secondary batteries

Abstract

A secondary battery according to one embodiment of the present invention includes an electrode assembly, an electrode lead attached to the electrode assembly, a case that houses the electrode assembly, a lead film that is formed to cover a portion of the outer surface of the electrode lead and is interposed between the electrode lead and the case, a vent region formed in at least a portion of the case, and a vent member that is inserted into the vent region and has a three-layer or more structure, wherein the vent member includes a linear low-density polyethylene having a comonomer with six or more carbon atoms in an outermost layer and a resin having a higher melting point than the linear low-density polyethylene having a comonomer with six or more carbon atoms in an intermediate layer.

Description

[Technical Field]

[0001] This application claims priority from Korean Patent Application No. 10-2021-0049379, filed on April 15, 2021.

[0002] The present invention relates to a secondary battery, and more particularly to a secondary battery provided with a vent member. [Background technology]

[0003] Secondary batteries, which can be applied to a variety of products and have excellent electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs). These secondary batteries are attracting attention as a new energy source that not only dramatically reduces the use of fossil fuels but is also environmentally friendly as no by-products are generated during the energy consumption process, and improves energy efficiency.

[0004] Currently widely used secondary batteries include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel metal hydride batteries, and nickel zinc batteries.

[0005] A secondary battery generally has a structure in which an electrode assembly including at least one unit cell having a positive electrode / separator / negative electrode structure is housed in a case made of a laminate sheet in which an outer layer, a metal barrier layer, and a sealant layer are sequentially stacked, and the electrode assembly is sealed by fusing a sealant resin in the sealant layer.

[0006] Conventionally, secondary batteries can catch fire due to various causes, such as short circuits inside the secondary battery, overcharging or over-discharging, temperature regulation, etc. When this happens, the internal temperature of the secondary battery rises rapidly, and at the same time, thermal propagation occurs, in which heat is transferred to adjacent cells, which can further spread the fire.

[0007] When thermal runaway occurs, i.e., when the internal temperature of a secondary battery rises, directional venting is required to minimize damage to the electrodes caused by gas. However, conventional secondary batteries have the problem of difficulty in directing gas discharge in a specific direction.

[0008] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a secondary battery having improved safety by guiding gas discharge in a specific direction. Summary of the Invention [Problem to be solved by the invention]

[0009] The problem to be solved by the present invention is to provide a secondary battery having improved safety by guiding gas discharge in a specific direction. [Means for solving the problem]

[0010] In order to achieve the above object, according to one aspect of the present invention, there is provided a secondary battery of the following embodiment.

[0011] The first embodiment is an electrode assembly; an electrode lead attached to the electrode assembly; a case for accommodating the electrode assembly therein; a lead film formed to cover a part of an outer surface of the electrode lead and interposed between the electrode lead and the case; a vent area formed in at least a portion of the case; a vent member inserted into the vent area and having a structure of three or more layers; The vent member relates to a secondary battery characterized in that the outermost layer contains linear low-density polyethylene having a comonomer with 6 or more carbon atoms, and the intermediate layer contains a resin having a higher melting point than the linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0012] According to the second embodiment, in the first embodiment, Venting may occur between the case and the outermost layer.

[0013] According to the third embodiment, in the first or second embodiment, The resin having a melting point higher than that of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a melting point higher than 120°C and not higher than 140°C.

[0014] According to the fourth embodiment, in any one of the first to third embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a melting point of 100°C to 120°C.

[0015] According to the fifth embodiment, in any one of the first to fourth embodiments, The resin having a melting point higher than that of linear low-density polyethylene having a comonomer having 6 or more carbon atoms may include high-density polyethylene, random polypropylene, or a mixture thereof.

[0016] According to the sixth embodiment, in any one of the first to fifth embodiments, The case may include a sealing portion formed to seal the electrode assembly, the sealing portion including a sealant resin, and the linear low-density polyethylene having a comonomer having 6 or more carbon atoms included in the vent member may have a melting point lower than that of the sealant resin.

[0017] According to the seventh embodiment, in any one of the first to sixth embodiments, The outermost layer may contain a linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0018] According to the eighth embodiment, in any one of the first to seventh embodiments, The vent member can melt at 100°C to 120°C to release gas.

[0019] According to the ninth embodiment, in the eighth embodiment, The vent member is capable of venting at a pressure of 1.5 atm or greater.

[0020] According to the tenth embodiment, in any one of the first to ninth embodiments, The vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100° C. or higher.

[0021] According to the eleventh embodiment, in any one of the first to tenth embodiments, The vent member may have an average sealing strength of less than 4.5 kgf / 15 mm at 100° C. or higher.

[0022] According to the twelfth embodiment, in any one of the first to eleventh embodiments, The vent member may have a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

[0023] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, The vent member may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

[0024] According to the 14th embodiment, in any one of the 1st to 13th embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be one polymerized in the presence of a metallocene catalyst.

[0025] According to the fifteenth embodiment, in any one of the first to fourteenth embodiments, The content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 15% by weight or less, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

[0026] According to the 16th embodiment, in any one of the 1st to 15th embodiments, The linear low density polyethylene having a comonomer having 6 or more carbon atoms may have a polydispersity index (PDI) of 4 or less.

[0027] According to the 17th embodiment, in any one of the 6th to 16th embodiments, The difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 10°C or less.

[0028] According to the eighteenth embodiment, in the seventeenth embodiment, The crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90°C to 115°C.

[0029] According to the 19th embodiment, in any one of the 1st to 18th embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a weight average molecular weight of 100,000 g / mol to 400,000 g / mol.

[0030] According to the 20th embodiment, in any one of the 6th to 19th embodiments, The vent area may be located in the sealing portion.

[0031] According to the 21st embodiment, in the 20th embodiment, The vent area may be located at a sealing portion on a corner side of the case.

[0032] According to the 22nd embodiment, in any one of the 1st to 21st embodiments, The secondary battery may be a pouch-type secondary battery. [Effects of the Invention]

[0033] A secondary battery according to one embodiment of the present invention includes a vent member having a three-layer or greater structure, in which an outermost layer includes a linear low-density polyethylene having a comonomer with six or more carbon atoms, and an intermediate layer includes a resin having a higher melting point than the linear low-density polyethylene having a comonomer with six or more carbon atoms. This structure allows gas to be vented to the vent region, and the rigidity of the vent member is improved, preventing premature venting before the target temperature and pressure are reached, thereby improving the safety of the battery.

[0034] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concepts of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters described in the drawings. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a plan view showing a secondary battery according to an embodiment of the present invention; [Figure 3] 4A and 4B are diagrams illustrating a state in which venting occurs in a secondary battery according to an embodiment of the present invention; [Figure 4] FIG. 10 is a plan view showing a secondary battery according to another embodiment of the present invention. [Figure 5] FIG. 10 is a plan view showing a secondary battery according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventors themselves can appropriately define the concepts of terms in order to best explain the invention.

[0037] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can be substituted for them at the time of this application.

[0038] A secondary battery according to one embodiment of the present invention includes an electrode assembly having an electrode lead attached thereto, a case for accommodating the electrode assembly therein, a lead film formed to enclose a portion of the outer surface of the electrode lead and interposed between the electrode lead and the case, a vent region formed in at least a portion of the case, and a vent member inserted in the vent region and having a three or more layer structure, wherein the vent member includes a linear low-density polyethylene having a comonomer with six or more carbon atoms in an outermost layer and a resin having a higher melting point than the linear low-density polyethylene having a comonomer with six or more carbon atoms in an intermediate layer.

[0039] 1 and 2 are diagrams showing a secondary battery according to an embodiment of the present invention.

[0040] Referring to FIGS. 1 and 2, a secondary battery 10 includes an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13.

[0041] The electrode assembly 12 includes a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly 12 may be formed by stacking the positive electrode plate and the negative electrode plate in order with the separator interposed therebetween.

[0042] The positive electrode plate may include a positive electrode current collector made of a highly conductive metal sheet, for example, aluminum (Al) foil, and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode plate may also include a positive electrode tab made of a metal material, for example, aluminum (Al), at one end. The positive electrode tab may protrude from one end of the positive electrode plate. The positive electrode tab may be welded to one end of the positive electrode plate or attached using a conductive adhesive.

[0043] The negative electrode plate may include a negative electrode current collector made of a conductive metal thin plate, for example, copper (Cu) foil, and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode plate may also include a negative electrode tab formed of a metal material, for example, nickel (Ni), at one end. The negative electrode tab may protrude from one end of the negative electrode plate. The negative electrode tab may be welded to one end of the negative electrode plate or attached using a conductive adhesive.

[0044] The separator is located between the positive electrode plate and the negative electrode plate to electrically insulate them. The separator may be a porous membrane that allows lithium ions to pass between the positive electrode plate and the negative electrode plate. The separator may be a porous membrane made of, for example, polyethylene (PE), polypropylene (PP), or a composite film thereof.

[0045] The surface of the separator may be provided with an inorganic coating layer, which may have a structure in which inorganic particles are bound to each other by a binder to form a pore structure (interstitial volume) between the particles.

[0046] The electrode assembly 12 may be a jelly roll (wound) electrode assembly having a structure in which long sheet-like positive and negative electrodes are wound with a separator interposed therebetween, a stacked electrode assembly having a structure in which a plurality of positive and negative electrodes cut into predetermined size units are stacked in order with a separator interposed therebetween, a bi-cell having a predetermined unit of positive and negative electrodes stacked with a separator interposed therebetween, or a stacked / folded electrode assembly having a structure in which a bi-cell or full-cell having a predetermined unit of positive and negative electrodes stacked with a separator interposed therebetween is wound up, etc.

[0047] The case 13 serves to house the electrode assembly 12 .

[0048] In one embodiment of the present invention, the case 13 may include a receiving portion 13a for receiving the electrode assembly 12 and a sealing portion 13b formed to seal the electrode assembly 12, as shown in FIG.

[0049] The sealing portion 13b may include a sealant resin, and the sealant resin may be fused along the outer circumferential surface of the receiving portion 13a to seal the electrode assembly 12.

[0050] In one embodiment of the present invention, the case 13 may be provided in the form of a multi-layered film including an outer layer for protection from external impact, a metal barrier layer for blocking moisture, and a sealant layer for sealing the case.

[0051] The outer layer may include a polyester film using polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, nylon, etc., and may be configured as a single layer or multiple layers.

[0052] The metal barrier layer may include aluminum, copper, and the like.

[0053] The sealant layer may include a sealant resin and may be composed of a single layer or multiple layers.

[0054] The sealant resin may include polypropylene (PP), acid-modified polypropylene (PPa), random polypropylene, ethylene-propylene copolymer, or two or more thereof. The ethylene-propylene copolymer may include, but is not limited to, ethylene-propylene rubber, ethylene-propylene block copolymer, etc.

[0055] In one embodiment of the present invention, the case 13 may be a pouch type.

[0056] The pouch-type battery case 13 may include an upper pouch and a lower pouch. When the case 13 includes an upper pouch and a lower pouch, the upper pouch and the lower pouch are arranged so that their sealant resins face each other, and then the opposing sealant resins are fused together by heat and pressure to seal the battery.

[0057] The sealing portion 13b can be fused by heat or ultrasonic waves, but there is no particular limitation as long as the sealing portion 13b can be fused.

[0058] In some embodiments, the sealing portion 13b may be four-sided or three-sided sealed around the periphery of the case 13. In the three-sided sealing structure, the upper pouch and the lower pouch are formed from a single pouch sheet, and then the boundary between the upper pouch and the lower pouch is folded to overlap the storage portions 13a formed in the upper pouch and the lower pouch, and the remaining three peripheries excluding the folded portion are sealed.

[0059] As shown in FIG. 1, the electrode lead 11 may be housed in the case 13 such that a portion of the electrode lead 11 is exposed to the outside of the case 13 .

[0060] A secondary battery 10 according to one embodiment of the present invention includes a lead film 14 .

[0061] The lead film 14 covers a portion of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the case 13. For example, the lead film 14 is interposed between the electrode lead 11 and a sealing portion 13b of the case 13 at a portion where the electrode lead 11 protrudes or extends from the case 13, thereby assisting in bonding the electrode lead 11 to the case 13.

[0062] 1 and 2, a secondary battery 10 according to an embodiment of the present invention includes a vent region (not shown) formed in at least a portion of the case 13, and a vent member 15 can be inserted into the vent region. When a thermal runaway phenomenon occurs, the vent member 15 can guide gas discharge in a specific direction, thereby improving the safety of the battery.

[0063] The vent member 15 and the case 13 may be overlapped by heat sealing. As another example, the vent member 15 and the case 13 may be overlapped by an adhesive such as glue. As yet another example, the vent member 15 and the case 13 may be physically connected by a clip or the like. As yet another example, at least a portion of the vent member 15 may be embedded in a film that constitutes the case 13, for example, a sealant resin.

[0064] The vent member 15 has a three or more layer structure. The vent member 15 includes an outermost layer 15a containing a linear low-density polyethylene having a comonomer with six or more carbon atoms, and an intermediate layer 15b containing a resin with a higher melting point than the linear low-density polyethylene having a comonomer with six or more carbon atoms.

[0065] Since the vent member 15 contains linear low-density polyethylene having a comonomer with 6 or more carbon atoms, the case 13 has excellent sealing properties within a normal temperature range, for example, room temperature to 60°C, but at high temperatures, for example, above 100°C, the sealing strength of the case into which the vent member 15 is inserted decreases, thereby realizing or inducing venting.

[0066] However, if only linear low-density polyethylene having a comonomer with 6 or more carbon atoms is contained, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may lack rigidity, and as the internal pressure of the battery increases, early venting may occur before the target temperature and pressure are reached.

[0067] The resin having a melting point higher than that of the linear low-density polyethylene having a comonomer having six or more carbon atoms serves to maintain the mechanical rigidity of the vent member 15. The improved rigidity of the vent member 15 allows for venting characteristics at high temperatures and prevents premature venting from occurring before the target temperature and pressure are reached.

[0068] 3 is a diagram illustrating a state in which venting occurs in a secondary battery according to an embodiment of the present invention, specifically, a cross-sectional view illustrating a vent member included in the secondary battery according to an embodiment of the present invention.

[0069] Referring to Figure 3, at temperatures where the battery normally operates, the vent member serves to seal the case from the outside. If the battery temperature rises excessively due to abnormal battery operation, the vent member melts, reducing the sealing strength of the area where the vent member is inserted. This allows gas to escape from this area. For example, if the pressure of the battery's internal gas is applied to the interface between the vent member and the case, a gap may form between the vent member and the case, allowing gas to escape through the gap.

[0070] For example, as shown in Figure 3, venting may occur between the case 13 and the outermost layer 15a. If the battery temperature rises excessively due to abnormal battery operation, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms melts, reducing the sealing strength of the portion where the vent member is inserted. This may cause venting between the case 13 and the outermost layer 15a.

[0071] In one embodiment of the present invention, the vent member 15 may be manufactured by inserting a resin having a higher melting point than linear low-density polyethylene having a comonomer with six or more carbon atoms between the linear low-density polyethylene having a comonomer with six or more carbon atoms, and then fusing the resin. For example, a resin having a higher melting point than linear low-density polyethylene having a comonomer with six or more carbon atoms may be heat-sealed between the linear low-density polyethylene having a comonomer with six or more carbon atoms. As another example, the resin may be fused using an adhesive such as glue.

[0072] In one embodiment of the present invention, the vent member 15 can vent at 100°C to 120°C and discharge or exhaust gas from the storage compartment to the outside of the battery. In particular, the vent member 15 can vent at 100°C to 120°C and a pressure of 1.5 atm or more. By venting using the vent member 15 within the above temperature range and / or pressure conditions, the battery can be sealed when the battery is operating normally, and gas can be discharged only when the battery is operating abnormally.

[0073] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm, less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm at temperatures above 100°C. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm, less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm at temperatures between 100°C and 120°C. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 3 kgf / 15 mm, less than 2 kgf / 15 mm, less than 1 kgf / 15 mm, or less than 0.5 kgf / 15 mm at temperatures above 120°C. If the vent member 15 satisfies the above-described sealing strength requirements within the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, making it easier to achieve venting characteristics.

[0074] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of 6 kgf / 15 mm or more, 8 kgf / 15 mm or more, 10 kgf / 15 mm or more, or 13 kgf / 15 mm or more at room temperature to 60°C. When the vent member 15 satisfies the above-described sealing strength within the above-described temperature range, the portion of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal battery operation, making it easy to ensure the hermeticity of the battery. Furthermore, the maximum sealing strength at room temperature to 60°C can be further improved compared to when the vent member 15 contains only linear low-density polyethylene having a comonomer having 6 or more carbon atoms. This improves the rigidity of the vent member 15, making it easier to prevent premature venting before the target temperature and pressure are reached.

[0075] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm at temperatures above 100°C and a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C. When the vent member 15 satisfies the above-mentioned sealing strength, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, and venting characteristics can be easily achieved. Furthermore, during normal battery operation, the case 13 has excellent sealing strength, making it easy to ensure the hermeticity of the battery.

[0076] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm or less than 3 kgf / 15 mm at temperatures above 100°C. In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm or less than 3 kgf / 15 mm at temperatures between 100°C and 120°C. In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 2 kgf / 15 mm, less than 1 kgf / 15 mm, or less than 0.5 kgf / 15 mm at temperatures above 120°C. If the vent member 15 satisfies the above-described sealing strength requirements within the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, making it easier to achieve venting characteristics.

[0077] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of 4.5 kgf / 15 mm or more, 5 kgf / 15 mm or more, 6 kgf / 15 mm or more, 7 kgf / 15 mm or more, or 8 kgf / 15 mm or more at room temperature to 60°C. When the vent member 15 satisfies the above-described sealing strength within the above-described temperature range, even with the vent member 15 inserted, the portion of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal battery operation, making it easy to ensure the hermeticity of the battery. In addition, the average sealing strength at room temperature to 60°C may be even higher than when the vent member 15 contains only linear low-density polyethylene having a comonomer having 6 or more carbon atoms. This improves the rigidity of the vent member 15, making it easier to prevent premature venting before the target temperature and pressure are reached.

[0078] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm at temperatures above 100°C and an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C. When the vent member 15 has the above-described sealing strength within the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, making it easy to achieve venting characteristics. Furthermore, the case 13 has excellent sealing strength during normal battery operation, making it easy to ensure the hermeticity of the battery.

[0079] The sealing strength of the vent member 15 according to temperature can be measured by cutting the portion of the case 13 where the vent member 15 is inserted into a piece 15 mm wide and 5 cm long, opening both ends 180°, fixing the piece to a UTM jig, and conducting a tensile test at a speed of 5 mm / min.

[0080] Here, the maximum sealing strength refers to the maximum value at which the case 13 breaks. In addition, the average sealing strength refers to the average value when the case 13 is stretched by 8 mm at 4.5 kgf / 15 mm if the maximum sealing strength is 4.5 kgf / 15 mm or more, and refers to the average value when the case 13 is stretched by 8 mm at the maximum sealing strength if the maximum sealing strength is less than 4.5 kgf / 15 mm.

[0081] In one embodiment of the present invention, the outermost layer 15a of the vent member 15 may contain linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0082] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may have a lower melting point than the sealant resin. If the melting point of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms is lower than that of the sealant resin, the linear low-density polyethylene may melt faster than the sealant resin at high temperatures. This reduces the sealing strength of the portion where the vent member 15 is inserted compared to the sealing strength of the case portion containing the sealant resin, making it easier to achieve venting characteristics. In particular, venting is easier between the case 13 and the outermost layer 15a.

[0083] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer with six or more carbon atoms may have a melting point of 100°C to 120°C, 105°C to 120°C, or 110°C to 120°C. When the linear low-density polyethylene having a comonomer with six or more carbon atoms satisfies the above-mentioned range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, above 100°C, making it easier to achieve venting properties. In particular, venting occurs more easily between the case 13 and the outermost layer 15a.

[0084] The melting point of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms can be measured using a differential scanning calorimeter (DSC). For example, the temperature of a sample is increased from 30°C to 280°C at 10°C / min, maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. The temperature of the sample is then increased from 30°C to 280°C at 10°C / min, and maintained at 280°C for 10 minutes, so that the melting point can be measured.

[0085] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is polymerized in the presence of a metallocene catalyst, it has more advantageous sealing strength and physical properties than when polymerized in the presence of a Ziegler-Natta catalyst.

[0086] In one embodiment of the present invention, the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 15 wt% or less, 12 wt% or less, 11.8 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, or 7.6 wt% or less, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. The content of the comonomer having 6 or more carbon atoms may be 5 wt% or more, 7.6 wt% or more, 8 wt% or more, 9.0 wt% or more, 10 wt% or more, 11.8 wt% or more, or 12 wt% or more, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. When the content of the comonomer having 6 or more carbon atoms is within the above range, it is possible to easily prevent a decrease in intermolecular packing density, which would otherwise result in a decrease in sealing strength during normal battery operation.

[0087] The content of the comonomer having 6 or more carbon atoms can be measured by H-NMR. For example, about 10 mg of a sample is completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, and then sampled into an NMR tube. 1 It can be measured using H-NMR.

[0088] In one embodiment of the present invention, the weight-average molecular weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 100,000 g / mol to 400,000 g / mol, 200,000 g / mol to 350,000 g / mol, or 230,000 g / mol to 300,000 g / mol. When the weight-average molecular weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above range, the sealing strength during normal operation of the battery may be further improved.

[0089] In one embodiment of the present invention, the polydispersity index (PDI) of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 4 or less, 3.8 or less, 3.796 or less, 3.5 or less, 3.023 or less, 3 or less, 2.7 or less, or 2.674 or less. The polydispersity index (PDI) may be 1.0 or more. When the polydispersity index of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above range, the molecular weight distribution is narrow, and thus the battery exhibits better sealing strength and physical properties during normal operation.

[0090] The weight average molecular weight and polydispersity index of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms can be measured by gel permeation chromatography (GPC) under the following conditions.

[0091] -Column: Tosoh HLC-8321 GPC / HT Solvent: TCB (trichlorobenzene) + 0.04% BHT (dried with 0.1% CaCl2) -Flow rate: 1.0ml / min -Sample concentration: 1.5mg / ml -Injection volume: 300μl -Column temperature: 160℃ -Detector: RI detector -Standard: Polystyrene (corrected by a cubic function)

[0092] In one embodiment of the present invention, the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be similar. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 10°C or less, or 5°C or less. Furthermore, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 0.1°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms satisfies the above-mentioned range, the fusion properties between the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms during normal operation of the battery are more excellent.

[0093] In one embodiment of the present invention, the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90°C to 115°C, 95°C to 110°C, 100°C to 110°C, or 105°C to 110°C. When the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above-mentioned range, the fusion properties between the sealant resin and the linear low-density polyethylene having a comonomer having 6 or more carbon atoms become more excellent.

[0094] In one embodiment of the present invention, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is 10°C or less, and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90°C to 115°C.

[0095] The crystallization temperature can be measured using a differential scanning calorimeter (DSC). For example, the temperature of a sample is increased from 30°C to 280°C at 10°C / min, then maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. The temperature of the sample is then increased from 30°C to 280°C at 10°C / min, and maintained at 280°C for 10 minutes to measure the crystallization temperature.

[0096] In one embodiment of the present invention, the melting point of the resin having a higher melting point than linear low-density polyethylene having a comonomer with six or more carbon atoms may be greater than 120° C. to 140° C., 130° C. to 140° C., or 132° C. to 138° C. When the melting point of the resin having a higher melting point than linear low-density polyethylene having a comonomer with six or more carbon atoms falls within the above-mentioned range, the rigidity of vent member 15 can be more easily improved.

[0097] In one embodiment of the present invention, the resin having a melting point higher than that of linear low-density polyethylene having a comonomer having 6 or more carbon atoms may include high-density polyethylene, random polypropylene, or a mixture thereof.

[0098] In one embodiment of the present invention, the vent member 15 may have various shapes so that the gas can be smoothly directed to the vent area. For example, the vent member 15 may have a film shape.

[0099] The vent member 15 may be formed to have a predetermined thickness.

[0100] In one embodiment of the present invention, as shown in Figures 1 and 2, the vent member 15 may be located at the sealing portion.

[0101] 2, the vent member 15 may be located in the sealing portion at a corner of the case. For example, the vent member 15 may be located at a corner of the sealing portion where the electrode leads 11 are exposed to the outside. Specifically, the vent member 15 may be located in the sealing portion close to the electrode leads 11, excluding the areas between the electrode leads 11. When the vent member 15 is located at a corner of the sealing portion where the electrode leads 11 are exposed to the outside, the amount of gas discharged toward the electrode leads 11 can be minimized, further improving the safety of the battery.

[0102] In one embodiment of the present invention, when the sealing portion 13b is sealed on three sides, the folded side of the case and one end of the vent member 15 can be in close contact with each other.

[0103] Furthermore, the vent member 15 may be inserted into the case 13 to vary the insertion length or to control the venting pressure and position, depending on the design. Here, the insertion length of the vent member refers to the maximum distance between one end and the other end of the vent member based on the protruding direction of the electrode lead.

[0104] In one embodiment of the present invention, the insertion length of the vent member 15 may be smaller than the width of the sealing portion 13b. For example, the insertion length of the vent member 15 may be less than about 50% of the width of the sealing portion 13b. Here, the width of the sealing portion 13b refers to the maximum distance between one end and the other end of the sealing portion 13b based on the protruding direction of the electrode lead 11.

[0105] In other embodiments of the present invention, the insertion length of the vent member 15 may be greater than the width of the sealing portion 13b. For example, the vent member 15 may be inserted through the storage portion 13a so as to be exposed to the outside of the case 13.

[0106] In one embodiment of the present invention, the vent member 15 may further include an adhesive layer for smoother placement.

[0107] FIG. 4 is a plan view showing a secondary battery according to another embodiment of the present invention.

[0108] Referring to FIG. 4, the vent member 15 may be located in the sealing portion except for the sealing portion where the electrode lead 11 is exposed to the outside.

[0109] FIG. 5 is a plan view showing a secondary battery according to still another embodiment of the present invention.

[0110] 5, the vent member 15 may be located in a sealing portion where the electrode leads 11 are exposed to the outside. For example, the vent member 15 may be located in a sealing portion between the electrode leads 11.

[0111] A secondary battery according to one embodiment of the present invention includes a vent member having a three-layer or greater structure, with the outermost layer including a linear low-density polyethylene having a comonomer with six or more carbon atoms and the middle layer including a resin with a higher melting point than the linear low-density polyethylene having a comonomer with six or more carbon atoms. This structure reduces sealing strength at high temperatures, enabling smoother and faster directional venting, allowing gas to be released in a specific direction. This minimizes damage to electrodes caused by gas when thermal runaway occurs, i.e., when the internal temperature of the secondary battery rises. Furthermore, the improved rigidity of the vent member prevents premature venting before the target temperature and pressure are reached.

[0112] In one embodiment of the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery, and particularly, the secondary battery may be a pouch-type secondary battery.

[0113] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0114] Example 1 Linear low-density polyethylene (ExxonMobil, Exceed) with a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst. TM High-density polyethylene (Sabic®, HDPE F04660, melting point: 135°C, weight-average molecular weight: 350,000 g / mol, crystallization temperature: 119°C) was inserted between two resins (1018) (melting point: 119°C, comonomer content relative to total resin content: 7.6 wt%, weight-average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C), and the resulting mixture was heat-sealed at 100°C. The resulting product was then cut to a width of 100 mm to produce a vent member.

[0115] An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0116] Thereafter, the manufactured vent member was inserted between the polypropylene resins, and then heat-sealed at 200° C. and 0.08 MPa for 1.5 seconds to manufacture a secondary battery.

[0117] Comparative Example 1 An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0118] Thereafter, the polypropylene resin was heat-sealed to manufacture a secondary battery. Comparative Example 2

[0119] An upper pouch and a lower pouch, each having polyethylene terephthalate / aluminum foil / polypropylene resin laminated in this order, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, each having a positive electrode / separator / negative electrode laminated in this order, was placed inside.

[0120] Thereafter, a linear low-density polyethylene (Exceed) having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst was placed between the polypropylene resins. TM , 1018) (melting point: 119°C, comonomer content relative to total resin content: 7.6 wt%, weight average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C) was inserted, and then heat-sealed at 200°C and 0.08 MPa for 1.5 seconds to manufacture a secondary battery.

[0121] Evaluation example 1: Measuring sealing strength according to temperature Using the secondary batteries manufactured in Example 1 and Comparative Example 2, the case where the vent member was inserted was cut into a 15 mm wide and 5 cm long piece at the temperature indicated below, and then both ends were opened 180°, fixed to a UTM jig, and a tensile test was performed at a speed of 5 mm / min. The sealing strength of the case is shown in Table 1 below.

[0122] Using the secondary battery manufactured in Comparative Example 1, the sealing portion of the case was cut to a width of 15 mm and a length of 5 cm at the following temperature, and then both ends were opened 180°, fixed to a UTM jig, and a tensile test was performed at a speed of 5 mm / min. The sealing strength of the case at this time is shown in Table 1 below.

[0123] In this case, the maximum sealing strength means the maximum value at which the case breaks, and the average sealing strength means the average value when the case is stretched by 8 mm at 4.5 kgf / 15 mm if the maximum sealing strength is 4.5 kgf / 15 mm or more, and means the average value when the case is stretched by 8 mm at the maximum sealing strength if the maximum sealing strength is less than 4.5 kgf / 15 mm.

[0124] [Table 1]

[0125] From Table 1, it can be seen that the maximum sealing strength and average sealing strength at room temperature to 60°C of the case portion into which the vent member is inserted in the secondary battery produced in Example 1 are higher than the maximum sealing strength and average sealing strength at room temperature to 60°C of the case portion into which the vent member is inserted in the secondary battery produced in Comparative Example 2. This improves the rigidity of vent member 15 compared to when it contains only linear low-density polyethylene having a comonomer with 6 or more carbon atoms, making it possible to prevent early venting before the target temperature and pressure are reached.

[0126] Furthermore, it was confirmed that the maximum sealing strength and average sealing strength at 100°C or higher of the case portion into which the vent member was inserted in the secondary battery manufactured in Example 1 were similar to the maximum sealing strength and average sealing strength at 100°C or higher of the case portion into which the vent member was inserted in the secondary battery manufactured in Comparative Example 2. As a result, the secondary battery manufactured in Example 1 was able to ensure appropriate sealing strength when the battery was operating normally, and at the same time, when the battery became too hot due to an abnormality, it was able to release gas through the vent member, the sealing strength of which was weakened.

[0127] Meanwhile, the maximum and average sealing strengths of the case of the secondary battery manufactured in Comparative Example 1 at room temperature to 60°C are similar to those of the case portion into which the vent member is inserted at room temperature to 60°C of the secondary battery manufactured in Example 1. However, the maximum and average sealing strengths at 100°C or higher are significantly higher than those of the case portion into which the vent member is inserted at 100°C or higher of the secondary battery manufactured in Example 1. If the battery becomes too hot due to an abnormal phenomenon, gas may be released in unspecified directions, which may cause a chain reaction fire of the battery. [Explanation of symbols]

[0128] 10 Secondary battery 11 Electrode Lead 12 Electrode assembly 13 cases 13a Storage area 13b Sealing part 14 Lead Film 15 Venting material

Claims

1. an electrode assembly; an electrode lead attached to the electrode assembly; a case for accommodating the electrode assembly therein; a lead film formed to cover a part of an outer surface of the electrode lead and interposed between the electrode lead and the case; a vent area formed in at least a portion of the case; a vent member inserted into the vent area and having a structure of three or more layers; the case includes a sealing portion formed to seal the electrode assembly, the vent member is located in a sealing portion other than a sealing portion where the electrode lead is exposed to the outside, the vent member includes, in an outermost layer, a linear low-density polyethylene having a comonomer having 6 or more carbon atoms, and, in an intermediate layer, a resin having a higher melting point than the linear low-density polyethylene having a comonomer having 6 or more carbon atoms; the resin having a melting point higher than that of linear low-density polyethylene having a comonomer having 6 or more carbon atoms comprises high-density polyethylene, random polypropylene, or a mixture thereof; the melting point of the resin having a higher melting point than the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is 132°C to 138°C; The linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a melting point of 100°C to 119°C.

2. The secondary battery of claim 1 , wherein venting occurs between the case and the outermost layer.

3. the sealing portion includes a sealant resin; The secondary battery according to claim 1 , wherein the linear low-density polyethylene having a comonomer having six or more carbon atoms contained in the vent member has a melting point lower than that of the sealant resin.

4. 4. The secondary battery according to claim 1, wherein the outermost layer contains a linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

5. 2. The secondary battery according to claim 1, wherein the vent member melts at 100° C. to 120° C. to release gas.

6. The secondary battery according to claim 5 , wherein the vent member vents at a pressure of 1.5 atm or more.

7. The secondary battery according to claim 1 , wherein the vent member has a maximum sealing strength of less than 6 kgf / 15 mm at 100° C. or higher.

8. 2. The secondary battery according to claim 1, wherein the vent member has an average sealing strength of less than 4.5 kgf / 15 mm at 100°C or higher.

9. 2. The secondary battery according to claim 1, wherein the vent member has a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

10. 2. The secondary battery according to claim 1, wherein the vent member has an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

11. 2. The secondary battery according to claim 1, wherein the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is 15% by weight or less, relative to 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

12. 2. The secondary battery according to claim 1, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a polydispersity index of 4 or less.

13. 4. The secondary battery according to claim 3, wherein the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is 10°C or less.

14. 14. The secondary battery according to claim 13, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a crystallization temperature of 90°C to 115°C.

15. 2. The secondary battery according to claim 1, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a weight-average molecular weight of 100,000 g / mol to 400,000 g / mol.

16. The secondary battery according to claim 1 , wherein the secondary battery is a pouch-type secondary battery.

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