Gas-permeable film, pouch outer packaging material containing the same, and secondary battery

Abstract

The gas-permeable film of the present invention includes a first polymer layer, a second polymer layer, and a third polymer layer disposed between the first and second polymer layers, wherein the third polymer layer contains polypropylene and polytetrafluoroethylene in a weight ratio of 9:1 to 1:9. Because the gas-permeable film has excellent gas permeability, when used in a secondary battery, it can effectively discharge gas generated inside the secondary battery.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0152797, filed November 15, 2022, and Korean Patent Application No. 10-2023-0157681, filed November 14, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a gas permeable film, and more particularly to a secondary battery in which the gas permeable film is applied to a pouch outer casing or a lead tab film in order to improve the gas permeability of the secondary battery. [Background technology]

[0003] Secondary batteries are widely used as power sources for mobile devices such as mobile phones, laptops, and camcorders. In particular, the use of lithium secondary batteries is rapidly increasing due to their advantages of high operating voltage and high energy density per unit weight.

[0004] Such lithium secondary batteries mainly use lithium-based oxides as positive electrode active materials and carbon materials as negative electrode active materials, and are generally classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of electrolyte used, and into cylindrical, prismatic, and pouch-type secondary batteries depending on the battery shape. Prismatic and pouch-type secondary batteries are typically in high demand due to their thin thickness and being applicable to products such as mobile phones.

[0005] Among them, pouch-type secondary batteries are attracting attention because they are not limited in shape or size, are easy to assemble through heat sealing, and have the effect of easily discharging gas or liquid in the event of abnormal behavior, and are particularly suitable for manufacturing lightweight, thin cells.

[0006] Meanwhile, secondary batteries are charged and discharged by repeatedly inserting and desorbing lithium ions from the lithium metal oxide cathode into the graphite anode. However, they are susceptible to various safety issues, such as internal short circuits caused by external impacts, heat generation due to overcharging and overdischarging, and electrolyte decomposition and thermal runaway caused by these.

[0007] In particular, as the energy density of secondary batteries increases, the amount of gas generated as a result of electrochemical reactions between electrolytes and electrode active materials due to repeated charging and discharging increases. This gas generation significantly shortens the lifespan of secondary batteries, and this problem is expected to become even more serious in the future.

[0008] Meanwhile, if moisture penetrates into a secondary battery, the moisture may react with the electrolyte of the secondary battery, resulting in a decrease in performance and gas generation of the secondary battery. Therefore, it is necessary to control the moisture penetration into the secondary battery.

[0009] However, there has been insufficient research into extracting gas generated inside a secondary battery to the outside and minimizing moisture permeating into the inside of the secondary battery from the outside. Summary of the Invention [Problem to be solved by the invention]

[0010] SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a film having improved gas releasing properties.

[0011] Another object of the present invention is to provide a secondary battery having an improved function of discharging internal gas by applying the gas-permeable film to a lead film of the secondary battery.

[0012] Another object of the present invention is to provide a pouch exterior material for a secondary battery, which has good durability due to excellent adhesive strength, an excellent effect of preventing moisture penetration from the outside, and an improved function of releasing internal gas, by applying the film to the pouch exterior material. [Means for solving the problem]

[0013] To achieve the above object, the gas-permeable film according to the present invention comprises a first polymer layer, a second polymer layer, and a third polymer layer disposed between the first and second polymer layers, and the third polymer layer is characterized in that it contains polypropylene and polytetrafluoroethylene in a weight ratio of 9:1 to 1:9.

[0014] In one embodiment, the first polymer layer and the second polymer layer each independently include a polyolefin-based polymer.

[0015] In one embodiment, the second polymer layer includes a modified polyolefin resin.

[0016] In one embodiment, the third polymer layer contains polypropylene and polytetrafluoroethylene in a weight ratio of 8:2 to 2:8.

[0017] In one embodiment, the first polymer layer has a thickness of 40 to 200 μm.

[0018] In one embodiment, the second polymer layer has a thickness of 40 to 200 μm.

[0019] In one embodiment, the third polymer layer has a thickness of 40 to 600 μm.

[0020] In one embodiment, a secondary battery according to the present invention includes an electrode assembly; a pouch outer casing that houses the electrode assembly; an electrode lead electrically connected to the electrode assembly; and a gas-permeable film adhered to at least one surface of the electrode lead, wherein the film is the gas-permeable film described above.

[0021] In one embodiment, the gas permeable film of the secondary battery according to the present invention is characterized in that the second polymer layer comprises a polypropylene acrylic acid copolymer.

[0022] In one embodiment, a pouch outer casing material according to the present invention is a pouch outer casing material for housing an electrode assembly, characterized in that the pouch outer casing material has a structure in which a metal layer and a polymer layer are laminated, the pouch outer casing material has one or more holes, and the one or more holes are sealed with the gas-permeable film described above.

[0023] In one embodiment, the pouch exterior material has an outer layer and an inner layer which are the polymer layer, and a deep layer interposed between the outer layer and the inner layer which is the metal layer.

[0024] In one embodiment, the outer layer of the pouch outer casing material comprises at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, and nylon.

[0025] In one embodiment, the deep layer of the pouch exterior material includes at least one selected from the group consisting of aluminum, copper, nickel, iron, carbon, chromium, manganese, and alloys containing at least two of these.

[0026] In one embodiment, the inner layer of the pouch outer casing comprises at least one material selected from the group consisting of polypropylene, acid-modified polypropylene, random polypropylene, and ethylene-propylene copolymer.

[0027] In one embodiment, the pouch outer casing is characterized in that the electrode assembly housed in the pouch outer casing includes an electrode lead electrically connected to the electrode assembly, the electrode lead is extended to the outside of the pouch outer casing, a gas collecting part is formed between the electrode assembly and a region where the electrode lead is extended to the outside of the pouch outer casing, and a hole is formed in the pouch outer casing region corresponding to the gas collecting part. [Effects of the Invention]

[0028] The gas-permeable film according to the present invention has excellent physical properties as a gas-permeable material and excellent durability due to excellent adhesive strength between the films constituting the gas-permeable film. Furthermore, when the gas-permeable film according to the present invention is applied to a hole formed in a pouch outer casing for a secondary battery, the excellent adhesive strength to the pouch outer casing can effectively prevent the penetration of external moisture, or when applied to a lead film for a secondary battery, the gas generated inside the secondary battery can be smoothly discharged to the outside. [Brief explanation of the drawings]

[0029] The following drawings in this specification illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention, and therefore the present invention should not be interpreted as being limited solely to the matters depicted in these drawings. [Figure 1] 1 is a cross-sectional view of a gas permeable film according to one embodiment of the present invention. [Figure 2] 1 is a perspective view of an electrode assembly according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view of an electrode assembly and a pouch outer casing according to an embodiment of the present invention. [Figure 4] 3 is an enlarged cross-sectional view of an electrode lead portion of a pouch outer casing according to an embodiment of the present invention. FIG. [Figure 5] 1 is an enlarged cross-sectional view of an electrode lead portion of a pouch exterior material according to one embodiment of the present invention, showing a case where a gas exhaust path is opened to the upper pouch side. FIG. [Figure 6]10 is an enlarged cross-sectional view of an electrode lead portion of a pouch exterior material according to one embodiment of the present invention, showing another example in which gas exhaust paths are opened to the upper and lower pouch sides. FIG. [Figure 7] 1 is a cross-sectional view of a pouch exterior material according to an embodiment of the present invention, showing a case where a hole is formed. [Figure 8] 3 is an enlarged cross-sectional view of a portion where a hole is formed in a pouch exterior material according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in detail below with reference to the drawings. The terms and phrases used in the specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, in accordance with the principle that an inventor may appropriately define the concepts of terms in order to best describe his or her invention.

[0031] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0032] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise stated in the phrase. The words "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0033] In this specification, when a part is said to include a certain component, this does not mean that it excludes other components, and that it may further include other components, unless otherwise specified.

[0034] In this specification, the expression "A and / or B" means A, or B, or A and B.

[0035] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0036] According to one aspect of the present invention, there is provided a gas-permeable film including a first polymer layer, a second polymer layer, and a third polymer layer positioned between the first and second polymer layers.

[0037] Here, the third polymer layer comprises polypropylene (PP) and polytetrafluoroethylene (PTFE), and the weight ratio of the two polymer materials may be 9:1 to 1:9, preferably 8:2 or less, 7:3 or less, or 6:4 or less, or 2:8 or more, or 3:7 or more. By including polytetrafluoroethylene in this range, the film of the present invention can effectively block moisture while venting gases, thereby improving inter-film adhesion. If the amount of either polypropylene or polytetrafluoroethylene is too low or too high, or if only one of them is present (e.g., if polypropylene is too high, gas permeability may be significantly reduced, resulting in swelling prevention issues), while if polytetrafluoroethylene is too high, inter-film adhesion may be poor, resulting in significantly reduced durability. Therefore, it is preferable to mix polypropylene and polytetrafluoroethylene in this range.

[0038] If the third polymer layer is exposed to the outside, for example, when it is the surface that is bonded to an electrode lead or the surface that is fused to a pouch, the polytetrafluoroethylene content cannot be increased sufficiently because it would affect adhesion. However, in the present invention, since the third polymer layer is located between the first and second polymer layers and is not exposed to the outside, the polytetrafluoroethylene content can be relatively increased, which can result in even better gas discharge performance.

[0039] Polypropylene is a material with good moldability and excellent dimensional stability. It is also lightweight yet has good chemical resistance, excellent flex fatigue resistance, and excellent heat resistance, making it suitable for use in various housings, exterior materials, films, and other applications. However, polypropylene is permeable to moisture, so using only polypropylene as the polymer layer results in insufficient moisture blocking properties. On the other hand, polytetrafluoroethylene is a material with good moisture blocking properties and particularly excellent gas permeability, but has poor adhesive properties.

[0040] In the present invention, by including a mixture of polypropylene and polytetrafluoroethylene as the third polymer layer, it is possible to exhibit both the excellent mechanical properties and adhesiveness of polypropylene and the moisture blocking effect of polytetrafluoroethylene, and it is possible to further improve the gas permeability of the gas-permeable film according to the present invention.

[0041] 1 is a cross-sectional view of a gas-permeable film 10 according to one embodiment of the present invention. A third polymer layer 13 is positioned between a first polymer layer 11 and a second polymer layer 12.

[0042] In an embodiment of the present invention, the first polymer layer and the second polymer layer may each independently include a polyolefin-based polymer, and the first polymer layer may include at least one selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), and polyimide (PI).

[0043] Specifically, the polypropylene resin may include a propylene polymer (homopolypropylene), a propylene copolymer (PP copolymer), a propylene terpolymer (PP terpolymer), etc. In addition, the propylene copolymer (PP copolymer) may include a propylene-ethyl block copolymer, etc., and the propylene terpolymer (PP terpolymer) may include a propylene-ethylene-butylene block copolymer, etc.

[0044] When the first polymer layer contains polypropylene, the water resistance of the film according to the present invention can be improved because polypropylene is a hydrophobic material. Furthermore, the high melting point of polypropylene allows the film according to the present invention to have excellent heat resistance and improve its sealing effect. Furthermore, the physical properties of the film according to the present invention, such as adhesive strength and mechanical strength, can be improved.

[0045] In addition, in an embodiment of the present invention, the second polymer layer may include at least one selected from the group consisting of poly(propylene-co-acrylic acid), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), and polyimide (PI).

[0046] When the second polymer layer contains polypropylene, the water resistance of the film according to the present invention can be improved because polypropylene is a hydrophobic material. Furthermore, because polypropylene has a high melting point, the film according to the present invention has excellent heat resistance and an improved sealing effect. Furthermore, physical properties such as adhesive strength and mechanical strength of the film according to the present invention can be improved. In particular, when the second polymer layer contains polypropylene-acrylic acid copolymer, the adhesive strength of the film according to the present invention can be improved. For example, when the second polymer layer is polypropylene-acrylic acid copolymer, the adhesive strength with the electrode lead can be excellent.

[0047] In one embodiment of the present invention, the thickness of the first polymer layer is 40 to 200 μm, 40 to 80 μm, or 80 to 200 μm. When the thickness of the first polymer layer falls within this range, the film according to the present invention is lightweight yet has excellent mechanical properties and heat resistance.

[0048] In one embodiment of the present invention, the second polymer layer has a thickness of 40 to 200 μm, 40 to 80 μm, or 80 to 200 μm. When the thickness of the second polymer layer falls within this range, the film according to the present invention is lightweight yet has excellent mechanical properties and heat resistance.

[0049] In one embodiment of the present invention, the thickness of the third polymer layer is 40 to 600 μm, 40 to 120 μm, or 120 to 600 μm. When the thickness of the third polymer layer falls within this range, the film of the present invention has sufficient gas permeability.

[0050] According to one aspect of the present invention, there is provided a secondary battery comprising: an electrode assembly; a pouch outer casing for accommodating the electrode assembly; an electrode lead electrically connected to the electrode assembly; and the gas-permeable film according to the present invention described above attached to at least one surface of the electrode lead.

[0051] In general, a secondary battery comprises an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between them, an electrolyte that transfers lithium ions through the separator, a pouch that contains the electrolyte, and an electrode lead that serves as a current path outside the pouch.

[0052] The electrode lead is electrically connected to the positive electrode (or the uncoated portion of the positive electrode or the positive electrode tab drawn from the positive electrode) and / or the negative electrode (or the uncoated portion of the negative electrode or the negative electrode tab drawn from the negative electrode) of the electrode assembly, and is used as a positive electrode terminal or a negative electrode terminal.

[0053] Here, the lead film is attached to the electrode lead to prevent short circuits from occurring in the electrode lead while sealing the electrode lead and the exterior material. When the gas-permeable film according to the present invention is applied to the lead film, it is possible to effectively discharge gas generated inside the pouch while maintaining hermeticity. Gas can be discharged by passing through the first, second, and third polymer layers of the gas-permeable film, but when the gas-permeable film according to the present invention is applied to the electrode lead, the amount of gas that moves through the third polymer layer when gas is discharged horizontally may be the largest.

[0054] The lead film may be formed on the upper and lower surfaces of the electrode lead, or may be formed to cover both surfaces including the upper and lower surfaces so as to cover the side surfaces of the electrode lead.

[0055] The lead film may be bonded to the pouch exterior material via an adhesive or may be heat-sealed to the pouch exterior material via heat fusion.

[0056] 2 shows an electrode lead 120 electrically connected to an electrode assembly 100 according to an embodiment of the present invention, with a gas-permeable film according to the present invention bonded to a lead film 110. Also, FIG. 3 is a cross-sectional view showing a secondary battery according to an embodiment of the present invention, in which a pouch outer casing includes an upper pouch 220a and a lower pouch 220b, and an electrode assembly 100 and an electrolyte (not shown) are accommodated in an internal space 300 formed by the upper pouch 220a and the lower pouch 220b. Sealing portions are formed on terrace portions 230 on the outer periphery of the upper pouch 220a and the lower pouch 220b to seal the internal space, and these sealing portions are bonded (sealed) to each other by a method such as heat fusion.

[0057] Such pouch exterior materials include a metal layer, such as an aluminum thin film, to protect internal components such as the electrode assembly 100 and electrolyte, complement the electrochemical properties of the electrode assembly 100 and electrolyte, and enhance heat dissipation. The metal layer is interposed between polymer layers made of insulating materials to ensure insulation. However, gas may be generated inside the pouch exterior material due to the reaction between the electrode assembly 100 and the electrolyte. However, the metal and polymer layers used in existing pouch exterior materials have poor gas permeability, which can cause the pouch exterior material to expand or explode. Therefore, it is necessary to efficiently vent the gas generated inside the pouch exterior material.

[0058] Therefore, by applying the gas-permeable film as described above to the lead film on the electrode lead, if the pressure resistance increases due to gas generated inside, the gas can be discharged horizontally from the film as a base through the gas-permeable lead film, or a gas discharge path can be formed as a result of a partial opening of the interface between the electrode lead and the lead film, allowing the gas to pass through and be discharged vertically from the film as a base through the gas-permeable film (lead film).

[0059] Although not specifically shown in the drawings, as shown in Figures 5 and 6, a film may be further included to allow a portion of the interface between the electrode lead and the lead film to be opened. The additional film may be a path-forming film, which may be disposed between the electrode lead and the lead film in a remaining region where the lead film and the electrode lead are bonded, excluding a portion of the outermost part in the protruding direction of the electrode lead. Such a path-forming film may function to weaken the adhesive strength between the electrode lead and the lead film so that the portion of the lead film can be opened when the internal pressure of the pouch increases. In this case, the portion of the outermost part in the protruding direction of the electrode lead in the region where the lead film and the electrode lead are bonded may be approximately 10% to 60% of the bonded region.

[0060] Specifically, referring to FIG. 4, a gas permeable film 210 may be disposed as the lead film 110 on the electrode leads 120 on the upper pouch 220a and lower pouch 220b sides.

[0061] When the pressure inside the battery increases due to gas generated inside, a portion of the interface between the electrode lead 120 and the lead film 110, i.e., the interface between the first polymer layer 11 of the gas permeable film 210 and the electrode lead 120, may open, forming a gas exhaust path 320, as shown in Fig. 5, or both the upper and lower pouch sides of the gas permeable film 210 may open, forming a gas exhaust path 320, as shown in Fig. 6. Gas passes through the gas permeable film 210 via this gas exhaust path 320 and is exhausted to the outside. This may result in a decrease in the withstand voltage of the battery.

[0062] According to one embodiment of the present invention, the second polymer layer of the gas-permeable film according to the present invention, which is adhered to the electrode lead, includes a polypropylene acrylic acid copolymer. Because the electrode lead is made of a metal material, the inclusion of a polypropylene acrylic acid copolymer in the second polymer layer of the film according to the present invention can improve adhesion to the metal. Therefore, when the gas-permeable film is adhered to the electrode lead, it is preferable that the second polymer layer faces the electrode lead.

[0063] The polypropylene acrylic acid copolymer of the second polymer layer can be prepared by treating a polypropylene layer with maleic anhydride.

[0064] According to one embodiment of the present invention, in the gas-permeable film according to the present invention attached to the electrode lead, the thickness of the first polymer layer is preferably 80 to 200 μm, 80 to 180 μm, 80 to 160 μm, 100 to 200 μm, 120 to 200 μm, 100 to 180 μm, or 120 to 160 μm. When the gas-permeable film according to the present invention is applied to a lead film attached to an electrode lead, gas generated inside the pouch permeates the film horizontally and is discharged to the outside. Therefore, when the thickness of the film applied to the lead film falls within the above range, appropriate horizontal gas permeability can be achieved and electrolyte sealing properties can be maintained.

[0065] According to one embodiment of the present invention, in the gas-permeable film according to the present invention attached to the electrode lead, the thickness of the second polymer layer is preferably 80 to 200 μm, 80 to 180 μm, 80 to 160 μm, 100 to 200 μm, 120 to 200 μm, 100 to 180 μm, or 120 to 160 μm. When the gas-permeable film according to the present invention is applied to a lead film attached to an electrode lead, gas generated inside the pouch permeates the film horizontally and is discharged to the outside. Therefore, when the thickness of the gas-permeable film applied to the lead film falls within the above range, appropriate horizontal gas permeability can be achieved and electrolyte sealing properties can be maintained.

[0066] According to one embodiment of the present invention, in the gas-permeable film according to the present invention attached to the electrode lead, the thickness of the third polymer layer is preferably 120 to 600 μm, 150 to 600 μm, 200 to 600 μm, 250 to 600 μm, 120 to 550 μm, 120 to 500 μm, 120 to 450 μm, 150 to 550 μm, 200 to 500 μm, 250 to 450 μm, or 300 to 400 μm. When the gas-permeable film according to the present invention is applied to a lead film attached to an electrode lead, gas generated inside the pouch permeates the gas-permeable film in the horizontal direction and is discharged to the outside. Therefore, when the thickness of the gas-permeable film applied to the lead film falls within the above range, appropriate horizontal gas permeability can be achieved and electrolyte sealing properties can be maintained.

[0067] According to an embodiment of the present invention, the metal conductor used as the electrode lead may be selected from the group consisting of copper (Cu), aluminum (Al), nickel (Ni), iron (Fe), carbon (C), chromium (Cr), manganese (Mn), and alloys containing two or more of these elements, but is not limited thereto, and any material that can be electrically connected to the electrode tab may be used without any particular limitation. The metal conductor may include aluminum, which may optionally be an alloy containing an element selected from the group consisting of silicon, boron, germanium, arsenic, antimony, copper, magnesium, manganese, zinc, lithium, iron, chromium, vanadium, titanium, bismuth, potassium, tin, lead zirconium, nickel, cobalt, and combinations thereof.

[0068] The metal conductor can be selected taking into consideration mechanical strength and flexibility. Preferably, aluminum is used for the positive electrode, and copper, nickel, or nickel-plated metal is used for the negative electrode, but these are not limited thereto. The metal conductor may have a thickness of 0.1 mm to 1.0 mm and a width of 1 mm to 200 mm, but these are not limited thereto, and may have specifications determined depending on the intended use of the secondary battery to be manufactured.

[0069] According to one aspect of the present invention, there is provided a pouch outer casing material for accommodating an electrode assembly, the pouch outer casing material having a structure in which a metal layer and a polymer layer are laminated, the pouch outer casing material having one or more holes, and the one or more holes being sealed with the gas-permeable film according to the present invention described above.

[0070] The portion of the pouch outer casing where the metal layer and polymer layer are laminated has low gas permeability, making it difficult for gas generated inside the pouch to escape. Therefore, by laminating the metal layer and polymer layer to form one or more holes vertically penetrating the same positions of each layer, and then sealing the one or more holes with the gas-permeable film according to the present invention, the pouch outer casing maintains its role of preventing electrolyte leakage and protecting the internal electrode assembly, while allowing gas to escape smoothly through the gas-permeable film according to the present invention. Specifically, because the first, second, and third polymer layers of the gas-permeable film according to the present invention have excellent gas permeability, gas generated inside the pouch outer casing can pass vertically through the gas-permeable film according to the present invention and be expelled to the outside.

[0071] The position of the hole formed in the pouch exterior material is not limited, and for example, the hole may be formed at a position that does not come into direct contact with the electrode assembly housed in the pouch exterior material.

[0072] 7 is a cross-sectional view of an electrode assembly and a pouch exterior material according to an embodiment of the present invention. When an electrode lead 120 electrically connected to the electrode assembly 100 is extended to the outside of the pouch exterior material 200, a gas collecting portion 310 may be formed between the electrode assembly 100 and the area where the electrode lead 120 is extended to the outside of the pouch exterior material 200. One or more holes may be formed in the area of ​​the pouch exterior material corresponding to the gas collecting portion 310, and the formed holes may be sealed with a gas permeable film 210 according to the present invention. In this case, the area of ​​the pouch exterior material corresponding to the gas collecting portion 310 may not be in direct contact with the electrode assembly. Therefore, when the gas permeable film 210 according to the present invention is positioned in the area of ​​the pouch exterior material corresponding to the gas collecting portion 310, the gas permeable film 210 may not be in direct contact with the electrode assembly 100.

[0073] Here, the sealing may be performed by heat sealing, but is not limited to this and may be performed by various methods commonly used for sealing. The lead film 110 may be the gas permeable film according to the present invention, or a commonly used lead film may be used.

[0074] In one embodiment of the present invention, when the gas permeable film according to the present invention is applied to a pouch exterior material, the lead film attached to the electrode lead electrically connected to the electrode assembly housed in the pouch exterior material may be the gas permeable film according to the present invention, or a lead film generally used in the technical field of secondary batteries may be used. For example, the lead film 110 may include polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polyimide, or two or more of these.

[0075] In one embodiment of the present invention, the gas-permeable film may be positioned on the inner layer side of the pouch outer material. Specifically, one or more holes may be formed in the pouch outer material, and then the gas-permeable film may be positioned on the inner layer of the pouch outer material and the holes may be sealed.

[0076] In one embodiment of the present invention, the gas-permeable film may be positioned on the outer layer side of the pouch outer covering material. Specifically, one or more holes may be formed in the pouch outer covering material, and the gas-permeable film may be positioned on the outer layer of the pouch outer covering material, and the holes may then be sealed. Here, the sealing may be performed by heat sealing, but is not limited to this and may be performed by various methods commonly used for sealing.

[0077] In one embodiment of the present invention, the size (diameter) of the hole formed in the pouch outer packaging material may be 0.5 mm to 20 mm, 1 mm to 10 mm, or 3 mm to 7 mm. If the hole size falls within this range, when the gas-permeable film according to the present invention seals the hole, gas generated within the pouch can be sufficiently released.

[0078] In one embodiment of the present invention, the hole formed in the pouch outer material may be circular, triangular, rectangular, or polygonal, but the shape of the hole is not limited thereto and may be any shape that can be selected by a person skilled in the art.

[0079] 8 shows a cross-section of a pouch exterior material according to one embodiment. The pouch exterior material is a laminate of metal layers and polymer layers, with the deep layer 223 being a metal layer and the inner layer 221 and outer layer 222 being polymer layers. Here, holes are formed at the same positions in each of the laminated metal and polymer layers, and the holes are sealed with the gas-permeable film 210 according to the present invention. A pouch exterior material formed only with conventional metal layers and polymer layers without the gas-permeable film 210 according to the present invention may have low gas permeability. However, the pouch exterior material according to the present invention includes the gas-permeable film 210, which has excellent gas permeability, allowing the pouch exterior material to smoothly release gas.

[0080] According to one embodiment of the present invention, in the gas-permeable film according to the present invention in which the one or more holes are sealed, the thickness of the first polymer layer is preferably 40 to 80 μm, 40 to 70 μm, 40 to 60 μm, 50 to 80 μm, 60 to 80 μm, 55 to 75 μm, or 50 to 70 μm. When the gas-permeable film according to the present invention is applied to a pouch exterior, gas generated inside the pouch passes through the film in a vertical direction and is discharged to the outside. Therefore, when the thickness of the film applied to the pouch exterior falls within the above range, appropriate gas permeability in the vertical direction can be achieved, and mechanical strength and electrolyte sealing ability can be maintained.

[0081] According to one embodiment of the present invention, in the gas-permeable film according to the present invention in which the one or more holes are sealed, the thickness of the second polymer layer is preferably 40 to 80 μm, 40 to 70 μm, 40 to 60 μm, 50 to 80 μm, 60 to 80 μm, 55 to 75 μm, or 50 to 70 μm. When the gas-permeable film according to the present invention is applied to a pouch exterior, gas generated inside the pouch passes through the film in a vertical direction and is discharged to the outside. Therefore, when the thickness of the film applied to the pouch exterior falls within the above range, appropriate gas permeability in the vertical direction can be achieved, and mechanical strength and electrolyte sealing ability can be maintained.

[0082] According to one embodiment of the present invention, in the film according to the present invention in which the one or more holes are sealed, the thickness of the third polymer layer is preferably 40 to 120 μm, 40 to 100 μm, 40 to 80 μm, 60 to 120 μm, 80 to 120 μm, 50 to 110 μm, or 60 to 100 μm. When the film according to the present invention is applied to a pouch exterior, gas generated inside the pouch permeates the film in a vertical direction and is discharged to the outside. Therefore, when the thickness of the film applied to the pouch exterior falls within the above range, appropriate gas permeability in the vertical direction can be achieved, and mechanical strength and electrolyte sealing ability can be maintained.

[0083] According to one embodiment of the present invention, the laminated metal layer and polymer layer of the pouch exterior material are characterized in that the outer and inner layers are polymer layers, and the metal layer is located in a deeper layer interposed between the outer and inner layers. That is, the outer and inner layers of the pouch exterior material may be polymer layers, and the deeper layer interposed between the outer and inner layers may be a metal layer.

[0084] The outer layer may include at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, and nylon, and may be configured as a single layer or multiple layers, but is not limited thereto and any material commonly used in the technical field of pouch outer covering materials may be used.

[0085] The deep layer may include at least one material selected from the group consisting of aluminum, copper, nickel, iron, carbon, chromium, manganese, and alloys containing two or more of these materials, and may be configured as a single layer or multiple layers, but is not limited thereto and may be any material commonly used in the technical field of pouch exterior materials.

[0086] The inner layer may include at least one material selected from the group consisting of polypropylene, acid-modified polypropylene, random polypropylene, and ethylene-propylene copolymer, and may be configured as a single layer or multiple layers, but is not limited thereto and may be any material commonly used in the technical field of pouch outer packaging materials.

[0087] The present invention will be described in more detail below through embodiments. However, the following embodiments are for illustrative purposes only and the scope of the present invention is not limited to these embodiments.

[0088] 1. Gas permeable film applied to lead film Example 1-1 (1) Manufacturing of gas-permeable films A 40 μm thick polypropylene layer was prepared as the first polymer layer, a 100 μm thick polypropylene acrylic acid copolymer layer was prepared as the second polymer layer, and a 60 μm thick mixture of polypropylene and polytetrafluoroethylene in a weight ratio of 3:7 was prepared as the third polymer layer.

[0089] Thereafter, the first polymer layer, the third polymer layer, and the second polymer layer were laminated in this order and then heat-sealed to produce a gas-permeable film.

[0090] (2) Manufacturing of pouch packaging materials A polyethylene terephthalate (PET) film measuring 266 mm wide, 50 m long, and 12 μm thick and a nylon film measuring 266 mm wide, 50 m long, and 25 μm thick were laminated on one side of an aluminum alloy thin film measuring 266 mm wide, 50 m long, and 60 μm thick, and a polypropylene film measuring 266 mm wide, 50 m long, and 80 μm thick was laminated on the other side, producing a pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / polypropylene film structure.

[0091] Here, the polyethylene terephthalate film and nylon film are base layers, the aluminum alloy thin film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0092] The pouch film laminate was molded to prepare a pouch-type case including a storage portion and a sealing portion.

[0093] (3) Secondary battery manufacturing The negative and positive electrodes and the porous polyethylene separator were stacked and then laminated to prepare an electrode assembly, and then an electrode lead was attached to the electrode assembly.

[0094] An electrolyte was prepared by dissolving LiPF6 in a solvent (EC:EMC:DMC = 3:3:4 volume ratio) to a concentration of 1.0 M. The electrode assembly was placed in the pouch-type case with the tip of the electrode lead extended to the outside, and the electrolyte was poured into the pouch-type case.

[0095] The gas-permeable film prepared above was laminated as a lead film on the upper surface of the electrode lead.

[0096] Thereafter, the sealing portion of the pouch-type case was sealed with a seal bar having an area of ​​200 mm x 10 mm under conditions of 220°C and 0.27 MPa for 2 seconds, and then left at 60°C for 4 hours to manufacture a pouch-type secondary battery. At this time, the portion of the sealing portion where the lead film was formed had a structure in which the lower case / lead film / electrode lead / gas exhaust part / lead film / upper case were sequentially stacked.

[0097] Example 1-2 A gas-permeable film was prepared in the same manner as in Example 1-1, except that a mixture of polypropylene and polytetrafluoroethylene in a weight ratio of 5:5 was used as the third polymer layer, and a pouch-type secondary battery was prepared in the same manner.

[0098] Examples 1-3 A gas-permeable film was prepared in the same manner as in Example 1-1, except that a mixture of polypropylene and polytetrafluoroethylene in a weight ratio of 7:3 was used as the third polymer layer, and a pouch-type secondary battery was prepared in the same manner.

[0099] Examples 1-4 A gas-permeable film was prepared in the same manner as in Examples 1-3, except that polypropylene was used as the second polymer layer instead of polypropylene acrylic acid copolymer.

[0100] Comparative Example 1-1 A 40 μm thick polypropylene was prepared as the first polymer layer, a 100 μm thick polypropylene acrylic acid copolymer was prepared as the second polymer layer, and a 60 μm thick polypropylene was prepared as the third polymer layer. The first polymer layer, the third polymer layer, and the second polymer layer were then laminated and heat-sealed to produce a gas-permeable film.

[0101] Thereafter, the pouch outer casing and the secondary battery were fabricated in the same manner as in Example 1-1.

[0102] Comparative Example 1-2 A gas-permeable film, a pouch outer casing, and a secondary battery were manufactured in the same manner as in Example 1-1, except that a polytetrafluoroethylene film was used as the third polymer layer.

[0103] Comparative Examples 1-3 A gas-permeable film, a pouch outer material, and a secondary battery were manufactured in the same manner as in Example 1-1, except that the first and second polymer layers were not formed and the third polymer layer was formed to a thickness of 200 μm.

[0104] 2. Gas-permeable film placed on the pouch outer packaging Example 2-1 (1) Manufacturing of gas-permeable films A gas-permeable film was prepared in the same manner as in Example 1-1, except that polypropylene was used as the second polymer layer instead of polypropylene acrylic acid copolymer.

[0105] (2) Manufacturing of pouch packaging materials A polyethylene terephthalate (PET) film measuring 266 mm wide, 50 m long, and 12 μm thick and a nylon film measuring 266 mm wide, 50 m long, and 25 μm thick were laminated on one side of an aluminum alloy thin film measuring 266 mm wide, 50 m long, and 60 μm thick, and a polypropylene film measuring 266 mm wide, 50 m long, and 80 μm thick was laminated on the other side, producing a pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / polypropylene film structure.

[0106] Here, the polyethylene terephthalate film and nylon film are base layers, the aluminum alloy thin film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0107] The pouch film laminate was molded to prepare a pouch exterior material including a storage portion and a sealing portion.

[0108] Thereafter, a hole having a diameter of 5 mm was punched in the storage area adjacent to the sealing part to form a through-hole, and the gas-permeable film prepared above was placed on the punched hole, facing the inner layer part, and heat-sealed onto the pouch film laminate through heat treatment to seal the hole formed in the pouch film laminate, thereby producing a pouch exterior material.

[0109] In this case, the pouch exterior material is manufactured in a shape that allows a gas collection part to be formed between the electrode assembly and the area where the electrode lead is pulled out into the pouch exterior material when the electrode assembly connected to the electrode lead is stored, and the hole is punched so as to be located in the pouch exterior material in the area corresponding to the gas collection part.

[0110] (3) Secondary battery manufacturing The negative and positive electrodes and the porous polyethylene separator were stacked and then laminated to prepare an electrode assembly, and then an electrode lead was attached to the electrode assembly.

[0111] An electrolyte was prepared by dissolving LiPF6 in a solvent (EC:EMC:DMC = 3:3:4 volume ratio) to a concentration of 1.0 M. The electrode assembly was placed in the pouch-type case with the tip of the electrode lead extended to the outside, and the electrolyte was poured into the pouch-type case.

[0112] Thereafter, the sealing portion of the pouch-type case was sealed with a seal bar having an area of ​​200 mm x 10 mm under conditions of 220°C and 0.27 MPa for 2 seconds, and then left at 60°C for 4 hours to manufacture a pouch-type secondary battery. At this time, the portion of the sealing portion where the lead film was formed had a structure in which the lower case / lead film / electrode lead / gas exhaust part / lead film / upper case were sequentially stacked.

[0113] Example 2-2 A gas-permeable film was prepared in the same manner as in Example 2-1, except that a mixture of polypropylene and polytetrafluoroethylene in a weight ratio of 5:5 was used as the third polymer layer, and a pouch-type secondary battery was prepared in the same manner.

[0114] Example 2-3 A gas-permeable film was prepared in the same manner as in Example 2-1, except that a mixture of polypropylene and polytetrafluoroethylene in a weight ratio of 7:3 was used as the third polymer layer, and a pouch-type secondary battery was prepared in the same manner.

[0115] Comparative Example 2-1 A 40 μm thick polypropylene was prepared as the first polymer layer, a 100 μm thick polypropylene acrylic acid copolymer was prepared as the second polymer layer, and a 60 μm thick polypropylene was prepared as the third polymer layer. The first polymer layer, the third polymer layer, and the second polymer layer were then laminated and heat-sealed to prepare a gas-permeable film, and a pouch-type secondary battery was fabricated in the same manner.

[0116] Comparative Example 2-2 A gas-permeable film and a pouch-type secondary battery were manufactured in the same manner as in Comparative Example 2-1, except that a polytetrafluoroethylene film was used as the third polymer layer.

[0117] Comparative Example 2-3 A gas-permeable film and a pouch-type secondary battery were manufactured in the same manner as in Example 2-1, except that the first and second polymer layers were not formed and the third polymer layer was formed to a thickness of 200 μm.

[0118] Experimental Example 1: Evaluation of adhesive strength of gas permeable film For the pouch-type secondary batteries manufactured in each of the Examples and Comparative Examples, the adhesive strength between the pouch film and the gas-permeable film and the adhesive strength between the laminated films in the gas-permeable film were evaluated, and for the set of Example 1 and Comparative Example 1, the adhesive strength with the electrode lead was also evaluated.

[0119] Specifically, CO2 gas was generated inside the pouch outer packaging, and then the pouch was stored in a chamber at 60°C for 5 days. The electrode lead was then broken by bending a portion 10 mm from one corner of the sealing portion. The ends of the lead assembly were then attached to the lower and upper jigs of the UTM, respectively, and the assembly was pulled 30 mm in a 180° direction at a speed of 50 mm / min. The average value (kgf / 15 mm) of the flat section of the adhesive strength graph was calculated. The results are shown in Tables 1 and 2 below.

[0120] Experimental Example 2: Gas Exhaust Rate Evaluation Using pressure-resistant equipment from ITS, CO2 was injected into the pouch-type secondary battery to increase the internal pressure of the pouch until the pressure difference between the inside and outside of the pouch reached 1.0 to 2.5 bar, and the battery was then stored in a chamber at 60°C for 1 to 2 days. The decrease in the internal pressure of the pouch during the storage period was confirmed, and the gas release rate was calculated based on the flow rate and pressure decrease, and is shown in Tables 1 and 2 below.

[0121] [Table 1]

[0122] [Table 2]

[0123] Referring to Table 1, it can be seen that the gas-permeable films of Examples 1-1 to 1-4 according to one embodiment of the present invention, when placed on an electrode lead, maintain excellent inter-film adhesion and also maintain excellent adhesion to the pouch outer casing, demonstrating excellent gas release performance. However, in the case of Example 1-4, the adhesion to the electrode lead was measured to be low. In this case, when the interface between the lead film and the electrode lead is opened to form a gas release path, if the withstand pressure increases somewhat, the lead film at the outer end may lose adhesion to the electrode lead and completely peel off, resulting in a venting phenomenon. Therefore, it can be seen that using a modified polyolefin-based polymer as the second layer is more preferable, as can be understood from the results of Examples 1-1 to 1-3.

[0124] On the other hand, in Comparative Example 1-2, in which only PTFE was used as the third layer, it was difficult to form a gas-permeable film due to adhesive strength issues, and the adhesive strength between the electrode lead and the pouch exterior material could not be measured. As a result, gas release performance could not be confirmed. In Comparative Example 1-1, in which only PP was used as the third layer without PTFE, the adhesive strength was similar to that of the Examples, but the gas release performance was significantly inferior to that of the Examples. Furthermore, in Comparative Example 1-3, in which a film was formed by blending PP and PTFE in a single layer, the film itself was able to be formed, but the adhesive strength between the pouch exterior material and the electrode lead was poor, resulting in the film completely peeling off and venting upon opening, confirming very low durability.

[0125] The gas-permeable films formed in the hole portions of the pouch outer packaging materials in Table 2 also showed results that were not particularly different from those in Table 1. In the examples, the adhesive strength between the films was superior to the comparative examples, and the gas discharge performance was also superior, but it was confirmed that comparative examples 2-1 to 2-3 had poor discharge performance or adhesive strength for the same reasons as comparative examples 1-1 to 1-3.

[0126] As described above, the present invention has been described using limited embodiments and drawings, but the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made by a person having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the claims set forth below. [Explanation of symbols]

[0127] 10: Gas permeable film 11: First polymer layer 12: Second polymer layer 13: Third polymer layer 100: Electrode assembly 110: Lead film 120: Electrode lead 200: Pouch outer packaging material 210: Gas permeable film 220a: Upper pouch 220b: Lower pouch 221: Inner layer 222: Outer layer 223:Deep 230: Terrace section 300: Interior space 310: Gas collection unit 320: Gas exhaust route

Claims

1. a first polymeric layer, a second polymeric layer, and a third polymeric layer disposed between the first and second polymeric layers; The gas-permeable film, wherein the third polymer layer contains polypropylene and polytetrafluoroethylene in a weight ratio of 9:1 to 1:

9.

2. The gas-permeable film according to claim 1 , wherein the first polymer layer and the second polymer layer each independently comprise a polyolefin-based polymer.

3. The gas-permeable film according to claim 1 , wherein the second polymer layer comprises a modified polyolefin resin.

4. 2. The gas-permeable film according to claim 1, wherein the third polymer layer comprises polypropylene and polytetrafluoroethylene in a weight ratio of 8:2 to 2:

8.

5. 2. The gas-permeable film according to claim 1, wherein the first polymer layer has a thickness of 40 to 200 [mu]m.

6. 2. The gas-permeable film according to claim 1, wherein the second polymer layer has a thickness of 40 to 200 [mu]m.

7. 2. The gas-permeable film according to claim 1, wherein the third polymer layer has a thickness of 40 to 600 [mu]m.

8. A secondary battery comprising: an electrode assembly; a pouch outer casing that houses the electrode assembly; an electrode lead electrically connected to the electrode assembly; and the gas-permeable film according to claim 1 that is adhered to at least one surface of the electrode lead.

9. The secondary battery according to claim 8, wherein the gas-permeable film has a second polymer layer comprising a polypropylene acrylic acid copolymer.

10. a pouch outer packaging material for housing an electrode assembly; The pouch exterior material has a structure in which a metal layer and a polymer layer are laminated, A pouch outer covering material, characterized in that the pouch outer covering material has one or more holes, and the one or more holes are sealed with the gas-permeable film according to claim 1.

11. the pouch exterior material has an outer layer portion and an inner layer portion each made of the polymer layer, 11. The pouch exterior packaging material according to claim 10, wherein the metal layer is a deep layer interposed between the outer layer and the inner layer.

12. 12. The pouch exterior material according to claim 11, wherein the outer layer portion comprises at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, and nylon.

13. 12. The pouch exterior packaging material according to claim 11, wherein the deep layer portion contains one or more selected from the group consisting of aluminum, copper, nickel, iron, carbon, chromium, manganese, and alloys containing two or more of these.

14. The pouch exterior material according to claim 11, wherein the inner layer portion comprises at least one material selected from the group consisting of polypropylene, acid-modified polypropylene, random polypropylene, and ethylene-propylene copolymer.

15. The accommodated electrode assembly includes an electrode lead electrically connected to the electrode assembly, The electrode lead is drawn out to the outside of the pouch outer packaging material, a gas collecting section is formed between the electrode assembly and a region where the electrode lead is drawn out of the pouch outer packaging material; The pouch outer casing according to claim 10, wherein the hole is formed in an area of ​​the pouch outer casing corresponding to the gas collecting portion.

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