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 formed by sequentially laminating and winding a first pole piece, a first diaphragm, a second pole piece and a second diaphragm, and in the winding direction of the electrode assembly, the ending end of the electrode assembly exceeds the ending end of the first pole piece and the ending end of the second pole piece; the insulating film is used for fixing the ending end of the electrode assembly and surrounds the electrode assembly by at least one circle, in a cross section perpendicular to a winding center line of the electrode assembly, the winding center line is orthographically projected on the cross section to form a projection point, and the ending end of the electrode assembly is connected with the projection point to form a first connecting line; the starting end of the insulating film is connected with the projection point to form a second connecting line, and in the winding direction of the electrode assembly, the first included angle between the second connecting line and the first connecting line is 50-190 degrees. According to the technical scheme, the tightening effect of the electrode assembly can be improved at least, the negative pole piece is prevented from being sunken, and lithium precipitation at the sunken edge is avoided.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of secondary battery, battery pack and electronic device. BACKGROUND

[0002] In the field of new energy power battery, the application of secondary battery is more and more widely, such as secondary battery (for example, lithium ion battery) can be applied to car, energy storage, mobile phone, tablet computer, wearable device, mobile power supply, electronic cigarette, digital product, power tool, power device, energy storage device and other electronic devices. One of the secondary battery is cylindrical battery, which includes a shell and an electrode assembly, the electrode assembly includes a positive electrode sheet, a first separator, a negative electrode sheet and a second separator, which are stacked in sequence and then wound into an electrode assembly, and then packaged in the shell. However, the existing secondary battery still needs to be further improved in some aspects. SUMMARY

[0003] In view of the problems in the related art, the purpose of the utility model is to provide a secondary battery, a battery pack and an electronic device, which can at least improve the tightening effect of the electrode assembly, prevent the negative electrode sheet from being concave, and prevent lithium precipitation at the concave edge.

[0004] To achieve the above-mentioned purpose, the embodiments of the present application provide a secondary battery, which includes an electrode assembly, a first electrode sheet, a first separator, a second electrode sheet and a second separator are stacked in sequence and then wound into an electrode assembly. In the winding direction of the electrode assembly, one end of the tail end of the first separator and the tail end of the second separator beyond constitutes the tail end of the electrode assembly, wherein the tail end of the electrode assembly beyond the tail end of the first electrode sheet and the tail end of the second electrode sheet. The secondary battery further includes an insulating film for fixing the tail end of the electrode assembly, and surrounds the electrode assembly at least one turn. In the cross section perpendicular to the winding center line of the electrode assembly, the winding center line forms a projection point on the cross section by orthogonal projection, the tail end of the electrode assembly and the projection point connect to form a first connecting line, and the starting end of the insulating film and the projection point connect to form a second connecting line, wherein in the winding direction of the electrode assembly, the first included angle of the second connecting line to the first connecting line is 50°-190°.

[0005] In some embodiments, in the winding direction of the electrode assembly, the distance between the tail end of the electrode assembly and the starting end of the insulating film is 20mm-70mm.

[0006] In some embodiments, in the cross section, the tail end of the insulating film and the projection point connect to form a third connecting line, wherein in the winding direction of the electrode assembly, the second included angle of the second connecting line to the third connecting line is 15°-35°.

[0007] In some embodiments, the starting end of the first tab, the ending end of the first tab, the starting end of the second tab and the ending end of the second tab are located within the range of the first included angle.

[0008] In some embodiments, in the cross section, the starting end of the second tab and the projection point form a fourth connecting line, and the ending end of the second tab and the projection point form a fifth connecting line, wherein the starting end of the first tab and the ending end of the first tab are located within the range from the fourth connecting line to the fifth connecting line in the winding direction.

[0009] In some embodiments, the number of the insulating film is 1, and the insulating film covers 50%-90% of the outer peripheral surface area of the electrode assembly; the secondary battery is a cylindrical battery, the first tab is a positive electrode tab, and the second tab is a negative electrode tab; the first separator is located on the side of the second tab facing the winding center line, the second separator is located on the side of the second tab away from the winding center line, and the second separator is located at the outermost circle of the electrode assembly; the adhesive value of the insulating film is greater than or equal to 2 N / cm; the tension of the first separator and the second separator at the tail of the electrode assembly is 200 N-400 N, and the tension of the first tab and the second tab at the tail of the electrode assembly is 800 N-1200 N.

[0010] In some embodiments, in the winding direction of the electrode assembly, the ending end of the second tab exceeds the ending end of the first tab; and in the opposite direction of the winding direction of the electrode assembly, the starting end of the second tab exceeds the starting end of the first tab.

[0011] In some embodiments, the secondary battery is a cylindrical battery, and the secondary battery further comprises: a shell comprising a circumferential side wall, one end of the circumferential side wall being formed with an opening, an end wall and the circumferential side wall surrounding to form a receiving cavity, and the electrode assembly being located in the receiving cavity, wherein the insulating film is located between the electrode assembly and the circumferential side wall and tightly fits the outer peripheral surface of the electrode assembly; a cover plate installed at the opening and electrically isolated from the circumferential side wall; and a pole post penetrating through the end wall, electrically connected to the electrode assembly and electrically isolated from the end wall.

[0012] Embodiments of the present application also provide a battery pack comprising any one of the secondary batteries described above.

[0013] Embodiments of the present application also provide an electronic device comprising at least one of any one of the secondary batteries described above and any one of the battery packs described above.

[0014] The beneficial technical effects of the present application are as follows:

[0015] The above-mentioned technical solution of this application, by configuring the first included angle A1 between the starting end of the insulating film and the ending end of the electrode assembly to be 50°-190°, can achieve a good electrode assembly tightening effect. Even when the adhesion of the insulating film is weakened after being soaked in electrolyte, it can still achieve the required electrode assembly tightening effect, improve the problem of concave deformation and color difference of the negative electrode sheet, and avoid lithium deposition at the concave edge. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

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

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

[0021] Figure 5A and Figure 5B These are partially enlarged schematic diagrams of the structures at the ends of the first and second separators in a secondary battery according to another embodiment of this application.

[0022] Figure 6 This is a front view schematic diagram of the electrode assembly and insulating film. Detailed Implementation

[0023] To better understand the spirit of the embodiments of this application, the following description is based on some preferred embodiments of this application.

[0024] Embodiments of this application will be described in detail below. Throughout this specification, identical or similar components and components having identical or similar functions are indicated by similar reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative and diagrammatic in nature and are intended to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0025] As used herein, the terms “approximately,” “substantially,” “substantially,” and “about” are used to describe and indicate minor variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately.

[0026] 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 (e.g., “horizontally,” “downward,” “upward,” etc.) should be interpreted as referring to the directions described in the discussion or depicted in the accompanying drawings. These relative terms are used for descriptive convenience only and do not require that this application be constructed or operated in a particular orientation.

[0027] For ease of description, the terms "first," "second," "third," etc., are 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. Furthermore, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] This application provides an electronic device 1000. For ease of explanation, the following embodiments use a vehicle as an example to illustrate the electronic device 1000. See also... Figure 1The vehicle has a battery pack 1002 installed inside, which can be located at the bottom, front, or rear of the vehicle body 1001. The battery pack 1002 can be used to power the vehicle; for example, it can serve as the vehicle's operating power source. The working part of the electronic device 1000 is electrically connected to the battery pack 1002 to obtain electrical power. The vehicle can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, but are not limited thereto. The working part is the vehicle body, and the battery pack 1002 is located at the bottom of the vehicle body, providing electrical power for the vehicle's movement or the operation of its internal electrical components. However, in some other embodiments, the electronic device 1000 can also be a mobile phone, portable device, laptop, ship, spacecraft, electric toy, and power tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; the working part can obtain electrical energy from the battery pack 1002 and perform corresponding functions, such as a fan blade rotation unit or a vacuum cleaner's suction unit. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric boat toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the aforementioned electronic device 1000.

[0029] Battery pack 1002 may include multiple secondary batteries (such as...) Figure 2 The secondary battery 100 and the casing that houses multiple secondary batteries are described below. In the following description, a cylindrical battery is used as an example for illustration. Figure 2 A perspective view of a secondary battery 100 according to an embodiment of this application is shown. Figure 3 A cross-sectional view of a secondary battery 100 according to an embodiment of this application is shown.

[0030] See also Figure 2 and Figure 3The secondary battery 100 is a cylindrical battery. The secondary battery 100 may include an electrode assembly 120, an electrolyte, a housing 200, and a cover plate 202. The housing 200 includes a peripheral sidewall 109 and an end wall 111 connected to one end of the peripheral sidewall 109. An opening 205 is provided at the other end of the peripheral sidewall 109 opposite to the end wall 111, and the cover plate 202 is installed in the opening 205. The end wall 111 and the peripheral sidewall 109 enclose a cavity within the housing 200 for accommodating the electrode assembly 20, the electrolyte, and other necessary battery components, and are covered by the cover plate 202. The connection between the end wall 111 and the peripheral sidewall 109 can be achieved in various ways, such as integral stamping, integral casting, or separate welding. The housing 200 can be made of any of a variety of available materials, such as copper, iron, aluminum, steel, or aluminum alloy. Furthermore, in embodiments where the secondary battery 100 is a cylindrical battery, the surface of the casing 200 may be pre-plated with nickel to prevent electrolyte corrosion. The casing 200 may be cylindrical and define a receiving cavity in which the electrode assembly 120 is disposed. The outer diameter of the casing 200 may be determined according to the specific diameter of the electrode assembly 120; for example, the outer diameter of the casing 200 may be, for example, 18 mm, 21 mm, 46 mm, etc. In some embodiments, the secondary battery 100 may be a 4680 cylindrical battery (outer diameter 46 mm, height 80 mm), or a 4695 cylindrical battery (outer diameter 46 mm, height 95 mm), or a 46120 cylindrical battery (outer diameter 46 mm, height 120 mm).

[0031] See Figure 3 The electrode assembly 120 may include a positive electrode, a first separator, a negative electrode, and a second separator that are sequentially stacked and wound (as shown in the following reference). Figure 4 As described, the electrode assembly 120 may have a winding center hole 120c and a winding center line Lc, the winding center line Lc being the axis of the winding center hole 120c.

[0032] The housing 200 also has an inwardly protruding crimping portion 203 (also called a groove) near the opening 205. Along the height Z direction 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 restricts the axial movement (movement in the height Z direction) of the electrode assembly 120 between the end wall 111 of the housing 200 and the crimping portion 203. In some embodiments, the cover plate 202 may have a weak portion. When thermal runaway occurs in the battery, the high-temperature, 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 discharge of the emissions.

[0033] The secondary battery 100 may also include an insulating seal 50 and a current collector. The insulating seal 50 surrounds the periphery of the cover plate 202 to insulate and seal the cover plate 202 and the housing 200. The negative current collector is disposed between the electrode assembly 120 and the cover plate 202 and is electrically connected to the negative electrode tab of the electrode assembly 120 and the housing 200. The connecting piece of the negative current collector is located on the side of the crimping portion 203 facing the electrode assembly 120 and is welded to the crimping portion 203. In this way, by setting the connecting piece of the negative current collector to be located on the side of the crimping portion 203 facing the electrode assembly 120 and welded to the crimping portion 203, the welding area of ​​the negative current collector and the negative electrode tab is located closer to the electrode assembly 120 than the crimping portion 203, thereby preventing the crimping portion 203 from affecting the welding area of ​​the negative electrode tab and the negative current collector, and thus improving the welding strength of the negative electrode tab and the negative current collector.

[0034] The end of the peripheral sidewall 109 of the housing 200 on the opening 205 side may be configured as a rolled edge 32, which extends radially inward along the housing 200. The rolled edge 32 and the pressing part 113 are arranged at intervals along the height direction Hd, and the pressing part 113 and the rolled edge 32 can jointly clamp the cover plate 220. The cover plate 220 is electrically insulated from the housing 200.

[0035] The electrode assembly 120 may have a positive electrode tab and a negative electrode tab respectively at both ends in the height direction Z of the secondary battery 100. In some embodiments, the positive electrode tab faces the end wall 111, and the negative electrode tab faces the opening 205. The negative electrode tab of the electrode assembly 120 can be electrically connected to the housing 200 through a negative current collector located between the cover plate 220 and the electrode assembly 120, thereby making the housing 200 negatively charged. The secondary battery 100 may also include a terminal post 160, which passes through the end wall 111 and is insulated from the end wall 111. The positive current collector can be disposed between the terminal post 160 and the end wall 111, and electrically connect the terminal post 160 to the positive electrode tab of the electrode assembly 120, thereby making the terminal post 160 positively charged.

[0036] In some embodiments, the secondary battery 100 is a cylindrical battery. Cylindrical batteries have advantages such as high energy density, long cycle life, and good safety performance. However, this is not a limitation; in other embodiments, the secondary battery 1 can also be a prismatic battery or other shaped batteries.

[0037] Furthermore, in one example where the secondary battery 100 of the present invention is a cylindrical battery, the method for manufacturing the secondary battery 100 of the present invention includes the following steps:

[0038] Winding: A winding structure formed by stacking and winding negative electrode sheet, separator and positive electrode sheet, the uncoated part of the negative current collector of negative electrode sheet and the positive current collector of positive electrode sheet is used as positive electrode tab and negative electrode tab, and the positive electrode tab and negative electrode tab are bent along the radial direction of electrode assembly 120 toward winding center hole 120c.

[0039] Welding of current collectors to electrode assemblies: The positive current collector and the negative current collector are welded to the surface areas of the bent positive and negative electrode tabs, respectively.

[0040] Installation: The electrode assembly 120, which has been welded to the negative current collector and the positive current collector, is installed into the housing 200 through the opening 205. The method of installing the electrode assembly 120 in this step is not limited. For example, it can be installed manually or by a robot.

[0041] Install pole 160.

[0042] Electrolyte injection: The method of electrolyte injection is not limited, and injection can be carried out through opening 205. In this embodiment, electrolyte is injected through opening 205, which reduces the step of opening an injection hole in the end wall 111. The existing opening 205 can be used directly for injection, simplifying the process and reducing costs.

[0043] Sealing: The cover plate 220 is sealed and installed on the opening 205. There are various sealing methods, and this is not limited to one. In some embodiments, a pressing portion 113 recessed towards the center of the housing 200 is first formed by rolling the outer periphery of the housing 200 to restrict the movement of the electrode assembly 120 in the height direction Z. Then, a mechanical sealing process is used to press and seal the cover plate 220 to form a rolled edge portion 32, thereby sealing and installing the cover plate 220 on the opening 205 of the housing 200. This step is a mature process, low in cost, and highly efficient.

[0044] Figure 4 This is a cross-sectional view of the electrode assembly 120 of a secondary battery according to an embodiment of this application, in a 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 Z direction (see...). 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 onto this cross-section. The electrode assembly 120 also has a winding center hole 120c, which is located in... Figure 4 The cross-section shown can have a circular shape. The projection point P can be the center of the circle surrounding the central hole 120c.

[0045] See Figure 4The electrode assembly 120 may include a first electrode 121, a first separator 141, a second electrode 122, and a second separator 142. The first electrode 121, the first separator 141, the second electrode 122, and the second separator 142 are sequentially stacked and wound along the winding direction D to form the electrode assembly 120. Furthermore, the secondary battery may also include an electrolyte, which may be located between the first electrode 121, the first separator 141, the second electrode 122, and the second separator 142. In some embodiments, the first electrode 121 is a positive electrode, and the second electrode 122 is a negative electrode.

[0046] The positive electrode 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 the positive electrode tab. The negative electrode 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 the negative electrode tab. Taking a lithium-ion battery as an example, the material of the positive current collector may be aluminum, and the positive active material layer may include a positive active material, such as lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide. The material of the negative current collector may be copper, and the negative active material layer may include a negative active material, such as carbon or silicon. In some embodiments, the materials of the first separator 141 and the second separator 142 may be, for example, PP (polypropylene) or PE (polyethylene).

[0047] 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 comes into 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 lithium ion activation process, which is also the battery charging process.

[0048] In the winding direction D, the terminal end 122e of the second electrode 122 extends beyond the terminal end 121e of the first electrode 121, allowing the second electrode 122 to cover the terminal end 121e of the first electrode 121. Therefore, lithium ions detached from the positive active material layer of the first electrode 121 (positive electrode) can be smoothly inserted into the negative active material layer of the second electrode 122 (negative electrode), thus preventing lithium plating at the terminal end of the second electrode 122 (negative electrode).

[0049] For similar reasons, in the direction opposite to the winding direction D, the starting end 122s of the second electrode 122 also extends beyond the starting end 121s of the first electrode 121. That is, at the beginning of the winding of the electrode assembly 120, the second electrode 122 is wound a longer distance than the first electrode 121. Therefore, lithium ions detached from the positive active material layer of the first electrode 121 (positive electrode) can be readily inserted into the negative active material layer of the second electrode 122 (negative electrode), thus avoiding lithium plating on the negative electrode at the starting end. However, lithium plating is still prone to occur on the outermost ring of the wound electrode assembly 120.

[0050] According to an embodiment of this application, along the winding direction D, the end 141e of the first diaphragm 141 and the end 142e of the second diaphragm 142 extending beyond each other constitute the end 120e of the electrode assembly 120. Figure 4 In the illustrated embodiment, the terminal ends 141e of the first diaphragm 141 and 142e of the second diaphragm 142 are substantially aligned. It should be understood that alignment in this application means that the terminal ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 differ by less than 5 mm. In such an embodiment, the extended ends of the terminal ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 constitute the terminal end 120e of the electrode assembly 120. When the terminal ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 differ by 0 mm, the terminal ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 can be used together as the terminal end 120e of the electrode assembly 120.

[0051] In other embodiments, the terminal ends 141e and 142e of the first diaphragm 141 and the second diaphragm 142 may not be aligned. Figure 5A and Figure 5B These are partially enlarged schematic diagrams showing the structures at the ends of the first and second separators in a secondary battery according to another embodiment of this application. (See reference) Figure 5A As shown, the terminal end 142e of the second diaphragm 142 extends beyond the terminal end 141e of the first diaphragm 141. In this embodiment, the terminal end 142e of the second diaphragm 142 is the outermost extension and constitutes the terminal end 120e of the electrode assembly 120. (See reference...) Figure 5B As shown, the end 141e of the first diaphragm 141 extends beyond the end 142e of the second diaphragm 142. In this embodiment, the end 141e of the first diaphragm 141 is the outermost end and constitutes the end 120e of the electrode assembly 120.

[0052] Return to reference Figure 4The secondary battery 100 may also include an insulating film 300, which can be used to fix the terminal end 120e of the electrode assembly 120. The insulating film 300 may be located between the electrode assembly 120 and the peripheral sidewall 109 (see...). Figure 3 The insulating film 300 is positioned between the electrode assembly 120 and in close contact with its outer peripheral surface. In this embodiment, the insulating film 300 surrounds the electrode assembly 120 at least once. The insulating film 300 surrounds the electrode assembly 120 along the winding direction D. In some embodiments, the insulating film 300 may be synthesized, for example, from 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 external environment.

[0053] Figure 6 This is a front view schematic diagram of the electrode assembly and insulating film. (Reference) Figure 6 and combined Figure 4 As shown, an insulating film 300 is disposed around the electrode assembly 120. In the height direction Z, the height H1 of the insulating film 300 is 50%-90% of the height H2 of the first diaphragm 141 and the second diaphragm 142. Height H2 refers to the height formed by the first diaphragm 141 and the second diaphragm 142 after winding. In some embodiments, the insulating film 300 covers 50%-90% of the outer peripheral surface area of ​​the electrode assembly 120.

[0054] The insulating film 300 can be an adhesive layer with adhesive strength, and the adhesive surface of the insulating film 300 faces the electrode assembly 120. In some embodiments, the adhesive strength of the insulating film 300 should be ≥2 N / cm to ensure that it can hold the diaphragm and tighten the electrode assembly. If the adhesive strength of the insulating film 300 is less than 2 N / cm, the adhesive strength of the insulating film 300 will weaken after immersion in the electrolyte, and it will not achieve a good tightening effect.

[0055] See again Figure 4 As shown, the terminal end 120e of the electrode assembly 120 extends beyond the terminal end 121e of the first electrode 121 and the terminal end 122e of the second electrode 122 to better isolate the first electrode 121 and the second electrode 122 from the outside. The terminal end 120e of the electrode assembly 120 is connected to the projection point P to form a first connection line L1. The starting end 300s of the insulating film 300 is connected to the projection point P to form a second connection line L2. In the winding direction D, a first included angle A1 is formed between the second connection line L2 and the first connection line L1. In some embodiments, the angle of the first included angle A1 is 50°-190°. Within the region of the first included angle A1, the starting section of the insulating film 300 overlaps with the terminal sections of the first diaphragm 141 and the second diaphragm 142.

[0056] If the starting end 300s of the insulating film 300 is located outside the first included angle A1, that is, within about half a circle after the ending end 120e of the electrode assembly 120, the inventors found that this would cause the electrode assembly 120 to not tighten, which in turn would cause the negative electrode sheet to have a concave deformation and color difference, resulting in lithium deposition at the concave edge of the negative electrode sheet.

[0057] The above-described technical solution of this application, by configuring the first included angle A1 between the starting end 300s of the insulating film 300 and the ending end 120e of the electrode assembly 120 to be 50°-190°, can achieve a good tightening effect on the electrode assembly. Even when the adhesion of the insulating film 300 weakens after immersion in the electrolyte, it can still achieve the required tightening effect on the electrode assembly, improve the problem of concave deformation and color difference of the negative electrode sheet, and avoid lithium deposition at the concave edge. If the first included angle A1 is less than 50° or greater than 190°, the tightening effect will not be good after the adhesion of the insulating film 300 is weakened by immersion in the electrolyte.

[0058] For cylindrical batteries, a good electrode assembly tightening standard should meet the following: the tension of the first separator 141 and the second separator 142 at the tail of the electrode assembly 120 should both be 200N-400N, and the tension of the first electrode 121 and the second electrode 122 at the tail of the electrode assembly 120 should both be 800-1200N. By configuring the first included angle A1 between the starting end 300s of the insulating film 300 and the ending end 120e of the electrode assembly 120 to be 50°-190°, the above standard for cylindrical batteries can be achieved, avoiding the negative electrode from being concave and deformed, thereby preventing lithium deposition at the concave edge.

[0059] In some embodiments, the first included angle A1 is 170°-190°, such that the starting section of the insulating film 300 overlaps with the ending sections of the first separator 141 and the second separator 142 by approximately half a circle around the outer perimeter of the electrode assembly. This can provide greater separator tension and electrode tension to better prevent the negative electrode from denting or deforming.

[0060] In the winding direction D, the distance between the end 120e of the electrode assembly 120 and the beginning 300s of the insulating film 300 is 20mm-70mm. This distance corresponds to the overlap between the beginning section of the insulating film 300 and the ending sections of the first diaphragm 141 and the second diaphragm 142. Therefore, the overlap between the beginning section of the insulating film 300 and the ending sections of the first diaphragm 141 and the second diaphragm 142 is 20mm-70mm. The minimum overlap of 20mm satisfies the aforementioned electrode assembly tightening standard. If the overlap is less than 20mm, the adhesion of the insulating film 300 weakens after immersion in the electrolyte, resulting in a tightening effect that does not meet the standard. If the overlap is greater than 70mm, the adhesion of the insulating film 300 weakens after immersion in the electrolyte, also resulting in a poor tightening effect that does not meet the standard.

[0061] refer to Figure 4 In the embodiment shown, the first diaphragm 141 is located on the second electrode 122 facing the winding center line Lc (in Figure 4 The second electrode 122 is located on one side of its projection point P, i.e., the side of the second electrode 122 facing inwards from the battery. The second separator 142 is located on the side of the second electrode 122 opposite to the winding center line Lc, i.e., the side of the second electrode 122 facing outwards from the battery. In this embodiment, the second separator 142 is on the outermost ring of the electrode assembly 120. Because the stress on the outer side of the second electrode 122 (negative electrode) is greater than that on the inner side, placing the second separator 142 on the outermost ring and then bonding it with the insulating film 300 will have a better tightening effect. Otherwise, in another case, if the second separator 142 on the outermost ring of the second electrode 122 is one less turn than the first separator 141 on the inner side, making the first separator 141 on the outermost ring, the second separator 142 will retract inwards, resulting in a poor tightening effect.

[0062] Furthermore, when the secondary battery 100 is a cylindrical battery, the side of the second electrode 122 facing inwards can be understood as the concave surface of the second electrode 122. The side of the second electrode 122 facing outwards can be understood as the convex surface of the second electrode 122. In the embodiment of the cylindrical battery, because the stress on the convex surface of the second electrode 122 (negative electrode) is greater than that on the concave surface, it is more likely that the second separator 142 will retract inwards if the first separator 141 is placed on the outermost ring. Therefore, by placing the second separator 142 on the convex side on the outermost ring, a standard tightening effect can be provided for the cylindrical battery.

[0063] The end 300e of the insulating film 300 is connected to the projection point P to form a third connecting line L3. In the winding direction D, the second connecting line L2 and the third connecting line L3 form a second included angle A2. In some embodiments, the angle of the second included angle A2 is 15°-35°. This angle range of the second included angle A2 can satisfy the requirement that the insulating film 300 has a good adhesion effect, tighten the electrode assembly 120, and avoid occupying space in the housing by winding multiple insulating films 300.

[0064] The starting end 121s and the ending end 121e of the first electrode 121, and the starting end 122s and the ending end 122e of the second electrode 122 are all located within the range of the first included angle A1. That is, the starting end and the ending end of each electrode are all set within the range between the starting end 300s of the insulating film 300 and the ending end 120e of the electrode assembly 120. This can help the insulating film 300 to tighten each electrode; in addition, this can also reduce the diameter difference of the electrode assembly and optimize the cylindricity of the electrode assembly.

[0065] In some embodiments, the starting end 121s of the first electrode 121, the ending end 121e of the first electrode 121, the starting end 122s of the second electrode 122, and the ending end 122e of the second electrode 122 do not overlap with each other in the radial direction of the electrode assembly, i.e., they are misaligned, to optimize the cylindricity of the electrode assembly.

[0066] The starting end 122s of the second electrode 122 is connected to the projection point P to form the fourth line L4, and the ending end 122e of the first electrode 122 is connected to the projection point P to form the fifth line L5. The starting end 121s and the ending end 121e of the first electrode 121 are located within the range from the fourth line L4 to the fifth line L5 in the winding direction D. This can further reduce the diameter range of the electrode assembly and optimize the cylindricity of the electrode assembly.

[0067] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises: an electrode assembly, a first electrode tab, a first separator, a second electrode tab and a second separator are sequentially stacked and then wound to form the electrode assembly, in the winding direction of the electrode assembly, one end of the first separator tail end and the second separator tail end beyond constitutes the tail end of the electrode assembly, wherein the tail end of the electrode assembly beyond the tail end of the first electrode tab and the tail end of the second electrode tab; and an insulating film for fixing the tail end of the electrode assembly, and surrounding the electrode assembly at least one circle, in the cross section perpendicular to the winding center line of the electrode assembly, the winding center line is orthogonally projected on the cross section to form a projection point, the tail end of the electrode assembly and the projection point form a first connecting line, and the starting end of the insulating film and the projection point form a second connecting line, wherein, in the winding direction of the electrode assembly, the first included angle of the second connecting line to the first connecting line is 50°-190°.

2. The secondary battery according to claim 1, wherein in the winding direction of the electrode assembly, the distance between the tail end of the electrode assembly and the starting end of the insulating film is 20mm-70mm.

3. The secondary battery according to claim 1, wherein in the cross section, the tail end of the insulating film and the projection point form a third connecting line, wherein, in the winding direction of the electrode assembly, the second included angle of the second connecting line to the third connecting line is 15°-35°.

4. The secondary battery according to claim 1, wherein the starting end of the first electrode tab, the tail end of the first electrode tab, the starting end of the second electrode tab and the tail end of the second electrode tab are located in the range of the first included angle.

5. The secondary battery according to claim 4, wherein in the cross section, the starting end of the second electrode tab and the projection point form a fourth connecting line, and the tail end of the second electrode tab and the projection point form a fifth connecting line, wherein the starting end of the first electrode tab and the tail end of the first electrode tab are located in the range between the fourth connecting line and the fifth connecting line in the winding direction.

6. The secondary battery according to claim 1, wherein the number of the insulating film is 1, and the insulating film covers 50%-90% of the peripheral surface area of the electrode assembly; the secondary battery is a cylindrical battery, the first electrode tab is a positive electrode tab, and the second electrode tab is a negative electrode tab; the first separator is located on the side of the second electrode tab facing the winding center line, the second separator is located on the side of the second electrode tab away from the winding center line, and the second separator is located in the outermost circle of the electrode assembly; the adhesive value of the insulating film is ≥2N / cm; the tension of the first separator and the second separator of the tail part of the electrode assembly is 200N-400N, and the tension of the first electrode tab and the second electrode tab of the tail part of the electrode assembly is 800N-1200N.

7. The secondary battery according to claim 1, wherein In a winding direction of the electrode assembly, the second tab's end exceeds the first tab's end; In a direction opposite to the winding direction of the electrode assembly, the second tab's end exceeds the first tab's end. 8.The secondary battery of claim 1, wherein The secondary battery is a cylindrical battery. The secondary battery further comprises: a housing including a circumferential side wall, one end of the circumferential side wall being formed with an opening, an end wall of the housing and the circumferential side wall enclosing a receiving cavity, the electrode assembly being located in the receiving cavity, wherein the insulating film is located between the electrode assembly and the circumferential side wall and tightly adheres to an outer circumferential surface of the electrode assembly; a cover plate installed at the opening and electrically isolated from the circumferential side wall; a pole post penetrating the end wall, electrically connected to the electrode assembly and electrically isolated from the end wall.

9. A battery pack characterized by comprising: The secondary battery of any one of claims 1 to 8.

10. An electronic device, comprising: The battery pack of claim 9.

Images