DE102024207809B3 - Method for separating a material bond between a cell connector and a battery cell - Google Patents

Abstract

The invention relates to a method for separating a material bond between a cell connector and a battery cell, comprising a provisioning step in which a first battery cell (3) is provided which is in a joining connection with a cell connector (7) in a first joining area (21) of the first battery cell (3). According to the invention, the method includes a separation step in which the cell connector (7) is separated from the first battery cell (3) by removing material at least partially and/or temporarily in the first joining area (21) of the first battery cell (3) and/or adjacent to the first joining area (21) of the first battery cell (3) using a laser beam generated by the ultrashort pulse laser (41).

Description

The invention relates to a method for separating a material bond between a cell connector and a battery cell according to the preamble of claim 1.

Traction batteries use cell stacks, which consist of several individual battery cells stacked in series. Adjacent battery cells within a cell stack are electrically connected via a cell connector. The cell connector is bonded to each of the battery cells by a weld. Each weld extends across a joint area. To allow for the disconnection of the cell connector from at least one of the battery cells during repairs, a generic method for separating the weld between the cell connector and the battery cell includes a separation step in which material is removed from the weld area using a laser, thus severing the weld between the cell connector and the battery cell. However, this laser separation step introduces heat not only into the weld area but also into the battery cells themselves. This heating can thermally destroy or at least damage the battery cell. Therefore, the method has the disadvantage that the battery cell is subjected to significant thermal stress when the cell connector is separated.

From the DE 10 2019 213 417 A1 A combined cutting/welding process for Al and Cu materials using heat accumulation of ultrashort laser pulses is known. DE 10 2017 216 149 A1 Disclosed is a method and a device for manufacturing an electrode stack for a battery cell. From the US 2022 / 0 263 060 A1 Laser ablation is a known treatment for lithium-ion batteries. WO 2020 / 192 845 A1 Disclosed is a device and a method for providing electrode strings and for manufacturing electrode arrangements. From the DE 10 2023 121 905 A1 A device and a method for cutting a workpiece using a laser beam are known. US 2021 /0 101 231 A1 reveals a laser processing method for thin-film structures.

One object of the invention is to provide a method by which a material bond between a cell connector and a battery cell can be separated without destroying or damaging the battery cell by heating.

This problem is solved by the features of the independent claim. Preferred embodiments of the invention are disclosed in the dependent claims.

The invention proposes a method for separating a material bond between a cell connector and a battery cell, comprising a provisioning step in which a first battery cell is provided which is in a joining connection with a cell connector in a first joining region of the first battery cell. The invention further provides that the method includes a separation step in which the cell connector is separated from the first battery cell by removing material at least partially and/or temporarily from the first joining region of the first battery cell using an ultrashort pulse laser or a laser beam generated by the ultrashort pulse laser, and/or preferably by removing material directly adjacent to the first joining region of the first battery cell. By using the ultrashort pulse laser, the material to be removed vaporizes and/or sublimates and/or is immediately converted into plasma without introducing heat into surrounding areas, such as the battery cells. Thus, the battery cells are neither thermally damaged nor destroyed in this method.

To ensure that the method can be used particularly efficiently and/or that reliable electrical contacting of the first battery cell is guaranteed, it is provided, by way of example, that the first battery cell has a cell terminal, and that the cell terminal of the first battery cell, preferably a contact plate of the cell terminal of the first battery cell for electrical contacting the first battery cell, particularly preferably directly, is in joining connection with the cell connector in the first joining area.

To achieve particularly good electrical conductivity, it is preferably provided that the material of the cell connector and/or the material of the cell terminal of the first battery cell, preferably a contact plate of the cell terminal of the first battery cell for electrical contacting of the first battery cell, is aluminum or an aluminum alloy.

In order to fully utilize the advantages of the process and/or to reliably and durably connect the first battery cell to the cell connector, it is exemplified that the joining connection in the first joining area is formed by a welded connection, preferably by a laser welded connection.

To prevent accidentally removing too much material during the separation step in the depth direction and thereby damaging the first battery cell, an exemplary embodiment provides that during the separation step the material in the first joining area of the first battery cell and/or, preferably immediately adjacent, next to the first joining area of the first battery cell is evaporated, preferably layer by layer, directly or immediately.

In order to achieve direct or immediate vaporization of the material to be removed, an exemplary embodiment provides that the ultrashort pulse laser has a pulse duration in the range of ^10⁻¹⁸ seconds to ^10⁻¹⁵ seconds, and/or that the ultrashort pulse laser is a titanium:sapphire laser.

In order to perform the separation step as efficiently as possible, an exemplary embodiment provides that the material is first removed and/or ablated using a pulsed and/or high-frequency standard laser and only towards the end of the separation step using the ultrashort pulse laser or the laser beam generated by the ultrashort pulse laser.

In order to separate the joining connection in the first joining area particularly gently and efficiently and above all without pressure, an exemplary embodiment provides that during the separation step the material of the cell connector and/or the cell terminal of the first battery cell and/or a contact plate of the cell terminal of the first battery cell in the first joining area or next to the first joining area is removed by ablation, preferably by means of the ultrashort pulse laser or the laser beam of the ultrashort pulse laser, preferably in a laser cutting system.

To prevent damage to surrounding components or the first battery cell itself during the separation step, an exemplary embodiment provides that, preferably exclusively, the material of the cell connector and/or the cell terminal of the first battery cell and/or a contact plate of the cell terminal of the first battery cell for electrical contacting of the first battery cell is removed during the separation step.

In order to achieve a reliable and process-safe separation of the cell connector from the first battery cell during the separation step, an exemplary embodiment provides that the cell connector is separated from the first battery cell during the separation step by removing, preferably exclusively, material, preferably of the cell connector, next to the first joining area, which preferably directly borders the first joining area.

In order to apply this method to remove a battery cell from the cell stack in a cost-effective and resource-saving manner, a preferred embodiment provides that a second battery cell is provided during the provisioning step, which is connected to the cell connector in a first joining area of the second battery cell.

To achieve a particularly high electrical performance of the cell stack, it is preferably provided that the first battery cell and the second battery cell are stacked one behind the other with an interlayer of cell spacer material, preferably along a stack axis. It is particularly preferred that the cell spacer material is formed by a welded-in powder.

The method is primarily suitable for prismatic battery cells. It is therefore preferred that the first battery cell and/or the second battery cell or all battery cells of the cell stack be prismatic battery cells.

To obtain a particularly space-saving cell stack, it is preferably provided that the cell connector in the area of the first joining area has a thickness in the range of 1 mm to 2 mm, and/or that the contact plate of the cell terminal of the first battery cell has a thickness in the range of 2 mm to 4 mm in the area of the first joining area.

To ensure that only enough material is removed to prevent damage to components and parts adjacent to the first joining area of the first battery cell and/or the first joining area of the second battery cell, an exemplary embodiment provides that, during the separation step, the material in the first joining area of the first battery cell and/or next to the first joining area of the first battery cell is removed from a cover surface of the cell connector in the direction of the first battery cell and/or in a depth direction to a depth in a range between 2 mm and 6 mm, preferably in a range of 4 mm to 5 mm, wherein it is preferably provided that the cover surface of the cell connector faces away from the first battery cell.

In order to be able to remove the material precisely during the separation step, a preferred embodiment provides that the first battery cell and/or the second battery cell are clamped in a clamping device during the separation step.

In order to remove the material with particular precision during the separation step, a particularly preferred embodiment provides that the material in the first joining area of the first battery cell and/or next to the first joining area of the first battery cell is removed automatically, preferably fully automatically, during the separation step.

The following are descriptions of embodiments of the invention with reference to the accompanying figures.

• 1 in einer Ansicht von oben einen Zellstapel mit einer ersten Batteriezelle und einer zweiten Batteriezelle und einem Zellverbinder;
• 2 in einer Seitenschnittansicht den Zellstapel der 1;
• 3 in der Seitenschnittansicht gemäß der 2 den Zellstapel in einer Laserschweißanlage während der Durchführung eines Trennschrittes;
• 4 in der Seitenschnittansicht gemäß der 2 den Zellstapel in der Laserschweißanlage nach der Durchführung des Trennschrittes;
• 5 in einer Ansicht von oben den Zellstapel gemäß der 4 nach der Durchführung des Trennschrittes;
• 6 in einer rein schematischen Seitenschnittansicht die Wirkungszone eines Ultrakurzpuls-Lasers bei dem Trennschritt, und
• 7 in einer rein schematischen, perspektivischen Ansicht eine aufgeraute Fläche oder Oberflächenstrukturierung, die durch einen Materialabtrag des Ultrakurzpuls-Lasers bei dem Trennschritt erzeugt wurde.

They show:

• 1 in a top view a cell stack with a first battery cell and a second battery cell and a cell connector;
• 2 in a side view the cell stack of 1 ;
• 3 in the side section view according to the 2 the cell stack in a laser welding system during the execution of a separation step;
• 4 in the side section view according to the 2 the cell stack in the laser welding system after the separation step has been carried out;
• 5 in a top view the cell stack according to the 4 after the separation step has been carried out;
• 6 in a purely schematic side-section view the area of effect of an ultrashort pulse laser during the separation step, and
• 7 In a purely schematic, perspective view, a roughened surface or surface structuring is shown, which was created by material removal by the ultrashort pulse laser during the separation step.

In the 1 A cell stack 1 is shown. The cell stack 1 comprises a first battery cell 3, which is prismatic here only as an example, and a second battery cell 5, which is prismatic here only as an example, as well as a cell connector 7. The first battery cell 3 has a cell terminal with a, for example in the 2 The illustrated contact plate 9 is for electrically contacting the first battery cell 3. The second battery cell 5 has a cell terminal with, for example, a 2 The illustrated contact plate 11 is used for the electrical contact of the second battery cell 5. The material of the cell connector 7 and the material of the contact plates 9 and 11 is shown here as an example only: an aluminum alloy.

The first battery cell 3 and the second battery cell 5 are stacked one behind the other along a stacking axis S. An intermediate cell material 13 of the cell stack 1 is arranged between the first battery cell 3 and the second battery cell 5. Here, the intermediate cell material 13 is merely an example of a sealed powder.

As this is shown in the 1 and 2 As shown, the cell connector 7 is located in a first joining area 21 or welded joint area of the first battery cell 3, which is here only by way of example cuboid or circular cylinder, and in a second joining area 23 or welded joint area of the first battery cell 3, which is here only by way of example cuboid or circular cylinder, each in a material-bonded connection, specifically in a laser welded connection, with the contact plate 9. As shown in the 1 and 2 As shown, the cell connector 5 is located in a first joining area 31 or weld joint area of the second battery cell 5, which is shown here only as an example of a cuboid or circular cylinder, and in a second, which is shown here The cell connector 7 has a thickness of, for example, 2 mm in the area of joining regions 21, 23, 31 and 33. The contact plate 9 has a thickness of, for example, 3 mm in the area of joining regions 21 and 23. The contact plate 11 has a thickness of, for example, 3 mm in the area of joining regions 31 and 33.

The following is based on the 1 to 7 a method for separating the material bond between the cell connector 5 and the first battery cell 3 in the first joining area 21, as described in particular in the 1 to 3 As shown, described. Naturally, this method is also applicable in the same way to the joining connections 23, 31 and 33, so that not only a single joining connection 21, 23, 31 and 33, but also the entire cell stack 1 can be separated using the method.

The process consists of a provisioning step and a separation step. The separation step follows the provisioning step in time.

In the provisioning step, cell stack 1 is provided first. As mentioned above, cell stack 1 includes at least cell connector 7, the first battery cell 3, and the second battery cell 5.

The separation step is then carried out. In the separation step, the cell connector 7 is separated from the first battery cell 3 by removing, preferably exclusively, material of the cell connector 7 and material of the contact plate 9 in the first joining area 21 and immediately adjacent to the first joining area 21 using an ultrashort pulse laser (USP laser) 41.

In the separation step, the material of the cell connector 7 and the material of the contact plate 9 are each removed starting from a cover surface 51 of the cell connector 7 in the depth direction T to a depth in the range of 2 mm to 6 mm, preferably in the range of 4 mm to 5 mm. The depth direction T extends perpendicular to the cover surface 51 that faces away from the first battery cell 3. In the separation step, the material of the cell connector 7 and the material of the contact plate 9 are removed fully automatically. This means that the ultrashort pulse laser 41 and/or the laser beam generated by the ultrashort pulse laser 41 are guided fully automatically during the separation step. The condition of the joining areas 21 and 31 after the separation step is described in the 4 and 5 shown.

The ultrashort pulse laser 41 can be a titanium-sapphire laser. The ultrashort pulse laser 41 belongs to a different laser class than, for example, a simply pulsed or high-frequency laser. This is because the ultrashort pulse laser 41 has a pulse duration in the range of ^10⁻¹⁸ seconds to ^10⁻¹⁵ seconds. For comparison, a standard pulsed laser has a pulse duration in the range of ^10⁻⁹ seconds to ^10⁻⁶ seconds. Due to the significantly shorter pulse duration of the ultrashort pulse laser 41, it exhibits a significantly higher laser beam intensity than, for example, a standard pulsed laser. Using the ultrashort pulse laser 41, the material is therefore vaporized or transitions directly into plasma during ablation or removal, unlike, for example, a standard pulsed laser which first heats, then melts, and then vaporizes it. In other words, the material sublimates under the influence of a laser beam generated by the ultrashort pulse laser 41. That is, it transitions directly from the solid to the liquid state. As a result, no heat is transferred to battery cells 3 and 5 during the separation step using the ultrashort pulse laser 41, and no heat-affected zone is formed because the material vaporizes faster than heat transfer or conduction to battery cells 3 and 5 can occur. Therefore, battery cells 3 and 5 do not heat up and are neither thermally nor mechanically damaged, as would otherwise happen, for example, during milling. These and other differences between the ultrashort pulse laser 41 and the pulsed or high-frequency standard laser are listed in the table below: Procedure parameters UKP laser qepulster standard laser Time scale pulse duration [s] ^10-18 to ^{10-15 10⁻⁹} to ^10⁻⁶ crystal Titanium:sapphire laser for example _CO2 ablation Direct evaporation (phase separation) Heating - Melting - Evaporation Heat stress no Heat-affected zone similar to welding Cracking no Microcracks due to thermal stress Material deformation small amount pronounced Structural parameters > 0.1 µm > 40 µm roughness > 1 µm > 2 µm Susceptibility to corrosion no Yes

As this is shown in the 6 As shown, the effective zone WZ or material ablation zone of the ultrashort pulse laser 41 or of the laser beam generated by the ultrashort pulse laser 41 has the shape of a circular cone. The circular cone-shaped effective zone WZ extends in the material to be removed or ablated such that one apex of the circular cone is located on the side facing away from the ultrashort pulse laser 41, as also shown in the 6 is shown. A further advantage of performing the separation step using an ultrashort pulse laser 41 is that, due to the shape of the effective zone WZ, a smooth surface 43 on the remaining material results in a surface 43 on the millimeter scale but structured on the micrometer scale when the material is removed. The structured surface 43 on the remaining material is in the 7 shown. Such a surface 43, smooth in the millimeter range and structured in the micrometer range, is ideally suited for re-welding one or the cell connector to the battery cells 3 and/or 5.

In principle, the material can be removed or ablated in various ways during the separation step, preferably layer by layer, with the ultrashort pulse laser 41 being used for the entire duration of the separation step or only for a limited time. For example, it is possible to first remove a large portion of the material to be removed with the pulsed or high-frequency standard laser and only towards the end of the separation step to use the ultrashort pulse laser 41 for material removal or ablation. This combines at least two advantages: the high material ablation rate of the pulsed or high-frequency standard laser compared to the ultrashort pulse laser 41, and the smooth, millimeter-scale, and micrometer-scale structured surface of the remaining material produced by the ultrashort pulse laser.

The ultrashort pulse laser 41 can be part of a laser cutting system 61. For the purpose of material removal, the laser cutting system 61 is operated with appropriate parameters so that the cutting step can be carried out with the laser cutting system 61. During the cutting step, the cell stack 1, that is, specifically the first battery cell 3 and the second battery cell 5, is clamped in a clamping device 63 of the laser cutting system 61. The laser cutting system 61 can have an extraction system (not shown). The extraction system allows the material vaporized during the cutting step to be extracted.

Reference symbol list

1

Cell stack

3

first battery cell

5

second battery cell

7

Cell connectors

9

Contact plate

11

Contact plate

13

Cellular intermediate material

21

first joining area of the first battery cell

23

second joining area of the first battery cell

31

first joining area of the second battery cell

33

second joining area of the second battery cell

41

Ultrashort pulse laser

43

textured surface

51

Cover surface

61

Laser cutting system

63

Clamping device

S

Stacking axis

T

Depth direction

WZ

Area of influence

Claims (9)

Method for separating a material connection between a cell connector and a battery cell, comprising: a provisioning step in which a first battery cell (3) is provided which is in a joining connection with a cell connector (7) in a first joining area (21) of the first battery cell (3), characterized in that the method comprises a separation step in which the cell connector (7) is separated from the first battery cell (3) by removing at least partially and/or temporarily material in the first joining area (21) of the first battery cell (3) and/or material adjacent to the first joining area (21) of the first battery cell (3) by means of a laser beam generated by an ultrashort pulse laser (41). Procedure according to Claim 1 , characterized in that during the separation step the material in the first joining area (21) of the first battery cell (3) and/or, preferably immediately adjacent, next to the first joining area (21) of the first battery cell (3), preferably layer by layer, is directly evaporated. Procedure according to Claim 1 or 2 , characterized in that the ultrashort pulse laser (41) has a pulse duration in the order of ^10⁻¹⁸ seconds to ^10⁻¹⁵ seconds, and/or that the ultrashort pulse laser (41) is a titanium:sapphire laser. Method according to one of the preceding claims, characterized in that in the separation step the material is first removed and/or ablated by means of a pulsed and/or high-frequency standard laser and only towards the end of the separation step by means of the laser beam generated by the ultrashort pulse laser (41). Procedure according to Claim 1 , characterized in that during the separation step the material of the cell connector (7) and/or a cell terminal of the first battery cell (3) and/or a contact plate (9) of a cell terminal of the first battery cell (3) is removed in the first joining area (21) or next to the first joining area (21) by means of ablation. Method according to one of the preceding claims, characterized in that in the separation step the cell connector (7) is separated from the first battery cell (3) by removing, preferably exclusively, material, preferably of the cell connector (7), next to the first joining area (21), which preferably directly adjoins the first joining area (21). Method according to one of the preceding claims, characterized in that in the provisioning step a second battery cell (5) is provided which is connected to the cell connector (7) in a first joining area (31) of the second battery cell (5). Method according to one of the preceding claims, characterized in that during the separation step the material in the first joining area (21) of the first battery cell (3) and/or next to the first joining area (21) of the first battery cell (3) is removed starting from a cover surface (51) of the cell connector (7) in the direction of the first battery cell (3) and/or in a depth direction (T) to a depth which lies in a range between 2 mm and 6 mm, preferably in a range of 4 mm to 5 mm, It is preferably provided that the cover surface (51) of the cell connector (7) faces away from the first battery cell (3). Method according to one of the preceding claims, characterized in that in the separation step the material in the first joining area (21) of the first battery cell (3) and/or next to the first joining area (21) of the first battery cell (3) is removed automatically, preferably fully automatically.