Pouch film for secondary battery exterior and secondary battery comprising same

Abstract

The present invention relates to a pouch film for secondary battery exterior, the pouch film comprising an outer layer, a barrier layer, and a sealant layer including a polyolefin-based resin, which are sequentially stacked, and having a delamination length of 3.0 mm or less, as measured according to measurement conditions. The description of the measurement conditions is as described in the present specification.

Description

Pouch film for secondary battery exterior 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. 10-2023-0129010, filed September 26, 2023, and Korean Patent Application No. 10-2024-0063137, filed May 14, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a pouch film for a secondary battery exterior and a secondary battery including the same.

[0005] Secondary batteries can be repeatedly charged and discharged, and can be classified into cylindrical secondary batteries, square secondary batteries, pouch-type secondary batteries, etc. depending on their structure and manufacturing method. Among these, pouch-type secondary batteries include a battery body (e.g., including a current collector, electrodes, etc., and further including a separator and / or electrolyte as necessary) and a pouch film that covers the battery body. Since their structure is relatively simple and their capacity per unit volume is relatively large, they are widely used in energy storage devices such as automobile batteries.

[0006] A method of enclosing a battery body with a pouch film generally involves bringing the innermost layers of the pouch films (e.g., sealant layers) into contact with each other, then applying heat and pressure to the innermost layers to thermally bond them together to form a seal, thereby sealing the battery body. In this way, a battery body sealed with a pouch film may not be substantially exposed to the external environment.

[0007] The aforementioned pouch film is required to have excellent sealing properties, which can be evaluated by the sealing strength of the heat-bonded sealing portion. In other words, if the pouch film has excellent sealing strength, the pouch film can be evaluated as having generally excellent sealing properties.

[0008] Meanwhile, conventional pouch films have had difficulty securing sufficient sealing strength at the sealing portion, and research on improving the sealing strength at the sealing portion has also been insufficient.

[0009] Accordingly, there is a growing demand for pouch films that can exhibit excellent sealing properties overall by securing sufficient sealing strength in the sealing portion of the pouch film.

[0010] In order to solve the aforementioned problem, the present invention provides a pouch film for a secondary battery exterior, which includes an outer layer, a barrier layer, and a sealant layer including a polyolefin resin, which are sequentially laminated, and has a peeling length of 3.0 mm or less measured under the following measurement conditions.

[0011] [Measurement conditions]

[0012] (1) Fold the secondary battery outer pouch film (width 200 mm, height 100 mm) in half and heat-bond (temperature 190°C, pressure 0.2 MPa, time 1.6 s) to form a sealing portion, then cut the sealing portion to a width of 15 mm to produce a specimen (width 15 mm, height 50 mm).

[0013] (2) At a measurement temperature of 25℃, the specimen is fixed between two jigs of a tensile tester (UTM) so that the sealing part of the specimen is positioned in the center (initial jig gap 30 mm), and then the sealing strength is measured while pulling at a measurement speed of 50 mm / min.

[0014] (3) When the gap between the two jigs of the tensile tester increases by 15 mm compared to the initial jig gap, the peeling length of the sealing portion in the direction in which the specimen is pulled is measured.

[0015] In addition, in order to solve the aforementioned problem, the present invention provides a lithium secondary battery externally covered with the secondary battery external pouch film.

[0016] According to the present invention, by applying a sealant layer in which the peeling length measured under the above-described measurement conditions satisfies the above-described numerical range, a pouch film for a secondary battery exterior can have excellent sealing strength characteristics.

[0017] Figures 1 and 2 are photographs showing specimens manufactured according to the conditions described in the measurement conditions of the present invention.

[0018] The present invention relates to a pouch film for external use of a secondary battery including an outer layer, a barrier layer, and a sealant layer laminated sequentially, and a lithium secondary battery externally covered with the pouch film for external use of the secondary battery.

[0019] outer layer

[0020] The above outer layer may be the outermost layer of the secondary battery outer pouch film, and may include a heat-resistant resin layer having a melting point higher than the heat-bonding temperature of the sealant layer described later. The type of the heat-resistant resin layer is not particularly limited, but may include at least one selected from the group consisting of polyamide, polyester, polyolefin, copolymers thereof, and blends thereof. Here, the outer layer may have a single-layer or multi-layer structure including at least one of the above-mentioned materials.

[0021] The outer layer may have an appropriate thickness within a range that ensures sufficient mechanical strength and formability as an exterior material. For example, the thickness of the outer layer may be appropriately selected within a numerical range of 15 µm to 140 µm, 25 µm to 110 µm, or 35 µm to 100 µm.

[0022] barrier layer

[0023] The barrier layer may be an intermediate layer of the 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 may include, but is not particularly limited to, at least one selected from the group consisting of aluminum, stainless steel, copper, titanium, and alloys thereof, and preferably may include aluminum.

[0024] The above barrier layer may have an appropriate thickness within a range that effectively prevents the intrusion of the aforementioned gases and / or moisture while ensuring sufficient formability. For example, the thickness of the barrier layer may be appropriately selected within a numerical range of 20 μm to 150 μm, 35 μm to 125 μm, or 60 μm to 90 μm.

[0025] sealant layer

[0026] The sealant layer may be the innermost layer of the pouch film for the secondary battery exterior. That is, the sealant layer may be in direct contact with the battery body (e.g., electrode, separator, and / or electrolyte). Therefore, the sealant layer must have excellent electrolyte resistance and excellent insulation.

[0027] To this end, the sealant layer may include at least a polyolefin resin. The polyolefin resin has excellent electrolyte resistance and excellent insulation properties, and accordingly, the sealant layer including the polyolefin resin may also have excellent electrolyte resistance and excellent insulation properties derived from the polyolefin resin.

[0028] 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.

[0029] In the case where the sealant layer includes the polyolefin-based resin, if the peeling length measured under the measurement conditions described below satisfies the numerical range described below, the type and content of the polyolefin-based resin, whether or not an additive (e.g., an elastomer-based additive) added to the sealant layer is added and the content, the characteristics of the polyolefin-based resin, etc. are not particularly limited. In addition, if the peeling length measured under the measurement conditions described below satisfies the numerical range described below, the sealant layer may have a single-layer structure, or may have a multi-layer structure including the same or different types of materials.

[0030] For example, the sealant layer may have a single-layer structure or a two-layer or more laminated structure formed by coextrusion, etc., and such a sealant layer may be adhered to the barrier layer through an adhesive layer provided on one surface of the barrier layer. Here, the adhesive layer may be a dried solvent-type adhesive, and in this case, a method of adhering the sealant layer to the barrier layer by drying such a solvent-type adhesive may be referred to as a solvent dry lamination method.

[0031] For another example, the sealant layer may be disposed on the barrier layer without a separate adhesive layer, and may include a first sealant layer disposed on the barrier layer on the opposite side from the outer layer, and a second sealant layer disposed on the first sealant layer. In this case, the secondary battery outer pouch film may include the second sealant layer, the first sealant layer, the barrier layer, and the outer layer in that order from the innermost layer to the outermost layer.

[0032] Here, the first sealant layer may be an extrusion coating layer obtained by extrusion coating the polyolefin-based resin, and the second sealant layer may be a film layer containing a polyolefin-based resin that is the same as or different from the resin contained in the first sealant layer, and may be adhered to the barrier layer by the first sealant layer, which is an extrusion coating layer. In this way, in the sealant layer containing the film layer and the extrusion coating layer, the method of adhering the film layer to the barrier layer by the extrusion coating layer may be referred to as an extrusion lamination method.

[0033] In one embodiment, the crystallization temperature (T) of the sealant layer is measured under a temperature decreasing condition of 10°C / min using a differential scanning calorimetry method. c ) can be 90~103℃, preferably 95~100℃.

[0034] Pouch film for secondary battery exterior

[0035] The pouch film for a secondary battery of the present invention includes the outer layer as the outermost layer, the barrier layer as the middle layer, and the sealant layer as the innermost layer.

[0036] The secondary battery external pouch film can be used to seal the battery main body. For example, the battery main body can be sealed by bringing the sealant layers of two different secondary battery external pouch films into contact with each other and then thermally bonding them to form a sealing portion. As another example, the battery main body can be sealed by folding a single secondary battery external pouch film in half so that the sealant layers touch each other and then thermally bonding the sealant layers that touch each other to form a sealing portion.

[0037] The above secondary battery external pouch film is required to have excellent sealing strength. Here, as a measure for evaluating the sealing strength characteristics of the secondary battery external pouch film, the peeling length of the sealing portion measured under the measurement conditions described below for the secondary battery external pouch film can be cited. The shorter the peeling length of the sealing portion measured under the measurement conditions described below (e.g., the length of the portion where sealant layers that were thermally bonded to each other are peeled and torn), the better the sealing strength of the secondary battery external pouch film at the sealing portion is.

[0038] [Measurement conditions]

[0039] (1) The secondary battery outer pouch film (width 200 mm, height 100 mm) is folded in half and heat-sealed (temperature 190°C, pressure 0.2 MPa, time 1.6 s) to form a sealing portion, and then the sealing portion is cut to have a width of 15 mm to manufacture a specimen (width 15 mm, height 50 mm) (the specific shape of the specimen is shown in FIGS. 1 and 2).

[0040] (2) At a measurement temperature of 25℃, the specimen is fixed between two jigs of a tensile tester (UTM) so that the sealing part of the specimen is positioned in the center (initial jig gap 30 mm), and then the sealing strength is measured while pulling at a measurement speed of 50 mm / min.

[0041] (3) When the gap between the two jigs of the tensile tester increases by 15 mm compared to the initial jig gap, the peeling length of the sealing portion in the direction in which the specimen is pulled is measured.

[0042] The secondary battery outer pouch film of the present invention may have a peeling length of 3.0 mm or less measured under the above measurement conditions, and thus may have excellent sealing strength characteristics.

[0043] Here, the peeling length measured according to the measurement conditions for the secondary battery outer pouch film is, for example, not only the material of the outer layer or barrier layer, but also the type or softness of the polyolefin resin included in the sealant layer, characteristics such as whether it is stretched or not, addition of various types of elastomer series additives known in the art (e.g., polyester elastomer, polyamide elastomer, polyurethane elastomer, polyolefin elastomer, polystyrene elastomer, polyurethane elastomer, polyolefin elastomer, polystyrene elastomer, polyester elastomer, acrylic elastomer, copolymers thereof, or blends thereof), the content of the added additive, the laminated configuration / material of the sealant layer and its crystallization temperature (e.g., 90 to 103°C), and the production of an extrusion coating film as the sealant layer. It is possible to control the temperature within a predetermined range by controlling the difference between the extrusion temperature of the city and the cooling roll temperature (e.g., 200 to 280°C).

[0044] Alternatively, as another example, the peeling length measured according to the measurement conditions for the secondary battery outer pouch film can be adjusted to a predetermined range by adjusting the material used for the barrier layer and / or the outer layer, its thickness, etc.

[0045] In one embodiment, the total thickness of the secondary battery outer pouch film, which can satisfy the above-described numerical range in terms of the peeling length measured according to the above-described measurement conditions, may be, for example, 120 µm or more and 300 µm or less, preferably 140 µm or more and 210 µm or less.

[0046] In this case, in one embodiment, the pouch film for external use of a secondary battery of the present invention may have a total thickness of 120 µm or more and 300 µm or less, and a peeling length of 3.0 mm or less measured under the above measurement conditions. More specifically, the pouch film for external use of a secondary battery of the present invention may have a total thickness of 140 µm or more and 190 µm or less, and a peeling length of 1.5 mm or less measured under the above measurement conditions. Alternatively, the pouch film for external use of a secondary battery of the present invention may have a total thickness of 195 µm or more and 210 µm or less, and a peeling length of 2.8 mm or less measured under the above measurement conditions.

[0047] In one embodiment, the ratio of the thickness of the sealant layer to the total thickness of the secondary battery external pouch film may be 1:0.3 to 0.6, and preferably 1:0.35 to 0.5. Here, when the thickness of the sealant layer satisfies the above-mentioned numerical range, the sealing strength characteristics of the secondary battery external pouch film are very excellent, and the peeling length measured according to the above-mentioned measurement conditions can be easily adjusted to match the above-mentioned numerical range.

[0048] In one embodiment, when measuring the peeling length according to the above measurement conditions, tearing may occur between the heat-bonded sealant layers of the secondary battery external pouch film. In this case, substantially no tearing may occur between the sealant layer and the barrier layer in the secondary battery external pouch film.

[0049] lithium secondary battery

[0050] The lithium secondary battery of the present invention includes the battery main body and the secondary battery external pouch film, and the battery main body is sealed by the secondary battery external pouch film.

[0051] The above battery body may include a negative electrode for a lithium secondary battery, a positive electrode for a lithium secondary battery, and an electrolyte.

[0052] 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 0.6 Mn 0.2 Co 0.2 ) may contain a positive electrode active material such as O2.

[0053] 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.

[0054] 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.

[0055] The above secondary battery external pouch film may have excellent sealing strength characteristics. Accordingly, the battery body sealed by the secondary battery external pouch film may not be exposed to the external environment.

[0056] Hereinafter, the present invention will be described in more detail through examples. However, these examples are provided solely to aid understanding of the present invention and are not intended to limit the scope of the present invention in any way.

[0057] Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0058] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 25 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, an 80 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC1) obtained by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 270°C), and a 50 ㎛ thick second sealant layer (CPP1) including a non-stretched polypropylene film bonded on the first sealant layer (EC1).

[0059] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC1) and the second sealant layer (CPP1) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC1) and the second sealant layer (CPP1) was 98°C (measurement error: ±2°C).

[0060] Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layers, barrier layers, and sealant layers

[0061] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 25 ㎛ thick nylon, and a 3 ㎛ thick outer adhesive layer are sequentially laminated as an outer layer, a 60 ㎛ thick aluminum foil bonded to the outer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC2) formed by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 250°C), and a 50 ㎛ thick second sealant layer (CPP2) comprising a non-stretched polypropylene film bonded on the first sealant layer (EC2).

[0062] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC2) and the second sealant layer (CPP2) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC2) and the second sealant layer (CPP2) was 98°C (measurement error: ±2°C).

[0063] Example 3: Pouch film for secondary battery exterior including sequentially laminated outer layers, barrier layers, and sealant layers

[0064] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 15 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, a 40 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC3) obtained by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 230°C), and a 50 ㎛ thick second sealant layer (CPP3) including a polypropylene film bonded on the first sealant layer (EC3).

[0065] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC3) and the second sealant layer (CPP3) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC3) and the second sealant layer (CPP3) was 98°C (measurement error: ±2°C).

[0066] Reference Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0067] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 25 ㎛ thick nylon, and a 3 ㎛ thick outer adhesive layer are sequentially laminated as an outer layer, an 80 ㎛ thick aluminum foil bonded to the outer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC4) obtained by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 260°C), and a 50 ㎛ thick second sealant layer (CPP4) including a non-stretched polypropylene film bonded on the first sealant layer (EC4).

[0068] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC4) and the second sealant layer (CPP4) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC4) and the second sealant layer (CPP4) was 111°C (measurement error: ±2°C).

[0069] Reference Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0070] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 25 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, a 60 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC5) obtained by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 265°C), and a 50 ㎛ thick second sealant layer (CPP5) including a non-stretched polypropylene film bonded on the first sealant layer (EC5).

[0071] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC5) and the second sealant layer (CPP5) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC5) and the second sealant layer (CPP5) was 111°C (measurement error: ±2°C).

[0072] Reference Example 3: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0073] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 15 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, a 40 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, a 30 ㎛ thick first sealant layer (EC6) obtained by extrusion-coating a polypropylene-based resin on the barrier layer as a sealant layer (the difference between the extrusion section temperature and the cooling roll temperature during the production of the extrusion-coated film: 280°C), and a 50 ㎛ thick second sealant layer (CPP6) including a polypropylene film bonded on the first sealant layer (EC6).

[0074] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC6) and the second sealant layer (CPP6) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the entire sealant layer including the first sealant layer (EC6) and the second sealant layer (CPP6) was 111°C (measurement error: ±2°C).

[0075] Comparative Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0076] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 25 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, a 60 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, and a first sealant layer (EC7) having a thickness of 80 ㎛ obtained by extrusion-coating a polypropylene resin on the barrier layer as a sealant layer (difference between the extrusion section temperature and the cooling roll temperature during the manufacture of the extrusion-coated film: 290°C).

[0077] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC7) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the first sealant layer (EC7) was 104°C (measurement error: ±2°C).

[0078] Comparative Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0079] A secondary battery outer pouch film was manufactured, which includes a laminate in which a 12 ㎛ thick PET, a 15 ㎛ thick nylon, and a 3 ㎛ thick outer layer adhesive layer are sequentially laminated as an outer layer, a 40 ㎛ thick aluminum foil bonded to the outer layer adhesive layer as a barrier layer, and a first sealant layer (EC8) having a thickness of 80 ㎛ obtained by extrusion-coating a polypropylene resin on the barrier layer as a sealant layer (difference between the extrusion section temperature and the cooling roll temperature during the manufacture of the extrusion-coated film: 300°C).

[0080] In the manufactured secondary battery outer pouch film, the sealant layer including the first sealant layer (EC8) was used such that the peeling length measured according to the measurement conditions described above satisfies the peeling length described in Table 1 below, and in this case, the crystallization temperature of the first sealant layer (EC8) was 104°C (measurement error: ±2°C).

[0081] Example 1 Example 2 Example 3 Reference Example 1 Reference Example 2 Reference Example 3 Comparative Example 1 Comparative Example 2 Peeling length #12.0mm1.2mm0.5mm4.0mm7.0mm7.5mm10mm6.0mm Peeling length #22.5mm0.9mm0.5mm5.0mm8.0mm6.0mm9.5mm5.0mm Peeling length #32.4mm1.1mm0.5mm5.2mm5.0mm8.5mm9.5mm7.0mm Average (#1~#3)2.3mm1.07mm0.5mm4.73mm6.67mm7.3mm9.6mm6.0mm

[0082] Referring to Table 1 above, it can be confirmed that the secondary battery external pouch films of Examples 1 to 3 all had peeling lengths of 3.0 mm or less when measured under the aforementioned measurement conditions. Here, in the case of the secondary battery external pouch films of Examples 1 to 3, in all measurement results (peeling length #1, peeling length #2, peeling length #3) when the peeling length was measured under the aforementioned measurement conditions, tearing occurred between the sealant layers that had been heat-bonded to each other. In contrast, it can be confirmed that the secondary battery external pouch films of Reference Examples 1 to 3, Comparative Example 1, and Comparative Example 2 all have peeling lengths exceeding 3.0 mm as measured under the aforementioned measurement conditions. In this case, the secondary battery external pouch film of Comparative Example 1 all has peeling lengths exceeding 10 mm as measured under the aforementioned measurement conditions, and the secondary battery external pouch film of Comparative Example 2 all has peeling lengths exceeding 6 mm as measured under the aforementioned measurement conditions, confirming that its sealing strength is inferior. In addition, in the case of the secondary battery external pouch films of Comparative Examples 1 and 2, in all measurement results (peel length #1, peel length #2, peel length #3) in the cases where the peeling length was measured under the aforementioned measurement conditions, tearing occurred between the sealant layer and the barrier layer.

[0083] Experimental Example 1: Evaluation of Sealing Strength

[0084] The secondary battery outer pouch films of Examples 1 to 3 and Reference Examples 1 to 3 were folded in half and heat-sealed (temperature 190°C, pressure 0.2 MPa, time 1.6 s) to form a sealing portion, and then the sealing portion was cut to a width of 15 mm to manufacture a specimen.

[0085] At a measurement temperature of 25℃, the specimen was fixed between two jigs of a tensile testing machine (UTM) so that the sealing part of the specimen was located in the center (initial jig gap 30 mm), and then pulled at a measurement speed of 50 mm / min to obtain a graph of the sealing strength's dependence on the jig gap change.

[0086] From this, the maximum value of the sealing strength was measured from the graph of the jig gap change dependence of the sealing strength, and the maximum value is shown in Table 2 below.

[0087] Example 1 Example 2 Example 3 Reference Example 1 Reference Example 2 Reference Example 3 Maximum Sealing Strength #1 219.6 N 186.2 N 161.2 N 176.0 N 161.8 N 151.0 N Maximum Sealing Strength #2 217.0 N 203.6 N 160.4 N 185.4 N 171.1 N 138.2 N Maximum Sealing Strength #3 204.9 N 210.6 N 159.8 N 165.3 N 182.0 N 142.7 N Average (#1 ~ #3) 213.8 N 200.1 N 160.5 N 175.6 N 171.6 N 143.9 N

[0088] Referring to Table 2, it can be seen that the secondary battery outer pouch films of Examples 1 to 3, which satisfy the peeling length of 3.0 mm or less according to the above-described measurement conditions, have a relatively higher maximum sealing strength compared to the secondary battery outer pouch films of Reference Examples 1 to 3, which satisfy the peeling length of more than 3.0 mm according to the above-described measurement conditions.

[0089] Acknowledgement

[0090] This application is the result of the following project support.

[0091] Assignment ID: 1415185612

[0092] Assignment Number: 20022450

[0093] Ministry Name: Ministry of Trade, Industry and Energy

[0094] Project Management (Professional) Agency Name: Korea Institute of Industrial Technology Planning and Evaluation

[0095] Research Project Name: Material and Components Technology Development

[0096] Research Project Title: Development of Next-Generation Secondary Battery Pouches Capable of Delivering More Than Double the Bonding Strength (60°C)

[0097] Contribution rate: 1 / 1

[0098] Project implementation organization name: Yulchon Chemical Co., Ltd.

[0099] Research period: January 1, 2023 - December 31, 2023

Claims

1. It comprises an outer layer, a barrier layer, and a sealant layer including a polyolefin resin that are sequentially laminated, A pouch film for a secondary battery exterior, the peeling length of which is 3.0 mm or less as measured under the following measurement conditions. [Measurement conditions] (1) Fold the secondary battery outer pouch film (width 200 mm, height 100 mm) in half and heat-bond (temperature 190°C, pressure 0.2 MPa, time 1.6 s) to form a sealing portion, then cut the sealing portion to a width of 15 mm to produce a specimen (width 15 mm, height 50 mm). (2) At a measurement temperature of 25℃, the specimen is fixed between two jigs of a tensile tester (UTM) so that the sealing part of the specimen is positioned in the center (initial jig gap 30 mm), and then the sealing strength is measured while pulling at a measurement speed of 50 mm / min. (3) When the gap between the two jigs of the tensile tester increases by 15 mm compared to the initial jig gap, the peeling length of the sealing portion in the direction in which the specimen is pulled is measured.

2. In claim 1, A secondary battery external pouch film having a total thickness of 120㎛ or more and 300㎛ or less.

3. In claim 1, A secondary battery external pouch film, wherein the ratio of the thickness of the sealant layer to the total thickness of the secondary battery external pouch film is 1:0.3 to 0.

6.

4. In claim 1, A pouch film for a secondary battery exterior, wherein the polyolefin-based resin comprises a polyolefin derived from an olefin or a derivative thereof, a copolymer thereof, or a blend comprising at least one of the above.

5. In claim 4, A pouch film for a secondary battery exterior, wherein the polyolefin resin comprises at least one selected from the group consisting of a copolymer derived from a monomer derived from polyethylene, polypropylene, polybutylene, ethylene and / or propylene and a monomer derived from alpha-olefin, or a blend thereof.

6. In claim 1, The total thickness of the secondary battery outer pouch film is 140㎛ or more and 190㎛ or less, A pouch film for external use of a secondary battery, the peeling length of which is 1.5 mm or less as measured under the above measurement conditions.

7. In claim 1, The total thickness of the secondary battery outer pouch film is 195㎛ or more and 210㎛ or less, A pouch film for external use of a secondary battery, the peeling length of which is 2.8 mm or less as measured under the above measurement conditions.

8. In claim 1, A pouch film for external use of a secondary battery, wherein when the peeling length is measured according to the above measurement conditions, peeling occurs between the heat-bonded sealant layers, and peeling does not occur between the sealant layer and the barrier layer.

9. In claim 1, A pouch film for a secondary battery exterior, wherein the barrier layer comprises at least one selected from the group consisting of aluminum, stainless steel, copper, titanium, and alloys thereof.

10. In claim 1, A pouch film for external use of a secondary battery, wherein the thickness of the barrier layer is 20㎛ or more and 150㎛ or less.

11. In claim 1, A pouch film for a secondary battery exterior, wherein the outer layer comprises at least one selected from the group consisting of polyamide, polyester, polyolefin, and copolymers thereof.

12. A lithium secondary battery externally packaged with a secondary battery external pouch film according to any one of claims 1 to 11.

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