Cylindrical battery cell having a spiral weld portion and battery module including the same

Abstract

The present invention relates to a cylindrical battery cell in which a cap assembly is mounted on an upper end of a battery case that houses an electrode assembly, the upper end of the battery case surrounds an outer periphery of the cap assembly and forms a crimped portion bent toward the center, the crimped portion is a negative electrode terminal, a top cap in the center of the cap assembly is a positive electrode terminal, and at least one of the negative electrode terminal and the positive electrode terminal is formed with a discontinuous spiral weld, and the present invention provides a cylindrical battery cell that improves safety by preventing over-welding from occurring in the positive electrode terminal and the negative electrode terminal.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2021-0142324 filed on October 25, 2021, and all contents disclosed in the document of the Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a cylindrical battery cell having a spiral welded portion and a battery module including the same. Specifically, the present invention relates to a cylindrical battery cell having a spiral welded portion formed to prevent overwelding when welding the cylindrical battery cell with a nanosecond pulsed laser, and a battery module including the same.

Background Art

[0003] As the safety improvement and capacity increase of rechargeable lithium secondary batteries are accelerated, the types of devices using the lithium secondary batteries as an energy source are increasing.

[0004] For example, the lithium secondary battery is widely used not only as an energy source for wireless mobile devices, which are multifunctional small products, or wearable devices worn on the body, but also as an energy source or a medium- to large-sized battery pack for use as an electric vehicle, a hybrid electric vehicle, etc., which are presented as alternatives to existing gasoline vehicles and diesel vehicles that cause air pollution, and as an energy storage system (ESS).

[0005] The lithium secondary battery is classified into a cylindrical secondary battery and a prismatic secondary battery in which an electrode assembly is built in a cylindrical or prismatic metal can according to the shape of the battery case, and a pouch-type secondary battery in which an electrode assembly is built in a pouch-shaped case of an aluminum laminate sheet. Among them, the cylindrical secondary battery has advantages of relatively large capacity and structural safety.

[0006] In order to manufacture the medium and large-sized battery pack, a process of electrically connecting a plurality of cylindrical battery cells is required. For example, a plurality of cylindrical battery cells can be electrically connected by bonding a bus bar or a metal plate to the positive and negative terminals of the cylindrical battery cell or by wire bonding.

[0007] Thus, a laser welding method can be used for the electrical connection between the positive and negative terminals of a plurality of cylindrical battery cells. As the laser welding, CW (Continuous Wave) laser welding, millisecond pulse laser welding, microsecond pulse laser welding, and nanosecond pulse laser welding can be used.

[0008] Generally, in a cylindrical battery cell, a crimping portion functions as a negative terminal and a top cap functions as a positive terminal. At this time, for the electrical connection through the negative terminal, welding is performed on the crimping portion in a linear pattern or a circular pattern. Here, CW (Continuous Wave) laser welding, millisecond pulse laser welding, or microsecond pulse laser welding is mainly used. However, in such welding methods, the input heat amount to the welded portion may become excessive, and the gasket may be damaged due to locally rapid heat conduction.

[0009] Thus, if the gasket is damaged and deformed, it may not only be difficult to prevent the leakage of the electrolytic solution, which is the original function, and may seriously affect the sealing performance of the cylindrical battery cell, but may also pose a problem in ensuring safety.

[0010] Therefore, it is appropriate to use a nanosecond pulse laser with a relatively low input heat amount to the welded portion.

[0011] However, since the nanosecond pulse laser has a small spot size, if a linear pattern or a circular pattern used in other welding methods is used, the weldability will decrease, and there is a problem that the time required for welding (tack time) is long and the workability decreases.

[0012] Therefore, when performing laser welding for electrical connection to the positive and negative terminals of a cylindrical battery cell, a technique is required that can minimize damage to the gasket, ensure weldability, and shorten the welding time by preventing overwelding.

Summary of the Invention

Problems to be Solved by the Invention

[0013] The present invention is for solving the above problems, and an object thereof is to provide a cylindrical battery cell in which a discontinuous spiral welding part is formed so as to prevent overwelding from occurring at the welding part for the electrode terminals of the cylindrical battery cell, and a battery module including the same.

Means for Solving the Problems

[0014] In order to achieve such an object, a cylindrical battery cell according to the present invention has a cap assembly mounted on the upper end of a battery case that houses an electrode assembly. The upper end of the battery case forms a crimping part that surrounds the outer periphery of the cap assembly and is bent in the central direction. The crimping part is a negative terminal, the top cap at the center of the cap assembly is a positive terminal, and at least one of the negative terminal and the positive terminal can form a discontinuous spiral welding part.

[0015] In the spiral welding part, the welding lines are formed so as not to overlap.

[0016] The spiral welding part can be formed so that the heat affected zones do not overlap.

[0017] The welding part can be formed by a nanosecond pulsed laser.

[0018] The spiral welding part formed on the negative electrode terminal can be formed by welding while moving a nanosecond pulse laser linearly and rotating it spirally.

[0019] The spiral welding part formed on the positive electrode terminal can be formed by welding while moving a nanosecond pulse laser circularly and rotating it spirally.

[0020] In this way, the post-welding line can be formed discontinuously so that the pre-welding line and the post-welding line do not overlap while rotating spirally.

[0021] The interval between unit spirals in the spiral welding part may be the same as the width of the unit spiral or larger than the width of the unit spiral at the negative electrode terminal, and may be smaller than the width of the unit spiral at the positive electrode terminal.

[0022] A bus bar, a wire, or a metal plate can be coupled to the spiral welding part.

[0023] The present invention provides a battery module including the cylindrical battery cell, and a plurality of cylindrical battery cells can be connected in series and in parallel by coupling a bus bar, a wire, or a metal plate.

[0024] Also, the present invention can be provided in a form in which various combinations of the means for solving the problems are combined.

Effects of the Invention

[0025] As described above, in the cylindrical battery cell according to the present invention, heat overlap can be minimized by the spiral welding part formed discontinuously, so that over-welding can be prevented from occurring at the welding part.

[0026] Further, since the spiral welding part is formed so that heat-affected zones do not overlap, formation of a softened region of the material can be prevented, and thus a decrease in tensile strength can be prevented.

[0027] In addition, since a wide area of the welded portion can be secured, the welding strength can be increased.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0029] Hereinafter, embodiments that enable a person having ordinary knowledge in the technical field to which the present invention pertains to easily implement the present invention will be described in detail with reference to the accompanying drawings. However, when it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the gist of the present invention in explaining the operating principle of a preferred embodiment of the present invention, the detailed description thereof will be omitted.

[0030] Also, the same reference numerals are used for parts having similar functions and operations throughout the drawings. Throughout the specification, when a part is described as being connected to another part, this includes not only the case where they are directly connected, but also the case where they are indirectly connected with other elements interposed therebetween. Also, including a certain component means, unless otherwise stated to the contrary, not excluding other components, but further capable of including other components.

[0031] Also, the descriptions for limiting or adding and specifying components are applicable to all inventions without special restrictions and are not limited to specific inventions.

[0032] Also, throughout the description and claims of the present invention, those expressed in the singular include the plural cases unless otherwise mentioned.

[0033] Also, throughout the description and claims of the present invention, "or" includes "and" unless otherwise mentioned. Therefore, "including A or B" means three cases: including A, including B, or including both A and B.

[0034] The present invention will be described in detail together with specific embodiments based on the drawings.

[0035] FIG. 1 is a perspective view of a cylindrical battery cell according to the present invention.

[0036] Referring to FIG. 1, in a cylindrical battery cell 100 according to the present invention, an electrode assembly is housed inside a battery case 110, and a cap assembly is mounted on the upper end of the battery case 110. The upper end of the battery case 110 forms a crimping portion 120 that surrounds the outer periphery of the cap assembly and is bent in the central direction.

[0037] The crimping portion 120 becomes a negative electrode terminal, the top cap 130 at the center of the cap assembly becomes a positive electrode terminal, and discontinuous spiral negative electrode welding portions 141 and continuous spiral positive electrode welding portions 142 are formed on the negative electrode terminal and the positive electrode terminal.

[0038] In this way, by forming the negative electrode welding part in a spiral shape, the area of the welding part can be increased, so that the welding strength can be ensured. Further, since a discontinuous spiral-shaped welding part is formed so as not to overlap at the meeting point of the spiral shapes, the problem of over-welding occurring at the meeting point of the spiral shapes can be prevented. Therefore, the problems of the gasket being damaged or the electrolyte leaking due to over-welding can be prevented.

[0039] Further, in the present invention, in order to prevent heat from concentrating on the negative electrode welding part 141 and the positive electrode welding part 142, a negative electrode welding part and a positive electrode welding part are formed using a nanosecond pulse laser with a relatively low input heat quantity.

[0040] Figure 2 is a photograph of the negative electrode welding part according to the present invention.

[0041] Referring to Figure 2, Figure 2 is a photograph of the negative electrode welding part formed on the crimping part that functions as a negative electrode terminal, and a discontinuous spiral-shaped welding part is formed. Specifically, since the crimping part is formed in an elongated shape along the circular end at the upper part of the battery case, the nanosecond pulse laser moves linearly and rotates in a spiral shape to form the welding line 210.

[0042] In this way, although the welding line 210 may be formed in a spiral shape to cause overlap, in the present invention, a discontinuous spiral shape is formed to prevent overlap.

[0043] Specifically, the subsequent welding line 212 is formed discontinuously so that the subsequent welding line 212 and the previous welding line 211 do not overlap while rotating in a spiral shape.

[0044] When using a nanosecond pulsed laser, the welded part will be formed narrower. The present invention forms a spiral welded part in order to secure a wider welded part. In the spiral welded part, when one spiral is referred to as a unit spiral, the interval between the unit spirals can be formed so that the heat affected zones do not overlap maximally, taking into account the width of the unit spiral.

[0045] In this way, by preventing the heat affected zones from overlapping, it is possible to prevent the gasket at the lower part of the welded part from being damaged by heat.

[0046] For example, the interval B between the unit spirals can be formed to be the same as or larger than the width D of the unit spiral in the negative electrode terminal where the welded part is generally formed linearly.

[0047] Figure 3 is a photograph of the positive electrode welded part according to the present invention.

[0048] Referring to Figure 3, a continuous spiral welded part is formed as the positive electrode welded part. Specifically, a welding line 210 is formed while moving the nanosecond pulsed laser circularly and rotating it spirally.

[0049] Therefore, compared with the case of welding only in a dot shape or a linear shape, the area of the welded part can be formed wider, so the welding strength of the positive electrode welded part can be improved.

[0050] The base material for the positive electrode welded part can be composed of an aluminum-based alloy material. Generally, it is as thick as 3.0T or more, so there is a low risk of penetration during nanosecond pulsed laser welding. Also, unlike the negative electrode welded part, there are no components at the lower part of the base material that may be damaged by welding heat. Therefore, the welding line of the positive electrode welded part can be formed in a continuous form without discontinuous sections in order to improve the welding strength.

[0051] In the positive electrode terminal, since the welding lines are arranged more densely than in the negative electrode welded part, the interval B between the unit spirals can be formed to be smaller than the width D of the unit spiral.

[0052] Also, the positive electrode welding part is generally thicker than the negative electrode welding part, with the thickness of the base material being 3.0T or more. Therefore, even if the welding lines are densely arranged, the heat-affected zones can be prevented from overlapping.

[0053] In the cylindrical battery cell of the present invention, a bus bar, a wire, or a metal plate is coupled to the positive electrode terminal and the negative electrode terminal, so that it can be connected in series and / or in parallel with other cylindrical battery cells, or electrically connected to a device.

[0054] With such a connection structure, it can be used as an energy source for devices that require high capacity and high output.

[0055] Hereinafter, embodiments of the present invention will be described with reference to examples, which are for easier understanding of the present invention and do not limit the scope of the present invention.

[0056] <Example 1>

[0057] To attach a metal plate made of an aluminum material to the crimping part of the cylindrical battery cell, nanosecond pulsed laser welding was performed to form a discontinuous spiral welding part as shown in FIG. 2. Here, the subsequent welding line was formed discontinuously so that the prior welding line and the subsequent welding line did not overlap.

[0058] FIG. 4 is a photograph of the heat-affected zone of the negative electrode welding part according to the present invention.

[0059] The heat-affected zone does not melt directly by the welding heat source, but means a part where the temperature rises due to the welding heat and the physical properties of the base material change. When the heat-affected zones overlap, a softening region of the base material is formed, so the welding strength may decrease and the tensile strength may decrease.

[0060] Referring to FIG. 4, it can be seen that a heat-affected zone 230 is formed around the welding line 210. Although the heat-affected zones may partially overlap at the portion where the pre-welding line and the post-welding line are formed adjacent to each other, by configuring as shown in FIG. 4, the overlapping area of the heat-affected zones can be minimized.

[0061] Thus, in the spiral welding portion for minimizing the overlap of the heat-affected zones and ensuring the welding strength, the optimal values of A to D, tack time, total number of spirals, and laser pulses per unit spiral shown in FIGS. 2 and 3 were derived as the numerical values shown in Table 1 below.

[0062]

Table 1

[0063] <Comparative Example 1> Spot welding was performed on the crimping portion and the top cap of the cylindrical battery cell with a micro-pulse laser. A welding portion in which a plurality of points were arranged side by side was formed on the negative electrode terminal formed on the crimping portion, and a welding portion in which 15 points were arranged in 3 rows and 5 columns was formed on the positive electrode terminal formed on the top cap.

[0064] A point constituting one of the spot welding portions can be configured in a spiral shape formed while rotating around the center, and the tack time required to form the welding portion with 15 such points is 0.3 seconds for the negative electrode and 1.5 seconds for the positive electrode.

[0065] Therefore, it can be seen that when performing spot welding, the tack time of the positive electrode increases compared to Example 1.

[0066] FIG. 5 is a photograph of the heat-affected zone of the welded portion where spot welding was performed.

[0067] Referring to FIG. 5, a heat affected zone 230 is formed along the periphery of the welding line 210, and an overlapping section of the heat affected zones occurs along the spiral welding line. Thus, when the heat affected zones overlap, the base material softens and the welding strength decreases, resulting in a possible decrease in the tensile strength.

[0068] <Comparative Example 2>

[0069] In the above Example 1, nanosecond pulsed laser welding was carried out in the same manner as in Example 1, except that the subsequent welding line was continuously formed so that the preceding welding line and the subsequent welding line overlapped.

[0070] <Laser Penetration Depth Measurement Experiment of Welded Part>

[0071] One hundred and ten cylindrical battery cells manufactured as in Example 1 and Comparative Example 2 were respectively prepared.

[0072] FIG. 6 is a photograph of a cross section of the welded part of the cylindrical battery cells manufactured in Example 1 and Comparative Example 2.

[0073] FIG. 6(a) shows a cross section of the welded part of Example 1, FIG. 6(b) shows a cross section of the welded part of Comparative Example 2, and the reference numerals 14, 15, 16 shown in FIG. 6(a) and the reference numerals 47, 48, 49 shown in FIG. 6(b) are identification numbers of the laser welded parts.

[0074] The laser penetration depths of the crimping parts at the welded parts 14, 15, 16 shown in FIG. 6(a) are 0.042 mm, 0.104 mm, and 0.190 mm respectively, and the laser penetration depths of the crimping parts at the welded parts 47, 48, 49 shown in FIG. 6(b) are 0.307 mm, 0.399 mm, and 0.311 mm respectively.

[0075] That is, it can be confirmed that it was measured that the laser penetration depth is deeper in the welded part of Comparative Example 2 formed such that the welding lines overlap. Therefore, when the welding lines are formed to overlap, there is a high possibility that the gasket at the lower part of the crimping part will be damaged by the welding heat.

[0076] <Air leakage experiment>

[0077] Figure 9 is a schematic diagram and a photograph of the apparatus for the air leakage experiment.

[0078] Using the apparatus for the air leakage experiment shown in Figure 9, the presence or absence of air leakage in the cylindrical battery cells manufactured in Example 1 and Comparative Example 2 was confirmed.

[0079] With the cylindrical battery cell 100 inserted into the holder, it was mounted on the air leakage test jig.

[0080] A gasket was interposed so that no space was created between the holder and the cylindrical battery cell 100, and the holder was filled with water.

[0081] An air injection hole was formed at the bottom of the cylindrical can, and while injecting air through the hole, it was confirmed with a camera whether bubbles were generated in the water.

[0082] The air injection pressure was maintained at a pressure lower than 20 kgf / cm 2 ~23 kgf / cm 2 and a method of gradually increasing the pressure in four steps was used. Specifically, it was carried out during the process of injecting air at 15 kgf / cm 2 for 1 minute, 16 kgf / cm 2 for 1 minute, 17 kgf / cm 2 for 1 minute, and 18 kgf / cm 2 for 2 minutes.

[0083] For the air injection, the RTK18 - 0003 model of PDK Co., Ltd. was used.

[0084] Figure 7 is a photograph taken while observing the injection of air at the lower part of the cylindrical battery cell manufactured in Example 1, and Figure 8 is a photograph showing the state of the cylindrical battery cell manufactured in Comparative Example 2 before and after air injection.

[0085] Referring to FIGS. 7 and 8, it can be confirmed that no generation of bubbles was observed in the cylindrical battery cells manufactured in Example 1, and no air leakage occurred in any of them. On the other hand, among 110 cylindrical battery cells manufactured in Comparative Example 2, bubbles were generated at the welding parts in 86 of them.

[0086] That is, when the welding part is formed such that the welding lines overlap at the spiral welding part, as a result, the laser penetration depth becomes deeper, and it can be understood that battery cells in which the gasket is damaged and judged as defective in the air leakage experiment were generated.

[0087] Those having ordinary knowledge in the field 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 content.

Explanation of Reference Numerals

[0088] 100 Cylindrical battery cell 110 Battery case 120 Crimping part 130 Top cap 141, 142 Welding part 210 Welding line 211 Pre-welding line 212 Post-welding line 230 Heat-affected part A Length of welding part B Spacing between unit spirals C Vertical width of unit spiral D Horizontal width of unit spiral

Claims

1. A cap assembly is mounted on the upper end of a battery case that houses an electrode assembly, The upper end of the battery case forms a crimping portion that surrounds the outer periphery of the cap assembly and is bent in the central direction, The crimping portion is a negative electrode terminal, and the top cap at the center of the cap assembly is a positive electrode terminal, At least one of the negative electrode terminal and the positive electrode terminal is formed with a discontinuous spiral welding portion, The discontinuous spiral welding portion is formed by moving a nanosecond pulse laser along the overall shape of the welding portion while circularly moving it so as to draw an overlapping loop-shaped locus. For the loop-shaped portion of the generated welding line, the subsequent welding line is formed to be discontinuous at the portion where it is supposed to overlap the previous welding line so that the previous welding line and the subsequent welding line do not overlap. A cylindrical battery cell.

2. The cylindrical battery cell according to claim 1, wherein in the discontinuous spiral welding portion, the welding lines are formed so as not to overlap.

3. The cylindrical battery cell according to claim 1, wherein the discontinuous spiral welding portion is formed so that heat affected zones do not overlap.

4. The cylindrical battery cell according to claim 1, wherein the discontinuous spiral welding portion is formed by the nanosecond pulse laser.

5. The cylindrical battery cell according to claim 1, wherein the discontinuous spiral welding portion formed on the negative electrode terminal is formed by moving the nanosecond pulse laser linearly and rotating it spirally while welding.

6. The cylindrical battery cell according to claim 1, wherein the discontinuous spiral welding portion formed on the positive electrode terminal is formed by moving the nanosecond pulse laser circularly and rotating it spirally while welding.

7. The cylindrical battery cell according to claim 5 or 6, wherein the rear welding line is discontinuously formed so that the front welding line and the rear welding line do not overlap while rotating spirally.

8. The cylindrical battery cell according to claim 1, wherein the interval between unit spirals in the discontinuous spiral welding portion is the same as or larger than the lateral width of the unit spiral at the negative electrode terminal and smaller than the lateral width of the unit spiral at the positive electrode terminal.

9. The cylindrical battery cell according to claim 1, wherein a bus bar, a wire, or a metal plate is coupled to the discontinuous spiral welding portion.

10. A battery module including the cylindrical battery cell according to claim 1, The battery module, wherein a plurality of cylindrical battery cells are connected in series and in parallel by coupling a bus bar, a wire, or a metal plate.

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