Secondary battery with improved safety

Abstract

The disclosed invention relates to a secondary battery including an electrode assembly in which a plurality of unit cells are stacked. In one example, electrode tabs of each unit cell extending from the electrode assembly are gathered together and electrically connected to an electrode terminal of the secondary battery, and the electrode tabs of each unit cell include an excess portion that accommodates swelling of the electrode assembly.

Description

Technical Field

[0001] The present invention relates to a secondary battery, and more particularly, to a secondary battery in which the safety of an electrode tab is maintained even when a swelling phenomenon of an electrode assembly occurs.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0045170 filed on April 12, 2022, and Korean Patent Application No. 10-2023-0039585 filed on March 27, 2023, and all of the contents disclosed in the documents of the Korean patent applications are incorporated herein by reference.

Background Art

[0003] Unlike a primary battery, a secondary battery is rechargeable and has been extensively studied and developed in recent years due to its potential for miniaturization and high capacity. With the increasing development of technology and demand for mobile devices, as well as the emergence of electric vehicles and energy storage systems in response to the contemporary requirements of environmental protection, the demand for secondary batteries as an energy source has increased even more rapidly.

[0004] Secondary batteries are classified into coin-type batteries, cylindrical batteries, prismatic batteries, and pouch-type batteries according to the shape of the battery case. An electrode assembly mounted inside the battery case in a secondary battery is a power generation element capable of charge and discharge, which has a laminated structure of electrodes and a separator.

[0005] The electrode assembly can be roughly classified into a jellyroll type in which a separator is interposed between a sheet-shaped positive electrode and a negative electrode coated with an active material and wound, a stack type in which a plurality of positive electrodes and negative electrodes are sequentially laminated with a separator interposed therebetween, and a stack and folding type in which a unit cell of the stack type is wound with a long separation film.

[0006] One of the problems that can occur when a secondary battery is used for a long time is the swelling phenomenon. The swelling phenomenon refers to the phenomenon in which a secondary battery that repeatedly charges and discharges gradually swells. The swelling phenomenon is that the lithium-ion electrolyte in the battery vaporizes and the battery swells due to the pressure, but it induces deformation of the case, and in severe cases, the electrolyte may leak and a fire or explosion may occur.

[0007] The swelling phenomenon affects not only the outer shape of the secondary battery but also its internal structure. That is, when the swelling phenomenon occurs in the electrode assembly, stress accumulates due to the tensile force acting on the electrode tab that extends from the electrode assembly and is welded to the electrode terminal. Once the swelling phenomenon occurs, it cannot be restored to a good state, so the electrode tab will continue to be pulled, and when the stress exceeds the limit, the electrode tab will break.

[0008] Therefore, in order to safely use the secondary battery for a long time, a structure that can prevent the disconnection of the electrode tab in response to the swelling phenomenon is required.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a secondary battery that can prevent disconnection of the electrode tab even when a swelling phenomenon occurs during use of the secondary battery.

[0011] However, the technical problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those of ordinary skill in the art from the description of the invention described below.

Means for Solving the Problems

[0012] The present invention relates to a secondary battery including an electrode assembly in which a plurality of unit cells are stacked. In one example, electrode tabs of each unit cell extending from the electrode assembly are gathered together and electrically connected to an electrode terminal of the secondary battery, and the electrode tabs of each unit cell are characterized by including a surplus length portion corresponding to swelling of the electrode assembly.

[0013] In one embodiment of the present invention, electrode tabs of each unit cell extending from the electrode assembly are supported by a clip electrically connected to the electrode terminal, and the surplus length portion is formed behind a binding portion of the clip.

[0014] And a welding portion is formed where an end portion of the surplus length portion is joined to the clip.

[0015] Depending on a specific embodiment, the surplus length portion may form a U-turn portion between the binding portion and the welding portion.

[0016] Also, according to one embodiment, a plurality of the electrode assemblies can be provided, and respective electrode tabs extending from the plurality of electrode assemblies may form binding portions independent of each other with respect to the clip.

[0017] In one example, a plurality of the clips corresponding to the number of the electrode assemblies are provided, each electrode assembly is supported by a binding portion of a corresponding clip, and an end portion of a surplus length portion included in an electrode tab extending from each electrode assembly forms a welding portion with respect to the corresponding clip.

[0018] In another example, the clip includes a plurality of binding portions corresponding to the number of the electrode assemblies, and each electrode assembly is supported by a corresponding binding portion.

[0019] And an end portion of a surplus length portion included in an electrode tab extending from each electrode assembly may form one welding portion with respect to the clip.

[0020] In addition, the extra length portions provided in each electrode tab extended from a plurality of electrode assemblies can form a U-turn portion between the above-described ligation portion and the welding portion.

[0021] On the other hand, according to another embodiment of the present invention, the clip can be provided with a friction reduction structure on the contact surface of the ligation portion that supports the electrode tab of the electrode assembly.

[0022] In one example, the friction reduction structure can be an embossing structure formed on the contact surface of the ligation portion.

[0023] In another example, the friction reduction structure can be a low friction coating layer formed on the contact surface of the ligation portion.

[0024] And, according to another embodiment of the present invention, the clip can be provided with an insertion guiding portion that assists in inserting the electrode tab of each unit cell into the ligation portion.

[0025] For example, the insertion guiding portion can be a groove that converges toward the ligation portion.

Advantages of the Invention

[0026] Even when a swelling phenomenon occurs in the electrode assembly due to battery degradation or impact caused by repeated charging and discharging in the secondary battery of the present invention having the above-described configuration, since the electrode tab has an extra length portion, excessive stress does not act on the welding portion. Therefore, in the secondary battery of the present invention, disconnection of the electrode tab can be prevented even when a swelling phenomenon occurs, and the safety of the secondary battery can be maintained well for a long time.

[0027] In addition, the present invention can be designed such that the electrode tab moves only by that amount in proportion to the swelling level by guiding the movement of the electrode tab accompanying swelling to sliding while supporting the middle portion of the electrode tab using a clip. Thereby, the extra length portion of the electrode tab can effectively cope with the swelling phenomenon of the electrode assembly, and dangers such as internal short circuits are eliminated by accurately controlling the position and movement of the extra length portion.

[0028] However, the technical effects that can be obtained by the present invention are not limited to the effects described above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

[0029] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention to be described later. Therefore, the present invention should not be construed as being limited only to the matters described in such drawings.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0031] Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be described in detail below.

[0032] However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0033] In the present invention, terms such as "comprising" and "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should not be construed as precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0034] Also, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is directly on the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, it includes not only the case where it is directly under the other part, but also the case where there is another part in between. Also, in this application, being "disposed on" can include not only the upper part but also the case of being disposed on the lower part.

[0035] The present invention relates to a secondary battery including an electrode assembly in which a plurality of unit cells are stacked. In one example, the electrode tabs of each unit cell extending from the electrode assembly are gathered together and electrically connected to the electrode terminals of the secondary battery, and the electrode tabs of each unit cell are provided with an extra length portion corresponding to the swelling of the electrode assembly.

[0036] In a specific embodiment, the secondary battery according to an embodiment of the present invention is supported by a clip in which the electrode tabs of each unit cell extending from the electrode assembly are electrically connected to the electrode terminals, and the extra length portion is formed after the tying portion of the clip.

[0037] Accordingly, even when the battery degrades due to repeated charging and discharging of the secondary battery, or the electrode assembly bulges due to impact, i.e., swelling occurs, the electrode tab has an extra length portion, so that excessive stress does not act on the welded portion. Therefore, the secondary battery according to an embodiment of the present invention can prevent disconnection of the electrode tab even when the swelling phenomenon occurs, and can maintain good safety of the secondary battery for a long time.

[0038] Also, by guiding the movement (tension by tensile force) of the electrode tab accompanying swelling to sliding while supporting the middle portion of the electrode tab using a clip, it can be controlled so that the electrode tab moves only by that amount in proportion to the swelling level. Thereby, the extra length portion of the electrode tab can effectively cope with the swelling phenomenon of the electrode assembly, and by accurately designing the position and movement of the extra length portion, risks such as internal short circuits are eliminated.

[0039] Hereinafter, specific embodiments of the secondary battery according to the present invention will be described in detail with reference to the accompanying drawings. For reference, the front-back, up-down, left-right directions designating relative positions used in the following description are for helping the understanding of the invention, and are based on the directions shown in the drawings unless otherwise defined.

[0040] (First Embodiment) FIG. 1 is an exploded perspective view illustrating a secondary battery 10 according to an embodiment of the present invention, and FIG. 2 is a drawing illustrating a coupling structure between an electrode tab 120 and a clip 300 of an electrode assembly 100.

[0041] As shown in the attached drawings, the present invention is applicable to a secondary battery 10 including an electrode assembly 100 in which a plurality of unit cells 110 are stacked. For example, as one example, it is applicable to a rectangular secondary battery 10 illustrated in the drawings. The electrode tabs 120 of each unit cell 110 extending from the electrode assembly 100 are gathered together and electrically connected to the electrode terminals 200 of the secondary battery 10. Each electrode tab 120 of the unit cell 110 is provided with an extra length portion 130 corresponding to the swelling of the electrode assembly 100.

[0042] The swelling phenomenon refers to the phenomenon in which the electrode assembly 100 that repeatedly charges and discharges gradually swells. The swelling phenomenon is that the lithium-ion electrolyte in the battery vaporizes and the battery swells due to its pressure, which induces deformation of the case 20. In severe cases, the electrolyte may leak and fires or explosions can occur.

[0043] As one of the problems that the swelling phenomenon has on the internal structure of the secondary battery 10, stress may be generated on the electrode tab 120. In the electrode assembly 100, for example, a stacked electrode assembly 100, the electrode tabs 120 (positive electrode tabs or negative electrode tabs) of the stacked unit cells 110 are joined to the electrode terminals 200 by welding. However, the distances from each unit cell 110 to the electrode terminals 200 are different from each other.

[0044] When the swelling phenomenon occurs in the electrode assembly 100 with such a structure, the relative position changes more greatly for the unit cell 110 that is farther away from the electrode terminal 200. As a result, a strong tensile force acts on the electrode tab 120 of the unit cell 110 that is farther away. When designing the welded portion 320 between the electrode tab 120 and the electrode terminal 200, only an extra amount for process deviation is considered. Therefore, when the battery deteriorates and the swelling phenomenon occurs, the electrode tab 120 on which the tensile force acts strongly is likely to short-circuit at the electrode terminal 200, and the disconnection of the electrode tab 120 will have an adverse effect on the safety of the secondary battery 10.

[0045] In order to prevent disconnection of the electrode tab 120 associated with such a swelling phenomenon, the electrode tab 120 of each unit cell 110 is configured to include a surplus length portion 130 corresponding to the swelling of the electrode assembly 100. Even if a swelling phenomenon occurs and the relative position between the unit cell 110 and the electrode terminal 200 changes significantly, the surplus length portion 130 changes in response to the variation in the relative position, so that no stress is generated in the electrode tab 120.

[0046] According to a specific embodiment of the present invention illustrated in FIGS. 1 and 2, the electrode tab 120 of each unit cell 110 extended from the electrode assembly 100 is supported by a clip 300 electrically connected to the electrode terminal 200, and the surplus length portion 130 is formed behind the binding portion 310 of the clip 300. Then, a welding portion 320 is formed where the end of the surplus length portion 130 is joined to the clip 300, whereby the electrode tab 120 is electrically connected to the electrode terminal 200 via the clip 300.

[0047] The clip 300 in an embodiment of the present invention means a component that physically grips and supports a bundle of electrode tabs 120 without being restricted by its form. For example, as illustrated in the drawings, the electrode tab 120 can be inserted between the slits provided in the clip 300 and temporarily fixed. Here, the temporary fixation means a fixed state in which the electrode tab 120 fitted in the clip 300 is normally fixed in its position, but relative movement can occur when a certain degree of tensile force acts.

[0048] The binding portion 310 of the clip 300 is a portion that compresses and temporarily fixes the electrode tab 120 (for example, the above-described slit), and the surplus length portion 130 formed behind the binding portion 310 of the clip 300 corresponds to the swelling of the electrode assembly 100. When the electrode assembly 100 swells and a tensile force acts on the electrode tab 120 of the unit cell 110, and the surplus length portion 130 passes through the binding portion 310 and moves toward the electrode assembly 100 side, the stress acting on the electrode tab 120 is greatly relieved.

[0049] For reference, although the polarities of the electrode tab 120 and the electrode terminal 200 are not particularly distinguished in the drawings, this is because the configuration of the extended portion 130 of the electrode tab 120 and the clip 300 can be widely applied regardless of whether it is a positive electrode or a negative electrode.

[0050] Depending on the specific embodiment, the extended portion 130 may form a U-turn portion 132 between the ligation portion 310 and the welding portion 320. The U-turn portion 132 forms a gentle curve toward the ligation portion 310 of the clip 300, thereby reducing the resistance that hinders the movement of the extended portion 130.

[0051] FIG. 3 is a drawing illustrating the change of the electrode tab 120 supported by the clip 300 when a swelling phenomenon occurs in the electrode assembly 100. Compared with FIG. 2, as the thickness of the electrode assembly 100 swells (the thickness increases from d to d'), a relative movement away from the ligation portion 310 of the clip 300 occurs for each outer unit cell 110. However, the extended portion 130 moves as much as the displacement of the electrode tab 120, thereby preventing the disconnection of the electrode tab 120.

[0052] As in the illustrated embodiment, when the movement of the electrode tab 120 due to swelling is induced to slide while supporting the middle portion of the electrode tab 120 using the clip 300, it can be accurately designed so that the electrode tab 120 moves only by that amount in proportion to the swelling level. Thereby, the extended portion 130 of the electrode tab 120 can effectively respond to the swelling phenomenon of the electrode assembly 100, and by accurately controlling the position and movement of the extended portion 130, risks such as internal short circuits are eliminated.

[0053] On the other hand, depending on the embodiment, a plurality of electrode assemblies 100 can be provided. In such a case, each electrode tab 120 extended from the plurality of electrode assemblies 100 can form a ligation portion 310 independent of each other with respect to the clip 300.

[0054] FIG. 4 is a drawing illustrating a case where a plurality of electrode assemblies 100 are supported by a plurality of clips 300. In other words, a plurality of clips 300 are provided, the number corresponding to the number of the plurality of electrode assemblies 100. Each electrode assembly 100 is supported by a ligating portion 310 of the clip 300 corresponding thereto. The end of the extra length portion 130 provided in the electrode tab 120 extending from each electrode assembly 100 forms a welding portion 320 with the corresponding clip 300. That is, the embodiment of FIG. 4 corresponds to an arrangement in which several of the embodiments of FIG. 2 are arranged in parallel.

[0055] Alternatively, as shown in FIG. 5, an embodiment in which a plurality of electrode assemblies 100 are supported by one clip 300 is also possible. Referring to FIG. 5, one clip 300 includes a plurality of ligating portions 310 corresponding to the number of electrode assemblies 100, and each electrode assembly 100 is supported by the corresponding ligating portion 310.

[0056] And the end of the extra length portion 130 provided in the electrode tab 120 extending from each electrode assembly 100 can form its own welding portion 320, but as shown in the drawing, a plurality of extra length portions 130 can also form one welding portion 320. The fewer the number of welding portions 320, the more advantageous it is in terms of process efficiency.

[0057] Here, as described above, it can be directly applied that the extra length portion 130 provided in each electrode tab 120 extending from the plurality of electrode assemblies 100 can form a U-turn portion 132 between the ligating portion 310 and the welding portion 320.

[0058] (Second Embodiment) The second embodiment of the present invention further includes a configuration for reducing the accompanying resistance when the extra length portion 130 temporarily fixed to the ligating portion 310 of the clip 300 slides due to a swelling phenomenon. That is, it is an embodiment for preventing an unintentional disconnection of the electrode tab 120 due to a strong resistance when the extra length portion 130 slides.

[0059] For this purpose, the second embodiment of the present invention includes a friction reduction structure 330 on the contact surface of the binding portion 310 of the clip 300 that supports the electrode tab 120 of the electrode assembly 100. By providing the friction reduction structure 330 on the contact surface of the binding portion 310 that compresses the electrode tab 120, the sliding of the surplus length portion 130 occurs smoothly.

[0060] The friction reduction structure 330 provided in the binding portion 310 can be embodied in various forms. For example, as shown in FIG. 6, an embossing structure 332 can be applied as the friction reduction structure 330 provided in the binding portion 310 of the clip 300. The embossing structure 332 similar to a hemispherical shape reduces the sliding resistance by reducing the contact area. In addition, protrusion structures of various shapes can also be applied as the friction reduction structure 330.

[0061] Alternatively, the low friction coating layer 334 shown in FIG. 7 can also be applied as the friction reduction structure 330. The low friction coating layer 334 means various coating layers that reduce the friction coefficient of the surface as the term implies. For example, a chemically stable Teflon (registered trademark) coating layer or a mechanically excellent DLC (Diamond-Like Carbon) coating layer can be applied.

[0062] (Third Embodiment) FIG. 8 illustrates the third embodiment of the present invention, and the third embodiment includes a structure in which an insertion guiding portion is provided in the clip.

[0063] The electrode assembly 100 in which a plurality of unit cells 110 are stacked includes a bundle of electrode tabs 120 corresponding to the number of unit cells 110, and this bundle of electrode tabs 120 must be gathered together and temporarily fixed to the binding portion 310 of the clip 300. The binding portion 310 can be formed of a slit structure in which the clip 300 as shown in FIG. 1 is thinly cut open along the longitudinal direction, for example.

[0064] When the thickness of the electrode assembly 100 increases due to the swelling phenomenon, in order for the electrode tabs 120 of each unit cell 110 to cancel it out while sliding relative to the binding part 310, the bundle of electrode tabs 120 must be smoothly inserted into the binding part 310 without causing damage to the electrode tabs 120. For example, when the thickness of the electrode assembly 100 increases due to an increase in capacitance, there may be a problem that when the bundle of electrode tabs 120 thickens accordingly and is inserted into the binding part 310, bending, breaking, tearing, etc. may occur.

[0065] The third embodiment is for preventing such problems. As shown in FIG. 8, the clip 300 is provided with an insertion guiding portion 312 for assisting the insertion of the electrode tabs 120 of each unit cell 110 into the binding part 310.

[0066] For example, the insertion guiding portion 312 can be provided as a groove that converges toward the binding part 310. The groove that converges toward the binding part 310 means a groove whose width gradually decreases toward the binding part 310. FIG. 8(a) shows the case where the insertion guiding portion 312 is formed as a wedge-shaped slope, and FIG. 8(b) shows the case where the insertion guiding portion 312 is formed as a semi-circular shape.

[0067] As long as it is in the form of a groove that converges toward the binding part 310, in addition to the forms exemplified, it would be suitable for application as the insertion guiding portion 312. Due to the convergence guiding action of the insertion guiding portion 312, a thick bundle of electrode tabs 120 can also smoothly enter the binding part 310, thereby significantly reducing the possibility of problems such as bending, breaking, and tearing occurring in the electrode tabs 120 during the insertion process.

[0068] The present invention has been described in more detail with reference to the drawings and embodiments. However, the configurations described in the drawings or embodiments described in this specification are only one embodiment of the present invention and do not represent all of the technical ideas of the present invention. It should be understood that there can be various equivalents and modifications that can replace these at the time of this application.

Description of Symbols

[0069] 10: Secondary battery 20: Case 100: Electrode assembly 110: Unit cell 120: Electrode tab 130: Excess length portion 132: U-turn portion 200: Electrode terminal 300: Clip 310: Binding portion 312: Insertion guiding portion 320: Welding portion 330: Friction reduction structure 332: Embossing structure 334: Low friction coating layer

Claims

1. In a secondary battery including an electrode assembly in which a plurality of unit cells are stacked, the electrode tabs of each unit cell extended from the electrode assembly are gathered together and electrically connected to the electrode terminal of the secondary battery, the electrode tabs of each unit cell are provided with a surplus length portion corresponding to the swelling of the electrode assembly, the electrode tabs of each unit cell extended from the electrode assembly are supported by a clip electrically connected to the electrode terminal, the surplus length portion is formed behind the binding portion of the clip, A secondary battery.

2. Form a welding portion where the end of the surplus length portion is joined to the clip, The secondary battery according to Claim 1.

3. The surplus length portion forms a U-turn portion between the binding portion and the welding portion, The secondary battery according to Claim 2.

4. A plurality of electrode assemblies are provided, each electrode tab extended from the plurality of electrode assemblies forms a binding portion independent of each other with respect to the clip, The secondary battery according to Claim 2.

5. A plurality of clips corresponding to the number of the electrode assemblies are provided, each electrode assembly is supported by the binding portion of the corresponding clip, the end of the surplus length portion provided in the electrode tab extended from each electrode assembly forms a welding portion with respect to the corresponding clip, The secondary battery according to Claim 4.

6. The clip includes a plurality of binding portions corresponding to the number of the electrode assemblies, each electrode assembly is supported by the corresponding binding portion, The secondary battery according to Claim 4.

7. The end of the surplus length portion provided in the electrode tab extended from each electrode assembly forms one welding portion with respect to the clip, The secondary battery according to Claim 6.

8. The surplus length portion provided in each electrode tab extended from the plurality of electrode assemblies forms a U-turn portion between the binding portion and the welding portion, The secondary battery according to Claim 4.

9. The clip is provided with a friction reduction structure on the contact surface of the binding portion that supports the electrode tabs of the electrode assembly, The secondary battery according to any one of Claims 1 to 8.

10. The friction reduction structure is an embossing structure formed on the contact surface of the binding portion, The secondary battery according to Claim 9.

11. The friction reduction structure is a low friction coating layer formed on the contact surface of the binding portion, The secondary battery according to Claim 9.

12. The clip is provided with an insertion guiding portion that assists the insertion of the electrode tabs of each unit cell into the binding portion, The secondary battery according to any one of claims 1 to 8.

13. The insertion guiding portion is a groove in a form converging toward the ligation portion. The secondary battery according to claim 12.

Images