Pouch-type battery case and lithium secondary battery including 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 to 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 applied and used not only in small products such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, and E-bikes, but also in large products that require high output such as electric vehicles and hybrid cars, power storage devices that store surplus generated electricity and newly renewable energy, and backup power storage devices.

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

[0005] Secondary batteries are divided into pouch type and can type depending on the material of the case that houses the electrode assembly. The pouch type houses the electrode assembly in a pouch made of a flexible polymer material.

[0006] The pouch-type battery case is manufactured by pressing a flexible pouch film laminate to form a cup portion for housing an electrode assembly, and then housing 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 such 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, as the demand for high-capacity batteries such as electric vehicle batteries and ESS batteries increases, the demand for battery cases capable of accommodating more electrode assemblies is also increasing. Accordingly, attempts have been made to increase the molding depth of the cup part of the pouch-type battery case or to form cup parts in the upper and lower cases to increase the volume of the storage space. However, when the molding depth of the cup part is increased or two-cup molding is performed, cracks and pinholes are likely to occur due to the increased tensile force applied to the pouch film laminate during the molding process, and there is a problem that cracks and pinholes are particularly likely to occur at the lower corners of the cup parts where stress is concentrated during stretching. If cracks or pinholes occur, the battery case becomes vulnerable to external impact, making it more likely to be damaged, and the safety of the battery is reduced.

[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 bonding an additional member to the edge of a cup part (storage part) or by varying the stretching pressure to thicken the barrier layer at the edge of the cup part during manufacturing of the secondary battery case. However, when an additional member is bonded to the edge of the cup part as described in Patent Document 1, the stretchability is reduced during molding, and a step is generated due to the bonding of the additional member, or the thickness of the sealant layer or the base material layer becomes uneven, which adversely affects the seal durability and insulation properties. In addition, there is a problem that the thickness of the pouch film laminate becomes uneven when the additional member is bonded, making it difficult to wind it up. Meanwhile, when the molding pressure is adjusted to thicken the edge of the cup part, stretching is performed unevenly, and wrinkles are generated after molding, which may adversely affect the 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 compromising moldability, sealing properties, and insulating 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 an object of the present invention is to provide a pouch-type battery case that can minimize the occurrence of cracks at the corners of the cup part, 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, the pouch-type battery case including 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 a periphery of the cup portion, the cup portion including 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 greater than 30 μm, preferably greater than 30 μm and not greater than 70 μm, 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 tensile strength of the cup portion can be 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. Effect of the Invention

[0020] The battery case according to the present invention uses a thick pouch film laminate with a gas barrier layer of 60 μm or more, and is formed so that the remaining thickness of the gas barrier layer at the corners of the cup part after cup formation is greater than 30 μm, thereby effectively preventing the occurrence of cracks such as cracks or pinholes at the corners of the cup part even under harsh stretching conditions. As such, the battery case according to the present invention has fewer cracks and pinholes at the corners of the cup part, and therefore has high resistance to external impacts that occur during logistics and charging and discharging, and can prevent electrolyte leakage and moisture penetration due to damage to the battery case, thereby ensuring battery stability.

[0021] In addition, the battery case according to the present invention can be sufficiently stretched so that the thickness of the gas barrier layer at the corners of the cup portion is 50% to 70% of the thickness of the gas barrier layer in the terraces, which are unformed areas, thereby making it possible to form a deep cup portion. As a result, the volume of the storage space for the electrode assembly can be increased, and a high energy density can be achieved. [Brief description of the drawings]

[0022] [Figure 1] 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; [Diagram 2] 13A and 13B are diagrams illustrating a battery case according to another embodiment of the present invention. [Diagram 3] FIG. 3 is a partial enlarged view of A in FIG. 1 and FIG. 2. [Figure 4] 1 is a cross-sectional view illustrating a pouch film laminate of the present invention. [Diagram 5] FIG. 4 is a diagram showing cutting positions of a battery case in Experimental Example 1. [Figure 6] 1 is a photograph of a cut sample and a cross section of the sample in Experimental Example 1. [Figure 7] FIG. 13 is a diagram showing cutting positions of a battery case for producing a sample for measuring tensile strength in Experimental Example 3. [Figure 8] 2 is a photograph showing the appearance of the battery case of Example 1. [Figure 9] 1 is a photograph showing the appearance of a battery case of Comparative Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0024] The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner 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 describe his / her invention.

[0025] The present inventors have conducted extensive research to manufacture a battery case that can provide a large storage space for a battery assembly and achieve a high energy density, and that can suppress damage due to external stress generated during logistics and charging / discharging, particularly damage to the corners of the cup portion, which are vulnerable portions, caused by stress. As a result, the present inventors have found that the above-mentioned object can be achieved when a battery case is formed such that the remaining thickness of the gas barrier layer at the corners of the cup portion after cup molding exceeds 30 μm, 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 part A in Fig. 1 and Fig. 2, and Fig. 4 is a diagram illustrating one embodiment of a pouch film laminate for manufacturing a battery case of the present invention. Hereinafter, the present invention will 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, “battery case”) and an electrode assembly 200 housed in the battery case 100 .

[0028] The pouch-type battery case 100 is manufactured by a method in which a flexible pouch film laminate is inserted into a press molding device and a punch is used to apply pressure 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 impacts 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 multi-layer structure, the thickness includes the thickness of the adhesive layer. When the substrate layer 10 satisfies the above range, it has excellent durability, insulation, and formability. If the substrate layer is too thin, the durability decreases and the substrate layer may be damaged during the forming process, and if the substrate layer is too thick, the 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. Here, it is preferable that the nylon film is disposed on the gas barrier layer 20 side, i.e., on the inside, 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, and when a PET film is placed on the surface side, it has excellent durability and insulation. However, in the case of a PET film, the adhesion to the aluminum alloy thin film constituting the gas barrier layer 20 is weak, and the stretching behavior is also different, so when a PET film is placed on the gas barrier layer side, peeling between the base layer and the gas barrier layer may occur during the molding process, and the gas barrier layer may not be stretched uniformly, resulting in a problem of reduced moldability. In contrast, since the stretching behavior of a nylon film is similar to that of the aluminum alloy thin film constituting the gas barrier layer 20, when a nylon film is placed between the polyethylene terephthalate and the gas barrier layer, it is possible to obtain an effect of improving moldability.

[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, the moldability and rigidity after molding are excellent.

[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 and from the secondary battery, and to prevent electrolyte leakage.

[0039] The gas barrier layer 20 may 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 molding depth of the cup part is formed deep, such as 6.5 mm or more, the remaining thickness of the gas barrier layer at the corner of the cup part can be formed to exceed 30 μm. In addition, when the thickness of the gas barrier layer of the pouch film laminate satisfies the above range, the moldability is improved, the molding depth of the cup part is increased, or even when two cups are molded, cracks and / or pinholes are less likely to occur, and resistance to external stress after molding is improved. 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 part to 30 μm or more after the cup part 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 becomes non-uniform and wrinkles may occur.

[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 1.2wt% to 1.7wt%, preferably 1.3wt% to 1.7wt%, more preferably 1.3wt% to 1.45wt%. If the iron (Fe) content in the aluminum alloy thin film is less than 1.2wt%, the strength of the aluminum alloy thin film is reduced, and cracks and pinholes may occur during forming, and if it exceeds 1.7wt%, the flexibility of the aluminum alloy thin film is reduced, and there is a limit to the improvement of formability and bendability.

[0043] The aluminum alloy thin film 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 the above range, the forming depth can be increased without the occurrence of pinholes or cracks during cup forming. When 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 disperse internal stress during stretching, increasing the occurrence of cracks and pinholes. When 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 with 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 is obtained using a scanning electron microscope, and the maximum diameters of any 30 crystal grains among the crystal grains observed in the SEM image are measured, and the average value of these is evaluated as the grain size.

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

[0046] Sealant Layer The sealant layer 30 is bonded by thermocompression 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 being molded into a battery case, and therefore must have insulating properties 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 them, it is particularly preferable to include 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 thickness of the sealant layer is too thin, the seal durability and insulation properties may decrease, and if the thickness 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 the above range, it is possible to minimize the reduction in battery accommodating space and the deterioration of sealing durability due to the increase in the thickness of the pouch laminate, and to increase the molding depth.

[0053] The pouch film laminate of the present invention as described above may be manufactured by a method for manufacturing a pouch film laminate well known in the art. For example, the pouch film laminate of the present invention may be manufactured by a method in which a base layer 10 is attached to an upper surface of a gas barrier layer 20 by an adhesive, and a sealant layer 30 is formed on a 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, and if the pressure is too high, squeezing may not be performed well, resulting in a reduced molding depth.

[0055] Meanwhile, the moving speed of the punch may be 20mm / min to 80mm / min, preferably 30mm / min to 70mm / min, more preferably 40mm / min to 60mm / min. If the moving speed of the punch is too fast, the peripheral surface 112 of the cup part 110 may not be sufficiently stretched and may be subjected to a compressive force, resulting in wrinkles due to buckling, whereas if the moving speed of the punch is too slow, the stress concentrated at the corners of the cup part during molding may increase, resulting in increased 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 a 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 further 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 among the plurality of peripheral surfaces 112 meet. Each of the edges 113, 114, 115 may be formed in a round shape having a predetermined radius of curvature.

[0061] In addition, the cup portion 110 may include a corner 116 where a pair of adjacent peripheral surfaces 112 among the plurality of peripheral surfaces 112 contact the bottom surface 111. That is, the corner 116 may be a portion where a pair of second edges 114 and third edges 115 that contact each other 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 a part where stretching stress is concentrated during molding of the cup part, and since it is stretched the most, it is formed thinner than other parts, and is also most susceptible to cracks and pinholes and is most vulnerable to external impact. In particular, when molding two cups, pressure is applied by two punches at a close distance, so that the stress concentrated at the corner increases and the problem tends to become even worse. In order to solve this problem, the present invention forms the gas barrier layer at the corner 116 of the cup part to a thickness of more than 30 μm, thereby suppressing the occurrence of cracks and minimizing damage caused by external impact.

[0065] On the other hand, the thickness of the gas barrier layer at the corner 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 terrace 120. If the gas barrier layer is stretched so that the thickness at the corner 116 is less than 50% of the thickness at the terrace 120, which is an unformed region, the stretching at the corner 116 will be excessive, increasing the occurrence of cracks, and if it exceeds 70%, the volume of the storage space B of the cup portion will decrease, decreasing the energy density of the battery.

[0066] On the other hand, the terrace 120 is an area where molding has not 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 the 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 with respect to the inner surface of the corner 116. If the radius of curvature of the corner 116 is too small, it is 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 storage space of the cup portion is reduced, which may result 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, and preferably 0.3 mm to 1 mm. When the clearance satisfies this range, the free space in 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 type battery case including two cup parts, in which a cup part 110 is formed in each of a lower case 101 and an upper case 102, as shown in Fig. 1, or may be a one-cup type battery case in which a cup part 110 is formed only in the lower case 101, as shown in Fig. 2. In the case of a two-cup type battery case, after accommodating an electrode assembly and an electrolyte, the upper case is folded so that the cup part of the upper case and the cup part of the lower case face each other, so that an electrode assembly having a greater thickness can be accommodated in the two-cup type battery case, which is advantageous in realizing 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 because the volume of the electrode assembly receiving space B is small. 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 forming 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, stores the electrode assembly 200 in the cup part 110, injects an electrolyte, and then folds 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 part 130 is formed apart from the cup part 110, and the distance between the folding part 130 and the cup part 110 may be about 0.5 mm to 3 mm, and preferably about 0.5 mm to 2 mm. If the folding part 130 is formed too close to the cup part 110, folding may not be performed smoothly, and if the folding part 130 is formed too far from the cup part 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 part may be formed to satisfy the distance between each cup part.

[0075] The battery case of the present invention has a large space for accommodating an electrode assembly, thereby realizing a high energy density, and has excellent rigidity of the cup portion, thereby minimizing damage caused by external stress during a logistics process or a charge / discharge process. Specifically, the battery case of the present invention has a high tensile strength of 200N or more, preferably 200N to 300N, and more preferably 210N to 260N, thereby providing excellent resistance to external impact. Here, the tensile strength of the cup portion refers to the strength at which breakage occurs when the cup portion of the battery case is cut into a sample having a width x length of 15mm x 80mm, and the sample is fixed in a UTM device with a grip gap of 30mm and pulled at a pulling speed of 50mm / min.

[0076] The electrode assembly 200 is housed in the battery case 100 as described above, 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 that are alternately stacked. The plurality of electrodes may include positive and negative electrodes having opposite polarities that are alternately stacked with separators interposed therebetween.

[0078] In addition, the electrode assembly 200 may 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 to the outside, and act as a passage through which electrons can move between the inside and the 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, the present invention is not limited thereto, and 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 to the outside of 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 an 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 can prevent electricity generated from the electrode assembly 200 from flowing to the battery case 100 through the lead 240, and can maintain the sealing of the battery case 100.

[0082] The electrolyte is for transferring 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 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 an external force.

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

[0084] Example 1 A 25μm-thick nylon film (product name: Nylon 6, manufacturer: HYOSUNG) and a 12μm-thick polyethylene terephthalate (PET) film (manufacturer: HYOSUNG) were laminated on one side of a 60μm-thick AA8021 aluminum (Al) alloy thin film (manufacturer: SAMA Aluminum) using a urethane adhesive by dry lamination to form a base layer. Next, an 80μm-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 to produce a pouch film laminate.

[0085] The pouch film laminate was cut to a size of 266 mm x 240 mm, and then attached to a two-cup molding device equipped with a die and a punch, and the punch was lowered at a pressure of 0.5 MPa and a speed of 50 mm / min to perform drawing to a molding depth of 9.1 mm, thereby manufacturing a battery case including two cup parts. Here, the mold conditions of the two-cup molding device are as 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 a 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 a 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 parts, i.e., at the corners in the direction of the folding parts, to manufacture samples. The cutting positions of the battery cases are shown in FIG. 5. The cut cross sections of the samples were then observed to measure the thickness of the gas barrier layer at the corners where the bottom surface and the periphery of the cup parts meet, and the percentage of the ratio of the thickness of the gas barrier layer at the corners after molding of the cup to the thickness of the gas barrier layer before molding was shown as the residual rate. The cut sample (A) and a photograph of the cross section of the sample (B) are shown in FIG. 6.

[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 to visually check whether cracks had occurred. If two or fewer of the ten battery cases had cracks, the battery case was marked as OK, and if three or more of the ten battery cases had cracks, the battery case was marked as NG. The measurement results are shown in Table 3 below.

[0099] Experimental Example 3: Tensile strength measurement 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 a width x length of 15 mm x 80 mm to manufacture samples. The cutting positions (box regions) of the battery cases are shown in FIG. 7. Then, each sample was fixed to a UTM device with a grip gap of 30 mm, and pulled at a pulling speed of 50 mm / min to measure the strength at which breakage occurred 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, show little occurrence of cracks 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, show high occurrence of cracks at the corners.

[0102] In addition, the battery cases of Examples 1 to 4 had a high tensile strength of 200 N or more in the cup portion, whereas Comparative Examples 1 and 2 had a low tensile strength of 200 N or less. In the cases 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 produced in Examples 1 and 5 were observed. Fig. 8 is a photograph showing the appearance of the battery case of Example 1, and Fig. 9 is a photograph showing 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 pouch-type battery case has a gas barrier layer having a thickness of more than 30 μm at a corner where a pair of adjacent peripheral surfaces and the bottom surface meet.

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

3. 2. The pouch-type battery case according to claim 1, wherein the thickness of the gas barrier layer on the terrace is 60 μm or more.

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

5. 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 onto an upper portion of the lower case to seal the cup portion, and a folding portion that connects the upper case and the lower case.

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

7. The pouch-type battery case according to claim 5 , wherein the upper case is formed with a cup portion.

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

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

10. 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.

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

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

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

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

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

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

17. 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, the pouch-type battery case being the pouch-type battery case according to any one of claims 1 to 16.

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