Pouch-type battery case and pouch-type secondary battery

Abstract

To provide a pouch-type battery case including a pouch film laminate including a sealant layer, a gas barrier layer, and a surface protective layer.SOLUTION: A sealant layer is formed as an innermost layer using a first polymer, a surface protective layer is formed as an outermost layer using a second polymer, and a gas barrier layer is laminated between the surface protective layer and the sealant layer and is formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a crystal grain size of 10 μm to 13 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0045542, filed on April 14, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a pouch-type battery case and a pouch-type secondary battery, and more particularly to a pouch-type battery case and a pouch-type secondary battery that have improved tensile strength and elongation and thus 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 laminate into a press and applying pressure to the pouch film laminate with a punch, thereby stretching the pouch film laminate. Pouch film laminates are formed from multiple layers, of which the inner gas barrier layer is made of metal. However, conventional pouch film laminates have limitations in forming a deeper cup portion and in reducing the filleting radius when filleting the bottom and opening corners of the cup portion. Furthermore, there are limitations in forming the outer wall of the cup portion nearly vertically. This increases dead space in the secondary battery, reduces the size of the electrode assembly, and reduces 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-type battery case and a pouch-type secondary battery that have improved tensile strength and elongation, and thus improved 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 problems, a pouch-type battery case according to an embodiment of the present invention is a pouch-type battery case that houses an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode, and the pouch-type battery case includes a pouch film laminate including: a sealant layer formed as the innermost layer using a first polymer; a surface protective layer formed as the outermost layer using a second polymer; and a gas barrier layer laminated between the surface protective layer and the sealant layer, the gas barrier layer being formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a crystal grain size of 10 μm to 13 μm.

[0011] The aluminum alloy thin film may contain 1.2 wt % to 1.7 wt % of iron.

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

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

[0014] The aluminum alloy thin film may have a crystal grain size of 10.5 μm to 12.5 μm.

[0015] The aluminum alloy thin film may have an alloy number of AA8021.

[0016] The gas barrier layer may have a thickness of 70 μm to 90 μm.

[0017] The thickness of the sealant layer may be 0.6 to 1.2 times the thickness of the gas barrier layer, for example, 30 μm to 90 μm.

[0018] The first polymer may also include polypropylene (PP).

[0019] The surface protection layer may have a thickness of 6 μm to 25 μm.

[0020] The second polymer can also include polyethylene terephthalate (PET).

[0021] The film may further include a stretching assist layer formed of a third polymer and laminated between the surface protective layer and the gas barrier layer.

[0022] The stretching auxiliary layer may have a thickness of 20 μm to 50 μm.

[0023] The third polymer may also include nylon.

[0024] The total thickness of the pouch film laminate can be 180 μm or more, preferably 180 μm to 210 μm.

[0025] In addition, the pouch film laminate may have a tensile strength of 200N / 15mm to 300N / 15mm and an elongation of 105% to 150% when measured by cutting into a size of 15mm x 80mm and pulling at a pulling speed of 50mm / min.

[0026] In order to solve the above problems, a pouch-type secondary battery according to an embodiment of the present invention 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. The battery case includes a sealant layer formed as an innermost layer using a first polymer, a surface protective layer formed as an outermost layer using a second polymer, and a gas barrier layer laminated between the surface protective layer and the sealant layer, the gas barrier layer being formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a crystal grain size of 10 μm to 13 μm.

[0027] Further details of the invention are included in the detailed description and drawings. [Effects of the Invention]

[0028] According to the embodiment of the present invention, at least the following effects are obtained.

[0029] The pouch-type battery case according to the present invention uses a pouch film laminate including an aluminum alloy thin film having a specific thickness and grain size as a gas barrier layer, thereby improving the tensile strength, elongation, and toughness of the pouch film laminate. The use of the pouch film laminate allows for increased molding depth without the occurrence of pinholes or cracks during cup molding, and also reduces the curvature radius of the cup corners, thereby increasing the volume of the storage space for the battery assembly.

[0030] Furthermore, the pouch film laminate according to the present invention has excellent puncture strength, and can more effectively protect the electrode assembly inside even if it is subjected to a large external pressure or is punctured by a sharp object.

[0031] The effects of the present invention are not limited to the above-mentioned examples, and various other effects are included in the present 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 laminate 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 tensile strength, elongation, and grain size 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 thin film of alloy number AA8021 used in Example 1 and an aluminum alloy thin film of alloy number AA8079 used in Comparative Example 3. [Figure 6] 1 is a graph showing the results of experiments on tensile strength and elongation percentage for pouch film laminates according to Production Examples of the present invention, Comparative Examples 1 and 2. [Figure 7] 1 is a graph showing the results of an experiment on the puncture strength of pouch film laminates according to a production example of the present invention, comparative example 1, and comparative example 2. 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. However, 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, and 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 the pouch film laminate 135 is molded to manufacture the pouch-type battery case 13. In addition, the pouch film laminate has excellent puncture strength, so that the internal electrode assembly can be more effectively protected even if it is subjected to large external pressure or is punctured by a sharp object.

[0039] To this end, the pouch-type battery case 13 according to one embodiment of the present invention is a pouch-type battery case 13 that houses an electrode assembly 10 formed by stacking a positive electrode, a separator, and a negative electrode, and includes a pouch film laminate 135 including a sealant layer 1351 formed as the innermost layer using a first polymer, a surface protective layer 1353 formed as the outermost layer using a second polymer, and a gas barrier layer 1352 laminated between the surface protective layer 1353 and the sealant layer 1351, and formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a crystal grain size of 10 μm to 13 μm.

[0040] In addition, 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 includes a pouch film laminate 135 that includes a sealant layer 1351 formed as the innermost layer using a first polymer, a surface protective layer 1353 formed as the outermost layer using a second polymer, and a gas barrier layer 1352 laminated between the surface protective layer 1353 and the sealant layer 1351, and formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a crystal grain size of 10 μm to 13 μm.

[0041] The electrode assembly 10 is formed by sequentially stacking a positive electrode, a separator, and a negative electrode. First, a slurry containing an electrode active material, a binder, a conductive material, etc. is applied to a positive electrode current collector and a negative electrode current collector to form a positive electrode and a negative electrode. These 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.

[0042] Specifically, the electrode assembly 10 includes two types of electrodes, such as 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 types of 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 active material slurry is typically formed by stirring a granular active material, a conductive material, a binder, and the like in a solvent. The solvent is removed in a subsequent process.

[0043] 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 one side of the electrode assembly 10 to form a path for electrons to move between the inside and outside of the electrode assembly 10. The 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 can 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 can protrude parallel to one another in the same direction from one side of the electrode assembly 10, as shown in FIG. 1, but are not limited thereto and can also protrude in different directions.

[0044] An electrode lead 12 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, thereby adhering 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-conductor that does not allow electricity to pass through easily. Typically, the insulating portion 14 is made of a relatively thin insulating tape that easily adheres 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 are capable of insulating the electrode lead 12.

[0045] 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. Furthermore, 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.

[0046] 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.

[0047] The battery case 13 is formed by molding a pouch film laminate made of a flexible material. Hereinafter, the battery case 13 will be described as a pouch. The battery case 13 accommodates and seals the electrode assembly 10 so that a portion of the electrode lead 12, i.e., the terminal portion, is exposed. As shown in FIG. 1, the battery case 13 includes a first case 131 and a second case 132. The second case 132 is formed with a cup portion 133 and is provided with a receiving space 1331 capable of accommodating the electrode assembly 10. The first case 131 covers the receiving space 1331 from above to prevent the electrode assembly 10 from falling out of the battery case 13. In this regard, as shown in FIG. 1, the first case 131 is also formed with a cup portion 133 with a receiving space 1331, so that the electrode assembly 10 can be accommodated from above. 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 are not limited thereto and may be manufactured in various ways, such as being separated from each other and manufactured separately.

[0048] 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 second case 132, and the first case 131 covers the space from above. An electrolyte solution is then poured into the interior, and the sealing portions 134 formed on the edges of the first case 131 and the second case 132 are sealed. The electrolyte solution transports lithium ions generated by an electrochemical reaction of the electrodes during charging and discharging of the secondary battery 1, and may include a non-aqueous organic electrolyte solution, which is a mixture of lithium salt and high-purity organic solvents, or a polymer using a polymer electrolyte. A pouch-type secondary battery 1 can be manufactured in this manner.

[0049] FIG. 2 is a cross-sectional view of a pouch film laminate 135 according to one embodiment of the present invention.

[0050] 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 laminate 135 includes a sealant layer 1351, a gas barrier layer 1352, and a surface protection layer 1353, as shown in FIG. 2, and may further include a drawing assistance layer 1354, if necessary.

[0051] The sealant layer 1351 is formed as the innermost layer using a first polymer and is in direct contact with the electrode assembly 10. Here, the innermost layer refers to the layer located last in the direction of the electrode assembly 10 relative to the gas barrier layer 1352. When the pouch film laminate 135 having the above-described laminated structure is drawn using a punch or the like, a portion is stretched to form a cup portion 133 including a bag-shaped receiving space 1331. After the electrode assembly 10 is placed inside the receiving space 1331, an electrolyte solution is injected. Thereafter, the upper pouch 131 and the lower pouch 132 are brought into contact with each other, and the sealing portion 134 is subjected to thermocompression bonding, whereby the sealant layers 1351 are bonded together to seal the pouch. In this case, the sealant layer 1351 must be insulating since it is in direct contact with the electrode assembly 10, and must also be corrosion-resistant since it is in contact with the electrolyte. Furthermore, since the interior must be completely sealed to prevent the transfer of substances 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 forming 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 form 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.

[0052] On the other hand, the thickness of sealant layer 1351 can be 0.6 to 1.2 times, preferably 0.7 to 1.1 times, and more preferably 0.8 to 1.1 times the thickness of the gas barrier layer described below. If the thickness of the sealant layer is less than 0.6 times the thickness of the gas barrier layer, seal durability may decrease, while if it exceeds 1.2 times, the total thickness of the pouch may become excessively thick, which may decrease formability. Furthermore, to ensure sufficient insulation, it is more preferable that the thickness of sealant layer 1351 be 0.8 times or more the thickness of the gas barrier layer.

[0053] Specifically, the thickness of the sealant layer 1351 can be 30 μm to 90 μm, preferably 50 μm to 90 μm, and more preferably 70 μm to 90 μm. If the thickness of the sealant layer 1351 is less than 30 μm, problems such as internal rupture during sealing may occur, resulting in reduced seal durability. If the thickness exceeds 90 μm, the pouch may become excessively thick, which may reduce moldability and reduce the battery energy density (energy per volume). Furthermore, to ensure sufficient insulation, the thickness of the sealant layer 1351 is preferably 70 μm or greater. If the sealant layer is too thin, the dielectric breakdown voltage of the pouch film laminate may decrease, resulting in reduced insulation. This may increase the defective rate when batteries are manufactured using a pouch film laminate with poor insulation.

[0054] The gas barrier layer 1352 is laminated between the surface protection layer 1353 and the sealant layer 1351 to ensure the mechanical strength of the pouch, block the entry and exit of gases or moisture from the outside of the secondary battery 1, and prevent leakage of the electrolyte.

[0055] The gas barrier layer 1352 is formed of an aluminum alloy thin film, and in particular, the gas barrier layer 1352 according to an embodiment of the present invention may be formed of an aluminum alloy thin film having a thickness of 60 μm to 100 μm and a grain size of 10 μm to 13 μm. The aluminum alloy thin film can ensure a predetermined level of mechanical strength, is lightweight, and can ensure the electrochemical properties of the electrode assembly 10 and the electrolyte, as well as heat dissipation.

[0056] More specifically, the aluminum alloy thin film according to one embodiment of the present invention may have a thickness of 60 μm to 100 μm, preferably 70 μm to 90 μm, and a grain size of 10 μm to 13 μm, preferably 10.5 μm to 12.5 μm, and more preferably 11 μm to 12 μm. When the thickness and grain size of the aluminum alloy thin film satisfy the above ranges, the forming depth can be increased without generating pinholes or cracks during cup forming.

[0057] Conventionally, the gas barrier layer 1352 has typically been formed to a thickness of 30 μm to 50 μm. However, when the gas barrier layer is 30 μm to 50 μm thick, even if the pouch film laminate 135 is draw-formed, the cup portion 133 becomes deep, or there is a limit to how far the outer wall of the cup portion 133 can be formed to be nearly vertical, and there is also a limit to how far the filleting curvature radius of the corner of the cup portion 133 can be reduced. In addition, there is a problem in that the puncture strength is weak, and the internal electrode assembly 10 is easily damaged when the battery case 13 receives an external impact.

[0058] To address this issue, the present invention forms the gas barrier layer 1352 with a thickness of 60 μm to 100 μm, particularly 70 μm to 90 μm. When the thickness of the gas barrier layer is within this range, the formability of the gas barrier layer 1352 is improved. This allows the cup portion 133 to be formed deeper during the draw-forming of the pouch film laminate 135. The outer wall of the cup portion 133 becomes more vertical, reducing the radius of curvature of the corners of the cup portion 133. This increases the volume of the housing space 1331, allowing more electrodes and separators to be stacked in the electrode assembly 10 housed therein, thereby improving the energy efficiency per volume. However, if the thickness of the gas barrier layer 1352 is greater than 100 μm, the overall thickness of the pouch becomes excessively thick, which may actually reduce the energy density per volume of the secondary battery 1.

[0059] In addition, when the thickness of the gas barrier layer satisfies the above range, the puncture strength of the pouch film laminate 135 is improved, and the internal electrode assembly 10 can be more effectively protected even if it is subjected to a large external pressure or is punctured by a sharp object. Here, excellent puncture strength means that the pouch film laminate 135 has high strength when a hole is made therein.

[0060] However, simply increasing the thickness of the aluminum alloy thin film can increase the forming depth, but pinholes and cracks occur in the aluminum alloy thin film after forming, causing problems with sealing durability. Therefore, the present inventors conducted extensive research and found that, when an aluminum alloy thin film with a grain size of 10 μm to 13 μm is used, the occurrence of pinholes and cracks can be suppressed even when the forming depth is increased, leading to the completion of the present invention. According to the inventors' research, when the grain size of the aluminum alloy thin film exceeds 13 μm, the strength of the aluminum alloy thin film decreases, increasing the occurrence of cracks and pinholes during forming, while when the grain size is less than 10 μm, the flexibility of the aluminum alloy thin film decreases, limiting the improvement of formability.

[0061] 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, an SEM image of the cross section 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.

[0062] The aluminum alloy thin film according to the present invention may contain one or more metal elements other than aluminum, such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0063] The iron (Fe) content of the aluminum alloy thin film may 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 may decrease, causing cracks and pinholes during forming, while if it exceeds 1.7 wt%, the flexibility of the aluminum alloy thin film may decrease, limiting the improvement of formability.

[0064] The aluminum alloy thin film may have a silicon (Si) content of 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.

[0065] Specifically, the aluminum alloy thin film according to the present invention can be an aluminum alloy with alloy number AA8021.

[0066] FIG. 3 is a graph showing the iron and silicon contents of an aluminum alloy of alloy number AA8079, which has been mainly used for battery pouches in the past, and an aluminum alloy of alloy number AA8021, which is used in the present invention.

[0067] As shown in Figure 3, alloy number AA8079 contains 0.6 wt% to 1.2 wt% iron and 0.05 to 0.3 wt% silicon. Generally, when an aluminum alloy contains a large amount of iron, its mechanical strength improves, and when the iron content is small, its flexibility improves. In the case of aluminum alloy number AA8079, which contains a relatively small amount of iron, when gas barrier layer 1352 is formed using this alloy, flexibility can be improved, but strength may decrease and formability may be limited.

[0068] On the other hand, alloy number AA8021 contains 1.2 wt% to 1.7 wt%, particularly 1.3 wt% to 1.7 wt%, of iron, and 0.05 to 1.9 wt%, particularly 0.08 to 0.19 wt%, of silicon, as shown in Figure 3. When the gas barrier layer 1352 is formed from an aluminum alloy with alloy number AA8021, the relatively high iron content can improve the tensile strength, elongation rate, and puncture strength.

[0069] FIG. 4 shows the tensile strength (Rm), elongation (A), and grain size of the aluminum alloy with alloy number AA8079 and the aluminum alloy with alloy number AA8021.

[0070] As shown in Figure 4, AA8079 has limited formability due to its low tensile strength and elongation, and its relatively large grain size of 13µm to 21µm means that internal stress is not sufficiently dispersed during stretching, resulting in the formation of many pinholes.

[0071] Meanwhile, AA8021 has high tensile strength and elongation, making it excellent in formability. Its relatively small grain size of 10 μm to 13 μm allows for better dispersion of internal stress during stretching, effectively preventing pinholes.

[0072] On the other hand, when a tensile force is applied to a certain 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 resistance to fracture; the higher the toughness, the more the material can be stretched before breaking. When the gas barrier layer 1352 is formed using aluminum alloy number AA8021, the tensile strength and elongation improve, which increases toughness and improves formability.

[0073] The surface protective layer 1353 is formed as the outermost layer of a second polymer. It protects the secondary battery 1 from external friction and impact while electrically insulating 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 excellent abrasion resistance and heat resistance. The surface protective layer 1353 may have a single-layer structure made of any one material or a mixed-layer structure made of two or more materials.

[0074] According to one embodiment of the present invention, the thickness of the surface protective layer 1353 can be 6 μm to 25 μm. If the thickness of the surface protective layer 1353 is thinner than 6 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.

[0075] 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.

[0076] According to one embodiment of the present invention, the battery case 13 may further include a stretching assist layer 1354 formed 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 and prevents the surface protective layer 1353 and the gas barrier layer 1352 from peeling off when they are stretched. The third polymer forming 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.

[0077] As described above, according to one embodiment of the present invention, the gas barrier layer 1352 has a thickness of approximately 60 μm to 100 μm, which improves the formability of the gas barrier layer 1352. To improve the formability of the stretching auxiliary layer 1354 as well, the stretching auxiliary layer 1354 may have a thickness of 20 μm to 50 μm, and preferably a thickness of 25 μm to 38 μm. If the stretching auxiliary layer 1354 is thinner than 20 μm, it may not be able to accommodate the improved formability of the gas barrier layer 1352 and may be damaged during stretching. Conversely, if the stretching auxiliary layer 1354 is thicker 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.

[0078] Meanwhile, the pouch film laminate according to the present invention may have a total thickness of 180 μm or more, preferably 180 μm to 210 μm. When the thickness of the pouch film laminate is 180 μm or more, a cup can be formed with a greater depth than conventional ones. On the other hand, if the total thickness of the pouch film laminate is excessively thick, the total volume of the secondary battery increases, which is not preferable.

[0079] Meanwhile, the pouch film laminate of the present invention has excellent tensile strength and elongation due to the inclusion of an aluminum alloy thin film having a specific thickness and crystal grain size. Specifically, the pouch film laminate of 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 105% to 150%, preferably 105% to 140%, and even more preferably 105% to 130%. Thus, the pouch film laminate of the present invention has high tensile strength and elongation, which increases toughness and reduces the occurrence of cracks even when the molding depth is large during cup molding.

[0080] Furthermore, the pouch film laminate according to the present invention has excellent puncture strength due to the inclusion of an aluminum alloy thin film having a specific thickness and crystal grain size. Specifically, the pouch film laminate according to the present invention can have a puncture strength of 30 N or more, preferably 30 N to 40 N.

[0081] The present invention will be described in more detail below with reference to specific examples.

[0082] Example 1 A nylon film having a width of 266 mm, a length of 50 m and a thickness of 25 μm, and a polyethylene terephthalate (PET) film having a width of 266 mm, a length of 50 m and a thickness of 12 μm were adhered in that order to one side of an aluminum (Al) alloy thin film of alloy number AA8021 having a width of 266 mm, a length of 50 m and a thickness of 80 μm by dry lamination using a urethane adhesive, to form a surface protection layer, an extension auxiliary layer and a gas barrier layer.

[0083] Next, non-oriented polypropylene (CPP) was melted at high temperature and co-extruded onto the other side of the aluminum (Al) alloy thin film to form a 60 μm thick sealant layer, producing a pouch film laminate with a total thickness of 183 μm.

[0084] Example 2 Except for forming the sealant layer to a thickness of 80 μm, a pouch film laminate was produced in the same manner as in Example 1. The total thickness of the pouch film laminate was 203 μm.

[0085] (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 of alloy number AA8021 was used as the gas barrier layer, a 15 μm thick nylon film was used as the stretching aid layer, and the sealant layer was formed to a thickness of 80 μm. The total thickness of the pouch film laminate was 153 μm.

[0086] (Comparative Example 2) A pouch film laminate was manufactured in the same manner as in Example 1, except that a 50 μm thick aluminum alloy thin film of alloy number AA8021 was used as the gas barrier layer. The total thickness of the pouch film laminate was 153 μm.

[0087] (Comparative Example 3) A pouch film laminate was produced in the same manner as in Example 1, except that an 80 μm thick aluminum alloy thin film of alloy number AA8079 was used as the gas barrier layer. The total thickness of the pouch film laminate was 183 μm.

[0088] Comparative Example 4 A pouch film laminate was produced in the same manner as in Example 2, except that an 80 μm thick aluminum alloy thin film of alloy number AA8079 was used as the gas barrier layer. The total thickness of the pouch film laminate was 203 μm.

[0089] (Comparative Example 5) A pouch film laminate was produced in the same manner as in Example 1, except that a 40 μm thick aluminum alloy thin film of alloy number AA8079 was used as the gas barrier layer, a 15 μm thick nylon film was used as the stretching assist layer, and the sealant layer was formed to a thickness of 80 μm. The total thickness of the pouch film laminate was 153 μm.

[0090] [Table 1]

[0091] (Experimental Example 1: Measurement of grain size) The cross sections of the aluminum alloy thin films AA8021 and AA8079 used as the gas barrier layers in Example 1 and Comparative Example 3 were observed with a scanning electron microscope (SEM) to measure the grain size. Specifically, the maximum diameters of 30 grains observed in the SEM images of the cross sections of the aluminum alloy thin films in the thickness direction obtained using the scanning electron microscope were measured, and the average value was calculated.

[0092] Figure 5 shows SEM images of the AA8021 aluminum alloy thin film and the AA8079 aluminum alloy thin film. The grain size was measured based on the SEM images and found to be 11.6 μm for AA8021 and 16.8 μm for AA8079.

[0093] (Experimental Example 2: Evaluation of formability) The pouch film laminates produced in Examples 1 and 2 and Comparative Examples 1 to 5 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 machine with a molding section measuring 32 mm wide x 55 mm long. The molding depth at which cracks occurred for each sample was recorded. The punch and molding section of the battery case molding machine were filleted (chamfered) 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. The measurement results are shown in Table 2 below.

[0094] [Table 2]

[0095] As shown in Table 2, the pouch film laminates according to Examples 1 and 2 of the present invention could be molded to a depth of 15.0 mm or more without cracking, whereas the pouch film laminates according to Comparative Examples 1 to 5, in which the thickness and / or crystal grain size of the gas barrier layer were outside the range of the present invention, cracked at a molding depth of less than 15.0 mm. Therefore, it can be confirmed that the moldability of the pouch film laminate is improved when the thickness and crystal grain size of the gas barrier layer according to the present invention are satisfied. For example, when a battery case is manufactured using the pouch film laminate according to the manufacturing example of the present invention, one cup portion is formed in each of the second case and the first case, resulting in a storage space of 30 mm or more in depth. Therefore, a thicker electrode assembly can be accommodated, and the energy efficiency per volume of the secondary battery can be increased.

[0096] (Experimental Example 3: Evaluation of tensile strength and elongation) The pouch film laminates produced in Examples 1 and 2 and Comparative Examples 1 to 5 were each cut into five pieces measuring 15 mm x 80 mm, and each sample was then secured to the lower fixture of a tensile strength tester (manufacturer: Shimadzu, model: AGX-V). Each sample was then secured to the upper fixture up to 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 to stretch the sample. The tensile strength and elongation of the pouch film laminates were then measured immediately before they broke. The measurement results are shown in Tables 3 and 4 below.

[0097] [Table 3]

[0098] [Table 4]

[0099] Fig. 6 is a graph showing the experimental results of the tensile strength and elongation percentage for the pouch film laminates according to Example 1 of the present invention and Comparative Examples 1 and 2. From Fig. 6 and Tables 3 and 4, it can be seen that the pouch film laminates according to Examples 1 and 2 have superior tensile strength and elongation percentage compared to the pouch film laminates according to Comparative Examples 1 to 5.

[0100] Meanwhile, in a graph between tensile strength and elongation, the area below represents the toughness of the material. As shown in FIG. 6, the graph area of ​​the pouch film laminate according to Example 1 of the present invention is larger than the graph areas of the pouch film laminates according to Comparative Examples 1 and 2, which indicates that the pouch film laminate of Example 1 according to the present invention has excellent toughness.

[0101] (Experimental Example 4: Evaluation of Puncture Strength) The pouch film laminates produced in Examples 1 and 2 and Comparative Examples 1 to 5 were each cut into 10 pieces of the same size, 90 mm x 80 mm, and then fixed horizontally to the jig of a puncture strength tester (manufacturer: Shimadzu, model: AGX-V). A pin with a diameter of 1.0 mm and a tip curvature of 0.5 mm was placed vertically above the placed samples. The pin was then dropped onto each sample to measure the puncture strength of the sample. The measurement results are shown in Table 5 below.

[0102] [Table 5]

[0103] Fig. 7 is a graph showing the results of an experiment on the puncture strength of pouch film laminates according to Example 1 of the present invention and Comparative Examples 1 and 2. Fig. 7 and Table 5 confirm that the pouch film laminates according to Examples 1 and 2 of the present invention have superior puncture strength compared to the pouch films according to Comparative Examples 1 to 5. That is, even if the pouch film laminate according to the present invention is subjected to a large external pressure or is punctured by a sharp object and damaged, it can more effectively protect the internal electrode assembly.

[0104] (Experimental Example 5: Evaluation of insulation properties) The pouch film laminates prepared in Examples 1 and 2 were each cut into identical pieces measuring 90 mm x 150 mm and stored in a vacuum oven at 60°C for 24 hours. The breakdown voltages were then measured in a dry room. Specifically, 5 mm-thick aluminum foils were placed on both sides of the pouch film laminate. The (+) electrode of the measuring device was connected to the gas barrier layer of the pouch film laminate, and the (-) electrode was connected to the aluminum foil in contact with the sealant layer. A voltage was applied at a rate of 100 V / s, and the applied voltage at which the measured leakage current was 0.5 mA or greater was evaluated as the breakdown voltage. The measurement results are shown in Table 6 below.

[0105] [Table 6]

[0106] From Table 6, it can be seen that the dielectric breakdown voltage of the pouch film laminate of Example 2, in which the sealant layer thickness is 80 μm, is higher than that of the pouch film laminate of Example 1, in which the sealant layer thickness is 60 μm. This indicates that the sealant layer has better insulation properties when the thickness is 80 μm.

[0107] 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]

[0108] 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 laminate 1331 Containment Space 1351 sealant layer 1352 Gas barrier layer 1353 Surface protective layer 1354 Stretched auxiliary layer

Claims

1. A pouch-type battery case that houses an electrode assembly formed by stacking a positive electrode, a separator, and a negative electrode, a sealant layer formed as an innermost layer from a first polymer; a surface protection layer formed as an outermost layer using a second polymer; a gas barrier layer formed of an aluminum alloy thin film and laminated between the surface protective layer and the sealant layer, The pouch film laminate has a total thickness of 180 μm or more, the thickness of the sealant layer is 0.6 to 1.2 times the thickness of the gas barrier layer; The pouch-type battery case, wherein the aluminum alloy thin film has a crystal grain size of 10.5 μm to 13 μm.

2. The aluminum alloy thin film is 2. The pouch-shaped battery case according to claim 1, containing 1.2 wt % to 1.7 wt % iron.

3. The aluminum alloy thin film is 2. The pouch-shaped battery case according to claim 1, which contains 0.2 wt % or less of silicon.

4. The aluminum alloy thin film is 2. The pouch-type battery case according to claim 1, wherein the alloy number is AA8021.

5. The gas barrier layer is 2. The pouch-type battery case according to claim 1, which has a thickness of 60 μm to 100 μm.

6. The sealant layer is 2. The pouch-type battery case according to claim 1, which has a thickness of 30 μm to 90 μm.

7. The first polymer is 10. The pouch-type battery case of claim 1, comprising polypropylene (PP).

8. The surface protective layer is 2. The pouch-type battery case according to claim 1, which has a thickness of 6 μm to 25 μm.

9. The second polymer is 10. The pouch-shaped battery case of claim 1, comprising polyethylene terephthalate (PET).

10. The pouch-type battery case according to claim 1 , further comprising an extension assist layer formed of a third polymer and laminated between the surface protective layer and the gas barrier layer.

11. The stretching assist layer is The pouch-type battery case according to claim 10, which has a thickness of 20 μm to 50 μm.

12. The third polymer is 11. The pouch-shaped battery case of claim 10, comprising nylon.

13. 2. The pouch-type battery case according to claim 1, wherein the pouch film laminate is cut into a size of 15 mm x 80 mm, and has a tensile strength of 200 N / 15 mm to 300 N / 15 mm and an elongation of 105% to 150% as measured while being pulled at a pulling rate of 50 mm / min.

14. The pouch-type battery case according to claim 1 , wherein the pouch film laminate has a puncture strength of 30 N or more.

15. 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 pouch-type battery case includes: a sealant layer formed as an innermost layer from a first polymer; a surface protection layer formed as an outermost layer using a second polymer; a gas barrier layer formed of an aluminum alloy thin film and laminated between the surface protective layer and the sealant layer, The pouch film laminate has a total thickness of 180 μm or more, the thickness of the sealant layer is 0.6 to 1.2 times the thickness of the gas barrier layer; The aluminum alloy thin film has a crystal grain size of 10.5 μm to 13 μm.

Images