Secondary batteries and electronic devices

Abstract

The present invention provides a secondary battery and electronic device in which, when the explosion-proof valve is opened, each blade of the current collector opens easily, and the flatness between each blade can be more easily maintained. [Solution] The secondary battery of the present invention comprises a housing, an electrode assembly, and a current collector, the housing comprising an end wall on which an explosion-proof valve is disposed; the electrode assembly is housed within the housing, and a tab extends from one end of the electrode assembly facing the explosion-proof valve; the current collector is welded to the tab, and the current collector comprises a first opening and a plurality of second openings, the first opening passing through the center of the current collector and extending radially along the current collector, the plurality of second openings distributed on both sides of the first opening, the portion between the end of the second openings near the first opening and the first opening constitutes an easily breakable portion of the current collector, and when the internal pressure of the secondary battery rises and the pressure is released through the explosion-proof valve, the current collector breaks at the easily breakable portion and folds away from the electrode assembly.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and more specifically to secondary batteries and electronic devices.

Background Art

[0002] In some secondary batteries, an explosion-proof valve is attached to one end wall of the battery housing. The function of the explosion-proof valve is to release the internal pressure when the abnormal pressure inside the battery rises, and prevent the explosion of the battery. Also, in order to effectively collect and conduct current, some secondary batteries are further provided with a current collector. The current collector is arranged corresponding to the explosion-proof valve. When the explosion-proof valve is opened under extreme conditions, in order to improve the pressure release effect, some current collectors can be broken and folded, and the airflow for pressure release and the substances discharged from the inside can pass through without being hindered much.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of the drawbacks of the prior art, the present invention provides a secondary battery and an electronic device in which when the explosion-proof valve is opened, each blade of the current collector can easily open, and the flatness on the same plane between each blade can be maintained more easily.

Means for Solving the Problems

[0004] A secondary battery provided by a first aspect of the present invention includes a housing, an electrode assembly, and a current collector. The housing includes an end wall on which an explosion-proof valve is disposed. The electrode assembly is housed within the housing, with a tab extending from one end facing the explosion-proof valve. The current collector is welded to the tab. The current collector includes a first opening and a plurality of second openings, the first opening extending radially through the center of the current collector, the plurality of second openings distributed on both sides of the first opening, and the portions between the ends of the second openings near the first opening and the first opening constitute an easily breakable portion of the current collector, and when the internal pressure of the secondary battery rises and the pressure is released through the explosion-proof valve, the current collector breaks at the easily breakable portion and folds away from the electrode assembly.

[0005] Optionally, the current collector has two second openings extending along the radial direction of the current collector, and the first and second openings divide the current collector into four independently foldable circumferential regions. According to this technical solution, by breaking only one easy-break section, the two blades of the current collector can be quickly folded to approximately half their area, further improving the ease of breaking and folding each blade and the response speed, and making the pressure-relieving airflow passage smoother.

[0006] Optionally, the current collector has four second openings extending radially along the current collector, and the first and second openings divide the current collector into six independently foldable circumferential regions. In some technical solutions, the folding of each blade of the current collector is limited by the size of the opening of the explosion-proof valve, and as the current collector is divided into more blades circumferentially, the angle at which each blade folds and opens also increases accordingly, which is advantageous in maintaining a smooth pressure release passage. At the same time, the number of second openings should not be too many, as too many increases the average number of easily breakable sections required to break each blade that is folded, making the current collector difficult to manufacture; therefore, evenly spaced four second openings is one preferred solution.

[0007] Optionally, the first opening has a central hole at a position corresponding to the center of the current collector, and the central hole has multiple corners, each of which is positioned toward the end of the second opening closest to the first opening. According to this technical solution, the corners can increase stress concentration at this position, making the easily breakable section more easily broken, and the breakage method tends to be in the direction of the connecting line from the central hole to the end of the second opening.

[0008] Arbitrarily, the maximum straight-line distance between the outer edges of multiple corners of the central hole is equal to the radial size of the central hole, d1 ≥ 8 mm. In particular, the opening angles of the multiple corners of the central hole are θ, where 45° ≤ θ ≤ 90°. Due to the presence of acute corners, molds used for processing this type of current collector are prone to wear and damage to the edges during the processing. According to this technical solution, if the radial size of the central hole is d1 ≥ 8 mm and the opening angles θ of the corners are 45° ≤ θ ≤ 90°, the service life of the molds used for processing the current collector can be effectively improved, and the increase in foreign matter due to mold wear can be avoided.

[0009] Optionally, the center of the electrode assembly contains a central hole, the diameter of the central hole is d2, and the maximum straight-line distance between the outer edges of multiple corners is d1, where d1 > d2. According to this technical solution, the central hole of the electrode assembly typically constitutes a passage for pressure-relieving airflow, and substances including electrolytes and particles are mainly discharged from the outer periphery of the passage. By making d1 > d2, substances such as electrolytes and particles directly collide with the corners, increasing the impact force on the corners and making the easily breakable parts more likely to break from the corners.

[0010] Optionally, multiple weld marks are formed between the current collector and the tab by welding, with each weld mark having a width of W ≤ 1 mm. According to this technical solution, when tab delamination occurs, the width of each weld mark is W ≤ 1 mm, which reduces the peeling force required in the initial stages of delamination. Furthermore, as the delamination process progresses, the relatively small width of each weld mark slows down the increase in peeling force during the delamination process, allowing the delamination to proceed in stages.

[0011] Optionally, multiple weld marks, including multiple straight weld marks, are formed between the current collector and the tab by welding. According to this technical solution, the straight weld marks allow for a relatively small peeling force required in the initial stages of folding and tab peeling, requiring only the peeling of the ends of the straight weld marks. Furthermore, the line width of the straight weld marks remains almost unchanged during the peeling process, and the magnitude of the peeling force during the peeling process also remains essentially unchanged. By combining multiple straight weld marks, the peeling force during the peeling process can be gradually changed from small to large while maintaining welding reliability, making it easier to guide the peeling process in the desired direction.

[0012] Optionally, the weld marks and connecting lines at the ends of the weld marks in a group of weld marks constitute the contour of the group of weld marks, which is close to the center of the current collector and has angles facing the current collector. Furthermore, the first and second openings divide the current collector into multiple circumferential regions along the circumferential direction, and the multiple straight weld marks are divided into multiple groups of weld marks depending on the circumferential region in which they are located. Each group of weld marks includes a central weld mark and multiple lateral weld marks, the central weld mark is located in the center of the circumferential region along the circumferential direction, and the lateral weld marks are distributed symmetrically on both sides of the central weld mark. According to this technical solution, this type of symmetrically arranged group of weld marks has symmetrical peeling forces that need to resist folding each blade (i.e., each circumferential region) of the current collector, thereby guiding the folding direction of each blade and making it easier for each blade of the current collector to fold along the extending direction of the central weld mark.

[0013] **Optionally, in each group of weld marks, the distance between the end of the central weld mark and the central hole of the current collector is the shortest compared to the lateral weld marks, and the length of the central weld mark is d3 ≥ 10 mm.** According to this technical solution, by configuring the end of the central weld mark to be closest to the central hole of the current collector, the folding process of each blade usually starts with peeling and folding near the central hole. Therefore, at the start of folding, only the weld fixing at the end of the central weld mark needs to be peeled, and the initial peeling force that needs to be resisted to start folding is relatively small. By setting the length d3 of the central weld mark to d3 ≥ 10 mm, internal resistance can be reduced.

[0014] Optionally, each group of weld marks includes multiple lateral weld marks positioned at different distances from the central weld mark, with the lateral weld marks further from the central weld mark also being further from the central hole. According to this technical solution, in the folding and tab peeling process of each blade, on the one hand, the symmetrical structure induces the folding and tab peeling process to proceed along the direction of the central axis, and on the other hand, as the folding and tab peeling proceeds along the direction of the central axis, peeling occurs sequentially until a new lateral weld mark needs to be peeled off. Therefore, the magnitude of the peeling force required for the folding and peeling process does not increase abruptly but gradually, and the folding and peeling process can proceed more gradually.

[0015] Arbitrarily, the capacity of the secondary battery is G Ah, the total area of ​​the weld marks is S, and S ≥ G / 8 mm². 2 According to this technical solution, the larger the area of ​​the weld, the larger the area of ​​the conductive current portion between the current collector and the tab, thereby reducing contact resistance.

[0016] Optionally, the projection plane of the explosion-proof valve on the current collector aligned with the height direction of the secondary battery is the explosion-proof valve projection range, and both the first and second openings extend outward along the radial direction of the current collector to the outside of the explosion-proof valve projection range. According to this technical solution, by arranging the first and second openings to extend to the outside of the explosion-proof valve projection range, the area of ​​the explosion-proof valve can be utilized as much as possible as a pressure relief passage, and the cross-sectional area of ​​the pressure relief passage can be increased.

[0017] Optionally, the current collector may further include positioning holes. Furthermore, the positioning holes are located at the outer end of the second opening along the radial direction of the current collector.

[0018] A second aspect of the present invention provides an electronic device having a secondary battery according to the first aspect of the present invention. [Effects of the Invention]

[0019] According to this technical solution, each blade of the current collector can be freely folded by having only one or two easily breakable sections, thus reducing the number of easily breakable sections that need to be broken in order to fold the blade freely, and thus allowing each blade to open more easily under the impact of the pressure-releasing airflow. Furthermore, since the blades of the current collector are interconnected at the center of the current collector, the coplanar flatness between the blades can be maintained at the center during processing and transportation, and when welding the current collector and tab, they can be firmly fixed and welded together, thus avoiding the occurrence of welding defects. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic diagram of the negative electrode current collector used in cylindrical batteries. [Figure 2] This is a schematic diagram of the structure of a secondary battery provided in some embodiments of the present invention. [Figure 3] The laminated structure of an electrode assembly provided in some embodiments of the present invention is shown. [Figure 4]It is a schematic diagram (front view) of the structure of the negative electrode current collector of the secondary battery provided in the first embodiment of the present invention. [Figure 5] It is a schematic diagram (front view) of the structure of the negative electrode current collector of the secondary battery provided in the second embodiment of the present invention. [Figure 6] It is a schematic diagram (front view) of the structure of the negative electrode current collector of the secondary battery provided in the third embodiment of the present invention. [Figure 7] It is a schematic diagram showing the physical quantity represented by the width W of the welding mark in some embodiments of the present invention. [Figure 8] It is a schematic diagram of the electronic device in the embodiment of the present invention.

Mode for Carrying Out the Invention

[0021] The technical solution of the embodiment of the present invention will be clearly and completely described below while referring to the accompanying drawings. Of course, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments that can be obtained by those skilled in the art without creative efforts are within the protection scope of the present invention.

[0022] When a numerical range is shown in the embodiment, it should be understood that, unless otherwise specified in the present invention, both end values of each numerical range and any value between the end values can be selected. Unless otherwise defined, all technical terms and scientific terms used in the present invention, as well as the prior art known to those skilled in the art and the description of the present invention, can be implemented using methods, devices, and materials of the prior art similar or equivalent to those described, used, or manufactured in the embodiments of the present invention.

[0023] <Terms and Their Explanation>

[0024] Terms such as "upper", "lower", "left", "right", "center", "one", etc. used in this specification are only used for the purpose of clarifying the description and are not intended to limit the scope of the present invention. Even if the relative relationship of these terms is changed or adjusted, as long as there is no substantial change in the technical content, it is considered to be within the scope of the present invention.

[0025] The term "easily fractured area" refers to a region that has relatively lower strength compared to the surrounding area, where stress concentrates and fracture is likely to occur.

[0026] Terms such as "radial direction" and "circumferential direction" are based on the axis of the object being described and are not limited to objects that are circular. For example, in the case of an elongated object with an elliptical cross-section, the so-called "axis" refers to the line connecting the intersections of the major and minor axes of each elliptical cross-section. In the case of an elongated object with a rectangular cross-section, the so-called "axis" refers to the line connecting the intersections of the diagonals of each rectangular cross-section.

[0027] The term "blade" refers to a unit of current collector that can be independently folded and unfolded, and in some embodiments, corresponds to one "circumferential region" of the current collector.

[0028] Figure 1 is a schematic diagram of the structure of a current collector. Referring to Figure 1, the current collector includes four foldable and unfoldable blades 1002 uniformly distributed in the circumferential direction. The blades 1002 are connected by easily breakable sections 1006 where stress concentration is likely to occur, and there are further weight-reducing holes 1004 between the blades 1002. However, in a current collector of this type, it is necessary to break four easily breakable sections 1006 in order to fold one blade 1002, making it difficult to completely break and fold all four blades 1002. In addition, the weight-reducing holes 1004 on the current collector reduce the impact force required to fold each blade 1002, making some blades 1002 more difficult to fold and unfold. Furthermore, due to uncertainty in the location of malfunctions that cause extreme conditions, the pressure-relieving airflow does not flow precisely in the direction of the central axis. In response, the main stress support of the current collector may shift by a certain angle relative to the central axis. In such a situation, some of the blades 1002 may open while others remain closed due to insufficient force, increasing the likelihood that the pressure-releasing airflow will be obstructed.

[0029] Similarly, current collectors with multiple foldable blades also exist, but the blades of this type of current collector are not fixed to each other. Although this type of current collector does not require each blade to be broken before folding, the lack of mutual fixation between the blades makes it difficult to maintain flatness between each blade during processing and transportation, which is disadvantageous for processing, and in particular, makes void welding problems more likely during the welding process.

[0030] <Secondary battery>

[0031] A schematic diagram of the structure of a secondary battery 500 provided in some embodiments of the present invention is shown in Figure 2. The secondary battery 500 may be, for example, a cylindrical battery and mainly comprises a housing 600, an electrode assembly 700, a positive electrode assembly 800, and a negative electrode assembly 900. The electrode assembly 700 is located inside the housing 600, and the positive electrode assembly 800 is located in the center of the upper end of the housing 600, and is electrically insulated from the housing 600 by an insulating seal 802. The negative electrode assembly 900 is located at the lower end of the housing 600, and the negative electrode assembly 900 and the housing 600 are electrically connected.

[0032] The structure, materials, and functional characteristics of each component of the secondary battery 500 in several embodiments of the present invention will be described in detail below, divided into several parts.

[0033] <Housing>

[0034] The shape of the housing 600 is such that it can effectively accommodate the wound electrode assembly 700, for example, a cylindrical shape. The material of the housing 600 may be a metal such as steel or aluminum, which has excellent thermal conductivity. Steel is preferred, as a steel housing 600 has excellent strength and can effectively suppress cell expansion, making it suitable for high-energy systems such as silicon-carbon anodes, and the secondary battery 50 itself can also function as a support for structural components.

[0035] The housing 600 includes an outer casing 602 and a cover plate 604. The outer casing 602 is a cylindrical can with an end plate 608 integrally formed or joined to the top of the can. A positive electrode terminal hole 606 is located in the center of the end plate 608. The positive electrode assembly 800, including the positive electrode terminal 804, is positioned to protrude from the top of the cylindrical can through the positive electrode terminal hole 606. The bottom of the outer casing 602 is sealed using the cover plate 604. Specifically, after housing the electrode assembly 700 in the outer casing 602, the negative electrode assembly 900 is placed at the other end of the outer casing 602, the electrolyte is injected, and the cover plate 604 is attached and sealed to obtain the secondary battery 500.

[0036] The specific size of the outer casing 602 can be determined according to the size of the electrode assembly 700, and may be, for example, an outer casing 602 with a diameter of 46 mm or more and a height of 80 mm or more. The thickness of the outer casing 602 may be 0.2 to 0.6 mm, and the surface may be nickel-plated for corrosion prevention and rust prevention.

[0037] After housing the electrode assembly 700 in the outer casing 602, a hob cutter can be used to form rolling grooves 610 around the housing 600 near the opening of the outer casing 602. The rolling grooves 610 are recessed inward from the side wall surface of the outer casing 602, thereby restricting the position of the electrode assembly 700 and preventing it from moving in the height direction Z of the secondary battery 500.

[0038] <Electrode Assembly>

[0039] Referring to Figure 3, the electrode assembly 700 of the cylindrical cell is manufactured by winding. Specifically, the positive electrode sheet 702, the negative electrode sheet 704, and the separator 706 are stacked and then wound to form a core. The separator 706 is placed between the positive electrode sheet 702 and the negative electrode sheet 704 to prevent short circuits caused by direct contact between them. Both the positive electrode sheet 702 and the negative electrode sheet 704 include a base material made of metal foil, a coated area 708 coated with active material, and an uncoated area 710 where no active material is coated. Here, the base material of the positive electrode sheet 702 is aluminum foil, and the positive electrode active material is coated on the main body, i.e., the lower part of the base material. The base material of the negative electrode sheet 704 is copper foil, and the negative electrode active material is coated on the main body, i.e., the upper part of the base material. The uncoated areas 710 of the positive electrode sheet 702 and the negative electrode sheet 704 are located at opposite ends to prevent conductive short circuits between the positive and negative electrodes caused by contact between them. Note that Figure 3 is merely an example, and in other embodiments of the present invention, the uncoated area 710 of the positive electrode sheet 702 may be placed at the bottom of the electrode assembly 700, and the uncoated area 710 of the negative electrode sheet 704 may be placed at the top of the electrode assembly 700. The present invention is not limited thereto.

[0040] The positive electrode sheet 702 is not coated with active material and is used as a positive electrode tab 714 for electrical connection. The lower part of the negative electrode sheet 704 is not coated with active material and is used as a negative electrode tab 716 for electrical connection. In some embodiments, the uncoated metal foil substrate 710 can be cut into a plurality of flag electrodes (not shown), the flag electrodes can be folded toward the electrode assembly central hole 712 of the electrode assembly 700, and then welded to the current collector.

[0041] The center of the core has an electrode assembly central hole 712, where a central roller is positioned during the core manufacturing process. Once core manufacturing is complete, the central roller is removed, leaving the electrode assembly central hole 712. The electrode assembly central hole 712 allows the welding rod to pass through during the welding process between the positive electrode terminal 804 and the positive electrode current collector 806, and also functions as a passage for releasing the gas pressure generated during thermal runaway.

[0042] An electrolyte is also injected into the chamber of the housing 600 that houses the electrode assembly 700. The electrolyte is a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these can be used. The non-aqueous solvent may also contain halogen-substituted compounds obtained by substituting at least some of the hydrogen in these solvents with halogen atoms such as fluorine. Furthermore, the non-aqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel-like polymer or the like. As the electrolyte salt, lithium salts such as LiPF6 can be used. Examples of non-aqueous solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone, methyl ethyl carbonate, γ-butyrolactone, or mixtures thereof.

[0043] The positive electrode active material mainly consists of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. Examples of positive electrode active materials include lithium cobalt oxide, lithium iron phosphate, ternary lithium, and lithium manganese oxide.

[0044] The positive electrode active material also includes a conductive agent and a binder. Examples of conductive agents include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binders include fluorine-based polymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. These resins can also be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) and its salts, and polyethylene oxide (PEO).

[0045] As the negative electrode active material, a carbon material capable of reversibly intercalating and releasing lithium ions is used. Preferred carbon materials include natural graphite such as flake graphite, lump graphite, and earthy graphite, as well as artificial graphite such as lump graphite and graphitized mesocarbon microbeads. The negative electrode mixture layer may also contain a Si-containing compound as the negative electrode active material. Furthermore, the negative electrode active material may be a metal that forms a lithium alloy other than Si, an alloy containing the said metal, or a compound containing the said metal.

[0046] As the binder used for the negative electrode active material, the same materials as those used for the positive electrode active material can be used, such as fluororesins, polyacrylonitriles, polyimide resins, acrylic resins, and polyolefin resins, but styrene-butadiene rubber (SBR) or a modified version thereof is preferred. In addition to SBR, the negative electrode active material may also contain carboxymethylcellulose or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0047] The separator 706 is made of a porous sheet material having ion permeability and insulating properties. Examples of porous sheet materials include porous films, woven fabrics, and nonwoven fabrics. Preferred materials for the separator 706 include polyethylene, olefin resins such as polypropylene, and cellulose. The separator 706 may have a single-layer structure or a laminated structure. A heat-resistant layer or the like may also be formed on the surface of the separator 706.

[0048] <Positive electrode assembly>

[0049] The positive electrode assembly 800 includes a positive electrode terminal 804, an insulating seal 802, and a positive electrode current collector 806.

[0050] The positive terminal 804 is typically secured to the positive terminal hole 606 of the housing 600 by riveting. The riveting method may involve extending the terminal into the housing 600 and riveting it from the inside of the housing 600, or extending the terminal out of the housing 600 and riveting it from the outside of the housing 600. The material of the positive terminal 804 is usually aluminum.

[0051] The positive terminal 804 includes a terminal body 810, an upper flange 812, and a lower flange 814. The upper flange 812 is located at one end of the terminal body 810, and the lower flange 814 is located at the other end of the terminal body 810, with both the upper flange 812 and the lower flange 814 projecting radially outward from the terminal body 810. In some embodiments, the housing 600 and the negative electrode of the electrode assembly 700 are electrically connected. To electrically insulate the positive terminal 804 from the housing 600, an insulating seal 802 is further provided. The insulating seal 802 includes an upper insulating member 816, a lower insulating member 818, and a seal ring 820. The upper insulating member 816 is positioned between the upper flange 812 and the end plate 608 of the housing 600, the lower insulating member 818 is positioned between the end plate 608 of the housing 600 and the lower flange 814 or the positive terminal tab 714, and the seal ring 820 is positioned between the end plate 608 and the positive terminal 804.

[0052] Each positive electrode tab 714 of the electrode assembly 700 is welded to the positive electrode current collector 806, and the positive electrode current collector 806 and the positive electrode terminal 804 are welded together so that current is collected through the current collector and then transmitted to the positive electrode terminal 804.

[0053] <Negative electrode assembly>

[0054] The negative electrode assembly 900 includes at least a negative electrode current collector 902 and an explosion-proof valve 904 integrally formed with the cover plate 604. In some embodiments of the present invention, the negative electrode tab 716 of the electrode assembly 700 is welded to the negative electrode current collector 902, and the negative electrode current collector 902 and the rolling groove 610 portion of the housing 600 are welded together, thereby making electrical contact between the negative electrode of the electrode assembly 700 and the housing 600. In other embodiments of the present invention, the negative electrode current collector 902 and the cover plate 604 may be directly welded together.

[0055] A vulnerable area can be provided on the cover plate 604 and used as an explosion-proof valve 904. In some embodiments of the present invention, the explosion-proof valve 904 is located in the center of the cover plate 604 on the negative electrode side. Specifically, the explosion-proof valve 904 is formed into a circular or other suitable shape by punching or subtractive processing, for example, by forming grooves or through holes in the circumferential direction of the cover plate 604. The explosion-proof valve 904 can open and release pressure when the internal pressure rises rapidly, preventing the battery from exploding.

[0056] <First Embodiment>

[0057] In the secondary battery provided in this embodiment, the negative electrode current collector 902A is arranged as shown in Figure 4.

[0058] In a first embodiment of the present invention, the negative electrode current collector 902A is circular in shape and includes one first opening 102 and two second openings 104.

[0059] The first opening 102 is a linear opening that extends radially upward from the circular negative electrode current collector 902A, and its length is slightly shorter than the diameter of the negative electrode current collector 902A. In other words, both ends of the first opening 102 are adjacent to the outer edge of the negative electrode current collector 902A, yet still spaced apart. The second openings 104 are also linear openings, and the two second openings 104 similarly extend radially along the negative electrode current collector 902A, both evenly distributed on both sides of the first opening 102. The direction of extension of the second openings 104 is perpendicular to the first opening 102. The one first opening 102 and the two second openings 104 evenly divide the negative electrode current collector 902A circumferentially into four blades 106, each with a circumferential angle of 90°. In the center of the negative electrode current collector 902A, the portion between the end of the second opening 104 closest to the first opening 102 and the first opening 102 constitutes an easily breakable portion 108 of the negative electrode current collector 902A, and the two blades 106 located on the same side as the first opening 102 are interconnected by the easily breakable portion 108.

[0060] In this embodiment, the first opening 102 and the second opening 104 are linear openings, but the invention is not limited thereto. In other embodiments of the present invention, the first opening 102 and the second opening 104 may be dashed or curved openings, and correspondingly, their extension direction will be approximately the extension direction of the dashed or curved line.

[0061] When the internal pressure of the secondary battery 500 rises and the pressure is released through the explosion-proof valve 904, the negative electrode current collector 902A breaks at the easy-break section 108 and folds away from the electrode assembly 700, i.e., downward as shown in Figure 2. Each negative electrode current collector 902A provided in this embodiment has only two corresponding easy-break sections 108. When either one of the two easy-break sections 108 breaks, two blades 106 of the negative electrode current collector 902A can be folded (corresponding to opening approximately half the area of ​​the negative electrode current collector 902A). When both of the two easy-break sections 108 break, all four blades 106 fold accordingly. In other words, in this embodiment, the average number of easy-break sections 108 that need to break in order to fold each blade 106 is 0.5. Compared to the conventional technical solution which requires breaking four easily breakable sections to fold one blade, the negative electrode current collector 902A provided in this embodiment can effectively reduce the number of easily breakable sections 108 required to fold each blade 106, and each blade 106 can be opened more easily under the impact of a pressure-releasing airflow. Furthermore, since the blades 106 of the negative electrode current collector 902A are interconnected by easily breakable sections 108 in the center of the negative electrode current collector 902A, the coplanar flatness between the blades 106 can be maintained by the easily breakable sections 108 during processing and transportation, thereby allowing the negative electrode current collector 902A and the negative electrode tab 716 to be firmly fixed and welded together, thus avoiding the problem of void welding.

[0062] In this embodiment, the end of the second opening 104 closest to the first opening 102 is a cleanly cut right-angle shape, but the present invention is not limited thereto. In other embodiments of the present invention, the end of the second opening 104 closest to the first opening 102 may have a variety of other different shapes to accommodate various battery design requirements and pressure relief requirements. For example, in some embodiments, the end of the second opening 104 closest to the first opening 102 may be configured as a rounded corner or an acute angle shape directed toward the center of the negative electrode current collector 902A.

[0063] Continuing to refer to Figure 4, in this embodiment, the negative electrode current collector 902A is evenly divided into four blades 106 by the first opening 102 and the second opening 104, i.e., divided into four circumferential regions 110 that are uniformly distributed in the circumferential direction. The negative electrode current collector 902A is welded to the negative electrode tab 716 via at least a number of straight welds. The number of straight welds is similarly evenly divided into four weld group 112, each weld group 112 including one central weld 114 and a number of lateral welds 116. Here, the central weld 114 is the longest of the weld group 112 and is located in the center of each blade 106, and the lateral welds 116 are distributed symmetrically on both sides of the central weld 114. Here, “located in the center” means located in the center of the circumferential region 110 along the circumferential direction of the negative electrode current collector 902A. In other embodiments, there may be two or more central weld marks 114 in each weld mark group 112. Specifically, in this embodiment, each blade 106 is a sector occupying a 90° circumferential angle. The central weld mark 114 is located in the center, extends radially, and further divides each blade 106 into two sectors with a 45° circumferential angle. Two lateral weld marks 116 are located on each side of the central weld mark 114. Since each lateral weld mark 116 is parallel to and substantially equidistant from the central weld mark 114, the uniformity of the weld distribution can be improved, and the integrity and reliability of the negative electrode tab 716 weld can be improved. Furthermore, during the folding process of each blade 106, this type of symmetrically arranged weld mark group 112 can provide a symmetrical peeling force distribution, thereby guiding the folding direction of each blade 106 so that each blade 106 folds along the extending direction of the central weld mark 114.

[0064] By positioning the central weld 114 as the longest, specifically by positioning the radial inner end of the central weld 114 closer to the center of the negative electrode current collector 902A than the inner end of the lateral weld 116, the magnitude of the initial peeling force required to initiate folding of each blade 106 can be reduced. Specifically, the folding process of each blade 106 usually begins with the breaking and folding of the easily breakable section 108, that is, folding usually begins from the center of the negative electrode current collector 902A. Therefore, once folding begins, there is a gradient in the distance between the central weld 114 and the lateral weld 116 and the distance between the center of the negative electrode current collector 902A. As a result, to initiate folding of each blade 106, it is not necessary to resist the joining forces of multiple welds, but only to resist or break the joining force of the radial inner end of the central weld 114. This significantly reduces the magnitude of the initial peeling force that needs to be resisted to initiate folding. More preferably, the length d3 of the central weld mark 114 is set to d3 ≥ 10 mm. By setting the central weld mark 114 to the preferred length range, the number of turns of the negative electrode tab 716 welded to the negative electrode current collector 902A can be increased, thereby reducing the internal resistance of the secondary battery.

[0065] Similarly, continuing to refer to Figure 4, the weld marks in the weld mark group 112 (including the central weld mark 114 and the lateral weld marks 116) and the connecting lines at the ends of the weld marks constitute the contour 132 of the weld mark group. The contour 132 is close to the center of the negative electrode current collector 902A and has an angle facing the center of the current collector 902A, i.e., the upper right corner of the contour 132 of the weld mark group in Figure 4. According to the above method, the bonding force that needs to be resisted to initiate folding of each blade 106 is relatively small, thereby reducing the magnitude of the initial peeling force that needs to be resisted to initiate folding and making the increase in peeling force more gradual.

[0066] The lateral weld marks 116 include a first lateral weld mark 118 and a second lateral weld mark 120. The distance between the first lateral weld mark 118 and the central weld mark 114 is closer than that between the second lateral weld mark 120. The distance between the radial inner end of the first lateral weld mark 118 and the center of the negative electrode current collector 902A is closer than that between the second lateral weld mark 120. In other words, among the multiple lateral weld marks 116, the distance between the lateral weld marks 116 further from the central weld mark 114 and the center of the current collector 902A is also greater. According to the above method, on the one hand, the symmetrical structure of the weld marks 112 induces the folding and peeling process of the blade 106 to proceed along the direction of the central weld mark 114, and on the other hand, as it is guided to peel along the direction of the central weld mark 114, the distance from different lateral weld marks 116 to the center of the negative electrode current collector 902A has a gradient, so the peeling edge moves sequentially to different positions where new lateral weld marks 116 need to be peeled off during the movement process. After folding begins, the folded portion of the negative electrode current collector 902A can gain kinetic energy to fold outwards and overcome the gradually increasing peeling force.

[0067] In this embodiment, both the central weld mark 114 and the lateral weld marks 116 are straight weld marks, and the width of a single straight weld mark is W ≤ 1 mm. By using straight weld marks within the above width range, the peeling force required in the initial stage of peeling becomes relatively small, and as the peeling process progresses, because the width of the weld marks is relatively small, even if the moving tip of the peeled area moves to a new weld mark during the peeling process, the increase in peeling force is relatively small, making it easy to gradually advance the peeling process. Furthermore, since the line width of the straight weld marks does not change substantially, the magnitude of the peeling force contributed by a single weld mark during the peeling process also does not change substantially. As a result, by using multiple straight weld marks in combination, it is possible to form a smooth peeling force gradient that gradually increases during the peeling process while maintaining the reliability of the weld, making it easier to advance the peeling process in the desired direction.

[0068] According to the method described above, when the explosion-proof valve 904 is opened, the secondary battery 500 provided in this embodiment can fully open its four blades 106 by simply breaking two easily breakable sections 108, making the breaking and folding process of the negative electrode tab 716 smoother and more efficient, thereby enabling the secondary battery 500 to achieve more reliable and efficient pressure release when faced with extreme conditions.

[0069] <Second Embodiment>

[0070] Figure 5 is a schematic diagram of the structure of the negative electrode current collector 902B of the secondary battery 500 provided by the second embodiment of the present invention.

[0071] Referring to Figure 5, the main difference between the structure of the negative electrode current collector 902B provided by the second embodiment and the structure of the negative electrode current collector 902A provided by the first embodiment is that, in the second embodiment, the first opening 102 has a central hole 122 located at a position corresponding to the center of the negative electrode current collector 902B, and the central hole 122 has two corners 124, each of which is positioned toward the ends of the two second openings 104 closer to the first opening 102. By positioning the corners 124, stress concentration at the fracture initiation end of the easily fractured portion 108 (i.e., the inner end along the radial direction of the easily fractured portion 108) is increased, making the easily fractured portion 108 easier to fracture, and furthermore, by positioning the corners 124, the fracture pattern of the easily fractured portion 108 is more likely to be in the direction of the connecting line from the central hole 122 to the end of the second opening 104.

[0072] The straight-line distance between the two corners 124 is the radial size d1 of the central hole 122, and in this embodiment, the radial size of the central hole 122 is d1 ≥ 8 mm. Because of the presence of the acute corners 124, the mold used to process this type of negative electrode current collector 902B is prone to wear and damage to its edges during the processing. By setting the radial size d1 of the central hole 122 to d1 ≥ 8 mm, the service life of the mold used to process the negative electrode current collector 902B can be effectively improved, and the increase in foreign matter due to mold wear can be avoided.

[0073] In this embodiment, the opening angle θ of the corner 124 is 90°. In some embodiments of the present invention, the opening angle θ of the corner 124 may be any other suitable value that satisfies the condition 45° ≤ θ ≤ 90°. The opening angle of the corner 124 should not be too large or too small. If the corner 124 is too large, stress concentration becomes difficult, and if the corner 124 is too small, machinability deteriorates. By setting the corner 124 within the above range, it is possible to achieve both stress concentration and machinability.

[0074] Furthermore, in this embodiment, a positioning hole 126 is provided at the radial outer end of the second opening 104. Since the negative electrode current collector 902B provided in the embodiment of the present invention has a relatively centrally symmetric and axially symmetric structure, by providing the positioning hole 126 at the radial outer end of the second opening 104, on the one hand, it can be machined integrally with the second opening 104, improving machining convenience. On the other hand, the positioning hole 126 can assist in positioning during the welding process and improve the positioning effect in the negative electrode tab 716 and negative electrode current collector 902B process. In some embodiments, the positioning hole 126 may be a positioning hole 126 that facilitates pallet positioning of the negative electrode current collector 902B during the transport process, or it may have a positioning function in both the welding process and the transport process. Furthermore, in this embodiment, the positioning hole 126 is described as being located at the outer end of the second opening 104 along the radial direction of the negative electrode current collector 902B. However, in other embodiments, the positioning hole 126 may be located at other suitable locations on the negative electrode current collector 902B, and the present invention is not limited thereto.

[0075] In this embodiment, the shape of the end of the second opening 104 closest to the first opening 102 corresponds to the corner 124 and is an acute angle positioned opposite the corner 124. By positioning it at an acute angle, the stress concentration in the easily fractured portion 108 is increased, which can further guide the fracture direction of the easily fractured portion 108, making it easier to fracture the easily fractured portion 108.

[0076] According to the method described above, the negative electrode current collector 902B provided in the second embodiment utilizes the characteristic that stress concentrates at the corners 124 by arranging the central hole 122 having the corners 124, thereby allowing the easily fractured portion 108 to fracture more easily and guiding the fracture direction.

[0077] <Third Embodiment>

[0078] Figure 6 is a schematic diagram (front view) of the structure of the negative electrode current collector 902C of a secondary battery provided by the third embodiment of the present invention.

[0079] Referring to Figure 6, the main difference between the structure of the negative electrode current collector 902C provided by the third embodiment and the structures of the negative electrode current collector 902C provided by the first and second embodiments is that, in the third embodiment, the negative electrode current collector 902C has four second openings 104 extending radially along the negative electrode current collector 902C, the angle between the second openings 104 is 60°, the angle between the first opening 102 and the second opening 104 is also 60°, and both the first opening 102 and the second opening 104 equally divide the negative electrode current collector 902C into six circumferential regions along the circumferential direction, i.e., divided into six blades 106 that, after the easily breakable portion 108 is completely broken, fold independently and peel off from the negative electrode tab 716.

[0080] The explosion-proof valve 904 is obtained by forming a circular notch or groove in the center of the cover plate 604 (or end wall). The projection plane of the explosion-proof valve 904 on the negative electrode current collector 902C along the Z direction is the explosion-proof valve projection range 128, which is the range shown by the dashed line in Figure 6. In this embodiment, the radial outer ends of both the first opening 102 and the second opening 104 extend beyond the explosion-proof valve projection range 128. In other words, both the first opening 102 and the second opening 104 extend radially beyond the explosion-proof valve projection range 128, thereby maximizing the use of the area of ​​the explosion-proof valve 904 as a pressure release passage and increasing the cross-sectional area of ​​the pressure release passage.

[0081] On the other hand, since both the first opening 102 and the second opening 104 extend outward radially to the outside of the explosion-proof valve projection range 128, the maximum opening angle / area when the six blades 106 are open is limited by the edge of the explosion-proof valve 904. Taking the left blade 106 in Figure 6 as an example, the maximum opening area of ​​each blade 106 is actually the area shown in the shaded area 130 in Figure 6. Compared to the case where the blades are divided into four blades 106 as in the first and second embodiments, although the arc length of each blade 106 decreases when the blades are divided into six blades 106, the proportion of the sum of the maximum opening areas of all blades 106 to the area of ​​the explosion-proof valve projection range 128 is actually larger. In other embodiments, the number of blades 106 may be more than six, but as the number of blades 106 increases, the difficulty of processing the current collector increases significantly, while the increase in the sum of the maximum opening areas is not so significant. Furthermore, the average number of easily breakable sections 108 that need to be broken in order to fold each blade 106 also increases accordingly. Therefore, more preferably, the number of blades 106 is four or six, and the number of corresponding second openings 104 is two or four.

[0082] In this embodiment, the center of the electrode assembly 700 has an electrode assembly central hole 712, the diameter of which is d2. Referring to Figure 6, in this embodiment, the number of corners 124 of the central hole 122 is also 4, corresponding to the number of second openings 104. The straight-line distance between the outer edges of the two furthest corners 124 (i.e., two non-adjacent corners 124) is the radial size d1 of the central hole 122, where d1 > d2. When the explosion-proof valve 904 is opened under extreme conditions, the electrode assembly central hole 712 typically constitutes a passage for pressure-relieving airflow, and the material flow of substances including electrolyte, particles, etc., is mainly discharged from the outer periphery of the airflow passage, and the impact force of the material flow is usually greater than that of the airflow. By making d1 > d2, the material flow directly collides with the corners 124, increasing the impact force on the corners 124, making the easily breakable portion 108 more likely to break from the corners 124.

[0083] Furthermore, in this embodiment, in each group of weld marks 112, one lateral weld mark 116 is symmetrically arranged on both sides of the central weld mark 114. The extension direction of the lateral weld marks 116 is inclined with respect to the central weld mark 114 and is parallel to the first opening 102 or second opening 104 adjacent to the lateral weld mark 116. This allows the lateral weld marks 116 to be arranged more uniformly, improving the uniformity of the weld mark distribution.

[0084] According to the method described above, the third embodiment of the present invention provides a negative electrode current collector 902C in which the sum of the maximum opening areas of each blade 106 is larger, thereby increasing the area of ​​the pressure release passage, which allows for rapid pressure release, while also providing ease of processing of the negative electrode current collector 902C.

[0085] In the above embodiment of the present invention, the capacity of the secondary battery 500 is G Ah, the total area of ​​the weld marks on the negative electrode current collector 902 is S, and S is S ≥ G / 8 mm 2 This satisfies the following conditions. The larger the area of ​​the weld marks, the larger the area of ​​the conductive current portion between the negative electrode current collector 902 and the negative electrode tab 716, thereby reducing contact resistance.

[0086] In the above embodiment of the present invention, the length of the easily fractured portion 108 is d4 (see Figure 4), and since the distance between the end of the second opening 104 closest to the first opening 102 and the first opening 102 is limited to d4 < 2 mm, the easily fractured portion 108 is a portion that fractures relatively easily.

[0087] In the above embodiment of the present invention, the weld marks in the group of weld marks 112 may be straight weld marks, or curved weld marks such as dashed lines or corrugated weld marks. Referring to Figure 7, in the case of dashed lines or curved weld marks, the width W of the weld mark is the characteristic size shown in Figure 7. By setting the width of the weld mark to W ≤ 1 mm, it is possible to prevent excessive tension between the negative electrode current collector 902 and the negative electrode tab 716 from affecting the folding of the negative electrode current collector 902.

[0088] <Electronic equipment>

[0089] Figure 8 shows a schematic diagram of the electronic device 400 in this embodiment. As shown in Figure 8, the electronic device 400 includes a battery pack 300 and an operating unit 200 electrically connected to the battery pack 300. For example, the electronic device 400 is a vehicle, which may be a gasoline vehicle, a natural gas vehicle, or a new energy vehicle. The new energy vehicle may be, but is not limited to, a pure electric vehicle, a hybrid electric vehicle, or an extended-range electric vehicle. The operating unit 200 is the vehicle body, and the battery pack 300 is located at the bottom of the vehicle body, providing support for the electrical energy necessary for the vehicle to run and for the operation of electrical components within the vehicle. However, in some other embodiments, the electronic device 400 may further be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, a power tool, etc. A spacecraft includes airplanes, rockets, space shuttles, spaceships, etc. The operating unit 200 is a unit component that can obtain electrical energy from the battery pack 300 and perform corresponding tasks, such as a fan blade rotation unit or a vacuum cleaner suction unit. Electric toys include stationary or mobile electric toys such as game consoles, electric car toys, electric boat toys, and electric airplane toys. Power tools include power tools for metal cutting, grinding, assembly, and railway power tools, and include, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. Embodiments of the present invention do not impose any special limitations on the electronic devices 400 described above.

[0090] The foregoing describes only preferred embodiments of the present invention and does not limit it. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are within the scope of protection of the present invention. [Industrial applicability]

[0091] The secondary battery and electronic device of this application can be applied in the field of battery technology. [Explanation of Symbols]

[0092] 1002: Blade 1004: Lightweight hole 1006: Easily fractured section 102: First opening 104: Second opening 106: Blade 108: Easily fractured section 110: Circumferential region 112: Group of weld marks 114: Central weld mark 116: Lateral weld marks 118: First lateral weld mark 120: Second lateral weld mark 122: Center hole 124: Corner 126: Positioning hole 128: Explosion-proof valve projection range 130:Shaded area 132: Outline of welding marks 200: Operating part 300: Battery pack 400:Electronic equipment 500: Secondary battery 600: Housing 602: Outer can 604: Cover plate 606: Positive terminal hole 608: End plate 610: Rolling groove 700: Electrode Assembly 702: Positive electrode sheet 704: Negative electrode sheet 706: Separator 708: Application area 710: Non-applied area 712: Electrode assembly center hole 714: Positive Tab 716: Negative electrode tab 800: Positive electrode assembly 802: Insulating seal 804: Positive terminal 806: Positive electrode current collector 810: Terminal body 812: Upper flange 814: Lower flange 816: Upper insulating material 818: Lower insulating member 900: Negative electrode assembly 902 / 902A / 902B / 902C: Negative electrode current collector 904: Explosion-proof valve

Claims

1. It is a secondary battery, A housing including an end wall, on which an explosion-proof valve is positioned, An electrode assembly housed within the housing, with a tab extending from one end facing the explosion-proof valve, A current collector is positioned between the end wall and the tab and welded to the tab, Includes, The current collector includes a first opening and a plurality of second openings, the first opening penetrates the center of the current collector and extends along the radial direction of the current collector, and the plurality of second openings are distributed on both sides of the first opening. The portion between the end of the second opening closest to the first opening and the first opening constitutes the easily breakable portion of the current collector. The easily breakable portion is configured such that when the internal pressure of the secondary battery rises and the pressure is released through the explosion-proof valve, the current collector breaks at the easily breakable portion and folds away from the electrode assembly. A secondary battery characterized by the following features.

2. The current collector has two of the second openings that extend along the radial direction of the current collector, The first and second openings divide the current collector into four independently foldable circumferential regions. A secondary battery according to claim 1, characterized in that...

3. The current collector has four of the second openings extending along the radial direction of the current collector, The first and second openings divide the current collector into six independently foldable circumferential regions. A secondary battery according to claim 1, characterized in that...

4. The first opening has a central hole at a position corresponding to the center of the current collector, The central hole has multiple corners, Each of the aforementioned corners is positioned toward the end of the plurality of the second openings that is closest to the first opening. A secondary battery according to claim 1, characterized in that...

5. The maximum straight-line distance between the outer edges of the multiple corners is the radial size d of the central hole. １ And, The radial size of the central hole is d １ It is ≥ 8 mm. The secondary battery according to claim 4, characterized in that

6. The opening angle of the aforementioned corner is θ, where 45° ≤ θ ≤ 90°. The secondary battery according to claim 5, characterized in that

7. The center of the electrode assembly includes a central hole in the electrode assembly. The diameter of the central hole of the electrode assembly is d ２ And, The maximum straight-line distance between the outer edges of the multiple corners is the radial size d of the central hole of the current collector. １ And, d １ >d ２ That is, The secondary battery according to claim 4, characterized in that

8. Multiple weld marks are formed between the current collector and the tab by welding. The first opening and the second opening divide the current collector into a plurality of circumferential regions along the circumferential direction. The multiple weld marks located in each of the circumferential regions form a single group of weld marks. The width of each weld mark is W ≤ 1 m. A secondary battery according to claim 1, characterized in that...

9. The aforementioned weld marks include multiple straight weld marks. The secondary battery according to claim 8, characterized in that

10. Each group of weld marks includes a central weld mark and multiple lateral weld marks. The aforementioned central weld mark is located in the center of the circumferential region along the circumferential direction. The lateral weld marks are distributed symmetrically on both sides of the central weld mark. The secondary battery according to claim 9, characterized in that

11. In each group of weld marks, the distance between the inner end of the central weld mark in the radial direction and the central hole is smaller than the distance between any of the lateral weld marks and the central hole. The length of the central weld mark is d ３ ≥ 10 mm The secondary battery according to claim 10, characterized in that

12. The capacity of the aforementioned secondary battery is G Ah, The total area of ​​the weld marks is S. S ≥ G / 8 mm ２ That is, The secondary battery according to claim 8, characterized in that

13. The projection plane of the explosion-proof valve on the current collector along the height direction of the secondary battery is the projection range of the explosion-proof valve. Both the first and second openings extend outward along the radial direction of the current collector to the outside of the explosion-proof valve projection range. A secondary battery according to claim 1, characterized in that...

14. The current collector further includes positioning holes, The positioning hole is located at the outer end of the second opening along the radial direction of the current collector. A secondary battery according to claim 1, characterized in that...

15. The length of the easily breakable portion is d ４ <2 mm, A secondary battery according to claim 1, characterized in that...

16. An electronic device characterized by having a secondary battery according to any one of claims 1 to 15.

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