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 cells (3), 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) including a working fluid, a condenser portion (9a) disposed in the immersed portion of the electrochemical cells (3), and an evaporator portion (9b) disposed in the emerged portion 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 cells in an electrical storage device. More particularly, the invention relates to an electrical storage device comprising a cooling plate equipped with a heat pipe.

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

[0003] These electrical modules do not tolerate operation well outside a specific temperature range. Therefore, they must be maintained within a given 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 remain within this temperature range regardless of atmospheric and operating conditions.

[0004] The most critical use case, the one that determines the cooling capacity, is encountered during thermal runaway events or ultra-fast charging. This rapid charging causes the electrical storage device to heat up, requiring greater cooling capacity.

[0005] A device for controlling the temperature of a battery with a hollow separating plate arranged between two electrical cells is also known from document JP5994345B2. This plate includes a cooling circuit within its hollow volume. However, this solution is complex and expensive to implement.

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

[0007] A storage device with partially immersed electrochemical cells, comprising a separation layer with a dielectric liquid supply line opening at the level of the exposed portion of the electrochemical cells, is also known from document FR3125635. However, such a solution may prove insufficient to cool the exposed portion of the electrochemical cells.

[0008] The invention aims to overcome the drawbacks of the prior art by proposing a system to improve 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 cooling circuit for 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 includes a heat pipe comprising a working fluid, a condenser part disposed in the immersed part of the electrochemical cells and an evaporator part disposed in the emerged part of the electrochemical cells.

[0009] The technical effect is to allow efficient management of the cooling of the 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 having 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 includes a first exhaust device arranged to release a portion of the working fluid out of 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 escape device is formed by a thermal fuse or a pressure relief valve.

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

[0016] In one embodiment, the cooling plate includes a reservoir 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 escape device is formed by a thermal fuse or a pressure relief valve.

[0018] In one embodiment, the cooling plate includes a second port for filling the reservoir with an inert gas, said second filling port being equipped 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 become apparent from the following description of a particular, non-limiting embodiment of the invention, made 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 plate of cooling according to 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 implementation of an electrical storage device according to the invention.

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

[0026] In the remainder of this description, the 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 illustrated example.

[0027] When there are several modules, they are grouped together in a container or housing 4 and then form a battery pack, this battery pack often being referred to by the English expression "battery pack".

[0028] Furthermore, the term electrochemical cell 3 shall 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), Ni-Mh, Ni-Cd or 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 serve to cool the electrochemical cells 3 in order to prevent thermal runaway of the electrical storage device 1. Preferably, each cooling plate 5 is made of sandwich 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 allows the electrochemical cells 3 to be kept under stress in order to prevent their swelling and to 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 referred to as "pouch" in English), the cooling plate being interposed between two cells.

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

[0032] The cooling circuit 6 includes a dielectric fluid circulation pump 6a 7 connected for example by means of a pipe to a dielectric fluid inlet 4a in the battery casing 4.

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

[0034] The pump 6a is advantageously controllable with variable flow or pressure, depending on the cooling requirements. To this end, the device includes means 8 for controlling the pump 6a.

[0035] Each cooling plate 5 includes 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 driven 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 that its condenser part 9a is in the immersed part of the cooling plate 5 and the electrochemical cells 3, and its evaporator part 9b is 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 can be an oscillating type heat pipe (also known as a Pulsating Heat Pipe, PHP). This type of heat pipe is characterized by its capillary-like coil shape. This coil is partially filled with the fluid, which divides into vapor pockets and liquid plugs. The pressure difference between two vapor pockets provides the driving force for fluid movement. The reduced thickness of a cooling plate with a heat pipe allows for a thickness lower than that 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 without 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] Figure 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 has, at its upper part, a first filling port 9d for the heat pipe 9. The upper part is understood to be the part intended to be in the emerged portion of the cooling plate and the electrochemical cells.

[0040] The cooling plate 5 has, at its upper part, a first exhaust device 9e arranged to release a part of the working fluid out of 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 the level of 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 escape device 9d can be formed by a thermal fuse comprising a wax that reacts according to temperature to allow the two-phase coolant to pass through. In a non-limiting 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 embodiment, the first escapement 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 escapement device 9d may be separate from each other.

[0045] In this embodiment illustrated in [Fig.2], the cooling plate 5 also includes a reservoir of an inert gas 10. By way of non-limitation, the inert gas contained may be carbon dioxide or nitrogen.

[0046] The cooling plate 5 further includes, at its upper part, a second filling port 10a for the inert gas reserve 10. In addition, the cooling plate 5 includes, 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] When 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 escape device 10b can be formed by a thermal fuse comprising a wax that reacts according to temperature to allow the two-phase coolant to pass through. In a non-limiting embodiment, the second temperature threshold is between 110°C and 150°C, typically 130°C.

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

[0050] In this non-limiting embodiment, the second escapement 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 escapement device 10b may be separate 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 a 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 thermal management of the electrical storage device 1 by efficiently extracting heat from the electrochemical cells 3 in normal operation and in malfunction during 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 embodiment, this support cooling 12 can be formed by the bottom of the electrical storage device 1 and be traversed by a conduit 13 allowing the passage of the dielectric fluid 7 ([Fig.l]).

[0054] Furthermore, in order to compensate for any potential swelling of the electrochemical cells 3 occurring during their charging and discharging, each cooling plate 5 has a thickness between 1.8 mm and 3.2 mm, typically 2 mm. The cooling plates 5 also provide compressive prestressing for all 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 can be machined into a first wall 5a and a second wall 5b can be welded to the first wall 5a. In this case, the second wall 5b forms 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 that reacts to an overpressure to allow the working fluid or inert gas to pass through.

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

[0058] Figure 4 shows a detail of another embodiment. This embodiment differs from the previous embodiments in that the cooling plate 5 has an additional portion 5c through which the heat pipe 9 extends and which covers the electrochemical cell 3 where the electrical connection 3a is located. In this arrangement, the heat pipe 9 is close to the electrical connection 3a, which allows for the cooling of this part of the electrochemical cell 3, which is subjected to stress, particularly during the charging and discharging phases. This embodiment improves the cooling management of the upper part of the electrochemical cell 3 and its electrical connection 3a.

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

[0060] The invention has the advantage of enabling efficient cooling of electrochemical cells via cooling plates equipped with a heat pipe with a Excellent temperature distribution within the battery. The presence of the cooling plate between the cells compresses them, protecting them from swelling and thus extending their lifespan. The invention also provides 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 thereby improved.

[0061] With partial immersion cooling, the amount of dielectric fluid is reduced compared to total cell immersion. The first consequence is a reduction in fluid-related costs, but above all, a reduction in the pump's energy consumption. Indeed, the fluid circulates only in the lower part (cold source), thus drastically reducing pressure losses and providing homogeneous cooling throughout the battery's lifespan and in all climates, ensuring battery longevity.

Claims

Demands

1. 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 comprising 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 condenser portion (9a) disposed in the immersed portion of the electrochemical cells (3) and an evaporator portion (9b) disposed in the emerged portion of the electrochemical cells (3),the cooling plate (5) comprising a first exhaust device (9e) arranged to release a portion of the working fluid out of the heat pipe (9) when this working fluid reaches a first predetermined threshold temperature or a first predetermined threshold pressure.

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 located.

4. Device according to any one of the preceding claims, characterized in that the first escape device (9e) is formed by a thermal fuse or a pressure relief valve.

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

6. Device according to any one of the preceding claims, characterized in that the cooling plate (5) has a reservoir (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.

7. Device according to the preceding claim, characterized in that the second escape device (10b) is formed by a thermal fuse or a pressure relief valve.

8. Device according to claim 6 or 7, characterized in that the cooling plate (5) has a second filling port (10a) for the reservoir (10) of an inert gas, said second filling port (10a) being provided with the second exhaust device (10b).

9. 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