EP3235022A1

EP3235022A1 - Lithium accumulator with a two-layered thermally insulating package and with a heat pipe for thermal management

Info

Publication number: EP3235022A1
Application number: EP15810636.9A
Authority: EP
Inventors: Fabien PERDU; Lionel Picard
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2014-12-16
Filing date: 2015-12-16
Publication date: 2017-10-25
Also published as: US20170352935A1; FR3030121A1; FR3030121B1; WO2016096974A1

Abstract

Lithium electrochemical accumulator including at least one first package housing at least one electrochemical cell, said first package including at least: one internal thermally insulating layer suitable for confining, to the interior of a first package, the heat given off even in case of abnormal operation of a cell C and for protecting the cell(s) from heat generated outside the first package; one external layer superposed on the internal layer, the external layer being mechanically strong and fire resistant; and one cooling device including at least one heat pipe the enclosure of which passes through the first package(s) in a seal-tight manner and such that the heated zone of the heat pipe(s) is located inside the first package(s) and that the cooled zone of the heat pipe(s) is located outside the first package(s).

Description

LITHIUM ACCUMULATOR WITH INSULATING PACKAGING

THERMALLY TWO LAYERS AND WITH HEAT PUMP FOR

THERMAL MANAGEMENT

Technical area

The present invention relates to the field of lithium electrochemical generators, which operate according to the principle of insertion or deinsertion, or in other words intercalation-deintercalation, of lithium in at least one electrode.

The invention particularly relates to a lithium electrochemical accumulator, in particular lithium-ion battery whose packaging is mechanically resistant and fireproof and thermally insulating, and whose thermal management is provided by a heat pipe, both in normal operation and in case of abnormal operation of the cell (s) electrochemical (s) of the accumulator.

Prior art

A lithium battery or accumulator usually comprises one or more electrochemical cells each consisting of an electrolyte constituent between a positive electrode or cathode and a negative or anode electrode, a current collector connected to the cathode, a current collector connected to a the anode and finally a package arranged to contain the electrochemical cell (s) with sealing while being traversed by a portion of the current collectors.

The primary function of a package is to separate the inside of the battery from the outside. The electrolyte of an electrochemical cell must never come into contact with traces of moisture, at the risk of producing hydrofluoric acid and greatly degrading the performance of the cell.

A package must also withstand high mechanical stresses coming either from the outside (shocks, vibrations) or from the inside (pressure in case of failure of the electrochemical cell).

A packaging also has thermal protection functions: it must allow the battery to withstand an external fire sufficiently long. Furthermore, it must be avoided that the thermal runaway of a cell can spread to neighboring cells, or a module grouping several cells to neighboring modules.

All of these safety constraints require the design of a strongest package, the most waterproof, and the most thermally insulating possible, and this while being careful not to penalize the mass and volume of the accumulator. On the other hand, the optimal functioning of cells in power and aging requires precise thermal management: thus, if the temperature inside the packaging is too high, the cell (s) age (s) prematurely even without to be solicited (s) in operation. Conversely, if the temperature inside the package is too low, the cell (s) is (are) unable to provide power because the electrical resistance is excessive and it (s) degrade (s) rapidly in charge due to the deposition of lithium metal on the negative electrode.

In addition, the cell (s) in normal operation gives off the heat that must be discharged outside the packaging, in order to avoid excessive temperature inside the packaging.

Many solutions have been devised to evacuate the internal heat to the packaging to prevent heating of one (of) cell (s) in normal operation.

The existing battery packs are most often metallic and rigid or flexible and in the form of laminated layers. The existing packages of module and battery-pack with several modules are most often metallic and rigid. In all these cases, the packages are thermally conductive, which is favorable in terms of operating conditions but unfavorable in terms of safety in the event of abnormal operation of the cell (s).

As for the cooling of the electrochemical cells, they can be cooled either by a flow of air, or by a liquid cooling circuit, sometimes by heat pipes. A heat pipe consists of a sealed enclosure containing a heat transfer fluid which absorbs heat by vaporizing in an area called heated zone or evaporator, and restores it by liquefying in another zone called cooled zone or condenser. A heat pipe allows to passively exchange heat flows two orders of magnitude higher than the best metals in the same geometry. We can refer to the publication [1].

Among the existing solutions that offer heat pipes to effectively remove the heat from the battery, mention may be made of the patent application CN103367837 A. One reproduces in FIG. 1A describes a battery 100 according to this patent application by using new numerical references. This battery 100 comprises a housing and a plurality of electrochemical cells C arranged in the lower compartment 301 of the housing. The electrochemical cells are cooled by pulsed heat pipes 201 and are in contact with the heated zone 240 of the heat pipes. The cooled zone 230 of these pulsed heat pipes 201 is in the upper housing compartment which comprises a phase change material with high thermal inertia. In addition, the upper housing compartment is connected to a heatsink not shown.

The patent application FR 2989323 A1 describes a battery module comprising cells arranged in a compartment, these cells being in direct contact with heat pipes operating by capillarity. The cooled zone of each heat pipe is integrated in a matrix with a phase change material. The phase change material is in contact with a heat sink.

The patent application US 2011/0206965 A1 describes a battery with a plurality of electrochemical cells and heat pipes inserted between two individual cells, the cells and heat pipes being all arranged in the same housing. The cooled zone of each heat pipe is equipped with fins to improve the cooling and to homogenize the temperature inside the housing.

The patent application US 2011/0000241 A1 describes a battery with a plurality of electrochemical cells and an associated heat pipe, arranged in the same housing, the cooled zone of the heat pipe being connected to an active cooling device which is a heat exchanger. .

These requests according to the state of the art provide solutions to the problems related to the thermal management of batteries in normal operation but do not provide effective protection against excessive heat outside a package.

It is thus understood that the set of known solutions favoring indoor / outdoor heat exchange is antinomic with the search for protection against fire, extreme temperatures, or the propagation of thermal runaway cell (s). Conversely, the use of highly insulating materials against fire, extreme temperatures or the propagation of runaway makes it more difficult to operate in power and life of the battery because the internal heat to the packaging becomes more difficult to evacuate.

The patent application FR 2,539,919 describes a battery 100, reproduced in FIG. 1B, comprising a plurality of electrochemical cells C arranged inside a thermal protection envelope 300 and a heat pipe 200. The heated zone 240 of the heat pipe located inside the casing 300 while being heated by a catalytic converter. However, in the disclosed configuration, the heat pipe brings heat from outside to the electrochemical cells C which in this case use double chloride of sodium and aluminum (NaAICU) as the electrolyte and which require high operating temperatures, typically between 300 ° C and 400 ° C. In other words, the disclosed heat pipe 200 only serves to heat the electrochemical cells and is not intended to evacuate the heat inside the package. Potassium is used as heat transfer fluid, and this potassium condenses at the cooled zone 230. Thus, FR 2 539 919 does not disclose in any case a cooling system of the electrochemical cells. Nothing in this application relates to the thermal management of a lithium battery which differs from that of a NaAICLt accumulator since it must be provided with heat and not cool in operation.

There is thus a need for improvement of batteries and lithium batteries, in particular to ensure both better thermal and mechanical protection of the electrochemical cell (s) and the most efficient thermal management possible of this (these) last (s), even in case of excessive heat inside and / or outside of the packaging which (the) lodge (s).

The object of the invention is to respond at least in part to this need.

Presentation of the invention

To do this, the subject of the invention is, in one of its aspects, an electrochemical lithium battery comprising at least a first package housing at least one electrochemical cell, said first package comprising at least:

an inner layer, thermally insulating, adapted to confine inside the first packaging the heat released even in the event of abnormal operation of a cell C and to protect the cell (s) from the external heat at first packaging,

an outer layer superimposed on the inner layer, the outer layer being mechanically resistant and fire-resistant, and

a cooling device comprising at least one heat pipe whose enclosure passes through the first package (s) in a sealed manner and that the heated zone of the heat pipe (s) is located at inside the first package (s) and that the cooled area of the heat pipe (s) is located outside the first package (s).

For the purposes of the invention, the term "heated zone of a heat pipe" denotes the usual technological meaning, namely the zone of the heat pipe where the heat transfer fluid of the heat pipe receives heat and evaporates. The heated zone is still usually called an evaporator. For the purposes of the invention, the term "cooled zone of a heat pipe" also refers to the usual technological meaning, namely the zone of the heat pipe where the heat transfer fluid of the heat pipe transmits heat and condenses. The cooled zone is still usually called a condenser. For more details, refer to the publication [1].

The accumulator according to the invention can house one or more electrochemical cells in a first package. A package according to the invention fulfills two functions: a function of mechanical protection and fire resistance, and a thermal insulation function. The thermal insulation must be sufficient to allow the electrochemical cell (s) to be protected from extreme heat outside, which can be caused in particular by the abnormal operation of a neighboring electrochemical cell outside. .

"Abnormal operation" means an increase in temperature and pressure beyond that expected in normal operation, which is large enough to cause degradation of the cell and / or thermal runaway of the ) cell (s) around.

Thus, the cooling device is adapted to evacuate the heat confined by the inner layer inside the accumulator even in case of abnormal operation of the electrochemical cell.

Thermal management of the accumulator in normal or abnormal operation is therefore ensured by the cooling device.

Typically, a heat pipe implemented in the invention comprises the following elements:

- a tabular envelope made of aluminum, steel (soft, stainless, ...), copper, ...

a diphasic fluid inside the tubular casing, at the temperature of use, such as, for example, water, ammonia, methanol, ethanol, acetone, toluene, heptane, .

where appropriate, a porous capillary medium such as a sintered metal cloth or powder, or grooves inside the tubular envelope.

It is ensured that the combination of the two-phase fluid and the shell material respects the constraints mainly related to corrosion.

Advantageously, the diameter of the heat pipe according to the invention is of the order of a few millimeters, preferably between 1 mm and 2 cm, more preferably between 2 mm and 2 cm. and 6 mm. The length of the heat pipe can be arbitrary, since it affects only very little thermal evacuation. For example, the heat pipe may protrude from the package of 1 mm to 2 cm.

According to an advantageous variant, the thermal conductivity K of the inner layer is less than 0,05W.m ^{"^} ^{K" 1.} A very low thermal conductivity of the inner layer makes it possible to confine with great efficiency the internal heat of the packaging according to the invention, in the event of abnormal operation of an electrochemical cell or to protect it from heat external to the packaging. .

According to another advantageous variant, the outer layer provides fire resistance according to the SAE J2464 standard.

According to another advantageous variant, the Young's modulus E of the outer protective layer is greater than 1GPa.

According to an advantageous embodiment, the cooled zone of the heat pipe is located above the first package, the heat pipe thus constituting a thermosiphon or heat pipe assisted by gravity. It is specified that in the context of the invention, the term "diphasic thermosiphon", the usual meaning known to those skilled in the art as defined in the publication [1]. Thus, a diphasic thermosiphon is a heat pipe that transfers heat by evaporation / condensation of a fluid inside an envelope without any capillary structure, that is to say with a gravity return of gravity inside the envelope.

A gravity-assisted heat pipe [1] is a heat pipe in which there is a capillary structure, usually grooves, but the return of condensates from the condenser to the evaporator is ensured by the gravity, the evaporator of the heat pipe being at a position lower than the condenser. The capillary structure is therefore not intended to reduce the condensates; but to improve the exchange coefficients in evaporation and condensation, and to push back the training limit.

According to an advantageous variant of the invention, at least one heat pipe constitutes a current output terminal of the accumulator. This advantageously makes it possible to dispense with a welding step of an output terminal on a part of the accumulator, as in the accumulators according to the state of the art.

According to one embodiment, the (the) heat pipe (s) is (are) adapted (s) to limit or even eliminate the liquid phase within its (their) enclosure in case of abnormal operation of the cell (s) (s) ) electrochemical (s) from which it (s) receives (wind) heat at its (their) heated zone. A heat pipe configured in such a manner has a saturation phenomenon as illustrated in FIG. 2: when the temperature becomes too great, the heat pipe is dimensioned so that the liquid phase evaporates completely.

Thus, the amount of heat transmitted by the heated zone to the cooled zone of the heat pipe reaches a maximum that does not increase significantly beyond the saturation temperature, which is chosen as the abnormal operating temperature of a cell. electrochemical. Excessive heat is thus completely confined by the packaging and the heat pipe.

According to an alternative embodiment of the inner layer, the latter comprises a thermosetting or thermoplastic polymer matrix, this matrix being mainly loaded with silica airgel or other particulate filler.

The material constituting the matrix of the inner layer is preferably chosen from urethane, acrylate, methacrylate, polyether and silicone, or is a vinylic polymer, in particular styrene, a polyolefin polymer which may or may not be crosslinked, a polymer of the type unsaturated polyester or an epoxy resin.

According to a variant of the outer protective layer, the latter comprises a thermosetting matrix in which is embedded a fibrous reinforcement.

The material constituting the matrix of the outer layer may advantageously be chosen from urethane, acrylate or methacrylate, or it may be a vinylic polymer, especially styrene, an unsaturated polyester polymer or an epoxy resin.

The material constituting the fibrous reinforcement may advantageously be short or long fibers, preferably glass fibers, carbon, an aromatic polyamide, silicon carbide SiC, bamboo fibers, flax, coconut fibers or hemp fibers. .

The enclosure (s) of the heat pipe (s) may be of circular or prismatic section. A heat pipe with such a chamber section may optionally be adapted to serve as a winding mandrel of a cell.

According to a preferred embodiment, the electrochemical cell C is in the form of a coil wound around the enclosure of the heat pipe.

According to another embodiment, the enclosure of at least one heat pipe is arranged on the periphery of the electrochemical cell (s) C in a gap inside the first package.

According to a first embodiment, the electrochemical accumulator comprises a plurality of a number of n first packages, of which a number equal to n-1 of the first Each package houses an electrochemical cell, the (n-1) first packages being themselves housed inside the other first package.

According to a second embodiment, the accumulator comprises a second metal alloy package, such as an aluminum alloy, housing the electrochemical cell (s), the second package being itself even housed tightly in the first package. According to this embodiment, the invention can be applied to metal alloy packaging batteries according to the state of the art.

According to this second embodiment, the first package comprises, on the inner layer, an electrically conductive coating. The electrically conductive coating may preferably be based on photon sintered metal particles or conductive graphites, preferably deposited as a paint or aerosol. Its role is to ensure the electromagnetic compatibility of the battery.

According to an alternative embodiment, the first package has on its inner face, a coating with a barrier function, adapted to ensure the chemical neutrality of the inner layer vis-à-vis the electrolyte of the electrochemical cell C

The material of the barrier coating may be chosen from polypropylene, polyethylene, a polymer of the polyaryletherketone (PAEK) family, preferably polyetheretherketone (PEEK ™), or a polymer of the polyimide family.

detailed description

Other advantages and features will emerge more clearly on reading the detailed description, given by way of illustration with reference to the following figures among which:

FIG. 1A represents a lithium-ion accumulator with a cooling device according to the state of the art,

FIG. 1B represents a NaAICU accumulator according to the state of the art,

FIG. 2 illustrates the phenomenon of saturation of a heat pipe,

FIG. 3 schematically illustrates the relative arrangement between the package in which an electrochemical cell is housed and a heat pipe of a lithium-ion accumulator according to the invention,

FIG. 4 illustrates an exemplary embodiment of a lithium-ion battery according to the invention,

FIG. 5 illustrates another exemplary embodiment of a lithium-ion battery according to the invention, FIG. 6 illustrates yet another embodiment of a lithium-ion battery according to the invention,

- Figure 7 illustrates yet another embodiment of a lithium-ion battery according to the invention.

Figures 1A to 2 have already been described in detail in the preamble. They are therefore not commented on below.

As represented in FIG. 3, the accumulator 1 according to the invention comprises a package 3 which houses at least one lithium electrochemical cell.

The package 3 comprises an outer layer 4 superimposed on an inner layer 5, thermally insulating.

The outer layer 4 is mechanically resistant and provides fire resistance. The outer layer 4 is preferably epoxy resin polymer, polyurethane resin, polyvinyl resin, polyester resin, optionally with reinforcements of the glass fiber type or carbon fiber. The thickness of the layer 4 is preferably between 300 μιη and 2 mm, more preferably of the order of 1 mm.

The inner layer 5 is preferably made of polyethylene (PE) or of polypropylene (PP), or of PTFE or of PFE, with possibly thermally insulating fillers of the type

nano-clay or alumina, for example. The thickness of the layer 5 is preferably less than 300 μιη preferably and greater than 20 nanometers (nm).

A coating 6 covers the inner layer 5. This coating 6 may have different functions as explained below.

The cooling device of the accumulator 1 comprises a heat pipe 2 comprising a sealed enclosure 21, inside which circulates a coolant 22. This heat transfer fluid is adapted to operate in linear mode at the operating temperature of a cell electrochemical lithium, and can typically be water.

The heat pipe 2 passes through the package 3 in a sealed manner. The heated zone 24 is located within the package 3. The cooled zone 23 is located outside the package 3.

Typically, the diameter of the heat pipe 2 is of the order of a few millimeters, preferably between 1 mm and 2 cm, more preferably between 2 and 6 mm. The length of heat pipe can be any, since it affects very little thermal evacuation. For example, the heat pipe may protrude from the package of 1 mm to 2 cm.

An exemplary embodiment of the invention is shown in FIG. 4. In this example, a single electrochemical cell C is arranged inside the first package 3. The electrochemical cell is in the form of a coil wound around the heat pipe 2 The enclosure 21 of the heat pipe 2 has a circular section. The positive 7 and negative 8 terminals also pass through the package 3 sealingly. According to one variant, it is possible to use the heat pipe itself as the output terminal of the current of the accumulator.

The coating 6 ensures the neutrality of the inner layer 5 vis-à-vis the electrolyte of the electrochemical cell C.

The first package 3 being very thermally insulating, with a thermal conductivity of the inner layer less than 0.05 Wm ^ .K ^"1 , the thermal management in normal operation of the cell 6 is provided by the heat pipe 2.

The heated zone 24 is inside the hollow cylinder formed by the cell C wound on itself, and in thermal contact therewith. Thus, a large amount of heat is transmitted from the cell C to the heated zone 24. The heat transfer fluid 22 then follows an evaporation and condensation cycle: it evaporates at the heated zone 24, and condenses at the level of the cooled zone 23. This cooled zone 23 may optionally comprise a thermal diffuser in order to evacuate the heat transmitted during the condensation of the fluid 22.

In this example, the heated zone 24 being located below the zone 23, the heat pipe 2 constitutes a thermosiphon and operates thanks to gravity: the condensed fluid falls by gravity to the heated zone 23 where it undertakes a new evaporation cycle and condensation.

In case of abnormal operation of the cell C, the inner layer 5 confines the heat inside the package 3. In addition, a heat pipe has a saturation limit as shown in FIG. 5. Beyond a certain temperature, it stops transmitting heat. Thus, in the event of abnormal operation of the cell C, the heat is also not transmitted by the heat pipe 2. The heat is thus effectively confined within the package 3 according to the invention.

On the other hand, in case of temperature outside the high packaging 3, the inner layer 5 prevents degradation of the electrochemical cell C or in other words, protects the electrochemical accumulator 1. The accumulator illustrated in FIG. 3 is made by winding around the enclosure of the heat pipe 2 the electrochemical cell C. The enclosure 21 of the heat pipe 2 is thus adapted to serve as a mandrel during the manufacture of the cell.

To achieve the different layers 4, 5 of the package, one can consider different manufacturing processes. An injection method can thus be advantageous for producing the thermal insulation layer 5, from a thermoplastic polymer and a low load K.

Conventional processes for the use of composites such as reactive injection, the various injection techniques known under the name "Sheet Molding Compound" (SMC), "Bulk Molding Compound" (BMC), "Resin Transfer Molding" (RTM) ), the contact molding can be used for the implementation of the outer layer 4 of thermosetting polymer.

A thermoplastic-thermosetting bi-material injection process can be envisaged for producing the two layers 4, 5, in a single step. Advantageously, the positive 7 and negative 8 terminals may already be present at the beginning of the injection process. It is conceivable to produce the layers 4, 5 by the injection method described and claimed in the patent application FR 14 51546 in the name of the applicant.

An embodiment of the packaging layers 4, 5 with a fibrous reinforcement matrix is now described.

This example consists in the creation of two half-shells which will be gathered around the electrochemical cell C. The introduction of the electrolyte is made at the time of the gathering of the two half-shells by injection before plastic welding / final bonding.

This example with fibrous reinforcement matrices can be realized according to a RTM technology, coupled to a thermoplastic injection with charge. The following successive steps are thus carried out:

1-introduction of the different thicknesses of the glass fiber fabric with the connection terminals 7, 8 into a previously heated RTM mold,

2- closing of the mold and evacuation of the mold,

3- injection of the precursors of the epoxy resin into the mold, which leads to the impregnation of the fibers,

4- baking the epoxy resin according to the recommended time at the recommended temperature, 5- adjustment of the mold temperature for the injection of thermoplastic material,

Opening of the valve in the mold to define the molding zone of the thermal reinforcement of the electrochemical cell,

7- injection of highly filled polyethylene (PE) with micron-sized particles, thermal insulation materials,

8- extraction of the mold from the formed object and trimming / unraveling of excess materials,

9- gathering of the two half-shells formed around the electrochemical cell C wound around its heat pipe 2 and thermoplastic welding around a double needle, by evacuation with one of the needles and simultaneous injection of the electrolyte by the other needles,

10- removal of the needles while completing the thermoplastic welding,

11- bonding of thermosetting material thermosetting areas to ensure homogeneity of reinforcement for fire resistance and mechanical reinforcement.

Another exemplary embodiment of the invention is illustrated in FIG. 5. According to this example, the accumulator 1 comprises a plurality of electrochemical cells C. Each electrochemical cell is arranged in a sealed manner within a package 3 'according to FIG. state of the art. This 3 'package is metal alloy type, such as aluminum alloy, or plastic. This packaging 3 'according to the state of the art is housed in a sealed manner in the package 3 according to the invention. Several heat pipes 2 pass tightly through the package 3 and have one of their ends arranged in interstices 9 within the package 3. Their heated zones 24 are thus in contact with the packages 3 'according to the state of the package. art, which are thermally conductive and thus which diffuse the heat released by the electrochemical cells C. The thermal contact between a heated zone 24 of heat pipe and the 3 'packaging of an electrochemical cell can be improved by interposing thermally conductive grease .

Preferably, in this example, an electrically conductive coating 6 covers the inside of the inner layer 5 of the package 3, in order to ensure the electromagnetic compatibility of the battery.

In case of abnormal operation of a cell C, the inner layer 5 confines the heat inside the package 3. Similarly, in case of heat outside the high packaging 3, the inner layer 5 prevents degradation electrochemical cells C and thus protects the electrochemical accumulator 1. Other variants and improvements may be envisaged without departing from the scope of the invention.

For example, it is possible to envisage an embodiment of an accumulator with several electrochemical cells C immersed in the same electrolyte in the package 3 according to the invention. Such a mode is illustrated in FIG. 6, in which three cells arranged in parallel in the same package 3 are seen, with a single heat pipe 2 of pulsed type, the heated zones 24 of which are inside and its cooled zones 23 at the same time. outside. This embodiment is particularly advantageous when it is desired to produce C cells of very large capacity.

It is also possible to envisage a "double packaging" mode according to which the electrochemical accumulator comprises a plurality of a number of n first packagings, of which a number equal to n-1 of the first packs each houses an electrochemical cell C, the (n -1) first packs being themselves housed inside the other first packaging. This mode is illustrated in FIG. 7, in which we see two cells arranged in parallel and each inside a package 3 according to the invention, a central heat pipe 2 being arranged between these two packages 3 themselves housed in a third peripheral package 3.

REFERENCE CITEE

[1]: Hello J, Lefevre F, Sartre V, Bertin Y, Romantant C, Ayel V and Platel V, "Diphasic Systems of Thermal Control - Thermosyphons and Heatpipes", Engineering Techniques, Vol. BE9545, 2011.

Claims

1. Lithium electrochemical accumulator (1), comprising:

At least one first package (3) housing at least one electrochemical cell, said first package (3) comprising at least one inner layer (5), thermally insulating, adapted to confine inside the first package the heat released even in case of abnormal operation of a cell C and to protect the cell (s) from external heat to the first package (3),

An outer layer (4) superimposed on the inner layer (5), the outer layer being mechanically resistant and fire-resistant,

and

- a cooling device comprising at least one heat pipe (2) whose enclosure (21) passes through the first package (s) (3) in a sealed manner and so that the heated zone (24) the heat pipe is located inside the first package (3) and that the cooled zone (23) of the heat pipe is located outside the first package (s) ) (3).

2. Electrochemical battery according to claim 1, the thermal conductivity K of the inner layer (5) being less than 0,05W.m ^{"^} ^{K" 1.}

3. Electrochemical accumulator according to one of the preceding claims, the Young's modulus E of the outer layer (4) being greater than 1GPa.

4. electrochemical accumulator according to one of the preceding claims, the cooled zone (23) of the heat pipe being located above the first package (3), the heat pipe (2) thus constituting a thermosiphon or heat pipe assisted by gravity.

5. electrochemical accumulator according to one of the preceding claims, at least one heat pipe (2) constituting an output terminal of the current of the accumulator.

6. electrochemical accumulator according to one of the preceding claims, the (s) heat pipe (s) being adapted (s) to limit or eliminate the liquid phase within his (their) enclosure in case of abnormal operation of (the) electrochemical cell (s).

7. Electrochemical accumulator according to one of the preceding claims, the inner layer (5) comprising a matrix of thermosetting or thermoplastic polymer, this matrix being mainly loaded with airgel silica or other particulate filler.

8. electro-chemical accumulator according to claim 7, the material constituting the matrix of the inner layer (5) being chosen from urethane, acrylate, methacrylate, polyether and silicone, or being a vinyl polymer including styrene, a polyolefin polymer crosslinked or not, an unsaturated polyester type polymer or an epoxy resin.

9. electrochemical accumulator according to one of the preceding claims, the outer layer (4) comprising a thermosetting matrix in which is embedded a fibrous reinforcement.

10. electrochemical accumulator according to claim 9, the material constituting the matrix of the outer layer being selected from urethane, acrylate, methacrylate, or being a vinyl polymer including styrenic, unsaturated polyester polymer or an epoxy resin .

Electrochemical accumulator according to claim 9 or 10, the material constituting the fiber reinforcement being short or long fibers, preferably glass fibers, carbon, an aromatic polyamide, silicon carbide SiC, bamboo fibers, flax, coconut fiber or hemp.

12. electrochemical accumulator according to one of the preceding claims, the (the) enclosure (s) of (the) pipe (s) (21) being of circular or prismatic section.

13. Electrochemical accumulator according to one of the preceding claims, the electrochemical cell C being in the form of a coil wound around the enclosure (21) of the heat pipe.

Electrochemical accumulator according to one of the preceding claims, the enclosure (21) being arranged on the periphery of the electrochemical cell (s) C in a gap (9) inside the first package (3). .

Electrochemical accumulator according to one of the preceding claims, comprising a plurality of a number of n first packages (3), of which a number equal to n-1 of the first packages (3) each housing an electrochemical cell, the (n -1) first packs being themselves housed inside the other first package (3).

16. Electrochemical accumulator according to one of claims 1 to 14 comprising at least a second packaging (3 ') based on a metal alloy, such as an aluminum alloy, housing the electrochemical cell (s) (s) ( s), the second package itself being sealed in the first package (3).

17. electrochemical accumulator according to claim 16, the first package (3) having, on the inner layer, a coating (6) electrically conductive.

Electrochemical accumulator according to Claim 17, the electrically conductive coating (6) being based on sintered metal particles by sintering. photonics or conductive graphites, preferably deposited in the form of paint or aerosol.

19. electrochemical accumulator according to one of claims 1 to 15 the first package (3) having on the inner layer a coating (6) barrier function, adapted to ensure the chemical neutrality of the inner layer (5) vis-à-vis the electrolyte of the electrochemical cell C.

20. Electrochemical accumulator according to claim 19, the material of the coating (6) barrier being selected from polypropylene, polyethylene, a polymer of the family of polyaryletherketones (PAEK), preferably polyetheretherketone (PEEK ™), or a polymer of the family of polyimides.