Pouch-type secondary battery

Abstract

The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a housing portion that houses the electrode assembly and a seal portion that seals the housing portion, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case via the seal portion, and a lead film disposed between the electrode lead and the pouch-type case, wherein the lead film includes a first layer disposed on the electrode lead, a second layer disposed on the first layer, and a third layer disposed on the second layer, and the difference in elastic modulus between any two layers selected from the first to third layers is 20% or less of the maximum elastic modulus of the first to third layers.

Description

[Technical Field]

[0001] The present invention claims the benefit of priority based on Korean Patent Application No. 10-2022-0179920 filed on December 20, 2022 and Korean Patent Application No. 10-2023-0183756 filed on December 15, 2023, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a pouch-type secondary battery, and more particularly to a pouch-type secondary battery including a lead film. [Background technology]

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

[0004] A secondary battery can be manufactured by placing an electrode assembly, which includes a positive electrode, a negative electrode, and a separator interposed between them, into a battery case, injecting an electrolyte, and then sealing the battery case. Secondary batteries are classified into pouch types, can types, and the like, depending on the material of the case that houses the electrode assembly. Among these, pouch-type batteries can be manufactured by pressing a flexible pouch film laminate to form a cup, placing the electrode assembly in the container space inside the cup, and sealing the seal.

[0005] Pouch-type secondary batteries can generate gas inside the pouch when operated at high temperatures, overcharged, or when a short circuit occurs. When the gas pressure inside the pouch increases, the sealed portion of the pouch can vent, causing an explosion or fire. Among the sealed portions, the joint between the electrode lead and the pouch-type film laminate, which are made of different materials, is particularly likely to vent. Therefore, a technology to improve the seal strength in this region is needed to ensure the durability of pouch-type secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to solve the above problems and provides a pouch-type secondary battery that can prevent the phenomenon of interface peeling at the joint between the electrode lead and the pouch-type film laminate due to gas generation inside the pouch. [Means for solving the problem]

[0007] According to one embodiment of the present invention, there is provided a pouch-type secondary battery including an electrode assembly, a pouch-type case including a housing that houses the electrode assembly and a seal that seals the housing, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case via the seal, and a lead film disposed between the electrode lead and the pouch-type case, the lead film including a first layer disposed on the electrode lead, a second layer disposed on the first layer, and a third layer disposed on the second layer, wherein the difference in elastic modulus between any two selected from the first to third layers is 20% or less of the maximum elastic modulus of the first to third layers, and the sum of the elastic moduli of the first to third layers is 2600 MPa or more, the elastic moduli being measured at room temperature using a UTM. Preferably, the difference in elastic modulus between the second and third layers is 20% or less of the maximum elastic modulus of the second and third layers. It is more preferable that the first to third layers have the same modulus of elasticity.

[0008] According to the present invention, the difference in modulus of elasticity between any two layers selected from the first to third layers may be 200 MPa or less.

[0009] According to the present invention, the sum of the elastic moduli of the first to third layers may be 2600 MPa to 3600 MPa, and the elastic moduli of the first to third layers may be 700 MPa to 1200 MPa.

[0010] The second layer may have a melting point of 140°C to 180°C. The second layer may contain polypropylene, which may be a homopolymer. The third layer may have a melting point of 130°C to 150°C. The third layer may contain polypropylene, which may be a copolymer. The first layer may contain an acid-modified polyolefin.

[0011] According to the present invention, one surface of the electrode lead that directly contacts the lead film may be coated with at least one inorganic material selected from the group consisting of chromium (Cr), nickel (Ni), zirconium (Zr), and titanium (Ti), aluminum oxide (Al2O3), and polyvinyl alcohol (PVA), acrylic, and / or epoxy resins that act as a binder.

[0012] The lead film may have a thickness of 150 μm to 250 μm. [Effects of the Invention]

[0013] According to the present invention, the lead film disposed on the electrode lead is designed so that the difference in elastic modulus between the first to third layers is 20% or less of the maximum elastic modulus among the first to third layers. With this design, the sealant layer of the pouch-type film laminate and the third and second layers of the lead film simultaneously deform during the process of sealing the pouch-type secondary battery, thereby mitigating the stress concentration phenomenon. This prevents the phenomenon of interface peeling at the joint between the electrode lead and the pouch-type film laminate due to gas generation inside the pouch, achieving high sealing strength and improving the safety of the pouch-type secondary battery.

[0014] The drawings attached to the specification illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention, and therefore the present invention should not be interpreted as being limited solely to the matters depicted in such drawings. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an exploded view of a pouch-type secondary battery according to the present invention; [Figure 2] FIG. 1 is a cross-sectional view of a sealed pouch-type secondary battery. [Figure 3] 1 is a cross-sectional view of a lead film according to the present invention. [Figure 4] 10 is a cross-sectional image of the lead assembly in Example 1 when the seal portion in which the lead assembly is disposed is opened. [Figure 5] 10 is a cross-sectional image of Comparative Example 2 after the seal portion in which the lead assembly is arranged has been opened. DETAILED DESCRIPTION OF THE INVENTION

[0016] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various different forms. The present embodiments are provided merely to complete the disclosure of the present invention and to enable those skilled in the art to fully understand the scope of the invention. The present invention is defined only by the claims. The same reference numerals refer to the same elements throughout the specification.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used herein will be used in the sense commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries will not be interpreted ideally or excessively unless clearly defined otherwise.

[0018] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise stated in the phrase. As used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements in addition to the elements being mentioned.

[0019] In this specification, when a part is said to include a certain component, it does not mean that it may further include other components, unless otherwise specified.

[0020] In this specification, the expression "A and / or B" means A, B, or A and B.

[0021] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0022] In this specification, the term "elastic modulus" refers to the Young's modulus in the MD (Machine Direction) direction of a polymer film measured at room temperature using a UTM.

[0023] The pouch-type secondary battery according to the present invention includes an electrode assembly, a pouch-type case including a housing that houses the electrode assembly and a seal that seals the housing, an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case via the seal, and a lead film disposed between the electrode lead and the pouch-type case. In this case, the lead film includes a first layer disposed on the electrode lead, a second layer disposed on the first layer, and a third layer disposed on the second layer, wherein the difference in elastic modulus between any two layers selected from the first to third layers is 20% or less of the maximum elastic modulus of the first to third layers, and the sum of the elastic moduli of the first to third layers is 2600 MPa or more. Here, the elastic moduli are measured at room temperature using a UTM.

[0024] Hereinafter, each component of the pouch-type secondary battery of the present invention will be described in more detail with reference to the drawings.

[0025] Fig. 1 is an exploded view of a pouch-type secondary battery 100 according to the present invention, and Fig. 2 is a cross-sectional view of the sealed pouch-type secondary battery 100. For ease of understanding, some of the components of the pouch-type secondary battery 100 are omitted in Fig. 2. As shown in Figs. 1 and 2, the pouch-type secondary battery 100 according to the present invention includes a pouch-type case 110, an electrode assembly 160, an electrode lead 180, and a lead film 190.

[0026] (1) Pouch-type case The pouch-type case 110 may house the electrode assembly 160 inside. The pouch-type case 110 may be manufactured by molding a pouch film laminate. In this case, the pouch film laminate may 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 may be laminated in this order.

[0027] The substrate layer is formed as the outermost layer of the pouch film laminate to protect the secondary battery from external friction and impact. The substrate layer is made of a polymer and can electrically insulate the electrode assembly from the outside.

[0028] The substrate layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber. The substrate layer is preferably made of polyethylene terephthalate (PET), nylon, or a combination thereof, which are abrasion-resistant and heat-resistant.

[0029] The substrate layer may have a single film structure made of any one material, or alternatively, the substrate layer may have a composite film structure made of two or more materials each formed as a layer.

[0030] 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 thickness of the entire pouch is not large, so that the energy density relative to the volume of the secondary battery is excellent.

[0031] The gas barrier layer is laminated between the base layer and the sealant layer to ensure the mechanical strength of the pouch, block the entry and exit of gases and moisture from outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type case.

[0032] The gas barrier layer may be formed of a metal, specifically, an aluminum alloy thin film. When an aluminum alloy thin film is used to form the gas barrier layer, it is possible to ensure a predetermined level of mechanical strength, a light weight, complement the electrochemical properties of the electrode assembly and the electrolyte, and ensure heat dissipation. The aluminum alloy thin film may contain at least one metal element other than aluminum (Al), such as iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0033] 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 during molding of the cup portion and the gas barrier performance are excellent.

[0034] The sealant layer is intended to completely seal the inside of the pouch-shaped case by thermally bonding the seal portions together when the pouch-shaped case accommodating the electrode assembly therein is sealed, and therefore may be made of a material having excellent thermal bonding strength.

[0035] The sealant layer may be formed of a material having insulating, corrosion-resistant, and sealing properties. Specifically, since the sealant layer is in direct contact with the electrode assembly and / or electrolyte inside the pouch-type case, it may be formed of a material having insulating and corrosion-resistant properties. Furthermore, since the sealant layer must completely seal the interior of the pouch-type case to prevent the transfer of substances between the interior and exterior, it may be formed of a material having high sealing properties (e.g., excellent thermal adhesive strength). To ensure such insulating, corrosion-resistant, and sealing properties, the sealant layer may be formed of a polymer material. For example, the sealant layer may include, but is not limited to, polypropylene.

[0036] The sealant layer may be made of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, Teflon (registered trademark), and glass fiber, and is preferably made of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). In this case, the polypropylene may be made of cast polypropylene (CPP), acid-modified polypropylene (PPa), polypropylene-ethylene copolymer, and / or polypropylene-butylene-ethylene terpolymer.

[0037] The thickness of the sealant layer may be 30 μm to 130 μm, specifically 50 μm to 120 μm, more specifically 70 μm to 100 μm. When the thickness of the sealant layer satisfies the above range, it is possible to ensure the formability of the pouch film laminate while ensuring the seal strength of the sealed portion.

[0038] The pouch film laminate may be drawn and stretched using a punch or the like to manufacture the pouch-type case 110. As a result, the pouch-type case 110 may include a cup portion 122 and a receiving portion 124. The receiving portion 124 is a portion that receives the electrode assembly, and may refer to a receiving space formed in a pocket shape inside the cup portion 122 by forming the cup portion 122.

[0039] According to an embodiment of the present invention, the pouch-type case 110 may include a first case 120 and a second case 130, as shown in Fig. 1. The first case 120 may include a receiving portion 124 that can receive the electrode assembly 160, and the second case 130 may cover the receiving portion 124 from above to prevent the electrode assembly 160 from falling out of the battery case 110. The first case 120 and the second case 130 may be manufactured with one side connected to each other as shown in Fig. 1, but the present invention is not limited thereto and may be manufactured in various ways, such as being separated from each other and separately manufactured.

[0040] According to another embodiment of the present invention, when forming cup portions in a pouch film laminate, two symmetrical cup portions 122, 132 may be adjacent to one another by drawing molding. In this case, the first case 120 and the second case 130 may be formed with the cup portions 122, 132, respectively, as shown in FIG. 1 . The electrode assembly 160 may be accommodated in the accommodation portion 124 provided in the cup portion 122 of the first case 120, and then the bridge portion 140 formed between the two cup portions 122, 132 may be folded so that the two cup portions 122, 132 face each other. In this case, the cup portion 132 of the second case 130 can accommodate the electrode assembly 160 from above. Therefore, since two cup portions 122, 132 accommodate one electrode assembly 160, a thicker electrode assembly 160 can be accommodated than when there is only one cup portion 122. In addition, since one edge of the secondary battery 100 is formed by folding the pouch-type case 110, the number of edges to be sealed in a subsequent sealing process is reduced, thereby improving the processing speed of the pouch-type secondary battery 100 and reducing the number of sealing processes.

[0041] The pouch-type case 110 may be sealed with the electrode assembly 160 housed therein so that a portion of the electrode lead 180, i.e., a terminal portion, described below, is exposed. Specifically, after the electrode lead 180 is connected to the electrode tab 170 of the electrode assembly 160 and a lead film 190 is formed on a portion of the electrode lead 180, the electrode assembly 160 may be housed in a housing portion 124 provided in the cup portion 122 of the first case 120, and the housing portion 124 may be covered from above by the second case 130. Next, an electrolyte may be injected into the housing portion 124, and the seal portions 150 formed on the edges of the first case 120 and the second case 130 may be sealed.

[0042] The sealing portion 150 serves to seal the receiving portion 124. Specifically, the sealing portion 150 may be formed along the edge of the receiving portion 124 to seal the receiving portion 124.

[0043] The temperature at which the seal portion 150 is sealed may be 180° C. to 250° C., specifically 200° C. to 250° C., and more specifically 210° C. to 240° C. When the sealing temperature is within the above range, the pouch-type case 110 can be thermally bonded to ensure sufficient seal strength.

[0044] (2) Electrode assembly The electrode assembly 160 may be inserted into the pouch-type case 110, and after the electrolyte is injected, the pouch-type case 110 may be sealed.

[0045] The electrode assembly 160 may be formed by sequentially stacking a positive electrode, a separator, and a negative electrode. Specifically, the electrode assembly 160 may include two types of electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes to insulate the electrodes from each other.

[0046] The positive electrode and the negative electrode may have a structure in which an active material slurry is applied to an electrode current collector in the form of a metal foil or a metal mesh containing aluminum and copper, respectively. The slurry may be formed by stirring a granular active material, a conductive additive, a binder, a conductive material, etc., in a solvent. The solvent may be removed in a subsequent process.

[0047] A slurry containing 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 form a positive electrode and a negative electrode, which are then stacked on both sides of a separator to form a predetermined shape of the electrode assembly 160. Types of the electrode assembly 160 include, but are not limited to, a stack type, a jelly roll type, and a stack-and-fold type.

[0048] The electrode assembly 160 may include an electrode tab 170 .

[0049] The electrode tabs 170 are connected to the positive and negative electrodes of the electrode assembly 160, respectively, and protrude from the electrode assembly 160 to serve as paths for electrons to move between the inside and outside of the electrode assembly 160. The electrode current collector included in the electrode assembly 160 may be composed of a portion coated with an electrode active material and an end portion, i.e., a plain portion, where the electrode active material is not coated. The electrode tabs 170 may be formed by cutting the plain portion or by connecting a separate conductive member to the plain portion using ultrasonic welding or the like. As shown in FIG. 1, the electrode tabs 170 may protrude in different directions from the electrode assembly 160, but are not limited thereto. They may be formed to protrude in various directions, such as protruding in parallel in the same direction from one side.

[0050] (3) Electrode lead The electrode lead 180 can supply electricity to the outside of the secondary battery 100. The electrode lead 180 may be connected to the electrode tab 170 of the electrode assembly 160 by spot welding or the like.

[0051] An electrode lead 180 may be connected to the electrode assembly 160 and may protrude to the outside of the pouch-type case 110 via the sealing part 150. Specifically, one end of the electrode lead 180 may be connected to the electrode assembly 160, particularly to the electrode tab 170, and the other end of the electrode lead 180 may protrude to the outside of the pouch-type case 110.

[0052] The electrode lead 180 may include a positive electrode lead 182 having one end connected to the positive electrode tab 172 and extending in the direction in which the positive electrode tab 172 protrudes, and a negative electrode lead 184 having one end connected to the negative electrode tab 174 and extending in the direction in which the negative electrode tab 174 protrudes. The other ends of the positive electrode lead 182 and the negative electrode lead 184 may protrude to the outside of the battery case 110. This allows electricity generated inside the electrode assembly 160 to be supplied to the outside. In addition, since the positive electrode tab 172 and the negative electrode tab 174 protrude in different directions, the positive electrode lead 182 and the negative electrode lead 184 may also extend in different directions. The positive electrode lead 182 and the negative electrode lead 184 may be made of different materials. That is, the positive electrode lead 182 may be made of aluminum (Al), the same material as the positive electrode current collector, and the negative electrode lead 184 may be made of copper (Cu) or nickel (Ni)-coated copper, the same material as the negative electrode current collector. The part of the electrode lead 180 that protrudes outside the battery case 110 may serve as a terminal portion and be electrically connected to an external terminal.

[0053] The surface of the electrode lead 180 that directly contacts the lead film 190 may be coated with at least one inorganic material selected from the group consisting of chromium (Cr), nickel (Ni), zirconium (Zr), and titanium (Ti), aluminum oxide (Al2O3), and polyvinyl alcohol (PVA), acrylic, and / or epoxy resins that act as a binder. In this case, corrosion resistance to the electrolyte and adhesion to the lead film 190 can be ensured.

[0054] (4) Lead film The lead film 190 is intended to prevent electricity generated from the electrode assembly 160 from flowing to the battery case 110 via the electrode lead 180 .

[0055] The lead film 190 may be disposed so as to surround the outer peripheral surface of the electrode lead 180. Specifically, at least a portion of the electrode lead 180 may be surrounded by the lead film 190. The lead film 190 may be located only in the seal portion 150 where the first case 120 and the second case 130 of the pouch-type case 110 are heat-sealed.

[0056] The lead film 190 may be disposed between the electrode lead 180 and the pouch-type case 110. For example, as shown in Fig. 2, the lower case 110, the lead film 190, the electrode lead 180, the lead film 190, and the upper case 110 may be sequentially stacked in the region of the sealing portion 150. Here, the lead film 190 may be in direct contact with the sealant layer of the battery case 110.

[0057] In the case of a pouch-type secondary battery using a conventional lead film, there is a problem in that the interface between the lead film and the sealant layer of the battery case 110 is opened under high pressure conditions due to gas generation inside the pouch, thereby reducing the durability and safety of the pouch. As a result of extensive research to solve this problem, the inventors discovered that reducing the difference in elastic modulus between the layers included in the lead film 190 prevents peeling at the interface between the lead film 190 and the sealant layer of the battery case 110, preventing premature venting of the pouch and achieving high seal strength, which led to the completion of the present invention.

[0058] 3 is a cross-sectional view of a lead film 190 according to the present invention. As shown in FIG. 3, the lead film 190 includes a first layer 210, a second layer 220, and a third layer 230 that are sequentially laminated. Specifically, the first layer 210 may be disposed on the electrode lead 180 during assembly of the pouch, the second layer 220 may be disposed on the first layer 210, and the third layer 230 may be disposed on the second layer 220.

[0059] According to the present invention, the difference in elastic modulus between any two layers selected from the first layer 210, the second layer 220, and the third layer 230 may be 20% or less, specifically 0% to 20%, more specifically 0% to 10%, of the maximum value of the elastic moduli of the first layer 210 to the third layer 230. If the difference in elastic modulus between any two layers selected from the first layer 210 to the third layer 230 exceeds 20% of the maximum value of the elastic moduli of the first layer 210 to the third layer 230, the large difference in elastic modulus between the layers causes stress to concentrate at the interface between the layers, resulting in the problem of interfacial peeling. On the other hand, in the present invention, when the difference in elastic modulus between two layers selected from the first layer 210 to the third layer 230 is 20% or less of the maximum value of the elastic modulus of the first layer 210 to the third layer 230, the sealant layer of the pouch film laminate and the first layer 210 to the third layer 230 of the lead film 190 deform simultaneously, thereby alleviating stress concentration and preventing interfacial peeling.

[0060] The difference in elastic modulus between the second layer 220 and the third layer 230 is preferably 20% or less, specifically 0% to 20%, more specifically 0% to 10%, of the maximum value of the elastic moduli of the second layer 220 and the third layer 230. When the difference in elastic modulus between the second layer 220 and the third layer 230 is 20% or less of the maximum value of the elastic moduli of the second layer 220 and the third layer 230, the sealant layer of the pouch film laminate and the second layer 220 and the third layer 230 of the lead film 190 deform simultaneously, thereby easing stress concentration and preventing peeling at the interface between the second layer 220 and the third layer 230. As a result, interfacial peeling does not occur in pouch-type secondary batteries, particularly in high-temperature environments, and high seal strength can be achieved.

[0061] In lead film 190 according to the present invention, it is more preferable that the modulus of elasticity of each of first layer 210 to third layer 230 is the same. When the modulus of elasticity of first layer 210 to third layer 230 is the same, concentration of deformation within lead film 190 is alleviated, and instead of only third layer 230 deforming, first layer 210 to third layer 230 deform uniformly, making peeling between layers less likely to occur, and as a result, a high sealing strength of the pouch can be achieved.

[0062] In the lead film 190 according to the present invention, the difference in elastic modulus between any two layers selected from the first layer 210, the second layer 220, and the third layer 230 may be 200 MPa or less, specifically 0 MPa to 200 MPa, and more specifically 0 MPa to 100 MPa. It is preferable that the difference in elastic modulus between the second layer 220 and the third layer 230 is 200 MPa or less, specifically 0 MPa to 200 MPa, and more specifically 0 MPa to 100 MPa. When the above range is satisfied, the sealant layer of the pouch film laminate and each layer of the lead film 190 deform simultaneously, thereby easing stress concentration and preventing interfacial peeling.

[0063] The sum of the moduli of elasticity of first layer 210, second layer 220, and third layer 230 is 2600 MPa or more, and may specifically be 2600 MPa to 3600 MPa, and more specifically may be 2700 MPa to 3000 MPa. When the sum of the moduli of elasticity of first layer 210, second layer 220, and third layer 230 satisfies the above numerical range, lead film 190 has excellent tensile strength, which increases the adhesive strength between lead film 190 and electrode lead 180 and improves the durability of the pouch.

[0064] The elastic modulus of each of the first layer 210, the second layer 220, and the third layer 230 may be 700 MPa to 1200 MPa, specifically 900 MPa to 1100 MPa, and more specifically 900 MPa to 1000 MPa. When the elastic modulus of each of the first layer 210 to the third layer 230 satisfies the above numerical range, the tensile strength of the lead film 190 is ensured, which is advantageous for a robust design of the pouch.

[0065] On the other hand, the first layer 210 is in direct contact with the electrode lead 180 and serves to bond the lead film 190 to the electrode lead 180 .

[0066] The first layer 210 may include any material that can be easily bonded to the electrode lead 180. Specifically, the first layer 210 may include an acid-modified polyolefin. For example, the first layer 210 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.

[0067] The melting point of first layer 210 may be 130° C. to 150° C., specifically 135° C. to 140° C. When the melting point of first layer 210 satisfies the above numerical range, first layer 210 melts within a specified tact time, thereby making it possible to easily fuse lead film 190 and electrode lead 180 together.

[0068] The thickness of the first layer 210 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 first layer 210 satisfies the above numerical range, it is effective in preventing through-type pinholes and leaks at the edge when the electrode lead and the lead film are fused together.

[0069] The second layer 220 may be a layer located in the center of the lead film 190 .

[0070] The melting point of the second layer 220 may be 140° C. to 180° C., specifically 145° C. to 165° C. When the melting point of the second layer 220 satisfies the above numerical range, excessive deformation of the lead film 190 due to heat applied during fusion (adhesion between the lead film and the electrode lead) or sealing (adhesion between the lead film and the pouch film laminate) can be suppressed, and the shape of the lead film 190 can be maintained.

[0071] The second layer 220 may contain, but is not limited to, polypropylene, polyolefin elastomer (POE), and / or additives such as colorants. Among these, the polymer contained in the second layer 220 may be a homopolymer. When the second layer 220 contains a homopolymer, the melting point of the second layer 220 can be controlled within the above-mentioned range, minimizing thermal deformation, which is advantageous in terms of ensuring insulation.

[0072] Additionally, the second layer 220 may not include a heat-resistant polymer or block copolymer containing cross-linking molecules to reduce the induction of interfacial delamination.

[0073] The thickness of second layer 220 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 second layer 220 satisfies the above numerical range, deformation due to heat applied during fusion and sealing is prevented, resulting in a robust design effect in terms of ensuring insulation.

[0074] The third layer 230 may be a layer that directly contacts the battery case 110, specifically the sealant layer of the pouch film laminate.

[0075] The melting point of the third layer 230 may be 130° C. to 150° C., specifically 135° C. to 140° C. When the melting point of the third layer 230 satisfies the above numerical range, the third layer 230 melts within a specified tact time, thereby easily sealing the lead film 190 and the battery case 110. The third layer 230 may include, but is not limited to, polypropylene or polyolefin elastomer (POE). Among these, the polymer included in the third layer 230 may be a copolymer. When the third layer 230 includes a copolymer, the melting point of the third layer 230 can be controlled within the above-mentioned range, and the copolymer has a melting point similar to that of the polymer in the sealant layer of the pouch film laminate, which is advantageous in ensuring the sealing process.

[0076] The thickness of the third layer 230 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 third layer 230 satisfies the above numerical range, there is an effect of ensuring a sufficient residual rate of the polymer (for example, polypropylene) to ensure strength when sealing the electrode lead and the pouch film laminate.

[0077] The lead film 190 may be formed of an insulating material that is non-conductive and does not easily conduct electricity. Generally, the lead film 190 is made of insulating tape, which is easy to attach to the electrode lead 180 and / or the pouch film laminate and has a relatively thin thickness, but is not limited to this, and any material that can insulate the electrode lead 180 may be used.

[0078] The thickness of the lead film 190 may be 150 μm to 250 μm, specifically 150 μm to 220 μm, and more specifically 180 μm to 220 μm. When the thickness of the lead film 190 satisfies the above numerical range, the tensile properties of the lead film are improved to ensure the durability of the pouch, while also ensuring sufficient seal strength, thereby preventing a decrease in cell energy density.

[0079] (5) Electrolyte The pouch-type secondary battery 100 according to the present invention may further include an electrolyte (not shown) injected into the pouch-type case 110. The electrolyte is used to transport lithium ions generated by an electrochemical reaction of the electrodes during charge / discharge of the secondary battery 100, and may include a non-aqueous organic electrolytic solution that is a mixture of a lithium salt and an organic solvent, or a polymer using a polymer electrolyte. The electrolyte may also include a sulfide-based, oxide-based, or polymer-based solid electrolyte, and such a solid electrolyte may have flexibility that makes it easily deformable under external force.

[0080] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative to aid in understanding the present invention and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present description, and it is obvious that such changes and modifications are included in the scope of the appended claims. [Example]

[0081] Examples and Comparative Examples Example 1 (1) Manufacturing of lead assemblies A lead film with a laminated structure including a 70 μm thick acid-modified polypropylene film (first layer), a 70 μm thick polypropylene homopolymer film (second layer), and a 60 μm thick polypropylene copolymer film (third layer) was manufactured using a three-layer co-extrusion method.The lead film was then placed around the outer periphery of a 60 μm thick electrode lead to manufacture a lead assembly.

[0082] (2) Manufacturing pouch-type cases A pouch film laminate with a polyethylene terephthalate / nylon / aluminum alloy thin film / polypropylene film structure was produced by laminating a polyethylene terephthalate (PET) film (266 mm wide, 50 mm long, 12 μm thick) and a nylon film (266 mm wide, 50 mm long, 25 μm thick) on one side of an aluminum alloy thin film (266 mm wide, 50 mm long, 60 μm thick) and laminating a polypropylene film (266 mm wide, 50 mm long, 50 μm thick) on the other side.

[0083] Here, the polyethylene terephthalate film and nylon film are base layers, the aluminum alloy thin film is a gas barrier layer, and the polypropylene film is a sealant layer.

[0084] The pouch film laminate was molded to produce a pouch-type case including a storage portion and a seal portion.

[0085] (3) Manufacturing of pouch-type secondary batteries The negative electrode, the positive electrode, and the porous polyethylene separator were stacked and then laminated to prepare an electrode assembly, and then a lead assembly was attached to the electrode assembly.

[0086] An electrolyte was prepared by dissolving LiPF6 in a solvent (volume ratio of EC:EMC:DMC = 3:3:4) to a concentration of 1.0 M. The electrode assembly was housed in the pouch-type case with the tip of the lead assembly extended to the outside, and the electrolyte was poured into the electrode assembly.

[0087] Thereafter, the seal portion of the pouch-type case was sealed under the conditions of a seal bar area of ​​200 mm × 10 mm, 220°C, and 0.27 MPa for 2 seconds, and then left at 60°C for 4 hours to manufacture a pouch-type secondary battery. Here, the portion of the seal portion where the lead assembly was formed had a structure in which the lower case / lead film / electrode lead / lead film / upper case were sequentially stacked.

[0088] Example 2 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer film applied to the second layer.

[0089] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0090] Example 3 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer film applied to the second layer.

[0091] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0092] Comparative Example 1 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer film applied to the second layer.

[0093] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0094] Comparative Example 2 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of the polypropylene base resin and the polyolefin-based elastomer softener added during extrusion was adjusted to adjust the elastic modulus of the polymer film applied to the third layer.

[0095] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0096] Comparative Example 3 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer films applied to the second and third layers, respectively.

[0097] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0098] Comparative Example 4 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer films applied to the second and third layers, respectively.

[0099] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0100] Comparative Example 5 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of the polypropylene base resin and the polyolefin-based elastomer softener added during extrusion was adjusted to adjust the elastic modulus of the polymer film applied to the third layer.

[0101] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0102] Comparative Example 6 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer films applied to the second and third layers, respectively.

[0103] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0104] Comparative Example 7 The lead assembly was manufactured in the same manner as in Example 1, except that the ratio of polypropylene, the base resin, and polyolefin-based elastomer, the softener, added during extrusion was adjusted to adjust the elastic modulus of the polymer films applied to the second and third layers, respectively.

[0105] A pouch-type case and a secondary battery were manufactured in the same manner as in Example 1, except that the lead assembly was used.

[0106] Experimental Example 1: Evaluation of the physical properties of polymer films Before the pouches were sealed, the physical properties of the polymer films applied to the first to third layers in Examples 1 to 3 and Comparative Examples 1 to 7 were measured.

[0107] Specifically, the melting point of the polymer film was measured by differential scanning calorimetry using a DSC 25 manufactured by TA Instruments.

[0108] The elastic modulus of the polymer film was measured in the MD (Machine Direction) direction of the polymer film at room temperature (25° C.) using a UTM (Universal Test Machine).

[0109] The results of the measurements are shown in Table 1 below.

[0110] [Table 1]

[0111] Experimental Example 2: Evaluation of the seal strength between the lead film and the pouch film laminate and the presence or absence of interfacial peeling In the pouch-type secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 7, the seal strength between the lead film and the pouch film laminate was evaluated.

[0112] Specifically, the sealed portion between the lead assembly and the pouch film laminate of a pouch-type secondary battery was cut at 15 mm intervals. The electrode lead was then attached to the lower fixture of the UTM, and the pouch film laminate was attached to the upper fixture. The battery was then pulled in a 180° direction at a rate of 5 mm / min at room temperature (25°C) and 60°C. The low-speed seal strength was calculated by averaging the seal strength over an 8 mm interval from the point exceeding 4.5 kgf / 15 mm. The results are shown in Table 2 below.

[0113] In addition, the cross section of the seal was photographed using an electron microscope AM4113ZT manufactured by Dino-Lite to check whether interfacial delamination occurred at the seal where the lead film and the pouch film laminate were sealed. The results are shown in Table 2 below and in Figures 4 and 5. ○: The interface between the second and third layers peeled off ×: The interface between the second layer and the third layer did not peel off.

[0114] Fig. 4 is a cross-sectional image of Example 1 when the sealed portion in which the lead assembly is disposed is being opened, and Fig. 5 is a cross-sectional image of Comparative Example 2 after the sealed portion in which the lead assembly is disposed is being opened. As shown in Fig. 4, in Example 1, the second layer, the third layer, and the sealant layer are simultaneously deformed, thereby alleviating the stress concentration phenomenon and preventing interfacial peeling between the layers. In contrast, as shown in Fig. 5, in Comparative Example 2, the second layer does not deform, causing peeling at the interface between the second and third layers, and leaving only the first and second layers of the lead film on the electrode lead.

[0115] Experimental Example 3: Evaluation of adhesive strength between electrode lead and lead film in lead assembly The electrolyte-resistant adhesive strength of the lead assemblies prepared in Examples 1 to 3 and Comparative Examples 1 to 7 was measured. Specifically, the lead assemblies were immersed in an electrolyte (EC:EMC:DMC = 3:3:4 volume ratio, LiPF61.0M) and then stored in an 80°C chamber for one day. The lead assemblies were removed from the electrolyte, the remaining electrolyte was washed off, and the assembly was left in the air for one hour. The lead assemblies were bent 10 mm from one edge to break the electrode leads. Then, both ends of the lead assemblies were attached to the lower and upper jigs of the UTM, respectively, and the assembly was pulled 30 mm in a 180° direction at a speed of 50 mm / min. The average value of the flat section of the measured adhesive strength graph was calculated. The results are shown in Table 2 below.

[0116] [Table 2]

[0117] According to Tables 1 and 2, in Examples 1 to 3, in which the difference in elastic modulus between two layers selected from the first to third layers is 20% or less of the maximum value of the elastic modulus of the first to third layers, the sealant layer and the second and third layers deform simultaneously, thereby alleviating stress concentration and resulting in a significantly higher low-speed sealing strength between the lead film and the pouch film laminate than in Comparative Examples 1 to 7, and it can be confirmed that no interfacial peeling occurred at the sealed portion where the lead film and the pouch film laminate were sealed.

[0118] In contrast, in Comparative Examples 1 to 7, in which the difference in elastic modulus between two layers selected from the first to third layers exceeds 20% of the maximum value of the elastic moduli of the first to third layers, the large difference in elastic modulus between the layers causes stress to concentrate at the interface between the layers, resulting in interfacial peeling between the second and third layers of the lead film under room temperature or high temperature conditions, and it can be confirmed that the low-speed sealing strength is significantly lower than in Examples 1 to 3. Furthermore, in Comparative Examples 2, 5, and 6, the sum of the tensile strengths of the layers of the lead film is relatively small, and the lead film is easily pulled (stretched), so it can be confirmed that the adhesive strength between the lead film and the electrode lead is lower than in Examples 1 to 3. [Explanation of symbols]

[0119] 100 Pouch-type secondary battery 110 Pouch-type case 120 Case 1 122 Cup section 124 Storage unit 130 Case 2 132 Cup section 140 Bridge section 150 Seal part 160 Electrode assembly 170 Electrode Tab 172 Positive electrode tab 174 Negative electrode tab 180 Electrode Lead 182 Positive lead 184 Negative lead 190 Lead Film 210 1st layer 220 2nd layer 230 3rd layer

Claims

1. A pouch-type secondary battery, an electrode assembly; a pouch-type case including a housing portion that houses the electrode assembly and a seal portion that seals the housing portion; an electrode lead connected to the electrode assembly and protruding to the outside of the pouch-type case via the seal portion; a lead film disposed between the electrode lead and the pouch-type case, the lead film includes a first layer disposed on the electrode lead, a second layer disposed on the first layer, and a third layer disposed on the second layer; a difference in elastic modulus between any two layers selected from the first to third layers is 20% or less of the maximum value of the elastic moduli of the first to third layers; the sum of the elastic moduli of the first to third layers is 2600 MPa or more; The pouch-type secondary battery, wherein the elastic modulus is measured at room temperature using a UTM.

2. 2. The pouch-type secondary battery according to claim 1, wherein a difference in elastic modulus between the second layer and the third layer is 20% or less of the maximum elastic modulus of the second layer and the third layer.

3. 2. The pouch-type secondary battery according to claim 1, wherein the first layer, the second layer, the third layer, and the third layer have the same modulus of elasticity.

4. 2. The pouch-type secondary battery according to claim 1, wherein a difference in elastic modulus between any two layers selected from the first to third layers is 200 MPa or less.

5. 2. The pouch-type secondary battery according to claim 1, wherein the sum of the elastic moduli of the first to third layers is 2600 MPa to 3600 MPa.

6. 2. The pouch-type secondary battery according to claim 1, wherein the first to third layers each have an elastic modulus of 700 MPa to 1200 MPa.

7. 2. The pouch-type secondary battery according to claim 1, wherein the second layer has a melting point of 140°C to 180°C.

8. the second layer comprises polypropylene; The pouch-type secondary battery according to claim 1 , wherein the polypropylene is a homopolymer.

9. 2. The pouch-type secondary battery according to claim 1, wherein the third layer has a melting point of 130°C to 150°C.

10. the third layer comprises polypropylene; The pouch-type secondary battery according to claim 1 , wherein the polypropylene is a copolymer.

11. The pouch-type secondary battery according to claim 1 , wherein the first layer includes an acid-modified polyolefin.

12. The surface of the electrode lead that is in direct contact with the lead film is made of at least one inorganic material selected from the group consisting of chromium (Cr), nickel (Ni), zirconium (Zr) and titanium (Ti), an aluminum oxide film (Al ２ O ３ 2. The pouch-type secondary battery according to claim 1, wherein the pouch-type secondary battery is coated with one or more resins selected from the group consisting of polyvinyl alcohol (PVA), acrylic, and / or epoxy resins that serve as a binder.

13. 2. The pouch-type secondary battery according to claim 1, wherein the lead film has a thickness of 150 μm to 250 μm.

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