Method for manufacturing battery case for secondary battery and gas exhaust part

Abstract

To provide a battery case for a secondary battery and a method of manufacturing a gas exhaustion part capable of exhausting gas inside a pouch to the exterior to adjust pressure when an internal pressure of the pouch increases.SOLUTION: A battery case for a secondary battery according to an embodiment of the present invention for solving the above problem is a battery case for a secondary battery including: a cup part provided with an accommodation space for accommodating an electrode assembly formed by laminating an electrode and a separator; a sealing part formed to extend in an outward direction of the cup part; and a gas exhaustion part attached to the inside of a hole formed by perforating at least one of the cup part and the sealing part and through which gas is transmitted. The gas exhaustion part includes: a gas exhaustion layer through which gas is transmitted; and an external functional layer formed on an outer lateral face of the gas exhaustion layer, and having a hydrophobic property.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0105417, filed on August 27, 2019, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a battery case for a secondary battery and a method for manufacturing a gas exhaust part, and more particularly to a battery case for a secondary battery and a method for manufacturing a gas exhaust part that can adjust the pressure by exhausting the internal gas to the outside when the internal pressure of the pouch increases. [Background technology]

[0003] Common types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries. These secondary batteries are used not only in small products such as digital cameras, P-DVDs, 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 vehicles, as well as in power storage devices that store surplus generated power and renewable energy, and as backup power storage devices.

[0004] Secondary batteries are classified 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 soft polymer material, while can types house the electrode assembly in a case made of metal or plastic.

[0005] Meanwhile, secondary batteries may generate gas due to an internal short circuit caused by an external impact, overcharging, over-discharging, etc. Also, when stored or preserved at high temperatures, the high temperature may rapidly promote the electrochemical reaction between the electrolyte and the electrode active material, resulting in gas generation.

[0006] In this case, the generated gas increases the internal pressure of the secondary battery, causing problems such as weakening of the bonding strength between components, damage to the secondary battery case, early activation of the protection circuit, deformation of the electrodes, internal short circuit, and explosion. To prevent this, can-type secondary batteries are equipped with protective members such as CID filters and safety vents. Therefore, when the pressure inside the case increases, the electrical connection is physically cut off. However, conventional pouch-type secondary batteries do not have sufficient protective members. Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a battery case for a secondary battery and a method for manufacturing a gas exhaust part that can adjust the pressure by exhausting the internal gas to the outside when the internal pressure of the pouch increases.

[0008] The objects of the present invention are not limited to the objects mentioned above, and other objects not mentioned above will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0009] To solve the above problems, a battery case for a secondary battery according to an embodiment of the present invention includes a cup portion having an accommodating space for accommodating an electrode assembly formed by stacking electrodes and separators; a sealing portion extending outward from the cup portion; and a gas discharge portion attached to the inside of a hole formed by perforating at least one of the cup portion or the sealing portion and through which gas can pass, the gas discharge portion including a gas discharge layer through which gas can pass, and a hydrophobic outer functional layer formed on an outer surface of the gas discharge layer.

[0010] The outer functional layer may be formed with a plurality of micro-projections distributed on the outer surface, and the micro-projections may have a diameter of 50 nm to 10 μm. The fine protrusions may have a diameter of 100 nm to 1 μm.

[0011] The outer functional layer may include an oil or wax component, and the oil may include at least one of a fluorocarbon oil, a silicone oil, a carbon-based oil, and a fatty acid amide.

[0012] The gas-releasing layer may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).The gas-releasing layer may further include an inner functional layer formed on the inner surface of the gas-releasing layer and having hydrophobic properties.

[0013] The sealing portion may include an inner region adjacent to the cup portion and an outer region positioned outside the inner region to form a rim and seal the cup portion, and the hole may be formed in the inner region of the sealing portion.

[0014] To solve the above problems, a method for manufacturing a gas exhaust part according to an embodiment of the present invention includes the steps of providing a gas exhaust layer through which gas can pass, stirring fine particles and a polymer solution to prepare a mixture, spraying the mixture onto at least one surface of the gas exhaust layer, and drying the mixture.

[0015] The gas release layer may contain at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

[0016] The polymer solution may contain at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

[0017] The fine particles may include at least one of silica particles, carbon nanotubes (CNTs), and alumina particles, and the silica particles may be contained in an amount of 0.1 to 2 wt %.

[0018] In addition, the step of spraying the mixture may involve spraying the mixture using a nozzle at a pressure of 0.2 to 0.5 MPa from a distance of 8 to 15 cm from the gas discharge layer. In addition, the step of spraying the mixture and the step of drying the mixture may be repeated two to four times.

[0019] A pouch-type secondary battery according to an embodiment of the present invention for solving the above problems includes: an electrode assembly formed by stacking electrodes and a separator; and a battery case that houses the electrode assembly therein. The battery case includes: a cup portion having an accommodation space that houses the electrode assembly; a sealing portion formed to extend outward from the cup portion; and a gas outlet portion attached to an inner side of a hole formed by perforating at least one of the cup portion or the sealing portion and through which gas can pass. The gas outlet portion includes a gas outlet layer through which gas can pass; and an outer functional layer that is formed on an outer surface of the gas outlet layer and has hydrophobic properties.

[0020] To solve the above problems, a method for manufacturing a pouch-type secondary battery according to an embodiment of the present invention includes the steps of: drawing a pouch film to form a cup portion; drilling a hole in at least one of the cup portion and a seal portion formed to extend outward from the cup portion; attaching a gas outlet portion, through which gas can pass, to the inside of the hole; accommodating an electrode assembly formed by stacking electrodes and a separator in an accommodating space defined in the cup portion; and thermocompression bonding the electrode assembly to the seal portion.

[0021] The gas release part may include a gas release layer that is permeable to gas and a hydrophobic outer functional layer formed on the outer surface of the gas release layer, the pouch film may include a sealant layer made of a polymer and positioned as an innermost layer, and the step of attaching the gas release part may involve sealing the outer functional layer by applying heat and pressure to the sealant layer. Other specific features of the present invention are included in the detailed description and drawings. [Effects of the Invention]

[0022] According to an embodiment of the present invention, at least the following effects can be achieved: Holes are drilled in the battery case, and a gas exhaust part through which gas can pass is attached to the hole, so that when the internal pressure of the secondary battery increases, the internal gas can be exhausted to the outside to adjust the pressure.

[0023] In addition, an external or internal functional layer is formed on the gas exhaust portion, which can prevent external moisture penetration and internal electrolyte leakage. In addition, the gas exhaust portion is attached to the inside of the hole, which can prevent the metal of the gas barrier layer exposed to the inner surface of the hole from being corroded by the electrolyte.

[0024] The effects of the present invention are not limited to the above-mentioned examples, and various other effects are included within the present specification. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is an assembly diagram of a pouch-type secondary battery according to one embodiment of the present invention. [Figure 2] 1 is a perspective view of a pouch-type secondary battery according to an embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view of a gas discharge section according to an embodiment of the present invention. [Figure 4] 4 is a flowchart illustrating a method for manufacturing a gas exhaust portion according to an embodiment of the present invention. [Figure 5] 1 is a cross-sectional view of a pouch film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains. The present invention is defined solely by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless clearly defined otherwise.

[0028] 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 form includes the plural form unless otherwise specified in the wording. 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.

[0029]

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is an assembly diagram of a pouch-type secondary battery 1 according to one embodiment of the present invention, and Fig. 2 is a perspective view of the pouch-type secondary battery 1 according to one embodiment of the present invention.

[0030] As shown in FIG. 1, a pouch-type secondary battery 1 according to one embodiment of the present invention includes an electrode assembly 10 formed by stacking electrodes such as a positive electrode and a negative electrode and a separator, and a pouch-type battery case 13 that houses the electrode assembly 10 therein.

[0031] To manufacture the pouch-type secondary battery 1, first, a slurry containing an electrode active material, a binder, and a plasticizer is applied to a positive electrode current collector and a negative electrode current collector to manufacture electrodes such as a positive electrode and a negative electrode. This is then laminated on both sides of a separator to form an electrode assembly 10 of a predetermined shape, and the electrode assembly 10 is then inserted into a battery case 13, filled with an electrolyte, and sealed.

[0032] Specifically, the electrode assembly 10 may be a laminated structure including two electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes or disposed on the left or right side of one of the electrodes to insulate the electrodes from each other. The laminated structure may be formed in various forms, including stacking positive and negative electrodes of a predetermined size with a separator interposed therebetween, or wound up in the form of a jelly roll. The two electrodes, i.e., the positive electrode and the negative electrode, are each formed by applying an active material slurry to a metal foil or metal mesh electrode collector containing aluminum and copper. The slurry may be formed by stirring a granular active material, an auxiliary conductor, a binder, a plasticizer, and the like in a solvent. The solvent is removed in a subsequent process.

[0033] As shown in FIG. 1, the electrode assembly 10 includes electrode tabs 11. The electrode tabs 11 are connected to the positive and negative electrodes of the electrode assembly 10, respectively, and protrude from the outside of the electrode assembly 10, providing 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 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion by ultrasonic welding or the like. The electrode tabs 11 may protrude in the same direction from one side of the electrode assembly 10, as shown in FIG. 1, but are not limited thereto and may protrude in different directions.

[0034] 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 within a seal portion 134 formed by heat-sealing an upper case 131 and a lower case 132 of the battery case 13, and is adhered to the battery case 13. The insulating portion 14 prevents electricity generated by the electrode assembly 10 from flowing to the battery case 13 through the electrode lead 12, thereby maintaining the sealing of the battery case 13. Therefore, the insulating portion 14 is made of a non-conductive material that does not conduct electricity well. Typically, the insulating portion 14 is made of insulating tape, which is easy to adhere to the electrode lead 12 and has a relatively thin thickness. However, the insulating portion 14 is not limited thereto, and various materials may be used as long as they are capable of insulating the electrode lead 12.

[0035] 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 to the outside of the battery case 13, thereby enabling electricity generated inside the electrode assembly 10 to be supplied to the outside. In addition, since the positive electrode tab 111 and the negative electrode tab 112 protrude in various directions, the positive electrode lead 121 and the negative electrode lead 122 can also extend in various directions.

[0036] 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). 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.

[0037] The battery case 13 is a pouch made of a flexible material. The battery case 13 accommodates and seals the electrode assembly 10 such 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 an upper case 131 and a lower case 132. The lower case 132 has a cup portion 133 formed therein and is provided with a receiving space 1331 capable of accommodating the electrode assembly 10, and the upper 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 case, as shown in FIG. 1 , the upper case 131 may also be formed with a cup portion 133 having the receiving space 1331, allowing the electrode assembly 10 to be accommodated from above. However, the present invention is not limited thereto, and various other configurations are possible, such as a cup portion 133 being formed only in the lower case 132. In addition, the upper case 131 and the lower 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.

[0038] The battery case 13 includes a gas-permeable gas exhaust part 136. The gas exhaust part 136 is attached to the inside of a hole 137 formed by drilling at least one of the cup part 133 and the sealing part 134.

[0039] The hole 137 is formed in at least one of the upper case 131 and the lower case 132. That is, the hole 137 may be formed in one or more. As shown in FIG. 1, the sealing portion 134, which is extended outward from the cup portion 133, includes an inner region 1341 adjacent to the cup portion 133 and an outer region 1342 located outside the inner region 1341 and sealing the cup portion 133 as a rim. In this case, it is preferable that the hole 137 is formed in the inner region 1341 of the sealing portion 134 rather than the outer region 1342. Then, when sealing the sealing portion 134, it is preferable that the inner region 1341 where the hole 137 is located is not sealed, and only the outer region 1342 is sealed. As a result, the two seal portions 134 of the upper and lower cases 131 and 132 normally contact each other and close the hole 137, preventing external moisture penetration and internal electrolyte leakage. When a large amount of gas is generated inside the secondary battery 1, the volume of the secondary battery 1 expands, causing the inner regions 1341 of the two seal portions 134 that were in contact with each other to separate. This opens the hole 137, allowing the gas to be discharged to the outside through the gas discharge portion 136. However, the present invention is not limited to this, and the hole 137 may be formed in various positions, such as on one side of the cup portion 133, as long as the gas can be easily discharged.

[0040] Gas can easily permeate through the gas exhaust part 136, but it is preferable that liquids such as water and electrolyte cannot easily permeate through the gas exhaust part 136. The gas exhaust part 136 will be described in detail later.

[0041] 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 defined in the cup portion 133 of the lower case 132, and the upper case 131 covers the space from above. An electrolyte solution is then poured into the interior, and the upper case 131 and the lower case 132 are sealed with the sealing portions 134 formed on the edges of the upper case 131 and the lower case 132. The electrolyte solution transports lithium ions generated by an electrochemical reaction at the electrodes during charging and discharging of the secondary battery 1. The electrolyte solution may include a non-aqueous organic electrolyte solution, which is a mixture of a lithium salt and a high-purity organic solvent, or a polymer using a polymer electrolyte. Using this method, a pouch-type secondary battery 1 can be manufactured, as shown in FIG. 2.

[0042] 3 is a cross-sectional view of a gas exhaust unit 136 according to an embodiment of the present invention. The gas exhaust unit 136 is attached to the inside of a hole 137 formed by drilling at least one of the cup portion 133 or the sealing portion 134, and is gas permeable. As shown in FIG. 3, the gas exhaust unit 136 includes a gas-permeable gas exhaust layer 1362 and an outer functional layer 1361 formed on the outer surface of the gas exhaust layer 1362 and having hydrophobic properties. The gas exhaust unit 1366 may further include an inner functional layer 1363 formed on the inner surface of the gas exhaust layer 1362 and having hydrophobic properties.

[0043] The gas release layer 1362 is preferably made of a semipermeable membrane that allows gas to easily pass through but does not allow liquids such as water and electrolyte to easily pass through. The gas release layer 1362 may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF). The gas release layer 1362 may be manufactured using a biaxial stretching method. That is, the gas release layer 1362 may be manufactured by extruding an original material containing the above-mentioned material into a film and then stretching it in the extrusion direction (MD, Mechanical Direction) and the transverse direction. However, without being limited thereto, a phase separation method may also be used. That is, the gas release layer 1362 may be manufactured by applying an original material containing the above-mentioned material into a film on a plate, evaporating the solvent at different temperatures, and then immersing the film in a water bath filled with the above-mentioned solution.

[0044] According to one embodiment of the present invention, there is no separate cover for opening and closing the hole 137 formed in the battery case 13. If a cover were present, it would be difficult to close the hole 137 again after the cover opened it. To solve this problem, a separate hinge would have to be provided so that the cover could open and close the hole 137, which would complicate the structure and reduce durability. However, if there was no cover, even if liquid could not easily permeate through the gas discharge layer 1362, a small amount of moisture could still permeate from the outside through the gas discharge layer 1362.

[0045] 3, a hydrophobic outer functional layer 1361 is formed on the outer surface of the gas discharge layer 1362. Here, the outer surface of the gas discharge layer 1362 refers to the surface formed on the outside of the secondary battery 1, i.e., the surface facing away from the electrode assembly 10, when the secondary battery 1 is manufactured.

[0046] According to one embodiment of the present invention, the outer functional layer 1361 may have a plurality of microprotrusions distributed on its outer surface. The microprotrusions may prevent moisture condensation on the outer surface of the outer functional layer 1361, thereby providing hydrophobicity. Here, the outer surface of the outer functional layer 1361 refers to the surface opposite to the surface bonded to the gas release layer 1362. The diameter of the microprotrusions may be 50 nm to 10 μm, preferably 100 nm to 1 μm. If the diameter of the microprotrusions is too small, the hydrophobicity may be reduced, and if the diameter is too large, the adhesion strength between the gas release portion 136 and the pouch film 135 may be reduced.

[0047] To achieve the distribution of these microprotrusions, the outer functional layer 1361 contains fine particles, which may include at least one of silica particles, carbon nanotubes (CNTs), and alumina particles, and most preferably carbon nanotubes (CNTs). The outer functional layer 1361 must be hydrophobic, while silica particles are hydrophilic. Therefore, if the fine particles contain silica particles, it is preferable to include only a very small amount of silica particles, approximately 0.1 to 2 wt% or less.

[0048] Meanwhile, according to another embodiment of the present invention, the outer functional layer 1361 may include an oil or wax component. The oil or wax has lipophilic properties that make it immiscible with water, and therefore may have hydrophobic properties. Here, the oil may include at least one of fluorocarbon oil, silicone oil, carbon-based oil, and fatty acid amide, and the wax may include at least one of paraffin wax and carbon-based wax.

[0049] If the hole 137 were not covered, not only would a small amount of moisture permeate, but a small amount of electrolyte would leak from the inside through the gas discharge layer 1362. Therefore, as shown in Fig. 3, an inner functional layer 1363 having hydrophobic properties may be formed on the inner surface of the gas discharge layer 1362. Here, the inner surface of the gas discharge layer 1362 refers to the surface formed toward the inside of the secondary battery 1, i.e., the electrode assembly 10, when the secondary battery 1 is manufactured.

[0050] According to one embodiment of the present invention, the inner functional layer 1363 may also have a plurality of micro-protrusions distributed on its outer surface. To this end, the inner functional layer 1363 may also include micro-particles, which may include at least one of silica particles, carbon nanotubes (CNTs), and alumina particles. Here, the outer surface of the inner functional layer 1363 refers to the surface opposite to the surface bonded to the gas discharge layer 1362.

[0051] Meanwhile, according to another embodiment of the present invention, the inner functional layer 1363 may have an oil or wax component. Here, the oil may include at least one of fluorocarbon oil, silicone oil, carbon-based oil, and fatty acid amide. By forming the outer functional layer 1361 and the inner functional layer 1363 in this manner, it is possible to more effectively prevent external moisture penetration and internal electrolyte leakage.

[0052] FIG. 4 is a flow chart illustrating a method for manufacturing a gas exhaust portion 136 according to one embodiment of the present invention. A method for manufacturing a gas exhaust part 136 according to one embodiment of the present invention includes the steps of providing a gas exhaust layer 1362 through which gas can pass, stirring fine particles and a polymer solution to prepare a mixture, spraying the mixture onto at least one surface of the gas exhaust layer 1362, and drying the mixture.

[0053] Specifically, first, a gas-permeable gas discharge layer 1362 is provided (S401). As described above, the gas discharge layer 1362 is preferably made of a semipermeable membrane that allows gas to easily pass through but does not allow liquids such as water and electrolyte to easily pass through. The gas discharge layer 1362 may include at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

[0054] The fine particles and the polymer solution are then stirred to prepare a mixture (S402). The fine particles may include at least one of silica particles, carbon nanotubes (CNTs), and alumina particles. The outer functional layer 1361 must be hydrophobic, while the silica particles are hydrophilic. Therefore, if silica particles are included, they are preferably included in a very small amount of about 0.1 to 2 wt% or less. The diameter of the fine particles may be 50 nm to 10 μm, preferably 100 nm to 1 μm. If the diameter of the fine particles is too small, the hydrophobicity may be reduced, and if the diameter is too large, the subsequent fusion strength between the gas exhaust portion 136 and the pouch film 135 may be reduced.

[0055] The polymer solution may contain at least one of polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF). That is, since the polymer solution contains the same or similar material as the gas release layer 1362, the outer functional layer 1361 or the inner functional layer 1363 can be easily laminated on the gas release layer 1362.

[0056] Then, the mixture is sprayed onto at least one surface of the gas discharge layer 1362 (S403). If the mixture is sprayed onto the outer surface of the gas discharge layer 1362, an outer functional layer 1361 is formed, and if the mixture is sprayed onto the inner surface of the gas discharge layer 1362, an inner functional layer 1363 is formed.

[0057] The mixture may be sprayed using a spray coating method. For example, the mixture may be sprayed using a nozzle at a pressure of about 0.2 to 0.5 MPa, particularly 0.4 MPa, from a distance of about 8 to 15 cm, particularly 10 cm, from the gas discharge layer 1362. However, the method is not limited thereto, and various other coating methods may be used.

[0058] Next, heat is applied to dry the mixture (S404). If the temperature of the applied heat is too low, it will take too long to dry the mixture, and if the temperature is too high, the shape of the gas discharge layer 1362 may be deformed. Therefore, it is preferable to apply heat at a temperature of 50 to 140°C, particularly 50 to 100°C.

[0059] This allows the formation of the outer functional layer 1361 or the inner functional layer 1363. Steps S403 and S404 may be repeated two to four times.

[0060] 5 is a cross-sectional view of a pouch film 135 according to one embodiment of the present invention. According to this embodiment, a hole 137 is perforated in the battery case 13, and a gas outlet 136 through which gas can pass is attached to the hole 137. When the internal pressure of the secondary battery 1 increases, the internal gas can be released to the outside to adjust the pressure. Furthermore, an outer functional layer 1361 or an inner functional layer 1363 is formed on the gas outlet 136, which prevents moisture penetration from the outside and electrolyte leakage from the inside. Furthermore, the gas outlet 136 is attached to the inside of the hole 137, which prevents corrosion of the metal of the gas barrier layer 1351 exposed to the inner circumferential surface 1371 of the hole 137 by the electrolyte.

[0061] To this end, according to one embodiment of the present invention, a battery case 13 for a secondary battery 1 includes a cup portion 133 having an accommodating space 1331 for accommodating an electrode assembly 10 formed by stacking electrodes and separators, a sealing portion 134 extending outward from the cup portion 133, and a gas-permeable gas outlet portion 136 attached to the inside of a hole 137 formed by perforating at least one of the cup portion 133 or the sealing portion 134. In this case, the gas outlet portion 136 includes a gas-permeable gas outlet layer 1362 and a hydrophobic outer functional layer 1361 formed on the outer surface of the gas outlet layer 1362. The battery case 13 may further include a hydrophobic inner functional layer 1363 formed on the inner surface of the gas outlet layer 1362.

[0062] To manufacture the battery case 13, first, a pouch film 135 is drawn and stretched to form the cup portion 133. As shown in FIG. 5 , the pouch film 135 includes a gas barrier layer 1351, a surface protection layer 1352, and a sealant layer 1353.

[0063] The gas barrier layer 1351 ensures the mechanical strength of the battery case 13, blocks the ingress and egress of gas or moisture from the secondary battery 1, and prevents leakage of the electrolyte. Generally, the gas barrier layer 1351 includes a metal, and aluminum foil is preferably used. Aluminum can ensure a certain level of mechanical strength while being lightweight, and can complement the electrochemical properties of the electrode assembly 10 and the electrolyte and ensure heat dissipation. However, the gas barrier layer 1351 is not limited thereto, and various materials may be used. For example, the gas barrier layer 1351 may be one or more substances selected from the group consisting of iron (Fe), carbon (C), chromium (Cr), manganese (Mn), nickel (Ni), and aluminum (Al). In this case, when the gas barrier layer 1351 is made of a material containing iron, its mechanical strength is improved, and when it is made of a material containing aluminum, its flexibility is improved. Therefore, the respective properties can be taken into consideration when selecting the gas barrier layer 1351.

[0064] The surface protective layer 1352 is made of a polymer and is positioned as the outermost layer. It protects the secondary battery 1 from external friction and impact and electrically insulates the electrode assembly 10 from the outside. Here, the outermost layer refers to the layer positioned furthest from the gas barrier layer 1351 in the opposite direction to the electrode assembly 10. The polymer used to form the surface protective layer 1352 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. It is particularly preferable to use a polymer such as nylon resin or polyethylene terephthalate (PET), which is primarily abrasion-resistant and heat-resistant. The surface protection layer 1352 may have a single film structure made of any one material, or a composite film structure made of two or more materials each forming a layer.

[0065] The sealant layer 1353 is made of a polymer and is positioned as the innermost layer, directly contacting the electrode assembly 10. Here, the innermost layer refers to the layer positioned furthest from the gas barrier layer 1351 in the direction in which the electrode assembly 10 is positioned. Therefore, as shown in FIG. 5, the gas barrier layer 1351 is laminated between the surface protective layer 1352 and the sealant layer 1353. The sealant layer 1353 must be insulating since it is in direct contact with the electrode assembly 10, and must be corrosion-resistant since it is in contact with the electrolyte. Furthermore, it must have high sealing properties because it must completely seal the interior and prevent material transfer between the interior and exterior. That is, the seal portion 134, where the sealant layers 1353 are bonded together, must have excellent thermal adhesive strength. Typically, the polymer used to form the sealant 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, polyolefin resins such as polypropylene (PP) or polyethylene (PE) are preferably used. Polypropylene (PP) is primarily used to form the sealant layer 1353 because of its excellent mechanical properties, such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance, as well as chemical properties, such as corrosion resistance. Furthermore, the sealant layer 1353 may be made of unstretched polypropylene (catenated polypropylene) or a polypropylene-butylene-ethylene terpolymer. The sealant layer 1353 may have a single-layer structure made of any one material, or a composite layer structure formed by layers of two or more materials.

[0066] Meanwhile, an adhesive layer 1354 for bonding the gas barrier layer 1351, the surface protective layer 1352, and the sealant layer 1353 together may be further formed between them. When the pouch film 135 having the above-described laminated structure is formed by drawing using a punch or the like, a portion of the film is stretched to form the cup portion 133 including the bag-shaped storage space 1331. Then, a hole 137 is punched in at least one of the cup portion 133 or the seal portion 134.

[0067] 5, a gas outlet 136 through which the produced gas passes is attached to the inside of the hole 137. Since the hole 137 may be formed in one piece or in multiple pieces, the gas outlet 136 may also be formed in one piece or in multiple pieces correspondingly.

[0068] In this case, if the gas exhaust part 136 were attached from the outside, the metal of the gas barrier layer 1351 exposed to the inner circumferential surface 1371 of the hole 137 would be corroded by the electrolyte. Therefore, by attaching the gas exhaust part 136 to the hole 137 from the inside, the metal of the gas barrier layer 1351 exposed to the inner circumferential surface 1371 of the hole 137 can be prevented from being corroded by the electrolyte.

[0069] When the gas exhaust part 136 is attached to the hole 137, the outer functional layer 1361 of the gas exhaust part 136 is bonded to one side of the sealant layer 1353, and is preferably sealed by applying heat and pressure to prevent easy detachment by the electrolyte. Therefore, in order to easily seal the outer functional layer 1361 to the sealant layer 1353, it is preferable that the sealant layer 1353 and the outer functional layer 1361 include the same or similar materials.

[0070] Once the electrode assembly 10 is placed inside the receiving space 1331 of the cup portion 133, an electrolyte is poured in. Then, the upper case 131 and the lower case 132 are brought into contact with each other and thermocompressed at the sealing portion 134, whereby the sealant layers 1353 are bonded together, thereby sealing the battery case 13. In this way, the secondary battery 1 according to one embodiment of the present invention can be manufactured.

[0071] Those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential characteristics 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 included within the scope of the present invention. [Explanation of symbols]

[0072] 1. Pouch-type secondary battery 10 Electrode assembly 13 Battery case 133 Cup section 134 Seal part 135 Pouch Film 136 Gas exhaust section 137 holes 1331 Containment Space 1341 Inner area 1342 outer area 1353 Sealant Layer 1361 External functional layer 1362 Gas Discharge Layer 1363 Internal functional layer

Claims

1. A pouch-type secondary battery case including a laminated pouch film, a cup portion having a receiving space for receiving an electrode assembly formed by stacking electrodes and separators; a seal portion extending outward from the cup portion; a gas outlet portion attached to an inner side of a hole formed by perforating at least one of the cup portion and the sealing portion, and through which gas passes; The gas exhaust unit is a gas-permeable gas-dissipating layer containing at least one material selected from the group consisting of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); a moisture permeation prevention layer formed on an outer surface of the gas-releasing layer, The pouch film includes a sealant layer located as an innermost layer, a pouch-type secondary battery case, wherein the moisture penetration prevention layer formed on the outer surface of the gas release layer is adhered to one surface of the sealant layer, and the moisture penetration prevention layer and the sealant layer are made of the same material.

2. The moisture penetration prevention layer is 2. The pouch-type secondary battery case according to claim 1, comprising at least one material selected from the group consisting of polypropylene (PP) and polyethylene (PE).

3. The gas discharge layer is The pouch-type secondary battery case according to claim 1 , comprising polytetrafluoroethylene (PTFE).

4. The pouch-type battery case for a secondary battery according to claim 1 , further comprising an electrolyte leakage prevention layer formed on an inner surface of the gas release layer.

5. The sealing portion is an interior region adjacent the cup portion; an outer region that is located outside the inner region and forms a rim, and that seals the cup portion by being sealed; The hole is The pouch-type battery case for a secondary battery according to claim 1 , wherein the seal portion is formed in the inner region.

6. The gas exhaust unit is The pouch-type battery case for a secondary battery according to claim 1 , which is formed from a plurality of battery cases.

7. an electrode assembly formed by stacking electrodes and separators; a battery case including a laminated pouch film that accommodates the electrode assembly therein; The battery case is a cup portion having a receiving space for receiving the electrode assembly; a seal portion extending outward from the cup portion; a gas outlet portion attached to an inner side of a hole formed by perforating at least one of the cup portion and the sealing portion, and through which gas passes; The gas exhaust unit is a gas-permeable gas-dissipating layer containing at least one material selected from the group consisting of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); a moisture permeation prevention layer formed on an outer surface of the gas-releasing layer, The pouch film includes a sealant layer located as an innermost layer, a pouch-type secondary battery, wherein the moisture penetration prevention layer formed on the outer surface of the gas release layer is bonded to one surface of the sealant layer, and the moisture penetration prevention layer and the sealant layer are made of the same material;

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