DE102018207693A1 - Method and device for integrally joining a number of arrester foils for producing a battery arrester - Google Patents

Abstract

The invention relates to a method for materially joining a number of arrester foils (14) for producing a battery conductor (10) and a device therefor, wherein the following method steps are carried out: a) applying a foil stack (16) of arrester foils (14) a hold-down force (26) through a holding-down device (18), b) throughflow of a flow channel (36) formed by the holding-down device (18) and the film stack (16) with a process gas stream (48), c) generation of a roughened region (34) the closest several Ableitfolien (14) of the film stack (16) delimiting the flow channel (36) and d) generating a joining seam (32) between the Ableitfolien (14) in the film stack (16) in the joining direction (50).

Description

Technical area

The invention relates to a method for materially joining a number of arrester foils for producing a battery drain for traction batteries for vehicles and to a device suitable for carrying out this method.

State of the art

In future production processes for the production of lithium-ion battery cells, collector tabs are to be produced by material bonding. The arrester lugs are made of up to 70 layers of copper with a thickness between 9 microns and 12 microns or aluminum in a thickness between 15 .mu.m and 20 .mu.m, preferably in the way of the laser welding process to meet the ever growing demands on the electrical contacting and power management become. For this purpose, up to 70 film layers, either of aluminum or of copper, must be mechanically pressed together in order to produce the zero gap between the individual conductor foils necessary for the laser welding process. In addition, the laser welding process is preferably carried out under an inert protective gas atmosphere.

If, for example, as a result of poor compression of the film stack from the arrester foils, no zero gap is achieved and if the flow guidance of the process gas stream of inert gas over the component surface is not optimal, voids, pores or cracks are formed in and at the edges of the weld seam. Furthermore, for example, for Cu, a high laser power is required when using an IR fiber laser, which is due to the high degree of reflection, since the absorption of the radiation increases only as a result of the molten bath and a Keyholeausbildung drastically. An inhomogeneous current density of uneven welds is the result. This can result in so-called "hot spots" within the battery cell, which can significantly accelerate battery cell aging and, in extreme cases, can lead to battery cell failure.

The insufficient quality of welds has various causes, such as insufficient compression of the film stack, which is present at individual points within the film stack no zero gap. Another cause is inadequate flow mechanics of non-optimized inert gas streams, such as helium, argon, CO ₂ or a mixture of these. Due to insufficient compression of the Ableiterfolien within the film stack material defects can occur, also the welding quality is reduced, as well as the process stability.

All in all, the previous joining methods are unsatisfactory, which is why we are looking for a remedy.

Presentation of the invention

1. a) Beaufschlagen eines Folienstapels aus Ableiterfolien mit einer Niederhaltekraft mittels eines Niederhalters,
2. b) Durchströmung eines durch den Niederhalter und den Folienstapel gebildeten Strömungskanals mit einem Inertgas,
3. c) Erzeugung eines aufgerauten Bereiches an der den Strömungskanal begrenzenden, nächstliegenden Ableiterfolie des Folienstapels und
4. d) Erzeugung einer Fügenaht zwischen den Ableiterfolien im Folienstapel in Fügerichtung.

According to the invention, a method is proposed for materially joining a number of conductor foils for producing a battery conductor, in which process at least the following method steps are performed:

1. a) applying a foil stack of arrester foils with a hold-down force by means of a hold-down,
2. b) flow through a flow channel formed by the hold-down device and the film stack with an inert gas,
3. c) Generation of a roughened area on the flow channel limiting, the nearest arrester foil of the film stack and
4. d) Generation of a joining seam between the arrester foils in the film stack in the joining direction.

By the method proposed according to the invention, on the one hand, a hold-down force is generated which acts on the entire film stack and, on the other hand, creates the possibility of carrying out the cohesive connection precisely at this time. According to the proposed method, a zero gap between the individual conductor sheets of the film stack can be maintained during the production of the integral connection, so that the quality of the resulting joint seam, in particular the laser-welded seam, is considerably improved.

In a further development of the method proposed according to the invention, a zero gap is generated in each case according to method step a) by the hold-down force in the film stack between the individual conductor foils and maintained during the production of the cohesive joining seam.

According to the invention, a completely inert protective gas atmosphere is created in the flow channel according to process step b) by an inert gas. As inert gases are noble gases such as helium, argon, krypton, radon or even, for example, CO ₂ or a mixture of these used.

According to the method proposed according to the invention, according to method step c), the roughened area is produced by producing raised structures in the μm / sub-μm range by direct structuring, interference structuring or laser scanning. induced periodic surface structuring (LIPSS). The roughened area considerably improves the laser beam injection and qualitatively greatly improves the finally formed cohesive joint seam.

In accordance with method step d), a refraction of the light can be effected either by the inert gas and / or a corresponding shaping of a part of the hold-down beam irradiated by the laser beam, for example of transparent BK7 glass in a rectangular, convex or concave form. In a further development of the method proposed according to the invention, a focusing or defocusing of the laser beam can be carried out. By means of an upstream VarioScan or an ExcelliShift, a focusing or defocusing can be achieved, whereby an adjustment of the focal plane takes place by means of optical elements. By targeted defocusing, the energy distribution for the process can be optimized.

A device for carrying out the method proposed according to the invention is characterized in that a holding-down device has a glass insert, for example made of BK7 glass, or is made entirely of transparent BK7 glass and at the same time offers a flow channel through which inert gas flows. Advantageously, the hold-down device simultaneously constitutes a welding cell with integrated flow channel, while at the same time being transparent to the laser beam on the side facing it.

Advantageously, the shaping of the flow channel on the coupling-in side of the laser beam can be such that it is either flat, convex in shape or concave in shape. By shaping, be it convex or concave, the focusing or defocusing of the laser beam can be made possible. For example, the use of the process gas can change the focus, which is due to the different refractive index in contrast to air. Furthermore, process gases and convective flows dissipate heat at the material surface other than "stagnant", i. a stagnant air flow in a process that is performed without process gas. By the proposed solution according to the invention, this change can be compensated by a suitably shaped flow channel.

The device proposed according to the invention may additionally comprise a metallic welding mask which has at least one hole for producing a spot weld and at least one groove for a line weld. The welding mask is used in this case as a hold-down, but also two different welding masks can be used.

In a further development of the solution proposed according to the invention, the hold-down device comprises a first leg and a second leg, which are interconnected by a bridge part, wherein in one embodiment the hold-down device is made entirely of transparent material, such as BK7 glass, or the hold-down device is such, that the first and the second leg are made, for example, of metallic material, and only the region of the hold-down, through which the coupling of the laser beam takes place, is made of a transparent material, such as BK7 glass.

Advantages of the invention

The proposed solution according to the invention allows a good compression of the individual Ableiterfolien within the film stack at the moment in which the cohesively produced joint seam is produced in the film stack. The optimized compression of the individual Ableiterfolien within the film stack leads to the achievement of a zero gap between the individual Ableiterfolien. The optimized hold-down device on the one hand represents a welding cell with integrated flow channel and is also transparent to the laser beam. The roughening of the first individual conductor sheets within the film stack by a ps / fs laser can significantly improve the degree of coupling in of the laser radiation.

With regard to the fluid mechanics, an optimized inert gas stream of inert gas, such as He, Ar, CO ₂ , Rn, Kr and other noble gases or a mixture of these can be achieved by the solution proposed by the invention. By means of the area of the arrester foil roughened by means of a ps / fs laser, structures in the μm / sub-μm range can be produced, which can be achieved by direct structuring, interference structuring or laser-induced periodic surface structuring (LIPSS). The roughening an absorption center for the coupled laser radiation can be achieved, the Einkoppelgrad be significantly improved, and the successful laser performance are favorably influenced, ie reduced. It is possible to achieve a more homogeneous molten bath in which significantly fewer spatters occur that would have to be removed by means of the inert gas flow within the flow duct. The flow channel for the protective gas flow is limited on the one hand by the hold-down and on the other hand by the overhead Ableiterfolien the film stack. Through the flow channel for the inert gas, a reduction of the plasma temperature can be achieved, which in turn to avoid Oxidation processes during the cohesive joining process, ie the welding process leads. By appropriate adjustment of an optimized inert gas flow within the flow channel, the removal of particles and spatter can be promoted. If a welding mask made of metallic material acts as a holding-down device, spot welds or line welding operations can be carried out in accordance with the position and orientation of grooves or bores.

Depending on the design of the exit surface of the laser beam from the transparent for this area of the blank holder as a flat surface, concave curved surface or convex curved surface, a refraction of light can be adjusted by appropriate shaping, which acts as an optical micron lens. In addition, the refraction of light within the flow channel can also be set by the selection of the inert gas used as the process gas.

With the formation of a suitable flow channel, depending on the Reynolds number, which is a function of the flow velocity of a characteristic geometric characteristic of the geometry of the flow channel and the viscosity of the fluid, the process gas flow can be controlled in its characteristic. The process gas stream may be either a laminar flow or a turbulent flow. As a result, in each case advantageous properties can be set for the process, in particular targeted cooling or also heating of the material surface are conceivable. Furthermore, it is possible to mix certain elements into the weld by means of the process gas flow.

list of figures

With reference to the drawing, the invention will be described below in more detail.

• 1 eine Seitenansicht einer ersten Ausführungsvariante des Niederhalters,
• 2.1 bis 2.3 verschiedene Formgebungen des Niederhalters aus transparentem Material,
• 3 eine perspektivische Darstellung des Niederhalters aus transparentem Material mit Strömungskanal und darunterliegendem Folienstapel,
• 4 eine weitere Ausführungsvariante des Niederhalters,
• 5 die Darstellung einer Schweißmaske aus metallischem Material, die als Niederhalter dient und
• 6 eine schematische Darstellung einer als Schweißnaht ausgebildeten Fügenaht ohne Defekte.

It shows:

• 1 a side view of a first embodiment of the blank holder,
• 2.1 to 2.3 different shapes of the hold-down made of transparent material,
• 3 a perspective view of the blank made of transparent material with flow channel and underlying film stack,
• 4 a further embodiment of the hold-down,
• 5 the representation of a welding mask of metallic material, which serves as hold-down and
• 6 a schematic representation of a weld formed as seam without defects.

variants

1 shows view of a proposed inventions hold-down.

From the illustration according to 1 it turns out that a hold-down 18 with a hold-down force 26 is charged. The hold down 18 compresses conductor foils 14 made of copper, nickel-coated copper or aluminum coated with a very thin carbon-containing layer within a film stack 16 , The film pile 16 forms an arrester banner 12 and puts a battery charger 10 In the case of copper, the thickness of the individual arrester foil lies between 9 μm and 12 μm and in the case of aluminum between 15 μm and 20 μm. The hold down 18 as shown in 1 has a first leg 20 and a second leg 22 on, passing through a bridge section 24 connected to each other. The hold down 18 is made of a transparent material, such as BK7 glass, which is powered by a laser beam 30 is irradiated. The laser may be a continuous wave laser or a pulsed IR fiber laser. Furthermore, suitable for the production of cohesive compounds, in particular welded joints, such as copper, a continuous wave laser with blue wavelength or a continuous wave laser or pulsed laser with green wavelength. By the application of the blank holder 18 with the hold-down force 26 is between the individual arrester foils 14 of the film stack 16 a zero gap 28 generated and maintained during the execution of the welding process. With reference number 32 is in 1 indicated by dashed lines the course of a joint seam within the film stack 16 , By the coupling of the laser beam 30 in one through the hold-down 18 and the film pile 16 formed flow channel 36 , which is traversed by a process gas stream, the generation of a roughened area 34 on the uppermost arrester foil 14 which is made of either Cu or Al. The by the coupling of the laser beam 30 generated structures 40 are in the 1 shown greatly enlarged and lie in the micron or sub-micron range. The structures 40 are generated by direct structuring, interference structuring or laser-induced periodic surface structuring (LIPSS). The structures 40 form the absorption center for the laser beam 30 and improve the Einkoppelgrad the laser beam 30 , In addition, through the structures 40 reached be that the laser power of the IR fiber laser can be reduced, as there is a higher absorption and thereby the introduced heat in the cell stack is reduced in delamination of active layers at grenzlagigen temperatures; furthermore, it can be defined by the roughened area 34 or the structures 40 achieve a more homogeneous melt pool and the number of weld spatter is significantly reduced.

The flow channel 36 - formed on the one hand by the hold-down 18 and on the other hand through the film stack 16 - Forms a flow space for a process gas stream of inert gas such as neon, helium, argon, krypton, radon or CO ₂ or a mixture of these to reduce the plasma temperature. Furthermore, by the process gas stream oxidation processes can be avoided during the welding process, also be discharged by the process gas flow, the above-mentioned spatter, as well as particles that the joint seam 32 contaminate and affect their durability.

The representations according to the 2.1 . 2.2 and 2.3 are different geometries of the blank holder 18 removable. According to the 2.1 . 2.2 . 2.3 can the flow channel 36 in terms of its channel cross-section 38 be such that the flow channel is essentially a rectangular shape 42 has, as in 2.1 is shown. In addition, there is according to 2.2 , the possibility of the flow channel 36 in convex form 44 train or, as in 2.3 is shown in concave form 46 , Due to the convex shape 44 or the concave shape 46 can be a focusing or defocusing of the laser beam 30 to be influenced. Furthermore, the shape of the refraction can be influenced by the shape of a flow cell, which acts as a micron optical lens. By appropriate shaping depending on whether the convex shape 44 or the concave shape 46 is selected, the process gas flow can be specified in terms of turbulent or laminar flow.

3 shows a perspective view of the in 1 from the side shown downholder 18 as well as the film stack 16 ,

From the perspective view according to 3 it turns out that the flow channel 36 that has a channel cross section here 38 in rectangular shape 42 has, from a process gas stream 48 is flowed through. In the process gas stream 48 it is an inert gas flow, or an inert gas flow mixture of helium, neon, argon, krypton, radon or CO ₂ or a mixture of these.

This flows through the flow channel 36 , Through the process gas flow 48 Welding spatters during the production of the joint seam 32 can emerge, as well as particles removed from the weld zone. Furthermore, by the process gas flow 48 a targeted cooling or heating of the surface of the weld zone done. It is possible to influence the weld quality by a favorable chemical or structural modification of the surface or the weld during the welding process, because an oxidation- and electrolyte-resistant weld quality can be achieved, furthermore, a less brittle weld shape can be represented. Like the perspective view according to 3 shows, the holddown extends 18 in joining direction 50 , ie in the direction in which the cohesive joining seam 32 is produced. The film pile 16 is continuous through the hold-down 18 with the hold-down force 26 so that within the film stack 16 or between the individual conductor foils 14 , the zero gap 28 while in the film stack 16 by coupling the laser beam 30 on the transparent side of the blank holder 18 ie the bridge part 24 the joint seam 32 , performed as a laser-welded weld, is generated. The quality of the joining direction 50 produced joint seam 32 is significantly improved because the Einkopplungsgrad the laser beam 30 through the roughened area 34 or the structures 40 on the top of the arrester foils 14 is significantly improved. As well as out 3 shows, is the flow channel 36 or its channel cross section 38 at the bottom of the film pile 16 and laterally through the first leg 20 and the second leg 22 , as well as this connecting bridge part 24 the hold-down 18 limited. In the in 3 The perspective view shown is the hold-down 18 from one for the laser beam 30 transparent material, for example made of BK7 glass.

4 shows a further embodiment of the blank holder 18 ,

From the illustration according to 4 it turns out that the hold down 18 a glass insert 52 made of a transparent material such as BK7 glass. This rests on the first leg 20 and the second leg 22 , which are made according to this embodiment of metallic material and the glass insert 52 take up. Through the glass insert 52 is according to this embodiment of the laser beam 30 in the flow channel 36 coupled, as shown in 4 a channel cross-section 38 in rectangular shape 42 having. Also according to this embodiment, the flow channel 36 from a process gas stream 48 (compare illustration according to 3 ) flows through. Through the coupled laser beam 30 becomes on the surface of the uppermost arrester foil 14 whether made of copper or made of aluminum, a roughened area 34 generated, the structures 40 includes, which lie in the micrometer / sub-micron range. This will cause the coupling of the laser beam 30 in the individual arrester foils 14 of the film stack 16 significantly improved.

Also by the in 4 illustrated hold-down 18 , whose first and second legs 20 respectively. 22 are made of metallic material, the hold-down force 26 in the film pile 16 , formed from the individual arrester foils 14 , coupled, so that within the film stack 16 between the individual conductor foils 14 the zero gap 28 what is the generation of the joint seam 32 significantly improved. At the in 4 illustrated embodiment, the laser beam 30 For example, by an IR fiber laser either pulsed or continuous wave in the flow channel 36 be coupled. Instead of an IR fiber laser, it is also possible, for example, to use blue wavelength continuous wave lasers and a continuous wave laser or a pulsed laser with a green wavelength. Although not shown in the drawing, the glass insert 52 preferably made of a transparent material, such as BK7 glass, on the exit side of the laser beam 30 in the flow channel 36 according to the in the 2.1 . 2.2 . 2.3 Variants shown either level, in convex shape 44 running or concave 46 running, be trained.

5 shows one as a hold-down 18 serving welding mask made of metallic material 54 ,

From the illustration according to 5 it turns out that above a foil stack 16 from individual arrester foils 14 a welding mask 54 which is the function of the hold-down 18 exercises.

As seen from the top view 5 shows, runs in the welding mask 54 made of metallic material a groove 56 ; Furthermore, there are several adjacent holes 58 intended. Through the groove 56 it is possible to create a line weld or a wobble weld while drilling 58 open up the possibility of making individual spot welds. When using a pulsed laser, for example, line welding or spot welding can be made. When using a continuous wave laser, it is preferable to perform line welding; spot welding is not possible with a continuous wave laser.

6 shows a joining seam 32 without defects.

From the illustration according to 6 shows in a schematic way that one between the individual Ableiterfolien 14 within the film stack 16 produced seam width 60 which is between 1 mm and 2 mm and the one depth 62 which is dimensioned so that the individual Ableiterfolien 14 within the film stack 16 are connected to each other cohesively.

6 further shows that on top of the topmost arrester foil 14 a vault 64 located.

For illustrative reasons are in 6 only five arrester foils 14 drawn. In the proposed method according to the invention can be up to seventy Ableiterfolien 14 be connected to each other.

As shown in the illustration 6 indicates that in 6 illustrated joint seam 32 without defects neither pores nor cracks, nor voids or the like more defects on which could arise within a battery cell "hot spots", which have the above-mentioned negative properties.

By the inventively proposed solution according to the above-described embodiments of the blank holder 18 can with regard to its fluid mechanics an optimized process gas flow 48 through the flow channel 36 be passed, the channel cross sections 38 can be varied as above. By inventively proposed optimized hold-down 18 on the one hand, a welding cell with integrated flow channel 36 on the other hand transparent for the on the coupling side in the flow channel 36 to be coupled laser beam 30 is. According to the invention, a further optimization of the joining process is achieved in that the respective overhead, the flow channel 36 limiting arrester foil 14 roughened with the ps / fs laser, therefore a roughened area 34 is generated, which the Einkoppelgrad the laser beam 30 greatly improved and forms the absorption center for the laser radiation.

As further laser sources, the inventively proposed cohesive joining method for joining the individual Ableiterfolien 14 of the film stack 16 A laser with a blue wavelength and a laser with a green wavelength can be mentioned. These shorter wavelengths compared to the IR laser have an increased absorption, for example for copper. The use of these laser sources, taking into account the above-mentioned points, the absorption can be further increased and the overall welding result can be qualitatively further improved.

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

Claims (13)

Method for materially joining a number of arrester foils (14) for producing a battery arrester (10) with the following method steps: a) applying a foil stack (16) of conductor sheets (14) with a hold-down force (26) by means of a hold-down device (18), b) flow through a flow channel (36) formed by the holding-down device (18) and the film stack (16) with a process gas stream (48), c) generating a roughened area (34) on the flow channel (36) limiting, closest, several Ableiterfolien (14) of the film stack (16) and d) generating a joining seam (32) between the arrester foils (14) in the film stack (16) in the joining direction (50). Method according to Claim 1 , characterized in that according to method step a) by the hold-down force (26) in the film stack (16) between the Ableiterfolien (14) in each case a zero gap (28) is present. Method according to Claim 1 , characterized in that according to process step b) by the process gas stream (48) of inert gas, a completely inert inert gas atmosphere in the flow channel (36) is created, or the process gas stream (48) is formed by an air flow. Method according to Claim 1 , characterized in that, according to method step c), the roughened region (34) is formed by producing raised structures (40) in the μm sub-μm range by direct structuring, interference structuring or laser-induced periodic surface structuring (LIPSS). Method according to Claim 1 , characterized in that according to process step d) a refraction of light by the inert gas and / or shaping of a laser beam (30) irradiated part (24, 52) made of transparent BK7 glass in a rectangular shape (42), convex shape (44) or concave shape (46). Method according to Claim 1 , characterized in that in step d), a focusing or defocusing of the laser beam (30) is performed. Method according to Claim 1 , characterized in that according to method step d) at least one joint seam (32) in the sweep welding process or with a metallic welding mask (54) is performed as a line or spot welding. Method according to Claim 1 , characterized in that the process gas stream (48) is such that it is designed with respect to the flow channel geometry of the flow velocity and the fluid viscosity such that a laminar or turbulent flow field is generated which the at least one joining seam (32) depending on the materials and Suture request by heating or cooling of the joint seam surface by chemical or structural influence of the surface or the joint seam (32) optimally form. Apparatus for carrying out the method according to one of Claims 1 - 8th , characterized in that a hold-down (18) has a glass insert (52) made of BK7 glass, or is made of this and a flow channel (36) which is traversed by a process gas stream (48). Device according to Claim 9 , characterized in that the flow channel (36) on the side, which is irradiated by the laser beam (30), even, in a convex shape (44) or in concave shape (46) is executed. Device according to Claim 9 , characterized in that a metallic welding mask (54) is provided, which has at least one bore (58) for generating a spot weld and at least one groove (56) for a line welding and acts as a hold-down (18) on the film stack (16). Device according to Claim 9 , characterized in that the hold-down (18) is a first leg (20), a second leg (22) and a bridge part (24) comprising, for example, made of transparent BK7 glass. Device according to Claim 9 , characterized in that the hold-down (18) has a first leg (20) and a second leg (22), which are made of metallic material and contains a made of BK7 glass glass insert (52).

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