Lithium Accumulator With A Two-Layered Thermally Insulating Package And With A Heat Pipe For Thermal Management

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).

Claims

1. A lithium electrochemical accumulator, including: at least one first package housing at least one electrochemical cell, said first package including at least one thermally insulating internal layer that is suitable for confining to the interior of the 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 that is 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 is located in the interior of the first package(s) and such that the cooled zone of the heat pipe is located on the exterior of the first package(s).

2. The electrochemical accumulator as claimed in claim 1, the thermal conductivity K of the internal layer being lower than 0.05 W.Math.m.sup.−1.Math.K.sup.−1.

3. The electrochemical accumulator as claimed in claim 1, the Young's modulus E of the external layer being higher than 1 GPa.

4. The electrochemical accumulator as claimed in claim 1, the cooled zone of the heat pipe being located above the first package, the heat pipe thus forming a gravity-assisted heat pipe or thermosiphon.

5. The electrochemical accumulator as claimed in claim 1, at least one heat pipe forming an output terminal for the current of the accumulator.

6. The electrochemical accumulator as claimed in claim 1 the heat pipe(s) being suitable for limiting or even suppressing the liquid phase within its (their) enclosure in case of abnormal operation of the electrochemical cell(s).

7. The electrochemical accumulator as claimed in claim 1, the internal layer comprising a matrix made of thermosetting or thermoplastic polymer, this matrix being mainly filled with silica aerogel or some other particulate filler.

8. The electrochemical accumulator as claimed in claim 7, the material forming the matrix of the internal layer being chosen from urethane, acrylate, methacrylate, polyether and silicone, or being a vinyl and in particular styrene polymer, an optionally cross-linked polyolefin polymer, an unsaturated polyester type polymer or an epoxy resin.

9. The electrochemical accumulator as claimed in claim 1, the external layer comprising a thermoset matrix in which a fibrous reinforcement is embedded.

10. The electrochemical accumulator as claimed in claim 9, the material forming the matrix of the external layer being chosen from urethane, acrylate, methacrylate, or being a vinyl and in particular styrene polymer, an unsaturated polyester type polymer or an epoxy resin.

11. The electrochemical accumulator as claimed in claim 9, the material forming the fibrous reinforcement being short- or long-fiber and preferably fibers of glass, of carbon, an aromatic polyamide, of silicon carbide SiC, fibers of bamboo, of linen, fibers of coconut or hemp.

12. The electrochemical accumulator as claimed in claim 1, the enclosure(s) of the heat pipe(s) being of prismatic or circular cross section.

13. The electrochemical accumulator as claimed in claim 1, the electrochemical cell C taking the form of a roll rolled around the enclosure of the heat pipe.

14. The electrochemical accumulator as claimed in claim 1, the enclosure being arranged on the periphery of the electrochemical cell(s) C in an interstice in the interior of the first package.

15. The electrochemical accumulator as claimed in claim 1, including a plurality of a number of n first packages, a number equal to n−1 of the first packages of which each houses an electrochemical cell, the (n−1) first packages themselves being housed in the interior of the other first package.

16. The electrochemical accumulator as claimed in claim 1, including at least one second package based on a metal alloy, such as an aluminum alloy, housing the electrochemical cell(s), the second package itself being housed in a seal-tight manner in the first package.

17. The electrochemical accumulator as claimed in claim 16, the first package including, on the internal layer, an electrically conductive coating.

18. The electrochemical accumulator as claimed in claim 17, the electrically conductive coating being based on metal particles sintered by photonic sintering or graphite conductors, said coating preferably being deposited in the form of a paint or aerosol.

19. The electrochemical accumulator as claimed in claim 1, the first package including on the internal layer a coating having a barrier function, said coating being suitable for ensuring the chemical neutrality of the internal layer with respect to the electrolyte of the electrochemical cell C.

20. The electrochemical accumulator as claimed in claim 19, the material of the barrier coating being chosen from polypropylene, polyethylene, a polymer from the family of the polyaryletherketones (PAEK), preferably polyetheretherketone (PEEK™), or a polymer from the family of the polyimides.

Description

DETAILED DESCRIPTION

[0061] Other advantages and features will become more clearly apparent on reading the detailed description, which is given with reference to the following figures, in which:

[0062] FIG. 1A shows a lithium-ion accumulator with a cooling device according to the prior art,

[0063] FIG. 1B shows an NaAlCl.sub.4 accumulator according to the prior art,

[0064] FIG. 2 illustrates the effect of saturation of a heat pipe,

[0065] FIG. 3 illustrates a schematic view of 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,

[0066] FIG. 4 illustrates an exemplary embodiment of a lithium-ion accumulator according to the invention,

[0067] FIG. 5 illustrates another exemplary embodiment of a lithium-ion accumulator according to the invention,

[0068] FIG. 6 also illustrates another exemplary embodiment of a lithium-ion accumulator according to the invention,

[0069] FIG. 7 also illustrates another exemplary embodiment of a lithium-ion accumulator according to the invention.

[0070] FIGS. 1A to 2 have already been described in detail in the preamble. They are therefore not discussed below.

[0071] As FIG. 3 shows, the accumulator 1 according to the invention comprises a package 3 that houses a least one lithium electrochemical cell.

[0072] The package 3 includes an external layer 4 that is superposed on a thermally insulating internal layer 5.

[0073] The external layer 4 is mechanically strong and provides fire resistance. The external layer 4 is preferably made of a polymer such as an epoxy resin, polyurethane resin, polyvinyl resin or a polyester resin, where appropriate reinforced with a glass-fiber or carbon-fiber type reinforcement. The thickness of the layer 4 is preferably comprised between 300 μm and 2 mm and more preferably is about 1 mm.

[0074] The internal layer 5 is preferably made of polyethylene (PE) or of polypropylene (PP), or of PTFE or PFE, and optionally contains thermally insulating fillers such as nanoclay or alumina fillers for example. The thickness of the layer 5 is preferably smaller than 300 μm and larger than 20 nanometers (nm).

[0075] A coating 6 covers the internal layer 5. This coating 6 may have various functions as explained below.

[0076] The cooling device of the accumulator 1 comprises a heat pipe 2 including a seal-tight enclosure 21, in the interior of which a heat-transfer fluid 22 flows. This heat-transfer fluid is suitable for operating in linear regime at the operating temperature of a lithium electrochemical cell, and may typically be water.

[0077] The heat pipe 2 passes through the package 3 in a seal-tight manner. The heated zone 24 is located within the package 3. The cooled zone 23 is located on the exterior of the package 3.

[0078] Typically, the diameter of the heat pipe 2 is about a few millimeters and preferably comprised between 1 mm and 2 cm and more preferably between 2 and 6 mm. The heat pipe may be any length, since its length has very little effect on the heat removal. For example, the heat pipe may protrude from the package by 1 mm to 2 cm.

[0079] One exemplary embodiment of the invention is shown in FIG. 4. In this example, a single electrochemical cell C is arranged in the interior of the first package 3. The electrochemical cell takes the form of a roll rolled around the heat pipe 2. The enclosure 21 of the heat pipe 2 has a circular cross section. The positive terminal 7 and negative terminal 8 also pass through the package 3 in a seal-tight manner. According to one variant, it is possible to use the heat pipe itself as an output terminal for the current of the accumulator.

[0080] The coating 6 for its part ensures the neutrality of the internal layer 5 with respect to the electrolyte of the electrochemical cell C.

[0081] Since the first package 3 is very thermally insulating, the internal layer 5 having a thermal conductivity lower than 0.05 W.Math.m.sup.−1.Math.K.sup.−1, thermal management in normal operation of the cell 6 is ensured via the heat pipe 2.

[0082] The heated zone 24 is located in the interior of the hollow cylinder formed by the cell C rolled about itself, and makes thermal contact with the latter. Thus, a large amount of heat is transmitted from the cell C to the heated zone 24. The heat-transfer fluid 22 then follows a cycle of evaporation and condensation: it evaporates in the heated zone 24, and condenses in the cooled zone 23. This cooled zone 23 may optionally include a heat spreader in order to remove the heat transmitted during the condensation of the fluid 22.

[0083] In this example, the heated zone 24 being located below the zone 23, the heat pipe 2 forms a thermosiphon and functions by virtue of gravity: the condensed fluid falls under gravity toward the heated zone 23 where it begins a new cycle of evaporation and condensation.

[0084] In case of abnormal operation of the cell C, the internal layer 5 confines the heat to the interior of the package 3. In addition, a heat pipe has a saturation limit as shown in FIG. 5. Beyond a certain temperature, it ceases to transmit heat. Thus, in case of abnormal operation of the cell C, the heat is no longer transmitted by the heat pipe 2. Heat is thus effectively confined to the interior of the package 3 according to the invention.

[0085] Furthermore, in case of high temperature outside the package 3, the internal layer 5 prevents the degradation of the electrochemical cell C, or in other words protects the electrochemical accumulator 1.

[0086] The accumulator illustrated in FIG. 3 is produced by rolling the electrochemical cell C around the enclosure of the heat pipe 2. The enclosure 21 of the heat pipe 2 is thus suitable for serving as a spool during the manufacture of the cell.

[0087] To produce the various layers 4, 5 of the package, various manufacturing processes may be envisioned. Thus, an injection molding process may be advantageous for producing the thermally insulating layer 5, from a thermoplastic polymer and a low-K filler.

[0088] Processes conventionally used to form composites such as reaction injection molding, the various injection molding techniques that employ sheet molding compounds (SMCs) or bulk molding compounds (BMCs), resin transfer molding (RTM) and contact molding may be used to form an external layer 4 made of thermosetting polymer.

[0089] A bi-material thermoplastic-thermoset injection molding process is envisionable for the production in a single step of the two layers 4, 5 of the package. Advantageously, the positive terminal 7 and negative terminal 8 may already be present at the start of the injection molding process. It is also possible to envision producing the layers 4, 5 using the injection molding process described and claimed in patent application FR 14 51546 in the name of the applicant.

[0090] An exemplary embodiment of the package layers 4, 5 comprising a fiber-reinforced matrix will now be described.

[0091] This example consists in creating two shell halves that will be closed around the electrochemical cell C. The electrolyte is introduced at the moment of closure of the two shell halves by injection before final adhesive bonding/plastic welding.

[0092] This example with fiber-reinforced matrices may be produced by injection molding a filled thermoplastic using an RTM technology. Thus, the following steps are carried out in succession:

[0093] 1—various thicknesses of glass fiber cloth are introduced with the connection terminals 7, 8 into a preheated RTM mold;

[0094] 2—the mold is closed and placed under vacuum;

[0095] 3—precursors of the epoxide resin are injected into the mold, this leading to impregnation of the fibers;

[0096] 4—the epoxide resin is baked for the recommended time at the recommended temperature;

[0097] 5—the temperature of the mold is set for the injection of thermoplastic;

[0098] 6—the valve in the mold is opened to define the molding zone of the thermal reinforcement of the electrochemical cell;

[0099] 7—polyethylene (PE) highly filled with micron-sized particles of thermally insulating materials is injected;

[0100] 8—the object formed is extracted from the mold and excess material is trimmed/degated;

[0101] 9—two shell halves are closed around the electrochemical cell C rolled around its heat pipe 2 with thermoplastic welding around two needles, one of the needles being used to create a vacuum and the other of the needles being used simultaneously to inject the electrolyte;

[0102] 10—the needles are removed while completing the thermoplastic weld;

[0103] 11—thermoset is adhesively bonded to the thermosetting zones in order to ensure reinforcement uniformity for the fire resistance and mechanical reinforcement.

[0104] 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 seal-tight manner within a package 3′ according to the prior art. This package 3′ is made of a metal alloy, such as an aluminum alloy, or of plastic. This package 3′ according to the prior art is housed in a seal-tight manner in the package 3 according to the invention. A plurality of heat pipes 2 pass, in a seal-tight manner, through the package 3 and have one of their ends arranged in interstices 9 within the package 3. Their heated zones 24 are thus located in contact with the packages 3′ according to the prior art, which are thermally conductive and which therefore spread the heat liberated by the electrochemical cells C. The thermal contact between a heated zone 24 of the heat pipe and the package 3′ of an electrochemical cell may be improved by interposing thermally conductive grease.

[0105] Preferably, in this example, an electrically conductive coating 6 covers the interior of the internal layer 5 of the package 3, in order to ensure the electromagnetic compatibility of the battery.

[0106] In case of abnormal operation of a cell C, the internal layer 5 confines heat to the interior of the package 3. Likewise, in case of a high temperature outside the package 3, the internal layer 5 prevents degradation of the electrochemical cells C and thus protects the electrochemical accumulator 1.

[0107] Other variants and improvements may be envisioned without however departing from the scope of the invention.

[0108] For example, an embodiment may be envisioned in which the accumulator comprises a plurality of electrochemical cells C submerged in the same electrolyte in a package 3 according to the invention. Such an embodiment is illustrated in FIG. 6, which shows three cells arranged in parallel in the same package 3, with a single pulsation heat pipe 2, the heated zones 24 of which are in the interior and the cooled zones 23 of which are on the exterior. This embodiment is particularly advantageous when it is desired to produce cells C of very high capacity.

[0109] It is also possible to envision a “dual package” embodiment in which the electrochemical accumulator includes a plurality of a number of n first packages, a number equal to n−1 of the first packages of which each houses an electrochemical cell C, the (n−1) first packages themselves being housed in the interior of the other first package. This embodiment is illustrated in FIG. 7, which shows two cells arranged in parallel and each in the interior of a package 3 according to the invention, a central heat pipe 2 being arranged between these two packages 3 that are themselves housed in a third peripheral package 3.

CITED REFERENCE

[0110] [1]: Bonjour J, Lefevre F, Sartre V, Bertin Y, Romestant C, Ayel V and Platel V, “Systèmes Diphasiques De Contrôle Thermique—Thermosiphons Et Caloducs”, Techniques de l'ingénieur, Vol. BE9545, 2011.