CN114361679A

CN114361679A - Welding device for producing an electrical contact in a battery module of a high-voltage battery

Info

Publication number: CN114361679A
Application number: CN202111170482.1A
Authority: CN
Inventors: F.格劳; D.贝姆; A.布鲁尔
Original assignee: Volkswagen Automotive Co ltd
Current assignee: Volkswagen Automotive Co ltd
Priority date: 2020-10-14
Filing date: 2021-10-08
Publication date: 2022-04-15
Also published as: DE102020212933A1

Abstract

The invention relates to a welding device for establishing an electrical contact between at least one cell electrode (3) and a busbar (5) of a high-voltage battery module in a welding process, in which, in a first process step, the cell electrode (3) and the busbar (5) can form a joint connection as a welding partner, and, in a second process step, the two welding partners (3, 5) are welded to one another at the joint connection. According to the invention, the welding process is implemented as a negative-pressure laser welding process, wherein a laser unit (9) applies a laser beam (11) to the weld spot (7). The welding installation has an evacuation unit which, during the welding process, at least applies a negative pressure to the environment adjacent to the welding spot (7).

Description

Welding device for producing an electrical contact in a battery module of a high-voltage battery

Technical Field

The invention relates to a welding device for producing an electrical contact between at least one cell and a cell electrode and a busbar according to the preamble of claim 1 and to a method for producing such a contact according to claim 14.

Background

When the battery module of the high-voltage battery is mounted, a certain number of battery cells are stacked in a stacking direction as a cell stack. The cell stack is then transferred to a welding installation of this type, in which the cell electrodes/arresters of the battery cells are welded to the busbars/busbars in order to electrically connect the battery cells to one another according to a predetermined connection scheme.

In this type of welding process, in a first process step, the cell electrode and the busbar are brought into a joint connection as a welding partner. In a second process step, the two welding partners are welded to one another at the joint connection.

It has been found that, for example, when laser welding is carried out in the atmosphere, welding defects occur, which impair the quality of the electrical contact between the cell electrode and the busbar. In this case, the electrical contacts need to be reworked, which is complicated in terms of production technology.

A welding device for establishing an electrical contact between a cell and a cell electrode and a busbar is known from CN 106956076 a.

Disclosure of Invention

The object of the present invention is to provide a welding device and a welding method, by means of which a process-safe and defect-free contact between the cell electrode and the busbar of a high-voltage battery can be achieved.

This object is achieved by the features of claim 1 or 14. Preferred embodiments of the invention are disclosed in the dependent claims.

The invention relates to a welding process in which, in a first process step, the respective cell electrode and busbar are brought into a joint connection (or butt connection) as a welding partner, and in a second process step, the two welding partners are welded to one another at the joint connection. According to the characterizing part of claim 1, the welding process is realized as a negative pressure laser welding process, wherein the laser unit applies a laser beam to the weld spot. The welding installation furthermore has a vacuum unit which, during the welding process, at least loads the adjacent (or immediate, direct) environment of the welding spot with a negative pressure.

In general, the invention relates to a laser beam welding system in which the mounting of parts of the arrester/cell electrode of one or more lithium ion cells to be connected relative to one or more busbars/busbars takes place. In this device, the connection is produced by laser beam welding under reduced atmospheric pressure or in a vacuum. The apparatus has at least one beam-entering glass (hereinafter referred to as an injection optic) that makes the directed laser radiation accessible to the weld spot. Furthermore, at least one tensioning element is integrated in the device, which produces a "zero" gap between the welded busbar/busbar and the arrester/cell electrode. Additionally, an electrically insulating layer is introduced between the beam entering the glass holder, the tensioning element of the welding enclosure (Schwei β mask or so-called welding mask) and the component to be welded, which layer prevents short-circuit currents between the cells and/or the device. The opening in the weld enclosure is oversized to correspond to the geometry of the desired weld shape. The vacuum chamber has an opening through which the gas present is discharged from the vacuum chamber and a vacuum is generated in the welding chamber. In order to be able to save additional process time when the arrester/cell electrode is in contact with a busbar or busbar, a plurality of laser units can be used in parallel.

Since the laser beam can propagate freely between the beam-escape glass of the welding device (exit optics of the laser unit) and the beam-entry glass (entry optics), a housing around the device and the laser beam exit (laser protection compartment) is necessary, or there is a laser radiation-tight encapsulation between the beam-escape glass of the laser optics and the beam-entry glass of the device. No additional encapsulation is then required to prevent laser radiation. In this case, it must be ensured by means of a sensor that the laser radiation is released only when the laser protection encapsulation is in engagement with the device. Such a laser protection package may be fixed directly to the welding optics or moved from welding to welding by a separate device.

Different application scenarios can be implemented for complete (parallel) and partial (individual) laser welding devices:

1. the welding device(s) continuously remain positioned in the laser installation. The setting-up process of the device relative to the laser device is therefore carried out only once. In this case, the cell stacks and busbars are inserted, or the busbars are already fixed to the cell stack and subsequently inserted into the apparatus. Subsequently, a negative pressure is generated, and then welding is performed.

2. In an application, a plurality of devices are in cyclic operation. Outside the laser installation, the single battery pack and bus bar are used to charge the device. Furthermore, the equipment outside the laser installation is closed and ventilated, while another equipment is already located in the laser installation and performs the welding. Thereby saving process time.

3. Depending on the module/cell configuration, the laser for welding can be radiated simultaneously by a plurality of lasers or by a laser system.

The contact of the arrester/cell electrode with the busbar can be achieved by means of a device in which a negative pressure is generated in order to increase the solderability of the material. The evacuation time is very short due to the small volume to be evacuated of the equipment in the vicinity of the soldered connection. Thereby reducing spray formation/holes and thereby increasing the electrical connection area. Due to the negative pressure, a higher feed speed can be obtained at the same laser power, or the laser power can be minimized at the same feed speed. Due to the higher feed speed or the minimized laser power, the amount of heat input to the member becomes smaller. Thereby, no or a smaller intensity drop in the heat affected zone occurs. This principle works regardless of the number of arresters/cell electrodes and busbars/busbars that are welded simultaneously with a single device. The negative pressure welding apparatus can be designed according to the type of joint of the splice partners to be welded. With the laser protection package, large space laser protection capsules can be avoided. The sensor ensures that the laser radiation is released only when the laser protection package engages with the welding device.

In an alternative embodiment, the device can be designed such that not only the welding region but also the entire component to be welded is subjected to a vacuum. The negative pressure/vacuum laser chamber is only slightly larger than the cladding geometry of the cell to be welded (including the busbar to be welded). In general, in this embodiment variant, the vacuum laser chamber has a much larger volume to be evacuated. The evacuation time is increased accordingly due to the volume.

Several aspects of the invention are highlighted in detail again below: the evacuation unit can therefore have at least one adapter part which delimits (or delimits) a vacuum chamber which is open in the direction of the weld spot. During the welding process, the adapter part can be placed with its open cavity side pressure-tightly on the side of the joining connection facing the laser unit, so that the adjacent environment of the weld spot is loaded with a negative pressure. Subsequently, the underpressure cavity in the adapter part can be loaded with underpressure.

In a technical implementation it is preferred that the laser unit is located outside the adapter part. In this case, the adapter part can have injection optics (or coupling-in optics). The laser beam generated by the laser unit is injected into the vacuum chamber via injection optics and is guided from there further to the weld spot.

In connection with defect-free welding processes, it is preferred that the vacuum unit has a prestressing device, by means of which the adapter part can be brought into indirect or direct pressure contact with the joint connection to be welded (between the cell electrode and the busbar) by means of a prestressing force.

With regard to the defect-free weld core formation at the weld points, it is preferred if the adapter part has a weld cap on its open chamber side, by means of which the weld points are bounded on the peripheral side. Furthermore, an electrically insulating layer may be provided between the solder mask and the bonding connection.

Furthermore, the adapter part may have an evacuation connection. The vacuum chamber can be fluidically connected to a vacuum source via a vacuum connection in order to apply a vacuum to the vacuum chamber.

Preferably, the laser unit is not integrated directly in the adapter part, but is spaced apart from the injection optics of the adapter part by a free optical path. In this case, it is preferable to shield the free optical path between the laser unit and the adapter part from the outside. This can advantageously be achieved by means of a laser protection capsule in which the exit optics of the laser unit and at least the joining connection to be welded (between the cell electrode and the busbar) are accommodated. Alternatively, a laser radiation-tight encapsulation may also be provided, which extends between the exit optics of the laser unit and the entry optics of the adapter part.

In a battery cell stack, a plurality of cell electrodes are welded to a bus bar. With regard to reducing the welding process time, it is preferred that not only one adapter part but also a plurality of adapter parts are provided in the welding installation. The adapter members may be arranged one after another as viewed in the stacking direction of the battery cells. Each adapter part can be assigned exactly one joint connection between a cell electrode and a busbar. Preferably, the adapter part can be connected to a carrier element, on which the pretensioning device acts. In this way, all adapter parts are in pressure contact with the assigned welding partners.

In the above-described embodiment variant, the laser beam can be radiated into the adapter part simultaneously by a plurality of laser units. Alternatively, the laser beam may be radiated by a single laser radiation unit. The laser irradiation unit may be movably disposed in a cell stacking direction. Thus, the movable laser units are in turn brought close to the adapter part.

In a further embodiment, the vacuum unit can have a vacuum housing which delimits a vacuum space. The negative pressure space can be slightly larger than the envelope geometry of the battery cell to be welded. In this case, the entire battery cell stack can be arranged in a negative pressure space, which can be coupled to a negative pressure source, not shown. All adapter parts can be connected with their vacuum chambers to one another and to the vacuum space in a flow-related manner.

Drawings

Embodiments of the present invention are described later on with reference to the drawings. Wherein:

fig. 1 shows a completed battery cell stack after a welding process in a sectional view;

FIG. 2 shows a facility sketch of a welding facility with an evacuation unit;

figures 3 to 5 show detail views of figure 2;

fig. 6 to 11 show further embodiments; and is

Fig. 12 shows different joint connections and adapter parts respectively matched to the joint connections.

Detailed Description

Fig. 1 shows the completed battery module after the welding process. The battery module has a cell stack having battery cells 1 stacked in sequence in a stacking direction. The battery cell 1 is illustratively a pouch cell. In fig. 1, the cell electrodes 3 of the battery cells 1 are soldered to one another in soldering points 7 by means of busbars 5, according to a predefined connection scheme, in order to electrically connect the battery cells 1 to one another.

Subsequently, a welding facility and a welding process for establishing electrical contact between the cell electrode 3 and the busbar 5 are described with reference to fig. 2 to 5. First, in a first process step, all the busbars 5 are joined together in a bonded connection with the not yet welded cell electrodes 3 of the battery cells 1 as welding partners. Subsequently, the battery cell stack, which has not yet been welded, is transferred into the welding installation shown in fig. 2. The welding installation has a laser unit 9, by means of which a laser beam 11 can be applied to the respective weld spot 7.

The core of the invention is that the welding process is realized as a negative pressure laser welding process. For this purpose, the welding installation has an evacuation unit, by means of which the adjacent environment of the respective weld spot 7 is loaded with a negative pressure during the welding process.

In the context of figures 2 and 3 of the drawings,the evacuation unit is formed by a plurality of adapter parts 15, which are arranged one behind the other, as seen in the stacking direction of the battery cells 1. Each adapter part 15 is assigned exactly one joining connection between the cell electrode 3 and the busbar 5. Furthermore, all adapter parts 15 are connected to the carrier element 17. A pretensioning device, not shown, acts on the carrier element 17, by means of which pretensioning force F can be used by all adapter parts 15_VIn pressure contact with the respectively assigned

welding partners

3, 5.

Fig. 4 and 5 show the adapter part 15 of the vacuum unit in a detail view. The adapter part 15 thus delimits a negative pressure chamber 19 which is open in the direction of the joining connection. During the welding process shown in fig. 2, the adapter part 15 is placed with its open chamber side pressure-tightly and spaced apart from the weld spot 7 on the side of the joining connection facing the laser unit 9. The vacuum chamber 19 is loaded with vacuum in this case. For this purpose, the adapter part 15 has an evacuation connection 21 (fig. 3) which is connected to a source of negative pressure, not shown.

The adapter part 15 has, on its side spaced apart from the joining connection, injection optics 23, by means of which the laser beam 11 generated by the laser unit 9 can be injected into the underpressure chamber 19 and from there be guided further to the weld spot 7. In fig. 4, the adapter part 15 is not directly in pressure contact with the joining connection, but rather a solder dome 25 and an electrically insulating layer 27 are present between them.

As further emerges from fig. 3, the laser beam 11 is radiated by a single laser unit 9 into the respective adapter part 15. The laser unit is movably arranged in the cell stacking direction so that the laser unit 9 can access the adapter member 15 in sequence.

As can be seen from fig. 3, the laser unit 9 is spaced apart from the injection optics 23 of the respective adapter part 15 by a free beam path f. In order to shield the free beam path f from the outside, the welding installation additionally has a laser protection compartment 29 in fig. 6, in which the laser unit 9 and the entire battery cell stack to be welded are arranged. Alternatively, in fig. 7 a laser radiation-tight encapsulation 31 is provided, which extends between the exit optics 33 of the laser unit 9 and the exit optics 23 of the adapter part 15. The laser radiation sealed package 31 is illustrated in detail in fig. 8.

Fig. 9a and 9b show a further exemplary embodiment, in which the vacuum unit has a vacuum housing 35. The negative pressure housing 35 delimits a negative pressure space 37. The negative pressure space is slightly larger than the envelope geometry of the battery cell stack to be welded. Accordingly, in fig. 9a and 9b, the entire battery cell stack is arranged in a negative pressure space 37, which can be coupled to a not shown negative pressure source. According to fig. 9, all adapter parts 15 are connected with their vacuum chambers 19 to each other and to the vacuum space 37 in terms of flow.

Modifications of the embodiment shown in fig. 9 are shown in fig. 10 and 11, respectively: in fig. 10, the welding installation therefore additionally has a laser protection compartment 29, in which the free beam path f is shielded to the outside. Alternatively, in fig. 11, the free beam path f is shielded to the outside by a laser radiation-sealed encapsulation 31, which has been described, for example, in accordance with fig. 7.

The adapter part 15 according to the invention can be adapted to the geometry of the joint connection to be welded in each case, as shown in fig. 12a to 12 f: in fig. 12a, the adapter part 15 is arranged on the side facing the laser unit 9 and is designed for welding the lap joint of the

counterpart

3, 5. In fig. 12b, the adapter part 15 is likewise designed for a lap joint, but is embodied in stages. In fig. 12c, the adapter part 15 is likewise positioned on the side of the joining connection facing the laser unit 9 on only one side. The joint connection is realized as a T-joint. In fig. 12d, the joining connection is realized as a butt joint, wherein the adapter part 11 is positioned on both sides on the side facing the laser unit 9 and on the opposite side of the joining connection, respectively. Correspondingly, fig. 12e and 12f also show a lap joint, on which the adapter parts 15 are positioned on both sides.

List of reference numerals

1 Battery cell

3 single cell electrode

5 bus bar

7 welding spot

9 laser unit

11 laser beam

15 adapter part

26 spring support

17 bearing element

19 negative pressure cavity

21 evacuation joint

23 injection optics

24 spring element

25 welding cover

27 electrically insulating layer

29 laser protection cabin

31 laser protection package

33-emission optical device

35 negative pressure shell

37 negative pressure space

Optical path of f freedom

F_VPre-tightening force.

Claims

1. Welding installation for establishing an electrical contact between at least one cell electrode (3) and a busbar (5) of a high-voltage battery module in a welding process in which, in a first process step, the cell electrode (3) and the busbar (5) can form a joint connection as a welding partner and, in a second process step, the two welding partners (3, 5) are welded to one another at the joint connection, characterized in that the welding process is implemented as a negative-pressure laser welding process, wherein a laser unit (9) applies a laser beam (11) to a welding spot (7), and in that the welding installation has an evacuation unit which, during the welding process, at least loads the adjacent environment of the welding spot (7) with a negative pressure.

2. Welding installation according to claim 1, characterized in that the evacuation unit has at least one adapter part (15) which delimits a vacuum chamber (19) which is open in the direction of the welding spot (7), and in that the adapter part (15) can be placed pressure-tightly with its open chamber side on the side of the joining connection facing the laser unit (9) during the welding process, so that the adjacent environment of the welding spot (7) can be loaded with a vacuum.

3. Welding plant according to claim 2, characterized in that the laser unit (9) is positioned outside the adapter part (15) and that the adapter part (15) has injection optics (23) by means of which the laser beam (11) generated by the laser unit (9) can be injected into the underpressure chamber (19) and further guided to the welding spot (7).

4. Welding installation according to claim 2 or 3, wherein the evacuation unit has a pretensioning device by means of which the adapter part (15) can utilize a pretensioning force (F)_V) The joining connection is in indirect or direct pressure contact.

5. Welding plant according to any one of claims 2 to 4, characterized in that the adapter part (15) has a welding cap (25) on its open cavity side, by means of which welding spot (7) is delimited.

6. Welding plant according to claim 5, characterized in that an electrically insulating layer (27) is provided between the welding enclosure (25) and the joint connection.

7. Welding plant according to any of claims 2 to 6, characterized in that the adapter part (15) has an evacuation connection (21) by means of which the negative pressure chamber (19) can be connected with a source of negative pressure.

8. The welding plant according to one of the claims 3 to 7, characterized in that the laser unit (9) is spaced apart from the injection optics (23) of the adapter part (15) by a free beam path (f) and in particular a laser protection compartment (29) is provided for shielding the free beam path (f), in which the laser unit (9) and at least the joining connection to be welded are accommodated.

9. Welding plant according to claim 8, characterized in that for shielding the free light path (f), a laser radiation-tight package (31) is provided alternatively between the exit optics (33) of the laser unit (9) and the entrance optics (23) of the adapter part (15).

10. The welding installation according to one of claims 2 to 9, characterized in that a plurality of adapter parts (15) are arranged one behind the other, as seen in the stacking direction of the battery cells (1), and that exactly one joint connection between the cell electrode (3) and the busbar (5) is assigned to each adapter part (15), and in particular that the adapter parts (15) are connected to a carrier element (17) on which the prestressing device acts, so that all adapter parts (15) are in pressure contact with the assigned welding partners (3, 5).

11. Welding plant according to claim 10, characterized in that the laser beam (11) is radiated into the adapter part (15) simultaneously by a plurality of laser units (9) or by only one laser unit (9), which laser units are movably arranged in the cell stacking direction, so that the laser units (9) approach the adapter part (15) in sequence.

12. Welding plant according to any of the preceding claims, characterized in that the evacuation unit has a negative pressure housing (35) which delimits a negative pressure space (37) which is slightly larger than the cladding geometry of the battery cells (1) to be welded, and in that the entire battery cell stack is arranged in the negative pressure space (37) which is coupled to a negative pressure source.

13. Welding installation according to claim 12, wherein all adapter parts (15) are connected with their underpressure chambers (19) to each other and to the underpressure space (37) in terms of flow.

14. A method for establishing an electrical contact between at least one cell electrode (3) and a busbar (5) of a high-voltage battery module, which method can be implemented in a welding installation according to any one of the preceding claims.