Battery cell

Abstract

Battery cell (14) with an electrode arrangement (18) arranged within a cell housing (16), wherein an overpressure equalization element (26) is incorporated into a wall (24) of the cell housing (16) and is connected to the electrode arrangement (18) in a gas-open manner, wherein a cover arrangement (30) is arranged in the cell housing (16) by means of which the overpressure equalization element (26) is electrolyte-tightly separated from an electrolyte (36) present in the cell housing (16), wherein the cover arrangement (30) comprises a membrane (32) arranged between the overpressure equalization element (26) and the electrode arrangement (18), wherein the entire wall (24) is covered by means of the membrane (32), wherein the membrane (32) is fluid-tightly attached to further inner walls (46) of the cell housing (16), and wherein the membrane (32) is corrugated.

Description

[0001] The invention relates to a battery cell and a method for manufacturing a battery cell. The battery cell has an electrode arrangement that is arranged inside a cell housing.

[0002] Increasingly, motor vehicles are being powered, at least partially, by an electric motor, resulting in electric or hybrid vehicles. A high-voltage battery, typically comprising several individual battery modules, is used to power the electric motor. These battery modules are usually identical in construction and electrically connected in series and / or parallel, so that the voltage applied to the high-voltage battery is a multiple of the voltage provided by each individual battery module. Each battery module, in turn, contains several battery cells, usually arranged in a common module housing, which are also electrically connected in series and / or parallel.

[0003] Each battery cell typically comprises several galvanic cells. These cells each have two electrodes, namely an anode and a cathode, as well as a separator between them and an electrolyte containing freely moving charge carriers. A liquid, for example, is used as such an electrolyte. Alternatively, the battery cell is designed as a solid-state battery, with the electrolyte in solid form. The anode and cathode, which form the electrodes of the battery cell, usually comprise a substrate that acts as a current collector. An active material is typically attached to this substrate; this active material is a component of a layer applied to the substrate, also known as the current collector. The electrolyte may already be present in this layer, or it may be added subsequently. At a minimum, however, the active material must be able 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 substrate material and a different layer material are used.

[0004] To protect the galvanic elements, these are usually arranged in a cell housing of the battery cell, which also protects the electrolyte from environmental influences.

[0005] The chemical reactions that occur during battery cell operation also lead to a minor, undesirable decomposition of the electrolyte or other forms of aging. These components of the electrolyte can subsequently no longer be used for operation. In other words, the work ions in these chemical substances are bound elsewhere and therefore cannot be absorbed by the electrodes. To ensure that sufficient electrolyte is available over a relatively long period, the cell casing is usually filled with a larger volume of electrolyte than is needed at the start of operation. In other words, an electrolyte reserve is available.

[0006] During unwanted chemical reactions, gases can be produced, and the required volume of gases exceeds the volume of the reactants. This increases the pressure inside the cell casing. To prevent uncontrolled rupture of the cell casing due to this additional volume, which would damage surrounding components, the cell casing typically incorporates a pressure relief element. This element reduces the excess pressure within the casing and usually vents the gases into the environment in a controlled manner. However, due to excess electrolyte in the cell casing, it is possible that the gases may not reach the pressure relief element.In other words, the gases are retained due to the electrolyte, and / or the functionality of the pressure relief element is impaired by the additional electrolyte. Therefore, it is possible that the pressure inside the cell casing will increase and lead to an uncontrolled rupture of the cell casing.

[0007] The invention is based on the objective of providing a particularly suitable battery cell and a particularly suitable method for manufacturing a battery cell, wherein material and / or manufacturing costs are advantageously reduced, and wherein a service life and / or operational reliability is suitably increased.

[0008] With regard to the battery cell, this problem is solved according to the invention by the features of claim 1, and with regard to the method by the features of claim 9. Advantageous further developments and embodiments are the subject of the respective dependent claims.

[0009] The battery cell, which in the following is also referred to simply as the battery, is preferably designed to be rechargeable and is expediently a secondary battery. Preferably, the battery cell, in its intended state, is a component of a motor vehicle. The battery cell is suitable for this purpose, and in particular is designed and configured accordingly. In its intended state, the battery cell is, for example, a component of an energy storage system of the motor vehicle, which comprises several such battery cells. Preferably, the battery cells are divided among several battery modules, which are identical in construction. The battery cells are, in particular, arranged in a housing of the energy storage system or the respective battery module and are electrically connected to each other in parallel and / or in series.Therefore, the electrical voltage applied to the energy storage / battery module is many times higher than the electrical voltage provided by each individual battery cell. Conveniently, all battery cells are identical in construction, which simplifies manufacturing.

[0010] The housing of the energy storage device or the respective battery module, which thus forms a group of such battery cells, is preferably made of a metal, for example, steel such as stainless steel, or an aluminum alloy. Manufacturing processes include, for example, die casting, deep drawing, casting presses, or extrusion. In particular, the housing of the energy storage device or the respective battery module is designed to be sealed. Advantageously, an interface is incorporated into the housing of the energy storage device or the respective battery module, which, for example, forms a connector for the energy storage device / battery module. This interface is electrically connected to the battery cells, so that electrical energy can be supplied to and / or withdrawn from the battery cells from outside the energy storage device, provided a corresponding mating connector is plugged into the connector.

[0011] The motor vehicle is, for example, a ship or boat. Preferably, however, the motor vehicle is land-based and preferably has a number of wheels, at least one, preferably several or all, of which are driven by a drive system. In particular, one, preferably several, of the wheels is designed to be steerable. Thus, it is possible to move the motor vehicle independently of a specific roadway, such as rails or the like. It is advantageously 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 truck or a bus. However, it is particularly preferred that the motor vehicle be a passenger car.

[0012] The drive system expediently propels the motor vehicle. For example, the drive system, particularly the main drive, is at least partially electric, and the motor vehicle is, for instance, an electric vehicle. The electric motor is powered, for example, by means of the energy storage device, which is suitably designed as a high-voltage battery. The high-voltage battery expediently provides a direct current voltage, the voltage being, 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 supplied to the electric motor is adjusted. Alternatively, the drive system also includes an internal combustion engine, so that the motor vehicle is designed as a hybrid vehicle.Alternatively, the energy storage device is used to power a low-voltage electrical system of the motor vehicle, and in particular, the energy storage device provides a direct current voltage of 12 V, 24 V or 48 V.

[0013] In another alternative, the battery cell is a component of a forklift, an industrial plant, or a handheld device, such as a power tool, especially a cordless screwdriver. In yet another alternative, the battery cell is part of a power supply system and is used, for example, as a buffer battery. In this case, the battery cell is used, for instance, within a power plant or a household / industrial facility. In another alternative, the battery cell is a component of a portable device, such as a mobile phone or wearable, or a computer. It is also possible to use such a battery cell in camping, model making, or for other outdoor activities.

[0014] The battery cell has an electrode arrangement with multiple electrodes. The electrodes are specifically divided into anodes and cathodes, with, for example, as many anodes as cathodes, or preferably an additional anode. Particularly preferably, all anodes and all cathodes are identical in construction, which simplifies manufacturing. The electrodes, i.e., the anodes and the cathodes, are, for example, planar and, in particular, substantially rectangular. Advantageously, the anodes and cathodes each have a support, which is also referred to as a surge arrester. In particular, the respective support is formed by means of a metal foil that is coated on one or both sides, at least partially, with a layer. For example, aluminum is used as the metal of the support / surge arrester for the cathodes, and copper as the metal of the surge arrester for the anodes.

[0015] The layer has a thickness of less than 1 mm. Advantageously, the supports have a thickness of less than 0.1 mm. Preferably, each layer comprises an active material, a binder, and / or a conductive additive, such as conductive carbon black. The active material serves to absorb working ions, such as lithium ions, and is suitable, designed, and configured for this purpose. For example, a lithium metal oxide, such as lithium cobalt(III) oxide (LiCoO2), NMC (e.g., NMC622 or NMC811), NCA, or LFP, is used as the active material for the cathode, and / or LTO or graphite, silicon-based, for the anode.

[0016] The electrodes, i.e., the anodes and cathodes, are stacked on top of each other to form a cell stack, with the stacking direction perpendicular to the direction of expansion of the electrodes, which are arranged parallel to each other. The anodes and cathodes alternate in the stacking direction of the cell stack. A separator of the cell stack is arranged between adjacent electrodes, i.e., between each anode and each cathode, and is preferably also planar. For example, all separators are identical in design. In particular, the electrodes are stacked essentially flush with each other, with, for example, all anodes projecting at least slightly beyond the cathodes. This prevents unwanted material buildup at the edges of the anodes during operation. Due to the stacking of the electrodes, the cell stack is also essentially cuboid in shape.In particular, the cell stack forms the electrode arrangement. 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," which in particular constitutes the electrode arrangement. In a further embodiment, the separator is formed by means of a band, a so-called separator band, which is folded several times in a Z-shape. The individual electrodes, which are in particular leaf-shaped, are inserted into the pockets formed in this way.

[0017] The battery cell further comprises a cell housing within which the electrode assembly is completely arranged. The cell housing is, for example, made of aluminum and is preferably rigid. The cell housing particularly includes a cell cup which is closed by means of a lid. In particular, the cell housing is cylindrical or cuboidal, and the battery cell is preferably designed as a so-called prismatic cell. Alternatively, the cell housing is, for example, made of a foil, which is, for instance, a coated aluminum foil. In other words, the battery cell is designed as a pouch cell. At a minimum, however, the cell housing is preferably designed to be fluid-tight, in particular electrolyte-tight. Thus, the electrode assembly is protected by the cell housing, and the ingress of foreign particles is prevented.

[0018] Advantageously, the cell housing has one or more openings, each through which a terminal passes. For example, the battery cell may include one, two, or more such terminals, each associated with one of the openings. The area between the terminals and the edge of the openings is also designed to be fluid-tight, and each terminal is electrically contacted with at least one of the electrodes of the electrode assembly. Thus, electrical energy can be supplied to and / or drawn from the electrode assembly from outside the cell housing via the terminals.

[0019] In particular, the cell housing is partially filled with an electrolyte after manufacturing, the electrolyte being tailored to the electrode arrangement, especially the active material used. The electrolyte provides, in particular, working ions. The electrolyte is preferably liquid. A larger volume of electrolyte is preferably present in the cell housing than is initially required for the operation of the electrode arrangement.

[0020] A pressure equalization element is incorporated into a wall of the cell housing, which may be rigid or flexible and is expediently designed to be essentially flat. The pressure equalization element is specifically not part of the wall, but rather separate from it. For example, the pressure equalization element is made of a different material than the cell housing wall. Preferably, a fluid-tight connection is provided between the pressure equalization element and the wall, thus preventing electrolyte leakage between the pressure equalization element and the wall. This also prevents the ingress of foreign particles into the cell housing. In summary, the pressure equalization element is therefore specifically not a component of any cell cup or lid made of a rigid metal, such as aluminum, nor is it a component of any film.The pressure relief element is not formed, even partially, by any of these components. Rather, the pressure relief element is a separate component from the cell cup / lid / film. Using the pressure relief element, it is possible, at least depending on certain conditions, to reduce and preferably equalize the overpressure within the cell housing compared to the ambient pressure, so that no pressure difference remains. For this purpose, gases from inside the cell housing, such as H2, CO, or CO2, which are present during operation due to unwanted chemical reactions, are vented from the cell housing to the environment.

[0021] The pressure equalization element is connected to the electrode assembly in a gas-open manner. In other words, the pressure at the pressure equalization element and the electrode assembly is the same, particularly during operation of the battery cell, and gas flow between the electrode assembly and the pressure equalization element is possible, or there is only a comparatively small, preferably negligible, flow resistance.

[0022] Furthermore, a cover assembly is arranged within the cell housing, by means of which the pressure equalization element is electrolyte-tightly separated from the electrolyte present in the cell housing. In other words, the cover assembly prevents the electrolyte from reaching the pressure equalization element and keeps the electrolyte away from the pressure equalization element. In summary, the pressure equalization element is covered from the electrolyte by the cover assembly, while preventing a pressure differential between the electrode assembly and the pressure equalization element.

[0023] The cover design ensures that the electrolyte does not impair the functionality of the pressure relief element, allowing any overpressure that may occur in the cell casing during operation to be relieved by the pressure relief element. This increases operational reliability. The cell casing can be filled with a larger volume of electrolyte than initially required for operation. Therefore, the battery cell can be used for an extended period, even if the electrolyte degrades. In other words, the battery cell's service life is increased. Furthermore, the cover design isolates the pressure relief element from the electrolyte, eliminating the need for the element to be resistant to the electrolyte.This reduces the material requirements for the pressure relief element, thereby lowering material and manufacturing costs. Furthermore, the cover arrangement ensures that no electrolyte escapes from the cell casing if gases are released into the environment via the pressure relief element, thus protecting the environment from the electrolyte. This further increases operational reliability and expands the battery cell's range of applications.

[0024] Advantageously, the cover arrangement also provides at least partial electrical insulation to the electrode assembly, particularly from the pressure equalization element and / or other components of the cell housing. For this purpose, the cover arrangement is specifically designed to be electrically insulated. This further increases the range of functions without requiring an additional component. Consequently, manufacturing costs are reduced and energy density is increased. Preferably, the cover arrangement also shields at least part of the cell housing from the electrolyte, thus preventing interaction with the electrolyte, such as corrosion. In other words, the cover arrangement separates the electrolyte from at least part of the cell housing. This further extends the service life of the battery cell and ensures comparatively long cycle stability.

[0025] For example, the pressure relief element is integrated into an edge region of the cell housing. However, it is particularly preferred that the pressure relief element is integrated into the bottom of the cell housing. In other words, the bottom forms the wall of the cell housing into which the pressure relief element is integrated. In a typical battery cell configuration, the bottom is the lower part of the cell housing in the vertical direction. If the battery cell is used in a motor vehicle, it is usually located below a passenger compartment. Since the pressure relief element is located on the bottom of the cell housing facing away from the passenger compartment, the gases are prevented from entering the passenger compartment of the motor vehicle.Furthermore, any connections or electrically contacted interconnection elements, which are expediently located in a vertical direction at the upper end of the cell housing, particularly in a lid, are not obstructed by the overpressure equalization element.

[0026] If the cell housing comprises a cell cup and a lid, the pressure relief element is integrated, in particular, into one of the walls of the cell cup, preferably the bottom. This allows the lid to be manufactured without a pressure relief element, thus simplifying the manufacturing costs of the lid, through which any connections are expediently routed. This design also achieves functional separation and simplifies assembly. Although the pressure relief element is located in the lower part of the cell housing where the electrolyte collects during operation, the cover arrangement prevents the electrolyte from escaping the pressure relief element.

[0027] For example, the pressure relief element includes a rupture disc. The pressure relief element may be formed by means of the rupture disc, or it may have one or more additional components. These components may be attached to the rupture disc or arranged separately. In particular, the wall has several openings, with the rupture disc inserted into one opening and the other component(s) inserted into the other. The rupture disc is designed to tear, or in particular to break, when the pressure inside the cell housing exceeds the pressure in the surrounding area by a certain threshold. The tearing / breaking process is irreversible. Despite the broken rupture disc, the escape of electrolyte is prevented by the cover arrangement.For example, if the pressure difference exceeds the limit, the rupture disc may rupture completely, or it may initially tear partially. Specifically, the rupture disc is designed so that the tearing stops when the pressure difference decreases. This prevents a complete failure of the battery cell, allowing it to continue to be used, at least to a limited extent. Alternatively, if the limit is exceeded, the rupture disc may rupture completely, allowing the pressure difference to dissipate relatively quickly, thus increasing safety. In summary, the rupture disc prevents the cell casing from bursting if an excessive amount of gas forms inside the battery casing due to an unwanted chemical reaction during operation.

[0028] In another alternative, the pressure relief element comprises a pressure relief valve. For example, the pressure relief element is formed by means of the pressure relief valve, or the pressure relief valve is, for example, the additional component of the rupture disc. In yet another alternative, the pressure relief element comprises the pressure relief valve and other components. The pressure relief valve is, in particular, reversibly actuated and is designed such that it opens when a further limit value is exceeded due to the pressure difference between the pressure in the cell housing and the environment of the cell housing, so that the pressure difference is reduced at least to the further limit value or a lower limit value. In particular, the pressure relief valve closes after the further / other limit value is undershot. Preferably, the pressure relief valve is designed in the manner of a check valve.This increases robustness and prevents foreign particles from entering the cell housing. The pressure relief valve ensures continuous degassing, particularly during battery cell operation, so that gases that would otherwise be produced during normal operation are always, or at least at certain times, vented into the surrounding environment. This allows for continuous operation of the battery cell while preventing excessive gas accumulation within the cell housing. The cover design prevents electrolyte from leaking out of the pressure relief valve and does not impair its functionality.

[0029] For example, the cover assembly is formed by means of a labyrinth seal or a type of siphon. Particularly preferably, however, the cover assembly comprises a membrane and is expediently formed by means of this membrane. The membrane is arranged between the pressure equalization element and the electrode assembly and is thus mechanically located between the electrode assembly and the pressure equalization element. Due to the use of the membrane, the required installation space is reduced, and thus the energy density of the battery cell is increased. The membrane is designed, in particular, to be gas-permeable but not permeable to the electrolyte. In other words, the membrane is designed to be gas-open and electrolyte-tight. For example, the membrane is made of a polymer or a polymer matrix.In particular, the membrane is made of an elastomer, for example a thermoplastic elastomer, the material being selected such that damage due to or interaction with the electrolyte is avoided. In other words, the material is inert to the electrolyte used. For example, polypropylene is used as the material. The membrane is particularly preferably designed as a multilayer membrane, with the individual layers being tailored to the respective application, so that the functions of being electrolyte-tight and gas-permeable can be distributed among the different layers. This increases the selection of usable materials and consequently also reduces manufacturing costs.

[0030] For example, the connection(s) are arranged such that they are spaced away from the membrane. Alternatively, at least one of the connections passes through the membrane. This increases design flexibility. In particular, the membrane is at least partially attached to the respective connection, for example, directly or via other components. Advantageously, the membrane is connected to the connection in a fluid-tight or, preferably, electrolyte-tight manner. For example, the connection is made in such a way that it is also gas-tight. This increases the tightness. However, due to the other components of the membrane, gas passage to the pressure equalization element is still possible, so the functionality is not restricted by the connection.

[0031] For example, the pressure equalization element is covered by the membrane, and the membrane is (also) attached to the wall, preferably in a fluid-tight manner. Particularly preferably, however, the entire wall is covered by the membrane, and the membrane is expediently attached to other inner walls of the cell housing in a fluid-tight manner. For example, the membrane is glued or welded to these other inner walls. A gap is preferably formed between the membrane and the wall. In this way, an area is provided in which any gases can collect. Gas passage is also permitted due to the relatively large surface area of ​​the membrane, even if the membrane is designed to be relatively dense. For example, an additional membrane is provided, which, for instance, also covers the wall of the cell housing opposite the wall.This provides a larger space for gas collection, and the electrolyte is kept free of any gases that may be produced. Alternatively, the membrane can be designed as a hollow cylinder and attached to two of its inner walls, while the rest of the cell housing is spaced away from the membrane. In other words, the membrane, and therefore the electrode array, is surrounded by a space formed between the membrane and the cell housing, which is kept free of the electrolyte. This provides a comparatively large area for gas accumulation and increases the surface area available for gas passage.

[0032] For example, the membrane can be flat or planar. If the membrane is hollow cylindrical, it can be continuously curved. A corrugated membrane is particularly preferred. This increases the membrane's surface area, thus facilitating gas passage. This allows the membrane to be made relatively dense, further improving electrolyte tightness.

[0033] In an alternative embodiment, for example, a sack is formed by means of the membrane, within which the electrode arrangement is positioned. For instance, the sack is attached to the inner walls, and thus also to the wall of the cell housing, which increases robustness. Alternatively, the sack is simply loosely inserted within the cell housing, which simplifies manufacturing. In other configurations, for example, the sack is designed to be closed, and the electrode arrangement is completely enclosed on the outside by the membrane. This increases the tightness. Preferably, the sack is arranged such that it is open at one end, preferably at the upper end in the vertical direction. This facilitates the filling of the electrolyte. Furthermore, this design allows the membrane to be manufactured from an electrolyte-tight and gas-tight material, thus reducing material costs.The gas-open connection between the electrolyte arrangement and the pressure equalization element is made via the open part of the bag.

[0034] Here, the membrane is advantageously located mechanically between the electrode assembly, and consequently also the electrolyte, and the pressure equalization element, and the electrolyte is advantageously contained within the bag. Particularly preferably, the bag extends upwards in a vertical direction with respect to the electrolyte level, so that even if the battery cell is tilted or shaken, the electrolyte is prevented from reaching the pressure equalization element. In particular, the membrane is located between the electrolyte and the pressure equalization element, so that even if the electrolyte splashes or bubbles form, the membrane prevents the electrolyte from reaching the pressure equalization element.

[0035] The method for manufacturing a battery cell with an electrode arrangement located within a cell housing, wherein a pressure equalization element is incorporated into a wall of the cell housing and is connected to the electrode arrangement in a gas-open manner, and wherein a cover arrangement is arranged in the cell housing by means of which the pressure equalization element is electrolyte-tightly separated from any electrolyte present in the cell housing, provides that the electrode arrangement, the cover arrangement, and the cell housing are first provided, wherein a separate pressure equalization element is incorporated into a wall of the cell housing. Preferably, the cell housing comprises several individual parts, which are not yet attached to one another. At a minimum, however, the cell housing is open.

[0036] In a subsequent step, the electrode assembly and the cover assembly are arranged in the cell housing such that the pressure relief element is connected to the electrode assembly in a gas-open manner, with the cover assembly is electrolyte-tightly separating the pressure relief element from any electrolyte present in the cell housing. For example, the electrolyte is then filled into the cell housing, unless this has already been done when arranging the cover assembly and / or the electrode assembly within the cell housing. Alternatively, the cell housing is first closed, and the electrolyte is then filled in through another opening.

[0037] In one embodiment, for example, the electrode assembly and the cover assembly are first positioned appropriately relative to each other and, for example, attached to one another. This assembly is then positioned in the cell housing. In an alternative, the cover assembly is first arranged within the cell housing, with the cover element covering, in particular, the wall or other walls of the cell housing. Subsequently, the electrode assembly is positioned in the cell housing and / or the cover assembly.

[0038] The invention further relates to an assembly of such battery cells, wherein the assembly is preferably a battery module or a high-voltage battery. The invention further relates to a motor vehicle, such as a passenger car, with such a battery cell, and in particular such an assembly. The battery cell is preferably used to power a main drive system of the motor vehicle.

[0039] The advantages and further training described in connection with the battery cell can also be applied analogously to the process / the system / the motor vehicle and to each other, and vice versa.

[0040] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 schematically simplified, a motor vehicle that has several identical battery cells, Fig. 2 schematically in a sectional view one of the battery cells, Fig. 3 a method for manufacturing the battery cell, Fig. 4, Fig. 5 each in a flowchart variants of the battery cell manufacturing process, and Fig. 6 - Fig. 8 each according to Fig. 2 other variants of the battery cell.

[0041] Corresponding parts are marked with the same reference symbols in all figures.

[0042] In Fig. Figure 1 schematically simplifies the representation of a motor vehicle 2 in the form of a passenger 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 includes an inverter that supplies power to the electric motor. 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 integrated into an energy storage housing 12 of the energy storage device 8, made of stainless steel.

[0043] Within the energy storage housing 12 of the energy storage unit 8, several identical battery modules (not shown in detail) are arranged, each comprising several battery cells 14. The battery cells 14 of each battery module are partially connected in series and partially in parallel. Some of the battery modules are connected in series, and these in turn are connected in parallel. The electrical connection of the battery modules is electrically contacted via the interface 10, so that when the drive 6 is operated, the battery modules, and thus also the battery cells 14, are discharged or charged (recuperated). Due to the electrical connection, the voltage provided at the interface 10, which is 400 V, is a multiple of the voltage provided by each of the battery modules and also by each of the battery cells 14.

[0044] In Fig. Figure 2 shows a schematically simplified cross-sectional view of one of the structurally identical battery cells 14. The battery cell 14 has a rigid, essentially cuboid cell housing 16 made of aluminum. Thus, the battery cell 14 is a prismatic cell. Inside the cell housing 16 is an electrode arrangement 18, shown with dashed lines, which comprises several electrodes not shown in detail. The electrodes are divided into anodes and cathodes, which are stacked on top of each other, with a separator between each. For example, the anodes, cathodes, and separators are initially separate and are attached to each other using suitable fasteners. Alternatively, for example, one anode, one cathode, and two separators are already attached to each other, forming a so-called monocell.The single cells are stacked on top of each other and form, in particular, the electrode arrangement 18. In another alternative, the electrode arrangement 18 is formed by means of a so-called "jelly roll" or comprises a separator band folded several times in a Z-shape, into which the anodes / cathodes are inserted.

[0045] The electrode arrangement 18 is electrically contacted via two terminals 20, wherein, for example, one of the terminals 20 is electrically contacted with all anodes and the other with all cathodes of the electrode arrangement 18. The two terminals 20 are guided through a boundary wall 22 that vertically limits the cell housing 16 upwards, for which purpose the boundary wall 22 has openings (not shown in detail). The area between the edge of the openings and the terminals 20 is designed to be fluid-tight, for which the terminals 20 are designed accordingly. An electrical voltage is present at the terminals 20 during operation, and this enables the extraction and supply of electrical energy to the electrode arrangement 18 during operation.

[0046] The boundary wall 22 is formed by a lid (not shown) of the cell housing 16, which is attached to a cup-shaped cell cup. A pressure relief element 26 is incorporated into the wall 24 opposite the boundary wall 22, which forms the bottom of the cell housing 16 when the battery cell 14 is used as intended. For this purpose, the wall 24 has an opening 28 that is completely filled by the pressure relief element 26, which is fluid-tightly attached to the wall 24. In this embodiment, the pressure relief element 26 is a rupture disc. The rupture disc is designed to rupture when a pressure difference between the pressure inside the cell housing 16 and the surrounding environment exceeds a certain limit.The rupture disc 26 initially tears open until the pressure difference decreases. If this does not occur, the rupture disc 26 tears open completely and thus breaks.

[0047] Within the cell housing 16, a cover assembly 30 is arranged, designed as a bag open vertically upwards, and made of a suitably folded membrane 32. The membrane 30 is designed to be both electrolyte- and gas-tight. The bag is fluid-tight and is simply loosely inserted into the cell housing 16, allowing gas to pass between the cell housing 16 and the membrane 32. In a variant not shown, the bag is attached to the cell housing 16 in sections. The electrode assembly 18 is inserted into the bag formed by the cover assembly 30, projecting vertically beyond the bag. This reduces the amount of material required for the membrane 32 and simplifies assembly and manufacturing.In this way, the electrode arrangement 18 is also connected to the pressure equalization element 26 in a gas-open manner, and gas passage from the electrode arrangement 18 to the pressure equalization element 26 is not prevented or hindered by the boundary wall 22. In summary, the cover arrangement 30 thus includes the membrane 32, which is mechanically arranged between the pressure equalization element 26 and the electrode arrangement 18.

[0048] The cover assembly 30, namely the bag, is filled with an electrolyte 36 up to a fill level 34. The fill level 34 is located vertically below the upper end of the bag formed by the membrane 32, so that even if the cell housing 16 is tilted, the electrolyte 36 does not leak out of the bag. Thus, the cover assembly 30 provides an electrolyte-tight seal between the pressure equalization element 26 and the electrolyte 36 present in the cell housing 16.

[0049] If unwanted chemical reactions occur during operation between the electrolyte 36 and the electrode arrangement 18, gases can be formed, and the volume of electrolyte 36 in the cell housing 16 decreases, causing the fill level 34 to drop. However, since a comparatively large amount of electrolyte 36 remains in the cell housing 16, the battery cell 14 can continue to operate unimpeded, namely by supplying or withdrawing electrical energy. Due to the gases, however, overpressure develops in the cell housing 16. The gases can then travel unimpeded to the pressure equalization element 26 and accumulate, in particular, at the bottom of the cell housing 16. If the overpressure exceeds the limit, the overpressure equalization element 26, designed as a rupture disc, ruptures, allowing the gases to escape from the cell housing 16.Due to the cover arrangement 30, the electrolyte 36 is prevented from escaping from the cell housing 16, so that the battery cell 14 can still be used.

[0050] In Fig. Figure 3 shows a method 38 for manufacturing identical battery cells 14. In a first step 40, the electrode assembly 18, the cover assembly 30, and the cell housing 16 are provided. The cell housing 16 already has the opening 28 in the wall 24 into which the pressure equalization element 26 is inserted. In other words, the pressure equalization element 26, which is a separate component from the wall 24, is integrated into the wall 24 of the cell housing 16.

[0051] In a subsequent second step 42, the electrode arrangement 18 and the cover arrangement 30 are arranged in the cell housing 16 such that the pressure equalization element 26 is connected to the electrode arrangement 18 in a gas-open manner, with the pressure equalization element 26 being electrolyte-tightly separated from the electrolyte 36 present in the cell housing 16 by means of the cover arrangement 30. For this purpose, the bag is positioned accordingly in the cell housing 16. Preferably, the electrolyte 36 is then filled into the bag and the cell housing 16 is sealed fluid-tight.

[0052] In Fig. Figure 4 shows a first variant of the process 38, namely the second step 42. In this step, the electrode assembly 18, to which the terminals 20 are already attached, is first inserted into the bag-like cover assembly 30. Subsequently, the assembly of electrode assembly 18 and cover assembly 30, which are loosely connected to each other, is inserted into the cell housing 16. In particular, the boundary wall 22 is formed by means of a separate cover, which, after the cover assembly 30 has been positioned in the cell housing 16, is attached to the other components of the cell housing 16, with the terminals 20 passing through the boundary wall 22.

[0053] In Fig. Figure 5 shows a modification of method 38. In the second step 45, the cover assembly 30 is first positioned inside the cell housing 16. The electrode assembly 18 is then inserted into the bag-like cover assembly 30 and thus also into the cell housing 16. Following this, the electrolyte 36 is added, and the boundary wall 22 is appropriately positioned and attached to other components of the cell housing 16.

[0054] In Fig. 6 is according to the representation of the Fig. Figure 2 shows a modification of the battery cell 14. In this variant, the boundary wall 22 is free of the openings containing the terminals 20, and the terminals 20 protrude through opposing side walls 44 of the cell housing 16 into the terminals 20. In this variant, the electrode arrangement 18 is also formed, for example, by means of a "jelly roll," whereby the electrode arrangement 18 remains electrically contacted with the terminals 20. The terminals 20 extend through the cover arrangement 30, which is also designed as a bag, with the membrane 32 being partially open to allow the terminals 20 to pass through. The membrane 32 is fluid-tightly attached to the terminals 20, thus preventing the electrolyte 36 from escaping the bag.

[0055] Wall 24 still features the opening 28 into which the pressure relief element 26 is fluid-tightly inserted. Wall 24 is again formed by the base of the cell housing 16. However, in contrast to the previous embodiment, the pressure relief element 26 is formed by a pressure relief valve. The pressure relief valve is designed such that it opens at a lower pressure difference, namely at a further threshold value, between the pressure in the cell housing 16 and the pressure in the environment of the cell housing 16, allowing the gases generated in the cell housing 16 to escape from the cell housing 16 via the pressure relief element 26. As soon as the pressure difference falls below another threshold value, the pressure relief valve, designed as a check valve, closes, thus preventing the ingress of foreign particles into the cell housing 16.In this variant of the battery cell 14, due to the design of the overpressure compensation element 26, essentially continuous degassing takes place during operation.

[0056] In Fig. Figure 7 shows a further modification of the battery cell 14, in which the cell housing 16, the electrode arrangement 18, and the terminals 20 remain unchanged. The pressure equalization element 26 also remains unchanged. Only the cover arrangement 30 is modified, although it still includes the membrane 32. The material of the membrane 32 is changed and is now gas-permeable, while the membrane 32 remains electrolyte-tight. To provide these functionalities, the membrane 32 has different layers formed from different materials.

[0057] The membrane 32 is hollow cylindrical and completely surrounds the electrode assembly 18. The opposite ends of the hollow cylinder thus formed are fluid-tight, namely by bonding or welding, attached to further inner walls 46 of the cell housing 16, which are provided by the two opposing side walls 44. The membrane 32 is spaced apart from the wall 24. Consequently, a circumferential space 48 is formed between the cell housing 16 and the membrane 32. The electrolyte 36 is located within the membrane 32, so that the space 48 is free of the electrolyte 36. In summary, the membrane 32 completely covers the wall 24, and a portion of the cell housing 16 is not in contact with the electrolyte 36. Consequently, corrosion is prevented in this area, and the service life of the battery cell 14 is increased.In this variant, the electrolyte 36 cannot reach the pressure equalization element 26 even in the event of a comparatively large shock or if the battery cell 14 tips over.

[0058] The gases unintentionally generated during operation enter the chamber 48 through the membrane 32. Due to the relatively large surface area of ​​the membrane 32, the gas passage is essentially unimpeded, so that the pressure inside the membrane 32 is essentially the same as outside the membrane 32, i.e., in the chamber 48. If the pressure difference between the pressure inside the cell housing 16 and the pressure outside the cell housing 16 exceeds the further limit value, the gases are released into the environment of the cell housing 16 via the pressure equalization element 26, without any escape of the electrolyte 36.

[0059] In Fig.Figure 8 shows a further modification of the battery cell 14, in which only the cover arrangement 30 is changed compared to the previous embodiment. The cover arrangement 30 again includes the membrane 32, which is made of the same material as in the previous variant. However, the membrane 32 is arranged essentially in a plane and is not curved. Due to waves introduced into the membrane 32, it is not completely in a plane. Consequently, the membrane 32 has an increased surface area compared to the completely flat embodiment. The wall 24 and the pressure equalization element 26 are completely covered by the membrane 32, which is arranged vertically above the wall 24 at a distance.The membrane 32 is in turn fluid-tightly attached to the other inner walls 46 and the other inner walls (not shown) by welding or gluing, the respective weld or glue seam being straight, which simplifies manufacturing. The electrolyte 36 is thus retained above the wall 24 by means of the membrane 32.

[0060] Vertically above the electrode arrangement 18, another membrane 50 is arranged, which is identical in design to the membrane 32 and is also fluid-tightly connected to the other inner walls 46. This creates an additional space 52, which is also free of the electrolyte 36 and in which the gases can collect. The additional space 52 is fluidically connected to the pressure equalization element 26 by means of a device shown in more detail, so that the gases can also be discharged from there. Due to the corrugated design of the membrane 32 and the additional membrane 50, the surface area available for gas passage is increased.

[0061] The invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived by a person skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in connection with the individual embodiments can also be combined with one another in other ways without departing from the subject matter of the invention. Reference symbol list 2 motor vehicles 4-wheeler 6 Drive 8 Energy storage 10 Interface 12 energy storage housings 14 battery cells 16 cell casings 18 Electrode arrangement 20 connection 22 Boundary wall 24 wall 26 Overpressure compensation element 28 Opening 30 Cover arrangement 32 Membran 34 Fill level 36 Electrolyte 38 procedures 40 first step 42 second step 44 side wall 46 more interior walls 48 Room 50 more membranes 52 additional spaces

Claims

[1] Battery cell (14) with an electrode arrangement (18) arranged within a cell housing (16), wherein an overpressure equalization element (26) is inserted into a wall (24) of the cell housing (16) which is connected to the electrode arrangement (18) in a gas-open manner, and wherein a cover arrangement (30) is arranged in the cell housing (16) by means of which the overpressure equalization element (26) is electrolyte-tightly separated from an electrolyte (36) present in the cell housing (16). [2] Battery cell (14) according to claim 1, characterized by , that the pressure equalization element (26) is inserted into a base of the cell housing (16). [3] Battery cell (14) according to claim 1 or 2, characterized by , that the overpressure equalization element (26) includes a rupture disc. [4] Battery cell (14) according to any one of claims 1 to 3, characterized by , that the pressure equalization element (26) includes a pressure relief valve. [5] Battery cell (14) according to any one of claims 1 to 4, characterized by , that the cover arrangement (30) comprises a membrane (32) which is arranged between the overpressure equalization element (26) and the electrode arrangement (18). [6] Battery cell (14) according to claim 5, characterized by , that the entire wall (24) is covered by means of the membrane (32), wherein the membrane (32) is fluid-tightly attached to further inner walls (46) of the cell housing (16). [7] Battery cell (14) according to claim 6, characterized by , that the membrane (32) is corrugated. [8] Battery cell (14) according to claim 5, characterized by , that a sack is formed by means of the membrane (32) within which the electrode arrangement (18) is arranged. [9] Method (38) for manufacturing a battery cell (14) according to any one of claims 1 to 8, wherein - an electrode arrangement (18), a cover arrangement (30) and a cell housing (16) are provided, wherein an overpressure equalization element (26) is incorporated into a wall (24) of the cell housing (16), - the electrode arrangement (18) and the cover arrangement (30) are arranged in the cell housing (16) such that the overpressure equalization element (26) is connected to the electrode arrangement (18) in a gas-open manner, wherein the overpressure equalization element (26) is electrolyte-tightly separated from an electrolyte (36) present in the cell housing (16) by means of the cover arrangement (30).

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