WO2025262009A1

WO2025262009A1 - Multi-layer connector and method for making same

Info

Publication number: WO2025262009A1
Application number: PCT/EP2025/066833
Authority: WO
Inventors: Edvin List Clausen; Christian Delfs
Original assignee: Hydro Extruded Solutions AS
Current assignee: Hydro Extruded Solutions AS
Priority date: 2024-06-18
Filing date: 2025-06-17
Publication date: 2025-12-26
Anticipated expiration: 2026-12-18

Abstract

It is disclosed a connector (1) for providing a flexible connection between battery cells of an electric vehicle battery system, a battery module, a battery system, and a method for manufacturing the connector (1). The connector (1) comprises: - a flexible portion (11), and - two connection portions (12) arranged on opposite sides of the flexible portion (11), wherein the flexible portion (11) and the connection portions (12) are coextruded, and the flexible portion (11) as extruded comprises at least one hollow chamber (13).

Description

Multi-layer connector and method for making same

TECHNICAL FIELD

The present invention relates to a multi-layer connector for connecting battery cells, in particular for battery cells in automotive vehicles.

BACKGROUND ART

Battery systems in electric cars comprise a plurality of battery cells connected by connectors. In use, these cells will expand and retract, for example when the battery is charged/discharged. Because of this, the distance between the cells will constantly vary. In order not to destroy the cells or the connections to these, the connectors need to be flexible.

One example of such a flexible connector is disclosed in JPH10125301A.

However, the flexibility in connectors is usually on the expense of increased weight and or production costs. One way of improving the conductive capacity is to make connectors with several flexible layers.

One example of such a flexible connector is disclosed in DE102019216740A1.

However, the manufacturing of multi-layered connectors is more complicated and typically involves additional assembly and/or joining steps.

The present invention is directed to a method and a connector that may solve or at least reduce at least one of the aforementioned problems or challenges.

SUMMARY OF INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

The present disclosure relates to a connector for providing a flexible connection between battery cells of an electric vehicle battery system. The connector comprises: a flexible portion; and two connection portions arranged on opposite sides of the flexible portion. Wherein the flexible portion and the connection portions are coextruded, and the flexible portion as extruded comprises at least one hollow chamber.

An advantage of the connector is that it offers improved flexibility, its flexible portion allows the battery cells to expand and retract with less force being transferred over the connector. As compared to a 1-layer connector, the present connector can provide the same conductivity and weight yet with improved flexibility.

Since the connector has higher flexibility than solid 1-layer connectors, its size can be reduced. The smaller connector benefits from lower weight and requires less space.

A further advantage of the higher flexibility is that annealing in some cases can be avoided for a cold formed connector.

An advantage of the connector being coextruded, i.e. the flexible portion and the connection portions being extruded as one, is that it does not require assembling. The connector can be used as extruded, i.e. extruded to its final shape, or the connector can be formed to a required shape after extrusion.

The hollow chamber may have curved, zigzag, or wavy walls to provide flexibility. The shape can e.g. be selected according to available space in the battery system.

Each wall extends between two connection points of the hollow chamber. At the connection point the hollow chamber is connected to another part of the connector such as another hollow chamber, a connection portion, or an intermediate connection portion.

The connection portions are configured to facilitate connection to the battery cells of a battery system. The connection portions are typically straight and arranged in the same plane.

The hollow chamber may have walls that form offset curves, i.e. spaced apart curves that follow the same curvature.

The hollow chamber may have walls that are brought into contact with each other after extrusion. The walls may be brought together by a forming process, e.g. rolling.

The hollow chamber may be symmetric, e.g. by having walls that mirror each other on opposite sides of an imaginary line.

An imaginary line extending between two connection portions may intersect the hollow chamber. The hollow chamber would then typically have one wall on each side of the imaginary line. An advantage of this shape is eliminated or at least reduced moment at the connection to the batteries.

The hollow chamber may be arranged on one side of an imaginary line extending between two connection portions. The hollow chamber would then have both/all walls on the same side of the imaginary line.

The hollow chamber has a first wall thickness, and the connection portions have a second wall thickness. The first wall thickness may then be equal or smaller than the second wall thickness. E.g. the walls of the hollow chamber may have a combined wall thickness being equal to the wall thickness of one connection portion. As an example, the first wall thickness may be 0.5x the second wall thickness.

The walls of the hollow chamber typically have equal wall thicknesses. The walls of the hollow chamber preferably have the same length, i.e. the distance they cover between the connection points, such that their electrical resistance is equal.

The connection portions typically have equal wall thicknesses.

The connection portions are configured for connection to battery cells. They can be provided with an area for laser welding or a hole for bolting or other suitable features to facilitate connection to the battery cells.

The connector may comprise a plurality of flexible portions.

Each flexible portion may comprise a plurality of hollow chambers, wherein the hollow chambers are arranged in parallel and/or in series.

The connector may comprise an intermediate connection portion arranged between two flexible portions. The intermediate connection portion will typically have the same geometry as the connection portions. The connection portions will typically be parallel and arranged in the same plane. However, in some embodiments of the invention, the connection portions may be arranged in different planes and /or be angled relative each other. The positioning of the connection portions will typically be set to match the arrangement of the battery cells they are configured to be connected to.

The connector may be made of aluminium or an aluminium alloy, such as a 1XXX series aluminium alloy, preferably AA1050.

The chemical composition of a 1050 aluminium alloy is: Aluminium: 99.5% min, Copper: 0.05% max, Iron: 0.4% max, Magnesium: 0.05% max, Manganese: 0.05% max, Silicon: 0.25% max, Titanium: 0.03% max, Vanadium: 0.05% max, and Zinc: 0.05% max.

The hollow chamber may preferably have walls configured to carry the same current. To configure the walls to carry the same current, the resistance of the walls should be balanced. The resistance is given by the formula: where R is the resistance, p is the resistivity of the material, L is the length of the wall, and A is the cross-sectional area. If the walls have different lengths, the same current flow can be achieved by adapting their cross-sectional areas accordingly. The longest wall should be thicker, and the shortest wall should be thinner to balance the resistance. By balancing the resistance, the walls (which are made from the same material) will carry the same current.

The present disclosure also relates to a battery module for an electric vehicle. The battery module comprises at least one connector as described herein and a plurality of battery cells. The battery cells are connected by means of the at least one connector.

The present disclosure also relates to a battery system for an electric vehicle. The battery system comprises a plurality of battery modules as described herein.

The present disclosure also relates to a method of manufacturing a connector as described herein. The method comprises the steps of providing an extrusion billet made of aluminium or an aluminium alloy; extruding a hollow profile comprising a flexible portion(s) and connection portions arranged on opposite sides of the flexible portion(s), wherein the flexible portion comprises at least one hollow chamber; and optionally forming the hollow profile to a predefined shape of a connector. If the as extruded hollow profile corresponds to the predefined shape of the connector, i.e. the required final shape of the connector, the forming step is not required.

The hollow extruded profile typically has a length (in the extrusion direction) that is longer than the required length of the connector, which allows the hollow profile to be cut into a plurality of connectors.

The method may comprise the step of cold rolling or cold forming the flexible portion and/or the connection portions. As the wall thickness can be reduced during cold rolling after extrusion, a thicker material can be extruded and thereby achieve higher productivity. The extruded profile will in this case obtain higher yield stresses and can then be cut/stamped without burrs as the elongation of the material is significantly reduced. Furthermore, the extrusion tolerances can be optimized.

The method may comprise the step of bending the flexible portion and/or the connection portions to obtain the predefined shape. The cold rolling, cold forming, and bending performed subsequent the extrusion process does not cause an intermetallic connection of the walls of the flexible portion.

The method may comprise the step of annealing the flexible portion and/or the connection portions after forming, preferably by means of induction.

BRIEF DESCRIPTION OF DRAWINGS

The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where:

Fig. 1 is a cross-sectional view of a prior art connector;

Fig. 2 is a cross-sectional view of a connector according to the invention;

Fig. 3 is a cross-sectional view of a connector according to the invention;

Fig. 4 is a cross-sectional view of a connector according to the invention;

Fig. 5 is a cross-sectional view of a connector according to the invention;

Fig. 6 is a cross-sectional view of a connector according to the invention;

Fig. 7 is a cross-sectional view of a connector according to the invention;

Fig. 8 is a cross-sectional view of a connector according to the invention;

Fig. 9 is a cross-sectional view of a connector according to the invention;

Fig. 10 is a cross-sectional view of a connector according to the invention;

Fig. 11 is a cross-sectional view of a connector according to the invention;

Fig. 12a-c are cross-sectional views of a sequence illustrating how the connector of Fig. 5 can be made by a process comprising extrusion, cold rolling and bending;

Fig. 13 is a side view of a cold rolling process leading to the state illustrated in Fig. 12b;

Fig. 14 is a cross-sectional view of Fig. 13;

Fig. 15 is a perspective view showing a finite element method (FEM) simulation performed on a prior art connector; and

Fig. 16 is a perspective view showing the same FEM simulation as in Fig. 15 performed on a connector according to the invention.

DETAILED DESCRIPTION

In the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings.

In the preceding description, various aspects of the disclosure have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the invention and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

Fig. 1 shows a cross-section view of a prior art connector 2 of a solid 1-layer construction. The prior art connector 2 is configured to connect battery cells of a battery system, typically used in electric vehicles.

The prior art connector 2 comprises two connection portions 22 configured for connection to one battery cell each. In use, these cells will expand and retract, for example when the battery is charged/discharged. Because of this, the distance between the cells will constantly vary. In order not to destroy the cells or the connections to these, the prior art connector 2 has a flexible portion 21 arranged between the connection portions 22.

Fig. 2 is a cross-sectional view of a connector 1 according to the invention. This connector 1 is also configured to provide a flexible connection between battery cells and therefore also comprises a flexible portion 11 and two connection portions 12 arranged on opposite sides of the flexible portion 11. However, this connector 1 has a hollow flexible portion 11, i.e. the flexible portion 11 comprises a hollow chamber 13. The hollow flexible portion 13 provides more flexibility than a solid flexible portion 21.

In Fig. 2, the hollow chamber 13 is defined by two curved walls 14. The shape of the walls 14 allow movement of the two connection portions 12 relative each other as the battery cells expand and retract. The walls 14 are curved in opposite directions (upwards and downwards in the figure) and form a symmetric hollow chamber 13. By imagining a line extending between the two connection portions 12, that imaginary line would intersect the hollow section 13 and split it into two identical portions. The symmetric hollow chamber 13 allows relative movement of the connection portions 12 without causing them to bend. The connection portions 12 can thus move with the battery cells without inducing a moment on them.

The connector 1 in Fig. 2 is made by an extrusion process in which the extruded profile comprises the flexible portion 11 and the connection portions 12, i.e. the flexible portion 11 and the connection portions 12 are coextruded. As such, the connection portions 12 and the flexible portion 11 is made of the same material. The preferred material is aluminium or an aluminium alloy, such as a 1XXX series aluminium alloy, preferably AA1050.

Fig. 2 illustrates a typical as extruded shape that may be intended to undergo further forming processes before reaching the final shape of the connector 1, or an as extruded shape that corresponds to the final shape of the connector 1, i.e. a shape that is not intended to undergo further forming processes.

The walls 14 may have a combined wall thickness corresponding to the wall thickness of the connection portion 12. The wall thickness of the wall 14 may thus be 0.5x the wall thickness of the connection portion 12.

In Fig. 2, the walls 14 extend between the two connection portions 12. The points where the two walls 14 meet and connect to the connection portion 12 can be considered connection points. These are not however the points where battery cells are connected.

Fig. 3 is a cross-sectional view of a connector 1 according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the shape of the flexible portion 11. In Fig. 3, the flexible portion 11 has a hollow chamber 13 wherein the walls 14 are bent after extrusion to form a zigzag pattern or at least a part of a zigzag pattern. As such, the walls 14 may have straight portions. In the embodiment of Fig. 3, the straight parts of the walls 14 are angled relative the connection portions 12.

Fig. 4 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the shape of the flexible portion 11. In Fig. 4, the flexible portion 11 has a hollow chamber 13 wherein the walls 14 have different lengths. The upper wall 14 in the figure is longer than the lower wall 14. This could also be the other way around, such that the upper wall 14 was the shortest. As a result, the two walls 14 have different curvatures.

The shape illustrated in Fig. 4 could be used when space is limited in the battery system. Since the hollow chamber 13 is not symmetric this shape may not prevent moment on the battery cells to the same extent as the shape of Figs. 2 and 3. The wall thicknesses can preferably be adapted to ensure the same current flow in both walls 14.

Fig. 5 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the shape of the flexible portion 11. Whereas the shapes of Figs. 2-4 illustrate typical as extruded shapes, the flexible portion 11 in Fig. 5 is typically achieved by subsequent forming after extrusion.

By again imagining a line extending between the two connection portions 12, that imaginary line would not intersect the hollow chamber 13 in Fig. 5. The shape illustrated in Fig. 5 with the hollow chamber 13 arranged on one side of the imaginary line can be more space efficient than the shapes of Figs. 2-4.

In Fig. 5, the walls 14 form offset curves that are partially brought into contact with each other. As a result, the volume of the hollow chamber 13 is significantly reduced as compared to the shape in Fig. 2. In some embodiments of the invention, the walls 14 can be completely brought into contact with each other. Forming after extrusion may be performed in-line with the extrusion process.

Fig. 6 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the shape of the flexible portion 11. In Fig. 6, the flexible portion 11 has two hollow chambers 13 arranged in parallel. The two hollow chambers 13 are defined by three walls 14, thus having one common wall 14. This common wall 14 is wave shaped and the two other walls 14 are curved like the walls 14 in Fig. 2. As illustrated in Fig. 6, the walls 14 may have the same length even though they have different shapes.

The two hollow chambers 13 are symmetric in Fig. 6. In other embodiments of the invention the flexible portion 11 may comprise asymmetric hollow chambers 13.

Fig. 7 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the number of flexible portions 11 and the addition of an intermediate connection portion 12'. In Fig. 7, the connector 1 comprises two flexible portions 11 arranged in series, two connecting portions 12, and an intermediate connecting portion 12'.

In Fig. 7 , the two flexible portions 11 are arranged on opposite sides of the intermediate connection portion 12'. The intermediate connection portion 12' is configured for connection to a battery cell. Thus, the connector in Fig. 7 is configured to connect three battery cells. In the example of Fig. 7 , the flexible portions 11 are identical and comprise one hollow chamber 13 each. In other embodiments of the invention the flexible portions 11 may be different from each other and/or comprise a plurality of hollow chambers 13.

Fig. 8 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 7. The difference is the shape of the flexible portions 11. In Fig. 8, the flexible portions 11 have hollow chambers 13 wherein the walls 14 are bent like the walls 14 in Fig. 3.

Fig. 9 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 7. The difference is the shape of the flexible portions 11. In Fig. 9, the flexible portions 11 have hollow chambers 13 wherein the walls 14 are bent like the walls 14 in Fig. 5.

Fig. 10 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 2. The difference is the shape of the flexible portion 11. In Fig. 10, the flexible portion 11 comprises two hollow chambers 13 arranged in series. The hollow chambers 13 are symmetrical and have the same shape as the hollow chamber of Fig. 2.

Fig. 11 is a cross-sectional view of a connector according to the invention. This connector 1 has substantially all the same features as the connector in Fig. 10. The difference is the shape of the flexible portion 11. In Fig. 11, the walls 14 of each hollow chamber 13 form offset curves that are partially brought into contact with each other in the same way as in Fig. 5. The two hollow chambers 13 are symmetric but curved in opposite directions. Together the two hollow chambers 13 form the flexible portion 11 which has a wave shape.

By again imagining a line extending between the two connection portions 12, that imaginary line would not intersect the hollow chambers 13 in Fig. 11.

Fig. 12a-c are cross-sectional views of a sequence illustrating how a connector 1 according to the invention can be made.

In Fig. 12a, an extrusion billet made of aluminium or an aluminium alloy has been extruded to a geometry similar to the connector 1 in Fig. 3. The extruded profile can be several meters long, whereas the connector 1 only needs to be some millimetres long. A plurality of connectors 1 can thus be made from one extruded profile. The illustrated cross-sectional views are perpendicular to this length direction.

The connector 1 of Fig. 12a could be used as extruded. However, further forming may provide some advantages.

In Fig. 12b, the connector 1 from Fig. 12a has been cold rolled. As compared to the geometry of Fig. 12a, the connector in Fig. 12b has a reduced wall thickness. In Fig. 12b the entire connector has been cold rolled; however, in some embodiments of the invention only a part of the connector 1 can be cold formed. Higher productivity in the extrusion process can thus be achieved.

In Fig. 12 b, the walls 14 are straight (i.e. not bent or curved) and will therefore not provide the desired flexibility. If the entire connector 1 is cold rolled, further forming of the connector 1 will therefore typically be required. Subsequent the cold rolling, the connector 1 will typically be formed to a predetermined final shape. In Fig. 12c, the connector 1 from Fig. 12b has been formed to a geometry similar to the connector 1 in Fig. 5. This forming does not cause an intermetallic connection between the walls 14 of the flexible portion 11, neither does the cold rolling in Figs. 12b, 13 and 14.

After the connector 1 has been formed to the geometry in Fig. 12c, it can be annealed, e.g. by means of induction. Either the entire connector 1 can be annealed, or alternatively only parts of the connector 1 can be annealed.

Fig. 13 is a side view of a cold rolling process performed between the states of Fig. 12a and Fig. 12b.

Fig. 14 is a cross-sectional view of the cold rolling process taking place in Fig. 13. The cold rolling may preferably be performed in a manner preventing cold welding of the walls 14.

Fig. 15 is a perspective view showing a finite element method (FEM) simulation performed on a prior art connector 2. The connector 2 in Fig. 15 is similar to the connector 2 of Fig. 1 and the simulation reflects how an expected movement of the battery cells will affect the connector 2.

Fig. 16 is a perspective view showing the same FEM simulation as in Fig. 15 performed on a connector 1 according to the invention. The connector 1 in Fig. 16 is the same as the connector 1 in Fig. 5, which has a comparable shape as the prior art connector 2 of Fig. 15, i.e. two connection portions 12 arranged in the same plane and an upwardly curved flexible portion 11. The flexible portion 11 of the connector 1 in Fig. 16 will reduce stress levels with approximately 40 % as compared to the prior art connector 2.

LIST OF REFERENCE NUMBERS

1 Connector

11 Flexible portion

12 Connection portion

12' Intermediate connection portion

13 Hollow chamber

14 Wall

2 Prior art connector

21 Flexible portion, of prior art connector

22 Connection portion, of prior art connector

3 Rolls

Claims

1. A connector (1) for providing a flexible connection between battery cells of an electric vehicle battery system, wherein the connector (1) comprises:

- a flexible portion (11); and

- two connection portions (12) arranged on opposite sides of the flexible portion (11); characterized in that the flexible portion (11) and the connection portions (12) are coextruded, and the flexible portion (11) as extruded comprises at least one hollow chamber (13).

2. The connector (1) according to claim 1, wherein the hollow chamber (13) has curved, zigzag, or wavy walls (14).

3. The connector (1) according to claim 1 or 2, wherein the hollow chamber (13) has walls (14) that form offset curves.

4. The connector (1) according to claim 1 or 2, wherein the hollow chamber (13) is symmetric.

5. The connector (1) according to any one of claims 1-4, wherein an imaginary line extends between two connection portions (12), and wherein the imaginary line intersects the hollow chamber (13).

6. The connector (1) according to any one of claims 1-3, wherein an imaginary line extends between two connection portions (12), and wherein the hollow chamber (13) is arranged on one side of the imaginary line.

7. The connector (1) according to any one of claims 1-6, wherein the hollow chamber (13) has a first wall thickness and the connection portions (12) have a second wall thickness; wherein the first wall thickness is equal or smaller than the second wall thickness.

8. The connector (1) according to any one of claims 1-7, wherein the flexible portion (11) comprises a plurality of hollow chambers (13), wherein the hollow chambers (13) are arranged in parallel and/or in series.

9. The connector (1) according to any one of claims 1-8, wherein the connector (1) comprises a plurality of flexible portions (11).

10. The connector (1) according to claim 9, wherein the connector (1) comprises an intermediate connection portion (12') arranged between two flexible portions (11).

11. The connector (1) according to any one of claims 1-10, wherein the connector is made of a 1XXX series aluminium alloy, preferably AA1050.

12. The connector (1) according to any one of the preceding claims, wherein the hollow chamber (13) has walls (14) configured to carry the same current.

13. A battery module for a battery system, wherein the battery module comprises:

- at least one connector (1) according to any one of the preceding claims; and - a plurality of battery cells; wherein the battery cells are connected by means of the at least one connector (1).

14. A battery system for an electric vehicle, wherein the battery system comprises:

- a plurality of battery modules according to claim 13.

15. A method of manufacturing a connector (1) according to any one of claims 1-12, wherein the method comprises the steps of:

- providing an extrusion billet made of aluminium or an aluminium alloy;

- extruding a hollow profile comprising a flexible portion (11) and two connection portions (12) arranged on opposite sides of the flexible portion (11), wherein the flexible portion (11) comprises at least one hollow chamber (13); and optionally

- forming the hollow profile to a predefined shape of a connector (1).

16. The method according to claim 15, wherein the method comprises the step of:

- cold rolling or cold forming the flexible portion (11) and/or the connection portions (12).

17. The method according to any one of claims 15-16, wherein the method comprises the step of: - bending the flexible portion (11) and/or the connection portions (12) to obtain the predefined shape.

18. The method according to any one of claims 15-17, wherein the method comprises the step of:

- annealing the flexible portion (11) and/or the connection portions (12) after forming, preferably by means of induction.