Lid assembly of a battery cell with permeation function

Abstract

The invention relates to a lid assembly of a battery cell, comprising a base plate (2) with at least one terminal (3, 4) for electrical contacting, and a permeation element (5) which closes a through-opening (9) in the base plate (2), wherein the permeation element (5) is configured to allow permeation (A) of a gas from an inner side (2a) of the base plate (2) to an outer side (2b) of the base plate (2).

Description

[0001] November 17, 2025 Mattausch

[0002] Applicant: Carl Freudenberg KG, 69469 Weinheim

[0003] Cover assembly of a battery cell with permeation function

[0004] Description

[0005] The present invention relates to a lid assembly of a battery cell, in particular a prismatic cell with a specially designed permeation element and a battery cell with a permeation function.

[0006] Battery cells, such as prismatic cells, are used in rechargeable battery systems, for example, lithium-based or sodium-based cells. A battery cell comprises a casing, made of materials such as aluminum or steel, and a lid assembly that is attached to the casing and seals it. The lid assembly's function is to close and seal the battery casing to protect the surrounding environment from the cell chemistry. Furthermore, the lid assembly allows for the connection of electrodes inside the battery cell and electrical contacts outside the cell. During operation, aging processes within the battery cell lead to the formation of gases, creating an overpressure within the cell relative to the surrounding environment. Carbon dioxide is a particularly significant component of these gases, comprising more than 30% of the total gas produced.Furthermore, carbon monoxide, hydrogen, and / or hydrocarbon gases are formed. The overpressure inside the cell leads to undesirable deformation of the casing and, in extreme cases, to the battery cell rupturing at the rupture disc. Impairment of cell function due to the gases produced cannot be ruled out.

[0007] The object of the invention is to provide a lid assembly and a battery cell with a permeation function for gases generated inside the battery cell to the outside of the battery cell, while being easy and cost-effective to manufacture.

[0008] This problem is solved by a lid assembly having the features of claim 1 and a battery cell having the features of claims 17 and 18.

[0009] The dependent claims describe preferred embodiments of the invention. The inventive lid assembly of a battery cell with the features of claim 1, in contrast, has the advantage that a defined permeation is possible, so that gases which form inside the battery cell during operation can be vented to the outside by means of permeation. This prevents an undesirable pressure increase due to gases forming inside the battery cell. As a result, damage during operation and / or undesirable deformation of housing components of the battery cell due to internal pressure build-up caused by gas formation can be avoided.

[0010] Furthermore, the displacement of electrolyte and thus the drying out of the electrode stack inside the battery cell by the gases produced can be prevented. Electrolyte displacement can, in particular, lower the electrolyte level in the battery cell, leading to a reduction in the battery cell's lifespan. For this purpose, the cover assembly comprises a base plate with at least one terminal for electrically contacting the battery cell and a permeation element. The permeation element seals a through-opening in the base plate. The permeation element can be positioned above, below, or within the through-opening. The permeation element is designed to allow permeation of a gas, which may be generated inside the battery cell during operation, from an inner to an outer surface of the base plate.Permeation from the interior to the exterior of the battery cell is possible via the lid assembly. The resulting gas is, in particular, a gaseous degradation product of the battery cell, specifically carbon dioxide, carbon monoxide, hydrogen, and / or a hydrocarbon. Thus, according to the invention, targeted and defined permeation through the specifically designed permeation element can prevent an undesirable pressure increase and the drying out of components within the battery cell.

[0011] Surprisingly, it has been shown that the typical degradation processes in a battery cell, and thus possible gas release processes in the battery cell, occur sufficiently slowly, so that a pressure reduction in the battery cell and a gas transfer to the outside of the battery cell are possible through permeation processes that are inherently slow, using a permeation element.

[0012] Since the typical degradation processes and thus gas releases in the cell occur slowly, a permeation process using the permeation element according to the invention is sufficient for gas transfer and thus pressure reduction. Compared to the conventional valve design, a permeation element has the significant advantage that no solids can enter from the outside of the battery cell to the inside. This is possible with a valve, which is intermittently open. Furthermore, the permeation element has no moving parts like a valve.

[0013] Furthermore, permeation is a continuous process, so no significant pressure increases occur inside the battery cell, not even reaching the opening pressure of a valve. Since permeation depends on a pressure difference between the inside and outside of the battery cell, a self-regulating effect results: increased pressure differences lead to increased permeation, and vice versa.

[0014] Preferably, the permeation element is made of a nonpolar material. This ensures that, in particular, the polar degradation products of the cell permeate selectively better than polar water molecules from any moisture present on the outside into the interior of the cell.

[0015] Preferably, the permeation element has a water-repellent coating on a side facing the outside of the lid assembly. This prevents water, as a liquid, from wetting the outside and, due to the resulting higher partial pressure, from permeating more readily into the permeation element. Preferably, the permeation element is configured primarily to permeate carbon dioxide.

[0016] The coating is preferably a hydrophobic coating of a chemical nature or a lotus-effect coating on which liquids bead up due to microscopic geometry. More preferably, the coating is a permeation-reducing coating, for example, a coating of EVOH (ethylene-vinyl alcohol copolymer), to reduce permeation from the outside to the inside. Preferably, the permeation element is made of a polymer-based material.

[0017] Preferably, the permeation element is produced by means of a shaping process.

[0018] Furthermore, the permeation element preferably exhibits at a temperature of 30 °C and an internal overpressure of 5 x 10 5 Pa one permeation per day in an area of ​​10 cm 3 / mm 2 / h up to 1000 cm 3 / mm 2 / h up.

[0019] The permeation element is preferably made of an elastic material. This has the advantage that, as the pressure inside the battery cell increases, the permeation element can bulge outwards. This increases the surface area of ​​the permeation element on both the inside and outside, while simultaneously reducing the wall thickness of the permeation element, thus enabling increased permeation through the permeation element as the internal pressure rises. A bulging permeation element also serves as an indicator, allowing for easy detection from the outside of the battery cell of an increasing pressure inside the cell. Measures can then be taken, if necessary, to limit and / or reduce the pressure increase.

[0020] The permeation element is preferably made of an elastic polymer, in particular ethylene propylene diene monomer (EPDM) rubber or a fluorocarbon rubber (FKM) compound. More preferably, multilayer materials can also be used, the inner surface of which is coated with polymers compatible with the battery cell chemistry. This coating can be a separate layer or a layer.

[0021] Preferably, the permeation element is made of a film-like material. Particularly preferably, the permeation element has a thickness between 0.3 mm and 3.0 mm, especially between 0.5 mm and 2.5 mm.

[0022] If it can be ruled out that the permeation element comes into contact with the electrolyte, other materials are also conceivable, for example silicone elastomers, which preferably have a thin design and high elasticity.

[0023] Preferably, the permeation element is also configured as a bursting element. Surface structures, such as linear reductions in material thickness, can preferably be incorporated into the permeation element to provide mechanical weakening. This allows the permeation element to provide burst protection for the battery cell in addition to permeation. This eliminates the need for a rupture disc and simplifies the design of the cover assembly.

[0024] Preferably, the through-opening where the permeation element is located is also configured for filling the battery cell. This allows a filling opening, which in the prior art is currently only used for filling the battery cell, to be closed after filling with the permeation element, thus integrating a permeation option into the lid assembly or the battery cell. This eliminates the need for additional openings in the lid assembly. In particular, if the permeation element is also used as a bursting element, only one opening needs to be provided in the lid assembly, which, in addition to its filling and bursting functions, also accommodates the permeation element.

[0025] Furthermore, preferably, a material-bonded fixing of the permeation element, e.g. by welding a polymer-based permeation element, can result in a lower risk of the release of metal particles than with welding the filling opening with metallic lids as previously carried out in the prior art.

[0026] Preferably, the permeation element has a central opening in which a terminal of the battery cell is arranged. The terminal can be the anode or the cathode. Preferably, the base plate has two terminals, with a permeation element arranged at each of the two terminals.

[0027] Preferably, the permeation element also insulates a terminal (cathode) from the base plate, which is typically made of aluminum or another metal. Thus, the permeation element can additionally provide electrical insulation between the terminals and the base plate of the battery cell. Alternatively, and preferably, the permeation element can also have a predetermined electrical conductivity, for example, to establish a defined potential between one of the terminals (anode) of the battery cell and the housing. This can be achieved, for example, by suitable fillers and / or a suitable coating.

[0028] Preferably, the permeation element has an annular flange on an inner side of the base plate, with a portion of the annular flange exposed to the inner side. This ensures permeation even when the permeation element is used to fix a terminal.

[0029] Preferably, the permeation element is bonded to the base plate or to a component connected to the base plate. Alternatively, the permeation element is attached to the base plate by means of an adhesive bond.

[0030] Preferably, the permeation element has an internal cavity and projects outwards from the base plate. The permeation element is preferably circular in cross-section, so that a hollow cylindrical section with a lid projects outwards from the base plate. This increases the surface area of ​​the permeation element on the outside. Similarly, the hollow permeation element preferably projects inwards from the base plate. This also increases the surface area of ​​the permeation element on the inside.

[0031] According to a further preferred embodiment of the invention, the permeation element has a pleated structure that projects outwards from the base plate and has an internal cavity. This also increases the surface area of ​​the permeation element. The pleated structure can, for example, be designed like a bellows. Preferably, the permeation element has an annular flange for fixing it to an inner side of the base plate. A portion of the annular flange is exposed on the inner side to allow permeation through the permeation element from the inside out.

[0032] Preferably, the permeation element has a slope on its outer surface relative to the base plate. This slope allows any liquid water that accumulates on the outer surface of the permeation element to bead off.

[0033] Furthermore, the present invention relates to a battery cell with a cover assembly according to the invention. The battery cell is preferably a prismatic battery cell. Preferably, both terminals are arranged in the cover assembly, or the battery cell has two cover assemblies, with exactly one terminal arranged in each cover assembly.

[0034] The invention more preferably relates to a battery cell with a housing, wherein a permeation element is arranged in an opening in a housing region, which is configured to allow permeation of gases from an inside of the battery cell to an outside of the battery cell. The permeation element is preferably arranged on an upwardly facing side of the battery cell, so that gases generated inside the battery cell can collect at the permeation element above an electrolyte level.

[0035] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows:

[0036] Fig. 1 shows a schematic, perspective view of a battery cell with a cover assembly according to a first preferred embodiment of the invention.

[0037] Fig. 2 is a schematic top view of the cover assembly of Fig. 1 ,

[0038] Fig. 3 shows a schematic partial sectional view of a permeation element of the first embodiment,

[0039] Fig. 4 shows a schematic top view of a cover assembly according to a second embodiment of the invention,

[0040] Fig. 5 is a schematic top view of a cover assembly according to a third embodiment of the invention, Fig. 6 is a schematic partial sectional view of a cover assembly according to a fourth embodiment of the invention,

[0041] Fig. 7 shows a perspective view of a battery cell with a cover assembly according to a fifth embodiment of the invention,

[0042] Fig. 7a shows a sectional view of a permeation element of the cover assembly of Fig. 7.

[0043] Fig. 8 shows a perspective view of a battery cell with a cover assembly according to a sixth embodiment of the invention,

[0044] Fig. 9 shows a perspective view of a battery cell with a cover assembly according to a seventh embodiment of the invention, and

[0045] Fig. 10 shows a perspective view of a battery cell with a cover assembly according to an eighth embodiment.

[0046] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawing. In the figures, identical or functionally equivalent parts are designated by the same reference numerals.

[0047] Figures 1 to 3 show a cover assembly 1 and a battery cell 10 according to a first preferred embodiment of the invention.

[0048] The cover assembly 1 comprises, as shown in Fig. 1, a metallic base plate 2, preferably made of aluminum. Several through-openings are formed in the metallic base plate 2.

[0049] A first terminal 3 (cathode) is arranged in one of the through-holes in the base plate 2, and a second terminal 4 (anode) is arranged in a second through-hole. The first and second terminals 3, 4 are geometrically identical and preferably have a rectangular shape.

[0050] The base plate 2 also includes a filling opening 6, which is designed for filling the battery cell 10 with a liquid electrolyte. After filling, the filling opening 6 is sealed fluid-tight with a plug or the like.

[0051] Reference numeral 7 designates a burst zone located above a further through-opening in the base plate 2. Structures 70 in the form of grooves for reducing material thickness or similar are provided on the burst zone 7. This allows for emergency opening of the battery cell 10 in the event of thermal runaway by bursting these mechanical weak points.

[0052] The lid assembly 1 further comprises a permeation element 5, which is arranged in a through-opening 9. The through-opening 9 is located in the base plate 2, as can be seen from Figures 1 and 2, between the first terminal 3 and the bursting area 7.

[0053] The diameter of the permeation element 5 is larger than the diameter of the filling opening 6.

[0054] As can be seen in Fig. 3, the permeation element 5 has an annular flange 50. The permeation element 5 is fixed to the annular flange 50 on an inner surface 2a of the base plate 2. The permeation element 5 completely fills the through-opening 9.

[0055] Furthermore, a surface of the permeation element 5 facing an outer surface 2b of the base plate 2 is provided with a coating 8. The coating 8 is a water-repellent coating, which prevents water from accumulating on the surface of the permeation element and thus prevents water vapor from being accelerated through the permeation element 5 into the interior of the battery cell 10 by means of permeation. A permeation element with a slope on its outer surface, allowing liquid water to bead off, would also be conceivable in this context. For clarity, the coating 8 is shown in Fig. 3 with a significantly greater thickness than in reality. Preferably, the coating completely covers the permeation element 5 and also covers the interface between the permeation element 5 and the base plate 2.

[0056] Thus, permeation of gases, as indicated by arrow A in Fig. 3, can pass through the specifically designed permeation element 5 from an inner side of the base plate 2 to an outer side. This prevents excessive pressure build-up inside the battery cell 10. A typical gas that can be produced as a decomposition product during operation is carbon dioxide. Other gases include carbon monoxide, hydrogen, and hydrocarbons, with carbon dioxide typically having a volume fraction greater than 50 vol%. The permeation and thus the gas removal also prevents excessive drying of components inside the battery cell.

[0057] Flexible EPDM is preferably used as the material for the permeation element 5.

[0058] Tests have shown that, for example, 100 ml of carbon dioxide can escape through a permeation element 5 in the base plate 2 within a period of 45 days if the permeation element 5 has a diameter of 15 mm, a thickness of 0.5 mm, a temperature of 30 °C, and a partial pressure of approximately 350 kPa. This ensures reliable protection of the battery cell against an undesirable pressure increase, which could lead to deterioration of the battery cell's performance, deformation of the battery cell housing, and, in extreme cases, bursting, particularly at the bursting area 7.

[0059] By specifically designing the permeation element 5 with a permeation area and thickness (permeation path length), a defined permeation can be achieved over a predetermined period. It is also conceivable to design the permeation element for varying cell chemistries or different cell operating modes. For example, the gas composition can change.

[0060] Fig. 4 shows a lid assembly 1 according to a second embodiment of the invention. In contrast to the first embodiment, the bursting function is additionally integrated into the permeation element 5 in the second embodiment. Here, the permeation element 5 has structures 51 corresponding to the structures of the bursting zone. Thus, the permeation element also assumes the safety function of the battery cell and provides a bursting zone if the pressure in the battery cell exceeds a predetermined setpoint pressure and the bursting zone opens. Therefore, the permeation element 5 of the second embodiment has the additional function of a bursting element.

[0061] Fig. 5 shows a third embodiment, which no longer has a separate filling opening. Here, the through-opening 9, in which the permeation element 5 is arranged, is also designed for filling the interior of the battery cell with electrolyte. For this purpose, the lid assembly is first connected to the rest of the battery cell housing, and then the electrolyte is filled into the battery cell through the through-opening 9. The through-opening 9 is then closed with the permeation element 5. This has the further advantage that there is no risk of metal shavings or debris from a welding process involving a metal closure opening to the metal lid assembly entering the interior of the battery cell when the through-opening 9 is closed.

[0062] Fig. 6 shows a fourth embodiment of the invention, wherein the permeation element 5 serves as a fixing element for the first terminal 3. The permeation element 5 has a central opening 52 for receiving the first terminal 3. The first terminal 3 also has an annular flange 30, and the permeation element 5 is configured with an annular flange 50 such that the annular flange 50 of the permeation element 5 lies between the annular flange 30 of the first terminal 3 and the base plate 2. A further annular area 50a is exposed to the inside of the battery cell to allow sufficient permeation through the permeation element 5. Additionally, the permeation element 5 can also be made of a material that is electrically insulating to a defined degree, particularly between 100 and 100. 9Ohm, to the base plate 2. The permeation element 5 also provides electrical insulation for the first terminal 3. In this embodiment, the first terminal 3 is the cathode of the battery cell. The permeation element 5 also provides electrical insulation for the cathode. The second terminal 4 is the anode in this embodiment, which can be fixed in the same way as the cathode with another permeation element. The permeation element at the second terminal 4 (anode) is designed such that the permeation element 5 has electrically conductive properties at the anode. This can be achieved, for example, by adding electrically conductive additives to the material of the permeation element 5.

[0063] Figures 7 and 7a show a fifth embodiment of a cover assembly 1 and a battery cell 10, the fifth embodiment being essentially identical to the first embodiment. However, the fifth embodiment features a cylindrical section 53 projecting outwards from the base plate 2, with an internal cavity 53a (see Figure 7a) on the permeation element 5. This cylindrical section increases the surface area of ​​the permeation element 5 exposed to the outside, thus allowing significantly increased permeation with the same opening diameter or cell size.

[0064] Figure 8 shows a sixth embodiment in which the surface area of ​​the permeation element 5 is increased on the outside by a folded structure 54. The folded structure 54 also projects outwards beyond the base plate 2 and increases the surface area and thus the permeation.

[0065] Regarding the fifth and sixth embodiments, it should also be noted that due to increasing pressure in the battery cell, the permeation element can deform in such a way that its wall thickness is reduced. This can also lead to increased permeation through the permeation element, resulting in a faster pressure reduction in the battery cell.

[0066] Fig. 9 shows a seventh embodiment of the invention in which the battery cell 10 is configured alternatively. Here, two cover assemblies are provided, arranged on opposite narrow sides of the battery cell 10. A terminal is arranged on each of the cover assemblies. A permeation element 5 is provided on at least one of the two cover assemblies. The permeation openings should be positioned as high as possible so that the gas inside is in contact with the permeation element. As can also be seen in Fig. 9, a burst area 7 is arranged on a longitudinal narrow side of a housing part 11 of the battery cell 10. As can be seen in Fig. 9, the permeation element 5 is arranged adjacent to an end of the base plate 2 that is located at the top during operation.If gases are produced during the operation of the battery cell, these will rise to the top of the cell, so that the gases then come into contact with the inside of the permeation element 5. This allows permeation through the permeation element 5 to the outside.

[0067] Fig. 10 shows an eighth embodiment of the invention, which essentially corresponds to the seventh embodiment. In contrast to the seventh embodiment, in the eighth embodiment the permeation element is arranged on a housing part 11 of the battery cell 10. The permeation element also performs the bursting function and therefore has corresponding bursting-supporting structures 50. The permeation element 5 is arranged on a longitudinal narrow side of the housing part 11, which is located at the top when the battery cell is installed. At least one filling opening 6 is provided in one of the base plates 2. The filling opening 6 is also located at an end of the base plate 2 that is located at the top when the battery cell is installed, in order to enable the most complete filling of the battery cell possible.It should be noted that the filling opening can also be omitted and filling can take place via the through-opening for the permeation element 5 provided in the housing part 11, and the permeation element 5 is then only fixed to the housing part 11 after filling.

[0068] In addition to the above written description of the invention, explicit reference is hereby made to the graphic representation of the invention in the figures for its supplementary disclosure.

Claims

Claims 1. Cover assembly of a battery cell, comprising: - a base plate (2) with at least one terminal (3, 4) for electrical contacting, and - a permeation element (5) which closes a through-opening (9) in the base plate (2), - wherein the permeation element (5) is configured to allow permeation (A) of a gas from an inside (2a) of the base plate (2) to an outside (2b) of the base plate (2).

2. Lid assembly according to claim 1, wherein the permeation element is made of a nonpolar material.

3. Lid assembly according to claim 1 or 2, further comprising a water-repellent coating (8) which is arranged on an outer-facing surface of the permeation element (9).

4. Lid assembly according to one of the preceding claims, wherein the permeation element (5) is made of a polymer-based material.

5. Cover assembly according to one of the preceding claims, wherein the permeation element (5) is made of an elastic material.

6. Lid assembly according to claim 5, wherein the permeation element (5) is made of an elastic polymer, in particular EPDM.

7. Lid assembly according to one of the preceding claims, wherein the permeation element (5) is made of a foil material.

8. Lid assembly according to one of the preceding claims, wherein the permeation element (5) is additionally configured as a bursting element and in particular has structures (51) for bursting support.

9. Cover assembly according to one of the preceding claims, wherein the through-opening (9) is also provided for filling the battery cell with an electrolyte.

10. Cover assembly according to one of the preceding claims, wherein the permeation element (5) has a central opening (52) in which a terminal (3, 4) is arranged.

11. Cover assembly according to claim 10, wherein the permeation element (5) electrically insulates the terminal (3) from the base plate (2).

12. Cover assembly according to claim 11, wherein the permeation element (5) has an annular flange (50) on an inner side of the base plate (2), wherein a partial area (50a) of the annular flange is exposed to the inner side.

13. Cover assembly according to one of the preceding claims, wherein the permeation element (5) is fixed to the base plate or to a component connected to the base plate in a materially bonded manner.

14. Cover assembly according to one of the preceding claims, wherein the permeation element (5) with an inner cavity (53a) projects outwards from the base plate, in particular cylindrically.

15. Cover assembly according to one of the preceding claims, wherein the permeation element (5) has a folded structure (54).

16. Cover assembly according to one of the preceding claims, wherein the permeation element (5) is configured to increase its surface area and reduce its wall thickness based on pressure changes.

17. Battery cell comprising a lid assembly according to any of the preceding claims.

18. Battery cell with a housing part (11), wherein a permeation element (5) is arranged in an opening in the housing part (11), wherein the permeation element (5) is configured to allow permeation of gases from an inside of the battery cell to the outside and in particular comprising a lid assembly according to any one of claims 1 to 16.

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