Battery cell provided with a cover capable of rupturing under excess pressure

Abstract

The invention relates to an electric cell for an electric vehicle, the cell (1) comprising: - a housing defining an interior space that contains an electrolyte and at least one stack of electrodes comprising a plurality of electrodes separated from one another by a porous separator film; - a cover (4) having a predetermined thickness closing the housing, in which cell (1) the cover (4) comprises a wall having an upper face (7) and a lower face opposite the upper face (7), wherein the wall comprises a groove (5) having a depth that varies along the groove (5), and in which cell (1) the cover (4) is made in one piece.

Description

Battery cell equipped with a cover capable of breaking under the effect of overpressure. Technical field of the invention

[0001] The invention relates to the field of rechargeable metal-ion batteries for electric vehicles. In particular, the invention relates to a metal-ion battery cell. More precisely, the invention relates to an electric cell comprising a cover having at least one groove of variable depth. Technical background

[0002] An electric battery cell comprises a stack of electrodes of opposite polarity separated from each other by a porous separator film.

[0003] The battery cell contains a liquid electrolyte.

[0004] 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.

[0005] 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. In the latter case, the pressure inside the casing can reach levels that could cause an explosion. An explosion can have dramatic consequences and must be avoided.

[0006] There are numerous safety devices. These safety devices prevent the pressure inside the cell casing from exceeding a predetermined value, which could damage the cell.

[0007] These safety devices are for single use only. Once the safety device is damaged, the pressure inside the housing drops and the cell is no longer operational.

[0008] Generally, cells include a safety device arranged beneath a cell cover. The safety device includes, for example, a groove cut into the device itself. The groove has a substantially constant depth.

[0009] In the event of overpressure inside the cell, these safety devices rupture at the groove. The rupture occurs approximately simultaneously at every point along the groove. This is referred to as uniform rupture.

[0010] A uniform rupture can lead to debris being projected and dispersed unpredictably, increasing the risk of damaging other cells in the module.

[0011] Another disadvantage of a uniform rupture is that said uniform rupture causes a rapid drop in pressure, increasing the risk of cell explosion.

[0012] The present invention therefore aims to solve the aforementioned problems.

[0013] To this end, it is proposed firstly an electric cell for an electric propulsion vehicle, said cell comprising: - a casing 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, - a lid of a predetermined thickness closing the casing, cell in which the lid has a wall having an upper face and a lower face opposite to the upper face, said wall comprising a groove having a depth which varies as one moves along said groove, the depth being measured along a longitudinal axis of the cell, cell in which the lid is made in one piece.

[0014] A groove whose depth varies along its length allows the rupture of the cover to be directed within the groove. The rupture begins where the groove is deepest and propagates down the groove as the depth decreases. By directing the rupture so that it occurs progressively along the groove, it becomes possible to prevent the projection of cover debris or other components initially located inside the casing around the damaged cell, and to gradually reduce the pressure inside the cell, significantly decreasing the risk of cell explosion. Furthermore, it is possible to control the propagation speed of the rupture. In particular, this allows the propagation speed to be slowed as one moves along the groove, thus preventing damage to the cover and the projection of debris.

[0015] Various additional features may be provided alone or in combination: - the groove has a constant maximum depth, said maximum depth being substantially between 70% and 90% of the thickness of the lid; - the maximum depth is substantially equal to 80% of the thickness of the lid; - the groove has a constant minimum depth measured along the longitudinal axis, said minimum depth being substantially between 5% and 20% of the thickness of the lid; - the minimum depth is substantially equal to 10% of the thickness of the lid; - the lid has an outer periphery and the groove has lateral edges located on the upper face, said lateral edges being located at a lateral distance from the periphery measured in a plane of the upper face, said lateral distance being greater than or equal to 5 millimeters;- the groove includes at least one maximum portion of maximum depth, said maximum portion having a predetermined length; - the groove includes at least one minimum portion of minimum depth, said minimum portion having a predetermined length; - the cover has substantially a disc-shaped cell in which the groove has an outer lateral edge located on the periphery side of the cover and an inner lateral edge substantially concentric with the outer lateral edge, said annular edges being arranged on the upper face and spaced apart from each other by a predetermined distance; - the maximum portion is defined by a first angular sector between 10 degrees and 60 degrees, said first angular sector being measured substantially from a center of the cover; - the first angular sector alpha is substantially equal to 30 degrees;- the minimum portion is defined by a second angular sector between 10 degrees and 60 degrees, said angular sector being measured substantially from a center of the lid; - the second angular sector of the minimum portion is substantially equal to 30 degrees; - the minimum and maximum portions are separated by separating portions whose depth varies as one moves along said separating portions; - the depth of the separating portions increases by 1% of the thickness of the lid for every 2 degrees of angle; - the separating portions are defined by a second angular sector between 120 degrees and 170 degrees; - the lateral distance is between 5 millimeters and 20 millimeters; - the groove spacing distance is substantially between 0.5 millimeters and 2 millimeters; - the lower face of the lid is located on the side of the internal volume of the housing of said cell;- the minimum and maximum portions are substantially symmetrical with respect to a center of the lid located in a plane of the upper face of said lid; - the groove has a U-shape with a flat bottom in cross-section; - the lid is an added piece. 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 according to the invention.

[0018] laest a cross-sectional view of laselon the section plane II-II.

[0019] This is a top view of the. Detailed description of the invention

[0020] On the image, a cell 1 of a battery for an electric propulsion vehicle is represented.

[0021] Advantageously, cell 1 comprises a cylindrical housing 2. By "cylindrical" it is understood that the housing 2 has rigid walls and a shape closely resembling that of a cylinder. The housing 2 includes an opening leading to an internal volume 3, 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 contains an electrolyte arranged within the housing 2.

[0022] The housing 2 is closed by a cover 4. The cover 4 has a wall on which is arranged a groove 5, said wall comprising a lower face 6 and an upper face 7 opposite to the lower face 6.

[0023] The cover 4 has a thickness 9 measured along a longitudinal X axis of cell 1. The longitudinal X axis is perpendicular to the lower face 6 and the upper face 7 and the housing 2 extends longitudinally along this longitudinal X axis.

[0024] As illustrated in the figure, the depth of groove 5 varies depending on how far one moves along said groove 5. The depth of groove 5 is measured along the longitudinal X axis.

[0025] A groove 5, whose depth varies along its length, allows the rupture of the cover 4 to be directed into the groove 5. The rupture begins where the groove 5 is deepest and propagates down the groove as the depth decreases. By directing the rupture so that it occurs progressively along the groove 5, it becomes possible to prevent debris from the cover 4 or from elements initially located inside the housing 2 from being projected around the damaged cell 1, and to progressively reduce the pressure inside the cell 1, significantly reducing the risk of its explosion. Furthermore, it is then possible to control the rate of propagation of the rupture.In particular, this slows the propagation speed as you move along groove 5 so that cover 4 is not damaged to avoid debris being thrown out.

[0026] Advantageously, the groove 5 has a maximum depth 8 measured along the longitudinal axis, substantially between 70% and 90% of the thickness 9 of the cover 4.

[0027] These conditions allow a maximum depth 8 to be obtained which is large enough to allow a break at the point of the maximum depth 8 of the groove 5, while ensuring that the groove 5 does not give way in normal operation of the cell.

[0028] Advantageously, the maximum depth 8 of the groove 5 is substantially equal to 80% of the thickness 9 of the cover 4.

[0029] This allows a maximum depth 8 to be obtained which is large enough to allow for localized rupture in case of overpressure while ensuring that the groove 5 does not give way in normal operation of the cell.

[0030] Advantageously, the groove 5 has a minimum depth 10 measured along the longitudinal X axis, said minimum depth 10 is substantially between 5% and 20% of the thickness 9 of the cover 4.

[0031] Thanks to a minimum depth 10 within this range, it becomes possible to locate the rupture in case of overpressure. This notably allows for better protection of surrounding cells in the event of a rupture of a given cell 1. Furthermore, a minimum depth 10 within the aforementioned range prevents uncontrolled destruction of the cover 4. It appears that without a minimum depth 10, the rupture propagates beyond the groove 5. There is then a risk of debris being projected around the damaged cell 1. This debris could be fragments of the cover 4 or elements located inside the housing 2.

[0032] Advantageously, the minimum depth 10 of the groove 5 is substantially equal to 10% of the thickness 9 of the cover 4.

[0033] This allows for better protection of surrounding cells in the event of a break in a given cell 1. Furthermore, it prevents uncontrolled destruction of the cover 4. It appears that without a minimum depth 10, the break propagates beyond the groove 5. There is then a risk of debris being projected around the damaged cell 1. This debris could be fragments of the cover 4 or elements located inside the housing 2.

[0034] With reference to Figures 2 and 3, the cover 4 advantageously comprises an outer periphery 11. The outer periphery 11 lies in a plane defined by the upper face 7 of the cover 4 of cell 1. The lateral edges of the groove 5 lie in the plane of the upper face 7 of the cover 4.

[0035] The lateral edges of the groove 5 are arranged at a predetermined lateral distance 12 from the outer periphery 11. The lateral distance 12 is measured in the plane of the upper face 7, along a straight line extending from the outer periphery 11 towards the lateral edges along the shortest path.

[0036] The lateral distance 12 is greater than or equal to 5 millimeters.

[0037] The presence of such a lateral distance 12 between the periphery of the cover 4 and the lateral edges of the groove 5 prevents damage that overpressure could cause to the housing 2 of cell 1. The integrity of the housing 2 of cell 1 could be compromised, potentially leading to electrolyte leaks or debris ejection. Such a situation could damage other cells in the module or even cause a fire.

[0038] As can be seen in the figure, the groove 5 advantageously includes at least one maximum portion 13, which has a maximum depth 8 and a predetermined length. In other words, there exists at least one portion of the groove 5 of a given length where the depth is substantially constant and at its maximum.

[0039] This ensures that the rupture occurs first in the maximum portion 13. In the event of overpressure in casing 2, the rupture will occur first in this maximum portion 13. This is particularly advantageous for preventing damage to the other cells in the module. Indeed, the first rupture is the one most likely to project debris outside cell 1 due to the pressure drop between the inside of casing 2 and the outside. By precisely locating this area of ​​initial rupture, the surrounding cells can be better protected.

[0040] As can be seen in the figure, the groove 5 advantageously includes at least one minimal portion 14, which has a minimum depth 10 and a predetermined length. In other words, there exists at least one portion of the groove 5 of a given length where the depth is substantially constant and minimal.

[0041] Such a minimal portion 14 prevents part of the lid 4 from detaching and being ejected. Thus, during overpressure in the cell, the minimal portion 14 acts as a hinge.

[0042] Advantageously, the cover 4 is substantially disc-shaped. The groove 5 has an outer lateral edge 15 located on the periphery side 11 of the cover 4 and an inner lateral edge 16 substantially concentric with the outer lateral edge 15. The lateral edges 15 and 16 are annular. The lateral edges 15 and 16 are arranged on the upper face 7 of the cover 4. The outer lateral edge 15 and the inner lateral edge 16 are located at a predetermined distance 17 from each other.

[0043] Groove 5 has a circular, annular shape. This maximizes the length of groove 5 to better dissipate the energy generated by a potential rupture. This reduces the risk of debris being ejected.

[0044] Advantageously, the maximum portion 13 extends along a first angular sector α. The first angular sector α is between 10° and 60°, measured from a center C of the lid 4. The center C is located in the plane of the upper face 7.

[0045] Such an amplitude makes it possible to define a portion of maximum depth 8 sufficient to control the location of the rupture of the lid 4.

[0046] Advantageously, the first angular sector α is approximately equal to 30 degrees.

[0047] This advantageously allows sufficient opening at the time of rupture so that the pressure drop is rapid in order to avoid damage to the cell while ensuring the location of the rupture.

[0048] Advantageously, the minimal portion 14 has a second angular sector β between 10° and 60°.

[0049] Such an amplitude makes it possible to control the location of the hinge and to define a minimum portion size 14 sufficient to retain at least a portion of the lid 4 broken under the effect of a suppression in the housing 2.

[0050] Advantageously, the second angular sector β of the minimal portion 14 is approximately equal to 30 degrees

[0051] This advantageously allows for the creation of a hinge capable of withstanding overpressures without altering the performance of the device.

[0052] Advantageously, the minimum portion 14 and the maximum portion 13 are separated from each other by two separating portions 20. The depth of the separating portions 20 varies as one moves along said separating portions 20. As can be seen in the figure, the separating portions 20 are arranged on either side of the minimum portion 14 and the maximum portion 13.

[0053] These 20 separating portions ensure the continuity of the groove 5, guiding the break of the groove from the maximum portion 13 to the minimum portion 14 so as to protect the rest of the cover 4.

[0054] The depth of the 20 separation portions increases by 1% of the thickness 9 every two degrees of angle.

[0055] The separation portions 20 have a depth that increases progressively and constantly so as not to create a break in slope in the groove 5. In case of overpressure in the housing 2, the rupture is soft and progressive, this makes it possible to control said rupture and in particular the speed of propagation of said rupture and therefore to avoid a projection of debris.

[0056] Advantageously, the separation portions 20 extend from the minimum portion 14 to the maximum portion 13. Thus, the separation portions 20 extend angularly along a third angular sector γ between 120° and 170°.

[0057] The 20 separating sections ensure the continuity of the groove 5 from the minimum section 14 to the maximum section 13. This optimizes the length of the groove 5. Thus, in the event of overpressure, the rupture occurs over a sufficient length to dissipate the energy caused by said rupture and therefore prevent the projection of debris.

[0058] Advantageously, the lateral distance 12 is between 5 millimeters and 20 millimeters.

[0059] Such a lateral distance helps to protect the lid against the risk of uncontrolled breakage.

[0060] Advantageously, the spacing distance is between 0.5 millimeters and 2 millimeters.

[0061] This interval makes it possible to locate the break without weakening the lid.

[0062] Advantageously, the lower face 6 of the lid 4 is in contact with the inner volume 3 of the cell.

[0063] Advantageously, groove 5 has in section substantially a "U" shape with a flat bottom.

[0064] This ensures a clean and precise cut without risking further damage to the lid 4. It also prevents the lid 4 from being crushed during the formation of the groove 5 and avoids cracking. This cut shape is suitable for creating guide lines such as a groove 5.

[0065] Advantageously, the lid is made in one piece. In other words, the cell only requires a lid to close it. No other parts are needed.

[0066] This simplifies the design and reduces production costs. Furthermore, the lid is more durable over time, unlike lids made from multiple parts which are particularly cumbersome to assemble and tend to be fragile.

[0067] In one embodiment, the cover 4 is an added component within the electrical cell 1, in other words, designed as a separate part. This advantageously results in greater assembly flexibility and better control of the manufacturing process.

[0068] Advantageously, the minimum portion 13 and the maximum portion 14 are substantially symmetrical with respect to the center C. Thus, portions 13, 14 face each other on the.

[0069] This allows for optimization of the groove length 5 to better dissipate energy during an overpressure event causing rupture. This reduces the risk of debris being ejected.

Claims

Electric cell (1) for an electric propulsion vehicle, said cell (1) comprising: - a housing (2) defining an internal volume (3) containing an electrolyte and at least one stack of electrodes comprising a plurality of electrodes separated from each other by a porous separator film, - a cover (4) of a predetermined thickness (9) closing the housing (2), cell (1) in which the cover (4) has a wall having an upper face (7) and a lower face (6) opposite the upper face (7), said wall comprising a groove (5) having a depth which varies as one moves along said groove (5), the depth being measured along a longitudinal axis (X) of the cell (1), cell (1) in which the cover (4) is made in one piece. Cell (1) according to claim 1 in which, the groove (5) has a constant maximum depth (8), said maximum depth (8) being substantially between 70% and 90% of the thickness (9) of the cover (4). Cell (1) according to claim 2 in which the maximum depth (8) is substantially equal to 80% of the thickness (9) of the lid (4). Cell (1) according to any one of the preceding claims in which, the groove (5) has a constant minimum depth (10) measured along the longitudinal axis (X), said minimum depth (10) being substantially between 5% and 20% of the thickness (9) of the cover (4). Cell (1) according to claim 4 in which the minimum depth (10) is substantially equal to 10% of the thickness (9) of the lid (4). Cell (1) according to any one of the preceding claims in which, the cover (4) has an outer periphery (11) and the groove (5) has lateral edges located on the upper face (7), said lateral edges being located at a lateral distance (12) from the periphery measured in a plane of the upper face (7), said lateral distance (12) being greater than or equal to 5 millimeters. Cell (1) according to any one of claims 2 or 3 and according to any one of claims 4 to 6 further dependent on claim 2, wherein the groove (5) comprises at least one maximum portion (13) of maximum depth (8), said maximum portion (13) having a predetermined length. Cell (1) according to any one of claims 4 or 5 and according to any one of claims 6 or 7 further dependent on claim 4, wherein the groove (5) comprises at least a minimum portion (14) of minimum depth (10), said minimum portion (14) having a predetermined length. Cell (1) according to any one of the preceding claims in which, the cover (4) has substantially a disc shape, cell (1) in which, the groove (5) has an outer lateral edge (15) located on the periphery side of the cover (4) and an inner lateral edge (16) substantially concentric with the outer lateral edge (15), said annular edges being arranged on the upper face (7) and at a distance from each other of a predetermined distance (17). Cell (1) according to claim 9 in which, the maximum portion (13) is defined by a first angular sector (α) between 10 degrees and 60 degrees, said first angular sector (α) being measured substantially from a center (C) of the lid (4). Cell (1) according to claim 10 in which the first angular sector (18) alpha is substantially equal to 30 degrees. Cell (1) according to any one of claims 9 to 11 wherein, the minimum portion (14) is defined by a second angular sector (β) between 10 degrees and 60 degrees, said angular sector (β) being measured substantially from a center (C) of the lid (4). Cell (1) according to claim 12 in which the second angular sector (β) of the minimum portion (14) is substantially equal to 30 degrees. Cell (1) according to any one of claims 12 or 13 in which the minimum portion (14) and the maximum portion (13) are separated by separation portions (20) whose depth varies as one moves along said separation portions (20). Cell (1) according to claim 14 in which the depth of the separation portions 20 increases by 1% of the thickness (9) of the lid (4) every 2 degrees of angle. Cell (1) according to claim 14 or 15 in which the portions of (20) separation are defined by a second angular sector (γ) between 120 degrees and 170 degrees. Cell (1) according to claim 6 and according to any one of claims 7 to 16 further dependent on claim 6 in which, the lateral distance (12) is between 5 millimeters and 20 millimeters. Cell (1) according to claim 17 in which the gap distance (17) of the groove (5) is substantially between 0.5 millimeter and 2 millimeters. Cell (1) according to any one of the preceding claims in which, the lower face (6) of the cover (4) is located on the side of the inner volume (3) of the housing (2) of said cell. Cell (1) according to claim 8 and according to any one of claims 9 to 19 further dependent on claim 8 in which the minimum portion (13) and the maximum portion (14) are substantially symmetric with respect to a center (C) of the cover (4) located in a plane of the upper face (7) of said cover (4). Cell (1) according to any one of the preceding claims in which the groove (5) has in section a U-shape with a flat bottom. Cell (1) according to any one of the preceding claims, wherein the cover (4) is an added part.

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