Pouch-type secondary battery with protective film having improved adhesive strength and manufacturing method thereof

Abstract

The present invention relates to a pouch-type secondary battery having a protective film with improved adhesive strength and a manufacturing method thereof, and more particularly, to a pouch-type secondary battery including a case having a laminate sheet structure, an electrode assembly housed inside the case, an electrode tab extending from the electrode assembly, an electrode lead connected to the electrode tab at one side and protruding out of the case at the other side, and protective films located on upper and lower surfaces of a welded portion W between the electrode tab and the electrode lead, the protective film including an ethylene-vinyl acetate copolymer-based adhesive layer in close contact with a surface of the welded portion, and a support layer made of one or more materials selected from the group consisting of polypropylene, cast polypropylene, and polyethylene terephthalate and located on one side of the adhesive layer.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0082085 filed on July 4, 2022, and Korean Patent Application No. 10-2023-0045688 filed on April 6, 2023, and all contents disclosed in the Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a pouch-type secondary battery having a protective film with improved adhesive strength and a manufacturing method thereof, and more particularly, to a pouch-type secondary battery having a protective film with improved adhesive strength, which can prevent the protective film from coming off its position even after an electrolyte wetting process by improving the adhesive strength of the protective film located at the welded portion between an electrode tab and an electrode lead, and a manufacturing method thereof. [Background technology]

[0003] Recently, the demand for secondary batteries that can store electrical energy produced by the development of alternative energy sources due to air pollution caused by the use of fossil fuels and energy depletion has increased. Rechargeable secondary batteries are closely related to daily life, being used in mobile devices, electric vehicles, hybrid electric vehicles, etc.

[0004] Secondary batteries are used as energy sources for various electronic devices that are essential in modern society, and the required capacity is increasing due to the increasing use and complexity of mobile devices and the development of electric vehicles, etc. To meet user demands, small devices are equipped with multiple battery cells, while automobiles and other devices use battery modules that electrically connect multiple battery cells or battery packs equipped with multiple such battery modules.

[0005] Meanwhile, battery cells have a protective film at the portion where the electrode tab and electrode lead are welded and connected, but the adhesive strength of the protective film can decrease during the electrolyte wetting process, causing the protective film to break or come off, leading to performance degradation and defects.

[0006] Fig. 1 is an exploded perspective view of a conventional battery cell. As shown in Fig. 1, the conventional battery cell includes an electrode assembly 10, a case 20 that houses the electrode assembly 10, an electrode tab 30 extending from one side of the electrode assembly 10, an electrode lead 40 that is connected to the electrode tab 30 on one side and protrudes outside the case 20 on the other side, and a ring-shaped protective film 50 that encloses the connection between the electrode tab 30 and the electrode lead 40.

[0007] In a battery cell according to the prior art, the connection between the electrode tab 30 and the electrode lead 40 is wrapped and attached with a protective film 50 coated with an acrylic resin adhesive, and the connection is then protected from impacts.

[0008] However, because the protective film 50 is fixed by tension due to the adhesive strength of the acrylic resin adhesive, the adhesive and fixing strength is insufficient, which can cause the electrode tab 30 and electrode lead 40 to move in the longitudinal direction during the electrolyte wetting process, resulting in displacement. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2009-0077420 Summary of the Invention [Problem to be solved by the invention]

[0010] In order to solve the above problems, the present invention aims to provide a pouch-type secondary battery including a protective film with improved adhesive strength, which can maintain high adhesive strength even after an electrolyte wetting process, thereby preventing the protective film from folding or coming off, and a method for manufacturing the same. [Means for solving the problem]

[0011] In order to achieve the above object, the pouch-type secondary battery with a protective film having improved adhesive strength according to the present invention includes a case (100) having a laminated sheet structure, an electrode assembly (200) housed inside the case (100), an electrode tab (300) extending from the electrode assembly (200), an electrode lead (400) connected to the electrode tab (300) at one side and protruding outside the case (100) at the other side, and a protective film (500) located on the upper and lower surfaces of a welded portion (W) between the electrode tab (300) and the electrode lead (400), the protective film (500) including an ethylene-vinyl acetate copolymer-based adhesive layer (520) in close contact with the surface of the welded portion, and a protective film (500) made of polypropylene, cast polypropylene, or polyethylene terephthalate (PET) located on one side of the adhesive layer (520). and a support layer (510) made of one or more materials selected from the group consisting of terephthalate (Tetraphthalate).

[0012] In addition, in the pouch-type secondary battery according to the present invention, the support layer (510) is made of cast polypropylene material.

[0013] In the pouch-type secondary battery according to the present invention, the support layer (510) is made of a polyethylene terephthalate material.

[0014] In addition, in the pouch-type secondary battery according to the present invention, the protective film (500) is located in the internal space of the case (100) without overlapping with the sealing part, and is in a state of completely enclosing the welded part (W).

[0015] In addition, in the pouch-type secondary battery according to the present invention, the thickness of the protective film (500) is equal to or greater than the height of the bead formed during welding.

[0016] In addition, in the pouch-type secondary battery according to the present invention, the protective film (500) includes a pair of protective films located on one side and the other side of the welded portion (W), respectively.

[0017] In addition, in the pouch-type secondary battery according to the present invention, the protective film (500) comprises a single protective film folded to enclose one side and the other side of the welded portion (W).

[0018] In addition, a method for manufacturing a pouch-type secondary battery according to the present invention includes a first step of preparing an electrode assembly (200), a second step of welding an electrode tab (300) extending from the electrode assembly (200) to an electrode lead (400), a third step of positioning a protective film (500) to cover a welded portion (W) between the electrode tab (300) and the electrode lead (400), a fourth step of thermocompressing the protective film (500), a fifth step of placing the electrode assembly (200) in a case (100), and a sixth step of sealing an edge of the case (100). The protective film (500) includes an ethylene-vinyl acetate copolymer adhesive layer (520) that is in close contact with the surface of the welded portion (W), and a polypropylene or cast polypropylene adhesive layer (520) that is located on one side of the adhesive layer. and a support layer (510) made of one or more materials selected from the group consisting of polypropylene and polyethylene terephthalate.

[0019] In addition, in the method for manufacturing a pouch-type secondary battery according to the present invention, the support layer (510) is made of cast polypropylene material.

[0020] In addition, in the method for manufacturing a pouch-type secondary battery according to the present invention, in the third step, the protective film (500) completely encloses the welded portion W, and in the fifth step, the protective film (500) is located in the internal space portion that does not overlap with the sealing portion of the case.

[0021] In addition, in the method for manufacturing a pouch-type secondary battery according to the present invention, the thickness of the protective film (500) is equal to or greater than the height of the bead formed during welding.

[0022] In addition, in the method for manufacturing a pouch-type secondary battery according to the present invention, the fourth step of thermocompression bonding is characterized in that a first thermocompression bonding step and a second thermocompression bonding step are sequentially performed, and a heating temperature during the second thermocompression bonding step is higher than a heating temperature during the first thermocompression bonding step.

[0023] In addition, in the method for manufacturing a pouch-type secondary battery according to the present invention, the heating temperature during the secondary thermocompression bonding is 100 to 145°C.

[0024] The present invention also provides a battery module including the above-mentioned pouch-type secondary battery. [Effects of the Invention]

[0025] As described above, the pouch-type secondary battery according to the present invention has an advantage in that it can maintain high adhesive strength by using an ethylene-vinyl acetate copolymer-based adhesive as the adhesive layer of the protective film, and as a result, it can prevent the protective film from folding or coming off even after the electrolyte wetting process.

[0026] In addition, the pouch-type secondary battery according to the present invention has an advantage in that a protective film with excellent adhesive strength is positioned at the welded portion between the electrode tab and the electrode lead, thereby preventing poor insulation resistance that may occur when the welded portion between the electrode tab and the electrode lead interferes with the case. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is an exploded perspective view showing a battery cell according to the prior art. [Figure 2] 1 is an exploded perspective view of a pouch-type secondary battery according to a first embodiment of the present invention; [Figure 3] 3A and 3B are vertical cross-sectional views of the protective film shown in FIG. 2, where (A) is a cross-sectional view taken along the aa direction in FIG. 2, and (B) is a cross-sectional view taken along the bb direction in FIG. [Figure 4] FIG. 10 is an exploded perspective view of a pouch-type secondary battery according to a second embodiment of the present invention. [Figure 5] 3 is a flowchart illustrating a method for manufacturing a pouch-type secondary battery according to a first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of an embodiment of the present invention that will enable a person skilled in the art to easily carry out the present invention. However, in describing the operation principle of the preferred embodiment of the present invention in detail, detailed description of related well-known functions or configurations will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0029] Furthermore, the same reference numerals are used throughout the drawings for parts that have similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element between them. Furthermore, unless otherwise specified, "including a certain element" does not mean that other elements are excluded, but that other elements may also be included.

[0030] Hereinafter, a pouch-type secondary battery having a protective film with improved adhesive strength according to the present invention and a method for manufacturing the same will be described with reference to the accompanying drawings.

[0031] FIG. 2 is an exploded perspective view of a pouch-type secondary battery according to the present invention, and FIG. 3 is a vertical cross-sectional view of a protective film according to the present invention, where (A) is a cross-sectional view taken along line aa in FIG. 2, and (B) is a cross-sectional view taken along line bb in FIG. 2.

[0032] As shown in FIGS. 2 and 3, the pouch-type secondary battery according to the present invention includes a case 100, an electrode assembly 200, an electrode tab 300, an electrode lead 400, and a protective film 500.

[0033] First, the case 100 may include an upper case and a lower case, and has a pocket-shaped receiving portion formed therein so as to receive the electrode assembly 200 therein.

[0034] In the case 100, a laminate sheet including an outer resin layer 110, a metal layer 120, and an inner resin layer 130 is molded to form a storage section.

[0035] The outer resin layer 110 is located on the outer periphery of the case 100. The outer resin layer 110 may be made of a heat-resistant polymer having excellent tensile strength, moisture-proof properties, and air-proof properties to ensure heat resistance and chemical resistance while protecting the electrode assembly 200. Examples of the outer resin layer 110 include, but are not limited to, nylon or polyethylene terephthalate.

[0036] The metal layer 120 in contact with the external resin layer 110 corresponds to a barrier layer that prevents moisture and various gases from penetrating into the interior of the battery from the outside, and a preferred material for such a metal layer is an aluminum thin film, which is lightweight yet has excellent formability.

[0037] Since the inner resin layer 130 is in direct contact with the electrode assembly 200, it must have insulating properties and electrolysis resistance. In addition, to seal against the outside, the sealing portion where the inner layers are thermally bonded must have excellent thermal adhesive strength.

[0038] The material of the inner resin layer 130 may be selected from polyolefin resins such as polypropylene, cast polypropylene (CPP), polyethylene, polyethylene acrylic acid, and polybutylene, which have excellent chemical resistance and sealing properties, polyurethane resins, and polyimide resins, but is not limited thereto. Polypropylene or cast polypropylene (CPP), which have excellent mechanical properties such as tensile strength, rigidity, surface hardness, and impact resistance, and excellent chemical resistance, are most preferred.

[0039] Although FIG. 2 shows a case in which both the upper case and the lower case are provided with storage sections, it is also possible to provide a storage section only in the upper case or only in the lower case.

[0040] Next, the electrode assembly 200 will be described. The electrode assembly 200 seated in the storage part of the case 100 can include, but is not limited to, a jelly roll type electrode assembly having a structure in which a separation membrane is interposed between a long sheet-like negative electrode and a positive electrode and then wound up, a stack type electrode assembly including unit cells having a structure in which a rectangular positive electrode and a negative electrode are laminated with a separation membrane interposed therebetween, a stack folding type electrode assembly in which unit cells are wound up by a long separation film, or a lamination stack type electrode assembly in which unit cells are laminated with a separation membrane interposed therebetween and adhered to each other.

[0041] Specifically, the negative electrode is manufactured by applying a slurry in which a negative electrode active material and a binder are mixed to a negative electrode current collector.

[0042] Here, examples of the negative electrode active material include carbon such as graphitizable carbon and graphite-based carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Si-based materials that are Si, SiO, SiO2 alone or mixtures thereof, etc. can be used, but are not limited only to these.

[0043] The positive electrode is manufactured by applying a slurry in which a positive electrode active material and a binder are mixed to a positive electrode current collector.

[0044] The positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x Ni-site type lithium nickel oxide represented by MxO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides expressed as LiMnO2 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu, or Zn); LiMn2O4, in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0045] Meanwhile, the negative electrode current collector and the positive electrode current collector include a coated portion coated with a slurry containing an active material and a plain portion not coated with the slurry. The plain portion is cut to form the electrode tab 300, or a separate conductive member is connected to the plain portion by ultrasonic welding or the like to form the electrode tab 300.

[0046] A pair of electrode leads 400 including a positive electrode lead and a negative electrode lead are electrically connected to electrode tabs 300 including a positive electrode tab and a negative electrode tab of the electrode assembly 200, respectively, and then exposed to the outside of the case.

[0047] The electrode tab 300 and the electrode lead 400 can be electrically connected to each other by welding, more specifically, ultrasonic welding. Such ultrasonic welding is performed by applying high-frequency vibrations generated by ultrasonic waves of approximately 20 kHz to the interface between the electrode tab and the electrode lead, and the vibration energy is converted into heat energy through friction as a horn and anvil are operated, resulting in rapid welding.

[0048] Meanwhile, after the electrode assembly 200 is housed, the edges of the upper and lower cases are sealed with a portion of the electrode lead 400 protruding to the outside. Here, since the sealing is performed by applying heat and pressure at a high temperature, the electrode lead 400 may be damaged, which may cause an electrical short circuit between the electrode lead and the case 100.

[0049] Therefore, in order to prevent such a short circuit, it is preferable that lead films 410 are positioned on the upper and lower surfaces of the electrode lead 400. Of course, the lead film 410 can be formed to cover the entire surface of the electrode lead 400, but since the purpose is to prevent damage to the electrode lead 400 and an electrical short circuit between the electrode lead 400 and the case 100 during sealing, it may be attached only to the portion of the electrode lead 400 that faces the case 100.

[0050] Next, a description will be given of the protective film 500. The protective film 500 is arranged so as to cover the portion where the electrode tab 300 and the electrode lead 400 overlap each other, that is, the welded portion W thereof.

[0051] As described above, since the electrode tab 300 and the electrode lead 400 are connected by welding, the surfaces of the electrode tab 300 and the electrode lead 400 may not be smooth. In other words, in the welding process between the electrode tab 300 and the electrode lead 400, a bead that melts and then hardens during laser welding is generally generated.

[0052] Therefore, if the surface of the welded portion W is not smooth due to a bead or the like, the welded portion W may come into contact with the case 100 upon external impact, causing damage to the case 100 and problems such as poor insulation. However, since the protective film 500 covers the welded portion W, the above-mentioned problems can be overcome.

[0053] The protective film 500 according to the present invention may include a support layer 510 and an adhesive layer 520. The protective film 500 is positioned on the upper and lower surfaces of the welded portion W, respectively, to completely enclose them.

[0054] Of course, it is preferable that the protective film 500 is positioned in the internal space of the case 100 so as not to overlap with the sealing portion.

[0055] Here, the support layer 510 may be made of an insulating material, and as an example, it is preferable that the support layer 510 is made of a polypropylene (PP), cast polypropylene (CPP), or polyethylene terephthalate (PET) material.

[0056] In particular, when the support layer 510 is made of the same material as the internal resin layer 130, cast polypropylene (CPP) or polypropylene (PP), there is an advantage that the adhesive strength is not reduced due to the same material even if the support layer 510 is unintentionally slightly removed from the attachment position.

[0057] Furthermore, when the support layer 510 is made of polyethylene terephthalate (PET), the melting temperature is about 160°C, which is higher than that of cast polypropylene (CPP), making it easier to perform the thermocompression bonding process of the protective film.

[0058] The adhesive layer 520 provided on one side of the support layer 510, in other words, the side facing the welded portion W, is preferably made of a material that exhibits adhesive strength when heated at a temperature above a certain temperature, and an ethylene-vinyl acetate copolymer adhesive is particularly preferred.

[0059] Since ethylene-vinyl acetate copolymer adhesives begin to melt at temperatures above approximately 80°C, excellent adhesive strength can be ensured by applying heat and pressure while one support layer 510 is positioned on the top and bottom surfaces of the welded portion W, facing each other.

[0060] Acrylic adhesives have been used as adhesive layer materials in the past. These acrylic adhesives provide adhesive strength when pressure is applied at room temperature, but due to their relatively low adhesive strength, the bonded parts can come off during the electrolyte wetting process, resulting in breakage, displacement, and in the worst case, separation from the welded part W, which can lead to quality degradation or product defects.

[0061] However, the protective film 500 of the present invention uses an ethylene-vinyl acetate copolymer adhesive, and exhibits excellent adhesive strength by performing the bonding process under heat and pressure conditions, thereby significantly reducing the occurrence of the above-mentioned problems.

[0062] On the other hand, the thickness of the protective film 500 is preferably the same as or slightly greater than the height of the bead so that the bead is not exposed. For example, if the height of the bead at the welded portion W is 110 μm or less, the thickness of the protective film 500 is preferably at least 110 μm.

[0063] Here, there are no particular limitations on the thickness of support layer 510 and adhesive layer 520 as long as they are within the thickness range of protective film 500. For example, when protective film 500 has a thickness of 110 μm, support layer 510 and adhesive layer 520 may have thicknesses of 90 μm and 20 μm, or 80 μm and 30 μm, respectively.

[0064] As the output of the secondary battery increases, the thickness of the electrode lead and electrode tab, and the height of the bead formed in the welding process, may also increase, so the thickness of the protective film 500 can be changed as much as desired.

[0065] 4 is an exploded perspective view of a pouch-type secondary battery according to a second embodiment of the present invention, which is identical in structure to the first embodiment described with reference to FIGS. 2 and 3 except for the outer shape of the protective film 500.

[0066] That is, in the pouch-type secondary battery according to the second embodiment of the present invention, the single protective film 500 is folded and positioned on the upper and lower surfaces of the welding portion W. Of course, it is clear that the adhesive layer 520 of the protective film 500 faces toward the welding portion W.

[0067] FIG. 5 is a flowchart illustrating a method for manufacturing a pouch-type secondary battery according to a first preferred embodiment of the present invention.

[0068] Referring to FIG. 5, the method for manufacturing a pouch-type secondary battery according to the first embodiment of the present invention includes a first step of preparing an electrode assembly 200, a second step of welding an electrode tab 300 extending from a side of the electrode assembly 200 to an electrode lead 400, a third step of positioning a protective film 500 to cover a welded portion W between the electrode tab 300 and the electrode lead 400, a fourth step of thermocompressing the protective film 500, a fifth step of placing the electrode assembly 200 in a case 100, and a sixth step of sealing an edge of the case.

[0069] First, the first step of preparing the electrode assembly 200 is to prepare the electrode assembly 200 in which one or more positive electrodes, one or more negative electrodes, and one or more separators are stacked and which has an electrode tab 300 extending outward.

[0070] The second step of welding the electrode tab 300 extending from the electrode assembly 200 to the electrode lead 400 is a step of overlapping the electrode tab 300 and a portion of the electrode lead 400, and then electrically connecting and fixing them using known joining means such as laser welding or resistance welding.

[0071] The third step of positioning the protective film 500 to cover the welded portion W where the electrode tab 300 and the electrode lead 400 are welded is a step of positioning a pair of protective films 500 on the upper and lower surfaces of the welded portion W, respectively, and then tightly adhering them.

[0072] The fourth step of thermocompression bonding the protective films 500 is a step of applying heat and pressure to the protective films 500 to melt a portion of the adhesive layer 520 of the protective films 500, thereby firmly bonding the pair of protective films 500 located on the upper and lower surfaces of the welded portion W. Of course, the adhesive layer 520 and the welded portion W are bonded in the portion where the protective films 500 and the welded portion W overlap, and the adhesive layers 520 located above and below are bonded in the portion that does not overlap the welded portion W.

[0073] Here, the thermocompression bonding step is preferably performed in two stages, i.e., after the first thermocompression bonding, the second thermocompression bonding is preferably performed, and the heating temperature during the second thermocompression bonding is preferably higher than that during the first thermocompression bonding. For example, the first thermocompression bonding may be performed at 80 to 90°C and 2 to 5 kgf / cm 2 for 2-4 seconds, and the secondary heat-compression bonding is performed at 100-160°C and 2-5 kgf / cm 2 This is done for 2 to 4 seconds.

[0074] The first thermocompression bonding step is a step of melting the adhesive layer 520 to fix the general position of the protective film 500 and temporarily bond it, and the second thermocompression bonding step is a step of applying heat and pressure again to the protective film 500 temporarily bonded in the first thermocompression bonding step to improve the fixing strength of the protective film 500.

[0075] The adhesive of conventional welding protection films is a material that exhibits adhesive strength at room temperature, so it is always in a sticky state. Therefore, when cutting the protection film or positioning it on the weld W, it is often not accurately attached to the desired position.

[0076] In contrast, the adhesive layer 520 of the present invention has no adhesive strength until heat is applied, so it can be positioned accurately in the desired location and is very advantageous in that it can be cut to or maintained at a fixed size.

[0077] The fifth step of storing the electrode assembly 200 in the case 100 is to store the electrode assembly 200 in the storage portion of the case 100 with the protective film 500 tightly attached to the upper and lower surfaces of the welded portion W. In this case, it is preferable that the protective film 500 is stored in the internal space of the case 100 so as not to overlap with the sealing portion of the case 100.

[0078] The sixth step of sealing the edges of the case involves pressing two or three edges of the case 100 at a certain temperature and pressure. This is followed by injecting an electrolyte solution and then performing an activation process. These processes are similar to those used in manufacturing pouch-type secondary batteries, so a detailed description will be omitted.

[0079] The present invention may also be a battery module including the pouch-type secondary battery described above, or may further be a battery pack including the battery module described above.

[0080] Examples and comparative examples of the present invention are given below. The following examples and comparative examples are provided for illustrative purposes to aid in understanding the present invention, and are not intended to limit the technical scope of the present invention.

[0081] Example 1 A two-layer protective film including an adhesive layer and a support layer was prepared, and then placed so as to encase the welded portion of the negative electrode lead made of nickel and the negative electrode tab made of copper.

[0082] Then, 130℃ and 5kgf / cm 2 The thermocompression bonding was carried out under the condition of 0.5°C for 3 seconds.

[0083] Here, the adhesive layer was made of an EVA resin composition containing 100 parts by weight of EVA resin and 18 parts by weight of crosslinking agent. The EVA resin had a vinyl acetate (VA) content of 18% by weight and a melt index (MFI) of 15 g / 10 min (measured at 190°C with a load of 2.16 kg). The crosslinking agent used was di-tert-butyl peroxide, a dialkyl peroxide with a one-hour half-life temperature (crosslinking reaction temperature) of 135 to 150°C.

[0084] The support layer has a tensile strength of 4.5 kgf / mm when measured in accordance with ASTM D882. 2 (Machine Direction, MD) and a cast polypropylene (CPP) having an elongation of 750% (Machine Direction, MD) when measured according to ASTM D882 was used.

[0085] Meanwhile, the bead thickness of the welded part is distributed in the range of 36 to 91 μm, the thickness of the adhesive layer and the support layer are 20 μm and 100 μm, respectively, and the total thickness is 120 μm.

[0086] Example 2 Except for the thicknesses of the adhesive layer and the support layer being 50 μm and 100 μm, respectively, and the total thickness being changed to 150 μm, the rest was the same as in Example 1. Meanwhile, the bead thickness of the weld was distributed in the range of 44 to 103 μm.

[0087] Example 3 A two-layer protective film including an adhesive layer and a support layer was fixed to the welded portion of the aluminum positive electrode lead and the aluminum positive electrode tab. At this time, the bead of the welded portion was distributed in the range of 48 to 108 μm, and the rest was the same as in Example 1.

[0088] Example 4 A two-layer protective film including an adhesive layer and a support layer was fixed to the welded portion of the aluminum positive electrode lead and the aluminum positive electrode tab. At this time, the weld bead was distributed in the range of 39 to 110 μm, and the rest was the same as in Example 2.

[0089] Example 5 The rest is the same as in Example 1, except that the bead of the weld is distributed in the range of 45 to 100 μm.

[0090] Example 6 The rest is the same as in Example 2, except that the bead of the weld is distributed in the range of 39 to 89 μm.

[0091] Example 7 The rest is the same as in Example 3, except that the bead of the weld is distributed in the range of 41 to 99 μm.

[0092] Example 8 The rest is the same as in Example 4, except that the bead of the weld is distributed in the range of 54 to 108 μm.

[0093] Example 9 A protective film having a two-layer structure including the same adhesive layer (EVA) and support layer (CPP) as in Example 1 was placed so as to enclose the welded portion of the aluminum positive electrode lead and aluminum positive electrode tab.

[0094] Then, 130℃ and 5kgf / cm 2 The thermocompression bonding was carried out under the condition of 0.5°C for 3 seconds.

[0095] On the other hand, the bead thickness of the weld was distributed in the range of 48 to 110 μm, and the thicknesses of the adhesive layer and the support layer were 50 μm and 100 μm, respectively, for a total thickness of 150 μm.

[0096] Example 10 A two-layer protective film including an adhesive layer and a support layer was placed so as to enclose the welded portion of the aluminum positive electrode lead and the aluminum positive electrode tab.

[0097] Then, 130℃ and 5kgf / cm 2 The thermocompression bonding was carried out under the condition of 0.5°C for 3 seconds.

[0098] Here, the adhesive layer was the same as in Example 1, and the support layer had a tensile strength of 26.6 kgf / mm when measured according to ASTM D882. 2 (Machine Direction, MD) and polyethylene terephthalate (PET) having an elongation of 114% (Machine Direction, MD) when measured according to ASTM D882 was used.

[0099] On the other hand, the bead thickness of the welded portion was distributed in the range of 39 to 89 μm on average, and the thicknesses of the adhesive layer and the support layer were 50 μm and 100 μm, respectively, for a total thickness of 150 μm.

[0100] Comparative Example 1 The adhesive layer was acrylic, and the support layer was a two-layer protective film containing unstretched polypropylene. The protective film was then placed to encase the welded portion of the nickel negative electrode lead and the copper negative electrode tab. The negative electrode was then heated at 120°C and 5 kgf / cm. 2 The pressure was applied for 3 seconds.

[0101] On the other hand, the thicknesses of the adhesive layer and the support layer were 10 μm and 100 μm, respectively, for a total thickness of 110 μm, and the weld bead was distributed in the range of 38 to 87 μm.

[0102] Comparative Example 2 A two-layer protective film containing acrylic and unstretched polypropylene was fixed to the welded portion of the aluminum positive electrode lead and aluminum positive electrode tab, as in Comparative Example 1. The remaining conditions were the same as in Comparative Example 1, except that the weld bead was distributed in the range of 49 to 98 μm.

[0103] Comparative Example 3 The remaining conditions were the same as those of Comparative Example 1, except that the bead thickness of the weld was distributed in the range of 36 to 89 μm.

[0104] Comparative Example 4 The remaining conditions were the same as those of Comparative Example 2, except that the bead of the weld was distributed in the range of 58 to 100 μm.

[0105] Comparative Example 5 The remaining conditions were the same as those of Comparative Example 2, except that the bead thickness of the weld was distributed in the range of 61 to 110 μm.

[0106] [Table 1]

[0107] Experimental Example 1 The protective films according to Examples 1-10 and Comparative Examples 1-5 were evaluated for thermal adhesion strength before and after impregnation with the electrolyte solution.

[0108] "Before electrolyte impregnation" refers to the result of measuring the thermal adhesion strength after a certain period of time has passed since the protective film was fixed to the welded portion and the film was not in contact with the electrolyte, and "after electrolyte impregnation" refers to the result of measuring the thermal adhesion strength after a certain period of time has passed since the protective film was fixed to the welded portion and the film was kept in continuous contact with the electrolyte.

[0109] The electrolyte contains 50 to 55 volume % of ethyl methyl carbonate, 30 to 35 volume % of ethylene carbonate, 10 to 15 volume % of lithium hexafluorophosphate, 0.1 to 5 volume % of vinylene carbonate, 0.1 to 5 volume % of 1,3,2-dioxathiolane, 0.1 to 5 volume % of lithium tetrafluoroborate, and 0.1 to 5 volume % of propane sultone.

[0110] Here, the thermal adhesive strength was measured between the negative electrode lead or the positive electrode lead and the protective film by applying a load that increased at a rate of 50 mm / min to an adhesive strength measuring instrument (Instron, Universal Material Tester 6800 Series Model).

[0111] The results of Examples 1-8 and Comparative Examples 1-4 are shown in Table 2. The measurements were taken two days before and after impregnation with the electrolyte.

[0112] [Table 2]

[0113] As can be seen from Table 2, in Comparative Examples 1 to 4, which used acrylic as the adhesive layer, the adhesive strength was in the range of 57 to 100 gf / 6.0 mm before impregnation with the electrolyte, but after impregnation with the electrolyte, it significantly decreased to 33 to 38 gf / 6.0 mm.

[0114] In contrast, in Examples 1 to 8, which used an EVA adhesive layer, although the adhesive strength varied depending on the bead height, it was in the range of 218 to 700 gf / 6.0 mm before impregnation with the electrolyte, demonstrating that the adhesive strength was significantly improved compared to the comparative examples.

[0115] It can also be seen that even after impregnation with the electrolyte, the adhesive strength remains at 235 to 700 gf / 6.0 mm without any particular decrease.

[0116] The results of Examples 9-10 and Comparative Example 5 are shown in Table 3 below. The results before impregnation with the electrolyte were measured immediately after thermocompression bonding, and then measurements were taken at regular intervals after impregnation.

[0117] [Table 3]

[0118] As can be seen from Table 3, in Comparative Example 5, in which acrylic was used as the adhesive layer, the adhesive strength was reduced by impregnation and could not be restored even after the impregnation time had elapsed.

[0119] On the other hand, it was confirmed that both Example 9, which used EVA as the adhesive layer and CPP as the support layer, and Example 10, which used EVA as the adhesive layer and PET as the support layer, maintained their adhesive strength regardless of impregnation, and were hardly affected by the impregnation time.

[0120] Example 11 The adhesive layer and support layer were 50 μm and 100 μm thick, respectively, and were positioned so as to enclose the welded portion of the positive electrode lead and positive electrode tab, the welded portion having a bead thickness ranging from 57 to 100 μm. The remaining procedures were the same as in Example 1, except that thermocompression bonding was performed at 120°C.

[0121] Example 12 The rest was the same as in Example 11, except that the thermocompression was carried out at 125°C.

[0122] Example 13 The rest was the same as in Example 11, except that the thermocompression was carried out at 130°C.

[0123] Example 14 The rest was the same as in Example 11, except that the thermocompression was carried out at 135°C.

[0124] Example 15 The rest was the same as in Example 11, except that the thermocompression was carried out at 140°C.

[0125] Example 16 The rest was the same as in Example 11, except that the thermocompression was carried out at 145°C.

[0126] Example 17 The rest was the same as in Example 11, except that the support layer was changed to the PET of Example 10, and the thicknesses of the adhesive layer and support layer were changed to 75 μm and 75 μm, respectively.

[0127] Example 18 The rest was the same as in Example 17, except that the thermocompression was carried out at 125°C.

[0128] Example 19 The rest was the same as in Example 17, except that the thermocompression was carried out at 130°C.

[0129] Example 20 The rest was the same as in Example 17, except that the thermocompression was carried out at 135°C.

[0130] Example 21 The rest was the same as in Example 17, except that the thermocompression was carried out at 140°C.

[0131] Example 22 The rest was the same as in Example 17, except that the thermocompression was carried out at 145°C.

[0132] Example 23 The rest was the same as in Example 17, except that the thermocompression was carried out at 150°C.

[0133] Example 24 The rest was the same as in Example 17, except that the thermocompression was carried out at 155°C.

[0134] Comparative Example 6 The rest was the same as in Example 11, except that the thermocompression was carried out at 150°C.

[0135] Comparative Example 7 The rest was the same as in Example 11, except that the thermocompression was carried out at 155°C.

[0136] Experimental Example 2 For the secondary thermocompression bonding conditions according to Examples 11-24 and Comparative Examples 6-7, the protective films were divided into those before impregnation with the electrolyte (after 2 days) and those after impregnation with the electrolyte (after 2 days), and the thermal adhesion strength was evaluated under the same conditions as in Experimental Example 1. Here, the presence or absence of shrinkage was visually confirmed to determine whether the film was good or bad.

[0137] [Table 4]

[0138] As shown in Table 4, in order to simultaneously achieve adhesive strength and function as a protective film, it is preferable to maintain the heating temperature at 155°C or less when the support layer is PET, and at 145°C or less when the support layer is CPP.

[0139] Those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content. [Explanation of symbols]

[0140] 100 cases 110 outer resin layer 120 metal layer 130 Internal resin layer 200 electrode assembly 300 Electrode Tab 400 electrode leads 410 lead film 500 protective films 510 Support layer 520 Adhesive layer W welded section

Claims

1. a case having a laminate sheet structure; an electrode assembly housed inside the case; an electrode tab extending from the electrode assembly; an electrode lead connected to the electrode tab at one side and protruding out of the case at the other side; and protective films positioned on the upper and lower surfaces of the welded portion W between the electrode tab and the electrode lead, The pouch-type secondary battery includes a protective film made of only an ethylene-vinyl acetate copolymer adhesive layer that is in close contact with the surface of the weld, and a support layer that is made of one or more materials selected from the group consisting of polypropylene, cast polypropylene, and polyethylene terephthalate and is positioned on one side of the adhesive layer.

2. The pouch-type secondary battery according to claim 1 , wherein the support layer is made of cast polypropylene.

3. The pouch-type secondary battery according to claim 1 , wherein the support layer is made of a polyethylene terephthalate material.

4. The pouch-type secondary battery according to claim 2 , wherein the protective film is positioned in an internal space of the case that does not overlap with a sealing portion of the case, and completely encloses the welded portion (W).

5. The pouch-type secondary battery according to claim 4 , wherein the thickness of the protective film is equal to or greater than the height of a bead formed during welding.

6. The pouch-type secondary battery according to claim 2 , wherein the protective film includes a pair of protective films positioned on one side and the other side of the welded portion W, respectively.

7. The pouch-type secondary battery according to claim 2 , wherein the protective film comprises a single protective film folded to enclose one side and the other side of the welded portion W.

8. a first step of providing an electrode assembly; a second step of welding an electrode tab extending from the electrode assembly to an electrode lead; a third step of positioning a protective film to cover the welded portion W between the electrode tab and the electrode lead; a fourth step of thermocompressing the protective film; a fifth step of housing the electrode assembly in a case; and a sixth step of sealing the edges of the case, the protective film is made of only an ethylene-vinyl acetate copolymer adhesive layer that is in close contact with the surface of the welded portion (W), and a support layer that is located on one side of the adhesive layer and is made of one or more materials selected from the group consisting of polypropylene, cast polypropylene, and polyethylene terephthalate.

9. The method for manufacturing a pouch-type secondary battery according to claim 8, wherein the support layer is made of cast polypropylene.

10. 10. The method of claim 9, wherein in the third step, the protective film completely encloses the welded portion W, and in the fifth step, the protective film is positioned in an internal space portion that does not overlap with a sealing portion of the case.

11. The method of manufacturing a pouch-type secondary battery according to claim 10 , wherein the thickness of the protective film is equal to or greater than the height of a bead formed during welding.

12. 10. The method of claim 9, wherein the fourth step of thermocompression bonding comprises sequentially performing a first thermocompression bonding step and a second thermocompression bonding step, and the heating temperature during the second thermocompression bonding step is higher than the heating temperature during the first thermocompression bonding step.

13. The method for manufacturing a pouch-type secondary battery according to claim 12, wherein the heating temperature during the secondary thermocompression bonding is 100 to 145°C.

14. A battery module comprising the pouch-type secondary battery according to any one of claims 1 to 7.

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