Ultrasonic welding apparatus, ultrasonic welding method, battery cell manufactured by ultrasonic welding method, battery pack and vehicle including same

Abstract

Disclosed are an ultrasonic welding apparatus capable of ensuring welding strength between a current collecting plate of a battery cell and a terminal (rivet), an ultrasonic welding method, a battery cell manufactured thereby, a battery pack, and a vehicle. The ultrasonic welding apparatus according to an embodiment of the present invention includes a welding horn that has a plurality of protrusions provided at the end of a welding tip to press at least one member to be welded among the current collecting plate and the rivet with a contact surface having recesses and protrusions. The plurality of protrusions protrude from the end surface toward the member to be welded. Among the plurality of protrusions, first protrusions arranged in the central region of a knurling portion are formed in a hexagonal cross-sectional shape, and the cross-sectional area of the first protrusions in the transverse direction decreases toward the member to be welded.

Description

Ultrasonic welding device, ultrasonic welding method, battery cell manufactured by the same, battery pack, and automobile including the same

[0001] The present invention relates to an ultrasonic welding device, an ultrasonic welding method, a battery cell and battery pack manufactured thereby, and an automobile including the same.

[0002] Secondary batteries are attracting attention as an energy source for improving eco-friendliness and energy efficiency because they have high energy density and the advantage of being able to drastically reduce the use of fossil fuels, as well as the advantage of not generating by-products from energy use. Due to these advantages, secondary batteries are widely applied not only to portable devices but also to electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electric power sources.

[0003] When a high output voltage is required, the output voltage can be supplied by a battery pack formed by connecting multiple unit secondary battery cells, i.e., battery cells, in series. Additionally, a battery pack can be configured by connecting multiple battery cells in parallel according to the required charge / discharge capacity of the battery pack. The number of battery cells included in the battery pack can be varied depending on the required output voltage and / or charge / discharge capacity.

[0004] Lithium secondary batteries are classified according to the shape of the battery case into prismatic and cylindrical secondary batteries (battery cells), in which the electrode assembly is housed in a metal can (battery housing), and pouch-type secondary batteries, in which the electrode assembly is housed in a pouch case made of an aluminum laminate sheet. In the case of cylindrical batteries, a terminal (rivet) provided on the closing side of the battery housing (battery can) penetrates the closing part and comes into contact with a current collector plate positioned on the inside of the battery can. The current collector plate and the terminal can be connected by ultrasonic welding. By performing ultrasonic welding by contacting a welding horn onto the current collector plate from the inside of the battery can, the contact area between the current collector plate and the terminal can be welded.

[0005] An ultrasonic welding device is equipped with an anvil on which a terminal is seated and a horn that presses against a collector plate. The horn of the ultrasonic welding device may be provided with a structure having multiple protrusions to increase friction and pressure with the workpiece to be welded. To increase energy capacity, it is necessary to reduce the size of the core around which the electrode assembly of a cylindrical battery cell is wound; in this case, the diameter of the ultrasonic welding horn inserted into the core of the electrode assembly must also be reduced. However, as the diameter of the welding device's horn is reduced, a problem may arise in which the weld joint strength decreases due to the reduction in the welding area.

[0006] Another problem arising during the ultrasonic welding process of the collector plate and the terminal is that it is difficult to apply a knurl pattern with an intact shape to the outermost edge of the weld zone between the collector plate and the terminal, and the failure to form a uniform knurl pattern at the outer edge of the weld zone results in a reduction of the total knurl area. Furthermore, excessive stress is concentrated in the unevenly formed knurl pattern in the outer region of the weld zone, leading to increased plastic deformation and the potential generation of foreign matter or burrs. Accordingly, a new knurl pattern is required to secure sufficient welding strength within a limited horn diameter. The background technology described above is intended to explain the background of the derivation of the present invention and does not imply that it is technology known prior to the filing of the present invention.

[0007] One objective of the present invention is to provide an ultrasonic welding device capable of securing welding strength between a current collector plate and a terminal (rivet) of a battery cell, an ultrasonic welding method, a battery cell, a battery pack, and an automobile manufactured thereby.

[0008] In addition, the present invention has the purpose of preventing excessive stress concentration at the outermost edge of the weld between the current collector plate and the terminal of a battery cell, thereby preventing an increase in plastic deformation and reducing foreign matter or burrs.

[0009] The technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description of the invention below.

[0010] An ultrasonic welding device according to an embodiment of the present invention includes a welding tip for joining a current collector plate of a cylindrical battery cell by ultrasonically welding it with a rivet. The welding tip includes a welding horn at the end of the welding tip to press at least one member to be welded, among the current collector plate and the rivet, with an uneven contact surface. The welding horn includes a knurling portion comprising a plurality of protrusions arranged on the end surface of the welding tip to press the member to be welded with the uneven contact surface. The plurality of protrusions of the knurling portion are formed to protrude from the end surface in a direction toward the member to be welded. Among the plurality of protrusions, first protrusions disposed in the central region of the knurling portion are formed in a hexagonal cross-sectional shape. The cross-sectional area of ​​the first protrusions decreases in the transverse direction as they move toward the member to be welded.

[0011] The first protrusions may be formed such that, with respect to the direction toward the welded member, the first cross-sectional shape at the end point and the second cross-sectional shape at the protrusion start point are each hexagonal cross-sectional shapes, and the first cross-sectional shape and the second cross-sectional shape are arranged coaxially.

[0012] The first protrusions mentioned above can be arranged in a honeycomb structure.

[0013] The plurality of protrusions may further include second protrusions disposed in an outer region surrounding the central region of the knurling portion.

[0014] The second protrusions may be formed in a shape different from the first protrusions.

[0015] The above second protrusions can be formed in a truncated cone shape.

[0016] The outermost protrusions among the first protrusions may be arranged spaced apart from each other. The second protrusions may be arranged between the outer protrusions.

[0017] The above second protrusions can be arranged at positions corresponding to the corner points of the hexagon.

[0018] An ultrasonic welding method according to an embodiment of the present invention comprises the steps of: preparing an ultrasonic welding device having a welding tip—the welding tip includes a welding horn at the end of the welding tip to press at least one member to be welded, among a current collector plate of a cylindrical battery cell and a rivet, with an uneven contact surface; and joining the current collector plate of a cylindrical battery cell to a rivet by ultrasonically welding it using the ultrasonic welding device.

[0019] The step of joining by ultrasonic welding described above includes the step of applying the welding horn, which has a knurling portion—the knurling portion comprises a plurality of protrusions arranged on the end surface of the welding tip, wherein the plurality of protrusions are formed to protrude from the end surface toward the workpiece—to the workpiece with an uneven contact surface.

[0020] Among the plurality of protrusions joined to the welded member, the first protrusions positioned in the central region of the knurling portion are formed in a hexagonal cross-sectional shape and are pressed against the welded member, and the cross-sectional area of ​​the first protrusions decreases in the transverse direction as they move toward the welded member.

[0021] In the step of joining by ultrasonic welding as described above, the first protrusions are arranged in a honeycomb structure and can be pressed against the member to be welded.

[0022] In the step of joining by ultrasonic welding as described above, among the plurality of protrusions, the second protrusions positioned in the outer region surrounding the central region of the knurling portion are formed in a truncated cone shape and can be pressed into the outer region of the weld portion of the member to be welded.

[0023] In the step of joining by ultrasonic welding, the outer protrusions positioned at the outermost of the first protrusions are spaced apart from each other and are pressed into the edge region of the center region of the weld portion of the member to be welded; and the second protrusions—the second protrusions are arranged at positions corresponding to the corner points of the hexagon—are arranged between the outer protrusions and can be pressed into the outer region of the weld portion of the member to be welded.

[0024] A cylindrical battery cell according to an embodiment of the present invention comprises: a cylindrical battery housing; a cylindrical electrode assembly that is received in the battery housing and is formed by winding a first electrode, a second electrode, and a separator around a winding axis; a current collector plate provided within the battery housing and electrically connected to at least one of the first electrode and the second electrode of the electrode assembly; and a rivet that is inserted at least a portion through an opening of the battery housing and joined to the current collector plate.

[0025] The collector plate and the rivet are joined by ultrasonic welding, and a plurality of indentations formed by ultrasonic welding are formed in the welded portion of the collector plate and the rivet. The plurality of indentations are formed by applying pressure to at least one workpiece among the collector plate and the rivet using the uneven contact surface of the welding horn provided at the end of the welding tip of the ultrasonic welding device. The plurality of indentations are formed with a hexagonal cross-sectional shape corresponding to a plurality of protrusions of the knurling portion arranged on the end surface of the welding tip. The plurality of indentations are formed by protruding from the end surface in a direction toward the workpiece.

[0026] Among the plurality of indentations above, the first indentations formed in the central region of the weld may include first indentation grooves formed by being pressed into the workpiece. The first indentation grooves may be formed in a truncated hexagonal pyramid shape in which the cross-sectional area decreases as the depth from the surface of the workpiece increases.

[0027] The plurality of indentations may include second indentation grooves disposed in an outer region surrounding the central region of the weld. The second indentation grooves may be formed in a truncated cone shape in which the cross-sectional area decreases as the depth from the surface of the workpiece increases.

[0028] According to an embodiment of the present invention, a battery pack comprising at least one cylindrical battery cell is provided.

[0029] According to an embodiment of the present invention, a vehicle comprising at least one battery pack is provided.

[0030] According to an embodiment of the present invention, an ultrasonic welding device capable of securing welding strength between a current collector plate of a battery cell and a terminal (rivet), an ultrasonic welding method, a battery cell manufactured thereby, a battery pack, and an automobile are provided.

[0031] In addition, according to an embodiment of the present invention, excessive stress concentration at the outermost edge of the weld between the current collector plate and the terminal of the battery cell can be prevented, thereby increasing the amount of plastic deformation and reducing foreign matter or burrs.

[0032] The effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by a person skilled in the art from the description of the invention below.

[0033] FIG. 1 is a perspective view showing a battery cell according to one embodiment of the present invention.

[0034] FIG. 2 is a cross-sectional perspective view of a battery cell according to an embodiment of FIG. 1.

[0035] FIG. 3 is a cross-sectional view of a battery cell according to an embodiment of FIG. 1.

[0036] FIG. 4 is a cross-sectional view showing the process of ultrasonically welding a current collector plate and a rivet of a battery cell according to an embodiment of the present invention.

[0037] FIG. 5 is a cross-sectional view showing the welding horn of a welding tip constituting an ultrasonic welding device according to an embodiment of the present invention.

[0038] FIG. 6 is a plan view showing a welding horn constituting an ultrasonic welding device according to an embodiment of the present invention.

[0039] FIG. 7 is a plan view showing an enlarged view of the protrusions of the welding horn constituting the ultrasonic welding device according to an embodiment of the present invention.

[0040] FIG. 8 is a side view showing an enlarged view of the protrusion of the welding horn constituting the ultrasonic welding device according to an embodiment of the present invention.

[0041] FIG. 9 is a cross-sectional view showing the welding horn of a welding tip constituting an ultrasonic welding device according to another embodiment of the present invention.

[0042] FIG. 10 is a plan view showing a welding horn constituting an ultrasonic welding device according to the embodiment of FIG. 9.

[0043] FIG. 11 is an enlarged side view showing the second projection of the welding horn constituting the ultrasonic welding device according to the embodiment of FIG. 9.

[0044] FIG. 12 is a drawing for explaining a battery pack including a battery cell according to an embodiment of the present invention.

[0045] FIG. 13 is a drawing for explaining a vehicle including the battery pack of FIG. 12.

[0046] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Accordingly, in some embodiments, well-known process steps, well-known device structures, and well-known techniques are not specifically described to avoid the present invention being interpreted ambiguously. Throughout the specification, like reference numerals refer to like components.

[0047] In drawings, thicknesses may be enlarged to clearly represent multiple layers and regions. Throughout the specification, the same reference numerals are used for similar parts. When a part such as a layer, film, region, or plate is described as being "above" another part, this includes not only cases where it is "immediately above" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately above" another part, it means that there is no other part in between. Furthermore, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only cases where it is "immediately below" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately below" another part, it means that there is no other part in between.

[0048] Hereinafter, an ultrasonic welding device and a cylindrical battery cell manufactured by the ultrasonic welding device according to an embodiment of the present invention will be described, and then the ultrasonic welding device and the ultrasonic welding device according to an embodiment of the present invention will be described. An ultrasonic welding device and an ultrasonic welding method according to one embodiment of the present invention apply a knurling portion in which protrusions with a hexagonal cross-sectional shape are arranged on the welding horn of a welding tip used for ultrasonic welding with a rivet to the collector plate of a cylindrical battery cell, thereby increasing the pressure area for the workpiece (collector plate, rivet) and ensuring sufficient weld joint strength. An ultrasonic welding device and an ultrasonic welding method according to another embodiment of the present invention apply a knurling portion in which protrusions with a hexagonal cross-sectional shape are arranged in the center of the welding tip and protrusions with a circular cross-sectional shape are arranged in the outer region, thereby preventing excessive stress concentration at the outermost edge of the weld between the collector plate and the terminal of the battery cell, which increases the amount of plastic deformation, and reducing foreign matter or burrs.

[0049] A cylindrical battery cell according to an embodiment of the present invention is provided with a structure in which an electrode assembly is inserted into a cylindrical battery housing. For convenience of explanation, in this specification, the direction following the longitudinal direction of the winding axis of the electrode assembly wound in a jelly roll shape is referred to as the "axial direction," "up-down direction," or "height direction." The direction surrounding the winding axis is referred to as the "circumferential direction" or "peripheral direction." The direction approaching the winding axis or moving away from the winding axis is referred to as the "radial direction." Among the radial directions, the direction approaching the winding axis may be referred to as the "centripetal direction," and the direction moving away from the winding axis may be referred to as the "centrifugal direction."

[0050] FIG. 1 is a perspective view showing a battery cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional perspective view of a battery cell according to the embodiment of FIG. 1. FIG. 3 is a cross-sectional view of a battery cell according to the embodiment of FIG. 1. Referring to FIG. 1 to 3, a battery cell (1) according to an embodiment of the present invention includes an electrode assembly (10), a battery housing (20), a current collector (30), a battery cap (40), a sealing gasket (50), a current collector plate (60), and a rivet (70). The battery cell of the present invention is not limited to the shape of the battery cell shown in FIG. 1 to 3 and can be applied to batteries of other shapes. To avoid obscuring the essence of the present invention, components such as a busbar for electrical connection, a cooling unit, and a power terminal are omitted from the illustration.

[0051] A battery cell (1) according to one embodiment of the present invention may be a cylindrical secondary battery (cylindrical battery cell). An electrode assembly (10) may be provided in a cylindrical shape having a core and an outer surface, wherein a first electrode (e.g., a negative electrode), a second electrode (e.g., a positive electrode), and a separator interposed between these electrodes are wound around a winding axis. The electrode assembly (10) may be a jelly-roll type electrode assembly. An additional separator may be provided on the outer surface of the electrode assembly (10) for insulation from the battery housing (20). The electrode assembly (10) may be provided to have a winding structure well known in the art of the present invention without limitation.

[0052] The first electrode comprises a first electrode current collector and a first electrode active material applied on one or both sides of the first electrode current collector. At one end (upper end) in the width direction of the first electrode (a direction parallel to the height direction of the battery cell shown in FIG. 1), there is a non-coated portion where the first electrode active material is not applied. That is, the first electrode includes a non-coated portion exposed to the outside of the separator, where the active material is not coated at one long end along the winding direction. The non-coated portion functioning as the first electrode tab is referred to as the first non-coated portion (11). The first non-coated portion (11) is provided at the upper end with respect to the height direction of the electrode assembly (10) housed within the battery housing (20). At least a portion of the first non-coated portion (11) is used as an electrode tab itself. The first non-coated portion (11) may be, for example, a negative electrode tab.

[0053] The second electrode comprises a second electrode current collector and a second electrode active material applied on one or both sides of the second electrode current collector. Based on the width direction (height direction) of the second electrode, there is a non-exposed portion at the other end where the second electrode active material is not applied. That is, the second electrode includes a non-exposed portion along the winding direction where the active material is not coated at the other long end and is exposed to the outside of the separator. The non-exposed portion functioning as a second electrode tab is referred to as the second non-exposed portion (12). The second non-exposed portion (12) is provided at the bottom based on the height direction of the electrode assembly (10) housed within the battery housing (20). At least a portion of the second non-exposed portion (12) is used as an electrode tab itself. The second non-exposed portion (12) may be, for example, a positive electrode tab.

[0054] The battery housing (20) is a roughly cylindrical receptacle with an opening formed on one side, and may be provided, for example, with a conductive metal material. The battery housing (20) is configured to accommodate the electrode assembly (10) of the secondary battery. The side of the battery housing (20) and the lower surface located opposite the opening (20a) may be formed integrally. The battery housing (20) may be provided with the upper end open and the lower end closed in the height direction. The lower surface of the battery housing (20) may have a roughly flat shape. The battery housing (20) is configured to accommodate the electrode assembly (10) and the electrolyte through the opening (20a) formed on its upper end.

[0055] The battery housing (20) may have a beading portion (21) formed in an end region adjacent to an opening (20a) provided at the top thereof, and a crimping portion (22) formed on the beading portion (21). The beading portion (21) has a shape in which the outer circumference of the battery housing (20) is pressed in to a predetermined depth. The beading portion (21) may have a shape in which it is pressed inward in the region between the opening (20a) of the battery housing (20) and the internal receiving space that accommodates the electrode assembly (10).

[0056] The beading portion (21) provides a support surface on which a sealing gasket (50) and a battery cap (40) can be seated. Additionally, the beading portion (21) can provide a support surface on which at least a portion of the edge perimeter of a current collector (30) can be seated and joined. At least a portion of the edge perimeter of the current collector (30), at least a portion of the edge perimeter of the sealing gasket (50), and at least a portion of the edge perimeter of the battery cap (40) can be seated on the upper surface of the beading portion (21). The beading portion (21) can be formed by pressing the outer circumference of the battery housing (20) inward in an area adjacent to the opening (20a) of the battery housing (20) while the electrode assembly (10) is received within the battery housing (20) through the opening (20a).

[0057] In order to stably support the current collector (30), the battery cap (40), and the sealing gasket (50), the upper surface of the beading portion (21) may have a shape that extends along a direction approximately parallel to the lower surface of the battery housing (20), that is, a shape that extends in a direction approximately perpendicular to the side wall of the battery housing (20). The beading portion (21) can function as a support portion on which the battery cap (40), etc., is seated, while preventing the electrode assembly (10), which has a size corresponding to the inner diameter of the internal receiving space of the battery housing (20), from coming out through the opening (20a) formed at the top of the battery housing (20).

[0058] The crimping portion (22) extends upward from the beading portion (21) and is formed on the upper part of the beading portion (21). The crimping portion (22) has a bent shape that extends to wrap around the edge perimeter and part of the upper surface of the battery cap (40) placed on the upper part of the beading portion (21). The battery cap (40) is fixed on the beading portion (21) by the crimping portion (22). The crimping portion (22) may have a shape that extends inwardly from the upper perimeter of the battery housing (20) in the radial direction (centripetal direction) of the battery cell (1). The crimping portion (22) is provided in an area corresponding to the edge perimeter of the upper surface of the battery cap (40) to fix the battery cap (40) and prevent the battery cap (40) from moving upward.

[0059] The upper portion of the crimping portion (22) is formed by bending so that it extends inward by a predetermined distance along the radial direction of the battery cell (1) to wrap around a part of the upper surface of the battery cap (40), thereby securing the perimeter of the upper surface of the battery cap (40). The perimeter area of ​​the battery cap (40) is interposed between the upper portion of the crimping portion (22) and the beading portion (21) and is secured to the battery housing (20), covering the opening (20a) of the battery housing (20).

[0060] The current collector (30) is housed inside the battery housing (20). The current collector (30) is made of a conductive metal material and can be electrically connected to the electrode assembly (10). The current collector (30) can be electrically connected to the battery housing (20). That is, the current collector (30) can electrically connect the first electrode of the electrode assembly (10) and the battery housing (20). The current collector (30) may have a support portion (31), a tab coupling portion (32), and a housing coupling portion (33).

[0061] The support portion (31) and the tab connecting portion (32) of the current collector (30) are positioned on the upper part of the electrode assembly (10). The support portion (31) is positioned on one side of the electrode assembly (10). The tab connecting portion (32) extends from the support portion (31) and is connected to the first non-reinforcing portion (11) of the electrode assembly (10). The tab connecting portion (32) can be connected to the electrode assembly (10), for example, by welding a certain area while seated on the first non-reinforcing portion (11) of the electrode assembly (10). The tab connecting portion (32) of the current collector (30) may be located below the lower surface of the beading portion (21).

[0062] A through hole (not shown) may be formed in the current collector (30) to allow flames generated inside the battery cell (1) to escape smoothly. Accordingly, even if a thermal runaway phenomenon occurs on the side of the electrode assembly (10), the flames and venting gas generated from the electrode assembly (10) can be smoothly discharged through the through hole without being blocked by the current collector (30) located on the upper side of the electrode assembly (10). Therefore, it is possible to prevent the flames from moving toward the beading part (21) located in the vicinity of the electrode assembly (10) and the current collector (30) and causing pinholes in the beading part (21), and to prevent the fire from spreading to other battery cells (1) located around the battery cell (1) where the fire occurred.

[0063] The support member (31) may have a current collector hole (H2) formed at a position corresponding to a winding hole (H1) formed approximately in the center of the electrode assembly (10). The winding hole (H1) and the current collector hole (H2), which are in communication with each other, may function as a passage for inserting a welding rod (welding tip) for welding between the electrode terminal of the electrode assembly (10) and the current collector (30) or between the electrode terminal and a lead tab (not shown).

[0064] If the diameter of the current collector hole (H2) is excessively smaller than the diameter of the winding hole (H1), the hole formed in the winding hole (H1) may be obscured, which may reduce liquid injection performance, and it may also be difficult to secure sufficient space for inserting a welding device or laser irradiation. Therefore, so that the current collector hole (H2) does not obscure the winding hole (H1) formed in the core of the electrode assembly (10), the winding hole (H1) of the electrode assembly (10) may have a diameter substantially equal to or larger than that of the current collector hole (H2).

[0065] The housing coupling portion (33) extends from the support portion (31) to a periphery area and is coupled to the inner surface of the battery housing (20). The housing coupling portion (33) may extend from the support portion (31) and be electrically coupled to the inner surface of the battery housing (20). For example, the housing coupling portion (33) may be coupled to the upper surface of the beading portion (21) on the inner surface of the battery housing (20).

[0066] The inner diameter of the battery housing (20) in the area where the beading portion (21) is formed is formed to be smaller than the diameter of the electrode assembly (10). For stable contact and connection, the beading portion (21) may have a shape that extends along a direction approximately parallel to the lower surface of the battery housing (20), that is, a direction approximately perpendicular to the side wall of the battery housing (20). The housing connection portion (33) may be welded to the upper surface of the beading portion (21). For welding the connection between the battery housing (20) and the current collector (30), for example, laser welding, ultrasonic welding, or spot welding may be applied.

[0067] A battery cap (40) is provided to cover an opening (20a) of a battery housing (20). The battery cap (40) may be coupled to the battery housing (20) to seal the opening (20a) of the battery housing (20) through a crimping process via a sealing gasket (50). The battery cap (40) may be provided with a venting portion (41) formed to prevent an increase in internal pressure caused by gas generated inside the battery housing (20).

[0068] The venting portion (41) may be configured to break when the internal pressure of the battery housing (20) increases above a certain level. The venting portion (41) is formed in a part of the battery cap (40) and may be a structurally weaker area than the surrounding area so that it can easily break when pressure is applied to the inside due to thermal runaway, etc. For example, the venting portion (41) may be an area having a thinner thickness compared to the surrounding area. The venting portion (41) may be formed as a roughly circular closed loop.

[0069] The battery cap (40) covers an opening (20a) formed on one side of the battery housing (20). The battery cap (40) can be secured by a crimping portion (22) formed on the top of the battery housing (20). To improve the fixing force and the sealing of the battery housing (20), a sealing gasket (50) is interposed between the battery housing (20) and the battery cap (40), and between the current collector (30) and the battery cap (40). Accordingly, the current collector (30) can be interposed between the beading portion (21) of the battery housing (20) and the sealing gasket (50). The current collector (30) interposed between the beading portion (21) and the sealing gasket (50) can be secured by bending the crimping portion (22) which extends upward from the beading portion (21).

[0070] The sealing gasket (50) is provided to surround the battery cap (40) and seal the space between the battery cap (40) and the battery housing (20). The sealing gasket (50) serves to maintain airtightness between the battery housing (20) and the battery cap (40). The sealing gasket (50) ensures good sealing performance, thereby preventing moisture from penetrating into the battery housing (20) or the electrolyte or gas inside the battery housing (20) from leaking out through the gap between the battery housing (20) and the battery cap (40).

[0071] The current collector plate (60) is housed inside the battery housing (20). The current collector plate (60) is made of a conductive metal material and can be electrically connected to the electrode assembly (10). The current collector plate (60) can be electrically connected to the second electrode of the electrode assembly (10). The current collector plate (60) is placed on the upper part of the electrode assembly (10). The current collector plate (60) is placed on the lower surface of the electrode assembly (10) and is coupled to the second non-conducting portion (12) of the electrode assembly (10). While the current collector plate (60) is seated on the second non-conducting portion (12) of the electrode assembly (10), it can be coupled to the electrode assembly (10) through welding of a certain area. For the welding to combine the battery housing (20) and the current collector plate (30), for example, laser welding, ultrasonic welding, or spot welding may be applied.

[0072] A rivet (70) is inserted into an opening formed in the bottom portion of a battery housing (20) and joined. An insulating portion (80) may be interposed between the rivet (70) and the opening of the battery housing (20). The insulating portion (80) can insulate the rivet (70) from the battery housing (20). FIG. 4 is a cross-sectional view showing the process of ultrasonically welding a current collector plate and a rivet of a battery cell according to an embodiment of the present invention. The current collector plate (60) and the rivet (70) of the battery cell can be welded together by an ultrasonically welding device. The ultrasonically welding device may include a welding tip (100). The welding tip (100) is inserted into a winding hole (H1) to ultrasonically weld the current collector plate (60) and the rivet (70), which are the members to be welded. The collector plate (60) and the rivet (70) can be joined by the weld (110) formed by the welding tip (100).

[0073] The rivet (70) may have a rivet body that is approximately cylindrical, and an upper protrusion and a lower protrusion that are formed by extending radially in a horizontal direction and parallel to the upper and lower surfaces of the rivet body, respectively, so that the rivet body may be positioned in an opening formed on the bottom surface of the battery housing (20). The rivet body of the rivet (70) may be positioned within an opening formed in the center of the bottom surface of the battery housing (20). To this end, the outer diameter of the rivet body may be formed to be smaller than the diameter of the opening formed on the bottom surface of the battery housing (20).

[0074] The upper protrusion of the rivet (70) can be inserted through an opening formed in the bottom surface of the battery housing (20) and interposed between the battery housing (20) and the current collector plate (60). The outer diameter of the upper protrusion can be formed to be larger than the diameter of the opening formed in the bottom surface of the battery housing (20). The lower protrusion of the rivet (70) is located outside the bottom surface of the battery housing (20). The outer diameter of the lower protrusion can be formed to be larger than the diameter of the opening formed in the bottom surface of the battery housing (20). In order to allow the rivet (70) to be smoothly inserted through the opening of the battery housing (20) and to allow the rivet (70) to be stably joined through the opening of the battery housing (20), the outer diameter of the lower protrusion can be formed to be larger than the outer diameter of the upper protrusion.

[0075] The insulating part (80) may have a shape corresponding to the rivet (70). Accordingly, the insulating part (80) may include a cylindrical insulating body, an upper insulating protrusion in the shape of a disc ring, and a lower insulating protrusion. The upper and lower heights of the insulating part (80) may be formed to be equal to the distance between the bottom surface of the upper protrusion and the top surface of the lower protrusion of the rivet (70). The inner diameter of the insulating body of the insulating part (80) may be formed to be equal to the diameter of the opening formed in the bottom surface of the battery housing (20), and the outer diameter may be formed to be equal to the outer diameter of the rivet body of the rivet (70).

[0076] The upper insulating protrusion of the insulating part (80) may be formed by extending and protruding in a radial direction parallel to the horizontal direction from the upper surface of the insulating body of the insulating part (80). The upper insulating protrusion is inserted through an opening formed in the bottom surface of the battery housing (20) and is interposed between the bottom surface of the battery housing (20) and the upper protrusion of the rivet (70). The outer diameter of the upper insulating protrusion may be formed to be larger than the diameter of the opening formed in the bottom surface of the battery housing (20).

[0077] The lower insulating protrusion of the insulating part (80) may be formed by extending and protruding in a radial direction parallel to the horizontal direction from the lower surface (bottom surface) of the insulating body. The lower insulating protrusion is located on the outer side of the bottom surface of the battery housing (20). The outer diameter of the lower insulating protrusion may be formed to be larger than the diameter of the opening formed in the bottom surface of the battery housing (20). In order for the insulating part (80) to be smoothly inserted through the opening of the battery housing (20) and stably coupled to the opening of the battery housing (20), the outer diameter of the lower insulating protrusion may be formed larger than the outer diameter of the upper insulating protrusion. To ensure the insulating performance of the insulating part (80), the outer diameter of the upper insulating protrusion may be formed larger than the outer diameter of the upper protrusion of the rivet (70), and the outer diameter of the lower insulating protrusion may be formed larger than the outer diameter of the lower protrusion of the rivet (70).

[0078] Next, an ultrasonic welding device for ultrasonically welding a rivet (70) to a current collector plate (60) of the battery cell described above will be described. FIG. 5 is a cross-sectional view showing the welding horn of a welding tip constituting an ultrasonic welding device according to an embodiment of the present invention. FIG. 6 is a plan view showing the welding horn constituting an ultrasonic welding device according to an embodiment of the present invention. FIG. 7 is a plan view showing an enlarged view of the protrusion of the welding horn constituting an ultrasonic welding device according to an embodiment of the present invention. FIG. 8 is a side view showing an enlarged view of the protrusion of the welding horn constituting an ultrasonic welding device according to an embodiment of the present invention.

[0079] Referring to FIGS. 5 to 8, the welding tip (100) includes a welding horn (200) having a plurality of protrusions (210) at the end of the welding tip (100) to press at least one member to be welded, among a collector plate (60) and a rivet (70), onto an uneven contact surface. The welding horn (200) includes a knurling portion having a plurality of protrusions (210) arranged on the end surface of the welding tip (100) to press the member to be welded onto an uneven contact surface.

[0080] A plurality of protrusions (210) constituting the knurling portion are formed by protruding from the end surface of the welding tip (100) toward the workpiece to be welded. The plurality of protrusions (210) may include first protrusions (210) disposed in the central area of ​​the knurling portion. The first protrusions (210) may be formed in a hexagonal cross-sectional shape and may be formed such that the transverse cross-sectional area decreases as it moves toward the workpiece to be welded.

[0081] The first protrusions (210) may be formed with a first cross-sectional shape at the end point (212) and a second cross-sectional shape at the protrusion start point (211), respectively, with respect to the direction toward the member to be welded. The first cross-sectional shape at the end point (212) and the second cross-sectional shape at the protrusion start point (211) of the first protrusions (210) may be formed to be arranged coaxially. That is, the first protrusions (210) may have a truncated cone shape. The first protrusions (210) may be arranged in a hexagonal honeycomb structure.

[0082] The first projection (210) may have six trapezoidal side sections (213) between a hexagonal protrusion starting point (211) and a hexagonal end point (212). The six side sections (213) of the first projection (210), together with the hexagonal end point (212), press the collector plate (60), which is the member to be welded, toward the rivet (70), thereby allowing the collector plate (60) and the rivet (70) to be ultrasonically welded together with a wide pressing area.

[0083] According to an embodiment of the present invention, by welding the current collector plate (60) and the rivet (70) of a battery cell using a welding horn having a knurl pattern with a hexagonal cross-sectional shape, the surface area in contact with the base material is increased, and a sufficient welding area can be secured. Accordingly, even if the diameter of the welding horn is reduced by decreasing the diameter of the winding hole (H1) to increase energy capacity, sufficient welding strength can be secured.

[0084] The first cross-sectional size (b) at the end point (212) of the first projection (210) may be formed to be smaller than the second cross-sectional size (a) at the protrusion start point (211). Accordingly, the six side portions (213) of the first projection (210) are formed as inclined surfaces. The first cross-section at the end point (212) of the first projection (210) and the six side portions (213) act as an area for applying pressure to the workpiece to be welded. In order to secure an appropriate pressure area for ultrasonic welding and to form an inclination angle suitable for applying pressure to the workpiece on the side portions (213), the first cross-sectional size (b) at the end point (212) of the first projection (210) may be designed to be within the range of 1 / 10 to 1 / 2 of the second cross-sectional size (a) at the protrusion start point (211).

[0085] In an embodiment of the present invention, in order to secure an appropriate pressure area for the member to be welded, the second cross-sectional size (a) at the protrusion starting point (211) of the first projection (210) may be designed to be within the range of 0.1 mm to 1 mm. In the embodiment of FIG. 6, the knurling portion of the welding horn (200) has 19 first projections (210). The pressure area (welding area) of one first projection (210) is 0.2 to 0.3 mm 2 In this case, the total pressurized area is 3.8 ~ 5.7 mm 2 It becomes.

[0086] In contrast, when the protrusions of the knurling portion are designed with a square cross-sectional shape (Comparative Example), the pressure area of ​​each protrusion is 0.3 to 0.4 mm 2 However, the knurling portion of the welding horn (200) of the same area includes 9 protrusions, so the total pressure area is 2.7 to 3.6 mm 2 This is the case. Accordingly, according to an embodiment of the present invention, the total pressurized area of ​​the welding horn of the ultrasonic welding device can be improved by about 40% or more compared to a welding horn with a square cross-sectional shape.

[0087] FIG. 9 is a cross-sectional view showing a welding horn of a welding tip constituting an ultrasonic welding device according to another embodiment of the present invention. FIG. 10 is a plan view showing a welding horn constituting an ultrasonic welding device according to the embodiment of FIG. 9. FIG. 11 is an enlarged side view showing a second projection of a welding horn constituting an ultrasonic welding device according to the embodiment of FIG. 9. In describing the embodiments of FIG. 9 to FIG. 11, redundant descriptions of components identical to or corresponding to the previously described embodiments may be omitted. Hereinafter, the description will focus on components that differ from the previously described embodiments.

[0088] Referring to FIGS. 9 to 11, the knurling portion of the welding horn (200) constituting the ultrasonic welding device according to an embodiment of the present invention may include first protrusions (220) formed in the central region (121) of the knurling portion and second protrusions (230) disposed in the outer region (122) surrounding the central region (121) of the knurling portion. The first protrusions (220) of FIGS. 9 to 11 may be provided with the same / similar shape as the first protrusions (210) of FIGS. 5 to 8.

[0089] The second protrusions (230) may be formed in a shape different from the first protrusions (220). The second protrusions (230) may be formed in a truncated cone shape. The outer protrusions positioned at the outermost of the first protrusions (220) may be arranged spaced apart from each other. The second protrusions (230) may be arranged between the outer protrusions of the first protrusions (220). The second protrusions (230) may be arranged at positions corresponding to the corner points of the hexagon.

[0090] The second protrusions (230) may be formed such that their transverse cross-sectional area decreases as they move toward the member to be welded. The second protrusions (230) may be formed such that the first cross-sectional shape at the end point (232) and the second cross-sectional shape at the protrusion start point (231) are each formed in a circular shape with respect to the direction toward the member to be welded. The first cross-sectional shape at the end point (232) and the second cross-sectional shape at the protrusion start point (231) of the second protrusions (230) may be formed to be arranged coaxially.

[0091] Since the shape of the first protrusion (220) is identical or similar to the first protrusion (210) of the previously described embodiment, a description thereof will be omitted. The first cross-sectional size (d) at the end point (232) of the second protrusion (230) may be formed smaller than the second cross-sectional size (c) at the protrusion start point (231). Accordingly, the side portion (233) of the second protrusion (230) is formed as an inclined surface. The first cross-section and the side portion (233) at the end point (232) of the second protrusion (230) act as an area that presses the member to be welded. In order to secure an appropriate pressure area for ultrasonic welding and to form an inclination angle suitable for applying pressure to the workpiece on the side portion (233), the first cross-sectional size (d) at the end point (232) of the first protrusion (230) can be designed to be within the range of 1 / 10 to 1 / 2 of the second cross-sectional size (c) at the protrusion start point (231).

[0092] According to the embodiments of FIGS. 9 to 11, the pressure surface area of ​​the welding horn in contact with the base material is increased through a combination of various knurl pattern protrusions, and the welding joint strength of the current collector plate (60) and the rivet (70) can be secured even within a limited horn diameter. Therefore, the energy capacity can be increased by reducing the winding core of the cylindrical battery cell. In addition, according to the embodiments of FIGS. 9 to 11, a knurl pattern with an intact shape can be applied to the outermost part through the alternating arrangement of a hexagonal cross-section knurl pattern and a circular cross-section knurl pattern, thereby reducing foreign matter and burr generation in the outer region of the weld. Furthermore, stress concentration caused by increased curvature can be prevented through the arrangement of a truncated cone knurl in the outer region of the welding horn, and the amount of plastic deformation can be reduced by reducing stress on the outer part of the horn where displacement is large due to torsional vibration.

[0093] An ultrasonic welding method according to an embodiment of the present invention may include the step of preparing an ultrasonic welding device as described above, and the step of joining a current collector plate (60) of a cylindrical battery cell by ultrasonic welding with a rivet (70) using a welding tip of an ultrasonic welding device having protrusions with a hexagonal cross-sectional shape or a rudder pattern combining protrusions with a hexagonal cross-sectional shape and protrusions with a circular cross-sectional shape.

[0094] As the ultrasonic welding method is performed by the ultrasonic welding device according to an embodiment of the present invention, a plurality of indentations (61, 62, 63) formed by ultrasonic welding corresponding to the knurling pattern (protrusions) of the welding tip (100) constituting the ultrasonic welding device may be formed in the weld portion (110) of the collector plate (60) and the rivet (70). The plurality of indentations (61, 62, 63) may be formed by applying pressure to at least one of the collector plate (60) and the rivet (70) with an uneven contact surface of the welding horn (200) provided at the end of the welding tip (100) of the ultrasonic welding device.

[0095] A plurality of indentations (61, 62, 63) may be formed with a hexagonal cross-sectional shape corresponding to a plurality of protrusions (210, 220, 230) of the knurling portion arranged on the end surface of the welding tip (100) (see FIG. 5), or may be formed to have an arrangement combining a hexagonal cross-sectional shape and a circular cross-sectional shape (see FIG. 9). A plurality of indentations (61, 62, 63) may be formed to protrude from the end surface in a direction toward the member to be welded.

[0096] Among the plurality of indentations (61, 62, 63), the first indentation (61, 62) formed in the central region (111, 121) of the weld (110) may include first indentation grooves formed by being pressed into the workpiece. The first indentation grooves may be formed in a truncated hexagonal pyramid shape, in which the cross-sectional area decreases as the depth from the surface of the workpiece increases. Among the plurality of indentations (61, 62, 63), the second indentation grooves of the second indentation (63) disposed in the outer region (112, 122) surrounding the central region (111, 121) of the weld (110) may be formed in a truncated cone shape, in which the cross-sectional area decreases as the depth from the surface of the workpiece increases.

[0097] A plurality of indentations (61, 62, 63) formed on at least one of the collector plate (60) and the rivet (70) to be welded appear as intaglio shapes corresponding to the knurling pattern (shape of protrusions) of the welding horn of the ultrasonic welding device, and the welding joint strength can be increased by increasing the pressure area due to the knurling of the welding horn of the ultrasonic welding device. In addition, according to an embodiment having indentations (63) corresponding to protrusions with hexagonal and circular cross sections, along with securing welding joint strength, it is possible to prevent excessive stress from concentrating at the outermost edge of the weld of the collector plate (60) and the rivet (70) and increase the amount of plastic deformation, and also provide the effect of reducing foreign matter or burrs.

[0098] FIG. 12 is a drawing for explaining a battery pack including battery cells according to an embodiment of the present invention. Referring to FIG. 12, a battery pack (3) according to an embodiment of the present invention includes a battery assembly in which a plurality of battery cells (1) according to an embodiment of the present invention as described above are electrically connected, and a pack housing (2) that accommodates the same. FIG. 13 is a drawing for explaining a vehicle including the battery pack of FIG. 12. Referring to FIG. 13, a vehicle (5) according to an embodiment of the present invention may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle, and includes a battery pack (3) according to an embodiment of the present invention. The vehicle (5) may include a four-wheeled vehicle and a two-wheeled vehicle. The vehicle (5) operates by receiving power from the battery pack (3) according to an embodiment of the present invention.

[0099] Although the present invention has been described above by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. A welding tip for joining a current collector plate of a cylindrical battery cell by riveting and ultrasonic welding; comprising, The above welding tip is A welding horn at the end of the welding tip is included to press at least one welded member among the current collector plate and the rivet with an uneven contact surface. The above welding horn is A knurling portion comprising a plurality of protrusions arranged on the end surface of the welding tip to press the above-mentioned workpiece against the above-mentioned contact surface, and A plurality of protrusions on the knurling portion are formed to protrude from the end surface in a direction toward the workpiece to be welded, and Among the plurality of protrusions, the first protrusions disposed in the central region of the knurling portion are formed in a hexagonal cross-sectional shape, and An ultrasonic welding device in which the first protrusions have a transverse cross-sectional area that decreases as they move toward the workpiece to be welded.

2. In Claim 1, The above first protrusions With respect to the direction toward the above-mentioned welded member, the first cross-sectional shape at the end point and the second cross-sectional shape at the protrusion start point are each hexagonal cross-sectional shapes, and An ultrasonic welding device in which the first cross-sectional shape and the second cross-sectional shape are formed to be arranged coaxially.

3. In Claim 1, An ultrasonic welding device in which the first protrusions are arranged in a honeycomb structure.

4. In Claim 1, The plurality of protrusions further include second protrusions disposed in an outer region surrounding the central region of the knurling portion, and An ultrasonic welding device in which the second protrusions are formed in a shape different from the first protrusions.

5. In Claim 4, An ultrasonic welding device in which the above-mentioned second protrusions are formed in a truncated cone shape.

6. In Claim 5, The outer protrusions positioned at the outermost of the first protrusions are spaced apart from each other, and An ultrasonic welding device in which the second protrusions are arranged between the outer protrusions.

7. In Claim 6, An ultrasonic welding device in which the second protrusions are arranged at positions corresponding to the corner points of a hexagon.

8. A step of preparing an ultrasonic welding device having a welding tip—the welding tip includes a welding horn at the end of the welding tip to press at least one member to be welded, among a current collector plate of a cylindrical battery cell and a rivet, against an uneven contact surface; and The above-described ultrasonic welding device includes the step of joining a current collector plate of a cylindrical battery cell by riveting and ultrasonic welding. The step of joining by ultrasonic welding mentioned above The method includes the step of applying the welding horn, which has a knurling portion—the knurling portion comprises a plurality of protrusions arranged on the end surface of the welding tip, wherein the plurality of protrusions are formed to protrude from the end surface toward the workpiece—to the workpiece with an uneven contact surface. An ultrasonic welding method in which, in the step of joining by ultrasonic welding, among the plurality of protrusions joined to the member to be welded, the first protrusions disposed in the central region of the knurling portion are formed in a hexagonal cross-sectional shape and are pressed against the member to be welded, and the cross-sectional area of ​​the first protrusions decreases in the transverse direction as they move toward the member to be welded.

9. In Claim 8, An ultrasonic welding method in which, in the step of joining by ultrasonic welding, the first protrusions are arranged in a honeycomb structure and pressed against the member to be welded.

10. In Claim 8, An ultrasonic welding method in which, in the step of joining by ultrasonic welding, among the plurality of protrusions, the second protrusions disposed in the outer region surrounding the central region of the knurling portion are formed in a truncated cone shape and are pressed into the outer region of the weld portion of the member to be welded.

11. In Claim 10, In the step of joining by ultrasonic welding as described above, The outer protrusions positioned at the outermost of the first protrusions are spaced apart from each other and are pressed into the edge region of the center region of the weldment of the member to be welded; An ultrasonic welding method in which the second protrusions—the second protrusions are arranged at positions corresponding to the corner points of a hexagon—are arranged between the outer protrusions and pressurized into the outer region of the weldment of the member to be welded.

12. Cylindrical battery housing; A cylindrical electrode assembly that is housed in the above-mentioned battery housing and is formed by winding a first electrode, a second electrode, and a separator around a winding axis; A current collector plate provided within the battery housing and electrically connected to at least one of the first electrode and the second electrode of the electrode assembly; and It includes a rivet that is inserted, at least a portion of which is inserted through the opening of the battery housing and joined to the current collector plate, and The above current collector plate and the above rivet are joined by ultrasonic welding, and a plurality of indentations formed by ultrasonic welding are formed in the welded portion of the above current collector plate and the above rivet. The above plurality of indentations A contact surface with an uneven shape of a welding horn provided at the end of the welding tip of an ultrasonic welding device is formed by applying pressure to at least one of the collector plate and the rivet to be welded, and The plurality of indentations are formed with a hexagonal cross-sectional shape corresponding to the plurality of protrusions of the knurling portion arranged on the end surface of the welding tip, and The plurality of indentations are formed by protruding from the end surface in a direction toward the workpiece to be welded, and Among the plurality of indentations above, the first indentations formed in the central region of the weldment include first indentation grooves formed by being pressed into the workpiece, The first indentation grooves are in the shape of a truncated hexagonal pyramid, the cross-sectional area of ​​which decreases as the depth from the surface of the member to be welded increases, Cylindrical battery cell.

13. In Claim 12, The above plurality of indentations It includes second press-fit grooves disposed in an outer region surrounding the central region of the weldment, and The second press-fit grooves are formed in a truncated cone shape such that the cross-sectional area decreases as the depth from the surface of the member to be welded increases. Cylindrical battery cell.

14. A battery pack comprising at least one cylindrical battery cell as described in Claim 12.

15. An automobile comprising at least one battery pack as described in Claim 14.

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