Battery provided with a cooling device comprising at least one heat pipe

Abstract

The invention relates to an electric battery (10) comprising a plurality of electrochemical cells (11) arranged inside a containment structure (12). The battery (10) is provided with a cooling device comprising at least one heat pipe (1) configured to contain a heat-transfer fluid that is intended to undergo an evaporation and condensation cycle, wherein calories are drawn from an evaporation end (4) of the heat pipe (1) arranged in contact with the cells (11) and delivered to a condensation end (5) of the heat pipe (1) to a cold source (F) located outside the confinement structure (12), the at least one heat pipe (1) being overmoulded onto a base (13) of the confinement structure (12).

Description

[0001] DESCRIPTION

[0002] TITLE: Battery equipped with a cooling device comprising at least one heat pipe

[0003] Technical field

[0004] The present invention relates to a battery comprising a cooling device, in particular in the field of aeronautics. The invention also relates to an aircraft equipped with such a battery.

[0005] Previous techniques

[0006] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those currently in operation, requiring the implementation of technological solutions to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0007] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental impacts with the aim of improving the energy efficiency of aircraft.

[0008] Ongoing research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aeronautical biofuels.

[0009] In the field of electric aircraft propulsion, the storage of electrical energy is carried out by means of batteries.

[0010] The term battery means a set of individual packs each comprising modules made up of power elements commonly called cells and configured in combination in series and / or in parallel in order to achieve the desired electrical voltage and electrical capacity.

[0011] Depending on the technology, batteries may require a cooling system to ensure performance, lifespan and safety.

[0012] In particular, lithium-ion batteries with a high energy density relative to mass require significant monitoring of their operating conditions, such as voltage or temperature, and a cooling system to keep them within a reduced temperature range.

[0013] Beyond a temperature threshold known as "thermal runaway", exothermic internal chemical reactions may begin. When the battery is no longer able to dissipate enough heat, the temperature of the cell increases until it is destroyed, a phenomenon commonly referred to as thermal runaway. In other words, thermal runaway occurs in a battery when the energy released by the exothermic reactions occurring inside it exceeds the capacity to dissipate it externally. This runaway may be followed by the generation of gas and an explosion and / or fire, which risks spreading the reaction to the other electrochemical cells in the battery.

[0014] To contain the thermal runaway phenomenon, aircraft batteries are enclosed in a dedicated containment structure.

[0015] It is therefore necessary to cool the batteries through the containment structure in place. Conventionally, this cooling is achieved by a single-phase cooling fluid circuit installed near the cells and / or by one or more cold plates installed in the containment structure using sealed connectors.

[0016] However, there are several disadvantages to installing a cold zone inside the battery containment structure. Thus, the integration rate, which is the ratio between the total mass of the equipment and the mass of the electrical power elements of the equipment, is reduced. The risk of the battery short-circuiting increases due to the condensation that can occur.

[0017] Furthermore, in the event of thermal runaway, the proximity between the cooling circuit and the battery cells can increase the risk of damage to the cooling system or even aggravate the thermal runaway reaction by an explosive interaction of the cooling fluid (water) with the chemical components (lithium) of the electric cells.

[0018] Statement of the invention

[0019] In view of the above, the invention aims to propose a cooling device which does not have the aforementioned drawbacks.

[0020] The invention relates to an electric battery comprising a plurality of electrochemical cells arranged inside a containment structure.

[0021] Said battery is provided with a cooling device comprising at least one heat pipe configured to contain a heat transfer fluid intended to undergo an evaporation and condensation cycle, taking calories through an evaporation end of said heat pipe arranged in contact with said cells and returning them through a condensation end of said heat pipe to a cold source located outside the confinement structure.

[0022] The integration of the cooling device of the invention, with a condensation end close to a cold source located outside the containment structure, makes it possible to relocate the cooling to an exchange point external to the containment structure, which makes the cooling independent in the event of thermal runaway of the battery without hindering the interface with the external circuit.

[0023] Advantageously, said at least one heat pipe is integrated by overmolding into a base of said confinement structure.

[0024] According to one characteristic, said at least one heat pipe comprises a capillary network arranged on the internal surface of said heat pipe, said network extending along an envelope of said heat pipe and surrounding an empty axial volume.

[0025] Advantageously, said at least one heat pipe comprises at least one zone of lower thermal resistance arranged at the evaporation end and made of a material capable of melting when the temperature inside the heat pipe exceeds a predefined threshold temperature and lower than the melting temperature of the heat pipe, so as to allow air to penetrate into the heat pipe.

[0026] For example, the material of the said zone of lower thermal resistance is a polyetheretherketone type polymer.

[0027] According to another characteristic, said containment structure is made of ceramic matrix composite material.

[0028] According to another aspect, the invention relates to a battery system comprising several batteries as described above, and comprising at least one cold source intended to simultaneously receive the calories taken from said batteries.

[0029] Advantageously, said cooling system comprises means for emergency stopping of the heat exchange between the cold source and the condensation ends of the heat pipes of the batteries, capable of urgently stopping said heat exchange in the event of thermal runaway of the batteries.

[0030] For example, said emergency stop means comprise spacing means capable of spacing the cold source F away from the condensation ends of the heat pipes in the event of thermal runaway of the batteries. According to another aspect, the invention relates to an aircraft comprising at least one battery as described above and / or at least one battery system as described above.

[0031] Brief description of the drawings

[0032] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0033] [Fig 1] is a sectional view of a heat pipe according to the invention;

[0034] [Fig 2] is a sectional view of a battery according to the invention; and [Fig 3] is a schematic plan view of a battery system according to the invention.

[0035] Detailed description of at least one embodiment

[0036] Figure 1 is a sectional view of a heat pipe 1 according to the invention. The heat pipe 1 comprises a sealed and thermally conductive casing 2. In the illustrated embodiment, the casing 2 has a flat shape and extends along a plane 3 of symmetry. The casing 2 comprises an evaporation end 4 which is placed in contact with a hot source, such as the electrochemical cells of a battery, to draw calories from this hot source. The other condensation end 5 is placed in contact with a cold source, to deliver the calories to this cold source. Between the two ends 4, 5 there is an adiabatic zone 6 in which the heat transfer between the heat pipe 1 and its environment is negligible compared to the heat exchanges taking place at the ends 4, 5. The length of the adiabatic zone 6 varies according to the applications by adapting to the locations of the hot and cold sources.

[0037] The heat pipe 1 comprises, for example, at least one steam chamber, designed to contain water in liquid and / or gaseous form. Since steam chambers are good thermal conductors, this configuration makes it possible to achieve good thermal cooling performance.

[0038] The heat pipe 1 comprises a capillary network 7 arranged on the internal lateral surface of the heat pipe 1 and which extends along the casing 2. The capillary network 7 allows the circulation by capillarity of a heat transfer fluid, from the condensation end 5 to the evaporation end 4. An axial volume 8 extending over the entire length of the heat pipe 1 is left free to allow the circulation in the other direction of the gas produced by the evaporation of this fluid in contact with the hot source.

[0039] The heat transfer fluid has an evaporation temperature which, taking into account the internal pressure in the heat pipe 1, is included in the operating temperature range of the hot source. The heat transfer fluid can be pure or made up of a binary mixture, it is chosen to have very good wettability of the capillary network 7.

[0040] Examples of heat transfer fluids available for cooling electrochemical battery cells are water, ammonia, acetone or ethanol. Preferably, during the manufacture of the heat pipe, the heat transfer fluid is introduced under vacuum into the heat pipe shell, in order to ensure improved heat transfer quality and reliability of the heat pipe compared to simpler techniques of expelling air from the shell after the introduction of the fluid.

[0041] The operating principle of the heat pipe 1 is as follows. In contact with the heat source, the calories are transmitted to one end 4 of the conductive envelope 2 containing the heat transfer fluid in the liquid state contained in the capillary network 7. This fluid evaporates, absorbing a latent heat of evaporation which cools this heat source.

[0042] The pressure of the vapors of the heat transfer fluid then conducts these gases through the empty axial volume 8, towards the other end 5 of the heat pipe 1 inserted in the cold source. In contact with the cold source, the vapors condense, releasing a latent heat of condensation which heats the cold source, and creates a drop in pressure which allows, with the increase in evaporation pressure, to circulate the gases.

[0043] The condensed heat transfer fluid is then conducted by capillarity in the capillary network 7 towards the hot source, which renews this fluid ready to undergo a new cycle.

[0044] The casing 2 of the heat pipe 1 has sufficient mechanical strength to withstand the internal pressure, as well as stability to prevent corrosion by the liquid or gas contained. Copper or aluminum can be used, in particular, which also have good thermal conductivity.

[0045] This produces a very efficient passive thermal conduction system, which conducts a much greater quantity of heat for a given volume than that transported by direct conduction with material remaining in the same phase.

[0046] The casing 2 of the heat pipe 1 comprises at least one zone 9 of lower thermal resistance arranged in the evaporation end 4 and made of a material capable of melting when the temperature inside the heat pipe 1 exceeds a predefined threshold temperature and lower than the melting temperature of the heat pipe 1. The threshold temperature is chosen so as to be representative of thermal runaway, while remaining lower than the melting temperature of the heat pipe 1. When the temperature inside the heat pipe 1 increases significantly compared to nominal operation, the material of the zone 9 of lower thermal resistance melts, causing the penetration of air into the casing 2 of the heat pipe. The penetration of air inside the casing 2 hinders the transfer of heat to the heat pipe because of the insulating properties of air.In this way, the heat exchange between the heat pipe 1 and the cold source F is drastically reduced in the event of thermal runaway of the battery 10.

[0047] Figure 2 is a partial sectional view of a battery 10 according to the invention.

[0048] The battery 10 comprises a succession of electrochemical cells 11 connected in series and / or in parallel and arranged inside a containment structure 12. The structure 12 of rectangular parallelepiped shape called “casing” in English, comprises a base 13, four vertical walls 14 and a cover 15, which are capable of containing any thermal runaway of the cells 11.

[0049] The battery 10 comprises a cooling device comprising at least one heat pipe 1. In the illustrated embodiment, a heat pipe 1 is arranged between the base 13 and the cells 11 while being fixed to the base 13. Preferably, the base 13 is overmolded onto the heat pipe 1 so as to fix the heat pipe 1 to the base 13. One face of the evaporation end 4 of the heat pipe is left free so as to be in contact with the cells 11. To guarantee the perfect fixing of the heat pipe 1 on the base 13, it is possible to provide in addition a mechanical assembly with inserts for example and / or gluing.

[0050] The cells 11 are in contact with the evaporation end 4 of the heat pipe 1 and represent a hot source C intended to be cooled by the heat pipe 1.

[0051] The calories extracted from the hot source are transmitted to a cold source F located outside the structure 12. The cold source F is preferably in contact with the condensation end 5 of the heat pipe 1. Alternatively, the cold source F could be only close to the condensation end 5, without being in contact with it. The cold source F is adapted according to the applications and can in particular take the form of a radiator or a cold plate.

[0052] The structure 12 is provided with a slot 16 formed on a vertical wall 14 and crossed by the heat pipe 1 in a sealed manner. The sealing is ensured by the overmolding of the base 13 and in particular by sealing gaskets 17 arranged around the slot 16 and the heat pipe 1.

[0053] In normal operation, the heat pipe 1 cools the battery 10 by evaporation-condensation cycles of the heat transfer fluid as described previously.

[0054] In the event of thermal runaway, the evaporation-condensation cycle is interrupted by the penetration of air inside the heat pipe 1, following the melting of the weak zone 9.

[0055] Figure 3 is a schematic plan view of a system 18 of batteries 10 comprising at least one cold source F intended to simultaneously receive the calories taken from several batteries 10. The cold source F may in particular comprise a heat exchanger making it possible to evacuate said calories to the outside of the system. The system 18 is configured to circulate a fluid, for example a cooling liquid to cool the cold source F.

[0056] The system 18 further comprises emergency stopping means 19 of the heat exchange between the cold source F and the condensation ends of the heat pipes of the batteries 10. The means 19 are capable of stopping said heat exchange in an emergency in the event of thermal runaway of the batteries 10. The stopping of a heat exchange corresponds to a drop in the heat exchange of at least one order of magnitude compared to the nominal heat exchange.

[0057] Said emergency stop means 19 may in particular comprise spacing means capable of spacing the cold source away from the condensation ends of the heat pipes. These spacing means may for example comprise mechanical levers or elastic elements coupled to holding systems which oppose the force of the elastic elements.

[0058] Said emergency stop means 19 can be controlled or can be triggered automatically in the event of thermal runaway of the batteries 10.

Claims

CLAIMS 1. Electric battery (10) comprising a plurality of electrochemical cells (11) arranged inside a containment structure (12), characterized in that said battery (10) is provided with a cooling device comprising at least one heat pipe (1) configured to contain a heat transfer fluid intended to undergo an evaporation and condensation cycle, taking calories through an evaporation end (4) of said heat pipe (1) arranged in contact with said cells (11) and returning them through a condensation end (5) of said heat pipe (1) to a cold source (F) located outside the containment structure (12), said at least one heat pipe (1) being integrated by overmolding to a base (13) of said containment structure (12).

2. Battery according to claim 1, wherein said at least one heat pipe (1) comprises a capillary network (7) arranged on an internal surface of said heat pipe (1), said network (7) extending along a casing (2) of said heat pipe (1) and surrounding an empty axial volume (8).

3. Battery according to claim 1 or 2, wherein said at least one heat pipe (1) comprises at least one zone (9) of lower thermal resistance arranged at the evaporation end (4) and made of a material capable of melting when the temperature inside the heat pipe exceeds a predefined threshold temperature and lower than the melting temperature of the heat pipe (1), so as to allow the penetration of air into the heat pipe (1).

4. Battery according to claim 3, in which the material of said zone (9) of lower thermal resistance is a polymer of the polyetheretherketone type.

5. Battery according to any one of claims 1 to 4, in which said confinement structure (12) is made of ceramic matrix composite material.

6. Battery system (18) comprising several batteries (10) according to any one of claims 1 to 5, and comprising at least a cold source (F) intended to simultaneously receive the calories taken from said batteries (10).

7. System according to claim 6, comprising means (19) for emergency stopping of the heat exchange between the cold source (F) and the condensation ends (5) of the heat pipes of the batteries (10), capable of urgently stopping said heat exchange in the event of thermal runaway of the batteries (10).

8. System according to claim 7, wherein said emergency stop means (19) comprise spacing means capable of spacing the cold source F from the condensation ends (5) of the heat pipes (1) in the event of thermal runaway of the batteries (10).

9. Aircraft comprising at least one battery (10) according to any one of claims 1 to 5 and / or at least one battery system (18) according to any one of claims 6 to 8.

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