Secondary battery

Abstract

The present invention relates to a secondary battery comprising: an electrode assembly having an electrode lead attached thereto; a case including a storage portion for storing the electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; a lead film covering a portion of an 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 including: a first layer including a resin having a melting point lower than that of the sealant resin; and a second layer located on at least one surface of the first layer and including an adhesive material, the second layer having a thickness of 5 μm or less.

Description

[Technical field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery provided with a vent member.

[0002] This application claims priority to Korean Patent Application No. 10-2022-0001217, filed on January 4, 2022, the entire contents of which are incorporated herein by reference in their entirety in the specification and drawings. [Background technology]

[0003] Secondary batteries, which have high applicability for each product group and electrical properties such as high energy density, are universally used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are driven by electrical sources. These batteries are attracting attention as a new energy source for improving energy efficiency, not only for their primary advantage of dramatically reducing the use of fossil fuels, but also for their environmental friendliness as they do not produce any by-products from the use of energy.

[0004] Currently, examples of widely used secondary batteries include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, and nickel zinc batteries.

[0005] Such secondary batteries are widely constructed in such a way that an electrode assembly including at least one unit cell having a positive electrode / separator / negative electrode structure is housed in a case, and the electrode assembly is sealed by fusing a sealant resin inside the case.

[0006] In the case of such conventional secondary batteries, fires can occur due to various reasons such as short circuits inside the secondary battery, overcharging or over-discharging, temperature control, etc. At this time, the internal temperature of the secondary battery rises rapidly and at the same time, a thermal runaway phenomenon occurs in which heat is transferred to adjacent cells, causing the fire to spread further.

[0007] In order to minimize damage to electrodes caused by gas when thermal runaway occurs, directional venting is required to exhaust gas in one direction when the internal temperature of the secondary battery rises. However, conventional secondary batteries have a problem in that it is difficult to induce gas exhaust in a specific direction. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a secondary battery having improved safety by directing gas discharge in a specific direction. [Means for solving the problem]

[0009] In order to achieve the above object, according to one aspect of the present invention, a secondary battery according to the following embodiment is provided.

[0010] The first embodiment is an electrode assembly having an electrode lead attached thereto; a case including a receiving portion for receiving the electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; a lead film that covers a part of an outer surface of the electrode lead and is interposed between the electrode lead and the case; a vent area formed in at least a portion of the case; a first layer including a resin having a melting point lower than that of the sealant resin, and a second layer including an adhesive substance located on at least one surface of the first layer; and a vent member inserted into the vent region; The present invention relates to a secondary battery, wherein the second layer has a thickness of 5 μm or less.

[0011] According to the second embodiment, in the first embodiment, The vent area may be located at the sealing portion.

[0012] According to the third embodiment, in the second embodiment, The vent member may be formed to be longer than the sealing portion, and the vent member may be exposed to both the inside and the outside of the case.

[0013] According to the fourth embodiment, in the third embodiment, The second layer may be located on at least one surface of the first layer exposed to the outside of the case.

[0014] According to the fifth embodiment, in any one of the first to fourth embodiments, The resin having a lower melting point than the sealant resin may include a linear low density polyethylene having a comonomer having six or more carbon atoms.

[0015] According to the sixth embodiment, in the fifth embodiment, The resin having a melting point lower than that of the sealant resin may include a linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0016] According to the seventh embodiment, in the fifth or sixth embodiment, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst.

[0017] According to the eighth embodiment, in any one of the fifth to seventh embodiments, 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 15% by weight or less, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

[0018] According to the ninth embodiment, in any one of the fifth to eighth embodiments, The linear low density polyethylene having a comonomer having 6 or more carbon atoms may have a polydispersity index (PDI) of 4 or less.

[0019] According to the tenth embodiment, in any one of the fifth to ninth embodiments, The difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 10° C. or less.

[0020] According to the eleventh embodiment, in any one of the fifth to tenth embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a crystallization temperature of 90°C to 115°C.

[0021] According to the twelfth embodiment, in any one of the fifth to eleventh embodiments, The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a weight average molecular weight of 100,000 g / mol to 400,000 g / mol.

[0022] According to the thirteenth embodiment, in any one of the first to twelfth embodiments, The vent member is capable of venting at 100°C to 120°C.

[0023] According to the 14th embodiment, in any one of the 1st to 13th embodiments, The vent member is capable of venting at a pressure of 1.5 atm or greater.

[0024] According to the fifteenth embodiment, in any one of the first to fourteenth embodiments, The vent member may have a maximum sealing strength of less than 6 kgf / 15 mm at 100° C. or higher.

[0025] According to the 16th embodiment, in any one of the 1st to 15th embodiments, The vent member may have an average sealing strength of less than 4.5 kgf / 15 mm at 100° C. or higher.

[0026] According to the seventeenth embodiment, in any one of the first to sixteenth embodiments, The vent member may have a maximum sealing strength of 6 kgf / 15 mm or more at room temperature to 60°C.

[0027] According to the 18th embodiment, in any one of the 1st to 17th embodiments, The vent member may have an average sealing strength of 4.5 kgf / 15 mm or more at room temperature to 60°C.

[0028] According to the 19th embodiment, in any one of the 1st to 18th embodiments, The resin having a lower melting point than the sealant resin may have a melting point of 100°C to 130°C.

[0029] According to the 20th embodiment, in any one of the first to 19th embodiments, The adhesive material may include an acrylic polymer, a polyurethane, an epoxy resin, a silicone, a butyl rubber, a polyisobutylene, or two or more of these.

[0030] According to the 21st embodiment, in any one of the 1st to 20th embodiments, The vent area may be located at a sealing portion at a corner side of the case.

[0031] According to the 22nd embodiment, in any one of the 1st to 21st embodiments, The secondary battery may be a pouch-type secondary battery. Effect of the Invention

[0032] According to an embodiment of the present invention, a secondary battery includes a vent member including a resin having a melting point lower than that of a sealant resin of a case, and thus gas can be discharged in a direction where the vent member is located, thereby improving the safety of the battery.

[0033] In the secondary battery according to an embodiment of the present invention, a second layer including an adhesive material is disposed on at least one surface of a first layer, thereby fixing the position of a vent member and improving the dimensional stability of the battery.

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

[0035] [Figure 1] FIG. 13 is a diagram showing a secondary battery in which the vent member does not include a layer containing an adhesive material. [Diagram 2] 1 is a diagram showing a secondary battery according to an embodiment of the present invention including a layer containing an adhesive material in a vent member; [Diagram 3] FIG. 2 is an enlarged view of a vent member according to an embodiment of the present invention. [Figure 4] FIG. 13 illustrates a secondary battery according to another embodiment of the present invention. [Diagram 5] 5 is a partially enlarged cross-sectional view of the vent member after the sealing portion of the secondary battery of FIG. 4 has been sealed. [Figure 6] 13 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 7] 13 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 8] 13 is a partially enlarged view of a vent member in a secondary battery according to still another embodiment of the present invention; FIG. [Figure 9] FIG. 3 is a cross-sectional view taken along line BB' in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[0038] According to one aspect of the present invention, there is provided a secondary battery comprising: an electrode assembly having an electrode lead attached thereto; a case including a housing for housing the electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; a lead film for wrapping a portion of an outer surface of the electrode lead and interposed between the electrode lead and the case; a vent region formed on at least a portion of the case; and a vent member including: a first layer including a resin having a lower melting point than the sealant resin; and a second layer located on at least one surface of the first layer and including an adhesive material, the second layer having a thickness of 5 μm or less.

[0039] 1 is a diagram showing a secondary battery in which the vent member does not include a layer containing an adhesive material. The secondary battery 10 includes an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13. The case 13 includes a receiving portion 13a for receiving the electrode assembly 12, and a sealing portion 13b formed to seal the electrode assembly 12. The secondary battery 10 includes a lead film 14. The lead film 14 covers a part of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the sealing portion 13b. The lead film 14 is interposed between the electrode lead 11 and the sealing portion 13b to assist in bonding between the electrode lead 11 and the sealing portion 13b.

[0040] 1, when the vent member 15 for inducing gas discharge in a specific direction does not include a layer containing an adhesive material, the vent member 15 is simply inserted into the case 13 and then the battery is sealed. However, when the vent member 15 is simply inserted into the case 13, the vent member 15 is not fixed until the case 13 is sealed, which causes a problem of reduced dimensional stability.

[0041] The inventors discovered that by positioning a layer containing an adhesive substance on at least one surface of the vent member, the vent member can be accurately fixed and dimensional stability can be ensured even before the case is sealed, which led to the completion of the present invention.

[0042] FIG. 2 is a diagram showing a secondary battery according to an embodiment of the present invention in which a vent member includes a layer containing an adhesive material.

[0043] Referring to FIG. 2, a secondary battery 10 according to an embodiment of the present invention includes an electrode assembly 12 having an electrode lead 11 attached thereto, and a case 13.

[0044] The electrode assembly 12 includes a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly 12 may include a positive electrode plate and a negative electrode plate that are sequentially stacked with a separator interposed therebetween.

[0045] The positive electrode plate may be formed including a positive electrode current collector made of a metal thin plate having excellent conductivity, for example, aluminum (Al) foil, and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode plate may also include a positive electrode tab made of a metal material, for example, aluminum (Al) material, at one end. The positive electrode tab may extend and protrude from one end of the positive electrode plate, or may be attached to one end of the positive electrode plate by welding or a conductive adhesive.

[0046] The negative electrode plate may be formed to include a negative electrode current collector made of a conductive metal sheet, for example, copper (Cu) foil, and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode plate may also include a negative electrode tab at one end of the negative electrode plate, which is made of a metal material, for example, copper (Cu) or nickel (Ni). The negative electrode tab may extend and protrude from one end of the negative electrode plate, or may be attached to one end of the negative electrode plate by welding or a conductive adhesive.

[0047] The separator may be formed in the form of a porous membrane that is interposed between the positive and negative electrode plates to electrically insulate the positive and negative electrode plates and allow lithium ions, etc., to pass between the positive and negative electrode plates. Such a separator may include, for example, a porous membrane using polyethylene (PE), polypropylene (PP), or a composite film thereof.

[0048] The surface of the separator may be provided with an inorganic coating layer. The inorganic coating layer may have a structure in which inorganic particles are bound to each other by a binder to form a pore structure (interstitial volume) between the particles.

[0049] Examples of the electrode assembly 12 include a jelly roll type (wound type) electrode assembly having a structure in which long sheet-like positive and negative electrodes are wound with a separator interposed therebetween, a stack type electrode assembly having a structure in which a plurality of positive and negative electrodes cut into units of a predetermined size are stacked in sequence with a separator interposed therebetween, and a stacked / folded type electrode assembly having a structure in which a bi-cell or a full-cell having positive and negative electrodes of a predetermined unit stacked with a separator interposed therebetween is wound up.

[0050] Referring to FIG. 2, the case 13 includes a receiving portion 13a for receiving the electrode assembly 12, and a sealing portion 13b for sealing the electrode assembly 12.

[0051] The sealing portion 13b includes a sealant resin, and the sealant resin is fused along the outer circumferential surface of the receiving portion 13a to seal the electrode assembly 12.

[0052] In one embodiment of the present invention, the case 13 may be provided in the form of a multi-layered film including an outer layer for protection from external impact, a metal barrier layer for blocking moisture, and a sealant layer for sealing the case.

[0053] The outer layer may include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, nylon, or other polyester-based film, and may be constructed as a single layer or multiple layers.

[0054] The metal barrier layer may include aluminum, copper, and the like.

[0055] The sealant layer may include a sealant resin and may be constructed as a single layer or multiple layers.

[0056] The sealant resin may include polypropylene (PP), acid modified polypropylene (PPa), random polypropylene, ethylene propylene copolymer, or two or more thereof. The ethylene propylene copolymer may include, but is not limited to, ethylene propylene rubber, ethylene-propylene block copolymer, etc.

[0057] In one embodiment of the present invention, the case 13 may be a pouch type.

[0058] In one embodiment of the present invention, when the case 13 is a pouch type, it 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 facing sealant resins may be fused to each other by heat and pressure to seal the battery.

[0059] The sealing portion 13b may be fused by heat or ultrasonic waves, but is not particularly limited as long as the sealing portion 13b can be fused.

[0060] The sealing portion 13b may be four-sided sealed or three-sided sealed at the periphery of the case 13. The three-sided sealed structure refers to a structure in which an upper pouch and a lower pouch are formed from one pouch sheet, and then the boundary between the upper pouch and the lower pouch is folded to overlap the storage portions 13a of the electrode assemblies formed in the upper pouch and the lower pouch, and the remaining three peripheries excluding the folded portion are sealed.

[0061] Referring to FIG. 2, the electrode lead 11 may be housed in the battery case 13 such that a portion of the electrode lead 11 is exposed to the outside of the battery case 13 .

[0062] Referring to FIG. 2, a secondary battery 10 according to an embodiment of the present invention includes a lead film 14.

[0063] The lead film 14 covers a part of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the sealing portion 13b. The lead film 14 is interposed between the electrode lead 11 and the sealing portion 13b to assist in bonding between the electrode lead 11 and the sealing portion 13b.

[0064] 2, a secondary battery 10 according to an embodiment of the present invention includes a vent area (not shown) formed in at least a portion of the case 13, and a vent member 15 may be inserted into the vent area. The vent member 15 may improve the safety of the battery by inducing gas discharge in a specific direction when a thermal runaway phenomenon occurs.

[0065] In one embodiment of the invention, the vent area may be located in the sealing portion 13b.

[0066] In one embodiment of the present invention, the vent region may be located in the sealing portion except for the sealing portion on the side where the electrode lead 11 is exposed to the outside.

[0067] In another embodiment of the present invention, the vent area may be located at the sealing portion on the side where the electrode lead 11 is exposed to the outside.

[0068] In yet another embodiment of the present invention, the vent area may be located at a corner sealing portion of the case 13. When the vent area is located at a corner sealing portion of the case 13, the amount of gas vented in a direction that directly contacts the electrode lead 11, i.e., toward the side of the electrode lead 11, can be minimized, and the safety of the battery can be further improved.

[0069] FIG. 3 is an enlarged view of a vent member according to one embodiment of the present invention.

[0070] Referring to FIG. 3, the vent member 15 includes a first layer 15a including a resin having a melting point lower than that of the sealant resin, and a second layer 15b located on at least one surface of the first layer 15a and including an adhesive material.

[0071] The vent member 15 includes a resin having a lower melting point than the sealant resin of the sealing portion 13b, so that the sealing strength of the portion where the vent member 15 is inserted is lower than the sealing strength of the portion of the sealant resin where the vent member 15 is not inserted under high temperatures, thereby making it easier to implement vent characteristics. As a result, when a thermal runaway phenomenon occurs, gas can be discharged in a specific direction, improving the safety of the battery.

[0072] In addition, the vent member 15 includes the second layer 15b including an adhesive material on at least one surface of the first layer 15a including a resin having a melting point lower than that of the sealant resin, so that the position of the vent member 15 can be easily fixed. That is, the positional deviation of the vent member 15 can be reduced. For example, the positional deviation of the vent member 15 can be within 0.5 mm.

[0073] In one embodiment of the present invention, at least a portion of the vent member 15 may be located in the sealing portion 13b.

[0074] In another embodiment of the present invention, at least a portion of the vent member 15 may be exposed to the outside of the case 13 .

[0075] FIG. 4 is a diagram showing a secondary battery according to another embodiment of the present invention.

[0076] 4, the vent member 15 may be formed longer than the sealing portion 13b, and the vent member 15 may be exposed to both the inside and outside of the case 13. That is, one end of the vent member 15 may be located closer to the inside of the battery than the inner end of the sealing portion 13b, and the other end of the vent member 15 may be located closer to the outside of the battery than the outer end of the sealing portion 13b. When the vent member 15 has such a structure, the vent effect can be further improved.

[0077] FIG. 5 is a partially enlarged cross-sectional view of the vent member after the sealing portion of the secondary battery of FIG. 4 has been sealed.

[0078] 5, when a portion of the vent member 15 is exposed to the outside of the case 13, the second layer 15b may be located on at least one surface of the first layer 15a exposed to the outside of the case 13. In the process of inserting the vent member including the second layer 15b into the case 13 and then sealing it, the second layer 15b may be pushed out of the case 13. As a result, the second layer 15b may not exist inside the case 13 but may exist only outside the case 13. That is, the second layer 15b may be located only on at least one surface of the first layer 15a exposed to the outside of the case 13. The adhesive material of the second layer 15b accurately fixes the vent member 15 at a desired position, but when the sealing portion 13b and the first layer 15a overlap, the adhesive material may hinder the overlapping of the sealing portion 13b and the first layer 15a, and the sealing strength between the sealing portion 13b and the first layer 15a may be reduced. When the second layer 15b is located on at least one surface of the first layer 15a exposed to the outside of the case 13, the problem of a decrease in the sealing strength between the sealing portion 13b and the first layer 15a can be more easily prevented.

[0079] The vent member 15 and the case 13 may be overlapped by heat fusion. As another example, the vent member 15 and the case 13 may be overlapped by an adhesive such as glue. As yet another example, the vent member 15 and the case 13 may be physically connected by a clip or the like. As yet another example, at least a portion of the vent member 15 may be embedded in a film constituting the case 13, for example, a sealant resin.

[0080] In the present invention, the thickness of the second layer 15b is 5 μm or less. For example, the thickness of the second layer 15b may be 100 nm to 5 μm or 1 to 5 μm. When the thickness of the second layer 15b satisfies the above-mentioned range, the battery is sealed during normal operation, and gas discharge can be induced only during abnormal operation of the battery.

[0081] If the thickness of the second layer 15b exceeds 5 μm, when the sealing portion 13b and the first layer 15a overlap, the second layer 15b containing the adhesive material becomes excessively thick, and the sealing strength between the sealing portion 13b and the first layer 15a decreases. As a result, it is difficult to ensure a desired sealing strength during normal operation of the battery. For example, the maximum sealing strength during normal operation of the battery may be 6 kgf / 15 mm or less.

[0082] In one embodiment of the present invention, the resin having a lower melting point than the sealant resin may include linear low-density polyethylene having a comonomer with a carbon number of 6 or more. By including linear low-density polyethylene having a comonomer with a carbon number of 6 or more as the resin having a lower melting point than the sealant resin, the case 13 has excellent sealing properties, and the sealing strength of the case 13 with the vent member 15 inserted therein decreases at high temperatures, making it possible to easily implement vent characteristics.

[0083] In one embodiment of the present invention, the resin having a lower melting point than the sealant resin may include linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

[0084] In one embodiment of the present invention, the resin having a lower melting point than the sealant resin may have a melting point of 100° C. to 130° C., 105° C. to 125° C., or 110° C. to 120° C. When the resin having a lower melting point than the sealant resin includes a linear low-density polyethylene having a comonomer having 6 or more carbon atoms, the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may have a melting point of 100° C. to 130° C., 105° C. to 125° C., or 110° C. to 120° C. When the resin having a lower melting point than the sealant resin has a melting point in the above-mentioned range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted is reduced at high temperatures, for example, 100° C. or higher, so that the vent characteristics can be more easily realized.

[0085] The melting point of the resin having a lower melting point than the sealant resin can be measured using a differential scanning calorimeter (DSC). For example, the temperature of the sample is raised from 30°C to 280°C at 10°C / min, then maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. Then, the temperature is raised from 30°C to 280°C at 10°C / min, and maintained at 280°C for 10 minutes to measure the melting point.

[0086] In one embodiment of the present invention, the vent member 15 can perform venting at 100°C to 120°C.

[0087] In one embodiment of the present invention, the vent member 15 is capable of venting at a pressure of 1.5 atm or more.

[0088] In one embodiment of the present invention, the vent member 15 can perform venting at 100° C. to 120° C. and at a pressure of 1.5 atm or more.

[0089] The vent member 15 vents within the above-mentioned temperature range and / or pressure conditions, so that the battery can be sealed during normal operation of the battery, and gas can be more easily discharged only during abnormal operation of the battery.

[0090] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm at temperatures of 100° C. or higher. If the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, at 100° C. or higher, so that the vent characteristics can be easily realized.

[0091] In addition, in one embodiment of the present invention, the maximum sealing strength of the vent member 15 may be 6 kgf / 15 mm or more at room temperature to 60° C. When the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, even if the vent member 15 is inserted, the battery can have excellent sealing strength during normal operation of the battery, and the hermeticity of the battery can be easily ensured.

[0092] In one embodiment of the present invention, the maximum sealing strength of the vent member 15 at 100° C. or higher may be less than 6 kgf / 15 mm, and the maximum sealing strength of the vent member 15 at room temperature to 60° C. may be 6 kgf / 15 mm or more. When the vent member 15 satisfies the above-mentioned sealing strength, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, making it easy to realize vent characteristics, and during normal operation of the battery, the vent member 15 has excellent sealing strength and can easily ensure the hermeticity of the battery.

[0093] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm at temperatures of 100° C. or more. If the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, the sealing strength of the portion of the case 13 where the vent member 15 is inserted decreases at high temperatures, making it easier to implement vent characteristics.

[0094] 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. When the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, it has excellent sealing strength during normal operation of the battery, and can easily ensure the hermeticity of the battery.

[0095] In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf / 15 mm at temperatures of 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 above-mentioned temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted decreases at high temperatures, making it easy to realize vent characteristics, and the vent member 15 has excellent sealing strength during normal operation of the battery, making it easy to ensure the hermeticity of the battery.

[0096] The sealing strength of the vent member 15 according to temperature can be measured by cutting the part of the case 13 into which the vent member 15 is inserted to a width of 15 mm and a length of 5 cm, opening both ends 180°, fixing them to a UTM jig, and conducting a tensile test at a speed of 5 mm / min.

[0097] Here, the maximum sealing strength means the maximum value at which the case 13 breaks. Also, the average sealing strength means the average value when the case 13 is stretched by 8 mm under the condition of 4.5 kgf / 15 mm or more when the maximum sealing strength is 4.5 kgf / 15 mm or more, and means the average value when the case 13 is stretched by 8 mm under the condition of 4.5 kgf / 15 mm or more when the maximum sealing strength is less than 4.5 kgf / 15 mm.

[0098] 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 is more advantageous in terms of sealing strength and physical properties than when it is polymerized in the presence of a Ziegler-Natta catalyst.

[0099] In one embodiment of the present invention, the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 15% by weight or less, 12% by weight or less, 11.8% by weight or less, 10% by weight or less, 9% by weight or less, 8% by weight or less, or 7.6% by weight or less, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. At the same time, the content of the comonomer having 6 or more carbon atoms may be 5% by weight or more, 7.6% by weight or more, 8% by weight or more, 9.0% by weight or more, 10% by weight or more, 11.8% by weight or more, or 12% by weight or more, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. When the content of the comonomer having 6 or more carbon atoms satisfies the above-mentioned range, the problem of the decrease in sealing strength during normal operation of the battery due to the decrease in intermolecular packing density can be easily prevented.

[0100] The content of the comonomer having 6 or more carbon atoms can be measured by H-NMR. For example, about 10 mg of a sample is completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, and then sampled in an NMR tube. 1 It can be measured using H-NMR.

[0101] 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, 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 above range, the sealing strength during normal operation of the battery can be further improved.

[0102] In one embodiment of the present invention, the polydispersity index (PDI) of the linear low density polyethylene having a comonomer with 6 or more carbon atoms may be 4 or less, 3.8 or less, 3.796 or less, 3.5 or less, 3.023 or less, 3 or less, 2.7 or less, or 2.674 or less. The polydispersity index (PDI) may be 1.0 or more. When the polydispersity index of the linear low density polyethylene having a comonomer with 6 or more carbon atoms satisfies the above range, the molecular weight distribution is narrow, and therefore the battery exhibits better sealing strength and physical properties during normal operation.

[0103] The weight average molecular weight and polydispersity index of the linear low density polyethylene having a comonomer having 6 or more carbon atoms may be measured by gel permeation chromatography (GPC) under the following conditions.

[0104] -Column: Tosoh Corporation, HLC-8321 GPC / HT -Solvent: TCB (trichlorobenzene) + 0.04% BHT (0.1% CaCl 2 (dried at 40°C) -Flow rate: 1.0ml / min -Sample concentration: 1.5mg / ml -Injection volume: 300μl -Column temperature: 160°C -Detector: RI detector -Standard: Polystyrene (corrected by a cubic function)

[0105] In one embodiment of the present invention, the crystallization temperature of the sealant resin may be similar to that of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms. 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. Also, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be 0.1° C. or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms satisfies the above-mentioned range, the fusion property between the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms during normal operation of the battery is more excellent.

[0106] In one embodiment of the present invention, the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be 90° C. to 115° C., 95° C. to 110° C., 100° C. to 110° C., or 105° C. to 110° C. When the crystallization temperature of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms satisfies the above-mentioned range, the fusion properties between the sealant resin and the linear low-density polyethylene having a comonomer having 6 or more carbon atoms become more excellent.

[0107] The crystallization temperature 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 10°C / min, then maintained at 280°C for 10 minutes, cooled to 30°C at 10°C / min, and maintained at 30°C for 10 minutes. Then, the temperature is increased from 30°C to 280°C at 10°C / min, and maintained at 280°C for 10 minutes to measure the crystallization temperature.

[0108] In one embodiment of the present invention, the vent member 15 may have a film shape.

[0109] The vent member 15 may be formed to have a predetermined thickness and may be inserted into the case 13 to allow for different insertion lengths or to control venting pressure and position depending on the design.

[0110] In one embodiment of the present invention, the insertion length of the vent member 15 may be 5 to 20 mm.

[0111] In an embodiment of the present invention, when the sealing portion 13b is sealed on three sides, the bent surface of the case and one end of the vent member 15 may be adjacent to each other.

[0112] In one embodiment of the present invention, the vent member 15 may have a shape that narrows toward the outside of the case 13. When the vent member 15 has a shape that narrows toward the outside of the case, the injection angle of the vented gas is reduced, thereby further improving the safety of the battery. In particular, when the vent member 15 is located in a sealing portion on the side where the electrode lead 11 is exposed to the outside or in a sealing portion on a corner side of the case, the amount of gas vented toward the side of the electrode lead 11 can be minimized, thereby further improving the safety of the battery.

[0113] 6 to 8 are partially enlarged views of a vent member in a secondary battery according to still another embodiment of the present invention.

[0114] 6 and 7, the shape of the vent member 15 may be, for example, elliptical or stepped, but the shape of the vent member 15 may be modified to be circular, triangular, trapezoidal, or the like.

[0115] 8, the vent member 15 may have an asymmetrical stepped shape. When the vent member 15 is located in a sealing portion on a side where the electrode lead 11 is exposed to the outside or in a sealing portion on a corner side of the case, the step of the step may be formed to correspond to the side of the electrode lead 11. In this case, the ejection direction of the vented gas can be separated from the side of the electrode lead 11 as far as possible.

[0116] In one embodiment of the present invention, the thickness of the vent member 15 may decrease continuously or discontinuously along the direction in which the electrode lead 11 protrudes.

[0117] FIG. 9 is a cross-sectional view taken along line BB' in FIG.

[0118] 9, the thickness of the vent member 15 may be decreased discontinuously in a stepwise manner as shown in FIG. 9(a) or may be decreased continuously as shown in FIG. 9(b).

[0119] In one embodiment of the present invention, the secondary battery may be a cylindrical, prismatic, or pouch-type secondary battery, and more preferably, the secondary battery may be a pouch-type secondary battery.

[0120] The present invention will be described in detail below with reference to specific examples. However, the examples according to the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0121] <Example 1> An upper pouch and a lower pouch in which polyethylene terephthalate / aluminum foil / polypropylene resin were laminated in this order were arranged so that the polypropylene resins faced each other, and then an electrode assembly in which a positive electrode / separator / negative electrode were laminated in this order was housed inside.

[0122] Thereafter, a linear low-density polyethylene film having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (ExxonMobil, Exceed (registered trademark), 1018, melting point: 119°C, comonomer content relative to total resin content: 7.6% by weight, weight average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C) was coated on both sides with a pressure-sensitive adhesive (PSA) (LG Chem, BPSA (Barrier Pressure-Sensitive Adhesives)) to a thickness of 5 μm, to manufacture a vent member.

[0123] The manufactured vent member was inserted between the polypropylene resins and then heat-sealed to manufacture a secondary battery.

[0124] <Example 2> A secondary battery was manufactured in the same manner as in Example 1, except that a linear low-density polyethylene having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (LG Chem, Lucene (registered trademark), SP311, melting point: 119°C, comonomer content relative to total resin content: 9.0 wt%, weight average molecular weight: 270,756 g / mol, polydispersity index: 2.674, crystallization temperature: 107°C) was used instead of the linear low-density polyethylene having a comonomer having 6 carbon atoms used in Example 1.

[0125] <Example 3> A secondary battery was manufactured in the same manner as in Example 1, except that a linear low-density polyethylene having a comonomer having a carbon number of 8 polymerized in the presence of a metallocene catalyst (Dow Chemical, Elite (registered trademark), 5401GT, melting point: 120°C, comonomer content relative to total resin content: 11.8 wt%, weight average molecular weight: 251,521 g / mol, polydispersity index: 3.796, crystallization temperature: 105°C) was used instead of the linear low-density polyethylene having a comonomer having a carbon number of 6 used in Example 1.

[0126] <Comparative Example 1> An upper pouch and a lower pouch in which polyethylene terephthalate / aluminum foil / polypropylene resin were laminated in this order were arranged so that the polypropylene resins faced each other, and then an electrode assembly in which a positive electrode / separator / negative electrode were laminated in this order was housed inside.

[0127] Then, a linear low-density polyethylene having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (Exceed (registered trademark), 1018, manufactured by ExxonMobil) was inserted between the polypropylene resins and heat-sealed to produce a secondary battery.

[0128] <Comparative Example 2> An upper pouch and a lower pouch in which polyethylene terephthalate / aluminum foil / polypropylene resin were laminated in this order were arranged so that the polypropylene resins faced each other, and then an electrode assembly in which a positive electrode / separator / negative electrode were laminated in this order was housed inside.

[0129] Thereafter, a linear low-density polyethylene film having a comonomer having 6 carbon atoms polymerized in the presence of a metallocene catalyst (ExxonMobil, Exceed (registered trademark), 1018, melting point: 119°C, comonomer content relative to total resin content: 7.6 wt%, weight average molecular weight: 289,053 g / mol, polydispersity index: 3.023, crystallization temperature: 106°C) was coated on both sides with a pressure-sensitive adhesive (PSA) (LG Chem, BPSA) to a thickness of 20 μm, to manufacture a vent member.

[0130] The manufactured vent member was inserted between the polypropylene resins and then heat-sealed to manufacture a secondary battery.

[0131] <Evaluation Example 1: Measurement of sealing strength of secondary battery> For the secondary batteries manufactured in Example 1, Comparative Example 1, and Comparative Example 2, the maximum sealing strength between the sealing portion and the vent member at room temperature was measured and is shown in Table 1 below.

[0132] The maximum sealing strength was measured by cutting the part of the case where the vent member was inserted to a width of 15 mm and a length of 5 cm, opening both ends 180° and fixing them to a UTM jig, and conducting a tensile test at 25°C and a speed of 5 mm / min. at which the maximum sealing strength was measured at which the case broke.

[0133] [Table 1]

[0134] From Table 1, it can be seen that the maximum sealing strength at room temperature between the vent member and the sealing portion of the secondary battery of Comparative Example 2, in which the thickness of the second layer exceeds 5 μm, is much lower than the maximum sealing strength at room temperature between the sealing portion and the vent member of the secondary battery manufactured in Example 1, in which the thickness of the second layer is 5 μm or less.

[0135] <Evaluation Example 2: Measurement of positional deviation of vent components> The positional deviation of the vent member produced in Example 1 and the vent member produced in Comparative Example 1 was measured.

[0136] The misalignment of the vent member was calculated by marking the position where the vent member was to be inserted on the sealant layer and outer layer of the secondary battery by drawing lines on each of them, and then attaching the vent members manufactured in Example 1 and Comparative Example 1 to the sealant layer and sealing them. After sealing, the distance where the vent member deviated from the line drawn on the outer layer was measured and calculated.

[0137] It can be seen that the positional deviation of the vent member in Example 1 is ±0.5 mm, whereas the positional deviation of the vent member in Comparative Example 1 is ±2 mm. [Explanation of symbols]

[0138] 10 Secondary battery 11 Electrode Lead 12 Electrode assembly 13 cases 13a Storage area 13b Sealing part 14 Lead Film 15 Venting material 15a Layer 1 15b Layer 2

Claims

1. An electrode assembly; a case including a receiving portion for receiving the electrode assembly and a sealing portion including a sealant resin and formed to seal the electrode assembly; a vent area formed in at least a portion of the case; a first layer including a resin having a melting point lower than that of the sealant resin, and a second layer including an adhesive substance and positioned on at least one surface of the first layer; and a vent member inserted into the vent region; The second layer has a thickness of 5 μm or less, The vent region is located in a sealing portion other than the sealing portion on the side where the electrode lead is exposed to the outside, The adhesive material comprises an acrylic polymer, a polyurethane, an epoxy resin, a silicone, a butyl rubber, a polyisobutylene, or two or more of these.

2. The secondary battery according to claim 1 , wherein the vent member is formed to be longer than the sealing portion, and the vent member is exposed to both the inside and the outside of the case.

3. The secondary battery according to claim 2 , wherein the second layer is located on at least one surface of the first layer exposed to the outside of the case.

4. The secondary battery according to claim 1 , wherein the resin having a melting point lower than that of the sealant resin contains a linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

5. 5. The secondary battery according to claim 4, wherein the resin having a melting point lower than that of the sealant resin comprises a linear low-density polyethylene having a comonomer having 6 to 8 carbon atoms.

6. 5. The secondary battery according to claim 4, wherein in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms, a content of the comonomer having 6 or more carbon atoms is 15% by weight or less relative to 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

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

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

9. 9. The secondary battery according to claim 8, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a crystallization temperature of 90° C. to 115° C.

10. 5. The secondary battery according to claim 4, wherein the linear low-density polyethylene having a comonomer having 6 or more carbon atoms has a weight average molecular weight of 100,000 g / mol to 400,000 g / mol.

11. The secondary battery according to claim 1 , wherein the vent member vents at 100° C. to 120° C.

12. The secondary battery according to claim 1 , wherein the vent member vents at a pressure of 1.5 atm or more.

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

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

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

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

17. 2. The secondary battery according to claim 1, wherein the resin having a melting point lower than that of the sealant resin has a melting point of 100°C to 130°C.

18. The electrode assembly has an electrode lead attached thereto, The secondary battery according to claim 1 , further comprising a lead film that covers a portion of an outer surface of the electrode lead and is interposed between the electrode lead and the case.

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

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