Secondary battery including gas exhaust unit for exhausting gas and method of manufacturing the secondary battery

Abstract

The present invention relates to a secondary battery and a method for manufacturing the secondary battery, which have improved performance and lifespan as well as safety by having a gas exhaust part that exhausts only gas. Specifically, the present invention relates to a secondary battery including an electrode assembly, a housing that accommodates the electrode assembly, a sealed part formed by sealing the periphery of the housing part, and a case that is disposed in the sealed part and has a gas exhaust part that has one end in contact with the housing part and the other end in contact with the outside and selectively exhausts only gas.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2020-0085641, filed on July 10, 2020, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 2021-0078634 dated June 17, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0003] The present invention relates to a secondary battery including a gas exhaust part and a method for manufacturing the secondary battery, and more particularly to a secondary battery including a case with a gas exhaust part that can selectively exhaust internal gas while blocking the inflow of moisture into the secondary battery, and a method for manufacturing the secondary battery. [Background technology]

[0004] In recent years, as devices using batteries have become more diverse, the demand for high-capacity and high-density batteries has increased. In particular, interest has been growing in pouch-type secondary batteries, which can achieve high-capacity and high-density batteries by reducing the thickness of an aluminum laminate sheet.

[0005] Pouch-type secondary batteries are generally formed by molding an aluminum laminate sheet to form a housing, and then housing an electrode assembly including a positive electrode, a separator, and a negative electrode in the housing. The aluminum laminate sheet is easily deformable and can be manufactured into various shapes, making it possible to form pouch-type secondary batteries that are compatible with various electronic devices. Furthermore, aluminum laminate sheets are lighter than conventional cylindrical or prismatic secondary batteries, which has the advantage of improving the energy density per weight of pouch-type secondary batteries.

[0006] FIG. 1 is a perspective view of a pouch-type secondary battery according to the prior art.

[0007] A conventional pouch-type secondary battery includes an electrode assembly 10 with protruding electrode leads 11 and a case 20 with a receiving portion 21 for receiving the electrode assembly 10. The pouch-type secondary battery includes the electrode assembly 10 received in the receiving portion 21, and then the periphery of the receiving portion 21 is sealed to form a sealed portion 22. The sealed portion 22 is formed to prevent materials present inside the pouch-type secondary battery from reacting with the outside air, but there is no separate member for removing gas generated inside the receiving portion. A pouch-type secondary battery with this structure has difficulty efficiently removing gas generated during charging and discharging. In particular, overcharging or heat generation due to malfunction of the secondary battery can cause the case to rupture or explode, resulting in the release of harmful gases or chemicals from the battery.

[0008] To improve the safety of the pouch-type case, conventional pouch-type secondary batteries have either included a gas-removing material inside to remove the gas or have a separate gas-retaining section outside the receptacle. However, when a gas-removing material is included, it interferes with the operation of the pouch-type secondary battery, reducing the efficiency of the battery, and when a gas-retaining section is included, there is a problem that the capacity per volume of the battery is reduced by including parts that are not related to the operation of the battery.

[0009] To solve this problem, Patent Document 1 discloses that a hydrogen permeable material is formed on at least a portion of the metal tab lead exposed to the outside of the exterior packaging, and this hydrogen permeable material exists continuously from the inside to the outside of the exterior packaging. However, because Patent Document 1 uses a hydrogen permeable material, it cannot prevent moisture from penetrating into the battery, which can hinder the function of the battery, and it has the disadvantage of being unable to efficiently discharge gases other than hydrogen.

[0010] In Patent Document 2, the electrode lead is formed to have a porous structure, and the inner surfaces of the pores of the electrode lead are coated with a gas adsorption material, but the gas adsorption material may act as resistance and reduce the efficiency of the entire battery.

[0011] Therefore, there is a need for a configuration that can improve the safety of the battery without reducing the performance and efficiency of the battery. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-212034 [Patent Document 2] Korean Patent Publication No. 2017-0082239 Summary of the Invention [Problem to be solved by the invention]

[0013] In order to solve the above problems, the present invention provides a gas exhaust part that selectively exhausts only gas at a sealed portion of the pouch-type secondary battery, thereby efficiently exhausting gas while preventing moisture from penetrating from the outside, thereby maintaining battery performance and improving safety.

[0014] Another object of the present invention is to provide a method for manufacturing a secondary battery that can easily discharge gas while reducing the battery defect rate by providing a method for sealing the gas exhaust part, the case, and the electrode lead together and successfully sealing the case. [Means for solving the problem]

[0015] To solve the above problems, a secondary battery according to the present invention may include a pouch-type case including a housing that houses an electrode assembly, a sealed portion formed by sealing the periphery of the housing, and a gas exhaust portion disposed in the sealed portion, one end of which contacts the housing and the other end of which contacts the outside, for selectively exhausting only gas.

[0016] The gas discharge part may be made of a gas discharge material having a gas permeability higher than a water permeability.

[0017] The gaseous emissions may have a moisture permeability of 50 ppm or less per year.

[0018] The gas-emitting material can be polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof.

[0019] The thickness of the gas exhaust portion may be 100 μm or more and 600 μm or less.

[0020] The gas exhaust portion may surround an electrode lead protruding from the electrode assembly.

[0021] The pouch-type case may include a laminate sheet, and the contact portion between the gas exhaust portion and the laminate sheet may be coated with polypropylene.

[0022] The secondary battery according to the present invention includes the pouch-type case and an electrode assembly. The present invention also provides a method for manufacturing a secondary battery, comprising: (S1) applying a gas-releasing material having a gas permeability higher than a water permeability to at least a portion of a surface of an electrode lead of the electrode assembly; and (S2) housing the electrode assembly in a housing inside a pouch-type case having a gas-releasing portion, and then sealing the housing.

[0023] In the method for manufacturing a secondary battery according to the present invention, the gas-emitting material may be polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof.

[0024] In the method for manufacturing a secondary battery according to the present invention, in step (S2), the gas releasing material and the pouch-type case may be bonded together by heat sealing at least once to ten times.

[0025] In the method for manufacturing a secondary battery according to the present invention, the gas exhaust part may be subjected to a surface modification process.

[0026] In the method for manufacturing a secondary battery according to the present invention, the gas exhaust portion may have a thickness of 100 μm or more and 600 μm or less.

[0027] The present invention can select and combine one or more of the above-mentioned configurations that are not contradictory to each other. [Effects of the Invention]

[0028] The secondary battery according to the present invention includes a gas exhaust unit that selectively exhausts only gas, thereby efficiently exhausting the internal gas and improving safety while maintaining the performance of the secondary battery.

[0029] In addition, the secondary battery has a low rate of moisture penetration into the battery, and therefore maintains safety even when a large number of electrode assemblies are housed inside the battery compared to conventional batteries, thereby improving the performance and life characteristics of the battery.

[0030] Furthermore, since the secondary battery can be manufactured in a simple manner and the sealing force is improved, the defective rate of the battery is reduced and the manufacturing cost of the secondary battery is also reduced. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a perspective view of a pouch-type secondary battery according to the prior art. [Figure 2] 1 is a perspective view of a pouch-type secondary battery according to the present invention; [Figure 3] 1 is a cross-sectional view of a first embodiment of a pouch-type secondary battery according to the present invention. [Figure 4] FIG. 3 is a cross-sectional view of a second embodiment of a pouch-type secondary battery according to the present invention. [Figure 5] 10 is a graph comparing moisture permeability when polypropylene is used in the gas exhaust section according to the present invention and when no gas exhaust section is provided. [Figure 6] 10 is a graph comparing gas permeability when polypropylene is used in the gas exhaust section according to the present invention and when no gas exhaust section is provided. DETAILED DESCRIPTION OF THE INVENTION

[0032] In this application, the terms "comprises," "has," or "has" are intended to specify the presence of features, numbers, steps, components, parts, or combinations thereof described in the specification, but should be understood as not precluding the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0033] Furthermore, the same reference numerals are used throughout the drawings for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element therebetween. Furthermore, unless otherwise specified, "including a certain element" does not mean that other elements are excluded, but that other elements may also be included.

[0034] Hereinafter, a secondary battery and a method for manufacturing the secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

[0035] FIG. 2 is a perspective view of a pouch-type secondary battery according to the present invention.

[0036] The pouch-type secondary battery according to the present invention includes an electrode assembly 100 from which an electrode lead 110 protrudes, a case 200 including a receiving portion 210 for receiving the electrode assembly 100, a sealing portion 220 formed by sealing the periphery of the receiving portion 210, and a gas exhaust portion 230 disposed in the sealing portion 220, one end of which contacts the receiving portion 210 and the other end of which contacts the outside, for selectively exhausting only gas.

[0037] The electrode assembly 100 may be, but is not limited to, a jelly-roll type assembly in which a separator is interposed between long sheet-shaped positive and negative electrodes and then wound up, a stack type assembly made up of unit cells in which rectangular positive and negative electrodes are stacked with a separator sandwiched between them, a stack folding type assembly in which unit cells are wound up with a long separator film, or a lamination stack type assembly in which unit cells are stacked with a separator sandwiched between them and then attached to each other. The electrode assembly according to the present invention preferably has a stack folding type or lamination stack type structure, which minimizes physical stress when forming a curved module.

[0038] The electrode lead 110 may have a structure in which it is electrically connected to the positive and negative electrode tabs of the electrode assembly 100, respectively, and then exposed to the outside of the case, or may have a structure in which the electrode lead 110 directly connects the electrode assembly 100 to the outside of the case 200 without the positive and negative electrode tabs, but is not limited thereto. Since the above-described secondary battery has a commonly known structure, further detailed description thereof will be omitted.

[0039] The case 200 typically has an inner layer / metal layer / outer layer laminate sheet structure. The inner layer, which comes into direct contact with the electrode assembly, must be insulating and electrolyte-resistant, and the sealing portion where the inner layers are thermally bonded must have excellent thermal adhesive strength to seal against the outside. Materials for the inner layer can be selected from polyolefin resins such as polypropylene, polyethylene, polyethylene acrylate, and polybutylene, polyurethane resins, and polyimide resins, which have excellent chemical resistance and sealing properties. However, polypropylene is most preferred because of its excellent mechanical properties, such as tensile strength, rigidity, surface hardness, and impact resistance, as well as chemical resistance.

[0040] The metal layer in contact with the internal layer corresponds to a barrier layer that prevents moisture and various gases from penetrating into the battery from the outside, and a suitable material for such a metal layer is an aluminum thin film, which is lightweight yet has excellent formability.

[0041] An outer layer is provided on the other side of the metal layer, and the outer layer may be made of a heat-resistant polymer having excellent tensile strength, moisture barrier properties, and air barrier properties to protect the electrode assembly and ensure heat resistance and chemical resistance, such as, but not limited to, nylon or polyethylene terephthalate.

[0042] The receiving portion 210 may be formed on both the upper and lower portions of the case 200, or may be formed on only one of the upper and lower portions. Here, forming the receiving portion 210 on only one of the upper and lower portions is more preferable since it can reduce the excess space of the terrace portion.

[0043] In addition, the case 200 seals the outer surface of the receiving portion 210 to prevent materials from being discharged from the receiving portion 210 to the outside. The sealed sealing portion 220 is bent toward the receiving portion 210 to improve the energy density of the battery module. Terrace portions of the sealing portion 220 from which the electrode leads 110 protrude in one or both directions protrude from the receiving portion 210.

[0044] The gas exhaust part 230 may be located in the sealing part 220. The gas exhaust part 230 may be located in any part of the sealing part 220. For example, the gas exhaust part 230 may be located in a part where the electrode lead 110 is located, as shown in FIG.

[0045] FIG. 3 is a cross-sectional view of a first embodiment of the pouch-type secondary battery according to the present invention.

[0046] In the first embodiment of the pouch-type secondary battery according to the present invention, the material constituting the gas exhaust part 230 is applied to the sealing part 220 of the case 200, i.e., the laminate sheet, so that the gas exhaust part 230 can be coupled to the electrode lead 110. This structure increases the coupling strength between the gas exhaust part 230 and the sealing part 220 and ensures a gas exhaust passage.

[0047] FIG. 4 shows a cross-sectional view of a pouch-type secondary battery according to a second embodiment of the present invention.

[0048] 4, the gas exhaust part 230 according to the second embodiment may be formed by applying a material constituting the gas exhaust part 230 to the surface of the electrode lead 110 and then combining the material with the case 200. This allows gas discharged through the gas exhaust part 230 to move smoothly while reducing the space where the electrode lead 110 is formed, i.e., the unsealed portion. The gas exhaust part 230 serves to connect the electrode lead 110 and the sealing part 220 between the electrode lead 110 and the sealing part 220. To enhance the bonding strength between the case 200 made of a laminate sheet, i.e., the sealing part 220 including the outer layer 221, the metal layer 222, and the inner layer 223, the gas exhaust part 230 may include a gas penetration part 231 located on the surface facing the electrode lead 110 and a coating part 232 on the surface facing the inner layer 223, which enhances the bonding strength.

[0049] The gas penetration part 231 may include one or more of fluorine-based, olefin-based, acrylic-based polymers, and ceramics. For fusion with the lower lead metal, the adhesive surface of the lead metal may be treated with MAH (maleic anhydride) or other chemical treatments that can form -OH (hydroxyl) groups. This is advantageous for improving the bonding strength between the two materials. The gas penetration part 231 may include a layer with pores for horizontal gas permeation.

[0050] The coating 232 may be directly coated on the gas exhaust portion 230, or may be coated on the inner layer 223 and then bonded to the gas exhaust portion 230. The coating 232 may be made of a material that has a high bonding strength with both the material constituting the gas exhaust portion 230 and the material constituting the inner layer 223. For example, the coating 232 may be made of a polypropylene material. In the present invention, the thickness of the coating 232 may be 50 μm to 500 μm. When the coating 232 is fused to the pouch, the thickness may be reduced due to heat and pressure, and if the coating 232 is too thin, the sealing strength may be reduced. The presence of the coating 232 allows for better sealing between the sealing portion 220 and the electrode lead 110.

[0051] The gas exhaust part 230 may be made of a gas exhaust material that is stable under the operating conditions of the secondary battery and has a gas permeability higher than its moisture permeability, and may have a moisture permeability of 50 ppm or less per year.

[0052] The gas-releasing material may be, for example, polypropylene, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, or a mixture thereof. Polypropylene, polyvinylidene difluoride, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, or a mixture thereof has the property of being able to release gases such as carbon dioxide, methane, and ethane while inhibiting moisture penetration, thereby enabling stable battery operation while releasing gases primarily generated in lithium-ion batteries. Considering the bonding strength with the laminate sheet, it is more preferable to use polypropylene or polyvinylidene difluoride, which have a stronger bonding strength with the laminate sheet and are easier to seal than other materials.

[0053] The thickness of the gas exhaust part 230 may be 100 μm or more and 600 μm or less. If the gas exhaust part 230 is 100 μm or less, the amount of gas passing through the gas exhaust part 230 may be limited, and the desired gas exhaust effect may not be obtained. If the gas exhaust part 230 is more than 600 μm, the gas exhaust part 230 may be too thick, which may increase the thickness of the secondary battery, and the desired sealing force may not be obtained.

[0054] A method for manufacturing a secondary battery according to the present invention may include the steps of (S1) applying a gas-releasing material having a gas permeability higher than a water permeability to at least a portion of a surface of an electrode lead of an electrode assembly, and (S2) housing the electrode assembly in a housing portion inside a case made of a laminate sheet and then sealing the housing portion.

[0055] Here, in step (S1), the gas releasing material may be applied to the case instead of the surface of the electrode lead, and the position of the gas releasing material may be changed depending on the bonding and sealing strength of the gas releasing material.

[0056] Examples of the gas-emitting material include polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof. Among these, polypropylene has a strong bonding strength with the electrode lead and the case, i.e., the laminate sheet, so it can be placed anywhere in the sealing portion of the case, but polytetrafluoroethylene requires a long time and high temperature for sealing, so it is preferable to place it in the part of the sealing portion through which the electrode lead passes, so as not to reduce the overall sealing strength of the secondary battery.

[0057] In step (S2), the gas emitting material and the case may be bonded by at least one to ten heat fusion processes. The number and duration of heat fusion processes may vary depending on the characteristics of the gas emitting material and the bonding strength between the electrode lead and the case. The heat fusion process may involve applying heat of 150°C to 250°C and applying a pressure of 1 kg / mm ​​to 100 kg / mm. If the pressure is higher than this temperature, the electrode assembly and the case may be damaged. If the pressure is lower than this temperature, the gas emitting material may not melt properly. In addition, if the pressure is too strong, the electrode lead may be damaged. If the pressure is too weak, the sealing force may be reduced, damaging the pouch-type secondary battery even during normal battery operation. Here, the heat fusion process may be performed using a laser in addition to heat.

[0058] In addition to the heat sealing method, the laminate sheet used as the case or the electrode lead may be coated by immersing it in a solution containing the gas-emitting material. Examples of such immersion methods include spin coating, slot die coating, doctor blading, bar coating, and dipping.

[0059] The gas exhaust portion may be subjected to a surface modification process to enhance bonding strength with the electrode lead or the case, and the surface modification process may be performed using ultraviolet curing, plasma, or the like.

[0060] The thickness of the gas exhaust portion may be from 100 μm to 600 μm. If the thickness of the gas exhaust portion is too small, gas cannot be smoothly exhausted and moisture penetrates, whereas if the thickness of the gas exhaust portion is too large, moisture penetrates easily due to the thickness of the gas exhaust portion, resulting in a decrease in battery performance.

[0061] <Experimental Example 1> A dummy cell without electrodes or a separator was formed in the shape according to the first embodiment of the present invention, where the gas exhaust part was coated with polypropylene having a thickness of 100 μm.

[0062] <Experimental Example 2> The gas exhaust section was coated with a 200 μm thick polypropylene film, but this was the same as Experimental Example 1, and so further explanation will be omitted.

[0063] <Comparative Example 1> The experiment was the same as Experimental Example 1 except that the gas exhaust section was not coated with anything, so further explanation will be omitted.

[0064] Water penetration measurement method The moisture penetration rate of the dummy cell was measured in an accelerated high-temperature, high-humidity environment. After accelerated storage, a portion of the solution in the sealed container was extracted and titrated using a titrator. To test the moisture penetration rate of the dummy cell, the sample was placed in a chamber set to high-temperature, high-humidity conditions (60°C, RH 90%) and the change in moisture penetration was measured over a period of one week. The amount of moisture that penetrated into the secondary battery was measured by the increase in the concentration of HF formed by the reaction of the electrolyte. In this invention, the moisture penetration rate is calculated as 16 weeks of moisture penetration in an accelerated moisture penetration environment, and 0.1 g of HF in the secondary battery corresponds to 500 ppm of moisture (H2O) penetration over 10 years.

[0065] FIG. 5 is a graph comparing the moisture permeability of a gas vent using polypropylene according to the present invention with that of a gas vent without a gas vent. As shown in FIG. 5, Experimental Examples 1 (Ex. 1) and 2 (Ex. 2) of the present invention have lower moisture permeability than Comparative Example 1 (Comp. Ex. 1). This is due to the characteristics of the unsealed pouch-type case, allowing some moisture to permeate. However, comparing Experimental Examples 1 and 2, it can be seen that moisture permeability decreases as the thickness of the gas vent increases. In other words, the presence of a gas vent allows for the adjustment of gas release within an acceptable moisture range. Therefore, polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof used in the present invention has lower moisture permeability and higher gas release than other materials, so as the thickness increases, moisture release decreases and gas release increases.

[0066] <Second Experimental Example 1> The change in pressure inside a pouch-type secondary battery according to the present invention, which has a gas outlet made of polypropylene (Ex. 1, Second Experimental Example 1) having a thickness of 100 μm, was measured for 24 hours.

[0067] <Second Comparative Example 1> The experiment was the same as the second experimental example 1 except that the target was a pouch-type secondary battery that was not provided with a gas exhaust portion, and therefore other explanations will be omitted.

[0068] Carbon dioxide gas, which is generated in large amounts from the secondary battery, was artificially injected into the pouch-type secondary battery from the outside at a pressure of about 0.0161 atm for 20 hours.

[0069] 6 is a graph comparing the gas permeability when a 100 μm thick polypropylene gas vent according to the present invention is used and when no gas vent is provided. As shown in FIG. 6, the gas vent amount in the second experimental example 1 (Ex. 1) is greater than that in the second comparative example 1 (Comp. Ex. 1), which indicates that the internal pressure of the pouch-type secondary battery is reduced.

[0070] As described above, when a material that selectively releases only gas is used for the gas release portion according to the present invention, that is, a material whose gas permeability is higher than its moisture permeability, it can be seen that gas can be released more smoothly.

[0071] Although specific portions of the contents of the present invention have been described in detail above, it will be apparent to those skilled in the art that such specific techniques are merely preferred embodiments and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it goes without saying that such changes and modifications also fall within the scope of the accompanying claims. [Explanation of symbols]

[0072] 10, 100 electrode assembly 11, 110 Electrode lead 20,200 cases 21, 210 Storage area 22, 220 Sealed part 221 Outer Layer 222 Metal layer 223 Inner layer 230 Gas exhaust section 231 Gas penetration 232 Coating Department

Claims

1. A pouch-type case including: a receiving section for receiving an electrode assembly; a sealed section formed by sealing a periphery of the receiving section; and a gas exhaust section disposed in the sealed section, one end of the gas exhaust section contacting the receiving section and the other end of the gas exhaust section contacting the outside, the gas exhaust section selectively exhausting only gas, the gas exhaust portion surrounds the electrode lead protruding from the electrode assembly to the outside, the gas exhaust portion connects the electrode lead and the sealing portion between the electrode lead and the sealing portion, In order to enhance the bonding strength between the sealing part, which is composed of an outer layer, a metal layer, and an inner layer, and the inner layer, the gas exhaust part includes a gas penetration part located on a surface facing the electrode lead, and a coating part that enhances the bonding strength on a surface facing the inner layer of the pouch-type case made of a laminate sheet, the gas exhaust portion undergoes a surface modification process, in which a bonding strength between the gas exhaust portion and the electrode lead or the pouch-type case is increased by ultraviolet curing or plasma curing; The gas penetration part is subjected to MAH (maleic anhydride) treatment on the bonding surface with the electrode lead, The pouch-type case is configured such that the gas discharge portion is made of a gas discharge material having a gas permeability higher than a moisture permeability.

2. 2. The pouch-type case according to claim 1, wherein the gas-emitting material has a moisture permeability of 50 ppm or less per year.

3. 3. The pouch-type case according to claim 2, wherein the gas-releasing material is polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof.

4. 4. The pouch-type case according to claim 1, wherein the gas discharge portion has a thickness of 100 μm or more and 600 μm or less.

5. The pouch-shaped case comprises a laminate sheet, 5. The pouch-type case according to claim 1, wherein a contact portion between the gas discharge portion and the laminate sheet is coated with polypropylene.

6. The pouch-type case according to any one of claims 1 to 5, and an electrode assembly.

7. (S1) applying a gas-releasing material having a gas permeability higher than a water permeability to at least a portion of a surface of an electrode lead of an electrode assembly; (S2) housing the electrode assembly in a housing portion inside a pouch-type case having a gas exhaust portion, and then sealing the housing portion; the gas exhaust portion surrounds the electrode lead protruding outward from the electrode assembly, the pouch-type case includes: a receiving portion that receives the electrode assembly; a sealing portion that is formed by sealing a periphery of the receiving portion; and a gas exhaust portion that is disposed in the sealing portion, one end of which contacts the receiving portion and the other end of which contacts the outside, and that selectively exhausts only gas; the gas exhaust portion connects the electrode lead and the sealing portion between the electrode lead and the sealing portion, In order to enhance the bonding strength between the sealing part, which is composed of an outer layer, a metal layer, and an inner layer, and the inner layer, the gas exhaust part includes a gas penetration part located on a surface facing the electrode lead, and a coating part that enhances the bonding strength on a surface facing the inner layer of the pouch-type case made of a laminate sheet, The gas exhaust part is subjected to a surface modification process, In the surface modification process, the bonding strength between the gas exhaust part and the electrode lead or the pouch-shaped case is increased by ultraviolet curing or plasma curing, The gas penetration portion is subjected to MAH (maleic anhydride) treatment on the bonding surface with the electrode lead. The gas discharge portion is made of a gas discharge material having a gas permeability higher than a water permeability.

8. The method for manufacturing a secondary battery according to claim 7 , wherein the gas-emitting material is polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), or a mixture thereof.

9. 9. The method of claim 7, wherein in step (S2), the gas-emitting material and the pouch-shaped case are bonded together by heat sealing at least once to ten times.

10. The method for manufacturing a secondary battery according to claim 7 , wherein the gas discharge portion has a thickness of 100 μm or more and 600 μm or less.

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