KR101054748B1 - Secondary battery cap assembly with excellent electrolyte sealing - Google Patents

Abstract

The present invention is connected to the device (current blocking safety device) that blocks the current when the high pressure in the battery is generated, the safety vent for discharging the gas when the high pressure generated more; A PTC device mounted on the safety vent and having an annular structure to block current when a high temperature is generated; A top cap mounted on the PTC element, having a through hole for discharging gas, and forming a protruding terminal; And a gasket sealing the outer circumferential surfaces of the devices. The outer circumferential end of the safety vent is vertically bent to correspond to the outer circumferential side of the PTC element and the top cap, and an annular gasket is formed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. Provided is a cap assembly, characterized in that the B).

Description

Cap Assembly of Second Battery Having Excellent Electrolyte Sealing Property}

1 is a schematic cross-sectional view showing the upper structure of a conventional cylindrical secondary battery;

2 is a schematic cross-sectional view showing an upper structure of a cylindrical secondary battery according to one embodiment of the present invention;

3 is a partial cross-sectional schematic diagram of the upper structure of the cap assembly in the cylindrical secondary battery of Figure 1;

4 is a partial cross-sectional schematic view of the upper structure of the cap assembly in the cylindrical secondary battery of FIG.

The present invention relates to a cap assembly for a secondary battery having excellent electrolyte sealing property, and more particularly, a device (current blocking safety device) that cuts off a current when a high pressure is generated in the battery is connected to a lower portion, and when a high pressure is generated, And a safety vent, a PTC element, a top cap, and a gasket (A) for discharging the safety vent, and an end portion of the outer circumferential surface of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, An annular gasket (B) is interposed between the bent portion and the outer peripheral side surfaces of the PTC element and the top cap.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

According to the shape of the battery case, secondary batteries are classified into cylindrical batteries and rectangular batteries in which the electrode assembly is embedded in a cylindrical or rectangular metal can, and pouch-type batteries in which the electrode assembly is embedded in a pouch type case of an aluminum laminate sheet. .

In addition, the electrode assembly embedded in the battery case is a power generator capable of charging and discharging composed of a laminated structure of the anode / separator / cathode, a jelly-roll type wound through a separator between the long sheet-type anode and cathode coated with the active material The structure is classified into a stacked structure in which a plurality of positive and negative electrodes of a predetermined size are sequentially stacked in a state where a separator is interposed therebetween. Among them, the jelly-roll type electrode assembly has advantages of easy manufacturing and high energy density per weight.

However, during charging and discharging of a battery, a jelly-roll type electrode assembly tends to deform while undergoing repeated expansion and contraction, and in this process, stress is concentrated to the center, and an electrode shorts through a separator and contacts a metal center pin. Tends to cause. The organic solvent may be decomposed by the heat generated by the internal short circuit to generate gas, and the battery may be ruptured due to the increase in gas pressure in the battery. This increase in gas pressure inside the battery may occur even when an internal short circuit occurs due to an external impact.

In order to solve the safety problem of the battery as described above, the cap assembly of the cylindrical battery has a safety vent for discharging high-pressure gas, a PTC device to cut off the current at a high temperature, a current interrupting device to cut off the current when the internal voltage rises (Current Interrupt) Safety elements such as a device (CID) and a top cap forming a protruding terminal for protecting the elements have a structure fixed by a gasket.

The structure of the cap assembly, by the gasket wraps the outer peripheral surface of the safety vent, PTC element, CID, top cap, etc., essentially prevents the electrolyte inside the battery to leak out. Therefore, if electrolyte is not leaked through the interface between the safety vent located at the innermost side of the battery and the gasket surrounding its outer circumference, the interface between the metal materials such as the interface between the safety vent and the PTC element and the interface between the PTC element and the top cap is No electrolyte leakage occurs.

However, due to the charging and discharging operation of the battery, dropping, external shock, and the like, substantially some electrolyte leaks through the interface between the gasket and the safety vent, and the leaked electrolyte may easily leak out through the interface between the metal materials. There is a problem. That is, since the interfacial portions between the metal materials are relatively inferior in adhesion, the electrolyte, once introduced into the interfacial surfaces of the metal materials, may be easily leaked to the outside compared to the interface portions of the gasket and related devices. Therefore, there is a high need for a technology capable of reducing the leakage of electrolyte in the cap assembly.

In this regard, Japanese Patent Application Laid-Open No. 2006-286561, Japanese Patent Application Laid-Open No. 2005-100927, Japanese Patent Application Laid-Open No. 2002-373711 and the like disclose a cap assembly provided with a gasket under the top cap. However, the cap assembly disclosed in these applications is not easy to manufacture because the shape of the gasket sealing the outer circumferential surface of the safety elements is complicated, and the interface between the metal materials (safety vent, PTC element and top cap) Since electrolyte leakage occurs at the site, the above problems cannot be solved fundamentally.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application, after in-depth study and various experiments, during the manufacture of the secondary battery, the end of the safety vent outer peripheral surface of the cap assembly is bent vertically corresponding to the outer peripheral side of the PTC element and the top cap, the vertical of the safety vent When the annular gasket is interposed between the bent portion and the outer circumferential side of the PTC element and the top cap, it is confirmed that the leakage of electrolyte at the interface between the metal materials (safety vent, PTC element and the top cap) can be minimized. The present invention has been completed.

Therefore, the secondary battery cap assembly according to the present invention,

(A) a safety vent that is connected to the lower element (current blocking safety device) that cuts off the current when a high pressure occurs in the battery, and discharges the gas when it bursts at a higher pressure;

(b) a PTC device having an annular structure mounted on the safety vent and blocking current when a high temperature occurs;

(c) a top cap mounted on the PTC element, having a through hole for gas discharge, and forming a protruding terminal; And

(d) a gasket sealing the outer circumferential surface of the elements;

It contains,

The outer circumferential end of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and an annular gasket B is interposed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. It is composed of a structure.

In general, the interfacial portion between the safety vent and the top cap, which is a metallic material, and the PTC element (hereinafter, referred to as 'metal materials'), which is a metal material, has an electrolyte as compared with the interface portion of the gasket and these elements, as described above. In the cap assembly of the present invention, the end of the outer circumferential surface of the safety vent is vertically bent, and an annular gasket is mounted between the bent portion, the top cap, and the PTC element, until the safety vent is shorted. The electrolyte may be prevented from leaking at the interface between the metal materials, thereby greatly improving the safety of the battery.

That is, even if the electrolyte passes through the interface between the safety vent positioned at the innermost side of the battery and the gasket A surrounding the outer circumferential surface thereof, the electrolyte flows directly into the interface between the safety vent and the PTC element and the interface between the PTC element and the top cap. Since it must not pass through the interface of another gasket (B), leakage of the electrolyte can be substantially prevented.

The thickness of the safety vent may vary depending on the material and structure, and the like, and may be particularly limited as long as it can expel gas at a predetermined high pressure, and may be 0.2 to 0.6 mm.

The thickness of the PTC device may also vary depending on materials, structures, and the like, and preferably, 0.2 to 0.4 mm. However, if the thickness of the PTC element is too thick, the internal resistance is increased, the size of the battery can be increased to reduce the capacity of the battery compared to the same standard. On the contrary, it is not preferable because the thickness of the PTC element is too thin, it is difficult to exert a desired current interruption effect at high temperature, and can be destroyed by a weak external impact. Therefore, the thickness of a PTC element can be suitably determined within the said range in consideration of these points.

The thickness of the top cap portion in contact with the top surface of the PTC device is not particularly limited as long as it can protect the devices of the cap assembly from the pressure applied from the outside, preferably may be 0.3 to 0.5 mm. If the thickness of the top cap portion is too thin, it is difficult to exert predetermined mechanical rigidity. On the contrary, if the thickness of the top cap portion is too thick, it is not preferable because the battery capacity can be reduced compared to the same standard by increasing the size and weight.

One of the important features of the present invention is that the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and another feature is between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. The point is that the annular gasket B is interposed.

First, the vertical bending height of the end portion of the safety vent outer peripheral surface is preferably made to match the sum of the thicknesses of the PTC element and the top cap, so that when the gasket A achieves sealing while surrounding the outer peripheral surface of the safety vent, the gasket ( By minimizing the separation space generated between the inner surface of the A) and the safety vent can maximize the sealing force between each other.

In addition, the height of the annular gasket (B) is preferably formed to match the sum of the thickness of the PTC element and the thickness of the top cap, so as described above, the gasket (A) surrounds the outer circumferential surface of the safety vent to seal When achieving, it is possible to maximize the sealing force between each other by minimizing the separation space generated between the inner surface of the gasket (A) and the top of the annular gasket (B).

As a result, with the above preferred structure, the outer peripheral surface bent end of the safety vent and the upper end of the gasket B coincide with the height of the top cap in contact with the gasket A, and the gasket A is in close contact with the site. Can be.

The gasket (A) and the annular gasket (B) is preferably made of an electrically insulating elastic material, and the material is not particularly limited as long as the material exhibits electrical insulating properties and predetermined elasticity and durability. Polypropylene (PP) can be used.

The width of the annular gasket B interposed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap is preferably so as to prevent leakage of the electrolyte at the mutual interface where the members come into contact with each other. 0.2 to 0.4 mm. Therefore, if the width of the annular gasket B is too thin, it may not be difficult to provide a predetermined electrical insulation and elasticity, and on the contrary, if the annular gasket B is too thick, the size of the battery may be increased, resulting in a decrease in battery capacity compared to the same standard. not.

The present invention also provides a secondary battery in which a wound electrode assembly ('jelly-roll') is embedded in a cylindrical can with an electrolyte impregnated thereon, and a cap assembly of the structure is mounted on an upper end of the cylindrical can.

In general, in the structure of a cylindrical secondary battery, the positive electrode tab welded to the positive electrode foil of the jelly-roll type electrode assembly is welded to the cap assembly and connected to the protruding terminal at the top of the battery, and the negative electrode tab welded to the negative electrode foil is a battery case ( Welded to the bottom of the cylindrical can) and the can itself constitutes the negative terminal. Electrolyte is injected in such a state that the mounting is made, and the cylindrical assembly is completed by sealing the cap assembly on the open top of the can. The material of the cylindrical can is not particularly limited, and preferably, may be formed of any one of stainless steel, steel, aluminum, or an equivalent thereof.

The battery according to the present invention may preferably be a lithium secondary battery of high energy density, discharge voltage, and output stability. Such lithium secondary batteries are composed of a positive electrode, a negative electrode, a separator, a lithium salt-containing nonaqueous electrolyte, and the like.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder onto a positive electrode current collector, followed by drying, and further, a filler may be further added as necessary. The negative electrode is also manufactured by coating and drying a negative electrode material on a negative electrode current collector, and if necessary, the components as described above may be further included.

The separator is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength is used.

The lithium salt-containing non-aqueous electrolyte solution consists of a nonaqueous electrolyte solution and a lithium salt, and a liquid nonaqueous electrolyte solution, a solid electrolyte, an inorganic solid electrolyte, and the like are used as the nonaqueous electrolyte solution.

Since the current collector, the electrode active material, the conductive material, the binder, the filler, the separator, the electrolyte, the lithium salt, and the like are known in the art, a detailed description thereof will be omitted herein.

The lithium secondary battery according to the present invention can be produced by conventional methods known in the art. That is, it may be prepared by inserting a porous separator between the anode and the cathode and injecting the electrolyte therein.

As described above, for example, the positive electrode may be manufactured by applying a slurry containing a lithium transition metal oxide active material, a conductive material, and a binder as a positive electrode active material onto a current collector, followed by drying and rolling. Similarly, the negative electrode can be produced by, for example, applying a slurry containing a carbon active material, a conductive material, and a binder as a negative electrode active material on a thin current collector, as described above, and then drying.

Hereinafter, the content of the present invention will be described in more detail with reference to the drawings according to an embodiment of the present invention, but the scope of the present invention is not limited thereto.

1 is a partial cross-sectional view schematically showing an upper structure of a conventional cylindrical secondary battery.

Referring to FIG. 1, the battery 100 inserts an electrode assembly 300 as a power generator into an inside of the can 200, injects electrolyte therein, and attaches a cap assembly 400 to an upper opening of the can 200. It is manufactured by mounting.

The cap assembly 400 is a PTC element 420 to block the top cap 410 and the over-current inside the hermetic gasket 500 mounted on the upper beading portion 210 of the can 200 and the internal pressure drop Safety vent for 430 is installed in close contact. The top cap 410 protrudes upward in the center to serve as a positive electrode terminal by connection with an external circuit, and a plurality of through holes (not shown) for gas discharge are perforated. The safety vent 430 has a lower end thereof connected to the anode of the electrode assembly 300 through the current blocking safety device 440 and the anode lead 310.

The safety vent 430 is a conductive thin plate, the center of which forms a downward indentation 432, and two notches having different depths are formed in the upper and lower bending portions of the indentation 432, respectively. have.

The current blocking safety device 440 that cuts off the current when the pressure rises above the threshold inside the battery is provided under the safety vent 430 as a conductive plate. The material of the current blocking safety device 440 is preferably made of the same material as the safety vent 430, and the auxiliary gasket 510 may prevent the current blocking safety device 440 and the safety vent 430 from being energized. It is made of polypropylene (PP) material.

For example, when the temperature of the battery 100 rises due to internal short circuit, overcharge, or the like caused by various causes, the amount of energizing current is greatly reduced by increasing the resistance of the PTC element 420. When the gas is generated as the electrolyte is decomposed due to the continuous rise of the temperature, and accordingly, the internal pressure increases, the inlet 432 of the safety vent 430 is lifted and the current blocking safety device 440 partially ruptures to block the current. To ensure safety. However, when the pressure rises continuously, the notch 436 of the safety vent 430 is ruptured, thereby discharging the high pressure gas to the outside of the battery 100 to ensure safety.

Figure 2 is a schematic cross-sectional view showing the upper structure of the cylindrical secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, in the cap assembly 400a of the secondary battery 100a according to the present invention, a current blocking safety device 440 that blocks current when a high voltage is generated in the battery is connected to a lower portion of the safety vent 430. The PTC element 420 that cuts off the current at a high temperature is mounted in an annular shape on the top of the safety vent 430, and the top cap 410 for forming the protruding terminal is formed with a through hole for gas discharge. It is mounted on the 420, the gasket (A) 500 is the same as the battery 100 of Figure 1 in that it is formed to seal surrounding the outer peripheral surface 610 of the elements.

On the other hand, the outer circumferential end of the safety vent 430a has a height corresponding to the outer circumferential side of the PTC element 420 and the top cap 410 and is bent vertically upward in an 'L' shape, and is an electrically insulating elastic material. An annular gasket 600 made of polypropylene (PP) is interposed between the vertical bending portion 438 of the safety vent 430a and the outer circumferential sides of the PTC element 420 and the top cap 410.

That is, the vertical bending portion 438 of the safety vent 430a and the annular gasket 600 are leaked to the upper portion of the cap assembly 400 until high pressure is generated in the battery and the safety vent 430a is ruptured. To prevent them.

3 is a partial cross-sectional schematic diagram of the upper structure of the cap assembly in the cylindrical secondary battery of Figure 1, Figure 4 is a top structure of the cap assembly in the cylindrical secondary battery of Figure 2 according to an embodiment of the present invention A partial cross-sectional schematic diagram is shown.

Referring to these figures, the top of the cap assembly (400, 400a) includes a top cap 410, PTC element 420 and safety vents (430, 430a), etc., among which PTC element 420 is a battery When the temperature increases, the resistance is greatly increased to block the current, and the safety vents 430 and 430a discharge the high pressure gas as the shape is reversed to the top of the cap assembly 400 and 400a when the internal pressure of the battery increases. Done.

As shown in FIG. 3, the cap assembly 400 has a structure in which the safety vent 430 is in close contact with the PTC element 420 having a disc shape, and the top cap 410 of the cap assembly 400 is provided. The height resulting from the PTC device 420 and safety vent 430 appears to correspond to the sum of the thicknesses of each device.

In the cap assembly 400 of FIG. 3, the gasket 500 covers the bottom surface of the safety vent 430 positioned at the innermost side of the battery in the cap assembly 400. It is in close contact with the outer peripheral side of the 420 and the top cap 410, and surrounds the upper end surface of the top cap 410. Therefore, once the electrolyte inside the battery flows into the bottom surface of the safety vent 430 and the interface S1 of the gasket 500, the interface S2 between the safety vent 430 and the PTC element 420 which is relatively inferior in adhesion strength. Or easily pass through the interface S3 between the PTC element 420 and the top cap 410 and leak.

On the other hand, according to the present invention, as shown in Figure 4, the safety vent 430a is bent vertically in the 'L' shape with respect to the outer peripheral side of the top cap 410 and the PTC element 420, the annular gasket ( The height H of the 600 is equal to the sum of the thicknesses of the PTC element 420 and the top cap 410, and thus has the same outer size as the cap assembly 400 of FIG. 3, and has a lower end portion of the gasket 500. And spaced apart space generated between the annular gasket 600 and maximize the sealing force between each other.

Furthermore, with the above structure, the interface S2 of the safety vent 430a and the PTC element 420 and the interface S3 of the PTC element 420 and the top cap 410 are in contact with the annular gasket 600. Therefore, even if the electrolyte inside the battery flows into the lower surface of the safety vent 430a and the interface S1 of the gasket 500, the annular gasket 600 passes through the vertical bending portion 438 of the safety vent 430a. Only after passing through can reach the interface (S2) and the interface (S3), the outflow of the electrolyte is substantially impossible.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

As shown in FIG. 2, a first notch having a diameter of 9.6 mm and a thickness of 0.10 mm is formed on an aluminum plate having an outer diameter of 16 mm and a thickness of 0.3 mm, and a second notch having a diameter of 4 mm and a thickness of 0.06 mm is formed. The safety vent is manufactured to have an indentation projecting downward by a depth of 0.65 mm, and the outer end of the safety vent is vertically bent corresponding to the outer peripheral side of the PTC element and the top cap, thereby matching the sum of the thicknesses of the PTC element and the top cap. To be prepared.

Further, a top cap was manufactured by drilling six radial holes of 1.5 mm in diameter radially into an aluminum plate having an outer diameter of 11 mm and a thickness of 0.5 mm, and forming protrusions having a diameter of 1.53 mm and a projecting height of 0.20 mm at the center. Then, three through-holes of width 0.6 mm and circumference length 2.61 mm were drilled at a distance of 1.5 mm from the center of the central protrusion, and a notch having a thickness of about 70 μm was formed on each bridge connecting the through holes, thereby forming CID. Prepared.

The CID was inserted along its outer circumference into a polypropylene auxiliary gasket and the bottom of the indent of the safety vent was attached by laser welding to the top of the protrusion.

Among the polypropylene gaskets (A and B), a gasket (B) having a thickness of 0.3 mm, similar to the thickness of the safety vent, is interposed between the vertical bending portion of the safety vent and the outer peripheral side surfaces of the PTC element and the top cap. The cap assembly was manufactured by wrapping the safety vent, the PTC device, and the top cap with the remaining gasket (A).

In addition, a jelly-roll electrode assembly in the form of a porous separator of polyethylene is inserted between a cathode composed of lithium cobalt oxide and a cathode composed of graphite in a cylindrical can, and then, the upper surface of the can is beaded and fixed. Cylindrical secondary batteries were prepared by inserting the cap assembly and pressing the top of the can inwards to crimp the gasket (A).

Comparative Example 1

In the same manner as in Example 1, except that the end of the outer peripheral surface of the safety vent was not bent vertically, and the gasket B was not interposed between the vertical bending portion of the safety vent and the outer peripheral side of the PTC element and the top cap. A cylindrical secondary battery was prepared.

Experimental Example 1

In the state of inverting the five batteries prepared in Example 1 and the five batteries prepared in Comparative Example 1, the short-circuit pressure, electrolyte leakage pressure and venting pressure of the CID were respectively applied while applying pressure to the inside of the cell up to 20 kgf. Measured. The results are shown in Table 1 below.

TABLE 1

As shown in Table 1, all of the batteries of Example 1 according to the present invention did not leak the electrolyte until the vent of the safety vent by a short circuit. On the other hand, in the batteries of Comparative Example 1, the leakage of the electrolyte occurred before the safety vent vented by a short circuit. Therefore, it can be seen that the batteries according to the present invention improve the safety of the battery by suppressing leakage of the electrolyte until the safety vent is shorted.

Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

As described above, the secondary battery according to the present invention vertically bends the outer circumferential end of the safety vent corresponding to the outer circumferential side of the PTC element and the top cap in the manufacture of the cap assembly, and between the bent portion and the top cap and the PTC element. By attaching the annular gasket B to the gasket B, the safety of the battery can be greatly improved by preventing the leakage of the electrolyte at the interface between the conventional gasket A and the safety vent until the safety vent is shorted.

Claims (13)

(A) a safety vent that is connected to the lower element (current blocking safety device) that cuts off the current when a high pressure occurs in the battery, and discharges the gas when it bursts at a higher pressure; (b) a PTC device having an annular structure mounted on the safety vent and blocking current when a high temperature occurs; (c) a top cap mounted on the PTC element, having a through hole for gas discharge, and forming a protruding terminal; And (d) a gasket sealing the outer circumferential surface of the elements; It contains, The outer circumferential end of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and the vertical bending height of the end of the safety vent outer circumferential surface coincides with the sum of the thickness of the PTC element and the top cap. Cap assembly, characterized in that the annular gasket (B) is interposed between the vertical bending portion of the PTC element and the outer peripheral side of the top cap. The cap assembly of claim 1, wherein the safety vent has a thickness of 0.2 to 0.6 mm. The cap assembly of claim 1, wherein the PTC device has a thickness of 0.2 to 0.4 mm. The cap assembly of claim 1, wherein the top cap has a thickness of 0.3 to 0.5 mm. delete 2. The cap assembly as claimed in claim 1, wherein the height of the annular gasket (B) coincides with the sum of the thickness of the PTC element and the thickness of the top cap. The cap assembly of claim 1, wherein the gasket (A) and the annular gasket (B) are made of an electrically insulating elastic material. 8. Cap assembly according to claim 7, wherein the gasket (A) and the annular gasket (B) are made of polypropylene (PP). 2. Cap assembly according to claim 1, wherein the annular gasket (B) has a width of 0.2 to 0.4 mm. A secondary battery in which a wound electrode assembly ('jelly-roll') is embedded in a cylindrical can with an electrolyte solution impregnated, and a cap assembly is mounted on an open upper end of the cylindrical can. (A) a safety vent that is connected to the bottom (current blocking safety device) that blocks the current when a high pressure occurs in the battery, and discharges gas while bursting at a higher pressure generated; (b) a PTC device having an annular structure mounted on the safety vent and blocking current when a high temperature occurs; (c) a top cap mounted on the PTC element, having a through hole for gas discharge, and forming a protruding terminal; And (d) a gasket sealing the outer circumferential surface of the elements; It contains, The outer circumferential end of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and an annular gasket B is interposed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. Secondary battery characterized in that. The secondary battery of claim 10, wherein the battery is a lithium secondary battery. (A) a safety vent that is connected to the lower element (current blocking safety device) that cuts off the current when a high pressure occurs in the battery, and discharges the gas when it bursts at a higher pressure; (b) a PTC device having an annular structure mounted on the safety vent and blocking current when a high temperature occurs; (c) a top cap mounted on the PTC element, having a through hole for gas discharge, and forming a protruding terminal; And (d) a gasket sealing the outer circumferential surface of the elements; It contains, The outer circumferential end of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and an annular gasket B is interposed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. And the height of the annular gasket (B) coincides with the sum of the thickness of the PTC element and the thickness of the top cap. (A) a safety vent that is connected to the lower element (current blocking safety device) that cuts off the current when a high pressure occurs in the battery, and discharges the gas when it bursts at a higher pressure; (b) a PTC device having an annular structure mounted on the safety vent and blocking current when a high temperature occurs; (c) a top cap mounted on the PTC element, having a through hole for gas discharge, and forming a protruding terminal; And (d) a gasket sealing the outer circumferential surface of the elements; It contains, The outer circumferential end of the safety vent is vertically bent in correspondence with the outer circumferential side of the PTC element and the top cap, and an annular gasket B is interposed between the vertical bent portion of the safety vent and the outer circumferential side of the PTC element and the top cap. The cap assembly, characterized in that the width of the annular gasket (B) is 0.2 to 0.4 mm.

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