Secondary battery and device including the same

Abstract

A secondary battery according to one embodiment of the present invention includes a current interrupt device (CID); a safety vent positioned on the current interrupt device and electrically connected to the current interrupt device; and a CID gasket surrounding the periphery of the current interrupt device, the CID gasket including a reinforcing material, the reinforcing material including at least one of glass fiber, carbon fiber, aramid fiber, cellulose, ceramic particles, and filler.

Description

[Technical Field]

[0001] Cross-reference to related application(s) This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0041436 filed on April 6, 2020, and Korean Patent Application No. 10-2021-0044214 filed on April 5, 2021, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a secondary battery and a device including the same, and more particularly to a secondary battery and a device including the same that have improved safety in high-temperature and high-pressure environments. [Background technology]

[0003] Recently, with the rapid increase in demand for portable electronic products such as laptops, video cameras, and mobile phones, and the full-scale development of electric vehicles, energy storage batteries, robots, satellites, and the like, much research has been conducted on secondary batteries used as the driving power source for these products.

[0004] The electrode assembly housed in the battery case is a chargeable / dischargeable power generating element having a stacked structure of a positive electrode, a separator, and a negative electrode. It is classified into a jelly roll type, a stack type, and a stack / folding type. The jelly roll type is a long sheet-like positive electrode and negative electrode coated with an active material, wound with a separator interposed between them. The stack type is a type in which multiple positive electrodes and negative electrodes of a predetermined size are stacked in sequence with a separator interposed between them. The stack / folding type is a combination of the jelly roll type and the stack type. Among these, the jelly roll type electrode assembly has the advantages of being easy to manufacture and having a high energy density per weight.

[0005] Secondary batteries are classified according to the shape of the battery case into cylindrical batteries, in which an electrode assembly is housed in a cylindrical metal can, prismatic batteries, in which an electrode assembly is housed in a prismatic metal can, and pouch batteries, in which an electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet. Of these, cylindrical batteries have the advantages of relatively large capacity and structural stability.

[0006] Meanwhile, secondary batteries include, for example, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium secondary batteries, etc. Among these, lithium secondary batteries have advantages over nickel-based secondary batteries, such as almost no memory effect, free charging and discharging, a very low self-discharge rate, a high operating voltage, and a high energy density per unit weight, and are therefore widely used in the field of cutting-edge electronic devices.

[0007] However, when a lithium secondary battery is exposed to high temperatures or a large current flows in a short period of time due to overcharging, an external short circuit, pinhole penetration, or localized damage, the battery heats up due to IR heating, which can lead to an explosion. In other words, when the pressure and temperature of the battery increase, decomposition reactions of the active material and various side reactions occur, causing the battery temperature to rise rapidly, which in turn accelerates the reaction between the electrolyte and the electrodes. Ultimately, a thermal runaway phenomenon occurs, in which the battery temperature rises rapidly. If the temperature rises above a certain level, the battery may ignite, and the increased internal pressure of the battery can cause the lithium secondary battery to explode.

[0008] Therefore, various methods are being discussed to effectively control lithium secondary batteries when they are placed in abnormal operating conditions such as high temperature, high pressure, etc. As part of efforts to ensure safety, there are methods such as attaching elements to the outside of the cell and using materials inside the cell, and safety vents that utilize changes in the battery's internal pressure fall into the former category.

[0009] A conventional cylindrical secondary battery equipped with a safety vent will be described below with reference to FIGS. 1 and 2. FIG.

[0010] FIG. 1 is a partial cross-sectional view of the upper part of a conventional cylindrical secondary battery.

[0011] Referring to FIG. 1, a cylindrical secondary battery 10 can be manufactured by housing a jelly-roll type electrode assembly 50 in a cylindrical case 20 and attaching a cap assembly 30 to the open top of the cylindrical case 20.

[0012] The cap assembly 30 includes a top cap 31 and an internal pressure drop safety vent 32, and the top cap 31 and the internal pressure drop safety vent 32 can form a tightly fitted structure.

[0013] The safety vent 32 may be electrically connected to the electrode assembly 50 through a current interrupt device (CID) 60. A CID gasket 70 may surround the periphery of the current interrupt device 60.

[0014] FIG. 2 is a partial cross-sectional view showing the cylindrical secondary battery of FIG. 1 when the internal pressure increases.

[0015] 2, when cylindrical secondary battery 10 is exposed to high temperatures or internal pressure increases due to internal heat generation, safety vent 32 reverses its shape, separating current interrupting member 60 into two parts to interrupt current. At this time, CID gasket 70 is positioned between safety vent 32 and current interrupting member 60, thereby preventing current from flowing between safety vent 32 and separated current interrupting member 60.

[0016] However, in a high-temperature and high-pressure environment, the CID gasket 70 may melt. Specifically, as shown in Fig. 2, a portion of the CID gasket 70 may melt, causing the current interruption member 60, which has risen due to internal pressure, to come into contact with the safety vent 32, resulting in reconnection without interrupting the current. Since the current cannot be interrupted, the temperature may continue to rise, ultimately leading to fire and explosion of the cylindrical secondary battery 10.

[0017] Therefore, there is a need to develop a CID gasket with a high heat distortion temperature so that it can maintain its insulating properties even when melted in a high-temperature and high-pressure environment. Summary of the Invention [Problem to be solved by the invention]

[0018] The embodiments of the present invention have been proposed to solve such problems in the previously proposed methods, and have an object to provide a secondary battery and a device including the same that have improved safety even in high-temperature and high-pressure environments.

[0019] However, the problems to be solved by the embodiments of the present invention are not limited to the above-mentioned problems, and may be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0020] A secondary battery according to one embodiment of the present invention includes a current interrupt device (CID); a safety vent positioned on the current interrupt device and electrically connected to the current interrupt device; and a CID gasket surrounding the periphery of the current interrupt device, the CID gasket including a reinforcing material, the reinforcing material including at least one of glass fiber, carbon fiber, aramid fiber, cellulose, ceramic particles, and filler.

[0021] The CID gasket may include a first portion surrounding the periphery of the current interrupting member, and a second portion positioned on the first portion and extending toward the center of the current interrupting member.

[0022] The second portion may extend between the safety vent and the current interruption member.

[0023] The CID gasket includes a polymer resin, and the polymer resin may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and perfluoroalkoxy alkane (PFA).

[0024] The CID gasket includes a polymer resin, and the polymer resin may include polybutylene terephthalate (PBT).

[0025] The current interrupting member includes an outer periphery and an interrupting portion surrounded by the outer periphery, and the interrupting portion can be separated from the outer periphery when the internal pressure of the secondary battery increases.

[0026] The safety vent may be electrically connected to the shutoff portion.

[0027] The secondary battery may further include an electrode assembly including a positive electrode, a negative electrode, and a separator, and the outer periphery may be electrically connected to the positive electrode through a positive electrode tab.

[0028] The secondary battery may further include a top cap positioned over and electrically connected to the safety vent.

[0029] The secondary battery may further include a cylindrical case. [Effects of the Invention]

[0030] The CID gasket according to an embodiment of the present invention includes a reinforcing material, which increases the heat resistance and heat distortion temperature, and therefore maintains its insulating properties even when melted under high temperature and pressure conditions, thereby enabling the manufacture of secondary batteries with improved safety. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a partial cross-sectional view of an upper portion of a conventional cylindrical secondary battery. [Figure 2] 2 is a partial cross-sectional view showing the cylindrical secondary battery of FIG. 1 when the internal pressure increases. FIG. [Figure 3] 1 is a partial cross-sectional view of an upper portion of a secondary battery according to an embodiment of the present invention; [Figure 4] 4 is a partial cross-sectional view showing the secondary battery of FIG. 3 when the internal pressure increases. FIG. [Figure 5] 1 is a graph showing the results of an external short circuit evaluation carried out on Example 1. [Figure 6] 10 is a graph showing the results of an external short circuit evaluation carried out on Example 2. [Figure 7] 10 is a graph showing the results of an external short circuit evaluation carried out on Comparative Example 1. [Figure 8] 10 is a graph showing the results of an external short circuit evaluation carried out on Comparative Example 2. [Figure 9] 10 is a graph showing the results of an external short circuit evaluation carried out on Example 3. [Figure 10] 10 is a graph showing the results of an external short circuit evaluation carried out on Example 4. [Figure 11] 10 is a graph showing the results of an external short circuit evaluation carried out on Comparative Example 3. [Figure 12] 10 is a graph showing the results of an external short circuit evaluation carried out on Comparative Example 4. [Figure 13] 10 is a photograph showing a CT image of Example 3 after the current interrupting member is separated, followed by a top cap and a sealing gasket. [Figure 14] 10 is a photograph showing a CT image, an upper end cap, and a sealing gasket after the current interrupting member is separated in Example 4. [Figure 15] 10 is a photograph showing a CT image of Comparative Example 3 after the current interrupting member is separated, an upper end cap, and a sealing gasket in that order. [Figure 16]10 is a photograph showing a CT image, an upper end cap, and a sealing gasket after the current interrupting member is separated from Comparative Example 4. [Figure 17] 10 is a graph showing the results of an external short circuit evaluation carried out on Example 5. [Figure 18] 10 is a graph showing the results of an external short circuit evaluation carried out on Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be embodied in various different forms and is not limited to the embodiments set forth herein.

[0033] In order to clearly explain the present invention, parts unnecessary for the explanation are omitted, and the same reference numerals are used throughout the specification to refer to the same or similar components.

[0034] Furthermore, the size and thickness of each component shown in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not necessarily limited to those shown in the drawings. In the drawings, thicknesses are exaggerated to clearly show multiple layers and regions. In the drawings, thicknesses of some layers and regions are exaggerated for the convenience of explanation.

[0035] Furthermore, when a layer, film, region, plate, or other part is said to be "above" another part, this does not only mean that it is "directly above" that part, but also includes cases where there are other parts in between. Conversely, when a part is said to be "directly above" another part, it means that there are no other parts in between. Furthermore, being "above" a reference part means being located above or below the reference part, and does not necessarily mean being "above" in the opposite direction of gravity.

[0036] Furthermore, throughout the specification, when a part is said to "comprise" a certain element, this does not mean that it excludes other elements and may further include other elements, unless specifically stated to the contrary.

[0037] Also, throughout the specification, "on a plane" means when the subject part is viewed from above, and "on a cross section" means when the subject part is cut vertically and viewed from the side.

[0038] FIG. 3 is a partial cross-sectional view of an upper portion of a secondary battery according to an embodiment of the present invention.

[0039] Referring to FIG. 3, a secondary battery 100 according to an embodiment of the present invention may be manufactured by inserting an electrode assembly 500 into a cylindrical case 200, injecting an electrolyte solution therein, and attaching a cap assembly 300 to the open top of the cylindrical case.

[0040] The electrode assembly 500 has a jelly-roll structure in which a separator 530 is interposed between a positive electrode 510 and a negative electrode 520, and a center pin (not shown) may be inserted into the center. The center pin is generally made of a metal material to provide a certain level of strength, and has a hollow cylindrical structure formed by bending a plate material into a circle. The center pin serves to fix and support the electrode assembly 500 and also serves as a passage for releasing gas generated by internal reactions during charge / discharge and operation.

[0041] The cap assembly 300 includes a top cap 310 and a safety vent 320. The top cap 310 is positioned on the safety vent 320 and may be electrically connected to the safety vent 320 by forming a tightly contacting structure therewith. The top cap 310 has a structure with an upward protrusion at the center and may be electrically connected to the positive electrode 510 of the electrode assembly 500 to function as a positive electrode terminal for connection to an external circuit. Specifically, the top cap 310 may be indirectly connected to the positive electrode 510 via the safety vent 320, the current interrupting member 600, and the positive electrode tab 511.

[0042] The cylindrical case 200 may include a beading portion 210 and a crimping portion 220 .

[0043] The beading portion 210 refers to a portion of the cylindrical case 200 that is recessed toward the center of the electrode assembly 500, and serves to securely bond the cap assembly 300 and prevent the electrode assembly 500 from moving.

[0044] The crimping portion 220 is located on top of the beading portion 210 and refers to the portion that surrounds the cap assembly 300, ensuring a stable connection of the cap assembly 300. The sealing gasket 400 is attached to the inner surfaces of the crimping portion 220 and the beading portion 210 to increase the sealing force between the cap assembly 300 and the cylindrical case 200. That is, the sealing gasket 400 is positioned between the cylindrical case 200 and the cap assembly 300, and the end of the cylindrical case 200 is bent to form the crimping portion 220. This allows the cap assembly 300 to be attached and the secondary battery 100 to be sealed.

[0045] Although not specifically shown, a negative electrode tab connected to the negative electrode 520 of the electrode assembly 500 may be bonded to the cylindrical case 200. This allows the cylindrical case 200 to function as a negative electrode terminal for connection to an external circuit.

[0046] Meanwhile, a current interrupt device (CID) 600 and a CID gasket 700 are located below the safety vent 320. This will be described in detail below.

[0047] The secondary battery 100 according to this embodiment includes a current interrupting member 600, a safety vent 320 positioned on and electrically connected to the current interrupting member 600, and a CID gasket 700 surrounding the periphery of the current interrupting member 600. The CID gasket 700 includes a reinforcing material, which may include at least one of glass fiber, carbon fiber, aramid fiber, cellulose, ceramic particles, and fillers.

[0048] Safety vent 320 is a thin film structure through which current flows, and has two grooves 321 and 322 formed therein, each having a different depth.

[0049] The current interrupting member 600 may include an outer periphery 610 as a conductive plate member, and a blocking portion 620 surrounded by the outer periphery 610. Although not specifically shown, a number of through holes may be formed for gas discharge. Meanwhile, the boundary between the outer periphery 610 and the blocking portion 620 may be designed to have relatively weak strength in order to separate the outer periphery 610 and the blocking portion 620, which will be described later.

[0050] The CID gasket 700 may include a first portion 710 that surrounds the periphery of the current interrupting member 600, and a second portion 720 that is located on the first portion 710 and extends toward the center of the current interrupting member 600. More specifically, the second portion 720 may extend between the safety vent 320 and the current interrupting member 600.

[0051] Fig. 4 is a partial cross-sectional view showing a state when the internal pressure of the secondary battery of Fig. 3 increases. Specifically, it shows a state in which the safety vent 320 and the current interrupting member 600 interrupt the current when the internal pressure of the secondary battery 100 increases.

[0052] 3 and 4, the outer periphery 610 is electrically connected to the positive electrode 510 of the electrode assembly 500 through the positive electrode tab 511, and the interrupting member 620 may be electrically connected to the bottom surface of the safety vent 320. There are no particular limitations on the electrical connection method, and the connection may be by welding. During normal operation of the secondary battery 100, the positive electrode tab 511, the current interrupting member 600, the safety vent 320, and the upper end cap 310 are electrically connected, connecting the secondary battery 100 to an external circuit.

[0053] However, when pressurized gas is applied to the safety vent 320 due to an increase in pressure inside the secondary battery 100, the shape of the safety vent 320 is reversed. As a result, the cutoff portion 620 is separated from the outer periphery 610, as shown in Fig. 4, and the electrical connection between the external circuit and the electrode assembly 500 is cut off. This prevents explosion or fire even if the secondary battery 100 is exposed to high temperatures or internal heat generation causes an increase in internal pressure.

[0054] In this case, the second portion 720 of the CID gasket 700 extends between the safety vent 320 and the outer periphery 610, preventing the safety vent 320 from contacting the outer periphery 610. That is, after the outer periphery 610 and the blocking portion 620 are separated, the second portion 720 prevents the safety vent 320 from contacting the outer periphery 610, thereby preventing reconnection, i.e., preventing current from flowing again.

[0055] As explained above, in the past, the CID gasket could melt or deform, making it impossible to block contact between the safety vent 320 and the outer periphery 610 .

[0056] In contrast, the CID gasket 700 according to an embodiment of the present invention includes a reinforcing material to increase heat resistance and heat distortion temperature. Therefore, even in high-temperature and high-pressure environments, the safety vent 320 and the outer periphery 610 can be prevented from contacting each other and insulation can be maintained. The reinforcing material according to this embodiment may include at least one of glass fiber, carbon fiber, aramid fiber, cellulose, ceramic particles, and fillers, and glass fiber is particularly preferred.

[0057] Meanwhile, the CID gasket 700 may be manufactured by injection molding using a polymer resin. Such polymer resins may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and perfluoroalkoxy alkane (PFA). Among these, polybutylene terephthalate (PBT) may be used. Super engineering plastic materials such as polyphenylene sulfide (PPS) have high rigidity, making them difficult to mold. Adding a reinforcing material to these materials can further adversely affect moldability. On the other hand, materials such as polybutylene terephthalate (PBT) and polypropylene (PP) are elastomers with good elasticity, and adding these materials improves injection molding, making it easier to mold the CID gasket 700. In other words, when a polymer resin such as polypropylene (PP) or polybutylene terephthalate (PBT) is included, as in this embodiment, the moldability and flexibility of the CID gasket 700 can be ensured, making injection molding easier and increasing contact with the current interrupting member 600.

[0058] Meanwhile, the safety vent 320 is often activated when the temperature and pressure inside the secondary battery 100 rises rapidly due to decomposition reactions of the active material and numerous side reactions, and the CID gasket 700 is a component directly exposed to such high-temperature, high-pressure gases. The CID gasket 700 does not require the same high-sealing properties as the sealing gasket 400, but its most important feature is its heat resistance. The CID gasket 700 according to this embodiment contains a polymer resin such as polypropylene (PP) or polybutylene terephthalate (PBT) to ensure moldability and flexibility, and also contains a reinforcing material such as glass fiber to maintain its insulating properties even in high-temperature, high-pressure environments.

[0059] Meanwhile, according to one embodiment of the present invention, the mass of the reinforcing material may be 15% to 50%, and more preferably 25% to 40%, of the mass of the CID gasket 700. For example, the CID gasket 700 may include polybutylene terephthalate (hereinafter, referred to as PBT) and glass fiber, and the mass of the glass fiber may be 15% to 50% of the total mass of the CID gasket including the PBT and the glass fiber.

[0060] If the mass of the reinforcing material is less than 15% of the mass of the CID gasket 700, the heat resistance and heat distortion temperature of the CID gasket 700 cannot be increased to the desired level. As a result, the safety vent 320 and the outer periphery 610 cannot be disconnected after the current interrupting device 600 is separated, which may result in reconnection. Meanwhile, a battery pack may be formed by assembling multiple secondary batteries 100. In this case, the mass of the reinforcing material relative to the mass of the CID gasket 700 is preferably 25% or more. If the mass of the reinforcing material is less than 25% of the mass of the CID gasket 700 per battery pack, the CID gasket 700 may melt due to its inability to withstand the heat and pressure inside the battery pack. This reconnection may lead to thermal runaway or explosion of the battery pack.

[0061] On the other hand, if the mass of the reinforcing material exceeds 50% of the mass of the CID gasket 700, it may hinder the moldability of the CID gasket 700. The CID gasket 700 can be manufactured by adding the reinforcing material to a polymer resin such as PBT and then injection molding it, but if the mass of the reinforcing material exceeds 50%, the resulting resin may have more rigidity than necessary, which may hinder successful injection molding.

[0062] Hereinafter, the CID gasket according to the present invention will be described with reference to specific examples and comparative examples.

[0063] Evaluation example 1: Heat distortion temperature measurement

[0064] [Table 1]

[0065] Table 1 compares the thermal properties of a CID gasket containing PBT and glass fiber (GF) with a gasket containing only PBT, as an experimental group and a comparative group. In the case of a CID gasket containing PBT and glass fiber, the mass of the glass fiber is 30% of the mass of the CID gasket.

[0066] Referring to Table 1, it can be seen that the melting points of both materials are similar, but the addition of glass fiber significantly increases the heat distortion temperature. In particular, there is a large difference between the values ​​of the two materials when measured at 1.8 MPa. This confirms that the addition of glass fiber improves the heat resistance of the CID gasket.

[0067] Evaluation example 2: External short circuit evaluation After preparing Examples 1 and 2 and Comparative Examples 1 and 2, an external short circuit evaluation was carried out.

[0068] Specifically, a CID gasket containing PBT and glass fiber was applied to an 18650 cylindrical battery to prepare Examples 1 and 2, and a CID gasket containing only PBT was applied to an 18650 cylindrical battery to prepare Comparative Examples 1 and 2. In both Examples 1 and 2, the mass of the glass fiber relative to the mass of the CID gasket was 30%.

[0069] In the case of external short circuit evaluation, external leads were connected to the positive and negative terminals of the cylindrical battery at a certain resistance value, and the behavior of the cylindrical battery was then confirmed.

[0070] In Evaluation Example 2, an external resistance of 25 mΩ was applied to the cylindrical batteries of Examples 1 and 2 and Comparative Examples 1 and 2 to check the behavior of each cylindrical battery. Specifically, the current value, voltage value, and CID gasket temperature of the cylindrical batteries were measured over time and are shown in Figures 5 to 8 and Table 2 below. Figures 5 to 8 are graphs showing the results of external short-circuit evaluations performed on Examples 1 and 2, Comparative Examples 1 and 2, respectively. Table 2 summarizes the results of the graphs.

[0071] Additionally, whether reconnection occurs after separation of the current interrupt device (CID) in an external short circuit evaluation was measured.

[0072] [Table 2]

[0073] 5 to 8 and Table 2, the point on the graph where the current and voltage values ​​of the cylindrical battery suddenly decrease and approach zero is the point where the current interrupt device (CID) separates due to an increase in internal pressure, cutting off the current and voltage. It can be seen that in Examples 1 and 2, the CID separated in the mid-30s, while in Comparative Examples 1 and 2, the CID separated after more than 40 seconds. Additionally, the maximum temperature (Max. temp) of the cylindrical battery was measured to be higher in Comparative Examples 1 and 2.

[0074] When examining the causes of this, it is understood that the temperature and pressure inside the cylindrical battery increased during the external short circuit evaluation, which should have caused the current interrupting device to separate and release, but in Comparative Examples 1 and 2, the CID gasket failed to function as a support and underwent thermal deformation, delaying the separation of the current interrupting device and increasing the maximum temperature of the cylindrical battery. On the other hand, in Examples 1 and 2, the addition of glass fiber improved the heat resistance of the CID gasket, allowing it to smoothly function as a support.

[0075] Meanwhile, in both Examples 1 and 2 and Comparative Examples 1 and 2, no reconnection occurred after the current interrupt device (CID) was separated.

[0076] Evaluation example 3: External short circuit evaluation After preparing Examples 3 and 4 and Comparative Examples 3 and 4, an external short circuit evaluation was carried out.

[0077] Specifically, a CID gasket containing PBT and glass fiber was applied to a 21700 cylindrical battery to prepare Examples 3 and 4, and a CID gasket containing only PBT was applied to a 21700 cylindrical battery to prepare Comparative Examples 3 and 4. In both Examples 3 and 4, the mass of glass fiber relative to the mass of the CID gasket was 30%.

[0078] In Evaluation Example 3, an external resistance of 20 mΩ was applied to the cylindrical batteries of Examples 3 and 4 and Comparative Examples 3 and 4 to check the behavior of each cylindrical battery. Furthermore, whether or not reconnection occurred after separation of the current interrupt device (CID) during external short circuit evaluation was measured. The experimental results are shown in Figures 9 to 12 and Table 3 below. Figures 9 to 12 are graphs showing the results of the external short circuit evaluation performed on Examples 3 and 4, Comparative Examples 3 and 4, respectively. Table 3 summarizes the results of the graphs.

[0079] [Table 3]

[0080] 9, 10, and Table 3, the current interrupting device separated at approximately 40 seconds in Examples 3 and 4, and FIG. 11, 12, and Table 3, the current interrupting device also separated at approximately 40 seconds in Comparative Examples 3 and 4. The time points at which the current interrupting device separated due to an increase in internal pressure were similar in Examples 3 and 4 and Comparative Examples 3 and 4. The maximum temperature (Max. temp) of the cylindrical batteries was also measured to be similar between Examples 3 and 4 and Comparative Examples 3 and 4.

[0081] However, in Comparative Examples 3 and 4, when the current flow was measured after the current interruption device (CID) was separated, resistances of 7.5 mΩ and 4.9 mΩ were measured, respectively. This means that the electrical connection between the safety vent and the current interruption device was not completely interrupted after the current interruption device (CID) was separated, and reconnection occurred. In contrast, in Examples 3 and 4, no reconnection occurred.

[0082] 13 to 16 are photographs sequentially showing CT images, the top cap, and the sealing gasket after the current interrupting device was separated for Example 3, Example 4, Comparative Example 3, and Comparative Example 4, respectively. The CT images show the top portion of the cylindrical battery where the cap assembly was located.

[0083] 13, 14 and Table 3, as described above, in Examples 3 and 4, no reconnection occurred, and no melting of the CID gasket or sealing gasket occurred.

[0084] On the other hand, referring to Figure 15 and Table 3, not only did reconnection occur, but both the CID gasket and the sealing gasket melted in Comparative Example 3. Next, referring to Figure 16 and Table 3, in Comparative Example 4, not only did reconnection occur, but the sealing gasket also melted.

[0085] To summarize the experimental results, Examples 3 and 4, which contained glass fiber, had improved heat resistance, did not experience thermal deformation, and effectively blocked reconnection between the safety vent and the current interrupting member. On the other hand, Comparative Examples 3 and 4, which did not contain glass fiber, were unable to block reconnection between the safety vent and the current interrupting member due to thermal deformation and melting of the CID gasket caused by the temperature rise.

[0086] Evaluation example 4: External short circuit evaluation After preparing Examples 5 and 6, an external short circuit evaluation was carried out.

[0087] Specifically, Examples 5 and 6 were prepared by varying the content of glass fiber in the CID gasket for the 18650 cylindrical battery. In addition, a battery pack was formed by configuring five 18650 cylindrical batteries (series) and two (parallel), and then an external short circuit evaluation was carried out.

[0088] In Example 5, the mass of the glass fiber relative to the mass of the CID gasket was 30%, and in Example 6, the mass of the glass fiber relative to the mass of the CID gasket was 20%.

[0089] In Evaluation Example 4, an external resistance of 80 mΩ was applied to battery packs containing multiple cylindrical batteries from Examples 5 and 6, respectively, to check the behavior of each battery pack. Additionally, whether or not reconnection occurred after separation of the current interrupt device (CID) during external short circuit evaluation was evaluated. The experimental results are shown in Figures 17 and 18 and Table 4 below. Figures 17 and 18 are graphs showing the results of the external short circuit evaluations performed on Examples 5 and 6, respectively. Table 4 summarizes the results of the graphs.

[0090] [Table 4]

[0091] 17, 18 and Table 4, in Example 5, the current interrupting member was separated at 50.6 seconds and no reconnection occurred thereafter. In contrast, in Example 6, the current interrupting member was separated at 49.4 seconds, but reconnection occurred thereafter, ultimately leading to an explosion.

[0092] In other words, if the mass of the glass fiber relative to the mass of the CID gasket in a battery pack is less than 25% and the reinforcing material is contained in small amounts, it will not be able to withstand the heat and pressure inside the battery pack, and the CID gasket may melt and reconnect, which may lead to thermal runaway or explosion of the battery pack.

[0093] In this embodiment, terms indicating directions such as front, back, left, right, up, and down are used, but these terms are merely for convenience of explanation and may change depending on the position of the object of interest, the position of the observer, etc.

[0094] One or more secondary batteries according to the present embodiment may be applied to various devices, particularly, but not limited to, transportation means such as electric bicycles, electric cars, and hybrid vehicles, and may be applied to various devices that can use secondary batteries.

[0095] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0096] 100: Secondary battery 200: Cylindrical case 300: Cap assembly 310: Top cap 320: Safety vent 400: Sealing gasket 500: Electrode assembly 600: Current interrupting member 700: CID gasket

Claims

1. Current Interrupt Device (CID); a safety vent located on and electrically connected to the current interruption member; and a CID gasket surrounding the periphery of the current interrupting member; the CID gasket includes a first portion surrounding a periphery of the current interrupting member, and a second portion located on the first portion and extending between the safety vent and the current interrupting member; the CID gasket includes a reinforcement material; the reinforcement material comprises glass fibers; The CID gasket includes a polymer resin, and the polymer resin includes polybutylene terephthalate (PBT). A secondary battery, wherein the mass of the reinforcing material relative to the mass of the CID gasket is 25% or more and 40% or less.

2. The secondary battery according to claim 1 , wherein the current interrupting member includes an outer periphery and an interrupting portion surrounded by the outer periphery, and when the internal pressure of the secondary battery increases, the interrupting portion is separated from the outer periphery.

3. The secondary battery of claim 2 , wherein the safety vent is electrically connected to the cutoff portion.

4. The battery further includes an electrode assembly including a positive electrode, a negative electrode, and a separator; The secondary battery of claim 2 , wherein the outer periphery is electrically connected to the positive electrode through a positive electrode tab.

5. The secondary battery of claim 1 , further comprising a top end cap positioned over and electrically coupled to the safety vent.

6. The secondary battery according to claim 1 , further comprising a cylindrical case.

7. A device comprising the secondary battery according to any one of claims 1 to 6.

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