Pouch film and pouch-type secondary battery case comprising same

Abstract

The present invention relates to a pouch film comprising: an inner sealant layer; a barrier layer including aluminum; and an outer layer, which are sequentially laminated, wherein the outer layer comprises: a first outer layer; and a second outer layer disposed between the first outer layer and the barrier layer, and a slope derived from a graph derived according to the following measurement method satisfies equation 1 below. [Equation 1] 0.9≤ RTD / RMD ≤1.6 In Equation 1, RTD is the slope of the increasing section between the upper yield point of the outer film measured when the outer film is stretched in the TD direction and the strength at a stroke of 25 mm, and RMD is the slope of the increasing section between the upper yield point of the outer film measured when the outer film is stretched in the MD direction and the strength at a stroke of 25 mm. [Measurement method] An outer film of the pouch film is peeled off to prepare a specimen 15 mm in width that does not include an inner sealant layer and a barrier layer. The specimen is fixed between two jigs of a tensile tester (UTM) (initial jig gap of 50 mm) at room temperature, and then measured for stroke (mm) and strength (N) while pulling the specimen in TD and MD directions at a measurement speed of 50 mm / min, each. In the graph derived from the measured values, the X-axis represents the stroke (mm) and the Y-axis represents the strength (N). In this case, RTD and RMD are obtained by measuring the slope of a straight line connecting the upper yield point and the strength at a stroke of 25 mm in a straight line.

Description

Pouch film and pouch-type secondary battery case containing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0070171, filed May 29, 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 pouch-type secondary battery case including the same.

[0006]

[0007] Secondary batteries can be repeatedly charged and discharged, and can be classified into cylindrical secondary batteries, square secondary batteries, and pouch-type secondary batteries depending on their structure and manufacturing method. Among these, a pouch-type secondary battery is a type in which an electrode assembly (cell) is built into a pouch made of a metal laminate sheet. Its structure is relatively simple and its capacity per unit volume is relatively large, so it is widely used in energy storage devices such as automobile batteries. The pouch, which is the case of the pouch-type secondary battery, is manufactured by performing press processing on a flexible pouch film 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. In this way, the battery body sealed by the pouch film can be substantially free from exposure to the external environment.

[0008] Meanwhile, to prevent the battery body from being exposed to the external environment, the pouch film is required to have excellent sealing properties, and in particular, excellent sealing properties are required to be maintained under various environmental conditions. This is because exposure of the battery body to the external environment may result in problems such as a decline in the function of the pouch-type secondary battery or an explosion.

[0009] Here, the sealability and retention characteristics of the pouch film can be evaluated by the sealing strength of the pouch film. Sealing strength is an indicator of the superiority of the thermal bonding strength at the sealing portion of the pouch film. If the sealing strength of the pouch film is excellent, the sealability of the pouch film can generally be considered excellent.

[0010] Meanwhile, conventional pouch films have struggled to ensure sufficient thermal bonding strength at the sealing area, and research into improving this strength has been limited. Conventional pouch films have struggled to ensure sufficient sealing strength, and venting of the thermally bonded sealing area has frequently occurred.

[0011] In addition, the mechanical properties and modulus characteristics of the outer layer, which is located at the outermost part of the existing pouch film, affect the mechanical properties of the entire pouch film, which can in turn be a factor in determining the formability of the pouch film. If the mechanical properties of the outer layer are poor, the recovery force after forming increases, making it difficult to achieve the desired level of deformation length. This can cause a margin of error in the accommodation space of the cup part, which can cause problems such as difficulty in accommodating an electrode assembly of the desired size.

[0012] (Patent Document 1) JP 6322577 B2

[0013]

[0014] The problem to be solved by the present invention is to provide a pouch film that improves formability by minimizing recovery force after forming, and a pouch-type secondary battery case including the same.

[0015]

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

[0017] (1) The present invention provides a pouch film comprising a sequentially laminated inner sealant layer; a barrier layer comprising aluminum; and an outer layer, wherein the outer layer comprises a first outer layer; and a second outer layer disposed between the first outer layer and the barrier layer, and wherein a slope derived from a graph derived according to the following measurement method satisfies the following equation 1.

[0018] [Formula 1]

[0019] 0.9≤ R TD / R MD ≤1.6

[0020] In the above equation 1,

[0021] The above R TD is the slope of the increasing section between the upper yield point of the outer layer measured when pulling the outer layer film in the TD direction and the strength at a stroke of 25 mm,

[0022] The above R MD is the slope of the increasing section between the upper yield point of the outer layer and the strength at a stroke of 25 mm, measured when the outer layer film is pulled in the MD direction.

[0023] [measurement method]

[0024] After peeling off the outer film of the above pouch film to prepare a specimen that does not include the inner sealant layer and barrier layer with a width of 15 mm, the specimen is fixed between two jigs of a tensile tester (UTM) at room temperature (initial jig gap 50 mm), 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. The X-axis of the graph derived from the measured values ​​is the stroke (mm), and the Y-axis is the strength (N). At this time, the R TD and R MDIt is the slope of the straight line connecting the strength at the above yield point and when the stroke is 25 mm.

[0025] (2) The present invention provides a pouch film in which, in the above (1), the strokes in the TD and MD directions corresponding to the breaking strength of the outer layer are each independently 30 mm or more and 100 mm or less.

[0026] (3) The present invention provides a pouch film in (1) or (2), wherein the first outer layer includes at least one compound selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate.

[0027] (4) The present invention provides a pouch film in which, in any one of the above (1) to (3), 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.

[0028] (5) In any one of the above (1) to (4), the formula 1 satisfies 0.9≤R TD / R MD A pouch film having a thickness of ≤1.35 is provided.

[0029] (6) The present invention is one of the above (1) to (5), wherein the R TD Wow R MD A pouch film is provided having an angle of 0 degrees or more and 25 degrees or less.

[0030] (7) The present invention provides a pouch film according to any one of the above (1) to (6), wherein the thickness of the barrier layer is 20 ㎛ or more and 80 ㎛ or less.

[0031] (8) The present invention provides a pouch film in which the thickness of the second outer layer is 10 µm or more and 40 µm or less in any one of the above (1) to (7).

[0032] (9) The present invention provides a pouch film having a ratio of loss modulus to storage modulus (loss modulus / storage modulus) of 0.09 or more and 0.12 or less in any one of the above (1) to (8).

[0033] (10) The present invention provides a pouch film in which, in any one of the above (1) to (9), when the thickness of the barrier layer is 30 µm or more and 50 µm or less and the thickness of the second outer layer is 10 µm or more and 20 µm or less, the ratio of loss modulus to storage modulus (loss modulus / storage modulus) is 0.11 or more and 0.12 or less.

[0034] (11) The present invention provides a pouch film having a ratio of loss modulus to storage modulus (loss modulus / storage modulus) of 0.09 to 0.10 when the thickness of the barrier layer is 50 µm to 70 µm and the thickness of the second outer layer is 20 µm to 30 µm in any one of the above (1) to (10).

[0035] (12) The present invention provides a pouch-type secondary battery case including a pouch film according to any one of (1) to (11).

[0036]

[0037] The pouch film of the present invention can have the effect of improving formability so that, when storing an electrode assembly within the pouch film, it can accommodate an electrode assembly of a desired size without an error in the accommodation space by minimizing the recovery force after processing and forming.

[0038]

[0039] Figure 1 is a schematic diagram showing the configuration of the pouch film of the present invention.

[0040] Figure 2 is a graph showing the results of a tensile elongation test in the MD direction of the outer layer of Comparative Example 1.

[0041] Figure 3 is a graph showing the results of a tensile elongation test in the TD direction of the outer layer of Comparative Example 1.

[0042] Figure 4 is a graph showing the results of a tensile elongation test in the MD direction of the outer layer of Example 1.

[0043] Figure 5 is a graph showing the results of a tensile elongation test in the TD direction of the outer layer of Example 1.

[0044]

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In the present specification, when each layer of the secondary battery pouch is included, it is not necessarily composed of only that layer, but additional layers may be included.

[0049] In this specification, being formed 'on' a specific layer includes not only being formed directly on that layer, but also being formed after interposing an additional layer.

[0050] In this specification, the extrusion lamination coating (EC) layer refers to an extrusion layer of a resin, such as a polyolefin-based resin, preferably a polypropylene-based resin, that is extruded for bonding with a barrier layer as a part of the sealant layer. The extrusion lamination coating (EC) layer of the sealant layer is located on the barrier layer side with respect to the polypropylene-based resin layer.

[0051] In this specification, the polypropylene (PP) layer of the sealant layer is a core resin layer forming the sealant layer and performs a sealing function, and may be formed of one or more layers made of polypropylene resin. It is in contrast to the aforementioned extrusion bonding coating (EC) layer for bonding with the barrier layer, and is located on the inner side of the pouch film (i.e., the side opposite the barrier layer) based on the aforementioned extrusion bonding coating (EC) layer.

[0052]

[0053] pouch film

[0054] The present invention provides a pouch film comprising: a sequentially laminated inner sealant layer; a barrier layer comprising aluminum; and an outer layer, wherein the outer layer comprises a first outer layer; and a second outer layer disposed between the first outer layer and the barrier layer, wherein a slope derived from a graph derived according to the following measurement method satisfies the following equation 1.

[0055] [Formula 1]

[0056] 0.9≤ R TD / R MD ≤1.6

[0057] In the above equation 1,

[0058] The above R TDis the slope of the increasing section between the upper yield point of the outer layer measured when pulling the outer layer film in the TD direction and the strength at a stroke of 25 mm,

[0059] The above R MD is the slope of the increasing section between the upper yield point of the outer layer and the strength at a stroke of 25 mm, measured when the outer layer film is pulled in the MD direction.

[0060] [measurement method]

[0061] After peeling off the outer film of the above pouch film to prepare a specimen that does not include the inner sealant layer and barrier layer with a width of 15 mm, the specimen is fixed between two jigs of a tensile tester (UTM) at room temperature (initial jig gap 50 mm), 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. The X-axis of the graph derived from the measured values ​​is the stroke (mm), and the Y-axis is the strength (N). At this time, the R TD and R MD It is the slope of the straight line connecting the strength at the above yield point and when the stroke is 25 mm.

[0062]

[0063] The outer layer included in the pouch film prevents contact with the outside and seals the electrode assembly accommodated inside, so it is required to have excellent processability and formability. The processability and formability are affected by the mechanical properties, and in particular, are greatly affected by the mechanical properties of the outer layer. The inventor of the present invention has discovered a problem that, in the case of a conventional pouch film, a forming process is performed according to the size of the electrode assembly in order to accommodate an electrode assembly having a desired size, but the desired level of deformation length is not achieved depending on the resilience (elasticity) of the pouch film, and errors occur, making the process difficult. In order to solve the above problem, the inventor of the present invention has developed a pouch film that has excellent mechanical properties and can minimize resilience to improve formability by controlling the relationship between the mechanical strength of the outer layer in the TD and MD directions and the relationship between the storage modulus and the loss modulus within a specific range.

[0064] Figure 1 illustrates the configuration of the pouch film of the present invention. The pouch film of the present invention includes a sealant layer on the inner side, an outer layer, and a barrier layer containing 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In addition, the outer layer of the pouch film of the present invention has a slope of an increasing section between the upper yield point and the strength when the stroke is 25 mm, which satisfies the following equation 1.

[0070] [Formula 1]

[0071] 0.9≤ R TD / R MD ≤1.6

[0072] In the above equation 1, the R TDis the slope of the increasing section between the upper yield point of the outer layer measured when pulling the outer layer film in the TD direction and the strength at a stroke of 25 mm,

[0073] The above R MD is the slope of the increasing section between the upper yield point of the outer layer and the strength at a stroke of 25 mm, measured when the outer layer film is pulled in the MD direction.

[0074] When measuring the tensile elongation of the outer layer of a conventional, commonly used pouch film, the tensile elongation when pulled in the TD direction was different from the tensile elongation when pulled in the MD direction, and when this was graphed, there was a deviation between the slopes of the TD and MD directions between the upper yield point and the breaking strength. In other words, most conventional, commonly used outer layer films contained anisotropic materials with different properties depending on the TD and MD directions, and when processing an outer layer containing such an anisotropic material, the storage modulus was high compared to the loss modulus, corresponding to a high level of recovery at room temperature, so a problem occurred in which the deformation length was reduced again after forming to the desired deformation length.

[0075] The pouch film of the present invention comprises an isotropic material in the outer layer controlled so that the deviation of the slopes of the TD and MD directions between the upper yield point and the breaking strength is minimized, and by including such an outer layer, the loss modulus is increased compared to the storage modulus, thereby lowering the recovery force, thereby having the effect of being able to be formed to a desired deformation length. Here, the upper yield point refers to the strength (N) when the outer layer receiving the force no longer maintains elasticity and begins to deform permanently, and the section before the upper yield point can be recovered to the elastic section. In addition, the breaking strength refers to the strength at which the outer layer breaks when force is applied. In addition, the stroke refers to the length by which the specimen is extended due to deformation of the specimen when pressure is applied.

[0076] Referring to Figures 2 to 5, even when pressure is continuously applied, a section where the stroke changes little suddenly occurs in a section where the stroke changes abruptly. The point where the stroke changes abruptly corresponds to the upper yield point. Furthermore, when pressure is continuously applied, the point where the measured specimen breaks as the stroke changes corresponds to the breaking strength.

[0077] Meanwhile, when the slope between the upper yield point and the breaking strength was measured multiple times, a problem occurred in which the slope deviation occurred as the number of measurements and the stroke increased. In order to measure the accurate parameter value, the slope from the upper yield point to the above strength was measured based on the strength measured when the stroke was 25 mm, which is the section before the slope deviation occurred.

[0078]

[0079] The above R TD / R MDIt can be between 0.9 and 1.6. For example, it may be 0.90 or more, 0.91 or more, 0.93 or more, 0.95 or more, 0.97 or more, 0.99 or more, 1.00 or more, 1.03 or more, 1.05 or more, 1.07 or more, 1.10 or more, 1.13 or more, 1.15 or more, 1.17 or more, 1.19 or more, 1.20 or more, 1.21 or more, 1.60 or less, 1.59 or less, 1.57 or less, 1.55 or less, 1.53 or less, 1.51 or less, 1.50 or less, 1.47 or less, 1.45 or less, 1.43 or less, 1.41 or less, 1.40 or less, 1.39 or less, 1.37 or less, 1.35 or less, 1.33 or less, 1.32 or less. And, specifically, it may be 0.90 or more and 1.60 or less, and more specifically, it may be 0.95 or more and 1.35 or less. The ratio (R) of the slope of the strength section when the upper yield point of the outer layer and the stroke is 25 mm measured when pulling in the TD direction and the slope of the strength section when the upper yield point of the outer layer and the stroke is 25 mm measured when pulling in the MD direction TD / R MD ) does not satisfy the above numerical range, the actual molding value may be lower than the target molding value, which may cause a problem of reduced process efficiency, and the mechanical strength in the MD direction and the TD direction is not the same / similar but different, which may make it difficult to flexibly respond to the cup sizes of MD and TD that change depending on the model. In addition, the shrinkage rates in the MD direction and the TD direction may also be different, resulting in the production of a mechanically unstable pouch film, and the resilience may also be reduced.

[0080] Referring to FIGS. 2 to 5, it can be confirmed that in the case of FIGS. 2 and 3, the difference in slope between the MD direction and the TD direction is large, and in the case of FIGS. 4 and 5, the difference in slope between the MD direction and the TD direction is small.

[0081] Meanwhile, the R of the present invention TD / RMD The ratio of the first outer layer (polyethylene terephthalate) and the second outer layer (nylon) may be affected by the draw ratio of the first outer layer (polyethylene terephthalate), the temperature conditions, pressure conditions, tensile speed, extrusion speed, type of resin, and orientation in the manufacturing process of the pouch film. In addition, the second outer layer may be manufactured by a blown method. The blown method is a method of melting a polymer, extruding it, and then injecting air to inflate the film like a balloon, and can be mainly used when producing a high-strength film such as nylon. Specifically, the blown method may be composed of extrusion, tube forming, blowing, cooling, platen, and winding steps. The extrusion refers to a step of heating a polymer pellet and then making it into a molten state through an extruder, and the tube forming refers to a step of extruding the melted polymer into a cylindrical tube shape through a die. The blowing is a step of injecting air into the center of the tube to inflate the tube, and the thickness of the film can be controlled in the blowing step. Thereafter, the second outer layer can be manufactured through a cooling step of cooling the expanded tube, a platen step of passing the cooled tube between compression rollers to form a film, and a winding step of winding the film into a roll. Since the second outer layer manufactured by the blown method can be stretched together with the barrier layer during molding, the formability of the pouch film can be excellent. In the case where a sequential stretching method or a biaxial stretching method is used other than the blown method, the tensile strength and durability can be improved, but the flexibility and elongation are very low, and there is a problem in that the formability can be inferior.

[0082] The present invention is to control the above conditions and R TD / R MDThe ratio of the film can be controlled, and thus a pouch film having optimal formability and maximum forming length capable of accommodating an electrode assembly of a desired size without an error in the accommodation space can be provided. For example, the stretching ratio can be adjusted to 7 times or more, 8 times or more, 9 times or more, 10 times or more, 11 times or more, 12 times or more, 15 times or less, 14 times or less, and 13 times or less, and the temperature condition can be adjusted to 10 ℃ or more, 11 ℃ or more, 13 ℃ or more, 15 ℃ or more, 17 ℃ or more, 19 ℃ or more, 20 ℃ or more, 21 ℃ or more, 23 ℃ or more, 25 ℃ or more, 40 ℃ or less, 39 ℃ or less, 37 ℃ or less, 35 ℃ or less, 33 ℃ or less, 31 ℃ or less, and 30 ℃ or less, and the tensile speed can be adjusted to 30 mm / min or more, 35 mm / min or more, 40 mm / min or more, 45 mm / min or more, 50 mm / min or more, and 70 mm / min or less, It can be adjusted to 65 mm / min or less, 60 mm / min or less, and 55 mm / min or less.

[0083] According to one embodiment of the present invention, the strokes in the TD and MD directions corresponding to the breaking strength of the outer layer may be independently 30 mm or more and 100 mm or less. When the breaking strength of the outer layer included in the pouch film of the present invention is measured based on the above-described measuring method, the strokes in the TD and MD directions can each independently be 30 mm or more and 100 mm or less, and for example, 30 mm or more, 31 mm or more, 33 mm or more, 35 mm or more, 37 mm or more, 39 mm or more, 40 mm or more, 41 mm or more, 43 mm or more, 45 mm or more, 47 mm or more, 49 mm or more, 50 mm or more, 51 mm or more, 53 mm or more, 55 mm or more, 57 mm or more, 59 mm or more, 60 mm or more, 100 mm or less, 97 mm or less, 95 mm or less, 93 mm or less, 91 mm or less, 90 mm or less, 89 mm or less, 87 mm or less, 85 mm or less, 83 mm or less, 81 mm or less, 80 mm or less. The above strokes independently represent the length of deformation before fracture when force is applied in the MD and TD directions. Furthermore, a longer stroke indicates higher elongation. Therefore, when the stroke satisfies the above numerical range, excellent formability can be ensured.

[0084]

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] According to one embodiment of the present invention, the X-axis of the graph and the R TD Wow R MD The angle between the two can be 0 degrees or more and 25 degrees or less. The above R TD Wow R MDis the slope of the TD and MD directions described above, which represents the relationship between the pressure applied to the outer layer and the stroke, and means an index indicating the extent to which the specimen is deformed in length depending on the applied pressure. Specifically, the slope means the increase in plastic deformation compared to the increase in stress, and for example, if the slope is large, the material becomes hard to withstand more load, and if the slope is small, the material is ductile and easily stretched. In addition, if the ratio of MD / TD of the slope is small, the material can be stretched evenly without being biased to a specific direction, and the entire material can be uniformly deformed because the stress is not concentrated during forming, so that excellent formability can be achieved. Here, the R TD Wow R MD When the angle between the two sides satisfies the above numerical range, the mechanical strength in the MD direction and the TD direction is similar, so that the cup sizes of MD and TD that change depending on the model can be flexibly responded to, and the shrinkage rate and recovery force can be excellent.

[0093]

[0094] According to one embodiment of the present invention, the ratio of loss modulus to storage modulus (loss modulus / storage modulus) may be 0.09 or more and 0.12 or less. The loss modulus is a factor representing viscosity, and refers to a factor that is viscously deformed by externally applied pressure. The higher the loss modulus, the more flexibly it can be deformed by the applied pressure. The storage modulus is a factor representing elasticity, and refers to a factor that can be confirmed not to elastically respond to externally applied pressure. The higher the storage modulus, the greater the resistance to pressure, and the greater the resilience to return to the original state after forming. Therefore, in order to maintain excellent processability and formability of the pouch film, an optimal ratio of loss modulus and storage modulus is important. The ratio of the loss modulus and storage modulus of the present invention may be 0.090 or more and 0.120 or less. For example, the ratio may be 0.09 or more, 0.091 or more, 0.093 or more, 0.095 or more, 0.097 or more, 0.098 or more, 0.099 or more, 0.10 or more, 0.120 or less, 0.119 or less, 0.117 or less, 0.115 or less, 0.113 or less, 0.111 or less, or 0.110 or less. When the ratio satisfies the numerical range, the recovery force after molding is small, so the error of the deformation length is small, and molding at a desired level of accuracy can be achieved. When the ratio is too high, outside the upper limit of the numerical range, the recovery force after molding is too low, so the processability may be deteriorated, and when it is outside the lower limit of the numerical range, the recovery force after molding is high, so molding at an accurate deformation length may be difficult.

[0095] According to one embodiment of the present invention, when the thickness of the barrier layer is 30 ㎛ or more and 50 ㎛ or less and the thickness of the second outer layer is 10 ㎛ or more and 20 ㎛ or less, the ratio of the loss modulus to the storage modulus (loss modulus / storage modulus) may be 0.11 or more and 0.12 or less. For example, the ratio may be 0.110 or more, 0.112 or more, 0.114 or more, 0.120 or less, 0.118 or less, or 0.116 or less.

[0096] In addition, according to one embodiment of the present invention, when the thickness of the barrier layer is 50 ㎛ or more and 70 ㎛ or less and the thickness of the second outer layer is 20 ㎛ or more and 30 ㎛ or less, the ratio of the loss modulus to the storage modulus (loss modulus / storage modulus) may be 0.09 or more and 0.10 or less. The ratio may be 0.090 or more, 0.091 or more, 0.093 or more, 0.095 or more, 0.097 or more, and 0.099 or less.

[0097] Meanwhile, the loss modulus, storage modulus, and their ratio may be affected by the draw ratio of the first outer layer and the second outer layer, the type of resin, the temperature conditions during the manufacturing process, the pressure conditions, the tensile speed, the extrusion speed, and the orientation. In addition, the loss modulus, storage modulus, and their ratio may be affected by the thickness of the barrier layer and the second outer layer constituting the pouch film. As the thickness of the barrier layer and the second outer layer becomes thicker, the ratio may increase, and as the thickness of the barrier layer and the second outer layer becomes thinner, the ratio may decrease. If there are different pouch films including the barrier layer and the second outer layer having the same thickness, the higher the ratio of the loss modulus and the storage modulus, the more optimal the formability and recoverability may be.

[0098] According to one embodiment of the present invention, the maximum formable deformation length of the pouch film of the present invention may be greater than 12 mm and less than or equal to 17 mm. For example, the maximum deformation length may be greater than 12 mm, 12.5 mm or more, 13.0 mm or more, 13.5 mm or more, 14.0 mm or more, 14.5 mm or more, 15.0 mm or more, 17 mm or less, 16.5 mm or less, or 16 mm or less. The maximum forming length refers to the maximum height of the space in which the electrode assembly in the pouch film can be accommodated, and the present invention can implement an accurate deformation length by reducing the recovery force, while simultaneously implementing a maximum deformation length compared to a conventional pouch film. When the maximum deformation length satisfies the above range, more electrode assemblies can be accommodated, which can have an excellent level in terms of electric capacity.

[0099]

[0100] Pouch-type secondary battery case and secondary battery

[0101] The secondary battery of the present invention includes a pouch-type secondary battery case including the battery body and the pouch film, and the battery 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 body may include a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and an electrolyte.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106]

[0107] 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.

[0108]

[0109] Example 1

[0110] 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. The nylon film was manufactured by a blown method, and the draw ratio and extrusion speed of the polyethylene terephthalate film and the nylon film, temperature, pressure conditions, etc. were controlled. At this time, the slope (R) in the TD and MD directions between the upper yield point of the outer layer and the strength when the stroke is 25 mm, as measured by Experimental Example 1 below, TD / R MD) was 1.21.

[0111]

[0112] Example 2

[0113] 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 25 ㎛) as the inner layer, the barrier layer is made of aluminum (thickness 60 ㎛), 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. The nylon film was manufactured by a blown method, and the draw ratio and extrusion speed of the polyethylene terephthalate film and the nylon film, temperature, pressure conditions, etc. were controlled. At this time, the slope (R) in the TD and MD directions between the upper yield point of the outer layer and the strength when the stroke is 25 mm, as measured by Experimental Example 1 below, TD / R MD) was 1.32.

[0114]

[0115] Comparative Example 1

[0116] 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 contains aluminum (thickness 60 ㎛), and the sealant layer (thickness 80 ㎛) is a polypropylene extrusion coating (EC) layer, and a pouch film in which the outer layer, the barrier layer, and the sealant layer are laminated was manufactured. The nylon film was manufactured by a simultaneous biaxial stretching method (5 or more (MD): 2 (TD)), and at this time, the R of the outer layer TD / R MD was 1.63.

[0117]

[0118] Comparative Example 2

[0119] 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 25 ㎛) as the inner layer, the barrier layer contains aluminum (thickness 60 ㎛), and the sealant layer (thickness 80 ㎛) is a polypropylene extrusion coating (EC) layer, and a pouch film in which the outer layer, the barrier layer, and the sealant layer are laminated was manufactured. The nylon film was manufactured by a simultaneous biaxial stretching method (5 or more (MD): 2 (TD)), and at this time, the R of the outer layer TD / R MD was 1.63.

[0120]

[0121] Experimental Example 1 - Measurement of the slope between the upper yield point and the strength when the stroke is 25 mm.

[0122] After peeling off the outer film of the above pouch film to prepare a specimen having a width of 15 mm and not including an inner sealant layer and a barrier layer, the specimen is fixed between two jigs of a tensile tester (UTM) at room temperature (initial jig gap 50 mm), and then 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. Based on the measured values, a graph was derived in which the X-axis represents the stroke (mm) and the Y-axis represents the strength (N), and the graphs are shown in FIGS. 2 to 5. At this time, the slope between the upper yield point in the TD direction and the strength when the stroke is 25 mm is the slope of the straight line connecting the strength values ​​when the upper yield point and the stroke are 25 mm.

[0123]

[0124] Yield point (N) in the direction of separation, the stroke unit below is mm. Stroke 25 (mm) Slope R TD / R MD Example 1 MD stroke: 1.6 Strength: 41 stroke: 25 Strength: 791.6 21.21 TD stroke: 1.2 Strength: 35 stroke: 25 Strength: 821.97 Example 2 MD stroke: 2.1 Strength: 50 stroke: 25 Strength: 1002.18 1.32 TD stroke: 1.4 Strength: 43 stroke: 25 Strength: 1112.88 Comparative example 1 MD stroke: 1.6 Strength: 37 stroke: 25 Strength: 721.5 1.63 TD stroke: 2 Strength: 33 stroke: 25 Strength 892.4 Comparative example 2 MD stroke: 1.7 Strength: 55 stroke: 25 Strength: 901.5 2.68 TD stroke 1.3 Strength: 38 strokes: 25 strength: 1344.05

[0125] Experimental Example 2 - Modulus and Max Forming Measurements

[0126] For the pouch films manufactured in the above examples and comparative examples, the loss modulus and storage modulus were measured from -15 degrees to 60 degrees using DMA (dynamic thermomechanical analysis), and the tangent delta (loss modulus / storage modulus) value at room temperature was derived.

[0127] 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. The loss modulus, storage modulus, and maximum molding length values ​​are shown in Table 2 below.

[0128]

[0129] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Storage Modulus (MPa) 13494171571334117070 Loss Modulus (MPa) 1523167714161668 Tangent Delta (Loss Modulus / Storage Modulus) 0.11290.097740.10610.09770 Maximum Forming Length (mm) 12.5159.512

[0130] Referring to Tables 1 and 2 above, the pouch films of Examples 1 and 2 have an R of the outer layer TD / R MD Since it falls within the numerical range of the present invention, it can have the optimal tangent delta value corresponding to the present invention, thereby maintaining excellent processability and formability. Specifically, when Example 1 and Comparative Example 1, in which the thicknesses of the barrier layer and the nylon layer are the same, are compared, Example 1 has superior storage modulus and loss modulus values ​​than Comparative Example 1, and also has a higher tangent delta value, so it can have excellent formability and can secure a higher maximum forming length. Similarly, when Example 2 is compared with Comparative Example 2, it can be confirmed that the maximum forming length of the pouch film of Example 2 is superior.

[0131]

[0132] Acknowledgement

[0133] The present invention is a result of the following task support.

[0134] [Project ID] 2410004468

[0135] [Assignment Number] 20022450

[0136] Ministry of Trade, Industry and Energy

[0137] [Name of Project Management (Specialist) Institution] Korea Institute of Industrial Technology Planning and Evaluation

[0138] [Research Project Name] Material and Components Technology Development (Leeum Company)

[0139] [Research Project Name] Development of a Next-Generation Secondary Battery Pouch Capable of Delivering More Than Double the Highest Adhesive Strength (60°C)

[0140] [Contribution rate] 1 / 1

[0141] [Name of Project Performing Organization] Yulchon Chemical Co., Ltd.

[0142] Research Period: January 1, 2024 - December 31, 2024

Claims

1. A sequentially laminated inner sealant layer; a barrier layer comprising aluminum; and an outer layer, The outer layer includes a first outer layer; and a second outer layer disposed between the first outer layer and the barrier layer, A pouch film having a slope derived from a graph derived according to the following measurement method that satisfies the following equation 1: [Formula 1] 0.9≤ R TD / R MD ≤1.6 In the above equation 1, The above R TD is the slope of the increasing section between the upper yield point of the outer layer measured when pulling the outer layer film in the TD direction and the strength at a stroke of 25 mm, The above R MD is the slope of the increasing section between the upper yield point of the outer layer and the strength at a stroke of 25 mm, measured when the outer layer film is pulled in the MD direction. [measurement method] After peeling off the outer film of the above pouch film to prepare a specimen that does not include the inner sealant layer and barrier layer with a width of 15 mm, the specimen is fixed between two jigs of a tensile tester (UTM) at room temperature (initial jig gap 50 mm), 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. The X-axis of the graph derived from the measured values ​​is the stroke (mm), and the Y-axis is the strength (N). At this time, the R TD and R MD It is the slope of the straight line connecting the strength at the above yield point and when the stroke is 25 mm.

2. In claim 1, A pouch film in which the strokes in the TD and MD directions corresponding to the breaking strength of the outer layer are each independently 30 mm or more and 100 mm or less.

3. In claim 1, A pouch film wherein the first outer layer comprises at least one compound selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate.

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

5. In claim 1, The above equation 1 is 0.9≤ R TD / R MD A pouch film having a thickness of ≤1.

35.

6. In claim 1, The above R TD Wow R MD A pouch film having an angle between 0 degrees and 25 degrees.

7. In claim 1, A pouch film wherein the thickness of the barrier layer is 20 ㎛ or more and 80 ㎛ or less.

8. In claim 1, A pouch film having a thickness of the second outer layer of 10 ㎛ or more and 40 ㎛ or less.

9. In claim 1, A pouch film having a ratio of loss modulus to storage modulus (loss modulus / storage modulus) of 0.09 or more and 0.12 or less.

10. In claim 1, A pouch film having a ratio of loss modulus to storage modulus (loss modulus / storage modulus) of 0.11 to 0.12 when the thickness of the barrier layer is 30 ㎛ to 50 ㎛ and the thickness of the second outer layer is 10 ㎛ to 20 ㎛.

11. In claim 1, A pouch film having a ratio of loss modulus to storage modulus (loss modulus / storage modulus) of 0.09 to 0.10 when the thickness of the barrier layer is 50 ㎛ to 70 ㎛ and the thickness of the second outer layer is 20 ㎛ to 30 ㎛.

12. A pouch-type secondary battery case comprising a pouch film according to claim 1.

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