A secondary battery

Abstract

A secondary battery according to one embodiment of the present invention comprises: an electrode assembly; an electrode lead attached to the electrode assembly; a case housing the electrode assembly inside; a lead film formed to surround 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 into the vent region and having a structure of three or more layers; wherein the vent member comprises linear low-density polyethylene having a comonomer having 6 or more carbon atoms in the outermost layer and a resin having a higher melting point than the linear low-density polyethylene having a comonomer having 6 or more carbon atoms in the middle layer.

Description

Technology Field

[0001] The present invention relates to a secondary battery, and more specifically, to a secondary battery having a vent member. Background Technology

[0002] Rechargeable batteries can be applied to a wide variety of products and possess excellent electrical characteristics, such as high energy density. They are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) powered by electricity. Rechargeable batteries are attracting attention as a new energy source for improving environmental friendliness and energy efficiency, as they can significantly reduce the use of fossil fuels and do not generate byproducts during the energy consumption process.

[0003] Currently widely used rechargeable batteries include lithium-ion batteries, lithium-polymer batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries.

[0004] A secondary battery generally has a structure in which an electrode assembly comprising at least one unit cell having a positive / separator / negative electrode structure is housed in a case of a laminate sheet in which an outer layer, a metal barrier layer, and a sealant layer are sequentially laminated, and the electrode assembly is sealed by fusing the sealant resin of the sealant layer.

[0005] In conventional secondary batteries, the battery may ignite due to various causes such as short circuits, overcharging or over-discharging, or temperature control. At this time, as the temperature inside the secondary battery rises rapidly, a thermal propagation phenomenon occurs in which heat is transferred to adjacent cells, which can cause the fire to become even larger.

[0006] In the event of thermal runaway, that is, when the internal temperature of the secondary battery rises, directional venting characteristics are required to expel gas in a specific direction in order to minimize electrode damage caused by gas. However, conventional secondary batteries have a problem in that it is difficult to induce gas expulsion in a specific direction.

[0007] Accordingly, the present invention aims to provide a secondary battery with improved safety by inducing gas discharge in a specific direction. The problem to be solved

[0008] Therefore, the problem that the present invention aims to solve is to provide a secondary battery with improved safety by being able to induce gas discharge in a specific direction. means of solving the problem

[0009] In order to solve the above problem, according to one aspect of the present invention, secondary batteries of the following embodiments are provided.

[0010] The first embodiment is,

[0011] Electrode assembly;

[0012] Electrode leads attached to the above electrode assembly;

[0013] A case housing the electrode assembly inside;

[0014] A lead film formed to wrap a portion of the outer surface of the electrode lead and interposed between the electrode lead and the case;

[0015] A vent area formed in at least a part of the above case; and

[0016] A vent member inserted into the above vent area and having a structure of three or more layers including a first resin in the lowest layer, a second resin in the upper layer, and a third resin in the middle layer; comprising

[0017] The second resin is a resin with a higher melting point than the first resin, and

[0018] The present invention relates to a secondary battery characterized in that the third resin has a higher melting point than the second resin.

[0019] The second embodiment is, in the first embodiment,

[0020] Venting may occur between the above middle layer and the above bottom layer.

[0021] The third embodiment is, in the first embodiment or the second embodiment,

[0022] The melting point of the first resin above may be 90°C or higher and less than 100°C.

[0023] The fourth embodiment is, in any one of the first to third embodiments,

[0024] The first resin above may be linear low-density polyethylene having a comonomer having 8 carbon atoms.

[0025] The fifth embodiment is, in any one of the first to fourth embodiments,

[0026] The Poly Dispersity Index (PDI) of the first resin may be less than 2.6.

[0027] The sixth embodiment is, in either the fourth embodiment or the fifth embodiment,

[0028] In the linear low-density polyethylene having the above-mentioned carbon-8 comonomer, the content of the above-mentioned carbon-8 comonomer may be 12 weight% or more relative to 100 weight% of the linear low-density polyethylene having the above-mentioned carbon-8 comonomer.

[0029] The seventh embodiment is, in any one of the first to sixth embodiments,

[0030] The crystallization temperature of the first resin above may be 80°C to 90°C.

[0031] The eighth embodiment is, in any one of the first to seventh embodiments,

[0032] The weight-average molecular weight of the first resin may be 100,000 g / mol to 250,000 g / mol.

[0033] The ninth embodiment is, in any one of the fourth to eighth embodiments,

[0034] The linear low-density polyethylene having the above-mentioned carbon-8 comonomer may be polymerized in the presence of a metallocene catalyst.

[0035] The 10th embodiment is, in any one of the 1st to 9th embodiments,

[0036] The above case may have a sealing portion formed to seal the electrode assembly, and the sealing portion may include a sealant resin, and the linear low-density polyethylene having a carbon-8 comonomer of the vent member may have a lower melting point than the sealant resin.

[0037] The 11th embodiment is, in any one of the 1st to 10th embodiments,

[0038] The melting point of the second resin above may be 100°C to 130°C.

[0039] The 12th embodiment is, in any one of the 1st to 11th embodiments,

[0040] The above second resin may be linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0041] The 13th embodiment is, in any one of the 1st to 12th embodiments,

[0042] The Poly Dispersity Index (PDI) of the second resin may be 2.6 or higher and 4 or lower.

[0043] The 14th embodiment is, in the 12th embodiment or the 13th embodiment,

[0044] In the linear low-density polyethylene having a comonomer with 6 or more carbon atoms, the content of the comonomer with 6 or more carbon atoms may be less than 12 weight percent relative to 100 weight percent of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0045] The 15th embodiment is, in any one of the 1st to 14th embodiments,

[0046] The crystallization temperature of the second resin above may be greater than 90°C and less than or equal to 115°C.

[0047] The 16th embodiment is, in any one of the 1st to 15th embodiments,

[0048] The weight-average molecular weight of the second resin may be greater than 250,000 g / mol and less than or equal to 400,000 g / mol.

[0049] The 17th embodiment is, in any one of the 12th to 16th embodiments,

[0050] The linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst.

[0051] The 18th embodiment is, in any one of the 1st to 17th embodiments,

[0052] The melting point of the third resin above may exceed 130℃.

[0053] The 19th embodiment is, in any one of the 1st to 18th embodiments,

[0054] The above third resin may include high-density polyethylene, random polypropylene, or two or more of these.

[0055] The 20th embodiment is, in any one of the 1st to 19th embodiments,

[0056] The above vent member may melt at 100°C or higher to vent gas.

[0057] The 21st embodiment is, in the 20th embodiment,

[0058] The above vent member may be vented at a pressure of 1.5 atm or higher.

[0059] The 22nd embodiment is, in any one of the 1st to 21st embodiments,

[0060] The above vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100°C or higher.

[0061] The 23rd embodiment is, in any one of the 1st to 22nd embodiments,

[0062] The average sealing strength of the above vent member at 100°C or higher may be less than 4.5 kgf / 15 mm.

[0063] The 24th embodiment is, in any one of the 1st to 23rd embodiments,

[0064] The above vent member may have a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

[0065] The 25th embodiment is, in any one of the 1st to 24th embodiments,

[0066] The above vent member may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

[0067] The 26th embodiment is, in any one of the 10th to 25th embodiments,

[0068] The above vent area may be located in the above sealing portion.

[0069] The 27th embodiment is, in the 26th embodiment,

[0070] The above vent area may be located in the corner side sealing portion of the above case.

[0071] The 28th embodiment is, in any one of the 1st to 27th embodiments,

[0072] The above secondary battery may be a pouch-type secondary battery. Effects of the invention

[0073] A secondary battery according to one embodiment of the present invention comprises a vent member having a structure of three or more layers, including a first resin in the bottom layer, a second resin with a melting point higher than that of the first resin in the top layer, and a third resin with a melting point higher than that of the second resin in the middle layer, so that gas discharge into the vent area is facilitated and the rigidity of the vent member can be improved. Accordingly, the safety of the battery is improved. Brief explanation of the drawing

[0074] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the aforementioned description; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings. FIG. 1 is an exploded perspective view of a secondary battery according to one embodiment of the present invention. FIG. 2 is a plan view showing a secondary battery according to one embodiment of the present invention. FIG. 3 is a diagram showing the state in which a vent occurs in a secondary battery according to one embodiment of the present invention. FIG. 4 is a plan view showing a secondary battery according to another embodiment of the present invention. FIG. 5 is a plan view showing a secondary battery according to another embodiment of the present invention. Specific details for implementing the invention

[0075] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0076] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0078] A secondary battery according to one aspect of the present invention comprises: an electrode assembly having an electrode lead attached thereto; a case housing the electrode assembly inside; a lead film formed to surround 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 into the vent region and having a structure of three or more layers, comprising a first resin in the bottom layer, a second resin in the top layer, and a third resin in the middle layer. In this case, the second resin is a resin with a higher melting point than the first resin, and the third resin is a resin with a higher melting point than the second resin.

[0080] FIGS. 1 and FIGS. 2 show a secondary battery according to one embodiment of the present invention.

[0081] Referring to FIGS. 1 and 2, the secondary battery (10) comprises an electrode assembly (12) to which an electrode lead (11) is attached, and a case (13).

[0082] The electrode assembly (12) includes an anode plate, a cathode plate, and a separator. The electrode assembly (12) may have an anode plate and a cathode plate stacked sequentially with a separator in between.

[0083] The positive plate may include a positive current collector made of a metal foil with excellent conductivity, for example, aluminum (Al) foil, and a positive active material layer coated on at least one surface thereof. Additionally, the positive plate may include a positive tab made of a metal material, such as aluminum (Al), at one end. The positive tab may protrude from one end of the positive plate. The positive tab may be welded to one end of the positive plate or joined using a conductive adhesive.

[0084] The cathode plate may include a cathode current collector made of a conductive metal foil, for example, copper (Cu) foil, and a cathode active material layer coated on at least one surface thereof. Additionally, the cathode plate may include a cathode tab formed of a metal material, such as nickel (Ni), at one end. The cathode tab may protrude from one end of the cathode plate. The cathode tab may be welded to one end of the cathode plate or joined using a conductive adhesive.

[0085] A separator is positioned between the positive plate and the negative plate to electrically insulate the positive plate and the negative plate from each other. The separator may be a porous membrane to allow lithium ions to pass between the positive plate and the negative plate. The separator may include a porous membrane using, for example, polyethylene (PE), polypropylene (PP), or a composite film thereof.

[0086] An inorganic coating layer may be provided on the surface of the separation membrane. The inorganic coating layer may have a structure in which inorganic particles are bonded to each other by a binder to form an interstitial volume between the particles.

[0087] The electrode assembly (12) may be a jelly-roll (wound type) electrode assembly having a structure in which long sheet-type positive and negative electrodes are wound with a separator interposed therebetween, a stack type (stacked type) electrode assembly having a plurality of positive and negative electrodes cut into units of a predetermined size and sequentially stacked with a separator interposed therebetween, or a stack / folding type electrode assembly having a structure in which bi-cells or full cells having a predetermined unit of positive and negative electrodes stacked with a separator interposed therebetween are wound.

[0089] The above case (13) serves to house the electrode assembly (12).

[0090] In one embodiment of the present invention, the case (13) may have a storage portion (13a) for housing an electrode assembly (12) as shown in FIG. 1, and a sealing portion (13b) formed to seal the electrode assembly (12).

[0091] The sealing portion (13b) may include a sealant resin, and the sealant resin may be fused along the outer surface of the storage portion (13a) to seal the electrode assembly (12).

[0092] In one embodiment of the present invention, the case (13) may be provided in the form of a film having a multilayer structure including an outer layer for protection against external impact, a metal barrier layer for blocking moisture, and a sealant layer for sealing the case.

[0093] The above outer layer may include a polyester-based film using poly(ethylene terephthalate; PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, nylon, etc., and may be composed of a single layer or multiple layers.

[0094] The above metal barrier layer may include aluminum, copper, etc.

[0095] The sealant layer may include a sealant resin and may be composed of a single layer or multiple layers.

[0096] The sealant resin may include polypropylene (PP), acid-modified polypropylene (PPA), random polypropylene, ethylene-propylene copolymer, or two or more of these. The ethylene-propylene copolymer may include ethylene-propylene rubber, ethylene-propylene block copolymer, etc., but is not limited thereto.

[0097] In one embodiment of the present invention, the case (13) may be in the form of a pouch.

[0098] A pouch-shaped 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 may be arranged so that the sealant resins face each other, and then the opposing sealant resins are fused together by heat and pressure to seal the battery.

[0099] The fusion of the sealing portion (13b) may be thermal fusion, ultrasonic fusion, etc., but is not particularly limited as long as the sealing portion (13b) can be fused.

[0100] In some embodiments, the sealing portion (13b) may be four-sided or three-sided sealing at the edge of the case (13). In a three-sided sealing structure, after the upper pouch and the lower pouch are formed on a single pouch sheet, the boundary surface between the upper pouch and the lower pouch is folded so that the storage portions (13a) formed in the upper pouch and the lower pouch overlap, and the edges of the remaining three sides excluding the folded portion are sealed.

[0102] As shown in FIG. 1, the electrode lead (11) can be housed in the case (13) such that a portion of the electrode lead (11) is exposed to the outside of the case (13).

[0103] A secondary battery (10) according to one embodiment of the present invention has a lead film (14).

[0104] 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) may be interposed between the electrode lead (11) and the sealing portion (13b) of the case (13) at the portion where the electrode lead (11) protrudes or extends from the case (13) to help secure the electrode lead (11) and the case (13).

[0106] Referring to FIGS. 1 and 2, a secondary battery (10) according to one embodiment of the present invention has a vent area (not shown) formed in at least a part of the case (13), and a vent member (15) may be inserted into the vent area. When a thermal runaway phenomenon occurs, the vent member (15) can induce the discharge of gas in a specific direction to improve the safety of the battery.

[0107] The vent member (15) and the case (13) may be overlapped through heat fusion. In another example, the vent member (15) and the case (13) may be overlapped through an adhesive such as glue. In yet another example, the vent member (15) and the case (13) may be physically joined together through a clip or the like. In yet another example, at least a portion of the vent member (15) may be embedded within a film constituting the case (13), such as a sealant resin.

[0108] The above vent member (15) has a structure of three or more layers. The above vent member (15) includes a first resin in the lowest layer (15a), a second resin in the uppermost layer (15b), and a third resin in the middle layer (15c). By including resins with different melting points on one side and the other side of the vent member (15), a vent can occur on one side of the vent member (15). Accordingly, it may be easy to control the direction of the vent in one direction. For example, a vent can occur on one side of the vent member (15) containing the first resin with the lowest melting point.

[0109] If the rigidity of the vent member (15) is insufficient, premature venting may occur under conditions prior to the desired temperature and pressure when the internal pressure of the battery increases. When the third resin is included, the third resin has a higher melting point than the first resin and the second resin, so the rigidity of the vent member (15) can be improved compared to when only the first resin and / or the second resin is included. Accordingly, premature venting can be prevented from occurring under conditions prior to the desired temperature and pressure when the internal pressure of the battery increases.

[0110] The above vent member (15) has excellent sealing performance of the case (13) in a normal temperature range, for example, at room temperature of 60°C, and can realize or induce venting by reducing the sealing strength of the case into which the vent member (15) is inserted at a high temperature, for example, 100°C or higher.

[0111] FIG. 3 is a diagram showing a state in which a vent occurs in a secondary battery according to one embodiment of the present invention. Specifically, FIG. 3 is a cross-sectional view illustrating a vent member in a secondary battery according to one embodiment of the present invention.

[0112] Referring to FIG. 3, at the normal operating temperature of the battery, the vent member serves to seal the case from the outside. If the temperature of the battery rises excessively due to abnormal operation of the battery, the vent member melts, and the sealing strength of the part where the vent member is inserted decreases. Consequently, gas can be discharged through this part. For example, as the pressure of the gas inside the battery is applied to the interface between the vent member and the case, a gap is formed between the vent member and the case, through which gas can be discharged.

[0113] For example, if the temperature of the battery rises excessively due to abnormal operation of the battery, the first resin contained in the lowest layer (15a), which has a lower melting point than the middle layer (15c) and the top layer (15b), melts. As the first resin melts, the sealing strength of the part where the vent member is inserted decreases. Since the second resin has a higher melting point than the first resin, the lowest layer (15a) melts faster than the top layer (15b). Accordingly, it is easier for a vent to occur in the lowest layer (15a) than in the top layer (15b). Since the third resin has a higher melting point than the first and second resins, the middle layer (15c) may not melt even if the temperature of the battery rises.

[0114] As described in FIG. 3, a vent may occur between the middle layer (15c) and the lowest layer (15a). Since the fusion characteristics between the middle layer (15c) and the lowest layer (15a) are inferior to the fusion characteristics between the lowest layer (15a) and the case (13), a vent may occur between the middle layer (15c) and the lowest layer (15a).

[0115] In one embodiment of the present invention, the vent member (15) can be manufactured by sequentially laminating a first resin, a third resin, and a second resin, and then fusing them together. For example, the first resin, the third resin, and the second resin can be sequentially laminated and then heat-fused. In another example, they can be fused using an adhesive such as glue.

[0117] In one embodiment of the present invention, the vent member (15) may be vented at 100°C or higher. The vent member (15) may vent earlier than when it contains only the second resin.

[0118] In one embodiment of the present invention, the vent member (15) can be vented at 100°C or higher, for example, from 100°C to 120°C, so as to discharge or exhaust gas from the storage portion to the outside of the battery. In particular, the vent member (15) can be vented at 100°C or higher and at a pressure of 1.5 atm or higher. As the vent member (15) is vented in the aforementioned temperature range and / or pressure conditions, the battery can be sealed when the battery is operating normally, while gas discharge can be induced only when the battery is operating abnormally.

[0119] In one embodiment of the present invention, the vent member (15) may have a lower maximum sealing strength at 100°C or higher than when it contains only the second resin. Accordingly, venting may occur earlier than when it contains only the second resin.

[0120] 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 100°C or higher, or less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm, or less than 3 kgf / 15 mm, or less than 2.6 kgf / 15 mm. 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 100°C to 120°C, or less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm, or less than 3 kgf / 15 mm, or less than 2.6 kgf / 15 mm. In one embodiment of the present invention, the vent member (15) may have a maximum sealing strength of less than 3 kgf / 15 mm, or less than 2 kgf / 15 mm, or less than 1 kgf / 15 mm, or less than 0.5 kgf / 15 mm, or less than 0.1 kgf / 15 mm, or less than 0.05 kgf / 15 mm at 120°C or higher. When the vent member (15) satisfies the sealing strength described above in the aforementioned temperature range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at a high temperature, e.g. 100°C or higher, making it easier to implement the vent characteristic.

[0121] In one embodiment of the present invention, the maximum sealing strength at room temperature to 60°C may be further improved than when the vent member (15) comprises only the second resin. Accordingly, the rigidity of the vent member (15) is improved, making it easier to prevent premature venting prior to the desired temperature and pressure.

[0122] In one embodiment of the present invention, the vent member (15) may have a maximum sealing strength of 6 kgf / 15 mm or more, or 8 kgf / 15 mm or more, or 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 sealing strength described above in the aforementioned temperature range, even if the vent member (15) is inserted, the part of the case (13) into which the vent member (15) is inserted may have excellent sealing strength during normal operation of the battery, making it easy to secure the sealing of the battery.

[0123] 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 100°C or higher, and the vent member (15) may have a maximum sealing strength of 6 kgf / 15 mm or higher at room temperature to 60°C. When the vent member (15) satisfies the aforementioned sealing strength, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at high temperatures, e.g., 100°C or higher, making it easier to implement vent characteristics. Additionally, during normal operation of the battery, the case (13) may have excellent sealing strength, making it easier to secure the sealing performance of the battery.

[0124] In one embodiment of the present invention, the vent member (15) may have a lower average sealing strength at 100°C or higher than when it contains only the second resin. Accordingly, venting may occur earlier than when it contains only the second resin.

[0125] 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 100°C or higher, or less than 3 kgf / 15 mm, or less than 2.1 kgf / 15 mm. 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 100°C to 120°C, or less than 3 kgf / 15 mm, or less than 2.1 kgf / 15 mm. In one embodiment of the present invention, the vent member (15) may have an average sealing strength of less than 2 kgf / 15 mm at 120°C or higher, or less than 1 kgf / 15 mm, or less than 0.5 kgf / 15 mm, or less than 0.1 kgf / 15 mm, or less than 0.05 kgf / 15 mm. When the vent member (15) satisfies the aforementioned sealing strength in the aforementioned temperature range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at a high temperature, for example, 100°C or higher, making it easier to implement the vent characteristic. When the vent member (15) satisfies the aforementioned sealing strength in the aforementioned temperature range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at a high temperature, for example, 100°C or higher, making it easier to implement the vent characteristic.

[0126] In one embodiment of the present invention, the average sealing strength at room temperature to 60°C may be further improved compared to when the vent member (15) comprises only the second resin. Accordingly, the rigidity of the vent member (15) is improved, making it easier to prevent premature venting prior to the desired temperature and pressure.

[0127] 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 at room temperature to 60°C, or 5 kgf / 15 mm or more, or 6 kgf / 15 mm or more, or 7 kgf / 15 mm or more, or 8 kgf / 15 mm or more. When the vent member (15) satisfies the sealing strength described above in the aforementioned temperature range, even if the vent member (15) is inserted, the part of the case (13) into which the vent member (15) is inserted may have excellent sealing strength during normal operation of the battery, making it easy to secure the sealing of the battery.

[0128] 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 100°C or higher, and an average sealing strength of 4.5 kgf / 15 mm or higher at room temperature to 60°C. When the vent member (15) has the aforementioned sealing strength in the aforementioned temperature range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at high temperatures, e.g. 100°C or higher, making it easier to implement vent characteristics. Additionally, the case (13) may have excellent sealing strength during normal operation of the battery, making it easier to secure the sealing performance of the battery.

[0129] The sealing strength of the vent member (15) according to temperature can be measured by cutting the case (13) of the part into which the vent member (15) is inserted to a width of 15 mm and a length of 5 cm, spreading both ends 180° and clamping them in a UTM jig, and then performing a tensile test at a speed of 5 mm / min.

[0130] At this time, the maximum sealing strength refers to the maximum value when the case (13) breaks, and the average sealing strength refers to the average value when the case (13) is stretched by 8 mm from 4.5 kgf / 15 mm when the maximum sealing strength is 4.5 kgf / 15 mm or more, and the average value when the case (13) is stretched by 8 mm from the maximum sealing strength when the maximum sealing strength is less than 4.5 kgf / 15 mm.

[0132] In one embodiment of the present invention, the melting point of the first resin may be less than 100°C. For example, the melting point of the first resin may be 90°C or higher and less than 100°C, or 90°C to 99°C, or 95°C to 99°C. When the melting point of the first resin satisfies the aforementioned range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at a high temperature, e.g. 100°C or higher, making it easier to implement vent characteristics. In particular, venting may occur earlier than when only the second resin is included.

[0133] Even if the melting point of the first resin is less than 100°C, it is used in the vent member (15) together with another resin that can compensate for this, so that venting at high temperatures is easier and the rigidity of the vent member (15) can be improved. For example, when the battery is in normal operation, the part of the case (13) into which the vent member (15) is inserted has excellent sealing strength, making it easy to ensure the sealing of the battery.

[0134] In this specification, the melting point of the resin can be measured using a differential scanning calorimeter (DSC). For example, the temperature of the sample is increased from 30°C to 280°C at a rate of 10°C / min, maintained at 280°C for 10 minutes, cooled down to 30°C at a rate of 10°C / min, and maintained at 30°C for 10 minutes. Afterward, the melting point can be measured by increasing the temperature of the sample from 30°C to 280°C at a rate of 10°C / min and maintaining the temperature at 280°C for 10 minutes.

[0135] In one embodiment of the present invention, the Poly Dispersity Index (PDI) of the first resin may be less than 2.6, or 2.59 or less, or 2.551 or less. The Poly Dispersity Index (PDI) of the first resin may be 1 or more. Venting may be more easily facilitated in the bottom layer of the vent member containing the first resin.

[0136] In one embodiment of the present invention, the weight-average molecular weight of the first resin may be 100,000 g / mol to 250,000 g / mol, or 15 g / mol to 25 g / mol, or 18 g / mol to 22 g / mol. When the weight-average molecular weight of the first resin satisfies the aforementioned range, the first resin may be more likely to have a low melting point, for example, a melting point of less than 100°C, and accordingly, the sealing strength of the vent member may be more easily lowered at high temperatures, for example, 100°C or higher, making it more easy to induce early venting.

[0137] In this specification, the weight-average molecular weight and polydispersity index of the resin may be measured by gel permeation chromatography (GPC) under the following conditions.

[0138] - Column: Tosoh HLC-8321 GPC / HT

[0139] - Solvent: TCB (Trichlorobenzene) + 0.04% BHT (after drying with 0.1% CaCl2)

[0140] - Flow rate: 1.0 ml / min

[0141] - Sample concentration: 1.5 mg / ml

[0142] - Infusion volume: 300 µl

[0143] - Column temperature: 160℃

[0144] - Detector: RI detector

[0145] - Standard: Polystyrene (corrected by a cubic function)

[0147] In one embodiment of the present invention, there may be a significant difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin may be 20°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin satisfies the aforementioned range, it may be easier for a vent to occur in the lowest layer of the vent member containing the first resin.

[0148] In one embodiment of the present invention, the crystallization temperature of the first resin may be 80°C to 90°C, or 80°C to 85°C. When the crystallization temperature of the first resin satisfies the aforementioned range, it may be easier for a vent to occur in the lowest layer of the vent member containing the first resin. In one embodiment of the present invention, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin is 20°C or more, and the crystallization temperature of the first resin may be 80°C to 90°C.

[0149] In this specification, the crystallization temperature can be measured using a differential scanning calorimeter (DSC). For example, the temperature of a sample can be increased from 30°C to 280°C at a rate of 10°C / min, maintained at 280°C for 10 minutes, cooled down to 30°C at a rate of 10°C / min, and maintained at 30°C for 10 minutes. Subsequently, the crystallization temperature can be measured by increasing the temperature of the sample from 30°C to 280°C at a rate of 10°C / min and maintaining the temperature at 280°C for 10 minutes.

[0150] In one embodiment of the present invention, the first resin may be linear low-density polyethylene having a comonomer having 8 carbon atoms. When the first resin is linear low-density polyethylene having a comonomer having 8 carbon atoms, it may be easier to reduce the sealing strength of the case into which the vent member (15) is inserted at a high temperature, for example, 100°C or higher.

[0151] In one embodiment of the present invention, the content of the comonomer having 8 carbon atoms in the linear low-density polyethylene having 8 carbon atoms may be 12 weight percent or more, or 12 weight percent to 20 weight percent, or 12 weight percent to 18 weight percent relative to 100 weight percent of the linear low-density polyethylene having 8 carbon atoms. When the content of the comonomer having 8 carbon atoms satisfies the aforementioned range, it may be easier for a vent to occur in the bottom layer of the vent member containing the first resin. In this specification, the content of the comonomer can be measured by H-NMR. For example, about 10 mg of the sample is completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, then sampled into an NMR tube, and 1 It can be measured using H-NMR.

[0152] In one embodiment of the present invention, the linear low-density polyethylene having the C8 comonomer may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having the C8 comonomer is polymerized in the presence of a metallocene catalyst, it may be more advantageous in terms of sealing strength and physical properties than when it is polymerized in the presence of a Ziegler-Natta catalyst.

[0153] In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a comonomer having 8 carbon atoms and a melting point of less than 100°C. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a comonomer having 8 carbon atoms and a Poly Dispersity Index (PDI) of less than 2.6. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a comonomer having 8 carbon atoms and a crystallization temperature of 80°C to 90°C. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a comonomer having 8 carbon atoms and a weight-average molecular weight of 100,000 g / mol to 250,000 g / mol.

[0154] In one embodiment of the present invention, the first resin may have a lower melting point than the sealant resin. When the first resin has a lower melting point than the sealant resin, the first resin may melt faster than the sealant resin at high temperatures. Accordingly, as the sealing strength of the portion into which the vent member (15) is inserted is lower than the sealing strength of the case portion containing the sealant resin, it may be easier to implement the vent characteristic.

[0156] In one embodiment of the present invention, the melting point of the second resin may be 100°C to 130°C, or 105°C to 130°C, or 110°C to 125°C, or 115°C to 125°C. When the melting point of the second resin satisfies the aforementioned range, the sealing strength of the part of the case (13) into which the vent member (15) is inserted is reduced at a high temperature, e.g. 100°C or higher, making it easier to implement vent characteristics.

[0157] In one embodiment of the present invention, the Poly Dispersity Index (PDI) of the second resin may be 4 or less, or 3.8 or less, or 3.796 or less, or 3.5 or less, or 3.023 or less, or 3 or less, or 2.7 or less, or 2.674 or less. Additionally, the Poly Dispersity Index may be 2.6 or higher. When the Poly Dispersity Index of the second resin satisfies the aforementioned range, the molecular weight distribution is narrow, so the sealing strength and physical properties may be even better during normal operation of the battery.

[0158] In one embodiment of the present invention, the weight-average molecular weight of the second resin may be greater than 250,000 g / mol and less than or equal to 400,000 g / mol, or between 200,000 g / mol and 350,000 g / mol, or between 230,000 g / mol and 300,000 g / mol. When the weight-average molecular weight of the second resin satisfies the aforementioned range, the sealing strength may be further improved during normal operation of the battery.

[0159] In one embodiment of the present invention, the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be similar. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be 10°C or less, or 5°C or less. Additionally, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be 0.1°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin satisfies the aforementioned range, the fusion characteristics of the sealant resin and the second resin during normal operation of the battery may be even better.

[0160] In one embodiment of the present invention, the crystallization temperature of the second resin may be greater than 90°C and less than or equal to 115°C, or between 95°C and 110°C, or between 100°C and 110°C, or between 105°C and 110°C. When the crystallization temperature of the second resin satisfies the aforementioned range, the fusion characteristics of the sealant resin and the second resin may be even better.

[0161] In one embodiment of the present invention, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin is 10°C or less, and the crystallization temperature of the second resin may be greater than 90°C and less than or equal to 115°C.

[0162] In one embodiment of the present invention, the second resin may be linear low-density polyethylene having a comonomer with 6 or more carbon atoms. When the second resin is linear low-density polyethylene having a comonomer with 6 or more carbon atoms, the sealing performance of the case (13) is excellent in a normal temperature range, e.g., room temperature of 60°C, while the sealing strength of the case with the vent member (15) inserted is reduced at a high temperature, e.g., 100°C or higher, thereby enabling or inducing venting. For example, the second resin may include linear low-density polyethylene having a comonomer with 6 to 8 carbon atoms.

[0163] In one embodiment of the present invention, in 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 less than 12 wt%, or 11.8 wt% or less, or 10 wt% or less, or 9 wt% or less, or 8 wt% or less, or 7.6 wt% or less, relative to 100 wt% of the linear low-density polyethylene having 6 or more carbon atoms. The content of the comonomer having 6 or more carbon atoms may be 5 wt% or more, or 7.6 wt% or more, or 8 wt% or more, or 9.0 wt% or more, or 10 wt% or more, or 11.8 wt% or more, relative to 100 wt% of the linear low-density polyethylene having 6 or more carbon atoms. When the content of a comonomer with 6 or more carbon atoms satisfies the aforementioned range, the intermolecular packing density is reduced, making it easier to prevent the problem of reduced sealing strength during normal operation of the battery.

[0164] 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 may be more advantageous in terms of sealing strength and physical properties than when it is polymerized in the presence of a Ziegler-Natta catalyst.

[0165] In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a comonomer with 6 or more carbon atoms and a melting point of 100°C to 130°C. In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a comonomer with 6 or more carbon atoms and a Poly Dispersity Index (PDI) of 2.6 or higher and 4 or lower. In one embodiment of the present invention, the crystallization temperature of the second resin may be greater than 90°C and less than or equal to 115°C and a linear low-density polyethylene having a comonomer with 6 or more carbon atoms. In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a comonomer with 6 or more carbon atoms and a weight-average molecular weight of 250,000 g / mol or greater than or equal to 400,000 g / mol.

[0166] In one embodiment of the present invention, the second resin may have a lower melting point than the sealant resin. Accordingly, it may be easier to induce a vent at a high temperature.

[0168] In one embodiment of the present invention, the melting point of the third resin may be greater than 130°C, or between 131°C and 140°C, or between 132°C and 138°C. When the melting point of the third resin satisfies the aforementioned range, it may be easier to improve the rigidity of the vent member (15).

[0169] In one embodiment of the present invention, there may be a significant difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin. For example, the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin is greater than the difference between the crystallization temperature of the first resin and the crystallization temperature of the sealant resin, so that the fusion characteristics between the third resin and the first resin are inferior to the fusion characteristics between the first resin and the sealant resin, and thus it may be easier for a vent to occur at the interface between the middle layer containing the third resin and the bottom layer of the vent member containing the first resin than at the interface between the first resin and the sealant resin.

[0170] In one embodiment of the present invention, the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin may be 30°C or more. When the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin satisfies the aforementioned range, it may be easier for a vent to occur between the middle layer containing the third resin and the bottom layer of the vent member containing the first resin.

[0171] In one embodiment of the present invention, the crystallization temperature of the third resin may be greater than 115°C. For example, the crystallization temperature of the third resin may be 116°C to 130°C, or 116°C to 120°C. When the crystallization temperature of the third resin satisfies the aforementioned range, it may be easier for a vent to occur between the middle layer containing the third resin and the bottom layer of the vent member containing the first resin.

[0172] In one embodiment of the present invention, the difference between the crystallization temperature of the third resin and the crystallization temperature of the first resin is 30°C or more, and the crystallization temperature of the third resin may be greater than 115°C.

[0173] In one embodiment of the present invention, the third resin may include high-density polyethylene, random polypropylene, or two or more of these.

[0175] In one embodiment of the present invention, the vent member (15) may have various shapes to facilitate gas flow toward the vent area. For example, the vent member (15) may have a film shape.

[0177] The above vent member (15) can be formed to have a predetermined thickness of a predetermined size.

[0178] In one embodiment of the present invention, as shown in FIGS. 1 and FIGS. 2, a vent member (15) may be located in a sealing portion.

[0179] Referring to FIG. 2, the vent member (15) may be located in the corner sealing portion of the case. For example, the vent member (15) may be located in the corner side of the sealing portion where the electrode lead (11) is exposed to the outside. Specifically, the vent member (15) may be located in the sealing portion next to the electrode lead (11), excluding the area between the electrode leads (11). When the vent member (15) is located in the corner side of the sealing portion where the electrode lead (11) is exposed to the outside, the amount of gas discharged toward the electrode lead (11) can be minimized, thereby further improving the safety of the battery.

[0180] In one embodiment of the present invention, when the sealing portion (13b) is sealed on three sides, the bent side of the case and one end of the vent member (15) can be in close contact.

[0181] Additionally, the vent member (15) can be inserted into the case (13) so that, depending on the design, the insertion length can be varied or the venting pressure and position can be controlled. Here, the insertion length of the vent member refers to the maximum value of the distance between one end and the other end of the vent member based on the protruding direction of the electrode lead.

[0182] 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 value of the distance between one end and the other end of the sealing portion (13b) with respect to the protruding direction of the electrode lead (11).

[0183] In another embodiment 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 so as to be exposed outside the case (13) through the storage portion (13a).

[0184] In one embodiment of the present invention, the vent member (15) may further include an adhesive layer for smoother placement.

[0186] FIG. 4 is a plan view showing a secondary battery according to another embodiment of the present invention.

[0187] Referring to FIG. 4, the vent member (15) may be located in the sealing portion excluding the sealing portion where the electrode lead (11) is exposed to the outside.

[0188] FIG. 5 is a plan view showing a secondary battery according to another embodiment of the present invention.

[0189] Referring to FIG. 5, the vent member (15) may be located in a sealing portion where the electrode lead (11) is exposed to the outside. For example, the vent member (15) may be located in a sealing portion between the electrode lead (11) and the electrode lead (11).

[0191] A secondary battery according to one embodiment of the present invention is provided with a vent member having a structure of three or more layers, comprising a first resin in the bottom layer, a second resin in the top layer, and a third resin in the middle layer, thereby enabling directional venting that allows gas to be discharged in a specific direction by reducing the sealing strength at high temperatures, so as to minimize damage to the electrode caused by gas when a thermal runaway phenomenon occurs, that is, when the internal temperature of the secondary battery rises. In addition, the rigidity of the vent member is improved, so premature venting before the desired temperature and pressure can be prevented.

[0193] In one embodiment of the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery. Among these, the secondary battery may be a pouch-type secondary battery.

[0195] Hereinafter, the present invention will be described in detail with reference to examples to aid in understanding. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the following embodiments. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

[0197] Example 1

[0198] Linear low-density polyethylene having a C6 comonomer polymerized in the presence of a metallocene catalyst with a thickness of 50 µm on one side of high-density polyethylene (Sabic®, HDPE F04660, melting point: 135°C, weight-average molecular weight: 350,000 g / mol, crystallization temperature: 119°C) (LG Chem, Lucene TM, SP311)(melting point: 119℃, comonomer content relative to total resin content: 9 wt%, weight-average molecular weight: 270,756 g / mol, polydispersity index: 2.674, crystallization temperature: 107℃) is laminated, and linear low-density polyethylene having a C8 comonomer polymerized in the presence of a metallocene catalyst having a thickness of 50 μm on the other side of the high-density polyethylene (LG Chem, Lucene TM A vent member was manufactured by laminating LF100 (melting point: 99℃, content of comonomer relative to total resin content: 16.3 wt%, weight average molecular weight: 205,603 g / mol, polydispersity index: 2.551, crystallization temperature: 83℃), heat-fusion at 100℃, and cutting it to a width of 100 mm.

[0199] An upper pouch and a lower pouch, each having poly(ethylene terephthalate) / aluminum foil / polypropylene resin stacked in sequence, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, stacked in the order of anode / separator / cathode, was housed.

[0200] Next, the vent member manufactured above was inserted between the polypropylene resins, and then heat-fused for 1.5 seconds under conditions of 200°C and 0.08 MPa to manufacture a secondary battery.

[0202] Comparative Example 1

[0203] An upper pouch and a lower pouch, each having poly(ethylene terephthalate) / aluminum foil / polypropylene resin stacked in sequence, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, stacked in the order of anode / separator / cathode, was housed.

[0204] Next, a secondary battery was manufactured by heat-fusing the above polypropylene resin.

[0206] Comparative Example 2

[0207] An upper pouch and a lower pouch, each having poly(ethylene terephthalate) / aluminum foil / polypropylene resin stacked in sequence, were arranged so that the polypropylene resins faced each other, and then an electrode assembly, stacked in the order of anode / separator / cathode, was housed.

[0208] Next, linear low-density polyethylene having a C6 comonomer polymerized in the presence of a metallocene catalyst having a thickness of 50 μm between the polypropylene resins ((LG Chem, Lucene TM A secondary battery was manufactured by inserting a vent member made of SP311 (melting point: 119℃, content of comonomer relative to total resin content: 9 wt%, weight-average molecular weight: 270,756 g / mol, polydispersity index: 2.674, crystallization temperature: 107℃) and then heat-fusing it for 1.5 seconds under conditions of 200℃ and 0.08 MPa.

[0210] Evaluation Example 1: Measurement of sealing strength according to temperature

[0211] In the secondary batteries prepared in Example 1 and Comparative Example 2, the case of the portion where the vent member was inserted was cut to a width of 15 mm and a length of 5 cm at the following temperature, then both ends were spread 180° and clamped in 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.

[0212] In the secondary battery manufactured in Comparative Example 1, the case of the sealing portion was cut to a width of 15 mm and a length of 5 cm at the following temperature, and then both ends were spread 180° and clamped in 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.

[0213] At this time, the maximum sealing strength refers to the maximum value when the case breaks, and the average sealing strength refers to the average value when the case is elongated by 8 mm from 4.5 kgf / 15 mm when the maximum sealing strength is 4.5 kgf / 15 mm or more, and the average value when the case is elongated by 8 mm from the maximum sealing strength when the maximum strength is less than 4.5 kgf / 15 mm.

[0215]

[0217] As can be seen in Table 1 above, it was confirmed that the maximum sealing strength and average sealing strength of the case portion with the vent member inserted in the secondary battery manufactured in Example 1 were higher than the maximum sealing strength and average sealing strength of the case portion with the vent member inserted in the secondary battery manufactured in Comparative Example 2 at room temperature to 60°C. Accordingly, the rigidity of the vent member (15) is improved compared to the case containing only the second resin, so that premature venting before the desired temperature and pressure can be prevented.

[0218] In addition, it was confirmed that the maximum sealing strength and average sealing strength of the case portion with the vent member inserted in the secondary battery prepared in Example 1 at temperatures above 100°C were lower than the maximum sealing strength and average sealing strength of the case portion with the vent member inserted in the secondary battery prepared in Comparative Example 2 at temperatures above 100°C. Accordingly, the secondary battery prepared in Example 1 is more easily vented when the battery reaches a high temperature due to abnormal phenomena compared to the secondary battery prepared in Comparative Example 2.

[0219] The secondary battery manufactured in Comparative Example 1 has a maximum sealing strength and average sealing strength of the case at room temperature to 60°C that is similar to the maximum sealing strength and average sealing strength of the case part with the vent member inserted in the secondary battery manufactured in Example 1 at room temperature to 60°C, but the maximum sealing strength and average sealing strength at 100°C or higher is significantly higher than the maximum sealing strength and average sealing strength of the case part with the vent member inserted in the secondary battery manufactured in Example 1 at 100°C or higher, so when the battery becomes high temperature due to an abnormal phenomenon, gas is discharged in an unspecified direction and a chain reaction of combustion of the battery may occur. Explanation of the symbols

[0220] 10: Secondary battery 11: Electrode lead 12: Electrode assembly 13: Case 13a: Storage compartment 13b: Sealing part 14: Lead film 15: Absence of vent 15a: Lowest level 15b: Top floor 15c: Middle layer

Claims

Claim 1 A secondary battery comprising: an electrode assembly; an electrode lead attached to the electrode assembly; a case housing the electrode assembly inside; a lead film formed to surround a portion of the 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; and a vent member inserted into the vent area and having a structure of three or more layers including a first resin in the bottom layer, a second resin in the top layer, and a third resin in the middle layer; wherein the second resin is a resin with a melting point higher than the first resin, the third resin is a resin with a melting point higher than the second resin, the melting point of the first resin is 90°C or higher and less than 100°C, and the melting point of the third resin is greater than 130°C. Claim 2 A secondary battery according to claim 1, characterized in that a vent occurs between the middle layer and the lowest layer. Claim 3 delete Claim 4 A secondary battery according to claim 1, characterized in that the first resin is linear low-density polyethylene having a comonomer having 8 carbon atoms. Claim 5 A secondary battery according to claim 1, characterized in that the Poly Dispersity Index (PDI) of the first resin is less than 2.

6. Claim 6 A secondary battery according to claim 4, characterized in that the content of the carbon-8 comonomer in the linear low-density polyethylene having the carbon-8 comonomer is 12 weight% or more relative to 100 weight% of the linear low-density polyethylene having the carbon-8 comonomer. Claim 7 A secondary battery according to claim 1, characterized in that the crystallization temperature of the first resin is 80°C to 90°C. Claim 8 A secondary battery according to claim 1, characterized in that the weight-average molecular weight of the first resin is 100,000 g / mol to 250,000 g / mol. Claim 9 A secondary battery according to claim 4, characterized in that the linear low-density polyethylene having the carbon-8 comonomer is polymerized in the presence of a metallocene catalyst. Claim 10 A secondary battery according to claim 4, wherein the case comprises a sealing portion formed to seal the electrode assembly, the sealing portion comprises a sealant resin, and the linear low-density polyethylene having a carbon-8 comonomer has a lower melting point than the sealant resin. Claim 11 A secondary battery according to claim 1, characterized in that the melting point of the second resin is 100°C to 130°C. Claim 12 A secondary battery according to claim 1, characterized in that the second resin is linear low-density polyethylene having a comonomer with 6 or more carbon atoms. Claim 13 A secondary battery according to claim 1, characterized in that the Poly Dispersity Index (PDI) of the second resin is 2.6 or higher and 4 or lower. Claim 14 A secondary battery according to claim 12, characterized in that the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having 6 or more carbon atoms is less than 12 weight percent relative to 100 weight percent of the linear low-density polyethylene having 6 or more carbon atoms. Claim 15 A secondary battery according to claim 1, characterized in that the crystallization temperature of the second resin is greater than 90°C and less than or equal to 115°C. Claim 16 A secondary battery according to claim 1, characterized in that the weight-average molecular weight of the second resin is greater than 250,000 g / mol and less than or equal to 400,000 g / mol. Claim 17 A secondary battery according to claim 12, characterized in that the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is polymerized in the presence of a metallocene catalyst. Claim 18 delete Claim 19 A secondary battery according to claim 1, characterized in that the third resin comprises high-density polyethylene, random polypropylene, or two or more of these. Claim 20 A secondary battery according to claim 1, characterized in that the vent member melts at 100°C or higher to vent gas. Claim 21 A secondary battery according to claim 20, characterized in that the vent member vents at a pressure of 1.5 atm or more. Claim 22 A secondary battery according to claim 1, characterized in that the vent member has a maximum sealing strength of less than 6 kgf / 15 mm at 100°C or higher. Claim 23 A secondary battery according to claim 1, characterized in that the average sealing strength of the vent member at 100°C or higher is less than 4.5 kgf / 15 mm. Claim 24 A 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. Claim 25 A 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. Claim 26 A secondary battery according to claim 10, characterized in that the vent area is located in the sealing portion. Claim 27 A secondary battery according to claim 26, characterized in that the vent area is located in the corner side sealing portion of the case. Claim 28 A secondary battery according to claim 1, characterized in that the secondary battery is a pouch-type secondary battery.

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