Pouch film for secondary battery exterior and secondary battery comprising same

Abstract

The present invention relates to a pouch film for a secondary battery exterior, comprising an outer layer, a barrier layer, and a sealant layer containing a polyolefin-based resin, which are sequentially stacked, wherein each of peak intensity reduction rates (R1, R2, R3) for the sealant layer is 58% to 72%, as measured according to measurement condition (A). For measurement condition (A), the description provided in the present specification is referenced.

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. 10-2023-0129009, filed September 26, 2023, and Korean Patent Application No. 10-2024-0063136, 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 above-mentioned problem, the present invention provides a pouch film for a secondary battery exterior, which comprises an outer layer, a barrier layer, and a sealant layer including a polyolefin resin, which are sequentially laminated, and in which the peak intensity reduction rates (R1, R2, R3) measured according to the following measurement conditions (A) for the sealant layer are 58% or more and 72% or less, respectively.

[0011] [Measurement conditions (A)]

[0012] (1) Using the FT-IR (Fourier Transform Infra-Red spectroscopy) method, the sealant layer before heat bonding was measured at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1) in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2) in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3) below

[0013] (2) After the sealant layers are in contact with each other, heat bonding (temperature 190℃, pressure 0.2 MPa, time 1.6 s) is performed to form a sealing part.

[0014] (3) After peeling off the heat-bonded sealant layers, the peeled part of the sealant layer was analyzed using the FT-IR method at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1') in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2') in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3') in the following range

[0015] (4) Measure the reduction rate according to Equation 1 below.

[0016] [Formula 1]

[0017] R n = ((A n - A n ') / A n )ㆍ100 [%]

[0018] (In the above equation 1, n is 1, 2, or 3, and R n is the rate of decrease in the nth peak intensity.)

[0019] 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.

[0020] According to the present invention, by applying a sealant layer in which the peak intensity reduction rate before and after thermal bonding of the first peak intensity, the second peak intensity, and the third peak intensity measured by the FT-IR method described above satisfies the numerical range described above, the sealing strength of the sealant layer can be improved, and accordingly, the pouch film for external use of a secondary battery can have excellent sealing strength characteristics.

[0021] Figure 1 is a graph showing the DSC evaluation results of the sealant layers of Examples 1 and 2, Comparative Examples 1 and 2, and Reference Example 1.

[0022] Figure 2a is a photograph showing the results of a tensile test of a specimen manufactured using the secondary battery outer pouch film of Example 1.

[0023] Figure 2b is a photograph showing the results of a tensile test of a specimen manufactured using the pouch film for the secondary battery exterior of Reference Example 1.

[0024] Figure 2c is a photograph showing the results of a tensile test of a specimen manufactured using the pouch film for the secondary battery exterior of Comparative Example 1.

[0025] 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.

[0026] outer layer

[0027] 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. 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.

[0028] 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.

[0029] barrier layer

[0030] 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.

[0031] 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, 55 μm to 125 μm, or 60 μm to 90 μm.

[0032] sealant layer

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The above sealant layer can form a sealing portion by thermal bonding (e.g., applying heat and pressure to the sealant layers that are in contact with each other to bond them). Therefore, by using this, the sealant layer of the secondary battery outer pouch film can be thermally bonded to form a sealing portion, thereby sealing the battery main body.

[0037] Here, the inventors of the present invention have found that when a sealant layer is used that satisfies peak intensity reduction rates (R1, R2, R3) of 58% or more and 72% or less, respectively, as measured under the following measurement conditions (A), the sealant layer has excellent sealing strength and the secondary battery external pouch film including the sealant layer can exhibit excellent sealing properties.

[0038] [Measurement conditions (A)]

[0039] (1) Using the FT-IR (Fourier Transform Infra-Red spectroscopy) method, the sealant layer before heat bonding was measured at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1) in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2) in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3) below

[0040] (2) After the sealant layers are in contact with each other, heat bonding (temperature 190℃, pressure 0.2 MPa, time 1.6 s) is performed to form a sealing part.

[0041] (3) After peeling off the heat-bonded sealant layers, the peeled part of the sealant layer was analyzed using the FT-IR method at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1') in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2') in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3') in the following range

[0042] (4) Measure the reduction rate according to Equation 1 below.

[0043] [Formula 1]

[0044] R n = ((A n - A n ') / A n )ㆍ100 [%]

[0045] (In the above equation 1, n is 1, 2, or 3, and R n is the rate of decrease in the nth peak intensity.)

[0046] Here, the first peak intensity may be derived from symmetrical bending vibration of CH bonds included in a methyl group (-CH3) in the sealant layer, the second peak intensity may be derived from asymmetrical bending vibration of CH bonds included in a methylene bridge (-CH2-) in the sealant layer, and the third peak intensity may be derived from asymmetrical bending vibration of CH bonds included in a methyl group (-CH3) in the sealant layer.

[0047] Meanwhile, if the peak reduction rate before and after thermal bonding analyzed by the FT-IR method satisfies the above-mentioned numerical range, the polyolefin resins constituting the sealant layer can effectively form an entanglement structure by forming an optimal network after thermal bonding, and accordingly, it is presumed that the sealing strength of the sealant layer is excellent.

[0048] In one embodiment, the melting point onset temperature (T) of the sealant layer measured under a temperature increase condition of 10°C / min using differential scanning calorimetry (DSC) m,onset ) is 105~125℃, preferably 110~120℃, and the melting point termination temperature (T m,offset ) may be 140 to 160°C, preferably 145 to 155°C, and the melting point (T) of the sealant layer here m ) may be 125 to 143°C, preferably 130 to 140°C. In this case, if the melting point start temperature and the melting point end temperature of the sealant layer satisfy the above-mentioned numerical range, and in particular, if the melting point of the sealant layer satisfies the above-mentioned numerical range, sufficient sealing strength can be secured even if the sealing temperature is lowered during thermal bonding of the sealant layer, and further, adhesion, diffusion, and entanglement can occur in a larger area during thermal bonding of the sealant layer, so that excellent sealing strength can be secured.

[0049] Meanwhile, the FT-IR peak intensity reduction rate before and after thermal bonding of the sealant layer depends on, for example, the material of the outer layer or barrier layer, as well as the type and softness of the polyolefin resin included in the sealant layer, whether it is stretched or not, the addition of various types of elastomer-based additives known in the art (e.g., polyester elastomer, polyamide 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 melting point (e.g., 125 to 143°C), the difference between the temperature of the molten resin and the cooling roll temperature during the production of the casting (non-stretched) film as the sealant layer (e.g., 190 to 230°C), etc. It is possible to adjust it to a certain range by adjusting it.

[0050] Here, when the sealant layer includes the polyolefin resin, as long as the FT-IR peak reduction rate before and after thermal bonding of the sealant layer satisfies the above-mentioned numerical range, the type and content of the polyolefin resin, whether the elastomer-based additive is added, the type and content of the elastomer-based additive added, the characteristics of the polyolefin-based resin, etc. are not particularly limited.

[0051] In addition, as long as the FT-IR peak reduction rate before and after thermal bonding of the sealant layer satisfies the above-mentioned numerical range, the sealant layer may have a single-layer structure, or may have a multi-layer structure including the same or different types of materials.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Pouch film for secondary battery exterior

[0056] 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.

[0057] 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.

[0058] The secondary battery outer pouch film including the sealing portion formed by thermal bonding of the sealant layer can exhibit excellent sealing properties derived from the excellent sealing strength of the sealant layer.

[0059] In one embodiment, the maximum value of the sealing strength measured according to the following measurement conditions (B) for the secondary battery external pouch film may be 90% or more of the breaking strength measured according to the following measurement conditions (C) for the secondary battery external pouch film. Here, when the maximum value of the sealing strength of the secondary battery external pouch film satisfies the above-described conditions, it can be seen that the sealing strength at the sealing portion of the secondary battery external pouch film is very excellent.

[0060] [Measurement conditions (B)]

[0061] (1) Fold the secondary battery outer pouch film in half and heat-bond (temperature 210°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 manufacture a specimen.

[0062] (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 the maximum value of the sealing strength is measured while pulling at a measurement speed of 50 mm / min.

[0063] [Measurement conditions (C)]

[0064] (1) Cut the secondary battery outer pouch film to produce a specimen with a width of 15 mm and no sealing portion.

[0065] (2) At a measurement temperature of 25℃, the specimen is fixed between two jigs of a tensile testing machine (UTM) (initial jig gap 30 mm), and the breaking strength of the specimen is measured while pulling at a measurement speed of 50 mm / min.

[0066] lithium secondary battery

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0075] A secondary battery outer pouch film (the melting point of the entire sealant layer including the first sealant layer (EC1) and the second sealant layer (CPP1) is shown in the measurement example below) 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, a 60 ㎛ 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, and a 50 ㎛ thick second sealant layer (CPP1) including a non-stretched polypropylene film bonded onto the first sealant layer (EC1) (the difference between the temperature of the molten resin and the cooling roll temperature during casting film production: 220°C).

[0076] 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 peak intensity reduction rates (R1, R2, R3) measured according to the above-described measurement conditions (A) satisfy the peak intensity reduction rates described in Table 1 below.

[0077] Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layers, barrier layers, and sealant layers

[0078] As a sealant layer, a first sealant layer (EC1) having a thickness of 30 μm obtained by extrusion-coating a polypropylene resin on a barrier layer so that the peak intensity reduction rate measured according to the above-described measurement conditions (A) satisfies the peak intensity reduction rate described in Table 1 below, and a second sealant layer (CPP1) having a thickness of 50 μm including a non-stretched polypropylene film bonded onto the first sealant layer (EC1) (difference between the temperature of the molten resin and the cooling roll temperature during casting film production: 230°C) were used, and the same procedure as in Example 1 was carried out to manufacture a pouch film for external use of a secondary battery (the melting point of the entire sealant layer including the first sealant layer (EC2) and the second sealant layer (CPP2) is shown in the measurement example below).

[0079] Reference Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0080] As a sealant layer, a first sealant layer (EC2) having a thickness of 30 μm obtained by extrusion-coating a polypropylene-based resin on a barrier layer as a sealant layer so that the peak intensity reduction rate measured according to the above-described measurement conditions (A) satisfies the peak intensity reduction rate described in Table 1 below, and a second sealant layer (CPP2) having a thickness of 50 μm including a non-stretched polypropylene film bonded onto the first sealant layer (EC2) (difference between the temperature of the molten resin and the cooling roll temperature during casting film production: 220°C) were used, and the same procedure as in Example 1 was used to manufacture a pouch film for external use of a secondary battery (the melting point of the entire sealant layer including the first sealant layer (EC2) and the second sealant layer (CPP2) is shown in the measurement example below).

[0081] Comparative Example 1: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0082] As a sealant layer, only the first sealant layer (EC3) having a thickness of 80 μm, which was formed by extrusion-coating a polypropylene resin on a barrier layer, was used so that the peak intensity reduction rate measured according to the measurement conditions (A) described above satisfied the peak intensity reduction rate described in Table 1 below. In this case, a pouch film for external use of a secondary battery (the melting point of the first sealant layer (EC3) is shown in the measurement example below) was manufactured in the same manner as in Example 1.

[0083] Comparative Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0084] As a sealant layer, a first sealant layer (EC1) having a thickness of 30 μm obtained by extrusion-coating a polypropylene resin on a barrier layer so that the peak intensity reduction rate measured according to the above-described measurement conditions (A) satisfies the peak intensity reduction rate described in Table 1 below, and a second sealant layer (CPP1) having a thickness of 50 μm including a non-stretched polypropylene film bonded onto the first sealant layer (EC1) (difference between the temperature of the molten resin and the cooling roll temperature during casting film production: 240°C) were used, and the same procedure as in Example 1 was used to manufacture a pouch film for external use of a secondary battery (the melting point of the entire sealant layer including the first sealant layer (EC2) and the second sealant layer (CPP2) is shown in the measurement example below).

[0085] Reduction rate after thermal bonding and pre-heat bonding [%] First peak intensity (A1) Second peak intensity (A2) Third peak intensity (A3) First peak intensity (A1') Second peak intensity (A2') Third peak intensity (A3') First peak intensity reduction rate (R1) Second peak intensity reduction rate (R2) Third peak intensity reduction rate (R3) Example 10.130.260.190.050.080.0761.569.263.2 Example 20.130.270.180.050.090.0761.566.661.1 Reference example 10.120.270.180.030.070.0475.074.077.8 Comparative example 10.120.270.180.10.230.1323.117.927.8 Comparative example 20.130.280.180.090.230.1430.717.522.2

[0086] In the above Table 1, the peak intensity reduction rates (R1, R2, R3) are measured according to the measurement conditions (A) described above, and represent the values ​​measured according to Equation 1 below. [Equation 1]

[0087] R n = [(A n - A n ') / A n ]ㆍ100 [%]

[0088] (In the above equation 1, n is 1, 2, or 3.)

[0089] Referring to Table 1, the sealant layer of the pouch film for the secondary battery exterior of Examples 1 and 2 satisfied the numerical ranges of 58% or more and 72% or less for the first peak intensity reduction rate, the second peak intensity reduction rate, and the third peak intensity reduction rate, respectively.

[0090] In contrast, the sealant layer of the pouch film for external use of a secondary battery of Reference Example 1 exceeded the numerical ranges described above in the first peak intensity reduction rate, the second peak intensity reduction rate, and the third peak intensity reduction rate, respectively, and the sealant layer of the pouch film for external use of a secondary battery of Comparative Examples 1 and 2 had the second peak intensity reduction rate, the second peak intensity reduction rate, and the third peak intensity reduction rate each falling short of the numerical ranges described above.

[0091] Measurement Example 1: Measurement of melting points of sealant layers of Examples 1 and 2, Reference Example 1, and Comparative Examples 1 and 2

[0092] For the sealant layers of Examples 1 to 2, Reference Example 1, and Comparative Examples 1 to 2, a DSC (DSC250 manufactured by TA) was used to obtain a DSC temperature increase curve while increasing the temperature at a rate of 10°C / min in the temperature range of 50 to 200°C, and the results are shown in Fig. 1.

[0093] Meanwhile, the melting point onset temperature (T) of the sealant layers of Examples 1 to 2, Reference Example 1, and Comparative Examples 1 to 2 measured from the DSC temperature increase curve (bottom) of Fig. 1 m,onset ), melting point termination temperature (T m,offset ), and melting point (T m ) are shown in Table 2 below.

[0094] Example 1 Example 2 Reference Example 1 Comparative Example 1 Comparative Example 2 Melting point onset temperature (T m,onset )116.3℃116.3℃149.5℃130.1℃130.1℃ Melting point termination temperature (T m,offset )150.2℃150.2℃167.5℃139.2℃139.2℃ Melting point (T m )135.2℃135.2℃162.1℃144.3℃144.3℃

[0095] Measurement Example 2: Comparison of maximum sealing strength and breaking strength

[0096] For the secondary battery outer pouch films of Examples 1 and 2, Reference Example 1, and Comparative Examples 1 and 2, the maximum value of the sealing strength was measured according to the measurement conditions (B) described above, and separately, the breaking strength was measured according to the measurement conditions (C) described above, and the results of comparing the maximum value of the sealing strength and the breaking strength are shown in Table 3 below.

[0097] In Table 3, if the maximum value of the sealing strength is 90% or more of the breaking strength, it is evaluated as 'S', if the maximum value of the sealing strength is 80% or more but less than 90% of the breaking strength, it is evaluated as 'A', if the maximum value of the sealing strength is 70% or more but less than 80% of the breaking strength, it is evaluated as 'B', if the maximum value of the sealing strength is 60% or more but less than 70% of the breaking strength, it is evaluated as 'C', and if the maximum value of the sealing strength is less than 60% of the breaking strength, it is evaluated as 'D'.

[0098] (Maximum value of sealing strength / breaking strength)ㆍ100 [%]Example 1SExample 2SReference Example 1BComparative Example 1DComparative Example 2C

[0099] Experimental Example 1: Evaluation of thermal bonding and maximum sealing strength under conditions of 210°C, 0.2 MPa, and 1.6 s.

[0100] The secondary battery outer pouch films of Examples 1 to 2, Reference Example 1, and Comparative Examples 1 to 2 were folded in half and heat-sealed (temperature 210°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.

[0101] Afterwards, the specimen was fixed between two jigs of a tensile testing machine (UTM) so that the sealing part of the specimen was positioned in the center at a measurement temperature of 25℃ (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 amount.

[0102] The maximum value of the sealing strength was measured from the graph of the jig gap change dependence of the sealing strength, and this measurement was repeated 10 times, and the average value of the measured values ​​(i.e., the average value of the maximum values ​​of 10 sealing strengths measured in 10 measurements) is shown in Table 4 below.

[0103] In addition, photographs of the tensile test results for specimens manufactured from the pouch films for secondary battery exteriors of Examples 1 and 2, Reference Example 1, and Comparative Examples 1 and 2 when the jig gap increased by 20 mm compared to the initial jig gap (i.e., when the jig gap change amount was 20 mm) are shown in FIGS. 2a, 2b, and 2c, respectively.

[0104] Example 1 Example 2 Reference Example 1 Comparative Example 1 Comparative Example 2 Maximum sealing strength (a) (average, TD direction) 210.1 N 209.2 N 180.4 N 120.0 N 131.2 N Maximum sealing strength (b) (average, MD direction) 195.7 N 193.3 N 168.6 N 91.5 N 103.7 N Difference (ab) 14.4 N 15.9 N 11.8 N 28.5 N 27.5 N

[0105] Referring to Table 4, it can be confirmed that the secondary battery external pouch film of Example 1 has a very excellent maximum sealing strength in both the TD direction and the MD direction compared to the secondary battery external pouch films of Reference Example 1 and Comparative Example 1. In addition, the secondary battery external pouch films of Examples 1 and 2 and Reference Example 1 were found to have a constant level of sealing strength characteristics regardless of their molding direction, but in contrast, the secondary battery external pouch films of Comparative Examples 1 and 2 have inferior maximum sealing strength values ​​in the MD direction, which causes a problem in that the molding direction is restricted when applied to a product. Meanwhile, referring to FIG. 2a, in the specimen manufactured with the secondary battery external pouch film of Example 1, when the jig gap variation was 20 mm, both tearing of the sealing part (i.e., Cohesive Failure) and fracture of the specimen in a part other than the sealing part (i.e., Material Failure) occurred. In addition, in the case of a specimen manufactured using the pouch film for external use of a secondary battery of Example 2, although publication of a separate photographic drawing was omitted, it was confirmed that almost the same results were obtained. This is understood to be because the sealing strength of the heat-bonded sealing portion is very high, corresponding to the breaking strength of the pouch film for external use of a secondary battery.

[0106] In contrast, referring to FIGS. 2b and 2c, in the specimens manufactured using the pouch films for external use in secondary batteries of Reference Example 1 and Comparative Example 1, only tearing of the sealing portion (Cohesive Failure) was observed, and virtually no breakage of the specimen (Material Failure) was observed.

[0107] In addition, as illustrated in FIGS. 2a and 2b, it was confirmed that the sealant layers that were thermally bonded to each other were torn off in the pouch films for external use of secondary batteries of Example 1 and Reference Example 1 as the amount of change in the jig gap increased. However, as illustrated in FIG. 2c, it was confirmed that the barrier layer and the sealant layer were torn off in the pouch films for external use of secondary batteries of Comparative Example 1 as the amount of change in the jig gap increased.

[0108] From this, it can be seen that the sealing strength of the sealing portion of the secondary battery outer pouch film of Example 1 is much superior to the sealing strength of the sealing portion of the secondary battery outer pouch film of Reference Example 1 and Comparative Example 1.

[0109] Experimental Example 2: Evaluation of the increase in sealing strength according to the increase in barrier layer thickness.

[0110] A pouch film for external use of a secondary battery according to Example 3 and Reference Example 2 was additionally manufactured. Here, the pouch film for external use of a secondary battery according to Example 3 and Reference Example 2 was manufactured as follows.

[0111] Example 3: Pouch film for secondary battery exterior including sequentially laminated outer layers, barrier layers, and sealant layers

[0112] A pouch film for external use of a secondary battery was manufactured in the same manner as in Example 1 (barrier layer thickness: 60 μm) except that the thickness of the barrier layer was increased to 80 μm.

[0113] Reference Example 2: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0114] A pouch film for external use of a secondary battery was manufactured in the same manner as in Reference Example 1 (barrier layer thickness: 60 μm) except that the thickness of the barrier layer was increased to 80 μm.

[0115] Afterwards, the secondary battery outer pouch films of Example 1, Example 3, Reference Example 1, and Reference Example 2 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 have a width of 15 mm to manufacture a specimen.

[0116] 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.

[0117] 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 5 below.

[0118] Example 1 Example 3 Reference Example 1 Reference Example 2 Maximum sealing strength (#1) 186.2N 219.6N 161.8N 176.0N Maximum sealing strength (#2) 203.6N 217.0N 171.1N 185.4N Maximum sealing strength (#3) 210.6N 204.9N 182.0N 165.3N Average (#1 ~ #3) 200.1N 213.8N 171.6N 175.6N

[0119] Referring to Table 5, the maximum average sealing strength for the secondary battery external pouch film of Example 1 was measured to be 200.1 N, and from this, it can be confirmed that the secondary battery external pouch film of Example 1 exhibits excellent sealing strength. In contrast, the average sealing strength maximum value for the secondary battery external pouch film of Example 1 and the secondary battery external pouch film of Reference Example 1, which are identical in thickness and type of the outer layer and metal layer, was measured to be 171.6 N, and from this, it was confirmed that the secondary battery external pouch film of Reference Example 1 was somewhat inferior in sealing strength. Meanwhile, the average sealing strength for the secondary battery external pouch film of Example 3, which differed only in the thickness of the barrier layer compared to the secondary battery external pouch film of Example 1, was measured to be 213.8 N, which was approximately 6.8% higher than the average sealing strength maximum value for the secondary battery external pouch film of Example 1.

[0120] In contrast, the average sealing strength of the secondary battery external pouch film of Reference Example 2, which differs only in the thickness of the outer layer compared to the secondary battery external pouch film of Reference Example 1, was measured to be 175.6 N, which was approximately 2.3% higher than the average sealing strength maximum value of the secondary battery external pouch film of Reference Example 1. That is, it can be confirmed that the improvement ratio of the average sealing strength maximum value in Reference Example 2 compared to Reference Example 1 is significantly lower than the improvement ratio of the average sealing strength maximum value in Example 3 compared to Example 1.

[0121] Experimental Example 3: Evaluation of Sealing Strength According to the Thickness of the Outer Layer and Barrier Layer

[0122] Pouch films for external use of secondary batteries of Example 4, Reference Example 3, and Comparative Example 3 were additionally manufactured. Here, the pouch films for external use of secondary batteries of Example 4, Reference Example 3, and Comparative Example 3 were manufactured as follows.

[0123] Example 4: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0124] A pouch film for external use of a secondary battery was manufactured in the same manner as in Example 1 (the thickness of the nylon in the outer layer was 25 ㎛, the thickness of the barrier layer was 60 ㎛), except that the thickness of the nylon in the outer layer was lowered to 15 ㎛ and the thickness of the barrier layer was lowered to 40 ㎛.

[0125] Reference Example 3: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0126] A pouch film for external use of a secondary battery was manufactured in the same manner as in Reference Example 1 (the thickness of the nylon in the outer layer was 25 ㎛, the thickness of the barrier layer was 60 ㎛), except that the thickness of the nylon in the outer layer was lowered to 15 ㎛ and the thickness of the barrier layer was lowered to 40 ㎛.

[0127] Comparative Example 3: Pouch film for secondary battery exterior including sequentially laminated outer layer, barrier layer, and sealant layer

[0128] A pouch film for external use of a secondary battery was manufactured in the same manner as in Comparative Example 1 (nylon thickness in the outer layer 25 ㎛, barrier layer thickness 60 ㎛), except that the thickness of the nylon in the outer layer was lowered to 15 ㎛ and the thickness of the barrier layer was lowered to 40 ㎛.

[0129] Afterwards, the secondary battery outer pouch films of Example 4, Reference Example 3, and Comparative Example 3 were folded in half and heat-sealed (temperature 200°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.

[0130] At a measurement temperature of 25℃, the specimen was fixed between two jigs of an unified tension tester (UTM) with the sealing portion of the specimen positioned 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 (in the TD and MD directions) dependent on the jig gap change amount. From this, the maximum value of the sealing strength was measured from the graph of the sealing strength dependent on the jig gap change amount, and the maximum value is shown in Table 7 below.

[0131] In addition, separately from the manufacture of the above specimens, specimens for measuring the breaking strength of the secondary battery outer pouch films of Example 4, Reference Example 3, and Comparative Example 3, which did not include a sealing portion and had a width of 15 mm, were manufactured, and using these, the specimens for measuring the breaking strength were fixed between two jigs of a tensile tester (UTM) at a measurement temperature of 25°C (initial jig gap 30 mm), and then the breaking strength (TD and MD directions) was measured while pulling at a measurement speed of 50 mm / min, and the results are shown in Table 6 below.

[0132] Example 4 Reference Example 3 Comparative Example 3 Maximum Sealing Strength TD 156 N 151 N 105 N MD 147 N 133 N 115 N Breaking Strength TD 168 N 166 N 159 N MD 159 N 158 N 177 N

[0133] Referring to Table 6, compared to the secondary battery external pouch films of Reference Example 3 and Comparative Example 3, the secondary battery external pouch film of Example 4 exhibited excellent maximum sealing strength in both the TD direction and the MD direction. In addition, it can be confirmed that the secondary battery external pouch film of Example 4 has the smallest absolute value of the difference between the maximum sealing strength in the TD direction and the maximum sealing strength in the MD direction, and from this, it can be seen that the secondary battery external pouch film of Example 4 exhibits excellent sealing strength regardless of the direction. In addition, it can be confirmed that the maximum sealing strength (156 N) of the secondary battery external pouch of Example 4 in the TD direction exceeded 90% of the breaking strength (168 N) in the TD direction, and the maximum sealing strength (147 N) in the MD direction also exceeded 90% of the breaking strength (159 N) in the MD direction.

[0134] In contrast, the secondary battery outer pouch film of Reference Example 3 had a maximum sealing strength (133 N) in the MD direction that was less than 90% of the breaking strength (158 N) in the MD direction, and it was confirmed that the secondary battery outer pouch film of Comparative Example 3 had maximum sealing strengths (TD: 105 N, MD: 115 N) in both the TD direction and MD direction that were less than the breaking strengths (TD: 159 N, MD: 177 N) in the TD direction and MD direction.

[0135] Acknowledgement

[0136] This application is the result of the following project support.

[0137] Assignment ID: 1415185612

[0138] Assignment Number: 20022450

[0139] Ministry Name: Ministry of Trade, Industry and Energy

[0140] Project Management (Professional) Agency Name: Korea Institute of Industrial Technology Planning and Evaluation

[0141] Research Project Name: Material and Components Technology Development

[0142] Research Project Title: Development of Next-Generation Secondary Battery Pouches Capable of Delivering More Than Double the Bonding Strength (60°C)

[0143] Contribution rate: 1 / 1

[0144] Project implementation organization name: Yulchon Chemical Co., Ltd.

[0145] 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 external use of a secondary battery, wherein the peak intensity reduction rates (R1, R2, R3) measured according to the following measurement conditions (A) for the sealant layer are 58% or more and 72% or less, respectively. [Measurement conditions (A)] (1) Using the FT-IR (Fourier Transform Infra-Red spectroscopy) method, the sealant layer before heat bonding was measured at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1) in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2) in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3) below (2) After the sealant layers are in contact with each other, heat bonding (temperature 190℃, pressure 0.2 MPa, time 1.6 s) is performed to form a sealing part. (3) After peeling off the heat-bonded sealant layers, the peeled part of the sealant layer was analyzed using the FT-IR method at 1450 cm -1 Ideal 1460cm -1 First peak intensity (A1') in the range below, 2910 cm -1 Height: 2920cm -1 The second peak intensity (A2') in the range below, and 2945 cm -1 Ideal 2955cm -1 Measure the third peak intensity (A3') in the following range (4) Measure the reduction rate according to Equation 1 below. [Formula 1] R n = ((A n - AM n ') / AM n )ㆍ100 [%] (In the above equation 1, n is 1, 2, or 3, and R n is the rate of decrease in the nth peak intensity.) 2. In claim 1, The above first peak intensity is derived from the symmetrical bending vibration of CH bonds contained in the methyl group (-CH3) in the sealant layer. The above second peak intensity is derived from the asymmetrical bending vibration of CH bonds included in the methylene bridge (-CH2-) in the sealant layer. A pouch film for external use of a secondary battery, wherein the third peak intensity is derived from the asymmetric bending vibration of CH bonds contained in the methyl group (-CH3) in the sealant layer.

3. 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.

4. In claim 3, A pouch film for a secondary battery exterior, wherein the polyolefin resin comprises at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, a copolymer derived from an ethylene-derived monomer and an alpha-olefin-derived monomer, a copolymer derived from a propylene-derived monomer and an alpha-olefin-derived monomer, or a blend thereof.

5. In claim 1, The above sealant layer has a melting point onset temperature (T) measured under a temperature increase condition of 10°C / min using differential scanning calorimetry (DSC). m,onset ) is 105~125℃, and the melting point termination temperature (T m,offset ) is a pouch film for external use of a secondary battery, having a temperature of 140 to 160°C.

6. In claim 5, The above sealant layer has a melting point (T) measured under a temperature increase condition of 10°C / min using the differential scanning calorimetry method. m ) A pouch film for external use of a secondary battery, having a temperature of 125 to 143°C.

7. 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.

8. 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.

9. 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.

10. In claim 1, A pouch film for external use of a secondary battery, wherein the thickness of the outer layer is 15㎛ or more and 140㎛ or less.

11. In claim 1, A secondary battery external pouch film, wherein the maximum value of the sealing strength measured according to the following measurement conditions (B) for the secondary battery external pouch film is 90% or more of the breaking strength measured according to the following measurement conditions (C) for the secondary battery external pouch film. [Measurement conditions (B)] (1) Fold the secondary battery outer pouch film in half and heat-bond (temperature 210°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 manufacture a specimen. (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 the maximum value of the sealing strength is measured while pulling at a measurement speed of 50 mm / min. [Measurement conditions (C)] (1) Cut the secondary battery outer pouch film to produce a specimen with a width of 15 mm and no sealing portion. (2) At a measurement temperature of 25℃, the specimen is fixed between two jigs of a tensile testing machine (UTM) (initial jig gap 30 mm), and the breaking strength of the specimen is measured while pulling at a measurement speed of 50 mm / min.

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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