Cell housing with protection of a burst region

Abstract

A cell housing 10 and an associated battery cell and vehicle, having at least one battery cell is cooled by a cooling medium flowing around the housing. At least one burst / degassing region 11 capabl

Description

The present application relates to a cell housing of a directly cooled battery cell and a battery cell having the cell housing according to the invention, as well as to a vehicle having a battery cell according to the invention. In particular, high-performance battery cells, for example in the form of a prismatic cell, must be cooled in order to be used safely and to provide optimum performance as well as to ensure the intended lifetime. For this purpose, a direct cooling is known in the prior art in which a cooling medium is provided, which flows directly past a cell housing of the battery cell and thus cools the cells by direct contact. Through an "event,” for example a short circuit or a deep discharge, a high heat energy can be released at once, wherein a portion of the electrolyte liquid located in the battery cell evaporates. The gas thus produced generates a positive pressure and is also highly combustible. If the temperature in the cell exceeds the flash point of the gas, there is a risk that it will ignite, which can lead to a sudden increase in pressure within the cell and a risk of fire. It is therefore important that positive pressure prevailing in the cell can be directly dissipated in a controlled manner. For this purpose, certain weakened regions in the cell housing of the battery cell, also referred to as burst regions in the context of this application, are provided in order to selectively dissipate a positive pressure in the cell interior and thus prevent the risk of fire or a chain reaction of the battery cells, a so-called "thermal runaway.” If a positive pressure forms in the interior of the cell housing, the burst region of the cell housing bursts, whereby the positive pressure can escape. Usually, these burst regions are designed so as to function at the ambient pressure in the manufacture of the battery cell, therefore as a rule approximately the atmospheric pressure of the air. A cell housing similar to the described embodiment is known, for example, from the patent DE 10 2012 222 870 A1, wherein an emergency degassing can be ensured via a safety valve. Such a cell housing 10 according to the prior art is shown schematically in Figs. 1a and 1b. Fig. 1a shows a cell housing 10 in the side view, wherein the cell housing 10 comprises a burst region 11. Fig. 1b shows a section through the cell housing 10 shown in Fig. 1a along the cutting line A-A. In Fig. 1b, the weakening of the cell housing 10 at the burst region 11 can be seen due to a significantly lower wall thickness of the cell housing 10. The burst region 11 thus constitutes a target breaking point in case of a positive pressure in the cell housing 10, which bursts at a defined positive pressure and dissipates the positive pressure from the cell housing 10. However, in direct cooling, there may well be pressure differentials in the cooling system, as a result of which the pressure of the cooling medium surrounding the cell housing cannot always be kept constantly at the designed pressure. As a result, under certain conditions, the positive pressure in the interior of the cell housing cannot be dissipated over the burst region as desired. In addition, there is the possibility that, under changing pressure conditions in the cooling system, so-called pressure strokes, the burst region of the cell housing will bulge slightly inward or outward and thereby become so weakened over time that crack formation and thus ultimately an undesired opening of the burst region or a leakage in the burst region can occur. The patent specification AT 515312 A4 also addresses the problem of dissipating a formed gas from a battery cell. It discloses a battery module in which a foam structure for receiving one or more battery cells comprises a target breaking point and a gas exiting via an adjacent channel is dissipated. A coolant line is arranged in the channel, wherein, in the event of a failure of this line, the coolant is also dissipated via the aforementioned channel, namely to a suitable location outside of the battery module. Document DE 10 2011 078 301 A1 discloses a battery cell with a burst disc, wherein this burst disc is protected against air humidity with a check valve and thus against chemical attack in connection with hydrofluorocarbons. Patent DE 10 2014 222 835 A1 further discloses a cover panel for a battery, which cover panel is formed in two layers with an arbitrarily thick lid layer and a safety layer, wherein a positive pressure recess, therefore a setback in the cover panel, is formed solely by the outer lid layer. Against the background of the described prior art, the present invention seeks to provide a cell housing for a battery cell cooled by a cooling medium, which further improves the safety of operation with direct cooling and avoids potentially occurring sources of error as described above during such operation. The present invention also seeks to provide a battery cell with a cell housing according to the invention as well as a vehicle with a battery cell according to the invention. Aspects of the invention are set out in the independent claims. Advantageous further developments of the invention are contained in the subclaims. The cell housing according to an aspect of the invention is configured so that a cooling medium flows directly around it. That is to say, in the installed state, it is directly in contact with the cooling medium, wherein the cooling medium is guided directly along the cell housing. The cell housing comprises at least one burst region configured so as to burst at a defined positive pressure inside the cell housing and to dissipate the positive pressure. Furthermore, the cell housing comprises a cover flap, which is fastened to the cell housing in a pressure-tight manner and extends completely across the burst region. Here, pressure-tight is defined such that the cover flap dissipates a defined positive pressure on its inner side to an environment, and the burst region is sealed against an ambient pressure surrounding the cell housing, therefore an ambient positive pressure, and is thus pressure-insulated. The inner side of the cover flap is defined as the side facing the burst region. The outer side is thus the side of the cover flap which is in contact with the environment, therefore the coolant. The burst region itself no longer comes into contact with the environment, and thus the coolant, due to the preferably rigid and not easily deformable cover flap. Pressure fluctuations in the cooling system are thus no longer directed to the burst region but are absorbed by the cover flap, whereby the burst region is not subjected to any mechanical stresses due to fluctuating ambient pressure. In a preferred embodiment of the invention, the cover flap is configured so as to burst in the event of a defined positive pressure on its inner side, thus dissipating the positive pressure to the environment. The bursting of the cover flap is preferably ensured by a target breaking point or the like in the cover flap. The bursting of the cover flap provides a convenient manner of ensuring the dissipation of positive pressure under certain conditions. Further preferable is an embodiment of the invention in which the cover flap is configured such that a defined positive pressure on its inner side exerts such a force on the cover flap that the latter detaches from the cell housing. In this embodiment, the fastening of the cover flap to the cell housing is thus configured such that it detaches at least in part in case of a specified force caused by the positive pressure on the inner side of the cover flap. This can alternatively or additionally be provided with a bursting of the cover flap itself. The detachment of the fastening creates the possibility to provide an embodiment in which the cover flap is not destroyed but rather can be used again under certain circumstances, which is particularly advantageous with respect to sustainability aspects. Preferably, the cover flap is further configured as a valve tongue, which is configured so as to detach from a valve seat at a defined positive pressure on the inner side of the cover flap and dissipate the positive pressure. This is a well-designable, functionally safe, and also cost-efficient alternative for dissipating the positive pressure. Further advantageous is an embodiment of the invention in which the cover flap is fastened to the cell housing in such a way that a sealing effect between the cover flap and the cell housing increases with increasing ambient pressure on the outer side of the cover flap and / or decreases with increasing pressure on the inner side. With an increasing sealing effect under increasing ambient pressure, the certainty can be increased that the burst region does not come into contact with the ambient pressure and thus a mechanical effect of the cooling system on the burst region occurs. The cover flap is preferably configured so as to curve outwardly from the cell housing, so that it has a convex shape on the outer side and a concave shape on the inner side. In a further advantageous embodiment of the invention, the cover flap is glued or welded onto the cell housing. In this way, a secure and pressure-tight connection between the cover flap and the cell housing can be provided. In a further advantageous embodiment of the invention, a gaseous volume is enclosed between the burst region and the cover flap, in particular in which there prevails a predefined standard pressure. By providing a gaseous volume, slight pressure fluctuations, which might be passed on to the burst region by slight deformations of the cover flap, can be buffered and thus mitigated so that the mechanical load in the burst region further decreases. In addition, by enclosing the volume with a predefined standard pressure, it can be ensured that a certain positive pressure in the cell interior, therefore in the inner region of the cell, reliably leads to the bursting of the burst region, because there is a constant predefined standard pressure prevailing on the outer side of the burst region. This can thus be taken into account in the design of the burst region. Thus, the functional safety and reliability of the cell housing is further improved. The battery cell according to the invention comprises a cell housing according to the invention, while the vehicle according to the invention comprises at least one battery cell according to the invention. Various advantageous aspects and embodiments of the invention will be explained in further detail below, making reference to the accompanying drawings. They show: Fig. 1 a shows a schematic illustration of a cell housing 10 according to the prior art in a side view. Fig. 1b shows a schematic illustration of the cell housing 10 from Fig. 1a in a sectional view. Fig. 2a shows a schematic illustration of an embodiment of a cell housing 10 according to the invention in a side view. Fig. 2b shows a schematic illustration of the cell housing 10 from Fig. 2a in a sectional view. Figs. 1a and 1b have already been discussed in further detail in the explanations regarding the prior art, therefore a more detailed description is omitted at this point and reference is made to the explanations regarding the prior art. Figs. 2a and 2b show schematic representations of an embodiment of the cell housing 10 according to the invention in the same views as Figs. 1a and 1 b. As in the prior art, the cell housing 10 comprises a burst region 11. It is completely covered by a cover flap 12, as indicated in Fig. 2a. Fig. 2b shows a sectional view of Fig. 2a along the cutting line A-A. The cover flap 12 is connected to the cell housing 10 around the burst region 11 by means of the fastening portion 13. The fastening portion 13 is provided as a solid connection in the form of an adhesive connection or a welded connection. A gaseous volume 20 with a defined standard pressure is enclosed between the cover flap 12 and the burst region 11. The standard pressure is the pressure for which the function of the burst region 11 is designed. This volume 20 is sealed against the environment of the cell housing 10 in a pressure-tight manner by the fastening of the cover flap 12 to the cell housing 10 on the fastening portion 13. If the cover flap 12 is welded to the cell housing 10, this is done prior to filling the cell with active material. If a fastening is carried out by means of an adhesive connection, the cover flap 12 can also be mounted after filling the cell with active material. A cooling medium (not shown) flowing around the cell housing 10 is shielded by the cover flap 12 and thus does not come into contact with the burst region 11. Therefore, a mechanical load on the burst region 11 can also be prevented by pressure strokes or pressure variations in the cooling system. With the enclosed volume 20, it can be ensured that the conditions for which the burst region 11 has been designed are given on the outer side of the burst region 11. Functional safety and reliability of the assembly are thus ensured. The cover flap 12 is designed so as to curve outwardly from the cell housing 10. Thus, a convex shape results on the outer side of the cover flap 12, in the drawing plane to the right of the cover flap 12, while a concave shape is given on the inner side of the cover flap 12. With this shape and the type of fastening using the full-surface fastening portion 13 enclosing the burst region 11, the cover flap 12 is pressed against the cell housing 10 at an increasing ambient pressure on its outer side, therefore an increasing pressure in the cooling system, whereby the sealing effect of the fastening portion 13 is further increased. The cover flap 12 does not necessarily have to be connected to the cell housing 10 at every point of the fastening portion 13, however, it must be ensured that the cover flap 12 is sealed with the cell housing 12 in a pressure-tight manner at every point of the fastening portion 13. If a pressure increase now occurs in the interior of the cell housing 10, wherein the positive pressure in the cell housing 10 exceeds a defined pressure, the burst region 11 initially bursts. Thus, the positive pressure of the interior of the cell housing 10 is now also present in the volume 20 and acts on the inner side of the cover flap 12. However, the latter is designed so as to already yield at a lower pressure than the burst region 11. Thus, even after the bursting of the burst region 11, with a negligible time delay, the cover flap 12 also bursts, whereby the positive pressure from the cell housing 10 can be dissipated in a controlled manner via the burst region 11 and the cover flap 12. In order to ensure a controlled bursting, and in particular a safe bursting, at a certain pressure level on the inner side of the cover flap 12, a target breaking point is preferably defined in the cover flap 12. Embodiments of the invention are also contemplated in which the cover flap 12 does not burst itself, but rather the pressure is dissipated in another way. For example, it is contemplated that the fastening of the cover flap 12 to the cell housing 10 yields in the event of a specified force acting on the inner side of the cover flap 12. The force results from the pressure on the inner side of the cover flap 12 and the surface of the cover flap 12. In this way, the cover flap 12 can itself remain intact and can be reused but is detached from the cell housing 10 in a controlled manner. Alternatively, an embodiment of the invention is also contemplated in which the cover flap 12 is configured as a reed valve and the valve seat is provided by the fastening portion 13. The reed valve is prestressed such that it seals the volume 20 enclosed between the burst region 11 and the cover flap 12 against the environment in a pressure-tight manner. In the event that the internal pressure in the volume 20 rises due to the burst region 11 that has burst, the reed valve detaches from the valve seat and thus allows the prevailing positive pressure in the interior of the cell housing 10 to be dissipated in a controlled manner. A reed valve can thus be used in order to establish a simple and safe method for pressure dissipation.

Claims

1. A cell housing of at least one battery cell directly cooled by a cooling medium, wherein the cell housing is configured so that the cooling medium flows directly around it, and the cell housingcomprises at least one burst region configured so as to burst at a defined positive pressure inside the cell housing and to dissipate the positive pressure, whereinthe cell housing further comprises a cover flap, which is fastened to the cell housing in a pressure-tight manner and extends across the burst region, wherein it is configured so as to dissipate a defined positive pressure on its inner side to an environment, and the burst region is sealed against an ambient positive pressure and is thus pressure-insulated.

2. A cell housing according to the preceding claim, wherein the cover flap bursts at a defined positive pressure on its inner side.

3. The cell housing according to any one of the preceding claims, wherein the cover flap is configured such that a defined positive pressure on its inner side exerts such a force on the cover flap that the latter detaches from the cell housing.

4. The cell housing according to the preceding claim, wherein the cover flap is provided in the form of a reed valve, which is configured so as to detach from a valve seat in the event of a defined positive pressure on the inner side of the cover flap.

5. The cell housing according to one of the preceding claims, wherein the cover flap is fastened to the cell housing in such a way that a sealing effect of the cover flap increases with increasing ambient positive pressure and / or decreases with increasing positive pressure on its inner side.

6. The cell housing according to the preceding claim, wherein the cover flap is configured so as to curve outwardly from the cell housing, so that it has a convex shape on its outer side and a concave shape on the inner side.

7. The cell housing according to any one of the preceding claims, wherein the cover flap is glued or welded onto the cell housing.

8. The cell housing according to any one of the preceding claims, wherein a gaseous volume is enclosed between the burst region and the cover flap, wherein the gaseous volume in particular has a predefined standard pressure.

9. A battery cell comprising a cell housing according to any one of the preceding claims.

10. A vehicle comprising at least one battery cell according to the preceding claim.