Method and device for producing a component for a battery cell and such a component

Description

[0001] The invention relates to a method for producing a component (e.g., for a (Li-ion) battery cell). The component comprises a plurality of stacked cell foils for storing electrical energy and at least one contact plate. The cell foils form a foil stack in a connecting section, and the foil stack is connected to the contact plate by at least one weld seam for electrically contacting the cell foils via the contact plate. The invention is used in particular in the production of lithium-ion batteries, for example, for electrified vehicles.

[0002] A battery cell is an energy storage device used, for example, in a motor vehicle to store electrical energy. In a battery cell, electrode foils (hereinafter also referred to as cell foils), i.e., anodes and cathodes, are stacked on top of each other, with different electrode foils separated from each other by separator foils or a separator material. The electrode foils are arranged in an electrolyte within a housing.

[0003] The electrode foils arranged inside the housing are connected to an electrical circuit outside the housing via so-called arresters. The arresters extend outwards through the gas-tight housing. Within the housing, the arresters are electrically connected to the numerous cell foils of the same type, i.e., anodes or cathodes. An arrester (hereinafter also referred to as a contact plate) is connected to a multitude of cell foils. The cell foils form a foil stack in a connection section, and the foil stack is connected to the contact plate via a welded connection. This welded connection is generally achieved by laser welding and, in particular, via spot welds.

[0004] The component described here includes in particular the electrode foils and the conductors of a battery cell.

[0005] Laser beam welding is the preferred joining method for the production of lithium-ion cells and batteries due to accessibility, heat input into the component, and mechanical stress on the joining partners. However, the reproducible, error-free production of Cu-Cu, Al-Al, and Al-Cu joints using laser beam welding is severely limited due to poor coupling of the laser light at a wavelength of approximately 1050 nm [nanometers] (infrared laser) and the high thermal conductivity of the materials to be welded. Furthermore, copper (Cu) exhibits an absorption jump when the material's state of aggregation changes from solid to liquid. This sudden behavior leads to sudden overheating of the Cu melt, which in turn causes the material to evaporate. This results in irregular formation of the weld joint and excessive spatter formation.Defects occur in the weld joint, which can lead to holes, pores, ejections, splashes, unbonded foils, etc., especially when forming longer welds (as opposed to short stitched welds with a weld seam extension of less than 5 millimeters or weld spots). These defects reduce the quality of the battery cells and increase the risk of failures during battery cell operation.

[0006] The process stability required for producing such welded joints under high-volume production conditions (e.g., more than 1,000 components per day) can currently only be achieved for short welded joints (e.g., stitched seams or spot welds). However, the defects that already occur in these cases limit the use of the battery cells produced to date in the manner described above.

[0007] At the same time, however, with increasing cell chemistry performance (e.g., fast-charging capability of battery cells), especially for battery cells of the same size, the demands on the quality and length of the welded joint increase. In particular, bonded connections between the foils and the arrester are required, providing a correspondingly large cross-sectional area to transmit the increased current volumes.

[0008] There is therefore a need to provide a process suitable for large-scale production of such welded joints, in particular a process that can be carried out using currently available laser devices, i.e. in particular using laser beams in the infrared range.

[0009] DE 10 2019 102 233 A1 discloses a method for producing a component assembly by laser welding. A region of the components to be joined by laser welding is arranged in a vacuum chamber. The vacuum chamber covers, for example, only a region of the components in which the weld seam is created.

[0010] DE 10 2018 221 843 A1 discloses an ultrasonic welding device for introducing an embossed surface into a stack of metal foils. The metal foils are subsequently welded together in the area of ​​the embossed surface using a laser beam.

[0011] Based on this, it is an object of the invention to at least partially solve the problems described in connection with the prior art. In particular, a method and a device for producing a component are to be provided, which enables a high-quality welded joint to be achieved.

[0012] These problems are solved by the features of independent claim 1. Further advantageous refinements of the solution proposed here are specified in the dependent patent claims. It should be noted that the features listed individually in the dependent patent claims can be combined with one another in any technically meaningful way and define further refinements of the invention. In addition, the features specified in the patent claims are more precisely defined and explained in the description, where further preferred refinements of the invention are presented.

[0013] A method for manufacturing a component is proposed. The component comprises a plurality of stacked cell foils for storing electrical energy and at least one contact plate. The cell foils form a foil stack in a connecting section, and the foil stack is connected to the contact plate by at least one weld seam (created by the method) for electrically contacting the cell foils via the contact plate.

[0014] The component described here comprises in particular the electrode foils and the conductors of a battery cell, in particular a lithium-ion battery cell.

[0015] The method for producing the at least one weld seam comprises at least the following steps: a) Providing the cell films and arranging the film stack with a stack height; b) Providing the contact sheet; c) Compacting at least the film stack by means of a compaction device; d) Arranging the film stack and the contact sheet relative to one another in a connecting position; e) Generating a negative pressure at least in a connecting region of the film stack and the contact sheet by means of a negative pressure device; f) Connecting the film stack to the contact sheet in the connecting region via the at least one weld seam generated by a laser welding process in the presence of the negative pressure.

[0016] The above (non-exhaustive) division of the process steps into a) to f) is primarily intended to serve as a distinction and does not enforce any order and / or dependency. The frequency of the process steps, for example, can also vary. It is also possible for process steps to overlap one another at least partially. Most preferably, process steps e) and f) take place at least partially in parallel. In particular, step c) is carried out immediately before or immediately after step d). The foil stack is therefore compacted either alone or together with the contact sheet. In particular, the negative pressure generated in step e) is maintained during step f). In particular, steps a) to f) are carried out in the order given.

[0017] The component is particularly suitable for storing electrical energy. The component can, for example, be a component for a (rechargeable) lithium-ion battery. In this context, the component can, for example, form a component for a (lithium-ion) cell. The component comprises at least one cell stack for storing electrical energy and at least one contact plate for electrically contacting the at least one cell stack. As a rule, after the cell stack and contact plate have been connected as described here, several components produced in this way can be connected to form a battery cell. The component can comprise a single cell stack. Furthermore, the component can comprise (exactly) two contact plates (or even more than two).

[0018] The method serves, in particular, to electrically connect the contact plate to the (individual) foil stack, so that the at least one foil stack can be connected to an electrical circuit via the contact plate. The contact plate forms, for example, an electrical connection of the component or an electrical connecting element of the component for connecting the component to external components or other components.

[0019] According to step a), the cell films are provided and the film stack is arranged with a stack height. In particular, the cell films are outside the respective

[0020] The connecting section is provided with a coating (e.g., active material), wherein the connecting sections (i.e., each cell film), which are in particular uncoated, are arranged to form a film stack with a stack height. In particular, the film stack comprises at least 10, preferably at least 20, particularly preferably at least 30, or even at least 50 or at least 75, cell films or connecting sections. In the connecting section, the cell films are also referred to below as films.

[0021] According to step b), the contact sheet is provided.

[0022] According to step c), the film stack is compacted by a compaction device.

[0023] According to step d), the foil stack and the contact sheet are arranged relative to each other in a connecting position. In this connecting position, the foil stack and the contact sheet are welded together in step f). The foil stack can be arranged on one side of the contact sheet or evenly or differently distributed on both sides of the contact sheet.

[0024] If necessary, after step b) and before step c) according to step d), the contact sheet can also be arranged on the foil stack so that the foil stack and the contact sheet are compacted according to step c).

[0025] As a result of compaction, air is displaced from the foil stack or between the foil stack and the contact plate. This air can otherwise lead to defects or faults in the weld seam, particularly during step f). According to the invention, compaction is achieved by applying pressure to the foil stack and, if necessary, also to the contact plate, which is superimposed with ultrasonic excitation. The ultrasonic excitation displaces and moves the individual components, at least relative to one another, so that air is successively displaced.

[0026] The pressure with which the compaction device acts on the component is between 0.75 and 2 bar, particularly at the contact point between the compaction device and the component (i.e. foil stack or contact sheet, if applicable).

[0027] The ultrasonic excitation comprises, in particular, a vibration transverse to the joining plane between the foils of the foil stack or the contact sheet and / or a vibration parallel to the joining plane. The frequency is preferably 20 kHz [kilohertz], preferably at most 40 kHz. The frequency is, in particular, at least 6 kHz. The amplitude of the ultrasonic excitation at the contact between the ultrasonic device and the component is, in particular, at most 60 µm [micrometers], preferably at most 20 µm.

[0028] In particular, a material bond between the foils of the foil stack and, if applicable, the contact sheet does not occur during compaction. However, the foils and, if applicable, the contact sheet are positively bonded to one another as a result of the ultrasonic excitation, in which the adjacent surfaces form tiny such connections.

[0029] Preferably, the foils of the foil stack and, if applicable, the contact sheet are at least partially bonded together by compacting.

[0030] According to step e), a vacuum is generated at least in a connecting region of the foil stack and the contact sheet by means of a vacuum device. The vacuum device, in particular, removes air from the area of ​​the weld seam to be created.

[0031] According to step f), the foil stack is connected to the contact sheet in the connection area via at least one weld seam created by a laser welding process under negative pressure, in particular a spot, stitch, or linear seam. The weld seam has a length along a welding direction of at least 5 millimeters, preferably at least 10 millimeters, particularly preferably at least 50 millimeters.

[0032] In particular, the laser beam is coupled via the contact plate or the foil stack. Preferably, the coupling occurs via the foil stack, so that the contact plate is connected only via the foil stack.

[0033] Due to the high quality of the weld seam produced by the proposed method, the root of a weld seam can also be located on a foil of the foil stack.

[0034] In particular, a foil and not the contact plate is arranged on the side of the connection area facing away from the laser source.

[0035] In particular, the components (films and, if applicable, contact sheet) connected to one another by compaction in step c) are secured in the connected position by a holding device at least up to step e), preferably also up to step f). This is intended, in particular, to prevent the connections between individual components created by compaction from being (re)detached, e.g., during transport of the component. The holding device particularly comprises clamping these components.

[0036] In particular, the weld seam is arranged exclusively in the area of ​​the foil stack or the contact sheet in which the connection was created by compaction in step c).

[0037] Within the scope of the present invention, it has been demonstrated for the first time that a high-quality weld seam can be produced only by combining the steps c) compaction and e) generation of a vacuum. In particular, this has enabled certain quality characteristics of the weld seam to be achieved for the first time.

[0038] In particular, the vacuum device comprises at least one chamber in which at least the foil stack and the contact plate are arranged. By arranging the foil stack and the contact plate in the chamber, air can also be removed from the areas between the foils of the foil stack or between the foil stack and the contact plate. However, the volume of the chamber is quite large, and thus large quantities of air must be removed, possibly for each component.

[0039] In particular, the vacuum device comprises a first device part and a second device part, each of which forms a sealing surface with at least the foil stack or the contact plate. The vacuum device thus forms at least two chambers, in each of which at least one vacuum is generated. Each chamber is formed at least partially by at least the foil stack or the contact plate.

[0040] In this design of the vacuum device, the areas between the foils or between the foil stack and the contact plate are located outside the vacuum device. However, by compacting the foil stack and, if applicable, the contact plate, air can be removed from these areas to such an extent that the quality of the welded joint is not compromised. The volume of each device part can be very small, so that only a small amount of air needs to be removed.

[0041] The respective sealing surface is in particular arranged completely on the foil stack and / or the contact sheet and thus comprises a surface section which is designed to be as small as possible, taking into account the position and length of the welded joint.

[0042] In particular, the foil stack is formed by a plurality of foils arranged one on top of the other, each foil having a first thickness, and the foils stacked one on top of the other, each with the first thickness, forming the stack height. The first thickness is between 4 and 30 µm [micrometers], and each foil of the foil stack comprises at least 99.0 wt.% either copper or aluminum. In particular, the first thickness is between 4 µm and 15 µm, preferably at most 10 µm.

[0043] In particular, each film comprises at most 0.5 wt% oxygen, preferably at most 0.1 wt%.

[0044] In particular, the stack height is formed by at least ten films stacked on top of one another. In particular, the film stack comprises at least 10, preferably at least 20, particularly preferably at least 30, cell films or connecting sections.

[0045] In particular, the contact sheet in the connection region has a second thickness that is between 0.2 and 3 millimeters and comprises at least 99.0 wt.% either copper or aluminum. In particular, the second thickness is between 20 µm and 1 (one) millimeter, preferably between 50 µm and 500 µm.

[0046] In particular, the contact sheet comprises at most 0.5 wt% oxygen, preferably at most 0.1 wt%.

[0047] In particular, the contact sheet has a coating having a third thickness of at most 2 µm and comprising at least 99.0 wt.% nickel. The third thickness is in particular at least 0.1 µm.

[0048] In particular, the negative pressure in the connecting region and / or in each chamber is less than 30 mbar [millibar], preferably less than 20 mbar, particularly preferably less than 10 mbar. In particular, the negative pressure can be more than 5 mbar.

[0049] In particular, the at least one weld seam is created by a laser beam with a wavelength on the component between 1,030 and 1,060 nm [nanometers].

[0050] In particular, the at least one weld seam is created by a laser beam with a wavelength on the component between 490 and 575 nm [nanometers] or even between 405 and 490 nm.

[0051] A component is presented, comprising at least a plurality of stacked cell foils for storing electrical energy and at least one contact sheet. The cell foils form a foil stack in a connecting section, and the foil stack is connected to the contact sheet by at least one weld seam in a butt joint or an overlap joint. The at least one weld seam is produced by the described method. The weld seam extends along a welding direction over a length and has a cross-section transverse to the welding direction. The component has a first material thickness in the cross-section and immediately adjacent to the weld seam, and all of the following conditions apply to at least 30% of the cross-sections present along the weld seam: if the foil stack and the contact sheet each comprise at least 99.0% copper: ∘ a minimum second material thickness of the weld seam is at least 70%, in particular at least 80%, preferably at least 90%, of the first material thickness; o a pore has a largest diameter of at most 0.02 millimeters, in particular of at most 0.01 millimeters; o a porosity of the weld seam is at most 20%, in particular of at most 10%, preferably of at most 5%, particularly preferably of at most 2%; if the foil stack and the contact sheet each comprise at least 99.0% aluminum: o a minimum second material thickness of the weld seam is at least 80% of the first material thickness, in particular at least 90%, preferably at least 95%; o a pore has a largest diameter of at most 0.04 millimeters, in particular of at most 0.02 millimeters, preferably of at most 0.01 millimeters;∘ a porosity of the weld seam is at most 20%, in particular at most 10%, preferably at most 5%, particularly preferably at most 2%; o at least 50%, preferably at least 75%, particularly preferably at least 85% or even at least 95%, of the films of the film stack are connected to the weld seam. ;

[0052] The first material thickness comprises in particular the foil stack or the contact sheet (in the case of a butt joint) or the foil stack and the contact sheet (in the case of an overlap joint) or their thickness; whereby only the material of the component is counted as having the first material thickness (without any free spaces or air arranged in between). In a butt joint, the components to be joined together via the weld seam are arranged in a known manner with opposite end faces contacting one another or spaced apart from one another by a welding gap. In a lap joint, the components to be joined via the weld seam are arranged on top of one another and the weld seam penetrates the component arranged at the top (towards the beam source) down to the lower component. In particular, in the case of an overlap joint, the contact sheet is arranged on the lower side.

[0053] The minimum second material thickness is, in particular, the smallest extension of the weld seam in the cross-section along the thickness direction. Pores, i.e., air or gas inclusions, are considered part of the second material thickness.

[0054] Each cross-section extends perpendicular to the welding direction and parallel to the material thickness of the respective component. The cross-section thus runs perpendicular to the largest side surface of the respective component. The cross-section can be evaluated using standard cross-sections of the weld seam. In particular, a magnification of at least 100 times, preferably at least 500 times, and particularly preferably at least 1,000 times, of the cross-section should be considered.

[0055] In particular, if the foil stack and the contact sheet each comprise at least 99.0% copper, at least one, preferably at least two or even at least three, of the following conditions additionally apply: in the overlap connection, a (shortest) connecting line (through the weld seam) between the foil stack and the contact sheet (or along the dividing line between the foil stack and the contact sheet) is pore-free (in particular less than 1% porosity); the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an elevation of a root of the weld seam is at most 0.04 millimeters, preferably at most 0.02 millimeters; the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an undercurvature of a root of the weld seam is at most 0.1 millimeters, preferably at most 0.05 millimeters; the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an elevation of a cover layer of the weld seam is at most 0.02 millimeters, preferably at most 0.01 millimeters;the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an undercurvature of a cover layer of the weld seam is at most 0.06 millimeters, preferably at most 0.03 millimeters; the weld seam is at least free of cracks or edge notches or root notches; at least 50%, preferably at least 75%, particularly preferably at least 85% or even at least 95%, of the films of the film stack are connected to the weld seam. ;

[0056] In particular, if the foil stack and the contact sheet each comprise at least 99.0% aluminum, at least one, preferably at least two or even at least three, of the following conditions additionally apply: in the overlap connection, a connecting line between the film stack and the contact sheet is pore-free (in particular less than 1% porosity); the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an elevation of a root of the weld seam is at most 0.07 millimeters, preferably at most 0.03 millimeters; the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an undercurvature of a root of the weld seam is at most 0.05 millimeters, preferably at most 0.02 millimeters; the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an elevation of a cover layer of the weld seam is at most 0.02 millimeters, preferably at most 0.01 millimeters;the first material thickness is at least one millimeter, preferably at least 1.5 millimeters, and an undercurvature of a cover layer of the weld seam is at most 0.02 millimeters, preferably at most 0.01 millimeters; the weld seam is at least free of cracks or edge notches or root notches.

[0057] A root overhang is in particular a protrusion of the weld seam in the cross-section under consideration compared to an imaginary straight line between the respective

[0058] Weld seam immediately adjacent underside (i.e. oriented away from the beam source) of the components connected by the weld seam.

[0059] An undercurvature of a root is in particular an undercut of the weld in the cross-section under consideration compared to an imaginary straight line between the respective underside of the components connected by the weld immediately adjacent to the weld.

[0060] An overhang of a cover layer is in particular an overhang of the weld seam in the cross-section under consideration compared to an imaginary straight line between the respective upper side immediately adjacent to the weld seam (i.e. oriented towards the beam source) of the components connected by the weld seam.

[0061] An undercurvature of a cover layer is in particular an undercut of the weld seam in the cross-section under consideration compared to an imaginary straight line between the respective upper side of the components connected by the weld seam immediately adjacent to the weld seam.

[0062] Crack-free means in particular that no cracks, i.e. gaps within the material of the weld, are visible or present in the cross-section under consideration.

[0063] Edge notches are particularly undercurvatures in the transition between the weld seam and the top of the component.

[0064] Root notches are particularly undercurvatures in the transition between the weld seam and the underside of the component.

[0065] Furthermore, a device for producing a component is proposed, wherein the component comprises a plurality of stacked cell foils for storing electrical energy and at least one contact plate. The cell foils form a foil stack in a connecting section, and the foil stack is connected to the contact plate by at least one weld seam for electrically contacting the cell foils via the contact plate. The device is designed to carry out the described method and comprises at least a compaction device for compacting at least the foil stack, a vacuum device for generating a vacuum at least in a connecting region of the foil stack and the contact sheet, and a laser device for connecting the foil stack to the contact sheet in the connecting region via at least one weld seam generated by a laser welding process in the presence of the vacuum.

[0066] The device is used in particular for carrying out the method described here and / or for producing the component described here and is suitably configured. The vacuum device can, for example, comprise at least one vacuum or negative pressure connection, e.g., per chamber, and / or at least one vacuum pump.

[0067] The laser device may comprise at least one laser source, in particular an infrared laser source.

[0068] The details, features, and advantageous embodiments discussed in connection with the method may also occur in the component and / or device presented here, and vice versa. In this respect, reference is made in full to the explanations therein for a more detailed characterization of the features.

[0069] The use of indefinite articles ("a", "an", "an" and "another"), particularly in the patent claims and the description reproducing them, is to be understood as such and not as a numeral. Terms or components introduced accordingly are therefore to be understood as appearing at least once and, in particular, as being able to appear multiple times.

[0070] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily specify any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or part of the majority of these components, but this is not mandatory.

[0071] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and, in particular, the illustrated proportions are only schematic. They show: Fig. 1: a cross-section through a weld seam produced by a known method; Fig. 2: a cross-section through another weld seam produced by a known method; Fig. 3: a first embodiment of a device with a component in a plan view according to steps e) and f); Fig. 4: the device according to Fig. 3 according to step c) in a side view; Fig. 5: the device according to Fig. 3 according to steps e) and f) in a side view; Fig. 6: a second embodiment of a device according to steps e) and f) in a side view; Fig. 7: a cross-section through a weld seam produced by the described method, in section; and Fig. 8: a cross-section through another weld seam produced by the described method, in section.

[0072] Fig. 1shows a cross-section 24 through a weld seam 6 produced by a known method. The component 1 comprises a contact sheet 3 with a second thickness 19 and a foil stack 5, which form an overlap connection. The foil stack 5 forms an upper side and is oriented toward the beam source. The weld seam 6 comprises large pores 27, a high porosity, and a strong undercurvature 30 of the root of the weld seam 6. The second material thickness 26 is significantly less than the first material thickness 25.

[0073] The first material thickness 25 is only indicated here, since the air or free spaces must be calculated out to determine the first material thickness.

[0074] The material of the foils 17 of the foil stack 5 and the material of the contact sheet 3 each comprises at least 99.0% aluminum. The foils 17 each have a first thickness 18.

[0075] A coating 20 of the contact sheet 3 with a third thickness 21 is only indicated here.

[0076] Fig. 2 shows a cross-section 24 through another weld seam 6, which was produced by a known method. The component 1 comprises a contact sheet 3 and a foil stack 5, which form an overlap connection. The foil stack 5 forms an upper side and is oriented towards the beam source. The weld seam 6 comprises large pores 27, a high porosity, and a strong undercurvature 30 of the root (on the underside of the component 1) and the cover layer (on the upper side of the component 1) of the weld seam 6. The second material thickness 26 is significantly less than the first material thickness 25. Only a small number of the foils 2 are connected to the contact sheet 3 via the weld seam 6.

[0077] The first material thickness 25 is only indicated here, since the air or free spaces must be calculated out to determine the first material thickness.

[0078] The material of the foils 17 of the foil stack 5 and the material of the contact sheet 3 each comprises at least 99.0% copper. The foils 17 each have a first thickness 18.

[0079] Fig. 3 shows a first embodiment of a device 31 with a component 1 in a plan view according to steps e) and f). Fig. 4 shows the device 31 after Fig. 3 according to step c) in a side view. Fig. 5 shows the device 31 after Fig. 3 according to steps e) and f) in a side view. The Fig. 3 to 5 are described together below.

[0080] The component 1 comprises a plurality of stacked cell foils 2 for storing electrical energy and at least one contact plate 3. The cell foils 2 form a foil stack 5 in a connecting section 4, and the foil stack 5 is connected to the contact plate 3 by a weld seam 6 for electrically contacting the cell foils 2 via the contact plate 3. The weld seam 6 is arranged adjacent to a sealing seam 33 of the battery cell, through which the housing of the battery cell is sealed. The weld seam 6 is later arranged within the housing of the battery cell, so that the contact plate 3 extends from the weld seam 6 over the sealing seam 33 to the outside of the housing.

[0081] The device 31 is designed to be suitable for carrying out the described method and, in order to produce the at least one weld seam 6, comprises a compaction device 8 for compacting at least the film stack 5, a vacuum device 11 for generating a vacuum at least in a connecting region 10 of the film stack 5 and the contact sheet 3, and a laser device 32 for connecting the film stack 5 to the contact sheet 3 in the connecting region 10 via at least one weld seam 6 produced by a laser welding process in the presence of the vacuum.

[0082] The method serves to electrically connect the contact plate 3 to the foil stack 5, so that the foil stack 5 can be connected to an electrical circuit via the contact plate 3. The contact plate 3 forms an electrical connection of the component 1 or an electrical connecting element of the component 1 for connecting the component 1 to external components or other components 1.

[0083] According to step a), the cell films 2 are provided and the film stack 5 is arranged with a stack height of 7. According to step b), the contact sheet 3 is provided. Contact sheet 3 and film stack 5 are arranged in a connection position 9 (here for an overlap connection) according to step d). According to step c), the film stack 5 and the contact sheet 3 are compacted by a compaction device 8 (see Fig. 4). In this connection position 9, the foil stack 5 and the contact sheet 3 are welded together in step f) by applying the laser beam 22 to the connection area 10.

[0084] Compaction is achieved by applying pressure to the foil stack 5 and additionally to the contact sheet 3, which is superimposed with an ultrasonic excitation ( Fig. 4 ). By means of ultrasonic excitation, the individual components 2, 3, 5, 17 are at least displaced and moved relative to each other, so that air is successively displaced.

[0085] According to step e), a vacuum is generated in a connecting area 10 of the foil stack 5 and the contact sheet 3 by a vacuum device 11. With the vacuum device 11, air is removed from the area of ​​the weld seam 6 to be created (see Fig. 5 and 6 ).

[0086] The vacuum device 11 comprises a first device part 14 and a second device part 15, each forming a sealing surface 16 with the foil stack 5 or the contact plate 3. The vacuum device 11 thus forms two chambers 12, 13, in each of which at least one vacuum is generated. The first chamber 12 is formed by the first device part 14 and the foil stack 5, and the second chamber 13 is formed by the second device part 15 and the contact plate 3.

[0087] In this embodiment of the vacuum device 11, the areas between the foils 17 and between the foil stack 5 and the contact plate 3 are located outside the vacuum device 11. However, due to the compaction of the foil stack 5 and the contact plate 3, air can be removed from these areas to such an extent that the quality of the welded joint is not compromised. The volume of the respective device part 14, 15 can be made very small, so that only a small amount of air needs to be removed.

[0088] The respective sealing surface 16 is arranged completely on the foil stack 5 or the contact plate 3 and thus comprises a surface section which is designed to be as small as possible, taking into account the position and length of the weld seam 6.

[0089] According to step f), the foil stack 5 is connected to the contact sheet 3 in the connecting region 10 via a weld seam 6 produced by a laser welding process in the presence of negative pressure. The weld seam 6 has, in particular, a length along a welding direction 23.

[0090] Fig. 6 shows a second embodiment of a device 31 according to steps e) and f) in a side view. In contrast to the first embodiment, the vacuum device 11 comprises only one chamber 12 in which the film stack 5 and the contact plate 3 are arranged. By arranging the film stack 5 and the contact plate 3 in the chamber 12, air can also be removed from the areas between the films 17 of the film stack 5 or between the film stack 5 and the contact plate 3. However, the volume of the chamber 12 is quite large and thus large quantities of air must be removed, possibly for each component 1.

[0091] Fig. 7 shows a cross section 24 through a weld seam 6 produced by the described method, in section.

[0092] The component 1 comprises a contact sheet 3 with a second thickness 19 and a foil stack 5, which form an overlap joint. The foil stack 5 forms an upper side and is oriented toward the beam source (the laser device 32). The weld seam 6 has almost no pores 27, thus low porosity, a slight elevation 29 of the root, and a slight undercurvature 30 of the cover layer of the weld seam 6. The second material thickness 26 is even greater than the first material thickness 25.

[0093] In the illustrated overlap joint, the material of the weld seam 6 is pore-free along a shortest connecting line 28 through the weld seam 6 between the foil stack 5 and the contact sheet 3, or along the dividing line between the foil stack 5 and the contact sheet 3. All foils 17 of the foil stack 5 are connected to the weld seam 6. The weld seam 6 is free of cracks, edge notches, and root notches.

[0094] The material of the foils 17 of the foil stack 5 and the material of the contact sheet 3 each comprises at least 99.0% aluminum. The foils 17 each have a first thickness 18.

[0095] Fig. 8 shows a cross section 24 through another weld seam 6, which was produced by the described method, in section.

[0096] The component 1 comprises a contact sheet 3 with a second thickness 19 and a foil stack 5, which form an overlap joint. The foil stack 5 forms an upper side and is oriented toward the beam source (the laser device 32). The weld seam 6 comprises only very small pores 27, thus providing low porosity, a slight undercurvature 30 of the root, and a slight undercurvature 30 of the cover layer of the weld seam 6. The second material thickness 26 is only slightly less than the first material thickness 25.

[0097] In the illustrated overlap joint, the material of the weld seam 6 is pore-free along a shortest connecting line 28 through the weld seam 6 between the foil stack 5 and the contact sheet 3, or along the dividing line between the foil stack 5 and the contact sheet 3. All foils 17 of the foil stack 5 are connected to the weld seam 6. The weld seam 6 is free of cracks, edge notches, and root notches.

[0098] The material of the foils 17 of the foil stack 5 and the material of the contact sheet 3 each comprises at least 99.0% aluminum. The foils 17 each have a first thickness 18. List of reference symbols

[0099] 1 Component 2 Cell film 3 Contact sheet 4 Connection section 5 Film stack 6 Weld seam 7 Stack height 8 Compaction device 9 Connection position 10 Connection area 11 Vacuum device 12 First chamber 13 Second chamber 14 First device part 15 Second device part 16 Sealing surface 17 Film 18 First thickness 19 Second thickness 20 Coating 21 Third thickness 22 Laser beam 23 Weld direction 24 Cross section 25 First material thickness 26 Second material thickness 27 Pore 28 Connection line 29 Superelevation 30 Undercurvature 31 Device 32 Laser device 33 Sealing seam

Claims

1. Method for producing a component (1), wherein the component has a multiplicity of cell foils (2), which are stacked on top of one another, for storing electrical energy and at least one contact sheet (3); wherein the cell foils (2) form a foil stack (5) in an attachment portion (4) and the foil stack (5) is connected to the contact sheet (3) by at least one weld seam (6) for electrical contacting of the cell foils (2) via the contact sheet (3), wherein the method for producing the at least one weld seam (6) comprises at least the following steps: a) providing the cell foils (2) and arranging the foil stack (5) with a stack height (7); b) providing the contact sheet (3); c) compacting at least the foil stack (5) by way of a compaction device (8); d) arranging the foil stack (5) and the contact sheet (3) relative to one another in a connecting position (9); e) generating a negative pressure at least in a connecting region (10) of the foil stack (5) and of the contact sheet (3) by way of a negative-pressure device (11); f) connecting the foil stack (5) to the contact sheet (3) in the connecting region (10) by way of the at least one weld seam (6) generated by a laser welding method in the presence of the negative pressure; characterized in that the compacting at least of the foil stack (5) is effected by applying a pressure which is superimposed with an ultrasonic excitation.

2. Method according to Patent Claim 1, wherein the negative-pressure device (11) comprises at least one chamber (12, 13) in which at least the foil stack (5) and the contact sheet (3) are arranged.

3. Method according to Patent Claim 1, wherein the negative-pressure device (11) comprises a first device part (14) and a second device part (15), each of which form a sealing surface (16) with at least the foil stack (5) or the contact sheet (3); with the result that the negative-pressure device (11) forms at least two chambers (12, 13) in which in each case at least one negative pressure is generated; wherein each chamber (12, 13) is at least partially formed at least by the foil stack (5) or by the contact sheet (3).

4. Method according to one of the preceding patent claims, wherein the foil stack (5) is formed by a multiplicity of foils (17) which are arranged on top of one another, wherein each foil (17) has a first thickness (18) and the foils (17) which are stacked on top of one another and each have the first thickness (18) form the stack height (7), wherein the first thickness (18) is between 4 and 30 µm and each foil (17) of the foil stack (5) comprises either copper or aluminium at least to an extent of 99.0% by weight.

5. Method according to one of the preceding patent claims, wherein the stack height (7) is formed by at least ten foils (17) stacked on top of one another.

6. Method according to one of the preceding patent claims, wherein the contact sheet (3) in the connecting region (10) has a second thickness (19) which is between 0.2 and 3 millimetres and comprises either copper or aluminium at least to an extent of 99.0% by weight.

7. Method according to one of the preceding patent claims, wherein the contact sheet (3) has a coating (20) which has a third thickness (21) of at most 2 µm and comprises nickel at least to an extent of 99.0% by weight.

8. Method according to one of the preceding patent claims, wherein the negative pressure in the connecting region (10) is less than 30 mbar.

9. Method according to one of the preceding patent claims, wherein the at least one weld seam (6) is generated by a laser beam (22) having a wavelength of between 405 and 575 nm.

10. Device (31) for producing a component (1), wherein the component has a multiplicity of cell foils (2), which are stacked on top of one another, for storing electrical energy and at least one contact sheet (3); wherein the cell foils (2) form a foil stack (5) in an attachment portion (4) and the foil stack (5) is connected to the contact sheet (3) by at least one weld seam (6) for electrical contacting of the cell foils (2) via the contact sheet (3); wherein the device (31) is embodied for carrying out the method according to one of the preceding Patent Claims 1 to 12 and, in order to produce the at least one weld seam (6), comprises at least • a compaction device (8) for compacting at least the foil stack (5), • a negative-pressure device (11) for generating a negative pressure at least in a connecting region (10) of the foil stack (5) and of the contact sheet (3), and • a laser device (32) for connecting the foil stack (5) to the contact sheet (3) in the connecting region (10) by way of at least one weld seam (6) generated by a laser welding method in the presence of the negative pressure; characterized in that the compacting comprises applying a pressure and an ultrasonic excitation.