Battery cell

Abstract

The invention relates to a battery cell (1) having a housing (2) which is encapsulated with active material, which is provided with a pressure relief element (6) on a side (3) of the housing (2), wherein the side (3) with the pressure relief element (6) is designed with a thermal insulation layer in the form of a potting compound (7) which is cured after casting and adheres to the housing (2). The battery cell according to the invention is characterized in that the potting compound (7) is arranged at least in the region of the area which is larger than the pressure relief element (6), and a flow guide element (8) is embedded in the potting compound (7), a partial region of which covers the pressure relief element (6).

Description

Technical Field

[0001] The present invention relates to a battery cell having a housing encapsulating active material, the housing having an overpressure relief element on the side of the housing. Background Technology

[0002] Battery cells with overpressure relief elements, such as those designed as explosion-proof devices, are known in the general prior art. These overpressure relief elements are used to ensure safety in the event of thermal runaway in an adjacent battery cell, such as a lithium-ion battery cell. In this context, thermal runaway is also referred to as “thermal propagation.” The overpressure relief element thus helps reduce the pressure within the battery cell. The explosion-proof element ruptures, or an overpressure relief element designed in other forms opens, allowing gases generated within the battery cell to escape. This process is also known as “cell venting.” Typically, these vented gases are very hot and may also be accompanied by flames and / or high-temperature particles or sparks. These particles may be designed to be abrasive and / or conductive. Therefore, they often also pose a threat to adjacent battery cells and components in the environment, and thus DE 10 2021 000 029 A1, which is cited herein by way of example only, describes a multi-layered protection element for a battery. This multi-layered protection element acts as a filter to trap flames, sparks, and high-temperature particles, thereby minimizing the hazards posed by the vented gases.

[0003] Furthermore, in general practice, the following structure is commonly accepted: attempting to protect adjacent battery cells from the high-temperature gases emitted by a runaway battery cell via a thermal insulation layer. In practice, this is typically achieved by coating the side of the overpressure relief element, which is highly susceptible to thermal effects, with a layer of silicate (mica). To ensure that this layer also cracks upon the response of the overpressure relief element and is not breached from below by high-temperature gases, it must be perforated in the area of ​​the overpressure relief element. This is complex in practice, and the perforation weakens the insulation effect precisely in areas where insulation is particularly critical. Moreover, this natural material is relatively expensive due to the complexity of its mining and preparation, especially for such applications.

[0004] Therefore, the applicant's unpublished German application DE 10 2023 128 877 A1 describes a thermal insulation layer made of potting compound adhered to the side of the battery casing to protect overvoltage relief elements from thermal effects primarily in the event of thermal runaway of adjacent batteries. A similar structure is also described in unpublished German application DE 10 2023 128 876 A1.

[0005] See also DE 20 20210 017 245 U1. This application describes a structure in which potting compound covers an overpressure relief element. An elastic pad is arranged in the middle, which is compressed during venting to create space for the flowing gas.

[0006] That is, if thermal runaway occurs in a battery cell, the exhaust gas flows out of the cell via the cell's overpressure relief element. After passing through the vent, this high-temperature, abrasive, and conductive particle-rich exhaust gas is distributed throughout the battery. This is based on the existing environmental geometry and pressure conditions. However, in certain areas, it is desirable to guide the exhaust gas out in a defined direction to avoid negative impacts on other battery cells and components. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a battery cell with an improved housing that is simple, efficient and inexpensive to manufacture, and provides a high level of protection against thermal effects in the event of thermal runaway in adjacent battery cells and components.

[0008] According to the invention, this objective is achieved by a battery cell having the features of claim 1. Advantageous designs and improvements are given in the dependent claims.

[0009] The battery cell according to the invention includes a housing encapsulating active material, one side of which has an overpressure relief element. Similar to the aforementioned unpublished German application DE 10 2023 128 877 A1, the side with the overpressure relief element is designed to have a heat insulation layer, which is in the form of a potting compound that is cured after casting and adhered to the housing.

[0010] According to the present invention, the potting compound is now arranged at least in a portion of the overpressure relief element with an area larger than the overpressure relief element, and a flow guiding element is embedded in the potting compound, a portion of which covers the overpressure relief element. This structure is very simple yet highly efficient. When the potting compound is applied to the side of the housing with the overpressure relief element, the flow guiding element can be simply inserted into the potting compound as an insert. If heat propagation occurs in the battery cell, the overpressure relief element, along with the potting compound and the flow guiding element, is torn apart. However, since the area of ​​the potting compound is larger than the overpressure relief element, a portion of the potting compound always remains on the housing and adheres to the housing. The flow guiding element (with only a portion of its area covering the overpressure relief element) then adheres to the housing along with the potting compound. Therefore, on such a side of the overpressure relief element, opposite the area of ​​the adhered potting compound and the area of ​​the flow guiding element adhered therein, a gap or opening is formed through which the exhaust gas can flow out. Therefore, by geometrically arranging the flow guiding elements within the potting compound relative to the position of the overpressure relief element, the direction of the exhaust gas flow can be structurally predetermined, thereby protecting components sensitive to, for example, electricity or heat from the effects of the exhaust gas. The flow guiding elements reinforcing the potting compound on the side of the overpressure relief element can be embedded in the potting compound in a space-saving manner.

[0011] In the battery cell according to the invention, the current-conducting element is formed of a metallic material. This metallic material is particularly thermally stable enough to withstand exhaust gases for a sufficiently long time together with the potting compound.

[0012] According to a highly advantageous improvement of the battery cell of the invention, the side of the casing with the overpressure relief element can be completely covered by potting compound. In particular, when the hot potting compound is designed to be not only electrically insulating but also thermally insulating, potting compound covering the entire surface of, for example, the upper side of the battery cell or its casing enables ideal protective functions.

[0013] Another highly advantageous design option is to configure the flow guiding element as elastic, or to have an elastic region in the transition area from the housing to the overpressure relief element. This allows for very easy lifting of the composite structure consisting of the potting compound and the flow guiding element, while maintaining adhesion to the housing on one side to achieve the desired effect. The elastic, or at least partially elastic, flow guiding element further reinforces the potting compound, preventing it from tearing completely around the overpressure relief element.

[0014] Preferably, the flow guiding element can be designed as a mesh element. This mesh element allows for a particularly good mechanical bond with the potting compound embedded therein, while being flexible enough to optimally achieve the composite structure consisting of the potting compound and the flow guiding element that guides the flow of exhaust gas. Furthermore, the mesh element is typically very thin and lightweight.

[0015] Another highly advantageous design of the battery cell according to the invention can be further configured such that the side having the overvoltage relief element additionally has cell terminals connected to the battery terminals, wherein these cell terminals protrude beyond the potting compound in the height direction. That is, the cell terminals always protrude beyond the potting compound, and even if the potting compound covers the entire side, the cell terminals are still easily accessible for electrical connection of the battery cell.

[0016] In principle, this structure can be implemented in any type of cell housing. For prismatic cell housings, this structure is particularly advantageous when the cross-section of the cell is rectangular, especially when one end face, particularly the larger end face, is used as the side equipped with the heat insulation layer.

[0017] For potting compounds, a variety of materials can be envisioned, and suitable fillers can be fitted to these materials to enable the potting compound to withstand particularly high thermal loads. Thus, polyurethane-based potting compounds can be used, for example. Silicone-based potting compounds have proven particularly suitable. The advantage of such silicone-based potting compounds is that silicon undergoes ceramization or vitrification on its surface upon contact with hot gases, thereby further optimizing the protective effect through the action of hot gases. Therefore, high-temperature, flammable exhaust gases will not reach the areas of the particularly vulnerable overvoltage relief elements of adjacent battery cells, thus reliably preventing or at least significantly delaying the spread of thermal events throughout the battery. Here, the material sold by Wacker under the brand name Elastosil, designated CM185, has proven particularly suitable. This material is referred to as "silicone rubber." Attached Figure Description

[0018] Advantageous design options and improvements are also derived from the embodiments, which are shown in more detail below with reference to the accompanying drawings.

[0019] in: Figure 1 A three-dimensional view showing a possible first embodiment of a battery cell according to the present invention; Figure 2 A possible second embodiment of the battery cell according to the present invention is shown; Figure 3 A schematic cross-sectional view showing the region through which the overvoltage discharge element passes through the battery cell; and Figure 4 The overvoltage discharge element of the battery cell is shown in response to the following. Figure 3 Similar illustrations. Detailed Implementation

[0020] exist Figure 1The illustration illustratively shows a prismatic battery cell 1 in the form of a lithium-ion battery cell. This cell includes a cell housing (denoted 2), on which two cell terminals 4 and 5, connected to battery electrodes, are arranged on the upper side 3. An overpressure relief element (denoted 6) is arranged between these two cell terminals 4 and 5. This overpressure relief element 6 can be, for example, a vent plate having a circular cross-section or, here preferably, an elliptical cross-section. The vent plate is connected only to the material surrounding the cell housing 2 or the side 3 via a correspondingly weakened material. Therefore, a predetermined break point is provided around or substantially around the vent plate in the circumferential direction. Typically, such a cell housing 2 is now made of a material with low elongation at break, low tensile strength, and low fracture strength, so that by determining the size of the predetermined break point, the internal pressure of the cell housing 2 at which the overpressure relief element 6 breaks can be determined. Thus, when a thermal event occurs in the battery cell 1, the pressure can be reduced by the broken overpressure relief element 6, specifically by releasing so-called exhaust gases through the resulting opening.

[0021] To protect the overpressure relief element 6, which is not visible here, from the high-temperature exhaust gases emitted by adjacent battery cells 1 that have experienced a thermal event, the side 3 of the cell housing 2 is provided with potting compound 7, shown here as a cross-shaded line, also known as potting material. This potting compound 7 is poured into the side 8 in liquid form, then adheres there and hardens. The potting compound bonds to the material of the cell housing 2 or the side 3, and thus reliably protects the area beneath it containing the overpressure relief element 6 when the potting compound 7 is swept by high-temperature gases, flames, abrasives, and / or high-temperature particles.

[0022] Specifically, silicone materials, such as the Elastosil CM185 mentioned above, can be used as potting compound 7. This material has ideal properties so that it can reliably crack in the event of a thermal response to the overpressure relief element 6 beneath the potting compound 7 without creating greater resistance to the outflowing gas than the overpressure relief element 6. On the other hand, this material used for potting compound 7 readily undergoes surface vitrification or ceramization when high-temperature gas passes through or is subjected to flames or high-temperature particles, thus providing excellent thermal protection for the underlying components. In addition to this material, other silicone-based or polyurethane potting compounds are also conceivable, with the addition of suitable fillers where appropriate to improve thermal insulation.

[0023] Figure 2 Showing from Figure 1 The structure is already known, in which only a small area of ​​side 3 is provided with potting compound 7. For reasons described below, this area with potting material should in any way be larger than the overpressure relief element 6.

[0024] Figure 3 A schematic cross-section of the region containing the overpressure relief element 6 and the potting material or potting compound 7, passing directly through the monocoque 2, is shown. Here, another important component is clearly visible: the flow guiding element 8, which is an insert within the potting compound 7. The bottom layer shown in the figure is the material of the monocoque 2. The overpressure relief element 6 is implemented by introducing two predetermined break points 9. The potting compound 7 is visible on the material of the monocoque 2, again indicated by cross-shading. The aforementioned flow guiding element 8 is inserted into this potting compound 7. It is surrounded by the potting compound 7. It can be designed, for example, as a metal mesh element, allowing it to be further permeated by the potting compound 7, forming a mechanically stable and load-bearing composite structure. Here, the material, geometry, and design specifications of the flow guiding element 8 can be adjusted according to the specific application, such as regarding temperature resistance, elasticity, size, and possibly its predetermined break points.

[0025] To achieve the desired function, the flow guiding element 8 now extends approximately from the area next to the overpressure relief element 6 shown on the left side here. Figure 3 The area to the right of the overpressure relief element 6 is the predetermined fracture point 9. If a thermal event occurs in the battery cell 1, the internal pressure increases until the predetermined fracture point 9 of the overpressure relief element 6 ruptures. Because the flow guiding element 8 used to reinforce the potting compound 7 is located to the right of the overpressure relief element 6 ( Figure 3 Above the predetermined fracture point 9 (as shown), the structure breaks on the left side. Additionally, this may also support the idea that the predetermined fracture point 9 was designed not to be completely circumferential, but rather interrupted on the right side, for example.

[0026] Along with the predetermined fracture point 9 (left), the potting compound 7 also cracks, as described in the applicant's unpublished German application (document number 10 2023 128 877.6). The flow guiding element 8 is pushed upward by the cracked potting compound 7. However, its right end remains fixed to the monolithic housing 2 along with the potting compound 7. This results in... Figure 4 As shown, the flow guiding element 8 deforms in the manner indicated by its elasticity or the elastic region above the predetermined break point 9 on the right side within the flow guiding element 8. Therefore, the exhaust gas indicated by arrow V in the figure flows primarily to the right. In the structural design exemplarily shown here, the area to the left of the dashed line is thus effectively protected from the exhaust gas. Of course, structural modifications can be made to this design to guide the exhaust gas to the right, backward, or forward.

Claims

1. A battery cell (1) having a housing (2) encapsulating an active material, the housing (2) having an overpressure relief element (6) on a side (3) of the housing, wherein the side (3) having the overpressure relief element (6) is designed to have a heat insulation layer, the heat insulation layer being in the form of a potting compound (7) that is cured after casting and adhered to the housing (2), wherein the potting compound (7) is arranged at least in a portion of the area larger than the overpressure relief element (6), and a flow guiding element (8) is embedded in the potting compound (7), a portion of the flow guiding element covering the overpressure relief element (6), and wherein the flow guiding element (8) is formed of a metallic material.

2. The battery cell (1) according to claim 1. Its features are, The side (3) of the housing (2) having the overpressure relief element (6) is completely covered by the potting compound.

3. The battery cell (1) according to claim 1 or 2. Its features are, The flow guiding element (8) is designed to be elastic, or has an elastic region in the transition area from the housing (2) to the overpressure relief element (6).

4. The battery cell (1) according to claim 1, 2 or 3. Its features are, The flow guiding element (8) is designed as a grid element.

5. The battery cell (1) according to any one of claims 1 to 4. Its features are, The side (3) having the overpressure relief element (6) additionally has a single terminal (4, 5) connected to the battery terminal, wherein the single terminal (4, 5) protrudes from the potting compound (7) in the height direction.

6. The battery cell (1) according to any one of claims 1 to 5. Its features are, The shell (2) is designed as a prismatic shell.

7. The battery cell (1) according to any one of claims 1 to 6. Its features are, The potting compound (7) is formed based on polyurethane or preferably based on silicone resin.

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