Compression pad with selectively permeable or semi-permeable separator layer and method for manufacturing a battery cell stack with said compression pad

Abstract

To provide a compression pad and a method for manufacturing a battery cell module that facilitates a process of inserting a battery cell packet into a housing.SOLUTION: A compression pad 3 for a battery cell stack includes an interior space having a filler material provided therein and a surface surrounding the interior space. The compression pad 3 is provided in various embodiments, at least part of a surface thereof of the compression pad 3 selectively including a permeable or semi-permeable separation layer. A method for manufacturing a battery cell module having the compression pad 3 is also provided.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a compression pad for a battery cell stack (battery cell packet). The present invention also relates to a method for manufacturing a battery cell stack having a compression pad that includes a selectively permeable or semi-permeable separator layer. [Background technology]

[0002] The driving range of an electric vehicle is primarily determined by the traction battery installed within it. Today, appropriately sized high-voltage batteries consisting of battery cell modules (also called battery modules), each of which contains several battery cells and each of which represents the smallest self-contained energy storage cell, are used to power modern electric vehicles. For example, the two-deck Performance Battery Plus used in some models of the Porsche Taycan comprises 33 cell modules, each consisting of 12 individual battery cells. Thus, the traction battery comprises a total of 396 battery cells, and lithium-ion batteries are used as the battery cells. The traction battery has a system voltage of 800 volts and a total capacity of 93.4 kWh.

[0003] Batteries are basically constructed using battery modules in which multiple cells are arranged in parallel, with a compression pad (also called a compression insert) placed between each two cells. The compression pads placed between the battery cells perform another important task: compensating for the increasing cell thickness (expansion). Expansion is the change in volume of a battery cell, especially a lithium-ion cell, which can be observed during charging and discharging, on the one hand, and on the other hand, caused by the aging of the battery cell on a slower time scale. Expansion is caused by structural changes in the active layer inside the battery cell, resulting from the redistribution of lithium ions in the cell. Expansion is particularly pronounced in the case of pouch cells, which are widely used in battery cell design. As mentioned above, placing compression pads between the battery cells in the stacking direction allows the pads to equalize the volumetric changes of the battery cells within the battery module through compression.

[0004] Compressible pads can also be used to accumulate force within a battery cell packet by clamping the battery cell packet into a housing (battery housing or module housing). To achieve good pretensioning, the outer dimensions of the battery cell packet usually differ only slightly from the inner dimensions of the housing. Pure foam pads that can be highly compressed are currently used as compression pads. Therefore, the battery cell packet is over-compressed during installation to temporarily reduce its dimensions and is then forced into the housing in this over-compressed state, which complicates the process of inserting the battery cell stack and results in a relatively complicated process. Next, the insertion process occurs using a certain insertion force, and the battery cell packet is pressed from the inside against the inside of the housing when inserted, resulting in frictional forces that can damage either the battery cells or the compression pad.

[0005] Patent document 1 describes a typical manufacturing process for a battery using a battery housing and multiple battery cells arranged adjacent to each other in the housing, in which a foam compression pad is placed between two adjacent battery cells, which is compressed during the assembly process and expanded after assembly.

[0006] Within the context of batteries, US Pat. No. 5,629,999 discloses the use of a separator to separate electrodes that expands when wetted.

[0007] Patent Document 3 discloses a battery using a plurality of adjacently arranged battery cells, in which a heat sink that also functions as a compression pad due to its elastic outer skin is arranged between every two adjacent battery cells. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2014 / 0141307 [Patent Document 2] British Patent Application Publication No. 1197468 [Patent Document 3] International Publication No. 2021 / 233778 Summary of the Invention [Problem to be solved by the invention]

[0009] Based on the compression pads known from the prior art, it has been found that the object of the present invention is to provide a compression pad and a corresponding manufacturing method that facilitates the process of inserting the battery cell packet into the housing. [Means for solving the problem]

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

[0011] According to the present invention, a compression pad for a battery cell stack is provided in various embodiments, the compression pad comprising an interior space in which a filler material is provided and a surface surrounding the interior space, at least a portion of the surface of the compression pad comprising a selectively permeable or semi-permeable separation layer, which may comprise, for example, a selectively permeable or semi-permeable membrane. For brevity, only semi-permeable separation layers are discussed below, although this can always include a selectively permeable separation layer.

[0012] The present invention achieves this basic objective by using a specific structure of compression pads, which in the assembled state have a smaller volume than in the later operating state, and no pressure needs to be actively applied to them. In other words, the assembled state can be understood as the deactivated state of the compression pad, while in the operating state, the compression pad according to the present invention is in an activated state. When the compression pad is in the assembled state, it is possible to build a cell stack that is small in size compared to its installation space in the housing and can therefore be easily inserted into a battery module or battery housing.

[0013] According to the invention, permeation is used to transition the compression pad according to the invention from the assembled state to the operational state. For this purpose, the compression pad according to the invention has a surface that at least partially comprises a semi-permeable separating layer, such as a corresponding membrane. The compression pad according to the invention may also be completely covered with the semi-permeable separating layer. Considering its mode of function, the compression pad according to the invention may also be called a permeable compression pad.

[0014] The compression pad according to the present invention can be incorporated into a cell stack placed in a suitable housing. Activation or transition of the compression pad according to the present invention to an operating state is performed within the housing by contacting a semi-permeable separating layer with a solvent. The semi-permeable separating layer can be permeable to the solvent so that the solvent can flow through the separating layer into the interior of the compression pad according to the present invention to equalize the concentration difference or difference between the chemical potentials of one or more substances in the phases separated by the membrane and their different concentrations inside and outside the semi-permeable separating layer. As a result, the compression pad according to the present invention increases in volume, thereby building up the necessary pressure on the battery cell to clamp it within the housing.

[0015] The internal space of the compression pad according to the present invention can accommodate the inflow fluid volume and, for that purpose, can include, for example, dispersed cavities. The initial flow of solvent into the internal space of the compression pad can be driven by capillary forces, in addition to the chemical potential or concentration difference of the separated phases when the membrane is wetted with the solvent. As the solvent flows into the internal space, osmotic pressure increases, allowing more solvent to flow from the outside through the semipermeable separating layer into the internal space of the compression pad. A substance may additionally be provided in the internal space of the compression pad according to the present invention, which is dissolved by the initial inflow solvent and creates a concentration gradient that further enhances the inflow of the solvent. In this case, the membrane may be impermeable to this substance. In the context of this specification, the solvent may be a fluid that is part of at least one of the phases separated by the membrane and can pass through the membrane to reduce the concentration difference or chemical potential difference between the two phases.

[0016] The portion of the surface of the compression pad that includes the semi-permeable separation layer may be an area of ​​the compression pad that does not rest against an inner battery cell of the battery cell stack constructed therewith, such as the upper and lower sides of a cube- or cushion-shaped compression pad, particularly when viewing the battery cell stack in transverse cross section.

[0017] The infiltration process, and thus the pressure build-up in the compression pad, can also be further caused by gases from the surroundings during assembly before the fluid is introduced into the cell in the subsequent filling process.

[0018] According to a further embodiment of the compression pad according to the invention, the filling material can comprise a substance that is elastic after the infiltration process, such as a plastic, in particular a porous plastic such as a foamed polymer. Alternatively, the filling material can comprise an elastomer, which can have perforations through which the solvent can flow. Before the infiltration process, the filling material does not have to be elastic but can be solid, or it can be elastic but have a greater material hardness.

[0019] According to a further embodiment of the compression pad according to the invention, the filler material may exhibit differences between chemical potentials and concentration differences between phases separated by a selectively permeable or semi-permeable separating layer.

[0020] The present invention also provides a method for manufacturing a battery cell module, which can also be used to create a higher-level entity of the battery cell module, i.e., a battery. In a first step, the method includes preparing a battery cell packet having an arrangement of battery cells, with a permeable compression pad according to one of the aforementioned embodiments being placed between every two battery cells. The battery cells may, for example, be in the form of a pouch cell. As a next step, the method includes inserting the battery cell packet into a housing, the battery cell packet being small compared to the installation space provided for the battery cell packet in the housing. The method then includes introducing a fluid or gas into the housing so that the fluid contacts the semi-permeable separating layer of the compression pad, flows through the separating layer, and into the compression pad to equalize the concentration difference. The fluid can be the aforementioned solvent.

[0021] According to a further embodiment of the manufacturing method according to the invention, the fluid can be a cooling medium. The battery cell module or the corresponding battery can be a directly cooled battery cell module or a directly cooled battery, characterized by a cooling system in which the cooling medium flows directly around the battery cells. The cooling medium also flows directly around the compression pads. Thus, in such an embodiment, a fluid is used that is also used as a cooling medium for the battery module or battery.

[0022] According to a further embodiment, a compression pad and Biryu The body can contain substances whose concentrations are higher in the compression pad than in the fluid. expensive In this case, the semi-permeable separating layer may simultaneously be impermeable to the substance, thereby establishing a concentration gradient that further drives fluid flow into the compression pad according to the present invention.

[0023] The present invention also presents the use of osmosis to induce expansion of compression pads disposed within the battery cell stack inside the housing and / or while fluid or gas flows around them.

[0024] It goes without saying that the features mentioned above and those to be described below may not only be used in the combinations specified respectively, but also in other combinations or alone without departing from the scope of the present invention.

[0025] Further advantages and configurations of the invention will become apparent from the description and accompanying drawings. [Brief explanation of the drawings]

[0026] [Figure 1] 1 illustrates the attachment of a battery cell stack having compression pads according to the present invention to a housing in an assembled state. [Figure 2] 1 illustrates a housing with an installed battery cell stack using compression pads in an operational state. DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 is a schematic diagram of a battery cell stack 4 immediately after it has been inserted into a housing 1. In the embodiment shown, the battery cell stack 4 comprises three battery cells 2 each separated from one another by a compression pad 3 according to the present invention. One such compression pad 3 is also provided at each end of the cell stack 4. Due to the compression pads 3 in the assembled, i.e. unexpanded state, the battery cell stack 4 is of small size and can be inserted relatively easily into the housing 1 without special measures.

[0028] FIG. 2 shows an operating battery cell stack 4 of an associated battery module or battery. Here, the compression pad 3 has been activated by passing a fluid 5 through a liquid cooling system flow path provided within the housing 1. Flow paths can be formed between the inner wall of the housing 1 and the surfaces of the battery cells 2 and compression pad 3, resulting in a directly cooled battery cell packet 4. As the fluid 5 flows through the housing 1, it contacts and flows through the semi-permeable separator layer of the compression pad 3, equalizing the concentration difference inside and outside the semi-permeable separator layer. As a result, the compression pad 3 increases in volume, thereby building up the necessary pressure on the battery cells 2 to clamp them within the housing 1. As FIG. 2 illustrates, there is no longer any axial free space between the battery cell stack 4 with the activated compression pad 3 and the inner wall of the housing 1.

[0029] As mentioned above, the compression pads can be activated by separately passing a fluid through the cooling system of the battery or battery module. Alternatively, a liquid cooling medium can function as the fluid so that a separate activation step is not required. To this end, the cooling medium can include additional additives to enhance penetration through the semi-permeable separating layer.

Claims

1. A compression pad (3) for a battery cell stack (4), comprising: an interior space within which a filler material is present; a surface surrounding the interior space, at least a portion of the surface of the compression pad comprising a selectively permeable or semi-permeable separating layer, the compression pad being configured to be expanded by osmosis.

2. 2. The compression pad (3) according to claim 1, wherein the filling material comprises a substance that is elastic after an infiltration process.

3. 3. A compression pad (3) according to claim 1 or 2, wherein the filling material exhibits a chemical potential difference or a concentration difference between phases separated by a selectively permeable or semi-permeable membrane.

4. 1. A method for manufacturing a battery cell module, comprising: providing a battery cell packet (4) including an arrangement of battery cells (2), wherein a compression pad (3) according to claim 1 or 2 is arranged between every two battery cells (2); inserting the battery cell packet (4) into the housing (1), the battery cell packet (4) being smaller than the installation space provided for the battery cell packet (4) in the housing (1); introducing a fluid or gas (5) into the housing (1) such that the fluid or gas contacts the selectively permeable or semi-permeable separating layer of the compression pad (3) and flows through the separating layer to the compression pad (3) to equalize the concentration difference.

5. The fluid (5) is a cooling medium. The method of claim 4.

6. 5. The method of claim 4, wherein the compression pad (3) and the fluid (5) contain a substance, the concentration of which is higher in the compression pad (3) than in the fluid (5).

7. The use of osmosis to cause expansion of the compression pad (3), which is disposed within the battery cell stack inside the housing, and in which at least a portion of the surface of the compression pad comprises a selectively permeable or semi-permeable separating layer around which fluid or gas flows.

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