Cap assembly and secondary battery including same

Abstract

The present invention relates to a cylindrical secondary battery, comprising a cap assembly to be coupled to an upper part of a can having an opening on one side and accommodating an electrode assembly therein, the cap assembly including: a top cap coupled to an upper part of the can; a safety vent located below the top cap and coupled to an end of the top cap; and a current interrupting element located below the safety vent and at least partially in contact with the safety vent, the current interrupting element comprising a material having a lower hardness than the safety vent.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0141748, filed with the Korean Intellectual Property Office on October 22, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a cap assembly and a secondary battery including the same, and more particularly to a cylindrical secondary battery that can effectively absorb external pressure due to the difference in physical properties between a safety vent and a current interruption element. [Background technology]

[0003] Depending on the shape of the battery case, secondary batteries are classified into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries, in which the electrode assembly is housed in a pouch-type case made of an aluminum laminate sheet.

[0004] Among these, cylindrical secondary batteries generally have a structure in which a top cap is attached to the top of a battery can and a safety vent is provided below the top cap. In addition, abnormal behavior of the secondary battery can cause the secondary battery to rise in temperature or pressure resistance. To prevent the risk of fire or explosion that can occur in such cases, a safety device is provided inside the secondary battery according to conventional technology.

[0005] Cylindrical secondary batteries are equipped with a safety vent and a current interrupt device (CID) as safety devices.

[0006] The stability test for a cylindrical secondary battery involves placing the cylindrical secondary battery between pressure plates and applying pressure to physically deform the cylindrical secondary battery. The stability test changes the overall shape of the cylindrical secondary battery, which also causes severe deformation of the cap assembly.

[0007] In this case, the safety vent and current interrupting element are made of a hard material, and instead of being deformed by external pressure, they penetrate the gasket and come into contact with the top of the can, causing a short circuit.

[0008] Therefore, there is an increasing need for a secondary battery structure that can fundamentally solve these problems and dramatically improve the defect rate problems such as fire and thermal runaway of cylindrical secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above-mentioned problems of the prior art, the present invention aims to provide a cap assembly in which a safety vent and a current interrupting element are made of materials with different physical properties, and a secondary battery including the same. [Means for solving the problem]

[0010] One embodiment of the present invention provides a cylindrical secondary battery, which is a cap assembly to be coupled to an upper part of a can having an open side and accommodating an electrode assembly therein, the cap assembly including: a top cap coupled to an upper part of the can; a safety vent located below the top cap and coupled to an end of the top cap; and a current interrupting element located below the safety vent and at least partially in contact with the safety vent, wherein the current interrupting element is made of a material having a lower hardness than the safety vent.

[0011] In one embodiment of the present invention, there is provided a cylindrical secondary battery, wherein the safety vent comprises aluminum or an aluminum alloy.

[0012] In one embodiment of the present invention, there is provided a cylindrical secondary battery, wherein the safety vent is provided at an angle of 0° to 30° with respect to the current interrupting element. [Effects of the Invention]

[0013] The cap assembly and secondary battery including the same according to the embodiment of the present invention include a safety vent and a current interruption element with different physical properties, and can effectively absorb external pressure and prevent deformation due to external pressure. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view illustrating a conventional cap assembly. [Figure 2] 1 is a cross-sectional view illustrating a cylindrical secondary battery according to an embodiment of the present invention. [Figure 3] 1 is a cross-sectional view illustrating a cap assembly according to one embodiment of the present invention. [Explanation of symbols]

[0015] 100 Cylindrical secondary battery 10...electrode assembly 20 cans 21 Beading section 22 Crimping section 30 Cap Assembly 31 Top Cap 32 Safety Vent 32a ···Curved center section 32b Venting section 32c...Frame part 32d notch 33 Current interruption element 33a...Central part 33b CID filter section 40 Gasket 50 CID gasket DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below with reference to the drawings. However, the drawings are for illustrative purposes only and the scope of the present invention is not limited by the drawings.

[0017] 2 is a cross-sectional view illustrating a cylindrical secondary battery 100 according to an embodiment of the present invention. The cylindrical secondary battery 100 according to an embodiment of the present invention may include an electrode assembly 10, a can 20, and a cap assembly 30.

[0018] The electrode assembly 10 is a chargeable and dischargeable power generating element having a laminated structure of an anode / separator / cathode, and may have a jelly roll structure in which a separator is interposed between a long sheet-like anode and cathode coated with an active material and wound up.

[0019] The cylindrical secondary battery 100 according to the present invention may have a first insulating plate (not shown) and a second insulating plate (not shown) respectively positioned on the top and bottom of the electrode assembly 10. The first insulating plate may provide insulation between the electrode assembly 10 and the cap assembly 30, and the second insulating plate may provide insulation between the electrode assembly 10 and the bottom of the can 20.

[0020] The electrode assembly 10 may further include a center pin (not shown) at the center. The center pin prevents the electrode assembly 10, which is wound in the form of a jelly roll, from unraveling and serves as a passage for gas movement inside the cylindrical secondary battery 100.

[0021] The can 20 may have a cylindrical structure with an internal space. The internal space of the can 20 may accommodate an electrode assembly 10 including electrodes and a separator, and an electrolyte (not shown). One side of the can 20 may be open, and the other side may be sealed. Here, the terms "one side" and "other side" refer to the ends located at the top and bottom along the direction of gravity or the central axis of the can 20.

[0022] A beading portion 21 folded toward the center of the cylindrical secondary battery 100 may be provided on one side of the open can 20. The can 20 may have a crimping portion 22 above the beading portion 21. That is, the crimping portion 22 may be located at the top of the can 20.

[0023] Can 20 may be constructed from a lightweight, conductive metallic material such as aluminum or an aluminum alloy.

[0024] 3 is a cross-sectional view illustrating a cap assembly 30 according to one embodiment of the present invention. The cap assembly 30 may be coupled to the top of the can 20 and may include a top cap 31, a safety vent 32, and a current interrupt device 33.

[0025] The top cap 31 may protrude from the top of the cap assembly 30 and serve as an electrode terminal for electrical connection to the outside. The top cap 31 may be coupled to the top of the can 20. That is, the top cap 31 may be coupled to the crimping portion 22 located at the top of the can 20.

[0026] The cylindrical secondary battery 100 according to the present invention may include a gasket 40 between the crimping portion 22 and the top cap 31. The gasket 40 can increase the sealing force of the can 20.

[0027] The safety vent 32 may be located below the top cap 31 and coupled to an end of the top cap 31. The safety vent 32 may be in contact with the end of the top cap 31 for a certain length, and the portion excluding the contact length may be spaced a certain distance from the top cap 31. More specifically, the distance between the safety vent 32 and the top cap 31 may increase from the end that contacts the top cap 31 toward the center. Here, the end may refer to a position corresponding to the position of the crimping portion 22 or the gasket 40.

[0028] In one embodiment, the safety vent 32 may be provided with an end perpendicular to the axial direction of the can 20. In this case, the top cap 31 may be provided perpendicular to the axial direction of the can 20, just like the safety vent 32. In other words, the safety vent 32 and the top cap 31 may be positioned horizontally.

[0029] In other embodiments, the safety vent 32 may be provided with a folded end that wraps around the outer periphery of the top cap 31 .

[0030] The safety vent 32 may be provided by being folded at least one time. The safety vent 32 may include a curved central portion 32a that is concave in the center, a frame portion 32c that is coupled to the edge of the top cap 31, i.e., the area where the top cap 31 is coupled to the can 20, and a venting portion 32b that connects the curved central portion 32a and the frame portion 32c. The safety vent 32 may also include one or more notches 32d between the curved central portion 32a and the frame portion 32c.

[0031] For example, the safety vent 32 may be provided with two notches 32d in a portion that does not contact the top cap 31. That is, the safety vent 32 may be bent by the notches 32d, and the center of the safety vent 32 may be recessed to form a curved central portion 32a. The safety vent 32 may then be formed with a venting portion 32b that connects the frame portion 32c that contacts the top cap 31 with the curved central portion 32a. In other words, the notches 32d may be provided in the region where the venting portion 32b and the curved central portion 32a contact each other and in the region where the venting portion 32b and the frame portion 32c contact each other.

[0032] The venting portion 32b of the safety vent 32 may be inclined, and the lower surface of the venting portion 32b may have an angle (θ) of 0° to 30° with respect to the upper or lower surface of the frame portion 32c of the safety vent 32. That is, the frame portion 32c of the safety vent 32 may be positioned parallel to the CID filter 33b (described later), and therefore the lower surface of the venting portion 32b may be provided at an angle of 0° to 30° with respect to the upper surface of the CID filter 33b.

[0033] If the venting portion 32b is inclined at an angle of more than 30° with respect to the CID filter 33b, the curved central portion 32a of the safety vent 32 may be deformed toward the top cap 31 during a stability test of the cylindrical secondary battery 100, which may result in a short circuit and deformation of the cap assembly 30.

[0034] The current interrupting element 33 may be located below the safety vent 32 and may be in at least partial contact with the safety vent 32 .

[0035] The current interrupting element 33 may include a central portion 33a protruding toward the safety vent 32 and a CID filter portion 33b located outside the central portion. Therefore, in the cap assembly 30, the central portion 33a of the current interrupting element 33 may contact the curved central portion 32a of the safety vent 32.

[0036] The cap assembly 30 according to the present invention may include a CID gasket 50 at the end of the CID filter portion 33b. The CID gasket 50 can prevent the safety vent 32 from contacting the current interruption device 33 at any portion other than the central portion 33a.

[0037] In the cap assembly 30 according to the present invention, the current interrupting element 33 may be made of a material having a lower hardness than the safety vent 32. If the current interrupting element 33 has a high hardness, deformation of the current interrupting element 33 due to a stability test or external pressure is minimized, and there is a problem in that the current interrupting element 33 may penetrate the CID gasket 50 and come into contact with the beading portion 21, increasing the possibility of fire.

[0038] The safety vent 32 may include a material with high hardness to reduce the rate of deformation of the safety vent 32 due to external pressure. That is, the safety vent 32 has a low rate of deformation of the safety vent 32 due to external pressure, and can reduce the overall deformation of the top cap 31.

[0039] Furthermore, since the safety vent 32 according to the present invention is formed with a recessed center, when external pressure is applied to the cylindrical secondary battery 100, the curved center of the safety vent 32 may be deformed toward the current interruption element 33.

[0040] At this time, the safety vent 32 applies pressure to the current interrupting element 33 due to deformation of the safety vent 32. However, the current interrupting element 33 is made of a brittle material and is subjected to a large amount of pressure applied by the safety vent 32. Therefore, the deformation rate of the current interrupting element 33 may increase.

[0041] The safety vent 32 may include aluminum or an aluminum alloy. In one embodiment, when the safety vent 32 is an aluminum alloy, it may be an aluminum-manganese alloy. For example, the safety vent 32 may include 85% to 98% by weight of aluminum, 7% or less by weight of manganese, 5% or less by weight of iron, and 5% or less by weight of silicon.

[0042] If the aluminum content in the aluminum alloy exceeds 98 wt %, the ductility increases, which may cause the shape of the cap assembly 30 to deform due to external pressure, resulting in problems such as fire or thermal runaway in the cylindrical secondary battery 100.

[0043] If the manganese content in an aluminum alloy exceeds 7% by weight, castability may decrease and workability may decrease due to stickiness. If the iron content exceeds 5% by weight, not only will ductility decrease, but extrudability and productivity may also decrease, leading to corrosion of the material and the formation of precipitates by combining with aluminum and silicon, which may decrease corrosion resistance. If the silicon content exceeds 5% by weight, not only will formability decrease, but the surface quality of the formed product may also decrease.

[0044] The safety vent 32 has a hardness of 15 kgf / mm 2 (147N / mm 2 ) ~35Kgf / mm 2 (343N / mm 2 ) , preferably with a hardness of 20 kgf / mm 2 (196N / mm 2 ) ~30Kgf / mm 2 (294N / mm 2) may be.

[0045] Safety vent 32 has a yield strength of 1 kgf / mm 2 (9.8N / mm 2 ) ~5Kgf / mm 2 (9.8N / mm 2 ) and preferably has a yield strength of 2 kgf / mm 2 (20N / mm 2 ) ~4Kgf / mm 2 (39N / mm 2 ) may be.

[0046] The safety vent 32 may have a stretch ratio of 35% to 45%, preferably 35% to 40%.

[0047] The current interrupting element 33 may include an aluminum material. More specifically, the current interrupting element 33 may include an aluminum material with a purity of 90% or more. If the aluminum purity of the current interrupting element 33 is less than 90%, the hardness of the current interrupting element 33 may increase, and the rate of deformation due to external pressure may increase.

[0048] The current interruption element 33 has a hardness of 10 kgf / mm 2 (98N / mm 2 ) ~30Kgf / mm 2 (294N / mm 2 ) , preferably with a hardness of 15 kgf / mm 2 (147N / mm 2 ) ~25Kgf / mm 2 (245N / mm 2 ) may be.

[0049] The current interruption element 33 has a yield strength of 2 kgf / mm2 (20N / mm 2 ) ~6Kgf / mm 2 (59N / mm 2 ) , preferably with a hardness of 3Kgf / mm 2 (29N / mm 2 ) ~4Kgf / mm 2 (39N / mm 2 ) may be.

[0050] The current interrupting element 33 may have an elongation ratio of 25% to 35%, preferably 25% to 30%.

[0051] The yield strength and elongation of the safety vent and current interrupting element were measured by measuring specimens of the safety vent and current interrupting element using a tensile testing machine based on KS B 0802 (standard tensile test method for metallic materials), and the Brinell hardness was measured by measuring specimens of the safety vent and current interrupting element using a hardness measuring instrument based on KS B 0805.

[0052] While the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. A cap assembly having an opening at one side and coupled to an upper portion of a secondary battery can, The cap assembly includes: a top cap that couples with the top of the can; a safety vent located under the top cap and coupled to an end of the top cap (excluding composite materials including a main component made of aluminum and a component made of an aluminum-manganese alloy); and a current interruption element located below the safety vent and in at least partial contact with the safety vent; the current interruption element comprises a material that is less hard than the safety vent; the safety vent comprises an aluminum alloy, and the current interruption element comprises an aluminum material; the safety vent has a hardness of 15 kgf / mm 2 (147 N / mm 2 ) to 35 kgf / mm 2 (343 N / mm 2 ); the current interrupting element has a hardness of 10 kgf / mm 2 (98 N / mm 2 ) to 30 kgf / mm 2 (294 N / mm 2 ); the safety vent includes a curved central portion having a recess in the center, a frame portion coupled to an end portion of the top cap, and a venting portion connecting the curved central portion and the end portion; a notch between the curved central portion and the rim; The lower surface of the venting portion forms an angle of 0° to 30° with the upper surface of the frame portion. Cap assembly.

2. 10. The cap assembly of claim 1, wherein the safety vent comprises 85% to 98% by weight aluminum, 0% to 7% or less by weight manganese, 0% to 5% or less by weight iron, and 0% to 5% or less by weight silicon, the sum of the aluminum, manganese, iron, and silicon contents being 100% by weight.

3. The cap assembly of claim 1 , wherein the current interrupting element comprises an aluminum material having a purity of 90% or more.

4. The safety vent has a yield strength of 1 kgf / mm ２ (9.8 N / mm ２ ) ~ 5 kgf / mm ２ (9.8 N / mm ２ ) and The current interrupting element has a yield strength of 2 kgf / mm ２ (20N / mm ２ ) ~ 6 kgf / mm ２ (59 N / mm ２ 10. The cap assembly of claim 1, wherein

5. the safety vent has an elongation ratio of 25% to 35%; The cap assembly of claim 1 , wherein the current interrupting element has an elongation ratio of 35% to 45%.

6. an electrode assembly in which a number of electrodes and separators are alternately stacked; a can having an open side and containing the electrode assembly; and A secondary battery comprising the cap assembly according to any one of claims 1 to 5.

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