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; 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, in the section perpendicular to the winding center line of the electrode assembly, the ending end of the first pole piece is connected with the projection point of the winding center line on the section to form a first connecting line, and the ending end of the second pole piece is connected with the projection point to form a second connecting line. The included angle between the first connecting line and the second connecting line is within the range of 80-100 degrees or within the range of 160-190 degrees. According to the embodiment of the invention, at least the pressure on the winding center hole can be reduced, the collapse of the winding center hole is avoided, and the life cycle of the secondary battery is prolonged.

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, which can at least reduce the pressure on the winding center hole, avoid collapse of the winding center hole, and extend the life cycle of the secondary battery.

[0004] To achieve the above-mentioned purpose, an embodiment of the present application provides a secondary battery, the secondary battery comprising 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 around a winding center line to form an electrode assembly; wherein, 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 in a cross section perpendicular to the winding center line of the electrode assembly, the tail end of the first electrode sheet is connected to the projection point of the winding center line on the cross section to form a first connecting line, and the tail end of the second electrode sheet is connected to the projection point to form a second connecting line, and the angle between the first connecting line and the second connecting line is in the range of 80°-100°, or in the range of 160°-190°. The angle (A1) between the first connecting line and the second connecting line is the angle formed by the first connecting line from the winding tail direction (that is, the winding direction from the tail end of the first electrode sheet to the tail end of the second electrode sheet) and the second connecting line.

[0005] In some embodiments, the included angle between the first connecting line and the second connecting line is in the range of 85°-95°, or in the range of 175°-185°.

[0006] In some embodiments, in the direction opposite to the winding direction of the electrode assembly, the starting end of the second pole piece exceeds the starting end of the first pole piece and exceeds the starting end of the first pole piece by at least one turn.

[0007] In some embodiments, the starting end of the second pole piece exceeds the starting end of the first pole piece by no more than 2 turns.

[0008] In some embodiments, in a direction opposite to the winding direction of the electrode assembly and toward the winding centerline, the first diaphragm and the second diaphragm extend beyond the starting end of the second pole piece in the inner circle of the electrode assembly, and the starting end of the first diaphragm and one end where the starting end of the second diaphragm extends beyond the starting end of the second pole piece by 1 to 2 circles.

[0009] In some embodiments, in the winding direction of the electrode assembly, the first diaphragm and the second diaphragm extend beyond the tail end of the second pole piece at the outer circle of the electrode assembly, and the tail end of the first diaphragm and one end of the tail end of the second diaphragm extend beyond the tail end of the second pole piece by 1.5 to 2 circles.

[0010] In some embodiments, the starting end of the first pole piece is connected to the projection point to form a third line, the starting end of the second pole piece is connected to the projection point to form a fourth line, and the angle between the third line and the fourth line is in the range of 30 to 120 degrees.

[0011] In some embodiments, the first connection line, the second connection line, the third connection line and the fourth connection line do not overlap with each other.

[0012] In some embodiments, the secondary battery further includes: an insulating film for fixing the tail end of the electrode assembly, wherein the insulating film surrounds the electrode assembly at least once in the winding direction of the electrode assembly.

[0013] 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.

[0014] An embodiment of the present application further provides a battery pack, which includes any one of the above-mentioned secondary batteries.

[0015] 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.

[0016] The beneficial technical effects of the utility model are:

[0017] By configuring the tail end of the second pole piece to exceed the tail end of the first pole piece and to wind at an angle within the range of 160°-190°, the pressure on the winding center hole position can be reduced, the pressure on the winding center hole can be close to the minimum, the winding center hole can be avoided from collapsing, and the life cycle of the secondary battery can be extended; or, the winding angle of the tail end of the second pole piece can be configured to be 80°-100°, thereby reducing the pressure on the winding center hole to an appropriate degree to avoid collapse, and at the same time avoiding material waste. By winding the starting end of the second pole piece at least one more circle on the inner circle of the electrode assembly from the starting end of the first pole piece, so that the second pole piece has at least one complete circle as support, the possibility of collapse at the center hole due to the influence of expansion after cycling is reduced, thereby avoiding problems such as failure of the electrode assembly, lithium deposition, short circuit, etc. caused by collapse, and extending the life cycle of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 A schematic diagram showing a case where the electronic device according to an embodiment of the present application is a vehicle.

[0020] Figure 2 A perspective view of a secondary battery according to an embodiment of the present application is shown.

[0021] Figure 3 A cross-sectional view of a secondary battery according to an embodiment of the present application is shown.

[0022] Figure 4 A schematic diagram of the structure of an existing electrode assembly after cycling is shown.

[0023] Figure 5 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.

[0024] FIG. 6A to FIG. 6D It shows the situation where the included angle between the first connecting line and the second connecting line is of different angle values.

[0025] Fig. 6E A schematic diagram of the structure of the electrode assembly of an embodiment of the present application after cycling is shown.

[0026] Fig. 7A It is a simplified schematic diagram of the starting points of the first and second pole pieces in the inner circle of an electrode assembly of a general secondary battery.

[0027] Figure 7B It is a simplified schematic diagram of the starting points of the first pole piece and the second pole piece of the inner circle of the electrode assembly according to an embodiment of the present application.

[0028] Fig. 8A and Figure 8B 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

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] For ease of description, "first", "second", "third", etc. may be used herein to distinguish different components of a figure or a series of figures. "First", "second", "third", etc. are not intended to describe corresponding components. In addition, the embodiments and features described in the embodiments of the present application may be combined with each other in the absence of conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] See also Figure 1For 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.

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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 5 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.

[0040] The first electrode sheet and the second electrode sheet may be a positive electrode sheet and a negative electrode sheet, respectively. The positive electrode sheet may 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 a positive electrode tab. The negative electrode sheet may 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 a negative electrode tab. Taking a lithium-ion battery as an example, the material of the positive current collector may be aluminum, the positive active material layer may include a positive active material, and the positive active material may be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc. The material of the negative current collector may be copper, the negative active material layer may include a negative active material, and the negative 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).

[0041] 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.

[0042] The electrode assembly 120 may be provided with a positive electrode tab and a negative electrode tab at both ends of the height direction of the secondary battery 100. 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 housing 200 is electrically connected to the negative electrode tab so that it is 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 housing 200.

[0043] See also Figure 4 For the electrode assembly 120' in a common secondary battery, especially for the current cylindrical battery, due to the large number of winding layers and the addition of silicon in the chemical system of the secondary battery, the radial expansion of the electrode assembly 120' will be aggravated. After the cycle, the rolling start position of the electrode assembly 120' will be affected by the expansion, and a collapse 125 will occur at the center hole 120c', which will lead to failure of the electrode assembly 120', lithium deposition, short circuit and other problems.

[0044] Figure 5 1 is a cross-sectional view of the electrode assembly of the secondary battery according to an embodiment of the present application in a cross section perpendicular to the winding center line. 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 5 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 5 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.

[0045] See also Figure 5 , 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 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.

[0046] The electrode assembly 120 has a winding direction D, which is the direction from the inner circle to the outer circle of the electrode assembly 120. According to an embodiment of the present application, in the winding direction D of the electrode assembly 120, the tail end 122e of the second pole piece 122 exceeds the tail end 121e of the first pole piece 121, so that the second pole piece 122 can cover the tail end 121e of the first pole piece 121. Then, the lithium ions separated from the positive active material layer of the first pole piece 121 (positive pole piece) can be smoothly embedded in the negative active material layer of the second pole piece 122 (negative pole piece), thereby avoiding the lithium deposition phenomenon on the negative pole piece at the tail end.

[0047] exist Figure 5 In the cross section shown, the tail end 121e of the first pole piece 121 is connected to the projection point P to form a first line L1, and the tail end 122e of the second pole piece 122 is connected to the projection point to form a second line L2. The angle A1 between the first line L1 and the second line L2 is the angle formed by the first line L1 in the winding tail direction (that is, along the winding direction from the tail end 121e of the first pole piece 121 to the tail end 122e of the second pole piece 122) and the second line L2. The angle A1 between the first line L1 and the second line L2 can reflect the angle that the tail end 122e of the second pole piece 122 is wound beyond the tail end 121e of the first pole piece 121.

[0048] Adjusting the amount by which the end 122e of the second pole piece 122 exceeds the end 121e of the first pole piece 121 will affect the characteristics of the secondary battery. The inventors have found that the angle A1 between the first connecting line L1 and the second connecting line L2 will affect the pressure level at the winding center hole 120c. FIG. 6A to FIG. 6D It shows the case where the included angle A1 between the first connecting line L1 and the second connecting line L2 has different angle values. Fig. 6A It shows that the angle A1 is less than 80°. Figure 6B It shows that the angle A1 = 90°, Figure 6C It shows that the angle A1>90°, Fig.6D An included angle A1 = 180° is shown.

[0049] The inventors have found that if the included angle A1 between the first connecting line L1 and the second connecting line L2 is within a range of <80°, Fig. 6A As shown, the pressure on the winding center hole will increase. If the angle A1 between the first connecting line L1 and the second connecting line L2 is equal to 180°, Fig.6D As shown, the pressure on the winding center hole position can be optimized and the pressure on the winding center hole is minimized.

[0050] In some embodiments, the angle A1 between the first line L1 and the second line L2 can be in the range of 160°-190°. It should be understood that in the description of the present application, within a certain numerical range refers to the end point value including the numerical range. By configuring the angle A1 within the range of 160°-190°, the pressure on the winding center hole position can be reduced, the pressure on the winding center hole can be close to the minimum, the collapse of the winding center hole can be avoided, and the life cycle of the secondary battery can be extended.

[0051] Optionally, the angle A1 between the first connecting line L1 and the second connecting line L2 can be in the range of 175°-185°. This can effectively optimize the pressure on the winding center hole position and minimize the pressure on the winding center hole, thereby effectively avoiding collapse at the winding center hole and extending the life cycle of the electrode assembly.

[0052] On the other hand, if the angle A1 between the first connection line L1 and the second connection line L2 is too large (e.g., 180°-190°), the second pole piece 122 will be used more and wasted more. Therefore, considering the two factors of reducing the pressure on the winding center hole and avoiding waste, in some embodiments, the angle between the first connection line L1 and the second connection line L2 can be in the range of 80° to 100°. By configuring the angle A1 in the range of 80° to 100°, the pressure on the winding center hole can be reduced to an appropriate degree to avoid collapse, and at the same time, material waste can be avoided.

[0053] Optionally, the angle A1 between the first connecting line L1 and the second connecting line L2 may be in the range of 85°-95°. Such a configuration of the angle A1 is a good compromise between reducing the pressure on the winding center hole and avoiding waste. Fig. 6E FIG. 1 shows a schematic diagram of the structure of the electrode assembly 120 after cycling according to an embodiment of the present application. Fig. 6E In the electrode assembly shown, the included angle A1 between the first connecting line L1 and the second connecting line L2 is about 88°. Fig. 6E As shown, no collapse 125 occurs at the roll-start position of the electrode assembly 120 after cycling.

[0054] See also Figure 5 In some embodiments, the first electrode sheet 121 and the second electrode sheet 122 have starting ends 121s and 122s, respectively. In the direction opposite to the winding direction D of the electrode assembly 120, that is, toward the winding center line Lc (at Figure 5The starting end 122s of the second pole piece 122 exceeds the starting end 121s of the first pole piece 121 in the direction of the projection point P in the figure. By configuring the starting end 122s of the second pole piece 122 to exceed the starting end 121s of the first pole piece 121, the lithium ions separated from the positive electrode active material layer of the first pole piece 121 (positive pole piece) can be smoothly embedded in the negative electrode active material layer of the second pole piece 122 (negative pole piece), thereby avoiding the lithium deposition phenomenon on the negative pole piece at the starting end. The amount by which the starting end 122s of the second pole piece 122 exceeds the starting end 121s of the first pole piece 121 can usually be adjusted according to the actual system.

[0055] Fig. 7A The figure is a simplified schematic diagram of the first pole piece 121' and the starting end of the second pole piece 122' at the inner circle of the electrode assembly of an existing secondary battery. Fig. 7A As shown, in a general secondary battery electrode assembly, the starting end 122s' of the second electrode sheet 122' generally exceeds the starting end 121s' of the first electrode sheet 121' by less than 1 / 4 of a circle.

[0056] Figure 7B 1 is a simplified schematic diagram of the starting ends of the first pole piece 121 and the second pole piece 122 at the inner circle of the electrode assembly according to an embodiment of the present application. According to an embodiment of the present application, in the direction opposite to the winding direction D of the electrode assembly 120, the starting end 122s of the second pole piece 122 exceeds the starting end 121s of the first pole piece 121 by at least one circle. The starting end 122s of the second pole piece 122 exceeds by at least one circle, so that the second pole piece 122 can have at least one complete circle as support. Due to the addition of this support, the possibility of collapse at the center hole due to the influence of expansion after the cycle is reduced, thereby avoiding the problems of electrode assembly failure, lithium deposition, short circuit, etc. caused by collapse, and extending the life cycle of the secondary battery. In an embodiment where the secondary battery is a cylindrical battery, the second pole piece 122 that exceeds the first pole piece 121 by at least one circle will be wound into a circle, which can play a better supporting role, thereby effectively reducing the possibility of collapse at the winding center hole of the cylindrical battery, avoiding the problems of electrode assembly failure, lithium deposition, short circuit, etc. of the cylindrical battery caused by collapse.

[0057] Refer to Figure 5 In some embodiments, the starting end 122s of the second pole piece 122 exceeds the starting end 121s of the first pole piece 121 by no more than 2 turns, that is, the starting end 122s of the second pole piece 122 may exceed by 1 turn to 2 turns. Since the second pole piece 122 exceeds too much, the energy density of the secondary battery will be affected. Therefore, the starting end 122s of the second pole piece 122 exceeds by no more than 2 turns, which can reduce the possibility of collapse at the center hole without excessively affecting the energy density.

[0058] In addition, the starting end 121s of the first pole piece 121 is connected to the projection point P to form a third line L3, and the starting end 122s of the second pole piece 122 is connected to the projection point P to form a fourth line L4, and any two of the first line L1, the second line L2, the third line L3, and the fourth line L4 do not overlap with each other. In other words, 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 configured without being aligned with each other. Such a misaligned configuration can reduce the winding ellipticity of the electrode assembly 120 and maintain the circularity of the winding.

[0059] In some embodiments, the angle A2 between the third connection line L3 and the fourth connection line L4 can be in the range of 30°-120°. By staggering the starting end 121s of the first pole piece 121 and the starting end 122s of the second pole piece 122 within the range of 30°-120°, and in conjunction with the angle A1 between the first connection line L1 and the second connection line L2, the winding ellipticity of the electrode assembly 120 can be effectively reduced, while reducing the pressure on the winding center hole position.

[0060] In addition, the first separator 141 and the second separator 142 may have tail ends 141e and 142e, respectively. The ends of the tail ends 141e and 142e of the first separator 141 and the second separator 142 that extend beyond the tail end 120e of the electrode assembly 120. Figure 5 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.

[0061] 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. Fig. 8A and Figure 8B 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. Fig. 8AAs shown, the tail end 142e of the second diaphragm 142 may exceed the tail end 141e of the first diaphragm 141, and in this embodiment, the tail end 142e of the second diaphragm 142 is an end that exceeds and may constitute the tail end 120e of the electrode assembly 120. Figure 8B As shown, the tail end 141e of the first diaphragm 141 may exceed the tail end 142e of the second diaphragm 142 , and in this embodiment, the tail end 141e of the first diaphragm 141 is the protruding end and may constitute the tail end 120e of the electrode assembly 120 .

[0062] Return to reference Figure 5 As shown, in the winding direction D of the electrode assembly 120, the end 120e of the electrode assembly 120 exceeds the end 122e of the second pole piece 122, and exceeds the end 122e of the second pole piece 122 by 1.5 to 2 turns. By increasing the winding length of the first diaphragm 141 and the second diaphragm 142, so that the first diaphragm 141 and the second diaphragm 142 exceed the end 122e of the second pole piece 122 by at least 1.5 turns in the outermost circle, the gap between the first pole piece 121 and the second pole piece 122 in the outermost circle can be reduced, so that the first pole piece 121 and the second pole piece 122 in the outermost circle are more closely attached, which can reduce the risk of lithium deposition in 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.

[0063] 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. Since over-winding will affect the energy density of the secondary battery, the tail end 120e of the electrode assembly 120 is wound no more than 2 times, which can reduce the risk of lithium deposition in the outermost circle and increase liquid absorption without affecting the energy density.

[0064] In addition, in the direction opposite to the winding direction D of the electrode assembly 120, that is, toward the winding center line Lc (at Figure 5The projection point in the figure is P), the first diaphragm 141 and the second diaphragm 142 can extend beyond the starting end 122s of the second pole piece 122 in the inner circle of the electrode assembly 120, and the end where the starting end of the first diaphragm 141 and the starting end of the second diaphragm extend beyond the starting end 122s of the second pole piece 122 by 1 to 2 turns. The first diaphragm 141 and the second diaphragm 142 extend beyond the starting end 122s of the second pole piece 122 in the inner circle by 1 to 2 turns, which can not only provide better electrical isolation, but also increase the liquid absorption of the electrode assembly 120 without affecting the energy density. For cylindrical batteries, it can especially solve the problems of difficult electrolyte infiltration and limited liquid retention. In addition, since winding the first diaphragm 141 and the second diaphragm 142 more in the inner circle can also increase a certain degree of adhesion, it can prevent the structure of the electrode assembly from changing, which can help reduce the possibility of collapse at the center hole of the cylindrical battery.

[0065] In some embodiments, the secondary battery may further include an insulating film 300, which may be used to fix the end of the electrode assembly 120. In some embodiments, the insulating film 300 may be made of, for example, PP, PE, PET (polyethyleneterephthalate), PVC (Polyvinyl chloride) or other high molecular polymer materials. The insulating film 300 may be used to electrically isolate the electrode assembly 120 from the outside.

[0066] In the present embodiment, the insulating film 300 may surround the electrode assembly 120 at least once in the winding direction D of the electrode assembly 120. The insulating film 300 is wound at least once in this way, which can maintain the winding tightness of the electrode assembly 120.

[0067] 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.

[0068] 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: comprising an electrode assembly, 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; Wherein, in the winding direction of the electrode assembly, the tail end of the second pole piece exceeds the tail end of the first pole piece, 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 first connecting line, and the tail end of the second pole piece is connected to the projection point to form a second connecting line, and the angle between the first connecting line and the second connecting line is in the range of 80°-100°, or in the range of 160°-190°.

2. The secondary battery according to claim 1, characterized in that: The included angle between the first connecting line and the second connecting line is in the range of 85°-95°, or in the range of 175°-185°.

3. The secondary battery according to claim 1, characterized in that: In the direction opposite to the winding direction of the electrode assembly, the starting end of the second pole sheet exceeds the starting end of the first pole sheet and exceeds the starting end of the first pole sheet by at least one turn.

4. The secondary battery according to claim 3, characterized in that: The starting end of the second pole piece exceeds the starting end of the first pole piece by no more than 2 turns.

5. The secondary battery according to claim 1, characterized in that: In a direction opposite to the winding direction of the electrode assembly and toward the winding centerline, the first diaphragm and the second diaphragm extend beyond the starting end of the second pole piece in the inner circle of the electrode assembly, and one end where the starting end of the first diaphragm and the starting end of the second diaphragm extend beyond the starting end of the second pole piece by 1 to 2 circles.

6. The secondary battery according to claim 1, characterized in that: In the winding direction of the electrode assembly, the first diaphragm and the second diaphragm extend beyond the tail end of the second pole piece at the outer circle of the electrode assembly, and one end of the tail end of the first diaphragm and the tail end of the second diaphragm extends beyond the tail end of the second pole piece by 1.5 to 2 turns.

7. The secondary battery according to claim 1, characterized in that: The starting end of the first pole piece is connected to the projection point to form a third line, the starting end of the second pole piece is connected to the projection point to form a fourth line, and the angle between the third line and the fourth line is in the range of 30 to 120 degrees.

8. The secondary battery according to claim 7, characterized in that: The first connecting line, the second connecting line, the third connecting line and the fourth connecting line do not overlap with each other.

9. The secondary battery according to claim 1, characterized in that: Also includes: The insulating film is used to fix the tail end of the electrode assembly, wherein in the winding direction of the electrode assembly, the insulating film surrounds the electrode assembly for at least one circle.

10. The secondary battery according to any one of claims 1 to 9, 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.

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

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

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