Pouch type secondary battery

Abstract

A pouch-type secondary battery according to the present invention comprises an electrode assembly, a pouch-type case including a receiving portion for housing the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding outside the pouch-type case via the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas induction portion disposed between the electrode lead and the lead film, wherein the gas induction portion comprises a first layer in contact with the lead film, and the first layer comprises a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

Description

Technology Field

[0001] The present invention relates to a pouch-type secondary battery, and more specifically, to a pouch-type secondary battery including a gas induction portion. Background Technology

[0003] Rechargeable batteries are used in a wide range of fields, including small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and E-bikes, as well as large products requiring high output such as electric vehicles and hybrid vehicles, and power storage devices and backup power storage devices that store surplus generated power or new and renewable energy. Types of rechargeable batteries include nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, and lithium-ion polymer batteries.

[0004] A secondary battery can be manufactured by housing an electrode assembly, in which a positive electrode, a negative electrode, and a separator interposed between them are alternately stacked, into a battery case, injecting an electrolyte, and then sealing the battery case. Secondary batteries are classified into pouch type and can type depending on the material of the case housing the electrode assembly. Among these, a pouch-type battery can be manufactured by forming a cup portion by press-forming a flexible pouch film laminate, housing the electrode assembly in the inner receiving space of the cup portion, and sealing the sealing portion.

[0005] In pouch-type secondary batteries, gas may be generated inside the pouch during high-temperature operation, overcharging, or short circuits. If the gas pressure inside the pouch increases, there is a problem where the pouch vents, leading to explosion or ignition. To solve this problem, conventionally, a gas discharge port was placed in the sealing portion of the pouch. In this case, when the gas pressure inside the pouch increases, the interface between the pouch and the gas discharge port opens, allowing the gas to be discharged to the outside of the pouch. However, in the past, even though the internal pressure of the pouch increased due to gas generation, the interface remained open, causing the internal pressure of the pouch to exceed a critical threshold and resulting in the pouch exploding. The problem to be solved

[0007] The present invention aims to solve the above-mentioned problems and provides a pouch-type secondary battery capable of releasing gas to the outside before the internal pressure of the pouch becomes excessively high. means of solving the problem

[0009] According to one embodiment of the present invention, a pouch-type secondary battery is provided, comprising an electrode assembly, a receiving portion for housing the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding outside the pouch-type case via the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas induction portion disposed between the electrode lead and the lead film. In this case, the gas induction portion comprises a first layer in contact with the lead film, and the first layer comprises a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

[0010] In a pouch-type secondary battery according to the present invention, the ratio (B / A) of the coefficient of thermal expansion of the polymer film measured at 60°C to 120°C and the coefficient of thermal expansion of the polymer film measured at -30°C to 10°C may be 1.2 to 3.0. At this time, the coefficient of thermal expansion of the polymer film measured at 60°C to 120°C (B) may be 25 μm / cm·°C or higher, and the coefficient of thermal expansion of the polymer film measured at -30°C to 10°C (A) may be 25 μm / cm·°C or higher.

[0011] In a pouch-type secondary battery according to the present invention, the air permeability of the polymer film may be 100 sec / 100cc or more. In addition, the water droplet contact angle of the polymer film may be 100° or more. The polymer film may include polytetrafluoroethylene (PTFE).

[0012] In a pouch-type secondary battery according to the present invention, the gas induction portion may further include a second layer in contact with an electrode lead. At this time, the electrode lead, the second layer, the first layer, and the lead film may be sequentially laminated. Additionally, the second layer may include an acid-modified polyolefin. Effects of the invention

[0014] According to the present invention, by placing a gas induction portion applied to a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C between an electrode lead and a lead film, the interface between the gas induction portion and the lead film is opened before the internal pressure of the pouch becomes excessively high, thereby allowing gas to be easily discharged to the outside of the pouch. Accordingly, the pouch-type secondary battery according to the present invention has excellent safety by preventing the problem of the pouch exploding due to the internal pressure of the pouch becoming excessively high caused by gas generation. Brief explanation of the drawing

[0016] The drawings attached to the specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is an exploded assembly diagram of a pouch-type secondary battery according to the present invention. Figure 2 is a cross-sectional view of a sealed pouch-type secondary battery. Figure 3 is an example of a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened. Figure 4 is an example of a cross-sectional view of a pouch-type secondary battery when the pouch-type case is opened. Figure 5 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened. Figure 6 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch-type case is opened. Specific details for implementing the invention

[0017] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0018] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0019] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0020] In this specification, when a part is described as including a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0021] In this specification, the description "A and / or B" means A, or B, or A and B.

[0022] In this specification, "%" means weight percent unless otherwise explicitly indicated.

[0023] In this specification, "storage modulus" refers to the storage modulus in the MD (Machine Direction) direction of a polymer film measured under a temperature condition of 100°C using dynamic mechanical analysis (DMA).

[0024] In this specification, "Coefficient of Thermal Expansion (CTE)" refers to the length increased in the MD direction when the temperature of a polymer film increases by 1°C.

[0025] In this specification, "air permeability" refers to the degree to which air passes through a polymer film.

[0026] In this specification, "water droplet contact angle" refers to the angle formed between water and the contact surface of the polymer film on the surface of the polymer film.

[0028] A pouch-type secondary battery according to the present invention comprises an electrode assembly, a pouch-type case including a receiving portion for housing the electrode assembly and a sealing portion for sealing the receiving portion, an electrode lead connected to the electrode assembly and protruding outside the pouch-type case via the sealing portion, a lead film disposed between the electrode lead and the pouch-type case, and a gas induction portion disposed between the electrode lead and the lead film. The gas induction portion comprises a first layer in contact with the lead film, and the first layer comprises a polymer film having a storage modulus of 30 MPa to 650 MPa measured at 100°C.

[0030] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the drawings.

[0031] FIG. 1 is an exploded assembly view of a pouch-type secondary battery (100) according to the present invention, and FIG. 2 is a cross-sectional view of a 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 FIG. 1 and FIG. 2, the pouch-type secondary battery (100) of the present invention includes a pouch-type case (110), an electrode assembly (160), an electrode lead (180), a lead film (190), and a gas induction part (200).

[0033] (1) Pouch-type case

[0034] The pouch-type case (110) can accommodate an 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 may include a substrate layer, a gas barrier layer, and a sealant layer. In the pouch film laminate, the substrate layer, the gas barrier layer, and the sealant layer may be laminated sequentially.

[0035] The substrate layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from friction and collision with the outside. The substrate layer is made of a polymer and can electrically insulate the electrode assembly from the outside.

[0036] The substrate layer may be composed of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber. Preferably, the substrate layer may be composed of polyethylene terephthalate (PET), nylon, or a combination thereof having wear resistance and heat resistance.

[0037] The substrate layer may have a single film structure made of any one material. In contrast, the substrate layer may have a composite film structure formed by two or more materials forming separate layers.

[0038] The thickness of the substrate layer may 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 the above range, the external insulation is excellent, and the overall thickness of the pouch is not thick, so the energy density relative to the volume of the secondary battery may be excellent.

[0039] The gas barrier layer is laminated between the substrate layer and the sealant layer to ensure the mechanical strength of the pouch, block the entry of gases or moisture from the outside of the secondary battery, and prevent electrolyte leakage from the inside of the pouch-type case.

[0040] The gas barrier layer can be formed from a metal, specifically an aluminum alloy thin film. When a gas barrier layer is formed using an aluminum alloy thin film, it is possible to secure mechanical strength above a certain level, while also ensuring light weight, complementing electrochemical properties of the electrode assembly and electrolyte, and heat dissipation. The aluminum alloy thin film may include one or more metal elements other than aluminum (Al), for example, selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0041] The thickness of the gas barrier layer may 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 the above range, the moldability and gas barrier performance are excellent when molding the cup portion.

[0042] The sealant layer is intended to completely seal the interior of a pouch-type case by mutually thermally bonding at the sealing portion when the pouch-type case, which accommodates an electrode assembly on the inside, is sealed. To this end, the sealant layer may be formed from a material having excellent thermal bonding strength.

[0043] The sealant layer can be formed from a material having insulating, corrosion-resistant, and sealing properties. Specifically, since the sealant layer comes into direct contact with the electrode assembly and / or electrolyte inside the pouch-type case, it can be formed from a material having insulating and corrosion-resistant properties. In addition, since the sealant layer must completely seal the inside of the pouch-type case to block material transfer between the inside and outside, it can be formed from a material having high sealing properties (e.g., excellent thermal bonding strength). To ensure these insulating, corrosion-resistant, and sealing properties, the sealant layer can be formed from a polymer material.

[0045] The pouch film laminate can be drawn and stretched by means of a punch or the like to manufacture a 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 place for housing an electrode assembly and may refer to a receiving space formed in the shape of a pocket inside the cup portion (122) as the cup portion (122) is formed.

[0046] According to one embodiment of the present invention, a 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) capable of receiving an electrode assembly (160), and the second case (130) may cover the receiving portion (124) from above so that the electrode assembly (160) does not escape to the outside of the battery case (110). The first case (120) and the second case (130) may be manufactured with one side connected to the other as shown in FIG. 1, but are not limited thereto and may be manufactured in various ways, such as being separated from each other and manufactured separately.

[0047] According to another embodiment of the present invention, when forming cup portions in a pouch film laminate, two symmetrical cup portions (122, 132) can be drawn and formed adjacent to each other in a single pouch film laminate. In this case, cup portions (122, 132) can be formed in the first case (120) and the second case (130) respectively as shown in FIG. 1. After receiving an electrode assembly (160) in a receiving portion (124) provided in the cup portion (122) of the first case (120), a bridge portion (140) formed between the two cup portions (122, 132) can 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 receive the electrode assembly (160) from above. Accordingly, since two cup portions (122, 132) accommodate one electrode assembly (160), an electrode assembly (160) with a thicker thickness than when there is only one cup portion (122) can be accommodated. Additionally, since one corner of the secondary battery (100) is formed by folding the pouch-type case (110), the number of corners to be sealed can be reduced when performing a sealing process later. Accordingly, the processing speed of the pouch-type secondary battery (100) can be improved and the number of sealing processes can be reduced.

[0048] The pouch-type case (110) can be sealed while accommodating the electrode assembly (160) so that a part of the electrode lead (180), which will be described later, i.e., the terminal part, 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 part of the electrode lead (180), the electrode assembly (160) is accommodated in the receiving portion (124) provided in the cup portion (122) of the first case (120), and the second case (130) can cover the receiving portion (124) from above. Subsequently, an electrolyte is injected into the interior of the receiving portion (124), and the sealing portion (150) formed on the edges of the first case (120) and the second case (130) can be sealed.

[0049] The sealing portion (150) can perform the function of sealing the receiving portion (124). Specifically, the sealing portion (150) can seal the receiving portion (124) by being formed along the edge of the receiving portion (124).

[0050] The temperature for sealing the sealing portion (150) may be 180°C to 250°C, specifically 200°C to 250°C, more specifically 210°C to 240°C. When the sealing temperature satisfies the above numerical range, the pouch-type case (110) can secure sufficient sealing strength by thermal bonding.

[0052] (2) Electrode assembly

[0053] The electrode assembly (160) can be inserted into a pouch-type case (110) and sealed by the pouch-type case (110) after the electrolyte is injected.

[0054] The electrode assembly (160) may be formed by sequentially stacking an anode, a separator, and a cathode. Specifically, the electrode assembly (160) may include two types of electrodes, an anode and a cathode, and a separator interposed between the electrodes to insulate them from one another.

[0055] The positive and negative electrodes may each have a structure in which an active material slurry is coated onto an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper. The slurry can typically be formed by stirring granular active material, an auxiliary conductor, a binder, and a conductive material with added solvent. The solvent can be removed in a subsequent process.

[0056] An electrode assembly (160) can be manufactured in a predetermined shape by applying a slurry, which is a mixture of an electrode active material and a binder and / or a conductive material, to an anode current collector and a cathode current collector to manufacture an anode and a cathode, and stacking them on both sides of a separator. The types of electrode assemblies (160) may include stack type, jelly roll type, stack and folding type, etc., but are not limited thereto.

[0057] The electrode assembly (160) may include an electrode tab (170).

[0058] The electrode tab (170) is connected to the positive and negative electrodes of the electrode assembly (160), respectively, and protrudes outward from the electrode assembly (160), serving as a path 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 a terminal portion not coated with an electrode active material, i.e., a non-coated portion. The electrode tab (170) may be formed by cutting the non-coated portion or by connecting a separate conductive member to the non-coated portion using ultrasonic welding or the like. As shown in FIG. 1, the electrode tab (170) may protrude in different directions from the electrode assembly (160), but is not limited thereto and may be formed to protrude in various directions, such as protruding in parallel from one side in the same direction.

[0060] (3) Electrode lead

[0061] The electrode lead (180) can supply electricity to the outside of the secondary battery (100). The electrode lead (180) can be connected to the electrode tab (170) of the electrode assembly (160) by spot welding or the like.

[0062] The electrode lead (180) is connected to the electrode assembly (160) and can protrude outside the pouch-type case (110) via the sealing portion (150). Specifically, one end of the electrode lead (180) is connected to the electrode assembly (160), specifically the electrode tab (170), and the other end of the electrode lead (180) can protrude outside the pouch-type case (110).

[0063] The electrode lead (180) may include a positive lead (182) that has one end connected to a positive tab (172) and extends in the direction in which the positive tab (172) protrudes, and a negative lead (184) that has one end connected to a negative tab (174) and extends in the direction in which the negative tab (174) protrudes. Both the positive lead (182) and the negative lead (184) may have their other ends protruding to the outside of the battery case (110). Thus, electricity generated inside the electrode assembly (160) can be supplied to the outside. Additionally, since the positive tab (172) and the negative tab (174) are each formed to protrude in various directions, the positive lead (182) and the negative lead (184) may also each extend in various directions. The positive lead (182) and the negative lead (184) may have different materials. That is, the positive lead (182) is made of the same aluminum (Al) material as the positive current collector, and the negative lead (184) may be made of the same copper (Cu) material as the negative current collector or copper material coated with nickel (Ni). A portion of the electrode lead (180) protruding outside the battery case (110) can be a terminal portion and electrically connected to an external terminal.

[0065] (4) Lead film

[0066] The lead film (190) prevents electricity generated from the electrode assembly (160) from flowing through the electrode lead (180) to the battery case (110) and can maintain the sealing of the battery case (110). To this end, the lead film (190) may be formed from a non-conductive insulating material that does not conduct electricity well. Generally, the lead film (190) is often made of insulating tape that is easy to attach to the electrode lead (180) and / or gas induction part (200) and is relatively thin, but is not limited thereto, and any material capable of insulating the electrode lead (180) may be used.

[0067] A lead film (190) according to one embodiment of the present invention may be a gas-permeable film and may be arranged to surround the outer surface of an electrode lead (180) and a gas guide (200). Specifically, the electrode lead (180) and the gas guide (200) are in contact with 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 located in a sealing portion (150) where the first case (120) and the second case (130) of the pouch-type case (110) are heat-fused, and the electrode lead (180) and the gas guide (200) may be bonded to the battery case (110).

[0068] The lead film (190) may be placed between the electrode lead (180) and / or the gas guide (200) and the pouch-type case (110). For example, as shown in FIG. 2, the lower case (110), lead film (190), electrode lead (180), gas guide (200), lead film (190), and upper case (110) may be arranged in a stacked state in order in the sealing part (150) area. Additionally, although not shown in the drawings, as another example, the lower case, lead film, gas guide, electrode lead, lead film, and upper case may be arranged in a stacked state in order, and as yet another example, the lower case, lead film, gas guide, electrode lead, gas guide, lead film, and upper case may be arranged in a stacked state in order.

[0069] According to one embodiment of the present invention, as shown in FIG. 3 or FIG. 5, the lead film (190) may be positioned such that one end protruding outward from the pouch-type case (110) protrudes further than one end of the gas guide (200) protruding outward from the pouch-type case (110) and comes into direct contact with the electrode lead (180). When the one end of the lead film (190) comes into direct contact with the electrode lead (180), that is, when the lead film (190) on the gas guide (200) is extended further than the lead film (180), it is easy to secure an area through which gas permeates through the lead film (190) when the lead film (190) on the gas guide (200) is opened while gas discharge is being performed, and compared to the case where the lead film (190) is not extended, the reduction in durability caused by the opening of the lead film (190) during gas discharge can be minimized due to the strong adhesive force between the lead film (190) and the electrode lead (180).

[0070] Additionally, according to another embodiment of the present invention, as shown in FIG. 3 or FIG. 6, the second layer (220) of the gas induction portion (200) may be formed to be longer in the outer direction of the pouch-type case (110) than the first layer (210), and one end of the lead film (190) protruding outwardly of the pouch-type case (110) may be arranged to be in direct contact with the second layer (220) rather than the first layer (210).

[0071] In particular, as shown in FIG. 3 above, when one end of the lead film (190) protrudes further in the direction of the electrode lead protrusion and contacts the electrode lead (180), and the second layer (220) of the gas induction part (200) extends further than the first layer (210) so that a part of the lead film (190) contacts the second layer (220), the adhesion between the lead film (190) and the gas induction part (200) can also be strongly maintained in addition to the adhesion between the lead film (190) and the electrode lead (180), so that the adhesion between the electrode lead (180) and the gas induction part (200) can also be synergistically maintained, thereby enabling the realization of a gas exhaust part with excellent durability.

[0072] Meanwhile, the lead film (190) may include one or more layers. Specifically, the lead film (190) may include a sequentially laminated metal adhesive layer, a core layer, and a pouch adhesive layer.

[0073] The metal adhesive layer is in direct contact with the electrode lead (180) and may be intended to adhere the lead film (190) to the electrode lead (180). The metal adhesive layer may include any material that facilitates adhesion to the electrode lead (180). Specifically, the metal adhesive layer may include an 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, more specifically 60 μm to 75 μm. When the thickness of the metal adhesive layer satisfies the above numerical range, it has the effect of preventing through-type pinholes and leaks at the edge portion when the electrode lead and the lead film are fused.

[0074] The core layer may be a layer located in the center of the lead film (190). The core layer may include, but is not limited to, additives such as polypropylene, polyolefin elastomer (POE), fluorinated polyolefin, and / or coloring agents. For example, the polymer included in the core layer may be a homopolymer. When a homopolymer is included in the core layer, the melting point of the core layer can be controlled within the above numerical range, and deformation due to heat can be minimized, which is advantageous in terms of securing insulation. As another example, the polymer included in the core layer may be a fluorinated polyolefin such as polytetrafluoroethylene, or a mixture of polytetrafluoroethylene and polypropylene, and if it is a mixture, it may be mixed in a weight ratio of 9:1 to 1:9. In this case, it may have superior gas permeability performance when gas is permeated into the lead film (190) through the gas induction part (200). The thickness of the core layer may be 40 μm to 70 μm, specifically 50 μm to 70 μm, and more specifically 60 μm to 70 μm. When the thickness of the core layer satisfies the above numerical range, it prevents deformation caused by heat applied during fusion and sealing, thereby providing a robust design effect in terms of ensuring insulation.

[0075] The pouch adhesive layer may be a layer that comes into direct contact with the battery case (110), specifically the sealant layer of the pouch film laminate. The pouch adhesive layer may include polypropylene and polyolefin elastomer (POE), but is not limited thereto. Among these, the polymer included in the pouch adhesive layer may be a copolymer. The melting point of the pouch adhesive layer containing a copolymer can be controlled to the above numerical range and has a melting point similar to that of the polymer in the sealant layer of the pouch film laminate, which is advantageous for ensuring sealing processability. 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 numerical range, it has the effect of securing a sufficient polymer (e.g., polypropylene) residual rate to ensure strength when sealing between the electrode lead and the pouch film laminate.

[0077] (5) Gas induction section

[0078] The gas guide (200) serves to form a path for discharging gas from inside the pouch-type case (110) to the outside. As shown in FIG. 2, the gas guide (200) of the present invention can be placed between the electrode lead (180) and the lead film (190).

[0079] 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 a pouch-type secondary battery when the pouch-type case is opened. As shown in FIG. 3 and FIG. 4, the gas induction part (200) includes a first layer (210) in contact with a lead film (190), and the first layer (210) includes a polymer film. When the internal pressure of the pouch-type case (110) increases, as shown in FIG. 4, the interface between the first layer (210) and the lead film (190) is opened, thereby forming a gas discharge path (300). However, in the case of a pouch-type secondary battery to which a conventional gas induction part is applied, there was a problem in which the gas induction part did not operate under high pressure conditions resulting from gas generation inside the pouch due to the high operating pressure of the gas induction part, causing the pouch to explode.

[0080] Accordingly, the inventors, through repeated research to solve this problem, discovered that by controlling the storage elasticity modulus of the gas induction part (200) to a specific numerical range, the interface between the gas induction part (200) and the lead film (190) can be opened before the internal pressure of the pouch becomes excessively high, thereby allowing gas to be discharged to the outside through the lead film (190), and thus completed the present invention.

[0081] Specifically, the storage elasticity of the first layer (210) can affect the adhesion and recovery force with the lead film (190) according to the shear stress generated when the internal pressure of the case (110) increases. That is, the lower the storage elasticity of the first layer (210), the more easily it opens as the internal pressure increases, thereby lowering the operating pressure of the gas induction part. When the internal pressure is lowered again through gas discharge, it is restored to its original state without lifting, thereby minimizing electrolyte leakage or moisture penetration. However, if the storage elasticity of the first layer (210) is too low, the lifted state is not restored to its original state even though the internal pressure is lowered after opening the lead film (190), and the first layer (210) fails to hold the lead film (190), allowing electrolyte to penetrate into the gas discharge path (300), increasing the possibility of moisture penetration from the outside, and there is a risk that the first layer (210) will melt during sealing. That is, 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 lowering the internal pressure of the pouch-type case (110) and preventing the explosion or ignition of the case (110).

[0082] 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, and may also be 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, there is a problem that the gas discharge path (300) is not formed because the first layer (210) melts when sealing the pouch-type case (110). If the storage modulus of the polymer film exceeds 650 MPa, there is a problem that the interface between the first layer (210) and the lead film (190) is not opened because the first layer (210) is not easily deformed.

[0083] According to the present invention, preferably, a first layer (210) comprising a polymer film in which the ratio of the coefficient of thermal expansion to the storage modulus is controlled may be applied. Specifically, the ratio (B / A) of the coefficient of thermal expansion (B) of the polymer film measured at 60°C to 120°C and the coefficient of thermal expansion (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 coefficient of thermal expansion of the polymer film satisfies the above numerical range, the first layer (210) does not melt during the sealing process, and when the internal pressure of the case (110) rises, the interface between the first layer (210) and the lead film (190) is opened to form a gas discharge path (300).

[0084] The ratio (B / A) of the thermal expansion coefficients mentioned above may indicate that the thermal expansion coefficient at high temperatures is greater than the thermal expansion coefficient at low temperatures. Since the environment in which gas is generated, i.e., the internal pressure of the case (110) increases, is generally high temperatures, a gas induction section having a low operating pressure can be implemented when the thermal expansion coefficient is high at high temperatures. Additionally, since a relatively low thermal expansion coefficient at low temperatures is applied, the opening of the unnecessary gas discharge path (300) can be prevented in environments where gas discharge is not required, thereby reducing the possibility of moisture penetration or electrolyte leakage. In this case, since gas discharge can be performed by controlling the storage modulus, it is desirable for the ratio of the thermal expansion coefficients to satisfy the aforementioned range.

[0085] At this time, the coefficient of thermal expansion (B) of the polymer film measured at 60°C to 120°C may be 25 μm / cm·°C or higher, specifically 100 μm / cm·°C to 450 μm / cm·°C, more specifically 150 μm / cm·°C to 300 μm / cm·°C. Additionally, the coefficient of thermal expansion (A) of the polymer film measured at -30°C to 10°C may be 25 μm / cm·°C or higher, specifically 30 μm / cm·°C to 200 μm / cm·°C, more specifically 90 μm / cm·°C to 150 μm / cm·°C.

[0087] *86

[0088] According to the present invention, the air permeability of the polymer film may be 100 sec / 100cc or more, specifically 100 sec / 100cc to 50,000 sec / 100cc, and more specifically 100 sec / 100cc to 40,000 sec / 100cc. The air permeability indicates the time it takes for 100cc of air to pass through the polymer film, and a lower value indicates superior air permeability. When the air permeability of the polymer film satisfies the above numerical range, the problem of not being able to form a gas discharge path due to the pores within the polymer film being blocked by the melted lid film during pouch sealing can be prevented.

[0090] According to the present invention, preferably, a first layer (210) comprising a polymer film having a contact angle controlled together with the ratio of the storage modulus and the coefficient of thermal expansion may be applied. Specifically, the droplet contact angle of the polymer film may be 100° or more, specifically 100° to 150°, more specifically 100° to 130°. When the 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) after sealing is reduced, and the gas discharge path (300) is formed early.

[0091] The polymer film may include at least one of polytetrafluoroethylene (PTFE) and polyimide (PI), but is not limited thereto. Among these, it is preferable that the polymer film includes polytetrafluoroethylene so that a gas discharge path (300) can be formed even under low internal pouch pressure conditions.

[0093] According to one embodiment of the present invention, the gas induction part (200) can form a gas discharge path (300) by causing the first layer (210) and the lead film (190) to be temporarily peeled off as the internal pressure of the pouch-type case (110) increases due to gas generation, thereby opening the interface thereof, and can form a gas discharge path (300) at a low internal pressure by applying a polymer film satisfying the aforementioned storage elasticity modulus to the first layer. When the internal pressure is lowered after the interface between the lead film (190) and the first layer (210) is opened and gas is discharged, it is easily restored to its original state by the first layer (210) with controlled storage elasticity modulus as described above, and this can also contribute to the effect of preventing moisture penetration and electrolyte leakage.

[0094] The mechanism for forming the aforementioned gas discharge path (300) can be implemented by applying a polymer film satisfying the storage modulus to the first layer (210) as described above, and according to another embodiment, it is preferable that the polymer film has a coefficient of thermal expansion at high temperature that is appropriately higher than the coefficient of thermal expansion at low temperature within the aforementioned range to satisfy the ratio of the coefficients of thermal expansion, and as another example, it can be optimally implemented when the polymer film satisfies the aforementioned contact angle range.

[0095] In addition, according to another embodiment of the present invention, the gas induction part (200) may adopt a structure such that, for durability, the lead film (190) protrudes further than the end of the gas induction part (200) in the direction of the outer side of the case (110) as described above and is arranged to come into direct contact with the electrode lead (180). In this case, even if the formation of the gas discharge path (300) occurs repeatedly, the strong adhesive force between the electrode lead (180) and the lead film (190) prevents the case (110) itself from opening and venting.

[0097] Additionally, the gas induction portion (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 be for attaching the gas induction portion (200) to the electrode lead (180). As described above, the second layer (220) may adopt a structure in which it protrudes further than the end of the first layer (210) in the direction of the outer side of the case (110) and is disposed to contact the lead film (190). In this case, the adhesion retention force between the electrode lead (180), the gas induction portion (200), and the lead film (190) is excellent, which can contribute to improved durability.

[0098] The second layer (220) may include any material that facilitates adhesion with the electrode lead (180). Specifically, the second layer (220) may include an acid-modified polyolefin. For example, the second layer (220) 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.

[0100] (6) Electrolyte

[0101] The pouch-type secondary battery (100) according to the present invention may further include an electrolyte (not shown) injected into the inside of a pouch-type case (110). The electrolyte is intended to move lithium ions generated by the electrochemical reaction of the electrodes during charging / discharging of the secondary battery (100), and may include a non-aqueous organic electrolyte, which 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 allows it to be easily deformed by an external force.

[0103] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are merely examples to aid in understanding the invention and do not limit the scope of the invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of this description, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0105] Examples and Comparative Examples

[0106] Example 1

[0107] (1) Manufacture of a pouch-type case

[0108] A pouch film laminate having a polyethylene terephthalate / nylon / aluminum alloy film / polypropylene film structure was manufactured by laminating a polyethylene terephthalate (PET) film with a width of 266 mm, a length of 50 m, and a thickness of 12 μm and a nylon film with a width of 266 mm, a length of 50 m, and a thickness of 25 μm on one side of an aluminum alloy film with a width of 266 mm, a length of 50 m, and a thickness of 50 μm, and laminating a polypropylene film with a width of 266 mm, a length of 50 m, and a thickness of 50 μm on the other side.

[0109] Here, the polyethylene terephthalate film and the nylon film are the substrate layer, the aluminum alloy thin film is the gas barrier layer, and the polypropylene film is the sealant layer.

[0110] A pouch-type case including a receiving portion and a sealing portion was manufactured by molding the above pouch film laminate.

[0112] (2) Manufacturing of secondary batteries

[0113] An electrode assembly was manufactured by assembling a cathode, an anode, and a porous polyethylene separator using a stacking method and then laminating them. Subsequently, an electrode lead was attached to the electrode assembly.

[0114] 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 drawn out to the outside, and the electrolyte was injected.

[0115] A gas induction portion was formed by sequentially laminating a 20 μm thick acid-modified polypropylene film (second layer) and a 50 μm thick polytetrafluoroethylene film (first layer) on the upper surface of the electrode lead. Subsequently, 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 induction portion, respectively.

[0116] Subsequently, a pouch-type secondary battery was manufactured by sealing the sealing portion of the above pouch-type case for 2 seconds under conditions of a seal bar area of ​​200mm × 10mm, 220℃, and 0.27MPa, and then leaving it at 60℃ for 4 hours. At this time, the portion of the sealing portion where the lead film is formed has a structure in which a lower case / lead film / electrode lead / gas induction portion / lead film / upper case are sequentially stacked.

[0118] Example 2

[0119] 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 sequentially laminated and used as the polymer film applied to the first layer.

[0121] Example 3

[0122] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polytetrafluoroethylene film with a thickness of 100 μm was used as the polymer film applied to the first layer.

[0124] Comparative Example 1

[0125] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polyurethane film with a thickness of 100 μm was used as the polymer film applied to the first layer.

[0127] Comparative Example 2

[0128] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a polyimide film with a thickness of 50 μm was used as the polymer film applied to the first layer.

[0130] Comparative Example 3

[0131] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that a 100 μm thick polypropylene film was used as the polymer film applied to the first layer.

[0133] Experimental Example 1: Evaluation of Physical Properties of Polymer Film

[0134] Before sealing the pouch, the physical properties of each polymer film (gas induction part) applied to the first layer in Examples 1 to 3 and Comparative Examples 1 to 3 were measured.

[0135] Specifically, the air permeability of the polymer film was calculated by measuring the time it takes for 100 ml of air with a pressure of 0.05 MPa to pass through the polymer film using Asahi Seiko's EG01-55-1MR.

[0136] The droplet contact angle of the polymer film was measured by using SEO's Phoenix mt to measure the static contact angle of each substrate at room temperature.

[0137] The storage modulus of the polymer film was measured in the MD (Machine Direction) direction using a DMA 850 from TA Instrument at a temperature of 100°C.

[0138] The coefficient of thermal expansion of the polymer film was measured using a TMA Q400 from TA Instrument, taking a sample with a width of 4.4 mm and a length of 50 mm. The measurement was performed under conditions of a preload of 0.1 N by purging with N2 at a heating rate of 5°C / min in a temperature range of -30°C to 120°C. Subsequently, the coefficient of thermal expansion ratio (B / A) was calculated by dividing the coefficient of thermal expansion (B) of the polymer film measured at 60°C to 120°C by the coefficient of thermal expansion (A) of the polymer film measured at -30°C to 10°C.

[0139] The above measurement results are shown in Table 1 below.

[0140] Air per 100cc Water droplet contact angle (°) Storage modulus (MPa) Thermal expansion coefficient ratio (B / A) Example 1 22,840 108 150 1.43 Example 2 36,811 107 55 1.67 Example 3 32,112 107 250 1.8 Comparative Example 1 19,642 91 10 1.13 Comparative Example 2 27,648 98 1700 0.907 Comparative Example 3 30,043 94 3 4.569

[0142] Experimental Example 2: Evaluation of operation of the gas induction unit

[0143] To evaluate whether the gas induction portion of the pouch-type secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3 would operate normally, the amount of a specific gas emitted from the pouch-type secondary battery was measured in a vacuum atmosphere. Specifically, using INFICON’s ELT3000, the flow rate of gaseous dimethyl carbonate (DMC) emitted from the inside of the pouch-type case to the outside was measured when a vacuum atmosphere was created outside the pouch-type secondary battery. The measurement results are shown in Table 2 below.

[0145] Experimental Example 3: Evaluation of Gas Emission Performance

[0146] To evaluate the performance of the gas induction section of the secondary batteries manufactured in Examples 1–3 and Comparative Examples 1–3, respectively, the gas discharge rate was measured and whether a gas discharge path was formed was verified. Specifically, CO2 was injected into the pouch-type secondary battery using a pressure-resistant device from 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, after which the battery was stored in a 60°C chamber for 1 to 2 days. During the storage period, the decrease in the internal pressure of the pouch was checked, and the gas discharge rate was calculated based on the flow rate and the pressure decrease values. In addition, the formation of a gas discharge path was evaluated by visually confirming the expansion of the sealing section. The results are shown in Table 2 below.

[0147] ○: Gas exhaust path formed

[0148] X: Gas exhaust path not formed

[0150] Gas discharge rate (cc / day, @60℃) Whether a gas discharge path is formed Operation status (mbar / s) Internal and external pressure difference (bar) 1.0 1.5 2.0 2.5 Example 1 3.18 5.68 8.33 11.09 O > 1.0 x 10 Example 2 3.82 5.33 7.51 10.41 O > 1.0 x 10 Example 3 3.41 3.96 6.11 7.62 O > 1.0 x 10 Comparative Example 1 - - - - X 1.5 x 10 -6 Comparative Example 2 0.50 0.77 1.00 9.6 O 1.0 x 10 -6 under Comparative Example 3 - - - - X 1.0 x 10 -6 under

[0151] According to Tables 1 and 2, in the case of Examples 1 to 3, where the storage modulus of the polymer film measured at 100°C falls within the range of 30 to 650 MPa, it can be seen from the measured amount of vapor that a gas discharge path is easily formed. In fact, as the pressure inside the pouch becomes relatively higher than the pressure outside the pouch, the formation of a gas discharge path can be visually confirmed, and it can be seen 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 inside and outside of the pouch is low. On the other hand, in the case of Comparative Examples 1 and 3, the storage modulus of the polymer film was too low, so the first layer of the gas induction part melted during pouch-type case sealing. Consequently, the measured amount of vapor was very small, so it was expected that a gas discharge path would not be formed, and in fact, a gas discharge path was not formed, making it impossible to measure the gas discharge rate.

[0152] In the case of Comparative Example 2, it was expected that no gas discharge path would be formed based on the measured steam amount data, but it was confirmed visually that a gas discharge path was formed when the actual internal pressure increased. However, because the storage modulus of the polymer film was too high, the gas induction part did not deform easily, and thus it was confirmed that the gas discharge rate was significantly smaller compared to the example. Explanation of the symbols

[0154] 100: Pouch-type secondary battery 110: Pouch-type case 120: First case 122: Cup 124: Reception Department 130: Second case 132: Cup 140: Bridge section 150: Sealing part 160: Electrode assembly 170: Electrode tab 172: Positive tab 174: Cathode tab 180: Electrode lead 182: Positive lead 184: Cathode Lead 190: Lead film 200: Gas induction section 210: 1st floor 220: 2nd floor 300: Gas exhaust path

Claims

Claim 1 A pouch-type secondary battery comprising: an electrode assembly; a pouch-type case including a receiving portion for housing 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 via the sealing portion; a lead film disposed between the electrode lead and the pouch-type case; and a gas induction portion disposed between the electrode lead and the lead film, wherein the gas induction portion comprises a first layer in contact with the lead film and a second layer in contact with the electrode lead; wherein the first layer comprises a polymer film and the polymer film comprises polytetrafluoroethylene (PTFE). Claim 2 A pouch-type secondary battery according to claim 1, wherein the polymer film has a ratio (B / A) of the coefficient of thermal expansion (B) measured at 60°C to 120°C and the coefficient of thermal expansion (A) measured at -30°C to 10°C of 1.2 to 3.

0. Claim 3 A pouch-type secondary battery according to claim 2, wherein the polymer film has a coefficient of thermal expansion (B) of 25 μm / cm·°C or more measured at 60°C to 120°C. Claim 4 A pouch-type secondary battery according to claim 2, wherein the polymer film has a coefficient of thermal expansion (A) of 25 μm / cm·°C or more measured at -30°C to 10°C. Claim 5 A pouch-type secondary battery according to claim 1, wherein the air permeability of the polymer film is 100 sec / 100cc or more. Claim 6 A pouch-type secondary battery according to claim 1, wherein the droplet contact angle of the polymer film is 100° or more. Claim 7 A pouch-type secondary battery according to claim 1, wherein the electrode lead, the second layer, the first layer, and the lead film are sequentially laminated. Claim 8 A pouch-type secondary battery according to claim 1, wherein the second layer comprises an acid-modified polyolefin. Claim 9 A pouch-type secondary battery according to claim 1, wherein the lead film is arranged such that one end protruding outwardly from the pouch-type case protrudes further than one end of the gas induction portion protruding outwardly from the pouch-type case and is in direct contact with the electrode lead. Claim 10 A pouch-type secondary battery according to claim 1, wherein the second layer of the gas induction portion is arranged such that one end protruding outwardly from the pouch-type case protrudes further than the first layer of the gas induction portion protruding outwardly from the pouch-type case and is in direct contact with the electrode lead. Claim 11 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 is opened to form a gas discharge path.

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