Battery cell and battery pack

Abstract

Battery cell, comprising: a housing configured to receive a first electrode assembly, the housing having a first wall; a first electrode terminal disposed on the first wall; a first electrode assembly and a first electrode tab portion, wherein the first electrode tab portion comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly, and the first electrode tab portion is electrically connected to the first electrode terminal, wherein a first welding mark and a second welding mark are arranged on the first electrode tab portion, an orthogonal projection of the second welding mark lies within an orthogonal projection of the first welding mark along a projection of a main surface of the first electrode tab portion, and the second welding mark is configured to weld the first electrode terminal to the first electrode tab portion, and wherein a roughness of the second weld mark is greater than a roughness of the first weld mark.

Description

Technical area

[0001] The present application relates to battery technology, in particular to a battery cell and a battery pack or battery set. background

[0002] In the related art, a battery includes an electrode assembly and a cover plate assembly. The cover plate assembly is connected to electrode tabs of the electrode assembly by torque welding. When the electrode tabs are welded to the cover plate assembly by torque welding, gaps between the electrode tabs may cause the edges of the weld marks to bulge and form protrusions after the surface of the electrode tabs is pressure-welded by the ultrasonic welding device, which can easily lead to the tearing of the electrode pieces and false welding. This results in insufficient welding strength between the electrode tabs and the terminals after welding, thereby compromising the reliability of the connection between the terminals and the electrode tabs. Summary

[0003] The present application relates to a battery cell and a battery pack which achieve the technical effect of improving the welding strength between electrode tabs and electrode terminals.

[0004] To achieve the above-mentioned objective, the present application comprises the following technical solutions: One embodiment of the present application relates to a battery cell comprising a housing, a first electrode terminal, a first electrode assembly, and a first electrode tab portion. The housing is configured to receive a / the first electrode assembly and has a first wall. The first electrode terminal is arranged on the first wall. The first electrode tab portion comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly, and the first electrode tab portion is electrically connected to the first electrode terminal. A first weld mark and a second weld mark are arranged on the first electrode tab portion. Along a projection of a main surface of the first electrode tab portion, an orthogonal projection of the second weld mark coincides with an orthogonal projection of the first weld mark.The second weld mark is configured to weld the first electrode terminal to the first electrode tab portion. A roughness of the second weld mark is greater than a roughness of the first weld mark.

[0005] In the battery cell provided by the embodiment of the present application, the first electrode tab pieces extend from at least one end of the first electrode assembly. At least two first electrode tab pieces are stacked and then pre-welded and joined under pressure to form the first weld mark, thereby reducing gaps between the first electrode tab pieces and also reducing curling or the formation of protrusions at the weld edges of the first electrode tab pieces. Then, the first electrode tab portion is welded to the first electrode terminal at the first weld mark to form the second weld mark.Along the projection of the main surface of the first electrode tab portion, the orthogonal projection of the second welding mark coincides with the orthogonal projection of the first welding mark, which means that the second welding mark is located within the range of the first welding mark, thereby improving the welding strength between the first electrode tab portion and the first electrode terminal.

[0006] In other words, when connecting the first electrode assembly to the first electrode terminal, one end of the first electrode tab portion is first connected to the first electrode assembly, the other ends of the first electrode tab portion are stacked and pre-welded to form the first weld mark, and then the first electrode tab portion is welded to the first electrode terminal within the range of the first weld mark to form the second weld mark. That is, the first electrode tab portion is pre-welded so that the metal sheets of the first electrode tab portion are connected to each other, and the structural strength of the first electrode tab portion is improved by the pre-welding.Therefore, when welding the first electrode tab portion to the first electrode terminal, the presence of the first welding mark improves the structural strength of the first electrode tab portion even when the welding energy is relatively high, thereby reducing damage to the first electrode tab portion during welding of the first electrode tab portion to the first electrode terminal.

[0007] To ensure a sufficient weld connection between the first electrode tab portion and the first electrode terminal and to improve the weld strength, the roughness of the second weld mark must be greater than the roughness of the first weld mark. If the roughness of the first weld mark is too high, the second weld mark may not fully contact each first electrode tab piece when the first electrode tab portion is welded to the first electrode terminal, which can easily lead to false welding and reduce the weld strength between the first electrode tab portion and the first electrode terminal.

[0008] The present application also relates to a battery cell comprising a housing, a first electrode terminal, a first electrode assembly, a first electrode tab portion, a second electrode assembly, and a second electrode tab portion. The housing is configured to receive the first electrode assembly and the second electrode assembly and has a first wall. The first electrode terminal is disposed on the first wall. The first electrode tab portion comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly, and the first electrode tab portion is electrically connected to the first electrode terminal.The second electrode tab portion comprises at least two second electrode tab pieces extending from at least one end of the second electrode assembly, and the second electrode tab portion is electrically connected to the first electrode terminal. The first electrode tab portion and the second electrode tab portion are stacked and welded to form a first weld mark and a second weld mark. Along a projection of a main surface of the first electrode tab portion or the second electrode tab portion, an orthogonal projection of the second weld mark coincides with an orthogonal projection of the first weld mark. The second weld mark is configured to weld at least one of the first electrode tab portion and the second electrode tab portion to the first electrode terminal.The roughness of the second weld mark is greater than the roughness of the first weld mark.

[0009] In the battery cell provided by the embodiment of the present application, when connecting the first electrode assembly and the second electrode assembly to the first electrode terminal, one end of the first electrode tab portion is first connected to the first electrode assembly, and one end of the second electrode tab portion is first connected to the second electrode assembly. Then, the other end of the first electrode tab portion and the other end of the second electrode tab portion are each stacked and pre-welded to form the first welding mark.Subsequently, the first electrode tab portion and the second electrode tab portion are stacked and welded to form the first welding mark, and then the first electrode tab portion and the second electrode tab portion are welded to the first electrode terminal within the range of the first welding mark to form the second welding mark. Since the thickness after stacking the first electrode tab portion and the second electrode tab portion is relatively large, in order to prevent false welding between the first and second electrode tab portions and the first electrode terminal, it is necessary to increase the depth of the second welding mark (ie,increase the roughness of the second weld mark) to ensure complete contact between the first and second electrode tab portions and the first electrode terminal, thereby improving the connection strength between the first and second electrode tab portions and the first electrode terminal.

[0010] The present application also relates to a battery pack comprising the battery cell according to one of the above embodiments.

[0011] In the battery pack provided by the embodiment of the present application, the first electrode tab portion is first pre-welded to form the first weld mark, then the first electrode tab portion is welded to the first electrode terminal within the range of the first weld mark to form the second weld mark, thereby reducing the probability of curling or cracking of the portion of the first electrode tab portion outside the range of the first weld mark.The roughness of the first weld mark is lower than the roughness of the second weld mark, thereby ensuring complete contact between the first electrode tab portion and the first electrode terminal, improving the connection strength between the first electrode tab portion and the first electrode terminal, and thereby increasing the structural stability of the battery pack. Brief description of the drawings

[0012] To more clearly illustrate the technical solutions in the specific embodiments of the present application or in the prior art, the drawings used in the description of the specific embodiments or the prior art are briefly presented below. It should be understood that the drawings described below represent some embodiments of the present application. Those skilled in the art can create additional drawings based on these drawings without creative effort. Fig. 1 is a structural diagram of a battery cell of the present application; Fig. 2 is a partial structural diagram of the battery cell in one embodiment of the present application; Fig. 3 is a diagram showing the projected areas of a first welding mark and a second welding mark along a projection of a main surface of a first electrode tab portion; Fig. 4 is a partial structural diagram of a battery cell in another embodiment of the present application; Fig. 5 is a partial structural diagram of a battery cell in another embodiment of the present application; Fig. 6 is a diagram showing the projected areas of a first weld mark, a second weld mark, a third weld mark, and a fourth weld mark along a projection of a main surface of a first electrode tab portion; Fig. 7 is a structural diagram of a first wall; Fig. 8 is a structural diagram of a first electrode tab portion. [Reference symbol]

[0013] 1: Housing; 11: First wall; 12: Electrode terminal 2: first electrode arrangement; 3: first electrode tab section; 31: first end; 32: second end; 33: first part; 34: second part; 35: bent part; 4: first weld mark; 41: first edge; 5: second weld mark; 51: second edge; 6: second electrode arrangement; 7: second electrode tab section; 71: third end; 72: fourth end 8: third weld mark; 9: fourth weld mark. Detailed description

[0014] To clarify the objectives, technical solutions, and advantages of the embodiments of the present application, the technical solutions in the embodiments of the present application are described clearly and completely in conjunction with the drawings in the embodiments of the present application. Of course, the described embodiments are only a part of the embodiments of the present application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort fall within the scope of the present application.

[0015] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terms used in the description of this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "comprising" and "having" and all variations thereof used in the description and claims of this application and the brief description of the drawings above are intended to effect non-exclusive inclusion. The terms "first", "second", etc.in the description and claims of the present application or the above brief description of the drawings are used to distinguish different objects, not to describe a particular order or primary-secondary relationship.

[0016] Throughout this application, reference to "embodiment" means that certain features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of this application. The appearance of this term in various places throughout the specification does not necessarily refer to the same embodiment, nor do they represent mutually exclusive, independent, or alternative embodiments. It will be understood by those skilled in the art, both explicitly and implicitly, that the embodiments described in this application may be combined with other embodiments.

[0017] In the description of the present application, it should be noted that terms such as "installed," "connected," "coupled," and "attached" are to be understood broadly unless expressly stated and limited otherwise. They may refer, for example, to a fixed connection, a detachable connection, or an integral connection; a direct connection or an indirect connection via intermediate media; or an internal communication between two elements. Those skilled in the art can understand the specific meanings of these terms in the present application based on the specific situations.

[0018] The term "and / or" in this application is merely a description of the associative relationship between associated objects and indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, both A and B exist, or B exists alone. Furthermore, the symbol " / " in this application generally denotes an "or" relationship between the associated objects before and after.

[0019] The term "a plurality of" in the present application refers to two or more (including two), likewise "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0020] In related art, a battery includes an electrode assembly and a cover plate assembly, with the cover plate assembly connected to electrode tabs of the electrode assembly. Currently, the electrode tabs are welded to the cover plate assembly by torque welding. Due to gaps between the electrode tabs, the edges of the weld marks curl upward after pressure welding is completed, forming protrusions, which can easily cause the electrode pieces to crack and false welding, resulting in insufficient weld strength between the electrode tabs and the terminals after welding.

[0021] In view of the above, with reference to the Fig. 1, Fig. 2 and Fig. 7, the present application provides a battery cell comprising a housing 1, a first electrode terminal 12, a first electrode assembly 2, and a first electrode tab portion 3. The housing is configured to receive the first electrode assembly 2 and has a first wall 11. The first electrode terminal 12 is arranged on the first wall 11. The first electrode tab portion 3 comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly 2, and the first electrode tab portion 3 is electrically connected to the first electrode terminal 12. A first weld mark 4 and a second weld mark 5 are arranged on the first electrode tab portion 3.Along a projection of a main surface of the first electrode tab portion 3, an orthogonal projection of the second weld mark 5 coincides with an orthogonal projection of the first weld mark 4. The second weld mark 5 is configured to weld the first electrode terminal 12 to the first electrode tab portion 3. A roughness of the second weld mark 5 is greater than a roughness of the first weld mark 4.

[0022] The housing is made of a metal material and is configured to accommodate the first electrode assembly 2. The housing 1 has a first wall 11, and the first electrode terminal 12 is arranged on the first wall 11. Each first electrode tab portion 3 has a first end 31 and a second end 32. The first end 31 of each first electrode tab portion 3 is connected to the first electrode assembly 2. The second ends 32 of each first electrode tab portion 3 are stacked and welded to form the first weld mark 4. The first weld mark 4 is used to press the first electrode tab portion 3 and connect the first electrode tab pieces. The first weld mark 4 is connected to the first electrode terminal 12 to form the second weld mark 5. The second weld mark 5 serves to weld the first electrode terminal 12 to the first electrode tab portion 3.Along the stacking direction of the plurality of second ends 32, the projection of the second weld mark 5 coincides with the projection of the first weld mark 4, and the roughness of the second weld mark 5 is greater than the roughness of the first weld mark 4.

[0023] In the battery cell provided by the embodiment of the present application, the first end 31 of the first electrode tab portion 3 is connected to the first electrode assembly 2. The second ends 32 of the first electrode tab portion 3 are stacked under pressure and pre-welded to form the first welding mark 4, thereby reducing gaps between the plurality of first electrode tab pieces in the first electrode tab portion 3 and also reducing curling or the formation of the protrusion at the welding edges of the plurality of first electrode tab pieces. Then, the first electrode tab portion 3 is welded to the first electrode terminal 12 at the first welding mark 4 to form the second welding mark 5.Along the stacking direction of the plurality of second ends 32, the projection of the second welding mark 5 coincides with the projection of the first welding mark 4, which means that the second welding mark 5 is located within the range of the first welding mark 4, thereby improving the welding strength between the first electrode tab portion 3 and the first electrode terminal 12.

[0024] In other words, during the joining of the first electrode assembly 2 to the first electrode terminal 12, the first end 31 of the first electrode tab portion 3 is first joined to the first electrode assembly 2, then the second ends 32 of the first electrode tab portion 3 are stacked and pre-welded to form the first weld mark 4. Subsequently, the first electrode tab portion 3 and the first electrode terminal 12 are welded within the range of the first weld mark 4 to form the second weld mark 5. That is, the second ends 32 of the first electrode tab portion 3 are stacked and pre-welded to join the metal sheets of the first electrode tab portion 3 to each other and improve the structural strength of the first electrode tab portion 3 by pre-welding.Therefore, when welding the first electrode tab portion 3 to the first electrode terminal 12, even if the welding energy is relatively high, the presence of the first welding mark 4 increases the structural strength of the first electrode tab portion 3, thereby reducing damage to the first electrode tab portion 3 when welding the first electrode tab portion 3 to the first electrode terminal 12.

[0025] In order to ensure a sufficient weld between the first electrode tab portion 3 and the first electrode terminal 12 and to improve the weld strength, the roughness of the second weld mark 5 must be greater than the roughness of the first weld mark 4. If the roughness of the first weld mark 4 is too high, the second weld mark 5 may not fully contact each first electrode tab piece when the first electrode tab portion 3 is welded to the first electrode terminal 12, which may easily lead to false welding and reduce the weld strength between the first electrode tab portion 3 and the first electrode terminal 12.

[0026] In the present application, the main surface of the first electrode tab portion 3 refers to the surface formed by flattening the first electrode tab portion 3 along the extension direction after the first electrode tab portion 3 is formed by stacking a plurality of first electrode tab pieces. In particular, the first electrode tab portion 3 comprises, with reference to Fig. 8 a first part 33 connected to the first electrode assembly 2, a second part 34 connected to the first electrode terminal 12, and a bent part 35 connecting the first part 33 and the second part 34, and the second part 34 refers to the main surface of the first electrode tab portion 3.

[0027] In the present application, the first electrode terminal 12 refers to a terminal, and the first electrode assembly 2 refers to a cell nucleus. One end of the first electrode terminal 12 is electrically connected to the bus bar, and the other end is electrically connected to the first electrode tab portion 3. The first electrode assembly 2 refers to a unit formed by winding or laminating a stacked portion, and the stacked portion includes a first electrode, a separator, and a second electrode. When the first electrode is a positive electrode, the second electrode is a negative electrode.

[0028] Optionally, the roughness of the second weld mark 5 is represented by a1, the roughness of the first weld mark 4 by a2, where, for example, 5≤a1 / a2≤300, a1 / a2 can be 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or 300, etc. The roughness of the second weld mark 5 is greater than that of the first weld mark 4, thereby reducing the problem of false welding between the first electrode tab portion 3 and the first electrode terminal 12, thereby improving the weld strength between the first electrode tab portion 3 and the first electrode terminal 12. However, if the roughness of the second weld mark 5 is too high, it may cause the second weld mark 5 to burn through the first electrode tab portion 3.

[0029] Optionally, the roughness a1 of the second weld mark 5 satisfies: 300 µm ≤ a1 ≤ 3000 µm; the roughness a2 of the first weld mark 4 satisfies: 10 µm ≤ a2 ≤ 500 µm.

[0030] The roughness a1 of the second weld seam 5 can be 300 µm, 400 µm, 500 µm, 600 µm, 700 µm, 800 µm, 1000 µm, 1100 µm, 1200 µm, 1300 µm, 1400 µm, 1500 µm, 1600 µm, 1700 µm, 1800 µm, 1900 µm, 2000 µm, 2100 µm, 2200 µm, 2300 µm, 2400 µm, 2500 µm, 2600 µm, 2700 µm, 2800 µm, 2900 µm or 3000 µm etc.

[0031] The roughness a2 of the first weld seam 4 can be 10 µm, 20 µm, 50 µm, 80 µm, 100 µm, 120 µm, 150 µm, 180 µm, 200 µm, 220 µm, 240 µm, 260 µm, 280 µm, 300 µm, 330 µm, 340 µm, 350 µm, 360 µm, 380 µm, 400 µm, 410 µm, 420 µm, 430 µm, 440 µm, 450 µm, 470 µm, 480 µm, 490 µm or 500 µm etc.

[0032] Optionally, the first welding mark 4 is formed by toothless welding. The first welding mark 4 is formed by toothless welding of the second ends 32 of the first electrode tab portion 3, thereby improving the surface flatness of the first electrode tab portion 3. When welding the first electrode tab portion 3 to the first electrode terminal 12, the first welding mark 4 formed by toothless welding can reduce the stress on the first electrode tab portion 3 during a second welding, thereby reducing damage to the first electrode tab portion 3 during the second welding.

[0033] Here, toothless welding refers to welding performed with a nearly toothless welding head. The depth of the teeth of the toothless welding head is relatively shallow, resulting in relatively flat concave sections in the weld area after welding is completed.

[0034] Optionally, the second welding mark 5 comprises a first welding area and a second welding area, wherein the second welding area is arranged on the outer peripheral side of the first welding area. A plurality of square welding marks are arranged in the first welding area, and a plurality of circular welding marks are arranged in the second welding area.

[0035] The second welding mark 5, formed by welding the first electrode tab portion 3 to the electrode terminal, includes two different types of welding areas: the first welding area and the second welding area located on the outer peripheral side of the first welding area. The first welding area includes a plurality of square welding marks with a greater depth to improve the connection strength between the first electrode tab portion 3 and the first electrode terminal 12. The second welding area includes a plurality of circular welding marks on the periphery of the second welding mark 5, which can relieve the stress between the second welding mark 5 and the portion of the first electrode tab portion 3 outside the second welding mark 5, thereby reducing the risk of tearing of the first electrode tab portion 3.

[0036] Optionally, with reference to Fig. 3, along a projection of the main surface of the first electrode tab portion 3, the projected area of ​​the first weld mark 4 is represented by S1, and the projected area of ​​the second weld mark 5 is represented by S2, where: 1≤S1 / S2≤10. That is, along the stacking direction of the second ends 32 of the first electrode tab portion 3, the projected area of ​​the first weld mark 4 is represented by S1, and the projected area of ​​the second weld mark 5 is represented by S2. Here S1 / S2 can be 1, 1.3, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.3, 3.5, 3.7, 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.6, 5.8, 6.0, 6.3, 6.5, 6.8, 7.2, 7.8, 8.0, 8.2, 8.6, 9.0, 9.3, 9.5, 9.8, 99 or 10 etc.After connecting the first electrode assembly 2 and the first electrode terminal 12, the connection area between the first electrode tab portion 3 and the first electrode terminal 12 must meet the following conditions to ensure sufficient current carrying capacity and reduce the risk of tearing off the first electrode tab portion 3: 1≤S1 / S2≤10.

[0037] If the area ratio between the second weld mark 5 and the first weld mark 4 is too small, this means that the area of ​​the second weld mark 5 is too small, resulting in a small connection area between the first electrode tab portion 3 and the first electrode terminal 12 and impairing the current-carrying capacity. If the area ratio between the second weld mark 5 and the first weld mark 4 is too large, this means that the area of ​​the second weld mark 5 is too large, which impairs the stress relief of the first weld mark 4 on the first electrode tab portion 3 at the edge of the first weld mark 4 and possibly leads to tearing of the first electrode tab portion 3.

[0038] Optionally, the projected area of ​​the first welding mark 4: 100 mm 2 ≤ S1 ≤ 2000 mm 2, and the projected area of ​​the second welding mark 5 meets: 20 mm 2 ≤ S2 ≤ 120 mm 2 .

[0039] The projected area S1 of the first welding mark 4 can be 100 mm 2 , 200 mm 2 , 300 mm 2 , 400 mm 2 , 500 mm 2 , 600 mm 2 , 700 mm 2 , 800 mm 2 , 900 mm 2 , 1000 mm 2 , 1100 mm 2 , 1200 mm 2 , 1300 mm 2 , 1400 mm 2 , 1500 mm 2 , 1600 mm 2 , 1700 mm 2 , 1800 mm 2 , 1900 mm 2 or 2000 mm 2 etc.

[0040] The projected area S2 of the second welding mark 5 can be 20 mm 2 , 25 mm 2 , 30 mm 2 , 35 mm 2 , 40 mm 2 , 45 mm 2 , 50 mm 2 , 55 mm 2 , 60 mm 2 , 65 mm 2 , 70 mm 2 , 75 mm 2 , 80 mm 2, 85 mm 2 , 90mm 2 , 95 mm 2 , 100 mm 2 , 105 mm 2 , 110 mm 2 , 115 mm 2 or 120 mm 2 etc.

[0041] Optionally, the first welding mark 4 has a first edge 41, the second welding mark 5 has a second edge 51, and the minimum distance c between the first edge 41 and the second edge 51 satisfies: 0.5 mm ≤ c ≤ 10 mm. The minimum distance c between the first edge 41 and the second edge 51 can be 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.5 mm, 2.7 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.5 mm, 3.8 mm, 4.0 mm, 4.1 mm, 4.3 mm, 4.5 mm, 4.8 mm, 5.0 mm, 5.2 mm, 5.6 mm, 5.8 mm, 6.0 mm, 6.3 mm, 6.7 mm, 7.0 mm, 7.3 mm, 7.8 mm, 8.1 mm, 8.4 mm, 8.6 mm, 8.9 mm, 9.1 mm, 9.4 mm, 9.6 mm, 9.8 mm or 10 mm etc.

[0042] To ensure sufficient connection strength between the first electrode tab portion 3 and the first electrode terminal 12 while preventing tearing of the first electrode tab portion 3, the minimum distance between the first edge 41 and the second edge 51 should satisfy the following condition: 0.5 mm ≤ c ≤ 10 mm. If the second edge 51 of the second weld mark 5 is too close to the first edge 41 of the first weld mark 4, it will exert a certain pressure on the portion of the first electrode tab portion 3 outside the first weld mark 4 during the second torque welding, causing the portion of the first electrode tab portion 3 to curl and possibly tear.If the second edge 51 of the second welding mark 5 is too far away from the first edge 41, this means that the welding area between the first electrode tab portion 3 and the first electrode terminal 12 is too small, which impairs the current carrying capacity between the first electrode assembly 2 and the first electrode terminal 12.

[0043] Optionally, the battery cell comprises, with reference to the Fig. 5 and Fig. 6 further comprises a second electrode assembly 6 and a second electrode tab portion 7, both disposed within the housing 1. The second electrode tab portion 7 includes at least two second electrode tab pieces extending from at least one end of the second electrode assembly 6, and the second electrode tab portion 7 is electrically connected to the first electrode terminal 12. A third welding mark 8 and a fourth welding mark 9 are disposed on the second electrode tab portion 7.Along a projection of the main surface of the first electrode tab portion 3, the projected area of ​​the first weld mark 4 is represented by S1; along a projection of the main surface of the second electrode tab portion 7, the projected area of ​​the third weld mark 8 is represented by S3, and the sum of the projected areas of the second weld mark 5 and the fourth weld mark 9 is represented by S4, where: S1+S3>S4.

[0044] The second electrode tab portion 7 has a third end 71 and a fourth end 72. A plurality of third ends 71 ​​are connected to the second electrode assembly 6, and the fourth ends 72 are stacked and welded to form the third weld mark 8. The third weld mark 8 is connected to the first electrode terminal 12 to form the fourth weld mark 9. The projection direction along the main surface of the first electrode tab portion 3 is the same as the projection direction along the main surface of the second electrode tab portion 7.

[0045] The first electrode tab portion 3 of the first electrode assembly 2 is pre-welded to form the first weld mark 4, and the second electrode tab portion 7 of the second electrode assembly 6 is pre-welded to form the third weld mark 8. Then, the first electrode terminal 12 is welded to the first electrode tab portion 3 within the area of ​​the first weld mark 4 to form the second weld mark 5, and the first electrode terminal 12 is welded to the second electrode tab portion 7 within the area of ​​the third weld mark 8 to form the fourth weld mark 9. That is, the first electrode tab portion 3 of the first electrode assembly 2 and the second electrode tab portion 7 of the second electrode assembly 6 are welded at different areas of the first electrode terminal 12.Compared to stacking the first electrode tab portion 3 and the second electrode tab portion 7, welding the first electrode tab portion 3 and the second electrode tab portion 7 at different regions of the first electrode terminal 12 can respectively reduce the joint thickness between the first electrode tab portion 3 and the second electrode tab portion 7, thereby reducing the false welds between the first electrode tab portion 3 and the first electrode terminal 12 and between the second electrode tab portion 7 and the first electrode terminal 12.

[0046] In addition, the area of ​​the first weld mark 4 formed after pre-welding the first electrode tab portion 3 should be larger than the area of ​​the second weld mark 5 formed by welding the first electrode tab portion 3 to the first electrode terminal 12. That is, the second weld mark 5 is located within the area of ​​the first weld mark 4. Similarly, the area of ​​the third weld mark 8 formed after pre-welding the second electrode tab portion 7 should be larger than the area of ​​the fourth weld mark 9 formed by welding the second electrode tab portion 7 to the plurality of first electrode terminals 12. That is, the fourth weld mark 9 is located within the range of the third weld mark 8.That is, the sum of the projected areas of the first welding mark 4 and the third welding mark 8 is larger than the sum of the projected areas of the second welding mark 5 and the fourth welding mark 9 in order to achieve sufficient connection strength between the first and second electrode tab sections 3 and 7 and the first electrode terminal 12 and at the same time to avoid problems with the protrusion or cracking of the section of the first electrode tab section 3 outside the first welding mark 4 and the section of the second electrode tab section 7 outside the third welding mark 8.

[0047] Specifically, the first welding mark 4 is formed after pre-welding the first electrode tab portion 3, and the third welding mark 8 is formed after pre-welding the second electrode tab portion 7, and then the first electrode tab portion 3 and the second electrode tab portion 7 are joined together. That is, the first welding mark 4 and the third welding mark 8 do not overlap. Then, the first electrode tab portion 3 and the second electrode tab portion 7 are welded to the first electrode terminal 12. The second welding mark 5 formed by welding the first electrode tab portion 3 to the first electrode terminal 12 may be either separate from or joined to the fourth welding mark 9 formed by welding the second electrode tab portion 7 to the second electrode terminal.

[0048] In an optional embodiment, the second ends 32 of the first electrode tab portion 3 are pre-welded to form the first weld mark 4, and the third ends 72 of the second electrode tab portion 7 are pre-welded to form the third weld mark 8. The first weld mark 4 and the third weld mark 8 may have a rectangular shape. Then, the first electrode tab portion 3 and the second electrode tab portion 7 are welded to the first electrode terminal 12 to form the second weld mark 5 and the fourth weld mark 9, respectively, which together form a circular weld mark, thereby establishing the weld connection between the first electrode tab portion 3 and the first electrode terminal 12 and between the second electrode tab portion 7 and the first electrode terminal 12.

[0049] Optionally, the roughness of the second weld mark 5 is represented by a1, the roughness of the first weld mark 4 by a2, the roughness of the fourth weld mark 9 by d1 and the roughness of the third weld mark 8 by d2, where the following conditions are satisfied: 5≤a1 / a2≤280, 5≤d1 / d2≤280.

[0050] Here, a1 / a2 can be 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 275 or 280 etc. d1 / d2 can be 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 275 or 280 etc.

[0051] Since the first electrode tab portion 3 and the second electrode tab portion 7 are joined together without overlapping after pre-welding and welded to the first electrode terminal 12, the thickness of the portions of the first electrode tab portion 3 and the second electrode tab portion 7 welded to the first electrode terminal 12 is relatively thin, so that the first electrode tab portion 3 and the second electrode tab portion 7 can be easily welded to the first electrode terminal 12 while achieving sufficient weld strength. Therefore, the roughness of the second weld mark 5 and the fourth weld mark 9 can be relatively reduced.

[0052] Optionally, the roughness of the second weld mark 5 satisfies: 300 µm ≤ a1 ≤ 2800 µm; the roughness of the first weld mark 4 satisfies: 10 µm ≤ a2 ≤ 500 µm; the roughness of the fourth weld mark 9 satisfies: 300 µm ≤ d1 ≤ 2800 µm; and the roughness of the third weld mark 8 satisfies: 10 µm ≤ d2 ≤ 500 µm, etc.

[0053] The roughness a1 of the second welding mark 5 can be 300 µm, 400 µm, 500 µm, 600 µm, 700 µm, 800 µm, 1000 µm, 1100 µm, 1200 µm, 1300 µm, 1400 µm, 1500 µm, 1600 µm, 1700 µm, 1800 µm, 1900 µm, 2000 µm, 2100 µm, 2200 µm, 2300 µm, 2400 µm, 2500 µm, 2600 µm, 2700 µm, 2750 µm or 2800 µm etc.

[0054] The roughness a2 of the first welding mark 4 can be 10 µm, 20 µm, 50 µm, 80 µm, 100 µm, 120 µm, 150 µm, 180 µm, 200 µm, 220 µm, 240 µm, 260 µm, 280 µm, 300 µm, 330 µm, 340 µm, 350 µm, 360 µm, 380 µm, 400 µm, 410 µm, 420 µm, 430 µm, 440 µm, 450 µm, 470 µm, 480 µm, 490 µm or 500 µm etc.

[0055] The roughness d1 of the third welding mark 8 can be 300 µm, 400 µm, 500 µm, 600 µm, 700 µm, 800 µm, 1000 µm, 1100 µm, 1200 µm, 1300 µm, 1400 µm, 1500 µm, 1600 µm, 1700 µm, 1800 µm, 1900 µm, 2000 µm, 2100 µm, 2200 µm, 2300 µm, 2400 µm, 2500 µm, 2600 µm, 2700 µm, 2750 µm or 2800 µm etc.

[0056] The roughness d2 of the fourth welding mark 9 can be 10 µm, 20 µm, 50 µm, 80 µm, 100 µm, 120 µm, 150 µm, 180 µm, 200 µm, 220 µm, 240 µm, 260 µm, 280 µm, 300 µm, 330 µm, 340 µm, 350 µm, 360 µm, 380 µm, 400 µm, 410 µm, 420 µm, 430 µm, 440 µm, 450 µm, 470 µm, 480 µm, 490 µm or 500 µm etc.

[0057] Optionally, the ratio satisfies: 0.9 ≤ S1 / S3 ≤ 1.1. Here, S1 / S3 can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.1, etc.

[0058] The projected area of ​​the first weld mark 4, formed after pre-welding the first electrode tab portion 3, is represented by S1, and the projected area of ​​the third weld mark 8, formed after pre-welding the second electrode tab portion 7, is represented by S3. To meet the current conduction requirements between the first electrode assembly 2 and the first electrode terminal 12, as well as between the second electrode assembly 6 and the first electrode terminal 12, the ratio should satisfy the following condition: 0.9 ≤ S1 / S3 ≤ 1.1. Preferably, the projected area S1 of the first weld mark 4 and the projected area S3 of the third weld mark 8 are approximately equal.

[0059] Optionally, the first welding mark 4 can have a rectangular shape. The rectangular shape of the first welding mark 4 increases the connecting area between the first electrode tab sections 3, thereby reducing the distances between the plurality of first electrode tab pieces and reducing the risk of tearing of the first electrode tab section 3.

[0060] Optionally, the second weld mark 5 may have a circular shape. The first electrode tab portion 3 is welded to the first electrode terminal 12 to form the second weld mark 5. Since the portion of the first electrode tab portion 3 at the edges of the first weld mark 4 is thinned and thus weakened by the first weld mark 4, the circular second weld mark 5 with a circular edge reduces the stress on the portion of the first electrode tab portion 3 at the edges of the first weld mark 4, thereby reducing the risk of tearing of the first electrode tab portion 3.

[0061] Optionally, along a protrusion of the main surface of the first electrode tab portion 3, the area of ​​the second welding mark 5 is represented by S2, and the end face of one end of the electrode terminal connected to the first electrode tab portion 3 is represented by S5, where: 0.25 ≤ S2 / S5 ≤ 0.95. That is, along the stacking direction of the second ends 32 of the first electrode tab portion 3, the area of ​​the second welding mark 5 is S2, and the end face of one end of the electrode terminal connected to the first electrode tab portion 3 is S5. Here S2 / S5 can be 0.25, 0.28, 0.3, 0.32, 0.33, 0.35, 0.36, 0.38, 0.4, 0.42, 0.46, 0.5, 0.52, 0.56, 0.6, 0.625, 0.28, 0.3, 0.32, 0.33, 0.35, 0.36, 0.38, 0.4, 0.42, 0.45, 0.47, 0.49, 0.51, 0.53, 0.56, 0.58, 0.6, 0.65, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.83, 0.86, 0.88, 0.9, 0.91, 0.93, 0.94 or 0.95 etc.The area of ​​the second welding mark 5 should ensure sufficient current carrying capacity between the first electrode arrangement 2 and the first electrode terminal 12, which is why the ratio S2 / S5 must meet the following condition: 0.25 ≤ S2 / S5 ≤ 0.95.

[0062] Optionally, the area of ​​the second welding mark 5: 20 mm 2 ≤ S2 ≤ 120 mm 2 ; and the end face of one end of the electrode terminal connected to the first electrode tab section 3 satisfies: 50 mm 2 ≤ S5 ≤ 300 mm 2 .

[0063] The projected area S2 of the second welding mark 5 can be 20 mm 2 , 25 mm 2 , 30 mm 2 , 35 mm 2 , 40 mm 2 , 45 mm 2 , 50 mm 2 , 55 mm 2 , 60 mm 2 , 65 mm 2 , 70 mm 2 , 75 mm 2 , 80 mm 2 , 85 mm 2 , 90mm 2 , 95 mm 2 , 100 mm 2, 105 mm 2 , 110 mm 2 , 115 mm 2 or 120 mm 2 etc.

[0064] The end face S5 of one end of the electrode terminal connected to the first electrode tab section 3 can be 50 mm 2 , 55 mm 2 , 60 mm 2 , 65 mm 2 , 70 mm 2 , 75 mm 2 , 80 mm 2 , 85 mm 2 , 90 mm 2 , 95 mm 2 , 100 mm 2 , 105 mm 2 , 110 mm 2 , 115 mm 2 , 120 mm 2 , 140 mm 2 , 160 mm 2 , 180 mm 2 , 200 mm 2 , 210 mm 2 , 220 mm 2 , 230 mm 2 , 240 mm 2 , 250 mm 2 , 260 mm 2 , 270 mm 2 , 280 mm 2 , 290 mm 2 or 300 mm 2 etc.

[0065] The present application also relates to a battery cell based on Fig.4 and comprises a housing 1, a first electrode terminal 12, a first electrode assembly 2, a first electrode tab portion 3, a second electrode assembly 6, and a second electrode tab portion 7. The housing 1 is configured to accommodate the first electrode assembly 2 and the second electrode assembly 6 and has a first wall 11. The first electrode terminal 12 is arranged on the first wall 11. The first electrode tab portion 3 comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly 2, and the first electrode tab portion 3 is electrically connected to the first electrode terminal 12.The second electrode tab portion 7 includes at least two second electrode tab pieces extending from at least one end of the second electrode assembly 6, and the second electrode tab portion 3 is electrically connected to the first electrode terminal 12. The first electrode tab portion 3 and the second electrode tab portion 7 are stacked and welded to form the first weld mark 4 and the second weld mark 5. Along a projection of the main surface of the first electrode tab portion 3 or the second electrode tab portion 7, an orthogonal projection of the second weld mark 5 coincides with an orthogonal projection of the first weld mark 4. The second weld mark 5 is configured to weld at least one of the first electrode tab portion 3 and the second electrode tab portion 7 to the first electrode terminal 12.The roughness of the second weld mark 5 is greater than the roughness of the first weld mark 4.

[0066] The first electrode tab portion 3 extends from the end of the first electrode assembly 2 and is electrically connected to the first electrode terminal 12. Both the first electrode assembly 2 and the first electrode tab portion 3 are arranged within the housing 1. The first electrode tab portion 3 has first ends 31 and second ends 32, wherein the first ends 31 are connected to the first electrode assembly 2. The second electrode tab portion 7 extends from the end of the second electrode assembly 6 and is electrically connected to the first electrode terminal 12. Both the second electrode assembly 6 and the second electrode tab portion 7 are arranged within the housing 1. The second electrode tab portion 7 has third ends 71 ​​and fourth ends 72, wherein the third ends 71 ​​are connected to the second electrode assembly 6.

[0067] The second ends 32 of the first electrode tab portion 3 and the fourth ends 72 of the second electrode tab portion 7 are stacked and welded to form the first weld mark 4, which serves to press the first electrode tab portion 3 and the second electrode tab portion 7 together and to connect the first electrode tab portion 3 to the second electrode tab portion 7. The first weld mark 4 is connected to the first electrode terminal 12 to form the second weld mark 5, which serves to weld the first electrode tab portion 3 to the first electrode terminal 12.Along the stacking direction of the second ends 32 of the first electrode tab portion 3 and the fourth ends 72 of the second electrode tab portion 7, the projection of the second weld mark 5 coincides with the projection of the first weld mark 4, and the roughness of the second weld mark 5 is greater than the roughness of the first weld mark 4.

[0068] In the battery cell provided by this embodiment of the present application, when connecting the first electrode assembly 2 and the second electrode assembly 6 to the first electrode terminal 12, first, the first ends 31 of the first electrode tab portion 3 are connected to the first electrode assembly 2, and the third ends 71 ​​of the second electrode tab portion 7 are connected to the second electrode assembly 6. Then, the second ends 32 of the first electrode tab portion 3 and the fourth ends 72 of the second electrode tab portion 7 are stacked and pre-welded to form the first weld mark 4. Subsequently, the stacked first electrode tab portion 3 and the second electrode tab portion 7 are welded to the first electrode terminal 12 within the range of the first weld mark 4 to form the second weld mark 5.Since the thickness after stacking the first electrode tab portion 3 and the second electrode tab portion 7 is relatively large, in order to prevent false welding between the first and second electrode tab portions 3 and 7 and the first electrode terminal 12, the depth of the second welding mark 5 needs to be increased, that is, the roughness of the second welding mark 5 needs to be increased so that the first and second electrode tab portions 3 and 7 can fully contact the first electrode terminal 12, thereby improving the joining strength of the first and second electrode tab portions 3 and 7 and the first electrode terminal 12.

[0069] Optionally, the roughness of the second weld mark 5 is represented by a1 and the roughness of the first weld mark 4 by a2, where 6≤a1 / a2≤300. Here, a1 / a2 can be 6, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or 300, etc. The roughness of the second welding mark 5 is greater than the roughness of the first welding mark 4, thereby reducing the problems of false welding and thus improving the welding strength of the first electrode tab portion 3 and the first electrode terminal 12.

[0070] Optionally, the roughness of the second weld mark 5 satisfies: 280 µm ≤ a1 ≤ 3000 µm; the roughness of the first weld mark 4 satisfies: 10 µm ≤ a2 ≤ 500 µm.

[0071] The roughness a1 of the second weld mark 5 can be 280 µm, 300 µm, 400 µm, 500 µm, 600 µm, 700 µm, 800 µm, 1000 µm, 1100 µm, 1200 µm, 1300 µm, 1400 µm, 1500 µm, 1600 µm, 1700 µm, 1800 µm, 1900 µm, 2000 µm, 2100 µm, 2200 µm, 2300 µm, 2400 µm, 2500 µm, 2600 µm, 2700 µm, 2800 µm, 2900 µm or 3000 µm etc.

[0072] The roughness a2 of the first weld mark 4 can be 10 µm, 20 µm, 50 µm, 80 µm, 100 µm, 120 µm, 150 µm, 180 µm, 200 µm, 220 µm, 240 µm, 260 µm, 280 µm, 300 µm, 330 µm, 340 µm, 350 µm, 360 µm, 380 µm, 400 µm, 410 µm, 420 µm, 430 µm, 440 µm, 450 µm, 470 µm, 480 µm, 490 µm or 500 µm etc.

[0073] In particular, due to the relatively large thickness after stacking the first electrode tab portion 3 and the second electrode tab portion 7, the roughness of the second weld mark 5 needs to be increased to prevent false welding between the first and second electrode tab portions 3 and 7 and the first electrode terminal 12 and to ensure full contact between the first and second electrode tab portions 3 and 7 and the first electrode terminal 12. However, if the roughness of the second weld mark 5 is too high, it may cause the second weld mark 5 to burn through the first and second electrode tab portions 3 and 7.

[0074] The present application also relates to a battery pack comprising the battery cell according to any one of the above embodiments. In the battery pack provided by this embodiment, the first electrode tab portion 3 is first pre-welded to form the first weld mark 4, then the first electrode tab portion 3 is welded to the first electrode terminal 12 within the range of the first weld mark 4 to form the second weld mark 5, thereby reducing the likelihood of curling or tearing of the portion of the first electrode tab portion 3 outside the range of the first weld mark 4.The lower roughness of the first welding mark 4 compared to the second welding mark 5 ensures complete contact between the first electrode tab portion 3 and the first electrode terminal 12, thereby improving the connection strength between the first electrode tab portion 3 and the first electrode terminal 12 and increasing the structural stability of the battery pack.

[0075] The present application also relates to an electrical device comprising the battery pack described in the above embodiments. The electrical device provided by this embodiment includes the first electrode assembly 2 and the first electrode terminal 12 in the above battery pack. The first electrode assembly 2 and the second electrode terminal are connected via the first electrode tab portion 3. The first electrode tab portion 3 is pre-welded to form the first weld mark 4, then the first electrode tab portion 3 is welded to the first electrode terminal 12 within the range of the first weld mark 4 to form the second weld mark 5, thereby reducing the likelihood of curling or tearing off the portion of the first electrode tab portion 3 outside the range of the first weld mark 4.The roughness of the first welding mark 4 is lower than that of the second welding mark 5, thereby ensuring complete contact between the first electrode tab portion 3 and the first electrode terminal 12, thereby improving the connection strength between the first electrode tab portion 3 and the first electrode terminal 12 and thereby improving the performance of the electrical device.

[0076] It should be noted that the terms "comprise," "include," or other variations thereof denote non-exclusive inclusion, such that a process, method, article, or device comprising a list of elements not only includes those elements, but may also include other elements not expressly listed or inherent in that process, method, article, or device. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the process, method, article, or device comprising the element. The various embodiments in this specification are described in a progressive manner, with reference to similar parts between the embodiments. Each embodiment focuses on describing its differences from other embodiments. In particular, for system embodiments, since these are substantially similar to method embodiments, their descriptions are relatively brief, and relevant details can be found in the method embodiment sections.

[0077] The above descriptions are merely embodiments of the present application and are not intended to limit the present application. The present application may be modified and varied in various ways by those skilled in the art. All modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the present application should be included within the scope of the claims of the present application.

[0078] Although the embodiments of the present application have been described in conjunction with the drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations fall within the scope defined by the appended claims.

Claims

[1] Battery cell, comprising: a housing configured to receive a first electrode assembly, the housing having a first wall; a first electrode terminal disposed on the first wall; a first electrode assembly and a first electrode tab portion, wherein the first electrode tab portion comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly, and the first electrode tab portion is electrically connected to the first electrode terminal, wherein a first welding mark and a second welding mark are arranged on the first electrode tab portion, an orthogonal projection of the second welding mark lies within an orthogonal projection of the first welding mark along a projection of a main surface of the first electrode tab portion, and the second welding mark is configured to weld the first electrode terminal to the first electrode tab portion, and wherein a roughness of the second weld mark is greater than a roughness of the first weld mark. [2] The battery cell according to claim 1, wherein the roughness of the second weld mark is represented by a1 and the roughness of the first weld mark is represented by a2, where 5≤a1 / a2≤300. [3] The battery cell according to claim 2, wherein the roughness of the second weld mark satisfies 300 µm ≤ a1 ≤ 3000 µm; and the roughness of the first weld mark satisfies 10 µm ≤ a2 ≤ 500 µm. [4] The battery cell according to claim 1, wherein the first welding mark is formed by toothless welding. [5] The battery cell according to claim 1, wherein the second welding mark comprises a first welding region and a second welding region, the second welding region is arranged on a peripheral outer side of the first welding region, a plurality of square welding marks are arranged in the first welding region, and a plurality of circular welding marks are arranged in the second welding region. [6] The battery cell according to claim 1, wherein along the projection of the main surface of the first electrode tab portion, a projected area of ​​the first welding mark is represented by S1 and a projected area of ​​the second welding mark is represented by S2, wherein 1 ≤ S1 / S2 ≤ 10 is satisfied. [7] Battery cell according to claim 6, wherein the projected area of ​​the first welding mark is 100 mm 2 ≤ S1 ≤ 2000 mm 2 fulfilled, and the projected area of ​​the second welding mark 20 mm 2 ≤ S2 ≤ 120 mm 2 fulfilled. [8] The battery cell according to claim 1, wherein the first welding mark has a first edge, the second welding mark has a second edge, and a minimum distance between the first edge and the second edge is represented by c and satisfies 0.5 mm ≤ c ≤ 10 mm. [9] The battery cell according to claim 1, wherein the battery cell further comprises: a second electrode assembly and a second electrode tab portion, wherein the second electrode assembly and the second electrode tab portion are both disposed in the housing, the second electrode tab portion comprises at least two second electrode tab pieces extending from at least one end of the second electrode assembly, and the second electrode tab portion is electrically connected to the first electrode terminal;and wherein a third welding mark and a fourth welding mark are arranged on the second electrode tab portion, a projected area of ​​the first welding mark is represented by S1 along the projection of the main surface of the first electrode tab portion, a projected area of ​​the third welding mark is represented by S3 along a projection of a main surface of the second electrode tab portion, and a sum of the projected areas of the second welding mark and the fourth welding mark is represented by S4, where S1+S3>S4 is satisfied.; [10] The battery cell according to claim 9, wherein the roughness of the second weld mark is represented by a1, the roughness of the first weld mark is represented by a2, a roughness of the fourth weld mark is represented by d1, and a roughness of the third weld mark is represented by d2, wherein 5≤a1 / a2≤280 and 5≤d1 / d2≤280 are satisfied. [11] The battery cell according to claim 10, wherein the roughness of the second weld mark satisfies the following condition: 300 µm ≤ a1 ≤ 2800 µm; the roughness of the first weld mark satisfies the following condition: 10 µm ≤ a2 ≤ 500 µm; the roughness of the fourth weld mark satisfies the following condition: 300 µm ≤ d1 ≤ 2800 µm; and the roughness of the third weld mark satisfies: 10 µm ≤ d2 ≤ 500 µm. [12] Battery cell according to claim 9, wherein 0.9≤S1 / S3≤1.1 is satisfied. [13] The battery cell according to claim 1, wherein the first welding mark has a rectangular shape. [14] Battery cell according to one of claims 1 to 13, wherein the second welding mark has a circular shape. [15] The battery cell according to claim 1, wherein along a projection of the main surface of the first electrode tab portion, a region of the second welding mark is represented by S2, an end face of an end of the electrode terminal connected to the first electrode tab portion is represented by S5, wherein 0.25 ≤ S2 / S5 ≤ 0.95 is satisfied. [16] The battery cell according to claim 15, wherein the area of ​​the second welding mark satisfies: 20 mm 2 ≤ S2 ≤ 120 mm 2 ; and the end face of the electrode terminal connected to the first electrode tab section 50 mm 2 ≤ S5 ≤ 300 mm 2 fulfilled. [17] Battery cell, comprising: a housing configured to receive a first electrode assembly and a second electrode assembly, the housing having a first wall; a first electrode terminal disposed on the first wall; a first electrode assembly and a first electrode tab portion, wherein the first electrode tab portion comprises at least two first electrode tab pieces extending from at least one end of the first electrode assembly, and the first electrode tab portion is electrically connected to the first electrode terminal; a second electrode assembly and a second electrode tab portion, wherein the second electrode tab portion comprises at least two second electrode tab pieces extending from at least one end of the second electrode assembly, and the second electrode tab portion is electrically connected to the first electrode terminal, wherein the first electrode tab portion and the second electrode tab portion are stacked and welded to form a first weld mark and a second weld mark, an orthogonal projection of the second weld mark lies within an orthogonal projection of the first weld mark along a projection of a main surface of the first electrode tab portion or the second electrode tab portion, and the second weld mark is configured to weld at least one of the first electrode tab portions and the second electrode tab portions to the first electrode terminal, and wherein a roughness of the second weld mark is greater than a roughness of the first weld mark. [18] The battery cell according to claim 17, wherein the roughness of the second weld mark is represented by a1 and the roughness of the first weld mark is represented by a2, where 6 ≤ a1 / a2 ≤ 300. [19] The battery cell according to claim 18, wherein the roughness of the second weld mark satisfies: 280 µm ≤ a1 ≤ 3000 µm; and the roughness of the first weld mark satisfies: 10 µm ≤ a2 ≤ 500 µm. [20] A battery pack comprising the battery cell according to any one of claims 1 to 19.

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