

[0152] The thickness of the barrier layer after the molding was measured by cutting the edge part of the manufactured pouch film using a microtome (cross-section cutting machine, manufacturer: Leica microsystems, model name: Ultracut UC7) to make a specimen of 266 mm (TD) x 240 mm (MD) x 15 mm (width), and then using a test mold machine with a specification of 30 mm x 75 mm, applying pressure of 0.3 Mpa to mold it to a molding depth of 17 mm, and then measuring the thickness of the barrier layer using an SEM (manufacturer: Hitachi, model name: SU3500). The measured residual thickness of the barrier layer after molding and the thickness residual ratio according to the following Equation 1 are shown in Table 1 below.

[0153] [Formula 1]

[0154] Thickness Retention Rate = (Thickness of barrier layer after molding / Thickness of barrier layer before molding) x 100

[0155]

[0156] (3) Max plasticity measurement evaluation

[0157] In addition, for the pouch films manufactured in the above examples and comparative examples, 1 cup molding was evaluated and the average value of the maximum molding length was measured using a vernier caliper.

[0158]

[0159] Classification 1 Outer layer (PET) / Barrier layer (Al) thickness ratio 1st outer layer (PET) / 2nd outer layer (Nylon) thickness ratio Crystallization elongation Max molding thickness Residual rate (%) Example 10.3 1 1 10% 400% 15 mm or more 61 Example 20.5 1 6 10% 400% 15 mm or more 63 Example 30.3 1 1 8% 400% 15 mm or more 62 Example 40.3 1 1 2 5% 400% 15 mm or more 64 Example 50.3 1 1 8% 200% 15 mm or more 58 Example 60.3 1 1 8% 300% 15 mm or more 59 Example 70.3 1 1 8% 500% 15 mm or more 62 Example 80.3 1 1 8% 600% 15 mm or more 64 Comparative example 10.20.4810%210%15mm or less50Comparative example 20.625210%210%15mm or less45Comparative example 30.31130%140%15mm or less41Comparative example 40.51.630%150%15mm or less40

[0160] Referring to Table 1 above, in the case of the embodiment, the thickness ratio of the first outer layer and the barrier layer and the thickness ratio of the first outer layer and the second outer layer satisfy the range of the present invention, and the crystallinity of the first outer layer is satisfied, so that the max molding value can be implemented as 15 mm or more, and it can be confirmed that the thickness residual ratio of the barrier layer after molding is 60% or more. Through this, it can be confirmed that the pouch film of the present invention has high moldability and, at the same time, can accommodate a large amount of electrode assemblies, so that it can have high electric capacity and efficiency.

[0161] On the other hand, in the case of Comparative Examples 1 and 2, it can be confirmed that the pouch films that deviate from the thickness ratio of the present invention have a max molding value of less than 15 mm and a thickness retention rate of 50% and 45%, which are significantly low. In addition, in the case of Comparative Examples 3 and 4, although the thickness ratio is satisfied, the crystallinity is not satisfied, and the elongation of the pouch films was measured to be 200% or less. Furthermore, it can be confirmed that the max molding value and the thickness retention rate are also significantly inferior to those of the examples.

[0162]

[0163] Acknowledgement

[0164] The present invention is a result of the following task support.

[0165] [Project ID] 2410004468

[0166] [Assignment Number] 20022450

[0167] Ministry of Trade, Industry and Energy

[0168] [Name of Project Management (Specialist) Institution] Korea Institute of Industrial Technology Planning and Evaluation

[0169] [Research Project Name] Material and Components Technology Development (Leeum Company)

[0170] [Research Project Name] Development of a Next-Generation Secondary Battery Pouch Capable of Delivering More Than Double the Highest Adhesive Strength (60°C)

[0171] [Contribution rate] 1 / 1

[0172] [Name of Project Performing Organization] Yulchon Chemical Co., Ltd.

[0173] Research Period: January 1, 2024 - December 31, 2024

Claims

1. Containing a sequentially laminated sealant layer, a barrier layer, a second outer layer, and a first outer layer, The above first outer layer comprises a resin composition having a crystallinity of 5.0% or more and 27.0% or less, The thickness ratio of the first outer layer to the barrier layer (thickness of the first outer layer (㎛) / thickness of the barrier layer (㎛)) is 0.25 or more and 0.6 or less, A pouch film, wherein a thickness ratio of the first outer layer to the second outer layer (thickness of the first outer layer (㎛) / thickness of the second outer layer (㎛)) is 0.5 or more and 1.8 or less.

2. In claim 1, A pouch film having a thickness of the first outer layer of 20 ㎛ or more and 40 ㎛ or less.

3. In claim 1, A pouch film having an elongation of 200% or more and 600% or less according to the following measurement method: [measurement method] According to ASTM D882, a specimen with a width of 15 mm of a pouch film is manufactured, and then the specimen is fixed between two jigs of a tensile testing machine (UTM) with an initial jig gap of 50 mm at room temperature, and the stroke (mm) and strength (N) of the specimen are measured while pulling at a measurement speed of 50 mm / min in the TD and MD directions, and then the crosshead (jig gap) increased by the tension is measured based on the increased length, and then calculated according to the following mathematical equation 1. [Mathematical Formula 1] Elongation = (length by which the jig gap has increased (moved distance) / initial gauge length) x 100 4. In claim 1, A pouch film wherein the thickness of the barrier layer is 70 ㎛ or more and 100 ㎛ or less.

5. In claim 1, A pouch film having a total thickness of 200 ㎛ or more and 250 ㎛ or less.

6. In claim 1, A pouch film wherein the first outer layer comprises at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber.

7. In claim 1, A pouch film wherein the first outer layer further comprises at least one polymer selected from the group consisting of a polyester polymer and a polyolefin polymer.

8. In claim 7, A pouch film wherein the polyolefin polymer comprises at least one material selected from the group consisting of ethylene-propylene copolymer (EPR), ethylene-butene copolymer (EBR), ethylene-hexene copolymer (EHR), ethylene-octene copolymer (EOR), propylene-butene copolymer (PBR), propylene-hexene copolymer (PHR), propylene-octene copolymer (POR), LLDPE resin, thermoplastic polyurethane (TPU) resin, and ethylene vinyl acetate (EVA) resin.

9. In claim 7, A pouch film wherein the polyester polymer comprises at least one material selected from the group consisting of isophthalic acid (IPA), naphthalene dicarboxylic acid, and cyclohexanedimethanol (CHDM).

10. In claim 1, A pouch film wherein the second outer layer comprises at least one compound selected from the group consisting of a polyamide-based compound, a polyester-based compound, a polyolefin-based compound, and a polyacrylic-based compound.

11. In claim 1, A pouch film, wherein the angle between the X-axis and the slope of the increasing section between the yield strength and the breaking strength in the graph derived according to the following measuring method of the first outer layer is 35 degrees or more and 80 degrees or less: [measurement method] After cutting the pouch film to produce a specimen with a width of 15 mm, the specimen is fixed between two jigs of a tensile testing machine (UTM) with an initial jig gap of 50 mm at a measurement temperature of 25°C, and the yield strength and breaking strength of the specimen are measured while pulling at a measurement speed of 50 mm / min. The X-axis of the resulting graph represents stroke (mm), and the Y-axis represents strength (N).

12. In claim 1, Including an adhesive layer between the second outer layer and the barrier layer, A pouch film wherein the thickness of the adhesive layer is 5 ㎛ or more and 8 ㎛ or less.

13. In claim 1, A pouch film having a thickness residual ratio of 60% or more according to the following formula 1 of the above barrier layer: [Formula 1] Thickness Residual Rate = (Thickness of barrier layer after molding / Thickness of barrier layer before molding) x 100 In the above equation 1, After the above molding, the thickness of the barrier layer is measured by cutting the edge of the manufactured pouch film using a microtome (cross-section cutting machine) to create a specimen measuring 266 mm (TD) x 240 mm (MD) x 15 mm (width), and then molding it using a test mold machine measuring 30 mm x 75 mm at a pressure of 0.3 MPa to a molding depth of 17 mm. The thickness of the barrier layer is then measured using an SEM.

14. A pouch-type secondary battery case including a pouch film according to claim 1.

15. An electrode assembly formed by laminating a positive electrode, a separator, and a negative electrode; and A secondary battery comprising a pouch-shaped secondary battery case according to claim 14 for accommodating the above electrode assembly.

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