Patent Application
20230411775
The invention relates to an energy storage device or battery pack comprising electrochemical cells and means for discharging the gas formed as a result of a malfunction of at least one electrochemical cell. The invention also relates to a motor vehicle including such an energy storage device.
Electric vehicles and hybrid vehicles include an energy storage device comprising electrochemical cells for supplying electrical energy to an electric motor. Several electrochemical cells are usually assembled in series or in parallel in an electrochemical module. The electrochemical modules are supported by a structure and connected to each other by electrical conductors, commonly referred to as “busbars”. During operation, significant differences in electrical potential can form between the different electrical conductors. The electrical conductors are therefore spaced far enough apart to prevent the formation of an electric arc.
Furthermore, electrochemical cells are liable to failures such as thermal runaway. Gases loaded with metal particles can then be released from the module including the faulty electrochemical cell. The presence of these gases between two electrical conductors with a large potential difference can lead to the formation of an electric arc. Such an electric arc can then create holes in the structure of the energy storage device, for example in a cover of the energy storage device. These holes can then facilitate the ingress of oxygen from the outside. The high temperatures inside the energy storage device combined with these electric arcs and an oxygen supply can then lead to a fire.
An energy storage device comprising a specific internal conduit designed to convey gases to the outside is known from document EP2654100. Such a storage device comprises numerous elements assembled together. Said storage device is complex to manufacture, heavy and bulky.
The purpose of the invention is to provide an energy storage device that overcomes the drawbacks mentioned above and improves the energy storage devices known in the prior art.
More specifically, one object of the invention is an energy storage device that is both simple to manufacture and reduces any risk of formation of an electric arc following failure of an electrochemical cell.
The invention relates to an energy storage device comprising a set of electrochemical modules and a casing containing said modules, the casing comprising a double-walled structure, each module comprising electrochemical cells and an envelope containing said electrochemical cells, the envelope being provided with at least one weak zone enabling gases contained inside the module to escape, said structure comprising an inner wall, an outer wall and at least one chamber formed between the inner wall and the outer wall, the inner wall being provided with a set of openings positioned opposite the at least one weak zone of each module, the outer wall being provided with at least one discharge opening.
Said structure may be an extruded structure, in particular an extruded aluminum structure.
The at least one weak zone formed in the envelope of each module may be an opening, in particular a circular opening.
The surface area of each opening in the inner walls of said structure may be strictly greater than the surface area of the opposing opening of the envelope.
The at least one weak zone may be arranged along a first side of each module, and the energy storage device may comprise electrical conductors connecting the modules together, the electrical conductors being arranged along a second side of each module, substantially opposite the first side, the electrical conductors notably being arranged substantially towards the center of the energy storage device.
The set of electrochemical modules may comprise two parallel rows of electrochemical modules, the energy storage device comprising electrical conductors arranged substantially in an interface zone between the two parallel rows.
The distance between each weak zone and the opening in the opposing inner wall may be equal to or less than 50 mm.
Said at least one chamber may form at least locally a gas discharge chamber towards the at least one discharge opening.
The energy storage device may comprise at least two distinct chambers defined between the inner wall and the outer wall of the structure, the at least two chambers forming at least locally two distinct gas discharge chambers towards at least two distinct discharge openings.
The energy storage device may comprise at least one valve designed to open gradually in the event of excess pressure in said at least one chamber, the at least one valve being arranged in the at least one discharge opening.
The energy storage device may comprise cross members separating adjacent electrochemical modules, the cross members being fastened to said structure.
The invention also relates to a motor vehicle comprising an energy storage device as defined above.
These objectives, features and advantages of the present invention are set out in detail in the description below of a specific embodiment provided as a non-limiting example with reference to the following attached figures:
The energy storage device 2, which could also be called a “battery pack” or for convenience “device 2”, comprises a set of electrochemical modules 3 and a casing containing the modules 3. The casing forms a closed envelope surrounding all the modules 3. Each module 3 comprises electrochemical cells, or accumulators, and an envelope surrounding these cells. The electrochemical cells can, for example, be lithium-ion cells or any other type of cell capable of storing energy in electrochemical form.
According to the embodiment shown in
The casing containing the modules 3 comprises a double-walled structure 4. The structure 4 extends laterally about the set of modules 3. The structure may be polygonal, having an overall rectangular or trapezoidal shape. The main function of the structure 4 may be to support all of the modules. The structure is therefore robust and rigid enough to bear the weight of the modules. Furthermore, the structure 4 forms a side protection for the different modules.
With reference to
The device 2 also includes cross members 6 separating adjacent electrochemical modules. The cross members 6 are fastened to the structure 4 and help to hold the different modules. In other words, the cross members 6 form compartments in which the modules 3 are arranged. The cross members 6 can extend parallel to each other between two opposite sides of the structure 4. Said cross members can extend parallel to a transverse axis of the vehicle.
The modules 3 are electrically connected to each other by electrical conductors 7, notably busbars. The electrical conductors 7 can for example be in the form of metal plates or bars and are able to carry high-intensity electrical currents. The metal conductors electrically connect two adjacent modules. Said metal conductors are arranged substantially towards the center of the storage device, i.e. substantially along a midline X separating the device 2 into two equal halves. In other words, the metal conductors are arranged substantially in an interface zone Zx defined between the two parallel rows of modules. The midline X can be substantially parallel to a longitudinal axis of the vehicle.
The envelope 31 further comprises two weak zones 34 arranged on the first side 32. Alternatively, the module may have a different number of weak zones: for example one, three, four or five weak zones, or even more. These weak zones may be positioned on different sides of the module 3. The weak zones 34 enable gases contained inside the electrochemical module to escape. In other words, when one or more of the electrochemical cells contained in the module 3 releases gas as a result of a malfunction, gas can escape from the envelope 31 via the weak zones 34 thereof.
According to one embodiment of the invention, these weak zones 34 may be simple openings in the envelope, for example circular openings. In this case, the envelope 31 is not sealed and the openings are the only openings in the envelope. In another variant embodiment, the weak zones may be zones of the envelope that are more fragile and liable to rupture as a result of an increase in pressure inside the envelope. For example, the weak zones may be made by thinning the envelope 31 locally or by pre-cutting an opening through only a portion of the envelope thickness. In this case, the envelopes may be sealed until the weak zones 34 are ruptured.
Furthermore, the electrical conductor 7 associated with the module 3 may preferably be arranged along a second side 35 of the envelope 31, opposite the first side 32. Thus, the electrical conductor 7 may be moved away from the weak zones along the greatest length of the module 3.
An example embodiment of the structure 4 is clearly visible in
The structure 4 may be formed by assembling different profile segments. These segments may advantageously be obtained by a material extrusion process, notably using aluminum. The inner wall 41 and the outer wall 42 may extend vertically substantially parallel to each other. The connecting walls 44 may extend substantially horizontally. Thus, a section of the structure 4 as shown in
The inner wall 41 of the structure 4 includes a set of openings 45 (shown schematically in
The openings 45 thus allow the volume containing the modules 3 to communicate with at least one of the chambers 43A, 43B, 43C. The outer wall 42 is provided with at least one discharge opening 46. In this case, two discharge openings 46 are arranged on either side of the midline X. The discharge openings 46 are not positioned opposite the openings 45 formed in the inner wall. Advantageously, at least one of the chambers 43A, 43B, 43C forms at least locally a gas discharge chamber 47 from the openings 45 towards the discharge openings 46. This discharge chamber is not an element attached to the device 2 but, on the contrary, is built directly into the structure 4 supporting the modules 3.
According to a first variant embodiment, all of the openings 45 may communicate with the same chamber 43A, 43B or 43C. In another variant embodiment, the individual openings 45 may communicate with separate chambers of the structure. In any case, discharge openings 46 are of course provided for each chamber that gases are liable to enter. This enables different gas flows to be handled differently, and in particular makes it possible to limit the risk of a gas that has entered a chamber through a first opening 45 from subsequently entering the volume containing the modules through a second opening 45.
Advantageously, the discharge openings 46 may be spaced apart from the openings 45 formed in the inner wall by a distance strictly greater than the distance separating the weak zones 34 from the openings 45. For example, this distance can be at least 60 mm, preferably at least 70 mm, or even at least 80 mm.
The device 2 also includes valves 9 that are arranged in each of the discharge openings 46 and designed to open gradually in the event of excess pressure in the chamber with which said valve communicates. These valves, an example embodiment of which is shown in
Advantageously, the surface area of the openings constituting the weak zones 34 is strictly smaller than the surface area of the openings 45 and strictly smaller than a flow area of the valves 9. The flow area of the valves 9 can be between the surface area of the weak zones 34 and the surface area of the openings 45. For example, an opening forming a weak zone 34 may have a surface area of between 300 mm2 and 400 mm2 inclusive. An opening 45 may have a surface area of between 500 mm2 and 700 mm2 inclusive. The flow opening of the valves 9 can be between 400 mm2 and 500 mm2 inclusive.
In order to manufacture the device 2 as set out above, the structure 4 can be manufactured by assembling extruded aluminum segments incorporating the openings 45 and 46. These openings can be made by simple drilling. Advantageously, the proposed dimensions for the openings 45, 46 are both small enough to have little effect on the rigidity of the structure 4 and large enough to efficiently discharge the gases. The valves 9 can be simply fitted into the corresponding openings 46. The modules 3 can be positioned inside the structure 4 between the cross members 6. The modules 3 are then fastened directly or indirectly to the structure 4 so that the weak zones 34 are positioned opposite the openings 45.
When the vehicle is running, electric currents can flow through the electrical conductors 7. Large potential differences may develop between adjacent electrical conductors. For example, this potential difference (illustrated by an arrow F1 in
If an electrochemical module 3 or an electrochemical cell contained within a module develops a fault, gas (illustrated by reference sign 10 in
Furthermore, hot gases escaping from one module are also prevented from heating up adjacent electrochemical modules, which would cause thermal runaway.
Advantageously, the presence of a valve prevents the fresh air from entering the device 2 in the opposite direction to the gases. This prevents oxygen from entering the device, which could lead to a fire.
Advantageously, the walls of the structure 4 have a high thermal inertia and enable the gases to be cooled as said gases are discharged. This reduces the risk of spontaneous combustion of the gases at the outlet of the valve.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20 10499 | Oct 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/078057 | 10/11/2021 | WO |
