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 a first pole piece, a first diaphragm, a second pole piece and a second diaphragm which are sequentially laminated and then wound to form an electrode assembly; in the winding direction of the electrode assembly, the ending end of the second pole piece exceeds the ending end of the first pole piece, the ending end of the electrode assembly is formed by the end, exceeding the ending end of the first diaphragm and the ending end of the second diaphragm, of the electrode assembly, and the ending end of the electrode assembly exceeds the ending end of the second pole piece; and at least 1.5 circles are wound on the outer ring of the electrode assembly from the ending end of the second pole piece. According to the embodiment of the invention, the lithium separation risk of the outermost ring of the electrode assembly of the cylindrical battery can be at least reduced.

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 diaphragm, a negative electrode sheet, and a second diaphragm, which are stacked in sequence and wound into an electrode assembly, and 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, so as to at least reduce the risk of lithium plating in the outermost circle of the electrode assembly of the secondary battery.

[0004] To achieve the above-mentioned purpose, an embodiment of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including: 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; in the winding direction of the electrode assembly, the tail end of the second electrode sheet exceeds the tail end of the first electrode sheet, and the tail end of the first diaphragm and the end where the tail end of the second diaphragm exceeds constitute the tail end of the electrode assembly, wherein the tail end of the electrode assembly exceeds the tail end of the second electrode sheet, and is wound at least 1.5 times more on the outer circle of the electrode assembly from the tail end of the second electrode sheet.

[0005] In some embodiments, the tail end of the electrode assembly is wound around the outer ring of the electrode assembly for no more than 2 turns.

[0006] In some embodiments, the electrode assembly has a winding center hole. In a cross section perpendicular to the winding center line of the electrode assembly, the tail end of the electrode assembly is connected to the projection point of the winding center line on the cross section to form a first reference line. The second reference line passes through the projection point and is perpendicular to the first reference line. The starting end of the second pole piece and the tail end of the electrode assembly are located on opposite sides of the second reference line.

[0007] In some embodiments, the starting end of the second electrode piece is connected to the projection point to form a first line, and the ending end of the electrode assembly is connected to the starting end of the second electrode piece to form a second line, wherein the ending end of the electrode assembly exceeds the first line, and the angle between the first line and the second line is in the range of 0 to 30 degrees.

[0008] In some embodiments, in the winding direction of the electrode assembly, the starting end of the second pole piece exceeds the starting end of the first pole piece, the starting end of the second pole piece is connected to the projection point to form a first line, and the starting end of the first pole piece is not located on the extension line of the first line.

[0009] In some embodiments, in a cross section perpendicular to the winding centerline of the electrode assembly, the starting end of the second pole piece is connected to the projection point to form a second line, and the starting end of the first pole piece is connected to the projection point of the winding centerline on the cross section to form a third line, wherein the angle between the third line and the first line is in the range of 30 to 120 degrees.

[0010] In some embodiments, in a cross section perpendicular to the winding center line of the electrode assembly, the tail end of the first pole piece is connected to the projection point of the winding center line on the cross section to form a fourth line, and the tail end of the second pole piece is connected to the projection point to form a fifth line, wherein the angle between the fourth line and the fifth line is in the range of 30 to 120 degrees.

[0011] In some embodiments, the secondary battery further comprises an insulating film for fixing the tail end of the electrode assembly, wherein a length of the insulating film in the winding direction of the electrode assembly is no greater than 0.1 times a circumference of the outermost circle of the electrode assembly.

[0012] In some embodiments, the first electrode piece is a positive electrode piece, the second electrode piece is a negative electrode piece, and the secondary battery is a cylindrical battery.

[0013] An embodiment of the present application further provides a battery pack, which includes any one of the above-mentioned secondary batteries.

[0014] An embodiment of the present application further provides an electronic device, which includes at least one of any one of the above-mentioned secondary batteries and any one of the above-mentioned battery packs.

[0015] The beneficial technical effects of the utility model are:

[0016] By increasing the winding length of the first diaphragm and the second diaphragm, so that the first diaphragm and the second diaphragm are wound at least 1.5 more times at the outermost circle than the tail end of the second pole piece, the gap between the first pole piece and the second pole piece at the outermost circle can be reduced, so that the first pole piece and the second pole piece at the outermost circle are more closely attached, which can reduce the risk of lithium deposition at the outermost circle. In addition, by increasing the length and mass of the first diaphragm and the second diaphragm, the liquid absorption of the electrode assembly can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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 paying any creative work.

[0018] Figure 1 A schematic diagram showing a case where the electronic device according to an embodiment of the present application is a vehicle.

[0019] Figure 2 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0020] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0021] Figure 4A 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.

[0022] Figure 4B A further detailed configuration of an electrode assembly of a secondary battery according to an embodiment of the present application is shown.

[0023] Figure 5A and Figure 5B They are respectively partial enlarged schematic diagrams of the structures at the tail ends of the first diaphragm and the second diaphragm in the secondary battery according to another embodiment of the present application. DETAILED DESCRIPTION

[0024] 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.

[0025] The embodiments of the present application will be described in detail below. In the full text of the present application specification, the same or similar components and components with the same or similar functions are represented by similar reference numerals. The embodiments of the accompanying drawings described herein are illustrative, graphical, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0026] As used herein, the terms "substantially," "substantially," "essentially," and "about" are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms may refer to instances where the event or circumstance occurred exactly as well as instances where the event or circumstance occurred very approximately.

[0027] 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 derivative terms (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 direction.

[0028] For convenience of description, “first”, “second”, “third”, etc. may be used herein to distinguish different components in one figure or a series of figures. “First”, “second”, “third”, etc. are not intended to describe the corresponding components.

[0029] See also Figure 1 For the convenience of explanation, the following embodiments are described by taking the electronic device as a vehicle 1000. However, it is not difficult to understand that the electronic device provided by the present application is not limited to a vehicle, and the electronic device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like.

[0030] The vehicle 1000 is provided with a battery pack 1002 inside, and the battery pack 1002 can be arranged at the bottom of the vehicle body 1001 (such as 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 A secondary battery 100) and a housing for accommodating a plurality of cylindrical batteries.

[0031] 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 jointly accommodate the electrode assembly 120 and the electrolyte. The material of the housing 200 may be any one of a variety of available materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The housing 200 may be cylindrical and define a housing cavity, and the electrode assembly 120 is disposed in the housing cavity. The diameter of the housing 200 may be determined according to the specific size of the electrode assembly 120, such as 18mm, 21mm, 46mm, etc. In some embodiments, the secondary battery 100 may be a 4680 cylindrical battery (diameter 46mm, height 80mm), the secondary battery 100 may be a 4695 cylindrical battery (diameter 46mm, height 95mm), or the secondary battery 100 may be a 46120 cylindrical battery (diameter 46mm, height 120mm).

[0032] The housing 200 can be connected to the negative electrode of the electrode assembly 120. The housing 200 may have a mounting opening 205 at one end along the height direction (direction Z), and the cover plate 202 is disposed at the mounting opening 205 and blocks the accommodating cavity. The secondary battery 100 may also have a pole 208 at one end relative to the cover plate 202, and the pole 208 may be connected to the positive electrode of the electrode assembly 120. It should be understood that the pole 208 and the housing 200 are in an insulated matching state to avoid battery short circuit.

[0033] See also Figure 3 , the position of the housing 200 adjacent to the mounting opening 205 is also provided with a crimping portion 203 protruding inward. Along the height direction of the secondary battery 100, the electrode assembly 120 is arranged between the end wall 111 and the crimping portion 203, and the crimping portion 203 can limit the axial movement (movement in the height direction) of the electrode assembly 120 between the end wall 111 of the housing 200 and the crimping portion 203. A weak portion may be provided on the cover plate 202. When the battery has thermal runaway, the high-temperature and high-pressure emissions inside can be discharged to the outside from the bottom of the battery, breaking through the weak portion on the cover plate 202, thereby achieving good drainage of the emissions.

[0034] 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) which are sequentially stacked and wound. Figure 4AAs described above, the first electrode sheet, the first diaphragm, the second electrode sheet and the second diaphragm may be wound around the winding center line Lc. In addition, the electrode assembly 120 also has a winding center hole 120c. The electrode assembly 120 is provided with a positive electrode tab and a negative electrode tab at both ends of the height direction of the secondary battery 100, respectively. In some embodiments, the positive electrode tab faces the end wall 111 and is electrically connected to the pole 208 so that the pole 208 is positively charged; the negative electrode tab faces the mounting port 205, and the outer shell 200 is electrically connected to the negative electrode tab so as to be negatively charged. However, in other embodiments, the negative electrode tab may be connected to the pole 208, and the positive electrode tab may be connected to the outer shell 200.

[0035] Figure 4A 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. Figure 4A , 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, and the first electrode sheet 121, the first separator 141, the second electrode sheet 122, and the second separator 142 are sequentially stacked and wound to form the electrode assembly 120. In addition, the secondary battery may further include an electrolyte, and the electrolyte may be located between the first electrode sheet 121, the first separator 141, the second electrode sheet 122, and the separator. 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 positive electrode plate may include a positive electrode current collector and a positive electrode active material layer coated on both sides of the positive electrode current collector. The portion of the positive electrode current collector not coated with the positive electrode active material layer constitutes a positive electrode tab. The negative electrode plate may include a negative electrode current collector and a negative electrode active material layer coated on both sides of the negative electrode current collector. The portion of the negative electrode current collector not coated with the negative electrode active material layer constitutes a negative electrode tab. Taking a lithium-ion battery as an example, the material of the positive electrode current collector may be aluminum, the positive electrode active material layer may include a positive electrode active material, and the positive electrode active material may be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc. The material of the negative electrode current collector may be copper, the negative electrode active material layer may include a negative electrode active material, and the negative electrode active material may be carbon or silicon, etc. In some embodiments, the material of the first diaphragm 141 and the second diaphragm 142 may be, for example, PP (polypropylene) or PE (polyethylene).

[0037] By coating a positive electrode active material layer on the positive electrode plate, 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 also the process of battery charging.

[0038] See also Figure 4A In the winding direction 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 separated from the positive electrode active material layer of the first electrode sheet 121 (positive electrode sheet) can be smoothly embedded in the negative electrode active material layer of the second electrode sheet 122 (negative electrode sheet), thereby avoiding the lithium deposition phenomenon on the negative electrode sheet at the tail end.

[0039] In some embodiments, in the winding direction of the electrode assembly 120, the starting end 122s of the second electrode sheet 122 exceeds the starting end 121s of the first electrode sheet 121. By configuring the starting end 122s of the second electrode sheet 122 to exceed the starting end 121s of the first electrode sheet 121. Thus, the lithium ions separated from the positive electrode active material layer of the first electrode sheet 121 (positive electrode sheet) can be smoothly embedded in the negative electrode active material layer of the second electrode sheet 122 (negative electrode sheet), thereby avoiding the lithium deposition phenomenon on the negative electrode sheet at the starting end. However, the outermost circle of the wound electrode assembly 120 is still prone to lithium deposition.

[0040] According to an embodiment of the present application, the end 141e of the first diaphragm 141 and the end 142e of the second diaphragm 142 that protrudes outward constitute the end 120e of the electrode assembly 120. Figure 4A In the illustrated embodiment, the tail end 141e of the first diaphragm 141 and the tail end 142e of the second diaphragm 142 are substantially aligned. It should be understood that alignment in the present application means that the tail ends 141e, 142e of the first diaphragm 141 and the second diaphragm 142 differ by 5 mm. In such an embodiment, the ends of the tail ends 141e, 142e of the first diaphragm 141 and the second diaphragm 142 that extend beyond constitute the tail end 120e of the electrode assembly 120. In the case where the tail ends 141e, 142e of the first diaphragm 141 and the second diaphragm 142 differ by 0 mm, the tail ends 141e, 142e of the first diaphragm 141 and the second diaphragm 142 can be used together as the tail end 120e of the electrode assembly 120.

[0041] 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 5B The following are partial enlarged schematic diagrams of the structures at the end of the first diaphragm and the second diaphragm 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. Figure 5B As shown, the tail end 141e of the first diaphragm 141 exceeds the tail end 142e of the second diaphragm 142, and in this embodiment, the tail end 141e of the first diaphragm 141 is the outermost end and constitutes the tail end 120e of the electrode assembly.

[0042] Return to reference Figure 4A As shown, the tail end 120e of the electrode assembly 120 exceeds the tail end 122e of the second pole piece 122, and is wound at least 1.5 more times on the outer circle of the electrode assembly 120 from the tail end 122e of the second pole piece 122. By increasing the winding length of the first diaphragm 141 and the second diaphragm 142, the first diaphragm 141 and the second diaphragm 142 are wound at least 1.5 more times on the outermost circle than the tail end 122e of the second pole piece 122, which can reduce the gap between the first pole piece 121 and the second pole piece 122 on the outermost circle, so that the first pole piece 121 and the second pole piece 122 on the outermost circle are more closely attached, which can reduce the risk of lithium deposition on the outermost circle. In addition, by increasing the length and mass of the first diaphragm 141 and the second diaphragm 142, the liquid absorption of the electrode assembly 120 for absorbing electrolyte can be increased.

[0043] For cylindrical batteries, the problem of difficulty in electrolyte infiltration is particularly obvious because of the high group margin of cylindrical batteries. In order to improve the energy density, the electrode assembly of the cylindrical battery will be wound very tightly, so that the spacing between the pole pieces is small. When the electrolyte injection amount is limited, the amount of liquid retained by the electrode assembly is limited. In the embodiment of the present application, the first diaphragm 141 and the second diaphragm 142 are wound at least 1.5 turns more than the tail end 122e of the second pole piece 122 in the outermost circle. Since the multi-wound first diaphragm 141 and second diaphragm 142 can increase the liquid absorption of the electrode assembly 120, the problem of difficulty in electrolyte infiltration and limited liquid retention of the cylindrical battery can be solved, and the tension of the electrode assembly of the cylindrical battery in the outer circle can be relieved to maintain the stability of the electrode assembly of the cylindrical battery.

[0044] In some embodiments, the tail end 120e of the electrode assembly 120 is wound around the outer circle of the electrode assembly 120 by no more than 2 turns. That is, the tail end 120e of the electrode assembly 120 is wound around the outer circle by 1.5 to 2 turns beyond the tail end 122e of the second pole piece 122. Since winding too much will affect the energy density of the secondary battery, winding the tail end 120e of the electrode assembly 120 by 1.5 to 2 turns can reduce the risk of lithium deposition in the outermost circle and increase liquid absorption without affecting the energy density.

[0045] It should be understood that the wound electrode assembly 120 has a winding center line Lc extending in the direction Z (see Figure 3 ), Figure 4AThe 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 4A 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.

[0046] The tail end 120e of the electrode assembly 120 is connected to the projection point P to form a first reference line La. The second reference line Lb is a straight line passing through the projection point P and perpendicular to the first reference line La. The starting end 122s of the second pole piece 122 and the tail end 120e of the electrode assembly 120 can be located on opposite sides of the second reference line Lb. In other words, the starting end 122s of the second pole piece 122 and the tail end 120e of the electrode assembly 120 can be basically arranged relative to the center of the winding center hole 120c. It should be understood that since the starting end 122s of the second pole piece 122 exceeds the starting end 121s of the first pole piece 121 on the inner side of the electrode assembly 120, this will cause the electrode assembly 120 to have a winding ellipticity to a certain extent. By configuring the tail end 120e of the electrode assembly 120 to be opposite to the starting end 122s of the second electrode sheet 122, the winding ellipticity of the electrode assembly 120 can be reduced, that is, the circularity of the winding of the electrode assembly 120 can be increased.

[0047] Figure 4B Detailed configuration of an electrode assembly of a secondary battery according to an embodiment of the present application is shown. Figure 4B As shown, in addition, the starting end 122s of the second pole piece 122 is connected to the projection point P to form a first connection line L1. The starting end 122s of the second pole piece 122 is connected to the tail end 120e of the electrode assembly 120 to form a second connection line L2. The tail end 120e of the electrode assembly 120 may exceed the first connection line L1 in the winding direction of the electrode assembly 120. In some embodiments, the angle A1 between the first connection line L1 and the second connection line L2 may be in the range of 0 to 30 degrees. In some embodiments, the angle A1 between the first connection line L1 and the second connection line L2 may be 0, that is, the tail end 120e of the electrode assembly 120 and the second connection line L2 of the starting end 122s of the second pole piece 122 may pass through the projection point P. By means of this configuration of the tail end 120e of the electrode assembly 120 and the starting end 122s of the second pole piece 122, the winding ellipticity of the electrode assembly 120 may be further reduced, and the circularity of the winding may be maintained.

[0048] In some embodiments, any two of the starting end 121s of the first pole piece 121, the ending end 121e of the first pole piece 121, the starting end 122s of the second pole piece 122, and the ending end 122e of the second pole piece 122 are misaligned and misaligned with each other. Specifically, as described above, the starting end 122s of the second pole piece 122 is connected to the projection point P to form a first line L1. In some embodiments, the starting end 121s of the first pole piece 121 is not located on the extension line of the first line (L1). This can be referred to as the starting end 121s of the first pole piece 121 and the starting end 122s of the second pole piece 122 being misaligned and misaligned with each other, and the ending end 120e of the electrode assembly 120 is arranged relative to the starting end 122s of the second pole piece 122, which can further reduce the winding ellipticity of the electrode assembly 120 and maintain the circularity of the winding.

[0049] In some embodiments, the starting end 121s of the first pole piece 121 is connected to the projection point P to form a three-line L3. The angle A2 between the third line L3 and the first line L1 can be in the range of 30 to 120 degrees. In other words, the starting end 121s of the first pole piece 121 and the starting end 122s of the second pole piece 122 are misaligned with each other, and the misalignment angle is in the range of 30 to 120 degrees. By misaligning the starting end 121s of the first pole piece 121 and the starting end 122s of the second pole piece 122 with each other, and coordinating the tail end 120e of the electrode assembly 120 with the starting end 122s of the second pole piece 122, the winding ellipticity of the electrode assembly 120 can be further reduced to maintain the circularity of the winding.

[0050] In some embodiments, the tail end 121e of the first pole piece 121 is connected to the projection point P to form a fourth line L4, and the tail end 122e of the second pole piece 122 may not be located on the fourth line L4, that is, the tail end 121e of the first pole piece 121 and the tail end 122e of the second pole piece 122 are also misaligned and misaligned with each other. The tail end 122e of the second pole piece 122 is connected to the projection point P to form a fifth line L5. In some embodiments, the angle A3 between the fourth line L4 and the fifth line L5 can be in the range of 30 to 120 degrees. That is to say, the tail end 121e of the first pole piece 121 and the tail end 122e of the second pole piece 122 are misaligned and misaligned with each other, and the misalignment angle is in the range of 30 to 120 degrees. By staggering the starting end 121s of the first pole piece 121, the starting end 122s of the second pole piece 122, the tail end 121e of the first pole piece 121 and the tail end 122e of the second pole piece 122, and arranging the tail end 120e of the electrode assembly 120 relative to the starting end 122s of the second pole piece 122, the winding ellipticity of the electrode assembly 120 can be further reduced and the circularity of the winding can be maintained.

[0051] In some embodiments, the secondary battery may further include an insulating film 300, which may be used to fix the tail end of the electrode assembly to maintain the tightness of the winding of the electrode assembly 120. In some embodiments, the insulating film 300 may be synthesized, for example, from PP, PE, PET (polyethylene terephthalate), PVC (Polyvinylchloride) or other high molecular polymer materials.

[0052] In the present embodiment, the insulating film 300 extends across the tail end 120e of the electrode assembly 120 and covers a portion of the electrode assembly 120 in the winding direction of the electrode assembly 120. In some embodiments, the length of the insulating film 300 in the winding direction of the electrode assembly 120 is not greater than 0.1 times the circumference of the outermost circle of the electrode assembly 120, that is, the length of the section of the electrode assembly 120 covered by the insulating film 300 is not greater than 0.1 times the circumference of the outermost circle of the electrode assembly 120. Figure 4A As shown, the outermost circle of the electrode assembly 120 can be circular, and the outermost circle of the electrode assembly 120 has a radius of the distance between the projection point P and the tail end 120e of the electrode assembly 120, and the circumference of the outermost circle of the electrode assembly 120 can be equal to 2π×the distance between the projection point P and the tail end 120e.

[0053] The end ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 may be covered by the insulating film 300 (eg Figure 5A and Figure 5B ). Figure 4A As shown, similar to the tail end 120e of the electrode assembly 120, the insulating film 300 and the starting end 122s of the second pole piece 122 are located on the opposite side of the second reference line Lb. By configuring the tail end 120e of the electrode assembly 120 to be opposite to the starting end 122s of the second pole piece 122, and combining with the insulating film 300 being designed to cover a smaller section of the electrode assembly 120, the winding ellipticity of the electrode assembly 120 can be further improved, and the circularity of the winding of the electrode assembly 120 can be increased.

[0054] The above describes the embodiments of the present application with the first electrode piece being a positive electrode piece and the second electrode piece being a negative electrode piece. However, it should be understood that in other embodiments, the first electrode piece may be a negative electrode piece and the second electrode piece may be a positive electrode piece.

[0055] The above description is only the preferred embodiment of the utility model, and is not intended to limit the utility model. For those skilled in the art, the utility model can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A secondary battery, characterized in that: An electrode assembly is included, wherein the electrode assembly includes: The first pole piece, the first diaphragm, the second pole piece and the second diaphragm are sequentially stacked and then wound to form the electrode assembly; In the winding direction of the electrode assembly, the tail end of the second pole sheet exceeds the tail end of the first pole sheet, and the tail end of the first diaphragm and the end beyond the tail end of the second diaphragm constitute the tail end of the electrode assembly, wherein the tail end of the electrode assembly exceeds the tail end of the second pole sheet, and is wound at least 1.5 turns more on the outer circle of the electrode assembly from the tail end of the second pole sheet.

2. The secondary battery according to claim 1, characterized in that: The tail end of the electrode assembly is wound around the outer ring of the electrode assembly for no more than 2 turns.

3. The secondary battery according to claim 1, characterized in that: in, The electrode assembly has a winding center hole. In a cross section perpendicular to the winding center line of the electrode assembly, the tail end of the electrode assembly is connected to the projection point of the winding center line on the cross section to form a first reference line. The second reference line passes through the projection point and is perpendicular to the first reference line. The starting end of the second pole piece and the tail end of the electrode assembly are located on opposite sides of the second reference line.

4. The secondary battery according to claim 3, characterized in that: The starting end of the second pole piece is connected to the projection point to form a first line, and the tail end of the electrode assembly is connected to the starting end of the second pole piece to form a second line, wherein the tail end of the electrode assembly exceeds the first line, and the angle between the first line and the second line is in the range of 0 to 30 degrees.

5. The secondary battery according to claim 3, characterized in that: In the winding direction of the electrode assembly, the starting end of the second pole piece exceeds the starting end of the first pole piece, The starting end of the second pole piece is connected to the projection point to form a first connecting line, and the starting end of the first pole piece is not located on an extension line of the first connecting line.

6. The secondary battery according to claim 4, characterized in that: In the cross section perpendicular to the winding center line of the electrode assembly, the starting end of the first pole piece is connected to the projection point to form a third line, wherein an angle between the third line and the first line is in the range of 30 to 120 degrees.

7. The secondary battery according to claim 4, characterized in that: In the cross section perpendicular to the winding center line of the electrode assembly, the tail end of the first pole piece is connected to the projection point to form a fourth line, and the tail end of the second pole piece is connected to the projection point to form a fifth line, wherein the angle between the fourth line and the fifth line is in the range of 30 to 120 degrees.

8. The secondary battery according to claim 1, characterized in that: Also includes: An insulating film is used to fix the tail end of the electrode assembly, wherein the length of the insulating film in the winding direction of the electrode assembly is not greater than 0.1 times the circumference of the outermost circle of the electrode assembly.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The first pole piece is a positive pole piece, the second pole piece is a negative pole piece, and the secondary battery is a cylindrical battery.

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

11. An electronic device, characterized in that: The invention comprises at least one of the secondary battery according to any one of claims 1 to 9 and the battery pack according to claim 10.

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