ELECTRICAL STORAGE DEVICE COMPRISING A COOLING PLATE EQUIPPED WITH A HEAT PIPE

Abstract

The present invention relates to an electrical storage device (1) comprising two adjacent electrochemical electrical storage cells (3), a cooling plate (5) for the two electrochemical cells (3), a cooling circuit (6) for the electrochemical cells by a dielectric liquid (7), the electrochemical cells (3) and the cooling plate (5) being partially immersed in this dielectric liquid (7), characterized in that the cooling plate (5) comprises a heat pipe (9) comprising a working fluid, a so-called condenser part (9a) arranged in the immersed part of the electrochemical cells (3) and a so-called evaporator part (9b) arranged in the emerged part of the electrochemical cells (3). Figure 1

Description

Title of the invention: ELECTRICAL STORAGE DEVICE COMPRISING A COOLING PLATE EQUIPPED WITH A HEAT PIPE

[0001] The present invention relates to the cooling of the cells of an electrical storage device. More particularly, the subject of the invention is an electrical storage device comprising a cooling plate equipped with a heat pipe.

[0002] Vehicles, whether fully electric or combining the use of a thermal engine and an electric motor, are equipped with electrical storage devices, generally comprising several electrical modules. These electrical modules comprise a plurality of electrical cells connected to each other.

[0003] These electrical modules do not tolerate operation well outside a specific temperature range. Therefore, it is necessary to maintain them within a specific temperature range. For example, lithium-ion batteries operate optimally between 0°C and 50°C. Effective thermal management is necessary to ensure that the cells are maintained within this temperature range regardless of atmospheric and operating conditions.

[0004] The most critical use case, the one that sizes the cooling capacity, is encountered during thermal runaway events or ultra-fast charging. This fast charging involves heating of the electrical storage device requiring a greater need for cooling.

[0005] Document JP5994345B2 also discloses a device for controlling the temperature of a battery with a hollow separation plate arranged between two electric cells, this plate comprising a cooling circuit in the hollow volume. However, this solution is complex and expensive to implement.

[0006] For cooling batteries, it is known, for example, from document FR3085547, to completely immerse the electric cells in a non-conductive fluid, otherwise known as a dielectric fluid. However, total immersion of the electric cells requires a significant quantity of dielectric fluid, which penalizes the weight of the system and its cost.

[0007] Document FR3125635 also discloses a storage device with partially submerged electrochemical cells comprising a separation section with a dielectric liquid supply pipe opening at the level of the emerged part of the electrochemical cells. However, such a solution may prove insufficient for cooling the emerged part of the electrochemical cells.

[0008] The invention aims to resolve the drawbacks of the prior art by proposing a system for improving battery cooling. To achieve this objective, the invention provides an electrical storage device comprising: - two adjacent electrochemical electrical storage cells, - a cooling plate for the two electrochemical cells (3), - a circuit for cooling the electrochemical cells using a dielectric liquid, -the electrochemical cells and the cooling plate being partially immersed in this dielectric liquid, characterized in that the cooling plate comprises a heat pipe comprising a working fluid, a part called a condenser arranged in the submerged part of the electrochemical cells and a part called an evaporator arranged in the emerged part of the electrochemical cells.

[0009] The technical effect is to enable efficient management of the cooling of electrochemical cells, with a compact arrangement.

[0010] Various additional features may be provided, alone or in combination:

[0011] In one embodiment, the heat pipe is an oscillating type heat pipe or a capillary heat pipe.

[0012] In one embodiment, the electrochemical cells are electrically connected to each other by means of electrical connectors, the cooling plate comprising an additional part in which the heat pipe extends, this additional part covering a part of the electrochemical cell where the electrical connection is placed.

[0013] In one embodiment, the cooling plate comprises a first exhaust device arranged to release a portion of the working fluid from the heat pipe when this working fluid reaches a first predetermined threshold temperature or a first predetermined threshold pressure.

[0014] In one embodiment, the first exhaust device is formed by a thermal fuse or a pressure relief valve.

[0015] In one embodiment, the heat pipe comprises a first working fluid filling port, this first filling port being provided with the first exhaust device.

[0016] In one embodiment, the cooling plate comprises a reserve of an inert gas and a second exhaust device arranged to release a portion of the inert gas when this inert gas reaches a second predetermined threshold temperature or a second predetermined threshold pressure.

[0017] In one embodiment, the second exhaust device is formed by a thermal fuse or a pressure relief valve.

[0018] In one embodiment, the cooling plate comprises a second port for filling the reserve of an inert gas, said second filling port being provided with the second exhaust device.

[0019] In one embodiment, the cooling plate is sandwiched between the two electrochemical cells.

[0020] Other features and advantages will appear on reading the following description of a particular, non-limiting embodiment of the invention, given with reference to the figures in which:

[0021] [Fig-1]: this figure schematically illustrates a device of electrical storage according to the invention.

[0022] [Fig.2]: this figure schematically represents an example of a re plate cooling in accordance with the invention.

[0023] [Fig.3]: this figure schematically represents an example of manufacturing of a cooling plate as illustrated in [Fig.2].

[0024] [Fig.4]: this figure schematically represents a detail of another example embodiment of an electrical storage device according to the invention.

[0025] [Fig.l] schematically illustrates an electrical storage device 1. This electrical storage device 1 can equip a motor vehicle comprising an electric motor for its traction.

[0026] In the remainder of this description, the term electrical storage device 1 will be understood to mean an assembly comprising at least one battery module 2, each battery module 2 containing electrochemical cells 3, six in the example illustrated.

[0027] When there are several modules, they are grouped in a tray or casing 4 and then form a battery block, this battery block often being designated by the English expression “battery pack”.

[0028] Furthermore, the term electrochemical cell 3 will be understood to mean an electrical energy storage cell. This electrochemical cell 3 is arranged to generate current by chemical reaction, for example of the lithium-ion (or Li-ion) type, of the Ni-Mh, or Ni-Cd or even lead type.

[0029] The electrochemical cells 3 are electrically connected to each other by means of electrical connectors 3a.

[0030] The electrical storage device 1 comprises several cooling plates 5. The cooling plates 5 have the function of cooling the electrochemical cells 3 in order to prevent thermal runaway of the electrical storage device 1. Preferably, each cooling plate 5 is sandwiched between two adjacent electrochemical cells 3, in other words the two adjacent electrochemical cells 3 are in thermal contact with a cooling plate 5. This makes it possible to keep the electrochemical cells 3 under constraints in order to prevent their swelling and homogenize the temperature in the electrochemical cells 3. This sandwich configuration is particularly suitable for so-called rectangular prismatic electrochemical cells or flat and flexible pocket-shaped electrochemical cells (also called "pouch" in English), the cooling plate being inserted between two cells.

[0031] The electrical storage device 1 further comprises a cooling circuit 6 for the electrochemical cells 3 of the battery modules 2 by a dielectric cooling liquid 7, i.e. a liquid which is not electrically conductive. Such a liquid is already used as an electrical insulator in high voltage applications, for example, transformers, capacitors.

[0032] The cooling circuit 6 comprises a pump 6a for circulating the dielectric liquid 7 connected for example by means of a pipe to an inlet 4a of dielectric liquid in the battery casing 4.

[0033] The casing 4 also comprises an outlet 4b for dielectric liquid 7 connected, for example, by means of a pipe to a dielectric liquid inlet 7 of a heat exchanger 6b. The heat exchanger 4b comprises a dielectric liquid outlet 7 connected, for example, by means of a pipe to the circulation pump 6a.

[0034] The pump 6a is advantageously of variable flow or pressure controllable according to the cooling requirements. For this purpose, the device comprises means 8 for controlling the pump 6a.

[0035] Each cooling plate 5 comprises a heat pipe 9. The heat pipe is a device that uses a liquid in equilibrium with its vapor phase, which we will also refer to as the working fluid, for heat transfer. These two-phase heat pipe systems have the particularity of dissipating heat from a hot source to a cold source by evaporation and circulation of the working fluid in a closed circuit moved without external mechanical energy.

[0036] The electrochemical cells 3 as well as the cooling plate 5 and its heat pipe 9 are partially immersed in the dielectric liquid 7. The heat pipe 9 is arranged in the cooling plate 5 so as to present its part called condenser 9a in the immersed part of the cooling plate 5 and the electrochemical cells 3 and its part called evaporator 9b in the emerged part of the cooling plate 5 and the electrochemical cells 3. The cold source of the heat pipe 9 is provided by the dielectric fluid which plays the role of partially cooling the cell and also the condensation zone of the heat pipe 9.

[0037] In an advantageous embodiment, the heat pipe 9 may be an oscillating heat pipe (also called a Pulsating Heat Pipe, PHP in English). This type of heat pipe has the particularity of being in the form of a coil of capillary dimension. This The latter is partially filled with fluid, which is divided into vapor pockets and liquid slugs. The pressure difference between two vapor pockets provides the driving force for fluid movement. The thickness of a cooling plate with heat pipe allows for a reduced thickness lower than the thicknesses of standard thermal insulators (e.g., Aerogel insulation) used between electrochemical cells.

[0038] The heat pipe 9 can also be a capillary heat pipe. Indeed, with a suitable capillary network, the heat pipe 9 can operate outside of gravity and in particular with the evaporator part 9b above the condenser part 9a, the circulation of the working fluid being based on the action of capillary forces.

[0039] [Fig.2] illustrates in front view an example of a cooling plate 5 with an oscillating type heat pipe 9 having a capillary coil 9c. The cooling plate 5 comprises, at its upper part, a first filling port 9d of the heat pipe 9. The upper part is understood to mean the part intended to be in the emerged part of the cooling plate and the electrochemical cells.

[0040] The cooling plate 5 comprises, at its upper part, a first exhaust device 9e arranged to release a portion of the working fluid from the heat pipe 9 when this working fluid reaches a first predetermined threshold temperature or a first predetermined threshold pressure.

[0041] As soon as the cooling plate 5 is positioned between two electrochemical cells 3, the first exhaust device 9d opens at a peripheral edge of the two electrochemical cells 3, formed in this example by the upper edge of the two electrochemical cells 3.

[0042] Such a first exhaust device 9d may be formed by a thermal fuse comprising a wax which reacts as a function of the temperature to allow the two-phase cooling fluid to pass. In a non-limiting exemplary embodiment, the first temperature threshold is between 110°C and 150°C, typically 130°C.

[0043] When the working fluid escapes from the heat pipe 9, this fluid vaporizes on the adjacent electrochemical cell 3 so as to promote its cooling.

[0044] In this non-limiting exemplary embodiment, the first exhaust device 9e is integrated into the first filling port 9d. It is understood that, in a different embodiment, the first filling port 9d and the first exhaust device 9d may be separated from each other.

[0045] In this embodiment illustrated in [Fig.2], the cooling plate 5 also comprises a reserve of an inert gas 10. In a non-limiting manner, the inert gas contained may be carbon dioxide or nitrogen.

[0046] The cooling plate 5 further comprises, at its upper part, a second filling port 10a for the inert gas reserve 10. In addition, the plate cooling device 5 comprises, at its upper part, a second exhaust device 10b arranged to release a portion of the inert gas when this inert gas reaches a second predetermined threshold temperature or a second predetermined threshold pressure.

[0047] As soon as the cooling plate 5 is positioned between two electrochemical cells 3, the second exhaust device 10b opens at a peripheral edge of the two electrochemical cells 3, formed in this example by the upper edge of the two electrochemical cells 3.

[0048] Such a second exhaust device 10b may be formed by a thermal fuse comprising a wax which reacts as a function of the temperature to allow the two-phase cooling fluid to pass. In a non-limiting exemplary embodiment, the second temperature threshold is between 110°C and 150°C, typically 130°C.

[0049] When the inert gas escapes from its reserve 10, it is vaporized onto the adjacent electrochemical cell 3 so as to prevent thermal runaway of this electrochemical cell 3 and the propagation of the thermal runaway to the other electrochemical cells.

[0050] In this non-limiting exemplary embodiment, the second exhaust device 10b is integrated into the second filling port 10a. It is understood that, in a different embodiment, the second filling port 10a and the second exhaust device 10b may be separated from each other.

[0051] Thus, in the heat pipe 9, a first filling port 9d is closed by a first thermal fuse 9e which allows the working fluid to escape during thermal runaway of the electrical storage device 1. This particular escape makes it possible to secure the electrical storage device 1 by lowering the temperature of the electrochemical cells 3.

[0052] Thus, these cooling plates 5 with heat pipe 9 interposed between the electrochemical cells 3 allow better management of the thermal performance of the electrical storage device 1 by efficiently extracting the heat from the electrochemical cells 3 in normal operation and in the event of a thermal runaway.

[0053] It should also be noted that the cooling plates 5 are placed on a cooling support 12. In a non-limiting exemplary embodiment, this cooling support 12 can be formed by the bottom of the electrical storage device 1 and be crossed by a conduit 13 allowing the passage of the dielectric fluid 7 ([Fig.l])•

[0054] Furthermore, in order to compensate for any possible swelling of the electrochemical cells 3 occurring during the charging and discharging thereof, each cooling plate The cooling plates 5 have a thickness of between 1.8 mm and 3.2 mm, typically 2 mm. The cooling plates 5 also provide compressive prestressing for all of the electrochemical cells 3. The cooling plates 5 can be made of a metallic or plastic material.

[0055] As illustrated in [Fig.3], in the case of a metallic material, the coil 9c of the heat pipe 9 may be machined in a first wall 5a and a second wall 5b may be welded to the first wall 5a. In this case, the second wall 5b forms a part of the wall of the coil 9c.

[0056] It should be noted that the first exhaust device 9e and the second exhaust device 10b are formed by a thermal fuse. In a different embodiment, the first exhaust device 9e and the second exhaust device 10b are formed by a pressure relief valve which reacts according to an overpressure to allow the working fluid or the inert gas to pass.

[0057] In a still different embodiment, the first exhaust device 9e is formed by a thermal fuse and the second exhaust device 110b is formed by a pressure relief valve or vice versa.

[0058] [Fig.4] shows a detail of another exemplary embodiment. This exemplary embodiment differs from the previous exemplary embodiments in that the cooling plate 5 has an additional part 5c in which the heat pipe 9 extends and which covers the electrochemical cell 3 where the electrical connection 3a is placed. In this arrangement, the heat pipe 9 is close to the electrical connection 3a, which makes it possible to cool this part of the electrochemical cell 3 which is stressed in particular during the charging and discharging phases. This embodiment improves the management of the cooling of the upper part of the electrochemical cell 3 and its electrical connection 3a.

[0059] As for the previous embodiment, this cooling plate 5 is provided with the first fuse 9e to release the working fluid from the heat pipe 9 and the second fuse (not visible in [Fig.4]) to release an inert gas stored in a reserve (not visible in [Fig.4]) within the cooling plate 5 supporting the heat pipe in order to avoid combustion.

[0060] The invention has the advantage of allowing efficient cooling of the electrochemical cells via the cooling plates equipped with heat pipes with very good temperature distribution in the battery. The presence of the cooling plate between the cells makes it possible to compress them and protect them against swelling and thus extend the life of the cells. The invention also allows protection against thermal runaway and its propagation thanks to the cooling plates containing the heat pipes and an inert gas. In addition to thermal management, safety is thus improved.

[0061] With partial immersion cooling, the quantity of dielectric fluid is reduced compared to total immersion of the cells. The first consequence is a reduction in costs related to the fluid but above all a reduction in the energy consumption of the pump. In fact, the fluid only circulates in the lower part (cold source), thus drastically reducing pressure losses and providing uniform cooling during all battery life situations and all climates to ensure battery durability.

Claims

Claims

1. Electrical storage device (1) comprising: - two adjacent electrochemical cells (3) for electrical storage, - a cooling plate (5) for the two electrochemical cells (3), - a cooling circuit (6) for the electrochemical cells using a dielectric liquid (7), - the electrochemical cells (3) and the cooling plate (5) being partially immersed in this dielectric liquid (7), characterized in that the cooling plate (5) comprises a heat pipe (9) comprising a working fluid, a part called a condenser (9a) arranged in the immersed part of the electrochemical cells (3) and a part called an evaporator (9b) arranged in the emerged part of the electrochemical cells (3).

2. Device according to claim 1, characterized in that the heat pipe (9) is an oscillating type heat pipe or a capillary heat pipe.

3. Device according to claim 1 or claim 2, characterized in that the electrochemical cells (3) are electrically connected to each other by means of electrical connectors (3a), the cooling plate (5) comprising an additional part (5c) in which the heat pipe (9) extends, this additional part (5c) covering a part of the electrochemical cell (3) where the electrical connection (3a) is placed.

4. Device according to claim 1 or claim 2, characterized in that the cooling plate (5) comprises a first exhaust device (9e) arranged to release a portion of the working fluid from the heat pipe (9) when this working fluid reaches a first predetermined threshold temperature or a first predetermined threshold pressure.

5. Device according to the preceding claim, characterized in that the first exhaust device (9e) is formed by a thermal fuse or a pressure relief valve.

6. Device according to claim 4 or 5, characterized in that the heat pipe (9) comprises a first filling port (9d) for working fluid, this first filling port (9d) being provided with the first exhaust device (9e).

7. Device according to any one of the preceding claims, ca-

8.

9.

10. characterized in that the cooling plate (5) comprises a reserve (10) of an inert gas and a second exhaust device (10b) arranged to release a portion of the inert gas when this inert gas reaches a second predetermined threshold temperature or a second predetermined threshold pressure. Device according to the preceding claim, characterized in that the second exhaust device (10b) is formed by a thermal fuse or a pressure relief valve. Device according to claim 7 or 8, characterized in that the cooling plate (5) comprises a second filling port (10a) for the reserve (10) of an inert gas, said second filling port (10a) being provided with the second exhaust device (10b). Device according to any one of the preceding claims, characterized in that the cooling plate (5) is sandwiched between the two electrochemical cells (3).

Images