Lead-tab laser welding method and lead-tab laser welding apparatus

Abstract

The present invention relates to a lead-tab laser welding method for bonding a lead part and a tab part. The lead-tab laser welding method comprises: a seating step of disposing a lead part and a tab part of a secondary battery to overlap each other; and a laser welding step of forming a plurality of beads in an overlapping area of the lead part and the tab part by a welding unit. In the laser welding step, with respect to a first position, a second position, and a third position sequentially located along a first direction in the overlapping area of the lead part and the tab part, the beads are formed in the order of the first position, the third position, and the second position.

Description

Lead-tab laser welding method and lead-tab laser welding device

[0001] The present invention relates to a lead-tab laser welding method and a lead-tab laser welding device, and more particularly, to a lead-tab laser welding method capable of minimizing welding defects and improving the mechanical strength of an overlapping area of ​​a lead and a tab, and a lead-tab laser welding device for performing the same.

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0082265, filed June 24, 2024, the entire contents of which are incorporated herein by reference.

[0003] With the recent rapid growth of the electric vehicle market, demand for large-capacity batteries is also increasing significantly. Lithium-ion batteries, which boast high energy density and safety, are primarily used for electric vehicles, and these are often manufactured in pouch-type cells. The welding process for connecting the electrodes and tabs is essential in the manufacture of pouch-type lithium-ion batteries, and the quality and reliability of these joints directly impact battery performance.

[0004] The secondary battery manufacturing process can be broadly divided into electrode manufacturing, electrode assembly, and battery activation. The electrode manufacturing process involves mixing the active materials of the positive and negative electrodes, conductive agents, and binders to create a slurry. This slurry is then coated onto a metal current collector, such as a copper or aluminum sheet, and dried. The electrode assembly process involves stacking the manufactured electrodes and separators to create the basic battery structure, followed by injecting and sealing the electrolyte. The battery activation process involves performing repeated charging and discharging cycles to activate the battery's performance.

[0005] Fig. 1 is an exploded perspective view showing the configuration of a typical pouch-type secondary battery (30). Fig. 2 is a cross-sectional view showing a portion of the inside of a typical secondary battery (30).

[0006] Referring to FIGS. 1 and 2, the pouch-type secondary battery (30) includes an electrode assembly (20) including a positive electrode (24) and a negative electrode (22) having an electrode active material applied to an electrode plate, and a separator (23) interposed between the positive electrode (24) and the negative electrode (22). In addition, positive electrode tabs (25) and positive electrode leads (51) extending to one side of a plurality of positive electrodes (24) are welded in an overlapping area (28) where they overlap with each other. In addition, negative electrode tabs (26) and negative electrode leads (52) extending to one side of a plurality of negative electrodes (22) are welded in an overlapping area (not shown) where they overlap with each other.

[0007] And, this electrode assembly (20) is accommodated in a receiving portion (21b1) formed in a lower pouch film (21b). At this time, the electrode assembly (20) has a plurality of electrode leads (51, 52), and the plurality of electrode leads can be divided into a positive electrode lead (51) and a negative electrode lead (52). In a state where this electrode assembly (20) is accommodated in the receiving portion (21b1), an electrolyte is injected, and after an initial charge / discharge (activation process) is performed, the edge portions (21b2) of the upper pouch film (21a) and the lower pouch film (21b) are heat-sealed and sealed in this order. In addition, the secondary battery may be provided with a protective film (27) for electrical insulation between the electrode leads and the pouch film (21b).

[0008] Laser welding has traditionally been widely used to weld electrode tabs (also known as tabs) and electrode leads (also known as lead portions). Previously, pulse welding using a multi-mode fiber laser was primarily performed in two rows.

[0009] Figure 3 schematically illustrates the configuration of a typical multi-mode fiber laser welding device (10).

[0010] Referring to FIG. 3, a multimode fiber laser welding device (10) is composed of a laser pumping source (11), an optical fiber (12), and a scanner (13). The laser pumping source (11) includes a plurality of laser diodes (14). The laser diodes (14) are semiconductor devices that convert electrical energy into optical energy and provide a pumping light source. The pumping light source from the laser diodes (14) is incident on an optical fiber (12) through a center beam combiner (17). At this time, the optical fiber (12) includes a plastic jacket (12-4), which is the outermost layer, a cladding (12-1) which is an inner layer, and a core (12-2) located at the center. The beam incident on the optical fiber (12) is trapped by the cladding (12-1) and is oscillated as a laser through a fiber (12-3), which is a medium for laser oscillation. Here, the center beam combiner (17) is configured to combine the outputs of multiple laser diodes (14) into one and transmit them to an optical fiber (12). Thereafter, the laser beam emitted from the optical fiber (12) is accelerated into parallel light by the collimating lens (16) of the scanner (13), and the accelerated parallel light is reflected by the mirror (15) and then focused by the focusing lens (19) to be irradiated onto the surface of the workpiece (20).

[0011] At this time, in the case of the multimode-fiber laser device (10), the optical fiber (12) includes a multimode optical fiber (12). That is, the multimode optical fiber (12) has a large core (12-2) diameter (e.g., 50 μm or more) and a large number of fibers (12-3) embedded inside the core (e.g., 3), so that more modes can be propagated compared to a single mode. Accordingly, the multimode-fiber laser device (10) can obtain high output, but on the other hand, because the laser beam diameter size is large (e.g., 300 μm to 400 μm) and the output is high, it is easy to cause thermal effects on the welded portion and surrounding components. Therefore, in the past, when welding the lead portion and the tab portion using the multimode-fiber laser device (10), spot welding was inevitable to reduce the thermal effects. Since the bead size that can be created per pulse is limited to a spot, it was inevitable to form beads in two or more rows to increase the welding area and thus increase the tensile strength.

[0012] For example, a multi-mode fiber laser device (10) can form multiple beads in a single line through pulse welding in the welding area of ​​the lead portion-tab portion, and then form beads that overlap in the same manner in a second line adjacent to the first line formed thereafter.

[0013] Fig. 4 is a partial cross-sectional view schematically showing the appearance of a lead-tab overlap area (28) that is pulse-welded in two lines using a general multi-mode fiber laser device (10).

[0014] Referring to FIGS. 3 and 4, in the lead-tab overlap region (28), a multi-mode fiber laser device (10) can perform pulse welding by having a laser beam (B) emitted from an optical fiber (12) pass through focusing lenses (19).

[0015] However, due to the characteristics of the multi-mode fiber laser device (10) described above, problems arose in which pulse welding had to be performed in more than two lines. First, pulse welding performed in two lines using a multi-mode fiber laser had a large bead protrusion height formed in the overlapping area (28), which was at risk of contact with internal components of the secondary battery (e.g., pouch). This could cause insulation breakdown of the secondary battery, which could act as a factor that lowers the safety and reliability of the battery.

[0016] In addition, the existing method had difficulty in ensuring uniformity in welding strength and quality, and there was a high possibility of the existence of defective welding areas with low bondability. If the bonding of the overlapping area (28) is incomplete, the electrical resistance of the lead-tab overlapping area (28) may increase, which may result in a decline in battery performance, and in severe cases, it may lead to fatal defects such as separation of the tab from the lead.

[0017] Furthermore, pulse welding using a multimode fiber laser device generates a large amount of spatter, posing a contamination problem around the overlapping area. The scattered spatter can adhere to the electrode surface, causing foreign matter defects, a major cause of battery durability and performance degradation.

[0018] In particular, the wide beam size of multimode fiber lasers and the characteristics of the pulse welding method cause problems such as excessive heat input in the overlapping area and heat overlap between adjacent overlapping areas. This excessive heat input and heat overlap cause excessive heat-affected zone (HAZ) formation in the overlapping area and softening of the overlapping area. This softening of the HAZ significantly reduces the strength of the overlapping area, adversely affecting the reliability of the joint and resulting in adverse effects such as shortened fatigue life and weakened corrosion resistance.

[0019] Therefore, there is an urgent need to develop a new laser welding technology that can improve joint strength and durability while minimizing overlapping area defects.

[0020] The present invention aims to solve problems associated with conventional lead-tab laser welding technology.

[0021] Specifically, the present invention aims to provide a lead-tab laser welding method and a lead-tab laser welding device capable of preventing excessive heat input in a lead-tab overlapping area and maximizing a bonding area through one embodiment of the present invention.

[0022] In addition, the present invention aims to provide a lead-tap laser welding method and a lead-tap laser welding device that can increase bondability and durability and reduce the amount of spatter generated through one embodiment of the present invention.

[0023] In addition, the present invention aims to provide a lead-tab laser welding method and a lead-tab laser welding device capable of obtaining even heat input distribution throughout the overlapping area and preventing tensile strength reduction due to excessive heat input by forming beads in the order of a first position, a third position, and a second position in the welding target of the overlapping area of ​​the lead portion and the tab portion through one embodiment of the present invention.

[0024] In addition, the present invention aims to provide a lead-tab laser welding method and a lead-tab laser welding device capable of minimizing deformation and defect occurrence in a lead-tab overlapping area and preventing tensile strength reduction due to excessive heat input by forming a plurality of beads by spacing them apart at a predetermined interval through a welding unit through one embodiment of the present invention.

[0025] In addition, the present invention aims to provide a lead-tap laser welding method and a lead-tap laser welding device that can reduce the risk of welding with weak bonding force and improve welding quality by obtaining high energy density with a small beam diameter using a single-mode fiber laser through one embodiment of the present invention.

[0026] In addition, the present invention aims to provide a lead-tap laser welding method and a lead-tap laser welding device that can minimize changes in mechanical and chemical properties of an overlapping region by reducing the instantaneous high temperature region and reducing the surrounding heat-affected zone compared to a pulse mode by irradiating a single-mode fiber laser in a continuous wave mode through an embodiment of the present invention.

[0027] In order to achieve the above-described purpose, according to one embodiment of the present invention, a lead-tab laser welding method is provided, including a laser welding step of forming a plurality of beads through a welding unit in an overlapping area of ​​a lead portion and a tab portion of a secondary battery, and in the laser welding step, forming beads in the order of the first position, the third position, and the second position for a first position, a second position, and a third position located sequentially along a first direction within the overlapping area of ​​the lead portion and the tab portion.

[0028] In addition, according to one embodiment of the present invention, there is provided a lead-tab laser welding method for joining a lead portion and a tab portion of a secondary battery, the method comprising: a mounting step of arranging the lead portion and the tab portion of the secondary battery to overlap each other; and a laser welding step of forming a plurality of beads in an overlapping area of ​​the lead portion and the tab portion by a welding unit, wherein in the laser welding step, beads are formed in the order of the first position, the third position, and the second position for a first position, a second position, and a third position sequentially located along a first direction within the overlapping area of ​​the lead portion and the tab portion.

[0029] The first position, the second position, and the third position are spaced apart from each other, and the interval between the first position and the second position can be set to be greater than the interval between the second position and the third position.

[0030] In the laser welding step, when the welding unit forms a plurality of beads along the first direction, the overlapping area can be divided into a first area and a second area based on the center of the first direction, and beads can be formed alternately in the first area and the second area.

[0031] In the above laser welding step, each bead can be formed by irradiating a single mode fiber laser.

[0032] The beam diameter of the above single mode fiber laser can be formed to be 13 μm to 25 μm.

[0033] In the above laser welding step, each bead can be formed by irradiating a single mode fiber laser in continuous wave mode.

[0034] In the above laser welding step, the plurality of beads can be formed in only one line along the first direction.

[0035] The above lead portion includes a positive lead and a negative lead, the tab portion includes a positive tab and a negative tab, and in the laser welding step, the welding unit can form a bead shape differently when welding the positive lead-positive tab and a bead shape differently when welding the negative lead-negative tab.

[0036] In the above laser welding step, when welding the positive lead-positive tab, the welding unit can form the bead so that the width of the bead along the width direction of the positive tab is smaller than the length of the bead along the length direction of the positive tab.

[0037] In the above laser welding step, when welding the positive lead-positive tab, the welding unit can form the bead in an open curved path with different positions of the welding start point and the welding end point.

[0038] The above curved path may have a rotational movement angle of less than 360 degrees from the starting point to the ending point.

[0039] In the above laser welding step, the welding unit can form a bead in an arc-shaped welding path when welding the cathode lead-cathode tab.

[0040] In addition, according to one embodiment of the present invention, a lead-tab laser welding device is provided, which includes a welding unit configured to form beads in the order of the first position, the third position, and the second position, with respect to a first position, a second position, and a third position sequentially located along a first direction within an overlapping area of ​​a lead portion and a tab portion of a secondary battery.

[0041] In addition, according to one embodiment of the present invention, a lead-tab laser welding device may be provided, including a lead-tab mounting portion that arranges a lead portion and a tab portion of a secondary battery to overlap each other; and a welding unit that is arranged to form beads in the order of the first position, the third position, and the second position, with respect to a first position, a second position, and a third position sequentially located along a first direction within an overlapping area of ​​the lead portion and the tab portion.

[0042] Additionally, the first position, the second position, and the third position may be spaced apart from each other, and the interval between the first position and the second position may be set to be greater than the interval between the second position and the third position.

[0043] In addition, when forming a plurality of beads along the width direction of the lead tab, the welding unit may be arranged to alternately form beads in the first region and the second region by dividing the first region and the second region based on the center of the width direction of the lead tab.

[0044] Additionally, the welding unit may be configured to form each bead by irradiating a single mode fiber laser.

[0045] Additionally, the welding unit may be configured to form each bead by irradiating a continuous wave mode fiber laser.

[0046] Additionally, the welding unit can irradiate the laser beam so that the welding bead is formed in only one line along the width direction of the lead portion-tab portion overlapping area.

[0047] In addition, the welding unit may be arranged so that, when welding the positive lead-positive tab, the width of the bead in the width direction of the positive tab is formed to be smaller than the length of the bead in the length direction of the positive tab.

[0048] In addition, the welding unit may include a laser oscillation unit that generates a laser beam of a single-mode fiber laser, a beam control unit that adjusts the diameter and path of the laser beam generated from the laser oscillator, and a focus control lens unit that focuses the laser beam passing through the beam control unit on a lead-tab overlapping area.

[0049] The lead-tab laser welding method and lead-tab laser welding device of the present invention can prevent excessive heat input during welding of the overlapping area of ​​the lead-tab, maximize the joining area, thereby improving joining properties and durability, and reducing the amount of spatter generated.

[0050] Specifically, the lead-tab laser welding method and lead-tab laser welding device according to one embodiment of the present invention can have sufficient time for cooling of the preceding bead when the welding unit cross-forms a plurality of beads in the first and second regions on the left and right of the lead-tab, so that the heat generated by the generation of the previously formed bead can have less of a thermal effect on the generation of the next adjacent bead, thereby preventing an increase in the bead size due to heat overlap and a decrease in the tensile strength of the welded lead-tab.

[0051] The lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention can minimize deformation and defects in the overlapping area of ​​the lead portion and the tab portion by forming a plurality of beads spaced apart at predetermined intervals by the welding unit. This can prevent a decrease in tensile strength due to excessive heat input due to the bead spacing of the conventional technology being too narrow.

[0052] Single-mode fiber lasers have the advantage of enabling precise welding due to their small beam diameter and short focal length. Therefore, the lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention can achieve high energy density with a small beam diameter using a single-mode fiber laser. This reduces the risk of welding with weak bonding strength and improves weld quality.

[0053] The lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention can continuously supply energy while lowering peak power compared to the pulse mode by irradiating a single-mode fiber laser in a continuous wave mode, thereby preventing the formation of an instantaneous high temperature in the overlapping area and reducing the formation of a heat-affected zone in the surrounding area.

[0054] The lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention form a single row of welding beads in the lead-tab overlapping area, thereby making it easier to control heat input for each bead and ensuring sufficient spacing between beads compared to the conventional case of forming welding beads in two or more rows, thereby preventing a decrease in tensile strength due to excessive heat input in the overlapping area.

[0055] The lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention can minimize the thermal influence between beads located on both sides of the welding direction and increase the melting area in the longitudinal direction of the electrode lead by forming a bead of an elongated curved path in the overlapping area of ​​the positive lead portion and the tab portion.

[0056] The lead-tap laser welding method and lead-tap laser welding device according to one embodiment of the present invention can prevent a decrease in tensile strength due to excessive heat input at the start and end points by forming a bead in an overlapping area of ​​the positive lead and the tab with an outer and inner open path where the welding start and end points do not meet each other.

[0057] The lead-tab laser welding method and lead-tab laser welding device according to one embodiment of the present invention can improve the bonding strength by maximizing the overlapping area area by adopting a circular path as the path of a bead to be formed in the overlapping area of ​​the cathode lead and the tab.

[0058] Figure 1 is an exploded perspective view schematically showing the configuration of a typical secondary battery.

[0059] Figure 2 is a cross-sectional view showing a portion of the inside of a typical secondary battery.

[0060] Figure 3 is a schematic diagram schematically showing the configuration of a typical multimode fiber laser device.

[0061] Fig. 4 is a partial cross-sectional view schematically showing the appearance of a lead-tab overlap area that is pulse-welded in two rows using a general multimode fiber laser device.

[0062] Figure 5 is a plan view schematically showing the appearance of a secondary battery according to one embodiment of the present invention.

[0063] FIG. 6 is a block diagram conceptually illustrating the configuration of a lead-tap laser welding device according to one embodiment of the present invention.

[0064] FIG. 7 is a schematic diagram schematically showing the configurations of a lead-tap laser welding device according to one embodiment of the present invention.

[0065] FIG. 8 is a partial cross-sectional view schematically showing the appearance of a positive lead-positive tab overlapping area welded using a lead-tab laser welding device according to one embodiment of the present invention.

[0066] FIG. 9 is a partial cross-sectional view schematically showing the appearance of a cathode lead-cathode tab overlapping region welded using a lead-tab laser welding device according to one embodiment of the present invention.

[0067] FIG. 10 is a perspective view schematically showing the appearance of a lead-tab overlapping area welded using a lead-tab laser welding device according to one embodiment of the present invention.

[0068] FIG. 11 is a partial plan view showing the formation order of a bead formed using a lead-tap laser welding device according to one embodiment of the present invention.

[0069] Fig. 12 is a partial plan view showing a bead path and bead shape formed during anode lead-tab welding in a lead-tab laser welding method according to one embodiment of the present invention.

[0070] Fig. 13 is a partial plan view showing the shape of a bead path formed during anode lead-tab welding in a lead-tab laser welding method according to another embodiment of the present invention.

[0071] FIG. 14 is a partial plan view showing the shape of a bead path formed during cathode lead-tab welding in a lead-tab laser welding method according to one embodiment of the present invention.

[0072] Figure 15 is a flowchart showing steps of a lead-tap laser welding method according to one embodiment of the present invention.

[0073] Hereinafter, a lead-tap laser welding device (100) and a lead-tap laser welding method (200) according to one embodiment of the present invention will be described in detail with reference to the attached drawings.

[0074] In addition, regardless of the drawing symbol, identical or corresponding components are given identical or similar reference numbers, and redundant descriptions thereof are omitted. For convenience of explanation, the size and shape of each component depicted may be exaggerated or reduced.

[0075] FIG. 5 is a plan view schematically showing a secondary battery (300) according to an embodiment of the present invention. FIG. 6 is a block diagram conceptually showing a configuration of a lead-tap laser welding device (100) according to an embodiment of the present invention. FIG. 7 is a schematic diagram schematically showing the configurations of a lead-tap laser welding device (100) according to an embodiment of the present invention. FIG. 8 is a partial cross-sectional view schematically showing a shape of an overlapping area (327) of a lead part (330) and a tab part (350) welded using a lead-tap laser welding device (100) according to an embodiment of the present invention. FIG. 9 is a partial cross-sectional view schematically showing a shape of an overlapping area of ​​a negative electrode lead and a negative electrode tab welded using a lead-tap laser welding device according to an embodiment of the present invention. And, FIG. 10 is a perspective view schematically showing the appearance of the overlapping area (327) of the lead part (330) and the tab part (350) welded using a lead-tab laser welding device (100) according to one embodiment of the present invention.

[0076] Referring to FIGS. 5 to 10, a lead-tab laser welding device (100) according to one embodiment of the present invention includes a lead-tab mounting portion (120) that arranges a lead portion (330) and a tab portion (350) of a secondary battery (300) to overlap each other. In addition, the lead portion (330) and the tab portion (350) of the secondary battery (300) are mounted on the lead-tab mounting portion (120) in a state of overlapping each other.

[0077] Here, the secondary battery (300) includes an electrode assembly (320) and a pouch case (360) containing an electrolyte, as in FIG. 5. As in FIG. 8, the electrode assembly (320) includes a positive electrode (324), a negative electrode (322), and a separator (326) interposed between the positive electrode (324) and the negative electrode (322). The secondary battery (300) may include a tab portion (350) provided on each of the positive electrode (324) and the negative electrode (322). For example, the tab portion (350) may include a positive electrode tab (351) and a negative electrode tab (353). Here, the positive electrode tab (351) may be an extension of a current collector (e.g., aluminum foil) to which a positive electrode active material is applied, and the negative electrode tab (353) may be an extension of a current collector (e.g., copper foil) to which a negative electrode active material is applied.

[0078] In addition, the secondary battery (300) must connect the tab portion (350) of the electrode assembly (320) and the lead portion (330) that serves as an external terminal to draw current outward. Here, the lead portion (330) may include a positive lead (331) and a negative lead (333). For example, the positive lead (331) may be formed of an aluminum alloy material, and the negative lead (333) may be formed of a copper alloy material. In the process of manufacturing the secondary battery (300), the lead portion (330) and the tab portion (350) are overlapped and joined by laser welding, and the positive lead (331) is joined to the positive tab (351), and the negative lead (333) is joined to the negative tab (353), respectively.

[0079] At this time, in order to manage the welding quality of the overlapping area (327) of the lead portion (330) and the tab portion (350), welding defects must be minimized and sufficient joint strength must be secured. For example, defects such as pores or cracks can reduce electrical performance and mechanical reliability. In addition, spatter generation must be suppressed to prevent electrode contamination, and thermal deformation and residual stress must be minimized to prevent electrode damage.

[0080] Meanwhile, the lead-tab mounting portion (120) of the present invention serves to overlap and position the lead portion (333) and the tab (350) of the secondary battery (300). Specifically, as shown in FIG. 8, the lead-tab mounting portion (120) is provided to arrange the positive lead (331) and the positive tab (351) so as to overlap and align them. As shown in FIG. 9, the lead-tab mounting portion (120) is provided to arrange the negative lead (333) and the negative tab (353) so as to overlap and align them.

[0081] FIG. 11 is a partial plan view showing the formation order of a bead formed using a lead-tap laser welding device (100) according to one embodiment of the present invention.

[0082] Referring to FIGS. 6, 10, and 11, the welding unit (110) of the lead-tab laser welding device (100) according to one embodiment of the present invention is arranged to form beads in the order of the first position (1 of FIG. 10), the second position (3 of FIG. 10), and the third position (2 of FIG. 10) located sequentially along the first direction (X-axis direction) within the overlapping area (327), in the first position (1), the third position (2), and the second position (3). Here, the first direction may be the width direction (W) of the lead or tab.

[0083] In this document, the X-axis direction may represent the width direction of the tab (or lead), the Z-axis direction may represent the stacking direction of the tab and lead, and the Y-axis direction may represent the length direction of the tab (or lead).

[0084] That is, the lead-tap laser welding device (100) of the present invention forms a bead (B1) at a first position (1) first, and then, rather than forming a bead at an immediately adjacent second position (3), forms a second bead (B2) at a third position (2) which is further in the first direction (X-axis direction, width direction of the electrode tab), and then forms a bead at a second position (3) located between the first position (1) and the third position (2). Of course, the remaining beads (B5, B6, B7, B8, B9, B10) can also be formed using this welding order rule. That is, the fifth bead (B5), the sixth bead (B6), the seventh bead (B7), the eighth bead (B8), the ninth bead (B9), and the tenth bead (B10) can be welded in this order.

[0085] In addition, in the present invention, the first position (1), the second position (3), and the third position (2) are spaced apart from each other, and the interval between the first position (1) and the second position (3) can be set to be greater than the interval between the second position (3) and the third position (2).

[0086] The welding unit (110) of the lead-tab laser welding device (100) of the present invention may be configured to form a plurality of beads along the width direction (W) of the lead-tab when welding the lead portion (330) and the tab portion (350), and to divide the lead portion (330) into a first region (Z1) and a second region (Z2) on the left and right based on the center of the width direction (W) of the lead portion, and to alternately form beads in the first region (Z1) and the second region (Z2) thus divided.

[0087] At this time, the welding unit (110) can form a first bead row (T1) and a second bead row (T2) arranged in the width direction (W) in each of the first region (Z1) and the second region (Z2). At this time, the first bead row (T1) may include a plurality of beads (B1, B3, B5, B7, B9), and the second bead row (T2) may include a plurality of beads (B2, B4, B6, B8, B10). For convenience of explanation in the drawing, an example of forming about 10 beads has been described, but the number of beads is not necessarily limited to 10. That is, the number of beads in the lead portion-tab portion overlapping area may be, for example, 28.

[0088] Referring to Fig. 11, when bead formation positions spaced at regular intervals from number 1 to 10 are designated on the lead portion (330), the left side can be defined as the first region (Z1) and the right side can be defined as the second region (Z2) based on the center of the width direction (W) of the lead portion (330) between 9 and 2.

[0089] The welding unit (110) can form beads one at a time by alternately selecting one bead (B1, B3, B5, B7, B9 sequentially selected) of the first region (Z1) and beads (B2, B4, B6, B8, B10 sequentially selected) of the second region (Z2) from among the first bead row (T1) of the first region (Z1) and the second bead row (T2) of the second region (Z2). Of course, when viewed from each of the first region (Z1) and the second region (Z2) of the lead (350), the beads (B1 to B10) are sequentially generated in the width direction (W).

[0090] In addition, the lead-tap laser welding device (100) of the present invention includes a welding unit (110). In addition, the welding unit (110) may be arranged to irradiate a single mode fiber laser to weld the overlapping lead portion (330) and tab portion (350) to each other.

[0091] More specifically, as shown in FIGS. 6 and 7, the welding unit (110) of the lead-tap laser welding device (100) according to one embodiment of the present invention includes a laser oscillation unit (130) that oscillates a laser beam of a single-mode fiber laser type. It may include a pumping source (131), an optical fiber (134), and a center beam combiner (137).

[0092] For example, a laser diode (132) is used as a pumping source (131), and pumping light generated from the laser diode (132) is incident into an optical fiber (134) through a center beam combiner (137). Here, the optical fiber (134) includes a cladding (134-1), a core (134-2), a fiber (134-3), and a plastic jacket (134-4). After the pumping light is incident, the pumping light is confined inside the core (134-2) by the cladding (134-1) within the optical fiber (134), and laser oscillation occurs through the fiber (134-3), which is a medium for laser oscillation.

[0093] Additionally, the optical fiber (134) used in the single-mode fiber laser method has a small core (134-1) diameter (about 14 μm) and operates in a single mode with one fiber (138).

[0094] In addition, as shown in FIG. 6, the welding unit (110) includes a beam control unit (112) that controls the diameter and path of the laser beam emitted from the laser oscillation unit (130). Here, the beam control unit (112) performs the function of optimizing the bead shape and penetration depth of the overlapping area (327) by controlling the focal size of the laser beam.

[0095] More specifically, as shown in FIG. 7, the beam control unit (112) may include a scanner (114). The scanner (114) may be equipped with a collimating lens (117) for controlling the beam diameter. The scanner (114) may include a mirror (118) for controlling the direction of propagation of the beam, i.e., the path of the beam.

[0096] Here, the collimating lens (117) functions to convert the divergent light from the laser oscillation unit (130) into parallel light. The divergent light tends to spread out as it moves away from the light source, causing the beam diameter to gradually increase. To prevent this, the beam diverged from the optical fiber (134) is passed through the collimating lens (117) to make the beam parallel. By adjusting the focal length of the collimating lens (117), the diameter of the parallel light, i.e., the beam diameter, can be adjusted to a desired size.

[0097] Additionally, the collimated beam is reflected by a mirror (118) inside the scanner (114) to change its direction of travel. Depending on the rotation angle of the mirror (118), the beam can be moved to a desired point on the surface of the overlapping area (327).

[0098] In addition, the welding unit (110) may include a control unit (114). The control unit (114) may be configured to control the laser oscillation unit (111), the beam control unit (112), and the focus adjustment lens unit (113). The user may use control software to set how the control unit (114) controls the laser oscillation unit (111), the beam control unit (112), the focus adjustment lens unit (113), etc. Through this, the user may designate the formation positions of a plurality of beads (B1 to B10) and the welding path (pattern) of the bead (B1). Accordingly, the control unit (114) controls each component according to the contents set by the user to perform the formation and welding process of the bead.

[0099] In addition, as shown in FIG. 6, the welding unit (110) may include a focus adjustment lens unit (113) that focuses the laser beam passing through the beam adjustment unit (112) onto the lead unit (330)-tab unit (350) overlapping area (327). The focus adjustment lens unit (113) precisely focuses the laser beam onto the surface of the overlapping area (327) to maximize energy transfer efficiency.

[0100] More specifically, as shown in FIG. 7, the focus adjustment lens unit (113) of the lead-tap laser welding device (100) according to one embodiment of the present invention may include an F-theta lens (116). The F-theta lens (116) is an optical system used to irradiate a laser beam with a uniform beam diameter onto a flat surface.

[0101] Additionally, the F-theta lens (116) is controlled by the control unit (114). The control unit (114) can control the F-theta lens (116) to move the focus of the beam in the first direction so as to form a plurality of beads lined up in the first direction (X-axis direction).

[0102] Additionally, the control unit (114) can control the F-theta lens (116) to move the laser beam to form a bead along a set welding path.

[0103] Meanwhile, the welding unit (110) of the lead-tap laser welding device (100) of the present invention can form each bead by irradiating a single mode fiber laser. Accordingly, high beam quality and a small beam size (approximately 14 μm) compared to a multimode fiber laser device can be obtained.

[0104] The welding unit (110) of the lead-tap laser welding device (100) of the present invention can form each bead by irradiating a continuous wave mode fiber laser.

[0105] Meanwhile, the welding unit (110) of the lead-tap laser welding device (100) according to one embodiment of the present invention can form a welding bead along the width direction of the overlapping area (327) of the lead portion (330) - the tab portion (350). At this time, the present invention can form a plurality of beads in at least one row in the width direction. However, compared to the case of one row, when two or more rows of beads are formed, there is a disadvantage in that the bead size easily increases and the tensile strength decreases due to excessive heat input between the beads of each of the two adjacent rows. Therefore, the present invention can preferably irradiate a laser beam so that the welding bead is formed in only one row along the width direction of the overlapping area (327) of the lead portion (330) - the tab portion (350).

[0106] FIG. 12 is a partial plan view showing a bead path and a bead shape formed when welding a positive lead (331) to a positive tab (351) in a lead-tab laser welding method (200) according to one embodiment of the present invention.

[0107] Referring to FIGS. 5, 8, 9, and 12, the positive electrode lead (331) of the secondary battery (300) may include an aluminum alloy material. In addition, the negative electrode lead (333) may include a copper alloy material. Here, aluminum is disadvantageous in securing welding strength due to differences in physical properties compared to copper. Accordingly, the positive electrode lead (331) - positive electrode tab (351) overlapping area (327) needs to have a welding path of a different form from the welding path applied to the negative electrode lead (333) - negative electrode tab (353) overlapping area (327) in order to obtain sufficient welding strength.

[0108] For example, the welding unit (110) of the lead-tab laser welding device (100) according to one embodiment of the present invention performs welding by irradiating a laser beam in a curved path elongated in the longitudinal direction (Y-axis direction of FIG. 5) of the anode lead (331) and the anode tab (351) when welding them. Specifically, as shown in FIG. 12, the welding unit (110) can form a plurality of beads (C1) in a curved path having a narrower path width (S) than the path length (L) in the direction (Y-axis direction) perpendicular to the welding direction (X-axis direction) of the lead-tab in the overlapping area (327) of the anode lead (331) and the anode tab (351). For example, the ratio of the length (L) and width (S) of the path may be 1: 0.45.

[0109] Fig. 13 is a partial plan view showing the shape of a path for generating a bead (C1) formed when welding a positive lead (331) and a positive tab (351) in a lead-tab laser welding method according to another embodiment of the present invention.

[0110] Referring to FIGS. 8, 12, and 13, the curved path applied by the welding unit (110) of the present invention may preferably have a form in which the outer and inner sides are open. That is, the curved path of the bead (C1) may have a form in which the start point and the end point do not meet and the two points are spaced apart by a predetermined distance. For example, as shown in FIG. 13, the welding unit (110) may form the bead (C1) by irradiating a laser beam in a curved path that is open from the inner side to the upper side in the overlapping area (327) of the positive lead (331) and the positive tab (351).

[0111] In addition, the lead-tab laser welding device (100) according to another embodiment of the present invention can form an open curved bead (C1) applied when welding anode lead (331) - anode tab (351) with a rotation range of less than 360 degrees. That is, the generation path of the bead (C1) formed by the welding unit (110) can be a path in the form of a partial arc in which the sum of the angles moving from the starting point to the ending point is less than 360 degrees.

[0112] For example, the generation path of the bead (C1) can be formed with a rotation range of 340 degrees. Accordingly, the open curved bead of the present invention exists at positions where the start and end points are spaced apart from each other.

[0113] FIG. 14 is a partial plan view showing the shape of a bead path formed when welding a cathode lead (333) and a cathode tab (353) in a lead-tab laser welding method (200) according to one embodiment of the present invention.

[0114] Referring to FIG. 14 together with FIG. 9, the welding unit (110) of the lead-tap laser welding device (100) according to one embodiment of the present invention may be arranged to form a bead (B1) in an arc-shaped path when welding the negative lead (333) - negative tab (353).

[0115] That is, as illustrated in FIG. 9, when the welding unit (110) irradiates a laser beam to the overlapping area (327) where the cathode lead (333) and the cathode tab (353) overlap, a bead (B1) is formed by drawing a circular trajectory. At this time, the end point of the continuous laser irradiation of the bead (B1) may be positioned adjacent to the starting point. However, the starting point and the end point of the arc-shaped path do not need to meet.

[0116] As previously explained, the cathode lead (333) and tab are primarily made of copper. Since copper has excellent thermal conductivity and low laser absorption, it is appropriate to secure a sufficient melting area.

[0117] Hereinafter, a lead-tap laser welding method (200) according to one embodiment of the present invention will be described.

[0118] FIG. 15 is a flowchart showing the steps of a lead-tap laser welding method (200) according to one embodiment of the present invention.

[0119] Referring to FIG. 15 together with FIGS. 6 to 14, a lead-tap laser welding method (200) according to one embodiment of the present invention will be described.

[0120] A lead-tab laser welding method (200) according to another embodiment of the present invention includes a mounting step (M01) of arranging the lead portion (330) and the tab portion (350) of the secondary battery (300) to overlap each other.

[0121] First, in the settling step (M01), the positive lead (331) and the positive tab (351), or the negative lead (333) and the negative tab (353) of the secondary battery (300) are aligned and placed so as to overlap each other by the lead-tab settling portion (120). At this time, the lead portion (330) and the tab portion (350) must overlap by an appropriate length in consideration of the electrical and mechanical characteristics of the overlapping area (327).

[0122] If the overlapping length is too short, contact resistance may increase, resulting in electrical loss. Conversely, if the overlapping length is excessively long, unnecessary space may be occupied, reducing the energy density of the battery. Therefore, in the settling step (M01), it is important to set the overlapping length so as to secure optimal conditions for the overlapping area (327) of the lead portion (330) and the tab portion (350).

[0123] Meanwhile, referring to FIG. 11, a lead-tab laser welding method (200) according to another embodiment of the present invention includes a laser welding step (M02). The laser welding step (M02) performs welding by irradiating a fiber laser to an overlapping area (327) of a lead portion (330) and a tab portion (350) disposed on a lead-tab mounting portion (120) by a welding unit (110).

[0124] A lead-tab laser welding method (200) according to another embodiment of the present invention includes a laser welding step (M02). As shown in FIG. 11, the laser welding step (M02) causes the welding unit (110) to form a plurality of beads spaced apart at predetermined intervals in a first position (1), a third position (2), and a second position (3) that are sequentially positioned along a first direction (X-axis direction) of an overlapping area (327) of a lead portion (330) and a tab portion (350) disposed on a lead-tab mounting portion (120). In addition, the first position (1), the second position (3), and the third position (2) are spaced apart from each other, and the interval between the first position (1) and the second position (3) may be set to be greater than the interval between the second position (3) and the third position (2).

[0125] According to one embodiment of the present invention, a lead-tab laser welding method (200) forms a plurality of beads along the width direction (W) of the lead-tab when the welding unit (110) welds the lead portion (330) and the tab portion (350) in the laser welding step (M02), and divides the lead-tab into a first region (Z1) and a second region (Z2) on the left and right based on the center of the width direction (W), and forms beads alternately in the first region (Z1) and the second region (Z2).

[0126] At this time, as shown in FIG. 11, the lead-tap laser welding method (200) of the present invention divides the lead portion (330) into a first region (Z1) and a second region (Z2) on the left and right based on the center in the width direction (W), and forms beads alternately within each region, and can form a single row of multiple beads (B1 to B10) arranged in the width direction (W) in each region.

[0127] For example, when bead formation positions are designated at regular intervals from number 1 to 10 along the width direction (W) length of the lead portion (330), the left side can be defined as the first region (Z1) and the right side can be defined as the second region (Z2) based on the center of the width direction (W) of the lead portion (330) between 5 and 6.

[0128] A lead-tap laser welding method (200) according to one embodiment of the present invention can form a bead by repeatedly moving the welding target forward and backward in the welding progress direction so that the welding unit (110) forms a bead in a first region (Z1) and a bead in a second region (Z2) at an intersection.

[0129] Meanwhile, in the laser welding step (M02), a single mode fiber laser may be irradiated to form each bead. In addition, the lead-tap laser welding method (200) according to one embodiment of the present invention may use a single mode fiber laser having a narrow beam diameter of between 13 μm and 25 μm, which is oscillated from the laser oscillation unit (130) of the welding unit (110) in the laser welding step (M02).

[0130] The present invention can form each bead by irradiating a single mode fiber laser in a continuous wave mode in the laser welding step (M02).

[0131] Meanwhile, the lead-tap laser welding method (200) according to one embodiment of the present invention can form only one row of welding beads (B1, B2, B3, B4, B5, B6, B7, B8, B9, B10) in the width direction (W) of the lead portion (330) and the tab portion (350).

[0132] Meanwhile, referring to FIG. 12, the lead-tab laser welding method (200) according to one embodiment of the present invention can form a bead shape differently when welding the positive lead (331) - positive tab (351) and a bead shape differently when welding the negative lead (333) - negative tab (353) in the laser welding step.

[0133] In addition, the lead-tab laser welding method (200) according to one embodiment of the present invention has a feature that, when welding the positive lead (331) - positive tab (351), the welding unit (110) forms a bead (C1) that is narrow in width (S) in the welding direction and long in the length (L) direction. This is to obtain a bead (C1) that is close to an elliptical shape that is vertically elongated along the welding line, unlike a conventional circular bead.

[0134] Meanwhile, referring to FIGS. 12 and 13, the welding method (200) of the present invention can form a bead (C1) of an open curved path in which the starting point and the ending point are at different positions when welding the positive lead (331) and the positive tab (351). For example, the path of the bead (C1) formed by the welding unit (110) can be a C-shape in which the starting point and the ending point of the bead do not meet.

[0135] That is, the curved path of the bead (C1) may be such that the start and end points do not meet, but are spaced apart by a predetermined distance. For example, the welding unit (110) may form a bead by irradiating a laser beam in a curved path that is open from the inside to the top in the overlapping area (327) of the positive lead (331) and the positive tab (351).

[0136] In addition, the lead-tab laser welding method (200) according to one embodiment of the present invention can form a rotation range of an open curved bead (C1) applied by a welding unit (110) when welding a positive lead (331) - a positive tab (351) to be less than 360 degrees. That is, the welding path of the bead (C1) formed by the welding unit (110) can be a path in the form of a partial arc in which the sum of the angles moving from the starting point to the ending point is less than 360 degrees.

[0137] For example, the path of the bead (C1) can be formed with a rotation range of 340 degrees. Accordingly, the open curved bead (C1) of the present invention exists at positions where the start and end points are spaced apart from each other.

[0138] Meanwhile, referring to FIGS. 9 and 14, a lead-tab laser welding method (200) according to one embodiment of the present invention can weld by forming a bead (B1) in an arc-shaped path when the welding unit (110) welds the negative lead (333) and negative tab (353).

[0139] That is, when the welding unit (110) irradiates a laser beam to the overlapping area (327) where the cathode lead (333) and the cathode tab (353) overlap, it forms a bead (B1) by drawing a circular trajectory, as shown in Fig. 14. At this time, the end point of the continuous laser irradiation of the bead (B1) may be positioned adjacent to the starting point. However, at this time, the starting point and the end point of the arc-shaped path do not need to meet.

[0140] Meanwhile, referring to FIGS. 5 to 9, the present invention provides a secondary battery (300) manufactured using a welding device (100) and a welding method (200) according to an embodiment of the present invention. Specifically, the secondary battery (300) may include a positive electrode lead (331), a positive electrode tab (351), and a negative electrode lead (333) and a negative electrode tab (353) welded together using the welding device (100) and the welding method (200). The secondary battery (300) of the present invention includes an electrode assembly (320), an electrolyte (not shown), and a pouch case (360).

[0141] As shown in Fig. 8, the electrode assembly (320) has a structure in which positive electrodes (322) and negative electrodes (324) are alternately laminated with a separator (326) therebetween. In addition, each of the plurality of negative electrodes (324) and the plurality of positive electrodes (322) provided in the electrode assembly (320) may have a structure in which they are electrically connected to the positive electrode tab (351) and the negative electrode tab (353). In addition, each bundle of positive electrode tabs (351) and negative electrode tabs (353) may be connected by welding to the positive electrode lead (331) and the negative electrode lead (333).

[0142] The manufacturing process of the pouch case (360) first involves processing the pouch film using a molding device (not shown) to form a receiving portion (362) capable of accommodating the electrode assembly (320). At this time, the molding device uses a mold to give the pouch film a concave shape corresponding to the receiving portion (362).

[0143] As shown in FIG. 5, the electrode assembly (320) can be stored in a receiving portion (362) inside a pouch case (360). Specifically, in the electrode insertion step, the electrode assembly (320) can be automatically inserted into the receiving portion (362) formed in the pouch manufacturing step using a loading device (not shown).

[0144] In addition, the pouch case (360) can be injected with an electrolyte (not shown) while the electrode assembly (320) is accommodated therein. The electrolyte injection is performed after the electrode assembly (320) is seated in the receiving portion (362) inside the pouch case (360).

[0145] The secondary battery (300) can be manufactured in a form in which a portion of each of the positive lead (331) and the negative lead (333), which are connected to each of the positive tab (351) and the negative tab (353), protrudes out of the pouch case (360) through a pouch film positioned relatively above and a pouch film positioned below.

[0146] At this time, the electrode lead portion (330) may be covered with a protective film (340) at a portion that comes into contact with the pouch case (360) to ensure electrical insulation from the pouch case (360). The protective film (340) may include an electrically insulating material.

[0147] The preferred embodiments of the present invention described above are disclosed for the purpose of illustration, and those skilled in the art having ordinary knowledge of the present invention will be able to make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions should be considered to fall within the scope of the following claims.

[0148] According to a lead-tab laser welding method and a lead-tab laser welding device related to one embodiment of the present invention, it is possible to prevent excessive heat input during welding of an overlapping area of ​​a lead-tab, maximize a joining area, thereby improving joining properties and durability, and reducing the amount of spatter generated.

Claims

1. Includes a laser welding step of forming a plurality of beads through a welding unit in an overlapping area of ​​a lead portion and a tab portion of a secondary battery, A lead-tab laser welding method in which, in the laser welding step, beads are formed in the order of the first position, the third position, and the second position, for a first position, a second position, and a third position located sequentially along the first direction within the overlapping area of ​​the lead portion and the tab portion.

2. In paragraph 1, A lead-tab laser welding method wherein the first position, the second position, and the third position are spaced apart from each other, and the distance between the first position and the second position is set to be greater than the distance between the second position and the third position.

3. In paragraph 1, In the above laser welding step, A lead-tap laser welding method in which, when the welding unit forms a plurality of beads along the first direction, the overlapping area is divided into a first area and a second area based on the center of the first direction, and beads are alternately formed in the first area and the second area.

4. In paragraph 1, A lead-tap laser welding method in which each bead is formed by irradiating a single mode fiber laser in the above laser welding step.

5. In paragraph 4, A lead-tap laser welding method for forming a beam diameter of the single mode fiber laser to 13 μm to 25 μm.

6. In paragraph 1, A lead-tap laser welding method in which each bead is formed by irradiating a single-mode fiber laser in a continuous wave mode in the above laser welding step.

7. In paragraph 1, In the above laser welding step, A lead-tap laser welding method for forming the plurality of beads in only one line along the first direction.

8. In paragraph 1, The above lead portion includes a positive lead and a negative lead, The above tab portion includes a positive tab and a negative tab, In the above laser welding step, A lead-tab laser welding method in which the welding unit forms a bead in a different shape when welding the positive lead-positive tab and a bead in a different shape when welding the negative lead-negative tab.

9. In paragraph 8, In the above laser welding step, A lead-tab laser welding method in which, during the above anode lead-anode tab welding, the welding unit forms the bead so that the width of the bead along the width direction of the anode tab is smaller than the length of the bead along the length direction of the anode tab.

10. In paragraph 9, In the above laser welding step, A lead-tab laser welding method in which, during the above-mentioned positive lead-positive tab welding, the welding unit forms a bead in an open curved path in which the positions of the welding start point and the welding end point are different.

11. In paragraph 8, A lead-tab laser welding method in which the welding unit forms a bead in an arc-shaped welding path when welding the cathode lead-cathode tab in the laser welding step.

12. A lead-tab laser welding device including a welding unit configured to form beads in the order of the first position, the third position, and the second position, with respect to a first position, a second position, and a third position sequentially located along a first direction within an overlapping area of ​​a lead portion and a tab portion of a secondary battery.

13. In paragraph 12, A lead-tap laser welding device in which the first position, the second position, and the third position are spaced apart from each other, and the interval between the first position and the second position is set to be greater than the interval between the second position and the third position.

14. In paragraph 12, A lead-tab laser welding device, wherein the welding unit is configured to alternately form beads in the first region and the second region by dividing the lead-tab into a first region and a second region based on the center of the lead-tab in the width direction when forming a plurality of beads along the width direction of the lead-tab.

15. In paragraph 12, The above welding unit is a lead-tap laser welding device that forms each bead by irradiating a single mode fiber laser.

16. In paragraph 12, The above welding unit is a lead-tap laser welding device that forms each bead by irradiating a continuous wave mode fiber laser.

17. In paragraph 12, The above welding unit is a lead-tab laser welding device that irradiates a laser beam so that a welding bead is formed in only one line along the width direction of the lead-tab overlapping area.

18. In paragraph 12, The above welding unit is a lead-tab laser welding device configured to form a bead width along the width direction of the anode tab smaller than the bead length along the length direction of the anode tab when welding anode lead-anode tab.

19. In paragraph 12, The above welding unit, A laser oscillation unit that oscillates a laser beam of a single-mode fiber laser; A beam control unit that controls the diameter and path of a laser beam emitted from the laser generator; and A lead-tab laser welding device including a focus adjustment lens unit that focuses a laser beam passing through the beam adjustment unit on a lead-tab overlapping area.

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