Secondary battery

Abstract

The present invention discloses a secondary battery having a vent member. The secondary battery according to one embodiment of the present invention includes an electrode assembly having electrode leads attached thereto, a case housing the electrode assembly, a lead film surrounding a portion of an outer surface of the electrode leads and interposed between the electrode leads and the case, and a vent member, wherein the case includes an outer layer, a metal barrier layer, and a sealant layer, and the sealant layer includes a thermally conductive layer.

Description

Technical Field

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

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0049399 filed on April 15, 2021, and all of the contents disclosed in the specification and drawings of the application are incorporated into this application.

Background Art

[0003] Secondary batteries can be applied to various products and have excellent electrical characteristics such as high energy density. Secondary batteries are used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) driven by electricity. Secondary batteries can significantly reduce the use of fossil fuels, are environmentally friendly in that no by-products are generated during the energy consumption process, and are attracting attention as a new energy source for improving energy efficiency.

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

[0005] A secondary battery generally has a structure in which an electrode assembly including at least one unit cell having a structure of a positive electrode / separator / negative electrode 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 welding a sealant resin of the sealant layer.

[0006] In conventional secondary batteries, the battery can catch fire due to various causes such as internal short circuit, overcharging or over-discharging, and temperature regulation of the secondary battery. At this time, a thermal runaway phenomenon (Thermal Propagation) occurs in which the internal temperature of the secondary battery rises rapidly and heat is transferred to adjacent cells, and the flame can become even larger.

[0007] When a thermal runaway phenomenon occurs, that is, when the internal temperature of a secondary battery rises, in order to minimize damage to the electrodes caused by gas, a directional venting characteristic for discharging gas in one direction is required. However, conventional secondary batteries have a problem in that it is difficult to induce gas discharge in a specific direction.

[0008] Therefore, an object of the present invention is to provide a secondary battery with improved safety by inducing gas discharge in a specific direction.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The problem to be solved by the present invention is to provide a secondary battery with improved safety by inducing gas discharge in a specific direction.

Means for Solving the Problems

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

[0011] The first embodiment is an electrode assembly, an electrode lead attached to the electrode assembly, a case for housing the electrode assembly therein, a lead film formed to surround a part of the outer surface of the electrode lead and interposed between the electrode lead and the case, a vent member, and includes wherein the case includes a sealant layer, and the sealant layer includes a heat conduction layer therein, and relates to a secondary battery.

[0012] The second embodiment is, in the first embodiment, the heat conduction layer may be located in the core of the sealant layer.

[0013] The third embodiment is, in the first embodiment or the second embodiment, The heat conduction layer may contain heat conductive particles.

[0014] In a fourth embodiment, in the third embodiment, The heat conductive particles may include boron nitride, aluminum nitride, or a mixture thereof.

[0015] In a fifth embodiment, in any one of the first to fourth embodiments, The heat conduction layer may be in the form of a film.

[0016] In a sixth embodiment, in the fifth embodiment, The heat conduction layer may be in the form of a film containing heat conductive particles and a binder.

[0017] In a seventh embodiment, in any one of the first to sixth embodiments, The case includes a sealing portion formed to seal the electrode assembly, and the vent member may be located at the sealing portion.

[0018] In an eighth embodiment, in the seventh embodiment, The vent member may be located at a corner-side sealing portion on the side where the electrode lead is exposed to the outside.

[0019] In a ninth embodiment, in the seventh or eighth embodiment, The sealing portion includes a sealant resin, and the vent member may have a melting point lower than that of the sealant resin.

[0020] In a tenth embodiment, in any one of the first to ninth embodiments, The vent member may be vented at 100°C to 120°C.

[0021] In an eleventh embodiment, in the tenth embodiment, The vent member may be vented at a pressure of 1.5 atm or more.

[0022] The 12th embodiment is any one of the 1st to 11th embodiments, the maximum sealing strength of the vent member at 100 °C or higher may be less than 6 kgf / 15 mm.

[0023] The 13th embodiment is any one of the 1st to 12th embodiments, the average sealing strength of the vent member at 100 °C or higher may be less than 4.5 kgf / 15 mm.

[0024] The 14th embodiment is any one of the 1st to 13th embodiments, the maximum sealing strength of the vent member at normal temperature to 60 °C may be 6 kgf / 15 mm or more.

[0025] The 15th embodiment is any one of the 1st to 14th embodiments, the average sealing strength of the vent member at normal temperature to 60 °C may be 4.5 kgf / 15 mm or more.

[0026] The 16th embodiment is any one of the 1st to 15th embodiments, the vent member may include linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0027] The 17th embodiment is the 16th embodiment, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst.

[0028] The 18th embodiment is the 16th embodiment or the 17th embodiment, in the linear low-density polyethylene having a comonomer with 6 or more carbon atoms, the content of the comonomer with 6 or more carbon atoms may be 15% by weight or less based on 100% by weight of the linear low-density polyethylene having a comonomer with 6 or more carbon atoms.

[0029] The 19th embodiment is any one of the 16th to 18th embodiments, the polydispersity index (PDI) of the linear low-density polyethylene having the comonomer with 6 or more carbon atoms may be 4 or less.

[0030] The 20th embodiment is any one of the 16th to 19th embodiments, the case includes a sealing part formed to seal the electrode assembly, the sealing part includes a sealant resin, and the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the linear low-density polyethylene having the comonomer with 6 or more carbon atoms may be 10°C or less.

[0031] The 21st embodiment is the 20th embodiment, the crystallization temperature of the linear low-density polyethylene having the comonomer with 6 or more carbon atoms may be 90°C to 115°C.

[0032] The 22nd embodiment is any one of the 1st to 21st embodiments, the vent member may have a melting point of 100°C to 130°C.

[0033] The 23rd embodiment is any one of the 16th to 22nd embodiments, the weight average molecular weight of the linear low-density polyethylene having the comonomer with 6 or more carbon atoms may be 100,000 g / mol to 400,000 g / mol.

[0034] The 24th embodiment is any one of the 1st to 23rd embodiments, the secondary battery may be a pouch-type secondary battery.

Advantages of the Invention

[0035] In the secondary battery according to an embodiment of the present invention, by including a heat conduction layer in the sealant layer of the case, it becomes easy to induce gas discharge in the direction where the vent member is located. As a result, the safety of the battery can be improved.

[0036] The following drawings attached to this specification illustrate desirable embodiments of the present invention and serve to further facilitate understanding of the technical concept of the invention together with the detailed description of the invention. The present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0038] Hereinafter, desirable 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 the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventor himself must interpret them according to the meaning and concept corresponding to the technical concept of the present invention in accordance with the principle that he can appropriately define the concept of the terms in order to explain the invention in the best way.

[0039] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most desirable embodiments of the present invention and do not represent all of the technical concepts of the present invention. At the time of this application, there can be various equivalents and modifications that can replace them.

[0040] A secondary battery according to an aspect of the present invention includes an electrode assembly to which an electrode lead is attached, a case that houses the electrode assembly therein, a lead film formed to surround a part of the outer surface of the electrode lead and interposed between the electrode lead and the case, and a vent member. The case includes a sealant layer, and the sealant layer includes a heat conduction layer.

[0041] Figure 1 is a diagram showing a secondary battery according to an embodiment of the present invention.

[0042] Referring to Figure 1, the secondary battery 10 includes an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13.

[0043] The electrode assembly 12 includes a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate and the negative electrode plate can be sequentially laminated with the separator interposed therebetween.

[0044] The positive electrode plate may include 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 thereof. Further, the positive electrode plate may include a positive electrode tab made of a metal material, for example, an aluminum material, at one end portion. The positive electrode tab may protrude from one end portion of the positive electrode plate. The positive electrode tab may be welded to one end portion of the positive electrode plate or joined using a conductive adhesive.

[0045] The negative electrode plate may include a negative electrode current collector made of a conductive metal thin plate, for example, copper (Cu) foil, and a negative electrode active material layer coated on at least one surface thereof. Further, the negative electrode plate may include a negative electrode tab formed of a metal material, for example, a nickel (Ni) material, at one end portion. The negative electrode tab may protrude from one end portion of the negative electrode plate. The negative electrode tab may be welded to one end portion of the negative electrode plate or joined using a conductive adhesive.

[0046] The separator is located between the positive electrode plate and the negative electrode plate and electrically insulates the positive electrode plate and the negative electrode plate from each other. The separator may be a porous membrane through which lithium ions can pass through each other between the positive electrode plate and the negative electrode plate. The separator may include, for example, a porous membrane using polyethylene (PE), or polypropylene (PP), or a composite film thereof.

[0047] 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 a pore structure (interstitial volume) between the particles.

[0048] The electrode assembly 12 can be a jelly roll type (winding type) electrode assembly having a structure in which a long sheet-like positive electrode and negative electrode are wound with a separation membrane interposed therebetween, a stack type (lamination type) electrode assembly in which a plurality of positive electrodes and negative electrodes cut out in a predetermined unit size are sequentially laminated with a separation membrane interposed therebetween, or a stack / folding type electrode assembly having a structure in which a bi-cell or full cell in which a positive electrode and a negative electrode of a predetermined unit are laminated with a separation membrane interposed therebetween is wound.

[0049] The case 13 serves to house the electrode assembly 12.

[0050] Figure 2 is a cross-sectional view taken along A-A' of Figure 1.

[0051] Referring to Figure 2, the case 13 includes a sealant layer and includes a heat conduction layer in the sealant layer. For example, the case 13 may be provided with a multi-layer structure including an outer layer 131 for protection from external impact, a metal barrier layer 132 for blocking moisture, a sealant layer 133 for sealing the case, a heat conduction layer 134, and the sealant layer 133.

[0052] The outer layer 131 can include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolyester, polycarbonate, nylon, and other polyester-based films, and can be composed of a single layer or multiple layers.

[0053] The metal barrier layer 132 can include aluminum, copper, etc.

[0054] The sealant layer 133 contains a sealant resin and may be composed of multiple layers. When the sealant layer 133 is multilayered, the heat conduction layer 134 may be located between the multiple sealant layers 133. For example, the heat conduction layer 134 may be located in the core portion of the sealant layer 133.

[0055] 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, but is not limited to, ethylene-propylene rubber, ethylene-propylene block copolymer, etc.

[0056] The heat conduction layer 134 can disperse local heat generation due to abnormal reactions of the battery throughout the case, effectively preventing local heat damage to the case. Also, the heat conduction layer 134 can transfer local heat generation to the vent member side, making it easier to discharge gas from the vent member.

[0057] When the temperature inside the secondary battery rises rapidly due to abnormal operation of the battery, the case may be damaged before venting occurs at the vent member. When a heat conduction layer 134 is provided as in a secondary battery according to an embodiment of the present invention, heat transfer to the case 13, for example, the metal barrier layer 132 of the case 13, can be prevented, thus preventing the problem of the case 13 being damaged before venting occurs.

[0058] In one embodiment of the present invention, the heat conduction layer 134 may be prevented from directly contacting the vent member 15 described later. Even if the heat conduction layer 134 does not directly contact the vent member 15, the heat conduction layer 134 can transfer local heat generation to the vent member side, making it easier to discharge gas from the vent member.

[0059] In one embodiment of the present invention, the heat conduction layer 134 can be inserted into the sealing layer 133 by an extrusion lamination method.

[0060] In one embodiment of the present invention, the heat conduction layer 134 may contain heat conductive particles. The heat conductive particles may include, for example, boron nitride, aluminum nitride, or a mixture thereof.

[0061] In one embodiment of the present invention, the heat conduction layer 134 may be in the form of a film. For example, the heat conduction layer 134 may be in the form of a film containing the heat conductive particles and a binder. The binder may be a non-conductive material. For example, the binder may include polypropylene and the like.

[0062] When the heat conduction layer 134 contains the heat conductive particles and a binder, the content of the heat conductive particles may be 10 to 80% by weight based on 100% by weight of the heat conduction layer 134. When the content of the heat conductive particles satisfies the above-described range, it may be easier to effectively prevent local heat damage of the case.

[0063] When the heat conduction layer 134 is in the form of a film, a mixture of the heat conductive particles and a binder may be extruded to form a film.

[0064] When the heat conduction layer 134 is in the form of a film, the thickness of the heat conduction layer 134 may be 20 to 40 μm.

[0065] In one embodiment of the present invention, the case 13 may include a storage portion 13a for storing the electrode assembly 12 and a sealing portion 13b formed for sealing the electrode assembly 12.

[0066] The sealing portion 13b can be welded along the outer peripheral surface of the storage portion 13a to seal the electrode assembly 12. The sealing layer of the case 13 can be welded to form the sealing portion 13b. The welding of the sealing portion 13b can be heat welding, welding by ultrasonic waves, etc., but is not particularly limited as long as the sealing portion 13b can be welded.

[0067] In one embodiment of the present invention, the case 13 can be in a pouch form.

[0068] The battery case 13 in the form of a pouch may include an upper pouch and a lower pouch. When the case 13 includes an upper pouch and a lower pouch, after arranging the upper pouch and the lower pouch so that the sealing resins face each other, the opposing sealing resins are welded to each other by heat and pressure to seal the battery.

[0069] The sealing portion 13b can be four-sided sealed or three-sided sealed at the peripheral edge of the case 13 in some embodiments. In the three-sided sealing structure, after the upper pouch and the lower pouch are formed on one pouch sheet, the boundary surface between the upper pouch and the lower pouch is bent so that the storage portions 13a formed in the upper pouch and the lower pouch are overlapped, and the remaining three peripheral edges except the bent portion are sealed.

[0070] As shown in FIG. 1, the electrode lead 11 can be housed in the case 13 such that a part of the electrode lead 11 is exposed outside the case 13.

[0071] Referring to FIG. 1, a secondary battery 10 according to an embodiment of the present invention includes a lead film 14.

[0072] The lead film 14 surrounds a part of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the case 13. For example, by interposing the lead film 14 between the electrode lead 11 and the sealing portion 13b of the case 13 where the electrode lead 11 protrudes or extends from the case 13, the binding between the electrode lead 11 and the case 13 can be assisted.

[0073] Referring to FIG. 1, a secondary battery 10 according to an embodiment of the present invention includes a vent member 15. When a thermal runaway phenomenon occurs, the vent member 15 can guide the discharge of gas in a specific direction to improve the safety of the battery.

[0074] FIG. 3 is a cross-sectional view taken along line B-B' of FIG. 1, and shows a state in which a vent occurs in a secondary battery according to an embodiment of the present invention. Specifically, FIG. 3 is a cross-sectional view showing a vent member in a secondary battery according to an embodiment of the present invention.

[0075] Referring to FIG. 3, at a temperature at which the battery operates normally, the vent member serves to seal the case from the outside. When the temperature of the battery rises excessively due to abnormal operation of the battery, the sealing strength of the portion where the vent member is inserted decreases while the vent member melts. As a result, gas can be discharged at that portion. For example, a gap can be formed between the vent member and the case by the pressure of the gas inside the battery being applied to the interface between the vent member and the case, and gas can be discharged therefrom.

[0076] Referring to FIG. 3, the vent member 15 can be located between the sealant layer 133 on the upper part of the case and the sealant layer 133 on the lower part of the case. The vent member 15 can be located between the sealant layer 133 on the upper part of the case and the sealant layer 133 on the lower part of the case by being welded.

[0077] The vent member 15 and the case 13 can be overlapped by thermal welding. In another example, the vent member 15 and the case 13 can be overlapped by an adhesive such as glue. In still another example, the vent member 15 and the case 13 can be physically coupled to each other by a clip or the like. In still another example, at least a part of the vent member 15 can be embedded in a film constituting the case 13, for example, a sealant resin (embedding).

[0078] In one embodiment of the present invention, the melting point of the vent member 15 may be lower than the melting point of the sealing resin. When the melting point of the vent member 15 is lower than that of the sealing resin, the vent member 15 can be melted faster than the sealing resin at high temperatures. By reducing the sealing strength of the portion where the vent member 15 is inserted compared to the sealing strength of other case portions including the sealing resin, the vent characteristics can be more easily realized.

[0079] In one embodiment of the present invention, the vent member 15 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 vent member 15 satisfies the above-mentioned range, at high temperatures, for example, 100°C or higher, the sealing strength of the case 13 portion where the vent member 15 is inserted decreases, and the vent characteristics can be more easily realized.

[0080] The melting point of the vent member 15 can be measured using a differential scanning calorimeter (DSC). For example, after increasing the temperature of the sample from 30°C to 280°C at a rate of 10°C / min, maintaining it at 280°C for 10 minutes, cooling it to 30°C at a rate of 10°C / min, and then maintaining it at 30°C for 10 minutes. Thereafter, after increasing the temperature of the sample from 30°C to 280°C at a rate of 10°C / min, the temperature can be maintained at 280°C for 10 minutes to measure the melting point.

[0081] Referring to FIGS. 1 and 3, the vent member 15 may be located at the sealing portion 13b.

[0082] Referring to FIG. 1, the vent member 15 may be located at the sealing portion on the corner side of the case. For example, the vent member 15 may be located at 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 at the sealing portion adjacent to the electrode lead 11 except for the region between the electrode leads 11. When the vent member 15 is located at 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, and the safety of the battery can be further improved.

[0083] In one embodiment of the present invention, when the sealing portion 13b is sealed on three sides, the bent side surface of the case and one end of the vent member 15 can be in close contact with each other.

[0084] In still another embodiment of the present invention, the vent member 15 can be located at the sealing portion excluding the sealing portion where the electrode lead 11 is exposed to the outside.

[0085] In another embodiment of the present invention, the vent member 15 can be located at the sealing portion where the electrode lead 11 is exposed to the outside. For example, the vent member 15 can be located at the sealing portion between the electrode lead 11 and the electrode lead 11.

[0086] In one embodiment of the present invention, the vent member 15 may further include an adhesive layer for a smoother arrangement.

[0087] In one embodiment of the present invention, the vent member 15 can discharge or exhaust gas from the storage portion to the outside of the battery by venting at 100°C to 120°C. In particular, the vent member 15 can be vented at a temperature of 100°C to 120°C and a pressure of 1.5 atm or more. By venting the vent member 15 under the above-described temperature range and / or the above-described pressure conditions, the battery can be sealed when the battery operates normally, while gas discharge can be induced only during abnormal operation of the battery.

[0088] In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm, or less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm at 100 °C or higher. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf / 15 mm, or less than 5 kgf / 15 mm, or less than 4.5 kgf / 15 mm at 100 °C to 120 °C. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 3 kgf / 15 mm, or 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 above-described sealing strength in the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted at a high temperature, for example, 100 °C or higher, decreases, and the vent characteristics can be more easily realized.

[0089] Also, 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 above-described sealing strength in the above-described temperature range, even if the vent member 15 is inserted, the portion of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal operation of the battery, and the battery sealing performance can be more easily ensured.

[0090] In one embodiment of the present invention, the vent member 15 has 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 more at room temperature to 60 °C. When the vent member 15 satisfies the above-described sealing strength, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted at a high temperature, for example, 100 °C or higher, decreases, and the vent characteristics can be easily realized. Also, during normal operation of the battery, the case 13 has excellent sealing strength, and the battery sealing performance can be more easily ensured.

[0091] 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 above-described sealing strength in the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted at a high temperature, for example, 100°C or higher, is reduced, and the vent characteristics can be more easily realized.

[0092] 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, or 5 kgf / 15 mm or more, or 6 kgf / 15 mm or more, or 7 kgf / 15 mm or more at normal temperature to 60°C. When the vent member 15 satisfies the above-described sealing strength in the above-described temperature range, even if the vent member 15 is inserted, the portion of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal operation of the battery, and the sealing performance of the battery can be more easily ensured.

[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 100°C or higher and an average sealing strength of 4.5 kgf / 15 mm or more at normal temperature to 60°C. When the vent member 15 has the above-described sealing strength in the above-described temperature range, the sealing strength of the portion of the case 13 into which the vent member 15 is inserted at a high temperature, for example, 100°C or higher, is reduced, and the vent characteristics can be more easily realized. Also, the case 13 has excellent sealing strength during normal operation of the battery, and the sealing performance of the battery can be more easily ensured.

[0094] The sealing strength of the vent member 15 due to temperature can be measured by cutting the case 13 at the portion where the vent member 15 is inserted into a width of 15 mm and a length of 5 cm, opening both ends by 180°, interposing them in a UTM jig, and then performing a tensile test at a speed of 5 mm / min.

[0095] At this time, the maximum sealing strength means the maximum value when the case 13 breaks, and the average sealing strength means the average value when the case 13 is stretched by 8 mm at 4.5 kgf / 15 mm when the maximum sealing strength is 4.5 kgf / 15 mm or more, and when the maximum sealing strength is less than 4.5 kgf / 15 mm, it means the average value when the case 13 is stretched by 8 mm at the maximum sealing strength.

[0096] In one embodiment of the present invention, the vent member 15 may include linear low-density polyethylene having a comonomer with 6 or more carbon atoms. By including linear low-density polyethylene having a comonomer with 6 or more carbon atoms in the vent member 15, the sealing property of the case 13 is excellent in the normal temperature range, for example, room temperature to 60°C, and at high temperatures, for example, 100°C or more, the sealing strength of the case into which the vent member 15 is inserted can be reduced to realize or induce venting.

[0097] In one embodiment of the present invention, the vent member 15 may include linear low-density polyethylene having a comonomer with 6 to 8 carbon atoms.

[0098] In one embodiment of the present invention, the linear low-density polyethylene having a comonomer with 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having a comonomer with 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 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 the comonomer having 6 or more carbon atoms is 15% by weight or less, or 12% by weight or less, or 11.8% by weight or less, or 10% by weight or less, or 9% by weight or less, or 8% by weight or less, or 7.6% by weight or less, based on 100% by weight of the linear low-density polyethylene having the comonomer having 6 or more carbon atoms. Further, the content of the comonomer having 6 or more carbon atoms can be 5% by weight or more, or 7.6% by weight or more, or 8% by weight or more, or 9.0% by weight or more, or 10% by weight or more, or 11.8% by weight or more, or 12% by weight or more, based on 100% by weight of the linear low-density polyethylene having the comonomer having 6 or more carbon atoms. When the content of the comonomer having 6 or more carbon atoms satisfies the above-described range, the problem of a decrease in sealing strength during normal operation of the battery can be easily prevented by a decrease in the packing density between molecules.

[0100] The content of the comonomer having 6 or more carbon atoms can be measured by H-NMR. For example, after completely dissolving about 10 mg of the sample in about 0.6 mL of trichloroethylene solvent using a heat gun, sampling is performed into an NMR tube, 1 and 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 the comonomer having 6 or more carbon atoms can 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 the comonomer having 6 or more carbon atoms satisfies the above-described range, the sealing strength can be further improved during normal operation of the battery.

[0102] In one embodiment of the present invention, the polydispersity index (PDI) of the linear low-density polyethylene having the 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. Further, the polydispersity index (PDI) may be 1.0 or more. When the polydispersity index of the linear low-density polyethylene having the comonomer with 6 or more carbon atoms satisfies the above-described range, the molecular weight distribution becomes narrow, and the sealing strength and physical properties can be further improved during the normal operation of the battery.

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

[0104] - Column: Tosoh HLC-8321 GPC / HT - Solvent: Trichlorobenzene (TCB) + 0.04% BHT (after drying with 0.1% CaCl2) - Flow rate: 1.0 ml / min - Sample concentration: 1.5 mg / ml - Injection volume: 300 μl - Column temperature: 160 °C - Detector: RI detector - Standard: Polystyrene (corrected with a cubic function)

[0105] 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. Further, 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-described range, the welding characteristics during the normal operation of the battery of the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms can be more excellent.

[0106] 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 above-described range, the welding characteristics of the sealant resin and the linear low-density polyethylene having a comonomer with 6 or more carbon atoms can be more excellent.

[0107] 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.

[0108] The crystallization temperature can be measured using a differential scanning calorimeter (DSC). For example, after increasing the temperature of the sample from 30 °C to 280 °C at 10 °C / min, maintaining it at 280 °C for 10 minutes, cooling it to 30 °C at 10 °C / min, and then maintaining it at 30 °C for 10 minutes. Then, after increasing the temperature of the sample from 30 °C to 280 °C at 10 °C / min and maintaining the temperature at 280 °C for 10 minutes, the crystallization temperature can be measured.

[0109] In one embodiment of the present invention, the vent member 15 may have various shapes such that gas flows toward the vent region. For example, the vent member 15 may have a film shape.

[0110] The vent member 15 may be formed to have a predetermined thickness with a preset size. Also, depending on the design, the insertion length of the vent member 15 may be made different, or the vent member 15 may be inserted into the case 13 such that the venting pressure and position can be controlled. Here, the insertion length of the vent member means the maximum value of the distance between one end and the other end of the vent member with reference to the protruding direction of the electrode lead.

[0111] In one embodiment of the present invention, the insertion length of the vent member 15 may be smaller than the width of the sealing portion 13b. For example, the insertion length of the vent member 15 may be less than about 50% of the width of the sealing portion 13b. Here, the width of the sealing portion 13b means the maximum value of the distance between one end and the other end of the sealing portion 13b with reference to the protruding direction of the electrode lead 11.

[0112] In another embodiment of the present invention, the insertion length of the vent member 15 may be larger 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.

[0113] In one embodiment of the present invention, the vent member 15 may further include an adhesive layer for smoother attachment.

[0114] In one embodiment of the present invention, the secondary battery may be a cylindrical, rectangular, or pouch-type secondary battery. Among them, the secondary battery may be a pouch-type secondary battery.

[0115] As described above, the present invention has been described with specific examples, but the examples according to the present invention can be deformed into various other forms, and it should not be construed that the scope of the present invention is limited to the following examples. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

Description of Symbols

[0116] 10 Secondary battery 11 Electrode lead 12 Electrode assembly 13 Case 13a Storage part 13b Sealing part 14 Lead film 15 Vent member 131 Outer layer 132 Metal barrier layer 133 Sealant layer 134 Heat conduction layer

Claims

1. An electrode assembly body, an electrode lead attached to the electrode assembly body, a case for housing the electrode assembly body therein, a lead film formed so as to surround a part of the outer surface of the electrode lead and interposed between the electrode lead and the case, and a vent member, wherein the case includes a sealant layer, and the sealant layer includes a heat conduction layer, the sealant layer includes a sealant resin, the sealant resin includes polypropylene, acid-modified polypropylene, random polypropylene, ethylene-propylene copolymer, or two or more thereof, the heat conduction layer includes heat conductive particles including boron nitride, aluminum nitride, or a mixture thereof, characterized in that it is a secondary battery.

2. The secondary battery according to claim 1, characterized in that the heat conduction layer is located in the core of the sealant layer.

3. The secondary battery according to claim 1, characterized in that the heat conduction layer is in the form of a film.

4. The secondary battery according to claim 3, characterized in that the heat conduction layer is in the form of a film including heat conductive particles and a binder.

5. The case includes a sealing portion formed for sealing the electrode assembly body, The secondary battery according to claim 1, characterized in that the vent member is located at the sealing portion.

6. The secondary battery according to claim 5, characterized in that the vent member is located at the corner side sealing portion on the side where the electrode lead is exposed to the outside.

7. The secondary battery according to claim 5, characterized in that the vent member has a melting point lower than that of the sealant resin.

8. The secondary battery according to claim 1, characterized in that the vent member is vented at 100°C to 120°C.

9. The secondary battery according to claim 8, characterized in that the vent member is vented at a pressure of 1.5 atm or more.

10. The secondary battery according to claim 1, characterized in that the maximum sealing strength of the vent member at 100°C or higher is less than 6 kgf / 15 mm.

11. The secondary battery according to claim 1, characterized in that the average sealing strength of the vent member at 100°C or higher is less than 4.5 kgf / 15 mm.

12. The secondary battery according to claim 1, characterized in that the maximum sealing strength of the vent member at room temperature to 60°C is 6 kgf / 15 mm or more.

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

14. The secondary battery according to any one of claims 1 to 13, wherein the vent member contains linear low density polyethylene having a comonomer with 6 or more carbon atoms.

15. In the linear low density polyethylene having a comonomer with 6 or more carbon atoms, the content of the comonomer with 6 or more carbon atoms is 15% by weight or less based on 100% by weight of the linear low density polyethylene having a comonomer with 6 or more carbon atoms. The secondary battery according to claim 14 is characterized by this.

16. The secondary battery according to claim 14, wherein a polydispersity index of the linear low density polyethylene having a comonomer with 6 or more carbon atoms is 4 or less.

17. The case includes a sealing portion formed to seal the electrode assembly. The sealing portion contains a sealant resin. The secondary battery according to claim 14, wherein a difference between a crystallization temperature of the sealant resin and a crystallization temperature of the linear low density polyethylene having a comonomer with 6 or more carbon atoms is 10°C or less.

18. The secondary battery according to claim 17, wherein a crystallization temperature of the linear low density polyethylene having a comonomer with 6 or more carbon atoms is 90°C to 115°C.

19. The secondary battery according to claim 1, wherein the vent member has a melting point of 100°C to 130°C.

20. The secondary battery according to claim 14, wherein a weight average molecular weight of the linear low density polyethylene having a comonomer with 6 or more carbon atoms is 100,000 g / mol to 400,000 g / mol.

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

Images