ULTRASONIC WELDING DEVICE AND METHOD FOR PRODUCING A METAL FOIL STACK

Abstract

The invention relates to an ultrasonic welding device for introducing an embossed surface into a metal foil stack for a cell of a lithium-ion battery, comprising a sonotrode and an anvil, wherein the anvil or the sonotrode has a number of first protrusions projecting from the working surface thereof, in order to form the, in particular strip-like, embossed surface by compacting the metal foil stack. The invention additionally relates to a method for producing a metal foil stack of metal foils for a cell of a lithium-ion battery, in particular using such an ultrasonic welding device.

Claims

1. An Ultrasonic welding device for introducing an embossed surface into a metal foil stack for a cell of a lithium-ion battery, comprising a sonotrode, and an anvil, wherein the anvil or the sonotrode has a number of first protrusions projecting from the working surface to form the, in particular strip-like, embossed surface by compacting the metal foil stack.

2. The Ultrasonic welding device according to claim 1, wherein, if the sonotrode has the first protrusions, then the anvil has a contour, or if the anvil has the first protrusions, then the sonotrode has the contour, the contour being formed by means of a number of second protrusions projecting from the relevant working surface, or by means of a number of recesses in the relevant working surface, which correspond to the first protrusions, and the anvil and the sonotrode being oriented with respect to one another such that the first protrusions and the second protrusions or the recess are opposite one another in a direction perpendicular to the working surfaces, or that the first protrusions are offset from the second protrusions, in particular in a grid-like manner, with respect to a direction parallel to the working surfaces.

3. The Ultrasonic welding device according to claim 1, wherein the first protrusions, the recess and/or the second protrusions are in the shape of a truncated prism or truncated pyramid, the prism-shaped protrusions extending transversely to a vibration direction of the sonotrode.

4. The Ultrasonic welding device according to claim 1, wherein the first protrusions, the recess and/or the second protrusions have a height of between 0.02 mm and 1.0 mm.

5. The Ultrasonic welding device according to claim 2, wherein the second protrusions have a smaller height than the first protrusions, for example less than half the height of the first protrusions, in particular less than a quarter of the height of the first protrusions,

6. The Ultrasonic welding device according to claim 1, wherein the sonotrode has a plurality of first protrusions extending in parallel with one another.

7. A Method for producing a metal foil stack of metal foils, in particular for a cell of a lithium-ion battery, comprising: providing metal foils which are stacked on top of one another, compacting the metal foils to form an embossed surface by means of an ultrasonic welding device designed in particular according to claim 1, and welding the metal foils to one another in the region of the embossed surface by means of a laser beam.

8. The Method according to claim 7, further comprising, in the course of the welding of the metal foils by means of the laser beam, welding an electrical cell arrester to the metal foils in the region of the embossed surface, or fixing the electrical cell arrester to the metal foils in the course of the compacting and subsequently welding the electrical cell arrester to the metal foils in the course of the welding of the metal foils by means of the laser beam in the region of the embossed surface, arranging the cell arrester between a laser device which generates the laser beam and the metal foils, or arranging the metal foils between the cell arrester and the laser device.

9. The Method according to claim 7, wherein for the purpose of compacting, a working surface of an anvil of the ultrasonic welding device is oriented with respect to a working surface of a sonotrode of the ultrasonic welding device, on the basis of reference points of the sonotrode and the anvil, and for the purpose of welding by means of the laser beam, the laser device is oriented with respect to the sonotrode, on the basis of the reference points thereof, such that the laser beam impinges on the region of the embossed surface or is moved or moves along the embossed surface.

10. A Metal foil stack for a cell of a lithium-ion battery, produced by means of the ultrasonic welding device according to claim 1.

11. A Metal foil stack for a cell of a lithium-ion battery, produced by means of the ultrasonic welding device according to the method of claim 7,

12. A Metal foil stack for a cell of a lithium-ion battery, produced by means of the ultrasonic welding device according to the method according to claim 7.

Description

[0037] Embodiments of the invention are explained in more detail below with reference to the drawings, which show:

[0038] FIG. 1 schematically, in a perspective view, an ultrasonic welding device comprising an anvil and a sonotrode, the sonotrode having first protrusions on the working surface thereof that extend in parallel with one another, by means of which an embossed surface introduced into a metal foil stack between the sonotrode and the anvil,

[0039] FIG. 2a to c the sonotrode in a schematic plan view, in each case with different embodiments of the first protrusions, FIG. 3a to d the anvil in a schematic plan view, in each case with different variants of a contour formed by means of second protrusions, the second protrusions projecting from the working surface of the anvil,

[0040] FIG. 4a the metal foil stack in a schematic front view, a cell arrester being arranged on the embossed surface, and the metal foils of the metal foil stack and the cell arrester being integrally joined to one another by means of a laser beam moved along the embossed surface,

[0041] FIG. 4b the metal foil stack and the cell arrester arranged thereon in a schematic plan view,

[0042] FIG. 5a schematically, in a lateral view, an alternative embodiment of the ultrasonic welding device, the anvil having the first protrusions and the sonotrode having the contour formed by a number of recesses, and

[0043] FIG. 5b schematically, in a lateral view, a further alternative embodiment of the ultrasonic welding device, the sonotrode having the first protrusions and the anvil having the contour formed by a number of recesses.

[0044] Corresponding parts and dimensions are always provided with the same reference signs in all figures.

[0045] FIG. 1 shows a portion of an ultrasonic welding device 2 which has a sonotrode 4 and an anvil 6. The sonotrode 4 is T-shaped with a vertical limb 4a and a horizontal limb 4b extending transversely thereto, the vertical limb 4a being connected to a vibration system (not further shown) by means of which the sonotrode 4 can be caused to vibrate in a vibration direction S extending along the vertical limb 4a. For example, the sonotrode in this case vibrates at a frequency of between 2 kHz and 40 kHz. One of the end faces of the horizontal limb 4b faces the anvil 6 in this case, said end face forming the working surface 4c of the sonotrode 4.

[0046] The sonotrode 4 has two first protrusions 8 on the working surface 4c thereof, which working surface faces the anvil 6 and against which the workpiece to be processed rests in the course of an ultrasonic welding process. The anvil 6 has a contour which is formed by means of three second protrusions 10, said protrusions projecting from the working surface 6a of the anvil 6. Both the first protrusions 8 and the second protrusions 10 are each parallel to one another and are prism-shaped, the prisms each having a trapezoid as the base, and the prisms extending in parallel with the working surface 4c or 6a. The first protrusions 8 and the second protrusions 10 extend transversely to the vibration direction S of the sonotrode 4.

[0047] The sonotrode 4 and the anvil 6 are oriented with respect to one another such that the first protrusions 8 and the second protrusions 10 are offset from one another in a grid-like manner in a direction parallel to the relevant working surface 4c or 6a and perpendicular to the extension direction of the prisms, i.e., in the vibration direction S of the sonotrode 4.

[0048] According to a variant which is not further shown, the anvil 6 and the sonotrode 4 are oriented with respect to one another such that the first protrusions 8 and the second protrusions 10 are opposite one another in a direction which extends perpendicularly to the working surfaces 4c and 6a; in other words, the first protrusions 8 and the second protrusions 10 are arranged in opposition with respect to this direction.

[0049] Metal foils 12 stacked on top of one another are introduced between the anvil 6 and the sonotrode 4. The metal foil stack 14 formed by the metal foils 12 stacked on top of one another is provided in particular for a cell (not further shown) of a lithium-ion battery, which is designed, for example, as what is referred to as a pouch cell. When the ultrasonic welding device 2 is used, i.e., in the course of the ultrasonic welding of the metal foils 12, said metal foils are pressed (compressed) by means of the first protrusions 8 to form an embossed surface 16. The embossed surface 16, which can be seen relatively well in particular in FIGS. 4a and 4b, is designed in a strip-like manner. The first protrusions 8 together with the second protrusions 10 in this case form a negative mold for compacting the metal foil stack 14. The embossed surface 16 introduced into the metal foil stack 14 during compaction defines a region or a strip for a laser beam 18 in the course of a laser beam welding process (laser welding process), which is shown in FIG. 4a. Due to the compression of the metal foil stack 16 in the region of the embossed surface 16, which is caused by the ultrasonic welding process, the formation of cavities between the metal foils 12 is prevented or at least reduced and constant (homogeneous) conditions for the laser beam welding are achieved. In this way, a particularly reliable connection of the metal foils 12 to one another can be achieved.

[0050] The metal foils only rest in portions on the working surface 6a of the anvil 6. The portions of the metal foils 12 shown in FIG. 1, which portions are provided to be joined to one another, are also referred to as flags. In a manner which is not shown in greater detail, the metal foils 12, with the exception of the flags, are positioned on a support.

[0051] In FIGS. 2a to 2c, the sonotrode 4 is shown in a plan view, in each case with different embodiments of the first protrusions 8. In this case, three rows are formed on first protrusions 8 in each case, which protrusions extend perpendicularly to a vibration direction S of the sonotrode 4. According to an embodiment which is not further shown, the rows of the first protrusions 8 extend in parallel with or at an angle to the vibration direction S of the sonotrode 4.

[0052] The three rows of the first protrusions 8 are in this case arranged so as to be spaced apart from one another. In FIG. 2a, the row of first protrusions 8 described above has two outer first protrusions 8 designed as pyramids, and a prism-shaped extension 8 arranged therebetween, the base of which is designed as a triangle. The middle row is in this case formed by means of a single prism-shaped first protrusion 8, and the third row is formed by three first protrusions 8, the two outer protrusions each being designed as a truncated pyramid, and the first protrusion 8, which is arranged therebetween and extends from one of the truncated pyramids to the other truncated pyramid of this row, being designed as a prism having a trapezoid as the basic shape.

[0053] In the embodiment of the sonotrode 4 shown in FIG. 2b, the middle and lower rows shown correspond to the middle and lower rows of the embodiment according to FIG. 2a. The row of the embodiment of the sonotrode 4 that is described above is formed analogously to the third row of first protrusions 8 thereof, i.e. has two outer truncated pyramid-shaped first protrusions 8 and a prism-shaped first protrusion 8 arranged therebetween.

[0054] In contrast to the embodiment in FIGS. 2a and 2b, the embodiment of the sonotrode 4 in FIG. 2c, in the row of first protrusions 8 described above, has three protrusions 8 which are each designed as a prism having a trapezoid as the base, the three prisms extending along a common direction.

[0055] The prisms of the embodiments in FIGS. 2a to 2c are beveled toward the working surface 4c at the end with respect to the extension direction thereof.

[0056] In FIGS. 3a to 3d, different variants of the second protrusions 10 projecting from the working surface 6a of the anvil 6 are shown. According to FIGS. 3a to 3c, four rows are in each case formed by means of the second protrusions 10, which rows extend in parallel with one another and are offset in a grid-like manner from the rows formed by means of the first protrusions 8 of the sonotrode 4 according to one of the variants of FIGS. 2a to 2c. In other words, the first protrusions 8 do not overlap with the second protrusions 10 in a direction perpendicular to the working surfaces 4c, 6a.

[0057] In FIG. 3a, the four rows are each formed by means of a single prism-shaped second protrusion 10. In FIG. 3b, the four rows are each formed by a plurality of pyramid-shaped second protrusions 10, the pyramids each having a square base and the pyramids of the relevant row being arranged next to one another such that one of the diagonals of the basic shapes of all of the pyramids lie on a common straight line.

[0058] In the variant of the anvil 6 shown in FIG. 3c, the four rows of the second protrusions 10 are also formed by means of pyramids having square bases. In this case, however, the pyramids are arranged in a row such that two opposite sides of the bases of all of the pyramids extend on two straight lines which are parallel to one another.

[0059] In FIG. 3d, a further embodiment of the anvil 6 is shown, in which the second protrusions 10 are each designed as pyramids. The pyramid-shaped second protrusions 10 are arranged in twelve rows, the twelve rows being divided into four groups of three rows each. The four groups are arranged at a distance from one another. In each of the groups, the pyramids are arranged in a checkerboard-like manner with respect to one another. Along the straight line parallel to the vibration direction S and parallel to the working surface 4c or 6a, the first protrusions 8 of the sonotrode 4, which are designed according to one of the embodiments in FIGS. 1 to 2c, and the second protrusions 10 are offset from one another in a grid-like manner in a ratio of 3:1. In other words, a first protrusion 8 and three second protrusions 10 are arranged alternately in this direction.

[0060] In further variants which are not shown, the first protrusions 8 and/or the second protrusions 10 are hemispherical or cylindrical, in particular semi-cylindrical.

[0061] The first protrusions 8 shown in FIGS. 2a to 2c and 3a to 3d and the second protrusions 10 shown there have a height of between 0.05 mm and 0.5 mm. The second protrusions 10 of FIGS. 3b to 3d have a smaller height than the first protrusions. The second protrusions 10 shown in FIG. 3d have less than a quarter of the height of the first protrusions of FIGS. 2a to 2c.

[0062] Furthermore, the sonotrode 4 and the anvil 6 each have two reference points R1 and R2 or R1′ and R2′, by means of which the anvil 6 is oriented with respect to the sonotrode 4. In the oriented state, the reference point R1 corresponds to the reference point R1′ and, analogously, the reference point R2 corresponds to the reference point R2′. The mutually corresponding reference points R1 and R1′ or R2 and R2′ are thus each arranged on a common straight line which extends in a direction perpendicular to the working surfaces 4c and 6a.

[0063] As can be seen in FIGS. 4a and 4b, the metal foil stack 14 rests on a cell arrester 20. In this case, the cell arrester 20 abuts the compacted region, i.e. in the region of the embossed surface 16 of the metal foil stack 14. The embossed surface 16 introduced into the metal foil stack 14 defines a region or a strip for the laser beam 18, such that, in the course of the laser beam welding process, the metal foils 12 are joined together and the metal foil stack 14 is joined to the cell arrester 20 by means of the laser beam 18. Therefore, due to the action of the laser beam 18, the metal foils 12 fuse to one another and with the cell arrester 20. The fused region B, which in particular forms a weld seam, is shown hatched for the purpose of improved visibility. Furthermore, for the laser beam welding process, a laser device 22 generating the laser beam 18 is oriented with respect to the sonotrode 4 such that the laser beam 18 moves along the embossed surface 16.

[0064] In a variant which is not further shown, the cell arrester 20 is already fixed, in particular tack welded, to the metal foil stack 16 in the course of the compacting of the metal foils 12 by the ultrasonic welding process and is subsequently welded to the metal foil stack 16 in the course of the welding of the metal foils 12 by means of the laser beam 18 in the region of the embossed surface 16.

[0065] According to an alternative of FIG. 4a, which is not further shown, the metal foil stack 14 also rests on the cell arrester 20, the cell arrester 20 abutting the compacted region, i.e. in the region of the embossed surface 16 of the metal foil stack 14. In comparison to the variant shown in FIG. 4a, however, the laser device 22 is oriented such that the laser beam 18 impinges on the cell arrester 20. The laser device 20 is oriented such that the laser beam 18 acts in the region of the embossed surface 16 of the metal foil stack 14. The cell arrester 20 is thus arranged between the laser device 22 and the metal foil stack 14.

[0066] In summary, in a method for producing the metal foil stack 14, metal foils 12 which are stacked on top of one another are provided in a first step. In a second step, the metal foils 12 are compacted to form the embossed surface 16 by means of the ultrasonic welding device 2, which is designed according to one of the embodiments in FIGS. 1 to 3, the working surface 6a of the anvil 6 of the ultrasonic welding device 2 being oriented with respect to the working surface 4c of the sonotrode 4 for this purpose. In a third step, the metal foils 12 are welded to one another in the region of the embossed surface 16 by means of the laser beam 18, the laser device 22 generating the laser beam 18 being correspondingly oriented with respect to the sonotrode 2.

[0067] FIGS. 5a and 5b each show an alternative embodiment of the ultrasonic welding device 2. According to the variant in FIG. 5a, the anvil 6 has the first protrusions 8. The sonotrode 4 has the contour formed by means of a number of recesses 11. According to FIG. 5b, the anvil the sonotrode 4 has the first protrusions 8, and the anvil 6 has the contour formed by means of the recesses 11 that correspond to the first protrusions 8.

[0068] The invention is not restricted to the embodiments described above. Rather, other variants of the invention can also be derived therefrom by a person skilled in the art without departing from the subject matter of the invention. In particular, all of the individual features described in connection with the embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

LIST OF REFERENCE SIGNS

[0069] 2 Ultrasonic welding device [0070] 4 Sonotrode [0071] 4a Vertical limb of the sonotrode [0072] 4b Horizontal limb of the sonotrode [0073] 4c Working surface of the sonotrode [0074] 6 Anvil [0075] 6a Working surface of the anvil [0076] 8 First protrusion [0077] 10 Second protrusion [0078] 11 Recess [0079] 12 Metal foil [0080] 14 Metal foil stack [0081] 16 Embossed surface [0082] 18 Laser beam [0083] 20 Cell arrester [0084] 22 Laser device [0085] B Fused region [0086] R1, R1′, R2, R2′ Reference points [0087] S Vibration direction of the sonotrode