Secondary battery

Abstract

A secondary battery is disclosed. According to one aspect of the present invention, a bent portion is formed at the upper end of the battery can by bent inward toward the top cap to fix the top cap. When the internal pressure of the battery can exceeds a certain value, the top cap or the bent portion is deformed, reducing the area of ​​the region (R) where the top cap and the bent portion overlap when viewed from above. As a result, the bonding force between the bent portion and the top cap is reduced, and a secondary battery is provided in which the entire area of ​​the top cap is separated from the battery can.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0013848 filed on February 1, 2019, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a secondary battery, and more particularly to a secondary battery having a structure capable of effectively discharging gas when the internal pressure of the secondary battery increases. [Background technology]

[0003] Secondary batteries capable of repeated charging and discharging may be classified into pouch-type secondary batteries, prismatic secondary batteries, cylindrical secondary batteries, etc., depending on their structures and manufacturing methods. Among these, cylindrical secondary batteries have a structure in which an electrode assembly is accommodated inside a cylindrical battery can and a top cap is attached to the top of the battery can.

[0004] Meanwhile, with an increasing demand for secondary batteries having a larger capacity per the same volume than before, research into the manufacture of such secondary batteries is also being actively carried out.

[0005] In order to manufacture a secondary battery having a larger capacity for the same volume, the content of nickel in the positive electrode active material in the positive electrode tends to increase. However, as the content of nickel in the positive electrode active material increases, there is a problem that the thermal stability of the positive electrode active material decreases. The decrease in thermal stability of the positive electrode active material means that the possibility of fire or explosion of the secondary battery increases due to an increase in temperature or pressure inside the secondary battery.

[0006] In order to solve these problems, methods of adding compounds that can improve the thermal stability of secondary batteries have been considered, but the reality is that there are limitations in terms of cost, productivity, etc. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the problem to be solved by the present invention is to eliminate the risk of fire or explosion of the secondary battery that may occur when the pressure or temperature inside the secondary battery increases by optimizing the structure of the secondary battery. [Means for solving the problem]

[0008] According to one aspect of the present invention to achieve the above object, there is provided a secondary battery comprising: an electrode assembly; a battery can that receives the electrode assembly and has an open top; and a top cap that is coupled to an upper part of the battery can, wherein an upper end of the battery can is formed with a bent portion that is bent inwardly toward the top cap to fix the top cap; and when an internal pressure of the battery can exceeds a certain value, a deformation of the top cap or the bent portion reduces an area of ​​a region (R) where the top cap and the bent portion overlap each other when viewed from above, and a bonding force between the bent portion and the top cap is reduced, so that the entire region of the top cap is separated from the battery can.

[0009] If the internal pressure of the battery can exceeds the certain value, the top cap may separate from the battery can in one piece without fragmenting into multiple components.

[0010] When the internal pressure of the battery can exceeds the certain value, the top cap may be separated from the battery can due to the degree to which the bent portion is relaxed.

[0011] When the internal pressure of the battery can exceeds the certain value, the center of the top cap may bend upward, causing the top cap to separate from the battery can.

[0012] The certain value may be a value in the range of 30 kgf to 60 kgf.

[0013] The battery can has a width (W), the bent portion has a bent length (A), and the ratio A / W of the bent length (A) of the bent portion to the width (W) of the battery can is 2.27×10 -2 From 7.5 × 10 -2 It may be.

[0014] The bent portion has a thickness (t1), the bent portion has a bent length (A), and A / t1, which is the ratio of the bent length (A) of the bent portion to the thickness (t1) of the bent portion, may be from 1.43 to 6.

[0015] The terminal area protruding upward from the top cap has a thickness (t2), the bent portion has a bent length (A), and A / t2, which is the ratio of the bent length (A) of the bent portion to the thickness (t2) of the terminal area of ​​the top cap, may be from 1 to 5.

[0016] The bent length (A) of the bent portion may be from 0.5 mm to 1.5 mm.

[0017] The width (W) of the battery can may be from 20mm to 22mm.

[0018] The thickness (t1) of the bent portion may be from 0.25 mm to 0.35 mm.

[0019] The thickness (t2) of the terminal area of ​​the top cap may be from 0.3 mm to 0.5 mm.

[0020] The battery can may include a material of iron (Fe) coated with nickel (Ni). Effect of the Invention

[0021] According to the present invention, the risk of fire or explosion of the secondary battery, which may occur when the pressure or temperature inside the secondary battery increases, can be eliminated by optimizing the structure of the secondary battery. [Brief description of the drawings]

[0022] [Figure 1] 1 is a side cross-sectional view showing the structure of a secondary battery according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the structure of the secondary battery according to the present invention will be described with reference to the drawings.

[0024] secondary battery FIG. 1 is a side cross-sectional view showing the structure of a secondary battery according to the present invention.

[0025] 1, a secondary battery 10 according to the present invention may include an electrode assembly (not shown), a battery can 100 that houses the electrode assembly and has an open top, and a top cap 200 that is coupled to the top of the battery can 100. As shown in FIG 1, the top cap 200 may have a structure in which a central portion thereof protrudes upward. Hereinafter, in this specification, the region protruding upward from the top cap 200 will be referred to as a "terminal region."

[0026] Meanwhile, the secondary battery according to the present invention may be, for example, a cylindrical secondary battery, but the type of secondary battery to which the present invention can be applied is not limited thereto. Also, the battery can 100 may have a cylindrical shape, but the shape of the battery can 100 is not limited thereto. Meanwhile, the battery can 100 may include a material of iron (Fe) containing nickel (Ni).

[0027] A gasket 300 for sealing may be provided between the upper inner portion of the battery can 100 and the outer periphery of the top cap 200. Also, a safety vent 400 may be provided in close contact with the lower surface of the top cap 200.

[0028] 1, the upper end of the battery can 100 may be formed with a bent portion 110 that is bent inwardly toward the top cap 200. As shown in FIG. 1, the bent portion 110 presses the gasket 300 downward, so that the top cap 200 may be fixed by the bent portion 110. A beading portion 120 having an inwardly curved shape may be formed at a lower portion of the bent portion 110 formed on the battery can 100.

[0029] At this time, as shown in FIG. 1, when the secondary battery 10 is viewed from above, a region (R) where the top cap 200 and the bent portion 110 overlap each other (hereinafter, referred to as an "overlapping region") may be formed.

[0030] The secondary battery 10 of the present invention may have a structure in which, when the pressure inside the secondary battery increases, the entire area of ​​the top cap 200 is separated from the battery can 100, thereby enabling gas inside the secondary battery 10 to be discharged to the outside.

[0031] For this reason, the secondary battery 10 according to the present invention may have a structure in which, when the pressure inside the secondary battery exceeds a certain value, the area of ​​the overlapping region (R) of the top cap 200 and the folding portion 110 when viewed from above decreases due to deformation of the shape of the top cap 200 or the folding portion 110, and the bonding force between the top cap 200 and the folding portion 110 decreases, so that the entire area of ​​the top cap 200 is separated from the battery can 100.

[0032] In the secondary battery 10 according to the present invention, when the internal pressure of the battery can 100 exceeds a certain value, the manner in which the entire area of ​​the top cap 200 is separated from the battery can 100 can be roughly divided into two types.

[0033] The first is a method in which, as the internal pressure of the secondary battery 10 increases, the top cap 200 and gasket 300, etc. apply upward pressure to the bent portion 110 formed at the upper end of the battery can 100, thereby reducing the degree to which the bent portion 110 is bent, causing the bent portion 110 and the top cap 200 to slide against each other in the overlap region (R), thereby separating the top cap 200 from the battery can 100 (hereinafter referred to as the ``first separation method'').

[0034] The second is a method in which an increase in the internal pressure of the secondary battery 10 presses upward on the underside of the center of the top cap 200, causing the center of the top cap 200 (i.e., the terminal area) to bend upward, thereby causing the bent portion 110 and the top cap 200 to slide against each other in the overlap area (R), thereby separating the top cap 200 from the battery can 100 (hereinafter referred to as the "second separation method").

[0035] The above two types of methods may occur simultaneously in a mixed state when the entire area of ​​the top cap 200 is separated from the battery can 100, rather than selectively occurring one after the other.

[0036] When the internal pressure of the secondary battery increases and the entire area of ​​the top cap is separated from the battery can, if the top cap is fragmented into multiple pieces when it is separated from the battery can, a safety hazard may occur as the multiple pieces fly in various directions.

[0037] In the secondary battery 10 according to the present invention, when the pressure inside the battery can 100 exceeds a certain value, the top cap 200 can be separated from the battery can 100 in an integrated state without fragmenting into multiple components.

[0038] As described above, in the secondary battery 10 according to the present invention, when the pressure inside the secondary battery exceeds a certain value, the entire area of ​​the top cap 200 may be separated from the battery can 100 due to deformation of the shape of the top cap 200 or the folding portion 110, and in this case, the certain value may be a value in the range of 30 kgf or more and 60 kgf or less.

[0039] If the certain value is less than 30 kgf, the bond between the top cap 200 and the battery can 100 becomes too weak, so that even if gas inside the secondary battery does not need to be discharged to the outside, a problem may occur in which the top cap 200 is separated from the battery can 100. On the other hand, if the certain value exceeds 60 kgf, the bond between the top cap 200 and the battery can 100 becomes too strong, so that even if gas needs to be discharged to the outside due to an increase in pressure inside the secondary battery, a problem may occur in which the top cap 200 is not separated from the battery can 100. More preferably, the certain value may be a value in the range of 30 kgf to 55 kgf.

[0040] Meanwhile, as shown in Fig. 1, in the secondary battery 10 according to the present invention, the battery can 100 may have a predetermined width (W). When the battery can 100 has a cylindrical shape, the width (W) shown in Fig. 1 may be regarded as the diameter of the battery can 100.

[0041] In addition, the bent portion 110 formed in the battery can 100 may have a bent length (A) that is a predetermined length by which the bent portion is bent inwardly of the battery can 100. The bent portion 110 may have a predetermined thickness (t1).

[0042] Meanwhile, the top cap 200 may have a predetermined thickness (t2). In this case, the top cap 200 may have a constant thickness over the entire area, but for convenience, the present specification will mainly describe the case where the thickness of the terminal area protruding upward from the top cap 200 is t2.

[0043] In the secondary battery 10 according to the present invention, the bent length (A) of the bent portion 110 may have a certain ratio to the width (W) of the battery can 100. That is, the ratio A / W of the bent length (A) of the bent portion 110 to the width (W) of the battery can 100 is 2.27×10 -2 From 7.5 × 10 -2 It may be.

[0044] A / W is 2.27 x 10 -2 If A / W is less than 7.5×10, the bonding strength between the battery can 100 and the top cap 200 becomes too weak, so that even if the internal pressure of the secondary battery 10 is normal, the degree to which the bent portion 110 is bent is reduced, and the top cap 200 may become separated from the battery can 100. -2 If the pressure exceeds this value, the bonding force between the battery can 100 and the top cap 200 will be excessively large, and even if the internal pressure of the secondary battery 10 is abnormal, the top cap 200 will not be separated from the battery can 100, which may cause the secondary battery 10 to explode.

[0045] In addition, in the secondary battery 10 according to the present invention, the bending length (A) of the bending portion 110 may also have a certain ratio to the thickness (t1) of the bending portion 110. That is, A / t1, which is the ratio of the bending length (A) of the bending portion 110 to the thickness (t1) of the bending portion 110, may be 1.43 to 6.

[0046] When A / t1 is less than 1.43, the thickness (t1) of the bent portion 110 is relatively large while the bent length (A) is relatively small, so that it is difficult to form the bent portion 110 at the upper end of the battery can 100, and the formability of the bent portion 110 may be reduced. On the other hand, when A / t1 exceeds 6, the thickness (t1) of the bent portion 110 is relatively small while the bent length (A) is relatively large, so that the durability of the area where the bent portion 110 is formed is reduced, and a problem may occur in which the bent portion 110 is damaged during the formation of the bent portion 110. More preferably, A / t1 may be 2.0 to 4.3.

[0047] In addition, in the secondary battery 10 according to the present invention, the bending length (A) of the bending portion 110 may also have a certain ratio to the thickness (t2) of the terminal region of the top cap 200. That is, the ratio A / t2 of the bending length (A) of the bending portion to the thickness (t2) of the terminal region of the top cap may be 1.0 to 5.0.

[0048] When A / t2 is less than 1.0, the thickness (t2) of the terminal region of the top cap 200 is relatively large while the bending length (A) is relatively small, so that deformation in the terminal region of the top cap 200 hardly occurs, and when the entire region of the top cap 200 is separated from the battery can 100 due to an increase in the internal pressure of the secondary battery 10, this is mainly achieved by the "first separating method". Conversely, when A / t2 exceeds 5.0, the thickness (t2) of the terminal region of the top cap 200 is relatively small while the bending length (A) is relatively large, so that relaxation to the extent that the top cap 200 is bent at the bending length (A) hardly occurs, and when the entire region of the top cap 200 is separated from the battery can 100 due to an increase in the internal pressure of the secondary battery 10, this is mainly achieved by the "second separating method". If the entire area of ​​the top cap 200 is separated from the battery can 100 only by relying on the first separation method, the top cap 200 may not be separated from the battery can 100 and the secondary battery 10 may explode if the first separation method does not work depending on the usage state of the secondary battery. This is also true when relying on the second separation method only. Therefore, in order to enable the top cap 200 to be separated from the secondary battery 10 regardless of the usage state of the secondary battery, it is necessary to set A / t2 so that the first and second separation methods can operate in harmony.

[0049] Meanwhile, the bent length (A) of the bent portion 110 of the secondary battery 10 according to the present invention may be from 0.5 mm to 1.5 mm.

[0050] If the bending length (A) of the bending portion 110 is less than 0.5 mm, the bending length (A) becomes too short, making it difficult to form the bending portion 110 at the upper end of the battery can 100, and the formability of the bending portion 110 may decrease, and the bonding strength between the battery can 100 and the top cap 200 by the bending portion 110 under normal conditions may decrease, resulting in a problem that the top cap 200 may be separated from the battery can 100 even under normal conditions. On the other hand, if the bending length (A) of the bending portion 110 exceeds 1.5 mm, the bending length (A) becomes too large, making the bonding strength between the battery can 100 and the top cap 200 by the bending portion 110 too large, and the top cap 200 may not be separated from the battery can 100 even in a situation where it should be separated due to an increase in the internal pressure of the secondary battery 10, which may cause the secondary battery 10 to explode.

[0051] In addition, the thickness (t1) of the bent portion 110 formed in the battery can 100 of the secondary battery 10 according to the present invention may be 0.25 mm to 0.35 mm.

[0052] If the thickness (t1) of the bent portion 110 is less than 0.25 mm, the durability of the area where the bent portion 110 is formed may decrease, and a problem may occur in that the bent portion 110 may be damaged during the molding of the bent portion 110. On the other hand, if the thickness (t1) of the bent portion 110 exceeds 0.35 mm, it may become difficult to mold the bent portion 110 at the upper end of the battery can 100, and the moldability of the bent portion 110 may decrease.

[0053] Moreover, the thickness (t2) of the top cap 200 of the secondary battery 10 according to the present invention may be from 0.3 mm to 0.5 mm.

[0054] When the thickness (t2) of the top cap 200 is less than 0.3 mm, the entire area of ​​the top cap 200 may be separated from the battery can 100 mainly by the "second separation method" when the internal pressure of the secondary battery 10 increases. On the other hand, when the thickness (t2) of the top cap 200 is more than 0.5 mm, the entire area of ​​the top cap 200 may be separated from the battery can 100 mainly by the "first separation method" when the internal pressure of the secondary battery 10 increases. More preferably, t2 may have a value between 0.35 mm and 0.45 mm.

[0055] In addition, for the sake of productivity of the secondary battery 10 and efficiency in using the secondary battery 10, the width (W) of the battery can 100 of the secondary battery 10 according to the present invention may be 20 mm to 22 mm.

[0056] Cylindrical secondary batteries are generally provided with a safety vent (see FIG. 1) 400. According to conventional technology, when the internal pressure of a cylindrical secondary battery increases, the safety vent breaks, releasing gas and electrolyte from inside the secondary battery to the outside, thereby preventing the secondary battery from exploding.

[0057] However, according to the conventional technology, even if the safety vent is broken, the outlet through which the gas and electrolyte inside the secondary battery are discharged to the outside is limited to the area broken by the safety vent, so that it is difficult to quickly discharge the gas and electrolyte. In particular, when the diameter or size of the secondary battery is large, for example, when the diameter of the secondary battery exceeds 11 mm, the gas and electrolyte need to be discharged to the outside as quickly as possible to prevent the secondary battery from exploding, but since the area broken by the safety vent is localized, the gas and electrolyte cannot be quickly discharged to the outside, so that the safety of the secondary battery cannot be guaranteed. In addition, even if the safety vent is broken, the top cap remains connected to the battery can, so that the safety vent is still constrained to the lower part of the top cap, and the size of the area opened by breaking the safety vent is limited by the top cap.

[0058] However, as described above, according to the present invention, when the internal pressure of the battery can 100 exceeds a certain value, the bonding force between the bent portion 110 of the battery can 100 and the top cap 200 decreases, and the entire area of ​​the top cap 200 is separated from the battery can 100, so that the gas and electrolyte inside the secondary battery can be quickly discharged to the outside. Also, since the top cap is separated from the battery can, the size of the area where the safety vent is broken and opened is not limited by the top cap. Therefore, the size of the area where the safety vent is broken increases, and the gas and electrolyte inside the secondary battery can be quickly discharged to the outside.

[0059] Example 1 A cylindrical secondary battery was manufactured. The diameter of the battery can was 21.05 mm, the thickness of the battery can was 0.3 mm, and the thickness of the bent part formed at the upper end of the battery can was also 0.3 mm. In addition, the thickness of the top cap combined with the bent part at the top of the battery can was 0.4 mm. In addition, the bent length of the bent part was 0.5 mm.

[0060] Example 2 A cylindrical secondary battery was produced in the same manner as in Example 1, except that the bent length of the bent portion was 1.5 mm.

[0061] Experimental Example While increasing the pressure inside the cylindrical secondary batteries manufactured according to Examples 1 and 2, the pressure inside the secondary batteries was measured when the entire area of ​​the top cap was separated from the battery can while remaining intact.

[0062] In the cylindrical secondary battery according to Example 1, the pressure inside the secondary battery was 33 kgf when the entire area of ​​the top cap was separated from the battery can while remaining intact.

[0063] In the cylindrical secondary battery according to Example 2, the pressure inside the secondary battery was 50 kgf when the entire area of ​​the top cap was separated from the battery can while remaining intact.

[0064] Although the present invention has been described above using limited examples and figures, the present invention is not limited thereto, and it is of course possible for a person having ordinary skill in the art to which the present invention pertains to implement various aspects of the present invention within the scope of the technical concept of the present invention and the equivalent scope of the claims.

Claims

1. An electrode assembly; a battery can housing the electrode assembly and having an open top; a top cap coupled to an upper portion of the battery can and having a structure in which a central portion is protruded upward, the protruding region being bent upward as an internal pressure of the battery can presses upward against a lower surface of a central portion of the top cap; comprising a bent portion is formed at an upper end of the battery can, the bent portion being bent inward toward the top cap to fix the top cap; When the internal pressure of the battery can exceeds a certain value, at least the area of ​​the region (R) where the top cap and the bent portion overlap each other when viewed from above is reduced due to deformation of the top cap, and the bonding force between the bent portion and the top cap is reduced, so that the entire region of the top cap is separated from the battery can, the battery can has a width (W); The bent portion has a bent length (A), The ratio A / W of the bent length (A) of the bent portion to the width (W) of the battery can is 2.27×10 －２ From 7.5 x 10 －２ That is, a secondary battery.

2. The secondary battery of claim 1 , wherein when the internal pressure of the battery can exceeds the certain value, the top cap is separated from the battery can in an integral state without fragmenting into multiple components.

3. A secondary battery as described in claim 2, wherein in addition to deformation of the top cap, the top cap is separated from the battery can due to relaxation of the degree to which the bent portion is bent.

4. The secondary battery of claim 2 , wherein when the internal pressure of the battery can exceeds the certain value, the top cap is separated from the battery can by bending a center portion of the top cap upward.

5. 5. The secondary battery according to claim 3, wherein the certain value is in the range of 30 kgf / cm2 or more and 60 kgf / cm2 or less.

6. The bent portion has a thickness (t １ ) The bent portion has a bent length (A), The thickness of the folded portion (t １ A / t is the ratio of the bent length (A) of the bent portion to the bent length (A) of the bent portion. １ The secondary battery according to claim 1 , wherein m is 1.43 to 6.

7. The terminal area protruding upward from the top cap has a thickness (t ２ ) The bent portion has a bent length (A), The thickness (t ２ A / t is the ratio of the bent length (A) of the bent portion to the bent length (A) of the bent portion. ２ The secondary battery according to claim 1 , wherein R is an integer from 1 to 5.

8. The secondary battery according to claim 1 , wherein a bent length (A) of the bent portion is 0.5 mm to 1.5 mm.

9. The secondary battery according to claim 1 , wherein the width (W) of the battery can is from 20 mm to 22 mm.

10. The thickness of the folded portion (t １ 7. The secondary battery according to claim 6, wherein the thickness of the first electrode is 0.25 mm to 0.35 mm.

11. The thickness of the terminal area of ​​the top cap (t ２ 8. The secondary battery according to claim 7, wherein the thickness of the first electrode is 0.3 mm to 0.5 mm.

12. The secondary battery according to claim 1 , wherein the battery can comprises a material of iron (Fe) coated with nickel (Ni).

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