Battery cell

Abstract

The invention relates to a battery cell (14) having a cell casing (26) in which a number of electrodes (20) are arranged. The cell casing (26) has an opening (28) that is is covered by a gas-permeable membrane (30), the exterior of the membrane (30) being covered by a cover element (34) in order to restrict the ingress of matter into the cell casing (26).

Description

[0001] Description

[0002] Battery cell

[0003] The invention relates to a battery cell. The battery cell has a cell housing in which several electrodes are arranged.

[0004] Motor vehicles are increasingly being powered at least partially by an electric motor, so that they are designed as electric vehicles or hybrid vehicles. A high-voltage battery comprising several individual battery modules is typically used to power the electric motor. The battery modules are usually identical in construction and are electrically connected in series and / or parallel, so that the electrical voltage applied to the high-voltage battery corresponds to a multiple of the electrical voltage provided by each of the battery modules. Each battery module, in turn, comprises several battery cells, which are usually arranged in a common module housing and are electrically connected in series and / or parallel.

[0005] Each of the battery cells, in turn, usually comprises several galvanic elements. These each have two electrodes, namely an anode and a cathode, as well as a separator arranged between them and an electrolyte with freely moving charge carriers. A liquid, for example, is used as such an electrolyte. In an alternative, the battery cell is designed as a solid-state battery, and the electrolyte is in the form of a solid. The anode and the cathode, which form the electrodes of the battery cell, usually comprise a carrier that acts as a current collector. An active material is usually attached to this carrier, which is a component of a layer applied to the carrier, which is also referred to as a collector. In this case, the electrolyte may already be present in the layer, or it may be added subsequently. At the very least, however, the active material is designed to absorb the working ions, e.g.Lithium-ion batteries are suitable. Depending on whether they are used as an anode or cathode, a different material is used for the carrier and a different type of layer material.

[0006] To protect the galvanic elements, they are usually arranged in a cell housing of the battery cell, which in some cases is also referred to as a cell cup. The cell housing also protects the electrolyte in particular, but also other components, from environmental influences. To ensure that a comparatively large capacity is provided by each battery cell, several such galvanic elements, usually up to 100, are usually arranged in the common cell housing. To use the available space comparatively efficiently and to simplify production, the individual components of the galvanic elements are designed to be flat and stacked on top of one another in one stacking direction, forming an essentially cuboid-shaped cell stack.In an alternative embodiment, for example, the separator is designed in a strip shape and is provided with several electrodes on opposite sides. The strip is wound into a roll, in particular a so-called "jelly roll."

[0007] The cell housing is shaped depending on the arrangement of the galvanic elements used. It can be rigid and made of aluminum, for example. The cell housing's shape is, for example, cuboidal. Such a battery cell is also called a prismatic cell. In an alternative embodiment, the cell housing is constructed using a foil wrapped around the galvanic elements. Such a battery cell is also called a pouch cell.

[0008] During operation of the battery cell, i.e. during charging and discharging, it is possible that gases are released due to unwanted chemical reactions. This increases the pressure within the cell casing, which on the one hand can lead to poorer ion conduction in some electrode areas, leading to a loss of performance of the battery cell. On the other hand, it is possible that the cell casing is deformed due to the increased pressure, which in particular has a mechanical impact on the area surrounding the battery cell. At a comparatively high pressure, the cell casing bursts, allowing the electrolyte to leak out and making the entire battery cell unusable. It is also possible that unwanted chemical reactions between the individual components of the battery cell and the environment occur.

[0009] To minimize such gas formation, a special combination of the individual materials of the electrodes and the electrolyte is required, which on the one hand increases manufacturing costs. On the other hand, the choice of less reactive electrode materials is often accompanied by a reduction in capacity and / or energy density. Alternatively, additional elements are present, for example, in the cell housing, by means of which the resulting gases are bound and / or converted. Due to the additional elements, however, the installation space and also the weight of the battery cell are increased, which therefore reduces the energy density. The object of the invention is to provide a particularly suitable battery cell, wherein operational reliability and / or energy density are advantageously increased.

[0010] According to the invention, this object is achieved by the features of claim 1. Advantageous further developments and refinements are the subject of the subclaims.

[0011] The battery cell is in particular designed to be rechargeable and is expediently a secondary battery. Preferably, in its intended state, the battery cell is a component of a motor vehicle. The battery cell is suitable, in particular provided and configured for this purpose. In its intended state, the battery cell is, for example, a component of an energy storage device of the motor vehicle which has a plurality of such battery cells. Preferably, the battery cells are divided into a plurality of battery modules which are in turn structurally identical to one another. The battery cells are in particular arranged in a housing of the energy storage device or the respective battery module and are electrically connected to one another in parallel and / or in series. Thus, the electrical voltage applied to the energy storage device / battery module is a multiple of the electrical voltage provided by each of the battery cells.Conveniently, all battery cells are identical to each other, which simplifies production.

[0012] The housing of the energy storage device or the respective battery module, which thus in particular forms a composite of such battery cells, is preferably made of a metal, for example a steel such as stainless steel, or an aluminum alloy. For production, for example, a die-casting process, deep-drawing process, casting molding, or extrusion molding is used. In particular, the housing of the energy storage device or the respective battery module is designed to be closed. An interface is expediently incorporated into the housing of the energy storage device or the respective battery module, which forms a connection of the energy storage device / battery module. The interface is electrically connected to the battery cells, so that electrical energy can be fed in and / or withdrawn from the battery cells from outside the energy storage device, provided a corresponding plug is plugged into the connection.

[0013] The motor vehicle is preferably land-based and preferably has a number of wheels, of which at least one, suitably several or all, are driven by a drive. In particular, one, preferably several, of the wheels is designed to be steerable. This makes it possible to move the motor vehicle independently of a specific roadway, for example rails or the like. In this case, it is expediently possible to position the motor vehicle essentially arbitrarily on a roadway, which is made in particular of asphalt, tar, or concrete. The motor vehicle is, for example, a commercial vehicle, such as a lorry (truck) or a bus. However, the motor vehicle is particularly preferably a passenger car (car).

[0014] The motor vehicle is expediently moved by means of the drive. For example, the drive, in particular the main drive, is at least partially electric, and the motor vehicle is, for example, an electric vehicle. The electric motor is operated, for example, by means of the energy storage device, which is suitably designed as a high-voltage battery. A direct electrical voltage is expediently provided by the high-voltage battery, wherein the electrical voltage is, for example, between 200 V and 800 V and, for example, substantially 400 V. Preferably, an electrical converter is arranged between the energy storage device and the electric motor, by means of which the current supply to the electric motor is adjusted. In an alternative, the drive additionally has an internal combustion engine, so that the motor vehicle is designed as a hybrid motor vehicle.In an alternative, the energy storage device is used to feed a low-voltage electrical system of the motor vehicle, and the energy storage device is used to provide, in particular, an electrical direct voltage of 12 V, 24 V or 48 V.

[0015] In another alternative, the battery cell is a component of an industrial truck, an industrial plant, or a handheld device, such as a tool, in particular a cordless screwdriver. In another alternative, the battery cell is a component of a power supply and is used there, for example, as a so-called buffer battery. In another alternative, the battery cell is a component of a portable device, such as a portable mobile phone or other wearable. It is also possible to use such a battery cell in camping, model making, or other outdoor activities.

[0016] The battery cell has a plurality of electrodes, for example two or preferably more. In particular, the electrodes are divided into anodes and cathodes, with expediently half of the electrodes forming the anodes and the other half the cathodes. However, there is preferably one more anode than cathodes. Particularly preferably, all anodes and all cathodes are identical in construction, which simplifies production. The electrodes are, for example, flat in design and in particular have a carrier, which is also referred to as a conductor. In particular, the respective carrier is formed by means of a metal foil which is coated on one or both sides with a layer, at least in sections. Aluminum is used, for example, as the metal of the carrier / conductor of the cathodes, and copper is used as the metal of the conductor of the anodes.

[0017] The layer has a thickness of less than 1 mm. The supports expediently have a thickness of less than 0.1 mm. Preferably, the respective layer comprises an active material, a binder and / or a conductive additive, such as conductive carbon black. The active material serves to absorb / release working ions, such as lithium ions, and is suitable, intended and configured for this purpose. The active material used for the cathode can be, for example, a lithium metal oxide, such as lithium cobalt (III) oxide (LiCoO2), NMC, for example NMC622 or NMC811, NCA, LNMO or Li-rich materials. Alternatives include olivines such as LFP. For the anode, for example, graphite, Si-based materials or mixtures thereof, lithium metal or LTO are used.

[0018] In particular, the electrodes are essentially rectangular. The electrodes are, for example, stacked one above the other to form a cell stack, wherein the stacking direction is perpendicular to the direction of extension of the electrodes, which are arranged parallel to one another. The anodes and cathodes preferably alternate in the stacking direction of the cell stack. Advantageously, a separator of the cell stack is arranged between adjacent electrodes, i.e. in particular between one of the anodes and one of the cathodes, which separator is preferably also designed to be flat. For example, all separators are structurally identical to one another. In particular, the electrodes are stacked essentially flush one above the other, wherein, for example, all anodes protrude at least slightly beyond the cathodes. Due to the stacking of the electrodes, the cell stack is therefore also essentially cuboid-shaped.

[0019] In an alternative embodiment, for example, all anodes, all cathodes, or the separator are formed by means of a common band, or they are attached to a common band. The band itself is rolled into a cylindrical shape or the like, forming a so-called "jelly roll."

[0020] The battery cell has a cell housing within which the electrodes are arranged, for example the cell stack or the "jelly roll". In particular, a volume between 0.1 dm3 and 10 dm3 is enclosed by the cell housing. For example, the cell housing is additionally at least partially filled with an electrolyte. The cell housing is preferably rigid. In other words, the battery cell is, in particular, a prismatic cell. In particular, the cell housing is made of a metal, such as aluminum, i.e., pure aluminum or an aluminum alloy. The cell housing has, for example, a cuboid shape. Alternatively, the cell housing is flexible and, for example, formed at least partially by a metal foil, which is, in particular, coated on one or both sides.The electrodes are folded over by means of the metal foil, and the metal foil is expediently sealed at the ends so that leakage of the electrolyte and / or entry of ambient air into the cell housing is prevented.

[0021] The electrodes are in particular arranged directly in the cell housing, so that the electrodes rest, for example, directly or via a further component against an inner wall of the cell housing and are thus stabilized by the latter. At least the cell housing directly serves to protect the electrodes and / or to prevent contact of the electrodes / electrolyte with ambient air or other particles. In other words, the electrodes within the cell housing are preferably not, or at least not completely, surrounded by a further component, so that the weight of the battery cell and material costs are reduced. In particular, there is no further housing in the cell housing by which the electrodes are surrounded. Consequently, it is possible to fill the cell housing essentially completely with the electrodes and any separator(s).

[0022] The cell housing suitably has at least one or two openings, through each of which a connection is led. By means of the connection(s), depending on the wiring of the electrodes, at least some of the electrodes arranged in the cell housing are electrically contacted, such that electrical energy can be fed in and / or drawn from outside the cell housing to or from the galvanic elements formed by the electrodes via the connection(s). If only a single connection is present, at least some of the electrodes are electrically contacted with the cell housing, such that an electrical potential of the cell housing is predetermined by means of these electrodes. In particular, the connection(s) are electrically insulated from the cell housing, wherein the connections are connected to the cell housing in a fluid-tight manner, such that leakage of the electrolyte in the region of the connections is prevented.

[0023] The cell housing has an opening, which is, for example, round or rectangular in shape. In particular, the area of ​​the opening is between 50 pm2 and 15 mm2, preferably between 0.2 mm2 and 3 mm2. The opening is covered by a gas-permeable membrane. In particular, the membrane is rigidly connected to the cell housing, preventing movement of the membrane relative to the cell housing. The membrane has a larger area than the opening, so that the membrane completely overlaps the opening. In particular, the area of ​​the membrane is smaller than the area of ​​any side of the cell housing that has the opening. This reduces material costs.

[0024] The membrane is preferably connected to the cell housing in a liquid-tight and / or gas-tight manner, so that the passage of liquids and / or gas between the membrane and the cell housing into the opening is prevented. The membrane is particularly preferably welded to the cell housing, suitably with a circumferential weld seam. Alternatively, for example, the membrane is positively and / or materially connected to the cell housing, in particular adhesively bonded. In this case, the opening is expediently completely surrounded by the adhesive or weld seam. For example, the connection is made directly adjacent to the opening, or a gap is formed between the opening and the connection of the membrane to the cell housing, for example the adhesive or weld seam. Consequently, gas can only escape from or into the cell housing through the opening, with the gas also being conducted through the membrane.

[0025] In particular, the membrane is selected such that it is permeable to preferably at least CO, CO2, H2 and / or CH4. For example, the membrane does not impede the passage of such gases or only impedes it to a comparatively small extent. However, the membrane's permeability to moisture, in particular water vapor, is lower. In particular, the membrane has a ratio of CO2 permeability to moisture permeability of at least 0.5 or of at least 1 or of at least 1.5. Preferably, the ratio is more than 0.5 and less than 3. In summary, the membrane is designed such that gases generated in the cell housing can pass through it and out of the cell housing through the opening, for which purpose the opening is used. The membrane makes it more difficult for moisture, in particular water vapor, to enter the cell housing.

[0026] The membrane itself is covered on the outside, i.e. offset outwards with respect to the cell housing, with a cover element. At least that part of the membrane which covers the opening is covered by the cover element. In particular, the opening is covered by the cover element. In this case, it is possible for the cover element to also be arranged inside the cell housing, but offset in the direction of the opening with respect to the membrane. Alternatively, the cover element is located outside the cell housing. For example, the cover element rests against the cell housing and / or the membrane or is spaced from one or both of them. In particular, the cover element is at least partially rigid. The cover element serves to limit the ingress of substances, in particular moisture, in particular water vapor, into the cell housing and is suitable, in particular provided and configured for this purpose.In this case, the ingress of substance to the membrane is preferably also limited by means of the cover element. In other words, the cover element is used in particular to adjust how much and / or whether a substance, such as a liquid or preferably a gas, enters the cell housing through the membrane and through the opening. In other words, the opening is preferably closed at least temporarily by means of the cover element. At least the cover element is preferably designed in such a way that the passage of gas through the membrane and the opening is limited or at least temporarily limited and thus adjusted. The cover element is preferably fluid-tight, for example always or at least when it is in a certain state, such as a closed state. In other words, in this state, any further transmission of liquid, in particular water, is largely excluded, preferably due to the principle and / or design.If or as long as no gases form within the cell housing, the cover element is preferably in the specific state.

[0027] The opening and the membrane allow gases generated in the cell housing to escape, preventing the buildup of excessive pressure within the cell housing, which could lead to damage to the electrodes and / or the cell housing. This increases operational reliability. Only the membrane and the cover element are required, which require only a comparatively small volume of space. Furthermore, it is possible to position the cover element outside the cell housing so that energy density is not negatively affected. The cover element at least partially protects the membrane from environmental influences outside the cell housing, preventing damage to the membrane.The cover element also at least temporarily / partially keeps particles from the environment away from the membrane, particularly in the specific state when gas ingress and / or egress is completely prevented by the cover element. Thus, the membrane is not exposed to any liquid, particularly water vapor, from outside the cell housing, so that despite the continued, albeit reduced, permeability of the membrane to liquids, penetration of these is completely prevented. If, on the other hand, gas escaping from the cell housing is temporarily possible by means of the cover element, water, for example, can also penetrate to the membrane for this period, although this is a comparatively small amount and is essentially completely retained by the membrane. Thus, penetration of water into the cell housing is almost completely prevented.

[0028] The membrane is made, in particular, of a polymer, for example, a film, such as a polymer film. Suitably, the membrane is made of or consists of PTFE, i.e., polytetrafluoroethylene. The membrane expediently has a crystallinity between 85% and 100% and a density between 0.2 g / cm3 and 2 g / cm3. Such a choice of material provides gas permeability, whereby the membrane prevents or at least impedes the penetration of moisture, in particular water vapor, into the cell housing. In particular, a membrane described in WO 2021 / 079163 A1 is used as the membrane.

[0029] For example, the opening can be positioned arbitrarily on the cell housing. However, if the battery cell is designed as a pouch cell, it is particularly preferably located in the region of one of the ends of the cylinder shape near the conductor, in which the foil, if any, is sealed (e.g., on the so-called gas pocket). In this case, the opening is expediently offset inward from the respective ends up to a maximum of one-third of the maximum length of the cell housing.

[0030] If the battery cell is a prismatic cell, the opening is preferably located in the region of the end faces and / or narrow sides, which in particular are not parallel to the electrodes layered to form the cell stack, if any. Alternatively, the opening is located in one of the sides of the cell housing that is parallel to the electrodes, but preferably in an edge region, i.e. offset inwards from the edge up to a maximum of one-third of the width of the side. Due to this position of the opening, construction is simplified and it is not necessary to modify an existing design of the cell stack. Furthermore, the opening is thus arranged in an area where gases that arise collect, thus enabling a comparatively efficient removal of the gases through the opening.

[0031] For example, the membrane is attached to the outside of the cell housing. In this way, the membrane does not fill the interior of the cell housing, so that a comparatively large volume is available there for the electrodes. This continues to ensure a high capacity of the battery cell. However, it is particularly preferred that the membrane is attached to an inner wall of the cell housing. In this way, even at a comparatively high pressure inside the cell housing, the membrane does not bulge excessively outwards if the design of the membrane does not allow immediate passage of gas. Consequently, the membrane is stabilized by the inner wall, which increases its robustness. In the event of excess pressure, the membrane is pressed against the inner wall, thus preventing gas from passing between the cell housing and the membrane.Consequently, the gas can only escape through the membrane, which is controlled. In summary, the membrane is arranged on either an outward-facing or inward-facing side of the cell casing.

[0032] For example, the cover element is actuated depending on a temperature. In this case, the cover element is expediently designed such that at a temperature below a limit value, gas ingress and / or egress is completely prevented, so that the cover element prevents the membrane from being exposed to a fluid from outside the cell housing. If, however, the temperature of the battery cell is greater than the limit value, the cover element is in particular adjusted such that it does not prevent gas from escaping from the cell housing. In other words, the membrane is exposed. As a result, however, it is possible for moisture, in particular water vapor, to reach the membrane from outside the cell housing.

[0033] The limit value is preferably between 25°C and 60°C. Due to such a limit value, the cover element is thus adjusted in such a way that gas escape is only possible when the battery cell is in operation, i.e., when electrical energy is being fed into the battery cell and / or drawn from the battery cell. Only during this period is the formation of gases that should escape possible. In contrast, when the battery cell is not in use, the cover element protects the membrane.

[0034] Alternatively, or in combination with this, the cover element is actuated as a function of a pressure difference between a pressure outside the cell housing and a pressure in a space formed between the cover element and the membrane. In particular, the volume of this space is less than 4 cm3, 1 cm3, or 0.5 cm3. The pressure in the space between the cover element and the membrane is, in particular, equal to the pressure inside the cell housing or slightly reduced due to the membrane.

[0035] The cover element is in particular actuated in such a way that gas escape from the cell housing is possible or at least simplified if the pressure in the space is greater than the pressure outside the cell housing, for example by more than 0.1 bar, 0.5 bar, 1 bar, 2 bar or 5 bar. Otherwise, the cover element is in particular closed, so that gas escape is completely prevented. The membrane is also protected by the cover element from liquids from outside the cell housing. Thus, protection of the membrane by the cover element is only reduced if the pressure on the side of the cover element facing the interior of the cell housing is higher than the pressure outside the cell housing. In this case, however, a flow direction of the gas is directed outside the cell housing. Thus, penetration of liquid up to the membrane is prevented due to the flow direction of the gas.When the pressure difference decreases, the gas velocity also decreases, making it possible for moisture, especially water vapor, to penetrate. However, the cover element is then closed again, which also prevents liquid penetration.

[0036] For example, the cover element is or comprises a porous element, wherein the pores are in particular open. For example, the porous element is a foam ceramic. By means of the porous element, the path length that the gas must travel is increased, so that increased resistance is provided for the escaping gas. Thus, the porous element limits the escape of gas from the cell housing. Due to the porous element, penetration of moisture, in particular water vapor, is prevented or at least made more difficult, particularly due to capillary effects. For example, the porous element is designed to be completely liquid and / or gas-impermeable, at least in certain areas, for example on one side, so that the path traveled by the gases and the liquid and thus the fluid resistance is further increased.In particular, the side of the porous element opposite the opening is designed in such a way that the path traveled by gases / liquids through the porous element is comparatively long. In particular, the porous element is essentially cuboid-shaped, which simplifies manufacturing.

[0037] Particularly preferably, the cover element comprises or is formed with a valve. The valve is actuated, for example, by means of an actuator, such as a piezo actuator. This makes it possible to control the gas outlet from the cell housing, in particular as a function of certain conditions, such as any pressure difference. Preferably, the cover element has a sensor, depending on which the actuator is controlled. Alternatively, the valve is spring-loaded, for example, and is designed, in particular, as a check valve. The valve is actuated, in particular, as a function of the pressure difference between the pressure prevailing outside the cell housing and the pressure in the space formed between the cover element and the membrane, i.e. when the pressure exceeds a certain predetermined limit. This allows adaptation to different areas of application and / or other requirements by exchanging the spring.

[0038] For example, the valve is a gas- and liquid-impermeable body, which is, for example, membrane-like / membrane-shaped. By means of the body, for example, the opening or the membrane is completely covered when the cover element / valve is in the closed state. By means of longitudinal displacement, in particular perpendicular to the direction of extension of the body and / or the membrane, the cover element is transferred into the open state, and the body is preferably mounted accordingly. Due to the longitudinal displacement, direct penetration of liquid to the opening is prevented even when the cover element is open. Alternatively, the cover element is designed in the manner of a flap and is thus mounted in particular so as to be pivotable with respect to and / or on the cell housing. For example, the body, if any, is mounted on the cell housing by means of a bearing or, particularly preferably, a film hinge.In this way, a construction is simplified.

[0039] In an alternative to this, the cover element has a plastic, preferably polymer layer, which is applied, for example, directly to another body, such as a film. The polymer layer comprises micro- or nanostructures, i.e. structures which have an extension between 100 pm and 1 nm. In particular, the structures repeat periodically so that a pattern is formed. This simplifies production. The structures are, for example, flaps and / or grasses. If they are grasses, they are directed away from the interior of the cell housing so that in the event of increased pressure outside the cell housing or when a liquid impacts on them, they are pressed flat against a base of the polymer layer, so that the cover element is designed to be comparatively tight.Alternatively, or in combination with this, the structures can be adjusted, for example, by applying an electrical voltage, so that gas and liquid passage is either permitted or prevented. Due to the micro- or nanostructures, mechanical robustness is increased and space requirements are reduced.

[0040] In a further alternative, the cover element has a plurality of cover wings, for example two cover wings, three cover wings, four cover wings, five cover wings or more cover wings. Expediently, the number of cover wings is fewer than ten, so that construction is simplified. The cover wings are connected to the cell housing, for example directly attached thereto or indirectly via another element. In this case, the cover wings are connected to one another at different points, namely a respective connection point, i.e. spaced from one another, on the cell housing. In particular, the connection points surround the opening. Suitably, the cover wings are only connected on one side. The cover wings at least partially overlap the membrane, i.e. in particular also the opening, or at least the part of the membrane by means of which the opening is covered. In addition, the cover wings overlap one another.In other words, each of the cover wings at least partially covers one or more of the remaining cover wings.

[0041] The cover wings are designed to be flexible, meaning they can be elastically deformed. In particular, the cover wings are made of a gas- and liquid-impermeable material. Due to their flexible design, they can be bent, releasing the membrane. The cover wings stabilize each other, so that inadvertent bending of one of the cover wings does not lead to the membrane being released. The forces required for this are also comparatively high. Due to the mutual overlap, a comparatively large creepage distance is also provided, so that the penetration of liquid between the cover wings and the membrane is essentially prevented, and the escape of gas in the opposite direction through the cover wings adjacent to the cell housing is essentially prevented.However, by bending open all or at least some of the cover wings, it is possible to release the membrane and thus allow gas to escape.

[0042] Particularly preferably, the cover wings are attached to the outside of the cell housing, preventing the cover wings from being indented, which could lead to damage to the membrane. For example, the cover wings are designed in such a way that they bend when pressure is increased on the membrane side, allowing gas to escape. Alternatively, the cover wings are made, for example, of two different materials that contract differently when the temperature increases. Thus, at elevated temperatures, the cover wings are bent, thus exposing the membrane and thus the opening.

[0043] The battery cell particularly preferably comprises a drying element for reducing moisture penetrating through the opening into the cell housing. The drying element is suitable, in particular provided and configured, for this purpose. Due to the drying element, moisture penetrating despite the cover element, such as water, for example in the liquid or gaseous state, is bound, thus preventing an unwanted reaction with the electrodes arranged in the housing and / or any electrolytes. Operational reliability is thus further increased. In particular, the drying element is designed such that it binds water, in particular absorbs water molecules.

[0044] For example, the drying element is arranged in the region of the opening and surrounds it, for example. In particular, the drying element has a plurality of silicon-containing groups that are bonded to the membrane. In other words, the membrane is functionalized with the silicon-containing groups. This reduces the space required. The drying element is particularly preferably membrane-shaped and, for example, placed loosely on the membrane or spaced apart from it. Due to its arrangement on the inside of the membrane, the drying element only stops that part of the liquid, in particular water, that passes through the membrane into the interior of the cell housing. In other words, the membrane initially serves to stop the moisture / liquid, and only subsequently is the drying element used.This also enables a comparatively long operation of the battery cell without the drying element being disabled.

[0045] For example, the membrane is designed to be tear-resistant. However, the membrane is particularly preferably designed such that it tears when a pressure difference between a pressure outside the cell housing and a pressure inside the cell housing exceeds a limit value. This prevents damage to the cell housing. For example, the membrane tears completely and thus breaks. Tearing expediently only occurs when the limit value is exceeded. When the pressure difference falls below the limit value again, the tearing is stopped. This prevents complete destruction of the membrane.

[0046] For example, the battery cell has several openings, each covered by a corresponding gas-permeable membrane, with each membrane covered on the outside with an associated cover element to limit the ingress of moisture into the cell housing. For example, several or all of the openings are covered with the same cover element. In particular, all openings / membranes / cover elements are structurally identical to one another, and their position on the cell housing differs. Alternatively, the cover elements and / or membranes are designed differently, so that they have different levels of permeability and / or are activated under different pressure differences or other conditions. This increases flexibility.

[0047] However, the battery cell particularly preferably has only a single opening, which simplifies production. In particular, the membrane rests against a stabilizing element at least in the region of the opening and is, for example, attached to it. In other words, the stabilizing element at least partially covers the opening. The stabilizing element is preferably rigid and made of a metal, for example. The stabilizing element is preferably attached to the cell housing, suitably by welding. The stabilizing element has further openings, each of which is covered by the opening. Thus, the effective area available for gas to escape from the cell housing is limited to the sum of the further openings, so that a comparatively large opening can be selected without excessive gas escaping or liquid entering the cell housing.

[0048] The stabilizing element is suitably offset outwards compared to the membrane. Thus, the additional openings specify maximum deformation of the membrane and thus stabilize the membrane. For example, the stabilizing element is designed such that it breaks when there is an increased pressure difference between the pressure inside the housing and the pressure outside the cell housing. For this purpose, the stabilizing element has, for example, one or more predetermined breaking points, which are created, for example, by means of a laser or embossing. The pressure difference at which this occurs can be adjusted relatively precisely. Alternatively, or in combination with this, the stabilizing element is designed such that it breaks when a certain temperature is exceeded. Due to the breakage, the membrane is no longer stabilized and is therefore also overloaded, causing it to tear.As a result, a comparatively large volume of gas can pass through the opening. In particular, the cover element also ruptures in this case, or is at least configured in such a way that gas escape is essentially unhindered. This allows for controlled degassing of the battery cell, and prevents uncontrolled destruction of the cell casing due to excessive pressure. Although this damages the battery cell and renders it unusable, the environmental impact is reduced. In other words, the membrane and the stabilizing element act like a rupture disc.

[0049] Alternatively or in combination with the previously described embodiments, the cell housing suitably has an integrated predetermined breaking point. The integrated predetermined breaking point is, for example, spatially separated from the opening or, for example, the integrated predetermined breaking point has the opening. In a further alternative, the predetermined breaking point is formed by the opening. For example, the predetermined breaking point is a surface of the cell housing with reduced wall thickness. Alternatively or in combination, the predetermined breaking point is, for example, a surface of the cell housing with an engraving and / or notch. In a further development, the predetermined breaking point is an additional opening in the cell housing closed with a rupture disc. In other words, the cell housing has the additional opening that is completely closed by the rupture disc. Suitably, the predetermined breaking point has a size of 0.01% and 50% of the surface area of ​​the cell housing.Preferably, the predetermined breaking point has a size between 0.1% and 40%, and in particular between 0.3% and 30%, of the area of ​​the complete cell housing. For example, the membrane has an area 50% larger than the opening.

[0050] For example, the membrane is arranged on an inward-facing side of the cell casing. Outside the openings, for example, the membrane is not in full physical contact with the cell casing. In an alternative, the membrane is partially spaced from the cell casing by spacers.

[0051] In a further alternative, the cell housing comprises, for example, an auxiliary opening which is closed with a rupture disc having the opening covered by the gas-permeable membrane. The rupture disc is formed, for example, by a reduction in the wall thickness of the cell housing or is a component that is initially separate from the cell housing and is fastened to the cell housing for assembly. In particular, any predetermined breaking point is formed by the rupture disc. The membrane is preferably fastened to an outward-facing side of the rupture disc. In this case, for example, the membrane rests on the outside against another or the possible stabilizing element that has a plurality of additional openings. The stabilizing element is preferably fastened to the rupture disc.In an alternative, the membrane is arranged on an inward-facing side of the rupture disc, with the membrane being partially supported on the rupture disc via spacers.

[0052] The invention further relates to a battery cell assembly of such battery cells, wherein the assembly is preferably a battery module or a high-voltage battery. Furthermore, the invention relates to a motor vehicle, such as a passenger car (PV), having such a battery cell, in particular such an assembly. The battery cell is used in particular to supply power to a main drive of the motor vehicle. The advantages and developments described in connection with the battery cell are also applicable mutatis mutandis to the assembly / motor vehicle and to each other, and vice versa.

[0053] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings:

[0054] Fig. 1 shows a simplified schematic representation of a motor vehicle having several identical battery cells,

[0055] Fig. 2 shows a schematic sectional view of one of the battery cells having a cell housing,

[0056] Fig. 3 - 6 schematically show a section of the cell housing, which has an opening for gas escape, at different pressures within the cell housing, wherein the opening is covered with a gas-permeable membrane, and wherein the membrane is covered on the outside with a cover element for limiting gas escape from the cell housing,

[0057] Fig. 7, 8 each schematically show an alternative embodiment of the battery cell,

[0058] Fig. 9, 10 in a plan view each show alternative embodiments of a stabilizing element,

[0059] Fig. 11 - 13 schematically show an alternative embodiment of the battery cell, and

[0060] Fig. 14 - 17 each schematically show an alternative embodiment of the cover element.

[0061] Corresponding parts are provided with the same reference numerals in all figures.

[0062] Figure 1 shows a simplified schematic representation of a motor vehicle 2 in the form of a passenger car (car). The motor vehicle 2 has a number of wheels 4, at least some of which are driven by a drive 6 comprising an electric motor. Thus, the motor vehicle 2 is an electric vehicle or a hybrid vehicle. The drive 6 has an inverter by means of which the electric motor is powered. The inverter of the drive 6, in turn, is powered by an energy storage device 8 in the form of a high-voltage battery. For this purpose, the drive 6 is connected to an interface 10 of the energy storage device 8, which is incorporated in an energy storage housing 12 of the energy storage device 8, which is made of stainless steel.

[0063] Arranged within the energy storage housing 12 of the energy storage device 8 are a plurality of identical battery modules (not shown in detail), each comprising a plurality of battery cells 14. The battery cells 14 of each battery module are partly electrically connected in series and partly electrically connected in parallel. The battery modules, in turn, are electrically connected in series and / or parallel. The electrical connection of the battery modules is electrically contacted with the interface 10, so that when the drive 6 is in operation, the battery modules and thus also the battery cells 14 are discharged or charged (recuperated). Due to the electrical wiring, the electrical voltage provided at the interface 10, which is 400 V or 800 V, is a multiple of the electrical voltage provided by each of the battery modules and also by each of the battery cells 14.

[0064] Figure 2 shows a sectional view of one of the identical battery cells 14. The battery cell 14 has a plurality of anodes 16 and cathodes 18, of which only two are shown at a time. The anodes 16 and the cathodes 18, which form the electrodes 20 of the battery cell 14, are each flat and are alternately layered on top of one another to form a cell stack, with a separator (not shown in detail) being arranged between adjacent anodes 16 and cathodes 18. The anodes 16 protrude beyond the cathodes 18 on a common side, namely a respective conductor, which is formed by means of a respective metal foil. In the region of the projection, the respective conductor is free of further components, but in the other regions a layer comprising an active material is applied to the respective conductor, which is also referred to as a carrier.The cathodes 18 also protrude beyond the anodes 16 in the same way, with the projections being located on opposite sides of the stack formed by the anode 16 and cathodes 18.

[0065] The projections of the anodes 16 and the cathodes 18 are each welded to a busbar 22 (tab) made of copper. A common busbar 22 is assigned to the anodes 16 and the cathodes 18. The busbars 22 each have a connection 24 that extends through a cell housing 26, within which the anodes 16 and the cathodes 18 are arranged. In other words, the electrodes 20 are arranged within the cell housing 26. The cell housing 26 is rigid and made of aluminum, i.e., a material containing aluminum. Thus, the battery cell 14 is a prismatic cell. The cell housing 26 is filled with a liquid electrolyte (not shown in detail).

[0066] Figures 3-6 show a schematic sectional view of the battery cell 14 during operation. The cell housing 26 has an opening 28 with an area of ​​50 mm². The opening 28 is located in the same wall of the cell housing 26 as the opening for one of the terminals 24. With the exception of the opening 28, the cell housing 26 is fluid-tight and gas-tight. Thus, the areas between the terminals 24 and the associated openings in the cell housing 26 are filled with a plastic (not shown in detail).

[0067] The opening 28 is covered with a gas-permeable membrane 30, which is attached to the inner wall 32 of the cell housing 26, which has the opening 28, by welding or gluing. In the example shown, the membrane 30 covers the entire inner wall 32 of the housing 26 and thus also completely covers the opening 28. The membrane 30 is made at least partially of PTFE. Thus, the passage of gases such as H2, CO, CH4 and CO2 through the membrane 30 is comparatively easy, whereas the passage of moisture, in particular water vapor, and other liquids is comparatively more difficult. The membrane 30, namely the part by which the opening 28 is covered, is covered on the outside of the cell housing 26 with a cover element 34. The cover element 34 is located on the outside of the cell housing 26 and is attached to it.The cover element 34 is gas- and liquid-tight and serves to limit the ingress of gas into the cell housing 26. Thus, the cover element 34 completely prevents the penetration of moisture from the environment, in particular water vapor, into the opening 28 and thus also to the membrane 30.

[0068] During operation of the battery cell 14, it is possible that gases 36, such as H2, CO, CH4 and / or CO2, form in the cell housing 26 due to unwanted chemical reactions, for example due to a comparatively high load or due to unwanted foreign particles. The gases 36 require a larger volume than the reactants, so that the pressure inside the cell housing 26 increases. As shown in Figure 4, the gases 36 can pass through the membrane 30 into the opening 28, i.e. a space 38 formed between the cover element 34 and the membrane 30, which in this embodiment is defined by the opening 28. If the pressure difference between the pressure outside the cell housing 26 and the pressure in the space 38 exceeds a limit value, such as 0.5 bar, the cover element 34 is actuated so that it is partially opened.As a result, gas escapes from the space 38 into the environment of the cell housing 26, as shown in Figure 5. Gases 36 also continue to flow from the interior of the cell housing 26 through the membrane 30 and the opening 28 into the environment. The membrane 30 prevents moisture from entering the cell housing 26 (see also below).

[0069] When the pressure difference between the pressure in the space 38 and the pressure outside the cell housing 26 has dropped again because the gases 36 have at least partially escaped, the cover element 34 is closed again, so that further escape of the gases 36 from the space 38 and thus from the cell housing 26 no longer occurs, as shown in Figure 6. Thus, the membrane 30 is subsequently completely covered again by the cover element 34, so that the ingress of moisture into the opening 28 is prevented.

[0070] Due to the design of the battery cell 14, moisture penetration from outside the battery cell 26 to the electrodes 20 would only be possible if the cover element 34 is actuated in such a way that gas passage is possible. In this case, however, the gases 36 flow outward from the interior of the cell housing 26, so that moisture penetration is prevented or at least greatly reduced due to the flow movement of the gases 36.

[0071] In an alternative embodiment, the actuation of the cover element 34 takes place additionally or alternatively only as a function of the temperature of the battery cell 14. In this case, the cover element 34 is actuated so that the gases 36 can escape when the temperature of the battery cell 14 exceeds a limit value, such as 40 °C.

[0072] The membrane 30 is further configured such that it ruptures when the pressure difference between the pressure outside the cell housing 26 and a pressure inside the cell housing 26 exceeds a (further, higher) limit value. The limit value, i.e., the further limit value, is 10% - 25% lower than the maximum pressure load on the cell housing 26, i.e., the pressure difference at which irreversible destruction of the cell housing 26 occurs. This pressure is, in particular, between 6 bar and 8 bar. In other words, the membrane 30 acts as a bursting membrane that ruptures to prevent destruction of the cell housing 26.

[0073] Thus, when a comparatively large volume of gases 36 is formed, they enter the chamber 28, actuating the cover element 34. As a result, the pressure in the chamber 28 essentially corresponds to the pressure in the environment of the cell housing 26, i.e., the pressure outside the cell housing 26. If the pressure difference between the pressure in the chamber 28 and the pressure inside the cell housing 26 exceeds the further limit value, the membrane 30 retracts in a controlled manner, so that the escape of the gases 36 from the interior of the cell housing 26 into the environment is accelerated due to the lack of or reduced fluid resistance of the membrane 30. This prevents damage to the housing 26 due to excessive pressure inside the cell housing 26.

[0074] When the pressure difference has fallen below the further limit value again, the membrane 30 stops tearing. Also, when a large portion of the gases 36 has escaped, so that the pressure difference between the environment of the cell housing 26 and the pressure in the space 28 falls below the limit value of 0.5 bar, the cover element 34 is actuated again, completely covering the opening 28. Thus, the cover element 34 again prevents moisture from penetrating the cell housing 26. Consequently, continued operation of the battery cell 14 is possible, although the torn membrane 30 allows liquid to penetrate at least temporarily and partially.

[0075] Figure 7 shows a modification of the battery cell 14 according to the illustration in Figure 3. In this variant, the battery cell 14 has a drying element 40. The drying element 40 consists of silicon-containing groups and is present as a layer by means of which the membrane 30 is coated on the inside, namely over its entire surface in this variant, and thus covered. In other words, the drying element 40 is a separate layer from the membrane 30. The drying element 40 does not impede, or only slightly impedes, the passage of the gases 36. However, the drying element 40 binds and / or absorbs the moisture that nevertheless penetrates through the opening 28 and the membrane 30, namely water (vapor), so that it cannot reach the electrodes 30 and / or the electrolyte. The drying element 40 thus serves to reduce the moisture penetrating the cell housing 26 through the opening 28.

[0076] Figure 8 shows a further modification of the battery cell 14 according to the illustration in Figure 3. In this variant, the opening 28 is covered on the outside by the membrane 30, and the membrane 30 is fastened to the outside of the cell housing 26, namely by welding or gluing. Furthermore, the battery cell 14 has a stabilizing element 42 made of a metal. The stabilizing element 42 is flat and lies fully against the membrane 30. Consequently, the membrane 30 also lies against the stabilizing element 42 in the region of the opening 28. The membrane 30 is arranged between the cell housing 26 and the stabilizing element 42, which is thus offset outwards with respect to the membrane 30.

[0077] Figures 9 and 10 each show a top view of an embodiment of the stabilizing element 42. These each have a plurality of additional openings 44. In the variant shown in Figure 9, the additional openings 44 are each provided separately from one another and by means of round recesses. In the variant shown in Figure 10, the additional openings 44 are strip-shaped.

[0078] The additional openings 44, or at least a portion thereof, are arranged above the opening 28, and the additional openings are thus covered by the opening 28. The stabilizing element 42 and thus also the membrane 30 are completely covered by the cover element 34, which is also arranged outside the cell housing 26. If the pressure inside the cell housing 26 increases and the cover element 34 is at least partially open, the membrane 30 bulges slightly outward only in the areas of the additional openings 44, thus preventing excessive deformation of the membrane 30.Only when the pressure difference between the interior of the cell housing 26 and the environment of the cell housing 26 exceeds the further limit value, namely 6 bar - 8 bar, does the stabilizing element 42 break, so that the membrane 30 is no longer stabilized by means of it, which thus tears, so that the escape of a comparatively large volume of the gases 36 is possible unhindered.

[0079] Figure 11 shows a plan view of a variant of the cover element 34. The cover element 34 has a plurality of cover wings 46, which are connected, namely fastened, to the cell housing 26 at connection points 48 spaced apart from one another. The connection points 48 surround the opening 28, and the cover wings 46 are arranged such that, at the end opposite the respective connection point 48, they at least partially cover each other and the opening 28, and therefore also the membrane 30. The cover wings 46 are flexible and made, for example, from a polymer. If the pressure difference exceeds the limit value, the cover wings 46 are lifted off the cell housing 26 at the free end spaced apart from the respective connection point 48, against which they otherwise rest flatly, due to the increased pressure, thus enabling gas to escape.If, however, the pressure difference is lower, gas escaping from within the cell housing 26 and / or moisture entering from outside the cell housing 26 into the opening 28 or at least to the membrane 30 is prevented due to the comparatively large creepage distance provided by the overlap. In an alternative, the cover wings 46 are made of two different materials that have different temperature behavior. The material of the part of the cover wings 46 facing the outside of the cell housing 26 is selected such that it contracts more intensively when the temperature rises. As a result, at an elevated temperature, the cover wings 46 are deformed such that the opening 28 and thus the membrane 30 are exposed.

[0080] Figure 12 again shows a simplified schematic cross-sectional view of a section of the battery cell 14. In this variant, the opening 28 is again covered on the outside by the membrane 30. The membrane 30, in turn, is completely covered by the cover element 34, which comprises a porous element 50, namely a foam ceramic or a foam. The porous element 50 has several open pores (not shown in detail). Due to the pores, gas passage is possible, although this passage is limited due to the increased fluid resistance.

[0081] On the side opposite the membrane 30, the cuboid-shaped porous element 50 is provided with a layer 52 that is completely fluid-tight. Layer 52 ensures that the escaping gases 36 travel a comparatively long path through the porous element 50 to the outlet, while not excessively increasing the size of the cover element 34. Layer 52 also ensures that impinging water also only reaches the opening 28 after traveling a comparatively long path through the porous element 50, which is comparatively significantly delayed due to capillary effects.

[0082] Figure 13 shows a further embodiment of the battery cell 14 according to Figure 12. Here, too, the membrane 30 is arranged on the outside of the cell housing 26 and covers the opening 28. The cover element 34 is also arranged on the outside of the housing 26. The cover element 34 comprises a valve 54 and is formed thereby in the illustrated embodiment. The valve 54 has a fluid-impermeable body 56 which is shaped such that the entire membrane 30 is enclosed when the body 56 rests against the edge of the cell housing 26. The body 56 is made of a plastic and is mounted perpendicular to the surface of the membrane 30 by means of guides (not shown in detail). In addition, the body is supported on a stop 58 by means of several springs 60, with the body 56 being located between the stop 58 and the membrane 30.The springs 60 are designed such that they press the body 56 against the membrane 30 and the cell housing 26 as long as the pressure difference between the pressure inside the housing 26 and the pressure surrounding the cell housing 26 is less than the limit value of 0.5 bar. If the limit value is exceeded, the pressure forces the body 56 away from the membrane 30, counter to the force applied by the springs 60, allowing the gases 36 to escape.

[0083] In a variant not shown in detail, the springs 60 are replaced by an actuator, or the actuator is additionally present. The actuator, such as a piezo actuator or a magnetic element, is actuated to space the body 56 from the membrane 30 when certain conditions exist, such as a certain temperature increase.

[0084] Figure 14 shows an alternative embodiment of the valve 54. In this embodiment, the body 56 is pivotally mounted on other components of the cover element 34 or the cell housing 26 by means of a hinge 62, such as a film hinge. In one variant, the valve 54 is designed like a check valve, so that liquid impinging on the body 56 from the outside causes the valve 54 to close. In a variant not shown in detail, the body 56 is additionally loaded by means of springs 60 (not shown in detail), by means of which the body 56 is pushed or pulled into the closed position when the pressure difference is less than the limit value. In a further variant not shown, the body 56 is additionally or alternatively actuated by means of the actuator.

[0085] Figures 15 and 16 show a modified form of the cover element 34. In one alternative, the polymer layer 64 is applied to a separate component, or a further membrane is formed using the polymer layer 64. The polymer layer 64 has a base 66 to which several nanostructures 68 are attached. The nanostructures 68 are spaced 200 nm apart from one another and arranged in a repeating pattern. Each nanostructure 68 has a peg 70 attached to the base 66 and pointing away therefrom, to which a thickened portion 72 is connected on the free end opposite the base 66. The extent of the thickened portion 72 depends on an applied electrical voltage.In the normal state of the cover element 34, i.e., when no electrical voltage is applied, the thickened portions 20 are inflated such that adjacent thickened portions 20 abut one another, preventing the gases 36 from passing through, as shown in Figure 15. If, however, an electrical voltage is applied, the thickened portions 72 contract, allowing adjacent thickened portions 20 to be spaced apart from one another. As a result, the gases 36 can pass through, as shown in Figure 16. Figure 17 shows a modification of the cover element 34, which is also formed by the polymer layer 64. In this modification, however, the nanostructures 68 are configured as micro-grasses. In other words, the individual pegs 70 merely protrude from the base 66 and are comparatively flexible. As in the previous embodiment, the pegs 70 point away from, or outward from, the cell housing 26.When a liquid drop hits from the outside, the pins 70 are bent toward the base 66, so that the pins 70 rest on top of each other and against each other. As a result, moisture penetration is prevented. Once the moisture is removed, the pins 70 essentially return to their original position. The passage of gases 36 from the opposite direction is always possible with the straight pins 70 aligned.

[0086] In a variant not shown in detail, the shape of the pins 70 is modified, and they are, for example, shortened and / or conical. In variants not shown in detail, the pins 70 are enlarged, so that the polymer layer 64 has microstructures instead of the nanostructures 68. In other words, the size of the pins 70 and their spacing from one another are increased. The shape of the pins 70, however, is essentially unchanged.

[0087] The invention is not limited to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by those skilled in the art without departing from the scope of the invention. In particular, all individual features described in connection with the individual exemplary embodiments can also be combined with one another in other ways without departing from the scope of the invention.

[0088] List of reference symbols

[0089] Motor vehicle

[0090] wheel

[0091] drive

[0092] Energy storage

[0093] interface

[0094] Energy storage housing

[0095] Battery cell

[0096] anode

[0097] cathode

[0098] electrode

[0099] Busbar

[0100] Connection

[0101] Cell housing opening membrane

[0102] interior wall

[0103] Cover element

[0104] gas

[0105] Space

[0106] Drying element

[0107] Stabilizing element further opening cover wing connection point porous element

[0108] layer

[0109] valve

[0110] Body

[0111] stop

[0112] Feather

[0113] hinge

[0114] polymer layer

[0115] Floor

[0116] Nanostructure

[0117] cones

[0118] thickening

Claims

Claims: A battery cell (14) with a cell housing (26) in which several electrodes (20) are arranged and which has an opening (28) covered by a gas-permeable membrane (30), wherein the membrane (30) is covered on the outside by a cover element (34) to limit the ingress of substances into the cell housing (26). A battery cell (14) according to claim 1, characterized in that the membrane (30) is attached to an inner wall (32) of the cell housing (26). A battery cell (14) according to claim 1 or 2, characterized in that the cover element (34) is actuated depending on a pressure difference between a pressure outside the cell housing (26) and a pressure in a space (38) formed between the cover element (28) and the membrane (30). A battery cell (14) according to any one of claims 1 to 3, characterized in that the cover element (34) comprises a valve (54).A battery cell (14) according to any one of claims 1 to 3, characterized in that the cover element (34) comprises a polymer layer (64) with micro- or nanostructures (68). A battery cell (14) according to any one of claims 1 to 3, characterized in that the cover element (34) comprises several flexible cover wings (46) that overlap each other and the membrane (30) at least partially and are attached to the cell housing (26) at intervals from each other. A battery cell (14) according to any one of claims 1 to 6, characterized by a drying element (40) for reducing moisture penetrating the cell housing (26) through the opening (28). A battery cell (14) according to claim 7, characterized in that the membrane (30) is covered on its inner surface by the drying element (40). A battery cell (14) according to any one of claims 1 to 8, characterized in that the membrane (30) is designed such that it tears when the pressure difference between a pressure outside the cell housing (26) and a pressure inside the cell housing (26) exceeds a limit value. A battery cell (14) according to any one of claims 1 to 9, characterized in that the membrane (30) in the region of the opening (28) abuts a stabilizing element (42) which has several further openings (44) each covered by the opening (28).

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