阅读说明：本技术 电芯卷绕方法及电芯 (Battery cell winding method and battery cell ) 是由 吴祖钰 易梓琦 张万财 张男 谢斌 于 2021-06-07 设计创作，主要内容包括：本申请涉及储能技术领域,尤其涉及一种电芯卷绕方法及电芯。该方法包括依次叠放第一极片、第一隔离膜、第二极片和第二隔离膜,使所述第一隔离膜和所述第二隔离膜在第一方向上的第一端超出所述第一极片和所述第二极片,分别形成第一延长部和第二延长部；将所述第一延长部和所述第二延长部连接；沿所述第一方向将所述第一极片、第一隔离膜、第二极片和第二隔离膜卷绕。本申请实施例提供的电芯卷绕方法及电芯不仅能够解决电芯在发生跌落等现象时,导致电芯松动,进而发生隔离膜内折,正负极片发生接触短路的问题,而且还能够解决电芯在卷绕的过程中,隔离膜回缩的问题。(The application relates to the technical field of energy storage, in particular to a battery cell winding method and a battery cell. The method comprises the steps of sequentially stacking a first pole piece, a first isolation film, a second pole piece and a second isolation film, wherein the first ends of the first isolation film and the second isolation film in a first direction exceed the first pole piece and the second pole piece to form a first extension part and a second extension part respectively; connecting the first extension and the second extension; and winding the first pole piece, the first isolation film, the second pole piece and the second isolation film along the first direction. The battery cell winding method and the battery cell provided by the embodiment of the application can solve the problems that when the battery cell falls and the like, the battery cell becomes loose, and then the isolating membrane is folded, and the positive and negative pole pieces are in short circuit contact, and can also solve the problem that the isolating membrane retracts in the winding process of the battery cell.)

1. A cell winding method, comprising:

sequentially stacking a first pole piece (1), a first isolating film (2), a second pole piece (3) and a second isolating film (4) to enable first ends of the first isolating film (2) and the second isolating film (4) in a first direction to exceed the first pole piece (1) and the second pole piece (3) to form a first extending portion (21) and a second extending portion (41) respectively;

-connecting the first extension (21) and the second extension (41);

and winding the first pole piece (1), the first isolating film (2), the second pole piece (3) and the second isolating film (4) along the first direction.

2. The cell winding method according to claim 1, wherein a first pole piece (1), a first isolation film (2), a second pole piece (3), and a second isolation film (4) are sequentially stacked, so that first ends of the first isolation film (2) and the second isolation film (4) in a first direction exceed the first pole piece (1) and the second pole piece (3) to form a first extension portion (21) and a second extension portion (41), respectively, and further comprising:

sequentially stacking a first pole piece (1), a first isolating film (2), a second pole piece (3) and a second isolating film (4) to enable second ends of the first isolating film (2) and the second isolating film (4) in a first direction to exceed the first pole piece (1) and the second pole piece (3) to form a third extending portion (22) and a fourth extending portion (42) respectively;

connecting the third extension (22) and the fourth extension (42).

3. The cell winding method of claim 2, further comprising:

sequentially stacking a first pole piece (1), a first isolating film (2), a second pole piece (3) and a second isolating film (4) to enable the first isolating film (2) and the second isolating film (4) to exceed the first pole piece (1) and the second pole piece (3) in a second direction to form a fifth extending part (23) and a sixth extending part (43) respectively;

after winding the first pole piece (1), first separator film (2), second pole piece (3) and second separator film (4) in the first direction, the method further comprises:

-connecting the fifth extension (23) and the sixth extension (43) together.

4. The cell winding method according to claim 3, wherein the connecting the fifth extension portion (23) and the sixth extension portion (43) together specifically comprises:

-joining together said fifth extension (23) and said sixth extension (43) by means of heat fusion; or the like, or, alternatively,

and bonding the fifth extension part (23) and the sixth extension part (43).

5. The cell winding method according to claim 2, characterized in that the first direction is a length direction (X) of the first and second separators (2, 4);

the second direction is a width direction (Y) of the first separator (2) and the second separator (4).

6. The cell winding method according to claim 2, wherein the third extension portion (22) and the fourth extension portion (42) are connected by means of heat fusion.

7. The cell winding method according to any of claims 1 to 6, characterized in that the first extension portion (21) and the second extension portion (41) are connected by means of heat fusion.

8. The cell winding method according to claim 7, wherein the connecting the first extension portion (21) and the second extension portion (41) by means of hot melting specifically comprises:

and cutting the first extending part (21) and the second extending part (41) by using a resistance wire heating cutter so as to connect the first extending part (21) and the second extending part (41) in a hot melting mode.

9. The cell winding method according to any one of claims 1 to 6, further comprising:

forming a first pole lug part on the first pole piece (1), wherein the first pole lug part is formed at a first end close to the first pole piece (1) in the second direction;

forming a second pole ear part (311) on the second pole piece (3), wherein the second pole ear part (311) is formed at a first end close to the second pole piece (3) in the second direction;

and a space (24) is formed on the first isolation film (2) and the second isolation film (4) at positions corresponding to the first pole ear part and the second pole ear part (311).

10. A battery cell, comprising:

the device comprises a first pole piece (1), a first isolating film (2), a second pole piece (3) and a second isolating film (4) which are sequentially stacked and wound;

the first ends of the first isolating film (2) and the second isolating film (4) in the first direction are respectively provided with a first extending part (21) and a second extending part (41) which exceed the first pole piece (1) and the second pole piece (3);

the ends of the first extension (21) and the second extension (41) are connected together.

11. The cell of claim 10, wherein the second ends of the first and second separator films (2, 4) in the first direction have a third and fourth extension (22, 42) beyond the first and second pole pieces (1, 3), respectively;

the ends of the third extension (22) and the fourth extension (42) are connected together.

12. The cell of claim 10, wherein the first and second separator films (2, 4) have, in the second direction, a fifth and a sixth extension (23, 43) beyond the first and second pole pieces (1, 3), respectively;

the ends of the fifth extension (23) and the sixth extension (43) are connected together.

13. The electrical core according to any of claims 10 to 12, wherein the first direction is a length direction (X) of the first separator (2) and the second separator (4);

the second direction is a width direction (Y) of the first separator (2) and the second separator (4).

14. The cell of any of claims 10 to 12, further comprising a first pole ear portion disposed on the first pole piece (1), and a second pole ear portion (311) disposed on the second pole piece (3);

the first pole lug part is formed at a first end close to the first pole piece (1) in the second direction;

the second pole lug part (311) is formed at a first end close to the second pole piece (3) in the second direction;

and the first isolation film (2) and the second isolation film (4) are respectively provided with a space avoidance part (24) corresponding to the first pole ear part and the second pole ear part (311).

15. The electrical core of any of claims 10 to 12, wherein the length of the first extension (21) is greater than or equal to 1 mm; the length of the second extension (41) is greater than or equal to 1 mm.

16. The cell of claim 15, wherein the first extension (21) has a length that is 1.5 times the inner perimeter of the cell;

the length of the second extension part (41) is 1.75 times of the outer periphery of the battery core.

Technical Field

The application relates to the technical field of energy storage devices, in particular to a battery cell winding method and a battery cell.

Background

With the enhancement of environmental awareness, energy storage batteries are increasingly being applied to various fields. The battery comprises a plurality of battery units, and each battery unit comprises a battery core, a top cover assembly and a shell. Wherein, the inside chamber that holds that forms of casing for hold electric core and electrolyte.

The battery cell comprises an electrode unit and a tab, wherein the electrode unit comprises a negative pole piece, a positive pole piece and an isolating film, and the isolating film is positioned between the adjacent negative pole piece and the positive pole piece and used for isolating the negative pole piece from the positive pole piece.

In the structure of the electrode unit, the isolating film is arranged between the positive pole piece and the negative pole piece, the width of the isolating film is slightly larger than that of the positive pole piece and the negative pole piece, and the exceeding part is the extension part of the isolating film. In the above scheme, the problem that the extending part of the isolating film is folded, dislocated or retracted into the gap between the positive electrode and the negative electrode exists, so that the edges of the pole pieces are in positive and negative electrode contact, and the positive and negative electrodes are in short circuit.

Disclosure of Invention

The application provides a battery cell winding method and a battery cell, which are used for solving the problem of battery short circuit caused by the fact that an isolating film is turned over, dislocated or retracted into a gap between a positive electrode and a negative electrode in the prior art.

The application provides a cell winding method, which comprises the following steps:

sequentially stacking a first pole piece, a first isolating film, a second pole piece and a second isolating film, so that the first ends of the first isolating film and the second isolating film in a first direction exceed the first pole piece and the second pole piece, and respectively forming a first extending part and a second extending part;

connecting the first extension and the second extension;

and winding the first pole piece, the first isolation film, the second pole piece and the second isolation film along the first direction.

In a possible embodiment, the method further includes stacking a first pole piece, a first isolation film, a second pole piece, and a second isolation film in sequence, so that a first end of the first isolation film and a first end of the second isolation film in a first direction exceed the first pole piece and the second pole piece to form a first extension portion and a second extension portion, respectively, and further including:

stacking a first pole piece, a first isolation film, a second pole piece and a second isolation film in sequence, wherein the second ends of the first isolation film and the second isolation film in the first direction exceed the first pole piece and the second pole piece, and a third extension part and a fourth extension part are respectively formed;

connecting the third extension and the fourth extension.

In one possible embodiment, the method further comprises:

stacking a first pole piece, a first isolating film, a second pole piece and a second isolating film in sequence, wherein the first isolating film and the second isolating film exceed the first pole piece and the second pole piece in a second direction to form a fifth extension part and a sixth extension part respectively;

after winding the first pole piece, first separator film, second pole piece, and second separator film in the first direction, the method further comprises:

attaching the fifth extension and the sixth extension together.

In a possible embodiment, the connecting the fifth extension and the sixth extension comprises:

connecting the fifth extension part and the sixth extension part together in a hot melting mode; or the like, or, alternatively,

and bonding the fifth extension portion and the sixth extension portion.

In one possible embodiment, the first direction is a length direction of the first and second separation films;

the second direction is a width direction of the first and second separation films.

In one possible embodiment, the third extension portion and the fourth extension portion are connected by heat fusion.

In one possible embodiment, the first extension portion and the second extension portion are connected by heat fusion.

In a possible embodiment, the attaching the first extension portion and the second extension portion by means of heat fusion specifically includes:

and cutting the first extending part and the second extending part by using a resistance wire heating cutter so as to connect the first extending part and the second extending part in a hot melting mode.

In one possible embodiment, the method further comprises:

forming a first pole lug part on the first pole piece, wherein the first pole lug part is formed at a first end close to the first pole piece in the second direction;

forming a second pole ear portion on the second pole piece, the second pole ear portion being formed near a first end of the second pole piece in a second direction;

and space avoidance parts are respectively formed on the first isolation film and the second isolation film at positions corresponding to the first pole ear part and the second pole ear part.

The application further provides a battery cell, wherein, include:

the first pole piece, the first isolating film, the second pole piece and the second isolating film are sequentially stacked and wound;

the first ends of the first isolating film and the second isolating film in the first direction are respectively provided with a first extending part and a second extending part which exceed the first pole piece and the second pole piece;

the ends of the first and second extensions are connected together.

In one possible embodiment, the second ends of the first and second isolation films in the first direction have third and fourth extensions beyond the first and second pole pieces, respectively;

the ends of the third and fourth extensions are connected together.

In a possible embodiment, the first and second separation films have, in the second direction, a fifth and a sixth extension beyond the first and second pole pieces, respectively;

the ends of the fifth extension and the sixth extension are connected together.

In one possible embodiment, the first direction is a length direction of the first and second separation films;

the second direction is a width direction of the first and second separation films.

In one possible embodiment, the battery cell further includes a first pole ear portion disposed on the first pole piece, and a second pole ear portion disposed on the second pole piece;

the first pole lug part is formed at a first end close to the first pole piece in the second direction;

the second pole ear part is formed close to a first end of the second pole piece in the second direction;

and the first isolating film and the second isolating film are respectively provided with a space avoiding part corresponding to the positions of the first polar ear part and the second polar ear part.

In one possible embodiment, the length of the first extension is greater than or equal to 1 mm; the length of the second extension is greater than or equal to 1 mm.

In one possible embodiment, the length of the first extension part is 1.5 times of the inner perimeter of the battery cell;

the length of the second extension part is 1.75 times of the outer periphery of the battery core.

According to the cell winding method and the cell, the first extension part and the second extension part are connected together, so that the first isolation film and the second isolation film cannot retract in the winding process, and the problem of short circuit caused by contact between the first pole piece and the second pole piece is avoided. The battery cell winding method provided by the embodiment of the application can solve the problems that when the battery cell falls and the like, the battery cell is loosened, the isolating membrane is folded, and the positive and negative pole pieces are in short circuit contact, and can also solve the problem that the isolating membrane retracts in the winding process of the battery cell.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings needed to be used in the detailed description of the present application or the prior art description will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a flowchart of a cell winding method according to an embodiment of the present application;

fig. 2 is a schematic view of a partial structure of a battery cell provided in an embodiment of the present application before winding;

fig. 3 is a main cross-sectional view of a structure of a battery cell provided in an embodiment of the present application;

FIG. 4 is an enlarged view of FIG. 3 at A;

fig. 5 is a flowchart of a cell winding method according to yet another embodiment of the present application;

fig. 6 is a flowchart of a cell winding method according to yet another embodiment of the present application;

fig. 7 is a structural side sectional view of a battery cell provided in an embodiment of the present application;

FIG. 8 is a schematic view of the cutting of the first and second extensions by a knife;

fig. 9 is a top view of a battery cell provided in an embodiment of the present application.

Reference numerals:

100-cell

1-a first pole piece;

11-a first tab;

2-a first barrier film;

21-a first extension;

22-a third extension;

23-a fifth extension;

24-an escape part;

3-a second pole piece;

31-a second tab;

311-second pole ear;

4-a second barrier film;

41-a second extension;

42-a fourth extension;

43-a sixth extension;

5-cutting tools.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

Detailed Description

The technical solutions of the present application will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.

It should be noted that the terms "upper", "lower", "left", "right", and the like used in the embodiments of the present application are described in terms of the angles shown in the drawings, and should not be construed as limiting the embodiments of the present application. In addition, in this context, it will also be understood that when an element is referred to as being "on" or "under" another element, it can be directly on "or" under "the other element or be indirectly on" or "under" the other element via an intermediate element.

As shown in fig. 1 to 4, an embodiment of the present application provides a cell winding method, including the following steps:

s1, stacking the first pole piece 1, the first isolation film 2, the second pole piece 3 and the second isolation film 4 in sequence, so that the first ends of the first isolation film 2 and the second isolation film 4 in the first direction exceed the first pole piece 1 and the second pole piece 3, and forming the first extension portion 21 and the second extension portion 41, respectively.

The first pole piece 1 may be a positive pole piece, and the second pole piece 3 may be a negative pole piece. The second pole piece 3 can also be a positive pole piece, and the first pole piece 1 can be a negative pole piece. The negative electrode plate comprises a negative electrode current collector (such as copper foil) and a negative electrode active material layer (such as carbon or silicon) coated on the surface of the negative electrode current collector, and the positive electrode plate comprises a positive electrode current collector (such as aluminum foil) and a positive electrode active material layer (such as ternary material, lithium iron phosphate or lithium cobalt oxide) coated on the surface of the positive electrode current collector.

The first separator 2 may completely cover the first pole piece 1, and the second separator 4 may completely cover the second pole piece 3. The first end of the first isolation film 2 in the first direction extends beyond the first pole piece 1 and the second pole piece 3 to form a first extension portion 21. The first end of the second isolation film 4 in the first direction extends beyond the first pole piece 1 and the second pole piece 3 to form a second extension portion 41. In this way it can be ensured that the first pole piece 1 and the second pole piece 3 are separated.

The first direction may be a longitudinal direction X of the first and second separators 2 and 4 before winding, which is also a width direction of the cell formed after the winding of the first and second separators 2 and 4.

S2, first extension portion 21 and second extension portion 41 are connected.

Specifically, the first extension portion 21 and the second extension portion 41 may be connected by a hot press or by an adhesive.

S3, the first pole piece 1, the first separator 2, the second pole piece 3, and the second separator 4 are wound in the first direction.

The first direction may be a length direction X of the first isolation film 2 and the second isolation film 4, and since the first extension portion 21 and the second extension portion 41 are connected together, the first isolation film 2 and the second isolation film 4 do not retract during the winding process, thereby avoiding the problem of short circuit caused by contact between the first pole piece 1 and the second pole piece 3.

The battery cell winding method provided by the embodiment of the application can solve the problems that when the battery cell falls and the like, the battery cell is loosened, the isolating membrane is folded, and the positive and negative pole pieces are in short circuit contact, and can also solve the problem that the isolating membrane retracts in the winding process of the battery cell.

As shown in fig. 5 and also referring to fig. 3, in the cell winding method provided in the embodiment of the present application, step S1 further includes:

the first pole piece 1, the first isolation film 2, the second pole piece 3 and the second isolation film 4 are stacked in sequence, so that the second ends of the first isolation film 2 and the second isolation film 4 in the first direction exceed the first pole piece 1 and the second pole piece 3, and a third extending portion 22 and a fourth extending portion 42 are formed respectively.

That is, the third extension portion 22 and the first extension portion 21 are located at opposite ends of the first isolation film 2 in the longitudinal direction X, respectively. The fourth extension portion 42 and the second extension portion 41 are located at opposite ends of the second isolation film 4 in the longitudinal direction X, respectively.

The cell winding method further comprises the following steps:

s4, third extension 22 and fourth extension 42 are connected.

Specifically, the third extension portion 22 and the fourth extension portion 42 are connected by heat pressing or by adhesion.

The sequence of the steps S4 and S2 is not particularly limited. Step S2 may be performed first, or step S4 may be performed first.

Before the battery core is formed by winding, two ends of the isolating membrane are fixed, so that the two ends of the isolating membrane are prevented from retracting.

As shown in fig. 6 and 7, in the cell winding method, step S1 further includes:

the first pole piece 1, the first isolation film 2, the second pole piece 3 and the second isolation film 4 are sequentially stacked, so that the first isolation film 2 and the second isolation film 4 exceed the first pole piece 1 and the second pole piece 3 in the second direction to form a fifth extension portion 23 and a sixth extension portion 43 respectively.

The second direction may be a width direction Y of the first and second separators 2 and 4 before winding, which is also a length direction of the cell formed after the winding of the first and second separators 2 and 4. In the embodiment shown in fig. 7, the second direction is the width direction Y before the separator is wound.

After step S3, the method further includes:

s5, the fifth extension part 23 and the sixth extension part 43 are connected together.

After the fifth extending portion 23 and the sixth extending portion 43 are connected, the end portions of the isolation films are fixed together, and the wound battery cell cannot turn inwards to cause short circuit.

In a possible embodiment, the fifth extension 23 and the sixth extension 43 are joined together by means of heat fusion; alternatively, the fifth extension 23 and the sixth extension 43 are bonded together.

In one possible embodiment, third extension 22 and fourth extension 42 are attached by heat staking.

In one possible embodiment, the first extension portion 21 and the second extension portion 41 are connected by heat fusion.

As shown in fig. 8, in a possible embodiment, the step of connecting the first extension part 21 and the second extension part 41 by heat fusion specifically includes:

the first extension portion 21 and the second extension portion 41 are cut by using the resistance wire heating cutter 5, so that the first extension portion 21 and the second extension portion 41 are connected in a hot melting mode.

The dimensions of the projecting lengths of the first extension 21 and the second extension 41 may be subject to errors from the set process parameters during lamination of the separator film to the pole pieces. In practical implementation, a certain amount of the first extending portion 21 and the second extending portion 41 can be reserved, and during the cutting process by the resistance wire heating cutter 5, the first extending portion 21 and the second extending portion 41 can be connected together in a hot melting mode, and meanwhile, an appropriate length can be reserved. Therefore, the resistance wire heating cutter 5 is used for cutting the first extending part 21 and the second extending part 41, the first extending part and the second extending part can be connected, optimal process parameters can be obtained, and the process is simplified.

In the present embodiment, the length of the first extension portion 21 and the length of the second extension portion 41 after cutting are respectively greater than or equal to 1mm, thereby avoiding the problems of folding or dislocation of the isolation film, and occupying a small space.

Referring to fig. 2 and fig. 9, in a possible implementation, the method further includes:

a first pole lug portion is formed on the first pole piece 1, and the first pole lug portion is formed near a first end of the first pole piece 1 in the second direction.

A second pole ear portion 311 is formed on the second pole piece 3, and the second pole ear portion 311 is formed near a first end of the second pole piece 3 in the second direction.

Space-avoiding portions 24 are formed in the first separator 2 and the second separator 4 at positions corresponding to the first pole lug portion and the second pole lug portion 311, respectively.

After winding, the first tab portions are connected to form the first tab 11, and the second tab portions 311 are connected to form the second tab 31.

The first tab portion may be formed by cutting directly on the first pole piece 1, or may be attached to the first pole piece 1 as a separate component.

The second pole ear portion 311 may be formed by cutting directly on the second pole piece 3, or may be connected to the second pole piece 3 as a separate component.

As shown in fig. 3 and fig. 9, an embodiment of the present application further provides a battery cell 100, which includes a first pole piece 1, a first separation film 2, a second pole piece 3, and a second separation film 4, which are sequentially stacked and wound.

The first ends of the first isolation film 2 and the second isolation film 4 in the first direction are respectively provided with a first extending part 21 and a second extending part 41 which exceed the first pole piece 1 and the second pole piece 3, and the ends of the first extending part 21 and the second extending part 41 are connected together.

The electric core that this application embodiment provided not only can solve electric core and when the emergence was fallen the scheduling phenomenon, lead to electric core not hard up, and then take place the barrier film and roll over, the problem of contact short circuit takes place for positive and negative pole piece, but also can solve electric core at the in-process of coiling, the barrier film problem of retracting.

In one possible embodiment, the second ends of the first and second isolating membranes 2, 4 in the first direction have a third and a fourth extension 22, 42, respectively, beyond the first and second pole pieces 1, 3. The ends of third extension 22 and fourth extension 42 are connected together.

Before the battery core 100 is wound and formed, both ends of the isolation film are fixed to prevent the retraction of the both ends of the isolation film.

In one possible embodiment, the first and second separating films 2, 4 have a fifth and a sixth extension 23, 43, respectively, beyond the first and second pole pieces 1, 3 in the second direction. The ends of the fifth extension 23 and the sixth extension 43 are connected together.

After the fifth extending portion 23 and the sixth extending portion 43 are connected, the end portions of the respective layers of the insulating films are fixed together, and the wound battery core 100 is not turned inward to cause a short circuit.

The first direction is a longitudinal direction (X) of the first and second separators 2, 4, and the second direction is a width direction (Y) of the first and second separators 2, 4.

In a possible embodiment, the battery cell further includes a first tab 11 disposed on the first pole piece 1, and a second tab 31 disposed on the second pole piece 3.

The first tab 11 is formed near a first end of the first pole piece 1 in the second direction, and the second tab 31 is formed near a first end of the second pole piece 3 in the second direction. The first separator 2 and the second separator 4 have a space 24 formed therein at positions corresponding to the first tab 11 and the second tab 31, respectively.

Since the first tab 11 and the second tab 31 are disposed on the outer layer of the battery cell 100, after the battery cell 100 is formed, the first tab 11 and the second tab 31 can be directly led out of the battery cell 100, and the first tab 11 and the second tab 31 do not need to be bent and led out, thereby ensuring the performance of the battery cell.

In one possible embodiment, the length of the first extension 21 is greater than or equal to 1mm and the length of the second extension 41 is greater than or equal to 1 mm.

In one possible embodiment, the length of the first extension portion 21 is 1.5 times the inner perimeter of the battery cell, and the length of the second extension portion 41 is 1.75 times the outer perimeter of the battery cell.

Since the second extension portion 41 is positioned on the outer ring of the first extension portion 21 after winding, the length of the second extension portion 41 is set to be longer than the length of the first extension portion 21, and the uniformity of stretching of the separator can be ensured.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.