Pouch-type battery case and lithium secondary battery including the same

Abstract

The present invention relates to a high-strength battery case that is less susceptible to cracking during molding and is less damaged by external impact. The battery case of the present invention is made of a pouch film laminate including a gas barrier layer, a base layer arranged on one side of the gas barrier layer, and a sealant layer arranged on the other side of the gas barrier layer, and includes at least one cup portion having a recessed shape so as to accommodate an electrode assembly, and a terrace located on at least a part of the periphery of the cup portion, the cup portion including a bottom surface and a plurality of peripheral surfaces surrounding the bottom surface, and the gas barrier layer has a thickness of more than 30 μm at a corner where the bottom surface and a pair of adjacent peripheral surfaces meet.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0187274, filed on December 24, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a pouch-type battery case, and more particularly to a high-strength battery case that is less susceptible to damage due to external stress, and a lithium secondary battery including the same. [Background technology]

[0003] 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 e-bikes, but also in large products that require high output such as electric vehicles and hybrid cars, power storage devices that store surplus generated power and renewable energy, and backup power storage devices.

[0004] Typically, a secondary battery is manufactured by coating a positive electrode active material slurry on a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, laminating these on both sides of a separator to form an electrode assembly of a predetermined shape, and then housing the electrode assembly in a battery case, injecting an electrolyte, and sealing the battery case.

[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.

[0006] The pouch-type battery case is manufactured by pressing a flexible pouch film laminate to form a cup portion for accommodating an electrode assembly, and then placing the electrode assembly in the cup portion of the battery case, injecting an electrolyte, and sealing the seal portion to manufacture a secondary battery.

[0007] Among these press processes, drawing is performed by inserting a pouch film into a press device and applying pressure to the pouch film laminate with a punch to stretch the pouch film laminate. The pouch film laminate is generally formed of multiple layers, with a polymer film such as polyethylene terephthalate laminated on one side of a gas barrier layer made of a metal material and a sealant layer laminated on the other side.

[0008] Recently, with the increasing demand for high-capacity batteries, such as electric vehicle batteries and ESS batteries, there has been an increasing need for battery cases that can accommodate more electrode assemblies. In response, attempts have been made to increase the molding depth of the cup portion of pouch-type battery cases or to use a two-cup molding method, in which cup portions are molded into both the upper and lower cases to increase the volume of the storage space. However, when increasing the molding depth of the cup portion or using two-cup molding, the increased tensile force applied to the pouch film laminate during the molding process makes it more likely to develop cracks and pinholes, especially at the lower corners of the cup portion where stress is concentrated during stretching. The occurrence of cracks and pinholes makes the battery case more susceptible to external impact damage and reduces battery safety.

[0009] Korean Patent Publication No. 10-2015-0130002 (Patent Document 1) discloses a secondary battery case that can suppress cracks and pinholes even during high-molding by either attaching an additional member to the edge of the cup (receptacle) or varying the stretching pressure to thicken the barrier layer at the edge of the cup. However, as described in Patent Document 1, attaching an additional member to the edge of the cup reduces stretchability during molding, causing unevenness due to the attachment of the additional member or uneven thickness of the sealant layer and base layer, which can adversely affect seal durability and insulation. Furthermore, attaching the additional member can cause uneven thickness of the pouch film laminate, making winding difficult. Meanwhile, adjusting the molding pressure to thicken the edge of the cup can result in uneven stretching, resulting in wrinkles after molding, which can adversely affect appearance and seal quality.

[0010] Therefore, there is a need for the development of a pouch-type battery case that can minimize the occurrence of cracks at the corners of the cup portion without deteriorating moldability, sealing properties, and insulation properties. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the above problems, and aims to provide a pouch-type battery case that can minimize the occurrence of cracks at the corners of the cup portion, and a secondary battery including the same. [Means for solving the problem]

[0012] In one aspect, the present invention provides a pouch-type battery case comprising a pouch film laminate including a gas barrier layer, a base layer disposed on one side of the gas barrier layer, and a sealant layer disposed on the other side of the gas barrier layer, wherein the pouch-type battery case includes at least one cup portion having a recessed shape to accommodate an electrode assembly, and a terrace located on at least a part of the periphery of the cup portion, the cup portion including a bottom surface and a plurality of peripheral surfaces surrounding the bottom surface, and the thickness of the gas barrier layer at a corner where a pair of adjacent peripheral surfaces and the bottom surface meet is greater than 30 μm, preferably greater than 30 μm and not greater than 70 μm, and more preferably greater than 30 μm and not greater than 60 μm.

[0013] The thickness of the gas barrier layer at the corners may be 50% to 70%, preferably 50% to 65%, and more preferably 55% to 65% of the thickness of the gas barrier layer at the terraces.

[0014] The radius of curvature of the corner may be 0.5 to 5.0 mm, preferably 1.0 to 4.0 mm, and more preferably 2.0 to 3.5 mm.

[0015] The battery case may include two cup portions and a folding portion formed between the two cup portions.

[0016] The thickness of the gas barrier layer on the terrace can be 60 μm or more, preferably 60 μm to 100 μm, and more preferably 60 μm to 80 μm.

[0017] The depth of the cup portion may be 5.0 mm or more, preferably 5.0 to 20 mm, and more preferably 6.5 mm to 20 mm.

[0018] The cup portion may have a tensile strength of 200N or more, preferably 200N to 300N, and more preferably 210N to 260N.

[0019] In another aspect, the present invention provides a secondary battery including: an electrode assembly formed by stacking 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 the pouch-type battery case according to the present invention. [Effects of the Invention]

[0020] The battery case according to the present invention uses a thick pouch film laminate with a gas barrier layer of at least 60 μm thick, and after cup formation, the remaining thickness of the gas barrier layer at the corners of the cup is thick enough to exceed 30 μm, thereby effectively preventing cracks or pinholes from forming at the corners of the cup, even under harsh stretching conditions. Because the battery case according to the present invention has fewer cracks or pinholes at the corners of the cup, it has high resistance to external impacts that occur during logistics and charging / discharging, and can prevent electrolyte leakage and moisture penetration due to damage to the battery case, thereby ensuring battery stability.

[0021] Furthermore, the battery case according to the present invention can be formed with a deep cup portion by sufficiently stretching the gas barrier layer at the corners of the cup portion so that the thickness of the gas barrier layer at the corners is 50% to 70% of the thickness of the gas barrier layer at the terraces, which are unformed regions. This allows the volume of the space for accommodating the electrode assembly to be increased, thereby achieving a high energy density. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; [Figure 2] 10A and 10B are diagrams illustrating a battery case according to another embodiment of the present invention. [Figure 3] FIG. 3 is an enlarged view of a portion A in FIGS. 1 and 2. [Figure 4] 1 is a cross-sectional view illustrating a pouch film laminate of the present invention. [Figure 5] 1 is a diagram showing cutting positions of a battery case in Experimental Example 1. FIG. [Figure 6] 1 shows photographs of a cut sample and a cross section of the sample in Experimental Example 1. [Figure 7] FIG. 10 is a diagram showing cutting positions of a battery case for producing a sample for measuring tensile strength in Experimental Example 3. [Figure 8] 1 is a photograph showing the appearance of a battery case of Example 1. [Figure 9] 10 is a photograph showing the appearance of the battery case of Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in more detail below.

[0024] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concept of a term in order to best explain his or her invention.

[0025] The present inventors have conducted extensive research to manufacture a battery case that can accommodate a large battery assembly and achieve a high energy density, and that can suppress damage due to external stresses that occur during logistics and charging / discharging, particularly damage to the corners of the cup, which are vulnerable parts. As a result, they have found that the above-mentioned objectives can be achieved when the battery case is formed so that the remaining thickness of the gas barrier layer at the corners of the cup exceeds 30 μm after cup molding, and have thus completed the present invention.

[0026] Fig. 1 is an exploded perspective view of a secondary battery 1 according to one embodiment of the present invention, and Fig. 2 is a diagram illustrating a battery case according to another embodiment of the present invention. Fig. 3 is a partially enlarged view of portion A in Figs. 1 and 2, and Fig. 4 is a diagram illustrating one embodiment of a pouch film laminate for manufacturing a battery case according to the present invention. The present invention will now be described with reference to Figs. 1 to 4.

[0027] Referring to FIG. 1, a secondary battery 1 according to the present invention may include a pouch-type battery case 100 (hereinafter, referred to as a “battery case”) and an electrode assembly 200 housed in the battery case 100 .

[0028] The pouch-type battery case 100 is manufactured by inserting a flexible pouch film laminate into a press molding device and applying pressure with a punch to a portion of the pouch film laminate to stretch it, thereby forming a recessed cup portion.

[0029] Here, as shown in FIG. 4, the pouch film laminate includes a gas barrier layer 20, a base layer 10 disposed on one side of the gas barrier layer 20, and a sealant layer 30 disposed on the other side of the gas barrier layer 20.

[0030] Hereinafter, each layer of the pouch film laminate used in the present invention will be specifically described with reference to FIG.

[0031] Base material layer The substrate layer 10 is disposed on the outermost layer of the battery case to protect the electrode assembly from external impact and to provide electrical insulation.

[0032] The substrate layer 10 may be made of a polymer material, for example, one or more polymer 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, and Teflon (registered trademark).

[0033] The substrate layer 10 may have a single layer structure, or may have a multi-layer structure in which different polymer films 12 and 14 are laminated, as shown in Fig. 4. When the substrate layer 10 has a multi-layer structure, an adhesive layer 16a may be interposed between the polymer films.

[0034] Meanwhile, the substrate layer 10 may have a total thickness of 10 μm to 60 μm, preferably 20 μm to 50 μm, and more preferably 30 μm to 50 μm. When the substrate layer has a multilayer structure, the thickness includes the thickness of the adhesive layer. When the substrate layer 10 satisfies the above range, it exhibits excellent durability, insulation properties, and formability. If the thickness of the substrate layer is too thin, durability decreases and the substrate layer may be damaged during the forming process. If the thickness of the substrate layer is too thick, formability may decrease, the total thickness of the pouch film laminate may increase, the battery storage space may decrease, and the energy density may decrease.

[0035] According to one embodiment, the base layer 10 may have a laminated structure of a polyethylene terephthalate (PET) film and a nylon film. Preferably, the nylon film is disposed on the gas barrier layer 20 side, i.e., the inner side, and the polyethylene terephthalate film is disposed on the surface side of the battery case.

[0036] Polyethylene terephthalate (PET) has excellent durability and electrical insulation properties, and when a PET film is placed on the surface side, it also has excellent durability and insulation properties. However, PET film has poor adhesion to the aluminum alloy thin film that constitutes the gas barrier layer 20 and its stretching behavior is different. Therefore, when a PET film is placed on the gas barrier layer side, peeling between the base layer and the gas barrier layer can occur during the molding process, resulting in uneven stretching of the gas barrier layer and reduced formability. In contrast, nylon film has a similar stretching behavior to the aluminum alloy thin film that constitutes the gas barrier layer 20, so when a nylon film is placed between the polyethylene terephthalate and the gas barrier layer, it can improve formability.

[0037] The polyethylene terephthalate film may have a thickness of 5 μm to 20 μm, preferably 5 μm to 15 μm, and more preferably 7 μm to 15 μm, and the nylon film may have a thickness of 10 μm to 40 μm, preferably 10 μm to 35 μm, and more preferably 15 μm to 25 μm. When the thicknesses of the polyethylene terephthalate film and the nylon film satisfy the above ranges, excellent formability and rigidity after forming are achieved.

[0038] Gas barrier layer The gas barrier layer 20 is intended to ensure the mechanical strength of the battery case, to block the entry and exit of external gases or moisture into the secondary battery, and to prevent electrolyte leakage.

[0039] The gas barrier layer 20 can have a thickness of 60 μm or more, preferably 60 μm to 100 μm, and more preferably 60 μm to 80 μm. When the thickness of the gas barrier layer of the pouch film laminate is 60 μm or more, even when the cup portion is formed to a deep depth of 6.5 mm or more, the remaining thickness of the gas barrier layer at the corners of the cup portion can be formed to exceed 30 μm. Furthermore, when the thickness of the gas barrier layer of the pouch film laminate satisfies the above range, moldability is improved, and even when the cup portion is formed to a deep depth or when two cups are formed, cracks and / or pinholes are reduced, improving resistance to external stress after molding. When the thickness of the gas barrier layer of the pouch film laminate is less than 60 μm, in order to maintain the thickness of the gas barrier layer at the corner of the cup portion to 30 μm or more after the cup portion is formed, it is necessary to reduce the forming depth or reduce the pressure when stretching the corner. However, if the forming depth is reduced, the volume of the space for accommodating the electrode assembly is reduced, making it difficult to achieve a high energy density, and if the corner stretching pressure is reduced, stretching may be uneven, resulting in the generation of wrinkles.

[0040] Meanwhile, the gas barrier layer 20 may be made of a metal material, specifically, an aluminum alloy thin film.

[0041] The aluminum alloy thin film may contain aluminum and 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).

[0042] Preferably, the aluminum alloy thin film has an iron (Fe) content of 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 improvements in formability and bendability.

[0043] The aluminum alloy thin film also includes an aluminum alloy thin film having a crystal 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 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 and it becomes difficult to distribute 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 and bendability.

[0044] 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.

[0045] Specifically, the aluminum alloy thin film may be an aluminum alloy of alloy number AA8021, but is not limited thereto.

[0046] Sealant layer The sealant layer 30 is bonded by thermocompression bonding to seal the battery case, and is located as the innermost layer of the pouch film laminate 1.

[0047] The sealant layer 30 is the surface that comes into contact with the electrolyte and the electrode assembly after the battery case is formed, and therefore must have insulating and corrosion resistance. It must also have high sealing properties because it must completely seal the interior and prevent material transfer between the interior and exterior.

[0048] The sealant layer 30 may be made of a polymer material, for example, one or more 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, and Teflon (registered trademark). Among these, it is particularly preferable to use polypropylene (PP), which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, and chemical properties such as corrosion resistance.

[0049] More specifically, the sealant layer 30 may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0050] The sealant layer 30 may have a single layer structure or a multi-layer structure including two or more layers made of different polymer materials.

[0051] The sealant layer may have a total thickness of 60 μm to 100 μm, preferably 60 μm to 90 μm, and more preferably 70 μm to 90 μm. If the sealant layer is too thin, the seal durability and insulation properties may decrease, while if the sealant layer is too thick, the flexibility may decrease, the total thickness of the pouch film laminate may increase, and the energy density relative to the volume may decrease.

[0052] 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.

[0053] The pouch film laminate of the present invention may be manufactured by a method known in the art for manufacturing a pouch film laminate. For example, the pouch film laminate of the present invention may be manufactured by a method in which a substrate layer 10 is attached to the upper surface of a gas barrier layer 20 with an adhesive, and a sealant layer 30 is formed on the lower surface of the gas barrier layer 20 by coextrusion or an adhesive layer, but is not limited thereto.

[0054] The pouch film laminate manufactured as described above is inserted into a molding device, and pressure is applied to a portion of the pouch film laminate with a punch to form a cup portion, thereby manufacturing the battery case 100. Here, the pressure may be about 0.3 MPa to 1 MPa, preferably 0.3 MPa to 0.8 MPa, and more preferably 0.4 MPa to 0.6 MPa. If the pressure is too low during molding of the cup portion, excessive squeezing may occur, resulting in wrinkles, while if the pressure is too high, squeezing may not be performed well, resulting in a small molding depth.

[0055] Meanwhile, the moving speed of the punch may be 20 mm / min to 80 mm / min, preferably 30 mm / min to 70 mm / min, and more preferably 40 mm / min to 60 mm / min. If the moving speed of the punch is too fast, the peripheral surface 112 of the cup portion 110 may not be sufficiently stretched, and a compressive force may act thereon, causing wrinkles due to buckling. If the moving speed of the punch is too slow, stress may be concentrated at the corners of the cup portion during molding, increasing the occurrence of pinholes and cracks.

[0056] 1 and 2, a battery case 100 according to the present invention includes a cup portion 110 having a concave shape and a terrace 120 located on at least a part of the periphery of the cup portion 110. As shown in FIG.

[0057] The cup portion 110 has an accommodating space B for accommodating the electrode assembly 200, and the terrace 120 refers to the portion not formed by the pouch film laminate, i.e., the remaining area other than the cup portion 110.

[0058] 3, the cup portion 110 may include a bottom surface 111 and a peripheral surface 112. The peripheral surface 112 may connect the bottom surface 111 and the terrace 120. A plurality of, more specifically, four peripheral surfaces 112 may be provided.

[0059] The bottom surface 111 may cover one side of the electrode assembly 200 , and the peripheral surface 112 may surround the periphery of the electrode assembly 200 .

[0060] The cup portion 110 may also include a first edge 113 where the peripheral surface 112 and the terrace 120 meet, a second edge 114 where the bottom surface 111 and the peripheral surface 112 meet, and a third edge 115 where a pair of adjacent peripheral surfaces 112 meet among the plurality of peripheral surfaces 112. Each of the edges 113, 114, and 115 may be rounded to have a predetermined radius of curvature.

[0061] The cup portion 110 may also include a corner 116 where a pair of adjacent peripheral surfaces 112 of the plurality of peripheral surfaces 112 meet the bottom surface 111. That is, the corner 116 may be a portion where a pair of adjacent second edges 114 and third edges 115 overlap each other. The corner 116 may have a predetermined radius of curvature.

[0062] Since the cup portion 110 has four peripheral surfaces 112, each of the edges 113, 114, 115 and corners 116 can also be formed in four pieces.

[0063] In the battery case according to the present invention, the thickness of the gas barrier layer at the corner 116 exceeds 30 μm, preferably exceeds 30 μm and does not exceed 70 μm, and more preferably exceeds 30 μm and does not exceed 60 μm.

[0064] The corner 116 is where stretching stress is concentrated during cup formation. Because it is the area where stretching occurs most frequently, it is formed thinner than other areas, and is therefore most susceptible to cracks and pinholes and vulnerable to external impacts. In particular, when forming a two-cup structure, pressure is applied by two punches at close range, which further increases the stress concentrated at the corner, exacerbating these problems. To solve this problem, the present invention forms a gas barrier layer at the corner 116 of the cup to a thickness of more than 30 μm, thereby suppressing crack formation and minimizing damage caused by external impacts.

[0065] On the other hand, the thickness of the gas barrier layer at the corners 116 can be 50% to 70%, preferably 50% to 65%, and more preferably 55% to 65% of the thickness of the gas barrier layer at the terraces 120. If the gas barrier layer is stretched so that the thickness at the corners 116 is less than 50% of the thickness at the terraces 120, which are unformed regions, excessive stretching at the corners 116 will increase the occurrence of cracks, and if the thickness exceeds 70%, the volume of the storage space B in the cup portion will decrease, resulting in a decrease in the energy density of the battery.

[0066] On the other hand, terrace 120 is an area where no molding has been performed, and the thickness of the gas barrier layer in this area is approximately the same as the thickness of the gas barrier layer of the pouch film laminate before molding. Therefore, the thickness of the gas barrier layer in terrace 120 can be 60 μm or more, preferably 60 μm to 100 μm, and more preferably 60 μm to 80 μm.

[0067] Meanwhile, the radius of curvature of the corner 116 may be 0.5 to 5.0 mm, preferably 1.0 to 4.0 mm, and more preferably 2.0 to 3.5 mm. The radius of curvature of the corner 116 may be the radius of curvature of the inner surface of the corner 116. If the radius of curvature of the corner 116 is too small, it may be difficult to maintain the thickness of the gas barrier layer at the corner to 30 μm or more, and if the radius of curvature is too large, the accommodation space of the cup portion may be reduced, resulting in a decrease in energy density.

[0068] Specifically, the clearance CL between the first edge 113 and the second edge 114 may be 2 mm or less, preferably 0.3 mm to 1 mm. When the clearance satisfies this range, the free space within the cup portion 110 is further reduced, thereby improving the energy density of the secondary battery and the appearance of the secondary battery. Here, the clearance CL may refer to the distance between an imaginary first vertical line perpendicularly passing through the boundary point between the first edge 113 and the peripheral surface 112, and an imaginary second vertical line perpendicularly passing through the boundary point between the second edge 114 and the peripheral surface 112.

[0069] Meanwhile, the battery case 100 according to the present invention may include a lower case 101, an upper case 102, and a folding part 130 connecting the lower case and the upper case.

[0070] Specifically, the battery case 100 according to the present invention may be a two-cup battery case having two cup portions, with a cup portion 110 formed in each of a lower case 101 and an upper case 102, as shown in Fig. 1, or a one-cup battery case having a cup portion 110 formed only in the lower case 101, as shown in Fig. 2. In the case of a two-cup battery case, after accommodating an electrode assembly and an electrolyte, the upper case is folded so that the cup portion of the upper case and the cup portion of the lower case face each other. This allows for the accommodation of a thicker electrode assembly than a one-cup battery case, which is advantageous in achieving a high energy density.

[0071] On the other hand, in the present invention, the depth of the cup portion can be 5.0 mm or more, preferably 5.0 to 20 mm, and more preferably 6.5 to 20 mm. More specifically, in the case of a one-cup battery case, the depth of the cup portion can be 7.0 to 17 mm, and preferably 9.0 to 15 mm, and in the case of a two-cup battery case, the depth of each cup portion can be 5.0 to 12 mm, preferably 6 to 10 mm, and more preferably 7 to 10 mm.

[0072] If the cup depth is less than 6.5 mm, it is difficult to achieve a high energy density due to the small volume of the electrode assembly receiving space B. On the other hand, if the cup depth is increased, it is advantageous in terms of energy density, but cracks or pinholes may occur during the cup formation process, which may reduce the safety of the battery.

[0073] Meanwhile, the folding part 130 connects the lower case 101 and the upper case 102, and is folded after the electrode assembly 200 is accommodated in the cup part 110 and the electrolyte is injected, so that the upper case 102 can seal the cup part 110 of the lower case 101. When the folding part 130 is included, the lower case 101 and the upper case 102 are connected together, thereby reducing the number of sides to be sealed during a sealing process, thereby improving processability.

[0074] The folding portion 130 is formed to be spaced apart from the cup portion 110, and the distance between the folding portion 130 and the cup portion 110 may be about 0.5 mm to 3 mm, and preferably about 0.5 mm to 2 mm. If the folding portion 130 is formed too close to the cup portion 110, folding may not be performed smoothly, and if the folding portion 130 is formed too far from the cup portion 110, the total volume of the secondary battery may increase, and the energy density per volume may decrease. In the case of a two-cup case, the folding portion may be formed to satisfy the distance from each cup portion.

[0075] The battery case of the present invention has a large storage space for an electrode assembly, enabling high energy density. The cup portion has excellent rigidity, minimizing damage caused by external stress during logistics and charging / discharging. Specifically, the battery case of the present invention has a high tensile strength of 200 N or more, preferably 200 N to 300 N, and more preferably 210 N to 260 N, providing excellent resistance to external impact. Here, the tensile strength of the cup portion refers to the strength at which breakage occurs when a sample is prepared by cutting the cup portion of the battery case to a size of 15 mm wide x 80 mm long, and then the sample is fixed in a UTM device with a grip gap of 30 mm and pulled at a pulling rate of 50 mm / min.

[0076] The electrode assembly 200 is placed in the battery case 100, an electrolyte is injected, and then the folding part 130 is folded so that the upper case 102 is positioned above the lower case 101, and the terrace 120 is sealed to manufacture a secondary battery.

[0077] The electrode assembly 200 may include a plurality of electrodes and a plurality of separators stacked alternately. The plurality of electrodes may include positive and negative electrodes having opposite polarities, stacked alternately with separators interposed therebetween.

[0078] The electrode assembly 200 may also include a plurality of electrode tabs 230 welded to each other. The plurality of electrode tabs 230 may be connected to the plurality of electrodes 210, protrude from the electrode assembly 200, and act as paths through which electrons can move between the inside and outside of the electrode assembly 200. The plurality of electrode tabs 230 may be located inside the battery case 100.

[0079] The electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may protrude in different directions from each other with respect to the electrode assembly 200. However, without being limited thereto, the electrode tab 230 connected to the positive electrode and the electrode tab 230 connected to the negative electrode may protrude in the same direction in parallel to each other.

[0080] A lead 240 for supplying electricity to the outside of the secondary battery may be connected to the plurality of electrode tabs 230 by spot welding, etc. One end of the lead 240 may be connected to the plurality of electrode tabs 230, and the other end may protrude outside the battery case 100.

[0081] A portion of the lead 240 may be surrounded by an insulating portion 250. For example, the insulating portion 250 may include insulating tape. The insulating portion 250 may be located between the terrace 120 of the lower case 101 and the upper case 102, and in this state, the terrace 120 and the upper case 102 may be heat-sealed to each other. In this case, the terrace 120 and a portion of the upper case 102 may be heat-sealed to the insulating portion 250. Therefore, the insulating portion 250 prevents electricity generated from the electrode assembly 200 from flowing to the battery case 100 through the lead 240, thereby maintaining the seal of the battery case 100.

[0082] The electrolyte is used to transport lithium ions generated by electrochemical reactions at the electrodes during charging and discharging of the secondary battery 1, and may include a non-aqueous organic electrolyte solution that is a mixture of lithium salt and high-purity organic solvents, or a polymer using a polymer electrolyte. Furthermore, the electrolyte may include a sulfide-based, oxide-based, or polymer-based solid electrolyte, and such a solid electrolyte may have flexibility that makes it easily deformed by external forces.

[0083] The present invention will be described in more detail below with reference to specific examples.

[0084] Example 1 A 25 μm-thick nylon film (product name: Nylon 6, manufacturer: HYOSUNG) and a 12 μm-thick polyethylene terephthalate (PET) film (manufacturer: HYOSUNG) were laminated on one side of a 60 μm-thick AA8021 aluminum (Al) alloy thin film (manufacturer: SAMA Aluminum) using a urethane adhesive by dry lamination to form a substrate layer. Next, an 80 μm-thick sealant layer was formed on the other side of the aluminum alloy thin film by co-extrusion of acid-modified polypropylene (PPa) and polypropylene, producing a pouch film laminate.

[0085] The pouch film laminate was cut to a size of 266 mm x 240 mm and then placed in a two-cup molding machine equipped with a die and punch. The punch was lowered at a pressure of 0.5 MPa and a speed of 50 mm / min to form a battery case with a depth of 9.1 mm, producing a battery case with two cups. The mold conditions for the two-cup molding machine are shown in Table 1 below.

[0086] [Table 1]

[0087] Example 2 A pouch film laminate and a battery case were produced in the same manner as in Example 1, except that an 80 μm thick AA8021 aluminum (Al) alloy thin film was used instead of the 60 μm thick AA8021 aluminum (Al) alloy thin film.

[0088] Example 3 A pouch film laminate and a battery case were produced in the same manner as in Example 1, except that drawing was performed so that the forming depth was 6.2 mm.

[0089] Example 4 A pouch film laminate and a battery case were manufactured in the same manner as in Example 1, except that an 80 μm thick AA8021 aluminum (Al) alloy thin film was used instead of the 60 μm thick AA8021 aluminum (Al) alloy thin film, and drawing was performed to a forming depth of 6.2 mm.

[0090] Example 5 A film laminate and a battery case were produced in the same manner as in Example 1, except that drawing was performed by lowering the punch at a pressure of 0.1 MPa and a speed of 50 mm / min to a forming depth of 11.5 mm.

[0091] Comparative Example 1 A pouch film laminate and a battery case were produced in the same manner as in Example 1, except that a 40 μm thick AA8021 aluminum (Al) alloy thin film was used instead of the 60 μm thick AA8021 aluminum (Al) alloy thin film.

[0092] Comparative Example 2 A pouch film laminate and a battery case were manufactured in the same manner as in Example 1, except that a 40 μm thick AA8021 aluminum (Al) alloy thin film was used instead of the 60 μm thick AA8021 aluminum (Al) alloy thin film, and drawing was performed to a forming depth of 6.2 mm.

[0093] Comparative Example 3 A pouch film laminate and a battery case were manufactured in the same manner as in Example 1, except that a 40 μm thick AA8021 aluminum (Al) alloy thin film was used instead of the 60 μm thick AA8021 aluminum (Al) alloy thin film, and drawing was performed to a forming depth of 11.5 mm.

[0094] Comparative Example 4 A pouch film laminate and a battery case were produced in the same manner as in Example 1, except that drawing was performed so that the forming depth was 11.5 mm.

[0095] Experimental Example 1 The battery cases manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 were cut at a 45-degree angle between the cup portions, i.e., at the corners facing the folding portion, to prepare samples. Figure 5 illustrates the cutting positions of the battery cases. The cut cross sections of the samples were then observed, and the thickness of the gas barrier layer at the corners where the bottom and rim of the cups met was measured. The percentage ratio of the thickness of the gas barrier layer at the corners after cup molding to the thickness of the gas barrier layer before molding was calculated and expressed as the residual rate. Figure 6 shows the cut sample (A) and a photograph of the cross section of the sample (B).

[0096] The measurement results are shown in Table 2 below.

[0097] [Table 2]

[0098] Experimental example 2: Evaluation of crack occurrence Ten battery cases were manufactured using the methods of Examples 1 to 5 and Comparative Examples 1 to 4, and the four corners of the cup of each battery case were then illuminated with an LED light and visually inspected for cracks. Battery cases in which two or fewer cracks occurred out of the ten were rated as "OK," and battery cases in which three or more cracks occurred were rated as "NG." The measurement results are shown in Table 3 below.

[0099] Experimental Example 3: Measurement of tensile strength The cup portions of the battery cases manufactured by the methods of Examples 1 to 5 and Comparative Examples 1 to 4 were cut to produce samples with dimensions of 15 mm wide x 80 mm long. The cutting positions (box regions) of the battery cases are shown in Figure 7. Each sample was then fixed to a UTM device with a grip gap of 30 mm and pulled at a pulling rate of 50 mm / min to measure the strength at which breakage occurred, which was taken as the tensile strength. The measurement results are shown in the table below.

[0100] [Table 3]

[0101] As shown in Table 3 above, the battery cases of Examples 1 to 4, in which the thickness of the gas barrier layer at the corners of the cup portion exceeds 30 μm, have little cracking at the corners, whereas the battery cases of Comparative Examples 1 to 4, in which the thickness of the gas barrier layer is 30 μm or less, have a high incidence of cracking at the corners.

[0102] Furthermore, the battery cases of Examples 1 to 4 were shown to have a high tensile strength of 200 N or more in the cup portion, whereas those of Comparative Examples 1 and 2 were shown to have a low tensile strength of 200 N or less. In the case of Comparative Examples 3 and 4, the battery cases broke immediately at the start of the test, making it impossible to measure the tensile strength.

[0103] Experimental Example 4 The appearances of the battery cases manufactured in Examples 1 and 5 were observed. Fig. 8 is a photograph of the appearance of the battery case of Example 1, and Fig. 9 is a photograph of the appearance of the battery case of Example 5.

[0104] As shown in Figures 8 and 9, no wrinkles were observed in the battery case of Example 1, but it was confirmed that wrinkles occurred in the terrace portion of the battery case of Example 5, which was molded by adjusting the pressure to a low level. [Explanation of symbols]

[0105] 1 Secondary battery 10 Base material layer 20 Gas barrier layer 30 Sealant Layer 100 Battery Case 101 Lower case 102 Upper case 110 Cup section 120 Terrace 130 Folding section 200 electrode assembly

Claims

1. A pouch-type battery case comprising a pouch film laminate including a gas barrier layer, a base layer disposed on one surface of the gas barrier layer, and a sealant layer disposed on the other surface of the gas barrier layer, the pouch-type battery case includes at least one cup portion for accommodating an electrode assembly, and a terrace located on at least a portion of a periphery of the cup portion; The cup portion includes a bottom surface and a plurality of peripheral surfaces surrounding the bottom surface, the thickness of the gas barrier layer at a corner where a pair of adjacent peripheral surfaces and the bottom surface meet is more than 30 μm and not more than 70 μm; The thickness of the gas barrier layer on the terrace is 60 μm to 100 μm.

2. 2. The pouch-type battery case according to claim 1, wherein the thickness of the gas barrier layer at the corners is 50% to 70% of the thickness of the gas barrier layer at the terraces.

3. 2. The pouch-shaped battery case according to claim 1, wherein the corner has a radius of curvature of 0.5 to 5.0 mm.

4. 2. The pouch-type battery case according to claim 1, wherein the pouch-type battery case includes: a lower case having the cup portion; an upper case that is folded over the lower case to seal the cup portion; and a folding portion that connects the upper case and the lower case.

5. 5. The pouch-type battery case according to claim 4, wherein the folding portion and the cup portion are spaced apart from each other by a distance of 0.5 mm to 3 mm.

6. The pouch-type battery case according to claim 4 , wherein the upper case has a cup portion formed therein.

7. 2. The pouch-type battery case according to claim 1, wherein the cup portion has a depth of 5.0 mm or more.

8. 2. The pouch-type battery case according to claim 1, wherein the cup portion has a tensile strength of 200 N or more.

9. 2. The pouch-type battery case according to claim 1, wherein the base layer has a laminated structure of a polyethylene terephthalate film and a nylon film.

10. The thickness of the polyethylene terephthalate film is 5 μm to 20 μm, 10. The pouch-type battery case according to claim 9, wherein the nylon film has a thickness of 10 μm to 30 μm.

11. The pouch-type battery case according to claim 1 , wherein the gas barrier layer includes an aluminum alloy thin film.

12. 12. The pouch-type battery case according to claim 11, wherein the aluminum alloy thin film contains 1.2 wt % to 1.7 wt % of iron.

13. 12. The pouch-type battery case according to claim 11, wherein the aluminum alloy thin film has a crystal grain size of 10 μm to 13 μm.

14. 2. The pouch-type battery case according to claim 1, wherein the sealant layer has a thickness of 60 μm to 100 μm.

15. 2. The pouch-type battery case according to claim 1, wherein the sealant layer comprises polypropylene, unstretched polypropylene, acid-modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

16. 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, wherein the pouch-type battery case is the pouch-type battery case according to any one of claims 1 to 15.

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