Busbar for a battery pack, intended to electrically connect at least one accumulator battery of the pack and to allow a heat transfer fluid to flow therein in order to optimally cool the accumulator battery and the pack, in particular in the case of thermal runaway

Abstract

A busbar for a battery pack, intended to electrically connect at least one electrochemical accumulator battery of the pack, preferably to electrically connect several electrochemical accumulator batteries of the pack to one another, including an electrically conductive and sealtight envelope itself intended to channel the current of the accumulator batteries and designed to contain a heat transfer liquid whose vaporization temperature is chosen so as to be between a value close to 90% of the self-heating temperature and a value close to 110% of the thermal runaway temperature of the accumulator batteries of the pack, the sealtight envelope being designed to guarantee an injection of heat transfer liquid as close as possible to each accumulator battery to which it is intended to be connected, preferably close to at least one of its output terminals.

Claims

1. A busbar for a battery pack, intended to electrically connect at least one electrochemical accumulator battery of the pack, the at least one accumulator battery having a self-heating temperature and a thermal runaway temperature, wherein the busbar comprises an electrically conductive and sealtight envelope intended to conduct a current of the accumulator batteries and configured to contain a heat transfer liquid having a vaporization temperature chosen so as to be comprised between a value close to 90% of the self-heating temperature and a value close to 110% of the thermal runaway temperature of the accumulator batteries of the pack, the sealtight envelope being configured to guarantee an injection of heat transfer liquid as close as possible to each accumulator battery to which the sealtight envelope is intended to be connected.

2. The busbar as claimed in claim 1, wherein the envelope is a sealtight finite volume containing the heat transfer liquid, configured to be arranged at least partly as close as possible to each accumulator battery to which the sealtight finite volume is intended to be connected.

3. The busbar as claimed in claim 1, wherein the sealtight envelope is part of a flow circuit for the heat transfer liquid, configured to be arranged at least partly as close as possible to each accumulator battery to which the sealtight envelope is intended to be connected.

4. The busbar as claimed in claim 1, wherein the sealtight envelope consists of two electrically conductive sheets that are joined together in a sealtight manner in order to internally define a heat transfer liquid container intended to be arranged facing or around an end face of each accumulator battery.

5. The busbar as claimed in claim 4, wherein the container is defined by the entire sheet surface intended to face the accumulator batteries, except for the areas intended to face spaces between accumulator batteries.

6. The busbar as claimed in claim 4, wherein the container is defined by the entire sheet surface intended to face the accumulator batteries, except for the areas intended to face end faces of the accumulator batteries.

7. The busbar as claimed in claim 4, wherein the envelope comprises through-holes passing through the two joined sheets outside of the liquid container, the through-holes being intended to evacuate gases emitted by at least one accumulator battery in thermal runaway.

8. The busbar as claimed in claim 7, wherein the through-holes are distributed in rings, each ring being intended to face an end face of an accumulator battery.

9. The busbar as claimed in claim 7, wherein the busbar comprises an additional sheet, said additional sheet being configured to recover the gases emitted through the holes, to channel said gases and to cool said gases with the heat transfer liquid.

10. The busbar as claimed in claim 4, wherein one of the two sheets has a thickness less than a thickness of the other of the two sheets, the sheet of lesser thickness being intended to be closer to the accumulator batteries to which the sealtight envelope is intended to be connected than the sheet of greater thickness.

11. The busbar as claimed in claim 9, wherein assembly welds between the two sheets are remote from areas intended to face output terminals of the accumulator batteries.

12. A battery pack comprising at least one module comprising: a plurality of accumulator batteries with a cylindrical geometry, each comprising at least one electrochemical cell formed of a cathode, of an anode and of an electrolyte interposed between the cathode and the anode, a housing designed to contain the electrochemical cell in a sealtight manner and two output terminals projecting from a cover and/or from a base of the housing; at least one busbar as claimed in claim 1, welded to one of the output terminals of at least some of the accumulator batteries, in order to electrically connect the accumulator batteries to one another.

13. The battery pack as claimed in claim 12, wherein the pack comprises a fluid circuit configured so as to channel a heat transfer fluid in the busbar.

14. The battery pack as claimed in claim 13, wherein the circuit is configured so as to passively allow, through gravity, a supply of the heat transfer liquid facing or around each accumulator battery.

15. The battery pack as claimed in claim 12, wherein the busbar is inclined with respect to an horizontal plane when the pack is in an operational configuration, so as to allow evacuation of gases resulting from vaporization of the heat transfer liquid through a top side of the pack.

16. The battery pack as claimed in claim 12, each accumulator battery being a Li-ion accumulator battery, wherein: the negative electrode(s) material is chosen from the group comprising graphite, lithium, lithium titanate oxide Li.sub.4TiO.sub.5O.sub.12; the positive electrode(s) material is chosen from the group comprising LiFePO.sub.4, LiCoO.sub.2, LiNi.sub.0.33Mn.sub.0.33Co.sub.0.33O.sub.2.

17. The busbar as claimed in claim 1, wherein each accumulator battery has two output terminals and the sealtight envelope is designed to guarantee an injection of heat transfer liquid close to at least one of the output terminals of each accumulator battery to which the sealtight envelope is intended to be connected.

18. The battery pack as claimed in claim 13, wherein the heat transfer fluid is a two-phase liquid-vapor heat transfer fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic perspective exploded view showing the various elements of a lithium-ion accumulator battery.

(2) FIG. 2 is a front view showing a lithium-ion accumulator battery with its flexible packaging according to the prior art.

(3) FIG. 3 is a perspective view of a lithium-ion accumulator battery according to the prior art with its rigid packaging consisting of a cylindrical housing.

(4) FIG. 4 is a perspective view of a lithium-ion accumulator battery according to the prior art with its rigid packaging consisting of a prismatic housing.

(5) FIG. 5 is a perspective view of an assembly, by way of busbars, of lithium-ion accumulator batteries according to the prior art, forming a battery pack.

(6) FIG. 6 is a perspective plan view of a battery pack module equipped with a busbar according to a first embodiment of the invention.

(7) FIG. 6A is a perspective and longitudinal sectional view of a module according to FIG. 6.

(8) FIG. 7 is a perspective plan view of a battery pack module equipped with a busbar according to a second embodiment of the invention.

(9) FIG. 7A is a perspective and longitudinal sectional view of a module according to FIG. 7.

(10) FIG. 7B is a detailed view of FIG. 7A.

(11) FIG. 7C is a schematic longitudinal sectional view of a module similar to that of FIG. 7 in an accumulator battery.

(12) FIG. 8 picks up from FIG. 7 and illustrates a flow of the heat transfer liquid within the busbar according to the second embodiment.

(13) FIG. 9 is a perspective view of a module according to FIG. 7, in an operational configuration with the busbar vertical, FIG. 9 showing the evacuation of the gases emitted when the heat transfer liquid is vaporized.

DETAILED DESCRIPTION

(14) FIGS. 1 to 5 relate to different examples of Li-ion accumulator batteries, flexible packagings and accumulator battery housings and a battery pack according to the prior art. These FIGS. 1 to 5 have already been commented on in the preamble and are therefore not commented on any more below.

(15) For the sake of clarity, the same references denoting the same elements according to the prior art and according to the invention are used for all of FIGS. 1 to 9.

(16) Throughout the present application, the terms “lower”, “upper”, “bottom”, “top”, “below” and “above” should be understood with reference to Li-ion accumulator battery housings that are inclined with respect to the vertical, that is to say with a busbar according to the invention inclined with respect to the horizontal.

(17) FIGS. 6 and 6A show a first example of a busbar 10 according to the invention in a module M1 of a battery pack P of Li-ion accumulator batteries, A1, A2, . . . , A17. In the illustrated examples, the accumulator batteries A1-A17 that are illustrated have housings in a cylindrical format, typically the 18650 or 21700 format.

(18) The accumulator batteries A1-A17 are supported by a support plate 20 and are connected electrically in parallel in groups by the busbar 10.

(19) The busbar 10 according to the invention is a sealtight envelope arranged above the cover 9 of the Li-ion accumulator batteries A1-A17. It is specified here that the term “above” should be considered here with the Li-ion accumulator batteries in the vertical position, and therefore with the busbar 10 arranged horizontally above, this not being the operational configuration of the modules M1, M2, in which the busbar 10 is inclined with respect to the horizontal.

(20) The sealtight envelope of the busbar 10 consists of two metal sheets 11, 12 joined to one another in a sealtight manner, by a weld S2, S3, in order to internally define a heat transfer liquid container V1 intended to be arranged facing the covers 9 of all of the accumulator batteries, from where their positive 4 or negative 5 output terminals project. The sheet 11 closer to the accumulator batteries has a lesser thickness than the outer sheet 12.

(21) The sheet 11 is fastened by a weld S1 to each negative output terminal 5 of the accumulator batteries.

(22) In this module M1, the busbar 10 therefore has a container V1 that forms a heat transfer liquid pocket, which is defined by the entire surface of the sheet 11 and the sheet 12 facing the accumulator batteries, except for the areas 13 facing the spaces between the accumulator batteries.

(23) This container V1 may be closed and therefore be a finite volume.

(24) An inlet 14 and an outlet 15 may also be provided at the ends of the volume V1 in order to allow heat transfer liquid to flow therein. Located at the upper part of the pack, the inlet 14 or outlet 15 may also be used to evacuate the vaporized gas from the heat transfer fluid. This flow of heat transfer liquid within the volume V1 is integrated into the heat transfer liquid circuit of the battery pack that incorporates the module M1, which will therefore make it possible to cool the plurality of accumulator batteries A1-A17 through the flow of heat transfer liquid within busbars 10 according to the invention.

(25) FIGS. 7 to 7C show a second example of a busbar 10 according to the invention in a module M2 of a battery pack P of Li-ion accumulator batteries, A1, A2, . . . , A17.

(26) The accumulator batteries A1-A17 are also supported by a support plate 20 and are connected electrically in parallel in groups by the busbar 10.

(27) The sealtight envelope of the busbar 10 also consists here of two metal sheets 11, 12 joined to one another in a sealtight manner, by a weld S2, S3, in order to internally define a heat transfer liquid container V2 intended to be arranged facing the covers 9 of all of the accumulator batteries, from where their positive 4 or negative 5 output terminals project. The sheet 11 closer to the accumulator batteries has a lesser thickness than the outer sheet 12. By way of example, the thickness e1 of the sheet 11 may be between 0.05 and 0.5 mm, typically equal to 0.1 mm, whereas that e2 of the sheet 12 may be between 0.1 and 2 mm, typically equal to 0.3 mm.

(28) With a sheet 11 of lesser thickness, the thermal barrier to be crossed between each accumulator battery and the heat transfer liquid in the container V2 is smaller. The flow cross section for the current is able to be provided by the thicker outer sheet 12, by spacing the terminals and the contact points between plates.

(29) The sheet 11 is also fastened by a weld S1 to each positive 4 or negative 5 output terminal of the accumulator batteries.

(30) The structural difference between the module M2 according to FIGS. 7 to 7C and that M1 of FIGS. 6, 6A is that, in this module M2, the busbar 10 has a container V2 that forms a heat transfer liquid pocket, which is defined by the entire surface of the sheet 11 facing the accumulator batteries, except for the areas 16 facing the end faces 9 of the accumulator batteries.

(31) Thus, as is able to be seen better in FIGS. 7B and 7C, in the areas 16, the sheet 11 to which the positive 4 or negative 5 output terminals are welded by the welds Si is exposed and in contact with the surroundings above the module M2.

(32) The sheet 11 furthermore comprises through-holes 17 outside of the areas of the liquid container V2. These through-holes 17 make it possible to evacuate the gases emitted by at least one accumulator battery in thermal runaway.

(33) Preferably, as shown in FIGS. 7 to 7B, the through-holes 17 are distributed in rings, each ring facing an end face 9 of an accumulator battery, around an output terminal via which the gases are able to escape.

(34) The assembly welds S2, S3 between the two sheets 11, 12 are remote from the areas 16 facing the output terminals of the accumulator batteries. This makes it possible to limit thermal conduction between accumulator batteries via the thicker sheet 12, i.e. the outer one.

(35) In order to allow optimized centering when positioning the busbar 10 with respect to each accumulator battery, it is possible to provide holes 18 that will each face an output terminal before the welds S1 are formed.

(36) The container V2 may also be closed and therefore be a finite volume.

(37) It is also possible to provide an inlet 14 and an outlet 15 at the ends of the volume V2 in order to allow heat transfer liquid to flow therein from the heat transfer liquid circuit of the battery pack, or even blowholes for evacuating the gas resulting from the vaporization of the heat transfer fluid.

(38) FIG. 8 illustrates the flow of dielectric heat transfer fluid F homogeneously everywhere facing the surfaces between the accumulator batteries A1-A17, as close as possible to the positive 4 or negative 5 output terminals.

(39) FIG. 9 shows an operational configuration in which the busbar of the module M2 is vertical and, in the form of an arrow, the evacuation of the gases G emitted during the vaporization of the heat transfer liquid caused by the thermal runaway of an accumulator battery within the module.

(40) The invention is not limited to the examples that have just been described; it is in particular possible to combine features of the examples illustrated within variants that are not illustrated.

(41) Other variants and improvements may be contemplated without otherwise departing from the scope of the invention.

(42) For example, although the busbar that has just been described comprises a sealtight envelope formed by joining exactly two sheets 11, 12 to one another, it is possible to provide a three-sheet assembly with an additional sheet.

(43) This additional sheet would have the role of recovering the gases emitted through the holes 17, channeling them in order to limit the impact of their toxicity and cooling them with the heat transfer fluid. This third sheet may in this case be thicker than the other two sheets 11, 12.

(44) Other holes or safety blowholes may be provided for the passage of the gases resulting from the phase change of the heat transfer fluid, since the latter will increase the volume necessary for the encapsulation thereof in the sealtight envelope of the busbar. These holes or blowholes in the upper part may be situated for example at the end of an inlet 14 or outlet 15 (FIGS. 6 to 9).

LIST OF CITED REFERENCES

(45) [1] Xuning Fenga, et al. “Key Characteristics for Thermal Runaway of Li-ion Batteries” Energy Procedia, 158 (2019) 4684-4689