Battery cell enclosure

Abstract

The invention relates to a battery cell envelope (1) arranged so as to surround an electric cell (2), the battery cell envelope delimiting a volume and comprising at least two adjacent walls (11, 12, 13, 14, 15, 17) connected to each other by an edge (10) forming a junction, the battery cell envelope comprising a developable surface forming a hollow protruding bead open towards the volume, extending along the edge and connecting the two walls. (Fig. 1)

Description

Title of the invention: Battery electric cell casing Technical field of the invention

[0001] The invention relates, in general, to the technical field of batteries, in particular batteries intended to equip hybrid or all-electric motor vehicles. More specifically, the invention relates to a battery cell casing. State of the prior art

[0002] Today, in the field of traction batteries intended for hybrid or all-electric motor vehicles, said traction batteries comprise a set of electric cells positioned adjacent to one another. The electric cell can be of the prismatic Li-ion type, widely available on the market. It comprises an envelope forming a rectangular parallelepiped. It is conventionally made of aluminum by stamping then by laser welding of an upper face. Inside is positioned a winding or a stack of anodes and cathodes (called stack in the remainder of the description).

[0003] With the aging of the electric cell due to parasitic chemical reactions, the active materials of the electric cell "grow" (mainly a progressive increase in the layer of the solid electrolyte interface by decomposition of the electrolyte). This creates a deformation and stresses in the stack. This will, as a result, touch and then deform the envelope of the electric cell. This creates an inhomogeneity of stresses / deformations of the stack in areas of the corners of the envelope of the electric cell. This "over-stress" in the corners tends to promote a deposition of solid lithium (also called "lithium-plating" according to English terminology) in these locations. This lithium deposition can cause durability problems, or even long-term safety problems for the electric cell.

[0004] Solutions already exist to avoid lithium deposition within an electric cell envelope. It is possible to reduce the size of the stack within the electric cell envelope. But the disadvantage of this solution is to reduce the capacity of the electric cell for the same envelope volume.

[0005] It is also possible to reduce the limits of the power mapping, i.e. reduce the maximum admissible current depending on the temperature and the state of charge of the cell. However, the disadvantage of such a solution is a reduction in the possible charging power (therefore, an increase in the charging time), and a reduction in the availability of the battery when cold. Statement of the invention

[0006] The invention aims to remedy all or part of the drawbacks of the state of the art by proposing in particular a solution making it possible to minimize the deposition of lithium within a battery cell envelope.

[0007] To do this, according to a first aspect of the invention, a battery cell envelope is proposed, arranged so as to surround an electric cell, the battery cell envelope delimiting a volume and comprising at least two adjacent walls connected to each other by an edge forming a junction, the battery cell envelope comprising a developable surface forming a hollow protruding bead open towards the volume, extending along the edge and connecting the two walls.

[0008] According to one embodiment, the envelope is of rectangular parallelepiped shape.

[0009] According to one embodiment, the battery cell envelope comprising a first side wall, the developable surface extends along at least one edge delimiting said first side wall.

[0010] According to one embodiment, the developable surface extends along three edges delimiting the first side wall.

[0011] According to one embodiment, the envelope comprising a second side wall extending opposite and at a distance from the first side wall, the developable surface extends along three edges delimiting the second side wall.

[0012] According to one embodiment, the envelope comprising a front wall, a rear wall and a bottom wall, the developable surface extends along the edge connecting the front wall and the bottom wall and / or the edge connecting the rear wall and the bottom wall.

[0013] According to one embodiment, the protruding hollow bead has a rounded shape in section.

[0014] According to one embodiment, the developable surface has a thickness equal to a thickness of the walls that it connects.

[0015] According to another aspect of the invention, there is provided a battery cell module comprising an electric cell and a battery cell envelope surrounding the electric cell, the battery cell envelope being an envelope having at least one of the preceding technical characteristics.

[0016] According to yet another aspect of the invention, there is provided a battery comprising at least one battery cell module having one of the preceding technical characteristics.

[0017] According to yet another aspect of the invention, there is provided a motor vehicle comprising a battery having one of the preceding technical characteristics. Brief description of the figures

[0018] Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, which illustrate: • [Fig.l]: schematic three-dimensional view of an embodiment of a battery cell module comprising a battery cell casing according to the invention. • [Fig.2]: Schematic top view of the battery cell module of [Fig.l]; • [Fig.3]: sectional view of the battery cell module of [Fig.l] new (BoL) and at end of life (EoL); and, • [Fig.4]: schematic top view of a battery comprising a assembly of battery cell modules of [Fig.l].

[0019] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. Detailed description of an embodiment

[0020] [Fig.l] illustrates a three-dimensional schematic view of an embodiment of a battery cell module 5 comprising an electric cell 2, here prismatic with a rectangular parallelepiped shape known per se. The battery cell module 5 further comprises a battery cell casing 1 according to the invention.

[0021] The battery cell casing 1 according to the invention is of the same shape as the electric cell 2, i.e. here a rectangular parallelepiped. The battery cell casing 1 according to the invention comprises a first 11 and second 13 side walls, a bottom wall 12, a top wall 14, a front wall 15 and a rear wall 17. The battery cell casing 1 according to the invention thus delimits a volume intended to receive the electric cell 2. The walls 11, 13, 12, 14, 15 and 17 adjacent in pairs are connected by an edge 10 forming a junction. The battery cell casing 1 according to the invention is formed from a sheet of material, such as aluminum.

[0022] With reference to [Fig. 2], along all or part of the edges 10, the battery cell envelope 1 according to the invention comprises a developable surface forming a projecting hollow bead, said developable surface then connecting the two adjacent walls 11, 13, 12, 14, 15, 17 considered. The projecting hollow bead is thus open towards the volume delimited by the battery cell envelope 1 according to the invention. The developable surface is integral with these two adjacent walls 11, 13, 12, 14, 15, 17 considered and therefore formed from the same sheet of material as said adjacent walls considered. The developable surface has, in this case, a thickness equal to a thickness of the walls that it connects. The cross-sectional shape of the developable surface is, for example, rounded, as illustrated in [Fig.2] or 3. The cross-sectional shape of the developable surface is defined by calculating the stresses that will appear in the stack forming the electric cell 2 during its lifetime when the active materials of said stack increase in size. The cross-sectional shape of the developable surface is chosen to allow the best homogeneity of stresses at the end of the life of the electric cell 2.

[0023] In particular, the developable surface is formed along the edges 10 which connect: • the front wall 15 with the first side wall 11 and / or the second side wall 13 and / or the bottom wall 12; and / or • the rear wall 17 with the first side wall 11 and / or the second side wall 13 and / or the bottom wall 12; and / or • the bottom wall 12 with the first side wall 11 and / or the second side wall 13.

[0024] The developable surface(s) provided on the battery cell envelope 1 according to the invention being integral with the walls of the battery cell envelope 1 according to the invention which it connects, said developable surface(s) is / are produced by stamping or hydroforming during the production of the battery cell envelope 1 according to the invention. After insertion of the electric cell 2 into the battery cell envelope 1 according to the invention, the top wall 14 is generally added and fixed to upper edges of the first 11 and second 13 side walls, of the front wall 15 and of the rear wall 17 by laser welding for example. It should be noted that other techniques and methods for producing the battery cell envelope 1 according to the invention may be used.

[0025] With reference to [Fig. 3], we will describe an evolution of the battery cell envelope 1 according to the invention which has just been described during the life of a battery cell module 5. On the left of [Fig. 3] is shown the new battery cell module 5 (BoL), therefore at the start of its life. To simplify the subject, we have simplified the representation of said battery cell module 5: we have drawn only a developable surface along the edges 10 connecting the front wall 15 with the first 11 and second 13 side walls of the battery cell envelope 1 according to the invention.

[0026] To the right of [Fig. 3], the battery cell module 1' is illustrated at the end of its life (EoL). Under the effect of the physicochemical changes of the electric cell 2' during its life, the front wall 15' of the battery cell envelope 1' according to the invention has deformed by swelling and causing in its deformation a deformation of the developable surface (which "unrolls" and "opens") of the edges 10' connecting the deformed front wall 15' with the first 11 and second 13 side walls. Thus the first 11 and second 13 side walls have not (or very little) deformed during the life of the battery cell module 5'. This has, moreover, made it possible to significantly reduce the stresses which have developed in the electric cell 2' during its life and therefore prevent the formation of a lithium deposit along the edges 10, 10' of the battery cell envelope 1' according to the invention.

[0027] With reference to [Fig. 4], we will briefly describe a battery 6 comprising battery cell modules 5 previously described. Within the battery 6, the battery cell modules 5 are “stacked” by interposing between two adjacent battery cell modules 5 a layer 8 of thermal insulation. Conventionally, the side walls 11 and 13 are the largest. Thus, the layer 6 of thermal insulation is sandwiched between the first side wall 11 of one of the two adjacent battery cell modules 5 and the second side wall 13 of the second of the two adjacent battery cell modules 5. The layer 6 of thermal insulation therefore extends opposite the aforementioned side walls except opposite the developable surface(s) extending along the edges 10 considered.For example, the developable surface of the battery cell envelope 1 according to the invention has a protruding dimension of the side wall 11, 13 of approximately a value of half the thickness of the thermal insulation layer 6. By way of illustration, the developable surface has a protruding dimension of approximately 1 mm for example.

[0028] The fact that during the life of the electric cell 2, the deformation of the developable surface(s) forming projecting hollow ridges makes it possible to best preserve the flatness of the facing side walls 11, 13 and therefore to best preserve the integrity of the layer 6 of thermal insulation between two battery cell modules 5 of the battery 6. Thus, the overall durability and safety of the battery 6 are best preserved.

[0029] Although the invention has been described in the context of a Li-ion electric cell, it is also usable in the context of other electric cell chemistries such as those which involve an addition of Si-Ox in the anode or solid state electric cells.

[0030] The invention which has just been described applies mainly to batteries for motor vehicles, in particular traction batteries for all-electric or hybrid motor vehicles.

[0031] Naturally, the invention is described in the foregoing by way of example. It is understood that the person skilled in the art is able to carry out different variant embodiments of the invention without departing from the scope of the invention.

[0032] It is emphasized that all the characteristics, as they emerge for a person skilled in the art from the present description, the drawings and the attached claims, even if concretely they have only been described in relation to other determined characteristics, both individually and in any combinations, can be combined with other characteristics or groups of features disclosed herein, unless expressly excluded or technical circumstances make such combinations impossible or meaningless.

Claims

Claims

1. Battery cell envelope (1) arranged so as to surround an electric cell (2), the battery cell envelope delimiting a volume and comprising at least two adjacent walls (11, 12, 13, 14, 15, 17) connected to each other by an edge (10) forming a junction, characterized in that the battery cell envelope comprises a developable surface forming a hollow protruding bead open towards the volume, extending along the edge and connecting the two walls.

2. Envelope according to claim 1, characterized in that the envelope is of rectangular parallelepiped shape.

3. Envelope according to claim 2, characterized in that, the battery cell envelope comprising a first side wall (11), the developable surface extends along at least one edge delimiting said first side wall.

4. Envelope according to claims 2 and 3, characterized in that the developable surface extends along three edges delimiting the first side wall.

5. Envelope according to claim 4, characterized in that, the envelope comprising a second side wall (13) extending opposite and at a distance from the first side wall, the developable surface extends along three edges delimiting the second side wall.

6. Envelope according to one of claims 2 to 5, characterized in that, the envelope comprising a front wall (15), a rear wall (17) and a bottom wall (12), the developable surface extends along the edge connecting the front wall and the bottom wall and / or the edge connecting the rear wall and the bottom wall.

7. Envelope according to one of claims 1 to 6, characterized in that the developable surface has a rounded shape in section.

8. Envelope according to one of claims 1 to 7, characterized in that the developable surface has a thickness equal to a thickness of the walls which it connects.

9. Battery cell module (5) comprising an electric cell (2) and a battery cell envelope (1) surrounding the electric cell, characterized in that the battery cell envelope is an envelope according to one of claims 1 to 8.

10.

11. Battery (6), characterized in that it comprises at least one battery cell module (5) according to claim 9. Motor vehicle, characterized in that it comprises a battery according to claim 10.

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