Pouch film laminate and secondary battery

Abstract

To provide a pouch film laminate which increases the seal strength of a pouch, and a secondary battery manufactured from the pouch film laminate.SOLUTION: The pouch film laminate according to the present invention includes a base material layer, a gas barrier layer, and a sealant layer which are sequentially laminated. The sealant layer includes a first sealant layer adjacent to the gas barrier layer and a second sealant layer laminated on the first sealant layer. ΔY in the following formula 1 is in the range of 66% to 120%: [Mathematical Formula 1] {(Yield strength of the second sealant layer-Yield strength of the first sealant layer) / Yield strength of the first sealant layer}×100.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0131121, filed on October 1, 2021, and all of the contents disclosed in the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a pouch film laminate and a secondary battery manufactured by molding the same, and more particularly, to a pouch film laminate for improving the seal strength of a pouch and a secondary battery manufactured by molding the same.

Background Art

[0003] Generally, types of secondary batteries include nickel cadmium batteries, nickel metal hydride batteries, lithium ion batteries, lithium ion polymer batteries, and the like. Such secondary batteries are used not only in small products such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also in large products that require high power such as electric vehicles and hybrid vehicles, as well as power storage devices for storing surplus generated power and new renewable energy and backup power storage devices.

[0004] To manufacture such a secondary battery, first, an electrode active material slurry is applied to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, and the positive electrode and the negative electrode are laminated on both sides of a separator to form an electrode assembly having a predetermined shape. Then, the electrode assembly is housed in a battery case, an electrolyte is injected, and then sealed.

[0005] Secondary batteries are classified into pouch type, can type, etc. according to the material of the case that houses the electrode assembly. The pouch type houses the electrode assembly in a pouch made of a flexible polymer material. The can type houses the electrode assembly in a case made of a material such as metal or plastic.

[0006] The pouch, which is the case of the pouch-type secondary battery, is manufactured by performing press working on a flexible pouch film laminate to form a cup portion. Once the cup portion is formed, the electrode assembly can be housed in the inner accommodation space of the cup portion and the seal portion can be sealed to manufacture the secondary battery.

[0007] Generally, the pouch film laminate is formed of a plurality of layers in which a polymer film such as polyethylene terephthalate is laminated on one surface of a metal gas barrier layer and a sealant layer is laminated on the other surface. However, in the case of such a conventional pouch film laminate, when the pouch-type secondary battery is exposed to harsh environmental conditions, the seal portion of the pouch may be vented. As a result, there has been a problem that contamination and malfunction occur in the electrode assembly housed inside the pouch.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention provides a pouch film laminate in which the yield strength of the sealant layer is optimized and the seal strength of the pouch is improved.

[0009] The problems of the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0010] According to an embodiment of the present invention, a pouch film laminate includes a base material layer, a gas barrier layer, and a sealant layer laminated in sequence. The sealant layer includes a first sealant layer disposed adjacent to the gas barrier layer and a second sealant layer laminated on the first sealant layer, and ΔY according to the following formula 1 is 66% to 120%.

[0011] [Equation 1] ΔY = { (Yield strength of the second sealant layer - Yield strength of the first sealant layer) / Yield strength of the first sealant layer} × 100

[0012] In the pouch film laminate of the present invention, the difference between the yield strength of the first sealant layer and the yield strength of the second sealant layer may be 8 N / 15 mm or less.

[0013] In the pouch film laminate of the present invention, the yield strength of the first sealant layer may be smaller than the yield strength of the second sealant layer.

[0014] In the pouch film laminate of the present invention, the yield strength of the first sealant layer may be 7 N / 15 mm to 15 N / 15 mm.

[0015] In the pouch film laminate of the present invention, the yield strength of the second sealant layer may be 10 N / 15 mm to 30 N / 15 mm.

[0016] In the pouch film laminate of the present invention, the ratio of the thickness of the first sealant layer to the thickness of the second sealant layer may be 1:0.3 to 1:3.

[0017] In the pouch film laminate of the present invention, the thickness of the first sealant layer may be 10 μm to 60 μm.

[0018] In the pouch film laminate of the present invention, the thickness of the second sealant layer may be 20 μm to 70 μm.

[0019] In the pouch film laminate of the present invention, the first sealant layer and the second sealant layer may contain polypropylene (PP), and the gas barrier layer may contain aluminum (Al).

[0020] In the pouch film laminate of the present invention, the peel strength between the gas barrier layer and the first sealant layer may exceed 23 N / 15 mm.

[0021] When two of the above-mentioned pouch film laminates are laminated such that the respective second sealant layers are in contact with each other and then sealed for 2 seconds under the conditions of 180°C and 0.4 MPa to form a sealed portion, the breaking strength of the sealed portion measured at 25°C is 100 N / 15 mm or more, and the breaking strength of the sealed portion measured at 60°C may be 80 N / 15 mm or more.

[0022] On the other hand, a secondary battery according to another embodiment of the present invention includes a pouch-type battery case manufactured by molding any one of the above-mentioned pouch film laminates, and an electrode assembly housed inside the pouch-type battery case.

Effect of the Invention

[0023] Conventionally, when manufacturing a pouch film laminate, in order to improve the adhesion to the gas barrier layer, which is a metal layer, the first sealant layer attached to the gas barrier layer is generally formed of a material having lower fluidity than the second sealant layer. However, in the case of a battery case manufactured using such a conventional pouch film laminate, when gas is generated inside the pouch or an external force is applied, there is a problem that the interface between the first sealant layer and the second sealant layer peels off and the seal durability is poor.

[0024] In order to solve the above problems, the pouch film laminate according to the present invention controls the difference in yield strength between the first sealant layer and the second sealant layer within a specific range, thereby suppressing the peeling of the interface between the first sealant layer and the second sealant layer due to external force, generation of gas, etc. As a result, the seal durability of the pouch manufactured by sealing the pouch film laminate is improved.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] The advantages, features, and methods for achieving them of the present invention will become apparent by referring to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be realized in various different forms. This embodiment is merely provided to complete the disclosure of the present invention and to enable those with ordinary knowledge in the technical field to which the present invention pertains to fully understand the scope of the invention. The present invention is only defined by the scope of the claims. Throughout the specification, the same reference numerals indicate the same components.

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall be construed in a manner that is commonly understood by one of ordinary skill in the art to which this invention belongs. Also, terms defined in commonly used dictionaries shall not be construed ideally or overly unless clearly and specifically defined herein.

[0028] The terms used herein are for the purpose of describing embodiments and are not intended to limit the present invention. In this specification, the singular forms also include the plural forms unless otherwise specified. The term "comprises and / or comprising" as used herein does not exclude the presence or addition of one or more other components in addition to the recited component.

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] In this specification, when a certain part includes a certain component, it means that, unless otherwise stated to the contrary, it does not exclude other components but may further include other components.

[0031] In this specification, the upper part of the drawing can be said to be the "upper part" or "upper side" of the configuration shown in the drawing, and the lower part can be said to be the "lower part" or "lower side". Also, the part between the upper and lower parts of the configuration shown in the drawing or other parts excluding the upper and lower parts can be said to be the "side part" or "side surface". Such relative terms as "upper part", "upper side", etc. are used to explain the relationship between the configurations shown in the drawing, and the present disclosure is not limited by such terms.

[0032] In this specification, the direction towards the internal space of a structure can be said to be the "inside", and the direction protruding into the open external space can be said to be the "outside". Such relative terms as "inside", "outside", etc. are used to explain the relationship between the configurations shown in the drawing, and the present disclosure is not limited by such terms.

[0033] In this specification, the description of "A and / or B" means A, or B, or A and B.

[0034] In this specification, when it is stated that a certain part is connected to another part, it includes not only the case where they are directly connected, but also the case where they are connected with other components interposed therebetween.

[0035] In this specification, the yield strength is the limit stress at which elastic deformation occurs, meaning the 0.2% offset stress, and is measured by pulling a 15 mm × 80 mm polypropylene film sample at a speed of 50 mm / min in an environment of a temperature of 25°C and a relative humidity of 40% using a measuring device UTM (Zwick).

[0036] In this specification, the breaking strength of the seal part means the stress when the seal part formed by sealing two pouch film laminates for 2 seconds under the conditions of 180°C and 0.4 MPa with their respective second sealant layers in contact is broken. Specifically, the breaking strength of the seal part means the maximum value of the tensile strength measured when, after cutting the sample on which the seal part is formed into a width of 15 mm, fastening one end of each of the pouch film laminates laminated vertically in the sample to the upper / lower jigs of a measuring device (UTM, Zwick) and then pulling it in the vertical direction at a speed of 5 mm / min until the seal part is broken.

[0037] Pouch film laminate The pouch film laminate according to the present invention is one in which a base material layer, a gas barrier layer, and a sealant layer are sequentially laminated. In this case, the sealant layer includes a first sealant layer disposed adjacent to the gas barrier layer and a second sealant layer laminated on the first sealant layer, and ΔY according to the following formula 1 is 66% to 120%.

[0038] [Equation 1] ΔY = {(Yield strength of the second sealant layer - Yield strength of the first sealant layer) / Yield strength of the first sealant layer} × 100

[0039] Hereinafter, with reference to FIG. 1, the pouch film laminate according to the present invention and each layer included in the pouch film laminate will be described in detail.

[0040] FIG. 1 is a cross-sectional view of a pouch film laminate 100 according to the present invention.

[0041] As shown in FIG. 1, the pouch film laminate 100 includes a base material layer 110, a gas barrier layer 120, and a sealant layer 130. The sealant layer 130 includes a first sealant layer 132 and a second sealant layer 134. In the pouch film laminate 100, the base material layer 110, the gas barrier layer 120, the first sealant layer 132, and the second sealant layer 134 may be sequentially laminated.

[0042] (1) Base material layer The base material layer 110 is formed on the outermost layer of the pouch film laminate 100 to protect the secondary battery from friction and collision with the outside. The base material layer 110 is made of a polymer and can electrically insulate the electrode assembly from the outside. The base material layer 110 may be made of one or more materials selected from the group consisting of, for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. Among them, it is particularly preferable that the base material layer 110 is made of polyethylene terephthalate (PET), nylon, or a combination thereof having abrasion resistance and heat resistance.

[0043] The base material layer 110 may have a single film structure composed of any one substance. Alternatively, the base material layer 110 may have a composite film structure formed by two or more substances each forming a layer.

[0044] The thickness of the base material layer 110 may be 5 μm to 50 μm, specifically 7 μm to 50 μm, and more specifically 7 μm to 40 μm. When the thickness of the base material layer 110 satisfies the above range, the pouch film laminate has excellent external insulation properties, and the thickness of the whole pouch does not increase, so it is excellent in energy density with respect to the volume of the secondary battery.

[0045] (2) Gas barrier layer The gas barrier layer 120 is laminated between the base material layer 110 and the sealant layer 130 to ensure the mechanical strength of the pouch, block the entry and exit of gas, moisture, etc. from the outside of the pouch-type battery case, and prevent the leakage of the electrolyte from the inside of the pouch-type battery case.

[0046] The gas barrier layer 120 may be made of a metal, specifically, it may be made of an aluminum alloy thin film. When the gas barrier layer is formed using an aluminum alloy thin film, mechanical strength above a predetermined level can be ensured, the weight is light, and complementarity of the electrochemical properties of the electrode assembly and the electrolyte, heat dissipation, etc. can be ensured. The aluminum alloy thin film may contain one or more selected from the group consisting of metal elements other than aluminum, such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0047] On the other hand, the thickness of the gas barrier layer 120 may be 40 μm to 100 μm, specifically 50 μm to 90 μm, and more specifically 55 μm to 85 μm. When the thickness of the gas barrier layer 120 satisfies the above range, it is excellent in formability and gas barrier performance during the forming of the cup portion.

[0048] (3) Sealant layer The sealing layer 130 is for completely sealing the inside of the pouch-type battery case from the outside when the pouch-type battery case (310 in FIG. 3) that houses the electrode assembly inside is sealed, such that the seal portions (350 in FIG. 3) are thermally adhered to each other. For this purpose, the sealing layer 130 may be formed of a material having excellent thermal adhesion strength.

[0049] The sealing layer 130 may have a composite film structure in which two or more substances are formed in layers respectively.

[0050] Specifically, the sealing layer 130 according to the present invention may include a first sealing layer 132 and a second sealing layer 134. In this case, the first sealing layer 132 is a layer disposed adjacent to the gas barrier layer 120, and the second sealing layer 134 may be a layer disposed on the first sealing layer 132. The first sealing layer 132 and the second sealing layer 134 may be made of materials having different materials and / or physical properties respectively.

[0051] An interface may exist between the first sealing layer 132 and the second sealing layer 134. This means that the first sealing layer 132 and the second sealing layer 134 are different layers and can be formed separately.

[0052] According to the present invention, ΔY according to the following formula 1 may be 66% to 120%, specifically 66% to 110%, more specifically 66% to 100%. Here, ΔY means a value indicating, in percentage, the difference between the yield strength of the first sealing layer 132 and the yield strength of the second sealing layer 134 with respect to the yield strength of the first sealing layer 132.

[0053] [Equation 1] ΔY = {(Yield strength of the second sealing layer - Yield strength of the first sealing layer) / Yield strength of the first sealing layer}×100

[0054] When the ΔY exceeds 120%, delamination may occur at the interface between the first sealant layer 132 and the second sealant layer 134 when an external force or gas is generated, and the seal durability of the pouch-type battery case (310 in FIG. 3) may decrease.

[0055] When the ΔY is less than 66%, during the production of the pouch film laminate, the extrusion processability of the sealant layer decreases, and during the sealing process for battery production after the production of the pouch film laminate, the low-temperature sealability may decrease.

[0056] The difference in yield strength between the first sealant layer 132 and the second sealant layer 134 may be 8 N / 15 mm or less, preferably 1 N / 15 mm to 8 N / 15 mm, more preferably 3 N / 15 mm to 7 N / 15 mm. When the difference in yield strength between the first sealant layer 132 and the second sealant layer 134 satisfies the above range, the possibility of delamination occurring at the interface between the first sealant layer 132 and the second sealant layer 134 when an external force or gas is generated is reduced, and the seal durability of the pouch-type battery case (310 in FIG. 3) is improved.

[0057] The yield strength of the first sealant layer 132 may be smaller than that of the second sealant layer 134. In this case, since the first sealant layer 132 has lower fluidity than the second sealant layer 134, it is easily attached to the gas barrier layer 120 when the pouch film laminate 100 is formed, and the adhesive force on the interface between the gas barrier layer 120 and the first sealant layer 132 is maintained high when an external force occurs.

[0058] The first sealant layer 132 and the second sealant layer 134 may be made of materials having different materials and / or physical properties. For example, the first sealant layer 132 may be made of a material having lower fluidity than the second sealant layer 134. In this case, the first sealant layer 132 having lower fluidity has a smaller yield strength than the second sealant layer 134.

[0059] The thickness ratio of the first sealant layer 132 to the second sealant layer 134 may be 1:0.3 to 1:3, preferably 1:0.6 to 1:2.2, and more preferably 1:1 to 1:1.7. When the thickness ratio of the first sealant layer 132 to the second sealant layer 134 satisfies the above range, the extrusion processability between the gas barrier layer 120 and the sealant layer 130 can be ensured, and at the same time, the effect of improving the breaking strength of the seal part can be obtained.

[0060] Hereinafter, each of the aforementioned first sealant layer 132 and second sealant layer 134 will be described in more detail.

[0061] 1) First sealant layer As described above, the first sealant layer 132 may be a layer disposed adjacent to the gas barrier layer 120.

[0062] The first sealant layer 132 may be made of a polymer material. Specifically, the first sealant layer 132 may be made of one or more substances selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber, and is preferably made of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be composed of cast polypropylene (CPP), acid modified polypropylene (PPa), or a polypropylene-butylene-ethylene terpolymer.

[0063] The first sealant layer 132 is particularly preferably made of acid modified polypropylene (PPa) in order to ensure the long-term adhesion performance between the gas barrier layer 120 and the first sealant layer 132. Here, the acid modified polypropylene may be maleic anhydride polypropylene (MAH PP).

[0064] In order to adjust the yield strength of the first sealant layer 132 to a desired value, an additive may be added to the polymer material forming the first sealant layer 132. For example, at least any one of carbon fiber, glass fiber, and aramid fiber may be added as an additive for improving the yield strength of the first sealant layer 132. For example, the additive may be contained at 5 vol% to 8 vol% with respect to the total volume of the first sealant layer, but is not limited thereto.

[0065] The yield strength of the first sealant layer 132 may be 7 N / 15 mm to 15 N / 15 mm, preferably 7.2 N / 15 mm to 9.0 N / 15 mm, more preferably 7.5 N / 15 mm to 8.5 N / 15 mm.

[0066] When the yield strength of the first sealant layer 132 is less than 7 N / 15 mm, the difference in the yield strength between the first sealant layer 132 and the second sealant layer 134 becomes large. As a result, when an external force or gas is generated, delamination may occur at the interface between the first sealant layer 132 and the second sealant layer 134, and the seal durability of the pouch-type battery case (310 in FIG. 3) may decrease.

[0067] When the yield strength of the first sealant layer 132 exceeds 15 N / 15 mm, the extrusion processability for laminating the gas barrier layer 120 and the first sealant layer 132 may decrease. Further, in order to increase the yield strength of the first sealant layer 132, it is necessary to improve the overall strength of the sealant layer 130. However, when the first sealant layer 132 and the second sealant layer 134 are extruded, problems such as necking may occur. Moreover, as the difference in the yield strength between the first sealant layer 132 and the gas barrier layer 120 becomes large, the adhesive force on the interface between the gas barrier layer 120 and the first sealant layer 132 may decrease.

[0068] The thickness of the first sealant layer 132 may be 10 μm to 60 μm, preferably 20 μm to 50 μm, more preferably 30 μm to 40 μm. When the thickness of the first sealant layer 132 is less than 10 μm, the seal durability and insulation of the seal portion (350 in FIG. 3) deteriorate, and there is a problem that the yield strength of the first sealant layer 132 decreases and the seal strength of the seal portion (350 in FIG. 3) becomes weak. When the thickness of the first sealant layer 132 is more than 60 μm, the thickness of the entire pouch film laminate becomes too thick and the moldability deteriorates. In the pouch-type battery case manufactured by molding the pouch film laminate, the accommodation space (324 in FIG. 3) for the electrode assembly decreases, and the energy density relative to the volume of the secondary battery may decrease.

[0069] 2) Second sealant layer As described above, the second sealant layer 134 may be a layer disposed on the first sealant layer 132.

[0070] The second sealant layer 134 may be made of a material having insulation, corrosion resistance, and sealability. Specifically, referring to FIG. 3, since the second sealant layer 134 is in direct contact with the electrode assembly (360 in FIG. 3) and / or the electrolyte inside the accommodation space (324 in FIG. 3), it may be made of a material having insulation and corrosion resistance. Further, since the second sealant layer 134 must completely seal the inside of the pouch-type battery case and block the movement of substances between the inside and the outside, it may be made of a material having high sealability (for example, excellent thermal adhesion strength).

[0071] In order to ensure such insulation, corrosion resistance, and sealing properties, the second sealant layer 134 may be made of a polymer material. Specifically, the second sealant layer 134 may be made of one or more substances selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. The second sealant layer 134 is preferably made of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be composed of unstretched polypropylene, acid-modified polypropylene (Acid Modified Polypropylene), or a polypropylene-butylene-ethylene terpolymer. Here, the acid-modified polypropylene may be maleic anhydride polypropylene (MAH PP). The second sealant layer 134 is more preferably made of unstretched polypropylene having heat-sealing properties and high tensile strength.

[0072] In order to adjust the yield strength of the second sealant layer 134 to a desired value, an additive may be added to the polymer material forming the second sealant layer 134. For example, at least one of carbon fiber, glass fiber, and aramid fiber may be added as an additive for improving the yield strength of the second sealant layer 134.

[0073] The yield strength of the second sealant layer 134 may be 10 N / 15 mm to 30 N / 15 mm, specifically 12 N / 15 mm to 17 N / 15 mm, and more specifically 14 N / 15 mm to 16 N / 15 mm. When the yield strength of the second sealant layer 134 is less than 10 N / 15 mm, breakage may occur along the pair of sealed second sealant layers 134 when an external force or gas is generated, and the seal durability of the pouch-type battery case (310 in FIG. 3) may decrease. When the yield strength of the second sealant layer 134 exceeds 30 N / 15 mm, the difference between the yield strength of the second sealant layer 134 and the yield strength of the first sealant layer 132 increases, increasing the risk of delamination at the interface between the first sealant layer 132 and the second sealant layer 134.

[0074] The thickness of the second sealant layer 134 may be 20 μm to 70 μm, preferably 30 μm to 70 μm, and more preferably 40 μm to 60 μm. When the thickness of the second sealant layer 134 is less than 20 μm, the seal durability and insulation of the seal portion (350 in FIG. 3) decrease, and there is a problem that the yield strength of the second sealant layer 134 decreases and the seal strength of the seal portion (350 in FIG. 3) becomes weak. When the thickness of the second sealant layer 134 is greater than 70 μm, the thickness of the entire pouch film laminate becomes too thick, the moldability decreases, the accommodation space (324 in FIG. 3) of the electrode assembly in the pouch-type battery case manufactured by molding the pouch film laminate decreases, and the energy density relative to the volume of the secondary battery may decrease.

[0075] Next, FIG. 2 is a cross-sectional view showing the seal portion 210 of the pouch-type battery case according to the present invention.

[0076] As shown in FIG. 2, the battery case manufactured by molding the pouch film laminate may be sealed after being laminated so that the second sealant layer 134 abuts. In this case, the seal portion 210 includes one or more sealant layers 130.

[0077] When pressure is applied to a battery case sealed by external force or gas generation, peeling occurs at the interface between layers with relatively weak adhesive force. For example, peeling occurs along the interface between the gas barrier layer 120 and the first sealant layer 132 (e.g., path A in FIG. 2), the interface between the second sealant layers 134 thermally adhered to each other (e.g., path B in FIG. 2), and / or the interface between the first sealant layer 132 and the second sealant layer 134 (e.g., path C in FIG. 2).

[0078] However, the battery case manufactured using the pouch film laminate according to the present invention has excellent adhesive force at all three of the above interfaces and exhibits excellent seal strength.

[0079] Specifically, in the pouch film laminate of the present invention, since the yield strength of the first sealant layer 132 has a value comparable to the yield strength of the gas barrier layer 120, the adhesive force on the interface between the gas barrier layer 120 and the first sealant layer 132 is maintained high when an external force occurs, and peeling is suppressed. For example, the peel strength between the gas barrier layer 120 and the first sealant layer 132 may exceed 23 N / 15 mm, preferably be 23.2 N / 15 mm or more, and more preferably be 23.5 N / 15 mm or more. When the peel strength between the gas barrier layer 120 and the first sealant layer 132 satisfies the above range, peeling is suppressed at the interface between the gas barrier layer 120 and the first sealant layer 132.

[0080] In addition, since the yield strength of the second sealant layer 134 formed in the seal portion 210 is high, a high restoring force acts when an external force occurs, so interface peeling between the second sealant layers 134 thermally adhered to each other is suppressed.

[0081] Moreover, since the difference in yield strength between the first sealant layer 132 and the second sealant layer 134 is small, interlayer peeling is suppressed at the interface between the first sealant layer 132 and the second sealant layer 134.

[0082] According to one embodiment of the present invention, the seal portion 210 may be formed by laminating two pouch film laminates such that their respective second sealant layers 134 are in contact with each other, and then sealing them at 180 °C and 0.4 MPa for 2 seconds.

[0083] In this case, the breaking strength of the seal portion 210 measured at 25 °C may be 100 N / 15 mm or more, preferably 110 N / 15 mm or more, more preferably 120 N / 15 mm or more.

[0084] Also, the breaking strength of the seal portion 210 measured at 60 °C may be 80 N / 15 mm or more, preferably 90 N / 15 mm or more, more preferably 100 N / 15 mm or more.

[0085] If the breaking strength of the seal portion 210 at 25 °C is less than 100 N / 15 mm or the breaking strength of the seal portion 210 at 60 °C is less than 80 N / 15 mm, the sealing strength of the seal portion 210 is low, and there is a problem that the battery case sealed by an external force or gas generation is likely to be vented.

[0086] The breaking strength of the seal portion 210 means the maximum value of the tensile strength measured when one end of each of the pouch film laminates laminated vertically in the sample in which the seal portion 210 is formed is fastened to the upper / lower jigs of the measuring device and then pulled at a speed of 5 mm / min in the vertical direction until the seal portion is broken. Also, the "25 °C" and the "60 °C" mean the temperature when pulling one end of each of the adjacent pouch film laminates 100 in the vertical direction.

[0087] Secondary battery Next, the secondary battery according to the present invention will be described.

[0088] FIG. 3 is an exploded assembly view of a secondary battery 300 according to the present invention.

[0089] 3, a secondary battery 300 according to the present invention may include a pouch-type battery case 310 and an electrode assembly 360 housed in the pouch-type battery case 310. The electrode assembly 360 may be formed by stacking a positive electrode, a separator, and a negative electrode, and may include an electrode tab 370, an electrode lead 380, and an insulating part 390. The secondary battery 300 may be manufactured by injecting an electrolyte with the electrode assembly 360 housed inside the pouch-type battery case 310 and then sealing the seal part 350.

[0090] The pouch-type battery case 310 may house the electrode assembly 360 inside. The pouch-type battery case 310 may be manufactured by molding the pouch film laminate 100 of Fig. 1 described above. The detailed configuration and physical properties of the pouch film laminate 100 are as described above, so a detailed description will be omitted.

[0091] To manufacture the pouch-type battery case 310, the pouch-type film laminate 100 may be drawn and stretched using a punch or the like to form a cup portion 322 including a pocket-shaped storage space 324 capable of accommodating the electrode assembly 360.

[0092] As shown in Fig. 3, the pouch-type battery case 310 may include a first case 320 and a second case 330. In one embodiment, the first case 320 includes a receiving space 324 in which a cup portion 322 is formed and capable of receiving an electrode assembly 360, and the second case 330 may cover the receiving space 324 from above so that the electrode assembly 360 does not fall out of the battery case 310. The first case 320 and the second case 330 may be manufactured by connecting one side to each other (e.g., reference numeral 340) as shown in Fig. 3, but the present invention is not limited thereto, and the first case 320 and the second case 330 may be manufactured in various forms, such as being separated from each other and separately manufactured.

[0093] In other embodiments, when forming the cup portions 322 in the pouch film laminate 100, two cup portions 322, 332 that are symmetric with respect to one pouch film laminate 100 may be formed adjacent to each other by drawing. In this case, as shown in FIG. 3, cup portions 322, 332 may be formed in the first case 320 and the second case 330, respectively. The electrode assembly 360 is housed in the accommodation space 324 provided in the cup portion 322 of the first case 320, and then the bridge portion 340 formed between the two cup portions 322, 332 may be folded so that the two cup portions 322, 332 face each other. In this case, the cup portion 332 of the second case 330 can house the electrode assembly 360 from above. Therefore, since the two cup portions 322, 332 house one electrode assembly 360, an electrode assembly 360 thicker than when there is one cup portion 322 can be housed. Further, since one edge of the secondary battery 300 is formed by folding the pouch-type battery case 310, the number of edges to be sealed during the subsequent sealing process is reduced. Thereby, the process speed of the secondary battery 300 can be improved and the number of sealing processes can be reduced.

[0094] The pouch-type battery case 310 may be sealed in a state where the electrode assembly 360 is accommodated such that a part of the electrode lead 380, that is, the terminal part, is exposed. Specifically, when the electrode lead 380 is connected to the electrode tab 370 of the electrode assembly 360 and an insulating part 390 is formed on a part of the electrode lead 380, the electrode assembly 360 may be accommodated in the accommodation space 324 provided in the cup part 322 of the first case 320, and the second case 330 may cover the accommodation space 324 from above. Next, an electrolyte may be injected into the accommodation space 324, and the seal part 350 formed at the edges of the first case 320 and the second case 330 may be sealed. The electrolyte is for moving lithium ions generated by the electrochemical reaction of the electrodes during charging / discharging of the secondary battery 300, and may contain a non-aqueous organic electrolyte which is a mixture of a lithium salt and organic solvents or a polymer using a polymer electrolyte. Further, the electrolyte may contain a sulfide-based, oxide-based or polymer-based solid electrolyte, and such a solid electrolyte has flexibility that is easily deformed by an external force.

[0095] Next, the electrode assembly 360 may be formed by alternately laminating electrodes and a separator. Specifically, the electrode assembly 360 may be manufactured by applying a slurry in which an electrode active material, a binder and / or a conductive material are mixed to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, and laminating them on both sides of a separator to form a predetermined shape. The electrode assembly 360 may be inserted into the pouch-type battery case 310, and after the electrolyte is injected, it may be sealed by the pouch-type battery case 310. In one embodiment, the types of the electrode assembly 360 include, but are not limited to, a stack type, a jelly roll type, a stack and folding type, etc.

[0096] In one embodiment, the electrode assembly 360 may include two types of electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other. The positive electrode and the negative electrode each have a structure in which an active material slurry is applied to a metal foil or a metal mesh current collector containing aluminum and copper. The slurry may usually be formed by stirring granular active material, auxiliary conductor, binder, conductive material, etc. with a solvent added. The solvent is removed in a subsequent process.

[0097] The electrode tabs 370 are respectively connected to the positive electrode and the negative electrode of the electrode assembly 360, protrude outward from the electrode assembly 360, and serve as a path through which electrons can move between the inside and the outside of the electrode assembly 360. The current collector of the electrode assembly 360 may be composed of a portion coated with the electrode active material and an end portion not coated with the electrode active material, that is, a plain portion. The electrode tab 370 may be formed by cutting the plain portion, or may be formed by connecting a separate conductive member to the plain portion by ultrasonic welding or the like. As shown in FIG. 3, the electrode tabs 370 may protrude in different directions of the electrode assembly 360, but are not limited thereto, and may be formed to protrude in various directions, such as protruding side by side in the same direction from one side.

[0098] The electrode lead 380 can supply electricity to the outside of the secondary battery 300. The electrode lead 380 may be connected to the electrode tab 370 of the electrode assembly 360 by spot welding or the like. At least a part of the electrode lead 380 may be surrounded by the insulating portion 390. In one embodiment, one end of the electrode lead 380 may be connected to the electrode tab 370, and the other end may protrude outside the battery case 310 respectively. The electrode lead 380 may include a positive electrode lead 382 having one end connected to the positive electrode tab 372 and extending in the direction in which the positive electrode tab 372 protrudes, and a negative electrode lead 384 having one end connected to the negative electrode tab 374 and extending in the direction in which the negative electrode tab 374 protrudes.

[0099] The positive electrode lead 382 and the negative electrode lead 384 may both have their other ends protruding outside the battery case 310. By doing so, the electricity generated inside the electrode assembly 360 can be supplied to the outside. Also, since the positive electrode tab 372 and the negative electrode tab 374 project in various directions respectively, the positive electrode lead 382 and the negative electrode lead 384 can also extend in various directions respectively. In one embodiment, the positive electrode lead 382 and the negative electrode lead 384 may have different materials. That is, the positive electrode lead 382 may be made of the same aluminum (Al) material as the positive electrode current collector, and the negative electrode lead 384 may be made of the same copper (Cu) material as the negative electrode current collector or a copper material coated with nickel (Ni). A part of the electrode lead 380 protruding outside the battery case 310 may serve as a terminal portion and may be electrically connected to an external terminal.

[0100] The insulating portion 390 can adhere the electrode lead 380 to the battery case 310 in a state where it is limited to and located at the seal portion 350 where the first case 320 and the second case 330 of the pouch-type battery case 310 are heat-sealed. Also, the insulating portion 390 can prevent the electricity generated from the electrode assembly 360 from flowing through the electrode lead 380 to the battery case 310 and can maintain the seal of the battery case 310. For this purpose, the insulating portion 390 may be manufactured from a non-conductive insulator having poor electrical conductivity. Generally, as the insulating portion 390, an insulating tape that is easy to attach to the electrode lead 380 and has a relatively thin thickness is often used, but it is not limited to this, and any member that insulates the electrode lead 380 may be used.

[0101] Hereinafter, the present invention will be described more specifically with specific examples. However, the following examples are merely illustrative for helping the understanding of the present invention and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea, and it is self-evident that such deformations and modifications are included in the appended claims.

Example

[0102] Examples and Comparative Examples Example 1 (Manufacture of Pouch Film Laminate) A polyethylene terephthalate film with a width of 266 mm, a length of 50 m, and a thickness of 12 μm and a nylon film with a width of 266 mm, a length of 50 m, and a thickness of 25 μm were laminated on one side of an aluminum alloy thin film with a width of 266 mm, a length of 50 m, and a thickness of 60 μm. An acid-modified polypropylene (PPa) with a width of 266 mm, a length of 50 m, and a thickness of 30 μm and an unstretched polypropylene (CPP) with a width of 266 mm, a length of 50 m, and a thickness of 50 μm were laminated on the other side to manufacture a pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / acid-modified polypropylene / unstretched polypropylene structure.

[0103] At this time, 8 vol% of a carbon fiber additive for improving the yield strength was added to the acid-modified polypropylene. After the acid-modified polypropylene was melted at a high temperature, it was extruded and laminated onto the aluminum alloy thin film and the unstretched polypropylene.

[0104] Here, the polyethylene terephthalate and nylon are the base material layers, the aluminum alloy thin film is the gas barrier layer, the acid-modified polypropylene is the first sealant layer, and the unstretched polypropylene is the second sealant layer.

[0105] Example 2 (Manufacture of Pouch Film Laminate) A pouch film laminate was manufactured in the same manner as in Example 1, except that 5 vol% of a carbon fiber additive for improving the yield strength was added to the first sealant layer.

[0106] Comparative Example 1 (Manufacture of Pouch Film Laminate) A pouch film laminate was manufactured in the same manner as in Example 1, except that no additive for improving the yield strength was added to the first sealant layer.

[0107] Comparative Example 2 (Manufacture of Pouch Film Laminate) A pouch film laminate was manufactured in the same manner as in Comparative Example 1, except that the thickness of the first sealant layer was formed to be 20 μm.

[0108] Comparative Example 3 (Manufacture of Pouch Film Laminate) A pouch film laminate was manufactured in the same manner as in Comparative Example 1, except that 10 vol% of a carbon fiber additive for improving the yield strength was added to the first sealant layer.

[0109] The materials and thicknesses of each layer of the pouch film laminates manufactured in Examples 1 to 2 and Comparative Examples 1 to 3 are as described in Table 1 below.

[0110]

Table 1

[0111] Experimental Example 1: Measurement of Yield Strength of Sealant Layer In the example or comparative example, after extruding the resin constituting each of the first sealant layer and the second sealant layer into a film shape, a stress-strain curve was measured to measure the yield strength of the first sealant layer and the second sealant layer. Then, using the measured yield strength, ΔY was calculated by the following formula 1. The values of the yield strength and ΔY are shown in Table 2 below.

[0112] [Equation 1] ΔY = {(Yield strength of the second sealant layer - Yield strength of the first sealant layer) / Yield strength of the first sealant layer} × 100

[0113] Experimental Example 2: Evaluation of Peel Strength between Gas Barrier Layer and Sealant Layer In the pouch film laminates manufactured in the examples and comparative examples, the peel strength between the gas barrier layer and the sealant layer was measured.

[0114] Specifically, as shown in FIG. 4, the 180-degree peel strength was measured by peeling the sealant layer from the pouch film laminate manufactured in the examples and comparative examples, respectively, and the average value of the strength in the 5-25 mm flat section was measured. The measurement results are shown in Table 2 below.

[0115] FIG. 4 shows a state of measuring the peel strength between the gas barrier layer and the sealant layer according to the present invention.

[0116] Experimental Example 3: Evaluation of the presence or absence of delamination between the first sealant layer and the second sealant layer When measuring the peel strength between the gas barrier layer and the sealant layer in Experimental Example 2, the presence or absence of delamination between the first sealant layer and the second sealant layer was visually confirmed. The measurement results are shown in Table 2 below.

[0117] Experimental Example 4: Evaluation of the breaking strength of the seal part Two pouch film laminates manufactured in the examples and comparative examples, respectively, were laminated so that the second sealant layer was in contact. Then, the sealant layer was sealed for 2 seconds under the conditions of a seal bar area of 200 mm × 10 mm, 180 ° C., and 0.4 MPa to form a seal part. Next, the sealed sample was cut to a width of 15 mm. Finally, as shown in FIG. 5, one end of each of the laminates laminated vertically in the cut sample was fastened to the upper / lower jigs of a measuring device (UTM, Zwick), and then pulled at a speed of 5 mm / min in the vertical direction to measure the maximum value of the tensile strength when the seal part was broken. The measurement results are shown in Table 2 below.

[0118] FIG. 5 shows a state of measuring the breaking strength of the seal part manufactured from the pouch film laminate according to the present invention.

[0119] The measurement results according to Experimental Examples 1 to 4 are as described in Table 2 below.

[0120]

Table 2

[0121] According to Experimental Example 1, ΔY was measured to be 82.5% in Example 1, 108.3% in Example 2, 125% in Comparative Example 1, 150% in Comparative Example 2, and 65.1% in Comparative Example 3. That is, ΔY in Examples 1 and 2 belongs to the numerical range of 66% to 120% which is the reference value of the present invention, while ΔY in Comparative Examples 1 to 3 was measured to deviate from the numerical range of 66% to 120% which is the reference value of the present invention.

[0122] On the other hand, the difference in yield strength between the first sealant layer and the second sealant layer was measured to be 6.6 N / 15 mm in Example 1, 7.8 N / 15 mm in Example 2, 8.5 N / 15 mm in Comparative Example 1, 9 N / 15 mm in Comparative Example 2, and 9.9 N / 15 mm in Comparative Example 3. That is, the difference in yield strength between the first sealant layer and the second sealant layer in Examples 1 and 2 was measured to be a value smaller than 8 N / 15 mm which is the reference value of the present invention, while the difference in yield strength between the first sealant layer and the second sealant layer in Comparative Examples 1 to 3 was measured to be a value larger than 8 N / 15 mm which is the reference value of the present invention.

[0123] According to Experimental Example 2, the peel strength between the gas barrier layer and the first sealant layer was measured to be 24 N / 15 mm in Example 1, 23.6 N / 15 mm in Example 2, 23 N / 15 mm in Comparative Example 1, 22 N / 15 mm in Comparative Example 2, and 20 N / 15 mm in Comparative Example 3. Therefore, the pouch-type battery case manufactured by heat-sealing the pouch film laminate of Examples 1 and 2 has a better seal strength than the pouch-type battery case manufactured by heat-sealing the pouch film laminate of Comparative Examples 1 to 3.

[0124] According to Experimental Example 3, in the pouch film laminates manufactured in Examples 1 and 2, no peeling was confirmed between the first sealant layer and the second sealant layer, while in the pouch film laminates manufactured in Comparative Examples 1 to 3, peeling was confirmed between the first sealant layer and the second sealant layer. Therefore, the pouch-type battery case manufactured by heat-sealing the pouch film laminate of Examples 1 and 2 has a better seal strength than the pouch-type battery case manufactured by heat-sealing the pouch film laminate of Comparative Examples 1 to 3.

[0125] According to Experimental Example 4, the breaking strength of the seal part manufactured using the pouch film laminates of Examples 1 and 2 was measured to be significantly higher at both 25°C and 60°C compared to the breaking strength of the seal part manufactured using the pouch film laminates of Comparative Examples 1 to 3. Therefore, the pouch-type battery case manufactured by thermally sealing the pouch film laminates of Examples 1 and 2 has a better sealing strength than the pouch-type battery case manufactured by thermally sealing the pouch film laminates of Comparative Examples 1 to 3.

Explanation of Signs

[0126] 100 Pouch film laminate 110 Base material layer 120 Gas barrier layer 130 Sealant layer 132 First sealant layer 134 Second sealant layer 210 Seal part 300 Secondary battery 310 Pouch-type battery case 320 First case 322 Cup part 324 Accommodation space 330 Second case 332 Cup part 340 Bridge part 350 Seal part 360 Electrode assembly 370 Electrode tab 372 Positive electrode tab 374 Negative electrode tab 380 Electrode lead 382 Positive electrode lead 384 Negative electrode lead 390 Insulating part

Claims

1. In a pouch film laminate in which a base material layer, a gas barrier layer, and a sealant layer are sequentially laminated, the sealant layer includes: a first sealant layer disposed adjacent to the gas barrier layer; and a second sealant layer laminated on the first sealant layer wherein the yield strength of the first sealant layer is less than the yield strength of the second sealant layer, and the difference between the yield strength of the first sealant layer and the yield strength of the second sealant layer is 8 N / 15 mm or less. A pouch film laminate.

2. The yield strength of the first sealant layer is 7 N / 15 mm to 15 N / 15 mm. The pouch film laminate according to claim 1.

3. The yield strength of the second sealant layer is 10 N / 15 mm to 30 N / 15 mm. The pouch film laminate according to claim 1.

4. The ratio of the thickness of the first sealant layer to the thickness of the second sealant layer is 1:0.3 to 1:

3. The pouch film laminate according to claim 1.

5. The thickness of the first sealant layer is 10 μm to 60 μm. The pouch film laminate according to claim 1.

6. The thickness of the second sealant layer is 20 μm to 70 μm. The pouch film laminate according to claim 1.

7. The first sealant layer and the second sealant layer contain polypropylene. The pouch film laminate according to claim 1.

8. The first sealant layer and / or the second sealant layer further contains at least one of carbon fiber, glass fiber, and aramid fiber. The pouch film laminate according to claim 7.

9. The gas barrier layer contains aluminum. The pouch film laminate according to claim 1.

10. The peel strength between the gas barrier layer and the first sealant layer exceeds 23 N / 15 mm. The pouch film laminate according to claim 1.

11. A pouch-type battery case including the pouch film laminate according to any one of claims 1 to 10; and A secondary battery including an electrode assembly housed inside the pouch-type battery case.

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