Pouch film laminate, pouch-type battery case, and pouch-type secondary battery

Abstract

To provide a pouch film laminate for preparing a pouch type battery case accommodating an electrode assembly.SOLUTION: A pouch film laminate of the present invention includes a sealant layer composed of a first polymer as an innermost layer, a surface protection layer composed of a second polymer as an outermost layer, and a gas barrier layer that includes an aluminum alloy thin film and is laminated between the surface protection layer and the sealant layer, as well as an elongation support layer that is composed of a third polymer and is laminated between the surface protection layer and the gas barrier layer. The pouch film laminate has a total thickness of 160 μm-200 μm. The thickness of the sealant layer is 1 to 2 times the thickness of the gas barrier layer. The ratio of the thickness of the elongation support layer to the thickness of the gas barrier layer is 1: 1.5-1: 2.5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0069917, filed on June 9, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a pouch film laminate, a pouch-type battery case, and a pouch-type secondary battery, and more particularly to a pouch film laminate, a pouch-type battery case, and a pouch-type secondary battery that have improved tensile strength and elongation and thereby improved formability. [Background technology]

[0003] Generally, types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, lithium-ion polymer batteries, etc. These secondary batteries are used not only in small products such as digital cameras, DVD players, MP3 players, mobile phones, PDAs, portable game devices, power tools, and electric bicycles, but also in large products requiring high output such as electric vehicles and hybrid vehicles, as well as in power storage devices and backup power storage devices that store surplus generated power and new renewable energy.

[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 form a positive electrode and a negative electrode, which are then stacked on both sides of a separator to form an electrode assembly of a predetermined shape.The electrode assembly is then placed in a battery case, an electrolyte is injected, and the battery case is sealed.

[0005] Secondary batteries are divided into pouch types and can types depending on the material of the case that houses the electrode assembly. Pouch types house the electrode assembly in a pouch made of a flexible polymer material, while can types house the electrode assembly in a case made of metal or plastic.

[0006] The pouch, which is the case of a pouch-type secondary battery, is manufactured by pressing a flexible pouch film laminate to form a cup portion. Once the cup portion is formed, an electrode assembly is placed in the receiving space of the cup portion and the sealing portion is sealed to manufacture the secondary battery.

[0007] Among these press processes, drawing is performed by inserting a pouch film into a press and applying pressure to the pouch film laminate with a punch, stretching the pouch film. Pouch film laminates are typically formed from multiple layers, with a polymer film such as polyethylene terephthalate laminated on one side of a metal gas barrier layer and a sealant layer laminated on the other side. The gas barrier layer is typically an aluminum metal alloy thin film approximately 40 μm thick. However, such conventional pouch film laminates have poor formability, limiting the depth of the cup. They also limit the reduction in filleting radius when filleting the bottom and opening corners of the cup. Furthermore, they also limit the ability to form the outer wall of the cup nearly vertically. This increases dead space in the secondary battery, reducing the size of the electrode assembly and resulting in reduced energy efficiency relative to the volume. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a pouch film laminate, a pouch-type battery case, and a pouch-type secondary battery that have improved tensile strength and elongation and excellent formability.

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

[0010] In order to solve the above problem, a pouch film laminate according to an embodiment of the present invention includes a sealant layer made of a first polymer and formed as the innermost layer, a surface protective layer made of a second polymer and formed as the outermost layer, and a gas barrier layer including an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm, laminated between the surface protective layer and the sealant layer, wherein the gas barrier layer has a thickness of 50 to 70 μm, and the sealant layer has a thickness of 70 to 100 μm.

[0011] The aluminum alloy thin film may be an aluminum alloy thin film of alloy number AA8021.

[0012] The aluminum alloy may contain 1.3 wt % to 1.7 wt % of iron.

[0013] The aluminum alloy may also contain silicon in an amount of 0.2 wt% or less.

[0014] The gas barrier layer may have a thickness of 55 μm to 65 μm.

[0015] The sealant layer may have a thickness of 75 μm to 85 μm.

[0016] The first polymer may also include polypropylene (PP).

[0017] The surface protection layer may have a thickness of 5 μm to 25 μm.

[0018] The surface protection layer may have a thickness of 7 μm to 12 μm.

[0019] The second polymer can also include polyethylene terephthalate (PET).

[0020] The film may further include a stretching assist layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer.

[0021] The stretching auxiliary layer may have a thickness of 20 μm to 50 μm.

[0022] The stretching auxiliary layer may have a thickness of 25 μm to 38 μm.

[0023] The thickness ratio of the stretching-assisting layer to the gas barrier layer may be 1:1.5 to 1:2.5.

[0024] The third polymer may also include nylon.

[0025] The pouch film laminate may have a total thickness of 160 μm to 200 μm, preferably 170 μm to 200 μm, and more preferably 180 μm to 200 μm. The pouch film laminate may have a tensile strength of 200 N / 15 mm to 300 N / 15 mm and an elongation of 120% to 150%, as measured after being cut into a size of 15 mm x 80 mm and pulled at a pulling rate of 50 mm / min.

[0026] A pouch-type battery case according to an embodiment of the present invention for solving the above problems is a pouch-type battery case that houses an electrode assembly and is manufactured by molding a pouch film laminate, wherein the pouch film laminate includes a sealant layer made of a first polymer and formed as the innermost layer, a surface protective layer made of a second polymer and formed as the outermost layer, and a gas barrier layer that includes an aluminum alloy thin film with a crystal grain size of 10 μm to 13 μm and is laminated between the surface protective layer and the sealant layer, wherein the gas barrier layer has a thickness of 50 μm to 70 μm and the sealant layer has a thickness of 70 μm to 100 μm.

[0027] A pouch-type secondary battery according to an embodiment of the present invention for solving the above problems includes an electrode assembly formed by laminating a positive electrode, a separator, and a negative electrode, and a pouch-type battery case that houses the electrode assembly, wherein the pouch-type battery case is manufactured by molding a pouch film laminate, and the pouch film laminate includes: a sealant layer made of a first polymer and formed as an innermost layer; a surface protective layer made of a second polymer and formed as an outermost layer; and a gas barrier layer that includes an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm and is laminated between the surface protective layer and the sealant layer, wherein the gas barrier layer has a thickness of 50 μm to 70 μm, and the sealant layer has a thickness of 70 μm to 100 μm.

[0028] Further details of the invention are included in the detailed description and drawings. [Effects of the Invention]

[0029] According to the embodiment of the present invention, at least the following effects are obtained.

[0030] The pouch film laminate according to the present invention has excellent tensile strength, elongation, and toughness due to the gas barrier layer and sealant layer meeting specific thicknesses and the use of an aluminum alloy thin film with a specific crystal grain size as the gas barrier layer. As a result, when using the pouch film laminate according to the present invention, the molding depth can be increased without generating pinholes or cracks during the molding of the cup section, especially during the molding of the two cup sections, and the curvature radius of the cup section corners can be reduced, thereby increasing the volume of the storage space for the battery assembly.

[0031] The effects of the present invention are not limited to the examples given above, and various other effects are included in this specification. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is an assembly diagram of a secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a pouch film according to one embodiment of the present invention. [Figure 3] 1 is a graph showing the iron and silicon contents of aluminum alloys with alloy number AA8079 and aluminum alloys with alloy number AA8021. [Figure 4] 1 is a graph showing the changes in tensile strength, elongation, and grain size depending on the iron content of an aluminum alloy having alloy number AA8079 and an aluminum alloy having alloy number AA8021. [Figure 5] 1 is an SEM photograph showing enlarged crystal grains of an aluminum alloy with alloy number AA8079 and an aluminum alloy with alloy number AA8021. DETAILED DESCRIPTION OF THE INVENTION

[0033] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided to fully disclose the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined only by the scope of the claims. The same reference symbols refer to the same elements throughout the specification.

[0034] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0035] The terms used in this specification are for the purpose of describing embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise stated in the phrase. The words "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0036] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] FIG. 1 is an assembly diagram of a secondary battery 1 according to one embodiment of the present invention.

[0038] According to one embodiment of the present invention, the tensile strength and elongation of the pouch film laminate 135 are improved, thereby increasing toughness and improving formability when molding the pouch film laminate 135 to manufacture a pouch-type battery case 13.

[0039] Pouch film laminate 135 according to one embodiment of the present invention includes sealant layer 1351 made of a first polymer and formed as the innermost layer, surface protective layer 1353 made of a second polymer and formed as the outermost layer, and gas barrier layer 1352, which includes an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm, laminated between surface protective layer 1353 and sealant layer 1351. In this case, gas barrier layer 1352 has a thickness of 50 μm to 70 μm, and sealant layer 1351 has a thickness of 70 μm to 100 μm. In particular, it is preferable that gas barrier layer 1352 has a thickness of 55 μm to 65 μm, and sealant layer 1351 has a thickness of 75 μm to 85 μm.

[0040] In accordance with one embodiment of the present invention, a pouch-type battery case 13 is provided, housing an electrode assembly, by forming a pouch film laminate 135. The pouch film laminate 135 includes a sealant layer 1351 formed as an innermost layer using a first polymer, a surface protective layer 1353 formed as an outermost layer using a second polymer, and a gas barrier layer 1352 formed between the surface protective layer and the sealant layer, the gas barrier layer 1352 including an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm. The gas barrier layer 1352 is preferably 50 to 70 μm thick, and the sealant layer is preferably 70 to 100 μm thick. It is particularly preferred that the gas barrier layer 1352 be 55 to 65 μm thick, and the sealant layer be 75 to 85 μm thick.

[0041] Furthermore, a secondary battery 1 according to one embodiment of the present invention includes an electrode assembly 10 formed by stacking a positive electrode, a separator, and a negative electrode, and a pouch-type battery case 13 that houses the electrode assembly 10. The battery case 13 is manufactured by molding a pouch film laminate 135. The pouch film laminate 135 includes a sealant layer 1351 made of a first polymer and formed as an innermost layer, a surface protective layer 1353 made of a second polymer and formed as an outermost layer, and a gas barrier layer 1352 that includes an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm and is laminated between the surface protective layer 1353 and the sealant layer 1351. The gas barrier layer 1352 has a thickness of 50 to 70 μm, and the sealant layer 1351 has a thickness of 70 to 100 μm. In particular, it is preferable that the gas barrier layer 1352 has a thickness of 55 to 65 μm, and the sealant layer 1351 has a thickness of 75 to 85 μm.

[0042] The electrode assembly 10 is formed by alternately stacking electrodes and separators. First, a slurry containing an electrode active material, a binder, and / or a conductive material is applied to a positive electrode current collector and a negative electrode current collector to form a positive electrode and a negative electrode, which are then stacked on both sides of a separator to form the electrode assembly 10 of a predetermined shape. The electrode assembly 10 is then inserted into a battery case 13, an electrolyte is injected, and the case is sealed.

[0043] Specifically, the electrode assembly 10 includes two electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate them from each other. Such electrode assemblies 10 include stack, jelly roll, and stack-and-fold types. The two electrodes, i.e., the positive electrode and the negative electrode, are each constructed by applying an active material slurry to an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper. The slurry is typically formed by stirring particulate active material, auxiliary conductor, binder, and conductive material in a solvent. The solvent is removed in a subsequent process.

[0044] As shown in FIG. 1, the electrode assembly 10 includes electrode tabs 11. The electrode tabs 11 are connected to the positive and negative electrodes of the electrode assembly 10, respectively, and protrude from the electrode assembly 10 to provide a path for electrons to move between the inside and outside of the electrode assembly 10. The electrode current collector of the electrode assembly 10 is composed of a portion coated with an electrode active material and an end portion, i.e., a plain portion, where the electrode active material is not coated. The electrode tabs 11 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion using ultrasonic welding or the like. The electrode tabs 11 may protrude in different directions from the electrode assembly 10 as shown in FIG. 1, but are not limited thereto and may protrude in various directions, such as protruding in parallel from one side in the same direction.

[0045] An electrode lead 12 that supplies electricity to the outside of the secondary battery 1 is connected to the electrode tab 11 of the electrode assembly 10 by spot welding or the like. A portion of the electrode lead 12 is surrounded by an insulating portion 14. The insulating portion 14 is located only at a sealing portion 134 where the first case 131 and the second case 132 of the battery case 13 are thermally sealed, and adheres the electrode lead 12 to the battery case 13. The insulating portion 14 also prevents electricity generated from the electrode assembly 10 from flowing to the battery case 13 via the electrode lead 12, thereby maintaining the sealing of the battery case 13. Therefore, the insulating portion 14 is made of a non-conductive material that does not allow electricity to pass through easily. Typically, the insulating portion 14 is made of a relatively thin insulating tape that is easily attached to the electrode lead 12. However, the insulating portion 14 is not limited to this, and various materials may be used as long as they can insulate the electrode lead 12.

[0046] The electrode lead 12 has one end connected to the electrode tab 11 and the other end protruding out of the battery case 13. That is, the electrode lead 12 includes a positive electrode lead 121 having one end connected to the positive electrode tab 111 and extending in the direction in which the positive electrode tab 111 protrudes, and a negative electrode lead 122 having one end connected to the negative electrode tab 112 and extending in the direction in which the negative electrode tab 112 protrudes. Meanwhile, as shown in FIG. 1 , the other ends of both the positive electrode lead 121 and the negative electrode lead 122 protrude out of the battery case 13. This allows electricity generated inside the electrode assembly 10 to be supplied to the outside. In addition, since the positive electrode tab 111 and the negative electrode tab 112 protrude in different directions, the positive electrode lead 121 and the negative electrode lead 122 can also extend in different directions.

[0047] The positive electrode lead 121 and the negative electrode lead 122 may be made of different materials. That is, the positive electrode lead 121 may be made of the same aluminum (Al) material as the positive electrode current collector, and the negative electrode lead 122 may be made of the same copper (Cu) material as the negative electrode current collector or a copper material coated with nickel (Ni). In addition, a portion of the electrode lead 12 protruding outside the battery case 13 serves as a terminal portion and is electrically connected to an external terminal.

[0048] The battery case 13 is a pouch made of a flexible material that houses the electrode assembly 10. Hereinafter, the battery case 13 will be described as a pouch. When a flexible pouch film laminate 135 is drawn using a punch or the like, a portion of the laminate is stretched to form a cup portion 133 that includes a bag-shaped storage space 1331, thereby manufacturing the battery case 13.

[0049] The battery case 13 accommodates and seals the electrode assembly 10 such that a portion of the electrode lead 12, i.e., a terminal portion, is exposed. As shown in FIG. 1, the battery case 13 includes a first case 131 and a second case 132. The first case 131 is formed with a cup portion 133 and is provided with an accommodation space 1331 in which the electrode assembly 10 can be accommodated, and the second case 132 covers the accommodation space 1331 from above to prevent the electrode assembly 10 from falling out of the battery case 13. The first case 131 and the second case 132 may be manufactured with one side connected to each other as shown in FIG. 1, but the present invention is not limited thereto and may be manufactured in various ways, such as being separated and separately manufactured.

[0050] When forming the cup portions 133 in the pouch film laminate 135, two cup portions 133 that are symmetrical with respect to one pouch film laminate 135 can be drawn adjacent to each other. As a result, as shown in FIG. 1 , a cup portion 133 is formed in each of the first case 131 and the second case 132. After the electrode assembly 10 is accommodated in the accommodation space 1331 formed in the cup portion 133 of the first case 131, the bridge 136 formed between the two cup portions 133 in the battery case 13 can be folded so that the two cup portions 133 face each other. As a result, the cup portion 133 of the second case 132 accommodates the electrode assembly 10 from above as well. Therefore, since two cup portions 133 accommodate one electrode assembly 10, an electrode assembly 10 that is thicker than when there is only one cup portion 133 can be accommodated. Furthermore, since one corner of the secondary battery 1 is formed by folding the battery case 13, the number of corners to be sealed in the subsequent sealing process can be reduced, thereby improving the process speed and reducing the number of sealing processes.

[0051] After the electrode lead 12 is connected to the electrode tab 11 of the electrode assembly 10 and an insulating portion 14 is formed on a portion of the electrode lead 12, the electrode assembly 10 is accommodated in the accommodation space 1331 formed in the cup portion 133 of the first case 131, and the second case 132 covers the space from above. An electrolyte is then injected into the accommodation space 1331, and the sealing portion 134 formed on the edges of the first case 131 and the second case 132 is sealed. The electrolyte is used to transport lithium ions generated by an electrochemical reaction of the electrodes during charging and discharging of the secondary battery 1. It may include a non-aqueous organic electrolyte solution, which is a mixture of lithium salt and organic solvents, or a polymer using a polymer electrolyte. The electrolyte may also include a sulfide-based, oxide-based, or polymer-based solid electrolyte, which may be flexible and easily deformed by external forces. A pouch-type secondary battery 1 may be manufactured using this method.

[0052] FIG. 2 is a cross-sectional view of a pouch film laminate 135 according to one embodiment of the present invention.

[0053] The pouch, which is the battery case 13 of the pouch-type secondary battery 1 according to one embodiment of the present invention, is manufactured by drawing a pouch film laminate 135. That is, the pouch film laminate 135 is stretched using a punch or the like to form a cup portion 133. According to one embodiment of the present invention, the pouch film 135 includes a sealant layer 1351, a gas barrier layer 1352, a surface protection layer 1353, and a drawing assistance layer 1354, as shown in FIG.

[0054] The sealant layer 1351 is made of a first polymer and is formed as the innermost layer, directly contacting the electrode assembly 10. Here, the innermost layer refers to the layer located last relative to the gas barrier layer 1352 in the direction toward which the electrode assembly 10 is located. The pouch is manufactured by drawing the pouch film laminate 135 having the above-described laminated structure using a punch or the like, thereby stretching a portion and forming a cup portion 133 including a bag-shaped receiving space 1331. Once the electrode assembly 10 is placed inside the receiving space 1331, an electrolyte is injected. The first case 131 and the second case 132 are then brought into contact with each other, and the sealing portion 134 is thermocompressed to bond the sealant layers 1351 together, thereby sealing the pouch. Since the sealant layer 1351 is in direct contact with the electrode assembly 10, it must be insulating. Since it also comes into contact with the electrolyte, it must be corrosion-resistant. Furthermore, since the interior must be completely sealed to prevent the transfer of materials between the interior and exterior, high sealing performance is required. That is, the sealing portion 134, where the sealant layers 1351 are bonded together, must have excellent thermal adhesive strength. Generally, the first polymer used to manufacture the sealant layer 1351 may be one or more materials 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, and glass fiber. In particular, polyolefin resins such as polypropylene (PP) or polyethylene (PE) are commonly used. Polypropylene (PP) is primarily used to manufacture the sealant layer 1351 because of its excellent mechanical properties, such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, as well as its excellent chemical properties, such as corrosion resistance. Furthermore, it may be made of oriented polypropylene (cation polypropylene), acid-modified polypropylene, or polypropylene-butylene-ethylene terpolymer.Here, the acid-treated polypropylene may be MAH PP (maleic anhydride polypropylene). Also, the sealant layer 1351 may have a single film structure made of one material or a mixed film structure made of two or more materials each forming a layer.

[0055] According to one embodiment of the present invention, the thickness of sealant layer 1351 may be 70 to 100 μm, and preferably 75 to 85 μm. If the thickness of sealant layer 1351 is thinner than 70 μm, there is a problem of reduced sealing durability, such as internal breakage during sealing. Furthermore, if the thickness of sealant layer 1351 is thicker than 100 μm, the overall thickness of the pouch becomes excessively thick, which may actually reduce the energy density relative to the volume of secondary battery 1.

[0056] Meanwhile, the thickness of the sealant layer 1351 may be 1 to 2 times, preferably 1.1 to 1.8 times, and more preferably 1.2 to 1.5 times, the thickness of the barrier layer (described below). When the thickness ratio of the sealant layer to the barrier layer satisfies this range, a pouch film laminate with excellent sealing durability and formability can be obtained. If the thickness of the sealant layer is smaller than that of the barrier layer, sealing durability and insulation properties may be adversely affected. If the sealant layer is too thick, formability may be reduced, and the space available to accommodate the electrode assembly may be reduced, resulting in a decrease in energy density.

[0057] The gas barrier layer 1352 is laminated between the surface protective layer 1353 and the sealant layer 1351 to ensure the mechanical strength of the pouch, block the ingress and egress of gas or moisture from the secondary battery 1, and prevent electrolyte leakage. The gas barrier layer 1352 is made of metal. In particular, the gas barrier layer 1352 according to one embodiment of the present invention may be made of an aluminum alloy thin film having a grain size of 10 to 13 μm, preferably 10.5 to 12.5 μm, and more preferably 11 to 12 μm. Aluminum can ensure a certain level of mechanical strength, is lightweight, and can complement the electrochemical properties of the electrode assembly 10 and the electrolyte, as well as provide heat dissipation. The thickness of the gas barrier layer may be 50 μm to 70 μm, and preferably 55 μm to 65 μm.

[0058] Conventionally, a gas barrier layer has generally been formed using an aluminum alloy thin film having a thickness of approximately 30 to 50 μm, particularly 40 μm. When the gas barrier layer has a thickness of 30 to 50 μm, the gas barrier layer may be broken if the cup portion 133 is drawn deeply during drawing, which limits the increase in drawing depth. In addition, it is difficult to draw the outer wall of the cup portion 133 nearly vertically, which limits the reduction in the filleting curvature radius of the corner of the cup portion 133.

[0059] Increasing the thickness of the gas barrier layer can have the effect of increasing the molding depth, but this not only increases manufacturing costs but also increases the overall thickness of the pouch, resulting in a problem of reduced energy density per volume of the secondary battery 1. Simply increasing the thickness of the aluminum alloy thin film alone can increase the molding depth, but pinholes and cracks may occur in the aluminum alloy thin film after molding, resulting in problems with sealing durability. Increasing the thickness of the gas barrier layer and decreasing the thickness of the sealant layer in order to reduce the overall thickness of the pouch also results in a problem of reduced sealing durability.

[0060] Therefore, as a result of extensive research, the inventors have found that when an aluminum alloy thin film having a specific crystal grain size is used as the material for the gas barrier layer and the thicknesses of the gas barrier layer and sealant layer are controlled within a specific range, it is possible to form a deep cup portion and maintain excellent sealing durability, which has led to the completion of the present invention.

[0061] Specifically, the gas barrier layer 1352 according to the present invention comprises an aluminum alloy thin film having a crystal grain size of 10 μm to 13 μm, preferably 10.5 to 12.5 μm, and more preferably 11 to 12 μm. When the crystal grain size of the aluminum alloy thin film satisfies this range, the forming depth can be increased without the occurrence of pinholes or cracks during cup forming. If the crystal grain size of the aluminum alloy thin film exceeds 13 μm, the strength of the aluminum alloy thin film decreases, making it difficult to disperse internal stress during stretching, increasing the occurrence of cracks and pinholes. If the crystal grain size is less than 10 μm, the flexibility of the aluminum alloy thin film decreases, limiting the improvement of formability.

[0062] Meanwhile, the grain size varies depending on the composition of the aluminum alloy thin film and the processing method of the aluminum alloy thin film, and can be measured by observing a cross section of the aluminum alloy thin film in the thickness direction using a scanning electron microscope (SEM). Specifically, in the present invention, a cross section SEM image of the aluminum alloy thin film in the thickness direction was obtained using a scanning electron microscope, and the maximum diameters of 30 randomly selected grains among the grains observed in the SEM image were measured, and the average value of these was evaluated as the grain size.

[0063] Meanwhile, the aluminum alloy thin film according to the present invention may contain metal elements other than aluminum, for example, one or more selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0064] The iron (Fe) content of the aluminum alloy thin film can be 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, and more preferably 1.3 wt% to 1.45 wt%. If the iron (Fe) content in the aluminum alloy thin film is less than 1.2 wt%, the strength of the aluminum alloy thin film will decrease, and cracks and pinholes may occur during forming. If the iron (Fe) content exceeds 1.7 wt%, the flexibility of the aluminum alloy thin film will decrease, and there will be a limit to the improvement of formability.

[0065] The silicon (Si) content of the aluminum alloy thin film may be 0.2 wt% or less, preferably 0.05 to 0.2 wt%, more preferably 0.08 to 0.19 wt%, and even more preferably 0.1 to 1.18 wt%. If the silicon content exceeds 0.2 wt%, formability may decrease.

[0066] Specifically, the aluminum alloy thin film according to the present invention can be an aluminum alloy with alloy number AA8021.

[0067] FIG. 3 is a graph showing the iron and silicon contents of aluminum alloys with alloy number AA8079 and aluminum alloys with alloy number AA8021.

[0068] When an aluminum alloy contains a large amount of iron, its mechanical strength improves, while when the iron content is small, its flexibility improves. As shown in Figure 3, alloy number AA8079 contains 0.6 wt% to 1.2 wt% iron and 0.3 wt% or less silicon. That is, when the gas barrier layer 1352 is manufactured using an aluminum alloy with alloy number AA8079, the relatively small amount of iron improves flexibility, but the strength decreases, and formability may be limited.

[0069] Meanwhile, among aluminum alloys, alloy number AA8021 may contain 1.2 wt% to 1.7 wt%, particularly 1.3 wt% to 1.7 wt%, of iron, and 0.2 wt% or less of silicon, as shown in Figure 3. When the gas barrier layer 1352 is manufactured using such an aluminum alloy with alloy number AA8021, the tensile strength and elongation rate can be improved due to the relatively high iron content.

[0070] On the other hand, when a tensile force is applied to a material, the relationship between tensile strength and elongation can be shown in a graph. In this case, if the vertical axis of the graph represents tensile strength and the horizontal axis represents elongation, the area under the graph represents the toughness of the material. Toughness indicates the material's ability to withstand fracture; the higher the toughness, the more the material can be stretched before breaking.

[0071] Therefore, when the gas barrier layer 1352 is manufactured using the aluminum alloy of alloy number AA8021, the tensile strength and elongation are improved, which increases toughness and improves formability.

[0072] FIG. 4 is a graph showing the changes in tensile strength (Rm), elongation (A), and grain size (grain) depending on the iron content of aluminum alloys with alloy numbers AA8079 and AA8021.

[0073] As shown in Figure 4, AA8079 has limited formability due to its low tensile strength and elongation, and its relatively large grain size of 13 to 21 μm means that internal stress is not sufficiently dispersed during stretching, resulting in the formation of many pinholes.

[0074] Meanwhile, AA8021 has high tensile strength and elongation, making it excellent in formability, and its relatively small grain size of 10-13 μm allows for better dispersion of internal stress during stretching, effectively suppressing the occurrence of pinholes. Therefore, when the gas barrier layer 1352 is manufactured using an aluminum alloy with alloy number AA8021, a pouch film laminate with excellent formability and sealing durability can be manufactured.

[0075] Meanwhile, the gas barrier layer 1352 may have a thickness of 50 μm to 70 μm, and preferably 55 μm to 65 μm. When the thickness of the gas barrier layer is within this range, the formability of the gas barrier layer 1352 is improved, and the cup portion 133 can be formed deeper when the pouch film 135 is drawn. The outer wall of the cup portion 133 becomes nearly vertical, and the radius of curvature of the corners of the cup portion 133 can also be reduced. This increases the volume of the receiving space 1331, allowing more electrodes and separators to be stacked in the electrode assembly 10 to be accommodated therein, thereby improving energy efficiency relative to the volume. Furthermore, the manufacturing cost does not increase significantly, and the overall thickness of the pouch does not increase significantly even if the thickness of the sealant layer 1351 is not reduced, and sealing durability does not decrease.

[0076] The surface protective layer 1353 is made of a second polymer and is formed as the outermost layer. It protects the secondary battery 1 from external friction and impact and electrically insulates the electrode assembly 10 from the outside. Here, the outermost layer refers to the layer located last in the opposite direction from the gas barrier layer 1352 toward the electrode assembly 10. The second polymer forming the surface protective layer 1353 may be one or more materials 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, and glass fiber. In particular, it is preferable to use a polymer such as polyethylene terephthalate (PET), which has wear resistance and heat resistance. The surface protective layer 1353 may have a single film structure made of any one material or a mixed film structure formed by layers of two or more materials.

[0077] According to one embodiment of the present invention, the thickness of the surface protective layer 1353 may be 5 to 25 μm, and preferably 7 to 12 μm. If the thickness of the surface protective layer 1353 is thinner than 5 μm, there is a problem of reduced external insulation. Conversely, if the thickness of the surface protective layer 1353 is thicker than 25 μm, the overall thickness of the pouch becomes thick, which may actually reduce the energy density relative to the volume of the secondary battery 1.

[0078] On the other hand, PET is inexpensive, durable, and has excellent electrical insulation properties, but it has poor adhesion to aluminum, which is often used for the gas barrier layer 1352, and the behavior of the two materials when stretched by applying stress differs. Therefore, if the surface protective layer 1353 and the gas barrier layer 1352 are directly bonded, the surface protective layer 1353 and the gas barrier layer 1352 may peel off during drawing. This can lead to problems such as the gas barrier layer 1352 not being stretched uniformly, reducing formability.

[0079] According to one embodiment of the present invention, the battery case 13 may further include a stretching assist layer 1354 made of a third polymer and laminated between the surface protective layer 1353 and the gas barrier layer 1352. The stretching assist layer 1354 is laminated between the surface protective layer 1353 and the gas barrier layer 1352 to prevent peeling between the surface protective layer 1353 and the gas barrier layer 1352 when they are stretched. The third polymer used to form the stretching assist layer 1354 may be one or more materials 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, and glass fiber. In particular, nylon resin is preferably used as the third polymer because it easily adheres to the polyethylene terephthalate (PET) of the surface protective layer 1353 and behaves similarly when stretched to the aluminum alloy of the gas barrier layer 1352. In addition, the stretching assisting layer 1354 may have a single film structure made of any one material, or a mixed film structure made of layers of two or more materials.

[0080] Conventionally, the gas barrier layer 1352 has a thickness of approximately 40 μm, and the stretching auxiliary layer 1354 has a correspondingly thin thickness of approximately 15 μm. That is, the thickness ratio of the stretching auxiliary layer 1354 to the gas barrier layer 1352 was 1:2.67, and the thickness ratio of the gas barrier layer 1352 was considerably high. However, as described above, according to one embodiment of the present invention, the gas barrier layer 1352 has a thickness of approximately 50 to 70 μm, particularly 55 to 65 μm, thereby improving the formability of the gas barrier layer 1352. In this case, to improve the formability of the stretching auxiliary layer 1354 as well, the stretching auxiliary layer 1354 preferably has a thickness of 20 to 50 μm, preferably 25 to 38 μm, and more preferably 27 to 35 μm. If the stretching auxiliary layer 1354 is thinner than 20 μm, it will not be able to accommodate the improved formability of the gas barrier layer 1352 and may be damaged during stretching. Conversely, if the thickness is greater than 50 μm, the overall thickness of the pouch increases, which may increase the volume of the secondary battery 1 and reduce the energy density. In particular, according to one embodiment of the present invention, the thickness ratio of the stretching aid layer 1354 to the gas barrier layer 1352 may be less than 1:2.5. That is, the thickness ratio of the stretching aid layer 1354 may be greater than in the past. However, because an excessively thick stretching aid layer 1354 increases the overall thickness of the pouch, it is preferable that the thickness ratio be greater than 1:1.5. That is, the thickness ratio may be 1:1.5 to 1:2.5, preferably 1:1.7 to 1:2.3, and more preferably 1:1.8 to 1:2.1.

[0081] Meanwhile, the pouch film laminate according to the present invention may have a total thickness of 160 μm to 200 μm, preferably 180 μm to 200 μm. When the thickness of the pouch film laminate satisfies this range, it is possible to minimize the reduction in battery accommodating space and the deterioration of sealing durability due to an increase in the thickness of the pouch laminate, and to increase the molding depth.

[0082] On the other hand, the pouch film laminate according to the present invention has excellent tensile strength and elongation. Specifically, the pouch film laminate according to the present invention, after being cut into a size of 15 mm x 80 mm, has a tensile strength of 200 N / 15 mm to 300 N / 15 mm, preferably 210 N / 15 mm to 270 N / 15 mm, and more preferably 220 N / 15 mm to 250 N / 15 mm, as measured at a pulling rate of 50 mm / min, and an elongation of 120% to 150%, preferably 120% to 140%, and even more preferably 120% to 130%. Thus, the pouch film laminate according to the present invention has high tensile strength and elongation, which increases toughness and reduces the occurrence of cracks during cup molding, even when the molding depth is large.

[0083] The pouch-type battery case 13 manufactured by molding such a pouch film laminate 135 has improved moldability, allowing the cup portion 133 to be formed deeper, the outer wall of the cup portion 133 to be nearly vertical, and the radius of curvature of the corners of the cup portion 133 to be reduced, making it possible to accommodate a larger and thicker electrode assembly 10. Therefore, the secondary battery 1 manufactured using such a battery case 13 can have improved energy efficiency relative to its volume.

[0084] The present invention will be described in more detail below with reference to specific examples.

[0085] Example 1 A nylon film measuring 266 mm wide, 50 mm long, and 60 μm thick with a grain size of 11.6 μm, and a polyethylene terephthalate (PET) film measuring 266 mm wide, 50 mm long, and 25 μm thick were laminated on one side of an AA8021 aluminum (Al) alloy thin film with a width of 266 mm, a length of 50 mm, and a thickness of 25 μm, and a polyethylene terephthalate (PET) film measuring 266 mm wide, a length of 50 mm, and a thickness of 12 μm were laminated on the other side, to produce a pouch film laminate with a PET / nylon / aluminum alloy thin film / CPP structure.

[0086] The nylon and PET films were bonded together using a urethane adhesive by dry lamination, and the CPP was melted at high temperature and then co-extruded onto the aluminum alloy. The aluminum alloy served as the gas barrier layer, the PET as the surface protection layer, the nylon as the stretching auxiliary layer, and the CPP as the sealant layer.

[0087] Example 2 A pouch film laminate was manufactured in the same manner as in Example 1, except that a nylon film having a thickness of 30 μm was used as the stretching assist layer and a polyethylene terephthalate (PET) film having a thickness of 7 μm was used as the surface protective layer.

[0088] Example 3 A pouch film laminate was produced in the same manner as in Example 1, except that a polyethylene terephthalate (PET) film having a thickness of 7 μm was used as the surface protective layer.

[0089] Comparative Example 1 A pouch film laminate was produced in the same manner as in Example 1, except that a 40 μm thick aluminum alloy thin film was used as the gas barrier layer and a 15 μm thick nylon film was used as the stretching assist layer.

[0090] Comparative Example 2 A pouch film laminate was produced in the same manner as in Example 1, except that an aluminum alloy thin film having a thickness of 80 μm was used as the gas barrier layer and the sealant layer was formed to a thickness of 60 μm.

[0091] Comparative Example 3 A pouch film laminate was manufactured in the same manner as in Example 1, except that an AA8079 aluminum (Al) alloy thin film with a crystal grain size of 16.8 μm was used as the gas barrier layer.

[0092] Comparative Example 4 A pouch film laminate was manufactured in the same manner as in Example 1, except that the gas barrier layer was made of an AA8079 aluminum (Al) alloy thin film having a thickness of 80 μm and a grain size of 16.8 μm, and the sealant layer was formed to a thickness of 60 μm.

[0093] Comparative Example 5 A pouch film laminate was manufactured in the same manner as in Example 1, except that an AA8079 aluminum (Al) alloy thin film having a thickness of 80 μm and a grain size of 16.8 μm was used as the gas barrier layer.

[0094] Comparative Example 6 A pouch film laminate was manufactured in the same manner as in Example 1, except that an AA8079 aluminum (Al) alloy thin film having a thickness of 40 μm and a grain size of 16.8 μm was used as the gas barrier layer, and a nylon film having a thickness of 15 μm was used as the stretching assist layer.

[0095] Comparative Example 7 A pouch film laminate was produced in the same manner as in Example 1, except that a 50 μm thick aluminum alloy thin film was used as the gas barrier layer and the sealant layer was formed to a thickness of 60 μm.

[0096] [Table 1]

[0097] Experimental Example 1: Measurement of grain size The cross section of the aluminum alloy thin film used as the gas barrier layer in Example 1 and Comparative Example 3 was observed with a scanning electron microscope (SEM) to measure the grain size. The grain size was measured by measuring the maximum diameter of 30 grains observed in the SEM image of the cross section of the aluminum alloy thin film in the thickness direction obtained using the scanning electron microscope, and then calculating the average value of these.

[0098] 5 shows SEM images of the AA8021 aluminum alloy thin film used in Example 1 and the AA8079 aluminum alloy thin film used in Comparative Example 3. When the grain sizes were measured based on the SEM images shown, the grain size of the AA8021 used in Example 1 was 11.6 μm, and the grain size of the AA8079 used in Comparative Example 3 was 16.8 μm.

[0099] Experimental Example 2: Evaluation of formability The pouch films produced in Examples 1 to 3 and Comparative Examples 1 to 7 were each cut to the same size of 90 mm x 150 mm, and then molded at various molding depths using a battery case molding device with one molding section measuring 32 mm wide x 55 mm long, and another with two molding sections. The molding depth at which cracks occurred was recorded for each sample. The punch and molding section of the battery case molding device had filleting (chamfering) at the corners. The punch corners had a curvature of 2 mm and the corners had a curvature of 1 mm, and the molding section corners had a curvature of 2.3 mm and the corners had a curvature of 1 mm. The clearance between the punch and molding section was 0.3 mm. In the battery case molding device with two molding sections, the distance between the two molding sections was 1 mm.

[0100] The measurement results are shown in Table 2 below.

[0101] [Table 2]

[0102] As shown in Table 2 above, in the pouch film laminates of Examples 1 to 3, in which the crystal grain size of the Al alloy thin film and the thicknesses of the gas barrier layer and sealant layer fall within the ranges of the present invention, the 1-cup formability and 2-cup formability are superior to those of Comparative Examples 1 to 7.

[0103] On the other hand, in the case of the pouch film laminate according to Comparative Example 2, the molding depth of the first cup portion is similar to that of Example 1, but it can be confirmed that the moldability is reduced when molding the second cup portion.

[0104] Experimental Example 3: Evaluation of tensile strength and elongation The pouch films produced in Examples 1 and 2 and Comparative Examples 1 to 7 were each cut into five pieces measuring 15 mm x 80 mm, and each sample was fixed to the lower fixture of a universal testing machine (manufacturer: Shimadzu, model: AGX-V). Each sample was then fixed to the upper fixture at a point 30 mm from the top end, and the upper fixture was then moved away from the lower fixture at a rate of 50 mm / min while pulling the sample. The tensile strength and elongation were measured. The measurement results are shown in Tables 3 and 4 below.

[0105] [Table 3]

[0106] [Table 4]

[0107] From Tables 3 and 4 above, it can be seen that the pouch film laminates of Examples 1 to 3, which satisfy the conditions of the present invention, have superior tensile strength and / or elongation to the pouch film laminates of Comparative Examples 1 to 7.

[0108] Those skilled in the art will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims set forth below rather than the above detailed description, and various embodiments derived from the meaning and scope of the claims and their equivalents should be construed as being within the scope of the present invention. [Explanation of symbols]

[0109] 1 Secondary battery 10 Electrode assembly 11 Electrode tab 12 electrode leads 13 Battery case 14 Insulation section 111 Positive electrode tab 112 Negative electrode tab 121 Positive lead 122 Negative lead 131 Case 1 132 Case 2 133 Cup section 134 Sealing section 135 Pouch Film 1331 Containment Space 1351 sealant layer 1352 Gas barrier layer 1353 Surface protective layer 1354 Stretched auxiliary layer

Claims

1. a sealant layer made of a first polymer and formed as an innermost layer; a surface protection layer made of a second polymer and formed as the outermost layer; a gas barrier layer including an aluminum alloy thin film and laminated between the surface protective layer and the sealant layer; a pouch film laminate including a stretch-assisting layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer; The total thickness of the pouch film laminate is 160 μm to 200 μm, the gas barrier layer has a thickness of 50 μm to 70 μm; the thickness of the sealant layer is 1 to 2 times the thickness of the gas barrier layer; A pouch film laminate, wherein the thickness ratio of the stretching assist layer to the gas barrier layer is 1:1.7 to 1:2.

3.

2. The pouch film laminate according to claim 1, wherein the pouch film laminate is cut into a size of 15 mm x 80 mm, and the tensile strength measured while being pulled at a pulling rate of 50 mm / min is 200 N / 15 mm to 300 N / 15 mm, and the elongation is 120% to 150%.

3. The sealant layer is The pouch film laminate according to claim 1, wherein the thickness is 1.1 to 1.8 times the thickness of the gas barrier layer.

4. The sealant layer is The pouch film laminate according to claim 1, having a thickness of 70 μm to 100 μm.

5. 2. The pouch film laminate of claim 1, wherein the aluminum alloy thin film is alloy number AA8021.

6. The first polymer is 10. The pouch film laminate of claim 1 comprising polypropylene (PP).

7. The surface protective layer is 2. The pouch film laminate according to claim 1, having a thickness of 5 μm to 25 μm.

8. The surface protective layer is 2. The pouch film laminate according to claim 1, having a thickness of 7 μm to 12 μm.

9. The second polymer is 10. The pouch film laminate of claim 1 comprising polyethylene terephthalate (PET).

10. The stretching assist layer is The pouch film laminate according to claim 1, having a thickness of 20 μm to 50 μm.

11. The stretching assist layer is The pouch film laminate according to claim 1, having a thickness of 25 μm to 38 μm.

12. The third polymer is 10. The pouch film laminate of claim 1 comprising nylon.

13. A pouch-type battery case that houses an electrode assembly and is manufactured by forming a pouch film laminate, The pouch film laminate comprises: a sealant layer made of a first polymer and formed as an innermost layer; a surface protection layer made of a second polymer and formed as the outermost layer; a gas barrier layer including an aluminum alloy thin film and laminated between the surface protective layer and the sealant layer; a pouch film laminate including a stretch-assisting layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer; The total thickness of the pouch film laminate is 160 μm to 200 μm, the gas barrier layer has a thickness of 50 μm to 70 μm; the thickness of the sealant layer is 1 to 2 times the thickness of the gas barrier layer; The pouch-type battery case has a thickness ratio of the stretching assist layer to the gas barrier layer of 1:1.7 to 1:2.

3.

14. an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode; a pouch-type battery case that houses the electrode assembly, The battery case is It is manufactured by molding a pouch film laminate, The pouch film laminate comprises: a sealant layer made of a first polymer and formed as an innermost layer; a surface protection layer made of a second polymer and formed as the outermost layer; a gas barrier layer including an aluminum alloy thin film and laminated between the surface protective layer and the sealant layer; a pouch film laminate including a stretch-assisting layer made of a third polymer and laminated between the surface protective layer and the gas barrier layer; The total thickness of the pouch film laminate is 160 μm to 200 μm, the gas barrier layer has a thickness of 50 μm to 70 μm; the thickness of the sealant layer is 1 to 2 times the thickness of the gas barrier layer; The pouch-type secondary battery has a thickness ratio of the stretching assist layer to the gas barrier layer of 1:1.7 to 1:2.3.

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