A pouch film for a secondary battery, a method of manufacturing the same, a secondary battery, and a method of manufacturing the same

Abstract

Disclosed are a pouch film for a secondary battery, a secondary battery using the pouch film for a secondary battery, and a method of manufacturing the same. The pouch film for a secondary battery is composed of a laminate of at least an outer layer, a barrier layer, and a sealant layer, and the sealant layer includes an extrusion (EC) layer and a polypropylene (PP) layer at a lower portion of the EC layer. The pouch film for a secondary battery has excellent normal temperature seal strength and high temperature seal strength, and has excellent normal temperature seal strength maintenance characteristics and high temperature seal strength maintenance characteristics. The pouch film for a secondary battery has excellent high temperature long-term reliability when a battery pack is manufactured, and thus can be effectively used for large and medium-sized batteries.

Description

Technical Field

[0001] This invention relates to a pouch film for secondary batteries with excellent sealing strength characteristics at both room temperature and high temperature, and a method for preparing the same, as well as a secondary battery using the same pouch film and a method for preparing the same. More specifically, it relates to a pouch film for secondary batteries and a method for preparing the same, and a secondary battery using the same pouch film and a method for preparing the same. This method not only makes the thermal bonding strength, i.e., sealing strength, of the pouch film excellent under both room temperature and high temperature conditions, but also achieves excellent room temperature sealing strength maintenance characteristics and high temperature sealing strength maintenance characteristics, thereby improving the long-term high-temperature reliability of the battery pack.

[0002] [Support the South Korean R&D project for this invention]

[0003] [Project Unique Number] 1415181922

[0004] [Project Number] 20022450

[0005] [Department Name] Trade, Industry and Resources Department

[0006] [Name of the Project Management (Specialized) Agency] Korea Institute for Industrial Technology Evaluation and Management

[0007] [Research Project Title] Materials and Components Packaging (Leading Enterprise)

[0008] [Research Project Title] Development of a New Generation of Secondary Battery Bags Achieving More Than 2 Times Higher Bonding Strength (60℃)

[0009] [Contribution Rate] 1 / 1

[0010] [Name of the Institution Conducting the Project] Kurimura Chemical Co., Ltd.

[0011] [Research Period] September 1, 2022 – December 31, 2022

[0012] [Project Unique Number] 1415185612

[0013] [Project Number] 20022450

[0014] [Department Name] Trade, Industry and Resources Department

[0015] [Name of the Project Management (Specialized) Agency] Korea Institute for Industrial Technology Evaluation and Management

[0016] [Research Project Title] Materials and Components Packaging (Leading Enterprise)

[0017] [Research Project Title] Development of a New Generation of Secondary Battery Bags Achieving More Than 2 Times Higher Bonding Strength (60℃)

[0018] [Contribution Rate] 1 / 1

[0019] [Name of the Institution Conducting the Project] Kurimura Chemical Co., Ltd.

[0020] [Research Period] January 1, 2023 – December 31, 2023 Background Technology

[0021] Lithium-ion batteries (LiB) are suitable for a variety of applications due to their high energy density and excellent output.

[0022] Secondary battery pouch film, as a multi-layered packaging film, is used to surround the electrode assembly and electrolyte of the aforementioned secondary battery. As a core component material, it determines the battery's safety, service life characteristics, and continuous operation. Therefore, it requires mechanical flexibility and strength, high oxygen / water vapor barrier properties, high thermal bonding strength, chemical resistance to electrolyte, electrical insulation, and high-temperature safety.

[0023] Typically, the bag film for secondary batteries consists of an outer layer, a barrier layer, and an inner sealant layer.

[0024] The outer or outermost layer is made of nylon or a blend of nylon and polyethylene terephthalate (PET), stretched polypropylene (OPP), polyethylene, etc. This outer or outermost layer needs to have properties such as heat resistance, pinhole resistance, chemical resistance, moldability, and insulation.

[0025] The barrier layer needs to be able to block water vapor or other gases and also be formable. Based on this, the barrier layer can be made of formable metals, such as aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), etc., with aluminum being the most commonly used currently.

[0026] The inner sealant layer serves as the contact layer for the electrolyte. In addition to thermal adhesion and moldability, it also needs to be resistant to electrolyte and have good insulation resistance.

[0027] On the other hand, as the application of lithium secondary batteries expands from small-scale applications to large and medium-sized applications such as automobiles or energy storage devices (ESS), the bag membranes for secondary batteries are also gradually required to have characteristics suitable for large and medium-sized applications with high safety requirements.

[0028] Therefore, in addition to sealing strength characteristics under normal temperature conditions, excellent sealing strength is especially required under high temperature (60°C) conditions. Furthermore, the sealing strength must be maintained without decrease under both normal and high temperature conditions. However, this characteristic significantly impacts battery safety. Particularly in the case of pouch films for medium and large-sized rechargeable batteries, since battery explosions can cause fatal accidents, there is a need to develop pouch films for rechargeable batteries that can ensure battery safety. Summary of the Invention

[0029] Technical issues

[0030] On the one hand, exemplary embodiments of the present invention provide a pouch film for secondary batteries and a method for preparing the same, a secondary battery using the pouch film for secondary batteries and a method for preparing the same, which not only makes the sealing strength excellent under both room temperature and high temperature conditions, but also achieves excellent room temperature sealing strength maintenance characteristics and high temperature sealing strength maintenance characteristics, thereby making the long-term high-temperature reliability of the battery pack excellent.

[0031] Technical solution

[0032] The exemplary embodiment of the present invention provides a pouch film for secondary batteries, which is composed of at least an outer layer, a barrier layer and a sealant layer stacked sequentially. The sealant layer is formed by extrusion (EC) layer stacking. When sealed under sealing conditions of 220°C, the maximum room temperature sealing strength of the pouch film for secondary batteries, measured by the following method, is 150 N / 15 mm or more and 205 N / 15 mm or less in both the longitudinal (MD direction) and transverse (TD direction).

[0033] [Method for determining the maximum room temperature seal strength under sealing conditions at 220°C]

[0034] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0035] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0036] Under normal temperature conditions, the sealing strength of the specimen in the MD and TD directions was determined using a sealing strength tester. The test was conducted under sealing conditions of 10mpm test speed and 30mm clamping gap.

[0037] The maximum value in the seal strength measurement is the maximum seal strength.

[0038] Furthermore, the secondary battery bag film provided in the exemplary embodiment of the present invention is composed of a laminate having at least an outer layer, a barrier layer, and a sealant layer stacked sequentially. The sealant layer is formed by extrusion (EC) layer stacking. When sealed under sealing conditions of 220°C, the maximum high-temperature sealing strength of the secondary battery bag film in at least one of the MD and TD directions (the sealing strength value measured after being placed at a temperature of 60°C for 3 minutes) measured according to the following method is 115 N / 15 mm to 170 N / 15 mm.

[0039] [Method for determining the maximum high-temperature seal strength under sealing conditions at 220°C]

[0040] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0041] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0042] After being placed at 60°C for 3 minutes, the sealing strength of the specimen in at least one of the MD and TD directions was measured using a sealing strength tester. The test was conducted under sealing conditions of 10mpm test speed and 30mm clamping gap (GripGap).

[0043] The maximum value in the seal strength measurement is the maximum seal strength.

[0044] In one exemplary implementation of the present invention, when sealing is performed under sealing conditions of 220°C, the following maximum sealing strength parameters related to the maximum sealing strength of the bag film for secondary batteries can be 1.1 or more and 1.8 or less.

[0045] [Maximum sealing strength parameter]

[0046] (Maximum sealing strength in the MD direction at room temperature × Maximum sealing strength in the TD direction at room temperature) / (Maximum sealing strength in the MD direction at high temperature × Maximum sealing strength in the TD direction at high temperature).

[0047] In one exemplary implementation of the present invention, when sealed under sealing conditions at 220°C, the room temperature energy in the TD direction of the above-mentioned secondary battery bag film, measured according to the following method, can be 2.0 KN×mm to 3.0 KN×mm.

[0048] [Method for determining room temperature energy in the TD direction under sealed conditions at 220℃]

[0049] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0050] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0051] With the specimen pulled in the TD direction, the change in sealing strength was measured using a sealing strength tester at room temperature. The measurement was conducted under the following conditions: test speed of 10mpm and clamping gap of 30mm.

[0052] When the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the room temperature energy. The area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke in the range of 0mm to 20mm.

[0053] In one exemplary implementation of the present invention, when sealed under a sealing condition of 220°C, the high-temperature energy in the TD direction of the above-mentioned secondary battery bag film, measured by the following method, can be 1.5KN×mm to 2.5KN×mm.

[0054] [Method for determining high-temperature energy in the TD direction under sealed conditions at 220℃]

[0055] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0056] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0057] Under high-temperature conditions of 60°C for 3 minutes, the change in sealing strength was measured using a sealing strength tester when the test piece was pulled in the TD direction. The test was conducted at a test speed of 10mpm and a clamping gap of 30mm (GripGap).

[0058] When the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the high-temperature energy. The area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke in the range of 0mm to 20mm.

[0059] In one exemplary implementation of the present invention, when the bag film for secondary batteries is sealed under a sealing condition of 220°C, the difference between the room temperature energy and the high temperature energy in the TD direction of the bag film, as measured by the following method, can be 0.4 KN×mm to 0.6 KN×mm.

[0060] [Method for determining the room temperature energy and high temperature energy in the TD direction under sealed conditions at 220℃]

[0061] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0062] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0063] Under normal temperature conditions or high temperature conditions after being placed at 60°C for 3 minutes, the change in sealing strength was measured using a sealing strength tester when the test piece was pulled in the TD direction. The test was conducted under the following conditions: test speed of 10mpm and clamping gap of 30mm.

[0064] When the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the normal temperature energy or high temperature energy. The area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke in the range of 0mm to 20mm.

[0065] Energy measured under normal temperature conditions is called normal temperature energy, and energy measured under high temperature conditions is called high temperature energy.

[0066] In one exemplary implementation of the present invention, when sealed under sealing conditions at 220°C, the maximum room temperature travel of the above-mentioned secondary battery bag film in the TD direction, as measured by the following method, can be 15mm to 25mm.

[0067] [Method for determining the maximum stroke in the TD direction at room temperature under sealing conditions of 220℃]

[0068] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0069] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0070] With the specimen pulled in the TD direction, the change in sealing strength was measured using a sealing strength tester at room temperature. The measurement was conducted under the following conditions: test speed of 10mpm and clamping gap of 30mm.

[0071] When the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the stroke (distance) when the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke.

[0072] In one exemplary implementation of the present invention, when sealed under a sealing condition of 220°C, the maximum high-temperature travel in the TD direction of the above-mentioned secondary battery bag film, measured by the following method, can be 18mm to 24mm.

[0073] [Method for determining the maximum high-temperature stroke in the TD direction under sealing conditions at 220℃]

[0074] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0075] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0076] Under high-temperature conditions of 60°C for 3 minutes, the change in sealing strength was measured using a sealing strength tester when the test piece was pulled in the TD direction. The test was conducted at a test speed of 10mpm and a clamping gap of 30mm (GripGap).

[0077] When the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the stroke (distance) when the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke.

[0078] Furthermore, an exemplary implementation of the present invention provides a secondary battery with an externally mounted secondary battery pouch film.

[0079] In one exemplary implementation of the present invention, the above-mentioned secondary battery can be used in electric vehicles or energy storage devices.

[0080] Furthermore, an exemplary implementation of the present invention provides a method for preparing a secondary battery, the method including the step of placing the aforementioned secondary battery bag membrane on the outside of the secondary battery.

[0081] The effects of the invention

[0082] The exemplary embodiment of the present invention provides a bag membrane that achieves excellent long-term high-temperature reliability during battery pack fabrication by controlling room-temperature density strength, high-temperature density strength, maximum stroke, room-temperature energy parameters, and high-temperature energy parameters. This type of bag membrane for secondary batteries is effectively used in large and medium-sized secondary battery bags for electric vehicles or energy storage devices that require both safety and high-temperature safety. Attached Figure Description

[0083] Figure 1 A simplified diagram illustrating a pouch membrane structure for a secondary battery prepared by pressing EC method, as an exemplary implementation of the present invention.

[0084] Figure 2a This is a schematic diagram of the fixture used in this experimental example. Figure 2b A photograph showing the battery pack sample and fixture combined in this experimental example. Detailed Implementation

[0085] Terminology Definition

[0086] In this specification, when described as comprising layers of a pouch film for secondary batteries, it means that it is not necessary to consist of only the respective layers, but may include additional layers.

[0087] In this specification, when it is said that something is formed "on" a particular layer, it includes not only the case where it is formed directly on the corresponding layer, but also the case where it is formed with other additional layers in between.

[0088] In this specification, yield strength refers to the force applied to the yield point, which is the point at which the elastic limit is exceeded during the process of the specimen being increased proportionally with the load, and then begins to increase disproportionately.

[0089] In this specification, the upper yield strength refers to the maximum value (peak value) of the yield strength. That is, the yield point is divided into the upper yield point (the point with the highest yield strength) and the lower yield point (the point with the lowest yield strength). The upper yield strength refers to the maximum yield strength (peak value) within the yield point [i.e., the yield strength at the upper yield point], and the lower yield strength refers to the minimum yield strength within the yield point [i.e., the yield strength at the lower yield point]. Depending on the object being measured, the upper and lower yield points may be the same.

[0090] In this specification, an extrusion coating (EC) layer refers to a resin, such as an extrusion coating of a polyolefin resin, applied for bonding with the barrier layer in the sealant layer [hereinafter simply referred to as an extrusion layer or extrusion (EC) layer]. The extrusion (EC) layer of the sealant layer is located on the barrier layer side with the polypropylene resin layer as a reference.

[0091] In this specification, the polypropylene resin layer of the sealant layer serves as the core resin layer constituting the sealant layer, performing a sealing function, and is composed of at least one layer. Corresponding to the aforementioned extrusion (EC) layer used for bonding with the barrier layer, it is located on the inner side of the bag film (i.e., the opposite side of the barrier layer) with reference to the aforementioned extrusion (EC) layer.

[0092] In this specification, energy refers to the item used to evaluate the sealing strength maintenance characteristics. When the change in sealing strength (Y-axis) value is measured based on the stroke (distance) [X-axis] of the sealing part, the area of ​​the curve representing the change in sealing strength in the stroke range (0mm to 20mm), that is, the integral value of the sealing strength change curve in the corresponding stroke range (0mm to 20mm) with respect to the stroke (distance) axis [X-axis], can be represented by the product of force and distance.

[0093] In this specification, maximum stroke is used as an item for evaluating the sealing strength maintenance characteristics. Maximum stroke refers to the stroke (distance) at which the sealing strength value reaches its maximum as the sealing strength increases with the stroke (distance) of pulling the sealing part.

[0094] Explanation of the exemplary implementation example

[0095] The following describes an exemplary implementation of the present invention.

[0096] When preparing a bag membrane for a secondary battery, the sealing layer can be prepared by extrusion lamination or solvent-dry lamination (SDL).

[0097] The solvent-drying lamination method involves bonding a barrier layer (metal layer) to a polypropylene (PP) layer using a solvent-based adhesive and then drying the corresponding solvent-based adhesive. The resulting sealant layer is composed of a polypropylene (PP) layer. Although some solvent-based adhesive may remain on the polypropylene (PP) layer after drying, its thickness is approximately 4 μm or less, and therefore can be disregarded.

[0098] On the other hand, the extrusion lamination method involves extruding a polyolefin resin while bonding a polypropylene resin layer, primarily used in the sealant layer, to the barrier layer (metal layer). Preferably, the polypropylene resin layer is a cast polypropylene (CPP) resin layer, and the polyolefin resin is a polypropylene resin. As a result, the sealant layer consists of an extrusion coating (EC) layer (primarily an extruded polypropylene layer) and a lower (inner side relative to the bag film) polypropylene (PP) resin layer, preferably a cast polypropylene (CPP) layer (see reference). Figure 1 ).

[0099] The inventors have discovered that, particularly in the extrusion lamination preparation method, by controlling the room temperature density strength characteristics and high temperature sealing strength characteristics of the secondary battery bag film, and by controlling the relevant factors of the room temperature sealing strength and high temperature sealing strength maintenance characteristics, the leakage test characteristics related to battery explosion are made excellent. Thus, the present invention has been realized through research.

[0100] Specifically, in an exemplary implementation of the present invention, the pouch film for secondary batteries may be composed of a laminate having at least an outer layer, a barrier layer, and a sealant layer stacked sequentially. The sealant layer may be composed of at least an extrusion (EC) layer and a polypropylene (PP) layer located below the extrusion (EC) layer as a sealing resin layer.

[0101] When sealed at 220°C, the maximum sealing strength (in N / 15mm) of the aforementioned secondary battery bag film in both the MD and TD directions, measured according to the following method, is 150 N / 15mm or more and 205 N / 15mm or less at room temperature. Within this range, the leakage test characteristics related to battery explosion become excellent.

[0102] [Method for determining the maximum room temperature seal strength under sealing conditions at 220°C]

[0103] Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0104] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2MPa, and a temperature of 220°C.

[0105] Under normal temperature conditions, the sealing strength of the specimen in the MD and TD directions was determined using a sealing strength tester. The test was conducted under sealing conditions of 10mpm test speed and 30mm clamping gap.

[0106] The maximum value in the seal strength measurement is the maximum seal strength.

[0107] In a non-limiting example of the present invention, when sealing is performed under sealing conditions of 220°C, the room temperature measured values ​​of the maximum sealing strength in the MD and TD directions can be 150N / 15mm or more, 155N / 15mm or more, 160N / 15mm or more, 165N / 15mm or more, 170N / 15mm or more, 175N / 15mm or more, 180N / 15mm or more, 185N / 15mm or more, 190N / 15mm or more, 195N / 15mm or more, or 200N / 15mm or more.

[0108] In one exemplary embodiment of the present invention, when sealed under sealing conditions at 220°C, the high-temperature measured value (measured after being placed at 60°C for 3 minutes) of the maximum sealing strength (in N / 15mm) of the above-mentioned secondary battery bag film in at least one of the MD and TD directions, as determined by the following method, is 115N / 15mm or more and 170N / 15mm or less. Within this range, the leakage test characteristics related to battery explosion become excellent.

[0109] In a non-limiting example of the present invention, when sealing is performed under the above-mentioned 220°C sealing conditions, the high-temperature measured values ​​of the maximum sealing strength in the MD and TD directions (values ​​measured after being placed at a temperature of 60°C for 3 minutes) can be 115N / 15mm or more, 120N / 15mm or more, 125N / 15mm or more, 130N / 15mm or more, 135N / 15mm or more, 140N / 15mm or more, 145N / 15mm or more, 150N / 15mm or more, 155N / 15mm or more, 160N / 15mm or more, or 165N / 15mm or more.

[0110] [Method for determining the maximum sealing strength under sealing conditions at 220°C]

[0111] Prepare a 100mm×200mm pouch film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction.

[0112] Perform the sealing under the following conditions: 200mm seal bar width × 10mm seal thickness, 2.0 seconds, 0.2 MPa, and a temperature of 220°C.

[0113] When the test piece is pulled in the MD or TD direction, the sealing strength (load) in the MD direction and the sealing strength (load) in the TD direction of the test piece are measured using a sealing strength tester (e.g., Shimadzu's AGS-X model UTM device). The measurement is performed under the conditions of a test speed of 10 mpm and a clamping gap of 30 mm.

[0114] The room temperature measurement value refers to the value measured under normal temperature (25℃) conditions, while the high temperature measurement value refers to the value measured after being placed at a temperature of 60℃ for 3 minutes. If the sealing strength is measured while the sealing part is being pulled, the maximum strength represents the maximum sealing strength.

[0115] In one exemplary implementation of the present invention, preferably, when sealed under sealing conditions at 220°C, the following maximum sealing strength parameter related to the maximum sealing strength of the bag film for the secondary battery is 1.1 or higher and 1.8 or lower. Within the above range, the leakage test characteristics related to battery explosion become excellent.

[0116] [Maximum sealing strength parameter]

[0117] (Maximum sealing strength in the MD direction at room temperature × Maximum sealing strength in the TD direction at room temperature) / (Maximum sealing strength in the MD direction at high temperature × Maximum sealing strength in the TD direction at high temperature)

[0118] In a non-limiting example of the present invention, for example, the above-mentioned maximum sealing strength parameter can be a value within the range of any two values ​​from 1.1, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, etc.

[0119] In one exemplary implementation of the present invention, the room temperature energy of the above-mentioned secondary battery bag membrane was measured to be 2.0 KN×mm to 3.0 KN×mm according to the following method.

[0120] In one exemplary implementation of the present invention, the high-temperature energy of the above-mentioned secondary battery bag membrane was measured to be 1.5KN×mm to 2.5KN×mm according to the following method.

[0121] In one exemplary implementation of the present invention, the difference between the room temperature energy and the high temperature energy of the above-mentioned secondary battery bag membrane was measured to be 0.4 KN×mm to 0.6 KN×mm according to the following method.

[0122] [Measuring Energy at Room Temperature and High Temperature]

[0123] The room temperature energy or high temperature energy is measured according to the above sealing strength test method. The difference is that the room temperature energy or high temperature energy is measured under the conditions of room temperature or high temperature (high temperature is measured after being placed at a temperature of 60°C for 3 minutes). When the X-axis is the stroke (distance) of pulling the sealing part and the Y-axis is the sealing strength, the area between the sealing strength change curve based on the stroke and the X-axis representing the stroke (i.e., the integral value between the sealing strength curve and the X-axis) is integrated. The stroke during integration is within the range of 0 mm to 20 mm.

[0124] When the above-mentioned room temperature energy characteristic values ​​and high temperature energy characteristic values ​​are met, the following leakage test characteristics related to battery explosion become excellent.

[0125] In one exemplary implementation of the present invention, the maximum stroke of the bag film for secondary batteries at room temperature was measured to be 15 mm to 25 mm according to the following method.

[0126] In one exemplary implementation of the present invention, the maximum high-temperature stroke of the above-mentioned secondary battery bag film was measured to be 18 mm to 24 mm according to the following method.

[0127] [Determination of maximum stroke at room temperature and maximum stroke at high temperature]

[0128] The maximum stroke at room temperature or the maximum stroke at high temperature is determined according to the sealing strength test method described above. The difference lies in that, under normal temperature or high temperature conditions (high temperature is measured after being placed at 60°C for 3 minutes), when the X-axis represents the stroke (distance) of pulling the sealing part and the Y-axis represents the sealing strength, the stroke (distance) at which the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke. The evaluation performed under normal temperature conditions is the maximum stroke at room temperature, and the evaluation performed under high temperature conditions is the maximum stroke at high temperature.

[0129] Within the aforementioned maximum stroke range at room temperature and maximum stroke range at high temperature, the leakage test characteristics related to battery explosion become excellent.

[0130] In the exemplary embodiment of the present invention, the thickness ratio of the polypropylene (PP) layer in the sealant layer is greater than 0.5, and the sealant layer, i.e., the sealant layer including the extruded (EC) layer and the polypropylene (PP) layer, has an upper yield strength (N / mm) in the MD direction. 2 The yield strength (N / mm²) in the TD direction is 17.50–19.99, more preferably 17.50–19.80. 2 The glass transition temperature (Tg) of the sealant layer is 17.00 to 19.99, more preferably 17.00 to 19.50, and preferably, the glass transition temperature (Tg) of the sealant layer is in the range of -20°C to -10°C.

[0131] In one exemplary embodiment of the present invention, the thickness ratio of the polypropylene (PP) layer in the sealant layer can be 0.500 or more, 0.525 or more, 0.550 or more, 0.575 or more, 0.600 or more, 0.625 or more, 0.650 or more, 0.675 or more, 0.700 or more, 0.725 or more, 0.750 or more, or 0.775 or more. Alternatively, it can be 0.800 or less, 0.775 or less, 0.750 or less, 0.725 or less, 0.700 or less, 0.675 or less, 0.650 or less, 0.625 or less, 0.600 or less, 0.575 or less, 0.550 or less, or 0.525 or less.

[0132] When the thickness ratio is less than 0.5, that is, when the thickness of the polypropylene (PP) layer is less than half the thickness of the sealant layer, it will be difficult to meet the above-mentioned room temperature density strength characteristics, high temperature density strength characteristics, room temperature density strength maintenance characteristics, and high temperature density strength maintenance characteristics (stroke, energy).

[0133] The requirement that the thickness ratio of the polypropylene (PP) layer in the sealant layer is 0.500 or more means that the thickness of the extruded (EC) layer should be less than the thickness of the polypropylene (PP) layer.

[0134] The thickness ratio of the polypropylene (PP) layer in the sealant layer can be determined by adjusting the thickness of the extrusion (EC) layer during the resin extrusion process, while selecting the thickness of the PP layer itself.

[0135] In an exemplary implementation of the present invention, the upper yield strength (N / mm) of the sealant layer in the MD direction is... 2 The yield strength (N / mm²) of the sealant layer is in the range of 17.50 to 19.99, and may have a numerical range between the following values ​​within the corresponding range. 2 When it deviates from the above range, it will be difficult to meet the above-mentioned room temperature density and strength characteristics, high temperature density and strength characteristics, room temperature density and strength maintenance characteristics, and high temperature density and strength maintenance characteristics (stroke, energy).

[0136] In a non-limiting example of the present invention, the upper yield strength (N / mm) of the above-mentioned sealant layer in the MD direction is... 2The values ​​can be 17.50 or higher, 17.51 ​​or higher, 17.52 or higher, 17.53 or higher, 17.54 or higher, 17.55 or higher, 17.56 or higher, 17.57 or higher, 17.58 or higher, 17.59 or higher, 17.60 or higher, 17.61 or higher, 17.62 or higher, 17.63 or higher, 17.64 or higher, 17.65 or higher, 17.66 or higher, 17.67 or higher, 17.68 or higher, 17.69 or higher, 17.70 or higher, 17.71 or higher, or 17.72. Above or below, 17.73 or below, 17.74 or below, 17.75 or below, 17.76 or below, 17.77 or below, 17.78 or below, 17.79 or below, 17.80 or below, 17.81 or below, 17.82 or below, 17.83 or below, 17.84 or below, 17.85 or below, 17.86 or below, 17.87 or below, 17.88 or below, 17.89 or below, 17.90 or below, 17.91 or below, 17.92 or below, 17.93 or below, 17.94 or below, 1 7.95 or below, 17.96 or below, 17.97 or below, 17.98 or below, 17.99 or below, 18.00 or below, 18.01 or below, 18.02 or below, 18.03 or below, 18.04 or below, 18.05 or below, 18.06 or below, 18.07 or below, 18.08 or below, 18.09 or below, 18.10 or below, 18.11 or below, 18.12 or below, 18.13 or below, 18.14 or below, 18.15 or below, 18.16 or below, 18.17 or above. Or below, 18.18 or above, 18.19 or above, 18.20 or above, 18.21 or above, 18.22 or above, 18.23 or above, 18.24 or above, 18.25 or above, 18.26 or above, 18.27 or above, 18.28 or above, 18.29 or above, 18.30 or above, 18.31 or above, 18.32 or above, 18.33 or above, 18.34 or above, 18.35 or above, 18.36 or above, 18.37 or above, 18.38 or above, 18.39 or above, 18.40 and below, 18.41 and below, 18.42 and below, 18.43 and below, 18.44 and below, 18.45 and below, 18.46 and below, 18.47 and below, 18.48 and below, 18.49 and below, 18.50 and below, 18.51 and below, 18.52 and below, 18.53 and below, 18.54 and below, 18.55 and below, 18.56 and below, 18.57 and below, 18.58 and below, 18.59 and below, 18.60 and below, 18.61 and below, 18.62 and below. 18.63 or below, 18.64 or below, 18.65 or below, 18.66 or below, 18.67 or below, 18.68 or below, 18.69 or below, 18.70 or below, 18.71 or below, 18.72 or below, 18.73 or below, 18.74 or below, 18.75 or below, 18.76 or below, 18.77 or below, 18.78 or below, 18.79 or below, 18.80 or below, 18.81 or below, 18.82 or below, 18.83 or below, 18.84 or below, 18.85 or above Below, 18.86 and below, 18.87 and below, 18.88 and below, 18.89 and below, 18.90 and below, 18.91 and below, 18.92 and below, 18.93 and below, 18.94 and below, 18.95 and below, 18.96 and below, 18.97 and below, 18.98 and below, 18.99 and below, 19.00 and below, 19.01 and below, 19.02 and below, 19.03 and below, 19.04 and below, 19.05 and below, 19.06 and below, 19.07 and below, 19.08 Above or below, 19.09 or below, 19.10 or below, 19.11 or below, 19.12 or below, 19.13 or below, 19.14 or below, 19.15 or below, 19.16 or below, 19.17 or below, 19.18 or below, 19.19 or below, 19.20 or below, 19.21 or below, 19.22 or below, 19.23 or below, 19.24 or below, 19.25 or below, 19.26 or below, 19.27 or below, 19.28 or below, 19.29 or below, 19.30 or below, 19.31 and below, 19.32 and below, 19.33 and below, 19.34 and below, 19.35 and below, 19.36 and below, 19.37 and below, 19.38 and below, 19.39 and below, 19.40 and below, 19.41 and below, 19.42 and below, 19.43 and below, 19.44 and below, 19.45 and below, 19.46 and below, 19.47 and below, 19.4 8 or below, 19.49 or below, 19.50 or below, 19.51 or below, 19.52 or below, 19.53 or below, 19.54 or below, 19.55 or below, 19.56 or below, 19.57 or below, 19.58 or below, 19.59 or below, 19.60 or below, 19.61 or below, 19.62 or below, 19.63 or below, 19.64 or below, 19.65 Above or below, 19.66 or below, 19.67 or below, 19.68 or below, 19.69 or below, 19.70 or below, 19.71 or below, 19.72 or below, 19.73 or below, 19.74 or below, 19.75 or below, 19.76 or below, 19.77 or below, 19.78 or below, 19.79 or below, 19.80 or below, 19.81 or below, 19.82 and below Above or below, 19.83 and below, 19.84 and below, 19.85 and below, 19.86 and below, 19.87 and below, 19.88 and below, 19.89 and below, 19.90 and below, 19.91 and below, 19.92 and below, 19.93 and below, 19.94 and below, 19.95 and below, 19.96 and below, 19.97 and below, 19.98 and below, or below 19.99.

[0137] In an exemplary implementation of the present invention, the upper yield strength (N / mm) of the sealant layer in the TD direction is... 2 Within the range of 17.00 to 19.99, the following numerical ranges may exist within the corresponding range. When the upper yield strength (N / mm) in the TD direction of the above-mentioned sealant layer... 2 When it deviates from the above range, it will be difficult to meet the above-mentioned room temperature density and strength characteristics, high temperature density and strength characteristics, room temperature density and strength maintenance characteristics, and high temperature density and strength maintenance characteristics (stroke, energy).

[0138] In a non-limiting example of the present invention, the upper yield strength (N / mm) of the above-mentioned sealant layer in the TD direction is... 2The values ​​can be 17.00 or higher, 17.01 or higher, 17.02 or higher, 17.03 or higher, 17.04 or higher, 17.05 or higher, 17.06 or higher, 17.07 or higher, 17.08 or higher, 17.09 or higher, 17.10 or higher, 17.11 or higher, 17.12 or higher, 17.13 or higher, 17.14 or higher, 17.15 or higher, 17.16 or higher, 17.17 or higher, 17.18 or higher, 17.19 or higher, 17.20 or higher, 17.21 or higher, or 17.22. Above or below, 17.23 or below, 17.24 or below, 17.25 or below, 17.26 or below, 17.27 or below, 17.28 or below, 17.29 or below, 17.30 or below, 17.31 or below, 17.32 or below, 17.33 or below, 17.34 or below, 17.35 or below, 17.36 or below, 17.37 or below, 17.38 or below, 17.39 or below, 17.40 or below, 17.41 or below, 17.42 or below, 17.43 or below, 17.44 or below, 1 7.45 or below, 17.46 or below, 17.47 or below, 17.48 or below, 17.49 or below, 17.50 or below, 17.51 ​​or below, 17.52 or below, 17.53 or below, 17.54 or below, 17.55 or below, 17.56 or below, 17.57 or below, 17.58 or below, 17.59 or below, 17.60 or below, 17.61 or below, 17.62 or below, 17.63 or below, 17.64 or below, 17.65 or below, 17.66 or below, 17.67 or above. Or below, 17.68 or above, 17.69 or above, 17.70 or above, 17.71 or above, 17.72 or above, 17.73 or above, 17.74 or above, 17.75 or above, 17.76 or above, 17.77 or above, 17.78 or above, 17.79 or above, 17.80 or above, 17.81 or above, 17.82 or above, 17.83 or above, 17.84 or above, 17.85 or above, 17.86 or above, 17.87 or above, 17.88 or above, 17.89 or above, 17.90 or below, 17.91 or below, 17.92 or below, 17.93 or below, 17.94 or below, 17.95 or below, 17.96 or below, 17.97 or below, 17.98 or below, 17.99 or below, 18.00 or below, 18.01 or below, 18.02 or below, 18.03 or below, 18.04 or below, 18.05 or below, 18.06 or below, 18.07 or below, 18.08 or below, 18.09 or below, 18.10 or below, 18.11 or below, 18.12 or below. 18.13 or below, 18.14 or below, 18.15 or below, 18.16 or below, 18.17 or below, 18.18 or below, 18.19 or below, 18.20 or below, 18.21 or below, 18.22 or below, 18.23 or below, 18.24 or below, 18.25 or below, 18.26 or below, 18.27 or below, 18.28 or below, 18.29 or below, 18.30 or below, 18.31 or below, 18.32 or below, 18.33 or below, 18.34 or below, 18.35 or above Below, 18.36 and below, 18.37 and below, 18.38 and below, 18.39 and below, 18.40 and below, 18.41 and below, 18.42 and below, 18.43 and below, 18.44 and below, 18.45 and below, 18.46 and below, 18.47 and below, 18.48 and below, 18.49 and below, 18.50 and below, 18.51 and below, 18.52 and below, 18.53 and below, 18.54 and below, 18.55 and below, 18.56 and below, 18.57 and below, 18.58 Above or below, 18.59 or below, 18.60 or below, 18.61 or below, 18.62 or below, 18.63 or below, 18.64 or below, 18.65 or below, 18.66 or below, 18.67 or below, 18.68 or below, 18.69 or below, 18.70 or below, 18.71 or below, 18.72 or below, 18.73 or below, 18.74 or below, 18.75 or below, 18.76 or below, 18.77 or below, 18.78 or below, 18.79 or below, 18.80 or below, 18.81 and below, 18.82 and below, 18.83 and below, 18.84 and below, 18.85 and below, 18.86 and below, 18.87 and below, 18.88 and below, 18.89 and below, 18.90 and below, 18.91 and below, 18.92 and below, 18.93 and below, 18.94 and below, 18.95 and below, 18.96 and below, 18.97 and below, 18.98 and below, 18.99 and below, 19.00 and below, 19.01 and below, 19.02 and below, 19.03 and below. 19.04 or below, 19.05 or below, 19.06 or below, 19.07 or below, 19.08 or below, 19.09 or below, 19.10 or below, 19.11 or below, 19.12 or below, 19.13 or below, 19.14 or below, 19.15 or below, 19.16 or below, 19.17 or below, 19.18 or below, 19.19 or below, 19.20 or below, 19.21 or below, 19.22 or below, 19.23 or below, 19.24 or below, 19.25 or below, 19.26 or above Below, 19.27 and below, 19.28 and below, 19.29 and below, 19.30 and below, 19.31 and below, 19.32 and below, 19.33 and below, 19.34 and below, 19.35 and below, 19.36 and below, 19.37 and below, 19.38 and below, 19.39 and below, 19.40 and below, 19.41 and below, 19.42 and below, 19.43 and below, 19.44 and below, 19.45 and below, 19.46 and below, 19.47 and below, 19.48 and below, 19.49 Above or below, 19.50 or below, 19.51 or below, 19.52 or below, 19.53 or below, 19.54 or below, 19.55 or below, 19.56 or below, 19.57 or below, 19.58 or below, 19.59 or below, 19.60 or below, 19.61 or below, 19.62 or below, 19.63 or below, 19.64 or below, 19.65 or below, 19.66 or below, 19.67 or below, 19.68 or below, 19.69 or below, 19.70 or below, 19.71 or below, 19.72 or below, 19.73 or below, 19.74 or below, 19.75 or below, 19.76 or below, 19.77 or below, 19.78 or below, 19.79 or below, 19.80 or below, 19.81 or below, 19.82 or below, 19.83 or below, 19.84 or below, 19.85 or below. 19.86 or below, 19.87 or below, 19.88 or below, 19.89 or below, 19.90 or below, 19.91 or below, 19.92 or below, 19.93 or below, 19.94 or below, 19.95 or below, 19.96 or below, 19.97 or below, 19.98 or below, or below 19.99.

[0139] In an exemplary implementation of the present invention, the upper yield strength (N / mm) of the sealant layer in the MD direction is... 2 ) and the upper yield strength in the TD direction (N / mm 2 The sum of () is 34.5 or more and 39.9 or less, preferably 34.5 or more and 39 or less, and more preferably 34.61 to 38.85.

[0140] In an exemplary implementation of the present invention, the upper yield strength (N / mm) of the sealant layer in the MD direction is... 2 It can be greater than the upper yield strength in the TD direction (N / mm). 2 In the process characteristics of extrusion coating (EC) and lamination of sealant layers using PP layers, fine stretching can occur in the MD direction (Machine Direction). Therefore, the upper yield strength in the MD direction can be relatively greater compared to the TD direction (Transverse Direction), where no stretching occurs.

[0141] In one exemplary embodiment of the present invention, the glass transition temperature (Tg) of the sealant layer is -20°C to -10°C, preferably a value within the range of -19°C to -11°C, and may have a value range between the following values ​​within the corresponding range. When the glass transition temperature (Tg) of the sealant layer deviates from the above-mentioned range of -20°C to -10°C, it will be difficult to meet the above-mentioned room temperature density strength characteristics, high temperature density strength characteristics, room temperature density strength maintenance characteristics, and high temperature density strength maintenance characteristics (stroke, energy).

[0142] In a non-limiting example of the present invention, the glass transition temperature (Tg) of the above-mentioned sealant layer can be above -20°C, above -19.5°C, above -19°C, above -18.5°C, above -18°C, above -17.5°C, above -17°C, above -16.5°C, above -16°C, above -15.5°C, above -15°C, above -14.5°C, above -14°C, above -13.5°C, above -13°C, above -12.5°C, above -12°C, above -11.5°C, above -11°C, or above -10.5°C. Alternatively, it can be below -10℃, below -10.5℃, below -11℃, below -11.5℃, below -12℃, below -12.5℃, below -13℃, below -13.5℃, below -14℃, below -14.5℃, below -15℃, below -15.5℃, below -16℃, below -16.5℃, below -17℃, below -17.5℃, below -18℃, or below -18.5℃.

[0143] Those skilled in the art to which this invention pertains can easily adjust the upper yield strength and glass transition temperature values. As is known, the upper yield strength and glass transition temperature can be determined based on the type or properties of the polypropylene (PP) resin in the sealant layer, such as its softness, and the content of additives such as the elastomer used in the sealant layer. Therefore, the upper yield strength and glass transition temperature can be adjusted by selecting appropriately typed and characteristic polypropylene and elastomer additives to achieve the desired upper yield strength and glass transition temperature.

[0144] In one exemplary embodiment of the present invention, the outer layer may be composed of nylon, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), a mixed layer of nylon and PET (a laminated film of nylon and PET), etc.

[0145] In one exemplary implementation of the present invention, in terms of formability, the thickness of the nylon film in the outer layer is preferably 20 μm or more, more preferably 25 μm or more. However, if the thickness of the nylon film is greater than 30 μm, it may lead to a decrease in the insulation breakdown voltage. Therefore, the thickness of the nylon film is preferably 20 μm to 30 μm, more preferably 25 μm to 30 μm.

[0146] In one exemplary embodiment of the present invention, the thinner the PET film and the thicker the nylon film in the outer layer, the better the formability. However, as the thickness of the PET film gradually decreases, it may become more unfavorable in terms of insulation breakdown voltage. Therefore, from this point of view, the thickness of the PET is preferably 7 μm to 12 μm.

[0147] In one exemplary implementation of the present invention, the metal layer may be made of metals such as aluminum, stainless steel (SUS), and copper.

[0148] In one exemplary embodiment of the present invention, the cast polypropylene (CPP) layer or cast polypropylene (CPP) film of the sealant layer may contain various additives (rubber, elastomer, lubricant, etc.) based on the desired physical properties.

[0149] In one exemplary implementation of the present invention, for example, the total thickness of the above-described secondary battery bag film can be 60 μm to 185 μm. In one embodiment, the above-described secondary battery bag film can be 153 μm or more or 113 μm or less.

[0150] In one exemplary implementation of the present invention, for example, the thickness of the metal layer is 20 μm to 80 μm, preferably 40 μm to 60 μm.

[0151] In one exemplary implementation of the present invention, for example, the thickness of the sealant layer can be 20 μm to 80 μm.

[0152] In one exemplary implementation of the present invention, for example, the thickness of the cast polypropylene (CPP) layer of the above-mentioned sealant layer can be 20 μm to 80 μm.

[0153] In one exemplary implementation of the present invention, for example, the thickness of the extruded polypropylene (PP) layer, which is the extrusion (EC) layer of the above-mentioned sealant layer, can be 0 μm to 60 μm.

[0154] On the other hand, an exemplary implementation of the present invention provides a secondary battery with an externally mounted pouch membrane for the aforementioned secondary battery. Typically, this secondary battery can be a lithium secondary battery, and in particular, it can be a large or medium-sized secondary battery for electric vehicles (EVs) or energy storage devices (ESS).

[0155] Furthermore, an exemplary implementation of the present invention provides a method for preparing a secondary battery, the method comprising the step of placing the aforementioned secondary battery bag membrane outside the secondary battery.

[0156] The following describes exemplary implementations of the present invention in further detail through examples. The embodiments disclosed in this specification are for illustrative purposes only, and the present invention can be implemented through various methods; the present invention is not limited to the embodiments described in this specification.

[0157] [Experimental Methods]

[0158] In the examples and comparative examples, the outer layer is composed of a composite layer of nylon (25 μm) and PET (12 μm), aluminum foil (60 μm) is used as the metal layer. As shown in Table 1 below, the yield strength and Tg value shown in Table 1 below are achieved by adjusting the thicknesses of the extrusion layer of the sealant layer and the polypropylene (CPP, cast polypropylene) layer. Moreover, each yield strength, Tg, and seal strength were evaluated according to the following methods. The overall thickness including the adhesive layer is 183 μm.

[0159] [Table 1]

[0160]

[0161]

[0162] <Yield Strength>

[0163] Preparation of test piece: After peeling off the sealant layer of the bag film, a test piece with a width of 15 mm × a length of 100 mm is prepared.

[0164] In the yield strength measurement method, the measurement is performed using an AGS-X model UTM device from SHIMADZU Corporation, under the conditions of a test speed of 50 mpm and a grip gap of 30 mm.

[0165] When the load on the test piece increases proportionally, if the elastic limit is exceeded, it will start to increase disproportionately, and this point is called the yield point. Since CPP does not have a lower yield point, the yield point is the upper yield point.

[0166] <Tg Measurement>

[0167] A DSC250 device from TA Instruments is used. The measurement is carried out in a temperature range of -50°C to 200°C, with a heating rate of 10°C / min and a cooling rate of -20°C / min. The calculation of the Tg value is performed by the analysis program (TRIOS) under the temperature condition of -50°C to 20°C, which is the approximate Tg range of PP.

[0168] <Maximum Sealing Strength Under Sealing Condition of 220°C>

[0169] Preparation of test piece: Prepare a bag film of 100 mm × 200 mm, fold and seal it, then cut it into test pieces with a width of 15 mm along the direction perpendicular to the sealing direction.

[0170] Sealing is performed under the following conditions: a seal bar with a width of 200 mm, a seal thickness of 10 mm, a sealing time of 2.0 seconds, a pressure of 0.2 Mpa, and a temperature of 220°C.

[0171] In the method for determining sealing strength, when the test piece is pulled in the MD direction or TD direction, the sealing strength (load) in the MD direction and the sealing strength (load) in the TD direction of the test piece are determined by a sealing strength tester (e.g., SHIMADZU AGS-X model UTM device). The test is conducted under the conditions of a test speed of 10mpm and a clamping gap of 30mm.

[0172] Ambient temperature measurement refers to measurement performed at room temperature, while high temperature measurement refers to measurement performed after being placed at 60°C for 3 minutes.

[0173] The maximum value among the measured sealing strength values ​​is the maximum sealing strength. That is, if the sealing strength is measured while the sealing part is being pulled, the maximum strength represents the maximum sealing strength.

[0174] <Measurement of room temperature energy, high temperature energy, maximum room temperature travel, and maximum high temperature travel in the TD direction under sealing conditions of 220℃>

[0175] To confirm the sealing strength maintenance characteristics in the TD direction, room temperature energy and high temperature energy were evaluated. Therefore, the sealing strength was measured according to the method described above for measuring sealing strength under 220°C sealing conditions. Under room temperature or high temperature (high temperature was measured after being placed at 60°C for 3 minutes), with the X-axis representing the stroke (distance) of the sealing part and the Y-axis representing the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke (i.e., the integral value of the sealing strength curve based on the stroke) was defined as room temperature energy (energy measured at room temperature) or high temperature energy (energy measured after being placed at 60°C for 3 minutes). The stroke during integration was within the range of 0 mm to 20 mm.

[0176] On the other hand, the maximum stroke at room temperature and the maximum stroke at high temperature were measured to confirm the TD direction sealing strength maintenance characteristics.

[0177] That is, the sealing strength is measured according to the method described above for sealing under 220°C conditions. Under normal or high temperature conditions (high temperature means measuring after being placed at 60°C for 3 minutes), when the X-axis represents the stroke (distance) of the sealing part pulled in the TD direction and the Y-axis represents the sealing strength, the stroke (distance) at which the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke. The evaluation performed under normal temperature conditions is the maximum stroke at normal temperature, and the evaluation performed under high temperature conditions is the maximum stroke at high temperature.

[0178] As described above, the maximum stroke and energy (the integral value between the stroke axis and the sealing strength curve) can be considered important factors in evaluating the sealing strength maintenance characteristics (reliability). That is, even if the maximum sealing strength, which is the peak value, is relatively large, it is difficult to judge the sealing strength maintenance characteristics based solely on the maximum sealing strength. However, based on the maximum stroke, the speed at which the maximum sealing strength reaches its maximum value and the subsequent decrease can be determined. Furthermore, based on the stroke and the area (integral value) constituting the sealing strength curve, it can be determined whether the sealing strength is well maintained, i.e., reliability can be evaluated.

[0179] In the case of medium and large batteries, such as those used in electric vehicles, which have various MD-direction molding models, the sealing characteristics in the MD direction are generally superior to those in the TD direction. Therefore, in the TD direction (Pouch to Pouch) seal, where the sealing characteristics are relatively weaker than those in the MD direction (Tap to Pouch seal), the focus is more on maintaining the seal strength. The change in seal strength based on the stroke variation in the TD direction is shown in the table below.

[0180] <Leakage Test>

[0181] In the examples and comparative examples, after forming a pouch film for secondary batteries using a molding machine (6mm molding), 20 simple battery pack samples (200mm × 110mm) were prepared. A label [Sumitomo Corporation product] was inserted into each battery pack sample. After inserting the battery pack samples into the zig clamps at appropriate intervals, the vertical spacing (6mm) of the zig clamps was fixed and the samples were joined. Figure 2a This is a schematic diagram of the fixture used in this experimental example. Figure 2b A photograph showing the battery pack sample and fixture combined in this experimental example.

[0182] At a temperature of 80°C, after 90 days, the occurrence of leakage was evaluated (to assess long-term reliability). The number of leaks (Fail) was determined out of a total of 20, as shown in Table 4 below.

[0183] <Density strength properties at room temperature and at high temperature, density strength retention properties at room temperature and density strength retention properties at high temperature>

[0184] Table 2 below shows the maximum sealing strength test results of the embodiments and comparative examples under sealing conditions of 220°C.

[0185] [Table 2]

[0186]

[0187]

[0188] Furthermore, the energy values ​​and maximum travel of the aforementioned sealed bags at room temperature and high temperature are shown in Table 3 below.

[0189] [Table 3]

[0190]

[0191]

[0192] <High-Temperature Long-Term Reliability Characteristics of Battery Packs - Leakage Test Characteristics>

[0193] Table 4 shows the leakage test results of the above-described embodiments and comparative examples.

[0194] [Table 4]

[0195] Example 1 2 / 20 Example 2 1 / 20 Example 3 0 / 20 Example 4 0 / 20 Example 5 1 / 20 Example 6 2 / 20 Example 7 2 / 20 Comparative Example 1 10 / 20 Comparative Example 2 20 / 20 Comparative Example 3 20 / 20 Comparative Example 4 8 / 10 Comparative Example 5 4 / 20

[0196] As shown in Tables 3 and 4, the embodiments not only exhibit excellent maximum density strength values ​​at both room temperature and high temperature, but also demonstrate superior room temperature energy, high temperature energy, maximum stroke at room temperature, and maximum stroke at high temperature compared to the comparative examples. Furthermore, in addition to excellent room temperature seal strength maintenance characteristics, high temperature seal strength maintenance characteristics are also superior. Moreover, based on the leakage test results, while possessing the same room temperature density strength characteristics, high temperature density strength characteristics, stroke characteristics, and energy characteristics as the embodiments, the leakage amount is significantly reduced compared to the comparative examples. Therefore, the battery pack demonstrates excellent long-term high-temperature reliability and excellent battery safety.

[0197] While the foregoing has described non-limiting illustrative embodiments of the present invention, the inventive concept is not limited to the accompanying drawings or the above description. It is evident that those skilled in the art can make various modifications without departing from the inventive concept, and such modifications also fall within the scope of protection claimed by the present invention.

Claims

1. A bag film for secondary batteries, characterized in that, It consists of a laminate composed of at least an outer layer, a barrier layer, and a sealant layer stacked in sequence. In the sealant layer comprising an extruded coating (EC) layer and a cast polypropylene (CPP) layer, the thickness proportion of the cast polypropylene (CPP) layer is greater than 0.

5. When sealed at 220°C, the maximum room-temperature sealing strength of the aforementioned secondary battery bag film, measured according to the following method, is 150 N / 15 mm or more and 205 N / 15 mm or less in both the MD and TD directions. The glass transition temperature (Tg) of the sealant layer is -20°C to -10°C. Methods for determining the maximum room temperature seal strength under sealing conditions at 220°C include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. Under normal temperature conditions, the sealing strength of the specimen in the MD and TD directions was measured using a sealing strength tester. The measurements were conducted under sealing conditions of a test speed of 10 mpm and a clamping gap of 30 mm. The maximum value in the seal strength measurement is the maximum seal strength.

2. The bag film for secondary batteries according to claim 1, characterized in that, When sealed at 220°C, the maximum high-temperature sealing strength of the aforementioned secondary battery bag film, measured according to the following method, is 115 N / 15 mm or more and 170 N / 15 mm or less in at least one of the MD and TD directions. This maximum high-temperature sealing strength is measured after being placed at 60°C for 3 minutes. Methods for determining the maximum high-temperature seal strength under sealing conditions at 220°C include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. After being placed at 60℃ for 3 minutes, the sealing strength of the specimen was measured in at least one of the MD and TD directions using a sealing strength tester, with the measurement conditions being a test speed of 10mpm and a clamping gap of 30mm; and The maximum value in the seal strength measurement is the maximum seal strength.

3. The bag film for secondary batteries according to claim 2, characterized in that, When sealed under 220°C conditions, the following maximum sealing strength parameters related to the maximum sealing strength of the aforementioned secondary battery bag film are 1.1 or higher and 1.8 or lower. Maximum sealing strength parameter = (maximum sealing strength in the MD direction at room temperature × maximum sealing strength in the TD direction at room temperature) / (maximum sealing strength in the MD direction at high temperature × maximum sealing strength in the TD direction at high temperature).

4. The bag film for secondary batteries according to claim 1, characterized in that, When sealed at 220°C, the room temperature energy in the TD direction of the aforementioned secondary battery bag membrane, measured according to the following method, is 2.0 kN × mm to 3.0 kN × mm. Methods for measuring room-temperature energy in the TD direction under sealed conditions at 220°C include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. While pulling the specimen in the TD direction, the change in sealing strength was measured using a sealing strength tester under normal temperature conditions. The measurement was conducted at a test speed of 10 mpm and a clamping gap of 30 mm. When the X-axis is set as the stroke (distance) of the sealing part pulled in the TD direction, and the Y-axis is set as the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the room temperature energy. The area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke in the range of 0mm to 20mm.

5. The bag film for secondary batteries according to claim 2, characterized in that, When sealed at 220°C, the high-temperature energy in the TD direction of the aforementioned secondary battery bag membrane, measured according to the following method, is 1.5 KN×mm~2.5 KN×mm. Methods for measuring high-temperature energy in the TD direction under sealed conditions at 220°C include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. Under high-temperature conditions (60℃ for 3 minutes), the test piece was pulled in the TD direction while the change in sealing strength was measured using a sealing strength tester. The measurement was conducted at a test speed of 10 MPa and a clamping gap of 30 mm. The X-axis is set as the stroke, i.e., the distance, of the sealing part pulled in the TD direction. When the Y-axis is set as the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the high-temperature energy. The area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke in the range of 0mm to 20mm.

6. The bag film for secondary batteries according to claim 2, characterized in that, When sealed at 220°C, the difference between the room temperature energy and the high temperature energy in the TD direction of the aforementioned secondary battery bag membrane, measured according to the following method, is 0.4 kN × mm to 0.6 kN × mm. Methods for determining the room-temperature energy and high-temperature energy in the TD direction under sealed conditions at 220℃ include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. Under normal temperature conditions or high temperature conditions after being placed at 60°C for 3 minutes, the test piece is pulled in the TD direction while the change in sealing strength is measured using a sealing strength tester. The test is conducted under the following conditions: test speed of 10mpm and clamping gap of 30mm. When the X-axis is set as the stroke (distance) of the sealing part pulled in the TD direction, and the Y-axis is set as the sealing strength, the area between the sealing strength variation curve based on the stroke and the X-axis representing the stroke is defined as the normal temperature energy or high temperature energy. This area is the integral value of the sealing strength variation curve based on the stroke, and the integral value is the integral of the stroke within the range of 0mm to 20mm. Energy measured under normal temperature conditions is called normal temperature energy, and energy measured under high temperature conditions is called high temperature energy.

7. The bag film for secondary batteries according to claim 1, characterized in that, When sealed at 220°C, the maximum TD-direction travel of the aforementioned secondary battery bag film at room temperature, measured according to the following method, is 15mm to 25mm. Methods for determining the maximum travel at room temperature in the TD direction under sealing conditions of 220℃ include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. While pulling the test piece in the TD direction, the change in sealing strength was measured using a sealing strength tester under normal temperature conditions. The measurement was conducted at a test speed of 10 mpm and a clamping gap of 30 mm. The X-axis is set as the stroke (distance) of the sealing part pulled in the TD direction. When the Y-axis is set as the sealing strength, the stroke at which the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke, and the stroke is the distance.

8. The bag film for secondary batteries according to claim 2, characterized in that, When sealed at 220°C, the maximum high-temperature travel in the TD direction of the aforementioned secondary battery bag membrane, measured according to the following method, is 18mm to 24mm. Methods for determining the maximum high-temperature stroke in the TD direction under sealing conditions at 220°C include: Prepare a 100mm×200mm bag film for secondary batteries, fold it in half and seal it, then cut it into test pieces with a width of 15mm along the direction perpendicular to the sealing direction. The sealing conditions are as follows: 200mm sealing strip width × 10mm sealing thickness, 2.0 seconds, 0.2Mpa, and a temperature of 220℃. Under high-temperature conditions (60℃ for 3 minutes), the test piece was pulled in the TD direction while the change in sealing strength was measured using a sealing strength tester. The measurement was conducted at a test speed of 10 MPa and a clamping gap of 30 mm. The X-axis is set as the stroke (distance) of the sealing part pulled in the TD direction. When the Y-axis is set as the sealing strength, the stroke at which the sealing strength value reaches its maximum as the stroke increases is evaluated as the maximum stroke, and the stroke is the distance.

9. A secondary battery, characterized in that, The secondary battery is packaged using the bag film according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, characterized in that, The aforementioned secondary batteries are used in electric vehicles or energy storage devices.

11. A method for preparing a secondary battery, characterized in that, The method includes the step of packaging the secondary battery with the secondary battery bag film according to any one of claims 1 to 8.

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