Cylindrical battery monomer and battery module

Abstract

The utility model relates to the technical field of batteries, particularly provides a cylindrical battery monomer and a battery module, and aims to solve the technical problems of small effective welding area, large internal resistance of the battery monomer and poor overcurrent capacity caused by unreasonable position arrangement of a welding area of an anti-explosion valve and a roll core on a cover plate. Therefore, the cylindrical battery monomer provided by the utility model comprises a shell with an opening; the electrode assembly is arranged in the shell; the cover plate is arranged at the opening; the cover plate comprises a weak part and a plurality of welding parts, the weak part is arranged around the center of the cover plate, and the welding parts are electrically connected with the electrode assembly; the partial welding part is arranged on the side, close to the center, of the weak part. The plurality of welding parts are arranged on the cover plate, and part of the welding parts are arranged on the side, close to the center, of the weak part, so that welding of the electrode assembly and the cover plate is more sufficient, the transmission path of electrons on the electrode assembly is shortened, the internal resistance of the single cylindrical battery is reduced, and the overcurrent capacity of the single cylindrical battery is enhanced.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, and specifically provides a cylindrical battery monomer and a battery module. Background Art

[0002] Lithium-ion batteries have outstanding advantages such as high energy density, low environmental pollution, high power density, long service life, wide adaptability, and small self-discharge coefficient. They are one of the most widely used batteries in the world today and an important part of the development of new energy.

[0003] With the continuous upgrading of market demand, cylindrical batteries have developed from 18650 and 21700 to the larger and more energy-dense 4680 series cylindrical batteries. Compared with 18650 and 21700 cylindrical cells, the 4680 cylindrical battery adopts a full-ear design, which effectively shortens the current path, promotes smoother movement of electrons inside the battery, reduces the internal resistance of the cell itself, and significantly reduces Joule heat loss. In addition, cylindrical batteries are made of stainless steel, have higher mechanical strength, and can effectively absorb the pressure caused by the expansion of the negative electrode, so they are more suitable for high-silicon and high-nickel systems.

[0004] In order to improve the space utilization of large cylindrical batteries in the height direction and the energy density of the batteries, and reduce the number of structural parts of the batteries, the existing technology is to cancel the negative electrode collector plate welded to the winding core and the shell, and weld the cover plate to the winding core and the shell, which puts higher requirements on the structural design of the cover plate. The problem with the structure of the cover plate in the existing technology is that the relative position of the explosion-proof valve and the winding core welding area on the cover plate is not properly set, resulting in a small effective welding area between the cover plate and the pole ear, and the cover plate is not completely welded to the pole ear, which increases the internal resistance of the battery cell and reduces the current capacity. Utility Model Content

[0005] The utility model aims to solve the above technical problems, namely, to solve the technical problems of small effective welding area, large internal resistance of battery cells and poor current capacity caused by unreasonable position setting of the welding area between the explosion-proof valve and the winding core on the cover plate.

[0006] In a first aspect, the utility model provides a cylindrical battery cell, comprising: a shell having an opening; an electrode assembly disposed in the shell; a cover plate disposed at the opening; the cover plate comprising: a weak portion and a plurality of welding portions, the weak portion being disposed around the center of the cover plate, the welding portions being electrically connected to the electrode assembly; wherein some of the welding portions are disposed on a side of the weak portion close to the center.

[0007] In the above technical solution, multiple welding parts are arranged on the cover plate, and some of the welding parts are arranged on the side close to the center of the weak part. Compared with the solution of setting the weak part on the inner side of the welding part in the prior art, the pole ear on the inner side of the weak part on the electrode assembly can also be welded to the welding part, shortening the transmission path of electrons on the pole piece, reducing the internal resistance of the battery cell, and enhancing the current carrying capacity of the battery cell.

[0008] In some embodiments, the weak portion includes a first arc, the welding portion includes a first convex portion, and the first convex portion intersects with the circle where the first arc is located.

[0009] In the above technical solution, since part of the welding portion is arranged on the side close to the center of the weak portion, the electrode assembly corresponding to the area where the weak portion is located cannot be welded to the cover plate, and the first protrusion intersects with the circle where the first arc of the weak portion is located. The setting of the first protrusion makes up for the area on the aforementioned cover plate that cannot be welded to the electrode assembly, shortens the transmission path of electrons on the electrode piece, reduces the internal resistance of the battery cell, and enhances the current carrying capacity of the battery cell.

[0010] In some embodiments, the weak portion includes a second arc, a first end of the first arc is connected to a first end of the second arc, a second end of the first arc is connected to a second end of the second arc, and the first convex portion is located inside the weak portion.

[0011] In the above technical solution, the weak portion is set as a closed figure with two ends of the first arc and the second arc connected, which reduces the difficulty of processing the weak portion; the first convex portion is arranged on the inner side of the weak portion. Compared with the existing solution, the welding between the cover plate and the electrode assembly is more sufficient, shortening the transmission path of electrons on the electrode piece, reducing the internal resistance of the battery cell, and enhancing the current carrying capacity of the battery cell.

[0012] In some embodiments, the welding portion includes a second protrusion, and the second protrusion is located on the inner side of the weakened portion.

[0013] In the above technical solution, by further providing a second protrusion on the cover plate, the welding area between the cover plate and the electrode assembly can be increased.

[0014] In some embodiments, the welding portion includes a third protrusion, and the third protrusion is located outside the weakened portion.

[0015] In the above technical solution, by further arranging a third protrusion on the cover plate, and the third protrusion is arranged on the outside of the weak portion, the welding area between the cover plate and the electrode assembly is increased while ensuring the valve opening area of ​​the weak portion.

[0016] In some embodiments, the second protrusion and the third protrusion are both arranged along the radial extension of the cover plate; and / or, there are multiple second protrusions and third protrusions, and the multiple second protrusions and / or third protrusions are arranged along the circumference of the cover plate.

[0017] In some embodiments, the first protrusion is arranged to extend along the radial direction of the cover plate.

[0018] In the above technical solution, the first protrusion, the second protrusion and the third protrusion are arranged to extend radially or circumferentially, and the positions of the first, second and third protrusions are reasonably arranged to reduce the processing difficulty and enhance the strength and welding flatness of the cover plate.

[0019] In some embodiments, the cover plate includes a fourth protrusion, the fourth protrusion is electrically connected to the shell, the cover plate and the side wall of the shell are interference fit, and the fourth protrusion abuts against the side wall.

[0020] In the above technical solution, the interference fit can increase the connection strength between the shell and the cover plate and improve the sealing performance.

[0021] In some embodiments, the shell includes a top wall, which is arranged opposite to the opening and connected to the top wall, and the top wall has an electrode lead-out hole; a pole is arranged in the electrode lead-out hole and is electrically connected to the electrode assembly.

[0022] In the above technical solution, the top wall and the pole can be used as two output poles of the battery cell, which can simplify the structure of the battery cell and ensure the current carrying capacity of the battery cell. The top wall and the pole are located at the same end of the battery cell, so that the current collecting component can be assembled to the same side of the battery cell, simplifying the assembly process and improving the efficiency of assembling multiple battery cells into groups.

[0023] In some embodiments, the fourth protrusion includes a vertical portion, and in the thickness direction of the cover plate, the end of the vertical portion away from the electrode assembly is a first outer end surface, and the side wall surrounding the opening is a second outer end surface, and the first outer end surface is flush with the second outer end surface.

[0024] In the above technical solution, the first outer end face and the second outer end face are arranged flush so that the edge of the cover plate is flush with the bottom wall of the shell. In this way, when the battery cell is assembled into the battery module, the height of the battery cell is consistent and will not tilt, which is also conducive to the installation and welding of the busbar.

[0025] In some embodiments, the fourth protrusion includes a guide portion, which is connected to an end of the vertical portion close to the electrode assembly, and the guide portion is arc-shaped to guide the fourth protrusion to be installed on the shell.

[0026] In the above technical solution, by providing a guide portion on the fourth protrusion, the fourth protrusion can be guided to be installed on the shell when the cover plate is assembled, thereby simplifying the assembly process and improving the assembly efficiency.

[0027] In some embodiments, in the thickness direction of the cover plate, the first protrusion, the second protrusion, or the third protrusion is closer to the electrode assembly than the fourth protrusion.

[0028] In a second aspect, the utility model further provides a battery module, wherein the battery module comprises a plurality of the above-mentioned cylindrical battery cells.

[0029] The advantages of the battery module and the cylindrical battery cell described above over the prior art are the same, and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only illustrate certain embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 is a cross-sectional view of a cylindrical battery cell provided by an embodiment of the utility model;

[0032] Figure 2 It is a structural schematic diagram of a cover plate provided by an embodiment of the utility model;

[0033] Figure 3 is a structural schematic diagram of a cover plate provided by another embodiment of the utility model;

[0034] Figure 4 It is a partial cross-sectional view of a cylindrical battery cell provided by an embodiment of the utility model;

[0035] Figure 5 yes Figure 4 Schematic diagram of the structure with a partial enlargement at point A in the middle.

[0036] List of reference numerals:

[0037] 1. Shell; 11. Side wall; 111. Second outer end surface; 12. Top wall; 13. Pole; 2. Electrode assembly; 3. Cover plate; 4. Weak portion; 41. First circular arc; 42. Second circular arc; 5. Welding portion; 51. First convex portion; 52. Second convex portion; 53. Third convex portion; 54. Fourth convex portion; 541. Vertical portion; 5411. First outer end surface; 542. Guide portion. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0039] It should be noted that in the description of the present invention, the terms "inside", "outside", "top", "bottom" and other terms indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings, which are only for the convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0040] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installation", "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0042] In the prior art, in order to improve the space utilization rate of large cylindrical batteries in the height direction and the energy density of the battery, and at the same time reduce the number of structural parts of the battery, the specific method is to cancel the negative electrode collector plate welded to the winding core and the shell, and weld the cover plate to the winding core and the shell. The inventor found that since the cover plate is also provided with a weak structure for timely explosion to prevent thermal runaway, the weak structure is usually set at the center of the cover plate, and at the same time, in order to ensure a stable valve opening area, the weak part occupies a large area at the center of the cover plate. After the negative electrode collector plate is cancelled, the cover plate is welded to the electrode assembly. Due to the relative position relationship between the weak structure and the cover plate, the welding area between the cover plate and the electrode assembly is small. In addition, due to the position of the weak structure, the pole ear on the electrode assembly corresponding to the weak structure cannot be welded to the welding part, resulting in a longer transmission path of electrons on the pole piece, increasing the internal resistance of the cylindrical battery cell, and reducing the current capacity. Based on this, the inventor provides a cylindrical battery cell that can solve the above-mentioned technical problems. The specific embodiment of the cylindrical battery cell of the utility model is described in detail below in conjunction with the accompanying drawings.

[0043] Please refer to Figures 1 to 5 , Figures 1 to 5 This is a schematic structural diagram of a cylindrical battery cell and a cover plate 3 provided in an embodiment of the utility model.

[0044] like Figures 1 to 3As shown, the cylindrical battery cell of the embodiment of the present application includes: a shell 1, which has an opening; an electrode assembly 2, which is arranged in the shell 1; and a cover plate 3, which is arranged at the opening of the shell 1. In this embodiment, the shell 1 is a hollow structure with an opening on one side, and the cover plate 3 covers the opening of the shell 1 and forms a sealed connection, which is used to accommodate the electrode assembly 2 and the electrolyte. The shape of the shell 1 can be determined according to the specific shape of the electrode assembly 2. In this embodiment, the electrode assembly 2 is a cylindrical structure, and the shell 1 is selected as a cylindrical shell 1. The shell 1 can be positively charged, negatively charged, or uncharged. In this embodiment, the shell 1 is directly connected to the electrode assembly 2, and the shell 1 is charged. Optionally, the cover plate 3 and the shell 1 can be connected by welding, so that the cover plate 3 and the shell 1 can have substantially the same potential. The cover plate 3 and the shell 1 can be made of the same material, for example, the base material of the cover plate 3 and the shell 1 is the same, both are steel, so that the welding strength of the shell 1 and the cover plate 3 can be ensured, and the sealing of the cylindrical battery cell can be improved; or they can be made of different materials.

[0045] In this embodiment, the cover plate 3 is a plate-like structure, which forms inner and outer surfaces that are arranged oppositely and parallel to each other in the thickness direction. A plurality of welding portions 5 are provided on the surface of the cover plate 3 close to the electrode assembly 2, and the plurality of welding portions 5 are used to be electrically connected to the electrode assembly 2. In some embodiments, the plurality of welding portions 5 are laser-penetrated and welded to the electrode assembly 2. Further, the cover plate 3 is provided with a weak portion 4, which is arranged around the center of the cover plate 3. The weak portion 4 is also processed on the surface of the cover plate 3 to face the electrode assembly 2 or away from the electrode assembly 2, or both sides are processed to have a thickness less than the thickness of the cover plate 3, so as to quickly explode and release the pressure to protect the safety of the cylindrical battery cell when the pressure increases due to thermal runaway inside the cylindrical battery cell. Further, part of the welding portion 5 is provided on one side of the weak portion 4 close to the center. Since the weak portion 4 is arranged around the center of the cover plate 3, the side of the weak portion 4 close to the center can be the inner side of the area enclosed by the weak portion 4. In the prior art, the negative electrode current collector is removed, and the welding portion 5 is set in the area on the cover plate 3 outside the weak portion 4. Since the valve opening area of ​​the weak portion 4 needs to be guaranteed, the weak portion 4 needs to occupy a certain area on the cover plate 3, which will cause the position of the cover plate 3 corresponding to the weak portion 4 to be unable to be welded with the electrode assembly 2, and the effective welding area between the electrode assembly 2 and the cover plate 3 is small, and the flow effect is poor. However, the present application sets a partial welding portion 5 on the side close to the center of the weak portion 4, which can ensure that the area inside the weak portion 4 of the cover plate 3 forms an effective weld with the electrode assembly 2, increases the welding area between the cover plate 3 and the electrode assembly 2, and significantly improves the flow effect.

[0046] In some embodiments of the present application, reference Figure 3As shown, the weak portion 4 is a first arc 41, and the shape of the first arc 41 can be C-shaped, which is not limited here. When the weak portion 4 is set as the first arc 41, in order to ensure the safety of the valve opening of the weak portion 4, the position of the first arc 41 on the cover plate 3 cannot be welded with the electrode assembly 2, resulting in that the electrode pieces of the electrode assembly 2 in the radial direction are not completely welded, increasing the transmission path of electrons on the electrode pieces and the internal resistance of the cylindrical battery cell, and the overcurrent efficiency is poor. In order to solve this problem, the welding portion 5 includes a first convex portion 51, and the first convex portion 51 is set to intersect the circle where the cover plate 3 and the first arc 41 are located (that is, the full circle where the first arc 41 is located), that is, the position where the first convex portion 51 is located makes up for the area where the circle where the first arc 41 is located on the cover plate 3 cannot be welded with the electrode piece, ensuring that the electrode pieces of each circle of the electrode assembly 2 can be effectively welded with the cover plate 3, shortening the transmission path of electrons on the electrode pieces, reducing the internal resistance of the cylindrical battery cell, and improving the overcurrent efficiency.

[0047] In other embodiments of the present application, reference Figure 2 As shown, the first end of the first arc 41 is connected to the first end of the second arc 42, and the second end of the first arc 41 is connected to the second end of the second arc 42, that is, the outer shape of the weak portion 4 is a closed figure in which the first arc 41 and the second arc 42 are connected end to end, and the first convex portion 51 is located on the inner side of the weak portion 4, that is, on the inner side of the closed figure. As a result, the area on the cover plate 3 where the circle where the first arc 41 is located cannot be welded to the pole piece is effectively compensated when the first convex portion 51 and the electrode assembly 2 are welded successfully, ensuring that the pole piece of each circle of the electrode assembly 2 can be effectively welded to the cover plate 3, shortening the transmission path of electrons on the pole piece, reducing the internal resistance of the cylindrical battery cell, and improving the current efficiency. In this embodiment, the first convex portion 51 is arranged to extend radially along the cover plate 3.

[0048] like Figures 2 to 3 As shown, in this embodiment, the welding part 5 includes a second convex part 52, which is located on the inner side of the weak part 4, and the number of the second convex parts 52 can be one or more, and in this embodiment, the number of the second convex parts 52 is five. The second convex part 52 is arranged along the radial direction of the cover plate 3, and the plurality of second convex parts 52 are arranged along the circumference of the cover plate 3. Further, the welding part includes a third convex part 53, which is located on the outer side of the weak part 4, and the number of the third convex parts 53 can be one or more, and in this embodiment, the number of the third convex parts 53 is five. The third convex part 53 is arranged along the radial direction of the cover plate 3, and the plurality of third convex parts 53 are arranged along the circumference of the cover plate 3. Further, the plurality of second convex parts 52 and the plurality of third convex parts 53 are arranged one by one. The first convex part 51, the second convex part 52 and the third convex part 53 are arranged to extend radially or to be arranged circumferentially, and the positions of the first, second and third convex parts 53 are arranged reasonably, so as to reduce the processing difficulty and enhance the strength and welding flatness of the cover plate 3.

[0049] like Figure 1 , Figure 4 and Figure 5 As shown, the cover plate 3 in this embodiment also includes a fourth protrusion 54, the fourth protrusion 54 is electrically connected to the shell 1, the fourth protrusion 54 is an annular structure surrounding the outside of the cover plate 3, and the fourth protrusion 54 is processed on the cover plate 3, and protrudes relative to the cover plate 3 facing the electrode assembly 2. The cover plate 3 and the side wall 11 of the shell 1 are interference fit, and the fourth protrusion 54 abuts against the side wall 11. The interference fit can increase the connection strength between the shell 1 and the cover plate 3 and improve the sealing performance. At the same time, the shell 1 and the cover plate 3 are interference fit, and no external equipment is required to fix the cover plate 3, which simplifies the assembly process. Optionally, the fourth protrusion 54 and the shell 1 are connected by laser welding. When welding the fourth protrusion 54 and the side wall 11 of the shell 1, the laser is irradiated at the connection between the second protrusion 52 and the side wall 11, and the laser partially melts and connects them together to achieve sealing and reduce the risk of electrolyte leakage from the connection. In some embodiments, the fourth protrusion 54 includes a vertical portion 541. In the thickness direction of the cover plate 3, the end of the vertical portion 541 away from the electrode assembly 2 is a first outer end face 5411, and the side wall 11 surrounds the opening as a second outer end face 111. The first outer end face 5411 and the second outer end face 111 are flush. The first outer end face 5411 and the second outer end face 111 are arranged flush, so that the edge of the cover plate 3 and the bottom wall of the shell 1 are flush, so that when the cylindrical battery cell is assembled into the battery module, the height of the cylindrical battery cell is consistent and will not tilt, which is also conducive to the installation and welding of the busbar. Further, the fourth protrusion 54 also includes a guide portion 542, which is connected to the end of the vertical portion 541 close to the electrode assembly 2, and the guide portion 542 is arc-shaped to guide the fourth protrusion 54 to be installed on the shell 1. The guide portion 542 and the side wall 11 are arranged at intervals, and the distance between the surface of the guide portion 542 close to the side wall 11 along the radial direction of the cover plate 3 gradually increases. By providing the arc-shaped guide portion 542, the fourth protrusion 54 can be guided to be inserted into the shell 1 when assembling the cover plate 3 and the shell 1, thereby simplifying the assembly process and improving the assembly efficiency. Furthermore, in the thickness direction of the cover plate 3, the first protrusion 51 or the second protrusion 52 or the third protrusion 53 is closer to the electrode assembly 2 than the fourth protrusion 54.

[0050] In this embodiment, if Figures 1 to 4As shown, in this embodiment, the shell 1 includes a side wall 11 and a top wall 12, and the top wall 12 is arranged opposite to the opening and connected to the side wall 11. The side wall 11 and the top wall 12 can be an integrally formed structure, that is, the shell 1 is an integrally formed component. In addition, the side wall 11 and the top wall 12 can also be two components arranged separately, and then connected together by welding or the like, which is not limited here. The side wall 11 is a cylindrical structure, and the top wall 12 is a plate-like structure, and its shape corresponds to the shape of the side wall 11. An opening is formed at one end of the side wall 11, and the top wall 12 is connected to the other end of the side wall 11 away from the opening. In some embodiments, the top wall 12 has an electrode lead-out hole, and the pole 13 is insulated and arranged on the top wall 12. The pole 13 can be fixed as a whole on the outside of the top wall 12, or it can extend into the interior of the shell 1 through the electrode lead-out hole. In this embodiment, an electrode lead-out hole for installing the pole 13 is formed on the top wall 12 by a hole-opening process. The top wall 12 is formed by processing the shell 1. The setting of the electrode lead-out hole will not affect the flatness of the top wall 12, and enhance the connection strength between the top wall 12 and the busbar. The top wall 12 and the pole 13 can be used as two output poles of the cylindrical battery cell, simplifying the structure of the cylindrical battery cell and ensuring the current capacity of the cylindrical battery cell. The top wall 12 and the pole 13 are arranged at the same end of the cylindrical battery terminal, so that the busbar can be assembled to the same side, simplifying the assembly process and improving the efficiency of assembling multiple cylindrical battery cells into groups. In some embodiments, the electrode assembly 2 has a positive pole ear and a negative pole ear, the positive pole ear is connected to the pole 13, and the negative pole ear is connected to the cover plate 3; it is also possible that the positive pole ear is connected to the cover plate 3 and the negative pole ear is connected to the pole 13. When the positive pole tab is connected to the pole 13 and the negative pole tab is connected to the cover plate 3, the pole 13 is the positive output pole of the cylindrical battery cell and the cover plate 3 is the negative output pole of the cylindrical battery cell; when the positive pole tab is connected to the cover plate 3 and the negative pole tab is connected to the pole 13, the pole 13 is the negative output pole of the cylindrical battery cell and the cover plate 3 is the positive output pole of the cylindrical battery cell. The positive pole tab and the negative pole tab are arranged at both ends of the electrode assembly 2, which can reduce the risk of conduction between the positive and negative pole tabs and increase the flow area of ​​the positive pole tab and the flow area of ​​the negative pole tab.

[0051] The utility model also provides a battery module having a plurality of cylindrical battery cells. The beneficial effects of the battery module are the same as the advantages of the cylindrical battery cells in this embodiment over the prior art, and will not be described in detail herein.

[0052] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A cylindrical battery cell, characterized in that: include: a housing having an opening; An electrode assembly, disposed in the housing; A cover plate is disposed at the opening; the cover plate comprises: a weak portion and a plurality of welding portions, the weak portion is disposed around the center of the cover plate, and the welding portion is electrically connected to the electrode assembly; Part of the welding portion is arranged on a side of the weak portion close to the center.

2. The cylindrical battery cell according to claim 1, characterized in that: The weak portion includes a first circular arc, and the welding portion includes a first convex portion, and the first convex portion intersects with a circle where the first circular arc is located.

3. The cylindrical battery cell according to claim 2, characterized in that: The weak portion includes a second arc, a first end of the first arc is connected to a first end of the second arc, a second end of the first arc is connected to a second end of the second arc, and the first convex portion is located inside the weak portion.

4. The cylindrical battery cell according to claim 3, characterized in that: The welding portion includes a second protrusion located at an inner side of the weak portion.

5. The cylindrical battery cell according to claim 4, characterized in that: The welding portion includes a third protrusion, and the third protrusion is located outside the weak portion.

6. The cylindrical battery cell according to claim 5, characterized in that: The second protrusion and the third protrusion are both arranged to extend in the radial direction of the cover plate; and / or, there are multiple second protrusions and multiple third protrusions, and the multiple second protrusions and / or the third protrusions are arranged along the circumferential direction of the cover plate.

7. The cylindrical battery cell according to any one of claims 2 to 6, characterized in that: The first protrusion is extended along the radial direction of the cover plate.

8. The cylindrical battery cell according to claim 5, characterized in that: The cover plate includes a fourth protrusion, the fourth protrusion is electrically connected to the shell, the cover plate and the side wall of the shell are interference fit, and the fourth protrusion abuts against the side wall.

9. The cylindrical battery cell according to claim 8, characterized in that: The shell includes a top wall, which is arranged opposite to the opening and connected to the top wall, and has an electrode lead-out hole; a pole, which is arranged in the electrode lead-out hole and is electrically connected to the electrode assembly.

10. The cylindrical battery cell according to claim 9, characterized in that: The fourth protrusion includes a vertical portion, and in the thickness direction of the cover plate, the end of the vertical portion away from the electrode assembly is a first outer end surface, and the side wall surrounding the opening is a second outer end surface, and the first outer end surface is flush with the second outer end surface.

11. The cylindrical battery cell according to claim 10, characterized in that: The fourth protrusion includes a guide portion, the guide portion is connected to one end of the vertical portion close to the electrode assembly, and the guide portion is arc-shaped to guide the fourth protrusion to be installed on the shell.

12. The cylindrical battery cell according to claim 8, characterized in that: In the thickness direction of the cover plate, the first protrusion, the second protrusion, or the third protrusion is closer to the electrode assembly than the fourth protrusion.

13. A battery module, characterized in that: The invention comprises a plurality of cylindrical battery cells according to any one of claims 1 to 12.

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