Battery pack including cooling circuit

Abstract

The present invention relates to a battery pack for an electric or hybrid vehicle, which comprises an upper casing (3) and a lower casing (2) and is provided with a cooling circuit that allows the circulation within the pack of a cooling fluid intended to be sprayed onto the battery modules by spray nozzles (30), characterized in that the cooling circuit is configured to ensure the circulation of the cooling fluid in a closed circuit inside the pack using a pump (7) arranged within the internal container of the pack, which allows the cooling fluid sprayed onto the modules and collected in a double bottom (23) arranged below the bottom wall (20) of the lower casing (2) to be recirculated to the spray nozzles by means of discharge openings (21) formed in the bottom wall of the lower casing.

Description

[Technical field]

[0001] The present invention relates to a battery pack for receiving at least one battery module including a plurality of interconnected cells and comprising a cooling circuit for circulating a cooling fluid within the pack.

[0002] The present invention has particular, but not exclusive, application to lithium-ion (Li-ion) batteries for powering the drivetrain of electric or hybrid vehicles. [Background technology]

[0003] Lithium-ion batteries are particularly suitable for powering the drivetrains of electric or hybrid vehicles due to their high voltage and high energy density. In such batteries, the lithium-ion cell is the basic building block, which includes a certain amount of electrolyte through which lithium ions can move between a cathode and an anode to store or deliver electrical energy. In lithium-ion batteries, a number of lithium-ion cells are first assembled and connected in series and / or parallel to form a module, and then a number of modules are assembled and connected in series and / or parallel to form a "pack". Thus, a battery pack generally comprises a number of interconnected modules, which are formed by a number of interconnected cells and supports for their various elements.

[0004] In the event of failure of one or more cells in a battery pack, a thermal runaway phenomenon may be triggered inside the cells. In the absence of a safety device, such as that implemented by the applicant, this thermal runaway phenomenon may spread throughout the pack and result in a fire as soon as a cell exceeds a temperature threshold. As this is a chemical fire, it is very difficult to extinguish, especially considering that the fire is contained within the almost sealed chamber formed by the pack.

[0005] Patent document CN106110537 discloses a device for preventing the risk of fire when thermal runaway of a lithium-ion battery occurs. Besides a temperature sensor, the battery is equipped with a water supply circuit and a liquid nitrogen supply circuit to enable water and liquid nitrogen to be circulated in the battery pack, respectively. When the detected temperature exceeds a certain threshold, one or the other of the two water supply circuits and liquid nitrogen supply circuits is activated to cool the battery during the early stage of thermal runaway of the battery cells, and, if necessary, to put out the fire when the battery is burning. Specifically, when the temperature is between a low temperature threshold and a high temperature threshold, the liquid nitrogen supply circuit is activated to spray liquid nitrogen onto the battery cells from above, and when the temperature is higher than the high threshold, the liquid nitrogen spray is stopped, while the water supply circuit is activated to spray water mist onto the battery cells from above.

[0006] This device is relatively complex to manufacture, since it requires providing the battery with two different cooling circuits, specifically a liquid nitrogen supply circuit and a water supply circuit, resulting in loss of space and cost. Moreover, the simple act of spraying liquid nitrogen or water from above onto the cells of the battery module may not be sufficient to prevent a fire in case of an excessive temperature rise or to ensure that the fire is completely extinguished. Summary of the Invention

[0007] SUMMARY OF THE DISCLOSURE It is therefore an object of the present invention to propose a battery pack which is free of at least one of the limitations mentioned above.

[0008] To this end, the invention relates to a battery pack for an electric or hybrid motor vehicle, formed by an upper housing and a lower housing which delimit an internal chamber in which at least one battery module comprising a plurality of interconnected electrochemical cells is accommodated, comprising a cooling circuit enabling the circulation in the pack of a cooling fluid intended to be sprayed by a spray nozzle onto said at least one module, characterized in that the cooling circuit is configured to ensure the circulation of the cooling fluid in a closed circuit within the pack by means of a pump arranged in the internal chamber capable of recirculating to the spray nozzle, by means of a discharge orifice formed in the bottom wall of the lower housing, the cooling fluid sprayed onto said at least one module and collected in a double bottom provided below the bottom wall of the lower housing.

[0009] This arrangement, which includes, on the one hand, discharge orifices formed in the bottom wall of the lower housing enabling the cooling fluid flowing down along the cells of said at least one module to be collected in the double bottom of the lower housing, and, on the other hand, a pump enabling this collected fluid to be recirculated to the spray nozzles, causes the cooling fluid to circulate in a closed circuit inside the pack, which is therefore particularly compact and not very bulky.

[0010] Advantageously, a heat-soluble sealing element is installed inside each discharge orifice, said sealing element being capable of dissolving to enable sealing of said at least one discharge orifice when a predetermined temperature threshold is reached, in order to enable immersion of the cells of said at least one module, and to prevent the discharge of the cooling fluid sprayed on said at least one module towards the double bottom of the lower housing.

[0011] With this configuration, each discharge orifice facing the double bottom can be closed in the event of an excessive temperature rise. The temperature threshold is configured to melt the thermofusible sealing element at the onset of a thermal runaway event in a cell that may ignite in the pack. This allows the level of the cooling fluid, which continues to be sprayed on the cells in said at least one module, to rise until it submerges the cells. This effectively stops the spread of a cell fire.

[0012] Advantageously, the spray nozzle is arranged on an inner wall of an upper housing, said upper housing having an outer wall spaced apart from said inner wall so as to form an internal cavity within said upper housing, and a pump is connected to the spray nozzle by a conduit leading to said internal cavity for injecting said cooling fluid into the internal cavity.

[0013] Advantageously, a through hole leading to the double bottom of the lower housing is formed in the bottom wall of the lower housing for the passage of cooling fluid, the pump having a suction spout engaged through the hole as mentioned above and penetrating into the double bottom.

[0014] Advantageously, the multiple cells are juxtaposed in the receiving space of each module with at least one space between two elementary cells of said at least one module to allow the passage of cooling fluid between the two cells of said at least one module.

[0015] Advantageously, the space is formed by a partition extending between two cells, said partition being grooved on both sides in order to create fluid-passing channels along the cells.

[0016] The invention also relates to a motor vehicle equipped with an electric drive train, characterized in that it comprises a battery pack as described above.

[0017] Further characteristics and advantages of the present invention will become apparent from the following description, given by way of example and in no way in a limiting manner, in connection with the accompanying drawings, in which: [Brief description of the drawings]

[0018] [Figure 1] 1 is a longitudinal cross-sectional view of a battery pack according to an exemplary embodiment of the present invention; [Diagram 2] FIG. 2 is a perspective view of the battery pack module shown in FIG. [Diagram 3] 2 is an exploded cross-sectional perspective view of a detail of a lower portion of the battery pack shown in FIG. 1. FIG. [Figure 4] 2 is an unexploded, cross-sectional perspective view of a detail of a lower portion of the battery pack shown in FIG. 1. FIG. [Diagram 5] 1A-1C are cross-sectional perspective views of details of a lower portion of a battery pack having two release orifices formed in the bottom of the lower housing shown in closed and unclosed configurations, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 shows a side cross-sectional view of a main battery pack 1 of an electric or hybrid motor vehicle with at least one electric drive train. The pack 1 is substantially formed by a lower housing 2, for example made of aluminium, which is closed by an upper housing 3, also made of aluminium. The lower and upper housings 2 and 3 delimit an internal chamber in which at least one and preferably several modules 4 of interconnected electrochemical cells 5 of the lithium-ion type are arranged. According to this example, the pack 1 encloses two modules 4 of ten interconnected electrochemical cells 5, preferably of parallelepiped shape. For each of the modules 4, the cells 5 are held parallel to each other and at a distance from each other by a partition plate 6, the role of which is to allow the passage between the cells of a cooling fluid sprayed from above the module. FIG. 2 shows a perspective view of a detail of the module 4 and of its inner partition plate 6, which are arranged at a certain distance apart and parallel to each other, between which the cells shown in FIG. 1 are inserted. The module 4 is formed by a casing with a substantially square cross section, including an upper opening 41 opposite a lower opening 42. Inside the casing 4, each of the partition plates 6 extends substantially over the entire height of the casing 4 and has two opposing surfaces 61, 62. The two opposing surfaces 61, 62 of the plate 6 are grooved. The two opposing surfaces 61, 62 therefore have a groove 63 that extends over the entire height of the plate 6 between the upper and lower openings of the module casing 4.

[0020] Referring again to FIG. 1, the upper housing 3 has an internal cavity 33 formed by two opposing, spaced apart walls extending along the two modules 4 of cells 5 housed in the battery pack 1, specifically an external wall 31 and an internal wall 32. The internal wall 32 is provided with a number of spray nozzles 30 facing the upper opening 41 of the module and the cells arranged in the module. The spray nozzles 30 are provided to allow the spraying of a cooling fluid injected into the internal cavity 33 of the upper housing 3 onto the battery modules 4 arranged in the internal chamber of the pack below the upper housing 3 of the pack, as will be explained in more detail below. The cooling fluid is a dielectric fluid, i.e. it is not a charge carrier so as not to short-circuit the cells. The heat transfer fluid is, for example, polyethylene glycol or mineral oil.

[0021] Therefore, the cooling fluid sprayed by the spray nozzle 30 onto the upper part of the battery module 4 flows along the grooves between the cells 5 and the partition plates 6 of the battery module to the bottom 20 of the lower housing 2. In this way, heat exchange takes place between the cells and the cooling fluid, so that the thermal energy released by the cells can be dissipated.

[0022] As best seen in Figures 3 and 4, which show a perspective view of a detail of the lower part of the pack 1 in exploded and non-exploded views, respectively, the heated cooling fluid is then intended to flow by gravity through the discharge orifices 21 formed in the bottom wall 20 of the lower housing 2, preferably including at least one discharge orifice formed opposite the lower opening 42 of each of the modules 4 arranged in the pack. The heated cooling fluid collected by the discharge orifices 21 is conveyed through these orifices 21 into the double bottom 23 of the lower housing 2, formed by the lower wall 22 of the lower housing 2 facing the bottom wall 20 of the lower housing 2, the two walls of the lower housing being spaced apart from each other, i.e. the lower wall 22 and the bottom wall 20. The double bottom 23 of the lower housing therefore extends below the bottom wall 20 of the lower housing 2 facing the lower opening of the module.

[0023] The double bottom 23 of the lower housing 2 and the internal cavity 33 of the upper housing 3 are connected to each other by a pump 7 placed in the chamber of the battery pack 1 adjacent to the module 4. For this purpose, the internal wall 32 of the upper housing 3 has an orifice 34, substantially along the pump 7, which leads into the internal cavity 33 of the upper housing 3. On said orifice 34 there is a connector fitted into a supply tube 8 which extends to the pump 7.

[0024] Furthermore, the bottom wall 20 of the lower housing 2 has a through hole 26 in the area of ​​the pump 7, said through hole leading to the double bottom 23 of the lower housing 2. The pump 7 has a suction spout 71 which is inserted through the through hole 26 into the double bottom 23 of the lower housing 2.

[0025] Thus, by switching on the pump 7, the cooling fluid circulates in a closed circuit inside the pack 1 as follows: First, the cooling fluid is drawn into the double bottom 23 of the lower housing through the through hole 26. The cooling fluid is considered to be at a low temperature in the through hole 26. Then, the cooling fluid is sucked through the suction spout 71 of the pump 7 and delivered under pressure through the supply line 8, as shown by the arrow F. Then, the cooling fluid flows under pressure into the internal cavity 33 of the upper housing 3. Then, the cooling fluid is sprayed under pressure through the spray nozzles 30 so as to form a spray mist P above the modules 4. Then, according to the arrow T, the cooling fluid flows by gravity along the cells 5 in the passage channels formed by the grooves 63 of the partition plates 6 arranged between the cells 5. When the cooling fluid comes into contact with the cells 5, it stores the thermal energy generated by the cells 5, and then flows by gravity on the bottom wall 20 of the lower housing 2, and then through the discharge orifices 21 inside the double bottom 23 of the lower housing 2. The thermal energy accumulated from contact with the cells then tends to be lost from the heated cooling fluid to the lower wall 22, which is exposed, for example, to the ambient air. Since the distance between the lower wall 22 and the bottom wall 20 is small compared to their surface areas, the cooling fluid is in the form of a thin layer passing through the double bottom 23 of the lower housing, and therefore its cooling is rapid. As a result, when the cooling fluid is sucked again through the through holes 26, it is considered to be at a low temperature, and therefore another cooling cycle of the cells 5 begins.

[0026] However, if thermal runaway of cells within one or more battery modules occurs, the battery cells may catch fire within the pack once the temperature threshold is exceeded, and the battery cell cooling cycle just described may not be sufficient to prevent or contain the spread of this fire.

[0027] Each discharge orifice 21 is therefore equipped with a thermofusible sealing element 24, which is incorporated in the orifice and is intended to enable said discharge orifice to be sealed in the event of an excessive temperature rise, thus allowing the module to be immersed. The thermofusible sealing elements 24 are in the form of pellets made of a thermofusible material, placed inside each discharge orifice 21 and having a central bore 25 for allowing the passage of a cooling fluid towards the double bottom 23 of the lower housing 2, each pellet having the ability to melt in order to block the discharge orifice 21 when a predetermined temperature is reached.

[0028] By way of example, and as can be seen most clearly in FIG. 5, each discharge orifice 21 formed in the bottom wall 20 of the lower housing 2 is bounded by a substantially frustoconical inner circumferential surface 210 that converges from top to bottom between an upper opening 211 on the side of the internal chamber and a lower opening 212 on the side of the double bottom 23 of the lower housing 2. A thermofusible pellet 24 is incorporated in the discharge orifice 21 so as to conform to the inner circumferential surface 210 of the discharge orifice 21, while a central bore 25 of the pellet provides a passage for a cooling fluid between the upper opening 211 and the lower opening 212 of the discharge orifice 21. Thus, by melting when a predetermined temperature is reached, the thermofusible material of the pellet 24 agglomerates in contact with the inner wall 22 at said opening until it flows into the double bottom 23 and forms a plug that blocks the lower opening 212 of the discharge orifice 21. The discharge orifice 21 on the left side of FIG. 5 is shown in this blocked configuration. Thus, the heat-soluble pellets 24 associated with each discharge orifice 21 make it possible, when a predetermined temperature is reached, to block the fluid passage formed under the module towards the double bottom 23 of the lower housing 2, thereby preventing the discharge of cooling fluid into the double bottom 23 of the lower housing 2.

[0029] The melting of the thermosoluble pellets 24 associated with the discharge orifices 21 placed under the modules 4 of the battery causes the modules to be filled with cooling fluid that continues to spray the cells from above, thus making it possible to at least partially immerse the cells within the module. This configuration is particularly effective in stopping the spread of fire at the onset of a thermal runaway phenomenon inside the cells.

Claims

1. A battery pack (1) for an electric or hybrid motor vehicle, the battery pack (1) being formed by an upper housing (3) and a lower housing (2) that delimit an internal chamber in which at least one battery module (4) comprising a plurality of interconnected electrochemical cells (5) is accommodated, and comprising a cooling circuit that allows the circulation in the battery pack of a cooling fluid intended to be sprayed by a spray nozzle (30) onto the at least one battery module (4), the cooling circuit being configured to ensure the circulation of the cooling fluid in a closed circuit within the battery pack by means of a pump (7) arranged in the internal chamber, capable of recirculating the cooling fluid sprayed onto the at least one battery module and collected in a double bottom (23) provided under the bottom wall of the lower housing (2) to the spray nozzle by means of a discharge orifice (21) formed in the bottom wall (20) of the lower housing, The battery pack (1) further comprises a heat-meltable sealing element (24) disposed inside each release orifice (21), the heat-meltable sealing element (24) melting when a predetermined temperature threshold is reached to seal the release orifice (21).

2. A battery pack as described in claim 1, characterized in that the cooling fluid sprayed onto the at least one battery module is prevented from discharging toward the double bottom of the lower housing, thereby immersing the multiple electrochemical cells of the at least one battery module.

3. 3. The battery pack according to claim 1, characterized in that the spray nozzle (30) is arranged on an inner wall (32) of the upper housing (3), the upper housing having an outer wall (31) spaced from the inner wall to form an internal cavity (33) in the upper housing, and the pump (7) is connected to the spray nozzle by a conduit (8) leading to the internal cavity for injecting the cooling fluid into the internal cavity.

4. 4. The battery pack according to claim 1, wherein a through hole (26) leading to the double bottom (23) of the lower housing is formed in the bottom wall (20) of the lower housing for the passage of the cooling fluid, and the pump (7) has a suction spout (71) engaged through the through hole into the double bottom.

5. 5. The battery pack according to claim 1, wherein the plurality of electrochemical cells are juxtaposed in a receiving space of the at least one battery module with at least one space between two elementary cells of the plurality of electrochemical cells of each battery module to allow passage of the cooling fluid between the plurality of electrochemical cells of the at least one battery module.

6. 6. The battery pack according to claim 5, characterized in that the space is formed by a partition plate (6) extending between the two elementary cells, the two faces of the partition plate being grooved to create fluid-passing channels (63) along the plurality of electrochemical cells.

7. 7. A battery pack according to claim 1, wherein said electrochemical cells are of the lithium-ion type.

8. 8. A motor vehicle equipped with an electric drivetrain, characterized in that it comprises a battery pack according to any one of claims 1 to 7.

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