Battery cell provided with a degassing device

Abstract

The invention relates to an electric cell (1) for an electrically-driven vehicle, the cell (1) comprising: - a housing (3) defining an interior volume (4) containing an electrolyte; and - at least one stack of electrodes comprising a plurality of electrodes separated from one another by a porous separator film, the at least one stack of electrodes being arranged in the housing (3), the cell (1) comprising a degassing device (2) arranged on the housing (3), which degassing device (2) comprises: - a first porous membrane located on the interior volume (4) side of the housing (3); and - a second porous membrane (6) that is separate from the first membrane and that is arranged facing the first membrane, the first membrane and second membrane (6) being arranged at a distance from one another.

Description

Battery cell equipped with a degassing device Technical field of the invention

[0001] The invention relates to the field of rechargeable metal-ion electric batteries for electric motor vehicles.

[0002] In particular, the invention relates to a metal-ion battery cell comprising an individual degassing device having at least one flexible and gas-permeable membrane. Technical background

[0003] An electric battery cell comprises a stack of electrodes of opposite polarity separated from each other by a porous separator film.

[0004] The battery cell contains a liquid electrolyte.

[0005] The so-called prismatic or cylindrical cells typically have a rigid casing in which the stack of electrodes is arranged and which contains, among other things, the electrolyte.

[0006] A known problem related to battery cell operation is the generation of gas inside the casing. This can occur under normal operating conditions or in the event of thermal runaway of the cell.

[0007] There are many degassing devices. These devices prevent the pressure inside the cell casing from exceeding a predetermined value, which could damage the cell.

[0008] These degassing devices thus make it possible to evacuate excess gas generated during the use of the cell.

[0009] In the event that the pressure in the casing were to reach too high a value, the degassing device breaks down as a safety measure, rendering the cell inoperative.

[0010] It has been observed that these degassing devices tend to break frequently, rendering the cell, or even the module comprising a plurality of cells, unusable.

[0011] The motor vehicle then experiences a decline in performance, or in the worst case, becomes unusable.

[0012] These degassing devices can therefore still be improved to enhance cell reliability while maintaining an acceptable level of safety for the end user.

[0013] To this end, it is proposed firstly an electric cell for an electric propulsion vehicle, said cell comprising: - a housing defining an internal volume containing an electrolyte, and - at least one stack of electrodes comprising a plurality of electrodes separated from each other by a porous separating film, said at least one stack of electrodes being arranged in the housing, the cell comprising a degassing device arranged on the housing, said degassing device comprising: - a first porous membrane located on the side of the internal volume of the housing, and - a second porous membrane distinct from the first membrane and arranged opposite the first membrane, said first membrane and second membrane being arranged at a distance from each other.

[0014] Due to the position of the first membrane, it is frequently subjected to mechanical stress, as the pressure inside the housing fluctuates continuously. This mechanical stress weakens the first membrane. If the first membrane ruptures, the venting system remains functional, since the second membrane has not been affected. The venting system is therefore more robust, increasing the cell's lifespan without posing any risk to the end user.

[0015] Various additional features may be provided alone or in combination: - the first membrane is flexible; - the second membrane is flexible; - the first membrane and the second membrane are separated from each other by a distance of between 1 millimeter and 3 millimeters, said separation distance being measured along an axis substantially perpendicular to a wall of the housing on which the degassing device is arranged; - the first membrane has a first porosity and the second membrane has a second porosity, in which the first porosity is different from the second porosity; - the degassing device is arranged on a cover attached to the housing, said cover comprising an inner face located on the side of the inner volume and an outer face opposite to the inner face;- the first membrane is arranged flush with the inner face and the second membrane is arranged flush with the outer face; - the degassing device includes a frame on which the first membrane and the second membrane are fixed; - the degassing device includes a frame comprising: - an inner plate on which the first membrane is fixed, - an outer plate on which the second membrane is fixed, - a junction wall connecting the inner plate to the outer plate, cell in which the inner plate and the outer plate are substantially parallel to each other and extend substantially in a plane of the cell lid; - the frame includes an orifice opening onto the inner volume, said orifice being covered by the first membrane and the second membrane, said orifice having an area between 10% and 30% of an area of ​​the cell lid;- the degassing device includes a buffer volume delimited by the chassis, the first membrane and the second membrane, said buffer volume being less than or equal to 5% of a total volume of the cell, said total volume being determined as the volume of the assembly including the housing and the cover mounted on said housing; the cell is of the prismatic type. Brief description of the figures

[0016] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0017] laest a perspective view of a cell comprising a degassing device according to the invention;

[0018] This is an exploded view of the degassing device;

[0019] laest a cross-sectional view of laselon the section plane III-III. Detailed description of the invention

[0020] Figure 1 shows a cell 1 of an electric battery for an electric vehicle. Cell 1 includes a degassing device 2.

[0021] Advantageously, cell 1 comprises a prismatic housing 3. By prismatic, we mean that the housing 3 is rigid and has a shape closely resembling that of a rectangular parallelepiped. The housing 3 includes an opening leading to an internal volume 4, through which an electrode stack is inserted. The electrode stack comprises a series of electrodes separated from each other by a porous separating film. Cell 1 includes, among other things, an electrolyte arranged within the housing 3.

[0022] In what follows, the invention will be described in a state of rest. By "rest," it is understood that the pressure inside the housing 3 is less than a predetermined deformation value of the degassing device 2.

[0023] The degassing device 2 is arranged on the housing 3 of cell 1.

[0024] With reference to the degassing device 2, it comprises: - a first porous membrane 5 located on the side of the volume 4 inside the cell 1, and - a second porous membrane 6 distinct from the first membrane 5 and arranged opposite the first membrane 5.

[0025] As can be seen in the drawings, the first membrane 5 and the second membrane 6 are arranged at a distance from each other.

[0026] Due to the position of the first membrane 5, it is frequently subjected to mechanical stress, as the pressure inside the housing 3 fluctuates continuously. This mechanical stress weakens the first membrane 5. If the first membrane 5 ruptures, the degassing device 2 remains functional, since the second membrane 6 has not been stressed. The degassing device 2 is therefore more robust, increasing the lifespan of the cell 1, without posing any risk to the end user.

[0027] Advantageously, the first membrane 5 is flexible. By "flexible," it is understood that the first membrane 5 is capable of elastic deformation. Thus, the membrane deforms under the effect of pressure variations inside the housing 3. In other words, the first membrane 5 can deform and then substantially return to its initial shape. In the event of overpressure in the housing 3, the first membrane 5 deforms while the second membrane 6 does not deform or deforms very little.

[0028] The deformable nature of the first membrane 5 makes the degassing device 2 more robust because it is thus less likely to break under the effect of pressure in the housing 3.

[0029] Advantageously, the second membrane 6 is flexible. By "flexible," it is understood that the second membrane 6 is capable of elastic deformation. Thus, it deforms under the effect of pressure variations. In other words, the second membrane 6 can deform and then substantially return to its initial shape. The second membrane 6 tends to deform when the first membrane 5 is ruptured and the second membrane 6 comes into direct contact with the internal volume 4 of the housing 3.

[0030] The deformable nature of the second membrane 6 makes the degassing device 2 more robust because it is thus less likely to break under the effect of pressure in the housing 3.

[0031] Advantageously, the first membrane 5 and the second membrane 6 are separated by a distance 7 of between 1 millimeter and 3 millimeters. The separation distance 7 is measured along an axis substantially perpendicular to a wall of the housing 3 on which the degassing device 2 is arranged.

[0032] This separation distance 7 allows a buffer volume 8 to be created between the first membrane 5 and the second membrane 6. The buffer volume 8 prevents the first membrane 5 from coming into direct contact with the second membrane 6 under the effect of pressure variations inside the housing 3. Contact between the first membrane 5 and the second membrane 6 is likely to damage them.

[0033] Advantageously, the first membrane 5 is gas-permeable and has a first porosity. The second membrane 6 is gas-permeable and has a second porosity different from the first porosity.

[0034] The porosity of the membranes varies depending on their position, namely whether they are in direct contact with the interior volume 4 or in contact with the external atmosphere. This varying porosity allows for the management of the specific characteristics of the environment with which the membrane is in direct contact. This optimizes degassing management.

[0035] Advantageously, the first porosity is greater than the second porosity. Porosity is defined as the ratio between the volume of voids in a given material and the volume of that material.

[0036] Degassing is thus optimized. A first porosity greater than the second porosity advantageously protects the inner volume 4 from the risk of contamination from the atmosphere outside cell 1, while preventing liquid present in the inner volume 4 from escaping from cell 1.

[0037] Cell 1 includes a cover 11, attached and mounted on the housing 3. The cover 11 includes an inner face 12 located on the side of the inner volume 4 and an outer face 13 opposite to the inner face 12, and in contact with the atmosphere outside cell 1. Advantageously, the degassing device 2 is arranged on the cover 11.

[0038] By positioning the degassing device 2 on the cover 11 in this way, the manufacturing of cell 1 is facilitated. Indeed, the dimensions of the cover 11 are smaller than those of the housing 3, which makes handling and drilling operations easier. Another advantage of this design is that the cover 11 is thicker than the rest of the housing 3, thus making it easier to position the degassing device 2 on the cover 11.

[0039] Advantageously, the first membrane 5 is flush with the inner face 12 and the second membrane 6 is flush with the outer face 13.

[0040] The separation distance 7 between the first membrane 5 and the second membrane 6 is maximized, thus increasing the buffer volume 8. The degassing device 2 is therefore made more robust.

[0041] With reference to the drawings, the device advantageously includes a frame 14. The first membrane 5 and the second membrane 6 are each attached to the frame 14.

[0042] Such an architecture allows the degassing device 2 to be manufactured independently of cell 1 and subsequently assembled to cell 1 and more specifically to the cover 11. The manufacture of cell 1 is thus facilitated.

[0043] As previously mentioned, the degassing device 2 comprises a frame 14. As can be seen in the figure, the frame 14 advantageously includes an inner plate 15 to which the first membrane 5 is fixed and an outer plate 16 to which the second membrane 6 is fixed. The frame 14 also includes a connecting wall 17 linking the inner plate 15 to the outer plate 16. The inner plate 15 and the outer plate 16 are substantially parallel to each other. Furthermore, the inner plate 15 and the outer plate 16 extend substantially in a plane of the cover 11.

[0044] This architecture allows for a robust and easy-to-manufacture degassing device 2. Furthermore, by extending in a plane of the cover 11, the attachment of the plates 15, 16 to the cover 11 is facilitated and made more robust.

[0045] Advantageously, the frame 14 includes an opening 18. The opening 18 leads, on the one hand, to the inner volume 4 and, on the other hand, to the atmosphere outside cell 1. The opening 18 is covered by the first membrane 5 and the second membrane 6. The area of ​​the opening 18 is between 10% and 30% of the area of ​​the lid 11 of cell 1. In the embodiment shown in the drawings, the opening 18 is delimited by the inner plate 15. In a preferred embodiment, the area of ​​the opening is approximately equal to 15% of the area of ​​the lid 11 of cell 1.

[0046] Such proportions ensure optimal safety with a robust degassing device 2 with improved longevity.

[0047] As previously mentioned, the degassing device 2 includes a buffer volume 8. The buffer volume 8 is delimited by the frame 14, the first membrane 5, and the second membrane 6. The cell 1 has a total volume calculated as the volume of the assembly including the housing 3 and the cover 11 mounted on said housing 3. The buffer volume 8 is less than or equal to 5% of the total volume.

[0048] Such proportions ensure optimal safety with a robust degassing device 2 with improved longevity.

Claims

Electric cell (1) for an electric propulsion vehicle, said cell (1) comprising: - a housing (3) defining an internal volume (4) containing an electrolyte, and - at least one electrode stack comprising a plurality of electrodes separated from each other by a porous separator film, said at least one electrode stack being arranged in the housing (3), the cell (1) comprising a degassing device (2) arranged on the housing (3), said degassing device (2) comprising: - a first porous and flexible membrane (5) located on the side of the internal volume (4) of the housing (3), and - a second porous membrane (6) distinct from the first membrane (5) and arranged opposite the first membrane (5), said first membrane (5) and second membrane (6) being arranged at a distance from each other. Cell (1) according to claim 1 in which the second membrane (6) is flexible. Cell (1) according to any one of the preceding claims in which the first membrane (5) and the second membrane (6) are separated from each other by a distance of between 1 millimeter and 3 millimeters, said separation distance (7) being measured along an axis substantially perpendicular to a wall of the housing (3) on which the degassing device (2) is arranged. Cell (1) according to any one of the preceding claims in which the first membrane (5) has a first porosity (9) and the second membrane (6) has a second porosity (10), cell (1) in which the first porosity (9) is different from the second porosity (10). Cell (1) according to claim 4 in which the first porosity (9) is greater than the second porosity (10). Cell (1) according to any one of the preceding claims wherein, the degassing device (2) is arranged on a cover (11) attached to the housing (3), said cover (11) comprising an inner face (12) located on the side of the inner volume (4) and an outer face (13) opposite the inner face (12). Cell (1) according to claim 6 in which the first membrane (5) is arranged flush with the inner face (12) and the second membrane (6) is arranged flush with the outer face (13). Cell (1) according to any one of the preceding claims in which, the degassing device (2) comprises a frame (14) on which the first membrane (5) and the second membrane (6) are attached. Cell (1) according to any one of the preceding claims, wherein the degassing device (2) comprises a frame (14) having: - an inner plate (15) on which the first membrane (5) is fixed, - an outer plate (16) on which the second membrane (6) is fixed, - a connecting wall (17) linking the inner plate (15) to the outer plate (16), cell (1) wherein the inner plate (15) and the outer plate (16) are substantially parallel to each other and extend substantially in a plane of the cover (11) of the cell (1). Cell (1) according to any one of claims 8 or 9 in which the frame (14) includes an opening (18) leading into the inner volume (4), said opening (18) being covered by the first membrane (5) and the second membrane (6), said opening (18) having an area between 10% and 30% of an area of ​​the lid (11) of the cell (1). Cell (1) according to any one of the preceding claims in which, the degassing device (2) comprises a buffer volume (8) delimited by the frame (14), the first membrane (5) and the second membrane (6), said buffer volume (8) being less than or equal to 5% of a total volume of the cell (1), said total volume being determined as the volume of the assembly including the housing (3) and the cover (11) mounted on said housing (3). Cell (1) according to any one of the preceding claims, wherein the cell is of the prismatic type.

Images