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 comprising linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

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] The present invention relates to a secondary battery characterized by comprising a vent member inserted in the vent region and comprising linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0017] The second embodiment is, in the first embodiment,

[0018] The above vent member may include linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

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

[0020] The above case may have a sealing portion formed to seal the electrode assembly, the sealing portion may include a sealant resin, and the linear low-density polyethylene of the vent member may have a lower melting point than the sealant resin.

[0021] The fourth embodiment is, in any one of the first to third embodiments,

[0022] The above vent member can be melted at 100°C to 120°C to vent gas.

[0023] The fifth embodiment is, in the fourth embodiment,

[0024] The above vent member can be vented at a pressure of 1.5 atm or higher.

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

[0026] The above vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100°C or higher.

[0027] The seventh embodiment is, in any one of the first to sixth embodiments,

[0028] The above vent member may have an average sealing strength of less than 4.5 kgf / 15 mm at 100°C or higher.

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

[0030] The above vent member may have a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

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

[0032] The above vent member may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

[0033] The 10th embodiment is, in any one of the 1st to 9th embodiments,

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

[0035] The 11th embodiment is, in any one of the 1st to 10th embodiments,

[0036] Based on 100 weight% of the above linear low-density polyethylene, the content of a comonomer with 6 or more carbon atoms may be 15 weight% or less.

[0037] The 12th embodiment is, in any one of the 1st to 11th embodiments,

[0038] The above linear low-density polyethylene may have a Poly Dispersity Index (PDI) of 4 or less.

[0039] The 13th embodiment is, in any one of the 3rd to 12th embodiments,

[0040] The difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene may be 10℃ or less.

[0041] The 14th embodiment is, in the 13th embodiment,

[0042] The crystallization temperature of the above linear low-density polyethylene may be 90°C to 115°C.

[0043] The 15th embodiment is, in any one of the 1st to 14th embodiments,

[0044] The above linear low-density polyethylene may have a melting point of 100°C to 130°C.

[0045] The 16th embodiment is, in any one of the 1st to 15th embodiments,

[0046] The weight-average molecular weight of the above linear low-density polyethylene may be 100,000 g / mol to 400,000 g / mol.

[0047] The 17th embodiment is, in any one of the 3rd to 16th embodiments,

[0048] The above vent area may be located in the above sealing portion.

[0049] The 18th embodiment is, in the 17th embodiment,

[0050] The above vent area may be located in the corner side sealing portion of the above case.

[0051] The 19th embodiment is, in any one of the 1st to 18th embodiments,

[0052] The above secondary battery may be a pouch-type secondary battery.

[0053] The 20th embodiment is, in any one of the 1st to 19th embodiments,

[0054] The above vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100°C to 120°C.

[0055] The 21st embodiment is, in any one of the 1st to 20th embodiments,

[0056] The above vent member may have an average sealing strength of less than 4.5 kgf / 15 mm at 100°C to 120°C.

[0057] The 22nd embodiment is, in any one of the 1st to 21st embodiments,

[0058] Based on 100 weight% of the above linear low-density polyethylene, the content of a comonomer with 6 or more carbon atoms may be 5 weight% to 15 weight%.

[0059] The 23rd embodiment is, in any one of the 1st to 22nd embodiments,

[0060] The above linear low-density polyethylene may have a polydispersity index (PDI) of 1 to 4.

[0061] The 24th embodiment is, in any one of the 1st to 23rd embodiments,

[0062] The above vent member may have a maximum sealing strength of less than 3 kgf / 15 mm at 120°C or higher.

[0063] The 25th embodiment is, in any one of the 1st to 24th embodiments,

[0064] The above vent member may have an average sealing strength of less than 2 kgf / 15 mm at 120°C or higher. Effects of the invention

[0065] A secondary battery according to one embodiment of the present invention is provided with a vent member comprising linear low-density polyethylene having a comonomer with 6 or more carbon atoms, thereby inducing gas discharge into a vent region. Accordingly, the safety of the battery is improved. Brief explanation of the drawing

[0066] 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. FIG. 6 is a plan view showing a secondary battery according to another embodiment of the present invention. FIG. 7 is a plan view showing a secondary battery according to another embodiment of the present invention. Specific details for implementing the invention

[0067] 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.

[0068] 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.

[0070] 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 comprising linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

[0072] FIGS. 1 and FIGS. 2 show a secondary battery according to one embodiment of the present invention.

[0073] The secondary battery (10) comprises an electrode assembly (12) with an electrode lead (11) attached, and a case (13).

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0081] The above case (13) serves to house the electrode assembly (12).

[0082] 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).

[0083] 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).

[0084] 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.

[0085] 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.

[0086] The above metal barrier layer may include aluminum, copper, etc.

[0087] The sealant layer may include a sealant resin and may be composed of a single layer or multiple layers.

[0088] 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.

[0089] In one embodiment of the present invention, the case (13) may be in the form of a pouch.

[0090] A pouch-shaped 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.

[0091] 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.

[0092] 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.

[0094] 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).

[0095] A secondary battery (10) according to one embodiment of the present invention has a lead film (14).

[0096] 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).

[0098] 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.

[0099] 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.

[0100] The above vent member (15) comprises linear low-density polyethylene having a comonomer with 6 or more carbon atoms. As the above vent member (15) comprises 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 into which the vent member (15) is inserted is reduced at a high temperature, e.g., 100°C or higher, thereby enabling or inducing venting.

[0101] 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.

[0102] 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 battery case, a gap is formed between the vent member and the battery case, through which gas can be discharged.

[0103] In one embodiment of the present invention, the vent member (15) may comprise linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0104] 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. When the linear low-density polyethylene having a conomer with 6 or more carbon atoms has a lower melting point than the sealant resin, the linear low-density polyethylene may melt faster than the sealant resin at high temperatures. 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.

[0105] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may have a melting point of 100°C to 130°C, or 105°C to 125°C, or 110°C to 120°C. When the melting point of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms 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.

[0106] The melting point of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms 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.

[0107] In one embodiment of the present invention, the vent member (15) can be vented at 100°C to 120°C 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 to 120°C 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.

[0108] 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. 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. In one embodiment of the present invention, the vent member (15) may have a maximum sealing strength of less than 3 kgf / 15 mm at 120°C or higher, or less than 2 kgf / 15 mm, or less than 1 kgf / 15 mm, or less than 0.5 kgf / 15 mm. When the above-described vent member (15) satisfies the above-described sealing strength in the above-described 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.

[0109] In addition, 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 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.

[0110] 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.

[0111] 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 100°C or higher. 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 100°C to 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 or less than 1 kgf / 15 mm or less than 0.5 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 vent characteristics.

[0112] 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. 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0117] 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.

[0118] 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 6 or more carbon atoms may be 15 weight% or less, or 12 weight% or less, or 11.8 weight% or less, or 10 weight% or less, or 9 weight% or less, or 8 weight% or less, or 7.6 weight% or less, relative to 100 weight% of the linear low-density polyethylene having 6 or more carbon atoms. At the same time, the content of the comonomer having 6 or more carbon atoms may be 5 weight% or more, or 7.6 weight% or more, or 8 weight% or more, or 9.0 weight% or more, or 10 weight% or more, or 11.8 weight% or more, or 12 weight% or more, relative to 100 weight% 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.

[0119] The content of the above comonomer with 6 or more carbon atoms can be measured by H-NMR. For example, about 10 mg of the sample can be completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, then sampled into an NMR tube and measured using H-NMR.

[0121] In one embodiment of the present invention, the weight-average molecular weight of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 100,000 g / mol to 400,000 g / mol, or 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 with 6 or more carbon atoms satisfies the aforementioned range, the sealing strength may be further improved during normal operation of the battery.

[0122] In one embodiment of the present invention, the Poly Dispersity Index (PDI) of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms 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 (PDI) may be 1.0 or higher. When the Poly Dispersity Index of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms 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.

[0123] The weight-average molecular weight and polydispersity index of linear low-density polyethylene having comonomers with 6 or more carbon atoms may be measured by gel permeation chromatography (GPC) under the following conditions.

[0124] - Column: Tosoh HLC-8321 GPC / HT

[0125] - Solvent: TCB (Trichlorobenzene) + 0.04% BHT (after drying with 0.1% CaCl2)

[0126] - Flow rate: 1.0 ml / min

[0127] - Sample concentration: 1.5 mg / ml

[0128] - Infusion volume: 300 µl

[0129] - Column temperature: 160℃

[0130] - Detector: RI detector

[0131] - Standard: Polystyrene (corrected by a cubic function)

[0133] 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. Additionally, 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 aforementioned range, the fusion characteristics of the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms during normal operation of the battery may be even better.

[0134] In one embodiment of the present invention, the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 90°C to 115°C, or 95°C to 110°C, or 100°C to 110°C, or 105°C to 110°C. When the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms satisfies the aforementioned range, the fusion characteristics of the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be even better.

[0135] 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 with 6 or more carbon atoms is 10°C or less, and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 90°C to 115°C.

[0136] The crystallization temperature can be measured using a differential scanning calorimeter (DSC). For example, the temperature of the 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. Afterward, 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.

[0138] 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.

[0140] The above vent member (15) can be formed to have a predetermined thickness of a predetermined size.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] For example, as illustrated in FIG. 4, 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).

[0146] Alternatively, as illustrated in FIG. 5, 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).

[0147] In one embodiment of the present invention, the vent member (15) may further include an adhesive layer for smoother placement.

[0149] FIG. 6 is a plan view showing a secondary battery according to another embodiment of the present invention.

[0150] Referring to FIG. 6, 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.

[0151] FIG. 7 is a plan view showing a secondary battery according to another embodiment of the present invention.

[0152] Referring to FIG. 7, 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).

[0154] A secondary battery according to one embodiment of the present invention is provided with a vent member comprising linear low-density polyethylene having a comonomer with 6 or more carbon atoms, thereby enabling directional venting that allows gas to be discharged in a specific direction by reducing sealing strength at high temperatures more smoothly and quickly, so that damage to the electrode caused by gas can be minimized when a thermal runaway phenomenon occurs, that is, when the internal temperature of the secondary battery rises.

[0156] 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.

[0158] 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.

[0160] Example 1

[0161] 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.

[0162] Next, linear low-density polyethylene having a carbon-6 comonomer polymerized in the presence of a metallocene catalyst between the polypropylene resins (ExxonMobile, Exceed TM A secondary battery was manufactured by inserting a vent member containing , 1018) and then heat-fusing it.

[0164] Example 2

[0165] Linear low-density polyethylene having a C6 comonomer polymerized in the presence of a metallocene catalyst (LG Chem, Lucene TM A secondary battery was manufactured in the same manner as in Example 1, except that a vent member including SP311) was inserted between the polypropylene resins.

[0167] Example 3

[0168] Linear low-density polyethylene having a C8 comonomer polymerized in the presence of a metallocene catalyst (Dow, Elite TMA secondary battery was manufactured in the same manner as in Example 1, except that a vent member including , 5401GT) was inserted between the polypropylene resins.

[0170] Comparative Example 1

[0171] 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.

[0172] Next, a secondary battery was manufactured by heat-fusing the above polypropylene resin.

[0174] Comparative Example 2

[0175] A secondary battery was manufactured in the same manner as in Example 1, except that a vent member comprising linear low-density polyethylene having a carbon-4 comonomer polymerized in the presence of a Ziegler-Natta catalyst was inserted between polypropylene resins.

[0177] Comparative Example 3

[0178] A secondary battery was manufactured in the same manner as in Example 1, except that a vent member comprising high-density polyethylene (SABIC®, HDPE F04660) was inserted between polypropylene resins.

[0180] Evaluation Example 1: Evaluation of physical properties of the resin used in the vent member

[0181] The melting point, comonomer content, weight-average molecular weight, polydispersity index, and crystallization temperature of the resin (also referred to as 'vent resin' in this specification) used in the vent members of Examples 1 to 3 and Comparative Example 2, and the sealant resin used in Comparative Example 1 were measured and are shown in Table 1 below.

[0183] (1) Measurement of melting point and crystallization temperature

[0184] The melting point and crystallization temperature of the sealant resin used in Comparative Example 1 and the vent resin used in the vent members of Examples 1 to 3 and Comparative Example 2 were measured in the following manner.

[0185] Using a differential scanning calorimeter (DSC), the temperature of the sample was increased from 30°C to 280°C at a rate of 10°C / min, maintained at 280°C for 10 minutes, cooled to 30°C at a rate of 10°C / min, and maintained at 30°C for 10 minutes. Subsequently, the temperature of the sample was increased from 30°C to 280°C at a rate of 10°C / min and maintained at 280°C for 10 minutes to measure the melting point and crystallization temperature.

[0187] (2) Measurement of comonomer content

[0188] The comonomer content of the sealant resin used in Comparative Example 1 and the vent resin used in the vent members of Examples 1 to 3 and Comparative Example 2 was measured using H-NMR.

[0189] About 10 mg of the sample was completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, then sampled into an NMR tube and measured using H-NMR.

[0191] (3) Measurement of weight-average molecular weight and polydispersity index

[0192] The weight-average molecular weight and polydispersity index of the sealant resin used in Comparative Example 1 and the vent resin used in the vent members of Examples 1 to 3 and Comparative Example 2 were measured using gel permeation chromatography (GPC) under the following conditions.

[0193] - Column: Tosoh HLC-8321 GPC / HT

[0194] - Solvent: TCB (Trichlorobenzene) + 0.04% BHT (after drying with 0.1% CaCl2)

[0195] - Flow rate: 1.0 ml / min

[0196] - Sample concentration: 1.5 mg / ml

[0197] - Infusion volume: 300 µl

[0198] - Column temperature: 160℃

[0199] - Detector: RI detector

[0200] - Standard: Polystyrene (corrected by a cubic function)

[0202]

[0204] Evaluation Example 2: Measurement of sealing strength according to temperature

[0205] In the secondary batteries prepared in Examples 1 to 3 and Comparative Examples 2 to 3, the case of the portion where the vent member is inserted was cut to a width of 15 mm and a length of 5 cm at the following temperatures, 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 2 below.

[0206] 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 2 below.

[0207] 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.

[0209]

[0211] As can be seen in Table 2 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 batteries prepared in Examples 1 to 3 at room temperature to 60°C were at a level similar to the maximum sealing strength and average sealing strength of the case of the secondary battery prepared in Comparative Example 1 at room temperature to 60°C. 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 batteries prepared in Examples 1 to 3 at 100°C or higher were at a significantly lower level compared to the maximum sealing strength and average sealing strength of the case of the secondary battery prepared in Comparative Example 1 at 100°C or higher.

[0212] Accordingly, the secondary battery equipped with the vent member manufactured in Examples 1 to 3 can secure appropriate sealing strength when the battery is operating normally, and can discharge gas through the vent member with weakened sealing strength when the battery becomes high temperature due to an abnormal phenomenon. On the other hand, the secondary battery manufactured in Comparative Example 1 can secure appropriate sealing strength when the battery is operating normally, but when the battery becomes high temperature due to an abnormal phenomenon, gas is discharged in an unspecified direction, which may cause a chain reaction of combustion in the battery.

[0213] The secondary batteries manufactured in Comparative Examples 2 and 3 had a maximum sealing strength and average sealing strength at room temperature to 60°C in the case portion with a vent member inserted, which were significantly lower than the secondary batteries manufactured in Examples 1 to 3, and at 100°C or higher, the sealing strength was too low to be measured. From this, it was confirmed that the secondary batteries manufactured in Comparative Examples 2 and 3 could not secure an appropriate sealing strength when the battery was operating normally. Explanation of the symbols

[0214] 10: Secondary battery 11: Electrode lead 12: Electrode assembly 13: Case 13a: Storage compartment 13b: Sealing part 14: Lead film 15: Absence of vent

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 region formed in at least a portion of the case; and a vent member inserted in the vent region and comprising linear low-density polyethylene having a comonomer with 6 or more carbon atoms; wherein the vent member has a maximum sealing strength of less than 6 kgf / 15 mm at 100°C or higher, and the vent member has a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C, and the content of the comonomer with 6 or more carbon atoms is 7.6 wt% or more and 11.8 wt% or less based on 100 wt% of the linear low-density polyethylene, and the linear low-density polyethylene has a Poly Dispersity Index (PDI) of 4 or less. Claim 2 A secondary battery according to claim 1, characterized in that the vent member comprises linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms. Claim 3 A secondary battery according to claim 1, wherein the case has a sealing portion formed to seal the electrode assembly, the sealing portion includes a sealant resin, and the linear low-density polyethylene of the vent member has a lower melting point than the sealant resin. Claim 4 A secondary battery according to claim 1, characterized in that the vent member melts at 100°C to 120°C to vent gas. Claim 5 A secondary battery according to claim 4, characterized in that the vent member vents at a pressure of 1.5 atm or higher. Claim 6 delete Claim 7 A secondary battery according to claim 1, characterized in that the vent member has an average sealing strength of less than 4.5 kgf / 15 mm at 100°C or higher. Claim 8 delete Claim 9 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 10 A secondary battery according to claim 1, characterized in that the linear low-density polyethylene is polymerized in the presence of a metallocene catalyst. Claim 11 delete Claim 12 delete Claim 13 A secondary battery according to claim 3, characterized in that the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene is 10℃ or less. Claim 14 A secondary battery according to claim 13, characterized in that the crystallization temperature of the linear low-density polyethylene is 90°C to 115°C. Claim 15 A secondary battery according to claim 1, characterized in that the linear low-density polyethylene has a melting point of 100°C to 130°C. Claim 16 A secondary battery according to claim 1, characterized in that the weight-average molecular weight of the linear low-density polyethylene is 100,000 g / mol to 400,000 g / mol. Claim 17 A secondary battery characterized in that, in paragraph 3, the vent area is located in the sealing portion. Claim 18 A secondary battery according to claim 17, characterized in that the vent area is located in the corner side sealing portion of the case. Claim 19 A secondary battery according to claim 1, characterized in that the secondary battery is a pouch-type secondary battery. Claim 20 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 to 120°C. Claim 21 A secondary battery according to claim 1, characterized in that the vent member has an average sealing strength of less than 4.5 kgf / 15 mm at 100°C to 120°C. Claim 22 delete Claim 23 delete Claim 24 A secondary battery according to claim 1, characterized in that the vent member has a maximum sealing strength of less than 3 kgf / 15 mm at 120°C or higher. Claim 25 A secondary battery according to claim 1, characterized in that the vent member has an average sealing strength of less than 2 kgf / 15 mm at 120°C or higher.

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