Pouch-type secondary battery

Abstract

The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a receiving portion that receives the electrode assembly and a sealing portion that seals the receiving portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas guide disposed between the electrode lead and the lead film, wherein the gas guide includes a first layer in contact with the lead film, and the first layer includes a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0159794 filed November 24, 2022 and Korean Patent Application No. 10-2023-0164379 filed November 23, 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 pouch-type secondary battery, and more particularly to a pouch-type secondary battery including a gas vent. [Background technology]

[0003] Secondary batteries are used in a wide range of fields, from small products such as digital cameras, DVD players, MP3 players, mobile phones, PDAs, portable game devices, power tools, and e-bikes to large products requiring high output such as electric and hybrid vehicles, as well as power storage devices and backup power storage devices for storing surplus generated electricity and new / renewable energy. Types of secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries, and lithium-ion polymer batteries.

[0004] A secondary battery can be manufactured by placing an electrode assembly, in which positive electrodes, negative electrodes, and separators interposed therebetween are alternately stacked, in a battery case, injecting an electrolyte, and sealing the battery case. Secondary batteries can be classified into pouch types and can types depending on the material of the case that houses the electrode assembly. Among these, a pouch-type battery can be manufactured by pressing a flexible pouch film laminate to form a cup, placing the electrode assembly in the inner space of the cup, and sealing the sealing portion.

[0005] Pouch-type secondary batteries can generate gas inside the pouch when operated at high temperatures, overcharged, or when a short circuit occurs. When the gas pressure inside the pouch increases, the pouch vents, potentially resulting in an explosion or fire. To address this issue, a gas exhaust port has been provided at the sealed portion of the pouch. In this case, when the gas pressure inside the pouch increases, the interface between the pouch and the gas exhaust port opens, allowing the gas to be released to the outside of the pouch. However, in the past, even when the internal pressure of the pouch increases due to gas generation, the interface remains unopened, causing the internal pressure of the pouch to exceed a critical value, resulting in an explosion of the pouch. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to solve the above problems, and provides a pouch-type secondary battery that can discharge gas to the outside before the internal pressure of the pouch becomes excessively high. [Means for solving the problem]

[0007] According to one embodiment of the present invention, there is provided a pouch-type secondary battery including an electrode assembly, a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas guide disposed between the electrode lead and the lead film. In this case, the gas guide includes a first layer in contact with the lead film, and the first layer includes a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

[0008] In the pouch-type secondary battery according to the present invention, the ratio (B / A) of the thermal expansion coefficient (B) of the polymer film measured at 60°C to 120°C to the thermal expansion coefficient (A) of the polymer film measured at -30°C to 10°C may be 1.2 to 3.0. Here, the thermal expansion coefficient (B) of the polymer film measured at 60°C to 120°C may be 25 μm / cm°C or more, and the thermal expansion coefficient (A) of the polymer film measured at -30°C to 10°C may be 25 μm / cm°C or more.

[0009] In the pouch-type secondary battery according to the present invention, the polymer film may have an air permeability of 100 sec / 100 cc or more, a water droplet contact angle of 100° or more, and may include polytetrafluoroethylene (PTFE).

[0010] In the pouch-type secondary battery according to the present invention, the gas guide may further include a second layer in contact with the electrode lead. Here, the electrode lead, the second layer, the first layer, and the lead film may be laminated in this order. In addition, the second layer may include an acid-modified polyolefin. [Effects of the Invention]

[0011] According to the present invention, by disposing a gas guide portion, which is made of a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C, between the electrode lead and the lead film, the interface between the gas guide portion and the lead film opens before the internal pressure of the pouch becomes excessively high, allowing the gas to be easily released to the outside of the pouch. Therefore, the pouch-type secondary battery according to the present invention has excellent stability by preventing the problem of the pouch exploding due to excessive internal pressure of the pouch caused by gas generation. [Brief explanation of the drawings]

[0012] The drawings attached to the specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, 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 such drawings.

[0013] [Figure 1] 1 is an exploded view of a pouch-type secondary battery according to the present invention; [Figure 2] FIG. 2 is a cross-sectional view of a sealed pouch-type secondary battery. [Figure 3] 1 is a cross-sectional view of an example of a pouch-type secondary battery before the pouch-type case is opened. [Figure 4] 1 is an example of a cross-sectional view of a pouch-type secondary battery when the pouch-type case is opened. [Figure 5] 10 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened. FIG. [Figure 6] 10 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to 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 embodied in various different forms. However, the present embodiments are provided to fully disclose the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains, and the present invention is defined only by the scope of the claims. The same reference symbols refer to the same elements throughout the specification.

[0015] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0016] 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 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.

[0017] In this specification, when a part is said to include a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified to the contrary.

[0018] In this specification, the phrase "A and / or B" means A, or B, or A and B.

[0019] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0020] In this specification, the term "storage modulus" refers to the storage modulus in the machine direction (MD) of a polymer film measured at a temperature of 100°C using dynamic mechanical analysis (DMA).

[0021] In this specification, the "coefficient of thermal expansion (CTE)" means the length of a polymer film stretched in the MD direction when the temperature of the polymer film increases by 1°C.

[0022] As used herein, "breathability" refers to the degree to which air passes through a polymer film.

[0023] In this specification, the term "water droplet contact angle" refers to the angle formed between water on the surface of a polymer film and the surface where the polymer film is in contact.

[0024] The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas guide disposed between the electrode lead and the lead film. The gas guide includes a first layer in contact with the lead film, and the first layer includes a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

[0025] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the drawings.

[0026] Fig. 1 is an exploded view of a pouch-type secondary battery 100 according to the present invention, and Fig. 2 is a cross-sectional view of the sealed pouch-type secondary battery 100. In Fig. 2, some of the components of the pouch-type secondary battery 100 are omitted for ease of understanding. As shown in Figs. 1 and 2, the pouch-type secondary battery 100 according to the present invention includes a pouch-type case 110, an electrode assembly 160, an electrode lead 180, a lead film 190, and a gas guide 200.

[0027] (1) Pouch-type case The pouch-type case 110 can house the electrode assembly 160 inside. The pouch-type case 110 can be manufactured by molding a pouch film laminate. In this case, the pouch film laminate can include a base layer, a gas barrier layer, and a sealant layer. In the pouch film laminate, the base layer, the gas barrier layer, and the sealant layer can be laminated in this order.

[0028] The substrate layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from external friction and impact. The substrate layer is made of a polymer and can electrically insulate the electrode assembly from the outside.

[0029] The substrate layer may be made of 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. Preferably, the substrate layer is made of polyethylene terephthalate (PET), nylon, or a combination thereof, which are abrasion-resistant and heat-resistant.

[0030] The substrate layer may have a single film structure made of any one material, or alternatively, the substrate layer may have a composite film structure made of two or more materials each formed into a layer.

[0031] The thickness of the substrate layer can be 5 μm to 50 μm, specifically 7 μm to 40 μm, more specifically 25 μm to 38 μm. When the thickness of the substrate layer satisfies this range, the external insulation is excellent and the overall thickness of the pouch is not large, so that the energy density relative to the volume of the secondary battery can be excellent.

[0032] The gas barrier layer is laminated between the base layer and the sealant layer to ensure the mechanical strength of the pouch, block the entry and exit of gas or moisture from outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type case.

[0033] The gas barrier layer may be formed of a metal, specifically, an aluminum alloy thin film. When an aluminum alloy thin film is used to form the gas barrier layer, it can ensure a certain level of mechanical strength, be lightweight, and ensure electrochemical compatibility between the electrode assembly and the electrolyte, as well as heat dissipation. The aluminum alloy thin film may contain at least one metal element other than aluminum (Al), such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0034] The thickness of the gas barrier layer can be 40 μm to 100 μm, specifically 50 μm to 90 μm, more specifically 55 μm to 85 μm. When the thickness of the gas barrier layer satisfies this range, excellent moldability and gas barrier performance are achieved when the cup portion is formed.

[0035] The sealant layer is thermally bonded to the sealing portion when the pouch-shaped case accommodating the electrode assembly therein is sealed, thereby completely sealing the inside of the pouch-shaped case. For this purpose, the sealant layer may be made of a material having excellent thermal adhesive strength.

[0036] The sealant layer may be formed of a material having insulating properties, corrosion resistance, and sealing properties. Specifically, since the sealant layer is in direct contact with the electrode assembly and / or electrolyte inside the pouch-type case, it may be formed of a material having insulating properties and corrosion resistance. Furthermore, since the sealant layer must completely seal the inside of the pouch-type case to prevent the transfer of materials between the inside and outside, it may be formed of a material having high sealing properties (e.g., excellent thermal adhesive strength). To ensure such insulating properties, corrosion resistance, and sealing properties, the sealant layer may be formed of a polymer material.

[0037] The pouch film laminate may be drawn and stretched using a punch or the like to manufacture the pouch-type case 110. As a result, the pouch-type case 110 may include a cup portion 122 and a receiving portion 124. The receiving portion 124 is a location for receiving the electrode assembly, and may refer to a bag-shaped receiving space formed inside the cup portion 122 as the cup portion 122 is formed.

[0038] According to an embodiment of the present invention, the pouch-type case 110 may include a first case 120 and a second case 130, as shown in Fig. 1. The first case 120 includes a receiving portion 124 that can receive the electrode assembly 160, and the second case 130 can cover the receiving portion 124 from above to prevent the electrode assembly 160 from falling out of the battery case 110. The first case 120 and the second case 130 may be manufactured with one side connected to each other as shown in Fig. 1, but are not limited to this and may be manufactured in various ways, such as being separated from each other and manufactured separately.

[0039] According to another embodiment of the present invention, when forming cup portions in a pouch film laminate, two symmetrical cup portions 122, 132 may be formed adjacent to each other by drawing one pouch film laminate. In this case, as shown in FIG. 1 , the first case 120 and the second case 130 may be formed with the cup portions 122, 132, respectively. After the electrode assembly 160 is accommodated in the accommodating portion 124 of the cup portion 122 of the first case 120, the bridge portion 140 formed between the two cup portions 122, 132 may be folded so that the two cup portions 122, 132 face each other. In this case, the cup portion 132 of the second case 130 can accommodate the electrode assembly 160 from above. Therefore, because two cup portions 122, 132 accommodate one electrode assembly 160, an electrode assembly 160 that is thicker than when there is only one cup portion 122 can be accommodated. In addition, folding the pouch-type case 110 forms one corner of the secondary battery 100, which reduces the number of corners to be sealed during a subsequent sealing process, thereby improving the processing speed of the pouch-type secondary battery 100 and reducing the number of sealing processes.

[0040] The pouch-type case 110 may be sealed with the electrode assembly 160 housed therein so that a portion of the electrode lead 180, i.e., a terminal portion, described below, is exposed. Specifically, when the electrode lead 180 is connected to the electrode tab 170 of the electrode assembly 160 and a lead film 190 is formed on a portion of the electrode lead 180, the electrode assembly 160 may be housed in a housing portion 124 provided in the cup portion 122 of the first case 120, and the second case 130 may cover the housing portion 124 from above. Next, an electrolyte may be injected into the housing portion 124, and the sealing portions 150 formed on the peripheries of the first case 120 and the second case 130 may be sealed.

[0041] The sealing part 150 may serve to seal the receiving part 124. Specifically, the sealing part 150 may be formed along the periphery of the receiving part 124 to seal the receiving part 124.

[0042] The temperature for sealing the sealing part 150 may be 180°C to 250°C, specifically 200°C to 250°C, and more specifically 210°C to 240°C. When the sealing temperature is within the above range, the pouch-type case 110 can be thermally bonded to ensure sufficient sealing strength.

[0043] (2) Electrode assembly The electrode assembly 160 may be inserted into the pouch-type case 110 and sealed by the pouch-type case 110 after the electrolyte is injected.

[0044] The electrode assembly 160 may be formed by sequentially stacking a positive electrode, a separator, and a negative electrode. Specifically, the electrode assembly 160 may include two electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other.

[0045] The positive and negative electrodes may each have a structure in which an active material slurry is applied to an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper, respectively. The slurry may be formed by stirring a granular active material, a supplemental conductor, a binder, a conductive material, and the like in a solvent. The solvent may be removed in a subsequent process.

[0046] A slurry containing a mixture of an electrode active material, a binder, and / or a conductive material is applied to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, which are then stacked on both sides of a separator to manufacture a predetermined shape of the electrode assembly 160. The electrode assembly 160 may be of a stack type, a jelly roll type, a stack and folding type, or the like, but is not limited thereto.

[0047] The electrode assembly 160 may include an electrode tab 170 .

[0048] The electrode tabs 170 are connected to the positive and negative electrodes of the electrode assembly 160, respectively, and protrude from the electrode assembly 160 to serve as paths for electrons to move between the inside and outside of the electrode assembly 160. The electrode current collector included in the electrode assembly 160 may be 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 170 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion by ultrasonic welding, for example. As shown in FIG. 1, the electrode tabs 170 may protrude in different directions from the electrode assembly 160, but are not limited thereto. They may protrude in various directions, such as protruding side by side in the same direction from one side.

[0049] (3) Electrode lead The electrode lead 180 may supply electricity to the outside of the secondary battery 100. The electrode lead 180 may be connected to the electrode tab 170 of the electrode assembly 160 by spot welding or the like.

[0050] The electrode lead 180 is connected to the electrode assembly 160 and may protrude to the outside of the pouch-type case 110 through the sealing portion 150. Specifically, one end of the electrode lead 180 is connected to the electrode assembly 160, particularly to the electrode tab 170, and the other end of the electrode lead 180 may protrude to the outside of the pouch-type case 110.

[0051] The electrode lead 180 may include a positive electrode lead 182 having one end connected to the positive electrode tab 172 and extending in the direction in which the positive electrode tab 172 protrudes, and a negative electrode lead 184 having one end connected to the negative electrode tab 174 and extending in the direction in which the negative electrode tab 174 protrudes. The other ends of both the positive electrode lead 182 and the negative electrode lead 184 may protrude to the outside of the battery case 110. This allows electricity generated inside the electrode assembly 160 to be supplied to the outside. In addition, since the positive electrode tab 172 and the negative electrode tab 174 protrude in different directions, the positive electrode lead 182 and the negative electrode lead 184 may also extend in different directions. The positive electrode lead 182 and the negative electrode lead 184 may be made of different materials. That is, the positive electrode lead 182 may be made of the same aluminum (Al) material as the positive electrode current collector, and the negative electrode lead 184 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 180 protruding outside the battery case 110 serves as a terminal portion and may be electrically connected to an external terminal.

[0052] (4) Lead film The lead film 190 prevents electricity generated from the electrode assembly 160 from flowing to the battery case 110 via the electrode lead 180, thereby maintaining the sealing of the battery case 110. To this end, the lead film 190 may be formed of an insulator that is electrically non-conductive and does not easily pass electricity. Typically, the lead film 190 is made of a relatively thin insulating tape that is easily attached to the electrode lead 180 and / or the gas guide 200, but is not limited thereto, and any material that can insulate the electrode lead 180 may be used.

[0053] The lead film 190 according to an embodiment of the present invention may be a gas-permeable film and may be disposed to wrap the outer periphery of the electrode lead 180 and the gas guide 200. Specifically, the electrode lead 180 and the gas guide 200 may contact each other on one side, and at least a portion of the electrode lead 180 and the gas guide 200 may be surrounded by the lead film 190. The lead film 190 may be positioned only in the sealing portion 150 where the first case 120 and the second case 130 of the pouch-type case 110 are heat-sealed, and may bond the electrode lead 180 and the gas guide 200 to the battery case 110.

[0054] A lead film 190 may be disposed between the electrode lead 180 and / or gas guide 200 and the pouch-type case 110. For example, as shown in Fig. 2, a lower case 110, a lead film 190, an electrode lead 180, a gas guide 200, a lead film 190, and an upper case 110 may be disposed in a stacked state in the region of the sealing unit 150. Although not shown in the drawings, in another example, a lower case, a lead film, a gas guide, an electrode lead, a lead film, and an upper case may be disposed in a stacked state in this order, or in yet another example, a lower case, a lead film, a gas guide, an electrode lead, a gas guide, a lead film, and an upper case may be disposed in a stacked state in this order.

[0055] 3 or 5, the lead film 190 may be disposed so that one end protruding outward from the pouch-type case 110 protrudes further than one end of the gas guide portion 200 protruding outward from the pouch-type case 110 and directly contacts the electrode lead 180. When one end of the lead film 190 is disposed so that it directly contacts the electrode lead 180, i.e., extends further than the gas guide portion 200 disposed on the electrode lead 180, an area through which gas can pass through the lead film 190 can be easily secured when gas is discharged and the lead film 190 on the gas guide portion 200 is opened. Furthermore, due to the strong adhesive strength between the lead film 190 and the electrode lead 180, a decrease in durability caused by opening the lead film 190 during gas discharge can be minimized compared to when the lead film 190 is not extended.

[0056] According to another embodiment of the present invention, similar to FIG. 3 or 6, the second layer 220 of the gas guide portion 200 may be formed longer toward the outside of the pouch-type case 110 than the first layer 210, and one end of the lead film 190 protruding toward the outside of the pouch-type case 110 may be positioned so as to be in direct contact with the second layer 220 rather than the first layer 210.

[0057] In particular, as shown in FIG. 3, when one end of the lead film 190 protrudes further in the protruding direction of the electrode lead to contact the electrode lead 180, and the second layer 220 of the gas guide unit 200 extends further than the first layer 210 so that a portion of the lead film 190 contacts the second layer 220, the adhesive strength between the lead film 190 and the electrode lead 180, as well as the adhesive strength between the lead film 190 and the gas guide unit 200, can be maintained strong, and a synergistic effect can be achieved in the adhesive strength between the electrode lead 180 and the gas guide unit 200, resulting in a gas exhaust component with excellent durability.

[0058] Meanwhile, the lead film 190 may include one or more layers, specifically, the lead film 190 may include a metal adhesive layer, a core layer, and a pouch adhesive layer, which are laminated in order.

[0059] The metal adhesive layer may be in direct contact with the electrode lead 180 and serve to adhere the lead film 190 to the electrode lead 180. The metal adhesive layer may include any material that easily adheres to the electrode lead 180. Specifically, the metal adhesive layer may include acid-modified polyolefin. For example, the metal adhesive layer may include at least one of PPa (acid modified polypropylene), PEa (acid modified polyethylene), and plasma-treated PP (plasma-treated polypropylene), but is not limited thereto. The thickness may be 50 μm to 80 μm, specifically 50 μm to 75 μm, and more specifically 60 μm to 75 μm. When the thickness of the metal adhesive layer satisfies the above numerical range, it is effective in preventing pinholes and leaks at the edges when the electrode lead and the lead film are fused together.

[0060] The core layer may be a layer located at the center of the lead film 190. The core layer may include, but is not limited to, additives such as polypropylene, polyolefin elastomer (POE), fluorine-based polyolefin, and / or colorants. For example, the polymer included in the core layer may be a homopolymer. When the core layer includes a homopolymer, the melting point of the core layer can be controlled within the above-mentioned range, minimizing thermal deformation and ensuring insulation. As another example, the polymer included in the core layer may be polytetrafluoroethylene as a fluorine-based polyolefin, or a mixture of polytetrafluoroethylene and polypropylene, which may be mixed in a weight ratio of 9:1 to 1:9. In this case, gas permeation performance may be superior to that when gas permeates the lead film 190 through the gas guide 200. The thickness of the core layer may be 40 μm to 70 μm, specifically 50 μm to 70 μm, more specifically 60 μm to 70 μm. When the thickness of the core layer satisfies the above range, deformation due to heat applied during fusion and sealing is prevented, and a robust design effect is achieved in terms of ensuring insulation.

[0061] The pouch adhesive layer may be a layer that directly contacts the battery case 110, specifically, the sealant layer of the pouch film laminate. The pouch adhesive layer may include, but is not limited to, polypropylene or polyolefin elastomer (POE). In particular, the polymer contained in the pouch adhesive layer may be a copolymer. The pouch adhesive layer containing a copolymer can have a melting point controlled within the above-mentioned range, which is similar to the melting point of the polymer in the sealant layer of the pouch film laminate, thereby ensuring ease of sealing. The thickness of the pouch adhesive layer may be 40 μm to 100 μm, specifically 40 μm to 80 μm, and more specifically 40 μm to 60 μm. When the thickness of the pouch adhesive layer satisfies the above-mentioned range, it is effective in ensuring a sufficient polymer (e.g., polypropylene) remaining rate to ensure strength during sealing between the electrode lead and the pouch film laminate.

[0062] (5) Gas induction section The gas guide 200 serves to form a path for discharging gas from the inside to the outside of the pouch-type case 110. As shown in FIG. 2, the gas guide 200 of the present invention can be disposed between the electrode lead 180 and the lead film 190.

[0063] FIG. 3 is a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened, and FIG. 4 is a cross-sectional view of the pouch-type secondary battery when the pouch-type case is opened. As shown in FIGS. 3 and 4, gas guide 200 includes first layer 210 in contact with lead film 190, and first layer 210 includes a polymer film. When the internal pressure of pouch case 110 increases, the interface between first layer 210 and lead film 190 opens, forming gas exhaust path 300, as shown in FIG. 4. However, in pouch-type secondary batteries using conventional gas guides, the operating pressure of the gas guide is high, and the gas guide does not operate under high pressure conditions due to gas generation inside the pouch, resulting in the pouch exploding.

[0064] As a result of extensive research into solving this problem, the inventors discovered that by controlling the storage modulus of the gas guide section 200 within a specific numerical range, the interface between the gas guide section 200 and the lead film 190 opens before the pressure inside the pouch becomes excessively high, allowing the gas to be discharged to the outside through the lead film 190, thereby completing the present invention.

[0065] Specifically, the storage modulus of the first layer 210 may affect the adhesive strength and restoring force with the lead film 190 due to shear stress generated when the internal pressure of the case 110 increases. That is, the lower the storage modulus of the first layer 210, the easier it is to open the case when the internal pressure increases, thereby reducing the operating pressure of the gas guide portion. Furthermore, when the internal pressure decreases again due to the gas being released, the first layer 210 returns to its original, non-lifted state, thereby minimizing electrolyte leakage and moisture penetration. However, if the storage modulus of the first layer 210 is too low, the lifted state may not return to its original state even when the internal pressure decreases after the lead film 190 is opened. This may cause the first layer 210 to be unable to hold the lead film 190, which may lead to electrolyte penetration into the gas exhaust path 300 and increase the possibility of moisture penetration from the outside, which may result in the first layer 210 melting during sealing. In other words, by controlling the storage modulus to an appropriate level, the gas inside the case 110 is discharged to the outside through the gas discharge path 300 before the internal pressure of the case 110 becomes excessively high, thereby reducing the internal pressure of the pouch-type case 110 and preventing the case 110 from exploding or catching fire.

[0066] According to the present invention, the storage modulus of the polymer film measured at 100°C is 30 MPa to 650 MPa, specifically, 600 MPa or less, 500 MPa or less, 450 MPa or less, 400 MPa or less, or 350 MPa or less, or 50 MPa or more, 70 MPa or more, or 100 MPa or more. If the storage modulus of the polymer film is less than 30 MPa, the first layer 210 melts during sealing of the pouch-type case 110, resulting in a problem of not forming a gas exhaust path 300. If the storage modulus of the polymer film is more than 650 MPa, the first layer 210 does not easily deform, resulting in a problem of not opening the interface between the first layer 210 and the lead film 190.

[0067] According to the present invention, first layer 210 preferably includes a polymer film having a controlled ratio of storage modulus and thermal expansion coefficient. Specifically, the ratio (B / A) of the thermal expansion coefficient (B) of the polymer film measured at 60°C to 120°C to the thermal expansion coefficient (A) of the polymer film measured at -30°C to 10°C may be 1.2 to 3.0, specifically 1.2 to 2.5, more specifically 1.3 to 2.0. When the ratio (B / A) of the thermal expansion coefficients of the polymer film satisfies the above range, first layer 210 does not melt during the sealing process, and when the internal pressure of case 110 increases, the interface between first layer 210 and lead film 190 opens, forming gas exhaust path 300.

[0068] The ratio of the thermal expansion coefficients (B / A) may mean that the thermal expansion coefficient at high temperatures is larger than the thermal expansion coefficient at low temperatures. This is because high temperatures are generally the environment in which gas is generated, i.e., the internal pressure of the case 110 increases. If the thermal expansion coefficient is high at high temperatures, a gas guide portion with low operating pressure can be realized. Furthermore, since a material with a relatively low thermal expansion coefficient at low temperatures is used, in an environment in which gas discharge is not required, unnecessary opening of the gas discharge path 300 can be prevented, thereby reducing the possibility of moisture penetration and electrolyte leakage. In this case, gas can be discharged by controlling the storage modulus, and it is preferable that the ratio of the thermal expansion coefficients satisfies the above-mentioned range.

[0069] Here, the thermal expansion coefficient (B) of the polymer film measured at 60°C to 120°C can be 25 μm / cm·°C or more, specifically 100 μm / cm·°C to 450 μm / cm·°C, more specifically 150 μm / cm·°C to 300 μm / cm·°C. Also, the thermal expansion coefficient (A) of the polymer film measured at -30°C to 10°C can be 25 μm / cm·°C or more, specifically 30 μm / cm·°C to 200 μm / cm·°C, more specifically 90 μm / cm·°C to 150 μm / cm·°C.

[0070] According to the present invention, the polymer film may have an air permeability of 100 sec / 100 cc or more, specifically 100 sec / 100 cc to 50,000 sec / 100 cc, and more specifically 100 sec / 100 cc to 40,000 sec / 100 cc. The air permeability indicates the time it takes for 100 cc of air to pass through the polymer film, and a lower value indicates better air permeability. When the air permeability of the polymer film satisfies the above numerical range, it is possible to prevent the problem of pores in the polymer film being clogged by a melted lead film during pouch sealing, preventing the formation of a gas discharge path.

[0071] According to the present invention, it is preferable to use the first layer 210 including a polymer film in which the ratio of the storage modulus and the thermal expansion coefficient as well as the contact angle are controlled. Specifically, the water droplet contact angle of the polymer film may be 100° or more, specifically 100° to 150°, more specifically 100° to 130°. When the water droplet contact angle of the polymer film satisfies the above numerical range, the van der Waals force between the first layer 210 and the lead film 190 is reduced after sealing, which has the effect of quickly forming the gas discharge path 300.

[0072] The polymer film may include at least one of polytetrafluoroethylene (PTFE) and polyimide (PI), but is not limited thereto. In particular, when the polymer film includes polytetrafluoroethylene, it is preferable because the gas discharge path 300 can be formed even under low internal pressure conditions of the pouch.

[0073] In the gas guide unit 200 according to an embodiment of the present invention, as the internal pressure of the pouch-type case 110 increases due to gas generation, the first layer 210 and the lead film 190 are temporarily peeled apart, and the interface between them is opened, thereby forming the gas exhaust path 300. The gas exhaust path 300 can be formed at a low internal pressure by applying a polymer film having the above-described storage modulus to the first layer. After the interface between the lead film 190 and the first layer 210 is opened, the gas is exhausted and the internal pressure decreases, and the first layer 210, which has a controlled storage modulus as described above, easily returns to its original state, thereby helping to prevent moisture penetration and electrolyte leakage.

[0074] The mechanism for forming the gas discharge path 300 described above can be realized when a polymer film satisfying the storage modulus is applied to the first layer 210, as described above. According to another embodiment, it is preferable when the polymer film satisfies the ratio of thermal expansion coefficients in the above-mentioned range, with the thermal expansion coefficient at high temperatures being appropriately higher than the thermal expansion coefficient at low temperatures. As another example, it can be optimally realized when the polymer film satisfies the above-mentioned contact angle range.

[0075] According to yet another embodiment of the present invention, for durability, the gas guide unit 200 may preferably have a structure in which the lead film 190 protrudes further outward from the case 110 than the end of the gas guide unit 200 and is disposed in direct contact with the electrode lead 180, as described above. In this case, even if the gas exhaust path 300 is repeatedly formed, the strong adhesive force between the electrode lead 180 and the lead film 190 can prevent the case 110 itself from opening and venting.

[0076] Furthermore, the gas guide 200 according to the present invention may further include a second layer 220 in contact with the electrode lead 180. Specifically, the second layer 220 may be disposed on the electrode lead 180, and the first layer 210 may be disposed on the second layer 220. The second layer 220 may serve to attach the gas guide 200 to the electrode lead 180. As described above, the second layer 220 may have a structure in which it protrudes further outward from the case 110 than the end of the first layer 210 and is disposed in contact with the lead film 190. In this case, the adhesion between the electrode lead 180, the gas guide 200, and the lead film 190 may be excellent, which may help improve durability.

[0077] The second layer 220 may include any material that can be easily bonded to the electrode lead 180. Specifically, the second layer 220 may include an acid-modified polyolefin. For example, the second layer 220 may include, but is not limited to, at least one of acid-modified polypropylene (PPa), acid-modified polyethylene (PEa), and plasma-treated polypropylene (PP).

[0078] (6) Electrolyte The pouch-type secondary battery 100 according to the present invention may further include an electrolyte (not shown) injected into the pouch-type case 110. The electrolyte is used to transport lithium ions generated by an electrochemical reaction of the electrodes during charging / discharging of the secondary battery 100, and may include a non-aqueous organic electrolyte solution that is a mixture of a lithium salt and an organic solvent, or a polymer using a polymer electrolyte. Furthermore, the electrolyte may include a sulfide-based, oxide-based, or polymer-based solid electrolyte, and such a solid electrolyte may have flexibility that makes it easily deformable under external force.

[0079] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for the purpose of facilitating understanding of the present invention and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0080] [Examples and Comparative Examples] Example 1 (1) Manufacturing pouch-type cases 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 50 μm thick was laminated on the other side to produce a pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / polypropylene film structure.

[0081] Here, the polyethylene terephthalate film and nylon film are the base layer, the aluminum alloy thin film is the gas barrier layer, and the polypropylene film is the sealant layer.

[0082] The pouch film laminate was molded to prepare a pouch-type case including a receiving portion and a sealing portion.

[0083] (2) Secondary battery manufacturing The negative and positive electrodes and a porous polyethylene separator were stacked and then laminated to prepare an electrode assembly, and then an electrode lead was attached to the electrode assembly.

[0084] An electrolyte was prepared by dissolving LiPF6 in a solvent (volume ratio of EC:EMC:DMC = 3:3:4) to a concentration of 1.0 M. With the tip of the electrode lead extended to the outside, the electrode assembly was placed in the pouch-type case, and the electrolyte was poured into it.

[0085] A 20 μm thick acid-modified polypropylene film (second layer) and a 50 μm thick polytetrafluoroethylene film (first layer) were laminated in this order on the upper surface of the electrode lead to form a gas guide. Next, a 200 μm thick polypropylene film (lead film) was laminated on the lower surface of the electrode lead and the upper surface of the gas guide, respectively.

[0086] Thereafter, the sealing portion of the pouch-type case was sealed for 2 seconds under the conditions of a seal bar area of ​​200 mm x 10 mm, 220°C, and 0.27 MPa, and then left for 4 hours at 60°C to manufacture a pouch-type secondary battery. Here, 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 guide / lead film / upper case were laminated in this order.

[0087] Example 2 A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a 50 μm thick polytetrafluoroethylene film and a 50 μm thick polypropylene film were laminated in that order as the polymer film applied to the first layer.

[0088] Example 3 A pouch-type case and a secondary battery were produced in the same manner as in Example 1, except that a polytetrafluoroethylene film having a thickness of 100 μm was used as the polymer film applied to the first layer.

[0089] Comparative Example 1 A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polyurethane film having a thickness of 100 μm was used as the polymer film applied to the first layer.

[0090] Comparative Example 2 A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polyimide film having a thickness of 50 μm was used as the polymer film applied to the first layer.

[0091] Comparative Example 3 A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polypropylene film having a thickness of 100 μm was used as the polymer film applied to the first layer.

[0092] Experimental Example 1: Evaluation of the physical properties of polymer films Before sealing the pouches, the physical properties of each polymer film (gas guide) applied to the first layer in Examples 1 to 3 and Comparative Examples 1 to 3 were measured.

[0093] Specifically, the breathability of the polymer film was calculated by measuring the time it took for 100 ml of air having a pressure of 0.05 MPa to pass through the polymer film using EG01-55-1MR manufactured by Asahi Seiko Co., Ltd.

[0094] The water droplet contact angle of the polymer film was measured as a static contact angle of each substrate at room temperature using Phoenix mt manufactured by SEO.

[0095] The storage modulus of the polymer film was measured in the MD (Machine Direction) direction at a temperature of 100°C using a DMA 850 manufactured by TA Instruments.

[0096] The thermal expansion coefficient of the polymer film was measured using a 4.4 mm wide, 50 mm long sample using a TA Instruments TMA Q400. The measurement was performed in the temperature range of -30°C to 120°C, at a heating rate of 5°C / min, with N2 purging and a preload of 0.1 N. The thermal expansion coefficient (B) of the polymer film measured at 60°C to 120°C was then divided by the thermal expansion coefficient (A) of the polymer film measured at -30°C to 10°C to calculate the ratio of the thermal expansion coefficients (B / A).

[0097] The measurement results are shown in Table 1 below.

[0098] [Table 1]

[0099] Experimental example 2: Evaluation of gas guide section operation In order to evaluate whether the gas guide parts of the pouch-type secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 functioned normally, the amount of a specific gas discharged from the pouch-type secondary batteries was measured in a vacuum atmosphere. Specifically, an ELT3000 manufactured by INFICON was used to measure the flow rate of gaseous dimethyl carbonate (DMC) discharged from the inside of the pouch-type case to the outside when a vacuum atmosphere was created outside the pouch-type secondary battery. The measurement results are shown in Table 2 below.

[0100] Experimental example 3: Gas emission performance evaluation To evaluate the performance of the gas guide parts of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, the gas discharge rate was measured to confirm the formation of a gas discharge path. Specifically, CO2 was injected into the pouch-type secondary battery using internal pressure equipment manufactured by ITS, and the internal pressure of the pouch was increased until the pressure difference between the inside and outside of the pouch reached 1.0 to 2.5 bar. The battery was then stored in a chamber at 60°C for approximately 1 to 2 days. The decrease in the internal pressure of the pouch during the storage period was confirmed, and the gas discharge rate was calculated based on the flow rate and the pressure decrease. The presence or absence of a gas discharge path was also evaluated by visually checking the expansion of the sealing part. The results are shown in Table 2 below.

[0101] ○: Gas discharge path formed ×: Gas discharge path not formed

[0102] [Table 2]

[0103] According to Tables 1 and 2, in Examples 1 to 3, where the storage modulus of the polymer film measured at 100°C is in the range of 30 to 650 MPa, the measured vapor amount indicates that a gas discharge path is easily formed, and in fact, as the internal pressure of the pouch becomes relatively higher than that of the exterior of the pouch, the formation of a gas discharge path can be visually confirmed, and it can be confirmed that the gas discharge rate is significantly higher than that of the comparative example. In particular, it can be confirmed that the pouch-type secondary batteries of Examples 1 to 3 have a high gas discharge rate even when the pressure difference between the interior and exterior of the pouch is low.

[0104] On the other hand, in the case of Comparative Examples 1 and 3, the storage modulus of the polymer film was too low, and the first layer of the gas guide melted when the pouch-shaped case was sealed. As a result, the measured amount of vapor was very small, and it was predicted that a gas discharge path would not be formed. In fact, a gas discharge path was not formed, and it was impossible to measure the gas discharge rate.

[0105] In the case of Comparative Example 2, it was predicted that no gas discharge path would be formed based on the measured vapor volume data. However, when the internal pressure increased, it was confirmed by visual inspection that a gas discharge path was formed. However, because the storage modulus of the polymer film was too high, the gas guide portion was not easily deformed, and it was confirmed that the gas discharge rate was significantly slower than in the Examples. [Explanation of symbols]

[0106] 100 Pouch-type secondary battery 110 Pouch-type case 120 Case 1 122 Cup section 124 Storage unit 130 Case 2 132 Cup section 140 Bridge section 150 sealing part 160 Electrode assembly 170 Electrode Tab 172 Positive electrode tab 174 Negative electrode tab 180 Electrode Lead 182 Positive lead 184 Negative lead 190 Lead Film 200 Gas induction section 210 1st layer 220 2nd layer 300 Gas Exhaust Route

Claims

1. an electrode assembly; a pouch-type case including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion; an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case through the sealing portion; a lead film disposed between the electrode lead and the pouch-shaped case; a gas guide portion disposed between the electrode lead and the lead film, the gas guide portion includes a first layer in contact with the lead film; The pouch-type secondary battery includes a polymer film having a storage modulus measured at 100° C. of 30 MPa to 650 MPa.

2. 2. The pouch-type secondary battery according to claim 1, wherein the ratio (B / A) of the thermal expansion coefficient (B) measured at 60°C to 120°C to the thermal expansion coefficient (A) measured at -30°C to 10°C is 1.2 to 3.

0.

3. 3. The pouch-type secondary battery according to claim 2, wherein the polymer film has a thermal expansion coefficient (B) measured at 60° C. to 120° C. of 25 μm / cm·° C. or more.

4. 3. The pouch-type secondary battery according to claim 2, wherein the polymer film has a thermal expansion coefficient (A) measured at -30°C to 10°C of 25 μm / cm·°C or more.

5. 2. The pouch-type secondary battery according to claim 1, wherein the polymer film has an air permeability of 100 sec / 100 cc or more.

6. The pouch-type secondary battery according to claim 1 , wherein the polymer film has a water droplet contact angle of 100° or more.

7. The pouch-type secondary battery according to claim 1 , wherein the polymer film contains polytetrafluoroethylene (PTFE).

8. 8. The pouch-type secondary battery according to claim 1, wherein the gas guide further includes a second layer in contact with the electrode lead.

9. 9. The pouch-type secondary battery according to claim 8, wherein the electrode lead, the second layer, the first layer, and the lead film are laminated in this order.

10. The pouch-type secondary battery according to claim 8 , wherein the second layer includes an acid-modified polyolefin.

11. 2. The pouch-type secondary battery according to claim 1, wherein one end of the lead film protruding outward from the pouch-type case protrudes further than one end of the gas guide portion protruding outward from the pouch-type case, and is positioned so as to be in direct contact with the electrode lead.

12. 9. The pouch-type secondary battery according to claim 8, wherein one end of the second layer of the gas guide portion protruding outward from the pouch-type case protrudes further than the first layer of the gas guide portion protruding outward from the pouch-type case, and is disposed so as to be in direct contact with the electrode lead.

13. 2. The pouch-type secondary battery according to claim 1, wherein when the pressure inside the pouch-type case increases, the interface between the lead film and the first layer opens, forming a gas release path.

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