Secondary battery, battery pack, and electronic device

Abstract

The embodiment of the utility model provides a secondary battery, a battery pack and an electronic device, the secondary battery comprises an electrode assembly, a first pole piece, a first diaphragm, a second pole piece and a second diaphragm which are sequentially laminated and then wound to form the electrode assembly; an insulating film for fixing the ending end of the electrode assembly; in the winding direction of the electrode assembly, the insulating film surrounds the electrode assembly for at least one circle, the extending ends of the ending end of the first diaphragm and the ending end of the second diaphragm form the ending end of the electrode assembly, the ending end of the second pole piece extends out of the ending end of the first pole piece, and the ending end of the electrode assembly extends out of the ending end of the second pole piece. The starting ends of the insulating films all exceed the ending ends of the electrode assemblies. According to the technical scheme, at least the cylindricity of the cylindrical battery can be improved.

Description

Technical Field

[0001] The utility model relates to a secondary battery, a battery pack and an electronic device. Background Art

[0002] In the field of new energy power batteries, the application of secondary batteries is becoming more and more extensive. For example, secondary batteries (such as lithium-ion batteries) can be applied to electronic devices such as cars, energy storage, mobile phones, tablets, wearable devices, mobile power supplies, electronic cigarettes, digital products, power tools, power devices, energy storage devices, etc. One type of secondary battery is a cylindrical battery, which includes a housing and an electrode assembly. The electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator. The electrode assembly is stacked in sequence and wound into an electrode assembly, which is then encapsulated in a housing. However, existing secondary batteries still need further improvement in some aspects. Utility Model Content

[0003] In view of the problems existing in the related art, the purpose of the present invention is to provide a secondary battery, a battery pack and an electronic device, which can at least improve the cylindricity of cylindrical batteries.

[0004] To achieve the above-mentioned purpose, an embodiment of the present application provides a secondary battery, which includes: an electrode assembly, a first electrode sheet, a first diaphragm, a second electrode sheet and a second diaphragm, which are stacked in sequence and wound to form an electrode assembly; an insulating film, used to fix the tail end of the electrode assembly; wherein, along the winding direction of the electrode assembly, the insulating film surrounds the electrode assembly at least one circle, the tail end of the first diaphragm and the end exceeding the tail end of the second diaphragm constitute the tail end of the electrode assembly, and the tail end of the second electrode sheet exceeds the tail end of the first electrode sheet, the tail end of the electrode assembly exceeds the tail end of the second electrode sheet, and the starting end of the insulating film exceeds the tail end of the electrode assembly.

[0005] In some embodiments, in the opposite direction of the winding direction of the electrode assembly, the starting end of the second electrode sheet exceeds the starting end of the first electrode sheet. In the cross section perpendicular to the winding center line of the electrode assembly, the positive projection of the winding center line on the cross section forms a projection point. The projection point and the tail end of the first electrode sheet form a first connecting line. The projection point and the starting end of the second electrode sheet form a second connecting line. The tail end of the second electrode sheet, the tail end of the electrode assembly, and the starting end and tail end of the insulating film are located in the area between the first connecting line and the second connecting line along the winding direction.

[0006] In some embodiments, in the winding direction of the electrode assembly, the tail end of the insulating film extends beyond the tail end of the electrode assembly.

[0007] In some embodiments, the projection point and the starting end of the first electrode sheet form a third line, and the angle formed by the third line and the second line along the winding direction is in the range of 170°-190°, and the tail end of the first electrode sheet is located in the area between the third line and the second line along the winding direction; or, in some embodiments, in the opposite direction of the winding direction of the electrode assembly, the starting end of the second electrode sheet exceeds the starting end of the first electrode sheet by 1 to 2 turns; or, in some embodiments, the angle formed by the first line and the second line along the winding direction is in the range of 80°-90°.

[0008] In some embodiments, the projection point and the tail end of the second pole piece form a fourth connecting line, and the angle formed by the first connecting line and the fourth connecting line along the winding direction is A1, 0°<A1≤30°.

[0009] In some embodiments, the projection point and the tail end of the second electrode form a fourth line, the projection point and the tail end of the electrode assembly form a fifth line, and the angle formed by the fourth line and the fifth line along the winding direction is A2, 0°<A2≤30°.

[0010] In some embodiments, the projection point and the tail end of the electrode assembly form a fifth line, the projection point and the starting end of the insulating film form a sixth line, and the angle formed by the fifth line and the sixth line along the winding direction is A3, 7.7°≤A3≤30°.

[0011] In some embodiments, the projection point and the starting end of the insulating film form a sixth line, the projection point and the ending end of the insulating film form a seventh line, and the angle formed by the sixth line and the seventh line along the winding direction is A4, 0°<A4≤30°.

[0012] An embodiment of the present application further provides a battery pack, which includes any one of the above-mentioned secondary batteries.

[0013] An embodiment of the present application further provides an electronic device, comprising at least one of any one of the aforementioned secondary batteries and any one of the aforementioned battery packs.

[0014] The beneficial technical effects of the present utility model are:

[0015] In the above technical solution, by setting the tail end of the insulating film behind the tail end of the electrode assembly, the overlapping part of the two layers of insulating film is located at a position where the thickness of the outer ring of the electrode assembly is thinner after the tail end of the electrode assembly, the diameter range of the electrode assembly can be reduced and the cylindricity of the electrode assembly can be optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 A schematic diagram showing an electronic device according to an embodiment of the present application is a vehicle.

[0018] Figure 2 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0019] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0020] Figure 4 is a cross-sectional view of an electrode assembly of a secondary battery according to an embodiment of the present application in a cross section perpendicular to a winding center line.

[0021] Figure 5A and Figure 5B They are respectively partial enlarged schematic diagrams of the structures at the tail ends of the first separator and the second separator in the secondary battery according to another embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to better understand the spirit of the embodiments of the present application, some preferred embodiments of the present application are further described below.

[0023] The embodiments of the present application will be described in detail below. Throughout this specification, identical or similar components and components having identical or similar functions are represented by similar reference numerals. The embodiments described herein with respect to the accompanying drawings are illustrative and diagrammatic and are intended to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0024] As used herein, the terms "substantially," "substantially," "essentially," and "about" are used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the terms may refer to instances where the event or circumstance occurred precisely as well as instances where the event or circumstance occurred very approximately.

[0025] In this specification, unless otherwise specified or limited, relative terms such as "central", "longitudinal", "lateral", "front", "rear", "right", "left", "inner", "outer", "lower", "higher", "horizontal", "vertical", "above", "below", "above", "below", "top", "bottom" and their derivatives (such as "horizontally", "downwardly", "upwardly", etc.) should be interpreted as referring to the directions described in the discussion or depicted in the drawings. These relative terms are only used for convenience of description and do not require that the present application be constructed or operated in a specific orientation.

[0026] For ease of description, "first," "second," "third," and the like may be used herein to distinguish different components within a figure or a series of figures. "First," "second," "third," and the like are not intended to describe corresponding components. Furthermore, the embodiments and features described in the embodiments of this application may be combined with one another unless there is a conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0027] See also Figure 1 For ease of explanation, the following embodiments are described using a vehicle 1000 as an electronic device. However, it is readily understood that the electronic device provided herein is not limited to vehicles. The electronic device may include vehicles, mobile phones, portable devices, laptop computers, ships, spacecraft, electric toys, electric tools, and the like.

[0028] The interior of the vehicle 1000 is provided with a battery pack 1002, which can be arranged at the bottom of the vehicle body 1001 (e.g. Figure 1 The battery pack 1002 may be used to power the vehicle 1000. For example, the battery pack 1002 may be used as an operating power source or a driving power source for the vehicle 1000. The battery pack 1002 may include a plurality of cylindrical batteries (such as Figure 2 The secondary battery 100) and a shell that accommodates multiple cylindrical batteries.

[0029] Figure 2 1 shows a perspective view of a secondary battery 100 according to an embodiment of the present application. Figure 3 1 shows a cross-sectional view of a secondary battery 100 according to an embodiment of the present application. In this embodiment, the secondary battery 100 is a cylindrical battery. Figure 2 and Figure 3, the secondary battery 100 may include an electrode assembly 120, an electrolyte, a housing 200 and a cover plate 202. The housing 200 and the cover plate 202 are components that together contain the electrode assembly 120 and the electrolyte. The housing 200 may be made of any of a variety of available materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The housing 200 may be cylindrical and define a receiving cavity, and the electrode assembly 120 is disposed in the receiving cavity. The diameter of the housing 200 may be determined according to the specific size of the electrode assembly 120, such as 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 may be a 4680 cylindrical battery (diameter 46 mm, height 80 mm), the secondary battery 100 may be a 4695 cylindrical battery (diameter 46 mm, height 95 mm), or the secondary battery 100 may be a 46120 cylindrical battery (diameter 46 mm, height 120 mm).

[0030] The outer shell 200 can be connected to the negative electrode of the electrode assembly 120. One end of the outer shell 200 along the height direction Z may have an installation opening 205. The cover plate 202 is positioned within the installation opening 205 and seals the storage cavity. The secondary battery 100 may also have a terminal 208 at the end opposite the cover plate 202. The terminal 208 can be connected to the positive electrode of the electrode assembly 120. It should be understood that the terminal 208 is insulated from the outer shell 200 to prevent battery short circuits.

[0031] See also Figure 3 , the outer shell 200 is also provided with an inwardly protruding crimping portion 203 at a position adjacent to the mounting opening 205. Along the height direction Z of the secondary battery 100, the electrode assembly 120 is disposed between the end wall 111 and the crimping portion 203. The crimping portion 203 can limit the axial movement (movement in the height direction Z) of the electrode assembly 120 between the end wall 111 and the crimping portion 203 of the outer shell 200. A weak portion can be provided on the cover plate 202. When thermal runaway occurs in the battery, the high-temperature and high-pressure emissions inside can be discharged to the outside through the bottom of the battery, breaking through the weak portion on the cover plate 202, thereby achieving good drainage of the emissions.

[0032] The electrode assembly 120 may include a first electrode sheet, a first separator, a second electrode sheet, and a second separator (as shown in the following reference) stacked and wound in sequence. Figure 4 As described above, the electrode assembly 120 may have a winding center line Lc. Also, the electrode assembly 120 may have a winding center hole 120c.

[0033] The electrode assembly 120 may be provided with a positive electrode tab and a negative electrode tab at each end in the height direction Z of the secondary battery 100. In some embodiments, the positive electrode tab faces the end wall 111 and is electrically connected to the terminal post 208, thereby providing a positive charge to the terminal post 208. The negative electrode tab faces the mounting opening 205 and is electrically connected to the outer casing 200, thereby providing a negative charge to the terminal post 208. However, in other embodiments, the negative electrode tab may be connected to the terminal post 208, while the positive electrode tab may be connected to the outer casing 200.

[0034] Figure 4 1 is a cross-sectional view of the electrode assembly 120 of the secondary battery according to an embodiment of the present application in a cross section perpendicular to the winding center line Lc. It should be understood that the wound electrode assembly 120 has a winding center line Lc extending in the direction Z (see FIG. Figure 3 ), Figure 4 The XY plane shown is a cross section perpendicular to the winding center line Lc, and point P is the projection point of the winding center line Lc on the cross section. The electrode assembly 120 also has a winding center hole 120c. Figure 4 The cross section shown may have a circular shape. The projection point P may be the center of the circle surrounding the central hole 120c.

[0035] See also Figure 4 The electrode assembly 120 may include a first electrode sheet 121, a first separator 141, a second electrode sheet 122, and a second separator 142. The first electrode sheet 121, the first separator 141, the second electrode sheet 122, and the second separator 142 are sequentially stacked and wound along a winding direction D to form the electrode assembly 120. In addition, the secondary battery may further include an electrolyte, which may be located between the first electrode sheet 121, the first separator 141, the second electrode sheet 122, and the second separator 142. In some embodiments, the first electrode sheet 121 is a positive electrode sheet, and the second electrode sheet 122 is a negative electrode sheet.

[0036] The first and second electrode sheets can be the positive and negative electrode sheets, respectively. The positive electrode sheet can include a positive current collector and a positive active material layer coated on both sides of the positive current collector. The portion of the positive current collector not coated with the positive active material layer constitutes the positive electrode tab. The negative electrode sheet can include a negative current collector and a negative active material layer coated on both sides of the negative current collector. The portion of the negative current collector not coated with the negative active material layer constitutes the negative electrode tab. Taking a lithium-ion battery as an example, the positive current collector can be made of aluminum, and the positive active material layer can include a positive active material such as lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The negative current collector can be made of copper, and the negative active material layer can include a negative active material such as carbon or silicon. In some embodiments, the first and second separators 141 and 142 can be made of materials such as polypropylene (PP) or polyethylene (PE).

[0037] By coating a positive electrode active material layer on the positive electrode sheet, the positive electrode active material layer contains lithium ions. When the positive electrode active material layer is in contact with the electrolyte and the battery is charged, the lithium ions in the positive electrode active material layer will move through the electrolyte to the negative electrode active material layer and be embedded in the negative electrode active material layer. This process is the process of lithium ion activation and is also the process of battery charging.

[0038] The secondary battery may also include an insulating film 300, which can be used to secure the end of the electrode assembly 120. In this embodiment, the insulating film 300 surrounds the electrode assembly 120 at least once. In some embodiments, the insulating film 300 can be made of, for example, PP, PE, PET (polyethylene terephthalate), PVC (polyvinyl chloride), or other polymer materials. The insulating film 300 can be used to electrically isolate the electrode assembly 120 from the outside world.

[0039] Continue to see Figure 4In the winding direction D of the electrode assembly 120, the tail end 122e of the second electrode sheet 122 exceeds the tail end 121e of the first electrode sheet 121, so that the second electrode sheet 122 can cover the tail end 121e of the first electrode sheet 121. Then, the lithium ions released from the positive active material layer of the first electrode sheet 121 (positive electrode sheet) can be smoothly embedded in the negative active material layer of the second electrode sheet 122 (negative electrode sheet), thereby avoiding the occurrence of lithium plating on the second electrode sheet 122 (negative electrode sheet) at the tail end. For similar reasons, in the direction opposite to the winding direction D, the starting end 122s of the second electrode sheet 122 exceeds the starting end 121s of the first electrode sheet 121, that is, at the starting point of the winding of the electrode assembly 120, the second electrode sheet 122 is wound a certain length longer than the first electrode sheet 121.

[0040] In some embodiments, in the winding direction D of the electrode assembly 120, the starting end 122s of the second electrode sheet 122 extends beyond the starting end 121s of the first electrode sheet 121. By configuring the starting end 122s of the second electrode sheet 122 to extend beyond the starting end 121s of the first electrode sheet 121, lithium ions released from the positive active material layer of the first electrode sheet 121 (positive electrode sheet) can be smoothly embedded in the negative active material layer of the second electrode sheet 122 (negative electrode sheet), thereby avoiding lithium plating on the negative electrode sheet at the starting end. However, the outermost ring of the wound electrode assembly 120 is still prone to lithium plating.

[0041] According to an embodiment of the present application, along the winding direction D of the electrode assembly 120, the end of the tail end 141e of the first separator 141 and the end of the tail end 142e of the second separator 142 extend beyond the end 120e of the electrode assembly 120. Figure 4 In the illustrated embodiment, the tail end 141e of the first separator 141 and the tail end 142e of the second separator 142 are substantially aligned. It should be understood that alignment, as used herein, means that the tail ends 141e, 142e of the first separator 141 and the second separator 142 are within 5 mm of each other. In such an embodiment, the ends of the tail ends 141e, 142e of the first separator 141 and the second separator 142 that extend beyond the tail end 120e of the electrode assembly 120. If the tail ends 141e, 142e of the first separator 141 and the second separator 142 are within 0 mm of each other, the tail ends 141e, 142e of the first separator 141 and the second separator 142 can collectively serve as the tail end 120e of the electrode assembly 120.

[0042] In other embodiments, the tail ends 141 e and 142 e of the first diaphragm 141 and the second diaphragm 142 may not be aligned. Figure 5A and Figure 5BThey are respectively partial enlarged schematic diagrams of the structures at the end of the first separator and the second separator in the secondary battery according to another embodiment of the present application. Figure 5A As shown, the tail end 142e of the second diaphragm 142 exceeds the tail end 141e of the first diaphragm 141, and in this embodiment, the tail end 142e of the second diaphragm 142 is the outermost end and constitutes the tail end 120e of the electrode assembly 120. Figure 5B As shown, the tail end 141 e of the first separator 141 exceeds the tail end 142 e of the second separator 142 , and in this embodiment, the tail end 141 e of the first separator 141 is the outermost end and constitutes the tail end 120 e of the electrode assembly 120 .

[0043] Return Reference Figure 4 As shown, along the winding direction D of the electrode assembly 120 , the tail end 120 e of the electrode assembly 120 extends beyond the tail end 122 e of the second electrode sheet 122 . The starting end 300 s of the insulating film 300 extends beyond the tail end 120 e of the electrode assembly 120 .

[0044] In the above technical solution, by setting the starting end 300s of the insulating film 300 behind the tail end 120e of the electrode assembly 120 along the winding direction D, the overlapping part of the two layers of insulating film 300 is located at a position where the thickness of the outer circle of the electrode assembly is thinner, which can reduce the diameter range of the electrode assembly and optimize the cylindricity of the electrode assembly.

[0045] The projection point P forms a first line L1 with the trailing end 121e of the first electrode sheet 121, and the projection point P forms a second line L2 with the starting end 122s of the second electrode sheet 122. The trailing end 122e of the second electrode sheet 122, the trailing end 120e of the electrode assembly 120, and the starting end 300s and the trailing end 300e of the insulating film 300 are located within the region between the first line L1 and the second line L2 along the winding direction D. That is, in the winding direction D, the trailing end 120e of the electrode assembly 120, the trailing end 122e of the second electrode sheet 122, and the starting end 300s and the trailing end 300e of the insulating film 300 do not extend beyond the starting end 122s of the second electrode sheet 122. The area between the tail end 121e of the first pole piece 121 and the starting end 122s of the second pole piece 122 (corresponding to the area between the first line L1 and the second line L2) is usually the area with the thinnest thickness of the outer circle of the electrode assembly. By arranging the tail end 122e of the second pole piece 122, the tail end 120e of the electrode assembly 120, and the insulating film 300, the starting end 300s and the tail end 300e in this area, the diameter range of the electrode assembly can be reduced and the cylindricity of the electrode assembly can be optimized.

[0046] In some embodiments, as Figure 4As shown, along the winding direction D, the tail end 300e of the insulating film 300 extends beyond the tail end 120e of the electrode assembly 120. Thus, the overlapping portion of the two insulating films 300 is located at a location where the thickness of the outer ring of the electrode assembly is relatively thin, that is, between the tail end 120e of the electrode assembly 120 and the starting end 122s of the second electrode sheet 122. This effectively reduces the diameter range of the electrode assembly and optimizes the cylindricity of the electrode assembly.

[0047] In some embodiments, in the direction opposite to the winding direction D, the starting end 122s of the second pole piece 122 extends beyond the starting end 121s of the first pole piece 121 by 1 to 2 turns. If the starting end 122s of the second pole piece 122 extends beyond the starting end 121s of the first pole piece 121 by less than 1 turn, lithium plating may not be effectively avoided. If the starting end 122s of the second pole piece 122 extends beyond the starting end 121s of the first pole piece 121 by more than 2 turns, the energy density of the battery may be adversely affected. Therefore, configuring the starting end 122s of the second pole piece 122 to extend beyond the starting end 121s of the first pole piece 121 by 1 to 2 turns can avoid lithium plating without excessively affecting the energy density.

[0048] In addition, the projection point P and the starting end 121s of the first pole piece 121 form a third line L3. Along the winding direction D, the angle formed by the third line L3 and the second line L2 is in the range of 170°-190°, preferably 180°. In this embodiment, in the opposite direction of the winding direction D, the starting end 122s of the second pole piece 122 extends about 1.5 turns beyond the starting end 121s of the first pole piece 121, so that the angle formed by the third line L3 and the second line L2 is in the range of about 180°. The tail end 121e of the first pole piece 121 is located in the area of ​​the angle formed by the third line L3 and the second line L2 ( Figure 4 Along the winding direction D, the angle formed by the first line L1 and the second line L2 is in the range of 80°-90°, preferably 90°. In some embodiments, the arc length between the first line L1 and the second line L2 is less than or equal to 35 mm (corresponding to the arc length within 90° of the circumference of the electrode assembly). In some embodiments, the arc length between the first line L1 and the second line L2 can be equal to the diameter of the electrode assembly × 3.14 / 4, that is, the arc length within 90° of the circumference of the electrode assembly. In some embodiments, for 46 series cylindrical batteries, the diameter of the electrode assembly can be approximately 44.7 mm.

[0049] The projection point P and the tail end 122e of the second electrode sheet 122 form a fourth line L4. The angle formed between the first line L1 and the fourth line L4 along the winding direction D is A1, where 0°<A1≤30°. In some embodiments, the arc length of the segment corresponding to the angle A1 ranges from 3 mm to 11.7 mm. In some embodiments, the arc length of the segment corresponding to the angle A1 can be equal to the diameter of the electrode assembly × 3.14 / 12, that is, the arc length within 30° of the circumference of the electrode assembly.

[0050] The projection point P and the tail end 1220e of the electrode assembly 120 form a fifth line L5. The angle formed by the fourth line L4 and the fifth line L5 along the winding direction D is A2. In some embodiments, 5°<A2<160°. Preferably, 0°<A2≤30°. In some embodiments, the arc length of the segment corresponding to the angle A1 ranges from 3 mm to 11.7 mm. In some embodiments, the arc length of the segment corresponding to the angle A2 can be equal to the diameter of the electrode assembly × 3.14 / 12.

[0051] The projection point P and the starting end 300s of the insulating film 300 form a sixth line L6. The angle formed by the fifth line L5 and the sixth line L6 along the winding direction D is A3, 7.7°≤A3≤30°. In some embodiments, the arc length of the segment corresponding to the angle A3 is greater than 3 mm.

[0052] The projection point P and the tail end 300e of the insulating film 300 form a seventh line L7. The angle formed between the sixth line L6 and the seventh line L7 along the winding direction D is A4, where 0°<A4≤30°. In some embodiments, the arc length of the segment corresponding to angle A4 ranges from 3 mm to 11.7 mm. In some embodiments, the arc length of the segment corresponding to angle A4 can be equal to the diameter of the electrode assembly × 3.14 / 12.

[0053] By designing the angle A1-A4 between the first connecting line L1 and the second connecting line L2, the thickness variation caused by the tail section 121e of the first pole piece 121, the tail section 122e of the second pole piece 122, and the starting end 300s and the tail end 300e of the insulating film 300 can be uniform, thereby further improving the cylindricity of the electrode assembly.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A secondary battery, characterized in that: include: An electrode assembly, comprising a first electrode sheet, a first diaphragm, a second electrode sheet, and a second diaphragm, which are sequentially stacked and then wound to form the electrode assembly; an insulating film for fixing the tail end of the electrode assembly; In which, along the winding direction of the electrode assembly, the insulating film surrounds the electrode assembly at least one circle, the tail end of the first diaphragm and the end exceeding the tail end of the second diaphragm constitute the tail end of the electrode assembly, and the tail end of the second pole piece exceeds the tail end of the first pole piece, the tail end of the electrode assembly exceeds the tail end of the second pole piece, and the starting end of the insulating film exceeds the tail end of the electrode assembly.

2. The secondary battery according to claim 1, wherein In the opposite direction of the winding direction of the electrode assembly, the starting end of the second pole piece exceeds the starting end of the first pole piece, In a cross section perpendicular to the winding center line of the electrode assembly, the orthographic projection of the winding center line on the cross section forms a projection point, the projection point and the trailing end of the first electrode sheet form a first connecting line, and the projection point and the starting end of the second electrode sheet form a second connecting line, The tail end of the second pole piece, the tail end of the electrode assembly, and the starting end and tail end of the insulating film are located in the area between the first connecting line and the second connecting line along the winding direction.

3. The secondary battery according to claim 1, wherein In the winding direction of the electrode assembly, the tail end of the insulating film exceeds the tail end of the electrode assembly.

4. The secondary battery according to claim 2, wherein: The projection point and the starting end of the first pole piece form a third connecting line, and the angle formed by the third connecting line along the winding direction and the second connecting line is in the range of 170°-190°. The tail end of the first pole piece is located in the area between the third connecting line and the second connecting line along the winding direction; or, In the opposite direction of the winding direction of the electrode assembly, the starting end of the second pole piece exceeds the starting end of the first pole piece by 1 to 2 turns; or, The angle formed by the first connecting line and the second connecting line along the winding direction is in a range of 80°-90°.

5. The secondary battery according to claim 2, wherein The projection point and the tail end of the second pole piece form a fourth connecting line, and the angle formed by the first connecting line and the fourth connecting line along the winding direction is A1, 0°<A1≤30°.

6. The secondary battery according to claim 2, wherein: The projection point and the tail end of the second pole piece form a fourth line, the projection point and the tail end of the electrode assembly form a fifth line, and the angle formed by the fourth line and the fifth line along the winding direction is A2, 0°<A2≤30°.

7. The secondary battery according to claim 2, characterized in that The projection point and the tail end of the electrode assembly form a fifth line, the projection point and the starting end of the insulating film form a sixth line, and the angle formed by the fifth line and the sixth line along the winding direction is A3, 7.7°≤A3≤30°.

8. The secondary battery according to claim 2, wherein The projection point and the starting end of the insulating film form a sixth connecting line, and the projection point and the ending end of the insulating film form a seventh connecting line. The angle formed by the sixth connecting line and the seventh connecting line along the winding direction is A4, 0°<A4≤30°.

9. A battery pack, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 8.

10. An electronic device, characterized in that: Comprising at least one of the batteries described in claim 9.

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