Degassing system for an electric vehicle battery pack

Abstract

Degassing system configured to manage a possible release of gas from a plurality of electrochemical cells (2) of an electric vehicle battery, the degassing system comprising a retention manifold (1) generally hermetically delimiting a buffer volume (V1), the retention manifold comprising opposite each cell an opening forming part of a selectively opening passage (PS) between an interior volume of the cell and the buffer volume (V1), each cell comprising a first relief valve (3), configured to communicate the interior volume of the cell with the retention manifold in the event of overpressure inside the cell, the degassing system comprising at least one second downstream relief valve (4) arranged on a wall of the retention manifold, configured to communicate the buffer volume with the ambient air in the event of overpressure inside. Abstract figure: Fig. 2

Description

Title of the invention: Degassing system for an electric vehicle battery pack

[0001] The present invention relates to a degassing system for an electric vehicle battery pack, and a vehicle comprising such a system.

[0002] The battery of an electric vehicle comprises electrochemical cells grouped in an assembly called in the trade 'battery pack'.

[0003] The most common traction batteries on electric vehicles are batteries based on Lithium-Ion electrochemistry. Among these, there are several types, namely for example NMC (Nickel Manganese Cobalt), LFP (Lithium Iron Phosphate / LifePo4) and others.

[0004] Each electrochemical cell contains chemical elements hermetically contained in a cell envelope.

[0005] It cannot be excluded that one (or more) lithium-ion battery cell(s) may be subject, in certain circumstances, to excessive heating which causes an internal release of gas and an increase in the pressure prevailing inside the cell envelope. Each electrochemical cell therefore has, in order to limit the increase in the internal pressure of the cell and thus avoid any risk of incident, a gas discharge device also called here a relief valve. When said discharge device opens, gases present inside the cell envelope escape; these gases are also very hot in the circumstances in question. This phenomenon is called here "degassing" of the cell.

[0006] Furthermore, it turns out that in practice, the risk of a phenomenon called "thermal runaway" cannot be completely eliminated.

[0007] This phenomenon of thermal runaway, also called "thermal runaway" in the trade, occurs when an electrochemical cell reaches too high a temperature and begins to burn while communicating sufficient heat energy to neighboring cells to increase the temperature of the neighboring cells so that they too begin to burn, which gradually leads to the destruction of the battery.

[0008] On motor vehicles, all precautionary measures are taken to avoid at all costs an unwanted inflammatory or incandescent event for the entire vehicle, including the battery.

[0009] To this end, electric and electrified motor vehicles are equipped with high-performance cooling systems to cool the electrochemical cells of their battery. Regarding the battery, it is also planned to limit the stress applied to the battery if the temperature approaches a predefined threshold (this is called voluntary performance capping, also called 'derating').

[0010] Despite all the appropriate precautions taken, the risk of excessive heating in a cell of the battery pack with degassing, or even local heating which spreads to neighboring cells with possible thermal runaway, cannot be completely excluded.

[0011] If such an event were to occur, even if it is of extremely low probability, the battery monitoring system ('BMS') is configured to detect it in order to alert the occupants of the vehicle in question in time, so that they can take all relevant and appropriate actions in view of the situation.

[0012] It is requested that the occupants of the vehicle in question have time to leave the vehicle if an event of the aforementioned type occurs.

[0013] The time that the occupants of the vehicle must have is at least five minutes.

[0014] Document US2022149477 discloses a solution that proposes a baffle system for channeling gases emanating from a cell in a degassing situation. The passage of the gases in the baffle system lowers the temperature and reduces the risk of ignition. But the release of the gases into the atmosphere, although slowed down, is not substantially delayed in time.

[0015] The inventors sought to improve the situation, in particular to delay or delay the effect of heating or even degassing of one or more cells.

[0016] For this purpose, a degassing system is proposed configured to manage a possible release of gas from a plurality of electrochemical cells (2) of an electric vehicle battery, the degassing system comprising a retention manifold (1) generally hermetically delimiting a buffer volume (VI), the retention manifold comprising opposite each cell an opening (12) forming part of a selectively opening passage between an interior volume of the cell and the buffer volume, each cell comprising a first discharge valve (3) with an opening directed towards the retention manifold, configured to communicate the interior volume of the cell with the retention manifold in the event of pressure inside the cell greater than a first threshold, through the selectively opening passage,the degassing system comprising at least one second relief valve (downstream of the first valve) arranged on a wall of the retention collector, configured to communicate the buffer volume with the ambient air in the event of pressure inside the retention collector exceeding a second threshold.

[0017] Thanks to these provisions, the retention manifold allows the gases emanating from a cell to be kept captive in a degassing situation. It is only from the moment when several cells have degassed in the retention manifold that the accumulation of gases in the retention manifold generates an increase in the pressure in the retention manifold and the second relief valve can then open to release gas into the atmosphere.

[0018] Expressed differently, the retention collector makes it possible to substantially delay in time the occurrence of the release, into the atmosphere, of the degassing gases emanating from the cells.

[0019] If a small number of cells vent, the retention collector can contain the vent gases without time limit.

[0020] Advantageously, the retention collector also makes it possible to lower the temperature of the gases before any possible release into the atmosphere, this limits any possible risks of combustion.

[0021] A possible phenomenon of degassing of the first cell is detected and known to the battery management computer which can issue an alert to the occupants of the vehicle. The occupants of the vehicle then have time to leave said vehicle before a possible second, third, (or even more) electrochemical cells degas in turn in the particular case of a runaway of the battery pack which ends up causing the opening of the second discharge valve, and therefore degassing to the atmosphere.

[0022] According to one embodiment, the buffer volume represents a volume greater than three times the internal volume of a cell, preferably greater than five times the internal volume of a cell. Whereby the retention manifold can accommodate the gases resulting from degassing of a problematic cell, without the second discharge valve opening. Depending on the volumes degassed by the cells, and the opening pressure thresholds of the second discharge valve, the retention manifold can accommodate the gases resulting from degassing of several problematic cells. The release of hot and potentially toxic gases is thus delayed / deferred, which gives the vehicle occupants time to move away.

[0023] According to one embodiment, the buffer volume represents a volume greater than 20 liters, and preferably greater than 30 liters. This is a substantial volume capable of storing a large quantity of gas emanating from a degassing cell.

[0024] According to one embodiment, each selectively opening passage comprises a third valve interposed between the first relief valve and the buffer volume. As a result, the third valve is downstream of the first relief valve and an isolation airlock is formed between the first relief valve and the third valve, in the normal configuration, i.e. in their closed state. This isolation airlock allows to prevent hot gases emanating from a problematic cell, after having filled the retention collector, from directly heating the mouth where the breakable membrane of a normally operating cell is located. This arrangement is therefore beneficial in preventing runaway or propagation of the problem from a problematic cell to other cells, via the buffer volume.

[0025] According to one embodiment, the first and / or second discharge valves are of the breakable membrane type. This is a cheap and well-controlled solution. A breakable membrane is also a very reliable solution; it does not risk getting stuck, it tears without a hitch as expected under a pressure differential across its faces, from a breaking point or a breaking zone.

[0026] According to one embodiment, the third valve is a breakable membrane or a non-return valve. In a normal initial configuration, this third valve remains closed and delimits the isolation airlock mentioned above. In the event of a pressure differential across its faces, the third valve opens. The third valve may typically have a lower trigger threshold than the first relief valve so that the third valve systematically opens if the first valve opens. The trigger threshold of the third valve may be adjusted to a third threshold chosen as a function of the respective volumes of cells and the retention collector.

[0027] According to one embodiment, the breakable membrane of the first relief valve has a breaking strength up to a first breaking strength threshold in response to a pressure difference, and the breakable membrane of the second relief valve has a breaking strength up to a second breaking strength threshold in response to a pressure difference across its faces. The first and second breaking strength thresholds may be identical but, depending in particular on the volume available inside the retention manifold, the first and second breaking strength thresholds may be differentiated. The breakable membrane of the third relief valve has a breaking strength up to a third breaking strength threshold in response to a pressure difference across its faces.

[0028] According to one embodiment, the retention collector comprises a main body and two end pieces forming a closure plate, the main body being obtained by extrusion, and the main body further comprises hollow channels resulting from extrusion and adapted to conduct cooling fluid.

[0029] Thus, the cooling fluid intended to cool the electrochemical cells also cools the buffer volume and contributes to lowering the temperature of the degassed gases before they are discharged into the open air.

[0030] According to one embodiment, the retention collector is arranged, in a local vertical direction Z, under the plurality of electrochemical cells. The retention collector thus naturally forms the mechanical support on which the electrochemical cells rest.

[0031] According to one embodiment, the degassing system may further comprise, for each cell, a cell support, mounted on the retention collector, then acting as a base for the cell supports, each cell being mounted individually on a cell support. Each cell support provides a mechanical holding function for the cell that it frames.

[0032] According to one embodiment, the degassing system further comprises a connection sleeve between each cell and the retention collector, associated with a cell support or forming part of the cell support.

[0033] According to one embodiment, heat transfer is provided by means of angled strips adjacent to a slice of the cell housing. For each cell, the angled strips make it possible to exchange calories with the cell over a fairly large surface area as well as to exchange calories with the upper wall of the retention collector over a fairly large surface area, which provides good cooling efficiency.

[0034] According to an alternative embodiment, the retention collector is arranged, in a local vertical direction Z, above the plurality of electrochemical cells. According to this configuration, the hot gases resulting from the degassing tend to be placed upwards in the interior volume of the retention collector, and they have less tendency to lick the first discharge valve of the other cells which are still operating normally.

[0035] The present invention also relates to a battery pack comprising a plurality of electrochemical cells, and a degassing system as described previously.

[0036] The present invention also relates to an electric or hybrid vehicle, comprising at least one degassing system as described previously.

[0037] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig. 1] illustrates a side view of an electric vehicle in which the present invention is implemented; - [Fig.2] represents a cross-sectional view of an example of a battery pack according to a first embodiment; - [Fig.3] illustrates a perspective view of an example of a retention collector; - [Fig.4] represents a cross-sectional view in exploded mode; - [Fig.5] illustrates a perspective view of an example of a retention collector with the cell supports mounted without the cells and without the cover; - [Fig.6] illustrates a perspective view of an example of a battery pack without the cover; - [Fig.7] illustrates a perspective view from below of the electrical connections between the cells; - [Fig.8] illustrates an exploded perspective view of an example of a cell support according to a first embodiment; - [Fig.9] shows in a detail view the area of ​​the connecting sleeve with the first relief valve and the third valve; - [Fig. 10] represents a perspective view of a variant of the first embodiment with cell supports according to an alternative embodiment; - [Fig. 11] illustrates a perspective view of an example of a cell support according to the embodiment variant of [Fig. 10]; - [Fig. 12] illustrates a perspective view of a set of cell supports according to the embodiment variant of [Fig. 10]; - [Fig. 13] represents a cross-section of an example of a battery pack according to the embodiment variant of [Fig. 10]; - [Fig. 14] represents a cross-sectional view of an example of a battery pack according to a second embodiment.

[0038] In the various figures, the same references designate identical or similar elements. For reasons of clarity of the description, certain elements are not necessarily represented to scale. It should be noted that the chemical elements contained inside the battery cells have not been represented in the figures.

[0039] With reference to the figures, a battery pack 19 used in an electric vehicle is now described. The battery pack comprises electrochemical cells. For example, electrochemical cells are based on Lithium-Ion type electrochemistry. However, it should be noted that the presentation can be applied to any electrochemical variant of electrochemical cells for traction batteries of electric vehicles.

[0040] Regarding the quantity of energy stored in the battery pack, we are talking in practice about a significant amount of energy, several tens of kWh. A 100% electric vehicle battery has an energy storage capacity typically between 40 kWh and 100 kWh, depending on the target autonomy, the weight and the consumption of said vehicle.

[0041] The number of electrochemical cells can range from 20 to 200, without excluding a larger number.

[0042] The battery pack 19 is installed in the floor area of ​​the vehicle 9 illustrated here. The vehicle can be of any type, private vehicle or utility vehicle, for example sedan, station wagon, SUV, minivan, van, van, truck. Off-road vehicles, for example recreational vehicles are also considered. Watercraft are also not excluded.

[0043] Advantageously, a degassing retention collector 1 is provided, arranged in the first embodiment below the electrochemical cells of the battery. The retention collector 1 may also be called a 'casing'.

[0044] A battery management computer 92 is provided (this computer is called in the jargon of the trade BMS for Battery Management System), responsible for monitoring the operation of the battery, periodically calculating its state of charge, isolating the battery pack from the rest of the high voltage electrical network of the vehicle if necessary, monitoring the temperature of the cells or cell modules and cooperating with a cooling system in order to maintain the cells in an optimal temperature range.

[0045] Turning to Figures 2 to 9, we now discuss the arrangement of the battery pack 19 according to a first embodiment.

[0046] By convention, a motor vehicle moves in an orthogonal spatial reference frame comprising a longitudinal axis X in a direction of movement of the vehicle, a transverse axis Y perpendicular to the longitudinal axis X, and a vertical axis Z perpendicular to the longitudinal axis X and to the transverse axis Y, the vertical axis being directed from bottom to top. The three axes in question are shown in Figures 2 and following.

[0047] The battery pack 19 comprises in the lower part the retention collector 1 already mentioned. On the retention collector are mounted cell supports 6. Each electrochemical cell 2 is mounted individually on a cell support 6. The cells are arranged in a row and are close to each other, but are not in direct contact with one or the other to avoid possible direct thermal conduction.

[0048] In the non-limiting example illustrated in the figures, there are 20 cells arranged in two rows of 10 cells.

[0049] Concerning the position of each electrochemical cell, it is noted that the electrical terminals, positive 22 and negative 23, are oriented downwards. Conversely, the bottom of the cell 20 is at the top. In other words, the cell is positioned upside down compared to a conventional position, with here its front interfacial face 21 oriented downwards.

[0050] The electrochemical cells 2 are prismatic, namely of general parallelepiped shape.

[0051] A metal frame 29 is provided which runs along the entire edge of the cell, i.e. on the 4 short sides of the parallelepiped. The frame can itself be the housing which contains the internal elements of the cell or a specific part attached to a housing made of synthetic material, plastic.

[0052] The thickness E2 in the X direction can be between 3 cm and 10 cm.

[0053] The height H2 along the Z axis can be between 10 cm and 20 cm

[0054] The length L2 along the Y axis can be between 15 cm and 40 cm.

[0055] The cell envelope delimits an internal cell volume marked V2. The volume The internal part of the cell contains electrode elements and an electrolyte (not shown in the figures).

[0056] The retention manifold 1 is a hollow part, made of extruded aluminum. The retention manifold 1 comprises hollow channels 34 produced by extrusion and adapted to channel cooling fluid.

[0057] The retention collector 1 generally hermetically delimits a buffer volume VI.

[0058] The retention manifold 1 comprises a main body 10 and two end pieces, a front end plate 15 and a rear end plate 16. The end plates form sealed closure plates hermetically joined to the main body 10 around the entire perimeter of the closure plates, by welding or structural bonding.

[0059] The main body 10 comprises a lower wall 14, two side walls 13 and an upper wall 11.

[0060] The main body 10 is a good thermal conductor, consequently the thermal gradient between the temperature of the fluid which flows through the hydraulic channels 34 and the average temperature of the main body 10 of the retention collector 1 remains low.

[0061] The cell support 6 comprises a horizontal sole 60 elongated along the axis Y6. Two uprights 61, 62 extend from the ends of the sole in the vertical direction to frame the cell. In the middle of each of the uprights 61, 6211 is provided a vertical notch 69 whose utility will be seen later.

[0062] The cell support 6 can be made of light alloy, or can be made of synthetic polymer for example based on polyethylene, polypropylene, polyamide, PVC or other.

[0063] In the middle of the horizontal sole 60, a core 65 is provided with a central bore 66 in which the sleeve 7 seen further on is received.

[0064] In addition, support surfaces 63 are provided on which the cells 2 rest. The weight of the cells is taken up by these support surfaces 63 and transferred to the retention collector which thus forms a main base for the entire battery pack.

[0065] Recesses 64 are provided to leave space for the nuts 78 which allow the bus bars connecting the cells electrically to each other to be screwed on.

[0066] For each cell, a selective opening passage PS is provided between the interior volume V2 of the cell and the buffer volume VI.

[0067] For this purpose, a connecting sleeve 7 is further provided between each cell 2 and the retention collector 1. The connecting sleeve 7 may be part of the cell support 6. In the example illustrated, the connecting sleeve 7 is a separate part associated with the cell support 6. More precisely, the sleeve is inserted into the central bore 66 already described above.

[0068] With reference to [Fig.2], the connecting sleeve 7 shown on the left has axis Z1 and the connecting sleeve shown on the right has axis Z2.

[0069] According to a particular option, the connection sleeve is metallic and acts as a heat pipe between the main body 10 of the retention collector and the metal casing or the cell frame 29.

[0070] As visible in [Fig.8], an annular layer of thermal grease 71 is provided between the connection sleeve 7 and the main body 10 of the retention collector, and in addition an annular layer of thermal grease 72 is also provided between the connection sleeve 7 and the metal frame 29 which surrounds the edge of the cell.

[0071] The connecting sleeve 7 and the layers of thermal grease 71 together form a thermal bridge between the cell and the main body 10 of the retention collector.

[0072] Thanks to these arrangements, in addition to the thermal conduction function, it is prevented that gas leaving the cell can escape on the sides of the connection sleeve. All the gas escaping from the cell arrives in the internal volume VI of the retention collector.

[0073] According to an alternative embodiment, annular sealing gaskets may be provided instead of the aforementioned thermal grease, the annular gaskets being made of a material which is a good thermal conductor.

[0074] As seen in Figures 3 and 9, the retention collector 1 comprises opposite each cell an opening 12 forming part of the selective opening passage PS between the interior volume of the cell V2 and the buffer volume VI.

[0075] Each cell comprises a first discharge valve 3 with an opening directed towards the retention collector, i.e. downwards here. The first discharge valve 3 is configured to communicate the interior volume of the cell with the retention collector in the event of pressure inside the cell exceeding a first threshold, through the selectively opening passage PS.

[0076] Referring to [Fig.9], the first relief valve 3 comprises a breakable membrane 30. The breakable membrane 30 has a breaking strength up to a first breaking strength threshold in response to a difference in pressure. A fixing ring 32 makes it possible to immobilize the discharge valve 3 relative to the cell frame 29.

[0077] The degassing system comprises at least one second downstream discharge valve 4 arranged on a wall of the retention collector. The second discharge valve 4 is configured to communicate the buffer volume VI with the ambient air in the event of pressure inside the retention collector exceeding a second threshold.

[0078] The second relief valve 4 comprises a breakable membrane 40. The breakable membrane 40 has a breaking strength up to a second breaking strength threshold in response to a pressure difference.

[0079] The two breakable membranes 30, 40 can be made of different plastic materials having a certain flexibility such as neoprene, Teflon™, but more generally any synthetic polymer of the polyamide, polyester, polyethylene type. A membrane made of rubber or polyurethane is also possible. A membrane in the form of a thin metal sheet or a metal / plastic composite sheet may also be suitable. A membrane in the form of a thin aluminum sheet may also be suitable.

[0080] Each of the breakable membranes 30, 40 has a constant general thickness of between 0.1 mm and 2 mm, preferably between 0.2 mm and 1 mm depending on the material chosen.

[0081] Advantageously, weakening lines are provided in the breakable membrane so as to control the breaking strength threshold.

[0082] Once the breakable membrane has been ruptured, it remains open; the rupture phenomenon is non-reversible.

[0083] According to one option, the second threshold may be equal to the first threshold. According to another option, the two thresholds are differentiated and chosen so as to obtain the desired confinement of gas in the internal volume of the retention collector.

[0084] In a side wall 13, a hole 47 with axis Y4 is provided to receive the second discharge valve 4.

[0085] It is noted that there could be several second discharge valves in parallel to evacuate the gas included in the interior volume VI of the retention manifold.

[0086] Each selective opening passage PS comprises a third valve 5 interposed between the first discharge valve 3 and the buffer volume VL

[0087] As illustrated in the detail view of [Fig.9], the third valve 5 is downstream of the first relief valve 3. An isolation airlock marked Vsas is thus formed between the first relief valve 3 and the third valve 5, in the normal configuration, that is to say in their closed state.

[0088] This Vsas isolation airlock makes it possible to prevent hot gases emanating from a problematic cell, after having filled the retention collector 1, from directly heating the wall of a normally operating cell. This arrangement is therefore favorable for preventing runaway through its closed membrane 30 and / or propagation of the problem from a problematic cell to other cells.

[0089] In an illustrated example, the third valve 5 comprises a breakable membrane 50 which operates in a manner similar to the breakable membranes already described.

[0090] In an alternative embodiment, the third valve may be formed as a non-return valve which allows gases to flow towards the buffer volume but not back up towards the internal volume of the cell.

[0091] Electrical connection bar buses 77 are provided, visible in [Fig.7], and nuts 78 as known per se and therefore not described in detail here.

[0092] To electrically connect a cell of the first row to a cell of the second row, the bus bar 77a passes through the aforementioned notch 69.

[0093] The channels 34 are in specific fluid communication with respective hydraulic fittings 35 (see [Fig.3]). It is noted that the end closure plates 15, 16 each have four holes 36. The holes 36 in the front and rear plates receive the hydraulic fittings.

[0094] In [Fig.2], it is noted that a cover 8 shown in dotted lines covers the plurality of cells. According to a particular embodiment, shims 84 are provided to constrain the cells 2 against the cell supports 6. Any other means of fixing the cells inside the battery pack is also considered in the context of the present invention. The cover 8 can be assembled by screwing onto the retention collector 1.

[0095] [Fig. 10] illustrates an alternative embodiment essentially concerning the cell supports and the heat pipe function. Anything not described in the following paragraphs is considered similar or identical to what was described for the first embodiment and therefore not described again.

[0096] According to the variant shown in Figures 10 to 13, the heat pipe function is performed differently from that of the first embodiment.

[0097] The cell support marked 6' can fully contain the function of the connection sleeve without the heat pipe function.

[0098] For the thermal conduction function between the cell 2 and the retention collector 1, there are here provided right-angled strips 55, 56 adjacent to the edge of the housing. A first portion 87, arranged horizontally, is in thermal contact with the upper wall of the retention collector. A second portion 88, arranged vertically, is in contact with a rising side of a cell. The first and second portions are connected by an elbow 89.

[0099] The right-angled strips 55, 56 are made of aluminum or any metal alloy that is a good thermal conductor.

[0100] The parts of the right-angled strip in contact with the cell 2 and in contact with the upper face 11 of the retention collector are coated with a thermal paste 82, 83.

[0101] Each electrochemical cell 2 is framed on the one hand on the left side by a first right-angled strip 55, and on the other hand on the right side by a second right-angled strip 56.

[0102] As seen in [Fig. 11], the cell support marked 6' includes previous lower lateral vertical uprights, but each upright, on the right and left side, includes two separate notches 75, 76.

[0103] Cleverly, the 2 right-angled strips are not opposite each other but are offset along the longitudinal axis X. This allows, as visible in figures 12 and 13, to have in the intermediate zone between the two rows of cells, an alternation of the right-angled strips, namely a right-angled strip which holds the cell on the left then a right-angled strip which holds the cell on the right, and so on. This gives a more compact physical integration, that is to say a single thickness of strip on the line marked 74 between the 2 rows of cells.

[0104] [Fig. 14] illustrates a second embodiment in which the retention collector 1 is arranged above the cells (instead of below the cells in the first embodiment presented above). In other words, the assembly is reversed in the vertical direction.

[0105] In this second embodiment, the internal volume of the retention collector has, as in the first embodiment, a substantial volume. In practice, a buffer volume VI of at least 20 liters, preferably at least 30 liters, is chosen.

[0106] The first relief valves 3 open upwards. The third relief valves 5 also open upwards if present.

[0107] The hydraulic cooling channels 34 remain below.

[0108] The second discharge valve 4 is on the side and directed downwards, so that the discharge of potentially hot gases is directed towards the ground.

[0109] In [Fig. 14], the path of the gases from the inside of the cell to the open air has been shown by the path illustrated in dotted lines marked Fl.

[0110] Generally, it should be noted that, in a single vehicle, several instances of the battery pack described above can be arranged one after the other along X, sharing the same hydraulic circuit along the X axis.

Claims

Claims

1. A degassing system configured to manage a possible release of gas from a plurality of electrochemical cells (2) of an electric vehicle battery, the degassing system comprising a retention manifold (1) generally hermetically delimiting a buffer volume (VI), the retention manifold comprising opposite each cell an opening (12) forming part of a selectively opening passage (PS) between an interior volume of the cell and the buffer volume (VI), each cell comprising a first discharge valve (3) with an opening directed towards the retention manifold, configured to communicate the interior volume of the cell with the retention manifold in the event of pressure inside the cell greater than a first threshold, through the selectively opening passage, the degassing system comprising at least one second downstream discharge valve (4) arranged on a wall of the retention manifold,configured to communicate the buffer volume with the ambient air in the event of pressure inside the retention collector being greater than a second threshold, in which the retention collector is arranged, in a local vertical direction (Z), under the plurality of electrochemical cells, and in which the buffer volume represents a volume greater than three times the interior volume of a cell, preferably greater than five times the interior volume of a cell.,

2. A degassing system according to claim 1, wherein the retention manifold is a hollow part, made of extruded aluminum and comprises hollow channels (34) adapted to channel cooling fluid.

3. A degassing system according to any one of claims 1 to 2, wherein each selectively opening passage comprises a third valve (5) interposed between the first relief valve and the buffer volume.

4. A degassing system according to any one of claims 1 to 3, wherein the first and / or second relief valves are of the breakable membrane type.

5. A degassing system according to claim 3, wherein the third valve is a breakable membrane (50) or a check valve.

6. A degassing system according to claim 4, wherein the breakable membrane (30) of the first relief valve (3) has a breaking strength up to a first breaking strength threshold in response to a pressure difference, the breakable membrane (40) of the second relief valve (4) has a breaking strength up to a second breaking strength threshold in response to a pressure difference.

7. A degassing system according to any one of claims 1 to 6, wherein the retention manifold comprises a main body (10) and two end pieces (15,16).

8. Degassing system according to any one of claims 1 to 7, further comprising, for each cell, a cell support (6), mounted on the retention collector then acting as a base for the cell supports, each cell being individually mounted on a cell support.

9. A degassing system according to any one of claims 1 to 8, further comprising a connecting sleeve (7) between each cell and the retention manifold, the connecting sleeve being associated with a cell support or forming part of the cell support.

10. A degassing system according to any one of claims 1 to 9, wherein heat transfer is provided by means of angled strips (55,56) adjacent to a slice of the cell housing.

11. A battery pack comprising a plurality of electrochemical cells, and a degassing system according to any one of claims 1 to 10.

12. Electric or hybrid vehicle, comprising at least one degassing system according to any one of claims 1 to 10.

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