Cell housing for battery electrodes, battery cell with a cell housing and method for manufacturing a cell housing

Abstract

A steel cell housing (10) for battery electrodes (12) has a prismatic geometry, wherein the cell housing (10) comprises a housing body (11) with side walls (16) and a rupture membrane (14) provided on one of the side walls (16), and wherein the rupture membrane (14) is plastically deformed such that it bulges inwards at room temperature and is inherently stable. Furthermore, a battery cell with such a cell housing is proposed, as well as a method for manufacturing the cell housing (10).

Description

[0001] The invention relates to a steel cell housing for battery electrodes, having a prismatic geometry, side walls, and a rupture membrane provided on one of the side walls. The invention further relates to a battery cell with such a cell housing and a method for manufacturing a cell housing.

[0002] Battery cells, also called accumulator cells, serve to chemically store electrical energy. One of the best-known battery cells is the lithium-ion battery cell. However, the present invention is not limited to such battery cells.

[0003] A battery cell typically comprises at least one battery electrode in the form of an electrode winding or an electrode stack, which in turn consists of at least one positive electrode, at least one negative electrode, and at least one separator arranged between the positive and negative electrodes. The battery electrodes, also called electrode units, may additionally have an insulating film wound around the electrode winding or electrode stack. To form a battery cell, the electrode unit is inserted into a cell housing. Depending on the design of the cell housing, the battery cell is configured as a cylindrical cell, a pouch cell, or a prismatic cell. The present invention relates to a prismatic cell, i.e., a cell with a prismatic cell housing.

[0004] In certain situations, such as a defect or improper handling, lithium-ion batteries can experience gas formation and a resulting overpressure within the battery cell. It is therefore known to provide a pressure relief valve or a rupture membrane functioning as a pressure relief valve within the cell housing of the battery cell body to vent the generated gases in a controlled manner and prevent thermal runaway of the battery cell. The rupture membrane is designed to burst at a specific pressure, thereby opening the cell housing at a predetermined point to release the overpressure.

[0005] The cell casing of prismatic cells is typically made of aluminum or an aluminum alloy, and the rupture membrane is integrated directly into the aluminum cell casing. The rupture membrane is therefore also made of aluminum or an aluminum alloy. Rupture membranes made of aluminum alloys usually have a predetermined breaking point subjected to tensile or shear stress. This point fails in a controlled manner when the tensile strength of the aluminum alloy is reached, causing the rupture membrane to burst and allowing pressure equalization between the inside and outside of the battery cell.

[0006] Alternatively, the cell casing of a prismatic battery cell, or at least the casing body, can be made of an iron-based material, i.e., iron or an iron alloy, particularly stainless steel. If the rupture membrane is then inserted into the cell casing, it, like the cell casing itself, is made of iron or an iron alloy. However, iron-based materials have a significantly higher tensile strength than aluminum, so a rupture membrane made of iron or an iron alloy also has a significantly higher tensile strength than a comparable rupture membrane made of aluminum or an aluminum alloy. Consequently, a rupture membrane made of an iron-based material will not rupture at all, or at least not as quickly and reliably, as a comparable rupture membrane made of aluminum. Therefore, rupture membranes with extremely thin walls must be used.This results in process engineering challenges in the precise manufacturing of predetermined breaking points to reliably maintain the required trigger pressure within the specified limits. A rupture membrane that is directly inserted or integrated into a cell housing made of iron or a material containing an iron alloy, i.e., formed as a single piece with it, is more difficult to implement technically and economically due to the properties of ferrous materials. Furthermore, the wall thickness in the area of ​​the rupture membrane is typically too high, and the incorporated predetermined breaking points must therefore be even thinner, making manufacturing difficult. For this reason, rupture membranes in iron cell housings are typically installed as separate components within the cell housing.

[0007] Simply welding steel foils as rupture membranes to the housing body has the disadvantage that the foil often warps during welding due to the locally high heat input into the thin foil material; in this case, the heat cannot be dissipated optimally, and there is no element to hold the foil in place during welding. Welding thin foils to the housing body thus carries the risk of sealing problems in the area of ​​the weld. Furthermore, a welded-in steel foil is subject to constant alternating stress due to the so-called swelling of the battery cell. This can be exacerbated if the cells are cooled by immersion cooling. This results in constantly changing pressure stresses from the internal cell pressure on the one hand and the externally imposed pressure stresses and pressure pulsations from the immersion cooling system on the other.This can lead to premature cell failure due to breakage of the bursting element foil as a result of material fatigue.

[0008] The object of the present invention is to provide a cell casing with a bursting device that overcomes the disadvantages known from the prior art and ensures reliable bursting of the bursting membrane.

[0009] The problem is solved according to the invention by a cell casing of the type mentioned above, in which the rupture membrane is plastically deformed such that it bulges inwards at room temperature and is inherently rigid. Without any internal or external load, the rupture membrane already has a dome-shaped form projecting into the interior of the cell casing; that is, it bulges inwards into the interior of the cell casing. In other words, the rupture membrane has an arc-shaped profile in all cross-sections passing through its center.

[0010] Due to the bulging, the burst membrane can absorb stresses more easily during both welding and operation compared to a conventional, flat burst membrane, without the alternating tensile or bending stresses leading to material fatigue.

[0011] If the rupture membrane has such a thickness and curvature that it tears open during an abrupt outward flip due to increased internal pressure, the kinetic energy during this abrupt flip will contribute to a sudden increase in stress within the rupture membrane, leading to its tearing. This opening can thus be predicted very precisely. During the flip, the rupture membrane snaps outwards at high speed, like a crackling sound, due to the increased internal pressure occurring within the cell casing in the event of a battery cell failure.

[0012] The degree of curvature allows for precise adjustment of the battery cell's internal pressure (limit internal pressure), which is necessary to trigger the rupture of the diaphragm. However, this internal pressure is never intended for normal battery cell use, but only when a critical internal pressure is exceeded, such as in the case of a thermal runaway or an internal short circuit of the battery cell.

[0013] This effect, without which, according to one variant of the invention, the destruction of the membrane would not be possible, is effective both in the case of a burst membrane as a separate part and in the case of a burst membrane that is integrally integrated into the housing body, i.e., was never a separate component.

[0014] Due to the energy released when the rupture membrane ruptures, leading to an abrupt stress peak within the membrane, the predetermined breaking points can be made comparatively thick. This increases strength and allows for greater tolerance of alternating pressure stresses. The battery cell's lifespan is extended, and cell casing failure is prevented.

[0015] Furthermore, the curvature of the rupture membrane can effectively prevent distortion or wrinkling during welding.

[0016] To more precisely adjust the internal pressure threshold at which the rupture diaphragm is destroyed, a frame element can be provided on the housing body, extending around the inwardly bulging area of ​​the rupture diaphragm. This frame element stiffens the corresponding side wall and is attached to the housing body by welding, soldering, gluing, or a mechanical connection. The housing body is thus stabilized in the edge zone of the bulging area, rendering the influence of the flexibility of this edge on the rupture process negligible.

[0017] Another option for precisely adjusting the internal pressure threshold at which the rupture membrane is destroyed is to incorporate reduced-thickness tear zones, particularly lines or points, into the membrane. These so-called predetermined breaking lines or points can be created by embossing or ablation, for example, using a laser.

[0018] The line framing the bulging area is specifically round, oval, elliptical or the like, so that the stresses are distributed evenly during operation and welding.

[0019] The rupture diaphragm will reliably burst at an opening pressure between 2 and 30 bar.

[0020] As already mentioned, the burst membrane can be a separate metal component, which is welded to the edge for attachment and closes a hole in the housing body.

[0021] The rupture membrane consists of metal, in particular steel or nickel or a nickel alloy, for example austenitic chromium-nickel steels e.g. 1.4301, or chromium-nickel-molybdenum steels e.g. 1.4401, 1.4404. For special applications, the use of nickel foils e.g. 2.4068 is conceivable.

[0022] The thickness of the weldable rupture membrane can be less than the thickness of the housing body, with the membrane thickness being measured outside of predetermined breaking lines, i.e., in the area where the rupture membrane is of uniform thickness.

[0023] The rupture membrane has a circumferential mounting edge for attachment; this edge is flat and surrounds the inwardly bulging area. This prevents the bulging area from being weakened by the weld seam.

[0024] The rupture membrane is welded to the inside of the housing body, or to an adjacent frame component that reinforces the edge of the hole, or the rupture membrane is positioned between an adjacent frame component that reinforces the edge of the hole and the housing body. In this process, the frame component, rupture membrane, and housing body are welded together in a single welding operation. This means the weld seam extends from the frame component through the rupture membrane into the housing body. This reduces the temperature peaks that occur during welding because the energy is distributed more effectively across the frame component. This eliminates welding defects, and the weld seam density, and consequently the overall tightness, safety, and lifespan of the battery cell, are significantly improved.As mentioned previously, the frame component also increases the rigidity of the cell housing, thus reducing deformation of the cell housing when a critical internal pressure occurs. This results in a precisely predictable triggering behavior of the rupture membrane.

[0025] The frame part can be located inside the housing body or on the outside, in particular in a recess in the housing body, the shape of which is adapted to the frame part.

[0026] The opening of the rupture membrane is improved by an external cutting edge, spaced away from the rupture membrane before the opening process, which is contacted by the rupture membrane when it flips outwards, causing it to tear open.

[0027] The cutting edge can be provided on a metal plate attached to the outer edge of the hole, projecting into the area of ​​the hole when viewed from above. Alternatively, the cutting edge can also be formed directly into the edge of the hole in the housing. Multiple cutting edges are also possible. Upon rupture, the bursting diaphragm strikes the cutting edge, causing it to penetrate the diaphragm.

[0028] The cutting edge is produced in particular by a simple punching and bending process.

[0029] The opening cross-section of the rupture membrane in the event of its destruction is preferably 20-5000 mm². 2 .

[0030] The opening pressure (limit internal pressure) of the bursting diaphragm is preferably in the range of 2-30 bar.

[0031] It is also advantageous to have at least one bridge that spans opposite areas of the edge of the hole and runs inwards in an arc, seamlessly merging into the opposite areas of the edge.

[0032] The bridge is preferably formed from the housing body and therefore typically has the same material thickness as the housing body itself. For example, the bridge can be produced by punching out sections of the hole from its sides, i.e., the bridge remains intact. While welding the bridge on afterwards is also conceivable, it is more economically problematic.

[0033] As the internal pressure within the cell casing increases, the rupture membrane exerts a force on at least one of its ribs. Above a certain force, the rupture membrane flips towards the outside of the cell as soon as the rib can no longer provide stabilization. The rib stabilizes the rupture membrane until the predetermined internal pressure limit is reached. Due to its thickness, or more generally, its cross-section, the rib is ideally suited to defining the internal pressure limit at which the rupture membrane flips and ruptures. Therefore, in this case, precise manufacturing of the rupture membrane is not the only crucial factor; rather, it can be manufactured with greater tolerances since the rib primarily determines the internal pressure limit. The rib can either flip along with the membrane or it can tear off at at least one of its ends.

[0034] The bridge is smooth on the underside, so that it does not damage the rupture membrane or cause it to tear.

[0035] Indentations at opposite ends of the bridge can weaken it at the transition to the housing body, making it easier to destroy.

[0036] The rib can also have one or more stiffening ribs to make it rigid at specific points, so that it ruptures selectively at weaker areas. For example, a stiffening element is provided at the lowest point of the rib, so that in this case the rib is not deformed outwards in this area, but may even only tear at the edges before the rupture membrane flips in the opposite direction.

[0037] The hole is particularly elongated and provided on a narrow side of the cell casing, with the longitudinal extent of the hole extending parallel to the longitudinal extent of this narrow side.

[0038] The housing body can be made in one piece or alternatively consist of a container part and a lid closing the container part, the lid having the hole which is closed by the bursting membrane.

[0039] According to the alternative embodiment, the bursting membrane is an integral part of the housing body and is therefore manufactured together with it.

[0040] A stiffening frame can also be attached to the housing body around the bulging section that forms the rupture membrane. This frame has an opening adapted to the bulging section and can be located on the inside or outside of the housing body, particularly in a recess in the housing body whose shape is adapted to the frame. This frame stabilizes the flat area, allowing the portion of the housing body forming the rupture membrane to spring outwards in a more defined manner. If the frame is located on the outside, it can be designed with the aforementioned cutting edge, which then strikes the rupture membrane as it springs outwards.

[0041] Generally, regardless of whether the rupture membrane is an integral part of the housing body or a separate component, it can be advantageous for the housing body to have stiffening elements at the edge of the hole. These stiffening elements serve to reinforce the edge or the entire side wall, including the edge. The stiffening elements can be ribs or beads, for example, or be an integral part of the housing body.

[0042] The invention further relates to a battery cell with a cell housing according to the invention and battery electrodes attached in the cell housing.

[0043] Furthermore, the invention also relates to a method for manufacturing a cell housing according to the invention, comprising the steps of: plastically forming a flat metal sheet or a flat section of a metal sheet to form a burst membrane with a bulge and a flat edge surrounding the bulge; manufacturing the housing body, wherein the burst membrane forms a part of the cell housing and the weakest point of the closed cell housing with respect to internal pressure in the cell housing.

[0044] If the rupture diaphragm is a separate part that is welded to the housing body, the flat material is preferably welded first, and then the bulge is produced by plastic deformation, or vice versa. This bulging of the initially flat part or section can be done by a punch or by applying hydraulic or pneumatic pressure that plastically deforms the rupture diaphragm in a die.

[0045] If the burst membrane forms a separate part, independent of the housing body, and closes a hole in the housing body, the burst membrane is positioned in the area of ​​the edge of the hole between the housing body and a frame part surrounding the hole, and the burst membrane, housing body, and frame part are welded together in one step.

[0046] Reduced thickness tear zones, especially lines or points, can be incorporated into the rupture membrane by mechanical or chemical ablation, embossing, or using a laser.

[0047] The cell casing wall thickness is 0.1 to 2 mm. However, the wall thickness is greater at the edge of the rupture membrane, as it is comprised of the membrane wall thickness and the frame wall thickness. The frame wall has a thickness of 0.2 to 3 mm, resulting in a total wall thickness of 0.3 to 5 mm in the area around the bulging section.

[0048] Further features and advantages of the invention will become apparent from the following description and from the accompanying drawings, to which reference is made. The drawings show: - Fig. 1 an exploded view of a variant of the cell housing of a battery cell according to the invention, - Fig. 2 a sectional view through the cell casing Fig. 1 along line II-II, - Fig. 3 a top view of a narrow side of the cell casing according to Fig. 1 in the area of ​​the rupture membrane, - Fig. 4 A perspective view of the rupture membrane, which forms during cell division. Fig. 1 is used, - Fig. 5 A perspective view of a reinforcing frame part, which is attached to the cell casing after Fig. 1 is used, - Fig. 6 a top view of another variant of the cell casing in the area of ​​the rupture membrane, - Fig. 7 a perspective view of a different variant of the cell casing in the area of ​​the rupture membrane, - Fig. 8 an enlarged top view of the in Fig. 7 shown jetty, - Fig. 9 a perspective view of an additional variant of the cell casing, - Fig. 10 a sectional view through the cell casing along line XX in Fig. 9, - Fig. 11 a perspective exploded view of a variant of the cell housing according to the invention without a bridge in the area of ​​the hole, - Fig. 12 a sectional view through a cell housing according to the invention with an externally attached frame part, - Fig. 13 a perspective view of a lid of a cell housing according to the invention, in which the hole with the burst membrane is provided, - Fig. 14 an exploded view of the lid according to Fig. 13, - Fig. 15 a perspective view of a rupture membrane with predetermined breaking lines, - Fig. 16 a perspective view of a rupture membrane with a singular predetermined breaking line, - Fig. 17 a perspective view of a cell housing according to the invention with a bursting membrane integrally integrated into the housing body, - Fig. 18 a sectional view of the cell casing according to Fig. 17 with external frame part, - Fig. 19 a sectional view of the cell casing with a burst membrane integrally integrated into the casing body and with an internal frame part, and - Fig. 20 to 26 different variations of the design of the predetermined breaking lines in the bursting membrane, whether as a separate part or as a bursting membrane that merges seamlessly into the housing body.

[0049] In Fig. Figure 1 shows a cell housing 10 with a housing body 11 made of steel, for example stainless steel, which has a prismatic geometry with pairwise opposing, parallel side walls.

[0050] The cell housing 10, together with battery electrodes 12, which are shown schematically, forms a battery cell of a larger vehicle battery. The cell housing 10 accommodates the battery electrodes 12. An electrolyte is also provided inside the cell housing 10.

[0051] In Fig. The following are omitted: on the front end face a cover and on the opposite end face a base, which are part of the housing body 11 and the rectangular in cross-section, integrally surrounding part of the housing body 11, which in Fig. 1 is visible, complete.

[0052] To reduce the pressure in the event of a defective battery cell where a critical internal pressure occurs, a type of pressure relief valve is incorporated.

[0053] This pressure relief valve is formed by a bursting diaphragm 14, which bursts open when a defined overpressure is reached.

[0054] In the embodiment according to Fig. Figure 1 shows the burst membrane 14 as a part formed separately from the housing body 11.

[0055] The housing body 11 has a hole 18 provided on a side wall 16, in particular an elongated hole, the longitudinal extent of which runs parallel to the longitudinal direction of the side wall 16, which in this case forms a narrow side of the cell housing and is therefore stiffer than the adjacent wide side walls.

[0056] This hole 18 is closed by the bursting membrane 14. The bursting membrane 14 is also available separately in Fig. 4 shown.

[0057] The rupture membrane 14 is an original plate-shaped part made of metal, in particular steel, stainless steel, nickel, or a nickel alloy, with a flat, circumferential mounting edge 20 that surrounds a bulging area 22. This bulging area 22 is adapted in size and to the hole 18 and corresponds in its dimensions, at least substantially, to those of the hole 18. The inherently rigid, bulging area 22 is always present due to the plastic deformation of the corresponding sheet metal when the battery cell is in its normal state, i.e., it is present at room temperature and also at the same internal and external pressure.

[0058] The side wall 16 is bordered in the area around the hole 18 by an adjacent frame part 24 (see also Fig. 5) reinforced on the inside, which also has a hole 26, the dimensions of which correspond to hole 18.

[0059] In the illustrated embodiment, the frame part 24 is located on the inside of the housing body 11, with the fastening edge 20 lying between the frame part 24 and the edge of the hole 18.

[0060] The frame part 24, the mounting edge 20 and the edge of the hole 18 are welded together in one step, with the weld passing through all parts.

[0061] For example, the burst membrane 14 is plastically deformed either after welding to create the bulging area or beforehand.

[0062] The burst membrane 14 has a thickness that is significantly less than the thickness of the housing body 11.

[0063] In the variant according to Fig. 1 a bridge 28 bridges opposite areas of the edge of the hole 18, the bridge 28 curving inwards, i.e. into the interior of the cell casing 10 and transitioning into the opposite areas.

[0064] The bridge 28 can be a welded-on separate part or, as shown, an integral part of the housing body 11 and thus transition into the opposite areas of the edge.

[0065] As in Fig. As can be seen in Figure 2, the bursting membrane 14 with its bulging area 22 lies against the bridge 28, even in the unloaded state of the bursting membrane 14, when the same pressure prevails on the inside and outside.

[0066] The bulging area 22 is produced by plastically deforming the previously flat metal sheet, which subsequently forms the rupture membrane 14, wherein the bulging area 22 is inherently rigid, i.e., it does not fold outwards when, for example, the cell housing 10 is shifted relative to its position after the Fig. 1 and Fig. 2 is turned around so that hole 18 points downwards.

[0067] In Fig. Figure 3 shows that on the outer side of the rupture membrane 14 on the housing body 11, a cutting edge 30 in the form of a point projects into the hole 18. In the normal state of the battery cell, the rupture membrane 14 is spaced apart from this cutting edge 30.

[0068] However, if the battery cell is defective, resulting in excessive internal pressure, the bursting membrane 14 will increasingly press on the bridge 28 once this limit internal pressure is reached, until the bridge, together with the bursting membrane 14, abruptly flips outwards, i.e., springs outwards like a cracking frog, causing the bursting membrane 14 to strike the cutting edge 30 at high speed and tear, thus releasing the hole 18.

[0069] Fig. Figure 6 shows another embodiment in which a cutting edge 30 is provided on each side of the bridge 28.

[0070] It can also be seen that in this variant, the bridge 28 transitions at its ends into the edge of the hole 18 with a radius, whereas according to Fig. 3 a 90° transition from the bridge 28 to the edge of the hole 18 is provided.

[0071] Depending on the design of the bridge 28, it can fold outwards or it can also tear.

[0072] In the Fig. 7 and Fig. 8 The bridge 28 is provided at its opposite ends in the area of ​​the transition to the edge of the hole 18 with indentations 34 which weaken the bridge 28 in this area, so that it tears when the defined limit internal pressure is reached and thus gives the burst membrane 14 the possibility to fold outwards.

[0073] In the variant according to the Fig. 7 and Fig. 8 even have more than two cutting edges 30 are provided.

[0074] However, in this case, the formation of the bridge 28 is not necessarily technically linked to the provision or number of cutting edges 30.

[0075] In the variant according to the Fig. 9 and Fig. Figure 10 shows that the bridge 28 has a stiffening bead 36 to make it stiffer in this area and to make it more difficult or even prevent it from flipping over, so that the bridge 28 does not tear at one or both ends when the burst membrane flips over when there is stress inside the battery cell, for example.

[0076] The variant according Fig. 11 corresponds to the one after Fig. 1 with the difference that there is no bridge 28 here.

[0077] As soon as a corresponding limit internal pressure is reached, the burst membrane 14, more precisely the bulging area 22, flips outwards and thereby meets at least one cutting edge 30.

[0078] Whereas in previous embodiments the stiffening frame part 24, which incidentally has a greater thickness than the adjacent side wall 16, is located on the outside of the housing body 11, in the variant according to Fig. 12 the side wall 16 outside a recess 40, which in its depth and dimensions is adapted to the frame part 24, so that the frame part 24 lies here outside the housing body 11 and is received in the recess 40.

[0079] Here too, the burst membrane14 lies between the edge of the hole 18 and the frame part 24 and is welded together with both.

[0080] While in previous embodiments the hole 18 is provided in a rectangular circumferential part of the housing body, more precisely in a narrow side wall 16, in the variant according to Fig. 13 is provided in a cover 42. A corresponding burst membrane 14 with an inwardly bulging area 22 and a mounting rim 20 is welded to the inside of the cover 42, optionally again using a frame part 24, which is not strictly necessary. Openings 44 are provided for the passage of electrodes 12.

[0081] Fig. Figure 15 shows a burst membrane 14 with intersecting tear lines 46, which are created by material weakening, for example by embossing, mechanical processing, chemical processing or by laser engraving.

[0082] In particular, one tear line 46 runs along the lowest point of the trough-like bulging area 22 and the other tear line 46 runs perpendicular to it in the area of ​​the middle, with respect to the longitudinal extent of the area 22.

[0083] At the burst membrane 14 after Fig. 16 there is only one tear line 46, namely along the lowest point of the trough-like bulging area 22.

[0084] The Fig. 17 and Fig. Figure 18 shows a cell casing with a casing body 11 in which the rupture membrane 14 is formed integrally, i.e., is a single part of the casing body 11. The rupture membrane 14 is formed by plastically deforming a side wall 16 inwards to create an inwardly bulging region 22, which then forms the rupture membrane 14.

[0085] Here too, a frame part 24 is provided, which is placed on the outside of the housing body 11 and which rests against the edge of the side wall 16 surrounding the burst membrane 14 in order to stiffen it.

[0086] Optionally, the side wall 16 can also have a recess 40 that accommodates the frame part 24, as Fig. 18 shows.

[0087] Here too, the frame part 24 is preferably welded to the housing body 11, although other connections such as soldering, gluing or mechanical connections are also possible.

[0088] The embodiment according to Fig. 19 differs from the one after Fig. 18 by the fact that the frame part 24 surrounds the burst membrane 14 on the inside and stiffens the edge that limits the burst membrane 14.

[0089] The Fig. Figures 20-26 show different forms of the tear lines 46, which are present both in a burst membrane 14 that is designed as a separate part and in a burst membrane 14 that is an integral part of the housing body 11 (as in Fig. 17-19), may be trained.

[0090] In Fig. 20, the tear line 46 is zigzag-shaped, in Fig. 21 wavy and in Fig. 22 crenellated.

[0091] Fig. Figure 23 shows a tear line 46 in the form of two “Y”s, whose central ribs merge into one another, with the diverging side ribs of the “Y” ending before the edge end 48 of the bulging area 22, while they Fig. 24 to this edge end 48 are sufficient.

[0092] To ensure that no parts can fly off after the burst membrane 14 ruptures, the variant according to Fig. 25 A tear line 46 is provided, which runs partially near the edge end 48 and has a partially circumferential contour, thus creating a kind of flap. This means that the rupture membrane 14 tears open at the tear line 46 near one edge end 48 and then pivots outwards in the area of ​​the opposite edge end 48, where no tear line 46 is provided. In this area, the rupture membrane 14 has a hinge-like function.

[0093] The same applies to the variant according to Fig. 26, wherein the tear line 46 runs in a U-shape along the edge end 48 along three sides of the end 48, with no tear line being provided on one side of the end 48, so that the rupturing burst membrane 14 pivots outwards around this area when it tears.

[0094] Cutting edges are not strictly necessary in these embodiments.

[0095] The cell casing 10 in its final form has a wall thickness of 0.1 to 2 mm outside the hole 18.

[0096] Hole 18 has a superelliptical shape, or is an oval made up of circular arcs and opposite straight lines.

[0097] Only in a bursting event, in which the pressure inside the cell casing 10 is in a range between 2 and 30 bar, does the bursting membrane 14 flip over.

[0098] To stiffen the edge of the opening, the side wall 16 can also have stiffening elements, in particular ribs 50 or beads 52, which are integrally integrated into the side wall 16, as shown by way of example in Fig. 3 are indicated, although this is only one option and possibly an alternative to frame part 24.

Claims

[1] Steel cell housing for battery electrodes, having a prismatic geometry, wherein the cell housing has a housing body with side walls and a burst membrane provided on one of the side walls and wherein the burst membrane is plastically deformed such that the burst membrane bulges inwards at room temperature and is inherently rigid. [2] Cell housing according to claim 1, wherein a frame part extending around the inwardly bulging area of ​​the rupture membrane is provided on the housing body, stiffening the corresponding side wall, and is attached to the housing body by welding, soldering, gluing or by means of a mechanical connection. [3] Cell casing according to claim 1 or 2, characterized by that the rupture membrane has reduced thickness areas where it tears, especially lines or points. [4] Cell housing according to one of the preceding claims, wherein the burst membrane is a separate component made of metal, in particular of steel or nickel or a nickel alloy, which is welded to the edge for fastening and closes a hole in the housing body. [5] Cell casing according to claim 4, characterized by , that the thickness of the rupture membrane is less than the thickness of the housing body. [6] Cell casing according to claim 4 or 5, wherein the rupture membrane has a circumferential mounting edge which is planar and surrounds the inwardly bulging area. [7] Cell casing according to one of claims 4-6, wherein • the membrane is welded to the inside or outside of the housing body or • is welded to an adjacent frame part that reinforces the edge of the hole or • between an adjacent frame part reinforcing the edge of the hole and the housing body, and the frame part, the bursting membrane and the housing body are welded together, wherein the frame part is located inside the housing body or on the outside, in particular in a recess in the housing body which is adapted in shape to the frame part. [8] Cell casing according to one of claims 4-7, wherein an external cutting edge spaced apart from the burst membrane is provided which is contacted by the burst membrane when the burst membrane flips outwards, causing it to rupture. [9] Cell housing according to claim 8, wherein the cutting edge is provided on a sheet metal attached to the outside of the edge of the hole, which, in a top view of the hole in the housing body, projects into the area of ​​the hole, or is formed on the edge of the hole in the housing body. [10] Cell casing according to one of claims 4 to 9, wherein at least one web bridges opposite areas of the edge of the hole and extends inwards in an arc shape and transitions into the opposite areas. [11] Cell casing according to claim 10, wherein the burst membrane rests on at least one web on opposite sides of the burst membrane at the same pressure. [12] Cell casing according to claim 10 or 11, characterized by that at least one of the bridges has lateral indentations and / or a stiffening rib at its opposite ends. [13] Cell casing according to one of claims 10 to 12, wherein the at least one bridge is designed such that it breaks upon flipping of the rupture membrane or flips over itself. [14] Cell housing according to any one of claims 4 to 9, wherein the hole is elongated and provided on a narrow side of the cell housing. [15] Cell housing according to any one of claims 4 to 14, wherein the housing body has a container part and a lid closing the container part, the lid having the hole which is closed by the burst membrane. [16] Cell casing according to any one of claims 1 to 3, wherein the burst membrane is an integral part of the casing body. [17] Cell housing according to claim 16, wherein a stiffening frame part is attached to the housing body around the bulging section forming the rupture membrane, with an opening adapted to the bulging section, wherein the stiffening frame part is located on the inside of the housing body or on the outside of the housing body, in particular in a recess in the housing body which is adapted in shape to the frame part. [18] Cell housing according to one of the preceding claims, wherein the housing body has stiffening elements at the edge of the hole to stiffen the edge or the entire side wall with the edge, wherein the stiffening elements are in particular ribs or beads. [19] Cell casing according to one of the preceding claims, wherein the rupture membrane has such a thickness and curvature that it ruptures when abruptly flipping outwards due to increased pressure on the inside. [20] Battery cell comprising a cell housing according to one of the preceding claims and battery electrodes housed in the cell housing. [21] Method for manufacturing a cell housing according to one of the preceding claims, comprising the steps of: plastically forming a flat metal sheet or a flat section of a metal sheet to form a rupture membrane with a bulge and a flat edge surrounding the bulge; and manufacturing the housing body, wherein the rupture membrane forms part of the cell housing and the weakest point of the closed cell housing with respect to internal pressure in the cell housing. [22] Method according to claim 21, wherein the bursting membrane forms a separate part which is separate from the housing body and closes a hole in the housing body, wherein the bursting membrane is positioned in the area of ​​the edge of the hole between the housing body and a frame part surrounding the hole and the bursting membrane, housing body and frame part are welded together. [23] Method according to claim 21 or 22, wherein the rupture membrane is formed by mechanical or chemical ablation, by embossing or by laser by means of reduced thickness rupture areas, in particular lines or points.

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