CN210136970U

CN210136970U - Secondary battery

Info

Publication number: CN210136970U
Application number: CN201921300882.8U
Authority: CN
Inventors: 陈雷
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2019-08-12
Filing date: 2019-08-12
Publication date: 2020-03-10
Anticipated expiration: 2029-08-12

Abstract

The utility model provides a secondary battery, it includes electrode subassembly, casing, top cap subassembly and insulating member. The case has an opening, the electrode assembly is housed in the case, and the cap assembly is connected to the case and seals the opening of the case. The insulating member is disposed between the case and the electrode assembly. The insulating member is integrally provided and includes a first insulating sheet, a second insulating sheet, a third insulating sheet and a fourth insulating sheet. The first insulation sheet and the second insulation sheet are respectively located on both sides of the electrode assembly in the thickness direction, the third insulation sheet extends from one end of the first insulation sheet in the length direction toward the direction close to the second insulation sheet, and the fourth insulation sheet extends from one end of the second insulation sheet in the length direction toward the direction close to the first insulation sheet. The third insulation sheet and the fourth insulation sheet are located on the same side of the electrode assembly in the length direction. The third insulation sheet and the fourth insulation sheet are at least partially overlapped in the length direction, and the third insulation sheet and the fourth insulation sheet are welded in the overlapped area and form a first welding area.

Description

Secondary battery

Technical Field

The utility model relates to a battery field especially relates to a secondary battery.

Background

A secondary battery generally includes an electrode assembly, which is received in a case, and a cap assembly, which is coupled to the case and seals the electrode assembly in the case. The case is mostly made of metal, and if the electrode assembly is in contact with the case, a short circuit risk is easily caused.

SUMMERY OF THE UTILITY MODEL

In view of the problems in the prior art, an object of the present invention is to provide a secondary battery, which can reduce the risk of contact between an electrode assembly and a case, and improve safety performance.

In order to accomplish the above object, the present invention provides a secondary battery including an electrode assembly, a case, a cap assembly, and an insulating member. The case has an opening, the electrode assembly is housed in the case, and the cap assembly is connected to the case and seals the opening of the case. The insulating member is disposed between the case and the electrode assembly. The insulating member is integrally provided and includes a first insulating sheet, a second insulating sheet, a third insulating sheet and a fourth insulating sheet. The first insulation sheet and the second insulation sheet are respectively located on both sides of the electrode assembly in the thickness direction, the third insulation sheet extends from one end of the first insulation sheet in the length direction toward the direction close to the second insulation sheet, and the fourth insulation sheet extends from one end of the second insulation sheet in the length direction toward the direction close to the first insulation sheet. The third insulation sheet and the fourth insulation sheet are located on the same side of the electrode assembly in the length direction. The third insulation sheet and the fourth insulation sheet are at least partially overlapped in the length direction, and the third insulation sheet and the fourth insulation sheet are welded in the overlapped area and form a first welding area.

The fourth insulation sheet is positioned at one side of the third insulation sheet close to the electrode assembly. In the thickness direction, the distance between the first insulating sheet and the second insulating sheet is D1, the size of the fourth insulating sheet is D2, and the value of D2/D1 is 0.01-0.2.

The dimension of the first fusion-bonded region in the thickness direction was D3, and the value of D3/D2 was 0.3 to 0.9.

In the height direction, a ratio of a size of the first fusion-bonding area to a size of the third insulation sheet is greater than 0.5.

The insulating member further includes a fifth insulating sheet extending from an end of the first insulating sheet, which is away from the third insulating sheet, toward a direction close to the second insulating sheet, and a sixth insulating sheet extending from an end of the second insulating sheet, which is away from the fourth insulating sheet, toward a direction close to the first insulating sheet. The fifth insulation sheet and the sixth insulation sheet are located on the same side of the electrode assembly in the length direction. The fifth insulation sheet and the sixth insulation sheet are at least partially overlapped in the length direction, and the fifth insulation sheet and the sixth insulation sheet are welded at the overlapped area and form a second welding area.

In the thickness direction, the size of the third insulation sheet is equal to the size of the sixth insulation sheet, and the size of the fourth insulation sheet is equal to the size of the fifth insulation sheet.

The insulating member further includes a seventh insulating sheet, an eighth insulating sheet, and a ninth insulating sheet. The seventh insulating sheet is located on one side of the electrode assembly, which is far away from the cap assembly, and two ends of the seventh insulating sheet are respectively connected to the first insulating sheet and the second insulating sheet. The eighth insulation sheet and the ninth insulation sheet extend from both ends of the seventh insulation sheet in the length direction toward a direction close to the top cap assembly, respectively. The eighth insulation sheet and the third insulation sheet are at least partially overlapped in the length direction, and the eighth insulation sheet and the third insulation sheet are welded in the overlapped area to form a third welding area, and the third welding area is connected to the first welding area. The ninth insulation sheet and the sixth insulation sheet are at least partially overlapped in the length direction, and the ninth insulation sheet and the sixth insulation sheet are welded at the overlapped area and form a fourth welding area, and the fourth welding area is connected to the second welding area.

The eighth insulating sheet is located on one side of the third insulating sheet away from the electrode assembly, and the ninth insulating sheet is located on one side of the sixth insulating sheet away from the electrode assembly.

The first welding zone, the second welding zone, the third welding zone and the fourth welding zone have the same width.

The top cover assembly includes a top cover plate connected to the case and covering the opening of the case, and an insulating frame disposed on one side of the top cover plate near the electrode assembly. The first insulating sheet and the second insulating sheet are welded to the insulating frame body.

The utility model has the advantages as follows: the insulating component is arranged on the outer side of the electrode assembly, so that the risk of contact between the electrode assembly and the shell can be reduced, and the safety performance is improved. Through butt fusion third insulating piece and fourth insulating piece, this application can avoid third insulating piece and fourth insulating piece to open at the in-process of going into the shell, reduces the risk that third insulating piece and fourth insulating piece were scraped brokenly, guarantees the insulating properties of insulating member.

Drawings

Fig. 1 is a schematic view of a secondary battery according to the present invention.

Fig. 2 is an enlarged view of the secondary battery of fig. 1 at a circle frame a.

Fig. 3 is a schematic view of an electrode assembly and an insulating member according to the present invention.

Fig. 4 is an enlarged view of fig. 3 at circle B.

Fig. 5 is a cross-sectional view of the electrode assembly and insulating member of fig. 3.

Fig. 6 is an enlarged view of fig. 5 at block C.

Fig. 7 is an enlarged view of fig. 5 at block E.

Fig. 8 is another sectional view of the electrode assembly and the insulating member of fig. 3.

Fig. 9 is an enlarged view of fig. 8 at block F.

Fig. 10 is a schematic view of an insulating member of a secondary battery according to the present invention before molding. Wherein the reference numerals are as follows:

1 electrode Assembly

2 casing

3 Top cover assembly

31 ceiling board

32 insulating frame

33 electrode terminal

4 insulating member

41 first insulating sheet

42 second insulating sheet

43 third insulating sheet

44 fourth insulation sheet

45 fifth insulating sheet

46 sixth insulating sheet

47 seventh insulating sheet

48 eighth insulation sheet

49 ninth insulating sheet

5 current collecting component

W1 first weld zone

W2 second weld zone

W3 third weld zone

W4 fourth weld zone

In the X longitudinal direction

Y thickness direction

Direction of Z height

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In the description of the present application, unless explicitly stated or limited otherwise, the terms "first", "second", "third", and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means more than two (including two); the term "coupled", unless otherwise specified or indicated, is to be construed broadly, e.g., "coupled" may be a fixed or removable connection or a connection that is either integral or electrical or signal; "connected" may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

In the description of the present application, it should be understood that the terms "upper" and "lower" used in the description of the embodiments of the present application are used in a descriptive sense only and not for purposes of limitation. The present application is described in further detail below with reference to specific embodiments and with reference to the attached drawings.

Referring to fig. 1, the secondary battery of the present application includes an electrode assembly 1, a case 2, a cap assembly 3, and an insulating member 4.

The electrode assembly 1 is a core member of the secondary battery that realizes the charge and discharge functions. The electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm, wherein the diaphragm separates the positive pole piece from the negative pole piece. The positive pole piece and the negative pole piece are both in a belt-shaped structure, and the positive pole piece, the diaphragm and the negative pole piece are sequentially stacked and wound into a flat shape. The positive pole piece comprises an aluminum foil and a positive active substance layer coated on the surface of the aluminum foil, wherein the positive active substance layer comprises a ternary material, lithium manganate or lithium iron phosphate. The negative pole piece comprises a copper foil and a negative active material layer coated on the surface of the copper foil, wherein the negative active material layer comprises graphite or silicon.

The housing 2 may have a hexahedral shape or other shapes. The case 2 forms a receiving chamber therein to receive the electrode assembly 1 and the electrolyte. The case 2 is formed with an opening at one end, and the electrode assembly 1 may be placed into the receiving cavity of the case 2 through the opening. The housing 2 may be made of a material of conductive metal, and preferably, the housing 2 is made of aluminum or aluminum alloy.

The top lid assembly 3 includes a top lid plate 31, an insulating frame 32, and an electrode terminal 33. The top cap plate 31 is disposed on the case 2 and covers the opening of the case 2, thereby sealing the electrode assembly 1 within the case 2. The top cover plate 31 may be a metal plate and is connected to the housing 2 by welding. The insulating frame 32 is disposed on one side of the top cap plate 31 close to the electrode assembly 1, and the insulating frame 32 can separate the electrode assembly 1 from the top cap plate 31 to reduce the risk of short circuit.

Two electrode terminals 33 are provided in the top lid plate 31, and the two electrode terminals 33 are a positive electrode terminal and a negative electrode terminal, respectively. The secondary battery of the present application may further include two current collecting members 5, one current collecting member 5 connecting the positive terminal and the positive electrode tab, and the other current collecting member 5 connecting the negative terminal and the negative electrode tab.

The top cover 31 is electrically connected to the positive terminal and is insulated from the negative terminal. Since the case 2 is welded to the top cover plate 31, the case 2 is positively charged. When the housing 2 is positively charged, the risk of corrosion of the housing 2 can be reduced. However, if the negative electrode tab in the electrode assembly 1 comes into contact with the case 2, a short circuit will be caused, causing a safety risk.

The top cover plate 31 may also be insulated from both the positive and negative terminals, and the housing 2 is not charged at this time. If the negative electrode plate in the electrode assembly 1 contacts the case 2, the case 2 is in a low potential state, and is easily corroded by the electrolyte, which affects the service life and safety performance of the secondary battery.

Therefore, in order to reduce the risk of the electrode assembly 1 coming into contact with the case 2 and improve safety performance, the present application preferably provides the insulating member 4 on the outside of the electrode assembly 1.

Referring to fig. 3 to 7, the insulating member 4 is disposed between the case 2 and the electrode assembly 1. The insulating member 4 is integrally provided. In other words, the insulating member 4 is an integrally formed member, and covers the outside of the electrode assembly 1 by bending or the like. The material of the insulating member 4 may be polypropylene. The thickness may be 0.1mm-0.2 mm.

Specifically, the insulating member 4 includes a first insulating sheet 41, a second insulating sheet 42, a third insulating sheet 43, and a fourth insulating sheet 44.

The first insulation sheet 41 and the second insulation sheet 42 are respectively located at both sides of the electrode assembly 1 in the thickness direction Y. The first and

second insulation sheets

41 and 42 may separate the case 2 from the electrode assembly 1 in the thickness direction Y. The first insulation sheet 41 and the second insulation sheet 42 are substantially flat plates perpendicular to the thickness direction Y. The area of the first insulation sheet 41 is substantially equal to the area of the second insulation sheet 42.

The third insulation sheet 43 extends from one end of the first insulation sheet 41 in the longitudinal direction X toward the second insulation sheet 42, and the fourth insulation sheet 44 extends from one end of the second insulation sheet 42 in the longitudinal direction X toward the first insulation sheet 41. The third insulation sheet 43 and the fourth insulation sheet 44 are located on the same side of the electrode assembly 1 in the length direction X. The third and

fourth insulation sheets

43 and 44 may separate the case 2 from the electrode assembly 1 in the length direction X.

The third insulation sheet 43 and the fourth insulation sheet 44 are substantially flat plates perpendicular to the length direction X. The area of the first insulation sheet 41 is larger than the areas of the third and

fourth insulation sheets

43 and 44.

Referring to fig. 6, the third insulation sheet 43 and the fourth insulation sheet 44 are at least partially overlapped in the length direction X. In other words, the projections of the third insulation sheet 43 and the projections of the fourth insulation sheet 44 at least partially overlap in a plane perpendicular to the length direction X.

Preferably, the edge of the fourth insulation sheet 44 remote from the second insulation sheet 42 is completely covered by the third insulation sheet 43. At this time, there is no gap between the third insulation sheet 43 and the fourth insulation sheet 44 in the thickness direction Y, thereby preventing the electrode assembly 1 from being exposed.

The third insulation sheet 43 is bent with respect to the first insulation sheet 41, and after the bending, a stress is present at a connection portion between the third insulation sheet 43 and the first insulation sheet 41, and the third insulation sheet 43 is easily opened by the stress. As does the fourth insulating sheet 44. If the third insulation sheet 43 and the fourth insulation sheet 44 are independent of each other without a fixed relationship therebetween, the third insulation sheet 43 and the fourth insulation sheet 44 are easily opened outward during the process of mounting the electrode assembly 1 and the insulating member 4 into the case 2, causing the third insulation sheet 43 and the fourth insulation sheet 44 to be scratched by the case 2, thereby causing a safety risk.

Therefore, it is preferable that the third insulation sheet 43 and the fourth insulation sheet 44 are welded at the overlapping area and form the first welding area W1. The first welding area W1 may connect the third insulation sheet 43 and the fourth insulation sheet 44, so as to prevent the third insulation sheet 43 and the fourth insulation sheet 44 from being opened, reduce the risk of the third insulation sheet 43 and the fourth insulation sheet 44 being scratched, and ensure the insulation performance of the insulation member 4.

Compared with the bonding mode, the first welding area W1 is resistant to electrolyte corrosion and does not cause connection failure due to electrolyte soaking.

The first insulation sheet 41 and the second insulation sheet 42 have a spacing D1 in the thickness direction Y. The value of D1 is substantially equal to the thickness of electrode assembly 1.

The fourth insulation sheet 44 is located at one side of the third insulation sheet 43 adjacent to the electrode assembly 1. The dimension of the third insulating sheet 43 in the thickness direction Y may be substantially equal to D1. At this time, the third insulation sheet 43 may separate the electrode assembly 1 from the case 2 in the longitudinal direction X.

In the present application, the electrode assembly 1 is in a winding structure, and one end of the electrode assembly 1 close to the third insulation sheet 43 is in a circular arc shape, so that a gap is left between the electrode assembly 1 and the third insulation sheet 43. The fourth insulation sheet 43 can be accommodated in the gap to prevent the fourth insulation sheet 43 from occupying additional space in the length direction X, thereby increasing the energy density of the secondary battery.

Therefore, it is preferable that the size of the fourth insulation sheet 44 in the thickness direction Y is D2, and the value of D2/D1 is 0.01-0.2. If D2/D1 is greater than 0.2, the fourth insulation sheet 44 is wide and may come into contact with the electrode assembly 1, causing the fourth insulation sheet 44 to occupy additional space in the length direction X, affecting the energy density of the secondary battery. On the other hand, if the value of D2/D1 is less than 0.01, the fourth insulation sheet 44 is narrow, which increases the difficulty of welding the third insulation sheet 43 and the fourth insulation sheet 44, making it difficult to ensure the connection strength between the third insulation sheet 43 and the fourth insulation sheet 44.

The first fusion-bonded region W1 has a dimension D3 and a value D3/D2 of 0.3 to 0.9 in the thickness direction Y. If the value of D3/D2 is too large, it is easily misaligned due to process errors during welding, and the risk of the third insulation sheet 43 being melted through is caused. If the value of D3/D2 is too small, insufficient connection strength between the third insulation sheet 43 and the fourth insulation sheet 44 is easily caused, and the third insulation sheet 43 and the fourth insulation sheet 44 are easily separated.

The third insulation sheet 43 and the fourth insulation sheet 44 have substantially the same size in the height direction Z. The third insulation sheet 43 has a larger dimension in the height direction Z, and if the dimension of the first fusion-bonding zone W1 in the height direction Z is smaller, there is still a risk that the third insulation sheet 43 and the fourth insulation sheet 44 open at a position away from the first fusion-bonding zone W1. Therefore, it is preferable that the ratio of the size of the first fusion-bonding zone W1 to the size of the third insulation sheet 43 in the height direction Z is greater than 0.5.

Referring to fig. 5 and 7, the insulating member 4 further includes a fifth insulating sheet 45 and a sixth insulating sheet 46, the fifth insulating sheet 45 extending from an end of the first insulating sheet 41 remote from the third insulating sheet 43 toward a direction close to the second insulating sheet 42, and the sixth insulating sheet 46 extending from an end of the second insulating sheet 42 remote from the fourth insulating sheet 44 toward a direction close to the first insulating sheet 41. The fifth insulating sheet 45 and the sixth insulating sheet 46 are located on the same side of the electrode assembly 1 in the length direction X. The fifth insulating sheet 45 and the sixth insulating sheet 46 are substantially flat plates perpendicular to the length direction X. The area of the first insulation sheet 41 is larger than the areas of the fifth and

sixth insulation sheets

45 and 46.

The fifth insulation sheet 45 and the sixth insulation sheet 46 are at least partially overlapped in the length direction X. In other words, the projection of the fifth insulating sheet 45 and the projection of the sixth insulating sheet 46 at least partially overlap in a plane perpendicular to the length direction X. Preferably, an edge of the fifth insulating sheet 45, which is away from the first insulating sheet 41, is completely covered by the sixth insulating sheet 46.

The fifth insulating sheet 45 and the sixth insulating sheet 46 are welded at the overlapping area and form a second welding area W2. The second welding area W2 can connect the fifth insulating sheet 45 and the sixth insulating sheet 46, so as to prevent the fifth insulating sheet 45 and the sixth insulating sheet 46 from opening, reduce the risk of the fifth insulating sheet 45 and the sixth insulating sheet 46 being scratched, and ensure the insulating property of the insulating member 4.

The fifth insulation sheet 45 is located at one side of the sixth insulation sheet 46 adjacent to the electrode assembly 1. In the thickness direction Y, the size of the third insulation sheet 43 is equal to the size of the sixth insulation sheet 46, and the size of the fourth insulation sheet 44 is equal to the size of the fifth insulation sheet 45.

The sixth insulation sheet 46 may space the electrode assembly 1 from the case 2 in the length direction X. The fifth insulating sheet 5 can utilize the gap between the sixth insulating sheet 46 and the electrode assembly 1 without additional occupied space in the length direction X, thereby improving the energy density of the secondary battery.

In addition, the first fusion-bonded zone W1 and the second fusion-bonded zone W2 are diagonally arranged, and the strength of the whole can be effectively improved. Meanwhile, the anti-blocking device can also play a role in preventing blocking and simplify the assembly process.

Referring to fig. 8 and 9, the insulation member 4 further includes a seventh insulation sheet 47, an eighth insulation sheet 48, and a ninth insulation sheet 49.

The seventh insulating sheet 47 is located at one side of the electrode assembly 1 away from the cap assembly 3, and both ends of the seventh insulating sheet 47 are connected to the first insulating sheet 41 and the second insulating sheet 42, respectively. The seventh insulating sheet 47 is a substantially flat plate perpendicular to the height direction Z, and the seventh insulating sheet 47 separates the bottom of the electrode assembly 1 from the case 2.

The eighth and

ninth insulation sheets

48 and 49 extend from both ends of the seventh insulation sheet 47 in the length direction X toward the direction close to the head cover assembly 3, respectively.

The eighth insulation sheet 48 and the third insulation sheet 43 are at least partially overlapped in the length direction X. In other words, the projection of the eighth insulating sheet 48 and the projection of the third insulating sheet 43 at least partially overlap in a plane perpendicular to the length direction X.

The eighth insulation sheet 48 and the third insulation sheet 43 are welded at the overlapping area and form a third welding area W3. The third welding area W3 can fix the eighth insulating sheet 48 to the third insulating sheet 43, avoiding the eighth insulating sheet 48 from opening, reducing the risk of being scratched, and ensuring the insulating properties of the insulating member 4.

Referring to fig. 4, the third welding-performed regions W3 are connected to the first welding-performed regions W1, so that the connection strength of the third, fourth and

eighth insulation sheets

43, 44 and 48 can be improved.

The ninth insulating sheet 49 and the sixth insulating sheet 46 are at least partially overlapped in the longitudinal direction X, and the ninth insulating sheet 49 and the sixth insulating sheet 46 are welded at the overlapped area and form a fourth welding area W4. The fourth welding area W4 can fix the ninth insulating sheet 49 to the sixth insulating sheet 46, avoiding the ninth insulating sheet 49 from opening, reducing the risk of being scratched, and ensuring the insulating properties of the insulating member 4. The fourth welding-together regions W4 are connected to the second welding-together regions W2 to improve the connection strength of the fifth insulating sheet 45, the sixth insulating sheet 46 and the ninth insulating sheet 49.

If the eighth insulation sheet 48 is positioned at a side of the third insulation sheet 43 close to the electrode assembly 1, the eighth insulation sheet 48 forms a step at the inner side of the third insulation sheet 43, and the electrode assembly 1 is liable to generate stress concentration at the step, causing a risk of lithium precipitation. Therefore, it is preferable that the eighth insulation sheet 48 is located at a side of the third insulation sheet 43 away from the electrode assembly 1.

Likewise, the ninth insulation sheet 49 is located at a side of the sixth insulation sheet 46 away from the electrode assembly 1.

The first weld zone W1, the second weld zone W2, the third weld zone W3 and the fourth weld zone W4 have the same width, so that the uniformity of the joining strength of the respective portions of the insulating member 4 can be ensured.

The first insulation sheet 41 and the second insulation sheet 42 are welded to the insulation frame 32. Preferably, the upper ends of the first insulation sheet 41, the second insulation sheet 42, the third insulation sheet 43, the fourth insulation sheet 44, the fifth insulation sheet 45, and the sixth insulation sheet 46 are all welded to the insulation frame 32, so that the insulation member 4 can be fixed, and the insulation member 4 is prevented from shaking.

The following describes in detail a molding method of an embodiment of the insulating member 4 of the present application.

i) By cutting, the PP film sheet was cut into a shape shown in fig. 10.

ii) bent along the lines L1 and L2 so that the first and second insulating

sheets

41 and 42 are formed to be perpendicular to the seventh insulating sheet 47.

iii) bending along line L3 to form the fourth insulating sheet 44, and then bending along line L4 to form the third insulating sheet 43. Similarly, the fifth insulating sheet 45 is formed by bending along the line L5, and then the sixth insulating sheet 46 is formed by bending along the line L6.

iv) bending along line L7 and forming eighth insulating sheet 48, and bending along line L8 and forming ninth insulating sheet 49.

v) the third insulation sheet 43 and the fourth insulation sheet 44 are welded to form a first welding area W1, the fifth insulation sheet 45 and the sixth insulation sheet 46 are welded to form a second welding area W2, the eighth insulation sheet 48 and the third insulation sheet 43 are welded to form a third welding area W3, and the ninth insulation sheet 49 and the sixth insulation sheet 46 are welded to form a fourth welding area W4.

Claims

1. A secondary battery characterized by comprising an electrode assembly (1), a case (2), a cap assembly (3), and an insulating member (4);

the shell (2) is provided with an opening, the electrode assembly (1) is accommodated in the shell (2), and the top cover assembly (3) is connected to the shell (2) and seals the opening of the shell (2);

an insulating member (4) is disposed between the case (2) and the electrode assembly (1);

the insulating member (4) is integrally provided and includes a first insulating sheet (41), a second insulating sheet (42), a third insulating sheet (43), and a fourth insulating sheet (44);

a first insulation sheet (41) and a second insulation sheet (42) are respectively positioned on two sides of the electrode assembly (1) along the thickness direction (Y), a third insulation sheet (43) extends from one end of the first insulation sheet (41) along the length direction (X) towards the direction close to the second insulation sheet (42), and a fourth insulation sheet (44) extends from one end of the second insulation sheet (42) along the length direction (X) towards the direction close to the first insulation sheet (41);

the third insulating sheet (43) and the fourth insulating sheet (44) are positioned on the same side of the electrode assembly (1) along the length direction (X);

the third insulation sheet (43) and the fourth insulation sheet (44) are at least partially overlapped in the longitudinal direction (X), and the third insulation sheet (43) and the fourth insulation sheet (44) are welded in the overlapped area and form a first welding area (W1).

2. The secondary battery according to claim 1,

the fourth insulation sheet (44) is positioned on one side of the third insulation sheet (43) close to the electrode assembly (1);

in the thickness direction (Y), the distance between the first insulation sheet (41) and the second insulation sheet (42) is D1, the size of the fourth insulation sheet (44) is D2, and the value of D2/D1 is 0.01-0.2.

3. The secondary battery according to claim 2, wherein the first fusion-bonded region (W1) has a size D3 and a value D3/D2 of 0.3 to 0.9 in the thickness direction (Y).

4. The secondary battery according to claim 1, wherein a ratio of a size of the first welding zone (W1) to a size of the third insulation sheet (43) in the height direction (Z) is greater than 0.5.

5. The secondary battery according to any one of claims 1 to 4,

the insulation member (4) further comprises a fifth insulation sheet (45) and a sixth insulation sheet (46), wherein the fifth insulation sheet (45) extends from one end of the first insulation sheet (41) far away from the third insulation sheet (43) to the direction close to the second insulation sheet (42), and the sixth insulation sheet (46) extends from one end of the second insulation sheet (42) far away from the fourth insulation sheet (44) to the direction close to the first insulation sheet (41);

the fifth insulating sheet (45) and the sixth insulating sheet (46) are positioned on the same side of the electrode assembly (1) in the length direction (X);

the fifth insulating sheet (45) and the sixth insulating sheet (46) are at least partially overlapped in the longitudinal direction (X), and the fifth insulating sheet (45) and the sixth insulating sheet (46) are welded in the overlapped area and form a second welding area (W2).

6. The secondary battery according to claim 5, wherein the size of the third insulation sheet (43) is equal to the size of the sixth insulation sheet (46) and the size of the fourth insulation sheet (44) is equal to the size of the fifth insulation sheet (45) in the thickness direction (Y).

7. The secondary battery according to claim 5,

the insulating member (4) further comprises a seventh insulating sheet (47), an eighth insulating sheet (48) and a ninth insulating sheet (49);

the seventh insulating sheet (47) is positioned on one side of the electrode assembly (1) far away from the top cover assembly (3), and two ends of the seventh insulating sheet (47) are respectively connected to the first insulating sheet (41) and the second insulating sheet (42);

the eighth insulation sheet (48) and the ninth insulation sheet (49) extend from two ends of the seventh insulation sheet (47) in the length direction (X) towards the direction close to the top cover assembly (3) respectively;

the eighth insulation sheet (48) and the third insulation sheet (43) are at least partially overlapped in the longitudinal direction (X), and the eighth insulation sheet (48) and the third insulation sheet (43) are welded in the overlapped area to form a third welding area (W3), the third welding area (W3) being connected to the first welding area (W1);

the ninth insulating sheet (49) and the sixth insulating sheet (46) are at least partially overlapped in the longitudinal direction (X), and the ninth insulating sheet (49) and the sixth insulating sheet (46) are welded at the overlapped area and form a fourth welding area (W4), the fourth welding area (W4) being connected to the second welding area (W2).

8. The secondary battery according to claim 7, wherein an eighth insulation sheet (48) is positioned at a side of the third insulation sheet (43) remote from the electrode assembly (1), and a ninth insulation sheet (49) is positioned at a side of the sixth insulation sheet (46) remote from the electrode assembly (1).

9. The secondary battery according to claim 7, wherein the widths of the first welding zone (W1), the second welding zone (W2), the third welding zone (W3), and the fourth welding zone (W4) are the same.

10. The secondary battery according to claim 1,

the top cover assembly (3) comprises a top cover plate (31) and an insulating frame body (32), the top cover plate (31) is connected to the shell (2) and covers the opening of the shell (2), and the insulating frame body (32) is arranged on one side, close to the electrode assembly (1), of the top cover plate (31);

the first insulating sheet (41) and the second insulating sheet (42) are welded to the insulating frame (32).