Battery cell

Abstract

The invention relates to a battery cell (14) having a cell housing (26), in which a plurality of electrodes (20) is disposed. The cell housing (262) comprises a wall (28) having a predetermined breaking region (30), the predetermined breaking region (30) comprising an opening (32) which is covered by means of a gas-permeable membrane (36). A recess (38) extending to the opening (32) is introduced into the wall (28) in the predetermined breaking region (30).

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 is also referred to as a cell cup. The cell housing also protects the electrolyte from environmental influences. In order to provide a comparatively large capacity from each battery cell, several such galvanic elements, usually up to 100, are usually arranged in the common cell housing. In order 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 a stacking direction, forming an essentially cuboid-shaped cell stack. In an alternative embodiment, for example, the separator is designed in a strip-shaped manner and is provided with several electrodes on opposite sides.The strip is wound into a roll, specifically a so-called "jelly roll." Thus, the galvanic elements are rolled into a cylindrical shape.

[0007] The cell housing is shaped depending on the arrangement of the galvanic elements used. It is possible to make it rigid and, for example, made of aluminum. In this case, the cell housing is cuboidal in shape. 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 can lead to the de-contacting of individual electrodes and 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 occur between the individual components of the battery cell and the environment.

[0009] To avoid such gas formation, a special selection of the individual electrode materials is necessary, which on the one hand increases manufacturing costs. On the other hand, such materials reduce the capacity of the battery cell. Alternatively, additional elements can be present in the cell housing, for example, by means of which the resulting gases are bound and / or converted. In another variant, the cell housing is designed to be comparatively robust, so that the pressure that leads to a rupture of the cell housing is never reached during operation of the battery cell. However, due to the additional elements and the robust design of the cell housing, the installation space and weight of the battery cell are increased, which therefore reduces the energy density.The invention is based on the object of specifying a particularly suitable battery cell, wherein operational reliability and / or energy density are advantageously increased, wherein manufacturing costs are expediently reduced.

[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 truck or a bus. However, the motor vehicle is particularly preferably a passenger car. Alternatively, the motor vehicle is, for example, a boat, an aircraft, a helicopter, a multicopter, a bicycle (pedelec), or a motorcycle.

[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. Preferably, however, there is one more anode than cathode. Particularly preferably, all anodes and all cathodes are structurally identical to one another, 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, for example, is used 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, 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, intended, and configured for this purpose. The active material used for the cathode is, for example, a lithium metal oxide, such as lithium cobalt(III) oxide (LiCoO2), NMC, for example NMC622 or NMC811, NCA, LMNO, or LFP, and / or for the anode, LTO or Si-based graphite.

[0018] In particular, the electrodes are substantially 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, which is preferably also designed to be flat, is arranged between adjacent electrodes, i.e. in particular between one of the anodes and one of the cathodes. For example, all separators are structurally identical to one another. In particular, the electrodes are stacked substantially flush one above the other, wherein, for example, all anodes protrude at least slightly beyond the cathodes. Particularly preferably, the protrusion on one of the sides is increased.Preferably, the cathodes also protrude beyond the anodes on one side, with the (enlarged) projections located on opposite sides of the cell stack. This simplifies contacting the anodes and cathodes with other components. Due to the stacking of the electrodes, the cell stack is 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 up into a cylindrical shape or the like, so that a so-called "jelly roll" is formed. The battery cell has a cell housing, within which the electrodes are arranged, for example the cell stack or the "jelly roll". Suitably, the cell housing has a base body, within which the electrodes are arranged. The base body is in this case pot-shaped, for example, and closed by means of a cover of the cell housing. This simplifies the arrangement of the electrodes. In particular, a volume between 0.1 dm3 and 10 dm3 is enclosed by the cell housing, preferably the base body.For example, the cell housing is additionally at least partially filled with an electrolyte, or the electrolyte is, for example, already partially formed by the respective active material. The cell housing, in particular any base body, is preferably rigid. In other words, the battery cell is a prismatic cell. In particular, the cell housing, preferably the base body and / or any cover, is made of a metal, such as aluminum, i.e. pure aluminum or an aluminum alloy. The cell housing, in particular the base body, has, for example, a cuboid shape. Alternatively, the cell housing, and preferably the base body, is flexible and, for example, at least partially formed by a metal foil, which is coated in particular 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.

[0020] 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 prevent contact of the electrodes / electrolytes 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).

[0021] 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), 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.

[0022] The cell housing, in particular the base body, has a wall with a predetermined breaking area. In other words, the wall has the predetermined breaking area. The wall is, for example, flat or curved / uneven. The predetermined breaking area thus covers a specific surface of the cell housing, in particular of the base body, namely a portion of the wall. The predetermined breaking area is designed such that it breaks at a specific pressure difference between the interior and exterior of the cell housing, thus enabling, in particular, a mass transfer between the interior of the cell housing and the environment. The breaking of the predetermined breaking area is irreversible. For example, if the pressure difference, which is also referred to below as bursting pressure, is exceeded, the predetermined breaking area breaks completely or only partially.In particular, the area of ​​the predetermined breaking area that breaks and is thus opened depends on the actual pressure difference.

[0023] The cell housing is particularly designed such that when the bursting pressure is exceeded, the cell housing initially only breaks in the predetermined breaking area, i.e., a portion of the wall, while the remaining components of the cell housing, in particular the base body, remain undamaged. These components are only damaged if the pressure difference increases further and, in this case, break in an uncontrolled manner. The bursting pressure is preferably selected such that it is lower than the pressure difference between a pressure inside the cell housing and a pressure outside the cell housing that would lead to the (uncontrolled) destruction of the cell housing, for example, a complete bursting or rupture. The bursting pressure is preferably between 70% and 90%, between 75% and 85%, or 80% of this pressure difference.

[0024] The predetermined breaking area has an opening, which is arranged in particular in a central region, i.e. offset inward from an edge of the predetermined breaking area. Suitably, the distance of the opening from an edge of the predetermined breaking area is greater than a quarter of the extent of the predetermined breaking area in the respective direction. In particular, the opening is located exactly in the center of the predetermined breaking area. The area of ​​the opening is smaller than the area of ​​the predetermined breaking area and in particular smaller than 50%, 20%, 10%, 5%, 1%, or 0.1% thereof.

[0025] The opening is covered by a gas-permeable membrane. In particular, the membrane is rigidly, i.e. immovably, connected to the cell housing, preferably the base body and / or the predetermined breaking region, such that movement of the membrane relative to the cell housing / base body is prevented. The area of ​​the membrane is at least equal to the area of ​​the opening or preferably larger, such that the membrane completely overlaps the opening. Preferably, the membrane is arranged such that passage of liquids and / or gas between the membrane and the predetermined breaking region is prevented. In other words, the membrane is connected to the cell housing in a gas- and fluid-tight manner, for example directly or via further components. For this purpose, the membrane is particularly preferably welded to the cell housing, e.g. the predetermined breaking region, suitably with a circumferential weld seam.For this purpose, for example, an ultrasonic, laser, or thermal welding process is used. Alternatively, the membrane is connected to the cell housing in a form-fitting and / or material-fitting manner, in particular by adhesive bonding. 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 there is a gap between the opening and the connection of the membrane to the cell housing, e.g., the adhesive or weld seam. Consequently, gas can only escape from or into the cell housing through the opening, with the gas also being guided through the membrane.

[0026] In particular, the membrane is selected such that it is permeable to 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 to water vapor, is preferably significantly lower. In particular, the membrane has a ratio of CO2 permeability to moisture permeability of at least 0.5, of at least 1, or at least 1.5. The ratio is preferably more than 0.5 and less than 3. In particular, the membrane acts as a barrier to the penetration of moisture, in particular water vapor, into the cell housing. 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 difficult or significantly reduces the penetration of moisture and liquids, particularly water, into the cell housing. 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 of between 85% and 100% and a density of between 0.2 g / cm3 and 2 g / cm3. Such a choice of material provides gas permeability, while the membrane prevents or at least impedes the penetration of moisture, particularly water vapor, into the cell housing. A membrane suitable for battery applications is described in WO 2021 / 079163 A1. For example, the membrane is flat. This simplifies production and reduces weight.

[0027] A recess is made in the wall which has the predetermined breaking area and is thus located in the predetermined breaking area. In particular, the recess is only located in the predetermined breaking area. The recess serves to reduce the wall thickness, i.e. the thickness of the wall, whereby the recess is only local. The recess preferably extends along a path which is, for example, straight, corrugated / bent or shaped in some other way. The recess is preferably elongated. For example, the recess is a notch and, in particular, has a V-shaped cross-section. Alternatively, the recess is designed in the manner of a bead or groove. The recess reaches as far as the opening, such that at least a section of the edge of the opening merges into the recess and / or comprises part of it.

[0028] Due to the gas-permeable membrane, essentially continuous degassing of the cell housing is possible, so that the formation of a pressure difference between a pressure outside the cell housing and a pressure inside the cell housing, in particular due to the unwanted formation of gases in the cell housing during operation of the battery cell, is avoided or slowed down. Due to the comparatively small area of ​​the opening, on the one hand, the mechanical integrity of the cell housing is only insignificantly reduced. On the other hand, the penetration of foreign substances such as moisture or liquids into the cell housing is only possible in principle in this area, which is comparatively unlikely. This enables comparatively safe operation of the battery cell over a comparatively long period of time, thus increasing operational reliability.In other words, during undisturbed operation of the battery cell, due to the essentially continuous release via the membrane, there is no excessive accumulation of gases within the cell casing, so that the pressure difference between the environment of the cell casing and the interior of the cell casing remains comparatively low. However, if, due to unwanted chemical reactions in the cell casing, for example, in the event of an overload, the pressure difference increases comparatively sharply and quickly, so that the resulting gases cannot be sufficiently discharged via the opening and the membrane, the predetermined breaking area breaks, and the cell casing is opened at a defined point, namely in the predetermined breaking area. Consequently, uncontrolled damage to the cell casing and an uncontrolled influence on the environment are avoided.Rather, this only occurs in the predetermined breaking point, making it possible to adapt the battery cell's installation situation accordingly. This increases operational reliability.

[0029] The breaking / tearing begins in the area of ​​the depression, which represents a mechanical weakening of the wall. Because the depression extends to the opening, the initial force required is reduced. The depression extending to the opening thus ensures that, on the one hand, if the burst pressure is exceeded, the predetermined breaking area actually and always tears, which increases safety. On the other hand, because the depression extends to the opening, the tearing / tearing begins at the opening and runs along the depression. This also determines the shape of the tear. If the burst pressure is only slightly exceeded, the predetermined breaking area does not tear completely, but only partially along the depression, so that the battery cell can still be operated afterwards if necessary.

[0030] For example, the predetermined breaking zone has a reduced wall thickness compared to the rest of the wall, with the wall thickness being reduced even further in the area of ​​the recess, i.e., the thickness of the wall. This ensures that if the bursting pressure is exceeded, the wall only tears in the area of ​​the predetermined breaking zone. Alternatively, the predetermined breaking zone, with the exception of any recess or other local reductions in wall thickness, has essentially the same wall thickness as the rest of the wall. This facilitates manufacturing. Furthermore, mechanical stress during assembly does not cause damage, thus increasing robustness.

[0031] Particularly preferably, the predetermined breaking region is integral with the rest of the wall and preferably pre-formed with it. In other words, the predetermined breaking region is not formed by means of an initially separate component that was inserted into a corresponding recess in the wall. This facilitates production. For example, the recess is already present when the wall is pre-formed or is preferably introduced subsequently, for example by etching, lasering or engraving. This facilitates production of the battery cell. To produce the battery cell, in particular, the cell housing having the (undamaged) wall is first created, for which an extrusion process is used, for example. The opening and the recess are then introduced into the wall; these are therefore not created by pre-forming the wall. The opening is then covered with the membrane, which is preferably attached to the cell housing.

[0032] For example, the membrane is attached to an outer surface of the cell housing / wall, for example, to an outer surface of the predetermined breaking area or any base body. In this way, the membrane prevents the interior of the cell housing from being filled, leaving a comparatively large volume available for the electrodes. This increases the capacity of the battery cell. This also makes it possible to select a membrane surface area larger than the area of ​​the opening. After the gases pass through the opening, an enlarged surface area is available for them to pass through the membrane.

[0033] In an alternative, the membrane is arranged on an inward-facing side of the predetermined breaking area. In other words, the membrane is offset from the predetermined breaking area into the interior of the cell casing. In this way, even at a comparatively high pressure within the cell casing, the membrane does not bulge excessively outwards if the design of the membrane does not allow immediate passage of gases. In this case, the membrane is at least partially pressed against the inward-facing side of the predetermined breaking area. Consequently, the membrane is stabilized by the predetermined breaking area, which increases robustness. The passage of gas between the predetermined breaking area and the membrane is also prevented, which increases tightness in this area.

[0034] Preferably, the opening is covered with a gas-permeable, hydrophobic, i.e., at least water-repellent, additional membrane. Preferably, the contact angle of the material of the additional membrane to water is greater than 80°, 90°, or 100°, especially if the material is also exposed to air or is in ambient air. The additional membrane thus keeps moisture away from the membrane, further impeding the penetration of moisture into the cell housing. At the very least, however, the additional membrane keeps moisture from penetrating from the outside out.

[0035] For example, the predetermined breaking area / 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 predetermined breaking area / opening is expediently offset inward from the respective ends up to a maximum of one-third of the maximum length of the cell housing.

[0036] If the battery cell is a prismatic cell, the predetermined breaking area / 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 predetermined breaking area / opening is thus arranged in an area where gases that arise collect, thus enabling comparatively efficient removal of the gases through the opening.

[0037] The predetermined breaking area is, for example, stadium-shaped, round, or rectangular. In particular, the area of ​​the predetermined breaking area is between 0.01 cm2 and 20 cm2, and preferably between 0.1 cm2 and 10 cm2. Suitably, the predetermined breaking area has a size of 0.01% and 50% of the area of ​​the cell housing. Preferably, the predetermined breaking area has a size of 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. Suitably, the opening has an area of ​​50 μm2 to 15 mm2, preferably of 0.2 mm2 to 3 mm2.

[0038] Preferably, the predetermined breaking area is delimited by a further recess. In other words, the edge of the predetermined breaking area is at least partially formed by the further recess, and at the edge of the predetermined breaking area, the wall thickness is thus locally reduced due to the further recess. The further recess also structurally weakens the wall, so that if the bursting pressure is exceeded, tearing also occurs along the further recess, which is why the predetermined breaking area is also opened at the edge.

[0039] For example, only part of the edge of the predetermined breaking area is formed by the further recess. If the bursting pressure is exceeded and the wall tears along the further recess, the tearing along the part of the edge of the predetermined breaking area that does not have the further recess will not occur. Consequently, even if the further recess is completely torn, the components of the predetermined breaking area remain on the wall and are bent outwards, forming a type of film hinge. This prevents individual fragments of the wall from moving away uncontrollably, which prevents damage to surrounding components. Alternatively, the further recess can be circumferential, so that the entire predetermined breaking area is enclosed by the further recess.Thus, if the burst pressure is exceeded and the entire further recess tears, the entire predetermined breaking area is separated from the rest of the wall, allowing for comparatively rapid pressure equalization. This prevents further uncontrolled destruction of the cell casing, thus increasing operational reliability.

[0040] For example, the depression is spaced apart from the further depression. However, it is particularly preferred if the depression extends to the further depression. In other words, the two depressions merge into one another. Consequently, when the bursting pressure is exceeded, the depression begins to tear at the opening and the tear is conducted to the further depression, which then also tears. In summary, the tearing of the predetermined breaking area begins at the opening, runs along the depression to the further depression and then along the further depression. This reduces the force required to initially tear the further depression. This ensures that the predetermined breaking area tears at least partially around the circumference, so that a comparatively large part of the wall is exposed. This achieves comparatively rapid pressure equalization.

[0041] For example, the angle between the depression and the further depression can be arbitrary or, for example, 90°. Particularly preferably, however, the angle between the depression and the further depression, as in the transition region, is greater than 110°. Expediently, the angle is greater than 140° or 170°. The intersection point of the depression with the further depression forms the apex of the angle. This ensures that the tearing of the depression is also carried over to the further depression, and the effort required to start tearing the further depression is reduced. For example, the depression and / or the further depression are straight in the area where they meet. Particularly preferably, however, the transition between them is curved. In this way, the effort required to start tearing the further depression is further reduced, which is why tearing can continue reliably once it has started.

[0042] For example, the predetermined breaking area only has the recess and optionally the further recess. However, it is particularly preferred if an additional recess is made in the wall in the predetermined breaking area, extending as far as the opening. The additional recess thus also provides a local reduction in wall thickness. Thus, when the bursting pressure is exceeded, the predetermined breaking area is also opened along the additional recess, so that a large part of the predetermined breaking area is released relatively quickly, thus enabling rapid pressure equalization. The additional recess is preferably located on the opposite side of the opening with respect to the recess. In particular, an angle between the recess and the additional recess, with the opening forming the apex of the angle, is greater than 160° or 170°. Preferably, the angle is equal to 180°.Suitably, the recess and the additional recess are S-shaped and, for example, point-symmetrical to each other with respect to the opening. Thus, a comparatively large area is quickly released when the burst pressure is exceeded.

[0043] Preferably, the additional depression also extends to the further depression, if present. Thus, the tearing of the further depression begins at two different points, namely in the region of the intersection with the depression and the region of the intersection with the additional depression, which is why the area released within a certain time due to tearing / breaking is further increased. For example, only the depression and the additional depression are present, which extend to the opening. Particularly preferably, further such additional depressions are present, which also extend to the opening, which is why the area released within a certain period of time after the bursting pressure is exceeded is further increased.

[0044] For example, the cell housing has only a single opening covered by the membrane. Alternatively, the cell housing comprises several such openings, each covered by the membrane. In this case, the membrane is, for example, continuous, or each of the openings is assigned a corresponding (separate) membrane. Particularly preferably, these openings are incorporated into the same wall.

[0045] In summary, in addition to the opening, the battery cell therefore has a second opening and optionally further such openings. For example, the second opening is arranged outside the predetermined breaking region. However, it is particularly preferred that the second opening is a component of the predetermined breaking region, and the second opening is arranged symmetrically with respect to the opening. The second opening is covered either with the membrane or with a further second membrane, so that gas can pass through here too, but moisture cannot enter the cell housing. For example, the edge surrounding the second opening is intact. In other words, the area around the second opening has a constant wall thickness. However, it is particularly preferred that a second depression extending as far as the second opening is made in the wall in the predetermined breaking region.For example, the second opening and / or the second recess are designed identically to the opening or recess respectively. Alternatively, they differ, for example in their dimensions, so that different optimizations can be carried out. Due to the second opening and the second recess, the predetermined breaking area also tears there when the bursting pressure is exceeded. This further increases the area released within a certain period of time after the bursting pressure is exceeded, while during normal operation there is no excessive structural weakening of the cell housing and penetration of foreign particles into the battery cell is not possible. Manufacturing costs are also not increased or only slightly increased, and the second opening and the second recess are introduced into the wall in particular in the same work step as the opening and the recess.

[0046] For example, there is an additional second recess extending to the second opening, so that the tearing also occurs in different directions starting from the second opening. If the additional recess is present, the second recess in particular extends to the further recess, which is why the tearing is directed to the further recess via the second recess.

[0047] For example, the area of ​​the wall between the two openings is undamaged. However, the two openings are particularly preferably connected by means of a connecting recess. In other words, the connecting recess is introduced into the wall, thus also a local reduction in wall thickness, with the connecting recess running between the two openings, i.e. reaching up to the two openings. Consequently, even if the bursting pressure is exceeded, the area between the two openings is torn by means of the connecting recess, with the tearing starting in particular from both openings. This further increases the speed at which a certain area is released after the bursting pressure is exceeded. For example, the connecting recess is straight or, particularly preferably, corrugated or curved.Thus, the length of the connecting recess is increased, which increases the area for gas passage after the burst pressure is exceeded, allowing comparatively rapid pressure equalization. Particularly preferably, several such second openings and corresponding second recesses are provided.

[0048] In particular, the size of the membrane is smaller than the size of the (complete) predetermined breaking area. In other words, the predetermined breaking area completely covers the membrane. This reduces material costs. Furthermore, the membrane surface can be optimized regardless of the size of the predetermined breaking area with regard to the necessary size and its connection to the predetermined breaking area / cell housing. Furthermore, after the recess has been torn and the predetermined breaking area has been opened, at least part of the area covered by the predetermined breaking area is not covered by the membrane, which is why comparatively unhindered pressure equalization can occur there. Alternatively, the size of the membrane is larger than the size of the predetermined breaking area, and the membrane overlaps the predetermined breaking area. In this way, when the membrane is attached to the cell housing, in particular at the edge, the predetermined breaking area is not influenced.

[0049] For example, the predetermined breaking area comprises further auxiliary recesses that are spaced apart from the opening or other openings. The auxiliary recesses extend, for example, to another of the existing recesses or are also spaced apart from them. The auxiliary recesses, which represent structural weakenings of the predetermined breaking area, are used in particular to specify a form of tearing so that the predetermined breaking area is opened in a desired manner. For example, the recesses in the predetermined breaking area differ from one another. However, it is particularly preferred that they have essentially the same depth, which facilitates production. This also means that if the bursting pressure is exceeded, these recesses tear in an undifferentiated manner, so that, for example, if one of the recesses malfunctions, the rest of the construction is not affected.Alternatively, or in combination with this, the cross-section of the recesses is identical to each other, allowing them to be manufactured with the same tool. In another alternative, at least one of the recesses has a different depth. This makes it possible to specify the tearing process of the predetermined breaking area and adapt it, for example, to the components surrounding the battery cell in the assembled state.

[0050] The invention further relates to a battery cell assembly of such 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.

[0051] The advantages and developments described in connection with the battery cell are also applicable to the assembly / motor vehicle and to each other, and vice versa. Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. In the drawings:

[0052] Fig. 1 shows a simplified schematic representation of a motor vehicle having several identical battery cells,

[0053] Fig. 2 shows a schematic sectional view of one of the battery cells having a cell housing with a predetermined breaking area,

[0054] Fig. 3 shows a schematic plan view of the predetermined breaking area,

[0055] Fig. 4 shows a schematic sectional view of the predetermined breaking area, and

[0056] Fig. 5 - 12 each show schematically in a plan view variants of the predetermined breaking area.

[0057] Corresponding parts are provided with the same reference numerals in all figures.

[0058] 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 into an energy storage housing 12 of the energy storage device 8, which is made of stainless steel.

[0059] 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 with one another and partly electrically connected in parallel with one another. Some of the battery modules are in turn electrically connected in series with one another, and these in turn are electrically connected in parallel with one another. 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, is a multiple of the electrical voltage provided by each of the battery modules and also by each of the battery cells 14.

[0060] 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.

[0061] The projections of the anodes 16 and the cathodes 18 are each welded to an associated busbar 22 made of copper. One of the busbars 22 is assigned to each of the anodes 16 and the cathodes 18. The busbars 22 each have a terminal 24 that extends through a cuboid cell housing 26, within which the anodes 16 and the cathodes 18 are arranged. The cell housing 26 is rigid and made of aluminum. Thus, the battery cell 14 is a prismatic cell. The cell housing 26 is filled with a liquid electrolyte (not shown in detail).

[0062] The cell housing 26 has a wall 28 with a predetermined breaking area 30 having an area of ​​5 cm². The predetermined breaking area 30 is designed such that, if a pressure difference between a pressure outside the cell housing 26 and a pressure inside the cell housing 26 exceeds a bursting pressure of 1 bar, the predetermined breaking area 30 ruptures, thus opening the cell housing 26 and allowing pressure equalization. The bursting pressure is 90% of the maximum pressure load on the cell housing 26, i.e., the pressure difference at which irreversible and uncontrolled destruction of the cell housing 26 occurs.

[0063] Figure 3 shows a schematic plan view and Figure 4 a sectional view of the predetermined breaking region 30. The predetermined breaking region 30, which is integral with the rest of the wall 28, is stadium-shaped and has an opening 32 and a second opening 34, each of which extends through the entire predetermined breaking region 30, i.e., the wall 28. On the inside, the opening 32 and the second opening 34 are covered by a gas-permeable membrane 36, which is attached to the inside of the wall 28, namely the inside of the predetermined breaking region 30, for example by welding. The size of the membrane 36 is smaller than the size of the predetermined breaking region 30, but the passage of particles from the interior of the cell housing 26 to the exterior and vice versa is only possible through the membrane 36. The membrane 36 is made of PTFE, so that it prevents the ingress of moisture into the interior of the cell housing 26.However, it is possible for CH4, for example, to escape from the cell housing 26 through the membrane 26 as well as the opening 32 and the second opening 34.

[0064] In the predetermined breaking area 30, a recess 38 extending to the opening 32 is formed, namely in the inside of the wall 28. The recess 38 has a wavy / curved profile and extends to the opening 32, wherein the recess 38 is partially covered by the membrane 36, and wherein the membrane 36 partially fills the recess 38. The recess 38 is a local reduction in the thickness of the wall 28 in the predetermined breaking area 30, wherein a cross-section of the recess 38 is rectangular in the example shown.

[0065] In addition, two additional recesses 40 are formed in the wall 28 in the predetermined breaking region 30, extending to the opening 32, said recesses also having a wavy or curved shape. The depth of the additional recesses 40 corresponds to the depth of the recess 38, and they are otherwise designed in the same way. One of the additional recesses 40 is arranged point-symmetrically to the recess 38 with respect to the opening 32. Thus, the recess 38 and this additional recess 40 meet at an angle of 180° at the opening 32. The remaining additional recess 40 is rotationally symmetrical with respect to the recess 38 and the other additional recess 40 with respect to the opening by an angle of 90°.

[0066] Also formed in the wall 28 in the predetermined breaking region 30 is a second recess 42 extending as far as the second opening 34, which is essentially structurally identical to the recess 38 but offset from the second opening 34. In other words, the course of the second recess 42 is the same as the course of the recess 38. Also associated with the second opening 34 are two additional second recesses 44 formed in the wall 28 in the predetermined breaking region 30 and extending as far as the second opening 34. One of the additional second recesses 44 is point-symmetrical to the second recess 42 with respect to the second opening 34, and the remaining additional second recess 44 is rotationally symmetrical by an angle of 90° to the second recess 42 and the other additional second recess 44 with respect to the second opening 42.The recess 38, the additional recesses 40, the second recess 42 and the additional second recesses 44 always have the same cross-section as well as the same length and the same course, whereby only the orientation and / or assignment to the respective opening 32, 34 is different.

[0067] The predetermined breaking area 30 is delimited by a further circumferential recess 46, which thus forms the edge of the predetermined breaking area 30. Consequently, the shape of the further recess 46 is stadium-shaped, with the cross-section of the further recess 46 corresponding to the cross-section of the recess 38. The recess 38, the additional recesses 40, the second recess 42 and the additional second recesses 44 extend to the further recess 46 and merge into it. Due to the curved shape of the recess 38, the additional recesses 40, the second recess 42 and the additional second recesses 44, the angle formed between these and the further recess 46 is greater than 110° at the intersection point, with an essentially continuous transition.

[0068] Furthermore, a connecting recess 48 is formed in the inside of wall 28, extending to opening 32 and to the second opening 34. In other words, the two openings 32, 34 are connected by means of the connecting recess 48. The depth and cross-section of the connecting recess 48 correspond to the respective value of the recess 38. The profile of the connecting recess 48 is corrugated, and this meets one of the additional recesses 40 at the opening 32 at an angle of 180°, and at the second opening 34 meets one of the additional second recesses 44, also at an angle of 180°.

[0069] During operation of the battery cell 14, it is possible that gases may develop in the cell housing 26 due to undesired chemical reactions. These gases can escape from the cell housing 26 to the outside via the membrane 36 and the two openings 32, 34, thus preventing an excessive pressure increase. In the event of a malfunction or excessive load, it is possible that the rate of gas dissipation may not be sufficient to limit the pressure increase within the cell housing 26. If the pressure difference between the interior of the cell housing 26 and the exterior exceeds a limit value, namely a burst pressure, the predetermined breaking region 30 begins to tear open, starting from the opening 28 along the recess 38 and the additional recess 40, as well as along the connecting recess 48.The predetermined breaking area 30 also begins to tear, starting from the second opening 34 along the second recess 42, the additional second recess 44, and the connecting recess 48. Due to the local reduction in wall thickness, the force required to initiate the tearing is reduced, so that tearing always begins when the burst pressure is exceeded. Due to the tearing, an area for gas escape is enlarged, thus limiting the pressure increase. As soon as the pressure stops increasing, the tearing stops, and the predetermined breaking area 30 remains partially open.

[0070] However, if a relatively serious malfunction occurs and the pressure difference continues to rise, the tearing will continue. The tearing will continue until the entire depression 38, the additional depressions 40, the connecting depression 48, the second depression 42 and the additional second depressions 44 have completely torn open. From these, the tearing will transfer to the further depression 46, which will then also begin to tear, namely at six different locations. Due to the transition from the individual depressions 38, 40, 42, 44 to the further depression 46, the further depression 46 will tear in a clockwise direction from the locations in the example shown. When the further depression 46 is completely torn, the individual components of the predetermined breaking region 30 are detached from the rest of the wall 28 and are detached from it due to the excess pressure in the cell casing 26.This provides a comparatively large surface area for pressure equalization, so that at least the pressure increase is stopped. This prevents the cell housing 26 from bursting uncontrollably. Consequently, other components of the motor vehicle 2 located in the vicinity of the battery cell 14 are not destroyed, even if the battery cell 14 is no longer operational.

[0071] Figures 5-11 show different embodiments of the predetermined breaking region 30 according to the illustration in Figure 3, although they are always stadium-shaped. Each predetermined breaking region 30 is also delimited by the further recess 46. In the variant shown in Figure 5, the membrane 36 and the two openings 32, 34 are not modified. The connecting recess 48, the additional recesses 40 and the additional second recesses 44 are not present. The recess 38 and the second recess 42, which extend to the respective opening 32, 34, are present. However, these are now designed to be straight and point away from the other opening 32, 34 in the direction of the further recess 46. The recess 38 and the second recess 42 are spaced apart from the further recess 46.In this embodiment, the area initially exposed by tearing open the two recesses 38, 42 is limited, so that operation of the battery cell 14 is still possible even with a comparatively small pressure increase. Only when the pressure difference is comparatively large does the further recess 46 tear open, thus exposing the entire predetermined breaking area 30. The modification of the predetermined breaking area 30 shown in Figure 6 is based on the variant shown in Figure 5. The only difference is that the recess 38 and the second recess 42 are extended and curved at the ends, so that they each open into the further recess 46 via an arc. Thus, after the recess 38 or the second recess 42 has completely torn open, the pressure is introduced into the further recess 46 via the respective intersection point. This essentially results in a continuous tearing and release of the predetermined breaking area 30.

[0072] Figure 7 shows a further modification, wherein here too the two openings 32, 34, the membrane 36 and the further recess 46 are present unchanged. The recess 38 again extends from the opening 32 to the further recess 46, and one of the additional recesses 40 is present, which is arranged point-symmetrically to the recess 38 with respect to the opening 32. The course of the recess 38 and the additional recess 40 is now straight and perpendicular to the course of the longitudinal axis of the stadium-like predetermined breaking region 30. In other words, the recess 38 and the additional recess 40 each open into the further recess 46 at an angle of 90°. The second recess 42 is designed correspondingly to the recess 38, and one of the additional second recesses 44 is present, which is shaped correspondingly to the additional recess 40.In this variant, the further depression 46 tears in both directions, starting from the intersection points with the other depressions 38, 40, 42, 44, after these have been completely torn, so that a speed with which the further depression 46 is completely torn is increased.

[0073] The variant of the predetermined breaking region 30 shown in Figure 8 essentially corresponds to the variant shown in Figure 7. Only the further recess 46 is modified and no longer circumferential. In other words, the further recess 46 is now divided into two subsections, and the predetermined breaking region 30 merges essentially continuously into the remainder of the wall 28 at two different points. The two points are located at opposite ends along the longitudinal axis of the predetermined breaking region 30, with the predetermined breaking region 30 being designed axially symmetrically with respect to the longitudinal axis. Due to the interrupted design of the further recess 46, some components of the predetermined breaking region 38 remain on the remainder of the wall 28 after it has completely torn. These components of the predetermined breaking region 30 are bent outwards with respect to the cell housing 26 due to the pressure difference.In this way, the formation of splinters, which would lead to unwanted interaction with the components surrounding the battery cell 14, is avoided. Figure 9 shows a further embodiment of the predetermined breaking region 30, wherein the two openings 32, 34 and the membrane 36 are present unchanged. The two openings 32, 34 are connected by means of the connecting recess 48, which is rectilinear and runs along the longitudinal axis of the stadium-like predetermined breaking region 30. On the side opposite the connecting recess 48 with respect to the opening 32, the recess 38, which is bent in an S-shape, opens into the opening 32. The opposite end of the recess 38 opens into the further recess 46. The second recess 42 is designed as a mirror image of this and is also S-shaped, so that it opens into the second opening 34 at the end of the connecting recess 48 opposite the latter.The further recess 46 is shortened and begins at the recess 38 and the second recess 42 into it. Thus, a portion of the predetermined breaking area 30 also remains on the rest of the wall 28 when all recesses 38, 42, 46, 48 are torn.

[0074] Figure 10 shows a further embodiment of the predetermined breaking region 30, wherein the further recess 46 is again designed to be circumferential. The membrane 36 is also present unchanged. The second opening 34 has been omitted, so that only the opening 32 remains, which is now arranged in the center of the predetermined breaking region 30. The rectilinear recess 38 and one of the rectilinear additional recesses 40 open into the opening 32 on opposite sides, namely at an angle of 180° to one another. The recess and the additional recess 40 each open into the further recess 46 at an angle of 120°. In this variant, production of the predetermined breaking region 30 is simplified.

[0075] Figure 11 shows a final embodiment of the predetermined breaking region 30, wherein the further recess 46 and the opening 32 are unchanged from the previously shown example. The recess 38 and the additional recess 40 are also present; they run straight and are located on opposite sides with respect to the opening 32. However, they are now arranged perpendicular to the course of the predetermined breaking region 30 and thus intersect the further recess 46 at an angle of 90°. The membrane 36 is extended in the longitudinal direction and covers the second opening 34, which is now arranged outside the predetermined breaking region 30. Mirror-symmetrical to the second opening 34, a further opening 50 is introduced into the wall 28 with respect to the opening 32 and is likewise covered by the extended membrane 36. In this illustrated variant, gas can escape via all three openings 32, 34, 50.If the predetermined breaking area 30 tears, the second opening 34 and the further opening 50 are not affected. In the example shown, the membrane 36 is narrower than the predetermined breaking area 30. In a variant not shown in detail, the membrane 36 is enlarged so that it completely covers the predetermined breaking area 30. This design of the membrane 36 can also be used in the other previous examples.

[0076] The variant shown in Figure 12 essentially corresponds to the embodiment shown in Figure 3. Only the membrane 36 is enlarged, so that it is now larger than the predetermined breaking area 30. The membrane 36 also completely overlaps the predetermined breaking area 30.

[0077] 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.

[0078] List of reference symbols

[0079] Motor vehicle

[0080] wheel

[0081] drive

[0082] Energy storage

[0083] interface

[0084] Energy storage housing

[0085] Battery cell

[0086] anode

[0087] cathode

[0088] electrode

[0089] Busbar

[0090] Connection

[0091] Cell housing

[0092] Wall

[0093] Predetermined breaking point

[0094] Opening second opening

[0095] membrane

[0096] Deepening additional deepening second deepening additional second deepening further deepening

[0097] Connection deepening further opening

Claims

A battery cell (14) having a cell housing (26) in which a plurality of electrodes (20) are arranged, and which has a wall (28) with a predetermined breaking region (30), wherein the predetermined breaking region (30) comprises an opening (32) which is covered by a gas-permeable membrane (36), and wherein a recess (38) extending as far as the opening (32) is introduced into the wall (28) in the predetermined breaking region (30). Battery cell (14) according to claim 1, characterized in that the predetermined breaking region (30) is delimited by a further recess (46). Battery cell (14) according to claim 2, characterized in that the further recess (46) is circumferential. Battery cell (14) according to claim 2 or 3, characterized in that the recess (38) extends as far as the further recess (46). Battery cell (14) according to claim 4, characterized in that an angle formed between the recess (38) and the further recess (46) is greater than 110°.Battery cell (14) according to one of claims 1 to 5, characterized in that an additional recess (40) extending as far as the opening (32) is introduced into the wall (28) in the predetermined breaking region (30). Battery cell (14) according to one of claims 1 to 6, characterized in that the predetermined breaking region (30) comprises a second opening (34), wherein a second recess (42) extending as far as the second opening (34) is introduced into the wall (28) in the predetermined breaking region (30). Battery cell (14) according to claim 7, characterized in that the two openings (32, 34) are connected by means of a connecting recess (48). Battery cell (14) according to one of claims 1 to 8, characterized in that a size of the membrane (36) is smaller than the size of the predetermined breaking region (30).

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