Compression Pad with Shape Memory Function and Related Manufacturing Method

Abstract

To provide a compression pad for facilitating an assembly process and a corresponding manufacturing method.SOLUTION: A compression pad 1 has a shape memory function relative to a battery cell stack and includes an internal space in which a filler material is present. The internal space is further filled with media 2 or the media 2 is machined in the filler material. The media 2 holds the compression pad 1 in a compressed shape as compared to a shape the compression pad 1 would take without the media 2. Furthermore, a method for manufacturing the compression pad 1 having the shape memory function as well as a method for manufacturing a battery cell module are provided.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention specifically relates to a compression pad having a shape memory function for use in a battery cell stack (battery cell packet). Further, the present invention relates to a manufacturing method for such a compression pad and additionally a battery cell stack having a compression pad with a shape memory function.

Background Art

[0002] The driving range of electric vehicles is mainly determined by the traction batteries attached to them. Today, high-voltage batteries of appropriate size are used to power modern electric vehicles consisting of battery cell modules (also referred to as battery modules), each of which in turn contains several battery cells, each representing the smallest self-sufficient energy storage cell. For example, the dual performance battery plus used in some models of the Porsche Taycan contains 33 cell modules, each consisting of 12 individual battery cells. Thus, the traction battery comprises a total of 396 battery cells, with lithium-ion accumulators being used as the battery cells. The traction battery has a system voltage of 800 volts and a total capacity of 93.4 kWh.

[0003] Generally, to construct a battery, a battery module is used in which a plurality of cells are arranged in parallel and compression pads (also referred to as compression inserts) are respectively arranged between two cells. The compression pads arranged between the battery cells perform a more important task, that is, providing an equilibrium against the growing cell thickness (swelling). Swelling is the volume change of the battery cell, especially the lithium-ion cell, which can be observed on the one hand during charging and discharging, and on the other hand can be observed on a slower time scale due to the aging of the battery cell. Swelling is caused by the structural change of the active layer in the battery cell and the rearrangement of lithium ions occurring therein. Swelling is particularly prominent in the case of pouch cells, which is a widely used design for battery cells. As described above, by arranging the compression pads in the stacking direction between the battery cells, the volume change of the battery cells in the battery module can be corrected compressively.

[0004] In addition, due to the compressible pads, force may be accumulated in the battery cell package, which may cause distortion in the housing (battery or module housing). To achieve good preloading, the outer dimensions of the battery cell package are usually only slightly different from the inner dimensions of the housing. Currently, pure foaming pads that can be greatly compressed are used as compression pads. Therefore, during installation, the battery cell packets are stacked to temporarily reduce their dimensions, and in this stacked state, the battery cell packets are pushed into the housing, which complicates the operation of sliding the battery cell stack, thereby making the process side relatively complicated. Next, when the battery cell packet is inserted from the inside, it is pressed against the inside of the housing, thereby generating frictional force, and in certain situations, it may damage either the battery cell or the compression pad, so the insertion process is performed under a specific insertion force.

[0005] Patent Document 1 discloses a battery having a battery case and a plurality of battery cells arranged adjacent to each other, and a foaming compression pad is arranged between two adjacent battery cells, which is compressed during the assembly process and expands after assembly.

[0006] Patent Document 2 discloses a battery having a plurality of battery cells and a plurality of compression and thermal protection pads disposed between two adjacent battery cells, and the compression pads contract as the temperature rises.

[0007] A battery cell packet is known from Patent Document 3, in which a plurality of battery cells are pushed between two terminal elements, and compression pads are disposed between the terminal elements and the battery cells.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Proceeding from the method of assembling a compression pad and a battery cell stack in a housing known from the prior art, the problem addressed by the present invention can be regarded as providing a compression pad and a corresponding manufacturing method that facilitate the assembly process.

Means for Solving the Problems

[0010] This problem is solved by the subject matter of the independent claims. Further preferred embodiments can be found in the dependent claims.

[0011] The present invention is based on the compression of a compression pad to a predetermined extent that occurs prior to the formation of a battery cell stack. This degree of compression is fixed by the holding force of an additional medium or material and is maintained, in particular, during the formation of the battery cell stack and its assembly in the housing. The predetermined degree of the compressed compression pad is selected such that the formed battery cell stack is smaller with respect to the design space provided for this purpose in the housing and can thus be more easily inserted into the housing. Subsequently, the compression pad expands or spreads within the housing and accumulates a desired compressive force on the battery cells to fix them in place within the housing.

[0012] Stabilizing or "freezing" the compressed state of the compression pad is achieved by filling or immersing the compression pad with a medium or by incorporating the medium as an additive into the filler material of the compression pad. In the first case, the medium can be the cooling medium of the battery's liquid cooling system, in particular, a directly cooled battery where the battery module is directly perfused by the cooling medium inside the housing. This medium becomes hard or very firm at a specific temperature, which is below the operating temperature of the battery cell stack during its intended use in the battery. On the other hand, at higher temperatures, particularly within the range of the operating temperature of the battery cell stack, the medium is soft or liquid. In other words, the strength is low at this temperature.

[0013] To provide the compression pad with a shape memory function, the compression pad is pressed together with the medium to a predetermined, for example, minimum thickness and cooled in this state, whereby the medium hardens or becomes firm and holds the compression pad in this state. This state is self-sustainedly compressed, i.e., without any further external force, the compression pad can be installed in the battery cell stack. As a result, the battery cell stack is smaller and can be more easily inserted into the battery module or the battery housing, especially without a tool for accumulating pressure on the battery cell stack.

[0014] In this case, the necessary temperature stroke can be carried out either from a temperature higher than room temperature (for example, a temperature within the operating temperature range of the battery cell stack) to room temperature or a lower temperature, or from a temperature within the range of room temperature to a lower temperature than room temperature, depending on the selected medium.

[0015] The shape memory function of the compression pad according to the present invention is exhibited when the compression pad stabilized in a compressed state by the medium is heated to a temperature at which the medium softens or liquefies and its holding force is reduced. From a specific temperature, when the expansion force of the filler material in the compression pad increases, it expands again according to its shape memory. The expanding compression pad compresses the battery cells in the battery module or the battery housing, thereby completing the assembly step.

[0016] The operating mechanism of the present invention can be illustrated based on a sponge as a compression pad and water as a medium. To manufacture a sponge having a shape memory function, first, water is filled / saturated, compressed, and frozen. After the completion of the freezing process, the compressed sponge is held in its shape as long as the water frozen in the sponge is thin. Then, the frozen sponge is pushed into its installation position in the housing. Since the sponge is smaller, it is easy to insert into the housing, and there are gaps on the left and right of the sponge with respect to the inner wall of the housing. Due to the high ambient room temperature, the sponge thaws and tries to return to its original shape. As a result, the sponge expands and presses against the inner wall of the housing.

[0017] According to the present invention, there is first provided a compression pad having a shape memory function for a battery cell stack, which includes an internal space in which a filler material is present. The internal space is further filled with the filler material or the medium is machined into the filler material. The medium, due to its strength, holds the compression pad in a compressed shape as compared to the shape that the compression pad would take without the medium. As a result, the state of the compression pad described herein corresponds to the compressed state, and the compressed state is fixed, so to speak, by the cooled medium.

[0018] According to a further embodiment of the compression pad, the filler can be elastic. For example, the filler material can include plastics such as foamed plastics.

[0019] According to a further embodiment of the compression pad, the medium can include the cooling medium of a battery's liquid cooling system. The cooling medium can be a non-conductive liquid having properties suitable for a cooling medium (heat capacity, viscosity, flash point). When using the cooling medium as the medium, the cooling fluid is released from the filler material to its environment and then released into the battery's cooling medium after installation and subsequent delayed compression, so that the same cooling medium used in an electric vehicle in the cooling system can be conveniently used. As a result, for example, when the escaped cooling medium was present in the internal space of the compression pad, undesirable contamination of the cooling medium circulating in the cooling circuit of the electric vehicle by other liquids can be avoided.

[0020] According to the present invention, a method for manufacturing a compression pad having a shape memory function for a battery cell stack is further provided. The method first includes inserting a medium into the compression pad. Inserting the medium can include filling the compression pad with the medium or immersing the compression pad in the medium. Alternatively, the insertion step can also include, for example, incorporating the medium in the form of an additive into the compression pad in its filler material.

[0021] In the next step, the manufacturing method according to the present invention includes compressing the compression pad filled with the medium. The compression pad is brought to a target size, for example, with respect to its expansion along the stacking direction of the battery cells in the battery cell stack.

[0022] In a further step, the method according to the invention includes cooling the compression pad to a temperature at which the compression pad can be held in its compressed shape by the cooling medium when no external force is acting. In other words, the cooling of the medium located in the compression pad results in a change in its material properties towards an increase in the holding force. The medium becomes harder or stronger such that its holding force exceeds the expansion force of the filler material of the compression pad, thereby being able to remain in the compressed shape.

[0023] The medium may also be used as a cryogenic storage device, extending the time until the compression pad warms up more slowly and thereby expands. For example, the compression pad can be compressed and frozen, but due to its low thermal mass, it rapidly heats up and expands through the ambient temperature and can then be installed at the end position. If this compression pad is pre-saturated in the cooling medium, its thermal mass can be increased. Repeating this can extend the time until the compression pad is heated and expands.

[0024] According to a further embodiment of the manufacturing method according to the invention, the medium can include the cooling medium of a liquid cooling system of a battery.

[0025] According to a further embodiment of the manufacturing method according to the invention, the medium can be an additive incorporated inside the compression pad. Thus, the additive can be incorporated into the manufacture of the compression pad or the filler material of the compression pad itself.

[0026] According to a further embodiment of the manufacturing method according to the invention, the temperature at which the compression pad is cooled can be below the operating temperature of the battery cell stack.

[0027] According to the present invention, there is further provided a method for manufacturing a battery cell module based on a battery cell stack to which a compression pad according to the present invention is attached. The method includes first providing a battery cell packet having an arrangement of battery cells, each compression pad being disposed between two battery cells manufactured according to the aforementioned method embodiments for manufacturing a compression pad according to the present invention.

[0028] The method further includes inserting the battery cell package into a housing, the battery cell package being smaller with respect to the design space provided within the housing.

[0029] According to a further embodiment of the manufacturing method according to the present invention, the method can further include heating the compression pad to a temperature at which the medium can no longer hold the compression pad in its compressed shape. In other words, the method according to the present invention includes expanding the compression pad by supplying heat, thereby reducing the strength of the medium.

[0030] According to a further embodiment of the manufacturing method according to the present invention, the heating of the compression pad can be caused by a fluid (liquid or gas) flowing through the battery cell module. For example, when the battery cells are assembled within the battery cell module, this can be caused by warm air passing through the battery cell module.

[0031] It goes without saying that the features described above and the features to be described hereinafter can be used not only within the specified combinations without departing from the scope of the present invention, but also within other combinations or alone.

[0032] Additional advantages and configurations of the present invention are obtained from the present specification and the accompanying drawings.

Brief Description of the Drawings

[0033]

Figure 1A

Figure 1B

Figure 1C

Figure 2A

Figure 2B

Figure 2C

DETAILED DESCRIPTION OF THE INVENTION

[0034] The method for manufacturing a compression pad having a shape memory function begins with providing a suitable compression pad 1. In this pad, a medium 2 that provides a holding force in a later phase of the method is already incorporated, or the compression pad 1 is filled or saturated with this medium 2.

[0035] In FIG. 1A, the start of compression is shown. For this purpose, the compression pad 1 with the medium 2 can be placed between two press arms 3 of a press. In FIG. 1B, the compression pad 1 is compressed to the desired extent. In FIG. 1C, there is a temperature drop while the compression pad 1 remains in the compressed state. The reduction in heat changes the material properties of the medium 2, and as a result, the medium 2 becomes stronger or stiffer, exerting a holding force that cancels out the expansion force of the compression pad 1 relative to its original dimensions (FIG. 1A), and exceeding the holding force from a specific temperature. When a stable state is achieved where the compression pad 1 remains in its compressed state to hold the medium 2 together, the manufacturing operation is completed and the compressed compression pad 1 can be removed.

[0036] The compressed compression pad 1 can then be used to manufacture a battery cell module or a battery, as shown in FIGS. 2A-2C. In FIG. 2A, a battery cell stack 5 is first constructed, which in the illustrated example comprises four battery cells 4, and the compressed compression pad 1 abuts laterally against each battery cell 4. The battery cells 4 may, for example, be adhered to the compression pad 1 or may be temporarily surrounded by a support structure such as a mesh sheath. FIG. 2B shows the assembly step in which the battery cell stack 5 is inserted into the housing 6 to form a battery cell module 8 or a battery. Since the battery cell stack 5 is smaller, it can be inserted very simply into the side walls of the battery stack 5 and the housing 6, especially without friction. During the assembly phase, a gap 7 is provided between the battery cell stack 5 and the side wall of the housing 6. After the battery cell stack 5 has been inserted into the housing 6, an expansion step of the compression pad 1 is carried out. The compression pad is heated passively through the room temperature or actively by passing a fluid through a cooling channel 9, such as the cooling fluid of the liquid cooling system of the battery module 8. As a result of the heating, the material properties of the medium 2 change such that its holding force decreases and the expansion force of the compression pad 1 prevails. As a result, the compression pad 1, which is compressed or pushed together, expands and then simultaneously presses against the battery cells 4 in the housing 6 (the gap 7 disappears).

[0037] The operation by which the medium 2 loses its holding force due to heat so that the compressed compression pad 1 can expand back to its original state can be initiated by different processes such as softening, melting, or sublimation again.

Claims

1. A method for manufacturing a battery cell module (8), comprising: providing a compression pad (1) having a shape memory function, wherein a medium (2) is additionally introduced into the internal space of the compression pad (1) in the presence of a filler material, or the medium (2) is incorporated as an additive into the filler material; compressing the compression pad (1) into which the medium (2) has been introduced or incorporated; and cooling the compressed compression pad (1) to a temperature at which its compressed shape can be maintained when no external force acts thereon; providing a battery cell package (5) including an arrangement of battery cells (4), wherein the cooled compression pad (1) is disposed between two of the battery cells (4) respectively; inserting the battery cell package (5) into a housing (6), wherein the battery cell package (5) is smaller than the design space provided for the battery cell package (5) in the housing (6); heating the compression pad (1) until the medium (2) can no longer hold the compression pad (1) in its compressed shape; A method comprising the above steps.

2. The method according to claim 1, wherein the filler material is elastic.

3. The method according to claim 1 or 2, wherein the medium (2) comprises a cooling medium of a liquid cooling system of the battery.

4. The method according to claim 1 or 2, wherein the temperature in the step of cooling the compression pad (1) is lower than the operating temperature of the battery cell package (5).

5. The method according to claim 1 or 2, wherein the compression pad (1) is actively heated by a fluid flowing through the battery cell module (8).

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