KR20090027316A - Cap assembly for secondary battery - Google Patents

Abstract

A secondary battery is provided to prevent the leakage of electrolyte due to external shock or internal pressure, by forming downward protrusions at the end of the circumferential surface of the safety vent to increase sealability by suppressing the gasket. A cap assembly(400) comprises a safety vent(420), a top cap(410) and a gasket(500). A downward protrusion for pressurizing a gasket is formed at the end of the circumferential surface of a safety vent. A device blocking current in generating overvoltage is connected to at the lower part of the safety vent. The safety vent ejects gas while bursting in generating overvoltage. The top cap is mounted on the safety vent, is formed with a through hole(412) for gas discharge and forms a protruded terminal. The gasket seals the circumference of devices.

Description

Cap Assembly for Secondary Battery

The present invention relates to a cap assembly, and more particularly, to a secondary battery cap assembly having a structure to prevent the leakage of electrolyte at the interface between the safety vent and the gasket by forming a downward projection on the end portion of the outer peripheral surface of the safety vent. .

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized on lithium secondary batteries with high energy density and high discharge voltage. It is widely used.

As the application fields and products of secondary batteries are diversified as described above, the types of batteries are also diversified to provide outputs and capacities suitable for them. For example, small mobile devices such as mobile phones, PDAs, digital cameras, notebook computers, etc. have one or two or four small, lightweight secondary batteries (unit cells) per device according to the miniaturization tendency of the products. .

Secondary batteries are classified into roughly cylindrical cells, square cells, and pouch-type cells according to their external and internal structural characteristics, and are mainly jelly-roll type (wound type) according to the structure of the electrode assembly of the anode / separation membrane / cathode structure constituting the secondary battery. ) And stacked (stacked).

Among them, a commonly used jelly-roll type electrode assembly is coated with an electrode active material or the like on a metal foil used as a current collector, dried and pressed, cut into bands of a desired width and length, and a negative electrode and a positive electrode using a separator. After the diaphragm is wound into a spiral is produced. Jelly-roll type electrode assemblies are mainly used in cylindrical batteries, and in some cases, they are compressed into plate shapes and applied to square or pouch type batteries.

1 is a vertical cross-sectional view of a structure of a conventional cylindrical secondary battery equipped with a jelly-roll type electrode assembly.

Referring to FIG. 1, a cylindrical secondary battery 10 generally includes a cylindrical can 20, a jelly-roll electrode assembly 30 accommodated in the can 20, and a cap coupled to an upper portion of the can 20. Assembly 40 and a crimping portion 50 for mounting the cap assembly 40.

The electrode assembly 30 has a structure in which the electrode assembly 30 is wound in a jelly-roll shape with a separator 33 interposed between the anode 31 and the cathode 32, and a cathode tab 34 is attached to the cathode 31. A negative electrode tab (not shown) is attached to the negative electrode 32, and is connected to the lower end of the can 20.

The cap assembly 40 includes an upper cap 41 for forming a positive electrode terminal, a positive temperature coefficient element 42 for blocking current due to a large increase in battery resistance when the temperature inside the battery increases, and a pressure increase inside the battery. Safety vents 43 for interrupting current and / or exhausting gas, insulating members 44 for electrically separating the safety vents 43 from the cap plate 45, except for certain parts, and connected to the anode 31. The cap plate 45 to which the positive electrode tab 34 is connected is sequentially stacked.

The crimping portion 50 is formed at the top of the can 20 so that the cap assembly 40 can be mounted on the open top of the can 20. More specifically, the crimping portion 50 forms an indentation portion 21 inwardly by beading an upper end portion of the can 20, and the cap plate 45, the insulating member 44, and the gasket 60. It is formed by inserting the outer circumferential surface of the safety vent 43 and the upper cap 41 in turn, and then bending the upper end. As a result, the cap assembly 40 is formed by enclosing the gasket 60 positioned on the inner surface of the crimping portion 50 and performing a crimping and pressing process.

However, in the secondary battery having such a structure, when the battery is exposed to a high temperature environment or a local internal short circuit occurs due to an external impact or the like, decomposition reaction of the electrolyte occurs at the electrode interface, whereby a large amount of gas is generated. Since the gas generated in such a large amount causes the internal pressure of the battery to increase, when the internal pressure rises above a predetermined pressure, the safety vent operates to discharge the high pressure gas.

In such a structure, the interfacial area between the metal materials such as the top cap, the PTC device, and the safety vent of the cap assembly has a high risk of leakage of the electrolyte compared to the interface area of the gasket and the devices. In the cap assembly, if no electrolyte leaks through the interface of the gasket and the safety vent, no electrolyte leak occurs at the interface between the metal materials, but substantially some of the electrolyte leaks through the interface of the gasket and the safety vent. The electrolyte is easily leaked to the outside through the interface between the metal materials as described above. The leaked electrolyte causes fire or explosion, which greatly reduces the safety of the battery.

Therefore, there is a high need for development of a cylindrical secondary battery capable of maintaining sealing property from external impact or internal pressure.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application form a downward protrusion at the end portion of the outer circumferential surface of the safety vent in the cap assembly of the secondary battery to strongly press the gasket, thereby greatly improving the sealing property. It has been found that the safety of the battery can be greatly improved by preventing the leakage of OH, and the present invention has been completed.

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

A safety vent for discharging gas while a high voltage in the battery is connected to a device (current blocking safety device) that blocks current when a high pressure is generated, and bursts at a higher pressure;

A top cap mounted on the safety vent and having a through hole for discharging gas and forming a protruding terminal; And

A gasket sealing the outer circumferential surfaces of the devices;

It contains,

The outer circumferential end portion of the safety vent is configured to have a downward protrusion for pressing the gasket during the battery manufacturing process.

The safety vent is a kind of safety member that discharges gas to the outside when the internal pressure of the battery increases due to abnormal operation of the battery or deterioration of battery components, thereby ensuring safety of the battery. For example, gas is generated inside the battery. When the internal pressure increases above the threshold, the safety vent is ruptured, and the gas discharged to the rupture portion is discharged to the outside through one or more gas outlets formed in the upper cap.

By forming a downward protrusion at the end portion of the outer peripheral surface of the safety vent to pressurize the gasket during the assembly of the battery to increase the sealability, the electrolyte is essentially prevented from leaking to the interface portion of the metal materials of the cap assembly.

In addition, the high sealing property according to the above structure can greatly improve safety by preventing the electrolyte from leaking to the outside while the sealing portion of the cap assembly is partially or temporarily released upon application of an external force or an increase in the internal pressure.

Between the safety vent and the top cap may be made of a structure that additionally includes a safety device (PTC device) of the annular structure to block the current at high temperature. As described above, the cap assembly to which the PCT element is mounted may be preferably used for the cap assembly of the cylindrical battery of, for example, a battery pack for a notebook computer.

In the present invention, the downward protrusion may be formed at the end of the outer peripheral surface of the safety vent. In the cap assembly, since the outer circumferential surface of the top cap and the safety vent are fixed by the form of the gasket, the downward protrusion formed on the outer circumferential surface of the safety vent is configured to pressurize the gasket adjacent to the safety vent to increase the sealing property.

In one preferred example, the downward protrusion may be formed by vertically bending the outer peripheral surface end of the safety vent, in which case the bent end may be configured to press the gasket, the structure of the downward protrusion Even with a simple manufacturing process, there is an advantage that a large sealing property can be secured.

In some cases, the downward protrusion may be molded together in the manufacturing process of the safety vent, or a separate member may be attached to the end of the safety vent to form the downward protrusion.

The height of the downward protrusion may be formed to have an effective sealing property. If the height of the downward protrusion is too large, a portion of the outer circumferential surface of the safety vent where the downward protrusion is not formed and the gasket are spaced apart from each other, and thus the sealing property is reduced or excessively strong. The gasket may be damaged by pressing, and on the contrary, if the height is too small, it may be difficult to expect a sealing effect by the downward protrusion according to the present invention. In consideration of this point, the downward protrusions preferably have a height of 0.05 to 0.2 mm.

The downward protrusion is not particularly limited as long as it presses the gasket to increase the sealing property, and various structures may be possible, and as one preferred example, may be a wedge-shaped structure. The downward protrusion of the wedge-shaped structure elastically presses the gasket resiliently during the crimping process to provide a high sealing property. On the other hand, if the end of the wedge is sharp, the gasket may be damaged while being pressed, so that the wedge-shaped structure having a gentle end is more preferable.

The safety vent is not particularly limited as a conductive material, and is preferably a material made of aluminum or an alloy thereof which is light and has a suitable mechanical rigidity that can be broken by its operation when the internal pressure of the battery reaches a predetermined threshold. The gasket may be used in a variety of materials having elasticity, fixing the top cap and the safety vent from the battery can, and sealing the electrolyte. Preferably, polypropylene (PP) may be used.

On the other hand, when a secondary battery is used as a power source for a mobile phone or a notebook, a secondary battery for stably providing a constant output is required, while when used as a power source of a power tool such as an electric drill, a high output is instantaneously provided. While there is a need for a secondary battery that can be stable against external physical shocks such as vibration and dropping.

That is, the secondary battery having the PTC element in the cap assembly is difficult to provide a high output instantaneously, it is difficult to provide a uniform output by increasing the resistance of the contact surface during an external impact such as vibration. Specifically, the PTC device generally exhibits an electrical resistance of about 7 to 32 mW even at room temperature, and also causes a steep increase in resistance with an increase in temperature, and thus may act as a large inhibitor in providing an instantaneous high output.

Therefore, the cap assembly for a secondary battery according to another embodiment of the present invention is a cap assembly that does not include a PTC element,

A safety vent connected to the lower portion of the current blocking safety element and discharging gas while bursting at a high pressure;

A top cap mounted on the safety vent and having a through hole for discharging gas and forming a protruding terminal; And

A gasket sealing the outer circumferential surfaces of the devices;

It contains,

The end of the safety vent is bent to surround the outer circumferential surface of the top cap, the outer circumferential surface of the safety vent in contact with the gasket may be composed of a protrusion that can press the gasket during the manufacturing process of the battery.

That is, the cap assembly as described above, by bending the end of the safety vent vertically, and close to the top cap so as to surround the outer peripheral surface of the top cap, by forming a protrusion on the outer peripheral surface of the safety vent in contact with the gasket, the safety vent and the top The electrolyte inside the battery may be prevented from leaking along the interface of the cap and the interface between the safety vent and the gasket.

For example, the length of the safety vent wrapped around the top cap may be about 5 to 40%, preferably 10 to 30% based on the radius of the top cap. This bending area is ultimately wrapped by the gasket.

The protrusion is not particularly limited as long as it can be formed on the outer circumferential surface of the safety vent as long as it can improve the sealing property with the gasket. Preferably, the protrusion protrudes downward to the end portion of the outer circumferential surface of the safety vent. The sealing property can be further improved.

In some cases, at the interface between the safety vent and the top cap, a groove may be further formed parallel to the outer circumferential surface of the top cap to prevent the leakage of electrolyte and the possibility of defects during assembly. More details on this structure are described in Korean Patent Application No. 2006-0022950 filed by the applicant, which is incorporated by reference in the context of the present invention.

The present invention also has a cylindrical structure in which a wound electrode assembly ('jelly-roll') is embedded in a cylindrical can with an electrolyte impregnated, and an open top of the cylindrical can is mounted with a cap assembly according to the present invention. It provides a secondary battery.

The battery according to the present invention may be preferably applied to a lithium secondary battery manufactured by impregnating a lithium-containing electrolyte in a state in which an electrode assembly is embedded in a battery case. 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 on 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, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

2 schematically shows a cap assembly structure in a secondary battery according to an embodiment of the present invention.

Referring to FIG. 2, the cylindrical secondary battery 100 inserts an electrode assembly 110 into the can 200, injects electrolyte therein, and places the cap assembly 400 on an open top of the can 200. It is manufactured by mounting.

The cap assembly 400 has an upper cap 410, a current blocking safety device (PTC device) 760, and an internal pressure drop inside the airtight gasket 500 mounted on the upper beading part 210 of the can 200. Dragon safety vent 420 is made of a structure that is in close contact. The upper cap 410 has a center projecting upward to serve as a positive electrode terminal by connection with an external circuit, and a through hole 412 through which the compressed gas inside the can 200 can be discharged along the periphery of the protrusion. Many are formed.

The safety vent 420 is a thin film structure through which a current flows, and a central portion thereof is recessed to form an indented central portion 421, and two notches having different depths at upper and lower bending portions of the central portion 421, respectively. Fields 422 and 423 are formed.

2 and 3, the first notch 422 formed at the upper portion of the notches 422 and 423 forms a closed curve, and the second notch 423 formed at the lower portion is an open curve at which one side is opened. It is structured. In addition, since the coupling force of the second notch 423 is made smaller than the coupling force of the first notch 422, the second notch 423 is dug deeper than the first notch 422.

When the internal pressure of the can 200 rises above the critical pressure, the second notch 423 of the safety vent 420 bursts without being able to withstand the pressure, so that the pressurized gas inside the can 200 is opened in the hole of the upper cap 410. Exit through 412.

In this process, the CID 700 is installed under the safety vent 420 to discharge the gas inside the battery and cut off the current. The CID 700 is provided with an auxiliary gasket 510 as a member of a conductive plate.

4 shows an example of a current blocking safety device (CID). CID 700 is formed with a plurality of through-holes 710 through which gas is discharged along a side surface, and an upwardly projecting protrusion 720 is formed at the center thereof, and three through-concentric lines are formed around the protrusion 720. The hole 730 and three bridges 740 connecting the through hole 730 are symmetrically formed. The notch 750 is formed in the bridge 740 so that when the pressurized gas is applied to the safety vent (FIG. 2: 420) due to the pressure rise inside the battery, the indented center portion 421 is lifted up and the indented center portion is lifted. The protrusion 720 welded to 421 is separated from the main body of the CID 700 as the notch 750 is cut off.

Referring back to Figure 2, the outer circumferential surface end 424 of the safety vent is formed with a downward protrusion, the corresponding portion of the gasket 500 in contact with the outer circumferential surface of the safety vent 420 is made of a structure that is pressed by the downward protrusion. have. An enlarged view of site A to identify more detailed structure of the site is shown in FIG. 5.

Referring to FIG. 5, the top cap 410, the PTC element 760, and the safety vent 420 are closely attached to each other and are wrapped and fixed by the gasket 500. A downward protrusion 426 is formed at an end of the outer circumferential surface of the safety vent 420, and the downward protrusion 426 strongly presses the gasket 500 having elasticity, so that the electrolyte inside the battery is supplied to the safety vent 420 and the gasket 500. To prevent leakage.

In comparison, FIG. 6 shows a corresponding structure of the cap assembly in which the downward protrusion is not formed at the end of the outer peripheral surface of the safety vent in the structure of FIG. 5.

Referring to FIG. 6, the top cap 410, the PTC element 760, and the safety vent 420 ′ are in close contact with each other and are wrapped and secured by the gasket 500. The difference is that the downward protrusion is not formed at the end of the outer peripheral surface of the vent 420 '. Therefore, once the electrolyte inside the battery flows into the bottom surface of the safety vent 420 'and the interface S1 of the gasket 500, the interface between the safety vent 420' and the PTC element 760 that is relatively inferior in adhesion. (S2) or leaks through the interface S3 between the PTC element 760 and the top cap 410 easily. Under normal conditions or operating conditions of the battery, the electrolyte solution does not flow into the interface (S1), but when the external force is applied or the internal pressure increases, the sealing state of the cap assembly is partially or temporarily released and the electrolyte flows into the interface (S1). Can be.

On the other hand, in the structure of FIG. 5, since the downward protrusion 426 is formed at the interface S1 between the safety vent 420 and the gasket 500, the sealing force is high, so that an external force is applied and the battery falls. Even if an increase in the internal pressure occurs, the electrolyte inside the battery may flow into the interface S2 of the safety vent 420 and the PTC element 760 and the interface S3 of the PTC element 760 and the top cap 410. There is little possibility.

7 is an enlarged cross-sectional view of an end portion of a safety vent according to another embodiment of the present invention.

Referring to FIG. 7, the wedge-shaped downward protrusion 428 is formed at the end of the safety vent 420, and the wedge-shaped downward protrusion 428 resiliently strengthens the gasket 500 when the battery is assembled. By pressurizing, the sealing property to electrolyte solution is further improved. The wedge end of the downward protrusion 428 has a non-sharp gentle structure to minimize damage to the gasket 500 by compression.

FIG. 8 is a schematic cross-sectional view showing an upper structure of a secondary battery according to still another embodiment of the present invention, and FIG. 9 is an enlarged view schematically illustrating a portion B of FIG. 8.

Referring to these drawings, the cylindrical secondary battery 101 is bent so that the outer peripheral surface end portion 420b of the safety vent 420a surrounds the outer peripheral surface of the top cap 410 for use as a power source of the power tool. Except that is not mounted, the same as the secondary battery 100 of FIG.

Since the outer circumferential surface end 420b of the safety vent 420a is vertically bent and is closely adhered to the top cap 410 while surrounding the outer circumferential surface of the top cap 410, the safety vent 420a may be exposed to external shock such as vibration. Since the contact surface resistance of the top cap 410 does not change, it may provide a uniform output, and the electrolyte inside the battery may be prevented from leaking along the interface thereof.

In addition, a downward protrusion 426a is formed at an end portion of the outer circumferential surface of the safety vent 420a, so that the sealing property between the safety vent 420a and the gasket 500 is improved, and the electrolyte solution inside the battery along the interface thereof. Leakage can be prevented.

Although described above with reference to the drawings according to an embodiment of the present invention, those of ordinary skill in the art will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

EXAMPLE

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

Using Ni-plated SPCE (cold rolled steel sheet), a top cap and a cylindrical can are fabricated, the electrode assembly is mounted on the cylindrical can, and then a crimping process is performed on a cylindrical can of a portion corresponding to the upper end of the electrode assembly. The site was formed and a gasket was inserted into the inner side of the crimping site to secure the top cap, PTC device and safety vent of the cap assembly. The safety vent was fabricated in such a way that the end of its outer circumferential surface was bent vertically downward to a height of 0.1 mm, forming a downward protrusion to press the gasket.

In this process, a cylindrical secondary battery of 18650 (diameter 18 mm, length 65 mm) was manufactured.

Comparative Example 1

A cylindrical secondary battery was manufactured in the same manner as in Example 1, except that the downward protrusion was not formed at the end of the outer circumferential surface of the safety vent.

Experimental Example 1

In the state in which 10 batteries manufactured in Example 1 and 10 batteries manufactured in Comparative Example 1 were inverted, pressure was applied to the inside of the cell to 15 kgf, and it was confirmed whether the electrolyte leaked before the current blocking safety device was short-circuited. The results are shown in Table 1 below.

TABLE 1

As shown in Table 1, in the battery of Example 1 according to the present invention, leakage of electrolyte did not occur in any case, whereas many of the cells of Comparative Example 1 were current blocking safety devices. The electrolyte leaked before and after the short circuit. Therefore, it can be seen that the cells having a downward protrusion at the end of the safety vent according to the present invention exhibit excellent sealing property against the electrolyte.

As described above, the secondary battery according to the present invention is formed on the outer circumferential end of the safety vent is formed with a downward protrusion to increase the sealing by pressing the gasket, it can prevent the leakage of the electrolyte due to the external impact or increase in the internal pressure It can greatly improve the safety.

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

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

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

3 and 4 are perspective views of the safety vent and the current blocking safety element used in the battery of FIG. 2;

5 is an enlarged view of a portion A of FIG. 2;

FIG. 6 is an enlarged view of a corresponding structure of a cap assembly in which the downward protrusion is not formed at the outer peripheral surface end of the safety vent in the structure of FIG. 5; FIG.

7 is an enlarged view of an end portion of a safety vent in accordance with another embodiment of the present invention;

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

9 is an enlarged view of a portion B of FIG. 8.

Claims (12)

A safety vent for discharging gas while a high voltage in the battery is connected to a device (current blocking safety device) that blocks current when a high pressure is generated, and bursts at a higher pressure; A top cap mounted on the safety vent and having a through hole for discharging gas and forming a protruding terminal; And A gasket sealing the outer circumferential surfaces of the devices; It contains, Cap assembly, characterized in that the lower end portion is formed on the outer peripheral surface end portion of the safety vent can press the gasket during the manufacturing process of the battery. The cap assembly as claimed in claim 1, further comprising an annular PTC element for blocking a current when a high temperature occurs between the safety vent and the top cap. The cap assembly according to claim 1, wherein the downward protrusion is formed at an outer circumferential end thereof. The cap assembly of claim 1, wherein the downward protrusion is formed by vertically bending an outer circumferential end thereof. The cap assembly of claim 1, wherein the height of the downward protrusions is between 0.05 and 0.2 mm. The cap assembly of claim 1, wherein the downward protrusion has a wedge-shaped structure. 2. The cap assembly of claim 1 wherein the safety vent is made of aluminum or an alloy thereof and the gasket is made of polypropylene (PP). A cap assembly that does not contain a PTC device, A safety vent connected to the lower portion of the current blocking safety element and discharging gas while bursting at a high pressure; A top cap mounted on the safety vent and having a through hole for discharging gas and forming a protruding terminal; And A gasket sealing the outer circumferential surfaces of the devices; It contains, The end of the safety vent is bent to surround the outer circumferential surface of the top cap, the cap assembly, characterized in that a protrusion for pressing the gasket during the manufacturing process of the battery is formed on the outer circumferential surface of the safety vent in contact with the gasket. The cap assembly of claim 8, wherein the protrusion protrudes downward from an end portion of an outer circumferential surface of the safety vent. 9. The groove of the safety vent and the top cap is further provided with a groove for preventing leakage of electrolyte and occurrence of defects in the assembling process, in parallel to an outer circumferential surface of the top cap. Cap assembly. A wound electrode assembly ('jelly-roll') is embedded in a cylindrical can while the electrolyte is impregnated, and the cap assembly according to any one of claims 1 to 10 is mounted on an open upper end of the cylindrical can. Cylindrical secondary battery, characterized in that. 12. The cylindrical secondary battery of claim 11, wherein the battery is a lithium secondary battery.

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