Methods for assembling rechargeable batteries, rechargeable batteries, battery packs, and electronic devices

Abstract

The present invention provides a method for assembling a secondary battery, a secondary battery, a battery pack, and an electronic device that can improve the stability of the welded structure of the current collector. [Solution] The method for assembling a secondary battery includes an assembly step of assembling a current collector and a pole pole and bringing the wall portion of the pole pole into contact with the current collector, and a welding step of irradiating a laser spot onto the wall portion and moving the laser spot along a spiral trajectory to weld the wall portion and the current collector to form a weld mark, wherein the weld mark extends from a first end to a second end on a cross section passing through the axis of the pole pole, the first end is located on the side of the wall portion facing away from the current collector, and the second end is located inside the current collector.

Description

[Technical Field]

[0001] This invention relates to the technical field of battery assembly, and more particularly to a method for assembling a secondary battery, a secondary battery, a battery pack, and an electronic device. [Background technology]

[0002] In conventional welding techniques, the electrode poles and current collectors of a battery are often welded together by applying welding energy from one side of the current collector. However, this welding method increases the likelihood of foreign matter being generated inside the battery because the welding slag produced directly comes into contact with the inside of the battery, thus affecting the safety performance of the battery.

[0003] In order to reduce foreign matter inside batteries and improve assembly efficiency, a method of welding the poles and current collectors to the outside of the poles using laser penetration welding is attracting attention in this field. However, laser penetration welding is difficult to control, and it is difficult to maintain a uniform and stable depth of the molten pool, which makes it prone to technical problems such as miswelding and burn-through. [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention provides a method for assembling a secondary battery, a secondary battery, a battery pack, and an electronic device that can improve the stability of the welded structure of the poles and current collectors. [Means for solving the problem]

[0005] A first aspect of the present invention provides a method for assembling a secondary battery. This method includes an assembly step of assembling a current collector and an electrode pole so that the wall portion of the electrode pole contacts the current collector, and a welding step of irradiating the wall portion with a laser spot and moving the laser spot along a spiral trajectory to weld the wall portion and the current collector to form a weld mark. Here, on a cross section passing through the axis of the electrode pole, the weld mark extends from a first end to a second end, the first end is located on the side of the wall portion facing away from the current collector, and the second end is located inside the current collector.

[0006] Selectively, during the welding step, the laser spot rotates from the inside out along a helical trajectory.

[0007] Selectively, a fluid injection hole is placed in the center of the wall, and during the welding step, the laser spot rotates around the fluid injection hole from the outside to the inside along a spiral trajectory.

[0008] Selectively, a fluid injection hole is placed in the center of the wall, and the welding step includes a first welding step in which a laser spot rotates around the fluid injection hole from the outside to the inside along the trajectory of a first helix to form a first helical weld mark, and a second welding step in which a laser spot rotates from the inside to the outside along the trajectory of a second helix to form a second helical weld mark, the second helical weld mark surrounding the first helical weld mark.

[0009] Selectively, the middle portion of the current collector has a projection that protrudes toward one side of the pole column, and the portion where the wall and the projection contact each other constitutes a contact surface, the contact surface having a central region and an edge region, and in the welding step, the movement of the laser spot starts from the central region and ends in the edge region, and the weld mark located in the edge region surrounds the weld mark located in the central region.

[0010] Selectively, during the welding step, the optical magnification ratio of the laser spot is 2.5 to 3.5 times.

[0011] Selectively, the wavelength of the laser spot is 600-1200 nm.

[0012] Selectively, spiral trajectories are Archimedean spiral trajectories.

[0013] Selectively, during the welding step, a laser galvanometer is used, moving the laser spot along a spiral trajectory at a speed of 300 mm / s or more.

[0014] Selectively, the laser spot's focal point is located on the side away from the current collector in the wall.

[0015] A second aspect of the present invention provides a secondary battery comprising a housing, an electrode assembly, and a current collector. The housing includes an end plate and a side wall surrounding the end plate, the end plate having an opening. The electrode assembly is housed inside the housing. The current collector is positioned between the electrode assembly and the end plate and is electrically connected to the electrode assembly. A pole is fixed to the end plate through the opening, and the pole includes a wall. The wall and the current collector are welded to form a weld, the weld having a helical trajectory. On a cross section passing through the axis of the pole, the weld extends from a first end to a second end, the first end located on the side of the wall facing away from the electrode assembly, and the second end located inside the current collector.

[0016] Selectively, the middle portion of the current collector has a projection that extends toward one side of the pole column, and the portion where the wall and the projection contact each other constitutes a contact surface, the contact surface having a central region and an edge region, the weld marks starting from the central region along the direction of movement of the laser spot and ending in the edge region, and the weld marks located in the edge region surround the weld marks located in the central region.

[0017] A third aspect of the present invention provides a battery pack comprising a plurality of secondary batteries, the secondary batteries being the secondary batteries provided in the second aspect of the present invention.

[0018] The fourth aspect of the present invention further provides an electronic device. The electronic device includes the battery pack provided by the third aspect of the present invention.

Advantages of the Invention

[0019] By adopting the central locus of the spiral-shaped laser spot in the technical solution of the present invention, in the path where the laser spot moves, the spot does not pass through the same point twice, so the heat influence between two adjacent curves of the welding mark can be reduced. As a result, the consistency of the penetration depth is improved and the stability of the welding process is ensured.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram of the internal structure of the secondary battery provided by the first embodiment of the present invention. [Figure 2] It is a cross-sectional view of the positive terminal assembly of the secondary battery provided by the first embodiment of the present invention. [Figure 3] It is a top view of the positive terminal assembly in FIG. 2. [Figure 4] It is a schematic diagram of the spiral movement locus of the laser spot in the first embodiment. [Figure 5] It is a schematic flow diagram of the method for assembling the secondary battery provided by the first embodiment. [Figure 6] It is a cross-sectional view of the positive terminal assembly in the second embodiment. [Figure 7] It is a schematic diagram of the central locus corresponding to the welding mark in the second embodiment, that is, a schematic diagram of the movement locus of the laser spot. [Figure 8] It is a schematic diagram of the battery pack provided by the embodiment of the present invention. [Figure 9] It is a schematic diagram of the electronic device provided by the embodiment of the present invention, specifically, a schematic diagram of a vehicle.

Modes for Carrying Out the Invention

[0021] The technical solutions in embodiments of the present invention will be clearly and completely described below in combination with the accompanying drawings. Clearly, the embodiments described are not all embodiments of the present invention, but only a few. All other embodiments that can be obtained based on embodiments of the present invention without creative work by an ordinary person of the art are all within the scope of protection of the present invention.

[0022] <Terminology and its interpretation>

[0023] The term "center trajectory" refers to the trajectory path formed as the laser spot moves its center. In this embodiment, since the weld mark is formed by the laser spot moving along a predetermined path, the centers of the two substantially overlap. Therefore, in the embodiment of the present invention, the center trajectory of the laser spot is the same as the center trajectory of the weld mark.

[0024] The term "arm" refers to a curved line segment within a 2π-angle range of a spiral. Adjacent "arms" are two curved line segments in polar coordinates whose rotation angle difference is 2π. For example, two curved line segments of a spiral with rotation angles of 0-2π and 2π-4π constitute an adjacent arm, and two curved line segments with rotation angles of 2π-4π and 4π-6π also constitute an adjacent arm.

[0025] In this invention, unless otherwise specified, the term "penetration depth" refers to the distance from the first end to the second end of the weld in the axial direction of the pole column. Due to variations in welding energy, this distance may differ at different welding locations.

[0026] <First Embodiment>

[0027] Figure 1 is a schematic diagram of the internal structure of the secondary battery 1 provided by the first embodiment of the present invention. Figure 2 is a cross-sectional view of the positive electrode terminal assembly 10 of the secondary battery 1 provided by the first embodiment of the present invention. Referring to Figures 1 and 2, in this embodiment, the secondary battery 1 is a cylindrical secondary battery 1, that is, a battery cell unit packaged using a cylindrical housing 101.

[0028] The housing 101 can be made of materials such as copper, iron, aluminum, steel, or aluminum alloy. The side walls 103 of the housing 101 are cylindrical, and the hollow portion is used to house the electrode assembly 20.

[0029] In Figure 1, the upper end of the housing 101 is used to form the positive electrode terminal assembly 10, and the lower end of the housing 101 is used to form the negative electrode terminal assembly 11. The negative electrode terminal assembly 11 electrically connects one electrode of the electrode assembly 20 to the housing 101. The positive electrode terminal assembly 10 electrically connects the other electrode of the electrode assembly 20 to the positive electrode pole 40, electrically isolating the positive electrode pole 40 from the housing 101.

[0030] Figure 2 shows the structure of the upper end of the housing 101 in Figure 1, that is, the end that forms the positive terminal assembly 10. At this end, the side wall portion 103 is bent inward and extended to form a substantially flat end plate 105. The end plate 105 has an opening 107 in the center, thereby forming the positive terminal assembly 10 in the opening 107. The end plate 105 and the side wall portion 103 may be integrally molded or may be separate structures.

[0031] The thickness of the side wall portion 103 of the housing 101 may be approximately 0.2 to 0.6 mm, and the thickness of the end plate 105 may be slightly greater than the thickness of the side wall portion 103. For example, the end plate 105 can have a thickness of approximately 0.6 to 1.0 mm. By making the thickness of the side wall portion 103 thinner, the volume of the electrode assembly 20 that can be housed can be increased, thereby improving the energy density of the secondary battery 1. At the same time, by not making the thickness of the side wall portion 103 too thin, the strength of the housing 101 is increased, and the safety performance of the secondary battery 1 is ensured. In some embodiments, corrosion and rust can be prevented by forming a nickel plating layer on the surface of the housing 101.

[0032] The electrode assembly 20 of the secondary battery 1 is housed in a cavity formed by being surrounded by the cylindrical side wall portion 103 of the housing 101.

[0033] The electrode assembly 20 includes a positive electrode sheet, a separator, and a negative electrode sheet wound around the axial direction of the housing 101. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, and a first coated region on the positive electrode sheet is formed where the positive electrode active material layer is coated and a first uncoated region is not coated. The first coated region and the first uncoated region are arranged along the axial direction of the housing 101, and the first uncoated region extends out of the separator toward one end in the height direction of the secondary battery 1, and forms a positive electrode tab that is folded toward the axis of the housing 101 and stacked. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector, and a second coated region on the negative electrode sheet is formed where the negative electrode active material layer is coated and a second uncoated region is not coated. The second coated area and the second uncoated area are arranged along the axial direction of the housing 101, and the second uncoated area extends beyond the separator toward the other end in the height direction of the secondary battery 1, and is folded toward the axis of the housing to form a stacked negative electrode tab. The separator is placed between the positive electrode sheet and the negative electrode sheet, separating the positive electrode active material layer and the negative electrode active material layer. Taking the lithium-ion secondary battery 1 as an example, the material of the positive electrode current collector may be aluminum, and the positive electrode active material layer contains positive electrode active material, which may be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The material of the negative electrode current collector may be copper, and the negative electrode active material layer contains negative electrode active material, which may be carbon or silicon, etc. The material of the separator may be polypropylene (PP) or polyethylene (PE), etc. While all well-known core structures in this field can be applied to the secondary battery 1 provided by the present invention, they will not be described in detail here.

[0034] The electrode assembly 20 may be immersed in an electrolyte (e.g., an electrolyte solution), which can be injected into the hollow chamber of the housing 101 through an injection hole. The location of the injection hole is not limited in this embodiment. The electrolyte may be a salt containing lithium ions, and the electrolyte can be used after being dissolved in an organic solvent.

[0035] As organic solvents, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or mixtures thereof can be selected.

[0036] The current collector 30 is made of a conductive metallic material, such as aluminum or copper. The longitudinal end of the electrode assembly 20 is bent and then extended in a direction parallel to the current collector 30, connecting the bent portion with the current collector 30 and completing the electrical connection between the current collector 30 and the electrode assembly 20. The side of the current collector 30 away from the electrode assembly 20 is connected to the positive pole column 40, thereby using the current collector 30 to collect and conduct current.

[0037] Referring to Figure 2, in this embodiment, the current collector member 30 of the positive terminal assembly 10 is positioned between the electrode assembly 20 and the positive pole 40, specifically on one side of the electrode assembly 20 closer to the positive pole 40. The lower surface of the current collector member 30 is coupled to the electrode assembly 20, and the upper surface of the current collector member 30 is welded and fixed to the positive pole 40 for electrical connection.

[0038] The main body of the positive pole column 40 is a cylindrical columnar portion 402 that penetrates the opening 107. Both ends of the columnar portion 402 have an outer flange portion 401 and an inner flange portion 403 that extend radially outward from the columnar portion. The outer flange portion 401 is connected to one end of the columnar portion 402 that is located on the outside of the housing 101, and the projection of the outer flange portion 401 along the axial direction covers the opening 107. The inner flange portion 403 is connected to one end of the columnar portion 402 that is located on the inside of the housing 101, and the projection of the inner flange portion 403 along the axial direction also covers the opening 107. The columnar portion 402 has a groove 409, and the bottom of the groove 409 is a flat wall portion 405. The position of the positive pole column 40 is fixed using the insulating portion 50 by fitting the shape and size of the outer flange portion 401 and the inner flange portion 403 with the shape and size of the insulating portion 50. The insulating section 50 is installed between the positive pole 40 and the housing 101, electrically isolating the positive pole 40 and the housing 101. The insulating section 50 includes a seal ring 502, and the sealing effect of this section is ensured by bringing both sides of the seal ring 502 into contact with the inner edge of the housing 101 and the outer edge of the positive pole 40, respectively. The material of the seal ring 502 may be ethylene propylene diene rubber, fluorosilicone rubber, or fluororubber, but the present invention is not limited thereto.

[0039] The plane on which the wall portion 405 is located is perpendicular to the axial direction of the cylindrical secondary battery 1 (i.e., the vertical direction in Figure 2), and the outer edge of the wall portion 405 is connected to the cylindrical portion of the positive electrode column 40. In this embodiment, by integrally molding the wall portion 405 and the cylindrical portion of the positive electrode column 40, the overall strength of the positive electrode column 40 is increased, and the convenience of automated assembly is improved.

[0040] The positive pole column 40 is welded and fixed to the current collector member 30 using the wall portion 405. Specifically, the welding of the wall portion 405 and the current collector member 30 is completed using laser penetration welding. The laser penetration welding device projects a laser spot onto the upper surface of the wall portion 405, and the thermal effect of the laser spot rapidly generates a large amount of heat locally, causing the local temperature to rise rapidly, melting the metal of the wall portion 405 and creating a molten pool. In addition, the localized high temperature not only penetrates and melts the wall portion 405, but the heat is also conducted through the wall portion 405 to the upper surface of the current collector member 30, melting a portion of the metal material on the upper surface of the current collector member 30. As a result, a weld mark 60 is formed that penetrates the wall portion 405 and fits into the current collector member 30 when viewed from the cross-sectional direction in Figure 2. Referring to Figure 2, in the direction from the positive pole column 40 to the current collector member 30, the weld mark 60 starts from the upper surface of the wall portion 405 of the positive pole column 40, penetrates the wall portion 405, and extends to a position where it fits into the current collector member 30.

[0041] Figure 3 is a top view of the positive terminal assembly 10 in Figure 2. In Figure 3, the shape of the central trajectory 602 in which the laser spot moves along the upper surface of the wall portion 405 is specifically shown. Referring to Figure 3, it can be seen that the central trajectory 602 of the laser spot is helical, and the trajectory of the weld mark 60 is also helical overall. The helical central trajectory 602 (i.e., the helical trajectory) has a starting end 604 and an ending end 606, and has a plurality of arms 608 between the starting end 604 and the ending end 606. The movement of the laser spot may start from the radially outer end of the helix, or it may start from the center 618 of the helix. In other words, the starting end 604 of the weld mark 60 may be located at the outer end of the helix, or it may be located at the center 618 of the helix. In Figure 3, the case in which the starting end 604 is located at the center 618 of the helix is ​​described, but this does not constitute a limiting description.

[0042] By employing a spiral-shaped central trajectory 602 of the laser spot, the laser spot does not pass through the same position twice. That is, the central trajectories 602 of the laser spot neither overlap nor intersect. In some embodiments, the spiral may be an Archimedean spiral, the distance between two adjacent arms 608 of the central trajectory 602 of the laser spot is constant, the distribution of weld marks 60 is uniform, and the thermal influence between each curved portion is small. In some other embodiments, the spiral may be of other forms, such as any suitable type of two-dimensional spiral, such as a Fermat spiral or an equiangular spiral.

[0043] When the laser spot passes over the same point two or more times, it can lead to increased localized penetration depth, metal splatter, and burst point problems. In this embodiment, by employing a spiral-shaped central trajectory 602 of the laser spot, the spot does not pass over the same point twice in its path, thereby reducing the thermal influence between two adjacent curves of the weld mark 60. This improves the consistency of the penetration depth and prevents burn-through of the current collector 30 and localized miswelding, thus ensuring the stability of the welding process.

[0044] It should be explained that the laser spot in laser penetration welding has a relatively small diameter, and when it moves along the trajectory in Figure 3, the laser spot does not pass through the same point. However, the amount of heat generated by the laser spot diffuses laterally (left-right direction in Figure 2) within the metal material, so the weld mark 60 formed by the movement of the laser spot has a certain width. Therefore, even if the laser spots do not overlap, overlap may occur between two adjacent curves of the weld mark 60 generated by the laser spot.

[0045] Furthermore, the heat generated by the laser spot can also diffuse vertically (up and down in Figure 2) within the metal material. During the heat conduction process, as the depth increases, the amount of heat that can be transferred to the deeper parts of the material also decreases accordingly, so the depth of the formed molten pool becomes narrower. Therefore, the overall cross-section of each weld mark 60 formed by laser penetration welding exhibits a triangle shape, where the upper surface is wider and the width gradually decreases as it gets deeper, i.e., a triangle with a wide upper surface and a gradually narrowing lower surface in Figure 2.

[0046] Referring to Figures 2 and 3, in this embodiment, by setting the laser output and the parameters of the central helical trajectory 602 on which the laser spot moves, for example by setting the parameter b in the polar coordinate equation r=a+bθ of the Archimedes spiral, the spacing between two adjacent arms 608 (for example, adjacent arms 608a and 608b in Figure 4) of the central helical trajectory 602 along the movement of the laser spot can be controlled, and furthermore, the overlap of two adjacent curves of the weld mark 60 (for example, the curve corresponding to arm 608a and the curve corresponding to arm 608b in Figure 4) can be controlled.

[0047] Specifically, the overlapping portion of two adjacent curves includes a first overlapping portion 610 and a second overlapping portion 612. In embodiments of the present invention, viewed based on the cross-sectional view in Figure 2, at the upper surface of the wall portion 405, that is, at the first end 60a of the weld mark 60 away from the electrode assembly 20, two adjacent curved portions of the weld mark 60 overlap each other. Specifically, refer to the first overlapping portion 610 in Figure 2. Also, at the upper end face of the current collector member 30, that is, at the end face where the current collector member 30 and the positive pole column 40 abut and are welded, two adjacent curved portions of the weld mark 60 also overlap each other. Specifically, refer to the second overlapping portion 612 in Figure 2.

[0048] On the other hand, at the lower end of the weld mark 60, that is, at the second end 60b of the weld mark 60 that is close to the electrode assembly 20, the two adjacent curved portions of the weld mark 60 are offset from each other. That is, they form a separation portion 620 between the two adjacent curved portions.

[0049] As can be seen by combining the above features, when viewed from the cross-sectional direction in Figure 2, the cross-section of the weld mark 60 is generally sawtooth-shaped, and the sawtooth-shaped weld mark 60 fits between the wall portion 405 and the current collector member 30, effectively reducing secondary welding of the molten pool and improving the weld strength between the wall portion 405 and the current collector member 30. In some embodiments, by applying the welding method provided by embodiments of the present invention, the pull-out force between the positive pole column 40 and the current collector member 30 can reach 50N or more. Pull-out force refers to the force applied in the direction along the axial direction of the positive pole column 40 and the current collector member 30, which separates the two. The measurement method can be an industry standard detection method, so it will not be described in detail here. Not only is it superior in terms of welding strength, but at the upper end face of the current collector member 30, two adjacent curved portions of the weld mark 60 overlap each other (second overlapping portion 612). Therefore, such a welded structure can effectively guarantee the welding area between the current collector member 30 and the wall portion 405, and furthermore, it can also guarantee the discharge capacity between the current collector member 30 and the positive electrode pole 40.

[0050] In this embodiment, a projection 302 is installed in the center of either the wall portion 405 or the current collector member 30, projecting toward the other. In this embodiment, the projection 302 is installed in the center of the current collector member 30 and projects toward the wall portion 405. The upper end surface of the projection 302 abuts against the center of the wall portion 405, and the positive pole column 40 is welded and fixed using the wall portion 405 and the upper end surface of the projection 302.

[0051] In a laser penetration welding system for mass-producing secondary batteries 1 for industrial applications, the laser emitter requires preheating in the initial stages of welding, and because the workpiece temperature is relatively low, the penetration depth of the molten pool obtained by welding is usually relatively shallow. On the other hand, in the initial stages of welding, the output of the laser emitter is usually unstable, and burst points occur with a certain probability. To improve the effective penetration depth and prevent leakage problems caused by the occurrence of burst points, in this embodiment, the laser beam (or laser spot) of the laser penetration welding starts irradiating from the center of the wall portion 405 and rotates from the inside to the outside along a spiral trajectory to obtain the weld mark 60. By setting the starting position of the laser beam to the center of the wall portion 405, even if the laser output is unstable at the start and the burst point phenomenon occurs, the location of the burst point is also surrounded by the outer peripheral region 407, and since burst points are less likely to occur in the outer peripheral region 407, welding can be performed relatively reliably. Since the path through which the electrolyte flows from the wall portion 405 of the outer peripheral region 407 to the current collector member 30 and towards the location where the burst point occurs is blocked by welding, leakage problems are less likely to occur even if the burst point phenomenon occurs.

[0052] In Figure 2, the penetration depth T at the midpoint of the weld mark 60 is shown for easier illustration in the drawing. i The penetration depth T at the edge position of the weld mark 60 o This only shows the case where it is equal to [the specified value]. However, depending on the laser power and the temperature of the workpiece, the penetration depth of the molten pool formed at the starting position of the laser beam is usually relatively shallow, and in the final weld mark 60, assuming the starting position of the laser beam is the helical center 618 and it rotates from the inside to the outside along the helical trajectory, the position where the penetration depth of the weld mark 60 is shallowest is correspondingly located at the helical center 618 of the weld mark 60. In other words, the penetration depth T at the intermediate position of the weld mark 60 on the cross section passing through the axis of the positive pole column 40. i This is the penetration depth T at the edge position of the weld mark 60. oSmaller. It should be explained that the comparison here is between the relative sizes of the penetration depths, i.e., the distance from the first end 60a to the second end 60b of the weld mark 60 near the central region and the distance from the first end 60a to the second end 60b of the weld mark 60 near the edge region. The point with the deepest penetration in the intermediate position does not need to be exactly at the helical center 618, nor does the point with the deepest penetration in the edge position need to be exactly at the edge line. Also, T i <T o The comparison is between the deepest penetration depth in each curved section and the deepest penetration depth in each curved section of the entire weld mark 60. In other words, T i <T o This indicates that the average penetration depth at the deepest point in the curved portion at the intermediate position is smaller than the average penetration depth at the deepest point in the curved portion at the edge position. Due to the short circumference of the intermediate position, even if the penetration depth at the intermediate position is shallow, its actual contribution to the effective penetration depth of the entire molten pool is still small. Therefore, compared to a scheme in which the laser spot starts from the outer end of the helix, the scheme in this embodiment in which the laser spot starts from the helix center 618 results in a deeper effective penetration depth of the final weld 60 and a higher weld strength.

[0053] Continuing to refer to FIG. 2, in this embodiment, the center of the columnar portion 402 of the positive electrode terminal 40 has a concave groove 409, the wall portion 405 is located at the bottom of the concave groove 409, and the concave groove 409 is wider at the upper end and narrower at the lower end. By exposing the wall portion 405 through the concave groove 409 that is wider at the upper end and narrower at the lower end, it becomes convenient to irradiate the wall portion 405 with a laser during welding. Furthermore, the concave groove 409 can be sealed using a sealing pin 411. The sealing pin 411 is fitted and inserted into the concave groove 409, and the upper surface of the sealing pin 411 is flush with the upper surface of the outer flange portion 401 of the positive electrode terminal 40. By using seam welding to weld and fix the sealing pin 411 and the positive electrode terminal 40, the sealing performance of the secondary battery 1 can be further improved. In some embodiments, referring to FIG. 2, by setting the roughness Rb of the upper surface of the outer flange portion 401 to satisfy Rb>0.5 mm, the absorption rate of the metal to the laser can be increased, and a more stable welding process can be formed.

[0054] In some more preferred embodiments, continuing to refer to FIG. 2, the diameter of the surface of the wall portion 405 on the side away from the electrode assembly 20 is d1, the outer diameter of the columnar portion 402 is D1, and d1 / D1<0.75. By the above setting method, not only can the positive electrode terminal 40 have a higher flexural strength, but when the internal pressure of the secondary battery 1 is relatively large, the acting force and its moment of the stress transmitted to the welded joint 60 are also relatively small. Therefore, when the internal pressure of the secondary battery 1 increases, the welded joint 60 is less likely to fail, and the safety performance of the battery can be improved.

[0055] Preferably, the diameter of the surface of the protruding portion 302 that abuts against the wall portion 405, that is, the upper end surface of the protruding portion 302 in FIG. 1, is d2, the diameter of the lower surface of the wall portion 405 is d3, and the welded joint 60 is centered on the axis of the wall portion 405 and is located within the range defined by a circle with d y as the diameter, d y , d2, and d3 are d y<2d2-d3 is satisfied. Due to the existence of assembly tolerances, the space between the projection 302 and the wall 405 may not be coaxial. The above method ensures that even if the axial misalignment between the projection 302 and the wall 405 is at its maximum, the weld mark 60 can connect the wall 405 and the projection 302 as long as it is positioned in the center of the wall 405 and its diameter satisfies the above-mentioned relation. This prevents miswelding by welding in a position where there is no corresponding projection 302 below, thereby making welding positioning easier and ensuring the stability of welding quality.

[0056] In some embodiments of the present invention, the thickness of the wall portion 405 is T, the thickness of the protrusion portion 302 is h, the range of the value of T is 0.3 to 1.5 mm, and the range of the value of T / h is 0.3 to 1. T / h is not appropriate if it is too large or too small. When the value is greater than 1, the excessively thick wall portion 405 is difficult to penetrate, and the required laser energy is large, making it easy for the molten pool to penetrate deeply into or directly through the protrusion portion 302 due to poor control, increasing the thermal impact on the separator inside the electrode assembly 20, and even causing a short circuit between the positive and negative electrodes due to the shrinkage of the separator. On the other hand, when the value of T / h is less than 0.3, the strength of the wall portion 405 itself is too low, making it easy to weld but prone to deformation after welding. When gas is generated inside the battery, it is prone to deformation due to the action of internal pressure, and the welded joint 60 is pulled, causing the welded joint 60 to rupture. For this reason, it is more preferable for T / h to be within the above range of values.

[0057] In some embodiments of the present invention, the roughness of the surface of the wall portion 405 away from the electrode assembly 20 (i.e., the upper surface of the wall portion 405 in Figure 2) is Ra > 0.5 mm. By increasing the roughness of the metal surface irradiated with the laser, the absorption rate of the metal to the laser can be effectively improved, thereby forming a more stable welding process and ensuring consistency in the penetration depth of the molten pool.

[0058] Figure 4 is a schematic diagram of the helical movement trajectory of the laser spot in this embodiment, i.e., the central trajectory 602 of the laser spot or weld mark 60. Referring to Figure 4, in a more preferred embodiment of the present invention, the distance A between two adjacent arms 608 of the helical movement trajectory of the laser spot, i.e., the distance A between the centers of two adjacent curved portions of the weld mark 60, satisfies A = 0.05 to 0.5 mm. Taking the case where the spiral is an Archimedean spiral as an example, its polar coordinate equation is r = a + bθ, and correspondingly, the distance between two adjacent arms 608 of the spiral is A = 2πb. The distance A is not appropriate if it is too large or too small. If A is too small, the mutual thermal influence between the two weld marks 60 increases, the rate at which the molten pool is secondary welded increases, the quality of the final molten pool deteriorates, and the risk of leakage increases. If A is too large, the total welding area between the current collector 30 and the positive pole column 40 will decrease, affecting the discharge capacity in the welded area 60. For these reasons, it is preferable that the spacing A is within the range of 0.05 to 0.5 mm.

[0059] Continuing to refer to Figure 2, in a more preferred embodiment of the present invention, the thickness of the projection 302 is h, where the thickness h is the thickness of the current collector 30 along the axial direction of the projection 302, and the depth to which the weld mark 60 penetrates the surface of the projection 302 is D2, where D2 / h = 0.08 to 0.7. Since the penetration depth of the weld mark 60 differs at different locations, the depth to which the weld mark 60 penetrates the surface of the projection 302 also differs slightly at different locations. Here, the limitation on the penetration depth D2 means that the depth D2 to which the same weld mark 60 penetrates the surface of the projection 302 at different locations must all satisfy the range of D2 / h = 0.08 to 0.7.

[0060] The shallowest point at which the weld mark 60 penetrates the surface of the protruding portion 302 must satisfy D2 / h ≥ 0.08. When D2 / h < 0.08, the depth D2 to which the weld mark 60 penetrates the surface of the current collector member 30 is too small, making it impossible to form an effective welded connection, and the welded surface becomes prone to tearing, thus making it impossible to guarantee weld strength.

[0061] The deepest point where the weld mark 60 is embedded in the surface of the protrusion 302 must satisfy D2 / h ≤ 0.7. When D2 / h > 0.7, the high temperature generated during welding is easily transmitted to the inside of the electrode assembly 20 corresponding to the current collector 30, potentially damaging the separator. As a result, the separator shrinks, preventing the formation of effective isolation between the positive and negative electrode sheets, creating a risk of short circuits inside the battery.

[0062] It should be explained that in this embodiment, the welding of the positive pole column 40 and the current collector member 30 of the positive terminal assembly 10 is described as an example. However, the welding method provided in this embodiment is also applicable to welding the negative pole column and the corresponding current collector member, and is therefore not limited to this embodiment.

[0063] This embodiment further provides a method for assembling a secondary battery 1. Figure 5 is a schematic flowchart of the assembly method. Referring to Figure 5, the assembly method includes an assembly step and a welding step, in which the current collector member 30 and the positive pole column 40 are assembled. Specifically, the protruding portion 302 of the current collector member 30 is brought into contact with the wall portion 405 of the positive pole column 40.

[0064] In the welding step, first, the laser beam is irradiated onto the central region 417 (see Figure 4) of the wall portion 405, and then the laser beam is moved from the inside to the outside along a helical trajectory and stopped at the edge region 415 (see Figure 4). This completes the welding between the wall portion 405 and the protrusion 302 using laser penetration welding, forming a weld mark 60. In this embodiment, by using a laser spot movement method that starts from the spiral center 618 and gradually moves outward along a helical trajectory, the edge region 415 becomes the end point, making it less likely for burst points to occur. The weld mark 60 surrounding the central region 417 isolates the central region 417, which is prone to burst points, from the outer peripheral region 407, which has a leakage path, thus preventing burst points from occurring in the area with the leakage path. This reduces the possibility of leakage due to burst points, improves the effective penetration depth of the weld mark 60, and improves the weld strength.

[0065] By the method described above, the welded portion between the positive electrode pole 40 and the current collector 30 of the secondary battery 1 provided in this embodiment has relatively high welding strength and excellent discharge capacity, and therefore has even better product safety and quality reliability compared to existing welding methods.

[0066] <Second Embodiment>

[0067] A second embodiment of the present invention provides a secondary battery 1. Figure 6 is a cross-sectional view of the positive electrode terminal assembly 10 in the second embodiment. The main structural difference between the second embodiment and the first embodiment of the secondary battery 1 is that in the second embodiment, the center of the wall portion 405 of the positive electrode pole 40 and the center of the protruding portion 302 of the current collector member 30 both have corresponding electrolyte injection holes 70 in size and position. The manufacturer can inject electrolyte into the housing 101 of the secondary battery 1 through these electrolyte injection holes 70.

[0068] Since the liquid injection hole 70 is located in the center of the wall portion 405 and the protruding portion 302, when the wall portion 405 and the protruding portion 302 are welded together, a burst point appears near the liquid injection hole 70, increasing the risk of leakage. The inventors of the present invention have found through research that when a burst point occurs around the liquid injection hole 70 in such a situation, the risk of leakage is even higher compared to when a burst point occurs in the outer peripheral region 407. In some embodiments of the present invention, a method for assembling a secondary battery 1 is provided. In the welding step, a laser spot rotates around the liquid injection hole 70 from the outside to the inside along a helical trajectory, and a single weld mark 60 is used to complete the welding between the wall portion 405 and the current collector member 30. Specifically, the starting end 604 can be located in the outer peripheral region 407, and the ending end 606 can be located in a region close to the liquid injection hole 70. That is, the central trajectory 602 starts from the outer end of the helix, extends from the outside to the inside, and ends near the liquid injection hole 70. In the latter half of the welding process, the output power is relatively high and the workpiece temperature is relatively high, so the movement path of such a laser spot is such that the penetration depth T at the intermediate position i The depth of penetration at the edge position T o It forms a larger weld mark 60.

[0069] In some other embodiments, a different method for assembling the secondary battery 1 is provided, which can solve the leakage problem at both intermediate and edge positions by dividing the welding into two steps to generate two weld marks 60.

[0070] Figure 7 is a schematic diagram of the central trajectory 602 corresponding to the weld mark 60 in this embodiment, that is, a schematic diagram of the laser spot's movement trajectory.

[0071] Referring to Figure 7, in this embodiment, the central trajectory 602 of the first helical weld is the first helix 614, and the central trajectory 602 of the second helical weld is the second helix 616. The first helix 614 and the second helix 616 may be different parts of the same helix, or they may be different helices.

[0072] The welding steps may include a first welding step and a second welding step. In the first welding step, the laser spot rotates around the injection hole 70 from the outside to the inside along the trajectory of the first helix 614. In the second welding step, the laser spot rotates from the inside to the outside along the trajectory of the second helix 616 to form a second helical weld. The second helical weld obtained in the second welding step surrounds the first helical weld obtained in the first welding step.

[0073] In Figure 7, the laser spot starts at point B on the first helix 614, moves from the outside to the inside, and ends at point C on the first helix 614, forming the first helical weld. Subsequently, the laser spot starts at point D on the second helix 616, moves from the inside to the outside, and ends at point E on the second helix 616, forming the second helical weld. The order in which the first and second helical welds are formed may be reversed.

[0074] When forming the first helical weld, the laser spot is prone to burst point phenomena at point B because the process starts from point B, but the output becomes relatively stable as it moves to point C. In other words, the area closer to the injection hole 70 is welded more reliably. Accordingly, by adopting the above-described direction of movement, the penetration depth T at the intermediate position of the first helical weld is achieved. i This is the penetration depth T at the edge position of the first helical weld. o It will get bigger.

[0075] When forming a second helical weld, the laser spot starts at point D, and the output is relatively stable as it moves from the inside to the outside at point E. In other words, the second helical weld more reliably welds the area closer to the outside. Correspondingly, the penetration depth T at the intermediate position of the second helical weld... i This is the penetration depth T at the edge position of the second helical weld. o It will become smaller.

[0076] It should be explained that, in this embodiment, the central trajectories of the first and second helical weld marks are not perfect helices and neither extends to the center of the helix. Therefore, the term "intermediate position" in this embodiment is used in a relative sense to the "edge position." That is, the intermediate position is closer to the center than the edge position, and the edge position is further from the center than the intermediate position.

[0077] By the method described above, if a burst point occurs at point B or D, both the area near the injection hole 70 and the outer circumference of the second helix 616 are reliably welded, effectively blocking the path through which the electrolyte flows towards the location where the burst point appears. Therefore, even if a burst point occurs, leakage problems are less likely to occur.

[0078] After the liquid injection is complete, the sealing performance of the secondary battery 1 can be improved by further filling the injection hole 70 with a sealing plug 71 (see Figure 6) to seal the injection hole 70. The sealing plug 71 may be a rubber stopper. After sealing the injection hole 70 with the sealing plug 71, a sealing pin 411 is further filled into the groove 409 to complete the welding of the sealing pin 411 to the positive electrode pole 40.

[0079] In this embodiment, the portion where the wall portion 405 and the protruding portion 302 come into contact with each other (i.e., the contact surface 413) is annular in shape, and the annular contact surface 413 has an annular central region 417 (i.e., the main portion of the contact surface 413), an inner edge region 415a (i.e., the annular portion of the contact surface 413 close to the injection hole 70), and an outer edge region 415b (i.e., the annular portion of the contact surface 413 away from the injection hole 70).

[0080] In the first welding step, the laser spot starts at point B located in the central region 417 along the first helix 614, rotates around the injection hole 70 from the outside inward, and ends at point C located in the inner edge region 415a. In the second welding step, the laser spot starts at point D located in the central region 417 along the second helix 616, rotates from the inside inward, and ends at point E located in the outer edge region 415b. The edge regions 415 on both sides (inner edge region 415a and outer edge region 415b) surround the weld mark 60 in the central region 417, but since both edge regions 415 are termination points, burst points are unlikely to occur, so the weld mark 60 has excellent quality and stable welding can be performed. Therefore, by creating isolation from both sides of the weld mark in the central region 417, the area where burst points may occur is separated from the area where leakage may occur, and the possibility of leakage can be reduced.

[0081] In the assembly method for the secondary battery 1 provided by the above embodiment of the present invention, the optical magnification ratio of the laser spot in the welding step is 2.5 to 3.5 times, for example, an optical magnification ratio of 3 times is adopted. By using an optical magnification ratio of 2.5 to 3.5 times, the beam waist radius can be increased and the depth of focus range can be improved, thereby obtaining a relatively wide penetration depth range, which is convenient for penetrating the wall portion 405 and reaching the current collector member 30.

[0082] In a method for assembling a secondary battery 1 provided by several embodiments of the present invention, the positive electrode column 40 is selected and used from aluminum. The laser used in the welding step is a red laser or an infrared laser with a wavelength of 600 to 1200 nm. Aluminum has a relatively good laser absorption rate in this wavelength range, and the laser is relatively inexpensive.

[0083] In some embodiments, a laser galvanometer is used to control the movement of the laser spot. Using a laser galvanometer can improve welding speed, resulting in superior production efficiency. For example, the laser spot's movement speed can be controlled to 300 mm / s or more.

[0084] Furthermore, the focal point of the laser spot can be positioned on the side of the wall 405 away from the current collector 30. By positioning the focal point of the laser spot above the welding surface, the energy of the laser spot weakens as the penetration depth of the molten pool increases. This control method makes it less likely for the current collector 30 to burn through, thereby reducing the possibility of leakage and improving the product yield.

[0085] Referring to Figure 8, the present invention further provides a battery pack 8, which includes a secondary battery 1 as provided in any one embodiment described above. In one embodiment of the battery pack 8 of the present invention, the battery pack 8 includes a box 81, a box cover 82, and a plurality of secondary batteries 1, which are arranged inside the box 81 and connected to each other in series or in parallel, or a combination of series and parallel. The box cover 82 covers the box 81 and protects the plurality of secondary batteries 1. It should be noted that, in addition to the secondary batteries 1 in embodiments of the present invention, the battery pack 8 may also include parts such as a thermal management system for the battery pack and a circuit board. The battery pack 8 may be a battery module, a battery pack, or a power storage cabinet, but each will not be described individually here.

[0086] Referring to Figure 9, the present invention further provides an electronic device 9, which includes the battery pack 8 described above. A work unit 91 is electrically connected to the battery pack 8 to receive support from electrical energy. As one example, the electronic device 9 is a vehicle, which may be a fuel-powered vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle, or a range-extender vehicle, etc., but the present invention is not limited thereto. The work unit 91 is the vehicle body, and the battery pack 8 is installed at the bottom of the vehicle body to provide support from electrical energy for the vehicle to run or for the operation of electrical components inside the vehicle. However, in some other embodiments, the electronic device 9 may further be a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and a power tool, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. The work unit 91 may also be a unit component that can perform a corresponding task by obtaining electrical energy from the battery pack 8, for example, a fan blade rotation unit, a vacuum cleaner dust collection work unit, etc. 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 metal cutting power tools, polishing power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers. Embodiments of the present invention do not particularly limit the electronic devices 9 described above.

[0087] The foregoing describes only more preferred embodiments of the present invention and is not intended to limit it. Any modifications, equivalent substitutions, and alterations made within the spirit and principles of the present invention shall all be within the scope of protection of the present invention. [Industrial applicability]

[0088] In the technical solution of the present invention, by employing a helical laser spot central trajectory, the laser spot does not pass through the same point twice in its moving path. This reduces the thermal influence between two adjacent curves of the weld, thereby improving the consistency of the penetration depth and ensuring the stability of the welding process. [Explanation of Symbols]

[0089] 1 Secondary battery 101 cabinets 103 Side wall section 20 Electrode Assembly 10 Positive terminal assembly 11. Negative terminal assembly 105 End Plate 107 Opening 30 Current collector 302 Protrusion 40 Positive Polarity Column 401 Outer flange section 403 Inner flange section 405 Wall 407 Outer area 409 Groove 411 Seal pin 413 Contact surface 415 Edge region 415a Inner edge region 415b Outer edge region 417 Central area 50 Insulation part 502 Seal Ring 60 Weld marks 60a End 1 60b 2nd end 602 Center locus 604 Starting end 606 Termination 608 Arm 610 1st overlap part 612 2nd overlap part 614 1st spiral 616 Second spiral 618 Spiral Center 620 Separation part 70 Liquid injection hole 71 Seal Plug 8 Battery Packs 81 Boxes 82 Box Cover 9 Electronic Devices 91 Work Unit

Claims

1. The assembly step involves assembling the current collector and the pole pole, and bringing the wall portion of the pole pole into contact with the current collector, A welding step involves irradiating the wall with a laser spot, moving the laser spot along a spiral trajectory, and welding the wall and the current collector to form a weld mark, A method for assembling a secondary battery, wherein, on a cross section passing through the axis of the pole column, the weld marks extend from a first end to a second end, the first end is located on the side of the wall portion facing away from the current collector, and the second end is located inside the current collector.

2. The method for assembling a secondary battery according to claim 1, wherein in the welding step, the laser spot rotates from the inside outward along the helical trajectory.

3. A method for assembling a secondary battery according to claim 1, wherein an injection hole is provided in the center of the wall portion, and in the welding step, the laser spot rotates around the injection hole from the outside to the inside along the spiral trajectory.

4. An injection hole is provided in the center of the wall portion, and the welding step is performed A first welding step in which the laser spot rotates around the injection hole from the outside to the inside along the trajectory of the first helix to form a first helical weld mark, The process includes a second welding step in which the laser spot rotates from the inside out along the trajectory of the second helix to form a second helical weld mark, The second helical weld mark surrounds the first helical weld mark. A method for assembling a secondary battery according to claim 1.

5. The middle portion of the current collector member has a projection that protrudes toward one side of the pole column, and the portion where the wall portion and the projection portion come into contact with each other constitutes a contact surface, and the contact surface has a central region and an edge region. The method for assembling a secondary battery according to claim 1, wherein in the welding step, the movement of the laser spot starts from the central region and ends in the edge region, and the weld mark located in the edge region surrounds the weld mark located in the central region.

6. The method for assembling a secondary battery according to claim 1, wherein in the welding step, the optical magnification ratio of the laser spot is 2.5 to 3.5 times.

7. The method for assembling a secondary battery according to claim 1, wherein the wavelength of the laser spot is 600 to 1200 nm.

8. The method for assembling a secondary battery according to claim 1, wherein the spiral trajectory is an Archimedean spiral trajectory.

9. The method for assembling a secondary battery according to claim 1, wherein in the welding step, a laser galvanometer is used to move the laser spot along the helical trajectory at a speed of 300 mm / s or more.

10. The method for assembling a secondary battery according to claim 1, wherein the focal point of the laser spot is located on the side of the wall away from the current collector.

11. Including an end plate and a side wall portion surrounding the end plate, the end plate comprises a housing having an opening, The electrode assembly housed inside the aforementioned housing, A current collector member is installed between the electrode assembly and the end plate and is electrically connected to the electrode assembly, The pole column is fixed to the end plate by passing through the opening, and the pole column includes a wall portion, and the wall portion and the current collector are welded together to form a weld mark, and the weld mark has a spiral trajectory to the pole column, A secondary battery comprising a cross-section passing through the axis of the pole column, wherein the weld marks extend from a first end to a second end, the first end located on the side of the wall portion facing away from the electrode assembly, and the second end located inside the current collector.

12. The secondary battery according to claim 11, wherein the middle portion of the current collector member has a projection that protrudes toward one side of the pole column, the portion where the wall portion and the projection portion contact each other constitutes a contact surface, the contact surface has a central region and an edge region, the weld marks start from the central region along the direction of movement of the laser spot and end in the edge region, and the weld marks located in the edge region surround the weld marks located in the central region.

13. A battery pack comprising a plurality of secondary batteries, wherein the secondary batteries are the secondary batteries described in claim 11 or 12.

14. An electronic device comprising a battery pack as described in claim 13.

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