Pouch-type secondary battery

Abstract

The pouch-type secondary battery according to the present invention comprises: an electrode assembly; a pouch-type case including an accommodating portion for accommodating the electrode assembly and a sealing portion for sealing the accommodating 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 provided between the electrode lead and the pouch type case; and a gas guide portion provided between the electrode lead and the lead film. The gas guide portion includes a first layer in contact with the lead film. The first layer includes a polymer film having a storage modulus, measured at 100 DEG C, of 30 MPa to 650 MPa.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10 - 2022 - 0159794, filed on November 24, 2022, and 10 - 2023 - 0164379, filed on November 23, 2023, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference.

[0004] The present invention relates to a pouch - type secondary battery, and more particularly to a pouch - type secondary battery including an exhaust part. Background Art

[0005] Secondary batteries can be used in various products, including small products such as digital cameras, P - DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, and electric bicycles, as well as large products that require high power such as electric vehicles and hybrid vehicles, power storage devices for storing surplus power or renewable energy, and backup power storage devices. Secondary batteries include nickel - cadmium batteries, nickel - metal hydride batteries, lithium - ion batteries, and lithium - ion polymer batteries.

[0006] A method of manufacturing a secondary battery may be to accommodate an electrode assembly (in which a positive electrode, a negative electrode, and a separator interposed therebetween are alternately stacked) in a battery case, inject an electrolyte, and then seal the battery case. According to the case material for accommodating the electrode assembly, secondary batteries can be classified into pouch - type secondary batteries and can - type secondary batteries. In particular, a pouch - type battery can be manufactured as follows: stamping is performed on a flexible pouch film laminate to form a cup part, then the electrode assembly is accommodated in the receiving space inside the cup part, and the sealing part is sealed.

[0007] Gas may be generated inside the pouch of a pouch - type secondary battery during operation at high temperatures, overcharging, or short - circuiting. When the gas pressure inside the pouch increases, the pouch may explode or catch fire during exhaust. To ensure prevention of the above problems, generally, an exhaust part is used and placed on the sealing part of the pouch. In this case, when the gas pressure inside the pouch increases, the interface between the pouch and the exhaust part opens, allowing the gas to be discharged to the outside of the pouch. However, there is a problem that even when the pressure inside the pouch increases due to gas generation, the interface does not open, so the pressure inside the pouch exceeds a critical level, resulting in the explosion of the pouch. Summary of the Invention

[0008] Technical Problem

[0009] One aspect of the present invention provides a pouch - type secondary battery capable of discharging gas to the outside before the pressure inside the pouch rises to an excessive level.

[0010] Technical Solution

[0011] According to one aspect of the present invention, there is provided a pouch-type secondary battery, which includes: an electrode assembly; a pouch-type housing 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 housing through the sealing portion; a lead film disposed between the electrode lead and the pouch-type housing; and a gas guiding portion disposed between the electrode lead and the lead film. In this case, the gas guiding portion includes a first layer in contact with the lead film, and the first layer includes a polymer film having a storage modulus measured at 100 °C of 30 MPa to 650 MPa.

[0012] In the pouch-type secondary battery according to the present invention, the ratio (B / A) of the coefficient of thermal expansion (B) of the polymer film measured at 60 °C to 120 °C to the coefficient of thermal expansion (A) of the polymer film measured at -30 °C to 10 °C may be in the range of 1.2 to 3.0. In this case, the coefficient of thermal expansion (B) of the polymer film measured at 60 °C to 120 °C may be 25 μm / cm·°C or greater, and the coefficient of thermal expansion (A) of the polymer film measured at -30 °C to 10 °C may be 25 μm / cm·°C or greater.

[0013] In the pouch-type secondary battery according to the present invention, the gas permeability of the polymer film may be 100 sec / 100 cc or greater. In addition, the water droplet contact angle of the polymer film may be 100° or greater. The polymer film may include polytetrafluoroethylene (PTFE).

[0014] In the pouch-type secondary battery according to the present invention, the gas guiding portion may further include a second layer in contact with the electrode lead. In this case, the electrode lead, the second layer, the first layer, and the lead film may be sequentially stacked. In addition, the second layer may include an acid-modified polyolefin.

[0015] Advantageous Effects

[0016] According to the present invention, a gas guiding portion is provided between the electrode lead and the lead film, and the gas guiding portion is applied with a polymer film having a storage modulus measured at 100 °C of 30 MPa to 650 MP, so that the interface between the gas guiding portion and the lead film is opened before the internal pressure of the pouch rises to an excessive level, thereby allowing gas to be easily discharged to the outside of the pouch. Therefore, it is possible to prevent the pouch from exploding under the excessive pressure inside the pouch caused by gas generation, thereby providing a pouch-type secondary battery according to the present invention with excellent safety. Description of the Drawings

[0017] The accompanying drawings of this document illustrate preferred embodiments of the present invention by way of examples, and together with the detailed description of the present invention given below are used to enable a further understanding of the technical concept of the present invention. Therefore, the present invention should not be construed solely by the content in these accompanying drawings.

[0018] Figure 1 is an exploded view of a pouch-type secondary battery according to the present invention;

[0019] Figure 2 is a cross-sectional view of a sealed pouch-type secondary battery;

[0020] Figure 3 is an example of a cross-sectional view of a pouch-type secondary battery before the pouch housing is opened;

[0021] Figure 4 is an example of a cross-sectional view of a pouch-type secondary battery when the pouch housing is opened;

[0022] Figure 5 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch housing is opened; and

[0023] Figure 6 is another example of a cross-sectional view of a pouch-type secondary battery before the pouch housing is opened. Detailed Description of the Embodiments

[0024] Advantages and features of the present disclosure and methods for achieving them can be more easily understood by referring to the accompanying drawings and the following detailed description of the embodiments. However, the present disclosure may be embodied in different forms, and these embodiments are provided only to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. Therefore, the present disclosure is defined only by the scope of the appended claims. Throughout the specification, like reference numerals denote like elements.

[0025] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are not to be construed ideally or overly unless clearly and specifically defined.

[0026] The terms used herein are not intended to limit the concept of the present invention, but are used to describe the embodiments. As used herein, the singular forms also include the plural forms unless the context clearly indicates otherwise. As used herein, the meanings of "comprising" and / or "containing" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0027] In this document, when an element "comprises" a component, it may mean that the element does not exclude other components unless otherwise clearly stated, but may also include other components.

[0028] In this text, the description of "A and / or B" means A or B or both A and B.

[0029] In this text, "%" means wt% unless otherwise specified.

[0030] In this text, the "storage modulus" refers to the storage modulus of the polymer film in the machine direction (MD) measured at 100 °C using dynamic mechanical analysis (DMA).

[0031] In this text, the "coefficient of thermal expansion (CTE)" refers to the length extended in the MD direction when the temperature of the polymer film is increased by 1 °C.

[0032] In this text, the "gas permeability" refers to the flow rate of air through the polymer film.

[0033] In this text, the "water droplet contact angle" refers to the angle formed between the water on the surface of the polymer film and the contact surface of the polymer film.

[0034] 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 via the sealing portion; a lead film provided between the electrode lead and the pouch-type case; and a gas guiding portion provided between the electrode lead and the lead film. The gas guiding portion 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.

[0035] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the accompanying drawings.

[0036] Figure 1 is an exploded view of the pouch-type secondary battery 100 according to the present invention, Figure 2 is a cross-sectional view of the sealed pouch-type secondary battery 100. In Figure 2 , for ease of understanding, some components of the pouch-type secondary battery 100 are not shown. As Figure 1 and Figure 2 shown, 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 guiding portion 200.

[0037] (1) Pouch-type case

[0038] The pouch-shaped housing 110 can store the electrode assembly 160 inside. The pouch-shaped housing 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 stacked in sequence.

[0039] The base layer is formed on the outermost layer of the pouch film laminate to protect the secondary battery from external friction and collision. Since the base layer is made of a polymer, it can electrically insulate the electrode assembly from the outside.

[0040] The base layer can be made of at least 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, poly(p-phenylene benzobisoxazole), polyarylate, Teflon, and glass fiber. Preferably, the base layer can be made of polyethylene terephthalate (PET), nylon, or a combination thereof, which has abrasion resistance and heat resistance.

[0041] The base layer can have a single film structure made of any one material. Alternatively, the base layer can have a composite film structure in which two or more materials are formed into layers respectively.

[0042] The thickness of the base layer can be 5 μm to 50 μm, specifically 7 μm to 40 μm, and more specifically 25 μm to 38 μm. When the thickness of the base layer satisfies the above range, the external insulation is excellent, and the whole pouch is not thick. Therefore, the relationship between the energy density and the volume of the secondary battery will be excellent.

[0043] The gas barrier layer is stacked 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 outside the secondary battery, and prevent the electrolyte from leaking from the inside of the pouch-shaped housing.

[0044] The gas barrier layer can be formed of a metal, specifically, it can be formed of an aluminum alloy thin film. When using an aluminum alloy thin film to form the gas barrier layer, the gas barrier layer can have a predetermined level of mechanical strength and a light weight, and can supplement the electrochemical properties caused by the electrode assembly and the electrolyte and obtain a heat dissipation effect. The aluminum alloy thin film can include metal elements other than aluminum (Al), for example, it can include at least one selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0045] The thickness of the gas barrier layer can be from 40 μm to 100 μm, specifically from 50 μm to 90 μm, and more specifically from 55 μm to 85 μm. When the thickness of the gas barrier layer satisfies the above range, the molding performance and gas barrier performance are excellent when molding the cup portion.

[0046] When sealing the bag-shaped housing that houses the electrode assembly to completely seal the interior of the bag-shaped housing, the sealant layers are thermally bonded together at the sealing portion. For this purpose, the sealant layer can be formed of a material having excellent heat-sealing strength.

[0047] The sealant layer can be formed of a material having insulation, corrosion resistance, and sealing characteristics. Specifically, since the sealant layer is in direct contact with the electrode assembly and / or electrolyte inside the bag-shaped housing, it can be formed of a material having insulation and corrosion resistance. In addition, the sealant layer should completely seal the interior of the bag-shaped housing and block the movement of materials between the inside and outside, so it can be formed of a material having high sealing characteristics (e.g., excellent heat-sealing strength). To ensure obtaining such insulation, corrosion resistance, and sealing characteristics, the sealant layer can be formed of a polymer material.

[0048] The bag film laminate can be rolled, molded, or stretched by stamping or the like to manufacture the bag-shaped housing 110. Therefore, the bag-shaped housing 110 can include a cup portion 122 and a receiving portion 124. The receiving portion 124 is a portion for storing the electrode assembly, and can represent a receiving space formed in a pocket shape inside the cup portion 122 when the cup portion 122 is formed.

[0049] According to an embodiment of the present invention, the bag-shaped housing 110 can include Figure 1 the first housing 120 and the second housing 130 as shown. The first housing 120 can include a receiving portion 124 capable of accommodating the electrode assembly 160, and the second housing 130 can cover the receiving portion 124 from above to prevent the electrode assembly 160 from separating to the outside of the battery housing 110. The first housing 120 and the second housing 130 can be manufactured such that one side of the first housing 120 and one side of the second housing 130 can be Figure 1 connected to each other as shown, but the embodiments of the present invention are not limited thereto, and the first housing 120 and the second housing 130 can be manufactured in different ways (e.g., manufactured separately by being separated from each other).

[0050] According to another embodiment of the present invention, when forming the cup portion with the bag film laminate, two symmetric cup portions 122 and 132 adjacent to each other can be formed by stretch molding with one bag film laminate. In this case, the cup portions 122 and 132 can be formed in the first housing 120 and the second housing 130, respectively, as Figure 1As shown. After the electrode assembly 160 is received in the receiving portion 124 provided in the cup portion 122 of the first housing 120, the bridging portion 140 formed between the two cup portions 122 and 132 can be folded so that the two cup portions 122 and 132 face each other. In this case, the cup portion 132 of the second housing 130 can receive the electrode assembly 160 from above. Thus, the two cup portions 122 and 132 accommodate one electrode assembly 160, and thus the accommodated electrode assembly 160 can be thicker than in the case where there is only one cup portion 122. In addition, one edge of the pouch-type secondary battery 100 is formed by folding the pouch-type housing 110, so that when the sealing process is performed later, the number of edges to be sealed can be reduced. Therefore, the processing speed of the pouch-type secondary battery 100 can be increased and the number of sealing processes can be reduced.

[0051] The pouch-type housing 110 can be sealed while accommodating the electrode assembly 160 so that a part (i.e., the terminal portion) of the electrode lead 180 to be described later is exposed. Specifically, when the electrode lead 180 is connected to the electrode joint 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 can be received in the receiving portion 124 provided in the cup portion 122 of the first housing 120, and the second housing 130 can cover the receiving portion 124 from above. Then, an electrolyte is injected into the receiving portion 124, and the sealing portion 150 formed on the edges of the first housing 120 and the second housing 130 can be sealed.

[0052] The sealing portion 150 can be used to seal the receiving portion 124. Specifically, the sealing portion 150 can be formed along the edge of the receiving portion 124, so that the receiving portion 124 can be sealed.

[0053] The temperature at which the sealing portion 150 is sealed can be 180°C to 250°C, specifically 200°C to 250°C, and more specifically 210°C to 240°C. When the sealing temperature satisfies the above numerical range, the pouch-type housing 110 can obtain sufficient sealing strength through thermal sealing.

[0054] (2) Electrode Assembly

[0055] The electrode assembly 160 can be inserted into the pouch-type housing 110 and sealed by means of the pouch-type housing 110 after electrolyte injection.

[0056] The positive electrode, the separator, and the negative electrode can be sequentially stacked to form the electrode assembly 160. Specifically, the electrode assembly 160 can include two types of electrodes (positive electrode and negative electrode) and a separator sandwiched between the electrodes to insulate the electrodes from each other.

[0057] The positive electrode and the negative electrode can each have a structure in which an active material paste is applied to an electrode current collector in the form of a metal foil or a metal mesh containing aluminum and copper. Generally, granular active material, auxiliary conductor, binder, and conductive material are stirred together with an added solvent to form a paste. The solvent can be removed in a subsequent process.

[0058] A paste mixed with 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, and the positive electrode and the negative electrode are stacked on both sides of a separator. Thus, the electrode assembly 160 can be manufactured into a predetermined shape. The types of the electrode assembly 160 can include a stacked type, a wound core type, and a stacked and folded type, but are not limited thereto.

[0059] The electrode assembly 160 can include an electrode tab 170.

[0060] The electrode tab 170 is connected to each of the positive electrode and the negative electrode of the electrode assembly 160 and protrudes outward from the electrode assembly 160. Thus, it can be used as a path for electrons to move between the inside and the outside of the electrode tab. The current collector included in the electrode assembly 160 can be provided with a portion where the electrode active material is applied and an end portion (i.e., a non-coated portion) where the electrode active material is not applied. The electrode tab 170 can be formed by cutting the non-coated portion, or by connecting a separate conductive member to the non-coated portion by ultrasonic welding or the like. As Figure 1 shown, the electrode tab 170 can protrude from the electrode assembly 160 in different directions, but is not limited thereto, and can be formed to protrude in various directions, such as protruding from one side in the same direction.

[0061] (3) Electrode lead

[0062] The electrode lead 180 can supply power 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.

[0063] The electrode lead 180 can be connected to the electrode assembly 160 and can protrude to the outside of the pouch-type case 110 via the sealing portion 150. Specifically, one end of the electrode lead 180 can be connected to the electrode assembly 160, particularly to the electrode tab 170, and the other end of the electrode lead 180 can protrude to the outside of the pouch-type case 110.

[0064] The electrode lead 180 may include: a positive electrode lead 182, one end of which is connected to the positive electrode terminal 172 and extends in the direction in which the positive electrode terminal 172 protrudes; and a negative electrode lead 184, one end of which is connected to the negative electrode terminal 174 and extends in the direction in which the negative electrode terminal 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. Thus, the electric power generated inside the electrode assembly 160 can be supplied to the outside. In addition, both the positive electrode terminal 172 and the negative electrode terminal 174 are formed to protrude in all directions, so the positive electrode lead 182 and the negative electrode lead 184 can also extend in all directions. The positive electrode lead 182 and the negative electrode lead 184 may be made of different materials from each other. 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 copper (Cu) or copper material coated with nickel (Ni) that is the same as the negative electrode current collector. The portions of the electrode lead 180 that protrude to the outside of the battery case 110 may serve as terminal portions and be electrically connected to external terminals.

[0065] (4) Lead film

[0066] The lead film 190 may prevent the electric power generated from the electrode assembly 160 from flowing to the battery case 110 via the electrode lead 180 and enable the battery case 110 to be kept sealed. For this purpose, the lead film 190 may be formed of a non-conductor having non-conductive properties in which electric power does not flow well. Generally, as the lead film 190, a relatively thin insulating tape that is easily attached to the electrode lead 180 and / or the gas guide portion 200 is widely used, but embodiments of the present invention are not limited thereto, so any member that can insulate the electrode lead 180 may be used.

[0067] The lead film 190 according to an embodiment of the present invention may be a breathable film and may be disposed to surround the outer peripheral surface of the electrode lead 180 and the gas guide portion 200. Specifically, the electrode lead 180 and the gas guide portion 200 are in contact with each other on one side, and in this case, at least a part of the electrode lead 180 and the gas guide portion 200 may be surrounded by the lead film 190. The lead film 190 may be placed so as to be restricted within 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 adhere the electrode lead 180 and the gas guide portion 200 to the battery case 110.

[0068] The lead film 190 may be disposed between the electrode lead 180 and / or the gas guide portion 200 and the pouch-type case 110. For example, as Figure 2As shown, the lower housing 110, the lead film 190, the electrode lead 180, the gas guide portion 200, the lead film 190, and the upper housing 110 can be sequentially stacked and disposed in the sealing portion 150. In addition, although not shown in the figure, as another embodiment, the lower housing, the lead film, the gas guide portion, the electrode lead, the lead film, and the upper housing can be sequentially stacked and disposed, and as another embodiment, the lower housing, the lead film, the gas guide portion, the electrode lead, the gas guide portion, the lead film, and the upper housing can be sequentially stacked and disposed.

[0069] According to an embodiment of the present invention, as Figure 3 or Figure 5 shown, in the lead film 190, one end protruding outward from the bag-shaped housing 110 protrudes further than one end of the gas guide portion 200 protruding outward from the bag-shaped housing 110, and thus can be arranged to directly contact the electrode lead 180. When one end of the lead film 190 is arranged to directly contact the electrode lead 180 (i.e., when it is arranged to extend further than the gas guide portion 200 provided on the electrode lead 180), when the lead film 190 on the gas guide portion 200 is opened by gas discharge, the area where gas permeates through the lead film 190 can be easily ensured, and compared with the case where the lead film 190 is not extended, the strong adhesion force between the lead film 190 and the electrode lead 180 can minimize the problem of durability deterioration caused by the opening of the lead film 190 during gas discharge.

[0070] In addition, according to another embodiment of the present invention, as Figure 3 or Figure 6 shown, the second layer 220 of the gas guide portion 200 can be formed to be longer than the first layer 210 in the outward direction of the bag-shaped housing 110, and one end of the lead film 190 protruding outward from the bag-shaped housing 110 can be arranged to directly contact the second layer 220 instead of the first layer 210.

[0071] In particular, as shown above Figure 3 shown, when one end of the lead film 190 further protrudes in the direction in which the electrode lead protrudes and contacts the electrode lead 180 and the second layer 220 of the gas guide portion 200 extends further than the first layer 210, such that a part of the lead film 190 is arranged to contact the second layer 220, in addition to the adhesion force between the lead film 190 and the electrode lead 180, the adhesion force between the lead film 190 and the gas guide portion 200 can also be maintained strongly, thereby producing a synergistic effect on the adhesion force between the electrode lead 180 and the gas guide portion 200 to obtain a gas discharge portion with excellent durability.

[0072] Meanwhile, the lead film 190 may include at least one layer. Specifically, the lead film 190 may include a metal adhesion layer, a core layer, and a pouch adhesion layer that are sequentially stacked.

[0073] The metal adhesion layer is in direct contact with the electrode lead 180 and can be used to adhere the lead film 190 to the electrode lead 180. The metal adhesion layer may include any material that is easily adherent to the electrode lead 180. Specifically, the metal adhesion layer may include acid-modified polyolefin. For example, the metal adhesion layer may include at least one of acid-modified polypropylene (PPa), acid-modified polyethylene (PEa), or plasma-treated polypropylene (PP), but is not limited thereto. The thickness of the metal adhesion layer 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 adhesion layer satisfies the above numerical range, it has the effect of preventing the occurrence of through holes and leakage at the edge portion when the electrode lead and the lead film are fused.

[0074] The core layer may be a layer placed at the center of the lead film 190. The core layer may include additives such as polypropylene, polyolefin elastomer (POE), fluorinated polyolefin, and / or colorant, but is not limited thereto. 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 the deformation caused by heat can be minimized, which better ensures insulation. As another exemplary embodiment, the polymer included in the core layer may be a fluorinated polyolefin, which may be polytetrafluoroethylene, or may be a mixture of polytetrafluoroethylene and polypropylene, and as a mixture, the components may be mixed in a weight ratio of 9:1 to 1:9. Compared with the case where gas permeates through the lead film 190 via the gas guiding portion 200, a greater gas permeability can be achieved in this case. 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, deformation caused by the heat applied during fusion and sealing can be prevented, resulting in a robust design effect in terms of ensuring insulation.

[0075] The pouch adhesive layer can be a layer that is in direct contact with the battery case 110 (specifically, the sealant layer of the pouch film laminate). The pouch adhesive layer can include polypropylene or polyolefin elastomer (POE), but is not limited thereto. In particular, the polymer included in the pouch adhesive layer can be a copolymer. The melting point of the pouch adhesive layer including the copolymer can be controlled within the above numerical range, and the melting point of the pouch adhesive layer is similar to the melting point of the polymer in the sealant layer of the pouch film laminate, which better ensures the sealing processability. The thickness of the pouch adhesive layer can 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, there is an effect of ensuring that the polymer (e.g., polypropylene) residue rate is sufficient to obtain the sealing strength between the electrode lead and the pouch film laminate.

[0076] (5) Gas guiding part

[0077] The gas guiding part 200 is used to form a path for gas to be discharged from the inside of the pouch-shaped case 110 to the outside. As Figure 2 shown, the gas guiding part 200 of the present invention can be provided between the electrode lead 180 and the lead film 190.

[0078] Figure 3 is a cross-sectional view of the pouch-type secondary battery before the pouch-shaped case is opened, and Figure 4 is a cross-sectional view of the pouch-type secondary battery when the pouch-shaped case is opened. As Figure 3 and Figure 4 shown, the gas guiding part 200 includes a first layer 210 that contacts the lead film 190, and the first layer 210 includes a polymer film. When the pressure inside the pouch-shaped case 110 increases, the interface between the first layer 210 and the lead film 190 can be opened as Figure 4 shown, thereby forming a gas discharge path 300. However, in the case of a pouch-type secondary battery with a typical gas guiding part, the operating pressure of the gas guiding part is very high, so the gas guiding part cannot function under high pressure caused by the gas generated inside the pouch, resulting in pouch explosion.

[0079] Therefore, as a result of repeated research by the inventors of the present invention to overcome this problem, it was found that controlling the storage modulus of the gas guiding part 200 to a specific numerical range enables the interface between the gas guiding part 200 and the lead film 190 to be opened before the pressure inside the pouch rises to an excessive level, so that the gas can be discharged to the outside through the lead film 190, and thus the present invention was completed.

[0080] Specifically, the storage modulus of the first layer 210 can affect the restoring force and adhesion force of the lead film 190 according to the shear stress generated when the pressure inside the housing 110 increases. That is, the lower the storage modulus of the first layer 210, the easier it is to open as the internal pressure increases, thereby reducing the operating pressure of the gas guiding portion. And when the internal pressure decreases again due to gas discharge, it can return to the original state without warping, thereby minimizing electrolyte leakage or moisture penetration. However, when the storage modulus of the first layer 210 is too low, even if the internal pressure drops after the lead film 190 is opened, it may not return to the original state from the warped state, and the first layer 210 cannot hold the lead film 190, thus enabling the electrolyte to penetrate into the gas discharge path 300, making it more likely for moisture to invade from the outside, and causing the first layer 210 to possibly melt during sealing. That is, by controlling the storage modulus to an appropriate level, before the pressure inside the housing 110 rises to an excessive level, the gas inside the housing 110 is discharged to the outside via the gas discharge path 300, thereby reducing the pressure inside the pouch-shaped housing 110 to prevent the housing 110 from exploding or catching fire.

[0081] According to the present invention, the storage modulus of the polymer film measured at 100 °C can be from 30 MPa to 650 MPa, specifically can be 600 MPa or lower, 500 MPa or lower, 450 MPa or lower, 400 MPa or lower, or 350 MPa or lower, and can be 50 MPa or higher, 70 MPa or higher, or 100 MPa or higher. When the storage modulus of the polymer film is less than 30 MPa, during the sealing of the pouch-shaped housing 110, the first layer 210 melts, thus unable to form the gas discharge path 300. When the storage modulus of the polymer film is greater than 650 MPa, the first layer 210 is not easily deformed, thus unable to open the interface between the first layer 210 and the lead film 190.

[0082] According to the present invention, preferably, the first layer 210 including a polymer film can be applied, wherein the ratio of the coefficient of thermal expansion is controlled together with the storage modulus. Specifically, the ratio (B / A) of the coefficient of thermal expansion (B) of the polymer film measured at 60 °C to 120 °C to the coefficient of thermal expansion (A) of the polymer film measured at -30 °C to 10 °C can be from 1.2 to 3.0, specifically from 1.2 to 2.5, more specifically from 1.3 to 2.0. When the ratio (B / A) of the coefficient of thermal expansion of the polymer film satisfies the above range, the first layer 210 does not melt during the sealing process, and when the pressure inside the housing 110 increases, the interface between the first layer 210 and the lead film 190 can be opened to form the gas discharge path 300.

[0083] The coefficient of thermal expansion ratio (B / A) can indicate that the coefficient of thermal expansion at high temperature is greater than that at low temperature. In this case, the condition for generating gas (i.e., the pressure inside the housing 110 increases) is usually high temperature. Therefore, when the coefficient of thermal expansion at high temperature is high, a gas guiding part with a low operating pressure can be obtained. In addition, a relatively low coefficient of thermal expansion at low temperature is adopted, so that the gas discharge path 300 can be prevented from being unnecessarily opened under conditions where gas discharge is not required, reducing the chance of moisture penetration or electrolyte leakage. And in this case, since gas discharge can be carried out by controlling the storage modulus, the ratio of the coefficient of thermal expansion preferably satisfies the above range.

[0084] In this case, the coefficient of thermal expansion (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. In addition, the coefficient of thermal expansion (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.

[0085] According to the present invention, the gas permeability of the polymer film can be 100 sec / 100 cc or more, specifically 100 sec / 100 cc to 50000 sec / 100 cc, more specifically 100 sec / 100 cc to 40000 sec / 100 cc. The gas permeability represents the time taken for 100 cc of air to pass through the polymer film, and the lower the value, the better the gas permeability. When the gas permeability of the polymer film satisfies the above numerical range, the problem that the gas discharge path cannot be formed due to the melting and blocking of the holes in the polymer film by the lead film during bag sealing can be prevented.

[0086] According to the present invention, preferably, a first layer 210 including a polymer film can be applied, and the contact angle of the first layer 210 is controlled together with the storage modulus and the coefficient of thermal expansion ratio. Specifically, the water droplet contact angle of the polymer film can 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 decreases after sealing, thereby bringing the effect of forming the gas discharge path 300 in the early stage.

[0087] The polymer film can include at least one of polytetrafluoroethylene (PTFE) or polyimide (PI), but is not limited thereto. In particular, it is preferred that the polymer film includes polytetrafluoroethylene because the gas discharge path 300 can be formed even under the condition of low pressure inside the bag.

[0088] In the gas guiding part 200 according to an embodiment of the present invention, the pressure inside the bag-shaped housing 110 increases due to gas generation. Therefore, the first layer 210 and the lead film 190 are temporarily separated to open the interface, thereby forming a gas discharge path 300. And a polymer film satisfying the above-mentioned storage modulus is applied to the first layer. Therefore, the gas discharge path 300 can be formed under a low internal pressure. When the interface between the lead film 190 and the first layer 210 is opened and gas is discharged to reduce the internal pressure, as described above, the first layer 210 with the controlled storage modulus is easily restored to the original state, and this can also contribute to preventing moisture intrusion and electrolyte leakage.

[0089] As described above, when a polymer film satisfying the storage modulus is applied to the first layer 210, a mechanism for forming the gas discharge path 300 can be realized. And according to another embodiment, it is preferable that the polymer film satisfies the thermal expansion coefficient ratio within the above range (the thermal expansion coefficient at high temperature is appropriately higher than that at low temperature). And as another example, when the above contact angle range is satisfied, the polymer film can be optimally implemented.

[0090] In addition, according to another embodiment of the present invention, as described above, for durability, the gas guiding part 200 may preferably have the following structure: the lead film 190 protrudes further in the outer direction of the housing 110 than the end of the gas guiding part 200 and is arranged in a structure in direct contact with the electrode lead 180. And in this case, even if the gas discharge path 300 is repeatedly formed, the strong adhesion force between the electrode lead 180 and the lead film 190 can prevent the housing 110 itself from opening and ventilation.

[0091] In addition, the gas guiding part 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 arranged on the electrode lead 180, and the first layer 210 may be arranged on the second layer 220. The second layer 220 can be used to make the gas guiding part 200 adhere to the electrode lead 180. As described above, the second layer 220 may have a structure in which the second layer 220 protrudes further in the outer direction of the housing 110 than the end of the first layer 210 and is arranged in contact with the lead film 190. In this case, the strong adhesion holding force between the electrode lead 180, the gas guiding part 200, and the lead film 190 can contribute to improving durability.

[0092] The second layer 220 may include any material that is easily adhered to the electrode lead 180. Specifically, the second layer 220 may include acid-modified polyolefin. For example, the second layer 220 may include at least one of acid-modified polypropylene (PPa), acid-modified polyethylene (PEa), or plasma-treated polypropylene (PP), but is not limited thereto.

[0093] (6) Electrolyte

[0094] 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 move lithium ions generated by an electrochemical reaction passing through the electrodes during charging / discharging of the secondary battery 100, and may include a non-aqueous organic electrolyte solution which is a mixture of a lithium salt and an organic solvent, or a polymer using a polymer electrolyte. In addition, the electrolyte may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a polymer-based solid electrolyte, and such a solid electrolyte may be flexible and thus is easily deformed under an external force.

[0095] Hereinafter, the present invention will be described in more detail by means of specific embodiments. However, the embodiments shown below are only for understanding the present invention, and the scope of the inventive concept is not limited thereto. It will be apparent to those skilled in the art that various modifications and changes are possible within the scope and technical scope of the present invention, and such modifications and changes fall within the scope of the claims included herein.

[0096] Examples and Comparative Examples

[0097] Example 1

[0098] (1) Manufacture of the pouch-type case

[0099] A polyethylene terephthalate (PET) film having a width of 266 mm, a length of 50 m, and a thickness of 12 μm and a nylon film having a width of 266 mm, a length of 50 m, and a thickness of 25 μm are stacked on one side of an aluminum alloy film having a width of 266 mm, a length of 50 m, and a thickness of 60 μm, and a polypropylene film having a width of 266 mm, a length of 50 m, and a thickness of 50 μm is stacked on the other side to prepare a pouch film laminate having a polyethylene terephthalate / nylon / aluminum alloy film / polypropylene film structure.

[0100] In this case, the polyethylene terephthalate film and the nylon film are base layers, the aluminum alloy film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0101] The pouch film laminate is molded to manufacture a pouch-type case including a receiving portion and a sealing portion.

[0102] (2) Manufacture of the secondary battery

[0103] A negative electrode, a positive electrode, and a porous polyethylene separator are assembled using a stacking method, and then laminated to manufacture an electrode assembly. Thereafter, electrode leads are connected to the electrode assembly.

[0104] LiPF6 was dissolved in a solvent (EC:EMC:DMC = 3:1:4 (volume ratio)) to 1.0 M to prepare an electrolyte. The electrode assembly was accommodated in a pouch-type case, where the front end of the electrode lead protruded to the outside, and the electrolyte was injected.

[0105] A 20-μm thick acid-modified polypropylene film (second layer) and a 50-μm thick polytetrafluoroethylene film (first layer) were sequentially stacked on the upper surface of the electrode lead to form a gas guiding portion. Then, a 200-μm thick polypropylene film (lead film) was stacked on each of the lower surface of the electrode lead and the upper surface of the gas guiding portion.

[0106] Thereafter, under the conditions of 220 °C, 0.27 MPa, and a sealing strip area of 200 mm × 10 mm, the sealing portion of the pouch-type case was sealed for 2 seconds, and then left at 60 °C for 4 hours to fabricate a pouch-type secondary battery. In this case, in the sealing portion, the portion where the lead film was formed had a structure in which the lower case / lead film / electrode lead / gas guiding portion / lead film / upper case were sequentially stacked.

[0107] Example 2

[0108] A pouch-type case and a secondary battery were fabricated 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 stacked as the polymer film applied to the first layer.

[0109] Example 3

[0110] A pouch-type case and a secondary battery were fabricated in the same manner as in Example 1, except that a 100-μm thick polytetrafluoroethylene film was used as the polymer film applied to the first layer.

[0111] Comparative Example 1

[0112] A pouch-type case and a secondary battery were fabricated in the same manner as in Example 1, except that a 100-μm thick polyurethane film was used as the polymer film applied to the first layer.

[0113] Comparative Example 2

[0114] A pouch-type case and a secondary battery were fabricated in the same manner as in Example 1, except that a 50-μm thick polyimide film was used as the polymer film applied to the first layer.

[0115] Comparative Example 3

[0116] A pouch-type case and a secondary battery were fabricated 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.

[0117] Experimental Example 1: Evaluation of Physical Properties of Polymer Films

[0118] Before sealing the bag, the physical properties of each polymer film (gas guiding part) applied to the first layer in Examples 1 to 3 and Comparative Examples 1 to 3 were measured.

[0119] Specifically, the gas permeability of the polymer film was calculated by measuring the time it took for 100 ml of air at a pressure of 0.05 MPa to pass through the polymer film using an EG01-55-1MR from Asahi Seiko.

[0120] The water droplet contact angle of the polymer film was measured by measuring the static contact angle of each substrate at room temperature using a Phoenix mt from SEO.

[0121] The storage modulus of the polymer film was measured in the longitudinal (MD) direction at 100 °C using a DMA 850 from TA Instrument.

[0122] The coefficient of thermal expansion of the polymer film was measured by taking a sample with a width of 4.4 mm and a length of 50 mm using a TMA Q400 from TA Instrument. The measurement was carried out under the following conditions: a preload of 0.1 N, purging with nitrogen (N2), a heating rate of 5 °C / min, and a temperature range of -30 °C to 120 °C. Thereafter, the coefficient of thermal expansion (B) of the polymer film measured at 60 °C to 120 °C was divided by the coefficient of thermal expansion (A) of the polymer film measured at -30 °C to 10 °C to calculate the coefficient of thermal expansion ratio (B / A).

[0123] The measurement results are shown in Table 1 below.

[0124] [Table 1]

[0125]

[0126] Experimental Example 2: Evaluation of the operation of the gas guiding part

[0127] To evaluate whether the gas guiding parts of the pouch-type secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were operating properly, the amount of a specific gas emitted from the pouch-type secondary batteries was measured in a vacuum atmosphere. Specifically, when a vacuum atmosphere was created outside the pouch-type secondary battery using an ELT3000 from INFICON, the flow rate of gaseous dimethyl carbonate (DMC) emitted from the inside of the pouch case to the outside was measured. The measurement results are shown in Table 2 below.

[0128] Experimental Example 3: Evaluation of gas emission performance

[0129] To evaluate the performance of the gas guiding part of the secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, the gas emission rate was measured and the formation of the gas emission path was determined. Specifically, CO2 was injected into the pouch-type secondary battery using a pressure-resistant device from ITS to increase the pressure inside the pouch until the pressure difference between the inside and outside of the pouch reached 1.0 to 2.5 bar, and then the resulting product was stored in a 60 °C chamber for about 1 to 2 days. The decrease in the pressure inside the pouch was determined during storage to calculate the gas emission rate based on the flow rate and the pressure decrease value. In addition, the formation of the gas emission path was evaluated by visually observing the swelling of the sealing part. The results are shown in Table 2 below.

[0130] O: Gas emission path formed

[0131] X: Gas emission path not formed

[0132] [Table 2]

[0133]

[0134] According to Tables 1 to 2, in the cases of Examples 1 to 3 (where the storage modulus of the polymer film measured at 100 °C is in the range of 30 MPa to 650 MPa), it can be seen that the gas emission path is easily formed from the measured amount of vapor. In fact, since the pressure inside the pouch is relatively greater than the pressure outside the pouch, the formation of the gas emission path is visually observed, and the gas emission rate is significantly higher than that of the comparative examples. In particular, it can be seen that the pouch-type secondary batteries of Examples 1 to 3 have a high gas emission rate even when the pressure difference between the inside and outside of the pouch is low.

[0135] Meanwhile, in the cases of Comparative Example 1 and Comparative Example 3, the storage modulus of the polymer film is very low, such that the first layer of the gas guiding part melts when sealing the pouch-type housing, so it is expected that no gas emission path will be formed due to the small measured amount of vapor. In fact, no gas emission path is formed and the gas emission rate is not measurable.

[0136] In the case of Comparative Example 2, based on the measured vapor amount data, it is expected that no gas emission path will be formed, but when the actual internal pressure increases, the formation of the gas emission path is visually observed. However, the storage modulus of the polymer film is too high, so the gas guiding part is not easily deformed, indicating that the gas emission rate is significantly lower than that of the examples.

[0137] [Reference Signs Explanation] 100: Pouch-type secondary battery 110: Pouch-type housing

[0138] 120: First housing

[0139] 122: Cup part

[0140] 124: Accommodating part

[0141] 130: Second housing

[0142] 132: Cup part

[0143] 140: Bridging part

[0144] 150: Sealing part

[0145] 160: Electrode assembly

[0146] 170: Electrode connector

[0147] 172: Positive electrode connector

[0148] 174: Negative electrode connector

[0149] 180: Electrode lead

[0150] 182: Positive electrode lead

[0151] 184: Negative electrode lead

[0152] 190: Lead film

[0153] 200: Gas guiding part 210: First layer

[0154] 220: Second layer 300: Gas discharge path.

Claims

1. A pouch-type secondary battery, the pouch-type secondary battery comprising: An electrode assembly; A pouch-type housing, the pouch-type housing including a receiving portion for receiving the electrode assembly and a sealing portion for sealing the receiving portion; An electrode lead, the electrode lead being connected to the electrode assembly and protruding to the outside of the pouch-type housing via the sealing portion; A lead film, the lead film being disposed between the electrode lead and the pouch-type housing; and A gas guiding portion, the gas guiding portion being disposed between the electrode lead and the lead film, wherein the gas guiding portion includes a first layer in contact with the lead film, and the first layer includes a polymer film having a storage modulus measured at 100 °C of 30 MPa to 650 MPa.

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

0.

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

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

5. The pouch-type secondary battery according to claim 1, wherein, The gas permeability of the polymer film is 100 sec / 100 cc or greater.

6. The pouch secondary battery according to claim 1, wherein The water droplet contact angle of the polymer film is 100° or greater.

7. The pouch secondary battery according to claim 1, wherein, The polymer film includes polytetrafluoroethylene (PTFE).

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

9. The pouch secondary battery according to claim 8, wherein, The electrode lead, the second layer, the first layer, and the lead film are stacked in sequence.

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

11. The pouch secondary battery according to claim 1, wherein, The lead film is disposed such that an end protruding outward from the pouch-type housing protrudes further than an end of the gas guiding portion protruding outward from the pouch-type housing and is in direct contact with the electrode lead.

12. The pouch secondary battery according to claim 8, wherein, The second layer of the gas guiding portion is disposed such that an end protruding outward from the pouch-type housing protrudes further than the first layer of the gas guiding portion protruding outward from the pouch-type housing and is in direct contact with the electrode lead.

13. The pouch secondary battery according to claim 1, wherein, When the pressure inside the pouch-type housing increases, the pouch-type secondary battery forms a gas discharge path when the interface between the lead film and the first layer is opened.

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